Lauren Nathan

Testosterone inhibits early atherogenesis by conversion to estradiol: Critical role of aromatase

The effects of testosterone on early atherogenesis and the role of aromatase, an enzyme that converts testosterone to estrogens, were assessed in low density lipoprotein receptor-deficient male mice fed a Western diet. Castration of male mice increased the extent of fatty streak lesion formation in the aortic origin compared with testes-intact animals. Administration of anastrazole, a selective aromatase inhibitor, to testes-intact males increased lesion formation to the same extent as that observed with orchidectomized animals. Testosterone supplementation of orchidectomized animals reduced lesion formation when compared with orchidectomized animals receiving the placebo. This attenuating effect of testosterone was not observed when the animals were treated simultaneously with the aromatase inhibitor. The beneficial effects of testosterone on early atherogenesis were not explained by changes in lipid levels. Estradiol administration to orchidectomized males attenuated lesion formation to the same extent as testosterone administration. Aromatase was expressed in the aorta of these animals as assessed by reverse transcription–PCR and immunohistochemistry. These results indicate that testosterone attenuates early atherogenesis most likely by being converted to estrogens by the enzyme aromatase expressed in the vessel wall.

Insulin Sensitivity and Insulin Secretion Determined by Homeostasis Model Assessment and Risk of Diabetes in a Multiethnic Cohort of Women: The Women's Health Initiative Observational Study

OBJECTIVE— The homeostasis model assessment (HOMA), based on plasma levels of fasting glucose and insulin, has been widely validated and applied for quantifying insulin resistance and β-cell function. However, prospective data regarding its relation to diabetes risk in ethnically diverse populations are limited. RESEARCH DESIGN AND METHODS— Among 82,069 women who were aged 50–79 years, free of cardiovascular disease or diabetes, and participating in the Womens Health Initiative Observational Study, we conducted a nested case-control study to prospectively examine the relations of HOMA of insulin resistance (HOMA-IR) and β-cell function (HOMA-B) with diabetes risk. During a median follow-up period of 5.9 years, 1,584 diabetic patients were matched with 2,198 control subjects by age, ethnicity, clinical center, time of blood draw, and follow-up time. RESULTS— Baseline levels of fasting glucose, insulin, and HOMA-IR were each significantly higher among case compared with control subjects, while HOMA-B was lower (all P values <0.0001). After adjustment for matching factors and diabetes risk factors, all four markers were significantly associated with diabetes risk; the estimated relative risks per SD increment were 3.54 (95% CI 3.02–4.13) for fasting glucose, 2.25 (1.99–2.54) for fasting insulin, 3.40 (2.95–3.92) for HOMA-IR, and 0.57(0.51–0.63) for HOMA-B. While no statistically significant multiplicative interactions were observed between these markers and ethnicity, the associations of both HOMA-IR and HOMA-B with diabetes risk remained significant and robust in each ethnic group, including whites, blacks, Hispanics, and Asians/Pacific Islanders. When evaluated jointly, the relations of HOMA-IR and HOMA-B with diabetes risk appeared to be independent and additive. HOMA-IR was more strongly associated with an increased risk than were other markers after we excluded those with fasting glucose ≥126 mg/dl at baseline. CONCLUSIONS— High HOMA-IR and low HOMA-B were independently and consistently associated with an increased diabetes risk in a multiethnic cohort of U.S. postmenopausal women. These data suggest the value of HOMA indexes for diabetes risk in epidemiologic studies.

Estradiol Inhibits Leukocyte Adhesion and Transendothelial Migration in Rabbits In Vivo: Possible Mechanisms for Gender Differences in Atherosclerosis

