Simple empirical assessment of beta-cell function by a constant infusion of glucose test in normal and type 2 (non-insulin-dependent) diabetic subjects

National trends in insulin resistance and β-cell dysfunction among adults with prediabetes: NHANES 2001-2016

Background

Insulin resistance is the central abnormality and mechanism underlying the progression of cardiometabolic-based chronic diseases. This study aimed to evaluate the trends in insulin resistance and β-cell dysfunction from 2001 to 2016 among US adults with undiagnosed diabetes, prediabetes, and normal glucose regulation and to provide sex-specific information using data from National Health and Nutrition Examination Surveys (NHANES) 2001–2016.

Methods

Data from 14,481 participants aged over 20 years from 8 consecutive 2-year cross–sectional cycles of the NHANES from 2001 to 2016 were used. Updated homoeostasis model assessment 2 (HOMA2: HOMA2%B for β-cell function and HOMA2IR for insulin resistance) was used as a surrogate measure. We defined the upper sex-specific tertile of HOMA2IR as insulin resistance and the lower corresponding tertile of HOMA2%B as low β-cell function.

Results

In both sexes with undiagnosed diabetes, HOMA2%B (men, P_trend = 0.118; women, P_trend = 0.184) and HOMA2IR (men, P_trend = 0.710; women, P_trend = 0.855) remained stable over time. In the prediabetes group, both sexes exhibited significant increasing trends in HOMA2%B (men, P_trend < 0.010; women, P_trend < 0.010) and HOMA2IR (men, P_trend < 0.010; women, P_trend < 0.050). Adjusting for waist circumference mildly attenuated the trend in HOMA2IR and insulin resistance in men (P_trend < 0.010), but it resulted in no significance in women (P_trend = 0.196). In regard to normal glucose regulation, both sexes presented significant decreasing trends in low β-cell function (men, P_trend < 0.050; women < 0.010) and attenuated trends in insulin resistance (men, P_trend = 0.196; women, P_trend = 0.121).

Conclusions

Over 16 years, insulin resistance demonstrated an increasing trend in adult US population with prediabetes, while β-cell function showed a compensatory increasing trend. Identifying people with prediabetes early and focusing on reducing insulin resistance as the intervention core, especially controlling central obesity, might increase the opportunity for cardiovascular and diabetes risk reduction.

Lixisenatide as add-on treatment among patients with different β-cell function levels as assessed by HOMA-β index

BACKGROUND

The effect of lixisenatide-a prandial once-daily glucagon-like peptide-1 receptor agonist-on glycaemic control in patients with inadequately controlled type 2 diabetes mellitus (T2DM), stratified by baseline β-cell function, was assessed.

METHODS

The 24-week GetGoal-M, -P and -S trials evaluated the efficacy and safety of lixisenatide in combination with oral antidiabetic agents. This post hoc analysis used data from patients receiving lixisenatide in these trials, divided into matched cohorts by propensity scoring, and stratified according to baseline homeostasis model assessment of β-cell function (HOMA-β) index levels, high HOMA-β: > median HOMA-β (28.49%); low HOMA-β: ≤ median.

RESULTS

The matched "low" and "high" HOMA-β index cohorts (N = 546 patients) had comparable baseline parameters. Mean change from baseline in glycated haemoglobin (HbA_1c ) was -0.85% and -0.94% for low and high HOMA-β cohorts, respectively (P = .2607). Reductions from baseline in fasting plasma glucose (FPG; -0.77 vs -1.04 mmol/L; P = .1496) and postprandial plasma glucose (PPG; -5.82 vs -5.61 mmol/L; P = .7511) were similar in the low versus high HOMA-β index cohorts. Reduction in body weight was significantly greater in the low versus high HOMA-β index cohort (-2.06 vs -1.13 kg, respectively; P = .0006).

CONCLUSIONS

In patients with T2DM, lixisenatide was associated with reduction in HbA_1c and improvements in both FPG and PPG, regardless of β-cell function, indicating that lixisenatide is effective in reducing hyperglycaemia, even in patients with more advanced stages of T2DM and poor residual β-cell function.

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).

Changes in insulin resistance indicators, IGFs, and adipokines in a year-long trial of aerobic exercise in postmenopausal women

