The effect of chronic sulfonylurea therapy on hepatic glucose production in non-insulin-dependent diabetes

Pancreatic regulation of glucose homeostasis

In order to ensure normal body function, the human body is dependent on a tight control of its blood glucose levels. This is accomplished by a highly sophisticated network of various hormones and neuropeptides released mainly from the brain, pancreas, liver, intestine as well as adipose and muscle tissue. Within this network, the pancreas represents a key player by secreting the blood sugar-lowering hormone insulin and its opponent glucagon. However, disturbances in the interplay of the hormones and peptides involved may lead to metabolic disorders such as type 2 diabetes mellitus (T2DM) whose prevalence, comorbidities and medical costs take on a dramatic scale. Therefore, it is of utmost importance to uncover and understand the mechanisms underlying the various interactions to improve existing anti-diabetic therapies and drugs on the one hand and to develop new therapeutic approaches on the other. This review summarizes the interplay of the pancreas with various other organs and tissues that maintain glucose homeostasis. Furthermore, anti-diabetic drugs and their impact on signaling pathways underlying the network will be discussed.

Synthesis and structure-activity relationship of non-phosphorus-based fructose-1,6-bisphosphatase inhibitors: 2,5-Diphenyl-1,3,4-oxadiazoles

With the aim of discovering a novel class of non-phosphorus-based fructose-1,6-bisphosphatase (FBPase) inhibitors, a series of 2,5-diphenyl-1,3,4-oxadiazoles were synthesized based on the hit compound (1) resulting from a high-throughput screening (HTS). Structure-activity relationship (SAR) studies led to the identification of several compounds with comparable inhibitory activities to AMP, the natural allosteric inhibitor of FBPase. Notably, compound 22 and 27b, bearing a terminal carboxyl or 1H-tetrazole, demonstrated remarkable inhibition to gluconeogenesis (GNG). In addition, both inhibition and binding mode to the enzyme were investigated by enzymatic kinetics and in silico experiments for representative compounds 16 and 22.

Efficacy of glimepiride/metformin fixed-dose combination vs metformin uptitration in type 2 diabetic patients inadequately controlled on low-dose metformin monotherapy: A randomized, open label, parallel group, multicenter study in Korea

Aims/Introduction

To compare the efficacy and safety of early combination therapy with glimepiride/metformin to metformin uptitration in reducing glycated hemoglobin (HbA1c) levels in Korean type 2 diabetic patients inadequately controlled on low-dose metformin monotherapy.

Materials and Methods

In a randomized, open label, parallel group, multicenter study, 209 Korean type 2 diabetic patients (HbA1c 7.0–10.0%, on metformin 500–1,000 mg/day) received glimepiride/metformin fixed-dose combination (G/M FDC) or metformin uptitration treatment (Met UP). The primary end-point was the change in HbA1c from baseline to week 24.

Results

G/M FDC therapy provided significantly greater adjusted mean decreases vs Met UP therapy in HbA1c (−1.2 vs −0.8%, P < 0.0001), and fasting plasma glucose (−35.7 vs −18.6 mg/dL, P < 0.0001). A significantly greater proportion of patients with G/M FDC therapy achieved HbA1c < 7% (74.7 vs 46.6%, P < 0.0001) at the end of the study. More patients experienced hypoglycemia with G/M FDC therapy compared with Met UP therapy (41 vs 5.6%, P < 0.0001), but there was no serious hypoglycemia in any group. A modest increase in mean bodyweight occurred in the patients who were treated with G/M FDC therapy (1.0 kg), whereas a slight decrease was observed in the patients who were treated with Met UP therapy (−0.7 kg).

Conclusion

The present study showed that glimepiride/metformin fixed-dose combination therapy was more effective in glycemic control than metformin uptitration, and was well tolerated in type 2 diabetic patients inadequately controlled by low-dose metformin monotherapy in Korea. This trial was registered with ClinicalTrial.gov (no. NCT00612144).

Colesevelam suppresses hepatic glycogenolysis by TGR5-mediated induction of GLP-1 action in DIO mice

Bile acid sequestrants are nonabsorbable resins designed to treat hypercholesterolemia by preventing ileal uptake of bile acids, thus increasing catabolism of cholesterol into bile acids. However, sequestrants also improve hyperglycemia and hyperinsulinemia through less characterized metabolic and molecular mechanisms. Here, we demonstrate that the bile acid sequestrant, colesevelam, significantly reduced hepatic glucose production by suppressing hepatic glycogenolysis in diet-induced obese mice and that this was partially mediated by activation of the G protein-coupled bile acid receptor TGR5 and glucagon-like peptide-1 (GLP-1) release. A GLP-1 receptor antagonist blocked suppression of hepatic glycogenolysis and blunted but did not eliminate the effect of colesevelam on glycemia. The ability of colesevelam to induce GLP-1, lower glycemia, and spare hepatic glycogen content was compromised in mice lacking TGR5. In vitro assays revealed that bile acid activation of TGR5 initiates a prolonged cAMP signaling cascade and that this signaling was maintained even when the bile acid was complexed to colesevelam. Intestinal TGR5 was most abundantly expressed in the colon, and rectal administration of a colesevelam/bile acid complex was sufficient to induce portal GLP-1 concentration but did not activate the nuclear bile acid receptor farnesoid X receptor (FXR). The beneficial effects of colesevelam on cholesterol metabolism were mediated by FXR and were independent of TGR5/GLP-1. We conclude that colesevelam administration functions through a dual mechanism, which includes TGR5/GLP-1-dependent suppression of hepatic glycogenolysis and FXR-dependent cholesterol reduction.

