Impact of New COVID-19 Variant on Stroke, Thrombosis and Neurological Impairment

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has devastated the world with coronavirus disease 2019 (COVID-19). SARS-CoV-2 is an RNA virus that has a high mutation rate producing a new variant with serious threats. Recently emerged delta variant (B.1.617.2) (India), and omicron (B.1.1.529) (South Africa) mutant makes more serious attention than others previously known. These variants exhibit many neurological complications. The new variants of COVID-19 are also involved in gut microbiota dysbiosis, thus enhancing inflammation process which in then causes stroke, diabetes and thrombosis. Administering vaccines is crucial due to continual mutation and the introduction of variants of concern. Therefore, variant modified vaccines have been thought of as potential vaccines.

1. Introduction

In December 2019 an outbreak of pneumonia and respiratory problems occurred in Wuhan city of China making it a complete lockdown within months. The virus which was associated with the outbreak was corona virus disease 2019 (COVID-19). The coronavirus disease is brought on by the enveloped, positive sense single stranded genome virus (++sRNA) known as SARS-CoV-2 (formerly known as 2019-nCoV). The symptoms consist of respiratory distress, fever, cough, fatigue and overall low immunity [1]. Thousands of people died all over the world and in 2020 WHO declared it as worldwide pandemic. SARS-CoV-2 virus was first identified by Tyrell and Bynoe in 1965 from the patients having common cold [2]. SARS CoV-2 has been rapidly evolving, leading to emergence of new strain which fostered the need of new and more adaptive diagnostic methods to tackle the strain. Every other strain showcases different range of symptoms within infected people [2]. SARS-CoV-2 detection methods mostly focus on anti-SARS-CoV-2 antibodies (serological testing), antigen specific viral protein or particular viral nucleic acid (molecular testing). Administering vaccines is crucial due to SARS-CoV-2’s continual mutation and the introduction of variants of concern. The majority of SARS-CoV-2 vaccines now on market are inactivated, live attenuated, viral vector, protein subunit, RNA and DNA vaccines. Comirnaty, spikevox and vaxveria, the precursor COVID-19 vaccines, received Emergency Use Authorization (EUA) in December 2020, less than a year after the epidemic. There were 40 vated EUA worldwide as of August 2022, with over 11 billion doses administered [3]. Despite this amazing accomplishments, fresh issues have emerged that pose a threat to the pandemics long term control. These issues include newly emerging viral variants with higher transmissibility and immune escape, waning immunity over time in those who have received vaccinations and uncommon but potentially serious vaccines associated adverse events. In this book chapter, we will cover the molecular mechanism of COVID-19 new variants, impact on gut microbiota and neurological complications. We will also discuss the bivalent, nasal and oral Vaccines against COVID-19, along with the variant modified COVID-19 vaccines.

2. Molecular mechanism of action of COVID-19 new variant

SARS-CoV-2 uses the S protein to attach to the host cell surface receptor ACE2 (angiotensin-converting enzyme 2) and enters the cell by membrane fusion using type II transmembrane serine protease (TMPRSS2) or cathepsin L and Furin [4]. The S protein is composed of S1 and S2 subunits [5]. The S1 subunit has the RBD (receptor-binding domain), which binds to ACE2. The S2 subunit has the transmembrane part of the S protein, which anchors the S protein to the membrane and helps the viral and cellular membranes fuse together [6, 7]. Several investigations have demonstrated that Omicron RBD binds ACE2 1.5–2.8 times better than the wild-type [8]. Cleavage of the S protein at the S1–S2 and S2 sites is required for virus to enter host cell. Cathepsin L and Furin are responsible for carrying this out. TMPRSS2 and cathepsin L can cleave the SARS-CoV-2 genome at the S2 location, which results in two distinct entry points for the virus into cells. Because it is located on the exterior of the cell, TMPRSS2 regulates the passage of substances via plasma membrane. The process of entering the endosome is regulated by cathepsin L, which is located within the endosome. [6, 9, 10, 11] Six distinct mutations on S2 (N764K, D796Y, N856K, Q954H, N969K, and L981F) are present in the Omicron variation and have not been found in prior VOCs [12]. Recent research has shown that the Omicron spike pseudo typed virus prefers endosomal entrance over plasma membrane entry, and that infection was decreased in TMPRSS2 expressing cells but enhanced in cells which promote endosomal entry [13, 14, 15]. The Omicron variant contains three mutations in the furin cleavage site region (P681H, H655Y, and N679K). Basic mutation P681H in the polybasic cleavage site (PBCS), which is also found in Alpha and Gamma, has been shown to speed up furin-mediated cleavage of the S protein, which could make the virus more infectious [16].

