Neuronal nitric oxide synthase inhibition improves diastolic function and reduces oxidative stress in ovariectomized mRen2.Lewis rats

Targeting estrogen receptor signaling for treating heart failure

Heart failure (HF) is a significant public health problem worldwide. It has long been noted that premenopausal women, compared to postmenopausal women and men, have lower rates for developing this disease, as well as subsequent morbidity and mortality. This difference has been attributed to estrogen playing a cardioprotective role in these women, though exactly how it does so remains unclear. In this review, we examine the presence of estrogen receptors within the cardiovascular system, as well as the role they play behind the cardioprotective effect attributed to estrogen. Furthermore, we highlight the underlying mechanisms behind their alleviation of HF, as well as possible treatment approaches, such as hormone replacement therapy and exercise regimens, to manipulate these mechanisms in treating and preventing HF.

Hypertension after the Menopause: What Can We Learn from Experimental Studies?

Hypertension is the most prevalent cardiovascular disease of the adult population and is closely associated with serious cardiovascular events. The burden of hypertension with respect to vascular and other organ damage is greater in women. These sex differences are not fully understood. The unique feature in women is their transition to menopause accompanied by profound hormonal changes that affect the vasculature that are also associated with changes of blood pressure. Results from studies of hormone replacement therapy and its effects on the cardiovascular system are controversial, and the timing of treatment after menopause seems to be important. Therefore, revealing potential sex- and sex hormone-dependent pathophysiological mechanisms of hypertension in experimental studies could provide valuable information for better treatment of hypertension and vascular impairment, especially in postmenopausal women. The experimental rat models subjected to ovariectomy mimicking menopause could be useful tools for studying the mechanisms of blood pressure regulation after menopause and during subsequent therapy.

Sex and the G Protein-Coupled Estrogen Receptor Impact Vascular Stiffness

[Figure: see text].

The Role of Estrogen Receptors in Cardiovascular Disease

Cardiovascular Diseases (CVDs) are the leading cause of death globally. More than 17 million people die worldwide from CVD per year. There is considerable evidence suggesting that estrogen modulates cardiovascular physiology and function in both health and disease, and that it could potentially serve as a cardioprotective agent. The effects of estrogen on cardiovascular function are mediated by nuclear and membrane estrogen receptors (ERs), including estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled ER (GPR30 or GPER). Receptor binding in turn confers pleiotropic effects through both genomic and non-genomic signaling to maintain cardiovascular homeostasis. Each ER has been implicated in multiple pre-clinical cardiovascular disease models. This review will discuss current reports on the underlying molecular mechanisms of the ERs in regulating vascular pathology, with a special emphasis on hypertension, pulmonary hypertension, and atherosclerosis, as well as in regulating cardiac pathology, with a particular emphasis on ischemia/reperfusion injury, heart failure with reduced ejection fraction, and heart failure with preserved ejection fraction.

Connecting sex differences, estrogen signaling, and microRNAs in cardiac fibrosis

Sex differences are evident in the pathophysiology of heart failure (HF). Progression of HF is promoted by cardiac fibrosis and no fibrosis-specific therapies are currently available. The fibrotic response is mediated by cardiac fibroblasts (CFs), and a central event is their phenotypic transition to pro-fibrotic myofibroblasts. These myofibroblasts may arise from various cellular origins including resident CFs and epicardial and endothelial cells. Both female subjects in clinical studies and female animals in experimental studies generally present less cardiac fibrosis compared with males. This difference is at least partially considered attributable to the ovarian hormone 17β-estradiol (E2). E2 signals via estrogen receptors to regulate genes are involved in the fibrotic response and myofibroblast transition. Besides protein-coding genes, E2 also regulates transcription of microRNA that modulate cardiac fibrosis. Sex dimorphism, E2, and miRNAs form multi-level regulatory networks in the pathophysiology of cardiac fibrosis, and the mechanism of these networks is not yet fully deciphered. Therefore, this review is aimed at summarizing current knowledge on sex differences, E2, and estrogen receptors in cardiac fibrosis, emphasizing on microRNAs and myofibroblast origins. KEY MESSAGES: • E2 and ERs regulate cardiac fibroblast function. • E2 and ERs may distinctly affect male and female cardiac fibrosis pathophysiology. • Sex, E2, and miRNAs form multi-level regulatory networks in cardiac fibrosis. • Sex-dimorphic and E2-regulated miRNAs affect mesenchymal transition.

