Abstract: The aim of the study was to investigate whether insulin combined with linazolid had both hypoglycemic antibacterial and α-hemolysin activity to inhibit diabetic bacterial pneumonia.The effect of insulin combined with linezolid on macrophage inflammation induced by high glucose and Staphylococcus aureus α-hemolysin was studied in vitro,and its mechanism was discussed.The antibacterial activity of insulin,linezolid alone or in combination with insulin was examined by measuring minimum inhibitory concentration (MIC) in drug sensitivity test and D_{600 nm} to draw growth curve.The inhibitory effect of drug combination on α-hemolysin activity was investigated by hemolysis test.The safety of drug combination in vitro was determined by cytotoxic test.Western blotting was used to analyze the effect of drug combination on inflammatory pathway protein.The results of drug sensitivity test showed that the MIC values of 8325-4 and DU1090 strains of Staphylococcus aureus were not detected in insulin group,and the MIC values of linezolid and insulin+linezolid groups for both strains of Staphylococcus aureus were 0.5 μg/mL.The results of growth curve showed that insulin did not inhibit the growth of Staphylococcus aureus in the normal group and the high glucose group,while in linezolid group and insulin+linezolid groups,0.25 to 4 μg/mL linezolid could inhibit the growth of Staphylococcus aureus.The results of hemolysis test showed that in normal group and high glucose group,insulin did not inhibit α-hemolysin activity,while 0.25 to 4 μg/mL linezolid could inhibit α-hemolysin activity.The cytotoxic test showed that the cell survival rate of normal group and high glucose group was more than 88.038%.The combination of 50 nmol/L insulin,0.25 μg/mL linezolid,50 nmol/L insulin +0.25 μ g/mL linezolid could improve the survival rate of MH-S cells induced by high glucose.The results of Western blotting showed that 50 nmol/L insulin alone did not inhibit the expression of TLR2,MAPKs and NLRP3 in mouse alveolar macrophages (MH-S cells) induced by high glucose and α-hemolysin,while 50 nmol/L insulin combined with 0.25 μg/mL linezolid could reduce the expression level of these proteins in MH-S cells induced by high glucose and α-hemolysin,and the inhibitory effect of linezolid was more significant than that of linezolid alone.In conclusion,insulin combined with linezolid could effectively inhibit the inflammatory response of MH-S cells by lowering high glucose,antibacterial and inhibiting α-hemolysin activity.

Key words: linezolid; insulin; Staphylococcus aureus; α-hemolysin; high glucose; MH-S cells