Effect of sulfonylurea treatment on in vivo insulin secretion and action in patients with non-insulin-dependent diabetes mellitus

Fasting insulin levels correlate with the frequency of hypoglycemic events in people with type 2 diabetes on treatment with sulfonylureas: A pilot study

AIMS AND OBJECTIVES:

We aimed to explore whether fasting insulin levels correlate with the risk of hypoglycemia in people with Type 2 diabetes (T2D) receiving sulfonylureas (SUs).

MATERIALS AND METHODS:

Our study included 58 individuals with T2D who had been on treatment with SUs, but not insulin, for more than 2 years. Confirmed hypoglycemic episodes during the past year were self-reported by the patients, and a potential relationship of hypoglycemic event frequency with fasting insulin levels was investigated.

RESULTS:

Fasting insulin concentrations were found to have a low positive and statistically significant correlation with the number of cases of mild hypoglycemia per year (ρ = 0.279/P = 0.034) and a moderately positive and statistically significant correlation with the number of severe hypoglycemic events per month (ρ = 0.349/P = 0.007) and per year (ρ = 0.39/P = 0.002).

CONCLUSION:

Our results suggest that fasting insulin levels might be a predictor of the risk of hypoglycemia in people with T2D on treatment with SUs.

Glucose Sensing by Skeletal Myocytes Couples Nutrient Signaling to Systemic Homeostasis

Skeletal muscle is a major site of postprandial glucose disposal. Inadequate insulin action in skeletal myocytes contributes to hyperglycemia in diabetes. Although glucose is known to stimulate insulin secretion by β cells, whether it directly engages nutrient signaling pathways in skeletal muscle to maintain systemic glucose homeostasis remains largely unexplored. Here we identified the Baf60c-Deptor-AKT pathway as a target of muscle glucose sensing that augments insulin action in skeletal myocytes. Genetic activation of this pathway improved postprandial glucose disposal in mice, whereas its muscle-specific ablation impaired insulin action and led to postprandial glucose intolerance. Mechanistically, glucose triggers K_ATP channel-dependent calcium signaling, which promotes HDAC5 phosphorylation and nuclear exclusion, leading to Baf60c induction and insulin-independent AKT activation. This pathway is engaged by the anti-diabetic sulfonylurea drugs to exert their full glucose-lowering effects. These findings uncover an unexpected mechanism of glucose sensing in skeletal myocytes that contributes to homeostasis and therapeutic action.

Skeletal Muscle TRIB3 Mediates Glucose Toxicity in Diabetes and High- Fat Diet-Induced Insulin Resistance

In the current study, we used muscle-specific TRIB3 overexpressing (MOE) and knockout (MKO) mice to determine whether TRIB3 mediates glucose-induced insulin resistance in diabetes and whether alterations in TRIB3 expression as a function of nutrient availability have a regulatory role in metabolism. In streptozotocin diabetic mice, TRIB3 MOE exacerbated, whereas MKO prevented, glucose-induced insulin resistance and impaired glucose oxidation and defects in insulin signal transduction compared with wild-type (WT) mice, indicating that glucose-induced insulin resistance was dependent on TRIB3. In response to a high-fat diet, TRIB3 MOE mice exhibited greater weight gain and worse insulin resistance in vivo compared with WT mice, coupled with decreased AKT phosphorylation, increased inflammation and oxidative stress, and upregulation of lipid metabolic genes coupled with downregulation of glucose metabolic genes in skeletal muscle. These effects were prevented in the TRIB3 MKO mice relative to WT mice. In conclusion, TRIB3 has a pathophysiological role in diabetes and a physiological role in metabolism. Glucose-induced insulin resistance and insulin resistance due to diet-induced obesity both depend on muscle TRIB3. Under physiological conditions, muscle TRIB3 also influences energy expenditure and substrate metabolism, indicating that the decrease and increase in muscle TRIB3 under fasting and nutrient excess, respectively, are critical for metabolic homeostasis.

Weight Loss and the Prevention and Treatment of Type 2 Diabetes Using Lifestyle Therapy, Pharmacotherapy, and Bariatric Surgery: Mechanisms of Action

Weight loss, whether achieved by lifestyle intervention, pharmacotherapy, or bariatric surgery, is highly effective as a primary interventional strategy in both the prevention and treatment of type 2 diabetes. In high-risk patients with prediabetes and/or metabolic syndrome, weight loss effectively prevents progression to type 2 diabetes mellitus (T2DM) and improves cardiovascular risk factors. These benefits are the result of improvements in insulin resistance, which is central to the pathophysiology of cardiometabolic disease. In patients with T2DM, weight loss improves glycemia, while reducing the need for conventional glucose-lowering medicines, by affecting all three processes that produce and sustain the hyperglycemic state, namely via increments in peripheral insulin sensitivity with improvements in insulin signal transduction at the cellular level, more robust insulin secretory responses, and reduced rates of hepatic glucose production. In both nondiabetic and diabetic subjects, hypocaloric feeding (e.g., treatment with very low-calorie diet or bariatric surgery) produces a rapid improvement in insulin sensitivity due to mobilization of fat from the intramyocellular, intrahepatocellular, and intra-abdominal compartments, and via a more long-term mechanism that correlates with the loss of total body fat. In diabetes, by improving glycemia, weight loss also enhances glucose homeostasis by reversing the defects in insulin action and secretion attributable to glucose toxicity. Regardless of the therapeutic approach, weight loss of ∼ 10 % maximally prevents future diabetes in patients with prediabetes or metabolic syndrome. In T2DM, greater degrees of weight loss lead to progressive improvements in glucose homeostasis. Therefore, when accompanied by greater weight loss, the metabolic benefits following bariatric surgery are generally more pronounced than those achieved following lifestyle and medical treatment. In addition, the mechanisms by which bariatric operations improve diabetes may include both weight-dependent and weight-independent mechanisms, and the latter may involve changes in gut hormones, bile acids, or gut microflora.

TRIB3 mediates glucose-induced insulin resistance via a mechanism that requires the hexosamine biosynthetic pathway

In the current study, we investigated the role of tribbles homolog 3 (TRIB3) in glucose-induced insulin resistance and whether the induction of TRIB3 by glucose is dependent on the nutrient-sensing hexosamine biosynthetic pathway (HBP) known to mediate glucose toxicity in diabetes. In diabetic rats, TRIB3 expression in skeletal muscle was increased after 10 days of hyperglycemia, and glycemia and muscle TRIB3 were both restored toward normal by insulin therapy. In L6 myocytes, the induction of TRIB3 by high glucose or glucosamine was reversible upon removal of these substrates. To assess the role of HBP in the induction of TRIB3, we demonstrated that the ability of high glucose to augment TRIB3 expression was prevented by azaserine, an inhibitor of glutamine: fructose-6-phosphate amidotransferase (GFAT), which is the rate-limiting enzyme in the HBP pathway. TRIB3 expression was also substantially stimulated by glucosamine, which bypasses GFAT, accompanied by a decrease in the insulin-stimulated glucose transport rate, and neither response was affected by azaserine. Further, knockdown of TRIB3 inhibited, and TRIB3 overexpression enhanced, the ability of both high glucose and glucosamine to induce insulin resistance. These data provide the mechanistic link between the HBP flux and insulin resistance and point to TRIB3 as a novel target for treatment of glucose-induced insulin resistance.

Glipizide does not affect absorption of glucose and xylose in diabetics without residual beta-cell function

We have previously demonstrated that oral glipizide suppresses the absorption of xylose in diabetics treated with diet alone. We suggested that glipizide might influence postprandial glucose levels by interfering with absorptive mechanisms. In the present study we have extended our observations to insulin-dependent diabetics (IDDM). Nine non-obese diabetics without residual beta-cell function and with normal respiratory sinus arrhythmia and Valsalva ratio were studied on two occasions. Their ordinary insulin treatment was discontinued 24 hours before the study and glucose control was maintained by i.v. insulin infusion. The experiments began at 8 a.m. after an overnight fast. Insulin was given as a continuous i.v. infusion of 0.01 U/kg/h at 8-11 a.m. and 0.005 U/kg/h at 11 a.m. -2 p.m. At 8 a.m. the patients ingested 25 g of xylose and 15 g of glucose in 300 ml of water. Glipizide (5 mg) or placebo were given 30 min prior to the glucose-xylose load in random order, each patient serving as his own control. Blood samples were taken every 60 min for analysis of glucose, xylose, C-peptide and glipizide. The rise in blood glucose in the control experiment was similar to that previously seen in non-insulin-dependent diabetics (NIDDM) given the same xylose-glucose load. Glipizide did not exert any effects on either blood C-peptide, glucose or xylose levels. We conclude that oral glipizide administered in a therapeutic dose does not reduce xylose absorption in IDDM, in contrast to its previously demonstrated effect in NIDDM.

