[Effect of exogenous carbon monoxide on sequestration of polymorphonuclear neutrophils in the lung following limb ischemia-reperfusion: an experimental study].

Objective: To investigate the effect of exogenous carbon monoxide (CO) in inhibiting the sequestration of polymorphonuclear neutrophils (PMNs) in the lung following limb ischemia-reperfusion (IR) and the mechanism thereof.

Methods: PMNs of peripheral blood were isolated from the venous blood of a healthy volunteer. Serum was collected from a patient undergoing bilateral knee joint replacement as IR serum. Human pulmonary microvascular endothelial cells (PMVECs) were cultured and divided into 4 groups: control group (cultured under the condition of room air containing 5% CO2 for 5 h and cultured in normal human serum instead of medium during the last 4 hours of experiment), IR group (cultured under the condition of air containing 5% CO2 for 5h and cultured in the serum of IR patient during the last 4 hours), IR + CO group (cultured under the condition of air containing 0.025% CO and 5% CO2 for 5 hours and cultured in IR serum during the last 4 hours), and control + CO group (cultured under the condition of air containing and 0.025% CO and 5% CO2 for 5 hours and cultured in normal human serum during the last 4 hours). Immunofluorescence flow cytometry was used to detect the expression of intercellular adhesion molecule (ICAM)-1 and integrin CD11b in the PMVECs. Human PMVECs were put into the wells of a 96-well plate and added with PMNs to calculate the PMVEC-PMN adhesion rate. Tourniquettes were bound at the bilateral hind thighs of 32 healthy male SD rats for 4 hours so as to establish a rate IR model. The rats were randomly divided into 4 equal groups: control group (undergoing the same operation without causing limb ischemia and exposed to room air), IR group (undergoing bilateral hind limb ischemia for 4 h and reperfusion for 4 h and exposed to room air), IR + CO group (exposed to the containing 0.025% CO one hour before reperfusion till 4 hours after reperfusion), and control + CO group (exposed to air containing 0.025% CO at the corresponding time point as that of the IR + CO group). Then the rats were killed and their middle pulmonary lobes were taken out for microscopy and calculation of the number of PMNs in alveolar septum. Western blotting was used to examine the ICAM-1 protein expression in the lung.

Results: The ICAM-1 expression and integrin CD11b expression of the IR group PMVECs were significantly stronger than those of the IR + CO group PMVECs (both P < 0.05) and there were no significant differences in the ICAM-1 expression and CD11b expression between the control + CO and control groups (both P > 0.05). The PMN-PMVEC adhesion rate of the IR group PMVECs was 30 +/- 2.9%, significantly higher than those of the IR + CO group and control group PMVECs (19.8 +/- 1.5% and 13.4 +/- 1.1% respectively, both P < 0.05) and there was no significant difference in the PMN-PMVEC adhesion rate between the CO + control group and control group (P > 0.05). The lung tissues of the IR group rats showed edema and hemorrhage. The number of PMNs in the alveolar septum was 60.6 +/- 1.7/10 high power fields, significantly higher than those of the IR + CO group and control group (36.4 +/- 1.6 and 22.5 +/- 1.6 respectively, both P < 0.05) and there was no significant difference between the latter 2 groups (P > 0.05). The ICAM-1 protein expression in the lung of the IR group was the strongest, followed by the IR + CO group, control + CO group, and control group.

Conclusion: Exogenous CO inhibits the limb/IR-induced PMN sequestration in the lung, probably by the mechanism of down-regulation of the expression of adhesion molecules and suppression of the PMN\PMVEC adhesion following IR.