Cyclooxygenases in the skin: pharmacological and toxicological implications

Cyclooxygenase-2 inhibitor nimesulide blocks ultraviolet B-induced photocarcinogenesis in SKH-1 hairless mice

Cyclooxygenase-2 (COX-2) inhibition can inhibit UVB-induced carcinogenesis in the skin. We have shown that COX-2 is overexpressed in UVB-induced squamous cell carcinomas (SCCs). Celecoxib, a specific inhibitor of COX-2, blocks UVB-induced papillomas and carcinomas in murine skin. However, as COX-2 inhibitors of this type are associated with an increased risk of adverse cardiovascular events, we decided to study nimesulide, a different class of COX-2 inhibitor, an N-arylmethanesulfonamide derivative not known to have these untoward effects. To assess the antitumor-promoting effects of nimesulide, 90 mice were equally divided into three groups. Group I animals received no test agent or UVB and served as age-matched controls; group II animals were irradiated with UVB (180 mJ cm(-2), twice weekly for 35 weeks) and group III animals received 300 p.p.m. nimesulide in drinking water and were irradiated with UVB as described for group-II. Nimesulide treatment reduced the growth of UVB-induced tumors both in terms of tumor number and tumor volume. By weeks 25, 30 and 35, the tumor numbers in the nimesulide-treated group were 79%, 49% and 53% less than the number occurring in UVB-treated animals whereas tumor volume was reduced 69%, 54% and 53%, respectively, compared to the UVB-irradiated control group. Nimesulide also inhibited the malignant progression of SCCs. The reduction in tumorigenesis was paralleled by a decrease in cell cycle regulatory proteins (cyclins A, B1, D1, E, CDK2/4/6) and the antiapoptotic protein (Bcl2); concomitantly there was an increase in proapoptotic markers, poly (ADP-ribose) polymerase (PARP) and caspase-3. Nimesulide also decreased ornithine decarboxylase expression and the nuclear accumulation of nuclear factor kappa B transcriptionally active protein complexes. These results show that alternative classes of COX-2 inhibitors may likely be efficacious as cancer chemopreventive agents and may have an improved therapeutic index.

Drug-metabolizing enzymes in the skin of man, rat, and pig

The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most drug metabolizing enzymes occur in the suprabasal (i.e. differentiating) layers of the epidermis, but the rat CYP1A1 rather in the basal layer and human UDP-glucuronosyltransferase rather in the stratum corneum. The pattern of drug metabolizing enzymes and their localization will impact not only the beneficial as well as detrimental properties of drugs for the skin but also dictate whether a drug reaches the blood flow unchanged or as activated or inactivated metabolite(s).

Ultraviolet light induced alteration to the skin

Solar light is the primary source of UV radiation for all living systems. UV photons can mediate damage through two different mechanisms, either by direct absorption of UV via cellular chromophores, resulting in excited states formation and subsequent chemical reaction, or by phosensitization mechanisms, where the UV light is absorbed by endogenous (or exogenous) sensitizers that are excited and their further reactions lead to formation of reactive oxygen species (ROS). These highly reactive species can interact with cellular macromolecules such as DNA, proteins, fatty acids and saccharides causing oxidative damage. Direct and indirect injuries result in a number of harmful effects such as disrupted cell metabolism, morphological and ultrastructural changes, attack on the regulation pathways and, alterations in the differentiation, proliferation and apoptosis of skin cells. Processes like these can lead to erythema, sunburn, inflammation, immunosuppression, photoaging, gene mutation, and development of cutaneous malignancies. The endogenous and exogenous mechanisms of skin photoprotection are discussed.

Delayed drug hypersensitivity reactions ? new concepts

Immune reactions to small molecular compounds such as drugs can cause a variety of diseases mainly involving skin, but also liver, kidney, lungs and other organs. In addition to the well-known immediate, IgE-mediated reactions to drugs, many drug-induced hypersensitivity reactions appear delayed. Recent data have shown that in these delayed reactions drug-specific CD4(+) and CD8(+) T cells recognize drugs through their T cell receptors (TCR) in an MHC-dependent way. Immunohistochemical and functional studies of drug-reactive T cells in patients with distinct forms of exanthems revealed that distinct T cell functions lead to different clinical phenotypes. Taken together, these data allow delayed hypersensitivity reactions (type IV) to be further subclassified into T cell reactions, which by releasing certain cytokines and chemokines preferentially activate and recruit monocytes (type IVa), eosinophils (type IVb), or neutrophils (type IVd). Moreover, cytotoxic functions by either CD4(+) or CD8(+) T cells (type IVc) seem to participate in all type IV reactions. Drugs are not only immunogenic because of their chemical reactivity, but also because they may bind in a labile way to available TCRs and possibly MHC-molecules. This seems to be sufficient to stimulate certain, probably preactivated T cells. The drug seems to bind first to the fitting TCR, which already exerts some activation. For full activation, an additional interaction of the TCR with the MHC molecules is needed. The drug binding to the receptor structures is reminiscent of a pharmacological interaction between a drug and its (immune) receptor and was thus termed the p-i concept. In some patients with drug hypersensitivity, such a response occurs within hours even upon the first exposure to the drug. The T cell reaction to the drug might thus not be due to a classical, primary response, but is due to peptide-specific T cells which happen to be stimulated by a drug. This new concept has major implications for understanding clinical and immunological features of drug hypersensitivity and a model to explain the frequent skin symptoms in drug hypersensitivity is proposed.

