Apoptosis of W256 carcinosarcoma cells of the monocytoid origin induced by NDGA involves lipid peroxidation and depletion of GSH: role of 12-lipoxygenase in regulating tumor cell survival

Real time changes in the expression of eicosanoid synthesizing enzymes during inflammation

Immune responses during inflammation involve complex, well-coordinated lipid signaling pathways. Eicosanoids are a class of lipid signaling molecules derived from polyunsaturated fatty acids such as arachidonic acid and constitute a major network that controls inflammation and its subsequent resolution. Arachidonic acid is metabolized by enzymes in three different pathways to form a variety of lipid metabolites that can be either pro- or anti-inflammatory. Therefore, an understanding of the time-dependent gene expression, lipid metabolite profiles and cytokine profiles during the initial inflammatory response is necessary, as it will allow for the design of time-dependent therapeutics. Herein, we investigate the multi-level regulation of this process. After stimulating RAW 264.7 cells, a mouse-derived macrophage cell line commonly used to examine inflammatory responses, we examine the gene expression of 44 relevant lipid metabolizing enzymes from the different eicosanoid synthesizing classes. We also measure the formation of lipid metabolites and production of cytokines at selected time points. Results reveal a dynamic relationship between the time-course of inflammation dependent gene expression of the three eicosanoid synthesizing enzymes.

Classic Phytochemical Antioxidant and Lipoxygenase Inhibitor, Nordihydroguaiaretic Acid, Activates Phospholipase D through Oxidant Signaling and Tyrosine Phosphorylation Leading to Cytotoxicity in Lung Vascular Endothelial Cells

Nordihydroguaiaretic acid (NDGA), a dicatechol and phytochemical polyphenolic antioxidant and an established inhibitor of human arachidonic acid (AA) 5-lipoxygenase (LOX) and 15-LOX, is widely used to ascertain the role of LOXs in vascular endothelial cell (EC) function. As the modulatory effect of NDGA on phospholipase D (PLD), an important lipid signaling enzyme in ECs, thus far has not been reported, here we have investigated the modulation of PLD activity and its regulation by NDGA in the bovine pulmonary artery ECs (BPAECs). NDGA induced the activation of PLD (phosphatidic acid formation) in cells in a dose- and time-dependent fashion that was significantly attenuated by iron chelator and antioxidants. NDGA induced the formation of reactive oxygen species (ROS) in cells in a dose- and time-dependent manner as evidenced from fluorescence microscopy and fluorimetry of ROS and electron paramagnetic resonance spectroscopy of oxygen radicals. Also, NDGA caused a dose-dependent loss of intracellular glutathione (GSH) in BPAECs. Protein tyrosine kinase (PTyK)-specific inhibitors significantly attenuated NDGA-induced PLD activation in BPAECs. NDGA also induced a dose- and time-dependent phosphorylation of tyrosine in proteins in cells. NDGA caused in situ translocation and relocalization of both PLD₁ and PLD₂ isoforms, in a time-dependent fashion. Cyclooxygenase (COX) inhibitors were ineffective in attenuating NDGA-induced PLD activation in BPAECs, thus ruling out the activation of COXs by NDGA. NDGA inhibited the AA-LOX activity and leukotriene C₄ (LTC₄) formation in cells. On the other hand, the 5-LOX-specific inhibitors, 5, 8, 11, 14-eicosatetraynoic acid and kaempferol, were ineffective in activating PLD in BPAECs. Antioxidants and PTyK-specific inhibitors effectively attenuated NDGA cytotoxicity in BPAECs. The PLD-specific inhibitor, 5-fluoro-2-indolyl deschlorohalopemide (FIPI), significantly attenuated and protected against the NDGA-induced PLD activation and cytotoxicity in BPAECs. For the first time, these results demonstrated that NDGA, the classic phytochemical polyphenolic antioxidant and LOX inhibitor, activated PLD causing cytotoxicity in ECs through upstream oxidant signaling and protein tyrosine phosphorylation.

Nordihydroguaiaretic Acid: From Herbal Medicine to Clinical Development for Cancer and Chronic Diseases

Nordihydroguaiaretic acid (NDGA) is a phenolic lignan obtained from Larrea tridentata, the creosote bush found in Mexico and USA deserts, that has been used in traditional medicine for the treatment of numerous diseases such as cancer, renal, cardiovascular, immunological, and neurological disorders, and even aging. NDGA presents two catechol rings that confer a very potent antioxidant activity by scavenging oxygen free radicals and this may explain part of its therapeutic action. Additional effects include inhibition of lipoxygenases (LOXs) and activation of signaling pathways that impinge on the transcription factor Nuclear Factor Erythroid 2-related Factor (NRF2). On the other hand, the oxidation of the catechols to the corresponding quinones my elicit alterations in proteins and DNA that raise safety concerns. This review describes the current knowledge on NDGA, its targets and side effects, and its synthetic analogs as promising therapeutic agents, highlighting their mechanism of action and clinical projection towards therapy of neurodegenerative, liver, and kidney disease, as well as cancer.

Arachidonic Acid Metabolite as a Novel Therapeutic Target in Breast Cancer Metastasis

Metastatic breast cancer (BC) (also referred to as stage IV) spreads beyond the breast to the bones, lungs, liver, or brain and is a major contributor to the deaths of cancer patients. Interestingly, metastasis is a result of stroma-coordinated hallmarks such as invasion and migration of the tumor cells from the primary niche, regrowth of the invading tumor cells in the distant organs, proliferation, vascularization, and immune suppression. Targeted therapies, when used as monotherapies or combination therapies, have shown limited success in decreasing the established metastatic growth and improving survival. Thus, novel therapeutic targets are warranted to improve the metastasis outcomes. We have been actively investigating the cytochrome P450 4 (CYP4) family of enzymes that can biosynthesize 20-hydroxyeicosatetraenoic acid (20-HETE), an important signaling eicosanoid involved in the regulation of vascular tone and angiogenesis. We have shown that 20-HETE can activate several intracellular protein kinases, pro-inflammatory mediators, and chemokines in cancer. This review article is focused on understanding the role of the arachidonic acid metabolic pathway in BC metastasis with an emphasis on 20-HETE as a novel therapeutic target to decrease BC metastasis. We have discussed all the significant investigational mechanisms and put forward studies showing how 20-HETE can promote angiogenesis and metastasis, and how its inhibition could affect the metastatic niches. Potential adjuvant therapies targeting the tumor microenvironment showing anti-tumor properties against BC and its lung metastasis are discussed at the end. This review will highlight the importance of exploring tumor-inherent and stromal-inherent metabolic pathways in the development of novel therapeutics for treating BC metastasis.

Lipoxygenase Inhibitors Nordihydroguaiaretic Acid and Fungus Lecanicillum lecanii Extract Induce Death of Lymphoid Leukemia Cells

We studied the effect of lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA) and fungus Lecanicillum lecanii extract on lymphatic leukemia P388 cells. The cells grown in the abdominal cavity of DBA2 mice for 7 days were transferred into a nutrient medium. The effect of lipoxygenase inhibitors was evaluated by changes in cell number, trypan blue staining, nucleus damage, and changes in cell distribution by DNA content after 22-h incubation. NDGA and fungus extract induced apoptotic death of lymphatic leukemia cells, which was seen from nucleus damage and reduced DNA content in cells. IC₅₀ for NDGA and fungus extract was 0.66 and 5.5 μg/ml, respectively.

