Attenuation of methamphetamine-induced effects through the antagonism of sigma (sigma) receptors: Evidence from in vivo and in vitro studies

Involvement of nucleus accumbens SERCA2b in methamphetamine-induced conditioned place preference

Methamphetamine (METH) is a highly addictive psycho-stimulant that induces addictive behaviour by stimulating increased dopamine release in the nucleus accumbens (NAc). The sarco/endoplasmic reticulum calcium ion transport ATPases (SERCA or ATP2A) is a calcium ion (Ca2+) pump in the endoplasmic reticulum (ER) membrane. SERCA2b is a SERCA subtype mainly distributed in the central nervous system. This study used conditioned place preference (CPP), a translational drug reward model, to observe the effects of SERCA and SERCA2b on METH-CPP in mice. Result suggested that the activity of SERCA was significantly decreased in NAc after METH-CPP. Intraperitoneal SERCA agonist CDN1163 injection or bilateral CDN1163 microinjection in the NAc inhibited METH-CPP formation. SERCA2b overexpression by the Adeno-associated virus can reduce the DA release of NAc and inhibit METH-CPP formation. Although microinjection of SERCA inhibitor thapsigargin in the bilateral NAc did not significantly aggravate METH-CPP, interference with SERCA2b expression in NAc by adeno-associated virus increased DA release and promoted METH-CPP formation. METH reduced the SERCA ability to transport Ca2+ into the ER in SHSY5Y cells in vitro, which was reversed by CDN1163. This study revealed that METH dysregulates intracellular calcium balance by downregulating SERCA2b function, increasing DA release in NAc and inducing METH-CPP formation. Drugs that target SERCA2b may have the potential to treat METH addiction.

Main targets of ibogaine and noribogaine associated with its putative anti-addictive effects: A mechanistic overview

BACKGROUND

There is a growing interest in studying ibogaine (IBO) as a potential treatment for substance use disorders (SUDs). However, its clinical use has been hindered for mainly two reasons: First, the lack of randomized, controlled studies informing about its safety and efficacy. And second, IBO's mechanisms of action remain obscure. It has been challenging to elucidate a predominant mechanism of action responsible for its anti-addictive effects.

OBJECTIVE

To describe the main targets of IBO and its main metabolite, noribogaine (NOR), in relation to their putative anti-addictive effects, reviewing the updated literature available.

METHODS

A comprehensive search involving MEDLINE and Google Scholar was undertaken, selecting papers published until July 2022. The inclusion criteria were both theoretical and experimental studies about the pharmacology of IBO. Additional publications were identified in the references of the initial papers.

RESULTS

IBO and its main metabolite, NOR, can modulate several targets associated with SUDs. Instead of identifying key targets, the action of IBO should be understood as a complex modulation of multiple receptor systems, leading to potential synergies. The elucidation of IBO's pharmacology could be enhanced through the application of methodologies rooted in the polypharmacology paradigm. Such approaches possess the capability to describe multifaceted patterns within multi-target drugs.

CONCLUSION

IBO displays complex effects through multiple targets. The information detailed here should guide future research on both mechanistic and therapeutic studies.

Revisiting the sigma-1 receptor as a biological target to treat affective and cognitive disorders

Depression and cognitive disorders are diseases with complex and not-fully understood etiology. Unfortunately, the COVID-19 pandemic dramatically increased the prevalence of both conditions. Since the current treatments are inadequate in many patients, there is a constant need for discovering new compounds, which will be more effective in ameliorating depressive symptoms and treating cognitive decline. Proteins attracting much attention as potential targets for drugs treating these conditions are sigma-1 receptors. Sigma-1 receptors are multi-functional proteins localized in endoplasmic reticulum membranes, which play a crucial role in cellular signal transduction by interacting with receptors, ion channels, lipids, and kinases. Changes in their functions and expression may lead to various diseases, including depression or memory impairments. Thus, sigma-1 receptor modulation might be useful in treating these central nervous system diseases. Importantly, two sigma-1 receptor ligands entered clinical trials, showing that this compound group possesses therapeutic potential. Therefore, based on preclinical studies, this review discusses whether the sigma-1 receptor could be a promising target for drugs treating affective and cognitive disorders.

Association of sigma-1 receptor with dopamine transporter attenuates the binding of methamphetamine via distinct helix-helix interactions

Dopamine transporter (DAT) and sigma-1 receptor (σ1R) are potential therapeutic targets to reduce the psychostimulant effects induced by methamphetamine (METH). Interaction of σ1R with DAT could modulate the binding of METH, but the molecular basis of the association of the two transmembrane proteins and how their interactions mediate the binding of METH to DAT or σ1R remain unclear. Here, we characterize the protein-ligand and protein-protein interactions at a molecular level by various theoretical approaches. The present results show that METH adopts a different binding pose in the binding pocket of σ1R and is more likely to act as an agonist. The relatively lower binding affinity of METH to σ1R supports the role of antagonists as inhibitors that protect against METH-induced effects. We demonstrate that σ1R could bind to Drosophila melanogaster DAT (dDAT) through interactions with either the transmembrane helix α12 or α5 of dDAT. Our results showed that the truncated σ1R displays stronger association with dDAT than the full-length σ1R. Although different helix-helix interactions between σ1R and dDAT lead to distinct effects on the dynamics of individual protein, both associations attenuate the binding affinity of METH to dDAT, particularly in the interactions with the helix α5 of dDAT. Together, the present study provides the first computational investigation on the molecular mechanism of coupling METH binding and the association of σ1R with dDAT.

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.

Contribution of Lysosome and Sigma Receptors to Neuroprotective Effects of Memantine Against Beta-Amyloid in the SH-SY5Y Cells

Purpose: Memantine is an approved drug for the treatment of Alzheimer’s disease (AD). Autophagy, lysosome dysfunction, and sigma receptors have possible roles in the pathophysiology of AD. Therefore, we aimed to investigate the contribution of sigma receptors and lysosome inhibition to the neuroprotective effects of memantine against amyloid-beta (Aβ)-induced neurotoxicity in SH-SY5Y cells.

Methods: We determined the neuroprotective effects of memantine (2.5 µM), dizocilpine (MK801, as a selective N-methyl-D-aspartate (NMDA) receptor antagonist) (5 μM) against Aβ25– 35 (2 μg/μL)-induced neurotoxicity. We used chloroquine (10, 20, and 40 μM) as a lysosome inhibitor and BD-1063 (1, 10, and 30 μM) as a selective sigma receptor antagonist. The MTT assay was used to measure the neurotoxicity in the SH-SY5Y cells. Data were analyzed using the one-way ANOVA.

Results: Memantine (2.5 µM), dizocilpine (5 µM), chloroquine (10 and 20 µM) and BD-1063 (1, 10 and 30 µM) decreased the neurotoxic effects of Aβ on the SH-SY5Y cells. However, chloroquine (40 µM) increased the neurotoxic effects of Aβ. Cell viability in the cells treated with memantine + Aβ + chloroquine (10, 20, and 40 μM) was significantly lower than the memantine + Aβ-treated group. Moreover, cell viability in the memantine + Aβ group was higher than the memantine + Aβ + BD-1063 (10 and 30 μM) groups.

