Therapeutic approaches to reducing insulin resistance in patients with noninsulin-dependent diabetes mellitus

Synthesis and in vivo antihyperglycemic activity of 5-(1H-pyrazol-3-yl)methyl-1H-tetrazoles

A series of 5-[(5-aryl-1H-pyrazol-3-yl)methyl]-1H-tetrazoles 3a-h have been synthesized and evaluated for their in vivo antihyperglycemic activity. Some of the synthesized compounds have shown significant glucose lowering activity in male Sprague-Dawley rats in sucrose loaded model. These compounds were also evaluated for their peroxisome proliferator activated receptor gamma agonistic property, but none of them displayed any significant activity.

Moderate caloric restriction, but not physiological hyperleptinemia per se, enhances mitochondrial oxidative capacity in rat liver and skeletal muscle--tissue-specific impact on tissue triglyceride content and AKT activation

The study aimed at determining, in lean tissues from nonobese rats, whether physiological hyperleptinemia with leptin-induced reduced caloric intake and/or calorie restriction (CR) per se: 1) enhance mitochondrial-energy metabolism gene transcript levels and oxidative capacity; and 2) reduce triglyceride content. Liver and skeletal muscles were collected from 6-month-old Fischer 344 rats after 1-wk leptin sc infusion (0.4 mg/kg . d: leptin + approximately 3-fold leptinemia vs. ad libitum-fed control) or moderate CR (-26% of those fed ad libitum) in pair-fed animals (CR). After 1 wk: 1) leptin and CR comparably enhanced transcriptional expression of mixed muscle mitochondrial genes (P < 0.05 vs. control); 2) CR independently increased (P < 0.05 vs. leptin-control) hepatic mitochondrial-lipooxidative gene expression and oxidative capacity; 3) hepatic but not muscle mitochondrial effects of CR were associated (P < 0.01) with increased activated insulin signaling at AKT level (P < 0.05 vs. leptin-control); 4) liver and muscle triglyceride content were comparable in all groups. In additional experiments, assessing time course of posttranscriptional CR effects, 3-wk superimposable CR (P < 0.05): 1) increased both liver and muscle mitochondrial oxidative capacity; and 2) selectively reduced muscle triglyceride content. Thus, in nonobese adult rat: 1) moderate CR induces early increments of mitochondrial-lipooxidative gene expression and time-dependent increments of oxidative capacity in liver and mixed muscle; 2) sustained moderate CR alters tissue lipid distribution reducing muscle but not liver triglycerides; 3) mitochondrial-lipid metabolism changes are tissue-specifically associated with hepatic AKT activation; 4) short-term physiological hyperleptinemia has no independent stimulatory effects on muscle and liver mitochondrial-lipooxidative gene expression. Increased lean tissue oxidative capacity could favor substrate oxidation over storage during reduced nutrient availability.

Synthesis and biological activity of novel substituted pyridines and purines containing 2,4-thiazolidinedione

A series of substituted pyridines and purines containing 2,4-thiazolidinedione were designed and synthesized from their corresponding pyridines and purines. These synthesized compounds (entry no. 6a-d, 12a-e, 18a-d, 23a-c) were evaluated for their effect on triglyceride accumulation in 3T3-L1 cells in vitro and their hypoglycemic and hypolipidemic activity in the genetically diabetic KKA(y) mice in vivo. On the basis of their biological activities, 5-(4-[2-[N-methyl-(5-phenyl-pyridin-2-yl)amino]ethoxy]benzyl)thiazolidine-2,4-dione (6d) was selected as a candidate for further pharmacological studies.

Novel 5-substituted-1H-tetrazole derivatives as potent glucose and lipid lowering agents

A series of 5-(4-alkoxyphenylalkyl)-1H-tetrazole derivatives, containing an oxazole-based group at the alkoxy moiety, was prepared and their antidiabetic effects were evaluated in two genetically obese and diabetic animal models, KKAy mice and Wistar fatty rats. Syntheses were performed by cyclization of the corresponding nitrites reacting with azide compounds. A large number of the 5-(4-alkoxyphenylalkyl)-1H-tetrazoles showed potent glucose and lipid lowering activities in KKAy mice. In particular, 5-[3-[6-(5-methyl-2-phenyl-4-oxazolyl-methoxy)-3-pyridyl]propyl]-1H-tetrazole had potent glucose lowering activity (ED25=0.0839 mg x kg(-1) x d(-1)), being 72 times more active than pioglitazone hydrochloride (ED25=6.0 mg x kg(-1) x d(-1)). This compound also showed strong glucose lowering (ED25=0.0873 mg x kg(-1) x d(-1)) and lipid lowering effects (ED25=0.0277 mg x kg(-1) x d(-1)) in Wistar fatty rats. The antidiabetic effects of this compound are considered to be due to its potent agonistic activity for peroxisome proliferator-activated receptor gamma (PPARgamma) (EC50 = 6.75 nM).

