Sigma-1 Receptor Stimulation with PRE-084 Ameliorates Myocardial Ischemia-Reperfusion Injury in Rats

Sigma-1 receptor modulation fine-tunes KV1.5 channels and impacts pulmonary vascular function

K_V1.5 channels are key players in the regulation of vascular tone and atrial excitability and their impairment is associated with cardiovascular diseases including pulmonary arterial hypertension (PAH) and atrial fibrillation (AF). Unfortunately, pharmacological strategies to improve K_V1.5 channel function are missing. Herein, we aimed to study whether the chaperone sigma-1 receptor (S1R) is able to regulate these channels and represent a new strategy to enhance their function. By using different electrophysiological and molecular techniques in X. laevis oocytes and HEK293 cells, we demonstrate that S1R physically interacts with K_V1.5 channels and regulate their expression and function. S1R induced a bimodal regulation of K_V1.5 channel expression/activity, increasing it at low concentrations and decreasing it at high concentrations. Of note, S1R agonists (PRE084 and SKF10047) increased, whereas the S1R antagonist BD1047 decreased, K_V1.5 expression and activity. Moreover, PRE084 markedly increased K_V1.5 currents in pulmonary artery smooth muscle cells and attenuated vasoconstriction and proliferation in pulmonary arteries. We also show that both K_V1.5 channels and S1R, at mRNA and protein levels, are clearly downregulated in samples from PAH and AF patients. Moreover, the expression of both genes showed a positive correlation. Finally, the ability of PRE084 to increase K_V1.5 function was preserved under sustained hypoxic conditions, as an in vitro PAH model. Our study provides insight into the key role of S1R in modulating the expression and activity of K_V1.5 channels and highlights the potential role of this chaperone as a novel pharmacological target for pathological conditions associated with K_V1.5 channel dysfunction.

Sigma-1 Receptor Signaling: In Search of New Therapeutic Alternatives for Cardiovascular and Renal Diseases

Cardiovascular and renal diseases are among the leading causes of death worldwide, and regardless of current efforts, there is a demanding need for therapeutic alternatives to reduce their progression to advanced stages. The stress caused by diseases leads to the activation of protective mechanisms in the cell, including chaperone proteins. The Sigma-1 receptor (Sig-1R) is a ligand-operated chaperone protein that modulates signal transduction during cellular stress processes. Sig-1R interacts with various ligands and proteins to elicit distinct cellular responses, thus, making it a potential target for pharmacological modulation. Furthermore, Sig-1R ligands activate signaling pathways that promote cardioprotection, ameliorate ischemic injury, and drive myofibroblast activation and fibrosis. The role of Sig-1R in diseases has also made it a point of interest in developing clinical trials for pain, neurodegeneration, ischemic stroke, depression in patients with heart failure, and COVID-19. Sig-1R ligands in preclinical models have significantly beneficial effects associated with improved cardiac function, ventricular remodeling, hypertrophy reduction, and, in the kidney, reduced ischemic damage. These basic discoveries could inform clinical trials for heart failure (HF), myocardial hypertrophy, acute kidney injury (AKI), and chronic kidney disease (CKD). Here, we review Sig-1R signaling pathways and the evidence of Sig-1R modulation in preclinical cardiac and renal injury models to support the potential therapeutic use of Sig-1R agonists and antagonists in these diseases.

Effects of sub-chronic, in vivo administration of sigma-1 receptor ligands on platelet and aortic arachidonate cascade in streptozotocin-induced diabetic rats

BACKGROUND

Diabetes mellitus is a chronic metabolic disorder which induces endothelial dysfunction and platelet activation. Eicosanoids produced from arachidonic acid regulate cellular and vascular functions. Sigma-1 receptors (S1R) are expressed in platelets and endothelial cells and S1R expression is protective in diabetes.

OBJECTIVES

Our aim was to examine the influence of sub-chronic, in vivo administered S1R ligands PRE-084, (S)-L1 (a new compound) and NE-100 on the ex vivo arachidonic acid metabolism of platelets and aorta in streptozotocin-induced diabetic rats.

