Cardiovascular Protective Effects of NP-6A4, a Drug with the FDA Designation for Pediatric Cardiomyopathy, in Female Rats with Obesity and Pre-Diabetes

BACKGROUND

Obese and pre-diabetic women have a higher risk for cardiovascular death than age-matched men with the same symptoms, and there are no effective treatments. We reported that obese and pre-diabetic female Zucker Diabetic Fatty (ZDF-F) rats recapitulate metabolic and cardiac pathology of young obese and pre-diabetic women and exhibit suppression of cardio-reparative AT2R. Here, we investigated whether NP-6A4, a new AT2R agonist with the FDA designation for pediatric cardiomyopathy, mitigate heart disease in ZDF-F rats by restoring AT2R expression.

METHODS

ZDF-F rats on a high-fat diet (to induce hyperglycemia) were treated with saline, NP-6A4 (10 mg/kg/day), or NP-6A4 + PD123319 (AT2R-specific antagonist, 5 mg/kg/day) for 4 weeks (n = 21). Cardiac functions, structure, and signaling were assessed by echocardiography, histology, immunohistochemistry, immunoblotting, and cardiac proteome analysis.

RESULTS

NP-6A4 treatment attenuated cardiac dysfunction, microvascular damage (-625%) and cardiomyocyte hypertrophy (-263%), and increased capillary density (200%) and AT2R expression (240%) (p < 0.05). NP-6A4 activated a new 8-protein autophagy network and increased autophagy marker LC3-II but suppressed autophagy receptor p62 and autophagy inhibitor Rubicon. Co-treatment with AT2R antagonist PD123319 suppressed NP-6A4's protective effects, confirming that NP-6A4 acts through AT2R. NP-6A4-AT2R-induced cardioprotection was independent of changes in body weight, hyperglycemia, hyperinsulinemia, or blood pressure.

CONCLUSIONS

Cardiac autophagy impairment underlies heart disease induced by obesity and pre-diabetes, and there are no drugs to re-activate autophagy. We propose that NP-6A4 can be an effective drug to reactivate cardiac autophagy and treat obesity- and pre-diabetes-induced heart disease, particularly for young and obese women.

Using cultured canine cardiac slices to model the autophagic flux with doxorubicin

Chemotherapy-induced impairment of autophagy is implicated in cardiac toxicity induced by anti-cancer drugs. Imperfect translation from rodent models and lack of in vitro models of toxicity has limited investigation of autophagic flux dysregulation, preventing design of novel cardioprotective strategies based on autophagy control. Development of an adult heart tissue culture technique from a translational model will improve investigation of cardiac toxicity. We aimed to optimize a canine cardiac slice culture system for exploration of cancer therapy impact on intact cardiac tissue, creating a translatable model that maintains autophagy in culture and is amenable to autophagy modulation. Canine cardiac tissue slices (350 μm) were generated from left ventricular free wall collected from euthanized client-owned dogs (n = 7) free of cardiovascular disease at the Foster Hospital for Small Animals at Tufts University. Cell viability and apoptosis were quantified with MTT assay and TUNEL staining. Cardiac slices were challenged with doxorubicin and an autophagy activator (rapamycin) or inhibitor (chloroquine). Autophagic flux components (LC3, p62) were quantified by western blot. Cardiac slices retained high cell viability for >7 days in culture and basal levels of autophagic markers remained unchanged. Doxorubicin treatment resulted in perturbation of the autophagic flux and cell death, while rapamycin co-treatment restored normal autophagic flux and maintained cell survival. We developed an adult canine cardiac slice culture system appropriate for studying the effects of autophagic flux that may be applicable to drug toxicity evaluations.

A role for misaligned gene expression of fetal gene program in the loss of female-specific cardiovascular protection in young obese and diabetic females

Healthy, premenopausal women have the advantage of female-specific cardiovascular protection compared to age-matched healthy men. However, pathologies such as obesity and Type 2 diabetes mellitus (T2DM) cause losing of this female-specific cardiovascular protection in young, obese and diabetic females. Molecular mechanisms underlying this loss of female-specific cardiovascular protection in young, obese and diabetic females are not clearly elucidated. This review takes a close look at the latest advances in our understanding of sex differences in adult cardiac gene expression patterns in health and disease. Based on the emerging data, this review proposes that female biased gene expression patterns in healthy adult hearts of human and pre-clinical models support the existence of active fetal gene program in healthy, premenopausal female heart compared to age-matched healthy male heart. However, the misalignment of gene expression pattern in this female-specific active cardiac fetal gene program caused by pathologies such as obesity and T2DM may contribute to the loss of female-specific cardiovascular protection in young, obese and diabetic females.

Transdermal Delivery of High Molecular Weight Antibiotics to Deep Tissue Infections via Droplette Micromist Technology Device (DMTD)

Wound infection by multidrug-resistant (MDR) bacteria is a major disease burden. Systemic administration of broad-spectrum antibiotics colistin methanesulfonate (CMS) and vancomycin are the last lines of defense against deep wound infections by MDR bacteria. However, systemic administration of CMS and vancomycin are linked to life-threatening vital organ damage. Currently there are no effective topical application strategies to deliver these high molecular weight antibiotics across the stratum corneum. To overcome this difficulty, we tested if high molecular weight antibiotics delivered by Droplette micromist technology device (DMTD), a transdermal delivery device that generates a micromist capable of packaging large molecules, could attenuate deep skin tissue infections. Using green fluorescent protein-tagged E. coli and live tissue imaging, we show that (1) the extent of attenuation of deep-skin E. coli infection was similar when treated with topical DMTD- or systemic IP (intraperitoneal)-delivered CMS; (2) DMTD-delivered micromist did not spread the infection deeper; (3) topical DMTD delivery and IP delivery resulted in similar levels of vancomycin in the skin after a 2 h washout period; and (4) IP-delivered vancomycin was about 1000-fold higher in kidney and plasma than DMTD-delivered vancomycin indicating systemic toxicity. Thus, topical DMTD delivery of these antibiotics is a safe treatment for the difficult-to-treat deep skin tissue infections by MDR bacteria.

Suppression of Inflammatory Cardiac Cytokine Network in Rats with Untreated Obesity and Pre-Diabetes by AT2 Receptor Agonist NP-6A4

Obesity affects over 42% of the United States population and exacerbates heart disease, the leading cause of death in men and women. Obesity also increases pro-inflammatory cytokines that cause chronic tissue damage to vital organs. The standard-of-care does not sufficiently attenuate these inflammatory sequelae. Angiotensin II receptor AT2R is an anti-inflammatory and cardiovascular protective molecule; however, AT2R agonists are not used in the clinic to treat heart disease. NP-6A4 is a new AT2R peptide agonist with an FDA orphan drug designation for pediatric cardiomyopathy. NP-6A4 increases AT2R expression (mRNA and protein) and nitric oxide generation in human cardiovascular cells. AT2R-antagonist PD123319 and AT2RSiRNA suppress NP-6A4-effects indicating that NP-6A4 acts through AT2R. To determine whether NP-6A4 would mitigate cardiac damage from chronic inflammation induced by untreated obesity, we investigated the effects of 2-weeks NP-6A4 treatment (1.8 mg/kg delivered subcutaneously) on cardiac pathology of male Zucker obese (ZO) rats that display obesity, pre-diabetes and cardiac dysfunction. NP-6A4 attenuated cardiac diastolic and systolic dysfunction, cardiac fibrosis and cardiomyocyte hypertrophy, but increased myocardial capillary density. NP-6A4 treatment suppressed tubulointerstitial injury marker urinary β-NAG, and liver injury marker alkaline phosphatase in serum. These protective effects of NP-6A4 occurred in the presence of obesity, hyperinsulinemia, hyperglycemia, and hyperlipidemia, and without modulating blood pressure. NP-6A4 increased expression of AT2R (consistent with human cells) and cardioprotective erythropoietin (EPO) and Notch1 in ZO rat heart, but suppressed nineteen inflammatory cytokines. Cardiac miRNA profiling and in silico analysis showed that NP-6A4 activated a unique miRNA network that may regulate expression of AT2R, EPO, Notch1 and inflammatory cytokines, and mitigate cardiac pathology. Seventeen pro-inflammatory and pro-fibrotic cytokines that increase during lethal cytokine storms caused by infections such as COVID-19 were among the cytokines suppressed by NP-6A4 treatment in ZO rat heart. Thus, NP-6A4 activates a novel anti-inflammatory network comprised of 21 proteins in the heart that was not reported previously. Since NP-6A4's unique mode of action suppresses pro-inflammatory cytokine network and attenuates myocardial damage, it can be an ideal adjuvant drug with other anti-glycemic, anti-hypertensive, standard-of-care drugs to protect the heart tissues from pro-inflammatory and pro-fibrotic cytokine attack induced by obesity.

Angiotensin Type 2 Receptors: Painful, or Not?

