Influence of aging and obesity on serum levels of free amino acids and other ninhydrin-positive substances in man

Abstract

hereinafter referred to as AA, were investigated in consecutive decennial age groups of male and female healthy individuals with normal weights and obese persons, ranging from neonatal (cord blood) to eighties, as a basic study on the amino acid metabolism. The study has revealed remarkably characteristic findings in relation to age, sex and obesity.
(1) Cord serum AA showed higher concentrations in males than in females but there was no significant difference between sexes in the cord blood AA/maternal blood AA ratio, ranging between 1.0 and 2.0 in both sexes. Of individual amino acids and ninhydrin-positive substances in the cord serum, phosphoserine, serine, asparagine, glutamic acid, glutamine, citrulline, cystathionine, methionine, isoleucine, ethanolamine, 1-methylhistidine, 3-methylhistidine, anserine and carnosine were found to be at significantly higher levels in males.
(2) Male infants and children disclosed a significantly greater value for serum total AA concentration than females. Of the individual AAs, asparagine, proline, citrulline, α-aminon-butylic acid, cystathionine, tyrosine, ornithine, phenylalanine, ethanolamine, lysine, anserine, carnosine and arginine showed significantly higher values in the male.
(3) The serum total AA level increased progressively with advancing age from the teens to the forties, reaching a peak in the forties, both male and female. At all ages the obese exhibited greater values for serum total AA than the normal weight groups.
(4) Serum essential and non-essential AA levels varied significantly between sexes as well as with aging. Particularly, serum levels of branched AAs in males reached peaks at the thirties and declined thereafter till the eighties, whereas in females, they fluctuated with peaks at the twenties and showed the lowest values at the fifties.
(5) Ketogenic AAs in the serum of males increased to peaks at the forties with subsequent gradual decline. In the ferrale, they increased to peaks at the thirties and then decline to the lowest levels at the fifties, followed by a trend of gradual elevation. The serum ketogenic AA levels were significantly higher in males throughout life except the seventies and eighties.
(6) Glycogenic AAs showed the highest concentrations in cord serum and fell markedly during infancy and childhood, followed by a progressive rise to reach peaks at the thirties in both males and females. They declined thereafter. All these five types of AAs exhibited increased concentrations in the serum of obese subjects at all ages, regardless of sex.