Respirable α-Quartz Silica Triggers Immune–Inflammatory–Fibrotic Initiation in Zebrafish Embryos via Hindbrain Ventricle Microinjection: Implications for Silicosis Early Risk Assessment

Silicosis, an irreversible occupational lung disease resulting from prolonged exposure to respirable crystalline silica, faces challenges due to limitations in existing mammalian models. This study evaluated whether laboratory-prepared respirable α-quartz silica could induce immune cell-inflammatory-fibrotic initiation related to silicosis in zebrafish embryos as a tool for early toxicity assessment. Zebrafish embryos at 48 h post-fertilization (hpf) were microinjected into hindbrain ventricle with respirable α-quartz silica (test material 3.056 μm vs. standard material 3.217 μm) derived from natural α-quartz ore. The results indicated a significant decrease in zebrafish survival rates and an increase in malformation rates following exposure respirable α-quartz silica materials. Additionally, alterations in midbrain and hindbrain lengths were observed, while body length remained unaffected. Behavioral assessments revealed reduced touch response rates, decreased average speed, and less time spent in the central zone during open field tests in the treatment groups. In vivo imaging demonstrated sequential recruitment of neutrophils (peak at 18 h post-injection) and macrophages (peak at 24 h post-injection). qPCR analysis revealed upregulation of inflammation-related genes (<i>tnf-α</i>, <i>il-6</i>, <i>il-1β</i>) and fibrosis-related genes (<i>tgf-β</i>, <i>acta-2</i>, <i>collagen</i>). Moreover, the hydroxyproline content, a marker for fibrosis, was significantly elevated, although no mature fibrosis was observed histologically. These findings demonstrate that respirable α-quartz silica elicits pathophysiological changes associated with silicosis early initiation in zebrafish embryos. This supports the utility of the zebrafish embryo as a practical tool for early toxicity assessment and mechanistic studies of silica-induced immune-inflammatory-fibrotic initiation, with potential implications for silica exposure early risk warning.