Preservation of ��-Cell Function in Autoantibody-Positive Youth With Diabetes

OBJECTIVE

To determine the extent of β-cell function in youth with diabetes and GAD65 and/or IA2 autoantibodies.

RESEARCH DESIGN AND METHODS

Fasting C-peptide levels from 2,789 GAD65- and/or IA2 autoantibody-positive youth aged 1–23 years from the SEARCH for Diabetes in Youth study were used. Preserved β-cell function was defined on the basis of cut points derived from the Diabetes Control and Complications Trial (DCCT) (fasting C-peptide ≥0.23 ng/ml) and from the U.S. adolescent population of the National Health and Nutrition Examination Survey (NHANES) 5th percentile for fasting C-peptide (≥1.0 ng/ml). We compared the clinical characteristics between those with and without preserved β-cell function.

RESULTS

Within the first year of diagnosis, 82.9% of youth had a fasting C-peptide ≥0.23 ng/ml and 31.2% had values ≥1.0 ng/ml. Among those with ≥5 years of diabetes duration, 10.7% had preserved β-cell function based on the DCCT cutoff and 1.0% were above the 5th percentile of the NHANES population.

CONCLUSIONS

Within the 1st year of diagnosis, four of five youth with autoantibody-positive diabetes have clinically significant amounts of residual β-cell function and about one-third have fasting C-peptide levels above the 5th percentile of a healthy adolescent population. Even 5 years after diagnosis, 1 of 10 has fasting C-peptide above a clinically significant threshold. These findings have implications for clinical classification of youth with diabetes as well as clinical trials aimed to preserve β-cell function after diabetes onset.Immune-mediated β-cell destruction, marked by the presence of diabetes autoantibodies, occurs before and continues after the clinical diagnosis of type 1 diabetes. This model has served as the foundation of pathophysiological studies of the disease process and clinical studies designed to identify future risk for diabetes and to modify clinical course. The resultant perception is that most individuals with type 1 diabetes will have complete destruction of β-cells within a few years after diagnosis without a targeted intervention to sustain β-cell function.Despite frequent use of this model in research and patient care, it represents only part of the picture. Data from placebo-controlled populations in clinical intervention trials suggest that some individuals with type 1 diabetes will have persistent β-cell function years after diagnosis (1,2). The screening phase of the Diabetes Control and Complications Trial (DCCT) demonstrated that 48% of adults had significant C-peptide levels within 5 years of diagnosis, and 8% had significant C-peptide 5–15 years after diagnosis (3). Another study reported similar findings in 15% of individuals with measurable C-peptide levels 8–15 years after diagnosis (4). Multiple studies have reported that the loss of β-cell function after diagnosis is related to age of onset as well as to factors linked to autoimmunity such as autoantibodies (5–11). Nonetheless, there is a common belief that persistence of β-cell function is rare in young children with type 1 diabetes.The SEARCH for Diabetes in Youth (SEARCH) study, designed to determine the prevalence, incidence, and characteristics of diabetes in U.S. youth, provides an opportunity to examine the frequency of residual β-cell function in a population-based sample of GAD65⁺ or IA2⁺ youth with diabetes.     

β-Cell Mass and Turnover in Humans: Effects of obesity and aging

OBJECTIVE

We sought to establish β-cell mass, β-cell apoptosis, and β-cell replication in humans in response to obesity and advanced age.

RESEARCH DESIGN AND METHODS

We examined human autopsy pancreas from 167 nondiabetic individuals 20–102 years of age. The effect of obesity on β-cell mass was examined in 53 lean and 61 obese subjects, and the effect of aging was examined in 106 lean subjects.

RESULTS

β-Cell mass is increased by ∼50% with obesity (from 0.8 to 1.2 g). With advanced aging, the exocrine pancreas undergoes atrophy but β-cell mass is remarkably preserved. There is minimal β-cell replication or apoptosis in lean humans throughout life with no detectable changes with obesity or advanced age.

CONCLUSIONS

β-Cell mass in human obesity increases by ∼50% by an increase in β-cell number, the source of which is unknown. β-Cell mass is well preserved in humans with advanced aging.The incidence of type 2 diabetes increases with obesity and aging (1). There is a deficit in β-cell mass with increased β-cell apoptosis in type 2 diabetes (2). Although there are numerous studies of changes in β-cell mass and turnover in rodents, inevitably the data is much more limited in humans. As there is an increasing appreciation that regulation of β-cell mass in humans and rodents can be quite different, additional studies in humans, where possible, is important. In the current study, we addressed the following questions.First, is β-cell mass adaptively increased in obese humans, and if so, is this through increased β-cell replication as widely reported in rodents? It has been reported that β-cell mass increases with obesity in age-matched individuals but β-cell replication was not reported (3). Second, is β-cell apoptosis increased with obesity? The increased β-cell apoptosis in type 2 diabetes (2) has been ascribed to lipotoxicity, based on increased β-cell apoptosis in rodents with obesity due to deficient leptin signaling (4). Since the relative fat content (fat-to-acinar ratio) accumulates in the pancreas in humans with obesity (5), if this is sufficient to induce increased β-cell apoptosis, then it would be anticipated that humans with marked obesity would have increased β-cell apoptosis.Third, we questioned if β-cell mass adaptively decreases with aging, and if so, is this due to increased β-cell apoptosis? β-Cell function declines in humans with aging (6). The exocrine pancreas undergoes marked atrophy after 60 years of age, but there is limited data available about the changes in β-cell mass with aging, with one study reporting a marginal decline with age (3) but providing no measure of β-cell turnover.     

