Role of tumor necrosis factor-alpha in methamphetamine-induced drug dependence and neurotoxicity

Dose-Ranging Effects of the Intracerebral Administration of Atsttrin in Experimental Model of Parkinson's Disease Induced by 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in Mice

Parkinson's disease is one of the most common neurodegenerative disorders characterized by a multitude of motor and non-motor clinical symptoms resulting from the progressive and long-lasting abnormal loss of nigrostriatal dopaminergic neurons. Currently, the available treatments for patients with Parkinson's disease are limited and exert only symptomatic effects, without adequate signs of delaying or stopping the progression of the disease. Atsttrin constitutes the bioengineered protein which ultrastructure is based on the polypeptide chain frame of the progranulin (PGRN), which exerts anti-inflammatory effects through the inhibition of TNFα. The conducted preclinical studies suggest that the therapeutic implementation of Atsttrin may be potentially effective in the treatment of neurodegenerative diseases that are associated with the occurrence of neuroinflammatory processes. The aim of the proposed study was to investigate the effect of direct bilateral intracerebral administration of Atsttrin using stereotactic methods in the preclinical C57BL/6 mouse model of Parkinson's disease inducted by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. The analysis of the dose dependency effects of the increasing doses of Atsttrin has covered a number of parameters and markers regarding neurodegenerative processes and inflammatory responses including IL-1α, TNFα, IL-6, TH, and TG2 mRNA expressions. Accordingly, the evaluation of the changes in the neurochemical profile included DA, DOPAC, 3-MT, HVA, NA, MHPG, 5-HT, and 5-HIAA concentration levels. The intracerebral administration of Atsttrin into the striatum effectively attenuated the neuroinflammatory reaction in evaluated neuroanatomical structures. Furthermore, the partial restoration of monoamine content and its metabolic turnover were observed. In this case, taking into account the previously described pharmacokinetic profile and extrapolated bioavailability as well as the stability characteristics of Atsttrin, an attempt was made to describe as precisely as possible the quantitative and qualitative effects of increasing doses of the compound within the brain tissue microenvironment in the presented preclinical model of the disease. Collectively, this findings demonstrated that the intracerebral administration of Atsttrin may represent a potential novel therapeutic method for the treatment of Parkinson's disease.

Human Immunodeficiency Virus-Human Pegivirus Coinfected Individuals Display Functional Mucosal-Associated Invariant T Cells and Follicular T Cells Irrespective of PD-1 Expression

Human pegivirus (HPgV) appears to alter the prognosis of HIV disease by modulating T cell homeostasis, chemokine/cytokine production, and T cell activation. In this study, we evaluated if HPgV had any 'favorable' impact on the quantity and quality of T cells in HIV-infected individuals. T cell subsets such as CD4lo, CD4hi, and CD8+ T cells, CD4+ MAIT cells, CD8+ MAIT cells, follicular helper T (TFH) cells, and follicular cytotoxic T (TFC) cells were characterized based on the expression of markers associated with immune activation (CD69, ICOS), proliferation (ki67), cytokine production (TNF-α, IFN-γ), and exhaustion (PD-1). HIV+HPgV+ individuals had lower transaminase SGOT (liver) and GGT (biliary) in the plasma than those who were HPgV-. HIV/HPgV coinfection was significantly associated with increased absolute CD4+ T cell counts. HIV+HPgV+ and HIV+HPgV- individuals had highly activated T cell subsets with high expression of CD69 and ICOS on bulk CD4+ and CD8+ T cells, CD4+ MAIT cells, CD8+ MAIT cells, and CXCR5+CD4+ T cells and CXCR5+CD8+ T cells compared with healthy controls. Irrespective of immune activation markers, these cells also displayed higher levels of PD-1 on CD4+ T and CD8+ T cells . Exploring effector functionality based on mitogen stimulation demonstrated increased cytokine production by CD4+ MAIT and CD8+ MAIT cells. Decrease in absolute CD4+ T cell counts correlated positively with intracellular IFN-γ levels by CD4lo T cells, whereas increase of the same correlated negatively with TNF-α in the CD4lo T cells of HIV+HPgV+ individuals. HIV/HPgV coinfected individuals display functional CD4+ and CD8+ MAIT, TFH, and TFC cells irrespective of PD-1 expression.

Injecting drug use and hepatitis C virus infection independently increase biomarkers of inflammatory disease risk which are incompletely restored by curative direct-acting antiviral therapy

Background

Hepatitis C virus (HCV) infections are more prevalent in people who inject drugs (PWID) who often experience additional health risks. HCV induces inflammation and immune alterations that contribute to hepatic and non-hepatic morbidities. It remains unclear whether curative direct acting antiviral (DAA) therapy completely reverses immune alterations in PWID.

Methods

Plasma biomarkers of immune activation associated with chronic disease risk were measured in HCV-seronegative (n=24) and HCV RNA+ (n=32) PWID at baseline and longitudinally after DAA therapy. Adjusted generalised estimating equations were used to assess longitudinal changes in biomarker levels. Comparisons between community controls (n=29) and HCV-seronegative PWID were made using adjusted multiple regression modelling.

Results

HCV-seronegative PWID exhibited significantly increased levels of inflammatory biomarkers including soluble (s) TNF-RII, IL-6, sCD14 and sCD163 and the diabetes index HbA1c as compared to community controls. CXCL10, sTNF-RII, vascular cell adhesion molecule-1 and lipopolysaccharide binding protein (LBP) were additionally elevated in PWID with viremic HCV infection as compared to HCV- PWID. Whilst curative DAA therapy reversed some biomarkers, others including LBP and sTNF-RII remained elevated 48 weeks after HCV cure.

Conclusion

Elevated levels of inflammatory and chronic disease biomarkers in PWID suggest an increased risk of chronic morbidities such as diabetes and cardiovascular disease. HCV infection in PWID poses an additional disease burden, amplified by the incomplete reversal of immune dysfunction following DAA therapy. These findings highlight the need for heightened clinical surveillance of PWID for chronic inflammatory diseases, particularly those with a history of HCV infection.

Interleukin-6 and tumor necrosis factor-α attenuate dopamine release in mice fed a high-fat diet, but not medium or low-fat diets

Chronic low-grade inflammation is associated with a state of diet-induced obesity that impacts systemic tissues and can cross the blood-brain barrier to act directly on the brain. The extent to which pro-inflammatory cytokines released in these conditions affect dopamine presynaptic neurotransmission has not been previously investigated. The purpose of this study was to examine how dopamine terminals are affected by pro-inflammatory cytokines, and to determine if dietary fat consumption potentiates cytokine effects on dopamine release and reuptake rate in the nucleus accumbens (NAc). Male and female C57BL/6J mice were fed high, medium, or low-fat diets (60%, 30%, or 10% total kcals from fat, respectively) for six weeks. Fast scan cyclic voltammetry (FSCV) was used to measure dopamine release and reuptake rate in the NAc core from ex vivo coronal brain slices. Electrically evoked dopamine release and the maximal rate of dopamine reuptake (Vmax) were significantly lower in mice fed the 30% and 60% high-fat diets compared to the 10% low-fat group (p < 0.05). IL-6 5 or 10 nM or TNFα 30 or 300 nM was added to artificial cerebrospinal fluid (aCSF) bathed over brain slices during FSCV. No effect on dopamine release or Vmax was observed with lower concentrations. However, 10 nM IL-6 and 300 nM TNFα significantly reduced dopamine release in the 60% fat group (p < 0.05). No effect of added cytokine was observed on Vmax. Overall, these data provide evidence that dietary fat increases neural responsiveness to cytokines, which may help inform comorbidities between diet-induced obesity and depression or other mood disorders.

