Free Radicals and Carcinogenesis

The role of free radicals and active states of oxygen in human cancer is as yet unresolved. Various lines of evidence provide strong but inferential evidence that free radical reactions can be of crucial importance in certain carcinogenic mechanisms. A central point in considering free radical reactions in carcinogenesis is that human cancer is really a group of highly diverse diseases for which the initial causation and the progression to clinical disease occur through a wide variety of mechanisms. Furthermore, for many human cancers it appears that there are alternate pathways capable of tumor initiation and tumor progression. While for certain of these pathways free radical reactions appear necessary, it is unlikely that there are human cancers for which free radicals, or any other mechanism, are sufficient for the entire processbeginning with the genetic alteration leading to a somatic mutation and eventually resulting in clinically overt disease. It is crucial that we view free radical reactions as aong a panoply of mechanisms leading to human cancer, and consider research about the role of free radicals in cancer as opportunities to prevent the initiation or progression of human cancer.     

病毒感染致病与自由基的损伤

以流感病毒A/FM1/1/47(H₁N₁)鼠适应株,鼻腔内接种感染小鼠为模型,探讨了病毒感染过程中,自由基的产生以及在致病过程中的作用.结果表明,感染病毒的小鼠肺组织中氧自由基水平和黄嘌呤氧化酶活性显著升高,并与肺组织损伤和死亡率之间呈正相关.提示,氧自由基参与了病毒感染小鼠的致病过程,是造成组织损伤的重要因素.     

吸烟、自由基与健康

吸烟有害健康,其中,吸烟过程中产生的大量自由基是损害健康的重要因素。研究吸烟产生的自由基及其损害健康的机理,以及减少乃至祛除吸烟危害、保护人类健康的策略,具有重要的社会意义。从学术角度来看,吸烟产生多种自由基,也是研究自由基的一个好模型。本文综述了吸烟、自由基与健康关系方面的研究进展,特别总结了我们实验室20多年在这方面的研究工作,供读者和同行参考。     

Direct Evidence for the Involvement of Free Radicals in Ischemic Insult to the Intestine

Ischemia of rat intestine was induced in vivo by occlusion of the superior mesenteric artery (SMA) for 15 min. Sodium salicylate, 100 mg/kg, given IP, 30 min prior to the ischemic event served as a specific trap for hydroxyl radicals and provided direct evidence for the involvement of free radicals during the ischemic insult. Portions of the bowel were sequentially isolated and removed. The hydroxylation products. dihyd-roxybenzoic acid (DHBA) derivatives were isolated, identified and qunatified by HPLC coupled with electrochemical detection (ECD). The level of 2,5-DHBA (Mean ± SE, ng/g tissue) in the preischemic bowel (N = 21) was 241.8 ± 10.0. It rose significantly to 313.3 ± 15.5 in the ischemic specimen (p = 0.0129) and remained unchanged in the reperfusion period (322.8 ± 15.5). The histological examination correlated well with these levels: mild villi damage in the ischemic period with no further damage in the reperfusion period.     

自由基和基质金属蛋白酶介导脑缺血血脑屏障损伤的研究进展

血脑屏障的破坏是引起脑缺血损伤及继发水肿、出血、炎症的微观原因。缺血缺氧和再灌注过程产生的自由基,以及后续基质金属蛋白酶的激活,是破坏血脑屏障结构和功能的重要分子机制。因而,在脑缺血早期及时抑制自由基产生并清除自由基,抑制基质金属蛋白酶的活性,是降低脑缺血血脑屏障损伤及其并发症的关键环节。本文将从血脑屏障损伤的角度,概述自由基与基质金属蛋白酶在脑缺血损伤过程中的作用。     

Enzymatic and Non-Enzymatic Formation of Free Radicals From Aflatoxin B1

Formation of free radicals from aflatoxin B₁ was demonstrated in systems of a) NADPH/microsome, b) H₂O₂/peroxidase, c) UV irradiation, d) silver oxide oxidation and e) alkaline dimethyl sulfoxide. In a) to c), radical spots were detected in thin-layer chromatograms. Among several known metabolites of aflatoxin B₁, aflatoxin M₁ was active in generation of free radical. These results suggest a possible role of free radical metabolites in the cytotoxicity of this hepatocarcinogen.     

