Viabilidade da implementação em campo da atividade fotodinâmica da curcumina para o controle de larvas do Aedes aegypti

Abstract

The use of insecticides is indispensable for the control of vectors. Since the 1960s, organophosphates are applied against populations of Aedes aegypti. With the indiscriminate use of these substances during a long period of time, there was a strong pressure selection, favoring the appearance of resistant populations. In an attempt to circumvent this problem, vector control programs have opted for the rotation of compounds with different mechanisms of action. Since few products are available for Aedes aegypti control, the search for new molecules and methods is pivotal. Taking this into account, the use of substances with photodynamic activity is strongly encouraged, due to its multi-target mechanism of action. These molecules act through photodynamic action, generating highly reactive oxygen species (ROS) in the presence of light and molecular oxygen. In this study, we evaluated the photodynamic activity of curcumin, a polyphenolic compound, found in turmeric Curcuma longa L. against Rockefeller strains (simulated field trials) and field populations of Aedes aegypti. The photolarvicidal action of curcumin was investigated in the presence of two sugars: sucrose and D-mannitol. The characterization of the molecular alterations involved in the activity of these compounds on Aedes aegypti was performed by Raman spectroscopy. In addition, the acute toxicity of curcumin in sugars was verified using the microcrustacean Daphnia magna and the fish Danio rerio, as well as the generation of ROS in these organisms. The biological effects of curcumin on Aedes aegypti were characterized by oxidative stress biomarkers (reduced glutathione (GSH) and catalase (CAT). This study also aimed to analyze and characterize the morphological changes caused by curcumin in the larval digestive tract by histological analysis. Additionally, microbiological water quality studies of curcumin-treated reservoirs with sucrose and D-mannitol were conducted to evaluate the impact of these formulations on the micro-environment. The results of this study showed the high photo-larvicidal potential of curcumin on Rockefeller strains in a simulated field. The LC50-24h values ranged from 0.01 to 0.11 mg.L-1, which are lower than other natural plant extracts. The analysis of the molecular mechanisms via Raman spectroscopy showed that curcumin in D-mannitol is highly permeable to the peritrophic membrane of the insect, causing irreversible damage to the simple columnar epithelium of the digestive tube. Both formulations of curcumin did not presented toxicity in D. magna and D. rerio up to 100 mg.L-1. ROS were generated in D. magna exposed to 50 mg.L-1 of curcumin in D-mannitol, and may be a consequence of detoxification processes or even the mechanism of action of these molecules. Regarding the biochemical response in Aedes aegypti, curcumin in D-mannitol did not alter CAT activity at any of the concentrations tested. On the other hand, GSH overproduction occurred at the lowest concentration (0.45 mg.L-1), indicating detoxification efforts due to possible ROS generation. In the histological analysis of the larvae submitted to curcumin in D-mannitol, we observed a great cellular disorganization in all the regions of the alimentary canal, that completely lost its characteristic of columnar epithelium. The curcumin in sucrose also caused serious damage to the midgut, however these changes were more punctual. Finally, studies on Rockefeller strains and field populations validated the efficacy of curcumin as a photo-larvicide against Aedes aegypti, evincing its high potential as an environmentally safe, economically feasible and rational alternative for the control of vector larvae.