Soy isoflavones affect platelet thromboxane A2 receptor density but not plasma lipids in menopausal women

It has been suggested that isoflavones protect the cardiovascular system, in part by improving lipid profile. The purpose of the present research was to examine the effect of a 12-week soy isoflavone supplementation on lipoprotein status and platelet thromboxane A2 receptor density.

Twenty-nine healthy postmenopausal women were invited to take part in a randomised study to receive either 100 mg/day isoflavone supplement (n=15) or identical placebo capsules (n=14). Blood samples obtained at baseline and after 12 weeks were analysed for isoflavones, total cholesterol, high density lipoprotein cholesterol, triglycerides, glucose, insulin, estradiol, testosterone, gonadotrophins, sex hormone-binding globulin (SHBG) and platelet thromboxane A2 receptor density. Blood pressure measurements, body mass index, subcutaneous fat at entrance and at the end of treatment were also registered. Changes in variables between groups were compared by ANOVA for repeated measures.

Blood pressure, body mass index, subcutaneous fat, insulin, serum lipoprotein, sex hormones and SHBG did not differ among groups. However, platelet thromboxane A2 receptor density declined significantly (from 181.9+/-30.9 to 115.2+/-16.2 fmol/10(8) platelets) in the experimental group, remaining mostly unchanged in the placebo group (176.3+/-27.3 to 170.4+/-28.2 fmol/10(8) platelets). The dissociation constant (Kd) values were unchanged. The change in platelet thromboxane A2 receptors correlated negatively with isoflavones serum concentration (r=-0.59, p<0.001).

In this study we demonstrated that the beneficial effects of isoflavones in menopausal women could be more related to platelet function than to improving classical cardiovascular risk factors.