Influence of atherosclerosis‐related risk factors on serum high‐sensitivity C‐reactive protein levels in patients with type 2 diabetes: Comparison of their influence in obese and non‐obese patients

Aims/Introduction

Increased levels of high‐sensitivity C‐reactive protein (hs‐CRP) likely leads to the development of atherosclerosis. Therefore, it is very important to know which factors largely influence hs‐CRP levels. In the present study, we examined the influence of various atherosclerosis‐related factors on hs‐CRP levels in patients with type 2 diabetes.

Materials and Methods

A total of 275 patients (176 men, 99 women) were enrolled in this study. We tested the relationship between the number of risk factors reaching a desired value and hs‐CRP levels. The Mann–Whitney U‐test was used to compare two groups. The Kruskal–Wallis test was used to carry out overall group comparisons, and the Steel–Dwass test was used to carry out between‐group comparisons. Spearman''s rank correlation was carried out to study the correlation between hs‐CRP levels and clinical parameters. Multivariate regression method was used to analyze the factors independently contributing to hs‐CRP levels.

Results

Hs‐CRP levels were lower in patients with a larger number of risk factors reaching a desired value. In particular, triglyceride and body mass index (BMI) were independent risk factors determining hs‐CRP levels in a multivariate regression analysis. Furthermore, we compared the influence of various factors on hs‐CRP levels in both obese (BMI ≥25 kg/m²) and non‐obese patients with type 2 diabetes (BMI <25 kg/m²). In obese groups, BMI and urinary albumin were independent risk factors determining hs‐CRP levels, whereas triglyceride and statin were independent risk factors in non‐obese patients.

Conclusions

There is some difference in the factors responsible for hs‐CRP levels in obese and non‐obese patients with type 2 diabetes.     

Combination therapy with an angiotensin‐converting‐enzyme inhibitor and an angiotensin II receptor antagonist ameliorates microinflammation and oxidative stress in patients with diabetic nephropathy

Aims/Introduction

Recent studies have pointed to the effectiveness of combination therapy with an angiotensin‐converting‐enzyme inhibitor (ACEI) and an angiotensin receptor blocker (ARB) for diabetic nephropathy. However, some controversy over this combination treatment remains and the mechanisms underlying its renoprotective effects have not been fully clarified. Therefore, we compared the renoprotective effects of imidapril (ACEI) and losartan (ARB) combination therapy with losartan monotherapy in patients with diabetic nephropathy. We also compared the anti‐inflammatory and anti‐oxidative stress effects of these two treatments.

Materials and Methods

A total of 32 Japanese patients with type 2 diabetes and nephropathy were enrolled. Patients were randomized to either 100 mg/day losartan (n = 16) or 50 mg/day losartan plus 5 mg/day imidapril (n = 16). We evaluated clinical parameters, serum concentrations of high‐sensitivity C‐reactive protein (hs‐CRP), soluble intercellular adhesion molecule‐1 (sICAM‐1), interleukin‐18 (IL‐18) and monocyte chemotactic protein‐1 (MCP‐1), and the urinary concentrations of IL‐18, MCP‐1 and 8‐hydroxy‐2′‐deoxyguanosine (8‐OHdG) at 24 and 48 weeks after starting treatment.

Results

Blood pressure was not significantly different between the two groups. The serum levels of hs‐CRP, sICAM‐1 and IL‐18, as well as urinary excretion of albumin, IL‐18 and 8‐OHdG decreased significantly in the combination therapy group at 48 weeks. The percent decreases in serum IL‐18 concentrations and urinary IL‐18 and 8‐OHdG were significantly greater in the combination therapy group than in the monotherapy group.

Conclusions

Combination therapy with an ACEI and an ARB could be beneficial for treating diabetic nephropathy through its anti‐inflammatory and anti‐oxidative stress effects.     

