Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced epidermal ornithine decarboxylase activity by lipoxygenase inhibitors: possible role of product(s) of lipoxygenase pathway

Nanokinetics of drug molecule transport into a single cell

Aims: To analyze drug transport at a single cell level, a mast cell line, RBL-2H3, was treated with cell-permeable fluorescent compounds, such as quinacrine, and was monitored by a fluorescence video microscope. Methods: Small areas in the video that corresponded to granules and part of the cytosol in a cell were chosen and the signal intensity in these areas was monitored sequentially. Results: The initial rate of quinacrine uptake through the cell membrane calculated from the fluorescent signal was correlated with quinacrine concentration, and it decreased at a lower temperature, showing that the transport was an energy-requiring process, such as active transport. The kinetics of the transport through the microgranular membrane did not depend on the temperature but the pH in the cytosol, therefore this process should be passive transport by pH gradient. Conclusion: These data indicate that the observation of video microscope-mediated drug transport using fluorescent dye is useful in kinetic analysis at the nanometer scale.

An antitumorigenic role for murine 8S-lipoxygenase in skin carcinogenesis

The levels of 8S-lipoxygenase (8S-LOX) expression and of its arachidonic acid metabolite, 8-hydroxyeicosatetraenoic acid (8-HETE), are highly elevated in the early stages of mouse skin carcinogenesis. On the other hand, several reports showing that 8-HETE is also closely associated with keratinocyte differentiation raise a question concerning the role of 8S-LOX/8-HETE in skin carcinogenesis. To address that question, here we conducted a series of gain-of-function studies. Skin targeted loricrin 8S-LOX/C57BL/6J transgenic mice showed a more differentiated epidermal phenotype as well as a 64% reduced papilloma development in a two-stage skin carcinogenesis protocol. Forced expression of 8S-LOX in MT1/2 cells, a murine papilloma cell line, also caused a more differentiated appearance as well as keratin 1 expression. Overexpression of 8S-LOX in CH72 cells, a murine carcinoma cell line, inhibited cell proliferation by 30% in vitro and by 86% in in vivo xenografts. Exogenous addition of 5 muM 8-HETE to CH72 cells caused cell cycle arrest at the G1 phase. Finally, immunohistochemical analyses showed 8S-LOX protein expression was strictly confined to the differentiated compartment of mouse skin and throughout tumorigenesis. Collectively, these data suggest that 8S-LOX plays a role as a prodifferentiating, antitumorigenic, and tumor suppressing gene in mouse skin carcinogenesis.

Identification and Characterization of a Phorbol Ester-responsive Element in the Murine 8S-Lipoxygenase Gene

Murine 8S-lipoxygenase (8S-LOX) is a 12-O-tetradecanoylphorbol-13-acetate (TPA)-inducible lipoxygenase. That is, it is not detected in normal mouse skin, however, a significant increase in expression is detected in the skin of TPA promotion-sensitive strains of mice after TPA treatment. In this study, we found TPA-induced 8S-LOX mRNA expression is a result of increased transcription in SSIN primary keratinocytes and further investigated transcriptional regulation of 8S-LOX expression by cloning its promoter. The cloned 8S-LOX promoter ( approximately 2 kb) in which a transcription initiation site was mapped at -27 from the ATG has neither a TATA box nor a CCAAT box. However, the promoter was highly responsive to TPA in TPA promotion-sensitive SSIN but not in TPA promotion-resistant C57BL/6J primary keratinocytes. We then identified a Sp1 binding site located -77 to -68 from the ATG that is a TPA-responsive element (TRE) of the promoter and that Sp1, Sp2, and Sp3 proteins bind to the TRE. We also found that the binding of these proteins to the TRE was significantly increased by TPA treatment and inhibition of the binding by mithramycin A decreased TPA-induced promoter activity as well as 8S-LOX mRNA expression. These data suggest that increased binding of Sp1, Sp2, and Sp3 to the TRE of the 8S-LOX promoter is a mechanism by which TPA induces 8S-LOX expression in keratinocytes.

Plant phenolics as potential cancer prevention agents

The frequent consumption of fresh fruits and vegetables is associated with a lower cancer incidence in humans, and in experimental carcinogenesis. There are several groups of substances in plant foods which may contribute to this inhibition of tumor development. Almost all fresh fruits, vegetables and cereal grains contain appreciable amounts of naturally occurring plant phenolics. A brief overview will be presented of the most common plant phenolics in human foods and their chemical and biochemical properties. Plant phenolics, originally hypothesized to inhibit mutagenesis and/or carcinogenesis by virtue of antioxidant or electrophile trapping mechanisms, can also act as potent modulators of arachidonic metabolism cascade pathways. Certain plant phenols can be effective inhibitors of chemical mutagens, in vitro, and/or carcinogenesis in vivo. The historical origins, hypotheses of actions, current status and potential adverse effects of the utility of plant phenolics to reduce risk of cancer are discussed, as well as future possibilities and needs and objectives for future research.