Effect of sulfonylurea on glucose, insulin and C-peptide responses to a meal stimulus in a patient with type 2 diabetes and liver disease

The influence of two sulfonylureas on blood glucose and plasma immunoreactive insulin (IRI) and C-peptide responses to a standardized meal was investigated in a patient with type 2 diabetes and a liver disease with enhanced peripheral levels of liver enzymes. The very high fasting values of plasma IRI and C-peptide were further elevated by the meal. This response to the meal was markedly enhanced by both sulfonylureas, glipizide and glibenclamide. The blood glucose increment after the meal was diminished by sulfonylureas. Sulfonylureas thus seem to have beneficial effects in this diabetic patient, who had a liver disease and markedly elevated basal levels of plasma IRI and C-peptide concentrations.

Metabolic effects of chronic glipizide gastrointestinal therapeutic system on serum glucose, insulin secretion, insulin sensitivity, and hepatic insulin extraction in glucose-tolerant, first-degree relatives of African American patients with type 2 diabetes: new insights on mechanisms of action

We examined the long-term metabolic effects of a potent sulfonylurea (SU), glipizide gastrointestinal therapeutic system (glipizide GITS) in normal glucose-tolerant (NGT), first-degree relatives of African American patients with type 2 diabetes in a randomized, placebo-controlled, double-blind manner for 24 months and 6 months after discontinuation of glipizide GITS. Fifty NGT African American first-degree relatives (n = 50)) were randomized to receive either glipizide GITS (GITS, 5 mg/d) or identical placebo (PLAC). The NGT consisted of NGT/GITS (n = 16; mean age, 43.1 +/- 8.7years; body mass index [BMI], 34.8 +/- 10) and NGT/PLAC (n = 34; 45.5 +/- 9.7 years; BMI, 31.3 +/- 3.1years). Each of the subjects underwent an oral glucose tolerance test (OGTT) and frequently sampled intravenous glucose tolerance test (FSIGT) at baseline and at yearly intervals for 2 years. Insulin sensitivity (Si) and glucose effectiveness (Sg) were determined by Bergman's minimal model method. Hepatic insulin extraction (HIE) was calculated as the molar ratio of C-peptide and insulin. The mean fasting serum glucose, insulin, and C-peptide levels in the NGT/GITS were not different from that of the NGT/PLAC. After oral glucose challenge, mean serum glucose responses slightly increased (P = not significant [NS]) at 12 and 24 months in the NGT/GITS group when compared with the baseline, 0 month, but remained unchanged in the NGT/PLAC group. In addition, serum insulin and C-peptide responses significantly increased in the NGT/GITS group, but were unchanged in the NGT/PLAC group at 12 and 24 months versus 0 month. The HIE, during OGTT, decreased by 30% from the baseline (0 month) values in the NGT/ GITS, but remained unchanged in the NGT/PLAC group at 12 and 24 months. Mean Si decreased by 30% from the baseline in the NGT/GITS group by 12 and 24 months, but remained unchanged in the NGT/PLAC group. However, the disposition index (DI) remained normal in the NGT/GITS and the NGT/PLAC groups. The DI data in the NGT/GITS group suggested that beta cells maintained the ability to compensate for the lower Si during the chronic GITS administration in our high risk African Americans. Chronic GITS was well tolerated without any symptoms of either hypoglycemia or weight gain in the NGT/IGTS group. After discontinuation of GITS, the altered metabolic parameters significantly improved, returning to baseline values in the NGT/IGTS group in 6 months. In summary, chronic glipizide GITS administration (5 mg/d) was associated with increased beta-cell secretion, peripheral hyperinsulinemia, reduced Si, and reduced HIE in glucose-tolerant, first-degree relatives of African American patients with type 2 diabetes. These metabolic changes were reversible within 6 months after discontinuation of glipizide GITS. Our study defines a unique mode of action of glipizide GITS in African Americans at high risk for type 2 diabetes. We conclude that the use of glipizide GITS in the primary prevention of type 2 diabetes in nondiabetic first-degree relatives of patients with type 2 diabetes impaired glucose homeostasis.

Influence of treatment with acarbose or glibenclamide on insulin sensitivity in type 2 diabetic patients

AIM

The aim of our double-blind, placebo-controlled study was to compare the effect of acarbose and glibenclamide on the insulin sensitivity in type 2 diabetes.

METHODS

We investigated 77 patients (mean age 58.7 years, mean BMI 27.3 kg/m2), treated by diet alone for at least 4 weeks. The subjects were randomized into three treatment groups for 16 weeks: 100 mg t.i.d. acarbose (n = 25) or 1 mg t.i.d. glibenclamide (n = 27) or one t.i.d. placebo (n = 25). Before and after therapy, the levels of fasting plasma glucose, glycosylated haemoglobin, fasting insulin, plasma glucose and insulin 1 h after a standardized breakfast were measured and insulin sensitivity determined by euglycaemic hyperinsulinaemic clamp test.

RESULTS

After the treatment period, BMI in the acarbose and placebo group decreased significantly, whereas in the glibenclamide group a significant increase was observed. Fasting plasma glucose was only significant reduced under glibenclamide. The postprandial glucose decreased significantly after acarbose (13.8 vs. 11.4 mmol/l, p < 0.05) and glibenclamide treatment (14.6 vs. 11.4 mmol/l, p < 0.05) and was unchanged under placebo (13.8 vs. 13.7 mmol/l). The fasting insulin levels remained unchanged in all three groups, whereas postprandial insulin values increased significantly under glibenclamide. Neither acarbose nor glibenclamide significantly changed insulin sensitivity [acarbose: glucose disposal rate before treatment 2.3 mg/kg body weight/min/insulin, after treatment 3.2; glibenclamide 2.2 vs. 2.1; placebo 2.6 vs. 3.0].

CONCLUSIONS

Our results show a more substantial improvement of glucose control under glibenclamide than under acarbose which, however, was not associated with an increase of insulin sensitivity.

Abnormality in fibre type distribution of soleus and plantaris muscles in non-obese diabetic Goto-Kakizaki rats

1. Fibre type distributions of the slow soleus and fast plantaris muscles were investigated in 5-, 9- and 20-week-old male Goto-Kakizaki (GK) rats, as an animal model of non-obese diabetes, and were compared with those of age-matched non-diabetic Wistar rats. 2. Bodyweight and both soleus and plantaris muscle weights were lower in GK rats than in Wistar rats, regardless of age. In addition, both relative soleus and plantaris muscle weights per bodyweight were lower in GK rats than in Wistar rats, regardless of age. 3. In the soleus muscle, a higher percentage of type I fibres and a lower percentage of type IIA fibres were observed in 5- and 9-week-old GK rats. In addition, there were no type IIA fibres in 20-week-old GK rats. 4. In the plantaris muscle, there were no differences in fibre type distribution of 5-week-old GK rats. However, a higher percentage of type IIB fibres and a lower percentage of type I and type IIA fibres were observed in 9- and 20-week-old GK rats. In addition, there were no type I fibres in 20-week-old GK rats. 5. These results indicate that the decreased percentage of high-oxidative fibres (e.g. type IIA fibres in the soleus muscle and type I and type IIA fibres in the plantaris muscle) of the diabetic animals is concerned with an impairment in insulin sensitivity and glucose metabolism and is not related to bodyweight.

Disruption of Sur2-containing K(ATP) channels enhances insulin-stimulated glucose uptake in skeletal muscle

ATP-sensitive potassium channels (K(ATP)) are involved in a diverse array of physiologic functions including protection of tissue against ischemic insult, regulation of vascular tone, and modulation of insulin secretion. To improve our understanding of the role of K(ATP) in these processes, we used a gene-targeting strategy to generate mice with a disruption in the muscle-specific K(ATP) regulatory subunit, SUR2. Insertional mutagenesis of the Sur2 locus generated homozygous null (Sur2(-/-)) mice and heterozygote (Sur2(+/-)) mice that are viable and phenotypically similar to their wild-type littermates to 6 weeks of age despite, respectively, half or no SUR2 mRNA expression or channel activity in skeletal muscle or heart. Sur2(-/-) animals had lower fasting and fed serum glucose, exhibited improved glucose tolerance during a glucose tolerance test, and demonstrated a more rapid and severe hypoglycemia after administration of insulin. Enhanced glucose use was also observed during in vivo hyperinsulinemic euglycemic clamp studies during which Sur2(-/-) mice required a greater glucose infusion rate to maintain a target blood glucose level. Enhanced insulin action was intrinsic to the skeletal muscle, as in vitro insulin-stimulated glucose transport was 1.5-fold greater in Sur2(-/-) muscle than in wild type. Thus, membrane excitability and K(ATP) activity, to our knowledge, seem to be new components of the insulin-stimulated glucose uptake mechanism, suggesting possible future therapeutic approaches for individuals suffering from diabetes mellitus.