Association of serum bilirubin levels with development and progression of albuminuria,and decline in estimated glomerular filtration rate in patients with type 2 diabetes mellitus

Aims/Introduction

Recent observational studies suggest elevated levels of bilirubin, an endogenous anti‐oxidant, might protect against kidney disease. We carried out an observational cohort study to assess whether higher baseline levels of bilirubin, within normal range, could predict the rate of development and progression of diabetic nephropathy in patients with type 2 diabetes.

Materials and Methods

Japanese type 2 diabetic patients with normo‐ or microalbuminuria and normal serum bilirubin (<1.2 mg/dL) were recruited from a single center, and categorized according to baseline serum bilirubin levels. Two independent end‐points were specified: development or progression of diabetic nephropathy, based on transition to a more advanced stage of albuminuria (albuminuria cohort), and the rate of change in estimated glomerular filtration rate (eGFR cohort).

Results

Albuminuria and eGFR cohorts were constructed consisting of 1,915 patients and 1,898 patients, respectively, with 1,738 patients overlapping. Mean follow up was 4.4 and 5.4 years for the two cohorts, respectively. Within the albuminuria cohort, 132 (9%) of 1,418 patients with normoalbuminuria developed microalbuminuria, and 56 (11%) of 497 patients with microalbuminuria developed macroalbuminuria. Higher baseline bilirubin levels were associated with significantly lower risk of progression from microalbuminuria to macroalbuminuria in both the univariate and multivariate analyses. In normoalbuminuric patients, an inverse association was found when restricted to a subgroup with elevated hemoglobin A1c levels. There was no relationship between bilirubin levels and the rate of change in eGFR.

Conclusions

Higher serum bilirubin levels, within normal range, might be predictive of a lower risk of progression of nephropathy in type 2 diabetic patients.     

Age‐associated changes of islet endocrine cells and the effects of body mass index in Japanese

Aims/Introduction

Impaired growth and premature death of β‐cells are implicated in the progression of islet pathology in type 2 diabetes. It remains unclear, however, how aging affects islet cells, or whether the islet change in diabetes is an augmented process of aging. We studied age‐related changes of the islet structure in Japanese non‐diabetic subjects and explored the underlying mechanism of the changes.

Materials and Methods

A total of 115 non‐diabetic autopsy cases were subjected to morphometric analysis for volume densities of islets, β‐ and non‐β‐cells, as well as their masses. Proliferation activity identified by Ki67, and expressions of pancreatic and duodenal homeobox (PDX)‐1, cell cycle inhibitor P16, and oxidative stress marker γH2AX were also examined.

Results

There was a gradual and marginal decline of volume densities of islets, β‐ and non‐β‐cells with aging, while masses of these components were increased during maturation and slowly decreased after the 40s. Islet density was high in the young, but reduced after maturation. There was only a minimal influence of increased body mass index (BMI) on the increase in β‐cell mass, but not on the other variables. Ki67 positivity and PDX‐1 expressions were high in the young, but low after maturation, whereas expressions of P16 and γH2AX were elevated in the aged.

Conclusions

Age‐associated decline of β‐cell mass is marginal after maturation, and the reduction of β‐cell mass could be a specific process in diabetes. The impact of BMI on the islet structure is limited in Japanese with normal glucose tolerance.     

Oral glucose‐stimulated serum C‐peptide predicts successful switching from insulin therapy to liraglutide monotherapy in Japanese patients with type 2 diabetes and renal impairment

Aims/Introduction

In Japan, liraglutide was recently approved for patients with type 2 diabetes. To our knowledge, there are no markers predicting successful switching from insulin therapy to liraglutide monotherapy in Japanese patients with type 2 diabetes and renal impairment. We therefore assessed clinical characteristics predicting successful switching.

Materials and Methods

We analyzed 21 patients with type 2 diabetes and estimated glomerular filtration rates <60 mL/min/1.73 m² receiving long‐term insulin in Shiga University of Medical Science Hospital, Otsu, Shiga, Japan. Their β‐cell function was assessed by measuring urinary C‐peptide and C‐peptide immunoreactivity (CPR) index, along with glucagon loading and oral glucose tolerance tests. Blood glucose concentration and blood pressure were measured daily before and after switching from insulin to liraglutide, and glycated hemoglobin (HbA1c; National Glycohemoglobin Standardization Program) was assessed 12 weeks after switching to liraglutide.

