氧化·疾病·抗氧化(Ⅳ)

<正> 2 氧化与疾病 人体内在氧的利用过程中,会因各种内因性或外因性原因而产生各种活性氧和自由基。但体内也有各种消除活性氧和自由基的防御系统,以免组织遭伤害。但当人体内出现各种各样负荷状态时,就会使活性氧和自由基的形成和消除之间平衡丧失,从而诱发各种组织损伤和疾病。     

氧化·疾病·抗氧化(XV)

<正> 4.7 维生素C抗氧化作用 维生素C有四种异构体,包括L-抗坏血酸、D-抗坏血酸、L-异抗坏血酸和D-异抗坏血酸,习惯上仅将L-抗坏血酸(AsA)称作V_C,因除D-异抗坏血酸有约1/20L-抗坏血酸所具有抗坏血病生理功效外,另两种均无活性。但在抗氧化性能方面,上述四种性能相同,故D-异抗坏血酸因生产成本低等因素而成为在食品中有用抗氧化剂。V_C是一种抗坏血病因子,因人、猿和豚鼠等难以在体内合成而列为必须微量营养素。     

氧化·疾病·抗氧化(ⅩⅢ)

<正> 4.2.1类胡萝卜素对单线态氧消除作用 类胡萝卜素能消除单线态氧,已于1968年由Foote和Denney[13]得到证实。由叶绿素之类光敏剂吸收光能后,引发三重态氧激发态,使三重态氧3O2引发反应而产生单线态氧1O2。类胡萝卜素吸收1O2能量而使之回复至三重态氧,自己成为吸附能量类胡萝卜素,经放出热能后重新回至普通类胡萝卜素,同时消除1O2(见图6)。这种消除1O2能力只能在有9个以上共轭双键的类胡萝卜素才具备,如只有五个共轭双键的视黄醇就无法消除1O2[14]。     

氧化·疾病·抗氧化(十八)

<正>4.9 辅酶Q 辅酶Q(coenzyme Q)亦称泛醌(ubiquinone),其还原型称泛醇(ubiquinol)。广泛存在于生物界,是线粒体在氧化还原循环中电子传递重要物质,是生物体内脂溶性维生素类物质,也是细胞自身产生天然抗氧化剂,能激活细胞呼吸,加速生产ATP,抑制线粒体过     

氧化·疾病·抗氧化(Ⅰ)

该文对自由基所引起的氧化胁迫和伤害,以及各种抗氧化防御系统进展,作一综述。     

氧化、疾病、抗氧化( III)

1.3.3修复和再生型抗氧化物 人体对氧化伤害第三道防线,是受到自由基DNA、脂类、膜脂质、蛋白和遗传因子等损伤部分的修复,以及酰基转移酶(acyltransferase)等酶类再生,其中担负主要作用的有磷脂酶、蛋白酶和核酸修复酶等.     

氧化·疾病·抗氧化(Ⅱ)

<正> 1.2.2 对蛋白质伤害 自由基对蛋白质伤害作用,主要可分为以下几类: 第一类是使蛋白质肽链断裂。 第二类是蛋白质分子发生交联聚合而生成变性高聚物,是蛋白质分子一种链式聚合作用。 第三类是蛋白质结构上氨基酸发生氧化脱氨之类反应。 第四类是自由基攻击酶蛋白,使其改变结构而导致酶的活力丧失。如自由基作用于酶蛋白中巯基,使成为二硫键结     

氧化·疾病·抗氧化(Ⅺ)

该文对氧化在衰老中作用和抗氧化物在抗衰老中作用等进展作一综述     

氧化·疾病·抗氧化(Ⅷ)

<正> 2.6氧化与消化道疾病2.6.1胃粘膜病变和抗氧化物质 曾有不少关于胃粘膜病变模型与活性氧之间关系文章,及给予活性氧消除剂后消除胃粘膜损伤报告[66.67]。有人[68]曾用接有反射分光光度计内窥镜,研究胃粘膜血流和氧的代谢变化时胃粘膜出血性病变形成所产生重大影响,而SOD和CAT能缓解胃粘膜     

氧化·疾病·抗氧化(Ⅹ)

