Gut as an Alternative Entry Route for SARS-CoV-2: Current Evidence and Uncertainties of Productive Enteric Infection in COVID-19

Mechanisms of enteric neuropathy in diverse contexts of gastrointestinal dysfunction

The enteric nervous system (ENS) commands moment-to-moment gut functions through integrative neurocircuitry housed in the gut wall. The functional continuity of ENS networks is disrupted in enteric neuropathies and contributes to major disturbances in normal gut activities including abnormal gut motility, secretions, pain, immune dysregulation, and disrupted signaling along the gut-brain axis. The conditions under which enteric neuropathy occurs are diverse and the mechanistic underpinnings are incompletely understood. The purpose of this brief review is to summarize the current understanding of the cell types involved, the conditions in which neuropathy occurs, and the mechanisms implicated in enteric neuropathy such as oxidative stress, toll like receptor signaling, purines, and pre-programmed cell death.

Attenuated replication and damaging effects of SARS-CoV-2 Omicron variants in an intestinal epithelial barrier model

Many COVID-19 patients suffer from gastrointestinal symptoms and impaired intestinal barrier function is thought to play a key role in Long COVID. Despite its importance, the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on intestinal epithelia is poorly understood. To address this, we established an intestinal barrier model integrating epithelial Caco-2 cells, mucus-secreting HT29 cells and Raji cells. This gut epithelial model allows efficient differentiation of Caco-2 cells into microfold-like cells, faithfully mimics intestinal barrier function, and is highly permissive to SARS-CoV-2 infection. Early strains of SARS-CoV-2 and the Delta variant replicated with high efficiency, severely disrupted barrier function, and depleted tight junction proteins, such as claudin-1, occludin, and ZO-1. In comparison, Omicron subvariants also depleted ZO-1 from tight junctions but had fewer damaging effects on mucosal integrity and barrier function. Remdesivir, the fusion inhibitor EK1 and the transmembrane serine protease 2 inhibitor Camostat inhibited SARS-CoV-2 replication and thus epithelial barrier damage, while the Cathepsin inhibitor E64d was ineffective. Our results support that SARS-CoV-2 disrupts intestinal barrier function but further suggest that circulating Omicron variants are less damaging than earlier viral strains.

Post-COVID dysautonomias: what we know and (mainly) what we don't know

Following on from the COVID-19 pandemic is another worldwide public health challenge that is referred to variously as long COVID, post-COVID syndrome or post-acute sequelae of SARS-CoV-2 infection (PASC). PASC comes in many forms and affects all body organs. This heterogeneous presentation suggests involvement of the autonomic nervous system (ANS), which has numerous roles in the maintenance of homeostasis and coordination of responses to various stressors. Thus far, studies of ANS dysregulation in people with PASC have been largely observational and descriptive, based on symptom inventories or objective but indirect measures of cardiovascular function, and have paid little attention to the adrenomedullary, hormonal and enteric nervous components of the ANS. Such investigations do not consider the syndromic nature of autonomic dysfunction. This Review provides an update on the literature relating to ANS abnormalities in people with post-COVID syndrome and presents a theoretical perspective on how the ANS might participate in common features of PASC.

Gut microbe-host interactions in post-COVID syndrome: a debilitating or restorative partnership?

Post-COVID syndrome (PCS) patients have reported a wide range of symptoms, including fatigue, shortness of breath, and diarrhea. Particularly, the presence of gastrointestinal symptoms has led to the hypothesis that the gut microbiome is involved in the development and severity of PCS. The objective of this review is to provide an overview of the role of the gut microbiome in PCS by describing the microbial composition and microbial metabolites in COVID-19 and PCS. Moreover, host-microbe interactions via the microbiota-gut-brain (MGB) and the microbiota-gut-lung (MGL) axes are described. Furthermore, we explore the potential of therapeutically targeting the gut microbiome to support the recovery of PCS by reviewing preclinical model systems and clinical studies. Overall, current studies provide evidence that the gut microbiota is affected in PCS; however, diversity in symptoms and highly individual microbiota compositions suggest the need for personalized medicine. Gut-targeted therapies, including treatments with pre- and probiotics, have the potential to improve the quality of life of affected individuals.

In vitro digestion of SARS-CoV-2 contaminated berries reveals high inactivation of infectious virus during gastrointestinal passage

IMPORTANCE

During the pandemic, news outlets occasionally reported on the detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) RNA on various foods, raising concerns over contaminated foods initiating infections. Coronavirus disease 2019 (COVID-19) patients often experience gastrointestinal symptoms and shed SARS-CoV-2 RNA in their feces. In addition, active virus replication in the gastrointestinal tract was shown; however, infectious viruses were rarely detected in feces. We previously showed that SARS-CoV-2 remained infectious on frozen berries for at least a month. Here, in vitro digestion models showed that SARS-CoV-2 on berries exhibits minimal inactivation at the oral phase and the virus may escape gastric inactivation early during feeding. However, high intestinal inactivation of the virus on berries suggested that SARS-CoV-2 was less likely to initiate infection in the small intestine. In contrast, the oral cavity is a potential site where infection might be initiated, providing more input for the gastrointestinal tract. High intestinal inactivation might explain the difficulty of detecting infectious SARS-CoV-2 in feces but not of virus RNA.

