Dietary supplementation with coenzyme Q (CoQ) has been proposed to have anti-atherogenic effects by virtue of its antioxidant capacity, To investigate this question, the leukocyte status of 5 males and 5 females (52-68 years) was evaluated before and after supplementation with 200mg CoQ/day for 5 and 10 weeks. CoQ was selectively taken up by mononuclear cells and alpha-tocopherol increased in polynuclear and mononuclear cells, The expression of beta2-integrin CD11b and complement receptor CD35 on the plasma membrane of resting and stimulated monocytes was significantly decreased upon dietary CoQ. Fatty acid and aldehyde analysis revealed that there was a selective increase of arachidonic acid and plasmalogens in only mononuclear cells. These selective lipid changes are not consistent with a general improvement in antioxidant status and indicate that CoQ most likely inhibits a phospholipase A,. Thus. these results strongly suggest that the anti-atherogenic effects of CoQ be mediated by other mechanisms beside its antioxidant protection. (C) 2002 Elsevier Science (USA). All rights reserved.