Effect of nordihydroguaiaretic acid on cell viability and glucose transport in human leukemic cell lines

The polyphenol nordihydroguaiaretic acid (NDGA) has antineoplastic properties, hence it is critical to understand its action at the molecular level. Here, we establish that NDGA inhibits glucose uptake and cell viability in leukemic HL‐60 and U‐937 cell lines. We monitored hexose uptake using radio‐labeled 2‐deoxyglucose (2DG) and found that the inhibition by NDGA followed a noncompetitive mechanism. In addition, NDGA blocked hexose transport in human red blood cells and displaced prebound cytochalasin B from erythrocyte ghosts, suggesting a direct interaction with the glucose transporter GLUT1. We propose a model for the mechanism of action of NDGA on glucose uptake. Our study shows for the first time that NDGA can act as inhibitor of the glucose transporter GLUT1.

Molecular response of 4T1-induced mouse mammary tumours and healthy tissues to zinc treatment

Breast cancer patients negative for the nuclear oestrogen receptor α have a particularly poor prognosis. Therefore, the 4T1 cell line (considered as a triple-negative model) was chosen to induce malignancy in mice. The aim of the present study was to assess if zinc ions, provided in excess, may significantly modify the process of mammary oncogenesis. Zn(II) ions were chosen because of their documented antitumour effects. Zn(II) is also known to induce the expression of metallothioneins (MT) and glutathion (GSH). A total dose of zinc sulphate per one gram of mouse weight used in the experiment was 0.15 mg. We studied the expression of MT1, MT2, TP53 and MTF-1 genes and also examined the effect of the tumour on antioxidant capacity. Tumour-free mice had significantly higher expression levels of the studied genes (p<0.003). Significant differences were also revealed in the gene expression between the tissues (p<0.001). The highest expression levels were observed in the liver. As compared to brain, lung and liver, significantly lower concentrations of MT protein were found in the primary tumour; an inverse trend was observed in the concentration of Zinc(II). In non-tumour mice, the amount of hepatic hydrosulphuryl groups significantly increased by the exposure to Zn(II), but the animals with tumour induction showed no similar trend. The primary tumour size of zinc-treated animals was 20% smaller (p=0.002); however, no significant effect on metastasis progression due to the zinc treatment was discovered. In conclusion, Zn(II) itself may mute the growth of primary breast tumours especially at their early stages.

Non-synonymous polymorphism (Gln261Arg) of 12-lipoxygenase in colorectal and thyroid cancers

12-lipoxygenase (12-LOX) pathway which produces 12-HETE and hepoxiline HXA3 and HXB3, and induces production of reactive oxygen species and inflammation is increasingly being implicated in variety of cancers, including those of colorectal and thyroid cancers. Hence, we examined whether the functional polymorphism of 12-LOX (mRNA A835G; Protein Gln261Arg) has any association with human colorectal and thyroid cancers. In this communication, we report that the mutation is linked to colorectal cancer and thyroid cancers. Further, we also observed that the heterozygous mutant (AG) is more prevalent in females than in males. Frequencies of AA, AG and GG, respectively were 62.5, 36.2 and 1.3 % in controls, 36.5, 61.5 and 2.0 % in colorectal cancer cases and 35.6, 62.4 and 2.0 % in thyroid cancer cases. The results obtained suggested a significant association of the heterogenous variant (AG) with the cancers. Relative risk of the cancers with the presence of the AG variant was found to be 2.9 and 4.0 for colorectal and thyroid cancers, respectively. However, the association of the variant (AG) was significant only in male colorectal cancer patients but not in female patients. On the other hand, prevalence of the AG variant is significantly higher in control females than in male control subjects. To the best of our knowledge, this is the first study that links the 12-LOX gene polymorphism with thyroid cancer and reveals a gender bias in the prevalence of the polymorphic variants in controls and colorectal cancer patients.

Inhibition of nicotinamide phosphoribosyltransferase modifies LPS-induced inflammatory responses of human monocytes

Recent studies have identified enzymes that use NAD as a substrate, thus contributing to its net consumption. To maintain the intracellular pool, NAD is re-synthesized by a salvage pathway using nicotinamide, the by-product generated by the enzymatic cleavage of NAD. Enzymes involved in NAD re-synthesis include nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide mononucleotide adenylyltransferase. Our studies show, that NAMPT was substantially up-regulated by LPS in primary human monocytes, suggesting that it may be especially required during the process of monocyte activation. To evaluate the contribution of the NAD rescue pathway to LPS-induced biological responses in human monocytes, we used APO866, a well-characterized inhibitor of NAMPT. Concomitant with the inhibition of NAMPT, LPS-induced TNF-α protein synthesis declined, while TNF-α mRNA levels were minimally affected. Moreover, APO866 strongly decreased the production of reactive oxygen species (ROS), increased surface expression of the NAD-consuming enzyme CD38, and modified the production of selective eicosanoids. We further demonstrate that protein ADP-ribosylation was strongly reduced, indicating a possible link between this post-translational protein modification and human monocyte inflammatory responses. Despite a substantial reduction in intracellular NAD levels, activated monocytes were resistant to apoptosis, while resting monocytes were not. Taken together, our data suggest that activated monocytes strongly depend on the NAD salvage pathway to mount an appropriate inflammatory response. Their survival is not affected by NAD-depletion, probably as a result of LPS-mediated anti-apoptotic signals.

Arachidonic acid inhibits neuronal nitric oxide synthase elicited by proinflammatory stimuli and promotes astrocyte survival with both exogenous and endogenous peroxynitrite via different mechanisms

Cytosolic phospholipase A(2)-inhibited astrocytes respond to the cocktail lipopolysaccharide/interferon-gamma with an immediate formation of peroxynitrite (ONOO(-)) and a delayed lethal response. Low concentrations of arachidonic acid (ARA; i.e., <0.1 microM) cause tyrosine kinase-dependent inhibition of neuronal nitric oxide synthase (nNOS) activity, thereby suppressing formation of ONOO(-) and the ensuing lethal response. ARA promoted its effects only when given to the cultures just prior to, or in parallel with, the proinflammatory mixture. High concentrations of ARA, i.e., >3 microM, promoted cytoprotection when applied to the cultures up to 50 min after the formation of endogenous ONOO(-) had been completed or up to 30 min after addition of exogenous ONOO(-). The mechanism(s) involved in these responses was, however, independent of tyrosine kinase activation and was in fact mediated by ARA metabolites of the lipoxygenase pathway. These results are consistent with a scenario in which astrocytes respond to low or high amounts of ARA with the triggering of different pathways involved in the inflammatory response. Early nNOS inhibition mediated by very low levels of ARA is indeed critical for nuclear factor-kappaB activation, which is otherwise effectively inhibited by constitutive nitric oxide, and for preventing early formation of ONOO(-). Greater ARA concentrations promote survival in astrocytes committed to death by ONOO(-), a species extensively released under inflammatory conditions, via a mechanism dependent on lipoxygenase metabolism and inhibition of downstream events leading to cell demise.

Singlet oxygen in plants: production, detoxification and signaling

Singlet oxygen ((1)O(2)) is a singular reactive oxygen species (ROS) that is produced constitutively in plant leaves in light via chlorophylls that act as photosensitizers. This (1)O(2) production is spatially resolved within thylakoid membranes and is enhanced under light stress conditions. (1)O(2) can also be produced by phytotoxins during plant-pathogen interactions. (1)O(2) is highly reactive, can be toxic to cells and can be involved in the signaling of programmed cell death or acclimation processes. Here, we summarize current knowledge on (1)O(2) management in plants and on the biological effects of this peculiar ROS. Compared with other ROS, (1)O(2) has received relatively little attention, but recent developments indicate that it has a crucial role in the responses of plants to light.

