Abstract
<title>Abstract</title> <p>Molnupiravir was approved by the U.S. Food and Drug Administration (U.S. FDA) in December 2021 for emergency use in adult patients infected with SARS-CoV-2 (COVID-19) who are at risk for progression to severe disease. While direct clinical evidence of Molnupiravir-induced cardiotoxicity is limited, its mechanism as a nucleoside analog raises theoretical concerns regarding mitochondrial injury and potential off-target cardiac effects. In this study, we utilized human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from a healthy Vietnamese donor as a platform to evaluate the cardiotoxicity of Molnupiravir and its active metabolite, β-D-N4-hydroxycytidine (NHC), across clinically relevant and supraclinical concentrations. At clinically relevant concentrations (1–20 µM), neither Molnupiravir nor NHC had significant effects on cell viability, sarcomere organization, mitochondrial structure, or cardiac gene expression. However, at supraclinical concentrations > = 30 µM, distinct phenotypic alterations emerged. NHC treatment induced noticeable Z-disk misalignment and significantly reduced the sarcomere width from 1.41 ± 0.06 µm to 1.36 ± 0.12 µm relative to that of the control. In contrast, Molnupiravir elicited an increase in sarcomere width, reaching 1.49 ± 0.09 µm, and produced a more regular and orderly arrangement of the Z-disk. Transcriptional analysis revealed that while structural gene expression remained stable, both compounds downregulated CaV1.2 ion channels, the ANP hypertrophic gene, and fibrosis genes (TGFB1, COL1A). Overall, NHC and Molnupiravir do not cause direct cardiotoxicity at therapeutic doses but may induce specific sarcomeric and transcriptomic alterations at the supraclinical level. These findings highlight the need for further investigation into the functional implications of these alterations and suggest exercising caution when Molnupiravir is administered to patients with preexisting cardiovascular conditions.</p>