Efficacy of a skin care cream with TRPV1 inhibitor 4-t-butylcyclohexanol in the topical therapy of perioral dermatitis.

BACKGROUND: Perioral dermatitis is a clinically distinctive reaction pattern of facial dermatitis, including redness, dryness, burning, pruritus and skin tightness. A gold standard treatment remains unclear. OBJECTIVES: Our study evaluates the clinical value of a skin care cream with the transient receptor potential vanilloid type 1 inhibitor 4-t-butylcyclohexanol in POD patients over 8 weeks. METHODS: This open, unblinded 8-week clinical trial included 48 patients. A skin care cream containing 4-t-butylcyclohexanol was applied over a period of 8 weeks. Standardized questionnaires were used at baseline, 4 and 8 weeks, for history documentation, objective and subjective severity scores, and quality of life assessments. Six different skin physiology parameters were assessed at all timepoints. RESULTS: The perioral dermatitis severity score decreased significantly during the treatment period. This was mirrored by significantly lower patients' subjective numerical rating score and an improved quality of life score. Transepidermal water loss, stratum corneum hydration and skin erythema improved significantly during the treatment period. CONCLUSION: This transient receptor potential vanilloid type 1 inhibitor-based skin care cream improved subjective and objective parameters of perioral dermatitis. Decreased transepidermal water loss values and increased stratum corneum hydration demonstrate a restored skin barrier function. Consequently, the topical inhibition of these receptors is a promising management option for POD.

Selective Nerve Fibre Activation in Patients with Generalized Chronic Pruritus: Hint for Central Sensitization?

Central sensitization induces pain augmentation in chronic pain states. An analogous mechanism is speculated for chronic pruritus. This study compared patients with chronic pruritus (n = 79) of different origins (atopic dermatitis, chronic pruritus on non-lesional skin, chronic prurigo) and healthy controls (HC, n = 54) with regard to itch intensity and qualities of sensory symptoms after selective peripheral nerve fibre activation by electrical stimulation at 5 Hz (surrogate for C-fibre function) and 2,000 Hz (surrogate for Aß-fibre function) using a Neurometer®. Electrically-induced itch was more intense in patients with chronic pruritus than in HC, but patients with chronic pruritus did not report "itch" more often than HC at 5 Hz. Stimulation at 2,000 Hz induced more pricking and tingling, but less throbbing in patients with chronic pruritus compared with HC. Treatment with cooling compound reduced clinical and experimental itch, but did not alter the distribution of sensory symptoms. These data show hyperknesis in chronic pruritus of various origins, arguing for common central sensitization mechanisms.

Efficacy and Tolerability of a Cosmetic Skin Care Product With Trans-4-t-butylcyclohexanol and Licochalcone A in Subjects With Sensitive Skin Prone to Redness and Rosacea.

BACKGROUND: Sensitive skin and rosacea are skin conditions, which may affect the quality of life of the patients considerably. In vitro and in vivo data indicated that the combination of trans-t-butylcyclohexanol and licochalcone A is an effective combination for alleviating the increased sensitivity of rosacea subtype I.

OBJECTIVE: Objective of this open dermocosmetic study was to investigate the efficacy and tolerability of a skin care product containing the anti-inflammatory licochalcone A and the TRPV1 antagonist trans-t-butylcyclohexanol in subjects with sensitive skin prone to redness and rosacea.

METHODS: 1221 subjects with sensitive skin and rosacea stage 0-II applied the test product twice daily for 4 weeks. Clinical assessment of sensitive skin and rosacea symptoms were performed at baseline and after 4 weeks. Additionally, at treatment end the test subjects filled a self-assessment questionnaire.

RESULTS: After 4 weeks of application, both, clinical and subjective assessment have shown improvement of all symptoms of sensitive skin and rosacea in a significant number of subjects (P less than 0.001). The test product was efficacious and very well tolerated also when used in conjunction with pharmacological treatments of the skin condition under scrutiny.