Anti-Apoptotic Effects of Arachidonic Acid and Prostaglandin E2 in Pancreatic β-Cells

BACKGROUND/AIMS

The polyunsaturated fatty acid arachidonic acid (AA) has been implicated in beta-cell defence mechanisms and prostaglandin (PG) products of cyclooxygenase (COX) 2 action confer resistance to alloxan-induced apoptosis in insulin-secreting RIN cells. We have now investigated the anti-apoptotic effects of AA and its metabolite, PGE(2), in the MIN6 mouse insulin-secreting beta-cell line and mouse islets.

METHODS

Apoptosis was determined in MIN6 beta-cell and mouse islet extracts by measurement of capase-3 activity, and COX2 mRNA levels were quantified by real-time RT-PCR.

RESULTS

Exposure of MIN6 cells to AA (3.1-12.5 microM) caused concentration-dependent reductions in apoptosis, and similar results were obtained when endogenous AA levels were elevated in cytosolic phospholipase A(2)-overexpressing MIN6 cells. 25mM glucose caused both a significant up-regulation of MIN6 cell COX2 mRNA levels and a decrease in apoptosis. Inhibition of MIN6 cell COX2 activity with a selective inhibitor, NS-398 (10-100 microM), increased apoptosis and exogenous PGE(2) (0.2-5 microM) reduced NS-398-induced apoptosis in a concentration-dependent manner. The protective effects of AA and PGE(2) were also observed in primary mouse islets.

CONCLUSION

These data show that AA and its COX2-generated metabolite, PGE(2), can protect beta-cells from apoptosis.

Chronic inflammation and oxidative stress in human carcinogenesis

A wide array of chronic inflammatory conditions predispose susceptible cells to neoplastic transformation. In general, the longer the inflammation persists, the higher the risk of cancer. A mutated cell is a sine qua non for carcinogenesis. Inflammatory processes may induce DNA mutations in cells via oxidative/nitrosative stress. This condition occurs when the generation of free radicals and active intermediates in a system exceeds the system's ability to neutralize and eliminate them. Inflammatory cells and cancer cells themselves produce free radicals and soluble mediators such as metabolites of arachidonic acid, cytokines and chemokines, which act by further producing reactive species. These, in turn, strongly recruit inflammatory cells in a vicious circle. Reactive intermediates of oxygen and nitrogen may directly oxidize DNA, or may interfere with mechanisms of DNA repair. These reactive substances may also rapidly react with proteins, carbohydrates and lipids, and the derivative products may induce a high perturbation in the intracellular and intercellular homeostasis, until DNA mutation. The main substances that link inflammation to cancer via oxidative/nitrosative stress are prostaglandins and cytokines. The effectors are represented by an imbalance between pro-oxidant and antioxidant enzyme activities (lipoxygenase, cyclooxygenase and phospholipid hydroperoxide glutathione-peroxidase), hydroperoxides and lipoperoxides, aldehydes and peroxinitrite. This review focalizes some of these intricate events by discussing the relationships occurring among oxidative/nitrosative/metabolic stress, inflammation and cancer.

Involvement of 5-lipoxygenase in survival of Epstein–Barr virus (EBV)-converted B lymphoma cells

Epstein-Barr Virus (EBV) is involved in the progression of lymphomas through still unknown mechanism involving increased resistance to induced apoptosis. We show here that in a set of apoptosis-resistant EBV-converted Burkitt's lymphoma clones, 5- and 12-lipoxygenases (LOXs) are over-expressed. Further investigations on 5-LOX showed that resistance to apoptosis increases parallely with the expression of 5-lipoxygenase (5-LOX). Inhibitors of 5-LOX: (a) decrease peroxides level, indicating that this enzyme promotes the generation of oxidative stress in EBV+ cells, and (b) potently induce apoptosis in the EBV resistant cell line E2R. 5- and 15-HETE, the products of the 5 and 15-LOXs, respectively, counteract 5-LOX inhibitor induced apoptosis, indicating that products of arachidonate metabolism, rather than peroxides, trigger a signal transduction that is required for survival of the EBV-converted cells. These findings suggest that 5- and, to a lesser extent, other LOXs, that are involved in tumor progression of several cell types, may also participate in lymphomagenesis, especially that EBV-mediated.

Stimulation of suicidal erythrocyte death by lipoxygenase inhibitor Bay-Y5884

The prostaglandin PGE(2), a metabolite of the cyclooxygenase pathway, activates Ca(2+)-permeable cation channels in erythrocyte cell membranes leading to entry of Ca(2+) with subsequent eryptosis, i.e. cell shrinkage, breakdown of phosphatidylserine (PS) asymmetry and membrane blebbing, all features typical for apoptosis in nucleated cells. PS exposing cells are recognized by macrophages, engulfed, degraded and thus cleared from circulating blood. The present study explored whether the specific lipoxygenase inhibitor Bay-Y5884 influences eryptosis. As determined by competitive ELISA, Bay-Y5884 (20 microM) enhanced the release of PGE(2) from human erythrocytes. According to whole-cell patch-clamp, Bay-Y5884 (20 microM) activated nonselective cation channels. The effect of Bay-Y5884 on cation channels was abolished by the cyclooxygenase inhibitor diclophenac (10 microM). Bay-Y5884 (30-40 microM) significantly increased erythrocyte free Ca(2+) concentration and PS exposure as analyzed in flow cytometry by Fluo3 fluorescence and annexin-V binding, respectively. PS exposure triggered by 20 microM (but not by 40 microM) Bay-Y5884 was blunted by cyclooxygenase inhibitors acetylsalicylic acid (50 microM) and diclophenac (10 microM). In conclusion, the lipoxygenase inhibitor Bay-Y5884 enhances erythrocyte PGE(2) formation with subsequent activation of non-selective cation channels, Ca(2+) entry and phospholipid scrambling.

Exploiting hypoxia in solid tumors to achieve oncolysis

Chemo- and radio-resistant cancer cells within solid tumors undermine the effectiveness of these approaches to achieving oncolysis. These resistant cells and clusters of cells typically thrive at low oxygen tensions and are reliant on anaerobic metabolic pathways that churn out lactate. This hypoxic state is one that can be exploited and in this paper a novel method is advanced involving tumor cell infiltration by bifidobacterium species which should bring about prodigious lactate synthesis; concomitant blocking of its enzymatic degradation by urea as well as export (from the cell) by use of quercetin; depletion of ATP using exogenous thyroid; and compromised oxidative catabolism of free fatty acids and amino acids via oral intake of l-hydroxycitrate, melatonin and nontoxic NDGA. This "anaerobic pathway cocktail", it is hypothesized, will bring about a profound reduction in intracellular pH and a compromised state of cellular energetics sufficient to effect oncolysis.

Role of 5-lipoxygenase pathway in the regulation of RAW 264.7 macrophage proliferation

Arachidonic acid (AA) metabolites control cell proliferation, among other physiologic functions. RAW 264.7 macrophages can metabolise AA through the cyclooxygenase and lipoxygenase (LOX) pathways. We aimed to study the role of AA-metabolites derived from 5-LOX in the control of RAW 264.7 macrophage growth. Our results show that zileuton, a specific 5-LOX inhibitor, and nordihydroguaiaretic acid (NDGA), a non-specific LOX inhibitor, inhibit cell proliferation and [(3)H]-thymidine incorporation in a concentration-dependent fashion. Growth inhibition induced by NDGA can be explained by an apoptotic process, while zileuton does not seem to induce apoptosis. Moreover, these treatments delay the cell cycle, as analysed by flow cytometry. On the other hand, the leukotriene (LT) B(4) receptor antagonist U-75302, the LTD(4) receptor antagonists LY-171883 and MK-571, and the cysteinyl-LT receptor antagonist REV-5901 also inhibit cell proliferation and [(3)H]-thymidine incorporation in a concentration-dependent manner, and delay the RAW 264.7 cell cycle. However, these antagonists did not induce annexin V staining, caspase activation or DNA fragmentation. Furthermore, we demonstrated that exogenous addition of LTB(4) or LTD(4) revert the cell growth inhibition induced by zileuton or the leukotriene receptor antagonists mentioned above. Finally, we observed that LTB(4) and LTD(4), in the absence of growth factors, have pro-proliferative effects on macrophages, and we obtained preliminary evidences that this effect could be through mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways. In conclusion, our results show that the interaction between LTB(4) and LTD(4) with its respective receptor is involved in the control of RAW 264.7 macrophage growth.

