Association between hepatitis C virus infection and Parkinson's disease

Risk of Parkinson's disease in hepatitis B and C populations: a systematic review and meta-analysis

Parkinson's disease (PD) is a common neurodegenerative disorder, and its association with viral hepatitis has been debated. We performed a meta-analysis to examine the association between PD risk and viral hepatitis. Medline, EMBASE, and the Cochrane library were searched from inception till July 2022. Meta-analysis was conducted using a fixed-effect model with the inverse variance method. Three groups were compared to controls: infection with either hepatitis B or C virus (HBV and HCV, respectively), or coinfection with both viruses. We found 551 records, and six studies comprising of 2,566,947 patients were included in the analysis. PD risk was increased in HCV-infected population (OR 1.10, 95% CI 1.03-1.17, p = 0.005) and (HR 1.37, 95% CI 1.26-1.49, p < 0.001). This increase was not observed for the HBV-infected and HBV-HCV-coinfected coinfection populations. For pooled OR, the risk was significantly lower in HBV-infected (OR 0.79, 95% CI 0.76-0.83, p < 0.001) but not significantly different in HBV-HCV-coinfected populations (OR 0.96, 95% CI 0.82-1.12, p = 0.57). For pooled HR, the risk was significantly higher in both HBV-infected (HR 1.22, 95% CI 1.14-1.31, p < 0.001) and HBV-HCV-coinfected populations (HR 1.29, 95% CI 1.05-1.58, p = 0.013). We found that the risk of PD was increased in the HCV-infected population, but results were inconsistent in those with HBV and HBV-HCV infections. Our findings provide impetus for further clinical and functional studies to unravel the role of the adaptive immune system in PD.

Microorganisms associated with increased risk of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects more than 7 million people worldwide. Its aetiology is unknown, although the hypothesis of a genetic susceptibility to environmental agents is accepted. These environmental agents include fungi, bacteria, and viruses. Three microorganisms are directly associated with a significantly increased risk of developing Parkinson's disease: the fungal genus Malassezia, the bacterium Helicobacter pylori, and the hepatitis C virus. If the host is vulnerable due to genetic susceptibility or immune weakness, these microorganisms can access and infect the nervous system, causing chronic neuroinflammation with neurodegeneration. Other microorganisms show an epidemiological association with the disease, including the influenza type A, Japanese encephalitis type B, St Louis, and West Nile viruses. These viruses can affect the nervous system, causing encephalitis, which can result in parkinsonism. This article reviews the role of all these microorganisms in Parkinson's disease.

Infectious Microorganisms Seen as Etiologic Agents in Parkinson’s Disease

Infections represent a possible risk factor for parkinsonism and Parkinson’s disease (PD) based on information from epidemiology and fundamental science. The risk is unclear for the majority of agents. Moreover, the latency between infection and PD seems to be very varied and often lengthy. In this review, the evidence supporting the potential involvement of infectious microorganisms in the development of Parkinson’s disease is examined. Consequently, it is crucial to determine the cause and give additional treatment accordingly. Infection is an intriguing suggestion regarding the cause of Parkinson’s disease. These findings demonstrate that persistent infection with viral and bacterial microorganisms might be a cause of Parkinson’s disease. As an initiating factor, infection may generate a spectrum of gut microbiota dysbiosis, engagement of glial tissues, neuroinflammation, and alpha-synuclein accumulation, all of which may trigger and worsen the onset in Parkinson’s disease also contribute to its progression. Still uncertain is the primary etiology of PD with infection. The possible pathophysiology of PD infection remains a matter of debate. Furthermore, additional study is required to determine if PD patients develop the disease due to infectious microorganisms or solely since they are more sensitive to infectious causes.

