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.
insulin; metabolic; signaling; heart
Angiotensin receptor (type 1) blockers (ARBs) can reduce both hypertension and insulin resistance induced by local and systemic activation of the renin-angiotensin-aldosterone system. The effectiveness of azilsartan medoxomil (AZIL-M), a novel imidazole-based ARB, to facilitate metabolic improvements in conditions of angiotensin II (Ang II)-associated insulin resistance is currently unknown. The aim of this study was to determine the impact of chronic AZIL-M treatment on glucose transport activity and key insulin signaling elements in red skeletal muscle of Ang II-treated rats. Male Sprague-Dawley rats were treated for 8 weeks with or without Ang II (200 ng/kg/min) combined with either vehicle or AZIL-M (1 mg/kg/day). Ang II induced significant (p < 0.05) increases in blood pressure, which were completely prevented by AZIL-M. Furthermore, Ang II reduced insulin-mediated glucose transport activity in incubated soleus muscle, and AZIL-M co-treatment increased this parameter. Moreover, AZIL-M treatment of Ang II-infused animals increased the absolute phosphorylation of insulin signaling molecules, including Akt [both Ser473 (81%) and Thr308 (23%)] and AS160 Thr642 (42%), in red gastrocnemius muscle frozen in situ. Absolute AMPKα (Thr172) phosphorylation increased (98%) by AZIL-M treatment, and relative Thr389 phosphorylation of p70 S6K1, a negative regulator of insulin signaling, decreased (51%) with AZIL-M treatment. These results indicate that ARB AZIL-M improves the in vitro insulin action on glucose transport in red soleus muscle and the functionality of the Akt/AS160 axis in red gastrocnemius muscle in situ in Ang II-induced insulin-resistant rats, with the latter modification possibly associated with enhanced AMPKα and suppressed p70 S6K1 activation.
Angiotensin II; Glucose transport; Red skeletal muscle; Akt; AS160; AMPK; p70 S6K1
The prevalence of obesity and diabetes continues to rise in the United States and worldwide. These findings parallel the expansion of childhood obesity and diabetes. Obesity is a central component of the cardiorenal metabolic syndrome (CRS) which increases the risk for cardiovascular disease (CVD) and chronic kidney disease (CKD). The hallmark of obesity, CRS, and early type 2 diabetes is insulin resistance, a result of decreased insulin metabolic signaling due, in part, to enhanced serine phosphorylation and/or proteasome-mediated degradation of the insulin receptor substrate. Cardiovascular and renal insulin resistance significantly contributes to endothelial dysfunction, impaired cardiac diastolic and vascular relaxation, glomerular injury, and tubular dysfunction. In this context, multiple factors including oxidative stress, increased inflammation, and inappropriate activation of the renin-angiotensin-aldosterone and the sympathetic nervous system contribute to overweight- and obesity-induced systemic and tissue insulin resistance. One common link between obesity and the development of insulin resistance appears to be a low-grade inflammatory response resulting from dysfunctional innate and adaptive immunity. In this regard, there has been recent work on the role of dipeptidyl peptidase-4 (DPP-4) in modulating innate and adaptive immunity. The direct effects of DPP-4 on immune cells and the indirect effects through GLP-1-dependent and -independent pathways suggest effects of DPP-4 inhibition may have beneficial effects beyond glycemic control in improving CVD and renal outcomes. Accordingly, this review addresses new insights into the role of DPP-4 in immune modulation and the potential beneficial effects of DPP-4 inhibitors in insulin resistance and associated CVD and CKD prevention.
DPP-4; Cardiorenal syndrome; Obesity; Diabetes; Insulin resistance
The mammalian target of rapamycin (mTOR) is a serine kinase that regulates phosphorylation (p) of its target ribosomal S6 kinase (S6K1), whose activation can lead to glomerular and proximal tubular cell (PTC) injury and associated proteinuria. Increased mTOR/S6K1 signaling regulates signaling pathways that target fibrosis through adherens junctions. Recent data indicate aldosterone signaling through the mineralocorticoid receptor (MR) can activate the mTOR pathway. Further, antagonism of the MR has beneficial effects on proteinuria that occur independent of hemodynamics.
