Sulfonylureas enhance in vivo the effectiveness of insulin in type 1 (insulin dependent) diabetes mellitus

Utilisation of the Prestwick Chemical Library to identify drugs that inhibit the growth of mycobacteria

Tuberculosis (TB) is an infectious bacterial disease that kills approximately 1.3 million people every year. Despite global efforts to reduce both the incidence and mortality associated with TB, the emergence of drug resistant strains has slowed any progress made towards combating the spread of this deadly disease. The current TB drug regimen is inadequate, takes months to complete and poses significant challenges when administering to patients suffering from drug resistant TB. New treatments that are faster, simpler and more affordable are urgently required. Arguably, a good strategy to discover new drugs is to start with an old drug. Here, we have screened a library of 1200 FDA approved drugs from the Prestwick Chemical library using a GFP microplate assay. Drugs were screened against GFP expressing strains of Mycobacterium smegmatis and Mycobacterium bovis BCG as surrogates for Mycobacterium tuberculosis, the causative agent of TB in humans. We identified several classes of drugs that displayed antimycobacterial activity against both M. smegmatis and BCG, however each organism also displayed some selectivity towards certain drug classes. Variant analysis of whole genomes sequenced for resistant mutants raised to florfenicol, vanoxerine and pentamidine highlight new pathways that could be exploited in drug repurposing programmes.

Efficacy of Sulfonylureas with Insulin in Type 2 Diabetes Mellitus

BACKGROUND:

In subjects with type 2 diabetes mellitus, glycemic control deteroriates while patients use sulfonylurea drugs during the course of the disease. Adjunctive therapy with insulin at this stage requires a lesser daily insulin dose in comparison with insulin monotherapy while restoring desirable glycemic control. However, data regarding direct comparison between various sulfonylureas in this regard are lacking.

OBJECTIVE:

To examine comparative efficacies of adjunctive therapy with insulin in subjects with type 2 diabetes manifesting lapse of glycemic control while receiving various individual sulfonylurea drugs.

METHODS:

Four groups of 10 subjects, each presenting with glycosylated hemoglobin (HbA1C) >8.0% while using either tolazamide, glyburide, glipizide Gastrointestinal Therapeutic System (GITS), or glimepiride, were recruited. Two from each group were randomized to receive placebo; the others continued the same drug. Pre-supper subcutaneous 70 NPH/30 regular insulin was initiated at 10 units and gradually increased and adjusted as necessary to attain fasting blood glucose levels between 80 and 120 mg/dL and maintain the same range for 6 months. Fasting plasma glucose, plasma C-peptide, and HbA1C concentrations were determined prior to the addition of insulin and at the end of the study. Daily insulin dose and changes in body weight (BW) were noted at the end of the study, and the number of hypoglycemic events during the last 4 weeks of the study was determined.

RESULTS:

Daily insulin dose (units/kg BW), weight gain, and number of hypoglycemic events were significantly lower (p < 0.01) in subjects receiving sulfonylureas in comparison with placebo. However, the daily insulin dose alone was significantly lower (p < 0.05) with glimepiride (0.49 ± 0.10; mean ± SE) than with other sulfonylureas (tolazamide 0.58 ± 0.12, glyburide 0.59 ± 0.12, glipizide GITS 0.59 ± 0.14). Finally, a significant correlation (r = 0.68; p < 0.001) was noted between suppression of plasma C-peptide level and the daily insulin dose among all participants.

CONCLUSIONS:

By lowering the daily insulin dose, sulfonylurea drugs appear to improve the sensitivity of exogenous insulin in subjects with type 2 diabetes mellitus manifesting lapse of glycemic control. Moreover, glimepiride appears to possess a greater insulin-sparing property than other sulfonylureas.

Effect of glimepiride on insulin-stimulated glycogen synthesis in cultured human skeletal muscle cells: a comparison to glibenclamide

OBJECTIVE

To examine the effect of glimepiride on insulin-stimulated glycogen synthesis in cultured human skeletal muscle cells in comparison with glibenclamide.

RESEARCH DESIGN AND METHODS

Myotubes derived from glucose-tolerant subjects were incubated with glimepiride or glibenclamide (0-100 micro mol/l) for 4 h and with or without insulin (100 nmol/l) for 2 h, and subsequently glycogen synthesis was determined.