<正> 3氧化与衰老 衰老是人体各器官功能开始逐步降低一种生理现象,是一个缓慢渐进过程,是一种不可避免自然规律。但这过程可因氧化而加速(如吸烟等),也可因抗氧化而延缓。     

氧化·疾病·抗氧化(十七)

<正>4.8.3维生素E对脂蛋白和血管保护作用 低密度脂蛋白(LDL)是人体血浆中携带大量胆固醇主要蛋白质,也含有大量亚油酸和花生四烯酸等不饱和脂肪酸,这些成分极易氧化变性而成为过氧化物,氧化LDL不能再结合到LDL受体上,而是与巨噬细胞清除受体相结合,并形成泡沫细胞,这是导致     

氧化·疾病·抗氧化( VI)

2.4氧化与糖尿病 　　人体每次进食后,血液中葡萄糖水平就会升高,使全身细胞周围葡萄糖浓度也升高,包括胰腺β-细胞.     

氧化·疾病·抗氧化(二十)

<正>5.2 茶叶多酚 茶叶消费已有数千年历史,并遍及五大洲,其除 诱人清香外,并因具种种药效和生理功能而成为人们 日常生活中不可或缺食物。据不完全统计,我国16 种古中医书中曾记载其有20项、219条药效,在4,700 多年前就有"神农尝百草,日遇七十二毒,得茶而解 之"记载。唐代《本草拾遗》中有"诸药为各病之药,茶 为万病之药"记载,说明其功效甚多。即使在边疆地 区,生活在青藏高原、蒙古高原及绵延数千里丝绸之 路两侧的蒙、藏、回等十多个少数民族,由于气候寒 冷、干燥,缺乏蔬菜,以牛羊和奶酪等为主食,砖茶就 成为他们特需品,故有"一日无茶则滞、三日无茶则 痛","宁可三日无粮,不可一日无茶"之说。仅内蒙一 地每年约需"边销茶"7,500吨。     

氧化·疾病·抗氧化(Ⅸ)

<正> 2.8 氧化与肝病 肝脏是人体内最大消化腺体,在人体内起着中央化学处理功能,即吸收来自小肠血液各种营养物质,分解各种不利毒物并排出各种废物。近年来,病毒性肝炎、脂肪肝、酒精性肝病、肝纤维化、肝硬化、中毒性肝脏病变、肝癌等发病率有不断上升趋势,尤其是由甲、乙、丙、丁、戊、己、庚型肝炎病毒所引起肝炎,面广量大,成为当今社会一大病源。据2003年初统计,全世界约有3亿乙肝病毒携带者,其中中国约有1.2亿,中国每年因肝病死亡人数达35万,每年约有75～120万名孕妇为乙肝病毒携带者,其中50％～90％婴儿     

Occurrence of dioxins (PCDDs,PCDFs) and polychlorinated biphenyls (PCBs) in wild,farmed and processed fish,and shellfish

Forty-eight composite samples of the most commonly consumed fish and shellfish species were prepared from up to 60 individual subsamples of each species and analysed for chlorinated dioxins (PCDD/Fs) and polychlorinated biphenyls (PCBs). These included 24 species of fresh wild fish, seven of farmed fish, seven of fresh shellfish, and ten processed fish and shellfish products. The ISO 17025-accredited analytical methodology used is consistent with the requirements given in European Commission Directive 2002/69/EC. Concentrations ranged from 0.03 ng kg^–1 PCDD/F plus PCB World Health Organization-toxic equivalent quantity (WHO-TEQ) for a sample of surimi, to approximately 6 ng kg^–1 for wild pilchards/sardines. The corresponding range for the ΣICES-6 PCBs was 0.04 μg kg^–1 to approximately 47 μg kg^–1. None of the samples showed concentrations above the European Union maximum permitted limits. Averaged PCDD/F and PCB concentrations for the two groups of farmed and wild fish show that there is little difference between the two categories, although individual species may show variations depending on factors such as the sampling location.     