Physical activity is a known modifiable lifestyle means for reducing postmenopausal breast cancer risk, but the biologic mechanisms are not well understood. Metabolic factors may be involved. In this study, we aimed to determine the effects of exercise on insulin resistance (IR) indicators, IGF1, and adipokines in postmenopausal women. The Alberta Physical Activity and Breast Cancer Prevention Trial was a two-armed randomized controlled trial in postmenopausal, inactive, cancer-free women. A year-long aerobic exercise intervention of 225  min/week (n=160) was compared with a control group asked to maintain usual activity levels (n=160). Baseline, 6- and 12-month serum levels of insulin, glucose, IGF1, IGF-binding protein 3 (IGFBP3), adiponectin, and leptin were assayed, and after data collection, homeostasis model assessment of IR (HOMA-IR) scores were calculated. Intention-to-treat analyses were performed using linear mixed models. The treatment effect ratio (TER) of exercisers to controls was calculated. Data were available on 308 (96.3%) women at 6 months and 310 (96.9%) women at 12 months. Across the study period, statistically significant reductions in insulin (TER=0.87, 95% confidence interval (95% CI)=0.81-0.93), HOMA-IR (TER=0.86, 95% CI=0.80-0.93), and leptin (TER=0.82, 95% CI=0.78-0.87), and an increase in the adiponectin/leptin ratio (TER=1.21, 95% CI=1.13-1.28) were observed in the exercise group compared with the control group. No significant differences were observed for glucose, IGF1, IGFBP3, adiponectin or the IGF1/IGFBP3 ratio. Previously inactive postmenopausal women who engaged in a moderate-to-vigorous intensity exercise program experienced changes in insulin, HOMA-IR, leptin, and adiponectin/leptin that might decrease the risk for postmenopausal breast cancer.

Randomized clinical trial to compare the effects of preoperative oral carbohydrate versus placebo on insulin resistance after colorectal surgery

Background

Preoperative oral carbohydrate (OCH) reduces postoperative insulin resistance (PIR). This randomized trial investigated whether this effect is related to insulin-induced activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) signalling pathway.

Methods

Patients with colorectal cancer scheduled for elective open resection were randomly assigned to preoperative OCH, fasting or placebo. Preoperative general well-being, insulin resistance before and immediately after surgery, and postoperative expression of PI3K, PKB, protein tyrosine kinase (PTK) and glucose transporter 4 (GLUT4) in rectus abdominis muscle were evaluated.

Results

Patient and operative characteristics did not differ between groups. Subjective well-being was significantly better in OCH and placebo groups than in the fasting group, primarily because of reduced thirst (P = 0·005) and hunger (P = 0·041). PIR was significantly greater in fasting and placebo groups (P &lt; 0·010). By the end of surgery, muscle PTK activity as well as PI3K and PKB levels were significantly increased in the OCH group compared with values in fasting and placebo groups (P &lt; 0·050), but GLUT4 expression was unaffected.

Conclusion

PIR involves the PI3K/PKB signalling pathway. Preoperative OCH intake improves preoperative subjective feelings of hunger and thirst compared with fasting, while attenuating PIR by stimulation of the PI3K/PKB pathway. Registration number: NCT00755729 (http://www.clinicaltrials.gov).

Evaluation of beta-cell mass and function in the Göttingen minipig

Increased knowledge about beta-cell mass and function is important for our understanding of the pathophysiology of type 2 diabetes (T2DM). The relationship between the two is difficult to study in humans, whereas animal models allow studies of consequences of, for example, reduction of beta-cell mass and induction of obesity and procurement of the pancreas for histological examination. An overview of results obtained in the Göttingen minipig in relation to beta-cell function, and mass is provided here. Effects of a primary reduction of beta-cell mass have indicated that not all of the defects of pulsatile insulin secretion in human T2DM can be explained by reduced beta-cell mass. Furthermore, induction of obesity has shown deterioration of beta-cell function and morphological changes in the pancreas. As in humans, obesity leads to an increased beta-cell volume in the minipig, and based on the increased number of islets, neogenesis of islets is an important factor in expansion of beta-cell mass in this species. Measurement of beta-cell function as an estimate of beta-cell mass is, at present, the only method possible in humans, and this approach has been validated using lean and obese minipigs with a range of beta-cell mass. The effects on beta-cell function and mass of obesity of longer duration and/or more pronounced hyperglycaemia remains to be determined, but the models developed so far represent a valuable tool for such investigations.

Measurements of insulin responses as predictive markers of pancreatic beta-cell mass in normal and beta-cell-reduced lean and obese Göttingen minipigs in vivo

At present, the best available estimators of beta-cell mass in humans are those based on measurement of insulin levels or appearance rates in the circulation. In several animal models, these estimators have been validated against beta-cell mass in lean animals. However, as many diabetic humans are obese, a correlation between in vivo tests and beta-cell mass must be evaluated over a range of body weights to include different levels of insulin sensitivity. For this purpose, obese (n = 10) and lean (n = 25) Göttingen minipigs were studied. Beta-cell mass had been reduced (n = 16 lean, n = 5 obese) with a combination of nicotinamide (67 mg/kg) and streptozotocin (125 mg/kg), acute insulin response (AIR) to intravenous glucose and/or arginine was tested, pulsatile insulin secretion was evaluated by deconvolution (n = 30), and beta-cell mass was determined histologically. AIR to 0.3 (r(2) = 0.4502, P < 0.0001) or 0.6 g/kg glucose (r(2) = 0.6806, P < 0.0001), 67 mg/kg arginine (r(2) = 0.5730, P < 0.001), and maximum insulin concentration (r(2) = 0.7726, P < 0.0001) were all correlated to beta-cell mass when evaluated across study groups, and regression lines were not different between lean and obese groups except for AIR to 0.3 g/kg glucose. Baseline pulse mass was not significantly correlated to beta-cell mass across the study groups (r(2) = 0.1036, NS), whereas entrained pulse mass did show a correlation across groups (r(2) = 0.4049, P < 0.001). This study supports the use of in vivo tests of insulin responses to evaluate beta-cell mass over a range of body weights in the minipig. Extensive stimulation of insulin secretion by a combination of glucose and arginine seems to give the best correlation to beta-cell mass.

