Pharmacokinetics and pharmacodynamics of different modes of insulin pump delivery. A randomized, controlled study comparing subcutaneous and intravenous administration of insulin aspart.

AIMS: To study the pharmacokinetics and pharmacodynamics of three different modes of insulin infusion delivered by means of an insulin pump: subcutaneous bolus insulin injection once an hour, continuous subcutaneous insulin infusion and continuous intravenous insulin infusion. METHODS: In random order, ten patients with Type 1 diabetes mellitus received insulin aspart with subcutaneous bolus insulin injection, continuous subcutaneous insulin infusion and continuous intravenous insulin infusion. The insulin aspart doses were individualized. RESULTS: A non-random, sinus-like variation of serum insulin aspart over time was found with subcutaneous bolus insulin injection compared with continuous subcutaneous insulin infusion and continuous intravenous insulin infusion (P<0.0001). Random variation of serum insulin aspart over time was significantly higher with continuous intravenous insulin infusion compared with subcutaneous bolus insulin injection (P=0.023) and continuous subcutaneous insulin infusion (P=0.013). Mean serum insulin aspart did not differ significantly between subcutaneous bolus insulin injection, continuous subcutaneous insulin infusion and continuous intravenous insulin infusion (P=0.17). Thus, absolute bioavailability was near 100% for both subcutaneous bolus insulin injection and continuous subcutaneous insulin infusion. Statistically significant differences were seen in mean plasma glucose and mean glucose infusion rate, with the highest mean plasma glucose and the lowest mean glucose infusion rate with continuous intravenous insulin infusion, suggesting a slightly lower bioefficacy of continuous intravenous insulin infusion compared with subcutaneous bolus insulin injection and continuous subcutaneous insulin infusion. CONCLUSIONS: Small but statistically significant differences in pharmacokinetics and pharmacodynamics between subcutaneous bolus insulin injection, continuous subcutaneous insulin infusion and continuous intravenous insulin infusion were observed. However, no major clinically relevant differences were found, suggesting that, for a basal subcutaneous insulin aspart pump therapy, relatively infrequent pump stroke frequency may suffice.

Insulin detemir is a fully efficacious, low affinity agonist at the insulin receptor.

AIM: To compare the properties of insulin detemir with human insulin or insulin aspart in various in vitro and in vivo experiments, thereby highlighting the importance of performing dose-response studies when investigating insulin analogues, in this study specifically insulin detemir. METHODS: Displacement of membrane-associated insulin receptors from human and rat hepatocytes, and from Chinese Hamster Ovary cells over-expressing human insulin receptor (CHO-hIR) at varying albumin concentrations is measured. Lipogenesis in primary rat adipocytes over time and the effects in the simultaneous presence of insulin detemir and human insulin or insulin aspart are assessed. The hyperinsulinaemic euglycaemic clamp technique in rats is used to establish dose-response curves for multiple metabolic endpoints and to investigate the effects of the simultaneous presence of insulin detemir and human insulin. RESULTS: Both in vitro and in vivo, insulin detemir shows full efficacy and right-shifted parallel dose-response curves compared with human insulin. The potency estimates are different between the in vivo and in vitro conditions and among different in vitro conditions, that is the potency decreases in vitro with increasing albumin concentration. The effects of insulin detemir and human insulin are additive both in vitro and in vivo. CONCLUSIONS: Insulin detemir is fully efficacious compared with human insulin on all metabolic endpoints measured in vitro and in vivo. The fact that the potency estimates are method-dependent emphasizes the importance of establishing full dose-response relationships when characterizing insulin detemir.

Synergistic effect of the human GLP-1 analogue liraglutide and a dual PPARalpha/gamma agonist on glycaemic control in Zucker diabetic fatty rats.

AIM/HYPOTHESIS: Combination therapies are increasingly common in the clinical management of type 2 diabetes. We investigated to what extent combined treatment with the human glucagon-like peptide-1 (GLP-1) analogue liraglutide and the dual PPARalpha/gamma agonist ragaglitazar would improve glycaemic control in overtly diabetic Zucker diabetic fatty (ZDF) rats. METHODS: Ninety overtly diabetic male ZDF rats were stratified into groups with matched haemoglobin A1c (HbA1c) (9.0+/-0.1%). Liraglutide (15 and 50 microg/kg subcutaneously twice daily), ragaglitazar (1 and 3 mg/kg perorally once daily) and their vehicles were studied as monotherapy and in combination in a 3x3 factorial design. RESULTS: After 4-week treatment, synergistic effects on HbA1c, non-fasting morning blood glucose (BG) and/or 24-h BG profiles were observed with three of the four combinations. The relationship between plasma insulin and BG in combination-treated animals approached that of historical lean ZDF rats representing normal glucose homeostasis, suggesting that insulin secretion and insulin sensitivity were markedly improved. Increased insulin immunostaining in islets further supports the improved beta-cell function and/or insulin sensitivity in combination-treated animals. The synergistic effect on glycaemic control was found without a similar synergistic increase in beta-cell mass in the combination groups. CONCLUSIONS/INTERPRETATION: Our data demonstrate that combination treatment with a human GLP-1 analogue and a dual PPARalpha/gamma agonist through distinct mechanism of actions synergistically improves glycaemic control in the ZDF rat.