Conclusion: The lysosomal and sigma receptors may contribute to the neuroprotective mechanism of memantine and other NMDA receptor antagonists. Moreover, the restoration of lysosomes function and the modulation of sigma receptors are potential targets in the treatment of AD.

Sigma-1 receptor ligand PD144418 and sigma-2 receptor ligand YUN-252 attenuate the stimulant effects of methamphetamine in mice

RATIONALE

Previous research indicates that the selective sigma-1 receptor ligand PD144418 and the selective sigma-2 ligands YUN-252 can inhibit cocaine-induced hyperactivity. The effects of these ligands on other stimulants, such as methamphetamine, have not been reported.

OBJECTIVES

The present study examined the effects of PD144418 and YUN-252 pretreatment on methamphetamine-induced hyperactivity after acute treatment.

METHODS

Mice (n = 8-14/group) were injected with PD144418 (3.16, 10, or 31.6 μmol/kg), YUN-252 (0.316, 3.16, 31.6 μmol/kg), or saline. After 15 min, mice injected with 2.69 μmol/kg methamphetamine or saline vehicle, where distance traveled during a 60-min period was recorded. Additionally, the effect of PD144418 on the initiation and expression of methamphetamine sensitization was determined by treating mice (n = 8-14/group) with PD144418, methamphetamine or saline repeatedly over a 5-day period, and testing said mice with a challenge dose after a 7-day withdrawal period.

RESULTS

Results indicate that both PD144418 and YUN-252, in a dose-dependent manner, attenuated hyperactivity induced by an acute methamphetamine injection. Specifically, 10 μmol/kg or 31.6 μmol/kg of PD144418 and 31 μmol/kg of YUN-252 suppressed methamphetamine-induced hyperactivity. In regard to methamphetamine sensitization, while 10 μmol/kg PD144418 prevented the initiation of methamphetamine sensitization, it did not have an effect on the expression.

CONCLUSIONS

Overall, the current results suggest an intriguing potential for this novel sigma receptor ligand as a treatment for the addictive properties of methamphetamine. Future analysis of this novel sigma receptor ligand in assays directly measuring reinforcement properties will be critical.

M100907 and BD 1047 attenuate the acute toxic effects of methamphetamine

There are no Food and Drug Administration approved pharmacotherapies for methamphetamine (METH) overdose, thus identifying novel drug targets to prevent this devastating adverse event is a public-health imperative. Previous research suggests that serotonin and sigma receptors may contribute to the adverse effects of METH. The present study assessed whether pretreatment with the 5-HT2A receptor antagonist M100907 or the sigma 1 (σ1) receptor antagonist BD 1047 attenuated METH-induced lethality, hyperthermia, convulsions, and seizures. Male, Swiss-Webster mice received intraperitoneal injections of M100907 (1 and 10 mg/kg), BD 1047 (10 mg/kg), or a combination of M100907 (1 mg/kg) and BD 1047 (10 mg/kg) prior to treatment with METH (78 mg/kg). Convulsions and lethality were assessed by observation, core body temperature was assessed by surgically implanted telemetric probes, and seizures were assessed by electroencephalography. M100907 reduced METH-elicited lethality from 67% to 33%, BD1047 reduced METH-elicited lethality from 67% to 50%, and combined administration of both agents eliminated lethality in all mice tested. Similarly, both agents and their combination reduced METH-elicited seizures and convulsions. None of the treatments decreased METH-induced hyperthermia. This research suggests that reducing METH-induced seizures is an important factor in reducing lethality associated with METH overdose. However, future studies should examine whether M100907 and BD 1047 modulate METH-induced hypertension and other adverse effects that may also contribute to METH overdose. Our data support the continued investigation of compounds that target 5-HT2A and σ1 receptors in METH-induced overdose, including their potential to yield emergency reversal agents.

The cellular basis of fetal endoplasmic reticulum stress and oxidative stress in drug-induced neurodevelopmental deficits

Prenatal substance exposure is a growing public health concern worldwide. Although the opioid crisis remains one of the most prevalent addiction problems in our society, abuse of cocaine, methamphetamines, and other illicit drugs, particularly amongst pregnant women, are nonetheless significant and widespread. Evidence demonstrates prenatal drug exposure can affect fetal brain development and thus can have long-lasting impact on neurobehavioral and cognitive performance later in life. In this review, we highlight research examining the most prevalent drugs of abuse and their effects on brain development with a focus on endoplasmic reticulum stress and oxidative stress signaling pathways. A thorough exploration of drug-induced cellular stress mechanisms during prenatal brain development may provide insight into therapeutic interventions to combat effects of prenatal drug exposure.

Methamphetamine Induces Apoptosis of Microglia via the Intrinsic Mitochondrial-Dependent Pathway

Methamphetamine (METH) is a drug of abuse, the acute and chronic use of which induces neurotoxic responses in the human brain, ultimately leading to neurocognitive disorders. Our goals were to understand the impact of METH on microglial mitochondrial respiration and to determine whether METH induces the activation of the mitochondrial-dependent intrinsic apoptosis pathway in microglia. We assessed the expression of pro- apoptosis genes using qPCR of RNA extracted from a human microglial cell line (HTHU). We examined the apoptosis-inducing effects of METH on microglial cells using digital holographic microscopy (DHM) to quantify real-time apoptotic volume decrease (AVD) in microglia in a noninvasive manner. METH treatment significantly increased AVD, activated Caspase 3/7, increased the gene expression levels of the pro- apoptosis proteins, APAF-1 and BAX, and decreased mitochondrial DNA content. Using immunofluorescence analysis, we found that METH increased the expression of the mitochondrial proteins cytochrome c and MCL-1, supporting the activation of mitochondrion-dependent (intrinsic) apoptosis pathway. Cellular bio-energetic flux analysis by Agilent Seahorse XF Analyzer revealed that METH treatment increased both oxidative and glycolytic respiration after 3 h, which was sustained for at least 24 h. Several events, such as oxidative stress, neuro-inflammatory responses, and mitochondrial dysfunction, may converge to mediate METH-induced apoptosis of microglia that may contribute to neurotoxicity of the CNS. Our study has important implications for therapeutic strategies aimed at preserving mitochondrial function in METH abusing patients.

The sigma-1 receptor as a regulator of dopamine neurotransmission: A potential therapeutic target for methamphetamine addiction

Methamphetamine (METH) abuse is a major public health issue around the world, yet there are currently no effective pharmacotherapies for the treatment of METH addiction. METH is a potent psychostimulant that increases extracellular dopamine levels by targeting the dopamine transporter (DAT) and alters neuronal activity in the reward centers of the brain. One promising therapeutic target for the treatment of METH addiction is the sigma-1 receptor (σ1R). The σ1R is an endoplasmic reticulum-localized chaperone protein that is activated by cellular stress, and, unique to this chaperone, its function can also be induced or inhibited by different ligands. Upon activation of this unique "chaperone receptor", the σ1R regulates a variety of cellular functions and possesses neuroprotective activity in the brain. Interestingly, a variety of σ1R ligands modulate dopamine neurotransmission and reduce the behavioral effects of METH in animal models of addictive behavior, suggesting that the σ1R may be a viable therapeutic target for the treatment of METH addiction. In this review, we provide background on METH and the σ1R as well as a literature review regarding the role of σ1Rs in modulating both dopamine neurotransmission and the effects of METH. We aim to highlight the complexities of σ1R pharmacology and function as well as the therapeutic potential of the σ1R as a target for the treatment of METH addiction.

