Exogenous carbon monoxide attenuates inflammatory responses in the small intestine of septic mice

AIM:To determine whether the carbon monoxide(CO)-releasing molecules(CORM)-liberated CO suppress inflammatory responses in the small intestine of septic mice.METHODS:The C57BL/6 mice(male,n = 36;weight 20 ± 2 g) were assigned to four groups in three respective experiments.Sepsis in mice was induced by cecal ligation and puncture(CLP)(24 h).Tricarbonyldichlororuthenium(Ⅱ) dimer(CORM-2)(8 mg/kg,i.v.) was administrated immediately after induction of CLP.The levels of inflammatory cytokines [interleukin-1(IL-1) and tumor necrosis factor-(TNF-)] in tissue homogenates were measured with enzyme-linked immunosorbent assay.The levels of malondialdehyde(MDA) in the tissues were determined.The levels of nitric oxide(NO) in tissue homogenate were measured and the expression levels of intercellular adhesion molecule 1(ICAM-1) and inducible nitric oxide synthase(iNOS) in the small intestine were also assessed.NO and IL-8 levels in the supernatants were determined after the human adenocarcinoma cell line Caco-2 was stimulated by lipopolysaccharide(LPS)(10 g/mL) for 4 h in vitro.RESULTS:At 24 h after CLP,histological analysis showed that the ileum and jejunum from CLP mice induced severe edema and sloughing of the villous tips,as well as infiltration of inflammatory cells into the mucosa.Semi-quantitative analysis of histological samples of ileum and jejunum showed that granulocyte infiltration in the septic mice was significantly increased compared to that in the sham group.Administration of CORM-2 significantly decreased granulocyte infiltration.At 24 h after CLP,the tissue MDA levels in the midileum and mid-jejunum significantly increased compared to the sham animals(103.68 ± 23.88 nmol/mL vs 39.66 ± 8.23 nmol/mL,89.66 ± 9.98 nmol/mL vs 32.32 ± 7.43 nmol/mL,P < 0.01).In vitro administration of CORM-2,tissue MDA levels were significantly decreased(50.65 ± 11.46 nmol/mL,59.32 ± 6.62 nmol/mL,P < 0.05).Meanwhile,the tissue IL-1 and TNF-levels in the mid-ileum significantly increased compared to the sham animals(6.66 ± 1.09 pg/mL vs 1.67 ± 0.45 pg/mL,19.34 ± 3.99 pg/mL vs 3.98 ± 0.87 pg/mL,P < 0.01).In vitro administration of CORM-2,tissue IL-1 and TNF-levels were significantly decreased(3.87 ± 1.08 pg/mL,10.45 ± 2.48 pg/mL,P < 0.05).The levels of NO in mid-ileum and mid-jejunum tissue homogenate were also decreased(14.69 ± 2.45 nmol/mL vs 24.36 ± 2.97 nmol/mL,18.47 ± 2.47 nmol/mL vs 27.33 ± 3.87 nmol/mL,P < 0.05).The expression of iNOS and ICAM-1 in the mid-ileum of septic mice at 24 h after CLP induction significantly increased compared to the sham animals.In vitro administration of CORM-2,expression of iNOS and ICAM-1 were significantly decreased.In parallel,the levels of NO and IL-8 in the supernatants of Caco-2 stimulated by LPS was markedly decreased in CORM-2-treated Caco-2 cells(2.22 ± 0.12 nmol/mL vs 6.25 ± 1.69 nmol/mL,24.97 ± 3.01 pg/mL vs 49.45 ± 5.11 pg/mL,P < 0.05).CONCLUSION:CORM-released CO attenuates the inflammatory cytokine production(IL-1 and TNF-),and suppress the oxidative stress in the small intestine during sepsis by interfering with protein expression of ICAM-1 and iNOS.