Crucial interactions between selective serotonin uptake inhibitors and sigma-1 receptor in heart failure

Sigmar1 ablation leads to lung pathological changes associated with pulmonary fibrosis, inflammation, and altered surfactant proteins levels

Sigma1 receptor protein (Sigmar1) is a small, multifunctional molecular chaperone protein ubiquitously expressed in almost all body tissues. This protein has previously shown its cardioprotective roles in rodent models of cardiac hypertrophy, heart failure, and ischemia-reperfusion injury. Extensive literature also suggested its protective functions in several central nervous system disorders. Sigmar1's molecular functions in the pulmonary system remained unknown. Therefore, we aimed to determine the expression of Sigmar1 in the lungs. We also examined whether Sigmar1 ablation results in histological, ultrastructural, and biochemical changes associated with lung pathology over aging in mice. In the current study, we first confirmed the presence of Sigmar1 protein in human and mouse lungs using immunohistochemistry and immunostaining. We used the Sigmar1 global knockout mouse (Sigmar1-/-) to determine the pathophysiological role of Sigmar1 in lungs over aging. The histological staining of lung sections showed altered alveolar structures, higher immune cells infiltration, and upregulation of inflammatory markers (such as pNFκB) in Sigmar1-/- mice compared to wildtype (Wt) littermate control mice (Wt). This indicates higher pulmonary inflammation resulting from Sigmar1 deficiency in mice, which was associated with increased pulmonary fibrosis. The protein levels of some fibrotic markers, fibronectin, and pSMAD2 Ser 245/250/255 and Ser 465/467, were also elevated in mice lungs in the absence of Sigmar1 compared to Wt. The ultrastructural analysis of lungs in Wt mice showed numerous multilamellar bodies of different sizes with densely packed lipid lamellae and mitochondria with a dark matrix and dense cristae. In contrast, the Sigmar1-/- mice lung tissues showed altered multilamellar body structures in alveolar epithelial type-II pneumocytes with partial loss of lipid lamellae structures in the lamellar bodies. This was further associated with higher protein levels of all four surfactant proteins, SFTP-A, SFTP-B, SFTP-C, and SFTP-D, in the Sigmar1-/- mice lungs. This is the first study showing Sigmar1's expression pattern in human and mouse lungs and its association with lung pathophysiology. Our findings suggest that Sigmar1 deficiency leads to increased pulmonary inflammation, higher pulmonary fibrosis, alterations of the multilamellar body stuructures, and elevated levels of lung surfactant proteins.

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.

Sigma-1 receptor: A potential target for the development of antidepressants

Though a great many of studies on the development of antidepressants for the therapy of major depression disorder (MDD) and the development of antidepressants have been carried out, there still lacks an efficient approach in clinical practice. The involvement of Sigma-1 receptor in the pathological process of MDD has been verified. In this review, recent research focusing on the role of Sigma-1 receptor in the etiology of MDD were summarized. Preclinical studies and clinical trials have found that stress induce the variation of Sigma-1 receptor in the blood, brain and heart. Dysfunction and absence of Sigma-1 receptor result in depressive-like behaviors in rodent animals. Agonists of Sigma-1 receptor show not only antidepressant-like activities but also therapeutical effects in complications of depression. The mechanisms underlying antidepressant-like effects of Sigma-1 receptor may include suppressing neuroinflammation, regulating neurotransmitters, ameliorating brain-derived neurotrophic factor and N-Methyl-D-Aspartate receptor, and alleviating the endoplasmic reticulum stress and mitochondria damage during stress. Therefore, Sigma-1 receptor represents a potential target for antidepressants development.

Activation of the sigma-1 receptor exerts cardioprotection in a rodent model of chronic heart failure by stimulation of angiogenesis

Background

Angiogenesis plays a critical role on post-infarction heart failure (PIHF), the presence of which facilitates additional blood supply to maintain the survival of residual cardiomyocytes. The sigma-1 receptor (S1R) has been substantiated to stimulate angiogenesis, with the effect on a model of PIHF remaining unknown.

Aims

This study aims to investigate the effects of S1R on PIHF and the underlying mechanisms involved.

Methods

Rats were implemented left anterior descending artery ligation followed by rearing for 6 weeks to induce a phenotype of heart failure. Daily intraperitoneal injection of S1R agonist or antagonist for 5 weeks was applied from 2nd week after surgery. The effects exerted by S1R were detected by echocardiography, hemodynamic testing, western blot, Sirius red dyeing, ELISA, immunohistochemistry and fluorescence. We also cultured HUVECs to verify the mechanisms in vitro.