Accordingly, hypertensive transgenic TG(mRen2)27 (Ren2) rats, with elevated serum aldosterone and proteinuria, and age-matched Sprague-Dawley rats were treated with either a low dose (1 mg/kg/day) or a conventional dose (30 mg/kg/day) of spironolactone (MR antagonist) or placebo for 3 weeks.
Ren2 rats displayed increases in urine levels of the PTC brush border lysosomal enzyme N-acetyl-β-aminoglycosidase (β-NAG) in conjunction with reductions in PTC megalin, the apical membrane adherens protein T-cadherin and basolateral α-(E)-catenin, and fibrosis. In concert with these abnormalities, Ren2 renal cortical tissue also displayed increased Ser2448 (p)/activation of mTOR and Thr389 (p)-S6K1 and increased 3-nitrotyrosine (3-NT) content, a marker for peroxynitrite. Low-dose spironolactone had no effect on blood pressure but decreased proteinuria and β-NAG comparable to a conventional dose of this MR antagonist. Both doses of spironolactone attenuated ultrastructural maladaptive alterations and led to comparable reductions in (p)-mTOR/(p)-S6K1, 3-NT, fibrosis, and increased expression of α-(E)-catenin, T- and N-cadherin.
Thereby, MR antagonism improves proximal tubule integrity by targeting mTOR/S6K1 signaling and redox status independent of changes in blood pressure.
Cadherin; Megalin; β-NAG; Proteinuria
Epidemiological studies support the notion that arterial stiffness is an independent predictor of adverse cardiovascular events contributing significantly to systolic hypertension, impaired ventricular-arterial coupling and diastolic dysfunction, impairment in myocardial oxygen supply and demand, and progression of kidney disease. Although arterial stiffness is associated with aging, it is accelerated in the presence of obesity and diabetes. The prevalence of arterial stiffness parallels the increase of obesity that is occurring in epidemic proportions and is partly driven by a sedentary life style and consumption of a high fructose, high salt, and high fat western diet. Although the underlying mechanisms and mediators of arterial stiffness are not well understood, accumulating evidence supports the role of insulin resistance and endothelial dysfunction. The local tissue renin-angiotensin-aldosterone system (RAAS) in the vascular tissue and immune cells and perivascular adipose tissue is recognized as an important element involved in endothelial dysfunction which contributes significantly to arterial stiffness. Activation of vascular RAAS is seen in humans and animal models of obesity and diabetes, and associated with enhanced oxidative stress and inflammation in the vascular tissue. The cross talk between angiotensin and aldosterone underscores the importance of mineralocorticoid receptors in modulation of insulin resistance, decreased bioavailability of nitric oxide, endothelial dysfunction, and arterial stiffness. In addition, both innate and adaptive immunity are involved in this local tissue activation of RAAS. In this review we will attempt to present a unifying mechanism of how environmental and immunological factors are involved in this local tissue RAAS activation, and the role of this process in the development of endothelial dysfunction and arterial stiffness and targeting tissue RAAS activation.
renin-angiotensin-aldosterone system; arterial stiffness; insulin resistance; endothelial dysfunction; obesity; diabetes
Angiotensin (Ang) II contributes to tubulointerstitial fibrosis. Recent data highlight mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) signaling in tubulointerstitial fibrosis; however, the mechanisms remain unclear. Thereby, we investigated the role of Ang II on mTOR/S6K1-dependent proximal tubule (PT) injury, remodeling, and fibrosis.
We utilized young transgenic Ren2 rats (R2-T) and Sprague-Dawley rats (SD-T) treated with the Ang type 1 receptor (AT1R) blocker telmisartan (2 mg · kg−1 · day−1) or vehicle (R2-C; SD-C) for 3 weeks to examine PT structure and function.