Results

Baseline HbA1c was significantly lower in successfully switched than in unsuccessfully switched patients. CPR index, urinary C‐peptide concentration and 6‐min post‐glucagon increment in CPR (ΔCPR) did not differ significantly in the two groups. ΔCPR 120 min after 75 g oral glucose was significantly higher in successfully than unsuccessfully switched patients. Mean blood glucose concentrations before breakfast, after breakfast, before lunch and after dinner were significantly lower in successfully switched patients. HbA1c did not change significantly in either group.

Conclusions

Measurement of oral glucose‐stimulated ΔCPR120 min is recommended when considering switching Japanese type 2 diabetes patients with renal impairment from insulin to liraglutide monotherapy.     

Albuminuria: Prevalence,associated risk factors and relationship with cardiovascular disease

Aims/Introduction

To investigate the prevalence and associated risk factors of microalbuminuria, and to explore the relationship between albuminuria and cardiovascular disease (CVD).

Materials and Methods

A nationally representative sample of 38,203 Chinese participants was categorized by different levels of urinary albumin‐to‐creatinine ratio (ACR; 0 –10 mg/g, 10 –20 mg/g, 20 –30 mg/g, 30 –300 mg/g). The prevalence of albuminuria was compared by using a single urinary ACR cut‐off point and by sex‐specific ACR cut‐off points. Factors associated with the presence of albuminuria, and the relationship between albuminuria and CVD were analyzed by logistic regression.

Results

Prevalence of albuminuria as measured by a single ACR cut‐point was significantly lower for men compared with women (13.9% vs 19.1% in the normal glucose tolerance group; 20.8% vs 26.8% in the impaired glucose tolerance group, P < 0.01). The prevalence of albuminuria, as measured by sex‐specific ACR cut‐points, was higher for men than women (31.4% vs 29.6% in the normal glucose tolerance group; 42.2% vs 39.3% in the impaired glucose tolerance group, P < 0.01). The independent risk factors for the presence of albuminuria were aging, female sex, hypertension, hyperglycemia, obesity, dyslipidemia, insulin resistance and metabolic syndrome. The subdivided normal ACR group did not show a linear or statistically significant relationship with CVD after adjusting for conventional CVD risk factors (P > 0.05).

Conclusions

The prevalence of albuminuria was high in the general Chinese population. Aging, female sex, hypertension, hyperglycemia, dyslipidemia, insulin resistance, obesity and metabolic syndrome were all independent risk factors for albuminuria. The causal relationship between ACR and CVD might require further follow‐up investigation.     

Sitagliptin improves albuminuria in patients with type 2 diabetes mellitus

Introduction

The aim of the present study was to determine the effect of sitagliptin on microalbuminuria in patients with type 2 diabetes mellitus.

Materials and Methods

A total of 85 patients with type 2 diabetes mellitus (age >20 years, <80 years, hemoglobin A1c [HbA1c] <8.4%) were randomized to patients taking sitagliptin 50 mg or other oral glucose‐lowering agents. The following parameters were evaluated at 0, 3 and 6 months after the treatment: bodyweight, blood pressure, HbA1c, fasting plasma glucose, fasting plasma insulin, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, triglycerides, estimated glomerular filtration rate and urinary albumin excretion. The primary outcome was changes in urinary albumin excretion at 6 months.

Results

Significant and comparable falls in HbA1c and fasting plasma glucose were found in both groups. However, sitagliptin significantly reduced urinary albumin excretion within 6 months, especially in patients with high urinary albumin at baseline. A total of 27 patients with normoalbuminuria showed a reduction in urinary albumin excretion, suggesting that sitagliptin prevents the development of albuminuria. A total of 15 patients with albuminuria showed a reduction in urinary albumin excretion, suggesting the beneficial effect of sitagliptin in the early stage of diabetic nephropathy. There was a significant correlation between improvement of proteinuria and that of diastolic blood pressure.

