维生素A、E对放射治疗鼻咽癌患者抗氧化水平的影响

放射治疗是鼻咽癌(nasopharyngealcarcinomaNPC)首选的治疗方法[1]。抗氧化剂是治疗肿瘤常用的辅助方法[2]。维生素A和维生素E是常用的抗氧化剂。抗氧化剂对保护机体免受自由基损害,降低肿瘤发病率有一定的作用。超氧化物歧化酶(superoxidedismutase,SOD)和谷胱甘肽过氧化物酶(     

淡豆豉多糖的提取及其清除自由基的活性研究

[目的]对淡豆豉中多糖进行分离提取,并研究其体外清除自由基的活性,为抗氧化剂的筛选提供科学依据.[方法]利用Fenton反应和邻苯三酚体系研究淡豆豉多糖对羟自由基和超氧阴离子的清除作用.[结果]淡豆豉多糖对化学体系产生的羟自由基和超氧阴离子有清除作用.[结论]淡豆豉多糖具有抗氧化活性.     

低剂量电离辐射对荷瘤小鼠某些免疫功能的影响

超氧化物自由基Ō2);氢氧自由基(·OH);激发态氧分子(¹O₂),过氧化氢(H₂O₂)和各类过氧化物(ROOH)是生物体内有氧代谢的产物,也是有氧条件下电离辐射与生物所产生的活性自由基^[1]。在生理情况下,自由基参于体内重要的新陈代谢过程。     

亚健康、氧化应激与抗氧化

人体处于躯体亚健康状态时,机体处于氧化应激态。躯体亚健康状态的起因、机制、预防和控制措施都与活性氧自由基在体内的作用机制和抗氧化剂的作用有关。抗氧化剂可以调节机体自由基代谢的平衡,对于缓解亚健康状态和预防疾病起到重要作用。已有的研究表明,含有多酚羟基的酚类衍生物和含巯基类的物质是两类典型的具有生物活性的抗氧化剂。它们在生物体内的抗氧化机制各有不同特点,本文对上述作简述。     

铜抗氧自由基作用的研究进展

铜是人类和动物机体必需的微量元素之一。铜不仅参与动物体内蛋白质、氨基酸、核酸、脂肪、碳水化合物、维生素等营养物质的代谢 ,而且还在骨骼发育、生殖、免疫、凝血、生物膜稳定等生理机能中担负着重要作用[1] 。其中 ,铜在自由基代谢中的作用是近年来国内外学者十分关注的课题 ,进行了广泛而深入的探讨 ,取得了丰硕的成果。1　氧自由基及其产生机制自由基 (Free Radical,FR)是指带有不成对电子的分子、原子、原子团或离子 [2 ]。生物体内产生的自由基主要是氧自由基 (Oxygen Free Radicals,OFR) ,约占机体内全部自由基的 95 %。这是…     

硫代碳酰腙法测定尿液超氧化物歧化酶活力

超氧化物歧化酶（SOD），是一种专一清除超氧阴离子（O2）的关键酶，是一种极其有效的抗氧化剂，能抵御超氧阴离子自由基对细胞的破坏。资料研究表明，超氧阴离子是生物体内重要的自由基。在许多情况下，对机体是有害的，是导致炎症、衰老及癌变的原因之一。SOD能有效的控制人体各种途径产生的超氧自由基，有保护机体组织免受损伤的作用。     

石墨炉原子吸收分光光度法测定血清中的硒

硒是人体必需元素 ,它既是一种营养元素 ,又是一种强氧化剂 ,具有清除人体内外有毒污染的作用及抗衰老作用[1] 。硒也是一种抗癌矿物质。微量元素硒是抗癌矿物质中效果最明显 ,抗癌力最强的元素。硒是很好的抗氧化剂 ,是吞食体内自由基最有效的物质 ,可保护细胞膜不受自由基的破坏 ,保持细胞核和基因成份的完整性。硒能启动谷胱甘肽过氧化酶的抗毒作用。这种酶是非常有效的吞食自由基的抗氧化剂 ,与硒配合能取得理想的抗癌效果[2 ] 。血清中痕量元素硒的测定可为多种人类疾病的诊断和治疗提供有价值的资料[3 ] 。硒测定的经典方法有 3.3-二…     