Insulin therapy improves insulin-stimulated endothelial function in patients with type 2 diabetes and ischemic heart disease

Blunted insulin-stimulated endothelial function may be a mechanism for the development of atherothrombotic disease in type 2 diabetes, but it is unknown whether hypoglycemic drug therapy can modulate this abnormality. We studied patients with type 2 diabetes and stable ischemic heart disease (n = 28) and lean, healthy control subjects (n = 31). Forearm blood flow was measured by venous occlusion plethysmography during dose-response studies of acetylcholine (ACh) and sodium nitroprusside (SNP) infused into the brachial artery. In the patients and 10 healthy control subjects, ACh was repeated after intrabrachial infusion of insulin. Patients were restudied after 2 months of insulin therapy with four daily subcutaneous injections (treatment group, n = 19) or without hypoglycemic drug therapy (time control group, n = 9). Insulin infusion raised venous serum insulin in the forearm to high physiological levels (133 +/- 14.6 mU/l in patients) with a minor increase in systemic venous serum insulin. This increased the ACh response by 149 +/- 47, 110 +/- 33, 100 +/- 45, and 106 +/- 44% during the four ACh doses in healthy control subjects (P < 0.0001) but had no effect in patients (P = 0.3). After 2 months, HbA(1c) in the treatment group had decreased from 10.0 +/- 0.4 to 7.5 +/- 0.2%. Although neither the ACh response (P = 0.09) nor the SNP response (P = 0.4) had changed significantly, insulin stimulation had a significant effect, as the ACh response increased by 58 +/- 25, 84 +/- 66, 120 +/- 93, and 69 +/- 36% (P = 0.0002). In the time control group, insulin stimulation remained without effect after 8 weeks (P = 0.7). In conclusion, insulin therapy partly restores insulin-stimulated endothelial function in patients with type 2 diabetes and ischemic heart disease.

Intermittent dietary restriction in eSS diabetic rats. Effects on metabolic control and skin morphology

eSS rats exhibit a non-insulin-dependent diabetic syndrome, significantly influenced by diet. Long-term effects of intermittent dietary restriction were studied in male eSS rats. Experimental animals were fed ad libitum during 48 h and food-deprived the next 24 h (R) while controls (L) of the same strain were freely fed every day. This schedule was maintained from 21 days of age until all rats were sacrificed. R animals were leaner than L rats at 5, 8 and 13 months of age. Moreover, an improved metabolic profile (i.e., lower levels in blood triglycerides, total blood cholesterol, basal blood glucose and blood glucose after an oral glucose load) was found. Histological examination of nuchal skin specimens showed a significant increase of dermal thickness and epidermal hypotrophy in free-fed animals. Collagenous fibers closely packed were found just beneath the dermo-epidermal junction in L rats. This finding was less pronounced in R rats. The above mentioned results suggest that eSS rats would draw advantage from living in environments where food availability is uncertain. The importance of early dietary restrictions in predisposed genotypes appears to be a valuable preventive measure against diabetic evolution and complications.

Insulin resistance and diabetes, mechanism and possible intervention

The issue of the peripheral resistance to insulin action has been getting a lot of attention over the last decade. The reason for this is that insulin is a major regulatory hormone and is involved in the metabolism of carbohydrates, lipids, protein and ions. To understand the pathophysiology of insulin resistance it is necessary to elucidate the methods for the assessment of insulin resistance and the molecular mechanism of insulin action. Insulin action is impaired in pathologic and physiologic states such as diabetes mellitus and obesity as well as in some rare syndromes. Further understanding of the pathophysiology of the impaired action of insulin improves the chances of defining new ways of treatment to improve the sensitivity to insulin action.

The hypoglycaemic and insulinotropic activity of Tinospora crispa: studies with human and rat islets and HIT-T15 B cells