Parkinsonism associated with viral infection

There are several known causes of secondary parkinsonism, the most common being head trauma, stroke, medications, or infections. A growing body of evidence suggests that viral agents may trigger parkinsonian symptoms, but the exact pathological mechanisms are still unknown. In some cases, lesions or inflammatory processes in the basal ganglia or substantia nigra have been found to cause reversible or permanent impairment of the dopaminergic pathway, leading to the occurrence of extrapyramidal symptoms. This chapter reviews current data regarding the viral agents commonly associated with parkinsonism, such as Epstein Barr virus (EBV), hepatitis viruses, human immunodeficiency virus (HIV), herpes viruses, influenza virus, coxsackie virus, and Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). We present possible risk factors, proposed pathophysiology mechanisms, published case reports, common associations, and prognosis in order to offer a concise overview of the viral spectrum involved in parkinsonism.

Neuroprotective approaches to halt Parkinson's disease progression

One of the most significant threats in Parkinson's disease (PD) is neurodegeneration. Neurodegeneration at both nigral as well as non-nigral regions of the brain is considered responsible for disease progression in PD. The key factors that initiate neurodegeneration are oxidative stress, neuroinflammation, mitochondrial complex-1 inhibition, and abnormal α-synuclein (SNCA) protein aggregations. Nigral neurodegeneration results in motor symptoms (tremor, bradykinesia, rigidity, shuffling gait, and postural instability) whereas; non-nigral neurodegeneration is responsible for non-motor symptoms (depression, cognitive dysfunctions, sleep disorders, hallucination, and psychosis). The available therapies for PD aim at increasing dopamine levels. The medications such as Monoamine oxidase B (MAO-B) inhibitors, catechol o-methyltransferase (COMT) inhibitors, Dopamine precursor (Levodopa), dopamine agonists, and dopamine reuptake inhibitors drastically improve the motor symptoms and quality of life only in the early stages of the disease. However, dopa resistant motor symptoms (abnormality in posture, speech impediment, gait, and balance problems), dopa resistant non-motor signs (sleep problems, autonomic dysfunction, mood, and cognitive impairment, pain), and drug-related side effects (motor fluctuations, psychosis, and dyskinesias) are considered responsible for the failure of these therapies. Further, none of the treatments, alone or in combination, are capable of halting the disease progression in the long run. Therefore, there is a need to develop safe and efficient neuroprotective agents, which can slow or stop the disease progression for the better management of PD. In this review, an effort has been made to discuss the various mechanisms responsible for progressive neurodegeneration (disease progression) in PD and also multiple strategies available for halting disease progression.

Reducing neuroinflammation via therapeutic compounds and lifestyle to prevent or delay progression of Parkinson's disease

Parkinson's disease (PD) is the second most common age-associated neurodegenerative disorder and is characterised by progressive loss of dopamine neurons in the substantia nigra. Peripheral immune cell infiltration and activation of microglia and astrocytes are observed in PD, a process called neuroinflammation. Neuroinflammation is a fundamental response to protect the brain but, when chronic, it triggers neuronal damage. In the last decade, central and peripheral inflammation were suggested to occur at the prodromal stage of PD, sustained throughout disease progression, and may play a significant role in the pathology. Understanding the pathological mechanisms of PD has been a high priority in research, primarily to find effective treatments once symptoms are present. Evidence indicates that early life exposure to neuroinflammation as a consequence of life events, environmental or behaviour factors such as exposure to infections, pollution or a high fat diet increase the risk of developing PD. Many studies show healthy habits and products that decrease neuroinflammation also reduce the risk of PD. Here, we aim to stimulate discussion about the role of neuroinflammation in PD onset and progression. We highlight that reducing neuroinflammation throughout the lifespan is critical for preventing idiopathic PD, and present epidemiological studies that detail risk and protective factors. It is possible that introducing lifestyle changes that reduce neuroinflammation at the time of PD diagnosis may slow symptom progression. Finally, we discuss compounds and therapeutics to treat the neuroinflammation associated with PD.