5-Hydroxyeicosatetraenoic acid is a key intermediate of the arachidonate-dependent protective signaling in monocytes/macrophages exposed to peroxynitrite

Endogenous generation of arachidonic acid via selective activation of cytosolic phospholipase A(2) has been implicated in the mechanism of monocytes/macrophage survival in the presence of peroxynitrite. In particular, the lipid messenger was shown to prevent the otherwise rapid onset of a mitochondrial permeability-transition (MPT)-dependent necrosis by causing the mitochondrial translocation of protein kinase Calpha (PKCalpha) and the ensuing cytosolic accumulation of the Bcl-2-antagonist of cell death (Bad), an event promoting the anti-MPT function of Bcl-2 (or Bcl-X(L)). Here, we show that the effects on PKCalpha are not mediated directly by arachidonate but rather, by downstream products of the enzyme 5-lipoxygenase (5-LO). Peroxynitrite elicited the nuclear membrane translocation of 5-LO and enhanced its enzymatic activity via a mechanism sensitive to low concentrations of inhibitors of 5-LO or the 5-LO-activating protein, as well as to genetic depletion of the latter enzyme. Inhibition of 5-LO activity was invariably associated with the cytosolic localization of PKCalpha, the mitochondrial accumulation of Bad, and a rapid MPT-dependent necrosis. All these events were prevented by nanomolar concentrations of the 5-LO product 5-hydroxyeicosatetraenoic acid.

Oxidative stress-driven mechanisms of nordihydroguaiaretic acid-induced apoptosis in FL5.12 cells

Nordihydroguaiaretic acid (NDGA), a general lipoxygenase (LOX) enzyme inhibitor, induces apoptosis independently of its activity as a LOX inhibitor in murine pro-B lymphocytes (FL.12 cells) by a mechanism that is still not fully understood. Glutathione depletion, oxidative processes and mitochondrial depolarization appear to contribute to the apoptosis induced by NDGA. The current data demonstrate that NDGA (20 microM)-induced apoptosis in FL5.12 cells is partially protected by N-acetylcysteine (NAC) (10 mM) and dithiothreitol (DTT) (500 microM) pretreatment, confirming a role for oxidative processes. In addition, the treatment of FL5.12 cells with NDGA led to an increase in phosphorylation and activation of the MAP kinases ERK, JNK and p38. Although pretreatment with ERK inhibitors (PD98059 or U0126) abolished ERK phosphorylation in response to NDGA, neither inhibitor had any effect on NDGA-induced apoptosis. SP600125, a JNK inhibitor, did not have any effect on NDGA-induced phosphorylation of JNK nor apoptosis. Pretreatment with the p38 inhibitor SB202190 attenuated NDGA-induced apoptosis by 30% and also abolished p38 phosphorylation, compared to NDGA treatment alone. NAC, but not DTT, also decreased the phosphorylation of p38 and JNK supporting a role for oxidative processes in activating these kinases. Neither NAC nor DTT blocked the phosphorylation of ERK suggesting that this activation is not related to oxidative stress. The release of cytochrome c and activation of caspase-3 induced by NDGA were inhibited by NAC. SB202190 slightly attenuated caspase-3 activation and had no effect on the release of cytochrome c. These data suggest that several independent mechanisms, including oxidative reactions, activation of p38 kinase and cytochrome c release contribute to NDGA-induced 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.

Differential effects of COX inhibitors against β-amyloid-induced neurotoxicity in human neuroblastoma cells

Retrospective epidemiological studies have suggested that chronic treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) provides some degree of protection from Alzheimer's disease (AD). Although most NSAIDs inhibit the activity of cyclooxygenase (COX), the rate-limiting enzyme in the production of prostanoids from arachidonic acid (AA), the precise mechanism through which NSAIDs act upon AD pathology remains to be elucidated. Classical NSAIDs like indomethacin inhibit both the constitutive COX-1 and the inducible COX-2 enzymes. In the present work, we characterize the protective effect of the indomethacin on the neurotoxicity elicited by amyloid-beta protein (A beta, fragments 25-35 and 1-42) alone or in combination with AA added exogenously as well as its effects on COX-2 expression. We also compared the neuroprotective effects of indomethacin with the selective COX-1, COX-2 and 5-LOX inhibitors, SC-560, NS-398 and NDGA, respectively. Our results show that indomethacin protected from A beta and AA toxicity in naive and differentiated human neuroblastoma cells with more potency than SC-560 while, NS-398 only protected neurons from AA-mediated toxicity. Present results suggest that A beta toxicity can be reversed more efficiently by the non-selective COX inhibitor indomethacin suggesting its role in modulating the signal transduction pathway involved in the mechanism of A beta neurotoxicity.

Arachidonic acid induces neuronal death through lipoxygenase and cytochrome P450 rather than cyclooxygenase

Arachidonic acid (AA) is released from membrane phospholipids during normal and pathologic processes such as neurodegeneration. AA is metabolized via lipoxygenase (LOX)-, cyclooxygenase (COX)-, and cytochrome P450 (CYP450)-catalyzed pathways. We investigated the relative contributions of these pathways in AA-induced neuronal death. Exposure of cultured cortical neurons to AA (50 microM) yielded significantly apoptotic neuronal death, which was attenuated greatly by LOX inhibitors (nordihydroguaiaretic acid, AA861, and baicalein), or CYP450 inhibitors (SKF525A and metyrapone), rather than COX inhibitors (indomethacin and NS398). AA (10 microM)-induced neurotoxicity was prevented by all kinds of inhibitors. Compared, the neurotoxic effects of three pathway metabolites, 12-hydroxyeicosatetraenoic acid (12-HETE), a major LOX metabolite, induced a significant neurotoxicity. AA also produced reactive oxygen species within 30 min, which was reduced by all inhibitors tested, including COX inhibitors, and AA neurotoxicity was abolished by the antioxidant Trolox. AA treatment also depleted glutathione levels; this depletion was reduced by the LOX or CYP450 inhibitors rather than by the COX inhibitors. Taken together, our data suggested that the LOX pathway likely plays a major role in AA-induced neuronal death with the modification of intracellular free radical levels.

Role of inflammation in pancreatic carcinogenesis and the implications for future therapy

BACKGROUND

The link between inflammation and pancreatic cancer has been observed for a number of gastrointestinal neoplasms. This review examines the role of inflammation in pancreatic carcinogenesis and how it can be utilised to develop new therapies against pancreatic cancer.

METHODS

A literature review of Pubmed, Medline and Web of Science databases was undertaken using the key words, pancreatic cancer, inflammation, inducible nitric oxide, interleukins, pro-inflammatory cytokines, cyclooxygenase-2, NF-kappa B, reactive oxygen species, DNA adducts, lipoxygenases, chemoprevention.

RESULTS

Epidemiological evidence and molecular studies both in vitro and in vivo all support the hypothesis that inflammation plays an important in the initiation and progression of pancreatic tumours.

CONCLUSION

Sustained damage caused by chronic inflammation may precede the onset of frank malignancy by a significant interval. As such, suppression of inflammatory changes and oxidative damage, may help delay or even prevent the inception of pancreatic neoplasia.

