8-methoxypsoralen plus UVA induces the 72 kDa heat shock protein in organ-cultured normal human skin

Fundamentals of light-cell-polymer interactions in photo-cross-linking based bioprinting

Biofabrication technologies that use light for polymerization of biomaterials have made significant progress in the quality, resolution, and generation of precise complex tissue structures. In recent years, the evolution of these technologies has been growing along with the development of new photocurable resins and photoinitiators that are biocompatible and biodegradable with bioactive properties. Such evolution has allowed the progress of a large number of tissue engineering applications. Flexibility in the design, scale, and resolution and wide applicability of technologies are strongly dependent on the understanding of the biophysics involved in the biofabrication process. In particular, understanding cell–light interactions is crucial when bioprinting using cell-laden biomaterials. Here, we summarize some theoretical mechanisms, which condition cell response during bioprinting using light based technologies. We take a brief look at the light–biomaterial interaction for a better understanding of how linear effects (refraction, reflection, absorption, emission, and scattering) and nonlinear effects (two-photon absorption) influence the biofabricated tissue structures and identify the different parameters essential for maintaining cell viability during and after bioprinting.

Heat shock proteins in the physiology and pathophysiology of epidermal keratinocytes

Heat shock proteins (HSPs), a large group of highly evolutionary conserved proteins, are considered to be main elements of the cellular proteoprotection system. HSPs are encoded by genes activated during the exposure of cells to proteotoxic factors, as well as by genes that are expressed constitutively under physiological conditions. HSPs, having properties of molecular chaperones, are involved in controlling/modulation of multiple cellular and physiological processes. In the presented review, we summarize the current knowledge on HSPs in the biology of epidermis, the outer skin layer composed of stratified squamous epithelium. This tissue has a vital barrier function preventing from dehydratation due to passive diffusion of water out of the skin, and protecting from infection and other environmental insults. We focused on HSPB1 (HSP27), HSPA1 (HSP70), HSPA2, and HSPC (HSP90), because only these HSPs have been studied in the context of physiology and pathophysiology of the epidermis. The analysis of literature data shows that HSPB1 plays a role in the regulation of final steps of keratinization; HSPA1 is involved in the cytoprotection, HSPA2 contributes to the early steps of keratinocyte differentiation, while HSPC is essential in the re-epithelialization process. Since HSPs have diverse functions in various types of somatic tissues, in spite of multiple investigations, open questions still remain about detailed roles of a particular HSP isoform in the biology of epidermal keratinocytes.

Can neuroimmune mechanisms explain the link between ultraviolet light (UV) exposure and addictive behavior?

High ultraviolet (UV) light exposure on the skin acts as a reinforcing stimulus, increasing sun-seeking behavior and even addiction-like sun seeking behavior. However, the physiological mechanisms that underlie this process remain to be defined. Here, we propose a novel hypothesis that neuroimmune signaling, arising from inflammatory responses in UV-damaged skin cells, causes potentiated signaling within the cortico-mesolimbic pathway, leading to increased sun-seeking behaviors. This hypothesized UV-induced, skin-to-brain signaling depends upon cell stress signals, termed alarmins, reaching the circulation, thereby triggering the activation of innate immune receptors, such as toll-like receptors (TLRs). This innate immune response is hypothesized to occur both peripherally and centrally, with the downstream signaling from TLR activation affecting both the endogenous opioid system and the mesolimbic dopamine pathway. As both neurotransmitter systems play a key role in the development of addiction behaviors through their actions at key brain regions, such as the nucleus accumbens (NAc), we hypothesize a novel connection between UV-induced inflammation and the activation of pathways that contribute to the development of addiction. This paper is a review of the existing literature to examine the evidence which suggests that chronic sun tanning resembles a behavioral addiction and proposes a novel pathway by which persistent sun-seeking behavior could affect brain neurochemistry in a manner similar to that of repeated drug use.

Expression of Heat Shock Protein 70 in Human Skin Cells as a Photoprotective Function after UV Exposure

BACKGROUND

Human skin is exposed to various environmental stresses, such as heat, cold, and ultraviolet (UV) radiation. Heat shock proteins (HSPs) induced by temperature elevations, as a physiologic response to mediate repair mechanisms and reduce cellular damage.

OBJECTIVE

The purpose of this study was to investigate the induction of HSPs in human skin cells after UV exposure.

