Reduction of oxidative stress and AT1 receptor expression by the selective oestrogen receptor modulator idoxifene

Protective effects of combining SERMs with estrogen on metabolic parameters in postmenopausal diabetic cardiovascular dysfunction: The role of cytokines and angiotensin II

INTRODUCTION

The beneficial effects of the administration of selective estrogen receptor modulators (SERMs) and estrogen (E2), alone or in combination with each other, have been reported in postmenopausal diabetic cardiovascular dysfunction. In the present study, we determined the mechanism of action of SERMs and E2 on inflammatory balance, angiotensin II (Ang II) serum levels, and glycemic profile in a postmenopausal diabetic rat model.

METHODS

Ovariectomized rats with type 2 diabetes received daily SERMs (tamoxifen and raloxifene) and E2 for one month. After treatment, cardiovascular risk indices, glycemic profile, and serum Ang II, TNF-α and IL-10 levels were measured.

RESULTS

Type 2 diabetes caused an abnormal glycemic profile, which was exacerbated by ovariectomy. All treatments inhibited the effects of diabetes and ovariectomy on the glycemic profile, with combined treatments (SERMs + E2) showing stronger effects. Cardiovascular risk indices that became abnormal by diabetes and worsened by ovariectomy were improved in all treatment modalities. Also, combined treatment reduced serum Ang II, TNF-α, and the ratio of TNF-α to IL-10, indicating an improvement in inflammatory balance.

CONCLUSION

Our study showed the administration of SERMs and E2, alone or in combination, could be an effective alternative in the treatment of menopausal diabetes, and generally, the beneficial effects of combined treatments were more effective than the effects of E2 or SERMs alone. It appears that E2 or SERMs benefit the cardiovascular system by improving inflammatory balance and reducing Ang II levels.

Acute improvement of endothelial functions after oral ingestion of isohumulones, bitter components of beer

Isohumulones, principal components of the bitter taste of beers, have antioxidant capacity. We studied i) the effects of oral ingestion of isomerized hop extract (IHE) on the endothelial functions in smokers as well as non-smokers and ii) the effects of IHE on cultured endothelial cells in high oxidative stress state. Twelve cigarette smokers and eleven non-smokers ingested IHE and placebo in a randomized crossover design. Flow-mediated vasodilatation (FMD) was measured using ultrasonography. We also studied the effects of isohumulones on i) the cell viability under hypoxia and ii) the levels of angiotensin II (AT-II)-induced reactive oxygen species (ROS) in the cultured human aortic endothelial cells (HAECs). At baseline, the FMDs of the smokers were significantly lower than those of the non-smokers. The FMDs increased significantly after 30 min and 120 min of IHE ingestion in both the smokers and the non-smokers. IHE protected the HAECs from hypoxia-induced cell death as assessed by cell viability. IHE also reduced the AT-II-induced intracellular ROS level. Oral ingestion of IHE appears to exert acute beneficial effects on the endothelial functions in both the smokers and non-smokers, and the in vitro experiments using HAECs suggested that the effect be through reducing intracellular oxidative stress.

Effects of estradiol and raloxifene on arterial thrombosis in ovariectomized mice

OBJECTIVE

The effects of estrogen and selective estrogen receptor modulators (eg, raloxifene) on arterial thrombosis are not well defined. This study assessed the manner and mechanism by which estrogen and raloxifene affect homeostatic pathways in ovariectomized mice after acute arterial injury.

DESIGN

Female mice (3 weeks old) underwent ovariectomy or sham operation. Five days after surgery, mice were assigned to treatment with estradiol (5.3 nmol/kg), raloxifene (2.7 micromol/kg), or placebo (n = 10-12/group). The biological effects of both treatments were assessed by measurements of bone mass and the degree of uterine atrophy. After 4 months of therapy, carotid artery thrombosis was induced by photochemical injury, and the time to vascular occlusion was measured.

