AA Oxidopathy Part One
Majid Ali, M.D.
The Core Pathogenetic Mechanism of Ischemic Heart Disease
Majid Ali, M.D., Omar Ali, M.D.
Ali M, Ali O. AA Oxidopathy: the core pathogenetic mechanism of ischemic heart disease.
J Integrative Medicine 1997;1:1-112.
From the Departments of Medicine, Capital University of Integrative Medicine, Washington, D.C., and Institute of Preventive Medicine, New York (MA and OA), and Department of Pathology, College of Physicians and Surgeons of Columbia University, New York (MA).
Outline of Part I
Spontaneity of Oxidation in Nature and Disease
Molecular Duality of Oxygen
Morphology of Atherosclerosis
Morphologic Patterns of AA Oxidopathy
AA Oxidopathy Is Consistent with All Known Molecular Dynamics of Ischemic Heart Disease (IHD)
Mycotoxicosis and AA Oxidopathy
Oxidative Cell and Plasma Membranes Dysfunction (Leaky Cell Membrane Dysfunction)
The Cholesterol Theory Has a Poor Explanatory Power for Atherogenesis and Related Clinical Phenomena
Outline of Part II
AA Oxidopathy Is the Common Denominator of IHD Risk Factors
AA Oxidopathy Hypothesis Versus and Other Proposed Theories of IHD
Why Therapies Based on the Cholesterol Theory Give Poor Results
Poor Long-Term Results of Mechanical Interventional Cardiology
The New Evolving Integrative Molecular Cardiology
Clinical Outcome Studies
Summary and Future Directions
We propose that ischemic heart disease (IHD) is caused by “AA oxidopathy”—a state of accelerated oxidative molecular injury to blood corpuscles and plasma components. Although AA oxidopathy eventually results in the formation of “microclots” and “microplaques” in the circulating blood, it begins with oxidative permutations of plasma sugars, proteins, lipids and enzymes, and is not merely confined to oxidative activation of recognized coagulation pathways that we collectively designate as “oxidative coagulopathy.” AA oxidopathy comprises localized areas of blood cell damage and congealing of plasma in its early stages, fibrin clots and thread formation with platelet entrapment in the intermediate stages, and “microclot” and “microplaque” formation in late stages. Such changes can be directly observed in peripheral blood smears with high-resolution phase-contrast and darkfield microscopy. As observed microscopically, the early changes of oxidative coagulopathy are reversible and constitute what we designate as “clotting-unclotting equilibrium (CUE).” The AA oxidopathy hypothesis seeks to establish oxidative “clotting-unclotting disequilibrium (CUD)” and related molecular and cellular events occurring in the circulating blood as the primary pathogenetic elements of IHD, and the patterns of tissue injuries taking place in the vessel wall (atheroma formation, scarring and rupture) as consequential events. Coronary vasospasm and membrane depolarization dysfunctions of myocytes as well as of the conducting system of myocardium are induced by AA oxidopathy and constitute nonatherogenic components of IHD. This hypothesis challenges two fundamental assumptions of the prevailing cholesterol, inflammatory, infectious, autoimmune and gene hypotheses: 1) that IHD is caused by initial tissue injury occurring in the arterial wall; and 2) that optimal therapeutic approaches must focus on lowering blood cholesterol levels and/or revascularization procedures such as angioplasty and coronary bypass surgery.
AA oxidopathy is caused by oxidant stressors of all types; however, our morphologic observations lead us to recognize the following five groups of oxidants as the principal factors in its pathogenesis: 1) chronic adrenergic hypervigilence associated with lifestyle stressors; 2) rapid glucose-insulin shifts and hyperinsulinemia; 3) mycotoxins and, to lesser degrees, other microbial oxidants; 4) dysequilibrium among nutrients with oxidant and antioxidant functions; and 5) ecologic oxidants. Native, unoxidized cholesterol, a weak antioxidant, plays no direct role in the pathogenesis of IHD, which is an oxidative phenomenon. Clinical outcome data obtained with nondrug, nonsurgical therapies that arrest and reverse AA oxidopathy without addressing issues of blood lipid levels validate the theoretical tenets of the proposed hypothesis.