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.

Hepatic glucose-6-phosphatase activity in non-insulin dependent diabetics. Effect of enzyme-inducing drugs

The role of glucose-6-phosphatase (G6Pase) in postreceptional glucose handling in non-insulin dependent diabetics ( NIDDs ) was in investigated by comparing the enzyme values in diagnostic liver biopsy samples with fasting blood glucose (BG), immunoreactive insulin (IRI) and plasma antipyrine half-life (T/2). The NIDDs , treated with sulphonylureas, had elevated serum aminotransferase and alkaline phosphatase values associated with fatty liver with or without fibrosis. G6Pase activity was reduced in the NIDDs compared with subjects who had undergone gallstone surgery (p less than 0.001), insulin dependent diabetics (p less than 0.001), and age- and sex-matched non-diabetics (p less than 0.001). G6Pase was inversely related to BG and antipyrine T/2, but not to IRI or conventional liver function tests. Therapy with phenobarbital and medroxyprogesterone acetate, known inducers, increased G6Pase activity, shortened antipyrine T/2, reduced BG and did not alter IRI, in four NIDDs . Low liver G6Pase activity in NIDDs may hence be one factor underlying the impaired glycemic control.

Glucokinase gene locus transgenic mice are resistant to the development of obesity-induced type 2 diabetes

Transgenic mice that overexpress the entire glucokinase (GK) gene locus have been previously shown to be mildly hypoglycemic and to have improved tolerance to glucose. To determine whether increased GK might also prevent or diminish diabetes in diet-induced obese animals, we examined the effect of feeding these mice a high-fat high-simple carbohydrate low-fiber diet (HF diet) for 30 weeks. In response to this diet, both normal and transgenic mice became obese and had similar BMIs (5.3 +/- 0.1 and 5.0 +/- 0.1 kg/m2 in transgenic and non-transgenic mice, respectively). The blood glucose concentration of the control mice increased linearly with time and reached 17.0 +/- 1.3 mmol/l at the 30th week. In contrast, the blood glucose of GK transgenic mice rose to only 9.7 +/- 1.2 mmol/l at the 15th week, after which it returned to 7.6 +/- 1.0 mmol/l by the 30th week. The plasma insulin concentration was also lower in the GK transgenic animals (232 +/- 79 pmol/l) than in the controls (595 +/- 77 pmol/l), but there was no difference in plasma glucagon concentrations. Together, these data indicate that increased GK levels dramatically lessen the development of both hyperglycemia and hyperinsulinemia associated with the feeding of an HF diet.

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.

The use of sulphonylureas in the elderly

Type 2 diabetes mellitus is a heterogeneous disorder characterised by defects in insulin secretion as well as reduced insulin action. During aging, glucose intolerance will gradually develop, and this is manifested primarily by an increase in the postprandial blood glucose response while fasting blood glucose levels are often less elevated. Abnormal beta-cell secretion of insulin is a main feature of this. Treatment of elderly patients with type 2 diabetes mellitus focuses on reduction of (hyperglycaemic) complaints and prevention of the development or progression of secondary complications. Although regular physical activity and dietary measures, aiming at bodyweight normalisation, are the cornerstones of therapy, pharmacological treatment with oral blood glucose lowering-agents often proves necessary to control the hyperglycaemia. In the United Kingdom Prospective Diabetes Study (UKPDS) it was clearly shown that patients with type 2 diabetes mellitus who were intensively treated with oral blood glucose-lowering agents or insulin developed less microvascular complications. The question whether achievement of strict metabolic control is also of benefit in elderly patients, is still unanswered. Sulphonylureas are drugs which stimulate insulin secretion by enhancing the release of insulin from the pancreatic beta-cells without an effect on insulin synthesis. They are frequently used in the treatment of type 2 diabetes mellitus, and several preparations are available. In general, there are no major differences in effectiveness between the various sulphonylureas. Long term treatment with sulphonylureas will decrease fasting and postprandial plasma glucose levels by 3 to 5 mmol/L, and glycosylated haemoglobin by 20%. However, after its initial decline, plasma glucose level will often go up slightly during the following months to years. Sulphonylureas are usually well tolerated. Hypoglycaemia is the most frequently occurring adverse effect, which may be very serious and damaging in the elderly. It has been associated primarily with long-acting sulphonylureas, like chlorpropamide and glibenclamide (glyburide). Hypoglycaemic episodes may trigger serious events like myocardial infarction or stroke. Therefore, shorter-acting compounds like tolbutamide and gliclazide have been relatively well tolerated and appear to be the best choice to treat elderly patients. It is advisable to start with a low dose and increase the dose, when needed, in small steps. The efficacy of sulphonylureas is much greater when they are taken before a meal. Because of the fact that type 2 diabetes mellitus is a progressive disease, and residual beta-cell function decreases with time, insulin therapy may ultimately be warranted in a significant number of patients.