Alteration at transcriptional level of cardiac renin-angiotensin system by letrozole treatment

INTRODUCTION

The use of aromatase inhibitors (AIs) for breast cancer led to a marked change in ventricular function. Since accumulating evidence indicates that overactivation of the cardiac renin-angiotensin system (RAS) plays an important role in the development of cardiovascular diseases such as hypertrophy and remodelling, we aimed to investigate whether letrozole alters the transcription level of RAS related genes in the cardiac tissue.

METHODS

Twenty four rats were randomly divided into four groups (n = 6 per group): two groups were letrozole treated (1 and 2 mg/kg/day orally), one group was vehicle treated (DMSO) and one group was the control group without any treatment. 12 weeks after beginning treatment with letrozole, we examined the rate of transcription of renin, angiotensinogen, AngII type 1a and 1b (AT1a and AT1b) and type 2 receptors (AT2) in the rat heart using real-time polymerase chain reaction.

RESULTS

The cardiac mRNA levels of several components of the RAS in the rats treated with letrozole were significantly increased including AT1a receptor (80%), renin (51%), and angiotensinogen (33%). Though not significant, AT2 receptor levels were observed to decrease with increasing doses of letrozole.

CONCLUSIONS

Letrozole can induce significant changes in some RAS related genes. These alterations are important to understand the pathways and consequences beyond cardiac events induced by breast cancer treatments.

G protein-coupled estrogen receptor (GPER) deficiency induces cardiac remodeling through oxidative stress

Oxidative stress has been implicated in the unfavorable changes in cardiac function and remodeling that occur after ovarian estrogen loss. Using ovariectomized rat models, we previously reported that the cardioprotective actions of estrogen are mediated by the G protein-coupled estrogen receptor (GPER). Here, in 9-month-old, female cardiomyocyte-specific GPER knockout (KO) mice vs sex- and age-matched wild-type (WT) mice, we found increased cardiac oxidative stress and oxidant damage, measured as a decreased ratio of reduced glutathione to oxidized glutathione, increased 4-hydroxynonenal and 8-hydroxy-2'-deoxyguanosine (8-oxo-DG) staining, and increased expression of oxidative stress-related genes. GPER KO mice also displayed increased heart weight, cardiac collagen deposition, and Doppler-derived filling pressure, and decreased percent fractional shortening and early mitral annular velocity compared with WT controls. Treatment of GPER KO mice for 8 weeks with phosphonium [10-(4,5-dimethoxy-2-methyl 3,6-dioxo-1,4-cyclohexadien-1-yl)decyl] triphenyl-,mesylate (MitoQ), a mitochondria-targeted antioxidant, significantly attenuated these measures of cardiac dysfunction, and MitoQ decreased 8-oxo-DG intensity compared with treatment with an inactive comparator compound, (1-decyl)triphenylphosphonium bromide (P <0.05). A real-time polymerase chain reaction array analysis of 84 oxidative stress and antioxidant defense genes revealed that MitoQ attenuates the increase in NADPH oxidase 4 and prostaglandin-endoperoxide synthase 2 and the decrease in uncoupling protein 3 and glutathione S-transferase kappa 1 seen in GPER KO mice. Our findings suggest that the cardioprotective effects of GPER include an antioxidant role and that targeted strategies to limit oxidative stress after early noncancerous surgical extirpation of ovaries or menopause may help limit alterations in cardiac structure and function related to estrogen loss.

Blunting of cardioprotective actions of estrogen in female rodent heart linked to altered expression of cardiac tissue chymase and ACE2

Background:

Diastolic dysfunction develops in response to hypertension and estrogen (E2) loss and is a forerunner to heart failure (HF) in women. The cardiac renin–angiotensin system (RAS) contributes to diastolic dysfunction, but its role with respect to E2 and blood pressure remain unclear.

