UV-irradiated Mice Research Articles

Effects of red ginseng extract on UVB irradiation-induced skin aging in hairless mice

Panax ginseng C.A. Meyer, Korean herb medicine, has been widely used in China and Japan for fatigue and enhancement of resistance to many diseases. Aim of the study This study is aimed to assess the effects of Korean red ginseng extract on UVB irradiation induced skin aging in hairless mice. Materials and methods Red ginseng extracts prepared with ethanol were used in this study. To standardize Korean red ginseng, it was analyzed by HPLC. And inhibitory effects of red ginseng extract on UVB irradiation-induced skin aging in hairless mice were determined by the measurement of wrinkle, expression of type I procollagen and MMP-1 and immunohistology. Results Based on the HPLC quantitative analysis, ginsenoside Rb1 content in Korean red ginseng was 43.5 mg/g of extract. In the result of body weight gain and food efficiency rate, body weights of all groups were increased during experimental periods. In the wrinkle measurement and image analysis of skin replicas, the results showed that the dietary supply containing red ginseng extract significantly inhibited wrinkle formation caused by chronic UVB irradiation. In the changes of expression of procollagen type I and MMP-1 in the skin of UV irradiated hairless mice fed dietary supplement containing 2.5% red ginseng extract, level of mRNA of procollagen type I was decreased. But protein level of that was increased. And in terms of MMP-1, either mRNA or protein levels of MMP-1 were significantly decreased. These results showed anti-wrinkle effect of Korean red ginseng involved the inhibition of collagen degradation rather than increased collagen synthesis. Conclusion It is shown that Korean red ginseng may be functional food candidate for skin photoaging.

Photoprotective effect of red ginseng against ultraviolet radiation‐induced chronic skin damage in the hairless mouse

To evaluate the ability of red ginseng (RG) to protect the skin from photodamage, the gross and microscopic changes in the skin of hairless mice and RG-treated mice exposed chronically to UV were examined. The skin of the UV-irradiated mice showed characteristic signs of photoaging, such as deep wrinkles across the back, increased epidermal thickness, numerous cell infiltration, and many enlarged keratinizing cysts. The RG-treated mice showed a significantly decreased wrinkling score, minimal epidermal hyperplasia, slightly increased dermal cellularity and lack of proliferation of cysts. By week 22, 88.9% (i.p. with saline) or 60.0% (topical administration with cream base) of the UV-irradiated mice developed at least one tumor. RG delayed tumor onset significantly. RG was also effective in reducing the occurrence of UV radiation-induced skin tumors and reduced the number of tumors per mouse. After 22 weeks of treatment, 57.1% (i.p.) or 85.7% (topical administration) of the mice treated with RG were tumor-free. Tumor multiplicity was reduced by 89.3% (i.p.) or 92.2% (topical administration) in the RG treated groups. It is noted that skin that is chronically exposed to UV is subject to photoaging and photocarcinogenesis and the regular use of RG would prevent these photodamaging effects of UV.

Inhibition of Photocarcinogenesis by Platelet-Activating Factor or Serotonin Receptor Antagonists

The UV radiation in sunlight is the primary cause of nonmelanoma skin cancer. Moreover, UV exposure induces immune suppression. Early steps in the cascade of events leading to immune suppression are the binding of UV-induced platelet-activating factor (PAF) to its receptor and the binding of cis-urocanic acid, a photoreceptor for UVB radiation, to the serotonin (5-HT(2A)) receptor. Here, we tested the hypothesis that blocking the binding of PAF and 5-HT(2A) to their receptors would also block skin cancer induction. Hairless mice were injected with PAF or serotonin receptor antagonists and then exposed to solar-simulated UV radiation. We noted a significant and substantial decrease in skin cancer incidence in mice treated with the PAF or 5-HT(2A) receptor antagonists. Also, the PAF and/or serotonin receptor antagonists blocked skin cancer progression. The PAF and serotonin receptor antagonists worked in a synergistic fashion to block skin cancer induction. We also measured the effect that injecting PAF and 5-HT(2A) receptor antagonists had on UV-induced skin damage after a single UV exposure. We noted a significant decrease in UV-induced hypertrophy, sunburn cell formation, and apoptosis when the mice were injected with PAF and/or 5-HT(2A) receptor antagonists. These data indicate that treating UV-irradiated mice with PAF and 5-HT(2A) receptor antagonists blocks skin cancer induction in vivo, in part by reversing UV-induced damage to the skin and by preventing the induction of immune suppression.

