Low acute insulin secretory responses in adult offspring of people with early onset type 2 diabetes

The offspring of Pima Indians with early onset type 2 diabetes are at high risk for developing diabetes at an early age. This risk is greater among those whose mothers were diabetic during pregnancy. To define the metabolic abnormalities predisposing individuals in these high-risk groups to diabetes, we conducted a series of studies to measure insulin secretion and insulin action in healthy adult Pima Indians. In 104 normal glucose-tolerant subjects, acute insulin secretory response (AIR) to a 25-g intravenous glucose challenge correlated with the age at onset of diabetes in the mother (r = 0.23, P = 0.03) and, in multiple regression analyses, the age at onset of diabetes in the father (P = 0.02), after adjusting for maternal age at onset and after allowing for an interaction between these terms. In contrast, insulin action (hyperinsulinemic glucose clamp) did not correlate with the age at onset of diabetes in the parents. To determine whether early onset diabetes in the parents affected insulin secretion in the offspring across a range of glucose concentrations, responses to a stepped glucose infusion were measured in 23 subjects. Insulin secretion rates were lower in individuals whose mothers had developed diabetes before 35 years of age (n = 8) compared with those whose parents remained nondiabetic until at least 49 years of age (n = 15) (average insulin secretory rates: geometric mean [95% CI] 369 [209-652] vs. 571 [418-780] pmol/min, P = 0.007). Finally, the AIR was lower in individuals whose mothers were diabetic during pregnancy (n = 8) than in those whose mothers developed diabetes at an early age but after the birth of the subject (n = 41) (740 [510-1,310] vs. 1,255 [1,045-1,505] pmol/l, P < 0.02). Thus, insulin secretion is lower in normal glucose tolerant offspring of people with early onset type 2 diabetes. This impairment may be worsened by exposure to a diabetic environment in utero.     

Evolution of abnormal insulin secretory responses during 48-h in vivo hyperglycemia

Recent in vitro studies have shown that insulin release caused by continuous exposure to high glucose concentration markedly falls within a few hours. We wanted to determine if a similar effect occurs in vivo with chronic intravenous infusions in normal rats. Male CD rats (200-250 g) were infused with 50% glucose at 2 ml/h for 6, 14, 24, or 48 h, whereas controls received 0.45% NaCl, and insulin responses were tested with the in vitro isolated perfused pancreas. Plasma glucose averaged 352 +/- 20 mg/dl after 4 h and 396 +/- 11 mg/dl after 24 h versus 137 +/- 5 mg/dl in controls; plasma insulin at the same times was 8.94 +/- 1.44 and 12.1 +/- 2.62 ng/ml versus 1.69 +/- 0.19 ng/ml in controls. The incremental insulin response caused by an increase in perfusate glucose from 2.8 to 16.7 mM was not significantly reduced after 24 h of glucose infusion; in contrast, paradoxical suppression was seen after 48 h. A second protocol examined glucose potentiation by giving 10 mM arginine at 2.8 and 16.7 mM glucose; a hyperresponse to arginine at the lower glucose level was present after just 14 h of infusion. Therefore, these results do not support the hypothesis that beta-cells lose their sensitivity to glucose within hours of being exposed to higher than normal glucose concentrations.     

Gastric secretory responses to modified sham feeding (MSF) and insulin after vagotomy

Modified sham feeding (MSF) and insulin tests were carried out in 28 patients after vagotomy. Basal and pentagastrin collections were also performed. Using the secretory data from 9 of the patients with endoscopically proven recurrent ulcer as a reference, 20 gastric secretory indices were studied and critical levels were chosen to provide the maximum sensitivity and specificity. The eleven most discriminating indices were then used to evaluate the remaining 19 patients. There was agreement between the responses to MSF and insulin as to the adequacy of vagotomy in 16 of the patients (84 per cent) and contradictory responses in 3 patients (16 per cent). Overall, MSF responses were as discriminating as the responses to insulin. A simplified ward test, based on crude volume measurements in response to MSF is proposed.     

