Angiotensin receptor-mediated oxidative stress is associated with impaired cardiac redox signaling and mitochondrial function in insulin-resistant rats

Mitochondrial Dysfunction in HFpEF: Potential Interventions Through Exercise

HFpEF is a prevalent and complex type of heart failure. The concurrent presence of conditions such as obesity, hypertension, hyperglycemia, and hyperlipidemia significantly increase the risk of developing HFpEF. Mitochondria, often referred to as the powerhouses of the cell, are crucial in maintaining cellular functions, including ATP production, intracellular Ca2+ regulation, reactive oxygen species generation and clearance, and the regulation of apoptosis. Exercise plays a vital role in preserving mitochondrial homeostasis, thereby protecting the cardiovascular system from acute stress, and is a fundamental component in maintaining cardiovascular health. In this study, we review the mitochondrial dysfunction underlying the development and progression of HFpEF. Given the pivotal role of exercise in modulating cardiovascular diseases, we particularly focus on exercise as a potential therapeutic strategy for improving mitochondrial function. Graphical abstract Note: This picture was created with BioRender.com.

Effects of telmisartan on metabolic syndrome components: a comprehensive review

Telmisartan is an antagonist of the angiotensin II receptor used in the management of hypertension (alone or in combination with other antihypertensive agents. It belongs to the drug class of angiotensin II receptor blockers (ARBs). Among drugs of this class, telmisartan shows particular pharmacologic properties, including a longer half-life than any other angiotensin II receptor blockers that bring higher and persistent antihypertensive activity. In hypertensive patients, telmisartan has superior efficacy than other antihypertensive drugs (losartan, valsartan, ramipril, atenolol, and perindopril) in controlling blood pressure, especially towards the end of the dosing interval. Telmisartan has a partial PPARγ-agonistic effect whilst does not have the safety concerns of full agonists of PPARγ receptors (thiazolidinediones). Moreover, telmisartan has an agonist activity on PPARα and PPARδ receptors and modulates the adipokine levels. Thus, telmisartan could be considered as a suitable alternative option, with multi-benefit for all components of metabolic syndrome including hypertension, diabetes mellitus, obesity, and hyperlipidemia. This review will highlight the role of telmisartan in metabolic syndrome and the main mechanisms of action of telmisartan are discussed and summarized. Many studies have demonstrated the useful properties of telmisartan in the prevention and improving of metabolic syndrome and this well-tolerated drug can be greatly proposed in the treatment of different components of metabolic syndrome. However, larger and long-duration studies are needed to confirm these findings in long-term observational studies and prospective trials and to determine the optimum dose of telmisartan in metabolic syndrome.

The β2-adrenergic receptor agonist formoterol restores mitochondrial homeostasis in glucose-induced renal proximal tubule injury through separate integrated pathways

Mitochondrial dysfunction drives the development and progression of diabetic kidney disease (DKD). Previously, we discovered that the β₂-adrenergic receptor (AR) agonist formoterol regulates mitochondrial dynamics in the hyperglycemic renal proximal tubule. The goal of this study was to identify signaling mechanisms through which formoterol restores the mitochondrial fission/fusion proteins Drp1 and Mfn1. Using primary renal proximal tubule cells (RPTC), the effect of chronic high glucose on RhoA/ROCK1/Drp1 and Raf/MEK1/2/ERK1/2/Mfn1 signaling was determined. In glucose-treated RPTC, RhoA became hyperactive, leading to ROCK1-induced activation of Drp1. Treatment with formoterol and/or pharmacological inhibitors targeting RhoA, ROCK1 and Drp1 blocked RhoA and Drp1 hyperactivity. Inhibiting this pathway also restored maximal mitochondrial respiration. By preventing Gβγ signaling with gallein, we determined that formoterol signals through the Gβγ subunit of the β₂-AR to restore RhoA and Drp1. Furthermore, formoterol restored this pathway by blocking binding of RhoA with the guanine nucleotide exchange factor p114RhoGEF. Formoterol also restored the mitochondrial fusion protein Mfn1 through a second Gβγ-dependent mechanism composed of Raf/MEK1/2/ERK1/2/Mfn1. Glucose-treated RPTC exhibited decreased Mfn1 activity, which was restored with formoterol. Pharmacological inhibition of Gβγ, Raf and MEK1/2 also restored Mfn1 activity. We demonstrate that glucose promotes the interaction between RhoA and p114RhoGEF, leading to increased RhoA and ROCK1-mediated activation of Drp1, and decreases Mfn1 activity through Raf/MEK1/2/ERK1/2. Formoterol restores these pathways and mitochondrial function in response to elevated glucose by activating separate yet integrative pathways that promote mitochondrial biogenesis, decreased fission and increased fusion in RPTC, further supporting its potential as a therapeutic for DKD.

Pharmacological Targeting of Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) in the United States and many other countries. DKD occurs through a variety of pathogenic processes that are in part driven by hyperglycemia and glomerular hypertension, leading to gradual loss of kidney function and eventually progressing to ESRD. In type 2 diabetes, chronic hyperglycemia and glomerular hyperfiltration leads to glomerular and proximal tubular dysfunction. Simultaneously, mitochondrial dysfunction occurs in the early stages of hyperglycemia and has been identified as a key event in the development of DKD. Clinical management for DKD relies primarily on blood pressure and glycemic control through the use of numerous therapeutics that slow disease progression. Because mitochondrial function is key for renal health over time, therapeutics that improve mitochondrial function could be of value in different renal diseases. Increasing evidence supports the idea that targeting aspects of mitochondrial dysfunction, such as mitochondrial biogenesis and dynamics, restores mitochondrial function and improves renal function in DKD. We will review mitochondrial function in DKD and the effects of current and experimental therapeutics on mitochondrial biogenesis and homeostasis in DKD over time. SIGNIFICANCE STATEMENT: Diabetic kidney disease (DKD) affects 20% to 40% of patients with diabetes and has limited treatment options. Mitochondrial dysfunction has been identified as a key event in the progression of DKD, and pharmacologically restoring mitochondrial function in the early stages of DKD may be a potential therapeutic strategy in preventing disease progression.

Simultaneous SGLT2 inhibition and caloric restriction improves insulin resistance and kidney function in OLETF rats

SGLT2 inhibitors (SGLT2i) are emerging as a novel therapy for type 2 diabetes due to their effective hypoglycemic and potential cardio- and nephroprotective effects, while caloric restriction (CR) is a common behavioral modification to improve adiposity and insulin resistance. Therefore, both interventions simultaneously may potentially further improve metabolic syndrome by enhancing carbohydrate metabolism. To test this hypothesis, cohorts of 10-week old, male Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats were treated with SGLT2i (10 mg luseoglifozin/kg/day x 4 wks) (OLETF only) and/or 30% CR (2 wks at 12 weeks of age). CR maintained body mass in both strains while SGLT2i alone did not have any effect on body mass. Simultaneous treatments decreased SBP in OLETF vs SGLT2i alone, decreased insulin resistance index (IRI), and increased creatinine clearance vs OLETF ad lib. Conversely, CR decreased albuminuria independent of SGLT2i. In conclusion, SGLT2i treatment by itself did not elicit significant improvements in insulin resistance, kidney function or blood pressure. However, when combined with CR, these changes where more profound than with CR alone without inducing chronic hypoglycemia.

Obesity and sudden cardiac death: Prevalence, pathogenesis, prevention and intervention

Obesity and sudden cardiac death (SCD) share common risk factors. Obesity, in and of itself, can result in the development of SCD. Numerous epidemiologic and clinical studies have demonstrated the close relationships between obesity and SCD, however, the underlying mechanisms remain incompletely understood. Various evidences support the significance of excess adiposity in determining the risk of SCD, including anatomical remodeling, electrical remodeling, metabolic dysfunction, autonomic imbalance. Weight reduction has improved obesity related comorbidities, and reversed abnormal cardiac remodeling. Indeed, it is still unknown whether weight loss contributes to decreased risk of SCD. Further high-quality, prospective trials are needed to strengthen our understanding on weight management and SCD.

