Transgenic overexpression of GTP cyclohydrolase 1 in cardiomyocytes ameliorates post-infarction cardiac remodeling

Exploring the therapeutic potential of tetrahydrobiopterin for heart failure with preserved ejection fraction: A path forward

A large number of patients are affected by classical heart failure (HF) symptomatology with preserved ejection fraction (HFpEF) and multiorgan syndrome. Due to high morbidity and mortality rate, hospitalization and mortality remain serious socioeconomic problems, while the lack of effective pharmacological or device treatment means that HFpEF presents a major unmet medical need. Evidence from clinical and basic studies demonstrates that systemic inflammation, increased oxidative stress, and impaired mitochondrial function are the common pathological mechanisms in HFpEF. Tetrahydrobiopterin (BH4), beyond being an endogenous co-factor for catalyzing the conversion of some essential biomolecules, has the capacity to prevent systemic inflammation, enhance antioxidant resistance, and modulate mitochondrial energy production. Therefore, BH4 has emerged in the last decade as a promising agent to prevent or reverse the progression of disorders such as cardiovascular disease. In this review, we cover the clinical progress and limitations of using downstream targets of nitric oxide (NO) through NO donors, soluble guanylate cyclase activators, phosphodiesterase inhibitors, and sodium-glucose co-transporter 2 inhibitors in treating cardiovascular diseases, including HFpEF. We discuss the use of BH4 in association with HFpEF, providing new evidence for its potential use as a pharmacological option for treating HFpEF.

SGLT2 Inhibitors: New Hope for the Treatment of Acute Myocardial Infarction?

Among all of the new antidiabetic drugs, an increasing number of studies have evaluated the relationship between the sodium-glucose cotransporter 2 inhibitors (SGLT2i) and acute myocardial infarction (AMI). Since SGLT2i like empagliflozin, canagliflozin, and recently, dapagliflozin have shown impressive positive effects in patients with chronic heart failure with reduced ejection fraction (HFrEF), it has increased research interest to explore the cardiac molecular mechanisms underlying the clinical benefits and attracted more attention to the effects of SGLT2i on a series of cardiovascular events. Experimental and clinical data on SGLT2i treatment after AMI is limited. This is a review of the clinical and preclinical effects of SGLT2i, focusing on available data on the effects of SGLT2i in AMI patients with a brief overview of ongoing trials.

Measurement of Tetrahydrobiopterin in Animal Tissue Samples by HPLC with Electrochemical Detection-Protocol Optimization and Pitfalls

Tetrahydrobiopterin (BH4) is an essential cofactor of all nitric oxide synthase isoforms, thus determination of BH4 levels can provide important mechanistic insight into diseases. We established a protocol for high-performance liquid chromatography/electrochemical detection (HPLC/ECD)-based determination of BH4 in tissue samples. We first determined the optimal storage and work-up conditions for authentic BH4 and its oxidation product dihydrobiopterin (BH2) under various conditions (pH, temperature, presence of antioxidants, metal chelators, and storage time). We then applied optimized protocols for detection of BH4 in tissues of septic (induced by lipopolysaccharide [LPS]) rats. BH4 standards in HCl are stabilized by addition of 1,4-dithioerythritol (DTE) and diethylenetriaminepentaacetic acid (DTPA), while HCl was sufficient for BH2 standard stabilization. Overnight storage of BH4 standard solutions at room temperature in HCl without antioxidants caused complete loss of BH4 and the formation of BH2. We further optimized the protocol to separate ascorbate and the BH4 tissue sample and found a significant increase in BH4 in the heart and kidney as well as higher BH4 levels by trend in the brain of septic rats compared to control rats. These findings correspond to reports on augmented nitric oxide and BH4 levels in both animals and patients with septic shock.

Myocardial ischemia/reperfusion injury: Mechanisms of injury and implications for management (Review)

Myocardial infarction is one of the primary causes of mortality in patients with coronary heart disease worldwide. Early treatment of acute myocardial infarction restores blood supply of ischemic myocardium and decreases the mortality risk. However, when the interrupted myocardial blood supply is recovered within a certain period of time, it causes more serious damage to the original ischemic myocardium; this is known as myocardial ischemia/reperfusion injury (MIRI). The pathophysiological mechanisms leading to MIRI are associated with oxidative stress, intracellular calcium overload, energy metabolism disorder, apoptosis, endoplasmic reticulum stress, autophagy, pyroptosis, necroptosis and ferroptosis. These interplay with one another and directly or indirectly lead to aggravation of the effect. In the past, apoptosis and autophagy have attracted more attention but necroptosis and ferroptosis also serve key roles. However, the mechanism of MIRI has not been fully elucidated. The present study reviews the mechanisms underlying MIRI. Based on current understanding of the pathophysiological mechanisms of MIRI, the association between cell death-associated signaling pathways were elaborated, providing direction for investigation of novel targets in clinical treatment.

