Effect of Dietary Methionine and Lysine on the Toxicity of Ingested Lead Acetate in the Chick

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Abstract
The interaction of methionine or lysine with lead in the diet of chicks was studied. In experiment 1, lead acetate to supply 0 or 1000 ppm lead was added to a diet that was either deficient in the total sulfur-containing amino acid (TSAA) content (62% of the requirement) or supplemented with DL-methionine to provide 100% of the requirement (NRC, 1977). Supplementing the 0 ppm lead diet with methionine improved body weight gain. Dietary addition of 1000 ppm lead significantly decreased body weight gain; however, supplemental methionine partially alleviated the lead-induced growth depression (methionine × lead interaction was significant). Liver glutathione levels were markedly increased by supplemental methionine and also by lead but no methionine × lead interaction was detected. In experiment 2, the interaction between an essential non-sulfur-containing amino acid, lysine, and dietary lead was investigated. Two levels of lead, 0 or 1000 ppm, were fed in diets either deficient or adequate in lysine (85 or 100% of the requirement, respectively). Addition of lysine to the lysine-deficient basal diet increased growth. The magnitude of the lead-induced growth depression was not affected by dietary lysine content. The lysine level of the diet did not influence the liver glutathione concentration. Lead significantly increased hepatic glutathione concentration, and this increase was greater in the lysine-deficient diet compared to the lysine-adequate diet. The data indicate that amelioration of lead toxicity by methionine may be related to methionine serving as a precursor of glutathione.