Activities of free radical metabolizing enzymes in tumours

9-Norbornyl-6-chloropurine (NCP) induces cell death through GSH depletion-associated ER stress and mitochondrial dysfunction

9-Norbornyl-6-chloropurine (NCP) is a representative of a series of antienteroviral bicycle derivatives with selective cytotoxicity towards leukemia cell lines. In this work we explored the mechanism of the antileukemic activity of NCP in T-cell lymphoblast cells (CCRF-CEM). Specifically, we searched for a potential link between its ability to induce cell death on the one hand and to modulate intracellular glutathione (GSH) that is necessary to its metabolic transformation via glutathione-S-transferase on the other hand. We have observed that GSH levels decreased rapidly in NCP-treated cells. Despite a complete regeneration following 24h of incubation with NCP, this profound drop in cellular GSH content triggered ER stress, ROS production and lipid peroxidation leading to the loss of mitochondrial membrane potential (MMP). These events induced concentration-dependent cell cycle arrest in G2/M phase and apoptosis. Both MMP loss and apoptosis were reversed by sulfhydryl-containing compounds (GSH, N-acetyl-l-cysteine). Furthermore, we have also shown that NCP-induced GSH decrease activated the Nrf2 pathway and its downstream targets

NAD(P)H

quinone oxidoreductase (NQO-1) and glutamate cysteine ligase modifier subunit (GCLm), thus explaining the fast restoration of GSH pool and ROS decrease. Importantly, we confirmed that the cell death-inducing properties of the compounds were co-dependent on their ability to diminish cellular GSH level by analyzing the relationships between the GSH-depleting potency and cytotoxicity in a series of other norbornylpurine analogs. Altogether, the results demonstrated that in CCRF-CEM cells NCP triggered apoptosis through GSH depletion-associated oxidative and ER stress and mitochondrial depolarization.

Alginic acid isolated from Sargassum wightii exhibits anti-inflammatory potential on type II collagen induced arthritis in experimental animals

The present study evaluated the anti-inflammatory potential of alginic acid isolated from the brown algae Sargassum wightii in type II collagen induced arthritic rats, a well established arthritic model that resembles more closely to human rheumatoid arthritis in its clinical, pathological, immunological and histological aspects. Type II collagen induced arthritic rats showed increased activities of inflammatory marker enzymes like cycloxygenase-2 (COX-2), lipoxygenase (5-LOX), xanthine oxidase (XO) and myeloperoxidase (MPO) along with increased concentration of rheumatoid factor (RF), ceruloplasmin and C-reactive protein (CRP). Treatment with alginic acid significantly reduced the activities of COX-2 and 5-LOX along with reduction in MPO, XO, RF and CRP. Alginic acid treatment reverted to the altered levels of hematological parameters like RBC count, WBC count and ESR in arthritic rats. Concentrations of proinflammatory cytokines like IL-1 β, TNF α and IL-6 were significantly higher in arthritic rats which were reduced on treatment with alginic acid. Increased activities of lysosomal enzymes that manifest the systemic damage during arthritis were significantly reduced by the treatment with alginic acid which indicates the reduction in the rupture and degradation of connective tissue. Histopathology of knee joint tissues showed that extensive bone degradation and synovial hyperplasia along with infiltrating cells and treatment with alginic acid reversed the histopathological changes which indicate the protective potential of alginic acid in rheumatoid arthritis.

Combined proteomic and molecular approaches for cloning and characterization of copper-zinc superoxide dismutase (Cu, Zn-SOD2) from garlic (Allium sativum)

Superoxide dismutases (SODs; EC 1.15.1.1) are key enzymes in the cells protection against oxidant agents. Thus, SODs play a major role in the protection of aerobic organisms against oxygen-mediated damages. Three SOD isoforms were previously identified by zymogram staining from Allium sativum bulbs. The purified Cu, Zn-SOD2 shows an antagonist effect to an anticancer drug and alleviate cytotoxicity inside tumor cells lines B16F0 (mouse melanoma cells) and PAE (porcine aortic endothelial cells). To extend the characterization of Allium SODs and their corresponding genes, a proteomic approach was applied involving two-dimensional gel electrophoresis and LC-MS/MS analyses. From peptide sequence data obtained by mass spectrometry and sequences homologies, primers were defined and a cDNA fragment of 456 bp was amplified by RT-PCR. The cDNA nucleotide sequence analysis revealed an open reading frame coding for 152 residues. The deduced amino acid sequence showed high identity (82-87%) with sequences of Cu, Zn-SODs from other plant species. Molecular analysis was achieved by a protein 3D structural model.

The oxidant/antioxidant status and cell death mode in oral squamous cell carcinoma

OBJECTIVE

Oxidative stress and imbalance in the oxidant/antioxidant system have a critical role in carcinogenesis by affecting necrosis and apoptosis. The aim of this study is to evaluate the oxidant/antioxidant status and cell death modes in patients with oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

Twenty-nine patients with OSCC and 29 control subjects were included in the study. The levels of malondialdehyde (MDA), advanced oxidation protein products (AOPP) and ferric reducing antioxidant power (FRAP) were determined in plasma samples of all subjects. The necrotic and apoptotic cell death modes were evaluated with M65 ELISA and M30 ELISA, respectively.

RESULTS

MDA and AOPP values as oxidative stress markers were higher in patients with OSCC than in the control group. FRAP values evaluating plasma antioxidant status increased in OSCC patients. M65 and M30 levels indicating necrosis and apoptosis were significantly higher in OSCC patients compared to controls. There were significant correlations between MDA, AOPP and FRAP; M65 and M30 values.

CONCLUSIONS

The elevated levels of oxidative stress markers together with the increase of antioxidant capacity and the presence of a strong correlation between MDA, AOPP and FRAP suggest an activation of antioxidant defense against accentuated oxidative stress determined in OSCC. Enhanced oxidation of lipids and proteins may cause decomposition of cell membranes with subsequent leakage of cytoskeletal cytokeratins as CK18 and caspase-cleaved CK18 (evaluated as M65 and M30, respectively) in the circulation, suggesting that both cell death modes are affected in OSCC.

