Background: Exposure to antibiotics (Abx) causes perturbation of the normal microbial balance increasing host susceptibility to gut dysbiosis and opportunistic pathogens. The microbiome damage can persist for months and have "non-target" health consequences. Catecholamines provide a survival advantage in adapting to common postnatal stressors such as hypoglycemia. We previously showed impaired basal and stress-induced epinephrine responses in mice with Abx induced gut dysbiosis. Recolonization restored gut bacterial overall diversity, but sympathoadrenal responses remained attenuated. We hypothesize that it is due to an altered microbial ecosystem functionality since cecal short chain fatty acids (SCFA) levels were reduced in this model.
Objective: To determine whether oral supplement with SCFA will alleviate the effect of Abx treatment on sympathoadrenal stress responses.
Methods: Groups of C57Bl6 male mice were given regular water (control); cocktail of Abx (vancomycin, erythromycin, neomycin, gentamycin and ampicillin in drinking water for 2 weeks; Abx); SCFA in the drinking water or Abx+SCFA. At 8 weeks postnatal age, mice were injected with insulin (2IU/kg) or saline. Urine and blood samples were used for hormone analysis, and fecal samples for whole genome shotgun metagenomics. The protocol was approved by IACUC, NYMC.
Results: Addition of SCFA to the drinking water of vehicle and Abx-treated animals did not affect daily fluid intake and body weights over the course of the experiment, but reversed glucose homeostasis (as evident by a glucose tolerance test) to control values. Exposure to hypoglycemia resulted in potentiated epinephrine response in the SCFA group, compared to water-consuming controls. Animals receiving Abx+SCFA displayed improved steady state and insulin-induced urinary epinephrine levels (compared to Abx alone group) consistent with other evidence that gut derived SCFA play a role in regulating stress responsivity in catecholaminergic pathways. To unravel which bacteria are making the molecular messages affecting peripheral epinephrine responses to stress, we performed whole genome shotgun sequence profiling of fecal samples from control, Abx and Abx+R (recolonization) cohorts. The reduction in bacterial diversity in Abx mice was associated with enrichment of Proteobacteria (common marker of dysbiosis) with a parallel reduction in the abundance of Firmicutes and Bacteroidetes. Significant difference comparison between control and Abx+R cohorts revealed nine microbes enriched in the control cohort, including SCFA producers.
Conclusion: This is the first evidence that Abx-induced gut dysbiosis results in prolonged sympathoadrenal hyporesponsiveness. The ability to respond to stress favorably correlates with the presence of Firmicutes and Bacteroides and the amount of SCFAs produced in the cecum. Dietary supplement with microbial-derived metabolites may preserve the functional phenotype and improve clinical outcomes.
