Methionine kinetics are altered in the elderly both in the basal state and after vaccination.
BACKGROUND
Inflammation is known to affect sulfur amino acid metabolism. Aging is associated with an increased prevalence of inflammatory conditions, but the metabolism of methionine has been poorly explored in the elderly.


OBJECTIVE
The aims of this study were to compare methionine kinetics between elderly and young subjects and to explore the effect of aging on the response to a mild inflammatory challenge induced by a vaccination.


METHODS
Seven elderly volunteers aged 66-76 y and 8 young volunteers aged 22-26 y were studied before and 2 d after a vaccination (diphtheria, tetanus, poliomyelitis, and typhoid vaccines). Methionine kinetics were measured by using an infusion of L-[1-13C, methyl-2H3]methionine in the postabsorptive and fed states.


RESULTS
Before vaccination, the contribution of homocysteine remethylation to methionine-methyl flux (Qm) and the ratio of remethylation to homocysteine transsulfuration were significantly lower in the elderly subjects than in the young subjects (P < 0.05). In contrast, the contribution of transsulfuration to methionine transmethylation was higher in the elderly (P < 0.05). Vaccination significantly increased the ratio of transsulfuration to transmethylation and decreased the ratio of remethylation to Qm (P < 0.05).


CONCLUSIONS
The preferential methionine metabolism toward cysteine synthesis observed after vaccination suggests an increased requirement of sulfur amino acids even in mild inflammatory situations. The main finding of this study is a higher proportion of methionine entering the transsulfuration pathway in elderly subjects before vaccination. This finding suggests an increased cysteine demand during aging.
Mercier
Sabine
S
Unité de Nutrition et Métabolisme Protéique, INRA Theix, Saint Genès Champanelle, France.
Breuillé
Denis
D
Buffière
Caroline
C
Gimonet
Johan
J
Papet
Isabelle
I
Mirand
Philippe Patureau
PP
Obled
Christiane
C
D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism* / Q000502:physiology; D002247:Carbon Isotopes; D003545:Cysteine / Q000096:biosynthesis / Q000378:metabolism; D003903:Deuterium; D005260:Female; D006710:Homocysteine / Q000378:metabolism; D006801:Humans; D007249:Inflammation / Q000378:metabolism*; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D008433:Mathematics; D008715:Methionine / Q000378:metabolism / Q000493:pharmacokinetics*; D008745:Methylation; D009751:Nutritional Requirements; D019518:Postprandial Period; D014611:Vaccination
D002247:Carbon Isotopes; D006710:Homocysteine; D008715:Methionine; D003903:Deuterium; D003545:Cysteine