胆红素自由基对人红细胞的损伤作用

为了进一步证明胆红素自由基对细胞造成的直接损伤,探讨胆红素对细胞表现毒性的机理以及在色素类结石形成中所起的作用,我们以胆红素自由基作用于人红细胞,用TBA法研究了完整人红细胞的脂质过氧化,用SDS-PAGE法研究了红细胞膜的损伤以及用荧光法研究了膜损伤后某些性质的改变。结果表明:胆红素自由基能引起人红细胞膜脂质过氧化,使膜蛋白发生降解,从而直接可测氨基减少,而溶液中游离氨基的含量却相应增加。根据以上事实,重点讨论了胆红素对细胞表现毒性的可能原因以及与色素类结石形成的关系。     

自由基、天然抗氧化剂与神经退行性疾病

神经退行性疾病,老年痴呆症(Alzheimer's disease,AD)、帕金森症(Parkinson'sDisease,PD)和中风(脑卒中)严重危害老年人的身体健康和生活质量。这些疾病的发病机制目前尚不完全清楚,也无有效治疗方法。目前的研究发现,氧化应激产生的活性氧和NO自由基在诱导细胞的凋亡和导致神经退行性疾病AD、PD和中风方面发挥了重要作用。该文章综述了神经退行性疾病的自由基机理和天然抗氧化剂对这些疾病的预防和治疗作用机理。天然抗氧化剂,如茶多酚,能够防止6-羟多巴胺(6-hydroxydopamine,6-OHDA)诱导的细胞凋亡,保护线粒体功能从而预防6-OHDP诱导大鼠的PD症状;大豆异黄酮和尼古丁作为抗氧化剂可以防止Amyloid-β(Aβ)诱导的海马细胞凋亡和转基因小鼠脑中Aβ的沉积,抑制6-OHDA诱导细胞凋亡过程线粒体细胞色素C释放。在转基因鼠海马CA1区的Aβ斑中,铜、铁浓度比周围神经明显增高,用尼古丁处理明显减少海马CA1区Aβ斑及其周围神经中铜和铁的浓度,尼古丁可以抑制分裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)的激活,核因子...     

Action of phorbol esters in cell culture: Mimicry of transformation,altered differentiation,and effects on cell membranes

The carcinogenic process is usually multifactor in its causation and multistep in its evolution. It is likely that entirely different molecular mechanisms underlie the many steps in this process. In contrast t o initiating carcinogens, the action of the tumor-promoting phorbol esters does not appear t o involve covalent binding t o cellular DNA and they are not mutagenic. Recent studies in cell culture have revealed two interesting biologic effects of the phorbol esters and related macrocyclic plant diterpenes. The first is that at nanomolar concentrations they induce several changes that resemble those seen in cells transformed by chemical carcinogens or tumor viruses. These include altered morphology and increased saturation density, altered cell surface fucose-glycopeptides, decrease in the LETS protein, increased transport of deoxyglucose, and increased levels of plasminogen activator and ornithine decarboxylase. In transformed cells exposed to phorbol esters the expression of these features is further accentuated. Phorbol esters do not induce normal cells to grow in agar but they do enhance the growth in agar of certain transformed cells. The second effect of the phorbol esters is inhibition of terminal differentiation. This effect extends to a variety of programs of differentiation and is reversible when the agent is removed. With certain cell culture systems induction of differentiation, rather than inhibition, is observed. Both the transformation mimetic and the differentiation effects are exerted by plant diterpenes that have tumor-promoting activity but not by congeners that lack such activity. The primary target of phorbol esters appears to be the cell membrane. Early membrane-related effects include enhanced uptake of 2-deoxyglucose and other nutrients, altered cell adhesion, induction of arachidonic acid release and prostaglandin synthesis, inhibition of the binding of epidermal growth factor t o cell surface receptors, altered lipid metabolism, and modifications in the activities of other cell surface receptors. A model of “two stage” carcinogenesis encompassing the known molecular and cellular effects of initiating carcinogens and tumor promoters is presented. According to this model, initiating carcinogens induce stable alterations in the cellular genome but these are not manifested until tumor promoters modulate programs of gene expression and induce the clonal outgrowth of the initiated cell.     

