Antimutagenic and antitumorigenic activities of nordihydroguaiaretic acid

Antigenotoxic, antiproliferative and antimetastatic properties of a combination of native medicinal plants from Argentina

ETHNOPHARMACOLOGICAL RELEVANCE

Jarilla is the common name of an appreciated group of native plants from the semi-arid region in Argentina (Larrea cuneifolia Cav., Larrea divaricata Cav. and Zuccagnia punctata Cav.) that have been historically consumed to heal respiratory, musculoskeletal and skin ailments, as well as recommended for weakness/tiredness, hypertension, diabetes and cancer treatment. It was previously reported that some biological properties could be improved when these plants are used jointly. Infusions of a defined mixture, composed by three Jarilla species, L. cuneifolia: L. divaricata: Z. punctata (0.5:0.25:0.25) (HM2) showed synergistic and additive effect on antioxidant activity even after passing through the gastro-duodenal tract.

AIM OF THE STUDY

The main purpose of this work was to evaluate antigenotoxic, antitumor, and anti-metastatic properties of the Jarilla species that grow in the Northwest of Argentina and a herbal combination of them.

MATERIAL AND METHODS

Infusions of Jarilla mixture (HM2), and of each single plant species were prepared. Phenolic profiles of infusions were analyzed by HPLC-ESI-MS/MS and two relevant chemical markers were quantified. The antigenotoxic activity was evaluated by using the Ames test and the Cytokinesis-Block Micronucleus (CBMN) assay against direct mutagens. Evaluations of both cytotoxicity and antiproliferative effects were conducted on tumor and non-tumor cell lines. Both in vivo tumoral growth and metastasis inhibition were evaluated by using a carcinoma model on Balb/c mice.

RESULTS

HM2 mix could suppress genetic and chromosome mutations induced by 4-nitro-o-phenylendiamine (4-NPD) and doxorubicin. Herbal mixture and single plant infusions showed cytotoxic effect against mammary, uterus, and brain tumoral cells without a selective action vs normal human cell line. HM2 mix was able to reduce mammary tumor mass on the Balb/c mice model and showed a significant reduction in the number of metastatic nodules in the lungs.

CONCLUSIONS

Our results suggest that the combinations of three Jarilla species from northwest Argentina would be a promising alternative to treat or slow down the development of chronic diseases, such as cancer.

Nordihydroguiaretic acid attenuates skin tumorigenesis in Swiss albino mice with the condition of topical co-administration of an immunosuppressant

Drug and chemically-induced immunosuppression has been implicated as a confounding factor for cancer development. Management of cancer in such situation is often a challenging task. We tested the efficacy of nordihydroguiaretic acid (NDGA) against immunosuppressant tacrolimus-induced augmentation of mouse skin tumorigenesis. It was observed that topical administration of tacrolimus significantly accelerated the tumor promotion events in dimethylbenz(a)anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA) promoted two-stage mouse skin carcinogenesis, which were accompanied by reduced CD4(+)/CD8(+) ratio of lymph nodes and serum IL-2 level. NDGA pre-treatment before each TPA application reduced the tumor incidence, its multiplicity and volume together with improvement in histopathological alterations and decrease in proliferating cell nuclear antigen (PCNA) labeling index (LI). However, NDGA had no significant influence on the immunosuppressive effect of tacrolimus. The present study demonstrates chemopreventive effect of NDGA in normal as well as in the condition of immunosuppression. Thus, NDGA has the potential to inhibit or delay the onset of tumor development during immunosuppressive regimen.

Phenolic compound production in relation to differentiation in cell and tissue cultures of Larrea divaricata (Cav.)

