Long-Lasting Improvements in Liver Fat and Metabolism Despite Body Weight Regain After Dietary Weight Loss

OBJECTIVE

Weight loss reduces abdominal and intrahepatic fat, thereby improving metabolic and cardiovascular risk. Yet, many patients regain weight after successful diet-induced weight loss. Long-term changes in abdominal and liver fat, along with liver test results and insulin resistance, are not known.

RESEARCH DESIGN AND METHODS

We analyzed 50 overweight to obese subjects (46 ± 9 years of age; BMI, 32.5 ± 3.3 kg/m²; women, 77%) who had participated in a 6-month hypocaloric diet and were randomized to either reduced carbohydrates or reduced fat content. Before, directly after diet, and at an average of 24 (range, 17–36) months follow-up, we assessed body fat distribution by magnetic resonance imaging and markers of liver function and insulin resistance.

RESULTS

Body weight decreased with diet but had increased again at follow-up. Subjects also partially regained abdominal subcutaneous and visceral adipose tissue. In contrast, intrahepatic fat decreased with diet and remained reduced at follow-up (7.8 ± 9.8% [baseline], 4.5 ± 5.9% [6 months], and 4.7 ± 5.9% [follow-up]). Similar patterns were observed for markers of liver function, whole-body insulin sensitivity, and hepatic insulin resistance. Changes in intrahepatic fat und intrahepatic function were independent of macronutrient composition during intervention and were most effective in subjects with nonalcoholic fatty liver disease at baseline.

CONCLUSIONS

A 6-month hypocaloric diet induced improvements in hepatic fat, liver test results, and insulin resistance despite regaining of weight up to 2 years after the active intervention. Body weight and adiposity measurements may underestimate beneficial long-term effects of dietary interventions.Increases in visceral and subcutaneous abdominal fat as well as ectopic fat deposition contribute to the development of metabolic abnormalities in obesity (1). In particular, intrahepatic fat accumulation is associated with increased insulin resistance and promotes the development of type 2 diabetes (2,3), independently of total or visceral fat mass (4,5). Excessive hepatic fat also predisposes to nonalcoholic steatohepatitis, which may progress to cirrhosis and hepatic cancer (6). Thus, interventions reducing hepatic fat address the root cause for both obesity-associated metabolic disease and liver disease. Lifestyle interventions including hypocaloric diets are a cornerstone of obesity management because diet-induced weight loss improves insulin sensitivity (7) while preventing type 2 diabetes (8). Weight reduction through caloric restriction decreased hepatic fat in studies lasting up to 12 months (9,10). The improvement in hepatic fat during dieting was primarily related to caloric restriction rather than macronutrient composition (11). Two important issues are involved in weight reduction studies. First, there may be dissociation between body weight changes and cardiovascular and metabolic risk factors over time. For example, whereas bariatric surgery decreases the risk for new-onset diabetes for many years, the risk for arterial hypertension may not be reduced despite sustained weight loss (12). Second, many subjects regain weight after diet-induced weight loss (13). Whether weight regain negates previous improvements in hepatic fat and liver function has not been investigated. Given the importance of hepatic fat in the pathogenesis of obesity-associated metabolic disease, we assessed long-term changes in visceral fat, subcutaneous fat, liver fat, liver test results, and insulin resistance after dietary weight loss in overweight or obese subjects.     

In Vivo Insulin Sensitivity and Lipoprotein Particle Size and Concentration in Black and White Children

OBJECTIVE

To examine sex-specific black/white differences in lipoprotein profile and the role of visceral adiposity and to assess the relationship between insulin sensitivity and lipoprotein profiles in each group.

RESEARCH DESIGN AND METHODS

Fasting lipoprotein particle size and concentration and visceral adipose tissue (VAT) were determined in 226 children (117 black, 101 male) aged 8 to <18 years. The relationship between lipoproteins and insulin sensitivity was evaluated in a subset of 194 children (100 black, 88 male) who underwent a hyperinsulinemic-euglycemic clamp.

RESULTS

Black male children had smaller VLDL and black female children had larger HDL size than their white counterparts. Overall, blacks had larger LDL size with no sex-specific race differences. After adjusting for VAT and sex, only VLDL size and concentrations remained significantly favorable in blacks. Analysis of lipoprotein particle size and concentration across insulin sensitivity quartiles revealed that in both racial groups, the most insulin-resistant children had higher concentrations of small dense LDL, small HDL, and large VLDL and smaller LDL and HDL sizes than their more insulin-sensitive counterparts.

CONCLUSIONS

The previously reported favorable lipoprotein profiles in black versus white children is partly due to race differences in VAT. In both groups, however, the most insulin-resistant youths have a high-risk atherogenic profile of small dense LDL, small HDL, and large VLDL, akin to the atherogenic lipoprotein pattern in adults with coronary artery disease.Type 2 diabetes and insulin resistance in children are associated with dyslipidemia (1,2), characterized by elevated triglycerides and LDL cholesterol and low concentrations of HDL cholesterol (1–3). In addition to traditional lipid profiles, evidence suggests that insulin resistance and type 2 diabetes are associated with changes in lipoprotein particle size and subclass concentration (2,4). These are important to assess, as traditional lipid measurements only partially predict disease risk (5). Recently, the SEARCH for Diabetes in Youth study (2) reported that 36% of youth with type 2 diabetes and 62% of those with poorly controlled diabetes had small dense LDL. Similarly, low proportions of large and high proportions of small HDL particles are found in children with type 2 diabetes and overweight, insulin-resistant children (4). However, whereas some investigators reported associations between LDL (6,7), HDL (8), and VLDL (6) particle size and fasting insulin, others did not (9). High triglyceride and low HDL cholesterol concentrations together with small, dense LDL in children with type 2 diabetes and insulin resistance are similar to the atherogenic lipoprotein phenotype in adults with coronary artery disease (10,11).Black children, despite being insulin resistant and hyperinsulinemic (12,13) compared with their white counterparts, have favorable lipid concentrations including lower LDL and triglyceride and higher HDL concentrations (3,14,15), larger HDL and LDL and smaller VLDL particles, and favorable lipoprotein subclass concentrations (6,8). Why black children have favorable lipoprotein profiles despite insulin resistance is not clear. One explanation could be lower visceral adiposity in black than in white children despite similar overall adiposity (15). In black adults insulin resistance is not a good marker of triglyceride or HDL cholesterol concentrations or lipoprotein particle size (16). Thus, the relationship between in vivo insulin sensitivity and lipoprotein profiles in black and white children needs to be examined if at-risk children are to be identified for early treatments to improve lipoprotein profiles and if those treatments are to be pertinent in children of different ethnicity.In the present study, therefore, we determined lipoprotein particle size and subclass concentrations in black and white children and measured in vivo insulin sensitivity to test the following hypotheses: 1) the favorable lipoprotein phenotype in black children is probably due to lower visceral adipose tissue (VAT) than in whites and 2) the relationship between insulin sensitivity and lipoprotein profile is similar between black and white children.     

Effect of elevated basal insulin on cancer incidence and mortality in cancer incident patients: the Israel GOH 29-year follow-up study

OBJECTIVE

Diabetes is associated with many forms of cancer. Recent evidence has suggested that some treatments for diabetes are associated with an increased cancer risk. Less is known about the association between endogenous insulin in the prediabetes state and cancer risk.

RESEARCH DESIGN AND METHODS

We investigated cumulative cancer incidence and cancer incidence density over 29 years, according to basal insulin, in a cohort of 1,695 nondiabetic men and women of four ethnic origins, aged 51.8 ± 8.0 years at baseline. Total mortality among the 317 subjects (18.7%) who developed cancer at least 2 years after baseline was assessed.

RESULTS

In a Cox proportional hazards model, the all-site hazard ratio of cancer incidence comparing the highest insulin quartile with the other three quartiles was 1.09 (95% CI 0.85–1.40), adjusted for age, sex, and ethnicity. BMI, smoking, and fasting blood glucose were not statistically significant in this model. Basal insulin level was not significantly associated with cancer of specific sites (breast, prostate, colon/rectum, or bladder). Fasting insulin in the upper quartile conferred a 37% increased risk for total mortality among cancer patients, adjusting for age, sex, and ethnic origin (95% CI 0.94–2.00, P = 0.097) compared with that of the lower quartiles. Male sex, older age, and North African origins were associated with a greater risk of mortality during follow-up time.

