Fecal microbiota transplantation regulates the cholinergic anti-inflammatory pathway in cerebral cortex of septic rats through intestinal microbiota

Abstract

To investigate the effects of fecal microbiota transplantation on septic gut flora and the cortex cholinergic anti-inflammatory pathway in rats. Sixty clean grade male Sprague-Dawley (SD) rats were divided into normal saline (NS) control group, sepsis model group and fecal microbiota transplantation group by random number table, with 20 rats in each group. The rat model of sepsis was reproduced by injection of 10 mg/kg lipopolysaccharide (LPS) via tail vein, the rats in the NS control group was given the same amount of NS. The rats in the fecal microbiota transplantation group received nasogastric infusion of feces from healthy donor on the 1st day, 2 mL each time, for 3 times a day, the other two groups were given equal dose of NS by gavage. Fecal samples were collected on the 7th day after modeling, the levels of intestinal microbiota composition was determined using the 16SrDNA gene sequencing technology. The brain function was evaluated by electroencephalogram (EEG), and the proportion of each waveform in EEG was calculated. After sacrifice of rats, the brain tissues were harvested, the levels of protein expression of α7 nicotinic acetylcholine receptor (α7nAChR) were determined by Western Blot, and positive cells of Iba-1 in brain tissue were detected by immunohistochemistry method. The levels of interleukins (IL-6 and IL-1β) and tumor necrosis factor-α (TNF-α) were determined by enzyme-linked immunosorbent assay (ELISA). Seven days after the reproduction of the model, all rats in the NS control group survived, while 10 rats and 8 rats died in the sepsis model group and fecal microbiota transplantation group, respectively, with mortality rates of 50% and 40% respectively. Finally, there were 20 rats in the NS control group, 10 in the sepsis model group and 12 in the fecal microbiota transplantation group. Compared with the NS control group, the diversity and composition of intestinal flora were changed, the incidence of abnormal EEG increased significantly, the expression of α7nAchR in the cortex decreased significantly, and the levels of Iba-1, TNF-α, IL-6 and IL-1β were significantly increased in the model group, suggested that the intestinal flora was dysbiosis, and severe inflammatory reaction occurred in the cerebral cortex, and brain function was impaired. Compared with the model group, the diversity of intestinal flora in the fecal microbiota transplantation group was significantly increased (species index: 510.24±58.76 vs. 282.50±47.42, Chao1 index: 852.75±25.24 vs. 705.50±46.50, both P < 0.05), the dysbiosis of intestinal flora at phylum, family, genus level induced by LPS were also significantly reversed, and with the improvement of intestinal flora, the incidence of abnormal EEG waveforms was lower in the fecal microbiota transplantation group compared with that in the model group [25.0% (3/12) vs. 80.0% (8/10), P < 0.05], and the expression of α7nAChR protein in the cerebral cortex was significantly increased (α7nAChR/β-actin: 1.56±0.05 vs. 0.82±0.07, P < 0.05), immunohistochemistry analysis showed that Iba-1 positive expression of microglia decreased significantly, and cerebral cortex TNF-α, IL-6, IL-1β levels were significantly decreased [TNF-α (ng/L): 6.28±0.61 vs. 12.02±0.54, IL-6 (ng/L): 28.26±3.15 vs. 60.58±4.62, IL-1β (ng/L): 33.63±3.48 vs. 72.56±2.25, all P < 0.05]. The results reveal that fecal microbiota transplantation has remarkably modulated the dysbiosis of intestinal microbiota and activated cholinergic anti-inflammatory pathway, and ameliorate the brain dysfunction in septic rats.