Inflammation, Dopaminergic Brain and Bilirubin

Dopamine is a well-known neurotransmitter due to its involvement in Parkinson's disease (PD). Dopamine is not only involved in PD but also controls multiple mental and physical activities, such as the pleasure of food, friends and loved ones, music, art, mood, cognition, motivation, fear, affective disorders, addiction, attention deficit disorder, depression, and schizophrenia. Dopaminergic neurons (DOPAn) are susceptible to stressors, and inflammation is a recognized risk for neuronal malfunctioning and cell death in major neurodegenerative diseases. Less is known for non-neurodegenerative conditions. Among the endogenous defenses, bilirubin, a heme metabolite, has been shown to possess important anti-inflammatory activity and, most importantly, to prevent DOPAn demise in an ex vivo model of PD by acting on the tumor necrosis factor-alpha (TNFα). This review summarizes the evidence linking DOPAn, inflammation (when possible, specifically TNFα), and bilirubin as an anti-inflammatory in order to understand what is known, the gaps that need filling, and the hypotheses of anti-inflammatory strategies to preserve dopamine homeostasis with bilirubin included.

Crosstalk between Mu-Opioid receptors and neuroinflammation: Consequences for drug addiction and pain

Mu-Opioid Receptors (MORs) are well-known for participating in analgesia, sedation, drug addiction, and other physiological functions. Although MORs have been related to neuroinflammation their biological mechanism remains unclear. It is suggested that MORs work alongside Toll-Like Receptors to enhance the release of pro-inflammatory mediators and cytokines during pathological conditions. Some cytokines, including TNF-α, IL-1β and IL-6, have been postulated to regulate MORs levels by both avoiding MOR recycling and enhancing its production. In addition, Neurokinin-1 Receptor, also affected during neuroinflammation, could be regulating MOR trafficking. Therefore, inflammation in the central nervous system seems to be associated with altered/increased MORs expression, which might regulate harmful processes, such as drug addiction and pain. Here, we provide a critical evaluation on MORs' role during neuroinflammation and its implication for these conditions. Understanding MORs' functioning, their regulation and implications on drug addiction and pain may help elucidate their potential therapeutic use against these pathological conditions and associated disorders.

Role of Microglia in Psychostimulant Addiction

The use of psychostimulant drugs can modify brain function by inducing changes in the reward system, mainly due to alterations in dopaminergic and glutamatergic transmissions in the mesocorticolimbic pathway. However, the etiopathogenesis of addiction is a much more complex process. Previous data have suggested that microglia and other immune cells are involved in events associated with neuroplasticity and memory, which are phenomena that also occur in addiction. Nevertheless, how dependent is the development of addiction on the activity of these cells? Although the mechanisms are not known, some pathways may be involved. Recent data have shown psychoactive substances may act directly on immune cells, alter their functions and induce various inflammatory mediators that modulate synaptic activity. These could, in turn, be involved in the pathological alterations that occur in substance use disorder. Here, we extensively review the studies demonstrating how cocaine and amphetamines modulate microglial number, morphology, and function. We also describe the effect of these substances in the production of inflammatory mediators and a possible involvement of some molecular signaling pathways, such as the toll-like receptor 4. Although the literature in this field is scarce, this review compiles the knowledge on the neuroimmune axis that is involved in the pathogenesis of addiction, and suggests some pharmacological targets for the development of pharmacotherapy.

Stress- and drug-induced neuroimmune signaling as a therapeutic target for comorbid anxiety and substance use disorders

Stress and substance use disorders remain two of the most highly prevalent psychiatric conditions and are often comorbid. While individually these conditions have a debilitating impact on the patient and a high cost to society, the symptomology and treatment outcomes are further exacerbated when they occur together. As such, there are few effective treatment options for these patients, and recent investigation has sought to determine the neural processes underlying the co-occurrence of these disorders to identify novel treatment targets. One such mechanism that has been linked to stress- and addiction-related conditions is neuroimmune signaling. Increases in inflammatory factors across the brain have been heavily implicated in the etiology of these disorders, and this review seeks to determine the nature of this relationship. According to the "dual-hit" hypothesis, also referred to as neuroimmune priming, prior exposure to either stress or drugs of abuse can sensitize the neuroimmune system to be hyperresponsive when exposed to these insults in the future. This review completes an examination of the literature surrounding stress-induced increases in inflammation across clinical and preclinical studies along with a summarization of the evidence regarding drug-induced alterations in inflammatory factors. These changes in neuroimmune profiles are also discussed within the context of their impact on the neural circuitry responsible for stress responsiveness and addictive behaviors. Further, this review explores the connection between neuroimmune signaling and susceptibility to these conditions and highlights the anti-inflammatory pharmacotherapies that may be used for the treatment of stress and substance use disorders.

Methamphetamine Induces Systemic Inflammation and Anxiety: The Role of the Gut–Immune–Brain Axis

Methamphetamine (METH) is a highly addictive drug abused by millions of users worldwide, thus becoming a global health concern with limited management options. The inefficiency of existing treatment methods has driven research into understanding the mechanisms underlying METH-induced disorders and finding effective treatments. This study aims to understand the complex interactions of the gastrointestinal–immune–nervous systems following an acute METH dose administration as one of the potential underlying molecular mechanisms concentrating on the impact of METH abuse on gut permeability. Findings showed a decreased expression of tight junction proteins ZO-1 and EpCAm in intestinal tissue and the presence of FABP-1 in sera of METH treated mice suggests intestinal wall disruption. The increased presence of CD45+ immune cells in the intestinal wall further confirms gut wall inflammation/disruption. In the brain, the expression of inflammatory markers Ccl2, Cxcl1, IL-1β, TMEM119, and the presence of albumin were higher in METH mice compared to shams, suggesting METH-induced blood–brain barrier disruption. In the spleen, cellular and gene changes are also noted. In addition, mice treated with an acute dose of METH showed anxious behavior in dark and light, open field, and elevated maze tests compared to sham controls. The findings on METH-induced inflammation and anxiety may provide opportunities to develop effective treatments for METH addiction in the future.

A review of basic to clinical studies of the association between hyperammonemia, methamphetamine

Methamphetamine (METH), an addictive psychostimulant drug, is the second most widely used type of drug all around the world. METH abusers are more likely to develop a psycho-neurological complication. Hyperammonemia (HAM) causes neuropsychiatric illnesses such as mental state changes and episodes of acute encephalopathy. Recently, there are some shreds of evidence about the relationship between METH complication and HAM. Both METH intoxication and HAM could induce psychosis, agitation, memory impairment, and psycho-neuronal disorders. They also have similar mechanisms of neuronal damages, such as excitotoxicity, oxidative stress, mitochondrial impairments, and inflammation responses, which can subsequently increase the glutamate level of the brain. Hence, the basic to clinical studies of the association between HAM and METH are reviewed by monitoring six case studies and a good body of animal studies literature. All instances of METH-associated HAM had changes in mental state and some level of confusion that were improved when the ammonia serum level returned to the normal level. Furthermore, most of them had typical vital signs. Several studies suggested some sources for METH-associated HAM, including METH-induced liver and renal damages, muscular hyperactivity, gut bacterial overgrowth, co-abuse of other substances, and using some forms of NH3 in METH cooking. In conclusion, it seems that mental status changes in METH abusers may be related to ammonia intoxication or HAM; therefore, it is important to assess the serum level of ammonia in METH intoxicated patients and resolve it.