Methods:

We compared the effects of ovariectomy (OVX) or sham surgery on the cardiac RAS, left ventricular (LV) structure/function, and systemic/intracardiac pressures of spontaneously hypertensive rats (SHRs: n = 6 intact and 6 OVX) and age-matched Wistar-Kyoto (WKY: n = 5 intact and 4 OVX) controls.

Results:

WKY rats were more sensitive to OVX than SHRs with respect to worsening of diastolic function, as reflected by increases in Doppler-derived filling pressures (E/e′) and reductions in myocardial relaxation (e′). This pathobiologic response in WKY rats was directly linked to increases in cardiac gene expression and enzymatic activity of chymase and modest reductions in ACE2 activity. No overt changes in cardiac RAS genes or activities were observed in SHRs, but diastolic function was inversely related to ACE2 activity.

Conclusion:

Endogenous estrogens exert a more significant regulatory role upon biochemical components of the cardiac RAS of WKY versus SHRs, modulating the lusitropic and structural components of its normotensive phenotype.

The Role of Estrogen in Cardiac Metabolism and Diastolic Function

Heart failure with preserved ejection fraction (HFpEF) has similar prevalence and prognosis as HF with reduced EF, but there is no approved treatment for HFpEF. HFpEF is common in postmenopausal women, which suggests that the absence of estrogen (E2) plays a role in its pathophysiology. With the country's growing elderly population, the prevalence of HFpEF is rapidly increasing. This has triggered a renewed urgency in finding novel approaches to preventing and slowing the progression of HFpEF. In this review, we address the role of E2 in left ventricular diastolic function and how it impacts women with HFpEF as well as animal models. We also discuss the primary potential mechanisms that represent critical nodes in the mechanistic pathways of HFpEF and how new treatments could be developed to target those mechanisms.

Hypolipidemic and cardioprotective benefits of a novel fireberry hawthorn fruit extract in the JCR:LA-cp rodent model of dyslipidemia and cardiac dysfunction

Hawthorn is a widely used herbal alternative medicine for the treatment of various cardiovascular diseases. However, the attributed health benefits, purported to be due to the presence of phenolic compounds, may depend on both the specific species and plant part. Studies to date investigating effects of hawthorn on heart disease(s) have used well-described European and/or Asian species, while little is known regarding the bioactivity of species native to North America. Six weeks of supplementation of both fireberry hawthorn berry (native Crataegus chrysocarpa) and English hawthorn leaf (C. monogyna, naturalized in North America) in the JCR:LA-cp rat, resulted in a significant reduction in heart weight, fasting LDL-C and improved heart function (p < 0.05). Fasting triglyceride and myocardial fibrosis were also reduced, but only by the berry extract. We demonstrate that both of the Canadian-sourced hawthorn extracts (introduced leaf and native berry) have cardioprotective benefits, likely via increased availability of nitric oxide.

Acute ascorbic acid infusion increases left ventricular diastolic function in postmenopausal women

OBJECTIVES

We tested the hypothesis that oxidative stress contributes to reductions in left ventricular diastolic (LV) function in estrogen-deficient postmenopausal women, related in part to reduced nitric oxide (NO) bioavailability.

STUDY DESIGN

LV diastolic function - recorded using transthoracic echocardiography and determined as the peak early (E) to late (A) mitral inflow velocity ratio and the E to peak early (e') mitral annular velocity ratio - and brachial artery flow mediated dilation (FMD), a biomarker of NO bioavailability, were measured during acute systemic infusions of saline (control) and ascorbic acid (experimental model to decrease oxidative stress) in healthy premenopausal women (N=14, 18-40 years) and postmenopausal women (N=23, 45-75 years).

RESULTS

The E/A ratio was lower (1.16[1.06-1.33] vs 1.65[1.5-2.3]; median[interquartile range]) and the E/e' ratio was elevated (8.8[7.6-9.9] vs. 6.6[5.5-7.3]) in postmenopausal compared with premenopausal women, indicating reduced LV diastolic function. E/A and E/e' were correlated with FMD (r=0.54 and r=-0.59, respectively, both P<0.01). Ascorbic acid infusion improved both FMD (5.4±2.0% to 7.8±2.6%) and E/e' (to 8.1[7.2-9.7], P=0.01) in postmenopausal women but not in premenopausal women. Ascorbic acid did not change E/A in either group.