CONCLUSIONS

This long-term cohort study may suggest a role for basal elevated insulin levels, mainly as a negative predictor in cancer prognosis.The American Diabetes Association and the American Cancer Society recently issued a consensus report showing cancer incidence to be associated with diabetes (1). Type 2 diabetes has been associated with increased incidence, in the range of 1.2–2.5 of cancers of the pancreas (2), breast (3), colon (4), and bladder (5). In addition, a recent meta-analysis of 23 studies found diabetes to be associated with an increased mortality hazard ratio (HR) of 1.41 (95% CI 1.28–1.55) among individuals with cancer (6). Furthermore, some treatments for diabetes have been implicated in increasing the risk of malignancy (7). The development of some types of insulin has been discontinued secondary to increased mitogenic side effects (8). The affinity of binding to the IGF-1 receptor (IGF-1R) has been implicated.We and others have shown basal hyperinsulinemia to predict type 2 diabetes (9,10). Further, elevated levels of circulating insulin and C-peptide have been associated with an increased risk of colorectal and pancreatic cancers (11). Though the risk of breast cancer was less certain in the latter study, two recent analyses of the Women''s Health Initiative found a positive association between insulin levels and breast cancer (12,13).Studies in animals (14–17) and in vitro (18,19) suggest a role for insulin in tumor progression. Glucose tolerance status from 2-h glucose tolerance tests has been shown to associate with the risk of cancer mortality (4). However, the effect of elevated basal insulin on cancer prognosis has not been investigated in vivo.The current study examined the effect, up to 29 years later (mean follow-up time 21.7 ± 6.5 years), of elevated levels of basal insulin on the cumulative incidence of cancer and on cancer survival in a cohort of the Jewish population, representing the four main ethnic origins of immigration to Israel.     

Abdominal Subcutaneous Adipose Tissue: A Protective Fat Depot?

OBJECTIVE

Obesity is associated with increased metabolic and cardiovascular risk. The ectopic fat hypothesis suggests that subcutaneous fat may be protective, but this theory has yet to be fully explored.

RESEARCH DESIGN AND METHODS

Participants from the Framingham Heart Study (n = 3,001, 48.5% women) were stratified by visceral adipose tissue (VAT) into sex-specific tertiles. Within these tertiles, age-adjusted abdominal subcutaneous adipose tissue (SAT) tertiles were examined in relation to cardiometabolic risk factors.

RESULTS

In the lowest VAT tertile, risk factor prevalence was low, although systolic blood pressure in women and rates of high triglycerides, impaired fasting glucose, hypertension, and the metabolic syndrome in men increased with increasing SAT tertile (all P < 0.04). In contrast, in the top VAT tertile, lower triglycerides were observed in men with increasing SAT (64.4% high triglycerides in SAT tertile 1 vs. 52.7% in SAT tertile 3, P = 0.03). Similar observations were made for women, although results were not statistically significant (50.6% high triglycerides in SAT tertile 1 vs. 41.0% in tertile 3, P = 0.10). Results in the highest VAT tertile were notable for a lack of increase in the prevalence of low HDL in men and women and in rates of impaired fasting glucose in men with increasing subcutaneous fat, despite sizable differences in BMI across SAT tertiles (27.1 to 36.3 kg/m²[women]; 28.1 to 35.7 kg/m²[men]).

CONCLUSIONS

Although adiposity increases the absolute risk of metabolic and cardiovascular disease, abdominal subcutaneous fat is not associated with a linear increase in the prevalence of all risk factors among the obese, most notably, high triglycerides.Obesity is associated with multiple cardiometabolic risk factors, including insulin resistance (1), diabetes (2), hypertension (3), and dyslipidemia (4). Variations in fat distribution may mediate such risks, with visceral adipose tissue (VAT) associated with more adverse risk factor profiles than abdominal subcutaneous adipose tissue (SAT) (5,6). The ectopic fat hypothesis proposes that obesity represents a failure of adipocyte growth and differentiation, resulting in “acquired lipodystrophy” and fat deposition in liver, skeletal muscle, and pancreatic β-cells (7). Such ectopic fat stores are hypothesized to contribute to the pathogenesis of impaired insulin secretion and insulin resistance and to mediate obesity-related cardiovascular disease (8).In addition to the detrimental effects of VAT, human and animal studies have suggested a possible protective role for subcutaneous fat. In humans, increased subcutaneous leg fat is associated with decreased risk of disturbed glucose metabolism and dyslipidemia, independent of abdominal fat (9). Thiazolidinedione treatment, which increases total fat mass, mostly in subcutaneous fat stores, improves insulin sensitivity (10). Removal of VAT by omentectomy results in decreased glucose and insulin levels in humans, (11), whereas removal of SAT by liposuction does not always result in improvements in glucose metabolism or lipid levels (12,13). Transplantation of subcutaneous fat into visceral compartments in mice produces decreases in body weight and total fat mass and improved glucose metabolism, suggesting that subcutaneous fat may be intrinsically different from visceral fat in ways that are beneficial (14).Therefore, the purpose of the present study was to test the hypothesis that abdominal subcutaneous fat is a protective fat depot in terms of cardiometabolic risk factor prevalence. We theorized that among those with similar levels of VAT, increasing SAT might be associated with decreases in cardiometabolic risk factor prevalence despite increasing BMI and total abdominal fat.     

Effect of longitudinal changes in visceral fat area and other anthropometric indices to the changes in metabolic risk factors in Japanese men: the Hitachi Health Study

OBJECTIVE

The effects of longitudinal changes in the visceral fat area (VFA), and other anthropometric indices, on the risk factors of metabolic syndrome were not studied. We calculated the changes in metabolic risk factors in relation to changes in certain anthropometric indices in a large-scale study of Japanese men.

RESEARCH DESIGN AND METHODS

The subjects were 1,106 men participating in the Hitachi Health Study who received a computed tomography examination in both 2004 and 2007. VFA, subcutaneous fat area (SFA), and waist circumference were measured using the computed tomography. We examined how longitudinal changes in each anthropometric index over a 3-year period influenced the value of each metabolic risk factor.

RESULTS

Changes (∆) over a 3-year period in body weight, SFA, and waist circumference strongly correlated, while the changes in body weight and VFA were weakly correlated. Changes in the VFA were associated with changes in metabolic risk factors, especially changes in triglyceride and HDL; we found these changes to be independent of the ∆body weight and ∆waist circumference.

CONCLUSIONS

Change in body weight is not a precise surrogate marker of ∆VFA, and repeated VFA measurements over time are useful. Adopting a lifestyle that does not increase the VFA is important in preventing metabolic syndrome.Cardiovascular disease (CVD) is one of the leading causes of morbidity and mortality in the world (1). Previous reports have shown that obesity plays a significant role in increasing cardiovascular risk (2). Certain indicators of obesity, such as the visceral fat area (VFA), or visceral adipose tissue, are more strongly associated with the risk of CVD than other indicators of obesity, such as waist circumference, BMI (3), or the subcutaneous fat area (SFA) (2). A large VFA is strongly related to a higher prevalence of impaired fasting glucose levels (4,5), diabetes (4,6,7), insulin resistance (4,8–10), hypertension (11,12), abnormality of lipid metabolism (13–16), and metabolic risk factors (14,17,18). Previous studies have examined the relationship between baseline VFA and metabolic risk factors. In a previous intervention study of 54 postmenopausal women, an increase in VFA strongly correlated with changes in triglyceride and HDL cholesterol levels compared with changes in the blood pressure and fasting blood glucose levels (19). In the current study, we examined the relationships between changes in the VFA, SFA, body weight, and waist circumference and changes in CVD risk factors to determine the relative contributions of the longitudinal changes in these anthropometric indices to the changes in metabolic risk factors over a 3-year period. Determining the relationships between the anthropometric indices and metabolic risk factors would be useful for preventing CVD in clinical settings.     

