Insulin secretory responses to rising and falling glucose concentrations are delayed in subjects with impaired glucose tolerance

Beta-cell sensitivity to glucose is impaired after gastric bypass surgery

AIMS

Patients who have undergone Roux-en-Y gastric bypass surgery (GB) have exaggerated postprandial insulin secretion, which has been attributed to increased meal glucose appearance and enhanced incretin effect. Here, we sought to determine β-cell glucose sensitivity in the absence of meal stimulation and insulinotropic gut factors.

MATERIALS AND METHODS

A total of 12 non-diabetic subjects with prior GB, and 7 matched non-surgical control subjects with normal glucose tolerance were studied. Blood glucose and insulin secretion rates were measured during a graded glucose infusion at increasing and then decreasing rates. Insulin sensitivity (S_I ) and glucose effectiveness (S_G ) were determined by the minimal model.

RESULTS

GB subjects had S_I comparable to that of control subjects. GB subjects had relative hyperglycaemia during the highest dose of glucose infusion associated with significantly reduced β-cell glucose sensitivity throughout both step-up (GB: 34 ± 6, CN: 82 ± 9 pmol min^-1 mM^-1 L, P < .0001) and step-down (GB: 31 ± 6, CN: 74 ± 9 pmol min^-1 mM^-1 L, P < .0001) phases of the glucose infusion. GB subjects also had reduced S_G (GB: 0.04 ± 0.00, CN: 0.07 ± 0.01 min^-1 , P = .004).

CONCLUSION

In the absence of enteric stimuli, β-cell sensitivity to changes in glycaemia is blunted among individuals with GB, indicating a significant shift in a fundamental property of β-cell function several years after surgery.

Polycystic ovarian syndrome: Assessment of approaches to diagnosis and cardiometabolic monitoring in UK primary care

INTRODUCTION

Polycystic ovarian syndrome (PCOS) is one of the commonest endocrine disorders affecting women of reproductive age. We examined the specific tests that are done in primary care to lead to the diagnosis of PCOS, and to support the diagnosis once made.

METHODS

One thousand seven hundred and ninety-seven women were identified from a pooled GP practice database. The search included all patients defined with PCOS or related terms. Records included demographic information, medical history (diagnoses), blood test results and whether a pelvic ultrasound scan had been performed.

RESULTS

The most common age of PCOS diagnosis was 20-29 years; 67.7% of the women had at least one concomitant Read-coded diagnosis. Most pelvic ultrasound scans were performed in the month immediately prior to diagnosis. In the 12 months prior to the diagnosis of PCOS being made, 30.5% of women underwent a measurement of their serum total testosterone level while 29.6% had their serum SHBG measured. For serum oestradiol, the corresponding statistics were 28.4%, LH 45.3% and for FSH 45.5% checked before diagnosis. Fasting blood glucose, random glucose and HbA1c were checked in 10.2%, 18.8% and 4.2%, of women before diagnosis, respectively, but in only 7.9%, 6.0% and 3.4% of women in the 24 months after diagnosis. There was a tendency for endocrine testing (oestradiol, LH, FSH, testosterone, SHBG) to peak in the weeks before diagnosis. For plasma glucose, testing was performed more evenly over time as for serum cholesterol. Of all women diagnosed with PCOS, 32.8% were prescribed metformin, 3.7% antihypertensives, 2.2% statins and 63.5% an oestrogen-containing contraceptive pill or HRT.

CONCLUSION

The underlying pathophysiology of PCOS is still not fully understood. As a result, treatment is often focused on individual symptoms, not the syndrome itself. Robust laboratory led protocols would provide the necessary information to enable an appropriate diagnostic evaluation/cardometabolic monitoring.

Review of methods for measuring β-cell function: Design considerations from the Restoring Insulin Secretion (RISE) Consortium

The Restoring Insulin Secretion (RISE) study was initiated to evaluate interventions to slow or reverse the progression of β-cell failure in type 2 diabetes (T2D). To design the RISE study, we undertook an evaluation of methods for measurement of β-cell function and changes in β-cell function in response to interventions. In the present paper, we review approaches for measurement of β-cell function, focusing on methodologic and feasibility considerations. Methodologic considerations included: (1) the utility of each technique for evaluating key aspects of β-cell function (first- and second-phase insulin secretion, maximum insulin secretion, glucose sensitivity, incretin effects) and (2) tactics for incorporating a measurement of insulin sensitivity in order to adjust insulin secretion measures for insulin sensitivity appropriately. Of particular concern were the capacity to measure β-cell function accurately in those with poor function, as is seen in established T2D, and the capacity of each method for demonstrating treatment-induced changes in β-cell function. Feasibility considerations included: staff burden, including time and required methodological expertise; participant burden, including time and number of study visits; and ease of standardizing methods across a multicentre consortium. After this evaluation, we selected a 2-day measurement procedure, combining a 3-hour 75-g oral glucose tolerance test and a 2-stage hyperglycaemic clamp procedure, augmented with arginine.

The β-cell burden index of food: A proposal

The quantity and quality of dietary fat and/or carbohydrate may alter one or more of the basic components of the insulin-glucose system, which in turn affect the pathways leading to alterations in glucose homeostasis and, possibly, to cardiovascular disease. This viewpoint article, reviewing some of the currently available tools aiming at quantifying the impact of dietary carbohydrates on the glucose-insulin homeostatic loop, highlights the unmet need of a more thorough assessment of the complex interaction between dietary factors and the glucose-insulin system. A novel index, the "β-cell burden index", may turn out to be a valuable tool to quantify the role played by the diet in shaping the risk of type 2 diabetes, cardiovascular disease and other metabolic and degenerative disorders, ideally orienting their prevention with strategies based on dietary modifications.