The mechanism by which estrogens protect against atherosclerosis is not known. We evaluated in vivo whether there is a gender difference in monocyte adhesion and subendothelial migration in hypercholesterolemic rabbits and whether any gender differences observed are due to estradiol. Monocyte adhesion and subendothelial migration were assessed in a blinded fashion by analyzing a standardized segment of aorta using a scanning electron microscope. We also assessed whether estradiol modulates induction of vascular cell adhesion molecule-1 (VCAM-1) protein using Western blot and flow cytometric analyses. We observed that male rabbits develop more monocyte adhesion and subendothelial migration than do female rabbits during hypercholesterolemia. We also observed that oophorectomized rabbits given physiological estradiol supplementation demonstrate fewer adherent and subendothelial monocytes than do oophorectomized rabbits given placebo. VCAM-1 protein expression was increased in aortae obtained from hypercholesterolemic, oophorectomized animals supplemented with placebo, and this increase was attenuated by estradiol. Finally, in cultured rabbit aortic endothelial cells stimulated with lysophosphatidylcholine, we observed an increase in VCAM-1 protein that was inhibited in a concentration-dependent fashion by estradiol. We have demonstrated in vivo that there is a gender difference in monocyte adhesion to endothelial cells and transendothelial migration after hypercholesterolemia and that this gender difference is due in part to estradiol. Our results also suggest that estradiol inhibits monocyte adhesion by inhibiting expression of VCAM-1.

Testosterone attenuates expression of vascular cell adhesion molecule-1 by conversion to estradiol by aromatase in endothelial cells: Implications in atherosclerosis

We previously reported that testosterone attenuated atherogenesis in LDLR−/− male mice, and that this effect of testosterone was most likely caused by its conversion to estradiol. Estradiol inhibits vascular cell adhesion molecule-1 (VCAM-1) expression, and expression of VCAM-1 is one of the early events in atherogenesis. We assessed the cellular mechanism(s) involved by which testosterone attenuates atherogenesis. We evaluated whether testosterone inhibited TNFα-induced VCAM-1 expression via its conversion to estradiol by the enzyme aromatase in human umbilical vein endothelial cells (HUVEC). Aromatase mRNA was dedected by reverse transcription–PCR in these cells. Testosterone (30 nM–1 μM) attenuated VCAM-1 mRNA expression in a concentration-dependent manner. The non aromatizable androgen, dihydrotestosterone, had no effect on VCAM-1 mRNA expression. Testosterone was less effective in attenuating VCAM-1 expression in the presence of anastrozole, an inhibitor of aromatase, indicating that testosterone inhibited VCAM-1 via conversion to estradiol. Estradiol also attenuated VCAM-1 mRNA expression, but this action was not abolished in the presence of anastrozole, indicating that anastrozole itself did not modulate VCAM-1 mRNA expression. The effect of testosterone on VCAM-1 mRNA expression was inhibited in the presence of the estrogen receptor antagonist, ICI-182780. Testosterone also attenuated TNFα-induced VCAM-1 protein expression, and this attenuation was abolished in the presence of anastrozole. In conclusion, testosterone inhibited VCAM-1 mRNA and protein expression in HUVEC by its conversion to estradiol via the enzyme aromatase present in the endothelial cells. Results from our study may help explain the mechanism by which testosterone may have beneficial effects on the cardiovascular system.

Estradiol Suppresses MCP-1 Expression In Vivo Implications for Atherosclerosis

The mechanisms by which 17beta-estradiol retards atherogenesis are not known. The adhesion of monocytes to endothelial cells followed by the migration of monocytes into the artery wall are key cellular events that occur throughout the entire atherogenic process and may be responsive to estradiol. Monocyte chemoattractant protein-1 (MCP-1), a chemokine that is expressed in atherosclerotic lesions, is thought to play a major role in stimulating the migration of blood monocytes into developing atherosclerotic lesions. We therefore assessed the effects of estradiol in vivo on MCP-1 protein and mRNA expression in the descending thoracic aorta of rabbits fed a cholesterol-enriched (0.5%) diet for 6 weeks and in animals fed normal chow. MCP-1 protein was quantified by Western blot analysis and monocyte chemotaxis bioassay, and reverse transcription-polymerase chain reaction was used to ascertain the level of MCP-1 mRNA expression. We observed that in both ovary-intact and ovariectomized (OVX) animals, MCP-1 protein and mRNA expression were significantly increased by 6 weeks in animals fed a high-cholesterol diet. The cholesterol-induced increase in MCP-1 protein and mRNA expression was significantly attenuated in OVX rabbits supplemented with estradiol pellets (1.5- and 10.0-mg 60-day-release pellets), which yielded a range of estradiol concentrations encompassing the physiological levels. MCP-1 protein and mRNA expression were increased in normocholesterolemic OVX rabbits compared with normocholesterolemic ovary-intact animals, and this increase was prevented in OVX animals supplemented with estradiol pellets. Our observations indicate that both basal and hypercholesterolemia-induced increases in MCP-1 protein are modulated by physiological concentrations of estradiol.