Salvia miltiorrhiza Protects Endothelial Dysfunction against Mitochondrial Oxidative Stress

Salvia miltiorrhiza (SM) is a common traditional Chinese medicine used in the treatment of cardiovascular and cerebrovascular diseases. Endothelial dysfunction plays an important role in the pathology of cardiovascular diseases. Endothelial dysfunction may induce inflammation and change vascular tone and permeability. The main pathological mechanism of endothelial dysfunction is the formation of reactive oxygen species (ROS). Mitochondria are the main source of energy and can also produce large amounts of ROS. Recent studies have shown that extracts of SM have antioxidative, anti-inflammatory, and antithrombus properties. In this review, we discuss the mechanism of oxidative stress in the mitochondria, endothelial dysfunction, and the role of SM in these oxidative events.

The Causes and Consequences of miR-503 Dysregulation and Its Impact on Cardiovascular Disease and Cancer

microRNAs (miRs) are short, non-coding RNAs that regulate gene expression by mRNA degradation or translational repression. Accumulated studies have demonstrated that miRs participate in various biological processes including cell differentiation, proliferation, apoptosis, metabolism and development, and the dysregulation of miRs expression are involved in different human diseases, such as neurological, cardiovascular disease and cancer. microRNA-503 (miR-503), one member of miR-16 family, has been studied widely in cardiovascular disease and cancer. In this review, we summarize and discuss the studies of miR-503 in vitro and in vivo, and how miR-503 regulates gene expression from different aspects of pathological processes of diseases, including carcinogenesis, angiogenesis, tissue fibrosis and oxidative stress; We will also discuss the mechanisms of dysregulation of miR-503, and whether miR-503 could be applied as a diagnostic marker or therapeutic target in cardiovascular disease or cancer.

SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) prevents cardiac remodeling after myocardial infarction through ERK/SMAD signaling pathway

In this study, we aimed to investigate the role of SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) in cardiac remodeling after myocardial infarction (MI) and explore the underlying molecular mechanism. MI model was established by ligation of the left anterior descending coronary artery. C57/BL6J mice were randomly administered with 3.0 mg/kg/day PHPS1 (PHPS1-treated group) or normal saline (model group) by intraperitoneal injection. After 4 weeks of infusion, the effects of PHPS1 on cardiac remodeling were evaluated. Echocardiography results showed that PHPS1 treatment aggravated the MI-induced deterioration of cardiac function, with worse cardiac function parameters. PHPS1 treatment significantly increased the infarcted area, as well as the fibrotic area and the expression of collagen I and collagen III. Western blots and immunofluorescence staining showed that PHPS1 treatment up-regulated the expression of p-GRK2, p-SMAD2/3 and p-ERK1/2, while U0126 reversed the effect of PHPS1. The present study indicated that PHPS1 treatment contributed to myocardial fibrosis and infarction by activating ERK/SMAD signaling pathway, suggesting that SHP-2 may be a promising treatment target for cardiac remodeling after MI.

Empagliflozin improves post-infarction cardiac remodeling through GTP enzyme cyclohydrolase 1 and irrespective of diabetes status

Sodium-glucose co-transporter-2 inhibitors (SGLT2i) have shown to prevent heart failure progression, although the mechanisms remain poorly understood. Here we evaluated the effect of empagliflozin (EMPA, SGLT2i) in cardiac remodeling after myocardial infarction, the interplay with diabetes status and the role of cardiac GTP enzyme cyclohydrolase 1 (cGCH1). A rat model of diabetes (50 mg/kg streptozotocin, i.p.) was subjected to myocardial infarction and left ventricular systolic dysfunction, by ligation of the left anterior descending coronary artery. EMPA therapy significantly improved cardiac remodeling parameters and ameliorated processes of fibrosis and hypertrophy, in both non-diabetic and diabetic rats. This cardioprotective effect related with a significant increase in myocardial expression levels of cGCH1, which led to activation of nNOS and eNOS, and inhibition of iNOS, and subsequently resulted in increasing of NO levels and decreasing O₂^.- and nitrotyrosine levels. These effects were replicated in a cardiomyocyte biomechanical stretching diabetic model, where silencing cGCH1 blocked the preventive effect of EMPA. The beneficial effects were observed irrespective of diabetes status, although the magnitude was greater in presence of diabetes. Empagliflozin improves myocardial remodeling after myocardial infarction through overexpression of cGCH1, and irrespective of diabetes status.

