Inhibitory effect of 18beta-glycyrrhetinic acid on 12-O-tetradecanoyl phorbol-13-acetate-induced cutaneous oxidative stress and tumor promotion in mice

Glycyrrhetinic acid is an aglycone of glycyrrhizic acid, another major active component of licorice roots. Licorice root extract has been used for a long time as a medicine and a natural sweetening additive. In the present study, we found that glycyrrhetinic acid inhibits 12-O-tetradecanoylphorbol-13-acetate (TPA) mediated oxidative stress and tumor promotion in murine skin. Topical application of TPA alone in mouse skin enhances ornithine decarboxylase activity and also increases [3H]-thymidine incorporation in DNA. Topical application of TPA also resulted in the depletion of glutathione, activities of glutathione metabolizing and antioxidant enzymes. Application of glycyrrhetinic acid prior to TPA treatment reduces this enhanced ODC activity, [3H]-thymidine incorporation in DNA and oxidative stress. Glycyrrhetinic acid was also found to inhibit DMBA/TPA-induced skin tumor formation at doses of 1.25 and 2.5 mg by reducing the number of tumors per mouse by 24% (P < 0.05) and 62% (P < 0.05), respectively. These results suggest that glycyrrhetinic acid, an antioxidant, is a potential chemopreventive agent that can inhibit DMBA/TPA-induced cutaneous oxidative stress and tumor promotion.     

12-0-Tetradecanoylphorbol-13-acetate induced alterations in mouse epidermal 3-hydroxy-3-methylglutaryl CoA reductase

Topical application of the tumor promoter 12-0-tetradecanoylphorbol-13-acetase to the mouse skin resulted in a significant initial increase (at 2 h) in the activity of epidermal hydroxymethylglutaryl CoA reductase followed by a significant decrease by 24 h. Phorbol and phorbol diacetate, which do not cause hyperplasia or promote skin tumor formation, has no effect on this enzyme. Ethylphenylpropiolate, a strong inducer of hyperplasia but a non-tumor promoter, also showed no effect on the reductase activity. Topical application of the products of hydroxymethylgutaryl CoA reductase viz. mevalanolactone or isopentenyl adenosine caused a decrease while cholesterol produced no change in hydroxymethylglutaryl CoA reductase activity. It is speculated that isopentenyladenosine or a closely related product, formed by the initial increase in hydroxymethylglutaryl CoA reductase activity following TPA application, might exert feedback inhibition.     

Antimutagenic and antitumorigenic activities of nordihydroguaiaretic acid.

Nordihydroguaiaretic acid (NDGA), which occurs in the resinous exudates of many plants is used as an antioxidant in fats and oils. In this study we show that NDGA inhibited the mutagenicity of methyl methanesulfonate, benzo[a]pyrene (BP), 2-aminofluorene, and aflatoxin B1 in Salmonella typhimurium strain TA100 or TA98 in the absence and presence of rat hepatic microsomal activation system. The addition of NDGA during and after nitrosation of methylurea (MU) resulted in a dose-dependent inhibition of mutagenicity induced by nitrosation products of MU. In a two-stage skin tumorigenesis protocol using 7,12-dimethylbenz[a]anthracene (DMBA) as the initiating agent followed by twice weekly applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) as tumor promoter, pretreatment of animals with NDGA prior to DMBA application, afforded significant protection against skin tumorigenicity in female SENCAR mice. In additional studies, skin application of NDGA also inhibited the binding of topically applied [3H]BP and [3H]DMBA to epidermal DNA. When assessed in the anti-tumor promotion protocol, pretreatment of animals with NDGA before each application of TPA in DMBA-initiated mouse skin, resulted in 72% decrease in the total number of tumors when compared to non-NDGA pretreated animals. The possible mechanism(s) of the antimutagenic and anti-tumorigenic activities may be due to the multiple effects of NDGA as inhibitor of the carcinogen metabolism and DNA-adduct formation, scavenger of carcinogen free radicals, and as inhibitor of TPA-induced ornithine decarboxylase activity.     