The protective effect of indomethacin on photocarcinogenesis in hairless mice

Orally administered indomethacin at 10-600 micrograms per mouse per day has been shown to inhibit UV radiation-induced erythema dose responsively. At the higher doses tested (200-600 micrograms) there was evidence of drug toxicity. Indomethacin administered orally at 20 micrograms per mouse daily during photocarcinogenesis induction both increased the probability of remaining tumour free and reduced the average tumour multiplicity. When indomethacin was administered only during the UV irradiation period (initiation), a reduction in tumour multiplicity and in the progression of tumours to malignant squamous cell carcinomas was observed; when administered only during the post-irradiation promotion period, there was a significant increase in the probability of remaining tumour free. Thus both tumour initiation and promotion by UV radiation appear to be indomethacin-sensitive, possibly affected by different mechanisms.

Modulating effects of ellagic acid, vanillin and quercetin in a rat medium term multi-organ carcinogenesis model

Effects of dietary supplementation with the antioxidants ellagic acid, quercetin and vanillin were examined using a medium term multi-organ carcinogenesis model in rats. Groups of 10-15 male F344 rats were given i.p. injections of diethylnitrosamine (DEN, 100 mg/kg body wt.) and N-methylnitrosourea (MNU, 20 mg/kg body wt), s.c. injections of 1,2-dimethylhydrazine (DMH, 40 mg/kg body wt.), together with 0.05% N-butyl-N-(4- hydroxybutyl)nitrosamine (BBN) and 0.1% 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN), both in the drinking water, for a total multiple initiation period of 4 weeks (DMBDD) treatment). Ellagic acid, quercetin or vanillin, each at a dose of 1% each in the diet were administered from 1 day before and throughout the carcinogen exposure period, or after completion of the initiation regimen. All surviving animals were sacrificed at the end of week 36, and major organs were examined histopathologically. In the small intestine, significant reductions in the incidence and number of tumors (adenomas and carcinomas) were observed in the groups administered ellagic acid during (8%, 0.08 +/- 0.29) or after (8%, 0.08 +/- 0.29) DMBDD treatment, and those receiving quercetin after DMBDD treatment (0%) compared to the control value (57%, 1.07 +/- 1.21). Although the incidences were not statistically significant, slightly decreased numbers of small intestinal tumors were found in the groups receiving vanillin during (0.33 +/- 0.72), or after (0.40 +/- 0.83) DMBDD treatment. The incidence of large intestinal carcinomas in the group treated with vanillin during DMBDD treatment was significantly higher (73%) than the control value (21%). These results indicated that while ellagic acid and quercetin exerted potent chemopreventive action in both the initiation and promotion stages in the present experimental system, their beneficial effects were restricted to the small intestine. Since small intestinal carcinomas are very infrequent in humans, the advantages of these phenolic compounds for human application as chemopreventors should not be overestimated.

Cepharanthine inhibits two-stage tumor promotion by 12-O-tetradecanoylphorbol 13-acetate and mezerein on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene

Cepharanthine, isolated from Stephania cepharantha, is one of the bisbenzylisoquinoline-type alkaloids. We have found that it inhibits tumor promotion after topical application in two-stage carcinogenesis in mouse skin. Epidermal ornithine decarboxylase activities inhibited by topical application of cepharanthine, with an 5 micrograms/mouse) and mezerein (5 micrograms/mouse) were found to be inhibited by topical application of cepharanthine, with a ED50 of 1.2 mumol and 1.4 mumol respectively. These inhibitory effects of cepharanthine are considered to be related to its antitumor activity in two-stage carcinogenesis in mouse skin. Cell-mediated immunosuppression by TPA was unaffected by topical application of cepharanthine. A diet containing 0.005% cepharanthine (about 0.5 mg mouse-1 day-1) slightly suppressed the two-stage promotion of skin tumors by twice-weekly applications of 2.5 micrograms TPA for 2 weeks (first stage) followed by twice-weekly applications of 2.5 micrograms mezerein for 23 weeks (second stage) in ICR mice following initiation by 50 micrograms 7,12-dimethylbenz[a]anthracene. Oral administration of cepharanthine inhibits the tumor promotion in two-stage carcinogenesis in mouse skin.

Assay of liver cytosol lipoxygenase by differential pulse polarography

Lipoxygenase activity assayed by differential pulse polarography was found to be more sensitive than that determined by the increase in absorption at 234 nm. The lipoxygenase activity level in the liver cytosol of rats fed oxidized palm oil was significantly higher than that of the control animals fed either saline or fresh palm oil. The effects of flavonoids on the inhibition of lipoxygenase activity level in liver cytosol of rats were in the decreasing order quercetin greater than myricetin greater than morin greater than phloretin. The observed free malonaldehyde (MDA) in liver cytosol of rats determined by high-performance liquid chromatography using malonaldehyde-dinitro-phenylhydrazine complex was 23, 25, and 51.2% for rats fed saline, fresh palm oil, and oxidized palm oil, respectively. A linear relationship between the lipoxygenase activity and the free liver cytosol MDA was shown. The assay of lipoxygenase by differential pulse polarography provides a simple, sensitive, and quantitative method for the study of liver lipid peroxidation.