Effects of an obesogenic diet on the oviduct depend on the duration of feeding

Research question

How long does it take for an obesogenic (high-fat/high-sugar, HF/HS) diet to influence the oviductal microenvironment? What are the affected cellular pathways and are they dependent on the genetic background of the mouse model?

Design

Female Swiss (outbred) and C57BL/6N (B6, inbred) mice were fed either a control (10% fat) or HF/HS (60% fat, 20% fructose) diet. Body weight was measured weekly. Mice were sacrificed at 3 days (3d), 1 week (1w), 4w, 8w, 12w and 16w on the diet (n = 5 per treatment per time point). Total cholesterol concentrations and inflammatory cytokines were measured in serum. Oviductal epithelial cells (OECs) were used to study the expression of genes involved in (mitochondrial) oxidative stress (OS), endoplasmic reticulum (ER) stress and inflammation using qPCR.

Results

Body weight and blood cholesterol increased significantly in the HF/HS mice in both strains compared to controls. In Swiss mice, HF/HS diet acutely increased ER-stress and OS-related genes in the OECs already after 3d. Subsequently, mitochondrial and cytoplasmic antioxidants were upregulated and ER-stress was alleviated at 1w. After 4-8w (mid-phase), the expression of ER-stress and OS-related genes was increased again and persisted throughout the late-phase (12-16w). Serum inflammatory cytokines and inflammatory marker-gene expression in the OECs were increased only in the late-phase. Some of the OEC stress responses were stronger or earlier in the B6.

Conclusions

OECs are sensitive to an obesogenic diet and may exhibit acute stress responses already after a few days of feeding. This may impact the oviductal microenvironment and contribute to diet-induced subfertility.

Glucose Increases Hepatic Mitochondrial Antioxidant Enzyme Activities in Insulin Resistant Rats Following Chronic Angiotensin Receptor Blockade

Non-alcoholic fatty liver disease (NAFLD) affects up to 20% of the world’s population. Overactivation of the angiotensin receptor type 1 (AT1) contributes to metabolic dysfunction and increased oxidant production, which are associated with NAFLD and impaired hepatic lipid metabolism. Nuclear factor erythroid-2-related factor 2 (Nrf2) regulates the expression of antioxidant phase II genes by binding to the antioxidant response element (ARE); however, the mechanisms by which AT1 contributes to this pathway during the progression of NAFLD remain unresolved. To investigate hepatic Nrf2 response to a hyperglycemic challenge, we studied three groups of rats (male, 10-weeks-old): (1) untreated, lean Long Evans Tokushima Otsuka (LETO), (2) untreated, obese Otsuka Long Evans Tokushima Fatty (OLETF), and (3) OLETF + angiotensin receptor blocker (OLETF + ARB; 10 mg olmesartan/kg/d × 6 weeks). Livers were collected after overnight fasting (T0; baseline), and 1 h and 2 h post-oral glucose load. At baseline, chronic AT1 blockade increased nuclear Nrf2 content, reduced expression of glutamate-cysteine ligase catalytic (GCLC) subunit, glutathione peroxidase 1 (GPx1), and superoxide dismutase 2 (SOD2), mitochondrial catalase activity, and hepatic 4-hydroxy-2-nonenal (4-HNE) content. The expression of hepatic interleukin-1 beta (IL-1β) and collagen type IV, which are associated with liver fibrosis, were decreased with AT1 blockade. Glucose increased Nrf2 translocation in OLETF but was reduced in ARB, suggesting that glucose induces the need for antioxidant defense that is ameliorated with ARB. These results suggest that overactivation of AT1 promotes oxidant damage by suppressing Nrf2 and contributing to hepatic fibrosis associated with NAFLD development.

Improved lipogenesis gene expression in liver is associated with elevated plasma angiotensin 1-7 after AT1 receptor blockade in insulin-resistant OLETF rats

Increased angiotensin II (Ang II) signaling contributes to insulin resistance and liver steatosis. In addition to ameliorating hypertension, angiotensin receptor blockers (ARBs) improve lipid metabolism and hepatic steatosis, which are impaired with metabolic syndrome (MetS). Chronic blockade of the Ang II receptor type 1 (AT1) increases plasma angiotensin 1-7 (Ang 1-7), which mediates mechanisms counterregulatory to AT1 signaling. Elevated plasma Ang 1-7 is associated with decreased plasma triacylglycerol (TAG), cholesterol, glucose, and insulin; however, the benefits of RAS modulation to prevent non-alcoholic fatty liver disease (NAFLD) are not fully investigated. To better address the relationships among chronic ARB treatment, plasma Ang 1-7, and hepatic steatosis, three groups of 10-week-old-rats were studied: (1) untreated lean Long Evans Tokushima Otsuka (LETO), (2) untreated Otsuka Long Evans Tokushima Fatty (OLETF), and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/d × 6 weeks). Following overnight fasting, rats underwent an acute glucose load to better understand the dynamic metabolic responses during hepatic steatosis and early MetS. Tissues were collected at baseline (pre-load; T0) and 1 and 2 h post-glucose load. AT1 blockade increased plasma Ang 1-7 and decreased liver lipids, which was associated with decreased fatty acid transporter 5 (FATP5) and fatty acid synthase (FASN) expression. AT1 blockade decreased liver glucose and increased glucokinase (GCK) expression. These results demonstrate that during MetS, overactivation of AT1 promotes hepatic lipid deposition that is stimulated by an acute glucose load and lipogenesis genes, suggesting that the chronic hyperglycemia associated with MetS contributes to fatty liver pathologies via an AT1-mediated mechanism.

Cardiac NF-κB Acetylation Increases While Nrf2-Related Gene Expression and Mitochondrial Activity Are Impaired during the Progression of Diabetes in UCD-T2DM Rats

The onset of type II diabetes increases the heart’s susceptibility to oxidative damage because of the associated inflammation and diminished antioxidant response. Transcription factor NF-κB initiates inflammation while Nrf2 controls antioxidant defense. Current evidence suggests crosstalk between these transcription factors that may become dysregulated during type II diabetes mellitus (T2DM) manifestation. The objective of this study was to examine the dynamic changes that occur in both transcription factors and target genes during the progression of T2DM in the heart. Novel UC Davis T2DM (UCD-T2DM) rats at the following states were utilized: (1) lean, control Sprague-Dawley (SD; n = 7), (2) insulin-resistant pre-diabetic UCD-T2DM (Pre; n = 9), (3) 2-week recently diabetic UCD-T2DM (2Wk; n = 9), (4) 3-month diabetic UCD-T2DM (3Mo; n = 14), and (5) 6-month diabetic UCD-T2DM (6Mo; n = 9). NF-κB acetylation increased 2-fold in 3Mo and 6Mo diabetic animals compared to SD and Pre animals. Nox4 protein increased 4-fold by 6Mo compared to SD. Nrf2 translocation increased 82% in Pre compared to SD but fell 47% in 6Mo animals. GCLM protein fell 35% in 6Mo animals compared to Pre. Hmox1 mRNA decreased 45% in 6Mo animals compared to SD. These data suggest that during the progression of T2DM, NF-κB related genes increase while Nrf2 genes are suppressed or unchanged, perpetuating inflammation and a lesser ability to handle an oxidant burden altering the heart’s redox state. Collectively, these changes likely contribute to the diabetes-associated cardiovascular complications.

