Lipid hydroperoxide-induced apoptosis: lack of inhibition by Bcl-2 over-expression

Peroxidised dietary lipids impair intestinal function and morphology of the small intestine villi of nursery pigs in a dose-dependent manner

The objective of this study was to investigate the effect of increasing degrees of lipid peroxidation on structure and function of the small intestine of nursery pigs. A total of 216 pigs (mean body weight was 6·5 kg) were randomly allotted within weight blocks and sex and fed one of five experimental diets for 35 d (eleven pens per treatment with three to four pigs per pen). Treatments included a control diet without added lipid, and diets supplemented with 6 % soyabean oil that was exposed to heat (80°C) and constant oxygen flow (1 litre/min) for 0, 6, 9 and 12 d. Increasing lipid peroxidation linearly reduced feed intake (P<0·001) and weight gain (P=0·024). Apparent faecal digestibility of gross energy (P=0·001) and fat (P<0·001) decreased linearly as the degree of peroxidation increased. Absorption of mannitol (linear,P=0·097) andd-xylose (linear,P=0·089), measured in serum 2 h post gavage with a solution containing 0·2 g/ml ofd-xylose and 0·3 g/ml of mannitol, tended to decrease progressively as the peroxidation level increased. Increasing peroxidation also resulted in increased villi height (linear,P<0·001) and crypt depth (quadratic,P=0·005) in the jejunum. Increasing peroxidation increased malondialdehyde concentrations (quadratic,P=0·035) and reduced the total antioxidant capacity (linear,P=0·044) in the jejunal mucosa. In conclusion, lipid peroxidation progressively diminished animal performance and modified the function and morphology of the small intestine of nursery pigs. Detrimental effects were related with the disruption of redox environment of the intestinal mucosa.

Cytotoxic effects of biosynthesized zinc oxide nanoparticles on murine cell lines

The aim of this study is to evaluate the in vitro cytotoxic activity and cellular effects of previously prepared ZnO-NPs on murine cancer cell lines using brown seaweed (Sargassum muticum) aqueous extract. Treated cancer cells with ZnO-NPs for 72 hours demonstrated various levels of cytotoxicity based on calculated IC50 values using MTT assay as follows: 21.7 ± 1.3 μg/mL (4T1), 17.45 ± 1.1 μg/mL (CRL-1451), 11.75 ± 0.8 μg/mL (CT-26), and 5.6 ± 0.55 μg/mL (WEHI-3B), respectively. On the other hand, ZnO-NPs treatments for 72 hours showed no toxicity against normal mouse fibroblast (3T3) cell line. On the other hand, paclitaxel, which imposed an inhibitory effect on WEHI-3B cells with IC50 of 2.25 ± 0.4, 1.17 ± 0.5, and 1.6 ± 0.09 μg/mL after 24, 48, and 72 hours treatment, respectively, was used as positive control. Furthermore, distinct morphological changes were found by utilizing fluorescent dyes; apoptotic population was increased via flowcytometry, while a cell cycle block and stimulation of apoptotic proteins were also observed. Additionally, the present study showed that the caspase activations contributed to ZnO-NPs triggered apoptotic death in WEHI-3 cells. Thus, the nature of biosynthesis and the therapeutic potential of ZnO-NPs could prepare the way for further research on the design of green synthesis therapeutic agents, particularly in nanomedicine, for the treatment of cancer.

Oleic acid promotes adaptability against oxidative stress in 3T3-L1 cells through lipohormesis

Although fatty acids are important components of biological membranes, energy sources, and signal transducers or precursors of lipid mediators, excess intake of fatty acids and their accumulation cause obesity and metabolic syndrome. Thus, fatty acid quantity is known to be an important factor for obesity-related diseases, but the effects of different types of fatty acids (i.e., fatty acid quality) on human health are not completely understood. We here focused on the relationship between fatty acid quality and oxidative stress by investigating whether resistibility to tert-butyl hydrperoxide (t-BuOOH)-induced oxidative stress in 3T3-L1 cells varied according to the fatty acid type. Among eight fatty acids (both saturated and unsaturated) tested, oleic acid (OA) exerted the most pronounced cytoprotective effects, with efficacy over a wide range of concentrations. OA treatment markedly enhanced the intracellular levels of lipid peroxidation markers, including N(ε)-(hexanoyl)lysine, 4-hydroxy-2-nonenal, and acrolein. The levels of these markers in OA-treated cells were decreased after t-BuOOH exposure, whereas the levels in untreated control cells were notably increased after t-BuOOH exposure. Our results suggested that unsaturated fatty acids, particularly OA, could promote an adaptive response and enhance cell tolerance through increased cellular antioxidative capacity via OA-induced mild lipid peroxidation (lipohormesis), and thus protect cells against subsequent oxidative stress-related injury.

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.

Quinestrol treatment induced testicular damage via oxidative stress in male Mongolian gerbils (Meriones unguiculatus)

The hypothesis that quinestrol exerts testicular damage via oxidative stress was investigated in male gerbils using a daily oral gavage of 3.5 mg/kg body weight for 2 weeks (the multidose-treated group) or 35 mg/kg body weight (the single-dose-treated group). The testicular histological morphology, antioxidant capacity and malondialdehyde (MDA) concentration in testicular tissue and plasma were assessed at 15, 30, and 60 days following treatment. The results showed that the activity of the antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxide (GSH-Px), and total antioxidant capacity (T-AOC), at 15 days after treatment in testicular tissue decreased, which led to the MDA concentration increasing while at the same time germ cells were rarefied and showed an irregular distribution in seminiferous tubules of quinestrol-treated gerbils. At 30 days, the testicular weight and antioxidant capacity continued to decrease, while the MDA concentration continued to increase, and testicular histopathological changes were more pronounced. Single-dose and multidose drug treatment had a similar effect on the antioxidant enzymes and MDA, but testicular damage was relatively severe at 15 and 30 days after multidose treatment. By 60 days of treatment withdrawal, however, the above parameters recovered to control levels. The results show that quinestrol causes reversible damage to gerbil testes that might be caused by the oxidative stress and that multidose treatment has more effects on testicular damage compared with one-dose treatment.

15-Lipoxygenase-1 as a tumor suppressor gene in colon cancer: is the verdict in?

15-Lipoxygenase-1 (15-LOX-1) is an inducible and highly regulated enzyme in normal human cells that plays a key role in the production of lipid signaling mediators, such as 13-hydroxyoctadecadienoic acid (13-HODE) from linoleic acid. 15-LOX-1 significantly contributes to the resolution of inflammation and to the terminal differentiation of normal cells. 15-LOX-1 is downregulated in human colorectal polyps and cancers. Emerging data support a tumor suppressor role for 15-LOX-1, especially in colon cancer. These data indicate that 15-LOX-1 promotes various anti-tumorigenic events, including cell differentiation and apoptosis, and inhibits chronic inflammation, angiogenesis, and metastasis. The transcriptional repression of 15-LOX-1 in colon cancer cells is complex and involves multiple mechanisms (e.g., histone methylation, transcriptional repressor binding). Re-expression of 15-LOX-1 in colon cancer cells can function as an important therapeutic mechanism and could be further exploited to develop novel treatment approaches for this common cancer.