Pharmacologic therapy for type 2 diabetes mellitus

Type 2 diabetes mellitus is a chronic metabolic disorder that results from defects in both insulin secretion and insulin action. An elevated rate of basal hepatic glucose production in the presence of hyperinsulinemia is the primary cause of fasting hyperglycemia; after a meal, impaired suppression of hepatic glucose production by insulin and decreased insulin-mediated glucose uptake by muscle contribute almost equally to postprandial hyperglycemia. In the United States, five classes of oral agents, each of which works through a different mechanism of action, are currently available to improve glycemic control in patients with type 2 diabetes. The recently completed United Kingdom Prospective Diabetes Study (UKPDS) has shown that type 2 diabetes mellitus is a progressive disorder that can be treated initially with oral agent monotherapy but will eventually require the addition of other oral agents, and that in many patients, insulin therapy will be needed to achieve targeted glycemic levels. In the UKPDS, improved glycemic control, irrespective of the agent used (sulfonylureas, metformin, or insulin), decreased the incidence of microvascular complications (retinopathy, neuropathy, and nephropathy). This review examines the goals of antihyperglycemic therapy and reviews the mechanism of action, efficacy, nonglycemic benefits, cost, and safety profile of each of the five approved classes of oral agents. A rationale for the use of these oral agents as monotherapy, in combination with each other, and in combination with insulin is provided.

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.

The biochemical basis of increased hepatic glucose production in a mouse model of type 2 (non-insulin-dependent) diabetes mellitus

The mechanism of increased hepatic glucose production in obese non-insulin-dependent diabetic (NIDDM) patients is unknown. The New Zealand Obese (NZO) mouse, a polygenic model of obesity and NIDDM shows increased hepatic glucose production. To determine the mechanism of this phenomenon, we measured gluconeogenesis from U-14C-glycerol and U-14C-alanine and relevant gluconeogenic enzymes. Gluconeogenesis from glycerol (0.07 +/- 0.01 vs 0.21 +/- 0.02 micromol.min-1.body mass index (BMI)-1, p < 0.005) and alanine (0.57 +/- 0.07 vs 0.99 +/- 0.07 micromol.min-1.BMI-1, p < 0.005) was elevated in control mice NZO vs as was glycerol turnover (0.25 +/- 0.02 vs 0.63 +/- 0.09 micromol.min-1.BMI-1, p < 0.05). Fructose 1,6-bisphosphatase activity (44.2 +/- 1.9 vs 55.7 +/- 4.1 nmol.min-1.mg protein-1, p < 0.05) and protein levels (6.9 +/- 1.1 vs 16.7 +/- 2.3 arbitrary units, p < 0.01) were increased in NZO mouse livers, as was the activity of pyruvate carboxylase (0.12 +/- 0.01 vs 0.17 +/- 0.02 nmol.min-1.mg protein-1, p < 0.05). To ascertain whether elevated lipid supply is responsible for these biochemical changes in NZO mice, we fed lean control mice a 60% fat diet for 2 weeks. Fat-fed mice were hyperinsulinaemic (76.37 +/- 4.06 vs 98.00 +/- 7.07 pmol/l, p = 0.05) and had elevated plasma non-esterified fatty acid levels (0.44 +/- 0.05 vs 0.59 +/- 0.03 mmol/l, p = 0.05). Fructose 1,6-bisphosphatase activity (43.86 +/- 2.54 vs 52.93 +/- 3.09 nmol.min-1.mg protein-1, p = 0.05) and protein levels (33.03 +/- 0.96 vs 40.04 +/- 1.26 arbitrary units, p = 0.005) and pyruvate carboxylase activity (0.10 +/- 0.003 vs 0.14 +/- 0.01 nmol.min-1.mg protein-1, p < 0.05) were elevated in fat-fed mice. We conclude that in NZO mice increased hepatic glucose production is due to elevated lipolysis resulting from obesity.

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.

The fourth musketeer--from Alexandre Dumas to Claude Bernard

Considerations of the pathophysiology of non-insulin dependent diabetes mellitus (NIDDM) usually focus on the respective roles of the so-called triumvirate-beta cell, muscle and liver [1]. Often overlooked in this context is the role of the adipose tissue, and attention is usually addressed to consideration of studies in which isolated adipocytes were used as a surrogate for muscle in studies of insulin action. The goal of this presentation will be to develop a radically different hypothesis, and marshal evidence that it is the loss of normal regulation of adipose tissue that plays the central role in both the hyperglycaemia and the dyslipidaemia that characterizes patients with NIDDM.

Hypoglycemia counterregulation in elderly humans: relationship to glucose levels

This study was designed to define the effect of human aging on hypoglycemia counterregulatory mechanisms. A hyperinsulinemic (2 mU.kg-1.min-1) glucose clamp procedure was used to control glucose and insulin levels during stepwise lowering of plasma glucose. Counterregulatory hormones, hepatic glucose production (HGP), glucose utilization, and symptoms of hypoglycemia were studied in 13 healthy young [age 24 +/- 1 (SE) yr] and 11 healthy old (age 65 +/- 1 yr) nondiabetic volunteers on two occasions: 1) at matched euglycemia and 70 and 60 mg/dl (study 1) and 2) at matched euglycemia and 60 and 50 mg/dl (study 2). The old had consistently lower epinephrine (P < 0.005), glucagon (P < 0.02), cortisol (P < 0.05), and pancreatic polypeptide (P < 0.02) responses at the 60-mg/dl glucose step in study 1. However, these differences were no longer detectable at the more severe hypoglycemic stimulus of 50 mg/dl in study 2. A consistent increase in HGP occurred in both groups only at the 50-mg/dl glucose step (study 2) and was not different between young and old. There were also no differences in symptom responses between young and old. In summary, we found that elderly individuals have a subtle impairment of the glucose counterregulatory response during moderate hypoglycemia, but this impairment is no longer detectable during more severe hypoglycemia.

