Chlorine dioxide enhances lipid peroxidation through inhibiting calcium-independent cellular PLA₂ in larvae of the Indianmeal moth, Plodia interpunctella

Polyunsaturated fatty acids usually undergo lipid peroxidation induced by reactive oxygen species (ROS). Calcium-independent cellular phospholipase A₂ (iPLA₂) can maintain fatty acid compositions in phospholipids depending on physiological conditions. An insect iPLA₂ (Pi-iPLA₂) was predicted from the transciptome of the Indianmeal moth, Plodia interpunctella. It encodes 835 amino acids. It possesses five ankyrin repeats in the N terminal and patatin lipase domain in the C terminal. Pi-iPLA₂ was expressed in all developmental stages of the Indianmeal moth. In the larval stage, it was expressed in all tissues tested. RNA interference (RNAi) specific to Pi-iPLA₂ was performed using specific double-stranded RNA (dsRNA). It resulted in almost 70% of reduction in gene expression. Under such RNAi condition, P. interpunctella exhibited significant accumulation of lipid peroxidation based on the amount of malondialdehyde. RNAi of Pi-PLA₂ expression also impaired cellular immune response of P. interpunctella. Chlorine dioxide (ClO₂), an insecticidal agent by generating ROS, increased lipid peroxidation in a dose-dependent manner. However, the addition of vitamin E (an antioxidant) reduced the formation of lipid peroxidation. ClO₂ treatment significantly reduced expression of Pi-iPLA₂ but increased lipid peroxidation in larval fat body of P. interpunctella. Furthermore, larvae treated with dsRNA specific to Pi-iPLA₂ were significantly susceptible to ClO₂ treatment. These results suggest that Pi-iPLA₂ plays a crucial role in repairing damaged fatty acids from phospholipids. Our results also suggest that ClO₂ can elevate lipid peroxidation through inhibiting Pi-iPLA₂ expression in addition to direct ROS production.