Avaliação da toxicidade e atividade biológica de nanopartículas de prata obtidas por síntese verde com extrato da planta Plectranthus neochilus no modelo animal Drosophila melanogaster

Abstract

Silver nanoparticles (AgNP) are promising nanomaterials, but its potential toxicity is still to be fully known. Green synthesis routes were developed to circumvent the use of the toxic sodium borohydride reagent with the use of another reducing agent, such as phenolic compounds from plants. Plectranthus neochilus has high levels of polyphenols, and plants of the same family have already been used in the synthesis of AgNP, evidencing its potential. Thus, the objective of this work was to and evaluate the biological activity of AgNP synthesized with Plectranthus neochilus extract. AgNP were obtained by green synthesis using extract from the plant Plectranthus neochilus. Formulations at concentrations of 0.50 to 0.10 ppm were administered for three days in the animal model Drosophila melanogaster, then evaluated mortality and negative geotaxis; total proteins, iron reducing capacity (FRAP), levels of oxidizing reactive species (ROS); and activities of catalase enzymes (CAT), glutathione s-transferase (GST) and acetylcholinesterase (AChE), from head and body. Exposure to AgNP did not generate mortality. The climbing ability increased by exposure to AgNP, which can be caused by decreased AChE activity in the head, which would increase the amount of acetylcholine in the synaptic cleft and thereby the excitatory and behavioral stimulus. The availability of reducing agents evaluated by FRAP and the levels of ROS are shown to be decreased, mainly for the head samples of the groups treated with AgNP. This can be attributed to the catalytic capacity of the AgNP, which by accelerating the neutralization reaction of oxidizing species, but also of the available reducing agents. Head CAT activity has also been decreased, and may be related to substrate decrease, hydrogen peroxide, leading to a negative regulation response. The activity of GST in the head decreases by exposure to the AgNP, and this result is in response to other findings about exposure to silver nanoparticles, which cause a decrease in the expression of messenger RNA to produce this enzyme, and consequently its activity. Total protein levels remained unchanged for body samples but were increased in the heads in the group exposed to AgNP 0.50 ppm and may be caused by an immune response of mobilization of cells and proteins in the face of redox imbalance. Thus, we concluded that the AgNP did not generate mortality in the animal model. Exposure to AgNP decreases AChE activity leading to greater excitability and increased locomotor activity. AgNP decreased rates of oxidizing reactive species, but also the availability of reducing species in the organism, suggesting a catalytic activity under the neutralization reactions of ROS. Also decreasing the activity of enzymes related to the antioxidant and detox mechanism such as CAT, and GST. The most expressive results were in the head of the groups exposed to AgNP, and although it presented a decrease of pro-oxidant agents, the reduction of the body's natural antioxidant barriers is a point for further investigation.