RESULTS

Both treatments increased bone mineral density (4.1%-7.85%). Reversal of macroscopic uterine atrophy was observed only in estrogen-treated mice. Ovariectomized mice had a shorter time to occlusion compared with sham-operated mice (70.8 +/- 7.4 vs 103 +/- 11.3 min), suggesting accelerated thrombosis. Both estradiol and raloxifene significantly inhibited intra-arterial thrombosis in ovariectomized mice, prolonging the time to occlusion to 136.33 +/- 13.5 and 141.43 +/- 9.26 min, respectively. Cyclooxygenase-2 levels in the lung tissue were significantly increased by both raloxifene and estradiol with endothelial nitric oxide synthase expression being unaltered. Platelet adhesion (measured by surface coverage under a shear rate of 1,800 s for 2 min) was significantly reduced in ovariectomized animals, being 4.63% +/- 1.47%, 5.78% +/- 1.58%, and 10.04% +/- 1.33% for raloxifene, estradiol, and placebo, respectively.

CONCLUSIONS

Ovariectomy amplifies thrombosis. We found that 4 months of treatment with both estradiol and raloxifene attenuates intravascular thrombosis. The antithrombotic effect was accompanied by increased expression of cyclooxygenase-2 and suppression of platelet surface adhesion.

Selective estrogen receptor modulators and risk for coronary heart disease

Coronary heart disease (CHD) is the leading cause of death in women in most countries. Atherosclerosis is the main biological process determining CHD. Clinical data support the notion that CHD is sensitive to estrogens, but debate exists concerning the effects of the hormone on atherosclerosis and its complications. Selective estrogen receptor modulators (SERMs) are compounds capable of binding the estrogen receptor to induce a functional profile distinct from estrogens. The possibility that SERMs may shift the estrogenic balance on cardiovascular risk towards a more beneficial profile has generated interest in recent years. There is considerable information on the effects of SERMs on distinct areas that are crucial in atherogenesis. The complexity derived from the diversity of variables affecting their mechanism of action plus the differences between compounds make it difficult to delineate one uniform trend for SERMs. The present picture, nonetheless, is one where SERMs seem less powerful than estrogens in atherosclerosis protection, but more gentle with advanced forms of the disease. The recent publication of the Raloxifene Use for The Heart (RUTH) study has confirmed a neutral effect for raloxifene. Prothrombotic states may favor occlusive thrombi at sites occupied by atheromatous plaques. Platelet activation has received attention as an important determinant of arterial thrombogenesis. Although still sparse, available evidence globally suggests neutral or beneficial effects for SERMs.

Lone atrial fibrillation: Pathologic or not?

Atrial fibrillation risk has been strongly associated with increasing age and visceral obesity. These characteristics are strongly associated with diabetes, decreased heart rate variability, and chronic inflammation. Lone atrial fibrillation (LAF) on the other hand exhibits a predilection for the physically fit and the middle aged, especially males. Given these opposing features it is postulated that pathologic AF is due to cardiac fibrosis and other age related changes while LAF is due to physiologic neurohormonal changes related to autonomic tone, insulin sensitivity, and electrolyte imbalance and that pathologic AF and LAF can be reliably differentiated via an anthropometric approach using weight, height, hip, and waist measurements. An anthropometric study is undertaken from an LAF database to test this hypothesis. Such individuals in addition to being younger and predominantly male appear to be taller with less central adiposity vs. those with pathologic AF. The ramifications of these findings with respect to insulin resistance, sympathetic tone, inflammation and hypertension, often associated with pathologic atrial fibrillation, are discussed. Speculation is drawn about possible etiologic link with mitral valve prolapse, which is commonly encountered in the tall and thin and which shares multiple clinical features with LAF.