3. Recent variants of COVID-19

The World Health Organisation (WHO) reported the Omicron variants as the most recent variant of concern (VOC) that emerged on November 26, 2021. The Omicron variant lineage is divided into the following sub-lineages: BA.1 (B.1.1.529 and BA.1.1), BA.2, BA.3, BA.4, and BA.5 [17]. The SARS-CoV-2 spike protein of omicron variant showed total 37 amino acid mutations, a few of which were found in the RBD [18]. The RBD is mostly found in the S protein, which binds to the host receptor angiotensin-converting enzyme 2 (ACE2) and may boost infectivity and facilitate escape from neutralising antibodies brought on by vaccination [19, 20, 21]. By February 2022, the first Omicron BA.1 lineage had been replaced by the BA.2 lineage, which has been found in various European and Asian countries [22, 23]. The BA.2 lineage is characterized by 57 mutations, 31 of which are found in the S protein. BA.1 and BA.2 share 12 RBD mutations, including G339D, S373P, S375F, K417N, N440K, S477N, T478K, E484A, Q493R, Q498R, N501Y, and Y505H in which BA.2 has two distinct mutations, S371F and R408S and shares T376A and D405N with BA.3 [24]. Although the BA.2 lineage continues to develop, giving rise to new subvariants as BA.2.12.1, BA.2.75, BA.4, and BA.5. In particular, the BA.4/5 and BA.2.75 subvariants have sparked further diversification of the circulating SARS-CoV-2, leading to the formation of a number of new subvariants, including the BA.4.6, BF.7, BQ.1, and BQ.1.1 (derived from BA.4/5), as well as BA.2.75.2 [25]. In contrast to BA.2.75, the BA.2.75.2 subvariant develops R346T, F486S, and D1199N mutations, notably those on RBD, which have raised concerns about additional immune escape [26]. One study also claimed that the F486S mutation substantially drives the enhanced neutralisation resistance of BA.2.75.2 [25]. In addition, BA.5 has taken over as the predominant subvariant in several countries. It should be noted that the successors of BA.5, such as BQ.1, BQ.1.1, and BF.7, are becoming more prevalent in more than 65 various countries, including China, India, Brazil, and the USA. By 19 November 2022, BQ.1, BQ.1.1, and BF.7 were responsible for 25.5%, 24.2%, and 7.8% of all cases in the United States, respectively [27, 28]. In the whole genome of the BF.7 subvariant of Omicron, 55 mutations have been found in which 32 mutations found in S-protein encoding gene. Furthermore, the BQ.1 and BQ.1.1 variant of omicron was also grown by N460K and K444T mutations which increase its neutralisation resistance to antibodies. In addition to the other mutations in the S-protein, the BQ.1.1 and BF.7 subvariant has a fundamental mutation in a crucial location, such as R346T. This mutation was associated with a greater capacity of the virus to evade neutralising antibodies (nAbs) brought on by prior infection or vaccination [26, 29]. A recent study showed that, compared to the original coronavirus, the BF.7 variant demonstrated 4.4 times greater resistance to neutralisation [25]. When compared with D614G, the BA.4.6, BF.7, BQ.1, and BQ.1.1 subvariants exhibited a 10.6-fold (p < 0.0001), 11.0-fold (p < 0.0001), 18.7- fold (p < 0.0001), and 22.9-fold (p < 0.0001) higher neutralization resistance, respectively [25].