DHA Hydroperoxides as a Potential Inducer of Neuronal Cell Death: a Mitochondrial Dysfunction-Mediated Pathway

During the lipid peroxidation reaction, lipid hydroperoxides are formed as primary products. Several lines of evidence suggest that lipid hydroperoxides can trigger cell death in many cell types, including neurons. In a screening of lipid hydroperoxides which can induce toxicity in neuronal cells, we found docosahexaenoic acid hydroperoxides (DHA-OOH) induced much severe levels of reactive oxygen species generation and cell death in human neuroblastoma SH-SY5Y cells compared to the hydroperoxides of linoleic acid and arachidonic acid. Therefore, we focused on DHA-OOH, and demonstrated that DHA-OOH apparently induced an apoptosis in the neuronal cells through several apoptotic hallmarks including nuclei condensation, DNA fragmentation, poly (ADP-ribose) polymerase cleavage and increased activity of caspase-3. We also found the signaling changes in mitochondria-mediated apoptosis, such as cytochrome c release and increased expression of Bcl-2, as well as a dose-dependent attenuation of mitochondrial membrane potential in the DHA-OOH treated cells. These data indicated DHA hydroperoxide as a potential inducer of apoptosis in human neuroblastoma SH-SY5Y cells, which may be mediated by mitochondria dysfunction pathway.

Programmed cell death of the megagametophyte during post-germinative growth of white spruce (Picea glauca) seeds is regulated by reactive oxygen species and the ubiquitin-mediated proteolytic system

The megagametophyte of white spruce (Picea glauca) seeds undergoes programmed cell death following seed germination. This process is characterized by distinct morphological and biochemical features, such as DNA fragmentation and the induction of proteases. Biphasic production of hydrogen peroxide was detected in the megagametophyte following seed germination. ROS scavengers or inhibitors of ROS production decreased caspase-like protease activity and slowed the progression of cell death. One catalase (CAT) of white spruce reacted with antibodies directed against cotton-seed CAT. The corresponding CAT gene was cloned and compared with the catalase genes of other plant species. The activity of the white spruce CAT enzyme was stimulated by tyrosine phosphorylation. The phosphorylated CAT was subjected to ubiquitination and degraded by the proteasome. Furthermore, the proteasome inhibitor MG132 inhibited the degradation of CAT and delayed cell death. These results suggest that the interplay of CAT and the ubiquitin-mediated proteolytic system is critical in the control of ROS production and subsequent cell death.

Lipid oxidation predominates over protein hydroperoxide formation in human monocyte-derived macrophages exposed to aqueous peroxyl radicals

In U937 and mouse myeloma cells, protein hydroperoxides are the predominant hydroperoxide formed during exposure to AAPH or gamma irradiation. In lipid-rich human monocyte-derived macrophages (HMDMs), we have found the opposite situation. Hydroperoxide measurements by the FOX assay showed the majority of hydroperoxides formed during AAPH incubation were lipid hydroperoxides. Lipid hydroperoxide formation began after a four hour lag period and was closely correlated with loss of cell viability. The macrophage pterin 7,8-dihydroneopterin has previously been shown to be a potent scavenger of peroxyl radicals, preventing oxidative damage in U937 cells, protein and lipoprotein. However, when given to HMDM cells, 7,8-dihydroneopterin failed to inhibit the AAPH-mediated cellular damage. The lack of interaction between 7,8-dihydroneopterin and AAPH peroxyl radicals suggests that they localize to separate cellular sites in HMDM cells. Our data shows that lipid peroxidation is the predominant reaction occurring in HMDMs, possibly due to the high lipid content of the cells.

Palatinose and oleic acid act together to prevent pancreatic islet disruption in nondiabetic obese Zucker rats

We showed previously that 8-wk consumption of a diet containing palatinose (P, a slowly-absorbed sucrose analogue) and oleic acid (O) ameliorates but a diet containing sucrose (S) and linoleic acid (L) aggravates metabolic abnormalities in Zucker fatty (fa/fa) rats. In this study, we aimed to identify early changes in metabolism in rats induced by certain combinations of carbohydrates and fatty acids. Specifically, male Zucker fatty rats were fed an isocaloric diet containing various combinations of carbohydrates (P; S) and fatty acids (O; L). After 4 wk, no significant differences in body weight, visceral fat mass, plasma parameters (glucose, insulin, lipids, and adipokines), hepatic adiposity and gene expression, and adipose inflammation were observed between dietary groups. In contrast, pancreatic islets of palatinose-fed (PO and PL) rats were smaller and less fibrotic than sucrose-fed (SO and SL) rats. The abnormal alpha-cell distribution and sporadic staining of active caspase-3 common to islets of linoleic-acid-fed rats were not observed in oleic-acid-fed (PO and SO) rats. Accordingly, progressive beta-cell loss was seen in SL rats, but not in PO rats. These findings suggest that pancreatic islets may be initial sites that translate the effects of different combinations of dietary carbohydrates and fats into metabolic changes.

Bioactive peroxides as potential therapeutic agents

Present review describes research on more than 280 natural anticancer agents isolated from terrestrial and marine sources and synthetic biologically active peroxides. Intensive searches for new classes of pharmacologically potent agents produced by terrestrial and marine organisms have resulted in the discovery of dozens of compounds possessing high cytotoxic, antibacterial, antimalarial, and other activities as an important source of leads for drug discovery.

Potent inhibitory effect of trans9, trans11 isomer of conjugated linoleic acid on the growth of human colon cancer cells

This study compared the growth inhibitory effects of pure conjugated linoleic acid (CLA) isomers [cis(c)9,c11-CLA, c9,trans(t)11-CLA, t9,t11-CLA, and t10,c12-CLA] on human colon cancer cell lines (Caco-2, HT-29 and DLD-1). When Caco-2 cells were incubated up to 72 h with 200 microM, each isomer, even in the presence of 10% fetal bovine serum (FBS), cell proliferation was inhibited by all CLA isomers in a time-dependent manner. The strongest inhibitory effect was shown by t9,t11-CLA, followed by t10,c12-CLA, c9,c11-CLA and c9,t11-CLA, respectively. The strongest effect of t9,t11-CLA was also observed in other colon cancer cell lines (HT-29 and DLD-1). The order of the inhibitory effect of CLA isomer was confirmed in the presence of 1% FBS. CLA isomers supplemented in the culture medium were readily incorporated into the cellular lipids of Caco-2 and changed their fatty acid composition. The CLA contents in cellular lipids were 26.2+/-2.7% for t9,t11-CLA, 35.9+/-0.3% for c9,t11-CLA and 46.3+/-0.8% for t10,c12-CLA, respectively. DNA fragmentation was clearly recognized in Caco-2 cells treated with t9,t11-CLA. This apoptotic effect of t9,t11-CLA was dose- and time-dependent. DNA fragmentation was also induced by 9c,11t-CLA and t10,c12-CLA. However, fragmentation levels with both isomers were much lower than that with t9,t11-CLA. t9t11-CLA treatment of Caco-2 cells decreased Bcl-2 levels in association with apoptosis, whereas Bax levels remained unchanged. These results suggest that decreased expression of Bcl-2 by t9t11-CLA might increase the sensitivity of cells to lipid peroxidation and to programmed cell death, apoptosis.

Effect of polyunsaturated fatty acid-enriched phosphatidylcholine and phosphatidylserine on butyrate-induced growth inhibition, differentiation and apoptosis in Caco-2 cells

Phospholipids are fascinating in terms of important bio-functional compounds. The present work investigated the effect of polyunsaturated phosphatidylcholine (PC) and phosphatidylserine (PS) on butyrate-induced growth inhibition, differentiation and apoptosis using Caco-2 cells. Growth inhibition of Caco-2 cells became apparent 24 h after addition of PC while it took 48 h with PS. Alkaline phosphatase activity of Caco-2 cells increased with combined PC or PS and sodium butyrate (NaBT) at 72 h, indicating that PC and PS enhanced cell differentiation in the presence of NaBT. An increased enrichment factor was also found when cells were treated with combinations of PC or PS and NaBT. These results suggest that marine PC and PS can be considered to be potentially useful colon cancer chemotherapy agents with high bio-availability.

