Cigarette smoking and COVID-19

Abstract

In a recent editorial published on tobacco and COVID-19, the Sociedade Portuguesa de Pneumologia raises doubts and caution about the data coming from the medical and scientific community regarding the hypothesis that cigarette smoking or nicotine could be ‘‘protective’’ against COVID19, recommending that this information should not be taken as an invitation to start smoking or to delay giving it up to avoid SARS-CoV-2 infection or its complications. The role of cigarette smoking/nicotine (or whatever else is contained within cigarette smoke) in the scientific discussion on COVID-19 ignores the fact that smoke cessation has to be discouraged to avoid COVID-19 pulmonary complications (this seems obvious for scientists and physicians) but references the scientific importance of the strong epidemiological data coming from all the countries that hospitalized patients with SARS-CoV-2 related pneumonia show quite low percentages of active smokers. Based on this we have to strongly support the importance of understanding of the possible mechanisms characterizing these aspects, i.e. how cigarette smoking dampens the inflammatory response during infection by SARS-CoV-2 strongly reducing the severe complications of SARS-CoV2 infection, mainly nterstitial pneumonia and ARDS. The reported evidence that among COVID-19 patients, those who are (and/or were) smokers show worse clinical progression with respect to never smokers is not in contradiction with the huge number of studies showing that there are few active smokers among hospitalized patients with SARS-CoV2 related pneumonia. However it is quite strange that a scientific society does not seem to understand the important scientific implications of such observations, bearing in mind that of course cigarette smoking has to be discouraged due to its well known dangerous effects. Thus we have to consider, without any preconceived position, on the one hand the notorious unhealthy effects of cigarette smoking, and on the other the possible important scientific information coming from different countries in the world showing that active smokers are somehow ‘protected’ from the severe complications of SARS-CoV-2 infection, namely interstitial pneumonia and ARDS. In this context a very recent paper reported decreased levels of the SARS-CoV-2 receptor ACE2 in both bronchial and alveolar epithelial cells from cigarette smoking-exposed versus air-exposed mice. Furthermore and more importantly, cigarette smoking treatment did not affect ACE2 levels but potently inhibited SARS-CoV-2 replication in Calu3 cells in vitro. On the other hand previous studies have reported the opposite effects of cigarette smoking on ACE2 expression in the lung, thus underlying the urge for further investigations to finally clarify the role of cigarette smoking on SARS-CoV-2 infection and its severe respiratory complications. Science proceeds by criticism and by analyzing objective data coming from scientists. In 1939 Winston Churchill said ‘‘Criticism may not be agreeable, but it is necessary. It fulfils the same function as pain in the human body; it calls attention to the development of an unhealthy state of things. If it is heeded in time, danger may be averted; if it is suppressed, a fatal distemper may develop’’. In the case of active smoking and COVID-19, to hide ones head in the sand will not help rapid scientific progress in the discovery of the pathophysiology of this disease and of its possible therapeutic strategies.