Mass recovery following caloric restriction reverses lipolysis and proteolysis, but not gluconeogenesis, in insulin resistant OLETF rats

Caloric restriction (CR) is one of the most important behavioral interventions to reduce excessive abdominal adiposity, which is a risk factor for the development of insulin resistance. Previous metabolomics studies have characterized substrate metabolism during healthy conditions; however, the effects of CR and subsequent mass recovery on shifts in substrate metabolism during insulin resistance (IR) have not been widely investigated. To assess the effects of acute CR and the subsequent mass recovery on shifts in substrate metabolism, a cohort of 15-week old Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats were calorie restricted (CR: 50% × 10 days) with or without partial body mass recovery (PR; 73% x 7 days), along with their respective ad libitum controls. End-of-study plasma samples were analyzed for primary carbon metabolites by gas chromatography (GC) time-of-flight (TOF) mass spectrometry (MS) data acquisition. Data analysis included PCA, Pearson correlation vs previously reported variables (adipose and body masses, and insulin resistance index, IRI), and metabolomics maps (MetaMapp) generated for the most significant group comparisons. All treatments elicited a significant group differentiation in at least one principal component. CR improved TCA cycle in OLETF, and increased lipolysis and proteolysis. These changes were reversed after PR except for gluconeogenesis. Plasma lipid concentrations were inversely correlated to IRI in LETO, but not OLETF. These shifts in substrate metabolism suggest that the CR-induced decreases in adipose may not be sufficient to more permanently alter substrate metabolism to improve IR status during metabolic syndrome.

Fibrosis of the diabetic heart: Clinical significance, molecular mechanisms, and therapeutic opportunities

In patients with diabetes, myocardial fibrosis may contribute to the pathogenesis of heart failure and arrhythmogenesis, increasing ventricular stiffness and delaying conduction. Diabetic myocardial fibrosis involves effects of hyperglycemia, lipotoxicity and insulin resistance on cardiac fibroblasts, directly resulting in increased matrix secretion, and activation of paracrine signaling in cardiomyocytes, immune and vascular cells, that release fibroblast-activating mediators. Neurohumoral pathways, cytokines, growth factors, oxidative stress, advanced glycation end-products (AGEs), and matricellular proteins have been implicated in diabetic fibrosis; however, the molecular links between the metabolic perturbations and activation of a fibrogenic program remain poorly understood. Although existing therapies using glucose- and lipid-lowering agents and neurohumoral inhibition may act in part by attenuating myocardial collagen deposition, specific therapies targeting the fibrotic response are lacking. This review manuscript discusses the clinical significance, molecular mechanisms and cell biology of diabetic cardiac fibrosis and proposes therapeutic targets that may attenuate the fibrotic response, preventing heart failure progression.

Application of Animal Models in Diabetic Cardiomyopathy

Diabetic heart disease is a growing and important public health risk. Apart from the risk of coronary artery disease or hypertension, diabetes mellitus (DM) is a well-known risk factor for heart failure in the form of diabetic cardiomyopathy (DiaCM). Currently, DiaCM is defined as myocardial dysfunction in patients with DM in the absence of coronary artery disease and hypertension. The underlying pathomechanism of DiaCM is partially understood, but accumulating evidence suggests that metabolic derangements, oxidative stress, increased myocardial fibrosis and hypertrophy, inflammation, enhanced apoptosis, impaired intracellular calcium handling, activation of the renin-angiotensin-aldosterone system, mitochondrial dysfunction, and dysregulation of microRNAs, among other factors, are involved. Numerous animal models have been used to investigate the pathomechanisms of DiaCM. Despite some limitations, animal models for DiaCM have greatly advanced our understanding of pathomechanisms and have helped in the development of successful disease management strategies. In this review, we summarize the current pathomechanisms of DiaCM and provide animal models for DiaCM according to its pathomechanisms, which may contribute to broadening our understanding of the underlying mechanisms and facilitating the identification of possible new therapeutic targets.

The Importance of Redox Status in the Frame of Lifestyle Approaches and the Genetics of the Lung Innate Immune Molecules, SP-A1 and SP-A2, on Differential Outcomes of COVID-19 Infection

The pandemic of COVID-19 is of great concern to the scientific community. This mainly affects the elderly and people with underlying diseases. People with obesity are more likely to experience unpleasant disease symptoms and increased mortality. The severe oxidative environment that occurs in obesity due to chronic inflammation permits viral activation of further inflammation leading to severe lung disease. Lifestyle affects the levels of inflammation and oxidative stress. It has been shown that a careful diet rich in antioxidants, regular exercise, and fasting regimens, each and/or together, can reduce the levels of inflammation and oxidative stress and strengthen the immune system as they lead to weight loss and activate cellular antioxidant mechanisms and reduce oxidative damage. Thus, a lifestyle change based on the three pillars: antioxidants, exercise, and fasting could act as a proactive preventative measure against the adverse effects of COVID-19 by maintaining redox balance and well-functioning immunity. Moreover, because of the observed diversity in the expression of COVID-19 inflammation, the role of genetics of innate immune molecules, surfactant protein A (SP-A)1 and SP-A2, and their differential impact on the local lung microenvironment and host defense is reviewed as genetics may play a major role in the diverse expression of the disease.

Aerobic exercise modulates cardiac NAD(P)H oxidase and the NRF2/KEAP1 pathway in a mouse model of chronic fructose consumption

The present study investigated the effects of exercise on the cardiac nuclear factor (erythroid-derived 2) factor 2 (NRF2)/Kelch-like ECH-associated protein 1 (KEAP1) pathway in an experimental model of chronic fructose consumption. Male C57BL/6 mice were assigned to Control, Fructose (20% fructose in drinking water), Exercise (treadmill exercise at moderate intensity), and Fructose + Exercise groups ( n = 10). After 12 wk, the energy intake and body weight in the groups were similar. Maximum exercise testing, resting energy expenditure, resting oxygen consumption, and carbon dioxide production increased in the exercise groups (Exercise and Fructose + Exercise vs. Control and Fructose groups, P < 0.05). Chronic fructose intake induced circulating hypercholesterolemia, hypertriglyceridemia, and hyperleptinemia and increased white adipose tissue depots, with no changes in blood pressure. This metabolic environment increased circulating IL-6, IL-1β, IL-10, cardiac hypertrophy, and cardiac NF-κB-p65 and TNF-α expression, which were reduced by exercise ( P < 0.05). Cardiac ANG II type 1 receptor and NAD(P)H oxidase 2 (NOX2) were increased by fructose intake and exercise decreased this response ( P < 0.05). Exercise increased the cardiac expression of the NRF2-to-KEAP1 ratio and phase II antioxidants in fructose-fed mice ( P < 0.05). NOX4, glutathione reductase, and catalase protein expression were similar between the groups. These findings suggest that exercise confers modulatory cardiac effects, improving antioxidant defenses through the NRF2/KEAP1 pathway and decreasing oxidative stress, representing a potential nonpharmacological approach to protect against fructose-induced cardiometabolic diseases.

NEW & NOTEWORTHY This is the first study to evaluate the cardiac modulation of NAD(P)H oxidase (NOX), the NRF2/Kelch-like ECH-associated protein 1 pathway (KEAP), and the thioredoxin (TRX1) system through exercise in the presence of moderate fructose intake. We demonstrated a novel mechanism by which exercise improves cardiac antioxidant defenses in an experimental model of chronic fructose intake, which involves NRF2-to-KEAP1 ratio modulation, enhancing the local phase II antioxidants hemoxygenase-1, thioredoxin reductase (TXNRD1), and peroxiredoxin1B (PDRX1), and inhibiting cardiac NOX2 overexpression.

