The Impact of SARS-CoV-2 Infection on the Development of Neurodegeneration in Multiple Sclerosis

Potential Mechanisms Underlying COVID-19-Mediated Central and Peripheral Demyelination: Roles of the RAAS and ADAM-17

Demyelination is among the most conspicuous neurological sequelae of SARS-CoV-2 infection (COVID-19) in both the central (CNS) and peripheral (PNS) nervous systems. Several hypotheses have been proposed to explain the mechanisms underlying demyelination in COVID-19. However, none have considered the SARS-CoV-2's effects on the renin-angiotensin-aldosterone system (RAAS). Therefore, our objective in this review is to evaluate how RAAS imbalance, caused by direct and indirect effects of SARS-CoV-2 infection, could contribute to myelin loss in the PNS and CNS. In the PNS, we propose that demyelination transpires from two significant changes induced by SARS-CoV-2 infection, which include upregulation of ADAM-17 and induction of lymphopenia. Whereas, in the CNS, demyelination could result from RAAS imbalance triggering two alterations: (1) a decrease in angiotensin type II receptor (AT2R) activity, responsible for restraining defense cells' action on myelin; (2) upregulation of ADAM-17 activity, leading to impaired maturation of oligodendrocytes and myelin formation. Thus, we hypothesize that increased ADAM-17 activity and decreased AT2R activity play roles in SARS-CoV-2 infection-mediated demyelination in the CNS.

SARS-CoV-2 Infection to Premature Neuronal Aging and Neurodegenerative Diseases: Is there any Connection with Hypoxia?

The pandemic of coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, has become a global concern as it leads to a spectrum of mild to severe symptoms and increases death tolls around the world. Severe COVID-19 results in acute respiratory distress syndrome, hypoxia, and multi- organ dysfunction. However, the long-term effects of post-COVID-19 infection are still unknown. Based on the emerging evidence, there is a high possibility that COVID-19 infection accelerates premature neuronal aging and increases the risk of age-related neurodegenerative diseases in mild to severely infected patients during the post-COVID period. Several studies correlate COVID-19 infection with neuronal effects, though the mechanism through which they contribute to the aggravation of neuroinflammation and neurodegeneration is still under investigation. SARS-CoV-2 predominantly targets pulmonary tissues and interferes with gas exchange, leading to systemic hypoxia. The neurons in the brain require a constant supply of oxygen for their proper functioning, suggesting that they are more vulnerable to any alteration in oxygen saturation level that results in neuronal injury with or without neuroinflammation. We hypothesize that hypoxia is one of the major clinical manifestations of severe SARS-CoV-2 infection; it directly or indirectly contributes to premature neuronal aging, neuroinflammation, and neurodegeneration by altering the expression of various genes responsible for the survival of the cells. This review focuses on the interplay between COVID-19 infection, hypoxia, premature neuronal aging, and neurodegenerative diseases and provides a novel insight into the molecular mechanisms of neurodegeneration.

The association between various viral infections and multiple sclerosis: An umbrella review on systematic review and meta-analysis

Multiple Sclerosis (MS) is one of the immune-mediated demyelinating disorders. Multiple components, including the environment and genetics, are possible factors in the pathogenesis of MS. Also, it can be said that infections are a key component of the host's response to MS development. Finally, we evaluated the relationship between different pathogens and MS disease in this umbrella research. We systematically collected and analysed multiple meta-analyses focused on one particular topic. We utilised the Scopus, PubMed, and Web of Science databases starting with inception until 30 May 2023. The methodological quality of the analysed meta-analysis has been determined based on Assessing the Methodological Quality of Systematic Reviews 2 and Grade, and graph construction and statistical analysis were conducted using Comprehensive Meta-Analysis. The Confidence Interval of effect size was 95% in meta-analyses, and p < 0.05 indicated a statistically meaningful relationship. The included studies evaluated the association between MS and 12 viruses containing SARS-CoV-2, Epstein-Barr virus (EBV), Hepatitis B virus, varicella-zoster virus (VZV), human herpesvirus 6 (HHV-6), HHV-7, HHV-8, HSV-1, HSV-2, Cytomegalovirus, Human Papillomavirus, and influenza. SARS-CoV-2, with a 3.74 odds ratio, has a significantly more potent negative effect on MS among viral infections. After that, EBV, HHV-6, HSV-2, and VZV, respectively, with 3.33, 2.81, 1.76, and 1.72 odds ratios, had a significantly negative relationship with MS (p < 0.05). Although the theoretical evidence mostly indicates that EBV has the greatest effect on MS, recent epidemiological studies have challenged this conclusion and put forward possibilities that SARS-CoV-2 is the culprit. Hence, it was necessary to investigate the effects of SARS-CoV-2 and EBV on MS.

