Red blood cell eNOS is cardioprotective in acute myocardial infarction

Erectile dysfunction in cardiovascular patients: A prospective study of the eNOS gene T-786C, G894T, and INTRON variable number of the tandem repeat functional interaction

BACKGROUND

Cardiovascular disease induces erectile dysfunction modulated by endothelial nitric oxide synthase enzyme and an impaired ejection fraction that restricts penis vascular congestion. However, the mechanisms regulating endothelial dysfunction are not understood.

OBJECTIVES

Exploring the functional impact of endothelial nitric oxide synthase genetic polymorphisms on erectile dysfunction and drug therapy optimization in high-risk cardiovascular disease patients.

MATERIALS AND METHODS

Patients with erectile dysfunction symptoms and candidates for andrology therapy were included (n = 112). Clinical data and endothelial nitric oxide synthase rs1799983 (G894T) and rs2070744 (T-786C), genotyped by fluorescence polarization assays, were registered. The 27-bp variable number of the tandem repeat polymorphism in intron 4 (intron4b/a) was analyzed by polymerase chain reaction-restriction fragment length polymorphism. Association analyses were run with the R-3.2.0 software.

RESULTS

A significant association between endothelial nitric oxide synthase 786-TT (p = 0.005) and the aa/ac of intron 4 variable number of the tandem repeat (p = 0.02) with higher erectile dysfunction susceptibility was observed in cardiovascular disease patients (60 ± 9 years, 66% severe erectile dysfunction, 56% ejection fraction). After 3-months of phosphodiesterase type 5 inhibitors, erectile dysfunction (International Index of Erectile Function, 50 ± 16 scores, the International Index of Erectile Function-Erectile Function 21 ± 10 scores, p < 0.001) and sexual quality of life (modified Sexual Life Quality Questionnaire 55 ± 23 scores, p < 0.001) had significantly improved. The cardiovascular ejection fraction was influenced positively with better sexual quality of life (0.1941), and also in the endothelial nitric oxide synthase G894-T allele (p = 0.076) carriers, which could merit future analyses. Erectile dysfunction was present as the primary clinical manifestation in 62% of cases, with cardiovascular disease occurring concurrently. Only former smokers and obese subjects debuted prior to cardiovascular disease than to erectile dysfunction.

CONCLUSIONS

Our study provides comprehensive insights into the functional interaction linking endothelial nitric oxide synthase gene polymorphisms, erectile function, and ejection fraction in high-risk cardiovascular disease patients. Future therapeutic strategies could target endothelial nitric oxide synthase activity by including lifestyle changes and epigenetic modulations.

Emerging concepts in the molecular cell biology and functions of mammalian erythrocytes

Erythrocytes, or red blood cells, are essential components of vertebrate blood, comprising approximately 45% of human blood volume. Their distinctive features, including small size, biconcave shape, extended lifespan (∼115 days), and lack of a nucleus or other membrane-bound organelles, make them unique among mammalian cell types. Traditionally regarded as passive carriers of oxygen and carbon dioxide, erythrocytes were long thought to function merely as hemoglobin-filled sacs, incapable of gene expression or roles beyond gas transport. However, advancements in molecular biology have revealed a more complex picture. Recent studies have identified various RNA types within erythrocytes, demonstrated globin mRNA translation, and uncovered miRNA-mediated defenses against Plasmodium infection. Beyond gas exchange, erythrocytes play critical roles in regulating regional blood flow via nitric oxide, contribute to innate immunity through toll-like receptors, transport amino acids between tissues, and maintain water homeostasis. Furthermore, emerging technologies have repurposed erythrocytes as drug-delivery vehicles, opening new avenues for therapeutic applications. This review highlights these recent discoveries and explores the expanding functional landscape of erythrocytes, shedding light on their multifaceted roles in physiology and medicine.

