Estrogen replacement stimulates fatty acid oxidation and impairs post-ischemic recovery of hearts from ovariectomized female rats

Loss of carnitine palmitoyltransferase 1a reduces docosahexaenoic acid-containing phospholipids and drives sexually dimorphic liver disease in mice

BACKGROUND AND AIMS

Genome and epigenome wide association studies identified variants in carnitine palmitoyltransferase 1a (CPT1a) that associate with lipid traits. The goal of this study was to determine the role of liver-specific CPT1a on hepatic lipid metabolism.

APPROACH AND RESULTS

Male and female liver-specific knockout (LKO) and littermate controls were placed on a low-fat or high-fat diet (60% kcal fat) for 15 weeks. Mice were necropsied after a 16 h fast, and tissues were collected for lipidomics, matrix-assisted laser desorption ionization mass spectrometry imaging, kinome analysis, RNA-sequencing, and protein expression by immunoblotting. Female LKO mice had increased serum alanine aminotransferase levels which were associated with greater deposition of hepatic lipids, while male mice were not affected by CPT1a deletion relative to male control mice. Mice with CPT1a deletion had reductions in DHA-containing phospholipids at the expense of monounsaturated fatty acids (MUFA)-containing phospholipids in whole liver and at the level of the lipid droplet (LD). Male and female LKO mice increased RNA levels of genes involved in LD lipolysis (Plin2, Cidec, G0S2) and in polyunsaturated fatty acid metabolism (Elovl5, Fads1, Elovl2), while only female LKO mice increased genes involved in inflammation (Ly6d, Mmp12, Cxcl2). Kinase profiling showed decreased protein kinase A activity, which coincided with increased PLIN2, PLIN5, and G0S2 protein levels and decreased triglyceride hydrolysis in LKO mice.

CONCLUSIONS

Liver-specific deletion of CPT1a promotes sexually dimorphic steatotic liver disease (SLD) in mice, and here we have identified new mechanisms by which females are protected from HFD-induced liver injury.

Loss of Carnitine Palmitoyltransferase 1a Reduces Docosahexaenoic Acid-Containing Phospholipids and Drives Sexually Dimorphic Liver Disease in Mice

Background and Aims

Genome and epigenome wide association studies identified variants in carnitine palmitoyltransferase 1a (CPT1a) that associate with lipid traits. The goal of this study was to determine the impact by which liver-specific CPT1a deletion impacts hepatic lipid metabolism.

Approach and Results

Six-to-eight-week old male and female liver-specific knockout (LKO) and littermate controls were placed on a low-fat or high-fat diet (HFD; 60% kcal fat) for 15 weeks. Mice were necropsied after a 16 hour fast, and tissues were collected for lipidomics, matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), kinome analysis, RNA-sequencing, and protein expression by immunoblotting. Female LKO mice had increased serum alanine aminotransferase (ALT) levels which were associated with greater deposition of hepatic lipids, while male mice were not affected by CPT1a deletion relative to male control mice. Mice with CPT1a deletion had reductions in DHA-containing phospholipids at the expense of monounsaturated fatty acids (MUFA)-containing phospholipids in both whole liver and at the level of the lipid droplet (LD). Male and female LKO mice increased RNA levels of genes involved in LD lipolysis ( Plin2 , Cidec , G0S2 ) and in polyunsaturated fatty acid (PUFA) metabolism ( Elovl5, Fads1, Elovl2 ), while only female LKO mice increased genes involved in inflammation ( Ly6d, Mmp12, Cxcl2 ). Kinase profiling showed decreased protein kinase A (PKA) activity, which coincided with increased PLIN2, PLIN5, and G0S2 protein levels and decreased triglyceride hydrolysis in LKO mice.

Conclusions

Liver-specific deletion of CPT1a promotes sexually dimorphic steatotic liver disease (SLD) in mice, and here we have identified new mechanisms by which females are protected from HFD-induced liver injury.

