key: cord-0981830-sq55xlyq authors: Stavropoulou, Elisavet; Bezirtzoglou, Eugenia title: Probiotics as a Weapon in the Fight Against COVID-19 date: 2020-12-15 journal: Front Nutr DOI: 10.3389/fnut.2020.614986 sha: 1acbac2c64f429fe4af240d36f70f2dfa28964ed doc_id: 981830 cord_uid: sq55xlyq nan together with protein E, and finally (c) protein E (envelope) which is the less abundant protein in the virion envelope possessing a single hydrophobic domain (HD) (16) . In addition, SARS-CoV-2 contains the nucleocapsid protein (N) (14) . It is believed that SARS-CoV E protein assembles into a homopentamer (15). Furtherly, SARS-CoV E can oligomerize and form a channel. Particularly, SARS-CoV E proteins create cation-selective ion channels, forming a viroporin (17, 18) . It is a proteolipidic pore with negatively charged planar lipids in bilayers which amplify ion conductance and cation selectivity (19) . It is reported that viral ion channels (viroporins) instigate a leakage in host cellular membranes influencing the membrane role (19) . Thus, viroporins set out a role of markers of a viral infection (20) . Coronaviruses usually possess three types of ion channels: E, 8a and 3a (21) . The 3a ion channel has 3 TMD (Trans-Membrane Domain), while the E and 8a ion channels have one TMD (21) . Yet, 3a and protein E were found to possess a common structural aminoacid PDZ domain-Binding Motif (PBM) which is known to play a key role in anchoring receptor proteins in the membrane (22, 23) . There is evidence that the last four aminoacids in the C-terminus PBM of the E protein are actively participating in the development of SARS-CoV disease resulting in the overexpression of cytokines, called the "cytokine storm" (23) . There has been some evidence that protein E is profusely expressed in the infected cell as it is found mainly in ERGIC (Endoplasmic Reticulum-Golgi Intermediate Compartment), while only a small protein fragment is found in the envelope of the virion (24) (25) (26) . It should be reported that the PBM is found only in several coronaviruses, specifically in the genera α and β, while it is not present in the γ genera (24) . Without any doubt, it should be interesting to investigate the role of the interaction patterns and whether they interact specifically with the protein E of SARS-CoV or also with protein E from other coronavirus species of the same genus (27) . Moreover, in coronaviruses, the ERGIC intercedes in between the endoplasmic reticulum and the Golgi for dispensing the virions from the infected cell (26) and accommodates Ca2+ transport (28) . As a result, activation of the NLRP3 inflammasome occurs going along with an overproduction of interleukin 1β (29) . E protein found in the ERGIC participates in the formation of the infectious virion SARS-CoV E protein involves a triple role; viral assembly, virion release, and viral pathogenesis (28, 29) . SARS-Cov E protein has been mentioned to connect to five host proteins (Bcl-xL, PALS1, syntenin, sodium/potassium (Na+/K+) ATPase α-1 subunit, and stomatin) (24) in SARS-1, permitting virus replication in the host. Studies have shown that administration of a p38 MAPK inhibitor boosted the survival rate in mice following SARS-CoV infection (30) defining its importance in SARS-CoV virulence. Thus, the PBM virulent domain of E protein activates the immunopathological mechanisms by using syntenin as a mediator of p38 MAPK induced inflammation (31) . Lactobacillus contains a HSP27-inducible polyphosphate (poly P) fraction. Probiotic-derived polyphosphates, strengthen the epithelial barrier function and keep intestinal homeostasis through the integrin-p38 MAPK pathway (32) . The importance of protein E in the pathogenesis of mutant SARS-CoV viruses is stated (18, 19) as mutant of SARS-CoV with inactive E protein in experimental mice model and in vitro cell culture able to retrograde protein E in its initial active status (24) . Further to the above, the absence of protein E viroporin is related to shrinking of pulmonary edema as well as to lower mortality rates in mice (33) . In this vein, other authors observed the absence of protein E to be related to inefficient viral maturation, incompetent progenitors and reduced viral levels (34) . Minor PBM mutations of protein E seems to be bearable while PBM main domain remains intact (24) . In this regard, knowledge on PBM mutants and their interaction capacity with host cell proteins