4. Impact of COVID-19 on gut microbiota

The gut microbiota is the variety of bacteria that populate the gastrointestinal (GI) tract as part of a complex and dynamic ecosystem [30, 31]. The term eubiosis refers to the balance of different genus or species of bacteria that belongs to the 4 phyla which includes, Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes [32]. Any alteration in the composition of the gut microbiota or abnormalities with the gut microbiota’s homeostasis is given the term dysbiosis [33]. Numerous studies have documented gut dysbiosis in patients suffering from COVID-19 [34, 35]. Patients with SARS-CoV2 infection have dysbiosis in their gut microbiome, which causes an increase in GI opportunistic bacteria, suggesting a potential connection between SARS-CoV2 and gut-lung axis [36, 37]. The gut microbiome dysbiosis reduces the beneficial commensals that are anti-inflammatory, like, Lachnospiraceae, Faecalibacterium prausnitzii and Roseburia, Eubacterium, and enriches the gut of the COVID-19 patients with opportunistic pathogens that cause bacteremia such as, Bacteroides nordii, Clostridium hathewayi, Actinomyces viscosus and Enterobacteriaceae, Enterococcus [38]. Important epithelial cells are altered by the gut microbiome dysbiosis, as seen in K18-hACE2 mice in a study. The ileum of infected mice had significantly more mucus-producing goblet cells and fewer Paneth cells. A decrease in the number of Paneth cells was accompanied by abnormalities, like, misplaced or deformed granules, reduction in the expression of antimicrobial factors like, serum amyloid A, lysozyme, Reg3γ and defensins. This resulted from the sharp variations in Akkermansiaceae concentration [39]. Patients with COVID-19 also showed a depletion of bacteria that produce SCFAs (short-chain fatty acid), such as Parabacteroides, Bacteroides, and Lachnospiraeae. In the presence of SARS-CoV-2, metabolomic studies of animal models observed alterations in SCFA synthesis, which decreased lung defenses, strengthened pathogen colonization and the development of bacterial infection [40, 41, 42].

5. Impact of new variant of COVID-19 on neurological complications

Research is ongoing on the clinical importance of SARS-CoV-2 brain infection. It has been discovered that brain infection and inflammation are linked to neurological symptoms in COVID-19 patients, including headache, dizziness, myalgia, disorientation, delirium, and altered mental status [43, 44]. The introduction of the delta (B1.617.2) mutation increased the probability of COVID-19 neurological diagnoses (such as cognitive disability, epilepsy or seizures, and ischemic strokes) [45]. The SARS-CoV-2 delta variant is more virulent than the early strain (Hu-1 variants) and causes severe neurotropic patterns. Histopathological examination of the brains of K18-hACE2 mice showed that B1.617.2 infects the brains more quickly and effectively than Hu-1. It was found that the early activation of several signature genes in delta-infected mice involves innate cytokines, and the necrosis-related response was more prominent than in Hu-1-infected mice [46]. The Omicron variety has currently taken over as the dominant strain, which has led to a pattern of development into the enduring and endemic COVID-19 [47]. Notably, despite the fact that the initial strain led to fatal brain infections in COVID-19 mice models, [48, 49] both adult human cases and animal models infected with Omicron allegedly did not exhibit these symptoms. However, because everyone’s immune status varies, the severity of SARS-CoV-2 variations is complex, therefore it’s important not to underestimate the pathogenicity brought on by the Omicron variant [50]. Recently, a neonate with the Omicron BA.1 mutation was discovered to have severe encephalopathy [51]. In another recent work, scientists employed K18-hACE mice to show that the Omicron version can infect the brain. Their findings demonstrated that abnormalities in lymphoid organs coexist with Omicron infection in the brain [50]. In comparison to earlier versions, the Omicron variant is also linked to seizures and decreased mental status in youngsters [52].

6. COVID-19, stroke and thrombosis

Based on clinical observation and initial case series, the COVID-19 pandemic is associated with stroke induced neurological impairment [53]. These reported neurological impairments were the anosmia, ageusia, cerebral haemorrhage and infarction [54]. The potential mechanism of ischemic stroke in the older age COVID-19 patients with various comorbidities and severe illness were observed. The uncommon reasons of stroke in the COVID-19 patients are atherosclerosis, hypertension and arterial fibrillation. SARS-CoV-2 virus binds to the angiotensin convertin enzyme-2 (ACE2) present on brain endothelial cells and smooth muscles cells [55, 56]. ACE2 is the key part of the renin angiotensin system (RAS) and the counter balance to the ACE1 and angiotensin II. Angiotensin II is proinflammatory, vasoconstrictive and promotes organ damage. Depletion of ACE2 by the SARS-CoV-2 may tip the balance in the favour of harmful ACE1/angiotensin II axis and promote tissue injury including stroke. Treatment with tissue plasminogen activator for COVID-19 related stroke and low molecular weight of heparinoids may reduce the thrombosis and mortality in sepsis-induced coagulopathy [57]. The three mechanistic pathways involved in the incidence of stroke are hypercoagulable state, vasculitis, and cardiomyopathy. The venous thrombosis has been reported in the patients with severe COVID-19 [58]. However, pathogenesis of hemorrhagic stroke in COVID-19 has not been fully elucidated. It has been postulated that affinity of SARS-CoV-2 for the ACE2 receptors, which are expressed in endothelial and arterial smooth muscles cells in the brain allow the virus to mechanical damage the intra-arterial arteries causing vessel wall rupture [55]. The COVID-19 patients, who had stroke were more likely to be older and have hypertension, diabetes, cancer and higher level of D-dimer [59]. The diagnostic investigations could not be completed in some COVID-19 patients, might have contributed to the high rate of cryptogenic strokes. The cytokine may also damage and result in blood brain barrier (BBB) leakage and cause hemorrhagic posterior reversible encephalopathy syndrome. Several nutritional components such as vitamin D and phytochemicals such as riboflavin and piperine can be essential nutraceutical components may involve in protection and prevention from the ischemic stroke injury (Figure 1) [60, 61, 62].