The Crosstalk Between Neurons and Glia in Methamphetamine-Induced Neuroinflammation

Methamphetamine (METH), an illicit psycho-stimulant, is widely known as an addictive drug that may cause neurotoxic effects. Previous researches on METH abuse have mainly focused on neurotransmitters, such as dopamine and glutamate. However, there is growing evidence that neuroinflammation also plays an important role in the etiology and pathophysiology of brain dysfunction induced by METH abuse. This has cast a spotlight on the research of microglia and astrocyte, which are critical mediators of neuroimmune pathology in recent years. In the central nervous system (CNS) immunity, abnormalities of the microglia and astrocytes have been observed in METH abusers from both postmortem and preclinical studies. The bidirectional communication between neurons and glia is essential for the homeostasis and biological function of the CNS while activation of glia induces the release of cytokines and chemokines during pathological conditions, which will affect the neuron-glia interactions and lead to adverse behavioral consequences. However, the underlying mechanisms of interaction between neurons and glia in METH-induced neuroinflammation remain elusive. Notably, discovering and further understanding glial activity and functions, as well as the crosstalk between neurons and glia may help to explain the pathogenesis of METH abuse and behavioral changes in abusers. In this review, we will discuss the current understanding of the crosstalk between neurons and glia in METH-induced neuroinflammation. We also review the existing microglia-astrocyte interaction under METH exposure. We hope the present review will lead the way for more studies on the development of new therapeutic strategies for METH abuse in the near future.

Toll-Like Receptor 4: A Novel Target to Tackle Drug Addiction?

Drug addiction is a chronic brain disease characterized by compulsive drug-seeking and drug-taking behaviors despite the major negative consequences. Current well-established neuronal underpinnings of drug addiction have promoted the substantial progress in understanding this disorder. However, non-neuronal mechanisms of drug addiction have long been underestimated. Fortunately, increased evidence indicates that neuroimmune system, especially Toll-like receptor 4 (TLR4) signaling, plays an important role in the different stages of drug addiction. Drugs like opioids, psychostimulants, and alcohol activate TLR4 signaling and enhance the proinflammatory response, which is associated with drug reward-related behaviors. While extensive studies have shown that inhibition of TLR4 attenuated drug-related responses, there are conflicting findings implicating that TLR4 signaling may not be essential to drug addiction. In this chapter, preclinical and clinical studies will be discussed to further evaluate whether TLR4-based neuroimmune pharmacotherapy can be used to treat drug addiction. Furthermore, the possible mechanisms underlying the effects of TLR4 inhibition in modulating drug-related behaviors will also be discussed.

Astrocyte-derived TNF and glutamate critically modulate microglia activation by methamphetamine

Methamphetamine (Meth) is a powerful illicit psychostimulant, widely used for recreational purposes. Besides disrupting the monoaminergic system and promoting oxidative brain damage, Meth also causes neuroinflammation, contributing to synaptic dysfunction and behavioral deficits. Aberrant activation of microglia, the largest myeloid cell population in the brain, is a common feature in neurological disorders triggered by neuroinflammation. In this study, we investigated the mechanisms underlying the aberrant activation of microglia elicited by Meth in the adult mouse brain. We found that binge Meth exposure caused microgliosis and disrupted risk assessment behavior (a feature that usually occurs in individuals who abuse Meth), both of which required astrocyte-to-microglia crosstalk. Mechanistically, Meth triggered a detrimental increase of glutamate exocytosis from astrocytes (in a process dependent on TNF production and calcium mobilization), promoting microglial expansion and reactivity. Ablating TNF production, or suppressing astrocytic calcium mobilization, prevented Meth-elicited microglia reactivity and re-established risk assessment behavior as tested by elevated plus maze (EPM). Overall, our data indicate that glial crosstalk is critical to relay alterations caused by acute Meth exposure.

Possible repair mechanisms of renin-angiotensin system inhibitors, matrix metalloproteinase-9 inhibitors and protein hormones on methamphetamine-induced neurotoxicity

Methamphetamine is a highly addictive central stimulant with extensive and strong neurotoxicity. The neurotoxicity of methamphetamine is closely related to the imbalance of dopamine levels and the destruction of the blood-brain barrier. An increase in dopamine may induce adverse effects such as behavioral sensitization and excessive locomotion. Damage to the blood-brain barrier can cause toxic or harmful substances to leak to the central nervous system, leading to neurotoxicity. The renin-angiotensin system is essential for the regulation of dopamine levels in the brain. Matrix metalloproteinase-9 causes reward effects and behavioral sensitization by inducing dopamine release. Prolactin has been shown to be involved in the regulation of tight junction proteins and the integrity of the blood-brain barrier. At present, the treatment of methamphetamine detoxification is still based on psychotherapy, and there is no specific medicine. With the rapid increase in global seizures of methamphetamine, the treatment of its toxicity has attracted more and more attention. This review intends to summarize the therapeutic mechanisms of renin-angiotensin inhibitors, matrix metalloproteinase-9 inhibitors and protein hormones (prolactin) on methamphetamine neurotoxicity. The repair effects of these three on methamphetamine may be related to the maintenance of brain dopamine balance and the integrity of the blood-brain barrier. This review is expected to provide the new therapeutic strategy of methamphetamine toxicity.

The Relationships between HIV-1 Infection, History of Methamphetamine Use Disorder, and Soluble Biomarkers in Blood and Cerebrospinal Fluid

Methamphetamine (METH) use disorder is highly prevalent among people with HIV (PWH) and is a significant public health problem. HIV and METH use are each associated with immune system dysfunction; however, the combined effects on the immune system are poorly understood. This cross-sectional project measured soluble immune biomarkers in plasma and cerebrospinal fluid (CSF) collected from a control group, people with a history of a METH use disorder (METH+), PWH with no history of METH use disorder (HIV+), and PWH with a history of METH use disorder (HIV+/METH+). HIV, METH, and immune dysfunction can also be associated with affective and cognitive deficits, so we characterized mood and cognition in our participants. Two factor analyses were performed for the plasma and CSF biomarkers. Plasma IL-8, Ccl2, VEGF, and 8-isoprostane loaded onto one factor that was highest in the HIV+/METH+ group (p < 0.047) reflecting worse inflammation, vascular injury, and oxidative stress. This plasma factor was also negatively correlated with delayed recall (R = -0.49, p = 0.010), which was worst in the HIV+/METH+ group (p = 0.030 compared to the control group). Overall, these data implicate that combined HIV-1 infection and METH use may exacerbate inflammation, leading to worse cognition.

Methamphetamine leads to the alterations of microRNA profiles in the nucleus accumbens of rats

CONTEXT

MicroRNA (miRNA) is an important regulator of gene expression. Methamphetamine (METH) induces a variety of alterations in different systems by affecting gene expression, but the effects of METH on miRNA profiles need to be elucidated.

OBJECTIVES

This study develops a rat model of METH addiction, and analyzes the expression profile alterations of miRNA in nucleus accumbens (NAc) of the METH-addicted rats.

MATERIALS AND METHODS

Sprague-Dawley rats were administered 10 mg/kg METH or vehicle twice a day for 4 weeks. The addictive behaviour of rats was estimated by CPP test. The pathological changes of brain tissues were then observed by HE and Glee silver staining. The miRNA profile analysis of the NAc of the rats was performed using an Illumina HiSeq™ 2500 sequencing system.