Combination of the insulin sensitizer, pioglitazone, and the long-acting GLP-1 human analog, liraglutide, exerts potent synergistic glucose-lowering efficacy in severely diabetic ZDF rats.

OBJECTIVE: Severe insulin resistance and impaired pancreatic beta-cell function are pathophysiological contributors to type 2 diabetes, and ideally, antihyperglycaemic strategies should address both. RESEARCH DESIGN AND METHODS: Therapeutic benefits of combining the long-acting human glucagon-like peptide-1 (GLP-1) analog, liraglutide (0.4 mg/kg/day), with insulin sensitizer, pioglitazone (10 mg/kg/day), were assessed in severely diabetic Zucker diabetic fatty rats for 42 days. Impact on glycaemic control was assessed by glycated haemoglobin (HbA(1C)) at day 28 and by oral glucose tolerance test at day 42. RESULTS: Liraglutide and pioglitazone synergistically improved glycaemic control as reflected by a marked decrease in HbA(1C) (liraglutide + pioglitazone: 4.8 +/- 0.3%; liraglutide: 8.8 +/- 0.6%; pioglitazone: 7.9 +/- 0.4%; vehicle: 9.7 +/- 0.3%) and improved oral glucose tolerance at day 42 (area under the curve; liraglutide + pioglitazone: 4244 +/- 445 mmol/l x min; liraglutide: 7164 +/- 187 mmol/l x min; pioglitazone: 7430 +/- 446 mmol/l x min; vehicle: 8093 +/- 139 mmol/l x min). A 24-h plasma glucose profile at day 38 was significantly decreased only in the liraglutide + pioglitazone group. In addition, 24-h insulin profile was significantly elevated only in the liraglutide + pioglitazone group. Liraglutide significantly decreased food intake alone and in combination with pioglitazone, while pioglitazone alone increased cumulated food intake. As a result, rats on liraglutide alone gained significantly less weight than vehicle-treated rats, whereas rats on pioglitazone alone gained significantly more body weight than vehicle-treated rats. However, combination therapy with liraglutide and pioglitazone caused the largest weight gain, probably reflecting marked improvement of energy balance because of reduction of glucosuria. CONCLUSIONS: Combination therapy with insulinotropic GLP-1 agonist liraglutide and insulin sensitizer, pioglitazone, improves glycaemic control above and beyond what would be expected from additive effects of the two antidiabetic agents.

Lack of control by glucose of ultradian insulin secretory oscillations in impaired glucose tolerance and in non-insulin-dependent diabetes mellitus.

Normal subjects demonstrate the presence of ultradian oscillations (period 80-150 min) in insulin secretion rate (ISR) tightly coupled to glucose oscillations of similar period. These oscillations appear to be a function of the feedback loop linking glucose and insulin. The present study was undertaken to determine whether the control by glucose of the ultradian oscillations in insulin secretion is altered in impaired glucose tolerance IGT and in non-insulin-dependent diabetes mellitus (NIDDM). Patients with NIDDM (n = 7), IGT (n = 4), and matched nondiabetic controls (n = 5) were studied under three separate protocols that involved administration of glucose at either a constant rate of 6 mg/kg per min for 28 h or in one of two oscillatory patterns at the same overall mean rate. The amplitude of the oscillations was 33% above and below the mean infusion rate, and their respective periods were 144 min (slow oscillatory infusion) or 96 min (rapid oscillatory infusion). Insulin, C-peptide, and glucose were sampled at 10-min intervals during the last 24 h of each study. ISRs were calculated by deconvolution of C-peptide levels. Analysis of the data showed that (a) the tight temporal coupling between glucose and ISR in the nondiabetic controls was impaired in the IGT and NIDDM groups as demonstrated by pulse analysis, cross-correlation analysis, and spectral analysis; (b) the absolute amplitude of the ISR pulses progressively declined with the transition from obesity to IGT to NIDDM; and (c) the absolute amplitude of the ISR oscillations failed to increase appropriately with increasing absolute amplitude of glucose oscillations in the IGT and NIDDM subjects compared with the control group. In conclusion, the present study demonstrates that important dynamic properties of the feedback loop linking insulin secretion and glucose are disrupted not only in established NIDDM but also in conditions where glucose tolerance is only minimally impaired. Further studies are needed to determine how early in the course of beta-cell dysfunction this lack of control by glucose of the ultradian oscillations in insulin secretion occurs and to define more precisely if this phenomenon plays a pathogenetic role in the onset of hyperglycemia in genetically susceptible individuals.

