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 performed an experimental study in 20 rabbits. In the experimental group animals (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 animals (n = 10) received normal distilled drinking water. Following 7- and 28-day periods, tissue sections obtained from kidneys were examined histopathologically under light microscopy for the presence and the degree of crystal deposition in the tubular lumen. Apoptotic changes in renal tubular cells were examined using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP in situ nick and labeling (TUNEL) method during the same follow-up period. Crystal deposition was evident in the tubular lumen of tissue sections obtained during the 7-day examination period. During the 28-day examination period, however, these findings were found to be either limited or to have disappeared. In relation to apoptotic changes, the percentage of positive nuclei stained using the TUNEL method was from 11 to 20% in the experimental 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 may be responsible for the pathologic course of urolithiasis.