Results

Stimulation of S1R significantly ameliorated the cardiac function resulted from PIHF, in addition to the observation of reduced fibrosis in the peri-infarct region and the apoptosis of residual cardiomyocytes, which were associated with augmentation of microvascular density in peri-infarct region through activation of the JAK2/STAT3 pathway. We also indicated that suppression of JAK2/STAT3 pathway by specific inhibitor in vitro reversed the pro-angiogenic effects of S1R on HUVECs, which further confirmed that angiogenesis, responsible for PIHF amelioration, by S1R stimulation was in a JAK2/STAT3 pathway-dependent manner.

Conclusion

S1R stimulation improved PIHF-induced cardiac dysfunction and ventricular remodeling through promoting angiogenesis by activating the JAK2/STAT3 pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00517-1.

Cardiovascular disease associated with methamphetamine use: a review

Methamphetamine abuse is a global epidemic associated with a wide-ranging array of adverse effects on the cardiovascular system including dilated cardiomyopathy, malignant and benign arrhythmias, coronary vasospasm, and atherosclerotic coronary artery disease. While the acute behavioral manifestations of amphetamine abuse are the most easily clinically identified, cardiovascular toxicity is common in this patient population and should be considered in this setting due to its high morbidity and mortality. The specific mechanisms for amphetamine cardiotoxicity have not been fully established, but new research implicates activation of several cellular targets including Sigma-1 receptors and trace amine-associated receptor 1 (TAAR1) leading to a myriad of negative downstream effects including increased reactive oxygenating species (ROS), mitochondrial dysfunction, and modulations of intracellular calcium. Additional pathologic effects are mediated by increased circulating catecholamines, which when chronically activated have well-established adverse effects on the cardiovascular system. In this article, we present a case report followed by a current review of the epidemiology, pathophysiology, diagnosis, and treatment modalities of amphetamine-induced cardiovascular disease.

Methamphetamine-Associated Cardiomyopathy: Addressing the Clinical Challenges

The growth in methamphetamine usage worldwide continues to present increasing societal and health care challenges. With the escalation of its usage in a variety of social demographics, the entity of methamphetamine-associated cardiomyopathy (MA-CMP) has emerged. This entity is increasingly responsible for an important proportion of heart failure burden in both admissions to hospital and in those individuals requiring chronic heart failure care. MA-CMP poses some unique challenges including its recognition, particularly in younger patients presenting with new-onset heart failure, its severity at presentation and complications as well as management options. The challenging nature of methamphetamine addiction and the necessity to achieve abstinence is a fundamental aspect of management of this condition. As methamphetamine use continues at high levels in Australia, the burden of MA-CMP will inevitably increase and, therefore, all clinicians responsible for heart failure management require an awareness of this disease entity and the specific clinical challenges of its care.

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.

Involvement of Chaperone Sigma1R in the Anxiolytic Effect of Fabomotizole

Sigma-1 receptor (chaperone Sigma1R) is an intracellular protein with chaperone functions, which is expressed in various organs, including the brain. Sigma1R participates in the regulation of physiological mechanisms of anxiety (Su, T. P. et al., 2016) and reactions to emotional stress (Hayashi, T., 2015). In 2006, fabomotizole (ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole dihydrochloride) was registered in Russia as an anxiolytic (Seredenin S. and Voronin M., 2009). The molecular targets of fabomotizole are Sigma1R, NRH: quinone reductase 2 (NQO2), and monoamine oxidase A (MAO-A) (Seredenin S. and Voronin M., 2009). The current study aimed to clarify the dependence of fabomotizole anxiolytic action on its interaction with Sigma1R and perform a docking analysis of fabomotizole interaction with Sigma1R. An elevated plus maze (EPM) test revealed that the anxiolytic-like effect of fabomotizole (2.5 mg/kg i.p.) administered to male BALB/c mice 30 min prior EPM exposition was blocked by Sigma1R antagonists BD-1047 (1.0 mg/kg i.p.) and NE-100 (1.0 mg/kg i.p.) pretreatment. Results of initial in silico study showed that fabomotizole locates in the active center of Sigma1R, reproducing the interactions with the site's amino acids common for established Sigma1R ligands, with the ΔGbind value closer to that of agonist (+)-pentazocine in the 6DK1 binding site.