RESULTS

CPP test indicated that METH significantly prolonged the residence time of the rats in the drug box (from 307 ± 97 to 592 ± 96 s). The pathological staining showed the distorted axons, and fewer polarized neurons in the METH-treated rats. We further identified 40 differential miRNAs (17 up- and 23 down-regulated) and three novel miRNAs (novel 237, 296 and 501) that responded to METH. The bioinformatic analysis for the potential targets of the differential miRNA suggests that the downstream were concentrated in the Wnt signalling pathway, tuberculosis, toxoplasmosis, spliceosome, lysosome, and axon guidance.

DISCUSSION AND CONCLUSIONS

A number of miRNAs responding to METH were identified in the NAc of rats. These METH-regulated miRNAs provide a new perspective for revealing the molecular mechanisms of METH addiction.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Association between TNF-alpha polymorphism and the age of first suicide attempt in chronic patients with schizophrenia

Patients with schizophrenia (SCZ) exhibit higher suicide rates than the general population. However, the molecular mechanism remains poorly understood. Tumor necrosis factor (TNF)-alpha polymorphisms have been repeatedly indicated to play a pathogenetic role in various mental disorders, but none of these studies focused on the susceptibility to suicidal behavior in SCZ. We recruited 1087 chronic inpatients with SCZ and 576 controls to assess the psychopathological symptoms of SCZ using the Positive and Negative Syndrome Scale scales. We selected 2 polymorphisms (-308G>A and -1031C>T) in the TNF-alpha gene and analyzed their associations with SCZ and suicide. Our results showed that TNF-alpha -308G>A and -1031C>T were not related to SCZ and suicide. However, we found that suicide attempters with the C allele carriers exhibited suicidal behaviors significantly later than those with TT genotype in the SCZ patients. The haplotype containing the T allele of the -1031 was significantly associated with the age of suicide initiation. Further logistic regression analysis showed that -1031C>T interacted with psychopathological symptoms and drinking, age of smoking, and related to the initiation age of suicide attempts. Our study demonstrated that the TNF-alpha variants may affect the age at which suicide attempts started among SCZ suicide attempters.

The effects of acute and repeated methylenedioxypyrovalerone (MDPV) administration on striatal transcriptome networks in male long evans rats

The psychoactive drug methylenedioxypyrovalerone (MDPV) elicits feelings of euphoria and hyperexcitability, but can also result in paranoia, agitation, and depression by unknown mechanisms. We identified molecular networks in the rat striatum that were affected by single or repeated exposure to MDPV. Male Long Evans rats were injected with either saline or MDPV (1 mg/kg) (single or repeated MDPV) over 5 days. To distinguish the effects of repeated MDPV from a single exposure, an additional group received saline over 4 days and then MDPV on the 5th day. Twenty-four hours after the final injection, the left dorsal striatum was processed for transcriptomics. The transcriptome response was subtle after 24 h, and a single gene passed an FDR correction (LOC103691845) following repeated MDPV treatment. Gene set and subnetwork enrichment analyses were conducted to improve data interpretation from a network perspective. Consistent with the mode of action of MDPV, networks related to the nigrostriatal dopaminergic system were altered in the rat striatum. Transcriptional networks related to cognition, short and long-term memory, and synaptic transmission were over-represented in the striatum of rats repeatedly injected with MDPV. This study identifies potential transcriptional networks altered by single or repeated MDPV exposure, which can be interrogated further to elucidate molecular mechanisms underlying cathinone abuse.

Methamphetamine Activates Toll-Like Receptor 4 to Induce Central Immune Signaling within the Ventral Tegmental Area and Contributes to Extracellular Dopamine Increase in the Nucleus Accumbens Shell

Methamphetamine (METH) is a globally abused, highly addictive stimulant. While investigations of the rewarding and motivational effects of METH have focused on neuronal actions, increasing evidence suggests that METH can also target microglia, the innate immune cells of the central nervous system, causing release of proinflammatory mediators and therefore amplifying the reward changes in the neuronal activity induced by METH. However, how METH induces neuroinflammatory responses within the central nervous system (CNS) is unknown. Herein, we provide direct evidence that METH creates neuroinflammation, at least in part, via the activation of the innate immune Toll-like receptor 4 (TLR4). Biophysical studies revealed that METH bound to MD-2, the key coreceptor of TLR4. Molecular dynamics simulations showed METH binding stabilized the active heterotetramer (TLR4/MD-2)₂ conformation. Classic TLR4 antagonists LPS-RS and TAK-242 attenuated METH induced NF-κB activation of microglia, whereas added MD-2 protein boosted METH-induced NF-κB activation. Systemically administered METH (1 mg/kg) was found to specifically up-regulate expression of both CD11b (microglial activation marker) and the proinflammatory cytokine interleukin 6 (IL-6) mRNAs in the ventral tegmental area (VTA), but not in either the nucleus accumbens shell (NAc) or prefrontal cortex (PFC). Systemic administration of a nonopioid, blood-brain barrier permeable TLR4 antagonist (+)-naloxone inhibited METH-induced activation of microglia and IL-6 mRNA overexpression in VTA. METH was found to increase conditioned place preference (CPP) as well as extracellular dopamine concentrations in the NAc, with both effects suppressed by the nonopioid TLR4 antagonist (+)-naloxone. Furthermore, intra-VTA injection of LPS-RS or IL-6 neutralizing antibody suppressed METH-induced elevation of extracellular NAc dopamine. Taken together, this series of studies demonstrate that METH-induced neuroinflammation is, at least in part, mediated by TLR4-IL6 signaling within the VTA, which has the downstream effect of elevating dopamine in the NAc shell. These results provide a novel understanding of the neurobiological mechanisms underlying acute METH reward that includes a critical role for central immune signaling and offers a new target for medication development for treating drug abuse.

Glial regulation of synaptic function in models of addiction

The glial regulation of synaptic function provides important modulation of the synaptic and behavioral changes induced by drugs of abuse. In some cases, this regulation is adaptive, reducing drug-induced change, and in other cases maladaptive, contributing to the induction or maintenance of these changes. Understanding the contribution of glia to addictive behaviors will be important to fully understand the development of addiction, and a critical entry into methods to potentially mitigate this affliction. This review will cover recent advances in elucidating the contribution of the major types of glia - microglia and astrocytes - to drug-induced synaptic plasticity.

The Main Molecular Mechanisms Underlying Methamphetamine- Induced Neurotoxicity and Implications for Pharmacological Treatment

Methamphetamine (METH) is a popular new-type psychostimulant drug with complicated neurotoxicity. In spite of mounting evidence on METH-induced damage of neural cell, the accurate mechanism of toxic effect of the drug on central nervous system (CNS) has not yet been completely deciphered. Besides, effective treatment strategies toward METH neurotoxicity remain scarce and more efficacious drugs are to be developed. In this review, we summarize cellular and molecular bases that might contribute to METH-elicited neurotoxicity, which mainly include oxidative stress, excitotoxicity, and neuroinflammation. We also discuss some drugs that protect neural cells suffering from METH-induced neurotoxic consequences. We hope more in-depth investigations of exact details that how METH produces toxicity in CNS could be carried out in future and the development of new drugs as natural compounds and immunotherapies, including clinic trials, are expected.