METHODS

We performed immunoblotting using a specific monoclonal antibody to the HSP70 family, one of the best-conserved stress proteins in humans, with cultured normal human keratinocytes, A431 cells, human melanocytes, SK30 cells, and human dermal fibroblasts (HDF).

RESULTS

Our results indicated that high expression of HSP70 in the unstressed state was noted in epidermal cells, including normal human keratinocytes, A431 cells, human melanocytes, and SK30 cells, but epidermal cells showed no additional up-regulation of HSP70 after UV irradiation. On the other hand, HDF expressed very small amounts of HSP70 at baseline, but significantly higher amounts of HSP70 after UV exposure.

CONCLUSION

These findings suggest that constitutive expression of HSP70 in epidermal cells may be an important mechanism for protection of the human epidermis from environmental stresses, such as sunlight exposure.

Heat shock proteins in the photobiology of human skin

All organisms respond to sudden environmental changes with the increased transcription of genes belonging to the family of heat shock proteins (hsps). Hsp-inducing stress factors include elevated temperatures, alcohol, heavy metals, oxidants, and agents leading to protein denaturation. The induction of heat shock proteins is followed by a transient state of increased resistance to further stress and the heat shock response is generally thought to represent an evolutionary conserved adaptive mechanism to cope with hostile environmental conditions. Since the skin as a barrier organ has to cope with the potentially harmful consequences of exposure to ultraviolet radiation (UV), it appears reasonable to question whether hsps constitute a natural defence mechanism against UV. Hsps have been detected in resting as well as in stressed epidermal and dermal cells and overexpression of hsps is associated with increased resistance to UV-induced cell death. Furthermore, UV itself is able to induce the expression of specific hsps. Thus, hsps might provide an adaptive cellular response to increasing UV and enhancing the expression of hsps might turn out as a new way to deal with the immediate and long-term consequences of UV exposure. Prerequisite for the utilization of this concept is the development of non-toxic heat shock inducers and their evaluation for clinical efficacy and safety.

Induction of radioresistance by a nitric oxide-mediated bystander effect

To elucidate whether nitric oxide secreted from irradiated cells affects cellular radiosensitivity, we examined the accumulation of inducible nitric oxide synthase, TP53 and HSP72, the concentration of nitrite in the medium of cells after X irradiation, and cellular radiosensitivity using two human glioblastoma cell lines, A-172, which has a wild-type TP53 gene, and a transfectant of A-172 cells, A-172/mp53, bearing a mutated TP53 gene. Accumulation of inducible nitric oxide synthase was caused by X irradiation of the mutant TP53 cells but not of the wild-type TP53 cells. Accumulation of TP53 and HSP72 in the wild-type TP53 cells was observed by cocultivation with irradiated mutant TP53 cells, and the accumulation was abolished by the addition of an inhibitor for inducible nitric oxide synthase, aminoguanidine, to the medium. Likewise, accumulation of these proteins was observed in the wild-type TP53 cells after exposure to conditioned medium from irradiated mutant TP53 cells, and the accumulation was abolished by the addition of a specific nitric oxide scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, to the medium. The radiosensitivity of wild-type TP53 cells was reduced when the cells were cultured in conditioned medium from irradiated mutant TP53 cells compared to conventional fresh growth medium. Collectively, these findings indicate the potential importance of an intercellular signal transduction pathway initiated by nitric oxide in the cellular response to ionizing radiation.

Enhancement of heat-induced heat shock protein (hsp)72 accumulation by doxorubicin (Dox) in vitro

Previous studies have shown that cellular thermotolerance develops in response to exposure to doxorubicin (Dox) and treatment with hyperthermia. In the present study, we evaluated the induction of thermotolerance and the accumulation of heat shock protein (hsp)72 after treatment with Dox and/or hyperthermia at 44 degrees C in Chinese hamster V-79 cells. Thermotolerance developed after exposure to Dox at 37 degrees C for 2 h in a dose-dependent manner. Western blot analysis showed no accumulation of hsp72 after exposure to Dox (0.2 microg/ml) for 2 h (lethal dose (LD)(15)). Hsp72 accumulated 12 h after hyperthermia at 44 degrees C for 35 min (LD(15)). However, when the cells were exposed to Dox (0.1 microg/ml) followed by heating at 44 degrees C for 25 min (LD(15)), accumulation of hsp72 was observed after 6 h. These results suggest that enhancement of induction of hsp72 accumulation by Dox may be involved in the development of thermotolerance induced by sequential treatment with Dox and hyperthermia.