Entrainment of pulsatile insulin secretion by oscillatory glucose infusion.

Ultradian "oscillations" or "pulses" of insulin secretion with periods around 120 min occur in man. It is not known whether glucose plays an active role in generating these oscillations, or if an intrapancreatic pacemaker generates oscillations in insulin secretion that entrain glucose passively. To determine if the frequency of pulses of insulin secretion could be modified by oscillatory glucose infusion, seven normal men were studied on three separate occasions. The first study involved a constant glucose infusion administered at a rate of 6 mg/kg per min for 28 h. During the two subsequent studies, the subjects received an oscillatory glucose infusion for 28 h with the same mean rate, an amplitude of 33% above and below the mean infusion rate, a sinusoidal waveshape and a period either 20% longer ("slow oscillatory infusion") or 20% shorter ("rapid oscillatory infusion") than the periodicity observed during constant glucose infusion. Samples for insulin, C-peptide, and glucose were drawn at 10-min intervals during the last 24 h of each study. Insulin secretion rates were calculated by deconvolution of C-peptide levels. During constant glucose infusion, the respective periods of oscillation of glucose and insulin secretion averaged 126 +/- 5 min and 118 +/- 3 min (mean +/- SEM). During the slow oscillatory infusion, the period of infusion was 155 +/- 7 min and the periods of insulin secretion and glucose were, respectively, 155 +/- 7 min and 150 +/- 5 min. During rapid oscillatory infusion, the period of infusion was 103 +/- 5 min and the period of both insulin secretion and glucose was 105 +/- 5 min. Thus the periodicity of both insulin secretion and plasma glucose changed in parallel with the exogenous periodicity, indicating complete entrainment of the secretory oscillations. These results suggest that the ultradian oscillations of insulin secretion are caused by the feedback loop linking glucose and insulin.

24-hour glucose profiles during continuous or oscillatory insulin infusion. Demonstration of the functional significance of ultradian insulin oscillations.

Under basal and stimulated conditions, normal insulin secretion oscillates with periods in the ultradian 100-150-min range. To test the hypothesis that oscillatory insulin delivery is more efficient in reducing blood glucose levels than continuous administration, nine normal young men were each studied on two occasions during a 28-h period including a period of polygraphically recorded sleep. Endogenous insulin secretion was suppressed by somatostatin, a constant intravenous glucose infusion was administered, and exogenous insulin was infused either at a constant rate or in a sinusoidal pattern with a period of 120 min. The mean glucose level over the 28-h period was 0.72 +/- 0.31 mmol/liter lower when insulin was infused in an oscillatory pattern than when the rate of infusion was constant (P < 0.05). The greater hypoglycemic effect of oscillatory versus constant infusion was particularly marked during the daytime, with the difference averaging 1.04 +/- 0.38 mmol/liter (P < 0.03). Serum insulin levels tended to be lower during oscillatory than constant infusion, although the same amount of exogenous insulin was administered under both conditions. Ultradian insulin oscillations appear to promote more efficient glucose utilization.

Insulin secretory defects in polycystic ovary syndrome. Relationship to insulin sensitivity and family history of non-insulin-dependent diabetes mellitus.

The increased prevalence of non-insulin-dependent diabetes mellitus (NIDDM) among women with polycystic ovary syndrome (PCOS) has been ascribed to the insulin resistance characteristic of PCOS. This study was undertaken to determine the role of defects in insulin secretion as well as familial factors to the predisposition to NIDDM seen in PCOS. We studied three groups of women: PCOS with a family history of NIDDM (PCOS FHx POS; n = 11), PCOS without a family history of NIDDM (PCOS FHx NEG; n = 13), and women without PCOS who have a family history of NIDDM (NON-PCOS FHx POS; n = 8). Beta cell function was evaluated during a frequently sampled intravenous glucose tolerance test, by a low dose graded glucose infusion, and by the ability of the beta cell to be entrained by an oscillatory glucose infusion. PCOS FHx POS women were significantly less likely to demonstrate appropriate beta cell compensation for the degree of insulin resistance. The ability of the beta cell to entrain, as judged by the spectral power for insulin secretion rate, was significantly reduced in PCOS FHx POS subjects. In conclusion, a history of NIDDM in a first-degree relative appears to define a subset of PCOS subjects with a greater prevalence of insulin secretory defects. The risk of developing NIDDM imparted by insulin resistance in PCOS may be enhanced by these defects in insulin secretion.

