Effects of chronic administration of benfluorex to rats on the metabolism of corticosterone, glucose, triacylglycerols, glycerol and fatty acid

Benfluorex, a hypotriglyceridemic drug, reduces lipid peroxidation and alleviates adverse metabolic complications of copper deficiency

The pathologies associated with copper deficiency in rats fed fructose may be induced, in part, by hypertriglyceridemia and lipid peroxidation. Reducing triacylglycerol levels in plasma may result in lowering lipid peroxidation, which in turn could ameliorate metabolic effects resulting from the combination of fructose feeding and copper deficiency. Benfluorex, a hypolipidemic factor able to reduce hypertriglyceridemia, was administered to weanling male rats fed either copper-deficient (0.6 microgram Cu/g) or adequate (6.0 micrograms Cu/g) diets containing fructose as the sole dietary carbohydrate. In copper-deficient rats, benfluorex (50 micrograms.kg-1.d-1) reduced plasma triacylglycerols from 45 to 31 mg/dL, reduced lipid peroxidation by approximately 50%, and prevented the enlargements of heart and liver size and the atrophy of the pancreas, and ameliorated anemia. It is suggested that lipid peroxidation associated with hypertriglyceridemia may be responsible for the pathologies induced by the combination of fructose consumption and copper deficiency.

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.

Research prospects with benfluorex

The recent recognition that insulin resistance is associated with a number of risk factors for atherosclerotic cardiovascular disease has increased the interest in agents that are able to improve insulin sensitivity. The capacity of benfluorex (Médiator) to enhance insulin action has led to much speculation regarding its mechanism of action. Chronic benfluorex treatment, in a variety of genetic and dietary animal models of diabetes and insulin resistance, has been shown to diminish, circulating insulin levels and to decrease blood glucose, triglycerides, and cholesterol concentrations. From these studies, it is possible to postulate a multifactorial mode of action of this drug that involves three independent but interactive processes: (1) a direct effect on insulin target tissues, mediated by mechanisms distal to the binding of insulin to its receptor, (2) modulation of the glucoregulatory hormone balance, including a diminution in both adrenal and sympathetic tone, leading to improved hepatic sensitivity to insulin, and (3) reduced hepatic and muscle lipid availability, leading to improved glucose utilization in skeletal muscle. The multiplicity of the neuroendocrine and biochemical effects of benfluorex cannot be explained by a single cellular or molecular action. It has been suggested that insulin sensitizers may act on key molecules involved in the sequence of biochemical events involving the insulin signal transduction process. The identification of these molecular targets and the determination of their relative importance in the treatment of type II diabetes remains to be established and constitutes the main subject of ongoing research with benfluorex.

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.

Effect of benfluorex on insulin secretion and insulin action in streptozotocin-diabetic rats

We have examined the effect of chronic (20 days) oral administration of benfluorex (35 mg/kg) in a rat model of non-insulin-dependent diabetes mellitus (NIDDM), as induced by injection of streptozotocin 5 days after birth and characterized by frank hyperglycaemia, hypoinsulinaemia, and hepatic and peripheral insulin resistance. In the benfluorex-treated diabetic rats, basal plasma glucose levels were decreased (7.9 +/- 0.2 mM as compared with 17.2 +/- 1.1 mM in the pair-fed untreated diabetic and 6.7 +/- 0.2 mM in the benfluorex-treated non-diabetic rats) while the basal and the glucose-stimulated (IVGTT) plasma insulin levels were not improved. The lack of improvement of glucose-induced insulin release after benfluorex treatment was confirmed under in vitro conditions (perfused pancreas). In the benfluorex-treated diabetic rats, basal glucose production and overall glucose utilization were normalized. Following hyperinsulinaemia (euglycaemic clamp), glucose production was normally suppressed while overall glucose utilization was not significantly improved. Since benfluorex exerts a predominant action on the liver in the present rat model of diabetes, and since increased basal hepatic glucose output is a major metabolic abnormality and is responsible for much of the elevated fasting blood glucose levels in NIDDM, the use of such a compound in NIDDM may be potentially relevant.

Sustained decreases in weight and serum insulin, glucose, triacylglycerol and cholesterol in JCR:LA-corpulent rats treated with D-fenfluramine

1. The effects of D-fenfluramine were studied in the JCR:LA-corpulent rat that is grossly obese, hyperphagic, hyperlipidaemic, hyperinsulinaemic and atherosclerosis-prone. 2. Daily doses of 1, 2.5 and 5 mg kg-1 of D-fenfluramine produced sustained decreases in body weight and food intake over a period of 30 days in 6 month old female rats fed ad libitum. This was accompanied by decreases in the circulating concentrations of glucose, triacylglycerol, free cholesterol and insulin. 3. Food restriction imposed by meal feeding also decreased circulating glucose, triacylglycerols, cholesterol and insulin and diminished the effect of D-fenfluramine on these parameters in male and female rats. 4. Addition of D-fenfluramine to drinking water to give a dose of about 0.25 mg kg-1 daily produced a sustained decrease in body weight and food intake of male and female rats over a nine week period. 5. The results show that the JCR:LA-corpulent rat is very sensitive to the pharmacological effects of D-fenfluramine. These rats should provide an appropriate animal model for determining the mechanisms of action of this anti-obesity agent and whether apparently beneficial changes in metabolism translate into long-term protection against premature atherosclerosis.

Decreased incorporation of glucose into lipids and increased lactate production by adipose tissue after long-term treatment of rats with D-fenfluramine

Male rats were treated with ten daily doses of 10 mg of D-fenfluramine/kg. Body weight decreased after days 1 and 2, but thereafter the weight gain paralleled that of the control rats. After the tenth injection there were decreases in the weights of the epididymal fat pads, their fat content, and the average size of the adipocytes after collaginase digestion. The rate of glucose uptake by incubated pieces of adipose tissue was maintained after D-fenfluramine treatment, and the production of lactate increased. The incorporation of glucose into fatty acids by adipose tissue pieces decreased by 65-74% after treatment with D-fenfluramine. This effect was not reversed by adding insulin or phenylisopropyladenosine to the incubations. D-Fenfluramine also decreased the incorporation of glucose into glyceride-glycerol, but this effect was less pronounced than that for fatty acid synthesis. Direct addition of D-fenfluramine to the incubation inhibited lipid synthesis from [14C]glucose but only at drug concentrations above 1 mM. It is concluded that the treatment of rats with D-fenfluramine modifies the metabolic balance of adipose tissue so as to direct glucose metabolism away from lipid synthesis and towards lactate production. This could be a significant mechanism in the overall loss of adipose tissue mass caused by the administration of D-fenfluramine.