An in vivo model for postinflammatory hyperpigmentation: an analysis of histological, spectroscopic, colorimetric and clinical traits.

BACKGROUND: Acne vulgaris is a common condition that occurs in all skin types. Postinflammatory hyperpigmentation (PIH) is often associated with acne in patients of darker skin types, making it a common complaint in dermatology offices. Despite this, there is limited understanding of and effective treatment options for PIH. OBJECTIVES: The study objective was to validate an in vivo model for PIH and to compare the clinical, histological and spectroscopic characteristics of artificially induced PIH and acne-induced PIH. METHODS: A nonblinded, nonrandomized pilot study was performed. Thirty subjects served as their own control in which four sites treated with 35% trichloroacetic acid (TCA) solution and four truncal acne pustules were followed for 8 weeks and were evaluated clinically and histologically, and by colorimetry and spectroscopy. RESULTS: The initial phases of inflammation between TCA- and acne-induced PIH differ. However, clinical evaluations were similar on and after day 14. Acne- and TCA-induced lesions were clinically, histologically and spectroscopically indistinguishable at day 28. CONCLUSIONS: Clinical, spectroscopic and histological similarities of acne-induced and TCA-induced PIH at day 28 suggest that TCA-induced PIH can be a reproducible model for the study of acne-induced PIH.

Does poor sleep quality affect skin ageing?

BACKGROUND: Sleep is important for growth and renewal of multiple physiological systems. The effects of chronic poor sleep quality on human skin function and visible signs of ageing have not been elucidated. AIM: To evaluate the effect of chronic poor sleep quality on measures of skin health and ageing. Self-perceived satisfaction with appearance was also assessed. METHODS: 60 healthy caucasian women, who were categorized as poor quality sleepers [Pittsburg Sleep Quality Index (PSQI) > 5, sleep duration ≤ 5 h] or good quality sleepers (PSQI ≤ 5, sleep duration 7-9 h). A validated clinical tool, SCINEXA(TM) , was used to assess intrinsic and extrinsic skin ageing. Dark under-eye circles were evaluated using standardized photos. Measurement of in vivo transepidermal water loss (TEWL) was used to assess recovery of the skin barrier after tape stripping. Subjects were exposed to simulated solar ultraviolet light, and recovery from erythema was monitored. Subjects also completed a questionnaire evaluating self-perception of attractiveness. RESULTS: Good sleepers had significantly lower intrinsic skin ageing scores by SCINEXA(TM) . At baseline, poor sleepers had significantly higher levels of TEWL. At 72 h after tape stripping, good sleepers had 30% greater barrier recovery compared with poor sleepers. At 24 h after exposure to ultraviolet light, good sleepers had significantly better recovery from erythema. Good sleepers also reported a significantly better perception of their appearance and physical attractiveness compared with poor sleepers. CONCLUSIONS: This study indicates that chronic poor sleep quality is associated with increased signs of intrinsic ageing, diminished skin barrier function and lower satisfaction with appearance.

Antioxidants add protection to a broad-spectrum sunscreen.

BACKGROUND: Exposure of human skin to ultraviolet radiation (UVR) results in erythema, pigment darkening, skin cancer and photoageing. In addition to conventional organochemical and the physical-mineral type sunscreens (SS), other non-SS protective strategies have been investigated, including antioxidants (AOx) and topical DNA repair enzymes. AIM: To investigate whether AOx could improve the protection provided by a broad-spectrum sunscreen (SS) preparation. METHODS: Volunteers were exposed to repetitive solar-simulated (ss)UVR at 1.5 times minimal erythema dose for four consecutive days. Thirty minutes before each exposure and 6, 24 and 48 h after the last exposure, the test materials [vehicle, SS (sun protection factor 25) alone, AOx alone and SS plus AOx] were applied to four different sites. Another two sites received ssUVR only, or SS plus AOx only, and a third site was left untreated (neither ssUVR or product). Erythema and pigmentation were measured using a Mexameter. Biopsy specimens were taken 72 h after the last irradiation. The thickness of the stratum corneum and epidermis were measured by microscopy. Expression of cytokeratins (CKs), matrix metalloproteinases (MMPs) and CD1a-positive Langerhans cells (LCs) analysed by immunohistochemical staining, and relative expression levels were compared between all seven sites. RESULTS: AOx alone did not reduce erythema. There was a significant reduction in pigmentation, and the product almost completely protected against LC depletion. AOx plus SS gave better protection against pigment formation and CK5/6 induction than SS alone. AOx alone protected against ssUVR-induced hyperproliferation, as shown by epidermal thickness and CK16 biomarkers, and was better than SS alone. Interestingly, although protection against induction of MMP-9, a marker of photoageing, did not reach significance when either SS or AOx were applied separately, there was complete protection against MMP-9 induction when these were combined. CONCLUSIONS: Non-SS materials such as AOx can contribute significantly to sun protection when added to a broad-spectrum SS and applied topically to human skin in vivo.