Reduced risk of colorectal cancer with metformin therapy in patients with type 2 diabetes: a meta-analysis

OBJECTIVE

Both in vitro and in vivo studies indicate that metformin inhibits cancer cell growth and reduces cancer risk. Recent epidemiological studies suggest that metformin therapy may reduce the risks of cancer and overall cancer mortality among patients with type 2 diabetes. However, data on its effect on colorectal cancer are limited and inconsistent. We therefore pooled data currently available to examine the association between metformin therapy and colorectal cancer among patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

The PubMed and SciVerse Scopus databases were searched to identify studies that examined the effect of metformin therapy on colorectal cancer among patients with type 2 diabetes. Summary effect estimates were derived using a random-effects meta-analysis model.

RESULTS

The analysis included five studies comprising 108,161 patients with type 2 diabetes. Metformin treatment was associated with a significantly lower risk of colorectal neoplasm (relative risk [RR] 0.63 [95% CI 0.50–0.79]; P < 0.001). After exclusion of one study that investigated colorectal adenoma, the remaining four studies comprised 107,961 diabetic patients and 589 incident colorectal cancer cases during follow-up. Metformin treatment was associated with a significantly lower risk of colorectal cancer (0.63 [0.47–0.84]; P = 0.002). There was no evidence for the presence of significant heterogeneity between the five studies (Q = 4.86, P = 0.30; I² = 18%).

CONCLUSIONS

From observational studies, metformin therapy appears to be associated with a significantly lower risk of colorectal cancer in patients with type 2 diabetes. Further investigation is warranted.Colorectal cancer is one of the most frequent malignant tumors and a leading cause of cancer-related death worldwide (1). The incidence of colorectal cancer continues to increase in economically transitioning countries such as Asia, Eastern Europe, and selected countries in South America (2,3), whereas a declining trend has been noted in several developed countries in recent years (1).Type 2 diabetes is also a common disease, and it is well established that type 2 diabetes is associated with a higher risk of colorectal cancer (4–8). Metformin is a relative of isoamylene guanidine and has been recommended as the initial glucose-lowering therapy for diabetes. Emerging evidence from both in vitro and in vivo studies indicates that metformin may inhibit cancer cell growth and reduce cancer risks. Previous research suggests that metformin may be involved in the tumor suppressor pathway by indirectly activating AMP-activated protein kinase (9)—a key sensor of cellular ATP and AMP balance—and plays a role on activating tumor suppressor genes, e.g., LKB1. Subsequent in vitro studies have shown that metformin inhibits cancer cell proliferation (10,11) and selectively kills cancer stem cells (12). Animal experiments concur with these findings. Rodent models have shown that metformin suppresses colonic epithelial proliferation and colorectal aberrant crypt foci formation (13,14). Similarly, animal models of colon cancer have shown that metformin inhibits colon carcinoma growth (11,15). Given these encouraging findings, interest has arisen that metformin could potentially serve as a new antineoplasm drug to prevent colorectal cancer.Results from preliminary studies conducted in humans are encouraging. In a short-term randomized clinical trial among nondiabetic patients with rectal aberrant crypt foci, a significant decrease in the mean number of aberrant crypt foci was observed after metformin treatment for 1 month as compared with no significant changes in the control group (16). Findings from several epidemiological studies also support an antineoplastic role of metformin on cancer risks (17,18). If metformin therapy ultimately proves effective on reducing the risk of colorectal cancer, it would likely be recommended for the overwhelming majority of diabetes patients for both blood glucose control and cancer prevention. Nonetheless, despite accumulating evidence from population studies that indicate a lower risk of cancer at large with metformin therapy (17,19,20), data on its effect on colorectal cancer are limited and inconsistent. Accordingly, we performed a meta-analysis to pool studies currently available to examine the effect of metformin treatment on colorectal cancer risk among patients with type 2 diabetes.     

Defining the Ideal Injection Techniques When Using 5-mm Needles in Children and Adults

OBJECTIVE

We aimed to establish the ideal injection techniques using 5-mm needles to reliably inject insulin into the subcutaneous fat in both children and adults and to quantify the associated pain and leakage of the test medium.

RESEARCH DESIGN AND METHODS

A total of 259 subjects (122 children/adolescents and 137 adults) were injected with sterile air corresponding to 20 IU insulin (200 μl) with 32-G 5-mm needles at 90° or 45°, in the abdomen and thigh, and with or without a pinched skin fold. Injection depth was assessed via ultrasonography. Subjects rated pain on a visual analog scale. Test medium injections into the abdomen and thigh (0.2–0.6 ml) were also administered to assess injection leakage.

RESULTS

Among children, 5.5% of injections were intramuscular (IM) and 0.5% were intradermal, while in adults, the incidence was 1.3 and 0.6%, respectively. The frequency of IM injections was greater in boys and negligible among adult women. Subcutaneous fat thickness was the primary predictor of the likelihood of IM injections (P < 0.001). A third of all patients reported experiencing no pain during insulin injection, with children/adolescents experiencing considerably more discomfort than adults. Some leakage of medium was observed, but was unrelated to injection volume and was generally minimal.

CONCLUSIONS

5-mm needles are reliably inserted into subcutaneous fat in both adults and children. These needles were associated with reduced pain and minimal leakage. We recommend an angled injection with a pinched skin fold for children, while in adults, the technique should be left to patient preference.Although there are many new technologies assisting in diabetes care, multiple daily injections remain the mainstay of therapy where insulin is required. Such injections aim to reliably deposit insulin into subcutaneous fat while minimizing inadvertent intramuscular (IM) injections (1). Intramuscular injections of regular, NPH, and glargine insulin have been associated with variability in glycemic control and an increased risk of severe hypoglycemia (2–6). Although no studies have systematically evaluated the frequency of IM injections among diabetic patients, these appear to be relatively common (6,7).The risk of IM insulin deposition is associated with a number of factors including younger age, male sex, lower BMI, injection technique (angle of insertion and a lifted or pinched skin fold), and needle length (5,8–11). Furthermore, the thinner a person''s skin or subcutaneous fat layer, the greater the chances of an accidental IM injection (5). Little information is known about skin thickness, although it appears to vary with age, obesity, and puberty (1).Not surprisingly, needle length has been shown to be an important variable determining site of insulin deposition (5,12). However, although decreasing the length of the insulin needle reduces the incidence of IM injections, the use of 5-mm needles may result in insulin being administered too superficially in the dermal layer (13,14). The consequence of intradermal insulin deposition is largely unknown, but may lead to increased immune response, injection pain, and insulin leakage (14).Despite this, there have been few studies examining injection technique. Perpendicular insertion of 6-, 8- and 12.7-mm needles has been associated with frequent IM injections in children and adolescents with rates of 42, 38, and 86%, respectively (1,5,8). By using an angled insertion of 6-mm needles, the risk of IM injections was markedly reduced (1). More recently, 4-mm needles inserted vertically were shown to be safe and effective in the majority of lean children and adults (12). However, no evidence-based recommendations exist for 5-mm needles, which are being used with increasing frequency. Although there are some data on children with other needle lengths (1,5,8), little information is available on adults, and it remains unclear how suitable shorter needles are for this group, especially for the obese.Our primary aim was to establish the ideal injection techniques required to reliably inject insulin into the subcutaneous fat in both children and adults using 5-mm needles. We also aimed to assess the level of discomfort associated with each technique and quantify the respective amounts of backflow or leakage of test medium to the skin surface.     

Sagittal Abdominal Diameter Is a Strong Anthropometric Measure of Visceral Adipose Tissue in the Asian General Population

OBJECTIVE

Finding the anthropometric measure of visceral obesity is essential to clinical practice, because it predicts cardiovascular and metabolic risks. Sagittal abdominal diameter (SAD) has been proposed as an estimate of visceral adipose tissue (VAT). The aim of the present study was to evaluate the usefulness of SAD in predicting visceral obesity by comparing SAD to other anthropometric measures.