Why should any hypothesis be put forth? One reason is to seek a simpler concept that integrates new observations with established knowledge. A second reason is to merge the seemingly incongruous parts to facilitate comprehension of the whole. In clinical medicine, the compelling justification for a new hypothesis is to provide the scientific basis and/or rationale for therapies that are more logical, safer and clinically more effective than those based on preexisting theories. We believe the proposed AA oxidopathy hypothesis meets all of the above three criteria. (Letters AA stand for the names of the two authors and are added to the term oxidopathy to differentiate it from the myriad oxidative phenomena in human biology in health and disease.) We introduce the term oxidative coagulopathy for a state of accelerated oxidative intravascular clotting involving known coagulative pathways. The term AA oxidopathy represents a much broader range of oxidative injury to all the components of circulating blood, as well as coronary arteries, cardiac myocytes and the conducting system of the heart, that play various roles in pathogenesis of IHD. In the context of coronary artery disease, our high-resolution, phase-contrast observations are new and are not explained by the existing cholesterol, inflammatory, autoimmune and gene activation/mutation theories of pathogenesis of atherosclerosis. The concept of AA oxidopathy is simple and integrates the new observations with established knowledge. Finally, as we demonstrate later in this article, AA oxidopathy provides a sound scientific basis for therapies that are more logical, safer and clinically more effective than those based on existing cholesterol, inflammatory, infectious, autoimmune and gene theories of atherosclerosis.
In introducing our hypothesis that AA oxidopathy is the core pathogenetic mechanism of IHD, we address the following five basic questions:
1. Since blood is the medium of the circulatory system, should inquiry into the pathogenesis of IHD be directed to the primary events occurring in the circulating blood rather than to secondary changes in the arterial wall that result in atheroma formation?
2. Since all the primary plasma and cell membrane events occurring in the circulating blood are oxidative in nature and since cholesterol is an antioxidant, is the prevailing focus on blood cholesterol as the centerpiece molecule under scrutiny in experimental and clinical research justified?
3. Do the cholesterol, inflammatory, infectious, autoimmune and gene hypotheses adequately explain the pathogenetic mechanisms of the established risk factors of IHD?
4. Does the proposed AA oxidopathy hypothesis completely explain the pathogenetic mechanisms of all of the established risk factors of IHD?
5. How effective are the long-term clinical outcomes of therapies for reversing IHD that are based on the cholesterol, inflammatory, infectious, autoimmune and gene mutation hypotheses? How effective are the therapies based on the AA oxidopathy hypothesis?
In 1983, one of us (MA) published the hypothesis that the phenomenon of spontaneity of oxidation in nature is the core mechanism of molecular and cellular injury in all diseases.1 Since the publication of that hypothesis, we have surveyed a host of natural oxidative phenomena and drawn support for the hypothesis.2-8 The notion that a single mechanism can serve as the core pathogenetic mechanism of molecular injury in all disease processes appears too simplistic to be valid. Yet, diligent search of the literature of oxidative phenomena in nature and biology fails to uncover any evidence to the contrary.9
Specifically, we have investigated oxidative phenomena in peripheral blood in a variety of clinical settings9-11 and have described reversibility of oxidatively induced erythrocyte membrane deformities by ascorbic acid in patients with chronic fatigue syndrome12 and dissociation of aggregates caused in vitro by norepinephrine, collagen and ADP by ascorbic acid in healthy subjects.13
The evolution of the core concepts of AA oxidopathy and oxidative coagulopathy was preceded by our recognition of the many roles of oxidative phenomena in our microscopic findings in patients with IHD and a host of other disorders.14-31 Specifically, we observed microscopic evidence of cardiac myocytolysis in cardiomyopathy14-15and myocardial fibrosis associated with iron,16-18 calcium19 and oxalate20-21 deposits in hemodialysis patients. Some parallel morphologic observations concerned vascular intimal proliferative changes and other vascular alterations in hemodialysis patients.22-23 We also documented anatomic and enzymatic evidence of ischemic myocardial injury unaccompanied by occlusive coronary artery disease.25-26 We have also discussed many clinical implications of the hypothesis of spontaneity of oxidation in integrative medicine in areas of clinical nutrition,27 fitness,28 adrenergic hypervigilence,29 and meditative and self-regulatory methods for reducing stress associated with lifestyle elements.9,30,31
