Fisetin attenuates oxidative and haemolytic damage induced by quinuclidine derivatives in human erythrocytes.

Quinuclidine derivatives are potent bioactive compounds investigated as cholinesterase inhibitors with potential intravenous therapeutic application. However, the cytotoxic properties of some, particularly those linked to oxidative stress, pose significant safety concerns. This study aimed to evaluate if flavonoid fisetin could protect cells from such toxic effects. Erythrocytes were chosen due to high susceptibility to reactive oxygen species (ROS) and well-characterised endogenous antioxidant system, making them a sensitive and physiologically relevant model. Over 24 h, human erythrocytes were exposed to QOH-C12-16 or QNOH-C12-16 derivatives to establish their 25, 50, and 75 % inhibitory concentrations (IC25, IC50, and IC75, respectively). As the compounds with the C12 side alkyl chain showed no significant haemolytic effects, they were excluded from further experimentation. In the next steps, we assessed the protective effects of fisetin (1, 10, 100 μmol/L) against quinuclidine-induced haemolysis over 24 h and against reactive oxygen species (ROS) generation and potential glutathione (GSH) and superoxide dismutase (SOD) depletion over 4 h. Fisetin at 10 and 100 μmol/L significantly reduced ROS to near-control levels, restored SOD activity, and decreased haemolysis by 10-40 %, most effectively in cells exposed to quinuclidines at IC50. However, GSH measurements in combined treatment were not reliable, as fisetin exhibited autofluorescence, but single quinuclidine exposure showed no significant effects on GSH levels. In summary, fisetin showed a promising potential to make quinuclidine intravenous therapies safer.