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Biomedical subjects

P P Agin

Publications and source records attributed to P P Agin.

At least 19 recordsLinked to original sources
PubMed1996

Chronic exposure of Sk-1 hairless mice to narrow-band ultraviolet A (320-355 nm)

Several recent investigations collectively suggest that the role of ultraviolet A (UVA) in chronic actinic skin damage may be greater than originally thought. In the present work, the output of a xenon-arc solar-simulator passed through a Bausch & Lomb monochromator in conjunction with a 2-mm Schott WG-320 filter produced narrow-band UVA centered at 338 nm, half-band width 24 nm, I0 = 3.4 +/- 0.3 mW/cm2. We chronically irradiated 10 Sk-1 albino hairless mice 5 times per week for 18 weeks, starting with 1.25 J/cm2, for 33 irradiation days, sequentially followed by 1.50 J/cm2 (34 days), 1.8 J/cm2 (10 days), 2.0 J/cm2 (22 days) to afford a total UVA dose of 154.3 J/cm2 over 99 irradiation days. Erythema was noted clinically by day 6, which persisted throughout the irradiation. During the irradiation period, some scaling, consistent with mild epidermal hyperplasia was noted during irradiation days 37-56. This response later regressed despite continued chronic irradiation. Hematoxylin and eosin examination immediately after the final irradiation revealed a mild inflammatory response, with some dermal restructuring. At the end of the experiment, no significant signs of epidermal hyperplasia or (pre)malignant lesions were seen, although some stratum corneum thickening was noted. Marked dermal collagen damage and moderate elastosis was also evident. We believe that the observed differences in results reported in previous studies are in large part due to differences in light sources and irradiation protocols.

Animals↗
PubMed1992

Dose-response of chronic ultraviolet exposure on epidermal forward scattering-absorption in SK-1 hairless mouse skin.

This work provides a dose-response model of UV-induced epidermal-stratum corneum thickening induced by irradiation at wavelength lambda. This model assumes that photobiochemical reaction(s) can give rise to hyperplasia in a manner which is predictable from a simple photochemical kinetic scheme. In this work, we derive an equation which predicts an approximately linear relationship between the logarithm of the increase in optical skin thickening measured at 320 nm (delta OD320) and total cumulative dose (DT) seen by the target cells in or near the basal layer. For each excitation wavelength lambda, the slope R(lambda) of the log delta OD320 vs DT plot is proportional to epsilon(lambda) phi rx, where epsilon(lambda) is the extinction coefficient for the target chromophore at excitation wavelength, and phi rx is the quantum yield for the photochemical reaction(s) leading to hyperplasia. Our data previously obtained from irradiation of SK-1 hairless mice with "monochromatic" UV wavebands at 280, 290, 300, 307 and 313 nm (Menter et al., 1988, Photochem. Photobiol. 47, 225-260.) and data from Sterenborg and van der Leun at 254 and 313 nm (1988, Photodermatology 5, 71-82) are in good agreement with this model, except for 254 and 280 nm excitation, which are greatly attenuated by epidermis-stratum corneum. For excitation at the latter wavelengths, "dark" regressive processes successfully compete with the "light" reaction(s) which lead to (pre)cancerous lesion. This difficulty notwithstanding, the "intrinsic" action spectrum for hyperplasia derived from these measurements indicates that the target chromophore preferentially absorbs in the UV-C region.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Diacylglycerol-induced melanogenesis in Skh-2 pigmented hairless mice.