During over a decade of our clinical work based on our concepts of oxidative injury, we examined freshly prepared and unstained smears of peripheral blood of several hundred patients with a host of degenerative, immune, nutritional, and ecologic disorders, as well as smears of healthy subjects, to establish a frame of reference for the range of high-resolution morphologic patterns in health and disease. For this report, we also examined 100 consecutive patients who presented with ischemic heart disease as assessed by clinical evaluation, electrocardiography, stress test, thallium perfusion scans and coronary angiography to define specifically the morphologic patterns of oxidative injury in IHD which we present here. In 1995, such experimental and clinical observations led us to define ischemic coronary artery disease as a specific example of disease processes that are initiated by oxidative injury.9 In a companion article in this issue of the Journal and two others appearing in the next issue, we present clinical outcome data obtained in patients with advanced IHD, periphery vascular and renal failure.32-34
Several lines of chemical and clinical evidence for the oxidation hypothesis of ischemic heart disease have been developed during the last 15 years.35-50 There have also been dissenting voices.51 The proponents of the oxidation theory assumed “that the oxidative modification of LDL occurs primarily in the arterial intima, in microdomains sequestered from antioxidants in plasma.”41 It has been further assumed that if oxidized LDL were to be generated in the circulating blood, it would be swept up within minutes by the liver.45 Hence, all research in atherogenesis has been exclusively directed to investigation of atherogenic changes in the vascular wall. It is important to note that these assumptions were made without benefit of direct microscopic observations of the oxidant phenomena in the circulating blood. Those assumptions are clearly not warranted in view of our morphologic observations of oxidative coagulopathy and AA oxidopathy documented in this report. Furthermore, the mechanisms of oxidation of LDL are deemed “unknown.” Here again the fundamental phenomenon of spontaneity of oxidation in the blood ecosystem has been ignored. Our observations also challenge the cholesterol hypothesis of IHD, thus clearing the way for a wholly novel view of pathogenesis of atherogenesis and ischemic coronary artery disease. The clinical implications of this view, as we show in Part II of this article, are vastly different from those of the prevailing cholesterol, infectious and gene mutation theories of IHD.
We introduce the terms AA oxidopathy and oxidative coagulopathy in this article for specific reasons. Our morphologic observations of peripheral blood indicate to us that the molecular events involved in recognized intrinsic and extrinsic coagulative pathways are oxidative in nature, though the redox dynamics of such pathways have not been fully investigated. Limited published studies on this subject support our view.52-55 Recently, a third coagulative pathway, the Bradford-Allen Coagulation Pathway, has been proposed that involves activation of sialidase enzyme by reactive oxidative species.56 It seems likely that additional oxidatively triggered coagulative pathways will be discovered and characterized in the future. We introduce the term oxidative coagulopathy as an all-encompassing term for all such oxidative coagulative events that result in formation of microclots (microscopic clots formed in circulating blood and composed of loosely held blood elements within a matrix of congealed plasma and microplaques (microscopic plaques formed within the circulating blood and composed of compacted necrotic debris and blood elements. We introduce the term AA oxidopathy for a broader spectrum of energetic-molecular dysregulations of the redox phenomena. In advanced stages, the morphologic evidence of such injury may be observed in freshly prepared peripheral blood smears with high-resolution phase-contrast microscopy. AA oxidopathy includes patterns of blood cell and plasma component damage that involve oxidative injury to lipids, sugars and protein moieties as well as diverse enzymatic pathways of intracellular, extracellular and interstitial compartments. In the context of IHD, it also includes cell membrane depolarization dysfunction of cardiac myocytes and the conducting system of the heart.
While the concepts of oxidative coagulopathy and AA oxidopathy evolved from our extensive high-resolution, phase-contrast microscopic studies of unstained peripheral blood smears in diverse clinicopathologic states, the subject of this article—that AA oxidopathy is the core pathogenetic mechanism of IHD—developed from peripheral blood findings of patients with advanced coronary artery disease, congestive heart failure, cardiac arrhythmias, poorly controlled diabetes, and in smokers before and after smoking.
We draw support for AA oxidopathy from many lines of evidence and recognize the oxidative nature of the involved processes as the common denominator. We also establish that the clinical implications of AA oxidopathy are radically different from those of other prevailing theories of IHD. Specifically, it requires that therapeutic strategies be directed to all aspects of blood ecology (initial redox phenomena occurring in the circulating blood) and not merely to aspects of vessel wall ecology (later atherogenic cellular and tissue changes taking place in the vascular wall).