Intercellular signaling initiated by nitric oxide produced in heat-shocked human glioblastoma cells

The accumulation of inducible nitric oxide synthase was caused by heat shock of human glioblastoma T98G cells but not of A-172 cells. The accumulation of hsp72 and p53 was observed in A-172 cells cocultivated with heat-shocked T98G cells, which was suppressed by the addition of aminoguanidine to the medium. The accumulation of these proteins was observed in A-172 cells after exposure to the conditioned medium of heat-shocked T98G cells, which was completely blocked by the addition of 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide to the medium. In addition, the accumulation of these proteins in A-172 cells was induced by the administration of S-nitroso-N-acetylpenicillamine to the medium. Finally, the thermosensitivity of A-172 cells was reduced in the conditioned medium of heat-shocked T98G cells compared with conventional fresh growth medium. Our findings demonstrate that the accumulation of stress-induced proteins and thermoresistance in NO recipient cells cocultivated with heat-shocked NO donor cells is induced through an intercellular signal transduction pathway initiated by NO without cell-to-cell interactions such as gap junctions.

DNA damage formation and p53 accumulation in mammalian cells exposed to the space environment

To determine the effects of the space environment on gene instability from the point of view of human health for long-term stays in space, we have studied the formation of DNA strand breaks and the induction of gene expression in mammalian cells. We previously measured DNA damage in human cultured cells and the accumulation of a tumor suppressor gene product, p53, in muscle and skin of rats after space flight, and the relative importance of microgravity and space radiation in causing these effects remains to be clarified. Our results suggest that the p53 pathway may play a role in safeguarding genomic stability against the stressful space environment. We review here the present knowledge on cellular stress signaling and present our space experimental data. The importance of the stress response to the space environment is also discussed.

Expression of the 72-kD heat shock protein is induced by ultraviolet A radiation in a human fibrosarcoma cell line

The 72-kD heat shock protein (hsp72) belongs to a family of stress inducible proteins (heat shock proteins, hsp) and its expression is associated with increased survival of cells in culture following exposure to ultraviolet radiation (UV). Hsp72 can be induced by a number of stresses, including heat, cold, and toxic chemicals. The purpose of this study was to evaluate whether UV is able to activate transcription of hsp72. The human fibrosarcoma cell line HT1080 was used for these experiments because hsp72 is not detectable in these cells under normal culture conditions. Cells were exposed to UVA and UVB using a solar simulating source and hsp72 was determined in whole cell extracts by immunoblotting. For inhibition of mRNA and protein synthesis cordycepin (20 microg/ml) and cycloheximide (10 microg/ml) were added to the cultures, respectively. UVA-induced lipid peroxidation was inhibited by alpha-tocopherol and butylated hydroxytoluene (BHT). UVA but not UVB induced hsp72 with maximal expression at 40 J/cm2, 8-12 h after exposure. Induction was blocked by cordycepin as well as by cycloheximide indicating that both, mRNA and protein synthesis, are required for UVA-induction of hsp72. Inhibition of cell lipid peroxidation with alpha-tocopherol and BHT had no effect on hsp72 expression. These results suggest that induction of hsp72 is part of an adaptive response mechanism in human cells to UV-related stress.

Heat shock transcription factor-1 regulates heat shock protein-72 expression in human keratinocytes exposed to ultraviolet B light

In response to ultraviolet radiation (UVR), skin keratinocytes increase expression of heat shock proteins that can protect cells from stress-induced damage. This heat shock response is known to be transcriptionally regulated in eukaryotic cells exposed to certain forms of environmental stress. In the skin, absorption of ultraviolet B light occurs primarily in the epidermis, and therefore, using primary cultures of normal human epidermal keratinocytes, we have examined whether transcriptional activation of the hsp72 gene occurs following UVB irradiation. Cultured keratinocytes were exposed to UVB (290-320 nm, 300 J per m2) and then incubated at 37 degrees C for various intervals before harvesting. Immediately following UV exposure, the heat shock transcription factor 1 (HSF1) dissociated from HSP72-HSF1 complexes, underwent trimerization and phosphorylation, and demonstrated DNA binding activity to the heat shock element in the promoter region of the hsp72 gene. UVB also increased hsp72 mRNA, with peak levels observed 1-3 h post-UVR. HSP72 protein was constitutively expressed in keratinocytes, and its expression was increased by UVB, with maximum levels at 6 h post-UVR. The stress response may be extremely important in the protection of human skin from UVB radiation, and modulation of heat shock protein expression and/or function offers a potential therapeutic target in the prevention of photoaging and skin cancer.