The Evolvement of OCT and OCT-A in Identifying Multiple Sclerosis Biomarkers

The prevalence of multiple sclerosis (MS) has been increasing among young people in developing countries over the last years. With the continuous development of new technology, the diagnosis and follow-up of these patients has received new parameters that physicians may use in their practice. This paper reviews the main biomarkers identified through Optical Coherence Tomography Angiography (OCT-A) involved in the development and progression of MS and investigates the role it may have in detecting changes to the central nervous system (CNS).

The association of upper respiratory infections with neuro-radiological course and attack rate of multiple sclerosis: Results from a large prospective cohort

Background

Although upper respiratory infections (URIs) are linked to multiple sclerosis (MS) attacks, SARS-COV2 has not been compared to URIs for attack rates.

Objectives

This study aimed to evaluate the attack rate and the results of neuroimaging in MS patients with URIs caused by COVID-19 and non-COVID-19 infections (NC-URI).

Methods

From May 2020 to April 2021, we followed 362 patients with relapsing-remitting MS in a prospective cohort design. Patients were monitored regularly every 12 weeks; an magnetic resonance imaging (MRI) scan was performed at enrollment and every time a relapse occurred. Poisson analysis was used to determine exacerbation rate ratios (RR) and the MRI parameters were tested using chi-square analysis.

Results

347 patients with an average age of 38 and a female ratio of 86% were included. A RR of 2.24 (p < 0.001) was observed for exacerbations during the at-risk period (ARP). Attacks related to COVID-19 (RR = 2.13, p = 0.001) and NC-URIs (RR = 2.39, p < 0.001) were comparable regarding the increased risk of exacerbation (p = 0.62). Exacerbations within or outside the ARP did not significantly alter the number of baseline GAD-enhancing lesions (p > 0.05 for both).

Conclusion

COVID-19 has been shown to increase the risk of MS exacerbations, like other viral URIs.

T cell responses to COVID-19 infection and vaccination in patients with multiple sclerosis receiving disease-modifying therapy

BACKGROUND

Multiple sclerosis (MS) is a neurological disorder marked by accumulating immune-mediated damage to the central nervous system. The dysregulated immune system in MS combined with immune effects of disease-modifying therapies (DMTs) used in MS treatment could alter responses to infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19). Most of the literature on immune response to SARS-CoV-2 infection and COVID-19 vaccination, in both the general population and patients with MS on DMTs, has focused on humoral immunity. However, immune response to COVID-19 involves multiple lines of defense, including T cells.

OBJECTIVE AND METHODS

We review innate and adaptive immunity to COVID-19 and expand on the role of T cells in mediating protective immunity against SARS-CoV-2 infection and in responses to COVID-19 vaccination in MS.

RESULTS

Innate, humoral, and T cell immune responses combat COVID-19 and generate protective immunity. Assays detecting cytokine expression by T cells show an association between SARS-CoV-2-specific T cell responses and milder/asymptomatic COVID-19 and protective immune memory.

CONCLUSION

Studies of COVID-19 immunity in people with MS on DMTs should ideally include comprehensive assessment of innate, humoral, and T cell responses.

COVID-19 and its implications on the clinico-radiological course of multiple sclerosis: A case-control study

BACKGROUND

Multiple sclerosis (MS) is an immune-mediated disease that has been related to several risk factors such as various viral infections. We carried out this study in order to establish a relationship between COVID-19 infection and MS severity.

