An experimental test of the nicotinic hypothesis of COVID-19

Proc Natl Acad Sci U S A. 2022 Nov;119(44):e2204242119. doi: 10.1073/pnas.2204242119. Epub 2022 Oct 24.

Abstract

The pathophysiological mechanisms underlying the constellation of symptoms that characterize COVID-19 are only incompletely understood. In an effort to fill these gaps, a "nicotinic hypothesis," which posits that nicotinic acetylcholine receptors (AChRs) act as additional severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptors, has recently been put forth. A key feature of the proposal (with potential clinical ramifications) is the suggested competition between the virus' spike protein and small-molecule cholinergic ligands for the receptor's orthosteric binding sites. This notion is reminiscent of the well-established role of the muscle AChR during rabies virus infection. To address this hypothesis directly, we performed equilibrium-type ligand-binding competition assays using the homomeric human α7-AChR (expressed on intact cells) as the receptor, and radio-labeled α-bungarotoxin (α-BgTx) as the orthosteric-site competing ligand. We tested different SARS-CoV-2 spike protein peptides, the S1 domain, and the entire S1-S2 ectodomain, and found that none of them appreciably outcompete [125I]-α-BgTx in a specific manner. Furthermore, patch-clamp recordings showed no clear effect of the S1 domain on α7-AChR-mediated currents. We conclude that the binding of the SARS-CoV-2 spike protein to the human α7-AChR's orthosteric sites-and thus, its competition with ACh, choline, or nicotine-is unlikely to be a relevant aspect of this complex disease.

Keywords: SARS-CoV-2; acetylcholine receptors; binding competition assays; nicotinic receptors; spike protein.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bungarotoxins
  • COVID-19*
  • Choline
  • Cholinergic Agents
  • Humans
  • Ligands
  • Nicotine
  • Receptors, Nicotinic* / metabolism
  • SARS-CoV-2
  • Spike Glycoprotein, Coronavirus / genetics
  • Spike Glycoprotein, Coronavirus / metabolism
  • alpha7 Nicotinic Acetylcholine Receptor

Substances

  • spike protein, SARS-CoV-2
  • Spike Glycoprotein, Coronavirus
  • Bungarotoxins
  • Nicotine
  • alpha7 Nicotinic Acetylcholine Receptor
  • Ligands
  • Receptors, Nicotinic
  • Cholinergic Agents
  • Choline

Grants and funding