Enhanced 15-HPETE production during oxidant stress induces apoptosis of endothelial cells

Oxidant stress plays an important role in the etiology of vascular diseases by increasing rates of endothelial cell apoptosis, but few data exist on the mechanisms involved. Using a unique model of oxidative stress based on selenium deficiency (-Se), the effects of altered eicosanoid production on bovine aortic endothelial cells (BAEC) apoptosis was evaluated. Oxidant stress significantly increased the immediate oxygenation product of arachidonic acid metabolized by the 15-lipoxygenase pathway, 15-hydroxyperoxyeicosatetraenoic acid (15-HPETE). Treatment of -Se BAEC with TNFalpha/cyclohexamide (CHX) exhibited elevated levels of apoptosis, which was significantly reduced by the addition of a specific 15-lipoxygenase inhibitor PD146176. Furthermore, the addition of 15-HPETE to PD146176-treated BAEC, partially restored TNF/CHX-induced apoptosis. Increased exposure to 15-HPETE induced apoptosis, as determined by internucleosomal DNA fragmentation, chromatin condensation, caspase-3 activation, and caspase-9 activation, which suggests mitochondrial dysfunction. The expression of Bcl-2 protein also was decreased in -Se BAEC. Addition of a caspase-9 inhibitor (LEHD-fmk) completely blocked 15-HPETE-induced chromatin condensation in -Se BAEC, suggesting that 15-HPETE-induced apoptosis is caspase-9 dependent. Increased apoptosis of BAEC as a result of oxidant stress and subsequent production of 15-HPETE may play a critical role in a variety of inflammatory based diseases.

Oxidative damage, aging and anti-aging strategies

The last two decades brought remarkable insight into the nature of normal aging in multicellular organisms. However, we are still far away from realizing extension of maximum lifespan in humans. An important modulator of lifespan is oxidative damage induced by reactive species, such as reactive oxygen species (ROS). Studies from yeast, Caenorhabditis and Drosophila primarily focused on (1) reduced generation or (2) elimination of ROS but have two principal shortcomings: (1) dietary restriction and single gene mutations are often associated with physiological impairments and (2) overexpression of components of the antioxidant system extend lifetime only under stress-induced conditions. Recent results from Drosophila indicate the involvement of an endogenous repair and elimination system for oxidatively damaged proteins in the process of aging. This system includes methionine sulfoxide reductase A (MSRA) and the carbonyl reductase Sniffer, the protein-ubiquitin ligase Parkin and the chaperone Hsp22. In this review we summarize different anti-aging strategies and discuss a synergistic interaction between protection against free radicals and specific repair/elimination of oxidative damage in lifespan extension primarily using the model system Drosophila. To achieve lifespan extension, available experiments are often methodically grouped into (1) caloric restriction, (2) single gene mutation, and (3) overexpression of genes. Here we summarize different strategies by a more causal classification: (1) prevention of ROS generation, (2) reducing free ROS level, and (3) repair and elimination of ROS-damaged proteins.

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.

Conjugated eicosapentaenoic acid (EPA) inhibits transplanted tumor growth via membrane lipid peroxidation in nude mice

Both conjugated linoleic acid (CLA) and eicosapentaenoic acid (EPA) have an antitumor effect. Hence, we hypothesized that a combination of conjugated double bonds and an (n-3) highly unsaturated fatty acid would produce stronger bioactivity. To verify the antitumor effect of conjugated EPA (CEPA), we transplanted DLD-1 human colon tumor cells into nude mice, and compared the tumor growth between CEPA-fed mice and CLA- and EPA-fed mice. After tumor cell inoculation, mice were assigned to 1 of 4 groups (control, CLA, EPA, and CEPA) consisting of 10 mice each. The control group received only safflower oil fatty acids, whereas the remaining groups received a mixture of safflower oil fatty acids and 20 g/100 g of total fatty acids as CLA, EPA, or CEPA. Mice were fed once every 2 d for 4 wk at a dose of 50 mg/mouse at each feeding. After 4 wk, tumor growth in CEPA-fed mice was significantly suppressed, compared with that in CLA- (P < 0.005) and EPA-fed mice (P < 0.001). DNA fragmentation in the tumor tissues of the CEPA-fed mice occurred more frequently than in the CLA- (P < 0.001) and EPA-fed mice (P < 0.001), suggesting that CEPA induced apoptosis in the tumor tissues. To further investigate the mechanism, the level of oxidative stress in the tumor tissues was determined. The CEPA-fed mice showed significant lipid peroxidation, compared with the CLA- (P < 0.001) and EPA-fed mice (P < 0.001). Therefore, we verified that CEPA has a stronger in vivo antitumor effect than EPA and CLA, and that CEPA acts through induction of apoptosis via lipid peroxidation.

Lipid Peroxidation during the Hypersensitive Response in Potato in the Absence of 9-Lipoxygenases

Hypersensitive cell death is an important defense reaction of plants to pathogen infection and is accompanied by lipid peroxidation processes. These may occur non-enzymatically by the action of reactive oxygen species or may be catalyzed by enzymes such as alpha-dioxygenases, lipoxygenases, or peroxidases. Correlative data showing increases in 9-lipoxygenase products in hyper-sensitively reacting cells have so far suggested that a large part of lipid peroxidation is mediated by a specific set of 9-lipoxygenases. To address the significance of 9-lipoxygenases for this type of pathogen response in potato, RNA interference constructs of a specific pathogen-induced potato 9-lipoxygenase were transferred to potato plants. Significantly reduced 9-lipoxygenase transcript levels were observed in transgenic plants after pathogen treatment. In addition, 9-lipoxygenase activity was hardly detectable, and levels of 9-lipoxygenase-derived oxylipins were reduced up to 12-fold after pathogen infection. In contrast to wild type plants, high levels of non-enzymatically as well as 13-lipoxygenase-derived oxylipins were present in 9-lipoxygenase-deficient plants. From this we conclude that during the normal hypersensitive response in potato, lipid peroxidation may occur as a controlled and directed process that is facilitated by the action of a specific 9-lipoxygenase. If 9-lipoxygenase-mediated formation of hydroperoxides is repressed, autoxidative lipid peroxidation processes and 13-lipoxygenase-mediated oxylipins synthesis become prominent. The unaltered timing and extent of necrosis formation suggests that the origin of lipid hydroperoxides does not influence pathogen-induced cell death in potato.

Bcl-2 overexpression increases survival in human retinal pigment epithelial cells exposed to H(2)O(2)

The integrity of the retinal pigment epithelium, especially that of the macula is essential for the preservation of vision into old age. The chronic exposure to sunlight and peroxidized lipids from phagocytized photoreceptor outer segments imposes a high level of oxidative stress on the retinal tissues, which increases with age as antioxidant protection declines and therefore could accelerate apoptosis. Bcl-2 known to facilitate mitochondrial DNA repair and cellular survival in other tissues was overexpressed in a single clone of human retinal pigment epithelium cells after stable transfection with humanbcl-2 in rhoSFV-neoexpression factor. Near confluent cells (2nd-4th generation permanently bcl-2 transfected) were protected from mitochondrial dysfunction after exposure to H(2)O(2) up to 150 microM. With 200 microM H(2)O(2), function in transfected cells declined by only 25% control activity as determined by MTT reduction assays, compared to wild type and vector only transfected cells expressing normal bcl-2 levels. Similarly the bcl-2 -transfected cells were more resistant to mitochondrial DNA damage after H(2)O(2) treatment than the other groups and suffered 50% less damage after exposure to 200 microM H(2)O(2), as assayed by quantitative polymerase chain reaction assays. These data suggest that bcl-2 overexpression protects human RPE cells from mitochondrial respiratory dysfuction, mitochondrial DNA damage and promotes cellular survival in response to oxidative stress induced by H(2)O(2).

