Skin Of Female ICR Mice Research Articles

Resveratrol inhibits phorbol ester‐induced cyclooxygenase‐2 expression in mouse skin: MAPKs and AP‐1 as potential molecular targets

Multiple lines of evidence from laboratory studies suggest that resveratrol, a polyphenolic antioxidant present in grapes, has potent chemopreventive activity. Resveratrol has been reported to inhibit chemically-induced carcinogenesis in mouse skin, but the underlying mechanisms remain unclarified. Since an abnormally elevated level of cyclooxygenase-2 (COX-2) has been implicated in carcinogenesis, we investigated the effect of resveratrol on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced COX-2 expression in mouse skin. Pretreatment of dorsal skin of female ICR mice with resveratrol inhibited TPA-induced COX-2 expression in a dose dependent manner. To elucidate the molecular mechanism underlying COX-2 inhibition by resveratrol, we examined its effect on TPA-induced activation of mitogen-activated protein kinases (MAPK) and transcription factors which regulate COX-2 expression. Resveratrol pretreatment resulted in a decrease in the phosphorylation of extracellular signal-regulated protein kinase (ERK) as well as the catalytic activity of ERK and p38 MAPK. In addition, resveratrol prevented TPA-induced DNA binding of activator protein-1 (AP-1). Taken together, suppression of COX-2 expression by blocking the activation of MAPKs and AP-1 may represent possible molecular mechanisms responsible for previously reported anti-tumor promoting effects of resveratrol on mouse skin carcinogenesis.

Celecoxib inhibits phorbol ester-induced expression of COX-2 and activation of AP-1 and p38 MAP kinase in mouse skin.

Celecoxib, the first US FDA-approved selective cyclooxygenase-2 (COX-2) inhibitor initially developed for the treatment of adult rheumatoid arthritis and osteoarthritis, was reported to reduce the polyp burden in patients with familial adenomatous polyposis. This specific COX-2 inhibitor also protects against experimentally induced carcinogenesis, but molecular mechanisms underlying its chemopreventive activities remain largely unresolved. In the present work, we found that celecoxib inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced expression of COX-2 in female ICR mouse skin when applied topically 30 min prior to TPA as determined by both immunoblot and immunohistochemical analyses. In another study, celecoxib attenuated the DNA binding activity of activator protein 1 (AP-1) through suppression of c-Jun and c-Fos expression in TPA-treated mouse skin. In addition, celecoxib inhibited both the catalytic activity and phosphorylation of p38 mitogen-activated protein (MAP) kinase. In the same animal model, TPA treatment resulted in rapid activation via phosphorylation of extracellular signal-regulated protein kinase (ERK)1/2 and p38 MAP kinase, which are upstream of AP-1 in mouse skin. In order to clarify the roles of p38 and ERK in TPA-induced AP-1 activation, we utilized the pharmacologic inhibitors of these enzymes. The p38 inhibitor SB203580 blocked TPA-mediated AP-1 activation, while the MEK1/2 inhibitor U0126 was not inhibitory despite suppression of c-Fos expression in mouse skin. Furthermore, SB203580 markedly inhibited COX-2 expression induced by TPA. Taken together, these findings suggest that celecoxib down-regulates COX-2 by blocking activation of p38 MAP kinase and AP-1, which may represent molecular mechanisms underlying antitumor promoting effects of this drug on mouse skin tumorigenesis.

Nitric oxide induces expression of cyclooxygenase-2 in mouse skin through activation of NF-kappaB.

Inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) are frequently overexpressed in tumor tissues or transformed cells. In the present work, we assessed the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on expression of iNOS and COX-2 in mouse skin. Topical application to the dorsal skin of female ICR mice of 10 nmol TPA led to maximal induction of iNOS and COX-2 protein expression at approximately 2 and 4 h, respectively. When applied topically onto shaven backs of mice 30 min prior to TPA, the NOS inhibitor aminoguanidine (AG) inhibited the expression of COX-2 protein at the pharmacologically effective dose. Pretreatment with a more specific iNOS inhibitor, N(G)-nitro-l-arginine-methyl ester, also suppressed TPA-induced COX-2 expression. Immunohistochemical analysis of TPA-treated mouse skin using an anti-nitrotyrosine antibody reveals enhanced levels of nitrotyrosine protein localized in epidermal and dermal layers. Topical application of NO donors, such as sodium nitroprusside (SNP) and S-nitroso-N-acetyl-d,l-penicillamine, induced expression of COX-2 in mouse skin, which was attenuated by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide. SNP treatment stimulated NF-kappaB activation in mouse skin, which was associated with the degradation of IkappaBalpha. Topical application of inhibitors of NF-kappaB, such as pyrrolidine dithiocarbamate or N-alpha-p-tosyl-l-lysine chloromethylketone, inhibited the SNP-induced COX-2 expression. SNP induced a weak but concentration-related increase in COX-2 expression in cultured mouse keratinocytes, which was abolished by treatment with SN50, a specific inhibitor of nuclear translocation of NF-kappaB. Mouse keratinocytes treated with SNP exhibited an elevated NF-kappaB-driven COX-2 promoter activity. Topical application of AG (10 micro mol) prior to each TPA treatment after initiation reduced the multiplicity of papillomas by 44% at 22 weeks. In conclusion, up-regulation of COX-2 by NO may be mediated by activation of NF-kappaB in mouse skin, which provides a molecular mechanism by which COX-2 is induced during tumor promotion.

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.

Curcumin inhibits phorbol ester-induced expression of cyclooxygenase-2 in mouse skin through suppression of extracellular signal-regulated kinase activity and NF-kappaB activation.

Recently, there have been considerable efforts to search for naturally occurring substances for the intervention of carcinogenesis. Many components derived from dietary or medicinal plants have been found to possess substantial chemopreventive properties. Curcumin, a yellow coloring ingredient of turmeric (Curcuma longa L., Zingiberaceae), has been shown to inhibit experimental carcinogenesis and mutagenesis, but molecular mechanisms underlying its chemopreventive activities remain unclear. In the present work, we assessed the effects of curcumin on 12-O- tetradecanoylphorbol-13-acetate (TPA)-induced expression of cyclooxygenase-2 (COX-2) in female ICR mouse skin. Topical application of the dorsal skin of female ICR mice with 10 nmol TPA led to maximal induction of cox-2 mRNA and protein expression at approximately 1 and 4 h, respectively. When applied topically onto shaven backs of mice 30 min prior to TPA, curcumin inhibited the expression of COX-2 protein in a dose-related manner. Immunohistochemical analysis of TPA-treated mouse skin revealed enhanced expression of COX-2 localized primarily in epidermal layer, which was markedly suppressed by curcumin pre-treatment. Curcumin treatment attenuated TPA- stimulated NF-kappaB activation in mouse skin, which was associated with its blockade of degradation of the inhibitory protein IkappaBalpha and also of subsequent translocation of the p65 subunit to nucleus. TPA treatment resulted in rapid activation via phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinases, which are upstream of NF-kappaB. The MEK1/2 inhibitor U0126 strongly inhibited NF-kappaB activation, while p38 inhibitor SB203580 failed to block TPA-induced NF-kappaB activation in mouse skin. Furthermore, U0126 blocked the IkappaBalpha phosphorylation by TPA, thereby blocking the nuclear translocation of NF-kappaB. Curcumin inhibited the catalytic activity of ERK1/2 in mouse skin. Taken together, suppression of COX-2 expression by inhibiting ERK activity and NF-kappaB activation may represent molecular mechanisms underlying previously reported antitumor promoting effects of this phytochemical in mouse skin tumorigenesis.

Silk protein, sericin, suppresses DMBA-TPA-induced mouse skin tumorigenesis by reducing oxidative stress, inflammatory responses and endogenous tumor promoter TNF-alpha.

This study was conducted to assess protective effect of an antioxidant protein, sericin, on tumor promotion in the 7,12-dimethylbenz (alpha) anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol 13-acetate (TPA)-promoted mouse skin tumorigenesis model. In experiment 1, sericin was applied topically to DMBA-initiated female ICR mouse skin at the doses of 2.5 and 5 mg twice per week for 16 weeks, 30 min prior to each promotion treatment with TPA. The protective effect of sericin was evident in terms of significant reduction in tumor incidence and tumor multiplicity at the doses of 2.5 and 5 mg per application, compared to the control group without receiving sericin. The expression of tumor necrosis factor (TNF)-alpha protein and the level of 4-hydroxynonenal (4-HNE) in normal epidermis were significantly reduced in both sericin treatment groups. In experiment 2, sericin at the dose of 5 mg was applied topically to the dorsal mouse skin 30 min before application of a TPA, and the same doses of TPA and sericin were applied twice at an interval of 24 h. Sericin treatment inhibited double TPA treatment-induced morphological changes reflecting inflammatory response, including leukocyte infiltration, hyperplasia and cell proliferation. Furthermore, sericin treatment significantly suppressed the elevation in 4-HNE level and elevated expressions of c-fos, c-myc and cyclooxygenase-2 (COX-2) in normal epidermis induced by double application of TPA. The results suggest that sericin possesses protective effect against tumor promotion in mouse skin by suppressing oxidative stress, inflammatory responses and TNF-alpha.