Noninvasive Imaging of Lipid Nanoparticle�CMediated Systemic Delivery of Small-Interfering RNA to the Liver

Mouse models with liver-specific expression of firefly luciferase were developed that enable a noninvasive and longitudinal assessment of small-interfering RNA (siRNA)–mediated gene silencing in hepatocytes of live animals via bioluminescence imaging. Using these models, a set of lipid nanoparticles (LNPs) with different compositions of cationic lipids, polyethylene glycol (PEG), and cholesterol, were tested for their abilities in delivering a luciferase siRNA to the liver via systemic administration. A dose-dependent luciferase knockdown by LNP/siRNA assemblies was measured by in vivo bioluminescence imaging, which correlated well with the results from parallel ex vivo analyses of luciferase mRNA and protein levels in the liver. RNA interference (RNAi)–mediated target silencing was further confirmed by the detection of RNAi-specific target mRNA cleavage. A single dose of LNP02L at 3 mg/kg (siRNA) caused 90% reduction of luciferase expression and the target repression lasted for at least 10 days. With identical components, LNPs containing 2% PEG are more potent than those with 5.4% PEG. Our results demonstrate that these liver-luciferase mouse models provide a powerful tool for a high-throughput evaluation of hepatic delivery platforms by noninvasive imaging and that the molar ratio of PEG lipid can affect the efficacy of LNPs in silencing liver targets via systemic administration.     

Carriers of Loss-of-Function Mutations in ABCA1 Display Pancreatic ��-Cell Dysfunction

OBJECTIVE

Abnormal cellular cholesterol handling in islets may contribute to β-cell dysfunction in type 2 diabetes. β-Cell deficiency for the ATP binding cassette transporter A1 (ABCA1), which mediates the efflux of cellular cholesterol, leads to altered intracellular cholesterol homeostasis and impaired insulin secretion in mice. We aimed to assess the impact of ABCA1 dysfunction on glucose homeostasis in humans.

RESEARCH DESIGN AND METHODS

In heterozygous carriers of disruptive mutations in ABCA1 and family-based noncarriers of similar age, sex, and BMI, we performed oral glucose tolerance tests (OGTTs) (n = 15 vs. 14) and hyperglycemic clamps (n = 8 vs. 8).

RESULTS

HDL cholesterol levels in carriers were less than half those in noncarriers, but LDL cholesterol levels did not differ. Although fasting plasma glucose was similar between groups, glucose curves after an OGTT were mildly higher in carriers than in noncarriers. During hyperglycemic clamps, carriers demonstrated lower first-phase insulin secretion than noncarriers but no difference in insulin sensitivity. The disposition index (a measure of β-cell function adjusted for insulin sensitivity) of the carriers was significantly reduced in ABCA1 heterozygotes.

CONCLUSIONS

Carriers of loss-of-function mutations in ABCA1 show impaired insulin secretion without insulin resistance. Our data provide evidence that ABCA1 is important for normal β-cell function in humans.The reasons for β-cell dysfunction in type 2 diabetes are incompletely understood. One hypothesis suggests that the accumulation of toxic lipid leads to the loss of insulin secretion characteristic of this disorder (1). Although the role of free fatty acids and triglycerides has been extensively studied (2), much less is known about the role of cholesterol in this process. The ATP-binding cassette transporter, subfamily A, member 1 (ABCA1) regulates the rate-limiting step in cholesterol transport out of cells and is thus a candidate molecule for influencing cholesterol metabolism in β-cells.In humans, homozygosity for naturally occurring loss-of-function mutations in ABCA1 leads to Tangier disease, an extremely rare disorder characterized by near absence of HDL cholesterol in plasma as well as a 30–40% reduction in LDL cholesterol, increased risk of coronary artery disease (CAD), and accumulation of cholesterol in tissues (3). Approximately 100 cases of Tangier disease have been reported worldwide. Heterozygous carriers of loss-of-function mutations in ABCA1, generally ascertained from Tangier disease pedigrees, also exhibit decreased HDL cholesterol levels and accelerated atherogenesis due to impaired removal of cholesterol from lipid-laden macrophages in the presence of relatively normal levels of total plasma cholesterol (4).Targeted deletion of β-cell Abca1 in mice results in accumulation of cholesterol in islets, reduced glucose-stimulated insulin secretion (GSIS), and impaired glucose tolerance (5). In addition, the common ABCA1 polymorphism R230C was shown to be associated with a fourfold increase in the occurrence of diabetes in a Mexican population (6). These novel findings imply an important role for ABCA1 in maintaining glucose-mediated insulin secretion.Interestingly, mice lacking Abca1 specifically in β-cells have a more severe impairment in β-cell function compared with mice lacking Abca1 globally, possibly because of the higher levels of total plasma cholesterol in mice with β-cell–specific deletion of Abca1. This finding suggests that the degree of β-cell dysfunction caused by ABCA1 deficiency may relate to the level of plasma cholesterol to which the islets are exposed. To assess whether deficiency of ABCA1 function influences β-cell function in humans, we therefore chose to study carriers of heterozygous ABCA1 mutations, with severe reductions in ABCA1 function but relatively normal total plasma cholesterol levels. We performed oral glucose tolerance tests (OGTTs) and hyperglycemic clamps in ABCA1 heterozygotes and family-based control subjects. Our data indicate that ABCA1 plays a significant role in insulin secretion and β-cell function in humans.     

Utility of Homeostasis Model Assessment of ��-Cell Function in Predicting Diabetes in 12,924 Healthy Koreans

OBJECTIVE

It is unclear how well homeostasis model assessment of β-cell function (HOMA-β) predicts diabetes development beyond its components, especially glucose.

RESEARCH DESIGN AND METHODS

We identified 12,924 nondiabetic Koreans who had fasting plasma glucose and insulin concentrations measured in 2003 and again in 2008. To minimize the impact of differences in baseline glucose concentration, individuals were divided into three glucose categories: normal fasting glucose (NFG, glucose <5.6 mmol/l), impaired fasting glucose (IFG-100) (5.6–6.0 mmol/l), and IFG-110 (6.1–6.9 mmol/l).

RESULTS

Diabetes developed in 29% of individuals in the IFG-110 group, compared with 5% in IFG-100 and 0.3% in NFG groups. Within each glucose category, those who progressed to diabetes had higher baseline glucose concentrations (P ≤ 0.04). Baseline HOMA-β, however, was not lower but higher in individuals who developed diabetes in the NFG group (P = 0.009) and similar in the IFG-100 and IFG-110 groups.