Acute insulin responses to glucose and arginine as predictors of beta-cell secretory capacity in human islet transplantation

Islet transplantation for type 1 diabetes can enable the achievement of near-normal glycemic control without severe hypoglycemic episodes. How much an islet (beta-cell) graft may be contributing to glycemic control can be quantified by stimulatory tests of insulin (or C-peptide) secretion. Glucose-potentiation of arginine-induced insulin secretion provides a measure of functional beta-cell mass, the beta-cell secretory capacity, as either AIR(pot) or AIR(max), but requires conduct of a hyperglycemic clamp. We sought to determine whether acute insulin responses to intravenous glucose (AIR(glu)) or arginine (AIR(arg)) could predict beta-cell secretory capacity in islet recipients. AIR(arg) was a better predictor of both AIR(pot) and AIR(max) (n=10, r2=0.98, P<0.0001 and n=7, r2=0.97, P<0.0001) than was AIR(glu) (n=9, r2=0.78, P=0.002 and n=6, r2=0.76, P=0.02). Also, the measures of beta-cell secretory capacity were highly correlated (n=7, r2=0.98, P<0.0001). These results support the use of AIR(arg) as a surrogate indicator of beta-cell secretory capacity in islet transplantation.     

The nature of insulin secretory defect in aging rats

We have attempted to define the nature of insulin secretory defect(s) in aged animals. In these studies, pancreatic islets were isolated from 2- and 18-mo-old Fischer 344 rats. Margination of secretion vesicles during exocytosis was assessed by measuring the recruitment of somatostatin (SRIF) receptors to the surface membrane. Section vesicle lysis was studied by measuring insulin release into the incubation media. Submaximal and maximal glucose-induced insulin secretion was significantly greater in islets isolated from younger rats (P less than 0.01). SRIF receptor recruitment was stimulated by glucose in both younger and older Fischer 344 rats. However, an increase in SRIF receptor recruitment was reduced in islets isolated from older animals (from 2.14 +/- 0.4 to 4.6 +/- 0.4 fmol/10 islets) (P less than 0.01) as compared with islets from younger animals (from 2.6 +/- 0.2 to 6.2 +/- 0.4 fmol/10 islets). When secretion vesicle lysis was inhibited by the presence of sodium isethionate in the incubation media, glucose (300 mg/dl) failed to stimulate secretion vesicle margination to the plasma membrane. In contrast, glyburide (0.6 micrograms/ml) continued to stimulate directly secretion vesicle margination in islets from aged animals (from 2.1 +/- 0.3 to 6.0 +/- 0.3 fmol/10 islets). We conclude that glucose-induced margination of secretion vesicles at the plasma membrane is impaired by the aging process. This impairment results in lower submaximal and maximal insulin secretory response to glucose. The fact that glyburide is capable of stimulating secretion vesicle margination suggests that glucose signal recognition and/or stimulus-secretion coupling may be the locus of impairment in the process of insulin secretion in older animals.     

Equivalent in vivo biological activity of insulin analogues and human insulin despite different in vitro potencies

In vivo biological potency of two human insulin analogues, AspB9,GluB27 insulin and AspB10 insulin with low and high affinity to the insulin receptor, respectively, was assessed by intravenous infusion of equimolar amounts in pigs, with the euglycemic clamp technique. Human insulin and the low- and high-affinity analogues showed equivalent glucose utilization rates in the steady state (mean +/- SE 14.7 +/- 1.4, 12.7 +/- 1.5, and 12.2 +/- 1.2 mg.kg-1.min-1, respectively; n = 7). The corresponding plasma insulin levels, however, were markedly different (329 +/- 25 and 856 +/- 46 pM, P less than 0.05; 197 +/- 19 pM, P less than 0.05). There was an inverse relationship between the insulin levels and the in vitro activities measured by binding to human hepatoma cells (HepG2; 100, 20, and 308%) or by incorporation of glucose into lipids in mouse free fat cells (100, 31, and 207%). The total amount of glucose infused during and after insulin infusion was equal for the three insulins, whereas glucose utilization as a function of time was somewhat different. By describing the individual plasma concentration courses with an open two-compartment model with elimination from the receptor compartment, the time courses for binding and elimination of the three insulins in the receptor compartment were estimated. The effect seems closely linked to the elimination of insulin from the receptors rather than to the amount of insulin bound to the receptors. In conclusion, the total effect of equimolar amounts of human insulin and the two insulin analogues on glucose utilization is equal regardless of the different receptor affinities of the insulins.     