The lignan nordihydroguaiaretic acid (NDGA) and its derivatives existing in Larrea divaricata species show a wide range of pharmacological activities which makes this genus an interesting target to consider the plant in vitro cultivation systems as a feasible alternative source for their production. These compounds are potentially useful in treating diseases related to heart condition, asthma, arteriosclerosis, viral and bacterial infections, inflammation and cancer. In the present study, calli, cell suspension cultures, and in vitro and wild plants of L. divaricata were investigated for their potential to synthesize phenolic compounds. Calli, both with and without organogenesis, produced NDGA and quercetin, as did plantlet and wild plants. NDGA was also produced by the cell suspension cultures, together with p-coumaric acid, ferulic acid and sinapyl alcohol. The capacity of undifferentiated tissues to form phenolic compounds is very limited, but when the calli underwent organogenesis, developing mainly adventitious shoots, the phenolic compound production increased significantly. Plantlets regenerated from adventitious shoots of L. divaricata calli did not show the same phenolic pattern as wild plants, with levels of NDGA and quercetin being 3.6- and 5.9-fold lower, respectively.

Nordihydroguaiaretic Acid from Creosote Bush (Larrea tridentata) Mitigates 12-O-Tetradecanoylphorbol-13-Acetate-Induced Inflammatory and Oxidative Stress Responses of Tumor Promotion Cascade in Mouse Skin

Nordihydroguaiaretic acid (NDGA) is a phenolic antioxidant found in the leaves and twigs of the evergreen desert shrub, Larrea tridentata (Sesse and Moc. ex DC) Coville (creosote bush). It has a long history of traditional medicinal use by the Native Americans and Mexicans. The modulatory effects of topically applied NDGA was studied on acute inflammatory and oxidative stress responses in mouse skin induced by stage I tumor promoting agent, 12-O-tetradecanoylphorbol-13-acetate (TPA). Double TPA treatment adversely altered many of the marker responses of stage I skin tumor promotion cascade. Pretreatment of NDGA in TPA-treated mice mitigated cutaneous lipid peroxidation and inhibited production of hydrogen peroxide. NDGA treatment also restored reduced glutathione level and activities of antioxidant enzymes. Elevated activities of myeloperoxidase, xanthine oxidase and skin edema formation in TPA-treated mice were also lowered by NDGA indicating a restrained inflammatory response. Furthermore, results of histological study demonstrated inhibitory effect of NDGA on cellular inflammatory responses. This study provides a direct evidence of antioxidative and anti-inflammatory properties of NDGA against TPA-induced cutaneous inflammation and oxidative stress corroborating its chemopreventive potential against skin cancer.

Antigenotoxic effect of nordihydroguaiaretic acid against chlormadinone acetate-induced genotoxicity in mice bone-marrow cells

Nordihydroguaiaretic acid (NDGA), a phenolic lignan, was tested for its antigenotoxic potential against chlormadinone acetate (CMA)-induced genotoxic damage in mice bone-marrow cells. Doses of about 22.50 mg/kg body weight of CMA were given along with 1, 5 and 10 mg/kg body weight of NDGA intraperitoneally. The treatment resulted in the reduction of sister chromatid exchanges and chromosomal aberrations induced by CMA, suggesting an antigenotoxic potential of NDGA. Earlier studies show that CMA generates reactive oxygen species, responsible for genotoxic damage. The free radical-scavenging property of NDGA is responsible for the reduction of genotoxic damage induced by CMA in mice bone-marrow cells.

A pilot dose-escalation study of the effects of nordihydroguareacetic acid on hormone and prostate specific antigen levels in patients with relapsed prostate cancer

OBJECTIVE

To assess the tolerability of the effects of nordihydroguareacetic acid (NDGA) and its effect on prostate-specific antigen (PSA) kinetics in patients with relapsed prostate cancer, as among the many biological effects of NDGA is the inhibition of the insulin-like growth factor 1 receptor (IGF-1R) tyrosine kinase.

PATIENTS AND METHODS

Eligible patients were those with an increasing PSA level after definitive local therapy, in either the non-castrate (androgen-dependent prostate cancer, ADPC) or the castrate state (castration-resistant prostate cancer, CRPC) with no evidence of metastatic disease by bone scan or computed tomography of the abdomen or pelvis. Treatment consisted of continuous oral daily dosing according to a planned dose escalation of 750, 1250, 1750, 2250 and 2500 mg of NDGA. PSA levels were measured every 28 days. Serial levels of testosterone, dihydrotestosterone, oestradiol and sex hormone-binding globulin were measured at baseline and monthly while on study therapy.