Jacaric acid, a linolenic acid isomer with a conjugated triene system, has a strong antitumor effect in vitro and in vivo

In this study, we compared the cytotoxic effects of natural conjugated linolenic acids (CLnAs) on human adenocarcinoma cells (DLD-1) in vitro, with the goal of finding CLnA isomers with strong cytotoxic effects. The antitumor effect of the CLnA with the strongest cytotoxic effect was then examined in mice. The results showed that all CLnA isomers have strong cytotoxic effects on DLD-1 cells, with jacaric acid (JA) having the strongest effect. Examination of the mechanism of cell death showed that CLnAs induce apoptosis in DLD-1 cells via lipid peroxidation. The intracellular levels of incorporated CLnAs were measured to examine the reason for differences in cytotoxic effects. These results showed that JA was taken into cells efficiently. Collectively, these results suggest that the cytotoxic effect of CLnAs is dependent on intracellular incorporation and induction of apoptosis via lipid peroxidation. JA also had a strong preventive antitumor effect in vivo in nude mice into which DLD-1 cells were transplanted. These results suggest that JA can be used as a dietary constituent for prevention of cancer.

Ameliorative effect of methanol extract of Rubia cordifolia in N-nitrosodiethylamine-induced hepatocellular carcinoma

CONTEXT

Rubia cordifolia Linn. (Rubiaceae) is a medicinal plant used in the ayurvedic system of medicine. It is also known as Indian Madder or Manjistha and is traditionally used as an antiinflammatory, antiseptic, and galactopurifier, but its anticancer propertis are yet not known.

OBJECTIVE

The ameliorative effect of the Rubia cordifolia methanol extract on N-nitrosodiethylamine-induced experimental hepatocellular carcinogenesis in rats.

MATERIALS AND METHODS

Changes in liver weight, serum markers of liver damage, hydroxyl radicals, lipid peroxidation, levels of enzymic and nonenzymic antioxidants; mitochondrial and respiratory chain enzymes were also investigated using various biochemical parameters and histopathological studies. Male albino rats of Wistar strain were divided into four groups for a study period of 3 months. Animals of group I and group IV served as control and drug control, respectively. Hepatocellular carcinoma was induced in animals of groups II and III with 0.02% N-nitrosodiethylamine.

RESULTS

Upon Rubia cordifolia methanol extract co-treatment (250, 500, and 750 mg/kg bodyweight) in group III alone levels of serum marker enzymes and antioxidants increased significantly in a dose-dependent manner. The levels of hydroxyl radicals and lipid peroxidation decreased. Mitochondrial enzymes and respiratory chain enzymes, which were decreased in N-nitrosodiethylamine-induced rats, increased significantly in RC treated rats. Further histological analysis of liver confirmed the prevention of pathological changes caused by N-nitrosodiethylamine on Rubia cordifolia supplementation.

DISCUSSION AND CONCLUSION

These findings demonstrate that Rubia cordifolia can be a source of potent antioxidants for treatment of diseases such as cancer.

Chronic unpredictable stress exacerbates 7,12-dimethylbenz (a) anthracene induced hepatotoxicity and nephrotoxicity in Swiss albino mice

Oxidative stress, a pervasive condition induced by stress has been implicated and recognized to be a prominent feature of various pathological states including cancer and their progression. The present study sought to validate the effectiveness of chronic unpredictable stress (CUS) on hepatic and renal toxicity in terms of alterations of various in vivo biochemical parameters, oxidative stress markers and the extent of DNA damage in Swiss albino mice. Animals were randomized into different groups based on their exposure to CUS alone, 7,12-dimethylbenz (a) anthracene (DMBA) alone (topical), DMBA-12-O-tetradecanoylphorbol-13-acetate (TPA) (topical), and exposure to CUS prior to DMBA or DMBA-TPA treatment, and sacrificed after 16 weeks of treatment. Prior exposure to CUS increased the pro-oxidant effect of carcinogen as depicted by significantly compromised levels of antioxidants; superoxide dismutase, catalase, glutathione-S-transferase, glutathione reductase, reduced glutathione in hepatic and renal tissues accompanied by a significant elevation of thiobarbituric acid reactive species (TBARS) as compared to DMBA alone or DMBA-TPA treatments. Loss of structural integrity at the cellular level due to stress-induced oxidative damage was demonstrated by significant increases in the hepatic levels of intracellular marker enzymes such as glutamate oxaloacetate transaminase, glutamate pyruvate transaminase and alkaline phosphatase, and significantly reduced levels of uric acid in kidney tissues. The results of DNA damage studies further positively correlated with all the above biochemical measurements. Thus, exposure to physical or psychological stress may significantly enhance the hepatotoxic and nephrotoxic potential of carcinogens through enhanced oxidative stress even if the treatment is topical.

Preparation of pH-sensitive liposomes retaining SOD mimic and their anticancer effect

We prepared an anticancer drug based on a pH-sensitive liposome retaining Fe-porphyrin as an SOD mimic. The liposomes contained cationic/anionic lipid combinations and were composed of Fe-porphyrin, 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine, dimethylditetradecylammonium bromide, sodium oleate, and Tween-80. The Fe-porphyrin was released from the liposome at low pH, and the cytotoxicity for cancer cells by the liposome depended on the acidic environments of the endosomes in the cells. Furthermore, although the liposome exhibited an excellent anticancer effect on a gastric cancer cell line, the SOD activity of Fe-porphyrin was shown to have a significant influence on the cytotoxicity toward cancer cells. These findings suggest that the pH-sensitive liposome retaining the Fe-porphyrin as an SOD mimic promises to be a novel anticancer drug for endosomal escape.

Effect ofVitex negundo leaf extract on the free radicals scavengers in complete Freund's adjuvant induced arthritic rats

The effect of the oral administration ofVitex negundo leaf extract on the levels of enzymic and non-enzymic antioxidants were studied in the adjuvant induced arthritic (AIA) rats The levels of antioxidant enzymes such as SOD, CAT, GPx, G6PD, GSH and Vit-C were estimated in various groups of the experimental rats. It was observed that the antioxidant enzyme levels in the AIA were significantly low when compared to normal rats. A significant decrease in enzymic antioxidant-SOD, CAT, GPx, G6PD and non-enzymic antioxidant-GSH, Vit-C were observed in the liver of AIA rats compared to the normal rats. These results suggest that the leaf extract ofVitex negundo possesses antioxidant activity.

