Regulation and inhibition of collagenase expression by long-wavelength ultraviolet radiation in cultured human skin fibroblasts

Phototherapy in systemic sclerosis: Review

Systemic scleroderma-also known as systemic sclerosis (SSc)-is a chronic systemic connective tissue disease characterized by collagen deposition in cutaneous and internal organs, leading to skin sclerosis and multiple organ fibrosis. The pathogenesis is complex and remains poorly understood. Treatment is based on organ involvement and requires a multidisciplinary approach. Skin sclerosis can cause disability, leading to decreasing quality of life. Various systemic antifibrotic therapies have been used; however, most have unsatisfactory results. Recently, phototherapy and in particular ultraviolet A (UVA) has been used to treat skin sclerosis in SSc patients with satisfactory results. The main mechanisms include lymphocyte apoptosis, cytokine alteration, inhibition of collagen synthesis and increased collagenase production, and neovascularization, leading to the breakdown of collagen fibrils resulting in skin softening or even healing digital ulcers. Most studies reported that psoralen plus UVA (PUVA) and UVA1 phototherapy improved clinical outcomes vis-à-vis skin sclerosis, joint mobility, ulcers, and histopathology. PUVA and UVA1 phototherapy therefore have potential as an alternative or adjunctive therapy for patients with SSc.

Iron sensitizes keratinocytes and fibroblasts to UVA-mediated matrix metalloproteinase-1 through TNF-α and ERK activation

Oestrogen deficiency is regarded as the main causative factor in postmenopausal skin ageing and photoageing. While women after menopause experience low levels of oestrogen because of cease of ovarian function, they are also exposed to high levels of iron as a result of cessation of menstruation. In this study, we investigated whether this increase in iron presents a risk to the postmenopausal skin. Because of the lack of appropriate animal models to closely mimic the low oestrogen and high iron conditions, we tested the hypothesis in a high iron and low oestrogen culture model. Here, we showed that primary human dermal fibroblasts exposed to iron did not affect the baseline levels of matrix metalloproteinase-1 (MMP-1) activity. However, the iron-exposed fibroblasts were sensitized to UVA exposure, which resulted in a synergistic increase in MMP-1. UVA activated the three members of MAPK family: ERKs, p38, and JNKs. Additional activation of ERKs by iron contributed to the synergistic increases. Primary normal human epidermal keratinocytes (NHEK) did not respond to iron or UVA exposure as measured by MMP-1, but produced tumor necrosis factor-alpha (TNF-α) in the media, which then stimulated MMP-1 in fibroblasts. Our results indicate that iron and UVA increase MMP-1 activity in dermal fibroblasts not only directly through ERK activation but also by an indirect paracrine loop through TNF-α released by NHEK. We conclude that in addition to oestrogen deficiency, increased iron as a result of menopause could be a novel risk factor by sensitizing postmenopausal skin to solar irradiation.

Temperature dependence of photochemical fluorescence fading in Skh-1 hairless mouse collagen

BACKGROUND

Type I mammalian collagens have several photolabile fluorescent moieties that absorb UV rays capable of reaching the dermis. We studied the temperature dependence of fluorescence fading as a marker of photochemical damage.

METHODS

Collagen solutions were exposed to radiation from 0 to 240 min from either a UVG-11 hand lamp, total dose=1.173 x 10(3) J/m(2); a UVL-21 hand lamp total dose=2.030 x 10(3) J/m(2); or the fluorometer, at 325+/-5 nm, total dose=0.156 x 10(3) J/m(2). We recorded intensities at excitation/emission wavelengths 270/300, 270/330, 270/360, 270/400, 325/400, and 370/450 nm at T=9.0-59.3 degrees C.

RESULTS

Results indicated simultaneous forward and reverse reactions. However, the 270/360 nm fluorophore could be analyzed as a second-order reaction. The Arrhenius curve showed two straight lines intersecting near the denaturation temperature, with helix activation energy E(a) approximately 0 and coil E(a)=7.6+/-0.6 kcal/mol (31.7+/-2.5 kJ/mol).

DISCUSSION

Collagen-bound fluorophores are not just passive markers of oxidative stress and age-related damage. Their photolability to wavelengths reaching the dermis may result in pathological conditions, particularly at elevated body temperatures.