Linearity of β-cell response across the metabolic spectrum and to pharmacology: insights from a graded glucose infusion-based investigation series

The graded glucose infusion (GGI) examines insulin secretory response patterns to continuously escalating glycemia. The current study series sought to more fully appraise its performance characteristics. Key questions addressed were comparison of the GGI to the hyperglycemic clamp (HGC), comparison of insulin secretory response patterns across three volunteer populations known to differ in β-cell function (healthy nonobese, obese nondiabetic, and type 2 diabetic), and characterization of effects of known insulin secretagogues in the context of a GGI. Insulin secretory response was measured as changes in insulin, C-peptide, insulin secretion rates (ISR), and ratio of ISR to prevailing glucose (ISR/G). The GGI correlated well with the HGC (r = 0.72 for ISR/G, P < 0.01). The insulin secretory response in type 2 diabetes (T2DM) was significantly blunted (P < 0.001), whereas it was significantly increased in obese nondiabetics compared with healthy nonobese (P < 0.001). Finally, robust (P < 0.001 over placebo) pharmacological effects were observed in T2DM and healthy nonobese volunteers. Collectively, the findings of this investigational series bolster confidence that the GGI has solid attributes for assessing insulin secretory response to glucose across populations and pharmacology. Notably, the coupling of insulin secretory response to glycemic changes was distinctly and uniformly linear across populations and in the context of insulin secretagogues. (Clinical Trial Registration Nos. NCT00782418, NCT01055340, NCT01373450).

Impact of a mild decrease in fasting plasma glucose on β-cell function in healthy subjects and patients with type 2 diabetes

Restoring euglycaemia for weeks or months improves insulin secretion in patients with type 2 diabetes (T2D). We tested whether mild decrements in fasting glucose (FPG) acutely affect β-cell function and insulin sensitivity. Thirteen normotolerant (NGT) and 10 T2D patients volunteered in pairs. In an isoglycemic test (Iso), after 100 min of stabilization, an incremental glucose infusion over 3 h was applied to raise plasma glucose to >22 mmol/l, followed by an arginine challenge; in a subisoglycemic test (Sub), a glucose infusion matching the plasma glucose time course of Iso was preceded by an insulin infusion period (100 min) aimed at maintaining a mild FPG reduction while avoiding hypoglycaemia. β-Cell function was assessed by mathematical modeling, whereas the acute insulin response (AIR) to arginine was determined from C-peptide levels. In the Sub, FPG was lowered by 17% in NGT and 31% in T2D patients. On the glucose ramp, total insulin release was lower in Sub than in Iso in both groups [from 106 (43) to 75 (39) nmol/m(-2) in NGT and from 71 (63) to 64 (41) nmol/m(-2) in T2D, P = 0.001]. In the Sub, β-cell glucose sensitivity was significantly (P = 0.008) reduced in NGT [from 50 (31) to 43 (21) pmol·min(-1)·m(-2)·mM(-1)] but not in T2D [19 (20) to 20 (20) pmol·min(-1)·m(-2)·mM(-1)]. Likewise, AIR was lowered in NGT [8.9 (4.6) to 7.1 (4.4) nmol/l, P = 0.048] but not in T2D [4.7 (3.3) to 5.3 (3.2) nmol/l]. Insulin sensitivity improved in NGT but only marginally in T2D. Prestimulatory glucose levels acutely influence both β-cell function and insulin sensitivity differentially in nondiabetic and type 2 diabetic individuals.

β-Cell Glucose Sensitivity Is Linked to Insulin/Glucagon Bihormonal Cells in Nondiabetic Humans

CONTEXT

Insulin resistance impacts virtually all tissues, including pancreatic β cells. Individuals with insulin resistance, but without diabetes, exhibit an increased islet size because of an elevated number of both β and α cells. Neogenesis from duct cells and transdifferentiation of α cells have been postulated to contribute to the β-cell compensatory response to insulin resistance.

OBJECTIVE

Our objective was to explore parameters that could potentially predict altered islet morphology.

METHODS

We investigated 16 nondiabetic subjects by a 2-hour hyperglycemic clamp to evaluate β-cell secretory function. We analyzed pancreas samples obtained during pancreatoduodenectomy in the same patients to examine glucagon and insulin double+ cells to assess islet morphology.

RESULTS

Among all the functional in vivo parameters of insulin secretion that were explored (basal, first phase and total secretion, glucose sensitivity, arginine-stimulated insulin secretion), β-cell glucose sensitivity was unique in exhibiting a significant correlation with both islet size and α-β double+ islet cells.

CONCLUSIONS

Our data suggest that poor β-cell glucose sensitivity is linked to islet transdifferentiation, possibly from α cells to β cells, in an attempt to cope with higher demands for insulin secretion. Understanding the mechanism(s) that underlies the adaptive response of the islet cells to insulin resistance is a potential approach to design tools to enhance functional β-cell mass for diabetes therapy.

Altered islet function and insulin clearance cause hyperinsulinemia in gastric bypass patients with symptoms of postprandial hypoglycemia

CONTEXT

Postprandial hypoglycemia, a late complication of gastric bypass (GB) surgery, is associated with an exaggerated insulin response to meal ingestion.

OBJECTIVE

The purpose of this study was to characterize insulin secretion and other glucoregulatory hormone responses to meal ingestion after GB based on hypoglycemia and clinical symptoms.