Graphical Summary

Circadian regulation of genetic and hormonal risk factors of cardiovascular disease in women

Cardiovascular disease is the leading cause of morbidity and mortality worldwide. However, sex differences can impact differently the etiology and outcome of cardiovascular disease when comparing men and women. Women have unique genetic and hormonal risk factors that can be associated with the development of cardiovascular diseases. Furthermore, certain phenotypes of cardiovascular diseases are more prevalent to women. Molecular clocks control circadian rhythms of different physiological systems in our body, including the cardiovascular system. Increased evidence in recent years points to a link between cardiovascular disease and regulation by circadian rhythms. However, the difference between circadian regulation of cardiovascular disease in women and men is poorly understood. In this review, we highlight the recent advances in circadian-regulated cardiovascular diseases with a specific focus on the pathogenesis of heart disease in women. Understanding circadian-regulated pathways and sex-specific differences between men and women may contribute to better diagnosis and development of sex-targeted interventions to better treat cardiovascular diseases.

Abdominal Obesity Is Associated with an Increased Risk of All-Cause Mortality in Males but Not in Females with HFpEF

Background. Association between abdominal obesity and development of heart failure (HF) with preserved ejection fraction (HFpEF) between the sexes is not completely understood. Objectives. This study evaluated the association between abdominal obesity and the risk of all-cause mortality in patients with HFpEF while performing a gender outcome comparison. Methods. A post hoc analysis was undertaken from the American cohort of the Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist (TOPCAT). The primary outcome (all-cause mortality) and the secondary outcomes (cardiovascular mortality, hospitalization for HF, stroke, and MI) were evaluated via Cox proportional hazards models to compare the hazard ratios (HRs) between sexes in HFpEF patients. Abdominal obesity was defined as a waist circumference of ≥102 cm in men and ≥88 cm in women. Results. A total of 3320 HFpEF patients (1620 men [48.80%] and 1700 women [51.20%]) were included in the analysis. The mean follow-up period was $3.4\pm 1.7$ years, with 503 patients dying during that time. After multivariable adjustment, abdominal obesity was significantly associated with an increased risk of all-cause mortality in males (adjusted HR: 1.32; 95% confidence interval [CI]: 1.02 to 1.71; $p=0.038$ ). Abdominal obesity was associated with hospitalization for HF in both male (adjusted HR: 1.39; 95% CI: 1.01 to 1.93; $p=0.045$ ) and female patients (adjusted HR: 1.15; 95% CI: 1.18 to 3.28; $p=0.010$ ). Conclusions. Abdominal obesity is associated with increased risks of all-cause mortality in the male but not the female HFpEF population and is associated with increased risks of hospitalization for HF in both sexes.

Intact mitochondrial substrate efflux is essential for prevention of tubular injury in a sex-dependent manner

The importance of healthy mitochondrial function is implicated in the prevention of chronic kidney disease (CKD) and diabetic kidney disease (DKD). Sex differences also play important roles in DKD. Our previous studies revealed that mitochondrial substrate overload (modeled by homozygous deletion of carnitine acetyl-transferase [CrAT]) in proximal tubules causes renal injury. Here, we demonstrate the importance of intact mitochondrial substrate efflux by titrating the amount of overload through the generation of a heterozygous CrAT-KO model (PT-CrATHET mouse). Intriguingly, these animals developed renal injury similarly to their homozygous counterparts. Mitochondria were structurally and functionally impaired in both sexes. Transcriptomic analyses, however, revealed striking sex differences. Male mice shut down fatty acid oxidation and several other metabolism-related pathways. Female mice had a significantly weaker transcriptional response in metabolism, but activation of inflammatory pathways was prominent. Proximal tubular cells from PT-CrATHET mice of both sexes exhibited a shift toward a more glycolytic phenotype, but female mice were still able to oxidize fatty acid-based substrates. Our results demonstrate that maintaining mitochondrial substrate metabolism balance is crucial to satisfying proximal tubular energy demand. Our findings have potentially broad implications, as both the glycolytic shift and the sexual dimorphisms discovered herein offer potentially new modalities for future interventions for treating kidney disease.