RESULTS

Fifteen patients were enrolled, including 11 with ADPC and four with CRPC. There were asymptomatic increases in transaminase in six patients, two of which were grade 3, all occurring at >or=3 months. The increases in transaminase resolved after stopping NDGA but recurred with repeated dosing. Doses of NDGA up to 2500 mg/day caused no other toxicities. A median (range) of 5.5 (1-13) cycles were delivered. Of the 11 patients with ADPC, one had a decline in PSA level of >50% of the baseline value and one a decline of <50%. Three patients with ADPC had a greater than three-fold increase in PSA doubling time while on therapy, one from 11 to 46 months (750 mg), one from 9.5 to 49.5 months (1750 mg), and one from 5.9 to 46.2 months (2500 mg). There were no reductions in PSA level in patients with CRPC. There were no significant effects on levels of testosterone, dihydrotestosterone, oestradiol or sex hormone-binding globulin.

CONCLUSIONS

Continuous daily dosing with NDGA is reasonably well tolerated but is associated with transaminitis in some patients, that occurs after several months on therapy. There were apparent effects on the rate of increase in PSA. Further study is required to determine the optimum pharmacokinetics and antitumour effects of this therapy.

Nordihydroguaiaretic acid increases endothelial nitric oxide synthase expression via the transcription factor AP-1

It has been previously reported that the antioxidant compound nordihydroguaiaretic acid (NDGA) increases endothelial nitric oxide synthase (eNOS) expression in cultured bovine aortic endothelial cells. However, the exact mechanism for this effect was unresolved. Thus, the purpose of this study was to further elucidate the effect of NDGA on eNOS protein expression and enzymatic activity in fetal pulmonary arterial endothelial cells (FPAECs), and to identify the transcription factors involved in this regulation. Following overnight exposure to 0-32 microM NDGA, we observed a 2- to 2.5-fold increase in eNOS protein expression in FPAECs, with a similar increase observed in eNOS activity. For eNOS gene promoter analysis, we initially used two promoter-reporter constructs: a 1.6 kb promoter fragment and an 840 bp construct, both of which include an AP-1-specific binding site. NDGA exposure induced a significant increase in eNOS promoter activity in both constructs. However, the NDGA-mediated increase was abolished when we used either a truncated promoter construct lacking the AP-1 element or a construct in which the AP-1 binding site was mutated. AP-1 binding efficiency was also determined by electrophoretic mobility shift assay, where we observed an increase in AP-1 binding in FPAECs treated with NDGA while the binding of AP-1 was found to be decreased when a mutated AP-1 consensus sequence was used. Further, supershift analyses indicated that the AP-1 complex consisted of c-Jun and FosB. We therefore conclude that NDGA antioxidant activity regulates eNOS expression via AP-1 and that antioxidant therapy could potentially be used to increase eNOS expression in diseases, such as persistent pulmonary hypertension of the newborn, where eNOS expression and activity are known to be reduced.

Inhibitory effect of nordihydroguaiaretic acid, a plant lignan, on Helicobacter pylori-associated gastric carcinogenesis in Mongolian gerbils

Recent epidemiological studies have demonstrated that consumption of certain natural products can lower cancer risk in humans. For example, plant-derived lignans have been shown to exert chemopreventive effects against cancer in vitro and in vivo. In the present study, the effects of three such lignans, termed arctiin, arctigenin, and nordihydroguaiaretic acid (NDGA), on the proliferation of Helicobacter pylori and the prevention of H. pylori-associated gastric cancer were investigated in Mongolian gerbils. To examine the effects of arctigenin and NDGA on stomach carcinogenesis, specific pathogen-free male, 5-week-old gerbils were infected with H. pylori, administered 10 p.p.m. N-methyl-N-nitrosourea in their drinking water and fed diets containing various concentrations of lignans until they were killed after 52 weeks. At a dietary level of 0.25%, NDGA significantly decreased the incidence of gastric adenocarcinomas. Arctigenin, in contrast, failed to attenuate neoplasia at a level of 0.1%. Both NDGA and arctigenin significantly reduced serum 8-hydroxy-2'-deoxyguanosine levels at doses of 0.25 and 0.05% (NDGA), and 0.1% (arctigenin). Administration of 0.25% NDGA significantly suppressed the formation of intestinal metaplasia both in the antrum and the corpus. Although all three lignans dose-dependently inhibited the in vitro proliferation of H. pylori, there were no differences in the titers of anti-H. pylori antibodies or the amount of the H. pylori-specific urease A gene among all H. pylori-infected groups. These results suggest that NDGA might be effective for prevention of gastric carcinogenesis. The possible mechanisms appear to be related to inhibitory effects on progression of gastritis and antioxidative activity rather than direct antimicrobial influence.