大蒜素对小鼠体内抗氧化酶的影响

<正> 现已证明,自由基的损伤作用与许多疾病和衰老的发生或发展有关系,因此,如何寻找有效的外源性抗氧化剂已成为自由基医学的前沿研究项目之一。我们在已往的体外实验中观察到大蒜及其有效成分大蒜素具有抗氧化的效能。为了进一步研究它是否可以增强机体抗自由基损伤的作用。我们就大蒜素对小鼠体内抗氧化酶的影响进行了实验观察。     

番茄红素对四氯化碳肝肾损伤的保护作用

番茄红素(Lycopene)属于烃类类胡萝卜素,存在于红色水果和蔬菜中,研究发现番茄红素具有淬灭单线态氧和清除自由基、阻断亚硝胺形成、抑制细胞增殖、诱导细胞分化、减少DNA损伤及诱导细胞间隙连接通讯等作用。番茄红素能够减缓动脉粥样硬化,防止冠心病的发生[1]。番茄红素的生物     

健身跑对老年人超氧化物歧化酶活力和含量的影响

机体各组织细胞在需氧代谢中不断地生成自由基,自由基浓度过高对人体极为有害,而超氧化物歧化酶(Superoxide dismutase,简称SOD)是机体清除超氧阴离子自由基的一种重要的酶,其活力和含量的高低与衰老及肿瘤、炎症等疾病有着十分密切的关系。一般认为,运动对延缓衰老有一定的作用,但有关长期坚持运动的老年人体内自由基产生或自由基防御能力的研究却很少报道。本文对SOD在人体红细胞和血清中的活力变化,及其含量的变化及相互关系进行研究和探讨。     

Free radicals,antioxidants, and nutrition

Radiation hazards in outer space present an enormous challenge for the biological safety of astronauts. A deleterious effect of radiation is the production of reactive oxygen species, which result in damage to biomolecules (e.g., lipid, protein, amino acids, and DNA). Understanding free radical biology is necessary for designing an optimal nutritional countermeasure against space radiation-induced cytotoxicity. Free radicals (e.g., superoxide, nitric oxide, and hydroxyl radicals) and other reactive species (e.g., hydrogen peroxide, peroxynitrite, and hypochlorous acid) are produced in the body, primarily as a result of aerobic metabolism. Antioxidants (e.g., glutathione, arginine, citrulline, taurine, creatine, selenium, zinc, vitamin E, vitamin C, vitamin A, and tea polyphenols) and antioxidant enzymes (e.g., superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidases) exert synergistic actions in scavenging free radicals. There has been growing evidence over the past three decades showing that malnutrition (e.g., dietary deficiencies of protein, selenium, and zinc) or excess of certain nutrients (e.g., iron and vitamin C) gives rise to the oxidation of biomolecules and cell injury. A large body of the literature supports the notion that dietary antioxidants are useful radioprotectors and play an important role in preventing many human diseases (e.g., cancer, atherosclerosis, stroke, rheumatoid arthritis, neurodegeneration, and diabetes). The knowledge of enzymatic and non-enzymatic oxidative defense mechanisms will serve as a guiding principle for establishing the most effective nutrition support to ensure the biological safety of manned space missions.     

Update on the Biological Characteristics of the Antioxidant Micronutrients: Vitamin C, Vitamin E, and the Carotenoids

Under normal circumstances, free radicals that are produced through biological processes and in response to exogenous stimuli are controlled by various enzymes and antioxidants in the body. Laboratory evidence suggests that oxidative stress, which occurs when free radical formation exceeds the ability to protect against them, may form the biological basis of several acute medical problems, such as tissue injury after trauma, and chronic conditions, such as atherosclerosis and cancer. A potential role for the antioxidant micronutrients (vitamin C, vitamin E, and the carotenoids) in modifying the risk for conditions that may result from oxidative stress has stimulated intense research efforts, increased interest in micronutrient supplements, and heightened consumer interest in these compounds. Much remains to be learned, however, about the bioavailability, tissue uptake, metabolism, and biological activities of these micronutrients. These biological characteristics will ultimately determine their clinical usefulness in modulating oxidative stress. Also, whether the antioxidant mechanism explains their relationship with risk for acute and chronic disease in epidemiologic studies remains to be determined. Increased knowledge in this area of nutrition science will have an impact on both clinical dietetics practice and public health nutrition guidelines. J Am Diet Assoc. 1996; 96:693–702.     

