Neurotoxic effects of the HCV core protein are mediated by sustained activation of ERK via TLR2 signaling

Neuroimmune modulation in liver pathophysiology

The liver, the largest organ in the human body, plays a multifaceted role in digestion, coagulation, synthesis, metabolism, detoxification, and immune defense. Changes in liver function often coincide with disruptions in both the central and peripheral nervous systems. The intricate interplay between the nervous and immune systems is vital for maintaining tissue balance and combating diseases. Signaling molecules and pathways, including cytokines, inflammatory mediators, neuropeptides, neurotransmitters, chemoreceptors, and neural pathways, facilitate this complex communication. They establish feedback loops among diverse immune cell populations and the central, peripheral, sympathetic, parasympathetic, and enteric nervous systems within the liver. In this concise review, we provide an overview of the structural and compositional aspects of the hepatic neural and immune systems. We further explore the molecular mechanisms and pathways that govern neuroimmune communication, highlighting their significance in liver pathology. Finally, we summarize the current clinical implications of therapeutic approaches targeting neuroimmune interactions and present prospects for future research in this area.

Role of hepatitis c virus in hepatocellular carcinoma and neurological disorders: an overview

The hepatitis C virus (HCV) causes serious issues, affecting 71 million people globally. The most common manifestations range from chronic hepatitis to liver cirrhosis, leading to hepatocellular carcinoma. Many mechanisms are known to play an important role in HCV-induced HCC. The interaction of viral proteins with host cells results in oxidative stress damage, liver inflammation, and irregularities in signaling pathways. These results in the activation of oncogenes and metabolic disturbances, liver fibrosis, and angiogenesis. Additionally, some non-coding RNAs (ncRNAs) and toll-like receptors have been identified and play a significant role in HCC development. This virus is also associated with impairment of the central nervous system, resulting in acute or sub-acute encephalopathy and inflammatory disorders. Neurological disorders are associated with the inflammatory responses of many cells, including microglia and astrocytes. Additionally, there are many other extrahepatic manifestations, including neurological disorders such as depression and fatigue, in 50% of infected patients. These manifestations include neuro-invasion, immune-mediated damage, neurotransmitter alterations, sensory-motor polyneuropathy, sensitivity loss, weakness of the leg, and cryoglobulinemia, which significantly results in a reduced quality of life. HCV infection may be improved using an appropriate diagnosis and direct antiviral therapy for sustained virological response. However, the success of therapy depends on the symptoms and organ damage, diagnosis, and therapeutic strategies applied. Some published reports have discussed that HCV is associated with both HCC and neurological disorders. Additionally, it has also been observed that individuals with HCC also develop neurological disorders compared with individuals with HCV alone. This review aims to provide an overview of the latest information about the relationship between HCV-induced HCC and their role in neurological disorders. Additionally, we have also discussed the progress made in the diagnosis, physio-pathological mechanisms, and strong antiviral therapies developed for HCV infection and HCC, as well as the latest advancements made in the study of the neurological disorders associated with HCV infection.

Brain metabolic and microstructural alterations associated with hepatitis C virus infection, autoimmune hepatitis and primary biliary cholangitis

BACKGROUND AND AIMS

Neuropsychiatric symptoms in hepatitis C (HCV) patients resemble those of patients with autoimmune hepatitis (AIH) or primary biliary cholangitis (PBC), whilst the mechanisms behind them are unknown. Here we looked for cerebral metabolic and/or microstructural alterations in patients with HCV, AIH or PBC as possible causes behind these symptoms.

METHODS

Patients with HCV infection (n = 17), AIH (n = 14) or PBC (n = 11) and age-adjusted healthy controls (n = 18) underwent brain magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS) and psychometric assessment of memory and attention. Brain relative proton density (PD) and T2 relaxation time (T2) were determined in 17 regions of interest (ROIs), as were the concentrations of N-acetyl-aspartate, choline, creatine, myo-inositol and glutamine + glutamate in frontal- (fWM) and parietal white matter (pWM). One-way analysis of variance and Kruskal-Wallis tests were used for group comparison. Correlations between altered neuropsychological findings and MRI/MRS observations were estimated with the Spearman ρ test.