Insulin secretory abnormalities in subjects with hyperglycemia due to glucokinase mutations.

Pancreatic beta-cell function was studied in six subjects with mutations in the enzyme glucokinase (GCK) who were found to have elevated fasting and postprandial glucose levels in comparison to six normoglycemic controls. Insulin secretion rates (ISRs) were estimated by deconvolution of peripheral C-peptide values using a two-compartment model and individual C-peptide kinetics obtained after bolus intravenous injections of biosynthetic human C-peptide. First-phase insulin secretory responses to intravenous glucose and insulin secretion rates over a 24-h period on a weight maintenance diet were not different in subjects with GCK mutations and controls. However, the dose-response curve relating glucose and ISR obtained during graded intravenous glucose infusions was shifted to the right in the subjects with GCK mutations and average ISRs over a glucose range between 5 and 9 mM were 61% lower than those in controls. In the controls, the beta cell was most sensitive to an increase in glucose at concentrations between 5.5 and 6.0 mM, whereas in the patients with GCK mutations the point of maximal responsiveness was increased to between 6.5 and 7.5 mM. Even mutations that resulted in mild impairment of in vitro enzyme activity were associated with a > 50% reduction in ISR. The responsiveness of the beta cell to glucose was increased by 45% in the subjects with mutations after a 42-h intravenous glucose infusion at a rate of 4-6 mg/kg per min. During oscillatory glucose infusion with a period of 144 min, profiles from the subjects with mutations revealed reduced spectral power at 144 min for glucose and ISR compared with controls, indicating decreased ability to entrain the beta cell with exogenous glucose. In conclusion, subjects with mutations in GCK demonstrate decreased responsiveness of the beta cell to glucose manifest by a shift in the glucose ISR dose-response curve to the right and reduced ability to entrain the ultradian oscillations of insulin secretion with exogenous glucose. These results support a key role for the enzyme GCK in determining the in vivo glucose/ISR dose-response relationships and define the alterations in beta-cell responsiveness that occur in subjects with GCK mutations.

Estimation of insulin secretion rates from C-peptide levels. Comparison of individual and standard kinetic parameters for C-peptide clearance.

Insulin secretion rates can be accurately estimated from plasma C-peptide levels with a two-compartment model for C-peptide distribution and degradation. In previous studies, the kinetic parameters of C-peptide clearance were derived in each subject from the decay curve observed after bolus intravenous injection of biosynthetic human C-peptide. To determine whether standard parameters for C-peptide clearance could be defined and used to calculate insulin secretion without obtaining a decay curve in each subject, we analyzed 200 decay curves of biosynthetic human C-peptide obtained in normal, obese, and non-insulin-dependent diabetes mellitus subjects studied in our laboratory. This analysis showed that the volume of distribution and kinetic parameters of C-peptide distribution and metabolism vary by less than 30% in a population highly heterogeneous in terms of age, sex, degree of obesity, and degree of glucose tolerance. The volume of distribution correlated with the degree of obesity as quantified by body surface area (BSA). This dependence of C-peptide distribution volume on BSA was more marked in men than in women. The long half-life was slightly longer in elderly subjects than in younger adults. When effects of BSA, sex, and age were taken into account, the parameters of C-peptide kinetics were very similar in normal, obese, and diabetic subjects. Based on these findings, a simple procedure to derive standard parameters for C-peptide clearance taking into account degree of obesity, sex, and age was defined. These standard parameters resulted in estimations of mean insulin secretion rates, which differed in each subject by only 10-12% from those obtained with individual parameters. The approach of using standard rather than individual parameters did not systematically underestimate or overestimate insulin secretion so that group values for the fasting secretion rate, the mean 24-h secretion rate, and the number and the amplitude of secretory pulses obtained with standard parameters differed by only 1-2% from the values obtained with individual parameters. Furthermore, the accuracy of measurements based on standard parameters was not different from that associated with replicate determinations of the parameters of C-peptide clearance in the same subject. We conclude that it is possible to estimate insulin secretion rates from plasma C-peptide levels with standard parameters for C-peptide clearance rather than individually derived parameters without significant loss of accuracy.