Loss of angiotensin-converting enzyme-2 leads to the late development of angiotensin II-dependent glomerulosclerosis

Angiotensin-converting enzyme-2 (ACE2), a membrane-bound carboxymonopeptidase highly expressed in the kidney, functions as a negative regulator of the renin-angiotensin system. Here we report early accumulation of fibrillar collagen in the glomerular mesangium of male ACE2 mutant (ACE2-/y) mice followed by development of glomerulosclerosis by 12 months of age whereas female ACE2 mutant (ACE2-/-) mice were relatively protected. Progressive kidney injury was associated with increased deposition of collagen I, collagen III and fibronectin in the glomeruli and increased urinary albumin excretion compared to age-matched control mice. These structural and functional changes in the glomeruli of male ACE2 mutant mice were prevented by treatment with the angiotensin II type-1 receptor antagonist irbesartan. Loss of ACE2 was associated with a marked increase in renal lipid peroxidation product formation and activation of mitogen-activated protein kinase and extracellular signal-regulated kinases 1 and 2 in glomeruli, events that are also prevented by angiotensin II type-1 receptor blockade. We conclude that deletion of the ACE2 gene leads to the development of angiotensin II-dependent glomerular injury in male mice. These findings have important implications for our understanding of ACE2, the renin-angiotensin system, and gender in renal injury, with ACE2 likely to be an important therapeutic target in kidney disease.

Pathophysiological regulation of the AT1-receptor and implications for vascular disease

BACKGROUND

Numerous studies have demonstrated that activation of the angiotensin II type 1 (AT1) receptor plays an important role in the pathogenesis of cardiovascular diseases.

RESULTS

AT1-receptor activation by angiotensin II is not only involved in the regulation of blood pressure, water and sodium homeostasis, and control of other neurohumoral systems, but also leads to excessive production of reactive oxygen species and to hypertrophy, proliferation, migration, and apoptosis of vascular cells. AT1-receptor-induced oxidative stress may cause nitric oxide inactivation, lipid oxidation, and activation of redox-sensitive genes, such as chemotaxis and adhesion molecules, pro-inflammatory cytokines, and matrix metalloproteinases, all of which are involved in the initiation and progression of endothelial dysfunction and manifested atherosclerosis. The expression levels of the AT1-receptor define the biological efficacy of angiotensin II. Many agonists, such as, for example, angiotensin II, growth factors, low-density lipoprotein cholesterol, insulin, glucose, estrogen, progesterone, reactive oxygen species, cytokines, nitric oxide, and many others, are known to regulate AT1-receptor expression in vascular cells. The pathophysiological relevance of dysregulated AT1-receptor expression has been demonstrated in many cell culture and animal studies and interventional trials in humans. Hypercholesterolemia, estrogen deficiency, and diabetes mellitus are associated with enhanced vascular AT1-receptor expression, increased oxidative stress, and endothelial dysfunction. Importantly, treatment with AT1-receptor blockers may inhibit the onset and progression of vascular oxidative stress and inflammation, endothelial dysfunction, atherosclerosis, and related organ damage.

CONCLUSION

Inhibition of AT1-receptor activation is presumably a primary treatment goal in patients suffering from cardiovascular risk factors or manifested atherosclerotic diseases.

Inhibitory effects of idoxifene on hepatic fibrosis in rats

AIM

To investigate the effects of a tissue-specific selective estrogen receptor modulator, idoxifene, on hepatic fibrosis in rats.

METHODS

Hepatic fibrosis was induced by dimethylnitrosamine (DMN) in male rats. The DMN model of hepatic fibrosis and the hepatocytes undergoing oxidative stress were treated with idoxifene respectively. The effect of idoxifene on hepatic fibrosis in the DMN model was examined by immunohistochemistry. Effects of idoxifene on antioxidant enzyme levels of copper, zinc-dependent superoxide dismutase (CuZn-SOD), and cellular glutathione peroxidase (GSHPx) were measured by ELISA. Effects of idoxifene on activation, proliferation, and apoptosis of culture-activated hepatic stellate cells (HSC) were analysed by immunohistochemistry, bromodeoxyuridine (BrdU) uptake, and flow cytometry, respectively.