Ultraviolet A phototherapy for sclerotic skin diseases: a systematic review

BACKGROUND

Ultraviolet (UV) A-1 phototherapy is now available for a variety of skin diseases. Increasingly since 1995, there have been investigations of the efficacy of UVA-1 (340-400 nm) therapy for sclerotic skin diseases. Most studies undertaken treated patients who had localized scleroderma, but UVA-1 phototherapy is currently also used for other sclerotic skin conditions.

OBJECTIVE

We sought to assess the efficacy, biological effects, and side effects of UVA-1 in a variety of sclerotic skin diseases (localized scleroderma, eosinophilic fasciitis, chronic graft-versus-host disease, lichen sclerosus et atrophicus, scleredema adultorum, necrobiosis lipoidica, POEMS disease, pansclerotic porphyria cutanea tarda, and drug-induced scleroderma-like disorders).

METHODS

The authors searched for publications dated between January 1996 and November 2007 in the computerized bibliographic database, PubMed. PubMed was searched using medical subject heading terms and open searches to retrieve the latest reports.

RESULTS

The evidence based on research concerning the effect of full-spectrum UVA (320-400 nm) and UVA-1 on these skin diseases is still growing, and appears promising. Up until now, good results are shown for all different doses (low, medium, and high) UVA-1 and UVA. There are insufficient data regarding use of high-dose UVA-1 and there are no comparative studies to make a clear assessment regarding the superiority of low-, medium-, or high-dose UVA-1 therapy. Although UVA-1 has various effects on, for instance, fibroblasts and inflammatory cells, the precise mode of action remains obscure. The main short-term side effects of UVA-1 therapy are erythema, pruritus, xerosis cutis, tanning, and recrudescence of herpes simplex infection. More studies are warranted to investigate the potential long-term risk of photoaging and skin cancer. Currently, UVA-1 is considered to be less carcinogenic than psoralen plus UVA (PUVA).

LIMITATIONS

Because of the limited availability of randomized controlled trials and large cohort studies, it is difficult to draw firm conclusions on the long-term efficacy, optimum dose, and best treatment regimens for UVA-1 when administered to patients with sclerosing skin disorders.

CONCLUSIONS

Full-spectrum UVA and UVA-1 phototherapy seem effective in the treatment of sclerotic skin diseases based on data retrieved from the literature. UVA-1 treatment can shorten the active period of localized scleroderma and pseudoscleroderma and prevent further disease progression, including contractures. Further investigations will be needed to determine any additional biological effects of UVA-1. Although long-term side effects are not yet known, UVA-1 might develop into a promising beneficial and well-tolerated treatment in the therapeutic armamentarium for sclerotic skin diseases. Long-term studies in large groups of patients are clearly needed.

Regulation of the extracellular matrix remodeling by lutein in dermal fibroblasts, melanoma cells, and ultraviolet radiation exposed fibroblasts

With aging and cancer there is increased expression or activity of matrix metalloproteinases (MMPs) that degrade and remodel the structural extracellular matrix (ECM). In addition, exposure of skin to ultraviolet (UV) radiation (photoaging) leads to loss of cell viability, membrane damage, and deposition of excessive elastotic material. Lutein has antioxidant, anti-inflammatory, photoprotective, and anti-carcinogenic properties. The goal of this research was to investigate lutein's anti-aging and anti-carcinogenic effects via the regulation of the extracellular matrix remodeling. To this purpose, the effects of lutein on the expression of MMPs and their inhibitors (TIMPs, tissue inhibitors of metalloproteinases) in dermal fibroblasts (intrinsic aging) and melanoma cells were examined. Further, for lutein's photoprotective effects, the regulation of cell viability, membrane integrity, and elastin expression in the non-irradiated, and UVA or UVB radiation exposed fibroblasts were analyzed. Lutein significantly inhibited MMP-1 expression, transcriptionally, and MMP-2 protein levels in dermal fibroblasts, without altering TIMPs expression. It significantly inhibited MMP-1 expression in melanoma cells while stimulating TIMP-2. Lutein did not alter fibroblast or melanoma cell viability or membrane integrity. In ultraviolet radiation exposed fibroblasts, lutein improved cell viability, membrane integrity and inhibited elastin expression, though more significantly in the UVB exposed fibroblasts. In summary, the mechanism to lutein's anti-aging and anti-carcinogenic effects include the inhibition of MMP to TIMP ratio in dermal fibroblasts and melanoma cells, and the inhibition of cell loss, membrane damage and elastin expression in ultraviolet radiation exposed fibroblasts.

