A obesidade associada a hiperglicemia compromete a indução de tolerância oral e agrava a alergia alimentar

Abstract

Obesity associated with hyperglycemia is directly correlated with intestinal barrier dysfunction and the risk for inflammatory bowel disorders. So, we decided to investigate whether the breakdown of intestinal homeostasis caused by obesity associated with hyperglycemia would interfere with the induction of oral tolerance, and would affect the occurrence of food allergy. First, we used C57/BL6 mice treated with a hypercaloric diet, rich in sugar and butter (HSB) for 13 weeks to induce obesity and comorbidities such as hyperglycemia. At the end of 13 weeks of treatment with the diet, the animals were obese and showed important changes in the intestinal mucosa such as increased intestinal permeability, higher frequency of goblet cells, and reduced frequency of regulatory T cells (Tregs) in duodenal and jejunal mesenteric lymph nodes. In addition, changes in the intestinal microbiota of obese animals were observed. Given the importance of intestinal mucosa homeostasis for the development of oral tolerance, it was evaluated whether the ability to induce oral tolerance was preserved. We observed that obese mice were resistant to the development of oral tolerance when considering the cellular and humoral responses. In addition, lean control mice that received oral OVA had an increased frequency of CD4+Foxp3+ regulatory T cells in lymph nodes, but no difference was found in the frequency of CD4+Foxp3+ T cells in obese mice that received oral OVA. Therefore, obese animals were refractory to the development of oral tolerance. There is an important correlation between hyperglycemia and disruption of intestinal homeostasis. In order to investigate whether hyperglycemia would play a role in resistance to oral tolerance induction, we treated obese mice with the glycemic modulator Metformin (1g/L) for 21 days, which reduced fasting glycemia in obese mice to the levels found in control mice. Treatment of obese mice with Metformin resulted in restoration of oral tolerance induction to OVA and improved intestinal permeability. Furthermore, mice with hyperglycemia caused by the treatment with streptozotocin (model of type 1 diabetes) also did not develop oral tolerance after oral administration of OVA. This confirms the relationship between hyperglycemia and resistance to oral tolerance induction. Failure to induce oral tolerance or disruption of intestinal homeostasis can result in food allergy. To verify the relationship between obesity and food allergy, after obesity induction, mice were immunized with OVA and challenged in drinking water. Allergic obese mice showed greater weight loss, significant increase in anti-Ova IgG1 compared to allergic lean control mice, and had a more intense passive cutaneous anaphylaxis reaction than lean animals, showing that obesity aggravates food allergy. To investigate the translation of our findings to clinical practice in humans, we compared the serum IgE levels of obese patients with hyperglycemia (DM2) with levels found in obese individuals with normal blood glucose. Individuals with DM2 have higher serum IgE levels when compared to obese patients without hyperglycemia. In addition, we evaluated gene expression in jejunal biopsies from obese patients with and without hyperglycemia. Among the genes, we identified the downregulation of IL-22, IL-10, Foxp3, ZO-1 and claudin 2, and the upregulation of IL-33 and IL-5 in hyperglycemic obese patients’ genes. The genes are related with gut homeostasis and allergic diseases. Together our data suggest that obesity associated with hyperglycemia makes it difficult to induce oral tolerance by breaking intestinal homeostasis, and that obesity can aggravate allergic phenomena. A better understanding of the relationship between obesity and mucosal immune responses may help to develop new therapeutic strategies for food allergy based on oral tolerance mechanisms.