Ren2 rats displayed increased systolic blood pressure, proteinuria and increased PT oxidant stress and remodeling. There were parallel increases in kidney injury molecule-1 and reductions in neprilysin and megalin with associated ultrastructural findings of decreased clathrin-coated pits, endosomes, and vacuoles. Ren2 rats displayed increased Serine2448 phosphorylation of mTOR and downstream S6K1, in concert with ultrastructural basement membrane thickening, tubulointerstitial fibrosis and loss of the adhesion molecule N-cadherin. Telmisartan treatment attenuated proteinuria as well as the biochemical and tubulointerstitial structural abnormalities seen in the Ren2 rats.
Our observations suggest that Ang II activation of the AT1R contributes to PT brush border injury and remodeling, in part, due to enhanced mTOR/S6K1 signaling which promotes tubulointerstitial fibrosis through loss of N-cadherin.
Angiotensin II; mTOR; N-Cadherin; Proximal tubule; Tubulointerstitial fibrosis
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.
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 pSer2448 of mTOR, pThr389 of S6K1, pSer235/236 of RPS6, pTyr1007/1008 of Jak2, pTyr701 of STAT1, and pThr172 of AMPK, respectively.
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).
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.
Nebivolol; Zucker obese; AMP kinase; mTORC1; Jak/STAT
The presence of a group of interacting maladaptive factors, including hypertension, insulin resistance, metabolic dyslipidemia, obesity, and microalbuminuria and/or reduced renal function, collectively constitutes the cardiorenal metabolic syndrome (CRS). Nutritional and other environmental cues during fetal development can permanently affect the composition, homeostatic systems, and functions of multiple organs and systems; this process has been referred to as ‘programming’. Since the original formulation of the notion that low birth weight is a proxy for ‘prenatal programming’ of adult hypertension and cardiovascular disease, evidence has also emerged for programming of kidney disease, insulin resistance, obesity, metabolic dyslipidemia, and other chronic diseases. The programming concept was initially predicated on the notion that in utero growth restriction due to famine was responsible for increased hypertension, and cardiovascular and renal diseases. On the other hand, we are now more commonly exposed to increasing rates of maternal obesity. The current review will discuss the overarching role of maternal overnutrition, as well as fetal undernutrition, in epigenetic programming in relation to the pathogenesis of the CRS in children and adults.
Albuminuria; Dyslipidemia; Fetal development; Hypertension; Insulin resistance; Malnutrition; Pediatric obesity
Overnutrition characterized by overconsumption of food rich in fat and carbohydrates is a significant contributor to hypertension, type 2 diabetes, and the cardiorenal syndrome. Overnutrition activates the renin-angiotensin-aldosterone system (RAAS) and causes chronic exposure of cardiovascular and renal tissue to increased circulating nutrients, insulin (INS), and angiotensin II (ANG II). Emerging evidence suggests that overnutrition, aldosterone, and ANG II promote INS resistance, a chronic condition that underlies these co-morbidities, through activation of the mammalian target of the rapamycin (mTOR)/S6 kinase 1 (S6K1) signaling pathway in cardiovascular tissue and the kidney. However, a novel ANG II type 2 receptor (AT2R)-mediated cross talk between the RAAS and mTOR pathways ameliorates overnutrition-induced activation of mTOR/S6K1 signaling in cardiovascular tissue of rats, mice, and humans and confers cardioprotection.
Overnutrition; Hypertension; Insulin metabolic signaling; Progressive kidney disease
Obesity has reached epidemic proportions with far-reaching health care and economic implications. Overnutrition, characterized by excess intake of carbohydrates and fats, has been associated with end-organ damage in several tissues, including the heart and the kidney. Furthermore, overnutrition is one of the most important modifiable and preventable causes of morbidity and mortality associated with cardiovascular and kidney diseases. Insulin resistance and compensatory hyperinsulinemia as well as associated mechanisms, including enhanced renin-angiotensin-aldosterone system activity, inflammation, and oxidative stress, have been implicated in obesity-related cardiorenal injury. In this review, the effect of overnutrition on heart and kidney disease is assessed in a rodent model of overnutrition and obesity, the Zucker obese rat.