RESULTS

HCV, AIH and PBC patients revealed similar alterations in brain PD and metabolites compared to controls: significantly decreased PD in 7/17 ROIs in the HCV group, 16/17 ROIs in the PBC group and 14/17 ROIs in the AIH group, significantly increased N-acetyl-aspartate in fWM in all patients, significantly increased choline in the PBC group in both fWM and pWM, in the AIH group only in pWM and with a trend in the HCV group in pWM. Correlation analysis did not reveal significant associations between MRI/MRS alterations and neuropsychological dysfunction.

CONCLUSION

The findings suggest similar pathophysiological mechanisms behind neuropsychiatric symptoms associated with HCV infection, AIH and PBC.

Enteropathogenic infections modulate intestinal serotonin transporter (SERT) function by activating Toll-like receptor 2 (TLR-2) in Crohn's disease

Serotonin (5-hydroxytryptamine [5-HT]) is an intestinal neuromodulator that regulates several essential enteric physiological functions such as absorption or secretion of fluids, and peristaltic reflexes. Availability of the intestinal 5-HT is dependent on serotonin transporter (SERT), which uptakes 5-HT and facilitates its degradation. Interestingly, Toll-like receptor 2 (TLR-2) is co-localized with 5-HT, which suggests a possible impact of neuroendocrine cells in the inflammatory response through TLR-2 activation. Serum 5-HT levels were measured in 80 Crohn's disease (CD) patients and 40 healthy control subjects. Additionally, fully differentiated Caco-2 monolayers were infected with Mycobacteria paratuberculosis (MAP), L. monocytogenes, or M. smegmatis in the presence of exogenous 5-HT at different concentrations. Cells were subsequently harvested and used for measuring SERT activity, RNA isolation followed by RT-PCR, protein quantification, and tissue damage markers (DHE, LDH, GSH and MDA). TLR-2 intracellular signaling pathways were assessed by pre-incubating Caco-2 monolayers with selective blockers of ERK, cAMP/PKA, p38 MAPK, and 5-HT₃ receptors. MAP-infected CD patients (N = 40) had higher serum 5-HT levels (462.95 ± 8.55 ng/mL, N = 40) than those without MAP infection (385.33 ± 10.3 ng/mL, N = 40). TLR-2 activation by enteropathogenic bacteria inhibited SERT activity in the presence of exogenous 5-HT by up to 50%. These effects were increasing gradually over 72 h, and MAP infection had the greatest effect on SERT inhibition when cells were exposed to 5-HT in a concentration dependent manner. Additionally, inhibition of SERT activity was accompanied with higher levels of pro-inflammatory cytokines (TNF-α, IL-6, IL-8) and oxidative stress markers (DHE, LDH and MDA), whereas SERT expression and protein level were downregulated. Consequently, inhibition of TLR-2 and p38 MAPK signaling or blocking 5-HT₃ receptors restored SERT activity and reduced the production of pro-inflammatory cytokines, as reflected by the downregulation of oxidative stress and tissue damage markers. The involvement of TLR-2 in the intestinal pathology might be concluded not only from its innate immune role, but also from its effect on modulating the intestinal serotonergic response. Ultimately, regulating the intestinal serotonergic system can be therapeutically exploited to mitigate other enteropathogenic infections, which will help in understanding the gut-microbiome-brain connection.

Neurological and psychiatric effects of hepatitis C virus infection

Hepatitis C virus (HCV) infection is widespread and affects 71 million people worldwide. Although hepatic manifestations are the most frequent, ranging from chronic hepatitis to cirrhosis and hepatocellular carcinoma, it is also associated with several extrahepatic manifestations. Infected patients may present non-specific neurological symptoms, regardless of the presence of liver cirrhosis. Several pathogenetic mechanisms underlying neurological symptoms have been hypothesized: neuroinvasion, immune-mediated damage, neurotransmitter alterations and cryoglobulinemia. Alterations of the central nervous system include cerebral vasculopathy, acute or subacute encephalopathy and inflammatory disorders. HCV infection may be responsible for neuropathies, of which the most frequent form is symmetrical axonal sensory or sensory-motor polyneuropathy which causes loss of leg sensitivity and weakness. Up to 50% of patients with HCV infection may experience cognitive decline and psychological disorders, such as depression and fatigue. HCV associated neurocognitive disorder is independent of the presence of liver cirrhosis and affects different domains than in patients with hepatic encephalopathy. It can be studied using specific tests that mainly explore executive functions, verbal learning and verbal recall. These disorders significantly reduce the quality of life. The new antiviral therapies improve the extrahepatic symptoms of HCV infection and their success depends on the achievement of sustained virological response. However, the effect of therapy may differ depending on the type of organ involved; neurological symptoms can be irreversible if there is organic liver damage. The aim of this review is to provide a critical overview of physiopathological mechanisms, diagnostic and therapeutic strategies of the neurological and psychiatric effects of HCV infection.