The expression pattern of prostaglandin E synthase and EP receptor isoforms in normal mouse skin and preinvasive skin neoplasms

Prostaglandin (PG) E(2), the predominant PG in skin, accumulates in experimentally produced mouse skin tumors. PGE(2) induces proliferation of mouse keratinocytes in vitro, epidermal hyperplasia and dysplasia, a promoted epidermis phenotype, and angiogenesis in keratin 5 promoter (K5) cyclooxygenase (COX)-2-transgenic NMRI mouse skin in vivo. PGE(2) is synthesized by COX-catalysed oxygenation of arachidonic acid to PGH(2) and its conversion to PGE(2) by prostaglandin E synthase (PGES) isoforms. PGE(2) signals via PGE(2) receptor isoforms EP1-EP4. Here, we investigated the expression profiles of PGES and EP receptors in wild type NMRI mouse skin constitutively expressing COX-1 when compared with the hyperplastic/dysplastic skin of homozygous K5 COX-2-transgenic mice and papillomas of both genotypes, which, in addition to COX-1, overexpress COX-2. The three PGES are constitutively expressed in normal and transgenic skin independent of the COX expression status. In papillomas, the increased PGE(2) levels correlate with an increased expression of mPGES-1 and cPGES. All four EP receptors were expressed in normal and transgenic skin. Only EP3 was slightly increased in transgenic skin. In papillomas of both genotypes, the expression levels of EP1 and EP4 were low when compared with those in wild type back skin. EP2 was the predominant receptor in papillomas of wild type and transgenic mice. In papillomas of wild type mice EP3 levels were slightly elevated when compared with transgenic tumors. EP1 and EP2 were localized in basal keratinocytes, sebaceous glands and CD31-positive vessels. Thus, normal and preinvasive mouse skin express the complete protein repertoire for PGE(2) biosynthesis and signalling.

Probing the skin permeation of fish oil/EPA and ketoprofen-3. Effects on epidermal COX-2 and LOX

This work employed immunocytochemistry (ICC) techniques to study the effect of topically applied fish oil and ketoprofen on cyclooxygenase (COX-2) and lipoxygenase (LOX) within freshly excised porcine ear skin. Maintained in Hanks buffer immediately post excision, full thickness membranes were mounted in Franz diffusion cells and dosed with 1 ml of individual formulations containing ketoprofen, fish oil or both. At different timepoints, the diffused areas were recovered and relative activities of COX-2 and LOX determined. It was found that the fish oil formulation qualitatively inhibited the expression of both COX-2 and LOX enzymes. As expected, ketoprofen had no effect upon LOX expression but a significant decrease on COX-2 expression was observed. The formulation containing both fish oil and ketoprofen proved to be the most effective at inhibiting the expression of both COX-2 and LOX. Considered together with data from earlier papers, a mechanism of EPA permeation enhancement by ketoprofen may be elucidated and also show the ability of such a formulation to inhibit these enzymes and thus indicate the efficacy of such a formulation.

Expression of tumor necrosis factor-α and cyclooxygenase-2 mRNA in porcine split-thickness wounds treated with epidermal growth factor by quantitative real-time PCR

Epidermal growth factor (EGF) accelerates the re-epithelialization of damaged epidermal cell layers in a wound, so it especially shortens the duration of wound healing. The effect of EGF on pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase-2 (COX-2), levels during wound healing has not been reported. We investigated the relationship between exogenous EGF treatment and the expression of TNF-alpha and COX-2 mRNA in porcine split-thickness wounds by real-time PCR. Twenty split-thickness wounds were created on the back of five pigs. Fifteen wounds were treated twice daily with EGF ointments (1 microg/g, 10 microg/g, and 50 microg/g) for 10 days and five wounds were untreated. Healing time until full-epithelialization was evaluated. We performed a quantitative analysis of TNF-alpha and COX-2 mRNA expression in wound biopsies using real-time PCR. Topical application of 1 microg/g EGF accelerated re-epithelialization more than treatments of EGF at 10 microg/g and 50 microg/g, and no treatment. The levels of TNF-alpha and COX-2 mRNA were significantly greater in wounds treated with 1 microg/g than those with 10 microg/g and 50 microg/g EGF, and no treatment. Topical treatment of EGF influences the level of TNF-alpha and COX-2 mRNA within porcine split-thickness wounds. EGF-dependent slightly up-regulation of TNF-alpha and COX-2 mRNA expression during the inflammatory phase of healing may create an optimal molecular environment for wound healing.

n-3 and n-6 polyunsaturated fatty acids induce the expression of COX-2 via PPARgamma activation in human keratinocyte HaCaT cells

Polyunsaturated fatty acids (PUFA) n-3 inhibit inflammation, in vivo and in vitro in keratinocytes. We examined in HaCaT keratinocyte cell line whether eicosapentaenoic acid (EPA) a n-3 PUFA, gamma-linoleic acid (GLA) a n-6 PUFA, and arachidic acid a saturated fatty acid, modulate expression of cyclooxygenase-2 (COX-2), an enzyme pivotal to skin inflammation and reparation. We demonstrate that only treatment of HaCaT with GLA and EPA or a PPARgamma ligand (roziglitazone), induced COX-2 expression (protein and mRNA). Moreover stimulation of COX-2 promoter activity was increased by those PUFAs or rosiglitazone. The inhibitory effects of GW9662 and T0070907 (PPARgamma antagonists), on COX-2 expression and on stimulation of COX-2 promoter activity by EPA and GLA suggest that PPARgamma is implicated in COX-2 induction. Finally, PLA2 inhibitor methyl arachidonyl fluorophosphonate blocked the PUFA effects on COX-2 induction, promoter activity and arachidonic acid mobilization suggesting involvement of AA metabolites in PPAR activation. These findings demonstrate that n-3 and n-6 PUFA increased PPARgamma activity is necessary for the COX-2 induction in HaCaT human keratinocyte cells. Given the anti-inflammatory properties of EPA, we suggest that induction of COX-2 in keratinocytes may be important in the anti-inflammatory and protective mechanism of action of PUFAs n-3 or n-6.