Novel Sigma-1 receptor antagonists: from opioids to small molecules: what is new?

Sigma-1 (σ1) receptor has been identified as a chaperone protein that interacts with other proteins, such as N-methyl-D-aspartate (NMDA) and opioid receptors, modulating their activity. σ1 receptor antagonists have been developed to obtain useful compounds for the treatment of psychoses, pain, drug abuse and cancer. Some interesting compounds such as E-5842 (5) and MS-377 (24), haloperidol and piperazine derivatives, respectively, were endowed with high affinity for σ1 receptors (Ki σ1 = 4 and 73 nM; Ki σ2 = 220 and 6900, respectively). They were developed for the treatment of psychotic disorders and 5 also underwent Phase II clinical trials suggesting interesting potential therapeutic applications. Here, σ1 receptor antagonists have been grouped based on chemical structure and reviewed according to structure-activity relationship and potential therapeutic role.

The sigma-1 receptor modulates methamphetamine dysregulation of dopamine neurotransmission

Dopamine neurotransmission is highly dysregulated by the psychostimulant methamphetamine, a substrate for the dopamine transporter (DAT). Through interactions with DAT, methamphetamine increases extracellular dopamine levels in the brain, leading to its rewarding and addictive properties. Methamphetamine also interacts with the sigma-1 receptor (σ1R), an inter-organelle signaling modulator. Using complementary strategies, we identified a novel mechanism for σ1R regulation of dopamine neurotransmission in response to methamphetamine. We found that σ1R activation prevents methamphetamine-induced, DAT-mediated increases in firing activity of dopamine neurons. In vitro and in vivo amperometric measurements revealed that σ1R activation decreases methamphetamine-stimulated dopamine efflux without affecting basal dopamine neurotransmission. Consistent with these findings, σ1R activation decreases methamphetamine-induced locomotion, motivated behavior, and enhancement of brain reward function. Notably, we revealed that the σ1R interacts with DAT at or near the plasma membrane and decreases methamphetamine-induced Ca2+ signaling, providing potential mechanisms. Broadly, these data provide evidence for σ1R regulation of dopamine neurotransmission and support the σ1R as a putative target for the treatment of methamphetamine addiction.

Role of microglia in methamphetamine-induced neurotoxicity

Methamphetamine (Meth) is an addictive psychostimulant widely abused around the world. The chronic use of Meth produces neurotoxicity featured by dopaminergic terminal damage and microgliosis, resulting in serious neurological and behavioral consequences. Ample evidence indicate that Meth causes microglial activation and resultant secretion of pro-inflammatory molecules leading to neural injury. However, the mechanisms underlying Meth-induced microglial activation remain to be determined. In this review, we attempt to address the effects of Meth on human immunodeficiency virus (HIV)-associated microglia activation both in vitro and in-vivo. Meth abuse not only increases HIV transmission but also exacerbates progression of HIV-associated neurocognitive disorders (HAND) through activation of microglia. In addition, the therapeutic potential of anti-inflammatory drugs on ameliorating Meth-induced microglia activation and resultant neuronal injury is discussed.

Sigma Receptors and Substance Use Disorders

Thanks to advances in neuroscience, addiction is now recognized as a chronic brain disease with genetic, developmental, and cultural components. Drugs of abuse, including alcohol, are able to produce significant neuroplastic changes responsible for the profound disturbances shown by drug addicted individuals. The current lack of efficacious pharmacological treatments for substance use disorders has encouraged the search for novel and more effective pharmacotherapies. Growing evidence strongly suggests that Sigma Receptors are involved in the addictive and neurotoxic properties of abused drugs, including cocaine , methamphetamine , and alcohol. The present chapter will review the current scientific knowledge on the role of the Sigma Receptor system in the effects of drugs and alcohol, and proposes that this receptor system may represent a novel therapeutic target for the treatment of substance use disorders and associated neurotoxicity.

Dissecting the Influence of Two Structural Substituents on the Differential Neurotoxic Effects of Acute Methamphetamine and Mephedrone Treatment on Dopamine Nerve Endings with the Use of 4-Methylmethamphetamine and Methcathinone

Mephedrone (MEPH) is a β-ketoamphetamine stimulant drug of abuse that is often a constituent of illicit bath salts formulations. Although MEPH bears remarkable similarities to methamphetamine (METH) in terms of chemical structure, as well as its neurochemical and behavioral effects, it has been shown to have a reduced neurotoxic profile compared with METH. The addition of a β-keto moiety and a 4-methyl ring substituent to METH yields MEPH, and a loss of direct neurotoxic potential. In the present study, two analogs of METH, methcathinone (MeCa) and 4-methylmethamphetamine (4MM), were assessed for their effects on mouse dopamine (DA) nerve endings to determine the relative contribution of each individual moiety to the loss of direct neurotoxicity in MEPH. Both MeCa and 4MM caused significant alterations in core body temperature as well as locomotor activity and stereotypy, but 4MM was found to elicit minimal dopaminergic toxicity only at the highest dose. By contrast, MeCa caused significant reductions in all markers of DA nerve-ending damage over a range of doses. These results lead to the conclusion that ring substitution at the 4-position profoundly reduces the neurotoxicity of METH, whereas the β-keto group has much less influence on this property. Although the mechanism(s) by which the 4-methyl substituent reduces METH-induced neurotoxicity remains unclear, it is speculated that this effect is mediated by a loss of DA-releasing action in MEPH and 4MM at the synaptic vesicle monoamine transporter, an effect that is thought to be critical for METH-induced neurotoxicity.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

Pridopidine selectively occupies sigma-1 rather than dopamine D2 receptors at behaviorally active doses

RATIONALE

Dopamine stabilizers have stimulatory actions under low dopamine tone and inhibitory actions under high dopamine tone without eliciting catalepsy. These compounds are dopamine D2 receptor (D2R) antagonists or weak partial agonists and may have pro-mnemonic and neuroprotective effects. The mechanism underlying their stimulatory and neuroprotective actions is unknown but could involve sigma-1R binding.

OBJECTIVES

The present study examined sigma-1R and D2R occupancy by the dopamine stabilizer pridopidine (ACR16) at behaviorally relevant doses in living rats.

METHODS

Rats were administered 3 or 15 mg/kg pridopidine, or saline, before injection of the radiotracer (11)C-SA4503 (sigma-1R) or (11)C-raclopride (D2R). Some animals received 60 mg/kg pridopidine and were only scanned with (11)C-raclopride. Cerebral (11)C-SA4503 binding was quantified using metabolite-corrected plasma input data and distribution volume (V T) calculated by Logan graphical analysis. (11)C-raclopride binding was quantified using striatum-to-cerebellum ratios and binding potentials calculated with a simplified reference tissue model.

RESULTS

Cunningham-Lassen plots indicated sigma-1R occupancies of 57 ± 2 and 85 ± 2% after pretreatment of animals with 3 and 15 mg/kg pridopidine. A significant (44-66%) reduction of (11)C-raclopride binding was only observed at 60 mg/kg pridopidine.

CONCLUSIONS

At doses shown to elicit neurochemical and behavioral effects, pridopidine occupied a large fraction of sigma-1Rs and a negligible fraction of D2Rs. Significant D2R occupancy was only observed at a dose 20-fold higher than was required for sigma-1R occupancy. The characteristics of dopamine stabilizers may result from the combination of high sigma-1R and low D2R affinity.