CONCLUSIONS

These data question the utility of using HOMA-β to predict the development of diabetes.The homeostasis model assessment of β-cell function (HOMA-β) is an index of insulin secretory function derived from fasting plasma glucose and insulin concentrations (1). It has been used to predict diabetes development in nondiabetic individuals in four studies (2–5), and the conclusion in each instance was that a decrease in insulin secretory function, as estimated by HOMA-β, predicted the development of diabetes and/or impaired glucose tolerance. However, because it was also shown in these studies that baseline glucose concentration was higher in individuals who developed diabetes, it could be argued that the lower values for HOMA-β may only be reflecting the difference in glucose concentration. The current analysis was initiated to see if HOMA-β provided a more sensitive assessment of the likelihood of developing type 2 diabetes than did knowledge of individual fasting plasma glucose and insulin concentrations.     

Effect of Ingested Interferon-�� on ��-Cell Function in Children With New-Onset Type 1 Diabetes

OBJECTIVE

To evaluate the safety and efficacy of ingested human recombinant interferon-α (hrIFN-α) for preservation of β-cell function in young patients with recent-onset type 1 diabetes.

RESEARCH DESIGN AND METHODS

Subjects aged 3–25 years in whom type 1 diabetes was diagnosed within 6 weeks of enrollment were randomly assigned to receive ingested hrIFN-α at 5,000 or 30,000 units or placebo once daily for 1 year. The primary outcome was change in C-peptide secretion after a mixed meal.

RESULTS

Individuals in the placebo group (n = 30) lost 56 ± 29% of their C-peptide secretion from 0 to 12 months, expressed as area under the curve (AUC) in response to a mixed meal. In contrast, children treated with hrIFN-α lost 29 ± 54 and 48 ± 35% (for 5,000 [n = 27] and 30,000 units [n = 31], respectively, P = 0.028, ANOVA adjusted for age, baseline C-peptide AUC, and study site). Bonferroni post hoc analyses for placebo versus 5,000 units and placebo versus 30,000 units demonstrated that the overall trend was determined by the 5,000-unit treatment group. Adverse events occurred at similar rates in all treatment groups.

CONCLUSIONS

Ingested hrIFN-α was safe at the doses used. Patients in the 5,000-unit hrIFN-α treatment group maintained more β-cell function 1 year after study enrollment than individuals in the placebo group, whereas this effect was not observed in patients who received 30,000 units hrIFN-α. Further studies of low-dose ingested hrIFN-α in new-onset type 1 diabetes are needed to confirm this effect.Residual β-cell function was shown to correlate with decreased complication rates in the Diabetes Control and Complications Trial (1). As a result, preservation of β-cell function is an important treatment goal in patients with type 1 diabetes. Over the past 25 years, multiple clinical trials attempted to prevent progressive β-cell destruction after the diagnosis of type 1 diabetes using immunosuppressive or immunomodulatory agents such as cyclosporin (2,3), cyclosporin in combination with bromocriptine (4), azathioprine with or without glucocorticoids (5,6), nicotinamide with or without glucocorticoids (7,8), and parenteral interferon-α (IFN-α) (9). More recent intervention trials used monoclonal antibody–based therapies such as rituximab (anti-CD-20) (clinical trial reg. no. NCT00279205), daclizumab (anti-CD25) in combination with mycophenolate mofetil (clinical trial reg. no. {"type":"clinical-trial","attrs":{"text":"NCT00100178","term_id":"NCT00100178"}}NCT00100178), anti-CD3 (10–12), and GAD (13). Although several studies are still ongoing and thus the results are pending, trials of anti-CD3 antibodies and GAD have demonstrated delayed decline of endogenous insulin secretion. However, none of these intervention trials have yet been translated into common clinical practice for two reasons: 1) the β-cell protective effect has been temporary, and 2) some of the agents available were associated with unacceptable side effects, such as impairment of renal function in the case of calcineurin inhibitors.The original observation that ingested type 1 interferon has an immunomodulatory effect was made in mice with chronic relapsing experimental autoimmune encephalomyelitis (14). Subsequently, a phase I trial demonstrated that 10,000–30,000 but not 100,000 units ingested IFN-α act as a biological response modifier without apparent toxicity in humans with multiple sclerosis (15), and a phase II trial suggested that 10,000 units may be more clinically effective than 30,000 units (16). The mechanism of action remains unclear. It is thought that ingested interferon, which is acid stable and therefore resists gastric digestion, binds to high-affinity receptors in the gut-associated lymphoid tissue where it transduces its signal. Serum levels do not change nor do other protein markers of interferon absorption (e.g., β₂-microglobulin, neopterin, and 2-5A synthetase) (17).A decade ago, ingested INF-α was reported to modify the onset of autoimmune diabetes in a commonly used animal model, the nonobese diabetic (NOD) mouse. Adoptive transfer of unstimulated splenocytes secreting interleukin (IL)-4 and IL-10 from mouse IFN-α–fed donors suppressed spontaneous diabetes in recipients, thus demonstrating the presence of ingested IFN-α–activated regulatory splenic cell populations that work via increased IL-4 or IL-10 production (18). A small, open-label pilot project in 10 children with recently diagnosed type 1 diabetes supported the safety of ingested interferon and helped with dose finding (19). The current study is the first randomized, controlled trial testing the safety and efficacy of ingested human recombinant (hr) IFN-α to preserve β-cell function in young patients with recent-onset type 1 diabetes.     