Pain in response to various types of acute injury can be a protective stimulus to prevent the organism from using the injured part and allow tissue repair and healing. On the other hand, neuropathic pain, defined as ‘pain caused by a lesion or disease of the somatosensory nervous system’, is a debilitating pathology. The TRPA1 neurons in the Dorsal Root Ganglion (DRG) respond to reactive oxygen species (ROS) and induce pain. In acute nerve injury and inflammation, macrophages infiltrating the site of injury undergo an oxidative burst, and generate ROS that promote tissue repair and induce pain via TRPA1. The latter discourages using the injured limb, with a lack of movement helping wound healing. In chronic inflammation caused by diabetes, cancer etc., ROS levels increase systemically and modulate TRPA1 neuronal functions and cause debilitating neuropathic pain. It is important to distinguish between drug targets that elicit protective vs. debilitating pain when developing effective drugs for neuropathic pain. In this context, the connection of the Angiotensin type 2 receptor (AT₂R) to neuropathic pain presents an interesting dilemma. Several lines of evidence show that AT₂R activation promotes anti-inflammatory and anti-nociceptive signaling, tissue repair, and suppresses ROS in chronic inflammatory models. Conversely, some studies suggest that AT₂R antagonists are anti-nociceptive and therefore AT₂R is a drug target for neuropathic pain. However, AT₂R expression in nociceptive neurons is lacking, indicating that neuronal AT₂R is not involved in neuropathic pain. It is also important to consider that Novartis terminated their phase II clinical trial (EMPHENE) to validate that AT₂R antagonist EMA401 mitigates post-herpetic neuralgia. This trial, conducted in Australia, United Kingdom, and a number of European and Asian countries in 2019, was discontinued due to pre-clinical drug toxicity data. Moreover, early data from the trial did not show statistically significant positive outcomes. These facts suggest that may AT₂R not be the proper drug target for neuropathic pain in humans and its inhibition can be harmful.

Challenges and New Therapeutic Approaches in the Management of Chronic Wounds

Chronic non-healing wounds are estimated to cost the US healthcare $28-$31 billion per year. Diabetic ulcers, arterial and venous ulcers, and pressure ulcers are some of the most common types of chronic wounds. The burden of chronic wounds continues to rise due to the current epidemic of obesity and diabetes and the increase in elderly adults in the population who are more vulnerable to chronic wounds than younger individuals. This patient population is also highly vulnerable to debilitating infections caused by opportunistic and multi-drug resistant pathogens. Reduced microcirculation, decreased availability of cytokines and growth factors that promote wound closure and healing, and infections by multi-drug resistant and biofilm forming microbes are some of the critical factors that contribute to the development of chronic non-healing wounds. This review discusses novel approaches to understand chronic wound pathology and methods to improve chronic wound care, particularly when chronic wounds are infected by multi-drug resistant, biofilm forming microbes.

Pro-Senescence and Anti-Senescence Mechanisms of Cardiovascular Aging: Cardiac MicroRNA Regulation of Longevity Drug-Induced Autophagy

Chronological aging as well as biological aging accelerated by various pathologies such as diabetes and obesity contribute to cardiovascular aging, and structural and functional tissue damage of the heart and vasculature. Cardiovascular aging in humans is characterized by structural pathologic remodeling including cardiac and vascular fibrosis, hypertrophy, stiffness, micro- and macro-circulatory impairment, left ventricular diastolic dysfunction precipitating heart failure with either reduced or preserved ejection fraction, and cardiovascular cell death. Cellular senescence, an important hallmark of aging, is a critical factor that impairs repair and regeneration of damaged cells in cardiovascular tissues whereas autophagy, an intracellular catabolic process is an essential inherent mechanism that removes senescent cells throughout life time in all tissues. Several recent reviews have highlighted the fact that all longevity treatment paradigms to mitigate progression of aging-related pathologies converge in induction of autophagy, activation of AMP kinase (AMPK) and Sirtuin pathway, and inhibition of mechanistic target of rapamycin (mTOR). These longevity treatments include health style changes such as caloric restriction, and drug treatments using rapamycin, the first FDA-approved longevity drug, as well as other experimental longevity drugs such as metformin, rapamycin, aspirin, and resveratrol. However, in the heart tissue, autophagy induction has to be tightly regulated since evidence show excessive autophagy results in cardiomyopathy and heart failure. Here we discuss emerging evidence for microRNA-mediated tight regulation of autophagy in the heart in response to treatment with rapamycin, and novel approaches to monitor autophagy progression in a temporal manner to diagnose and regulate autophagy induction by longevity treatments.

AT2R agonist NP-6A4 mitigates aortic stiffness and proteolytic activity in mouse model of aneurysm

Clinical and experimental studies show that angiotensin II (AngII) promotes vascular pathology via activation of AngII type 1 receptors (AT1Rs). We recently reported that NP-6A4, a selective peptide agonist for AngII type 2 receptor (AT2R), exerts protective effects on human vascular cells subjected to serum starvation or doxorubicin exposure. In this study, we investigated whether NP-6A4-induced AT2R activation could mitigate AngII-induced abdominal aortic aneurism (AAA) using AngII-treated Apoe^-/- mice. Male Apoe^-/- mice were infused with AngII (1 µg/kg/min) by implanting osmotic pumps subcutaneously for 28 days. A subset of mice was pre-treated subcutaneously with NP-6A4 (2.5 mg/kg/day) or vehicle for 14 days prior to AngII, and treatments were continued for 28 days. NP-6A4 significantly reduced aortic stiffness of the abdominal aorta induced by AngII as determined by ultrasound functional analyses and histochemical analyses. NP-6A4 also increased nitric oxide bioavailability in aortic tissues and suppressed AngII-induced increases in monocyte chemotactic protein-1, osteopontin and proteolytic activity of the aorta. However, NP-6A4 did not affect maximal intraluminal aortic diameter or AAA incidences significantly. These data suggest that the effects of AT2R agonist on vascular pathologies are selective, affecting the aortic stiffness and proteolytic activity without affecting the size of AAA.

Deficiency of IL12p40 (Interleukin 12 p40) Promotes Ang II (Angiotensin II)-Induced Abdominal Aortic Aneurysm

Objective- Abdominal aortic aneurysm is caused by the accumulation of inflammatory cells in the aortic wall. Our recent studies demonstrated that inhibition of Notch signaling attenuates abdominal aortic aneurysm formation by shifting the macrophage balance towards anti-inflammatory (M2) phenotype. Using IL12p40^-/- (interleukin 12 p40) mice, we investigated the effects of M2-predominant macrophages on the development of abdominal aortic aneurysm. Approach and Results- Male (8-10 week-old) wild-type and IL12p40^-/- mice (n=15) on C57BL/6 background were infused with Ang II (angiotensin II, 1000 ng/kg per minute) by implanting osmotic pumps subcutaneously for 28 days. In the IL12p40^-/- mice, Ang II significantly increased the maximal intraluminal diameter (9/15) as determined by transabdominal ultrasound imaging. In addition, IL12p40-deletion significantly increased aortic stiffness in response to Ang II as measured by pulse wave velocity and atomic force microscopy. Histologically, IL12p40^-/- mice exhibited increased maximal external diameter of aorta and aortic lesions associated with collagen deposition and increased elastin fragmentation compared with wild-type mice infused with Ang II. Mechanistically, IL12p40 deficiency by siRNA (small interfering RNA) augmented the Tgfβ2-mediated Mmp2 expression in wild-type bone marrow-derived macrophages without affecting the expression of Mmp9. No such effects of IL12p40 deficiency on MMP2/MMP9 was observed in human aortic smooth muscle cells or fibroblasts. Depletion of macrophages in IL12p40^-/- mice by clodronate liposomes significantly decreased the maximal external diameter of aorta and aortic stiffness in response to Ang II as determined by imaging and atomic force microscopy. Conclusions- IL12p40 depletion promotes the development of abdominal aortic aneurysm, in part, by facilitating recruitment of M2-like macrophages and potentiating aortic stiffness and fibrosis mediated by Tgfβ2.

Cell-Specific Protective Signaling Induced by the Novel AT2R-Agonist NP-6A4 on Human Endothelial and Smooth Muscle Cells

Cardiovascular disease incidence continues to rise and new treatment paradigms are warranted. We reported previously that activation of Angiotensin II receptor (encoded by the X-linked Agtr2 gene) by a new peptide agonist, NP-6A4, was more effective in protecting mouse cardiomyocyte HL-1 cells and human coronary artery vascular smooth muscle cells (hCAVSMCs) from acute nutrient deficiency than other drugs tested. To elucidate further the protective effects of NP-6A4 in human cells, we studied the effects of NP-6A4 treatment on functions of human coronary artery endothelial cells (hCAECs), and hCAVSMCs. In hCAVSMCs, NP-6A4 (1 μM) increased Agtr2 mRNA (sixfold, p < 0.05) after 12-h exposure, whereas in hCAECs, significant increase in Agtr2 mRNA (hCAECs: eightfold) was observed after prolonged exposure. Interestingly, NP-6A4 treatment (1 μM, 12 h) increased AT2R protein levels in all human cells tested. Pre-treatment with AT2R-antagonist PD123319 (20 μM) and anti-AT2R siRNA (1 μM) suppressed this effect. Thus, NP-6A4 activates a positive feedback loop for AT2R expression and signaling in hCAVSMCs and hCAECs. NP-6A4 (1–20 μM) increased cell index (CI) of hCAVSMCs as determined by real time cell analyzer (RTCA), indicating that high concentrations of NP-6A4 were not cytotoxic for hCAVSMCs, rather promoting better cell attachment and growth. Seahorse Extracellular Flux Assay revealed that NP-6A4 (1 μM) treatment for 7 days increased whole cell-based mitochondrial parameters of hCAVSMCs, specifically maximal respiration (p < 0.05), spare respiratory capacity (p < 0.05) and ATP production (p < 0.05). NP-6A4 (1 μM; 7 days) also suppressed Reactive Oxygen Species (ROS) in hCAVSMCs. Exposure to Doxorubicin (DOXO) (1 μM) increased ROS in hCAVSMCs and this effect was suppressed by NP-6A4 (1 μM). In hCAECs grown in complete medium, NP-6A4 (1 μM) and Ang II (1 μM) exerted similar changes in CI. Additionally, NP-6A4 (5 μM: 12 h) increased expression of eNOS (sixfold, p < 0.05) and generation of nitric oxide (1.3-fold, p < 0.05) in hCAECs and pre-treatment with PD123319 (20 μM) suppressed this effect partially (65%). Finally, NP-6A4 decreased phosphorylation of Jun-N-terminal kinase, implicated in apoptosis of ECs in atherosclerotic sites. Taken together, NP-6A4, through its ability to increase AT2R expression and signaling, exerts different cell-specific protective effects in human VSMCs and ECs.