Arginase is overactive in psoriatic skin.

BACKGROUND: Psoriatic keratinocytes are poorly differentiated and hyperproliferative. Low concentrations of nitric oxide (NO) induce keratinocyte proliferation, while high concentrations induce differentiation. The NO-producing enzyme inducible NO synthase is overexpressed in psoriatic skin, but so is arginase. The overexpressed arginase competes for arginine, the common substrate for both enzymes, and may reduce NO production. OBJECTIVES: To determine whether arginase activity is elevated in psoriatic skin and whether exogenous NO will improve psoriatic plaques. METHODS: Tape strips were taken from healthy skin of eight control subjects and nonlesional skin of eight patients with psoriasis and L-arginine, L-citrulline and L-ornithine concentrations measured by high-performance liquid chromatography. In a second study, four psoriatic patients with a pair of similar symmetrical plaques were treated with an NO donor and vehicle control. Plaques were scored for size, erythema, induration and scaling at the start and after 6 weeks of treatment. RESULTS: Ornithine, the end-product of arginase, was at higher concentrations in nonlesional psoriatic than in healthy skin (mean +/- SEM 2.08 +/- 0.98 vs. 1.13 +/- 0.44 microg mg(-1) protein; P = 0.0002). Arginine, its substrate, was at lower concentrations. Topical application of an NO donor improved psoriatic plaques clinically [mean +/- SD reduction in severity from baseline score (100%) to 35% +/- 16% in active NO donor and to 93% +/- 10% in control]. CONCLUSIONS: Arginase is overactive in psoriatic skin, leading to a relative increase in the consumption of arginine. We therefore hypothesize a relative decrease in NO synthase-derived NO production. NO donors may be effective topical treatments for psoriasis.

Psychological stress perturbs epidermal permeability barrier homeostasis: implications for the pathogenesis of stress-associated skin disorders.

BACKGROUND: A large number of skin diseases, including atopic dermatitis and psoriasis, appear to be precipitated or exacerbated by psychological stress. Nevertheless, the specific pathogenic role of psychological stress remains unknown. In 3 different murine models of psychological stress, it was recently shown that psychological stress negatively impacts cutaneous permeability barrier function and that coadministration of tranquilizers blocks this stress-induced deterioration in barrier function. OBJECTIVES AND METHODS: The relationship between psychological stress and epidermal permeability barrier function was investigated in 27 medical, dental, and pharmacy students without coexistent skin disease. Their psychological state was assessed with 2 well-validated measures: the Perceived Stress Scale and the Profile of Mood States. Barrier function was assessed simultaneously with the stress measures at periods of presumed higher stress (during final examinations) and at 2 assumed, lower stress occasions (after return from winter vacation [approximately 4 weeks before final examinations] and during spring vacation [approximately 4 weeks after final examinations]). RESULTS: The subjects as a group demonstrated a decline in permeability barrier recovery kinetics after barrier disruption by cellophane tape stripping, in parallel with an increase in perceived psychological stress during the higher vs the initial lower stress occasions. During the follow-up, presumed lower stress period, the subjects again displayed lower perceived psychological stress scores and improved permeability barrier recovery kinetics, comparable to those during the initial lower stress period. Moreover, the greatest deterioration in barrier function occurred in those subjects who demonstrated the largest increases in perceived psychological stress. CONCLUSION: These studies provide the first link between psychological status and cutaneous function in humans and suggest a new pathophysiological paradigm, ie, stress-induced derangements in epidermal function as precipitators of inflammatory dermatoses.