Primary Defects in ��-Cell Function Further Exacerbated by Worsening of Insulin Resistance Mark the Development of Impaired Glucose Tolerance in Obese Adolescents

OBJECTIVE—Impaired glucose tolerance (IGT) is a pre-diabetic state of increasing prevalence among obese adolescents. The purpose of this study was to determine the natural history of progression from normal glucose tolerance (NGT) to IGT in obese adolescents.RESEARCH DESIGN AND METHODS—We determined the evolution of β-cell function, insulin sensitivity (S_I), and glucose tolerance in a multiethnic group of 60 obese adolescents over the course of approximately 30 months. Each subject underwent three serial 3-h oral glucose tolerance tests. Dynamic, static, and total β-cell responsivity (Φ_d, Φ_s, and Φ_tot, respectively) and S_i were assessed by oral C-peptide and glucose minimal models. The disposition index (DI), which adjusts insulin secretion for S_i, was calculated.RESULTS—At baseline, all 60 subjects had NGT. Seventy-seven percent (46 subjects) maintained NGT over the three testing periods (nonprogressors), whereas 23% (14 subjects) developed IGT over time (progressors). At baseline, percent fat and BMI Z score were comparable between the groups. Fasting plasma glucose, 2-h glucose, glucose area under the curve at 180 min, and Φ_d were significantly different between the two groups at baseline, whereas S_i was comparable between the two groups. Over time, although S_i remained unchanged in nonprogressors, it steadily worsened by ∼45% (P > 0.04) in progressors. β-Cell responsivity decreased by 20% in progressors, whereas it remained stable in nonprogressors. The DI showed a progressive decline in progressors compared with a modest improvement in nonprogressors (P = 0.02).CONCLUSIONS—Obese adolescents who progress to IGT may manifest primary defects in β-cell function. In addition, progressive decline in S_i further aggravates β-cell function, contributing to the worsening of glucose intolerance.Understanding the underlying putative metabolic defects leading to the development of type 2 diabetes requires studies that focus on the earliest stages of the disease before the onset of any alterations in glucose tolerance. In adults, type 2 diabetes is the final stage in the progression of the disease (1–3), characterized by a progressive worsening in both insulin resistance and secretion (4–7). Whether a similar profile also occurs in youth developing type 2 diabetes is unknown. Much of the understanding of type 2 diabetes in youth originates from cross-sectional studies performed in obese adolescents with overt disease (8) or with impaired glucose tolerance (IGT) (9,10). One longitudinal study in obese adolescents with IGT at baseline indicated that over a period of 23 months, 45% reverted to normal glucose tolerance (NGT), 30% maintained IGT, and 25% developed type 2 diabetes(11). Thus, youth with IGT are at high risk for developing type 2 diabetes because of the presence of both insulin resistance and β-cell dysfunction.To assess the metabolic sequence of events that might be implicated in the transition from NGT to IGT, we performed serial oral glucose tolerance tests (OGTTs) along with anthropometric measures in a group of obese adolescents over a period of approximately 3 years. Using the oral minimal model (OMM) (12,13), we determined β-cell responsivity (Φ), insulin sensitivity (S_i), and disposition index (DI) and thus have repeated measures of both insulin secretion and insulin action before and during the evolution of IGT in obese adolescents. In a longitudinal study, we tested the hypothesis that preexisting β-cell dysfunction, further exacerbated by a progressive worsening in S_i, characterizes the onset of IGT in childhood obesity.     

��-Cell Function Declines Within the First Year Postpartum in Women With Recent Glucose Intolerance in Pregnancy

OBJECTIVE

Both gestational diabetes mellitus (GDM) and mild glucose intolerance in pregnancy identify women at increased risk of future type 2 diabetes. In this context, we queried whether metabolic changes that occur in the 1st year postpartum vary in relation to gestational glucose tolerance status.

RESEARCH DESIGN AND METHODS

Three-hundred-and-ninety-two women underwent glucose challenge test (GCT) and oral glucose tolerance test (OGTT) in pregnancy followed by repeat OGTT at both 3 months'' postpartum and 12 months'' postpartum. The antepartum testing defined four gestational glucose tolerance groups: GDM (n = 107); gestational impaired glucose tolerance (GIGT) (n = 75); abnormal GCT with normal glucose tolerance (NGT) on OGTT (abnormal GCT NGT) (n = 137); and normal GCT with NGT on OGTT (normal GCT NGT) (n = 73).

RESULTS

The prevalence of dysglycemia progressively increased across the groups from normal GCT NGT to abnormal GCT NGT to GIGT to GDM at both 3 months'' postpartum (2.7% to 10.2% to 18.7% to 34.6%, P < 0.0001) and 12 months'' postpartum (2.7% to 11.7% to 17.3% to 32.7%, P < 0.0001). Between 3 and 12 months'' postpartum, the groups did not differ with respect to changes in waist circumference, weight, or insulin sensitivity. Importantly, however, they exhibited markedly different changes in β-cell function (Insulin Secretion-Sensitivity Index-2 [ISSI-2]) (P = 0.0036), with ISSI-2 declining in both the GDM and GIGT groups. Furthermore, on multiple linear regression analysis, both GDM (t = −3.06, P = 0.0024) and GIGT (t = −2.18, P = 0.03) emerged as independent negative predictors of the change in ISSI-2 between 3 and 12 months'' postpartum.

CONCLUSIONS

Women with GDM and GIGT exhibit declining β-cell function in the 1st year postpartum that likely contributes to their future diabetic risk.The diagnosis of gestational diabetes mellitus (GDM) identifies a population of young women who are at high risk of developing type 2 diabetes on the order of 20–60% in the first 5 years following an index pregnancy (1–3). A systematic review of studies evaluating the risk of progression to type 2 diabetes following GDM has demonstrated that the cumulative incidence of diabetes increases markedly in the first 5 years'' postpartum and appears to plateau after 10 years (3). Thus, events in the early postpartum years are likely to be important in determining diabetic risk in this patient population. At present, however, little is known about the pathophysiologic changes that take place in these early years following a pregnancy complicated by GDM.A recent series of reports have demonstrated that even women with mild glucose intolerance in pregnancy (i.e., less severe than GDM) have an increased risk of ultimately developing pre-diabetes and diabetes (4–9). The magnitude of this risk is proportional to the degree of gestational dysglycemia, with the highest risk in women with GDM and proportionately lower risk in women with milder abnormalities of gestational glucose tolerance (4). It thus emerges that the spectrum of abnormal glucose homeostasis in pregnancy identifies a continuum of risk for future diabetes and, based on the temporal findings pertaining to GDM, pathophysiologic changes that occur in the early postpartum years may be relevant to the manifestation of this risk potential. Therefore, in the current study, our objective was to perform a longitudinal evaluation of the metabolic changes that take place in the 1st year postpartum in a well-characterized cohort of women representing the full spectrum of glucose tolerance in pregnancy and hence a broad range of future diabetic risk.     