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.

Methamphetamine-induced toxicity: an updated review on issues related to hyperthermia

Reports of methamphetamine-related emergency room visits suggest that elevated body temperature is a universal presenting symptom, with lethal overdoses generally associated with extreme hyperthermia. This review summarizes the available information on methamphetamine toxicity as it pertains to elevations in body temperature. First, a brief overview of thermoregulatory mechanisms is presented. Next, central and peripheral targets that have been considered for potential involvement in methamphetamine hyperthermia are discussed. Finally, future areas of investigation are proposed, as further studies are needed to provide greater insight into the mechanisms that mediate the alterations in body temperature elicited by methamphetamine.

SN79, a sigma receptor antagonist, attenuates methamphetamine-induced astrogliosis through a blockade of OSMR/gp130 signaling and STAT3 phosphorylation

Methamphetamine (METH) exposure results in dopaminergic neurotoxicity in striatal regions of the brain, an effect that has been linked to an increased risk of Parkinson's disease. Various aspects of neuroinflammation, including astrogliosis, are believed to be contributory factors in METH neurotoxicity. METH interacts with sigma receptors at physiologically relevant concentrations and treatment with sigma receptor antagonists has been shown to mitigate METH-induced neurotoxicity in rodent models. Whether these compounds alter the responses of glial cells within the central nervous system to METH however has yet to be determined. Therefore, the purpose of the current study was to determine whether the sigma receptor antagonist, SN79, mitigates METH-induced striatal reactive astrogliosis. Male, Swiss Webster mice treated with a neurotoxic regimen of METH exhibited time-dependent increases in striatal gfap mRNA and concomitant increases in GFAP protein, indicative of astrogliosis. This is the first report that similar to other neurotoxicants that induce astrogliosis through the activation of JAK2/STAT3 signaling by stimulating gp-130-linked cytokine signaling resulting from neuroinflammation, METH treatment also increases astrocytic oncostatin m receptor (OSMR) expression and the phosphorylation of STAT3 (Tyr-705) in vivo. Pretreatment with SN79 blocked METH-induced increases in OSMR, STAT3 phosphorylation and astrocyte activation within the striatum. Additionally, METH treatment resulted in striatal cellular degeneration as measured by Fluoro-Jade B, an effect that was mitigated by SN79. The current study provides evidence that sigma receptor antagonists attenuate METH-induced astrocyte activation through a pathway believed to be shared by various neurotoxicants.

Sigma (σ) receptors as potential therapeutic targets to mitigate psychostimulant effects

Many psychostimulants, including cocaine and methamphetamine, interact with sigma (σ) receptors at physiologically relevant concentrations. The potential therapeutic relevance of this interaction is underscored by the ability to selectively target σ receptors to mitigate many behavioral and physiological effects of psychostimulants in animal and cell-based model systems. This chapter begins with an overview of these enigmatic proteins. Provocative preclinical data showing that σ ligands modulate an array of cocaine and methamphetamine effects are summarized, along with emerging areas of research. Together, the literature suggests targeting of σ receptors as an innovative option for combating undesired actions of psychostimulants through both neuronal and glial mechanisms.

Neuroprotective targets through which 6-acetyl-3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one (SN79), a sigma receptor ligand, mitigates the effects of methamphetamine in vitro

Exposure to high or repeated doses of methamphetamine can cause hyperthermia and neurotoxicity, which are thought to increase the risk of developing a variety of neurological conditions. Sigma receptor antagonism can prevent methamphetamine-induced hyperthermia and neurotoxicity, but the underlying cellular targets through which the neuroprotection is conveyed remain unknown. Differentiated NG108-15 cells were thus used as a model system to begin elucidating the neuroprotective mechanisms targeted by sigma receptor antagonists to mitigate the effects of methamphetamine. In differentiated NG108-15 cells, methamphetamine caused the generation of reactive oxygen/nitrogen species, an increase in PERK-mediated endoplasmic reticulum stress and the activation of caspase-3, -8 and -9, ultimately resulting in apoptosis at micromolar concentrations, and necrotic cell death at higher concentrations. The sigma receptor antagonist, 6-acetyl-3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one (SN79), attenuated methamphetamine-induced increases in reactive oxygen/nitrogen species, activation of caspase-3, -8 and -9 and accompanying cellular toxicity. In contrast, 1,3-di(2-tolyl)-guanidine (DTG), a sigma receptor agonist, shifted the dose response curve of methamphetamine-induced cell death towards the left. To probe the effect of temperature on neurotoxicity, NG108-15 cells maintained at an elevated temperature (40 °C) exhibited a significant and synergistic increase in cell death in response to methamphetamine, compared to cells maintained at a normal cell culture temperature (37 °C). SN79 attenuated the enhanced cell death observed in the methamphetamine-treated cells at 40 °C. Together, the data demonstrate that SN79 reduces methamphetamine-induced reactive oxygen/nitrogen species generation and caspase activation, thereby conveying neuroprotective effects against methamphetamine under regular and elevated temperature conditions.

Chlorophenylpiperazine analogues as high affinity dopamine transporter ligands

Selective σ2 ligands continue to be an active target for medications to attenuate the effects of psychostimulants. In the course of our studies to determine the optimal substituents in the σ2-selective phenyl piperazines analogues with reduced activity at other neurotransmitter systems, we discovered that 1-(3-chlorophenyl)-4-phenethylpiperazine actually had preferentially increased affinity for dopamine transporters (DAT), yielding a highly selective DAT ligand.

Pharmacological evaluation of SN79, a sigma (σ) receptor ligand, against methamphetamine-induced neurotoxicity in vivo

Methamphetamine is a highly addictive psychostimulant drug of abuse, causing hyperthermia and neurotoxicity at high doses. Currently, there is no clinically proven pharmacotherapy to treat these effects of methamphetamine, necessitating identification of potential novel therapeutic targets. Earlier studies showed that methamphetamine binds to sigma (σ) receptors in the brain at physiologically relevant concentrations, where it "acts in part as an agonist." SN79 (6-acetyl-3-(4-(4-(4-florophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one) was synthesized as a putative σ receptor antagonist with nanomolar affinity and selectivity for σ receptors over 57 other binding sites. SN79 pretreatment afforded protection against methamphetamine-induced hyperthermia and striatal dopaminergic and serotonergic neurotoxicity in male, Swiss Webster mice (measured as depletions in striatal dopamine and serotonin levels, and reductions in striatal dopamine and serotonin transporter expression levels). In contrast, di-o-tolylguanidine (DTG), a well established σ receptor agonist, increased the lethal effects of methamphetamine, although it did not further exacerbate methamphetamine-induced hyperthermia. Together, the data implicate σ receptors in the direct modulation of some effects of methamphetamine such as lethality, while having a modulatory role which can mitigate other methamphetamine-induced effects such as hyperthermia and neurotoxicity.