Lipoxygenase inhibitors induce death receptor 5/TRAIL-R2 expression and sensitize malignant tumor cells to TRAIL-induced apoptosis

Lipoxygenases induce malignant tumor progression and lipoxygenase inhibitors have been considered as promising anti-tumor agents. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for new cancer therapeutics. Combined treatment with nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and TRAIL markedly induced apoptosis in Jurkat T-cell leukemia cells at suboptimal concentrations for each agent. The combined treatment efficiently activated caspase-3, -8 and -10, and Bid. The underling mechanism by which NDGA enhanced TRAIL-induced apoptosis was examined. NDGA did not change the expression levels of anti-apoptotic factors, Bcl-x(L), Bcl-2, cIAP-1, XIAP and survivin. The expression of death receptor-related genes was investigated and it was found that NDGA specifically up-regulated the expression of death receptor 5 (DR5) at mRNA and protein levels. Down-regulation of DR5 by small interfering RNA prevented the sensitizing effect of NDGA on TRAIL-induced apoptosis. Furthermore, NDGA sensitized prostate cancer and colorectal cancer cells to TRAIL-induced apoptosis. In contrast, NDGA neither enhanced TRAIL-induced apoptosis nor up-regulated DR5 expression in normal peripheral blood mononuclear cells. Another lipoxygenase inhibitor, AA861, also up-regulated DR5 and sensitized Jurkat and DU145 cells to TRAIL. These results indicate that lipoxygenase inhibitors augment the apoptotic efficiency of TRAIL through DR5 up-regulation in malignant tumor cells, and raise the possibility that the combination of lipoxygenase inhibitor and TRAIL is a promising strategy for malignant tumor treatment.

Prooxidant activity and toxicity of nordihydroguaiaretic acid in clone-9 rat hepatocyte cultures

Nordihydroguaiaretic acid (NDGA) is a polyphenol. It is present at high concentrations in the leaves of the evergreen desert shrub, Larrea tridentate (Creosote bush), which has a long history of medicinal use traditionally by the native Americans and Mexicans. It is generally believed that the antioxidant properties of NDGA are responsible for the medicinal value of this desert shrub. The clone-9 rat hepatocyte cultures were used as an in vitro model to assess the hepatotoxic potential of NDGA and to determine whether it exhibits any prooxidant activity. The hepatocyte cultures were treated with NDGA for 2 h at 37 degrees C at concentrations of 0-100 microM. After the treatment period the cells, the culture supernatants and cell lysates were assayed for evaluation of prooxidant activity and toxicity of NDGA. Oxidative stress level and oxidative cell injury as measured by the peroxidation of membrane lipids and DNA double-strand breaks were used to index prooxidant activity. Cytotoxicity as measured by the leakage of the liver enzyme lactate dehydrogenase (LDH) into the culture medium, mitochondrial function and extent of cell proliferation were used as the endpoints of toxicity. Significant concentration-dependent differences were observed in these biomarkers over the concentration range examined demonstrating the prooxidant activity and toxicity of NDGA in clone-9 rat hepatocyte cultures.