METHODS

We conducted a cross-sectional analysis of insulin secretion rate and islet and gastrointestinal hormone responses to liquid mixed meal ingestion in 65 subjects with GB and 11 body mass index-matched controls without surgery. The GB subjects were stratified by clinical history for analysis of their responses to the test meal.

RESULTS

The glucose and insulin responses to meal ingestion were shifted upward and to the left after GB, with the largest early insulin response and the lowest nadir glucose levels in patients with a history of hypoglycemia, particularly those with neuroglycopenic symptoms. Hypoglycemic GB subjects had lower postprandial insulin clearance rates and higher insulin secretion rates during the glucose decline after the test meal. Meal-induced glucagon was enhanced in all GB subjects but did not differ between subjects who did and did not develop hypoglycemia. Plasma gastric inhibitory polypeptide and glucagon-like peptide-1 concentrations did not differ between asymptomatic and neuroglycopenic GB subjects.

CONCLUSION

Among GB subjects with a clinical history of hypoglycemia, hyperinsulinemia is the result of inappropriate insulin secretion and reduced insulin clearance. In subjects with symptoms of postprandial hypoglycemia, insulin secretion is higher in the latter stages of meal glucose clearance, and despite elevated meal-induced glucagon, there is no further response to hypoglycemia. These abnormalities in islet function are most pronounced in subjects who report neuroglycopenic symptoms.

Epidemiology, diagnosis, and management of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common heterogeneous endocrine disorder characterized by irregular menses, hyperandrogenism, and polycystic ovaries. The prevalence of PCOS varies depending on which criteria are used to make the diagnosis, but is as high as 15%–20% when the European Society for Human Reproduction and Embryology/American Society for Reproductive Medicine criteria are used. Clinical manifestations include oligomenorrhea or amenorrhea, hirsutism, and frequently infertility. Risk factors for PCOS in adults includes type 1 diabetes, type 2 diabetes, and gestational diabetes. Insulin resistance affects 50%–70% of women with PCOS leading to a number of comorbidities including metabolic syndrome, hypertension, dyslipidemia, glucose intolerance, and diabetes. Studies show that women with PCOS are more likely to have increased coronary artery calcium scores and increased carotid intima-media thickness. Mental health disorders including depression, anxiety, bipolar disorder and binge eating disorder also occur more frequently in women with PCOS. Weight loss improves menstrual irregularities, symptoms of androgen excess, and infertility. Management of clinical manifestations of PCOS includes oral contraceptives for menstrual irregularities and hirsutism. Spironolactone and finasteride are used to treat symptoms of androgen excess. Treatment options for infertility include clomiphene, laparoscopic ovarian drilling, gonadotropins, and assisted reproductive technology. Recent data suggest that letrozole and metformin may play an important role in ovulation induction. Proper diagnosis and management of PCOS is essential to address patient concerns but also to prevent future metabolic, endocrine, psychiatric, and cardiovascular complications.

Quantification of β-cell insulin secretory function using a graded glucose infusion with C-peptide deconvolution in dysmetabolic, and diabetic cynomolgus monkeys

BACKGROUND

Quantitation of β-cell function is critical in better understanding of the dynamic interactions of insulin secretion, clearance and action at different phases in the progression of diabetes. The present study aimed to quantify β-cell secretory function independently of insulin sensitivity in the context of differential metabolic clearance rates of insulin (MCRI) in nonhuman primates (NHPs).

METHODS

Insulin secretion rate (ISR) was derived from deconvolution of serial C-peptide concentrations measured during a 5 stage graded glucose infusion (GGI) in 12 nondiabetic (N), 8 prediabetic or dysmetabolic (DYS) and 4 overtly diabetic (DM) cynomolgus monkeys. The characterization of the monkeys was based on the fasting glucose and insulin concentrations, glucose clearance rate measured by intravenous glucose tolerance test, and insulin resistance indices measured in separate experiments. The molar ratio of C-peptide/insulin (C/I) was used as a surrogate index of hepatic MCRI.

RESULTS

Compared to the N monkeys, the DYS with normal glycemia and hyperinsulinemia had significantly higher basal and GGI-induced elevation of insulin and C-peptide concentrations and lower C/I, however, each unit of glucose-stimulated ISR increment was not significantly different from that in the N monkeys. In contrast, the DM monkeys with β-cell failure and hyperglycemia had a depressed GGI-stimulated ISR response and elevated C/I.

CONCLUSIONS

The present data demonstrated that in addition to β-cell hypersecretion of insulin, reduced hepatic MCRI may also contribute to the development of hyperinsulinemia in the DYS monkeys. On the other hand, hyperinsulinemia may cause the saturation of hepatic insulin extraction capacity, which in turn reduced MCRI in the DYS monkeys. The differential contribution of ISR and MCRI in causing hyperinsulinemia provides a new insight into the trajectory of β-cell dysfunction in the development of diabetes. The present study was the first to use the GGI and C-peptide deconvolution method to quantify the β-cell function in NHPs.

