Thiamin as a therapeutic agent for lead poisoning

Lead poisoning is still a serious problem in children and young animals. The artificial chelating agents most commonly used in treatment of lead poisoning (CaEDTA, BAL and d-penicillamine) are by no means totally effective and may be potentially toxic. Recently, thiamin was recommended as a therapeutic agent for lead toxicity by some researches. This study was undertaken to evaluate the role of thiamin as an antidote for lead poisoning. Clinical, analytical, histopathologtical and neurophysiological effects of thiamin were evaluated in Sprague-Dawley rats exposed to 1,000 ppm of lead acetate in drinking water and treated thiamin (25 mg or 50mg/kg body weight), CaEDTA (50mg/kg b.w.) or their combination for 8 weeks. Thiamin decreased the blood, liver, and kidney lead concentrations. Both pre-and posttreatment of thiamin enhanced excretion of lead. The pretreatment with thiamin more effectively promoted excretion of lead. Thiamin also reduced the organ retention of lead (kidney, liver) although thiamin produced varied effects on the whole body retention and the organ distribution of lead depending upon variables such as route of administration, dose and treatment combination. The combined pretreatment (thiamin 50mg/kg and CaEDTA) and the CaEDTA treatment alone reduced the whole body retention of lead most effectively. Thiamin, CaEDTA and the combined treatments decreased the absorption of lead 203 and the biological halflife of retained lead 203 following oral or intraperitoneal lead exposure. Latency periods associated with the brainstem evoked responses (BAERs) were increased after 4 weeks of lead exposure. The neurophysiological alterations induced by lead exposure were prevented by thiamin or CaEDTA treatment. The latency periods in the lead exposed rats treated with thiamin, CaEDTA or the combined treatment did not increase in a similar fashion, but resembled more closely the latency periods observed in the rats which were not exposed to lead. The higher dose of thiamin(50mg/kg) was more effective than the lower dose (25mg/kg) in the comparable treatment groups. Histopathological examination of the animals did not reveal any pathological changes in the brain, although lesions often associated with lead toxicity were observed in the kidney. The severity of the lesions was not influenced by thiamin or CaEDTA treatment. It was concluded that CNS in the presence of neurophysiological alterations, indicates that functional deficits may be observed prior to histological evidence of pathological damage and that thiamin has useful effects as an antidote and that especially thiamin in combination with another chelator was a more effective therapeutic agent for lead poisoning.