METHODS

In a case-control study, we recruited patients with relapsing-remitting multiple sclerosis (RRMS). Patients were divided into two groups based on positive COVID-19 PCR at the end of the enrollment phase. Each patient was prospectively followed for 12 months. Demographical, clinical, and past medical history were collected during routine clinical practice. Assessments were performed every six months; MRI was performed at enrollment and 12 months later.

RESULTS

Three hundred and sixty-two patients participated in this study. MS patients with COVID-19 infection had significantly higher increases in the number of MRI lesions (p: 0.019, OR(CI): 6.37(1.54-26.34)) and EDSS scores (p: 0.017), but no difference was found in total annual relapses or relapse rates. COVID-19 infections were positively correlated with EDSS progression (p: 0.02) and the number of new MRI lesions (p: 0.004) and predicted the likelihood of the number of new MRI lesions by an odds of 5.92 (p: 0.018).

CONCLUSION

COVID-19 may lead to higher disability scores in the RRMS population and is associated with developing new Gd-enhancing lesions in MRI imaging. However, no difference was observed between the groups regarding the number of relapses during follow-up.

COVID-19 and its implications on the clinico-radiological course of multiple sclerosis: A case-control study

Background

Multiple sclerosis (MS) is an immune-mediated disease that has been related to several risk factors such as various viral infections. We carried out this study in order to establish a relationship between COVID-19 infection and MS severity.

Methods

In a case-control study, we recruited patients with relapsing-remitting multiple sclerosis (RRMS). Patients were divided into two groups based on positive COVID-19 PCR at the end of the enrollment phase. Each patient was prospectively followed for 12 months. Demographical, clinical, and past medical history were collected during routine clinical practice. Assessments were performed every six months; MRI was performed at enrollment and 12 months later.

Results

Three hundred and sixty-two patients participated in this study. MS patients with COVID-19 infection had significantly higher increases in the number of MRI lesions (p: 0.019, OR(CI): 6.37(1.54-26.34)) and EDSS scores (p: 0.017), but no difference was found in total annual relapses or relapse rates. COVID-19 infections were positively correlated with EDSS progression (p: 0.02) and the number of new MRI lesions (p: 0.004) and predicted the likelihood of the number of new MRI lesions by an odds of 5.92 (p: 0.018).

Conclusion

COVID-19 may lead to higher disability scores in the RRMS population and is associated with developing new Gd-enhancing lesions in MRI imaging. However, no difference was observed between the groups regarding the number of relapses during follow-up.

The Effects of SARS-CoV-2 Infection on the Cognitive Functioning of Patients with Pre-Existing Dementia

Background

Cognitive postscripts of COVID-19, codenamed as 'cognitive COVID' or 'brain fog,' characterized by multidomain cognitive impairments, are now being reckoned as the most devastating sequelae of COVID-19. However, the impact on the already demented brain has not been studied.

Objective

We aimed to assess the cognitive functioning and neuroimaging following SARS-CoV-2 infection in patients with pre-existing dementia.

Methods

Fourteen COVID-19 survivors with pre-existing dementia (four with Alzheimer's disease, five with vascular dementia, three with Parkinson's disease dementia, and two with the behavioral variant of frontotemporal dementia) were recruited. All these patients had detailed cognitive and neuroimaging evaluations within three months before suffering from COVID-19 and one year later.

Results

Of the 14 patients, ten required hospitalization. All developed or increased white matter hyperintensities that mimicked multiple sclerosis and small vessel disease. There was a significant increase in fatigue (p = 0.001) and depression (p = 0.016) scores following COVID-19. The mean Frontal Assessment Battery (p < 0.001) and Addenbrooke's Cognitive Examination (p = 0.001) scores also significantly worsened.