Effects of brief cutaneous JP-8 jet fuel exposures on time course of gene expression in the epidermis

The jet fuel jet propulsion fuel 8 (JP-8) has been shown to cause an inflammatory response in the skin, which is characterized histologically by erythema, edema, and hyperplasia. Studies in laboratory animal skin and cultured keratinocytes have identified a variety of changes in protein levels related to inflammation, oxidative damage, apoptosis, and cellular growth. Most of these studies have focused on prolonged exposures and subsequent effects. In an attempt to understand the earliest responses of the skin to JP-8, we have investigated changes in gene expression in the epidermis for up to 8 h after a 1-h cutaneous exposure in rats. After exposure, we separated the epidermis from the rest of the skin with a cryotome and isolated total mRNA. Gene expression was studied with microarray techniques, and changes from sham treatments were analyzed and characterized. We found consistent twofold increases in gene expression of 27 transcripts at 1, 4, and 8 h after the beginning of the 1-h exposure that were related primarily to structural proteins, cell signaling, inflammatory mediators, growth factors, and enzymes. Analysis of pathways changed showed that several signaling pathways were increased at 1 h and that the most significant changes at 8 h were in metabolic pathways, many of which were downregulated. These results confirm and expand many of the previous molecular studies with JP-8. Based on the 1-h changes in gene expression, we hypothesize that the trigger of the JP-8-induced, epidermal stress response is a physical disruption of osmotic, oxidative, and membrane stability which activates gene expression in the signaling pathways and results in the inflammatory, apoptotic, and growth responses that have been previously identified.

Ultraviolet A exposure might increase metastasis of mouse melanoma: a pilot study

BACKGROUND

The major sources of long-wave ultraviolet A radiation (UVA; 320-400 nm) exposure are extensive sunbathing and tanning in solaria. While the carcinogenic effects of mid-wave ultraviolet B radiation (UVB; 280-320 nm) are well recognized, the potentially hazardous effects of UVA are less understood. Several studies have shown that a variety of physiological processes in the cell are modified by UVA exposure, some of which might be involved in the regulation of tumor metastasis. In this study we suggest that UVA radiation could lead to the increase of metastatic capability of melanoma cells in mice.

METHOD/RESULT

A pilot in vivo study was executed using C57BL/6 mice and syngeneic B16 melanoma cell lines. Mice were intravenously (i.v.) injected with either B16-F1 or B16-F10 melanoma cells into the tail vein and then immediately exposed to UVA. Fourteen days after melanoma injection, lungs were collected and the quantity and quality of metastases were determined under a dissecting microscope. As an outcome of the pilot study we observed that i.v. injected melanoma cells formed more lung metastases in the UVA-exposed mice in comparison with the control mice.

CONCLUSION

This result suggests that the UVA exposure of mice, with melanoma cells present in blood circulation, increases the formation of melanoma metastases in lungs. Further studies should determine whether a similar pro-metastatic effect, as observed in mice, could occur in humans and whether other than melanoma tumors might be susceptible.

Ultraviolet A exposure alters adhesive properties of mouse melanoma cells

BACKGROUND

We have examined whether ultraviolet A (UVA) irradiation could alter adhesive properties of melanoma cells. As an experimental in vitro model, we have used C57BL/6 mouse-derived B16- F1 and B16-F10 melanoma cell lines and the syngeneic MS-1 endothelial cell line.

METHOD/RESULT

The melanoma cells were exposed to different doses of UVA irradiation. We have determined that a single dose of UVA at 8 and 12 J/cm(2) causes an 88% (P<0.001) and a 32% (P<0.05) increase in B16-F1 melanoma cell adhesiveness to the non-irradiated endothelial monolayer, respectively. The peak of the response was 24 h after the irradiation. The UVA dose of 8 J/cm(2) delivered in four doses separated by 1 h intervals (4 x 2 J/cm(2)) had led to a caused 149% (P<0.001) increase of B16-F1 melanoma adhesiveness already at 1 h after the last dose of UVA. Besides the induction of increase in the melanoma-endothelial cell adhesion, UVA exposure has induced a rapid decline (1 h after exposure) in homotypic melanoma-melanoma cell adhesion (clustering). The clustering decline of B16-F1 cells with a single dose of UVA at 8 J/cm(2) was by 61% (P<0.05) and by 35% (P<0.05) with 4 x 2 J/cm(2). Pilot experiments have shown that the changes of the adhesive properties of melanoma cells were accompanied by an increase in N-cadherin expression and a decline in E-cadherin expression. Such a change in cadherin expression profile has been shown to be an indicator of the increased metastatic potential.