Suppression of phorbol ester-induced NF-kappaB activation by capsaicin in cultured human promyelocytic leukemia cells.

Capsaicin, a major pungent constituent of red pepper (Capsicum annuum L.) possesses a vast variety of pharmacologic and physiologic activities. Despite its irritant properties, the compound exerts anti-inflammatory and anti-nociceptive effects. Previous studies from this laboratory revealed that capsaicin, when topically applied onto dorsal skin of female ICR mice, strongly attenuated activation of NF-kappaB and AP-1 induced by the typical tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), which may account for its anti-tumor promoting activity in mouse skin. In the present work, we have found that capsaicin suppresses TPA-stimulated activation of NF-kappaB through inhibition of IkappaB alpha degradation and blockade of subsequent nuclear translocation of p65 in human promyelocytic leukemia HL-60 cells. Methylation of the phenolic hydroxyl group of capsaicin abolished its inhibitory effect on NF-kappaB DNA binding. Likewise, TPA-induced activation of AP-1 was mitigated by capsaicin treatment.

Capsaicin suppresses phorbol ester-induced activation of NF-κB/Rel and AP-1 transcription factors in mouse epidermis

Capsaicin, the principal pungent ingredient of hot chili peppers, has anti-inflammatory and analgesic properties and is currently used as a topical cream for the management of various neuropathic conditions. In the present study, topical application of capsaicin onto dorsal skin of female ICR mice strongly suppressed phorbol ester-stimulated activation of NF-κB via blockade of IκB-α degradation with subsequent inhibition of nuclear translocation of the functionally active NF-κB subunit, p65. Likewise, phorbol ester-induced activation of activator protein-1 (AP-1) was abolished by capsaicin pretreatment. Since altered transactivation of NF-κB and AP-1 has been implicated for neoplastic transformation and progression, the suppression of these transcription factors by capsaicin may account for its previously reported chemopreventive effects on mouse skin tumorigenesis as well as inflammation.

A simple phenolic antioxidant protocatechuic acid enhances tumor promotion and oxidative stress in female ICR mouse skin: dose-and timing-dependent enhancement and involvement of bioactivation by tyrosinase.

The modifying effects of topical application of the phenolic antioxidant protocatechuic acid (PA) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse skin tumor promotion were investigated. Dimethylbenz[a]anthracene-initiated female ICR mice were treated with TPA (1.6 nmol) twice weekly for 20 weeks to promote papilloma formation. Pre-treatment with 16nmol PA 30 min prior to each TPA treatment significantly inhibited the number of papillomas per mouse by 52% (P < 0.05). On the other hand, PA pre-treatment at a high dose (1600 nmol) significantly enhanced tumor numbers by 38% (P < 0.05). Interestingly, in the group treated with a quite high dose (20000 nmol) of PA 5 min prior to each TPA application, the average number of tumors per mouse was reduced by 38%, whereas the same PA dose 3 h before TPA treatment significantly enhanced tumor numbers by 84% (P < 0.01). These results suggested that topically applied PA was converted to compound(s) lacking antioxidative properties and/or rather possessing the potential to enhance tumor development. A similar tendency was also observed in the short-term experiment of TPA-induced inflammation and oxidative stress; i.e. two groups pre-treated with PA at 20000 nmol, 30min and 3h before TPA treatment, did not show suppression or even significantly enhanced TPA-induced leukocyte infiltration, H(2)O(2) generation, thiobarbituric acid-reacting substances level and proliferating cell nuclear antigen index, while PA treatment together with TPA significantly suppressed these parameters. Treatment with a high dose (20000 nmol) of PA alone for 3h enhanced oxidative stress by reducing glutathione levels in mouse skin, which was counteracted by the tyrosinase inhibitor arbutin. Oxidative stress responses such as leukocyte infiltration and H(2)O(2) generation were also counteracted by arbutin. These results suggested that tyrosinase-dependent oxidative metabolism of PA was at least partially involved in the enhanced effects of PA on TPA-induced inflammatory responses and thus tumor promotion.

