Potential role of P-glycoprotein to modulate silver nanoparticle toxicity elucidated in a novel electrophysiology study

Abstract

In biological systems, the first line of defence against toxicants is mediated by transmembrane transporter proteins which pump out a variety of xenobiotics. Exposure to high levels of anthropogenic pollutants and natural toxins can induce over-expression of these proteins or sometimes block them. A well characterised transporter is P-glycoprotein (P-gp) which is encoded by the gene ABCB1. A real-time quantitative polymerase chain reaction was developed to measure ABCB1 gene transcription.A novel electrophysiological technique was used to compare the ecotoxicity of silver (Ag) nanoparticles (NPs) with that of silver nitrate (AgNO3) by measuring conduction velocity (CV) in the medial giant fibres (MGF) of earthworms and worms. Based on the LC10 and LC50 values, AgNP was 2- to 3-fold more toxic than AgNO3 and this was most marked in the juvenile earthworms. The CV in the juvenile earthworm A. caliginosa were measured at 0, 1, 3, 6, 8, 24, and 48 h following exposure to AgNP and AgNO3 concentrations of LC0.001, LC0.01, LC0.1, LC1, LC2, and L.variegatus to concentrations of LC1, LC5, LC10, and LC20. MGF CV progressively decreased in L. variegatus and A. caliginosa exposed to both AgNP and AgNO3 up to 8 h and then gradually increased. To eliminate the possible degradation of the Ag compounds, the AgNP and AgNO3 solutions were renewed every 3 h and CV measurements taken at hourly intervals for 7 h. Antibiotic rifampicin induced the ABCB1 expression in A. caliginosa. It is proposed that the oligochaetes adapt to excessive exposure of AgNP and AgNO3 via the elimination of chemicals via P-gp transporters.