Carotid artery intimal medial thickness, brachial artery flow-mediated vasodilation and cardiovascular risk factors in diabetic and non-diabetic indigenous Australians

BACKGROUND

Indigenous Australians are at high risk for cardiovascular disease and type 2 diabetes. Carotid artery intimal medial thickness (CIMT) and brachial artery flow-mediated vasodilation (FMD) are ultrasound imaging based surrogate markers of cardiovascular risk. This study examines the relative contributions of traditional cardiovascular risk factors on CIMT and FMD in adult Indigenous Australians with and without type 2 diabetes mellitus.

METHOD

One hundred and nineteen Indigenous Australians were recruited. Physical and biochemical markers of cardiovascular risk, together with CIMT and FMD were measured for all subjects.

RESULTS

Fifty-three Indigenous Australians subjects (45%) had type 2 diabetes mellitus. There was a significantly greater mean CIMT in diabetic versus non-diabetic subjects (p=0.049). In the non-diabetic group with non-parametric analyses, there were significant correlations between CIMT and: age (r=0.64, p<0.001), systolic blood pressure (r=0.47, p<0.001) and non-smokers (r=-0.30, p=0.018). In the diabetic group, non-parametric analysis showed correlations between CIMT, age (r=0.36, p=0.009) and duration of diabetes (r=0.30, p=0.035) only. Adjusting for age, sex, smoking and history of cardiovascular disease, Hb(A1c) became the sole significant correlate of CIMT (r=0.35, p=0.01) in the diabetic group. In non-parametric analysis, age was the sole significant correlate of FMD (r=-0.31, p=0.013), and only in non-diabetic subjects. Linear regression analysis showed significant associations between CIMT and age (t=4.6, p<0.001), systolic blood pressure (t=2.6, p=0.010) and Hb(A1c) (t=2.6, p=0.012), smoking (t=2.1, p=0.04) and fasting LDL-cholesterol (t=2.1, p=0.04). There were no significant associations between FMD and examined cardiovascular risk factors with linear regression analysis

CONCLUSIONS

CIMT appears to be a useful surrogate marker of cardiovascular risk in this sample of Indigenous Australian subjects, correlating better than FMD with established cardiovascular risk factors. A lifestyle intervention programme may alleviate the burden of cardiovascular disease in Indigenous Australians by reducing central obesity, lowering blood pressure, correcting dyslipidaemia and improving glycaemic control. CIMT may prove to be a useful tool to assess efficacy of such an intervention programme.

Beta-cell function and islet morphology in normal, obese, and obese beta-cell mass-reduced Göttingen minipigs

Herein, we bridge beta-cell function and morphology in minipigs. We hypothesized that different aspects of beta-cell dysfunction are present in obesity and obesity with reduced beta-cell mass by using pulsatile insulin secretion as an early marker. Measures for beta-cell function (glucose and arginine stimulation plus baseline and glucose-entrained pulsatile insulin secretion) and islet morphology were studied in long-term (19-20 mo) obese (n = 5) and obese beta-cell-reduced [nicotinamide + streptozotocin (STZ), n = 5] minipigs and normal controls, representing different stages in the development toward type 2 diabetes. Acute insulin response (AIR) to glucose and arginine were, surprisingly, normal in obese (0.3 g/kg glucose: AIR = 246 +/- 119 vs. 255 +/- 61 pM in control; 67 mg/kg arginine: AIR = 230 +/- 124 vs. 214 +/- 85 pM in control) but reduced in obese-STZ animals (0.3 g/kg glucose: AIR = 22 +/- 36, P < 0.01; arginine: AIR = 87 +/- 92 pM, P < 0.05 vs. control). Baseline pulsatile insulin secretion was reduced in obese (59 +/- 16 vs. 76 +/- 16% in control, P < 0.05) and more so in obese-STZ animals (43 +/- 13%, P < 0.01), whereas regularity during entrainment was increased in obese animals (approximate entropy: 0.85 +/- 0.14 vs. 1.13 +/- 0.13 in control, P < 0.01). Beta-cell mass (mg/kg body wt) was normal in obese and reduced in obese-STZ animals, with pancreatic fat infiltration in both groups. In conclusion, obesity and insulin resistance are not linked with a general reduction of beta-cell function, but dynamics of insulin secretion are perturbed. The data suggest a sequence in the development of beta-cell dysfunction, with the three groups representing stages in the progression from normal physiology to diabetes, and assessment of pulsatility as the single most sensitive marker of beta-cell dysfunction.

