Immune-oxidative and apoptotic response to titanium dioxide nanoparticle (TiO2-NP) exposure in an aquatic lower vertebrate, rohu (Labeo rohita).

Titanium dioxide nanoparticles (TiO2-NPs) are one of the most commercially manufactured and widely applied NPs. However, often TiO2-NPs leak into the environment and make aquatic animals exposure inevitable. Consequently, a deeper comprehension of TiO2-NPs toxicity is utmost important. The 96-hour lethal concentration of TiO2-NP in rohu (Labeo rohita) was 77.49 mg/L. An in-vivo toxicity assessment of TiO2-NP was conducted at sub lethal concentration of 1 mg/L (2%), 2.5 mg/L (5%), and 5 mg/L (10%) at 24 hours post exposure (hpe), 4 days post exposure (dpe), and 14 dpe in an aquatic lower vertebrate, rohu. Quantitative bioaccumulation analysis showed highest TiO2-NPs bioaccumulation in intestine followed by liver, gill, kidney, spleen, and negligible in muscle. TiO2-NP at 5 mg/L concentration induced the immunotoxic response by destabilization of serum lysozyme and antiprotease activity which was further potentiated by increased production of myeloperoxidase, respiratory burst activity leading to higher production of reactive oxygen species that contribute to oxidative stress, inflammation and cellular damage. Molecular study demonstrated that TiO2-NP is recognized and processed by signaling PRR, TLR22 leading to initiation of the downstream immune-signaling cascade and pro-inflammatory cytokines production. The TiO2-NP induced the oxidative stress gene (SOD, CAT, and GPx) expression significantly at 1, 2.5 and 5 mg/L. Nevertheless, apoptotic biomarker (caspase3, BAX and p53) were induced significantly on 14th dpe at 5 mg/L dose exposure. Our study infer that TiO2-NP induced immunotoxic response at higher concentration of 5 mg/L, nevertheless it acts as immunostimulator at lower concentration of 1 mg/L in L. rohita.