Partial Body Mass Recovery After Caloric Restriction Abolishes Improved Glucose Tolerance in Obese, Insulin Resistant Rats

Caloric restriction, among other behavioral interventions, has demonstrated benefits on improving glycemic control in obesity-associated diabetic subjects. However, an acute and severe intervention without proper maintenance could reverse the initial benefits, with additional metabolic derangements. To assess the effects of an acute caloric restriction in a metabolic syndrome model, a cohort of 15-week old Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats were calorie restricted (CR: 50% × 10 days) with or without a 10-day body mass (BM) recovery period, along with their respective ad libitum controls. An oral glucose tolerance test (oGTT) was performed after CR and BM recovery. Both strains had higher rates of mass gain during recovery vs. ad lib controls; however, the regain was partial (ca. 50% of ad lib controls) over the measurement period. Retroperitoneal and epididymal adipose masses decreased 30% (8.8 g, P < 0.001) in OLETF; however, this loss only accounted for 11.5% of the total BM loss. CR decreased blood glucose AUC 16% in LETO and 19% in OLETF, without significant decreases in insulin. Following CR, hepatic expression of the gluconeogenic enzyme, PEPCK, was reduced 55% in OLETF compared to LETO, and plasma triglycerides (TG) decreased 86%. Acute CR induced improvements in glucose tolerance and TG suggestive of improvements in metabolism; however, partial recovery of BM following CR abolished the improvement in glucose tolerance. The present study highlights the importance of proper maintenance of BM after CR as only partial recovery of the lost BM reversed benefits of the initial mass loss.

Simultaneous angiotensin receptor blockade and glucagon-like peptide-1 receptor activation ameliorate albuminuria in obese insulin-resistant rats

Insulin resistance increases renal oxidant production by upregulating NADPH oxidase 4 (Nox4) expression contributing to oxidative damage and ultimately albuminuria. Inhibition of the renin-angiotensin system (RAS) and activation of glucagon-like peptide-1 (GLP-1) receptor signalling may reverse this effect. However, whether angiotensin receptor type 1 (AT1) blockade and GLP-1 receptor activation improve oxidative damage and albuminuria through different mechanisms is not known. Using insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rats, we tested the hypothesis that simultaneous blockade of AT1 and activation of GLP-1r additively decrease oxidative damage and urinary albumin excretion (U_alb V) in the following groups: (a) untreated, lean LETO (n = 7), (b) untreated, obese OLETF (n = 9), (c) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d; n = 9), (d) OLETF + GLP-1 mimetic (EXE; 10 µg exenatide/kg/d; n = 7) and (e) OLETF + ARB +exenatide (Combo; n = 6). Mean kidney Nox4 protein expression and nitrotyrosine (NT) levels were 30% and 46% greater, respectively, in OLETF compared with LETO. Conversely, Nox4 protein expression and NT were reduced to LETO levels in ARB and EXE, and Combo reduced Nox4, NT and 4-hydroxy-2-nonenal levels by 21%, 27% and 27%, respectively. At baseline, U_alb V was nearly double in OLETF compared with LETO and increased to nearly 10-fold greater levels by the end of the study. Whereas ARB (45%) and EXE (55%) individually reduced U_alb V, the combination completely ameliorated the albuminuria. Collectively, these data suggest that AT1 blockade and GLP-1 receptor activation reduce renal oxidative damage similarly during insulin resistance, whereas targeting both signalling pathways provides added benefit in restoring and/or further ameliorating albuminuria in a model of diet-induced obesity.

AMPK: a balancer of the renin-angiotensin system

The renin-angiotensin system (RAS) is undisputedly well-studied as one of the oldest and most critical regulators for arterial blood pressure, fluid volume, as well as renal function. In recent studies, RAS has also been implicated in the development of obesity, diabetes, hyperlipidemia, and other diseases, and also involved in the regulation of several signaling pathways such as proliferation, apoptosis and autophagy, and insulin resistance. AMP-activated protein kinase (AMPK), an essential cellular energy sensor, has also been discovered to be involved in these diseases and cellular pathways. This would imply a connection between the RAS and AMPK. Therefore, this review serves to draw attention to the cross-talk between RAS and AMPK, then summering the most recent literature which highlights AMPK as a point of balance between physiological and pathological functions of the RAS.

Nrf2-related gene expression is impaired during a glucose challenge in type II diabetic rat hearts

Diabetic hearts are susceptible to damage from inappropriate activation of the renin angiotensin system (RAS) and hyperglycemic events both of which contribute to increased oxidant production. Prolonged elevation of oxidants impairs mitochondrial enzyme function, further contributing to metabolic derangement. Nuclear factor erythriod-2-related factor 2 (Nrf2) induces antioxidant genes including those for glutathione (GSH) synthesis following translocation to the nucleus. We hypothesized that an acute elevation in glucose impairs Nrf2-related gene expression in diabetic hearts, while AT1 antagonism would aid in Nrf2-mediated antioxidant production and energy replenishment. We used four groups (n = 6-8/group) of 25-week-old rats: 1) LETO (lean strain-control), 2) type II diabetic OLETF, 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 8 wks), and 4) ARBM (4 weeks on ARB, 4 weeks off) to study the effects of acutely elevated glucose on cardiac mitochondrial function and Nrf2 signaling in the diabetic heart. Animals were gavaged with a glucose bolus (2 g/kg) and groups were dissected at T0, T180, and T360 minutes. Nrf2 mRNA was 32% lower in OLETF rats compared to LETO and remained suppressed in response to glucose. LETO Nrf2 mRNA increased 25% at T360 in response to glucose while no changes were observed in diabetic hearts. GCLC and GCLM mRNA decreased in diabetic hearts 33% and 44% respectively and remained suppressed in response to glucose while ARB treatment increased GCLM transcripts 90% at T180. These data illustrate that during T2DM and in response to glucose, cardiac Nrf2's adaptive response to environmental stressors such as glucose is impaired in diabetic hearts and that ARB treatment may aid Nrf2's impaired dynamic response.

Angiotensin II induces oxidative stress and upregulates neuroprotective signaling from the NRF2 and KLF9 pathway in dopaminergic cells

Nuclear factor-E2-related factor 2 (NRF2) is a transcription factor that activates the antioxidant cellular defense in response to oxidative stress, leading to neuroprotective effects in Parkinson's disease (PD) models. We have previously shown that Angiotensin II (AngII) induces an increase in reactive oxygen species (ROS) via AngII receptor type 1 and NADPH oxidase (NOX), which may activate the NRF2 pathway. However, controversial data suggest that AngII induces a decrease in NRF2 signaling leading to an increase in oxidative stress. We analyzed the effect of AngII and the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) in culture and in vivo, and examined the effects on the expression of NRF2-related genes. Treatment of neuronal cell lines Mes23.5, N27 and SH-SY5Y with AngII, 6-OHDA or a combination of both increased ROS production and reduced cell viability. Simultaneously, these treatments induced an increase in expression in the NRF2-regulated genes heme oxygenase 1 (Hmox1), NAD(P)H quinone dehydrogenase 1 (Nqo1) and Kruppel like factor 9 (Klf9). Moreover, overexpression of KLF9 transcription factor caused a reduction in the production of ROS induced by treatment with AngII or 6-OHDA and improved the survival of these neuronal cells. Rats treated with AngII, 6-OHDA or a combination of both also showed an increased expression of NRF2 related genes and KLF9. In conclusion, our data indicate that AngII induces a damaging effect in neuronal cells, but also acts as a signaling molecule to activate NRF2 and KLF9 neuroprotective pathways in cellular and animal models of PD.

