Short Chain Fatty Acids: Fundamental mediators of the gut-lung axis and their involvement in pulmonary diseases.

The human microbiota is fundamental to correct immune system development and balance. Dysbiosis, or microbial content alteration in the gut and respiratory tract, is associated with immune system dysfunction and lung disease development. The microbiota's influence on human health and disease is exerted through the abundance of metabolites produced by resident microorganisms, where short-chain fatty acids (SCFAs) represent the fundamental class. SCFAs are mainly produced by the gut microbiota through anaerobic fermentation of dietary fibers, and are known to influence the homeostasis, susceptibility to and outcome of many lung diseases. This article explores the microbial species found in healthy human gastrointestinal and respiratory tracts. We investigate factors contributing to dysbiosis in lung illness, and the gut-lung axis and its association with lung diseases, with a particular focus on the functions and mechanistic roles of SCFAs in these processes. The key focus of this review is a discussion of the main metabolites of the intestinal microbiota that contribute to host-pathogen interactions: SCFAs, which are formed by anaerobic fermentation. These metabolites include propionate, acetate, and butyrate, and are crucial for the preservation of immune homeostasis. Evidence suggests that SCFAs prevent infections by directly affecting host immune signaling. This review covers the various and intricate ways through which SCFAs affect the immune system's response to infections, with a focus on pulmonary diseases including chronic obstructive pulmonary diseases, asthma, lung cystic fibrosis, and tuberculosis. The findings reviewed suggest that the immunological state of the lung may be indirectly influenced by elements produced by the gut microbiota. SCFAs represent valuable potential therapeutic candidates in this context.

Associations of disordered eating with the intestinal microbiota and short-chain fatty acids among young adults with type 1 diabetes.

BACKGROUND AND AIMS: Disordered eating (DE) in type 1 diabetes (T1D) includes insulin restriction for weight loss with serious complications. Gut microbiota-derived short chain fatty acids (SCFA) may benefit host metabolism but are reduced in T1D. We evaluated the hypothesis that DE and insulin restriction were associated with reduced SCFA-producing gut microbes, SCFA, and intestinal microbial diversity in adults with T1D. METHODS AND RESULTS: We collected stool samples at four timepoints in a hypothesis-generating gut microbiome pilot study ancillary to a weight management pilot in young adults with T1D. 16S ribosomal RNA gene sequencing measured the normalized abundance of SCFA-producing intestinal microbes. Gas-chromatography mass-spectrometry measured SCFA (total, acetate, butyrate, and propionate). The Diabetes Eating Problem Survey-Revised (DEPS-R) assessed DE and insulin restriction. Covariate-adjusted and Bonferroni-corrected generalized estimating equations modeled the associations. COVID-19 interrupted data collection, so models were repeated restricted to pre-COVID-19 data. Data were available for 45 participants at 109 visits, which included 42 participants at 65 visits pre-COVID-19. Participants reported restricting insulin "At least sometimes" at 53.3% of visits. Pre-COVID-19, each 5-point DEPS-R increase was associated with a -0.34 (95% CI -0.56, -0.13, p = 0.07) lower normalized abundance of genus Anaerostipes; and the normalized abundance of Lachnospira genus was -0.94 (95% CI -1.5, -0.42), p = 0.02 lower when insulin restriction was reported "At least sometimes" compared to "Rarely or Never". CONCLUSION: DE and insulin restriction were associated with a reduced abundance of SCFA-producing gut microbes pre-COVID-19. Additional studies are needed to confirm these associations to inform microbiota-based therapies in T1D.

Possible role of gut microbes and host's immune response in gut-lung homeostasis.

The vast diversity of microbial communities reside in various locations of the human body, and they are collectively named as the 'Human Microbiota.' The majority of those microbes are found in the gastrointestinal and respiratory tracts. The microorganisms present in the gastrointestinal and the respiratory tracts are called the gut microbiota and the airway microbiota, respectively. These microbial communities are known to affect both the metabolic functions and the immune responses of the host. Among multiple factors determining the composition of gut microbiota, diet has played a pivotal role. The gut microbes possess enzymatic machinery for assimilating dietary fibers and releasing different metabolites, primarily short-chain fatty acids (SCFAs). The SCFAs modulate the immune responses of not only the gut but other distal mucosal sites as well, such as the lungs. Dysbiosis in normal gut flora is one of the factors involved in the development of asthma and other respiratory disorders. Of note, several human and murine studies have indicated significant cross-talk between gut microbiota and lung immunity, known as the gut-lung axis. Here, in this review, we summarize the recent state of the field concerning the effect of dietary metabolites, particularly SCFAs, on the "gut-lung axis" as well as discuss its impact on lung health. Moreover, we have highlighted the role of the "gut-lung axis" in SARS-CoV-2 mediated inflammation. Also, to analyze the global research progress on the gut-lung axis and to identify the knowledge gap in this field, we have also utilized the bibliographic tools Dimension database and VOS viewer analysis software. Through network mapping and visualization analysis, we can predict the present research trend and the possibility to explore new directions.

