Vascular Redox Processes

Group Leader: Professor Roland Stocker

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Overview of Research

The "Oxidative Modification Theory of Atherosclerosis" predicts that oxidative modification of low-density lipoprotein (LDL) is an early event in and a cause of atherogenesis. Indeed, heightened oxidative stress and oxidative modifications to LDL are key features of atherosclerosis and related diseases. However, atherosclerosis-associated oxidative modifications are not specific for, or limited to, LDL. Also, large prospective studies testing the protective role of natural antioxidants such as vitamin E on cardiovascular disease outcome have yielded disappointing results. This questions the relationship of LDL oxidation and atherosclerosis, as well as the role antioxidants may play in these processes. Past work of our group has helped explain why vitamin E fails to provide protection against atherosclerosis. We have also shown that, in contrast to vitamin E, the synthetic antioxidant probucol consistently prevents atherosclerotic vascular diseases in animals. This protection does not depend on inhibition of LDL oxidation in diseased vessels, but instead requires the drug to induce the protein heme oxygenase-1 (HO-1). We have identified the chemical parts of probucol required for its in vivo efficacy and, in conjunction with industry, are aiming at developing some of our patented novel compounds as anti-atherosclerotic drugs.

Our research aims to understanding how redox processes contribute to atherosclerosis, related disorders and diabetes; and how this can be exploited to develop novel therapeutics.

Current Work

1. A major focus of our work is increasing the existing knowledge in HO-1 biology, at the cellular, tissue, and whole body level. The aim is to better understand how induction of the enzyme results in so many different biological benefits, including anti-inflammatory activity, increased protection provided to the endothelium against injury and dysfunction, and the control of cell growth. An immerging interest is the role of HO ‑ 1 in diabetes.
2. We continue studying the regulation and biological function of the enzyme indoleamine 2,3-dioxygenase (IDO), with a particular focus on its role in the control of vascular tone under conditions of inflammation and oxidative stress, including cardiovascular diseases.
3. We are assessing the utility of a recently generated monoclonal antibody that recognizes oxidized high-density lipoprotein as a diagnostic for cardiovascular disease.
4. We are developing analytical tools to assess the occurrence of oxidative processes in different cellular compartments and quantify their contribution to cellular functions.

Research Approach and Equipment

Our research approach is multidisciplinary, ranging from chemical synthesis to human applications, the latter through our links with the Department of Cardiology at the Royal Prince Alfred Hospital. We utilize purified enzymes, yeast genetics, mammalian cell culture, blood vessels and other tissue, histology, various animal models of atherosclerotic vascular disease and diabetes, and human tissue. The technologies employed include analytical tools (in biochemistry, chemistry and physics), cell and molecular biological tools, functional studies related to blood vessels, histology and immunohistochemistry, microscopy and state-of-the art imaging, as well as morphometry and whole body metabolic tests.

Recent Milestones and Important Events

1. Licensed IP related to novel molecules as anti-atherosclerotic agents to pharmaceutical company in the United States.
2. Identified cytochrome b 5 as a cellular reductant for the enzyme indoleamine 2,3-dioxygenase.
3. Dr Sabine Wimmer-Kleikamp, a CJ Martin Fellow, joined the group in February 2008.

Current Projects (all suitable for PhD Students)

1. The role of HO - 1 in diabetes, and novel HO ‑ 1 inducers as anti-diabetic agents
2. HO - 1-mediated mobilization of progenitor cells and their participation in tissue repair
3. Cellular signaling related to HO - 1 induction and downstream effector molecules
4. Cellular responses to adversity: protection against oxidative damage in yeast
5. Identify how probucol and related molecules induce HO-1, and how this translates into the various protective cellular effects
6. The role of an tryptophan-metabolizing enzyme in the formation of a novel endothelium-derived vascular relaxing factor produced during inflammation in animals and humans
7. Cross-regulation of indoleamine 2,3-dioxygenase and other enzymes involved in the regulation of vascular tone
8. Sensitive and specific methods to determine compartmentalized cellular oxidative stress
9. Novel markers of oxidative stress and their utility in the diagnosis of cardiovascular disease

Group Members

Key Publications

Maghzal G, Thomas SR, Hunt NH, Stocker R. Cytochrome b 5, not superoxide anion radical, is the major reductant of indoleamine 2,3 - dioxygenase in human cells. J Biol Chem 2008;in press.

Wu BJ, Di Girolamo N, Beck K, Hanratty CG, Choy K, Hou JY, Ward MR, Stocker R. Probucol retards compensatory arterial remodeling in apolipoprotein E deficient mice by decreasing macrophage and matrix metalloproteinases-2 and -9. J Pharmacol Exp Ther 2007;321:477-484

Witting PK, Rayner BS, Wu BJ, Ellis NA, Stocker R. Hydrogen peroxide promotes vascular dysfunction by decreasing nitric oxide bioavailability. Cell Physiol Biochem 2007;20:255-268

Thomas SR, Terentis AC, Cai H, Takikawa O, Levina A, Lay PA, Freewan M, Stocker R. Post-translational regulation of human indoleamine 2,3-dioxygenase activity by nitric oxide. J Biol Chem 2007;282:23778-23787

Hunt NH , Stocker R. Heme moves to center stage in cerebral malaria. Nat Med 2007;13:667-669

Wu BJ, Kathir K, Witting PK, Beck K, Choy K, Li C, Croft KD, Mori TA, Tanous D, Adams MR, Lau AK, Stocker R. Antioxidants protect from atherosclerosis by a heme oxygenase-1 pathway that is independent of free radical scavenging. J Exp Med 2006;203:1117-1127

Stocker R, Perrella MA. Heme oxygenase ‑ 1: A novel drug target for atherosclerotic diseases? Circulation 2006;114:2178-2189

Rayner BS, Wu BJ, Raftery M, Stocker R, Witting PK. Human S-nitroso-myoglobin is a store of vasoactive nitric oxide. J Biol Chem 2005;280:9985-9993

Witting PK, Wu BJ, Raftery M, Southwell-Keely P, Stocker R. Probucol protects against hypochlorite-induced endothelial dysfunction: identification of a novel pathway of probucol oxidation to a biologically active intermediate. J Biol Chem 2005;280:15612-15618

Deng YM, Wu B, Witting PK, Stocker R. Probucol protects against smooth muscle cell proliferation by up-regulating heme oxygenase-1. Circulation 2004;110:1861-1866

Stocker R, Keaney JF, Jnr. The role of oxidative modifications in atherosclerosis. Physiol Rev 2004;84:1381-1478