Direct effects of secretory products of immune cells on neurons and glia

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

Inflammation in multiple sclerosis: consequences for remyelination and disease progression

Despite the large number of immunomodulatory or immunosuppressive treatments available to treat relapsing-remitting multiple sclerosis (MS), treatment of the progressive phase of the disease has not yet been achieved. This lack of successful treatment approaches is caused by our poor understanding of the mechanisms driving disease progression. Emerging concepts suggest that a combination of persisting focal and diffuse inflammation within the CNS and a gradual failure of compensatory mechanisms, including remyelination, result in disease progression. Therefore, promotion of remyelination presents a promising intervention approach. However, despite our increasing knowledge regarding the cellular and molecular mechanisms regulating remyelination in animal models, therapeutic increases in remyelination remain an unmet need in MS, which suggests that mechanisms of remyelination and remyelination failure differ fundamentally between humans and demyelinating animal models. New and emerging technologies now allow us to investigate the cellular and molecular mechanisms underlying remyelination failure in human tissue samples in an unprecedented way. The aim of this Review is to summarize our current knowledge regarding mechanisms of remyelination and remyelination failure in MS and in animal models of the disease, identify open questions, challenge existing concepts, and discuss strategies to overcome the translational roadblock in the field of remyelination-promoting therapies.

Neuroinflammatory Response in Reward-Associated Psychostimulants and Opioids: A Review

Substance abuse is one of the significant problems in social and public health worldwide. Vast numbers of evidence illustrate that motivational and reinforcing impacts of addictive drugs are primarily attributed to their ability to change dopamine signaling in the reward circuit. However, the roles of classic neurotransmitters, especially dopamine and neuromodulators, monoamines, and neuropeptides, in reinforcing characteristics of abused drugs have been extensively investigated. It has recently been revealed that central immune signaling includes cascades of chemokines and proinflammatory cytokines released by neurons and glia via downstream intracellular signaling pathways that play a crucial role in mediating rewarding behavioral effects of drugs. More interestingly, inflammatory responses in the central nervous system modulate the mesolimbic dopamine signaling and glutamate-dependent currents induced by addictive drugs. This review summarized researches in the alterations of inflammatory responses accompanied by rewarding and reinforcing properties of addictive drugs, including cocaine, methamphetamine, and opioids that were evaluated by conditioned place preference and self-administration procedures as highly common behavioral tests to investigate the motivational and reinforcing impacts of addictive drugs. The neuroinflammatory responses affect the rewarding properties of psychostimulants and opioids.

Possible Receptor Mechanisms Underlying Cannabidiol Effects on Addictive-like Behaviors in Experimental Animals

Substance use disorder (SUD) is a serious public health problem worldwide for which available treatments show limited effectiveness. Since the legalization of cannabis and the approval of cannabidiol (CBD) by the US Food and Drug Administration, therapeutic potential of CBD for the treatment of SUDs and other diseases has been widely explored. In this mini-review article, we first review the history and evidence supporting CBD as a potential pharmacotherapeutic. We then focus on recent progress in preclinical research regarding the pharmacological efficacy of CBD and the underlying receptor mechanisms on addictive-like behavior. Growing evidence indicates that CBD has therapeutic potential in reducing drug reward, as assessed in intravenous drug self-administration, conditioned place preference and intracranial brain-stimulation reward paradigms. In addition, CBD is effective in reducing relapse in experimental animals. Both in vivo and in vitro receptor mechanism studies indicate that CBD may act as a negative allosteric modulator of type 1 cannabinoid (CB1) receptor and an agonist of type 2 cannabinoid (CB2), transient receptor potential vanilloid 1 (TRPV1), and serotonin 5-HT_1A receptors. Through these multiple-receptor mechanisms, CBD is believed to modulate brain dopamine in response to drugs of abuse, leading to attenuation of drug-taking and drug-seeking behavior. While these findings suggest that CBD is a promising therapeutic candidate, further investigation is required to verify its safety, pharmacological efficacy and the underlying receptor mechanisms in both experimental animals and humans.

