Heme is a potent inducer of inflammation in mice and is counteracted by heme oxygenase

Various pathologic conditions, such as hemorrhage, hemolysis and cell injury, are characterized by the release of large amounts of heme. Recently, it was demonstrated that heme oxygenase (HO), the heme-degrading enzyme, and heme are able to modulate adhesion molecule expression in vitro. In the present study, the effects of heme and HO on inflammation in mice were analyzed by monitoring the biodistribution of radiolabeled liposomes and leukocytes in conjunction with immunohistochemistry. Small liposomes accumulate in inflamed tissues by diffusion because of locally enhanced vascular permeability, whereas leukocytes actively migrate into inflammatory areas through specific adhesive interactions with the endothelium and chemotaxis. Exposure to heme resulted in a dramatic increase in liposome accumulation in the pancreas, but also intestines, liver, and spleen exhibited significantly increased vascular permeability. Similarly, intravenously administered heme caused an enhanced influx of radiolabeled leukocytes into these organs. Immunohistochemical analysis showed differential up-regulation of the adhesion molecules ICAM-1, P-selectin, and fibronectin in liver and pancreas in heme-treated animals. Heme-induced adhesive properties were accompanied by a massive influx of granulocytes into these inflamed tissues, suggesting an important contribution to the pathogenesis of inflammatory processes. Moreover, inhibition of HO activity exacerbated heme-induced granulocyte infiltration. Here it is demonstrated for the first time that heme induces increased vascular permeability, adhesion molecule expression, and leukocyte recruitment in vivo, whereas HO antagonizes heme-induced inflammation possibly through the down-modulation of adhesion molecules.

Distinct effect of retroviral-mediated IFN-alpha gene transfer on human erythroleukemic and CD34+ cell growth and differentiation

Human interferon-alpha (IFN-alpha) has been used in the management of leukemia, but its diverse adverse effects may influence the ability of IFN-alpha to treat this disease. We constructed two retroviral vectors, LSN-IFN-alpha and LNC-IFN-alpha, in which IFN-alpha cDNA was driven by viral LTR and CMV promoters, respectively. After transduction into the PA317 and PG13 retroviral packaging cells, high titers of retrovirus were produced and were used to infect K562 and human BM CD34+ hematopoietic cells. The IFN-alpha gene expression in transduced K562 cells was confirmed by Northern blot, RT-PCR, RIA, and biologic assay. Cell proliferation and cell viability in IFN-alpha-transduced K562 cells were significantly suppressed as compared with control K562 cells. Although the IFN-alpha expression in K562 cells did not affect BCR/ABL expression, it apparently upregulated the production of adhesion molecules (VLA-4 and Mac-1). We evaluated the effect of IFN-alpha gene transfer on human CD34+ cells infected with LSN-IFN-alpha retrovirus with the aid of fibronectin (FN) fragment CH-296 and growth factors. RIA showed that IFN-alpha-transduced CD34+ cells produced 72.2+/-15 U/ml of IFN-alpha compared with 4.3+/-1.2 U/ml in control CD34+ cells. Methylcellulose clonogenic assay indicated that IFN-alpha-transduced CD34+ cells produced similar numbers of burst-forming units-erythrocytes (BFU-E)/colony-forming units-GM (CFU-GM) colonies as compared with control CD34+ cells. Selected colonies expressed IFN-alpha and neo(r) mRNA, as measured by RT-PCR. These studies indicate that retrovirus-mediated IFN-alpha gene transfer may provide a useful tool for studying the effect of IFN-alpha gene transfer on leukemic cells and long-lived CD34+ cells.

