The molecular fingerprint of neuroinflammation in COVID-19: A comprehensive discussion on molecular mechanisms of neuroinflammation due to SARS-COV2 antigens

Abstract:

Background and objective: Severe acute respiratory syndrome coronavirus 2 attacks the neural system directly and indirectly via various systems, such as the nasal cavity, olfactory system, and facial nerves. Considering the high energy requirement, lack of antioxidant defenses, and high amounts of metal ions in the brain, oxidative damage is very harmful to the brain. Various neuropathic pain conditions, neurological disorders, and neuropsychiatric complications were reported in Coronavirus disease 2019, prolonged Coronavirus disease 2019, and after Coronavirus disease 2019 immunization. This manuscript offers a distinctive outlook on the interconnectedness between neurology and neuropsychiatry through its meticulous analysis of complications.

Discussion: After recovering from Coronavirus disease 2019, approximately half of the patients reported developing Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Long Coronavirus disease 2019 imaging reports illustrated the hypometabolism in various parts of the brain, such as olfactory bulbs, limbic/paralimbic domains, the brainstem, and the cerebellum. Ninety imaging and neuropathological studies of Coronavirus disease 2019 have shown evidence of white matter, brainstem, frontotemporal, and oculofrontal lesions. Emotional functions, such as pleasant, long/short-term memory, movement, cognition and cognition in decision-making are controlled by these regions. The neuroinflammation and the mechanisms of defense are well presented in the discussion. The role of microglia activation, Inducible NO synthase, Cyclooxygenases ½, Reactive oxygen species, neurotoxic toxins and pro-inflammatory cytokines, such as Interleukin-1 beta, Interleukin-6 and Tumor Necrosis Factor-alpha are highlighted in neuronal dysfunction and death. Nuclear factor kappa-light-chain-enhancer of activated B cells, Mitogen-activated protein kinase, Activator Protein 1, and Interferon regulatory factors are the main pathways involved in microglia activation in Coronavirus disease 2019 neuroinflammation.

Conclusion: The neurological aspect of Coronavirus disease 2019 should be highlighted. Neurological, psychological, and behavioral aspects of Coronavirus disease 2019, prolonged Coronavirus disease 2019, and Coronavirus disease 2019 vaccines can be the upcoming issues. We need a global awareness where this aspect of the disease should be more considered in health research.

Source: Zayeri ZD, Torabizadeh M, Kargar M, Kazemi H. The molecular fingerprint of neuroinflammation in COVID-19: A comprehensive discussion on molecular mechanisms of neuroinflammation due to SARS-COV2 antigens. Behav Brain Res. 2024 Jan 20;462:114868. doi: 10.1016/j.bbr.2024.114868. Epub ahead of print. PMID: 38246395. https://www.sciencedirect.com/science/article/abs/pii/S016643282400024X

Long-term neurological implications of severe acute respiratory syndrome coronavirus 2 infections in neonates: Innate immune memory and chronic neuroinflammation

Abstract:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can cause long-term neurological complications in adults. However, the mechanisms by which early-life SARS-CoV-2 infection increases the risk of abnormal neurodevelopment remain unknown.

Recent studies have shown an association with chronic proinflammatory cytokine/chemokine production in the central nervous system (CNS). Therefore, it was hypothesised that innate immune activation and induction of innate immune memory may play a potential role in the neonatal brain. Haematopoietic stem cells in the bone marrow are exposed to SARS-CoV-2, SARS-CoV-2 envelope protein (E protein), lipopolysaccharide (LPS)-bound spike proteins (S1 and S2 proteins), and damage-associated molecular patterns (DAMPs). Myeloid progenitors enter the stroma of the choroid plexus and are further directed to incessantly supply the brain parenchyma with resident innate immune cells. The S proteins-LPS complex can cross the blood–brain barrier and plays an important role in microglial and astrocytic inflammatory responses and innate immune memory.

Persistently activated microglia with memory release pro-inflammatory cytokines/chemokines which contribute to abnormal synaptic development in the frontal lobe and cerebellum, potentially leading to long-term neurological complications, similar to those observed in autism spectrum disorder (ASD). In addition, this hypothesis suggests that bacterial and fungal products may act as adjuvants to S proteins and may also explain why S proteins alone are insufficient to induce neuroinflammation in neonates.