Synergistic interaction between vinorelbine and gamma-linolenic acid in breast cancer cells

It has been suggested that exogenous unsaturated fatty acids (UFAs) may increase the cytotoxic activity of cancer chemotherapeutic agents. We examined how y-linolenic acid (GLA; 18: 3n-6), the most promising UFA in the treatment of human tumors, affects the effectiveness of the lipophilic drug vinorelbine (VNR) on human breast carcinoma cell lines. Cells were exposed simultaneously to VNR and GLA or sequentially to GLA followed by VNR. Cell viability was determined by MTT assay. The increase in VNR-induced cell growth inhibition was measured by dividing the IC50 and IC70 values (50 and 70% inhibitory concentrations, respectively) that were obtained when the cells were exposed to VNR alone with those with VNR plus GLA. We found that GLA enhanced in a dose-dependent manner the cell growth inhibitory activity of VNR on MCF-7 cells (up to 9-fold). As GLA by itself showed anti-proliferative effects, possible GLA-VNR interactions at the cellular level were assessed employing the isobologram analysis and the combination index (CI) method of Chou-Talalay. Both methods showed an overall synergism between GLA and VNR in MCF-7 cells. At a high level of cell kill, the synergism was greater when a 24 h GLA pre-exposure or co-exposures were tested. Synergy was likewise observed with the GLA-VNR combination in MDA-MB-231, T47D, and SK-Br3 breast cancer cells. In all cell lines, the synergism was independent of the treatment schedule and the exposure time. Under conditions inhibiting lipid peroxidation using Vitamin E (dl-alpha-tocopherol), the enhancing effect of GLA (an easily oxidizable UFA) on VNR activity was partially abolished. However, when Vitamin E was used in combination, a similar synergistic increase in growth inhibition was obtained. These latter observations strongly implies that the synergistic effects of GLA with VNR are not mediated through a mechanism involving a generation of lipoperoxides. For comparison, the effects of other UFAs were examined on VNR chemosensitivity: GLA was the most potent at enhancing VNR activity, followed by docosahexaenoic acid (22: 6n-3), eicosapentaenoic acid (20: 5n-3) and alpha-linolenic acid (18: 3n-3), whereas linoleic acid (18: 2n-6) and arachidonic acid (20: 4n-6) did not increase VNR chemosensitivity. Very high concentrations of oleic acid (OA; 18:1 n-9), an UFA inversely correlated with breast cancer risk, also enhanced VNR effectiveness. Thus, various types of UFAs were not equivalent with respect to their actions on VNR effectiveness. In conclusion, our results give experimental support to the hypothesis that some UFAs can be used as modulators of tumor cell chemosensitivity and provide the rationale for in vivo preclinical investigation.

Macrophages, oxidation, and endometriosis

Retrograde menstruation has been suggested to be the cause for the presence of endometrial cells in the peritoneal cavity. However, little is known about the events that lead to the adhesion and growth of these cells that ultimately result in endometriosis, considering the fact that the disease occurs only in certain women despite the common occurrence of retrograde menstruation in most women. We postulate that, in normal women, the endometrial cells and tissue that arrive in the peritoneal cavity during menstruation are effectively removed by macrophages that are chemoattracted and become resident tissue macrophages in the peritoneal cavity. In contrast, the peritoneal macrophages in women with endometriosis are nonadherent and ineffectively scavenged, resulting in the sustained presence and growth of the endometrial cells. We also postulate that the peritoneal fluid is not a passive reservoir of the factors secreted by cells of the peritoneum, but actively promotes endometriosis. The peritoneal fluid is rich in lipoproteins, particularly low-density lipoprotein, which generates oxidized lipid components in a macrophage-rich inflammatory milieu. The oxidants exacerbate the growth of endometriosis by inducing chemoattractants such as MCP-1 and endometrial cell growth-promoting activity. We provide evidence for the presence of oxidative milieu in the peritoneal cavity of women with endometriosis, the nonscavenging properties of macrophages that are nonadherent, and the synergistic interaction between macrophages, oxidative stress, and the endometrial cells. For example, the peritoneal fluid lipoproteins of subjects with endometriosis have increased the propensity to undergo oxidation as compared with plasma lipoproteins, and the subjects also have increased titer of autoantibodies to oxidatively modified proteins. If the oxidative proinflammatory nature of the peritoneal fluid is an important mediator of endometriosis growth, anti-inflammatory agents and antioxidants might afford protection against endometriosis.

Fatty acid oxidation and signaling in apoptosis

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.

Evidence for oxidative stress involved in physiological leaf spot formation in winter and spring barley

ABSTRACT A leaf spot disease with unknown etiology has become more pronounced in spring and winter barley in Germany in recent years. The symptoms are similar to net blotch and Ramularia leaf spots, but the causal agents of these diseases are not identified. The symptom expression varied much on cultivars. Cultivars most affected by the disease of both spring and winter barley showed a significantly higher level of superoxide (O(2) ) production and lipid peroxidation (malondialdehyde), but a lower level of antioxidant potential expressed as superoxide dismutase (SOD) activity, catalase activity, and integral water-soluble antioxidant capacity (ACW) than insensitive cultivars. A high positive correlation between O(2) production and leaf spot development between ear emergence and milk ripeness was established in the most sensitive winter barley cv. Anoa (r(2) = 0.9622) and spring barley cv. Barke (r(2) = 0.9434). Leaf H(2)O(2) levels increased with the severity of leaf spots. The histochemical localization of O(2) and H(2)O(2) in the tissues adjacent to leaf spots indicated that these two active oxygen species (AOS) are involved in the formation of leaf spots. Reduction of symptom severity by applying strobilurin and azole fungicides was always associated with elevated SOD activity and ACW content and suppressed O(2) production. However, peroxidase activities were significantly higher in sensitive cultivars and in more severely affected tissues and decreased by applying fungicides. Thus, it is assumed that a possible genetic mechanism based on the imbalanced AOS metabolism contributes to formation of physiological leaf spots.

Lipoxygenase activity in altered gravity

Lipoxygenases are a family of enzymes which dioxygenate unsaturated fatty acids, thus initiating lipoperoxidation of membranes or the synthesis of signalling molecules, or inducing structural and metabolic changes in the cell. This activity is the basis for the critical role of lipoxygenases in a number of pathophysiological conditions, both in animals and plants. We review the effects of microgravity on the catalytic efficiency of purified soybean (Glycine max) lipoxygenase-1, as well as the modulation of the activity and expression of 5-lipoxygenase in human erythroleukemia K562 cells subjected to altered gravity. We also outline the molecular properties of the lipoxygenase family and discuss its possible involvement in space-related processes, such as apoptosis (programmed cell death) and immuno-depression. Finally, we discuss the modulation of cyclooxygenase activity and expression in K562 cells exposed to altered gravity, because cyclooxygenase catalyzes the oxidation of arachidonate through a pathway different from that catalyzed by lipoxygenase activity.

