Study On The Pathogenesis Of Intestinal Flora Involved In Acute Ischemic Stroke

The incidence,the recurrence rate,and the mortality and disability rate of stroke are high in China.It has jumped to the top of the national death causes.According to the nationwide population survey,there are about 2.4 million new stroke cases and 1.1 million stroke-related deaths in China every year,which brings huge economic burden to the country and individuals.Ischemic stroke,also known as cerebral infarction,accounts for 87% of all stroke cases.It is mainly caused by blockage or stenosis of intracranial arteries leading to interruption of blood flow.The most important pathophysiological mechanism of ischemic stroke is atherosclerosis caused by lipid deposition in vascular wall and activation of inflammatory factors.Tissue plasminogen activator(TPA)is a commonly used treatment for ischemic stroke,but many patients lose the opportunity of treatment because they fail to reach the hospital within the prescribed time window,resulting in permanent neurological deficits.According to the statistics of China National Stroke Registry,21.5% of patients with acute ischemic stroke rushed to the emergency department within 3 hours of onset,12.6% were eligible for thrombolytic therapy,but only 1.6% received TPA intravenously.Therefore,it is very important to clarify the mechanism of atherosclerosis in ischemic stroke,to prevent the occurrence of ischemic stroke and to treat it after the occurrence of stroke.However,the basic mechanism of the occurrence and development of atherosclerosis is complex.There are many theories in the academic circles,including inflammatory response theory,lipid infiltration theory,oxidative stress theory,thrombosis theory,genetics theory and proteomics theory.The former two theories are widely accepted and accepted.In recent decades,more and more studies have proved that microorganisms,especially intestinal microorganisms,participate in the process of atherosclerosis.Several epidemiological studies have found that microorganisms including Chlamydia pneumoniae,Helicobacter pylori and Porphyromonas gingivalis are associated with atherosclerosis.The presence of bacterial DNA in human atherosclerotic plaques has been confirmed by genetic techniques in different patients.Subsequent clinical trials found that microbial populations were closely associated with the development of a variety of diseases,including obesity,type 2 diabetes and cardiovascular diseases.Humans coevoluted with these microbes in a symbiotic way.Microorganisms have many physiological functions,including the production of essential vitamins(such as vitamin B and vitamin K),participation in carbohydrate digestion,the establishment of the immune system,regulation of metabolism including cholesterol and lipid metabolism,and production of signaling molecules such as short-chain fatty acids and secondary bile acids.At the same time,microorganisms play an important role in many diseases,including nervous system diseases.Several studies have found that the intestinal microflora has strong signal transduction with the central nervous system through nervous,immune and direct humoral signal transduction pathways.The central nervous system can also change the intestinal microenvironment by regulating intestinal motility and secretion.Therefore,it is called bi-directional brain-gut signal,which is known as the "brain-gut axis theory".Animal and human studies have shown that intestinal microflora is involved in the pathogenesis of autism,autoimmune encephalomyelitis,optic neuromyelitis and Parkinson's disease.Are intestinal microflora associated with the pathogenesis or some risk factors of acute ischemic stroke? These hypotheses can further elaborate the theory of brain-gut axis and provide theoretical basis for the prevention and treatment of acute ischemic stroke.Some animal experimental studies abroad have found changes in the composition of intestinal microflora in animal models of stroke.Tascillar et al.reported that intestinal bacteria migrated to the parenteral tract in a mouse model of middle cerebral artery occlusion.Swidsinski et al.observed transient colonitis and the disappearance of several intestinal bacterial flora after acute brain injury in experimental animals.However,there are few studies on the clinical correlation between intestinal microflora and acute ischemic stroke.Therefore,the exact mechanism of intestinal microflora in the pathogenesis of acute ischemic stroke deserves further study.In order to explore this mechanism,40 subjects(31 patients with acute ischemic stroke in the experimental group and 9 healthy controls in the same age group)were selected to detect the difference of intestinal microbial composition between the two groups by 16 S rRNA gene sequencing.Linear regression analysis and KEGG analysis were used to explore intestinal microflora.Relevance with risk factors of acute ischemic stroke.The main results of this study are as follows:1.There was no significant difference in intestinal flora diversity between patients with acute ischemic stroke and healthy controls.In this study,a total of 40 blood and fecal samples were collected from 31 patients with acute ischemic stroke and 9 healthy controls.The basic clinical characteristics of the two groups showed that the levels of WBC,TC,TG and LP(a)in patients with acute ischemic stroke were significantly higher than those in healthy controls,however HDL was significantly lower than that of healthy control group.In addition,the rates of smoking and hypertension in stroke group were significantly higher than those in control group,with statistical significance.However,the diversity of species richness,evenness of the microbial community indicated and the number of community species that no significant difference in gut flora diversity could be identified between these two groups.2.There were statistical differences in intestinal bacterial species between patients with acute ischemic stroke and healthy controls.In contrast,from different taxa abundance(Phylum,Class,Family,Genus,Order and Species)in gut microbiota showed significant differences at the species level between patients with Acute Cerebral Infarction and healthy controls.The bacterial species with the highest relative abundances were Blautia obeum,Streptococcus infantis and Prevotella copri.The most remarkable difference was found in Blautia obeum.The presence of Blautia obeum is relatively lower in the patient group while Streptococcus infantis and Prevotella copri are relatively higher in cerebral infarction patients compared to the control group.3.Abnormal expression of three intestinal bacteria is associated with risk factors of acute ischemic stroke.After identifying three abnormally-expressed gut microbiota species,we analyzed whether there were associations between bacteria and cardiovascular risk factors using linear regression.We show that Blautia was negatively associated with white blood cell count.Streptococcus showed positive correlation with creatinine and lipoprotein.To predict the abundance of gene families and related functional pathways of microbial communities in fecal contents,KEGG functional pathway analysis,a predictive metabolism approach,was performed based on the 16 S rRNA gene sequencing and Green Genes database.The results showed that many bacterial pathways such as lipopolysaccharide metabolism,secretory function and flagellum assembly were significantly regulated in patients with acute ischemic stroke.To sum up,this study found that there were three abnormal bacteria in the acute ischemic stroke group : Blautia obeum,Streptococcus infantis and Pretella copri.We have revealed that these three bacteria may be related to the occurrence and development of acute ischemic stroke,because they are related to risk factors and multiple functional metabolic pathways of ischemic stroke.These findings suggest that altered intestinal bacteria may be involved in the pathogenesis of ischemic stroke and may be potential targets for the treatment of cerebrovascular diseases and metabolic diseases.