Preventive Effects of Bacillus licheniformis on Heat Stroke in Rats by Sustaining Intestinal Barrier Function and Modulating Gut Microbiota.

Lei Li,Sheng Wang,Changquan Ling,Zhuoran Xu,Chaoyu Xie,Meitang Wang,Jinfeng Li,Dong Liu,Jiqianzhu Zhang,Jianghong Wu,Xinyu Xia,Shuogui Xu,Jiangbo Zhu,Man Wang,Jikuai Chen,Shaokang Wang

doi:10.3389/fmicb.2021.630841

Abstract

Heat stroke (HS) models in rats are associated with severe intestinal injury, which is often considered as the key event at the onset of HS. Probiotics can regulate the gut microbiota by inhibiting the colonization of harmful bacteria and promoting the proliferation of beneficial bacteria. Here, we investigated the preventive effects of a probiotic Bacillus licheniformis strain (BL, CMCC 63516) on HS rats as well as its effects on intestinal barrier function and gut microbiota. All rats were randomly divided into four groups: control (Con) + PBS (pre-administration with 1 ml PBS twice a day for 7 days, without HS induction), Con + BL group (pre-administration with 1 ml 1 × 108 CFU/ml BL twice a day for 7 days, without HS induction), HS + PBS (PBS, with HS induction), and HS + BL (BL, with HS induction). Before the study, the BL strain was identified by genomic DNA analysis. Experimental HS was induced by placing rats in a hot and humid chamber for 60 min until meeting the diagnostic criterion of HS onset. Body weight, core body temperature, survival rate, biochemical markers, inflammatory cytokines, and histopathology were investigated to evaluate the preventive effects of BL on HS. D-Lactate, I-FABP, endotoxin, and tight-junction proteins were investigated, and the fluorescein isothiocyanate-dextran (FD-4) test administered, to assess the degree of intestinal injury and integrity. Gut microbiota of rats in each group were analyzed by 16S rRNA sequencing. The results showed that pre-administration with BL significantly attenuated hyperthermia, reduced HS-induced death, alleviated multiple-organ injury, and decreased the levels of serum inflammatory cytokines. Furthermore, BL sustained the intestinal barrier integrity of HS rats by alleviating intestinal injury and improving tight junctions. We also found that BL significantly increased the ratios of two probiotic bacteria, Lactobacillus and Lactococcus. In addition, Romboutsia, a candidate biomarker for HS diagnosis, was unexpectedly detected. In summary, BL pre-administration for 7 days has preventative effects on HS that may be mediated by sustaining intestinal barrier function and modulating gut microbiota.

Highlights

Heat stroke (HS) is a life-threatening disease characterized by extreme hyperthermia (usually core body temperature (Tc) > 40.5◦C), central nervous system dysfunction, systemic inflammatory response syndrome (SIRS), and multiple-organ injury dysfunction syndrome (MODS) (Epstein and Yanovich, 2019)
No differential species were determined for taxa of Linear discriminant analysis (LDA) >3.5 and only a tiny number of species were found when the LDA >2.0 between the Con + BL and HS + BL groups. These results collectively indicate that BL pre-administration and HS induction each modulated the gut microbiota of rats, and BL helped make the gut microbiota more probiotic and more heat-tolerable as characterized by the notable increase of Lactobacillus and the tiny alternations of gut microbiota of rats in the HS + BL group compared with the Con + BL group
We demonstrated that BL pre-administration for 7 days exerted preventive effects on HS in rats, including attenuating hyperthermia, reducing HS-induced death, decreasing systematic inflammatory responses, and minimizing multiple-organ injury, by sustaining intestinal barrier function and modulating gut microbiota under HS

Summary

Introduction

Heat stroke (HS) is a life-threatening disease characterized by extreme hyperthermia (usually core body temperature (Tc) > 40.5◦C), central nervous system dysfunction, systemic inflammatory response syndrome (SIRS), and multiple-organ injury dysfunction syndrome (MODS) (Epstein and Yanovich, 2019). Tc can rise continually and lead to a cascade of events that includes SIRS, disseminated intravascular coagulation (DIC), MODS, and even death. At this stage, even if multiple adjuvant treatments and intensive care therapy are adopted, the case-fatality rate of HS patients is difficult to reduce and the occurrence of sequelae might be inevitable. Considering the lack of specific and effective drugs for HS, prevention is critical rather than treatment after onset (Epstein and Yanovich, 2019)

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Conclusion