Slc7a11 (xCT) protein expression is not altered in the depressed brain and system xc- deficiency does not affect depression-associated behaviour in the corticosterone mouse model

Inhibition of xCT by sulfasalazine alleviates the depression-like behavior of adult male mice subjected to maternal separation stress

Maternal separation (MS) can induce emotional disorders. Our previous study reported that MS resulted in depression-like behavior. In this study, we aimed to explore the role of xCT in depression-like behavior in adult mice subjected to MS stress. Pups were divided into the control group, the control + sulfasalazine (SSZ, 75 mg/kg/day, i.p.) group, the MS group, and the MS+SSZ group. After MS, all pups were raised until PD60. Then, the depression-like behavior was detected by the novelty suppressed feeding (NSF) test, the forced swimming test (FST), and the tail suspension test (TST). The synaptic plasticity was examined by electrophysiological recordings and molecular biotechnology. The data showed that, compared with the control group, the mice in the MS group presented depression-like behavior, impairment of long-term potentiation (LTP), a reduction in the number of astrocytes, and activation of the microglia. Moreover, the expression of xCT was increased in the prefrontal cortex of MS mice, the EAAT2 and the Group Ⅱ metabotropic glutamate receptors (mGluR2/3) were decreased, and the level of pro-inflammatory factors was increased in the prefrontal cortex. After the administration with SSZ, the depression-like behavior and the impairment of LTP were alleviated, the number of astrocytes was increased, and the microglial activation was inhibited. Moreover, the levels of EAAT2 and mGluR2/3 were ameliorated, the over-activation of the microglia was mitigated, and the levels of glutamate and pro-inflammatory factors were decreased. In conclusion, the inhibition of xCT by SSZ could alleviate depression-like behavior partly via modulating the homeostasis of the glutamate system and dampening neuroinflammation.

Is depression the missing link between inflammatory mediators and cancer?

Patients with cancer are at greater risk of developing depression in comparison to the general population and this is associated with serious adverse effects, such as poorer quality of life, worse prognosis and higher mortality. Although the relationship between depression and cancer is now well established, a common underlying pathophysiological mechanism between the two conditions is yet to be elucidated. Existing theories of depression, based on monoamine neurotransmitter system dysfunction, are insufficient as explanations of the disorder. Recent advances have implicated neuroinflammatory mechanisms in the etiology of depression and it has been demonstrated that inflammation at a peripheral level may be mirrored centrally in astrocytes and microglia serving to promote chronic levels of inflammation in the brain. Three major routes to depression in cancer in which proinflammatory mediators are implicated, seem likely. Activation of the kynurenine pathway involving cytokines, increases tryptophan catabolism, resulting in diminished levels of serotonin which is widely acknowledged as being the hallmark of depression. It also results in neurotoxic effects on brain regions thought to be involved in the evolution of major depression. Proinflammatory mediators also play a crucial role in impairing regulatory glucocorticoid mediated feedback of the hypothalamic-pituitary-adrenal axis, which is activated by stress and considered to be involved in both depression and cancer. The third route is via the glutamatergic pathway, whereby glutamate excitotoxicity may lead to depression associated with cancer. A better understanding of the mechanisms underlying these dysregulated and other newly emerging pathways may provide a rationale for therapeutic targeting, serving to improve the care of cancer patients.

Chronic Sulfasalazine Treatment in Mice Induces System xc - - Independent Adverse Effects

Despite ample evidence for the therapeutic potential of inhibition of the cystine/glutamate antiporter system x_c⁻ in neurological disorders and in cancer, none of the proposed inhibitors is selective. In this context, a lot of research has been performed using the EMA- and FDA-approved drug sulfasalazine (SAS). Even though this molecule is already on the market for decades as an anti-inflammatory drug, serious side effects due to its use have been reported. Whereas for the treatment of the main indications, SAS needs to be cleaved in the intestine into the anti-inflammatory compound mesalazine, it needs to reach the systemic circulation in its intact form to allow inhibition of system x_c⁻. The higher plasma levels of intact SAS (or its metabolites) might induce adverse effects, independent of its action on system x_c⁻. Some of these effects have however been attributed to system x_c⁻ inhibition, calling into question the safety of targeting system x_c⁻. In this study we chronically treated system x_c⁻ - deficient mice and their wildtype littermates with two different doses of SAS (160 mg/kg twice daily or 320 mg/kg once daily, i.p.) and studied some of the adverse effects that were previously reported. SAS had a negative impact on the survival rate, the body weight, the thermoregulation and/or stress reaction of mice of both genotypes, and thus independent of its inhibitory action on system x_c⁻. While SAS decreased the total distance travelled in the open-field test the first time the mice encountered the test, it did not influence this parameter on the long-term and it did not induce other behavioral changes such as anxiety- or depressive-like behavior. Finally, no major histological abnormalities were observed in the spinal cord. To conclude, we were unable to identify any undesirable system x_c⁻-dependent effect of chronic administration of SAS.

