In vitro influence of benfluorex and its main metabolites on rat liver microsomal membrane properties

Benfluorex metabolism complemented by electrochemistry-mass spectrometry

The hypolipidemic and hypoglycemic drug benfluorex was widely applied to treat type 2 diabetes mellitus and metabolic syndrome in overweight patients since 1976. However, benfluorex was connected to multiple cases of valvular heart disease and pulmonary arterial hypertension later on. Similar adverse drug reactions were previously found to be associated to the structurally related drug fenfluramine, which was attributed to the formation of its N-deethylated metabolite norfenfluramine. Even though norfenfluramine was known to be a common metabolite of fenfluramine and benfluorex, only fenfluramine was withdrawn from European and United States markets in 1997 while benfluorex remained available until 2009. In this work, the metabolism of benfluorex is simulated by an online hyphenation of electrochemistry and mass spectrometry and the observed transformation products are further characterized using liquid chromatography and high-resolution tandem mass spectrometry. Using this approach, norfenfluramine is found to be the main electrochemical transformation product of benfluorex. Considering the knowledge about norfenfluramine toxicity, rapid metabolite screening using electrochemistry hyphenated to mass spectrometry could have been used to predict the potential of benfluorex for adverse drug reactions early on, showcasing the value of electrochemical metabolism mimicry for rapid drug safety evaluation.

Metabolic and anti-atherogenic effects of long-term benfluorex in dyslipidemic insulin-resistant sand rats (Psammomys obesus)

Benfluorex is a clinical lipid-lowering agent with antihyperglycemic properties. The effect of long-term oral treatment (10 mg/kg/day for 7.5 months) on carbohydrate and lipid metabolism and aortic morphology was investigated in 24 insulin-resistant sand rats receiving a standard laboratory diet supplemented with cholesterol (2%). Untreated controls (n=34) developed impaired glucose tolerance, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia and elevated plasma LDL- and VLDL-cholesterol, positively correlated with the proportion of the thoracic aorta displaying oil red O-positive atherosclerosis; ultrastructural examination showed intimal lipid deposits, foam cells, polymorph infiltrates and fibrosis. Benfluorex-treated animals showed significant decreases in glucose intolerance, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia, and plasma LDL- and VLDL-cholesterol, with no evidence of aortic atheroma. The metabolic benefits of benfluorex may protect against the long-term development of atherosclerosis in the insulin-resistant dyslipidemic syndrome.

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.