Differential effects of heme oxygenase isoforms on heme mediation of endothelial intracellular adhesion molecule 1 expression

Heme oxygenase (HO), by catabolizing heme to bile pigments, down-regulates cellular hemoprotein, hemoglobin, and heme; the latter generates pro-oxidant products, including free radicals. Two HO isozymes, the products of distinct genes, have been described; HO-1 is the inducible isoform, whereas HO-2 is suggested to be constitutively expressed. We studied the inducing effect of several metal compounds (CoCl(2), stannic mesoporphyrin, and heme) on HO activity. Additionally, we studied HO-1 expression in experimental models of adhesion molecule expression produced by heme in endothelial cells, and the relationship of HO-1 expression to the induced adhesion molecules. Flow cytometry analysis showed that heme induces intracellular adhesion molecule 1 (ICAM-1) expression in a concentration (10-100 microM)- and time (1-24 h)-dependent fashion in human umbilical vein endothelial cells. Pretreatment with stannic mesoporphyrin, an inhibitor of HO activity, caused a 2-fold increase in heme-induced ICAM-1 expression. In contrast, HO induction by CoCl(2) decreased heme-induced ICAM-1 expression by 33%. To examine the contribution of HO-1 and HO-2 to endothelial HO activity, specific antisense oligonucleotides (ODNs) of each isoform were tested for their specificity to inhibit HO activity in cells exposed to heme. Endothelial cells exposed to heme elicited increased HO activity, which was prevented (70%) by HO-1 antisense ODNs. HO-2 antisense ODN inhibited heme-induced HO activity by 21%. Addition of HO-1 antisense ODNs prevented heme degradation and resulted in elevation of microsomal heme. Western blot analysis showed that HO-1 antisense ODNs selectively inhibited HO-1 protein and failed to inhibit HO-2 protein. Incubation of endothelial cells with HO-1 antisense enhanced heme-dependent increase of ICAM-1. In contrast, addition of HO-2 antisense to endothelial cells failed to increase adhesion molecules. The role of glutathione, an important antioxidant, was examined on heme-induced ICAM-1 expression. Endothelial cells pretreated with a glutathione precursor, N-acetylcysteine, or glutathione ester, showed a decrease in heme-induced ICAM-1 expression of 37 and 44%, respectively, suggesting that the mechanism of ICAM-1 induction by heme may be partly dependent on the levels of antioxidant. It is possible that amelioration of the heme-induced oxidative stress and expression of ICAM-I is due, in part, to the induction of HO-1 activity. Regulation of HO activity in this manner may have clinical applications.

Heme induces the expression of adhesion molecules ICAM-1, VCAM-1, and E selectin in vascular endothelial cells

Heme is an important immunostimulating agent and oxidative factor contributing to endothelial cell activation. To investigate the mechanism of heme-induced endothelial cell activation, we analyzed the effect of heme and the inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), on the expression of the heme-degrading stress protein, heme oxygenase (HO), and adhesion molecules in human umbilical vein endothelial cells (HUVEC). Indirect immunofluorescence double labeling studies demonstrated a simultaneous increase of ICAM-1 and HO-1 after exposure of cells to heme for 24 hr. Co-expression of HO-1 and ICAM-1 was also demonstrated in TNF-alpha-exposed cells. Dot blot immunoassay and quantitative analysis by ELISA demonstrated that heme treatment for 24 hr caused a 2-fold increase in ICAM-1 expression (P < 0.002) compared with quiescent cells, while in cells stimulated by TNF-alpha for 24 hr ICAM-1 gene expression increased by 5-fold. Moreover, heme exposure also resulted in a marked increase in VCAM-1 and E selectin expression (three and four times over control levels, respectively). On the other hand, TNF-alpha treatment showed similar expression levels for VCAM-1 and E selectin, compared with stimulation by heme (100 microM). The level of HO activity in endothelial cells exposed to heme or TNF-alpha was increased from 24.7 +/- 5.7 pmol bilirubin/mg protein/min in control to 70.0 +/- 9.5 and 36.7 +/- 3.1 pmol bilirubin/mg protein/min in heme- and TNF-alpha-stimulated cells, respectively. These results suggest that upregulation of ICAM-1, VCAM-1, and E selectin expression is associated with oxidative stress induced by hemoglobin/heme and that HO-1 may play a modulating role via its ability to degrade heme to a substance with antioxidant properties.