Effect of ring-constrained phenylpropyloxyethylamines on sigma receptors

A series of ring-constrained phenylpropyloxyethylamines, partial opioid structure analogs and derivatives of a previously studied sigma (σ) receptor ligand, was synthesized and evaluated at σ and opioid receptors for receptor selectivity. The results of this study identified several compounds with nanomolar affinity at both σ receptor subtypes. Compounds 6 and 9 had the highest selectivity for both σ receptor subtypes, compared to μ opioid receptors. In addition, compounds 6 and 9 significantly reduced the convulsive effects of cocaine in mice, which would be consistent with antagonism of σ receptors.

The evaluation of AZ66, an optimized sigma receptor antagonist, against methamphetamine-induced dopaminergic neurotoxicity and memory impairment in mice

Sigma (σ) receptors have recently been identified as potential targets for the development of novel therapeutics aimed at mitigating the effects of methamphetamine. Particularly, σ receptors are believed to mitigate some of the neurotoxic effects of methamphetamine through modulation of dopamine, dopamine transporters and body temperature. Furthermore, recent evidence suggests that targeting σ receptors may prevent cognitive impairments produced by methamphetamine. In the present study, an optimized σ receptor antagonist, AZ66, was evaluated against methamphetamine-induced neurotoxicity and cognitive dysfunction. AZ66 was found to be highly selective for σ receptors compared to 64 other sites tested. Pretreatment of male, Swiss Webster mice with i.p. dosing of AZ66 significantly attenuated methamphetamine-induced striatal dopamine depletions, striatal dopamine transporter reductions and hyperthermia. Additionally, neurotoxic dosing with methamphetamine caused significant memory impairment in the object recognition test, which was attenuated when animals were pretreated with AZ66; similar trends were observed in the step-through passive avoidance test. Taken together, these results suggest that targeting σ receptors may provide neuroprotection against the neurotoxicity and cognitive impairments produced by methamphetamine.

SN79, a sigma receptor ligand, blocks methamphetamine-induced microglial activation and cytokine upregulation

Methamphetamine (METH) abuse is associated with several negative side effects including neurotoxicity in specific brain regions such as the striatum. The precise molecular mechanisms by which METH usage results in neurotoxicity remain to be fully elucidated, with recent evidence implicating the importance of microglial activation and neuroinflammation in damaged brain regions. METH interacts with sigma receptors which are found in glial cells in addition to neurons. Moreover, sigma receptor antagonists have been shown to block METH-induced neurotoxicity in rodents although the cellular mechanisms underlying their neuroprotection remain unknown. The purpose of the current study was to determine if the prototypic sigma receptor antagonist, SN79, mitigates METH-induced microglial activation and associated increases in cytokine expression in a rodent model of METH-induced neurotoxicity. METH increased striatal mRNA and protein levels of cluster of differentiation 68 (CD68), indicative of microglial activation. METH also increased ionized calcium binding adapter molecule 1 (IBA-1) protein expression, further confirming the activation of microglia. Along with microglial activation, METH increased striatal mRNA expression levels of IL-6 family pro-inflammatory cytokines, leukemia inhibitory factor (lif), oncostatin m (osm), and interleukin-6 (il-6). Pretreatment with SN79 reduced METH-induced increases in CD68 and IBA-1 expression, demonstrating its ability to prevent microglial activation. SN79 also attenuated METH-induced mRNA increases in IL-6 pro-inflammatory cytokine family members. The ability of a sigma receptor antagonist to block METH-induced microglial activation and cytokine production provides a novel mechanism through which the neurotoxic effects of METH may be mitigated.

Ultra-performance liquid chromatography tandem mass spectrometry method for the determination of AZ66, a sigma receptor ligand, in rat plasma and its application to in vivo pharmacokinetics

Methamphetamine abuse continues as a major problem in the USA owing to its powerful psychological addictive properties. AZ66, 3-[4-(4-cyclohexylpiperazine-1-yl)pentyl]-6-fluorobenzo[d]thiazole-2(3H)-one, an optimized sigma receptor ligand, is a promising therapeutic agent against methamphetamine. To study the in vivo pharmacokinetics of this novel sigma receptor ligand in rats, a sensitive ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed in rat plasma and validated. The developed method requires a small volume of plasma (100 μL) and a simple liquid-liquid extraction. The chromatographic separations were achieved in 3.3 min using an Acquity UPLC BEH Shield RP18 column. The mass spectrophotometric detection was carried out using a Waters Micromass Quattro MicroTM triple-quadrupole system. Multiple reaction monitoring was used for the quantitation with transitions m/z 406 → m/z 181 for AZ66 and m/z 448 → m/z 285 for aripiprazole. The method was validated over a concentration range of 1-3500 ng/mL and the lower limit of quantitation was determined to be 1 ng/mL. Validation of the assay demonstrated that the developed UPLC/MS/MS method was sensitive, accurate and selective for the determination of AZ66 in rat plasma. The present method has been successfully applied to an i.v. pharmacokinetic study in Sprague-Dawley rats.

Inhibitory effects of sigma-2 receptor agonists on T lymphocyte activation

Sigma (σ) receptor ligands are essentially known for their effects on the nervous system although recent studies have shown their potential effects modulating some other pathophysiological processes as cell proliferation, cancer, and the immune response. Here, we have analyzed the actions of σ-1 and σ-2 receptors ligands on T cell activation. Our results show that treatment of Jurkat T cells with σ-2 agonists decreased the induction of the expression of Interleukin (IL)-2, Tumor necrosis factor (TNF)-α, and Cyclooxygenase (COX)-2 by activated T cells in a dose-dependent manner. These effects take place at the transcriptional level since σ-2 agonists BD-737 and CB-184 diminished the activity of the promoters of those genes. Those immunosuppressive effects could be attributable to interference with transcription factor activation. Induced transcription mediated by Nuclear factor (NF)-κB or Nuclear Factor of Activated T cells (NFAT) was inhibited by σ-2 agonists. These effects seem to be specific for σ-2 agonists as no significant effects on T cell activation by σ-1 ligands PRE-084 and BD-1063 were found. Our results provide new insights into the immunomodulatory actions of σ ligands and describe a new property of σ-2 agonists, through inhibition of activation of transcription factors as NFAT by which these compounds are regulating gene expression. This may have important consequences on the possible therapeutic use of those compounds.

New positron emission tomography (PET) radioligand for imaging σ-1 receptors in living subjects

σ-1 receptor (S1R) radioligands have the potential to detect and monitor various neurological diseases. Herein we report the synthesis, radiofluorination, and evaluation of a new S1R ligand 6-(3-fluoropropyl)-3-(2-(azepan-1-yl)ethyl)benzo[d]thiazol-2(3H)-one ([(18)F]FTC-146, [(18)F]13). [(18)F]13 was synthesized by nucleophilic fluorination, affording a product with >99% radiochemical purity (RCP) and specific activity (SA) of 2.6 ± 1.2 Ci/μmol (n = 13) at end of synthesis (EOS). Positron emission tomography (PET) and ex vivo autoradiography studies of [(18)F]13 in mice showed high uptake of the radioligand in S1R rich regions of the brain. Pretreatment with 1 mg/kg haloperidol (2), nonradioactive 13, or BD1047 (18) reduced the binding of [(18)F]13 in the brain at 60 min by 80%, 82%, and 81%, respectively, suggesting that [(18)F]13 accumulation in mouse brain represents specific binding to S1Rs. These results indicate that [(18)F]13 is a promising candidate radiotracer for further evaluation as a tool for studying S1Rs in living subjects.