A Need for A Unifying Concept of Atherogenesis
The need for innovative research into the pathogenetic mechanisms of IHD was emphasized recently.57 The relationship between flow-limiting stenosis and ischemic coronary disease is weak.58 Reduction in the extent of atherosclerosis does not correlate with reduced mortality.59-63 Many persons with myocardial infarction have normal blood cholesterol levels.64-66 Treatment with lipid-lowering drugs does not reduce overall mortality in men in some studies,65 and decreases total and IHD mortality in women to a much lesser degree than in men.66,67 The paradox of IHD coexisting with normal coronary arteriogram is well recognized.68-70 Excess body stores of iron,71,72copper73,74 and mercury75,76 are risk factors for heart disease, while deficiencies of selenium77,78 and chromium79,80 increase risk of IHD. In the past, such associations between IHD and excess of pro-oxidants and deficiency of minerals with antioxidant roles have been assumed to contribute to oxidative modification of LDL cholesterol. We believe such assumptions are not warranted in view of our microscopic findings. Similar assumptions were made about the protective roles of natural antioxidants such as vitamins C,81,82 E,83,84 beta carotene,85,86and coenzyme Q10,87,88 as well as about synthetic antioxidants such as probucol89,90 and EDTA.91,92 The antiatherogenic roles of chronic alcohol intake—the so-called French paradox93,94—and risk of IHD associated with hyperhomocysteinemia95,96 are usually paid little attention by the proponents of the cholesterol hypothesis. A large body of experimental and epidemiological evidence points to a significant pathogenetic role of chronic inflammation.97-106 Among normal men, base line serum levels of C-reactive protein, an acute-phase reactant, correlate well with future myocardial infarction and stroke, and the increased risk is independent of lipid-related and non-lipid-related risk factors of atherosclerosis.107 Intriguingly, the benefits of aspirin in risk reduction diminish significantly with decreasing serum levels of C-reactive protein. Other evidence points to the roles of leukocyte activation and an autoimmune process.108-113 Several lines of evidence support the critical roles played by platelets, monocytes, macrophages, endothelial cells, myocytes and fibroblasts that are unequivocally independent of blood lipid levels.114-120 Recent investigations into the molecular basis of IHD have revealed activation of genes that encode for several mediator molecules such as platelet aggregation, vasoactive and chemotactic factors, as well as cytokines and interleukins.121-128
The prevailing cholesterol theory of coronary artery disease ascribes the primary pathogenetic mechanism of coronary artery disease to a disturbance of cholesterol metabolism. This view holds up to careful scrutiny neither on theoretical grounds nor on the basis of known experimental and clinical observations. The clinical benefits of lipid-lowering drugs are limited,129-136 and their toxicity, including carcinogenicity, is increasingly recognized.137-145 The advocacy of some proponents of the cholesterol theory for use of such drugs for persons without raised blood cholesterol levels is disturbing.146.
Below, we include a brief survey of pertinent literature as a frame of reference for presenting our AA oxidopathy hypothesis.
In 1842, T.W. Jones, a British physician, asked the question: Why doesn’t the blood circulating in the vessels coagulate?147 This question has intrigued blood coagulation researchers ever since. In 1845, Rudolph Virchow, the German physician and father of pathology, responded to the question raised by Jones by stating that under certain circumstances circulating blood does coagulate, and he speculated what those pathologic states might be.148Almost simultaneously, A. Trousseau, a French physician, observed that circulating blood does coagulate in the vessels in certain conditions and reported clinical observations to support Virchow’s speculation.149 Trousseau’s syndrome is the name still used when thrombophlebosis is associated with malignant diseases.
