This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Patterson, C. Articles by Runge, M. S. Search for Related Content PubMed PubMed Citation Articles by Patterson, C. Articles by Runge, M. S. Related Collections Oxidant stress Other Vascular biology ACE/Angiotension receptors Cell biology/structural biology Cell signalling/signal transduction

(Circulation Research. 2000;87:1074.)
© 2000 American Heart Association, Inc.

Editorial

The Oxidative Paradox

Another Piece in the Puzzle

Cam Patterson, Nageswara R. Madamanchi, Marschall S. Runge

From the University of North Carolina at Chapel Hill, Program in Molecular Cardiology, Division of Cardiology and Department of Medicine (C.P., N.R.M., M.S.R.) and Lineberger Comprehensive Cancer Center (C.P.), Chapel Hill, NC.

Correspondence to Marschall S. Runge, MD, PhD, Chairman, Department of Medicine, University of North Carolina at Chapel Hill, 3033 Old Clinic Building, Campus Box 7005, Chapel Hill, NC 27599-7005. E-mail mrunge{at}med.unc.edu

Key Words: atherosclerosis • oxidantstress • vascularbiology

	Introduction

Top Introduction References

 
Because atherosclerosis is a disease of many risk factors, a complex pathology, and diverse clinical manifestations, the as yet unattained Holy Grail of atherosclerosis research is a unifying pathway to explain its many aspects and provide a single point at which to measure risk or intervene in its clinical course. If vascular biology possesses such a relic, it would have many of the characteristics attributed to oxidative stress. Risk factors for atherosclerosis, such as hypertension¹ and hyperlipidemia,² are potent stimuli for the generation of reactive oxygen species (ROS) in experimental systems, and it is likely that cigarette smoking and diabetes mellitus share oxidative heritages. At the molecular level, signaling in response to proatherogenic agents, such as -thrombin,³ platelet-derived growth factor,⁴ and angiotensin II,^{5 6} requires the generation of ROS via oxidase systems. In fact, many of the hallmarks of atherosclerosis, including endothelial dysfunction, smooth muscle cell (SMC) proliferation, and inflammatory recruitment, occur in response to ROS. In this issue of Circulation Research, Schieffer et al⁷ contribute to our understanding of these events by demonstrating that angiotensin II–induced cytokine activation via the Janus kinase/signal transducer and activator of transcription (STAT) pathway requires oxidant generation by the NAD(P)H oxidase in SMCs. Their data are consistent with the notion that ROS are central mediators of adverse events in atherosclerosis. The oxidative paradox, then, is the inability of clinical investigators to definitively demonstrate that modulation of ROS by the use of antioxidant therapies has any effect on atherogenesis.

Angiotensin II is the best-characterized stimulus for ROS generation in SMCs.^{5 6} The study by Schieffer et al⁷ describes the role of ROS as stimuli for inflammatory events that may contribute to plaque instability. Although many of the issues raised in this study have been addressed previously,^{3 5} the nature of the NAD(P)H oxidase that likely generates ROS in SMCs merits attention. The classical NAD(P)H oxidase described in neutrophils consists of several components, p22^phox, p67^phox, p47^phox, gp91^phox, and a rac GTPase, that are recruited to create the oxidative burst. The study by Schieffer et al⁷ is the second to implicate a particular component of this oxidase, p47^phox, in the oxidase of SMCs.³ Using electroporated antibodies to target p47^phox, they find that this protein (and presumably the oxidase in which it participates) is necessary for ROS generation, STAT activation, and interleukin-6 synthesis elicited by angiotensin II. It should be noted that their data, although compelling, are not conclusive in this regard. Decreased p47^phox protein in cells electroporated with an anti-p47^phox antibody may indicate decreased de novo p47^phox protein synthesis. However, neutralizing-antibody experiments are notoriously difficult to interpret, and alternative explanations include the possibility that p47^phox-antibody complexes are insoluble or that antibody binding to p47^phox elicits its degradation.

p47^phox is not the only component of the SMC oxidase shared with the neutrophil oxidase. There is also good evidence that p22^phox is present in both.⁸ However, equally compelling evidence points to critical differences in the phagocytic and nonphagocytic oxidases. First, these oxidases have important differences in substrate use. The neutrophil oxidase consumes NADPH preferentially, whereas the SMC oxidase favors NADH.^{3 6} Second, the amounts of ROS generated by these oxidases differ by several orders of magnitude and also differ in the rate by which ROS is generated. Third, evidence is mounting that the components of these two oxidases differ structurally. A member of the gp91^phox family, NOX1, probably participates in the SMC oxidase in place of gp91^phox9 ; and p67^phox has been difficult to detect in SMCs,³ indicating that it may either be dispensable or replaced by another component.

