Thiyl radicals in biosystems: inhibition of the prostaglandin metabolism by the cis–trans-isomerization of arachidonic acid double bonds

This paper describes parallel and comparative experiments on the enzymatic cyclooxygenase (COX) driven conversion of arachidonic acid (AA, all-cis-5,8,11,14-eicosatetraenoic acid) into prostaglandins by using pure arachidonic acid and AA samples containing relatively small amounts of thiyl radical induced trans-isomers. The experiments were performed in a liquid aqueous model system using COX-1 as well as by the in vitro feeding of VD3-differentiated and LPS-stimulated promyelocytic HL-60 cells using the cell’s own COX-2. In the model solution, all the different test methods used (oxygen consumption, ROS induced luminescence, and TMPD oxidation) indicated the greatly disproportionate, non-stoichiometric inhibition of the prostaglandin metabolism by the trans-isomers. Accordingly, measurements performed in the cell system gave comparable results: both luminescence ROS detection and the ELISA test on PGE2 expression resulted in the strong inhibition of the prostaglandin metabolism. We interpret these findings as enzyme blocking caused by just one mono-trans-isomerized double bond of AA.