Effects of acute insulin excess and deficiency on gluconeogenesis and glycogenolysis in type 1 diabetes

To determine whether insulin induces acute changes in endogenous glucose production (EGP) via changes in gluconeogenesis (GNG), glycogenolysis (GL), or both, we measured GNG (with (2)H(2)O) and GL (EGP-GNG) in nine patients with type 1 diabetes during acute insulin excess produced by subcutaneous injection of insulin and during insulin deficiency which developed between 5 and 8 h after insulin injection. During insulin excess, free insulin concentration rose fivefold (from 36 to 180 pmol/l). Plasma glucose was maintained between 6.2 and 6.7 mmol/l for approximately 4 h with IV glucose. EGP (with 6,6-(2)H glucose) decreased from 17.1 to 9.8 micro mol. kg(-1). min(-1) after 1 h. This decrease was almost completely accounted for by a decrease in GL (from 10.7 to 4.6 micro mol. kg(-1). min(-1)). During insulin deficiency, plasma glucose rose from 6.2 to 10.5 mmol/l and EGP from 9.5 to 14.3 micro mol/kg min. The increase in EGP again was accounted for by an increase in GL. We conclude that in type 1 diabetes acute regulation of EGP by insulin is mainly via changes in GL while GNG changes little during the early hours of acute insulin excess or deficiency.     

Glucagon-like peptide 1 increases secretory burst mass of pulsatile insulin secretion in patients with type 2 diabetes and impaired glucose tolerance

The insulinotropic gut hormone glucagon-like peptide (GLP)-1 increases secretory burst mass and the amplitude of pulsatile insulin secretion in healthy volunteers without affecting burst frequency. Effects of GLP-1 on secretory mechanisms in type 2 diabetic patients and subjects with impaired glucose tolerance (IGT) known to have impaired pulsatile release of insulin have not yet been studied. Eight type 2 diabetic patients (64+/-9 years, BMI 28.9+/-7.2 kg/m2, HbA1c 7.7+/-1.3%) and eight subjects with IGT (63+/-10 years, BMI 31.7+/-6.4 kg/m2, HbA1c 5.7+/-0.4) were studied on separate occasions in the fasting state during the continued administration of exogenous GLP-1 (1.2 pmol x kg(-1) x min(-1), started at 10:00 P.M. the evening before) or placebo. For comparison, eight healthy volunteers (62+/-7 years, BMI 27.7+/-4.8 kg/m2, HbA1c 5.4+/-0.5) were studied only with placebo. Blood was sampled continuously over 60 min (roller-pump) in 1-min fractions for the measurement of plasma glucose and insulin. Pulsatile insulin secretion was characterized by deconvolution, autocorrelation, and spectral analysis and by estimating the degree of randomness (approximate entropy). In type 2 diabetic patients, exogenous GLP-1 at approximately 90 pmol/l improved plasma glucose concentrations (6.4+/-2.1 mmol/l vs. placebo 9.8+/-4.1 mmol/l, P = 0.0005) and significantly increased mean insulin burst mass (by 68%, P = 0.007) and amplitude (by 59%, P = 0.006; deconvolution analysis). In IGT subjects, burst mass was increased by 45% (P = 0.019) and amplitude by 38% (P = 0.02). By deconvolution analysis, insulin secretory burst frequency was not affected by GLP-1 in either type 2 diabetic patients (P = 0.15) or IGT subjects (P = 0.76). However, by both autocorrelation and spectral analysis, GLP-1 prolonged the period (lag time) between subsequent maxima of insulin concentrations significantly from approximately 9 to approximately 13 min in both type 2 diabetic patients and IGT subjects. Under placebo conditions, parameters of pulsatile insulin secretion were similar in normal subjects, type 2 diabetic patients, and IGT subjects based on all methodological approaches (P > 0.05). In conclusion, intravenous GLP-1 reduces plasma glucose in type 2 diabetic patients and improves the oscillatory secretion pattern by amplifying insulin secretory burst mass, whereas the oscillatory period determined by autocorrelation and spectral analysis is significantly prolonged. This was not the case for the interpulse interval determined by deconvolution. Together, these results suggest a normalization of the pulsatile pattern of insulin secretion by GLP-1, which supports the future therapeutic use of GLP-1-derived agents.     

Risk for ESRD in type 1 diabetes remains high despite renoprotection

Historically, patients with type 1 diabetes and macroalbuminuria had high competing risks: cardiovascular death or renal failure. Here, we assessed these risks in patients receiving therapies implemented during the last 30 years. Between 1991 and 2004, we enrolled 423 white patients with type 1 diabetes who developed macroalbuminuria (albumin excretion rate, ≥300 μg/min). With follow-up for 98% through 2008, ESRD developed in 172 patients (incidence rate, 5.8/100 person-years), and 29 died without ESRD (mortality rate, 1/100 person-years). The majority of these outcomes occurred between ages 36 and 52 years with durations of diabetes of 21 to 37 years. The 15-year cumulative risks were 52% for ESRD and 11% for pre-ESRD death. During the 15 years of follow-up, the use of renoprotective treatment increased from 56 to 82%, and BP and lipid levels improved significantly; however, the risks for both ESRD and pre-ESRD death did not change over the years analyzed. There were 70 post-ESRD deaths, and the mortality rate was very similar during the 1990s and the 2000s (11/100 person-years versus 12/100 person-years, respectively). Mortality was low in patients who received a pre-emptive kidney transplant (1/100 person-years), although these patients did not differ from dialyzed patients with regard to predialysis eGFR, sex, age at onset of ESRD, or duration of diabetes. In conclusion, despite the widespread adoption of renoprotective treatment, patients with type 1 diabetes and macroalbuminuria remain at high risk for ESRD, suggesting that more effective therapies are desperately needed.     