Diabetic Cardiomyopathy: Impact of Biological Sex on Disease Development and Molecular Signatures

Diabetic cardiomyopathy refers to a unique set of heart-specific pathological variables induced by hyperglycemia and insulin resistance. Given that cardiovascular disease (CVD) is the leading cause of death in the world, and type 2 diabetes incidence continues to rise, understanding the complex interplay between these two morbidities and developing novel therapeutic strategies is vital. Two hallmark characteristics specific to diabetic cardiomyopathy are diastolic dysfunction and cardiac structural mal-adaptations, arising from cardiac cellular responses to the complex toxicity induced by hyperglycemia with or without hyperinsulinemia. While type 2 diabetes is more prevalent in men compared to women, cardiovascular risk is higher in diabetic women than in diabetic men, suggesting that diabetic women take a steeper path to cardiomyopathy and heart failure. Accumulating evidence from randomized clinical trials indicate that although pre-menopausal women have lower risk of CVDs, compared to age-matched men, this advantage is lost in diabetic pre-menopausal women, which suggests estrogen availability does not protect from increased cardiovascular risk. Notably, few human studies have assessed molecular and cellular mechanisms regarding similarities and differences in the progression of diabetic cardiomyopathy in men versus women. Additionally, most pre-clinical rodent studies fail to include female animals, leaving a void in available data to truly understand the impact of biological sex differences in diabetes-induced dysfunction of cardiovascular cells. Elegant reviews in the past have discussed in detail the roles of estrogen-mediated signaling in cardiovascular protection, sex differences associated with telomerase activity in the heart, and cardiac responses to exercise. In this review, we focus on the emerging cellular and molecular markers that define sex differences in diabetic cardiomyopathy based on the recent clinical and pre-clinical evidence. We also discuss miR-208a, MED13, and AT2R, which may provide new therapeutic targets with hopes to develop novel treatment paradigms to treat diabetic cardiomyopathy uniquely between men and women.

Abstract 710: Deficiency of IL12p40 Promotes Angiotensin II-Induced Abdominal Aortic Aneurysm

Introduction: Abdominal aortic aneurysm (AAA) is caused by the immune and inflammatory cell accumulation of the aortic wall, leading to enhanced inflammation and aneurysm formation. Our recent studies demonstrate that inhibition of Notch signaling attenuates AAA formation by shifting the macrophage balance towards anti-inflammatory (M2) phenotype. Using IL12p40 knockout (KO) mice, we investigated the direct effects of M2-like macrophages in the development of AAA.

Methods and Results: Male (8-10 week-old) wild-type (WT) and IL12p40-KO mice (n=10) on C57BL/6 background were infused with angiotensin-II (AngII, 1,000 ng/kg/min) by implanting osmotic pumps subcutaneously for 28 days. Comparable increase in mean, systolic and diastolic arterial blood pressure was observed between WT and IL12p40-KO mice in response to AngII. Unexpectedly, AngII significantly increased the AAA-associated mortality (2/10) and luminal expansion (7/10) in IL12p40-KO mice as determined by transabdominal ultrasound. In addition, IL12p40-deficiency significantly increased aortic stiffness in the abdominal aortas in response to AngII than WT as measured by pulse wave velocity (PWV) and atomic force microscopy (AFM). Macroscopic and histological examination also showed that IL12p40-KO mice exhibited severe abdominal aortic lesion formation and increased maximal aortic width compared to WT mice. Increased elastin fragmentation and collagen deposition was detected in aorta of AngII-infused IL12p40-KO mice compared to AngII-infused WT mice. Further, there was no significant change in the total cholesterol, triglycerides and HDL-cholesterol levels in the serum of WT and IL12p40-KO mice treated with AngII. Importantly, bone marrow derived macrophages (BMDM) from IL12p40-KO mice showed increased mRNA expression of M2-markers (TGF-β1 and IL10) and decreased expression of M1-markers (iNOS and TNF-α) at basal level compared to WT BMDM.

Conclusions: IL12p40 deficiency may promote the development of AAA, in part, by facilitating recruitment of M2-like macrophages and potentiating aortic-stiffness and fibrosis mediated by TGF-β1 and IL10. In summary, optimal M1/M2 balance rather than predominance of M2-phenotype may be prerequisite to prevent AAA formation.

Cardiovascular disease progression in female Zucker Diabetic Fatty rats occurs via unique mechanisms compared to males

Population studies have shown that compared to diabetic men, diabetic women are at a higher risk of cardiovascular disease. However, the mechanisms underlying this gender disparity are unclear. Our studies in young murine models of type 2 diabetes mellitus (T2DM) and cardiovascular disease show that diabetic male rats develop increased cardiac fibrosis and suppression of intracardiac anti-fibrotic cytokines, while premenopausal diabetic female rats do not. This protection from cardiac fibrosis in female rats can be an estrogen-related effect. However, diabetic female rats develop early subclinical myocardial deformation, cardiac hypertrophy via elevated expression of pro-hypertrophic miR-208a, myocardial damage, and suppression of cardio-reparative Angiotensin II receptor 2 (Agtr2). Diabetic rats of both sexes exhibit a reduction in cardiac capillary density. However, diabetic female rats have reduced expression of neuropilin 1 that attenuates cardiomyopathy compared to diabetic male rats. A combination of cardiac hypertrophy and reduced capillary density likely contributed to increased myocardial structural damage in diabetic female rats. We propose expansion of existing cardiac assessments in diabetic female patients to detect myocardial deformation, cardiac hypertrophy and capillary density via non-invasive imaging, as well as suggest miR-208a, AT2R and neuropilin 1 as potential therapeutic targets and mechanistic biomarkers for cardiac disease in females.

Abstract P353: Attenuation of Cardiac Fibrosis, Hypertrophy and Myopathy by AT2R Agonist NP-6A4

Adverse cardiac remodeling (hypertrophy, fibrosis and myopathy) underlies cardiac dysfunction and heart failure. Male Zucker obese (ZO:fa/fa) rat that suffers from cardiac dysfunction, adverse remodeling, and heart failure with preserved ejection fraction is a useful model to study the effects of cardioprotective drugs. We reported that NP-6A4 (Novopyxis Inc. Cambridge, MA), a peptide agonist of the Angiotensin II Type 2 Receptor (AT2R), protected mouse cardiomyoblast HL-1 cells and human coronary artery vascular smooth muscle cells (hCAVSMCs) from acute nutrient serum deficiency stress better than β-AR-Blockers, ARBs, and AT2R agonist CGP42112A. This effect was inhibited by AT2R-specific antagonist PD123319, confirming that NP-6A4 acts through AT2R. AT2R is a cardiac and vascular reparative molecule that protects the heart and vasculature from structural damage and fibrosis. No current drugs increase AT2R expression. We report that NP-6A4 treatment (1μM) increased AT2R mRNA (up to 4 fold; p≤0.05) in hCAVSMCs and human coronary artery endothelial cells (up to 8 fold; p≤0.05). This effect was inhibited by PD123319 (10 μM). Treatment of 11-week old male ZO rats with heart disease with NP-6A4 (1.8mg/kg/day in saline, delivered once daily subcutaneously; N=7) increased cardiac AT2R expression and mitigated cardiac dysfunction and adverse remodeling. Quantitative RT-PCR and immunohistochemistry analysis showed that 2 weeks of NP-6A4 treatment increased cardiac AT2R mRNA (up to 9 fold) and protein (1.5-3 fold) compared to controls (N=6) receiving saline (p<0.01). NP-6A4 treatment improved cardiac parameters; endocardial circumferential strain (p≤0.05), myocardial performance index (MPI) (p≤0.005), and E/E’ ratio (p≤0.002). NP-6A4 treatment also increased cardiac capillary density (118% compared to saline treatedl; p≤0.002), and reduced interstitial fibrosis (77% compared to saline treated; p≤0.039.) At 19-weeks (after 8 weeks of treatment), cardiac tissues from 5 out of 6 control rats exhibited regions of myopathy. Only 2 out 7 NP-6A4 treated rats exhibited similar levels of myopathy in the heart. We propose that NP-6A4 attenuates adverse remodeling and improves cardiac function by increasing AT2R expression in cardiac cells.

mTORC1 inhibitors rapamycin and metformin affect cardiovascular markers differentially in ZDF rats

Mammalian target for rapamycin complex 1 (mTORC1) is a common target for the action of immunosuppressant macrolide rapamycin and glucose-lowering metformin. Inhibition of mTORC1 can exert both beneficial and detrimental effects in different pathologies. Here, we investigated the differential effects of rapamycin (1.2 mg/kg per day delivered subcutaneously for 6 weeks) and metformin (300 mg/kg per day delivered orally for 11 weeks) treatments on male Zucker diabetic fatty (ZDF) rats that mimic the cardiorenal pathology of type 2 diabetic patients and progress to insulin insufficiency. Rapamycin and metformin improved proteinuria, and rapamycin also reduced urinary gamma glutamyl transferase (GGT) indicating improvement of tubular health. Metformin reduced food and water intake, and urinary sodium and potassium, whereas rapamycin increased urinary sodium. Metformin reduced plasma alkaline phosphatase, but induced transaminitis as evidenced by significant increases in plasma AST and ALT. Metformin also induced hyperinsulinemia, but did not suppress fasting plasma glucose after ZDF rats reached 17 weeks of age, and worsened lipid profile. Rapamycin also induced mild transaminitis. Additionally, both rapamycin and metformin increased plasma uric acid and creatinine, biomarkers for cardiovascular and renal disease. These observations define how rapamycin and metformin differentially modulate metabolic profiles that regulate cardiorenal pathology in conditions of severe type 2 diabetes.

