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Xenograft rejection are due to the activation of endothelial cells and the expression of a series of proinflammatory genes encoding adhesion molecules, cytokines/chemokines and procoagulant molecules,leading to endothelial cell injury and apoptosis. HO-1 which acts as a cytoprotective gene can suppress a variety of inflammatory responses to prevent graft rejection. In this study, The plasmid containing HO-1 cDNA was constructed and transfected into human vascular endothelial cells (HUVEC) for expression using DOTAP lipsomal transfection reagents. Cells were homogenized in cell culture lysis reagent (CCLR) and the activity of HO-1 was measured. The apoptosis of HUVEC induced by tumor necrosis factor (TNF)-alpha was analyzed by flow cytometry. Meanwhile, Heme and Sn-protoporphyrin (SnPP) were added respectively to evaluate the apoptosis rate of HUVEC. The results showed that the expression of HO-1 gene can be significantly up-regulated in HUVEC transfected with pcDNA3HO1. The apoptosis rate of cells treated with Heme was less than 20% but significantly increased when cells treated with SnPP, the maximum arrived at 95%. The apoptosis rate in heme induced cells was 5-20 times lower than that in SnPP inhibited cells. The apoptosis rate was a negative relation to HO-1 expression. HO-1 protein can inhibit apoptosis in HUVEC. The results provide evidence to support the essential role of HO-1 in the cytoprotective function.

Human Heme Oxygenase-1 (hHO-1) is the rate-limiting enzyme in the catabolism reaction of heme, which directly regulates the concentration of bilirubin in human body. The mutant structure was simulated by Swiss-pdbviewer procedure, which showed that the structure of active pocket was changed distinctly after Ala25 substituted for His25 in active domain, but the mutated enzyme still binded with heme. On the basis of the results, the expression vectors, pBHO-1 and pBHO-1(M), were constructed, induced by IPTG and expressed in E. coli DH5alpha strain. The expression products were purified with 30%-60% saturation (NH4)2SO4 and Q-Sepharose Fast Flow column chromatography. The concentration of hHO-1 in 30%-60% saturation (NH4)2SO4 components and in fractions through twice column chromatography was 3.6-fold and 30-fold higher than that in initial product, respectively. The activity of wild hHO-1 (whHO-1) and mutant hHO-1 (deltahHO-1) showed that the activity of deltahHO-1 was reduced 91.21% compared with that of whHO-1. The study shows that His25 is of importance for the mechanism of hHO-1, and provides the possibility for effectively regulating the activity to exert biological function.