Thiyl radicals in biosystems: effects on lipid structures and metabolisms.

Thiyl radicals are intermediates of enzyme- and radical-driven biochemical processes, and their potential as reactive species in the biological environment has been somehow underestimated. From organic chemistry, however, it is known that thiyl radicals isomerize the double bonds of unsaturated fatty acids to a mixture with very dominating trans isomers. Recently, this reaction has been particularly studied for biosystems, focusing on the effect of thiyl radicals on the natural all-cis double bonds of unsaturated phospholipids, which undergo a conversion to the unnatural trans form.

Trans lipid formation induced by thiols in human monocytic leukemia cells.

Trans lipids in humans originate exogenously from the ingestion of isomerized fats. An endogenous path comprising a thiyl radical-catalyzed cis-trans isomerization of cis-unsaturated phospholipids was proposed. However, whether an isomerization process might be feasible in eukaryotic cells remained to be established.

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 VD(3)-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.