Induction of prosurvival molecules by apoptotic stimuli: involvement of FOXO3a and ROS

Most cancer therapeutics fails to eradicate cancer because cancer cells rapidly develop resistance to its proapoptotic effects. The underlying mechanisms remain incompletely understood. Here we show that three representative apoptotic stimuli, that is, serum starvation, a mitochondrial toxin, and a DNA-damaging agent (etoposide), rapidly induce several distinct classes of prosurvival molecules, in particular, Bcl-2/Bcl-X(L) and superoxide dismutase (SOD; including both MnSOD and Cu/ZnSOD). At the population level, the induction of these prosurvival molecules occurs prior to or concomitant with the induction of proapoptotic molecules such as Bim and Bak. Blocking the induction using siRNAs of the prosurvival or proapoptotic molecules facilitates or inhibits apoptosis, respectively. One master transcription factor, FOXO3a, is involved in the transcriptional activation of some of these prosurvival (e.g., MnSOD) and proapoptotic (e.g., Bim) molecules. Interestingly, in all three apoptotic systems, FOXO3a itself is also upregulated at the transcriptional level. Mechanistic studies indicate that reactive oxygen species (ROS) are rapidly induced upon apoptotic stimulation and that ROS inhibitors/scavengers block the induction of FOXO3a, MnSOD, and Bim. Finally, we show that apoptotic stimuli also upregulate prosurvival molecules in normal diploid human fibroblasts and at subapoptotic concentrations. Taken together, these results suggest that various apoptotic inducers may rapidly mobilize prosurvival mechanisms through ROS-activated master transcription factors such as FOXO3a. The results imply that effective anticancer therapeutics may need to combine both apoptosis-inducing and survival-suppressing strategies.

Ibuprofen-induced Walker 256 tumor cell death: cytochrome c release from functional mitochondria and enhancement by calcineurin inhibition

The participation of mitochondria in the mechanism of tumor cell death induced by non-steroid anti-inflammatory drugs is uncertain. Here we show that ibuprofen induces death of Walker 256 tumor cells independently on mitochondrial depolarization as estimated by flow cytometry using DioC(6)(3). Oligomycin increased mitochondrial transmembrane potential in both ibuprofen-treated and non-treated cells, indicating that ATP synthesis was sustained during cell death. Cyclosporin A, but not bongkrekic acid, both mitochondrial permeability transition inhibitors, increased the percentage of cell death in the presence of ibuprofen. FK506, a calcineurin inhibitor like cyclosporin A, also increased ibuprofen-induced cell death. Moreover, we showed that cytochrome c was released during ibuprofen-induced cell death. In conclusion, death of Walker 256 tumor cells induced by ibuprofen does not impair mitochondrial function, involves cytochrome c release and is accompanied by a rescue pathway via calcineurin activation.

Antisense glutaminase inhibition decreases glutathione antioxidant capacity and increases apoptosis in Ehrlich ascitic tumour cells

Glutamine is an essential amino acid in cancer cells and is required for the growth of many other cell types. Glutaminase activity is positively correlated with malignancy in tumours and with growth rate in normal cells. In the present work, Ehrlich ascites tumour cells, and their derivative, 0.28AS-2 cells, expressing antisense glutaminase mRNA, were assayed for apoptosis induced by methotrexate and hydrogen peroxide. It is shown that Ehrlich ascites tumour cells, expressing antisense mRNA for glutaminase, contain lower levels of glutathione than normal ascites cells. In addition, 0.28AS-2 cells contain a higher number of apoptotic cells and are more sensitive to both methotrexate and hydrogen peroxide toxicity than normal cells. Taken together, these results provide insights into the role of glutaminase in apoptosis by demonstrating that the expression of antisense mRNA for glutaminase alters apoptosis and glutathione antioxidant capacity.

In vitro proliferation of fibrosarcoma cells depends on intact functions of lipoxygenases and cytochrome P-450-monooxygenase

Proliferation of mouse fibrosarcoma cells G:5:113 was studied in vitro after affecting particular pathways of arachidonic acid metabolism by selected inhibitors. After 48 hours of cultivation with nonspecific lipoxygenase inhibitors, nordihydroguaiaretic acid (NDGA) and esculetin; a specific 12-lipoxygenase inhibitor, baicalein; and inhibitor of five-lipoxygenase activating protein, MK-886, markedly suppressed the number of cells and induced significant changes in cell cycle distribution in a dose-dependent manner. While proadifen, an inhibitor of cytochrome P-450-monooxygenase, applied in low concentrations, increased the cell number, at higher concentrations, it inhibited cell proliferation and significantly changed the cell cycle. Cyclooxygenase inhibitors, ibuprofen, flurbiprofen, and diclofenac suppressed cell numbers only moderately without any changes in the cell cycle. The occurrence of apoptosis was not significant for any of the selected drugs in comparison with untreated control cells. Moreover, not even one of the drugs caused the specific cleavage of poly (ADP-ribose) polymerase to the 89-kDa fragment, however, a decrease in total amount of this protein was observed after treatment with NDGA and esculetin. We conclude that the proliferation ability of fibrosarcoma cells G:5:113 in vitro depends on intact functions of 5-lipoxygenase, 12-lipoxygenase, and cytochrome P-450-monooxygenases, and that the effects of inhibitors do not include regulation of apoptosis.

Prostaglandin F2α is protective for apoptosis stimulated synergistically with 12-O-tetradecanoyl phorbol-β-acetate and nordihydroguaiaretic acid in Madin-Darby canine kidney cells

We recently found that 12-O-tetradecanoyl phorbol-beta-acetate (TPA) induced apoptosis in cultured Madin-Darby canine kidney (MDCK) cells. The present study shows that the apoptosis was mediated by the activation of caspases including caspase-3 and -7. Moreover, nordihydroguaiaretic acid (NDGA), a general lipoxygenase (LOX) inhibitor, synergistically stimulated the TPA-induced apoptosis despite no activation with NDGA alone. TPA preferentially increased the transcription of cyclooxygenase (COX)-2 in MDCK cells, whereas the expression of LOXs was almost negligible. These findings suggested that the effect of NDGA was independent of the inhibition of LOXs. The study using a cell-permeable 2',7'-dichlorofluorescin diacetate confirmed the more remarked production of reactive oxygen species at 6 h after the cells were treated with a mixture of TPA and NDGA. Calcium ionophore A23187 was markedly effective to attenuate the TPA-induced apoptosis, indicating that elevated endogenous prostaglandins (PGs) served as survival factors through not only the activation of phospholipase A(2) by A23187 but also the induction of COX-2 by TPA. Consistent with this indication, exogenous addition of PGF(2alpha), a predominant prostanoid in MDCK cells, was the most potent to protect the cells from the apoptosis induced by a mixture of TPA and NDGA.

Five-lipoxygenase-activating protein inhibitor MK-886 induces apoptosis in gastric cancer through upregulation of p27kip1 and bax

BACKGROUND AND AIM

Products of the arachidonic acid metabolizing enzyme, 5-lipoxygenase (5-LOX), stimulate the growth of several cancer types. Inhibitors of 5-LOX and 5-LOX-activating protein (FLAP) induce apoptosis in some cancer cells. Here, the authors investigated the effect of a FLAP inhibitor, MK-886, on the inhibition of proliferation and induction of apoptosis in gastric cancer.

METHODS

Cell proliferation in gastric cancer cells was measured using an 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide assay. Apoptosis was measured using acridine orange staining and flow cytometry. Protein expression of apoptosis-related genes p53, p21waf1, p27kip1, bcl-2 families, cytochrome c, and the caspases were examined using Western blotting. Caspase-3 activity was measured using colorimetric assay of substrate cleavage.