The novel structure of the SMC oxidase (and perhaps other nonphagocytic oxidases) may explain how these oxidases mediate nonmicrobicidal functions, particularly by generation of ROS at slower rates and lower intracellular concentrations. Perhaps more importantly, it is possible that the function of the SMC oxidase can be regulated independently of oxidase systems in other cell types, a significant point if oxidases in nonvascular cells are essential for other purposes. The present study provides confirmatory evidence that p47^phox is a component of the SMC oxidase. Identification and reconstitution of the SMC oxidase, which we anticipate would include additional novel components in comparison with the neutrophil oxidase, will be crucial to our understanding of the atherogenic role of ROS. It should also be emphasized that a component of the SMC oxidase, the Rac1 GTPase, may also regulate signaling independently of ROS generation by directly interacting with and activating STAT proteins.¹⁰ The relevance of such interactions, as demonstrated in the study by Schieffer et al,⁷ provides additional justification for the complete characterization of the SMC oxidase.

Regardless of how ROS are generated, it is easy to overwhelm their production with reducing agents and antioxidants in experimental studies, which is the crux of the oxidative paradox of atherosclerosis. The data regarding the use of antioxidants (eg, vitamin E) for prevention of atherosclerosis do not presently support their use in cardiovascular diseases^{11 12 13 14} (see Table). This conundrum poses perhaps the greatest challenge to vascular biologists interested in the role of ROS in atherogenesis. How can there be such a divergence between clinical data and studies in experimental models? It is worth considering the following possibilities.

View this table: [in this window] [in a new window]   Table 1. Randomized Trials of Vitamin E Supplementation in Patients With Coronary Artery Disease

First, the vitamin preparations may not be efficient oxidant scavengers in vivo. Redox reactions are complicated, and the potential exists for paradoxical electron transfer by antioxidant vitamins that results in additional oxidant generation.¹⁵ In addition, some vitamin formulations available for human use (vitamin E in particular) are relatively inefficient in their antioxidant functions in vivo.¹⁶ Our understanding of how the antioxidants available for human use affect oxidative stress in the circumstances described by Schieffer et al⁷ is still at a relatively superficial level.

Second, ROS that are detrimental to vascular function may be compartmentalized at designated sites within the cell. For example, production of ROS occurs by different mechanisms in the cytoplasm and mitochondria, and distinct cellular mechanisms exist to detoxify ROS present in these two compartments. Accumulation of oxidative injury in mitochondria may be particularly detrimental to vascular cells.¹⁷

Third, antioxidants may have subtle toxicities that mask their beneficial effects on vascular functions in vivo. Cells have evolved means to generate ROS for a reason, and quenching them randomly may have undesired effects, especially when administered on a chronic basis.¹⁸ Cell type–specific delivery of antioxidants may be one means to maximize the therapeutic benefit of these agents.

Fourth, similar to hypertension or hyperlipidemia, increased oxidative stress may be a risk factor for only a subset of patients with atherosclerosis, albeit a subset we presently have no easy way to identify. Measuring markers of oxidative injury, such as circulating lipid peroxides¹⁹ or mitochondrial DNA damage,¹⁷ is a promising, but as yet unproven, means to identify patients who might benefit from antioxidant therapy.

Although several important studies, including the present work by Schieffer et al,⁷ emphasize the role ROS play in cellular events critical to atherosclerosis, we need to recognize that our understanding of the relationship between oxidative stress and vascular lesion formation is still fairly naive. We are far enough along to recognize that there is an oxidative paradox but not far enough along to solve it.

	Footnotes

 
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.

	References

Top Introduction References

 