METHODS

The serum level of the S1R ligands was detected by LC-MS/MS before the ex vivo analysis. Sigma-1 receptor and cyclooxygenase gene expression in platelets were determined by RT-qPCR. The eicosanoid synthesis was examined with a radiolabelled arachidonic acid substrate and ELISA.

RESULTS

One month after the onset of STZ-induced diabetes, in vehicle-treated, diabetic rat platelet TxB2 and aortic 6-k-PGF1α production dropped. Sub-chronic in vivo treatment of STZ-induced diabetes in rats for one week with PRE-084 enhanced vasoconstrictor and platelet aggregator and reduced vasodilator and anti-aggregator cyclooxygenase product formation. (S)-L1 reduced the synthesis of vasodilator and anti-aggregator cyclooxygenase metabolites and promoted the recovery of physiological platelet function in diabetic rats. The S1R antagonist NE-100 produced no significant changes in platelet arachidonic acid metabolism. (S)-L1 decreased the synthesis of vasoconstrictor and platelet aggregator cyclooxygenase metabolites, whereas NE-100 increased the quantity of aortic vasodilator and anti-aggregator cyclooxygenase products and promoted the recovery of diabetic endothelial dysfunction in the aorta. The novel S1R ligand, (S)-L1 had similar effects on eicosanoid synthesis in platelets as the agonist PRE-084 and in aortas as the antagonist NE-100.

CONCLUSIONS

S1R ligands regulate cellular functions and local blood circulation by influencing arachidonic acid metabolism. In diabetes mellitus, the cell-specific effects of S1R ligands have a compensatory role and aid in restoring physiological balance between the platelet and vessel.

Effects of sub-chronic, in vivo administration of sigma non-opioid intracellular receptor 1 ligands on platelet and aortic arachidonate cascade in rats

Platelets regulate cell-cell interactions and local circulation through eicosanoids from arachidonic acid. Sigma non-opioid intracellular receptor 1 (sigma-1 receptor) expressed in platelets and endothelial cells can regulate intracellular signalization. Our aim was to examine the influence of sub-chronic, in vivo-administered sigma-1 receptor ligands 2-morpholin-4-ylethyl 1-phenylcyclohexane-1-carboxylate (PRE-084); N-benzyl-2-[(1S)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-1-yl]ethan-1-amine; dihydrochloride, a new compound ((S)-L1); and N-[2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethyl]-N-propylpropan-1-amine (NE-100) on the ex vivo arachidonic acid metabolism of the platelets and aorta of male rats. The serum level of sigma-1 receptor ligands was determined by liquid chromatography-mass spectrometry. Sigma-1 receptor and cyclooxygenase gene expression in the platelets were determined by a reverse transcription-coupled quantitative polymerase chain reaction. The eicosanoid synthesis was examined using a radiolabeled arachidonic acid substrate and enzyme-linked immunosorbent assay. We confirmed the absorption of sigma-1 receptor ligands and confirmed that the ligands were not present during the ex vivo studies, so their acute effect could be excluded. We detected no changes in either sigma-1 receptor or cyclooxygenase mRNA levels in the platelets. Nevertheless, (S)-L1 and NE-100 increased the quantity of cyclooxygenases there. Both platelet and aortic eicosanoid synthesis was modified by the ligands, although in different ways. The effect of the new sigma-1 receptor ligand, (S)-L1, was similar to that of PRE-084 in most of the parameters studied but was found to be more potent. Our results suggest that sigma-1 receptor ligands may act at multiple points in arachidonic acid metabolism and play an important role in the control of the microcirculation by modulating the eicosanoid synthesis of the platelets and vessels.