Suppression of heat-induced HSF activation by CDDP in human glioblastoma cells

PURPOSE

The kinetics of the accumulation of inducible 72-kD heat shock protein (hsp72) and the activation of heat shock transcriptional factor (HSF) after hyperthermia and/or CDDP treatment in two human glioblastoma cell lines, A-172 having the wild-type p53 gene and T98G having the mutated p53 gene were evaluated.

METHODS AND MATERIALS

Western blot analysis of hsp72, gel-mobility shift assay of HSF, cell survival, and development of thermotolerance were examined.

RESULTS

The prominent suppression of heat-induced hsp72 accumulation by CDDP was seen in A-172 cells, but not in T98G cells. This was due to the p53-dependent inhibition of heat-induced HSF activation by CDDP. The interactive hyperthermic enhancement of CDDP cytotoxicity was observed in A-172 cells, but not in T98G cells. In addition, the heat-induced thermotolerance was suppressed by the presence of CDDP in the pretreatment.

CONCLUSION

Suppression of heat-induced hsp72 accumulation by CDDP contributes to an interactive hyperthermic enhancement of CDDP cytotoxicity in the cells bearing the wild-type p53 gene.

Suppression of heat-induced hsp72 accumulation by cisplatin in human glioblastoma cells

The accumulation of the inducible hsp72 (72-kDa heat shock protein) after hyperthermia and/or cisplatin treatment in human glioblastoma cell line (A-172) was studied by Western blot analysis. The level of hsp72 increased to eight-fold 10 h after hyperthermia alone (44 degrees C for 20 min, D50) and to three-fold 10 h after cisplatin treatment (5 microg/ml) at 37 degrees C for 15 min (D50). In contrast, when the cells were simultaneously heated with cisplatin, the accumulation of hsp72 was suppressed. The level of hsp72 increased to about six-fold and two-fold 10 h after hyperthermia (44 degrees C, 15 min) in the presence of 1 and 10 microg/ml (D50 or D10) of cisplatin, respectively. In addition, we found both the enhancement of thermosensitivity and the suppression of thermotolerance by the simultaneously combined treatment of hyperthermia and cisplatin. It has been reported that the enhancement of cisplatin cytotoxicity by hyperthermia is due to increase of both cisplatin uptake and DNA damage by hyperthermia. Our results suggest that the interactive cytotoxic enhancement by the combination of hyperthermia and cisplatin may be also due to the suppression of heat-induced hsp72 accumulation by cisplatin.

DNA-damaging agents induce the 72-kD heat shock protein in SV40 transformed normal human fibroblasts

In order to elucidate the involvement of DNA damage in the induction of heat shock proteins (stress proteins), we examined the induction of 72-kD heat shock protein (HSP72) in an SV40-transformed human fibroblast cell line (WI38VA13) which was exposed to various DNA-damaging agents, including 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3 -nitro-methylmethane sulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, and 4-nitroquinoline-N-oxide. Induction of HSP72 was detected by the indirect immunofluorescence method using a monoclonal antibody. All the DNA-damaging agents used in this study induced HSP72 on human fibroblasts. This result indicates that DNA damage is one trigger for the induction of HSP72.

Stress proteins in the cellular response to ultraviolet radiation

Virtually all cells-from prokaryotes to highly differentiated mammalian tissues-respond to a sudden increase in temperature with increased production of a limited set of proteins, called heat shock proteins or stress proteins (hsp). Other stress factors such as alcohol, heavy metals, oxidants and agents leading to protein denaturation are equally able to induce a similar response. Induction of hsp is followed by a transient state of increased resistance to further stress. Many hsp function as "molecular chaperones" by binding to partially folded or misfolded proteins thus preventing their irreversible denaturation during stress exposure. The high evolutionary conservation of this reaction suggests its importance for the survival of cells and tissues under hostile environment conditions. Ultraviolet radiation (UV) exerts many potentially harmful effects on prokaryotic and eukaryotic cells and hsp may help the cell to cope with UV-induced damage. This review will focus on the role of hsp in the cellular response of mammalian skin to UV. Hsp have been detected in resting as well as stress exposed epidermal and dermal cells and experimental evidence points to the fact that these proteins mediate protection from UV induced cell death in vitro and in vivo. Experimental studies further indicate that UV itself might be able to induce the expression of specific hsp. Thus, hsp might provide an adaptive cellular response to increasing exposure to UV. Furthermore, UV-activation of hsp synthesis may provide a valuable model for investigation of the transcription regulation of UV-induced gene expression.