RESULTS

Glimepiride had no significant effect on basal glycogen synthesis; in contrast, glimepiride caused a dose-dependent increase of insulin-stimulated glycogen synthesis, with a maximal effect of 39.97 +/- 8.4% (mean +/- SEM, n = 4, P < 0,02). The time course of this glimepiride effect on insulin-stimulated glycogen synthesis showed a peak after 12 h incubation with a half maximal effect after 4 h. Preincubation of the myotubes with wortmannin (100 nmol/l), an inhibitor of phosphatidylinositol (PI)- 3 kinase, caused an inhibition of this glimepiride effect on insulin-stimulated glycogen synthesis. In contrast to glimepiride, incubation of myotubes with glibenclamide (0-100nmol/l), a second generation sulfonylurea, had no significant effect on basal or insulin-stimulated glycogen synthesis.

CONCLUSIONS

Incubation of cultured human skeletal muscle cells derived from glucose-tolerant subjects with glimepiride caused a dose-dependent increase of insulin-stimulated glycogen synthesis using therapeutic glimepiride concentrations. This glimepiride effect seems to be mediated via the PI3 kinase pathway. In contrast to glimepiride, glibenclamide had no significant effect on basal or insulin-stimulated glycogen synthesis. These results suggest that glimepiride, beside its well-known effect to stimulate insulin secretion, possess an insulin-sensitizing action in cultured human skeletal muscle cells in support of the concept of an extrapancreatic action of glimepiride.

Acute effect of glimepiride on insulin-stimulated glucose metabolism in glucose-tolerant insulin-resistant offspring of patients with type 2 diabetes

OBJECTIVE

This study addressed whether acute infusion of glimepiride influences glucose metabolism independent of its effect on insulin secretion.

RESEARCH DESIGN AND METHODS

Ten healthy, glucose-tolerant but insulin-resistant probands were subjected to a placebo-controlled, double-blind, cross-over study. Each individual received infusions of either 0.15 mol/l saline or glimepiride in randomized order on two separate occasions. A three-step hyperinsulinemic (0.5, 1.0, and 1.5 mU. kg(-1). min(-1))-euglycemic glucose clamp was performed on both occasions to determine insulin sensitivity. Glimepiride-induced insulin secretion was inhibited by octreotide. Endogenous glucose production and glucose elimination were measured with the "hot" glucose infusion method using U-[(13)C]glucose as tracer. Glucose oxidation was determined from indirect calorimetry. Lipolysis was evaluated by measurements of nonesterified fatty acid (NEFA) and glycerol concentration and measurement of glycerol production.

RESULTS

Plasma glucose and insulin concentrations were not significantly different between glimepiride or saline infusions. There was a significant increase in the rate of glucose infusion necessary to maintain euglycemia during infusion of glimepiride during the low- (12.2 +/- 1.1 vs. 16.1 +/- 1.7 micro mol. kg(-1). min(-1)) and intermediate-dose insulin infusion (24.4 +/- 1.7 vs. 30.0 +/- 2.8 micro mol. kg(-1). min(-1)). This was explained by an increased rate of glucose elimination and to a lesser degree by a decrease in glucose production. Glucose oxidation rate was not different. NEFA and glycerol concentration and glycerol production were equally suppressed.

CONCLUSIONS

Glimepiride improves peripheral glucose uptake and decreases endogenous glucose production independent of its insulin secretagogue action. The effects shown in this acute study are, however, too small to be considered therapeutically beneficial for the individual patient.

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.

More uniform diurnal blood glucose control and a reduction in daily insulin dosage on addition of glibenclamide to insulin in type 1 diabetes mellitus: role of enhanced insulin sensitivity

Combination therapy with insulin and sulphonylurea has gained acceptance in management of subjects with Type 2 (non-insulin-dependent) diabetes mellitus. However, its role in management of Type 1 (insulin-dependent) diabetes mellitus remains controversial. In this study, the effect of combination therapy with insulin and glibenclamide on metabolic control, daily insulin dosage, and insulin sensitivity was assessed in subjects with Type 1 diabetes mellitus. Ten men with Type 1 diabetes mellitus participated in a randomized, double-blind, crossover, clinical trial with three treatment regimens, namely (1) insulin alone, (2) insulin and placebo, (3) insulin and glibenclamide, each lasting 3 months. Combination therapy induced: (1) reduction in daily insulin dosage; (2) more uniform blood glucose control as reflected by a lower average 24 h blood glucose level, a smaller difference between mean preprandial and 2 h postprandial blood glucose concentrations, decreased 24 h urine glucose excretion, and a decline in number of hypoglycaemic events; (3) improved insulin sensitivity as expressed by more rapid plasma glucose disappearance rate, without a significant alteration in fasting plasma glucagon and 1h postprandial serum C-peptide levels; when compared with treatment with either insulin alone or with insulin and placebo. Therefore, it is apparent that the addition of glibenclamide to insulin reduces daily insulin dosage and renders a greater uniformity to diurnal blood glucose control, most probably secondary to enhancement of insulin sensitivity.