Inflammasome Activation by Methamphetamine Potentiates Lipopolysaccharide Stimulation of IL-1β Production in Microglia

Methamphetamine (Meth) is an addictive psychostimulant abused worldwide. Ample evidence indicate that chronic abuse of Meth induces neurotoxicity via microglia-associated neuroinflammation and the activated microglia present in both Meth-administered animals and human abusers. The development of anti-neuroinflammation as a therapeutic strategy against Meth dependence promotes research to identify inflammatory pathways that are specifically tied to Meth-induced neurotoxicity. Currently, the exact mechanisms for Meth-induced microglia activation are largely unknown. NLRP3 is a well-studied cytosolic pattern recognition receptor (PRR), which promotes the assembly of the inflammasome in response to the danger-associated molecular patterns (DAMPs). It is our hypothesis that Meth activates NLRP3 inflammasome in microglia and promotes the processing and release of interleukin (IL)-1β, resulting in neurotoxic activity. To test this hypothesis, we studied the effects of Meth on IL-1β maturation and release from rat cortical microglial cultures. Incubation of microglia with physiologically relevant concentrations of Meth after lipopolysaccharide (LPS) priming produced an enhancement on IL-1β maturation and release. Meth treatment potentiated aggregation of inflammasome adaptor apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), induced activation of the IL-1β converting enzyme caspase-1 and produced lysosomal and mitochondrial impairment. Blockade of capase-1 activity, lysosomal cathepsin B activity or mitochondrial ROS production by their specific inhibitors reversed the effects of Meth, demonstrating an involvement of inflammasome in Meth-induced microglia activation. Taken together, our results suggest that Meth triggers microglial inflammasome activation in a manner dependent on both mitochondrial and lysosomal danger-signaling pathways.

PKCδ-dependent p47phox activation mediates methamphetamine-induced dopaminergic neurotoxicity

Protein kinase C (PKC) has been recognized to activate NADPH oxidase (PHOX). However, the interaction between PKC and PHOX in vivo remains elusive. Treatment with methamphetamine (MA) resulted in a selective increase in PKCδ expression out of PKC isoforms. PKCδ co-immunoprecipitated with p47phox, and facilitated phosphorylation and membrane translocation of p47phox. MA-induced increases in PHOX activity and reactive oxygen species were attenuated by knockout of p47phox or PKCδ. In addition, MA-induced impairments in the Nrf-2-related glutathione synthetic system were also mitigated by knockout of p47phox or PKCδ. Glutathione-immunoreactivity was co-localized in Iba-1-labeled microglial cells and in NeuN-labeled neurons, but not in GFAP-labeled astrocytes, reflecting the necessity for self-protection against oxidative stress by mainly microglia. Buthionine-sulfoximine, an inhibitor of glutathione biosynthesis, potentiated microglial activation and pro-apoptotic changes, leading to dopaminergic losses. These neurotoxic processes were attenuated by rottlerin, a pharmacological inhibitor of PKCδ, genetic inhibitions of PKCδ [i.e., PKCδ knockout mice (KO) and PKCδ antisense oligonucleotide (ASO)], or genetic inhibition of p47phox (i.e., p47phox KO or p47phox ASO). Rottlerin did not exhibit any additive effects against the protective activity offered by genetic inhibition of p47phox. Therefore, we suggest that PKCδ is a critical regulator for p47phox activation induced by MA, and that Nrf-2-dependent GSH induction via inhibition of PKCδ or p47phox, is important for dopaminergic protection against MA insult.

Alpha-PVP induces the rewarding effect via activating dopaminergic neuron

A synthetic cathinone, 1-phenyl-2-(1-pyrrolidinyl)-1-pentanone (α-PVP), was occasionally found in the "bath salt" type of designer drugs, as an active ingredient. It has been reported that drivers who consumed α-PVP were in an excited state and incapable of controlling their behavior, causing traffic accidents. Despite its acute excitatory effects, there is no information on the psychological dependency elicited by α-PVP use. The purpose of the present study was to clarify whether the reward pathway is activated with repeated doses of α-PVP in experimental animals. Treatment of male C57BL/6j mice with α-PVP (25 mg/kg, i.p.), once a day, for 3 days significantly increased the conditioned place preference scores. Therefore, repeated doses of α-PVP were shown to induce palatability in mice. α-PVP increases extracellular dopamine levels in the nucleus accumbens shell immediately after administration. The number of cells immunopositive for phosphorylated cAMP-regulatory element binding protein (CREB) was significantly increased in the α-PVP-treated mice in our study. These results indicate that the administration of α-PVP activates the phosphorylation of CREB in the nucleus accumbens shell. Our results suggest that α-PVP stimulates the reward pathway by increasing the extracellular dopamine levels and CREB phosphorylation in the nucleus accumbens shell, eventually causing positive reinforcement in mice.

Involvement of the accumbal osteopontin-interacting transmembrane protein 168 in methamphetamine-induced place preference and hyperlocomotion in mice

Chronic exposure to methamphetamine causes adaptive changes in brain, which underlie dependence symptoms. We have found that the transmembrane protein 168 (TMEM168) is overexpressed in the nucleus accumbens of mice upon repeated methamphetamine administration. Here, we firstly demonstrate the inhibitory effect of TMEM168 on methamphetamine-induced behavioral changes in mice, and attempt to elucidate the mechanism of this inhibition. We overexpressed TMEM168 in the nucleus accumbens of mice by using an adeno-associated virus vector (NAc-TMEM mice). Methamphetamine-induced hyperlocomotion and conditioned place preference were attenuated in NAc-TMEM mice. Additionally, methamphetamine-induced extracellular dopamine elevation was suppressed in the nucleus accumbens of NAc-TMEM mice. Next, we identified extracellular matrix protein osteopontin as an interacting partner of TMEM168, by conducting immunoprecipitation in cultured COS-7 cells. TMEM168 overexpression in COS-7 cells induced the enhancement of extracellular and intracellular osteopontin. Similarly, osteopontin enhancement was also observed in the nucleus accumbens of NAc-TMEM mice, in in vivo studies. Furthermore, the infusion of osteopontin proteins into the nucleus accumbens of mice was found to inhibit methamphetamine-induced hyperlocomotion and conditioned place preference. Our studies suggest that the TMEM168-regulated osteopontin system is a novel target pathway for the therapy of methamphetamine dependence, via regulating the dopaminergic function in the nucleus accumbens.

Adolescent stress leads to glutamatergic disturbance through dopaminergic abnormalities in the prefrontal cortex of genetically vulnerable mice

BACKGROUND

Stress during the adolescent period influences postnatal maturation and behavioral patterns in adulthood. Adolescent stress-induced molecular and functional changes in neurons are the key clinical features of psychiatric disorders including schizophrenia.

OBJECTIVE

In the present study, we exposed genetically vulnerable mice to isolation stress to examine the molecular changes in the glutamatergic system involving N-methyl-d-aspartate (NMDA) receptors via dopaminergic disturbance in the prefrontal cortex (PFc).

RESULTS

We report that late adolescent stress in combination with Disrupted-in-Schizophrenia 1 (DISC1) genetic risk elicited alterations in glutamatergic neurons in the PFc, such as increased expression of glutamate transporters, decreased extracellular levels of glutamate, decreased concentration of d-serine, and impaired activation of NMDA-Ca2+/calmodulin kinase II signaling. These changes resulted in behavioral deficits in locomotor activity, forced swim, social interaction, and novelty preference tests. The glutamatergic alterations in the PFc were prevented if the animals were treated with an atypical antipsychotic drug clozapine and a dopamine D1 agonist SKF81297, which suggests that the activation of dopaminergic neurons is involved in the regulation of the glutamatergic system.

CONCLUSION

Our results suggest that adolescent stress combined with dopaminergic abnormalities in the PFc of genetically vulnerable mice induces glutamatergic disturbances, which leads to behavioral deficits in the young adult stage.