Topically applied vitamin E prevents massive cutaneous inflammatory and oxidative stress responses induced by double application of 12-O-tetradecanoylphorbol-13-acetate (TPA) in mice

Vitamin E (alpha-tocopherol) is a promising chemopreventive and pharmacologically safe agent, which can be exploited or tested against skin cancer. It is an established antioxidant with an ability to ameliorate the UV-induced skin damage and chemically induced inflammation in lungs. However, there are some conflicting reports about its role as a modulator of chemically induced promotion. We evaluated its efficacy in preventing the inflammatory and oxidative stress responses in a double 12-O-tetradecanoylphorbol-13-acetate (TPA) application tumor skin promotion protocol. Double application of TPA was undertaken to produce massive inflammatory and oxidative stress responses. Topical TPA treatment adversely altered many of the marker responses of stage I skin tumor promotion. Vitamin E application 30 min prior to TPA treatment (10 nmol) inhibited induction of hydrogen peroxide, myeloperoxidase (MPO) activity, xanthine oxidase (XO) activity and lipid peroxidation (LPO). Vitamin E also positively modulated altered antioxidants of mouse skin. Histological examination also revealed marked improvement. These results confirm the efficacy of vitamin E against early inflammatory and oxidative stress responses, which are hallmark of tumor promotion and provide rational basis for chemopreventive action of vitamin E in skin cancer.     

Progressive iron overload enhances chemically mediated tumor promotion in murine skin

Iron overload has been shown to enhance chemically mediated cutaneous tumor promotion in animals. However, the majority of these animal studies have used high concentrations of iron before initiating tumor development. The current study was designed to evaluate the effect of small doses of iron on the promotion stage of chemically mediated cutaneous carcinogenesis. We found an increased tumor response in mice initiated with dimethylbenz(a)anthracene (DMBA) when iron at the dose levels of 0.5, 1.0, and 1.5mg/mouse was injected (intramuscularly) once a week into mice at the promotion stage of skin carcinogenesis, employing 12-O-tetradecanoyl phorbol-13-acetate (TPA)/benzoyl peroxide (BPO) as tumor promoter. The appearance of first papilloma and the number of tumors/mouse were recorded weekly. When compared to the control (non-iron-treated) group, the iron-treated groups showed an augmented incidence of tumors and number of tumors/mouse. In iron-treated mice, tumors appeared earlier than in the control group. TPA/BPO treatment resulted in a significant decrease in the activities of antioxidant enzymes and depletion in the level of epidermal reduced glutathione (GSH). TPA treatment in non-iron-treated mice resulted in approximately 20-40% decrease in GSH level and in the activities of antioxidant enzymes, whereas 1.5-mg iron treatment along with TPA treatment resulted in about approximately 30-70% decrease in GSH level and in the activities of antioxidant enzymes. Similarly, treatment of iron along with BPO treatment resulted in a dose-dependent higher depletion of GSH and the antioxidant enzymes as compared to non-iron-treated animals treated with BPO. Further, TPA/BPO-mediated induction in ornithine decarboxylase activity and [3H]thymidine incorporation in cutaneous DNA was approx two- to threefold higher in mice treated with iron as compared to non-iron-treated mice. Cutaneous lipid peroxidation and iron levels were also higher in mice treated with iron as compared to non-iron-treated mice. These data suggest that progressive iron overload can enhance the tumor promotion ability of TPA/BPO in DMBA-initiated murine skin.     

Effect of Onosma echioides on DMBA/croton oil mediated carcinogenic response, hyperproliferation and oxidative damage in murine skin

The current study unveils the effect of O. echioides extract on two-stage skin carcinogenesis and on tumor promoter induced markers and oxidative stress in Swiss mice. Treatment of dorsal shaven cutaneous portions of the mice with single topical application of benzoyl peroxide (BPO) followed by exposure to ultraviolet B (UVB) radiation induced significant oxidative stress and elevated the marker parameters of tumor promotion. Similar effects were observed with 12-O-tetradecanoyl phorbol-13-acetate (TPA) treatment. Pretreatment of O. echioides extract (5 mg & 10 mg/Kg b.wt) in both the studies with BPO+UVB and TPA restored the levels of reduced glutathione (GSH) and cellular protective enzymes (p < 0.05). Concomitantly, malondialdehyde (MDA) formation and hydrogen peroxide (H2O2) content were also reduced significantly (p < 0.05) at both the doses. The promotion parameters tested (ornithine decarboxylase activity and DNA synthesis) were also significantly suppressed (p < 0.05). Thereafter, we proceeded with studies on mouse skin carcinogenesis. After ten days of 7,12-dimethylbenz(a)anthracene (DMBA) treatment, twice-weekly applications of croton oil for 20 weeks resulted in 100% incidence of tumors in the animals. However, O. echioides showed reduction in the number of tumors/ mouse and percentage of tumor bearing mice at the end of the study. The study was further histologically confirmed. The protective activity of the plant might be due to the two major constituents (alkannins and shikonins) present in the plant. O. echioides is thus, proposed to be helpful in prevention of experimental skin carcinogenesis.     

