Ruiping Song

Carbon monoxide suppresses arteriosclerotic lesions associated with chronic graft rejection and with balloon injury

Carbon monoxide (CO), one of the products of heme oxygenase action on heme, prevents arteriosclerotic lesions that occur following aorta transplantation; pre-exposure to 250 parts per million of CO for 1 hour before injury suppresses stenosis after carotid balloon injury in rats as well as in mice. The protective effect of CO is associated with a profound inhibition of graft leukocyte infiltration/activation as well as with inhibition of smooth muscle cell proliferation. The anti-proliferative effect of CO in vitro requires the activation of guanylate cyclase, the generation of cGMP, the activation of p38 mitogen-activated protein kinases and the expression of the cell cycle inhibitor p21Cip1. These findings demonstrate a protective role for CO in vascular injury and support its use as a therapeutic agent.

Carbon Monoxide Induces Cytoprotection in Rat Orthotopic Lung Transplantation via Anti-Inflammatory and Anti-Apoptotic Effects

Successful lung transplantation has been limited by the high incidence of acute graft rejection. There is mounting evidence that the stress response gene heme oxygenase-1 (HO-1) and/or its catalytic by-product carbon monoxide (CO) confers cytoprotection against tissue and cellular injury. This led us to hypothesize that CO may protect against lung transplant rejection via its anti-inflammatory and antiapoptotic effects. Orthotopic left lung transplantation was performed in Lewis rat recipients from Brown-Norway rat donors. HO-1 mRNA and protein expression were markedly induced in transplanted rat lungs compared to sham-operated control lungs. Transplanted lungs developed severe intraalveolar hemorrhage, marked infiltration of inflammatory cells, and intravascular coagulation. However, in the presence of CO exposure (500 ppm), the gross anatomy and histology of transplanted lungs showed marked preservation. Furthermore, transplanted lungs displayed increased apoptotic cell death compared with the transplanted lungs of CO-exposed recipients, as assessed by TUNEL and caspase-3 immunostaining. CO exposure inhibited the induction of IL-6 mRNA and protein expression in lung and serum, respectively. Gene array analysis revealed that CO also down-regulated other proinflammatory genes, including MIP-1alpha and MIF, and growth factors such as platelet-derived growth factor, which were up-regulated by transplantation. These data suggest that the anti-inflammatory and antiapoptotic properties of CO confer potent cytoprotection in a rat model of lung transplantation.

Carbon Monoxide Inhibits T Lymphocyte Proliferation via Caspase-Dependent Pathway

T lymphocyte activation and proliferation is involved in many pathological processes. We have recently shown that carbon monoxide (CO), an enzymatic product of heme oxyenase-1 (HO-1), confers potent antiproliferative effects in airway and vascular smooth muscle cells. The purpose of this study was to determine whether CO can inhibit T lymphocyte proliferation and then to determine the mechanism by which CO can modulate T lymphocyte proliferation. In the presence of 250 parts per million CO, CD3-activated T lymphocyte proliferation was, remarkably, inhibited by 80% when compared with controls. We observed that the antiproliferative effect of CO in T lymphocytes was independent of the mitogen-activated protein kinase or cGMP signaling pathways, unlike what we demonstrated previously in smooth muscle cells. We demonstrate that CO inhibited caspase-3 and caspase-8 expression and activity, and caspase inhibition with benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK pan-caspase inhibitor) blocked T lymphocyte proliferation. Furthermore, in caspase-8-deficient lymphocytes, the antiproliferative effect of CO was markedly attenuated, further supporting the involvement of caspase-8 in the antiproliferative effects of CO. CO also increased the protein level of p21Cip1, and CO-mediated inhibition of caspase activity is partially regulated by p21Cip1. Taken together, these data suggest that CO confers potent antiproliferative effects in CD3-activated T lymphocytes and that these antiproliferative effects in T lymphocytes are mediated by p21Cip1-dependent caspase activity, in particular caspase-8, independent of cGMP and mitogen-activated protein kinase signaling pathways.

