Apoptosis in kidney tissue of senior and geriatric cats with chronic kidney disease.

Apoptosis, an important pathological event associated with kidney disease progression, is expected to be a therapeutic target in chronic kidney disease (CKD). However, its role in naturally occurring CKD in aged cats remains unclear. Therefore, here, we investigated kidney tissues from aged cats (≥10 years) with or without azotemic CKD to evaluate apoptotic events using a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay. The positive TUNEL signals of the renal cells were quantified and statistically analyzed for correlation with the severity of plasma creatinine (pCre) concentration, renal lesions (glomerulosclerosis, interstitial cell infiltration, peritubular capillaries, and interstitial fibrosis), and oxidative damage of the kidney tissue. Oxidative damage was evaluated using immunohistochemistry for 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxynonenal (4-HNE). In the TUNEL assay, regardless of azotemia, positive nuclear signals were observed in the tubular epithelial and intraluminal cells, interstitial infiltrating cells, and glomerular cells. Quantitative TUNEL scores showed no significant differences between the azotemic and non-azotemic groups in any compartment of the kidney tissues. In the azotemic group, TUNEL scores did not correlate with pCre or renal lesion severity. However, the scores showed a significant positive correlation with the scores of 8-OHdG and 4-HNE. These findings suggest that apoptosis associated with oxidative damage in renal tissue is an initial pathological event that leads to CKD, rather than a change following CKD progression, in aged cats. Inhibiting apoptosis by antioxidant treatment may be a key strategy to prevent the development of CKD.