We investigated the effect of topically applied diacylglycerols (DG) on melanogenesis in Skh-2 pigmented hairless mouse skin. Groups of mice were treated according to 4 different regimens of either 1,2-dioctanoyl-sn-glycerol (DOG) or 1-oleyl-2-acetyl-sn-glycerol (OAG) with or without ultraviolet irradiation (UVR). After the treatment regimens were completed, separated epidermal tissue was stained with L-dopa and thin sections of whole skin were stained by the Warthin-Starry method to detect melanin deposition. Quantification of the stained areas by digital image analysis disclosed that DOG treatment without UVR increased the dopa-positive area in skin in a dose-dependent manner but had no effect on melanin deposition. DG treatment acted synergistically with UVR to enhance melanogenesis, with synergism being more pronounced for melanin deposition than for dopa staining. DOG treatment prior to UVR also resulted in an enhanced melanogenic response to UVR, suggesting that DG increases the sensitivity of melanocytes to subsequent UVR by inducing dopa oxidase activity. OAG also enhanced UVR-induced melanogenesis in a dose-dependent manner and was at least as potent an inducer as was DOG. Because DG is known to activate protein kinase C, our results suggest that a protein kinase C-dependent process is involved in melanogenesis.

Administration, Cutaneous↗
PubMed1990

A method for the determination of UVA protection for normal skin.

Although the UVB portion of the electromagnetic spectrum (290 to 320 nm) is responsible for most of the harmful effects of sunlight on the skin, wavelengths in the UVA region also contribute to photodamage. A simple and rapid clinical test, the sun protection factor determination, is available to assess the sunburn protective effect of a sunscreen, primarily a UVB effect. However, no practical test has been proposed to measure a sunscreen's UVA protection. We described a method for the calculation of UVA protection in normal subjects. The determination of UVA protection involves three steps: (1) the UV absorbance spectrum of the sunscreen on skin is determined spectrophotometrically; (2) a convolution spectrum is calculated by multiplying the solar spectrum with the Commission Internationale de l'Eclairage UV Hazard Spectrum; and (3) the sunscreen transmission spectrum is then incorporated into the convolution spectrum to obtain the UVA effectiveness ratio, which can be expressed as the UVA protection percentage. Because the UVA protection percentage value is based both on normal erythemic risk and on standard sunlight, the protection for any product can be easily measured. The procedure is simple, and values generated can be reproduced in other laboratories.

Erythema↗
PubMed1987

Phosphorylated mixed isomers of L-dopa increase melanin content in skins of Skh-2 pigmented hairless mice.

Dopa phosphates, a new class of compounds, contain phosphate-ester linkages at the 3- and/or 4- positions of the phenylalanine ring of L-dopa. Dopa phosphates have been shown to increase pigment production in the epidermis of hairless mice. Groups of Skh-2 pigmented hairless mice were treated topically with various concentrations of dopa phosphates daily for five weeks. Half of each group received suberythemal UVB radiation three times weekly for four weeks from a bank of filtered FS20 lamps. UVB and dopa phosphates alone each caused a modest increase in epidermal pigmentation. However, treatment of mice with dopa phosphates plus UVB radiation resulted in a marked increase in pigmentation, greater than with either treatment alone. The optimal concentration of dopa phosphates was 0.01% (100 micrograms/ml Tris-glycerol buffer) whether or not they were applied in conjunction with UVB radiation. Histological analyses revealed that dopa phosphates and UVB radiation each caused an increase in the number of pigmented melanocytes in the epidermis. Control groups treated with Tris-glycerol buffer alone, or buffer containing L-phenylalanine or L-dopa showed no significant changes in pigmentation. Our results indicate that dopa phosphates stimulate the production of melanin and affect the development and distribution of melanocytes in the skin of Skh-2 mice. By these criteria, dopa phosphates and UVB act in a similar manner to increase melanin content in the skin. The processes may be related to those recently observed in cultured mouse melanoma cells where dopa phosphates are incorporated into melanin, presumably following enzymatic hydrolysis by cellular phosphatases with the resultant production of L-dopa and inorganic phosphate.

Animals↗
PubMed1987

A novel model for testing enhancers of pigmentation.

Mouse skin, unlike human skin, does not contain active epidermal melanocytes, with the exception of the ear and tail skin in some pigmented strains. We have investigated enhancement of pigmentation in inbred C3H- mice using tail skin as a model for testing the effects of phosphorylated DOPA (DP) and ultraviolet radiation. Mice were restrained by cage dividers and treated with various doses of DP in dimethylsulphoxide (DMSO) or DMSO alone with or without the addition of UV radiation. Each tail served as its own control since only the dorsal surface was treated and irradiated. Pigmentation was graded blindly on histologic sections stained with Fontana-Masson. UV radiation caused a marked increase in epidermal and dermal pigmentation and this was enhanced in a dose-dependent manner by DP. However, there was minimal effect from DP alone.