A mathematical computer stimulation model for the development of colonic polyps and colon cancer

Currently known information about the development and progression of colon polyps and cancer is summarized and organized into a mathematical computer simulation model that successfully predicts the natural history of colon polyp and cancer development for an average patient with (1) familial polyposis coli (2) genetic susceptibility as measured by a positive family history, and (3) negative family history with a high fat diet. The mathematical model uses four distinct types of cells (normal, transformed, polypoid, and cancerous) and two kinetic processes (mutation and promotion). Arachidonic acid metabolites play a role in the model in the promotion of cancer from polyps, and account for that promotion through: (1) their effect on encouraging more polypoid cells in mitosis to move toward cancer; and (2) their immunosuppressive effect over time. The model also shows that one defect in allowing more cells to mutate to the transformed state is sufficient to account for the chain of events leading to the clinical sequelae of familial polyposis coli. A second genetic effect at another point in the process is unnecessary. The mechanism of action of Sulindac on colon polyps is explained by the model through inhibition of production of arachidonic acid metabolites, most notably prostaglandin E.

Effects of butylated hydroxyanisole on ornithine decarboxylase activity and its gene expression induced by phorbol ester tumor promoter

Butylated hydroxyanisole (BHA) is a phenolic antioxidant that has been found to suppress the activity of skin tumor promoters. In this study, we investigated the effect of BHA on the activity of ornithine decarboxylase (ODC, an indicator of tumor promotion) and its gene expression induced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in mouse skin. TPA-induced ODC activity was markedly inhibited by the topical application of 55 mumol of BHA (the inhibition rate at 6 h was about 80%). In Northern and dot-blot analysis, the TPA-induced increase in ODC mRNA was shown to be markedly reduced by the same dose of BHA (the inhibition rate at 4 h was about 60%). These results suggest the involvement of a decrease in ODC gene expression in the mechanism of the inhibition of ODC activity by BHA.

Inhibitory effect of curcumin and some related dietary compounds on tumor promotion and arachidonic acid metabolism in mouse skin

Topical application of curcumin, the major yellow pigment in turmeric and curry, has a potent inhibitory effect on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced tumor promotion in mouse skin. The structurally related compounds chlorogenic acid, caffeic acid and ferulic acid are less potent inhibitors. Curcumin is a potent inhibitor of TPA-induced ornithine decarboxylase activity and inflammation in mouse skin whereas chlorogenic acid, caffeic acid and ferulic acid are only weakly active or inactive. Curcumin is a potent inhibitor of arachidonic acid-induced inflammation in vivo in mouse skin, and this compound is also a potent inhibitor of epidermal lipoxygenase and cyclooxygenase activity in vitro. Although chlorogenic acid is only weakly active as an inhibitor of epidermal lipoxygenase activity and TPA-induced ear inflammation, it is more active than caffeic acid and ferulic acid. The inhibitory effects of curcumin, chlorogenic acid, caffeic acid and ferulic acid on TPA-induced tumor promotion in mouse skin parallel their inhibitory effects on TPA-induced epidermal inflammation and epidermal lipoxygenase and cyclooxygenase activities. Examination of the structural features of curcumin required for its biological activity indicate that free hydroxyl groups on the benzene rings are not required for inhibition of TPA-induced ornithine decarboxylase activity and inflammation in mouse skin.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-enhanced transformation in vitro by inhibitors of phospholipid metabolism

The effects of some inhibitors of phospholipid metabolism were studied using a two-stage transformation assay system in vitro with 3-methylcholanthrene (3-MC) initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion in BALB/3T3 cells. Inhibitors of phospholipid metabolism such as hydrocortisone (HC), p-bromophenacyl bromide (BPB), nordihydroguaiaretic acid (NDGA), quercetin and indomethacin (IM) were used. They were demonstrated to inhibit strongly TPA-promoted transformation. In particular, HC at 1 microgram/ml inhibited the in vitro transformation completely. All the inhibitors used inhibited transformation in a dose-dependent manner. The results suggest that phospholipid metabolism is important for the promotion stage of transformation in BALB/3T3 cells.

Inhibition of benzoyl peroxide-mediated tumor promotion in 7,12-dimethylbenz(a)anthracene-initiated skin of Sencar mice by antioxidants nordihydroguaiaretic acid and diallyl sulfide

Benzoyl peroxide (BPO), a free radical generating compound, is widely used in topical medications prescribed for acne vulgaris and in cosmetic products. It has been shown to possess tumor-promoting activity in murine skin initiated with chemical carcinogens such as 7,12-dimethylbenz(a)anthracene (DMBA). In the present study we assessed the effect of the antioxidants nordihydroguaiaretic acid (NDGA) and diallyl sulfide (DAS) against BPO-mediated tumor promotion in murine skin. Pretreatment of Sencar mice with NDGA and DAS prior to skin application of BPO resulted in a time- and dose-dependent inhibition of epidermal ODC induction caused by BPO. Tumor initiation was achieved by a single topical application of DMBA (10 micrograms/animal) to Sencar mice. Ten days later tumor promotion was begun by twice-weekly topical application of BPO (20 mg/animal). The anticarcinogenic effects of NDGA (25 mumol/mouse) and DAS (20 mumol/mouse) were evaluated by administering these agents topically 60 min prior to each BPO application. After 26 weeks on test, the number of benign papillomas/mouse were 0.10 +/- 0.07 and 2.15 +/- 0.30 in the NDGA and DAS pretreated group of animals as compared to 4.40 +/- 1.14 in animals receiving BPO alone. After 51 weeks on test, the number of squamous cell carcinomas/mouse were 0.00 +/- 0.00, 0.35 +/- 0.10 in the NDGA and DAS pretreated group of animals as compared to 0.65 +/- 0.12 in animals receiving BPO alone. From these data we suggest that the antioxidants NDGA and DAS can abrogate the tumor-promoting effects of BPO in murine skin and that NDGA is substantially more effective than DAS in this regard.

