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.