In 1893, Dastre first proposed the term “fibrinolyse” for his observations on the dissolution of blood clots.150However, his were not among the earliest observations on fibrinolysis. John Hunter, the eighteenth-century London surgeon, included his observation on clot dissolution in his famous treatise on blood.151 In 1887, Green’s publication of his studies of the effect of sodium chloride on the dissolution of plasma clots also preceded those of Dastre.152 In 1903, Delezenne and Pozerski reported activation of serum proteolytic activity by chloroform,153 and four years later, Opie and Barker separated albumin from globulin and proteolytic activity was associated with the globulin fraction.154 In 1933, rapid lysis of plasma clots by extracts of beta-hemolytic streptococci was noted by Tillet and Garner,155 and in 1944 Kaplan demonstrated that the streptococcal factor was an activator for the proteolytic enzyme precursor in human plasma.156
Coagulative and Fibrinolytic Pathways
The twin coagulative and fibrinolytic systems are similar in many ways and have been extensively investigated and reviewed.157-160 Both systems are activated, amplified and counterbalanced in biologic phenomena involving injury, inflammation, repair responses, metastatic cancer of spread and degenerative disorders. Both systems are composed of inactive precursors that are converted into active enzymes of serine protease type.161 Both systems involve intrinsic (plasma) and extrinsic (tissue) activation mechanisms which trigger a common pathway. In the coagulative system, the final common pathway involves polymerization of fibrinogen into fibrin, while that in the fibrinolytic system it involves activation of plasminogen. And, as we show later in this article, the primary mechanisms underlying both systems are related to oxidant phenomena in the circulating blood (which we designate as oxidative coagulopathy) as well as those which affect cell and plasma membranes and cytosol (which we collectively designate as AA oxidopathy). Even though the coagulative and fibrinolytic systems are generally regarded as two discrete enzymatic pathways, in reality the intrinsic pathways of the fibrinolytic system is coupled to the intrinsic pathways of the coagulative, so that clot formation and resolution are initiated concurrently and perpetuated in tandem. We introduce the term clotting-unclotting equilibrium (CUE) in this article to integrate the oxidative nature of events that lead to the concurrent phenomena of clot formation and clot resolution.
Abnormal coagulative phenomena within the circulating blood occur in diverse clinicopathologic entities such as eclampsia, anaphylaxis, localized and generalized Shwartzman reactions, hemorrhagic diathesis in clinical and experimental acute viral infections, bacterial endotoxic shock and others.157 Some turn-of-the-century investigators mistook such coagulative phenomena within the vascular lumina—fibrin threads and amorphous deposits, as well as the classical thrombi—as postmortem events. However, this mistake was recognized by Ingerslev and Teilum, who in 1946 described fibrin thrombi in hepatic periportal sinusoids in the liver of women who survived eclampsia.162 Even though the concepts of pre-thrombotic and hypercoagulable states have drawn considerable interest158-161,163,164; however, the definitions of such states varies from author to author and discussions of the subjects have been confined to clinical thrombotic-hemorrhagic events. To our knowledge the central role of chronic, insidious clotting-unclotting disequilibrium in the pathogenesis of IHD has not been recognized.
The occurrence and patterns of free radical injury to the myocardium, the conducting system of the heart, and coronary arteries have been investigated extensively with ischemia-perfusion studies.165-170 Specifically, free radicals, particularly superoxide anion (O2._) and hydroxyl radical (OH*), are produced during and after ischemia and reperfusion, and cause oxidative functional and structural injury to the heart, including the loss of myocardial contractile function. Superoxide anion is a relatively weak oxidant and owes most of its destructive potential to its ability to generate hydrogen peroxide by reacting with molecular oxygen. Hydrogen peroxide, in turn, generates highly toxic OH* radicals in the presence of transition metals such as iron and copper.
Fibrinolysis is generally assumed to occur only as a part of the spectrum of pathologic coagulative disorders. Our morphologic observations challenge this assumption. We sometimes observe congealed plasma and microclots in healthy subjects without history or demonstrable evidence of any coagulative disorders. We have also observed, as illustrated in this article, that such congealing of plasma and microclot formation is easily reversed by addition of antioxidants, proving that such coagulopathy is oxidative in nature. Our microscopic findings show that clotting and unclotting within circulating blood occurs with high frequency in a variety of cardiovascular disorders as well as in otherwise healthy subjects with established risk factors of IHD. In states of accelerated oxidative molecular injury, the rate of oxidative coagulation exceeds that of fibrinolysis, and the various patterns of oxidative coagulopathy and AA oxidopathy are readily observed. Clinicopathologic entities that are associated with disseminated intravascular coagulation, in our view, represent more advanced stages of the same process. While disseminated intravascular clotting in many acute and chronic disorders has been thoroughly studied, the occurrence and extent of such phenomena in the insidious development of molecular and cellular lesions that lead to IHD, to our knowledge, has not been previously recognized.
