BackgroundThe diagnosis of sepsis associated encephalopathy (SAE) remains challenging in clinical settings because of a lack of specific biomarkers. Functional magnetic resonance imaging (fMRI) and proton magnetic resonance spectroscopy (1H-MRS) can be used to aid in the diagnosis of cognition related diseases. This study investigated changes in functional activities and brain metabolites in the hippocampus in SAE rats by fMRI and 1H-MRS.Materials and methodsSepsis associated encephalopathy rats underwent cecal ligation and perforation (CLP) surgery. The Morris water maze (MWM) test was then used to evaluate cognitive function. Resting state-fMRI and 1H-MRS scanning were performed 7 and 14 days after CLP surgery to reveal spontaneous neuronal activity and metabolite changes in the hippocampus. The amplitude of low-frequency fluctuation (ALFF) was used to evaluate spontaneous neuronal activity in the hippocampus. Creatine (Cr), Myo-inositol (mI), and glutamine/glutamate (Glx) levels were measured with 1H-MRS scanning. Immunofluorescence and levels of interleukin (IL)-1β, interleukin (IL)-6, and C-reactive protein (CRP) in the hippocampus were additionally detected to evaluate microglial mediated inflammatory responses. Statistical analysis was performed to evaluate correlations between hippocampal metabolism and behavioral findings.ResultsCecal ligation and perforation treated rats exhibited impaired learning and memory function in the MWM test at days 7 and 14. Elevation of IL-1β in the hippocampus, as well as immunofluorescence results, confirmed severe neuro inflammation in the hippocampus in SAE rats. Compared with the sham group, the ALFF of the right CA-1 area of the hippocampus was higher at day 7after CLP surgery. The Glx/Cr and mI/Cr ratios were enhanced at day 7 after CLP surgery and slightly lower at day 14 after CLP surgery. The ALFF value, and Glx/Cr and mI/Cr ratios were negatively correlated with time spent in the target quadrant in the MWM test.ConclusionSpontaneous neuronal activity and metabolites showed significant alterations in SAE rats. The elevated ALFF value, Glx/Cr ratio, and mI/Cr ratio in the hippocampus were positively associated with cognitive deficits. Changes in ALFF and metabolites in hippocampus may serve as potential neuroimaging biomarkers of cognitive disorders in patients with SAE.

ObjectiveThis study aims to analyze the changes of fecal short chain fatty acids (SCFAs) content and gut microbiota composition in sepsis associated encephalopathy (SAE) mice, further evaluating the effect of SCFAs on cognitive function and the underlying mechanism in SAE mice.MethodsA total of 55 male adult C57BL/6 mice (2–3 months of age, 20–25 g) were divided into four groups randomly: sham group (n = 10), cecal ligation and puncture group (CLP group, n = 15), CLP+SCFAs group (n = 15), and CLP+SCFAs+GLPG0974 group (n = 15). Seven days after surgery, fecal samples were collected for microbiota composition and SCFA analysis from 6 mice in each group randomly. Behavioral test was applied to assess cognitive impairment at the same time. After that, mice were sacrificed and brain tissue was harvested for inflammatory cytokines analysis.ResultsThe levels of acetic acid (.57 ± 0.09 vs 2.00 ± 0.24, p < 0.001) and propionic acid (.32 ± 0.06 vs .66 ± 0.12, p = 0.002) were significantly decreased in the CLP group compared with the sham group. The administration of SCFAs significantly increased the levels of acetic acid (1.51 ± 0.12 vs. 0.57 ± 0.09, p < 0.001) and propionic acid (0.54 ± 0.03 vs. 0.32 ± 0.06, p = 0.033) in CLP+SCFAs group compared with CLP group. Relative abundance of SCFAs-producing bacteria, including Allobaculum (0.16 ± 0.14 vs. 15.21 ± 8.12, p = 0.037), Bacteroides (1.82 ± 0.38 vs. 15.21 ± 5.95, p = 0.002) and Bifidobacterium (0.16 ± 0.06 vs. 2.24 ± 0.48, p = 0.002), significantly decreased in the CLP group compared with the sham group. The behavioral tests suggested that cognitive function was impaired in SAE mice, which could be alleviated by SCFAs pretreatment. ELISA tests indicated that the levels of IL-1β, IL-6, and TNF-α were elevated in SAE mice and SCFAs could lower them. However, the GPR43 antagonist, GLPG0974, could reverse the cognitive protective effect and anti-neuroinflammation effect of SCFAs.ConclusionOur study suggested that in SAE, the levels of acetate and propionate decreased significantly, accompanied by gut microbiota dysbiosis, particularly a decrease in SCFAs-producing bacteria. GPR43 was essential for the anti-neuroinflammation and cognitive protective effect of SCFAs in SAE.

Background: Sepsis-associated encephalopathy (SAE) is one of the most serious complications of sepsis, along with brain function and cognitive behavioral changes. The process of efferocytosis with microglia was restrained in SAE rats’ hippocampus. We have previously shown that milk fat globule EGF factor 8 protein (MFG-E8) evoked efferocytosis in SAE rats’ brain, and alleviated the inflammnation in hippocampus. The present study investigated the the contribution of MFG-E8 to the brain functional connectivity (FC) of hippocampus and lateral entorhinal cortex in SAE rats by resting-state functional MRI scan.Methods: Sixty adult male Sprague Dawley rats were divided randomly into Sham operation group, cecal ligation and puncture (CLP) group, CLP+MFGE8 group, and CLP+MFGE8+Cilengitide group. After cecal ligation and puncture (CLP) surgery, MFGE8 (3.3ug) was injected intracerebroventricularly (i.c.v.) and cilengitide (10 mg/kg) was injected intraperitoneal. The Morris water maze (MWM) and open filed test (OFT) were performed continuously for five days. Rats were detected by T2-MRI and rs-fMRI scan 8 days post-surgery, then brain tissues were taken for western blotting and pathological observation by HE stained. One-way ANOVA with Tukey’s post-test of all pair of columns was employed statistical analyses.Results: MFGE8 improved performance of neurobehavioral tests in MWM test and OFT. Expression of IL-1β and the proteins of MFGE8, Rac1, and LC3 were up regulated in CLP+MFGE8 group. On the contrary, expression of IL-6, Rac1, and LC3 were down regulated in CLP+MFGE8+cilengitide group. MFGE8 significantly decreased the hyperintense region in hippocampus detected by T2-MRI, and increased ALFF value in SAE rats’ bilateral sensory cortex, motor cortex and visual cortex by rs-fMRI. In addition, MFGE8 increased FC of CA1 and LEnt in same side of cerebral hemisphere, and the FC of CA1 and LEnt was consistent with the behavior result in Morris water maze test.Conclusions: MFGE8 activated efferocytosis with microglia and improved brain function and functional connectivity between CA1 and LEnt which were reflected in behavior tests and fMRI.