ABSTRACT
To investigate how aging alters B-group vitamin metabolism, rats were fed with niacin-free 20% casein diet from 3 to 80 wk old, and the urinary excretions of the B group vitamins were periodically measured. The blood and liver B-group vitamin levels in 80-wk-old rats were also compared with those in 8-wk-old rats. The urinary excretion of thiamin, riboflavin, vitamin B6 metabolite 4-pyridoxic acid, pantothenic acid, folic acid and biotin were not altered during 540 d. The urinary vitamin B12 increased by 8-fold at 29 wk old, and further increased at 80 wk old. Conversion of nicotinamide from tryptophan gradually decreased to 60% from 29 to 48 wk old. Plasma PLP, vitamin B12 and folate levels in 80-wk-old rats were lower than those in 8-wk-old rats, consistent with lower liver vitamin B6 and folate levels in aged rats. Plasma and liver biotin levels in aged rats were higher than those in young rats. Other B-group vitamins such as vitamin B1, vitamin B2, niacin and pantothenic acid levels in blood and liver from aged rats were same as those from young rats. Alteration of vitamin B6 metabolism in particular is similar to the observations in elderly humans reported previously. Our findings suggest that aged rats can be useful models to investigate aging-related B-group vitamin metabolism.
Subject(s)
Aging/metabolism , Liver/metabolism , Vitamin B Complex/metabolism , Age Factors , Animals , Biotin/metabolism , Body Weight , Eating , Folic Acid/metabolism , Male , Models, Animal , Niacinamide/metabolism , Pyridoxal Phosphate/metabolism , Rats , Tryptophan/metabolism , Vitamin B 12/metabolism , Vitamin B Complex/blood , Vitamin B Complex/urineABSTRACT
We investigated a useful chemical index for an excessive nicotinamide intake and how this excessive nicotinamide intake affects the tryptophan-nicotinamide metabolism in rats. Weaning rats were fed on a tryptophan-limited and nicotinic acid-free diet containing no, 0.003%, 0.1%, 0.2%, or 0.3% nicotinamide for 21 days. Urine samples were collected on the last day and analyzed the intermediates and metabolites on the tryptophan-nicotinamide pathway. Nicotinamide N-oxide, nicotinic acid and nicotinuric acid, metabolites of nicotinamide, were detected when nicotinamide at more than 0.1% had been taken. An intake of nicotinamide of more than 0.1% increased the urinary excretion of quinolinic acid, an intermediate on the pathway. Nicotinamide N-oxide and nicotinuric acid increased with increasing dietary concentration of nicotinamide. These results show that the measurements of nicotinamide N-oxide and nicotinuric acid in urine would be useful indices for an excessive nicotinamide intake.
