Approaches to novel antidiabetic therapy.
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Insulin elicits a spectrum of biological responses by binding to its cell surface receptor. In a screen for small molecules that activate the human insulin receptor tyrosine kinase, a nonpeptidyl fungal metabolite (L-783,281) was identified that acted as an insulin mimetic in several biochemical and cellular assays. The compound was selective for insulin receptor versus insulin-like growth factor I (IGFI) receptor and other receptor tyrosine kinases. Oral administration of L-783,281 to two mouse models of diabetes resulted in significant lowering in blood glucose levels. These results demonstrate the feasibility of discovering novel insulin receptor activators that may lead to new therapies for diabetes.
A longitudal study was carried out to separate the effects of treatment with diet from those of treatment with glibenclamide and phenformin on the oral glucose tolerance test (OGTT) plasma sugar and insulin levels in 118 patients with maturity-onset diabetes mellitus. Both drugs improved glucose tolerance and random blood sugar levels more than diet alone. The improved glucose tolerance with both drugs was due to a combination of a reduced fasting plasma sugar level and an improved tolerance to the glucose load. Treatment with glibenclamide increased insulin secretion but phenformin had no significant effect. Mean body weight fell slightly during phenformin administration, whereas a small but insignificant rise in patients receiving glibenclamide.
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OBJECTIVE: To investigate whether blood flow in normal and post-stenotic coronary arteries is altered by therapeutic doses of the sulfonylurea agent glibenclamide. PATIENTS: 12 patients with a high grade stenosis of the left anterior descending coronary artery (n = 10) or left circumflex coronary artery (n = 2), and an angiographically normal corresponding left circumflex artery or left anterior descending artery, respectively. DESIGN: Two Doppler ultrasound wires were positioned in the "normal" and post-stenotic artery for simultaneous measurements of coronary blood flow velocity under baseline conditions and after intravenous glibenclamide, 0.05 mg/kg body weight. Local coronary blood flow was calculated from the average peak velocity and the cross sectional area derived from quantitative coronary angiographic analysis. Coronary flow reserve was determined after intracoronary injection of 30 microg adenosine and 12 mg papaverine. RESULTS: One hour after glibenclamide, serum insulin increased from (mean (SD)) 7.4 (2.0) to 44.8 (25.5) mU/l (p < 0.005), and C peptide from 1.4 (0.4) to 3.4 (1.2) ng/l (p = 0.005). In normal coronary arteries coronary flow reserve was 2.6 (0.4) after adenosine and 3.0 (0.4) after papaverine, while in post-stenotic arterial segments it was 1.2 (0.3) after adenosine (p = 0.005) and 1.3 (0.3) after papaverine (p = 0.005). There was no significant difference after glibenclamide. In non-stenotic arteries, average peak velocity (18.8 (5.2) cm/s) and calculated coronary blood flow (23.8 (10.7) ml/min) were not altered by glibenclamide (18.3 (5.2) cm/s and 22.8 (10.4) ml/min, respectively). In post-stenotic arteries, baseline average peak velocity was 13.3 (4.9) ml/min and coronary blood flow was 9.1 (3.0) ml/min, without significant change after glibenclamide (13.3 (5.2) cm/s, 9.0 (3.2) ml/min). CONCLUSIONS: Glibenclamide, 0.05 mg/kg intravenously, is effective in increasing serum insulin, suggesting a K(ATP) channel blocking effect in pancreatic beta cells. It does not compromise coronary blood flow and vasodilatation in response to adenosine and papaverine in post-stenotic and angiographically normal coronary arteries at rest.
