The cystine-glutamate transporter in the accumbens: a novel role in cocaine relapse

Conditional deletion of the AMPA-GluA1 and NMDA-GluN1 receptor subunit genes in midbrain D1 neurons does not alter cocaine reward in mice

Synaptic plasticity in the mesolimbic dopamine (DA) system contributes to the neural adaptations underlying addictive behaviors and relapse. However, the specific behavioral relevance of glutamatergic excitatory drive onto dopamine D1 receptor (D1R)-expressing neurons in mediating the reinforcing effect of cocaine remains unclear. Here, we investigated how midbrain AMPAR and NMDAR function modulate cocaine reward-related behavior using mutant mouse lines lacking the glutamate receptor genes Gria1 or Grin1 in D1R-expressing neurons (GluA1D1CreERT2 or GluN1D1CreERT2, respectively). We found that conditional genetic deletion of either GluA1 or GluN1 within this neuronal sub-population did not impact the ability of acute cocaine injection to increase intracranial self-stimulation (ICSS) ratio or reduced brain reward threshold compared to littermate controls. Additionally, our data demonstrate that deletion of GluA1 and GluN1 receptor subunits within D1R-expressing neurons did not affect cocaine reinforcement in an operant self-administration paradigm, as mutant mice showed comparable cocaine responses and intake to controls. Given the pivotal role of glutamate receptors in mediating relapse behavior, we further explored the impact of genetic deletion of AMPAR and NMDAR onto D1R-expressing neurons on cue-induced reinstatement following extinction. Surprisingly, deletion of AMPAR and NMDAR onto these neurons did not impair cue-induced reinstatement of cocaine-seeking behavior. These findings suggest that glutamatergic activity via NMDAR and AMPAR in D1R-expressing neurons may not exclusively mediate the reinforcing effects of cocaine and cue-induced reinstatement.

The nucleus accumbens in reward and aversion processing: insights and implications

The nucleus accumbens (NAc), a central component of the brain's reward circuitry, has been implicated in a wide range of behaviors and emotional states. Emerging evidence, primarily drawing from recent rodent studies, suggests that the function of the NAc in reward and aversion processing is multifaceted. Prolonged stress or drug use induces maladaptive neuronal function in the NAc circuitry, which results in pathological conditions. This review aims to provide comprehensive and up-to-date insights on the role of the NAc in motivated behavior regulation and highlights areas that demand further in-depth analysis. It synthesizes the latest findings on how distinct NAc neuronal populations and pathways contribute to the processing of opposite valences. The review examines how a range of neuromodulators, especially monoamines, influence the NAc's control over various motivational states. Furthermore, it delves into the complex underlying mechanisms of psychiatric disorders such as addiction and depression and evaluates prospective interventions to restore NAc functionality.

The Roles of Iron and Ferroptosis in Human Chronic Diseases

Ferroptosis, an iron-dependent novel type of cell death, has been characterized as an excessive accumulation of lipid peroxides and reactive oxygen species. A growing number of studies demonstrate that ferroptosis not only plays an important role in the pathogenesis and progression of chronic diseases, but also functions differently in different diseases. As a double-edged sword, activation of ferroptosis could potently inhibit tumor growth and increase sensitivity to chemotherapy and immunotherapy in various cancer settings. Therefore, the development of more efficacious ferroptosis agonists or inhibitors remains the mainstay of ferroptosis-targeting strategy for cancer therapeutics or cardiovascular and cerebrovascular diseases and neurodegenerative diseases therapeutics.

Geniposide Possesses the Protective Effect on Myocardial Injury by Inhibiting Oxidative Stress and Ferroptosis via Activation of the Grsf1/GPx4 Axis

Reactive oxygen species (ROS) produced in the ischemic myocardium can induce cardiomyocyte injury and death, resulting in cardiac remodeling. Ferroptosis, known as a newly type of cell death caused by iron-dependent oxidative stress, which is an essential death mechanism in cardiomyocytes. However, it is unclear whether oxidative stress products can further induce ferroptosis and aggravate cardiomyocyte injury. Geniposide (GEN), a major active component of Gardenia jasminoides J. Ellis, possesses the natural antioxidant activity and cardioprotective effect. Herein, we evaluated the role of ferroptosis in myocardial oxidative injury and the protective effect of GEN on myocardial ferroptosis. We first detected iron overload, massive ROS, and lipid peroxidation in ferric ammonium citrate (FAC)-treated cardiomyocytes, which were typical characteristics of ferroptosis. The iron overload-induced oxidative stress and ferroptosis aggravated cardiomyocyte injury, which were significantly alleviated by GEN treatment. Similar phenotypic changes of ferroptosis were consistently discovered in hydrogen peroxide (H₂O₂)-induced cells, which were reversed by GEN treatment as well. Interestingly, the RNA-binding protein Grsf1, which directly upregulated Gpx4 at the translational level, was activated by GEN following myocardial oxidative injury. The specific knockdown of Grsf1 increased their sensitivity to ferroptosis and weakened the cardioprotective effect of GEN in H₂O₂-treated cardiomyocytes. Moreover, GEN treatment reduced iron overload and lipid peroxidation in myocardial infarction (MI) rats, thereby fighting against the cardiac ischemic injury. Collectively, our study revealed the pathogenesis of oxidative stress and ferroptosis associated with myocardial ischemia, and indicated the antioxidant and anti-ferroptosis effects of GEN on preventing myocardial injury by activating the Grsf1/GPx4 axis, serving as a potential therapeutic target.