RESULTS

Idoxifene could markedly suppress DMN-induced hepatic fibrosis in male rats. A treatment of 0.4 mg x kg(-1) x d(-1) of idoxifene reduced the protein levels of collagen in the DMN model by 41.19% (P<0.05). Protein level of CuZn-SOD and activitiy of GSHPx in liver treated with DMN plus 0.4 mg/kg/d of idoxifene were 2.65 times (P<0.05) and 2.08 times greater (P<0.05) than that of liver treated with DMN alone respectively. The protein level of CuZn-SOD and activity of GSHPx in cultured rat hepatocytes treated with ferric nitrilotriacetate (FeNTA) plus 1 multiply 10(-7) mol/L of idoxifene were 3.43 times (P<0.05) and 2.52 times (P<0.05) greater than that treated with FeNTA alone. Idoxifene could inhibit HSC activation. Compared with the control, the uptake of BrdU in HSC cultured with 1 multiply 10(-7) mol/L of idoxifene was reduced by 51.87 % (P<0.05), and the number of apoptotic HSCs cultured with 1 multiply 10(-7) mol/L of idoxifene increased by 94.52% (P<0.05).

CONCLUSION

Idoxifene showed inhibitory action on hepatic fibrosis in male rats.

Genistein Inhibits Expressions of NADPH Oxidase p22phox and Angiotensin II Type 1 Receptor in Aortic Endothelial Cells from Stroke-Prone Spontaneously Hypertensive Rats

Phytoestrogens are considered to be natural selective estrogen receptor modulators exerting antioxidant activity and improving vascular function. However, the mechanisms responsible for their antioxidative effects remain largely unknown. This study tested the hypothesis that genistein may provide significant endothelial protection by antioxidative effects through attenuating NADPH oxidase expression and activity. The results showed that genistein suppressed the expressions of the p22phox NADPH oxidase subunit and angiotensin II (Ang II) type 1 (AT1) receptor in a concentration- and time-dependent manner in aortic endothelial cells from stroke-prone spontaneously hypertensive rats examined by Western blot analysis. Treatment with genistein also remarkably reduced the Ang II-induced superoxide by the reduction of nitroblue tetrazolium, inhibited nitrotyrosine formation, and attenuated endothelin-1 production by ELISA via the stimulation of Ang II. However, when cells were pretreated with ICI-182780, an estrogen-receptor antagonist, at a concentration of 50 micromol/l for 30 min and then co-incubated with ICI-182780 and genistein for 24 h, the inhibitory effect of genistein was not blocked. In contrast, the inhibitory effect of genistein treatment was partially reversed by 30-min pretreatment of endothelial cells with GW9662, a peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist. Genistein thus appears to act as an antioxidant at the transcription level by the downregulation of p22phox and AT1 receptor expression. Our data also showed that the PPARgamma pathway was involved, at least in part, in the inhibitory effect of genistein on the expression of p22phox and AT1 receptors. The endothelial-protective effects of phytoestrogen may contribute to improvement of cardiovascular functions.

Estrogen reduces angiotensin II-induced nitric oxide synthase and NAD(P)H oxidase expression in endothelial cells

OBJECTIVE

Angiotensin II (AII) has been shown to increase endothelial NAD(P)H oxidase activity, which is a source of superoxide anion that in turn may induce the formation of peroxynitrite. Estrogen (E2) has been reported to have vascular protective effects. In this study, we hypothesized that E2 reduces the AII-induced expression of NAD(P)H oxidase and peroxynitrite in endothelial cells.

METHODS AND RESULTS

Endothelial cells were cultured and stimulated with AII in the absence or presence of E2. Western blots were used to assess nitric oxide synthase (NOS) and NAD(P)H oxidase expression. Immunofluorescence of nitrotyrosine provided evidence of peroxynitrite formation. Our data indicate that AII increased the expression of endothelial NOS, inducible NOS, and NAD(P)H oxidase in a dose-dependent manner, which was attenuated by incubation with either E2, superoxide dismutase, or the AII type 1 receptor (AT1R) inhibitor candesartan. Estrogen as well as superoxide dismutase also inhibited AII-induced AT(1)R expression and nitrotyrosine staining. The effects of E2 on the AII responses were not inhibited by the E2 receptor antagonist ICI-182,780.

