Gas chromatographic characterization of free D-amino acids in the blood serum of patients with renal disorders and of healthy volunteers.

A capillary gas chromatographic method, using the chiral stationary phase Chirasil-L-Val, after treatment and isolation with Dowex 50W X8 cation exchanger and conversion into trifluoroacetyl-1-propyl esters or pentafluoropropionyl-1 (or 2)-propyl esters, has been developed for the determination of the relative amounts of free D-amino acids in the blood serum of eighteen patients with renal failure (continuous ambulatory peritoneal dialysis (CAPD), n = 11; hemodialysis, n = 5; nephrotic syndrome, n = 2) and compared with data obtained from healthy volunteers (n = 5). Significant amounts of D-Ala (0.5-13%) and D-Asx (1.5-7.7%; Asx = Asp + Asn) were found in all serum samples. D-Ser was detected in the serum of all patients with renal disorders and, in addition, D-Pro (0.6-2.5%) was found in the serum of all patients undergoing hemodialysis and with nephrotic syndrome. D-Ser (2.9-3.1%) and D-Pro (0.6-0.9%) were also found in the samples of three volunteers. D-Leu (1.2-1.7%) was present in three patients with CAPD, and D-Glx (0.3-1.3%; Glx = Glu + Gln) was present in eight of eighteen patients with renal malfunction. Linear regression analysis of the relative amounts of D-amino acids and the serum creatinine levels of all donors revealed positive correlation factors for D-Asx (r = 0.748) and D-Ser-(r = 0.667), but not for D-Pro and D-Ala. Remarkably high amounts of D-Ser (12.1 and 19.8%) were found in two hemodialysates investigated. Participation of intestinal bacteria and nutrition are discussed as possible sources of serum D-amino acids. An increase of some D-amino acids in the serum of patients with renal diseases might be explained, in part, by decreased activity of renal D-amino acid oxidase.