Angiotensin receptor and tumor necrosis factor-α activation contributes to glucose intolerance independent of systolic blood pressure in obese rats

Pathological activation of the renin-angiotensin system and inflammation are associated with hypertension and the development of metabolic syndrome (MetS). The contributions of angiotensin receptor type 1 (AT1) activation, independent of blood pressure, and inflammation to glucose intolerance and renal damage are not well defined. Using a rat model of MetS, we hypothesized that the onset of glucose intolerance is primarily mediated by AT1 activation and inflammation independent of elevated systolic blood pressure (SBP). To address this hypothesis, we measured changes in SBP, adiposity, plasma glucose and triglyceride levels, and glucose tolerance in six groups of rats: 1) lean, strain control Long-Evans Tokushima Otsuka (LETO; n = 5), 2) obese Otsuka Long-Evans Tokushima Fatty (OLETF; n = 8), 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg; n = 8), 4) OLETF + tumor necrosis factor-α (TNF-α) inhibitor (ETAN; 1.25 mg etanercept/kg; n = 6), 5) OLETF + TNF-α inhibitor + angiotensin receptor blocker (ETAN+ARB; 1.25 mg etanercept/kg + 10 mg olmesartan/kg; n = 6), and 6) OLETF + calcium channel blocker (CCB; 5 mg amlodipine/kg; n = 7). ARB and ETAN+ARB were most effective at decreasing SBP in OLETF, and ETAN did not offer any additional reduction. Glucose tolerance improved in ARB, ETAN, and ETAN+ARB compared with OLETF, whereas CCB had no detectable effect. Furthermore, all treatments reduced adiposity, whereas ETAN alone normalized urinary albumin excretion. These results suggest that AT1 activation and inflammation are primary factors in the development of glucose intolerance in a setting of MetS and that the associated increase in SBP is primarily mediated by AT1 activation.

Adipose transcriptome analysis provides novel insights into molecular regulation of prolonged fasting in northern elephant seal pups

The physiological and cellular adaptations to extreme fasting in northern elephant seals ( Mirounga angustirostris, NES) are remarkable and may help to elucidate endocrine mechanisms that regulate lipid metabolism and energy homeostasis in mammals. Recent studies have highlighted the importance of thyroid hormones in the maintenance of a lipid-based metabolism during prolonged fasting in weaned NES pups. To identify additional molecular regulators of fasting, we used a transcriptomics approach to examine changes in global gene expression profiles before and after 6-8 wk of fasting in weaned NES pups. We produced a de novo assembly and identified 98 unique protein-coding genes that were differentially expressed between early and late fasting. Most of the downregulated genes were associated with lipid, carbohydrate, and protein metabolism. A number of downregulated genes were also associated with maintenance of the extracellular matrix, consistent with tissue remodeling during weight loss and the multifunctional nature of blubber tissue, which plays both metabolic and structural roles in marine mammals. Using this data set, we predict potential mechanisms by which NES pups sustain metabolism and regulate adipose stores throughout the fast, and provide a valuable resource for additional studies of extreme metabolic adaptations in mammals.

Standardized Kaempferia parviflora Extract Enhances Exercise Performance Through Activation of Mitochondrial Biogenesis

Exercise enhances mitochondrial biogenesis in skeletal muscle. Increased mitochondrial function and content can contribute to the improvement in skeletal muscle function and the benefits of exercise by increasing the response to energy demands. The effect of standardized Kaempferia parviflora extract (KPE) on exercise performance was accessed in L6 myotubes and C57BL/6J mice. KPE significantly activated peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and increased mitochondrial density in L6 myotubes. KPE also upregulated the expression of transcription factors for mitochondrial biogenesis (estrogen-related receptor-α [ERRα], nuclear respiratory factor-1 [NRF-1], and mitochondrial transcription factor A [Tfam]) through activation of PGC-1α in L6 myotubes. In vivo models including normal diet mice and high-fat diet obese mice showed that KPE effectively enhanced running endurance and increased the skeletal muscle weight/body weight ratio. Furthermore, these observations were associated with a significant upregulation of mitochondrial biogenesis regulatory genes in skeletal muscle tissue. KPE enhanced the protein expression of the sirtuin 1 (SIRT1)/adenosine monophosphate (AMP)-activated protein kinase (AMPK)/PGC-1α/peroxisome proliferator-activated receptor-δ (PPARδ) signaling pathway components in vitro and in vivo, acting as an exercise metabolism regulator. These results suggest that KPE has the potential to enhance exercise performance through mitochondrial biogenesis and the SIRT1/AMPK/PGC-1α/PPARδ signaling pathways.

Angiotensin receptor blockade improves cardiac mitochondrial activity in response to an acute glucose load in obese insulin resistant rats

Hyperglycemia increases the risk of oxidant overproduction in the heart through activation of a multitude of pathways. Oxidation of mitochondrial enzymes may impair their function resulting in accumulation of intermediates and reverse electron transfer, contributing to mitochondrial dysfunction. Furthermore, the renin-angiotensin system (RAS) becomes inappropriately activated during metabolic syndrome, increasing oxidant production. To combat excess oxidant production, the transcription factor, nuclear factor erythriod-2- related factor 2 (Nrf2), induces expression of many antioxidant genes. We hypothesized that angiotensin II receptor type 1 (AT1) blockade improves mitochondrial function in response to an acute glucose load via upregulation of Nrf2. To address this hypothesis, an oral glucose challenge was performed in three groups prior to dissection (n = 5–8 animals/group/time point) of adult male rats: 1) Long Evans Tokushima Otsuka (LETO; lean strain-control), 2) insulin resistant, obese Otsuka Long Evans Tokushima Fatty (OLETF), and 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 6 weeks). Hearts were collected at T0, T60, and T120 minutes post-glucose infusion. ARB increased Nrf2 binding 32% compared to OLETF at T60. Total superoxide dismutase (SOD) and catalase (CAT) activities were increased 45% and 66% respectively in ARB treated animals compared to OLETF. Mitochondrial enzyme activities of aconitase, complex I, and complex II increased by 135%, 33% and 66%, respectively in ARB compared to OLETF. These data demonstrate the protective effects of AT1 blockade on mitochondrial function during the manifestation of insulin resistance suggesting that the inappropriate activation of AT1 during insulin resistance may impair Nrf2 translocation and subsequent antioxidant activities and mitochondrial function.

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ARB increases cardiac mitochondrial enzyme activity in insulin resistant rats.

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Nrf2 binding activity increases when AT1 receptor activation is blocked.

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Glucose suppresses total cardiac GPx and CAT activities during insulin resistance.

Exogenous thyroxine improves glucose intolerance in insulin-resistant rats

Both hypothyroidism and hyperthyroidism are associated with glucose intolerance, calling into question the contribution of thyroid hormones (TH) on glucose regulation. TH analogues and derivatives may be effective treatment options for glucose intolerance and insulin resistance (IR), but their potential glucoregulatory effects during conditions of impaired metabolism are not well described. To assess the effects of thyroxine (T4) on glucose intolerance in a model of insulin resistance, an oral glucose tolerance test (oGTT) was performed on three groups of rats (n = 8): (1) lean, Long Evans Tokushima Otsuka (LETO), (2) obese, Otsuka Long Evans Tokushima Fatty (OLETF) and (3) OLETF + T4 (8.0 µg/100 g BM/day × 5 weeks). T4 attenuated glucose intolerance by 15% and decreased IR index (IRI) by 34% in T4-treated OLETF compared to untreated OLETF despite a 31% decrease in muscle Glut4 mRNA expression. T4 increased the mRNA expressions of muscle monocarboxylate transporter 10 (Mct10), deiodinase type 2 (Di2), sirtuin 1 (Sirt1) and uncoupling protein 2 (Ucp2) by 1.8-, 2.2-, 2.7- and 1.4-fold, respectively, compared to OLETF. Activation of AMP-activated protein kinase (AMPK) and insulin receptor were not significantly altered suggesting that the improvements in glucose intolerance and IR were independent of enhanced insulin-mediated signaling. The results suggest that T4 treatment increased the influx of T4 in skeletal muscle and, with an increase of DI2, increased the availability of the biologically active T3 to upregulate key factors such SIRT1 and UCP2 involved in cellular metabolism and glucose homeostasis.