Nutrient infusion bypassing duodenum-jejunum improves insulin sensitivity in glucose-tolerant and diabetic obese subjects

The mechanisms of type 2 diabetes remission after bariatric surgery is still not fully elucidated. In the present study, we tried to simulate the Roux-en-Y gastric bypass with a canonical or longer biliary limb by infusing a liquid formula diet into different intestinal sections. Nutrients (Nutrison Energy) were infused into mid- or proximal jejunum and duodenum during three successive days in 10 diabetic and 10 normal glucose-tolerant subjects. Plasma glucose, insulin, C-peptide, glucagon, incretins, and nonesterified fatty acids (NEFA) were measured before and up to 360 min following. Glucose rate of appearance (Ra) and insulin sensitivity (SI), secretion rate (ISR), and clearance were assessed by mathematical models. SI increased when nutrients were delivered in mid-jejunum vs. duodenum (SI × 10⁴ min⁻¹·pM⁻¹: 1.11 ± 0.44 vs. 0.62 ± 0.22, P < 0.015, in controls and 0.79 ± 0.34 vs. 0.40 ± 0.20, P < 0.05, in diabetic subjects), whereas glucose Ra was not affected. In controls, Sensitivity of NEFA production was doubled in mid-jejunum vs. duodenum (2.80 ± 1.36 vs. 1.13 ± 0.78 × 10⁶, P < 0.005) and insulin clearance increased in mid-jejunum vs. duodenum (2.05 ± 1.05 vs. 1.09 ± 0.38 l/min, P < 0.03). Bypass of duodenum and proximal jejunum by nutrients enhances insulin sensitivity, inhibits lipolysis, and increases insulin clearance. These results may further our knowledge of the effects of bariatric surgery on both insulin resistance and diabetes.

Modulation of β-cell function: a translational journey from the bench to the bedside

Both decreased insulin secretion and action contribute to the pathogenesis of type 2 diabetes (T2D) in humans. The insulin receptor and insulin signalling proteins are present in the rodent and human β-cell and modulate cell growth and function. Insulin receptors and insulin signalling proteins in β-cells are critical for compensatory islet growth in response to insulin resistance. Rodents with tissue-specific knockout of the insulin receptor in the β-cell (βIRKO) show reduced first-phase glucose-stimulated insulin secretion (GSIS) and with aging develop glucose intolerance and diabetes, phenotypically similar to the process seen in human T2D. Expression of multiple insulin signalling proteins is reduced in islets of patients with T2D. Insulin potentiates GSIS in isolated human β-cells. Recent studies in humans in vivo show that pre-exposure to insulin increases GSIS, and this effect is diminished in persons with insulin resistance or T2D. β-Cell function correlates to whole-body insulin sensitivity. Together, these findings suggest that pancreatic β-cell dysfunction could be caused by a defect in insulin signalling within β-cell, and β-cell insulin resistance may lead to a loss of β-cell function and/or mass, contributing to the pathophysiology of T2D.

Distinct β-cell defects in impaired fasting glucose and impaired glucose tolerance

To characterize the defects in β-cell function in subjects with impaired fasting glucose (IFG) and compare the results to impaired glucose tolerance (IGT) and normal glucose tolerance (NGT) subjects, β-cell glucose sensitivity and rate sensitivity during the oral glucose tolerance test were measured with the model by Mari in 172 Mexican Americans. A subgroup (n=70) received a 2-h hyperglycemic clamp (+125 mg/dL), and first- and second-phase insulin secretion were quantitated. Compared with NGT, subjects with IFG and IGT manifested a decrease in β-cell glucose sensitivity; IFG subjects, but not IGT subjects, had decreased β-cell rate sensitivity. In IFG subjects, the defect in β-cell glucose sensitivity was time dependent, began to improve after 60 min, and was comparable to NGT after 90 min. The incremental area under the plasma C-peptide concentration curve during the first 12 min of the hyperglycemic clamp (ΔC-pep[AUC]0-12) was inversely related with the increase in FPG concentration (r=-36, r=0.001), whereas ΔC-pep[AUC]15-120 positively correlated with FPG concentration (r=0.29, r<0.05). When adjusted for the prevailing level of insulin resistance, first-phase insulin secretion was markedly decreased in both IFG and IGT, whereas second-phase insulin secretion was decreased only in IGT. These results demonstrate distinct defects in β-cell function in IFG and IGT.

Exogenous insulin enhances glucose-stimulated insulin response in healthy humans independent of changes in free fatty acids

CONTEXT

Islet β-cells express both insulin receptors and insulin signaling proteins. Recent studies suggest insulin signaling is physiologically important for glucose sensing.

OBJECTIVE

Preexposure to insulin enhances glucose-stimulated insulin secretion (GSIS) in healthy humans. We evaluated whether the effect of insulin to potentiate GSIS is modulated through regulation of free fatty acids (FFA).

DESIGN AND SETTING

Subjects were studied on three occasions in this single-site study at an academic institution clinical research center.

PATIENTS

Subjects included nine healthy volunteers.

INTERVENTIONS

Glucose-induced insulin response was assessed on three occasions after 4 h saline (low insulin/sham) or isoglycemic-hyperinsulinemic (high insulin) clamps with or without intralipid and heparin infusion, using B28 Asp-insulin that could be distinguished from endogenous insulin immunologically. During the last 80 min of all three clamps, additional glucose was administered to stimulate insulin secretion (GSIS) with glucose concentrations maintained at similar concentrations during all studies.

MAIN OUTCOME MEASURE

β-Cell response to glucose stimulation was assessed.

RESULTS

Preexposure to exogenous insulin increased the endogenous insulin-secretory response to glucose by 32% compared with sham clamp (P = 0.001). This was accompanied by a drop in FFA during hyperinsulinemic clamp compared with the sham clamp (0.06 ± 0.02 vs. 0.60 ± 0.09 mEq/liter, respectively), which was prevented during the hyperinsulinemic clamp with intralipid/heparin infusion (1.27 ± 0.17 mEq/liter). After preexposure to insulin with intralipid/heparin infusion to maintain FFA concentration, GSIS was 21% higher compared with sham clamp (P < 0.04) and similar to preexposure to insulin without intralipid/heparin (P = 0.2).

CONCLUSIONS

Insulin potentiates glucose-stimulated insulin response independent of FFA concentrations in healthy humans.

