Apoptotic Death of Renal Tubular Cells in Experimental Sepsis

Background and Purpose: Renal dysfunction attributable to sepsis was long considered a result of hemodynamic instability and subsequent local ischemia. Recent data show that apoptosis may be implicated also. The purpose of this study was to evaluate the role of apoptosis and the expression of the bax, bcl-2, caspase-8, and cytochrome c proteins in the renal parenchymal cells of rats with sepsis. Methods: Sepsis was induced using cecal ligation and puncture (CLP) in 62 male Wistar rats, which were euthanized 6, 12, 24, 36, 48, or 60 h later. Ten sham-treated animals served as a control group. Another group of 50 animals were subjected to CLP and then supervised for 60 h. Renal apoptosis was evaluated using light and transmission electron microscopy, in situ nick-end labeling (TUNEL), and flow cytometry using 7-amino-actinomycin D (7-AAD). Caspase-mediated apoptosis was assessed using M30 antibody. The expression of the apoptosis-regulator proteins B-cell lymphoma 2 (bcl-2), bcl-2-associated x protein (bax), caspase-8, and cytochrome c was detected immunohistochemically. Results: Sepsis increased inflammatory infiltration (p < 0.001) and necrosis (p < 0.001) in renal parenchyma. Apoptosis was significantly more common than in the kidneys of control animals (p = 0.02). Nuclei stained by the TUNEL technique were predominant in the tubular cells of non-survivors (p = 0.05). The time distribution of all types of cell death was increased significantly 6 h after the induction of sepsis, and declined subsequently. Caspase-generated cytokeratin 18 (CK18) new epitope (M30) was significantly more abundant in the kidneys of animals with sepsis than in control rats, with peaks at 6 h and 60 h post-procedure (p < 0.001). In addition, cells initiating apoptosis were significantly more common at 6 h than at 48 h post-CLP (p = 0.014). Caspase-8 protein immunodetection followed the same time pattern as cell death, increasing as early as 6 h post-CLP and decreasing thereafter (p = 0.013). Bax protein expression was elevated significantly early in the course of sepsis (p = 0.037), whereas the other members of the mitochondrial-dependent pathway remained constant. Animals dying from sepsis had a significantly greater prevalence of bax- (p = 0.037) and caspase-8- (p = 0.031) immunoreactive renal cells. Conclusion: Apoptosis in renal tissue was significantly more common in animals with sepsis than in controls. The time distribution of cell death markers showed a consistent pattern, making early sepsis the likely initiator of the apoptotic events.