Selective poly(ADP-ribose)-polymerase inhibition affects neither DNA repair nor cell senescence after ischemia-reperfusion

Background

Poly(ADP-ribose)-polymerase (PARP) inhibition has been beneficial in different models (sepsis, ischemia-reperfusion [I/R], hemorrhage) where oxidative stress induced DNA damage and subsequent PARP activation plays an important role. The effect of PARP inhibition on DNA repair in this context, however, is unknown. We therefore tested the effect of the selective PARP-1 blocker INO-1001 on DNA repair and cell senescence in a porcine model of thoracic aortic cross-clamping.

Materials and methods

After instrumentation, anesthetized and mechanically ventilated pigs received vehicle (n = 9) or INO-1001 (n = 9, 2 mg/kg each before clamping and during reperfusion, respectively). Norepinephrine (NE) was infused after declamping as required to maintain mean arterial pressure ≥ 80% of the preclamping level. Hemodynamic and metabolic data were recorded before clamping as well as prior to and 2 and 4 hours after declamping. The effect of INO-1001 on DNA damage and repair (single-cell gel electrophoresis, 'comet assay') was evaluated ex vivo in isolated lymphocytes (Ficoll gradient) that were sampled immediately before clamping, subsequently exposed to 4 bar of 100% O₂ in a hyperbaric chamber (HBO) for 2 hours and analyzed before as well as immediately 1 and 2 hours after HBO. Surgery and I/R-related DNA damage in vivo was assessed in whole blood samples taken before surgery, before clamping, and before and 2 hours after declamping. At the end of the experiment the spinal cord, gut, liver, and kidney tissue specimens were sampled for immonuhistochemistry of cyclin-dependent kinase inhibitor (p21 and p27) gene expression as a measure of cell senescence. Data are median (minimum–maximum).

Results

Significantly shorter NE infusion time (53 [23–93] vs 70 [41–83] min, P = 0.042) with reduced total NE doses (12 [6–19] vs 22 [9–38] μg/kg, P = 0.034) were needed for hemodynamic management in the INO-1001-treated animals. The time course of both the HBO-induced and surgery and I/R-related oxidative DNA damage was identical in the two groups. There were no differences in p21 and p27 expression, either.

Conclusion

The markedly reduced NE infusion time and dose needed for post-I/R hemodynamic stabilization confirm the well-known positive inotropic effect of selective PARP-1 blockers [1]. INO-1001 proved to be safe with respect to DNA repair and cell senescence.