DNA fragmentation reduced by antioxidants following ischaemia-reperfusion in the isolated perfused rat kidney

The role of oxygen-derived free radicals (OFR) in modifying structure and function after ischaemia-reperfusion (IR) injury was studied in isolated perfused rat kidneys (IPRK). Control kidneys were studied after 20 min of ischaemia followed by 15 or 60 min of reperfusion. The xanthine oxidase inhibitor allopurinol and the hydroxyl radical scavenger dimethylthiourea (DMTU) were used to prevent OFR-related damage. Morphological injury was assessed in cortex, inner and outer medulla and compared with indices of global renal function (inulin clearance, fractional sodium excretion and renal vascular resistance). Apoptosis was assessed using both morphological criteria and in situ end-labelling (ISEL) to identify DNA fragmentation. Tubular damage, as evidenced by cellular blebbing, tubular cast formation, epithelial necrosis, and occasional apoptosis, was greatest in the straight proximal tubule and thick ascending limb (TAL) in the outer zone of the outer medulla. Pretreatment with allopurinol or DMTU did not significantly improve renal function. However, structural damage and luminal debris were diminished in allopurinol- and DMTU-treated kidneys. These changes may lead to functional improvement after more prolonged reperfusion. In situ end-labelling was more frequent in distal tubular epithelial cells after IR than either morphological evidence of apoptosis or necrosis. Decreased ISEL was observed after pretreatment with both allopurinol and DMTU. The data demonstrate that OFR produce DNA damage after IR, increasing ISEL. This probably represents reversible DNA damage rather than incipient apoptosis. Thus, antioxidants reduce or prevent DNA and cellular injury after IR and may reduce functional impairment after prolonged reperfusion.