The renin angiotensin system, oxidative stress and mitochondrial function in obesity and insulin resistance

Obesity is a complex disease characterized by excessive expansion of adipose tissue and is an important risk factor for chronic diseases such as cardiovascular disorders, hypertension and type 2 diabetes. Moreover, obesity is a major contributor to inflammation and oxidative stress, all of which are key underlying causes for diabetes and insulin resistance. Specifically, adipose tissue secretes bioactives molecules such as inflammatory hormone angiotensin II, generated in the Renin Angiotensin System (RAS) from its precursor angiotensinogen. Accumulated evidence suggests that RAS may serve as a strong link between obesity and insulin resistance. Dysregulation of RAS also occurs in several other tissues including those involved in regulation of glucose and whole body homeostasis as well as insulin sensitivity such as muscle, liver and pancreas and heart. Here we review the scientific evidence for these interactions and potential roles for oxidative stress, inflammation and mitochondrial dysfunction in these target tissues which may mediate effects of RAS in metabolic diseases. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Activation of AMPK and its Impact on Exercise Capacity

Activation of the adenosine monophosphate (AMP)-activated kinase (AMPK) contributes to beneficial effects such as improvement of the hyperglycemic state in diabetes as well as reduction of obesity and inflammatory processes. Furthermore, stimulation of AMPK activity has been associated with increased exercise capacity. A study published in 2008, directly before the Olympic Games in Beijing, showed that the AMPK activator AICAR (5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide) increased the running capacity of mice without any training and thus, prompted the World Anti-Doping Agency (WADA) to include certain AMPK activators in the list of forbidden drugs. This raises the question as to whether all AMPK activators should be considered for registration or whether the increase in exercise performance is only associated with specific AMPK-activating substances. In this review, we intend to shed light on currently published AMPK-activating drugs, their working mechanisms, and their impact on body fitness.

Anesthetic Propofol-Induced Gene Expression Changes in Patients Undergoing Coronary Artery Bypass Graft Surgery Based on Dynamical Differential Coexpression Network Analysis

We aimed to determine the influence of anesthetic propofol on gene expression in patients treated by coronary artery bypass graft (CABG) surgery based on differential coexpression network (DCN) and to further reveal the novel mechanisms of the cardioprotective effects of propofol. Firstly, we constructed the DCN for disease condition based on Pearson correlation coefficient (PCC) and weight value. Secondly, the inference of modules was applied to search modules from DCN with same members but varied connectivity. Furthermore, we measured the statistical significance of the modules for selecting differential modules (DMs). Finally, attract method was used for DMs analysis to select key modules. Based on the δ value, 11928 edges and 2956 nodes were chosen to construct DCNs. A total of 29 seed genes were selected. Moreover, by quantifying connectivity changes in shared gene modules across different conditions, 8 DMs with higher connectivity dynamics were identified. Then, we extracted key modules using attract method, there were 8 key modules, and the top 3 modules were module 1, 2, and 3. Furthermore, GCG, PPY, and PON1 were initial seed genes of these 3 key modules, respectively. Accordingly, GCG and PON1 might exert important roles in the cardioprotective effects of propofol during CABG.

The brain renin-angiotensin system plays a crucial role in regulating body weight in diet-induced obesity in rats

BACKGROUND AND PURPOSE

Reduced weight gain after treatment with AT1 receptor antagonists may involve a brain-related mechanism. Here, we investigated the role of the brain renin-angiotensin system on weight regulation and food behaviour, with or without additional treatment with telmisartan.

METHODS

Transgenic rats with a brain-specific deficiency in angiotensinogen (TGR(ASrAOGEN)) and the corresponding wild-type, Sprague Dawley (SD) rats were fed (3 months) with a high-calorie cafeteria diet (CD) or standard chow. SD and TGR(ASrAOGEN) rats on the CD diet were also treated with telmisartan (8 mg·kg(-1) ·d(-1) , 3 months).

RESULTS

Compared with SD rats, TGR(ASrAOGEN) rats (i) had lower weights during chow feeding, (ii) did not become obese during CD feeding, (iii) had normal baseline leptin plasma concentrations independent of the feeding regimen, whereas plasma leptin of SD rats was increased due to CD, (iv) showed a reduced energy intake, (v) had a higher, strain-dependent energy expenditure, which is additionally enhanced during CD feeding, (vi) had enhanced mRNA levels of pro-opiomelanocortin and (vii) showed improved glucose control. Weight gain and energy intake in rats fed the CD diet were markedly reduced by telmisartan in SD rats but only to a minor extent in TGR(ASrAOGEN) rats.

CONCLUSIONS

The brain renin-angiotensin system affects body weight regulation, feeding behaviour and metabolic disorders. When angiotensin II levels are low in brain, rats are protected from developing diet-induced obesity and obesity-related metabolic impairments. We further suggest that telmisartan at least partly lowers body weight via a CNS-driven mechanism.

Diabetes-associated cardiac fibrosis: Cellular effectors, molecular mechanisms and therapeutic opportunities

Both type 1 and type 2 diabetes are associated with cardiac fibrosis that may reduce myocardial compliance, contribute to the pathogenesis of heart failure, and trigger arrhythmic events. Diabetes-associated fibrosis is mediated by activated cardiac fibroblasts, but may also involve fibrogenic actions of macrophages, cardiomyocytes and vascular cells. The molecular basis responsible for cardiac fibrosis in diabetes remains poorly understood. Hyperglycemia directly activates a fibrogenic program, leading to accumulation of advanced glycation end-products (AGEs) that crosslink extracellular matrix proteins, and transduce fibrogenic signals through reactive oxygen species generation, or through activation of Receptor for AGEs (RAGE)-mediated pathways. Pro-inflammatory cytokines and chemokines may recruit fibrogenic leukocyte subsets in the cardiac interstitium. Activation of transforming growth factor-β/Smad signaling may activate fibroblasts inducing deposition of structural extracellular matrix proteins and matricellular macromolecules. Adipokines, endothelin-1 and the renin-angiotensin-aldosterone system have also been implicated in the diabetic myocardium. This manuscript reviews our current understanding of the cellular effectors and molecular pathways that mediate fibrosis in diabetes. Based on the pathophysiologic mechanism, we propose therapeutic interventions that may attenuate the diabetes-associated fibrotic response and discuss the challenges that may hamper clinical translation.

Contractile apparatus dysfunction early in the pathophysiology of diabetic cardiomyopathy

Diabetes mellitus significantly increases the risk of cardiovascular disease and heart failure in patients. Independent of hypertension and coronary artery disease, diabetes is associated with a specific cardiomyopathy, known as diabetic cardiomyopathy (DCM). Four decades of research in experimental animal models and advances in clinical imaging techniques suggest that DCM is a progressive disease, beginning early after the onset of type 1 and type 2 diabetes, ahead of left ventricular remodeling and overt diastolic dysfunction. Although the molecular pathogenesis of early DCM still remains largely unclear, activation of protein kinase C appears to be central in driving the oxidative stress dependent and independent pathways in the development of contractile dysfunction. Multiple subcellular alterations to the cardiomyocyte are now being highlighted as critical events in the early changes to the rate of force development, relaxation and stability under pathophysiological stresses. These changes include perturbed calcium handling, suppressed activity of aerobic energy producing enzymes, altered transcriptional and posttranslational modification of membrane and sarcomeric cytoskeletal proteins, reduced actin-myosin cross-bridge cycling and dynamics, and changed myofilament calcium sensitivity. In this review, we will present and discuss novel aspects of the molecular pathogenesis of early DCM, with a special focus on the sarcomeric contractile apparatus.