Protective effect of nordihydroguaiaretic acid (NDGA) against norgestrel induced genotoxic damage

Nordihydroguaiaretic acid (NDGA) is a phenolic lignan and possesses antioxidant and number of properties potentially useful to man. The effect of NDGA was studied against norgestrel induced genotoxic damage, using sister chromatid exchanges (SCEs), chromosomal aberrations (CAs), mitotic index (MI) and replication index (RI) as parameters. Amounts of 5, 10 and 20 microM of norgestrel was tested for its genotoxic effect in the absence as well as presence of S9 mix, and was found to be genotoxic at 10 and 20 microM in the presence of S9 mix. Again, 10 microM of norgestrel was treated with 0.5 and 1 microM of NDGA, separately, in the presence of S9 mix. Similar treatment was given with 20 microM of norgestrel. Treatments given with NDGA result in the reduction of SCE, CA and increase of MI as well as RI, suggesting its protective action on human lymphocytes in vitro against the norgestrel induced genotoxic damage.

Arachidonic acid cascade inhibitors modulate phorbol ester-induced oxidative stress in female ICR mouse skin: differential roles of 5-lipoxygenase and cyclooxygenase-2 in leukocyte infiltration and activation

We recently developed a short-term assay for skin H2O2 generation induced by double 12-O-tetradecanoylphorbol-13-acetate (TPA) applications for mechanistic study on skin epidermal carcinogenesis. In the present study, we investigated the individual roles of arachidonic acid metabolism in H2O2 generation in mouse skin inflammation. The experiments using inhibitors of arachidonic acid (AA) metabolism showed that corticosteroid and a lipoxygenase (LO) inhibitor expectedly suppressed double TPA application-induced H2O2 generation through the interference of chemotactic action but not by direct decomposition or scavenging. We also demonstrated that the treatment of AA (1 mumol) and 5-LO metabolites including leukotriene B4 (LTB4) partly mimicked, though soybean LO-derived lipid hydroperoxide and prostaglandins did not, the priming effect evaluated by edema formation and leukocyte infiltration. We also confirmed that inflammatory leukocytes accumulated by LTB4 generated a significant amount of H2O2 by TPA stimulation. These results suggested that 5-LO metabolites of AA are the potential key molecules in the TPA-induced priming event. Interestingly, the cyclooxygenase (COX-) 2-selective inhibitor nimesulide (NS) and celecoxib (CXB) showed different responses than those of other inhibitors. These agents showed no specific potential to inhibit the priming event but significantly suppressed H2O2 generation, lipid peroxidation, and hyperplasia in mouse skin. From the results based on an in vitro leukocyte differentiation model, we speculated that the antioxidant effect of the COX-2 inhibitors might be partly associated with both counteraction of proinflammatory cytokine-enhanced ROS generation and inhibition of CD11b, an important molecule for cell adhesion, expression. Indeed, the topical application of NS attenuated the number of infiltrated leukocytes induced by TPA in mouse skin. Thus, these gathered data indicated the differential roles of 5-LO and COX-2 in leukocyte adhesion, infiltration, and H2O2 generation.

Inhibition of peroxisome proliferator-activated receptor (PPAR)-mediated keratinocyte differentiation by lipoxygenase inhibitors

Lipoxygenase (LOX) metabolites from arachidonic acid and linoleic acid have been implicated in atherosclerosis, inflammation, keratinocyte differentiation and tumour progression. We previously showed that peroxisome proliferator-activated receptors (PPARs) play a role in keratinocyte differentiation and that the PPARalpha ligand 8S-hydroxyeicosatetraenoic acid is important in this process. We hypothesized that blocking LOX activity would block PPAR-mediated keratinocyte differentiation. Three LOX inhibitors, nordihydroguaiaretic acid, quercetin and morin, were studied for their effects on primary keratinocyte differentiation and PPAR activity. All three LOX inhibitors blocked calcium-induced expression of the differentiation marker keratin 1. In addition, activity of a PPAR-responsive element was inhibited in the presence of all three inhibitors, and this effect was mediated primarily through PPARalpha and PPARgamma. LOX inhibitors decreased the activity of a chimaeric PPAR-Gal4-ligand-binding domain reporter system and this effect was reversed by addition of PPAR ligands. Ligand-binding studies revealed that the LOX inhibitors bind directly to PPARs and demonstrate a novel mechanism for these inhibitors in altering PPAR-mediated gene expression.