Mitochondria-associated membrane-modulated Ca2+ transfer: A potential treatment target in cardiac ischemia reperfusion injury and heart failure

Effective Ca²⁺ dependent mitochondrial energy supply is imperative for proper cardiac contractile activity, while disruption of Ca²⁺ homeostasis participates in the pathogenesis of multiple human diseases. This phenomenon is particularly prominent in cardiac ischemia and reperfusion (I/R) and heart failure, both of which require strict clinical intervention. The interface between endoplasmic reticula (ER) and mitochondria, designated the mitochondria-associated membrane (MAM), is now regarded as a crucial mediator of Ca²⁺ transportation. Thus, interventions targeting this physical and functional coupling between mitochondria and the ER are highly desirable. Increasing evidence supports the notion that restoration, and maintenance, of the physiological contact between these two organelles can improve mitochondrial function, while inhibiting cell death, thereby sufficiently ameliorating I/R injury and heart failure development. A better understanding regarding the underlying mechanism of MAM-mediated transport will pave the way for identification of novel treatment approaches for heart disease. Therefore, in this review, we summarize the crucial functions and potential mechanisms of MAMs in the pathogenesis of I/R and heart failure.

Methamphetamine induces cardiomyopathy by Sigmar1 inhibition-dependent impairment of mitochondrial dynamics and function

Methamphetamine-associated cardiomyopathy is the leading cause of death linked with illicit drug use. Here we show that Sigmar1 is a therapeutic target for methamphetamine-associated cardiomyopathy and defined the molecular mechanisms using autopsy samples of human hearts, and a mouse model of "binge and crash" methamphetamine administration. Sigmar1 expression is significantly decreased in the hearts of human methamphetamine users and those of "binge and crash" methamphetamine-treated mice. The hearts of methamphetamine users also show signs of cardiomyopathy, including cellular injury, fibrosis, and enlargement of the heart. In addition, mice expose to "binge and crash" methamphetamine develop cardiac hypertrophy, fibrotic remodeling, and mitochondrial dysfunction leading to contractile dysfunction. Methamphetamine treatment inhibits Sigmar1, resulting in inactivation of the cAMP response element-binding protein (CREB), decreased expression of mitochondrial fission 1 protein (FIS1), and ultimately alteration of mitochondrial dynamics and function. Therefore, Sigmar1 is a viable therapeutic agent for protection against methamphetamine-associated cardiomyopathy.

Chaperone Sigma1R and Antidepressant Effect

This review analyzes the current scientific literature on the role of the Sigma1R chaperone in the pathogenesis of depressive disorders and pharmacodynamics of antidepressants. As a result of ligand activation, Sigma1R is capable of intracellular translocation from the endoplasmic reticulum (ER) into the region of nuclear and cellular membranes, where it interacts with resident proteins. This unique property of Sigma1R provides regulation of various receptors, ion channels, enzymes, and transcriptional factors. The current review demonstrates the contribution of the Sigma1R chaperone to the regulation of molecular mechanisms involved in the antidepressant effect.

ER membranes associated with mitochondria: Possible therapeutic targets in heart-associated diseases

Cardiovascular system cell biology is tightly regulated and mitochondria play a relevant role in maintaining heart function. In recent decades, associations between such organelles and the sarco/endoplasmic reticulum (SR) have been raised great interest. Formally identified as mitochondria-associated SR membranes (MAMs), these structures regulate different cellular functions, including calcium management, lipid metabolism, autophagy, oxidative stress, and management of unfolded proteins. In this review, we highlight MAMs' alterations mainly in cardiomyocytes, linked with cardiovascular diseases, such as cardiac ischemia-reperfusion, heart failure, and dilated cardiomyopathy. We also describe proteins that are part of the MAMs' machinery, as the FUN14 domain containing 1 (FUNDC1), the sigma 1 receptor (Sig-1R) and others, which might be new molecular targets to preserve the function and structure of the heart in such diseases. Understanding the machinery of MAMs and its function demands our attention, as such knowledge might contribute to strengthen the role of these relative novel structures in heart diseases.