RESEARCH DESIGN AND METHODS

Estimation of subcutaneous and visceral adipose tissue and measurement of SAD and transverse abdominal diameter using computed tomography at the umbilical level were obtained in 5,257 men and women who were enrolled in a health checkup program in Korea. To compare SAD to other anthropometric measures, linear regression analyses were used to determine correlations between anthropometrics and visceral obesity.

RESULTS

SAD showed a stronger correlation to VAT than waist circumference, BMI, and transverse abdominal diameter in the both sexes (men: r = 0.804, women: r = 0.724). Waist circumference showed generally stronger associations to subcutaneous adipose tissue (SAT) than to VAT (men: r = 0.789 vs. 0.705, women: r = 0.820 vs. 0.636). Even after subdividing according to age or BMI in both sexes and analyzing multiple regressions, SAD showed the strongest correlation to VAT.

CONCLUSIONS

SAD showed the strongest correlation to VAT irrespective of age, sex, and the degree of obesity compared with other anthropometric measures, whereas waist circumference may have a stronger correlation to SAT than to VAT. The clinical use of SAD has advantages over other anthropometric measures in predicting VAT.Although abdominal obesity has been considered a risk factor compromising health in only Western countries, where its presence has been relatively high, the prevalence of abdominal obesity has recently increased in Asian countries because of sedentary lifestyles and westernized diet. Abdominal obesity frequently leads to diabetes or metabolic disorders and can induce cardiovascular diseases with a risk of early death (1,2). Several studies have suggested that, compared with subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT) has a stronger correlation to these obesity-related disorders (3,4). Thus, accurate measurement of VAT is required to predict the risk of obtaining such diseases. Computed tomography (CT) or magnetic resonance imaging is the most accurate method for estimating VAT (5). However, since the high costs of these tests make them clinically impractical, much effort has been made to find inexpensive, easily obtainable anthropometric measures to clinically evaluate the relationship between VAT and metabolic diseases.Waist circumference (WC) has been widely used to measure abdominal obesity (6), and it serves as one of the criteria for the diagnosis of metabolic syndrome (7,8). However, WC does not distinguish visceral from subcutaneous abdominal adipose tissue (9–11). Pou et al. (11) revealed that WC may misclassify individuals in terms of VAT. Their result implies that other anthropometric measures to correlate with VAT are needed.Sagittal abdominal diameter (SAD), which measures the anteroposterior diameter of the abdomen, reflects VAT based on the fact that subcutaneous fat is displaced inferiorly by gravity (12). Since SAD was introduced as a means of estimating visceral obesity (12), a few studies have been conducted on the usefulness of SAD in the evaluation of visceral obesity (13–15) as well as cardiovascular and metabolic risks (16,17) in comparison to other anthropometric measures. However, there were still insufficient evidences to draw any conclusions whether SAD more accurately represents visceral obesity due to the small number of subjects and selection process in the previous studies. Larger population-based studies are still needed to determine it. Moreover, the previous studies on SAD have been carried out in Western countries; there have been little data in the Asian population.Transverse abdominal diameter (TAD) was the largest spanned width, whereas SAD was the largest spanned height of the abdomen (12). TAD has been presented on correlation to SAT (12,13,15). However, TAD has never previously been investigated in terms of its correlation to the amount of adipose tissue in the Asian population.Therefore, the present study was conducted to compare SAD to other anthropometric measures in predicting the amount of CT-measured adipose tissue in a large, apparently healthy population.     

Lower risk of cancer in patients on metformin in comparison with those on sulfonylurea derivatives: results from a large population-based follow-up study

OBJECTIVE

Numerous studies have suggested a decreased risk of cancer in patients with diabetes on metformin. Because different comparison groups were used, the effect magnitude is difficult to estimate. Therefore, the objective of this study was to further analyze whether, and to what extent, use of metformin is associated with a decreased risk of cancer in a cohort of incident users of metformin compared with users of sulfonylurea derivatives.

RESEARCH DESIGN AND METHODS

Data for this study were obtained from dispensing records from community pharmacies individually linked to hospital discharge records from 2.5 million individuals in the Netherlands. The association between the risk of cancer in those using metformin compared with those using sulfonylurea derivatives was analyzed using Cox proportional hazard models with cumulative duration of drug use as a time-varying determinant.

RESULTS

Use of metformin was associated with a lower risk of cancer in general (hazard ratio 0.90 [95% CI 0.88–0.91]) compared with use of sulfonylurea derivatives. When specific cancers were used as end points, similar estimates were found. Dosage-response relations were identified for users of metformin but not for users of sulfonylurea derivatives.

CONCLUSIONS

In our study, cumulative exposure to metformin was associated with a lower risk of specific cancers and cancer in general, compared with cumulative exposure to sulfonylurea derivatives. However, whether this should indeed be seen as a decreased risk of cancer for the use of metformin or as an increased risk of cancer for the use sulfonylurea derivatives remains to be elucidated.As the drug of first choice in type 2 diabetes, metformin is the most widely prescribed oral glucose-lowering drug (OGLD) (1,2). However, the decision to prescribe metformin also depends on patient characteristics: metformin use is contraindicated in those with renal failure, cardiac, or hepatic failure (2).A statistically nonsignificant relationship between use of metformin and the risk of colon cancer was described in 2004 (3). However, 1 year later, metformin was found to be associated with a decreased risk of cancer in general in a case-control study in a diabetic population (4). Numerous studies followed; among which studies confirming the association between use of metformin and a decreased risk of cancer in general (5–8) or in specific cancers (5,6,9–14). However, for breast cancer (5,6) and prostate cancer (5,14), the decreased risk was not consistently demonstrated; for other cancers, no association with use of metformin was found (6,12). Hence, there is heterogeneity among published studies on cancer in patients with diabetes on metformin (15), partly because different comparison groups were used, such as nonmetformin users, users of other OGLDs, or users of insulin. Higher endogenous insulin levels have been linked to an increased risk of certain cancers (16). Moreover, specifically for insulin glargine, the debate whether this specific insulin increases the risk of cancer is ongoing (17–21).Owing to factors such as different drugs used to attain metabolic control, the duration of diabetes, and the presence of other diseases, the assessment of cancer risk in diabetic patients remains difficult. Therefore, the objective of this study was to analyze whether, and to what extent, use of metformin is associated with a decreased risk of cancer in a cohort of incident users of metformin compared with use of sulfonylurea derivatives.     

Fasting insulin level is positively associated with incidence of hypertension among American young adults: a 20-year follow-up study

OBJECTIVE

Although hyperinsulinemia, a surrogate of insulin resistance, may play a role in the pathogenesis of hypertension (HTN), the longitudinal association between fasting insulin level and HTN development is still controversial. We examined the relation between fasting insulin and incidence of HTN in a large prospective cohort.

RESEARCH DESIGN AND METHODS

A prospective cohort of 3,413 Americans, aged 18–30 years, without HTN in 1985 (baseline) were enrolled. Six follow-ups were conducted in 1987, 1990, 1992, 1995, 2000, and 2005. Fasting insulin and glucose levels were assessed by a radioimmunoassay and hexokinase method, respectively. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% CIs of incident HTN (defined as the initiation of antihypertensive medication, systolic blood pressure ≥140 mmHg, or diastolic blood pressure ≥90 mmHg).

RESULTS

During the 20-year follow-up, 796 incident cases were identified. After adjustment for potential confounders, participants in the highest quartile of insulin levels had a significantly higher incidence of HTN (HR 1.85 [95% CI 1.42–2.40]; P_trend < 0.001) compared with those in the lowest quartile. The positive association persisted in each sex/ethnicity/weight status subgroup. A similar dose-response relation was observed when insulin-to-glucose ratio or homeostatic model assessment of insulin resistance was used as exposure.

