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ARS Home » Southeast Area » Little Rock, Arkansas » Arkansas Children's Nutrition Center » Research » Publications at this Location » Publication #208445

Title: Soy Isoflavones Attenuate Human Monocyte Adhesion to Endothelial Cell–Specific CD54 by Inhibiting Monocyte CD11a1


Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2006
Publication Date: 9/1/2006
Citation: Nagarajan, S., Stewart, B.W., Badger, T.M. 2006. Soy isoflavones attenuate human monocyte adhesion to endothelial cell–specific CD54 by inhibiting monocyte CD11a1. Journal of Nutrition. 136(9):2384-2390.

Interpretive Summary: Heart attacks are caused by reduced blood flow to the heart, caused by thickening of blood vessels. Recent studies have shown that soy diets prevent thickening of blood vessels. However, we do not know how soy diet does this? Thickening of blood vessels is due to the attachment of blood cells to blood vessels. The attachment is controlled by a group of proteins called cell adhesion molecules. We studied whether the phytochemicals present in soy diet block the contact between these cells. The results from this study suggest that dietary soy protects the thickening of blood vessels by blocking blood cell and blood vessel cell contact. Collectively, our results suggest that soy-based diet prevents cellular interactions attributed to early development of atherosclerosis. Future studies will determine what factors in soy can cause these effects and whether there are permanent effects of early soy consumption, such as in people who were fed soy formula as infants.

Technical Abstract: Soy-based diets have been shown to protect against the development of atherosclerosis; however, the underlying mechanism(s) remain unknown. Interaction between activated monocytes and inflamed endothelial cells is an early event in atherogenesis. Therefore, we examined whether treatment of monocytes with soy phytochemicals could inhibit their adhesion to the endothelial cell–specific protein, CD54, a key factor in monocyte adhesion. Female Sprague-Dawley rats were fed AIN-93G diets containing soy protein isolate or casein. Sera from soy-fed rats inhibited CD54-dependent monocyte adhesion, whereas sera from casein-fed rats did not. To determine whether isoflavones in the sera of soy-fed rats were involved in this inhibition, monocytes were preincubated with soy isoflavones. Isoflavone treatment inhibited monocyte adhesion to CD54 protein, as well as to endothelial cells expressing CD54. Monocyte expression of CD11a, the cognate receptor for CD54, was unaffected by isoflavones. However, binding of the activation epitope–specific antibody mAb24, which binds specifically to the active form of CD11a, was significantly lower in soy isoflavone–treated monocytes than in media-treated cells. These findings suggest that inhibition of CD54-dependent monocyte adhesion by soy isoflavones is mediated in part by affinity regulation of CD11a. Inhibition of monocyte adhesion to endothelial cells by isoflavones resulted in reduced expression of the inflammatory cytokines IL-6 and IL-8. Collectively, these data suggest that the athero-protective effect of soy diets may be mediated by blocking monocyte-endothelial cell interaction.