Oxidative stress and ER-mitochondrial dysfunction contribute to carbon dot-induced cardiac developmental toxicity in zebrafish larvae.

Abstract

Carbon dots (CDs) are increasingly used carbonaceous nanoparticles whose potential environmental and developmental hazards remain insufficiently characterized. Because the embryonic heart is the first organ to develop and is highly dependent on mitochondrial energy supply, it may be particularly vulnerable to nanoparticle-induced oxidative injury. Here, we used zebrafish larvae to investigate CDs-induced cardiac developmental toxicity and its underlying mechanisms. CDs exposure during developmental stages caused dose-dependent cardiotoxicity, including increased SV-BA distance, reduced heart rate and blood flow velocity, and dysregulated expression of cardiac developmental genes. Transcriptomic profiling revealed extensive reprogramming, with differentially expressed genes enriched in mitochondrial, calcium-signaling, and stress-response pathways, and identified tlr4, myd88, and nlrp3 as candidate hub genes. CDs elevated cardiac and mitochondrial reactive oxygen species, induced mitochondrial swelling and cristae loss, decreased mitochondrial membrane potential, and triggered endoplasmic reticulum (ER) stress. These changes were accompanied by disrupted ER-mitochondria Ca²⁺ homeostasis, increased pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), neutrophil recruitment, and elevated apoptosis-related transcripts. Co-treatment with the antioxidant NAC, the mitochondria-targeted antioxidant Mito-tempo, or the ER-stress inhibitor 4-PBA substantially reversed these alterations, supporting convergent roles of oxidative stress, mitochondrial dysfunction, and ER stress. These findings provide a cardiac-focused mechanistic assessment of CD developmental toxicity and propose quantifiable endpoints for screening nanoparticle cardiotoxicity.