Topical Thymidine Dinucleotide Treatment Reduces Development of Ultraviolet-Induced Basal Cell Carcinoma in Ptch-1+/− Mice

Treatment with thymidine dinucleotide (pTT) has well documented DNA-protective effects and reduces development of squamous cell carcinoma in UV-irradiated mice. The preventive effect of pTT on basal cell carcinoma (BCC) was evaluated in UV-irradiated Ptch-1(+/-) mice, a model of the human disease Gorlin syndrome. Topical pTT treatment significantly reduced the number and size (P < 0.001) of BCCs in murine skin after 7 months of chronic irradiation. Skin biopsies collected 24 hours after the final UV exposure showed that pTT reduced the number of nuclei positive for cyclobutane pyrimidine dimers by 40% (P < 0.0002) and for 8-hydroxy-2'-deoxyguanosine by 61% (P < 0.01 compared with vehicle control). Immunostaining with an antibody specific for mutated p53 revealed 63% fewer positive patches in BCCs of pTT-treated mice compared with controls (P < 0.01), and the number of Ki-67-positive cells was decreased by 56% (P < 0.01) in pTT-treated tumor-free epidermis and by 76% (P < 0.001) in BCC tumor nests (P < 0.001). Terminal dUTP nick-end labeling staining revealed a 213% increase (P < 0.04) in the number of apoptotic cells in BCCs of pTT-treated mice. Cox-2 immunostaining was decreased by 80% in tumor-free epidermis of pTT-treated mice compared with controls (P < 0.01). We conclude that topical pTT treatment during a prolonged period of intermittent UV exposure decreases the number and size of UV-induced BCCs through several anti-cancer mechanisms.

Mast Cell Migration from the Skin to the Draining Lymph Nodes upon Ultraviolet Irradiation Represents a Key Step in the Induction of Immune Suppression

The UV radiation in sunlight is the primary cause of skin cancer. UV is also immunosuppressive and numerous studies have shown that UV-induced immune suppression is a major risk factor for skin cancer induction. Previous studies demonstrated that dermal mast cells play a critical role in the induction of immune suppression. Mast cell-deficient mice are resistant to the immunosuppressive effects of UV radiation, and UV-induced immune suppression can be restored by injecting bone marrow-derived mast cells into the skin of mast cell- deficient mice. The exact process however, by which mast cells contribute to immune suppression, is not known. In this study, we show that one of the first steps in the induction of immune suppression is mast cell migration from the skin to the draining lymph nodes. UV exposure, in a dose-dependent manner, causes a significant increase in lymph node mast cell numbers. When GFP(+) skin was grafted onto mast cell-deficient mice, we found that GFP(+) mast cells preferentially migrated into the lymph nodes draining the skin. The mast cells migrated primarily to the B cell areas of the draining nodes. Mast cells express CXCR4(+) and UV exposure up-regulated the expression of its ligand CXCL12 by lymph node B cells. Treating UV-irradiated mice with a CXCR4 antagonist blocked mast cell migration and abrogated UV-induced immune suppression. Our findings indicate that UV-induced mast cell migration to draining lymph nodes, mediated by CXCR4 interacting with CXCL12, represents a key early step in UV-induced immune suppression.

A dicyanotriterpenoid induces cytoprotective enzymes and reduces multiplicity of skin tumors in UV-irradiated mice

Inducible phase 2 enzymes constitute a primary line of cellular defense. The oleanane dicyanotriterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-onitrile (TP-225) is a very potent inducer of these systems. Topical application of TP-225 to SKH-1 hairless mice increases the levels of NAD(P)H-quinone acceptor oxidoreductase 1 (NQO1) and heme oxygenase 1 (HO-1) and protects against UV radiation-induced dermal thickening. Daily topical treatments of 10 nmol of TP-225 to the backs of mice that were previously subjected to low-level chronic UVB radiation (30 mJ/cm 2/session, twice a week for 17 weeks), led to 50% reduction in multiplicity of skin tumors. In addition, the total tumor burden of squamous cell carcinomas was reduced by 5.5-fold. The identification of new agents for protection against UV radiation-induced skin cancer and understanding of their mechanism(s) of action is especially important in view of the fact that human skin cancers represent a significant source of increasing morbidity and mortality.