will provide us information on the virus pathogenicity. It is known that SARS-CoV protein M is participating also in the viral envelope assembly and release of the virions (35) but in spite of that there is no evidence of protein M role in membrane morphology (35) . Membrane deviating morphology seems to be exclusively related to the protein E in SARS-CoV (35) . Moreover, analysis of viral proteins by VaxiJen software in order to test the probability of antigenic proteins showed evidence that protein E was the most antigenic (36) . Here we report the Avian infectious bronchitis virus (IBV) which prerequisites grounds in the hydrophobic domain (HD) of protein E (17) . There is biochemical evidence of 2 different oligomeric forms of protein E in IBV; the one is involved in the IBV assembly and the other form participates in the disarray of the secretory pathway (17) . It is then expected that broader knowledge of the SARS-CoV protein E will supply us with novel therapeutic targets (37) . Successfully, antiviral drugs that target viroporins were designed (36) . Antiviral drugs either inhibit proton conduction in the channel and directly block the channel passage or bind to six sites located outside the channel cavity and inhibit cation conduction with an allosteric mechanism (38) . In this context, amantadine and rimantadine were proposed for the treatment of influenza viruses (39) . As stated previously, evidence of additional interaction partners for SARS-CoV E protein could offer a real targeted therapeutic option for the disease treatment (24) . Probiotics interact with protein E and result in the internalization of the virion stimulating macrophages, dendritic and mast cells thus, releasing cytokines and chemokines (24) and stimulating the host immunity (40) . Despite the meaningful research progress on viroporins' structure and on the role of SARS-CoV protein E in viral replication, such as assembly, membrane functioning, virion release, inflammation, autophagy and apoptosis, major challenges lie ahead in research in order to get knowledge on the implicated physio-pathological mechanisms and settle therapeutic approaches for the treatment of COVID-19. Medications deactivating the enzymes implicated in these mechanisms should be hopeful as potential antiviral treatments. Current research is focused on the use of probiotics as a carrier of exogenous antigens into the mucosa, where they can boost IgA production and develop an enhanced T cell response (41) (42) (43) . In this vein, Lactobacillus sp. were used to release influenza H9N2 hemagglutinin or even H1N1 M2e protein as an approach to enhance the influenza virus vaccine efficacy (42) (43) (44) . Another study reported that oral administration of probiotics can differentially affect gene expression, and may boost the antiviral activity (45, 46) . All the above, suggest the potential effect of probiotics as a potential therapeutic approach for COVID-19. Nevertheless, probiotics should be used with caution, especially in critically ill patients (1). They are not recommended in immunocompromised patients or those with prosthetic valves due to their potential of invasive infections (1). Moreover, some of them have been incriminated as potential recipients of resistance genes (vanA gene cluster due to E. faecium SF68 strain) (47) . Finally, some have high enzymatic activity, expressing CYP enzymes, specifically P450 that could interfere in drugs' metabolism and bioavailability (48, 49) . Yet, a clearer understanding of the implicated mechanisms of action of probiotics, specification of the biochemical profile of the enigmatic SARS protein E and clinical trials are needed, in order to assign a probiotic as efficient in the prophylaxis or field therapy of COVID-19. All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication. Probiotics in medicine: a long debate Probiotics and COVID-19: one size does not fit all Using probiotics to attend the curve of coronavirus disease COVID-2019 pandemic The brain-lung-brain axis Enrichment of the lung microbiome with gut bacteria in sepsis and the acute respiratory distress syndrome Host innate immune responses to sepsis Gut microbiome composition predicts infection risk during chemotherapy in children with acute lymphoblastic leukemia Role of the intestinal microbiota in the immunomodulation of influenza virus infection. 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