Nanoparticulate TiO2 Protection of Midgut Damage in the Silkworm (Bombyx mori) Following Phoxim Exposure

Bombyx mori (B. mori) is often subjected to phoxim poisoning in China due to phoxim exposure, which leads to a decrease in silk production. Nanoparticulate (NP) titanium dioxide (nano-TiO2) has been shown to attenuate damages in B. mori caused by phoxim exposure. However, little is known about the molecular mechanisms of midgut injury due to organophosphorus insecticide exposure and its repair by nano-TiO2 pretreatment. In this study, phoxim exposure for 36 h led to significant decreases in body weight and survival and increased oxidative stress and midgut injury. Pretreatment with nano-TiO2 attenuated the phoxim-induced midgut injury, increased body weight and survival, and decreased oxidative stress in the midgut of B. mori. Digital gene-expression data showed that exposure to phoxim results in significant changes in the expression of 254 genes in the phoxim-exposed midgut and 303 genes in phoxim + nano-TiO2-exposed midgut. Specifically, phoxim exposure led to upregulation of Tpx, alpha-amylase, trypsin, and glycoside hydrolase genes involved in digestion and absorption. Phoxim exposure also led to the downregulation of Cyp450 and Cyp4C1 genes involved in an antioxidant capacity. In contrast, a combination of both phoxim and nano-TiO2 treatment significantly decreased the change in alpha-amylase, trypsin, and glycoside hydrolases (GHs), which are involved in digestion and absorption. These results indicated that Tpx, alpha-amylase, trypsin, GHs, Cyp450, and Cyp4C1 may be potential biomarkers of midgut toxicity caused by phoxim exposure and the attenuation of these toxic impacts by nano-TiO2.