Endothelium, 11:211–220, 2004 Copyright c  Taylor & Francis Inc. ISSN: 1062-3329 print / 1029-2373 online DOI: 10.1080/10623320490512435 Modulation of Nitric Oxide and 6-keto-Prostaglandin F 1α Production in Bovine Aortic Endothelial Cells by Conjugated Linoleic Acid Paul M. Coen, Philip M. Cummins, Yvonne A. Birney, Rosaleen Devery, and Paul A. Cahill Vascular Health Research Centre, School of Biotechnology, Faculty of Science and Health, Dublin City University, Glasnevin, Dublin, Ireland Conjugated linoleic acid (CLA) refers to a group of polyunsatu- rated fatty acids that exist as positional (18:2) and stereo (cis/trans) isomers of conjugated dienoic octadecadienoate. Reports consis- tently indicate that CLA may inhibit both the onset and progression of atherosclerosis, via an as yet unknown mechanism(s). In an effort to identify the putative biochemical effects of CLA on bovine aortic endothelial cells (BAECs), the authors examined both the temporal and dose-dependent effects of a commercial CLA isomeric mixture on the expression and enzymatic function of endothelial nitric oxide synthase (eNOS) and cyclooxygenase-I/II (COX-I/II) in these cells. Initial investigations indicated that CLA mix (0 to 10 μg/mL, 0 to 24 h) failed to regulate either the expression or activity of eNOS in BAECs under basal conditions. Pretreatment of BAECs with CLA mix (10 μg/mL) for either 3 or 24 h, followed by incubation with 5 μM bradykinin (BK) for 3 h, however, increased BK-stimulated nitrite release by 2.4 ± 0.6- and 3.0 ± 0.4-fold, respectively, more than control cells (BK-stimulation without CLA pretreatment). Under basal conditions, CLA mix (10 μg/mL, 0 to 24 h) had no significant effect on either COX-I or COX-II expression, genes that could be readily induced in response to hemodynamic stim- uli. CLA could, however, significantly attenuate BAEC release of 6-keto-prostaglandin F 1α (6k-PGF 1α ), a stable breakdown prod- uct of prostaglandin I 2 (PGI 2 ) within the cyclooxygenase pathway, in a dose- and time-dependent manner. In conclusion, therefore, the results suggest that CLA may potentiate agonist-stimulated eNOS activation whilst attenuating COX-dependent PGI 2 synthe- sis in BAECs. This ability to increase agonist-stimulated nitric ox- ide (NO) levels, whilst reducing production of inflammatory me- diators within vascular ECs, supports a putative atheroprotective role for CLA and provides an important biochemical insight into Received 16 January 2004; accepted 29 May 2004. The authors gratefully acknowledge the generous financial sup- port of the Dublin City University Educational Trust (Coen/Cummins), Health Research Board of Ireland (Cummins), and the Wellcome Trust (Birney/Cahill). Address correspondence to Philip M. Cummins, PhD, Vascular Health Research Centre, Faculty of Science and Health, Dublin City University, Glasnevin, Dublin 9, Ireland. E-mail: phil.cummins@dcu.ie its purported ability to modulate endothelium-mediated vascular homeostasis. Keywords Conjugated Linoleic Acid, Cyclooxygenase, Endothelial, Nitric Oxide, Prostaglandin Central to the maintenance of vascular homeostasis is the en- dothelial cell (EC) monolayer or endothelium, which constitutes a dynamic interface between the vessel wall and bloodstream, maintaining vascular homeostatic mechanisms. ECs exert pro- found paracrine and endocrine actions through their influence on the underlying smooth muscle cells, or on circulating blood elements such as platelets and white blood cells (Diodati et al. 1998). Under basal conditions, ECs are intimately involved in maintaining the nonthrombogenic blood/tissue interface by reg- ulating platelet adherence, thrombosis, and thrombolysis. In re- sponse to chemical (i.e., thrombin, brady kinin (BK), acetyl- choline, dietary constituents, etc.) and mechanical (i.e., shear stress, cyclic strain) stimuli, they produce and release a variety of vasoactive substances such as prostacyclins and nitric oix- ide (NO) (Sumpio 1991; Davies et al. 1992; Cahill et al. 2001), both of which inhibit platelet aggregation and attenuate vas- cular tone. As a consequence, discordant stimulation of ECs and/or endothelial dysfunction are key events in many vascular pathologies such as atherosclerosis and hypertension (Drexler and Zeiher 1991; Zeiher et al. 1991; Drexler 1999). Conjugated linoleic acid (CLA) refers to a group of polyun- saturated fatty acids that exist as positional (18:2) and stereo (cis/trans) isomers of conjugated dienoic octadecadienoate. CLA is found in foods such as beef and lamb, as well as dairy foods derived from these ruminant sources (Ma et al. 1999). Trace quantities have also been found in seafood and vegetable oils. Recent surveys indicate that total dietary CLA intake is re- ported to range from 151 and 212 mg/day for women and men, 211