SPONTANEITY OF OXIDATION IN NATURE AND DISEASE
We include below brief comments about some fundamental aspects of the phenomenon of oxidation as a framework for our discussion of oxidative coagulopathy. Oxidation is a spontaneous process—it requires neither an expenditure of energy nor any outside cues. A flower wilts spontaneously; a wilted flower does not “unwilt” spontaneously. Fish rot spontaneously; rotten fish do not “unrot” spontaneously. Cut grass decomposes spontaneously; decomposed grass does not “undecompose” spontaneously. Thus, spontaneity of oxidation in nature is the natural phenomenon that provides the core mechanism of molecular injury in biology. Stated in another way, spontaneity of oxidation is nature’s grand scheme to assure that no oxygen-utilizing form of life remains immune to the immutable law of oxidative death. Oxidation plays a similar role in the decay of inanimate matter as well. Iron rusts spontaneously; rusted iron does not “unrust” spontaneously. Reduction, the other side of the redox equation of life, requires expenditure of energy.
What is the energetic basis of spontaneity of oxidation in nature? A simple analogy may be used to answer this question. A boy is playing with a ball attached to a string. He keeps the ball flying in an orbit around him by moving his extended arm in a circle above his head. In this circumstance, the kinetic energy of the ball seeks to move the ball away from the boy, but it is counterbalanced by the pull of the string on it so that the ball stays in a circular orbit. If the boy lets go of the string, the ball will spontaneously fly away. The same thing would happen if the boy were to spin the ball with a greater force than can be sustained by the string. The above analogy may be completed by imagining that the ball moves in elliptical orbits—the string has extreme elasticity and pulls the ball closer to the boy’s head by shrinking at one time and allows the ball to move far away from the boy by stretching at another time. (Physicists believe that atoms exist in a simultaneous particle-wave state determined by a particle-wave probability distribution.) A similar set of conditions governs the motion of electrons as they spin around the nucleus of an atom. Thus, spontaneity of oxidation (electron loss) is in reality a function of the kinetic energy of electrons that favors their outward movement, hence their loss. Thus no external source of energy is required in oxidation.
Electrons within atoms and molecules do not orbit the nucleus of an atom in the sense that the earth orbits the sun. Rather, electrons occupy regions of space called orbitals, which can hold no more than two electrons. A characteristic of electrons in a given orbital is that they demonstrate opposite spins. Within a molecule, two electrons sharing the same orbital exist in a bond called a covalent bond. A lone electron within an orbital is considered unpaired. This leads us to the definition of a free radical: any atomic or molecular species capable of an independent (“free”) existence that contains one or more unpaired electrons in one or more orbitals. We may point out that carbon- and sulfur-centered radicals generally react with oxygen with greater affinity than others included in the table given below.
A partial list of common naturally occurring free radicals is shown in the following table adopted from Halliwell.171
Types of Radical Examples Oxygen-centered Superoxide O2*-
Lipid peroxyl lipid-O*
Hydrogen-centered Hydrogen atom H* Carbon-centered Tichloromethyl Ccl3* Sulfur-centered Glutathione GS* Delocalized electrons Phenoxyl (delocalized into benzene ring) C6H5O*
Nitric oxide NO*
Ali M, Ali O. AA Oxidopathy:
the core pathogenetic mechanism of ischemic heart disease.
J Integrative Medicine 1997;1:1-112.
MOLECULAR DUALITY OF OXYGEN
Oxygen: A Molecular Dr. Jekyll and Mr. Hyde
Oxygen ushers in life. Oxygen terminates life. We believe the comprehension of the molecular duality of oxygen is essential to understanding both oxidative coagulopathy and AA oxidopathy—and, hence, to an understanding of atherogenesis. At a fundamental level, life is stored energy of carbon in its various reduced forms. Life is sustained by release of that energy as carbon-containing compounds are oxidized by oxygen to produce water and carbon dioxide. This elemental aspect of living matter—and its profound implications in health and disease—is seldom given due attention in clinical medicine.
