25-hydroxyvitamine D and tubular lesions in chronic kidney disease
According to experimental and clinical studies, in chronic kidney disease, the 25-hydroxyvitamin D (25OHD) level may be reduced by the catabolic enzyme CYP24 in damaged tubules and increase of 25OHD renal excretion. In the context of new data, the study of the association between the 25OHD level and pathological changes in the kidney is of significant interest. The aim. To investigate the relationship between 25OHD level and tubulointerstitial changes in patients with chronic kidney disease. Material and methods. The study included patients with morphologically confirmed glomerulopathies (n=90, age 38 (30-50), M:F 37:53) and an initial decrease in the estimated glomerular filtration rate (eGFR=64 (33-90) ml/min/1.73 m2). The control group consisted of 10 apparently healthy individuals of comparable age with normal eGFR values. The creatinine concentration was measured by the modified Jaffe method (Beckman Coulter, USA), eGFR was calculated using the CKD-EPI formula. The protein concentration in urine was determined by the pyrogallol red method (Beckman Coulter, USA). To standardize the results, daily proteinuria was calculated. The concentration of intact parathyroid hormone (PTH) in the blood serum of patients was measured using the Intact PTH test system (Beckman Coulter, USA), the concentration of 25OHD - ARCHITECT 25OH vitamin D (Abbott Laboratories, USA). The morphological examination of the kidney included seven standard stains and semi-quantitative morphometry of tubulointerstitial changes (scores). Results. Most of the examined patients had a lack or deficiency of 25-hydroxyvitamin D. The level of PTH was higher in patients with eGFR <60 ml/min/1.73 m2 (p=0.028). There was no correlation between serum 25OHD and PTH concentrations (r= -0.03, p=0.86). A significant relationship was found between pathological changes in the nephron tubules and a decrease in 25OHD (granular tubular dystrophy: r= -0.39, p<0.05; hyalinedrop tubular dystrophy r= -0.39, p<0.05) and proteinuria (fig. 3). In multiple regression analysis, the severity of tubular dystrophy was associated with 25OHD concentration (β= -0.33±0.11, p=0.046), despite the inclusion of proteinuria (β=0.22±0.11, p=0.062) in the regression models. Conclusion. Low serum concentrations of 25OHD are associated with more pronounced degenerative changes in the renal tubular epithelium in patients with chronic kidney disease.