Avaliação dos efeitos do tratamento com ácidos graxos de cadeia curta sobre a infecção pelo vírus sincicial respiratório

Abstract

Introduction: Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infections in children under two years of age. There is still no vaccine available for this virus and the development of new therapeutic strategies to mitigate disease lethality are a priority. Short-chain fatty acids (SCFAs), such as acetate, propionate and butyrate, are substrates generated from the metabolization of fermentable dietary fibers by intestinal bacteria. Recently, both SCFAs and fermentable fibers have been studied for their action on intestinal homeostasis, since they influence several physiological, cellular and molecular functions, and play an antiinflammatory role in some diseases. Objective: To evaluate the effects of SCFAs treatment on RSV infection In vitro and In vivo, as well as to investigate the effects generated by a diet rich in fermentable fibers on RSV infection. Methods: Human pulmonary A549 and MRC-5 cells were pretreated with the SCFAs (acetate, propionate and butyrate) in different doses (60 μM, 120 μM, 200 μM, 260 μM) for 6 h, 12 h, and 24 h. Afterward they were infected with RSV (1x104 PFU/ml) for 96 hours and analyzed by cellular cytotoxicity assay. In addition, real-time PCR was performed to identify viral load in A549 cells. A bioinformatics analysis was performed to identify targets involved in the mechanism. In the In vivo experiments, for pretreatment, the animals were pretreated in drinking water with SCFAs at the final concentration of 200mM for 3 weeks and infected intranasally with RSV (107 PFU/ml) and on the fifth day after infection the data were collected and analyzed. For the simultaneous treatment and infection the animals began the treatment and were infected in the same day and in the fifth-day post infection the data were analyzed. In another experiment, the animals received a diet rich in fermentable fiber or poor control diet in fermentable fibers for 4 weeks and were infected as previously described. Results: SCFAs pretreatment protected cells from cell death caused by RSV infection at all times and concentrations, especially in pulmonary cells. In addition, acetate and butyrate significantly reduced viral load in A549 cells. The results of the bioinformatics analysis indicated that Cyclins, IL-8 and HDAC as possible targets of the mechanism involved with the antiviral activity of butyrate. However, we have seen that the mechanism involved in protection against RSV of SCFAs in vitro is not dependent on IL-8 and nor on cell cycle modulation. In vivo, SCFAs pretreatment, especially acetate, protected the animals from viral infection, reducing or abolishing viral load in the lung. Moreover, the treatment prevented weight loss caused by the virus, reduced the number of cells in the bronco alveolar lavage and decreased the production of proinflammatory cytokines (TNF-α and IL-1β) in the lungs. Acetate significantly increased the expression of IFN-α in the lungs. Simultaneous treatment and infection also protected animals from RSV infection. Although all SCFAs protected animals, acetate was the only one to abolish viral load in the lungs, in addition to increasing the expression of IFN-β in the lungs. The high-fiber diet also protected the animals from RSV infection compared to the control fiber group. In addition, the high fiber diet evidently increased the expression of both type I IFNs (IFN-α and IFN-β) in the lung. Conclusion: Our study demonstrated that treatment with the SCFAs, as well as the fermentable fibers, appear to protect against RSV infection. In addition, acetate was shown to have a greater protective effect. Furthermore, our findings suggest that type 1 IFN is involved in the observed protective mechanism. Finally, the results support the possible use of these easily obtained compounds in the diet as a potential treatment for acute viral bronchiolitis caused by RSV.