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.

Inhibitory effect of nordihydroguaiaretic acid on the frequency of micronuclei induced by methyl methanesulfonate in vivo

Nordihydroguaiaretic acid (NDGA) is an antioxidant originally obtained from plants of the genus Larrea. This chemical has shown antigenotoxic activity measuring gene mutations and sister-chromatid exchanges. The aim of this investigation was to determine if NDGA is also an antigenotoxic agent and can inhibit the induction of micronucleus (MN) formation by methyl methanesulfonate (MMS) in mouse. The frequency of micronucleated polychromatic erythrocytes (MPE) was scored for 4 days, and a MN induction curve by a single injection of MMS (40 mg/kg) was obtained. The results of this experiment showed that the highest MN incidence was reached at the second day of exposure with a mean of 13.2%+/-1.0. This value is more than 4 times the control mean. Thus, the modulatory study by NDGA was established at a 2-day exposure time using three doses (6.0, 11.0, and 17.0 mg/kg) against the damage induced by 40 mg/kg of MMS. The results of this study showed a significant reduction of the clastogenic damage at the two highest doses, where the inhibitory values corresponded to 62.2% and 66.7%, respectively. With respect to the ratio polychromatic erythrocytes/normochromatic erythrocytes, a marked toxicity was detected with 2 days of MMS exposure; however, the combination of the two high doses of NDGA plus MMS significantly reduced the cytotoxic damage produced by MMS alone.

Piperine modulation of carcinogen induced oxidative stress in intestinal mucosa

Reactive oxygen species (ROS) and reactive metabolic intermediates generated from various chemical carcinogens are known to play an important role in cell damage and in the initiation and progression of carcinogenesis. Many radical scavengers, interestingly naturally occuring antioxidants have been found to be effective in inhibiting the induction of carcinogenesis by a wide variety of chemical carcinogens. Studies have also indicated that various spice principles form an important group as antioxidants. In the present study our goal was to investigate whether piperine an pungent principle of black and long peppers was able to inhibit or reduce the oxidative changes induced by chemical carcinogens in rat intestinal model. Carcinogenesis was initiated in intestinal lumen of male rats with 7,12,dimethyl benzanthracene, dimethyl amino-methyl azobenzene and 3-methyl cholenthrene. Oxidative alterations were assessed by determining thiobarbituric reactive substances, mainly malonaldehyde (as a measure of lipid peroxidation), thiol status and expression of gamma-GT and Na+-K+-ATPase activity in intestinal mucosa. Data indicated that carcinogens treatment induced GSH depletion with substantial increase in thiobarbituric reactive substances and enzyme activities. Piperine treatment with carcinogens resulted in inhibition of thiobarbituric reactive substances. It mediated a significant increase in the GSH levels and restoration in gamma-GT and Na+-K+-ATPase activity. The studies thus indicate a protective role of piperine against the oxidative alterations by carcinogens. It may be suggested that piperine modulates the oxidative changes by inhibiting lipid peroxidation and mediating enhanced synthesis or transport of GSH thereby replenishing thiol redox.

In vivo and in vitro antigenotoxic effect of nordihydroguaiaretic acid against SCEs induced by methyl methanesulfonate

Nordihydroguaiaretic acid (NDGA) is a phenolic lignan which has shown to cause a variety of actions potentially useful for human health; therefore, in this investigation we determined its capacity for inhibiting the rate of sister chromatid exchanges (SCEs) induced by methyl methanesulfonate (MMS). We tested the effect of 0.25, 0.50, 1.0, and 2.0 microM of NDGA on the damage exerted by 55 microM of MMS. Cultured human lymphocytes from two female donors were used for the experiment. The best result concerning its modulatory action was obtained with 1.0 microM of NDGA; with this dose the mean inhibitory index including both donors reached 68.2%. The values obtained for the mitotic and proliferative indexes were not significantly modified with respect to the basal data. We also used the mouse bone marrow in vivo system to evaluate the inhibitory effect of the chemical. In this study we tested 1.0, 6.0, and 11.0 mg/kg of NDGA intraperitoneally (i.p.) administered 1 h before an i.p. injection of MMS (40 mg/kg). The best inhibitory index in this model corresponded to the dose of 11 mg/kg of NDGA (86.9%). The mitotic index and the average generation time showed no significant variation with respect to the control data. Our study established that NDGA produces antigenotoxic action in mammalian cells in vitro and in vivo.