Conclusions

The results suggested that sitagliptin improved albuminuria, in addition to improving glucose. The mechanism of the reduction of albuminuria by sitagliptin could be a direct effect, as well as an increase in active glucagon‐like peptide‐1, independently affecting blood pressure, bodyweight and glucose metabolism. This trial was registered with the University Hospital Medical Information Network (UMIN no. #000010871).     

Significance of renal biopsy in patients with presumed diabetic nephropathy

Aims/Introduction

Patients with diabetic nephropathy (DN) typically show varying degrees of proteinuria and renal impairment. Because these clinical signs are frequently observed in other glomerulopathies, renal biopsy is required to make a definitive diagnosis of DN. We carried out the present study to evaluate the significance of renal biopsy for patients who have been presumptively diagnosed with DN.

Materials and Methods

A total of 55 patients with type 2 diabetes mellitus (DM), and proteinuria, hematuria and/or renal impairment were enrolled in this study.

Results

Renal biopsy showed that just 30 patients (54.5%) were histologically diagnosed with DN. Fasting plasma glucose and glycated hemoglobin levels were associated with the presence of DN, whereas baseline renal function showed no statistically significant relationship to DN. The duration of DM was not associated with the presence of DN. Patients with DN had a higher rate of diabetic retinopathy (DR) than those with non‐DN (DN 18 patients vs non‐DN three patients, P = 0.00029). DN patients with DR showed a more severe renal histology than those without.

Conclusions

These data suggest that, even for patients with long‐term DM, renal biopsy should be carried out in patients with presumed DN. Because treatment options differ between DN and primary glomerulopathies, renal biopsy should especially be considered for presumed DN without DR.     

Secretory units of islets in transplantation index is a useful predictor of insulin requirement in Japanese type 2 diabetic patients

Aims/Introduction

The objective of the present study was to clarify the validity of β‐cell function‐related parameters for predicting the insulin requirement of Japanese type 2 diabetic patients.

Materials and Methods

In 188 patients with type 2 diabetes who had been admitted to the University of Toyama Hospital (Toyama, Japan) without receiving insulin therapy, we carried out a cross‐sectional study examining the relationship between the homeostasis model assessment of β‐cell function (HOMA‐β) and C‐peptide‐based indices, and also carried out a retrospective study to examine the utility for predicting insulin requirement of several β ‐cell function‐related indices using a receiver operating characteristic (ROC) curve analysis.

Results

The secretory units of islets in transplantation index (SUIT) had the strongest correlation with HOMA‐β, followed by the fasting serum C‐peptide immunoreactivity index (CPI); the fasting serum C‐peptide immunoreactivity itself (F‐CPR) had the least correlation. The CPI, HOMA‐β and SUIT were significantly lower in the insulin‐requiring group than in the non‐insulin‐requiring group, even after adjustments for confounding factors (P < 0.01). The areas under the ROC curve for insulin requirement were 0.622, 0.774, 0.808, and 0.759 for F‐CPR, CPI, SUIT, and HOMA‐β, respectively. The cut‐off values of SUIT, CPI, and HOMA‐β for an over 80% specificity for the prediction of insulin therapy were 23.5, 1.00, and 14.9, respectively.

Conclusions

The present study shows that SUIT is the best predictor of insulin requirement among these β‐cell function‐related markers.     

Postprandial C‐peptide to glucose ratio as a predictor of β‐cell function and its usefulness for staged management of type 2 diabetes

Aims/Introduction

Type 2 diabetes is characterized by progressive deterioration of β‐cell function. Recently, it was suggested that the C‐peptide‐to‐glucose ratio after oral glucose ingestion is a better predictor of β‐cell mass than that during fasting. We investigated whether postprandial C‐peptide‐to‐glucose ratio (PCGR) reflects β‐cell function, and its clinical application for management of type 2 diabetes.