New Dosage Formulations for Targeted Delivery of Cyclo-Oxygenase-2 Inhibitors

NSAIDs are a widely used class of analgesic and anti-inflammatory drugs that act by inhibiting the cyclo-oxygenase (COX) enzyme. However, because of their nonspecificity of action, use of these agents as long-term therapy for chronic pain in diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA) is often discouraged. Among NSAIDs, COX-2 inhibitors are promising candidates for long-term therapy of chronic diseases, particularly in the elderly, because of their reduced incidence of gastrointestinal adverse effects. However, in recent times these agents have also been shown to cause adverse effects such as cardiovascular effects (myocardial infarction, stroke and hypertension) and renal effects (decreased renal blood flow/glomerular filtration rate), which in 2004 led to the withdrawal of rofecoxib and in 2005 the withdrawal of valdecoxib from the US market. Importantly, these adverse effects can be effectively reduced by achieving site specific/targeted delivery through new formulation approaches. These formulations not only restrict the drug supply to specific organs but also reduce the dose required. As a result, use of new delivery systems such as nanoparticles, microparticles, microemulsions and nanogels has gained widespread applicability in the management of chronic disease, especially in the elderly, and particularly when there is a need to decrease dose-dependent adverse effects (as is the case with COX-2 inhibitors). This article reviews various new approaches to the delivery of COX-2 inhibitors and highlights issues related to the development of delivery systems for these agents for RA, OA, cancer (familial adenomatous polyposis, prostate, breast and non-small cell lung cancer), ocular diseases (such as diabetic retinopathy) and inflammatory diseases of the skin, with emphasis on their potential for use in the elderly. Emphasis is also placed on the preparation of these particulate systems, their release profile and behaviour in biological systems.

Anti-inflammatory drugs in the 21st century

Historically, anti-inflammatory drugs had their origins in the serendipitous discovery of certain plants and their extracts being applied for the relief of pain, fever and inflammation. When salicylates were discovered in the mid-19th century to be the active components of Willow Spp., this enabled these compounds to be synthesized and from this, acetyl-salicylic acid or Aspirin was developed. Likewise, the chemical advances of the 19th-20th centuries lead to development of the non-steroidal anti-inflammatory drugs (NSAIDs), most of which were initially organic acids, but later non-acidic compounds were discovered. There were two periods of NSAID drug discovery post-World War 2, the period up to the 1970's which was the pre-prostaglandin period and thereafter up to the latter part of the last century in which their effects on prostaglandin production formed part of the screening in the drug-discovery process. Those drugs developed up to the 1980-late 90's were largely discovered empirically following screening for anti-inflammatory, analgesic and antipyretic activities in laboratory animal models. Some were successfully developed that showed low incidence of gastro-intestinal (GI) side effects (the principal adverse reaction seen with NSAIDs) than seen with their predecessors (e.g. aspirin, indomethacin, phenylbutazone); the GI reactions being detected and screened out in animal assays. In the 1990's an important discovery was made from elegant molecular and cellular biological studies that there are two cyclo-oxygenase (COX) enzyme systems controlling the production of prostanoids [prostaglandins (PGs) and thromboxane (TxA2)]; COX-1 that produces PGs and TxA2 that regulate gastrointestinal, renal, vascular and other physiological functions, and COX-2 that regulates production of PGs involved in inflammation, pain and fever. The stage was set in the 1990's for the discovery and development of drugs to selectively control COX-2 and spare the COX-1 that is central to physiological processes whose inhibition was considered a major factor in development of adverse reactions, including those in the GI tract. At the turn of this century, there was enormous commercial development following the introduction of two new highly selective COX-2 inhibitors, known as coxibs (celecoxib and rofecoxib) which were claimed to have low GI side effects. While found to have fulfilled these aims in part, an alarming turn of events took place in the late 2004 period when rofecoxib was withdrawn worldwide because of serious cardiovascular events and other coxibs were subsequently suspected to have this adverse reaction, although to a varying degree. Major efforts are currently underway to discover why cardiovascular reactions took place with coxibs, identify safer coxibs, as well as elucidate the roles of COX-2 and COX-1 in cardiovascular diseases and stroke in the hope that there may be some basis for developing newer agents (e.g. nitric oxide-donating NSAIDs) to control these conditions. The discovery of the COX isoforms led to establishing their importance in many non-arthritic or non-pain states where there is an inflammatory component to pathogenesis, including cancer, Alzheimer's and other neurodegenerative diseases. The applications of NSAIDs and the coxibs in the prevention and treatment of these conditions as well as aspirin and other analogues in the prevention of thrombo-embolic diseases now constitute one of the major therapeutic developments of the this century. Moreover, new anti-inflammatory drugs are being discovered and developed based on their effects on signal transduction and as anti-cytokine agents and these drugs are now being heralded as the new therapies to control those diseases where cytokines and other nonprostaglandin components of chronic inflammatory and neurodegenerative diseases are manifest. To a lesser extent safer application of corticosteroids and the applications of novel drug delivery systems for use with these drugs as well as with NSAIDs also represent newer technological developments of the 21st century. What started out as drugs to control inflammation, pain and fever in the last two centuries now has exploded to reveal an enormous range and type of anti-inflammatory agents and discovery of new therapeutic targets to treat a whole range of conditions that were never hitherto envisaged.

Mechanisms underlying the inhibitory actions of the pentacyclic triterpene alpha-amyrin in the mouse skin inflammation induced by phorbol ester 12-O-tetradecanoylphorbol-13-acetate

The present study evaluated some of the mechanisms through which alpha-amyrin, a pentacyclic triterpene isolated from Protium Kleinii and other plants, exerts its effects against 12-O-tetradecanoylphorbol-acetate (TPA)-induced skin inflammation in mice. Topical application of alpha-amyrin (0.1-1 mg/ear) dose-dependently inhibited TPA-induced increase of prostaglandin E2 (PGE2) levels. In contrast with the selective cyclooxygenase (COX)-1 SC560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole] or COX-2 rofecoxib inhibitors, alpha-amyrin failed to alter either COX-1 or COX-2 activities in vitro. Western blot analysis revealed that alpha-amyrin dose-dependently inhibited TPA-induced COX-2 expression in the mouse skin. The evaluation of nuclear factor-kappaB (NF-kappaB) pathway revealed that topical treatment with alpha-amyrin is able to prevent IkappaB alpha degradation, p65/RelA phosphorylation and NF-kappaB activation. Moreover, alpha-amyrin given topically dose-dependently inhibited the activation of upstream protein kinases, namely extracellular signal-regulated protein kinase (ERK), p38 mitogen-activated protein kinase (MAPK) and protein kinase C (PKC)alpha, following topical TPA treatment. Collectively, present results suggest that topical skin application of alpha-amyrin exerts a strong and rapid onset inhibition of TPA-induced inflammation. These effects seem to be associated with the suppression of skin PGE2 levels by mechanisms involving the suppression of COX-2 expression, via inhibition of upstream protein kinases--namely ERK, p38 MAPK and PKCalpha--and blocking of NF-kappaB activation. These results indicate that alpha-amyrin-derivative could be potentially relevant for the development of a topical agent for the management of inflammatory diseases.

