Modified expression of antioxidant genes in lobster cockroach, Nauphoeta cinerea exposed to methylmercury and monosodium glutamate

Abstract

Methylmercury (MeHg) is a neurotoxicant that poses risk to human health and the environment, while glutamate homeostasis is necessary for the proper functioning of the brain. We have previously shown an increase in oxidative stress after cockroach exposure to diet containing monosodium glutamate (MSG), both separately and combined with a low dose of methylmercury. We herein seek to corroborate these findings by quantifying the expression levels of certain antioxidant genes in Nauphoeta cinerea exposed to MeHg and MSG. Cockroaches were fed with the basal diet alone, basal diet +2% NaCl, basal diet +2% MSG; basal diet +0.125mg/g MeHg, basal diet +0.125mg/g MeHg +2% NaCl; and basal diet +0.125mg/g MeHg +2% MSG for 21 days and mRNA from head homogenate was used to quantify the expression of antioxidant genes such as glutathione-s-transferase (GstS, GstT, GstD), thioredoxin (Trx1, Trx2, Trx5), peroxiredoxin (prx4), superoxide dismutase (Sod), catalase (Cat). MeHg, NaCl and MSG alone downregulated mRNA levels of GstS and Trx5, in contrast, co-exposure of MeHg+MSG, upregulated these genes. MeHg+NaCl upregulated the mRNA levels of Cat and Sod but these genes were downregulated by NaCl alone. MeHg+NaCl and MeHg+MSG upregulated GstD and GstT. MeHg alone upregulated the transcription levels of Trx1, Trx2 and Prx4. The disruptions in the transcription levels of various genes by MeHg and MSG, reinforce the toxicity of these neurotoxicants. In general, the data suggest their additive effects and support the use of N. cinerea as a model for toxicological studies.