Papilloma and carcinoma production in DMBA-initiated, onion oil-promoted mouse skin

Groups of 20 females Ha/ICR mice were initiated with 25 micrograms 7,12-dimethylbenz[a]anthracene (DMBA) and promoted one week later with topical treatments three times per week of 5 micrograms phorbol myristate acetate (PMA) and/or onion oil or garlic oil. Promotion was continued for 49 weeks in most experiments. Promotion was continued for 60 weeks in the experiment that evaluated the effect of time intervals between PMA and garlic oil. All experiments were conducted with 0.2 ml acetone solutions of agents. Onion oil, but not garlic oil, was a weak promoter in mouse skin. A 1-mg dose produced five papillomas in three mice and one carcinoma in 330 days (18 survivors). The 10-mg dose was more effective; it produced cumulative yields of 56 papillomas in 14 mice and 7 carcinomas in 4 mice in 345 days (14 survivors). Onion oil is neither an initiator nor a whole carcinogen. The effects of intervals between PMA and a 1-mg dose of onion or garlic oil were determined. These intervals were -2 hrs, -1 hr, -0.5 hr, +0.5 hr, +1 hr, and +2 hrs with respect to time of PMA application. Maximal inhibition of papillomas by onion oil was observed at the +0.5-hr interval and was similar to that previously reported. Garlic oil is not a promoter. It inhibited papillomas at the +0.5-hr, +1.0-hr, and +2.0-hr intervals but did not appear to affect carcinoma production.

Eicosapentaenoic and arachidonic acid: comparison of metabolism and activity in murine epidermal cells

The biological activity, including metabolism and modulation of ornithine decarboxylase activity and DNA synthesis, of arachidonic acid (AA) and eicosapentaenoic acid (EPA) were compared in epidermal cells from SENCAR mice. Radiolabelled AA and EPA were found to be similarly incorporated into and released from membrane phospholipids of unstimulated cultures. However, when cells were stimulated with the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA), the release of AA was significantly higher than the release of EPA. The extent of metabolism of AA and EPA to prostaglandins was determined in both freeze-thawed cell preparations and in viable cultured cells. In the freeze-thawed preparations, use of AA as a substrate resulted in significantly more PGF than when EPA was used as the substrate. However, more PGE3 was formed than PGE2. PGD levels were the same for either fatty acid precursor. Prostaglandin production was also determined in viable cultured cells since other influences such as phospholipase A2 activity can modify prostaglandin production. Control cultures prelabelled with either AA or EPA produced similar amounts of the respective PGF, PGE, and PGD. However, TPA-stimulated cultures produced significantly higher amounts of each prostaglandin in cultures prelabelled with AA compared to cells prelabelled with EPA. HETE or HEPE production was the same both for cultured cells prelabelled with AA or EPA and for homogenates from uncultured cells incubated directly with the radiolabelled fatty acids. TPA-induced ornithine decarboxylase (ODC) was significantly higher in AA-treated cultures compared to EPA-treated cultures. AA supports DNA synthesis to a greater extent than EPA, either alone or in the presence of TPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidants--carcinogenic and chemopreventive properties

Synthetic and naturally occurring antioxidants have a wide variety of biological actions in rodents in addition to their primary antioxidant activity. Some of the included biological effects are of direct interest in relation to studies of carcinogenicity and/or modulation of carcinogenesis. Since the synthetic antioxidant BHA was first found to exert carcinogenic potential in rat and hamster forestomach epithelium, many other synthetic and naturally occurring antioxidants have been examined for their ability to induce proliferative activity in the alimentary canal. These studies have revealed that caffeic acid and sesamol are also tumorigenic for rat forestomach epithelium, whereas catechol and p-methylcatechol induce neoplasia in rat glandular stomach epithelium. Although the proliferative response is very rapid, with inflammation and ulceration, it takes a very long time before carcinomas develop. The proliferative lesions in the forestomach induced by BHA or caffeic acid are largely reversible, in contrast to those induced by genotoxic carcinogens, which generally persist and develop into cancer. Therefore, chronic irritation is considered to be responsible for the induction of stomach cancer by antioxidants. Butylated hydroxyanisole can undergo oxidative metabolism in vitro, and some of the metabolites formed have the potential for binding to proteins. Neither BHA nor its metabolites binds to DNA in vivo, but protein binding in the forestomach was greater than 10 times higher than that in the glandular stomach. It is thus conceivable that BHA is oxidatively metabolized in the forestomach epithelium (possibly entering into redox cycling), and reactive metabolites including semiquinone radicals or active oxygen species are responsible for the carcinogenesis by a mechanism involving binding to macromolecules. Many antioxidants have been shown to modify carcinogenesis, and as a rule, they inhibit the initiation stage by reducing the interaction between carcinogen and DNA. However, both promotion and inhibition have been reported for second-stage carcinogenesis, depending on the organ site, species of animal, or initiating carcinogen. They can also block reaction of amine and nitrite to form nitrosamines or reduce TPA promotion of skin carcinogenesis. Generally high doses of antioxidants are required for carcinoma induction or modification of chemical carcinogenesis. The significance of the reported tumorigenicity and strong promoting activity of antioxidants for forestomach epithelium of animals to the development of human cancer appears limited mainly because humans do not have a forestomach. The carcinogenic and strong promoting activities of catechol and its structurally related compounds on rat glandular stomach epithelium are of greater concern because this tissue is directly analogous to human gastric epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Antioxidants and multistage carcinogenesis in mouse skin