Cannabidiol modulates the expression of neuroinflammatory factors in stress- and drug-induced reinstatement of methamphetamine in extinguished rats

Methamphetamine (METH) is a highly potent and addictive psychostimulant that is frequently abused worldwide. Although the biggest challenge to the efficient treatment of drug dependence is relapse, its mechanism is completely unclear. Plenty of evidence suggests that inflammation contributes to drug-induced reward especially in brain regions that are involved in the reward system, but there is no document about relapse. Cannabidiol (CBD) is a nonpsychoactive cannabinoid that has powerful anti-inflammatory and immunosuppressive properties. A previous research in our laboratory has demonstrated that CBD prevents reinstatement of METH even in 24-hour rapid eye movement (REM) sleep-deprived (RSD) rats. The aim of this study was to assess whether CBD prevents reinstatement of METH through change of gene expression of cytokines such as interleukin-1β, interleukin-6, interleukin-10, and tumor necrosis factor α (TNF-α) in extinguished rats. Real-time polymerase chain reaction (PCR) was used in this research to assay gene expression of cytokines. We found that stress- and drug-induced reinstatement of METH enhanced mRNA expression of cytokines in the prefrontal cortex (PFC) and hippocampus. Furthermore, CBD treatment significantly reduced the mRNA expression of cytokines in the PFC and hippocampus, but CBD treatment in RSD rats increased expression of cytokines in the hippocampus. It seems that enhancement of cytokines leads to change in neurotransmission and so triggers reinstatement of METH.

Role of Oligodendrocyte Dysfunction in Demyelination, Remyelination and Neurodegeneration in Multiple Sclerosis

Oligodendrocytes (OLs) are the myelinating cells of the central nervous system (CNS) during development and throughout adulthood. They result from a complex and well controlled process of activation, proliferation, migration and differentiation of oligodendrocyte progenitor cells (OPCs) from the germinative niches of the CNS. In multiple sclerosis (MS), the complex pathological process produces dysfunction and apoptosis of OLs leading to demyelination and neurodegeneration. This review attempts to describe the patterns of demyelination in MS, the steps involved in oligodendrogenesis and myelination in healthy CNS, the different pathways leading to OLs and myelin loss in MS, as well as principles involved in restoration of myelin sheaths. Environmental factors and their impact on OLs and pathological mechanisms of MS are also discussed. Finally, we will present evidence about the potential therapeutic targets in re-myelination processes that can be accessed in order to develop regenerative therapies for MS.

Insight into the mechanisms of action of estrogen receptor β in the breast, prostate, colon, and CNS

Estrogen and its receptors (ERs) influence many biological processes in physiology and pathology in men and women. ERs are involved in the etiology and/or progression of cancers of the prostate, breast, uterus, ovary, colon, lung, stomach, and malignancies of the immune system. In estrogen-sensitive malignancies, ERβ usually is a tumor suppressor and ERα is an oncogene. ERβ regulates genes in several key pathways including tumor suppression (p53, PTEN); metabolism (PI3K); survival (Akt); proliferation pathways (p45(Skp2), cMyc, and cyclin E); cell-cycle arresting factors (p21(WAF1), cyclin-dependent kinase inhibitor 1 (CDKN1A)), p27(Kip1), and cyclin-dependent kinases (CDKs); protection from reactive oxygen species, glutathione peroxidase. Because they are activated by small molecules, ERs are excellent targets for pharmaceuticals. ERα antagonists have been used for many years in the treatment of breast cancer and more recently pharmaceutical companies have produced agonists which are very selective for ERα or ERβ. ERβ agonists are being considered for preventing progression of cancer, treatment of anxiety and depression, as anti-inflammatory agents and as agents, which prevent or reduce the severity of neurodegenerative diseases.