Free radical-dependent inhibition of prostaglandin endoperoxide H Synthase-2 by nitro-arachidonic acid.

Prostaglandin endoperoxide H synthase (PGHS) is a heme-enzyme responsible for the conversion of arachidonic acid (AA) to prostaglandin H2 (PGH2). PGHS have both oxygenase (COX) and peroxidase (POX) activities and is present in two isoforms (PGHS-1 and -2) expressed in different tissues and cell conditions. It has been reported that PGHS activity is inhibited by the nitrated form of AA, nitro-arachidonic acid (NO2AA), which in turn could be synthesized by PGHS under nitro-oxidative conditions. Specifically, NO2AA inhibits COX in PGHS-1 as well as POX in both PGHS-1 and -2, in a dose and time-dependent manner. NO2AA inhibition involves lowering the binding stability and displacing the heme group from the active site. However, the complete mechanism remains to be understood. This review describes the interactions of PGHS with NO2AA, focusing on mechanisms of inhibition and nitration. In addition, using a novel approach combining EPR-spin trapping and mass spectrometry, we described possible intermediates formed during PGHS-2 catalysis and inhibition. This literature revision as well as the results presented here strongly suggest a free radical-dependent inhibitory mechanism of PGHS-2 by NO2AA. This is of relevance towards understanding the underlying mechanism of inhibition of PGHS by NO2AA and its anti-inflammatory potential.

A facilitated approach to evaluate the inhibitor mode and potency of compounds targeting microsomal prostaglandin e synthase-1.

Microsomal prostaglandin E(2) synthase-1 (MPGES1) catalyzes the formation of prostaglandin E(2) from the endoperoxide prostaglandin H(2). MPGES1 expression is induced in inflammatory diseases, and this enzyme is regarded as a potential drug target. To aid in the drug discovery effort, a simple method for determination of inhibition mechanism and potency toward both prostaglandin H(2) and glutathione (GSH) has been developed. Using an assay with thiobarbituric acid-based detection, the inhibitory effects of six MPGES1 inhibitors were evaluated. The IC(50) values obtained at three substrate (S) concentrations ([S]K(M)) were used to estimate inhibition modality and inhibition constant values. This facilitated strategy is a useful and general screening method to evaluate the inhibitory effects of new drug compounds.

New developments on thromboxane and prostacyclin modulators part I: thromboxane modulators.

The pathogenesis of numerous cardiovascular, pulmonary, inflammatory, and thromboembolic diseases can be related to arachidonic acid (AA) metabolites. One of these bioactive metabolites of particular importance is thromboxane A(2) (TXA(2)). It is produced by the action of thromboxane synthase on the prostaglandin endoperoxide H(2)(PGH(2)), which results from the enzymatic degradation of AA by the cyclooxygenases. TXA(2) is a potent inducer of platelet aggregation, vasoconstriction and bronchoconstriction. It is involved in a series of major pathophysiological states such as asthma, myocardial ischemia, pulmonary hypertension, and thromboembolic disorders. Therefore, TXA(2) receptor antagonists, thromboxane synthase inhibitors and drugs combining both properties have been developed by several pharmaceutical companies since the early 1980s. Several compounds have been launched on the market and others are under clinical evaluation. Moreover, the recent literature reported the interest of thromboxane modulators, which combine another pharmacological activity such as, platelet activating factor antagonism, angiotensin II antagonism, or 5-lipoxygenase inhibition. In this review, we will propose a description of the recently described thromboxane modulators of major interest from both a pharmacological and a chemical point of view.