Evaluating the effects of carbon monoxide releasing molecule-2 against myocardial ischemia-reperfusion injury in ovariectomized female rats

PURPOSE

Cardioprotective effect of carbon monoxide, a gasotransmitter against myocardial ischemia-reperfusion injury (I/R), is well established in preclinical studies with male rats. However, its ischemic tolerance in post-menopausal animals has not been examined due to functional perturbations at the cellular level.

METHODS

The protective role of carbon monoxide releasing molecule-2 (CORM-2) on myocardial I/R was studied in female Wistar rats using the Langendorff apparatus. The animals were randomly divided into normal and ovariectomized (Ovx) female rats and were maintained 2 months post-surgery. Each group was further divided into 4 subgroups (n = 6/subgroup): normal, I/R, CORM-2-control (20 μmol/L), and CORM-2-I/R. The cardiac injury was estimated via myocardial infarct size, lactate dehydrogenase, and creatine kinase levels in coronary effluent and cardiac hemodynamic indices. Mitochondrial functional activity was assessed by measuring mitochondrial electron transport chain enzyme activities, swelling behavior, mitochondrial membrane potential, and oxidative stress.

RESULTS

Hemodynamic indices were significantly lower in ovariectomized rat hearts than in normal rat hearts. Sixty minutes of reperfusion of ischemic heart exhibited deteriorated cardiac physiological recovery in both ovariectomized and normal groups, where prominent decline was observed in ovariectomized rat. However, preconditioning the isolated heart with CORM-2 improved hemodynamics parameters significantly in both ovariectomized and normal rat hearts challenged with I/R, but with a limited degree of protection in ovariectomized rat hearts. The protective effect of CORM-2 was further confirmed via a reduction in cardiac injury, preservation of mitochondrial enzymes, and reduction in oxidative stress in all groups.

CONCLUSION

CORM-2 administration significantly attenuated myocardial I/R injury in ovariectomized rat hearts by attenuating I/R-associated mitochondrial perturbations and reducing oxidative stress.

Effects of high fructose intake on liver injury progression in high fat diet induced fatty liver disease in ovariectomized female mice

Epidemiology shows that the morbidity of nonalcoholic fatty liver disease (NAFLD) is increased in postmenopausal women and chronic high fructose intake induces NAFLD progression. To analyze the effects of high fructose intake on estrogen deficiency, we evaluated liver disease progression using ovariectomized mice fed with a high fat diet (HFD) for 12 weeks. Hepatic steatosis developed in all HFD groups. Fructose intake significantly increased the liver weight and serum alanine aminotransferase, which was not exacerbated by ovariectomy alone. Ovariectomy enhanced the hepatic inflammatory activity shown by tumor necrosis factor α upregulation in the groups with or without fructose intake. Both fructose intake and ovariectomy increased the hepatocytes with ballooning degeneration and hepatic macrophage infiltration and activated hepatic stellate cells. Coexistence of fructose intake and ovariectomy markedly enhanced liver cell destruction, macrophage accumulation, and progression of fibrosis. Liver damage was ameliorated by 17β-estradiol supplementation. These findings suggest that high fructose intake enhanced the progression of NAFLD in ovariectomized female mice.

Estrogenic Impact on Cardiac Ischemic/Reperfusion Injury

The increase in cardiovascular disease and metabolic syndrome incidence following the onset of menopause has highlighted the role of estrogen as a cardiometabolic protective agent. Specifically regarding the heart, estrogen induced an improvement in cardiac function, preserved calcium homeostasis, and inhibited the mitochondrial apoptotic pathway. The beneficial effects of estrogen in relation to cardiac ischemia/reperfusion (I/R) injury, such as reduced infarction and ameliorated post-ischemic recovery, have also been shown. Nevertheless, controversial findings exist and estrogen therapy is reported to be related to a higher rate of thromboembolic events and atrial fibrillation in post-menopausal women. Therefore, greater clarification is needed to evaluate the exact potential of estrogen use in cases of cardiac I/R injury. This article reviews the effects of estrogen, in both acute and chronic treatment, and collates the studies with regard to their in vivo, in vitro, or clinical trial settings in cases of cardiac I/R injury and myocardial infarction.