CONCLUSION

The current study provides evidence that oxidative stress contributes to reduced LV diastolic function in estrogen-deficient postmenopausal women, possibly by reducing the availability of NO.

Effect of Age, Estrogen Status, and Late-Life GPER Activation on Cardiac Structure and Function in the Fischer344×Brown Norway Female Rat

Age-associated changes in cardiac structure and function, together with estrogen loss, contribute to the progression of heart failure with preserved ejection fraction in older women. To investigate the effects of aging and estrogen loss on the development of its precursor, asymptomatic left ventricular diastolic dysfunction, echocardiograms were performed in 10 middle-aged (20 months) and 30 old-aged (30 months) female Fischer344×Brown-Norway rats, 4 and 8 weeks after ovariectomy (OVX) and sham procedures (gonads left intact). The cardioprotective potential of administering chronic G1, the selective agonist to the new G-protein-coupled estrogen receptor (GPER), was further evaluated in old rats (Old-OVX+G1) versus age-matched, vehicle-treated OVX and gonadal intact rats. Advanced age and estrogen loss led to decreases in myocardial relaxation and elevations in filling pressure, in part, due to reductions in phosphorylated phospholamban and increases in cardiac collagen deposition. Eight weeks of G-protein-coupled estrogen receptor activation in Old-OVX+G1 rats reversed the adverse effects of age and estrogen loss on myocardial relaxation through increases in sarcoplasmic reticulum Ca²⁺ ATPase expression and reductions in interstitial fibrosis. These findings may explain the preponderance of heart failure with preserved ejection fraction in older postmenopausal women and provide a promising, late-life therapeutic target to reverse or halt the progression of left ventricular diastolic dysfunction.

Role of estrogen in diastolic dysfunction

The prevalence of left ventricular diastolic dysfunction (LVDD) sharply increases in women after menopause and may lead to heart failure. While evidence suggests that estrogens protect the premenopausal heart from hypertension and ventricular remodeling, the specific mechanisms involved remain elusive. Moreover, whether there is a protective role of estrogens against cardiovascular disease, and specifically LVDD, continues to be controversial. Clinical and basic science have implicated activation of the renin-angiotensin-aldosterone system (RAAS), linked to the loss of ovarian estrogens, in the pathogenesis of postmenopausal diastolic dysfunction. As a consequence of increased tissue ANG II and low estrogen, a maladaptive nitric oxide synthase (NOS) system produces ROS that contribute to female sex-specific hypertensive heart disease. Recent insights from rodent models that mimic the cardiac phenotype of an estrogen-insufficient or -deficient woman (e.g., premature ovarian failure or postmenopausal), including the ovariectomized congenic mRen2.Lewis female rat, provide evidence showing that estrogen modulates the tissue RAAS and NOS system and related intracellular signaling pathways, in part via the membrane G protein-coupled receptor 30 (GPR30; also called G protein-coupled estrogen receptor 1). Complementing the cardiovascular research in this field, the echocardiographic correlates of LVDD as well as inherent limitations to its use in preclinical rodent studies will be briefly presented. Understanding the roles of estrogen and GPR30, their interactions with the local RAAS and NOS system, and the relationship of each of these to LVDD is necessary to identify new therapeutic targets and alternative treatments for diastolic heart failure that achieve the cardiovascular benefits of estrogen replacement without its side effects and contraindications.