Conclusions: The study confirmed the good tolerability and efficacy of the skin care product in the management of sensitive skin prone to redness and rosacea when used alone or in combination with other therapies.

J Drugs Dermatol. 2017;16(6):605-611.

Dynamic Pruritus Score: Evaluation of the Validity and Reliability of a New Instrument to Assess the Course of Pruritus.

Currently valid itch intensity scales, such as the visual analogue scale (VAS), are indispensable, but they can be influenced by the patient's overall health status. The aim of this study was to evaluate the reliability and validity of the Dynamic Pruritus Score (DPS), a new instrument comparing reduction in current pruritus with a defined earlier time-point. Eighty-one randomly selected adults (50 females, mean age 53.9 years) recorded their pruritus at visit 1 and repeatedly at visit 2 on the DPS, VAS, numerical rating scale, and on health status questionnaires (EuroQol; EQ-5D), skin-related quality of life (Dermatology Life Quality Index; DLQI), anxiety and depression (Hospital Anxiety and Depression Scale; HADS) and patient benefit (Patient Benefit Index; PBI). Intraclass correlation showed high reliability for both DPS and VAS (r < 0.9, p < 0.001), while the DPS has shown higher concurrent validity (rDPS to PBI = 0.570; p < 0.001). The DPS can then be considered an alternative instrument to the VAS for assessment of pruritus in adults. Further research is needed to confirm these results with a more representative sample size.

Impaired glyoxalase activity is associated with reduced expression of neurotrophic factors and pro-inflammatory processes in diabetic skin cells.

Patients suffering from type II diabetes develop several skin manifestations including cutaneous infections, diabetic dermopathy, diabetic bullae and acanthosis nigricans. Diabetic micro- and macroangiopathy as well as diabetic neuropathy are believed to play a crucial role in the development of diabetic skin disorders. A reduced cutaneous nerve fibre density was reported in diabetic subjects, which subsequently leads to impaired sensory nerve functions. Using an innervated skin model, we investigated the impact of human diabetic dermal fibroblasts and keratinocytes on porcine sensory neurons. Diabetic skin cells showed a reduced capacity to induce neurite outgrowth due to a decreased support with neurotrophic factors, such as NGF. Furthermore, diabetic keratinocytes displayed insulin resistance and increased expression of pro-inflammatory cytokines demonstrating the persistent effect of diabetes mellitus on human skin cells. Dysregulations were related to a significantly reduced glyoxalase enzyme activity in diabetic keratinocytes as experimentally reduced glyoxalase activity mimicked the increase in pro-inflammatory cytokine expression and reduction in NGF. Our results demonstrate an impaired crosstalk of diabetic skin cells and sensory neurons favouring hypo-innervation. We suggest that reduced methylglyoxal detoxification contributes to an impaired neurocutaneous interaction in diabetic skin.

Efficacy and Tolerability of Steroid-Free, Over-the-Counter Treatment Formulations in Infants and Children With Atopic Dermatitis.

BACKGROUND: Two steroid-free, over-the-counter skin protectant products have been developed for the care and treatment of atopic dermatitis (AD)-Eucerin Eczema Relief Body Crème (Body Cream) for daily skin moisturization and Eucerin Eczema Relief Instant Therapy cream (Instant Therapy) for treatment of AD flare-ups. We tested the efficacy and tolerability of these formulations in infants and children with AD. METHODS: Study 1: Body Cream was applied twice daily to the lower legs of 64 children with a history of AD (aged 3 months to 12 years) for 14 days. Study 2: Instant Therapy was applied to active lesions and surrounding skin of 29 children (aged 3 months to 12 years) with active atopic lesions. Assessments were performed at baseline and Days 7 and 14. Symptoms were assessed using the Atopic Dermatitis Severity Index in Study 2. RESULTS: Body Cream significantly improved skin hydration and reduced itching, burning/stinging, erythema, and tactile roughness. Instant Therapy significantly improved skin hydration and AD symptoms, notably pruritus, erythema, and lichenification. Both products were safe and well tolerated. DISCUSSION: Body Cream and Instant Therapy were effective and well tolerated in the treatment of AD in children. These products provide steroid-free, nonprescription therapy for the maintenance and treatment of acute eczema and were proven effective and safe in infants as young as 3 months.