The two-step initiation-promotion protocol for the induction of skin tumors in mice is a convenient model to elucidate what molecular events are involved in the multistage process of carcinogenesis and how they can be modulated. The current theories concerning the mechanisms of skin tumor initiation, stages 1 and 2 of tumor promotion, and tumor progression are reviewed. Because chemical carcinogens and tumor promoters may, directly or indirectly, generate reactive oxygen species (ROS) and because various antioxidants inhibit effectively some of the biochemical and biological events linked to tumor initiation, promotion and/or progression, it is conceivable that different sequences and levels of free radical-induced macromolecule damage may contribute to the evolution of the epidermal target cells from the preneoplastic stage to the malignant stage.

The generation of oxygen radicals: a positive signal for lymphocyte activation

The induction of ornithine decarboxylase (ODC) activity in lymphocytes is associated with activation and the initiation of cellular proliferation. ODC is also an essential component in tumor promotion. Phorbol myristic acetate (PMA) is a mitogen for lymphocytes, but can also promote tumor formation. Tumor promotion is linked to the generation of free radicals induced by PMA. Modulation of intracellular glutathione is associated lymphocyte activation and in protection of cells from damage due to oxygen radicals. We examined the interaction between ODC activity and intracellular glutathione concentrations in EL4 murine lymphoblastoid cells. The intracellular glutathione concentration could be augmented in EL4 cells when cultured with the cysteine delivery agents 2-oxothiazolidine 4-carboxylate (OTC) and 2-mercaptoethanol (2-ME) and suppressed with the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine (BSO). OTC and 2-ME suppressed ODC activity in fresh serum and PMA-activated EL4 cells. BSO had no effect on ODC activity of EL4 cells cultured in the presence of PMA. While both OTC and 2-ME augmented the total intracellular glutathione concentration, PMA enhanced only the level of oxidized glutathione. To determine if the mechanism by which PMA or fresh serum altered intracellular glutathione and ODC activity was through the generation of oxygen radicals, EL4 cells were cultured with free radical scavengers. The nonpermeant electron acceptor potassium ferricyanide, and the H2O2 scavenger catalase, lowered ODC activity in both serum-stimulated and PMA-activated EL4 cells. Similarly, incubation of EL4 cells with either potassium ferricyanide or catalase elevated intracellular glutathione concentrations. These data suggest that (a) modulation of intracellular glutathione in the EL4 lymphoblastoid cell line alters ODC activity induced by fresh serum and by the mitogen PMA; (b) activation of EL4 cells by PMA alone alters intracellular glutathione metabolism, which may be associated with its role as a mitogen in lymphocyte activation; and (c) the generation of free radicals in EL4 cells may play a positive role in cellular activation.

Interaction of flavonoids with 1,1-diphenyl-2-picrylhydrazyl free radical, liposomal membranes and soybean lipoxygenase-1

The interaction of the antiperoxidative flavonoids namely, quercetin, quercetrin, rutin, myricetin, phloretin, phloridzin, catechin, morin and taxifolin with the 1,1,-diphenyl-2-picrylhydrazyl (DPPH) free radical was demonstrated. Flavonoid-DPPH interaction was looked at in the absence and presence of liposomes so as to reveal some information on bilayers. Perturbations in the lipid bilayers were monitored with the fluorescent probe, dansylhexadecylamine (DSHA). It was observed that the interaction of the flavonoids on the lipid bilayer occurred in the polar zone of the lipid bilayers. The flavonoids were able to scavenge free radicals and could do so in biomembranes. It is suggested that the DPPH free radical abstracts the phenolic hydrogen of the flavonoid molecule and that this could be the general mechanism of the scavenging action of the antiperoxidative flavonoids. The effects of the flavonoids on soybean lipoxygenase-1 were investigated both in buffer and also in liposomal suspension. All the flavonoids studied showed inhibition of the enzyme in both systems but the inhibition was greater in the liposomal suspension. Quercetin was the most potent and it inhibited the lipoxygenase in the liposomal suspension by about 42% while the other flavonoids inhibited the enzyme by about 14-23%. We observed that the effect of myricetin and quercetin on the enzyme was pH dependent.

The induction of ornithine decarboxylase caused by 12-O-tetradecanoylphorbol-13-acetate in isolated epidermal cells is inhibited by lipoxygenase inhibitors but not by cyclooxygenase inhibitors

The effects of lipoxygenase and cyclooxygenase inhibitors on ornithine decarboxylase (ODC) induction by a potent tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) were examined in vitro in isolated mouse epidermal cells. Lipoxygenase inhibitors such as quercetin, nordihydroguaiaretic acid (NDGA), 3,4,2',4'-tetrahydroxychalcone, 3-amino-1-(3-trifluoromethylphenyl)-2-pyrazoline (BW755C) inhibited the TPA-caused ODC induction. Indomethacin, a selective cyclooxygenase inhibitor, failed to inhibit it. These results suggest that the lipoxygenase inhibitors inhibit TPA-caused epidermal ODC induction in mouse skin at least in part by acting directly on epidermal cells while cyclooxygenase inhibitor inhibits it indirectly by acting on cells other than epidermal cells, e.g. cells which are involved in the prostaglandin-dependent inflammatory process.

