Soy isoflavones attenuate human monocyte adhesion to endothelial cell-specific CD54 by inhibiting monocyte CD11a.Author: Nagarajan S, Stewart BW, Badger TM. Publication: J Nutr. 2006 Sep;136(9):2384-90.
Previous studies have shown that the consumption of soy and soy protein reduces serum cholesterol levels but also protects against the development of atherosclerosis. Studies show that the isoflavones genistein and daidzein inhibit platelet aggregation. Atherosclerosis starts with the interaction of activated monocytes with inflamed endothelial cells of the arteries. Monocytes contain integrin receptor CD11a which adhere to CD54 protein on endothelial cells. The exact mechanism by which soy isoflavones influence the attachment of monocytes is not known.
The aim of this study is to identify the exact mechanism for the protective action of soy isoflavones on the development of atherosclerosis. The study was carried out on female rats, which were fed with a standard diet, containing either soy protein or casein as protein source. They found that the serum from rats fed with soy protein inhibited CD54-dependent monocyte adhesion, whereas serum from rats fed with casein showed no inhibition. The researchers then tried to determine if the inhibition was caused by soy isoflavones. They used a mixture of isoflavones aglycones (genistein, daidzein and equol) which are normally present in serum and tissue of animals fed with soy. When the monocytes were first treated with soy isoflavones their adhesion to the CD54 protein was inhibited in a dose-dependant manner. The inhibition of adhesion was up to 50% at high isoflavones levels but even at physiological levels the inhibition was significant. The binding of the antibody mAb24, which binds to the active form of CD11a, was significantly reduced after treatment with soy isoflavones. This indicates that the adhesion of monocytes is partly influenced by the changed affinity CD11a. Isoflavones also caused a reduced expression of the inflammatory cytokines.
Another recent study (2006) by Friedrich et al, entitled "Beta-Estradiol Inhibits Monocytes Adhesion via Down-Regulation" showed that 17-beta-estradiol reduces the adhesion of monocytes to endothelial cells. This suggests that the soy isoflavones act by their phytoestrogenic activity. The study concluded that the anti-atherosclerosis effect of soy isoflavones is caused by inhibiting the interaction between monocytes and endothelial cells.Dietary isoflavones: biological effects and relevance to human health. J Nutr. 1999 Mar;129(3):758S-767S