Oxidative stress in the pathogenesis of skin disease

Skin is the largest body organ that serves as an important environmental interface providing a protective envelope that is crucial for homeostasis. On the other hand, the skin is a major target for toxic insult by a broad spectrum of physical (i.e. UV radiation) and chemical (xenobiotic) agents that are capable of altering its structure and function. Many environmental pollutants are either themselves oxidants or catalyze the production of reactive oxygen species (ROS) directly or indirectly. ROS are believed to activate proliferative and cell survival signaling that can alter apoptotic pathways that may be involved in the pathogenesis of a number of skin disorders including photosensitivity diseases and some types of cutaneous malignancy. ROS act largely by driving several important molecular pathways that play important roles in diverse pathologic processes including ischemia-reperfusion injury, atherosclerosis, and inflammatory responses. The skin possesses an array of defense mechanisms that interact with toxicants to obviate their deleterious effect. These include non-enzymatic and enzymatic molecules that function as potent antioxidants or oxidant-degrading systems. Unfortunately, these homeostatic defenses, although highly effective, have limited capacity and can be overwhelmed thereby leading to increased ROS in the skin that can foster the development of dermatological diseases. One approach to preventing or treating these ROS-mediated disorders is based on the administration of various antioxidants in an effort to restore homeostasis. Although many antioxidants have shown substantive efficacy in cell culture systems and in animal models of oxidant injury, unequivocal confirmation of their beneficial effects in human populations has proven elusive.

Effects of anti-inflammatory biflavonoid, ginkgetin, on chronic skin inflammation

Ginkgetin, a biflavonoid from Ginkgo biloba leaves (Ginkgoaceae), was previously demonstrated to inhibit phospholipase A2 and to suppress proinflammatory gene expression such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase. In this study, the effects of ginkgetin were examined on an animal model of chronic skin inflammation and proinflammatory gene expression. When topically applied to ICR mouse ear, ginkgetin (20-80 microg/ear/treatment) inhibited ear edema (22.8-30.5%) and prostaglandin E2 production (30.2-31.1%) induced by multiple treatment of 12-O-tetradecanoylphorbol-13-acetate (TPA) for 7 consecutive days. By histological comparison, ginkgetin was also found to reduce epidermal hyperplasia. The expression of proinflammatory gene, interleukin-1beta, was suppressed by ginkgetin. From the results, it is suggested that ginkgetin may be beneficial against chronic skin inflammatory disorders like atopic dermatitis.

Role of COX-1 and COX-2 on skin PGs biosynthesis by mechanical scratching in mice

We examined the involvement of cyclooxygenase (COX)-1 and COX-2 on mechanical scratching-induced prostaglandins (PGs) production in the skin of mice. The dorsal regions of mice were scratched using a stainless brush. COXs expressions in the skin were analyzed using real-time PCR and Western blotting. The effect of acetylsalicylic acid (ASA) on the ability of PGs production were determined based on skin PGs level induced by arachidonic acid (AA) application. Mechanical scratching increased PGD2, PGE2, PGI2 and PGF(2 alpha). COX-1 was constitutively expressed and COX-2 expression was enhanced by scratching. Intravenous administration of ASA inhibited PGs biosynthesis in the normal skin. PGs levels of the skin 6h after ASA administration (ASA 6 h) were almost equal to those of the skin 10 min after ASA administration (ASA 10 min). In the scratched skin, AA-induced PGE2 and PGI2 of ASA 6 h were significantly higher than those of ASA 10 min. The skin PGD2 and PGF(2 alpha) of ASA 10 min were almost same to those of ASA 6 h. In the normal skin of COX-1-deficient mice, skin PGD2 level was lower than that of wild-type mice, although PGE2, PGI2 and PGF(2 alpha) levels were almost equal to those of wild type. In the scratched skin of COX-1-deficient mice, PGD2, PGE2, PGI2 and PGF(2 alpha) levels were lower than those of wild-type mice. These results suggested that cutaneous PGD2 could be mainly produced by COX-1, and PGE2 and PGI2 could be produced by COX-1 and COX-2, respectively, in mice.

Biphasic regulation by bile acids of dermal fibroblast proliferation through regulation of cAMP production and COX-2 expression level

We have previously reported that the bile acids chenodeoxycholate (CDCA) and ursodeoxycholate (UDCA) decreased PGE1-induced cAMP production in a time- and dose-dependent manner not only in hepatocytes but also in nonhepatic cells, including dermal fibroblasts. In the present study, we investigated the physiological relevance of this cAMP modulatory action of bile acids. PGE1 induced cAMP production in a time- and dose-dependent manner. Moreover, PGE1 (1 microM), forskolin (1-10 microM), and the membrane-permeable cAMP analog CPT-cAMP (0.1-10 microM) decreased dermal fibroblast proliferation in a dose-dependent manner with a maximum inhibition of approximately 80%. CDCA alone had no significant effect on cell proliferation at a concentration up to 25 microM. However, CDCA significantly reduced PGE1-induced cAMP production by 80-90% with an EC(50) of approximately 20 microM. Furthermore, at concentrations < or =25 microM, CDCA significantly attenuated the PGE-1-induced decreased cell proliferation. However, at concentrations of 50 microM and above, while still able to almost completely inhibit PGE-1-induced cAMP production, CDCA, at least in part through an increased cyclooxygenase-2 (COX-2) expression level and PGE2 synthesis, produced a direct and significant decrease in cell proliferation. Indeed, the CDCA effect was partially blocked by approximately 50-70% by both indomethacin and dexamethasone. In addition, overexpression of COX-2 cDNA wild type resulted in an increased efficacy of CDCA to block cell proliferation. The effects of CDCA on both cAMP production and cell proliferation were similar to those of UDCA and under the same conditions cholate had no effect. Results of the present study underline pathophysiological consequences of cholestatic hepatobiliary disorders, in which cells outside of the enterohepatic circulation can be exposed to elevated bile acid concentrations. Under these conditions, low bile acid concentrations can attenuate the negative hormonal control on cell proliferation, resulting in the stimulation of cell growth, while at high concentrations these bile acids provide for a profound and prolonged inhibition of cell proliferation.