Effects of cellular ATP depletion on glucose transport and insulin signaling in 3T3-L1 adipocytes

Glucosamine induced insulin resistance in 3T3-L1 adipocytes, which was associated with a 15% decrease in cellular ATP content. To study the role of ATP depletion in insulin resistance, we employed sodium azide (NaN3) and dinitrophenol (DNP), which affect mitochondrial oxidative phosphorylation, to achieve a similar 15% ATP depletion. Unlike glucosamine, NaN3 and DNP markedly increased basal glucose transport, and the increased basal glucose transport was associated with increased GLUT-1 content in the plasma membrane without changes in total GLUT-1 content. These agents, like glucosamine, did not affect the early insulin signaling that is implicated in insulin stimulation of glucose transport. In cells with a severe 40% ATP depletion, basal glucose transport was similarly elevated, and insulin-stimulated glucose transport was similar in cells with 15% ATP depletion. In these cells, however, early insulin signaling was severely diminished. These data suggest that cellular ATP depletion by glucosamine, NaN3, and DNP exerts differential effects on basal and insulin-stimulated glucose transport and that ATP depletion per se does not induce insulin resistance in 3T3-L1 adipocytes.

Pathophysiology and pharmacological treatment of insulin resistance

Diabetes mellitus type 2 is a world-wide growing health problem affecting more than 150 million people at the beginning of the new millennium. It is believed that this number will double in the next 25 yr. The pathophysiological hallmarks of type 2 diabetes mellitus consist of insulin resistance, pancreatic beta-cell dysfunction, and increased endogenous glucose production. To reduce the marked increase of cardiovascular mortality of type 2 diabetic subjects, optimal treatment aims at normalization of body weight, glycemia, blood pressure, and lipidemia. This review focuses on the pathophysiology and molecular pathogenesis of insulin resistance and on the capability of antihyperglycemic pharmacological agents to treat insulin resistance, i.e., a-glucosidase inhibitors, biguanides, thiazolidinediones, sulfonylureas, and insulin. Finally, a rational treatment approach is proposed based on the dynamic pathophysiological abnormalities of this highly heterogeneous and progressive disease.

Glucosamine-induced insulin resistance in 3T3-L1 adipocytes

To study molecular mechanisms for glucosamine-induced insulin resistance, we induced complete and reversible insulin resistance in 3T3-L1 adipocytes with glucosamine in a dose- and time-dependent manner (maximal effects at 50 mM glucosamine after 6 h). In these cells, glucosamine impaired insulin-stimulated GLUT-4 translocation. Glucosamine (6 h) did not affect insulin-stimulated tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 and -2 and weakly, if at all, impaired insulin stimulation of phosphatidylinositol 3-kinase. Glucosamine, however, severely impaired insulin stimulation of Akt. Inhibition of insulin-stimulated glucose transport was correlated with that of Akt activity. In these cells, glucosamine also inhibited insulin stimulation of p70 S6 kinase. Glucosamine did not alter basal glucose transport and insulin stimulation of GLUT-1 translocation and mitogen-activated protein kinase. In summary, glucosamine induced complete and reversible insulin resistance in 3T3-L1 adipocytes. This insulin resistance was accompanied by impaired insulin stimulation of GLUT-4 translocation and Akt activity, without significant impairment of upstream molecules in insulin-signaling pathway.

Metformin treatment leads to an increase in basal, but not insulin-stimulated, glucose disposal in obese patients with impaired glucose tolerance

AIMS

This study was initiated to test the hypothesis that metformin treatment leads to enhanced glucose disposal at ambient insulin concentrations.

METHODS

Nineteen obese patients with impaired glucose tolerance (IGT) were treated with either metformin or placebo in a randomized, double-blind, placebo-controlled, cross-over study. Insulin secretion and insulin resistance were quantified using the homeostasis model assessment (HOMA) and insulin-stimulated glucose disposal were measured by determining the steady-state plasma glucose (SSPG).

RESULTS

The average benefit of metformin was 0.6 mmol/l for glucose (95% confidence interval (CI) 0.2-0.9 P = 0.002), 2.8 pmol/l for insulin (95% CI 0.2-5.4, P = 0.019). Insulin resistance, as quantified by HOMA, was improved by 1.1 (95% CI 0.2-2.0, P = 0.004), without any change in insulin secretion. Basal and insulin-stimulated glucose oxidation were comparable in the placebo and metformin-treated groups at the end of each treatment period, as was the SSPG concentration. However, both systolic and diastolic blood pressures fell significantly following metformin administration as compared to treatment with placebo.

CONCLUSIONS

These results indicate that metformin administration to patients with IGT is associated with enhanced glucose disposal at baseline insulin concentrations and a fall in blood pressure. In contrast, neither glucose oxidation nor glucose disposal were increased in association with metformin treatment under conditions of physiological hyperinsulinaemia.

Delayed enhancement of myocardial FDG uptake on glucose loading FDG-PET in NIDDM patient

We report a case of delayed enhancement of myocardial FDG uptake in NIDDM patient after oral glucose loading. A 65-year-old man who had a past history of NIDDM received FDG-PET examination during fasting and glucose loading. In neither condition, was an accumulation of FDG in the myocardium, and myocardial blood flow was normal. An oral glucose tolerance test (OGTT) was performed to find the best time for FDG injection and 3 hours after loading, the serum insulin concentration was increased significantly. When the interval between glucose loading and the injection of FDG was set at 3 hours, enhancement of myocardial FDG uptake was demonstrated. To know the best time for the FDG injection in advance is thought to be important in obtaining better image quality and interpreting the myocardial viability when FDG-PET examination during glucose loading is performed in NIDDM patients.

The effects of obesity on the pharmacokinetics and pharmacodynamics of glipizide in patients with non-insulin-dependent diabetes mellitus

The pharmacokinetics and pharmacodynamics of glipizide were evaluated in 20 patients with non-insulin-dependent diabetes mellitus (NIDDM). The group consisted of 12 obese subjects (seven women, five men; mean +/- SD age, 53.5 +/- 8.5 years; total body weight (TBW), 95.5 +/- 17.2 kg; percentage > IBW (ideal body weight), 57.8 +/- 31.7%); and eight nonobese subjects (two women, six men; age, 57.8 +/- 11.7 years; TBW, 80.8 +/- 9.9 kg; percentage > IBW, 15.6 +/- 10.3%). After a 2-week antidiabetic drug-free period, patients were started on glipizide therapy for 12 weeks. Glipizide dosages were titrated to achieve specified therapeutic goals or a maximum daily dose of 40 mg. Glipizide pharmacokinetics were assessed by serum concentrations obtained during a 24-h pharmacokinetic evaluation performed after the first 5-mg dose (SD) and after 12 weeks of chronic therapy (CD). Glipizide pharmacodynamics were evaluated with serum glucose, insulin, and C-peptide responses to Sustacal tolerance test done at baseline, after SD, and after CD. No statistically significant differences in the SD pharmacokinetic parameters (Tmax = 3.1 +/- 1.2 vs. 2.8 +/- 1.6 h; Cmax = 332.5 +/- 92.5 vs. 420.8 +/- 142 g/L; area under the curve extrapolated to infinity (AUCI) = 2,598.3 +/- 1,148 vs. 3,138.9 +/- 1,847 g/h/L; oral clearance/bioavailability (CL/F), 2.3 +/- 1.0 vs. 2.0 +/- 1.0 L/h; volume of distribution/bioavailability (V/F), 19.5 +/- 4.4 vs. 17.2 +/- 4.3 L; t1/2 = 5.0 +/- 2.3 vs. 5.2 +/- 2.0 h) were observed between the obese and nonobese groups, respectively. The pharmacokinetic parameters assessed under CD conditions were also closely matched in the two groups. No differences in glucose responses to Sustacal challenge at baseline, SD, and CD (AUC0-->4.glucose:baseline, 52.3 +/- 18.0 vs. 44.9 +/- 9.8; SD, 50.4 +/- 20.9 vs. 36.1 +/- 11.0; CD, 37.8 +/- 10.7 vs. 36.6 +/- 8.5 mM/h) were noted between the obese and nonobese groups, respectively. However, glucose concentrations increased more and decreased to a smaller extent after SD in the obese as compared to nonobese subjects. Mean fasting serum insulin and C-peptide concentrations were not statistically different between the two groups. However, obese subjects exhibited higher fasting insulin (114.0 +/- 69 vs. 68.8 +/- 52 pM) at week 12 evaluation and C-peptide concentrations (0.83 +/- 0.2 vs. 0.63 +/- 0.2 nM) after SD as compared to the nonobese group. A smaller percentage increase in C peptide in response to Sustacal challenge was observed in the obese compared to the nonobese subjects (baseline, 60 +/- 25 vs. 117 +/- 117; SD, 119 +/- 39 vs. 193 +/- 149; and CD, 97 +/- 56 vs. 163 +/- 67%). In summary, the influence of obesity on glipizide pharmacokinetics appeared to be of little clinical significance. The observed differences in pharmacodynamics require further evaluation.