Ultraviolet-B exposure of human skin induces cytochromes P450 1A1 and 1B1.

The cytochromes P450 belong to a multigene superfamily and are responsible for the metabolic activation of both xenobiotics and endobiotics. The expression of cytochrome P450 genes in target cells is an important determinant of human susceptibility to cancers and other chemically initiated diseases. In this study using immunohistochemistry, reverse transcription polymerase chain reaction, and western blot analysis, we investigated the cellular distribution and localization of cytochrome P450 1A1 and cytochrome P450 1B1 in human skin, and their induction by ultraviolet-B. Through the use of immunohistochemistry, cytochrome P450 1A1 was found to be primarily localized in the basal cell layer of the epidermis in non-ultraviolet-B exposed skin, whereas cytochrome P450 1B1 was localized in the epidermal cells other than the basal cell layer. Thus, localizations of cytochrome P450 1A1 and cytochrome P450 1B1 in human skin are different and may be related to keratinocyte differentiation. Ultraviolet-B exposure to solar-ultraviolet-protected skin (buttock site) resulted in an ultraviolet-B dose-dependent (0-4 minimal erythema doses) and time-dependent (0-48 h) induction of both cytochrome P450 1A1 and cytochrome P450 1B1 in the epidermis. Reverse transcription polymerase chain reaction and western blot analyses revealed that exposure of human skin to ultraviolet-B (4 minimal erythema doses) resulted in enhanced expression of mRNA and protein of both cytochrome P450 1A1 and cytochrome P450 1B1 in the epidermis. Ultraviolet-B induction of both cytochrome P450 1A1 and cytochrome P450 1B1 in human skin will probably result in enhanced bioactivation of polycyclic aromatic hydrocarbons and other environmental pollutants to which humans are exposed, which in turn could make the human skin more susceptible to ultraviolet-B-induced skin cancers or allergic and irritant contact dermatitis.

Kinetics of UV light-induced cyclobutane pyrimidine dimers in human skin in vivo: an immunohistochemical analysis of both epidermis and dermis.

It is well known that UV exposure of human skin induces DNA damage, and the cumulative effect of such repeated damage is an important contributor to the development of skin cancer. Here, we demonstrate UV dose- and time-dependent induction of DNA damage in the form of cyclobutane pyrimidine dimers (CPD) in skin cells following a single exposure of human skin to UV radiation. CPD+ cells were identified by an immunohistochemical technique using monoclonal antibodies to thymine dimers. The percentage of CPD+ cells was UV dose-dependent, even a suberythemal (0.5 minimal erythemal dose [MED]) dose resulted in detectable level of cells that contained pyrimidine dimers. Forty-eight hours after irradiation the percent of total epidermal cells positive for CPD ranged from 19 +/- 8, 36 +/- 10, 57 +/- 12 and 80 +/- 10, and total percent dermal cells positive for CPD ranged from 1 +/- 1, 7 +/- 3, 16 +/- 3 and 20 +/- 5, respectively, following 0.5, 1.0, 2.0 and 4.0 MED. CPD were also observed in deeper reticular dermis, which suggest the penetrating ability of UV radiation into the skin. The change in CPD+ cells from 0.5 to 240 h post-UV exposure in both epidermal and dermal compartments of the skin was also quantitated. CPD+ cells were observed in skin biopsies at early time points after UV exposure which remained elevated for 48 h, then declined significantly by 3 days post-UV. A close examination of the skin at and after 3 days following UV exposure indicates the significant removal of DNA damaged cells from the epidermis. Ten days after UV exposure the levels of CPD+ cells in both epidermis and dermis were not significantly different from that in unirradiated skin.

Polyphenolic antioxidant (-)-epigallocatechin-3-gallate from green tea reduces UVB-induced inflammatory responses and infiltration of leukocytes in human skin.