Prevalence and Determinants of Impaired Glucose Metabolism in Frail Elderly Patients: The Belgian Elderly Diabetes Survey (BEDS)

BACKGROUND

Although diabetes in elderly persons is generally type 2, the metabolic abnormalities associated with aging suggest that elderly persons may differ from younger persons with type 2 diabetes. In addition, nonobese elderly persons with type 2 diabetes show a marked impairment in insulin release accompanied by mild insulin resistance, whereas obese elderly persons have marked insulin resistance in the presence of "adequate" levels of insulin. Other factors that could adversely affect glucose tolerance in aging include drug use, associated disease, and other stressful conditions commonly encountered in geriatric inpatients units. The authors' objectives in this study were 1) to prospectively assess the prevalence of glucose homeostasis abnormalities among elderly hospitalized patients and the degree to which it reflects abnormalities in insulin secretion or insulin sensitivity using homeostasis model assessment of fasting glucose, insulin, and C-peptide; and 2) to define the social, functional, pathologic, and nutritional characteristics of persons with impaired glucose tolerance or diabetes.

METHODS

Ninety-eight patients underwent a comprehensive geriatric assessment. Determinants of glucose homeostasis were assessed using the homeostasis model assessment, which provides estimates of beta-cell function (%B) and insulin sensitivity (%S).

RESULTS

Twelve patients (12%) had fasting glucose concentrations greater than 110 mg/dl. Four patients had impaired fasting glucose levels greater than 110 mg/dl but less than 126 mg/dl (IFG group), and 8 patients had levels greater than 126 mg/dl (type 2 diabetes group). Except for a higher proportion of women in the IFG-diabetes group, the latter did not exhibit significant differences in functional, morbidity, or nutritional characteristics compared with the normal glucose tolerance group. The entire cohort (n=98) presented with a mean (+/-SD) %B of 71%+/-47% and a mean %S of 208%+/-198%. Compared with the normal glucose tolerance group, the IFG-diabetes group had a fasting glycemia level of 142+/-24 mg/dl (vs 92+/-9 mg/dl), a %B of 43%+/-21% (vs 74%+/-45%), and a mean %S of 126%+/-113% (vs 219%+/-205%).

CONCLUSIONS

These data confirm the high prevalence of impaired glucose metabolism among elderly people, although the usual risk factors were not significantly increased. Marked beta secretory defects seem to be the rule, whereas a significant degree of insulin resistance is unusual.

Use and abuse of HOMA modeling

Homeostatic model assessment (HOMA) is a method for assessing beta-cell function and insulin resistance (IR) from basal (fasting) glucose and insulin or C-peptide concentrations. It has been reported in >500 publications, 20 times more frequently for the estimation of IR than beta-cell function. This article summarizes the physiological basis of HOMA, a structural model of steady-state insulin and glucose domains, constructed from physiological dose responses of glucose uptake and insulin production. Hepatic and peripheral glucose efflux and uptake were modeled to be dependent on plasma glucose and insulin concentrations. Decreases in beta-cell function were modeled by changing the beta-cell response to plasma glucose concentrations. The original HOMA model was described in 1985 with a formula for approximate estimation. The computer model is available but has not been as widely used as the approximation formulae. HOMA has been validated against a variety of physiological methods. We review the use and reporting of HOMA in the literature and give guidance on its appropriate use (e.g., cohort and epidemiological studies) and inappropriate use (e.g., measuring beta-cell function in isolation). The HOMA model compares favorably with other models and has the advantage of requiring only a single plasma sample assayed for insulin and glucose. In conclusion, the HOMA model has become a widely used clinical and epidemiological tool and, when used appropriately, it can yield valuable data. However, as with all models, the primary input data need to be robust, and the data need to be interpreted carefully.

A genomewide search for type 2 diabetes-susceptibility genes in indigenous Australians

The prevalence of type 2 diabetes among Australian residents is 7.5%; however, prevalence rates up to six times higher have been reported for indigenous Australian communities. Epidemiological evidence implicates genetic factors in the susceptibility of indigenous Australians to type 2 diabetes and supports the hypothesis of the "thrifty genotype," but, to date, the nature of the genetic predisposition is unknown. We have ascertained clinical details from a community of indigenous Australian descent in North Stradbroke Island, Queensland. In this population, the phenotype is characterized by severe insulin resistance. We have conducted a genomewide scan, at an average resolution of 10 cM, for type 2 diabetes-susceptibility genes in a large multigeneration pedigree from this community. Parametric linkage analysis undertaken using FASTLINK version 4.1p yielded a maximum two-point LOD score of +2.97 at marker D2S2345. Multipoint analysis yielded a peak LOD score of +3.9 <1 cM from marker D2S2345, with an 18-cM 3-LOD support interval. Secondary peak LOD scores were noted on chromosome 3 (+1.8 at recombination fraction [theta] 0.05, at marker D3S1311) and chromosome 8 (+1.77 at theta=0.0, at marker D8S549). These chromosomal regions are likely to harbor novel susceptibility genes for type 2 diabetes in the indigenous Australian population.