Source: Tatsuro Nobutoki. Long-term neurological implications of severe acute respiratory syndrome coronavirus 2 infections in neonates: Innate immune memory and chronic neuroinflammation. Medical Hypotheses, Volume 181, December 2023, 111204 https://www.sciencedirect.com/science/article/pii/S0306987723002001 (Full text)

Brain fog in long COVID: A glutamatergic hypothesis with astrocyte dysfunction accounting for brain PET glucose hypometabolism

Abstract:

Brain [18F]FDG-PET scans have revealed a glucose hypometabolic pattern in patients with long COVID. This hypometabolism might reflect primary astrocyte dysfunction. Astrocytes play a key role in regulating energy metabolism to support neuronal and synaptic activity, especially activity involving glutamate as the main neurotransmitter.

Neuroinflammation is one of the purported mechanisms to explain brain damage caused by infection with SARS-CoV-2. Microglial activation can trigger reactive astrogliosis, contributing to neuroinflammatory changes. These changes can disturb glutamatergic homeostasis, ultimately leading to cognitive fatigue, which has been described in other clinical situations.

We hypothesize that glutamatergic dysregulation related to astrocyte dysfunction could be the substrate of brain PET hypometabolism in long COVID patients with brain fog. Based on these elements, we propose that therapeutics targeting astrocytic glutamate regulation could help mitigate long COVID neurological manifestations.

Source: Tatiana Horowitz, Luc Pellerin, Eduardo R. Zimmer, Eric Guedj. Brain fog in long COVID: A glutamatergic hypothesis with astrocyte dysfunction accounting for brain PET glucose hypometabolism. Medical Hypotheses, Volume 180, 2023, 111186, ISSN 0306-9877, https://doi.org/10.1016/j.mehy.2023.111186. https://www.sciencedirect.com/science/article/pii/S0306987723001822 (Full text)

Role of Microglia, Decreased Neurogenesis and Oligodendrocyte Depletion in Long COVID-Mediated Brain Impairments

Abstract:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of a recent worldwide coronavirus disease-2019 (COVID-19) pandemic. SARS-CoV-2 primarily causes an acute respiratory infection but can progress into significant neurological complications in some. Moreover, patients with severe acute COVID-19 could develop debilitating long-term sequela.

Long-COVID is characterized by chronic symptoms that persist months after the initial infection. Common complaints are fatigue, myalgias, depression, anxiety, and “brain fog,” or cognitive and memory impairments. A recent study demonstrated that a mild COVID-19 respiratory infection could generate elevated proinflammatory cytokines and chemokines in the cerebral spinal fluid.

This commentary discusses findings from this study, demonstrating that even a mild respiratory SARS-CoV-2 infection can cause considerable neuroinflammation with microglial and macrophage reactivity. Such changes could also be gleaned by measuring chemokines and cytokines in the circulating blood. Moreover, neuroinflammation caused by mild SARS-CoV-2 infection can also impair hippocampal neurogenesis, deplete oligodendrocytes, and decrease myelinated axons.

All these changes likely contribute to cognitive deficits in long-COVID syndrome. Therefore, strategies capable of restraining neuroinflammation, maintaining better hippocampal neurogenesis, and preserving oligodendrocyte lineage differentiation and maturation may prevent or reduce the incidence of long-COVID after SARS-CoV-2 respiratory infection.

Source: Wei ZD, Liang K, Shetty AK. Role of Microglia, Decreased Neurogenesis and Oligodendrocyte Depletion in Long COVID-Mediated Brain Impairments. Aging Dis. 2023 Sep 24. doi: 10.14336/AD.2023.10918. Epub ahead of print. PMID: 37815903. https://www.aginganddisease.org/EN/10.14336/AD.2023.10918 (Full text)

Cognitive impairment after Long COVID-19: Current Evidence and Perspectives

Abstract:

COVID-19 is a respiratory infectious disease caused by the SARS-CoV-2 virus. Most patients recover after treatment, but COVID-19 treatment may lead to cognitive impairment. Recent studies have found that some recoverers experience cognitive impairments such as decreased memory and attention, and sleep disorder, indicating that COVID-19 may have longerterm effects on cognitive function.