UV radiation induces CXCL5 expression in human skin.

CXCL5 has recently been identified as a mediator of UVB-induced pain in rodents. To compare and to extend previous knowledge of cutaneous CXCL5 regulation, we performed a comprehensive study on the effects of UV radiation on CXCL5 regulation in human skin. Our results show a dose-dependent increase in CXCL5 protein in human skin after UV radiation. CXCL5 can be released by different cell types in the skin. We presumed that, in addition to immune cells, non-immune skin cells also contribute to UV-induced increase in CXCL5 protein. Analysis of monocultured dermal fibroblasts and keratinocytes revealed that only fibroblasts but not keratinocytes displayed up regulated CXCL5 levels after UV stimulation. Whereas UV treatment of human skin equivalents, induced epidermal CXCL5 mRNA and protein expression. Up regulation of epidermal CXCL5 was independent of keratinocyte differentiation and keratinocyte-keratinocyte interactions in epidermal layers. Our findings provide first evidence on the release of CXCL5 in UV-radiated human skin and the essential role of fibroblast-keratinocyte interaction in the regulation of epidermal CXCL5.

Licochalcone A activates Nrf2 in vitro and contributes to licorice extract-induced lowered cutaneous oxidative stress in vivo.

The retrochalcone licochalcone A (LicA) has previously been shown to possess antimicrobial and anti-inflammatory properties. In this study, we focused on pathways responsible for the antioxidative properties of LicA. In vitro, LicA protected from oxidative stress mediated by reactive oxygen species (ROS) by activating the expression of cytoprotective phase II enzymes. LicA induced nuclear translocation of NF-E2-related factor 2 (Nrf2) in primary human fibroblasts and elevated the expression of the cytoprotective and anti-inflammatory enzymes heme oxygenase 1 and glutamate-cysteine ligase modifier subunit. LicA-treated cells displayed a higher ratio of reduced to oxidized glutathione and decreased concentrations of ROS in UVA-irradiated human dermal fibroblasts, as well as in activated neutrophils. In vivo, ultraweak photon emission analysis of skin treated with LicA-rich licorice extract revealed a significantly lowered UVA-induced luminescence, indicative for a decrease in oxidative processes. We conclude from these data that topical application of licorice extract is a promising approach to induce Nrf2-dependent cytoprotection in human skin.

Steroid-free emollient formulations reduce symptoms of eczema and improve quality of life.

Two over-the-counter products have been clinically tested for efficacy and tolerability in the treatment of atopic dermatitis. Study 1 evaluated a daily maintenance Body Cream (Eucerin Eczema Relief Body Crème) applied twice daily for 14 days, followed by treatment withdrawal for 5 days (regression period) in subjects with a history of atopic dermatitis. Study 2 evaluated an acute treatment (Eucerin Eczema Relief Instant Therapy [Instant Therapy]) for active atopic dermatitis lesions administered for 14 days. Skin barrier function, hydration, tolerability, and relief of symptoms were assessed at baseline, day 7, and day 14. Study 2 also measured itch relief and treatment impact on work, social activities, and sleep. Body Cream significantly improved skin hydration and barrier function (P<.001) at 14 days, with improvements persisting through the 5-day regression phase. Itching was significantly improved in 93.8% of subjects (P<.001). Instant Therapy treatment of atopic dermatitis lesions significantly improved skin hydration and barrier function, as well as symptoms of erythema, pruritus, excoriation, and lichenification, with rapid improvement of itch reported within minutes of the first treatment application. Instant Therapy significantly reduced itch intensity and frequency, and demonstrated beneficial improvements in subjects' quality of life. Body Cream and Instant Therapy were both safe and well tolerated.

