Testosterone does not eliminate the attenuating effect of estrogen on progressive glomerular injury in estrogen-treated hypercholesterolemic male Imai rats

Rat mesangial cells exhibit sex-specific profibrotic and proinflammatory phenotypes

BACKGROUND

Chronic renal disease progresses more rapidly in males compared to females. This study investigated whether there were any inherent differences between male and female mesangial cells that could contribute to this phenomenon and whether these differences could be modulated by sex hormones.

METHODS

Experiments were carried out on cultured mesangial cells derived from adult male and female Wistar rat kidneys. Fibronectin, TNFalpha and IL-1beta levels were measured in control and macrophage-conditioned medium (MCM)-injured cells in the presence and absence of 17beta estradiol or testosterone.

RESULTS

Male mesangial cells expressed higher baseline fibronectin levels compared to female cells. Similarly, basal levels of the proinflammatory cytokines TNFalpha and IL-1beta were higher in male cells. Fibronectin and IL-1beta levels were enhanced proportionately between the sexes in response to MCM stimulation, whilst the increase in TNFalpha levels was greater in MCM-stimulated female cells. Treatment with 10(-8) M estradiol down-regulated baseline fibronectin levels in female mesangial cells but had no effect on basal levels in male cells. Estradiol had no effect on MCM-stimulated fibronectin levels in female mesangial cells but further increased stimulated levels in male cells. Testosterone had no effect on basal fibronectin levels of either sex but further enhanced MCM-stimulated fibronectin levels in mesangial cells of both sexes. Sex hormone treatment had no effect on cytokine levels in male mesangial cells. However, in female cells estradiol decreased TNFalpha levels and increased IL-1beta levels, while testosterone increased the levels of both cytokines.

CONCLUSION

These data would suggest that male mesangial cells inherently exhibit greater profibrotic and proinflammatory characteristics than female cells. The inherent gender phenotypes are further modulated by sex hormones. This sexual dimorphism in mesangial cells may play a contributory role in the faster rate of progression to end-stage renal disease in males.

Isoflavones made simple - genistein's agonist activity for the beta-type estrogen receptor mediates their health benefits

Soy isoflavones, the focus of much research and controversy, are often referred to as "weak estrogens". In fact, genistein is a relatively potent agonist for the recently characterized beta isoform of the estrogen receptor (ERbeta). The low nanomolar serum concentrations of unconjugated free genistein achieved with high-nutritional intakes of soy isoflavones are near the binding affinity of genistein for this receptor, but are about an order of magnitude lower than genistein's affinity for the "classical" alpha isoform of the estrogen receptor (ERalpha). Moreover, these concentrations are far too low to inhibit tyrosine kinases or topoisomerase II, in vitro activities of genistein often cited as potential mediators of its physiological effects. The thesis that these physiological effects are in fact mediated by ERbeta activation provides a satisfying rationale for genistein's clinical activities. Hepatocytes do not express ERbeta; this explains why soy isoflavones, unlike oral estrogen, neither modify serum lipids nor provoke the prothrombotic effects associated with increased risk for thromboembolic disorders. The lack of uterotrophic activity of soy isoflavones reflects the fact that ERalpha is the exclusive mediator of estrogen's impact in this regard. Vascular endothelium expresses both ERalpha and ERbeta, each of which has the potential to induce and activate nitric oxide synthase; this may account for the favorable influence of soy isoflavones on endothelial function in postmenopausal women and ovariectomized rats. The ERbeta expressed in osteoblasts may mediate the reported beneficial impact of soy isoflavones on bone metabolism. Suggestive evidence that soy-rich diets decrease prostate cancer risk, accords well with the observation that ERbeta appears to play an antiproliferative role in healthy prostate. In the breast, ERalpha promotes epithelial proliferation, whereas ERbeta has a restraining influence in this regard - consistent with the emerging view that soy isoflavones do not increase breast cancer risk, and possibly may diminish it. Premenopausal women enjoy a relative protection from kidney failure; since ERbeta is an antagonist of TGF-beta signaling in mesangial cells, soy isoflavones may have nephroprotective potential. Estrogen also appears to protect women from left ventricular hypertrophy, and recent evidence suggests that this effect is mediated by ERbeta. In conjunction with reports that isoflavones may have a modestly beneficial impact on menopausal symptoms - perhaps reflecting the presence of ERbeta in the hypothalamus - these considerations suggest that soy isoflavone regimens of sufficient potency may represent a safe and moderately effective alternative to HRT in postmenopausal women. Further clinical research is required to characterize the impact of optimal genistein intakes on endothelial and bone function in men. Studies with ERbeta-knockout mice could be helpful for clarifying whether ERbeta does indeed mediate the chief physiological effects of low nanomolar genistein. S-equol, a bacterial metabolite of daidzein, has an affinity for ERbeta nearly as high as that of genistein; whether this compound contributes meaningfully to the physiological efficacy of soy isoflavones in some individuals is still unclear.