Treatment of type I diabetes with a combination of glyburide and insulin

OBJECTIVE

To assess the ability of a combination of insulin and an oral hypoglycemic agent (glyburide) to improve the overall glycemic control in a population of patients with type I diabetes.

DESIGN

Randomized, placebo-controlled, double-blind trial.

SETTING

Community-based, university-affiliated, family medicine group.

PATIENTS

Men and women between 18 and 68 years of age with type I diabetes.

INTERVENTIONS

Subjects were observed and titrated on an insulin-only regimen for 12 weeks (phase I). Subjects were then randomized to receive either placebo or glyburide 10 mg/d for an additional 12 weeks (phase II).

MAIN OUTCOME MEASURES

Glucose measurements were taken at breakfast, lunch, supper, and bedtime. Each patient also was followed sequentially for serum lipids, glycosylated hemoglobin, (Hb A1c) and daily insulin utilization.

RESULTS

Average fasting blood glucose (FBG) measurements were significantly lower in the glyburide-treated group during phase II (9.22 +/- 0.55 mmol/L) compared with baseline (10.27 +/- 0.93 mmol/L) and phase I (10.41 +/- 0.55 mmol/L). A decrease in the average Hb A1c concentration in the glyburide group was evident by week 4 and was sustained for the duration of the study. The average daily insulin dose rose significantly in the glyburide but not the placebo group compared with baseline. Total cholesterol, triglycerides, and low-density lipoprotein cholesterol did not change significantly in either group over the course of the study. High-density lipoprotein cholesterol increased significantly over baseline in the glyburide group during phase II. Several patients experienced dramatic improvements in glycemic parameters after the addition of glyburide to their insulin regimens.

CONCLUSIONS

Improvements were observed in the FBG and Hb A1c measurements of this heterogeneous population of patients with type I diabetes after the addition of glyburide to their insulin regimens. The study failed to find consistent trends in glycemic control when evaluating mean changes in FBG measurements.

Acute effect of glipizide on glucose tolerance in obesity and diabetes mellitus (NIDDM)

The attempt has been made to identity the lowest dose of glipizide, a second generation sulphonylurea, capable of improving glucose tolerance in overweight and obese subjects with various degrees of glucose tolerance. Thirty one obese subjects, 12 with non insulin dependent diabetes mellitus (NIDDM), 9 with impaired glucose tolerance (IGT) and 10 with normal glucose tolerance (NGT) each underwent four OGTTS (75 g), at 1 week intervals, after administration in random order of placebo or glipizide 0.5, 1.0 or 2.5 mg 30 min before glucose. Glucose tolerance in all groups was progressively improved by the increasing doses of glipizide and was normalized by 1.0 mg glipizide in impaired glucose tolerance (IGT) and by 2.5 mg glipizide in NIDDM. Insulin release was not significantly affected by glipizide in the three groups of subjects. The data indicate that it is possible, at least in acute experiments, to improve glucose tolerance in overweight and obese subjects with IGT, with NGT and with NIDDM, with doses of glipizide that do not affect insulin release.

Modified protocols improve insulin sensitivity estimation using the minimal model

We attempted to improve the precision of the estimation of insulin sensitivity (S1) from the minimal model technique by modifying insulin dynamics during a frequently sampled intravenous glucose tolerance test (FSIGT). Tolbutamide and somatostatin (SRIF) were used to change the insulin dynamics without directly affecting insulin sensitivity. Injection of tolbutamide (100 mg) at t = 20 min provoked an immediate secondary peak in insulin response, resulting in a greater integrated incremental insulin than the standard FSIGT. SRIF, injected at t = -1 min, delayed insulin secretion in proportion to the dose without any change in magnitude. Computer simulation was used to assess the precision of S1 estimation. Insulin dynamics from both standard and modified protocols were adjusted in magnitude, with the shape unchanged and analyzed to determine the effect of the magnitude of insulin response. Fractional standard deviation was reduced from 73% with the standard insulin profile to 23% with tolbutamide and 18% with the highest dose of SRIF. In addition, the fractional standard deviation of S1 estimates decreased exponentially with increasing magnitude of insulin response. Modified FSIGTs require a smaller insulin response than the standard protocol to achieve the same precision.