Bedtime dosing of glyburide and the treatment of type II diabetes mellitus

Suppression of nocturnal hepatic glucose production is key in the treatment of noninsulin-dependent diabetes mellitus (NIDDM). In this article, the authors compare the effectiveness of dosing glyburide at bedtime versus in the morning on glycemic control in patients with NIDDM under suboptimal control. In a placebo-controlled, double-blind crossover trial, 32 patients with NIDDM with suboptimal control on chronic glyburide treatment fulfilling entry criteria were randomized to receive one of two regimens: (1) glyburide at bedtime and placebo in morning or (2) placebo at bedtime and glyburide in the morning. After 6 months of a regimen, patients crossed over to the other treatment and completed an additional 6-month period. After baseline assessment, fasting blood sugar, history, physical exam, and compliance assessments were performed monthly. HbA1c was measured bimonthly and Sustacal tolerance tests were performed at the end of each 6-month treatment period. During the initial 6-month comparison fasting, blood sugar concentration decreased 5% in bedtime ingesters and rose 10% in the morning patients. These changes were not statistically significant. HbA1c decreased significantly in the morning group but remained unchanged in the bedtime group. At the end of 12 months, nighttime dosing resulted in better home glucose monitoring values, fasting blood sugar results, and Sustacal tolerance profiles, but the differences were not statistically significant. No hypoglycemia was observed in the monitored data collected. Bedtime dosing of glyburide resulted in measurable improvement in fasting blood sugar and carbohydrate tolerance curves, but not to a degree justifying general recommendation of this technique in patients with NIDDM with secondary failure to oral agents.

Interstitial insulin concentrations determine glucose uptake rates but not insulin resistance in lean and obese men

Insulin action and obesity are both correlated with the density of muscle capillary supply in humans. Since the altered muscle anatomy in the obese might affect interstitial insulin concentrations and reduce insulin action, we have cannulated peripheral lymphatic vessels in lean and obese males, and compared peripheral lymph insulin concentrations with whole body glucose uptake during a euglycemic, hyperinsulinemic clamp. Lymph insulin concentrations in the lower limb averaged only 34% of arterial insulin concentrations during 150 min of insulin infusion. Obese subjects had the highest arterial (P < or = 0.0001) and lymph insulin (P < 0.005) concentrations, but the lowest glucose uptake rates (P < 0.002). In contrast to the initial steep rise then plateau of arterial insulins, both lymph insulin and whole body glucose uptake rates rose slowly and did not consistently reach a plateau. In each individual, the glucose uptake closely correlated with peripheral lymphatic insulin concentrations (mean r2 = 0.95). The coupling between glucose uptake and lymph insulin (glucose uptake/pmol insulin) was much steeper in lean subjects than in the obese (P < or = 0.0001). These results indicate that even if insulin diffusion into tissues is rate limiting for insulin action, a tissue defect rather than an insulin diffusion defect causes insulin resistance in obese subjects.

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)

Pharmacotherapy of Oral Hypoglycemic Agents

The use of sulfonylurea in conjunction with a diet and exercise regimen continues to be the primary treatment modality for obese type II diabetics in the United States. These agents work to lower plasma glucose by several proposed mechanisms. Pancreatic mechanisms of action improve efficiency of the islet beta cells, and extrapancreatic mechanisms of action increase peripheral insulin-receptor sensitivity. Sulfonylureas are extensively metabolized in the liver. Depending on the specific agent, renally excreted metabolites with hypoglycemic activity may be produced and pose a threat to patients with impaired renal function. Accumulation of these metabolites can result in hypoglycemia, a common adverse reaction seen with the sulfonylurea. Other adverse reactions and their prevalence, presentation, and treatment are also presented. Clinically significant drug interactions of the sulfonylurea are tabulated and discussed. Because the sulfonlyureas have equivalent efficacy to each other, proper agent selection must be based on the metabolism and excretion characteristics, adverse reaction potential, and concurrent drug profile of the patient for whom the sulfonylurea is being selected. In patients who have not achieved adequate blood glucose control, combination therapy is sometimes initiated. Sulfonylurea-sulfonylurea and various sulfonylurea-insulin regimens are discussed. The importance of diabetic patient education is reviewed, including some basic instructions pharmacists can give to diabetics. The investigation of other oral hypoglycemic agents continues. Information of selected agents undergoing clinical trials in the United States is also reviewed.

Twenty-four-hour energy expenditure in Pima Indians with type 2 (non-insulin-dependent) diabetes mellitus