Activation of TLR4/STAT3 signaling in VTA contributes to the acquisition and maintenance of morphine-induced conditioned place preference

Morphine, commonly used to relieve the acute or chronic pain, has a high potential for addiction and exerts rewarding effects via a critical role for mesolimbic dopamine system. Studies suggest that addiction-related behavior is highly associated with inflammatory immune response, but the mechanisms are poorly understood. The present study showed that intra-VTA microinjection of TLR4 antagonist LPS-RS prevented the acquisition and maintenance, but not the expression, of morphine-induced CPP in rats. In addition, chronic morphine treatment significantly activated STAT3 on day 6 and 11 in VTA, and bilateral microinjection of STAT3 inhibitor S3I-201 into the VTA suppressed the acquisition and maintenance of morphine-induced CPP in rats. Furthermore, local knockout of STAT3 by injection of the AAV-Cre-GFP into the VTA area of STAT3^flox/flox mice also significantly impaired the acquisition of morphine CPP. Importantly, the TLR4 expression is colocalized with p-STAT3-positive cell in VTA, and repeated injection of LPS-RS significantly attenuated the STAT3 activation in VTA induced by chronic morphine treatment. Collectively, these data suggest that TLR4/STAT3 signaling pathway in VTA might play a critical role in the acquisition and maintenance of morphine CPP, and provides new evidence that TLR4/STAT3 signaling pathway might be a potential target for treatment of morphine addiction.

Impact of chronic methamphetamine treatment on the atherosclerosis formation in ApoE-/- mice fed a high cholesterol diet

Background

We previously reported that methamphetamine could promote atherosclerosis (AS) in ApoE−/− mice fed normal chow. We herein observed the impact of methamphetamine on AS in ApoE−/− mice fed a high cholesterol diet and explored the potential mechanisms.

Results and Materials and Methods

Male ApoE−/− mice fed a high cholesterol diet were treated with saline (NS, n = 5) or methamphetamine [8 mg/kg/day (M8, n = 6) through intraperitoneal injection] for 24 weeks. Afterwards, the percentage area of atheromatous plaque in aortic root (44.31 ± 3.21% vs. 32.91 ± 3.58%, P < 0.01) and atherosclerotic lesion area on Oil red O stained en face aorta (32.74 ± 6.97% vs. 18.72 ± 3.65%, P < 0.01) were significantly higher in M8 group than in NS group. The percentages of Th1 cells and Th17 cells in spleen were significantly higher while the percentages of Th2 cells and CD4⁺CD25⁺Foxp3⁺ Tregs were significantly lower in M8 group than in NS group. mRNA expressions of TNF-α, IFN-γ, and IL-17 were significantly up-regulated, IL-4, IL-10, Foxp3, and TGF-β were significantly down-regulated in carotid artery and in spleen in M8 group compared to NS group.

Conclusions

Chronic methamphetamine treatment can enhance atherosclerotic plaque formation possibly through promoting proinflammatory cytokine secretions in ApoE−/− mice fed a high cholesterol diet.

Methamphetamine induces Shati/Nat8L expression in the mouse nucleus accumbens via CREB- and dopamine D1 receptor-dependent mechanism

Shati/Nat8L significantly increased in the nucleus accumbens (NAc) of mice after repeated methamphetamine (METH) treatment. We reported that Shati/Nat8L overexpression in mouse NAc attenuated METH-induced hyperlocomotion, locomotor sensitization, and conditioned place preference. We recently found that Shati/Nat8L overexpression in NAc regulates the dopaminergic neuronal system via the activation of group II mGluRs by elevated N-acetylaspartylglutamate following N-acetylaspartate increase due to the overexpression. These findings suggest that Shati/Nat8L suppresses METH-induced responses. However, the mechanism by which METH increases the Shati/Nat8L mRNA expression in NAc is unclear. To investigate the regulatory mechanism of Shati/Nat8L mRNA expression, we performed a mouse Shati/Nat8L luciferase assay using PC12 cells. Next, we investigated the response of METH to Shati/Nat8L expression and CREB activity using mouse brain slices of NAc, METH administration to mice, and western blotting for CREB activity of specific dopamine receptor signals in vivo and ex vivo. We found that METH activates CREB binding to the Shati/Nat8L promoter to induce the Shati/Nat8L mRNA expression. Furthermore, the dopamine D1 receptor antagonist SCH23390, but not the dopamine D2 receptor antagonist sulpiride, inhibited the upregulation of Shati/Nat8L and CREB activities in the mouse NAc slices. Thus, the administration of the dopamine D1 receptor agonist SKF38393 increased the Shati/Nat8L mRNA expression in mouse NAc. These results showed that the Shati/Nat8L mRNA was increased by METH-induced CREB pathway via dopamine D1 receptor signaling in mouse NAc. These findings may contribute to development of a clinical tool for METH addiction.

Role of astrocyte-synapse interactions in CNS disorders

Astrocytes comprise half of the cells in the brain. Although astrocytes have traditionally been described as playing a supportive role for neurons, they have recently been recognized as active participants in the development and plasticity of dendritic spines and synapses. Astrocytes can eliminate dendritic spines, induce synapse formation, and regulate neurotransmission and plasticity. Dendritic spine and synapse impairments are features of many neurological disorders, including autism spectrum disorder, schizophrenia, and Alzheimer's disease. In this review we will present evidence from multiple neurological disorders demonstrating that changes in astrocyte-synapse interaction contribute to the pathologies. Genomic analysis has connected altered astrocytic gene expression with synaptic deficits in a number of neurological disorders. Alterations in astrocyte-secreted factors have been implicated in the neuronal morphology and synaptic changes seen in neurodevelopmental disorders, while alteration in astrocytic glutamate uptake is a core feature of multiple neurodegenerative disorders. This evidence clearly demonstrates that maintaining astrocyte-synapse interaction is crucial for normal central nervous system functioning. Obtaining a better understanding of the role of astrocytes at synapses in health and disease will provide a new avenue for future therapeutic targeting.

PKCδ knockout mice are protected from para-methoxymethamphetamine-induced mitochondrial stress and associated neurotoxicity in the striatum of mice

Para-methoxymethamphetamine (PMMA) is a para-ring-substituted amphetamine derivative sold worldwide as an illegal psychotropic drug. Although PMMA use has been reported to lead to severe intoxication and even death, little is known about the mechanism(s) by which PMMA exerts its neurotoxic effects. Here we found that PMMA treatment resulted in phosphorylation of protein kinase Cδ (PKCδ) and subsequent mitochondrial translocation of cleaved PKCδ. PMMA-induced oxidative stress was more pronounced in mitochondria than in the cytosol. Moreover, treatment with PMMA consistently resulted in significant reductions in mitochondrial membrane potential, mitochondrial complex I activity, and mitochondrial Mn superoxide dismutase-immunoreactivity. In contrast, PMMA treatment led to a significant increase in intramitochondrial Ca²⁺ level. Treatment with PMMA also significantly increased ionized calcium binding adaptor molecule 1 (Iba-1)-labeled microglial activation and upregulated tumor necrosis factor alpha (TNF-α) gene expression. PKCδ knockout attenuated these mitochondrial effects and dampened the neurotoxic effects of PMMA. Importantly, TNF-α knockout mice were significantly protected from PMMA-induced increases in phospho-PKCδ expression, mitochondrial translocation of cleaved PKCδ, and Iba-1-labeled microgliosis. Both rottlerin, a pharmacological inhibitor of PKCδ, and etanercept, a pharmacological inhibitor of TNF-α, significantly protected against PMMA-mediated induction of apoptosis, as assessed by terminal deoxynucleotidyl transferase dUDP nick end labeling (TUNEL) assays. In addition, PKCδ knockout and TNF-α knockout both resulted in decreased PMMA-mediated induction of dopaminergic loss. Therefore, our results suggest that PKCδ mediates PMMA-induced neurotoxicity by facilitating oxidative stress (mitochondria > cytosol), mitochondrial dysfunction, microglial activation, and pro-apoptotic signaling. Our results also indicate that PMMA-induced PKCδ activation requires the proinflammatory cytokine TNF-α.