The NO/ONOO-cycle as the central cause of heart failure

The NO/ONOO-cycle is a primarily local, biochemical vicious cycle mechanism, centered on elevated peroxynitrite and oxidative stress, but also involving 10 additional elements: NF-κB, inflammatory cytokines, iNOS, nitric oxide (NO), superoxide, mitochondrial dysfunction (lowered energy charge, ATP), NMDA activity, intracellular Ca(2+), TRP receptors and tetrahydrobiopterin depletion. All 12 of these elements have causal roles in heart failure (HF) and each is linked through a total of 87 studies to specific correlates of HF. Two apparent causal factors of HF, RhoA and endothelin-1, each act as tissue-limited cycle elements. Nineteen stressors that initiate cases of HF, each act to raise multiple cycle elements, potentially initiating the cycle in this way. Different types of HF, left vs. right ventricular HF, with or without arrhythmia, etc., may differ from one another in the regions of the myocardium most impacted by the cycle. None of the elements of the cycle or the mechanisms linking them are original, but they collectively produce the robust nature of the NO/ONOO-cycle which creates a major challenge for treatment of HF or other proposed NO/ONOO-cycle diseases. Elevated peroxynitrite/NO ratio and consequent oxidative stress are essential to both HF and the NO/ONOO-cycle.

Characterization of the cardiac renin angiotensin system in oophorectomized and estrogen-replete mRen2.Lewis rats

The cardioprotective effects of estrogen are well recognized, but the mechanisms remain poorly understood. Accumulating evidence suggests that the local cardiac renin-angiotensin system (RAS) is involved in the development and progression of cardiac hypertrophy, remodeling, and heart failure. Estrogen attenuates the effects of an activated circulating RAS; however, its role in regulating the cardiac RAS is unclear. Bilateral oophorectomy (OVX; n = 17) or sham-operation (Sham; n = 13) was performed in 4-week-old, female mRen2.Lewis rats. At 11 weeks of age, the rats were randomized and received either 17 β-estradiol (E2, 36 µg/pellet, 60-day release, n = 8) or vehicle (OVX-V, n = 9) for 4 weeks. The rats were sacrificed, and blood and hearts were used to determine protein and/or gene expression of circulating and tissue RAS components. E2 treatment minimized the rise in circulating angiotensin (Ang) II and aldosterone produced by loss of ovarian estrogens. Chronic E2 also attenuated OVX-associated increases in cardiac Ang II, Ang-(1–7) content, chymase gene expression, and mast cell number. Neither OVX nor OVX+E2 altered cardiac expression or activity of renin, angiotensinogen, angiotensin-converting enzyme (ACE), and Ang II type 1 receptor (AT1R). E2 treatment in OVX rats significantly decreased gene expression of MMP-9, ACE2, and Ang-(1–7) mas receptor, in comparison to sham-operated and OVX littermates. E2 treatment appears to inhibit upsurges in cardiac Ang II expression in the OVX-mRen2 rat, possibly by reducing chymase-dependent Ang II formation. Further studies are warranted to determine whether an E2-mediated reduction in cardiac chymase directly contributes to this response in OVX rats.

Estrogen therapy, independent of timing, improves cardiac structure and function in oophorectomized mRen2.Lewis rats

OBJECTIVE

mRen2.Lewis rats exhibit exacerbated increases in blood pressure, left ventricular (LV) remodeling, and diastolic impairment after the loss of estrogens. In this same model, depletion of estrogens has marked effects on the cardiac biopterin profile concomitant with suppressed nitric oxide release. With respect to the establishment of overt systolic hypertension after oophorectomy (OVX), we assessed the effects of timing long-term 17β-estradiol (E2) therapy on myocardial function, myocardial structure, and the cardiac nitric oxide system.

METHODS

OVX (n = 24) or sham operation (Sham; n = 13) was performed in 4-week-old female mRen2.Lewis rats. After randomization, OVX rats received E2 immediately (OVX + E2-early; n = 7), E2 at 11 weeks of age (OVX + E2-late; n = 8), or no E2 at all (OVX; n = 9).

RESULTS

E2-early was associated with lower body weight, less hypertension-related cardiac remodeling, and decreased LV filling pressure compared with OVX rats without E2 supplementation. E2-late similarly attenuated the adverse effects of ovarian hormone loss on tissue Doppler-derived LV filling pressures and perivascular fibrosis, and significantly improved myocardial relaxation or mitral annular velocity (e'). Early and late exposures to E2 decreased dihydrobiopterin, but only E2-late yielded significant increases in cardiac nitrite concentrations.