Specific inhibition of phorbol diester-induced granulocyte-macrophage progenitor cell (GM-CFU) differentiation by lipoxygenase inhibitors

The induction of differentiation of SENCAR murine granulocyte-macrophage precursor cells (GM-CFU) by the tumor-promoting phorbol diester 12-O--tetradecanoyl-phorbol-13-acetate (TPA) was inhibited by agents reported to inhibit specific aspects of arachidonic acid metabolism. These agents included phospholipase A2 inhibitors, and eicosatetraynoic acid (ETYA), a competitive inhibitor of arachidonic acid oxygenases. Whereas inhibitors reported specific for lipoxygenases were also active, no comparable effect was observed for inhibitors of the corresponding cyclooxygenase. These findings are therefore consistent with the hypothesis that induced differentiation of GM-CFU cells is regulated by products of arachidonic acid metabolism formed principally via lipoxygenase activity.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced induction of Epstein-Barr virus early antigen in Raji cells by some inhibitors of tumor promotion

The effects of some compounds, which have been reported to inhibit tumor promotion in vivo, on the induction of the early antigen (EA) of Epstein-Barr virus (EBV) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells were examined. The inhibitors of the cascade process involving arachidonic acid, indomethacin, nordihydroguaiaretic acid, phenidone and p-bromophenacyl bromide, effectively inhibited EBV-EA induction by TPA. Two flavonoids, morin and kaempferol also inhibited EA induction. Among antioxidants, butylated hydroxytoluene effectively inhibited EA induction, though alpha-tocopherol did not show any inhibition of EA induction at concentrations of up to 150 micrograms/ml. N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide, a calmodulin antagonist, and esculetin showed inhibitory effects on EA induction, though slight cytotoxicity was observed. L-1-p-Tosylamino-2-phenylethyl chloromethyl ketone, a protease inhibitor, showed cytotoxicity and no specific inhibition of EA induction. Five kinds of steroids, cortisone, hydrocortisone, prednisolone, dexamethasone and fluocinolone acetonide showed no inhibitory effect on EA induction at concentrations of up to 100 micrograms/ml. In addition, the relationship between the inhibition of EBV-EA induction and that of tumor promotion is discussed.

Some properties of lipoxygenase activities in cytosol and microsomal fractions of mouse epidermal homogenate

Lipoxygenase activity in microsomal fraction of mouse epidermal homogenate was characterized in comparison with cytosol lipoxygenase activity. The major activity was identified as 12-lipoxygenase in microsomal fraction as well as in cytosol fraction by the analyses with high-performance liquid chromatography and gas chromatography-mass spectrometry. Apparent Km values of cytosol and microsomal 12-lipoxygenase for arachidonic acid were 5.0 microM and 6.2 microM respectively. Apparent Vmax values were 14 pmol/min/mg protein for the cytosol enzyme and 32 pmol/min/mg protein for the microsomal enzyme. Net activities of cytosol and microsomal 12-lipoxygenase were 214 and 109 pmol/min/g wet tissue, respectively. Both cytosol and microsomal lipoxygenase activities were neither dependent on calcium nor ATP. Carbon monoxide failed to affect these enzyme activities. There were considerable differences either in the effect of glutathione or in the sensitivities toward several lipoxygenase inhibitors, indicating that the cytosol and the microsomal 12-lipoxygenase activities are derived from two different enzymes. Alternatively, the differences could be attributable to the different microenvironments of these enzymes.

Effects of chalcone derivatives on lipoxygenase and cyclooxygenase activities of mouse epidermis

The effects of chalcone derivatives on 12-lipoxygenase and cyclooxygenase of mouse epidermis were investigated. The chalcone derivatives which have 3,4-dihydroxycinnamoyl structure in the molecule, such as 3,4-dihydroxychalcone, 3,4,2'-trihydroxychalcone, 3,4,4'-trihydroxychalcone and 3,4,2'4'-tetrahydroxychalcone, potently inhibited epidermal 12-lipoxygenase activity. Although some of them also inhibited cyclooxygenase activity at relatively high concentrations, the inhibitory effects of these chalcone derivatives on 12-lipoxygenase were 10 times or more potent than their effects on cyclooxygenase. The chalcone derivatives which have cinnamoyl or 4-hydroxycinnamoyl structure, instead of 3,4-dihydroxycinnamoyl structure, in the molecule, showed little or no inhibitory effects on either 12-lipoxygenase or cyclooxygenase activities. The inhibitory effects of chalcone derivatives on 12-lipoxygenase and cyclooxygenase of mouse epidermis are dependent on the particular structure, i.e. 3,4-dihydroxycinnamoyl structure, of the chalcone derivatives.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced increase in vascular permeability in mouse skin by lipoxygenase inhibitors