Figure 1.

Impact of new COVID-19 variant on gut microbiota which enhances the inflammation process in various metabolic disease as well as thrombosis.

7. Bivalent, nasal and oral vaccines against COVID-19

A recent report from the World Health Organization (WHO) revealed that seven vaccines (Covishield, Janssen/Ad26, Moderna COVID-19, Sinopharm, Sinovac-CoronaVac, Pfizer/BioNtech, and COVAXIN) have been approved for use against SARS-CoV2 in humans. Most of these immunisations are given as intramuscular injections [63, 64, 65, 66, 67, 68]. However, it’s crucial to remember that the intramuscular vaccinations only cause a systemic immune response; they have no effect on the mucous membranes. For SARS-CoV2 to be successfully neutralised in the upper respiratory system, mucosal immunity is essential. It aids in preventing the virus’s transmission to the lower respiratory system and the development of serious disease. The probability of SARS-CoV2 transmission from immunised persons who might still get the virus and disseminate it increases in the absence of mucosal protection, which entails the generation of local secretory immunoglobulin A (sIgA) antibodies [69]. Fortunately, there has been significant progress in developing mucosal vaccines that can be administered orally or intranasally. These vaccines offer a non-invasive delivery method and can generate mucosal immunity, in addition to humoral and cellular immunity, effectively providing protection against COVID-19 [70, 71]. Vaccines administered orally or intravenously can produce a significant B and T cell–mediated immune response in addition to the intended mucosal protection. A specific study focused on improving the mucosal vaccination for Omicron variants and developed ChAd-SARS-CoV-2-BA.5-S. This vaccine was evaluated in both monovalent and bivalent forms for its efficacy against circulating variations, including BQ.1.1 and XBB.1.5, and produces a pre-fusion and surface-stabilized S protein of the BA.5 strain. According to the study, these vaccinations did not protect against the antigenically distant XBB.1.5 Omicron strain in passive transfer tests because the serum neutralising antibody responses they produced were insufficient. The study did, however, show encouraging outcomes for nasally administered bivalent ChAd-vectored vaccinations. These vaccinations offered immunity to WA1/2020 D614G and Omicron variants BQ.1.1 and XBB.1.5 in both the upper and lower respiratory tracts by inducing strong antibody and spike-specific memory T cell responses in the respiratory mucosa [72].