N-acetylcysteine as a new prominent approach for treating psychiatric disorders

N-acetylcysteine (NAC) is a well-known and safe mucolytic agent, also used in patients with paracetamol overdose. In addition to these effects, recent preclinical and clinical studies have shown that NAC exerts beneficial effects on different psychiatric disorders. Many potential mechanisms have been proposed to underlie the therapeutic effects of NAC, including the regulation of several neurotransmitters, oxidative homeostasis, and inflammatory mediators. In this paper, we summarize the current knowledge on the ability of NAC to ameliorate symptoms and neuropathologies related to different psychiatric disorders, including attention deficit hyperactivity disorder, anxiety, bipolar disorder, depression, obsessive-compulsive disorder, obsessive-compulsive-related disorder, posttraumatic stress disorder, and schizophrenia. Although preclinical studies have shown a positive effect of NAC on animal models of psychiatric disorders, the clinical efficacy of NAC is not fully established. NAC remains a strong candidate for adjunct treatment for many psychiatric disorders, but additional preclinical and clinical studies are needed.

Oroxylin A regulates the turnover of lipid droplet via downregulating adipose triglyceride lipase (ATGL) in hepatic stellate cells

Proliferation and differentiation of hepatic stellate cells (HSCs) are the most noticeable events in hepatic fibrosis, in which the loss of lipid droplets (LDs) is the most important feature. However, the complex mechanisms of LD disappearance have not been fully elucidated. In the current study, we investigated whether oroxylin A has the pharmacological activity of reversing LDs in activated HSCs, and further examined its potential molecular mechanisms. Using genetic, pharmacological, and molecular biological measure, we found that LD content significantly decreased during HSC activation, whereas oroxylin A markedly reversed LD content in activated HSCs. Interestingly, oroxylin A treatment observably decreased the expression of adipose triglyceride lipase (ATGL) without large differences in classical LD synthesis pathway, LD-related transcription factors, and autophagy pathway. ATGL overexpression could completely impair the effect of oroxylin A on reversing LD content. Importantly, reactive oxygen species (ROS) signaling pathway mediated oroxylin A-induced ATGL downregulation and LD revision in activated HSCs. ROS specific stimulant buthionine sulfoximine (BSO) could dramatically diminish the antioxidant effect of oroxylin A, and in turn, abolish reversal effect of oroxylin A on LD content. Conversely, ROS specific scavenger N-acetyl cystenine (NAC) can significantly enhance the pharmacological effect of oroxylin A on LD revision. Taken together, our study reveals the important molecular mechanism of anti-fibrosis effect of oroxylin A, and also suggests that ROS-ATGL pathway is a potential target for reversing LDs.

Genetic deletion of xCT attenuates peripheral and central inflammation and mitigates LPS-induced sickness and depressive-like behavior in mice

The communication between the immune and central nervous system (CNS) is affected in many neurological disorders. Peripheral injections of the endotoxin lipopolysaccharide (LPS) are widely used to study this communication: an LPS challenge leads to a biphasic syndrome that starts with acute sickness and is followed by persistent brain inflammation and chronic behavioral alterations such as depressive-like symptoms. In vitro, the response to LPS treatment has been shown to involve enhanced expression of system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>x</mml:mi></mml:mrow> <mml:mrow><mml:mi>c</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> . This cystine-glutamate antiporter, with xCT as specific subunit, represents the main glial provider of extracellular glutamate in mouse hippocampus. Here we injected male xCT knockout and wildtype mice with a single intraperitoneal dose of 5 mg/kg LPS. LPS-injection increased hippocampal xCT expression but did not alter the mainly astroglial localization of the xCT protein. Peripheral and central inflammation (as defined by cytokine levels and morphological activation of microglia) as well as LPS-induced sickness and depressive-like behavior were significantly attenuated in xCT-deficient mice compared with wildtype mice. Our study is the first to demonstrate the involvement of system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>x</mml:mi></mml:mrow> <mml:mrow><mml:mi>c</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> in peripheral and central inflammation in vivo and the potential therapeutic relevance of its inhibition in brain disorders characterized by peripheral and central inflammation, such as depression.