Neurotrophic effects of Botulinum neurotoxin type A in hippocampal neurons involve activation of Rac1 by the non-catalytic heavy chain (HCC/A)

Botulinum neurotoxins (BoNTs) are extremely potent naturally occurring poisons that act by silencing neurotransmission. Intriguingly, in addition to preventing presynaptic vesicle fusion, BoNT serotype A (BoNT/A) can also promote axonal regeneration in preclinical models. Here we report that the non-toxic C-terminal region of the receptor-binding domain of heavy chain BoNT/A (HCC/A) activates the small GTPase Rac1 and ERK pathway to potentiate axonal outgrowth, dendritic protrusion formation and synaptic vesicle release in hippocampal neurons. These data are consistent with HCC/A exerting neurotrophic properties, at least in part, independent of any BoNT catalytic activity or toxic effect.

Characterising lipoteichoic acid as an in vitro model of acute neuroinflammation

Toll-like receptor 2 (TLR2) is a primary sensor for pathogens, including those derived from gram-positive bacteria. It can also mediate the effects of endogenous inflammatory signals such as β-amyloid peptide (Aβ), thus promoting the microglial activation and subsequent neuronal dysfunction, characteristic of chronic neuroinflammatory conditions. More recently, a role for TLR2 has been proposed in the pathogenesis of disorders associated with acute inflammation, including anxiety and depression. The current study aims to characterise the acute effects of the TLR2 agonist lipoteichoic acid (LTA) on microglial activation and neuronal integrity, and to evaluate the influence of LTA exposure on sensitivity to the inflammation and neuronal dysfunction associated with Aβ. Using BV2 and N2a cells as an in vitro model, we highlight that acute exposure to LTA robustly promotes inflammatory cytokine and nitric oxide (NO) production in microglia but also in neurons, similar to that reported under longer-term and chronic inflammatory conditions. Moreover, we find that exposure to LTA can enhance sensitivity to subthreshold Aβ, promoting an 'M1'-like phenotype in microglia and provoking dysregulation of neuronal activity in acute hippocampal slices. Anti-inflammatory agents, including mimetics of brain-derived neurotrophic factor (BDNF), have proven effective at alleviating chronic neuroinflammatory complications. We further examined the effects of 7,8,3-trihydroxyflavone (7,8,3-THF), a small-molecule TrkB agonist, on LTA-induced microglial activation. We report that 7,8,3-THF can significantly ameliorate interleukin (IL)-6 and NO production in LTA-stimulated BV2 cells. Taken together, our findings offer support for exploration of TLR2 as a potential target for therapeutic intervention into acute neuroinflammatory conditions. Moreover we propose that exposure to gram-positive bacterial pathogens may promote sensitivity to the inflammatory changes characteristic of the aged brain.

Cytokines and serum amyloid A in the pathogenesis of hepatitis C virus infection

Expression of the acute phase protein serum amyloid A (SAA) is dependent on the release of the pro-inflammatory cytokines IL-1, IL-6 and TNF-α during infection and inflammation. Hepatitis C virus (HCV) upregulates SAA-inducing cytokines. In line with this, a segment of chronically infected individuals display increased circulating levels of SAA. SAA has even been proposed to be a potential biomarker to evaluate treatment efficiency and the course of disease. SAA possesses antiviral activity against HCV via direct interaction with the viral particle, but might also divert infectivity through its function as an apolipoprotein. On the other hand, SAA shares inflammatory and angiogenic activity with chemotactic cytokines by activating the G protein-coupled receptor, formyl peptide receptor 2. These latter properties might promote chronic inflammation and hepatic injury. Indeed, up to 80 % of infected individuals develop chronic disease because they cannot completely clear the infection, due to diversion of the immune response. In this review, we summarize the interconnection between SAA and cytokines in the context of HCV infection and highlight the dual role SAA could play in this disease. Nevertheless, more research is needed to establish whether the balance between those opposing activities can be tilted in favor of the host defense.