The Role of Pathogens and Anti-Infective Agents in Parkinson's Disease, from Etiology to Therapeutic Implications

Parkinson's disease is a debilitating neurodegenerative disorder whose etiology is still unclear, hampering the development of effective treatments. There is an urgent need to identify the etiology and provide further effective treatments. Recently, accumulating evidence has indicated that infection may play a role in the etiology of Parkinson's disease. The infective pathogens may act as a trigger for Parkinson's disease, the most common of which are hepatitis C virus, influenza virus, and Helicobacter pylori. In addition, gut microbiota is increasingly recognized to influence brain function through the gut-brain axis, showing an important role in the pathogenesis of Parkinson's disease. Furthermore, a series of anti-infective agents exhibit surprising neuroprotective effects via various mechanisms, such as interfering with α-synuclein aggregation, inhibiting neuroinflammation, attenuating oxidative stress, and preventing from cell death, independent of their antimicrobial effects. The pleiotropic agents affect important events in the pathogenesis of Parkinson's disease. Moreover, most of them are less toxic, clinically safe and have good blood-brain penetrability, making them hopeful candidates for the treatment of Parkinson's disease. However, the use of antibiotics and subsequent gut dysbiosis may also play a role in Parkinson's disease, making the long-term effects of anti-infective drugs worthy of further consideration and exploration. This review summarizes the current evidence for the association between infective pathogens and Parkinson's disease and subsequently explores the application prospects of anti-infective drugs in Parkinson's disease treatment, providing novel insights into the pathogenesis and treatment of Parkinson's disease.

Microorganisms that are related with increased risk for Parkinson's disease

Parkinson's disease is a neurodegenerative disorder that affects more than 7 million people worldwide. Its aetiology is unknown, although the hypothesis of a genetic susceptibility to environmental agents is accepted. These environmental agents include fungi, bacteria, and viruses. Three microorganisms are directly associated with a significantly increased risk of developing Parkinson's disease: the fungal genus Malassezia, the bacterium Helicobacter pylori, and the hepatitis C virus. If the host is vulnerable due to genetic susceptibility or immune weakness, these microorganisms can access and infect the nervous system, causing chronic neuroinflammation with neurodegeneration. Other microorganisms show an epidemiological association with the disease, including the influenza type A, Japanese encephalitis type B, St Louis, and West Nile viruses. These viruses can affect the nervous system, causing encephalitis, which can result in parkinsonism. This article reviews the role of all these microorganisms in Parkinson's disease.

Association between viral hepatitis infection and Parkinson's disease: A population-based prospective study

The association between hepatitis virus infection and Parkinson's disease remains controversial. To determine whether hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are associated with an increased risk of Parkinson's disease in Korean aged ≥40 years, we completed a population-based prospective study including patients without infections and those with HBV, HCV and HBV/HCV infections from 2005 to 2015. We used the International Classification of Diseases 10th Revision to identify Parkinson's disease (G20) and chronic hepatitis C virus (B18.2) and chronic hepatitis B virus infections (B18.0 or B18.1). To identify Parkinson's disease risk, competing risk analysis adjusted for age, sex, comorbidities and death was performed. Overall, 1 010 317 patients (358 052, noninfection; 488 990, hepatitis B; 144 459 hepatitis C; and 18 680 hepatitis B/C) were included. The incidence density of Parkinson's disease per 10 000 person-years was highest in the hepatitis C group (8.0), followed by the hepatitis B/C (6.8) and hepatitis B (5.0) groups. Hypertension, ischaemic heart disease, epilepsy, stroke and depressive disorder increased the hazard of Parkinson's disease in all groups. The adjusted hazard ratios were 1.25 (95% confidence interval: 1.17-1.35), 1.39 (95% confidence interval: 1.27-1.52) and 1.46 (95% confidence interval: 1.14-1.85) in the HBV, HCV, and HBV/HCV groups, respectively. Our findings suggest that adult patient of 40 years and older with HBV and HCV infections should be monitored for signs of Parkinson's disease so that early intervention and accurate treatment can be provided for minimizing the development and consequences of Parkinson's disease.