Biochemistry, pharmacology, and in vivo function of arginases

The enzyme arginase catalyzes the hydrolysis of l-arginine into l-ornithine and urea. The 2 existing isoforms Arg1 and Arg2 exhibit different cellular localizations and metabolic functions. Arginase activity is crucial for nitrogen detoxification in the urea cycle, synthesis of polyamines, and control of l-arginine bioavailability and nitric oxide (NO) production. Despite significant progress in the understanding of the biochemistry and function of arginases, several open questions remain. Recent studies have revealed that the regulation and function of Arg1 and Arg2 are cell type-specific, species-specific, and profoundly different in mice and humans. The main differences are in the distribution and function of Arg1 and Arg2 in immune and erythroid cells. Contrary to what was previously thought, Arg1 activity appears to be only partially related to vascular NO signaling under homeostatic conditions in the vascular wall, but its expression is increased under disease conditions and may be targeted by treatment with arginase inhibitors. Arg2 appears to be mainly a catabolic enzyme involved in the synthesis of l-ornithine, polyamine, and l-proline but may play a putative role in blood pressure control, at least in mice. The immunosuppressive role of arginase-mediated arginine depletion is a promising target for cancer treatment. This review critically revises and discusses the biochemistry, pharmacology, and in vivo function of arginases, focusing on the insights gained from the analysis of cell-specific Arg1 and Arg2 knockout mice and human studies using arginase inhibitors or pegylated recombinant arginase. SIGNIFICANCE STATEMENT: Further basic and translational research is needed to deepen our understanding of the regulation of Arg1 and Arg2 in different cell types in consideration of their localization, species-specificity, and multiple biochemical and physiological roles. This will lead to better pharmacological strategies to target arginase activity in liver, cardiovascular, hematological, immune/infectious diseases, and cancer.

Generation and characterization of a conditional eNOS knock out mouse model for cell-specific reactivation of eNOS in gain-of-function studies

Nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS) in the vessel wall regulates blood pressure and cardiovascular hemodynamics. In this study, we generated conditional eNOS knock out (KO) mice characterized by a duplicated/inverted exon 2 flanked with two pairs of loxP regions (eNOSinv/inv); a Cre-recombinase activity induces cell-specific reactivation of eNOS, as a result of a flipping of the inverted exon 2 (eNOSfl). This work aimed to test the efficiency of the Cre-mediated cell-specific recombination and the resulting eNOS expression/function. As proof of concept, we crossed eNOSinv/inv mice with DeleterCrepos (DelCrepos) mice, expressing Cre recombinase in all cells. We generated heterozygous eNOSfl/inv or homozygous eNOSfl/fl mice, and eNOSinv/inv littermate mice. We found that both eNOSfl/fl and eNOSfl/inv mice express eNOS and the overall expression level depends on the number of mutated alleles, while eNOSinv/inv mice did not show any eNOS expression. Vascular endothelial function was restored in eNOSfl/fl and eNOSfl/inv mice, as determined by ACh-dependent vasodilation of aortic rings. Cre-dependent reactivation of eNOS in eNOSfl/fl and eNOSfl/inv mice rescued eNOSinv/inv (phenotypically global eNOS KO) mice from hypertension. These findings demonstrate that eNOS expression is restored in eNOSfl/fl mice at comparable physiological levels of WT mice, and its functional activity is independent on the number of the reactivated alleles. Therefore, eNOSinv/inv mice are a useful model for studying the effects of conditional reactivation of eNOS and gene dosage effects in specific cells for gain-of-function studies.

Red blood cells from patients with ST-elevation myocardial infarction and elevated C-reactive protein levels induce endothelial dysfunction

Endothelial dysfunction is an early consequence of vascular inflammation and a driver of coronary atherosclerotic disease leading to myocardial infarction. The red blood cells (RBCs) mediate endothelial dysfunction in patients at cardiovascular risk, but their role in patients with acute myocardial infarction is unknown. This study aimed to investigate if RBCs from patients with ST-elevation myocardial infarction (STEMI) induced endothelial dysfunction and the role of systemic inflammation in this effect. RBCs from patients with STEMI and aged-matched healthy controls were coincubated with rat aortic segments for 18 h followed by evaluation of endothelium-dependent (EDR) and endothelium-independent relaxation (EIDR). RBCs and aortic segments were also analyzed for arginase and oxidative stress. The patients were divided into groups depending on C-reactive protein (CRP) levels at admission. RBCs from patients with STEMI and CRP levels ≥2 mg/L induced impairment of EDR, but not EIDR, compared with RBCs from STEMI and CRP <2 mg/L and healthy controls. Aortic expression of arginase 1 was increased following incubation with RBCs from patients with STEMI and CRP ≥2, and arginase inhibition prevented the RBC-induced endothelial dysfunction. RBCs from patients with STEMI and CRP ≥2 had increased reactive oxygen species compared with RBCs from patients with CRP <2 and healthy controls. Vascular inhibition of NADPH oxidases and increased dismutation of superoxide improved EDR. RBCs from patients with STEMI and low-grade inflammation induce endothelial dysfunction through a mechanism involving arginase 1 as well as increased RBC and vascular superoxide by NADPH oxidases.NEW & NOTEWORTHY Red blood cells from patients with STEMI and systemic inflammation induce endothelial dysfunction ex vivo. The RBC-induced endothelial dysfunction is mediated through increased arginase 1 and a shift in the redox balance toward oxidative stress. Inhibition of arginase or free radicals attenuates the impairment of endothelial function. The study suggests that red blood cells deserve attention as a key player in systemic inflammation and STEMI.