Chemopreventive action of Phyllanthus urinaria Linn on DMBA-induced skin carcinogenesis in mice

The inhibition of tumor incidence by hydro-alcoholic extract of the whole plant of P. urinaria was evaluated in 6-7 weeks old female albino mice on two-stage process of skin carcinogenesis induced by a single application of 7,12-dimethylbenz(a)anthracene (50 microg/50 microl of acetone), and 2 weeks later, promoted by repeated application of croton oil (1% in acetone/three times a week) till the end of the experiment (15 weeks). Topical application of the extract at a dose of 5 mg/kg body weight/day for 15 weeks at the peri-initiational stage (i.e., 7 days before and 7 days after DMBA application), promotional stage (i.e., from the time of croton oil application) and both peri and post-initiational stages (i.e., 7 days prior to DMBA application and continued till the end of the experiment) on the shaven backs of the mice recorded a significant reduction in tumor incidence to 50, 33.3 and 16.7% respectively in comparison to the control (i.e., the mice treated with DMBA and croton oil only) where tumor incidence was found to be 81.8%. The average number of papillomas per mouse was also significantly reduced. The results suggest a possible chemopreventive property of P. urinaria against DMBA-induced skin papillomagenesis in mice.     

Inhibition of phorbol ester-caused synthesis of mouse epidermal ornithine decarboxylase by retinoic acid

The mechanisms by which topically applied retinoic acid to mouse skin inhibits tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced epidermal ornithine decarboxylase activity were analyzed. Retinoic acid inhibition of the induction of epidermal ornithine decarboxylic activity was not the result of nonspecific cytotoxicity, production of a soluble inhibitor of ornithine decarboxylase, or direct effect on its activity. In addition, inhibition of TPA-caused increased ornithine decarboxylase activity does not appear to be due to enhanced degradation and/or post-translational modification of ornithine decarboxylase by transglutaminase-mediated putrescine incorporation. We found that retinoic acid inhibits the synthesis of ornithine decarboxylase caused by TPA. Application of 10 nmol TPA to mouse skin led to a dramatic induction of epidermal ornithine decarboxylase activity which was paralled by increased [3H]difluoromethylornithine binding and an increased incorporation of [35S]methionine into the enzyme. Application of 17 nmol retinoic acid 1 h prior to application of 10 nmol TPA to skin resulted in inhibition of the induction of activity which accompanied inhibition of [3H]difluoromethylornithine binding and [35S]methionine incorporation into ornithine decarboxylase protein as determined by the tube-gel electrophoresis of the enzyme immunoprecipitated with monoclonal antibodies to it. Inhibition of ornithine decarboxylase synthesis was not the result of the inhibitory effect of retinoic acid on general protein synthesis. The results indicate that retinoic acid possibly inhibits TPA-caused synthesis of ornithine decarboxylase protein selectively.     

Glycyrrhizin exhibits potential chemopreventive activity on 12-O-tetradecanoyl phorbol-13-acetate-induced cutaneous oxidative stress and tumor promotion in Swiss albino mice

Glycyrrhizin and its aglycone, glycyrrhetic acid has been found useful for various therapeutic purposes. Glycyrrhizin has been shown to possess many physiological functions like anti-inflammatory activity, detoxification and inhibition of carcinogenic promoters. 12-O-Tetradecanoyl phorbol-13-acetate (TPA), a well-known phorbal ester is known for its tumor promotion activity. The induction of inflammation in skin mediated by TPA is believed to be governed by cyclooxygenase (COX), lipoxygenase and ornithine decarboxylase (ODC). These markers of inflammatory responses are important for skin tumor promotion. In our present study, we studied the chemopreventive effect of glycyrrhizin on TPA (20 nmol/0.2 mL acetone/animal, topically)-induced oxidative stress and hyperproliferation markers in skin. TPA enhanced lipid peroxidation with reduction in the level of catalase, glutathione, glutathione peroxidase, glutathione reductase and glutathione-s-transferase. TPA treatment also enhanced ODC activity and [3H] thymidine incorporation into cutaneous DNA. Prophylactic treatment of mice with glycyrrhizin (2.0 & 4.0 mg/0.2 mL acetone/animal, topically) resulted in a significant decrease in cutaneous microsomal lipid peroxidation (P < 0.001) and recovery of cutaneous glutathione content (P < 0.001) and its dependent enzymes. A significant inhibition in ODC activity and DNA synthesis (P < 0.001) was also observed. Thus, the results demonstrate that pretreatment with glycyrrhizin is protective against TPA-induced oxidative stress and tumor promotion in Swiss albino mice.     