To assess the impact of Type 2 (non-insulin-dependent) diabetes mellitus on energy metabolism, 24-h energy expenditure, basal metabolic rate and sleeping metabolic rate were measured in a respiratory chamber in 151 Pima Indians, 102 with normal glucose tolerance (67 male/35 female, (mean +/- SD) 28 +/- 7 years, 99 +/- 24 kg, 32 +/- 9% body fat) and in 49 with Type 2 diabetes (22 male/27 female, 35 +/- 11 years, 107 +/- 33 kg, 39 +/- 7% body fat), after at least 3 days on a weight maintaining diet. After adjustment for differences in fat-free mass, fat mass, age and sex, 24-h energy expenditure, basal metabolic rate and sleeping metabolic rate were significantly higher in diabetic patients than in control subjects (72 kcal/day, p less than 0.05; 99 kcal/day, p less than 0.005; 99 kcal/day, p less than 0.001 respectively). Spontaneous physical activity was similar in both groups whereas the thermic effect of food, calculated as the mean energy expenditure corrected for activity throughout the day above sleeping metabolic rate and expressed as a percentage of energy intake, was significantly lower in Type 2 diabetic patients (17.1 +/- 7.1 vs 19.8 +/- 5.6%, p less than 0.05). Adjusted values of 24-h energy expenditure, basal metabolic rate and sleeping metabolic rate were correlated with hepatic endogenous glucose production (r = 0.22, p less than 0.05; r = 0.22, p less than 0.05; r = 0.31, p less than 0.01 respectively). Therefore, increased basal and sleeping metabolic rates, resulting in increased 24-h sedentary energy expenditure may play a role in the weight loss so often observed in Type 2 diabetic subjects in addition to the energy loss from glycosuria.

Inhibition of gluconeogenesis in isolated rat hepatocytes after chronic treatment with phenobarbital

Gluconeogenesis was studied in hepatocytes isolated from phenobarbital-pretreated rats fasted for 24 h. In closed vial incubations, glucose production from lactate (20 mmol/l) and pyruvate (2 mmol/l), alanine (20 mmol/l) or glutamine (20 mmol/l) was suppressed by about 30-45%, although glycerol metabolism was not affected. In hepatocytes perifused with lactate and pyruvate (ratio 10:1), glucose production was inhibited by 50%, even at low gluconeogenic flux. From the determination of gluconeogenic intermediates at several steady states of gluconeogenic flux, we have found a single relationship between phosphoenolpyruvate and the rate of glucose production (Jglucose), and two different curves between cytosolic oxaloacetate and Jglucose in controls and in phenobarbital-pretreated hepatocytes. By using 3-mercaptopicolinate to determine the flux control coefficient of phosphoenolpyruvate carboxykinase we found that phenobarbital pretreatment led to an increase in this coefficient from 0.3 (controls) to 0.8 (phenobarbital group). These observations were confirmed by the finding that the activity of phosphoenolpyruvate carboxykinase was decreased by 50% after phenobarbital treatment. Hence we conclude that the inhibitory effect of phenobarbital on gluconeogenesis is due, at least partly, to a decrease in the flux through phosphoenolpyruvate carboxykinase.

Mechanisms for hyperglycemia in type II diabetes mellitus: therapeutic implications for sulfonylurea treatment--an update

Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by fasting hyperglycemia associated with defects in the pancreatic islet, the liver, and the peripheral tissues, which together comprise a feedback loop responsible for maintenance of glucose homeostasis. This review focuses on the key role of the endocrine pancreas alpha and beta cells to coordinate glucose output from the liver with glucose utilization. The basal rate of hepatic glucose utilization. The basal rate of hepatic glucose production is elevated in subjects with NIDDM, and this is positively correlated with the degree of fasting hyperglycemia. This increased rate of glucose release by the liver results from impaired hepatic sensitivity to insulin, reduced insulin secretion, and increased glucagon secretion. Though basal immunoreactive insulin levels in patients with NIDDM may appear normal when compared with healthy individuals, islet function testing at matched glucose levels reveals impairments of basal, steady-state, and stimulated insulin secretion due to a reduction in beta-cell secretory capacity and a reduced ability of glucose to suppress glucagon. The degree of impaired beta-cell responsiveness to glucose is closely related to the degree of fasting hyperglycemia but in a curvilinear fashion. The efficiency of glucose uptake by the peripheral tissues is also impaired due to a combination of decreased insulin secretion and defective cellular insulin action. This impairment becomes more important to the hyperglycemia as the islet alpha- and beta-cell function declines. Therapeutic interventions, to be effective, must reduce hepatic glucose production either by improving islet dysfunction and raising plasma insulin levels, or improving the effectiveness of insulin on the liver. Both result in a decline in the fasting glucose levels regardless of the cause of hyperglycemia. We conclude that NIDDM is characterized by a steady-state re-regulation of plasma glucose concentration at an elevated level in which islet dysfunction plays a necessary role. Treatment should be based on this physiologic understanding.

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.

Rationale for the association of sulfonylurea and insulin

Approximately 20-30% of patients with non-insulin-dependent diabetes mellitus (NIDDM) started on sulfonylureas fail to respond to treatment (primary failure); in the remaining patients, secondary failure to sulfonylurea therapy occurs at a rate of 5-10% per year. On the other hand, in insulin-treated NIDDM patients a progressive increase in insulin requirement can occur without significant improvement in glucose control. In these patients the combination of oral agents with insulin therapy may be useful. The rationale behind this therapeutic approach resides in the synergistic action of the two agents on specific mechanisms responsible for glucose intolerance and hyperglycemia. Long-acting insulin, administered as a single dose at supper or bedtime, should restrain excessive overnight hepatic glucose production, thus allowing a significant reduction in fasting glucose concentrations. A lower ambient glucose level should favor the stimulatory effect of sulfonylureas on insulin secretion. Sulfonylurea treatment should increase the portal inflow of secreted insulin with a resultant increase in insulin levels draining into liver, thus reducing postprandial hepatic glucose output. Moreover, sulfonylureas might improve insulin action on its target tissue (i.e., muscle), thus increasing overall insulin-mediated glucose metabolism. The reduction in prevailing plasma glucose levels will reduce the toxic effect of hyperglycemia on the beta-cell and on insulin-sensitive tissues. On this basis, NIDDM patients with secondary failure of monotherapy may benefit from combined therapy. Nevertheless, the effects of combined therapy should be strictly monitored and intensive insulin therapy promptly started if poor control persists.