Correlation of gut microbiota and metabolic functions with the antibody response to the BBIBP-CorV vaccine.

Increasing evidence indicates that gut microbiota may play a key role in vaccination immunity. Here, we investigate whether the human gut microbiota and metabolic function correlate with the BBIBP-CorV vaccine response. A total of 207 participants who received the BBIBP-CorV vaccine are enrolled. The gut microbiome and metabolic functions are investigated using metagenomic sequencing and metabolomic assays. We find that BBIBP-CorV vaccination is accompanied by altered microbiome composition and functional pathways, and the gut microbiome and its functional profiles correlate with the vaccine response. The levels of short-chain fatty acids (SCFAs) are much higher in the high antibody response group compared to the low response group, and several SCFAs display a positive correlation with the antibody response. Our study highlights that the gut microbiome and its function is associated with the BBIBP-CorV vaccine response, providing evidence for further exploration of microbiome modulation to improve COVID-19 vaccine efficacy.

Different methods of eubiotic feed additive provision affect the health, performance, fermentation, and metabolic status of dairy calves during the preweaning period.

BACKGROUND: This study aimed to evaluate whether different methods of providing eubiotic feed additives to neonatal calves, during the preweaning period, can improve the calves' health, performance, ruminal fermentation, and metabolic status. Forty-four (3-day-old) Holstein-Friesian dairy calves (22 female and 22 male) were divided into four treatment groups for the duration of the 8-week trial. The eubiotic feed additive consisted of a combination of probiotic Lactobacillus spp. (multiple-strains at a dose of 250 mg/calf/day) and phytobiotics containing rosmarinic acid, as the main bioactive compound (at a dose of 50 mg/calf/day). The groups were named: CON (control, without eubiotic in either the milk replacer or the starter feed), MR (eubiotic in the milk replacer), SF (eubiotic in the starter feed), MRS (eubiotic in both the milk replacer and the starter feed). The individual intake of starter feed and the fecal scores were measured daily, and body weight and biometric measurements were taken weekly until calves were 56 days of age. Blood samples were collected on day 3 and then every 14 days to determine concentrations of insulin-like-growth-factor-I, ß-hydroxybutyrate, non-esterified fatty acids, and blood urea nitrogen. Ruminal fluid was collected on days 28 and 56 for short-chain fatty acids, NH3-N, and pH measurements. RESULTS: The body weight of the calves of the MR treatment group was higher compared to all other groups on days 28 and 56. Including the eubiotic feed additive in the milk replacer increased average daily gain, starter intake, and total dry matter intake from day 29 to day 56 and the overall experimental period compared to the CON group. The calves with MR treatment had lower fecal scores from days 3 to 28, a number of parasite oocysts/cysts per gram of feces on day 28, and the occurrences of fecal consistency scores of 3 (mild diarrhea) and 4 (severe diarrhea) were 3.2 and 3.0 times lower, respectively, compared with the CON group. The MR group had higher ruminal concentrations of short-chain-fatty-acids, propionate, and butyrate on day 56 than the CON group. Adding eubiotics into milk replacer resulted in the highest concentrations of blood insulin-like-growth-factor-I and ß-hydroxybutyrate from days 29 to 56 and the overall experimental period. CONCLUSION: The addition of eubiotic feed additives into the milk replacer can improve health, performance, ruminal fermentation, and biochemical blood indices in dairy calves during the preweaning period.

Plant Polysaccharides Modulate Immune Function via the Gut Microbiome and May Have Potential in COVID-19 Therapy.

