Biotin is involved in carbon fixation reaction as a coenzyme of carboxylase and plays an important role in gluconeogenesis, synthesis of fatty acids and amino acids, and energy metabolism. Lysine is an essential amino acid and plays a role in protein synthesis and liver function enhancement necessary for the body such as internal organs, muscles, bones, and the brain. In this study, we investigated the effects on growth and development and biotin metabolism by feeding with excess biotin and excess lysine for a long term in young male mice. The four-week-old Slc:ICR male mice were divided into four groups (n = 4 for each group), and the control group was given CE-2 powder diet (CLEA Japan, Inc., Tokyo), and the experimental groups were given CE-2 diet with excess biotin (5 g/kg diet), excess lysine (5 g/kg diet), or excess biotin (5 g/kg diet) + excess lysine (5 g/kg diet). After feeding for five weeks, serum, liver, spleen, kidney, testis and brown adipocyte were sampled. Biotin was determined by the microbiological assay using Lactobacillus ATCC 8014, and lysine in serum was determined by HPLC. No effect of excess biotin and lysine diets on mouse growth and development was observed. As for organ weight, the excess biotin group had less weight of the spleen and liver than in other groups, but there was no significant difference in relative weight among these groups. The concentration of biotin in serum was 40.4 times higher in the excess biotin group than in the control group, but 9.5 times in the excess biotin + excess lysine group compared to the control group. The concentration of biotin in organs was also lower in the excess biotin + lysin group than in the excess biotin group. These findings suggest that excess lysine intake may affect the pharmacokinetics of biotin in vivo.