α-Synuclein-specific T cell reactivity is associated with preclinical and early Parkinson's disease

A diagnosis of motor Parkinson’s disease (PD) is preceded by a prolonged premotor phase with accumulating neuronal damage. Here we examined the temporal relation between α-synuclein (α-syn) T cell reactivity and PD. A longitudinal case study revealed that elevated α-syn-specific T cell responses were detected prior to the diagnosis of motor PD, and declined after. The relationship between T cell reactivity and early PD in two independent cohorts showed that α-syn-specific T cell responses were highest shortly after diagnosis of motor PD and then decreased. Additional analysis revealed significant association of α-syn-specific T cell responses with age and lower levodopa equivalent dose. These results confirm the presence of α-syn-reactive T cells in PD and show that they are most abundant immediately after diagnosis of motor PD. These cells may be present years before the diagnosis of motor PD, suggesting avenues of investigation into PD pathogenesis and potential early diagnosis.

α-Synuclein-specific T cell reactivity is preferentially associated with Parkinson’s disease (PD) patients, but the temporal relation with diagnosis was previously unknown. This study reveals that α-syn-reactive T cells are highest before and shortly after diagnosis of motor PD, and then decrease.

G2019S-LRRK2 mutation enhances MPTP-linked Parkinsonism in mice

Parkinson's disease (PD) is a common neurodegenerative disease with a heterogeneous etiology that involves genetic and environmental factors or exogenous. Current LRRK2 PD animal models only partly reproduce the characteristics of the disease with very subtle dopaminergic neuron degeneration. We developed a new model of PD that combines a sub-toxic MPTP insult to the G2019S-LRRK2 mutation. Our newly generated mice, overexpressing mutant G2019S-LRRK2 protein in the brain, displayed a mild, age-dependent progressive motor impairment, but no reduction of lifespan. Cortical neurons from G2019S-LRRK2 mice showed an increased vulnerability to stress insults, compared with neurons overexpressing wild-type WT-LRRK2, or non-transgenic (nTg) neurons. The exposure of LRRK2 transgenic mice to a sub-toxic dose of MPTP resulted in severe motor impairment, selective loss of dopamine neurons and increased astrocyte activation, whereas nTg mice with MPTP exposure showed no deficits. Interestingly, mice overexpressing WT-LRRK2 showed a significant impairment that was milder than for the mutant G2019S-LRRK2 mice. L-DOPA treatments could partially improve the movement impairments but did not protect the dopamine neuron loss. In contrast, treatments with an LRRK2 kinase inhibitor significantly reduced the dopaminergic neuron degeneration in this interaction model. Our studies provide a novel LRRK2 gene-MPTP interaction PD mouse model, and a useful tool for future studies of PD pathogenesis and therapeutic intervention.

Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies

AIMS

Recent studies showed that patients with various bacterial, viral, and fungal infections might be at increased risk of Parkinson's disease (PD). However, the risk of PD in patients with each specific infection varied. This meta-analysis estimated the association between various infections and PD risk.

METHODS

Literature published from January 1965 to October 2019 in PubMed and EMBASE databases was searched. Data were extracted and pooled using random/fixed effects model. Sensitivity analysis and meta-regression were also performed to analyze the source of heterogeneity. Publication bias was estimated by the trim and fill.

RESULTS

Twenty-three out of 6,609 studies were included. Helicobacter pylori (HP; pooled OR = 1.653, 1.426-1.915, p < .001), hepatitis C virus (HCV; pooled OR = 1.195, 1.012-1.410, p = .035), Malassezia (pooled OR = 1.694, 1.367-2.100, p < .001), and pneumoniae (pooled OR = 1.595, 1.020-2.493, p = .041) infection were associated with increased PD risk. Influenza virus, herpes virus, hepatitis B virus, scarlet fever, mumps virus, chicken pox, pertussis, German measles, and measles were not associated with PD risk. After antiviral treatment against HCV reduced the risk of PD in patients with HCV infection (OR = 0.672, 0.571-0.791, p < .001). Significant heterogeneity exists among the included studies.