Recent advances in metabolic imaging

Abnormalities in myocardial substrate metabolism play a central role in the manifestations of most forms of cardiac disease such as ischemic heart disease, heart failure, hypertensive heart disease, and the cardiomyopathy due to either obesity or diabetes mellitus. Their importance is exemplified by both the development of numerous imaging tools designed to detect the specific metabolic perturbations or signatures related to these different diseases, and the vigorous efforts in drug discovery/development targeting various aspects of myocardial metabolism. Since the prior review in 2005, we have gained new insights into how perturbations in myocardial metabolism contribute to various forms of cardiac disease. For example, the application of advanced molecular biologic techniques and the development of elegant genetic models have highlighted the pleiotropic actions of cellular metabolism on energy transfer, signal transduction, cardiac growth, gene expression, and viability. In parallel, there have been significant advances in instrumentation, radiopharmaceutical design, and small animal imaging, which now permit a near completion of the translational pathway linking in-vitro measurements of metabolism with the human condition. In this review, most of the key advances in metabolic imaging will be described, their contribution to cardiovascular research highlighted, and potential new clinical applications proposed.

The cardioprotective effect of different doses of vasopressin (AVP) against ischemia-reperfusion injuries in the anesthetized rat heart

The aim of the present study was to investigate the protective effect of various doses of exogenous vasopressin (AVP) against ischemia-reperfusion injury in anesthetized rat heart. Anesthetized rats were randomly divided into seven groups (n=4-13) and all of them subjected to prolonged 30 min regional ischemia and 120 min reperfusion. Group I served as saline control with ischemia, in treatment groups II, III, IV and V, respectively different doses of AVP (0.015, 0.03, 0.06 and 1.2 μg/rat) were infused within 10 min prior to ischemia, in group VI, an AVP-selective V1 receptor antagonist (SR49059, 1mg/kg, i.v.) was administrated prior to effective dose of AVP injection and in group VII, SR49059 (1 mg/kg, i.v.) was only administrated prior to ischemia. Various doses of AVP significantly prevented the decrease in heart rate (HR) at the end of reperfusion compared to their baseline and decreased infarct size, biochemical parameters [LDH (lactate dehydrogenase), CK-MB (creatine kinase-MB) and MDA (malondialdehyde) plasma levels], severity and incidence of ventricular arrhythmia, episodes and duration of ventricular tachycardia (VT) as compared to control group. Blockade of V1 receptors by SR49059 attenuated the cardioprotective effect of AVP on ventricular arrhythmias and biochemical parameters, but partially returned infarct size to control. AVP 0.03 μg/rat was known as effective dose. Our results showed that AVP owns a cardioprotective effect probably via V1 receptors on cardiac myocyte against ischemia/reperfusion injury in rat heart in vivo.

Biphasic protective effect of oxytocin on cardiac ischemia/reperfusion injury in anaesthetized rats

Oxytocin (OT) is well known for its role in reproduction. However, evidence has emerged suggesting a role in cardiovascular system. The aim of this study was to investigate the cardioprotective effect of oxytocin on ischemia/reperfusion (I/R) injury in an in vivo rat. Myocardial ischemia, was surgically induced by means of left anterior descending coronary artery occlusion for 25 min followed by reperfusion for 120 min. Infarct size was evaluated using the staining agent 2,3,5-triphenyltetrazolium chloride. Creatine kinase-MB isoenzyme (CK-MB) and lactate dehydrogenase (LDH) levels in plasma were analyzed to assess the degree of cardiac injury. Intraperitoneal administration of OT 0.001, 0.01 and 0.1 microg significantly reduced infarct size, LDH and CK-MB levels as compared to control (I/R) group and it had a biphasic effect on the reduction of ischemia/reperfusion injury. This biphasic effect was revealed as a U-shaped curve in which efficacy was optimal between very low and very high doses. Furthermore there were no significant differences in mean arterial pressure or heart rate between the OT treatment groups and control group during I/R. Blockade of specific OT receptors by atosiban (10(-6)M) abolished or attenuated the effect of OT preconditioning. The result of this study shows that OT possess a dose-dependent cardioprotective effect against ischemia/reperfusion injury and so study of OT preconditioning may provide a new target site for therapeutic exploitation.