The relationship between the insulin resistance syndrome and insulin sensitivity in the first-degree relatives of subjects with non-insulin dependent diabetes mellitus

Non-insulin dependent diabetes mellitus (NIDDM) has a substantial genetic component. Impaired insulin secretion, insulin insensitivity in muscle and adipose tissue, and elevated hepatic glucose production are the major pathophysiological features of NIDDM. Insulin insensitivity is also a feature of the insulin resistance syndrome, which describes the epidemiological association of glucose intolerance, upper body obesity, hyperinsulinaemia, hypertension, increased triglyceride levels and decreased high-density-lipoprotein (HDL)-cholesterol concentrations. Insulin insensitivity has been found to be a familial trait, and this raises the hypothesis that the insulin resistance syndrome may also occur as a familial trait in caucasian families in association with the development of NIDDM. The 90 first degree relatives of 50 caucasian subjects with NIDDM were studied with a continuous infusion glucose tolerance test to quantitate glucose tolerance, insulin sensitivity and beta-cell function. Body mass index (BMI), blood pressure, fasting triglyceride and HDL-cholesterol measurements were obtained, and the intercorrelations between these variables were examined. As a group the first degree relatives had a median insulin sensitivity of 65% (interquartile range 46-99%). Insulin sensitivity was univariately correlated with systolic and diastolic blood pressure, triglyceride and HDL-cholesterol. These associations were present in both the hyperglycaemic and the normoglycaemic relatives. The hyperglycaemic relatives were significantly more insulin insensitive than the normoglycaemic relatives, but this additional insulin insensitivity was not associated with significant differences in blood pressure, triglyceride or HDL-cholesterol concentrations. Our data indicate that the insulin insensitivity present in the first degree relatives of subjects with NIDDM is correlated with the cardiovascular risk factors which make up the insulin resistance syndrome, and that glycaemic status does not appear to be the major determinant of these associations. Interventions targeting obesity and insulin insensitivity in these subjects may reduce cardiovascular risk.

Insulin secretion and insulin resistance determined by euglycemic clamp

Obesity among children is increasingly recognized and linked to several metabolic problems. In this study, 47 children, aged 5-14 yr, with exogenous obesity were compared to 20 normal (non-obese) children to show alterations in glucose metabolism. All the obese children had body mass index > 95th percentile and weight for age > 120%. Basal and stimulated insulin and C-peptide levels were obtained during oral glucose tolerance test (OGTT). Seven children from the obese group had impaired OGTT according to WHO criteria. Mean fasting insulin levels were 26.7 +/- 14.6 microIU/ml in obese and 10.99 +/- 4.36 microIU/ml in controls; postprandial insulin levels were 70.4 +/- 56.4 microIU/ml and 22.23 +/- 6.55 microIU/ml, respectively (p < 0.001). The euglycemic glucose clamp technique was applied to 8 normal and 22 obese children. The amount of metabolized glucose (M) during clamp test is measured to identify glucose sensitivity. Mean M values were 3.24 +/- 1.35 mg/kg/min in obese and 6.525 +/- 0.770 mg/kg/min in control children (p < 0.001). As a result of this study, it seems reasonable to consider all obese children and adults as being at risk for hyperinsulinism and insulin resistance.

Clinical characteristics of subjects with a missense mutation in glucokinase

The clinical characteristics of subjects with a missense glucokinase mutation, gly299-->arg, were studied in a large pedigree, BX, initially characterized by some members having Maturity Onset Diabetes of the Young (MODY). Glucose tolerance, beta cell function and insulin sensitivity were measured with Homeostasis Model Assessment (HOMA) and with a 'Continuous Infusion of Glucose with Model Assessment' (CIGMA) test. Diabetic complications were clinically assessed. Subjects with glucokinase gly299-->arg were the same age, height, and obesity as the subjects without the mutation. Diabetes was usually asymptomatic at diagnosis and was treated with diet alone in 15 of the 18 subjects. Five of the 11 adult females had been diagnosed when they developed gestational diabetes. The fasting plasma glucose concentrations at the time of study were 4.3-12.6 mmol l-1, with the higher levels being in the more obese (p < 0.05) and in the older subjects (p < 0.05). In subjects with the mutation, beta cell function was impaired, being geometric mean 63% (normal-100%) compared with 126% in the subjects without the mutation (p < 0.001) measured by HOMA and in a subset assessed by CIGMA 59% and 127% (p < 0.01), respectively. There was no difference in fasting insulin concentrations, insulin sensitivity, lipid concentrations or blood pressure between the groups. The haemoglobin A1c was raised (mean 6.5% compared with 5.5% in the subjects without the mutation), but microvascular and macrovascular complications were uncommon. The subjects with the mutation did not have microalbuminuria but had an impaired vibration perception threshold compared with subjects without the mutation.(ABSTRACT TRUNCATED AT 250 WORDS)

