Famotidine activates the vagus nerve inflammatory reflex to attenuate cytokine storm (preprint)

Background. Severe COVID-19 is characterized by pro-inflammatory cytokine release syndrome (cytokine storm) which causes high morbidity and mortality. Recent observational and clinical studies suggest famotidine, a histamine 2 receptor (H2R) antagonist widely used to treat gastroesophageal reflux disease , attenuates the clinical course of COVID-19. Because evidence is lacking for a direct antiviral activity of famotidine, a proposed mechanism of action is blocking the effects of histamine released by mast cells. Here we hypothesized that famotidine activates the inflammatory reflex, a brain-integrated vagus nerve mechanism which inhibits inflammation via alpha 7 nicotinic acetylcholine receptor ( α7nAChR ) signal transduction, to prevent cytokine storm. Methods. The potential anti-inflammatory effects of famotidine and other H2R antagonists was assessed in mice exposed to lipopolysaccharide (LPS)-induced cytokine storm. As the inflammatory reflex is integrated and can be stimulated in the brain, and H2R antagonists penetrate the blood brain barrier poorly, famotidine was administered by intracerebroventricular (ICV) or intraperitoneal (IP) routes. Results. Famotidine administered IP significantly reduced serum and splenic LPS-stimulated tumor necrosis factor α and interleukin-6 concentrations, significantly improving survival. The effects of ICV famotidine were significantly more potent as compared to the peripheral route. Mice lacking mast cells by genetic deletion also responded to famotidine, indicating the anti-inflammatory effects are not mast cell dependent. Either bilateral sub-diaphragmatic vagotomy or genetic knock-out of α7nAChR abolished the anti-inflammatory effects of famotidine, indicating the inflammatory reflex as famotidine’s mechanism of action. While the structurally similar H2R antagonist tiotidine displayed equivalent anti-inflammatory activity, the H2R antagonists cimetidine or ranitidine were ineffective even at very high dosages. Conclusions. These observations reveal a previously unidentified vagus nerve-dependent anti-inflammatory effect of famotidine in the setting of cytokine storm which is not replicated by high dosages of other H2R antagonists in clinical use. Because famotidine is more potent when administered intrathecally, these findings are also consistent with a primarily central nervous system mechanism of action.

Monoclonal Antibodies Capable of Binding SARS-CoV-2 Spike Protein Receptor Binding Motif Specifically Prevent GM-CSF Induction. (preprint)

A severe acute respiratory syndrome (SARS)-like coronavirus (SARS-CoV-2) has recently caused a pandemic COVID-19 disease that infected more than 25.6 million and killed 852,000 people worldwide. Like the SARS-CoV, SARS-CoV-2 also employs a receptor-binding motif (RBM) of its envelope spike protein for binding the host angiotensin-converting enzyme 2 (ACE2) to gain viral entry. Currently, extensive efforts are being made to produce vaccines against a surface fragment of a SARS-CoV-2, such as the spike protein, in order to boost protective antibody responses. It was previously unknown how spike protein-targeting antibodies would affect innate inflammatory responses to SARS-CoV-2 infections. Here we generated a highly purified recombinant protein corresponding to the RBM of SARS-CoV-2, and used it to screen for cross-reactive monoclonal antibodies (mAbs). We found two RBM-binding mAbs that competitively inhibited its interaction with human ACE2, and specifically blocked the RBM-induced GM-CSF secretion in both human monocyte and murine macrophage cultures. Our findings have suggested a possible strategy to prevent SARS-CoV-2-elicited "cytokine storm", and provided a potentially useful criteria for future assessment of innate immune-modulating properties of various SARS-CoV-2 vaccines. One Sentence SummaryRBM-binding Antibodies Inhibit GM-CSF Induction.