Post-immune UV irradiation induces Tr1-like regulatory T cells that suppress humoral immune responses

It is well documented that UV radiation present in sunlight suppresses immune responses, especially T(h)1-driven cellular immune responses, resulting in the exacerbation of skin cancer and infectious diseases. However, the effects of UV irradiation on humoral immune responses remain less clearly defined. In addition, the majority of studies documenting immunosuppressive effects of UV irradiation has been demonstrated in animals exposed to UV radiation before immunization. In the present study, therefore, we examined the effects of UV irradiation on humoral immune responses in mice that had been immunized before UV irradiation. Both T(h)1- and T(h)2-associated Ig responses were significantly suppressed by UV irradiation given 7 days after immunization in an antigen-specific manner. Adoptive transfer experiments revealed that CD4(+) T cells from UV-irradiated mice are responsible for the UV-induced suppression of antibody responses. These CD4(+) regulatory T cells suppressed proliferation of conventional CD4(+) T cells in vivo and in vitro and contained IL-10-producing cells that did not express Foxp3. Mice depleted of CD25(+) cells also exhibited reduced antibody responses by UV irradiation. Finally, we showed that CD4(+) T cells from UV-irradiated mice treated with anti-IL-10 mAb failed to suppress antibody responses upon transfer. These results indicate that UV irradiation after immunization suppresses T(h)1- and T(h)2-mediated humoral immunity via the generation of Tr1-like regulatory T cells, in the process of which IL-10 appears to be important. Possible detrimental effects of UV irradiation after vaccination are also discussed.

Sequential Down-regulation of E-Cadherin with Squamous Cell Carcinoma Progression: Loss of E-Cadherin via a Prostaglandin E2-EP2–Dependent Posttranslational Mechanism

The incidence of skin cancer is on the rise, with over 1 million new cases yearly. Although it is known that squamous cell cancers (SCC) are caused by UV light, the mechanism(s) involved remains poorly understood. In vitro studies with epithelial cells or reports examining malignant skin lesions suggest that loss of E-cadherin-mediated cell-cell contacts may contribute to SCCs. Other studies show a pivotal role for cyclooxygenase-dependent prostaglandin E2 (PGE2) synthesis in this process. Using chronically UV-irradiated SKH-1 mice, we show a sequential loss of E-cadherin-mediated cell-cell contacts as lesions progress from dysplasia to SCCs. This E-cadherin down-regulation was also evident after acute UV exposure in vivo. In both chronic and acute UV injury, E-cadherin levels declined at a time when epidermal PGE2 synthesis was enhanced. Inhibition of PGE2 synthesis by indomethacin in vitro, targeted deletion of EP2 in primary mouse keratinocyte (PMK) cultures or deletion of the EP2 receptor in vivo abrogated this UV-induced E-cadherin down-regulation. In contrast, addition of PGE2 or the EP2 receptor agonist butaprost to PMK produced a dose- and time-dependent decrease in E-cadherin. We also show that UV irradiation, via the PGE2-EP2 signaling pathway, may initiate tumorigenesis in keratinocytes by down-regulating E-cadherin-mediated cell-cell contacts through its mobilization away from the cell membrane, internalization into the cytoplasm, and shuttling through the lysosome and proteasome degradation pathways. Further understanding of how UV-PGE2-EP2 down-regulates E-cadherin may lead to novel chemopreventative strategies for the treatment of skin and other epithelial cancers.

What's new in photoimmunology?

What's new in photoimmunology?

Ultraviolet radiation triggers apoptosis of fibroblasts and skin keratinocytes mainly via the BH3-only protein Noxa

To identify the mechanisms of ultraviolet radiation (UVR)–induced cell death, for which the tumor suppressor p53 is essential, we have analyzed mouse embryonic fibroblasts (MEFs) and keratinocytes in mouse skin that have specific apoptotic pathways blocked genetically. Blocking the death receptor pathway provided no protection to MEFs, whereas UVR-induced apoptosis was potently inhibited by Bcl-2 overexpression, implicating the mitochondrial pathway. Indeed, Bcl-2 overexpression boosted cell survival more than p53 loss, revealing a p53-independent pathway controlled by the Bcl-2 family. Analysis of primary MEFs lacking individual members of its BH3-only subfamily identified major initiating roles for the p53 targets Noxa and Puma. In the transformed derivatives, where Puma, unexpectedly, was not induced by UVR, Noxa had the dominant role and Bim a minor role. Furthermore, loss of Noxa suppressed the formation of apoptotic keratinocytes in the skin of UV-irradiated mice. Collectively, these results demonstrate that UVR activates the Bcl-2–regulated apoptotic pathway predominantly through activation of Noxa and, depending on cellular context, Puma.