HLA-DQ2/8 and COVID-19 in Celiac Disease: Boon or Bane

The SARS-CoV-2 pandemic continues to pose a global threat. While its virulence has subsided, it has persisted due to the continual emergence of new mutations. Although many high-risk conditions related to COVID-19 have been identified, the understanding of protective factors remains limited. Intriguingly, epidemiological evidence suggests a low incidence of COVID-19-infected CD patients. The present study explores whether their genetic background, namely, the associated HLA-DQs, offers protection against severe COVID-19 outcomes. We hypothesize that the HLA-DQ2/8 alleles may shield CD patients from SARS-CoV-2 and its subsequent effects, possibly due to memory CD4 T cells primed by previous exposure to human-associated common cold coronaviruses (CCC) and higher affinity to those allele's groove. In this context, we examined potential cross-reactivity between SARS-CoV-2 epitopes and human-associated CCC and assessed the binding affinity (BA) of these epitopes to HLA-DQ2/8. Using computational methods, we analyzed sequence similarity between SARS-CoV-2 and four distinct CCC. Of 924 unique immunodominant 15-mer epitopes with at least 67% identity, 37 exhibited significant BA to HLA-DQ2/8, suggesting a protective effect. We present various mechanisms that might explain the protective role of HLA-DQ2/8 in COVID-19-afflicted CD patients. If substantiated, these insights could enhance our understanding of the gene-environment enigma and viral-host relationship, guiding potential therapeutic innovations against the ongoing SARS-CoV-2 pandemic.

Spatiotemporal observations of host-pathogen interactions in mucosa during SARS-CoV-2 infection indicate a protective role of ILC2s

IMPORTANCE

Our study revealed the spatial interaction between humanized ACE2 and pseudovirus expressing Spike, emphasizing the role of type 2 innate lymphoid cells during the initial phase of viral infection. These findings provide a foundation for the development of mucosal vaccines and other treatment approaches for both pre- and post-infection management of coronavirus disease 2019.

Gut Microbiota and Mitochondria: Health and Pathophysiological Aspects of Long COVID

The current understanding of long COVID (LC) is still limited. This review highlights key findings regarding the role of gut microbiota, mitochondria, and the main pathophysiological aspects of LC revealed by clinical studies, related to the complex interplay between infection, intestinal dysbiosis, dysfunctional mitochondria, and systemic inflammation generated in a vicious circle, reflecting the molecular and cellular processes from the "leaky gut" to the "leaky electron transport chain (ETC)" into a quantum leap. The heterogeneity of LC has hindered progress in deciphering all the pathophysiological mechanisms, and therefore, the approach must be multidisciplinary, with a special focus not only on symptomatic management but also on addressing the underlying health problems of the patients. It is imperative to further assess and validate the effects of COVID-19 and LC on the gut microbiome and their relationship to infections with other viral agents or pathogens. Further studies are needed to better understand LC and expand the interdisciplinary points of view that are required to accurately diagnose and effectively treat this heterogeneous condition. Given the ability of SARS-CoV-2 to induce autoimmunity in susceptible patients, they should be monitored for symptoms of autoimmune disease after contracting the viral infection. One question remains open, namely, whether the various vaccines developed to end the pandemic will also induce autoimmunity. Recent data highlighted in this review have revealed that the persistence of SARS-CoV-2 and dysfunctional mitochondria in organs such as the heart and, to a lesser extent, the kidneys, liver, and lymph nodes, long after the organism has been able to clear the virus from the lungs, could be an explanation for LC.

CIAO: a living experiment in interdisciplinary large-scale collaboration facilitated by the Adverse Outcome Pathway framework

Introduction

The CIAO project was launched in Spring 2020 to address the need to make sense of the numerous and disparate data available on COVID-19 pathogenesis. Based on a crowdsourcing model of large-scale collaboration, the project has exploited the Adverse Outcome Pathway (AOP) knowledge management framework built to support chemical risk assessment driven by mechanistic understanding of the biological perturbations at the different organizational levels. Hence the AOPs might have real potential to integrate data produced through different approaches and from different disciplines as experienced in the context of COVID-19. In this study, we aim to address the effectiveness of the AOP framework (i) in supporting an interdisciplinary collaboration for a viral disease and (ii) in working as the conceptual mediator of a crowdsourcing model of collaboration.

Methods

We used a survey disseminated among the CIAO participants, a workshop open to all interested CIAO contributors, a series of interviews with some participants and a self-reflection on the processes.

Results

The project has supported genuine interdisciplinarity with exchange of knowledge. The framework provided a common reference point for discussion and collaboration. The diagram used in the AOPs assisted with making explicit what are the different perspectives brought to the knowledge about the pathways. The AOP-Wiki showed up many aspects about its usability for those not already in the world of AOPs. Meanwhile their use in CIAO highlighted needed adaptations. Introduction of new Wiki elements for modulating factors was potentially the most disruptive one. Regarding how well AOPs support a crowdsourcing model of large-scale collaboration, the CIAO project showed that this is successful when there is a strong central organizational impetus and when clarity about the terms of the collaboration is brought as early as possible.

Discussion

Extrapolate the successful CIAO approach and related processes to other areas of science where the AOP could foster interdisciplinary and systematic organization of the knowledge is an exciting perspective.

COVID-19 and Gastrointestinal Disease: Current Insights and Future Management

The first case of coronavirus disease 2019 (COVID-19) was reported in Wuhan, Hubei Province, China, in December 2019, marking a pivotal moment in human history [...].