Relations of Dietary Magnesium Intake to Biomarkers of Inflammation and Endothelial Dysfunction in an Ethnically Diverse Cohort of Postmenopausal Women

OBJECTIVE Although magnesium may favorably affect metabolic outcomes, few studies have investigated the role of magnesium intake in systemic inflammation and endothelial dysfunction in humans. RESEARCH DESIGN AND METHODS Among 3,713 postmenopausal women aged 50–79 years in the Womens Health Initiative Observational Study and free of cardiovascular disease, cancer, and diabetes at baseline, we measured plasma concentrations of high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), turnor necrosis factor-α receptor 2 (TNF-α-R2), soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), and E-selectin. Magnesium intake was assessed using a semiquantitative food frequency questionnaire. RESULTS After adjustment for age, ethnicity, clinical center, time of blood draw, smoking, alcohol, physical activity, energy intake, BMI, and diabetes status, magnesium intake was inversely associated with hs-CRP (P for linear trend = 0.003), IL-6 (P < 0.0001), TNF-α-R2 (P = 0.0006), and sVCAM-1 (P = 0.06). Similar findings remained after further adjustment for dietary fiber, fruit, vegetables, folate, and saturated and trans fat intake. Multivariable-adjusted geometric means across increasing quintiles of magnesium intake were 3.08, 2.63, 2.31, 2.53, and 2.16 mg/l for hs-CRP (P = 0.005); 2.91, 2.63, 2.45, 2.27, and 2.26 pg/ml for IL-6 (P = 0.0005); and 707, 681, 673, 671, and 656 ng/ml for sVCAM-1 (P = 0.04). An increase of 100 mg/day magnesium was inversely associated with hs-CRP (−0.23 mg/l ± 0.07; P = 0.002), IL-6 (−0.14 ± 0.05 pg/ml; P = 0.004), TNF-α-R2 (−0.04 ± 0.02 pg/ml; P = 0.06), and sVCAM-1 (−0.04 ± 0.02 ng/ml; P = 0.07). No significant ethnic differences were observed. CONCLUSIONS High magnesium intake is associated with lower concentrations of certain markers of systemic inflammation and endothelial dysfunction in postmenopausal women.

The role of nitric oxide in the altered vascular reactivity of pregnancy in the rat

1 Pregnancy is characterized by a decrease in systemic vascular resistance and a blunting of the angiotensin II (AII) pressor response. We studied the role of nitric oxide (NO) and prostanoids in these vascular changes of pregnancy in anaesthesized, ganglion blocked non‐pregnant and pregnant rats. 2 Inhibition of NO synthesis with NG‐nitro‐l‐arginine methyl ester (l‐NAME) led to an increase in mean arterial pressure (MAP) which was of a significantly greater magnitude in pregnant rats in late gestation than in non‐pregnant rats, or rats in mid‐gestation. 3 The pressor response to varying doses of AII was attenuated during late pregnancy, and this attenuation was partially reversed by l‐NAME. 4 The pressor response to varying doses of a vasocontrictor, phenylephrine (PE), was also attenuated in late pregnancy. However, this attenuation was not reversed by l‐NAME. 5 Inhibition of prostanoid biosynthesis with meclofenamate did not alter basal MAP, nor the pressor response to varying doses of AII or PE in pregnant and non‐pregnant animals. 6 It is concluded that (a) increased NO synthesis occurs during late gestation and contributes both to the decrease in systemic vascular resistance, as well as the blunting of the pressor response to AII during pregnancy, and (b) prostaglandins are not important in the maintenance of basal vascular tone, or the blunting of the pressor response to AII during pregnancy.

FTO Polymorphisms Are Associated With Obesity but Not Diabetes Risk in Postmenopausal Women