1. Somers MJ, Mavromatis K, Galis ZS, Harrison DG. Vascular superoxide production and vasomotor function in hypertension induced by deoxycorticosterone acetate-salt. Circulation. 2000;101:1722–1728.[Abstract/Free Full Text]
2. Galle J, Schneider R, Heinloth A, Wanner C, Galle PR, Conzelmann E, Dimmeler S, Heermeier K. Lp(a) and LDL induce apoptosis in human endothelial cells and in rabbit aorta: role of oxidative stress. Kidney Int. 1999;55:1450–1461.[Medline] [Order article via Infotrieve]
3. Patterson C, Ruef J, Madamanchi NR, Barry-Lane P, Hu Z, Horaist C, Ballinger CA, Brasier AR, Bode C, Runge MS. Stimulation of a vascular smooth muscle cell NAD(P)H oxidase by thrombin. J Biol Chem. 1999;274:19814–19822.[Abstract/Free Full Text]
4. Sundaresan M, Yu Z-X, Ferrans VJ, Irani K, Finkel T. Requirement for generation of H₂O₂ for platelet-derived growth factor signal transduction. Science. 1995;270:296–299.[Abstract/Free Full Text]
5. Zafari AM, Ushio-Fukai M, Akers M, Yin Q, Shah A, Harrison DG, Taylor WR, Griendling KK. Role of NADH/NADPH oxidase-derived H₂O₂ in angiotensin II-induced vascular hypertrophy. Hypertension. 1998;32:488–495.[Abstract/Free Full Text]
6. Griendling KK, Minieri CA, Ollerenshaw JD, Alexander RW. Angiotensin II stimulates NADH and NADPH oxidase activity in cultured vascular smooth muscle cells. Circ Res. 1994;74:1141–1148.[Abstract/Free Full Text]
7. Schieffer B, Luchtefeld M, Braun S, Hilfiker A, Hilfiker-Kleiner D, Drexler H. Role of NAD(P)H oxidase in angiotensin II–induced JAK/STAT signaling and cytokine induction. Circ Res. 2000;87:1195–1201.[Abstract/Free Full Text]
8. Ushio-Fukai M, Zafari AM, Fukui T, Ishizaka N, Griendling KK. p22^phox Is a critical component of the superoxide-generating NADH/NADPH oxidase system and regulates angiotensin II-induced hypertrophy in vascular smooth muscle cells. J Biol Chem. 1996;271:23317–23321.[Abstract/Free Full Text]
9. Suh YA, Arnold RS, Lassegue B, Shi J, Xu X, Sorescu D, Chung AB, Griendling KK, Lambeth JD. Cell transformation by the superoxide-generating oxidase Mox1. Nature. 1999;401:79–82.[Medline] [Order article via Infotrieve]
10. Simon AR, Vikis HG, Stewart S, Fanburg BL, Cochran BH, Guan K-L. Regulation of STAT3 by direct binding to the Rac1 GTPase. Science. 2000;290:144–147.[Abstract/Free Full Text]
11. Yusuf S, Dagenais G, Pogue J, Bosch J, Sleight P. Vitamin E supplementation and cardiovascular events in high-risk patients. N Engl J Med. 2000;342:154–160.[Abstract/Free Full Text]
12. GISSI-Prevenzione Investigators. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Lancet. 1999;354:447–455.[Medline] [Order article via Infotrieve]
13. Rapola JM, Virtamo J, Ripatti S, Huttunen JK, Albanes D, Taylor PR, Heinonen OP. Randomised trial of -tocopherol and ß-carotene supplements on incidence of major coronary events in men with previous myocardial infarction. Lancet. 1997;349:1715–1720.[Medline] [Order article via Infotrieve]
14. Stephens NG, Parsons A, Schofield PM, Kelly F, Cheeseman K, Mitchinson MJ. Randomised controlled trial of vitamin E in patients with coronary artery disease: Cambridge Heart Antioxidant Study (CHAOS). Lancet. 1996;347:781–786.[Medline] [Order article via Infotrieve]
15. Podmore ID, Griffiths HR, Herbert KE, Mistry N, Mistry P, Lunec J. Vitamin C exhibits pro-oxidant properties. Nature. 1998;392:559.[Medline] [Order article via Infotrieve]
16. Patterson C, Ballinger S, Stouffer GA, Runge MS. Antioxidant vitamins: sorting out the good and not so good. J Am Coll Cardiol. 1994;34:1216–1218.
17. Ballinger SW, Patterson C, Yan CN, Doan R, Burow DL, Young CG, Yakes FM, Van Houten B, Ballinger CA, Freeman BA, Runge MS. Hydrogen peroxide- and peroxynitrite-induced mitochondrial DNA damage and dysfunction in vascular endothelial and smooth muscle cells. Circ Res. 2000;86:960–966.[Abstract/Free Full Text]
18. Rowe PM. ß-Carotene takes a collective beating. Lancet. 1996;347:249.[Medline] [Order article via Infotrieve]
19. Li H, Lawson JA, Reilly M, Adiyaman M, Hwang SW, Rokach J, FitzGerald GA. Quantitative high performance liquid chromatography/tandem mass spectrometric analysis of the four classes of F(2)-isoprostanes in human urine. Proc Natl Acad Sci U S A. 1999;96:13381–13386.[Abstract/Free Full Text]

This article has been cited by other articles:

				N. R. Madamanchi, A. Vendrov, and M. S. Runge Oxidative Stress and Vascular Disease Arterioscler. Thromb. Vasc. Biol., January 1, 2005; 25(1): 29 - 38. [Abstract] [Full Text] [PDF]

				M. Mehrabian, H. Allayee, J. Wong, W. Shih, X.-P. Wang, Z. Shaposhnik, C. D. Funk, and A. J. Lusis Identification of 5-Lipoxygenase as a Major Gene Contributing to Atherosclerosis Susceptibility in Mice Circ. Res., July 26, 2002; 91(2): 120 - 126. [Abstract] [Full Text] [PDF]

				C. Patterson, G. A. Stouffer, N. Madamanchi, and M. S. Runge New Tricks for Old Dogs : Nonthrombotic Effects of Thrombin in Vessel Wall Biology Circ. Res., May 25, 2001; 88(10): 987 - 997. [Abstract] [Full Text] [PDF]

				G. A. Stouffer, C. Patterson, N. Madamanchi, and M. S. Runge Role of Reactive Oxygen Species in Angiotensin II Signaling : The Plot Thickens Arterioscler. Thromb. Vasc. Biol., April 1, 2001; 21(4): 471 - 472. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Patterson, C. Articles by Runge, M. S. Search for Related Content PubMed PubMed Citation Articles by Patterson, C. Articles by Runge, M. S. Related Collections Oxidant stress Other Vascular biology ACE/Angiotension receptors Cell biology/structural biology Cell signalling/signal transduction