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Poly(ADP-ribose) polymerase (PARP EC 2.4.2.30) is a key enzyme in the DNA repair machinery, but its excessive stimulation during reperfusion after ischemia could play a critical role in cell death. Our previous study indicated that the PARP inhibitor 3-aminobenzamide (3-AB) significantly protected neuronal cells against death after a short ischemic insult. In this study we investigated the effect of 3-AB on the ischemia-evoked alterations in intracellular organelles. Gerbils were submitted to 3 min of transient forebrain ischemia followed by reinstitution of recirculation for 1-7 days. Electron microscopy showed only the signs of necrotic cell death after ischemia-reperfusion. The examination of specimens revealed a pronounced protective effect of 3-AB on the swelling of astrocytes and neurons 1 day after the ischemic insult. 3-AB also decreased the swelling of pericytes, but it had no effect on the accumulation of osmiophilic inclusions and fibril formation in astrocytes. 3-AB decreased the ischemia-induced swelling of mitochondria. The protective effects of 3-AB on cellular ultrastructure were also observed 7 days after reperfusion. These findings indicate that the inhibition of PARP may have a protective effect on cell swelling and on the state of intracellular organelles after a short-term ischemic episode.
 1-methylnicotinamide (MNA) is a primary metabolite of nicotinamide. In recent years several activities of MNA have been described, such as anti-inflammatory activity in skin diseases, induction of prostacyclin synthesis via COX-2, aortal endothelium protection in diabetes and hypertriglyceridaemia and increased survival rate of diabetic rats. 1-methylnicotinamide was also suggested to protect pancreatic cells from streptozotocin in vivo. Streptozotocin toxicity is known to be mediated by poly-ADP-ribose polymerase. Nicotinamide and its derivatives have been shown to ameliorate poly-ADP-ribose polymerase-dependent nucleotide pool reduction. We aimed to verify if 1-methylnicotinamide and its metabolite, N-methyl-2-pyridone-5-carboxamide, can protect insulinoma cells from streptozotocin-induced toxicity. We found that N-methyl-2-pyridone-5-carboxamide, but not 1-methylnicotinamide, restores the pool of ATP and NAD+ in streptozotocin-treated cells, but neither compound improved the cell viability. We conclude that inhibition of poly-ADP-ribose polymerase-dependent nucleotide pool reduction may not be sufficient to protect cells from streptozotocin toxicity.
Poly(ADP-ribose) polymerase (PARP) is a conserved enzyme involved in the regulation of DNA repair and genome stability. The role of PARP during aging is not well known. In this study PARP activity was investigated in nuclear fractions from hippocampus, cerebellum, and cerebral cortex of adult (4 months), old adult (14 months) and aged (24-27 months) rats. Concomitantly, the free radical evoked lipid peroxidation was estimated as thiobarbituric acid reactive substances (TBARS). The specific activity of PARP in adult brain was about 25, 21 and 16 pmol/mg protein per min in hippocampus, cerebellum and cerebral cortex, respectively. The enzyme activity was higher in all investigated parts of the brain of old adults. In aged animals PARP activity was lower in hippocampus by about 50%, and was unchanged in cerebral cortex and in cerebellum comparing to adult rats. The concentration of TBARS was the same in all parts of the brain and remained unchanged during aging. There is no direct correlation between PARP activity and free radical evoked lipid peroxidation during brain aging. The lowered enzyme activity in aged hippocampus may decrease DNA repair capacity which subsequently may be responsible for the higher vulnerability of hippocampal neurons to different toxic insults.
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