Pathophysiological Role of Neuroinflammation in Neurodegenerative Diseases and Psychiatric Disorders

Brain diseases and disorders such as Alzheimer disease, Parkinson disease, depression, schizophrenia, autism, and addiction lead to reduced quality of daily life through abnormal thoughts, perceptions, emotional states, and behavior. While the underlying mechanisms remain poorly understood, human and animal studies have supported a role of neuroinflammation in the etiology of these diseases. In the central nervous system, an increased inflammatory response is capable of activating microglial cells, leading to the release of pro-inflammatory cytokines including interleukin (IL)-1β, IL-6, and tumor necrosis factor-α. In turn, the pro-inflammatory cytokines aggravate and propagate neuroinflammation, degenerating healthy neurons and impairing brain functions. Therefore, activated microglia may play a key role in neuroinflammatory processes contributing to the pathogenesis of psychiatric disorders and neurodegeneration.

Microglial TNF-α Suppresses Cocaine-Induced Plasticity and Behavioral Sensitization

Repeated administration of cocaine results in the development of behavioral sensitization, accompanied by a decrease in excitatory synaptic strength in the nucleus accumbens (NAc) through an unknown mechanism. Furthermore, glial cells in the NAc are activated by drugs of abuse, but the contribution of glia to the development of addictive behaviors is unknown. Tumor necrosis factor alpha (TNF-α), an inflammatory cytokine released by activated glia, can drive the internalization of synaptic AMPA receptors on striatal medium spiny neurons. Here we show that repeated administration of cocaine activates striatal microglia and induces TNF-α production, which in turn depresses glutamatergic synaptic strength in the NAc core and limits the development of behavioral sensitization. Critically, following a period of abstinence, a weak TLR4 agonist can reactivate microglia, increase TNF-α production, depress striatal synaptic strength, and suppress cocaine-induced sensitization. Thus, cytokine signaling from microglia can regulate both the induction and expression of drug-induced behaviors.

Cecal Ligation and Puncture Results in Long-Term Central Nervous System Myeloid Inflammation

Survivors of sepsis often experience long-term cognitive and functional decline. Previous studies utilizing lipopolysaccharide injection and cecal ligation and puncture in rodent models of sepsis have demonstrated changes in depressive-like behavior and learning and memory after sepsis, as well as evidence of myeloid inflammation and cytokine expression in the brain, but the long-term course of neuroinflammation after sepsis remains unclear. Here, we utilize cecal ligation and puncture with greater than 80% survival as a model of sepsis. We found that sepsis survivor mice demonstrate deficits in extinction of conditioned fear, but no acquisition of fear conditioning, nearly two months after sepsis. These cognitive changes occur in the absence of neuronal loss or changes in synaptic density in the hippocampus. Sepsis also resulted in infiltration of monocytes and neutrophils into the CNS at least two weeks after sepsis in a CCR2 independent manner. Cellular inflammation is accompanied by long-term expression of pro-inflammatory cytokine and chemokine genes, including TNFα and CCR2 ligands, in whole brain homogenates. Gene expression analysis of microglia revealed that while microglia do express anti-microbial genes and damage-associated molecular pattern molecules of the S100A family of genes at least 2 weeks after sepsis, they do not express the cytokines observed in whole brain homogenates. Our results indicate that in a naturalistic model of infection, sepsis results in long-term neuroinflammation, and that this sustained inflammation is likely due to interactions among multiple cell types, including resident microglia and peripherally derived myeloid cells.

Apocynin prevents mitochondrial burdens, microglial activation, and pro-apoptosis induced by a toxic dose of methamphetamine in the striatum of mice via inhibition of p47phox activation by ERK

BACKGROUND

Activation of NADPH oxidase (PHOX) plays a critical role in mediating dopaminergic neuroinflammation. In the present study, we investigated the role of PHOX in methamphetamine (MA)-induced neurotoxic and inflammatory changes in mice.

METHODS

We examined changes in mitogen-activated protein kinases (MAPKs), mitochondrial function [i.e., mitochondrial membrane potential, intramitochondrial Ca(2+) accumulation, mitochondrial oxidative burdens, mitochondrial superoxide dismutase expression, and mitochondrial translocation of the cleaved form of protein kinase C delta type (cleaved PKCδ)], microglial activity, and pro-apoptotic changes [i.e., cytosolic cytochrome c release, cleaved caspase 3, and terminal deoxynucleotidyl transferase dUDP nick-end labeling (TUNEL) positive populations] after a neurotoxic dose of MA in the striatum of mice to achieve a better understanding of the effects of apocynin, a non-specific PHOX inhibitor, or genetic inhibition of p47phox (by using p47phox knockout mice or p47phox antisense oligonucleotide) against MA-induced dopaminergic neurotoxicity.

RESULTS

Phosphorylation of extracellular signal-regulated kinases (ERK1/2) was most pronounced out of MAPKs after MA. We observed MA-induced phosphorylation and membrane translocation of p47phox in the striatum of mice. The activation of p47phox promoted mitochondrial stresses followed by microglial activation into the M1 phenotype, and pro-apoptotic changes, and led to dopaminergic impairments. ERK activated these signaling pathways. Apocynin or genetic inhibition of p47phox significantly protected these signaling processes induced by MA. ERK inhibitor U0126 did not exhibit any additional positive effects against protective activity mediated by apocynin or p47phox genetic inhibition, suggesting that ERK regulates p47phox activation, and ERK constitutes the crucial target for apocynin-mediated inhibition of PHOX activation.

CONCLUSIONS

Our results indicate that the neuroprotective mechanism of apocynin against MA insult is via preventing mitochondrial burdens, microglial activation, and pro-apoptotic signaling process by the ERK-dependent activation of p47phox.

The danger-associated molecular pattern HMGB1 mediates the neuroinflammatory effects of methamphetamine

Methamphetamine (METH) induces neuroinflammatory effects, which may contribute to the neurotoxicity of METH. However, the mechanism by which METH induces neuroinflammation has yet to be clarified. A considerable body of evidence suggests that METH induces cellular damage and distress, particularly in dopaminergic neurons. Damaged neurons release danger-associated molecular patterns (DAMPs) such as high mobility group box-1 (HMGB1), which induces pro-inflammatory effects. Therefore, we explored the notion here that METH induces neuroinflammation indirectly through the release of HMGB1 from damaged neurons. Adult male Sprague-Dawley rats were injected IP with METH (10mg/kg) or vehicle (0.9% saline). Neuroinflammatory effects of METH were measured in nucleus accumbens (NAcc), ventral tegmental area (VTA) and prefrontal cortex (PFC) at 2h, 4h and 6h after injection. To assess whether METH directly induces pro-inflammatory effects in microglia, whole brain or striatal microglia were isolated using a Percoll density gradient and exposed to METH (0, 0.1, 1, 10, 100, or 1000μM) for 24h and pro-inflammatory cytokines measured. The effect of METH on HMGB1 and IL-1β in striatal tissue was then measured. To determine the role of HMGB1 in the neuroinflammatory effects of METH, animals were injected intra-cisterna magna with the HMGB1 antagonist box A (10μg) or vehicle (sterile water). 24h post-injection, animals were injected IP with METH (10mg/kg) or vehicle (0.9% saline) and 4h later neuroinflammatory effects measured in NAcc, VTA, and PFC. METH induced robust pro-inflammatory effects in NAcc, VTA, and PFC as a function of time and pro-inflammatory analyte measured. In particular, METH induced profound effects on IL-1β in NAcc (2h) and PFC (2h and 4h). Exposure of microglia to METH in vitro failed to induce a pro-inflammatory response, but rather induced significant cell death as well as a decrease in IL-1β. METH treatment increased HMGB1 in parallel with IL-1β in striatum. Pre-treatment with the HMGB1 antagonist box A blocked the neuroinflammatory effects (IL-1β) of METH in NAcc, VTA and PFC. The present results suggest that HMGB1 mediates, in part, the neuroinflammatory effects of METH and thus may alert CNS innate immune cells to the toxic effects of METH.

