Direct effects of cigarette smoke extract from heated tobacco products on cardiomyocyte: Comparison with combustible cigarettes

Smoking of combustible cigarettes is a risk factor for cardiovascular disease. Heated tobacco products (HTPs) have recently increased in use due to their perceived lower toxicity compared with combustible cigarettes, yet their direct effects on cardiomyocytes remain unclear. In the present study, we compared the effects of nicotine- and tar-free cigarette smoke extracts (CSE) from two HTPs (‘HTP-1’ and ‘HTP-2’) and a combustible reference cigarette (RF) on cultured neonatal rat ventricular myocyte. All CSEs reduced cell viability and the spontaneous beating rate, with toxicity ranked as RF > HTP-2 > HTP-1. HTP-2 and RF also induced intracellular Ca 2+ -overload, contractile dysfunction, and mitochondrial reactive oxygen species production, whereas HTP-1 did not. Mitochondrial respiration and ATP production were suppressed by all CSEs, while glycolysis was upregulated only by HTP-2 and RF, indicating different metabolic alterations. Acrolein, a shared toxicant in all products, also reduced cell viability, suggesting its involvement in CSE-induced cardiotoxicity. In summary, we revealed that HTPs, like combustible cigarettes, exhibit direct cardiomyocyte toxicity, but the underlying mechanisms appear to differ between different cigarette products with regard to abnormal Ca 2+ regulation and metabolic inhibition. These findings raise concern regarding the cardiac safety of HTPs.