Identification of natural products capable of affording protection against UVB radiation-induced inflammatory responses and generation of oxidative stress may have important human health implications. The UVB exposure-induced skin injury and oxidative stress has been associated with a variety of skin disease conditions including photoaging, inflammation and cancer. Tea is a popular beverage consumed worldwide. In several mouse skin models, topical application as well as oral consumption of green tea has been shown to afford protection against chemical and UVB-induced carcinogenesis and inflammatory responses. In the present study, we investigated in human skin, whether topical application of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent in green tea, inhibits UVB-induced infiltration of leukocytes (macrophage/neutrophils), a potential source of generation of reactive oxygen species (ROS), and generation of prostaglandin (PG) metabolites. Human subjects were UVB irradiated on sun-protected skin to four times their minimal erythema dosage (MED) and skin biopsies or keratomes were obtained either 24 h or 48 h later. We found that topical application of EGCG (3 mg/2.5 cm2) before UVB (4 MED) exposure to human skin significantly blocked UVB-induced infiltration of leukocytes and reduced myeloperoxidase activity. These infiltrating leukocytes are considered to be the major source of generation of ROS. In the same set of experiments we found that topical application of EGCG before UVB exposure decreased UVB-induced erythema. In additional experiments, we found that microsomes from EGCG pretreated human skin and exposed to UVB, compared to UVB exposure alone, produced significantly reduced PG metabolites, particularly PGE2. The PG metabolites play a critical role in free radical generation and skin tumor promotion in multistage skin carcinogenesis. Careful microscopic examination of skin sections, stained with hematoxylin and eosin, under higher magnification (x400) also revealed that EGCG pretreated and UVB-exposed human skin contained fewer dead cells in the epidermis with comparison to nonpretreated UVB-exposed skin. Taken together, our data demonstrate that EGCG has the potential to block the UVB-induced infiltration of leukocytes and the subsequent generation of ROS in human skin. This may explain the possible mechanism involved in anti-inflammatory effects of green tea. We suggest that EGCG may be useful as a topical agent for protection against UVB-induced ROS-associated inflammatory dermatoses, photoaging and photocarcinogenesis. Further studies are warranted in this direction.

Ultraviolet radiation B induces differentiation and protein kinase C in normal human epidermal keratinocytes.

Mid-wave ultraviolet radiation (UVB, 280-320 nm) is highly efficient at inducing erythema, pyrimidine dimers in DNA, oncogene expression and initiation of cutaneous tumors. These UVB-induced responses of epidermal cells have been correlated with the direct effects of UVB on DNA. However, UVB has also been shown to have biologic effects at the cellular level that appear to mimic some of the membrane-associated effects produced by phorbol ester tumor promoters such as 12-O-tetradecanoyl phorbol-13-acetate (TPA). For example, we have previously shown that both UVB irradiation and TPA treatment are followed by release of arachidonic acid and a rapid, dose-dependent inhibition of epidermal growth factor (EGF) binding. TPA generates cellular responses through activation of a phospholipid-dependent, calcium-sensitive protein kinase, protein kinase C (PKC). The primary goal of the studies described here was to compare the cellular effects of TPA with those of UVB with special regard to PKC and keratinocyte growth control, using normal human epidermal keratinocytes. The results obtained showed that both TPA and UVB radiation induced differentiation in normal human keratinocytes. UVB radiation, however, increased both cytosolic and membrane-associated levels of PKC, in contrast to TPA, which increased PKC primarily in the membrane fraction. PKC is probably not the initial chromophore or target molecule of UVB, but because activation of PKC has been shown to be essential for keratinocyte differentiation, differentiation induced by UVB may be caused by activation of PKC by UVB-induced release of diacylglycerol or arachidonic acid.

Effect of benzoyl peroxide on protein kinase C in cultured human epidermal keratinocytes.