The painting of mouse dorsal skin with 12-O-tetradecanoylphorbol-13-acetate (TPA) (0.2-2.5 nmol/mouse) induced a dose-related increase in vascular permeability, which was determined by pontamine sky blue exudation into the skin 5 hr after the TPA treatment. Marked infiltration of neutrophils in the dermal interstitium was also observed 5 hr after TPA treatment. Treatment of mice with nordihydroguaiaretic acid (NDGA) (10 mumol/mouse). 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861) (10 mumol/mouse) and quercetin (3 mumol/mouse) significantly inhibited the TPA-induced dye exudation. However, indomethacin (250-1000 nmol/mouse) tended to inhibit the TPA-induced dye exudation, but the inhibition was not statistically significant. Treatment with AA861 (10 mumol/mouse) also caused a marked inhibition of TPA-induced neutrophil infiltration. Quercetin, NDGA and AA861 inhibited epidermal lipoxygenase activity, but indomethacin failed to inhibit it. On the other hand, indomethacin inhibited epidermal cyclooxygenase, but quercetin, NDGA and AA861 failed to inhibit it. The present study suggests involvement of a lipoxygenase product(s) in the mechanism of the TPA-induced increase in vascular permeability in the dorsal skin of mice.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced nitroblue tetrazolium reduction in mouse peritoneal macrophages by various tumor promotion inhibitors

The effects of various inhibitors on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced reduction of nitroblue tetrazolium (NBT) in mouse peritoneal macrophages were investigated. The reduction was inhibited by phospholipase A2 inhibitors, such as dibromoacetophenone, the lipoxygenase inhibitor nordihydroguaiaretic acid, an NADH-dehydrogenase inhibitor, the microfilament inhibitor cytochalasin B, oxygen radical scavengers such as superoxide dismutase, antioxidants such as butyl hydroxyanisole and non-specific inhibitors such as retinoic acid. The reduction was not affected by the cyclooxygenase inhibitor indomethacin or the H2O2 scavenger catalase.

Induction of ornithine decarboxylase activity by 1-oleoyl-2-acetyl-glycerol in isolated mouse epidermal cells

1-Oleoyl-2-acetyl-glycerol induced a rise in ornithine decarboxylase activity in isolated epidermal cells in a concentration-dependent manner. The time course of the induction of ornithine decarboxylase by 1-oleoyl-2-acetyl-glycerol was similar to that by 12-O-tetradecanoylphorbol-13-acetate. A23187 did not enhance the enzyme induction caused by 1-oleoyl-2-acetyl-glycerol. Palmitoyl-DL-carnitine prevented the induction of the enzyme either by 1-oleoyl-2-acetyl-glycerol or 12-O-tetradecanoyl-phorbol-13-acetate. These results suggest that the activation of protein kinase C is an initial and essential event in the process of ornithine decarboxylase induction caused by 12-O-tetradecanoyl-phorbol-13-acetate.

Inhibition of teleocidin-caused epidermal ornithine decarboxylase induction by phospholipase A2-, cyclooxygenase- and lipoxygenase-inhibitors

Teleocidin (5 micrograms/mouse), a potent tumor promoting indole alkaloid from Streptomyces, induced epidermal ornithine decarboxylase (ODC) in CD-1 mice. Teleocidin-caused ODC induction was inhibited by the treatment of indomethacin (2 mumol/mouse), a selective cyclooxygenase inhibitor, and p-bromophenacyl bromide (BPB) (30 mumol/mouse), a phospholipase A2 inhibitor. Teleocidin-caused ODC induction inhibited by indomethacin was completely restored by concurrent application of prostaglandin E2 (PGE2) (140 nmol/mouse). On the other hand, teleocidin-caused ODC induction inhibited by BPB was not restored by the treatment of mice with PGE2, but partially restored by the treatment with arachidonic acid (1 mumol/mouse). Treatment of mice with lipoxygenase inhibitors such as BW755C (30 mumol/mouse), nordihydroguaiaretic acid (NDGA) (30 mumol/mouse), quercetin (10 mumol/mouse), and 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861) (10 mumol/mouse) clearly suppressed ODC induction by teleocidin. Moreover, both NDGA (30 mumol/mouse) and quercetin (10 mumol/mouse) inhibited the restoring effect of PGE2. Therefore, our present results suggest that arachidonate metabolites, i.e., not only cyclooxygenase product(s) but also lipoxygenase product(s), are involved in the mechanism of ODC induction by teleocidin.

Inhibition of mouse epidermal 12-lipoxygenase by 2,3,4-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinon e (AA861)

2,3,5-Trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861) strongly inhibited epidermal lipoxygenase activity which was determined by the formation of [14C]12-hydroxy-5,8,10,14-eicosatetraenoic acid by incubating [14C]arachidonic acid with cytosol fraction of epidermal homogenate of CD-1 mice. AA861 failed to inhibit epidermal cyclooxygenase activity. The present results indicate that AA861 is a potent inhibitor of 12-lipoxygenase in mouse epidermis (IC50 1.9 microM).