CONCLUSIONS

AII stimulation of endothelial cells increases expression of NAD(P)H oxidase and NOS, which may contribute to oxidative stress, as evidenced by peroxynitrite formation. E2 inhibits these AII effects, possibly through reduced AT1R expression.

Mechanisms linking angiotensin II and atherogenesis

PURPOSE OF REVIEW

The concept that angiotensin II plays a central role in early atherogenesis, progression to atherosclerotic plaque, and the most serious clinical sequelae of coronary artery disease is the subject of considerable current interest. Results from recent large clinical trials confirm that blunting of the renin-angiotensin system through either angiotensin converting enzyme inhibition or angiotensin II type 1 receptor blockade incurs significant beneficial outcomes in patients with coronary artery disease. The exact mechanisms for these effects are not yet clear, but are suggested by studies demonstrating that suppression of the renin-angiotensin system is associated with muted vascular oxidative stress.

RECENT FINDINGS

As most of the biological effects of the renin-angiotensin system occur through stimulation of the angiotensin II type 1 receptor, the focus of this review is on changes in the vascular wall mediated by this receptor and primarily related to endothelial and vascular smooth muscle cells, monocyte/macrophages and platelets. The interactions between angiotensin II and nitric oxide exert particular demands on the vascular capacity to adapt to dyslipidemia, hypertension, estrogen deficiency and diabetes mellitus that appear to exacerbate atherogenesis. Associated with each of these conditions is angiotensin II-mediated stimulation of macrophages, platelet aggregation, plasminogen activator inhibitor 1, endothelial dysfunction, vascular smooth muscle cell proliferation and migration, apoptosis, leukocyte recruitment, fibrogenesis and thrombosis.

SUMMARY

Inhibition of the actions of angiotensin II serves a dual purpose: indirectly through reduction of mechanical stress on the vascular wall, and directly by diminished stimulation for vascular restructuring and remodeling. Collectively, data from studies published over the last year confirm and extend the notion that angiotensin II is a true cytokine prevalent at all stages of atherogenesis.

Angiotensin II and cAMP regulate AT(1)-mRNA expression in rat cardiomyocytes by transcriptional mechanism

Mechanisms of angiotensin II and cAMP regulating the expression of angiotensin II type 1 (AT(1)) receptor mRNA were studied in neonatal rat cardiomyocytes. Angiotensin II induced a transient decrease of AT(1)-mRNA expression in time- and dose-dependent manner. Maximal decrease (49.2 +/- 9.5% of control) occurred at 6 h of angiotensin II (10 nmol/l) treatment. AT(1) receptor antagonists 4-ethyl-2-n-propyl-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imidazole-5-carboxylic acid (DMP811) and losartan as well as 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) reversed the down-regulation of AT(1)-mRNA expression. 6 h of phorbol 12-myristate 13-acetate (PMA) stimulation caused a decrease of AT(1)-mRNA level. Treatment by angiotensin II plus actinomycin D for 6 h produced the same effect as actinomycin D alone. These results suggest that angiotensin II down-regulates AT(1)-mRNA level of rat cardiomyocytes by inhibiting the transcription of AT(1) gene, which is mediated by AT(1) receptor and related to the activation of protein kinase C. Stimulation by forskolin plus 3-isobutyl-1-methyl-xanthine (IBMX) decreased the expression of AT(1)-mRNA to 68.1 +/- 21.5% of control at 6 h treatment; while increased to 207.9 +/- 27.1% of control at 48 h treatment. A series of 5'-upstream deletion mutants of AT(1A) promoter were produced and then were recombined with pGL(3) basic vector utilizing luciferase as reporter gene. Among all the constructors, p(-201/+ 74)Luc was of the highest luciferase activity (5.9 times higher than control) after stimulation by forskolin for 48 h. Further deletion from -201 to -61 resulted in a large decrease of activity. These results indicate that cAMP induces a time-dependent bi-directional regulation of AT(1)-mRNA expression. The cAMP responsible element (CRE) cis-element located in the region -201/-61 of rat AT(1A) promoter is forskolin inducible, which may mediate the up-regulation of AT(1)-mRNA expression induced by cAMP long-lasting stimulation.