8. Variant modified COVID-19 vaccines

The COVID-19 vaccine offers significant protection against both symptomatic and severe disease. However, the efficacy of existing vaccination regimens, which are based on the ancestor (Wuhan-like) variant, has been significantly decreased by the introduction of antigenically unique SARS-CoV-2 variants [73]. Current vaccines, such as those based on nucleic acids, viral vectors, subunit vaccines, and inactivated vaccines, were developed based on the generation of potent immune responses against the spike (S) protein of SARS-CoV-2 [74]. The increase in SARS-CoV-2 variants with novel mutations, especially those with appealing mutations collectively referred to as variants of concern (VOCs), have been thought of as potential spike proteins for antigen-based vaccines. The primary causes of immunological escape, resistance to neutralising antibodies, and low efficiency of existing vaccines to prevent infection are the subsequent appearance of SARS-CoV-2 variants bearing novel mutations in the receptor binding domain (RBD) of spike protein [75]. A new phase of the SARS-CoV-2 pandemic may result from Omicron sub-lineages easily recombining and fusing with one another, according to recent findings. As a result, developing a multivalent vaccination can be a successful strategy for combating the new SARSCoV-2 variants, which predominantly emerged as a result of recombination between hybrid forms. In order to offer a greater range of protection against new SARS-CoV-2 variants, the Moderna firm recently created new multivalent vaccines, such as mRNA-1273.351 (targeting the B.1.351) and mRNA-1273.351 (targeting the B.1.351) [76]. Due to having a considerably larger fraction possessing important all RBD epitopes, being much easier to make, having lower production costs, and being more immunogenic, multivalent vaccines may be able to provide stronger immune protection against novel SARS-CoV-2 variants [77]. According to a recent study, multivalent S2-based vaccinations offer extensive protection against VOCs. It was shown that vaccination with S2-based constructs produced an IgG antibody response that was broadly cross-reactive and recognized the spike proteins of VOCs. Importantly, vaccination decreased the viral titers in respiratory tissues of animals exposed to SARS-CoV-2 variants B.1.351 (beta), B.1.617.2 (delta), and BA.1 (omicron) [78]. The current intramuscular COVID-19 vaccinations are at risk of losing their effectiveness due to the emergence of SARS-CoV-2 VOCs. Researchers tested trivalent COVID-19 vaccines expressing spike-1, nucleocapsid, and RdRp antigens in mice models using adenoviral vectors (Ad) of human and chimpanzee origin. They demonstrated that intranasal immunisation, particularly with chimpanzee Ad-vectored vaccine, induces a tripartite protective immunity consisting of local and systemic antibody responses, mucosal tissue-resident memory T cells, and mucosal trained innate immunity, which is superior to intramuscular immunisation. Such intranasal immunisation offers defence against the two VOC, B.1.1.7 and B.1.351, as well as the ancestor SARS-CoV-2. According to their research, an efficient next-generation COVID-19 vaccination method to generate overall mucosal immunity against existing and future VOC is respiratory mucosal administration of the Ad-vectored multivalent vaccine [79, 80].

9. Conclusion and future direction of therapy

The Omicron variant has garnered global attention due to its numerous mutations. There are significant concerns regarding other VoCs, such as Alpha (B.1.1.7), Beta (B.1.351), Gamma (B.1.1.28.1), and Delta (B.1.617.2), as they are associated with higher infectivity, transmission rates, and potential immune evasion mechanisms. A substantial percentage of COVID-19-infected patients, around 15–20%, experience a severe form of acute infection, characterized by hyperinflammatory cytokine storms, resulting in more morbidity and mortality than the actual cytotoxicity of the virus. Furthermore, recent findings suggest the correlation between microbial gut dysbiosis and the severity of the COVID-19 sickness. This has prompted researchers to investigate possible preventative and therapeutic targets including probiotics and dietary changes. Although clinical data suggests that immunopathogenesis, neuroinvasion, neuroinflammation, hypoxia, and neuroinflammation are all involved in the emergence of CNS symptoms, the precise molecular mechanism of COVID-19 neurotoxicity is still not fully characterised. Additionally, a hypercoagulable condition brought on by COVID-19 infection seems to be associated with an increased risk of thrombosis, including cases of ischemic stroke from large-vessel blockage. Given the catastrophic effects of COVID-19 on human lives, the WHO has sped up vaccine development to guarantee that people everywhere may obtain high-quality, safe, and effective vaccinations against SARS-CoV2. According to a recent study, mucosal vaccinations given intranasally after the first intramuscular vaccination may operate as booster doses, triggering a strong immune response that aids in preventing the reproduction of SARS-CoV2 in the upper and lower respiratory tracts. Future examination of the vaccines now under development, including the assessment of extensive clinical investigations and trials, may pave the way for the availability of prospective mucosal vaccines and associated medicines. This can result in their inclusion in international immunisation campaigns.

Abbreviations

COVID-19	coronavirus disease of 2019
SARS-CoV-2	severe acute respiratory syndrome coronavirus 2
WHO	World Health Organization
ACE2	angiotensin-converting enzyme 2
TMPRSS2	transmembrane serine protease 2
PBCS	polybasic cleavage site
RBD	receptor-binding domain
VOC	variant of concern
nAbs	neutralising antibodies
GI	gastrointestinal (GI) tract
SCFA	short-chain fatty acids