Avaliação da barata Nauphoeta cinerea como organismo modelo para o estudo de sepse

Abstract

Studies using model organisms, such as insects, are growing and have sought to investigate, in a preliminary way, the mechanisms involved in the progression of infectious diseases, examine potential pharmacological targets and access bacterial virulence factors. Insects have organs and systems analogous to mammals, conserved metabolic pathways, short lifetimes and, in general, are easy to create and manipulate. However, few insect species have been used in studies to understand immune reactions. Thus, this work aimed to investigate the bases of the immune defense of the cockroach Nauphoeta cinerea and evaluate its potential as an alternative animal for the study of bacterial infection. Different amounts of colony-forming units (CFU) of Staphylococcus aureus were injected into the nymphs' thorax in the last juvenile stage. Survival, number of nymphs that reached the adult stage, changes in biochemical parameters in the hemolymph and fat body were verified and CFU was counted in the hemolymph, after inoculation of the microorganism. The potential immunological memory (priming) was evaluated in the face of repeated bacterial challenges, as well as behavioral changes associated with infection and the phenoloxidase (FO) enzyme activity in the hemolymph. The available transcriptome of N. cinerea, of the head and fat body, was used to investigate the relative basal expression of genes involved in the FO cascade and to analyze phylogenetic comparison of amino acids from other insects. The infection caused a decrease in metabolites in the hemolymph (glucose, amino acids, proteins and cholesterol) and inhibition of FO activity after 24 h post injection. Nymphs infected with the highest concentrations of S. aureus (2 x 108 and 2 x 1010 CFU/cockroach), when compared to control nymphs, showed an increase in mortality, permanent morphological changes in adults, an increase in CFU in hemolymph over time, decreased levels of protein in the fat body, decreased aggregation behavior and antenna grooming. Nymphs inoculated with 2 x 107 CFU/cockroach showed a decrease in CFU in the hemolymph over time, increased levels of protein in the fat body, increased locomotor activity and exploration. There was no change in FO activity in the acute phase of infection (up to 4 h). Priming with 2 x 107 CFU / cockroach, or saline, did not promote an increase in FO activity after the second challenge with 2 x 1010 CFU/cockroach. The survival and protection of cockroaches primed with sublethal concentration of S. aureus varied according to the bacterial metabolic condition. The FO sequence shares a high identity with insects of the Neoptera infraclass, especially for the copper B binding site. The results of the relative expression showed that the serine proteases and FO are more expressed in the head than in the fat body of N. cinerea nymphs. Based on the results, N. cinerea proved to be a promising model organism for use in studies related to bacterial infection.