Adjusting Glucose-Stimulated Insulin Secretion for Adipose Insulin Resistance: An Index of β-Cell Function in Obese Adults

OBJECTIVE

The hyperbolic relationship between insulin secretion and sensitivity has been used to assess in vivo β-cell function (i.e., the disposition index). The disposition index emphasizes the importance of taking into account both skeletal muscle and hepatic insulin resistance to depict insulin secretion. However, we propose that adipose tissue insulin resistance also needs to be accounted for when characterizing glucose-stimulated insulin secretion (GSIS) because elevated plasma free fatty acids (FFAs) impair β-cell function.

RESEARCH DESIGN AND METHODS

To characterize the adipose disposition index, we used [1-¹⁴C] palmitate infusion to determine basal FFA turnover rate/adipose insulin resistance and an oral glucose tolerance test to characterize the first (i.e., 0–30 min) and second phase (i.e., 60–120 min) of GSIS. We validated a simplified version of the tracer infusion calculation as the product of (1/plasma FFA concentration × plasma insulin concentration) × GSIS in 44 obese insulin-resistant subjects.

RESULTS

The plasma FFA and palmitate tracer infusion calculations of the first- and second-phase disposition index were strongly correlated (r = 0.86, P < 0.000001 and r = 0.89, P < 0.000001, respectively). The first- and second-phase adipose disposition index derived from plasma FFA also was tightly associated with fasting hyperglycemia (r = −0.87, P < 0.00001 and r = −0.89, P < 0.00001, respectively) and 2-h glucose concentrations (r = −0.86, P < 0.00001 and r = −0.90, P < 0.00001).

CONCLUSIONS

Adjusting GSIS for adipose insulin resistance provides an index of β-cell function in obese subjects across the glucose spectrum. Plasma FFA–derived calculations of β-cell function may provide additional insight into the role of adipose tissue in glucose regulation.     

Restoring Insulin Secretion (RISE): Design of Studies of β-Cell Preservation in Prediabetes and Early Type 2 Diabetes Across the Life Span

OBJECTIVE

The Restoring Insulin Secretion (RISE) Consortium is testing interventions designed to preserve or improve β-cell function in prediabetes or early type 2 diabetes.

RESEARCH DESIGN AND METHODS

β-Cell function is measured using hyperglycemic clamps and oral glucose tolerance tests (OGTTs). The adult medication protocol randomizes participants to 12 months of placebo, metformin alone, liraglutide plus metformin, or insulin (3 months) followed by metformin (9 months). The pediatric medication protocol randomizes participants to metformin or insulin followed by metformin. The adult surgical protocol randomizes participants to gastric banding or metformin (24 months). Adult medication protocol inclusion criteria include fasting plasma glucose 95–125 mg/dL (5.3–6.9 mmol/L), OGTT 2-h glucose ≥140 mg/dL (≥7.8 mmol/L), HbA_1c 5.8–7.0% (40–53 mmol/mol), and BMI 25–40 kg/m². Adult surgical protocol criteria are similar, except for fasting plasma glucose ≥90 mg/dL (≥5.0 mmol/L), BMI 30–40 kg/m², HbA_1c <7.0% (<53 mmol/mol), and diabetes duration <12 months. Pediatric inclusion criteria include fasting plasma glucose ≥90 mg/dL (≥5.0 mmol/L), 2-h glucose ≥140 mg/dL (≥7.8 mmol/L), HbA_1c ≤8.0% (≤64 mmol/mol), BMI >85th percentile and ≤50 kg/m², 10–19 years of age, and diabetes <6 months.

RESULTS

Primary outcomes are clamp-derived glucose-stimulated C-peptide secretion and maximal C-peptide response to arginine during hyperglycemia. Measurements are made at baseline, after 12 months on treatment, and 3 months after treatment withdrawal (medication protocols) or 24 months postintervention (surgery protocol). OGTT-derived measures are also obtained at these time points.

CONCLUSIONS

RISE is determining whether medication or surgical intervention strategies can mitigate progressive β-cell dysfunction in adults and youth with prediabetes or early type 2 diabetes.     

Effects of Exenatide Alone and in Combination With Daclizumab on ��-Cell Function in Long-Standing Type 1 Diabetes

OBJECTIVE

In patients with long-standing type 1 diabetes, we investigated whether improved β-cell function can be achieved by combining intensive insulin therapy with agents that may 1) promote β-cell growth and/or limit β-cell apoptosis and 2) weaken the anti–β-cell autoimmunity.

RESEARCH DESIGN AND METHODS

For this study, 20 individuals (mean age 39.5 ± 11.1 years) with long-standing type 1 diabetes (21.3 ± 10.7 years) were enrolled in this prospective open-label crossover trial. After achieving optimal blood glucose control, 16 subjects were randomized to exenatide with or without daclizumab. Endogenous insulin production was determined by repeatedly measuring serum C-peptide.

RESULTS

In 85% of individuals with long-standing type 1 diabetes who were screened for participation in this trial, C-peptide levels ≥0.05 ng/ml (0.02 nmol/l) were found. Residual β-cells responded to physiological (mixed-meal) and pharmacological (arginine) stimuli. During exenatide treatment, patients lost 4.1 ± 2.9 kg body wt and insulin requirements declined significantly (total daily dose on exenatide 0.48 ± 0.11 vs. 0.55 ± 0.13 units · kg⁻¹ · day⁻¹ without exenatide; P = 0.0062). No signs of further activation of the underlying autoimmune disease were observed. Exenatide delayed gastric emptying, suppressed endogenous incretin levels, but did not increase C-peptide secretion.