The FTO gene was recently identified as a susceptibility locus for both obesity and type 2 diabetes by whole‐genome association analyses of several European populations. We tested for an association between FTO risk alleles and obesity and diabetes in a well‐characterized multiethnic cohort of postmenopausal women in the United States. We genotyped two most significantly associated single‐nucleotide polymorphisms (SNPs) (rs9939609 and rs8050136) in intron 1 of FTO gene in a nested case‐control study of 1,517 diabetes cases and 2,123 controls from the Womens Health Initiative‐Observational Study (WHI‐OS). The allelic frequencies of either rs9939609 or rs8050136 differed widely across four ethnic groups. The frequency of the rare allele A of rs9939609 among controls was much lower in Asians/Pacific Islanders (17%) than in blacks (45%), whites (40%), and Hispanics (31%). We found significant associations of rs9939609 with BMI and waist circumference in white and Hispanic women, but not among black and Asian/Pacific Islander women. On average, each copy of the risk‐allele A at rs9939609 was significantly associated with 0.45 kg/m2 increase in BMI (95% confidence interval (CI): 0.16–0.74; P = 0.004) and 0.97 cm increase in waist circumference (95% CI: 0.21–0.65; P = 0.0002). Similar results were observed for rs8050136. However, we found no significant genetic associations with diabetes risk, either within the full study sample or in any ethnic group. In conclusion, common genetic variants in the intron 1 of FTO gene may confer a modest susceptibility to obesity in an ethnicity‐specific manner, but may be unlikely to contribute to a clinically significant diabetes risk.

17-epiestriol, an estrogen metabolite, is more potent than estradiol in inhibiting vascular cell adhesion molecule 1 (VCAM-1) mRNA expression.

17-β estradiol (17-β E2) attenuates the expression of vascular cell adhesion molecule 1 (VCAM-1)in vivo at physiological levels (pg/ml), whereas supraphysiological concentrations of 17-β E2 (ng/ml) are required in vitro. We assessed whether a metabolite of estrogen, which could only be generated in vivo, might be a more potent inhibitor of VCAM-1 expression and thereby explain this discrepancy. We report here that 17-epiestriol, an estrogen metabolite and a selective estrogen receptor (ER) β agonist, is ∼400× more potent than 17-β E2 in suppressing tumor necrosis factor (TNF) α-induced VCAM-1 mRNA as well as protein expression in human umbilical vein endothelial cells. Genistein, an ERβ agonist, at low concentrations (1 and 10 nm) also suppressed TNFα-induced VCAM-1 mRNA expression. These actions of 17-epiestriol and genistein were significantly attenuated in the presence of the estrogen receptor antagonist ICI-182780. Other estrogenic compounds such as ethinyl estradiol and estrone did not have any effect on TNFα-induced VCAM-1 expression at the concentrations tested. We further show that, 1) 17-epiestriol induces the expression of endothelial nitric-oxide synthase mRNA and protein, 2) 17-epiestriol prevents TNFα-induced migration of NFκB into the nucleus, 3) NG-nitro-l-arginine methyl ester, an inhibitor of NO synthesis, abolishes 17-epiestriol-mediated inhibition of TNFα-induced VCAM-1 expression and migration of NFκB from the cytoplasm to the nucleus. Our results indicate that 17-epiestriol is more potent than 17-β E2 in suppressing TNFα-induced VCAM-1 expression and that this action is modulated at least in part through NO.

Arthritis Increases the Risk for Fractures---Results from the Women’s Health Initiative

Objective. To examine the relationship between arthritis and fracture. Methods. Women were classified into 3 self-reported groups at baseline: no arthritis (n = 83,295), osteoarthritis (OA; n = 63,402), and rheumatoid arthritis (RA; n = 960). Incident fractures were self-reported throughout followup. Age-adjusted fracture rates by arthritis category were generated, and the Cox proportional hazards model was used to test the association between arthritis and fracture. Results. After an average of 7.80 years, 24,137 total fractures were reported including 2559 self-reported clinical spinal fractures and 1698 adjudicated hip fractures. For each fracture type, age-adjusted fracture rates were highest in the RA group and lowest in the nonarthritic group. After adjustment for several covariates, report of arthritis was associated with increased risk for spine, hip, and any clinical fractures. Compared to the nonarthritis group, the risk of sustaining any clinical fracture in the OA group was HR 1.09 (95% CI 1.05, 1.13; p < 0.001) and HR 1.49 (95% CI 1.26, 1.75; p < 0.001) in the RA group. The risk of sustaining a hip fracture was not statistically increased in the OA group (HR 1.11; 95% CI 0.98, 1.25; p = 0.122) compared to the nonarthritis group; however, the risk of hip fracture increased significantly (HR 3.03; 95% CI 2.03, 4.51; p < 0.001) in the RA group compared to the nonarthritis group. Conclusion. The increase in fracture risk confirms the importance of fracture prevention in patients with RA and OA.