Antioxidant and Anticancer Properties of Metalloporphyrins Embedded in Liposomes

Reactive oxygen species (ROS) are implicated in many disease such as inflammation, arteriosclerosis, cancer. Therefore, a water-soluble cationic metalloporphyrins with SOD activity are studied widely as antioxidant drugs. Further, liposomes are applied to drug delivery system (DDS) as drug carriers and investigated for example disposition and stability. We designed PEG modified liposomes for avoiding reticuloendothelial system (RES) and embedded cationic metalloporphyrins for DDS, evaluated antioxidant and anticancer property. Preservation of these particle size measured DLS in an in vitro system, in order to simulate in vivo conditions of flow. Result of this measurement, we found Pluronic F-68/ liposomes have a long circulation property, and avoid fusion with plasma protein. SOD activity was determined by the stopped-flow analysis and cytochrome c assay, which allowed the evaluation of k(cat) and IC(50) for the reaction with a superoxide anion radical (.O(2)(-)). Anti cancer property was measured by cell viability test. We found that F-68/ liposomes were the most effective catalyst as antioxidant and anticancer. These results revealed that porphyrin-embedded PEG-liposomes had the property of long circulation in blood and that this compound was effective as a SOD model compound with a drug carrier capacity.

Superoxide dismutase as a target enzyme for Fe-porphyrin-induced cell death

The cell viability of human cancer cell lines treated with [5,10-bis(N-methyl-4-pyridyl)-15,20-diphenyl]porphinatoiron(III) (cis-FeMPy(2)P(2)P) has been estimated. The cis-FeMPy(2)P(2)P is a superoxide dismutase (SOD) mimic in vitro that exhibited a significant toxicity in cancer cell lines. This toxicity is rather due to pro-oxidant properties of the iron-porphyrin in vivo. We have demonstrated that there was the relationship between the LD(50) values calculated from the viability of cancer cell lines treated with cis-FeMPy(2)P(2)P and the SOD activities of the cell lines. Furthermore, the inhibition of SOD by antisense S-oligonucleotide increased the cytotoxic effect of cis-FeMPy(2)P(2)P against cancer cells. These results suggest that SOD is a target enzyme for the cell death induced by cis-FeMPy(2)P(2)P as a new class of anticancer agents.

Synthesis of the conjugated trienes 5E,7E,9E,14Z,17Z-eicosapentaenoic acid and 5Z,7E,9E,14Z,17Z-eicosapentaenoic acid, and their induction of apoptosis in DLD-1 colorectal adenocarcinoma cells

During the course of our recent study on the anti-tumor effect of conjugated eicosapentaenoic acids (CEPA), we found that acid mixtures prepared by treating EPA with KOH in ethylene glycol induced potent apoptotic cell death in human tumor cells via membrane phospholipid peroxidation. Interestingly, the KOH-treated CEPA mixtures were more cytotoxic than EPA and CLA and had no effect on normal human fibroblast cells. To identify the specific cytotoxic FA in the CEPA mixture, we synthesized possible candidates for the active species. Here, we report the synthesis of (5E,7E,9E, 14Z, 17Z)-5,7,9,14,1 7-eicosapentaenoic acid (E-CEPA) and its 5-(Z) isomer (Z-CEPA), both of which are conjugated trienes that exist naturally in red algae (Ptilota filicina J. Agardh). E-CEPA and Z-CEPA were synthesized from methyl 5-oxopentanoate in six steps, using three types of Wittig reactions as the key steps. Next, we examined the cytotoxicity of E-CEPA and Z-CEPA in human tumor cells and confirmed their bioactivity. Both E-CEPA and Z-CEPA had a strong cytotoxic reaction in tumor cells, and this effect occurred through induction of apoptosis.

Cell death by reactive oxygen species generated from water-soluble cationic metalloporphyrins as superoxide dismutase mimics

We investigated the effect on cell death of reactive oxygen species induced by water-soluble cationic metalloporphyrins with superoxide dismutase (SOD) activity. The SOD activity of 5,10,15,20-tetrakis(4-N-methylpyridyl)]porphine (MPy(4)P) containing Fe, Mn or Cu was measured using a cytochrome c assay by the xanthine/xanthine oxidase system and stopped-flow kinetic analysis. Cell viability of four cell lines treated with metalloporphyrins, mitomycin c (MMC), or cisplatin was estimated by a trypan blue exclusion assay. FeMPy(4)P with a high SOD activity showed a significant cytotoxicity compared with MMC and cisplatin, while CuMPy(4)P without SOD activity exhibited no cytotoxicity. However, MnMPy(4)P showing an SOD activity as high as that of FeMPy(4)P did not indicate cytotoxicity. These findings suggest that FeMPy(4)P as SOD mimic converts intracellular O2(*-) to H(2)O(2) and that it rapidly reacts with H(2)O(2) to form *OH, causing DNA damage and inducing cell death. On the other hand, MnMPy(4)P did not participate in the Fenton reaction, so that DNA damage in the cells treated with MnMPy(4)P was not observed. In addition, the cytotoxicity by the metalloporphyrin was inversely correlated with the SOD activity of the cells and the selective damage at cellular and DNA levels was confirmed. We believe that for an anticancer drug with antioxidant ability O(2)(*-) is useful as a target molecule to induce selective cell death between cancer and normal cells and that metalloporphyrins showing SOD activity and Fenton-like reaction are a new class of anticancer agents.

Antioxidant status, erythrocyte membrane lipid peroxidation and osmotic fragility in malignant lymphoma patients

We studied erythrocyte and leukocyte superoxide dismutase and catalase activities, erythrocyte malondialdehyde (MDA) and osmotic fragility and plasma L-ascorbic acid and L-dehydroascorbic acid levels in adult patients with acute lymphoblastic leukemia (ALL), Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL) before and after treatment. SOD activity was elevated in leukocytes of ALL and HD patients before treatment, and borderlike-significantly elevated in leukocytes of the same patients after treatment in comparison to the control subjects. SOD activity was not changed in NHL patients before or after chemotherapy. Erythrocyte superoxide dismutase and catalase activities were elevated in the three groups of lymphomas before and after treatment. MDA level and osmotic fragility of red blood cells of patients with lymphomas were increased before and after treatment in comparison to the control group. Plasma L-ascorbic acid concentrations were decreased, whereas L-dehydroascorbic acid concentrations were increased in ALL, HD and NHL patients before and after treatment. There were also significant differences in the activities of the antioxidant enzymes, concentrations of antioxidants, MDA and osmotic fragility in the most of the malignant lymphoma patients. The present data suggest that hematological complications and autoimmune hemolytic anemia might be attributed to the oxidative stress produced by malignant lymphomas.