Sulphonylurea stimulates glucose uptake in rats through an ATP-sensitive K+ channel dependent mechanism

We studied the effect of gliclazide, a second-generation sulphonylurea, on rat skeletal muscle glucose uptake using perfused hindquarter muscle preparations. Gliclazide at concentrations of 10 to 1000 microgram/ml increased (p < 0.05) the basal glucose uptake. The effect of gliclazide on glucose uptake was immediate and dose-dependent, reaching a plateau at a concentration of 300 micrograms/ml; the half-maximal effect was obtained between 25 and 50 micrograms/ml. The glucose uptake stimulated by gliclazide (300-1000 micrograms/ml) did not differ from that achieved by 10(-9) mol/l insulin, and was lower (p < 0.05) than that obtained with 10(-7) mol/l insulin. The combination of gliclazide (300 micrograms/ml) and 10(-9) mol/l insulin produced an increase in glucose uptake (7.7 +/- 0.6 mumol.g-1.h-1, n = 8, mean +/- SEM) which was higher (p < 0.05) than that achieved with 10(-9) mol/l insulin (5.6 +/- 0.7 mumol.g-1.h-1, n = 11) and not different from that obtained with 10(-7) mol/l insulin (9.8 +/- 1.0 mumol.g-1.h-1, n = 11). Diazoxide (100 mumol/l), an ATP-sensitive K+ channel opener, reversed the stimulatory effect of gliclazide (100 microgram/ml) on muscle glucose uptake from 3.1 +/- 0.4 to 0.5 +/- 0.2 mumol.g-1.h-1, (n = 7, p < 0.001). The addition of diazoxide prior to gliclazide into the perfusion medium blocked the gliclazide-induced glucose uptake by the hindquarter muscle preparations. In conclusion, gliclazide alone has an immediate stimulatory effect on glucose uptake by skeletal muscle and together with insulin has an additive effect on muscle glucose uptake. The effect of gliclazide on muscle glucose uptake seems to be due to the inhibition of ATP-sensitive K+ channels.

Glucosamine induces insulin resistance in vivo by affecting GLUT 4 translocation in skeletal muscle. Implications for glucose toxicity

Glucosamine (Glmn), a product of glucose metabolism via the hexosamine pathway, causes insulin resistance in isolated adipocytes by impairing insulin-induced GLUT 4 glucose transporter translocation to the plasma membrane. We hypothesized that Glmn causes insulin resistance in vivo by a similar mechanism in skeletal muscle. We performed euglycemic hyperinsulinemic clamps (12 mU/kg/min + 3H-3-glucose) in awake male Sprague-Dawley rats with and without Glmn infusion at rates ranging from 0.1 to 6.5 mg/kg/min. After 4h of euglycemic clamping, hindquarter muscles were quick-frozen and homogenized, and membranes were subfractionated by differential centrifugation and separated on a discontinuous sucrose gradient (25, 30, and 35% sucrose). Membrane proteins were solubilized and immunoblotted for GLUT 4. With Glmn, glucose uptake (GU) was maximally reduced by 33 +/- 1%, P < 0.001. The apparent Glmn dose to reduce maximal GU by 50% was 0.1 mg/kg/min or 1/70th the rate of GU on a molar basis. Control galactosamine and mannosamine infusions had no effect on GU. Relative to baseline, insulin caused a 2.6-fold increase in GLUT 4 in the 25% membrane fraction (f), P < 0.01, and a 40% reduction in the 35%f, P < 0.05, but had no effect on GLUT 4 in the 30% f, P= NS. Addition of Glmn to insulin caused a 41% reduction of GLUT 4 in the 25%f, P < 0.05, a 29% fall in the 30%f, and prevented the reduction of GLUT 4 in the 35% f. The 30%f membranes were subjected to a second separation with a 27 and 30% sucrose gradient. Insulin mobilized GLUT 4 away from the 30%f, P < 0.05, but not the 27% f. In contrast, Glmn reduced GLUT 4 in the 27%f, P < 0.05, but not the 30%f. Thus Glmn appears to alter translocation of an insulin-insensitive GLUT 4 pool. Coinfusion of Glmn did not alter enrichment of the sarcolemmal markers 5'-nucleotidase, Na+/K+ATPase, and phospholemman in either 25, 30, or 35% f. Thus Glmn completely blocked movement of Glut 4 induced by insulin. Glmn is a potent inducer of insulin resistance in vivo by causing (at least in part) a defect intrinsic to GLUT 4 translocation and/or trafficking. These data support a potential role for Glmn to cause glucose-induced insulin resistance (glucose toxicity).

Characterization of the binding sites for [3H]glibenclamide in rat liver membranes

The specific binding sites for sulfonylureas in the rat liver membrane fraction were demonstrated and characterized. [3H]Glibenclamide binding to the liver membrane was specific, time- and temperature-dependent, and reversible. Scatchard analysis showed a single class binding site. The dissociation constant (Kd) for glibenclamide was 1.1 microM and the binding capacity (Bmax) was 50 pmol/mg protein. [3H]Glibenclamide binding could be displaced by other sulfonylureas. Half-maximal inhibition of binding (IC50) for glimepiride, gliclazide, acetohexamide, tolbutamide and chlorpropamide was 4.2 microM, 74 microM, 0.33 mM, 0.60 mM, 1.2 mM, respectively. Each value is close to the reported blood concentration when a therapeutic dose of each drug is administered orally. The order of IC50 values is coincident with the order of potency of the clinical hypoglycemic effect of these drugs. We had shown that these concentrations of sulfonylureas stimulate 6-phosphofructo-2-kinase in the liver or hepatocytes and inhibit phosphoenolpyruvate carboxykinase in the hepatoma cells. The specific binding sites demonstrated here may play some roles when sulfonylureas affect carbohydrate metabolism in the liver.

Effect of glipizide treatment on postprandial lipaemia in patients with NIDDM

The primary goal of the present study was to examine the effects of improved glycaemic control associated with glipizide treatment on postprandial lipaemia in non-insulin-dependent diabetic patients. The metabolism of triglyceride-rich lipoproteins of intestinal origin was assessed by measuring the retinyl palmitate content in plasma and the Svedberg flotation index (Sf) > 400 and Sf 20-400 lipoprotein fractions. Fasting plasma glucose concentrations (14.5 +/- 0.5 vs 9.0 +/- 0.5 mmol/l), glycated haemoglobin levels (13.1 +/- 0.6 vs. 9.7 +/- 0.6%), and daylong plasma glucose concentrations were all significantly lower after glipizide treatment (p < 0.001). The improvement in glycaemic control was associated with increases in insulin-mediated glucose uptake (p < 0.001) and plasma post-heparin lipoprotein and hepatic lipolytic activities (p < 0.02). Both fasting plasma triglyceride (3.09 +/- 0.51 vs 2.37 +/- 0.34 mmol/l), and postprandial triglyceride concentrations (p < 0.05-0.001) were lower following glipizide treatment, associated with a significant fall in retinyl palmitate content in all three lipoprotein fractions (p < 0.02-0.001), with the most substantial decrease seen in the Sf20-400 fraction. These data indicate that glipizide-induced improvement in glycaemic control was associated with changes in the metabolism of triglyceride-rich lipoproteins of intestinal origin that would be anticipated to reduce risk of coronary heart disease in non-insulin-dependent diabetic patients.

Effects of glipizide on glucose metabolism and muscle content of the insulin-regulatable glucose transporter (GLUT 4) and glycogen synthase activity during hyperglycaemia in type 2 diabetic patients

To examine whether sulphonylureas influence hyperglycaemia-induced glucose disposal and suppression of hepatic glucose production (HGP) in type 2 diabetes mellitus, a 150-min hyperglycaemic (plasma glucose 14 mmol/l) clamp with concomitant somatostatin infusion was used in eight type 2 diabetic patients before and after 6 weeks of glipizide (GZ) therapy. During the clamp a small replacement dose of insulin was given (0.15 mU/kg per min). Isotopically determined glucose-induced glucose uptake was similar before and after GZ administration which led to improved glycaemic control (basal plasma glucose 12.2 +/- 1.3 vs 8.9 +/- 0.7 mmol/l; P < 0.01). Glucose-induced suppression of HGP was, however, more pronounced during GZ treatment (0.96 +/- 0.14 vs 1.44 +/- 0.20 mg/kg per min; P < 0.02). Following GZ treatment hyperglycaemia failed to stimulate glycogen synthase activity. Moreover, GZ resulted in a significant increase in the immunoreactive abundance of the insulin-regulatable glucose transport protein (GLUT 4) (P < 0.02). In conclusion, these results suggest that GZ therapy in type 2 diabetic patients enhances hepatic sensitivity to hyperglycaemia, while glucose-induced glucose uptake remains unaffected. In addition, GZ tends to normalize the activity of glycogen synthase and increases the content of GLUT 4 protein in skeletal muscle.