Involvement of Free Radicals in Excitotoxicity In Vivo

Abstract: Recent evidence has linked excitotoxicity with the generation of free radicals. We examined whether free radical spin traps can attenuate excitotoxic lesions in vivo. Pretreatment with N-tert -butyl-α-(2-sulfophenyl)-nitrone (S-PBN) significantly attenuated striatal excitotoxic lesions in rats produced by N -methyl- d -aspartate (NMDA), kainic acid, and α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA). In a similar manner, striatal lesions produced by 1-methyl-4-phenylpyridinium (MPP⁺), malonate, and 3-acetylpyridine were significantly attenuated by either S-PBN or α-phenyl- N-tert -butylnitrone (PBN) treatment. Administration of S-PBN in combination with the NMDA antagonist MK-801 produced additive effects against malonate and 3-acetylpyridine toxicity. Malonate injections resulted in increased production of hydroxyl free radicals (^•OH) as assessed by the conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid (DHBA). This increase was significantly attenuated by S-PBN, consistent with a free radical scavenging effect. S-PBN had no effects on malonate-induced ATP depletions and had no significant effect on spontaneous striatal electrophysiologic activity. These results provide the first direct in vivo evidence for the involvement of free radicals in excitotoxicity and suggest that antioxidants may be useful in treating neurologic illnesses in which excitotoxic mechanisms have been implicated.     

Alcohol-Induced Hepatotoxicity: A Role for Oxygen Free Radicals

Perfusion of isolated rat livers with ethanol at a concentration of 2g/l (%o) resulted in a release of glutamate-pyruvate-transaminase (GPT) and sorbitol dehydrogenase (SDH) into the perfusate as markers of toxicity. Inhibition of alcohol dehydrogenase by 4-methylpyrazole or of aldehyde dehydrogenase by cyanamide totally abolished ethanol hepatotoxicity despite of a severalfold increase in acetaldehyde concentration in the perfusate. Addition of superoxide dismutase or catalase clearly suppressed the ethanol-induced release of GPT and SDH, suggesting that 0₂～ and H₂0, are involved in this process. Also. chelation of iron ions by means of desferrioxamine displayed a clear inhibitory action, suggesting the involvement of an iron-catalyzed Haber-WeiB-reaction leading to the formation of OH radicals in the hepatotoxic response to ethanol. Our data suggest that during the metabolism of acetaldehyde primary reactive oxygen species ('0₂～, H₂0₂) are produced which may interact to yield hydroxyl or OH-like radicals, which possibly represent the hepatotoxic principle of ethanol.     

Alcohol-Induced Hepatotoxicity: A Role for Oxygen Free Radicals

Perfusion of isolated rat livers with ethanol at a concentration of 2g/l (%o) resulted in a release of glutamate-pyruvate-transaminase (GPT) and sorbitol dehydrogenase (SDH) into the perfusate as markers of toxicity. Inhibition of alcohol dehydrogenase by 4-methylpyrazole or of aldehyde dehydrogenase by cyanamide totally abolished ethanol hepatotoxicity despite of a severalfold increase in acetaldehyde concentration in the perfusate. Addition of superoxide dismutase or catalase clearly suppressed the ethanol-induced release of GPT and SDH, suggesting that 0₂∼ and H₂0, are involved in this process. Also. chelation of iron ions by means of desferrioxamine displayed a clear inhibitory action, suggesting the involvement of an iron-catalyzed Haber-WeiB-reaction leading to the formation of OH radicals in the hepatotoxic response to ethanol. Our data suggest that during the metabolism of acetaldehyde primary reactive oxygen species ('0₂∼, H₂0₂) are produced which may interact to yield hydroxyl or OH-like radicals, which possibly represent the hepatotoxic principle of ethanol.     