CONCLUSIONS

In long-standing type 1 diabetes, which remains an active autoimmune disease even decades after its onset, surviving β-cells secrete insulin in a physiologically regulated manner. However, the combination of intensified insulin therapy, exenatide, and daclizumab did not induce improved function of these remaining β-cells.In the past 2 decades, several lines of research dominated the field of type 1 diabetes: trials to alter the immunological response against β-cells and attempts to develop and replace β-cells. The latter, represented by islet transplantation in the clinical arena, has led to the realization that lasting insulin independence could not be achieved (1), but progress was made by gaining insight into β-cell development (2–4) and immunomodulation. Experimental therapies such as administration of the monoclonal antibody anti-CD3 and the β-cell antigen GAD65 slowed β-cell destruction when administered soon after disease onset (5,6). Currently, however, no therapy is available that results in a complete halt or reversal of β-cell failure.We initiated this trial in patients with well-controlled long-standing type 1 diabetes who had evidence of endogenous insulin production documented by measurable C-peptide concentrations ≥0.3 ng/ml (0.1 nmol/l). The study participants received exenatide, a glucagon-like peptide (GLP)-1 agonist, to stimulate β-cell recovery and possibly regeneration (7,8); 50% of patients also received daclizumab to diminish the underlying autoimmunity and to curb a potential autoimmune reactivation. β-Cell function was repeatedly assessed by measuring basal and stimulated C-peptide concentrations (9). We speculated that the difference between greater β-cell mass and improved function could be determined by observing the duration of any treatment effect; i.e., if the intervention resulted in increased β-cell mass, improved pancreatic insulin production would be expected to persist beyond the exenatide treatment. Daclizumab was chosen as a mild immunosuppressive agent because of its safety profile and its demonstrated efficacy in other T-cell–mediated autoimmune conditions such as uveitis and multiple sclerosis (10,11).     

Predicting the Peritoneal Absorption of Icodextrin in Rats and Humans Including the Effect of α-Amylase Activity in Dialysate

♦ Background:

Contrary to ultrafiltration, the three-pore model predictions of icodextrin absorption from the peritoneal cavity have not yet been reported likely, in part, due to difficulties in estimating the degradation of glucose-polymer chains by α-amylase activity in dialysate. We incorporated this degradation process in a modified three-pore model of peritoneal transport to predict ultrafiltration and icodextrin absorption simultaneously in rats and humans.

♦ Methods:

Separate three-pore models were constructed for humans and rats. The model for humans was adapted from PD Adequest 2.0 including a clearance term out of the peritoneal cavity to account for the absorption of large molecules to the peritoneal tissues, and considering patients who routinely used icodextrin by establishing steady-state plasma concentrations. The model for rats employed a standard three-pore model in which human kinetic parameters were scaled for a rat based on differences in body weight. Both models described the icodextrin molecular weight (MW) distribution as five distinct MW fractions. First order kinetics was applied using degradation rate constants obtained from previous in-vitro measurements using gel permeation chromatography. Ultrafiltration and absorption were predicted during a 4-hour exchange in rats, and 9 and 14-hour exchanges in humans with slow to fast transport characteristics with and without the effect of amylase activity.

♦ Results:

In rats, the icodextrin MW profile shifted towards the low MW fractions due to complete disappearance of the MW fractions greater than 27.5 kDa. Including the effect of amylase activity (60 U/L) resulted in 21.1% increase in ultrafiltration (UF) (7.6 mL vs 6.0 mL) and 7.1% increase in icodextrin absorption (CHO) (62.5% with vs 58.1%). In humans, the shift in MW profile was less pronounced. The fast transport (H) patient absorbed more icodextrin than the slow transport (L) patient during both 14-hour (H: 47.9% vs L: 40.2%) and 9-hour (H: 37.4% vs L: 31.7%) exchanges. While the UF was higher during the longer exchange, it varied modestly among the patient types (14-hour range: 460 – 509 mL vs 9-hour range: 382 – 389 mL). When averaged over all patients, the increases in UF and CHO during the 14-hour exchange due to amylase activity (7 U/L) were 15% and 1.5%, respectively.

♦ Conclusion:

The icodextrin absorption values predicted by the model agreed with those measured in rats and humans to accurately show the increased absorption in rats. Also, the model confirmed the previous suggestions by predicting an increase in UF specific to amylase activity in dialysate, likely due to the added osmolality by the small molecules generated as a result of the degradation process. As expected, this increase was more pronounced in rats than in humans because of higher dialysate concentrations of amylase in rats.     

Declining ��-Cell Function Relative to Insulin Sensitivity With Increasing Fasting Glucose Levels in the Nondiabetic Range in Children

OBJECTIVE

In adults, higher fasting plasma glucose (FPG) levels, even within the normoglycemic range, are associated with increased diabetes risk. This investigation tested the hypothesis that β-cell function relative to insulin sensitivity decreases with increasing FPG in youth.

RESEARCH DESIGN AND METHODS

A total of 223 youth with FPG <126 mg/dl underwent evaluation of first- and second-phase insulin secretion during a 2-h hyperglycemic (∼225 mg/dl) clamp, insulin sensitivity during a 3-h hyperinsulinemic-euglycemic clamp, body composition, and abdominal adiposity with dual-energy X-ray absorptiometry and computed tomographic scan. β-Cell function relative to insulin sensitivity was calculated as the product of first-phase insulin and insulin sensitivity, i.e., glucose disposition index (GDI). The subjects were divided into three FPG categories: ≤90, >90–<100, and ≥100–<126 mg/dl.

RESULTS

GDI decreased significantly across the three categories as FPG increased (1,086 ± 192 vs. 814 ± 67 and 454 ± 57 mg/kg/min, P = 0.002). This decline remained significant after adjustment for race, sex, BMI, and percent body fat or visceral fat. Within each FPG category, GDI declined with increasing BMI percentiles.