RESULTS

MK-886 inhibited cell growth in a dose- and time-dependent manner. Apoptosis was induced in gastric cancer cells and was characterized by upregulation of p27kip1 and bax, with release of cytochrome c from mitochondria into cytosol, which initiated caspase-3 activation. Specific caspase-3 inhibitors partially blocked MK-886-induced apoptosis.

CONCLUSION

The present results suggest that MK-886 induces apoptosis in gastric cancer cells through upregulation of p27kip1 and bax, and that MK-886 is a potentially useful drug in gastric cancer prevention and therapy.

Overexpression of leukocyte-type 12-lipoxygenase promotes W256 tumor cell survival by enhancing alphavbeta5 expression

The metabolism of arachidonic acid (AA) leads to the generation of biologically active metabolites that have been implicated in cell growth and proliferation, as well as survival and apoptosis. We have previously demonstrated that rat Walker 256 (W256) carcinosarcoma cells express the platelet-type 12-lipoxygenase (12-LOX) and synthesize 12(S)- and 15(S)-HETE as their major LOX metabolites. Here we show that Walker 256 cells also express leukocyte-type 12-LOX and that its overexpression in these cells significantly extends their survival and delays apoptosis when cells are cultured under serum-free conditions. Under serum-free conditions, the expression of leukocyte-type 12-LOX is upregulated. 12-LOX-transfected W256 cells had a more spread morphology in culture compared with wild-type or mock-transfected cells. Examination of W256 cells showed that the cells expressed a number of integrins on their surface. Overexpression of 12-LOX enhanced the surface expression and focal adhesion localization of integrin alphavbeta5, while not affecting other integrins. Also, the 12-LOX-transfected W256 cells exhibited higher levels of microfilament content. Treatment of cells with monoclonal antibody to alphavbeta5 or cytochalasin B (a microfilament-disrupting agent), but not antibodies to other integrin receptors, resulted in significant apoptosis, characterized by rapid rounding up and detachment from the substratum. These results show that the 12-LOX pathway is a regulator of cell survival and apoptosis, by affecting the expression and localization of the alphavbeta5 integrin and actin microfilaments in Walker 256 cells.

Effects of several polyhydroxylated flavonoids on the growth of B16F10 melanoma and Melan-a melanocyte cell lines: influence of the sequential oxidation state of the flavonoid skeleton

The response of B16F10 melanoma and Melan-a melanocyte cell lines to treatment with five polyhydroxylated flavonoids and gallic acid, after 24 and 72 h of exposure, was determined, and the relationship between any antiproliferative effects observed and the chemical structure is discussed. After 24 h, none of the studied compounds showed significant cytotoxic activity in the B16F10 cell line, whereas compounds with an adjacent trihydroxylated substitution pattern did affect the viability of the Melan-a cell line. After 72 h of exposure, myricetin, baicalein and gallic acid significantly inhibited both B16F10 and Melan-a cell cultures, whereas luteolin and quercetin had only a moderate effect. Eriodictyol only had an effect on Melan-a cell viability, which was reduced slightly. These results suggest that the presence of a C2-C3 double bond and three adjacent hydroxyl groups in the flavonoid A- or B-rings confers greater antiproliferative activity to the flavonoid.

Lipoxygenase and cyclooxygenase metabolism: new insights in treatment and chemoprevention of pancreatic cancer

The essential fatty acids, linoleic acid and arachidonic acid play an important role in pancreatic cancer development and progression. These fatty acids are metabolized to eicosanoids by cyclooxygenases and lipoxygenases. Abnormal expression and activities of both cyclooxygenases and lipoxygenases have been reported in pancreatic cancer. In this article, we aim to provide a brief summary of (1) our understanding of the roles of these enzymes in pancreatic cancer tumorigenesis and progression; and (2) the potential of using cyclooxygenase and lipoxygenase inhibitors for pancreatic cancer treatment and prevention.

Early mitochondrial activation and cytochrome c up-regulation during apoptosis

Apoptosis induced by many stimuli requires the mitochondrial respiratory chain (MRC) function. While studying the molecular mechanisms underlying this MRC-dependent apoptotic pathway, we find that apoptosis in multiple cell types induced by a variety of stimuli is preceded by an early induction of MRC proteins such as cytochrome c (which is encoded by a nuclear gene) and cytochrome c oxidase subunit II (COX II) (which is encoded by the mitochondrial genome). Several non-MRC proteins localized in the mitochondria, e.g. Smac, Bim, Bak, and Bcl-2, are also rapidly up-regulated. The up-regulation of many of these proteins (e.g. cytochrome c, COX II, and Bim) results from transcriptional activation of the respective genes. The up-regulated cytosolic cytochrome c rapidly translocates to the mitochondria, resulting in an accumulation of holocytochrome c in the mitochondria accompanied by increasing holocytochrome c release into the cytosol. The increased cytochrome c transport from cytosol to the mitochondria does not depend on the mitochondrial protein synthesis or MRC per se. In contrast, cytochrome c release from the mitochondria involves dynamic changes in Bcl-2 family proteins (e.g. up-regulation of Bak, Bcl-2, and Bcl-x(L)), opening of permeability transition pore, and loss of mitochondrial membrane potential. Overexpression of cytochrome c enhances caspase activation and promotes cell death in response to apoptotic stimulation, but simple up-regulation of cytochrome c using an ecdysone-inducible system is, by itself, insufficient to induce apoptosis. Taken together, these results suggest that apoptosis induced by many stimuli involves an early mitochondrial activation, which may be responsible for the subsequent disruption of MRC functions, loss of Deltapsi(m), cytochrome c release, and ultimately cell death.

Neurons overexpressing mutant presenilin-1 are more sensitive to apoptosis induced by endoplasmic reticulum-Golgi stress

Most early-onset cases of familial Alzheimer's disease (FAD) are linked to mutations in two related genes, ps1 and ps2. FAD-linked mutant PS1 alters proteolytic processing of the amyloid precursor protein and increases vulnerability to apoptosis induced by various cell stresses. In transfected cell lines, mutations in ps1 decrease the unfolded-protein response (UPR), which is the response to the increased amounts of unfolded proteins that accumulate in the endoplamic reticulum (ER), indicating that these mutations may increase vulnerability to ER stress by altering the UPR signalling pathway. Here we report that, in primary cultured neurons from cortices of transgenic mice, overexpression of mutated PS1 (M146L mutation) but not PS1 wild-type (wt) enhanced spontaneous neuronal apoptosis that involved oxidative stress and caspase activation. In PS1M146L cultures, neurons displaying immunoreactivity for human PS1 were threefold more vulnerable to spontaneous apoptosis than the overall neuronal population. In addition, PS1M146L transgenic neurons were more sensitive to apoptosis induced by various stresses, including two ER-Golgi toxins, nordihydroguaiatric acid and brefeldin A (also known to induce UPR), as well as staurosporine. In contrast, PS1 wt transgenic neurons were resistant to apoptosis induced by Golgi-ER toxins but displayed a comparable vulnerability to staurosporine. Our study demonstrates that, as previously reported, overexpression of FAD-linked mutant PS1 enhances neuronal vulnerability to spontaneous and induced apoptosis. In addition, we show that this vulnerability was correlated with mutant PS1 protein expression and that PS1 wt overexpression selectively prevented ER-Golgi stress-induced apoptosis. These data indicate that PS1 interferes with a specific apoptotic pathway that results from a dysfunction of the ER-Golgi compartment.