The genetics and pathophysiology of type II and gestational diabetes

The development of both type II diabetes and gestational diabetes is probably governed by a complex and variable interaction of genes and environment. Molecular genetics has so far failed to identify discrete gene mutations accounting for metabolic changes in NIDDM. Both beta cell dysfunction and insulin resistance are operative in the manifestation of these disorders. Specific and sensitive immunoradiometric assays found fasting hyperproinsulinemia and first-phase hypoinsulinemia early in the natural history of the disorder. A lack of specificity of early radioimmunoassays for insulin resulted in measuring not only insulin but also proinsulins, leading to overestimation of insulin and misleading conclusions about its role in diabetes. The major causes of insulin resistance are the genetic deficiency of glycogen synthase activation, compounded by additional defects due to metabolic disorders, receptor downregulation, and glucose transporter abnormalities, all contributing to the impairment in muscle glucose uptake. The liver is also resistant to insulin in NIDDM, reflected in persistent hepatic glucose production despite hyperglycemia. Insulin resistance is present in many nondiabetics, but in itself is insufficient to cause type II diabetes. Gestational diabetes is closely related to NIDDM, and the combination of insulin resistance and impaired insulin secretion is of importance in its pathogenesis.

Insulin secretion and clearance during low-dose graded glucose infusion

The present study was undertaken in normal volunteers to define the alterations in beta-cell responsiveness to glucose associated with different physiological states, including fasting and refeeding, and after prolonged intravenous glucose infusion. A low-dose graded glucose infusion protocol was used to explore the dose-response relationship between glucose and insulin secretion. Studies were performed in 10 normal volunteers, and insulin secretion rates (ISR) were calculated by deconvolution of peripheral C-peptide levels using a two-compartment model utilizing individual kinetic parameters. From 5 to 9 mmol/l glucose, the relationship between glucose and ISR was linear. After a 42-h glucose infusion at a rate of 4 mg.kg-1.min-1, the ISR increased by 53% over the same glucose concentration range (P < 0.002), resulting in a shift of the dose-response curve to the left. Insulin clearance rates decreased 27% after the 42-h glucose infusion (P < 0.001). After a 72-h fast, ISR decreased by 32% from baseline over the 5-8 mmol/l glucose range (P = 0.056), resulting in a shift of the dose-response curve to the right. This shift was reversed by a 42-h period of refeeding, after which ISR was increased by 77% compared with the fasting study (P < 0.02). Refeeding enhanced the beta-cell responsiveness, and ISR increased by 31% after refeeding compared with the baseline study (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of three methods for the quantification of beta-cell function and insulin sensitivity

The purpose of this study was to compare two techniques for the quantification of beta-cell function and insulin sensitivity. Sixteen subjects (2 with newly diagnosed non-insulin-dependent diabetes mellitus, 8 with impaired glucose tolerance (IGT) and 6 with normal glucose tolerance (NGT)), aged 40-65 years underwent an oral glucose tolerance test (OGTT), a continuous infusion of glucose with model assessment (CIGMA) and a hyperglycaemic clamp (10 mmol/l) in random order. As measures of beta-cell function we used the clamp derived area under the curve from 0-10 min (first phase insulin response) and the mean insulin level during the last 20 min of the clamp (second phase insulin response). Insulin sensitivity was reflected by the ratio of the glucose infusion rate and the mean insulin level during the last 20 min of the clamp (M/I ratio). Measures for beta-cell function and insulin sensitivity derived from OGTT and CIGMA appeared to correlate only moderately (0.5-0.7) with the corresponding clamp measures. It is concluded that OGTT and CIGMA derived measures of beta-cell function and insulin sensitivity should be interpreted with caution.