Hypoglycemic thresholds for cognitive dysfunction in IDDM.

Fourteen poorly controlled insulin-dependent diabetes mellitus (IDDM) patients (HbA1c 11 +/- 0.5%) with a mean +/- SE duration of disease of 15 +/- 2 yr were studied to evaluate the hypoglycemic threshold for cognitive dysfunction under insulin-induced hypoglycemia. The P300 event-related potential, a measure of cognitive function, and reaction time (RT) in response to visual stimuli under euglycemic conditions and at plasma glucose concentrations of 3.5 and 2.5 mM (63 and 45 mg/dl, respectively) during a constant insulin infusion were recorded. Baseline P300 latency was similar to that of a nondiabetic control group, but baseline RT was greater in the IDDM group. There was no increase in P300 latency or RT under euglycemic clamp conditions or at a plasma glucose level of 3.5 mM (63 mg/dl). However, when plasma glucose was lowered to 2.5 mM (45 mg/dl), there was an increase in P300 latency and a prolongation of RT. As plasma glucose returned to baseline, P300 latency and RT remained prolonged. After administration of intravenous glucose and a meal, P300 latency and RT returned to baseline. P140, an event-related potential reflecting sensory processes, was not altered. Because P300 latency changes paralleled RT changes, hypoglycemia appears to slow decision-making processes in IDDM. This study revealed that 1) baseline P300 latency is not elevated in poorly controlled IDDM patients, suggesting no cumulative cognitive dysfunction.

Insulin secretory profiles and C-peptide clearance kinetics at 6 months and 2 years after kidney-pancreas transplantation.

Glucose, insulin secretion, and insulin secretory pulses were measured by deconvolution of peripheral C-peptide concentrations in 10 IDDM recipients of a combined kidney-pancreas allograft 6 mo post-transplantation and were compared with 10 matched nondiabetic control subjects. Seven of the 10 recipients were restudied 2 yr post-transplantation. To control for immunosuppressive therapy, 6 patients with a kidney allograft also were studied. Pancreatic insulin secretion rates were evaluated over a 24-h period with three mixed meals. Six months post-transplantation, fasting (5.3 +/- 0.1 vs. 5.3 +/- 0.1 mM), average 24-h (6.0 +/- 0.1 vs. 5.7 +/- 0.1 mM), and meal-related (6.1 +/- 0.3 vs. 5.8 +/- 0.2 mM) plasma glucose levels were not different in control subjects and recipients, respectively. Total 24-h insulin secretion rates were similar between the two groups (150 +/- 15 vs. 182 +/- 24 nmol.m-2.24 h-1). However, post-transplantation, the relationship between basal and meal-stimulated insulin secretion was altered with increased basal insulin secretion (52.2 +/- 6.4 vs. 97.4 +/- 12.5 pmol.m-2.min-1, P less than 0.004) and reduced meal-related secretion. The proportion of total 24-h insulin secretion comprised by basal secretion was 44 +/- 4% in the control subjects vs. 73 +/- 5% in recipients. The number of ultradian oscillations of insulin secretion identified in each 24-h period by pulse analysis was similar in control subjects and recipients (11.9 +/- 0.9 vs. 10.4 +/- 0.5 oscillations/24 hr).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in pancreatic islet glucokinase and hexokinase activities with increasing age, obesity, and the onset of diabetes.