Materials and Methods

We carried out a two‐step retrospective study of 919 Korean participants with type 2 diabetes. In the first step, we evaluated the correlation of PCGR level with various markers for β‐cell function in newly diagnosed and drug‐naïve patients after a mixed meal test. In the second step, participants with well‐controlled diabetes (glycated hemoglobin <7%) were divided into four groups according to treatment modality (group I: insulin, group II: sulfonylurea and/or dipeptityl peptidase IV inhibitor, group III: metformin and/or thiazolidinedione and group IV: diet and exercise group).

Results

In the first step, PCGR was significantly correlated with various insulin secretory indices. Furthermore, PCGR showed better correlation with glycemic indices than homeostatic model assessment of β‐cell function (HOMA‐β). In the second step, the PCGR value significantly increased according to the following order: group I, II, III, and IV after adjusting for age, sex, body mass index and duration of diabetes. The cut‐off values of PCGR for separating each group were 1.457, 2.870 and 3.790, respectively (P < 0.001).

Conclusions

We suggest that PCGR might be a useful marker for β‐cell function and an ancillary parameter in the choice of antidiabetic medication in type 2 diabetes.     

Impact of cigarette smoking on impaired insulin secretion and insulin resistance in Japanese men: The Saku Study

Aims/Introduction

To assess the impact of smoking on impaired insulin secretion and insulin resistance in Japanese men.

Materials and Methods

This study included 1,199 men aged 30–79 years without diabetes, impaired insulin secretion and insulin resistance at baseline who underwent a comprehensive medical check‐up between April 2006 and March 2007 at Saku Central Hospital. Smoking status was categorized as current, ex‐smoker and never‐smoker. Insulinogenic index and homeostasis model assessment‐insulin resistance were determined using a standard 75‐g oral glucose tolerance test. The Japan Diabetes Society criteria were used to define impaired insulin secretion and insulin resistance. Participants were followed up until March 2011.

Results

A total of 449 and 99 men developed impaired insulin secretion and insulin resistance during 3,403 and 4,092 person‐years follow up, respectively. The multivariable‐adjusted hazard ratios (HRs) for impaired insulin secretion were 1.06 (95% confidence interval [CI] 0.84–1.33) in ex‐smokers and 1.95 (95% CI 1.44–2.63) in current smokers compared with never‐smokers after adjustment for age, familial history of diabetes, alcohol consumption, exercise, systolic blood pressure, triglyceride, γ‐glutamyltransferase, waist circumference, leukocyte count, changes in smoking status and changes in waist circumference. The number of pack‐years was positively associated with the risk for impaired insulin secretion in a dose‐dependent manner (P‐values for trend <0.001). The multivariable‐adjusted HRs for insulin resistance were 0.95 (95% CI 0.56–1.61) in ex‐smokers and 1.11 (95% CI 0.67–1.79) in current smokers compared with never‐smokers.

Conclusions

Cigarette smoking is a modifiable risk factor for impaired insulin secretion. The findings might also be important for other Asian populations, which have low insulin secreting ability.     

Obesity as an effect modifier of the association between leptin and diabetic kidney disease

Aims/Introduction

Obesity has been shown to be a modifier of the association between leptin levels and cardiovascular events. We examined whether obesity modifies the association between serum leptin levels and the progression of diabetic kidney disease.

Materials and Methods

This was an observational longitudinal study on patients with type 2 diabetes. We enrolled 410 and 348 patients in the eGFR and ACR cohorts, respectively. Patients were classified into three groups by sex‐specific tertile of leptin levels. Obesity was defined as body mass index ≥25 kg/m². Outcomes were the rate of change in estimated glomerular filtration rate (eGFR) and progression to a more advanced stage of albuminuria.

