Abstract
Bombyx mori (B. mori), silkworm, is one of the most important economic insects in the world, while phoxim, an organophosphorus (OP) pesticide, impact its economic benefits seriously. Phoxim exposure can damage the brain, fatbody, midgut and haemolymph of B. mori. However the metabolism of proteins and carbohydrates in phoxim-exposed B. mori can be improved by Titanium dioxide nanoparticles (TiO2 NPs). In this study, we explored whether TiO2 NPs treatment can reduce the phoxim-induced brain damage of the 5th larval instar of B. mori. We observed that TiO2 NPs pretreatments significantly reduced the mortality of phoxim-exposed larva and relieved severe brain damage and oxidative stress under phoxim exposure in the brain. The treatments also relieved the phoxim-induced increases in the contents of acetylcholine (Ach), glutamate (Glu) and nitric oxide (NO) and the phoxim-induced decreases in the contents of norepinephrine (NE), Dopamine (DA), and 5-hydroxytryptamine (5-HT), and reduced the inhibition of acetylcholinesterase (AChE), Na+/K+-ATPase, Ca2+-ATPase, and Ca2+/Mg2+-ATPase activities and the activation of total nitric oxide synthase (TNOS) in the brain. Furthermore, digital gene expression profile (DGE) analysis and real time quantitative PCR (qRT-PCR) assay revealed that TiO2 NPs pretreatment inhibited the up-regulated expression of ace1, cytochrome c, caspase-9, caspase-3, Bm109 and down-regulated expression of BmIap caused by phoxim; these genes are involved in nerve conduction, oxidative stress and apoptosis. TiO2 NPs pretreatment also inhibited the down-regulated expression of H+ transporting ATP synthase and vacuolar ATP synthase under phoxim exposure, which are involved in ion transport and energy metabolism. These results indicate that TiO2 NPs pretreatment reduced the phoxim-induced nerve toxicity in the brain of B. mori.
Highlights
Silkworm, Bombyx mori (B. mori, Bombycidae: Lepidoptera), is one of the most important economic insects in Asia, Africa, Europe and Latin America
The TiO2 NPs + phoxim-treated group did not show such pathological changes (Fig. 2d). It demonstrated that phoxim exposure caused brain damages, while TiO2 NPs treatments were able to reduce such damages
We observed that phoxim exposure significantly inhibited the activities of AChE, Na+/K+-ATPase, Ca2+-ATPase, and Ca2+/Mg2+-ATPase and promoted the activity of total nitric oxide synthase (TNOS) in the brain, while TiO2 NPs significantly promoted the activities of AChE, Na+/K+-ATPase, Ca2+-ATPase, Ca2+/Mg2+-ATPase, and AChE and inhibited the activity of TNOS (Fig. 4b). These results demonstrated that phoxim exposure altered the releases of neurotransmitters and the activities of several important enzymes in the nerve conduction in B. mori larvae brain, while TiO2 NPs were able to reverse such changes
Summary
Bombyx mori (B. mori, Bombycidae: Lepidoptera), is one of the most important economic insects in Asia, Africa, Europe and Latin America. B. mori has been domesticated for about 5,700 years in China, and it produces more than 80% of raw silk around the world [1]. B. mori is highly sensitive to adverse environmental conditions, especially pesticides. Pesticide contamination causes as much as 30% of the reduction in raw silk production in China [2]. Due to its short growth cycle and pesticide sensitivity, B. mori has been a widely used model insect for pesticide toxicology studies. Phoxim is an efficient broadspectrum organophosphorus (OP) pesticide, but its indiscriminate use has generated serious environmental problems
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