We examined changes in high- and low-Km glucose phosphorylating activity in pancreatic islet extracts from the prediabetic Zucker diabetic fatty (ZDF) rat between 5-6 weeks and 12 weeks of age (after the onset of diabetes). Comparisons were made between the activity observed in the ZDF rat and that seen in the ZDF lean control (ZLC) rat and the obese nondiabetic Zucker fatty (ZF) rat. At 5-6 weeks of age, insulin resistant ZDF and ZF rats were hyperinsulinemic, compared with the ZLC rat, but had normal plasma glucose levels. Kinetic parameters (Vmax and Km for glucose) of hexokinase (HK) and Km of glucokinase (GCK) did not differ between groups. Islet GCK activity for ZDF and ZF rats was 1.7-fold greater than in ZLC rats (P < 0.02 and P < 0.001, respectively). By 12 weeks of age, hypersecretion of insulin at 5.0 mmol/l glucose was observed in perifused islets from both obese groups relative to the ZLC rat. Islets from ZDF rats failed to increase insulin secretion in response to increased glucose concentration. Group differences in the kinetic parameters for GCK or in the Km values for HK were not significant. Islet HK activity for ZDF and ZF rats was 1.9-fold (P < 0.05) and 1.7-fold (P < 0.05) greater, respectively, than for ZLC rats. Compared with the 5- to 6-week-old animals, HK activity increased 3.1-fold (P < 0.001), 2.5-fold (P < 0.002), and 2.0-fold (P < 0.05) for ZDF, ZF, and ZLC rats, respectively. Differences in GCK activity between 5- to 6- and 12-week-old rats were not significant for any of the groups. We conclude: 1) increased islet glucose phosphorylating activity is present in insulin resistant and hyperinsulinemic ZF and ZDF rats, relative to the ZLC rat; 2) at 12 weeks of age, hyperinsulinemic ZDF and ZF rats demonstrated significant increases in HK activity, compared with lean controls; and 3) deficiency in GCK activity does not explain failure of diabetic ZDF islets to respond to glucose, since differences between diabetic ZDF and nondiabetic ZF rats were not statistically significant. Increases in pancreatic islet phosphorylating activity seem to be important in maintaining basal hyperinsulinemia in insulin-resistant animals, but do not appear to play a role in the progression to glucose intolerance and diabetes.

Defects in insulin secretion and action in women with a history of gestational diabetes.

Gestational diabetes mellitus (GDM) is associated with defects in insulin secretion and insulin action, and women with a history of GDM carry a high risk for the development of non-insulin-dependent diabetes mellitus (NIDDM). Assessment of subjects with a history of GDM who are currently normoglycemic should help elucidate some of the underlying defects in insulin secretion or action in the evolution of NIDDM. We have studied 14 women with normal oral glucose tolerance who had a history of GDM. They were compared with a group of control subjects who were matched for both body mass index (BMI) and waist-to-hip ratio (WHR). All subjects underwent tests for the determination of oral glucose tolerance, ultradian oscillations in insulin secretion during a 28-h glucose infusion, insulin secretion in response to intravenous glucose, glucose disappearance after intravenous glucose (Kg), and insulin sensitivity (SI) as measured by the Bergman minimal model method. The BMI in the post-GDM women was similar to that in the control subjects (24.9 +/- 1.2 vs. 25.4 +/- 1.4 kg/m2, respectively), as was the WHR ratio (0.80 +/- 0.01 vs. 0.76 +/- 0.01, respectively). The post-GDM women were slightly older (35.2 +/- 0.9 vs. 32.1 +/- 1.4 years, P = 0.04). The fasting plasma glucose levels were significantly higher in the post-GDM group than in the control group (4.9 +/- 0.1 vs. 4.4 +/- 0.1 mmol/l, respectively, P < 0.001) and remained higher at each of the subsequent determinations during the oral glucose tolerance test, although none had a result indicative of either diabetes or impaired glucose tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of physiological plasma glucose excursions to entrain high-frequency pulsatile insulin secretion in type 2 diabetes.

Insulin is released in high-frequency pulsatile bursts at intervals of 6-13 min. Intrapancreatic mechanisms are assumed to coordinate pulsatile insulin release, but small oscillations in plasma glucose concentrations may contribute further. To gain additional insight into beta-cell (patho)physiology, we explored the ability of repetitive small glucose infusions (6 mg/kg over 1 min every 10 min) to modify rapid pulsatile insulin secretion in 10 type 2 diabetic individuals (plasma glucose 9.3 +/- 1.0 mmol/l, HbA1c 7.9 +/- 0.5%, mean +/- SE) and 10 healthy subjects. All subjects were investigated twice in randomly assigned order: during saline and during glucose exposure. Blood was collected every minute for 90 min to create a plasma insulin concentration time-series for analysis using 3 complementary algorithms: namely, spectral analysis, autocorrelation analysis, and approximate entropy (ApEn). During saline infusion, none of the algorithms were able to discriminate between diabetic and control subjects (P > 0.20). During glucose entrainment, spectral density peaks (SP) and autocorrelation coefficients (AC) increased significantly (P < 0.001), and ApEn decreased (P < 0.01), indicating more regular insulin time-series in the healthy volunteers. However, no differences were observed in the diabetic individuals between the glucose and saline conditions. Furthermore, in spite of identical absolute glucose excursions (approximately 0.3 mmol/l) glucose pulse entrainment led to a complete (SP: 4.76 +/- 0.62 [range 2.08-7.60] vs. 17.24 +/- 0.93 [11.70-20.58], P < 0.001; AC: 0.01 +/- 0.05 [0.33-0.24] vs. 0.64 +/- 0.05 [0.35-0.83], P < 0.001) or almost complete (ApEn: 1.59 +/- 0.02 [1.48-1.67] vs. 1.42 +/- 0.05 [1.26-1.74], P < 0.005) separation of the insulin time-series in diabetic and control subjects. Even elevating the glucose infusion rate in the diabetic subjects to achieve comparable relative (and hence higher absolute) glucose excursions (approximately 4.9%) failed to entrain pulsatile insulin secretion in this group. In conclusion, the present study demonstrates that failure to respond adequately with regular oscillatory insulin secretion to recurrent high-frequency and (near)-physiological glucose excursion is a manifest feature of beta-cell malfunction in type 2 diabetes. Whether the model will be useful in unmasking subtle (possible prediabetic) defects in beta-cell sensitivity to glucose drive remains to be determined.