Problems and pitfalls of sulphonylurea therapy in older patients

The prevalence of non-insulin-dependent diabetes mellitus (type II) increases with age, so that approximately half of all known patients in English-speaking countries are over 65 years of age. There is no reason to believe that the criteria for blood glucose control should be any less stringent for elderly patients unless they have a limited life expectancy. Sulphonylurea drugs remain an effective means of achieving blood glucose control after failure of dietary therapy alone in older patients. However, changes in normal metabolism of drugs with age and the development of other pathologies in elderly patients make it important that these drugs are prescribed with care. Severe symptomatic hypoglycaemia is the most serious adverse effect of sulphonylurea drugs and this becomes progressively more likely with increasing age, depending primarily on the substantial reduction of renal function with normal aging. Other adverse effects are much less commonly of clinical importance. To minimise the risk of hypoglycaemia, it is important that patients receive closely supervised dietary management with education about their disease for at least 3 months before sulphonylurea drugs are prescribed. In elderly patients a short-acting agent with no active metabolites should be used. As patients become older, those receiving long-acting agents can be changed to short-acting agents before problems arise. If blood glucose control appears satisfactory on treatment, then symptoms of hypoglycaemia should be sought. If control is poor, then the criteria for introduction of insulin, with appropriate education, do not differ from those in younger patients.

Does glibenclamide influence the clearance of insulin and glucose uptake in patients with type 2 diabetes mellitus?

Sulphonylureas have been proposed to decrease the clearance of insulin based on the finding that they increase peripheral insulin concentrations more than C-peptide concentrations. However, direct evidence for such an effect has so far been lacking. The aim of this study was to investigate whether glibenclamide affects clearance of insulin in Type 2 diabetic patients. Nine patients with Type-2 diabetes participated in the study. Insulin clearance and glucose metabolism was assessed with a 240 min euglycaemic insulin clamp in combination with infusion of somatostatin (400 micrograms h-1) to completely suppress endogenous insulin secretion. Either saline or glibenclamide was infused throughout the clamp in random order. During both the glibenclamide and the saline protocol the C-peptide level declined to < 0.07 nmol l-1 within 150 min, indicating that insulin secretion was completely suppressed. However, peripheral clamp insulin concentrations remained similar during both saline and glibenclamide protocols (3374 +/- 258 vs. 3350 +/- 265 pmol l-1 x 240 min, p = NS). There was no significant difference in the metabolic clearance rate of insulin during the glibenclamide compared to the saline experiment neither during the first 120 min (796 +/- 36 vs. 757 +/- 34 ml m-2min-1) nor during the last 2 h of the clamp (780 +/- 43 vs. 724 +/- 35 ml m-2min-1). Total glucose metabolism during the first two (14 +/- 2 vs. 15 +/- 2 mumol kg-1 min-1) and the last 2 h of the clamp was similar both during saline and glibenclamide infusions (27 +/- 4 vs. 28 +/- 4 mumol kg-1min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

The sulphonylurea drug, glimepiride, stimulates release of glycosylphosphatidylinositol-anchored plasma-membrane proteins from 3T3 adipocytes

Sulphonylurea drugs stimulate glucose transport and metabolism in muscle and fat cells in vitro. The molecular basis for the insulin-mimetic extrapancreatic effects of these oral antidiabetic therapeutic agents is unknown at present. Here we demonstrate that incubation of 3T3 adipocytes with the novel sulphonylurea, glimepiride, causes a time- and concentration-dependent release of the glycosylphosphatidylinositol (GPI)-anchored ecto-proteins, 5'-nucleotidase, lipoprotein lipase and a 62 kDa cyclic AMP (cAMP)-binding protein from the plasma membrane into the culture medium. The change in the localization is accompanied by conversion of the membrane-anchored amphiphilic proteins into their soluble hydrophilic versions, as judged by pulse-chase experiments and Triton X-114 partitioning, and by appearance of anti-cross-reacting determinant (CRD) immunoreactivity of the released proteins as shown by Western blotting. Metabolic labelling of cells with myo-[14C]inositol demonstrates that inositol is retained in the major portion of released lipoprotein lipase and cAMP-binding ectoprotein. The identification of inositol phosphate after deamination of these proteins with nitrous acid suggests cleavage of their GPI membrane anchor by a GPI-specific phospholipase C. However, after longer incubation with glimepiride the amount of soluble versions of the GPI-proteins lacking inositol and anti-CRD immunoreactivity increases, which may be caused by additional drug-stimulated hydrolytic events within their GPI structure or C-termini. Since insulin also stimulates membrane release of these GPI-modified proteins, and in combination with glimepiride in a synergistic manner, sulphonylurea drugs may exert their peripheral actions in adipose tissue by using (part of) the insulin postreceptor signalling cascade at the step of activation of a GPI-specific phospholipase C.

Insulin resistance in Werner's syndrome

Insulin resistance in Werner's syndrome (WS) was studied using the glucose clamp technique, and compared with physiologically aged and young subjects. Fasting immuno-reactive insulin (IRI) was increased in patients with Werner's syndrome compared with aged and young subjects. Metabolic clearance rate (MCR) of glucose was decreased in the aged and WS. A rightward shift of the dose-response curves of insulin and MCR of glucose was observed in the aged and WS with a more pronounced shift in the latter. MCR of insulin was also decreased in WS. [125I]insulin binding to erythrocytes was similar in the three groups. These results suggest that insulin resistance associated with WS is due to a post-binding defect manifested by a rightward shift of the dose-response curve of insulin-induced glucose disposal and a decrease in insulin clearance rate.

Studies on the mechanism of action of sulphonylureas in type II diabetic subjects: gliquidone

The mechanism of action of sulphonylureas is not completely understood. In the present study we evaluated the effects of gliquidone, a second-generation compound, on several metabolic parameters in 22 patients with untreated newly-diagnosed type II (noninsulin-dependent) diabetes mellitus. After either 1 or 6 months of treatment with gliquidone plus isocaloric diet we observed: 1) a significant decrease in fasting plasma glucose and glycemic profile after oral glucose load; 2) unchanged fasting and postglucose plasma insulin levels; 3) no change in fasting C-peptide levels but a significant increase in C-peptide concentrations after glucose challenge; 4) a significant increase in glucose disappearance rate from plasma following iv insulin injection; 5) an increase in the insulin-induced reduction of plasma levels of free-fatty acids; 6) no change in plasma C-peptide levels following iv insulin injection; 7) a significant increase in specific insulin binding to monocytes. After 6 but not 1 month of gliquidone therapy we also found an increase in the activity of hexokinase in circulating mononuclear leukocytes. These results suggest that the hypoglycemic effect of gliquidone occurs through either an increased beta cell response to glucose stimulus or an enhanced insulin sensitivity. The latter effect seems to depend on both receptor and postreceptor mechanisms.

Hepatic sensitivity to insulin: effects of sulfonylurea drugs

Insulin regulation of hepatic glucose production (HGP) is altered in non-insulin-dependent diabetes mellitus (NIDDM), resulting in increased glucose output by the liver; this contributes to the elevation in plasma glucose concentration observed both in the basal state and postprandially. Therefore, restoration of normal insulin action in the liver must be a goal of hypoglycemic therapy. Sulfonylureas have been widely used for treatment of NIDDM over the past 30 years. In addition to their stimulatory effect on insulin secretion, these compounds seem to possess extrapancreatic effects. Early in vitro studies showed that addition of sulfonylureas to the perfusion medium of liver preparations could exert a significant suppressive effect on HGP. Subsequent experience suggested that these compounds could act at the level of the insulin receptor as well as at various postreceptor sites. These studies showed that sulfonylureas may inhibit glycogenolysis and gluconeogenesis while stimulating glycogen synthesis. Results obtained in vivo in NIDDM patients are in agreement with the in vitro studies. Long-term treatment with sulfonylureas is associated with a decline in fasting plasma glucose concentration and a parallel reduction in HGP. Nevertheless, the direct effect of sulfonylurea administration on the liver remains unclear, since the reduction in HGP that occurs during sulfonylurea treatment may be secondary to an overall improvement in insulin secretion. It is also of interest that in insulin-dependent diabetic patients, sulfonylurea administration in combination with insulin injections is not followed by a significant change in HGP. Possible effects of sulfonylureas on glucagon secretion and on the metabolism of free fatty acids (FFAs) may also contribute to improved sensitivity of the liver to the suppressive action of insulin, since these agents appear to reduce plasma glucagon and FFA concentrations. Thus, present data support an extrapancreatic action of sulfonylureas on the liver. However, it does appear that a certain degree of residual insulin secretion is required for sulfonylurea agents to elicit their hepatic effect.