Impaired beta-cell sensitivity to glucose and maximal insulin secretory capacity in adolescents with type 2 diabetes

BACKGROUND

Adults with type 2 diabetes mellitus (T2DM) have broad impairments in beta-cell function, including severe attenuation of the first-phase insulin response to glucose, and reduced beta-cell mass. In adolescents with T2DM, there is some evidence that beta-cell dysfunction may be less severe. Our objective was to determine beta-cell sensitivity to glucose and maximal insulin secretory capacity (AIR(max)) in teenagers with T2DM.

METHODS

Fifteen adolescents with T2DM [11 F/4 M, age 18.4 +/- 0.3 yr, body mass index (BMI) 39.8 +/- 2.2 kg/m(2)] and 10 non-diabetic control subjects (7 F/3 M, age 17.4 +/- 0.5 yr, BMI 41.5 +/- 2.2 kg/m(2)) were studied. T2DM subjects had a mean duration of diabetes of 48.8 +/- 6.4 months, were treated with conventional therapies, and had good metabolic control [hemoglobin A1c (HbA1c) 6.7 +/- 1.2%]. Insulin and C-peptide were determined before and after a graded glucose infusion and after intravenous arginine at a whole blood glucose level of >or=22 mM.

RESULTS

The insulin response to increasing plasma glucose concentrations was blunted in the diabetic compared with control subjects (34.8 +/- 11.9 vs. 280.5 +/- 57.8 pmol/mmol; p < 0.0001), and AIR(max) was also significantly reduced in the diabetic group (1868 +/- 330 vs. 4445 +/- 606; p = 0.0005).

CONCLUSION

Even adolescents with well-controlled T2DM have severe impairments of insulin secretion. These data support beta-cell dysfunction as central in the pathogenesis of T2DM in young people, and indicate that these abnormalities can develop over a period of just several years.

Insulin secretion rate and beta-cell sensitivity from oral glucose tolerance test in normotensive and normoglycemic humans

Aim of the study was to test the reproducibility of estimates of static, Phi s, and dynamic, Phi d, beta-cell sensitivity to glucose, and predictions of the insulin secretion rate, SR(t), provided by the C-peptide oral minimal model (COMM) applied to oral glucose tolerance tests (OGTT) of various complexity. The study involved six volunteer, normotensive and normoglycemic subjects who underwent a 300-minute OGTT. Results from a full 22-sampling schedule (OGTT300/22), were compared with those from two reduced schedules consisting of 11 samples in 300 min (OGTT300/11) and 7 samples in 120 min (OGTT120/7). Our results showed that both reduced-sample protocols did not affect significantly the estimates of Phi d. Intraclass correlation coefficients were higher than 0.9. The Phi s appeared more sensitive to reductions of protocol complexity. Nevertheless, intraclass correlation coefficients kept higher than 0.7. No significant differences were found in model predictions of SR(t) profiles among all tested OGTT protocols. These findings confirm the COMM as a potentially useful tool to quantify beta-cell sensitivity and insulin secretion rate in pathophysiological studies, from relatively low-cost OGTT.

Le syndrome des ovaires polykystiques (SOPK)

Polycystic ovaries syndrome (PCOS) is one of the most common female hormonal disorders. Its multiple components--reproductive, metabolic, neoplasic and cardiovascular--have a major impact on the public health. Androgen excess and resistance to insulin, probably from genetic origin, are responsible for most of the clinical symptomatology. Resistance to insulin seems to be accompanied by a greater risk of glucose intolerance, type 2 diabetes, lipidic anomalies and can involve the development of cardiovascular diseases. In addition, sleep apnea syndrome is more progressively described in PCOS. Infertility, menses disorders and hirsutism often push these patients to consult their physician. A better understanding of the physiopathological mechanisms led to the emergence of new therapeutic options increasing the sensitivity to insulin. Besides the pregnancy wishes, cares aim to attenuate the marks of the hyper-androgenism (hormonal treatment and cosmetic) and to correct cardiovascular, respiratory and gynaecological risk factors. In case of infertility by anovulation, cares must be performed by trained experts to minimize the risk of ovarian hyper-stimulation syndrome and multiple pregnancies. A gradation from loose weight to clomiphene citrate ovulation induction, ovarian drilling, low dose gonadotropin, in vitro fertilisation, or in vitro maturation of oocytes should bring back good reproduction potential.

Feasibility of automating insulin delivery for the treatment of type 1 diabetes

An automated closed-loop insulin delivery system based on subcutaneous glucose sensing and subcutaneous insulin delivery was evaluated in 10 subjects with type 1 diabetes (2 men, 8 women, mean [+/-SD] age 43.4 +/- 11.4 years, duration of diabetes 18.2 +/- 13.5 years). Closed-loop control was assessed over approximately 30 h and compared with open-loop control assessed over 3 days. Closed-loop insulin delivery was calculated using a model of the beta-cell's multiphasic insulin response to glucose. Plasma glucose was 160 +/- 66 mg/dl at the start of closed loop and was thereafter reduced to 71 +/- 19 by 1:00 p.m. (preprandial lunch). Fasting glucose the subsequent morning on closed loop was not different from target (124 +/- 25 vs. 120 mg/dl, respectively; P > 0.05). Mean glucose levels were not different between the open and closed loop (133 +/- 63 vs. 133 +/- 52 mg/dl, respectively; P > 0.65). However, glucose was within the range 70-180 mg/dl 75% of the time under closed loop versus 63% for open loop. Incidence of biochemical hypoglycemia (blood glucose <60 mg/dl) was similar under the two treatments. There were no episodes of severe hypoglycemia. The data provide proof of concept that glycemic control can be achieved by a completely automated external closed-loop insulin delivery system.