Lack of weight gain after angiotensin AT1 receptor blockade in diet-induced obesity is partly mediated by an angiotensin-(1-7)/Mas-dependent pathway

BACKGROUND AND PURPOSE

Angiotensin AT1 receptor antagonists induce weight loss; however, the mechanism underlying this phenomenon is unknown. The Mas receptor agonist angiotensin-(1-7) is a metabolite of angiotensin I and of angiotensin II . As an agonist of Mas receptors, angiotensin-(1-7) has beneficial cardiovascular and metabolic effects.

EXPERIMENTAL APPROACH

We investigated the anti-obesity effects of transgenically overexpressed angiotensin-(1-7) in rats. We secondly examined whether weight loss due to telmisartan (8 mg·kg(-1) ·d(-1) ) in diet-induced obese Sprague Dawley (SD) rats can be blocked when the animals were co-treated with the Mas receptor antagonist A779 (24 or 72 μg·kg(-1) ·d(-1) ).

KEY RESULTS

In contrast to wild-type controls, transgenic rats overexpressing angiotensin-(1-7) had 1.) diminished body weight when they were regularly fed with chow; 2.) were protected from developing obesity although they were fed with cafeteria diet (CD); 3.) showed a reduced energy intake that was mainly related to a lower CD intake; 5.) remained responsive to leptin despite chronic CD feeding; 6.) had a higher, strain-dependent energy expenditure, and 7.) were protected from developing insulin resistance despite CD feeding. Telmisartan-induced weight loss in SD rats was partially antagonized after a high, but not a low dose of A779.

CONCLUSIONS AND IMPLICATIONS

Angiotensin-(1-7) regulated food intake and body weight and contributed to the weight loss after AT1 receptor blockade. Angiotensin-(1-7)-like agonists may be drug candidates for treating obesity.

How exercise may amend metabolic disturbances in diabetic cardiomyopathy

SIGNIFICANCE

Over-nutrition and sedentary lifestyle has led to a worldwide increase in obesity, insulin resistance, and type 2 diabetes (T2D) associated with an increased risk of development of cardiovascular disorders. Diabetic cardiomyopathy, independent of hypertension or coronary disease, is induced by a range of systemic changes and may through multiple processes result in functional and structural cardiac derangements. The pathogenesis of this cardiomyopathy is complex and multifactorial, and it will eventually lead to reduced cardiac working capacity and increased susceptibility to ischemic injury.

RECENT ADVANCES

Metabolic disturbances such as altered lipid handling and substrate utilization, decreased mechanical efficiency, mitochondrial dysfunction, disturbances in nonoxidative glucose pathways, and increased oxidative stress are hallmarks of diabetic cardiomyopathy. Interestingly, several of these disturbances are found to precede the development of cardiac dysfunction.

CRITICAL ISSUES

Exercise training is effective in the prevention and treatment of obesity and T2D. In addition to its beneficial influence on diabetes/obesity-related systemic changes, it may also amend many of the metabolic disturbances characterizing the diabetic myocardium. These changes are due to both indirect effects, exercise-mediated systemic changes, and direct effects originating from the high contractile activity of the heart during physical training.

FUTURE DIRECTIONS

Revealing the molecular mechanisms behind the beneficial effects of exercise training is of considerable scientific value to generate evidence-based therapy and in the development of new treatment strategies.

Pre-treatment with metformin activates Nrf2 antioxidant pathways and inhibits inflammatory responses through induction of AMPK after transient global cerebral ischemia

Global cerebral ischemia arises in patients who have a variety of clinical conditions including cardiac arrest, shock and asphyxia. In spite of advances in understanding of the brain ischemia and stroke etiology, therapeutic approaches to improve ischemic injury still remain limited. It has been established that metformin can attenuate cell death in cerebral ischemia. One of the main functions of metformin is proposed to be conducted via AMP-activated protein kinase (AMPK)-dependent pathway in the experimental cerebral ischemia model. It is also established that metformin can suppress inflammation and activate Nuclear factor erythroid 2-related factor (Nrf2) pathways in neurons. In the current study, the role of metformin in regulating inflammatory and antioxidant pathways in the global cerebral ischemia was investigated. Our results indicated that pretreatment of rats by metformin attenuated cellular levels of nuclear factor-κB, Tumor Necrosis Factor alpha and Cyclooxygenase-2 which are considered as three important proteins involved in the inflammation pathway. Pretreatment by metformin increased the level of Nrf2 and heme oxygenase-1 in the hippocampus of ischemic rats compared with untreated ischemic group. Moreover, pretreatment by metformin enhanced the level of glutathione and catalase activities compared with them in ischemic group. Such protective changes detected by metformin pretreatment were reversed by injecting compound c, an AMPK inhibitor. These findings suggested that metformin might protect cells through modulating inflammatory and antioxidant pathways via induction of AMPK. However, more experimental and clinical trial studies regarding neuroprotective potential of metformin and the involved mechanisms, especially in the context of cerebral ischemic injuries, are necessary.

Updating experimental models of diabetic cardiomyopathy

Diabetic cardiomyopathy entails a serious cardiac dysfunction induced by alterations in structure and contractility of the myocardium. This pathology is initiated by changes in energy substrates and occurs in the absence of atherothrombosis, hypertension, or other cardiomyopathies. Inflammation, hypertrophy, fibrosis, steatosis, and apoptosis in the myocardium have been studied in numerous diabetic experimental models in animals, mostly rodents. Type I and type II diabetes were induced by genetic manipulation, pancreatic toxins, and fat and sweet diets, and animals recapitulate the main features of human diabetes and related cardiomyopathy. In this review we update and discuss the main experimental models of diabetic cardiomyopathy, analysing the associated metabolic, structural, and functional abnormalities, and including current tools for detection of these responses. Also, novel experimental models based on genetic modifications of specific related genes have been discussed. The study of specific pathways or factors responsible for cardiac failures may be useful to design new pharmacological strategies for diabetic patients.

Obesity, metabolic dysfunction, and cardiac fibrosis: pathophysiological pathways, molecular mechanisms, and therapeutic opportunities

Cardiac fibrosis is strongly associated with obesity and metabolic dysfunction and may contribute to the increased incidence of heart failure, atrial arrhythmias, and sudden cardiac death in obese subjects. This review discusses the evidence linking obesity and myocardial fibrosis in animal models and human patients, focusing on the fundamental pathophysiological alterations that may trigger fibrogenic signaling, the cellular effectors of fibrosis, and the molecular signals that may regulate the fibrotic response. Obesity is associated with a wide range of pathophysiological alterations (such as pressure and volume overload, metabolic dysregulation, neurohumoral activation, and systemic inflammation); their relative role in mediating cardiac fibrosis is poorly defined. Activation of fibroblasts likely plays a major role in obesity-associated fibrosis; however, inflammatory cells, cardiomyocytes, and vascular cells may also contribute to fibrogenic signaling. Several molecular processes have been implicated in regulation of the fibrotic response in obesity. Activation of the renin-angiotensin-aldosterone system, induction of transforming growth factor β, oxidative stress, advanced glycation end-products, endothelin 1, Rho-kinase signaling, leptin-mediated actions, and upregulation of matricellular proteins (such as thrombospondin 1) may play a role in the development of fibrosis in models of obesity and metabolic dysfunction. Moreover, experimental evidence suggests that obesity and insulin resistance profoundly affect the fibrotic and remodeling response after cardiac injury. Understanding the pathways implicated in obesity-associated fibrosis may lead to the development of novel therapies to prevent heart failure and attenuate postinfarction cardiac remodeling in patients with obesity.