CONCLUSIONS

Fasting serum insulin levels or hyperinsulinemia in young adulthood was positively associated with incidence of HTN later in life for both men and women, African Americans and Caucasians, and those with normal weight and overweight. Our findings suggested that fasting insulin ascertainment may help clinicians identify those at high risk of HTN.Hypertension (HTN), a leading cause of cardiovascular morbidity and mortality, has become an important public health burden worldwide (1). It has been well established that HTN tends to coexist with diabetes (2,3), either preceding or being the complication of diabetes. In addition, the risk factors for HTN and diabetes are prone to cluster together, and it has been hypothesized that hyperinsulinemia, a surrogate measure of insulin resistance, might provide the pathophysiological mechanism underlying these observations (4).Some epidemiological studies, including both cross-sectional and longitudinal studies, have indicated that insulin levels are associated with blood pressure (BP) as well as incidence of HTN (5–7). However, inconsistent findings (8,9), especially in a specific sex or ethnic subgroup (10,11), made this topic a controversy. In addition, among the limited prospective studies on the association of insulin level with incidence of HTN (5,6,9,12–14), most have been conducted in only one sex or one ethnic group (9,12–14). Few studies have examined the association in both men and women, and African Americans (AAs) and Caucasians (5,6). Therefore, we prospectively examined fasting insulin level in relation to incidence of HTN in a large biracial cohort of American men and women over 20 years of follow-up using data from the Coronary Artery Risk Development in Young Adults (CARDIA) study.     

Improved Plasma FFA/Insulin Homeostasis Is Independently Associated With Improved Glucose Tolerance After a 1-Year Lifestyle Intervention in Viscerally Obese Men

OBJECTIVE

Elevated plasma free fatty acids (FFAs) are one important link between excess visceral adiposity, insulin resistance, and the development of type 2 diabetes. Effects of lifestyle interventions on FFA metabolism are poorly known. This open-label study was conducted to test the effects of a 1-year healthy eating/physical activity intervention program on plasma FFA homeostasis in 117 viscerally obese men with dyslipidemia associated with insulin resistance (waist circumference ≥90 cm, triglycerides ≥1.69 mmol/L, and/or HDL-cholesterol <1.03 mmol/L).

RESEARCH DESIGN AND METHODS

Body weight, body composition, and fat distribution were assessed by dual-energy X-ray absorptiometry/computed tomography. Oral loads of lipid (60 g fat/m² body surface area) and glucose (75 g) were measured before and after the intervention.

RESULTS

After 1 year of lifestyle intervention, visceral adiposity was reduced by −26% (95% CI −29 to −23), whereas cardiorespiratory fitness improved by +20% (95% CI +16 to +24). After 1 year, the suppression of FFAs after the glucose load improved, whereas insulin concentrations were drastically reduced. After the oral lipid load, the late increase in FFA was reduced together with reduced circulating insulin. We calculated an insulin sensitivity index to reflect the concentration of insulin needed to manage plasma FFAs after the oral lipid load, which increased after the intervention and was associated with improved glucose tolerance, independent of changes in visceral or total adiposity.

CONCLUSIONS

A 1-year healthy eating/physical activity intervention improved the suppression of FFAs after oral glucose and lipid load tests in viscerally obese men, possibly due to improved responsiveness to insulin. This insulin-mediated regulation of postprandial plasma FFA levels could be a link between visceral obesity and impaired glucose homeostasis.Excess visceral adiposity has been associated with deteriorated cardiometabolic risk profile (1,2) and increased risk of developing type 2 diabetes and cardiovascular diseases (3,4). In both fasting and postprandial conditions (5), obese patients have increased concentrations of plasma free fatty acids (FFAs) compared with lean patients (6,7). Although visceral adiposity lipolysis accounts for less than 20% of systemic circulating FFA in obese patients, these FFAs are released directly into the portal vein, thereby exposing the liver to more FFA than would be predicted from systemic FFA (6). Moreover, in vitro studies have shown that visceral adipocytes are characterized by increased lipolysis compared with subcutaneous adipocytes (8) because visceral fat is much less sensitive to lipolysis inhibition by insulin than subcutaneous fat (9). Thus, increased visceral fat increases delivery of deleterious levels of FFA to the liver via the portal vein, leading to elevated hepatic triglyceride concentration and hepatic insulin resistance. Therefore, abdominal adiposity is an important determinant of postprandial plasma FFA flux (10). Increased plasma FFA, especially in the postprandial state, seems to be one important link between excess visceral adiposity, ectopic fat deposition, insulin resistance, and the development of type 2 diabetes (see Carpentier [11] and Giacca et al. [12] for review).Few studies have addressed the effect of lifestyle intervention on FFA homeostasis, particularly in relation to changes in visceral adiposity. An ancillary study from the LookAHEAD trial was conducted in obese patients with type 2 diabetes who participated to the intensive lifestyle intervention arm. In this study, Albu et al. (13) assessed insulin sensitivity and FFAs during a hyperinsulinemic euglycemic clamp in 26 men and 32 women. One year of intensive lifestyle intervention elicited an increase in exogenous insulin-mediated glucose uptake as well as a decrease in FFA concentrations during the clamp, demonstrating improved insulin sensitivity of both glucose metabolism and lipolysis inhibition. Furthermore, Johnson et al. (14) performed a study of 19 obese patients with impaired glucose tolerance (12 in the intervention and 7 in the control arm) to evaluate the effects of 4 weeks of aerobic exercise training on fat distribution and metabolism. They found that fasting FFA concentrations decreased in the intervention group in association with a reduction in hepatic triglyceride concentration. While these studies show that fasting FFA concentrations decrease after a diet or exercise intervention program, or both, it is still not known whether postprandial FFA metabolism may be improved with a lifestyle intervention.The current study was conducted to test the effects of a 1-year healthy eating/physical activity intervention program on plasma FFA homeostasis in viscerally obese men. Two complementary lipid and glucose oral loads were performed at baseline and after 1 year of intervention to test plasma FFA response to dynamic, oral, thus physiologic tests, in parallel with observed changes in fat accumulation and distribution.     

Maternal and Neonatal Circulating Markers of Metabolic and Cardiovascular Risk in the Metformin in Gestational Diabetes (MiG) Trial: Responses to maternal metformin versus insulin treatment

OBJECTIVE

This study was designed to compare glucose, lipids, and C-reactive protein (CRP) in women with gestational diabetes mellitus treated with metformin or insulin and in cord plasma of their offspring and to examine how these markers relate to infant size at birth.

RESEARCH DESIGN AND METHODS

Women with gestational diabetes mellitus were randomly assigned to metformin or insulin in the Metformin in Gestational Diabetes trial. Fasting maternal plasma glucose, lipids, and CRP were measured at randomization, 36 weeks’ gestation, and 6–8 weeks postpartum as well as in cord plasma. Women with available cord blood samples (metformin n = 236, insulin n = 242) were included.

RESULTS

Maternal plasma triglycerides increased more from randomization to 36 weeks’ gestation in women treated with metformin (21.93%) versus insulin (9.69%, P < 0.001). Maternal and cord plasma lipids, CRP, and neonatal anthropometry did not differ between treatments. In logistic regression analyses adjusted for confounders, the strongest associations with birth weight >90th centile were maternal triglycerides and measures of glucose control at 36 weeks.

CONCLUSIONS

There were few differences in circulating maternal and neonatal markers of metabolic status and no differences in measures of anthropometry between the offspring of women treated with metformin and the offspring of women treated with insulin. There may be subtle effects of metformin on maternal lipid function, but the findings suggest that treating gestational diabetes mellitus with metformin does not adversely affect lipids or CRP in cord plasma or neonatal anthropometric measures.Gestational diabetes mellitus is carbohydrate intolerance first diagnosed during pregnancy (1) and affects up to 18% of pregnancies. The prevalence varies depending on maternal demographics and diagnostic criteria (2). The prevalence of gestational diabetes mellitus is increasing, which is likely driven by the rising population prevalence of overweight and obesity and increasing maternal age at pregnancy (3). Gestational diabetes mellitus increases maternal and infant morbidity and mortality during pregnancy (4). Women with a history of gestational diabetes mellitus are at risk for metabolic syndrome, type 2 diabetes (5), and cardiovascular disease in later life (6). Children born to women with gestational diabetes mellitus have higher rates of type 2 diabetes and obesity (7).Treating gestational diabetes mellitus improves pregnancy outcomes for both mother and infant (8). Current therapies include modification of diet, increased physical activity, and drug therapy with insulin and oral hypoglycemic agents, including metformin. In addition to improving insulin sensitivity and hyperglycemia, metformin therapy in the setting of type 2 diabetes reduces triglycerides (9), total cholesterol, LDL cholesterol (10), and VLDL cholesterol; increases HDL cholesterol (9); and reduces markers of inflammation and thrombosis (11). Metformin therapy in gestational diabetes mellitus achieves maternal glucose control and pregnancy outcomes similar to insulin therapy (12,13).In contrast to insulin, metformin crosses the placenta (14) and, therefore, could directly influence fetal metabolism. Our recent follow-up studies in 2-year-old offspring of women enrolled in the Metformin in Gestational Diabetes (MiG) trial showed increased subcutaneous fat measurements with no increase in abdominal adiposity or total fat (15). Further assessments are required to determine whether metformin actually reduces visceral/ectopic fat. Therefore, we hypothesized that metformin would be more effective than insulin in improving markers of insulin sensitivity and cardiovascular risk during pregnancy and postpartum in women with gestational diabetes mellitus and in their newborns.     