Metabolism of n -9, n -6 and n -3 fatty acids in hepatoma Morris 7777 cells. Preferential accumulation of linoleic acid in cardiolipin

The objective of this study was to investigate, using a pulse-chase technique, the different incorporation of (1-(14)C) n -9, n -6 and n 3 fatty acids into hepatoma lipids and their secretion to the culture medium. Docosahexaenoic acid (DHA) accumulated preferentially into the triacylglycerol while arachidonic acid (AA) did into the phospholipid fraction. DHA was poorly secreted to the culture medium whereas AA was secreted to a large extent. The fatty acids were initially esterified mainly into phosphatidylcholine and phosphatidylethanolamine. During the 24 h chase, a general shift from phosphatidylcholine to phosphatidylethanolamine was observed. Linoleic acid was esterified in cardiolipin to a much greater extent than any other fatty acid and it was not converted to more polyunsaturated fatty acids. The supplementation of the culture medium with polyunsaturated fatty acids had no inhibitory effect on the growth of the hepatoma cells, in marked contrast to observations made in other tumoral cells. The reasons for the resistance of the hepatoma cells to polyunsaturated fatty acid toxicity, including the possible antioxidant effect of linoleic acid accumulation in cardiolipin, are also discussed.

Do conjugated eicosapentaenoic acid and conjugated docosahexaenoic acid induce apoptosis via lipid peroxidation in cultured human tumor cells?

Conjugated eicosapentaenoic acid (CEPA) and conjugated docosahexaenoic acid (CDHA) with triene structure, isomerized by alkaline treatment, showed intensive cytotoxicity with LD(50) at 12 and 16 microM, respectively, in DLD-1 cells (colorectal adenocarcinoma), while they had no effect on normal human fibroblast cell lines such as MRC-5, TIG-103, and KMS-6 cells. Cytotoxic action of CEPA and CDHA was also demonstrated in other tumor cell lines including HepG2, A549, MCF-7, and MKN-7 cells. alpha-Tocopherol suppressed cytotoxicity of CEPA and CDHA in tumor cells, and the cytotoxicity involved membrane phospholipid peroxidation. CEPA and CDHA induced DNA condensation and fragmentation in DLD-1 cells, indicating the involvement of apoptosis in this cytotoxic mechanism. Furthermore, previous reports have shown that lipid peroxidation product induces cell death, including apoptotic cell death in different cell lines. CEPA and CDHA have been demonstrated in cultured cells to cause cell death via lipid peroxidation and apoptosis in the absence of alpha-tocopherol.

Inhibition of drug-naive and -resistant leukemia cell proliferation by low molecular weight thiols

The aim of these studies was to investigate the ability of cysteamine and its congeners to arrest the proliferation of leukemic cells and to determine the physico-chemical properties responsible for this ability. Fifteen low molecular weight thiol-bearing compounds were shown to arrest the proliferation of CCRF-CEM cells and a methotrexate-resistant subline, with IC50 values between 10(-5) and 10(-4) M. Cysteamine arrested proliferation by slowing the passage of cells through S phase. These cells subsequently resumed cycling, although a proportion went on to die by apoptosis. The antiproliferative action of cysteamine was shown to depend, in part, on H2O2 production. This ability to generate peroxide is shared by many thiol compounds, and molecular modeling indicated that thiol groups were required for the antiproliferative actions of the congeners of cysteamine. Molecular modeling also revealed that the most efficacious antiproliferative agents were those that had their amino acid and thiol moieties separated by an intramolecular distance of 3.17 to 5.9 A, as exemplified by WR 1065 and the aminothiophenols. These findings indicate that thiol-bearing compounds may have some efficacy in the treatment of drug-naive and -resistant leukemia cells.

Effects of polyunsaturated fatty acids and their n-6 hydroperoxides on growth of five malignant cell lines and the significance of culture media

We examined effects of polyunsaturated fatty acids (PUFA), their corresponding hydroperoxy fatty acids (hp-PUFA), as well as various pro- and antioxidants on the growth of tumor cells in culture. When cultured in RPMI 1640 medium, A-427 and WEHI clone 13 cells were both highly sensitive to hydroperoxy docosahexaenoic acid (hp-DHA), but they were far less sensitive in minimum essential medium (MEM). In contrast, A-427 cells were also sensitive to DHA in both culture media, while WEHI clone 13 cells, as well as other cell lines, tested in their respective media, were resistant. The lower sensitivity of the cell lines to hp-DHA in MEM-medium was apparently due to a more rapid reduction of hp-DHA to the corresponding hydroxy-DHA in MEM-medium. Addition of glutathione (GSH) to the culture medium abolished the effects of hp-DHA, but not the effects of DHA, while depletion of intracellular GSH levels by L-buthionine-S,R-sulfoximine strongly enhanced the cytotoxic effect of hp-DHA, but not the cytotoxic effect of DHA. alpha-Tocopherol protected A-427 cells against the toxic effect of DHA and abolished the induced lipid peroxidation, while it did not protect against the toxic effects of hp-DHA in A-427 or WEHI clone 13 cells. Ascorbic acid reduced the cytotoxic effect of DHA, but potentiated the toxic effect of hp-DHA while selenite essentially abolished the toxicity of both DHA and hp-DHA. These results indicate that sensitivity of tumor cell lines to PUFA and their oxidation products depends on their antioxidant defense mechanisms, as well as culture conditions, and establishes hp-DHA as a major, but probably not the sole, metabolite responsible for cytotoxicity of DHA.

Salubrious effect of Semecarpus anacardium against lipid peroxidative changes in adjuvant arthritis studied in rats

Oxygen derived free radicals are known to play an important role in the etiology of tissue injury in rheumatoid arthritis. The effect of milk extract of Semecarpus anacardium nuts at the dose level of 150 mg/kg body weight for 14 days on adjuvant arthritis was studied for gaining insight into the intrigue disease in relation to the lipid peroxidation and antioxidant defence system. Increased lipid peroxides' levels in both plasma and tissues (liver, kidney and heart) of adjuvant arthritis was significantly decreased by the administration of the drug. The antioxidant defence system studied in tissues of arthritic animals were altered significantly as evidenced by the decreased level of non-enzymatic antioxidants (GSH, vitamin E, vitamin C, NPSH and TSH) and enzymatic antioxidants (catalase and GPx except SOD). Administration of Semecarpus anacardium nut extract brings back the altered antioxidant defence components to near normal levels. These observations suggest that the diseased state of adjuvant arthritis may be associated with augmented lipid peroxidation and the administration of the drug may exert its antiarthritic effect by retarding lipid peroxidation and causing a modulation in cellular antioxidant defence system.