[The role of ferroptosis in chronic diseases]

Recently, ferroptosis, an iron-dependent novel type of cell death, has been characterized as an excessive accumulation of lipid peroxides and reactive oxygen species. Emerging studies demonstrate that ferroptosis not only plays an important role in the pathogenesis and progression of chronic diseases, but also functions differently in the different disease context. Notably, it is shown that activation of ferroptosis could potently inhibit tumor growth and increase sensitivity to chemotherapy and immunotherapy in various cancer settings. As a result, the development of more efficacious ferroptosis agonists remains the mainstay of ferroptosis-targeting strategy for cancer therapeutics. By contrast, in non-cancerous chronic diseases, including cardiovascular & cerebrovascular diseases and neurodegenerative diseases, ferroptosis functions as a risk factor to promote these diseases progression through triggering or accelerating tissue injury. As a matter of fact, blocking ferroptosis has been demonstrated to effectively prevent ischemia-reperfusion heart disease in preclinical animal models. Therefore, it is a promising field to develope potent ferroptosis inhibitors for preventing and treating cardiovascular & cerebrovascular diseases and neurodegenerative diseases. In this article, we summarize the most recent progress on ferroptosis in chronic diseases, and draw attention to the possible clinical impact of this recently emerged ferroptosis modalities.

Contribution of cystine-glutamate antiporters to the psychotomimetic effects of phencyclidine

Altered glutamate signaling contributes to a myriad of neural disorders, including schizophrenia. While synaptic levels are intensely studied, nonvesicular release mechanisms, including cystine-glutamate exchange, maintain high steady-state glutamate levels in the extrasynaptic space. The existence of extrasynaptic receptors, including metabotropic group II glutamate receptors (mGluR), pose nonvesicular release mechanisms as unrecognized targets capable of contributing to pathological glutamate signaling. We tested the hypothesis that activation of cystine-glutamate antiporters using the cysteine prodrug N-acetylcysteine would blunt psychotomimetic effects in the rodent phencyclidine (PCP) model of schizophrenia. First, we demonstrate that PCP elevates extracellular glutamate in the prefrontal cortex, an effect that is blocked by N-acetylcysteine pretreatment. To determine the relevance of the above finding, we assessed social interaction and found that N-acetylcysteine reverses social withdrawal produced by repeated PCP. In a separate paradigm, acute PCP resulted in working memory deficits assessed using a discrete trial t-maze task, and this effect was also reversed by N-acetylcysteine pretreatment. The capacity of N-acetylcysteine to restore working memory was blocked by infusion of the cystine-glutamate antiporter inhibitor (S)-4-carboxyphenylglycine into the prefrontal cortex or systemic administration of the group II mGluR antagonist LY341495 indicating that the effects of N-acetylcysteine requires cystine-glutamate exchange and group II mGluR activation. Finally, protein levels from postmortem tissue obtained from schizophrenic patients revealed significant changes in the level of xCT, the active subunit for cystine-glutamate exchange, in the dorsolateral prefrontal cortex. These data advance cystine-glutamate antiporters as novel targets capable of reversing the psychotomimetic effects of PCP.

The x(c)- cystine/glutamate antiporter: a potential target for therapy of cancer and other diseases

The x(c) (-) cystine/glutamate antiporter is a major plasma membrane transporter for the cellular uptake of cystine in exchange for intracellular glutamate. Its main functions in the body are mediation of cellular cystine uptake for synthesis of glutathione essential for cellular protection from oxidative stress and maintenance of a cystine:cysteine redox balance in the extracellular compartment. In the past decade it has become evident that the x(c) (-) transporter plays an important role in various aspects of cancer, including: (i) growth and progression of cancers that have a critical growth requirement for extracellular cystine/cysteine, (ii) glutathione-based drug resistance, (iii) excitotoxicity due to excessive release of glutamate, and (iv) uptake of herpesvirus 8, a causative agent of Kaposi's sarcoma. The x(c) (-) transporter also plays a role in certain CNS and eye diseases. This review focuses on the expression and function of the x(c) (-) transporter in cells and tissues with particular emphasis on its role in disease pathogenesis. The potential use of x(c) (-) inhibitors (e.g., sulfasalazine) for arresting tumor growth and/or sensitizing cancers is discussed.

Novel pharmacotherapeutic targets for the management of drug addiction

Despite individual variation in the liability to the abuse of psychoactive substances, there is substantial commonality shared by drugs of abuse. The knowledge of these common mechanisms together with the continued elucidation of the neurobiological underpinnings of withdrawal symptoms, drug intake, craving, relapse, and co-morbid psychiatric associations are critically important for the development of new therapeutic strategies. The present review will focus on recent advances in the development of innovative pharmacotherapeutic agents, which should promote higher efficacy (abstinence, prevention of relapse, long-term recovery) and patient compliance, as well as improved safety profiles.