The "Goldilocks Zone" from a redox perspective-Adaptive vs. deleterious responses to oxidative stress in striated muscle

Consequences of oxidative stress may be beneficial or detrimental in physiological systems. An organ system's position on the “hormetic curve” is governed by the source and temporality of reactive oxygen species (ROS) production, proximity of ROS to moieties most susceptible to damage, and the capacity of the endogenous cellular ROS scavenging mechanisms. Most importantly, the resilience of the tissue (the capacity to recover from damage) is a decisive factor, and this is reflected in the disparate response to ROS in cardiac and skeletal muscle. In myocytes, a high oxidative capacity invariably results in a significant ROS burden which in homeostasis, is rapidly neutralized by the robust antioxidant network. The up-regulation of key pathways in the antioxidant network is a central component of the hormetic response to ROS. Despite such adaptations, persistent oxidative stress over an extended time-frame (e.g., months to years) inevitably leads to cumulative damages, maladaptation and ultimately the pathogenesis of chronic diseases. Indeed, persistent oxidative stress in heart and skeletal muscle has been repeatedly demonstrated to have causal roles in the etiology of heart disease and insulin resistance, respectively. Deciphering the mechanisms that underlie the divergence between adaptive and maladaptive responses to oxidative stress remains an active area of research for basic scientists and clinicians alike, as this would undoubtedly lead to novel therapeutic approaches. Here, we provide an overview of major types of ROS in striated muscle and the divergent adaptations that occur in response to them. Emphasis is placed on highlighting newly uncovered areas of research on this topic, with particular focus on the mitochondria, and the diverging roles that ROS play in muscle health (e.g., exercise or preconditioning) and disease (e.g., cardiomyopathy, ischemia, metabolic syndrome).

Triggering the succinate receptor GPR91 enhances pressure overload-induced right ventricular hypertrophy

BACKGROUND

Pulmonary arterial hypertension (PAH) leads to pressure overload in the right ventricle (RV) and induces right ventricular hypertrophy (RVH). GPR91 is an orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate, which increases in RVH; however, its role remains unknown.

METHODS AND RESULTS

We studied succinate-GPR91 signaling in a pulmonary arterial banding (PAB) model of RVH in the SD rats due to pressure overload. We report that GPR91 was located in cardiomyocytes. We found that the expressions of GPR91 and p-Akt in the RV significantly increased in the PAB model compared with the sham. In the PAB rats, the treatment of succinate further increased the p-Akt levels and aggravated RVH in vivo. In in vitro studies, succinate stimulated the up-regulation of the hypertrophic gene marker anp. All these effects were inhibited by the antagonist of PI3K, wortmannin, both in vivo and in vitro. Finally, we found that the GPR91-PI3K/Akt axis was also up-regulated compared with the sham in human RVH.

CONCLUSIONS

Our results suggest that succinate-GPR91 is involved in RVH via PI3K/Akt signaling in vivo and in vitro. GPR91 may be a novel therapeutic target for RVH induced by pressure overload.

Heart remodeling and ischemia-reperfusion arrhythmias linked to myocardial vitamin d receptors deficiency in obstructive nephropathy are reversed by paricalcitol

Cardiovascular disease is often associated with chronic kidney disease and vice versa; myocardial vitamin D receptors (VDRs) are among the probable links between the 2 disorders. The vitamin D receptor activator paricalcitol protects against some renal and cardiovascular complications. However, the structural and electrophysiological effects of myocardial vitamin D receptor modification and its impact on the response to ischemia-reperfusion are currently unknown. This work attempted to determine whether obstructive nephropathy induced myocardial changes (in rats) linked to vitamin D receptor deficiency and to ventricular arrhythmias in Langendorff-perfused hearts. Unilateral ureteral-obstructed and Sham-operated rats were treated with either paricalcitol (30 ng/kg/d intraperitoneal) or vehicle for 15 days. In 5 hearts from each group, we found that obstructed rats showed a reduction in VDRs and an increase in angiotensin II type 1 receptor expression (messenger RNA and protein), suffered fibrosis (determined by Masson trichrome stain) and myofibril reduction with an increase in mitochondrial size, and had dilated crests (determined by electron microscopy). These changes were reversed by paricalcitol. In 8 additional hearts per group, we found that obstructed rats showed a higher incidence of ventricular fibrillation during reperfusion (after 10 minutes of regional ischemia) than did those treated with paricalcitol. The action potential duration was prolonged throughout the experiment in paricalcitol-treated rats. We conclude that the reduction in myocardial vitamin D receptor expression in obstructed rats might be related to myocardial remodeling associated with an increase in arrhythmogenesis and that paricalcitol protects against these changes by restoring myocardial vitamin D receptor levels and prolonging action potentials.

DanQi Pill protects against heart failure through the arachidonic acid metabolism pathway by attenuating different cyclooxygenases and leukotrienes B4

Background

Chinese herbal formulae are composed of complex components and produce comprehensive pharmacological effects. Unlike chemical drugs that have only one clear single target, the components of Chinese herbal formulae have multiple channels and targets. How to discover the pharmacological targets of Chinese herbal formulae and their underlying molecular mechanism are still under investigation.

Methods

DanQi pill (DQP), which is one of the widely prescribed traditional Chinese medicines, is applied as an example drug. In this study, we used the drug target prediction model (DrugCIPHER-CS) to examine the underlying molecular mechanism of DQP, followed by experimental validation.

Results

A novel therapeutic effect pattern of DQP was identified. After determining the compounds in DQP, we used DrugCIPHER-CS to predict their potential targets. These potential targets were significantly enriched in well-known cardiovascular disease-related pathways. For example, the biological processes of neuroactive ligand–receptor interaction, calcium-signaling pathway, and aminoacyl–tRNA biosynthesis were involved. A new and significant pathway, arachidonic acid (AA) metabolism, was also identified in this study. This predicted pathway alteration was validated with an animal model of heart failure (HF). Results show that DQP had effect both on thromboxane B2 (TXB2) and Prostaglandin I2 (PGI2) in different patterns. It can down-regulate the TXB2 and up-regulate the PGI2 in diverse way. Remarkably, it also had effect on cyclooxygenase (COX)-1 and COX2 by suppressing their levels, which may be the critical and novel mechanism of cardiacprotective efficacy for DQP. Furthermore, leukotrienes B4 (LTB4) receptor, another key molecule of AA metabolism which finally mediated gastrotoxic leukotrienes, was also reduced by DQP.

Conclusions

The combination of drug target prediction and experimental validation provides new insights into the complicated mechanism of DQP.

Antioxidants supplementation in elderly cardiovascular patients

Supplementation with antioxidants and its benefit-risk relationship have been largely discussed in the elderly population. We evaluated whether antioxidants supplementation improved the biochemical profile associated with oxidative metabolism in elderly cardiovascular patients. Patients (n = 112) received daily supplementation with α-TP 400 mg, beta-carotene 40 mg, and vitamin C 1000 mg for 2 months (treatment). Plasma concentrations of alpha-tocopherol (α-TP), β-carotene (βC), ubiquinol-10 (QH-10), glutathione, and thiobarbituric acid reactive substances (TBARS) were determined before and after treatment. Response to treatment was dependent on pretreatment α-TP and βC levels. Increase in α-TP and βC levels was observed only in patients with basal levels <18  μM for α-TP (P < 0.01) and <0.30  μM for βC (P < 0.02). Ubiquinol-10, glutathione, and TBARS were unaffected by treatment: QH-10 (+57%, F(1,110) = 3.611, P < 0.06, and N.S.), glutathione (+21%, F(1,110) = 2.92, P < 0.09, and N.S.), and TBARS (-29%, F(1,110) = 2.26, P < 0.14, and N.S.). Treatment reduced oxidative metabolism: 5.3% versus 14.6% basal value (F(1,110) = 9.21, P < 0.0003). Basal TBARS/α-TP ratio was higher in smokers compared to nonsmokers: 0.11 ± 0.02 versus 0.06 ± 0.01 (F(32,80) = 1.63, P < 0.04). Response to antioxidant supplementation was dependent on basal plasma levels of α-TP and βC. Smoking status was strongly associated with atherosclerotic cardiovascular disease and high TBARS/α-TP ratio (lipid peroxidation).