Sex dimorphism in cardiac pathophysiology: experimental findings, hormonal mechanisms, and molecular mechanisms

The higher cardiovascular risk in men and post-menopausal women implies a protective action of estrogen. A large number of experimental studies have provided strong support to this concept. However, the recent clinical trials with negative outcomes regarding hormone replacement therapy call for "post hoc" reassessment of existing information, models, and research strategies as well as a summary of recent findings. Sex steroid hormones, in particular estrogen, regulate numerous processes that are related to the development and progression of cardiovascular disease through a variety of signaling pathways. Use of genetically modified models has resulted in interesting information on diverse actions mediated by steroid receptors. By focusing on experimental findings, we have reviewed hormonal, cellular, and signaling mechanisms responsible for sex dimorphism and actions of hormone replacement therapy and addressed current limitations and future directions of experimental research.

Impact of hormone replacement on myocardial fatty acid metabolism: potential role of estrogen

BACKGROUND

Estrogen increases fatty acid utilization and oxidation and may decrease glucose use in human skeletal muscle, whereas these effects are attenuated by progesterone. Whether these ovarian hormones exhibit similar effects on myocardial metabolism is unknown.

METHODS AND RESULTS

Myocardial blood flow and oxygen consumption, as well as glucose and fatty acid metabolism, were examined retrospectively by use of positron emission tomography in 24 postmenopausal women receiving estrogen (n = 7), estrogen plus progesterone (n = 8), or no hormone replacement (n = 9) and in 22 age-matched men. Myocardial blood flow was higher in women regardless of hormone replacement status. Myocardial oxygen consumption was higher in women taking estrogen only when compared with men (7.3 +/- 1.6 micromol.g(-1).min(-1) vs 4.6 +/- 1.2 micromol.g(-1).min(-1), P < .001). Glucose utilization was not affected by gender or hormone replacement. Whereas fatty acid levels and the degree of myocardial fatty acid uptake were not distinguished by gender or hormone use, myocardial fatty acid utilization was higher in women taking estrogen when compared with men (259 +/- 68 nmol.g(-1).min(-1) vs 176 +/- 50 nmol.g(-1).min(-1), P = .01) and trended higher when compared with women not receiving hormonal therapy (185 +/- 46 nmol.g(-1).min(-1), P = .07) but was not different from that of women taking estrogen plus progesterone (205 +/- 58 nmol.g(-1).min(-1), P = not significant).

CONCLUSIONS

In postmenopausal women, estrogen use is associated with increased myocardial fatty acid utilization. Thus, when the cardiac effects of hormone replacement therapy are being assessed, alterations in myocardial substrate metabolism should be considered.

Bone Marrow Cells from Normal and Ovariectomized Rats Respond Differently to Basic Fibroblast Growth Factor and Bone Morphogenetic Protein 2 Treatmentin Vitro