Expert opinion on managing chronic HCV in patients with neuropsychiatric manifestations

Neurological manifestations of HCV infection appear to be under-recognized in clinical practice despite the majority of HCV-infected patients experiencing symptoms such as fatigue, depression and cognitive dysfunction. There is also growing evidence for a link between HCV infection and an increased risk of Parkinson's disease. The mechanism underpinning the association between HCV and these neuropsychiatric syndromes still requires further investigation. Here we review the pre-clinical and clinical evidence for a link between HCV and effects on the central nervous system leading to neuropsychiatric syndromes. Lastly, we describe how improvements in neuropsychiatric manifestations of HCV following treatment have been observed, which is subsequently reflected in an overall improvement in health-related quality of life.

HCV Extrahepatic Manifestations

Hepatitis C virus (HCV) has been shown to affect many tissues other than liver. However, of the many extrahepatic manifestations (EMs) that have been associated with HCV, including cryoglobulinemia, lymphoma, insulin resistance, type 2 diabetes and neurological disorders, only a few have been shown to be directly related to HCV infection of extrahepatic tissues. HCV-triggered immune-mediated mechanisms account for most of the EMs. It is estimated that up to 74% of patients with chronic hepatitis C can develop at least one EM. All HCV patients with EMs should be considered for antiviral therapy, although not all will resolve with sustained virological response.

Serum‑derived hepatitis C virus can infect human glioblastoma cell line SF268 and activate the PI3K‑Akt pathway

Extra‑hepatic manifestations are frequently observed in hepatitis C virus (HCV)‑infected patients; however the underlying mechanisms remain largely unknown. In the present study, the human glioblastoma SF268 cell line (the precise origin of the cell type is not clear) was infected with HCV using HCV‑positive serum, and viral replication was assessed by immunofluorescence, reverse transcription‑polymerase chain reaction (PCR), quantitative PCR and western blotting following infection. HCV core protein and HCV RNA were detected in HCV‑positive serum‑infected SF268 cells at day 4 post‑infection, while no infection was observed in cells exposed to HCV‑negative serum. The mean HCV RNA levels at day 4 post‑infection were up to 5.00 IU/ml log10; however, HCV RNA and immunostaining for core protein were negative when cultured to day 6 or longer. The data suggest that human glioblastoma SF268 cells were transiently infected with HCV. AKT serine/threonine kinase phosphorylation was also detected in HCV‑infected SF268 cells at day 4 post‑infection. To the best of our knowledge, this is the first demonstration that a human glioblastoma cell line can be infected with serum‑derived HCV. The results provide evidence that HCV infection can occur in cells of the central nervous system. Neurological disorder‑associated phosphoinositide 3‑kinase‑AKT signaling pathway was activated in parallel with HCV infection, suggesting that SF268 may serve as an in vitro model for investigating HCV‑nervous system cell interactions.

Mechanisms of neuropathogenesis in HIV and HCV: similarities, differences, and unknowns

HIV and hepatitis C virus (HCV) have both been associated with cognitive impairment. Combination antiretroviral therapy (cART) has dramatically changed the nature of cognitive impairment in HIV-infected persons, while the role of direct-acting antivirals (DAA) in neurocognition of HCV-infected individuals remains unclear. Also, whether HIV and HCV interact to promote neurocognitive decline or whether they each contribute an individual effect continues to be an open question. In this work, we review the virally mediated mechanisms of HIV- and HCV-mediated neuropathogenesis, with an emphasis on the role of dual infection, and discuss observed changes with HIV viral suppression and HCV functional cure on neurocognitive impairments.