Results

In the eGFR cohort, the mean eGFR change during the median follow‐up period of 4.7 years was −1.4 mL/min/1.73 m²/year. An interaction between leptin levels (low, medium or high) and obesity (present or absent) on the change in eGFR was detected (P interaction = 0.003). In the lean group, adjusted eGFR decline in patients with low leptin was steeper than that in patients with medium leptin (2.1 and 0.8 mL/min/1.73 m²/year, P = 0.023). In the obese group, patients with high leptin had a steeper adjusted eGFR decline than those with medium leptin (1.7 and 0.6 mL/min/1.73 m²/year, P = 0.044). In the ACR cohort, 29 patients showed progression of albuminuria during the median follow‐up period of 3.9 years. There was no interaction between leptin levels and obesity on the outcome (P interaction = 0.094).

Conclusions

Obesity might modify the effects of leptin on kidney function decline in patients with type 2 diabetes.     

Association between serum adipocytokine levels and microangiopathies in patients with type 2 diabetes mellitus

Aims/Introduction

It is thought that adipocytokines contribute to the increased risk of vascular complications in type 2 diabetes. However, there is still limited information on the relationship between microangiopathies and adipocytokines, such as adiponectin, leptin and tumor necrosis factor‐α (TNF‐α) in patients with type 2 diabetes.

Materials and Methods

The present study examined the relationship between fasting serum adiponectin, leptin, and TNF‐α levels and microangiopathies in Korean type 2 diabetes. A total of 153 patients were recruited and evaluated for diabetic nephropathy, retinopathy and neuropathy. Serum adiponectin, TNF‐α and leptin levels were measured.

Results

Serum adiponectin levels were significantly lower in patients with nephropathy than in those without nephropathy (P = 0.017), and were significantly higher in patients with retinopathy or neuropathy than those without retinopathy or neuropathy (P = 0.01 and P = 0.002, respectively). The mean levels of leptin were significantly higher in patients with neuropathy than in those without neuropathy (P = 0.002). The mean levels of TNF‐α were not significantly different according to any of the three microangiopathies. Multivariate logistic regression analysis showed that the odds ratio for the presence of neuropathy in the highest tertile of adiponectin was 4.3 (95% confidence interval 1.59–11.62), as compared with the patients in the lowest tertile of adiponectin level.

Conclusions

Levels of adipocytokines were significantly different according to the presence of each microangiopathy. In particular, higher serum adiponectin was independently associated with increased odds for the presence of neuropathy. Future prospective studies with larger numbers of patients are required to establish a direct relationship between plasma adipocytokine concentrations and the development or severity of diabetic microangiopathies.     

Effect of serum 25‐hydroxyvitamin D3 on insulin resistance and β‐cell function in newly diagnosed type 2 diabetes patients

Aims/Introduction

To evaluate serum 25‐hydroxyvitamin D₃ (25(OH)D₃) in newly diagnosed type 2 diabetes patients and to explore the associations of 25(OH)D₃ with insulin resistance and β‐cell function.

Materials and Methods

A total of 97 newly diagnosed type 2 diabetes patients and 69 healthy controls were recruited. Serum 25(OH)D₃ was determined using high‐pressure liquid chromatography. Insulin resistance was measured using a homeostasis model assessment of insulin resistance (HOMA‐IR). β‐Cell function was determined using the HOMA β‐cell function index (HOMA‐β), early‐phase insulin secretion index (ΔI30/ΔG30) and area under the insulin curve (AUCins). Correlation analysis was carried out using Pearson''s correlation and multiple stepwise regression analysis.

Results

Serum 25(OH)D₃ was much lower in patients with newly diagnosed type 2 diabetes (t = −13.00, P < 0.01), and the prevalence of hypovitaminosis 25(OH)D₃ was 62.9% (61/97) in diabetic patients. Among the diabetic patients, patients with hypovitaminosis 25(OH)D₃ showed higher glycosylated hemoglobin and AUCglu (P < 0.01) as well as lower HOMA‐β, ΔI30/ΔG30 and AUCins. Serum 25(OH)D₃ was independently positively correlated with ΔI30/ΔG30 and AUCins (P < 0.05), but was not significantly correlated with either HOMA‐IR or HOMA‐β. Only triglycerides, glycosylated hemoglobin and ΔI30/ΔG30 emerged as independent factors associated with serum 25(OH)D₃ in both diabetes patients and the health control group.

