The phytoestrogen biochaninA weakens acute cardiac allograft rejection without affecting the reproductive system

Since the two estrogen receptor isoforms ERalpha and ERbeta have been discovered it is unclear by which receptor immunomodulating or feminizing effects are mediated. In this study, the effects of the two selective ERalpha- and ERbeta-agonists ethinylestradiol and biochaninA, respectively, on acute cardiac allograft rejection, uterus growth, vascular adhesion molecule and MHC-II expression were investigated and verified using in vitro cell culture.

Heterotopic Lewis to ovarectomized F344 cardiac transplantations were performed. The study groups received supplemental biochaninA or ethinylestradiol, the control group received no treatment. Grafts and uteri were harvested on the fifth postoperative day and blood was taken for hormone plasma level quantifications. Purified Lewis aortic endothelial cell cultures were pre-treated with biochaninA or ethinylestradiol and stimulated with TNF-alpha or IFN-gamma for quantification of ICAM-1/VCAM-1 and MHC-II expression. Endothelium-lymphocyte adhesion assays were performed using purified F344 lymphocytes.

Both biochaninA and ethinylestradiol treatment significantly reduced graft mononuclear infiltration of CD8(+) and ED1(+) cells and markedly reduced ISHLT grading compared to untreated controls. Either agent significantly inhibited lymphocyte adhesion, endothelial VCAM-1 upregulation during graft rejection and during TNF-alpha-stimulation in vitro, whereas no effect was observed for ICAM-1 upregulation. BiochaninA but not ethinylestradiol significantly reduced endothelial MHC-II upregulation in vivo and in vitro. Only ethinylestradiol treatment strongly affected uterus growth in ovarectomized recipients.

Only the treatment with the phytoestrogen biochaninA reduced endothelial MHC-II expression in vivo and in vitro and weakened allograft rejection without affecting the reproductive system. Supplemental phytoestrogens may therefore provide further benefits in the clinical setting.