Relationship of serum levels of TNF-α, IL-6 and IL-18 and schizophrenia-like symptoms in chronic ketamine abusers

OBJECTIVE

Exposing to NMDAR receptor antagonists, such as ketamine, produces schizophrenia-like symptoms in humans and deteriorates symptoms in schizophrenia patients. Meanwhile, schizophrenia is associated with alterations of cytokines in the immune system. This study aims to examine the serum TNF-α, IL-6 and IL-18 levels in chronic human ketamine users as compared to healthy subjects. The correlations between the serum cytokines levels with the demographic, ketamine use characteristics and psychiatric symptoms were also assessed.

METHODS

155 subjects who fulfilled the criteria of ketamine dependence and 80 healthy control subjects were recruited. Serum TNF-α, IL-6 and IL-18 levels were measured using an enzyme-linked immunosorbent assay (ELISA). The psychiatric symptoms of the ketamine abusers were assessed using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

Serum IL-6 and IL-18 levels were significantly higher, while serum TNF-α level was significantly lower among ketamine users than among healthy controls (p<0.05). Serum TNF-α levels showed a significant negative association with PANSS total score (r=-0.210, p<0.01) and negative subscore (r=-0.300, p<0.01). No significant association was found between PANSS score and serum levels of IL-6 and IL-18.

CONCLUSIONS

Serum levels of TNF-α, IL-6 and IL-18 were altered in chronic ketamine abusers which may play a role in schizophrenia-like symptoms in chronic ketamine abusers.

Evaluating Exercise as a Therapeutic Intervention for Methamphetamine Addiction-Like Behavior

The need for effective treatments for addiction and dependence to the illicit stimulant methamphetamine in primary care settings is increasing, yet no effective medications have been FDA approved to reduce dependence [1]. This is partially attributed to the complex and dynamic neurobiology underlying the various stages of addiction [2]. Therapeutic strategies to treat methamphetamine addiction, particularly the relapse stage of addiction, could revolutionize methamphetamine addiction treatment. In this context, preclinical studies demonstrate that voluntary exercise (sustained physical activity) could be used as an intervention to reduce methamphetamine addiction. Therefore, it appears that methamphetamine disrupts normal functioning in the brain and this disruption is prevented or reduced by engaging in exercise. This review discusses animal models of methamphetamine addiction and sustained physical activity and the interactions between exercise and methamphetamine behaviors. The review highlights how methamphetamine and exercise affect neuronal plasticity and neurotoxicity in the adult mammalian striatum, hippocampus, and prefrontal cortex, and presents the emerging mechanisms of exercise in attenuating intake and in preventing relapse to methamphetamine seeking in preclinical models of methamphetamine addiction.

Recent advances in methamphetamine neurotoxicity mechanisms and its molecular pathophysiology

Methamphetamine (METH) is a sympathomimetic amine that belongs to phenethylamine and amphetamine class of psychoactive drugs, which are widely abused for their stimulant, euphoric, empathogenic, and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, METH produces persistent damage to dopamine and serotonin release in nerve terminals, gliosis, and apoptosis. This review summarized the numerous interdependent mechanisms including excessive dopamine, ubiquitin-proteasome system dysfunction, protein nitration, endoplasmic reticulum stress, p53 expression, inflammatory molecular, D₃ receptor, microtubule deacetylation, and HIV-1 Tat protein that have been demonstrated to contribute to this damage. In addition, the feasible therapeutic strategies according to recent studies were also summarized ranging from drug and protein to gene level.

Methamphetamine effects on blood-brain barrier structure and function

Methamphetamine (Meth) is a widely abuse psychostimulant. Traditionally, studies have focused on the neurotoxic effects of Meth on monoaminergic neurotransmitter terminals. Recently, both in vitro and in vivo studies have investigated the effects of Meth on the BBB and found that Meth produces a decrease in BBB structural proteins and an increase in BBB permeability to various molecules. Moreover, preclinical studies are validated by clinical studies in which human Meth users have increased concentrations of toxins in the brain. Therefore, this review will focus on the structural and functional disruption of the BBB caused by Meth and the mechanisms that contribute to Meth-induced BBB disruption. The review will reveal that the mechanisms by which Meth damages dopamine and serotonin terminals are similar to the mechanisms by which the blood-brain barrier (BBB) is damaged. Furthermore, this review will cover the factors that are known to potentiate the effects of Meth (McCann et al., 1998) on the BBB, such as stress and HIV, both of which are co-morbid conditions associated with Meth abuse. Overall, the goal of this review is to demonstrate that the scope of damage produced by Meth goes beyond damage to monoaminergic neurotransmitter systems to include BBB disruption as well as provide a rationale for investigating therapeutics to treat Meth-induced BBB disruption. Since a breach of the BBB can have a multitude of consequences, therapies directed toward the treatment of BBB disruption may help to ameliorate the long-term neurodegeneration and cognitive deficits produced by Meth and possibly even Meth addiction.

Liposomal melatonin rescues methamphetamine-elicited mitochondrial burdens, pro-apoptosis, and dopaminergic degeneration through the inhibition PKCδ gene

We have demonstrated that mitochondrial oxidative damage and PKCδ overexpression contribute to methamphetamine-induced dopaminergic degeneration. Although it is recognized that antioxidant melatonin is effective in preventing neurotoxicity induced by methamphetamine, its precise mechanism remains elusive. C57BL/6J wild-type mice exhibited a similar degree of dopaminergic deficit when methamphetamine was administered during light and dark phases. Furthermore, dopaminergic neuroprotection by genetic inhibition of PKCδ during the light phase was comparable to that during the dark phase. Thus, we have focused on the light phase to examine whether melatonin modulates PKCδ-mediated neurotoxic signaling after multiple high doses of methamphetamine. To enhance the bioavailability of melatonin, we applied liposomal melatonin. Treatment with methamphetamine resulted in hyperthermia, mitochondrial translocation of PKCδ, oxidative damage (mitochondria > cytosol), mitochondrial dysfunction, pro-apoptotic changes, ultrastructural mitochondrial degeneration, dopaminergic degeneration, and behavioral impairment in wild-type mice. Treatment with liposomal melatonin resulted in a dose-dependent attenuation against degenerative changes induced by methamphetamine in wild-type mice. Attenuation by liposomal melatonin might be comparable to that by genetic inhibition (using PKCδ((-/-)) mice or PKCδ antisense oligonucleotide). However, liposomal melatonin did not show any additional protective effects on the attenuation by genetic inhibition of PKCδ. Our results suggest that the circadian cycle cannot be a key factor in modulating methamphetamine toxicity under the current experimental condition and that PKCδ is one of the critical target genes for melatonin-mediated protective effects against mitochondrial burdens (dysfunction), oxidative stress, pro-apoptosis, and dopaminergic degeneration induced by methamphetamine.