Conclusion

The rapid progression of dementia, the addition of further impairments/deterioration of cognitive abilities, and the increase or new appearance of white matter lesion burden suggest that previously compromised brains have little defense to withstand a new insult (i.e., 'second hit' like infection/dysregulated immune response, and inflammation). 'Brain fog' is an ambiguous terminology without specific attribution to the spectrum of post-COVID-19 cognitive sequelae. We propose a new codename, i.e. 'FADE-IN MEMORY' (i.e., Fatigue, decreased Fluency, Attention deficit, Depression, Executive dysfunction, slowed INformation processing speed, and subcortical MEMORY impairment).

Characteristics and management of multiple sclerosis patients during the Omicron era: is there a concern about the MS course in the face of the new variant of COVID-19?

INTRODUCTION

The Omicron variant of COVID-19 is highly transmissible, triggering unprecedented infection rates. The present study aimed to investigate the course of multiple sclerosis (MS) in the Omicron era among Iranian patients with MS.

METHODS

This observational study was designed on MS patients of the national MS registry of Iran through a self-designed online questionnaire. A questionnaire was prepared as a Google Form for MS patients during the Omicron outbreak from 1 March to 30 April 2022.

RESULTS

One hundred seventy-four patients with a mean age of 37.3 ± 9.04 were enrolled. Of the patients, 95.97% used DMT, the most common of which were rituximab and fingolimod. Of the patients, 77.58% were fully vaccinated for COVID-19. Regardless of the COVID-19 vaccination status, 76 patients developed COVID-19, which was mild to moderate. Except for recent corticosteroid therapy and secondary progressive MS (SPMS), other demographic and MS characteristics were not significantly associated with the severity of COVID-19. There was also a marginal association between the Expanded Disability Status Scale (EDSS) and the severity of COVID-19. In addition, 17.10% of patients reported MS relapse following COVID-19 leading to escalation therapy in eight patients.

CONCLUSION

Our study demonstrated that in the Omicron era, most patients developed mild COVID-19. Although the predominant COVID-19 variant in this period was Omicron, we could not separate the pathogenic variants. The risk factors for COVID-19 during the Omicron era were not different from other pandemic waves. Our preliminary results revealed that the MS relapse following COVID-19 was higher than in previous waves.

Survival and Neurogenesis-Promoting Effects of the Co-Overexpression of BCLXL and BDNF Genes on Wharton’s Jelly-Derived Mesenchymal Stem Cells

The main problem with using MSC (mesenchymal stem cells) to treat the deficient diseases of the central nervous system is the low cell survival rate after the transplant procedure and their low ability to spontaneously differentiate into functional neurons. The aim of this study was to investigate the effects of genetically modifying MSC. A co-overexpression of two genes was performed: BCLXL was supposed to increase the resistance of the cells to the toxic agents and BDNF was supposed to direct cells into the neuronal differentiation pathway. As a result, it was possible to obtain the functional overexpression of the BCLXL and BDNF genes. These cells had an increased resistance to apoptosis-inducing toxicants (staurosporine, doxorubicin and H₂O₂). At the same time, the genes of the neuronal pathway (CHAT, TPH1) were overexpressed. The genetically modified MSC increased the survival rate under toxic conditions, which increased the chance of surviving a transplant procedure. The obtained cells can be treated as neural cell progenitors, which makes them a universal material that can be used in various disease models. The production of neurotransmitters suggests that cells transplanted into the brain and subjected to the additional influence of the brain’s microenvironment, will be able to form synapses and become functional neurons.

SARS-CoV-2 infection in multiple sclerosis patients: interaction with treatments, adjuvant therapies, and vaccines against COVID-19

The SARS-CoV-2 pandemic has raised particular concern for people with Multiple Sclerosis, as these people are believed to be at increased risk of infection, especially those being treated with disease-modifying therapies. Therefore, the objective of this review was to describe how COVID-19 affects people who suffer from Multiple Sclerosis, evaluating the risk they have of suffering an infection by this virus, according to the therapy to which they are subjected as well as the immune response of these patients both to infection and vaccines and the neurological consequences that the virus can have in the long term. The results regarding the increased risk of infection due to treatment are contradictory. B-cell depletion therapies may cause patients to have a lower probability of generating a detectable neutralizing antibody titer. However, more studies are needed to help understand how this virus works, paying special attention to long COVID and the neurological symptoms that it causes.