Plant polysaccharides can increase the number and variety of beneficial bacteria in the gut and produce a variety of active substances, including short-chain fatty acids (SCFAs). Gut microbes and their specific metabolites have the effects of promoting anti-inflammatory activity, enhancing the intestinal barrier, and activating and regulating immune cells, which are beneficial for improving immunity. A strong immune system reduces inflammation caused by external viruses and other pathogens. Coronavirus disease 2019 (COVID-19) is still spreading globally, and patients with COVID-19 often have intestinal disease and weakened immune systems. This article mainly evaluates how polysaccharides in plants can improve the immune system barrier by improving the intestinal microecological balance, which may have potential in the prevention and treatment of COVID-19.

Short-chain fatty acid acetate triggers antiviral response mediated by RIG-I in cells from infants with respiratory syncytial virus bronchiolitis.

BACKGROUND: Gut microbiota-derived short-chain fatty-acid (SFCA) acetate protects mice against RSV A2 strain infection by increasing interferon-ß production and expression of interferon-stimulated genes (ISGs). However, the role of SFCA in RSV infection using strains isolated from patients is unknown. METHODS: We first used RSV clinical strains isolated from infants hospitalized with RSV bronchiolitis to investigate the effects of in vitro SCFA-acetate treatment of human pulmonary epithelial cells. We next examined whether SCFA-acetate treatment is beneficial in a mouse model of RSV infection using clinical isolates. We sought to investigate the relationship of gut microbiota and fecal acetate with disease severity among infants hospitalized with RSV bronchiolitis, and whether treating their respiratory epithelial cells with SCFA-acetate ex-vivo impacts viral load and ISG expression. We further treated epithelial cells from SARS-CoV-2 infected patients with SCFA-acetate. FINDINGS: In vitro pre-treatment of A549 cells with SCFA-acetate reduced RSV infection with clinical isolates and increased the expression of RIG-I and ISG15. Animals treated with SCFA-acetate intranasally recovered significantly faster, with reduction in the RSV clinical isolates viral load, and increased lung expression of IFNB1 and the RIG-I. Experiments in RIG-I knockout A549 cells demonstrated that the protection relies on RIG-I presence. Gut microbial profile was associated with bronchiolitis severity and with acetate in stool. Increased SCFA-acetate levels were associated with increasing oxygen saturation at admission, and shorter duration of fever. Ex-vivo treatment of patients' respiratory cells with SCFA-acetate reduced RSV load and increased expression of ISGs OAS1 and ISG15, and virus recognition receptors MAVS and RIG-I, but not IFNB1. These SCFA-acetate effects were not found on cells from SARS-CoV-2 infected patients. INTERPRETATION: SCFA-acetate reduces the severity of RSV infection and RSV viral load through modulation of RIG-I expression. FUNDING: FAPERGS (FAPERGS/MS/CNPq/SESRS no. 03/2017 - PPSUS 17/2551-0001380-8 and COVID-19 20/2551-0000258-6); CNPq 312504/2017-9; CAPES) - Finance Code 001.

Alteration of the gut microbiota following SARS-CoV-2 infection correlates with disease severity in hamsters.

Mounting evidence suggests that the gut-to-lung axis is critical during respiratory viral infections. We herein hypothesized that disruption of gut homeostasis during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection may associate with early disease outcomes. To address this question, we took advantage of the Syrian hamster model. Our data confirmed that this model recapitulates some hallmark features of the human disease in the lungs. We further showed that SARS-CoV-2 infection associated with mild intestinal inflammation, relative alteration in intestinal barrier property and liver inflammation and altered lipid metabolism. These changes occurred concomitantly with an alteration of the gut microbiota composition over the course of infection, notably characterized by a higher relative abundance of deleterious bacterial taxa such as Enterobacteriaceae and Desulfovibrionaceae. Conversely, several members of the Ruminococcaceae and Lachnospiraceae families, including bacteria known to produce the fermentative products short-chain fatty acids (SCFAs), had a reduced relative proportion compared to non-infected controls. Accordingly, infection led to a transient decrease in systemic SCFA amounts. SCFA supplementation during infection had no effect on clinical and inflammatory parameters. Lastly, a strong correlation between some gut microbiota taxa and clinical and inflammation indices of SARS-CoV-2 infection severity was evidenced. Collectively, alteration of the gut microbiota correlates with disease severity in hamsters making this experimental model valuable for the design of interventional, gut microbiota-targeted, approaches for the control of COVID-19.Abbreviations: SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; COVID-19, coronavirus disease 2019; SCFAs, short-chain fatty acids; dpi, day post-infection; RT-PCR, reverse transcription polymerase chain reaction; IL, interleukin. ACE2, angiotensin converting enzyme 2; TMPRSS2, transmembrane serine protease 2.