CONCLUSIONS

Although there are some similarities between E2-early and E2-late treatments in relation to preservation of diastolic function and cardiac structure after OVX, the lusitropic potential of E2 is most consistent with late supplementation. The cardioprotective effects of E2-late are independent of blood pressure and may have occurred through regulation of cardiac biopterins and nitric oxide production.

Cyclic stretch stimulates nitric oxide synthase-1-dependent peroxynitrite formation by neonatal rat pulmonary artery smooth muscle

Peroxynitrite, the reaction product of nitric oxide and superoxide, contributes to the pathogenesis of chronic pulmonary hypertension in immature animals by stimulating proliferation of pulmonary arterial smooth muscle cells (PASMCs). Pulmonary vasoconstriction, secondary to hypoxia and other stimuli, leads to enhanced pulsatile stretch of cells in the vascular wall, particularly in smooth muscle, which we hypothesized would cause increased peroxynitrite generation. Our objectives in this study were to determine whether cyclic mechanical stretch, at supraphysiologic levels, would cause increased production of reactive oxygen species (ROS), nitric oxide, and peroxynitrite in vitro. Early passage neonatal rat PASMCs were seeded and grown to subconfluence on collagen-coated elastomer-bottom plates and subjected to cyclic mechanical stretch (10% ("physiologic") or 20% ("supraphysiologic") at 0.5 Hz) for up to 24 h. Compared to nonstretched controls and to cells subjected to 10% stretch, 20% stretch increased H2O2 (stable marker of ROS) and nitrate/nitrite (stable marker of nitric oxide) in conditioned medium. These effects were accompanied by increased peroxynitrite, as evidenced by increased in situ dihydroethidium fluorescence and immunoreactive nitrotyrosine and by increased expression of nitric oxide synthase (NOS)-1 and NADPH oxidase 4 (NOX4), but not NOS-2. Stretch-induced H2O2 release and increased dihydroethidium fluorescence were prevented by pretreatment with a superoxide scavenger, nonspecific inhibitors of NADPH oxidase or NOS, or a peroxynitrite decomposition catalyst. Short-interfering RNA-mediated knockdown of NOS-1 or NOX4 attenuated increased nitric oxide and H2O2 content, respectively, in stretched-cell-conditioned medium. Knockdown of NOS-1 also attenuated increased immunoreactive nitrotyrosine content and stretch-induced proliferation, whereas knockdown of NOS-2 had no effect. We conclude that increased peroxynitrite generation by neonatal rat PASMCs subjected to supraphysiologic levels of cyclic stretch is NOS-1-dependent and that increased ROS production is predominantly mediated by NADPH oxidase, specifically NOX4.

Amelioration of renal injury and oxidative stress by the nNOS inhibitor L-VNIO in the salt-sensitive mRen2.Lewis congenic rat

Salt sensitivity is a key risk factor for cardiovascular disease and renal injury. Alterations in renal nitric oxide may contribute to salt-dependent increases in blood pressure and tissue damage. Therefore, we assessed the expression of nitric oxide synthase (NOS) isoforms in the kidney and the effects of nNOS inhibition on renal injury, inflammation, and oxidative stress in the female mRen2.Lewis rat (mRen), a model of salt-sensitive hypertension. We find that a high-salt diet (4% sodium) significantly reduced endothelial NOS mRNA (2.6-fold) and protein (1.5-fold) but increased nNOS mRNA (2.4-fold) and protein (1.9-fold) in the renal cortex of these animals. Immunostaining for nNOS also seemed higher in macula densa and cortical tubules of the rats fed a high-salt diet. Circulating nitrate and nitrite levels were reduced, including the tissue levels of the NOS cofactor tetrahydrobiopterin. Cortical markers of oxidative stress (4HNE, 8-OH-deoxyguanosine) and fibrosis were increased; however, mRNA levels of the NAD(P)H oxidase components NOX4, p22phox, and p47phox were reduced. Chronic treatment with the nNOS inhibitor N-(1-Imino-3-butenyl)-L-ornithine did not influence systolic blood pressure after 4 weeks but significantly attenuated albuminuria, renal fibrosis, inflammation, and indices of oxidative stress. We conclude that an increase in nNOS expression in conjunction with reduced levels of cortical tetrahydrobiopterin may stimulate oxidative stress and renal injury in the salt-sensitive female mRen2.Lewis rat.

