Investigating the risk of cardiac fibrosis due to heat-not-burn cigarettes through human cardiac stromal cells

Background The use of alternative smoking devices, such as heat-not-burn cigarettes (HNBC), is increasing on a global scale, and their impact on health is still uncertain. Objective To investigate the effects of circulating molecules in HNBC chronic smokers on the fibrotic specification and paracrine function of cardiac stromal cells (CSCs). Methods Resident CSCs were isolated from the atrial tissue of patients with cardiovascular diseases, and exposed to the serum of 60 young healthy subjects, stratified in exclusive HNBC smokers, traditional combustion cigarette (TCC) smokers, or non-smokers (NS) as reference. Results CSCs treated with TCC serum displayed impaired 3D growth and migration, as well as increased expression and/or release of pro-inflammatory and pro-fibrotic cytokines. Cells cultured with HNBC serum showed increased mRNA levels of pro-fibrotic genes, and reduced expression of the gap junction protein CX43. Nonetheless, both TCC and HNBC sera reduced the release of angiogenic and protective factors from CSCs. In fact, their paracrine support to tube-formation by endothelial cells and to preserved cell viability of cardiomyocytes in culture was significantly impaired. Treatment with the sera of both types of smokers also increased the expression of NOX isoforms and the release of H 2 O 2 by CSCs. Conclusion The circulating molecules in the serum of chronic HNBC smokers induce fibrotic specification in CSCs. They also reduce the beneficial paracrine effects of stromal cells on endothelial cells and cardiomyocytes, albeit to a reduced extent for some features. These results point to a potential risk for atrial fibrosis development triggered by chronic HNBC use. CONDENSED ABSTRACT The use of alternative smoking devices, such as heat-not-burn cigarettes (HNBC), is increasing on a global scale, and their impact on health is still uncertain. We isolated human stromal cells from the atrial tissue of patients with cardiovascular diseases, and exposed them to the serum of young healthy subjects, that are exclusive HNBC smokers. Results showed significant alterations in the phenotype of CSCs exposed to HNBC serum, suggesting a specification towards fibrosis, reduced support to parenchymal cells, and increased oxidative stress production. Data point to a potential risk for atrial fibrosis development triggered by chronic HNBC use.