The protein growth factors basic fibroblast growth factor (bFGF) and bone morphogenetic protein 2 (BMP-2) are being actively pursued for bone tissue engineering. Although both proteins are capable of stimulating osteogenic activity of bone marrow cells (BMCs), no studies have addressed the effect of estrogen deficiency on the growth factor responsiveness of BMCs. This study investigated the osteogenic response of BMCs from normal and ovariectomized (OVX) rats to bFGF and BMP- 2. In the absence of growth factors, a higher number of total colony-forming units (t-CFU) and alkaline phosphatase-expressing CFU (ALP-CFU) were obtained with BMCs derived from OVX rats. The percentage of ALP-CFU, however, was not significantly different between BMCs from the two groups of rats. Whereas BMP-2 did not influence the t-CFU and percentage of ALP-CFU, bFGF decreased t-CFU in BMCs derived from OVX rats and reduced the percentage of ALP-CFU in BMCs from both types of rats. Consistent with the higher t-CFU, the number of mineralized colonies (min-CFU) was also higher for BMCs derived from OVX rats. The number of min-CFU was not influenced by BMP-2 treatment, but was reduced with bFGF treatment. Comparison of the growth factor effects on a per-cell (DNA) basis confirmed the expected stimulatory effect of BMP-2 on ALP activity and mineralization in BMCs from normal rats, but these two parameters were not unequivocally stimulated in BMCs from OVX rats. We conclude that BMCs derived from normal and OVX rats exhibited significant differences in their osteogenic response to bFGF and BMP-2 treatment.

Effect of obesity and insulin resistance on myocardial substrate metabolism and efficiency in young women

BACKGROUND

Obesity is a risk factor for impaired cardiac performance, particularly in women. Animal studies suggest that alterations in myocardial fatty acid metabolism and efficiency in obesity can cause decreased cardiac performance. In the present study, we tested the hypothesis that myocardial fatty acid metabolism and efficiency are abnormal in obese women.

METHODS AND RESULTS

We studied 31 young women (body mass index [BMI] 19 to 52 kg/m2); 19 were obese (BMI >30 kg/m2). Myocardial oxygen consumption (MVO2) and fatty acid uptake (MFAUp), utilization (MFAU), and oxidation (MFAO) were quantified by positron emission tomography. Cardiac work was measured by echocardiography, and efficiency was calculated as work/MVO2. BMI correlated with MVO2 (r=0.58, P=0.0006), MFAUp (r=0.42, P<0.05), and efficiency (r=-0.40, P<0.05). Insulin resistance, quantified by the glucose area under the curve (AUC) during an oral glucose tolerance test, correlated with MFAUp (r=0.55, P<0.005), MFAU (r=0.62, P<0.001), and MFAO (r=0.58, P<0.005). A multivariate, stepwise regression analysis showed that BMI was the only independent predictor of MVO2 and efficiency (P=0.0005 and P<0.05, respectively). Glucose AUC was the only independent predictor of MFAUp, MFAU, and MFAO (P<0.05, <0.005, and <0.005, respectively).

CONCLUSIONS

In young women, obesity is a significant predictor of increased MVO2 and decreased efficiency, and insulin resistance is a robust predictor of MFAUp, MFAU, and MFAO. This increase in fatty acid metabolism and decrease in efficiency is concordant with observations made in experimental models of obesity. These metabolic changes may play a role in the pathogenesis of decreased cardiac performance in obese women.

Effect of estrogen replacement treatment on ischemic preconditioning in isolated rat hearts

In the present study, we tested the effects of long-term estrogen replacement treatment on myocardial ischemia-reperfusion injury and on the cardioprotection of ischemic preconditioning in isolated hearts from ovariectomized rats. Ovariectomized rats were treated with 17β-estradiol (30 µg/kg/d, s.c.) for 12 weeks. Isolated rat hearts were perfused in the Langendorff mode. Heart rate, coronary flow, left ventricular pressure and its first derivative (±LVdp/dtmax) were recorded. Fifteen-min global ischemia and 30-min reperfusion caused a significant decrease of cardiac mechanical function, which were not affected by ovariectomy or estrogen replacement treatment. The isolated hearts in all groups could be preconditioned, and the cardioprotection afforded by preconditioning in the sham-operated rats was greater compared with ovariectomized rats with or without estrogen treatment. These results suggest that long-term estrogen replacement treatment exerts no effect on the inhibition of mechanical function after ischemia-reperfusion, and this study also suggests that estrogen does not affect ischemic preconditioning in isolated hearts of ovariectomized rats.Key words: ERT (estrogen replacement treatment), ischemia-reperfusion, ischemic preconditioning, heart, rat.