The hidden role of the Sigma1 receptor in muscle cells

This review describes the very specific role of Sigma1 receptor in different types of muscle cells. Sigma1 receptor is a transmembrane protein residing in such structures like MAM. It has chaperoning activity supporting function of many proteins, particularly ion channels, including Ca2+ channels. This latter function is of particular meaning for muscle cells, due to their calcium-based/regulated metabolism. Here we discuss new reports pointing to participation of Sigma1 receptor in muscle specific processes like contraction, EC-coupling, calcium currents and in diseases like left ventricular hypertrophy, transverse aortic stenosis and hypertension-induced heart dysfunction.

Examination of Cardioprotective Effects of Fabomotizole Hydrochloride in Translational Rat Model of Chronic Heart Failure

A translational rat model of chronic heart failure was employed to examine the cardioprotective effect of fabomotizole hydrochloride. Fabomotizole therapy for 28 days (15 mg/kg/day intraperitoneally) restored inotropic function of the left ventricle and increased ejection fraction from 54±3 to 65±3% (p=0.001). The inotropic function returned to normal against the background of significantly reduced myocardial expression of angiotensin (p=0.01) and glucocorticoid (p=0.03) receptors and significant increased expression of sigma-1 receptors (p=0.04). Inhibition of abnormal expression of angiotensin and glucocorticoid receptors responsible for activation of the pathological cascades underlying the postinfarction remodeling of the left ventricle as well as activation of the expression of cytoprotective sigma-1 receptors are viewed as the key features of the cardioprotective action of fabomotizole hydrochloride.

Cardiac sigma receptors - an update

More than four decades passed since sigma receptors were first mentioned. Since then, existence of at least two receptor subtypes and their tissue distributions have been proposed. Nowadays, it is clear, that sigma receptors are unique ubiquitous proteins with pluripotent function, which can interact with so many different classes of proteins. As the endoplasmic resident proteins, they work as molecular chaperones - accompany various proteins during their folding, ensure trafficking of the maturated proteins between cellular organelles and regulate their functions. In the heart, sigma receptor type 1 is more dominant. Cardiac sigma 1 receptors regulate response to endoplasmic reticulum stress, modulates calcium signaling in cardiomyocyte and can affect function of voltage-gated ion channels. They contributed in pathophysiology of cardiac hypertrophy, heart failure and many other cardiovascular disorders. Therefore, sigma receptors are potential novel targets for specific treatment of cardiovascular diseases.

Spinal Sigma-1 Receptor-mediated Dephosphorylation of Astrocytic Aromatase Plays a Key Role in Formalin-induced Inflammatory Nociception

Aromatase is a key enzyme responsible for the biosynthesis of estrogen from testosterone. Although recent evidence indicates that spinal cord aromatase participates in nociceptive processing, the mechanisms underlying its regulation and its involvement in nociception remain unclear. The present study focuses on the potential role of astrocyte aromatase in formalin-induced acute pain and begins to uncover one mechanism by which spinal aromatase activation is controlled. Following intraplantar formalin injection, nociceptive responses were quantified and immunohistochemistry/co-immunoprecipitation assays were used to investigate the changes in spinal Fos expression and the phospho-serine levels of spinal aromatase. Intrathecal (i.t.) injection of letrozole (an aromatase inhibitor) mitigated both the late phase formalin-induced nociceptive responses and formalin-induced spinal Fos expression. Furthermore, formalin-injected mice showed significantly reduced phospho-serine levels of aromatase, which is associated with the rapid activation of this enzyme. However, sigma-1 receptor inhibition with i.t. BD1047 blocked the dephosphorylation of aromatase and potentiated the pharmacological effect of letrozole on formalin-induced nociceptive responses. In addition, i.t. administration of a sub-effective dose of BD1047 potentiated the pharmacological effect of cyclosporin A (a calcineurin inhibitor) on both the formalin-induced reduction in phospho-serine levels of aromatase and nociceptive behavior. These results suggest that dephosphorylation is an important regulatory mechanism involved in the rapid activation of aromatase and that spinal sigma-1 receptors mediate this dephosphorylation of aromatase through an intrinsic calcineurin pathway.

