POTENTIAL EFFECT OF METABOLIC-ACIDOSIS ON BETA-2-MICROGLOBULIN GENERATION - IN-VIVO AND IN-VITRO STUDIES

beta 2-Microglobulin (beta 2M) is responsible for dialysis-associated amyloidosis. Levels of beta 2M in plasma increase during chronic renal failure; however, retention does not appear to be the sole mechanism responsible. The effect of metabolic acidosis on beta 2M production wa s examined, Thirty-six patients with stable chronic renal insufficienc y, 12 uremic patients before their first dialysis, 8 hemodialysis pati ents who were assigned to acetate or bicarbonate dialysate and then cr ossed over to the alternative regimen, and 6 normal subjects given NH4 Cl to initiate metabolic acidosis were studied. In vitro studies in th e human myeloid cell line U 937 were also performed. beta 2M protein w as measured with ELISA, beta 2M mRNA was measured with reverse transcr iption polymerase chain reaction, and the U 937 cells were studied at two pH levels with FACScan flow cytometry. The cells were exposed in v itro up to 60 min in a buffered incubation medium to either pH 5.10 or pH 7.34. An inverse correlation was found between beta 2M and bicarbo nate concentrations in plasma in the stable chronic renal failure pati ents (r = -0.54; P < 0.05) and in the uremic patients before their fir st dialysis (r = -0.72; P < 0.05). In hemodialysis patients, blood pH and plasma bicarbonate values were lower (P < 0.05) and beta 2M concen trations in plasma were higher (P < 0.05) with acetate than with bicar bonate dialysate. In normal men, NH4Cl resulted in an increase (P < 0. 05) in beta 2M mRNA expression in lymphocytes by an average factor of 1.5 (range, 1.1 to 1.8), In U 937 cells, the cell surface expression o f beta 2M and HLA Class I heavy chain assembled with beta 2M decreased at low pH compared with normal pH, Concomitantly, an increase in beta 2M release into the supernatant was observed, possibly as the result of beta 2M dissociation from cell surface HLA Class I complex. The res ults suggest that metabolic acidosis may enhance cellular beta 2M gene ration and release.