Cardiorenal syndrome; Heart/kidney disease; Obesity; Overnutrition; Zucker rat model
Recent data implicate oxidative stress as a mediator of pulmonary hypertension (PH) and of the associated pathological changes to the pulmonary vasculature and right ventricle (RV). Increases in reactive oxygen species (ROS), altered redox state, and elevated oxidant stress have been demonstrated in the lungs and RV of several animal models of PH, including chronic hypoxia, monocrotaline toxicity, caveolin-1 knock-out mouse, and the transgenic Ren2 rat which overexpresses the mouse renin gene. Generation of ROS in these models is derived mostly from the activities of the nicotinamide adenine dinucleotide phosphate oxidases, xanthine oxidase, and uncoupled endothelial nitric oxide synthase. As disease progresses circulating monocytes and bone marrow-derived monocytic progenitor cells are attracted to and accumulate in the pulmonary vasculature. Once established, these inflammatory cells generate ROS and secrete mitogenic and fibrogenic cytokines that induce cell proliferation and fibrosis in the vascular wall resulting in progressive vascular remodeling. Deficiencies in antioxidant enzymes also contribute to pulmonary hypertensive states. Current therapies were developed to improve endothelial function, reduce pulmonary artery pressure, and slow the progression of vascular remodeling in the pulmonary vasculature by targeting deficiencies in either NO (PDE-type 5 inhibition) or PGI2 (prostacyclin analogs), or excessive synthesis of ET-1 (ET receptor blockers) with the intent to improve patient clinical status and survival. New therapies may slow disease progression to some extent, but long term management has not been achieved and mortality is still high. Although little is known concerning the effects of current pulmonary arterial hypertension treatments on RV structure and function, interest in this area is increasing. Development of therapeutic strategies that simultaneously target pathology in the pulmonary vasculature and RV may be beneficial in reducing mortality associated with RV failure.
Pulmonary arterial hypertension; Rosuvastatin; Oxidative stress; Nicotinamide adenine dinucleotide phosphate oxidase; Statins
Insulin resistance is associated with obesity and may be accompanied by left ventricular diastolic dysfunction and myocardial remodeling. Decreased insulin metabolic signaling and increased oxidative stress may promote these maladaptive changes. In this context, the β-blocker nebivolol has been reported to improve insulin sensitivity, increase eNOS activity, and reduce NADPH oxidase-induced superoxide generation. We hypothesized that nebivolol would attenuate diastolic dysfunction and myocardial remodeling by blunting myocardial oxidant stress and promoting insulin metabolic signaling in a rodent model of obesity, insulin resistance, and hypertension. Six week old male Zucker obese (ZO) and age-matched Zucker lean (ZL) rats were treated with nebivolol (10 mg·kg−1·day−1) for 21 days and myocardial function was assessed by cine magnetic resonance imaging. Compared to untreated ZL rats, untreated ZO rats exhibited prolonged diastolic relaxation time (27.7±2.5 vs 40.9±2.0 ms; P<0.05) and reduced initial diastolic filling rate (6.2±0.5 vs 2.8±0.6 μl/ms; P<0.05) in conjunction with increased HOMA-IR (7±2 vs 95±21; P<0.05), interstitial and pericapillary fibrosis, abnormal cardiomyocyte histoarchitecture, 3-nitrotyrosine, and NADPH oxidase-dependent superoxide. Nebivolol improved diastolic relaxation (32.8±0.7 ms; P<0.05 vs untreated ZO), reduced fibrosis and remodeling in ZO rats, in concert with reductions in nitrotyrosine, NADPH oxidase-dependent superoxide, and improvements in the insulin metabolic signaling, eNOS activation, and weight gain (381±7 vs 338±14 g; P<0.05). Results support the hypothesis that nebivolol reduces myocardial structural maladaptive changes and improves diastolic relaxation in concert with improvements in insulin sensitivity, and eNOS activation, concomitantly with reductions in oxidative stress.