Activation of GPR30 attenuates diastolic dysfunction and left ventricle remodelling in oophorectomized mRen2.Lewis rats

AIMS

GPR30 is a novel oestrogen receptor expressed in various tissues, including the heart. We determined the role of GPR30 in the maintenance of left ventricular (LV) structure and diastolic function after the surgical loss of ovarian hormones in the female mRen2.Lewis rat, a model emulating the cardiac phenotype of the post-menopausal woman.

METHODS AND RESULTS

Bilateral oophorectomy (OVX) or sham surgery was performed in study rats; the selective GPR30 agonist, G-1 (50 µg/kg/day), or vehicle was given subcutaneously to OVX rats from 13-15 weeks of age. Similar to the cardiac phenotype of sham rats, G-1 preserved diastolic function and structure relative to vehicle-treated OVX littermates independent of changes in blood pressure. G-1 limited the OVX-induced increase in LV filling pressure, LV mass, wall thickness, interstitial collagen deposition, atrial natriuretic factor and brain natriuretic peptide mRNA levels, and cardiac NAD(P)H oxidase 4 (NOX4) expression. In vitro studies showed that G-1 inhibited angiotensin II-induced hypertrophy in H9c2 cardiomyocytes, evidenced by reductions in cell size, protein content per cell, and atrial natriuretic factor mRNA levels. The GPR30 antagonist, G15, inhibited the protective effects of both oestradiol and G-1 on this hypertrophy.

CONCLUSION

These data show that the GPR30 agonist G-1 mitigates the adverse effects of oestrogen loss on LV remodelling and the development of diastolic dysfunction in the study rats. This expands our knowledge of the sex-specific mechanisms underlying diastolic dysfunction and provides a potential therapeutic target for reducing the progression of this cardiovascular disease process in post-menopausal women.

Testosterone deficiency accelerates neuronal and vascular aging of SAMP8 mice: protective role of eNOS and SIRT1

Oxidative stress and atherosclerosis-related vascular disorders are risk factors for cognitive decline with aging. In a small clinical study in men, testosterone improved cognitive function; however, it is unknown how testosterone ameliorates the pathogenesis of cognitive decline with aging. Here, we investigated whether the cognitive decline in senescence-accelerated mouse prone 8 (SAMP8), which exhibits cognitive impairment and hypogonadism, could be reversed by testosterone, and the mechanism by which testosterone inhibits cognitive decline. We found that treatment with testosterone ameliorated cognitive function and inhibited senescence of hippocampal vascular endothelial cells of SAMP8. Notably, SAMP8 showed enhancement of oxidative stress in the hippocampus. We observed that an NAD⁺-dependent deacetylase, SIRT1, played an important role in the protective effect of testosterone against oxidative stress-induced endothelial senescence. Testosterone increased eNOS activity and subsequently induced SIRT1 expression. SIRT1 inhibited endothelial senescence via up-regulation of eNOS. Finally, we showed, using co-culture system, that senescent endothelial cells promoted neuronal senescence through humoral factors. Our results suggest a critical role of testosterone and SIRT1 in the prevention of vascular and neuronal aging.

Associations of plasma phospholipid omega-6 and omega-3 polyunsaturated Fatty Acid levels and MRI measures of cardiovascular structure and function: the multiethnic study of atherosclerosis