Studies have found that COVID-19 may cause cognitive decline by damaging key brain regions such as the hippocampus and anterior cingulate cortex. Studies have also found that COVID-19 patients have active neuroinflammation, mitochondrial dysfunction, and microglial activation, suggesting that neuroinflammation, mitochondrial stress, and neurodegenerative changes may be potential mechanisms leading to cognitive impairment.

In summary, the possibility of cognitive impairment after COVID-19 treatment deserves close attention. Large-scale follow-up studies will help further explore the impact of COVID-19 on cognitive function and provide evidence to support clinical treatment and rehabilitation practices. Neuropathological and biological studies can explore precise mechanisms in-depth and provide a theoretical basis for prevention, treatment, and intervention research.

Given the risks of long-term COVID-19 and reinfection, it is necessary to integrate basic and clinical research data to maximize the maintenance of patient’s cognitive function and life quality. This also provides important experience in responding to similar public health events. This article integrates clinical and basic evidence of cognitive impairment after COVID-19 and discusses potential mechanisms and future research directions.

Source: Zhi-Tao Li, ZHANG ZHEN, Zhuoya Zhang, Zhi-Yong Wang, Hao Li. Cognitive impairment after Long COVID-19: Current Evidence and Perspectives. Front. Neurol. Sec. Neuroinfectious Diseases. Volume 14 – 2023 | doi: 10.3389/fneur.2023.1239182 https://www.frontiersin.org/articles/10.3389/fneur.2023.1239182/abstract

Evidence of neuroinflammation in fibromyalgia syndrome: a [18F]DPA-714 positron emission tomography study

Abstract:

This observational study aimed to determine whether individuals with fibromyalgia (FM) exhibit higher levels of neuroinflammation than healthy controls (HCs), as measured with positron emission tomography using [18F]DPA-714, a second-generation radioligand for the translocator protein (TSPO).
Fifteen women with FM and 10 HCs underwent neuroimaging. Distribution volume (VT) was calculated for in 28 regions of interest (ROIs) using Logan graphical analysis and compared between groups using multiple linear regressions. Group (FM vs HC) was the main predictor of interest and TSPO binding status (high- vs mixed-affinity) was added as a covariate. The FM group had higher VT in the right postcentral gyrus (b = 0.477, P = 0.033), right occipital gray matter (GM; b = 0.438, P = 0.039), and the right temporal GM (b = 0.466, P = 0.042). The FM group also had lower VT than HCs in the left isthmus of the cingulate gyrus (b = −0.553, P = 0.014).
In the subgroup of high-affinity binders, the FM group had higher VT in the bilateral precuneus, postcentral gyrus, parietal GM, occipital GM, and supramarginal gyrus. Group differences in the right parietal GM were associated with decreased quality of life, higher pain severity and interference, and cognitive problems.
In support of our hypothesis, we found increased radioligand binding (VT) in the FM group compared with HCs in several brain regions regardless of participants’ TSPO binding status. The ROIs overlapped with prior reports of increased TSPO binding in FM. Overall, increasing evidence supports the hypothesis that FM involves microglia-mediated neuroinflammation in the brain.
Source: Mueller C, Fang YD, Jones C, McConathy JE, Raman F, Lapi SE, Younger JW. Evidence of neuroinflammation in fibromyalgia syndrome: a [18F]DPA-714 positron emission tomography study. Pain. 2023 Jun 15. doi: 10.1097/j.pain.0000000000002927. Epub ahead of print. PMID: 37326674. https://pubmed.ncbi.nlm.nih.gov/37326674/

A neuroinflammatory paradigm can explain Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome and Post-COVID-19 Fatigue Syndrome

Abstract

This thesis illustrates the development of a neuroinflammatory paradigm for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), applicable to Long-COVID related “Post-COVID-19 Fatigue Syndrome” (PCFS).

The brain being devoid of nociceptors, in combination with neuroimaging technology lacking sufficient sensitivity, helps to explain why the chronic but low-level neuroinflammation purported to be present in the brains of ME/CFS (and PCFS) sufferers has gone unreported by patients, and has been largely undetected by scientists, until more recently. Over-activation of microglia and astrocytes is increasingly being proposed to be at the heart of ME/CFS (and PCFS) pathophysiology.