Polyunsaturated fatty acids increase the sensitivity of 36B10 rat astrocytoma cells to radiation-induced cell kill

Polyunsaturated fatty acids (PUFA) such as gamma-linolenic acid (GLA, 18:3n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) have been shown to be cytotoxic to tumor cells. The objective of this work was to study the effects of PUFA on the radiation response of a 36B10 rat astrocytoma cell line. Supplementation of the astrocytoma cells with 15-45 microM GLA, EPA, or DHA produced marked changes in the fatty acid profiles of their phospholipids and neutral lipids. The methylene bridge index of these lipids increased significantly. These PUFA also exerted cytotoxic effects, as determined using the clonogenic cell survival assay. While GLA and DHA produced a moderate cell-killing effect, EPA was extremely cytotoxic, especially at a concentration of 45 microM. The monounsaturated oleic acid (OA, 18:1n-9) did not affect cell survival. Further, all three PUFA, and particularly GLA, increased the radiation-induced cell kill; OA did not enhance the effect of radiation. alpha-Tocopherol acetate blocked the enhanced radiation sensitivity of GLA- and DHA-supplemented cells. In conclusion, GLA, EPA, and DHA supplementation prior to, during, and after irradiation can enhance the radiation-induced cytotoxicity of rat astrocytoma cells. GLA and DHA supplementation post-irradiation also enhanced the radiation response of the 36B10 cells. Because GLA maximally increases the radioresponsiveness of a rat astrocytoma, this PUFA might prove useful in increasing the therapeutic efficacy of radiation in the treatment of certain gliomas.

Effect of cis-unsaturated fatty acids on cellular oxidant stress in macrophage tumor (AK-5) cells in vitro

Cis-unsaturated fatty acids (c-UFAs) induced decreased survival of macrophage tumor (AK-5) cells in vitro. The cytotoxic action of c-UfAs was associated with an increase in free radical generation and lipid peroxidation process. In addition, exposure of AK-5 cells to various c-UFAs for a short period (1 h) decreased the cellular concentrations of anti-oxidants: superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione reductase, glutathione and vitamin E. However, prolonged (24 h) exposure of AK-5 cells to c-UFAs enhanced the levels of SOD with little or no change in the concentrations of catalase, glutathione peroxidase and glutathione reductase. These results indicate that c-UFAs can enhance free radical generation and lower the concentrations of various anti-oxidants in the tumor cells which may explain the cytotoxic action of c-UFAs.

Antioxidant and glutathione-associated enzymes in Wilms' tumour after chemotherapy

The present study demonstrates the activities of antioxidant and glutathione-associated enzymes and the level of glutathione in Wilms' tumour (nephroblastoma) samples after chemotherapy (mainly actinomycin D and vincristine). We observed higher activity of superoxide dismutase in Wilms' tumour compared to adjacent morphologically unchanged kidney. On the other hand, in this tumour lower activities of catalase and the glutathione-associated enzymes glutathione synthetase, gamma-glutamyl transpeptidase, glutathione reductase and total glutathione S-transferases (GST) were found. Using isoelectric focusing we separated different forms of GST in tested tissues and revealed lower activities of the basic enzymes in Wilms' tumour, which may be responsible for the decrease of total GST activity. Moreover, we found the acidic isoenzymes to be the predominant class of GST in nephroblastoma. In Wilms' tumours with unfavourable histology a high activity of these isoenzymes together with a high level of GSH were observed. We suggest that these parameters may participate in the known phenomenon of anticancer drug resistance of tumours with unfavourable histology.

Free radical-dependent suppression of growth of mouse myeloma cells by alpha-linolenic and eicosapentaenoic acids in vitro

Alpha-linolenic acid (ALA) and eicosapentaenoic acid (EPA) exhibited potent cytotoxic action on SP 2/0 mouse myeloma cells in vitro. Both SOD and vitamin E could inhibit the action of ALA and EPA indicating a role for reactive oxygen species and lipid peroxides. In addition, both ALA and EPA enhanced the formation of superoxide anion, hydrogen peroxide and lipid peroxides, and caused a reduction in the levels of antioxidant enzymes: SOD, catalase and glutathione peroxidase and induced significant damage to DNA in SP 2/0 cells. Thus, ALA and EPA inhibit antioxidant defenses of the cell and damage the DNA, which can ultimately lead to tumor cell lysis.

Status of antioxidant systems in human carcinoma of uterine cervix

Lipid peroxides, glutathione content and the activities of antioxidant enzymes were estimated in patients who had carcinoma of the uterine cervix, and the values were compared with those of normal. The results showed a remarkable reduction in glutathione content and in the activities of catalase and superoxide dismutase in neoplastic tissue in stages II, III and IV (P < 0.001) whereas the activities of glutathione peroxidase and glutathione reductase were significantly lower in stage III and IV patients than that of normal controls. The tissue level of lipid peroxides and the activity of glutathione-S-transferase were found to be significantly higher than that of normals from stage II onwards. These observations suggested the impaired antioxidant status in carcinoma of the uterine cervix.

Lipid peroxidation and prostaglandins in colorectal cancer

Dietary fat, arachidonic acid metabolism and lipid peroxidation have all been implicated in colorectal carcinogenesis. Fatty acids, prostaglandins (PGE2, PGF2 alpha) and malondialdehyde (MDA), the stable end-product of lipid peroxidation of polyunsaturated fatty acids (PUFAs), were studied in paired tumour and normal mucosa of 20 patients with colorectal cancer. Levels of arachidonic acid and total PUFAs were increased in the phospholipid fraction of tumours (P < 0.05). Levels of PGE2 and MDA were also higher in tumours (P < 0.001) and there was a significant correlation between MDA and PGE2 concentrations (rs = 0.69, P < 0.01). In contrast to previously reported in vitro studies, this work suggests that lipid peroxidation may be enhanced in human colorectal tumours. As PGE2 and MDA have been shown to be involved in carcinogenesis, these may be considered potential therapeutic targets for preventing or treating colorectal carcinoma.