Reduced capacity and affinity of skeletal muscle for insulin-mediated glucose uptake in noninsulin-dependent diabetic subjects. Effects of insulin therapy

We have estimated the capacity and affinity of insulin-mediated glucose uptake (IMGU) in whole body and in leg muscle of obese non-insulin-dependent diabetics (NIDDM, n = 6) with severe hyperglycemia, glycohemoglobin (GHb 14.4 +/- 1.2%), lean controls (ln, n = 7) and obese nondiabetic controls (ob, n = 7). Mean +/- SEM weight (kg) was 67 +/- 2 (ln), 100 +/- 7 (ob), and 114 +/- 11 (NIDDM), P = NS between obese groups. NIDDM were also studied after 3 wk of intensive insulin therapy, GHb post therapy was 10.1 +/- 0.9, P less than 0.01 vs. pretherapy. Insulin (120 mu/m2 per min) was infused and the arterial blood glucose (G) sequentially maintained at approximately 4, 7, 12, and 21 mmol/liter utilizing the G clamp technique. Leg glucose uptake (LGU) was calculated as the product of the femoral arteriovenous glucose difference (FAVGd) and leg blood flow measured by thermodilution. Compared to ln, ob and NIDDM had significantly lower rates of whole body IMGU and LGU at all G levels. Compared to ob, the NIDDM exhibited approximately 50% and approximately 40% lower rates of whole body IMGU over the first two G levels (P less than 0.02) but did not differ at the highest G, P = NS. LGU was 83% lower in NIDDM vs. ob, P less than 0.05 at the first G level only. After insulin therapy NIDDM were indistinguishable from ob with respect to whole body IMGU or LGU at all G levels. A significant correlation was noted between the percent GHb and the EG50 (G at which 1/2 maximal FAVGd occurs) r = 0.73, P less than 0.05. Thus, (a) insulin resistance in NIDDM and obese subjects are characterized by similar decreases in capacity for skeletal muscle IMGU, but differs in that poorly controlled NIDDM display a decrease in affinity for skeletal muscle IMGU, and (b) this affinity defect is related to the degree of antecedent glycemic control and is reversible with insulin therapy, suggesting that it is an acquired defect.

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)

Mechanism of increased gluconeogenesis in noninsulin-dependent diabetes mellitus. Role of alterations in systemic, hepatic, and muscle lactate and alanine metabolism

To assess the mechanisms responsible for increased gluconeogenesis in noninsulin-dependent diabetes mellitus (NIDDM), we infused [3-14C]lactate, [3-13C]alanine, and [6-3H]glucose in 10 postabsorptive NIDDM subjects and in 9 age- and weight-matched nondiabetic volunteers and measured systemic appearance of alanine and lactate, their release from forearm tissues, and their conversion into plasma glucose (corrected for Krebs cycle carbon exchange). Systemic appearance of lactate and alanine were both significantly greater in diabetic subjects (18.2 +/- 0.9 and 5.8 +/- 0.4 mumol/kg/min, respectively) than in the nondiabetic volunteers (12.6 +/- 0.7 and 4.2 +/- 0.3 mumol/kg/min, respectively, P less than 0.001 and P less than 0.01). Conversions of lactate and alanine to glucose were also both significantly greater in NIDDM subjects (8.6 +/- 0.5 and 2.4 +/- 0.1 mumole/kg/min, respectively) than in nondiabetic volunteers (4.2 +/- 0.4 and 1.8 +/- 0.1 mumol/kg/min, respectively, P less than 0.001 and P less than 0.025). The proportion of systemic alanine appearance converted to glucose was not increased in NIDDM subjects (42.7 +/- 1.9 vs. 44.2 +/- 2.9% in nondiabetic volunteers), whereas the proportion of systemic lactate appearance converted to glucose was increased in NIDDM subjects (48.3 +/- 3.8 vs. 34.2 +/- 3.8% in nondiabetic volunteers, P less than 0.025); the latter increased hepatic efficiency accounted for approximately 40% of the increased lactate conversion to glucose. Neither forearm nor total body muscle lactate and alanine release was significantly different in NIDDM and nondiabetic volunteers. Therefore, we conclude that increased substrate delivery to the liver and increased efficiency of intrahepatic substrate conversion to glucose are both important factors for the increased gluconeogenesis of NIDDM and that tissues other than muscle are responsible for the increased delivery of gluconeogenic precursors to the liver.

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.

Parenteral nutrition in patients with diabetes mellitus: theoretical and practical considerations

It is estimated that there are 11 million diabetics in the United States. Increasing recognition of the importance of nutrition in clinical medicine coupled with the frequent hospitalizations of the diabetic patient has heightened interest in their nutritional therapy. Patients with diabetes mellitus exhibit many abnormalities in the regulation of carbohydrate metabolism which may be accentuated during illness as part of the metabolic response to injury. An understanding of the effect of injury/illness, parenteral nutrition, and diabetes mellitus on carbohydrate metabolism is essential for the development of a rational approach to the initiation and maintenance of nutritional support in the diabetic patient.

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.