A key Positron Emission Tomography/Magnetic Resonance Imaging (PET/MRI) study (2014) provided evidence of glial-cell over-activity, implicating neuroinflammation within the brain’s limbic system, of ME/CFS patients. Other cerebral spinal fluid and neuroimaging studies, including a more recent Magnetic Resonance Spectroscopy (MRS)/MRI Thermometry study (2019), have added support to this concept.

Resultant dysfunction of the limbic system and its closely-connected hypothalamus, which in turn leads to a disturbed autonomic nervous system (ANS) and dysfunctional hypothalamic-pituitary-adrenal-axis (HPA-axis) could then account for the diverse range of symptoms reported in ME/CFS (and PCFS). These symptoms include chronic fatigue, flu-like malaise, mood, memory and cognitive problems (limbic system), sleep, taste, visual and thermostatic-control problems (hypothalamus), gastro-intestinal disturbance, cardiovascular problems and hypotension (ANS), as well as increased frequency of urination and lower blood cortisol levels (HPA-axis).

A dysfunctional hypothalamic paraventricular nucleus (PVN), a potentially vulnerable site, within the brains of genetically susceptible people, which functions normally as a stress-control integrator, is proposed to be at the core of ME/CFS (and PCFS) aetiology and pathophysiology.

It is proposed that all triggers of ME/CFS, be they viral (Epstein-Barr Virus is the most common trigger), or non-viral; including other infectious diseases, multiple vaccinations, emotional trauma or chemical toxin shock, share a common triggering mechanism. They are each proposed to manifest themselves as severe physiological stressors, which by a combination of humoral and neural routes, target, the hypothalamic PVN, of genetically susceptible individuals. By exceeding an intrinsic stress-threshold pertaining to the complex neurological circuitry, within the hypothalamic PVN, the triggering stressor is proposed to overload it into a (permanently) iii dysfunctional state.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), which causes Coronavirus Disease 2019 (COVID-19), in common with the triggering stressors of ME/CFS, also manifests itself as a severe physiological stressor, due to a cytokine surge at the site of the primary infection (the lungs). This particular stressor is, also, proposed to target the hypothalamic PVN, in genetically susceptible people, thus triggering PCFS. Life’s ongoing physiological stressors, such as physical, mental overexercise, chemical toxin exposure, emotional and financial stress, all of which are known to exacerbate and perpetuate ME/CFS (as well as PCFS) could do so by then targeting a now “compromised” (possibly inflamed) stress-sensitive hypothalamic PVN, by similar routes.

Then if an alternative, but variable (according to fluctuating neuroinflammation of the hypothalamic PVN, itself) stress threshold was exceeded, commonly reported post-exertional malaise (PEM) episodes, more problematic flare-ups, and even more severe prolonged and characteristic relapses could ensue.

It is proposed that a dysfunctional hypothalamic PVN, thereby, acts as an epicentre to a radiating neuroinflammatory response within the brains of ME/CFS (and PCFS) sufferers. A neuroinflammatory pathway, as proposed to be shared by the early-onset stages of several progressive neuroinflammatory (neurodegenerative) diseases could also be shared by ME/CFS, and PCFS. Indeed, this pathway could be shared by other potentially nonprogressive neuroinflammatory disorders, such as the closely-related fibromyalgia, mental health disorders, epilepsy, and migraines.

Might then the “drivers” of the inflammatory process, which sustain glial-cell activation (and neuroinflammation), in ME/CFS (and PCFS), be the perpetuating stressors, themselves, acting in combination with a now “compromised” and stress-sensitive hypothalamic PVN? If so, what then might be the mechanistic detail linking a stressor-targeted hypothalamic PVN and microglial activation in ME/CFS (and PCFS)?

One attractive scenario requiring further investigation involves the release of corticotrophin releasing hormone (CRH), which is released naturally by the hypothalamic PVN due to stress. The chronic release of CRH from a stress-sensitive, dysfunctional hypothalamic PVN might induce microglia activation, leading to chronic neuroinflammation, via the stimulation of mast-cells.