Regulation of the cardioprotective adiponectin and its receptor AdipoR1 by salt

Both circulating adiponectin (APN) and cardiac APN exert cardioprotective effects and improve insulin sensitivity and mitochondrial function. Low circulating APN serves as a biomarker for cardiovascular risk. Ablation of adiponectin receptor 1 (AdipoR1) causes myocardial mitochondrial dysfunction. Although high salt intake is a contributor to cardiovascular disease, how it modulates the expression of APN or AdipoR1 in cardiomyocytes is not known. We report that APN mRNA expression was attenuated in a dose-dependent manner in mouse cardiomyocyte cell line HL-1 exposed to salt concentrations ranging from 0.75% to 1.5% for 12 h. High-salt exposure (0.88% and 1.25% for 12 h) also suppressed APN and AdipoR1 protein expression significantly in rat cardiac muscle H9c2 cells. Co-immunostaining for AdipoR1 and mitochondrial complex 1 indicated that AdipoR1 may be co-localized with mitochondria. These data show for the first time that high salt is an important suppressor of cardiovascular protective APN and AdipoR1.

Loss of Nlrp3 Does Not Protect Mice from Western Diet-Induced Adipose Tissue Inflammation and Glucose Intolerance

We tested the hypothesis that loss of Nlrp3 would protect mice from Western diet-induced adipose tissue (AT) inflammation and associated glucose intolerance and cardiovascular complications. Five-week old C57BL6J wild-type (WT) and Nlrp3 knockout (Nlrp3-/-) mice were randomized to either a control diet (10% kcal from fat) or Western diet (45% kcal from fat and 1% cholesterol) for 24 weeks (n = 8/group). Contrary to our hypothesis that obesity-mediated white AT inflammation is Nlrp3-dependent, we found that Western diet-induced expression of AT inflammatory markers (i.e., Cd68, Cd11c, Emr1, Itgam, Lgals, Il18, Mcp1, Tnf, Ccr2, Ccl5 mRNAs, and Mac-2 protein) were not accompanied by increased caspase-1 cleavage, a hallmark feature of NLRP3 inflammasome activation. Furthermore, Nlrp3 null mice were not protected from Western diet-induced white or brown AT inflammation. Although Western diet promoted glucose intolerance in both WT and Nlrp3-/- mice, Nlrp3-/- mice were protected from Western diet-induced aortic stiffening. Additionally, Nlrp3-/- mice exhibited smaller cardiomyocytes and reduced cardiac fibrosis, independent of diet. Collectively, these findings suggest that presence of the Nlrp3 gene is not required for Western diet-induced AT inflammation and/or glucose intolerance; yet Nlrp3 appears to play a role in potentiating arterial stiffening, cardiac hypertrophy and fibrosis.

The two faces of miR-29

Diabetes mellitus is a metabolic homeostasis disease that contributes to additional comorbidities such as cardiovascular disease (CVD) and cancer. It has a long undiagnosed latent period during which there can be irreparable damage to the pancreas and cardiovascular tissues. Recent studies have highlighted the roles of several microRNAs in CVD. Determining the microRNAs that link diabetes mellitus and CVD is an important topic to be explored. In the present review, we discuss the microRNAs that contribute to the progression of diabetes mellitus and CVD and focus on the miR-29 family microRNAs whose expression is upregulated by hyperglycemia and proinflammatory cytokines, the hallmarks of diabetes mellitus. Upregulation of miR-29 expression is a key factor in the loss of pancreatic β cells and development of the first stage of type 1 diabetes mellitus (T1DM). Additionally, miR-29-mediated suppression of myeloid cell leukemia 1 (MCL-1), an important prosurvival protein, underlies Marfan's syndrome, abdominal aortic aneurysm, and diabetes mellitus-associated cardiomyocyte disorganization. Suppression of miR-29 expression and subsequent increase in the prosurvival MCL-1, however, promotes tumor development. Therefore, miR-29 mimics that suppress MCL-1 are hailed as tumor suppressors. The critical question is whether an increase in miR-29 levels is well tolerated in conditions of comorbidities in which insulin resistance is an underlying disease. In light of increasing awareness of the interconnection of diabetes mellitus, CVD, and cancer, it is of utmost importance to understand the mechanism of action of current treatment options on all of the comorbidities and careful evaluation of cardiovascular toxicity must accompany any treatment paradigm that increases miR-29 levels.

Regulation of cardiac miR-208a, an inducer of obesity, by rapamycin and nebivolol

OBJECTIVE

Resistance to obesity is observed in rodents and humans treated with rapamycin (Rap) or nebivolol (Neb). Because cardiac miR-208a promotes obesity, this study tested whether the modes of actions of Rap and Neb involve inhibition of miR-208a.

METHODS

Mouse cardiomyocyte HL-1 cells and Zucker obese (ZO) rats were used to investigate regulation of cardiac miR-208a.

RESULTS

Angiotensin II (Ang II) increased miR-208a expression in HL-1 cells. Pretreatment with an AT1 receptor (AT1R) antagonist, losartan (1 μM), antagonized this effect, whereas a phospholipase C inhibitor, U73122 (10 μM), and an NADPH oxidase inhibitor, apocynin (0.5 mM), did not. Ang II-induced increase in miR-208a was suppressed by Rap (10 nM), an inhibitor of nutrient sensor kinase mTORC1, and Neb (1 μM), a 3rd generation β-blocker that suppressed bioavailable AT1R binding of (125) I-Ang II. Thus, suppression of AT1R expression by Neb, inhibition of AT1R activation by losartan, and inhibition of AT1R-induced activation of mTORC1 by Rap attenuated the Ang II-induced increase in miR-208a. In ZO rats, Rap treatment (750 μg kg(-1)  day(-1) ; 12 weeks) reduced obesity despite similar food intake, suppressed cardiac miR-208a, and increased cardiac MED13, a suppresser of obesity.

CONCLUSIONS

Rap and Neb suppressed cardiac miR-208a. Suppression of miR-208a and increase in MED13 correlated with attenuated weight gain despite leptin resistance.

Abstract P623: Nutrient Stress Response of Cardiovascular Cells to β-Blockers, ARB and AT2R Agonists

To determine how cardioprotective drugs modulate cell response to nutrient starvation, we investigated the effects of β-blockers (Nebivolol [Neb], Carvedilol [Car], Metoprolol [Met] and Atenolol [Aten] (3μM each), Angiotensin II (Ang II) (300nM), AT1R blocker (ARB-Losartan (1μM)) and AT2R agonists (CGP42112A [CGP] and a novel peptide agonist NP-6A4 (300nM each)) on serum-starved HL-1 cardiomyocytes. The Xcelligence Real-Time Cell Analyzer (RTCA), which measures area covered by cells in microtiter plates and displays it as a unitless quantity called Cell Index (CI), was used to assess cellular changes in response to drug treatment. To find whether changes in CI are due to altered proliferation or cell size, we utilized the MTS Proliferation Assay, a colorimetric assay that measures formazan dye produced by viable cells, and fluorophore-conjugated Wheat Germ Agglutinin (WGA) labeling to measure cell size respectively. Difference in CI units is reported as % of CI units of cells treated with vehicle. CI units were suppressed by β-blockers (Aten≤15%; Met≤15%; Neb≤17%; Car≤8%), increased by Ang II (≥9.6%), CGP (≥14%) and NP-6A4 (≥25%), but not by losartan (n≥4 and p≤0.05 for all treatments). MTS assay revealed that only NP-6A4 increased (19%) formazan dye as measured at 490nm (n=3, p<0.05). Differences in cell size of WGA stained cells was calculated as % of size of cells treated with vehicle. Neb and Car decreased cell size (Neb≤14%, Car≤10%, p<0.05 and p<0.1 respectively), suggesting their mechanism for decrease in CI. Other treatments showed no significant change. Next, we determined changes in Myeloid cell leukemia 1 (MCL-1) levels, an essential protein for cardiomyocyte survival, in response to drug treatments by immunoblotting and immunofluorescence. β-Blockers suppressed MCL-1 expression in HL-1 cardiomyocytes (Neb≤26%, Car≤24%, Met≤24%, Aten≤16%) while AT2R agonists increased (CGP≥17%, NP-6A4≥28%, n=3; p<0.05 for all). Treatment of Female Human Coronary Artery Vascular Smooth Muscle Cells by these drugs also showed a similar expression pattern of expression for MCL-1 (CGP≥23%, NP-6A4≥43%). Therefore, AT2R agonist NP-6A4 is more effective in protecting serum starved cardiovascular cells.