Animals↗
PubMed1985

The relationship of immediate pigment darkening to minimal erythemal dose, skin type, and eye color.

Immediate pigment darkening (IPD) was recorded in over 1,300 volunteers participating in routine sun protection factor (SPF) testing. Medical history obtained included skin type, hair color, eye color, sunburn sensitivity, tanning ability, and current medications. The presence of IPD and the energy needed to produce it were recorded immediately following exposure to a filtered 2500 W xenon are solar simulator. Minimal erythemal dose (MED) values were recorded 16-24 hours post-exposure. The average MED was lowest for skin type I and highest for skin type IV. The IPD dose was also lowest for skin type I and highest for skin type IV. However, the average IPD dose was greater than the MED for skin type I and lower than the MED for skin type IV. For skin types II and III, the average IPD dose and MED were almost equivalent. For skin type I, 64% required equivalent or greater energy to produce IPD than their MED, and 30% showed no IPD at energy levels sufficient to produce erythema, whereas all skin type IV's had a measurable IPD response. For volunteers of skin type II and III showing no measurable IPD, the predominant eye color was blue or green (74%). Sunscreen usage altered the IPD response for all 4 skin types.

Dose-Response Relationship, Radiation↗
PubMed1982

A novel method for purification of plasma fibronectin.

Plasma fibronectin was purified from a gelatin-affinity chromatography column by elution with glucose. This procedure was effective only if the gelatin was particulate when it was attached to the Sepharose 4B. Glucose could not elute fibronectin from the gelatin if the gelatin was melted before it was attached to the Sepharose 4B. This new purification technique has the advantage of using very mild conditions for the isolation of plasma fibronectin.

Chromatography, Affinity↗
PubMed1981

Changes in epidermal forward scattering absorption after UVA or UVA-UVB irradiation.

Groups of skh-1 (albino) and Skh-2 (pigmented) hairless mice were irradiated for 125 hr using a modified GE F8T5-BL black light with and without a 3-mm plate glass filter to remove light below 320 nm. The epidermis was examined by forward scattering and by histological section postirradiation at 48 hr, 96 hr, 9 days, and 23 days. Changes in the epidermis of all animals were compared to control groups. Although no differences were seen between Skh-1 and Skh-2 mice, both the magnitude and shape of the forward scattering absorption curves were changed by the irradiation used. In both strains, differences which were detected at 48 hr postirradiation had returned to normal visually by 23 days, with no augmented pigmentation occurring in Skh-2 animals. At 23 days postirradiation, however, residual optical alterations were observed. This phenomenon, detected optically, may be skin acclimatization.

Absorption↗
PubMed1979

Photoprotection by melanin--a comparison of black and Caucasian skin.

The photoprotective role of melanin was evaluated by comparing the transmission of ultraviolet (UV) radiation through skin samples of blacks and Caucasians, using both biologic and spectroscopic techniques. UVA transmission was measured using fluoranthene, which causes a phototoxic response to UVA wavelength. UVB was measured by monitoring erythema produced by either a 150-watt xenon arc or FS-20 sunlamps. It was found that on the average, five times as much ultraviolet light (UVB and UVA) reaches the upper dermis of Caucasians as reaches that of blacks. Differences in transmission between the stratum corneum of blacks and of Caucasians were far less striking. The main site of UV filtration in Caucasians is the stratum corneum, whereas in blacks it is the malpighian layers. Melanin acts as a neutral density filter, reducing all wavelengths of light equally. The superior photoprotection of black epidermis is due not only to increased melanin content but also to other factors related to packaging and distribution of melanosomes. Not only are these data consistent with epidemiologic evidence, but they also may indicate why blacks are less disposed to phototoxic drug responses as well as less susceptible to acute and chronic actinic damage.

Adult↗