Porphyrins, porphyrias, cancer and photodynamic therapy--a model for carcinogenesis

Porphyrins are the only and most powerful photosensitizers synthesized internally. To understand better the involvement of porphyrins in photosensitization reactions, the heme biosynthetic pathway is first described, as well as the main features of its regulation in both erythroid and hepatic cells. Most disorders of porphyrin metabolism, known as porphyrias, are characterized by porphyrin accumulation. A full discussion of these diseases, their classification and relevant biochemical and clinical signs are presented. Abnormalities in heme biosynthesis in disorders other than porphyrias, such as iron-deficient and sideroblastic anemias, lead poisoning, hereditary tyrosinemia, chronic renal disease and alcoholism, are briefly considered. A complete survey of the experimental research on the biosynthesis of porphyrins in tumors and of the important association between cancer and porphyrias is dealt with. The link to photodynamic therapy (PDT) emerges naturally and this is treated from the point of view of using porphyrins endogenously formed by the tumors for their localization and PDT. Finally, considering the nature of the alterations occurring in heme metabolism in tumors, and porphyrias and their ubiquity, a model is discussed where the abnormality of heme synthesis is involved in the initiating lesion of carcinogenesis. The model strongly predicts that the incidence of cancer will be high in cells with abnormal heme metabolism, suggesting that porphyric patients may be at greater risk of the development of cancer.

Effect of synthetic protease inhibitor on histologic changes and free radical activity in hamsters with pancreatic cancer

To investigate the effects of synthetic trypsin inhibitors on pancreatic cancer, camostat (FOY-305) was administered orally to hamsters with experimental pancreatic cancer induced by diisopropanol nitrosamine (DIPN). The effect of free radicals on carcinogenesis was examined by measuring the tissue levels of the scavengers superoxide dismutase (SOD) and glutathione peroxidase (GSX-Px), and pancreatic tissues were examined histologically. Cancers developed in all hamsters that survived 24 weeks in the DIPN group and the FOY group, but 80% of the cancers in the DIPN group were tubular adenocarcinomas, and 91% of those in the FOY group papillary adenocarcinomas. The SOD activity in the DIPN group was significantly lower in the cancerous area and the borderline region than in the non-cancerous region and normal tissue. SOD activity in the cancerous and borderline regions was higher in the FOY groups than in the DIPN group. GSH-Px levels in the borderline and non-cancerous regions were significantly higher in the FOY group than in the DIPN group. These results suggest that the synthetic protease inhibitor slows the progress of pancreatic cancer by its free radical scavenging activity.

The consequences of doxorubicin quinone reduction in vivo in tumour tissue

A clear role for quinone reduction in the mechanism of action of doxorubicin has still to be established. There are three possible outcomes of this form of doxorubicin metabolism: (1) drug free radical formation, redox cycling and generation of reactive oxygen species (ROS) resulting in lipid peroxidation and DNA damage; (2) covalent binding of reactive drug intermediates to DNA; and (3) formation of an inactive 7-deoxyaglycone metabolite. In this work, the occurrence of each of these pathways has been studied in vivo in a subcutaneously growing rat mammary carcinoma (Sp 107). Doxorubicin was administered by direct intratumoural injection either as the free drug or incorporated in albumin microspheres (10-40 microns diameter). There was no evidence of an increase in lipid peroxidation over background after either treatment at any time point studied. In fact, doxorubicin administration resulted in a statistically significant reduction in lipid peroxidation at the later time points studied compared to control (no drug treatment), e.g. 24 hr: control, 21.7 +/- 2.8 SD nmol malondialdehyde/g tissue; free doxorubicin (70 micrograms drug), 14.5 +/- 4.0 SD nmol/g (P < 0.01 Student's t-test) and doxorubicin microspheres (70 micrograms drug), 17.4 +/- 1.1 nmol/g (P < 0.05). Covalent binding to DNA was measured by a 32P-post-labelling technique. Low levels of four putative drug-DNA adducts were detected; however, there were no qualitative or quantitative differences in profiles between free drug and microspheres. High 7-deoxyaglycone metabolite concentrations comparable to the parent drug itself were detected after administration of microspheres (3.0 micrograms/g +/- 1.7 SD at 24 hr and 3.1 micrograms/g +/- 1.1 SD at 48 hr). In contrast, these metabolites were present at levels close to the limit of detection of our HPLC assay after free drug (0.04 microgram/g +/- 0.03 SD at 24 hr and 0.02 microgram/g +/- 0.03 SD at 48 hr). Thus, 7-deoxyaglycone metabolite formation can occur in tumour tissue (indicating active drug quinone reduction) without concomitant increases in the level of lipid peroxidation or the levels of drug-DNA adducts. In conclusion, the main biological consequence of doxorubicin quinone reduction in vivo in tumour tissue would appear to be drug inactivation to a 7-deoxyaglycone metabolite rather than drug activation to DNA reactive species or ROS.

Reduced superoxide dismutase activity in UVB-induced hyperproliferative pig epidermis

Decreased superoxide dismutase (SOD) activity has been reported in various hyperproliferative keratinocytes. In order to elucidate the relationship between epidermal SOD activity and keratinocyte proliferation, we employed in vivo UVB irradiation. Following UVB irradiation at twice the minimum erythema dose, pig epidermis revealed an initial decrease in thymidine incorporation and mitotic counts for at least 48 h, followed by a marked increase, the peak of which was observed at 96 h after irradiation, and a return to basal levels by 5-7 days. The SOD activity remained constant during the initial 48 h and then decreased to about 50% at 96 h, mainly due to a decreased Cu,Zn-SOD activity. Our results indicate that the increased keratinocyte proliferation induced by UVB irradiation is accompanied by a decrease in SOD activity, and that this decrease is mainly due to a decreased Cu,Zn-SOD activity. No alteration in SOD activity was noted during the initial hypoproliferative phase following irradiation.

Superoxide dismutase in psoriasis, squamous cell carcinoma and basal cell epithelioma: an immunohistochemical study

Monoclonal antibodies against human Cu,Zn-superoxide dismutase (SOD) and Mn-SOD were used to stain frozen sections of normal and abnormal human skin. In normal human epidermis, the Cu,Zn-SOD antibody almost exclusively stained the basal cells. Mn-SOD antibody weakly stained the whole of the epidermis but more predominantly the basal cell layer. In psoriasis, Cu,Zn-SOD antibody mainly stained the basal cells of the lowest parts of the elongated rete ridges. Basal cells corresponding to the tip of the dermal papillae were weakly stained. Mn-SOD staining was considerably decreased in the psoriatic epidermis. In squamous cell carcinoma, staining with both Cu,Zn-SOD and Mn-SOD antibodies was decreased, and single cells positive for Cu,Zn-SOD were scattered throughout the tumour nests. In basal cell epithelioma, Cu,Zn-SOD staining was intense and diffusely distributed throughout the tumour nests, while Mn-SOD staining was absent.