Benzoyl peroxide (BzPO) has been the most widely used topical agent for acne since the 1960s. This is true despite numerous reports that BzPO can enhance the development of carcinomas from murine epidermal papillomas. Because activation of protein kinase C (PKC) is considered to mediate cellular responses to other epidermal tumor promotors, we wished to investigate the relationship between BzPO and PKC in cultured human epidermal keratinocytes (NHEK). We assayed (a) direct effects of BzPO on PKC activity in a cell-free system using semipurified human keratinocyte PKC, (b) BzPO effects on the subcellular distribution of PKC, and (c) BzPO modulation of NHEK proliferation and phorbol ester-induced differentiation. NHEK maintained in serum-free media (0.15 mM Ca2+) were treated with concentrations of BzPO in acetone from 100 nM to 500 microM, with concentrations of acetone not exceeding 0.1%. No short-term translocation of PKC from cytosol to membrane was observed at any BzPO concentration. BzPO did not downregulate subcellular levels of PKC activity after 24 h of exposure. BzPO did not significantly antagonize phorbol ester-induced inhibition of proliferation or differentiation but did weakly antagonize Ca(2+)-induced differentiation. Consistent with a PKC-mediated mechanism for Ca(2+)-induced differentiation, BzPO inhibited both human and murine PKC in a cell-free system. These results suggest that BzPO does not promote malignant conversion through a PKC-dependent mechanism, and in fact, inhibits PKC activity in vitro.

Ultraviolet radiation induces phosphorylation of the epidermal growth factor receptor.

Ultraviolet light in solar radiation is responsible for more than 600,000 malignancies each year in the United States alone, making it the most efficient environmental carcinogen known. Ultraviolet radiation-induced direct DNA damage is thought to be responsible for its initiating properties, while the promotional aspects of such radiation are poorly defined and only recently gaining attention. We show here for the first time that physiologically relevant doses of ultraviolet radiation induce phosphorylation of the epidermal growth factor receptor in A431 keratinocytes at tyrosine sites within 30 min. Such alteration of this major signal transduction system is probably an important step in the ultraviolet radiation-induced, epidermal cell-signalling cascade.

Long-wave ultraviolet radiation induces protein kinase C in normal human keratinocytes.

Skin tumor promotion by phorbol ester is believed to be mediated by the phospholipid-dependent ser/thr kinase, protein kinase C (PKC). Long-wave ultraviolet radiation (320-400 nm, UVA), which has also been shown to promote skin tumors, induces elevated levels of PKC in murine fibroblasts, suggesting that UVA may promote the development of basal and squamous cell skin cancers by a mechanism involving PKC. To examine UVA effects on PKC in a model relevant to skin, we maintained normal human epidermal keratinocytes (NHEK) in serum-free medium and exposed the cultured cells to various doses of UVA or to the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). Fifty minutes after exposure to UVA (5-20 J/cm2), PKC activity was elevated up to three-fold in NHEK cytosolic fractions, and membrane-associated PKC activity was elevated up to two-fold by UVA. The TPA treatment induced a 10-fold increase in membrane-associate PKC activity only. Immunoblot analysis suggested that a UVA-induced increase in PKC protein occurred. Both UVA and TPA reduced the cell number by 50-75% in the first 24-48 h; however, irradiated cultures began to recover at 72 h post-UVA due to an increased proliferative rate beginning after 48 h. Treatment with TPA induced a high level of differentiation as measured by cornified envelope formation. Ultraviolet A irradiation exposure was not followed by increased differentiation. These findings suggest that acute UVA exposure elevates PKC activity in human keratinocytes and may act through PKC to promote actinic skin cancer. The molecular mechanism is like to differ from that of the phorbol esters, however.

Protein kinase C agonist and antagonist effects in normal human epidermal keratinocytes.

Several lines of evidence implicate protein kinase C (PKC) in the development of basal cell and squamous cell carcinomas, tumors which originate from epidermal keratinocytes. To examine PKC in a model relevant to human skin, we exposed normal human epidermal keratinocytes (NHEK) in serum-free media to a variety of PKC agonists and antagonists. NHEK PKC activity increased up to 10-fold within the 1st hour of exposure to tetradecanoyl phorbol acetate (TPA), and gradually returned to control values within 72 h. TPA-induced PKC activity was enhanced by pretreatment of cultures with protein and RNA synthesis inhibitors. TPA-induced growth arrest and differentiation was antagonized by staurosporine. Down-regulation by bryostatin pretreatment blocked TPA-stimulated differentiation. Our overall conclusion is that activation of PKC in cultured human keratinocytes is required for differentiation. These results are crucial to the analysis of compounds suspected of promoting or inhibiting epidermal tumors.

