Ramatroban as a potential Treatment for COVID-19

COVID-19 is known to cause blood clotting (thrombosis) leading to deep vein thrombosis, pulmonary embolism, and stroke. The SARS-CoV-2 virus does this by attacking endothelial cells lining blood vessels and causing endothelial dysfunction and damage. In turn, damaged endothelial cells release mediators including thromboxane A2 that activates platelets and subsequent blood clotting. Thromboxane A2 is elRamatroban inhibits thromboxane induced platelet activation 100-times more potently than aspirin (Kariyazono et al, Blood Coagulation and Fibrinolysis, 2004). 

Activated platelets in COVID-19 expression P-selectin, a protein that activates neutrophils. This platelet-neutrophil partnership leads to release of neutrophil extracellular traps (NETs) from neutrophils which are web-like chromatic structures containing DNA and histones. Normally geared to fight parasites and larger pathogens, NETs in COVID-19 fuel thromboinflammation characterized by formation of inflammatory blood clots and subsequent multiorgan failure (Nicolai et al, Circulation, 2020). Myeloperoxidase is a marker of NET formation. Ramatroban was shown to reduce myeloperoxidase levels in the lungs, ileum and heart in a rat model of endotoxic shock with similar pathology to COVID-19 (Altavilla et al, Pharmacol Res, 1994).

Blood clots in COVID-19 obstruct blood flow to the organs, starving cells of oxygen and causing ischemia. In rats with splanchnic artery ischemia-reperfusion injury, while blood levels of thromboxane B2 were increased about 7-fold, ramatroban prevented hypotension, improved survival, restored phagocytic function of peritoneal macrophages partially, inhibited plasma myocardial depressant factor activity about 50%, and inhibited tissue infiltration by neutrophils as measured by decline in ilium myeloperoxidase activity > 50% and lung myeloperoxidase activity > 80% (Canale et al, Pharmacology, 1994). Therefore, as an anti-platelet agent, ramatroban has the potential to prevent organ damage in COVID-19.

Interferon lambda (IFN-λ) is the first line of defense against pathogens. SARS-CoV-2 virus suppresses the host innate immune response by suppressing production of IFN-λ by epithelial, endothelial and myeloid cells (Blanco-Melo et al, Cell, 2020; Broggi et al, Science, 2020). Respiratory viruses stimulate PGD2 production by barrier epithelial cells, dendritic cells, Th2 cells, mast cells, eosinophils and macrophages (Werder et al, Sci Transl Med, 2018). Prostaglandin D2 (PGD2), which is elevated in severe COVID-19 (Archambault et al, FASEB, 2021), inhibits IFN-λ production via the DPr2 receptor which is restored by blocking the DPr2 receptor during respiratory syncytial virus infection (RSV) (Werder et al, Sci Transl Med, 2018). Blocking the DPr2 receptor in RSV also limits virus replication and load in the upper respiratory tract, thereby preventing the virus from traveling down the respiratory tract and into the lungs, while reducing viral transmission to household or workplace contacts. As a DPr2 antagonist, Ramatroban may restore IFN-λ response to COVID-19 and limit virus progression.

SARS-CoV-2 virus shifts the immune response from a type 1 to a type 2 immune response, a hallmark of helminthic infection or allergic inflammation. Type 2 immune response is mediated by PGD2 simulation of the DPr2 receptor.  DPr2 stimulation on Th2 and ILC2 cells leads to release of IL-4, IL-5 and IL-13 which are high in COVID-19 (Lucas et al, Nature, 2020). IL-13 stimulates proliferation of myeloid derived suppressor cells which suppress the cell mediated immune response and induces lymphopenia (Trabanelli et al, Nat Commun, 2017) while IL-5 stimulates eosinophilia. Plasma PGD2 levels are markedly elevated in hospitalized COVID-19 patients (Prof. S. Reddy, UCLA, personal communication). Plasma PGD2 levels are known to increase with aging and obesity. Therefore,  more severe disease in the elderly and the obese infected with COVID-19 coincides with higher levels of PGD2 and more immunosuppression compared to the rest of the population. 

D-dimers, which are a marker of blood clotting and thrombosis, are reportedly elevated in approximately 25% of patients 4-months post-SARS-CoV-2 infection (Townsend et al, jth, 2021). Sustained hypercoagulability and thrombosis can obstruct blood flow to the brain leading to brain fog and difficulty performing daily tasks. Potentially prolonged elevations of lipid mediators including thromboxane A2 may fuel the persisting hypercoagulable state in convalescent COVID-19. Ramatroban has the potential to reduce the  neurological symptoms of post-COVID by abrogating platelet activation and promoting perfusion of the brain and other organs.

Long haul COVID is often accompanied by impaired quality of life secondary to persistent "brain fog" and fatigue in 85% and 81% of long haulers, respectively (Graham et al, Ann Clin Transl Neurol, 2021). Hypercoagulability and reduced blood flow to organs including the brain likely contributes to the neurological symptoms in Long haul COVID. Lack of blood flow and oxygen deprivation is referred to as hypoxia. During brain hypoxia, there is a 90-fold increased in the production of the lipid mediator, prostaglandin D2 (PGD2) (Taniguchi et al, J Neurosci, 2007). PGD2 via the DPr2 receptor has been shown to mediate depression-related behavior. As a DPr2 antagonist, Ramatroban has been shown to rescue impaired social interaction and depression-related behavior (Onaka et al, Behav Brain Res, 2015 ; Haba et al, J Neurosci, 2014).