CONCLUSION

Our results suggest that UVA radiation appears to alter the adhesive properties of melanoma cells in vitro, by diminishing the melanoma-melanoma adhesion and by increasing melanoma adhesion to the endothelium. This suggests that UVA exposure might increase the metastatic capability of the melanoma cells.

UVA/UVA1 phototherapy and PUVA photochemotherapy in connective tissue diseases and related disorders: a research based review

BACKGROUND

Broad-band UVA, long-wave UVA1 and PUVA treatment have been described as an alternative/adjunct therapeutic option in a number of inflammatory and malignant skin diseases. Nevertheless, controlled studies investigating the efficacy of UVA irradiation in connective tissue diseases and related disorders are rare.

METHODS

Searching the PubMed database the current article systematically reviews established and innovative therapeutic approaches of broad-band UVA irradiation, UVA1 phototherapy and PUVA photochemotherapy in a variety of different connective tissue disorders.

RESULTS

Potential pathways include immunomodulation of inflammation, induction of collagenases and initiation of apoptosis. Even though holding the risk of carcinogenesis, photoaging or UV-induced exacerbation, UVA phototherapy seems to exhibit a tolerable risk/benefit ratio at least in systemic sclerosis, localized scleroderma, extragenital lichen sclerosus et atrophicus, sclerodermoid graft-versus-host disease, lupus erythematosus and a number of sclerotic rarities.

CONCLUSIONS

Based on the data retrieved from the literature, therapeutic UVA exposure seems to be effective in connective tissue diseases and related disorders. However, more controlled investigations are needed in order to establish a clear-cut catalogue of indications.

Predominant effects of Polypodium leucotomos on membrane integrity, lipid peroxidation, and expression of elastin and matrixmetalloproteinase-1 in ultraviolet radiation exposed fibroblasts, and keratinocytes

BACKGROUND

Polypodium leucotomos has been reported to have antioxidant, anti-inflammatory and photoprotective properties. Exposure of skin to ultraviolet (UV) radiation can lead to deposition of excessive elastotic material, reduction in collagen, and increased expression of matrix metalloproteinases (MMPs).

OBJECTIVE

The goal of this research was to determine the effects of P. leucotomos in the absence or presence of UVA or UVB radiation on membrane damage, lipid peroxidation, and expression of elastin and MMP-1 in fibroblasts and keratinocytes, respectively.

METHODS

Fibroblasts and keratinocytes, respectively, were irradiated by a single exposure to UVA (0.6, 1.8 or 3.6 J) or UVB radiation (0.75, 2.5 or 7.5 mJ), and then incubated with, or without, P. leucotomos (0.01, 0.1 and 1%) and examined for membrane damage, lipid peroxidation, expression of elastin (protein levels) and MMP-1 (protein levels or MMP-1 promoter activity).

RESULTS

UV radiation did not significantly alter membrane integrity, lipid peroxidation or MMP-1 expression, but increased elastin expression. P. leucotomos significantly improved membrane integrity, inhibited lipid peroxidation, increased elastin expression, and inhibited MMP-1 expression in both fibroblasts, and keratinocytes. The effects of P. leucotomos predominated in the presence of UVA or UVB in both fibroblasts and keratinocytes, respectively, with the exception of inhibition of MMP-1 protein levels in fibroblasts only in combination with UV radiation.

CONCLUSION

Lower concentration of P. leucotomos (lower than 0.1%), may be beneficial in preventing photoaging by improving membrane integrity and inhibiting MMP-1, without increasing elastin expression. Higher concentration (greater than 0.1%) of P. leucotomos may reverse the loss of normal elastic fibers associated with intrinsic aging.

