Effects of cardiopulmonary bypass on tight junction protein expressions in intestinal mucosa of rats

Abstract

Aim: To investigate the tight junction protein expressions of intestinal mucosa in an experimental model of cardiopulmonary bypass (CPB) in rats.

Methods: Thirty anesthetized rats were randomly divided into two groups: Group S (n = 10) served as sham operation and group C (n = 20) served as CPB which underwent CPB for 1 h. Expression of occludin and zonula occludens-1 (ZO-1) were determined by Western blotting and immunotochemistry, respectively. Plasma levels of diamine oxidase (DAO) and d-lactate were determined using an enzymatic spectrophotometry.

Results: Immunohistochemical localization of occludin and ZO-1 showed disruption of the tight junctions in enterocytes lining villi at the end of CPB and 2 h after CPB. The intensities of the occludin and ZO-1 at the end of CPB were lower than those of control group (76.4% +/- 22.5% vs 96.5% +/- 28.5% and 62.4% +/- 10.1% vs 85.5% +/- 25.6%, P < 0.05) and were further lower at 2 h after CPB (50.5% +/- 10.5% and 45.3% +/- 9.5%, P < 0.05). Plasma d-lactate and DAO levels increased significantly (8.688 +/- 0.704 vs 5.745 +/- 0.364 and 0.898 +/- 0.062 vs 0.562 +/- 0.035, P < 0.05) at the end of CPB compared with control group and were significantly higher at 2 h after CPB than those at the end of CPB (9.377 +/- 0.769 and 1.038 +/- 0.252, P < 0.05). There were significant negative correlations between occludin or ZO-1 expression and DAO (r(2) = 0.5629, r(2) = 0.5424, P < 0.05) or d-lactate levels (r(2) = 0.6512, r(2) = 0.7073, P < 0.05) both at the end of CPB and 2 h after CPB.

Conclusion: CPB markedly down-regulates the expression of occludin and ZO-1 proteins in intestinal mucosa of rats. The close correlation between expression of tight junctions (TJs) and plasma levels of DAO or d-lactate supports the hypothesis that intestinal permeability increases during and after CPB because of decreases in the expressions of TJs.

Figure 1

Immunohistochemical expression of occludin in the rat terminal ileum (× 40). A: Control, sham-operated, the total of epithelia cell lining villi express occludin; B: End of CPB, loss of occludin expression in about 50% enterocytes at the villi; C: 2 h after CPB, loss of occludin expression in about 85% enterocytes at the villi.

Figure 2

Immunohistochemical expression of ZO-1 in the rat terminal ileum (× 40). A: Control, shame-operated: the total of epithelia cell lining villi express ZO-1; B: End of CPB: loss of ZO-1 expression in about 50% enterocytes at the villi; C: 2 h after CPB: loss of ZO-1 expression in about 80% enterocytes at the villi.

Figure 3

Western blot analysis of occludin and ZO-1 in terminal ileums. Lane 1: Control group; Lane 2: End of CPB; Lane 3: 2 h after CPB. A: Oclludin protein expression; B: ZO-1 protein expression. Total protein was extracted from rat terminal ileums. Band densities were normalized to the mean density of saline bands and expressed as % relative content. Gel staining was used as a loading control. Bars are mean % relative content ± SE, n = 10 for each group.

Figure 4

Effect of CPB on the ileum epithelia cells (× 7200). A: CPB group, epithelia damage was demonstrated by swollen mitochondria and loss of cristae, tight junction was disrupted; B: Control group, regularly-aligned microvilli in intestinal epithelium, integral mitochondria and RER and distinct junction complex were observed.