Sodium valproate treatment reverses endothelial dysfunction in aorta from rabbits with acute myocardial infarction

Sodium valproate (VPA), a histone deacetylase (HDAC) inhibitor, could be a promising candidate to treat acute myocardial infarction (AMI). In this study, AMI was induced in New Zealand White rabbits by occluding the left circumflex coronary artery for 1 h, followed by reperfusion. The animals were distributed into three experimental groups: the sham-operated group (SHAM), the AMI group and the AMI + VPA group (AMI treated with VPA 500 mg/kg/day). After 5 weeks, abdominal aorta was removed and used for isometric recording of tension in organ baths or protein expression by Western blot, and plasma for the determination of nitrate/nitrite (NOx) levels by colorimetric assay. Our results indicated that AMI induced a reduction of the endothelium-dependent response to acetylcholine without modifying the endothelium-independent response to sodium nitroprusside, leading to endothelial dysfunction. VPA treatment reversed AMI-induced endothelial dysfunction and even increased NO sensitivity in vascular smooth muscle. This response was consistent with an antioxidant effect of VPA, as it was able to reverse the superoxide dismutase 1 (SOD 1) down-regulation induced by AMI. Our experiments also ruled out that the VPA mechanism was related to eNOS, iNOS, sGC and arginase expression or changes in NOx plasma levels. Therefore, we conclude that VPA improves vasodilation by increasing NO bioavailability, likely due to its antioxidant effect. Since endothelial dysfunction was closely related to AMI, VPA treatment could increase aortic blood flow, making it a potential agent in reperfusion therapy that can prevent the vascular damage.

Modulation of the nitric oxide/cGMP pathway in cardiac contraction and relaxation: Potential role in heart failure treatment

Evidence exists that heart failure (HF) has an overall impact of 1-2 % in the global population being often associated with comorbidities that contribute to increased disease prevalence, hospitalization, and mortality. Recent advances in pharmacological approaches have significantly improved clinical outcomes for patients with vascular injury and HF. Nevertheless, there remains an unmet need to clarify the crucial role of nitric oxide/cyclic guanosine 3',5'-monophosphate (NO/cGMP) signalling in cardiac contraction and relaxation, to better identify the key mechanisms involved in the pathophysiology of myocardial dysfunction both with reduced (HFrEF) as well as preserved ejection fraction (HFpEF). Indeed, NO signalling plays a crucial role in cardiovascular homeostasis and its dysregulation induces a significant increase in oxidative and nitrosative stress, producing anatomical and physiological cardiac alterations that can lead to heart failure. The present review aims to examine the molecular mechanisms involved in the bioavailability of NO and its modulation of downstream pathways. In particular, we focus on the main therapeutic targets and emphasize the recent evidence of preclinical and clinical studies, describing the different emerging therapeutic strategies developed to counteract NO impaired signalling and cardiovascular disease (CVD) development.

Hypoxic erythrocytes mediate cardioprotection through activation of soluble guanylate cyclase and release of cyclic GMP

Red blood cells (RBCs) mediate cardioprotection via nitric oxide-like bioactivity, but the signaling and the identity of any mediator released by the RBCs remains unknown. We investigated whether RBCs exposed to hypoxia release a cardioprotective mediator and explored the nature of this mediator. Perfusion of isolated hearts subjected to ischemia-reperfusion with extracellular supernatant from mouse RBCs exposed to hypoxia resulted in improved postischemic cardiac function and reduced infarct size. Hypoxia increased extracellular export of cyclic guanosine monophosphate (cGMP) from mouse RBCs, and exogenous cGMP mimicked the cardioprotection induced by the supernatant. The protection induced by hypoxic RBCs was dependent on RBC-soluble guanylate cyclase and cGMP transport and was sensitive to phosphodiesterase 5 and activated cardiomyocyte protein kinase G. Oral administration of nitrate to mice to increase nitric oxide bioactivity further enhanced the cardioprotective effect of hypoxic RBCs. In a placebo-controlled clinical trial, a clear cardioprotective, soluble guanylate cyclase-dependent effect was induced by RBCs collected from patients randomized to 5 weeks nitrate-rich diet. It is concluded that RBCs generate and export cGMP as a response to hypoxia, mediating cardioprotection via a paracrine effect. This effect can be further augmented by a simple dietary intervention, suggesting preventive and therapeutic opportunities in ischemic heart disease.