Use of Metformin for Ovulation Induction in Women Who Have Polycystic Ovary Syndrome With or Without Evidence of Insulin Resistance

OBJECTIVE

To determine whether women with polycystic ovary syndrome (PCOS) and abnormal insulin levels treated with metformin had different rates of ovulation and pregnancy from women with PCOS and normal insulin levels.

METHODS

The outcomes of treatment with metformin in 146 infertile women with PCOS were analyzed using a retrospective cohort study design. Baseline characteristics and initial blood work results were recorded. The follow-up period was three months, and the primary outcome was ovulation.

RESULTS

Of the 146 women with PCOS, one third had elevated fasting insulin levels. After treatment with metformin, cumulative rates of ovulation were similar in women with elevated fasting serum insulin levels (48.8%) and those with normal levels (44.7%). Rates of ovulation were also similar in women with normal and abnormal glucose to insulin ratios. There was no difference in cumulative pregnancy rates based on fasting insulin levels. A fasting insulin level above 20 mU/L correlated with an abnormal glucose to insulin ratio (98%).

CONCLUSION

In anovulatory women with PCOS, fasting insulin levels and glucose to insulin ratios do not predict the ovulatory response to metformin.

Multiple defects in counterregulation of hypoglycemia in modestly advanced type 2 diabetes mellitus

In type 2 diabetes mellitus (T2DM), little is known about hormonal responses to hypoglycemia. In particular, beta-cell responses to hypoglycemia have not been carefully investigated and potentially because of confounding factors or insufficient power, conflicting data have been obtained regarding growth hormone responses. We therefore compared hormonal responses including rates of insulin secretion during a 2-hour hyperinsulinemic hypoglycemic clamp in a relatively large number of nondiabetic (n=21) and moderately insulin-deficient subjects with T2DM (homeostasis model assessment of beta-cell function [HOMA-%B], 751+/-160 vs 1144+/-83 [pmol/L]/[mmol/L], P<.04) (n=14) matched for age, sex, and body mass index. Subjects with T2DM were excluded for antecedent hypoglycemia, and baseline glycemia was controlled by a variable infusion of insulin overnight. Although both groups of subjects had indistinguishable plasma glucose levels at baseline and virtually identical levels of plasma insulin and glucose throughout the hypoglycemic clamp, insulin secretion decreased more slowly in the subjects with T2DM. The time required for insulin secretion to decline to half its baseline level was markedly increased (38.9+/-4.9 vs 22.3+/-1.3 minutes [SD], P<.01), and insulin secretion decreased to a lesser extent (-0.79+/-0.17 vs -1.51+/-0.09 [pmol/L]/kg per minute, P<.002). Moreover, responses of glucagon (28.3+/-7.3 vs 52.8+/-7.0 ng/L, P<.05) and growth hormone (2.9+/-0.8 vs 6.3+/-0.9 ng/mL, P<.04) were reduced in the subjects with T2DM, whereas responses of epinephrine, norepinephrine, and cortisol were similar to those in nondiabetic subjects (all P>0.6). We conclude that multiple defects exist in hormonal responses to hypoglycemia in T2DM with moderate beta-cell failure. These include delayed and reduced decreases in insulin secretion, and impaired increases of plasma glucagon and growth hormone.

Contributions of beta-cell dysfunction and insulin resistance to the pathogenesis of impaired glucose tolerance and impaired fasting glucose

Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are intermediate states in glucose metabolism that exist between normal glucose tolerance and overt diabetes. Epidemiological studies demonstrate that the two categories describe distinct populations with only partial overlap, suggesting that different metabolic abnormalities characterize IGT and IFG. Insulin resistance and impaired beta-cell function, the primary defects observed in type 2 diabetes, both can be detected in subjects with IGT and IFG. However, clinical studies suggest that the site of insulin resistance varies between the two disorders. While subjects with IGT have marked muscle insulin resistance with only mild hepatic insulin resistance, subjects with IFG have severe hepatic insulin resistance with normal or near-normal muscle insulin sensitivity. Both IFG and IGT are characterized by a reduction in early-phase insulin secretion, while subjects with IGT also have impaired late-phase insulin secretion. The distinct metabolic features present in subjects with IFG and IGT may require different therapeutic interventions to prevent their progression to type 2 diabetes.

Coordinate changes in plasma glucose and pancreatic beta-cell function in Latino women at high risk for type 2 diabetes

The purpose of this study was to examine longitudinally the relationship among glucose levels, pancreatic beta-cell function, and insulin resistance in women at high risk for type 2 diabetes. Oral glucose tolerance tests (OGTTs) and intravenous glucose tolerance tests (IVGTTs) were performed at 15-month intervals for up to 5 years or until fasting plasma glucose exceeded 140 mg/dl in Hispanic women with recent gestational diabetes. Data were analyzed 1) to compare changes in insulin sensitivity, beta-cell function, and glucose levels between women who had diabetes at one or more visits and women who remained diabetes free and 2) to determine longitudinal patterns of change in glucose levels and acute beta-cell compensation for insulin resistance. Seventy-one women provided data from a total of 280 paired OGTTs and IVGTTs during a median follow-up of 46 months. Compared with the 47 women who remained free of diabetes, the 24 who either had diabetes (n = 9) or developed it during follow-up (n = 15) had higher baseline glucose levels and lower acute beta-cell compensation for insulin resistance. Baseline insulin sensitivity was low in both groups and did not change significantly during follow-up. Fasting and 2-h glucose levels increased more rapidly in the diabetic group despite a decline in acute beta-cell compensation that was significantly slower than the decline in women who did not develop diabetes. This paradox was explained by an accelerated rise in glucose levels for any decline in beta-cell compensation when beta-cell compensation reached approximately 10% of normal, a level that was reached in the women who had or developed diabetes but not in the women who remained diabetes free. These findings define a pathogenesis for type 2 diabetes in one high-risk group that is characterized by a relatively long-term decline in acute beta-cell compensation for chronic insulin resistance that is attended by slowly rising glucose levels. Only relatively late in this process do glucose levels rise rapidly and into the diabetic range.