Abstract P635: Improvement of Cardiovascular Outcomes in Diabetic Rats by a Novel Angiotensin II Receptor Peptide Agonist

Diabetes Mellitus (DM) is an independent predictor of cardiovascular disease (CVD). Recent reports show that Angiotensin II type 2 receptor (AT2R) promotes cardiac repair after myocardial infarction. Therefore, we hypothesized that activation of AT2R would improve cardiac function in diabetic rats. Male Zucker obese (ZO) rats are leptin receptor–deficient and exhibit hyperphagia, obesity, insulin resistance and hyperlipidemia. They are a widely used rodent model for early stage Type 2 DM (T2DM). We and others have reported that male ZO rats exhibit diastolic and systolic dysfunction. Therefore we investigated whether a two week treatment with an AT2R agonist could improve cardiac functions of young male ZO rats. Thirteen-week old male ZO rats were subjected to daily intraperitoneal injections (0.9mg/kg/day) with a novel peptide AT2R agonist, NP-6A4 (from Novopyxis, Inc.) dissolved in saline (n=7) or saline only (n=6) for two weeks. Conventional echocardiography and speckle tracking strain analysis were performed using a Vevo 2100 (visualsonics) small animal ultrasound system. Fasting (6 hours) plasma analysis showed that triglycerides (mg/dL) were significantly reduced in response to treatment (ZO+ Saline=1229±164; ZO+NP-6A4= 610±109; p<0.015). Importantly, NP-6A4 treatment improved E/E’ ratio (ZO+Saline= 32.3±2.06; ZO+NP-6A4= 26±2.1; p<0.005), which indicates a significant improvement in diastolic dysfunction. A unit rise in the E/E' ratio is associated with a 17% increment in risk of a cardiac event. Moreover, myocardial performance index of NP-6A4 treated rats was also reduced (ZO+ Saline= 0.516±0.03; ZO+ NP-6A4= 0.389±0.02; p<0.006). Finally, circumferential strain (deg/sec) of endocardium (short axis view) was also significantly improved in response to treatment, while no significant changes were observed in radial or longitudinal strains (ZO+ Saline= -20.56±1.65; ZO+ NP-6A4= -26.11±2.47; p<0.024). Collectively, these data suggest that activation of the AT2R by NP-6A4 had significant lipid lowering effect and improved diastolic and systolic functions in diabetic rats.

Abstract P636: Sex Differences in Cardioprotective AT2R Expression in Diabetic Rats and Its Correlation with Myocardial Damage

Diabetes mellitus (DM) is an independent risk factor for cardiovascular disease (CVD). Healthy, young women are protected from CVD, while diabetic women are more susceptible to CVD compared to age-matched diabetic men and non-diabetic women. Underlying mechanisms for this sex difference in CVD are not fully elucidated. The angiotensin II type 2 receptor (AT2R) is a member of the protective, vasodilative arm of the renin angiotensin system. The Agtr2 gene that codes for AT2R is X-linked, and increased Agtr2 expression is reported in female vasculature of rodent models. We hypothesized that a sex difference might exist in DM-associated regulation of cardiac AT2R expression. To test this, we used hyperglycemic, male and female Zucker diabetic fatty (ZDF) rats and age- and sex-matched normoglycemic Zucker lean (ZL) rats. The male ZDF (ZDF-M) rat is an established model of type 2 DM. We have reported previously that hyperglycemic, female ZDF (ZDF-F) rats had the highest body fat and lowest lean muscle mass compared to male and female lean rats (ZL-M, ZL-F) and ZDF-M. Cardiac Agtr2 expression was measured by qRT-PCR at 5-months, cardiac function by echocardiography was compared at 3- and 5-months, and histopathology of cardiac tissue was assessed at 5-months. ZL-F had a nearly 2-fold increase of Agtr2 compared to ZL-M (p<0.01). Relative to lean controls, ZDF-M had no significant change in Agtr2, while ZDF-F exhibited ~60% suppression (Rq=0.42) of Agtr2 (p<0.001). Echocardiography data revealed evidence of compensated systolic function in all groups since fractional shortening was >50% at both ages, while heart rate and stroke volume were similar. However, diastolic dysfunction was observed in both ZDF-F and ZDF-M, relative to their lean counterparts, due to increased isovolumic relaxation time and decreased early:late ventricular filling ratio (E/A). ZDF-F exhibited the highest cardiomyocyte hypertrophy (≥35% over ZL-F, ZL-M and ZDF-M). Both ZDF and ZDF-M showed mitochondrial clustering and disrupted spatial orientation of mitochondria relative to the sarcomere (assessed by TEM). Based on our results, we propose that myocardial remodeling, diastolic dysfunction and loss of cardioprotective AT2R may underlie greater susceptibility of diabetic females to CVD.

Abstract P622: Regulation of Neuroprotective Myeloid Cell Leukemia 1 by Rapamycin and AT2R Agonists in Dopaminergic Neuronal Cell-line

Myeloid Cell Leukemia I (MCL-1) is a critical protein for neuronal cell survival. MCL-1 is one of the anti-apoptotic proteins in the Bcl2 family. In neurons, MCL-1 regulates the rate of programmed cell death during development and after neuronal damage. It is now well established that without sufficient MCL-1 dopaminergic neuronal cells succumb to cell death under conditions of oxidative stress that result in neurodegenerative diseases such as Parkinsonism. Therefore, identifying drugs that can up-regulate the expression of MCL-1 in neuronal cells is critical for enhancing neuronal resistance to oxidative stress and improving neuronal survival. Aim of this study was to evaluate the effects of treatments with Rapamycin and a novel AT2R peptide agonist NP-6A4 on the MCL-1 expression in SH-SY5Y neuronal cell line. SH-SY5Y cells are a human-derived in vitro model of neuronal function and differentiation, expressing both adrenergic and dopaminergic markers. This cell line is a highly translational model for Parkinson's disease. Cells were maintained in a 1:1 mixture of DMEM and Ham's F-12 with 10% FBS. Cells were subjected to serum starvation and were treated with Rap (10nM), NP-6A4 (300nM) or their combination for 6 hours. MCL-1 protein expression was assessed by immunofluorescence using anti-MCL-1 antibody and a fluorophore-conjugated secondary antibody. Cells were imaged using a confocal microscope and fluorescence was quantified using Leica LAS AF software. It was observed that Rap treatment significantly suppressed MCL-1 expression in SH-SY5Y cells (~40% suppression, p<0.001), whereas Rap+NP-6A4 treatment reversed the Rap-mediated suppression of MCL-1 (p<0.0002). This data indicates that Rapamycin suppresses MCL-1 in dopaminergic neuronal cells and AT2R agonist, NP-6A4 is capable of reversing this effect.

Mineralocorticoid receptor antagonism treats obesity-associated cardiac diastolic dysfunction

Patients with obesity and diabetes mellitus exhibit a high prevalence of cardiac diastolic dysfunction (DD), an independent predictor of cardiovascular events for which no evidence-based treatment exists. In light of renin-angiotensin-aldosterone system activation in obesity and the cardioprotective action of mineralocorticoid receptor (MR) antagonists in systolic heart failure, we examined the hypothesis that MR blockade with a blood pressure-independent low-dose spironolactone (LSp) would treat obesity-associated DD in the Zucker obese (ZO) rat. Treatment of ZO rats exhibiting established DD with LSp normalized cardiac diastolic function, assessed by echocardiography. This was associated with reduced cardiac fibrosis, but not reduced hypertrophy, and restoration of endothelium-dependent vasodilation of isolated coronary arterioles via a nitric oxide-independent mechanism. Further mechanistic studies revealed that LSp reduced cardiac oxidative stress and improved endothelial insulin signaling, with no change in arteriolar stiffness. Infusion of Sprague-Dawley rats with the MR agonist aldosterone reproduced the DD noted in ZO rats. In addition, improved cardiac function in ZO-LSp rats was associated with attenuated systemic and adipose inflammation and an anti-inflammatory shift in cardiac immune cell mRNAs. Specifically, LSp increased cardiac markers of alternatively activated macrophages and regulatory T cells. ZO-LSp rats had unchanged blood pressure, serum potassium, systemic insulin sensitivity, or obesity-associated kidney injury, assessed by proteinuria. Taken together, these data demonstrate that MR antagonism effectively treats established obesity-related DD via blood pressure-independent mechanisms. These findings help identify a particular population with DD that might benefit from MR antagonist therapy, specifically patients with obesity and insulin resistance.