Targeting sigma receptors: novel medication development for drug abuse and addiction

Psychostimulant abuse is a serious health and societal problem in industrialized and developing countries. However, the identification of an effective pharmacotherapy to treat it has remained elusive. It has long been known that many psychostimulant drugs, including cocaine and methamphetamine, interact with sigma receptors in the brain and heart, offering a logical target for medication development efforts. However, selective pharmacological agents and molecular biological tools have only recently become available to rigorously evaluate these receptors as viable medication development targets. The current review will summarize provocative preclinical data, demonstrating the ability of sigma receptor antagonists and antisense oligonucleotides to ameliorate cocaine-induced convulsions, lethality, locomotor activity and sensitization, and conditioned place-preference in rodents. Recent studies suggest that the protective effects of sigma receptor antagonists also extend to actions produced by methamphetamine, 3,4-methylenedioxymethamphetamine, ethanol and other abused substances. Together, the data indicate that targeting sigma receptors, particularly the σ(1)-subtype, may offer an innovative approach for combating the effects of cocaine, and perhaps other abused substances.

A 96-well filtration method for radioligand binding analysis of σ receptor ligands

σ receptors represent a potential drug target for numerous therapeutic indications including cancer, depression, psychostimulant abuse, and stroke. Most published radioligand binding studies for σ receptors utilize a low throughput method employing a "cell harvester." Higher throughput methods are required to facilitate efficient screening of large numbers of novel compounds. In this study, a series of reference compounds was analyzed with a new medium-throughput 96-well filtration method and the results were compared to those obtained using the conventional cell harvester-based method. The 96-well assay utilized rat liver membranes for the determination of both known σ receptor subtypes (σ(1) and σ(2)) because this tissue contains high densities of both subtypes and fulfills criteria required for reliable use with the 96-well format. The new method gave comparable K(i) values for reference ligands analyzed in parallel with samples prepared in rat brain membranes and processed on the traditional cell harvester. For σ(1) receptors, equivalent affinity values were observed for both methods/tissues. For σ(2) receptors, approximately 2-fold higher affinities were observed for most compounds in liver, as compared to brain membranes, but excellent correlation with brain-derived values was maintained. To further demonstrate the utility of the new method it was used to screen a novel series of 2(3H)-benzothiazolone compounds, resulting in the identification of several analogues with nanomolar affinity and greater than 50-fold specificity for σ(1) versus σ(2) receptors.

Sigma receptor antagonists attenuate acute methamphetamine-induced hyperthermia by a mechanism independent of IL-1β mRNA expression in the hypothalamus

Methamphetamine is currently one of the most widely abused drugs worldwide, with hyperthermia being a leading cause of death in methamphetamine overdose situations. Methamphetamine-induced hyperthermia involves a variety of cellular mechanisms, including increases in hypothalamic interleukin-1 beta (IL-1β) expression. Methamphetamine also interacts with sigma receptors and previous studies have shown that sigma receptor antagonists mitigate many of the behavioral and physiological effects of methamphetamine, including hyperthermia. The purpose of the current study was to determine if the attenuation of methamphetamine-induced hyperthermia by the sigma receptor antagonists, AZ66 and SN79, is associated with a concomitant attenuation of IL-1β mRNA expression, particularly in the hypothalamus. Methamphetamine produced dose- and time-dependent increases in core body temperature and IL-1β mRNA expression in the hypothalamus, striatum, and cortex in male, Swiss Webster mice. Pretreatment with the sigma receptor antagonists, AZ66 and SN79, significantly attenuated methamphetamine-induced hyperthermia, but further potentiated IL-1β mRNA in the mouse hypothalamus when compared to animals treated with methamphetamine alone. These findings suggest sigma receptor antagonists attenuate methamphetamine-induced hyperthermia through a different mechanism from that involved in the modulation of hypothalamic IL-1β mRNA expression.

Synthesis and pharmacological characterization of a novel sigma receptor ligand with improved metabolic stability and antagonistic effects against methamphetamine

Methamphetamine interacts with sigma receptors at physiologically relevant concentrations suggesting a potential site for pharmacologic intervention. In the present study, a previous sigma receptor ligand, CM156, was optimized for metabolic stability, and the lead analog was evaluated against the behavioral effects of methamphetamine. Radioligand binding studies demonstrated that the lead analog, AZ66, displayed high nanomolar affinity for both sigma-1 and sigma-2 receptors (2.4 ± 0.63 and 0.51 ± 0.15, respectively). In addition, AZ66 had preferential affinity for sigma receptors compared to seven other sites and a significantly longer half-life than its predecessor, CM156, in vitro and in vivo. Pretreatment of male, Swiss Webster mice with intraperitoneal (10-20 mg/kg) or oral (20-30 mg/kg) dosing of AZ66 significantly attenuated the acute locomotor stimulatory effects of methamphetamine. Additionally, AZ66 (10-20 mg/kg, i.p.) significantly reduced the expression and development of behavioral sensitization induced by repeated methamphetamine administration. Taken together, these data indicate that sigma receptors can be targeted to mitigate the acute and subchronic behavioral effects of methamphetamine and AZ66 represents a viable lead compound in the development of novel therapeutics against methamphetamine-induced behaviors.

Synthesis and σ1 Receptor Binding of Halogenated N,N'-Diphenethylethylenediamines

Eight halogenated N,N'-diphenethylethylenediamines were synthesized, characterized and evaluated for σ₁ receptor binding affinity in vitro. Measurements of lipophilicity also were obtained. The substitution pattern on one of the aromatic rings remained constant as 3,4-dichloro, while the substituents on the other aromatic ring were varied to include fluorine, bromine or iodine in either the 2-, 3- or 4- positions. Two main structure activity relationships were observed. First, halogen substitution on the 3- or 4-positions of the aromatic ring conferred higher binding affinities (K_i values 6.35 - 15.82 nM) than the corresponding substitutions at the 2-position (K_i values 12.08 - 43.15 nM). Second, derivatives containing either a bromo or fluoro substituent at a given position showed higher σ₁ receptor binding affinities than derivatives with a corresponding iodo substituent. The data indicate that σ₁ receptor affinity for this structural series is sensitive to steric bulk at the 2-position. Log k'_w measurements for the halogenated N,N'-diphenethylethylenediamines were determined by high performance liquid chromatography, and varied from 2.54 - 3.71. In particular, the 3-fluoro analog exhibited a log k'_w = 2.54 accompanied by a σ₁ receptor K_i = 7.8 nM. These novel N,N'-diphenethylethylenediamines warrant further investigation in behavioral assays, and radiolabeled versions may prove suitable for in vivo studies of σ₁ receptors.