Cyclooxygenases and lipoxygenases as potential targets for treatment of pancreatic cancer

Pancreatic adenocarcinoma is characterized by poor prognosis, late diagnosis and lack of response to conventional therapies. The incidence of this disease shows no sign of declining in the Western world. Thus, new targets need to be identified for pancreatic cancer treatment. In particular, new chemotherapeutic agents would be extremely beneficial for control of unresectable cancer and metastatic lesions as well as for prevention of this deadly disease. Mounting evidence suggests that both lipoxygenases (LOXs) and cyclooxygenases (COXs), the key enzymes for arachidonic acid metabolism, have a profound influence on the development and progression of several human cancers. Recent evidence suggests that both COX and LOX pathways are important in pancreatic cancer. Results from immunocytochemical, RT-PCR, and Western blotting studies have shown that COX, specifically COX-2, is upregulated in human pancreatic cancer cell lines as well as human pancreatic cancer tissues compared with normal ductal cells and normal pancreas specimens. Agents that block COX enzymes significantly inhibit pancreatic cancer growth both in vitro and in vivo, in parallel with induction of apoptosis. Expression of both 5-LOX and 12-LOX is also seen in pancreatic cancer, although compared to the expression of COX this has not been extensively investigated. Chemical inhibitors or antisense oligonucleotides that block either 5-LOX or 12-LOX cause marked inhibition of pancreatic cancer cell proliferation. On the other hand, LOX metabolites stimulate growth of the tumor cells and reverse LOX-inhibitor-induced growth inhibition, suggesting the specific role of LOX in regulating pancreatic cancer cell proliferation. Although questions still need to be answered, such as the underlying mechanisms for COX and LOX-induced growth inhibition, both COX and LOX pathways are potential targets for pancreatic cancer treatment and chemoprevention. COX and LOX enzyme inhibitors are available and have been shown to be relatively safe in the treatment of other diseases.

Arachidonate 12-lipoxygenases

Arachidonate 12-lipoxygenase introduces a molecular oxygen at carbon 12 of arachidonic acid to generate a 12-hydroperoxy derivative. The enzymes generate 12-hydroperoxy derivatives with either S- or R-configurations. There are three isoforms of 12S-lipoxygenases named after the cells where they were first identified; platelet, leukocyte and epidermis. The leukocyte-type enzyme is widely distributed among cells, but the tissue distribution varies substantially from species to species. The platelet and epidermal enzymes are present in only a relatively limited number of cell types. Although the structures and enzymatic properties of the three isoforms of 12S-lipoxygenases have been elucidated, the physiological roles of the 12S-lipoxygenases are not yet fully understood. There are important roles for the enzymes and their products in several biological systems including those involved in atherosclerosis and neurotransmission.

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.

Material properties of polymerized NDGA-collagen composite fibers: development of biologically based tendon constructs

Methods for stabilizing collagen-based materials with catechol containing monomers were developed in order to produce fibers with mechanical properties in tension comparable to those of normal tendon. Fibers produced from pepsin solubilized, bovine tendon type I collagen were polymerized with the di-catechol nordihydroguaiaretic acid (NDGA). Polymerization was based on the chemical oxidation of the constituent o-catechols to reactive o-quinone functionalities. NDGA caused a dose dependent increase in the tensile strength and stiffness of the type I collagen fibers. A second treatment with NDGA improved the tensile properties significantly. Comparison of the effects of NDGA with those of biologically relevant mono-catechols indicated that the bi-catechol functionality of NDGA was responsible for generation of the superior tensile properties. Elimination of unreacted intermediates from the treated fibers with ethanol increased the effectiveness of the cross-linking process while simultaneously sterilizing the material. Catalyzing oxidation by saturating the reaction buffer with oxygen increased the effectiveness of polymerization and the resulting tensile properties of the treated fibers. The ultimate tensile strength of the optimized NDGA-treated fibers averaged 90 MPa; the elastic modulus of these fibers averaged 580 MPa. Both values are comparable to native tendon. The material properties of the NDGA cross-linked fibers exceed the properties of collagen fibers treated with other cross-linking strategies such as glutaraldehyde and carbodiimide. These results indicate that NDGA cross-linking may provide a viable approach to stabilizing collagenous materials for use in repair of ruptured, lacerated or surgically transected tendons, as well as other biomaterial constructs for surgical repair of musculoskeletal injuries and disease.

gamma-Linolenic acid and eicosapentaenoic acid induce modifications in mitochondrial metabolism, reactive oxygen species generation, lipid peroxidation and apoptosis in Walker 256 rat carcinosarcoma cells

The polyunsaturated fatty acids gamma-linolenic acid (GLA) and eicosapentaenoic acid (EPA) are cytotoxic to tumour cells. GLA inhibits Walker 256 tumour growth in vivo, causing alterations in mitochondrial ultrastructure and cellular metabolism. The objective of the present study was to investigate the mechanisms behind fatty acid inhibition of Walker 256 tumour growth under controlled in vitro conditions. At a concentration of 150 microM, both GLA and EPA caused a decrease in cell proliferation and an increase in apoptotic index. Increases in reactive oxygen species (ROS) and lipid peroxide production were identified, as well as alterations in energy metabolism and the deposition of large amounts of triacylglycerol in the form of lipid droplets. Mitochondrial respiratory chain complexes I+III and IV had significantly decreased activity and mitochondrial membrane potential was greatly diminished. Intracellular ATP concentrations were maintained at 70-80% of control values despite the decreased mitochondrial function, which may be in part due to increased utilisation of glucose for ATP generation. Cytochrome c release from mitochondria was found, as was caspase-3-like activation. DNA fragmentation in situ revealed many apoptotic events within the cell population. The mechanism(s) by which ROS and lipid peroxides induce apoptosis remains unclear, but the effects of GLA and EPA appear to involve the mitochondrial pathway of apoptosis induction leading to cytochrome c release, caspase activation, loss of mitochondrial membrane potential and DNA fragmentation.

A novel form of platelet-type 12-lipoxygenase mRNA in human vascular smooth muscle cells

The lipoxygenase pathway has been implicated in the growth, migration, and contraction of vascular smooth muscle cells (VSMCs). However, the precise type of lipoxygenase present in the vascular wall has not been characterized. In this study, we used a specific reverse-transcriptase polymerase chain reaction method with 2 sets of specific primers on total RNA and polyA (+)RNA of normal human VSMCs prepared from umbilical artery. Two forms of platelet-type 12-lipoxygenase mRNA were present in human VSMCs: the already published form cloned from human erythroleukemia cells and a variant form of platelet-type 12-lipoxygenase, which includes 2 additional sequences consistent with the 2 introns (D and E). This novel form of 12-lipoxygenase poly A (+)RNA was downregulated by lipopolysaccharide (10 ug/ml) and upregulated by epidermal growth factor (100 ng/ml) but was not affected by angiotensin II (10(-7) mol/l). We developed a rabbit anti-human platelet-type 12-lipoxygenase polyclonal antibody directed against a 24-amino acid peptide encoded within exon 4. Western immunoblotting of protein extracted from VSMCs and umbilical artery and platelet extract with this antibody showed a coordinate 110-kDa protein and the already-described 70-kDa band detected in platelets and cord homogenate. Another 120-kDa protein was consistently detected in cord extracts but not in platelet or VSMC homogenates. The immunohistochemistry study performed with the same antibody showed extensive cytoplasmic staining of VSMCs. The specific role of these different forms of platelet-type 12-lipoxygenase is subject to further investigation.