Corticosteroids Mediate Heart Failure-Induced Depression through Reduced σ1-Receptor Expression

Cardiovascular diseases are risk factors for depression in humans. We recently proposed that σ1 receptor (σ1R) stimulation rescued cardiac hypertrophy and heart failure induced by transverse aortic constriction (TAC) in mice. Importantly, σ1R stimulation reportedly ameliorates depression-like behaviors in rodents. Thus, we hypothesized that impaired σ1R activity in brain triggers depression-like behaviors in animals with cardiovascular disease. Indeed, here we found that cardiac hypertrophy and heart failure induced by TAC were associated with depression-like behaviors concomitant with downregulation of σ1R expression in brain 6 weeks after surgery. σ1R levels significantly decreased in astrocytes in both the hippocampal CA1 region and dentate gyrus. Oral administration of the specific σ1R agonist SA4503 (0.3-1.0mg/kg) significantly improved TAC-induced depression-like behaviors concomitant with rescued astrocytic σ1R expression in CA1 and the dentate gyrus. Plasma corticosterone levels significantly increased 6 weeks after TAC, and chronic treatment of mice with corticosterone for 3 weeks elicited depression-like behaviors concomitant with reduced astrocytic σ1R expression in hippocampus. Furthermore, the glucocorticoid receptor antagonist mifepristone antagonized depressive-like behaviors and ameliorated decreased hippocampal σ1R expression in TAC mice. We conclude that elevated corticosterone levels trigger hippocampal σ1R downregulation and that σ1R stimulation with SA4503 is an attractive therapy to improve not only cardiac dysfunction but depression-like behaviors associated with heart failure.

Haloperidol aggravates transverse aortic constriction-induced heart failure via mitochondrial dysfunction

Haloperidol is an antipsychotic drug that inhibits the dopamine D2 receptor among others. Haloperidol also binds the sigma-1 receptor (σ1R) and inhibits it irreversibly. A serious outcome of haloperidol treatment of schizophrenia patients is death due to sudden cardiac failure. Although the cause remains unclear, we hypothesized that these effects were mediated by chronic haloperidol inhibition of cardiac σ1R. To test this, we treated neonatal rat cardiomyocytes with haloperidol, exposed them to angiotensin II and assessed hypertrophy, σ1R expression, mitochondrial Ca(2+) transport and ATP levels. In this context, haloperidol treatment altered mitochondrial Ca(2+) transport resulting in decreased ATP content by inactivating cardiac σ1R and/or reducing its expression. We also performed transverse aortic constriction (TAC) and then treated mice with haloperidol. After two weeks, haloperidol-treated mice showed enhanced heart failure marked by deteriorated cardiac function, reduced ATP production and increasing mortality relative to TAC only mice. ATP supplementation via sodium pyruvate rescued phenotypes seen in haloperidol-treated TAC mice. We conclude that σ1R inactivation or downregulation in response to haloperidol treatment impairs mitochondrial Ca(2+) mobilization, depleting ATP depletion from cardiomyocytes. These findings suggest a novel approach to mitigate haloperidol-related adverse effects in schizophrenia patients by ATP supplementation.

Potential Molecular Mechanisms on the Role of the Sigma-1 Receptor in the Action of Cocaine and Methamphetamine

The sigma-1 receptor (Sig-1R) is an endoplasmic reticulum membrane protein that involves a wide range of physiological functions. The Sig-1R has been shown to bind psychostimulants including cocaine and methamphetamine (METH) and thus has been implicated in the actions of those psychostimulants. For example, it has been demonstrated that the Sig-1R antagonists mitigate certain behavioral and cellular effects of psychostimulants including hyperactivity and neurotoxicity. Thus, the Sig-1R has become a potential therapeutic target of medication development against drug abuse that differs from traditional monoamine-related strategies. In this review, we will focus on the molecular mechanisms of the Sig-1R and discuss in such a manner with a hope to further understand or unveil unexplored relations between the Sig-1R and the actions of cocaine and METH, particularly in the context of cellular biological relevance.

Sigma receptors [σRs]: biology in normal and diseased states

This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ₁R) and sigma receptor two (σ₂R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ₁Rs are intracellular receptors acting as chaperone proteins that modulate Ca²⁺ signaling through the IP₃ receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ₁R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K⁺ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ₁R modulation of Ca²⁺ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ₁Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.

Sigma-1 receptors and animal studies centered on pain and analgesia

INTRODUCTION

Neuropathic pain is difficult to relieve with standard analgesics and tends to be resistant to opioid therapy. Sigma-1 receptors activated during neuropathic injury may sustain pain. Neuropathic injury activates sigma-1 receptors, which results in activation of various kinases, modulates the activity of multiple ion channels, ligand activated ion channels and voltage-gated ion channels; alters monoamine neurotransmission and dampens opioid receptors G-protein activation. Activation of sigma-1 receptors tonically inhibits opioid receptor G-protein activation and thus dampens analgesic responses. Therefore, sigma-1 receptor antagonists are potential analgesics for neuropathic and adjuvants to opioid therapy.