Chemosensory information processing between keratinocytes and trigeminal neurons.

Trigeminal fibers terminate within the facial mucosa and skin and transmit tactile, proprioceptive, chemical, and nociceptive sensations. Trigeminal sensations can arise from the direct stimulation of intraepithelial free nerve endings or indirectly through information transmission from adjacent cells at the peripheral innervation area. For mechanical and thermal cues, communication processes between skin cells and somatosensory neurons have already been suggested. High concentrations of most odors typically provoke trigeminal sensations in vivo but surprisingly fail to activate trigeminal neuron monocultures. This fact favors the hypothesis that epithelial cells may participate in chemodetection and subsequently transmit signals to neighboring trigeminal fibers. Keratinocytes, the major cell type of the epidermis, express various receptors that enable reactions to multiple environmental stimuli. Here, using a co-culture approach, we show for the first time that exposure to the odorant chemicals induces a chemical communication between human HaCaT keratinocytes and mouse trigeminal neurons. Moreover, a supernatant analysis of stimulated keratinocytes and subsequent blocking experiments with pyrodoxalphosphate-6-azophenyl-2',4'-disulfonate revealed that ATP serves as the mediating transmitter molecule released from skin cells after odor stimulation. We show that the ATP release resulting from Javanol® stimulation of keratinocytes was mediated by pannexins. Consequently, keratinocytes act as chemosensors linking the environment and the trigeminal system via ATP signaling.

Oxytocin modulates proliferation and stress responses of human skin cells: implications for atopic dermatitis.

The neuropeptide hormone oxytocin (OXT) mediates a wide spectrum of tissue-specific actions, ranging from cell growth, cell differentiation, sodium excretion to stress responses, reproduction and complex social behaviour. Recently, OXT expression was detected in keratinocytes, but expression of its receptor and function are still unexplored in human skin. Here, we showed that both OXT and its receptor are expressed in primary human dermal fibroblasts and keratinocytes. OXT-induced dose-dependent calcium fluxes in both cell types demonstrating that the OXT receptor (OXTR) is functionally expressed. We also showed that OXT decreases proliferation of dermal fibroblasts and keratinocytes in a dose-dependent manner. In order to further investigate OXT-mediated functions in skin cells, we performed OXTR knockdown experiments. OXTR knockdown in dermal fibroblasts and keratinocytes led to elevated levels of reactive oxygen species and reduced levels of glutathione (GSH). Moreover, OXTR-depleted keratinocytes exhibited an increased release of the pro-inflammatory cytokines IL6, CCL5 and CXCL10. Our data indicate that the OXT system modulates key processes which are dysregulated in atopic dermatitis (AD) such as proliferation, inflammation and oxidative stress responses. Furthermore, we detected a downregulation of the OXT system in peri-lesional and lesional atopic skin. Taken together, these data suggest that the OXT system is a novel neuroendocrine mediator in human skin homoeostasis and clinically relevant to stressed skin conditions like AD.

Role of fibroblasts in the pathogenesis of atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) is a common dermatosis that highly impairs a patient's quality of life. The recent discovery that epidermal barrier defects caused by an aberrant differentiation process of keratinocytes are comparably important to the well-characterized changes in immune response patterns attributed a crucial role to the keratinocytes. Fibroblasts are able to alter proliferation and differentiation of keratinocytes, but their role in AD is not yet fully understood. OBJECTIVE: We sought to determine the role of fibroblasts in skin proliferation and differentiation in patients with AD. METHODS: We used human 3-dimensional organotypic skin cultures consisting of atopic fibroblasts and healthy keratinocytes, as well as healthy fibroblasts and atopic keratinocytes, and compared them with their controls. The expression of differentiation markers in these organotypic cultures were analyzed by using immunohistology and quantitative RT-PCR. Furthermore, the fundamental role of fibroblast-secreted leukemia inhibitory factor was assessed by using small interfering RNA-mediated knockdown cultures. RESULTS: We observed that atopic fibroblasts influence the proliferation of keratinocytes and the terminal differentiation process, resulting in an in vivo-like morphology of AD. Subsequently, healthy fibroblasts were able to restore the structural deficits of the epidermis consisting of atopic keratinocytes. Partially, these effects were due to a reduced expression of the differentiation-associated cytokine leukemia inhibitory factor by atopic fibroblasts. CONCLUSION: These data demonstrate that fibroblasts and the modulation of fibroblast-derived factors might be new therapeutic targets for the alleviation of AD.