Effects of sulfonylureas on adipocyte and skeletal muscle insulin action in patients with non-insulin-dependent diabetes mellitus

The effect of glibenclamide treatment on insulin action in isolated fat cells was studied in eight moderately obese patients with non-insulin-dependent diabetes mellitus (NIDDM). Insulin receptor binding and the effect of insulin on glucose transport and lipogenesis were determined before and after 3 months of glibenclamide therapy. At the end of the treatment period, mean daytime plasma glucose concentrations were reduced (10.8 +/- 0.4 versus 7.0 +/- 0.3 mmol/L, p less than 0.001) whereas mean daytime plasma insulin level was increased (40 +/- 12 versus 71 +/- 9 mU/L, p less than 0.001). Adipocyte insulin receptor binding as well as basal glucose transport and metabolism were unaffected by drug treatment. In contrast, insulin-stimulated glucose transport and lipogenesis were both significantly enhanced (p less than 0.05). These findings are comparable to those of another study involving seven moderately obese subjects with NIDDM who had biopsies of the lateral vastus muscle taken for measurement of insulin receptor function and glycogen synthase activity before and during 2 months of gliclazide treatment. In that study insulin receptors purified with wheatgerm agglutinin showed unchanged insulin binding and receptor kinase activity. Moreover, gliclazide had no impact on maximal glycogen synthase activity. However, under physiologic hyperinsulinemic conditions gliclazide therapy was associated with an increased sensitivity of glycogen synthase for its allosteric activation by glucose-6-phosphatase (p less than 0.04). In conclusion, sulfonylurea treatment of NIDDM enhances insulin-stimulated peripheral glucose utilization in part through a potentiation of insulin action on adipose tissue glucose transport and lipogenesis and skeletal muscle glycogen synthase.

The effect of sulphonylurea therapy on skeletal muscle glycogen synthase activity and insulin secretion in newly presenting type 2 (non-insulin-dependent) diabetic patients

Ten newly presenting, Type 2 (non-insulin-dependent), Caucasian diabetic patients were studied before and after 8 weeks treatment with the sulphonylurea gliclazide, and in parallel 13 similar patients were studied before and after 8 weeks treatment with diet alone. Eight non-diabetic subjects were also studied. Insulin action was assessed by measuring activation of skeletal muscle glycogen synthase (GS) prior to and during a 4-h hyperinsulinaemic euglycaemic clamp (100 mU kg-1 h-1). Fasting plasma glucose (+/- SE) and glycosylated haemoglobin decreased to a greater extent in the gliclazide treated patients (fall of 6.2 +/- 0.7 vs 2.1 +/- 0.5 mmol l-1, p less than 0.005 and 4.7 +/- 0.5 vs 2.1 +/- 0.5%, p less than 0.005). This was accompanied by an increase in fasting serum insulin concentrations in the gliclazide treated patients (7.0 +/- 1.3 to 10.1 +/- 1.1 mU l-1, p less than 0.005), but no change in the diet treated patients. Fractional GS activity did not increase during the clamp at presentation in either treatment group (change +2.9 +/- 1.8 and -1.5 +/- 1.9%, respectively) whereas it increased markedly in the control subjects (+16.4 +/- 3.4%, both p less than 0.001). After 8-week treatment there was a significant increase in GS activity during the clamp in the patients receiving gliclazide (+6.9 +/- 2.7%, p less than 0.05), but no change in GS activity in the patients on diet alone (+0.5 +/- 1.4%). The difference in post-treatment muscle insulin action was significant (p less than 0.05). There was no correlation between the degree of improvement in metabolic control and the improvement in response of GS to insulin in the gliclazide treated patients (r = -0.06), suggesting a possible direct drug effect on skeletal muscle. Glucose requirement during the clamp at presentation was markedly lower in both treatment groups than in the non-diabetic subjects (gliclazide 2.1 +/- 0.3, diet 2.0 +/- 0.6 vs 7.8 +/- 0.4 mg kg-1 min-1, both p less than 0.001), and despite a marked improvement in both groups after treatment (4.3 +/- 0.4 and 3.1 +/- 0.5 mg kg-1 min-1, both p less than 0.001) remained lower than in the non-diabetic subjects (p less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in carbohydrate metabolism in association with glipizide treatment of type 2 diabetes

Nineteen patients with Type 2 diabetes were treated with glipizide for 2.5-6 months, and measurements made of metabolic variables before and after glipizide treatment. For purposes of analysis, the glipizide associated decrease in fasting plasma glucose concentration was used to divide patients into 'good' responders (decrease of 4.0 mmol l-1 or more, n = 9) or 'fair' responders (decrease of 3.0 mmol l-1 or less, n = 10). Good responders had a significantly greater fall in their mean (+/- SE) hourly plasma glucose (6.3 +/- 0.6 vs 2.7 +/- 0.3 mmol l-1, p less than 0.001) and NEFA (164 +/- 40 vs 60 +/- 37 mumol l-1, p less than 0.05) concentrations from 0800 to 1600 h in response to meals (0800 and 1200 h) than did the fair responders. However, the increase in hourly plasma insulin concentration following glipizide treatment was the same in the good (323 +/- 103 to 413 +/- 124 pmol l-1) and fair (276 +/- 42 to 345 +/- 43 pmol l-1) responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin release and peripheral sensitivity at the oral glucose tolerance test

With the use of a 75 g oral glucose tolerance test, both insulin release (IRG) and the degree of peripheral sensitivity (SI) were evaluated simultaneously in groups with normal (NGT) and impaired (IGT) glucose tolerance as well as NIDDM. IRG was expressed as the ratio of the area under the insulin curve to that of the glucose curve above fasting levels. The peripheral glucose uptake rate (M) during the OGTT was measured as the difference between the glucose load and the increase in the amount of glucose in the glucose space during the oral glucose tolerance test (OGTT). SI was expressed as the ratio of the metabolic clearance rate (M/mean blood glucose) to log mean serum insulin. In the non-obese groups, both mean IRG and mean SI values were decreased with an increasing degree of hyperglycemia from NGT to NIDDM. Decreased mean SI values were also found in obese subjects. IGT-subjects given 3 months of diet and exercise achieved improved SI values. A non-obese NIDDM-group had higher mean IRG and mean SI values after 6 months of treatment with glipizide. The results were comparable to data obtained with more complicated techniques, such as the insulin clamp and suppression tests, and should be easy to apply on a large scale in epidemiological studies.

Effects of glyburide on in vivo insulin-mediated glucose disposal

The purpose of this study was to examine the effects of glyburide on peripheral (muscle) and hepatic insulin sensitivity in patients with non-insulin-dependent diabetes mellitus (NIDDM) and insulin-dependent diabetes mellitus (IDDM) as well as in healthy control subjects. In protocol 1, 10 patients with NIDDM and seven young healthy control subjects were studied. Changes in insulin sensitivity (40 mU/m2.min euglycemic insulin clamp), hepatic glucose production (3-[3H]glucose turnover), and insulin secretion (+125 mg/dL hyperglycemic clamp) were measured before and after 3 months (in patients with NIDDM) and 6 weeks (in young control subjects) of glyburide therapy. In protocol 2, five patients with IDDM and eight patients with insulin-treated NIDDM were evaluated before and after two months of glyburide therapy (20 mg per day). Changes in daily insulin requirements, 24-hour plasma glucose profiles, glycohemoglobin, glucagon-stimulated C-peptide secretion, insulin sensitivity, and hepatic glucose production were measured. In protocol 1, glyburide significantly improved insulin sensitivity (p less than 0.01) and insulin secretion (p less than 0.01) in the NIDDM patients. The elevated rates of hepatic glucose production (2.4 +/- 0.3 mg/kg.min) were reduced after glyburide therapy (1.7 +/- 0.2 mg/kg.min; p less than 0.01) and were highly correlated with an improvement in fasted plasma glucose levels (r = 0.92; p less than 0.001). Insulin sensitivity also improved in the young healthy control subjects after glyburide therapy (6.5 +/- 0.5 to 7.6 +/- 0.7 mg/kg.min; p less than 0.05). In protocol 2, glyburide treatment produced no change in daily insulin requirement (54 +/- 8 versus 53 +/- 7 units per day), mean 24-hour glucose levels (177 +/- 20 versus 174 +/- 29 mg/dL), glycohemoglobin (10.1 +/- 1.0 percent versus 9.5 +/- 7 percent), C-peptide secretion, insulin sensitivity, or basal hepatic glucose production (p values not significant) in the IDDM patients. In contrast, the insulin-treated NIDDM patients had significant reductions in mean daily insulin requirement (72 +/- 6 versus 58 +/- 9 units per day; p = 0.05), mean 24-hour plasma glucose levels (153 +/- 10 to 131 +/- 5 mg/dL; p less than 0.05), and glycohemoglobin levels (10.3 +/- 0.7 percent to 8.0 +/- 0.4 percent; p less than 0.05) and an improvement in C-peptide secretion (0.24 +/- 0.07 to 0.44 +/- 0.09 pmol/mL; p = 0.08). Stimulated C-peptide levels were highly correlated with a reduction in insulin dose observed during the 2-month treatment period (r = 0.93; p less than 0.001). Insulin sensitivity improved slightly but not significantly after glyburide treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of glyburide on beta cell responsiveness to glucose in non-insulin-dependent diabetes mellitus