CONCLUSIONS

The impairment in β-cell function relative to insulin sensitivity is apparent even within the nondiabetic FPG range in children. At the current cutoff of 100 mg/dl for impaired fasting glucose (IFG), there is an ∼49% decline in the GDI independent of obesity and race. This observation may reflect a heightened risk of β-cell dysfunction and progression to diabetes in these children. Considering the near doubling of IFG prevalence among youth between National Health and Nutrition Examination Survey 1999–2000 and 2005–2006, our findings have important public health implications.Higher fasting plasma glucose (FPG) levels within the currently accepted normoglycemic range seem to have an impact on diabetes risk in adults (1–3). FPG levels >125 mg/dl indicate a provisional diagnosis of diabetes (4). FPG levels below this cutoff but above normal increase the risk of developing diabetes (5) and are associated with a higher cardiovascular disease risk (6,7). The American Diabetes Association classifies this intermediate state of FPG as impaired fasting glucose (IFG) (4) and initially defined it as fasting glucose of 110–125 mg/dl (8), which was lowered to 100 mg/dl in 2003 to better identify subjects at risk of diabetes development (9). Several studies in adults suggested that future diabetes risk increases continually with increasing FPG even below this lower cutoff for normoglycemia (1,2). In adults, fasting glucose levels of 90–94 mg/dl conferred a 49% greater risk of developing diabetes compared with levels <85 mg/dl (2). FPG levels in the top quintiles (95–99 mg/dl) of the normoglycemic range constituted an independent risk factor for type 2 diabetes among young men in the Israeli army after adjustment for several risk factors (1). In a Mauritius population-based study, parameters related to diabetes and cardiovascular disease such as higher BMI, cholesterol, triglycerides, and hypertension were positively correlated with higher FPG values in an approximately linear relationship (3). In addition, a meta-analysis of prospective studies showed a continuous relationship between baseline fasting glucose and subsequent cardiovascular risk (10). These observations raise a fundamental question: are insulin secretion and sensitivity impaired at higher levels of FPG but within the normal range? Few studies in adults have investigated this question, and results are conflicting (11–13). However, none of these studies used robust methodologies of assessing in vivo insulin secretion and sensitivity to derive a glucose disposition index (GDI), which is accepted to be the best indicator of β-cell dysfunction (14). Currently there are no published data assessing the relationship between high-normal fasting glucose levels and insulin sensitivity and secretion in children. The pre-diabetes cutoff levels for FPG in pediatrics are based on adult data and not on data generated in pediatric populations.In this study, we investigated the relationship between levels of fasting glucose and insulin secretion relative to insulin sensitivity, i.e., GDI, in children. Based on adult observations we hypothesized that β-cell function relative to insulin sensitivity decreases as FPG concentrations increase within the currently accepted nondiabetic range in children.     

No Effect of the Altered Peptide Ligand NBI-6024 on ��-Cell Residual Function and Insulin Needs in New-Onset Type 1 Diabetes

OBJECTIVE

This randomized, four-arm, placebo-controlled, dose-ranging phase 2 trial was conducted to determine whether repeated subcutaneous injections of the altered peptide ligand, NBI-6024, designed to inhibit autoreactive T-cells, improves β-cell function in patients with recently diagnosed type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 188 patients, aged 10–35 years, with recently diagnosed type 1 diabetes were randomly assigned for a treatment consisting of the subcutaneous administration of placebo or 1, 0.5, or 0.1 mg NBI-6024 at baseline, weeks 2 and 4, and then monthly until month 24. Fasting, peak, and area under the curve (AUC) C-peptide concentrations during a 2-h mixed-meal tolerance test were measured at 3-month intervals during treatment. Immune function parameters (islet antibodies and CD4 and CD8 T-cells) were also studied.

RESULTS

The mean peak C-peptide concentration at 24 months after study entry showed no significant difference between the groups treated with 0.1 mg (0.59 pmol/ml), 0.5 mg (0.57 pmol/ml), and 1.0 mg NBI-6024 (0.48 pmol/ml) and the placebo group (0.54 pmol/ml). Fasting, stimulated peak, and AUC C-peptide concentrations declined linearly in all groups by ∼60% over the 24-month treatment period. The average daily insulin needs at month 24 were also comparable between the four groups. No treatment-related changes in islet antibodies and T cell numbers were observed.

CONCLUSIONS

Treatment with altered peptide ligand NBI-6024 at repeated doses of 0.1, 0.5, or 1.0 mg did not improve or maintain β-cell function.Type 1 diabetes results from a T-cell–mediated autoimmune attack against the insulin-producing cells of the pancreatic islets (1–3). There is no curative treatment available to control these autoreactive T-cells, rendering the patients dependent on insulin injections for normoglycemia. A treatment that could stop or reduce autoimmune destruction of pancreatic β-cells would be a major advance in diabetes treatment and could potentially prevent diabetes in individuals genetically predisposed to developing the disease (4).There is potential to target specific populations of autoreactive T-cells by identifying the dominant antigens responsible for their activation and producing a soluble altered peptide ligand (APL) to block or change this response. The insulin B (9-23) peptide has been shown to be an important antigen of T-cells in autoimmune diabetes in animals and humans (5). NBI-6024 is an APL and contains two natural l-amino acid substitutions in the (9-23) sequence of the B-chain of insulin. Alanine is substituted for tyrosine at position 16, which is a key contact site at the T-cell receptor and at position 19 for cysteine. The resulting APL (Ala^16,19), known as NBI-6024, does not activate insulin B (9-23)–reactive murine or human T-cells (6). Nonobese diabetic mice treated with NBI-6024 are protected from developing diabetes, even though other T-cells with different antigenic specificities were present, suggesting that the immune response induced by the APL may regulate pathogenic T-cells through the production of regulatory cytokines such as interleukin-4 (6).Preliminary results of three studies in adult male patients with type 1 diabetes had indicated that NBI-6024 administration is safe and well tolerated (7,8). To investigate the pharmacological potential of NBI-6024 to improve β-cell function, a multicenter, randomized, four-arm, placebo-controlled phase 2 trial was performed. The primary objective of the trial was to assess the effect of repeated administrations of NBI-6024 on endogenous insulin production as measured by C-peptide concentration in adult and adolescent patients with recent-onset type 1 diabetes. Insulin usage, glycemic control, and immune function were also assessed.     

