Guanidino compounds after creatine supplementation in renal failure patients and their relation to inflammatory status

Background. Specific guanidino compounds have been described as uraemic toxins and their concentrations are increased in renal failure due to dimished glomerular filtration, whereas the guanidino compound creatine is used as a performance-enhancing substance in athletes. The present study investigates the effects of creatine supplementation on plasma guanidino compounds in a chronic haemodialysis population. Methods. Twenty male haemodialysis patients were included in a placebo-controlled cross-over trial. Patients were treated with creatine (2 g/day) or placebo during two treatment periods of 4 weeks, separated by a washout of 4 weeks. Plasma guanidino compounds and routine biochemical parameters were determined, as well as the prognostic inflammatory and nutritional index (PINI). Results. Upon creatine supplementation, guanidinoacetate concentrations decreased by 15%, due to inhibition of creatine synthesis. Concentrations of alpha-keto-delta-guanidinovaleric acid increased three-fold and argininic acid concentrations doubled. Guanidinosuccinate concentrations did not change, but correlated inversely with CRP (r = -0.736; P = 0.001), PINI-score (r = -0.716; P= 0.002) and correlated positively with plasma urea concentration (r = 0.54; P = 0.02). Conclusions. Creatine supplementation in haemodialysis patients significantly altered the concentration of specific guanidino compounds. Guanidinosuccinate correlated positively with plasma urea and negatively with inflammation markers