Different effects of carbon tetrachloride on carcinogen-induced hepatocellular carcinoma and normal liver of the rat: lowered lipid peroxidation and accelerated necrosis in cancer

To investigate molecular responses to lipid peroxidative stimuli in neoplastic cells, lipid peroxidation was induced in liver of rats bearing 3'-methyl-4-dimethylaminoazobenzene-induced hepatocellular carcinoma by injecting a high dose of carbon tetrachloride (CCl4), a strong lipoperoxidative reagent. Normal rat livers with or without CCl4 treatment served as controls. CCl4 administration markedly provoked fatty metamorphosis, visualized by oil red O staining, in normal livers while minimal fatty changes were seen in hepatocellular carcinomas, where necrosis was often observed instead. After CCl4 treatment, the thiobarbituric acid values (representing levels of lipid peroxides in the tissue) were increased two-fold in the untreated normal liver, but were unchanged in the cancer tissue. Levels of vitamin C, an acutely reactive antioxidant, measured by high-performance liquid chromatography were not influenced by the CCl4 injection in the cancer tissue whereas a significant decrease was evident in normal livers. The total fatty acid content, measured by gas chromatography, was significantly lower in the cancer tissue than in the normal liver while the ratio of polyunsaturated fatty acids (PUFAs) in total fatty acids was little changed. Resistance of hepatocellular cancer cells to fatty metamorphosis and their susceptibility to necrosis induced by free radicals may be due to the paucity of the target PUFAs in their cell membrane fraction, resulting in low levels of lipid peroxides. Peroxidation of PUFAs might act as a "shock absorber" against free radical-induced toxic cell death in normal cells.

Arachidonic acid and docosahexaenoic acid are increased in human colorectal cancer

Increased arachidonic acid concentrations in experimental rodent colonic cancer have been described recently. In humans, a reduced erythrocyte stearic acid to oleic acid ratio has been reported in patients with colorectal cancer and it has been proposed that similar changes exist in the cancer tissue. The long chain fatty acids in the cancers of 15 patients with colorectal cancer were measured and compared with values in the unaffected mucosa. The values were expressed as mean (SD) mg fatty acid/g tissue and compared by analysis of variance. In the cancer tissue arachidonic acid was increased (0.703 (0.109) mg/g v 0.603 (0.127) mg/g, p less than 0.05) as was docosahexaenoic acid (0.211 (0.066) mg/g v 0.148 (0.039) mg/g, p less than 0.001). In contrast, the stearic acid to oleic acid ratio in the cancer tissue was increased rather than decreased, as previously suggested (0.36 (0.05) v 0.29 (0.7), p less than 0.01). Increased arachidonic acid and docosahexaenoic acid concentrations may be related to reduced lipid peroxidation, which is a feature of rapidly growing cells. Alternatively, the increased arachidonic acid values could be due to enhanced desaturase activity upon linoleic and linolenic acid, leading perhaps to increased formation of prostaglandins and other lipoxygenase products.

Free radicals, antioxidant enzymes, and carcinogenesis

Free radicals are found to be involved in both initiation and promotion of multistage carcinogenesis. These highly reactive compounds can act as initiators and/or promoters, cause DNA damage, activate procarcinogens, and alter the cellular antioxidant defense system. Antioxidants, the free radical scavengers, however, are shown to be anticarcinogens. They function as the inhibitors at both initiation and promotion/transformation stage of carcinogenesis and protect cells against oxidative damage. Altered antioxidant enzymes were observed during carcinogenesis or in tumors. When compared to their appropriate normal cell counterparts, tumor cells are always low in manganese superoxide dismutase activity, usually low in copper and zinc superoxide dismutase activity and almost always low in catalase activity. Glutathione peroxidase and glutathione reductase activities are highly variable. In contrast, glutathione S-transferase 7-7 is increased in many tumor cells and in chemically induced preneoplastic rat hepatocyte nodules. Increased glucose-6-phosphate dehydrogenase activity is also found in many tumors. Comprehensive data on free radicals, antioxidant enzymes, and carcinogenesis are reviewed. The role of antioxidant enzymes in carcinogenesis is discussed.

Comparison of the inhibitory effect of polyunsaturated fatty acids on prostaglandin synthesis I oral squamous carcinoma cells

Polyunsaturated fatty acids (PUFAs) have been shown to suppress the growth rate of human osteogenic sarcoma cells and to have selective cytotoxic activity against human cancer cells. The purpose of this study was to investigate the efficacy of various PUFAs on inhibition of prostaglandin (PG) synthesis by oral squamous carcinoma cells (SCC-25). A significant inhibition of PGE2 and PGF2 alpha synthesis in SCC-25 was observed by all PUFAs tested except in the case of linoleic acid (LA) at 10 microM level. At 10 microM level the rank order of inhibition of PG synthesis by PUFAs was docosahexaenoic (DHA) greater than eicosapentaenoic (EPA) + DHA greater than dihomogamma-linolenic (DGLA) greater than EPA greater than alpha-linolenic (ALA) greater than linoleic (LA). At 50, 75, 100 microM the rank order of inhibition was DGLA greater than EPA greater than EPA + DHA greater than DHA greater than ALA greater than LA.

Polyunsaturated fatty acids stimulate superoxide formation in tumor cells: a mechanism for specific cytotoxicity and a model for tumor necrosis factor?

Some neoplastic cell lines are readily killed when incubated in the presence of polyunsaturated fatty acids (PUFA). In an attempt to elucidate this phenomenon, we studied PUFA-driven superoxide (O2-) production by cultured NS-1 cells (murine lymphoid tumor cells). We find: (1) Even in the absence of added PUFA, NS-1 cells generate O2- (i.e., reduce nitroblue tetrazolium). (2) addition of PUFA increases O2- by greater than 50%. (3) Artificial loading of NS-1 cells with liposome encapsulated superoxide dismutase prevents the majority of spontaneous and PUFA-driven NBT reduction. We conclude that PUFA drives O2- generation by tumor cells, that this generation is largely intracellular, and that this phenomenon may help explain toxicity of PUFA for tumor cells.