Chronic Sigma 1 receptor activation alleviates right ventricular dysfunction secondary to pulmonary arterial hypertension

Sigma 1 receptor (S1R) has shown a preferable protective effect on left ventricular function, but whether it protects right ventricular (RV) function is still elusive.This study aimed to determine the effects of S1R on RV dysfunction secondary to pulmonary arterial hypertension.Sixty wild-type male Sprague–Dawley rats were randomly divided into the control group, the fluvoxamine group, the pulmonary arterial hypertension group and the pulmonary arterial hypertension combined with fluvoxamine group. Monocrotaline (60 mg/kg) was administered to induce pulmonary arterial hypertension, and fluvoxamine was given for 21 consecutive days to activate S1R after one week of monocrotaline administration. Echocardiographic, serologic, and histologic parameters, qRT-PCR, and western blotting were conducted after 4 weeks of monocrotaline administration.The expression of S1R was decreased in the right ventricle in pulmonary arterial hypertension. TAPSE, and the FAC of the right ventricle were significantly decreased, and RV EDP and the plasma concentration of N-terminal pro-B-type natriuretic peptide was increased in the pulmonary arterial hypertension group, but fluvoxamine partly restored those abnormalities (all P < 0.05). Moreover, pulmonary arteriole remodeling, and fibrosis and hypertrophy in the RV were shown in the pulmonary arterial hypertension group; interestingly, fluvoxamine recovered RV structural remodeling (all P < 0.05) but neither alleviated pulmonary arteriole remodeling nor reduced pulmonary artery pressure. Furthermore, S1R activation protects RV function by upgrading the NRF 2/HO 1-mediated antioxidant stress pathway. In conclusion, chronic S1R activation ameliorates structural remodeling and RV dysfunction secondary to pulmonary arterial hypertension without altering pulmonary artery pressure.

Oxycodone protects cardiac microvascular endothelial cells against ischemia/reperfusion injury by binding to Sigma-1 Receptor

Endothelial dysfunction is an important mechanism involved in myocardial ischemia-reperfusion (I/R) injury. We aimed to explore the effects of Oxycodone on myocardial I/R injury in vivo and in vitro to reveal its mechanisms related to Sigma-1 Receptor (SIGMAR1). A rat model of I/R-induced myocardial injury was developed. The ischemic area and myocardial histopathological changes after oxycodone addition were evaluated by TTC staining and H&E staining. LDH, CK-MB and cTnI levels were used to assess myocardial function. Then, the endothelial integrity was reflected by the expressions of ZO-1, Claudin-1 and Occludin. Afterward, ELISA, RT-qPCR, western blot and immunofluorescence assays were adopted for the detection of inflammation-related genes. SIGMAR1 expression in myocardial tissues induced by I/R and cardiac microvascular endothelial cells (CMECs) under hypoxic/reoxygenation (H/R) was determined using RT-qPCR and western blotting. Subsequently, after SIGMAR1 silencing or BD1047 addition (a SIGMAR1 antagonist), cell apoptosis and endothelial integrity were analyzed in the presence of Oxycodone in H/R-stimulated CMECs. Results indicated that Oxycodone decreased the ischemic area and improved myocardial function in myocardial I/R injury rat. Oxycodone improved myocardial histopathological injury and elevated endothelial integrity, evidenced by upregulated ZO-1, Claudin-1 and Occludin expressions. Moreover, inflammatory response was alleviated after Oxycodone administration. Molecular docking suggested that SIGMAR1 could directly bind to Oxycodone. Oxycodone elevated SIGMAR1 expression and SIGMAR1 deletion or BD1047 addition attenuated the impacts of Oxycodone on apoptosis and endothelial integrity of CMECs induced by H/R. Collectively, Oxycodone alleviates myocardial I/R injury in vivo and in vitro by binding to SIGMAR1.

Emerging Benefits: Pathophysiological Functions and Target Drugs of the Sigma-1 Receptor in Neurodegenerative Diseases

The sigma-1 receptor (Sig-1R) is encoded by the SIGMAR1 gene and is a nonopioid transmembrane receptor located in the mitochondrial-associated endoplasmic reticulum membrane (MAM). It helps to locate endoplasmic reticulum calcium channels, regulates calcium homeostasis, and acts as a molecular chaperone to control cell fate and participate in signal transduction. It plays an important role in protecting neurons through a variety of signaling pathways and participates in the regulation of cognition and motor behavior closely related to neurodegenerative diseases. Based on its neuroprotective effects, Sig-1R has now become a breakthrough target for alleviating Alzheimer's disease and other neurodegenerative diseases. This article reviews the most cutting-edge research on the function of Sig-1R under normal or pathologic conditions and target drugs of the sigma-1 receptor in neurodegenerative diseases.