SARS-CoV-2 infection in patients with neuroimmunological disorders in a tertiary referral centre from the north of Portugal

Introduction

The impact of COVID-19 in patients with neuroimmunological disorders is not fully established. There is some evidence suggesting an increased risk of more severe infection associated with the use of immunosuppressors in this population.

Objective

To characterize SARS-CoV-2 infection in patients followed in the neuroimmunology outpatient clinic of a tertiary centre from the north of Portugal.

Methods

Retrospective analysis of neuroimmunological patients with PCR-proven SARS-CoV-2 infection during the observational period of 20 months.

Results

Ninety-one patients were infected, 68.1% female, with a mean age of 48.9±16.7 years. The median disease duration was 11.0 (IQR 6.0-19.0) years. Sixty-one patients (67.0%) had Multiple Sclerosis, of which 50 with relapsing-remitting course, 12 (13.2%) Myasthenia Gravis (MG), 6 (6.6%) Autoimmune Encephalitis and 6 (6.6%) Chronic Inflammatory Demyelinating Polyneuropathy. Seventy-six patients (83.5%) were taking disease-modifying therapy, 77.6% of which were on immunosuppressants, including anti-CD20 in 12 (13.2%). Most patients had mild COVID-19 (84.6%), with 3 cases (3.3%) of severe disease and, 7 cases (7.7%) of critical disease being reported. In total, 13 patients were hospitalized and 4 died. Patients with severe to critical disease were significantly older than patients with milder forms (69.4±21.0 versus 46.5±14.4 years, p<0.01). MG was also associated with more severe disease (p=0.02). There was no association between comorbidities or use of immunosuppressors (including anti-CD20) and COVID-19 severity.

Conclusions

Greater age and MG were associated with severe or critical COVID-19. We found no association between a specific DMT, including anti-CD20, and outcome. Clinical recovery was achieved by 93.4%.

Self-Assembled Nanoscale Materials for Neuronal Regeneration: A Focus on BDNF Protein and Nucleic Acid Biotherapeutic Delivery

Enabling challenging applications of nanomedicine and precision medicine in the treatment of neurodegenerative disorders requires deeper investigations of nanocarrier-mediated biomolecular delivery for neuronal targeting and recovery. The successful use of macromolecular biotherapeutics (recombinant growth factors, antibodies, enzymes, synthetic peptides, cell-penetrating peptide–drug conjugates, and RNAi sequences) in clinical developments for neuronal regeneration should benefit from the recent strategies for enhancement of their bioavailability. We highlight the advances in the development of nanoscale materials for drug delivery in neurodegenerative disorders. The emphasis is placed on nanoformulations for the delivery of brain-derived neurotrophic factor (BDNF) using different types of lipidic nanocarriers (liposomes, liquid crystalline or solid lipid nanoparticles) and polymer-based scaffolds, nanofibers and hydrogels. Self-assembled soft-matter nanoscale materials show favorable neuroprotective characteristics, safety, and efficacy profiles in drug delivery to the central and peripheral nervous systems. The advances summarized here indicate that neuroprotective biomolecule-loaded nanoparticles and injectable hydrogels can improve neuronal survival and reduce tissue injury. Certain recently reported neuronal dysfunctions in long-COVID-19 survivors represent early manifestations of neurodegenerative pathologies. Therefore, BDNF delivery systems may also help in prospective studies on recovery from long-term COVID-19 neurological complications and be considered as promising systems for personalized treatment of neuronal dysfunctions and prevention or retarding of neurodegenerative disorders.