Compensation in pancreatic beta-cell function in subjects with glucokinase mutations.

The relationship between the in vivo insulin secretory responsiveness of the pancreatic beta-cell to glucose and the flux of glucose through the enzyme glucokinase was investigated in six subjects with heterozygous glucokinase mutations and in six matched control subjects. This was done by combining data published previously on the in vivo dose-response relationships between glucose and insulin secretion and on the in vitro enzymatic properties of wild-type and mutant forms of glucokinase. The flux of glucose through glucokinase (GK flux) in these subjects was estimated using a model based on the approximate Michaelis-Menten kinetics of wild-type and mutant forms of the enzyme. In two subjects with glucokinase mutations, which resulted in only a small reduction in enzymatic activity, the decrease in insulin secretion was directly proportional to the decrease in GK flux predicted using a Michaelis-Menten model for both mutant and wild-type glucokinase. However, in four subjects with glucokinase mutations, which resulted in severe reductions in enzymatic activity, insulin secretion was reduced compared with control subjects but less than predicted. This latter result implies the existence of a compensatory change in the beta-cells of such subjects, which results in a relative increase in insulin secretory response. We propose modifications to the simple model relating glucose concentration and GK flux, including glucose-induced overexpression of the normal allele and a role of glucokinase regulatory protein. The modifications take into account the possibility that the degree of compensation may be directly related to the severity of the mutation.

Abnormal insulin secretion, not insulin resistance, is the genetic or primary defect of MODY in the RW pedigree.

Maturity-onset diabetes of the young (MODY) is a form of non-insulin-dependent diabetes mellitus (NIDDM) associated with autosomal-dominant inheritance. In the RW pedigree, MODY is associated with polymorphic DNA markers on chromosome 20q. To determine the early abnormalities of insulin action and insulin secretion in MODY, we studied nondiabetic members of the RW pedigree with and without the gene marker. Six nondiabetic marker-negative and 5 nondiabetic marker-positive members of the RW pedigree were studied, as were 4 diabetic marker-positive family members. Unrelated, young, healthy subjects served as comparison groups. Insulin action and insulin secretion were assessed with a frequently sampled intravenous glucose tolerance test. Insulin secretion was further assessed during constant glucose infusion by deconvolution of plasma C-peptide and by pulse analysis. The nondiabetic marker-positive group had normal sensitivity to insulin and unimpaired acute insulin response to intravenous glucose (AIRglu). However, the nondiabetic marker-positive group had decreased mean plasma C-peptide concentration and reduced absolute amplitude of insulin secretory oscillations during prolonged glucose infusion. These responses to prolonged glucose infusion were similar to those observed in the diabetic group. No alterations of insulin secretion were observed in the nondiabetic marker-negative family members. Deranged and deficient insulin secretion, and not insulin resistance, appears to be the genetic or primary abnormality that characterizes nondiabetic individuals who are predisposed to MODY in the RW pedigree.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of beta-cell dysfunction in the male Zucker diabetic fatty rat.