The antioxidants--vitamin C,vitamin E, selenium, and carotenoids

This is the second in a series of articles reviewing the recent revisions of the Recommended Dietary Allowances (RDA) and the resulting Dietary Reference Intakes (DRI). In April of 2000, the Food and Nutrition Board of the National Academy of Sciences released Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. The central premise of the report did not perpetuate the prevailing popular thought that large doses of antioxidants will prevent chronic diseases. Instead the panel concluded that at this time, insufficient scientific evidence exists to sustain claims that ingesting megadoses of dietary antioxidants can prevent certain chronic illnesses such as cardiovascular disease or cancer. In some instances recommended nutrient levels were reduced from the previous report in 1989; e.g., for the first time upper tolerable levels of ingestion (UL) were established to prevent the harmful effects of over consumption of essential nutrients, such as vitamin C, vitamin E, and selenium. Although dietary recommendations do exist for vitamin A, the panel did not set recommendations for beta-carotene or the other carotenoids due to lack of sufficient research to support recommended intakes or upper tolerable levels of intake. However, the panel advises the public to avoid intakes of provitamin A compounds, such as the numerous carotenoids, beyond the levels required to prevent vitamin A deficiency. Changes were also made with regard to estimating the amount of provitamin A carotenoids required to make a unit of retinal. The revised estimate suggests a twofold higher conversion rate than previously believed. Although this comprehensive report on the dietary reference intakes for vitamin C, vitamin E, selenium, and the carotenoids did not decisively confirm the role of antioxidants for the prevention of chronic diseases in humans, many research studies have generated new data to support this concept. Additional research is needed to define the attributes of antioxidants as studies progress from in vitro and animal studies to human nutrition.     

The role of antioxidants in prevention

The imbalance between free radical formation and the mechanisms involved in eliminating them results in oxidative stress which lies at the baseline of many diseases. There are many pathological conditions that can be prevented or even be cured by the application of antioxidants. Food containing plenty of natural antioxidants is very important in the maintenance of health and in the prevention of many illnesses. In some diseases supplementation of antioxidants in the proper form and dosage may be irrelevant. According to nutrigenomics the biologically active components of nutrition, including antioxidants, have an influence on the body in every single cell at all levels. Therefore the quality of nutrients is one of the important factors determining the appropriate cell function.     

Flavonoid basics: chemistry, sources, mechanisms of action, and safety

In our efforts to understand how various dietary factors can influence the risk and progression of chronic disease, much recent research has focused on phytochemicals. Phytochemicals are defined as nonessential nutrients found in plant-based food, many of which have been established as bioactive and thus may affect human health. The largest group of phytochemicals is the polyphenols, comprised principally of the flavonoids, which are characterized chemically by two benzene rings joined by a linear carbon chain. Evidence from observational studies indicates that regular consumption of foods containing flavonoids may reduce the risk several chronic conditions, including neurodegenerative diseases, atherosclerosis, and certain forms of cancer. These results have generated considerable interest in flavonoids, although much basic information about their nutrient characteristics in humans remains limited, e.g., their bioavailability and metabolism, interactions with other dietary factors, mechanisms of action, and intakes associated with specific health outcomes. Although flavonoids are commonly defined as dietary antioxidants and their putative health benefits commonly attributed to this mechanism, it now appears their principal actions are mediated in vivo via other biochemical and molecular pathways.     

Knowledge of antioxidants and breast cancer risk among women attending breast cancer risk assessment clinics

This qualitative study used semistructured interviews to examine the accuracy of knowledge concerning antioxidants and health among a convenience sample of 79 women attending a breast cancer risk assessment clinic. Despite a high level of familiarity (98%) with the word antioxidant, few participants could name more than one of these compounds and most relied on print media (41.6%) and radio/TV (22.2%) for antioxidant information. Thematic content analysis revealed participants' beliefs that antioxidants were strongly linked to reduced breast cancer risk and improved health. They described antioxidant functions that take place before (e.g., "Prevention . . . a best defense mechanism" and "To boost strength and good health") or after (e.g., "Fights diseases, free radicals, and cancer," "Acts as a cleanser or purifier," and "Undoes the harm that I am consciously or unconsciously doing to my body") a health threat. Participants' understandings of the links between antioxidant intake and breast cancer risk did not accurately reflect the scientific evidence. This large priority population group needs tailored, evidence-based nutrition communications to address inaccurate understandings about antioxidant intake and breast cancer risk.     

