Mechanisms for the effects of benfluorex on the obese-diabetic-dyslipidemic syndrome

The Ultrastructure of Skeletal Muscle Capillaries of Streptozotocin Diabetic Rats and the Therapeutic Effect of Benfluorex

Diabetes mellitus is a serious disease worldwide and causes other associated diseases. In this study, we observed the effect of streptozotocin (STZ)-induced diabetes and benfluorex treatment on muscular capillary ultrastructure. Adult male rats were used as the test subjects and each individual was intraperitoneally injected with one dose of STZ (45 mg/kg) to induce diabetes. Doses (50 mg/kg) of benfluorex were given to the subjects with tap water by intragastric gavage application once daily for 21 days. At the end of day 21, muscle tissues were obtained from animals and examined under transmission electron microscopy. From the data obtained with the electron microscope, it was observed that the control group had typical continuous capillary vascular structures in their muscles, while STZ caused disruptive disorder of the muscle cells in the capillary wall of the STZ-diabetic group. Additionally, the thickening of the basement membrane around endothelial cells, loss of mitochondrial crista in the muscle cells, enlarged endothelial cells, and narrowed vessel lumen were observed in the muscle tissue. The findings of our study revealed that STZ-induced diabetes disrupted the vascular structure, while benfluorex partially improved it.

Identification of alverine and benfluorex as HNF4α activators

The principal finding of this study is that two drugs, alverine and benfluorex, used in vastly different clinical settings, activated the nuclear receptor transcription factor HNF4α. Both were hits in a high-throughput screen for compounds that reversed the inhibitory effect of the fatty acid palmitate on human insulin promoter activity. Alverine is used in the treatment of irritable bowel syndrome, while benfluorex (Mediator) was used to treat hyperlipidemia and type II diabetes. Benfluorex was withdrawn from the market recently because of serious cardiovascular side effects related to fenfluramine-like activity. Strikingly, alverine and benfluorex have a previously unrecognized structural similarity, consistent with a common mechanism of action. Gene expression and biochemical studies revealed that they both activate HNF4α. This novel mechanism of action should lead to a reinterpretation of previous studies with these drugs and suggests a path toward the development of therapies for diseases such as inflammatory bowel and diabetes that may respond to HNF4α activators.

Antiatherogenic effects of long-term benfluorex treatment in male insulin resistant JCR:LA-cp rats

The JCR:LA-corpulent rat is an animal model that, if homozygous for the cp gene (cp/cp), spontaneously exhibits obesity and a severe insulin resistance, with a resultant hyperinsulinemia and hypertriglyceridemia. The obese male rats show defective nitric oxide-mediated vascular relaxation, advanced atherosclerosis, and ischemic myocardial lesions. Benfluorex has both anorectic and metabolic effects that lower body weight and improve insulin sensitivity in obesity and type 2 diabetes. Male cp/cp rats that were treated with benfluorex (or pair-fed to the treated animals) from the time of weaning, at 3 weeks of age, showed a marked delay in the development of postprandial hyperinsulinemia. At 12 weeks of age benfluorex-treated cp/cp rats did not show the extreme insulin response to a test meal that was observed in untreated or pair-fed rats. Both benfluorex-treated and pair-fed rats had a significant increase in sensitivity to acetylcholine-induced (nitric oxide-mediated) vascular relaxation. Corpulent male rats were also treated from 6 to 39 weeks of age with benfluorex in the feed at a dose of approximately 36 mg/kg/day at 12 weeks of age and decreasing to 23 mg/kg/day at 39 weeks to determine the effects on cardiovascular outcomes. The rats showed a sustained decrease in food consumption and body weight, although they exhibited 50% of the excess body weight of the controls and were grossly obese. Both fasting insulin concentrations and the hyperplasia of the islets of Langerhans were decreased by approximately 50%. Serum triglyceride concentrations were decreased by 44%, and free cholesterol and cholesteryl esters by 30%. The severity of the atherosclerotic lesions on the aortic arch was decreased (P < 0.05). There was also a decrease in the size of early ischemic myocardial lesions that are characterized by cell lysis and chronic inflammatory cell infiltration. Mature, scarred myocardial lesions were essentially absent in the hearts of 39-week-old benfluorex-treated rats. Long-term major food restriction (18 g/day) decreased the body weights of obese rats to essentially those of lean control animals, with similar beneficial effects on the insulin resistance and hyperlipidemia. While myocardial lesion frequency was reduced in these much thinner animals, lesions remained and the apparent effect was not statistically significant. This evidence shows that the beneficial metabolic effects of benfluorex are associated with long-term effects on the vessel wall and delay the onset of insulin resistance and cardiovascular disease in an animal model.