Deletion of Prostaglandin E2 EP2 Receptor Protects against Ultraviolet-Induced Carcinogenesis, but Increases Tumor Aggressiveness

Ultraviolet (UV) light is a complete carcinogen inducing and promoting squamous-cell carcinoma (SCC) of the skin. Recent work has shown that SCC initiation and promotion are enhanced by prostaglandin E2 (PGE2). PGE2 interacts with specific EP receptors to regulate cellular functions. Previous work from our group has shown that the prostaglandin E2 EP2 receptor is a powerful regulator of keratinocyte growth. SKH-1 hairless mice lacking the EP2 receptor were therefore studied to understand how this growth signaling pathway contributes to photocarcinogenesis. Our data indicate that UV-irradiated mice lacking EP2 receptors exhibit decreased proliferation and a poor capacity for epidermal hypertrophy in response to UV injury. In a chronic irradiation model, these animals were protected from tumor formation, developing 50% fewer tumors than wild-type controls. Despite this capacity to protect against tumorigenesis, animals lacking EP2 receptors grew tumors that were larger in size, with a more aggressive phenotype. Further study suggested that this susceptibility may be associated with synthesis of active metalloproteinase enzymes in greater quantities than keratinocytes expressing the EP2 receptor, thereby enhancing the invasive potential of EP2-/- cells.

A Role for Inflammatory Mediators in the Induction of Immunoregulatory B Cells

UV exposure suppresses the immune response to a variety of microbial, fungal, and viral Ags. In addition, UV radiation is a complete carcinogen and the immune suppression induced by UV radiation is a major risk factor for skin cancer induction. In this study, we examined the mechanisms underlying the induction of immune suppression and tolerance induction by UV radiation. Transferring lymph nodes cells from UV-irradiated, FITC-sensitized mice into normal recipients transferred immune tolerance. Contrary to expectations, the cell responsible was an FITC(+), IL-10-secreting, CD19(+), B220(+) B cell. Because the lipid mediator of inflammation, platelet-activating factor (PAF) is released by UV-irradiated keratinocytes and is essential for the induction of immune suppression, we determined its role in tolerance induction. When UV-irradiated mice were injected with PCA 4248, a selective PAF receptor (PAFR) antagonist, transfer of tolerance was suppressed. However, immune suppression was not transferred when FITC(+) cells from the draining lymph nodes of UV-irradiated, PAFR-deficient donor mice were injected into the recipients. Because PCA 4248 also blocks serotonin receptor binding, we measured the effect that blocking both serotonin and PAFR binding has on the transfer of immune suppression. Only when both PAF and serotonin binding were blocked could we inhibit tolerance induction. These data identify a novel function for PAF and serotonin in modulating immune function, the activation of immunoregulatory B cells.

E6/E7 Expression of Human Papillomavirus Type 20 (HPV-20) and HPV-27 Influences Proliferation and Differentiation of the Skin in UV-Irradiated SKH-hr1 Transgenic Mice

The functional role of UV irradiation, in combination with the E6 and E7 proteins of the cutaneous human papillomavirus (HPV) types in the malignant conversion of benign papillomatous lesions, has not been elucidated. Transgenic SKH-hr1 hairless mice expressing HPV-20 and HPV-27 E6 and E7 proteins in the suprabasal compartment were generated and exposed to chronic UV irradiation. Histological and immunohistochemical examination of skin samples revealed enhanced proliferation of the epidermal layers and papilloma formation in both transgenic strains in comparison to what was observed with nontransgenic mice. Squamous cell carcinoma developed in the HPV-20 E6/E7 transgenic line as well as in the HPV-27 E6/E7 transgenic line. Several weeks after cessation of UV-B exposure, enhanced proliferation, as measured by BrdU incorporation, was maintained only in HPV-20 transgenic skin. Keratin 6 expression was increased in the transgenic mice throughout all cell layers. Expression of the differentiation markers involucrin and loricrin was reduced and disturbed. p63alpha expression was differentially regulated with high levels of cytoplasmic expression in clusters of cells in the granular layer of the skin in the transgenic lines 20 weeks after cessation of UV-B exposure, in contrast to uninterrupted staining in the nontransgenic lines. p53 was expressed in clusters of cells in nontransgenic and HPV-27 transgenic mice, in contrast to an even distribution in a higher number of cells in HPV-20 transgenic animals.