Abstract 609: Differential Effects of Rapamycin Treatment on Cardiac Pathology in Lean and Obese Rats

Rapamycin (Rap) is a widely-used drug in organ transplant prophylaxis, drug eluting stents to prevent coronary restenosis, and cancer therapy. Rap is also considered as an anti-aging drug that improves health and life-span. However, evidence also suggests that new-onset diabetes mellitus (DM) is an adverse outcome of Rap treatment. Since DM is an independent risk factor for heart disease, it is unclear whether chronic Rap treatment would be beneficial or detrimental for myocardium. To test the hypothesis that chronic Rap treatment would have differential effects on cardiac pathology in lean and obese insulin resistant individuals, we investigated the effect of 12-week Rap treatment (via subcutaneous implantation of Rap pellets delivering Rap at a concentration of 750μg/kg/day) on young (8-20 weeks), Zucker lean (ZL) rats and insulin resistant Zucker obese (ZO) rats. While Rap treatment significantly suppressed body weight, heart weight, fasting plasma levels of cholesterol, triglycerides, and LDL in ZO rats (p<0.05), it also worsened DM as indicated by severe hyperglycemia, polydipsia and polyuria (p<0.05). Conversely, Rap-treated ZL rats did not develop DM. Echocardiography showed that 14-week old ZO rats exhibited abnormalities in diastolic parameters, including decreases in the tissue doppler E’/A’ ratio, mitral inflow propagation velocity (Vp) indicative of impaired active phase relaxation, as well as increases in LV filling pressure (E/E’ and E/Vp ratios), isovolumic relaxation time (IVRT) and myocardial performance index (Tei index of global cardiac function) compared to age-matched ZL rats. With the exception of IVRT, these abnormalities were improved in ZO rats treated for 6 weeks with Rap. However, an additional 6 weeks of Rap treatment reversed this improvement in diastolic abnormalities. IVRT, Vp and E/Vp ratio tended to be more impaired in ZO rats with 12 week Rap treatment, although none of the trends reached statistical significance. Histopathology analysis revealed that Rap treatment induced significant cardiomyofibril disarray in both ZL and ZO rats (p<0.05). These observations suggest that Rap treatment advances DM in obese, insulin resistant rats and induces cardiac structural damage in both healthy and obese rats.

Abstract 629: Gender Differences In The Expression Of Cardioprotective Myeloid Cell Leukemia 1 (Mcl-1) In Diabetic Male And Female Rats

Diabetes Mellitus (DM) is an important risk factor for cardiovascular disease (CVD) and young, diabetic women are more susceptible to CVD compared to age-matched men and non-diabetic women. It is unclear how the progression of DM differentially affects cardiac pathology in males and females. In this context, recent studies have shown that myeloid cell leukemia 1 (MCL-1) plays an important role in cardiac protection and cardiac-specific ablation of Mcl-1 causes fatal dilated cardiomyopathy. We hypothesized that there is a gender difference in the expression of cardiac MCL-1 in young, diabetic males and females. To test this, we compared cardiac Mcl-1 expression in young rats (ages 11-12 weeks): diabetic males [ZDF obese (n=8)], non-diabetic females [ZDF lean (n=5)], and non-diabetic males [ZDF lean (n=8)] on Purina 5008 diet to young, diabetic female rats [ZDF obese (n=5)] on Research Diets D12468. Body composition analysis by EchoMRI showed that both male and female lean rats had increased muscle mass compared to their obese, diabetic counterparts, whereas obese, diabetic male and female rats had >5-fold increase in body fat than the corresponding lean controls (p<0.05). Fasting plasma insulin levels in lean female rats were lower than that seen in lean male rats; there was a 49-fold increase in diabetic females, and only a 12-fold increase in diabetic males, compared to lean counterparts (p<0.05). Fasting plasma glucose levels increased 2-3 fold in diabetic males and females, compared to lean controls (p<0.05). Quantitative RT-PCR analysis of mRNA isolated from cardiac tissues of lean and diabetic male and female rats showed that there was a 45% decrease in Mcl-1 mRNA in diabetic males compared to lean males, whereas there was an over 90% suppression of Mcl-1 mRNA in diabetic females compared to lean females (p<0.05). Previously, we have shown that insulin improves MCL-1 expression in female mouse cardiomyocytes. Data presented here suggest that although diabetic female rats have more severe hyperinsulinemia compared to diabetic male rats, loss of cardiac MCL-1 expression is more severe in diabetic females compared to diabetic males.This may underlie the loss of cardioprotective benefits in diabetic females.

Regulation of cardiac expression of the diabetic marker microRNA miR-29

Diabetes mellitus (DM) is an independent risk factor for heart disease and its underlying mechanisms are unclear. Increased expression of diabetic marker miR-29 family miRNAs (miR-29a, b and c) that suppress the pro-survival protein Myeloid Cell Leukemia 1(MCL-1) is reported in pancreatic β-cells in Type 1 DM. Whether an up-regulation of miR-29 family miRNAs and suppression of MCL-1 (dysregulation of miR-29-MCL-1 axis) occurs in diabetic heart is not known. This study tested the hypothesis that insulin regulates cardiac miR-29-MCL-1 axis and its dysregulation correlates with DM progression. In vitro studies with mouse cardiomyocyte HL-1 cells showed that insulin suppressed the expression of miR-29a, b and c and increased MCL-1 mRNA. Conversely, Rapamycin (Rap), a drug implicated in the new onset DM, increased the expression of miR-29a, b and c and suppressed MCL-1 and this effect was reversed by transfection with miR-29 inhibitors. Rap inhibited mammalian target of rapamycin complex 1 (mTORC1) signaling in HL-1 cells. Moreover, inhibition of either mTORC1 substrate S6K1 by PF-4708671, or eIF4E-induced translation by 4E1RCat suppressed MCL-1. We used Zucker diabetic fatty (ZDF) rat, a rodent model for DM, to test whether dysregulation of cardiac miR-29-MCL-1 axis correlates with DM progression. 11-week old ZDF rats exhibited significantly increased body weight, plasma glucose, insulin, cholesterol, triglycerides, body fat, heart weight, and decreased lean muscle mass compared to age-matched lean rats. Rap treatment (1.2 mg/kg/day, from 9-weeks to 15-weeks) significantly reduced plasma insulin, body weight and heart weight, and severely dysregulated cardiac miR-29-MCL1 axis in ZDF rats. Importantly, dysregulation of cardiac miR-29-MCL-1 axis in ZDF rat heart correlated with cardiac structural damage (disorganization or loss of myofibril bundles). We conclude that insulin and mTORC1 regulate cardiac miR-29-MCL-1 axis and its dysregulation caused by reduced insulin and mTORC1 inhibition increases the vulnerability of a diabetic heart to structural damage.

The β-blocker Nebivolol Is a GRK/β-arrestin biased agonist

Nebivolol, a third generation β-adrenoceptor (β-AR) antagonist (β-blocker), causes vasodilation by inducing nitric oxide (NO) production. The mechanism via which nebivolol induces NO production remains unknown, resulting in the genesis of much of the controversy regarding the pharmacological action of nebivolol. Carvedilol is another β-blocker that induces NO production. A prominent pharmacological mechanism of carvedilol is biased agonism that is independent of Gα_s and involves G protein-coupled receptor kinase (GRK)/β-arrestin signaling with downstream activation of the epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase (ERK). Due to the pharmacological similarities between nebivolol and carvedilol, we hypothesized that nebivolol is also a GRK/β-arrestin biased agonist. We tested this hypothesis utilizing mouse embryonic fibroblasts (MEFs) that solely express β₂-ARs, and HL-1 cardiac myocytes that express β₁- and β₂-ARs and no detectable β₃-ARs. We confirmed previous reports that nebivolol does not significantly alter cAMP levels and thus is not a classical agonist. Moreover, in both cell types, nebivolol induced rapid internalization of β-ARs indicating that nebivolol is also not a classical β-blocker. Furthermore, nebivolol treatment resulted in a time-dependent phosphorylation of ERK that was indistinguishable from carvedilol and similar in duration, but not amplitude, to isoproterenol. Nebivolol-mediated phosphorylation of ERK was sensitive to propranolol (non-selective β-AR-blocker), AG1478 (EGFR inhibitor), indicating that the signaling emanates from β-ARs and involves the EGFR. Furthermore, in MEFs, nebivolol-mediated phosphorylation of ERK was sensitive to pharmacological inhibition of GRK2 as well as siRNA knockdown of β-arrestin 1/2. Additionally, nebivolol induced redistribution of β-arrestin 2 from a diffuse staining pattern into more intense punctate spots. We conclude that nebivolol is a β₂-AR, and likely β₁-AR, GRK/β-arrestin biased agonist, which suggests that some of the unique clinically beneficial effects of nebivolol may be due to biased agonism at β₁- and/or β₂-ARs.

Renin inhibition and AT(1)R blockade improve metabolic signaling, oxidant stress and myocardial tissue remodeling

OBJECTIVE

Strategies that block angiotensin II actions on its angiotensin type 1 receptor or inhibit actions of aldosterone have been shown to reduce myocardial hypertrophy and interstitial fibrosis in states of insulin resistance. Thereby, we sought to determine if combination of direct renin inhibition with angiotensin type 1 receptor blockade in vivo, through greater reductions in systolic blood pressure (SBP) and aldosterone would attenuate left ventricular hypertrophy and interstitial fibrosis to a greater extent than either intervention alone.

MATERIALS/METHODS

We utilized the transgenic Ren2 rat which manifests increased tissue expression of murine renin which, in turn, results in increased renin-angiotensin system activity, aldosterone secretion and insulin resistance. Ren2 rats were treated with aliskiren, valsartan, the combination (aliskiren+valsartan), or vehicle for 21 days.