Two papers were published in relation to this neuroinflammatory paradigm for ME/CFS (2018, 2019), followed by another paper (2021), in which a paradigm was presented to explain the more recently emergent, but equally perplexing, Long-COVID related “PostCOVID-19 Fatigue Syndrome” (PCFS).

The neuroinflammatory model presented is both iv coherent and unifying for all triggering stressors and perpetuating stressors of ME/CFS (& PCFS), without the need for subtypes (as many other models require), but it does require validation. To this effect, it is hoped that this neuroinflammatory model will be both thought-provoking, as well as providing a framework for scientific researchers to test, critique, modify, and develop, into the future.

More brain-focussed research, using increasingly sophisticated neuroimaging technology (especially enhanced PET/MRI) is recommended. Then, a brain-signature for both ME/CFS (and PCFS) might even become attainable, within the next decade, perhaps.

Long-COVID related PCFS, affecting millions of people worldwide, presents a golden opportunity for in-depth longitudinal neuroimaging studies (following patients through relapse-recovery cycles) to develop a better understanding of PCFS (and ME/CFS) pathophysiology.

Source: Mackay, A. A neuroinflammatory paradigm can explain Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome and Post-COVID-19 Fatigue Syndrome. PhD Thesis. University of Otago, New Zealand.  https://ourarchive.otago.ac.nz/bitstream/handle/10523/15089/MackayAngus2021PhD.pdf?sequence=1&isAllowed=y (PDF file)

Brain autopsies of critically ill COVID-19 patients demonstrate heterogeneous profile of acute vascular injury, inflammation and age-linked chronic brain diseases

Abstract:

Background: This study examined neuropathological findings of patients who died following hospitalization in an intensive care unit with SARS-CoV-2.

Methods: Data originate from 20 decedents who underwent brain autopsy followed by ex-vivo imaging and dissection. Systematic neuropathologic examinations were performed to assess histopathologic changes including cerebrovascular disease and tissue injury, neurodegenerative diseases, and inflammatory response. Cerebrospinal fluid (CSF) and fixed tissues were evaluated for the presence of viral RNA and protein.

Results: The mean age-at-death was 66.2 years (range: 26-97 years) and 14 were male. The patient’s medical history included cardiovascular risk factors or diseases (n = 11, 55%) and dementia (n = 5, 25%). Brain examination revealed a range of acute and chronic pathologies. Acute vascular pathologic changes were common in 16 (80%) subjects and included infarctions (n = 11, 55%) followed by acute hypoxic/ischemic injury (n = 9, 45%) and hemorrhages (n = 7, 35%). These acute pathologic changes were identified in both younger and older groups and those with and without vascular risk factors or diseases. Moderate-to-severe microglial activation were noted in 16 (80%) brains, while moderate-to-severe T lymphocyte accumulation was present in 5 (25%) brains. Encephalitis-like changes included lymphocytic cuffing (n = 6, 30%) and neuronophagia or microglial nodule (most prominent in the brainstem, n = 6, 30%) were also observed. A single brain showed vasculitis-like changes and one other exhibited foci of necrosis with ball-ring hemorrhages reminiscent of acute hemorrhagic leukoencephalopathy changes. Chronic pathologies were identified in only older decedents: 7 brains exhibited neurodegenerative diseases and 8 brains showed vascular disease pathologies. CSF and brain samples did not show evidence of viral RNA or protein.

Conclusions: Acute tissue injuries and microglial activation were the most common abnormalities in COVID-19 brains. Focal evidence of encephalitis-like changes was noted despite the lack of detectable virus. The majority of older subjects showed age-related brain pathologies even in the absence of known neurologic disease. Findings of this study suggest that acute brain injury superimposed on common pre-existing brain disease may put older subjects at higher risk of post-COVID neurologic sequelae.