Regulation of Expression of Hyperalgesic Priming by Estrogen Receptor α in the Rat

Hyperalgesic priming, a sexually dimorphic model of transition to chronic pain, is expressed as prolongation of prostaglandin E2-induced hyperalgesia by the activation of an additional pathway including an autocrine mechanism at the plasma membrane. The autocrine mechanism involves the transport of cyclic adenosine monophosphate (AMP) to the extracellular space, and its conversion to AMP and adenosine, by ecto-5′phosphodiesterase and ecto-5′nucleotidase, respectively. The end product, adenosine, activates A1 receptors, producing delayed onset prolongation of prostaglandin E2 hyperalgesia. We tested the hypothesis that the previously reported, estrogen-dependent, sexual dimorphism observed in the induction of priming is present in the mechanisms involved in its expression, as a regulatory effect on ecto-5′nucleotidase by estrogen receptor α (EsRα), in female rats. In the primed paw AMP hyperalgesia was dependent on conversion to adenosine, being prevented by ecto-5′nucleotidase inhibitor α,β-methyleneadenosine 5′-diphosphate sodium salt and A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. To investigate an interaction between EsRα and ecto-5′nucleotidase, we treated primed female rats with oligodeoxynucleotide antisense or mismatch against EsRα messenger RNA. Whereas in rats treated with antisense AMP-induced hyperalgesia was abolished, the A1 receptor agonist N⁶-cyclopentiladenosine still produced hyperalgesia. Thus, EsRα interacts with this autocrine pathway at the level of ecto-5′nucleotidase. These results demonstrate a sexually dimorphic mechanism for the expression of priming.

Contrast-enhanced MRI of the small bowel in Crohn��s disease

Recently, magnetic resonance imaging has emerged as a valuable tool in evaluation of small bowel Crohn’s disease. MRI provides several advantages to other imaging modalities, including the lack of ionizing radiation, multiplanar capability, and functional information. Intravenous contrast administration is a routine portion of MR enterography protocol, and aids in detection of disease extent, extramural complications such as fistula and abscess, and assessment of activity. Additionally, promising techniques such as dynamic contrast-enhanced MRI may provide quantitative measures to assess bowel perfusion, which may enhance evaluation of disease activity. This article will provide an overview of the technical aspects of contrast-enhanced MR enterography, describe common pathologic findings involving the small bowel in Crohn’s disease, summarize its role in determination of activity with an emphasis on endoscopic and histologic correlation, and compare its efficacy with other imaging modalities.     

No Protective Effect of Calcitriol on ��-Cell Function in Recent-Onset Type 1 Diabetes: The IMDIAB XIII trial

OBJECTIVE

We investigated whether supplementation of the active form of vitamin D (calcitriol) in recent-onset type 1 diabetes can protect β-cell function evaluated by C-peptide and improve glycemic control assessed by A1C and insulin requirement.

RESEARCH DESIGN AND METHODS

Thirty-four subjects (aged 11–35 years, median 18 years) with recent-onset type 1 diabetes and high basal C-peptide >0.25 nmol/l were randomized in a double-blind trial to 0.25 μg/day calcitriol or placebo and followed-up for 2 years.

RESULTS

At 6, 12, and 24 months follow-up, A1C and insulin requirement in the calcitriol group did not differ from the placebo group. C-peptide dropped significantly (P < 0.001) but similarly in both groups, with no significant differences at each time point.

CONCLUSIONS

At the doses used, calcitriol is ineffective in protecting β-cell function in subjects (including children) with recent-onset type 1 diabetes and high C-peptide at diagnosis.Vitamin D deficiency has been associated with type 1 diabetes (1). Several studies suggest that vitamin D supplementation in early childhood decreases the risk of developing type 1 diabetes (2,3). The aim of this pilot trial was to investigate whether the supplementation of the active form of vitamin D (calcitriol) in subjects with recent-onset type 1 diabetes is able to protect residual β-cell function (C-peptide) and to improve metabolic control.     

Impact of Islet Autoimmunity on the Progressive β-Cell Functional Decline in Type 2 Diabetes

OBJECTIVECross-sectional studies have suggested that islet autoimmunity may be more prevalent in type 2 diabetes (T2D) than previously appreciated and may contribute to the progressive decline in β-cell function. In this study, we longitudinally evaluated the effect of islet autoimmune development on the progressive β-cell dysfunction in T2D patients.RESULTSOf the 23 patients, 6 (26%) remained negative for islet autoimmunity (Ab−T−), 14 (61%) developed Ab+ and/or T+, and 3 (13%) were unclassifiable because they developed islet autoimmunity at only one study visit. Islet Ab+ was observed to be less stable than islet-specific T-cell responses. Development of islet autoimmunity was significantly associated with a more rapid decline in fasting (P < 0.0001) and glucagon-stimulated (P < 0.05) C-peptide responses.CONCLUSIONSThese pilot data suggest that the development of islet autoimmunity in T2D is associated with a significantly more rapid β-cell functional decline.     

Association of Vitamin D With Insulin Resistance and ��-Cell Dysfunction in Subjects at Risk for Type 2 Diabetes

OBJECTIVE

To examine cross-sectional associations of serum vitamin D [25-hydroxyvitamin D, 25(OH)D] concentration with insulin resistance (IR) and β-cell dysfunction in 712 subjects at risk for type 2 diabetes.

RESEARCH DESIGN AND METHODS

Serum 25(OH)D was determined using a chemiluminescence immunoassay. Insulin sensitivity/resistance were measured using the Matsuda insulin sensitivity index for oral glucose tolerance tests (IS_OGTT) and homeostasis model assessment of insulin resistance HOMA-IR. β-Cell function was determined using both the insulinogenic index (IGI) divided by HOMA-IR (IGI/IR) and the insulin secretion sensitivity index-2 (ISSI-2).

RESULTS

Linear regression analyses indicated independent associations of 25(OH)D with IS_OGTT and HOMA-IR (β = 0.004, P = 0.0003, and β = −0.003, P = 0.0072, respectively) and with IGI/IR and ISSI-2 (β = 0.004, P = 0.0286, and β = 0.003, P = 0.0011, respectively) after adjusting for sociodemographics, physical activity, supplement use, parathyroid hormone, and BMI.

CONCLUSIONS

Vitamin D may play a role in the pathogenesis of type 2 diabetes, as 25(OH)D concentration was independently associated with both insulin sensitivity and β-cell function among individuals at risk of type 2 diabetes.Emerging evidence suggests a role for vitamin D in the etiology of type 2 diabetes (1). However, associations of vitamin D with insulin resistance (IR) and especially β-cell dysfunction have been inconsistent (2–7). Therefore, our objective was to assess the association of serum vitamin D concentration with IR and β-cell dysfunction in a large, ethnically-diverse, North American cohort at risk of type 2 diabetes.