Depression, fatigue and neurocognitive deficits in chronic hepatitis C

Patients with chronic hepatitis C virus (HCV) infection experience a range of symptoms including depression, fatigue and neurocognitive deficits, impairing quality of life. Depression, in particular, may be reactive to increased psychosocial stress, and the physical symptoms of advanced HCV or associated comorbidities. However, even patients at an early stage of HCV infection, with minimal hepatic inflammation or comorbidities, report more depressive symptoms and fatigue than the general population. Similarly, specific neurocognitive deficits occur in early stage HCV infection and are independent of the presence of depression or encephalopathy. Therefore, intracerebral neurobiological changes associated with HCV may potentially explain these symptoms. These changes may arise from infiltration of the brain by peripherally induced cytokines, as well as direct neuropathic effects of HCV viral particles penetrating the blood-brain barrier. These phenomena parallel those reported in human immunodeficiency virus (HIV) infection. HCV-associated intracerebral changes include upregulated inflammatory responses, altered neurotransmitter levels, hormonal dysregulation, and release of neurotoxic substances. These may subsequently lead to abnormal neuronal conduction and function in areas of the brain governing affective responses, emotional processing, motivation, attention and concentration. Although direct-acting antiviral medications lead to high rates of HCV clearance, intracerebral changes may not be subsequently reversed and symptoms of depression, fatigue and neurocognitive deficits may persist. There is an ongoing role for multidisciplinary care and pharmacotherapy to manage these symptoms in HCV patients. Furthermore, there may be opportunities for future therapies to specifically target and ameliorate HCV-associated intracerebral changes.

Hepatitis C Virus Infection in the Older Patient

Hepatitis C virus (HCV) is the most common blood-borne infection in the United States and is of concern in older adults. HCV infection is associated with not only hepatic but also extrahepatic comorbidities common to the aging patient including diabetes, kidney and cardiovascular diseases, and neurocognitive impairment. The effect of direct-acting antiviral agents to treat HCV on these outcomes is limited. This article summarizes the literature regarding the epidemiology and natural history of HCV infection; the impact of age on clinical outcomes in HCV-infected persons; and current knowledge regarding safety and efficacy of HCV treatment regimens in the older patient.

Intestinal Serotonin Transporter Inhibition by Toll-Like Receptor 2 Activation. A Feedback Modulation

TLR2 is a microbiota recognition receptor that has been described to contribute to intestinal homeostasis and to ameliorate inflammatory intestinal injury. In this context, serotonin (5-HT) has shown to be an essential intestinal physiological neuromodulator that is also involved in intestinal inflammatory diseases. Since the interaction between TLR2 activation and the intestinal serotoninergic system remains non-investigated, our main aim was to analyze the effect of TLR2 on intestinal serotonin transporter (SERT) activity and expression and the intracellular pathways involved. Caco-2/TC7 cells were used to analyze SERT and TLR2 molecular expression and SERT activity by measuring 5-HT uptake. The results showed that apical TLR2 activation inhibits SERT activity in Caco-2/TC7 cells mainly by reducing SERT protein level either in the plasma membrane, after short-term TLR2 activation or in both the plasma membrane and cell lysate, after long-term activation. cAMP/PKA pathway appears to mediate short-term inhibitory effect of TLR2 on SERT; however, p38 MAPK pathway has been shown to be involved in both short- and long-term TLR2 effect. Reciprocally, 5-HT long-term treatment yielded TLR2 down regulation in Caco-2/TC7 cells. Finally, results from in vivo showed an augmented intestinal SERT expression in mice Tlr2^-/-, thus confirming our inhibitory effect of TLR2 on intestinal SERT in vitro. The present work infers that TLR2 may act in intestinal pathophysiology, not only by its inherent innate immune role, but also by regulating the intestinal serotoninergic system.

Hepatitis C virus infection, and neurological and psychiatric disorders - A review

An association between hepatitis C virus infection and neuropsychiatric symptoms has been proposed for some years. A variety of studies have been undertaken to assess the nature and severity of these symptoms, which range from fatigue and depression to defects in attention and verbal reasoning. There is evidence of mild neurocognitive impairment in some patients with HCV infection, which is not fully attributable to liver dysfunction or psychosocial factors. Further evidence of a biological cerebral effect has arisen from studies using magnetic resonance spectroscopy; metabolic abnormalities correlate with cognitive dysfunction and resemble the patterns of neuroinflammation that have been described in HIV infection. Recent research has suggested that, in common with HIV infection, HCV may cross the blood brain barrier leading to neuroinflammation. Brain microvascular endothelial cells, astrocytes and microglia may be minor replication sites for HCV. Importantly, patient reported outcomes improve following successful antiviral therapy. Further research is required to elucidate the molecular basis for HCV entry and replication in the brain, and to clarify implications and recommendations for treatment.