Interleukin-6 increases rat metalloproteinase-13 gene expression through stimulation of activator protein 1 transcription factor in cultured fibroblasts

The role of IL-6 in collagen production and tissue remodeling is controversial. In Rat-1 fibroblasts, we measured the effect of IL-6 on matrix metalloproteinase-13 (MMP-13), c-jun, junB, and c-fos gene expression, binding of activator protein 1 (AP1) to DNA, amount of AP1 proteins, immunoreactive MMP-13 and TIMP-1 proteins, and Jun N-terminal kinase activity. We show that IL-6 increased MMP-13-mRNA and MMP-13 protein. These effects were exerted by acting on the AP1-binding site of the MMP-13 promoter, as shown by transfecting cells with reporter plasmids containing mutations in this element. Mobility shift assays demonstrated that IL-6 induced the DNA binding activity of AP1. This effect was accompanied by a marked increase in c-Jun, JunB, and c-Fos mRNA, as well as in c-Jun protein and its phosphorylated form. The latter is not due to increased Jun N-terminal kinase activity but to a decreased serine/threonine phosphatase activity. We conclude that IL-6 increases interstitial MMP-13 gene expression at the promoter level. This effect seems to be mediated by the induction of c-jun, junB, and c-fos gene expression, by the binding of AP1 to DNA, by increasing phosphorylated c-Jun, and by the inhibition of serine/threonine phosphatase activity. These effects of IL-6 might contribute to remodeling connective tissue.

Transcriptional activation of endogenous retroviral sequences in human epidermal keratinocytes by UVB irradiation

Ultraviolet radiation is a pathogenic factor in various diseases, e. g., autoimmune disorders such as lupus erythematosus. On the other hand, endogenous retroviruses are discussed as etiologic agents in lupus erythematosus. Therefore, we investigated the influence of ultraviolet irradiation on expression of human endogenous retroviral sequences and human endogenous retroviral sequence promoter-driven transcription of cellular genes using human epidermal keratinocytes as a model system. First, conserved sequences of endogenous retroviral pol genes were amplified from cellular mRNA by reverse transcriptase polymerase chain reaction with degenerate oligonucleotide primers. Polymerase chain reaction products were hybridized in a reverse dot blot hybridization assay to a representative number of distinct cloned human endogenous retroviral pol fragments. Using this method, we could show that irradiation with 30 mJ per cm2 ultraviolet B activates transcription of various endogenous retroviral pol sequences in primary epidermal keratinocytes as well as in a spontaneously immortalized keratinocyte cell line (HaCaT). Interestingly, some of these sequences were found to be closely related to pol sequences of human endogenous retroviral sequences which have been shown to be expressed in autoimmune patients. Analysis of human endogenous retroviral pol expression in vivo using skin biopsies of lupus erythematosus patients revealed similar activation patterns. In a second approach, ultraviolet B- induced chimeric transcripts were isolated which are initiated by human endogenous retroviral promoters and proceed into cellular sequences using a newly established modified differential display polymerase chain reaction technique. The activation of human endogenous retroviral sequence transcription by ultraviolet B may contribute to the pathogenesis of lupus erythematosus, where inappropriate antigenic presentation of ultraviolet B-induced viral and cellular proteins could stimulate autoantibody production.

Translocation of protein kinase Cepsilon and protein kinase Cdelta to membrane is required for ultraviolet B-induced activation of mitogen-activated protein kinases and apoptosis

UV-induced signal transduction may be involved in tumor promotion and induction of apoptosis. The role of protein kinase C (PKC) in UVB-induced signal transduction is not well understood. This study showed that UVB markedly induced translocation of membrane-associated PKCepsilon and PKCdelta, but not PKCalpha, from cytosol to membrane. Dominant negative mutant (DNM) PKCepsilon or PKCdelta inhibited UVB-induced translocation of PKCepsilon and PKCdelta, respectively. UVB-induced activation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH2-terminal kinases (JNKs) was strongly inhibited by DNM PKCepsilon and PKCdelta, whereas the DNM of PKCalpha was less effective on the UVB-induced phosphorylation of Erks and JNKs. Among the PKC inhibitors used only rottlerin, a selective inhibitor of PKCdelta, markedly inhibited the UVB-induced activation of Erks and JNKs, but not p38 kinases. Safingol, a selective inhibitor for PKCalpha, did not show any inhibitory effect on UVB-induced mitogen-activated protein kinase activation. GF109203X is a stronger inhibitor of classical PKC than novel PKC. Lower concentrations of GF109203X (<10 microM) had no effect on UVB-induced activation of Erks or JNKs. However, at higher concentrations (over 20 microM), GF109203X inhibited UVB-induced activation of JNKs, Erks, and even p38 kinases. Meanwhile, rottlerin and GF109203X markedly inhibited UVB-induced apoptosis of JB6 cells, whereas safingol had little inhibitory effect. DNM-Erk2 cells and PD98059, a selective inhibitor for mitogen-activated protein kinase/extracellular signal-regulated kinase 1 that directly activates Erks, inhibited UVB-induced apoptosis. DNM-JNK1 cells also blocked UVB-induced apoptosis, whereas SB202190, a specific inhibitor for p38 kinases, did not produce the inhibitory effect. These data demonstrate that PKCdelta and PKCepsilon, but not PKCalpha, mediate UVB-induced signal transduction and apoptosis in JB6 cells through activation of Erks and JNKs.