Pancreatic beta-cell-to-beta-cell interactions are required for integrated responses to nutrient stimuli: enhanced Ca2+ and insulin secretory responses of MIN6 pseudoislets.

The effect of cell-to-cell contact on Ca2+ influx and secretory responses in the beta-cell line MIN6 was studied using MIN6 pseudoislets, which are three-dimensional islet-like cell aggregates that develop when MIN6 cells are cultured for 6-8 days on gelatin. The formation of pseudoislets is dependent on the Ca2+-dependent adhesion molecule E-cadherin (E-CAD), since the process can be inhibited by incubation in the absence of Ca2+ or in the presence of an anti-E-CAD antibody. Glucose and alpha-ketoisocaproic acid (KIC) evoked a Ca2+ influx in only a small fraction of the MIN6 monolayer cells, whereas >80% of cell groups within the pseudoislets responded to both nutrients. In contrast, changes in the intracellular free Ca2+ concentration ([Ca2+]i) were observed in all or most monolayer cells or pseudoislet cell groups in response to physical or pharmacological depolarizing stimuli. No significant increase in insulin release was observed from MIN6 monolayer cells in response to nutrient or nonnutrient insulin secretagogues. Conversely, pseudoislets were found to respond significantly to both nutrients and nonnutrients. These results suggest that close cell-to-cell contact improves the functional responsiveness of MIN6 cells and that pseudoislets may therefore serve as a useful research model in the study of beta-cell function.     

Effects of fetal insulin secretory deficiency on metabolism in fetal lamb

Fetal insulin secretion may be of importance in determining both fetal metabolic rate and glucose homeostasis in the resting state. To investigate this question, streptozocin (STZ) was injected into 10 late-gestation fetal lambs, and the effects of STZ on fetal pancreatic insulin storage and secretion, fetal metabolic rate, and umbilical glucose uptake were then studied. Fetal STZ injection caused a relative fetal hyperglycemia by 24 h after injection. Fetal hyperglycemia reached a maximum by 72 h and persisted for at least 10 days after injection. Neonates delivered after fetal injection were frankly diabetic. Fetal STZ injection was associated with complete suppression of both glucose- and tolbutamide-stimulated insulin release, although no changes in peripheral insulin concentration were observed when compared with controls. Fetal pancreatic insulin content was only 13% of that expected on the basis of gestational age. In a subgroup of 7 STZ-treated fetal lambs, fetal hyperglycemia was related to decrements in umbilical venoarterial difference of glucose, umbilical glucose uptake, and glucose-O2 quotient. No changes in maternal glucose homeostasis or in fetal O2 consumption were noted. The data suggest that deficient fetal insulin storage and secretion are associated with a decrement in exogenous fetal glucose entry but not in fetal metabolic rate. Whether the observed fetal changes relate to enhanced endogenous fetal glucose production with a passive decrease in maternofetal glucose transfer or are simply due to a decrease in overall fetal glucose utilization is not known. It is speculated that a quantitative decrease in pancreatic insulin secretion is responsible for the observed changes.     

Increased proinsulin levels and decreased acute insulin response independently predict the incidence of type 2 diabetes in the insulin resistance atherosclerosis study