HCV encephalopathy - an artefact due to medical care?

Anti-HCV positive individuals frequently complain about chronic disabling fatigue, mood alterations and deficits in concentration and memory. Several data provide evidence that such alterations are unrelated to hepatitis C virus (HCV) viremia. Thus, merely being exposed to HCV in the past may be sufficient to trigger, but the HCV exposure itself. This commentary reviews the available data upon this topic with special reference to the paper by Lowry and colleagues published in this issue of the Journal of Viral hepatitis. We will carefully discuss scientific reasons, why HCV may be directly involved in the development of neuropsychiatric symptoms independent from ongoing detectable viremia, as suggested by epidemiological data.

Systemic manifestations of hepatitis C infection

Chronic hepatitis C (HCV) is a common infection affecting 185 million people worldwide. The most common manifestation of chronic HCV is progressive liver fibrosis, cirrhosis, liver failure and hepatocellular carcinoma. However, several systemic manifestations of HCV have been recognized and reported in the literature. The purpose of this review is to assimilate published literature based on evidence to categorize these extrahepatic manifestations with the likelihood of a causal association with HCV. Exciting recent developments have resulted in simple all oral interferon-free highly effective therapy for HCV. However, this treatment is also expensive and less accessible to most affected individuals as treatment recommendations are based on stage of liver fibrosis. Expanding the scope of HCV therapy to those with extrahepatic manifestations beyond what is currently recommended will significantly reduce the morbidity and mortality in this aging population.

Extrahepatic manifestations of hepatitis C infection: navigating CHASM

This article describes the importance of extrahepatic systemic manifestations of chronic hepatitis C virus (HCV) infection. While most HCV literature focuses on liver injury and fibrosis progression, a spectrum of systemic disease processes, collectively called C hepatitis-associated systemic manifestations (CHASMs), are present in a high proportion of infected persons. These include thyroid disease (Hashimoto's thyroiditis, Graves disease, and thyroid cancer), cardiovascular disease (atherosclerosis, carotid artery disease, and coronary artery disease), renal disease (MPGN and glomerulosclerosis), eye disease (Mooren's ulcers and sicca syndrome), skin disease (PCT, vasculitis, and lichen planus), lymphomas (NHL and splenic T-cell), and diabetes. Mechanistic understanding of how HCV leads to CHASM processes could lead to development of new interventions. The role of early HCV treatment and cure may result in preventive strategies for a variety of complex disease states. Key Points • Systemic extrahepatic complications of HCV comprise a spectrum of disease states in many organs and systems.• Effective treatment of HCV may reduce or eliminate some but not all of these systemic complications.• Further research into early treatment intervention as a prevention strategy for systemic disease is warranted.

Hepatitis C virus-associated neurocognitive and neuropsychiatric disorders: Advances in 2015

Since its identification in 1989, hepatitis C virus (HCV) has emerged as a worldwide health problem with roughly 185 million chronic infections, representing individuals at high risk of developing cirrhosis and liver cancer. In addition to being a frequent cause of morbidity and mortality due to liver disease, HCV has emerged as an important trigger of lymphoproliferative disorders, owing to its lymphotropism, and of a wide spectrum of extra-hepatic manifestations (HCV-EHMs) affecting different organ systems. The most frequently observed HCV-EHMs include mixed cryoglobulinemia and cryoglobulinemic vasculitis, B-cell non-Hodgkin’s lymphoma, nephropathies, thyreopathies, type 2 diabetes mellitus, cardiovascular diseases, and several neurological conditions. In addition, neuropsychiatric disorders and neurocognitive dysfunction are reported in nearly 50% of patients with chronic HCV infection, which are independent of the severity of liver disease or HCV replication rates. Fatigue, sleep disturbance, depression and reduced quality of life are commonly associated with neurocognitive alterations in patients with non-cirrhotic chronic HCV infection, regardless of the stage of liver fibrosis and the infecting genotype. These manifestations, which are the topic of this review, typically occur in the absence of structural brain damage or signal abnormalities on conventional brain magnetic resonance imaging (MRI), although metabolic and microstructural changes can be detected by in vivo proton magnetic resonance spectroscopy, perfusion-weighted and diffusion tensor MRI, and neurophysiological tests of cognitive processing. Several lines of evidence, including comparative and longitudinal neuropsychological assessments in patients achieving spontaneous or treatment-induced viral clearance, support a major pathogenic role for HCV in neuropsychiatric and neurocognitive disorders.