Calming the Cytokine Storm - Splenic Ultrasound for Treating Inflammatory Disorders and Potentially COVID-19 (preprint)

Hyperinflammation and uncontrolled cytokine release, which can be seen in severe cases of COVID-19, require therapy to reduce the innate immune response without hindering necessary adaptive immune mechanisms. Here, we show results from the first in-human trials using non-invasive ultrasound stimulation of the spleen to reduce cytokine release in the context of both an acute response in healthy subjects and a chronic inflammatory condition in rheumatoid arthritis patients. Splenic ultrasound results in a reduction in TNF serum levels, as well as IL-1B; and IL-8 transcript levels in monocytes. There is also a down regulation of pathways involved in TNF and IL-6 production, and IFNgamma- and NFKB-regulated genes. Many of these cytokines or pathways are upregulated in COVID-19 patients. There is also a reduction in chemokine transcript levels and other components of the chemotactic response, suggesting that reduction of cellular migration may contribute to the therapeutic effects of ultrasound. There is no inhibition of the adaptive immune response with ultrasound treatment relating to antibody production. This is consistent with a pre-clinical animal model where enhanced antibody production was achieved with splenic ultrasound. Therefore, this new splenic ultrasound approach has the potential to treat acute and chronic hyper-inflammatory diseases, as it lowers cytokine levels without disrupting the normal adaptive immune response. Portable ultrasound technologies are currently being developed and translated to the clinic to treat various inflammatory disorders, with more recent efforts directed towards combatting the hyperinflammation or cytokine storm in COVID-19 patients.

HIV protease inhibitors saquinavir and nelfinavir are potent inhibitors of cathepsin L activity: A potential treatment for COVID-19 patients (preprint)

The 2019 coronavirus disease pandemic (COVID-19) has mobilized efforts worldwide, and several ongoing clinical trials aimed at developing a drug-based treatment for its control. Cathepsin L is an endosomal cysteine protease that mediates the cleavage of the S1 subunit of the coronavirus surface spike glycoprotein. This cleavage is necessary for coronavirus entry into human host cells and viruses/host cell endosome membrane fusion. Therefore, cathepsin L is a potential target for the treatment of COVID-19 patients. In this report, we describe a previously unknown inhibitory effect of two FDA-approved drugs, saquinavir and nelfinavir, on human cathepsin L activity. Whether the pivotal role for cathepsin L in Sars-Cov-2 infection described in vitro can be translated to humans, our results support immediate clinical trials of saquinavir or nelfinavir as a potential treatment for COVID-19 patients.

Famotidine Use is Associated with Improved Clinical Outcomes in Hospitalized COVID-19 Patients: A Retrospective Cohort Study (preprint)

Background and Aims: No medications are proven to improve clinical outcomes in COVID-19. Famotidine is commonly used for gastric acid suppression but has recently gained attention as an antiviral that may inhibit SARS-CoV-2 replication. This study tested whether famotidine use is associated with improved clinical outcomes in patients with COVID-19 initially hospitalized to a non-intensive care setting. Methods: This was retrospective cohort study conducted among consecutive hospitalized patients with COVID-19 infection from February 25 to April 13, 2020 at a single medical center. The primary exposure was famotidine, received within 24 hours of hospital admission. The primary outcome was intubation or death. Propensity score matching was used to balance the baseline characteristics of patients who did and did not use famotidine. Results: 1,620 hospitalized patients with COVID-19 were identified including 84 (5.1%) who received famotidine within 24 hours of hospital admission. 340 (21%) patients met the study composite outcome of death or intubation. Use of famotidine was associated with reduced risk for death or intubation (adjusted hazard ratio (aHR) 0.42, 95% CI 0.21-0.85) and also with reduced risk for death alone (aHR 0.30, 95% CI 0.11-0.80). After balancing baseline patient characteristics using propensity score matching, these relationships were unchanged (HR for famotidine and death or intubation 0.43, 95% CI 0.21-0.88). Proton pump inhibitors, which also suppress gastric acid, were not associated with reduced risk for death or intubation. Conclusion: Famotidine use is associated with reduced risk of intubation or death in hospitalized COVID-19 patients. Randomized controlled trials are warranted to determine whether famotidine therapy improves outcomes in hospitalized COVID-19 patients.