S1R agonist modulates rat platelet eicosanoid synthesis and aggregation

Sigma-1 receptor (S1R) is detected in different cell types and can regulate intracellular signaling pathways. S1R plays a role in the pathomechanism of diseases and the regulation of neurotransmitters. Fluvoxamine can bind to S1R and reduce the serotonin uptake of neurons and platelets. We therefore hypothesized that platelets express S1R, which can modify platelet function. The expression of the SIGMAR1 gene in rat platelets was examined with a reverse transcription polymerase chain reaction and a quantitative polymerase chain reaction. The receptor was also visualized by immunostaining and confocal laser scanning microscopy. The effect of S1R agonist PRE-084 on the eicosanoid synthesis of isolated rat platelets and ADP- and AA-induced platelet aggregation was examined. S1R was detected in rat platelets both at gene and protein levels. Pretreatment with PRE-084 of resting platelets induced elevation of eicosanoid synthesis. The rate of elevation in thromboxane B₂ and prostaglandin D₂ synthesis was similar, but the production of prostaglandin E₂ was higher. The concentration-response curve showed a sigmoidal form. The most effective concentration of the agonist was 2 µM. PRE-084 increased the quantity of cyclooxygenase-1 as detected by ELISA. PRE-084 also elevated the ADP- and AA-induced platelet aggregation. S1R of platelets might regulate physiological or pathological functions.

Sigmar1's Molecular, Cellular, and Biological Functions in Regulating Cellular Pathophysiology

The Sigma 1 receptor (Sigmar1) is a ubiquitously expressed multifunctional inter-organelle signaling chaperone protein playing a diverse role in cellular survival. Recessive mutation in Sigmar1 have been identified as a causative gene for neuronal and neuromuscular disorder. Since the discovery over 40 years ago, Sigmar1 has been shown to contribute to numerous cellular functions, including ion channel regulation, protein quality control, endoplasmic reticulum-mitochondrial communication, lipid metabolism, mitochondrial function, autophagy activation, and involved in cellular survival. Alterations in Sigmar1’s subcellular localization, expression, and signaling has been implicated in the progression of a wide range of diseases, such as neurodegenerative diseases, ischemic brain injury, cardiovascular diseases, diabetic retinopathy, cancer, and drug addiction. The goal of this review is to summarize the current knowledge of Sigmar1 biology focusing the recent discoveries on Sigmar1’s molecular, cellular, pathophysiological, and biological functions.

Chronic sigma-1 receptor activation ameliorates ventricular remodeling and decreases susceptibility to ventricular arrhythmias after myocardial infarction in rats

The present study aimed to assess the effect of sigma-1 receptor (S1R) stimulation on ventricular remodeling and susceptibility to ventricular arrhythmias (VAs) after myocardial infarction (MI) in rats. Wild-type male rats were placed into one of the following four treatment groups. For four weeks, animals in the Sham group and MI group received intraperitoneal (i.p.) injections of 0.9% saline (1 ml/kg/day); those in the MI + F group received fluvoxamine (FLV) (0.3 mg/kg/day); and those in the MI + F + BD group received FLV plus BD1047 (0.3 mg/kg/day). After that, the ventricular electrophysiological parameters were measured via the langendorff system. Ventricular fibrosis quantification was determined with Masson staining. Cardiac function was evaluated by echocardiography. The protein levels of S1R, connexin (Cx)43, Cav1.2, Kv4.2, Kv4.3, tyrosine hydroxylase (TH), nerve growth factor (NGF), growth-associated protein 43 (GAP43) were detected by Western blot assays. Our results indicated that fluvoxamine significantly prolonged the ventricular effective refractory period (ERP), shortened action potential duration (APD), reduced susceptibility to VAs after MI. Masson staining showed a decrease in ventricular fibrosis in the MI + F group. Furthermore, the contents of Cx43, S1R, Cav1.2, Kv4.2, Kv4.3 were increased in the MI + F group compared with the MI group (all P < 0.05). The contents of TH, NGF, GAP43 were reduced in the MI + F group compared with the MI group. (all P < 0.05). However, BD1047 reduces all of these effects of FLV. The results suggest that S1R stimulation reduces susceptibility to VAs and improves cardiac function by improving myocardial fibrosis, lightning sympathetic remodeling, electrical remodeling, gap junction remodeling and upregulating S1R content.