Proteolytic loss of bcl-x(L) in FL5.12 Cells undergoing apoptosis induced by MK886

Apoptosis induced in the IL3-dependent murine pro-B lymphocytic (FL5.12) cell line by the 5-lipoxygenase activating protein inhibitor MK886 is accompanied by the rapid loss of the anti-apoptotic bcl-x(L) and bcl-2, but not the proapoptotic bax proteins (Datta et al., J. Biol. Chem. 273, 28163-28169, 1998). Since several reports indicate important roles for noncaspase proteases in apoptosis, the participation of lysosomes, as well as serine, cysteine, or aspartic acid proteases, in the effects of MK886 were investigated. Consistent with the involvement of various proteases, lysosomal degranulation was evident, as observed by a decrease in acridine orange fluorescence at 2 h and an increase in cytosolic beta-hexosaminidase activity at 4 h after treating FL5.12 cells with 10 microM MK886. The disappearance of bcl-x(L) from FL5.12 cells upon MK886 treatment was prevented in a dose-dependent manner by pretreatment with leupeptin, pepstatin, phenylmethylsulfonyl fluoride, or the broad-spectrum caspase inhibitor Boc-D-FMK. Each of the noncaspase protease inhibitors partially inhibited MK886-induced apoptosis as measured by phosphatidylserine externalization and DNA fragmentation. The noncaspase inhibitors also blocked about half of the increase in caspase-3-like activity. Boc-D-FMK completely inhibited this enzyme and prevented apoptosis. None of the inhibitors were able to directly inhibit activated caspase-3 in cell lysates, suggesting their effects were upstream of caspase activation. These observations suggest the involvement of various proteases, possibly originating from lysosomes, upstream of active caspase-3, in the loss of bcl-x(L) protein and in the signaling pathway of MK886-induced apoptosis in FL5.12 cells. This pathway may be unique to MK886 since these same protease inhibitors had only minimal effects on etoposide-induced apoptosis and the accompanying moderate loss of bcl-x(L) in FL5.12 cells.

Baicalein protects cortical neurons from beta-amyloid (25-35) induced toxicity

Accumulation of amyloid beta peptide (Abeta) has been suggested to contribute to neurodegeneration in Alzheimer's disease (AD). Since chronic inflammation occurs in AD pathogenesis and lipoxygenases are important mediators of inflammatory processes, we evaluated the effect of lipoxygenase inhibitors on apoptosis induced by Abeta on rat cortical cells. The 12-lipoxygenase inhibitor baicalein attenuated both neuronal apoptosis and c-jun protein over-expression induced by Abeta(25- 35), whereas no protection was found with the broad spectrum lipoxygenase inhibitor nordihydroguaiaretic acid or the 5-lipoxygenase inhibitor caffeic acid. These results suggest that 12-lipoxygenase participates in a c-jun-dependent apoptosis pathway triggered by Abeta(25-35), and that specific 12-lipoxygenase inhibitors might be of interest in AD.

Inhibitors of arachidonic acid metabolism potentiate tumour necrosis factor-alpha-induced apoptosis in HL-60 cells

We investigated whether and how could various modulators of arachidonic acid metabolism affect apoptosis induced by tumour necrosis factor-alpha (TNF-alpha) in human myeloid leukaemia HL-60 cells. These included arachinonyltrifluoromethyl ketone (AACOCF3; cytosolic phospholipase A2 inhibitor), indomethacin (cyclooxygenase inhibitor), MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2-dimethyl propanoic acid; 5-lipoxygenase-activating protein inhibitor), nordihydroguaiaretic acid (general lipoxygenase inhibitor), and arachidonic acid itself. Incubation of HL-60 cells with nordihydroguaiaretic acid resulted in apoptosis and it was characterised by mitochondria membrane depolarisation, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. Indomethacin and nordihydroguaiaretic acid synergistically potentiated TNF-alpha-induced apoptosis, while arachidonic acid, AACOCF3 and MK-886 did not modulate its effects. Furthermore, indomethacin potentiated apoptosis in cells treated with a differentiating agent, all-trans retinoic acid, which induces resistance to TNF-alpha. However, the observed effects were probably not associated either with the cyclooxygenase- or lipoxygenase-dependent activities of indomethacin and nordihydroguaiaretic acid, respectively. Since indomethacin may reportedly activate peroxisome proliferator-activated receptors (PPARs), the effects of specific ligands of PPARs on apoptosis were studied as well. It was found that selective PPARs ligands had no effects on TNF-alpha-induced apoptosis. The findings suggest that arachidonic acid metabolism does not play a key role in regulation of apoptosis induced by TNF-alpha in the present model. Nevertheless, our data raise the possibility that indomethacin could potentially be used to improve the treatment of human myeloid leukaemia.

Biocompatibility of NDGA-polymerized collagen fibers. I. Evaluation of cytotoxicity with tendon fibroblasts in vitro

The material properties of tendon type I collagen fibers polymerized with nordihydroguaiaretic acid (NDGA) are equivalent to native tendon, suggesting that NDGA crosslinking may provide a viable approach to stabilizing collagenous materials for repairing ruptured, lacerated, or surgically transected fibrous tissues, such as tendon and ligament (Koob & Hernandez, Biomaterials, in press). Using standard cytotoxicity tests, the present study evaluated the biocompatibility of these fibers with cultured bovine tendon fibroblasts. Primary fibroblasts obtained from calf digital extensor tendons were exposed to NDGA, reaction products generated from the polymerization protocol, and the crosslinked fibers. NDGA was cytotoxic to these cells at concentrations above 100 microM. NDGA oxidation products were similarly cytotoxic. At concentrations below 100 microM, fibroblast viability was not affected by NDGA or its oxidation products. At these lower concentrations, fibroblast proliferation was unaffected compared to controls not exposed to NDGA. Fibers crosslinked with NDGA contained no unreacted NDGA, but they did contain soluble reaction products that were cytotoxic to tendon fibroblasts in both the elution and the direct contact tests. Washing the fibers in 70% ethanol and phosphate-buffered saline eliminated cytotoxicity of the fibers. Ethanol simultaneously sterilized the fibers. Tensile tests established that the ethanol/phosphate buffer wash did not adversely affect the material properties of the fibers. The results of these experiments indicate that NDGA-crosslinked fibers can be rendered nontoxic to tendon fibroblasts and may provide a novel approach for producing biologically based, biocompatible, tendon bioprostheses.

Disparate effects of similar phenolic phytochemicals as inhibitors of oxidative damage to cellular DNA

Phenolic phytochemicals are natural plant substances whose cellular effects have not been completely determined. Nordihydroguaiaretic acid (NDGA) and curcumin are two phenolic phytochemicals with similar molecular structures, suggesting that they possess comparable chemical properties particularly in terms of antioxidant activity. To examine this possibility in a cellular system, this study evaluated the capacities of NDGA and curcumin to function as antioxidants in inhibiting oxidative damage to DNA. Jurkat T-lymphocytes were pre-incubated for 30 min with 0-25 microM of either NDGA or curcumin to allow for uptake. The phenolic phytochemical-treated cells were then oxidatively challenged with 25 microM hydrogen peroxide (H2O2). Afterwards, cells were subjected to alkaline micro-gel electrophoresis (i.e. comet assay) to assess the extent of single-strand breaks in DNA. In a concentration-dependent manner, NDGA inhibited H2O2-induced DNA damage, whereas curcumin did not. In fact, incubating Jurkat T-lymphocytes with curcumin alone actually induced DNA damage. This effect of curcumin on DNA did not appear to reflect the DNA fragmentation associated with apoptosis because there was no proteolytic cleavage of poly-(ADP-ribose)-polymerase, which is considered an early marker of apoptosis. Curcumin-induced damage to DNA was prevented by pre-treatment of the cells with the lipophilic antioxidant, alpha-tocopherol, suggesting that curcumin damaged DNA through oxygen radicals. Therefore, it is concluded that NDGA has antioxidant activity but curcumin has prooxidant activity in cultured cells based on their opposite effects on DNA.