Protein kinase C in normal human epidermal keratinocytes during proliferation and calcium-induced differentiation.

Recent evidence has implicated protein kinase C (PKC) in the etiology of hyperproliferative diseases such as psoriasis and non-melanoma skin cancer. In this study, PKC activity, immunoreactive protein, and phorbol ester-binding kinetics were examined in primary cultures of normal human epidermal keratinocytes (NHEK) in order to elucidate the relationship between PKC and NHEK proliferation and differentiation. NHEK were maintained in a proliferative phase in serum-free low-calcium (0.15 mM) medium, and then were exposed to high calcium (1.6 mM) in order to stimulate growth arrest and differentiation. Staurosporine was inhibitory to Ca(++)-induced differentiation. Scatchard analysis of phorbol binding indicated that exposure to high calcium for 24 h increased the number of binding sites (Bmax) by fivefold. In correlation with the ligand-binding results, PKC activity was extremely low in proliferating (low-calcium) NHEK compared to differentiating cells (high calcium). When assayed after 24, 48, and 72 h, high calcium induced tenfold or greater increases in Ca++/phospholipid-dependent phosphotransferase activity. Immunoblot analysis of NHEK PKC using antibodies directed against the hinge region of PKC alpha/beta also indicated that exposure to high calcium resulted in higher levels of immunoreactive protein. Therefore, PKC in NHEK appears to be upregulated under conditions of Ca(++)-induced growth arrest and differentiation. In addition, NHEK and other human skin cell particulate fractions contain a protein of approximately 116 kDa that is highly immunoreactive to an antibody to PKC alpha/beta, which coelutes from DEAE-sephacel under the same buffer conditions as the 80-kDa PKC.

Longwave ultraviolet radiation and promotion of skin cancer.

Exposure to solar ultraviolet (UV) radiation is recognized as an important cause of skin cancer. The carcinogenic effects of UV radiation have been attributed almost entirely to wavelengths in the mid-range (UVB, 290-320 nm). However, the development of potent UVB sunscreens has allowed individuals to increase the length of time that they spend sunbathing and, as a consequence, they may be exposed to massive doses of longwave UV radiation (UVA, 320-400 nm). There is now much evidence to suggest that UVA acts to promote tumors that have been initiated by UVB. This review considers possible mechanisms by which UVA promotes tumorigenesis. Evidence is presented which suggests that UVA acts through modulation of protein kinase C.

Effects of specific fatty acids on cell transformation induced by an activated c-H-ras oncogene.

An increase in dietary lipid has been associated with an increase in the development of certain forms of cancer, notably breast and colon cancer, both in experimental animal studies and in human epidemiology studies. The underlying mechanisms are not, however, known with certainty. In the present studies we have examined whether certain specific fatty acids (FA) might act by enhancing the role of an activated oncogene in a model cell culture system. We found that when the rat fibroblast cell line Rat 6 was transfected with an activated human c-H-ras oncogene and the cells subsequently grown in medium supplemented with myristic acid, palmitic acid or stearic acid (20-80 microM) there was a marked enhancement of the number of transformed foci obtained. On the other hand arachidonic acid had a marked inhibitory effect in this transformation assay. However, this inhibitory effect can be partially reversed by indomethacin, an inhibitor of cyclo-oxygenase, at dose response manner. Control studies indicated that these results were not simply due to the effects of the FAs on growth of the Rat 6 cells or the process of transfection per se. Lipid analyses of cells grown in the presence of stearic acid indicated that the added FA was extensively incorporated into the major lipid classes of the cell and produced transient changes in lipid composition. This simple cell culture system may be useful for elucidating the mechanisms by which various dietary lipids and nutritional factors influence the carcinogenic process.

Induction of protein kinase C activity by ultraviolet radiation.