Low doses of ultraviolet A radiation stimulate adhesion of human dermal fibroblasts by integrins in a protein kinase C-dependent pathway

In this work, we have studied the modulation of fibroblast-extracellular matrix interactions by physiological doses of ultraviolet A (UV-A) radiation using an adhesion assay on collagen. We have shown that low doses of UV-A (20 kJ/m2) stimulate fibroblast adhesion while higher doses (100 and 200 kJ/m2) inhibit it. By measurement of the thiobarbituric acid reactive substances (TBARS) and use of the chain-breaking antioxidant vitamin E, no role of lipid peroxidation can be detected in these effects. By incubating fibroblasts with a specific protein kinase C (PKC) inhibitor, GF109203X, we have demonstrated that the stimulation of the adhesion by low doses of UV-A involves, at least in part, a PKC-dependent mechanism. In addition, using function-blocking antibodies of alpha 1, alpha 2 or alpha 5 integrin chains involved in extracellular matrix anchorage, we have shown that they decrease the stimulation of adhesion following low doses of UV-A radiation, demonstrating the involvement of these three integrin chains in this UV-A effect. In parallel, 20 kJ/M2 of UV-A are found to rapidly stimulate membrane expression of alpha 1, alpha 2 and alpha 5 integrin chains. This work, which underlines the involvement of integrins in UV-A effects, contributes to the evaluation of the mechanisms by which cell-matrix interactions modulate cell behaviour.

Correlation of skin phototype with facial wrinkle formation

Facial wrinkle formation is a representative sign of photoaging. Skin can be divided into different skin phototypes (SPTs) depending on its sensitivity to solar radiation. We have determined the relationship between SPTs and deep and fine wrinkle scores on the faces of 230 Japanese subjects. This group was chosen because it is relatively easy to quantify acute and chronic sun damage in Japanese individuals. SPT in the Japanese subjects was classified into one of four groups, SPT-I to -IV according to Fitzpatrick's classification method. The subjects were further classified into indoor or outdoor workers. After photographing the outer canthus, deep and fine wrinkles were discriminated visually and scored from 1-11 and from 1-9, respectively. UV light was used as a photographic light source for clear depiction of the fine wrinkles. Higher scores were recorded for deep wrinkles in individuals with SPT-I, who are more sensitive to sunlight than those with SPT-III or IV, who are more tolerant to sunlight. However, the same tendency did not seem to be apparent for fine wrinkle scores. A high incidence of SPT-IV was seen in outdoor workers. Early detection of SPT-I in individuals who are sensitive to sunlight, may help to predict and prevent photoaging of deep wrinkles. Sensitivity to sunlight may play a part in determining an individual's choice of working environment.

Modulation of the UVA activation of haem oxygenase, collagenase and cyclooxygenase gene expression by epigallocatechin in human skin cells

We have investigated the modifying effects of epigallocatechin, a major polyphenolic constituent of green tea, on ultraviolet-A-activated gene expression in human fibroblasts and keratinocytes using the stress responsive enzymes: haem oxygenase-1, interstitial collagenase and cyclooxygenase-2. Although epigallocatechin strongly reduced ultraviolet-A-induced haem oxygenase-1 activation in skin-derived 'fibroblasts, the same compound activated collagenase and cyclooxygenase expression. In a keratinocyte cell line, ultraviolet-A-mediated haem oxygenase-1 over-expression was low and epigallocatechin failed to modulate it further. In contrast to the results with fibroblasts, ultraviolet-A activation of cyclooxygenase in keratinocytes was reduced by epigallocatechin. The results indicate that the effect of this green tea polyphenol on cellular stress responses is complex and may involve direct effects on signal transduction as well as changes that may be associated with its antioxidant activity.