HIV-1, HCV and alcohol in the CNS: potential interactions and effects on neuroinflammation

Approximately 25% of the HIV-1 positive population is also infected with HCV. The effects of alcohol on HIV-1 or HCV infection have been a research topic of interest due to the high prevalence of alcohol use in these infected patient populations. Although it has long been known that HIV-1 infects the brain, it has only been a little more than a decade since HCV infection of the CNS has been characterized. Both viruses are capable of infecting and replicating in microglia and increasing the expression of proinflammatory cytokines and chemokines, including IL-6 and IL-8. Investigations focusing on the effects of HIV-1, HCV or alcohol on neuroinflammation have demonstrated that these agents are capable of acting through overlapping signaling pathways, including MAPK signaling molecules. In addition, HIV-1, HCV and alcohol have been demonstrated to increase permeability of the blood-brain barrier. Patients infected with either HIV-1 or HCV, or those who use alcohol, exhibit metabolic abnormalities in the CNS that result in altered levels of n-acetyl aspartate, choline and creatine in various regions of the brain. Treatment of HIV/HCV co-infection in alcohol users is complicated by drug-drug interactions, as well as the effects of alcohol on drug metabolism. The drug-drug interactions between the antiretrovirals and the antivirals, as well as the effects of alcohol on drug metabolism, complicate existing models of CNS penetration, making it difficult to assess the efficacy of treatment on CNS infection.

Chronic hepatitis C virus infection and neurological and psychiatric disorders: An overview

Hepatitis C virus (HCV) infection is considered a systemic disease because of involvement of other organs and tissues concomitantly with liver disease. Among the extrahepatic manifestations, neuropsychiatric disorders have been reported in up to 50% of chronic HCV infected patients. Both the central and peripheral nervous system may be involved with a wide variety of clinical manifestations. Main HCV-associated neurological conditions include cerebrovascular events, encephalopathy, myelitis, encephalomyelitis, and cognitive impairment, whereas “brain fog”, depression, anxiety, and fatigue are at the top of the list of psychiatric disorders. Moreover, HCV infection is known to cause both motor and sensory peripheral neuropathy in the context of mixed cryoglobulinemia, and has also been recently recognized as an independent risk factor for stroke. These extrahepatic manifestations are independent of severity of the underlying chronic liver disease and hepatic encephalopathy. The brain is a suitable site for HCV replication, where the virus may directly exert neurotoxicity; other mechanisms proposed to explain the pathogenesis of neuropsychiatric disorders in chronic HCV infection include derangement of metabolic pathways of infected cells, alterations in neurotransmitter circuits, autoimmune disorders, and cerebral or systemic inflammation. A pathogenic role for HCV is also suggested by improvement of neurological and psychiatric symptoms in patients achieving a sustained virologic response following interferon treatment; however, further ad hoc trials are needed to fully assess the impact of HCV infection and specific antiviral treatments on associated neuropsychiatric disorders.

Hepatitis C virus (HCV) interaction with astrocytes: nonproductive infection and induction of IL-18

Hepatitis C virus (HCV) infection causes the central nervous system (CNS) abnormalities in more than 50 % of chronically infected subjects. However, the underlying mechanisms are largely unknown. In this study, we characterized the HCV interactions with astrocytes, one of the putative HCV target cells in the brain. We demonstrated that primary human astrocytes (PHA) were very inefficiently infected by HCV, either in the cell-free form or through cell-cell contact. We then determined the potential restriction steps of HCV infection and replication in these cells. PHA expressed all known HCV receptors but failed to support HCV entry. HCV IRES-mediated RNA translation was functional in PHA and further enhanced by miR122 expression. Nevertheless, PHA did not support HCV replication regardless of miR122 expression. To our great surprise, we found that HCV exposure induced robust IL-18 expression in PHA and exhibited direct neurotoxicity. Taken together, these results showed that astrocytes did not support productive HCV infection and replication, but HCV interactions with astrocytes and neurons alone might be sufficient to cause CNS dysfunction.

