COVID-19 pathophysiology: interactions of gut microbiome, melatonin, vitamin D, stress, kynurenine and the alpha 7 nicotinic receptor: Treatment implications

Abstract

As data emerges on the pathophysiological underpinnings of severe acute respiratory syndrome coronavirus (SARS-CoV)-2, it is clear that there are considerable variations in its susceptibility and severity/fatality, which give indications as to its pathophysiology and treatment. SARS-CoV-2 modulatory factors include age, vitamin D levels, cigarette smoking, gender and ethnicity as well as premorbid medical conditions, including diabetes, cancer, obesity, cardiovascular disease, and immune-compromised conditions. A complex picture is emerging, with an array of systemic physiological processes interacting including circadian, immune, intestinal, CNS and coagulation factors. This article reviews data on SARS-CoV-2 pathoetiology and pathophysiology. It is proposed that a decrease in pineal and systemic melatonin is an important driver of SARS-CoV-2 susceptibility and severity, with the loss of pineal melatonin's induction of the alpha 7 nicotinic acetylcholine receptor (α7nAChR) in pulmonary epithelial cells and immune cells being a powerful regulator of susceptibility and severity, respectively. Stress, including discrimination stress, and decreased vitamin D also regulate SARS-CoV-2, including via gut dysbiosis and permeability, with a resultant decrease in the short-chain fatty acid, butyrate, and increase in circulating lipopolysaccharide. Stress and cytokine induction of the kynurenine pathways, leads to aryl hydrocarbon receptor activation, which primes platelets for heightened activity, coagulation and thrombin production, thereby driving elevations in thrombin that underpin many SARS-CoV-2 fatalities. On the basis of these pathophysiological changes, prophylactic and symptomatic treatments are proposed, including the use of melatonin and α7nAChR agonism.