8-methoxypsoralen and ultraviolet a radiation activate the human elastin promoter in transgenic mice: in vivo and in vitro evidence for gene induction

Treatment of skin diseases with the combination of 8-methoxypsoralen and ultraviolet A radiation (PUVA) results in clinical alterations in treated skin that resemble those observed in chronically photodamaged skin. The PUVA-treated patients develop nonmelanoma skin cancers, pigmentary alterations and wrinkling characteristic of sun-induced changes. The major alteration in the dermis of sun-damaged skin is the deposition of abnormal elastic fibers, termed solar elastosis. Up-regulation of elastin promoter activity in dermal fibroblasts explains the excess elastic tissue but not the reason for the aberrant morphology of the elastotic material. In order to study photoaging in an experimental system, we utilized a transgenic mouse line that expresses the human elastin promoter/chloramphenicol acetyltransferase construct in a tissue-specific and developmentally regulated manner. Although UVB radiation has been demonstrated to increase promoter activity in vitro, UVA fails to demonstrate a similar effect at the doses utilized. In this study, we demonstrate the ability of PUVA treatment to up-regulate elastin promoter activity both in vitro and in vivo. These data help to explain the development of photoaging in sun-protected PUVA-treated skin. We attribute the up-regulation of elastin promoter activity in response to PUVA to the formation of DNA photoadducts, which do not occur in response to UVA radiation alone.

Induction of the low-molecular-weight stress protein HSP27 in organ-cultured normal human skin

To examine the inducibility of 27-kD-molecular-weight heat shock protein (HSP27) in human skin, an indirect immunofluorescence (IF) study was performed on organ-cultured normal human skin by using a monoclonal antibody specific for HSP27. After heat treatment at 45 degrees C for 1 h, nuclear IF was observed in the epidermal cells. When the organ-cultured skin explants were exposed to 10.0 micrograms/ml or 100.0 micrograms/ml 8-methoxypsoralen (8-MOP) for 1 h and then irradiated with UVA (320-400 nm), positive nuclear IF was also observed 6 h after UVA irradiation. Considering these results with the previous reports about HSP72, it appears that, in human skin, HSP27 as well as HSP72 plays an important role in resisting various environmental stresses.

Epidermal expression of 65 and 72 kd heat shock proteins in psoriasis and AIDS-associated psoriasiform dermatitis

BACKGROUND

Psoriasiform dermatitis is common in patients with AIDS. The expression of heat shock proteins by keratinocytes has been postulated to be a significant factor in the physiopathology of psoriasis and might be subject to modulation in HIV-infected patients.

OBJECTIVE

We sought to evaluate the epidermal expression of 65 and 72 kd heat shock proteins (HSPs) in lesions of AIDS-associated psoriasiform dermatitis (AIDS-PD) and compare it with that in psoriasis vulgaris and seborrheic dermatitis in patients not infected with HIV.

METHODS

Sections from paraffin-embedded blocks of biopsy specimens of AIDS-PD (eight cases), psoriasis vulgaris (eight cases), seborrheic dermatitis (four cases), and normal skin (four cases) in non-HIV-infected patients were immunohistochemically stained by the avidin-biotin-peroxidase method and two monoclonal antibodies directed against the major 65 kd HSP antigen (HSP65) and against 70/72 kd HSP. The intensity, distribution, and cellular pattern of the epidermal stain were graded and assessed blindly.

RESULTS

The epidermal expression of HSP65 in biopsy specimens from AIDS-PD lesions was irregular, with less intensity and less tendency to perinuclear arrangement than in psoriasis or seborrheic dermatitis not associated with AIDS. The expression of HSP72 was also less intense and more uniform in AIDS-PD.