Antioxidants in liver protection

Great importance has been attributed to antioxidants in the prevention and treatment of conditions associated with oxidative stress for many years. At the same time the antioxidants are free radicals themselves, and they can exert prooxidant activity depending on the concentration. They influence the cell redox homeostasis by their prooxidant and antioxidant activity as well. Drugs of chronic liver diseases should be considered, because free radicals are generated during the activity of the monooxygenase system, which affect the tissue oxidised status. Combined antioxidant treatment is more favourable compared with monotherapy, because antioxidants have scavenger-, compartment- and tissue-specificity and they regenerate each other directly, too. Beside their antioxidant property they may also directly regulate many important processes, e.g. cell cycle. We have some favourable results with regard combined antioxidant therapy of liver disease of different etiology.     

Oxidative stress and liver disease

Several papers have been published on the important role of oxidative stress on living cells and cell responses e.g. apoptosis and necrosis, which leads to cell death. At the same time mild oxidative stress can modulate signal transduction cascades and redirect gene expression, and influence many cellular responses, e.g. proliferation, differentiation, reproduction. Regulations of the cell cycle depend on intracellular redox state. Critical steps in the signal transduction cascade are sensitive to oxidative stress and antioxidants. Heavy metal accumulation in higher concentration may inhibit enzyme activities influence the acute phase protein synthesis and gene expression, as well as the pro-oxidant and antioxidant forms of scavenger molecules. Polyphenols and flavonoid type antioxidants may influence the signal transduction routes as well. Ethanol inducible cytochrome P450 2EI isoenzyme oxidise ethanol and acetaldehyde and numerous potentially toxic xenobiotic and produce toxic oxygen free radicals, which are implicated in the pathogenesis of alcoholic liver diseases. Natural preparations, e.g. tea infusions contains trace elements and polyphenol type antioxidants in high concentration, therefore may influence the redox homeostasis, and especially dangerous with interaction of other medicines and alcohol.     

ANTIOXIDANT STATUS AND ALCOHOL-RELATED DISEASES

Chronic ethanol consumption is associated with increased incidenceof a variety of illnesses, including cancer Studies have shownthat ethanol consumption may result in increased oxidative stresswith formation of lipid peroxides and free radicals. The susceptibilityof a given tissue to peroxidation is, however, a function ofthe overall balance between prooxidants and antioxidant defencesystems. The latter involve both intracellular and extracellularprotective factors were nutrients play an important role. Impairednutritional status of different vitamins and trace elementshave been reported in alcoholics. Reduced levels of vitaminE have been found in serum of alcoholics with and without liverdisease and in liver biopsies from alcoholics with cirrhosis.These findings may be due to the increased oxidative stressas reported in experimental animals, and may be of importancesince vitamin E is the major, if not the only, hpid-solublefree radical scavenger in some tissues. Reduced antioxidantcapacity has been found in several tissues and may promote thegeneration of free radicals and lipid peroxides which may damagecells directly, induce inflammation and accelerate collagensynthesis. These events may progress to tissue damage and disease.The importance of radicals in cancer initiation and promotionis presently of great interest. The role of lipid peroxidesand free radicals in alcohol-related disease and cancer remainsunresolved. Further research is required to establish the roleof these reactive species in the pathogenesis of alcohol-relateddisease, and to evaluate the role of nutrition in favour ofthe antioxidant defence mechanisms.     

Free radicals in skin and muscle: damaging agents or signals for adaptation?

Much of the current literature regarding the biological effects of antioxidant nutrients has concentrated on their potential role in inhibiting or preventing tissue damage induced by free radical species produced during metabolism. Recent findings indicate that antioxidants may also have more subtle roles, regulating changes in gene expression induced by oxidizing free radical species. There is increasing evidence that free radicals act as signals for cell adaptation in a variety of cell types and the nature of the mechanisms by which free radical species influence gene expression is the subject of much current research. Processes such as these may be particularly important in tissues regularly exposed to varying amounts of oxidative stress as part of their normal physiological functions. Examples of such tissues include skin exposed to u.v. light and skeletal muscle subjected to repeated bouts of exercise.