CONCLUSION

Patients with infection of HP, HCV, Malassezia, pneumoniae might be an increased risk of PD. Antiviral treatment of HCV could reduce the risk of PD.

Antiviral Therapy in Patients With Chronic Hepatitis C Is Associated With a Reduced Risk of Parkinsonism

BACKGROUND

The risk of parkinsonism after antiviral treatment against chronic hepatitis C (CHC) is unclear.

OBJECTIVES

To investigate the association between CHC and parkinsonism and the efficacy of antiviral therapy.

METHODS

Using the National Health Insurance Research Database of Taiwan from 2004 to 2012, patients with and without CHC, patients receiving pegylated interferon-based antiviral therapy, and those without such therapy were matched by age, gender, and comorbidities by propensity scores and followed for new diagnoses of parkinsonism and Parkinson's disease (PD). Multivariable Cox proportional hazards regression analyses were performed.

RESULTS

Overall, 49,342 patients with CHC were matched with 49,342 non-CHC patients. After adjustment for confounding factors, there was a significantly increased risk (31%) of parkinsonism (hazard ratio [HR] 1.306; 95% confidence interval [CI], 1.208-1.412) in those with CHC and the risk of parkinsonism requiring anti-Parkinson medication (HR 1.323; 95% CI, 1.214-1.441). Furthermore, 23,647 untreated CHC patients were matched with 23,647 patients receiving antiviral therapy. Patients receiving antiviral therapy had a significantly lower risk of developing parkinsonism (38%; HR 0.618; 95% CI, 0.498-0.765) and a reduced risk of parkinsonism requiring anti-Parkinson medication (HR 0.651; 95% CI, 0.515-0.823). In sensitivity analyses, antiviral therapy significantly reduced the risk of parkinsonism and PD after adjustment for detection, selection, disease latency biases, and competing mortality. Our results suggest successful antiviral therapy associates with a reduced risk of hepatitis C virus-related parkinsonism compared with those with treatment failure.

CONCLUSIONS

CHC infection is associated with an increased risk of parkinsonism or PD. Antiviral therapy against CHC is associated with a reduced risk of parkinsonism or PD. © 2019 International Parkinson and Movement Disorder Society.

Impact of infection on risk of Parkinson's disease: a quantitative assessment of case-control and cohort studies

Identifying modifiable risk factors for Parkinson's disease (PD) to help prevent this disease has attracted increasing interest in recent years for the limited effective drugs at present. Despite many studies indicated that infection acts as a risk factor for PD, there is no quantitative assessment of the impact of viral and bacterial infections on the risk of developing PD. The present study performed a meta-analysis on the basis of 38 datasets from 13 studies covering 287,773 PD cases and 7,102,901 controls to ascertain the association between PD and infection and the differences in the strength of the viral and bacterial infections. The overall meta-analytic results indicated that individuals with infection had a 20% increased risk of PD compared with controls (OR 1.20, 95%CI 1.07-1.32). The subgroup analysis according to the type of infection found that bacterial infection had a significant impact on increased risk of PD (OR 1.40, 95%CI 1.32-1.48). The present analysis indicated that infection could increase the risk of developing PD, and physician should be aware of the risk of developing PD in subjects with infection.

Triggers, Facilitators, and Aggravators: Redefining Parkinson's Disease Pathogenesis

We hypothesize that Parkinson's disease (PD) pathogenesis can be divided into three temporal phases. During the first phase, 'triggers', such as viral infections or environmental toxins, spark the disease process in the brain and/or peripheral tissues. Triggers alone, however, may be insufficient, requiring 'facilitators' like peripheral inflammation for PD pathology to develop. Once the disease manifests, 'aggravators' spur further neurodegeneration and exacerbate symptoms. Aggravators are proposed to include impaired autophagy and cell-to-cell propagation of α-synuclein pathology. We believe clinical trials need to consider these three phases and target potential therapies at the appropriate stage of the disease process in order to be effective.