Effectiveness of a Computerized Insulin Order Template in General Medical Inpatients With Type 2 Diabetes: A cluster randomized trial

OBJECTIVE

To determine whether an electronic order template for basal-bolus insulin ordering improves mean blood glucose in hospitalized general medical patients with hyperglycemia and type 2 diabetes.

RESEARCH DESIGN AND METHODS

We randomly assigned internal medicine resident teams on acute general medical floors to the use of an electronic insulin order template or usual insulin ordering. We measured diabetes care parameters for 1 month on all patients with type 2 diabetes and blood glucose <60 mg/dl or >180 mg/dl treated by these physicians.

RESULTS

Intervention group patients (n = 65) had mean glucose of 195 ± 66 mg/dl. Control group patients (n = 63) had mean glucose of 224 ± 57 mg/dl (P = 0.004). In the intervention group, there was no increase in hypoglycemia.

CONCLUSIONS

Access to a computer insulin order template was associated with improved mean glucose levels without increasing hypoglycemia in patients with type 2 diabetes.Physiological, basal-bolus insulin prescribing is safe, effective (1), and the standard of care in hospitalized patients with type 2 diabetes and hyperglycemia (2). Yet only about half of such patients are prescribed basal insulin in the hospital (3). Order templates to support basal-bolus insulin prescribing (usually as part of a comprehensive inpatient diabetes quality improvement program) have been effective in improving glycemia in observational trials (4–8). Randomized trials have shown more modest effects (9,10). Knowledge of appropriate insulin ordering is a barrier to ordering basal-bolus insulin among inpatient providers (11–13).We tested the hypothesis that giving internal medicine residents access to an electronic insulin order template would be more effective than usual insulin ordering in lowering mean blood glucose in medical inpatients with type 2 diabetes.     

Minimal Contribution of Fasting Hyperglycemia to the Incidence of Type 2 Diabetes in Subjects With Normal 2-h Plasma Glucose

OBJECTIVE

To assess the relative contribution of increased fasting and postload plasma glucose concentrations to the incidence of type 2 diabetes in subjects with a normal 2-h plasma glucose concentration.

RESEARCH DESIGN AND METHODS

A total of 3,450 subjects with 2-h plasma glucose concentration <140 mg/dl at baseline were followed up in the San Antonio Heart Study (SAHS) and the Botnia Study for 7–8 years. The incidence of type 2 diabetes at follow-up was related to the fasting, 1-h, and 2-h plasma glucose concentrations.

RESULTS

In subjects with 2-h plasma glucose <140 mg/dl, the incidence of type 2 diabetes increased with increasing fasting plasma glucose (FPG) and 1-h and 2-h plasma glucose concentrations. In a multivariate logistic analysis, after adjustment for all diabetes risk factors, the FPG concentration was a strong predictor of type 2 diabetes in both the SAHS and the Botnia Study (P < 0.0001). However, when the 1-h plasma glucose, but not 2-h plasma glucose, concentration was added to the model, FPG concentration was no longer a significant predictor of type 2 diabetes in both studies (NS). When subjects were matched for the level of 1-h plasma glucose concentration, the incidence of type 2 diabetes markedly increased with the increase in 1-h plasma glucose, but the increase in FPG was not associated with a significant increase in the incidence of type 2 diabetes.

CONCLUSIONS

An increase in postload glycemia in the normal range is associated with an increase in the incidence of type 2 diabetes. After controlling for 1-h plasma glucose concentration, the increase in FPG concentration is not associated with an increase in the incidence of type 2 diabetes.Impaired fasting glucose (IFG) was introduced in 1997 by the American Diabetes Association (ADA) (1), and, analogous with impaired glucose tolerance (IGT), it was meant to represent an intermediate stage in the transition from normal glucose tolerance (NGT) to overt type 2 diabetes. Both IFG and IGT indicate an increased risk for future type 2 diabetes (2–4). Previously (5–7), we have shown that the 1-h plasma glucose concentration has better predictive power than either fasting plasma glucose (FPG) or 2-h plasma glucose, suggesting that the 1-h plasma glucose concentration may have greater utility in identifying subjects at increased risk for type 2 diabetes in routine clinical practice.Previous studies have reported that IFG and IGT represent separate clinical entities, which are characterized by distinct metabolic abnormalities (8–13). Subjects with IGT manifest insulin resistance in skeletal muscle (9–12) and impaired β-cell function (both early and late phases of insulin secretion) (10,14–16), whereas subjects with IFG are characterized by increased hepatic insulin resistance (9,16), impaired early insulin response (12), and decreased non–insulin-dependent glucose clearance (15). Because of the prominent role of progressive β-cell failure in the development of hyperglycemia (17), the impairment in β-cell function in subjects with IGT represents a major pathogenic factor for their increased risk for future type 2 diabetes. Although the increase in fasting plasma glucose is associated with a decrease in first-phase insulin secretion (11–13,18), subjects with IFG have robust second-phase insulin secretion, and, when related to their prevailing level of insulin resistance, they have second-phase insulin secretion comparable with that of subjects with NGT (12,13). Thus, impaired β-cell function cannot fully explain the increased incidence of type 2 diabetes associated with the increase in FPG concentration, e.g., in subjects with isolated IFG.Previously we have shown a strong correlation between insulin resistance in skeletal muscle and liver (16). Thus, a strong correlation between FPG and postload plasma glucose concentrations is anticipated. Therefore, we hypothesized that the increased type 2 diabetes risk associated with the increase in FPG, at least in part, is due to the increased postprandial plasma glucose concentration associated with the increase in FPG and is not due to the increase in FPG per se. The aim of this study was to test this hypothesis.     

TRAF-interacting Protein (TRIP): A Novel Component of the Tumor Necrosis Factor Receptor (TNFR)- and CD30-TRAF Signaling Complexes That Inhibits TRAF2-mediated NF-κB Activation