Inhibition of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse skin ornithine decarboxylase and protein kinase C by polyphenolics from grapes

Ornithine decarboxylase is the rate-limiting enzyme in the biosynthesis of polyamines, which are believed to play an essential role in diverse biological processes including cell proliferation and differentiation. We have previously reported [J. Bomser, K. Singletary, M. Wallig, M. Smith, Inhibition of TPA-induced tumor promotion in CD-1 mouse epidermis by a polyphenolic fraction from grape seeds, Cancer Letters 135 (1999) 151-157] that pre-application of a grape polyphenolic fraction (GPF) to mouse skin epidermis inhibits 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase (ODC) activity, as well as 7, 12-dimethylbenz[a]anthracene (DMBA)-initiated, TPA-promoted mouse skin tumorigenesis. The present studies were designed to further characterize the effect of time and dose of application of GPF on TPA-induced ODC activity and protein expression, and on protein kinase C activity in mouse skin epidermis. In addition, the effect of GPF on ODC kinetics in vitro was examined. Application of 5, 10, and 20 mg of GPF 20 min prior to treatment with TPA resulted in a significant decrease in epidermal ODC activity of 54, 53, 90%, respectively, compared with controls. Yet, ODC protein levels (Western blot) in the 10 and 20 mg GPF groups were significantly increased by 1.8 and 1.9-fold, respectively, compared with controls. A similar response was observed with the ODC inhibitor 2-difluoromethylornithine (DFMO), which served as a positive control. Application of grape polyphenolics (20 mg) at 60 and 30 min prior to treatment with TPA inhibited ODC activity by 62 and 68%, respectively, compared with controls (P<0.05). In contrast, application of grape polyphenolics (20 mg) at 60, 120 and 240 min after treatment with TPA resulted in no significant changes in ODC activity. A similar increase in epidermal ODC protein was observed in these GPF-treated animals, similar to that observed when GPF application preceded TPA. When applied to mouse skin prior to TPA, GPF was associated with a decrease in subsequent PKC activity compared with controls at 10 and 30 min following TPA treatment. The GPF-associated decrease in PKC activity preceded the decrease in ODC activity. In a separate in vitro study, kinetic analyses indicated that GPF is a competitive inhibitor of ODC activity. Collectively these data suggest that the grape polyphenolic fraction is effective as an inhibitor of ODC activity when applied before TPA, and that the magnitude of inhibition is independent of epidermal ODC protein content. In addition, GPF is a competitive inhibitor of ODC activity in vitro. The decrease in TPA-induced ODC activity due to GPF treatment is preceded by an inhibition of TPA-induced PKC activity. Thus, the polyphenolic fraction from grapes warrants further examination as a skin cancer chemopreventive agent that interferes with cellular events associated with TPA promotion.     

Glycyrrhizin exhibits potential chemopreventive activity on 12-O-tetradecanoyl phorbol-13-acetate-induced cutaneous oxidative stress and tumor promotion in swiss albino mice

Glycyrrhizin and its aglycone, glycyrrhetic acid has been found useful for various therapeutic purposes. Glycyrrhizin has been shown to possess many physiological functions like anti-inflammatory activity, detoxification and inhibition of carcinogenic promoters. 12-O-Tetradecanoyl phorbol-13-acetate (TPA), a well-known phorbal ester is known for its tumor promotion activity. The induction of inflammation in skin mediated by TPA is believed to be governed by cyclooxygenase (COX), lipoxygenase and ornithine decarboxylase (ODC). These markers of inflammatory responses are important for skin tumor promotion. In our present study, we studied the chemopreventive effect of glycyrrhizin on TPA (20 nmol/0.2 mL acetone/animal, topically)-induced oxidative stress and hyperproliferation markers in skin. TPA enhanced lipid peroxidation with reduction in the level of catalase, glutathione, glutathione peroxidase, glutathione reductase and glutathione-s-transferase. TPA treatment also enhanced ODC activity and [³H] thymidine incorporation into cutaneous DNA. Prophylactic treatment of mice with glycyrrhizin (2.0 & 4.0 mg/0.2 mL acetone/animal, topically) resulted in a significant decrease in cutaneous microsomal lipid peroxidation (P < 0.001) and recovery of cutaneous glutathione content (P < 0.001) and its dependent enzymes. A significant inhibition in ODC activity and DNA synthesis (P < 0.001) was also observed. Thus, the results demonstrate that pretreatment with glycyrrhizin is protective against TPA-induced oxidative stress and tumor promotion in Swiss albino mice.     

