Cobinamide, a Vitamin B₁₂ Analog, Attenuates Benzo[a]pyrene and Pyrene Toxicity Through Selective Redox Modulation

Polycyclic aromatic hydrocarbons (PAHs) are common environmental contaminants formed during the incomplete combustion of organic material. Their persistence, bioaccumulation, and metabolic activation contribute to mutagenic and cytotoxic outcomes. Among these are benzo[a]pyrene (B[a]P), the most studied PAH and a benchmark compound for PAH carcinogenicity, and pyrene, a PAH whose urinary metabolite 1-hydroxypyrene is widely used as a biomarker of PAH exposure. B[a]P undergoes CYP1A1-mediated oxidation to generate reactive oxygen species (ROS) via epoxide and quinone redox cycling, whereas pyrene produces ROS primarily through pyrene-quinone redox cycling. We investigated cobinamide, a vitamin B₁₂/cobalamin analog with potent antioxidant properties, for mitigating benzo[a]pyrene- and pyrene-induced injury. In H9C2 rat embryonic cardiomyoblasts and A549 human lung epithelial cells exposed to B[a]P (10 μM) or pyrene (10-100 μM), cobinamide (5-10 μM) attenuated PAH-induced reductions in cell number in both models, while in H9C2 cells, it also attenuated decreases in metabolic activity and reduced apoptosis. Cobinamide also returned JNK/p38 phosphorylation to near baseline levels, decreased DNA and protein oxidation and DNA strand breaks. Transcriptionally, cobinamide suppressed inflammatory (TNF-α, IL-1β, and IL-6) and oxidative stress genes (HMOX1 and NOX4), while enhancing oxidative response (SOD2) and xenobiotic metabolism (CYP1A1). In Drosophila melanogaster exposed to 5 mM B[a]P/pyrene, 2 mM cobinamide improved survival and fully restored locomotion, outperforming cobalamin (minimal benefit) and N-acetylcysteine (partial rescue). Spectroscopic analyses showed no direct cobinamide-PAH binding. These findings demonstrate that cobinamide efficiently limits ROS-mediated PAH injury through redox modulation while preserving xenobiotic metabolism, suggesting its potential therapeutic use to mitigate PAH-induced toxicity.