Through their interaction with the TNF receptor–associated factor (TRAF) family, members of the tumor necrosis factor receptor (TNFR) superfamily elicit a wide range of biological effects including differentiation, proliferation, activation, or cell death. We have identified and characterized a novel component of the receptor–TRAF signaling complex, designated TRIP (TRAF-interacting protein), which contains a RING finger motif and an extended coiled-coil domain. TRIP associates with the TNFR2 or CD30 signaling complex through its interaction with TRAF proteins. When associated, TRIP inhibits the TRAF2-mediated NF-κB activation that is required for cell activation and also for protection against apoptosis. Thus, TRIP acts as a receptor–proximal regulator that may influence signals responsible for cell activation/proliferation and cell death induced by members of the TNFR superfamily.Members of the TNF receptor (TNFR)¹ superfamily play important roles in the induction of diverse signals leading to cell growth, activation, and apoptosis (1). Whether the signals induced by a given receptor leads to cell activation or death is, however, highly cell-type specific and tightly regulated during differentiation of cells. For example, the TNFRs can exert costimulatory signals for proliferation of naive lymphocytes but also induce death signals required for deletion of activated T lymphocytes (1). The cytoplasmic domains of these receptors lack intrinsic catalytic activity and also exhibit no significant homology to each other or to other known proteins. Exceptions to this include Fas(CD95) and TNFR1 that share a significant homology within an 80–amino acid region of their cytoplasmic tails (called the “death domain”; 2, 3). Therefore, it is suggested that the TNFR family members can initiate different signal transduction pathways by recruiting different types of intracellular signal transducers to the receptor complex (1).Indeed, several types of intracellular signal transducers have been identified that initiate distinct signal transduction pathways when recruited to the members of TNFR superfamily (4–19). Recent biochemical and molecular studies showed that a class of signal-transducing molecules are recruited to Fas(CD95) or TNFR1 via interaction of the death domains (2, 3, 6, 12, 17, 20). For example, Fas(CD95) and TNFR1 recruit FADD(MORT1)/RIP or TRADD/FADD (MORT1)/RIP through the interactions of their respective death domains (2, 3, 6, 12, 17, 20, 21). Clustering of these signal transducers leads to the recruitment of FLICE/ MACH, and subsequently, to cell death (13, 14).The TNFR family members can also recruit a second class of signal transducers called TRAFs (TNFR-associated factor), some of which are responsible for the activation of NF-κB or JNK (9, 20, 22). TRAF proteins were identified by their biochemical ability to interact with TNFR2, CD40, CD30, or LT-βR (4, 5, 10, 11, 15, 23–27). These receptors interact directly with TRAFs via a short stretch of amino acids within their cytoplasmic tails, but do not interact with the death domain containing proteins (4, 5, 15, 24–27). To date, five members of the TRAF family have been identified as signaling components of the TNFR family members. All TRAF members contain a conserved TRAF domain, ∼230 amino acids in length, that is used for either homo- or heterooligomerization among the TRAF family, for interactions with the cytoplasmic regions of the TNFR superfamily, or for interactions with downstream signal transducers (4, 5, 8, 10, 11, 19, 23–25, 28). In addition to the TRAF domain, most of the TRAF family members contain an NH₂-terminal RING finger and several zinc finger structures, which appear to be important for their effector functions (4, 5, 10, 11, 23–25).Several effector functions of TRAFs were revealed by recent experiments based on a transfection system. TRAF2, first identified by its interaction with TNFR2 (4), was subsequently shown to mediate NF-κB activation induced by two TNF receptors, CD40 and CD30 (9, 28–30). TRAF5 was also implicated in NF-κB activation mediated by LTβR (10), whereas TRAF3 (also known as CRAF1, CD40bp, or LAP1; references 5, 11, 24, and 25) was shown to be involved in the regulation of CD40-mediated CD23 upregulation in B cells (5). The role of other TRAF members in the TNFR family–mediated signal transduction is not clear. They may possess some effector functions as yet to be revealed, or work as adapter proteins to recruit different downstream signal transducers to the receptor complex. For example, TRAF1 is required for the recruitment of members of the cellular inhibitor of apoptosis protein (c-IAP) family to the TNFR2-signaling complex (7). In addition to the signal transduction by the TNFR family members, TRAFs may regulate other receptor-mediated signaling pathways. For example, TRAF6 is a component of IL-1 receptor (IL1R)–signaling complex, in which it mediates the activation of NF-κB by IL-1R (31). Since TRAFs form homo- or heterooligomers, it is suggested that the repertoire of TRAF members in a given cell type may differentially affect the intracellular signals triggered by these receptors. This may be accomplished by the selective interaction of TRAFs with a specific set of downstream signal transducers. Although many aspects of TRAF-mediated effector functions leading to cellular activation have been defined, it needs to be determined whether TRAF proteins will also mediate the apoptotic signals induced by the “death-domain-less” members of the TNFR superfamily (1, 27, 32–36).Here we report the isolation and characterization of a novel component of the TNFR superfamily/TRAFs signaling complex, named TRIP (TRAF-interacting protein). TRIP associates with the receptor/TRAF signaling complex, and inhibits the TRAF2-mediated NF-κB activation. Biochemical studies indicate that TRIP associates with the TNFR2 or CD30 receptor complex via its interaction with TRAF proteins, suggesting a model which can explain why the ligation of these receptors can promote different cell fates: proliferation or death.     

A New Mechanism of NK Cell Cytotoxicity Activation: The CD40–CD40 Ligand Interaction

NK recognition is regulated by a delicate balance between positive signals initiating their effector functions, and inhibitory signals preventing them from proceeding to cytolysis. Knowledge of the molecules responsible for positive signaling in NK cells is currently limited. We demonstrate that IL-2–activated human NK cells can express CD40 ligand (CD40L) and that recognition of CD40 on target cells can provide an activation pathway for such human NK cells. CD40-transfected P815 cells were killed by NK cell lines expressing CD40L, clones and PBLderived NK cells cultured for 18 h in the presence of IL-2, but not by CD40L-negative fresh NK cells. Cross-linking of CD40L on IL-2–activated NK cells induced redirected cytolysis of CD40-negative but Fc receptor-expressing P815 cells. The sensitivity of human TAP-deficient T2 cells could be blocked by anti-CD40 antibodies as well as by reconstitution of TAP/MHC class I expression, indicating that the CD40-dependent pathway for NK activation can be downregulated, at least in part, by MHC class I molecules on the target cells. NK cell recognition of CD40 may be important in immunoregulation as well as in immune responses against B cell malignancies.NK cells represent a distinct lineage of lymphocytes that are able to kill a variety of tumor (1), virus-infected (2), bone marrow transplanted (3), and allogeneic target cells (4). NK cells do not express T cell receptors or immunoglobulins and are apparently normal in mice with defects in the recombinase machinery (5, 6).Our knowledge about NK cell specificity has increased considerably in the last years. NK cells can probably interact with target cells by a variety of different cell surface molecules, some involved in cell adhesion, some activating the NK cytolytic program (7, 8), and other ones able to inhibit this activation by negative signaling (as reviewed in reference 9).A common feature of several inhibitory NK receptors is the capability to bind MHC class I molecules (10, 11), as predicted by the effector inhibition model within the missing self hypothesis of recognition by NK cells (12–14). Interestingly, the MHC class I receptors identified so far belong to different gene families in mouse and man; these are the p58/p70/NKAT or killer cell inhibitory receptors (KIR)¹ of the immunoglobulin superfamily in man and the Ly49 receptors of the C-type lectin family in the mouse. There is also evidence that MHC class I molecules can be recognized as triggering signals in NK cells of humans, rats as well as mice (13). The inhibitory receptors allow NK cells to kill tumor or normal cell targets with deficient MHC class I expression (12, 14). This does not exclude that other activating pathways can override inhibition by MHC class I molecules (15) and, even in their absence, there must be some activating target molecules that initiate the cytolytic program. Several surface molecules are able to mediate positive signals in NK cells. Some of these structures, like NKRP1 (16), CD69 (17), and NKG2 (18) map to the NK complex region (NKC) of chromosome 6 in mice and of chromosome 12 in humans (13). CD2 (19) and CD16 (20) molecules can also play a role in the activation pathway.NK cells resemble T cells in many respects, both may arise from an immediate common progenitor (21, 22), and share the expression of several surface molecules (23). NK cells produce cytokines resembling those secreted by some helper T cell subsets (24) and contain CD3 components in the cytoplasm (21). The expression of some surface structures, involved in TCR-dependent T cell costimulation, like CD28 in human (25), has been described on NK cells, but the functional relevance of these molecules for NK activation processes has not been fully established.Another T cell molecule of interest is CD40L, which interacts with CD40, a 50-kD membrane glycoprotein expressed on B cells (26), dendritic cells (27), and monocytes (28). CD40 is a member of the tumor necrosis factor/nerve growth factor receptor family (29) which includes CD27 (30), CD30 (31), and FAS antigen (32). Murine and human forms of CD40L had been cloned and found to be membrane glycoproteins with a molecular mass of ∼39 kD induced on T cells after activation (33). Also mast cells (34), eosinophils (35), and B cells (36) can be induced to express a functional CD40L. The CD40L–CD40 interaction has been demonstrated to be necessary for T cell–dependent B cell activation (33, 37). Mutations in the CD40L molecule cause a hyper-IgM immunodeficiency condition in man (38, 39, 40). On the other hand, CD40–CD40L interactions also orchestrate the response of regulatory T cells during both their development (41, 42) and their encounter with antigen (43, 44).NK cells have also been suggested to play a role in B cell differentiation and immunoglobulin production (45). Therefore, it was of interest to investigate whether NK cells could use a CD40-dependent pathway in their interactions with other cells. Therefore, we have investigated the ability of target cells expressing CD40 to induce activation of NK cytotoxicity.     