Conclusions

The present results further showed a low serum 25(OH)D₃ concentration in patients with newly diagnosed type 2 diabetes. 25(OH)D₃ deficiency is associated with disturbances in glucose metabolism and lipid metabolism. Serum 25(OH)D₃ is not correlated with basal insulin resistance or β‐cell function, but is significantly positively correlated with glucose‐stimulated insulin secretion and β‐cell function.     

Transgenic zebrafish model of the C43G human insulin gene mutation

Aims/Introduction

The human insulin gene/preproinsulin protein mutation C43G disrupts disulfide bond formation and causes diabetes in humans. Previous in vitro studies showed that these mutant proteins are retained in the endoplasmic reticulum (ER), are not secreted and are associated with decreased secretion of wild‐type insulin. The current study extends this work to an in vivo zebrafish model. We hypothesized that C43G‐green fluorescent protein (GFP) would be retained in the ER, disrupt β‐cell function and lead to impaired glucose homeostasis.

Materials and Methods

Islets from adult transgenic zebrafish expressing GFP‐tagged human proinsulin mutant C43G (C43G‐GFP) or wild‐type human proinsulin (Cpep‐GFP) were analyzed histologically across a range of ages. Blood glucose concentration was determined under fasting conditions and in response to glucose injection. Insulin secretion was assessed by measuring circulating GFP and endogenous C‐peptide levels after glucose injection.

Results

The majority of β‐cells expressing C43G proinsulin showed excessive accumulation of C43G‐GFP in the ER. Western blotting showed that C43G‐GFP was present only as proinsulin, indicating defective processing. GFP was poorly secreted in C43G mutants compared with controls. Despite these defects, blood glucose homeostasis was normal. Mutant fish maintained β‐cell mass well into maturity and secreted endogenous C‐peptide.

Conclusions

In this model, the C43G proinsulin mutation does not impair glucose homeostasis or cause significant loss of β‐cell mass. This model might be useful for identifying potential therapeutic targets for proper trafficking of intracellular insulin or for maintenance of β‐cell mass in early‐stage diabetic patients.     

Palmitate induces reactive oxygen species production and β‐cell dysfunction by activating nicotinamide adenine dinucleotide phosphate oxidase through Src signaling

Aims/Introduction

Chronic hyperlipidemia impairs pancreatic β‐cell function, referred to as lipotoxicity. We have reported an important role of endogenous reactive oxygen species (ROS) overproduction by activation of Src, a non‐receptor tyrosine kinase, in impaired glucose‐induced insulin secretion (GIIS) from diabetic rat islets. In the present study, we investigated the role of ROS production by Src signaling in palmitate‐induced dysfunction of β‐cells.

Materials and Methods

After rat insulinoma INS‐1D cells were exposed to 0.6 mmol/L palmitate for 24 h (palmitate exposure); GIIS, ROS production and nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity were examined with or without exposure to10 μmol/L 4‐amino‐5‐(4‐chlorophenyl)‐7‐(t‐butyl)pyrazolo[3,4‐d]pyrimidine (PP2), a Src inhibitior, for 30 or 60 min.

Results

Exposure to PP2 recovered impaired GIIS and decreased ROS overproduction as a result of palmitate exposure. Palmitate exposure increased activity of NOX and protein levels of NOX2, a pathological ROS source in β‐cells. Palmitate exposure increased the protein level of p47^phox, a regulatory protein of NOX2, in membrane fraction compared with control, which was reduced by PP2. Transfection of small interfering ribonucleic acid of p47^phox suppressed the augmented p47^phox protein level in membrane fraction, decreased augmented ROS production and increased impaired GΙIS by palmitate exposure. In addition, exposure to PP2 ameliorated impaired GIIS and decreased ROS production in isolated islets of KK‐A^y mice, an obese diabetic model with hyperlipidemia.