Previous studies have indicated that beta-cell dysfunction predicts the development of diabetes, although it is unknown whether the use of combinations of insulin secretory measures further improves prediction. The Insulin Resistance Atherosclerosis Study is a prospective, multicenter, epidemiological study of the relationship between insulin sensitivity and the risk of diabetes and cardiovascular disease. At baseline, fasting concentrations of insulin, intact proinsulin (PI), and split PI were measured, and acute insulin response (AIR) was determined during a frequently sampled intravenous glucose tolerance test (FSIGTT). Subjects who were nondiabetic at baseline (n = 903) were reexamined after 5 years of follow-up; 148 had developed diabetes. In separate logistic regression models adjusted for age, sex, clinic, and ethnicity, 1 SD differences in measures of beta-cell dysfunction were associated with diabetes incidence (AIR: odds ratio [OR] 0.37, 95% CI 0.27-0.52; intact PI: OR 1.90, 95% CI 1.57-2.30; split PI: OR 1.94, 95% CI 1.63-2.31). After additional adjustment for BMI, impaired glucose tolerance, and insulin sensitivity, these measures continued to be significantly associated with risk of diabetes (all P < 0.0001). Furthermore, in models that included both PI and AIR, each was an independent predictor, and individuals who had combined low AIR and high PI experienced the highest diabetes risk. In conclusion, both low AIR and high PI independently predicted diabetes in a well-characterized multiethnic population. Although fasting PI is simpler to assess, determining AIR from an FSIGTT may further improve prediction. If pharmacological agents to prevent diabetes are proved to be efficacious in ongoing clinical trials, then it may be beneficial to perform FSIGTTs to identify better (for intensive intervention) prediabetic subjects who would ultimately require lifelong pharmacological therapy.     

Hypoglycemia with insulin in post-transplant diabetes mellitus

IntroductionTo prevent hypoglycemic episodes, the management of insulin therapy against post-transplant diabetes mellitus (PTDM) is important. We compared glargine (long-acting insulin) versus NPH isophane (intermediate-acting insulin) as an armamentarium against PTDM. Indeed, the study evaluated PTDM patients with hypoglycemic episodes treated with isophane or glargine.Material and methodsWe evaluated a total number of 231 living-donor renal transplant recipients with PTDM of age ≥ 18 years admitted to the hospital between January 2017 and September 2021. However, patients taking hypoglycemic agents before transplantation were excluded from this study. Out of 231 patients, 52 (22.15%) suffered from PTDM out of whom 26 were treated with glargine or isophane.ResultsAfter applying exclusion criteria, out of 52 PTDM patients 23 were included in the study: 13 PTDM patients were treated with glargine, whereas 10 PTDM patients with isophane. Our analysis revealed 12 episodes of hypoglycemia in glargine-treated PTDM patients compared to 3 in isophane-treated PTDM patients (p = 0.056). Clinically, 9 out of 15 hypoglycemic episodes were nocturnal (60%). Furthermore, no other risk factors were observed in our study population. Detailed analysis showed that both groups had equivalent doses of immunosuppressants and oral hypoglycemic agents. The odds ratio for hypoglycemia in the group treated with isophane compared to that treated with glargine was 0.224 (95% CI, 0.032–1.559). Glargine users recorded significantly lower blood sugar levels before lunch, dinner and at bedtime with p-values of 0.001, 0.009 and 0.001 respectively. A better hemoglobin A1c (HbA1c) level was seen in the glargine vs. isophane group (6.98 ± 0.52 vs. 7.45 ± 0.49, p-value 0.03).ConclusionThe study shows better blood sugar control with long-acting insulin analog, glargine, than with intermediate-actin analog, isophane. Overall, a higher number of hypoglycemic episodes was nocturnal. Long term safety of long-acting insulin analogs needs to be further studied.     

Different regulated expression of the tyrosine phosphatase-like proteins IA-2 and phogrin by glucose and insulin in pancreatic islets: relationship to development of insulin secretory responses in early life

IA-2 and phogrin are tyrosine phosphatase-like proteins that may mediate interactions between secretory granules and cytoskeleton in islets and neuroendocrine tissues. We investigated factors that regulate IA-2 and phogrin expression and their relationship to maturation of insulin secretory responses that occur after birth. Islet content of IA-2, but not phogrin, increased during the first 10 days of life in rats, when insulin secretion in response to glucose increased to adult levels. In cultured 5-day-old rat islets, IA-2 protein and mRNA was increased by glucose and agents that potentiate insulin secretion by the cAMP pathway. Addition of insulin increased IA-2 protein levels and insulin biosynthesis without affecting IA-2 mRNA. Blocking insulin secretion with diazoxide or insulin action with insulin receptor antibodies inhibited glucose-induced increases in IA-2 protein, but not those of mRNA. Phogrin expression was unchanged by all agents. Thus, IA-2 is regulated at the mRNA level by glucose and elevated cAMP, whereas locally secreted insulin modulates IA-2 protein levels by stimulating biosynthesis. In contrast, phogrin expression is insensitive to factors that modify beta-cell function. These results demonstrate differential regulation of two closely related secretory granule components and identify IA-2 as a granule membrane protein subject to autocrine regulation by insulin.