Oxidative stress and eicosanoids in the kidneys of hyperglycemic rats treated with dehydroepiandrosterone

Oxidative stress plays a crucial role in the pathogenesis of chronic diabetic complications. Normoglycemic and streptozotocin-diabetic rats were treated with dehydroepiandrosterone (DHEA) (4 mg/d per rat) for 3 weeks. At the end of treatment, hydroxynonenal, hydroperoxyeicosatetraenoic acids and antioxidant levels, as well as Na/K-ATPase activity and membrane fatty acids composition were evaluated in kidney homogenates. Chronic hyperglycemia caused a marked increase of both hydroxynonenal and lipoxygenase pathway products and a drop in both GSH levels and membrane Na/K-ATPase activity. DHEA treatment restored the antioxidant levels to close to the control value and considerably reduced hydroxynonenal and hydroperoxyeicosatetraenoic acid levels. Moreover, DHEA counteracted the detrimental effect of hyperglycemia on membrane function: the drop of Na/K-ATPase activity in diabetic animals was significantly inhibited by DHEA treatment. These results show that DHEA reduces oxidative stress and the consequent increase of lipoxygenase pathway products induced by experimental diabetes in rat kidney; they also suggest that, by reducing the inflammatory response to oxidative stress, DHEA treatment might delay the progression of diabetic kidney disease.

Enhancement of hyperthermia-induced apoptosis by a free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride, in human histiocytic lymphoma U937 cells

To elucidate the mechanism how a free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH), induces cell death at hyperthermic temperatures, apoptosis in a human histiocytic lymphoma cell line, U937, was investigated. Free radical formation deriving from the thermal decomposition of AAPH was examined by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). An assay for DNA fragmentation, observation of nuclear morphological changes, and flow cytometry for phosphatidylserine (PS) externalization were used to detect apoptosis and revealed enhancement of 44.0 degrees C hyperthermia-induced apoptosis by free radicals due to AAPH. However, free radicals alone derived from AAPH did not induce apoptosis. Hyperthermia induced the production of lipid peroxidation (LPO), an increase in intracellular Ca2+ concentration ([Ca2+]i) and enhanced expression of the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1). The effects of hyperthermia on LPO and [Ca2+]i were enhanced markedly by the combination with AAPH. A significant decrease in Bcl-2 expression, increase in Bax expression, a loss of mitochondrial membrane potential (delta psi m) and a marked increase in cytochrome c expression were found only in cells treated with hyperthermia and AAPH. Although an intracellular Ca2+ ion chelator, BAPTA-AM, completely inhibited DNA fragmentation, water-soluble vitamin E, Trolox, only partially suppressed DNA fragmentation and the increase in [Ca2+]i. In contrast, LPO was inhibited completely by Trolox, but no inhibition by BAPTA-AM was found. These results suggest that apoptosis induced by hyperthermia alone is due to the increase in [Ca2+]i arising from increased expression of IP3R1 and LPO. Additional increase in [Ca2+]i due to increased LPO and the activation of mitochondria-caspase dependent pathway play a major role in the enhancement of apoptosis by the combination with hyperthermia and AAPH.

Lipoxygenases and their involvement in programmed cell death

Lipoxygenases are a family of enzymes which dioxygenate unsaturated fatty acids, thus initiating lipoperoxidation of membranes and the synthesis of signaling molecules. Consequently, they induce structural and metabolic changes in the cell in a number of pathophysiological conditions. Recently, a pro-apoptotic effect of lipoxygenase, and of the hydroperoxides produced thereof, has been reported in different cells and tissues, leading to cell death. Anti-apoptotic effects of lipoxygenases have also been reported; however, this has often been based on the use of enzyme inhibitors. Here we review the characteristics of the lipoxygenase family and its involvement in the initiation of oxidative stress-induced apoptosis. Finally, we discuss the role of lipoxygenase activation in apoptosis of animal and plant cells, suggesting a common signal transduction pathway in cell death conserved through evolution of both kingdoms.

Inhibition of peroxisome-proliferator-activated receptor (PPAR)alpha by MK886

Although MK886 was originally identified as an inhibitor of 5-lipoxygenase activating protein (FLAP), recent data demonstrate that this activity does not underlie its ability to induce apoptosis [Datta, Biswal and Kehrer (1999) Biochem. J. 340, 371--375]. Since FLAP is a fatty-acid binding protein, it is conceivable that MK886 may affect other such proteins. A family of nuclear receptors that are activated by fatty acids and their metabolites, the peroxisome-proliferator-activated receptors (PPARs), have been implicated in apoptosis and may represent a target for MK886. The ability of MK886 to inhibit PPAR-alpha, -beta and -gamma activity was assessed using reporter assay systems (peroxisome-proliferator response element--luciferase). Using a transient transfection system in monkey kidney fibroblast CV-1 cells, mouse keratinocyte 308 cells and human lung adenocarcinoma A549 cells, 10--20 microM MK886 inhibited Wy14,643 activation of PPAR alpha by approximately 80%. Similar inhibition of PPAR alpha by MK886 was observed with a stable transfection reporter system in CV-1 cells. Only minimal inhibitory effects were seen on PPAR beta and PPAR gamma. MK886 inhibited PPAR alpha by a non-competitive mechanism as shown by its effects on the binding of arachidonic acid to PPAR alpha protein, and a dose-response study using a transient transfection reporter assay in COS-1 cells. An assay assessing PPAR ligand-receptor interactions showed that MK886 prevents the conformational change necessary for active-complex formation. The expression of keratin-1, a protein encoded by a PPAR alpha-responsive gene, was reduced by MK886 in a culture of mouse primary keratinocytes, suggesting that PPAR inhibition has functional consequences in normal cells. Although Jurkat cells express all PPAR isoforms, various PPAR alpha and PPAR gamma agonists were unable to prevent MK886-induced apoptosis. This is consistent with MK886 functioning as a non-competitive inhibitor of PPAR alpha, but may also indicate that PPAR alpha is not directly involved in MK886-induced apoptosis. Although numerous PPAR activators have been identified, the results show that MK886 can inhibit PPAR alpha, making it the first compound identified to have such an effect.

Evidence that increased 12-lipoxygenase activity induces apoptosis in fibroblasts

The 12-lipoxygenase (LO) enzyme has been implicated in playing a role in pancreatic beta cell inflammatory damage and atherosclerosis. 12-LO reacts with fatty acids to form hydroperoxides which may alter cellular growth. In this study we investigated the direct effect of mouse leukocyte type 12-LO cDNA overexpression on apoptosis in Chinese hamster ovary fibroblast cells that also stably overexpress the angiotensin II type 1a receptor. CHO-AT1a cells expressing background levels of 12-LO exhibited clear increases in growth in response to angiotensin II. In contrast, the new 12-LO transfected cells (CHO-AT1a/ML12-LO cells) displayed reduced basal and angiotensin Il-induced growth compared to CHO-AT1a cells. Furthermore, serum-deprivation resulted in a significantly greater number of non-viable cells in clones having the greatest magnitude of 12-LO overexpression. These results suggested that reduction of the proliferation rate of CHO-AT1a/ML12-LO cells was due to an increasing rate of cell death. To determine whether the increase in cell death was due to apoptosis, we evaluated nuclear DNA fragmentation, cell morphologic changes, and activation of caspase-3. Cells overexpressing 12-LO cDNA displayed all these changes characteristic of apoptosis. In addition the 12-LO product, 12-hydroperoxyeicosatetraenoic acid (12-HPETE), directly induced apoptosis in CHO-AT1a cells. These results demonstrate for the first time that 12-LO activation can lead to apoptosis in fibroblasts, suggesting a role of 12-LO in leading to inflammatory mediated cellular damage.