AREAS COVERED

This article reviews the importance of sigma-1 receptors as pain generators in multiple animal models in order to illustrate both the importance of these unique receptors in pathologic pain and the potential benefits to sigma-1 receptor antagonists as analgesics.

EXPERT OPINION

Sigma-1 receptor antagonists have a great potential as analgesics for acute neuropathic injury (herpes zoster, acute postoperative pain and chemotherapy induced neuropathy) and may, as an additional benefit, prevent the development of chronic neuropathic pain. Antagonists are potentially effective as adjuvants to opioid therapy when used early to prevent analgesic tolerance. Drug development is complicated by the complexity of sigma-1 receptor pharmacodynamics and its multiple targets, the lack of a specific sigma-1 receptor antagonist, and potential side effects due to on-target toxicities (cognitive impairment, depression).

Selective sigma-1 receptor antagonists for the treatment of pain

The sigma-1 receptor (σ1R) is located in areas of the CNS key for pain control and belongs to a unique target class with chaperoning functions over different molecular targets involved in transmission and amplification of nociceptive messages. Preclinical evidence supports a role for σ1R antagonists in the treatment of pain states where hypersensitivity develops as hyperalgesia and allodynia, two common symptoms encountered in neuropathic and other chronic pain conditions. Additionally, σ1R antagonists increase opioid analgesia without increasing opioid-related unwanted effects, which point to their potential use as opioid adjuvant therapy. This review summarizes the structure and function of the σ1R as well as the medicinal chemistry and pharmacological studies directed to the identification of σ1R antagonists for the treatment of pain.

A neuroendocrine mechanism of co-morbidity of depression-like behavior and myocardial injury in rats

Depression is generally a recurrent psychiatric disorder. Evidence shows that depression and cardiovascular diseases are common comorbid conditions, but the specific pathological mechanisms remain unclear. The purpose of this study is to determine the effects of depression induced by chronic unpredictable mild stress (CUMS) on myocardial injury and to further elucidate the biological mechanism of depression. Rats were used as a model. The CUMS procedure lasted for a total of 8 weeks. After 4 weeks of CUMS, treated rats exhibited a reduced sucrose preference and changes in scores on an open field test, body weight and content of 5-HT in the brain as compared with the values of these variables in controls. These changes indicated depression-like changes in CUMS rats and demonstrated the feasibility of the depression model. In addition, pathological changes in the myocardium and increased cardiomyocyte apoptosis demonstrated that myocardial injury had occurred after 6 weeks of CUMS and had increased significantly by the end of 8 weeks of CUMS. Plasma serotonin (5-HT), norepinephrine (NE) and epinephrine (E), all depression-related neuroendocrine factors, were measured by HPLC-ECD techniques, and the content of plasma corticosterone (GC) was evaluated by an I(125)-cortisol radioactivity immunoassay in control and CUMS rats. The results indicated that 5-HT had decreased, whereas NE, E and GC had increased in CUMS rats, and these factors might be associated with depression-induced myocardial injury. The effects of 5-HT, NE and GC on the survival rate of cultured cardiomyocytes were determined using an orthogonal design. The results showed that 5-HT was a more important factor affecting cell survival than GC or NE. The results suggested that normal blood levels of 5-HT had a cytoprotective effect. The neuroendocrine disorders characterized by decreased 5-HT combined with increased GC and NE mediated the occurrence of depression-induced myocardial injury.

ARF-Like (ARL) Proteins

The ARF-like (ARL) proteins, within the ARF family, are a collection of functionally diverse GTPases that share extensive (>40 %) identity with the ARFs and each other and are assumed to share basic mechanisms of regulation and a very incompletely documented degree of overlapping regulators. At least four ARLs were already present in the last eukaryotic common ancestor, along with one ARF, and these have been expanded to >20 members in mammals. We know little about the majority of these proteins so our review will focus on those about which the most is known, including ARL1, ARL2, ARL3, ARL4s, ARL6, ARL13s, and ARFRP1. From this fragmentary information we extract some generalizations and conclusions regarding the sources and extent of specificity and functions of the ARLs.