Beta-cell function and insulin sensitivity contribute to the shape of plasma glucose curve during an oral glucose tolerance test in non-diabetic individuals

To clarify whether beta-cell function and/or insulin resistance contributes to the shape of plasma glucose curve during an oral glucose tolerance test (OGTT), we investigated 583 Japanese subjects with normal glucose tolerance (NGT, n = 306) or impaired glucose tolerance (IGT, n = 277). Each subject was subdivided into three shapes of plasma glucose curve as follows: monophasic pattern (M type), biphasic pattern (B type) and two peaks (T type). Homeostasis model assessment of insulin resistance, quantitative insulin sensitivity check index and insulinogenic index were assessed by plasma glucose and insulin concentrations obtained at fasting or during an OGTT. There was a greater proportion of M type in the IGT group (M = 80.9%, B = 15.5% and T = 3.6%), whereas the prevalence of B and T types was much higher in the NGT group (M = 66.6%, B = 26.5% and T = 6.9%). There were significant differences in the proportions of shape types between the NGT and IGT groups (p = 0.0006). Among the NGT category, insulin sensitivity was significantly higher in the B type than in the M type, and beta-cell function adjusted for insulin resistance was significantly higher in the B and T types than in the M type. Among the IGT category, no significant differences were seen among the three shape types with respect to insulin sensitivity, but the beta-cell function adjusted for insulin resistance was significantly lower in the M type than in the B and T types. In conclusion, both impaired insulin secretion and insulin resistance may contribute to the underlying mechanisms of the shape of plasma glucose curve in Japanese subjects.

Impaired beta-cell compensation to dexamethasone-induced hyperglycemia in women with polycystic ovary syndrome

Deterioration in glucose tolerance occurs rapidly in women with polycystic ovary syndrone (PCOS), suggesting that pancreatic beta-cell dysfunction may supervene early. To determine whether the compensatory insulin secretory response to an increase in insulin resistance induced by the glucocorticoid dexamethasone differs in women with PCOS and control subjects, we studied 10 PCOS and 6 control subjects with normal glucose tolerance. An oral glucose tolerance test (OGTT) and a graded glucose infusion protocol were performed at baseline and after subjects took 2.0 mg of dexamethasone orally. Basal (Phi(b)), static (Phi(s)), dynamic (Phi(d)), and global (Phi) indexes of beta-cell sensitivity to glucose were derived. Insulin sensitivity (S(i)) was calculated using the minimal model; a disposition index (DI) was calculated as the product of S(i) and Phi. PCOS and control subjects had nearly identical fasting and 2-h glucose levels at baseline. Phi(b) was higher, although not significantly so, in the PCOS subjects. The Phi(d), Phi(s), and Phi indexes were 28, 19, and 20% higher, respectively, in PCOS subjects. The DI was significantly lower in PCOS (30.01 +/- 5.33 vs. 59.24 +/- 7.59) at baseline. After dexamethasone, control subjects averaged a 9% increase (to 131 +/- 12 mg/dl) in 2-h glucose levels; women with PCOS had a significantly greater 26% increase to 155 +/- 6 mg/dl. The C-peptide-to-glucose ratios on OGTT increased by 44% in control subjects and by only 15% in PCOS subjects. The accelerated deterioration in glucose tolerance in PCOS may result, in part, from a relative attenuation in the response of the beta-cell to the demand placed on it by factors exacerbating insulin resistance.

Evaluation of insulin sensitivity and beta-cell function indexes obtained from minimal model analysis of a meal tolerance test

Modeling analysis of glucose, insulin, and C-peptide following a meal has been proposed as a means to estimate insulin sensitivity (S(i)) and beta-cell function from a single test. We compared the model-derived meal indexes with analogous indexes obtained from an intravenous glucose tolerance test (IVGTT) and hyperglycemic clamp (HGC) in 17 nondiabetic subjects (14 men, 3 women, aged 50 +/- 2 years [mean +/- SE], BMI 25.0 +/- 0.7 kg/m(2)). S(i) estimated from the meal was correlated with S(i) estimated from the IVGTT and the HGC (r = 0.59 and 0.76, respectively; P < 0.01 for both) but was approximately 2.3 and 1.4 times higher (P < 0.05 for both). The meal-derived estimate of the beta-cell's response to a steady-state change in glucose (static secretion index) was correlated with the HGC second-phase insulin response (r = 0.69; P = 0.002), but the estimated rate-of-change component (dynamic secretion index) was not correlated with first-phase insulin release from either the HGC or IVGTT. Indexes of beta-cell function obtained from the meal were significantly higher than those obtained from the HGC. In conclusion, insulin sensitivity and beta-cell indexes derived from a meal are not analogous to those from the clamp or IVGTT. Further work is needed before these indexes can be routinely used in clinical and epidemiological studies.