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Treatment of obese (ob/ob) mice with the beta 3-adrenergic receptor (beta 3-AR) agonist BRL-35135 (1 mg.kg body wt-1.day-1 for 20 days) normalized plasma glucose levels and significantly decreased plasma insulin and nonesterified fatty acid levels. The time frame for the hypoglycemic effect, which reached a maximum after 10 days of treatment, paralleled an increase in brown adipose tissue DNA and protein content. The basal level of mRNA for the beta 3-AR and mitochondrial uncoupling protein was found to be markedly decreased in the ob/ob animals relative to the lean group. Chronic treatment of ob/ob mice for 20 days resulted in a twofold increase in beta 3-AR mRNA and a fivefold increase in uncoupling protein mRNA in brown adipose tissue relative to the placebo group. These findings indicate that chronic treatment of ob/ob animals with a beta 3-AR agonist results in proliferation of brown adipose tissue, with an upregulation of the beta 3-AR, which is associated with a decrease in plasma glucose, insulin, and nonesterified fatty acid levels.
The dried sap of the aloe plant (aloes) is one of several traditional remedies used for diabetes in the Arabian peninsula. Its ability to lower the blood glucose was studied in 5 patients with non-insulin-dependent diabetes and in Swiss albino mice made diabetic using alloxan. During the ingestion of aloes, half a teaspoonful daily for 4-14 weeks, the fasting serum glucose level fell in every patient from a mean of 273 +/- 25 (SE) to 151 +/- 23 mg/dl (p less than 0.05) with no change in body weight. In normal mice, both glibenclamide (10 mg/kg twice daily) and aloes (500 mg/kg twice daily) induced hypoglycaemia after 5 days, 71 +/- 6.2 and 91 +/- 7.6 mg/dl, respectively, versus 130 +/- 7 mg/dl in control animals (p less than 0.01); only glibenclamide was effective after 3 days. In the diabetic mice, fasting plasma glucose was significantly reduced by glibenclamide and aloes after 3 days. Thereafter only aloes was effective and by day 7 the plasma glucose was 394 +/- 22.0 versus 646 +/- 35.9 mg/dl, in the controls and 726 +/- 30.9 mg/dl in the glibenclamide treated group (p less than 0.01). We conclude that aloes contains a hypoglycaemic agent which lowers the blood glucose by as yet unknown mechanisms.
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Impaired glucose tolerance (IGT) is associated with defects in both insulin secretion and action and carries a high risk for conversion to non-insulin-dependent diabetes mellitus (NIDDM). Troglitazone, an insulin sensitizing agent, reduces glucose concentrations in subjects with NIDDM and IGT but is not known to affect insulin secretion. We sought to determine the role of beta cell function in mediating improved glucose tolerance. Obese subjects with IGT received 12 wk of either 400 mg daily of troglitazone (n = 14) or placebo (n = 7) in a randomized, double-blind design. Study measures at baseline and after treatment were glucose and insulin responses to a 75-g oral glucose tolerance test, insulin sensitivity index (SI) assessed by a frequently sampled intravenous glucose tolerance test, insulin secretion rates during a graded glucose infusion, and beta cell glucose-sensing ability during an oscillatory glucose infusion. Troglitazone reduced integrated glucose and insulin responses to oral glucose by 10% (P = 0.03) and 39% (P = 0.003), respectively. SI increased from 1.3+/-0.3 to 2.6+/-0.4 x 10(-)5min-1pM-1 (P = 0.005). Average insulin secretion rates adjusted for SI over the glucose interval 5-11 mmol/liter were increased by 52% (P = 0.02), and the ability of the beta cell to entrain to an exogenous oscillatory glucose infusion, as evaluated by analysis of spectral power, was improved by 49% (P = 0.04). No significant changes in these parameters were demonstrated in the placebo group. In addition to increasing insulin sensitivity, we demonstrate that troglitazone improves the reduced beta cell response to glucose characteristic of subjects with IGT. This appears to be an important factor in the observed improvement in glucose tolerance.
