4.6. Role of the Intestinal Microbiota
Evidently, the pharmacokinetic relationship between oral spermidine intake and spermidine/spermine plasma concentrations is not simply additive, and the underlying mechanisms remain rather speculative. Obviously, dietary spermidine is subject to extensive presystemic metabolism. In this context, it has been suggested that the intestinal microbiota is involved in the presystemic metabolism of dietary polyamines. Matsumoto et al. reported that the administration of probiotic bifidobacteria increased spermine—but not spermidine—concentrations in the feces of animals and humans [