Cancer chemoprevention: inhibitory effect of soybeans fermented with basidiomycetes on 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate-induced mouse skin carcinogenesis

In a two-stage skin carcinogenesis model, mice initiated with 7,12-dimethylbenz[a]anthracene and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 12 weeks developed an average of 15.8 skin tumours per mouse with 100% tumour incidence. Topical application of polysaccharides from soybeans fermented with either Phellinus igniarius or Agrocybe cylindracea together with TPA twice weekly for 12 weeks inhibited the number of skin tumours per mouse by 70 or 88%, respectively, and the percentage of mice with tumours was lowered by 70 or 30%, respectively.     

Inhibition of skin tumors in DMBA-induced complete carcinogenesis system in mice by garlic (Allium sativum)

The chemopreventive action of garlic extract on DMBA-induced complete skin carcinogenesis system was studied in random bred, 6-7 weeks old, male Swiss albino mice. Topical weekly application of DMBA for 25 weeks at two dose levels, i.e. 200 nmol during the first week followed by 100 nmol during subsequent weeks, or 400 nmol during the first week followed by 200 nmol during subsequent weeks, resulted in 73.9% and 100% tumor incidences respectively. When garlic extract was topically applied twice daily for 3 days every week prior to above-stated dose schedules of DMBA, the incidences of tumors were reduced to 31.8% (P less than 0.01) and 43.4% (P less than 0.01) respectively.     

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.     

Anti-inflammatory and anti-allergic effect of rosmarinic acid (RA); inhibition of seasonal allergic rhinoconjunctivitis (SAR) and its mechanism

The present study was undertaken to determine whether oral supplementation with rosmarinic acid (RA) is an effective intervention for patients with SAR. In addition, the anti-inflammatory mechanism of RA also estimated in the ear edema models. CLINICAL TRIAL: Patients were treated daily with RA (200 mg or 50 mg) or placebo for 21 days. Patients recorded symptoms daily and profiles of infiltrating cells and concentration of cytokines were measured in nasal lavage fluid. Compared to placebo, supplementation with RA resulted in a significant decrease in responder rates for each symptom. RA also significantly decreased the numbers of neutrophils and eosinophils in nasal lavage fluid. ANIMAL STUDY: Topical application RA showed anti-inflammatory activity 5-hours after 12-tetradecanoylphorbol 13-acetate (TPA) treatment with marked inhibition of neutrophil infiltration. Up regulation of ICAM-1, VCAM-1 cyclooxygenase-2 (COX-2), KC and MIP-2 by TPA were markedly reduced by pre-treatment with extract of perilla (PE) or RA. Reactive oxygen radical production detected as thiobarbituric acid reactive substance (TBARS), lipid peroxide (LPO) and 8-hydroxy-2'deoxyguanosine (8OH-dG), by double treatment of TPA was reduced by pretreatment with PE or RA. RA is an effective intervention for SAR that is mediated by inhibition of PMNL infiltration. This effect of RA is due to two independent mechanisms: inhibition of the inflammatory response and scavenging of ROS.     

Chemopreventive effects of sage oil on skin papillomas in mice.