Prevention of nitrogen mustard-induced apoptosis in normal and transformed lymphocytes by ebselen

The alkylating agent, nitrogen mustard (HN2), is thought to cause apoptosis through production of free oxygen radicals. To explore the mechanism of HN2-induced apoptosis, we utilized ebselen, a selenoorganic compound with potent antioxidant activity. We examined whether ebselen would inhibit apoptosis in BALB/c mouse spleen lymphocytes and human MOLT-4 leukemia cells treated with HN2 (2.5 microM) in vitro. Non-toxic concentrations (<50 microM) of ebselen were found to prevent HN2-induced apoptosis of murine lymphocytes in a dose-dependent manner, as measured by cell viability, hypodiploid DNA formation, and phosphatidylserine externalization. However, ebselen was ineffective at preventing spontaneous apoptosis in these cells, pointing to the selectivity of its action. Furthermore, pretreatment with ebselen at 1-10 microM for 72 hr protected MOLT-4 cells from HN2-induced apoptosis and maintained cell viability and proliferation as monitored by the above-mentioned parameters. This was accompanied by the preservation of mitochondrial transmembrane potential and elevated glutathione levels and by a blockage of caspase-3 and -9 activation. In vivo, ebselen also had a marked protective effect against spleen weight loss associated with lymphocyte apoptosis in mice treated by HN2. Therefore, ebselen provides an efficient protection against HN2-induced cell death in normal and tumoral lymphocytes and might prove useful as an antidote against alkylating agents.

Docosahexaenoic acid is a potent inducer of apoptosis in HT-29 colon cancer cells

Some studies have shown that dietary intake of polyunsaturated fatty acids of the n-3 series may have inhibitory effect on the growth of tumor cells both in vivo and in vitro. However, the cellular and molecular mechanisms by which n-3 fatty acids reduce the growth of tumor cells remain poorly understood. In the present studies, we compared the potency of a variety of n-3 and n-6 fatty acids in modulating the apoptotic cell death in HT-29 colon cancer cells. Of all fatty acids examined, we found that docosahexaenoic acid (22:6n-3; DHA) is a potent inducer of apoptosis in a time- and dose-dependent manner. Indomethacin, a cyclooxygenase inhibitor, is ineffective in blocking the apoptosis induced by DHA, suggesting that DHA-induced apoptosis in HT-29 cells is not mediated through the cyclooxygenase pathway. In contrast, the DHA-induced apoptosis is partially reversed by a synthetic antioxidant, butylated hydroxytoluene, indicating that lipid peroxidation may be involved in apoptotic signaling pathway induced by DHA. DHA treatment decreased bcl-2 levels in association with apoptosis, whereas bax levels remained unchanged. These results suggest that decreased expression of bcl-2 by DHA might increase the sensitivity of cells to lipid peroxidation and to programmed cell death.

The Haber-Weiss reaction and mechanisms of toxicity

The concept that the highly reactive hydroxyl radical (HO) could be generated from an interaction between superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)) was proposed (with Joseph Weiss) in Professor Haber's final paper published in 1934. Until it was recognized that free radicals are produced in biological systems, this finding seemed to have no relevance to biology. However, following the discovery that O(2)(-) was a normal cellular metabolite, it was quickly recognized that the Haber-Weiss reaction (O(2)(-)+H(2)O(2) -->HO+O(2)+HO(-)) might provide a means to generate more toxic radicals. Although the basic reaction has a second order rate constant of zero in aqueous solution and thus cannot occur in biological systems, the ability of iron salts to serve as catalysts was discussed by these authors. Because transition metal ions, particularly iron, are present at low levels in biological systems, this pathway (commonly referred to as the iron-catalyzed Haber-Weiss reaction) has been widely postulated to account for the in vivo generation of the highly reactive HO. Recent data documenting the importance of redox regulation of various cellular signaling pathways makes it clear that free radicals are essential for normal cellular function. However, this also makes it obvious that disruptions of free radical production or defenses at many different levels can lead to adverse effects on cells. While the generation of HO, which is by far the most reactive oxygen species, is generally indicative of an overtly toxic event, it is through studies at this level that we have reached a better understanding of free radicals as both signaling molecules and toxic species.

Lipoxygenases and atherosclerosis: protection versus pathogenesis

15 lipoxygenase (15LO) is a lipid-oxidizing enzyme that is considered to contribute to the formation of oxidized lipids in atherosclerotic lesions. Monocyte-macrophages are the key cells that express 15LO in atherosclerotic lesions. In this review, we examine the evidence for 15LO involvement in atherogenesis and explore and evaluate the potential mechanisms whereby 15LO may contribute to the oxidation of LDL by monocyte-macrophages. We also describe several possible pro- versus anti-atherogenic functions that may be mediated by various products of 15LO lipid oxidation. Central pathways involved in regulating 15LO expression and activity that may serve as future targets for intervention and regulation of this enzyme are also reviewed.

Activation of different lipoxygenase isozymes induces apoptosis in human erythroleukemia and neuroblastoma cells

We investigated the ability of different hydroperoxides generated by lipoxygenase isozymes to induce programmed cell death (PCD) in human cells. Erythroleukemia K562 and neuroblastoma CHP100 cells were used, because they showed high basal activity of lipoxygenase. The hydroperoxides generated by 5-, 12-, or 15-lipoxygenases from linoleate, linolenate, or arachidonate, and the corresponding hydroxides, were able to induce PCD in both cell types, in a concentration- and time-dependent manner. After 24 h, K562 and CHP100 cells showed 2.5- to 3.5-fold more apoptotic bodies than the untreated controls. PCD elicited by lipoxygenase products was independent of intracellular glutathione concentration, and did not require mRNA transcription or protein synthesis. On the other hand, lipoxygenase products evoked an immediate and sustained rise in cytoplasmic calcium (within seconds), followed by mitochondrial uncoupling (within hours). Unlike the hydro(pero)xides, the terminal products of the arachidonate cascade (i.e., leukotrienes, prostaglandins and thromboxane) were not cytotoxic.

Correlations between plasma platelet-activating factor acetylhydrolase (PAF-AH) activity and PAF-AH genotype, age, and atherosclerosis in a Japanese population

Platelet-activating factor acetylhydrolase (PAF-AH), a plasma enzyme that hydrolyzes PAF and oxidized phospholipids, is thought to be involved in protecting cells against oxidative stress. A G(994) (M allele)-->T (m allele) mutation in the plasma PAF-AH gene, which results in a Val(279)-->Phe substitution in the mature protein, leads to a loss of catalytic activity. To elucidate the relationships among PAF-AH enzyme activity, genotype, age, and atherosclerosis, we assayed these parameters in a large Japanese population (n=3932) that consisted of three groups; a control group (healthy individuals; n=1684), a risk-factor group (individuals having at least one conventional risk factor for atherosclerosis; n=1398), and a diseased group (patients who had suffered a myocardial infarction or stroke; n=850). We observed a significantly increased frequency of the m allele in the diseased group as compared with the control or risk-factor groups. Plasma PAF-AH activity increased significantly with age in women in the control group with the MM and Mm genotypes, and in men in the control group with the MM genotype, but not in men with the Mm genotype. In both the risk-factor and diseased groups, however, no correlation was observed between plasma PAF-AH activity and age in subjects with either genotype. These results suggest that in individuals with the MM genotype, plasma PAF-AH activity may be increased in response to stresses induced by PAF and/or oxidized phospholipids that might accumulate with age, but that this response is not evident or reduced in healthy individuals with the m allele, or in subjects with atherosclerotic disease, or having risk factors. Together with our previous findings, the G(994)-->T mutation in the PAF-AH gene may be one of the genetic determinants for atherosclerotic disease in the Japanese population.

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.