Differential protein expression in the epidermis of wild-type and COX-2 transgenic mice

Cyclooxygenases (COX) 1 and 2 are the key enzymes of prostaglandin biosynthesis. Like in many tissues, in adult skin COX-1 is a constitutive 'housekeeping' enzyme, while COX-2 is induced transiently in stress situations such as tissue damage and regeneration. In human skin carcinomas and corresponding early-stage cancer lesions, permanent COX-2 expression and activation is a consistent feature. Knockout and various transgenic approaches and pharmacologic studies show strong evidence for a cause-and-effect relationship between the aberrant COX-2 activation and tumor formation. In skin epidermis, keratin 5 promoter-driven overexpression of COX-2 caused hyperplasia and dysplasia, and sensitized skin for carcinogenesis. Therefore, this model offers the unique possibility of identifying COX-2-dependent and prostaglandin-mediated molecular pathways leading to the formation and malignant progression of early-stage cancer lesions.

Mechanisms of drug-induced delayed-type hypersensitivity reactions in the skin

Cutaneous drug reactions (CDRs) are the most commonly reported adverse drug reactions. These reactions can range from mildly discomforting to life threatening. CDRs can arise either from immunological or nonimmunological mechanisms, though the preponderance of evidence suggests an important role for immunological responses. Some cutaneous eruptions appear shortly after drug intake, while others are not manifested until 7 to 10 days after initiation of therapy and are consistent with delayed-type hypersensitivity. This review discusses critical steps in the initiation of delayed-type hypersensitivity reactions in the skin, which include protein haptenation, dendritic cell activation/migration and T-cell propagation. Recently, an alternative mechanism of drug presentation has been postulated that does not require bioactivation of the parent drug or antigen processing to elicit a drug-specific T-cell response. This review also discusses the role of various immune-mediators, such as cytokines, nitric oxide, and reactive oxygen species, in the development of delayed-type drug hypersensitivity reactions in skin. As keratinocytes have been shown to play a crucial role in the initiation and propagation of cutaneous immune responses, we also discuss the means by which these cells may initiate or modulate CDRs.

Differential expression of E prostanoid receptors in murine and human non-melanoma skin cancer

Enhanced prostaglandin production via upregulated cyclooxygenase-2 (COX-2) expression is a likely contributing factor in ultraviolet B (UVB)-induced non-melanoma skin cancer (NMSC), which consists primarily of squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). The four E prostanoid (EP) receptors, designated EP1 through EP4, are known to bind prostaglandin E2 (PGE2), the major prostaglandin present in the skin. We used murine models of UVB-induced SCC and BCC, as well as human NMSC from sun-exposed sites, to investigate the expression of EP receptors during UVB-induced tumorigenesis. We observed that UVB-induced murine SCC are associated with markedly altered expression patterns of the EP receptors when compared with non-irradiated skin. In contrast, expression of all EP receptors was largely absent in UVB-induced murine BCC. We also observed expression of all four EP receptors in human SCC, with altered expression of their mRNA levels as compared with adjacent tumor-free skin. Consistent with our murine studies, no EP receptor expression was detected in human BCC, and their mRNA expression levels showed no change from the adjacent non-tumor-bearing skin. These data suggest that altered EP receptor expression may play a differential role in the development of UVB-induced SCC and BCC in murine and human skin.

Current directions for COX-2 inhibition in breast cancer

Chemotherapy is effective against breast cancer. COX-2 has been implicated in the progression and angiogenesis of cancers. Celecoxib, a cyclooxygenase type 2 (COX-2) inhibitor, has both apoptotic and antiangiogenic activities, and may be of use in treatment of breast tumors which overexpress the COX-2 enzyme. Preliminary clinical trials have shown that the combination of chemotherapy with celecoxib has minimal additional toxicity and it may enhance the effects of the chemotherapy. Beside chemotherapy, celecoxib may promulgate the effect of aromatase inhibitor in breast cancer cells. Animal studies have shown that there are fewer and smaller tumors treated by combining exemestane and celecoxib. Larger clinical trials should be initiated to study the potential anti-cancer effects of celecoxib in breast cancer.

Differential expression of COX-1 and COX-2 in the gastrointestinal tract of the rat

The aim of this study was to use immunohistochemistry with morphometry to investigate COX-1 and COX-2 expression in the normal rat gastrointestinal (GI) tract and examine if sites of ulceration previously observed with long-term COX-2 inhibitor administration in mice correlate with differential COX-1/COX-2 expression. COX-2 positive cells were observed predominantly in the apical lamina propria of intestinal villi with fewer cells in the mucosal epithelium. The highest level of COX-2 expression was observed at the ileocaecal junction (ICJ). COX-2 expression was also present in parasympathetic ganglia of the submucosa and muscularis. In the stomach, the highest grade of COX-2 expression was observed in the apical lamina propria of the fundus adjacent to the junctional ridge. In contrast, COX-1 positive cells within the lamina propria were evenly distributed along the GI tract but were present in higher numbers than COX-2 positive cells. The mean level of COX-1 expression at the ICJ was not significantly different from the ileum and caecum. Evidence that the highest level of COX-2 expression in normal rats is located on the ileal side of the ICJ provides the first mechanism to explain spontaneous ulceration and perforation of the distal ileum in COX-2 -/- animals.