The molecular basis for the beta-cell dysfunction that characterizes non-insulin-dependent diabetes mellitus (NIDDM) is unknown. The Zucker diabetic fatty (ZDF) male rat is a rodent model of NIDDM with a predictable progression from the prediabetic to the diabetic state. We are using this model to study beta-cell function during the development of diabetes with the goal of identifying genes that play a key role in regulating insulin secretion and, thus, may be potential targets for therapeutic intervention aimed at preserving or improving beta-cell function. As a first step, we have characterized morphology, insulin secretion, and pattern of gene expression in islets from prediabetic and diabetic ZDF rats. The development of diabetes was associated with changes in islet morphology, and the islets of diabetic animals were markedly hypertrophic with multiple irregular projections into the surrounding exocrine pancreas. In addition, there were multiple defects in the normal pattern of insulin secretion. The islets of prediabetic ZDF rats secreted significantly more insulin at each glucose concentration tested and showed a leftward shift in the dose-response curve relating glucose concentration and insulin secretion. Islets of prediabetic animals also demonstrated defects in the normal oscillatory pattern of insulin secretion, indicating the presence of impairment of the normal feedback control between glucose and insulin secretion. The islets from diabetic animals showed further impairment in the ability to respond to a glucose stimulus. Changes in gene expression were also evident in islets from prediabetic and diabetic ZDF rats compared with age-matched control animals. In prediabetic animals, there was no change in insulin mRNA levels. However, there was a significant 30-70% reduction in the levels of a large number of other islet mRNAs including glucokinase, mitochondrial glycerol-3-phosphate dehydrogenase, voltage-dependent Ca2+ and K+ channels, Ca(2+)-ATPase, and transcription factor Islet-1 mRNAs. In addition, there was a 40-50% increase in the levels of glucose-6-phosphatase and 12-lipoxygenase mRNAs. There were further changes in gene expression in the islets from diabetic ZDF rats, including a decrease in insulin mRNA levels that was associated with reduced islet insulin levels. Our results indicate that multiple defects in beta-cell function can be detected in islets of prediabetic animals well before the development of hyperglycemia and suggest that changes in the normal pattern of gene expression contribute to the development of beta-cell dysfunction.

Altered insulin secretory responses to glucose in subjects with a mutation in the MODY1 gene on chromosome 20.

This study was undertaken to test the hypothesis that the diabetes susceptibility gene on chromosome 20q12 responsible for maturity-onset diabetes of the young (MODY) in a large kindred, the RW family, results in characteristic alterations in the dose-response relationships between plasma glucose concentration and insulin secretion rate (ISR) that differentiate this form of MODY from MODY in subjects with glucokinase mutations. Ten marker-positive subjects and six matched nondiabetic marker-negative subjects from the RW family received graded intravenous glucose infusions on two occasions separated by a 42-h continuous intravenous glucose infusion designed to prime the beta-cell to secrete more insulin in response to glucose. ISR was derived by deconvolution of peripheral C-peptide levels. Basal glucose and insulin levels were similar in marker-negative and marker-positive groups (5.3 +/- 0.2 vs. 5.0 +/- 0.2 mmol/l, P > 0.2, and 86.1 +/- 3.9 vs. 63.7 +/- 12.1 pmol/l, P > 0.1, respectively). However, the marker-positive subjects had defective insulin secretory responses to an increase in plasma glucose concentrations. Thus, as the glucose concentration was raised above 7 mmol/l, the slope of the curve relating glucose and ISR was significantly blunted in the marker-positive subjects (13 +/- 4 vs. 68 +/- 8 pmol.min-1.mmol-1 x 1, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Oscillatory insulin secretion after pancreas transplant.

In vivo studies of beta-cell secretory function have demonstrated the existence of rapid insulin oscillations of small amplitude recurring every 8-15 min in normal subjects. This study evaluated the effects of pancreas transplant on rapid insulin oscillations. Samples for glucose, insulin, and C-peptide were drawn during constant glucose infusion at 2-min intervals for 90 min from six successful Px patients with type I diabetes mellitus, from six normal nondiabetic control subjects, and from three Kx subjects. A computerized algorithm (ULTRA) was used for pulse detection. In the Px group, the average insulin pulse period was significantly shorter than in both the control and Kx groups (Px 8.1 +/- 0.5, control 12.5 +/- 0.7, Kx 12.4 +/- 0.5 min, P < 0.0005). By contrast, the C-peptide pulse periods (Px 16.8 +/- 2.3, control 14.7 +/- 1.2, Kx 15.3 +/- 1.5 min) were similar in the three groups. Spectral analysis confirmed that the frequency of the insulin pulses was increased in the Px group. The absolute amplitude of the insulin pulses was greater in the Px group (P < 0.001) while the amplitude of the C-peptide pulses did not differ between the groups. Cross-correlation analysis demonstrated maximal correlation coefficients at a lag of 0 min between insulin and C-peptide (control r = 0.33, P < 0.0001; Kx r = 0.17, P = 0.06) and between insulin and glucose (control r = 0.21, P < 0.001; Kx r = 0.20, P < 0.02) in the control and Kx groups, respectively, whereas no significant correlations were observed at any lag in the Px group.(ABSTRACT TRUNCATED AT 250 WORDS)