Potential Association Between Dietary Fibre and Humoral Response to the Seasonal Influenza Vaccine.

Influenza vaccination is an effective public health measure to reduce the risk of influenza illness, particularly when the vaccine is well matched to circulating strains. Notwithstanding, the efficacy of influenza vaccination varies greatly among vaccinees due to largely unknown immunological determinants, thereby dampening population-wide protection. Here, we report that dietary fibre may play a significant role in humoral vaccine responses. We found dietary fibre intake and the abundance of fibre-fermenting intestinal bacteria to be positively correlated with humoral influenza vaccine-specific immune responses in human vaccinees, albeit without reaching statistical significance. Importantly, this correlation was largely driven by first-time vaccinees; prior influenza vaccination negatively correlated with vaccine immunogenicity. In support of these observations, dietary fibre consumption significantly enhanced humoral influenza vaccine responses in mice, where the effect was mechanistically linked to short-chain fatty acids, the bacterial fermentation product of dietary fibre. Overall, these findings may bear significant importance for emerging infectious agents, such as COVID-19, and associated de novo vaccinations.

Probiotic Supplements: Their Strategies in the Therapeutic and Prophylactic of Human Life-Threatening Diseases.

Chronic diseases and viral infections have threatened human life over the ages and constitute the main reason for increasing death globally. The rising burden of these diseases extends to negatively affecting the economy and trading globally, as well as daily life, which requires inexpensive, novel, and safe therapeutics. Therefore, scientists have paid close attention to probiotics as safe remedies to combat these morbidities owing to their health benefits and biotherapeutic effects. Probiotics have been broadly adopted as functional foods, nutraceuticals, and food supplements to improve human health and prevent some morbidity. Intriguingly, recent research indicates that probiotics are a promising solution for treating and prophylactic against certain dangerous diseases. Probiotics could also be associated with their essential role in animating the immune system to fight COVID-19 infection. This comprehensive review concentrates on the newest literature on probiotics and their metabolism in treating life-threatening diseases, including immune disorders, pathogens, inflammatory and allergic diseases, cancer, cardiovascular disease, gastrointestinal dysfunctions, and COVID-19 infection. The recent information in this report will particularly furnish a platform for emerging novel probiotics-based therapeutics as cheap and safe, encouraging researchers and stakeholders to develop innovative treatments based on probiotics to prevent and treat chronic and viral diseases.

Neuropsychiatric Ramifications of COVID-19: Short-Chain Fatty Acid Deficiency and Disturbance of Microbiota-Gut-Brain Axis Signaling.

COVID-19-associated neuropsychiatric complications are soaring. There is an urgent need to understand the link between COVID-19 and neuropsychiatric disorders. To that end, this article addresses the premise that SARS-CoV-2 infection results in gut dysbiosis and an altered microbiota-gut-brain (MGB) axis that in turn contributes to the neuropsychiatric ramifications of COVID-19. Altered MGB axis activity has been implicated independently as a risk of neuropsychiatric disorders. A review of the changes in gut microbiota composition in individual psychiatric and neurological disorders and gut microbiota in COVID-19 patients revealed a shared "microbial signature" characterized by a lower microbial diversity and richness and a decrease in health-promoting anti-inflammatory commensal bacteria accompanied by an increase in opportunistic proinflammatory pathogens. Notably, there was a decrease in short-chain fatty acid (SCFA) producing bacteria. SCFAs are key bioactive microbial metabolites with anti-inflammatory functions and have been recognized as a critical signaling pathway in the MGB axis. SCFA deficiency is associated with brain inflammation, considered a cardinal feature of neuropsychiatric disorders. The link between SARS-CoV-2 infection, gut dysbiosis, and altered MGB axis is further supported by COVID-19-associated gastrointestinal symptoms, a high number of SARS-CoV-2 receptors, angiotensin-cleaving enzyme-2 (ACE-2) in the gut, and viral presence in the fecal matter. The binding of SARS-CoV-2 to the receptor results in ACE-2 deficiency that leads to decreased transport of vital dietary components, gut dysbiosis, proinflammatory gut status, increased permeability of the gut-blood barrier (GBB), and systemic inflammation. More clinical research is needed to substantiate further the linkages described above and evaluate the potential significance of gut microbiota as a diagnostic tool. Meanwhile, it is prudent to propose changes in dietary recommendations in favor of a high fiber diet or supplementation with SCFAs or probiotics to prevent or alleviate the neuropsychiatric ramifications of COVID-19.