Exposure to ultraviolet (UV) radiation has been well correlated with skin cancer incidence. Long wave UV radiation (320-400 nm, UVA) is a major component of natural sunlight and cosmetic tanning 'salon' light, and has been shown not only to damage DNA and to act as a complete carcinogen, but also to promote ultraviolet B (280-320 nm, UVB) carcinogenesis. The mechanism by which the latter occurs is unknown, but it is believed to be related to the inflammation and irritation which results from UV exposure. In order to examine the possibility that UVA stimulates the same signalling pathway as do the phorbol esters, a class of much more thoroughly characterized skin tumor promoters, we exposed cells in culture to UVA radiation and measured cellular responses related to protein kinase C (PKC) activation. The data presented here demonstrate that a low, physiologic dose of UVA inhibits epidermal growth factor binding and increases PKC activity in cultured mammalian fibroblasts. The increase in cytosolic activity is not completely translocated to the membrane, and can be partially suppressed by puromycin and cycloheximide but not by actinomycin D. These observations are the first evidence to suggest that a protein which has been strongly linked to chemical tumor promotion may also be a critical mediator for UV-induced promotion. The response of cells to UVA is also unique, in that it does not cause a 12-O-tetradecanoyl phorbol-13-acetate-like rapid redistribution of PKC activity followed by down regulation.

Ultraviolet-B (290-320 nm)-irradiation inhibits epidermal growth-factor binding to mammalian cells.

Mitogens, such as polypeptide growth factors and phorbol ester tumor promoters, act by binding to specific receptors and inducing a pleiotropic response in cultured mammalian cells, which results in the induction of cellular proliferation. An early effect of such agents is the inhibition of binding of epidermal growth factor (EGF) to its receptor. Ultraviolet radiation has also been shown to induce a proliferative response in vivo and in vitro and to act as a tumor promoter in animal skin. We, therefore, examined the effect of ultraviolet radiation (UVB - 290-320 nm) on EGF binding to cells in culture. We found that UVB (100-300 J/m2) induced a rapid, dose-dependent inhibition of EGF binding in a mouse fibroblast cell line, which resulted from a decrease in both number and affinity of binding sites. Phosphorylation of the EGF receptor by protein kinase C (PKC) is not likely to be the mechanism for inhibition, since UVB treatment did not result in PKC activation or modulation of phorbol diester binding.

Nutrition in the prevention of neoplastic disease in the elderly.

This review focuses on specific effects of diet on cancer risk and the relevance of these dietary effects to the risk of cancer in the elderly. The authors address the impact of certain dietary factors on cancer risk by reviewing their roles in two distinct phases of carcinogenesis: "imitation" and "promotion."

Fatty acid modification of C3H 10T 1/2 fibroblast cells: changes in benzo(a)pyrene metabolism and phorbol ester binding.

The mouse embryo fibroblast cell line, C3H 10T 1/2 Cl8, was studied as an in vitro experimental model to investigate the mechanism and specificity behind the modulation of carcinogenesis by dietary lipid. The cells were grown in medium supplemented with 95 microM stearate, linoleate, or palmitate as fatty acid/albumin complexes, during which time they maintained normal growth and morphology characteristics. After 5 days of supplementation total cellular lipid fatty acid was enriched in the supplemented fatty acid. By Day 40, however, fatty acid profiles of all groups were the same. Cellular uptake and utilization of 14C-radiolabeled fatty acids were measured. Within 24 h of supplementation, label was incorporated into cholesterol and diglycerides, cholesterol ester, alkyldiacylglycerols, and phospholipids. Approximately half of the radiolabel was found in phosphatidylcholine. Supplementation significantly increased the rate of benzo(a)pyrene metabolism, but did not affect DNA modification by benzo(a)pyrene. Phorbol dibutyrate binding to C3H 10T 1/2 cells at 4 degrees C was modified by lipid supplementation. At 37 degrees C and 23 degrees C, phorbol dibutyrate binding was characterized by both high- and low-affinity sites for linoleate- and stearate-supplemented cells. At 4 degrees C high-affinity binding was absent in stearate- and palmitate-supplemented cells, but was maintained in linoleate-supplemented cells. These studies suggest that the unsaturated fatty acid content of the diet may not significantly affect the initiation stage of benzo(a)pyrene carcinogenesis, but may instead affect promotion. One possible mechanism for this could involve changes in the lipid microenvironment of membrane receptors involved in tumor promotion.