In vivo and in vitro induction of sister-chromatid exchanges by nordihydroguaiaretic acid

Nordihydroguaiaretic acid (NDGA) is a phenolic lignan previously used as an antioxidant in commercial products, and with a number of properties potentially useful to man. As its genotoxic capacity has been poorly evaluated, in this investigation we determined its effect on the production of sister-chromatid exchanges (SCEs), and on the level of mitotic index (MI) in cultured human lymphocytes and in mouse bone marrow cells in vivo. The proliferative index (PI), and the average generation time (AGT) were also determined for human lymphocytes and in mouse bone marrow cells respectively. The in vitro study was made in two donors using NDGA doses of 1.1, 3.6, 6.7, 13.5, and 27.0 microM; and for the in vivo study the tested doses were 8.8, 17.6, 35.3, and 70.7 mg/kg of body weight. The results concerning SCE induction in human lymphocytes showed a dose-dependent response with a maximum mean increase of 5.52 SCE in relation to the control level, and with respect to MI and PI a decrement of more than 50% and a cell cycle delay was detected only with the high dose. In the study with bone marrow cells, a statistically significant difference was determined with the high two doses (an increase of 1.06 SCEs with 70.7 mg/kg in relation to the control level). The MI decreased only with the high dose and no modification was observed with respect to AGT. In conclusion, in both used models the study demonstrated that NDGA produced genotoxic and cytotoxic effects.

Inhibition of skin tumor initiation, promotion, and progression by antioxidants and related compounds

Antioxidants have been shown to inhibit the induction of cancer by a wide variety of chemical carcinogens and radiation at many target sites in mice, rats, hamsters, and man. Evidence is accumulating that suggests that free radicals are important in all stages of chemical carcinogenesis. Both carcinogens and tumor promoters have also been shown to decrease the cellular activity of superoxide dismutase and catalase. A number of antioxidants and related compounds were tested to determine if they would inhibit either skin tumor initiation, promotion, or progression. In terms of skin tumor initiation, compounds such as BHT, vitamins E and C, and CuDIPS have been found to inhibit DMBA skin tumor initiation. The mechanism of action of these compounds appears to be related to their effect on the metabolism of DMBA, as BHT and CuDIPS do not inhibit the initiating activity of BP-diol-epoxide and MNNG. Although several antioxidants do inhibit skin tumor initiation by procarcinogens, antioxidants are in general much more effective inhibitors of skin tumor promotion. BHT, BHA, parahydroxyanisole, disulfiran, and vitamins E and C as well as many other antioxidants are very effective inhibitors of skin tumor promotion. We also determined the effect of free radical scavengers on the progression process. Of the agents tested, glutathione and N-acyl dehydroalamines were the most effective in reducing carcinoma incidence. Diethyl maleate, a chemical that reduces glutathione levels, was effective in enhancing progression. In addition, overexpression of gamma-glutamyltranspeptidase (GGT), which leads to a reduction in cellular glutathione levels, also enhances progression.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of the induction of cancer by antioxidants