The influence of microbiota-derived metabolites on viral infections.

Intestinal microbiota have profound effects on viral infections locally and systemically. While they can directly influence enteric virus infections, there is also an increasing appreciation for the role of microbiota-derived metabolites in regulating virus infections. Because metabolites diffuse across the intestinal epithelium and enter circulation, they can influence host response to pathogens at extraintestinal sites. In this review, we summarize the effects of three types of microbiota-derived metabolites on virus infections. While short-chain fatty acids serve to regulate the extent of inflammation associated with viral infections, the flavonoid desaminotyrosine and bile acids generally regulate interferon responses. A common theme that emerges is that microbiota-derived metabolites can have proviral and antiviral effects depending on the virus in question. Understanding the molecular mechanisms by which microbiota-derived metabolites impact viral infections and the highly conditional nature of these responses should pave the way to developing novel rational antivirals.

Virtualized clinical studies to assess the natural history and impact of gut microbiome modulation in non-hospitalized patients with mild to moderate COVID-19 a randomized, open-label, prospective study with a parallel group study evaluating the physiologic effects of KB109 on gut microbiota structure and function: a structured summary of a study protocol for a randomized controlled study.

OBJECTIVES: These 2 parallel studies (K031 and K032) aim to evaluate the safety of KB109 in addition to supportive self-care (SSC) compared with SSC alone in outpatients with mild to moderate coronavirus disease 2019 (COVID-19). KB109 is a novel synthetic glycan that was formulated to modulate the gut microbiome composition and metabolic output in order to increase beneficial short-chain fatty acid (SCFA) production in the gut. The K031 study is designed to evaluate the safety of KB109 and characterize its impact on the natural progression of COVID-19 in patients with mild to moderate disease. The K032 study is evaluating the effect of KB109 on the gut microbiota structure and function in this same patient population. Additionally, both studies are evaluating measures of health care utilization, quality of life (QOL), laboratory indices, biomarkers of inflammation, and serological measures of immunity in patients who received SSC alone or with KB109. Noteworthy aspects of these outpatient studies include study design measures aimed at limiting in-person interactions to minimize the risk of infection spread, such as use of online diaries, telemedicine, and at-home sample collection. STUDY DESIGN: K031 and K032 are randomized, controlled, open-label, clinical food studies. PARTICIPANTS: Inclusion Criteria: • Adults ≥18 years of age • Patients willing and able to give informed consent • Screening/randomization telemedicine visit within 2 days of testing positive test for COVID-19 ○ In K031 study, symptomatic patients at COVID-19 testing must report new or worsening symptoms at baseline that have not been present for more than 5 days ▪ Cardinal COVID-19 symptoms include fever, chills/repeated shaking with chills, cough, shortness of breath, headache, muscle pain, anosmia/ageusia, and sore throat. The 5 additional symptoms include gastrointestinal (GI) disturbance/symptoms (other than diarrhea), diarrhea, fatigue, nasal congestion, and chest tightness ○ In K031, at COVID-19 testing, pre-symptomatic patients must report new cardinal COVID-19 symptoms within 7 days of a positive test and they must be screened and randomized within 5 days of developing symptoms • Mild to moderate COVID-19 and self-reported outpatient management ○ In K032, mild to moderate COVID-19 was defined as having the following symptoms for no more than 72 hours before COVID-19 testing: a self- reported fever or cough (new or exacerbated) or presence of at least 2 of the following: anosmia, sore throat, or nasal congestion • Ability to adhere to the study visit schedule and other protocol requirements • Consistent internet or cell phone access with a data plan and access to a smartphone, tablet, or computer • The K031 and K032 studies are currently being conducted at 17 clinical institutions throughout the United States. EXCLUSION CRITERIA: • In the primary investigator's (PI) judgement, patients likely to require hospitalization for COVID-19 • Patients who are hospitalized for in-patient treatment or currently being evaluated for potential hospitalization at the time of informed consent for conditions other than COVID-19 • History of chronic lung disease with chronic hypoxia • History of documented cirrhosis or end-stage liver disease • Ongoing requirement for oxygen therapy • Shortness of breath in resting position • Diagnosis of sleep apnea requiring bilevel positive airway pressure (BIPAP)/continuous positive airway pressure (CPAP) • Female patients who are pregnant, trying to become pregnant, or lactating • Concurrent use of immunomodulatory agent within 12 months; systemic antibiotics, antifungals, or antivirals for treatment of active infection within 28 days; systemic immunosuppressive therapy within 3 months; or drugs or other compounds that modulate GI motility (eg, stool softeners, laxatives, or fiber supplements) taken currently, or within 7 days. Antacid (histamine 2 blockers and proton pump inhibitors) and antidiarrheal agents are not prohibited • History of GI surgery (6 months prior to randomization), including but not limited to bariatric surgery and bowel resection, or history of, or active GI disease(s) that may affect assessment of tolerability, including but not limited to inflammatory bowel disease, irritable bowel syndrome, autoimmune disease, or GI malignancy • Participation in an interventional clinical trial or use of any investigational agent within 30 days before randomization • Clinically significant or uncontrolled concomitant medical condition that would put the patient at risk or jeopardize the objectives of the study in the opinion of the PI • In the opinion of the PI, patient unlikely for any reason to be able to comply with study procedures • Contraindications, sensitivities, or known allergy to the use of the study product or its components INTERVENTION AND COMPARATOR: Patients will be randomized (1,1) to receive either SSC and KB109 or SSC alone. During SSC, patients should follow the steps as instructed by their healthcare provider to care for themselves and protect other people in the home and community from potentially contracting COVID-19. Management of COVID-19-related symptoms with over-the-counter cough, cold, and anti-pyretic medications by patients is permitted in accordance with the medications' respective drug facts label or as instructed by the patient's healthcare provider. Following randomization, patients assigned to receive KB109 and SSC will receive a Kaleido Biosciences, Inc at-home study kit including a thermometer, pulse oximeter, and KB109. During the Intake Period (days 1-14), KB109 will be reconstituted in water by the patient and consumed by the patient twice daily (at least 8 hours apart), following an up-titration dosing schedule: Days 1 to 2: 9 g twice daily for a total daily dose of 18 g Days 3 to 4: 18 g twice daily for a total daily dose of 36 g Days 5 to 14: 36 g twice daily for a total daily dose of 72 g During the intake period, patients will record their daily COVID-19-related symptoms, selected COVID-19 signs (as self-measured using the provided thermometer and pulse oximeter), responses to questions related to QOL measures, health care use measures, and concomitant medications taken in the previous 24 hours. Wellness visits by telephone will be conducted between days 1 and 14 to follow up on patient's health status and to ascertain compliance with KB109 and completion of questions. On day 14, all patients will undergo a telemedicine visit where the following will be conducted: abbreviated physical examination, assessment of safety and other protocol-specified measures of health, and an evaluation of whether follow-up treatment is recommended owing to a progression of COVID-19 symptoms. If feasible, blood samples for clinical chemistries, biomarkers and serological measure of immunity, and nasal/oropharyngeal swabs for quantitative viral load assessments will be collected. Beginning on day 15, patients in both groups will enter the follow-up period (days 15-35) where COVID-19 signs, symptoms, and health care use indices will be collected. Wellness visits by telephone will be conducted on days 21, 28, and 35 to follow-up on the patient's health status. On day 35, all patients will undergo a telemedicine visit where the same information as the day 14 telemedicine visit will be collected, including any blood samples. MAIN OUTCOMES: The primary outcome for the K031 and K032 studies is to evaluate the safety of KB109 in addition to SSC compared with SSC alone in outpatients with mild to moderate COVID-19 by assessing the number of patients experiencing KB109-related treatment-emergent adverse events (TEAEs) during the study. K031 will also evaluate duration of symptoms among outpatients with mild to moderate COVID-19. This will be as an assessment made during the intake and/or follow-up periods of the following: • Time to resolution of the 13 overall and the 8 cardinal COVID-19-related symptoms from day 1 until the day at which the composite score of the 13 overall and 8 cardinal COVID-19-related symptoms becomes 0 or 1 and remains at 0 or 1 for the rest of the intake period and