Tryptophan as a surrogate prognostic marker for diabetic nephropathy

AIMS/INTRODUCTION Diabetic nephropathy is one of the leading causes of end-stage renal disease. Unfortunately, reliable surrogate markers for predicting the prognostic outcome of diabetic nephropathy are as yet absent. In order to find new markers in predicting the progression of diabetic nephropathy, we carried out a prospective study by investigating the correlation between serum metabolites and the annual change of estimated glomerular filtration rate (eGFR). MATERIALS AND METHODS From September 2013 to September 2015, 52 diabetes patients at various stages of chronic kidney disease were enrolled. While serum levels of 175 metabolites were measured by AbsoluteIDQ™ p180 kit, only those with a significant difference in advancing chronic kidney disease stages were selected. After then, serial renal function change of these patients was followed up for 12 months, the outcome of renal function with each selected metabolite was compared according to the occurrence of a rapid decline (sustained annual decrement rate ≥5%) of eGFR. RESULTS A total of 26 metabolites were found to be significantly associated with the severity of chronic kidney disease. Tryptophan (Trp) showed a significant association with the event of rapid decline in eGFR (P = 0.036). Serum concentration of Trp <44.20 μmol/L showed the most valuable predictive value with 55.6% sensitivity and 87% specificity. CONCLUSIONS A lower level of Trp, especially <44.20 μmol/L, was related to a rapid decline in eGFR. Accordingly, Trp might be regarded as a potential prognostic marker for diabetic nephropathy.