NOS cofactor tetrahydrobiopterin contributes to anesthetic preconditioning induced myocardial protection in the isolated ex vivo rat heart

Anesthetic preconditioning (APC) may decrease the myocardium injury nearly 50% following ischemia/reperfusion (I/R) by enhancing recovery of cardiac function, reducing myocardial enzyme release and lowering infarct size when utilized as pretreatment or posttreatment agents. I/R increases nitric oxide (NO) production through endothelial NO synthase (NOS3) and heat shock protein 90 (HSP90). The present study aimed to observe the role of BH4 availability and the association of HSP90 with NOS3 in APC‑mediated cardioprotection against I/R injury. Isolated rat hearts were subjected to no‑flow ischemia for 30 min and reperfusion for 120 min. Sevoflurane (3.5%) was administered for 15 min followed by a 15 min washout prior to ischemia. 2,4-Diamino-6-hydroxypyrimidine (DAHP) or sepiapterin (SP) was administered for 40 min until the onset of ischemia. The results revealed that compared with pre‑ischemic basal levels, BH4 levels decreased and BH2 levels increased following I/R. BH4 levels were significantly increased and BH2 levels were significantly decreased in the APC + I/R hearts compared with the I/R group hearts. The BH4:BH2 ratio in the APC‑treated hearts was also increased compared with that in the I/R group hearts. SP increased the recovery of contractile function and the production of NO, and decreased the production of superoxide anion (O2·‑) in I/R heart, but did not elicit these effects in APC‑treated hearts. DAHP treatment inhibited the APC‑mediated recovery of contractile function, increased O2·‑ levels and decreased NO production, but had no effect in I/R hearts. The cardioprotection of APC was demonstrated to be modulated by the BH4 precursor SP, which increased BH4 levels, or DAHP, which inhibited GTP cyclohydrolase I. Both APC and SP treatments increased the combination of HSP90 and NOS3, which improved the NOS3 activity and function. The results suggested that BH4, which servesas a cofactor for NOS, mediated the resistance of APC to I/R injury by promoting the binding of HSP90 and NOS3.

Vascular endothelial growth factor regulation of endothelial nitric oxide synthase phosphorylation is involved in isoflurane cardiac preconditioning

Aims

Previous studies indicate that nitric oxide derived from endothelial nitric oxide synthase (eNOS) serves as both trigger and mediator in anaesthetic cardiac preconditioning. The mechanisms underlying regulation of eNOS by volatile anaesthetics have not been fully understood. Therefore, this study examined the role of vascular endothelial growth factor (VEGF) in isoflurane cardiac preconditioning.

Methods and results

Wistar rats underwent 30 min of coronary artery occlusion followed by 2 h of reperfusion. Isoflurane given prior to ischaemia/reperfusion significantly decreased myocardial infarct size from 60 ± 1% in control to 40 ± 3% (n = 8 rats/group, P < 0.05). The beneficial effects of isoflurane were blocked by neutralizing antibody against VEGF (nVEGF). Coronary arterial endothelial cells (ECs) alone or together with cardiomyocytes (CMs) were subjected to hypoxia/reoxygenation injury. The expression of VEGF and eNOS was analysed by western blot, and nitric oxide was measured by ozone-based chemiluminescence. In co-cultured CMs and ECs, isoflurane administered before hypoxia/reoxygenation attenuated lactate dehydrogenase activity and increased the ratio of phosphorylated eNOS/eNOS and nitric oxide production. The protective effect of isoflurane on CMs was compromised by nVEGF and after VEGF in ECs was inhibited with hypoxia inducible factor-1α short hairpin RNA (shRNA). The negative effect of hypoxia inducible factor-1α shRNA was restored by recombinant VEGF.

Conclusion

Isoflurane cardiac preconditioning is associated with VEGF regulation of phosphorylation of eNOS and nitric oxide production.

Exercise training augments neuronal nitric oxide synthase dimerization in the paraventricular nucleus of rats with chronic heart failure

Exercise training (ExT) is an established non-pharmacological therapy that improves the health and quality of life in patients with chronic heart failure (CHF). Exaggerated sympathetic drive characterizes CHF due to an imbalance of the autonomic nervous system. Neuronal nitric oxide synthase (nNOS) in the paraventricular nucleus (PVN) produce nitric oxide (NO•), which is known to regulate the sympathetic tone. Previously we have shown that during CHF, the catalytically active dimeric form of nNOS is significantly decreased with a concurrent increase in protein inhibitor of nNOS (PIN) expression, a protein that dissociates dimeric nNOS to monomers and facilitates its degradation. Dimerization of nNOS also requires (6R)-5,6,7,8-tetrahydrobiopterin (BH4) for stability and activity. Previously, we have shown that ExT improves NO-mediated sympathetic inhibition in the PVN; however, the molecular mechanism remains elusive. We hypothesized; ExT restores the sympathetic drive by increasing the levels and catalytically active form of nNOS by abrogating changes in the PIN in the PVN of CHF rats. CHF was induced in adult male Sprague-Dawley rats by coronary artery ligation, which reliably mimics CHF in patients with myocardial infarction. After 4 weeks of surgery, Sham and CHF rats were subjected to 3 weeks of progressive treadmill exercise. ExT significantly (p < 0.05) decreased PIN expression and increased dimer/monomer ratio of nNOS in the PVN of rats with CHF. Moreover, we found decreased GTP cyclohydrolase 1(GCH1) expression: a rate-limiting enzyme for BH4 biosynthesis in the PVN of CHF rats suggesting that perhaps reduced BH4 availability may also contribute to decreased nNOS dimers. Interestingly, CHF induced decrease in GCH1 expression was increased with ExT. Our findings revealed that ExT rectified decreased PIN and GCH1 expression and increased dimer/monomer ratio of nNOS in the PVN, which may lead to increase NO• bioavailability resulting in amelioration of activated sympathetic drive during CHF.