RESULTS

Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic blood pressure, elevated serum aldosterone levels, cardiac tissue hypertrophy, interstitial fibrosis and ultrastructural remodeling. These biochemical and functional alterations were accompanied by increases in the NADPH oxidase subunit Nox2 and 3-nitrotyrosine content along with increases in mammalian target of rapamycin and reductions in protein kinase B phosphorylation. Combination therapy contributed to greater reductions in systolic blood pressure and serum aldosterone but did not result in greater improvement in metabolic signaling or markers of oxidative stress, fibrosis or hypertrophy beyond either intervention alone.

CONCLUSIONS

Thereby, our data suggest that the greater impact of combination therapy on reductions in aldosterone does not translate into greater reductions in myocardial fibrosis or hypertrophy in this transgenic model of tissue renin overexpression.

Angiotensin type 1 receptor resistance to blockade in the opossum proximal tubule cell due to variations in the binding pocket

Blockade of the angiotensin (ANG) II receptor type 1 (AT(1)R) with angiotensin receptor blockers (ARBs) is widely used in the treatment of hypertension. However, ARBs are variably effective in reducing blood pressure, likely due, in part, to polymorphisms in the ARB binding pocket of the AT(1)R. Therefore, we need a better understanding of variations/polymorphisms that alter binding of ARBs in heterogeneous patient populations. The opossum proximal tubule cell (OKP) line is commonly used in research to evaluate renal sodium handling and therefore blood pressure. Investigating this issue, we found natural sequence variations in the opossum AT(1)R paralleling those observed in the human AT(1)R. Therefore, we posited that these sequence variations may explain ARB resistance. We demonstrate that OKP cells express AT(1)R mRNA, bind (125)I-labeled ANG II, and exhibit ANG II-induced phosphorylation of Jak2. However, Jak2 phosphorylation is not inhibited by five different ARBs commonly used to treat hypertension. Additionally, nonradioactive ANG II competes (125)I-ANG II efficiently, whereas a 10-fold molar excess of olmesartan and the ANG II receptor type 2 blocker PD-123319 is unable to block (125)I-ANG II binding. In contrast, ANG II binding to OKP cells stably expressing rat AT(1A)Rs, which have a conserved AT(1)R-binding pocket with human AT(1)R, is efficiently inhibited by olmesartan. A novel observation was that resistance to ARB binding to opossum AT(1)Rs correlates with variations from the human receptor at positions 108, 163, 192, and 198 within the ARB-binding pocket. These observations highlight the potential utility of evaluating AT(1)R polymorphisms within the ARB-binding pocket in various hypertensive populations.

RAS-Mediated Adaptive Mechanisms in Cardiovascular Tissues: Confounding Factors of RAS Blockade Therapy and Alternative Approaches

Since the classic experiments by Tigerstedt and Bergman that established the role of renin in hypertension a century ago, aggressive efforts have been launched to effectively block the renin-angiotensin system (RAS). Blockade of RAS is advocated at multiple levels by direct renin inhibitor, angiotensin-converting enzyme inhibitor and/or angiotensin II type 1 receptor blocker, or aldosterone inhibitor (spironolactone), and has now become part of the standard of care to control hypertension and related metabolic diseases including diabetes. However, recent lessons learned from randomized clinical trials question the wisdom of blocking RAS at multiple levels. In this context, it is highly pertinent that components of RAS are evolutionarily conserved, and novel physiological/adaptive/protective roles for renin and angiotensin-converting enzyme are currently emerging. Angiotensin II, the classical RAS effector peptide responsible for hypertension, hypertrophy, fluid retention and fibrosis, manifests its cardiovascular protective effect when it activates the angiotensin II type 2 receptor. Additionally, angiotensin-converting enzyme 2 and the angiotensin II metabolite Ang-(1-7) that acts through the Mas proto-oncogene constitute the cardiovascular and renal protective branch of RAS. It is conceivable that modulating this vasodilative/anti-inflammatory branch of RAS by activation of the RAS components that constitute this branch may offer a safer long-term treatment strategy to balance RAS activity and achieve homeostasis compared to chronic multilevel RAS inhibition.

Abstract 652: Regulation of Cardiac MicroRNA miR-208a by Angiotensin II and the Beta-Adrenergic Receptor Blocker Nebivolol

The microRNA miR-208a is a pathologic myo-miR required for hemodynamic pressure overload induced cardiac fibrosis. It is unclear how cardio-deleterious hormones and cardioprotective drugs regulate expression of miR-208a. We hypothesized that the pro-inflammatory hormone angiotensin II (Ang II) and anti-inflammatory drugs rapamycin (Rap: inhibitor of the nutrient sensor kinase mTOR) and nebivolol (Neb: a 3 rd generation β1 adrenergic receptor [β1-AR] blocker that exhibits β3-AR agonism) modulate miR-208a expression in cardiomyocytes.

Methods and Results: In mouse atrial cardiomyocyte HL-1 cells, 12 hour treatment with Ang II (100nM) increased miR-208a by 6 fold as determined by real-time RT-PCR analysis (P<0.05; n=5). AT1 receptor (AT1R) blocker losartan (10μM), but not AT2 receptor (AT2R) blocker PD123319 (10μM), inhibited this effect. Pre-treatment (1hr) with Rap (10nM) and Neb (1μM), but not apocynin (500μM: NADPH oxidase inhibitor) or U73122 ((10μM: Phospholipase C inhibitor) attenuated Ang II-induced increases in miR-208a levels (P<0.05). Thus, the AT1R-mediated activation of mTOR up-regulates miR-208a in cardiomyocytes. Immunoblotting revealed that Ang II increased phosphorylation (p) of mTOR (pSer 2448 ), S6K1 (pThr 389 ) and RPS6 (pSer 235/236 ) by 1.5 to 2 fold in HL-1 cells and Rap and Neb suppressed this effect (P<0.05). Neb-induced β3-AR agonism was not involved in miR-208a suppression since β3-AR antagonist SR52930 (1μM) did not reverse Neb-induced suppression of miR-208a and β3-AR mRNA was not detected in HL-1 cells by real time RT-PCR. Interestingly, a 12 hour treatment of HL-1 cardiomyocytes with 1μM Neb attenuated 125 I-Ang II binding to the AT1R by (70%: P<0.05); however a 15 minute pre-incubation with 1μM Neb did not prevent 125 I-Ang II binding to HL-1 cells. Thus, chronic Neb treatment down-regulates AT1R function in cardiomyocytes.

Conclusions: We show for the first time that Ang II increases miR-208a expression in cardiomyocytes via activation of mTOR-S6K1 signaling pathway. Nebivolol, a β-blocker, inhibits Ang II-induced miR-208a expression and mTOR signaling. Moreover, chronic Neb treatment down-regulates AT1R in cardiomyocytes. Regulation of AT1R-mTOR-miR-208a axis by Neb is a novel cardioprotective mechanism.

Over-nutrition and metabolic cardiomyopathy

Cardiovascular disease, which accounts for the highest morbidity and mortality in the United States, has several major risk factors, including aging and diabetes. Overweight and obesity, especially abdominal obesity, have been increasingly implicated as independent risk factors in the development of cardiovascular disease. Metabolic and/or diabetic cardiomyopathy has been especially associated with excess body weight caused by chronic over-nutrition and high-fat feeding. In the initial stages, obesity is now understood to cause significant dysregulation of cardiac fatty acid and glucose metabolism. These abnormalities are due, in part, to increased oxidative stress, which in turn can cause deleterious effects on intracellular signaling pathways that control cellular growth and proliferation. This increase in oxidative stress is coupled with reduced anti-oxidant species and dysregulation of metabolic signaling pathways. The cardiomyopathy seen with obesity is associated with increased interstitial fibrosis and diastolic dysfunction. Over time, evolving abnormalities include hypertrophy and systolic dysfunction, eventually leading to heart failure.

Abstract 321: Combination Dri With At1R Blockade Does Not Confer Additional Benefit to Improvement in Myocardial Tissue Hypertrophy and Fibrosis

Data support the notion that direct renin inhibition and angiotensin type 1 receptor (AT 1 R) blockade improve myocardial hypertrophy and fibrosis. Even with contemporary use of AT 1 R blockade and renin inhibition, the burden of heart failure remains high. Thereby, we sought to determine if combination of direct renin inhibition with AT 1 R blockade in vivo , through greater reductions in systolic blood pressure (SBP) and aldosterone would attenuate left ventricular (LV) hypertrophy and interstitial fibrosis to a greater extent than either intervention alone. We utilized the transgenic Ren2 rat which manifests increased expression of murine renin which, in turn, results in increased tissue RAS activity, aldosterone secretion and elevated SBP. Ren2 rats were treated with renin inhibition (aliskiren), AT 1 R blockade (valsartan), the combination (aliskiren+valsartan), or vehicle for 21 days. Compared to Sprague-Dawley controls, Ren2 rats displayed increased SBP, serum aldosterone levels, LV and cardiomyocyte hypertrophy, interstitial fibrosis and ultrastructural remodeling. These biochemical and functional alterations were accompanied by increases in LV tissue NADPH oxidase subunit Nox2 and 3-nitrotyrosine (3-NT) content along with increases in mammalian target of rapamycin (mTOR) and reductions in protein kinase B phosphorylation. Combination therapy contributed to greater reductions in SBP and serum aldosterone but did not result in greater improvement in metabolic signaling or markers of oxidative stress, fibrosis or hypertrophy beyond either intervention alone. Thereby, our data suggest that the greater impact of combination therapy on reductions in aldosterone does not translate into greater reductions in myocardial fibrosis or hypertrophy in this transgenic model of tissue renin overexpression.

