Prostaglandin H synthase (PHS)‐1/2‐dependent oxidative DNA damage and cytotoxicity caused by neurotransmitters, their precursors and metabolites

PHS‐1 and PHS‐2 are implicated in neurodegeneration, but the mechanism is unclear. Neurotransmitters, their precursors and metabolites may serve as substrates for PHS‐1/2‐dependent bioactivation in the brain to free radicals that generate potentially neurotoxic reactive oxygen species ( ROS ). To assess this hypothesis, ovine PHS‐1 was incubated in vitro with DNA and dopamine ( DA ) or its precursor or metabolites. DA (p<0.05), L‐dihydroxyphenylalanine ( L‐DOPA ) (p<0.05) and dihydroxyphenylacetic acid ( DOPAC ) (p<0.05) were oPHS‐1 substrates, resulting in PHS‐dependent ROS formation that initiated DNA oxidation, quantified as 8‐oxo‐2′‐deoxyguanosine. CHO‐K1 cell lines expressing human PHS‐2 ( hPHS‐2 ) and untransformed CHO‐K1 cells were used to investigate hPHS‐2‐dependent cytotoxicity. PHS activity, quantified by the conversion of arachidonic acid ( AA ) to prostaglandin E2, was up to 40‐fold higher in hPHS‐2 cells compared to untransformed CHO‐K1 cells and activities were reduced by withholding AA (p<0.01). Cytotoxicity, measured by lactate dehydrogenase release, was higher in hPHS‐2 cells treated with DA, L‐DOPA, DOPAC or homovanillic acid versus vehicle control after a 6 hour incubation (p<0.001). AA‐activation increased hPHS‐2 cytotoxicity (p<0.05), while cytotoxicity was lower in untransformed CHO‐K1 cells (p<0.05). These results show that DA, its precursor and metabolites are substrates for PHS‐1/2‐dependent bioactivation, causing ROS‐mediated oxidative DNA damage and cytotoxicity. This mechanism may be involved in neurodegenerative changes associated with aging and drugs like amphetamines, which initiate neurotransmitter release. [Support: CIHR, CIHR/Rx&D HRF]