Epidermal nerve fibers modulate keratinocyte growth via neuropeptide signaling in an innervated skin model.

Atopic eczema is a chronic inflammatory skin disease characterized by cutaneous nerve fiber sprouting and epidermal hyperplasia, pointing to an involvement of the peripheral nervous system in cutaneous homeostasis. However, the interaction of sensory neurons and skin cells is poorly understood. Using an innervated skin model, we investigated the influence of sensory neurons on epidermal morphogenesis. Neurons induced the proliferation of keratinocytes, resulting in an increase in the epidermal thickness. Inhibition of calcitonin gene-related peptide (CGRP), but not substance P (SP) signaling, reversed this effect. Human CGRP enhanced keratinocyte proliferation and epidermal thickness in skin models, demonstrating a key role of CGRP in modulating epidermal morphogenesis, whereas SP had only a moderate effect. Innervated skin models composed of atopic skin cells showed increased neurite outgrowth, accompanied by elevated CGRP release. As atopic keratinocytes were sensitized to CGRP owing to higher expression levels of the CGRP receptor components, receptor activity-modifying protein 1 (RAMP1) and receptor component protein (RCP), atopic innervated skin models displayed a thicker epidermis than did healthy controls. We conclude that neural CGRP controls local keratinocyte growth. Our results show that the crosstalk of the cutaneous peripheral nervous system and skin cells significantly influences epidermal morphogenesis and homeostasis in healthy and atopic skin.

Atopic keratinocytes induce increased neurite outgrowth in a coculture model of porcine dorsal root ganglia neurons and human skin cells.

Skin of patients suffering from atopic eczema displays a higher epidermal nerve fiber density, associated with neurogenic inflammation and pruritus. Using an in vitro coculture system, allowing a spatially compartmented culture of somata from porcine dorsal root ganglion neurons and human primary skin cells, we investigated the influence of dermal fibroblasts and keratinocytes on neurite outgrowth. In comparison with dermal fibroblasts, keratinocytes induced more branched and less calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers. By adding neutralizing antibodies, we showed that nerve growth factor (NGF) and glial cell-line-derived neurotrophic factor (GDNF) are pivotal neurotrophic factors of skin cell-induced neurite outgrowth. Keratinocytes and dermal fibroblasts secreted different ratios of neurotrophic factors, influencing morphology and CGRP immunoreactivity of neurites. To investigate changes of the peripheral nervous system in the pathogenesis of atopic eczema in vitro, we analyzed neurite outgrowth mediated by atopic skin cells. Atopic keratinocytes produced elevated levels of NGF and mediated an increased outgrowth of CGRP-positive sensory fibers. Our results demonstrate the impact of dermal fibroblasts and keratinocytes on skin innervation and emphasize the role of keratinocytes as key players of hyperinnervation in atopic eczema.

UV radiation induces the release of angiopoietin-2 from dermal microvascular endothelial cells.