Inflammatory Murine Skin Responses to UV-B Light Are Partially Dependent on Endothelin-1 and Mast Cells

Endothelin (ET-1) has been shown to crucially contribute to UV-induced skin responses such as tanning. To test whether ET-1 is also involved in early cutaneous reactions to UV, we assessed ET-1 skin levels in UV-irradiated mice. In correlation with the levels of UV-induced skin inflammation, ET-1 concentrations increased substantially and continually. Moreover, blocking of ET-1 receptors (ETA) resulted in significantly decreased cutaneous inflammation following UV irradiation. When we assessed skin responses to ET-1 injections, we observed prominent mast cell degranulation and mast cell-dependent inflammation. Since mast cells also critically contributed to UV-induced inflammation, we determined the ET-1-dependent inflammatory response to UV in the absence and presence of these cells. Interestingly, ETA blockade did not decrease UV-induced inflammation in mast cell-deficient mice, unless these mice had been adoptively transferred with mast cells before irradiation. This indicates that skin inflammation due to UV irradiation is caused in part by ET-1 acting on skin mast cells.

Ultraviolet radiation-induced non-melanoma skin cancer in the Crl:SKH1:hr-BR hairless mouse: augmentation of tumor multiplicity by chlorophyllin and protection by indole-3-carbinol

Over 1 million new cases of ultraviolet radiation-induced non-melanoma skin cancers (NMSC) per year now occur in the USA and the incidence of these diseases continues to increase. New preventative strategies are required. The hypothesis tested was that dietary administration of the putative cancer chemopreventatives sodium-copper-chlorophyllin (Chlor) or indole-3-carbinol (I3C) would inhibit UV-induced skin carcinogenesis in the Crl:SKH1:hr-BR hairless mouse. Groups of 20 mice were pre-fed isocaloric/isonutritive 20% corn-oil AIN-76a based diets that contained either Chlor (1.52 g%), I3C (5.08 g%) or no chemopreventative (control) for 2 weeks followed by exposure of their dorsal skin to a 10 week incremental, sub-erythemal, carcinogenic simulated solar UV exposure regime. Feeding was continued for the duration of the experiment. Matched non-UV exposed dietary groups were also included in the experimental design. The diets had no significant (p > 0.05) effect on body weight, feed consumption, cutaneous methanol-extractable UV photoprotective substances or on cutaneous UV-reflective characteristics. By day 180, UV-irradiated mice fed the Chlor had a significantly (p < 0.05) higher tumor multiplicity (33.6 +/- 4.72; mean +/- SEM) than UV-irradiated control animals (22.8 +/- 4.25). UV-irradiated mice fed I3C had a significantly (p < 0.001) lower tumor multiplicity (13.0 +/- 2.42) than that of both the UV-irradiated control and UV-irradiated Chlor-fed mice. The Chlor or I3C diets did not significantly (p > 0.05) affect UV-induced systemic suppression of contact hypersensitivity responses. These results demonstrate augmentation of the UV-induced cutaneous carcinogenic process by dietary chlorophyllin and protection from this carcinogenic process by indole-3-carbinol via mechanisms that do not involve changes in skin optical properties, modulation of photoimmunosuppression or caloric/nutrient effects.

A210 UV照射マウスシワ皮膚の二軸引張特性の計測(A2-2 組織・器官のバイオメカニクス2)

A210 UV照射マウスシワ皮膚の二軸引張特性の計測(A2-2 組織・器官のバイオメカニクス2)

544 シワモデルマウスを用いたシワ部周辺の力学的環境の微視的解析(GS-16 : 軟組織(2))

544 シワモデルマウスを用いたシワ部周辺の力学的環境の微視的解析(GS-16 : 軟組織(2))

UV-Induced B-Cell Lymphomas in p53 Heterozygous Mice.