In Malaysia, Tinospora crispa extract is taken orally by Type 2 (non-insulin-dependent) diabetic patients to treat hyperglycaemia. We have evaluated the claimed hypoglycaemic property by adding aqueous extract to the drinking water of normal and alloxan-diabetic rats. After one week, fasting blood glucose levels were significantly (p less than 0.01) lower and serum insulin levels were significantly (p less than 0.01) higher in treated diabetic animals (10.4 +/- 1.0 mmol/l and 12.8 +/- 1.1 muU/ml respectively) compared to untreated diabetic controls (17.4 +/- 1.7 mmol/l and 8.0 +/- 0.7 muU/ml respectively). The insulinotropic action of T. crispa was further investigated in vitro using isolated human or rat islets of Langerhans and HIT-T15 cells. In static incubations with rat islets and HIT-T15 B cells, the extract induced a dosage dependent stimulation and potentiation of basal and glucose-stimulated insulin secretion respectively. This insulinotropic effect was also evident in perifused human and rat islets and HIT-T5 B-cells. The observations that (i) in all three models insulin secretory rates rapidly returned to basal levels on removal of the extract and (ii) in rat islets, a second challenge with T. crispa induced an additional, stimulated response, are all consistent with physiological release of insulin by B cells. Moreover, the rate of HIT-T15 glucose utilisation was not affected by incubation with T. crispa, suggesting that the cells were viable throughout. These are the first studies to provide biochemical evidence which substantiates the traditional claims for an oral hypoglycaemic effect of Tinospora crispa, and which also show that the hypoglycaemic effect is associated with increased insulin secretion.

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

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

Evaluation of first-generation sulfonylureas and glipizide in non-insulin-dependent diabetes mellitus

The current study examines the impact of glipizide, a second-generation sulfonylurea, on diabetes control in patients in whom adequate control was not achieved while receiving treatment with first-generation agents. The interim results of this multicenter study are presented in which patients in whom euglycemia was not achieved based on fasting and two-hour postprandial plasma glucose criteria with first-generation sulfonylureas were given glipizide therapy for 24 weeks. Twenty-three percent of the patients who had only fair results with first-generation sulfonylureas (fasting plasma glucose level of more than 140 mg/dl, postprandial plasma glucose level of more than 175 mg/dl) had good to excellent results with glipizide therapy alone (fasting plasma glucose level of less than 140 mg/dl or less than 115 mg/dl, respectively). Overall, 15.4 percent of patients with fair to poor control using first-generation agents had good to excellent control using glipizide. At least a 25-mg/dl decrease in fasting plasma glucose and postprandial plasma glucose levels was also seen in 47 and 46 percent of patients given treatment with glipizide who had poor control (fasting plasma glucose level of more than 200 mg/dl, postprandial plasma glucose level of more than 235 mg/dl) with first-generation agents. Glipizide was extremely well tolerated, with no significant side effects. Preliminary data indicate that glipizide may provide a significant advantage in terms of safety and efficacy over first-generation agents.

Guar sprinkled on food: effect on glycaemic control, plasma lipids and gut hormones in non-insulin dependent diabetic patients

The effects of guar granules sprinkled over food on carbohydrate and lipid metabolism were studied in a double-blind cross-over trial in 18 patients with non-insulin-dependent diabetes mellitus (mean +/- SEM age 61.3 +/- 2.5 years). Five-gram guar granules (Guarem, Rybar Laboratories, Amersham, Bucks) were sprinkled over food at each main meal for 4 weeks, and during a 4-week placebo period (separated by a 2-week 'wash-out' period), 5 g wheat bran was taken in the same way. Diabetic treatment was not changed during the study. Mean fasting plasma glucose (FPG) concentration and glycosylated haemoglobin (HbA1) concentration after treatment were significantly lower than after the placebo period (FPG 8.29 +/- 0.47 vs 8.78 +/- 0.53 mmol/l, p less than 0.05; HbA1: 8.70 +/- 0.39 vs 9.09 +/- 0.39%, p less than 0.05). There was a 50% reduction in the incremental area under the postprandial glycaemic curve when guar was eaten with a standardized test meal. Total plasma cholesterol decreased from 5.79 +/- 0.29 to 5.19 +/- 0.22 mmol/l (p less than 0.05) after the guar treatment period. Guar ingestion reduced postprandial insulin and enteroglucagon responses, the latter significantly so, but had no apparent effect on gastric inhibitory polypeptide, pancreatic glucagon, gastrin, and pancreatic polypeptide.

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

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

Delaying carbohydrate absorption in noninsulin-dependent diabetes mellitus: useful therapy?

Epidemiological and psychological studies have revealed major difficulties in motivating diabetic patients to observe a long-term dietary regimen. Therefore, manipulation of intestinal digestion or absorption appears to be a feasible therapeutic approach in the management of diabetes. The addition of natural or chemically processed fiber has been shown to decrease both the postprandial and fasting blood glucose in type-2 diabetics by delaying carbohydrate absorption. Recently, selective enzyme inhibitors of glycoside hydrolases in the upper intestine have been found which create a moderate degree of malabsorption of carbohydrates. The postprandial blood sugar response can be reduced by 50%. However, both these forms of treatment may not be accepted by patients because of impalatability or gastrointestinal side effects. At present only short-term studies with each group of substances are available. Whether the reduction of hyperglycemia is sufficient for the prevention of complications must be clarified in long-term trials.