Abstract
Abstract
Heme metabolism regulates the availability of heme, an iron-containing molecule essential for oxygen transport, mitochondrial respiration, electron transfer, and enzymatic reactions. Increasing evidence implicates heme metabolism in regulating viral infection, potentially representing an important innate antiviral mechanism. Components of both heme biosynthesis and degradation pathways exhibit antiviral activity against different viruses; however, their contributions and conservation across human coronaviruses remain incompletely defined. We investigated the impact of modulating heme metabolism on infection by seasonal human coronaviruses HCoV-OC43 and HCoV-229E. Treatment with 5-aminolevulinic acid (5-ALA) produced cell line-dependent antiviral effects, with robust inhibition in H1299 cells and selective HCoV sensitivity in MRC-5 cells. These differences correlated with intracellular accumulation of protoporphyrin IX (PPIX), suggesting that cellular metabolic capacity influences antiviral efficacy. In contrast, components of the heme degradation pathway, including heme oxygenase-1 (HO-1), carbon monoxide, and biliverdin, did not exhibit antiviral effects against HCoV-OC43 or HCoV-229E. PPIX and synthetic porphyrin CoPPIX inhibited early infection through direct viral inactivation. Collectively, these findings indicate that antiviral effects of heme metabolism against seasonal human coronaviruses are primarily driven by direct inactivation by PPIX rather than cellular antiviral responses induced by the heme degradation pathway.