Therapeutic effect of benfluorex in type II diabetic patients on diet regimen alone

A randomized double-blind study of benfluorex (150 mg x 3 daily) versus placebo was conducted over 3 months in 32 type II diabetic patients (24 men and 8 women, aged 52 +/- 8.4 years) with mild stable obesity [body-mass index (BMI) 27 +/- 1.6 kg/ m2], moderate fasting hyperglycemia (fasting blood glucose 9 +/- 0.5 mmol/L, HbA1c 6.7 +/- 0.9%) and moderate hyperinsulinemia (18.6 +/- 3.0 microU/mL) when on treatment with diet alone. After a 1-month placebo run-in period, subjects were randomized to benfluorex or placebo three tablets daily. Inclusion parameters and end-of-study measures were body weight, BMI, fasting blood glucose, glycemic profile, HbA1c, fasting insulinemia, basal and stimulated C-peptide, and an insulin tolerance test (0.1 U/kg). The groups were homogeneous at baseline, except for glycemic profile (higher postprandial glycemia in the group randomized to benfluorex). At the end of the study, the groups did not differ in body weight or BMI; however, HbA1c decreased more with benfluorex (6.0 +/- 1.0% versus 6.8 +/- 0.9%, p = 0.024), as did the mean glycemic profile (7.8 +/- 1.4 versus 8.5 +/- 1.7 mmol/L, p < 0.001), including a particular decrease in postprandial glycemia. The decreases in fasting blood glucose and insulinemia appeared larger with benfluorex (7.7 +/- 1.3 versus 8.4 +/- 1.6 mmol/L and 13.5 +/- 4.5 versus 16.1 +/- 5.1 microU/mL, respectively), but were not statistically significant. The increase in the insulin sensitivity index (Kitt) was greater with benfluorex (+0.54 +/- 1.4 versus +0.25 +/- 1.3%/mn), but the difference was not statistically significant. The same was observed for the stimulated C-peptide. In type II diabetics with mild obesity and hyperglycemia previously managed with diet alone, benfluorex has significant long-term effect on HbA1c and mean daily blood glucose, and tends to lower insulinemia.

Effects of benfluorex metabolites on membrane fluidity and insulin-related processes

As little work has dealt with the antihyperglycemic property of benfluorex at the hepatocyte level, we studied the effects of its main metabolites, S422 and S1475, on membrane fluidity and on insulin binding, internalization and action in healthy rat hepatocytes. Both metabolites were effective fluidizing agents. Neither one affected insulin binding. Only S422 favored the bound insulin-receptor internalization process. The metabolites produced no change in basal alpha-aminoisobutyric acid uptake. Only S422 promoted the insulin-stimulated alpha-aminoisobutyric acid uptake in a dose-dependent way. Therefore, our study demonstrated that: (i) the effects of S422 on insulin-related processes in isolated hepatocytes were direct, specific and not due to any membrane fluidizing mechanism; (ii) S422 improved hepatocyte response to insulin at a post-binding level. These results in vitro give an additional explanation, at the cellular level, of the benefit of benfluorex treatment for non insulin-dependent diabetes patients.