Pipecolic acid, a metabolite of
lysine, is found in human physiological fluids. It is known that plasma
pipecolic acid levels are elevated in patients with
Zellweger syndrome, a
genetic disorder, and chronic
liver diseases. However, it is uncertain if this
acid originates directly from food intake or from mammalian or intestinal bacterial
enzyme metabolism. To characterize the relationship between plasma
pipecolic acid and diet, we analyzed the contents of
pipecolic acid in 17 edible plants and changes in plasma and urinary
pipecolic acid levels following soybean juice ingestion by 4 healthy volunteers. Our study revealed that some of the plants contained high concentrations of total
pipecolic acid, and a higher portion of L-isomer than D-isomer. Loading tests demonstrated that plasma levels and urinary excretion of D-isomer increased significantly 2 h after soybean juice ingestion. Plasma
lysine levels showed a similar increase to that of D-isomer. These findings suggest that plasma
pipecolic acid, particularly the D-isomer, originates mainly from the catabolism of dietary
lysine by intestinal bacteria rather than by direct food intake and that D- and L-isomer may have different mechanisms of metabolism. Moreover, these findings may be important for clarifying the pathogenesis of
peroxisomal disorders.