Diatomic oxygen in ambient air is considered a radical because it contains two unpaired electrons. This structural characteristic of oxygen, according to thermodynamics, should allow oxygen to cause immediate combustion of all organic molecules that come in contact with it. Why does that not happen? The explanation is that the two unpaired electrons of diatomic oxygen in two different orbitals have the same spin quantum number. If oxygen were to directly oxidize organic molecules, it would have to accept two electrons from a donor with spins that are opposite to its own two unpaired electrons so as to be properly accommodated into the vacant spaces in oxygen’s two orbitals containing unpaired electrons. This, of course, cannot be achieved by electrons in covalent bonds, which spin in opposite directions. Such spin restriction explains oxygen’s poor reactivity even though it is a good oxidizer.(Diatomic oxygen accepts electrons more efficiently than other electron acceptors such as NO3-, CO2 and SO42-, and to organic compounds such as NAD+ and quinones.) This explains why organic molecules do not spontaneously undergo combustion in oxygen. This also explains why glucose in oxygen, like ATP in water, is kinetically stable even though it is thermodynamically unstable. For oxygen to be reduced, it requires a paramagnetic catalyst such as heme iron or a copper chelate, which scrabble, so to speak, the electron spin in the donor. More than 90% of the oxygen used in the human body is utilized by mitochondrial cytochrome oxidase, which transfers four electrons into an oxygenmolecule to produce two molecules of water:
O2 + 4H+ + 4e- = 2H2O
Under ordinary circumstances, reduction of oxygen by cytochrome oxidases in the above reaction does not release reactive oxygen radicals. This is assured by transitional metal ions such as iron, copper, vanadium and titanium, which are carried in the active sites of cytochrome oxidases. Such metal ions occur in variable states of oxidation, and changes in such states facilitate transfer of single electrons in an orderly fashion in which various partially reduced forms of oxygen are held bound to the metal ions. These ions also play essential roles in spontaneous oxidation (autoxidation) of several nonradical compounds including ascorbic acid; thiols such as cysteine, homocysteine and reduced glutathione; catecholamines such as epinephrine and norepinephrine; and a host of amines such as 3,4-dihydroxyphenylalanine (DOPA) and 6-hydroxydopamine.
Molecular oxygen has an interesting “love-hate” relationship with electrons. It avidly picks up free electrons in its vicinity, then just as avidly spins them out. In a vacuum, electrons travel at the speed of light. Even though the speed of an electron in tissues would be expected to be drastically reduced, the electron-oxygen transactions must still take place at amazingly fast speeds. During oxidative phosphorylation in the generation of ATP, molecular oxygen accepts an electron—is reduced—to become superoxide. Superoxide then loses its electrons spontaneously—is oxidized—in initiating the free radical chain reactions that result in the formation of peroxides, oxyacids, aldehydes and hydroxyl radicals. Such free radicals oxidize proteins of coagulation cascades, thus triggering oxidative coagulopathy, which further fans the fires of AA oxidopathy. However, our high-resolution microscopic observations described in this article lead us to conclude that accelerated oxidative stress on components of circulating blood is neither confined to oxidative injury of coagulation pathways nor, indeed, are the coagulative phenomena the initial events. We introduce the term AA oxidopathy to encompass a broad range of oxidative events that include: 1) peroxidation of plasma and cell membrane lipids; 2) oxidative permutations of plasma and cell membrane sugars and proteins; 3) accelerated autoxidation of nonenzymatic plasma antioxidants such as thiols and ascorbic acid; 4) inactivation or saturation of plasma enzymatic antioxidant mechanisms; 5) endothelial injury; and 6) later oxidative injury to subendothelial collagen and the muscularis of the arterial wall. Oxidative modification of LDL cholesterol—widely believed to be the critical event in atherogenesis—is, in our view, a relatively less significant event. We return to this essential issue later in this paper.
How Do Cells Autoregulate?
Human cells regulate themselves, just as unicellular organisms do. In medical literature, the discussions of cellular growth and regulation are generally limited to how cells maintain their structure and function by affecting key transcription factors. One commonly used mechanism by which cells turn key proteins on and off is adding or removing phosphate groups. In the context of our discussion of spontaneity of oxidation in nature, molecular duality and human redox dynamics—as well as from a teleologic standpoint, oxygen may be expected to play central roles in cellular growth, differentiation and autoregulation. The prevailing notions of human cell biology hold that greater the oxygen supply to cells, the more efficient their growth and the better their structural integrity and functional stability. Such simplification, however, ignores the diverse roles oxygen plays under different conditions. We cite here the example of cytotrophoblastic growth and differentiation to illustrate this important point.