A new hypothesis for Parkinson's disease pathogenesis: GTPase-p38 MAPK signaling and autophagy as convergence points of etiology and genomics

The combination of genetics and genomics in Parkinson´s disease has recently begun to unveil molecular mechanisms possibly underlying disease onset and progression. In particular, catabolic processes such as autophagy have been increasingly gaining relevance as post-mortem evidence and experimental models suggested a participation in neurodegeneration and alpha-synuclein Lewy body pathology. In addition, familial Parkinson´s disease linked to LRRK2 and alpha-synuclein provided stronger correlation between etiology and alterations in autophagy. More detailed cellular pathways are proposed and genetic risk factors that associate with idiopathic Parkinson´s disease provide further clues in dissecting contributions of single players. Nevertheless, the fine-tuning of these processes remains elusive, as the initial stages of the pathways are not yet clarified.In this review, we collect literature evidence pointing to autophagy as the common, downstream target of Parkinsonian dysfunctions and augment current knowledge on the factors that direct the subsequent steps. Cell and molecular biology evidence indicate that p38 signaling underlies neurodegeneration and autoptic observations suggest a participation in neuropathology. Moreover, alpha-synuclein and LRRK2 also appear involved in the p38 pathway with additional roles in the regulation of GTPase signaling. Small GTPases are critical modulators of p38 activation and thus, their functional interaction with aSyn and LRRK2 could explain much of the detailed mechanics of autophagy in Parkinson´s disease.We propose a novel hypothesis for a more comprehensive working model where autophagy is controlled by upstream pathways, such as GTPase-p38, that have been so far underexplored in this context. In addition, etiological factors (LRRK2, alpha-synuclein) and risk loci might also combine in this common mechanism, providing a powerful experimental setting to dissect the cause of both familial and idiopathic disease.

Failure of Isoflurane Cardiac Preconditioning in Obese Type 2 Diabetic Mice Involves Aberrant Regulation of MicroRNA-21, Endothelial Nitric-oxide Synthase, and Mitochondrial Complex I

BACKGROUND

Diabetes impairs the cardioprotective effect of volatile anesthetics, yet the mechanisms are still murky. We examined the regulatory effect of isoflurane on microRNA-21, endothelial nitric-oxide synthase, and mitochondrial respiratory complex I in type 2 diabetic mice.

METHODS

Myocardial ischemia/reperfusion injury was produced in obese type 2 diabetic (db/db) and C57BL/6 control mice ex vivo in the presence or absence of isoflurane administered before ischemia. Cardiac microRNA-21 was quantified by real-time quantitative reverse transcriptional-polymerase chain reaction. The dimers and monomers of endothelial nitric-oxide synthase were measured by Western blot analysis. Mitochondrial nicotinamide adenine dinucleotide fluorescence was determined in Langendorff-perfused hearts.

RESULTS

Body weight and fasting blood glucose were greater in db/db than C57BL/6 mice. Isoflurane decreased left ventricular end-diastolic pressure from 35 ± 8 mmHg in control to 23 ± 9 mmHg (P = 0.019, n = 8 mice/group, mean ± SD) and elevated ±dP/dt 2 h after post-ischemic reperfusion in C57BL/6 mice. These beneficial effects of isoflurane were lost in db/db mice. Isoflurane elevated microRNA-21 and the ratio of endothelial nitric-oxide synthase dimers/monomers and decreased mitochondrial nicotinamide adenine dinucleotide levels 5 min after ischemia in C57BL/6 but not db/db mice. MicroRNA-21 knockout blocked these favorable effects of isoflurane, whereas endothelial nitric-oxide synthase knockout had no effect on the expression of microRNA-21 but blocked the inhibitory effect of isoflurane preconditioning on nicotinamide adenine dinucleotide.

CONCLUSIONS

Failure of isoflurane cardiac preconditioning in obese type 2 diabetic db/db mice is associated with aberrant regulation of microRNA-21, endothelial nitric-oxide synthase, and mitochondrial respiratory complex I.