超氧化物歧化酶在氧自由基所引起的癌变中的作用

超氧化物歧化酶是一类抗氧化酶,它能催化超氧阴离子自由基的歧化反应,对机体起保护作用。氧自由基在某些情况下会对机体产生损伤作用。文章就氧自由基的产生、氧自由基与致癌的关系,以及超氧化物歧化酶在氧自由基所引起的癌变中的作用等方面进行了综述。     

Phospholipid Degradation and Cellular Edema Induced by Free Radicals in Brain Cortical Slices

Abstract: Cellular edema and increased lactate production were induced in rat brain cortical slices by xanthine oxidase and xanthine, in the presence of ferric ions. Lipid peroxidation, as measured by thiobarbituric acid-reactive malon-dialdehyde, was increased 174%. Among the various subcellular fractions of brain cortex, xanthine oxidase-stimulated lipid peroxidation was highest in myelin, mitochondria, and synaptosomes, followed by microsomes and nuclei. Antioxidants, catalase, chlorpromazine, and butylated hydroxytoluene inhibited lipid peroxidation in both homogenates and synaptosomes, indicating H₂O₂ and radicals were involved. Further, several free fatty acids, especially oleic acid (18:1), arachidonic acid (20:4), and docosahexaenoic acid (22:6) were released from the phospholipid pool concomitant with the degradation of membrane phospholipids in xanthine oxidase-treated synaptosomes. These data suggest that Upases are activated by free radicals and lipid peroxides in the pathogenesis of cellular swelling.     

Active Oxygen Radicals Induce Peroxidase Activity in Rice Blade Tissues

The relationship between active oxygen radicals and peroxidase induction on disease resistance in rice blades was investigated. Nitric oxide was produced in the whole blade stimulated by blast fungus elicitor. The induction of peroxidase activity was detected in active oxygen radical-treated rice blades 1 hour after treatment and thereafter. These results suggest that active oxygen radicals produced by stimulation with the elicitor could trigger peroxidase induction.     

自由基与细胞凋亡

细胞凋亡是指细胞在生理和病理情况下的一种死亡模式,广泛涉及到肿瘤、衰老和退行性病变等一系列疾病．最近有实验表明自由基与细胞凋亡有密切的关系．凋亡细胞内活性氧自由基（ROS）生成增加,同时消除ROS的能力下降.大多数凋亡障碍的细胞表现出ROS分子大量减少,若调节细胞内ROS含量,死亡率能随之改变;离子辐射能通过经自由基引起细胞的凋亡,培养细胞在无血清或撤除生长因子后发生的死亡也大多与细胞内自由基代谢酶如过氧化氢酶等的活性变化有关.提示自由基是参与调节细胞凋亡的重要因素之一.     

Effect of Oxygen-Derived Free Radicals and Oxidants on the Degradation in vitro of Membrane Phospholipids

The abilities of chemically generated hydroxyl radical (OH), superoxide anion (O^?) and hydrogen peroxide (H₂O₂) to degrade rat myocardial membrane phospholipids previously lableed with [1 -¹⁴C]arachidonic acid were studied. HO and H₂O₂ but not O₂^?_?, caused the degradation of phospha-tidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). With OH' and H₂O₂, the loss of radiolable in PC was accompanied by an increase in the radiolabel of lysophosphatidylcholine (LPC), but not in that of free fatty acid (FFA). These results suggest the hydrolysis of l-oxygen ester bond of PC by HO' and that H₂O₂ and that HO' and H₂O₂, but not O^?, are detrimental to the structure and function of membrane phospholipids. However, since μM amounts of HO' and mM amounts of H₂O₂ were necessary to affect the membrane phospholipids, it is likely that in the reprefused myocardium only HO', but not H₂O₂, may directly cause the breakdown of membrane phospholipids.     

