Study On The Level And Effects Of Short-chain Fatty Acids In The Airway Of Asthmatic Patients

Background and objectiveAsthma is one of the most common chronic airway diseases in the world.There are increasing evidence that short-chain fatty acids（SCFAs）play an important role in the development of asthma,especially TH2 type asthma.Previous studies mainly focus on intestinal SCFAs,the effects of SCFAs in the airway are still unclear.The purpose of this study was to explore the distribution of airway SCFAs in asthmatic patients,the association between SCFAs,TH2 inflammation,and other clinical features.And to verify the role of airway SCFAs by animal experiments according to the clinical analysis.Methods:25 asthmatic patients and 9 healthy volunteers in Tongji hospital were finally included from March 2015 to January 2019 retrospectively.Demographic information,medical history,blood routine,serum total Ig E,pulmonary function data and fasting induced sputum samples were collected.Exhaled nitric oxide,ACT score and HAD score data were also collected from patients with asthma.The contents of sputum supernatant SCFAs were determined by gas chromatography-tandem mass spectrometry,and the SCFAs’level of sputum supernatant between asthmatic patients and healthy controls as well as between different asthma subgroups were compared.Meanwhile,the correlation between sputum supernatant SCFAs and other clinical indicators in bronchial asthma patients was explored.20 C57BL/6J mice were divided into control group,50m M isovalerate group,500m M isovalerate group and strained stress group with a random blocks design according to the baseline weight,cage,and total distance.Mice in the first three groups received aerosol inhalation for 30 minutes a day,and mice in the strained stress group were simultaneously strained for 2 hours a day.After 3 weeks’intervention,all mice were tested by the open field test and the tail-suspension test.Bronchoalveolar lavage fluids were collected for cell classification and counting and lung tissues were taken to measure m RNA relative expression of IL-1,IL-8,IL-6,IL-4,IL-5 and IL-13 in the first three groups.The left lung of mice was taken for pathological section.Results:The concentration of total SCFAs in the sputum supernatant of all volunteers was 153.6（99.9-218.7）μM（median,quartile）.Acetate and propionate were major components,accounting for 69%and 24%respectively.There was no significant difference in SCFAs concentration and percentage between the healthy control group and the asthma group.The levels of airway butyrate[0.27（0.16-0.39）μM vs 0.14（0.11-0.30）μM,p=0.064]and valerate[5.19（3.20-17.50）μM vs 2.56（1.21-8.91）μM,p=0.064]in patients with high TH2 asthma tended to be higher than those with non-high TH2 asthma.In addition,patients with sputum eosinophil percentage≥3%had higher sputum supernatant valerate concentration[0.31（0.19-0.48）M vs 0.14（0.11-0.29）M,p=0.020]than patients with sputum eosinophil percentage<3%.And butyrate concentration of patients with sputum eosinophils≥3%also tended to be higher[10.85（3.33-18.13）μM vs 3.07（1.35-7.61）μM,p=0.059]than patients with sputum eosinophil percentage<3%.All SCFAs components’concentrations were negatively correlated with FEV₁%（p<0.05）or had a negative correlation trend.The percentage of sputum neutrophils was positively correlated with isovalerate and iso-butyrate（p<0.05）.The total HAD score of asthmatic patients was negatively correlated with the percentage of propionate（p=0.04）,and negatively correlated with valerate/isovalerate ratio（p=0.01）.There was no significant difference in weight change,total distance,percentage of center distance,numbers of standing and immobile time among the four groups.And there was also no significant difference in the BALF cell count and classification count among control group,50m M isovalerate group and 500m M isovalerate group.Macrophages were dominant in each group,followed by epithelial cells,lymphocytes and neutrophils were rare,and eosinophil was not observed.Compared with the control group,the isovalerate group consist of two isovalerate groups had lower relative expression of IL-4（p=0.03）and IL-13（p=0.04）.Conclusions:There was no significant difference in the sputum supernatant SCFAs between the asthma group and the healthy control group.The levels of airway butyrate and valerate in patients with high TH2 asthma tended to be higher than those with non-high TH2 asthma,which could be seen in asthma patients with sputum eosinophils≥3%and sputum eosinophils<3%.Inhalation of isovalerate aerosol has no effect on promoting anxiety and depression in healthy mice.Isovalerate has no direct pro-inflammatory effect or pathological damage on the lungs of healthy mice,but decreases the relative expression of TH2 inflammatory cytokines IL-4 and IL-13 in lung tissues of healthy mice.