Lack of protein-mediated alpha-tocopherol transfer between membranes in the cytoplasm of ascites hepatomas

Transfer-stimulating activity for alpha-tocopherol and the concentration of alpha-tocopherol and peroxidized lipids in rat ascites hepatoma cells were compared with those from normal and regenerating liver. The ability of supernatants from ascites hepatomas (AH-13, AH-60C, AH-109A) to enhance the transfer of alpha-tocopherol was much lower than that from normal livers. The alpha-tocopherol per mg protein of supernatant from ascites hepatomas was lower than that from normal liver. Regenerating liver showed almost the same values as normal liver in activity to stimulate the transfer of alpha-tocopherol and alpha-tocopherol content of the supernatant. By gel filtration, about 60% of alpha-tocopherol in the supernatant of normal liver was detected in the fractions containing the 30 K protein, which stimulates transfer of alpha-tocopherol between membranes, whereas no significant amount of alpha-tocopherol was detected in 30 K protein fractions of AH-60C supernatant. Little stimulating activity for alpha-tocopherol transfer was detected in AH-60C, AH-109A and AH-13. All ascites hepatomas tested contained less arachidonic acid and docosahexaenoic acid than normal and regenerating liver. An absorption peak with maximum intensity at 233 nm, which is due to conjugated dienes, was observed in UV-absorption spectra of ascites hepatoma total lipids, indicating that peroxidized lipids accumulate in these cells. With normal and regenerating liver, no significant peak due to conjugated dienes was detected.

In vitro modulation of antioxidant enzymes in normal and malignant renal epithelium

The activities of three antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase, were monitored in isolated human renal adenocarcinoma tissues and in cultured human renal adenocarcinoma cells. The results were compared to the activities of these enzymes in the proposed cell of origin, isolated human proximal tubular tissues, and cultured proximal tubular epithelial cells. Strong modulation of these enzymes by culture conditions was observed in normal cells but not in carcinoma cells. Low levels of cellular lipid peroxidation, as assessed by levels of malondialdehyde (MDA), were observed in adenocarcinoma cells under the culture conditions tested with one exception: greatly elevated MDA was observed in renal adenocarcinoma cells grown on plastic in serum-free, chemically defined medium. This increased lipid peroxidation correlated with a loss of cell viability under these conditions.

Factor analysis of the activities of superoxide dismutase, catalase and glutathione peroxidase in normal tissues and neoplastic cell lines

Exploratory factor analysis of reported specific activities of the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase in normal human tissues, normal mouse tissues, vertebrate red blood cells and neoplastic human cell lines shows that the activities of copper-zinc superoxide dismutase, catalase and glutathione peroxidase in normal tissues are influenced by a single factor. Catalase activity has the highest loading and correlation with this factor, suggesting a catalase- or hydrogen peroxide-related influence. The activity of manganese superoxide dismutase is influenced by a separate factor. The activities of copper-zinc and manganese superoxide dismutases in normal tissues therefore appear to be dichotomously regulated. The activities of superoxide dismutase and glutathione peroxidase in vertebrate red blood cells are influenced by a single factor. The activity of catalase is influenced by a separate factor. The roles of glutathione peroxidase and catalase in hydrogen peroxide catabolism in red blood cells in fact differ. In neoplastic human cell lines, two bipolar factor factors appear to influence the activities of catalase and manganese superoxide dismutase, and glutathione peroxidase and copper-zinc superoxide dismutase, respectively. The factors are, however, mainly catalase and glutathione peroxidase activity factors as the loadings and correlations of manganese superoxide dismutase on the one hand and copper-zinc superoxide dismutase on the other, with the respective factors, are relatively small. Potentially low superoxide production and intrinsically low peroxidizability of tumour cell membranes underlie the peculiar variation of antioxidant enzyme activities in tumour cells. Factor analysis is proposed as a heuristic data reduction and hypothesis-creating technique for the variation of antioxidant and other functionally-linked enzyme activities in normal and pathological cells and tissues.

Studies on lipid peroxidation in normal and tumour tissues. The Novikoff rat liver tumour

A study has been made of the factors that contribute to the decreased rates of lipid peroxidation under different pro-oxidant conditions in intact Novikoff tumour cells, and in microsomal suspensions prepared from Novikoff tumour cells, compared with isolated normal rat hepatocytes and microsomal suspensions prepared from normal rat liver. The pro-oxidant conditions were the addition of either NADPH, NADPH + ADP + iron, NADPH + CCl4 or ascorbate+iron to the experimental systems used, or exposure to gamma-radiation. Contributory factors to the lower rates of lipid peroxidation observed include: a significant decrease in the polyunsaturated fatty acid content of Novikoff cells or Novikoff microsomes; the decreases are especially marked for the C20:4 and C22:6 fatty acids; a very marked reduction in NADPH-cytochrome c reductase; and no detectable content of cytochrome P-450. Another, and in our opinion critical, contribution to the diminished rate of lipid peroxidation in the tumour material is the substantial increase in alpha-tocopherol relative both to total lipid and to methylene-interrupted double bonds in fatty acids. Moreover, the alpha-tocopherol is the major contributor to lipid-soluble chain-breaking antioxidant in lipid extracts of normal liver and of Novikoff tumour material.

Antioxidant systems in tumour cells: the levels of antioxidant enzymes, ferritin, and total iron in a human hepatoma cell line

The human hepatoma cell line Hep 3B, which has the hepatitis B virus genome, shows over 80% decrease of copper/zinc superoxide dismutase activity, over 90% decrease of manganese superoxide dismutase activity, over 70% decrease of catalase activity, absence of glutathione peroxidase and glutathione S-transferase activities, over 270-fold increase of ferritin content and 25-fold increase of total iron compared to normal autopsy liver. These conditions of low antioxidant enzyme activities and iron overload are those which support the accumulation of oxygen free-radicals and DNA damage commonly considered to be carcinogenic mechanisms.

The importance of free radicals and catalytic metal ions in human diseases

The study of free radical reactions is not an isolated and esoteric branch of science. A knowledge of free radical chemistry and biochemistry is relevant to an understanding of all diseases and the mode of action of all toxins, if only because diseased or damaged tissues undergo radical reactions more readily than do normal tissues. However it does not follow that because radical reactions can be demonstrated, they are important in any particular instance. We hope that the careful techniques needed to assess the biological role of free radicals will become more widely used.