Since the introduction of glyburide in 1984, many studies have evaluated the effects of this oral hypoglycemic agent on beta cell function in patients with non-insulin-dependent diabetes mellitus. The early studies, which were performed in patients receiving concomitant insulin therapy, may have underestimated the true effect of glyburide on insulin secretion. The more recent studies demonstrate that both short- and long-term glyburide therapy increase C-peptide levels in diabetic as well as nondiabetic subjects and that the effects of glyburide are comparable to those of the other second-generation sulfonylurea, glipizide. The effects of glyburide on insulin secretory rates calculated from plasma C-peptide levels were recently evaluated using individually derived C-peptide kinetic parameters and a validated open two-compartment model of peripheral C-peptide kinetics. Glyburide did not influence fasting insulin secretion (196 +/- 34 versus 216 +/- 23 pmol/min) but did cause an increase in the total amount of insulin secreted over a 24-hour period (447 +/- 58 versus 561 +/- 55 nmol). This increase in the production of insulin was generated by an increase in amplitude of secretory pulses occurring after lunch and dinner rather than by a greater number of pulses. The full effect of glyburide on the beta cell became evident when glucose concentrations were clamped at the hyperglycemic level of 300 mg/dL both before and during treatment for a 3-hour period. During that time, insulin secretion rates increased by 221 percent in response to glyburide. Glyburide did not, however, completely reverse the beta cell secretory defect characteristic of non-insulin-dependent diabetes mellitus. In the patients receiving glyburide, the sluggish insulin secretory response to breakfast persisted, and the insulin secretory response during the hyperglycemic clamping was less than the response normally seen in nondiabetic subjects. These experiments suggest that the primary effect of glyburide on the beta cell is to increase its responsiveness to glucose. Although the precise mechanism of action of glyburide at the cellular level is unclear, in vitro studies suggest that its effect is mediated through binding with specific receptors on the beta cell membrane, which in turn leads to alterations in the cellular efflux of potassium ions and influx of calcium ions.

Effects of the sulfonylureas on muscle glucose homeostasis

The sulfonylureas have pharmacologic effects both on insulin secretion by pancreatic beta cells and on responsiveness to insulin in peripheral tissues. The effects of the sulfonylureas on skeletal muscle may have a particularly significant influence on glucose homeostasis because of the important role of muscle as a peripheral site of glucose clearance. Under most physiologic conditions, the rate-limiting step for glucose utilization in muscle is its uptake across the plasma membrane; for this reason, the effects of the sulfonylureas on glucose transport have been a focus for study. In muscle tissue, the sulfonylureas appear to augment the stimulation of glucose uptake by insulin but not to alter glucose homeostasis in the absence of insulin. The mechanism of this effect, which requires several hours of exposure to a sulfonylurea, has not been defined. Although studies with cultured muscle cells have yielded inconsistent findings, recent work with the L6 rat skeletal muscle cell line demonstrated that the sulfonylureas exerted effects similar to those in muscle tissue both in time course and in requirement for co-stimulation by insulin. Mechanistic studies in L6 cells have shown that the sulfonylureas induce increased glucose transporter messenger ribonucleic acid levels and increased total cellular content of transporter proteins even in the absence of insulin, but that insulin is required for augmented glucose uptake activity. Based on these data, it has been suggested that insulin may cause the activation of transporters synthesized in response to sulfonylureas. The definition of the mechanism of this synergistic response to insulin and the sulfonylureas in L6 muscle cells may give insight into the in vivo molecular events involved in the action of the sulfonylureas in skeletal muscle.

The effects of long term gliclazide administration on insulin secretion and insulin sensitivity

Gliclazide (80 mg bd) was administered to nine subjects with type 2 (non insulin dependent) diabetes inadequately controlled on diet only. Twenty-four hour glucose, insulin and c-peptide profiles were obtained before and after one week and four months of therapy. Insulin sensitivity was assessed by euglycemic hyperinsulinemic clamp before and after four months of treatment. Twenty-four hour glucose levels were significantly lowered after one week and four months. Insulin secretion, as assessed by the areas under the insulin and c-peptide curves, was enhanced after one week. The increase was most noted during the day in response to meals. The enhancement was maintained after four months of treatment with the increase in the postabsorptive phase becoming significant. Glucose utilisation rate was significantly increased at four months. It is concluded that both acute and prolonged gliclazide therapy directly or indirectly 1) enhances both meal stimulated and post absorptive insulin secretion and 2) increases insulin sensitivity. The relative contribution of each to improved diabetic control has not been established.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

Relationship between glucose tolerance, insulin secretion, and insulin action in non-obese individuals with varying degrees of glucose tolerance

Plasma glucose and insulin concentration following a 75 g oral glucose challenge and glucose uptake during a hyperinsulinaemic glucose clamp study were determined in 50 non-obese individuals. The study population was divided into five groups on the basis of their glucose tolerance: normal, impaired glucose tolerance, Type 2 (non-insulin-dependent) diabetes mellitus with fasting plasma glucose of less than 8 mmol/l, between 8-15 mmol/l, and more than 15 mmol/l. The plasma insulin response was significantly greater (p less than 0.001) than normal in those with either impaired glucose tolerance or Type 2 diabetes and a fasting plasma glucose concentration less than 8 mmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulphonylurea antidiabetic drugs. An update of their clinical pharmacology and rational therapeutic use

Apart from the amelioration of symptoms, a major aim of the treatment of non-insulin-dependent diabetes mellitus (NIDDM, type 2 diabetes) should be the prevention of cardiovascular complications. These are associated with the chronic hyperglycaemia that is characteristic of NIDDM, and the risk of complications is already increased in subjects with impaired glucose tolerance (IGT). For these reasons, and because hyperglycaemia appears to be a self-perpetuating condition, treatment should be introduced as early as possible and should be aimed at normalisation of blood glucose. To enable early detection and intervention, screening is necessary. As diet regulation alone rarely suffices to normalise blood glucose, addition of sulphonylurea drugs is indicated in many cases. If introduced in the IGT phase, sulphonylureas drugs combined with diet regulation may postpone the development of IGT to manifest NIDDM, and may reduce the increased risk of cardiovascular morbidity and mortality. Sulphonylureas stimulate insulin release, possibly via interaction with receptors in the pancreatic B cells. In addition, such treatment enhances the reduced insulin action. This might be a primary effect but is also a consequence of the increased access to insulin and the subsequent reduction of hyperglycaemia. Sulphonylureas may enhance insulin availability by reducing insulin clearance. Effects on blood lipids are probably secondary phenomena. Fast and short acting sulphonylureas may improve the impaired meal-induced acute insulin release. If combined with weight-reducing diet regulation and introduced early, such treatment can maintain (near) normal blood glucose levels and an improved insulin action for several years without increasing basal insulin secretion, without chronic hyperinsulinaemia, and without weight increase. If not combined with diet regulation, sulphonylurea therapy is likely to fail. If introduced when NIDDM is advanced, the efficacy of these drugs is limited, with secondary failures developing at a rate of 5 to 10% per year. Continuous (24-hour-a-day) exposure to drug treatment could possibly desensitise the B cell to sulphonylurea stimulation. 'Second-generation' sulphonylurea drugs have a higher potency than 'first-generation' drugs, but this need not signify a greater clinical efficacy. The effect of several of these drugs may be increased if they are ingested half an hour before meal(s). Short acting sulphonylureas may be safer than long acting ones, which seem more likely to cause long lasting and fatal hypoglycaemia, at least in elderly patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin binding to monocytes and in vivo peripheral insulin sensitivity are normal in Graves' disease

Insulin resistance in hyperthyroidism seems to depend on increased glucose production rather than on decreased glucose utilization. A decreased insulin binding on different target cells has been reported in patients in whom an in vivo evaluation of peripheral insulin sensitivity was lacking. In 20 patients with Graves' disease (6 males, 14 females), aged 40.0 +/- 2.0 yr, BMI 23.7 +/- 0.7, and in 20 well-matched controls we performed the following tests: 75 g o.G.T.T., euglycemic-hyperinsulinemic clamp at 50 microU/ml combined with D-[3-3H] glucose infusion in tracer amounts, in vitro insulin binding on circulating monocytes. Fasting plasma glucose values were similar in the two groups, whereas plasma insulin values were significantly higher in hyperthyroids (21.4 +/- 2.5 vs 10.6 +/- 0.6 microU/ml, p less than 0.01). The values of peripheral glucose utilization (5.61 +/- 0.24 vs 6.01 +/- 0.22 mg/kg-min) and of total specific insulin binding (4.07 +/- 0.20 vs 4.39 +/- 0.23% bound to 10(7) cells/ml) were not significantly different in the two groups. These results indicate that in vitro and in vivo data, when recorded in the same patients, are concordant to confirm a normal peripheral tissue sensitivity to insulin in Graves' disease.

