Renal tubular injury induced by hyperoxaluria: evaluation of apoptotic changes

In order to evaluate the injurious effect of hyperoxaluria on renal tubular epithelium, as judged by apoptotic changes in the renal parenchyma, we per formed an experimental study in 20 rabbits. In the experimental group anima ls (n = 10) severe hyperoxaluria was induced by continuous ethylene glycol (EG; 0.75%). Histologic alterations, including crystal formation, together with apoptotic changes were evaluated after 7 and 28 days. Control group an imals (n = 10) received normal distilled drinking water. Following 7- and 2 8-day periods, tissue sections obtained from kidneys were examined histopat hologically under light microscopy for the presence and the degree of cryst al deposition in the tubular lumen. Apoptotic changes in renal tubular cell s were examined using the terminal deoxynucleotidyl transferase (TdT)-media ted dUTP in situ nick and labeling (TUNEL) method during the same follow-up period. Crystal deposition was evident in the tubular lumen of tissue sect ions obtained during the 7-day examination period. During the 28-day examin ation period, however, these findings were found to be either limited or to have disappeared. In relation to apoptotic changes, the percentage of posi tive nuclei stained using the TUNEL method was from 11 to 20% in the experi mental group and 5.6% in the control group. Our findings indicate that both calcium oxalate (CaOx) crystals and hyperoxaluria itself may be injurious to renal tubular cells, as indicated by apoptotic changes. These changes ma y be responsible for the pathologic course of urolithiasis.