PRE-084 as a tool to uncover potential therapeutic applications for selective sigma-1 receptor activation

The discovery of a highly selective putative sigma-1 (σ1) receptor agonist, PRE-084, has revealed the numerous potential uses of this receptor subtype as a therapeutic target. While much work has been devoted to determining the role of σ1 receptors in normal and pathophysiological states in the nervous system, recent work suggests that σ1 receptors may be important for modulating functions of other tissues. These discoveries have provided novel insights into σ1 receptor structure, function, and importance in multiple intracellular signaling mechanisms. These discoveries were made possible by σ1 receptor-selective agonists such as PRE-084. The chemical properties and pharmacological actions of PRE-084 will be reviewed here, along with the expanding list of potential therapeutic applications for selective activation of σ1 receptors.

Noscapine protects the H9c2 cardiomyocytes of rats against oxygen-glucose deprivation/reperfusion injury

Noscapine is an antitumor alkaloid derived from Papaver somniferum plants. Our previous study has demonstrated that exposure of noscapine on primary murine fetal cortical neurons exposed to oxygen-glucose deprivation/reperfusion (OGD/R) has neuroprotective effects. In current study, the effects of noscapine on cardiomyocytes (H9c2 cells) damage caused by 120 minutes (min) of OGD/R were evaluated and we determined whether the addition of BD1047, sigma-one receptor antagonist, prevents the protective effects of noscapine in H9c2 cells through the production of nitric oxide (NO) and apoptosis. To initiate OGD, H9c2 cells was transferred to glucose-free DMEM, and placed in a humidified incubation chamber. Cell viability was assessed with noscapine (1-5 μM) in the presence or absence of BD1047, 24 hours (h) after OGD/R. Cell viability, NO production and apoptosis ratio were evaluated by the MTT assay, the Griess method and the quantitative real-time PCR. Noscapine considerably improved the survival of H9c2 cells compared to OGD/R. Also, noscapine was extremely capable of reducing the concentrations of NO and Bax/Bcl-2 ratio expression. While the BD1047 administration alone diminished cell viability and increased the Bax/Bcl-2 ratio and NO levels. The addition of noscapine in the presence of BD1047 did not increase the cell viability relative to noscapine alone. Noscapine exerted cardioprotective effects exposed to OGD/R-induced injury in H9c2 cells, at least partly via attenuation of NO production and Bax/Bcl-2 ratio, which indicates that the sigma-one receptor activation is involved in the protection by noscapine of H9c2 cells injured by OGD/R.

Is the sigma-1 receptor a potential pharmacological target for cardiac pathologies? A systematic review

Sigma-1 receptors are ligand-regulated chaperone proteins, involved in several cellular mechanisms. The aim of this systematic review was to examine the effects that the sigma-1 receptor has on the cardiovascular system. The interaction targets and proposed mechanisms of action of sigma-1 receptors were explored, with the aim of determining if the sigma-1 receptor is a potential pharmacological target for cardiac pathologies. This systematic review was conducted according to the PRISMA guidelines and these were used to critically appraise eligible studies. Pubmed and Scopus were systematically searched for articles investigating sigma-1 receptors in the cardiovascular system. Papers identified by the search terms were then subject to analysis against pre-determined inclusion criteria. 23 manuscripts met the inclusion criteria and were included in this review. The experimental platforms, experimental techniques utilised and the results of the studies were summarised. The sigma-1 receptor is found to be implicated in cardioprotection, via various mechanisms including stimulating the Akt-eNOS pathway, and reduction of Ca2 + leakage into the cytosol via modulating certain calcium channels. Sigma-1 receptors are also found to modulate other cardiac ion channels including different subtypes of potassium and sodium channels and have been shown to modulate intracardiac neuron excitability. The sigma-1 receptor is a potential therapeutic target for treatment of cardiac pathologies, particularly cardiac hypertrophy. We therefore suggest investigating the cardioprotective mechanisms of sigma-1 receptor function, alongside proposed potential ligands that can stimulate these functions.