Conclusions

Activation of NOX through Src signaling plays an important role in ROS overproduction and impaired GΙIS caused by chronic exposure to palmitate, suggesting a lipotoxic mechanism of β‐cell dysfunction of obese mice.     

Usefulness of the insulin tolerance test in patients with type 2 diabetes receiving insulin therapy

Aims/Introduction

To establish the validity of the plasma glucose disappearance rate (KITT), derived from an insulin‐tolerance test (ITT), for evaluating the insulin sensitivity of patients with type 2 diabetes after insulin therapy.

Materials and Methods

In the first arm of the study, 19 patients with poorly controlled diabetes were treated with insulin and underwent an ITT and a euglycemic clamp test (clamp‐IR). The relationship between the insulin resistance index, as assessed by both the clamp‐IR and KITT tests, was examined. In the second arm of the study, the relationships between KITT values and various clinical parameters were investigated in 135 patients with poorly controlled diabetes, after achieving glycemic control with insulin.

Results

In study 1, a close correlation between KITT and the average glucose infusion rate during the last 30 min of the standard clamp‐IR test (M‐value) was noted (P < 0.001). In study 2, body mass index (P = 0.0011), waist circumference (P = 0.0004), visceral fat area (P = 0.0011) and the log‐transformed homeostasis model assessment of insulin resistance value (P = 0.0003) were negatively correlated with the log‐transformed KITT. High‐density lipoprotein cholesterol (P = 0.0183), low‐density lipoprotein cholesterol (P = 0.0121) and adiponectin (P = 0.0384) levels were positively correlated with the log‐transformed KITT.

Conclusions

The ITT is a valid and useful test for evaluating the insulin sensitivity of patients with diabetes, even after treatment with insulin.     

Dipeptidyl peptidase‐4 inhibitors are effective in Japanese type 2 diabetic patients with sustained endogenous insulin‐secreting capacity,a higher body mass index and insulin resistance

Aims/Introduction

Recently, dipeptidyl peptidase‐4 (DPP‐4) inhibitors have become available in Japan. It has not yet been clarified what clinical parameters could discriminate DPP‐4 inhibitor‐effective patients from DPP‐4 inhibitor‐ineffective patients.

Materials and Methods

We reviewed 33 consecutive patients with type 2 diabetes admitted to Osaka University Hospital for glycemic control. All of the patients were treated with medical nutrition therapy plus insulin therapy to improve fasting plasma glucose (FPG) and postprandial glucose below 150 and 200 mg/dL, respectively. After insulin secretion and insulin resistance were evaluated, insulin was replaced by DPP‐4 inhibitors. The efficacy of DPP‐4 inhibitors was determined according to whether glycemic control was maintained at the target levels.

Results

Dipeptidyl peptidase‐4 inhibitors were effective in 16 of 33 patients. DPP‐4 inhibitor‐effective patients were younger than DPP‐4 inhibitor‐ineffective patients. Body mass index (BMI) was significantly higher in DPP‐4 inhibitor‐effective patients. Endogeneous insulin‐secreting capacity, including insulinogenic index (II), fasting plasma C‐peptide (F‐CPR) and C‐peptide index (CPI), was more sustained in DPP‐4 inhibitor‐effective patients than DPP‐4 inhibitor‐ineffective patients. Insulin resistance evaluated by homeostasis model assessment of insulin resistance (HOMA‐IR) was significantly higher in DPP‐4 inhibitor‐effective patients than DPP‐4 inhibitor‐ineffective patients. In receiver operating characteristic analyses, the cut‐off values for predicting the efficacy of DPP‐4 inhibitors were 0.07 for II, 1.5 ng/mL for F‐CPR, 1.0 for CPI, 23.0 kg/m² for BMI, 1.3 for HOMA‐IR and 67.5 years for age.

Conclusions

Dipeptidyl peptidase‐4 inhibitors were effective in Japanese type 2 diabetic patients with sustained endogenous insulin‐secreting capacity, a higher BMI and insulin resistance.