Rats, bred to suffer from high blood pressure (hypertension), were found to benefit from dietary supplementation of genistein, with restoration of levels of endothelial nitric oxide synthase (eNOS), an enzyme linked to improved synthesis of nitric oxide (NO) and better vascular health, reports the study in the Journal of Nutrition .
"Our data suggest that genistein has direct genomic effects on the vascular wall that are unrelated to its known actions, leading to increased eNOS expression and NO synthesis, thereby improving hypertension," wrote Hongwei Si and Dongmin Liu from Virginia Polytechnic Institute and State University.
High blood pressure (hypertension),defined as having a systolic and diastolic blood pressure (BP) greater than 140 and 90 mmHg, is a major risk factor for cardiovascular disease (CVD) - a disease that causes almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169bn ($202bn) per year.
Si and Liu tested genistein in both human cells - primary human aortic EC (HAEC) and human umbilical vein EC (HUVEC) - and in spontaneously hypertensive rats.
The researchers report that the isoflavone enhanced the expression of eNOS by 1.8 to 2.6-fold of control, and the subsequent synthesis of NO in both HAEC and HUVEC when used in doses between one and 10 micromoles per litre.
These concentrations are "physiologically achievable concentrations in individuals consuming soy products," they said.
Nitric oxide (NO) is a molecule used by the endothelium (cells lining the surface of blood vessels) to signal surrounding muscle to relax, leading to a reduction in blood pressure, reduced blood clotting and protection against myocardial infarction and strokes.
Interestingly, the effects were not achieved by activating oestrogen signalling, a result that challenges previous results that suggested a role for oestrogen to act directly to enhance NO synthesis in vascular endothelial cells (EC).
Isoflavones are well known phytoestrogens - active substances derived from plants that have a weak oestrogen-like action.
When the rats were supplemented with genistein, the researchers observed a restoration of eNOS levels in the aorta, in addition to improvements in aortic wall thickness.
The hypertension of the animals was eased, wrote Si and Liu.
The research adds and expands the science linking isoflavones to improvements in cardiovascular health.
Previously, studies have reported improvements in blood cholesterol levels, and easing blood clotting.
However, the link between soy and cholesterol is controversial and a recent scientific statement by the American Heart Association (AHA) in the journal Circulation concluded that soy had little effect on cholesterol levels, and raised doubts about health claims associated with soy. Source: Journal of Nutrition February 2008, Volume 138, Pages 297-304 "Genistein, a Soy Phytoestrogen, Upregulates the Expression of Human Endothelial Nitric Oxide Synthase and Lowers Blood Pressure in Spontaneously Hypertensive Rats" Authors: Hongwei Si and Dongmin Liu