Racial and Ethnic Differences in an Estimated Measure of Insulin Resistance Among Individuals With Type 1 Diabetes

OBJECTIVE

Insulin resistance is greater in racial/ethnic minorities than in non-Hispanic whites (NHWs) for those with and without type 2 diabetes. Because previous research on insulin resistance in type 1 diabetes was limited to NHWs, racial/ethnic variation in an estimated measure of insulin resistance in type 1 diabetes was determined.

RESEARCH DESIGN AND METHODS

The sample included 79 individuals with type 1 diabetes diagnosed at age <18 years (32.9% NHWs, 46.8% non-Hispanic black [NHB], 7.6% other/mixed, and 12.7% Hispanic) and their families. Estimated glucose disposal rate (eGDR) (milligrams per kilogram per minute; a lower eGDR indicates greater insulin resistance) was calculated using A1C, waist circumference, and hypertension status.

RESULTS

Mean current age was 13.5 years (range 3.2–32.5) and diabetes duration was 5.7 years (0.1–19.9). eGDR was inversely associated with age. Compared with that in NHWs, age-adjusted eGDR was significantly lower among nonwhites (NHB, other/mixed, and Hispanic: Δ = −1.83, P = 0.0006). Age-adjusted eGDR was negatively associated with body fat, triglycerides, urinary albumin/creatinine, acanthosis nigricans, parental obesity, and parental insulin resistance and positively related to HDL and sex hormone–binding globulin. In multivariable analysis, lower eGDR was significantly associated with older age, nonwhite race/ethnicity, acanthosis, and lower HDL.

CONCLUSIONS

Minorities with type 1 diabetes are significantly more insulin resistant, as measured by eGDR, than NHWs. Exploring potential mechanisms, including disparities in care and/or physiological variation, may contribute to preventing racial/ethnic differences in insulin resistance–associated outcomes.Insulin resistance is common in type 2 diabetes (1) and seems to play a role in the natural history (2) and risk of complications (3) in type 1 diabetes as well. Measurement of insulin resistance in type 1 diabetes is difficult because methods used in nondiabetic and type 2 individuals, e.g., insulin or homeostasis model assessment (4), cannot be used in hypoinsulinemia. The euglycemic-hyperinsulinemic clamp has been used; however, it is labor-intensive and invasive and therefore is not suitable for population-based studies. In response, a derived measure of insulin resistance, the estimated glucose disposal rate (eGDR), has been developed using clinical measures and is strongly correlated with clamp-measured insulin resistance (5).Consistent with clamp studies in type 1 diabetes (2), lower eGDR is associated with older age (6), longer duration of diabetes (6), greater adiposity (6), family history of type 2 diabetes (5), poor glycemic control (5), and elevated lipids (6). Low eGDR predicts incident retinopathy (3), nephropathy (3,6), neuropathy (7), and cardiovascular disease in type 1 diabetes (3,6). These findings are primarily based on non-Hispanic white (NHW) adults.Previous research shows racial/ethnic differences in insulin resistance for healthy individuals and those with type 2 diabetes. For example, minority adults with and without type 2 diabetes were more insulin resistant than their NHW counterparts (1,8). Similarly, in nondiabetic youth, minorities were more insulin resistant than NHWs (9,10). Despite these findings, to our knowledge, there are no data on insulin resistance in minorities with type 1 diabetes.Therefore, we sought to determine 1) whether racial/ethnic differences in insulin resistance, as measured by eGDR, exist in type 1 diabetes and 2) whether the association of eGDR with factors traditionally related to insulin resistance differed by race/ethnicity. It was hypothesized that insulin resistance is greater in minorities than in whites and that associations with insulin resistance are consistent across race/ethnicity.     

A Study of Dapagliflozin in Patients With Type 2 Diabetes Receiving High Doses of Insulin Plus Insulin Sensitizers: Applicability of a novel insulin-independent treatment

OBJECTIVE

To determine whether dapagliflozin, which selectively inhibits renal glucose reabsorption, lowers hyperglycemia in patients with type 2 diabetes that is poorly controlled with high insulin doses plus oral antidiabetic agents (OADs).

RESEARCH DESIGN AND METHODS

This was a randomized, double-blind, three-arm parallel-group, placebo-controlled, 26-center trial (U.S. and Canada). Based on data from an insulin dose-adjustment setting cohort (n = 4), patients in the treatment cohort (n = 71) were randomly assigned 1:1:1 to placebo, 10 mg dapagliflozin, or 20 mg dapagliflozin, plus OAD(s) and 50% of their daily insulin dose. The primary outcome was change from baseline in A1C at week 12 (dapagliflozin vs. placebo, last observation carried forward [LOCF]).

RESULTS

At week 12 (LOCF), the 10- and 20-mg dapagliflozin groups demonstrated −0.70 and −0.78% mean differences in A1C change from baseline versus placebo. In both dapagliflozin groups, 65.2% of patients achieved a decrease from baseline in A1C ≥0.5% versus 15.8% in the placebo group. Mean changes from baseline in fasting plasma glucose (FPG) were +17.8, +2.4, and −9.6 mg/dl (placebo, 10 mg dapagliflozin, and 20 mg dapagliflozin, respectively). Postprandial glucose (PPG) reductions with dapagliflozin also showed dose dependence. Mean changes in total body weight were −1.9, −4.5, and −4.3 kg (placebo, 10 mg dapagliflozin, and 20 mg dapagliflozin). Overall, adverse events were balanced across all groups, although more genital infections occurred in the 20-mg dapagliflozin group than in the placebo group.

CONCLUSIONS

In patients receiving high insulin doses plus insulin sensitizers who had their baseline insulin reduced by 50%, dapagliflozin decreased A1C, produced better FPG and PPG levels, and lowered weight more than placebo.Treatment of hyperglycemia in patients with type 2 diabetes remains a challenge, particularly in those who require insulin as the disease progresses (1,2). Various combinations of insulin with oral antidiabetic agents (OADs) have been investigated (2–8). Often, these combination therapies become less effective in controlling hyperglycemia over time, particularly as a result of weight gain and worsening insulin resistance as well as progressive failure of insulin secretion.Hypoglycemia, weight gain, and subsequent increased insulin resistance are significant factors that limit optimal titration and effectiveness of insulin (2). Weight gain with insulin therapy, used alone or with OADs (7–9), is in part a consequence of reducing glucosuria (10,11). Among commonly used OADs, thiazolidinediones (TZDs) and sulfonylureas intrinsically contribute to weight gain, whereas metformin causes weight loss and dipeptidyl peptidase-4 inhibitors are weight neutral. Overall, there is a need for novel agents that can be safely administered to help achieve glycemic targets without increasing the risks of weight gain or hypoglycemia.A novel approach to treating hyperglycemia targets receptors for renal glucose reabsorption (12). Agents that selectively block sodium-glucose cotransporter 2 (SGLT2), located in the proximal tubule of the kidney, inhibit glucose reabsorption and induce its elimination through urinary excretion (13). Preclinical models have shown that SGLT2 inhibition lowers blood glucose independently of insulin (14–17). Dapagliflozin, a highly selective inhibitor of SGLT2, has demonstrated efficacy, alone or in combination with metformin, in reducing hyperglycemia in patients with type 2 diabetes (18,19) but has not been tested in patients requiring insulin. This study was designed to determine whether dapagliflozin is effective in lowering blood glucose in patients with type 2 diabetes who have not responded adequately to insulin combined with oral therapies that act through insulin-dependent mechanisms.