Islet dysfunction in non-insulin-dependent diabetes mellitus

Non-insulin-dependent diabetes mellitus is characterized by fasting hyperglycemia associated with defects in the pancreatic islet, the liver, and the peripheral tissues, which together comprise a feedback loop responsible for maintenance of glucose homeostasis. This review focuses on the key role of the endocrine pancreas A and B cells to coordinate glucose output from the liver with glucose utilization. The basal rate of hepatic glucose production is elevated in subjects with non-insulin-dependent diabetes mellitus and this is positively correlated with the degree of fasting hyperglycemia. This increased rate of glucose release by the liver results from impaired hepatic sensitivity to insulin and reduced insulin secretion. Though basal insulin levels in patients with non-insulin-dependent diabetes mellitus may appear normal when compared with those of healthy persons, islet function testing at matched glucose levels reveals impairments of basal and stimulated insulin secretion due to a reduction in B cell secretory capacity. The degree of impaired beta-cell responsiveness to glucose is closely related to the degree of fasting hyperglycemia but in a curvilinear fashion. The efficiency of glucose uptake by the peripheral tissues is also impaired due to a combination of decreased insulin secretion and defective cellular insulin action. This impairment becomes more important to the hyperglycemia as the islet dysfunction declines. Therapeutic interventions either improve islet dysfunction and raise plasma insulin levels, reduce hepatic glucose production, or improve the efficiency of tissue glucose uptake. All result in a decline in the fasting glucose level regardless of the cause of hyperglycemia. It is concluded that non-insulin-dependent diabetes mellitus is characterized by a steady-state re-regulation of plasma glucose concentration at an elevated level in which islet dysfunction plays a necessary role.

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)

Impaired insulin-stimulated muscle glycogen synthase activation in vivo in man is related to low fasting glycogen synthase phosphatase activity

Insulin-mediated glycogen synthase activity in skeletal muscle correlates with the rate of insulin-mediated glycogen deposition and is reduced in human subjects with insulin resistance. To assess the role of glycogen synthase phosphatase as a possible mediator of reduced glycogen synthase activity, we studied 30 Southwestern American Indians with a broad range of insulin action in vivo. Percutaneous biopsies of the vastus lateralis muscle were performed before and during a 440-min euglycemic clamp at plasma insulin concentrations of 89 +/- 5 and 1,470 +/- 49 microU/ml (mean +/- SEM); simultaneous glucose oxidation was determined by indirect calorimetry. After insulin stimulation, glycogen synthase activity was correlated with the total and nonoxidative glucose disposal at both low (r = 0.73, P less than 0.0001; r = 0.68, P less than 0.0001) and high (r = 0.75, P less than 0.0001; r = 0.74, P less than 0.0001) plasma insulin concentrations. Fasting muscle glycogen synthase phosphatase activity was correlated with both total and nonoxidative glucose disposal rates at the low (r = 0.48, P less than 0.005; r = 0.41, P less than 0.05) and high (r = 0.47, P less than 0.05; r = 0.43, P less than 0.05) plasma insulin concentrations. In addition, fasting glycogen synthase phosphatase activity was correlated with glycogen synthase activity after low- (r = 0.47, P less than 0.05) and high- (r = 0.50, P less than 0.01) dose insulin stimulations. These data suggest that the decreased insulin-stimulated glucose disposal and reduced glycogen synthase activation observed in insulin resistance could be secondary to a low fasting glycogen synthase phosphatase activity.

Relationship between plasma glucose and insulin concentration, glucose production, and glucose disposal in normal subjects and patients with non-insulin-dependent diabetes

The changes in hepatic glucose production (Ra), tissue glucose disposal (Rd), and plasma glucose and insulin concentration that took place over a 16-h period from 10 to 2 p.m. were documented in 14 individuals; 8 with non-insulin-dependent diabetes mellitus (NIDDM) and 6 with normal glucose tolerance. Values for Ra were higher than normal in patients with NIDDM at 10 p.m. (4.73 +/- 0.41 vs. 3.51 +/- 0.36 mg/kg per min, P less than 0.001), but fell at a much faster rate throughout the night than that seen in normal subjects. As a consequence, the difference between Ra in normal individuals and patients with NIDDM progressively narrowed, and by 2 p.m., had ceased to exist (1.75 +/- 0.61 vs. 1.67 +/- 0.47 mg/kg per min, P = NS). Plasma glucose concentration also declined in patients with NIDDM over the same period of time, but they remained quite hyperglycemic, and the value of 245 +/- 27 mg/dl at 2 p.m. was about three times greater than in normal individuals. Plasma insulin concentrations also fell progressively from 10 to 2 p.m., and were similar in both groups throughout most of the 16-h study period. Thus, the progressive decline in Ra in patients with NIDDM occurred despite concomitant falls in both plasma glucose and insulin concentration. Glucose disposal rates also fell progressively in both groups, but the magnitude of the fall was greater in patients with NIDDM. Consequently, Rd in patients with NIDDM was higher at 10 p.m. (3.97 +/- 0.48 vs. 3.25 +/- 0.13 mg/kg per min, P less than 0.001) and lower the following day at 2 p.m. (1.64 +/- 0.21 vs. 1.97 +/- 0.35 mg/kg per min, P less than 0.01). These results indicate that a greatly expanded pool size can exist in patients with NIDDM at a time when values for Ra are identical to those in normal subjects studied under comparable conditions, which suggests that fasting hyperglycemia in NIDDM is not simply a function of an increase in Ra.