Nicotine attenuates arachidonic acid-induced neurotoxicity in cultured spinal cord neurons

Arachidonic acid release from cellular membranes due to spinal cord trauma may be one of the principal destructive events that can lead to progressive injury to spinal cord tissue. Exposure to arachidonic acid can compromise neuronal survival and viability. Because nicotine is known to be a neuroprotective agent, we propose that it can prevent arachidonic acid-induced neurotoxicity. To study this hypothesis, effects of nicotine on mitochondrial function, cellular energy content and apoptotic cell death were measured in cultured spinal cord neurons treated with arachidonic acid. Nicotine attenuated arachidonic acid-induced compromised cell viability and cellular ATP levels in spinal cord neurons. Nicotine exerted these protective effects when used at the concentration of 10 microM and only after a 2-h pre-treatment before a co-exposure to arachidonic acid. Antagonists of nicotinic receptors, such as alpha-bungarotoxin or mecamylamine, only partially reversed these neuroprotective effects of nicotine. In addition, nicotine prevented arachidonic acid-induced activation of caspase-3 activity and apoptotic cell death. These results indicate that nicotine pre-treatment can exert a protective effect against arachidonic acid-induced injury to spinal cord neurons.

Involvement of lipoxygenase-dependent production of fatty acid hydroperoxides in the development of the hypersensitive cell death induced by cryptogein on tobacco leaves

Lipid peroxidation was investigated in relation with the hypersensitive reaction in cryptogein-elicited tobacco leaves. A massive production of free polyunsaturated fatty acid (PUFA) hydroperoxides dependent on a 9-lipoxygenase (LOX) activity was characterized during the development of leaf necrosis. The process occurred after a lag phase of 12 h, was accompanied by the concomitant increase of 9-LOX activity, and preceded by a transient accumulation of LOX transcripts. Free radical-mediated lipid peroxidation represented 10% of the process. Inhibition and activation of the LOX pathway was shown to inhibit or to activate cell death, and evidence was provided that fatty acid hydroperoxides are able to mimic leaf necrotic symptoms. Within 24 h, about 50% of leaf PUFAs were consumed, chloroplast lipids being the major source of PUFAs. The results minimize the direct participation of active oxygen species from the oxidative burst in membrane lipid peroxidation. They suggest, furthermore, the involvement of lipase activity to provide the free PUFA substrates for LOX. The LOX-dependent peroxidative pathway, responsible for tissue necrosis, appears as being one of the features of hypersensitive programmed cell death.

The early phase of apoptosis in human neuroblastoma CHP100 cells is characterized by lipoxygenase-dependent ultraweak light emission

Human neuroblastoma CHP100 cells were forced into apoptosis (programmed cell death, PCD) or necrosis by treatment with calcium chloride or sodium nitroprusside (a nitric oxide donor), respectively. Cellular luminescence, a marker of membrane lipid peroxidation, was increased by calcium but not by nitroprusside, and reached a maximum of 4-fold the control value 2 hours after treatment. The increase in luminescence was paralleled by increased 5-lipoxygenase (up to 250% of the control value) and decreased catalase (down to 50%) activity within the same time window. Consistently, incubation of CHP100 cells with inhibitors of 5-lipoxygenase (5,8,11,14-eicosatetraynoic acid and MK886) reduced light emission and PCD, whereas inhibition of catalase by 3-amino-1, 2,4-triazole enhanced both processes. Treatment of CHP100 cells with retinoic acid or cisplatin, unrelated PCD inducers reported to activate the lipoxygenase pathway, also gave enhanced light emission parallel to PCD increase. Altogether, these results suggest that cellular luminescence is an early marker of apoptotic, but not necrotic, program(s) involving generation of hydrogen peroxide and activation of 5-lipoxygenase.

4-Hydroxynonenal induces dysfunction and apoptosis of cultured endothelial cells

Lipolytic products of triglyceride-rich lipoproteins, i.e., free fatty acids, may cause activation and dysfunction of the vascular endothelium. Mechanisms of these effects may include lipid peroxidation. One of the major and biologically active products of peroxidation of n-6 fatty acids, such as linoleic acid or arachidonic acid, is the aldehyde 4-hydroxynonenal (HNE). To study the hypothesis that HNE may be a critical factor in endothelial cell dysfunction caused by free fatty acids, human umbilical endothelial cells (HUVEC) were treated with up to160 microM of linoleic or arachidonic acid. HNE formation was detected by immunocytochemistry in cells treated for 24 h with either fatty acid, but more markedly with arachidonic acid. To study the cellulareffects of HNE, HUVEC were treated with different concentrations of this aldehyde, and several markers of endothelial cell dysfunction were determined. Exposure to HNE for 6 and 9 h resulted in increased cellular oxidative stress. However, short time treatment with HNE did not cause activation of nuclear factor-kappaB (NF-kappaB). In addition, HUVEC exposure to HNE caused a dose-dependent decrease in production of both interleukin-8 (IL-8) and intercellular adhesion molecule-1 (ICAM-1). On the other hand, HNE exerted prominent cytotoxic effects in cultured HUVEC, manifested by morphological changes, diminished cellular viability, and impaired endothelial barrier function. Furthermore, HNE treatment induced apoptosis of HUVEC. These data provide evidence that HNE does not contribute to NF-kappaB-related mechanisms of the inflammatory response in HUVEC, but rather to endothelial dysfunction, cytotoxicity, and apoptotic cell death.

Antioxidants in the prevention of renal disease

In view of the role of oxidative processes in inflicting damage that leads to glomerulosclerosis and renal medullary interstitial fibrosis, more attention could be paid to the use of antioxidant food constituents and the usage of drugs with recognized antioxidant potential. In any case atherosclerosis is an important component of chronic renal diseases. There is a wide choice of foods and drugs that could confer benefit. Supplementation with vitamins E and C, use of soy protein diets and drinking green tea could be sufficient to confer remarkable improvements.

Tissue-specific functions of individual glutathione peroxidases

The family of glutathione peroxidases comprises four distinct mammalian selenoproteins. The classical enzyme (cGPx) is ubiquitously distributed. According to animal, cell culture and inverse genetic studies, its primary function is to counteract oxidative attack. It is dispensible in unstressed animals, and accordingly ranks low in the hierarchy of glutathione peroxidases. The gastrointestinal isoenzyme (GI-GPx) is most related to cGPx and is exclusively expressed in the gastrointestinal tract. It might provide a barrier against hydroperoxides derived from the diet or from metabolism of ingested xenobiotics. The extreme stability in selenium deficiency ranks this glutathione peroxidase highest in the hierarchy of selenoproteins and points to a more vital function than that of cGPx. Plasma GPx (pGPx) behaves similar to cGPx in selenium deficiency. It is directed to extracellular compartments and is expressed in various tissues in contact with body fluids, e.g., kidney, ciliary body, and maternal/fetal interfaces. It has to be rated as an efficient extracellular antioxidant device, though with low capacity because of the limited extracellular content of potential thiol substrates. Phospholipid hydroperoxide glutathione peroxidase (PHGPx), originally presumed to be a universal antioxidant enzyme protecting membrane lipids, appears to have adopted a variety of specific roles like silencing lipoxygenases and becoming an enzymatically inactive structural component of the mitochondrial capsule during sperm maturation. Thus, all individual isoenzymes are efficient peroxidases in principle, but beyond their mere antioxidant potential may exert cell- and tissue-specific roles in metabolic regulation, as is evident for PHGPx and may be expected for others.