Characteristics of GABA Release Induced by Free Radicals in Mouse Hippocampal Slices

The release of the inhibitory neurotransmitter GABA is generally enhanced under potentially cell-damaging conditions. The properties and regulation of preloaded [³H]GABA release from mouse hippocampal slices were now studied in free radical-containing medium in a superfusion system. Free radical production was induced by 0.01% of H₂O₂ in the medium. H₂O₂ markedly potentiated GABA release, which was further enhanced about 1.5-fold by K⁺ stimulation (50 mM). In Ca²⁺-free media this stimulation was not altered, indicating that the release was mostly Ca²⁺-independent. Moreover, omission of Na⁺ increased the release, suggesting that it is mediated by Na⁺-dependent transporters operating outwards, a conception confirmed by the enhancement with GABA homoexchange. Inhibition of the release with the ion channel inhibitors diisothiocyanostilbene-2,2′-disulphonate and 4-acetamido-4′-isothiocyanostilbene-2,2′-disulphonate indicates that Cl⁻ channels also participate in the process. This release was not modified by the adenosine receptor (A₁ and A_2a) agonists and ionotropic glutamate receptor agonists kainate, N-methy-d-aspartate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, whereas the agonists of metabotropic glutamate receptors of group I [(S)-3,5-dihydroxyphenylglycine] and of group II [(2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate] enhanced it by receptor-mediated mechanisms, the effects being abolished by their respective antagonists. The group III agonist l(+)-2-amino-4-phosphonobutyrate reduced the evoked GABA release, but this was not affected by the antagonist. Furthermore, the release was reduced by activation of protein kinase C by 4β-phorbol 12-myristate 13-acetate and by inhibition of tyrosine kinase by genistein and of phoshoplipase by quinacrine. On the other hand, increasing cGMP levels with the phosphodiesterase inhibitor zaprinast, selective for PDE5, 6 and 9, and NO production with the NO-generating compounds hydroxylamine, sodium nitroprusside and S-nitroso-N-penicillamine enhanced the release. The regulation of GABA release induced by free radical production proved thus to be rather complex. Under potentially cell-damaging conditions, the potentiation of GABA release may be a mechanism to counteract hyperactivity and reduce the effects of excitatory amino acid release. On the other hand, reduction of GABA release could be harmful and contribute to excitotoxic damage and neuronal degeneration.     

Effect of Free Radicals and Temperature on Sister Chromatid Exchanges in Hordeum vulgare L.

The clastogenic (chromosome-damaging) effect of many chemical and physical agents is believed to be mediated by reactive oxygen-detived radicals. The interaction of these free radicals with DNA and the significance of the radical-induced DNA lesions in mutagenesis and carcinogenesis have been the subjects of increasing interest during recent years. Sister chromatid exchange (SCE) reflects an interchange between DNA molecules at homologous loci within a replicating chromosome. SCE analysis was found to have increased use for monitoring the exposure of cell to mutagenic carcinogens. The authors found that the induction of SCEs in cells of Hordeum vulgare L. by ascorbic acid, mitomycin C, adriamycin and maleic hydrazid was through the action of free radicals. They also studied the influence of growth temperature on average generation time(AGT) and SCEs. and disclosed a close correlation between AGT and SCEs. The Brdu-Giemsa techniques were used for the detection of SCEs and AGT in cytological preparations of metaphase chromosomes.     

Endothelial Cells as A Source of Oxygen-Free Radicals An Esr Study

Endothelial cells were subjected to anoxia/reoxygenation in order to simulate some of the free radical mechanisms occurring in ischaemialreperfusion. With ESR and spin trapping using the spin traps 5.5-dimethyl-l-pyrroline-l-oxide (DMPO) and 3,3,5,5-dimethyl-l-pyrroline-l-oxide (M₄PO), the results show that upon reoxygenation of endothelial cells, following a period of anoxia, these cells generate superoxide (0₂). Cytotoxicity of the spin traps was measured by standard trypan blue exclusion methods. Cell injury or death was measured at various times during reoxygenation by lactate dehydrogenase (LDH) release. Experiments using oxypurinol, SOD, CAT and a combination of SOD and CAT show that while oxypurinol partially prevents spin adduct formation. the combination of SOD and CAT is more effective in doing so. These results suggest that the majority of the oxygen radicals produced by endothelial cells are done so exogenously. The results also suggest that endothelial cells are not only a source of oxygen radicals but also a target.