Journal of Pharmaceutics & Pharmacology

Review Article

Repurposing of Adamantanes with Transmitter Receptor Antagonist Properties for the Prevention/Treatment of COVID-19

Brenner SR1*, and Butterworth RF2

1Department of Neurology, Saint Louis University, USA
2Department of Medicine, University of Montreal, Canada
*Address for Correspondence: Brenner SR, Department of Neurology, Saint Louis University, (retired) St. Louis, Missouri, USA; E-mail: sbren20979@aol.com
Submission: 08 October 2020; Accepted: 12 November 2020; Published: 24 November 2020
Copyright: 2020 Brenner SR. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Members of the adamantane family of agents in general and two such members, amantadine and memantine, in particular, have established beneficial actions across a wide range of infectious diseases including those caused by coronaviruses. Increasing evidence suggests that the protective effects of these agents is the result of actions on neurotransmitter systems namely the NMDA receptor subclass of the glutamatergic system and by the α7-nACh subclass of nicotinic cholinergic receptor. The potent NMDA receptor antagonist, memantine, prevents motor disabilities and reduces replication of the neuroinvasive/neurotropic human respiratory virus HCoV-OC43 dose-dependently. Moreover, the lysosomotrophic adamantanes amantadine and memantine also limit viral replication. Known lysomotrophic agents such as ammonium chloride inhibit cellular entry of SARS-CoV-2 on laboratory testing. Inhibiting clathrinmediated endocytosis (cellular entry) of the SARS-CoV-2/ACE2 complex by amantadine or rimantadine may block viral entry into vulnerable cellular populations, and also reduce platelet activating factor-priming of Polymorphonuclear [PMN] cells, potentially lessening PMN cell-mediated tissue damage and excess Neutrophil Extracellular Traps [NETs] seen in advanced cases of COVID-19. Rimantadine has inhibitory effects of SARS-CoV-1, a closely-related virus to SARS-CoV-2, which may indicate the need for further evaluation as a treatment for COVID-19. Amantadine increases Dopamine [DA] release and blocks its reuptake, increasing its action on DA receptors on T cells thus activating resting effector T cells and suppressing regulator T cells, which may have a beneficial immunomodulating function in infectious diseases. Proposed adverse effects of smoking on COVID-19 outcomes are attributed to the effects of nicotine via the α7-nACh receptor located on bronchial and alveolar epithelial cells. As an antagonist of this receptor, memantine has the potential to prevent the entry of SARSCoV- 2 into these cells. Independent case reports provide evidence of protective effects of amantadine and/or memantine against COVID-19. Additional epidemiologic studies however indicate a lower incidence of smoking in hospitalized patients, stimulating investigations of nicotine-related aspects, and amino acid sequence analysis indicate homologous sequences with those of neurotoxins seen in snake venoms blocking the α7-nAChR suggesting that COVID-19 may be a disease of the nicotinic cholinergic system; α7-nAChR is involved in the cholinergic anti-inflammatory pathway or reflex. COVID-19 is a biphasic disease, the initial aspect involved with the initial infection and viral replication which stimulates a prominent innate immune response. This then transitions to the adaptive immune response with suppression of infection and recovery, while the innate response is suppressed via the cholinergic anti-inflammatory pathway. Severe disease may occur when the initial innate immune response continues, the cholinergic anti-inflammatory pathway being arrested by the neurotoxin inherent in the viral amino acid sequence, causing a runaway innate immune response. Memantine, being an inhibitor of α7-nACHR, could possibly make COVID-19 worse should it be α7-nACHR inhibitor. Tilorone, a lysosomotrophic agent and α7-nACHR agonist could also have potential as a treatment for COVID-19. Further studies are necessary to determine whether repurposing of adamantanes is beneficial in COVID-19, and for further investigations of pharmacological and pathophysiological properties of SARS-CoV-2.