Dasgupta Ph. D / Dasgupta / Klein BS Antioxidants in Food, Vitamins and Supplements

Prevention and Treatment of Disease
1. Auflage 2014
ISBN: 978-0-12-405917-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 360 Seiten

Antioxidants in Food, Vitamins and Supplements bridges the gap between books aimed at consumers and technical volumes written for investigators in antioxidant research. It explores the role of oxidative stress in the pathophysiology of various diseases as well as antioxidant foods, vitamins, and all antioxidant supplements, including herbal supplements. It offers healthcare professionals a rich resource of key clinical information and basic scientific explanations relevant to the development and prevention of specific diseases. The book is written at an intermediate level, and can be easily understood by readers with a college level chemistry and biology background. - Covers both oxidative stress-induced diseases as well as antioxidant-rich foods (not the chemistry of antioxidants) - Contains easy-to-read tables and figures for quick reference information on antioxidant foods and vitamins - Includes a glycemic index and a table of ORAC values of various fruits and vegetables for clinicians to easily make recommendations to patients

Amitava Dasgupta received his Ph. D in chemistry from Stanford University and completed his fellowship training in Clinical Chemistry from the Department of Laboratory Medicine at the University of Washington School of Medicine at Seattle. He is board certified in both Toxicology and Clinical Chemistry by the American Board of Clinical Chemistry. Currently, he is a tenured Full Professor of Pathology and Laboratory Medicine at the University of Kansas Medical Center and Director of Clinical Laboratories at the University of Kansas Hospital. Prior to this appointment he was a tenured Professor of Pathology and Laboratory Medicine at the University of Texas McGovern medical School from February 1998 to April 2022. He has 252 papers to his credit. He is in the editorial board of four journals including Therapeutic Drug Monitoring, Clinica Chimica Acta, Archives of Pathology and Laboratory Medicine, and Journal of Clinical Laboratory Analysis.

Autoren/Hrsg.