K18- and CAG-hACE2 Transgenic Mouse Models and SARS-CoV-2: Implications for Neurodegeneration Research

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global pandemic that might lead to very serious consequences. Notably, mental status change, brain confusion, and smell and taste disorders along with neurological complaints have been reported in patients infected with SARS-CoV-2. Furthermore, human brain tissue autopsies from COVID-19 patients show the presence of SARS-CoV-2 neuroinvasion, which correlates with the manifestation of meningitis, encephalitis, leukocyte infiltration, and neuronal damage. The olfactory mucosa has been suggested as a way of entry into the brain. SARS-CoV-2 infection is also known to provoke a hyper-inflammatory reaction with an exponential increase in the production of pro-inflammatory cytokines leading to systemic responses, even in the absence of direct infection of brain cells. Angiotensin-converting enzyme 2 (ACE2), the entry receptor of SARS-CoV-2, has been extensively demonstrated to be present in the periphery, neurons, and glial cells in different brain regions. To dissect the details of neurological complications and develop therapies helping COVID-19 survivors regain pre-infection quality of life, the development of robust clinical models is highly warranted. Several human angiotensin-converting enzyme 2 (hACE2) transgenic mouse models have been developed and used for antiviral drug screening and vaccine development, as well as for better understanding of the molecular pathogenetic mechanisms of SARS-CoV-2 infection. In this review, we summarize recent results from the studies involving two such mouse models, namely K18- and CAG-hACE2 transgenics, to evaluate the direct and indirect impact of SARS-CoV-2 infection on the central nervous system.

SARS-CoV-2-Mediated Neuropathogenesis, Deterioration of Hippocampal Neurogenesis and Dementia

A significant portion of COVID-19 patients and survivors display marked clinical signs of neurocognitive impairments. SARS-CoV-2-mediated peripheral cytokine storm and its neurotropism appear to elicit the activation of glial cells in the brain proceeding to neuroinflammation. While adult neurogenesis has been identified as a key cellular basis of cognitive functions, neuroinflammation-induced aberrant neuroregenerative plasticity in the hippocampus has been implicated in progressive memory loss in ageing and brain disorders. Notably, recent histological studies of post-mortem human and experimental animal brains indicate that SARS-CoV-2 infection impairs neurogenic process in the hippocampus of the brain due to neuroinflammation. Considering the facts, this article describes the prominent neuropathogenic characteristics and neurocognitive impairments in COVID-19 and emphasizes a viewpoint that neuroinflammation-mediated deterioration of hippocampal neurogenesis could contribute to the onset and progression of dementia in COVID-19. Thus, it necessitates the unmet need for regenerative medicine for the effective management of neurocognitive deficits in COVID-19.

Elucidating the Neuropathologic Mechanisms of SARS-CoV-2 Infection

The current pandemic caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a public health emergency. To date, March 1, 2021, coronavirus disease 2019 (COVID-19) has caused about 114 million accumulated cases and 2.53 million deaths worldwide. Previous pieces of evidence suggest that SARS-CoV-2 may affect the central nervous system (CNS) and cause neurological symptoms in COVID-19 patients. It is also known that angiotensin-converting enzyme-2 (ACE2), the primary receptor for SARS-CoV-2 infection, is expressed in different brain areas and cell types. Thus, it is hypothesized that infection by this virus could generate or exacerbate neuropathological alterations. However, the molecular mechanisms that link COVID-19 disease and nerve damage are unclear. In this review, we describe the routes of SARS-CoV-2 invasion into the central nervous system. We also analyze the neuropathologic mechanisms underlying this viral infection, and their potential relationship with the neurological manifestations described in patients with COVID-19, and the appearance or exacerbation of some neurodegenerative diseases.

Can coronavirus disease 2019 (COVID-19) trigger exacerbation of multiple sclerosis? A retrospective study

The effect of coronavirus disease (COVID-19) on the risk of relapse in multiple sclerosis (MS) have been unknown. In this retrospective study of 41 relapsing-remitting MS patients, number of relapses in pre-defined at risk-period (ARP) was compared with the previous two years. During the previous two years, a total of 32 attacks was reported, which 5 (15.6%) were during the at-risk period. After adjusting for age and sex, there was an increased risk of attack during ARP compared to the previous two years (RR: 2.566, 95%CI: 1.075-6.124, P=0.034). Our preliminary study suggested that COVID-19 can trigger exacerbation of MS.