Immunolocalization of Low-Affinity Prostaglandin E2 Receptors, EP1 and EP2, in Adult Human Epidermis

Four prostaglandin (PG)E(2) receptors have been described, termed E-series prostaglandin receptors (EP(1)-EP(4)), that can be further subclassified as low-affinity (EP(1) and EP(2)) or high-affinity (EP(3) and EP(4)) receptors. Activation of the low-affinity PGE(2) receptors is likely to be important in mediating the actions of the high levels of PGE(2) found in various pathologic processes. The pattern of expression of these receptors in epidermis, however, is unknown. We therefore examined the immunolocalization of the EP(1) and EP(2) receptors in human epidermis. The EP(1) and EP(2) receptors demonstrated both plasma membrane and perinuclear or nuclear staining within the basal and spinous layers. Within the granular layer, both receptors were expressed in the cytoplasm with a grainy or granular appearance. The major differences were that the EP(2) receptor demonstrated a zone of decreased to absent plasma membrane staining in the superficial spinous layer and only scattered cellular staining within the granular layer. In contrast, the EP(1) receptor was prominently expressed throughout the stratum granulosum and the plasma membrane staining pattern was seen throughout the spinous layer. In cultured primary human keratinocytes, we also verified the presence of functional EP(1) receptor coupled to intracellular calcium mobilization and EP(2) receptor coupled to cAMP production.

Wound inflammation in diabetic ob/ob mice: functional coupling of prostaglandin biosynthesis to cyclooxygenase-1 activity in diabetes-impaired wound healing

This study focused on the regulation of prostaglandin (PG) production in diabetes-impaired wound tissue. Cyclooxygenase (COX)-1 and -2 expression and activity were severely dysregulated in chronic wounds of diabetic ob/ob mice. Those wounds were characterized by a reduced expression of COX-1 and the presence of strongly elevated levels of COX-2 when compared with conditions observed in healthy animals. Resolution of the diabetic and impaired wound-healing phenotype by systemic administration of leptin into ob/ob mice increased COX-1 expression in wound margin keratinocytes and decreased COX-2 expression in inner wound areas to levels found in wild-type animals. Notably, improved wound healing was characterized by a marked increase in PGE2/PGD2 biosynthesis that colocalized with induced COX-1 in new tissue at the margin of the wound. COX-2 expression did not significantly contribute to PGE2/PGD2 production in impaired wound tissue. Accordingly, only late wound tissue from SC-560-treated (selective COX-1 inhibitor) but not celecoxib-treated (selective COX-2 inhibitor) ob/ob mice exhibited a severe loss in PGE2, PGD2, and prostacyclin at the wound site, and this change was associated with reduced keratinocyte numbers in the neo-epithelia. These data constitute strong evidence that a dysregulation of COX-1-coupled prostaglandin contributes to diabetes-impaired wound healing.

Epithelium-mesenchyme interactions control the activity of peroxisome proliferator-activated receptor beta/delta during hair follicle development

Hair follicle morphogenesis depends on a delicate balance between cell proliferation and apoptosis, which involves epithelium-mesenchyme interactions. We show that peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) and Akt1 are highly expressed in follicular keratinocytes throughout hair follicle development. Interestingly, PPARbeta/delta- and Akt1-deficient mice exhibit similar retardation of postnatal hair follicle morphogenesis, particularly at the hair peg stage, revealing a new important function for both factors in the growth of early hair follicles. We demonstrate that a time-regulated activation of the PPARbeta/delta protein in follicular keratinocytes involves the up-regulation of the cyclooxygenase 2 enzyme by a mesenchymal paracrine factor, the hepatocyte growth factor. Subsequent PPARbeta/delta-mediated temporal activation of the antiapoptotic Akt1 pathway in vivo protects keratinocytes from hair pegs against apoptosis, which is required for normal hair follicle development. Together, these results demonstrate that epithelium-mesenchyme interactions in the skin regulate the activity of PPARbeta/delta during hair follicle development via the control of ligand production and provide important new insights into the molecular biology of hair growth.

Inhibition of cyclooxygenase activity, platelet aggregation and thromboxane B2 production by two environmental toxicants: m- and o-cresol

Cresol is a well-known environmental pollutant, toluene metabolite, uremic toxicant and accidental poisoning product. Formocresol, a preparation of formalin and cresol, is also used as a root canal medicament and for pulpotomy of primary teeth. However, little is known about its effect on cardiovascular system. In this study, m-cresol inhibited the AA-induced platelet aggregation by 43-97% at concentrations ranging from 0.25 to 1 mM. Collagen-induced platelet aggregation was also inhibited by 0.25-1 mM of m-cresol by 47-98%. Accordingly, o-cresol (0.1-0.5 mM) also inhibited the AA-induced platelet aggregation by 46-96% and the collagen-induced platelet aggregation by 35-88% at concentrations of 0.1-1 mM. AA- and collagen-induced platelet thromboxane B(2) (TXB(2)) production was inhibited by even 0.1 mM of m-cresol with 88 and 54% of inhibition, respectively. The o-cresol (0.1 mM) also inhibited the AA- and collagen-induced platelet TXB(2) production with 91 and 97% respectively. Although m- and o-cresol (<1 mM) showed little effect on thrombin-induced platelet aggregation, they effectively inhibited the thrombin-induced platelet TXB(2) production. The m-cresol (2 and 5 mM) inhibited the COX-1 activity by 55-99%, but showed little effect on COX-2 enzyme activity. Moreover, o-cresol (0.5 and 1 mM) inhibited the COX-1 activity by 40-95%. COX-2 enzyme activity was inhibited by 68% at a concentration of 5 mM o-cresol. These results indicate that acute cresol-poisoning, direct root canal medication with formocresol or long-term occupational exposure to cresol and toluene may potentially suppress blood clot formation and lead to tissue hemorrhage via inhibition of platelet aggregation, TXB(2) production and COX enzyme activity.

Early signals for fracture healing

Fracture healing requires the cooperation of multiple molecular signaling pathways. To better understand this cascade of transcriptional events, we compared the gene expression profiles between intact bone and fractured bone at days 1, 2, and 4 using a rat femur model of bone healing. Cluster analysis identified several groups of genes with dynamic temporal expression patterns and stage-specific functions. The immediate-response genes are highlighted by binding activity, transporter activity, and energy derivation. We consider these activities as critical signals for initiation of fracture healing. The continuously increased genes are characterized by those directly involved in bone repair, thus, representing bone specific forefront workers. The constantly upregulated genes tend to regulate general cell growth and are enriched with genes that are involved in tumorigenesis, suggesting common pathways between two processes. The constantly downregulated genes predominantly involve immune response, the significance of which remains for further investigation. Knowledge acquired through this analysis of transcriptional activities at the early stage of bone healing will contribute to our understanding of fracture repair and bone-related pathological conditions.