Background. The association between plasma omega-6 fatty acids and cardiovascular disease (CVD) is unclear, and discrepancy remains concerning the cardiovascular benefit of the omega-3 fatty acid alpha-linolenic acid. Methods. Associations of plasma phospholipid fatty acid levels (arachidonic acid, linoleic acid, eicosapentaenoic acid, docosahexaenoic acid (DHA), and alpha-linolenic acid) with cardiac magnetic resonance imaging measures of left ventricular (LV) mass, LV volume, ejection fraction, stroke volume, and aortic distensibility were investigated in 1,274 adults. Results. Results of multivariate analysis showed no statistically significant associations of plasma omega-6 or omega-3 levels with cardiac magnetic resonance imaging measures. Stratification by gender revealed a positive association between DHA and LV mass in women (β = 1.89, P = 0.02; P interaction = 0.003) and a trend for a positive association between DHA and ejection fraction in men (β = 0.009, P = 0.05; P interaction = 0.03). Conclusion. Additional research is warranted to clarify the effects of plasma DHA on cardiac structure and function in women versus men.

Tetrahydrobiopterin restores diastolic function and attenuates superoxide production in ovariectomized mRen2.Lewis rats

After oophorectomy, mRen2.Lewis rats exhibit diastolic dysfunction associated with elevated superoxide, increased cardiac neuronal nitric oxide synthase (nNOS) expression, and diminished myocardial tetrahydrobiopterin (BH₄) content, effects that are attenuated with selective nNOS inhibition. BH₄ is an essential cofactor of nNOS catalytic activity leading to nitric oxide production. Therefore, we assessed the effect of 4 wk BH₄ supplementation on diastolic function and left ventricular (LV) remodeling in oophorectomized mRen2.Lewis rats compared with sham-operated controls. Female mRen2.Lewis rats underwent either bilateral ovariectomy (OVX) (n = 19) or sham operation (n = 13) at 4 wk of age. Beginning at 11 wk of age, OVX rats were randomized to receive either BH₄ (10 mg/kg · d) or saline, whereas the sham rats received saline via sc mini-pumps. Loss of ovarian hormones reduced cardiac BH₄ when compared with control hearts; this was associated with impaired myocardial relaxation, augmented filling pressures, increased collagen deposition, and thickened LV walls. Additionally, superoxide production increased and nitric oxide decreased in hearts from OVX compared with sham rats. Chronic BH₄ supplementation after OVX improved diastolic function and attenuated LV remodeling while restoring myocardial nitric oxide release and preventing reactive oxygen species generation. These data indicate that BH₄ supplementation protects against the adverse effects of ovarian hormonal loss on diastolic function and cardiac structure in mRen2.Lewis rats by restoring myocardial NO release and mitigating myocardial O₂⁻ generation. Whether BH₄ supplementation is a therapeutic option for the management of diastolic dysfunction in postmenopausal women will require direct testing in humans.

Changes in cardiac heparan sulfate proteoglycan expression and streptozotocin-induced diastolic dysfunction in rats

Background

Changes in the proteoglycans glypican and syndecan-4 have been reported in several pathological conditions, but little is known about their expression in the heart during diabetes. The aim of this study was to investigate in vivo heart function changes and alterations in mRNA expression and protein levels of glypican-1 and syndecan-4 in cardiac and skeletal muscles during streptozotocin (STZ)-induced diabetes.

Methods

Diabetes was induced in male Wistar rats by STZ administration. The rats were assigned to one of the following groups: control (sham injection), after 24 hours, 10 days, or 30 days of STZ administration. Echocardiography was performed in the control and STZ 10-day groups. Western and Northern blots were used to quantify protein and mRNA levels in all groups. Immunohistochemistry was performed in the control and 30-day groups to correlate the observed mRNA changes to the protein expression.

Results

In vivo cardiac functional analysis performed using echocardiography in the 10-day group showed diastolic dysfunction with alterations in the peak velocity of early (E) diastolic filling and isovolumic relaxation time (IVRT) indices. These functional alterations observed in the STZ 10-day group correlated with the concomitant increase in syndecan-4 and glypican-1 protein expression. Cardiac glypican-1 mRNA and skeletal syndecan-4 mRNA and protein levels increased in the STZ 30-day group. On the other hand, the amount of glypican in skeletal muscle was lower than that in the control group. The same results were obtained from immunohistochemistry analysis.

Conclusion

Our data suggest that membrane proteoglycans participate in the sequence of events triggered by diabetes and inflicted on cardiac and skeletal muscles.