Effects of the combination of insulin and glibenclamide in type 2 (non-insulin-dependent) diabetic patients with secondary failure to oral hypoglycaemic agents

The effects of combined insulin and sulfonylurea therapy on glycaemic control and B-cell function was studied in 15 Type 2 (non-insulin-dependent) diabetic patients who had failed on treatment with oral hypoglycaemic agents. The patients were first treated with insulin alone for four months. Five patients were given two daily insulin doses and ten patients one dose. During insulin treatment the fasting plasma glucose fell from 14.5 +/- 0.8 to 8.8 +/- 0.4 mmol/l and the HbA1 concentration from 12.6 +/- 0.4 to 9.2 +/- 0.2%. This improvement of glycaemic control was associated with a suppression of basal (from 0.31 +/- 0.04 to 0.10 +/- 0.02 nmol/l) and glucagon-stimulated (from 0.50 +/- 0.08 to 0.19 +/- 0.04 nmol/l) C-peptide concentrations. Four months after starting insulin therapy the patients were randomised to a four-month double-blind cross-over treatment with insulin combined with either 15 mg glibenclamide per day or with placebo. Addition of glibenclamide to insulin resulted in a further reduction of the fasting plasma glucose (7.9 +/- 0.5 mmol/l) and HbA1 (8.3 +/- 0.2%) concentration whereas the basal (0.21 +/- 0.03 nmol/l) and glucagon-stimulated C-peptide concentrations (0.34 +/- 0.06 nmol/l) increased again. Addition of placebo to insulin had no effect. The daily insulin dose could be reduced by 25% after addition of glibenclamide to insulin, while it remained unchanged when insulin was combined with placebo. The fasting free insulin concentration did not differ between the glibenclamide and placebo periods (28 +/- 6 vs 30 +/- 5 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperglycemia stimulates carbohydrate oxidation in humans

We examined whether hyperglycemia stimulates carbohydrate oxidation independent of insulin. Rates of total glucose disposal and substrate oxidation (indirect calorimetry) were measured at 4 insulin concentrations and at each level of insulin at 4 glucose concentrations in 88 separate studies in 22 normal volunteers. The insulin sensitivity of carbohydrate and lipid oxidation was independent of glycemia, but glucose, independent of insulin, increased the absolute rate of carbohydrate oxidation and decreased lipid oxidation. To compare the ability of glucose and insulin to stimulate carbohydrate oxidation, oxidation rates were examined at similar rates of total glucose disposal induced by hyperinsulinemia or hyperglycemia. At physiological matched rates of glucose disposal, insulin stimulated carbohydrate oxidation 2.4-fold more than glucose. The free fatty acids (FFA) were significantly lower in the presence of hyperinsulinemia than hyperglycemia. When compared at similar (supraphysiological) rates of total glucose disposal, where the FFA were completely suppressed, the rate of carbohydrate oxidation was related to the total rate of glucose disposal rather than the ambient glucose or insulin concentrations. We conclude that both glucose and insulin can increase carbohydrate oxidation in humans. We propose that the rate of carbohydrate oxidation is determined by FFA availability and by glucose availability independent of the FFA level in glucose-consuming tissues. Although FFA availability is almost solely determined by insulin, both glucose and insulin can increase carbohydrate oxidation by increasing glucose availability.

Skeletal muscle capillary density and fiber type are possible determinants of in vivo insulin resistance in man

We have compared the capillary density and muscle fiber type of musculus vastus lateralis with in vivo insulin action determined by the euglycemic clamp (M value) in 23 Caucasians and 41 Pima Indian nondiabetic men. M value was significantly correlated with capillary density (r = 0.63; P less than or equal to 0.0001), percent type I fibers (r = 0.29; P less than 0.02), and percent type 2B fibers (r = -0.38; P less than 0.003). Fasting plasma glucose and insulin concentrations were significantly negatively correlated with capillary density (r = -0.46, P less than or equal to 0.0001; r = -0.47, P less than or equal to 0.0001, respectively). Waist circumference/thigh circumference ratio was correlated with percent type 1 fibers (r = -0.39; P less than 0.002). These results suggest that diffusion distance from capillary to muscle cells or some associated biochemical change, and fiber type, could play a role in determining in vivo insulin action. The association of muscle fiber type with body fat distribution may indicate that central obesity is only one aspect of a more generalized metabolic syndrome. The data may provide at least a partial explanation for the insulin resistance associated with obesity and for the altered kinetics of insulin action in the obese.

Regulation of glycogen synthase and phosphorylase activities by glucose and insulin in human skeletal muscle

We examined the insulin dose-response characteristics of human muscle glycogen synthase and phosphorylase activation. We also determined whether increasing the rate of glucose disposal by hyperglycemia at a fixed insulin concentration activates glycogen synthase. Physiological increments in plasma insulin but not glucose increased the fractional activity of glycogen synthase. The ED50: s for insulin stimulation of whole body and forearm glucose disposal were similar and unaffected by glycemia. Glycogen synthase activation was exponentially related to the insulin-mediated component of whole body and forearm glucose disposal at each glucose concentration. Neither insulin nor glucose changed glycogen phosphorylase activity. These results suggest that insulin but not the rate of glucose disposal per se regulates glycogen synthesis by a mechanism that involves dephosphorylation of glycogen synthase but not phosphorylase. This implies that the low glycogen synthase activities found in insulin-resistant states are a consequence of impaired insulin action rather than reduced glucose disposal.