Brain viral burden, neuroinflammation and neurodegeneration in HAART-treated HIV positive injecting drug users

The long-term impact of chronic human immunodeficiency virus (HIV) infection on brain status in injecting drug users (IDU) treated with highly active antiretroviral therapy (HAART) is unknown. Viral persistence in the brain with ongoing neuroinflammation may predispose to Alzheimer-like neurodegeneration. In this study, we investigated the brains of ten HAART-treated individuals (six IDU and four non-DU), compared with ten HIV negative controls (six IDU and four non-DU). HIV DNA levels in brain tissue were correlated with plasma and lymphoid tissue viral loads, cognitive status, microglial activation and Tau protein and amyloid deposition. Brain HIV proviral DNA levels were low in most cases but higher in HIV encephalitis (n = 2) and correlated significantly with levels in lymphoid tissue (p = 0.0075), but not with those in plasma. HIV positive subjects expressed more Tau protein and amyloid than HIV negative controls (highest in a 58 year old), as did IDU, but brain viral loads showed no relation to Tau and amyloid. Microglial activation linked significantly to HIV positivity (p = 0.001) and opiate abuse accentuated these microglial changes (p = 0.05). This study confirms that HIV DNA persists in brains despite HAART and that opiate abuse adds to the risk of brain damage in HIV positive subjects. Novel findings in this study show that (1) plasma levels are not a good surrogate indicator of brain status, (2) viral burden in brain and lymphoid tissues is related, and (3) while Tau and amyloid deposition is increased in HIV positive IDU, this is not specifically related to increased HIV burden within the brain.

ERK signaling is triggered by hepatitis C virus E2 protein through DC-SIGN

Dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is a binding receptor for hepatitis C virus (HCV). Binding of HCV envelope protein E2 to target cells is a prerequisite to DC-SIGN-mediated signaling. Using cell lines with stable or transient expression of DC-SIGN, we investigated effects of soluble HCV E2 protein on ERK pathway. MEK and ERK are activated by the E2 in NIH3T3 cells stably expressing DC-SIGN. Treatment of the cells with antibody to DC-SIGN results in inhibition of the E2 binding as well as the E2-induced MEK and ERK activation. In HEK293T cells transiently expressing DC-SIGN, activation of MEK and ERK is also induced by the E2. Activation of ERK pathway by HCV E2 through DC-SIGN provides useful information for understanding cellular receptor-mediated signaling.

ERK2-dependent activation of c-Jun is required for nontypeable Haemophilus influenzae-induced CXCL2 upregulation in inner ear fibrocytes

The inner ear, composed of the cochlea and the vestibule, is a specialized sensory organ for hearing and balance. Although the inner ear has been known as an immune-privileged organ, there is emerging evidence indicating an active immune reaction of the inner ear. Inner ear inflammation can be induced by the entry of proinflammatory molecules derived from middle ear infection. Because middle ear infection is highly prevalent in children, middle ear infection-induced inner ear inflammation can impact the normal development of language and motor coordination. Previously, we have demonstrated that the inner ear fibrocytes (spiral ligament fibrocytes) are able to recognize nontypeable Haemophilus influenzae, a major pathogen of middle ear infection, and upregulate a monocyte-attracting chemokine through TLR2-dependent NF-κB activation. In this study, we aimed to determine the molecular mechanism involved in nontypeable H. influenzae-induced cochlear infiltration of polymorphonuclear cells. The rat spiral ligament fibrocytes were found to release CXCL2 in response to nontypeable H. influenzae via activation of c-Jun, leading to the recruitment of polymorphonuclear cells to the cochlea. We also demonstrate that MEK1/ERK2 signaling pathway is required for nontypeable H. influenzae-induced CXCL2 upregulation in the rat spiral ligament fibrocytes. Two AP-1 motifs in the 5'-flanking region of CXCL2 appeared to function as a nontypeable H. influenzae-responsive element, and the proximal AP-1 motif was found to have a higher binding affinity to nontypeable H. influenzae-activated c-Jun than that of the distal one. Our results will enable us better to understand the molecular pathogenesis of middle ear infection-induced inner ear inflammation.