Stimulation of Erythrocyte Soluble Guanylyl Cyclase Induces cGMP Export and Cardioprotection in Type 2 Diabetes

Reduced nitric oxide (NO) bioactivity in red blood cells (RBCs) is critical for augmented myocardial ischemia-reperfusion injury in type 2 diabetes. This study identified the nature of "NO bioactivity" by stimulating the intracellular NO receptor soluble guanylyl cyclase (sGC) in RBCs. sGC stimulation in RBCs from patients with type 2 diabetes increased export of cyclic guanosine monophosphate from RBCs and activated cardiac protein kinase G, thereby attenuating ischemia-reperfusion injury. These results provide novel insight into RBC signaling by identifying cyclic guanosine monophosphate from RBC as a mediator of protection against cardiac ischemia-reperfusion injury induced by sGC stimulation in RBCs.

Plasma-derived extracellular vesicles released after endurance exercise exert cardioprotective activity through the activation of antioxidant pathways

Cardiovascular diseases (CVD) can cause various conditions, including an increase in reactive oxygen species (ROS) levels that can decrease nitric oxide (NO) availability and promote vasoconstriction, leading to arterial hypertension. Physical exercise (PE) has been found to be protective against CVD by helping to maintain redox homeostasis through a decrease in ROS levels, achieved by increased expression of antioxidant enzymes (AOEs) and modulation of heat shock proteins (HSPs). Extracellular vesicles (EVs) circulating in the body are a major source of regulatory signals, including proteins and nucleic acids. Interestingly, the cardioprotective role of EVs released after PE has not been fully described. The aim of this study was to investigate the role of circulating EVs, obtained through Size Exclusion Chromatography (SEC) of plasma samples from healthy young males (age: 26.95 ± 3.07; estimated maximum oxygen consumption rate (VO_2max): 51.22 ± 4.85 (mL/kg/min)) at basal level (Pre_EVs) and immediately after a single bout of endurance exercise (30' treadmill, 70% heart rate (HR) -Post_EVs). Gene ontology (GO) analysis of proteomic data from isolated EVs, revealed enrichment in proteins endowed with catalytic activity in Post_EVs, compare to Pre_EVs, with MAP2K1 being the most significantly upregulated protein. Enzymatic assays on EVs derived from Pre and Post samples showed increment in Glutathione Reductase (GR) and Catalase (CAT) activity in Post_EVs. At functional level, Post_EVs, but not Pre_EVs, enhanced the activity of antioxidant enzymes (AOEs) and reduced oxidative damage accumulation in treated human iPS-derived cardiomyocytes (hCM) at basal level and under stress conditions (Hydrogen Peroxide (H₂O₂) treatment), resulting in a global cardioprotective effect. In conclusion, our data demonstrated, for the first time, that a single 30-min endurance exercise is able to alter the cargo of circulating EVs, resulting in cardioprotective effect through antioxidant activity.

Erythrocytes from patients with ST-elevation myocardial infarction induce cardioprotection through the purinergic P2Y13 receptor and nitric oxide signaling

Red blood cells (RBCs) are suggested to play a role in cardiovascular regulation by exporting nitric oxide (NO) bioactivity and ATP under hypoxia. It remains unknown whether such beneficial effects of RBCs are protective in patients with acute myocardial infarction. We investigated whether RBCs from patients with ST-elevation myocardial infarction (STEMI) protect against myocardial ischemia-reperfusion injury and whether such effect involves NO and purinergic signaling in the RBCs. RBCs from patients with STEMI undergoing primary coronary intervention and healthy controls were administered to isolated rat hearts subjected to global ischemia and reperfusion. Compared to RBCs from healthy controls, RBCs from STEMI patients reduced myocardial infarct size (30 ± 12% RBC healthy vs. 11 ± 5% RBC STEMI patients, P < 0.001), improved recovery of left-ventricular developed pressure and dP/dt and reduced left-ventricular end-diastolic pressure in hearts subjected to ischemia-reperfusion. Inhibition of RBC NO synthase with L-NAME or soluble guanylyl cyclase (sGC) with ODQ, and inhibition of cardiac protein kinase G (PKG) abolished the cardioprotective effect. Furthermore, the non-selective purinergic P2 receptor antagonist PPADS but not the P1 receptor antagonist 8PT attenuated the cardioprotection induced by RBCs from STEMI patients. The P2Y₁₃ receptor was expressed in RBCs and the cardioprotection was abolished by the P2Y₁₃ receptor antagonist MRS2211. By contrast, perfusion with PPADS, L-NAME, or ODQ prior to RBCs administration failed to block the cardioprotection induced by RBCs from STEMI patients. Administration of RBCs from healthy subjects following pre-incubation with an ATP analog reduced infarct size from 20 ± 6 to 7 ± 2% (P < 0.001), and this effect was abolished by ODQ and MRS2211. This study demonstrates a novel function of RBCs in STEMI patients providing protection against myocardial ischemia-reperfusion injury through the P2Y₁₃ receptor and the NO-sGC-PKG pathway.