Carbon Monoxide Suppresses Bleomycin-Induced Lung Fibrosis

Idiopathic pulmonary fibrosis is an incurable fibrosing disorder that progresses relentlessly to respiratory failure. We hypothesized that a product of heme oxygenase activity, carbon monoxide (CO), may have anti-fibrotic effects. To test this hypothesis, mice treated with intratracheal bleomycin were exposed to low-concentration inhaled CO or ambient air. Lungs of mice treated with CO had significantly lower hydroxyproline accumulation than controls. Fibroblast proliferation, thought to play a central role in the progression of fibrosis, was suppressed by in vitro exposure to CO. CO caused increased cellular levels of p21(Cip1) and decreased levels of cyclins A and D. This effect was independent of the observed suppression of MAPKs phosphorylation by CO but was dependent on increased cGMP levels. Further, CO-exposed cells elaborated significantly less fibronectin and collagen-1 than control cells. This same effect was seen in vivo. Suppression of collagen-1 production did not depend on MAPK or guanylate cyclase signaling pathways but did depend on the transcriptional regulator Id1. Taken together, these data suggest that CO exerts an anti-fibrotic effect in the lung, and this effect may be due to suppression of fibroblast proliferation and/or suppression of matrix deposition by fibroblasts.

Hepatocyte Growth Factor Protects against Hypoxia/Reoxygenation-induced Apoptosis in Endothelial Cells

Hypoxia/reoxygenation causes cellular injury and death associated with a number of pathophysiological conditions, including myocardial ischemia/reperfusion injury and stroke. The cell death pathways induced by hypoxia/reoxygenation and their underlying regulatory mechanisms remain poorly understood. Recent studies have shown that hypoxia/reoxygenation can induce Bax translocation and cytochrome c release. Using murine lung endothelial cells as a model, we found that the induction of apoptosis by hypoxia/reoxygenation involved the activation of both Bax-dependent and death receptor-mediated pathways. We demonstrated the activation of the death-inducing signal complex and Bid pathway after hypoxia/reoxygenation. Hepatocyte growth factor markedly inhibited hypoxia/reoxygenation-induced endothelial cell apoptosis. The cytoprotection afforded by hepatocyte growth factor was mediated in part by the stimulation of FLICE-like inhibiting protein expression, the attenuation of death-inducing signal complex formation, and the inhibition of Bid and Bax activation. Hepatocyte growth factor also prevented cell injury and death by increasing the expression of the antiapoptotic Bcl-XL protein. The inhibition of Bid/Bax-induced cell death by hepatocyte growth factor primarily involved p38 MAPK and in part Akt-dependent pathways but not ERK1/ERK2.

Heme Oxygenase-1 and Transplantation

The discovery of nitric oxide (NO) in 1987 unraveled the novel concept that an endogenous production of a gaseous substance such as NO can impart diverse and critical functional effects on a wide spectrum of biological and pathological processes. These investigations have led to numerous fruitful discoveries, enhancing our understanding of many disease processes including lung disorders. Interestingly though, we have known for a longer period of time that there exists another gaseous molecule, carbon monoxide (CO), which can be generated endogenously; that is, the heme oxygenase (HO) enzyme system generates the majority, if not, all of the endogenous CO’. Since the isolation of the HO enzyme in 1968, the major focus of HO research was in the study of HO in heme metabolism based on the known fact that the HO enzyme serves as the rate-limiting enzyme in the degradation of heme. However, in recent years, due to the emerging role of HO in a variety of biological processes, interest in HO has continued to grow beyond its role in heme metabolism and expanded into many scientific disciplines. The recent discovery of the HO enzyme system not only in yeast, but also in the prokaryotic bacterial system and in plants further highlights the functional importance of a highly conserved enzyme throughout the evolution of living organisms’.