Prevalence and pathophysiology of impaired glucose tolerance in three different high-risk white groups

Insulin resistance and beta-cell function were assessed by a continuous infusion of glucose in the following three groups of white subjects at risk of developing impaired glucose tolerance and diabetes: 41 subjects who were the offspring of patients with type II diabetes, 26 general-population subjects with an increased fasting plasma glucose level of at least 5.6 mmol/L on screening, and 22 subjects who had had gestational diabetes but were now nondiabetic. Subjects had a mean (+/- 1 SD) age of 43 +/- 9 years and a body mass index (BMI) of 27 +/- 5 kg/m2. Subjects with previously increased fasting glucose levels were significantly more insulin resistant than a control group, taking into account BMI, age, and gender (% normal insulin sensitivity [%], 59 [50 to 79] v 87 [73 to 96]; P < .005), and previously gestationally diabetic subjects showed greater impairment of beta-cell function (% normal beta-cell function [% beta], 69 [60 to 87] v 97 [89 to 105]; P < .005). Diabetes (defined by World Health Organization criteria) or impaired glucose tolerance (defined as an achieved plasma glucose concentration [APG] > 95th percentile of an age- and weight-matched population) was identified in 22% of family members, 31% of fasting hyperglycemic subjects, and 41% of previously gestationally diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperglycaemic progression in subjects with impaired glucose tolerance: association with decline in beta cell function

Impaired glucose tolerance is associated with an increased risk of Type 2 diabetes. This prospective cohort study has examined the variables associated with hyperglycaemic progression in order to elucidate the aetiology of this deterioration. The 5 mg glucose.kg ideal body weight.min-1 continuous infusion of glucose with model assessment (CIGMA) test was used to quantitate glucose tolerance, beta cell function, and insulin sensitivity. Twenty-two Caucasian subjects who had impaired glucose tolerance identified on two separate tests underwent repeat testing after a median period of 24 months. At follow-up, 2 of the 22 subjects (9%) had Type 2 diabetes, 18 (82%) had impaired glucose tolerance, and 2 (9%) were normoglycaemic. The fasting and achieved (60-min) glucose levels were significantly higher at follow-up (mean +/- SD) (5.7 +/- 0.8 vs 5.5 +/- 0.5 mmol l-1, p = 0.029 and 10.0 +/- 0.9 vs 9.6 +/- 0.6 mmol l-1, p = 0.021, respectively), and beta cell function was significantly lower (median and interquartile range): 75% (50-93%) vs 90% (70-135%), p = 0.009. The changes in fasting plasma glucose were found to correlate with change in body mass index (rs = 0.46, p = 0.03). We conclude that impaired glucose tolerance is associated with decline in beta cell function, and denotes substantial risk of hyperglycaemic progression. Randomized controlled trials are warranted to determine whether exercise programmes, dietary advice, and attentive follow-up and effective preventive strategies for subjects with impaired glucose tolerance.

Association of low birth weight with beta cell function in the adult first degree relatives of non-insulin dependent diabetic subjects

OBJECTIVE

To examine the relation between birth weight and beta cell function in the first degree relatives of non-insulin dependent diabetic subjects.

DESIGN

Cross sectional study of 101 adults of known birth weight from 47 families which had at least one member with non-insulin dependent diabetes.

SUBJECTS

101 white adults aged mean 43 (SD 7) years.

SETTING

Oxfordshire, England.

MAIN OUTCOME MEASURES

Glucose tolerance was measured by continuous infusion glucose tolerance test. beta cell function and insulin sensitivity were calculated from the fasting plasma glucose and insulin concentrations with homeostasis model assessment. beta cell function was standardised to allow for the confounding effects of age and obesity.

RESULTS

Twenty seven subjects had non-insulin dependent diabetes, 32 had impaired glucose tolerance, and 42 were normoglycaemic. Birth weight correlated with the beta cell function of the complete cohort (rs = 0.29, p = 0.005), the non-insulin dependent diabetic subjects (rs = 0.50, p = 0.023), and the non-diabetic subjects (rs = 0.29, p = 0.013). The non-insulin dependent diabetic (n = 27) and the non-diabetic (n = 74) subjects had similar mean (inter-quartile range) centile birth weight 50% (19%-91%), and 53% (30%-75%) respectively. Non-insulin dependent diabetic subjects had significantly lower beta function than the non-diabetic subjects: 69% (48%-83%) v 97% (86%-120%), p < 0.001.

CONCLUSIONS

The cause of the association between low birth weight and reduced beta cell function in adult life is uncertain. Impaired beta cell function in non-insulin dependent diabetic subjects was not accounted for by low birth weight, and genetic or environmental factors are likely to be necessary for development of diabetes.