Cellular mechanisms of insulin resistance in non-insulin-dependent (type II) diabetes

Recent studies have led to an enhanced understanding of cellular alterations that may play an important role in the pathophysiology of non-insulin-dependent diabetes mellitus (NIDDM). The insulin receptor links insulin binding at the cell surface to intracellular activation of insulin's effects. This transducer function involves the tyrosine kinase property of the beta-subunit of the receptor. It was found that adipocytes from subjects with NIDDM had a 50 to 80 percent reduction in insulin-stimulated receptor kinase activity compared with their non-diabetic counterparts. This defect was relatively specific for the diabetic state since no decrease was observed in insulin-resistant non-diabetic obese subjects. The reduction in kinase activity was accounted for by changes in the ratio of two pools of receptors, both of which bind insulin but only one of which is capable of tyrosine autophosphorylation and subsequent kinase activation; 43 percent of the receptors from non-diabetic subjects were capable of autophosphorylation compared with only 14 percent in the NIDDM group. A major component of cellular insulin resistance in NIDDM involves the glucose transport system. Exposure of cells to insulin normally results in enhanced glucose transport mediated by translocation of glucose transporters from a low-density microsomal intracellular pool to the plasma membrane. It was found that cells from NIDDM subjects had a marked depletion of glucose transporters in both plasma membranes and low-density microsomes, relative to obese non-diabetic control participants. Obese non-diabetic persons had a normal number of plasma membrane transporters but a reduced number of low-density microsome transporters in the basal state compared with lean control volunteers; insulin induced the translocation of relatively fewer transporters from the low-density microsome to the plasma membrane in the obese subgroups. In addition to the diminished number of glucose transporters, cells from both NIDDM and obese subjects had impaired functional activity of glucose carriers since decreased whole-cell glucose transport rates could not be entirely explained by the magnitude of the decrement in the number of plasma membrane transporters. Thus, impaired glucose transport is due to both a numerical and functional defect in glucose transporters. The cellular content of high-density microsomal transporters was the same in lean and obese control volunteers and NIDDM subjects, suggesting that transporter synthesis is normal and that cellular depletion results from increased protein turnover once transporters leave the high-density microsomal subfraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Oral hypoglycemic agents

The sulfonylureas remain the most important oral agents, although their chronic hypoglycemic actions are still unexplained and the evidence on their relative efficacy is inconclusive. Data on relative safety suggest that chlorpropamide is the most toxic sulfonylurea but glyburide causes dangerous hypoglycemia as often as chlorpropamide. For many patients, good blood glucose control will be achieved by taking tolbutamide or another sulfonylurea 30 minutes before breakfast and the main evening meal. The biguanide metformin, which is as safe as glyburide, is of use in treating overweight diabetic patients who do not have cardiovascular, hepatic, or renal dysfunction.

Diet only or diet and sulfonylureas in mild type II diabetes (NIDDM)? Pathophysiologic and therapeutic implications

Plasma glucose, insulin and C-peptide responses to a test meal were studied in 7 nonobese patients with type II diabetes mellitus (NIDDM) treated with diet alone and after 6 months of gliclazide therapy, as well as in 6 matched controls. The glycemic levels were significantly higher (p less than 0.05) in patients under diet alone than in controls and after gliclazide treatment (peak: 12.8 +/- 1.0; 7.9 +/- 0.4 and 10.0 +/- 0.5 mmol/l, respectively; means +/- SEM). Diet and gliclazide treated patients showed a reduced B-cell response during the first hour after the meal as indicated by insulin and C-peptide values and areas (insulin areas 0-60 min: controls 57.9 +/- 10.9; p less than 0.01 vs diet alone 14.2 +/- 2.7 and vs gliclazide 22.1 +/- 2.8 microU/ml/min). The hypoinsulinemic phase lasted from 20 to 60 min before gliclazide, and from 20 to 45 min after gliclazide. The first significant C-peptide increase, detected at 10 min in controls and at 30 min under diet alone, was advanced to 15 min after gliclazide treatment.

IN CONCLUSION

patients with mild, diet-treated NIDDM show a sluggish and attenuated B-cell response to a physiologic challenge (test meal); this secretory impairment is present even after a complete post-prandial glycemic normalization, supporting the idea of a persistent defect. Nevertheless, the slight improvement observed in insulin secretion after gliclazide treatment may be promoting, at least partially, the normalization of prandial hyperglycemia. The benefits of this normalization in diabetic patients previously controlled by diet only await further investigation.

Rapid improvement in insulin binding to erythrocyte insulin receptors in non-insulin-dependent diabetes mellitus during therapy

Insulin binding to erythrocyte receptors was studied in 36 newly diagnosed male subjects with NIDDM, treated with diet alone (Group I; n = 10) or diet + glibenclamide (Group II; n = 12) or diet + glibenclamide + metformin (Group III; n = 14). Fourteen matched non-diabetic subjects were also studied as controls. Initially, mean (+/- SD) specific insulin binding was lower in NIDDM patients than in controls (p less than 0.001), due to decreased receptor number and affinity. Control of diabetes with short-term therapy (10 +/- 2 days) resulted in significantly increased specific insulin binding in Groups II and III (p less than 0.001). A marginal increase was observed in Group I (p less than 0.01). The improved insulin binding observed in Group II and III patients after short-term therapy was maintained even after long-term therapy (9 +/- 1 months). Analysis of the insulin binding data by Scatchard plots and average affinity profiles indicated increased receptor number and affinity after short-term therapy. However, changes in affinity were reversed with long-term therapy in Groups II and III and the predominant effect appeared to be an increase in the number of binding sites.

Effects of short-term insulin therapy upon therapeutic response to glipizide

The effect of glipizide alone and glipizide preceded by a short course of insulin therapy (10 weeks) was studied in 69 patients with non-insulin-dependent diabetes mellitus (NIDDM) in a 10-month study. The patients were obese, had poor glycemic control, and, in all patients, first-generation sulfonylurea therapy had failed. The majority were Mexican-Americans, an ethnic population with a high incidence of NIDDM and insulin resistance. Plasma glucose levels were monitored using the eight-point [Saarstedt] series. In the group receiving glipizide alone, mean fasting plasma glucose levels decreased from 255.9 mg/dl at baseline to 228.7 mg/dl at the end of the study; two-hour postprandial glucose levels decreased from 280.1 to 260.5 mg/dl; glycosylated hemoglobin decreased from 9.1 to 7.4 percent; and post-Sustacal C-peptide levels increased from 0.7 to 1.0 pmol/ml. In the group receiving insulin/glipizide, mean fasting plasma glucose levels decreased from 241.1 mg/dl at baseline to 217.0 mg/dl; two-hour postprandial glucose levels increased from 267.2 to 279.0 mg/dl; glycosylated hemoglobin decreased from 9.1 to 7.5 percent; and post-Sustacal C-peptide levels increased from 0.6 to 1.0 pmol/ml. At the end of 10 weeks, insulin administration was associated with a more rapid decrease in the levels of fasting plasma glucose, two-hour postprandial glucose, and glycosylated hemoglobin, but there was no significant difference between the two therapies by the end of the study. Both regimens had a positive influence on reducing the total cholesterol/high-density lipoprotein ratio. More patients in the group receiving insulin/glipizide withdrew from the study, which may have been due to difficulties associated with insulin administration. In conclusion, there does not appear to be a prolonged effect of insulin treatment on the post-receptor defect. Some patients in whom first-generation oral agents fail may not have to be given permanent insulin therapy, especially those with fasting plasma glucose levels of less than 200 mg/dl. There was no overall difference between these treatments with respect to glycemic control or lipoprotein profiles. In the interests of simplifying both therapy and monitoring, enhancing patient compliance, and achieving cost reductions, therapy with glipizide alone ultimately may be sufficient for cases in which immediate control is unnecessary (for example, patients with asymptomatic hyperglycemia, and in the absence of hyperlipidemia and vascular disease).

Combined therapy of insulin and tolazamide decreases insulin requirement and serum triglycerides in obese patients with noninsulin-dependent diabetes mellitus

Insulin requirements, C-peptide levels, and serum lipids have been assessed in 12 obese, insulin-requiring (greater than 60 U/day) patients with type II diabetes mellitus, in a randomized crossover fashion with two treatment regimens: NPH alone and combined NPH and tolazamide, over a period of 3 months each, with maintenance of weight and glycemic control (HgA1, 2hpp and mean 24h glucose profile) at comparable levels. Serum cholesterol improved in both groups compared to their respective baseline values (p less than 0.05). In addition, serum triglyceride was lower (p less than 0.05) in the combined therapy as compared with NPH alone therapy. Insulin requirements were decreased by 23% (p less than 0.002) in the combined therapy group, without significant change in weight, glycemic control, or C-peptide levels. However, C-peptide increments in the combined therapy group were significantly higher than the baseline by 70% (p less than 0.02). NPH plus tolazamide therapy as compared with NPH alone lowers insulin requirement in obese, type II diabetic women without significant alteration in glycemic control, possibly by an increased tissue sensitivity to insulin, and decreases serum triglyceride levels.