Topical antiinflammatory effects of the ether extract from Protium kleinii and alpha-amyrin pentacyclic triterpene

Protium kleinii (Burseraceae), a native Brazilian medicinal plant is claimed to be useful to treat some inflammatory states. Now we reported that topical application of either the ether extract or the main active constituent from P. kleinii the pentacyclic triterpene alpha-amyrin, all caused a dose-related inhibition of both ear oedema (ID50 values are 0.55 and 0.31 mg/ear, respectively) and influx of polymorphonuclear cells (ID50 values are 0.72 and 0.45 mg/ear, respectively) in response to topical application of 12-O-tetradecanoylphorbol-acetate (TPA) in the of mice ear. In terms of the efficacy, the maximal obtained inhibition for both ear oedema and neutrophil influx was very similar to that produced by the topical application of the steroidal antiinflammatory drug dexamethasone (DE; with inhibition of 70+/-5%, 66+/-3%, and 87+/-4% for oedema and 83+/-6%, 73+/-5%, and 91+/-3% for neutrophil influx, for the ether extract, alpha-amyrin, and dexamethasone, respectively). Likewise, both the ether extract and alpha-amyrin given topically dose-dependently prevented the increase of the proinflammatory cytokine interleukin-1beta levels in response to topical application of TPA. The calculated mean ID50 values are 1.81 and 0.53 mg/ear, respectively. Again, the efficacy of the extract and alpha-amyrin was very similar to that produced by dexamethasone (63+/-6%, 61+/-5%, and 74+/-5%, respectively). In marked contrast to phenidone, a lipo and cyclooxygenase inhibitor, neither the ether extract nor the alpha-amyrin inhibited arachidonic acid-mediated ear oedema in mice. Collectively, these results indicate that the active constituents present in the ether extract of P. kleinii including the pentacyclic triterpene alpha-amyrin are good candidates to develop a skin permeable antiinflammatory drug.

Docosahexaenoic acid attenuates mycotoxin-induced immunoglobulin a nephropathy, interleukin-6 transcription, and mitogen-activated protein kinase phosphorylation in mice

The purpose of this investigation was to evaluate the dose-dependent effects of docosahexaenoic acid (DHA) on deoxynivalenol (DON)-induced IgA nephropathy in mice and their relation to proinflammatory gene expression and mitogen-activated protein kinase (MAPK) activation. Consumption of a modified AIN-93G diet containing 1, 5, and 30 g/kg DHA resulted in dose-dependent increases of DHA in liver phospholipids with concomitant decreases in arachidonic acid compared with control diets. DHA dose dependently inhibited increases in serum IgA and IgA immune complexes (IC) as well as IgA deposition in the kidney in DON-fed mice; the 30 g/kg DHA diet had the earliest detectable effects and maximal efficacy. Both splenic interleukin-6 (IL-6) mRNA and heterogeneous nuclear RNA (hnRNA), an indicator of IL-6 transcription, were significantly reduced in DON-fed mice that consumed 5 and 30 g/kg DHA; a similar reduction was observed for cyclooxygenase (COX-2) mRNA. In a subsequent study, acute DON exposure (25 mg/kg body weight) induced splenic IL-6 mRNA and hnRNA as well as COX-2 mRNA in mice fed the control diet, whereas induction of both RNA species was significantly inhibited in mice fed 30 g/kg DHA. These latter inhibitory effects corresponded to a reduction in DON-induced phosphorylation of p38, extracellular-signal related kinase 1/2, and c-Jun N-terminal kinase 1/2 MAPKs in the spleen. Taken together, the results indicate that DHA dose-dependently inhibited DON-induced IgA dysregulation and nephropathy, and that impairment of MAPK activation and expression of COX-2 and IL-6 are potential critical upstream mechanisms.

Targeting signal transduction pathways by chemopreventive agents

Cancer is a dynamic process that involves many complex factors, which may explain why a "magic bullet" cure for cancer has not been found. Death rates are still rising for many types of cancers, which possibly contributes to the increased interest in chemoprevention as an alternative approach to the control of cancer. This strategy for cancer control is based on the presumption that because cancer develops through a multi-step process, each step may be a prospective target for reversing or suppressing the process. Thus, the design and development of chemopreventive agents that act on specific and/or multiple molecular and cellular targets is gaining support as a rational approach to control cancer. Nutritional or dietary factors have attracted a great deal of interest because of their perceived ability to act as highly effective chemopreventive agents. They are professed as being generally safe and may have efficacy as chemopreventive agents by preventing or reversing premalignant lesions and/or reducing second primary tumor incidence. Many of these dietary compounds appear to act on multiple target signaling pathways. Some of the most interesting and well documented are resveratrol and components of tea, including EGCG, theaflavins and caffeine. This review will focus on recent work regarding three well-accepted cellular/molecular mechanisms that may at least partially explain the effectiveness of selected food factors, including those indicated above, as chemopreventive anti-promotion agents. These food compounds may act by: (1) inducing apoptosis in cancer cells; (2) inhibiting neoplastic transformation through the inhibition of AP-1 and/or NF-kappaB activation; and/or (3) suppressing COX-2 overexpression in cancer cells.