Source: Agrawal S, Farfel JM, Arfanakis K, Al-Harthi L, Shull T, Teppen TL, Evia AM, Patel MB, Ely EW, Leurgans SE, Bennett DA, Mehta R, Schneider JA. Brain autopsies of critically ill COVID-19 patients demonstrate heterogeneous profile of acute vascular injury, inflammation and age-linked chronic brain diseases. Acta Neuropathol Commun. 2022 Dec 17;10(1):186. doi: 10.1186/s40478-022-01493-7. PMID: 36528671; PMCID: PMC9758667. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9758667/ (Full text)

Molecular and cellular similarities in the brain of SARS-CoV-2 and Alzheimer’s disease individuals

Abstract:

Infection with the etiological agent of COVID-19, SARS-CoV-2, appears capable of impacting cognition, which some patients with Post-acute Sequelae of SARS-CoV-2 (PASC). To evaluate neuro-pathophysiological consequences of SARS-CoV-2 infection, we examine transcriptional and cellular signatures in the Broadman area 9 (BA9) of the frontal cortex and the hippocampal formation (HF) in SARS-CoV-2, Alzheimer’s disease (AD) and SARS-CoV-2 infected AD individuals, compared to age- and gender-matched neurological cases. Here we show similar alterations of neuroinflammation and blood-brain barrier integrity in SARS-CoV-2, AD, and SARS-CoV-2 infected AD individuals. ‘

Distribution of microglial changes reflected by the increase of Iba-1 reveal nodular morphological alterations in SARS-CoV-2 infected AD individuals. Similarly, HIF-1α is significantly upregulated in the context of SARS-CoV-2 infection in the same brain regions regardless of AD status. The finding may help to inform decision-making regarding therapeutic treatments in patients with neuro-PASC, especially those at increased risk of developing AD.

Source: Griggs E, Trageser K, Naughton S, Yang EJ, Mathew B, Van Hyfte G, Hellmers L, Jette N, Estill M, Shen L, Fischer T, Pasinetti GM. Molecular and cellular similarities in the brain of SARS-CoV-2 and Alzheimer’s disease individuals. bioRxiv [Preprint]. 2022 Nov 23:2022.11.23.517706. doi: 10.1101/2022.11.23.517706. PMID: 36451886; PMCID: PMC9709800. https://www.biorxiv.org/content/10.1101/2022.11.23.517706v1.full (Full text)

Role of neuroinflammation mediated potential alterations in adult neurogenesis as a factor for neuropsychiatric symptoms in Post-Acute COVID-19 syndrome-A narrative review

Abstract:

Persistence of symptoms beyond the initial 3 to 4 weeks after infection is defined as post-acute COVID-19 syndrome (PACS). A wide range of neuropsychiatric symptoms like anxiety, depression, post-traumatic stress disorder, sleep disorders and cognitive disturbances have been observed in PACS. The review was conducted based on PRISMA-S guidelines for literature search strategy for systematic reviews.

A cytokine storm in COVID-19 may cause a breach in the blood brain barrier leading to cytokine and SARS-CoV-2 entry into the brain. This triggers an immune response in the brain by activating microglia, astrocytes, and other immune cells leading to neuroinflammation. Various inflammatory biomarkers like inflammatory cytokines, chemokines, acute phase proteins and adhesion molecules have been implicated in psychiatric disorders and play a major role in the precipitation of neuropsychiatric symptoms. Impaired adult neurogenesis has been linked with a variety of disorders like depression, anxiety, cognitive decline, and dementia.

Persistence of neuroinflammation was observed in COVID-19 survivors 3 months after recovery. Chronic neuroinflammation alters adult neurogenesis with pro-inflammatory cytokines supressing anti-inflammatory cytokines and chemokines favouring adult neurogenesis. Based on the prevalence of neuropsychiatric symptoms/disorders in PACS, there is more possibility for a potential impairment in adult neurogenesis in COVID-19 survivors. This narrative review aims to discuss the various neuroinflammatory processes during PACS and its effect on adult neurogenesis.

Source: Saikarthik J, Saraswathi I, Alarifi A, Al-Atram AA, Mickeymaray S, Paramasivam A, Shaikh S, Jeraud M, Alothaim AS. Role of neuroinflammation mediated potential alterations in adult neurogenesis as a factor for neuropsychiatric symptoms in Post-Acute COVID-19 syndrome-A narrative review. PeerJ. 2022 Nov 4;10:e14227. doi: 10.7717/peerj.14227. PMID: 36353605; PMCID: PMC9639419. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9639419/ (Full text)