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Potential effect of metabolic acidosis on beta 2-microglobulin generation: in vivo and in vitro studies
M Sonikian1, J Gogusev, J Zingraff
1INSERM U90, Départment de Néphrologie, Paris, France.
Abstract:
Beta 2-microglobulin (beta 2M) is responsible for dialysis-associated amyloidosis. Level 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 was examined. Thirty-six patients with stable chronic renal insufficiency, 12 uremic patients before their first dialysis, 8 hemodialysis patients who were assigned to acetate or bicarbonate dialysate and then crossed over to the alternative regimen, and 6 normal subjects given NH4Cl to initiate metabolic acidosis were studied. In vitro studies in the human myeloid cell line U 937 were also performed. beta 2M protein was measured with ELISA, beta 2M mRNA was measured with reverse transcription polymerase chain reaction, and the U 937 cells were studied at two pH levels with FACScan flow cytometry. The cells were exposed in vitro 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 bicarbonate concentrations in plasma in the stable chronic renal failure patients (r = -0.54; P < 0.05) and in the uremic patients before their first dialysis (r = -0.72; P < 0.05). In hemodialysis patients, blood pH and plasma bicarbonate values were lower (P < 0.05) and beta 2M concentrations in plasma were higher (P < 0.05) with acetate than with bicarbonate 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 of 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 results suggest that metabolic acidosis may enhance cellular beta 2M generation and release.
Insights
Metabolic acidosis may increase beta 2-microglobulin (beta 2M) production and release, contributing to dialysis amyloidosis. This study investigated the link between acidosis and beta 2M levels in renal failure patients and cell models.
Area of Science:
- Nephrology
- Biochemistry
- Immunology
Background:
- Beta 2-microglobulin (beta 2M) accumulation is linked to dialysis-associated amyloidosis.
- While chronic renal failure increases beta 2M plasma levels, retention alone doesn't explain the elevation.
- The role of metabolic acidosis in beta 2M production requires investigation.
Purpose of the Study:
- To examine the effect of metabolic acidosis on beta 2-microglobulin (beta 2M) production and release.
- To correlate beta 2M levels with acid-base balance in renal insufficiency and hemodialysis patients.
- To investigate the in vitro impact of pH on beta 2M expression and release.
Main Methods:
- Studied patients with chronic renal insufficiency, uremic patients, hemodialysis patients, and normal subjects.
- Utilized ELISA for beta 2M protein and RT-PCR for beta 2M mRNA.
- Performed in vitro studies on U937 cells at varying pH levels using flow cytometry.
Main Results:
- Found inverse correlations between beta 2M and bicarbonate in renal failure patients.
- Hemodialysis with acetate dialysate led to lower pH, lower bicarbonate, and higher beta 2M compared to bicarbonate dialysate.
- Metabolic acidosis induced by NH4Cl increased beta 2M mRNA in lymphocytes; low pH decreased cell surface beta 2M and increased its release in U937 cells.
Conclusions:
- Metabolic acidosis is associated with increased beta 2M levels in chronic renal failure and hemodialysis.
- Acidosis may enhance beta 2M generation and release, potentially contributing to amyloidosis.
- Cellular mechanisms involving pH-dependent beta 2M expression and release are implicated.