Bile salt stimulation of colonic epithelial proliferation. Evidence for involvement of lipoxygenase products

Prostaglandin E2 (PGE2) and several other prostaglandins synthesized by colon suppress the proliferative activity of colonic epithelium. However, bile salts stimulate colonic epithelial proliferation despite the actions of bile salts to enhance the release of arachidonate and consequent colonic synthesis of PGE2. The current study was conducted to assess whether bile salt-induced increases in colonic formation of arachidonate metabolites other than PGE2 were linked to the stimulation of the proliferative activity of colonic epithelium. Within 10 min of addition, deoxycholate markedly stimulated the in vitro release of [14C]arachidonate from prelabeled rat colon. When given in vivo by intracolonic instillation deoxycholate (10 mumol) increased colonic accumulation of immunoreactive prostaglandin E (PGE), thromboxane B2 (TXB2), and the lipoxygenase product 12-hydroxyeicosatetraenoic acid (12-HETE) by two to fourfold over control in 30 min. This effect of intracolonic deoxycholate was followed by a ninefold increase in mucosal ornithine decarboxylase activity (4 h), and a subsequent two to threefold increase in [3H]thymidine [( 3H]Thd) incorporation into DNA of either mucosal scrapings or isolated pools of proliferative colonic epithelial cells (24 h). Intracolonic instillation of indomethacin (50 mumol) suppressed to low or undetectable levels both basal colonic accumulation of PGE and TXB2 and the increases in each parameter induced by subsequent instillation of deoxycholate. By contrast, indomethacin enhanced accumulation of 12-HETE in both control colons and those subsequently exposed to deoxycholate. The increases in 12-HETE induced by indomethacin alone were correlated with stimulation of mucosal ornithine decarboxylase activity and [3H]Thd incorporation into mucosal DNA. Indomethacin also enhanced the increases in these parameters induced by deoxycholate. Intracolonic instillation of phenidone (25-100 mumol) suppressed accumulation of PGE, TXB2, and 12-HETE in control colons and the increases in these parameters induced by a subsequent instillation of deoxycholate. Phenidone alone did not alter mucosal ornithine decarboxylase activity or [3H]thymidine incorporation into mucosal DNA. However, phenidone suppressed or abolished increases in these parameters induced by a subsequent instillation of deoxycholate. 4-(2-[IH-imidazol-1-yl]ethoxy) benzoic acid hydrochloride UK 37,248, which selectively reduced colonic TXB2 to undetectable levels without altering PGE or 12-HETE, had no effect on control or deoxycholate-induced increases in mucosal ornithine decarboxylase activity or [3H]Thd incorporation into DNA. Neither indomethacin nor phenidone altered the increases in [(14)C]arachidonate release induced in vitro by deoxycholate. Chenodeoxycholate and cholate also stimulated [(14)C]arachidonate release from colon in vitro within 10 min, and increased colonic 12-HETE (30 min) and mucosal ornithine decarboxylase activity (4 h) upon intracolonic installation. Prior installation of phenidone inhibited the increases in both 12-HETE and ornithine decarboxylase activity induced by these bile salts. The results support a role for bile salt-induced increases in colonic accumulation of lipoxygenase products, as reflected by 12-HETE, in the subsequent stimulation of the proliferative activity of colonic epithelium.

Differential effects of nordihydroguaiaretic acid (NDGA) on B-cell subsets: reversal of NDGA-induced antibody suppression by cyclic GMP is subset specific

Nordihydroguaiaretic acid (4,4'-[2,3-dimethyl tetramethylene]-dipyrpcatechol) (NDGA), a reportedly specific lipoxygenase inhibitor, suppressed the in vitro murine plaque-forming cell (PFC) response to a thymus-dependent (TD) antigen, and the two subclasses of thymus-independent (TI) antigens, TI1 and TI2, at a final concentration of 33 microM. Suppression kinetics were inconsistent with those observed in previous experiments for other lipoxygenase inhibitors, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in that BHA and BHT exert suppression early in the 5-day PFC culture system, whereas NDGA suppressed through the 96th h of the 120 h culture period. The sulfhydryl-protective agent 2-mercaptoethanol (2ME) protected both the TD and TI responses. Dibutyryl cyclic GMP (dbcGMP) failed to restore NDGA-suppressed TD and TI1 PFC responses but restored the TI2 response when added at 0-, 24-, 48-, 72-, and 96-h at concentrations of 1-2 mM. NDGA inhibited lipopolysaccharide- (LPS-) induced increases in murine splenocyte cyclic GMP (cGMP) levels, and dbcGMP failed to accelerate the onset of the TI2 PFC response appreciably. The results of these and other laboratory studies indicated that NDGA may not be a specific inhibitor of lipoxygenase. Furthermore, the B-cell subset responding to TI2 antigens may be separated from the TD- and TI1-responding subsets because of the ability of dbcGMP to restore NDGA-suppressed TI2 responses but not the TD or TI1 response. The results suggest a fundamental difference in the biochemical pathways of B-cell subsets, and that cGMP metabolism in some cells may be linked to specific protein synthesis.

Insulinotropic effect of the tumor promoter teleocidin in isolated pancreatic islets

A tumor promoter teleocidin induced insulin secretion from isolated pancreatic islets in a concentration-dependent manner. The teleocidin-induced secretion was inhibited by p-bromophenacyl bromide, nordihydroguaiaretic acid, 3-amino-1-(3-trifluoromethylphenyl)-2-pyrazoline and 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone, but not by indomethacin. Insulinotropic concentrations of teleocidin stimulated 6-keto-prostaglandin F1 alpha release from pancreatic islets. These results suggest that phospholipase A2 activation and lipoxygenase product(s) are involved in the mechanism of teleocidin-induced insulin secretion.