Association of viral hepatitis and bipolar disorder: a nationwide population-based study

Background

Bipolar disorder (BD), a type of psychiatric mood disorder, is manifested by chronic and recurrent mood fluctuations. This study aims to determine whether hepatitis B virus (HBV) or hepatitis C virus (HCV) infection is a risk factor for BD.

Methods

A total of 48,215 patients with newly diagnosed viral hepatitis from 2000 to 2010 were identified and frequency-matched with 192,860 people without hepatitis. Both groups were followed until diagnosis with BD, withdrawal from the national health insurance program, or the end of 2011. Patients with viral hepatitis were grouped into 3 cohorts: HBV infection, HCV infection, and HBV/HCV coinfection. The association between viral hepatitis and BD were examined using Cox proportional hazards regression models.

Results

The incidence of BD was higher in HBV/HCV coinfection than in the control group, with an adjusted hazard ratio of 2.16 (95% confidence interval 1.06–4.41) when adjusted for sex, age, and comorbidity. After further adjustment, we noted that an age more than 65 years and female may be associated with an increased risk of BD in patients with chronic hepatitis B and C.

Conclusion

Viral hepatitis may be associated with increased risk of subsequent BD.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1542-3) contains supplementary material, which is available to authorized users.

Hepatitis C virus infection and risk of Parkinson's disease: a systematic review and meta-analysis

BACKGROUND/OBJECTIVE

Hepatitis C virus (HCV) infection is one of the most common infections worldwide. Recent epidemiologic studies have suggested that patients with HCV infection might be at an increased risk of Parkinson's disease. However, the data on this relationship remain inconclusive. This meta-analysis was conducted with the aim to summarize all available evidence.

PATIENTS AND METHODS

A literature search was performed using MEDLINE and EMBASE database from inception to May 2017. Studies that reported relative risks, odd ratios (ORs), or hazard ratios comparing the risk of Parkinson's disease among HCV-infected patients versus participants without HCV infection were included. Pooled OR and 95% confidence interval were calculated using a random-effect, generic inverse variance method.

RESULTS

Of 468 studies, five studies with 323 974 participants met our eligibility criteria and were included in the analysis. We found a higher risk of Parkinson's disease among patients with chronic HCV infection compared with participants without HCV infection with the pooled OR of 1.35 (95% confidence interval: 1.19-1.52). The statistical heterogeneity of this study was insignificant (I=3%). The main limitation of this meta-analysis was the limited accuracy of diagnosis in the primary studies as they were coding-based studies.

CONCLUSION

This study demonstrated a higher risk of Parkinson's disease among HCV-infected patients. Further studies are required to clarify how this risk should be addressed in the clinical picture.

Evidence for association between hepatitis C virus and Parkinson's disease

Parkinson's disease (PD) is a globally prevalent neurodegenerative disorder, characterized by progressive neuronal loss in the substantia nigra and formation of Lewy bodies. These pathological characteristics are clinically translated into motor symptoms, such as bradykinesia, rigidity, resting tremors, and postural instability. Emerging data from epidemiological studies suggest a possible association between PD and hepatitis C virus (HCV) infection, which affects up to 71 million individuals worldwide. Preclinical studies have shown that HCV can penetrate and replicate within the brain macrophages and microglial cells, increasing their production of pro-inflammatory cytokines that can directly cause neuronal toxicity. Other studies reported that interferon, previously used to treat HCV infection, can increase the risk of PD through inhibition of the nigrostriatal dopaminergic transmission or induction of neuroinflammation. In this article, we provide a comprehensive review on the possible association between HCV infection and PD and highlight recommendations for further research and practice in this regard.