AC927, a σ receptor ligand, blocks methamphetamine-induced release of dopamine and generation of reactive oxygen species in NG108-15 cells

Methamphetamine is a highly addictive psychostimulant drug of abuse that causes neurotoxicity with high or repeated dosing. Earlier studies demonstrated the ability of the selective σ receptor ligand N-phenethylpiperidine oxalate (AC927) to attenuate the neurotoxic effects of methamphetamine in vivo. However, the precise mechanisms through which AC927 conveys its protective effects remain to be determined. With the use of differentiated NG108-15 cells as a model system, the effects of methamphetamine on neurotoxic endpoints and mediators such as apoptosis, necrosis, generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), and dopamine release were examined in the absence and presence of AC927. Methamphetamine at physiologically relevant micromolar concentrations caused apoptosis in NG108-15 cells. At higher concentrations of methamphetamine, necrotic cell death was observed. At earlier time points, methamphetamine caused ROS/RNS generation, which was detected with the fluorigenic substrate 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescin diacetate, acetyl ester, in a concentration- and time-dependent manner. N-Acetylcysteine, catalase, and l-N(G)-monomethyl arginine citrate inhibited the ROS/RNS fluorescence signal induced by methamphetamine, which suggests the formation of hydrogen peroxide and RNS. Exposure to methamphetamine also stimulated the release of dopamine from NG108-15 cells into the culture medium. AC927 attenuated methamphetamine-induced apoptosis, necrosis, ROS/RNS generation, and dopamine release in NG108-15 cells. Together, the data suggest that modulation of σ receptors can mitigate methamphetamine-induced cytotoxicity, ROS/RNS generation, and dopamine release in cultured cells.

Role of sigma receptors in methamphetamine-induced neurotoxicity

Methamphetamine (METH) is a widely abused substance world over. Currently, there is no effective pharmacotherapy to treat its effects. This necessitates identification of potential novel therapeutic targets. METH interacts with sigma (σ) receptors at physiologically relevant micromolar concentrations. In addition, σ receptors are present in organs like the brain, heart, and lungs at which METH acts. Additionally, σ receptors have been implicated in various acute and subchronic effects like locomotor stimulation, development of sensitization and neurotoxicity, where σ receptor antagonists attenuate these effects. σ Receptors may also have a role in METH-induced psychiatric complications such as depression, psychosis, cognitive and motor deficits. The neurotoxic effects of METH, which are cause for concern, can be prevented by σ receptor antagonists in mice. Mechanistically, METH-induced neurotoxicity involves factors like dopamine release, oxidative stress, endoplasmic reticulum stress, activation of mitochondrial death cascades, glutamate release, apoptosis, microglial activation, and hyperthermia. This review compiles studies from the literature that suggests an important role for σ receptors in many of the mechanisms of METH-induced neurotoxicity.

Effects of the selective sigma receptor ligand, 1-(2-phenethyl)piperidine oxalate (AC927), on the behavioral and toxic effects of cocaine

BACKGROUND

Sigma receptors represent a unique structural class of proteins and they have become increasingly studied as viable medication development targets for neurological and psychiatric disorders, including drug abuse. Earlier studies have shown that cocaine and many other abused substances interact with sigma receptors and that antagonism of these proteins can mitigate their actions.

METHODS

In the present study, AC927 (1-(2-phenethyl)piperidine oxalate), a selective sigma receptor ligand, was tested against the behavioral and toxic effects of cocaine in laboratory animals.

RESULTS

Acute administration of AC927 in male, Swiss Webster mice significantly attenuated cocaine-induced convulsions, lethality, and locomotor activity, at doses that alone had no significant effects on behavior. Subchronic administration of AC927 also attenuated cocaine-induced conditioned place preference in mice, at doses that alone had no effects on place conditioning. In drug discrimination studies in male, Sprague-Dawley rats, AC927 partially substituted for the discriminative stimulus effects of cocaine. When it was administered with cocaine, AC927 shifted the cocaine dose-response curve to the left, suggesting an enhancement of the discriminative stimulus effects of cocaine. In non-human primates, AC927 was self-administered, maintaining responding that was intermediate between contingent saline and a maintenance dose of cocaine.

CONCLUSION

The ability of AC927 to elicit some cocaine-like appetitive properties and to also reduce many cocaine-induced behaviors suggests that it is a promising lead for the development of a medication to treat cocaine abuse.

Synthesis and pharmacological evaluation of indole-based sigma receptor ligands

A series of novel indole-based analogs were prepared and their affinities for sigma receptors were determined using in vitro radioligand binding assays. The results of this study identified several compounds with nanomolar sigma-2 affinity and significant selectivity over sigma-1 receptors. In particular, 2-(4-(3-(4-fluorophenyl)indol-1-yl)butyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (9f) was found to display high affinity at sigma-2 receptors with good selectivity (σ-1/σ-2 = 395). The pharmacological binding profile for this compound was established with other relevant non-sigma sites.

CM156, a high affinity sigma ligand, attenuates the stimulant and neurotoxic effects of methamphetamine in mice

Methamphetamine (METH) is a highly addictive psychostimulant drug of abuse. Low and high dose administration of METH leads to locomotor stimulation, and dopaminergic and serotonergic neurotoxicity, respectively. The behavioral stimulant and neurotoxic effects of METH can contribute to addiction and other neuropsychiatric disorders, thus necessitating the identification of potential pharmacotherapeutics against these effects produced by METH. METH binds to σ receptors at physiologically relevant concentrations. Also, σ receptors are present on and can modulate dopaminergic and serotonergic neurons. Therefore, σ receptors provide a viable target for the development of pharmacotherapeutics against the adverse effects of METH. In the present study, CM156, a σ receptor ligand with high affinity and selectivity for σ receptors over 80 other non-σ binding sites, was evaluated against METH-induced stimulant, hyperthermic, and neurotoxic effects. Pretreatment of male, Swiss Webster mice with CM156 dose dependently attenuated the locomotor stimulation, hyperthermia, striatal dopamine and serotonin depletions, and striatal dopamine and serotonin transporter reductions produced by METH, without significant effects of CM156 on its own. These results demonstrate the ability of a highly selective σ ligand to mitigate the effects of METH.

The sigma receptor agonist SA4503 both attenuates and enhances the effects of methamphetamine

BACKGROUND

Methamphetamine's behavioral effects have been attributed to its interaction with monoamine transporters; however, methamphetamine also has affinity for sigma receptors.

METHOD

The present study investigated the effect of the sigma receptor agonist SA 4503 and the sigma receptor antagonists BD-1047 and BD-1063 on methamphetamine-evoked [(3)H]dopamine release from preloaded rat striatal slices. The effect of SA 4503 on methamphetamine-induced hyperactivity and on the discriminative stimulus properties of methamphetamine also was determined.

RESULTS

SA 4503 attenuated methamphetamine-evoked [(3)H]dopamine release in a concentration-dependent manner. BD-1047 and BD-1063 did not affect release. SA 4503 dose-dependently potentiated and attenuated methamphetamine-induced hyperactivity. SA 4503 pretreatment augmented the stimulus properties of methamphetamine.

CONCLUSIONS

Our findings indicate that SA 4503 both enhances and inhibits methamphetamine's effects and that sigma receptors are involved in the neurochemical, locomotor stimulatory and discriminative stimulus properties of methamphetamine.