Insulin secretion in type 1 diabetes

Type 1 diabetes, a chronic autoimmune disease, causes destruction of insulin-producing beta-cells over a period of years. Although many markers of the autoimmune process have been described, none can convincingly predict the rate of disease progression. Moreover, there is relatively little information about changes in insulin secretion in individuals with type 1 diabetes over time. Previous studies document C-peptide at a limited number of time points, often after a nonphysiologic stimulus, and under non-steady-state conditions. Such methods do not provide qualitative information and may not reflect physiologic responses. We have studied qualitative and quantitative insulin secretion to a 4-h mixed meal in 41 patients with newly diagnosed type 1 diabetes and followed the course of this response for 24 months in 20 patients. Newly diagnosed diabetic patients had an average total insulin secretion in response to a mixed meal that was 52% of that in nondiabetic control subjects, considerably higher than has been described previously. In diabetic patients there was a decline of beta-cell function at an average rate of 756 +/- 132 pmol/month to a final value of 28 +/- 8.4% of initial levels after 2 years. There was a significant correlation between the total insulin secretory response and control of glucose, measured by HbA(1c) (P = 0.003). Two persistent patterns of insulin response were seen depending on the peak insulin response following the oral meal. Patients with an early insulin response (i.e., within the first 45 min after ingestion) to a mixed meal, which was also seen in 37 of 38 nondiabetic control subjects, had a significantly accelerated loss of insulin secretion, as compared with those in whom the insulin response occurred after this time (P < 0.05), and significantly greater insulin secretory responses at 18 and 24 months (P < 0.02). These results, which are the first qualitative studies of insulin secretion in type 1 diabetes, indicate that the physiologic metabolic response is greater at diagnosis than has previously been appreciated, and that the qualitative insulin secretory response is an important determinant of the rate of metabolic decompensation from autoimmune destruction.

Upregulation of insulin receptor substrate-2 in pancreatic beta cells prevents diabetes

The insulin receptor substrate-2 (Irs2) branch of the insulin/IGF signaling system coordinates peripheral insulin action and pancreatic beta cell function, so mice lacking Irs2 display similarities to humans with type 2 diabetes. Here we show that beta cell-specific expression of Irs2 at a low or a high level delivered a graded physiologic response that promoted beta cell growth, survival, and insulin secretion that prevented diabetes in Irs2-/- mice, obese mice, and streptozotocin-treated mice; and that upon transplantation, the transgenic islets cured diabetes more effectively than WT islets. Thus, pharmacological approaches that promote Irs2 expression in beta cells, especially specific cAMP agonists, could be rational treatments for beta cell failure and diabetes.

Predominant role of reduced beta-cell sensitivity to glucose over insulin resistance in impaired glucose tolerance

AIMS/HYPOTHESIS

Impaired glucose tolerance (IGT) is an insulin-resistant state and a risk factor for Type 2 diabetes. The relative roles of insulin resistance and insulin deficiency in IGT have been disputed.

METHODS

In 40 IGT subjects and 63 sex-, age-, and weight-matched controls with normal glucose tolerance (NGT), we measured (i) indices of insulin sensitivity of fasting glucose production (by tracer glucose) and glucose disposal (M value on a 240 pmol x min(-1) x m(-2) insulin clamp) and (ii) indices of beta-cell function (glucose sensitivity, rate sensitivity, and potentiation) derived from model analysis (Am J Physiol 283:E1159-E1166, 2002) of the insulin secretory response (by C-peptide deconvolution) to oral glucose.

RESULTS

In comparison with NGT, IGT were modestly insulin resistant (M=29+/-2 vs 35+/-2 micromol x min(-1) x kg(FFM)(-1), p=0.01); insulin sensitivity of glucose production also was reduced, in approximate proportion to M. Despite higher baseline insulin secretion rates, IGT was characterized by a 50% reduction in glucose sensitivity [53 (36) vs 102 (123) pmol x min(-1) x m(-2) x mM(-1), median (interquartile range), p=0.001] and impaired potentiation [1.6 (0.8) vs 2.0 (1.5) units, p<0.04] of insulin release, whereas rate sensitivity [1.15 (1.15) vs 1.38 (1.28) nmol x m(-2) x mM(-1)] was not significantly reduced. Glucose sensitivity made the single largest contribution (approximately 50%) to the observed variability of glucose tolerance.

CONCLUSION/INTERPRETATION

In IGT the defect in glucose sensitivity of insulin release quantitatively predominates over insulin resistance in the genesis of the reduced tolerance to oral glucose.

Modeling beta-cell insulin secretion--implications for closed-loop glucose homeostasis

Glucose sensing and insulin delivery technology can potentially be linked to form a closed-loop insulin delivery system. Ideally, such a system would establish normal physiologic glucose profiles. To this end, a model of beta-cell secretion can potentially provide insight into the preferred structure of the insulin delivery algorithm. Two secretion models were evaluated for their ability to describe plasma insulin dynamics during hyperglycemic clamps (humans; n=7), and for their ability to establish and maintain fasting euglycemia under conditions simulated by the minimal model. The first beta-cell model (SD) characterized insulin secretion as a static component that had a delayed response to glucose, and a dynamic component that responded to the rate of increase of glucose. The second model (PID) described the response in terms of a proportional component without delay, an integral component that adjusted basal delivery in proportion to hyper/hypoglycemia, and a derivative component that responded to the rate of glucose change. Both models fit the beta-cell response during the clamp, and established fasting euglycemia under simulated closed-loop conditions; however, the SD model did not maintain euglycemia following simulated changes in insulin sensitivity or glucose appearance, whereas the PID model did. The PID model was more stable under the simulated closed-loop conditions. Both the SD and PID models described beta-cell secretion in response to a rapid increase in glucose. However, the PID model could maintain fasting euglycemia and was more stable under closed-loop conditions, and thus is more suited for such conditions.