Decreased 13-S-hydroxyoctadecadienoic acid levels and 15-lipoxygenase-1 expression in human colon cancers

13-S-Hydroxyoctadecadienoic acid (13-S-HODE), the product of 15-lipoxygenase (15-LOX) metabolism of linoleic acid, enhances cellular mitogenic responses to certain growth factors. Other observations have questioned whether 13-S-HODE has tumorigenic effects. Our study evaluated the hypothesis that 15-LOX-1 is overexpressed in colon cancers resulting in an increase in intracellular 13-S-HODE. 15-LOX-1 and 13-S-HODE were quantified using western blots, ELISA and immunohistochemistry in 18 human colon cancers with paired normal colonic mucosa. Additionally, 15-LOX-1 expression was measured by western blots in three transformed colonic cell lines and in a human umbilical vein endothelial cell line. Next, we evaluated 13-S-HODE effects on cellular proliferation, cell cycle distribution and apoptosis in a transformed colonic cell line (RKO). Cell cycle distributions were measured by flow cytometry and apoptosis was assessed by phase contrast microscopy, electron microscopy, flow cytometry and DNA fragmentation assay. 15-LOX-1 immunohistochemistry staining scores were reduced in tumor tissues (P </= 0.0001) and 15-LOX-1 expression was absent in three transformed colonic cell lines. 13-S-HODE levels were also reduced in tumors tissues compared with normal controls by ELISA (median 3.3-fold, P = 0.02) and by immunohistochemistry (P </= 0.0001). In vitro 13-S-HODE inhibited RKO cell proliferation and induced cell cycle arrest and apoptosis. 13-S-HODE produced similar effects in HT-29 cells. Our observations indicate that: (i) human colon cancers are associated with a down-regulation in 15-LOX-1 expression and a reduction in 13-S-HODE intracellular levels; (ii) 13-S-HODE can suppress cell proliferation and induce apoptosis in transformed colonic epithelial cells.

Vitamin C protects human vascular smooth muscle cells against apoptosis induced by moderately oxidized LDL containing high levels of lipid hydroperoxides

Vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque "necrotic" core, cap rupture, and thrombosis. Oxidatively modified low-density lipoproteins (LDLs) are implicated in the pathogenesis of atherosclerosis, and dietary antioxidants are thought to protect the vasculature against LDL-induced cytotoxicity. Because LDL oxidative modification may vary within atherosclerotic lesions, we examined the effects of defined, oxidatively modified LDL species on human arterial smooth muscle cell apoptosis and the cytoprotective effects of vitamin C. Moderately oxidized LDL (0 to 300 microg protein/mL), which has the highest content of lipid hydroperoxides, induced smooth muscle cell apoptosis within 6 hours, whereas native LDL and mildly and highly oxidized LDL had no effect. Moderately oxidized LDL increased cellular DNA fragmentation, release of fragmented DNA into the culture medium, and annexin V binding and decreased mitochondrial dehydrogenase activity and expression of the antiapoptotic mediator Bcl-x(L). Treatment of cells with native LDL together with the lipid hydroperoxide 13(S)-hydroperoxyoctadeca-9Z,11E-dienoic acid (HPODE, 200 micromol/L, 6 to 24 hours) also induced apoptotic cell death. Pretreatment of smooth muscle cells with vitamin C (0 to 100 micromol/L, 24 hours) attenuated the cytotoxicity and apoptosis induced by both moderately oxidized LDL and HPODE. Our findings suggest that moderately oxidized LDL, with its high lipid hydroperoxide content, rather than mildly or highly oxidized LDL, causes apoptosis of human smooth muscle cells and that vitamin C supplementation may provide protection against plaque instability in advanced atherosclerosis.

Resveratrol prevents apoptosis in K562 cells by inhibiting lipoxygenase and cyclooxygenase activity

The natural polyphenolic compound resveratrol (trans-3,4', 5-trihydroxystilbene) is shown to prevent apoptosis (programmed cell death) induced in human erythroleukemia K562 cells by hydrogen peroxide and other unrelated stimuli. Resveratrol reversed the elevation of leukotriene B4 (from 6.40 +/- 0.65 to 2.92 +/- 0.30 pmol.mg protein-1) and prostaglandin E2 (from 11.46 +/- 1.15 to 8.02 +/- 0.80 nmol.mg protein-1), induced by H2O2 challenge in K562 cells. The reduction of leukotriene B4 and prostaglandin E2 correlated with the inhibition of the 5-lipoxygenase activity, and the cyclooxygenase and peroxidase activity of prostaglandin H synthase, respectively. Resveratrol also blocked lipoperoxidation induced by hydrogen peroxide in K562 cell membranes. Resveratrol was found to act as a competitive inhibitor of purified 5-lipoxygenase and 15-lipoxygenase and prostaglandin H synthase, with inhibition constants of 4.5 +/- 0.5 microM (5-lipoxygenase), 40 +/- 5.0 microM (15-lipoxygenase), 35 +/- 4.0 microM (cyclooxygenase activity of prostaglandin H synthase) and 30 +/- 3.0 microM (peroxidase activity of prostaglandin H synthase). Altogether, the results reported here suggest that the anti-apoptotic activity of resveratrol depends on the direct inhibition of the main arachidonate-metabolizing enzymes.

Zinc nutrition and apoptosis of vascular endothelial cells: implications in atherosclerosis

Little is known about the requirements and function of zinc in maintaining endothelial cell integrity, especially during stressful conditions, such as the inflammatory response in cardiovascular disease. There is evidence that zinc requirements of the vascular endothelium are increased during inflammatory conditions such as atherosclerosis, where apoptotic cell death is also prevalent. Apoptosis is a morphologically distinct mechanism of programmed cell death which involves the activation of a cell-intrinsic suicide program, and there is evidence that factors such as inflammatory cytokines (e.g., tumor necrosis factor [TNF]) and pure or oxidized lipids are necessary to induce the cell death pathway. Because of its constant exposure to blood components, including prooxidants, diet-derived fats, and their derivatives, the endothelium is very susceptible to oxidative stress and to apoptotic injury mediated by blood lipid components, prooxidants, and cytokines. Thus, it is likely that the cellular lipid environment, primarily polyunsaturated fatty acids, can potentiate the overall endothelial cell injury by increasing cellular oxidative stress and cytokine release in proximity to the endothelium, which then could further induce apoptosis and disrupt endothelial barrier function. Our data suggest that zinc deficiency exacerbates the detrimental effects of specific fatty acids (e.g., linoleic acid) and inflammatory cytokines, such as TNF, on vascular endothelial functions. We propose that a major mechanism of zinc protection against disruption of endothelial cell integrity during inflammatory conditions, is by the ability of zinc to inhibit the pathways of signal transduction leading to apoptosis and especially mechanisms that lead to upregulation of caspase genes.

Lipid peroxidation is an early event in necrosis of wheat hybrid

We previously reported enhanced superoxide anion generation in an F1 necrotic hybrid produced from normal parents (Khanna-Chopra et al., Biochem. Biophys. Res. Commun. (1998) 248, 712-715). Further investigation of the mechanism of necrosis shows the possibility of lipid peroxidation as an early event in the death of necrotic leaves. Lipid peroxidation resulting from the inability of free radical scavenging is often associated with cell death. In this study the accumulation of malondialdehyde, an end product of lipid peroxidation, was measured in hybrid leaves and those of the parents. Lipid peroxidation was higher in the hybrid leaves through out the leaf ontogeny. This was accompanied by increased membrane permeability. Cell viability measured by a TTC reduction test showed a significant correlation with conductivity. There was no apparent effect on photosynthetic pigments and maximum efficiency of PSII (Fv/Fm) until the appearance of necrotic lesions on the hybrid leaf. There seems to be a close relationship among lipid peroxidation, membrane permeability, and cell viability in the leaves undergoing necrosis. This suggests the possibility of a genetic mechanism whereby the scavenging of free radical is impaired, leading to enhanced lipid peroxidation and membrane permeability, resulting in necrosis and death of the hybrid leaves in wheat.