Potentials and limitations of the natural antioxidants RRR-alpha-tocopherol, L-ascorbic acid and beta-carotene in cutaneous photoprotection

Sun exposure has been linked to several types of skin damage including sun burn, photoimmunosuppression, photoaging and photocarcinogenesis. In view of the increasing awareness of the potentially detrimental long term side effects of chronic solar irradiation there is a general need for safe and effective photoprotectants. One likely hypothesis for the genesis of skin pathologies due to solar radiation is the increased formation of reactive oxidants and impairment of the cutaneous antioxidant system. Consequently, oral antioxidants that scavenge reactive oxidants and modulate the cellular redox status may be useful; systemic photoprotection overcomes some of the problems associated with the topical use of sunscreens. Preclinical studies amply illustrate the photoprotective properties of supplemented antioxidants, particularly RRR-alpha-tocopherol, L-ascorbate and beta-carotene. However, clinical evidence that these antioxidants prevent, retard or slow down solar skin damage is not yet convincing. The purpose of this review is to provide the reader with current information on cutaneous pathophysiology of photoxidative stress, to review the literature on antioxidant photoprotection and to discuss the caveats of the photo-oxidative stress hypothesis.

Effects of simulated solar radiation on type I and type III collagens, collagenase (MMP-1) and stromelysin (MMP-3) gene expression in human dermal fibroblasts cultured in collagen gels

Understanding the mechanisms responsible for photodamage to the skin is most important for dermatology. 3-D cultures have been used as tools to mimic the in vivo situation for several years. We irradiated such a system containing human dermal fibroblasts cultured in collagen gels, a well-known model considered to be a dermal equivalent, which reproduces the interaction between cells and the surrounding extracellular matrix. The effects of solar irradiation (315-800 nm) on the steady-state levels of the mRNAs of extracellular matrix components (type I and III collagens) and their degrading enzymes (interstitial collagenase, MMP-1 and stromelysin 1, MMP-3) were measured. Exposure to low levels of solar radiation (0-10 J cm-2 in the UVA, i.e. suberythemal UVA doses) caused a transient decrease in type I procollagen mRNA, an increase in MMP-mRNA, and no change in type III procollagen mRNA steady-state levels. These results describe the early changes in the connective tissue of the skin following exposure to low-level solar stimulation, and may help explain the long-term changes in photodamaged skin.

Two-photon excitation of 4'-hydroxymethyl-4,5',8-trimethylpsoralen

Psoralens are a class of pharmaceutical agents commonly used to treat several cutaneous disorders. When irradiated with a mode-locked titanium: sapphire (Ti:sapphire) laser tuned to 730 nm, an aqueous solution of 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) emits blue light. The emission spectrum is centered at 452 nm and is identical to that obtained by one-photon excitation with UVA excitation, and its magnitude depends quadratically on the intensity of laser excitation. These results suggest that two-photon excitation occurs to a potentially photochemically active state. To estimate the two-photon absorption cross section, it was first necessary to measure the emission quantum yield of HMT using 365 nm excitation at room temperature that resulted in a value of 0.045 +/- 0.007. The two-photon absorption cross section of HMT at 730 nm is therefore estimated to be 20 x 10(-50) cm4 s (20 Göppert-Mayer). The excited-state photophysics and photochemistry of psoralens suggest potential applications to cutaneous phototherapy in diseases such as psoriasis and dystrophic epidermolysis bullosa.

UV-induced signal transduction

Irradiation of cells with wavelength ultraviolet (UVA, B and C) induces the transcription of many genes. The program overlaps with that induced by oxidants and alkylating agents and has both protective and other functions. Genes transcribed in response to UV irradiation include genes encoding transcription factors, proteases and viral proteins. While the transcription factor encoding genes is initiated in minutes after UV irradiation (immediate response genes) and depends exclusively on performed proteins, the transcription of protease encoding occurs only many hours after UV irradiation. Transcription factors controlling the activity of immediate response genes are activated by protein kinases belonging to the group of proline directed protein kinases immediately after UV irradiation. Experimental evidence suggests that these kinases are activated in UV irradiated cells through pathways which are used by growth factors. In fact, the first cellular reaction detectable in UV irradiated cells is the phosphorylation of several growth factor receptors at tyrosine residues. This phosphorylation does not depend on UV induced DNA damage, but is due to an inhibition of the activity of tyrosine phosphatases. In contrast, for late cellular reactions to UV, an obligatory role of DNA damage in transcribed regions of the genome can be demonstrated. Thus, UV is absorbed by several target molecules relevant for cellular signaling, and it appears that numerous signal transduction pathways are stimulated. The combined action of these pathways establishes the genetic program that determines the fate of UV irradiated cells.