Dasgupta Ph. D, Dabcc

Dasgupta, Amitava

Klein BS, Md

Klein, Kimberly

Leseproben

Chapter 1 Introduction to Free Radicals and the Body’s Antioxidant Defense
Free radicals are generated during normal cellular function and are part of the natural physiological process of all living beings. Free radicals also play important physiological roles, including signal transduction and gene expression, but the majority of free radicals generated must be neutralized by the body’s antioxidant defense for optimal health. The body has many antioxidants that are classified under two broad categories: water-soluble and fat-soluble. Water-soluble antioxidants, such as vitamin C, glutathione, lipoic acid, and uric acid, are major antioxidants present in human blood. Fat-soluble antioxidants, such as carotenes, vitamin E, and coenzyme Q10, can be found in both blood and cells. In addition, several enzymes also act as antioxidants, most notably superoxide dismutase, catalase, and peroxidases. Keywords
Reactive oxygen species; superoxide anion; nitric oxide; antioxidant enzymes Contents 1.1 Introduction 1.2 Free Radicals 1.2.1 Various Sources of Free Radicals 1.2.2 Damage of Biomolecules by Free Radicals 1.2.3 Physiological Role of Free Radicals 1.3 The Body’s Antioxidant Defense 1.3.1 Enzymes as Antioxidants 1.3.2 Chain-Breaking Antioxidants 1.3.3 Exercise and Antioxidant Status of Blood 1.3.4 Markers for Oxidative Stress in Human Blood 1.4 Conclusion References 1.1 Introduction
The “oxygen paradox” is defined by the fact that aerobic organisms require oxygen for survival but oxygen is also inherently toxic to these organisms due to its association with free radical generation and oxidative stress. Various free radicals are common products of respiration and other biochemical reactions in cells that are normal physiological processes essential for survival. To survive in an unfriendly oxygen environment, living organisms generate water- and lipid-soluble antioxidants that can neutralize these highly reactive free radicals [1]. For healthy living, a delicate balance must be maintained between oxidative stress and antioxidant defense of the body. If the body’s antioxidant mechanism does not operate optimally, excess free radicals can damage various biomolecules, including lipids, proteins, carbohydrates, and nucleic acids. 1.2 Free Radicals
A free radical is defined as an atom or molecule containing one or more unpaired electrons that are capable of free existence. Free radicals can be generated as products of homolytic, heterolytic, or redox reaction, and they usually consist of reactive oxygen species or reactive nitrogen species. Reactive oxygen species include oxygen-carrying free radicals as well as other reactive oxygen species such as hydrogen peroxide, which is not a free radical. Similarly, reactive nitrogen species include both nitrogen-containing free radicals and other reactive molecules in which the reactivity center is nitrogen [2]. Common free radicals and oxidants are summarized in Box 1.1. Box 1.1 Common Free Radicals and Oxidants Encountered in Human Physiology Free Radicals  Superoxide anion radical  Hydroxyl radical  Hydroperoxyl radical  Peroxyl radical  Lipid radical  Lipid peroxyl radical  Lipid alkoxyl radical  Nitric oxide  Nitrosyl cation  Thiyl radical  Protein radical Oxidants  Singlet oxygen  Ozone  Hydrogen peroxide  Hypochlorite  Nitrous acid  Peroxynitrous acid  Nitrous oxide Free radicals are generated during normal respiration and cellular functions. Under normal physiological conditions, approximately 2% of oxygen consumed by the human body during respiration is converted into superoxide anion free radical, which is negatively charged (O2•-) [3]. The human body also contains approximately 4.5 mg of iron, most of which is found in hemoglobin and other proteins. However, a small amount of iron that is found forming complexes with a variety of small molecules can react with hydrogen peroxide, producing the hydroxyl radical (Fenton reaction). In general, oxygen-centered free radicals (reactive oxygen species), such as superoxide, the hydroxyl radical, peroxyl radical, and alkoxy radical, and nitrogen oxide, play an important role in inducing oxidative stress [4]. Nitric oxide (NO•) is synthesized from L-arginine by many cell types through nitric oxide synthesis. Nitric oxide and superoxide are the major reactive species produced in cells. Both superoxide and nitric oxide can react with other species, producing reactive oxygen species and reactive nitrogen species, respectively. Nitric oxide can also bind to transition metals such as ferrous ions, and it plays an important role in the formation of cyclic guanosine monophosphate, a second messenger [5]. In general, superoxide anion radicals and nitric oxide are primary free radicals generated by cells during normal physiological functions. 1.2.1 Various Sources of Free Radicals
There are two sources of free radicals: endogenous sources and exogenous sources. Major endogenous sources of free radicals are summarized in Table 1.1. The most common reactive oxygen species are superoxide anion, hydrogen peroxide, hydroxyl radicals, peroxyl radicals, singlet oxygen, and ozone. The production of superoxide occurs mostly within mitochondria. The mitochondrial electron transport chain is the main source of energy that is stored in adenosine triphosphate (ATP) molecules. Movement of electrons from oxidizable organic molecules to molecular oxygen is responsible for ATP production by the mitochondrial electron transport system. During this process, superoxide anions are generated due to leaking of electrons to oxygen. Superoxide is also formed enzymatically in the process of reduction of molecular oxygen mediated by nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) and xanthine oxidase in mitochondria. Superoxide has a relatively longer half-life than that of other free radicals, but it is less reactive than the hydroxyl radical. Inflammatory cells also produce relatively large amounts of superoxide. Superoxide is membrane impermeable but can diffuse within cells [5]. Table 1.1 Endogenous Sources of Free Radicals Physiological Process Comment Mitochondrial respiration Essential process of life that generates superoxide anion radical. Autoxidation Autoxidation of many biological molecules (hemoglobin, myoglobin, catecholamines, etc.) in the human body can produce free radicals. Superoxide is the primary free radical formed. Enzymatic reaction Many enzymatic reactions involving xanthine oxidase, lipoxygenase, aldehyde oxidase, etc. can generate free radicals. Respiratory burst This is a process in which phagocytes consume a large amount of oxygen during phagocytosis. Metal ions Metal ions such as copper ion and ferrous ion, which are essential for the body, can react with hydrogen peroxide to produce free radicals. Strenuous exercise May activate xanthine oxidase, producing free radicals. Infection May produce free radicals because the immune system may try to neutralize invading microorganisms with a burst of free radicals. Ischemia/reperfusion May activate xanthine oxidase, causing free radical generation. Peroxisomes are another significant source for free radicals. Peroxisomes are specialized cytoplasmic organelles that carry out important physiological functions such as ß-oxidation of long-chain and very-long-chain fatty acids and degradation of uric acid. Peroxisomal oxidase is capable of generating hydrogen peroxide. The reaction of xanthine and xanthine oxidase produces the superoxide anion and hydrogen peroxide through one-electron and two-electron reduction of molecular oxygen, respectively, to form uric acid. Hydrogen peroxide is a relatively stable agent that is permeable to cell membranes. Hydrogen peroxide can generate free radicals such as the hydroxyl radical but cannot directly oxidize lipid or DNA. Therefore, cytotoxicity of hydrogen peroxide is due to its ability to produce hydroxyl radicals through metal-catalyzed reactions such as the Fenton reaction. However, hydroxyl radicals are highly reactive and can damage any biomolecules close to their site of generation. These radicals are some of the most dangerous free radicals encountered in physiology [6]. Singlet oxygen is an electronically excited form of oxygen, but it is not a free radical. However, singlet oxygen is a reactive oxygen species generated during dismutation of superoxide anion in...