Salvia libanotica (sage) extract is a popular plant remedy used by Middle Eastern people to treat common complaints such as colds and abdominal pain. In this study, the chemopreventive effects of sage oil on 7,12 dimethylbenz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted skin papillomas was investigated. Furthermore, its growth inhibitory and cytotoxic effects on a mouse papilloma-derived cell line (SP-1) were studied using 3H-thymidine incorporation, cell count and trypan blue dye exclusion assays. Sage oil was either applied topically to mouse skin at concentrations of 5, 50 and 100% in acetone, injected intraperitoneally at concentrations of 4 (37 mg/ml) and 8% (75 mg/ml) in saline or given by gavage at 100% twice per week for 20 weeks, 20 minutes prior to each promotion treatment with TPA. The topically applied 100% oil extract delayed tumor appearance by 4 weeks and inhibited tumor incidence and yield by 19 and 61%, respectively, at week 20. Topical application of 50% and 5% sage oil inhibited tumor yield by 41% at week 20. Tumor weight was decreased by 75% and 80% following treatment of mouse skin with 50% and 100% oil, respectively. Intraperitoneal injections and gavage treatments failed to inhibit the promotion of tumors in mouse skin, but significantly decreased tumor weight and volume. Sage oil displayed strong growth inhibitory effects on the SP-1 papilloma derived cell line following 24 hrs of treatment with estimated IC50 of 50 microg/ml. This observed growth inhibition was due to cytostatic and not cytotoxic effects. Our results suggest that the oil extract of the sage plant has potent suppressive activities against tumor promotion in mouse skin and thus could be an effective chemopreventive agent against skin cancer.     

Inhibition of benzoyl peroxide and ultraviolet-B radiation induced oxidative stress and tumor promotion markers by cycloartenol in murine skin

The chemopreventive potential of cycloartenol on benzoyl peroxide and UVB radiation-induced cutaneous tumor promotion markers and oxidative stress in murine skin is assessed. Benzoyl peroxide treatment (20 mg/animal/0.2 ml acetone) and UVB radiation (0.420 J/m(2)/s) caused a decrease in the activities of cutaneous antioxidant enzymes namely, catalase, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase, phase II metabolizing enzyme such as glutathione-S-transferase and quinone reductase and depletion in the level of cutaneous glutathione. There was also enhancement in cutaneous microsomal lipid peroxidation, xanthine oxidase activity, [(14)C]-ornithine decarboxylase activity and [(3)H]-thymidine incorporation into cutaneous DNA. Cycloartenol was topically applied prior to the application of benzoyl peroxide at dose levels of 0.2 mg and 0.4 mg/kg body weight in acetone, which resulted in significant inhibition of epidermal ornithine decarboxylase activity and DNA synthesis (P < 0.001). There was also significant reduction of lipid peroxidation and xanthine oxidase activity (P < 0.001). In addition, the depleted levels of glutathione, inhibited activities of antioxidant and phase II metabolizing enzymes, were also recovered to a significant level (P < 0.001). The data indicate that cycloartenol is an effective chemopreventive agent in skin carcinogenesis.     

Benzyl isothiocyanate inhibits oxidative stress in mouse skin: Involvement of attenuation of leukocyte infiltration

The exposure of benzyl isothiocyanate (BITC) to mouse skin resulted in the attenuation of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced oxidative damage through not only inhibition of the NADPH oxidase system but also leukocyte clearance at inflamed region. In spite of little ability to affect TPA-induced edema formation, pretreatments of mouse skin with BITC before the first or second TPA treatment significantly decrease the H2O2 level. A histological study also demonstrated that BITC enhanced the terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL)-positive index in mouse skin, suggesting that BITC might accelerate the disappearance of infiltrated leukocytes. Thus, these gathered data further supported that BITC has a potential as an anti-inflammatory agent.     

Cancer preventive agents. Part 1: chemopreventive potential of cimigenol, cimigenol-3,15-dione, and related compounds

In continuation of our previous report, cimigenol (1) and 15 related compounds were screened as potential antitumor promoters by using the in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)--induced Epstein-Barr virus early antigen (EBV-EA) activation assay. Cimigenol-3,15-dione (2) displayed the greatest potency (100% inhibition at 1000 mol ratio/TPA) and consequently was further examined for antitumor-promoting activity in a two-stage carcinogenesis assay of mouse skin tumors (DMBA/TPA). In this assay, compound 2 showed significant activity, reducing the number of papillomas per mouse to 48% of the control group at 20 weeks. In addition, compounds 1 and 2 were examined for antitumor-initiating activity in a two-stage carcinogenesis assay of mouse skin tumors induced by peroxynitrite as an initiator and TPA as a promoter. Results showed that these two triterpenoids were almost equipotent with epigallocatechin gallate (EGCG) and slightly more potent than tocinol (group V), the positive controls. Thus, compounds 1 and 2 exhibited not only strong antitumor-promoting activity but also significant antitumor-initiating effect on mouse skin. These data suggest that both compounds might be valuable chemopreventors.