An in vivo and in ovo evaluation of the toxicity of Sibutramine

Abstract

Sibutramine hydrochloride monohydrate is a weight loss agent banned from most global markets due to reports of serious adverse events including death. It is classified as a serotonin-norepinephrine reuptake inhibitor and acts within the central nervous system by inhibiting the reuptake of these neurotransmitters essentially influencing satiety and also energy expenditure. Despite its ban, sibutramine is still available for use in some countries and is often an unlisted ingredient in herbal or natural weight loss products. This leads to the oblivious and unintentional consumption of this compound which is of great concern especially if used by pregnant women. The aim of this study was to investigate the possible toxic and teratogenic effects of sibutramine by using a Spraque Dawley rat and an in ovo chick embryo model. The Sprague Dawley rat was used as in vivo model and animals were divided into three experimental groups, each consisting of 12 animals (6 males, 6 females). Rats were administered sibutramine over a 28 day period according to their assigned experimental groups namely control (C; sterile H2O), Low dose (LD; 1.32 mg/kg) and High Dose (HD; 13.2 mg/kg). On the day of termination blood was collected for various analyses which included biochemical tests for liver and kidney function, hormonal changes as well as the investigation of coagulation profiles. Brain, heart, lung, kidney and liver tissue of each animal was harvested for investigation of tissue and cellular structure. Rats were weighed daily and this data suggested that sibutramine was well tolerated by all animals, with only the female rats in the HD group showing a significant 8.2% decrease in their rate of weight gain. Biochemical data of liver and kidney function in all groups were normal. Thyroid hormone levels were comparable to control values though cortisol levels were lowered in the HD female group, a finding which correlates with the observed weight loss. Investigations of the ultrastructural morphology of the platelets and fibrin networks revealed differences between the experimental groups that are consistent with changes associated with a procoagulable state. Brain, kidney and liver tissue morphology appeared normal upon investigation, the latter confirming the biochemical findings. Examination of cardiac tissue revealed a slight increase in collagen deposition between the muscle fibers and ultrastructural analysis of lung tissue showed thickening of the alveolar walls, decreased intra-alveolar space and drastic increases in collagen deposition in the sibutramine-exposed groups. These findings were dosage dependant. The in ovo model was implemented with ephedrine, a known teratogen, as positive control. Three control groups were included to ensure the efficacy of the method. Eight experimental groups, each containing sixteen eggs, were exposed to four different concentrations of each drug (i.e. 0.5, 2.5, 5.0, 10.0 μmol). The brain, heart, liver and kidneys were harvested on embryonic day thirteen for morphological analysis. Macroscopic evaluation revealed that both drugs caused congenital abnormalities which included ventral wall and limb defects as well as growth retardation and increased mortality. Sibutramine was found to have a greater teratogenic potential than ephedrine. Histological investigation of kidney and brain samples of embryos revealed no morphological differences between the various experimental groups. Livers and hearts of embryos exposed were severely affected by both compounds in a dose dependant manner. Replacement of myocardium with adipose and connective tissue was observed in cardiac tissue, which is characteristic of muscular dystrophy. Severe liver steatosis was also evident. In conclusion, results from this animal-based study show that, at concentrations which are not toxic to the liver or kidneys, sibutramine administration led to increased coagulation, moderate cardiac and excessive lung fibrosis within the Sprague Dawley rat model. This indicates significant toxicity with the cardiac and respiratory system being more susceptible targets. In addition sibutramine was shown to possess greater teratogenic effects than ephedrine. Both drugs caused cardiac dystrophy and liver steatosis resulting in extensive liver and heart damage. Understanding the underlying mechanisms involved in the pathogenesis of these findings strongly emphasize an important area for future research.