Reduced sulfur mustard-induced skin toxicity in cyclooxygenase-2 knockout and celecoxib-treated mice

Sulfur mustard (SM), a potent vesicant and chemical warfare agent, induces tissue damage involving an inflammatory response, including vasodilatation, polymorphonuclear infiltration, production of inflammatory mediators, and cyclooxygenase activity. To evaluate the role of cyclooxygenase-1 and -2 (COX-1, COX-2) in sulfur mustard-induced skin toxicity, we applied the agent to the ears of wildtype (WT) and COX-1- and COX-2-deficient mice. In the latter, ear swelling 24 and 48 h after exposure was significantly reduced (P < 0.05) by 55% and 30%, respectively, compared to WT. Quantitative histopathology revealed no epidermal ulceration in COX-2-deficient mice but some degree of severity in WT. COX-2-deficient mice showed significant reductions (P < 0.05) in severity of epidermal necrosis (29%), acute inflammation (42%), and hemorrhage (25%), compared to the WT mice. COX-1 deficiency resulted in significant exacerbation (P < 0.05) in severity of some parameters, including increases of 4.6- and 1.2-fold in epidermal ulceration and epidermal necrosis, respectively, compared to WT. Postexposure treatment of normal male ICR mice with the selective COX-2 inhibitor celecoxib resulted in significant reductions of 27% (P < 0.05) and 28% (P < 0.01) in ear swelling at intervals of 40 and 60 min between exposure and treatment, respectively. Histopathological evaluation revealed significant reductions (P < 0.05) in subepidermal microblister formation (73%) and dermal necrosis (32%), compared to the control group. These findings may indicate that COX-2 participates in the early stages of sulfur mustard-induced acute skin toxicity and that COX-1 might exert some protective function against this chemical insult.

Cyclooxygenasen in der Haut. Cyclooxygenases in the skin

Cyclooxygenases (COX)-1 and COX-2 catalyse the key steps of prostaglandin biosynthesis and are the major target for non-steroidal anti-inflammatory drugs. In general, COX-1 but not COX-2 is expressed in healthy tissues of adults. After incision or acute irritant dermatitis, COX-2 is induced transiently. The development of UV-induced erythema and edema as well as of skin tumours is significantly governed by COX-2 activity. Squamous cell carcinomas and actinic keratoses are prominent examples of epithelial tumours with COX-2 overexpression in the tumour parenchyma, inflammatory infiltrate and associated vessels. According to multi-stage carcinogenesis studies in mouse skin and experiments with transgenic mice, there is a causal relationship between aberrant COX-2 expression and activity in the epithelium and tumour promotion and tumour progression. The transgenic overexpression of COX-2 causes an "autopromoted" skin phenotype, i.e. it dramatically sensitizes the tissue for the development of squamous cell carcinomas. Vice versa, the genetic ablation of COX-2, as well as of COX-1, results in a reduced tumour burden in murine skin. A major mechanism by which COX-2 contributes to epidermal tumour formation seems to be the disturbance of terminal keratinocyte differentiation. Because of these data, selective COX-2 inhibitors are ranked among the most promising agents for skin cancer prevention and therapy.

TGF‐β signaling and the fibrotic response

The cause of fibrotic diseases, pathologies characterized by excessive production, deposition, and contraction of extracellular matrix, is unknown. To understand the molecular basis of fibrotic disease, it is essential to appreciate how matrix deposition is normally controlled and how this process is dysregulated in fibrogenesis. This review discusses the current state of knowledge concerning interactions among the profibrotic proteins transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF, CCN2), and ED-A fibronectin (ED-A FN) and the antifibrotic proteins tumor necrosis factor-alpha (TNF-alpha) and gamma-interferon (IFN-gamma).

Photoprotective effects of sulindac against ultraviolet B-induced phototoxicity in the skin of SKH-1 hairless mice

Sulindac is a nonsteroidal anti-inflammatory drug with demonstrated potency as a chemopreventive agent in animal models of carcinogenesis and in patients with familial adenomatous polyposis. Because tumor promotion is generally associated with exposure to pro-inflammatory stimuli, it is likely that anti-inflammatory agents may have potent antitumor effects. In human skin, sulindac reduces bradykinin-induced edema. In this study, we tested the hypothesis that the cyclooxygenase inhibitor sulindac can protect against ultraviolet (UVB)-induced injury that is crucial for the induction of cancer. Exposure of SKH-1 hairless mice to two consecutive doses of UVB (230 mJ/cm2) induces various inflammatory responses including erythema, edema, epidermal hyperplasia, infiltration of polymorphonuclear leukocytes, etc. Topical application of sulindac (1.25-5.0 mg/0.2 ml acetone) to the dorsal skin of SKH-1 hairless mice either 1 h before or immediately after UVB exposure substantially inhibited these inflammatory responses in a dose-dependent manner. Oral administration of sulindac in drinking water (160 ppm) for 15 days before and during UVB irradiation similarly reduced these inflammatory responses. These potent anti-inflammatory effects of sulindac suggested the possibility that the drug could inhibit signaling processes that relate to carcinogenic insult by UVB. Accordingly, studies were conducted to assess the efficacy of sulindac in attenuating the expression of UVB-induced early surrogate molecular markers of photodamage and carcinogenesis. UVB exposure enhanced the expression of p53, c-fos, cyclins D1 and A, and PCNA 24 h after irradiation. Treatment of animals with either topical or oral administration of sulindac largely abrogated the expression of these UVB-induced surrogate markers. These results indicate that the cyclooxygenase inhibitor sulindac is effective in reducing UVB-induced events relevant to carcinogenesis and that this category of topically applied or orally administered drugs may prove to be effective chemopreventive agents for reducing the risk of photocarcinogenesis in human populations.

Inhibitory effects of [6]-gingerol on PMA-induced COX-2 expression and activation of NF-kappaB and p38 MAPK in mouse skin

[6]-Gingerol, a major pungent ingredient of ginger (Zingiber officinale Roscoe, Zingiberaceae), has a wide array of pharmacologic effects. Previous studies have demonstrated that [6]-gingerol inhibits mouse skin tumor promotion and anchorage-independent growth of cultured mouse epidermal cells stimulated with epidermal growth factor. Cyclooxygenase-2 (COX-2), a key enzyme in the prostaglandin biosynthesis, has been recognized as a molecular target for many anti-inflammatory as well as chemopreventive agents. Topical application of [6]-gingerol inhibited phorbol 12-myristate 13-acetate -induced COX-2 expression. One of the essential transcription factors responsible for COX-2 induction is NF-kappaB. [6]-Gingerol suppressed NF-kappaB DNA binding activity in mouse skin. In addition, [6]-gingerol inhibited the phoshorylation of p38 mitogen-activated protein kinase which may account for its inactivation of NF-kappaB and suppression of COX-2 expression.