In human skin, ultraviolet radiation (UVR)-induced erythema is characterized by the inflammatory and angiogenic activation of dermal endothelial cells. Recently, it has been shown that the release of angiopoietin-2 (Ang-2) from cytoplasmic storages of activated endothelial cells is crucial for the induction of inflammation and angiogenesis. Therefore, we hypothesized that UVR exposure induces the release of Ang-2 from endothelial cells controlling the early steps of erythema formation. In an in vivo study, suction blister fluids generated from UV-irradiated skin showed significantly increased concentrations of Ang-2, vascular endothelial growth factor (VEGF) and tumor necrosis factor-α (TNFα). Likewise, in vitro UVR exposure of human dermal microvascular endothelial cells (HDMECs) triggered the release of Ang-2 that enhanced the pro-inflammatory response of these cells and facilitated their detachment from smooth muscle cells as evidenced by employing a three-dimensional co-culture spheroid model. These effects were inhibited by angiopoietin-1 (Ang-1), which competes with Ang-2 for binding the endothelial cell Tie2 receptor. Collectively, these observations suggest that UVR triggers the release of endothelial Ang-2 which may promote the destabilization and pro-inflammatory phenotype of the microvascular endothelium. As Ang-1 counteracts UVR-induced effects, stimulating the Ang-1 activity may represent a strategy to stabilize the dermal microcirculatory system, thus protecting against UVR-induced skin damages.

TRP-channel-specific cutaneous eicosanoid release patterns.

Analyzing mechanisms and key players in peripheral nociception nonneuronal skin cells are getting more and more into focus. Herein we investigated the functional expression of TRPV1 and TRPA1 in human keratinocytes and fibroblasts and assessed proinflammatory lipid mediator release upon their stimulation as well as sensory effects after topical application, combining in vitro and in vivo approaches. In vitro, the expression of functional TRPV1 and TRPA1 channels on fibroblasts and keratinocytes was confirmed via immunofluorescence, qualitative real time (RT) polymerase chain reaction, and cellular Ca(2+) influx measurements. Additionally, the agonists allyl isothiocyanate (TRPA1) and capsaicin (TRPV1) induce a differential secretion pattern of the eicosanoids PGE(2) and LTB(4) in human dermal fibroblasts and keratinocytes, which was also detectable invivo, analyzing suction blister fluid at various times after short-term topical application. Capsaicin provoked the release of LTB(4) at 2 and 24 hours. In contrast, PGE(2) levels were reduced upon stimulation. Allyl isothiocyanate, however, increased PGE(2) levels only at 24 hours, but did not alter LTB(4) levels. In parallel, heat pain thresholds were reduced by both agents after short-term topical application, but only AITC provoked a long-lasting local erythema. In conclusion, the agonist-induced activation of nociceptors by TRPA1 and TRPV1 elicits painful sensations, whereas nonneuronal tissue cells respond with differential release of inflammatory mediators, thus influencing local vasodilatation and neuronal sensitization. These results have implications for the application of transient receptor potential antagonists to improve inflammatory skin conditions and pain management.

Expression of cyclooxygenase isozymes during morphogenesis and cycling of pelage hair follicles in mouse skin: precocious onset of the first catagen phase and alopecia upon cyclooxygenase-2 overexpression.

