#618 Hydroxyproline as a urinary biomarker in renal transplantation

Abstract Background and Aims Interstitial fibrosis/tubular atrophy in kidney transplantation is an unspecific lesion induced by immune and non-immune factors, which determines the progression of chronic kidney disease. Hydroxyproline is an imino acid in relation to collagen metabolism, a fundamental component of fibrosis. The aim of this study was to assess hydroxyproline in urine microvesicles as a marker of fibrosis in the renal transplant patient. Method Observational cross-sectional study in 46 renal transplant patients who had undergone renal biopsy with diagnostic intention, and 19 healthy controls. Clinical, histological and laboratory variables were collected at the time of marker determination and 2 years later (renal function). Hydroxyproline was measured in urine microvesicles. Results Renal transplant patients showed higher microvesicular concentration of hydroxyproline com-pared to the control group (median (interquartile IQR range): 28.024 (5.53) ng/ml vs 2.51 (1.16) ng/ml, P < 0.001. In the transplanted patients, patients in whom biopsy showed some score of total cortical parenchymal inflammation (ti) displayed significantly higher concentration of hydroxy-proline in urine microvesicles than those patients who did not score for cortical parenchymal inflammation (29.91 ± 2.797 ng/ml vs 22.72 ± 8.697 ng/ml, P = 0.034). No significant correlation was observed between urinary markers and serum creatinine, calcium and parathyroid hormone (PTH). Conclusion Concentration of hydroxyproline in urinary microvesicles is increased in renal transplant patients relative to healthy controls. Hydroxyproline in urinary microvesicles is a marker of chronic renal inflammation in transplanted patients and further studies are required to confirm this finding in other pathologies, as well as the association with fibrosis and evolution of renal function.