Pathological Evaluation Of Liver Injury In Obese Mice Infected With Escherichia Coli By Nasal Drip

Obesity is considered an important risk factor for adverse results of various diseases,and increases morbidity and mortality from many chronic inflammatory disease.However,recent research shows that obesity also exerts protective effects that benefit survival and improve outcomes in patients with pneumonia.Our previous studies suggest that the high-fat diet-induced-obese(DIO)mice exhibited less severe lung injury and lipid metabolic disorders than the normal mice after Escherichia coli(E.coli)intranasal infection.But,pathological evaluation of liver injury in obese mice infected with E.coli by nasal drip have not been reported.In this study,we investigated the effects of E.coli intranasal infection on the histopathology and apoptosis of liver in the high-fat diet induced-obese mice by using histopathology,ELISA,flow cytometry,qRT-PCR and western-blot techniques.A total of144 three weeks old male ICR mice were casually subdivided into 2 groups:Normal group(64)fed with regular diet and DIO group(80)fed with high-fat-diet.After 8 weeks of feeding,the Normal group mice were subdivided into Normal-PBS group(32)and Normal-E.coli group(32).Mice in the DIO group which reached to the obesity standard were chosen and subdivided into DIO-PBS group(32)and DIO-E.coli group(32).The Normal-E.coli and DIO-E.coli groups were intranasally instilled by 40?L bacterial suspension which contained approximately 4×10~9 CFUs/mL E.coli,while the Normal-PBS and DIO-PBS groups were given 40?L PBS,respectively.The liver parameters including body weight,Lee's index,serum triglyceride(TG)and total cholesterol(TC)levels,liver weight,liver index,liver histopathological injury,liver cytokine and adipocytokine levels,liver oxidative stress status and liver apoptosis were detected at 0h(pre-infection),12h,24h,and 72h(post-infection).Results were as follow:(1)After feeding with the high-fat diets or normal diets for 8 weeks,the body weight,Lee's index and serum TG and TC levels in the DIO group mice were markedly raised compared with the Normal group.(2)Before infected with E.coli,the liver weight in the DIO-PBS group was higher than that in the Normal-PBS group,but the liver index showed no significant difference.After infected with E.coli,compared with the Normal-PBS and DIO-PBS group,the liver weight and liver index in the Normal-and DIO-E.coli group were markedly increased.(3)The hepatic cords were disorganized,and hepatic sinusoids appeared narrow due to the swelling of hepatocytes,and hepatocyte steatosis and vesicular degeneration were observed in both the Normal-and DIO-E.coli groups.The lipid droplets contents in the Normal-and DIO-E.coli groups were dramatically elevated in comparison to the PBS groups,whereas the contents of hepatic glycogen was remarkably decreased,respectively.(4)Before infection,TNF-?,IL-6,Resistin,and Leptin contents of the DIO-PBS group in the liver were dramatically higher than those in the Normal-PBS group.After infection,the values of TNF-?,IL-1?,IL-6,IL-8,Resistin,and Leptin in the Normal-E.coli and DIO-E.coli groups were dramatically increased in comparison to the PBS groups,respectively.(5)Before infected with E.coli,the content of MDA and activity of GSH-Px in the liver of DIO-PBS group were higher than those in the Normal-PBS group.After infection,the contents of MDA,and GSH and the activities of GSH-Px,CAT,and SOD in the Normal-and DIO-E.coli groups were markedly raised in comparison to the Normal-PBS group and DIO-PBS group,respectively.(6)Before being treated with E.coli,the percentages of hepatic apoptotic cells showed no significant difference between the Normal-and DIO-PBS groups.After being infected with E.coli,the percentages of hepatic apoptotic cells in the Normal-E.coli group or DIO-E.coli group were significantly elevated in comparison to the Normal-and DIO-PBS group,respectively.(7)Before infected with E.coli,the DIO-PBS group led to the generally up-regulation of Caspase-3,Caspase-9,and Bax mRNAs and proteins as well as Bax/Bcl-2 ratio in the liver,while down-regulation of Bcl-2 expression in comparison to the Normal-PBS group.E.coli infection generally induced the elevated levels of Caspase-3,Caspase-9,and Bax mRNAs and proteins and the ratio of Bax/Bcl-2,and the lowered Bcl-2 contents in both Normal-and DIO-E.coli groups in comparison to the PBS groups,respectively.(8)Under the condition of E.coli intranasal infection,the relative changes of the above indexes in the DIO mice were less than those in the Normal mice.In summary,E.coli intranasal infection caused hepatic histopathological damage and increased apoptosis which may resulted from oxidative damages,and raised levels of cytokines and adipocytokines.The increased apoptosis of liver cells may be closely related to the mitochondrial pathway after E.coli infection.The above change range of DIO mice was significantly lower than that of Normal mice following E.coli intranasal infection.However,further research are needed to illustrate the mechanisms.