Inhibitory effects of curcumin and capsaicin on phorbol ester-induced activation of eukaryotic transcription factors, NF-kappaB and AP-1.

Recently, considerable attention has been focused on identifying dietary and medicinal phytochemicals that can inhibit, retard or reverse the multi-stage carcinogenesis. Spices and herbs contain phenolic substances with potent antioxidative and chemopreventive properties. Curcumin, a yellow colouring agent from turmeric and capsaicin, a pungent principle of red pepper exhibit profound anticarcinogenic and antimutagenic activities. Two well-defined eukaryotic transcription factors, nuclear factor-kappa B (NF-kappaB) and activator protein 1 (AP-1) have been implicated in pathogenesis of many human diseases including cancer. These transcription factors are known to be activated by a wide array of external stimuli, such as tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), tumor necrosis factor, reactive oxygen species, bacterial lipopolysaccharide, and ultraviolet. In the present study, we found that topical application of TPA onto dorsal skin of female ICR mice resulted in marked activation of epidermal NF-kappaB and AP-1. Curcumin and capsaicin, when topically applied prior to TPA, significantly attenuated TPA-induced activation of each transcription factor in mouse skin. Likewise, both compounds inhibited NF-kappaB and AP-1 activation in cultured human promyelocytic leukemia (HL-60) cells stimulated with TPA. Based on these findings, it is likely that curcumin and capsaicin exert anti-tumor promotional effects through suppression of the tumor promoter-induced activation of transcription factors, NF-kappaB and AP-1.

Inhibitory effects of curcumin and tetrahydrocurcuminoids on the tumor promoter-induced reactive oxygen species generation in leukocytes in vitro and in vivo.

The inhibitory effects of curcumin and two tetrahydrocurcuminoids on tumor promoter‐induced oxidative stress in vitro and in vivo were investigated. Curcumin, tetrahydrocurcumin (THC) and dihydroxytetrahydrocurcumin (DHTHC) exhibited significant inhibitory effects on 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA)‐induced O2‐generation in differentiated HL‐60 cells. The inhibitory activity of THC was weaker than that of curcumin. This tendency was the inverse of the results of previous studies on in vitro antioxidative activity against lipid peroxidation. The curcuminoids inhibited TPA‐induced intracellular peroxide formation in differentiated HL‐60 cells. THC exhibited much weaker inhibition of intracellular peroxide formation than curcumin, suggesting that this inhibition might be attributable to the inhibition of O2‐generation. The inhibitory effects of curcuminoids on TPA‐induced H2O2 formation in female ICR mouse skin were further examined using the double‐TPA‐application model. Each TPA application induces two distinct biochemical events, 1) recruitment of inflammatory cells to the inflammatory regions and 2) activation of oxidant‐producing cells. Double pretreatment of mice with curcuminoids before each TPA treatment significantly suppressed double TPA application‐induced H2O2 formation in the mouse skin. Coadministrations of curcumin with either first or second TPA treatment significantly inhibited H2O2 formation. In addition, THC tends to show weaker inhibitory activities than curcumin in bioassays related to tumor promotion, i.e., inhibition of tumor promoter‐induced inflammation in mouse skin and Epstein‐Barr virus activation. These tendencies were parallel to those in the tumor‐suppressive potential of curcumin and THC in mouse skin, as previously reported. Thus, we concluded that curcuminoids significantly suppress TPA‐induced oxidative stress via both interference with infiltration of leukocytes into the inflammatory regions and inhibition of their activation.

Inhibitory effect of topical application of polymerized ferulic acid, a synthetic lignin, on tumor promotion in mouse skin two-stage tumorigenesis.

A dehydrogenation polymer of ferulic acid (DHP-FA), a synthetic lignin, was evaluated for its ability to inhibit tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) in the 7,12-dimethylbenz[a]anthracene-treated skin of female ICR mice. Topical application of DHP-FA inhibits TPA-induced tumor promotion, whereas a monomeric ferulic acid does not show the inhibitory effect.