Plasma concentrations of alpha-melanocyte-stimulating hormone are elevated in patients on chronic haemodialysis

Background. Clinical and/or laboratory signs of systemic inflammation occur frequently in patients undergoing long-term haemodialysis. It is likely, therefore, that a compensatory release of endogenous anti-inflammatory molecules occurs to limit host reactions. The aim of the present research was to determine if the potent anti-inflammatory peptide α-melanocyte-stimulating hormone (α-MSH), a pro-opiomelanocortin derivative, is increased in plasma of haemodialysis patients. Because endotoxin and cytokines induce α-MSH in vivo and in vitro, we also measured plasma concentrations of endotoxin, interleukin-6 (IL-6), and tumour necrosis factor α (TNF-α), and the two circulating products of activated monocytes, nitric oxide (NO) and neopterin. Methods. Thirty-five chronic haemodialysis patients, 20 patients with chronic renal failure not yet on dialysis, and 35 normal controls were included in the study. In the haemodialysis group, blood samples were obtained before and at the end of a dialysis session. Plasma α-MSH was measured using a double antibody radioimmunoassay, and IL-6, TNF-α, and neopterin using specific enzyme-linked immunosorbent assays. Plasma nitrites were determined by a colorimetric method, and endotoxin with the quantitative chromogenic LAL (limulus amoebocyte lysate) method. Results. Mean plasma α-MSH was higher in haemodialysis patients than in control subjects, with the peptide concentrations being particularly elevated in dialysed patients with detectable endotoxin. High α-MSH concentrations were observed in the pre-dialysis samples, with no substantial change at the end of the dialysis session. Plasma concentrations of IL-6, TNF-α, neopterin, and NO were generally elevated in chronic haemodialysis patients and there was a negative correlation between circulating α-MSH and IL-6. In patients with renal failure not yet on dialysis, mean plasma α-MSH was similar to that of normal subjects. Conclusions. α-MSH is increased in tire circulation of chronic haemodialysis patients and particularly so in case of detectable endotoxaemia. Reduction of renal clearance is unlikely to contribute to the observed rise of the peptide because α-MSH concentration is not increased in patients with chronic renal failure who are not yet on dialysis. It is likely that dialysis-associated endotoxaemia, directly and/or through cytokine release, enhances the production of the anti-inflammatory mediator α-MSH that limits host reactions.