Structure-activity relationship for toxicity of α-pyrrolidinophenones in human aortic endothelial cells

In this study, we found that exposure of 20 μM α-pyrrolidinooctanophenone (α-POP), a new synthetic cathinone, time- and dose-dependently reduced viability of human aortic endothelial (HAE) cells, and the 50% lethal concentration (LC₅₀) for α-POP in its 48-h treatment was 15.6 μM. In addition, the LC₅₀ comparison of α-POP and α-pyrrolidinoheptanophenone (α-PHPP) toxicity against ten human cells exhibited that vascular (HAE and human aortic smooth muscle) and bronchial epithelial BEAS-2B cells were more susceptible to the cytotoxicity than neuronal (SK-N-SH and A172), gastrointestinal (DLD1 and MKN45), hepatic HepG2, renal HEK293 and pulmonary A549 cells. The results suggest that abuse of the lipophilic α-pyrrolidinophenones (PPs), such as α-POP and α-PHPP, is more likely to cause damage to the vascular, respiratory and central nervous systems. Structure-activity relationship study of 18 PPs with different alkyl chain lengths and substituents revealed that the endothelial cell toxicity depends on the alkyl chain length (α-POP > α-PHPP > PPs with shorter chains), and the presence of 4′-fluoro or 3′,4′-methylenedioxy group on α-POP and α-PHPP increased the cytotoxicity. In order to understand the cytotoxic mechanism of α-POP and F-α-POP that showed the most potent toxicity, the contribution of reactive oxygen species (ROS) production, caspase-3 activation and DNA fragmentation were investigated. The treatment of HAE cells with α-POP or F-α-POP resulted in remarkable ROS production, and the ROS production and apoptotic events were significantly prevented by pretreating the cells with an antioxidant N-acetyl-l-cysteine, suggesting that ROS-dependent signaling is primarily responsible for endothelial cell apoptosis elicited by the lipophilic synthetic cathinones.