During the first trimester, there is a discrepancy between the growth of the embryo and the placenta so that the placenta grows rapidly to prepare for the growth spurts in the embryo which are delayed well into the second trimester. The molecular basis of this phenomenon was unknown until recently when Genbacev et al.172 discovered that human placental development is regulated by the responsiveness of cytotrophoblast to changes in oxygen tension. They observed that cytotrophoblast in culture continue to proliferate and do not differentiate well under hypoxic conditions (2 percent oxygen), but stop proliferation and begin to differentiate when oxygen tension was raised with 20 percent oxygen—thus creating a paradox of a more rapid cellular growth occurring with lower oxygen tension. There are other lines of evidence that show that human cells may autoregulate by responding to oxygen and oxidant phenomena in other ways. For example, hypoxia induces the generation of vascular endothelial growth factor which stimulates endothelial proliferation. Hydrogen peroxide is involved in the signaling pathway of platelet-derived growth factor, which stimulates proliferation of vessel wall myocytes.173 Other examples of autoregulation of cells by employing their oxidants include activation of nuclear factor kB, which turns on genes for some mediators of inflammation, and inactivation of AP-1, which controls some genes involved with growth. Nature seems to have yet simpler and more elegant ways to allow individual cells to autoregulate via manipulation of oxygen and other oxidizing species. For example, it assigns important cell signaling functions to molecular oxygen by simply adding an electron to it. Recently, it has been shown that superoxides relay Ras protein’s oncogenic message in transformed fibroblasts.174 We include the above brief comments about cellular autoregulation and oxygen in our discussion of IHD to suggest that there may yet be other mechanisms by which oxidant phenomena in the circulating blood contribute to (or abate) oxidative coagulopathy and AA oxidopathy.
MORPHOLOGY OF ATHEROSCLEROSIS
By gross morphology, atherosclerosis is a simple process that progresses in three stages. In the first stage, a yellow-gray fatty streak appears on the inner surface of the vessel wall. Histologically, it comprises foamy, lipid-laden macrophages in the subendothelial space. The second stage is characterized by a fibrous plaque formation. The plaque is composed of a central necrotic, acellular area of fatty deposits covered by a fibrous cap, which in reality is made up of proliferating myocytes and fibroblasts in a matrix of collagen. In the third stage, hemorrhage occurs within the central necrotic area, resulting in a thrombus composed of fibrin threads with trapped platelets. The smooth fatty streak is often present in children and progresses to the two later stages with time.
The common atheromatous plaque is a raised area of white-gray-yellow discoloration on the inside wall of a vessel. As plaque grows in size, it protrudes into the vascular lumen and begins to reduce the inner caliber of the vessel. Plaques may vary in size from 0.1 to 2 cm in diameter, but may grow to much larger sizes when they coalesce. In the aorta and larger arteries, plaques may extend for several centimeters. The luminal surfaces of plaques are usually irregular and indurated; small erosions covered with fibrin thrombi are commonly observed. On section, the center of large plaques often exudes viscous, yellow-gray-brown gummous material—hence, the name atheroma from the Greek word for gruel. Histologically, plaques are composed of necrotic tissue with cholesterol crystals and other lipid deposits, degeneration and necrosis of the collagen and the muscle in the vascular wall, smooth muscle proliferation, and fibrous scarring at the periphery of the plaque. In advanced stages, hemorrhage and dystrophic calcification frequently occur in necrotic tissues.
It is the presence of cholesterol crystals and other lipid deposits in the plaque that has misled generations of pathologists and cardiologists into thinking that cholesterol is the cause of atherosclerosis—just as a prior generation of pathologists made a similar error in mistaking deposits of dystrophic calcification in injured tissues as evidence for dysregulated calcium metabolism. In atherosclerosis, cholesterol deposits occur as a consequence of oxidative coagulopathy, just as calcium deposits are often seen in organized hematomas. As we mention briefly in the abstract of this paper and discuss at length below, cholesterol is an antioxidant and cannot cause the lesions of coronary artery disease that are produced as a result of oxidative injury.