A large body of evidence shows the harmful effects of cigarette smoke to oral and systemic health. More recently, a link between smoking and susceptibility to coronavirus disease 2019 (COVID-19) was proposed. COVID-19 is due to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which uses the receptor ACE2 and the protease TMPRSS2 for entry into host cells, thereby infecting cells of the respiratory tract and the oral cavity. Here, we examined the effects of cigarette smoke on the expression of SARS-CoV-2 receptors and infection in human gingival epithelial cells (GECs). We found that cigarette smoke condensates (CSC) upregulated ACE2 and TMPRSS2 expression in GECs, and that CSC activated aryl hydrocarbon receptor (AhR) signaling in the oral cells. ACE2 was known to mediate SARS-CoV-2 internalization, and we demonstrate that CSC treatment potentiated the internalization of SARS-CoV-2 pseudovirus in GECs in an AhR-dependent manner. AhR depletion using small interference RNA decreased SARS-CoV-2 pseudovirus internalization in CSC-treated GECs compared with control GECs. Our study reveals that cigarette smoke upregulates SARS-CoV-2 receptor expression and infection in oral cells. Understanding the mechanisms involved in SARS-CoV-2 infection in cells of the oral cavity may suggest therapeutic interventions for preventing viral infection and transmission.

Passive leg movement (PLM) elicits rapid vasodilation in the microvasculature that is primarily dependent on nitric oxide. PLM‐induced vasodilation (PLM‐D) therefore, provides an index of lower‐limb microvascular endothelial function. PLM‐D is lower in advanced aging and clinical populations vs. young and healthy controls, demonstrating that PLM‐D provides a useful assessment of vascular responses. However, there is currently limited information regarding the reliability of PLM‐D and no information on the reliability of PLM‐D in women. Therefore, the purpose of this study was to test the hypothesis that PLM‐D in women is reliable when measured over two separate days. Seventeen, young healthy women (22 ± 3 yrs) participated in two identical experimental visits during the early follicular (low‐estrogen) phase of the menstrual cycle. Each visit included three standardized trials of PLM involving one minute of baseline, two minutes of PLM and two minutes of recovery. During the two minutes of PLM an experimenter moved the participant's leg from 90° flexion to 180° extension and back at a set pace of 1 cycle/s. Using duplex ultrasound PLM‐D was characterized by six commonly utilized factors; peak leg blood flow (LBF) and vascular conductance (LVC), peak change above baseline (Δpeak) for LBF and LVC, and area under the curve above baseline (ΔAUC) during the first 60s of PLM for LBF and LVC. The day‐to‐day reliability of PLM‐D was quantified by calculating the Pearson correlation coefficient (r value), intraclass correlation coefficient (ICC) and coefficient of variation (CV). The results demonstrated good day‐to‐day reliability of PLM‐D characterized as peak LBF (r = 0.84, p < 0.001; ICC = 0.84; CV = 13.2%), peak LVC (r = 0.82, p < 0.001; ICC = 0.79; CV = 14.4%), Δpeak LBF (r = 0.83, p < 0.001; ICC = 0.82; CV = 17.8%) and Δpeak LVC (r = 0.83, p < 0.001; ICC = 0.80; CV = 16.5%). Characterization of PLM as ΔAUC demonstrated moderate day‐to‐day reliability; ΔAUC LBF (r = 0.71, p< 0.05; ICC = 0.70; CV = 31.2%) and ΔAUC LVC (r = 0.78, p < 0.001; ICC = 0.74; CV = 27.1%). In conclusion, this study demonstrates that PLM‐D has good day‐to‐day reliability, however, characterization of PLM‐D as peak and Δpeak LBF and LVC is more reliable than ΔAUC. These findings support the use of PLM‐D in future studies as a reliable method to assess lower‐limb microvascular endothelial function in women.

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