Abstract 458: Obesity-related Alterations in Cardiac Lipid Profile During the Transition to Diastolic Dysfunction

Myocardial accumulation of fatty acids and lipid intermediates may contribute to cardiac dysfunction, but the interrelationship between different lipid species to diastolic dysfunction is not clearly understood. Herein, we examined changes in levels and composition of different lipid species during the progression to diastolic dysfunction in a clinically relevant model of obese insulin-resistant db/db mice at 12 and 15 wks of age. Obese db/db mice manifested loss of circadian BP dipping and diastolic dysfunction at 15 wks. Myocardial lipidomic analysis demonstrated elevated ceramides and fatty acids in db/db at 12 wks, but their levels were decreased at 15 wk and this was accompanied by increased fatty acid oxidation and enhanced production of reactive oxygen species. Triacylglyceride and diacylglyceride levels remained elevated at both 12 and 15 wk, but their composition changed to consist of more saturated and less unsaturated fatty acyl at 15 wks of age compared to 12 wk. Dysregulation of phospholipid metabolism persisted at 15 wk in db/db. Changes in triacylglyceride and diacylglyceride composition, phospholipid metabolism, β-oxidation, and oxidative stress that are temporally related to non-dipping of BP and diastolic dysfunction suggest a switch in metabolism of lipid intermediates contributes to the development of diastolic dysfunction in over-nutrition.

Regulation of Overnutrition-Induced Cardiac Inflammatory Mechanisms

BACKGROUND: Unlike conventional β-blockers, nebivolol, a third-generation β-adrenergic receptor blocker with vasodilator properties, promotes insulin sensitivity. Objective: The objective of this study was to determine whether nebivolol regulates overnutrition-induced activation of cardiac nutrient sensor kinases and inflammatory signaling. METHODS: Young Zucker obese (ZO) rats, a rodent model for overnutrition, and age-matched Zucker lean rats were treated with nebivolol (10 mg/kg/day; 21 days) and cardiac function was monitored by echocardiography and pressure volume loop analysis. Activation status of nutrient sensor serine/threonine kinases mammalian target for rapamycin (mTOR), and p70 S6kinase (S6K1) and S6K1-substrate RPS6, inflammatory marker Janus kinase 2 (Jak2) and its substrate STAT1, and energy sensor AMP-dependent kinase (AMPK) were monitored by determining phosphorylation status of pSer(2448) of mTOR, pThr(389) of S6K1, pSer(235/236) of RPS6, pTyr(1007/1008) of Jak2, pTyr(701) of STAT1, and pThr(172) of AMPK, respectively. RESULTS: Nebivolol reduced weight and improved cardiac function of ZO rats as shown by improvements in the myocardial performance index and a decrease in the diastolic parameter tau (τ), the time constant of isovolumic relaxation. Nebivolol also attenuated excessive activation of the nutrient sensor kinases mTOR and S6K1 and their substrate RPS6 as well as the inflammatory marker Jak2 and substrate STAT1 in ZO myocardium (p < 0.05). Moreover, nebivolol reversed suppression of the energy sensor kinase AMPK in ZO hearts (p < 0.05). CONCLUSION: We report for the first time that nebivolol regulates overnutrition-induced activation of cardiac mTOR and Jak/STAT signaling and reverses suppression of AMPK. Since it also suppresses weight gain, nebivolol appears effective in the treatment of overnutrition-related cardiac inflammation and diastolic dysfunction.

Combination of direct renin inhibition with angiotensin type 1 receptor blockade improves aldosterone but does not improve kidney injury in the transgenic Ren2 rat

Enhanced renin-angiotensin-aldosterone system (RAAS) activation contributes to proteinuria and chronic kidney disease by increasing glomerular and tubulointerstitial oxidative stress, promotion of fibrosis. Renin activation is the rate limiting step in angiotensin (Ang II) and aldosterone generation, and recent work suggests direct renin inhibition improves proteinuria comparable to that seen with Ang type 1 receptor (AT(1)R) blockade. This is important as, even with contemporary use of AT(1)R blockade, the burden of kidney disease remains high. Thereby, we sought to determine if combination of direct renin inhibition with AT(1)R blockade in vivo, via greater attenuation of kidney oxidative stress, would attenuate glomerular and proximal tubule injury to a greater extent than either intervention alone. We utilized the transgenic Ren2 rat with increased tissue RAS activity and higher serum levels of aldosterone, which manifests hypertension and proteinuria. Ren2 rats were treated with renin inhibition (aliskiren), AT(1)R blockade (valsartan), the combination (aliskiren+valsartan), or vehicle for 21days. Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic pressure (SBP), circulating aldosterone, proteinuria and greater urine levels of the proximal tubule protein excretory marker beta-N-acetylglucosaminidase (β-NAG). These functional and biochemical alterations were accompanied by increases in kidney tissue NADPH oxidase subunit Rac1 and 3-nitrotyrosine (3-NT) content as well as fibronectin and collagen type III. These findings occurred in conjunction with reductions in the podocyte-specific protein podocin as well as the proximal tubule-specific megalin. Further, in transgenic animals there was increased tubulointerstitial fibrosis on light microscopy as well as ultrastructural findings of glomerular podocyte foot-process effacement and reduced tubular apical endosomal/lysosomal activity. Combination therapy led to greater reductions in SBP and serum aldosterone, but did not result in greater improvement in markers of glomerular and tubular injury (i.e. β-NAG) compared to either intervention alone. Further, combination therapy did not improve markers of oxidative stress and podocyte and proximal tubule integrity in this transgenic model of RAAS-mediated kidney damage despite greater reductions in serum aldosterone and BP levels.

Nebivolol improves diastolic dysfunction and myocardial remodeling through reductions in oxidative stress in the transgenic (mRen2) rat

Angiotensin II contributes to myocardial tissue remodeling and interstitial fibrosis through NADPH oxidase-mediated generation of oxidative stress in the progression of heart failure. Recent data have suggested that nebivolol, a third-generation β-blocker, improves diastolic dysfunction by targeting nitric oxide (NO) and metabolic pathways that decrease interstitial fibrosis. We sought to determine if targeting NO would improve diastolic function in a model of tissue renin-angiotensin system overactivation. We used the transgenic (TG) (mRen2)27 rat, which overexpresses the murine renin transgene and manifests insulin resistance and left ventricular dysfunction. We treated 6- to 7-wk-old TG (mRen2)27 rats and age-matched Sprague-Dawley control rats with nebivolol (10 mg·kg(-1)·day(-1)) or placebo via osmotic minipumps for a period of 21 days. Compared with Sprague-Dawley control rats, TG (mRen2)27 rats displayed a prolonged diastolic relaxation time and reduced initial filling rate associated with increased interstitial fibrosis and left ventricular hypertrophy. These findings were temporally related to increased NADPH oxidase activity and subunits p47(phox) and Rac1 and increased total ROS and peroxynitrite formation in parallel with reductions in the antioxidant heme oxygenase as well as the phosphorylation/activation of endothelial NO synthase and PKB/Akt. Treatment with nebivolol restored diastolic function and interstitial fibrosis through increases in the phosphorylation of 5'-AMP-activated protein kinase, Akt, and endothelial NO synthase and reductions in oxidant stress. These results support that targeting NO with nebivolol treatment improves diastolic dysfunction through reducing myocardial oxidative stress by enhancing 5'-AMP-activated protein kinase and Akt activation of NO biosynthesis.

Overweight female rats selectively breed for low aerobic capacity exhibit increased myocardial fibrosis and diastolic dysfunction

The statistical association between endurance exercise capacity and cardiovascular disease suggests that impaired aerobic metabolism underlies the cardiovascular disease risk in men and women. To explore this connection, we applied divergent artificial selection in rats to develop low-capacity runner (LCR) and high-capacity runner (HCR) rats and found that disease risks segregated strongly with low running capacity. Here, we tested if inborn low aerobic capacity promotes differential sex-related cardiovascular effects. Compared with HCR males (HCR-M), LCR males (LCR-M) were overweight by 34% and had heavier retroperitoneal, epididymal, and omental fat pads; LCR females (LCR-F) were 20% heavier than HCR females (HCR-F), and their retroperitoneal, but not perireproductive or omental, fat pads were heavier as well. Unlike HCR-M, blood pressure was elevated in LCR-M, and this was accompanied by left ventricular (LV) hypertrophy. Like HCR-F, LCR-F exhibited normal blood pressure and LV weight as well as increased spontaneous cage activity compared with males. Despite normal blood pressures, LCR-F exhibited increased myocardial interstitial fibrosis and diastolic dysfunction, as indicated by increased LV stiffness, a decrease in the initial filling rate, and an increase in diastolic relaxation time. Although females exhibited increased arterial stiffness, ejection fraction was normal. Increased interstitial fibrosis and diastolic dysfunction in LCR-F was accompanied by the lowest protein levels of phosphorylated AMP-actived protein kinase [phospho-AMPK (Thr(172))] and silent information regulator 1. Thus, the combination of risk factors, including female sex, intrinsic low aerobic capacity, and overweightness, promote myocardial stiffness/fibrosis sufficient to induce diastolic dysfunction in the absence of hypertension and LV hypertrophy.