Papaverine Blocks Vasospasm but Induces ROS in Cardiac Mitochondria

Objectives: Arterial grafts are widely used in coronary bypass surgery. Because of its vasodilatory effect, papaverine is often used to prevent vasospasm. But as a matter of fact, it also causes endothelial damage. Papaverine is a potent inhibitor of mitochondrial complex I. Therefore, this study addresses its inhibitory effect, production of reactive oxygen species (ROS), and the myocardial bioenergetics status, especially in relation to the known ischemic accumulation of succinate and the respiratory status in reperfusion.

Methods: After harvesting the hearts from Wistar rats (male, weight: 250–300 g, permission EX 8-2018), mitochondria were prepared according to the standard procedures of isolation using sucrose density gradient centrifugation. Mitochondrial respiratory data and control ratios were measured by polarography in the presence of 5 mM Glutamate/5 mM Malate (G + M) or 5 mM Succinate (S), respectively. Measurements of mitochondrial ROS formation ( mol/L/min) were performed using EPR spectrometer NOXYSCAN, spin probe CMH (cyclic hydroxylamine 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine).

Results: Measurements of mitochondrial ADP- dependent respiration showed that the addition of G + M results in an O2 rate of 48.0 ± 6.1 nm/mL vs. 89.8 ± 17.5 nm/mL when S was used as a substrate (p < 0.05, respiratory control RC G + M = 3.91 vs. RC S = 2.06). Inhibitory effect was seen in case of G + M (p < 0.05), but not with S (ΔO2 G + M = 43.29 ± 6.64 nm/mL but O2 S = 86.52 ± 18.14). Moreover, respiration in the presence of Rotenone was additionally reduced by 0.5 μg/μL papaverine by up to 82.9 ± 2.6% (G + M) and 81.3 ± 2.7% (S) independent of the substrates. Supplemented Calcium (0.5, 1.0, and 2.0 μmol) also resulted in an inhibitory effect of papaverine (83.5 ± 2.5 G + M % vs. 80.63 ± 3.6 S %). In parallel, we found 207.32 μmol/L/min basic production of ROS which was stimulated by 10 μM Papaverine by up to 250.8 μmol/L/min and finally till 356.3 μmol/L/min.

Conclusion: (1) Succinate almost double the ADP dependent mitochondrial respiration and elucidate higher postischemic oxygen consumption of the heart. (2) Although Rotenone is definitively an efficient complex-I inhibitor, here its inhibitory effect was augmented by Papaverine indicating this PDE10A inhibitor must have an additional pathway. (3) Inhibitory effect of Papaverine is obvious in G + M, as well as in S stimulated respiration. (4) Even with Calcium same inhibition is found. (5) Inhibitory effect of papaverine is accompanied clearly by initial increase of ROS production.