The novel hypoglycemic agent nateglinide is pharmacologically distinct from oral hypoglycemic agents such as sulfonylureas and repaglinide. The present study investigated the effects in healthy volunteers of multiple doses of nateglinide on the pharmacokinetics and pharmacodynamics of warfarin. The study comprised a randomized two-group, two-way crossover, open-label design in 12 healthy male subjects. One group of 6 subjects initially received a single oral dose of warfarin 30 mg and then, after a 7- to 14-day washout, received both warfarin and nateglinide (120 mgnateglinide, 10 min before meals for 4 days and a single dose of 30 mg warfarin on the second day). The alternate group of 6 subjects received treatments in the opposite order. Pharmacokinetic profiles were derived from plasma warfarin and nateglinide concentrations. Prothrombin measurements were evaluated in both periods as a measure of warfarin activity. When administered alone or in combination, there were no statistically significant differences in mean warfarin (R- and S-enantiomers) or nateglinide pharmacokinetic parameters. The concurrent administration of nateglinide and warfarin did not affect the maximal change in prothrombin time that follows warfarin administration. In this study, there was no evidence of an effect of coadministration of nateglinide on the pharmacodynamic action of warfarin or any pharmacokinetic interaction between warfarin and nateglinide.
Bioavailability of pioglitazone and metformin, in 2 dose strengths, given either as a fixed-dose combination tablet or as coadministration of commercial tablets (coad), was studied in young healthy subjects in 2 separate studies. In study I (n = 63), single oral doses of 15-mg pioglitazone/500-mg metformin fixed-dose combination tablets or equivalent doses of commercial tablets were administered, in a fasting state, in an open-label, randomized, crossover study with a 7-day washout period between treatments. Study II (n = 61) was similar in design to study I, except the 15/850-mg fixed-dose combination tablet and coad treatments were evaluated. Least squares mean (fixed-dose combination/coad) ratios and 90% confidence intervals of the ratios for the 15/500-mg dose strength for the maximum observed serum concentration (Cmax) and area under the serum concentration-time curve from time 0 to infinity (AUC(infinity)) were 0.95 (0.86-1.05) and 1.02 (0.98-1.08), respectively, for pioglitazone and 0.99 (0.95-1.03) and 1.03 (0.98-1.08), respectively, for metformin. Bioequivalency for pioglitazone and metformin between fixed-dose combination tablets and coad treatments was met for both strengths of fixed-dose combination tablets. In a post hoc meta-analysis of combined data from the 2 studies (n = 124), there was considerable overlapping in AUC(infinity) values between gender and race (Caucasians, Blacks, and Hispanics), making neither gender- nor racial-based dosing of pioglitazone or metformin necessary.
An open-label, randomized, crossover study involving 28 healthy subjects was conducted to compare the peak (Cmax) and total (AUC(lqc), AUC(infinity)) exposures to pioglitazone and metformin after single-dose administration of a fixed-dose combination tablet containing 15 mg of pioglitazone plus 850 mg metformin when given under fasted versus fed states, with a washout period of 7 days between treatments. Two different fixed-dose combination formulations (bilayer and pioglitazone-micronized fixed-dose combination tablets) were tested. The pioglitazone-micronized fixed-dose combination formulation was selected for clinical development and regulatory approval; the present study describes food effect results with this formulation. For pioglitazone, least squares mean ratios (fed/fasted) and the 90% confidence intervals of these ratios were 1.05 (0.93-1.18) for Cmax, 1.13 (1.02-1.25) for AUC(lqc), and 1.11 (1.01-1.22) for AUC(infinity). For metformin, these values were 0.72 (0.65-0.79) for Cmax, 0.87 (0.81-0.94) for AUC(lqc), and 0.87 (0.81-0.94) for AUC(infinity). Dosing with food resulted in median prolongation of tmax values by 1.5 hours for metformin and 2.0 hours for pioglitazone. Because bioequivalency criteria were met (fed/fasted 90% confidence interval between 0.80 and 1.25) for both pioglitazone and metformin AUC, fixed-dose combination tablets can be taken with or without food, but to minimize gastrointestinal adverse effects of metformin, the fixed-dose combination tablets are recommended to be taken with food.
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