CONCLUSION

The altered interplay of T cells and keratinocytes in a situation of immune derangement such as AIDS might account for the differences observed in the expression of HSP65 and HSP72 by keratinocytes in psoriasis and AIDS-PD.

Cell stress and implications of the heat-shock response in skin

Heat-shock proteins (HSPs), or so-called 'stress proteins' may play an important role in cutaneous pathophysiology. HSPs are a group of highly conserved molecules that are expressed by all cells when subjected to heat or other forms of physical or chemical stress. The physiological roles of stress proteins are varied and are important in stress and nonstress conditions. They bind to other cellular proteins and participate in protein folding pathways during stress and also during the synthesis of new polypeptides. HSPs are also essential for thermotolerance and for prevention and repair of damage caused in DNA after ultraviolet exposure. Although HSPs are expressed in the skin in both epidermis and dermis, HSPs may influence many other cellular processes in the inflammatory and immune skin response. Many authors have speculated on a link between HSPs and human skin disease characterized by inflammation and proliferation.

Role of the chaperone protein Hsp104 in propagation of the yeast prion-like factor [psi+]

The yeast non-Mendelian factor [psi+] has been suggested to be a self-modified protein analogous to mammalian prions. Here it is reported that an intermediate amount of the chaperone protein Hsp104 was required for the propagation of the [psi+] factor. Over-production or inactivation of Hsp104 caused the loss of [psi+]. These results suggest that chaperone proteins play a role in prion-like phenomena, and that a certain level of chaperone expression can cure cells of prions without affecting viability. This may lead to antiprion treatments that involve the alteration of chaperone amounts or activity.

Heat shock proteins and molecular chaperones: implications for adaptive responses in the skin

Recent advances in the biology of heat-shock proteins (hsps) are reviewed. These abundant and evolutionarily highly conserved proteins (also called stress proteins) act as molecular escorts. Hsps bind to other cellular proteins, help them to fold into their correct secondary structures, and prevent misfolding and aggregation during stress. Cytoplasmic hsp70 and hsp60 participate in complicated protein-folding pathways during the synthesis of new polypeptides. Close relatives of hsp70 and hsp60 assist in the transport and assembly of proteins inside intracellular organelles. Hsp90 may have a unique role, binding to the glucocorticoid receptor in a manner essential for proper steroid hormone action. Hsps may also be essential for thermotolerance and for prevention and repair of damage caused by ultraviolet B light. A unique class of T lymphocytes, the gamma delta T cells, exhibits a restricted specificity against hsps. These T cells may constitute a general, nonspecific immune mechanism directed against the hsps within invading organisms or against very similar hsps within invading organisms or against very similar hsps expressed by infected (stressed) keratinocytes. Immunologic cross-reactivity between hsps of foreign organisms and of the host may play a role in some autoimmune diseases. Although hsps are expressed in the skin, many questions remain about their role during injury, infection, and other types of cutaneous pathophysiology.

Psoralen-protein photochemistry--a forgotten field

8-Methoxypsoralen in combination with long wavelength ultraviolet light is employed for the treatment of several cutaneous disorders, such as psoriasis, vitiligo and mycosis fungoides. It is common to attribute the efficacy of the photochemotherapy to the formation of psoralen DNA photoadducts. Thus, the main research effort has been directed towards the elucidation of nucleic acid photochemistry and related subsequent events (mutagenicity, toxicity). However, psoralens have been shown to undergo photoaddition reactions with other cellular components. In this review the status of psoralen-DNA photobiology is briefly summarized. The main focus, however, is on a survey of psoralen photochemical modification of proteins and the ways by which these additional photobiological events can impact the antigenicity and potentially immunogenicity of treated cells. Some preliminary results show the extent of psoralen-amino acid photoadduct formation and their impact on enzymatic processing.

The effect of N-acetylcysteine on the UVB-induced inhibition of epidermal DNA synthesis in rat skin

The effect of N-acetylcysteine (NAC), on the UVB-induced inhibition of epidermal DNA synthesis in rat skin was investigated. Topical application of NAC, 30 min prior to UVB irradiation (20 kJ m-2), significantly reduced the UVB-induced inhibition of the epidermal (methyl-1',2'-3H)-thymidine uptake. These results indicate that NAC affords protection against at least some of the damaging effects of UVB radiation on epidermal DNA, probably by neutralization of UVB induced reactive species.