The association between ultraviolet (UV) irradiation and skin cancer induction is well known. Recently, UV exposure was associated with the induction of internal lymphoid malignancies in UV-irradiated p53 heterozygous mice. Here we characterize the non-skin cancer that develops in the lymphoid organs of UV-irradiated mice and found that UV exposure promotes the induction of a B-cell lymphoma. p53 heterozygous mice were exposed to UVB irradiation (10KJ/m2; three times a week) supplied by a bank of FS40 sunlamps. After thirty weeks, we collected spleen cells from 5 irradiated mice, prepared single suspensions, pooled the cells and injected 2X106 cells/flank (subcutaneous injection) into Rag2−/−mice. The subcutaneous tumors that developed in the Rag2−/−mice were successfully transplanted into other Rag2−/−mice and adapted to grow in vitro. Flow cytometric analysis indicated that enlarged cells were positive for CD19, B220, IgM, CD24, CD40, B7-1, B7-2, but negative for CD43, BP-1, CD127, CD3, CD4, CD8, CD49b, NK1.1, Thy1.2, Gr-1. This phenotype is compatible with a mature B cell but also express CD5, CD11b, CD117. Immunohistchemical analysis confirmed that the tumor cells were of B-cell origin and southern blot analysis demonstrated rearrangement of Immunoglobulin heavy chain. Chromosomal analysis revealed a translocations, t (14;19). Subcutaneous injection of the tumor cells into Rag2−/− mice resulted in an aggressive tumor that infiltrated into the lymph nodes, the spleen and the bone marrow. After establishing the cell line from this B-cell lymphoma, we transfected GFP by using lentiviral vector to mark and injected into Rag2−/− mice. First, the cells bearing GFP infiltrated into the lymph nodes, and then into the spleen and the bone marrow. We also found that this cell line produced IL-10, which can promote lymphoma growth and can cause systemic immunosuppression (Masood et al., 1995 Blood 85:3423–30; Rivas et al., 1994 J Leukoc Biol. 59:769–75). The B-cell lymphoma, which grew progressively in immune compromised Rag2−/−mice, was rejected when injected into wild type mice and syngeneic UV-irradiated C57Bl/6 mice. This data indicates that UV induced B-cell lymphoma in p53 heterozygous mice does not express UV common antigen found on UV-induced skin cancer because UV irradiated mice are unable to reject UV induced tumor cells bearing this antigen as previously reported (Kripke et al., 1974 J.Natl Cancer Inst. 53:1333–6). Since sunlight exposure has been associated with the development of non-Hodgkin's lymphomas in humans, tumor development in UV-irradiated p53 heterozygous mice may provide a useful animal model for lymphoma development in humans.

Development of UV-induced squamous cell carcinomas is suppressed in the absence of SPARC.

SPARC (Secreted Protein Acidic and Rich in Cysteine) is a multifunctional glycoprotein belonging to a group of matrix-associated factors that mediate cell-extracellular matrix interactions but have no structural roles. In the present study we investigated the contribution of SPARC to factors that influence the development of skin tumors in response to UV irradiation. A hairless SPARC-null mouse was developed and compared to control SKH1 hairless mice in terms of skin tumor induction and extracellular matrix changes occurring in response to UV-irradiation. Following 23 weeks of exposure to UVB totaling 14.5 J per cm(2), tumor development in the wild-type mice was severe, with an average of over 20 tumors per mouse, many of which were squamous cell carcinomas. Conversely, the SPARC-null mice were strikingly tumor-resistant, developing no squamous cell carcinomas and averaging less than one small papilloma per mouse. SPARC was undetectable immunohistochemically in skin from the non-irradiated control group yet was present in relatively high quantities in the basal and superficial areas of the tumor mass. The SPARC-null mice also exhibited a limited contact hypersensitivity response and were refractory to UV induced immune suppression. In conclusion, SPARC appears to have a crucial role in mediating tumor formation in response to UV irradiation.

CO2 laser resurfacing and photocarcinogenesis: an experimental study.

To examine whether carbon dioxide (CO2) laser treatment has a carcinogenic potential or may influence ultraviolet (UV)-induced carcinogenesis. Hairless mice (n = 211) were treated with a Sharplan CO2 laser with FeatherTouch scanner. Simulated solar irradiations were administrated either pre-operatively or pre- and post-operatively. Weekly clinical assessments of skin tumors were performed blinded during the entire observation period of 12 months. No tumors appeared (a) in mice just treated with CO2 laser, (b) in mice exposed to UV irradiation only before CO2 laser treatment or (c) in untreated control mice. Tumors developed in CO2 laser treated mice that were exposed to UV-irradiation both pre- and post-operatively and in UV-irradiated control mice. The time to first, second, and third tumors ranged from 18 to 20 weeks and no significant differences were demonstrated. CO2 laser treatment does not have a carcinogenic potential in itself, nor does CO2 laser treatment influence UV-induced carcinogenesis.