Metabolic acidosis and malnutrition in dialysis patients.

Acidosis is a classic uremic toxin that causes protein catabolism, mainly by selective breakdown of skeletal muscle protein. However, the importance of acidosis is often overlooked in dialysis patients. In the presence of acidosis, there is activation of the ubiquitin-proteasome machinery as well as the branched-chain keto acid dehydrogenase, resulting in catabolism of muscle protein. Acidosis acts synergistically with other catabolic factors, such as inflammatory cytokines and insulin resistance, in inducing protein catabolism. There is ample laboratory evidence showing that correction of acidosis prevents the up-regulation of the ubiquitin-proteasome machinery and reduces protein degradation. Randomized control trials further show that acidosis in dialysis patients can be treated successfully by a higher dialysate bicarbonate or lactate concentration, or by oral bicarbonate supplement. Correction of mild acidosis in dialysis patients is effective in improving nutritional status and reducing the duration of hospitalization.