for the follow-up period • Proportion of patients with a reduction from baseline in each of the 13 overall COVID-19-related symptoms • Proportion of patients in whom symptoms (present at baseline) become absent for each of the 13 overall COVID-19-related symptoms • Change from baseline in the overall composite score of the 13 overall COVID-19-related symptoms and the 8 cardinal COVID-19-related symptoms • Time to resolution of fever (defined as from day 1 until the day at which a patient's daily maximum temperature achieves and remains below 100.4°F without antipyretic medication) • Proportion of patients with oxygen saturation <95% and <98% on days 14 and 35 • Measures collected from the health care provider wellness visits • Proportion of patients experiencing hospital admissions (all cause and COVID-19-related) • Health care use K032 will evaluate the effect of KB109 in addition to SSC compared with SSC alone on the gut microbiota structure and function in outpatients with mild to moderate COVID-19. Before days 1, 14, and 35, microbiota structure (eg, magnitude of change in gut microbiome structure, composition of gut microbiome) will be analysed by methods such as nucleic acid sequencing and gut microbiome function will be analysed via levels of stool inflammatory biomarkers (eg, lipocalin) and gut microbiome metabolites (eg, SCFA). The health of outpatients with mild to moderate COVID-19 will be evaluated during the intake and follow- up periods by: measures of QOL; measures collected from the healthcare provider wellness visits; the proportion of patients experiencing hospital admissions; health care use, the proportions of patients with oxygen saturation <95% and <98%, and the proportionof patients with temperature below 100.4 °F without an anti-pyretic medication. Potential exploratory outcome measures may include: changes from baseline (day 1) in laboratory measures, specific biomarkers of infection, serology, inflammation (eg, D-dimer, lipocalin, cytokines, IgM/IgG sero-conversion, and neutralization assays), and viral load in outpatients with mild to moderate COVID-19 in the presence and absence of KB109. RANDOMISATION: All patients deemed eligible for the studies will be randomized in a 1:1 ratio to KB109 in addition to SSC or SSC alone group using an interactive response technology system. Randomization will be stratified by study site/center, age groups (≥18-<45 years, ≥45-<65 years, ≥65 years), and comorbidity status (yes, no). BLINDING (MASKING): These studies are open-label; therefore, no blinding is necessary. NUMBERS TO BE RANDOMISED (SAMPLE SIZE): K031 will enroll approximately 350 to 400 (175-200 patients per group) whereas K032 will enroll approximately 50 patients (25 per group). STUDY STATUS: K031 protocol version 4, December 9, 2020; recruitment started in August, 2020, and the study is estimated to be completed in March 2021. This study is active and enrollment was completed in January, 2021. K032 protocol version 2, June 30, 2020; recruitment is estimated to start in July, 2020. This study is recruiting and the study is estimated to be completed in March 2021. STUDY REGISTRATION: K031 is registered with the US National Library of Medicine, Identifier NCT04414124 as of June 4, 2020. K032 is registered with the US National Library of Medicine, Identifier NCT04486482 as of July 24, 2020. FULL PROTOCOL: The full protocols are attached as additional files (Additional files 1 and 2), accessible from the ClinicalTrials.gov website. In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this letter serves as a summary of the key elements of the full protocols. The study protocols have been reported in accordance with the Standard Protocol Items: Recommendations for Clinical Interventional Trials (SPIRIT) guidelines (Additional files 3 and 4).

Microbiota-derived short-chain fatty acids do not interfere with SARS-CoV-2 infection of human colonic samples.

Microbiota-derived molecules called short-chain fatty acids (SCFAs) play a key role in the maintenance of the intestinal barrier and regulation of immune response during infectious conditions. Recent reports indicate that SARS-CoV-2 infection changes microbiota and SCFAs production. However, the relevance of this effect is unknown. In this study, we used human intestinal biopsies and intestinal epithelial cells to investigate the impact of SCFAs in the infection by SARS-CoV-2. SCFAs did not change the entry or replication of SARS-CoV-2 in intestinal cells. These metabolites had no effect on intestinal cells' permeability and presented only minor effects on the production of anti-viral and inflammatory mediators. Together our findings indicate that the changes in microbiota composition of patients with COVID-19 and, particularly, of SCFAs do not interfere with the SARS-CoV-2 infection in the intestine.