A simple method for quantitation of insulin sensitivity and insulin release from an intravenous glucose tolerance test

Both insulin secretion and insulin sensitivity are important in the development of diabetes but current methods used for their measurements are complex and cannot be used for epidemiological surveys. This study describes a simplified approach for the estimation of first phase insulin release and insulin sensitivity from a standard 40-min intravenous glucose tolerance test (IVGTT), and compares these parameter estimations with the sophisticated minimal model analysis of a frequently sampled 3-h IVGTT and the euglycaemic clamp technique. For the simplified IVGTT, first phase insulin release was measured as the insulin area above basal post glucose load unit-1 incremental change (i.e. peak rise) in plasma glucose over 0-10 min, and insulin sensitivity as a rate of glucose disappearance (Kg) unit-1 insulin increase above basal from 0-40 min post-glucose load in 18 subjects who were studied twice, either basally or in a perturbed pathophysiological state (i.e. pre- and post-ultramarathon race, n = 5; pre- and post-20 h pulsatile hyperinsulinaemia, n = 8; pre- and post-thyrotoxic state, n = 5). A further 12 subjects were compared by IVGTT, and glucose clamp. In addition, seven dogs were studied three times by IVGTT during normal saline infusion and after short-term (1/2 hour) or long-term (72 hour) adrenaline infusions. First phase insulin release and insulin sensitivity estimated from the simplified IVGTT as calculated by the two methods correlated closely (rs = 0.89 and rs = 0.87, respectively), although less precisely in markedly insulin-resistant subjects and the slopes and y intercepts of the linear regression lines were similar in the basal and perturbed states.(ABSTRACT TRUNCATED AT 250 WORDS)

Type II diabetes: search for primary defects

Type 2 diabetes is a familial disease, but recent analysis of nuclear families indicates it is unlikely to be due to a single dominant gene with high penetrance and that it could be polygenic. Insulin resistance is a major feature, with obesity being a major determinant. Beta cell deficiency is a sine qua non of Type 2 diabetes. It is possible that obesity, insulin resistance independent from obesity and impaired beta cell function are independently inherited factors. None of these can be said to be 'primary' as diabetes usually results from the interaction of several geometric and environmental factors. This makes linkage analysis of Type 2 diabetes of uncertain benefit, since heterogeneity can occur within a pedigree. The only mutation so far discovered is of glucokinase producing maturity-onset diabetes of the young, that has a clearly defined and unusual phenotype. Identification of genes that cause classical Type 2 diabetes is likely to come from population association studies, molecular scanning techniques and direct sequencing of candidate genes rather than linkage analysis.

Linkage of type 2 diabetes to the glucokinase gene

Maturity-onset diabetes of the young (MODY) is a subtype of type 2 diabetes that presents from the second decade and has an autosomal dominant mode of inheritance. We have investigated the glucokinase gene, a candidate gene for diabetes, in two MODY pedigrees. In a large 5-generation pedigree (BX) with 15 diabetic members, use of a microsatellite polymorphism revealed linkage of diabetes to the glucokinase locus on chromosome 7p. A peak lod score of 4.60 was obtained at a recombination fraction (theta) of zero. This finding suggests that a defective glucokinase gene contributes to the diabetes phenotype in this pedigree. This is not universal in MODY since linkage to the glucokinase locus was excluded in a second pedigree M (lod score = -7.36 at theta = 0). The affected members in pedigree BX were diagnosed either when young (in pregnancy or on screening) or when they presented symptomatically in middle and old age; most of them were treated by diet alone. Defects in the glucokinase gene may play an important part in the pathogenesis of type 2 diabetes.

Immunoradiometric assay of insulin, intact proinsulin and 32-33 split proinsulin and radioimmunoassay of insulin in diet-treated type 2 (non-insulin-dependent) diabetic subjects

Plasma insulin, intact proinsulin and 32-33 split proinsulin measured by specific immunoradiometric assays and insulin and C-peptide measured by radioimmunoassay were measured during a constant infusion of glucose test in ten diet-treated subjects with a history of Type 2 (non-insulin-dependent) diabetes (termed diabetic subjects), mean fasting plasma glucose 6.0 +/- 1.0 mmol/l (mean +/- SD), and 12 non-diabetic control subjects. Immunoreactive insulin concentrations measured by radioimmunoassay were 33% higher than insulin and 16% higher than the sum of insulin and its precursors by immunoradiometric assay. The diabetic and non-diabetic subjects had similar fasting concentrations of insulin, intact proinsulin and 32-33 split proinsulin. The ratio of fasting intact proinsulin to total insulin was greater in the diabetic than the non-diabetic group 12.0% (6.8-21.0%, 1 SD range) and 6.3% (4.0-9.8%), respectively, p less than 0.01), though the groups overlapped substantially. After glucose infusion, diabetic and non-diabetic subjects had similar intact proinsulin concentrations (geometric mean 4.9 and 5.2 pmol/l, respectively), but the diabetic group had impaired insulin secretion by immunoradiometric assay (geometric means 55 and 101 pmol/l, p less than 0.05) or by radioimmunoassay C-peptide (geometric means 935 and 1410 pmol/l, p less than 0.05), though not by radioimmunoassay insulin (87 and 144 pmol/l, p = 0.12), respectively. Individual immunoradiometric assay insulin responses to glucose expressed in terms of obesity were subnormal in nine of ten diabetic subjects. Radioimmunoassay insulin and C-peptide gave less complete discrimination (subnormal responses in six of ten and eight of ten, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)