氧化·疾病·抗氧化(Ⅻ)

<正> 4食品中维生素类抗氧化作用 人体内抗氧化防御系统成分及其大致情况,参见表1。各种酶类和蛋白基本上属于内源性抗氧化物。外源性抗氧化物则为各种抗氧化维生素、组成抗氧化酶微量元素及具有抗氧化能力植物化学成分,包括多酚类、类黄酮、花色素苷类、酚酸类等。     

氧化·疾病·抗氧化(ⅩⅥ)

<正>4.8维生素E抗氧化作用4.8.1概述 近年来,活性氧和自由基对各种疾病之间关系日益明显,在各种疾病发生和病症中,自由基起着重要角色,因此如何抑制自由基以防治各种疾病已引起广泛关注。 维生素E(VE)是防御体内脂质过氧化反应第一道防线。VE能中止自由基对各种生物膜攻击和伤害,能     

氧化.疾病.抗氧化(V)

2.3氧化与肿瘤 据统计,2000年全世界癌症患者共约1,400万人,每年死亡约600万人.据WHO 2002年7月1日研究报告认为,今后20年新患癌症人数将达1,500万/年,死亡数将达1,000万/年.     

氧化·疾病·抗氧化(十九)

<正>5 食品多酚类物质抗氧化作用 5.1 概述 在整个植物界,存有的多酚或酚类化合物及其衍 生物在6500种以上,这些化合物都是植物代谢过程 中次生副产物。它们存在于许多普通水果、蔬菜等 中,如葡萄、苹果、茶叶、葡萄柚、洋葱、茄子及各种香 辛料、谷物、豆类及果仁等,是人们每天从饮食中摄取 数量最多的抗氧化物质,见表30。     

Temporal trends, congener patterns, and sources of octa-, nona-, and decabromodiphenyl ethers (PBDE) and hexabromocyclododecanes (HBCD) in Swiss lake sediments

With the recent ban of pentabromodiphenyl ether (technical PentaBDE) and octabromodiphenyl ether (technical OctaBDE) mixtures in the European Union (EU) and in parts of the United States, decabromodiphenyl ether (technical DecaBDE) remains as the only polybrominated diphenyl ether (PBDE) based flame retardant available, today. The EU risk assessment report for DecaBDE identified a high level of uncertainty associated with the suitability of the current risk assessment approach for secondary poisoning by debromination of DecaBDE to toxic lower brominated diphenylethers. Addressing this still open question, we investigated concentrations and temporal trends of DecaBDE, NonaBDE, and OctaBDE congeners in the sediments of Greifensee, a small lake located in an urban area close to Zürich, Switzerland. PBDE appeared first in sediment layers corresponding to the mid 1970s. While total Tri-HeptaBDE (BDE-28, -47, -99, -100, -153, -154 and -183) concentrations leveled off in the mid 1990s to about 1.6 ng/g dw (dry weight), DecaBDE levels increased steadily to 7.4 ng/g dw in 2001 with a doubling time of 9 years. Hexabromocyclododecanes (HBCD) appeared in Greifensee sediments in the mid 1980s. They are an important class of flame retardants that are being used in increasing amounts, today. As was observed for DecaBDE, HBCD concentrations were continuously increasing to reach 2.5 ng/g dw in 2001. Next to DecaBDE, all 3 NonaBDE congeners (BDE-208, BDE-207, and BDE-206) and at least 7 out of the 12 possible OctaBDE congeners (BDE-202, BDE-201, BDE-197/204, BDE-198/203, BDE-196/200, BDE-205, and BDE-194) were detected in the sediments of Greifensee. Highest concentrations were found in the surface sediments with 7.2, 0.26, 0.14, and 1.6 ng/g dw for Deca-, Nona-, Octa-, and the sum of Tri-HeptaBDE, respectively. While DecaBDE and NonaBDE were found to increase rapidly, the increase of OctaBDE was slower. Congener patterns of Octa- and NonaBDE present in sediments of Greifensee did not change with time. Consequently, there was no evidence for sediment mediated long-term transformation of PBDE within the observed time span of almost 30 years. Despite the high persistence of DecaBDE, environmental debromination occurs, as shown by the detection of a shift in congener patterns of Octa- and NonaBDE in sediments, compared to the respective congener patterns in technical PBDE products. The OctaBDE congener BDE-202 was detected in sediments, representing a transformation product that is not reported in any of the technical PBDE products. Comparison of OctaBDE congener patterns in sediments with OctaBDE congener patterns from known sources reveals that (i) they were distinctively different from the congener patterns in technical PBDE products and (ii) that they were similar to the OctaBDE patterns in house dust and photodegradation products of DecaBDE, suggesting contributions from these sources.