Synthesis and pharmacological evaluation of 6-acetyl-3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one (SN79), a cocaine antagonist, in rodents

Cocaine interacts with monoamine transporters and sigma (σ) receptors, providing logical targets for medication development. In the present study, in vitro and in vivo pharmacological studies were conducted to characterize SN79, a novel compound which was evaluated for cocaine antagonist actions. Radioligand binding studies showed that SN79 had a nanomolar affinity for σ receptors and a notable affinity for 5-HT(2) receptors, and monoamine transporters. It did not inhibit major cytochrome P450 enzymes, including CYP1A2, CYP2A6, CYP2C19, CYP2C9*1, CYP2D6, and CYP3A4, suggesting a low propensity for potential drug-drug interactions. Oral administration of SN79 reached peak in vivo concentrations after 1.5 h and exhibited a half-life of just over 7.5 h in male, Sprague-Dawley rats. Behavioral studies conducted in male, Swiss Webster mice, intraperitoneal or oral dosing with SN79 prior to a convulsive or locomotor stimulant dose of cocaine led to a significant attenuation of cocaine-induced convulsions and locomotor activity. However, SN79 produced sedation and motor incoordination on its own at higher doses, to which animals became tolerant with repeated administration. SN79 also significantly attenuated the development and expression of the sensitized response to repeated cocaine exposures. The ability of SN79 to significantly attenuate the acute and subchronic effects of cocaine provides a promising compound lead to the development of an effective pharmacotherapy against cocaine.

Sigma (σ) receptor ligand, AC927 (N-phenethylpiperidine oxalate), attenuates methamphetamine-induced hyperthermia and serotonin damage in mice

Methamphetamine interacts with sigma (σ) receptors and AC927, a selective σ receptor ligand, protects against methamphetamine-induced dopaminergic neurotoxicity. In the present study, the effects of AC927 on methamphetamine-induced hyperthermia and striatal serotonergic neurotoxicity were evaluated. Male, Swiss Webster mice were injected (i.p.) every 2 h, for a total of four times, with one of the following treatments: Saline+Saline; Saline+Methamphetamine (5 mg/kg); AC927 (5, 10, 20 mg/kg)+Methamphetamine (5 mg/kg); or AC927 (5, 10, 20 mg/kg)+Saline. Pretreatment with AC927 (10 mg/kg) significantly attenuated methamphetamine-induced striatal serotonin depletions, striatal serotonin transporter reductions, and hyperthermia. At the doses tested, AC927 itself had no significant effects on serotonin levels, serotonin transporter expression, or body temperature. To evaluate the effects of higher ambient temperature on methamphetamine-induced neurotoxicity, groups of mice were treated at 37 °C. Overall, there was an inverse correlation between the body temperature of the animals and striatal serotonin levels. Together, the data suggest that AC927 (10 mg/kg) protects against methamphetamine-induced neurotoxicity. The reduction of methamphetamine-induced hyperthermia by AC927 may contribute to the observed neuroprotection in vivo.

Antiproliferative activity of phenylbutyrate ester of haloperidol metabolite II [(±)-MRJF4] in prostate cancer cells

Complex mechanisms of prostate cancer progression prompt to novel therapeutic strategies concerning a combination of drugs or of single molecules able to interact with more crucial targets. Histone deacetylase inhibitors and sigma ligands with mixed σ(1) antagonist and σ(2) agonist properties were proposed as new potential tools for treatment of prostate cancer. (±)-MRJF4 was synthesized as phenylbutyrate ester of haloperidol metabolite II, which is a molecule consisting of a histone deacetilase inhibitor (4-phenylbutyric acid) and a sigma ligand (haloperidol metabolite II). Antiproliferatives activities of 4-phenylbutyric acid, haloperidol metabolite II, equimolar mixture of both compounds and (±)-MRJF4 were evaluated in vitro on LNCaP and PC3 prostate cancer cells. Preliminary binding studies of (±)-MRJF4 for σ(1), σ(2), D(2) and D(3) receptors and inhibition HDAC activity were reported. MTT cell viability assays highlighted a notable increase of antiproliferative activity of (±)-MRJF4 (IC(50) = 11 and 13 μM for LNCaP and PC3, respectively) compared to 4-phenylbutyric acid, haloperidol metabolite II and the respective equimolar pharmacological association. (±)-MRJF4 was also used in combination with σ(1) agonist (+)-pentazocine and σ(2) antagonist AC927 in order to evaluate the role of σ receptor subtypes in prostate cancer cell death.

The effect of the pyridyl nitrogen position in pyridylpiperazine sigma ligands

A series of pyridylpiperazines was synthesized and analyzed for sigma receptor binding affinity to determine the optimal pyridyl nitrogen position and chain length for the sigma(1) and sigma(2) receptor recognition. The (3-pyridyl)piperazines and (4-pyridyl)piperazines favor sigma(1) receptors, while previously studied (2-pyridyl)piperazines favor sigma(2) receptors.

Regulation of sigma-1 receptors and endoplasmic reticulum chaperones in the brain of methamphetamine self-administering rats

sigma-1 Receptors are endoplasmic reticulum (ER) chaperones that are implicated in the neuroplasticity associated with psychostimulant abuse. We immunocytochemically examined the distribution of sigma-1 receptors in the brain of drug-naive rats and then examined the dynamics of sigma-1 receptors and other ER chaperones in specific brain subregions of rats that self-administered methamphetamine, received methamphetamine passively, or received only saline injections. sigma-1 Receptors were found to be expressed in moderate to high levels in the olfactory bulb, striatum, nucleus accumbens shell, olfactory tubercle, amygdala, hippocampus, red nucleus, ventral tegmental area, substantia nigra, and locus ceruleus. Methamphetamine, whether self-administered or passively received, significantly elevated ER chaperones including the sigma-1 receptor, BiP, and calreticulin in the ventral tegmental area and substantia nigra. In the olfactory bulb, however, only the sigma-1 receptor chaperone was increased, and this increase occurred only in rats that actively self-administered methamphetamine. Consistent with an increase in sigma-1 receptors, extracellular signal-regulated kinase was found to be activated and protein kinase A attenuated in the olfactory bulb of methamphetamine self-administering rats. sigma-1 Receptors in the olfactory bulb were found to be colocalized with dopamine D1 receptors. These results indicate that methamphetamine induces ER stress in the ventral tegmental area and substantia nigra in rats whether the drug is received actively or passively. However, the changes seen only in rats that actively self-administered methamphetamine suggest that D1 and sigma-1 receptors in the olfactory bulb might play an important role in the motivational conditioning/learning aspects of methamphetamine self-administration in the rat.

A novel substituted piperazine, CM156, attenuates the stimulant and toxic effects of cocaine in mice

Cocaine is a highly abused drug without effective pharmacotherapies to treat it. It interacts with sigma (sigma) receptors, providing logical targets for the development of medications to counteract its actions. Cocaine causes toxic and stimulant effects that can be categorized as acute effects such as convulsions and locomotor hyperactivity and subchronic effects including sensitization and place conditioning. In the present study, 3-(4-(4-cyclohexylpiperazin-1-yl)butyl)benzo[d]thiazole-2(3H)-thione (CM156), a novel compound, was developed and tested for interactions with sigma receptors using radioligand binding studies. It was also evaluated against cocaine-induced effects in behavioral studies. The results showed that CM156 has nanomolar affinities for each of the sigma receptor subtypes in the brain and much weaker affinities for non-sigma binding sites. Pretreatment of male Swiss-Webster mice with CM156, before administering either a convulsive or locomotor stimulant dose of cocaine, led to a significant attenuation of these acute effects. CM156 also significantly reduced the expression of behavioral sensitization and place conditioning evoked by subchronic exposure to cocaine. The protective effects of CM156 are consistent with sigma receptor-mediated actions. Together with previously reported findings, the data from CM156 and related sigma compounds indicate that sigma receptors can be targeted to alleviate deleterious actions of cocaine.