nebivolol; oxidative stress; insulin resistance; diastolic relaxation; MRI
Emerging evidence indicates that mineralocorticoid receptor (MR) blockade reduces the risk of cardiovascular events beyond those predicted by its blood pressure (BP)-lowering actions; however, the underlying mechanisms remain unclear. To investigate whether protection elicited by MR blockade is through attenuation of vascular apoptosis and injury, independently of BPlowering, we administered a low dose of the MR antagonist spironolactone or vehicle for 21 days to hypertensive transgenic Ren2 rats with elevated plasma aldosterone levels. Although Ren2 rats developed higher systolic BPs compared to Sprague-Dawley (SD) littermates, low dose spironolactone treatment did not reduce systolic BP compared with untreated Ren2 rats. Ren2 rats exhibited vascular injury as evidenced by increased apoptosis, hemidesmosome-like structure loss, mitochondrial abnormalities, and lipid accumulation compared with SD, and these abnormalities were attenuated by MR antagonism. Protein kinase B (Akt) activation is critical to vascular homeostasis via regulation of cell survival and expression of apoptotic genes. Akt serine473 phosphorylation was impaired in Ren2 aortas, and restored with MR antagonism. In vivo MR antagonist treatment promoted anti-apoptotic effects by increasing phosphorylation of BAD serine136 and expression of Bcl-2 and Bcl-xL, decreasing cytochrome c release and BAD expression, and suppressing caspase-3 activation. Furthermore, MR antagonism substantially reduced the elevated NADPH oxidase activity and lipid peroxidation, expression of angiotensin II, angiotensin type 1 receptor and MR, in Ren2 vasculature. These results demonstrate that MR antagonism protects the vasculature from aldosterone-induced vascular apoptosis and structural injury via rescuing Akt activation, independent of BP effects.
Aldosterone; Oxidative Stress; Akt Activation; Vascular Apoptosis and Injury
Activation of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase by angiotensin II is integral to the formation of oxidative stress in the vasculature and the kidney. 3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibition is associated with reductions of oxidative stress in the vasculature and kidney and associated decreases in albuminuria. Effects of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibition on oxidative stress in the kidney and filtration barrier integrity are poorly understood. To investigate, we used transgenic TG(mRen2)27 (Ren2) rats, which harbor the mouse renin transgene and renin-angiotensin system activation, and an immortalized murine podocyte cell line. We treated young, male Ren2 and Sprague-Dawley rats with rosuvastatin (20 mg/kg IP) or placebo for 21 days. Compared with controls, we observed increases in systolic blood pressure, albuminuria, renal NADPH oxidase activity, and 3-nitrotryosine staining, with reductions in the rosuvastatin-treated Ren2. Structural changes on light and transmission electron microscopy, consistent with periarteriolar fibrosis and podocyte foot-process effacement, were attenuated with statin treatment. Nephrin expression was diminished in the Ren2 kidney and trended to normalize with statin treatment. Angiotensin II–dependent increases in podocyte NADPH oxidase activity and subunit expression (NOX2, NOX4, Rac, and p22phox) and reactive oxygen species generation were decreased after in vitro statin treatment. These data support a role for increased NADPH oxidase activity and subunit expression with resultant reactive oxygen species formation in the kidney and podocyte. Furthermore, statin attenuation of NADPH oxidase activation and reactive oxygen species formation in the kidney/podocyte seems to play roles in the abrogation of oxidative stress-induced filtration barrier injury and consequent albuminuria.
angiotensin II; albuminuria; glomerular filtration barrier; transgenic Ren2 rat; rosuvastatin