Cyclooxygenase (COX)-1 and -2 catalyze the key reaction in prostaglandin biosynthesis. Whereas COX-1 is found in most tissues, COX-2, with a few exceptions, is not expressed in normal tissues but becomes transiently induced in the course of inflammatory reactions. In many neoplastic epithelia, COX-2 is constitutively overexpressed. Here we show that COX isozymes are spatiotemporally expressed during morphogenesis of dorsal skin epithelium of NMRI mice. COX-1 and COX-2 mRNA and protein were detected in embryonic and postnatal epidermal tissue by RT-PCR, northern blot, and immunoblot analysis indicating that both isoforms may contribute to prostaglandin production. Being barely detectable in interfollicular epidermis and resting hair follicles of adult mice, COX-2 protein appeared in embryonic skin first in epidermal precursor cells and later on in the basal cells and the peridermal layer of the stratified epidermis. In the course of pelage hair follicle morphogenesis, COX-2 remained expressed in the basal interfollicular compartment and, in addition, became apparent in elongated hair germs and hair pegs and later on in the outer root sheath cells of the distal and proximal hair follicles as well as in basal sebaceous gland cells. During the subsequent synchronous phases of hair cycling, COX-2 expression declined in catagen, was barely detectable in telogen, and was reinduced in the basal outer root sheath and basal sebaceous gland cells of anagen hair follicles. COX-1 immunosignals were detected predominantly in the interfollicular spinous and granular layers of the developing, neonatal, and adult epidermis but not in follicular epithelial cells of developing or cycling hair follicles. Dendritic cells in the interfollicular epidermis and distal hair follicles were also COX-1-positive. Transgenic overexpression of COX-2 under the control of a keratin 5 promoter in basal cells of the interfollicular and follicular epidermis induced a precocious entry into the first catagen stage of postnatal hair follicle cycling and a subsequent disturbance of hair follicle phasing. Furthermore, transgenic mice developed an alopecia. Inhibition of transgenic COX-2 activity by feeding the specific COX-2 inhibitor valdecoxib suppressed the development of alopecia, indicating that COX-2-mediated prostaglandin synthesis is involved in hair follicle biology.

Mouse skin as a model for cancer chemoprevention by nonsteroidal anti-inflammatory drugs.

The mouse skin model of multistage carcinogenesis has demonstrated that cancer results from a synergism between genotoxic and nongenotoxic factors. The former induce irreversible genetic alterations, whereas the latter promote tumor development by favoring the clonal outgrowth of the genetically altered cells. While therapeutic gene repair is a still unrealized dream, tumor promotion provides an attractive target for cancer prevention. A key event in epithelial tumor development is an aberrant constitutive overexpression of cyclooxygenase-2 (COX-2), being detectable already in premalignant lesions and leading to an overproduction of prostaglandins. In the mouse skin model, prostaglandin F2alpha has been identified as an endogenous tumor promoter. The well-established chemopreventive effect of nonsteroidal anti-inflammatory drugs seems to be mainly due to COX-2 inhibition. Targeted transgenic overexpression of COX-2 in mouse epidermis induces a preneoplastic phenotype and renders the tissue extremely sensitive to genotoxic carcinogens; i.e., for the induction of skin tumor development, tumor promoter treatment can be omitted in those animals. It is concluded that COX-2 acts as an endogenous tumor promoter and that its overexpression represents a first order risk factor for cancer development. Conversely, specific COX-2 inhibitors rank among the most promising agents for cancer chemoprevention.

Transgenic cyclooxygenase-2 overexpression sensitizes mouse skin for carcinogenesis.

Genetic and pharmacological evidence suggests that overexpression of cyclooxygenase-2 (COX-2) is critical for epithelial carcinogenesis and provides a major target for cancer chemoprevention by nonsteroidal antiinflammatory drugs. Transgenic mouse lines with keratin 5 promoter-driven COX-2 overexpression in basal epidermal cells exhibit a preneoplastic skin phenotype. As shown here, this phenotype depends on the level of COX-2 expression and COX-2-mediated prostaglandin accumulation. The transgenics did not develop skin tumors spontaneously but did so after a single application of an initiating dose of the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). Long-term treatment with the tumor promoter phorbol 12-myristate 13-acetate, as required for tumorigenesis in wild-type mice, was not necessary for transgenics. The ratios of squamous cell carcinomas to papillomas and of sebaceous gland adenomas to papillomas plus squamous cell carcinomas were increased markedly in transgenic mice treated with DMBA alone compared with DMBA/phorbol 12-myristate 13-acetate-treated transgenic and wild-type mice. Thus, COX-2 overexpression, which leads to high levels of epidermal prostaglandin E(2), prostaglandin F(2alpha), and 15-deoxy(delta12,14)-PGJ(2), is insufficient for tumor induction but transforms epidermis into an "autopromoted" state, i.e., dramatically sensitizes the tissue for genotoxic carcinogens.