Many different antioxidants have been shown to inhibit the induction of cancer by a wide variety of chemical carcinogens and/or radiation at many target sites in mice, rats, and hamsters. Evidence is accumulating that suggests that free radicals are important in all stages of chemical carcinogenesis. Both carcinogens and tumor promoters have also been shown to decrease the cellular activity of superoxide dismutase and catalase. A number of antioxidants and related compounds were tested to determine if they would inhibit either skin tumor initiation, promotion, and/or progression. In terms of skin tumor initiation, BHT, vitamin E and C and CuDIPS have been found to inhibit DMBA skin tumor initiation by approximately 50%. The mechanism of action of these compounds appears to be related to their effect on the metabolism of DMBA, since BHT and CuDIPS do not inhibit the initiating activity of BP-diol-epoxide and MNNG. Although several antioxidants do inhibit skin tumor initiation by procarcinogens, antioxidants are in general much more effective inhibitors of skin tumor promotion. BHT, BHA, parahydroxyanisole, disulfiran, and vitamin E and C inhibit skin tumor promotion by TPA and benzoyl peroxide by greater than 90%. We also determined the effect of free radical scavengers on the progression process. Of the agents tested glutathione and N-acyl dehydroalamines were the most effective in reducing carcinoma incidence. Diethyl maleate, a chemical that reduces glutathione levels, was effective in enhancing progression. In addition overexpression of g-glutamylt-ranspeptidase (GGT) which leads to a reduction in cellular glutathione levels also enhances progression. These results suggest that GGT has a functional role in skin tumor progression, and that a number of antioxidants are either effective inhibitors of skin tumor initiation, promotion, and/or progression.

Inhibition of tumoral cell respiration and growth by nordihydroguaiaretic acid

The effects of nordihydroguaiaretic acid (NDGA), best known as an inhibitor of lipoxygenase activities, on the culture growth, oxygen consumption, ATP level, viability, and redox state of some electron carriers of intact TA3 and 786A ascites tumor cells have been studied. NDGA inhibited the respiration rate of these two tumor cell lines by preventing electron flow through the respiratory chain. Consequently, ATP levels, cell viability and culture growth rates were decreased. NDGA did not noticeably inhibit electron flow through both cytochrome oxidase and ubiquinone-cytochrome b-c1 complex. Also, the presence of NDGA changed to redox state of NAD(P)+ to a more reduced level, and the redox states of ubiquinone, cytochrome b and cytochromes c + c1 changed to a more oxidized level. These observations suggest that the electron transport in the tumor mitochondria was inhibited by NDGA at the NADH-dehydrogenase-ubiquinone level (energy-conserving site 1). As a consequence, mitochondrial ATP synthesis would be interrupted. This event could be related to the cytotoxic effect of NDGA.

(-)-Epigallocatechin-3-gallate in Camellia sinensis leaves from Himalayan region of Sikkim: inhibitory effects against biochemical events and tumor initiation in Sencar mouse skin

Recently, we and others showed that the components of green tea may be useful cancer chemopreventive agents. It has been suggested that (-)-epigallocatechin-3-gallate (EGCG), the major constituent in green tea, may possess antitumor-promoting and/or anticarcinogenic effects in rodent tumor bioassay systems. During the chemical analysis of various green tea products, we found a traditionally preserved preparation of green tea used by tribes in the Himalayan region of Sikkim, India that was rich in EGCG. EGCG was isolated from this tea product, and its inhibitory effects were evaluated against the binding of topically applied 3H-labeled polycyclic aromatic hydrocarbons (PAHs) to epidermal DNA and 12-O-tetradecanoylphorbol-13-acetate (TPA) caused induction of epidermal ornithine decarboxylase (ODC) activity in Sencar mice, the short-term markers of tumor initiation and tumor promotion, respectively. Preapplication of EGCG resulted in significant inhibition (p less than 0.05) in the binding of [3H]PAH to epidermal DNA. Similarly, the topical application of EGCG resulted in significant inhibition (p less than 0.005) in TPA-caused induction of epidermal ODC activity. In further studies, we assessed the anti-skin tumor-initiating effect of EGCG in Sencar mice in an initiation-promotion protocol. The application of EGCG before challenge with 7,12-dimethylbenz[a]anthracene as tumor initiator resulted in significant reduction both in percentage of mice with tumors and number of tumors per mouse compared with a non-EGCG-pretreated group of animals. The results of the present study suggest that the green tea preparation from Sikkim may be a good source for the isolation of EGCG and that this compound may have significant potential as a cancer chemopreventive agent.