Nikiforos Kollias

New trends in photobiology: Photoprotection by melanin

Abstract This paper is an attempt to summarize the current state of information on melanin and epidermal melanin pigmentation (EMP) as photoprotective agents. The chemistry and biochemistry of melanin (the particle) and its interaction, in its various forms, with UV radiation are considered. Methods of attenuation of UV radiation are discussed in terms of structure and chemical constituents. Photoprotection by constitutive and facultative pigmentation is reviewed with minimum erythema dose (MED) as the end point. The issue of acclimatization to UV radiation is discussed in terms of UVB phototherapy for psoriasis. Finally, skin cancer is considered as an end point and the reduction of its incidence with pigment level is discussed. It is concluded that whilst EMP provides protection, its extent depends on the end point chosen for evaluation. MED is a convenient photobiological end point but is rather insensitive, whereas skin cancer is sensitive but impractical for laboratory studies. Our current state of knowledge of melanin lacks information on its absorption and scattering coefficients and its refractive index. Methods for the quantitative measurement of EMP are also urgently required.

In vivo Fluorescence Spectroscopy of Nonmelanoma Skin Cancer

Abstract In vivo and ex vivo tissue autofluorescence (endogenous fluorescence) have been employed to investigate the presence of markers that could be used to detect tissue abnormalities and/or malignancies. We present a study of the autofluorescence of normal skin and tumor in vivo, conducted on 18 patients diagnosed with nonmelanoma skin cancers (NMSC). We observed that both in basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) the endogenous fluorescence due to tryptophan residues was more intense in tumor than in normal tissue, probably due to epidermal thickening and/or hyperproliferation. Conversely, the fluorescence intensity associated with dermal collagen crosslinks was generally lower in tumors than in the surrounding normal tissue, probably because of degradation or erosion of the connective tissue due to enzymes released by the tumor. The decrease of collagen fluorescence in the connective tissue adjacent to the tumor loci was validated by fluorescence imaging on fresh-frozen tissue sections obtained from 33 NMSC excised specimens. Our results suggest that endogenous fluorescence of NMSC, excited in the UV region of the spectrum, has characteristic features that are different from normal tissue and may be exploited for noninvasive diagnostics and for the detection of tumor margins.

Microfine Zinc Oxide is a Superior Sunscreen Ingredient to Microfine Titanium Dioxide

Background. Microfine zinc oxide and microfine titanium dioxide are particulate sunscreen ingredients that absorb broad‐spectrum ultraviolet (UV) irradiation. Objective. We compare microfine zinc oxide and microfine titanium dioxide for their abilities to attenuate UVA radiation and their relative whiteness in cosmetic formulations. Methods. UVA attenuation was measured by diffuse reflectance spectroscopy on normal human skin in vivo. Whiteness was determined by reflectance density of dried coatings on a black background of the two particulates at varying concentrations. Results. Microfine zinc oxide demonstrates superior protection compared to microfine titanium dioxide in the UV spectrum between 340 and 380 nm. Microfine zinc oxide is less white than titanium dioxide at all concentrations. Conclusion. Microfine zinc oxide is superior to microfine titanium dioxide as a sunscreen ingredient. It is more protective against long‐wave UVA and is less white at a given concentration.

Fluorescence photography in the evaluation of acne

BACKGROUND Quantification of acne remains a challenge. It may be difficult to identify lesions by standard flash photography. Previous studies have shown that foci of light in fluorescence photographs correspond to high protoporphyrin IX production by Propionibacterium acnes in open comedones, follicles, and inflammatory lesions. OBJECTIVE Our purpose was to study the utility of fluorescence photography for evaluation of acne. METHODS Forty subjects with mild to moderate acne vulgaris were randomly selected to apply either clindamycin 1% topical solution or vehicle twice daily. Counts of acne lesions and flash and fluorescence photographs were obtained at baseline, and at 4, 8, and 12 weeks. RESULTS At 12 weeks, the treatment group had a larger percentage change in open comedones, less fluorescence in all areas assessed, and a larger percent decrease in fluorescence than the vehicle group. CONCLUSION Fluorescence photography appears to be a useful tool to chart the course of acne treatment.

Effects of photodynamic therapy with topical application of 5-aminolevulinic acid on normal skin of hairless guinea pigs

Photodynamic therapy (PDT) is a relatively new approach to the treatment of neoplasms which involves the use of photoactivatable compounds to selectively destroy tumors. 5-Aminolevulinic acid (ALA) is an endogenous substance which is converted to protoporphyrin IX (PpIX) in the synthetic pathway to heme. PpIX is a very effective photosensitizer. The goal of this study was to evaluate the effect of PDT using topical ALA on normal guinea pig (g.p.) skin and g.p. skin in which the stratum corneum was removed by being tape-stripped (TS). Evaluation consisted of gross examination, PpIX fluorescence detection, reflectance spectroscopy, and histology. There was no effect from the application of light or ALA alone. Normal non-TS g.p. skin treated with ALA and light was unaffected unless high light and ALA doses were used. Skin from which the stratum corneum was removed was highly sensitive to treatment with ALA and light: 24 h after treatment, the epidermis showed full thickness necrosis, followed by complete repair within 7 d. Time-dependent fluorescence excitation and emission spectra were determined to characterize the chromophore and to demonstrate a build-up of the porphyrin in the skin. These data support the view that PDT with topical ALA is a promising approach for the treatment of epidermal cutaneous disorders.

Topical Drug Delivery in Humans with a Single Photomechanical Wave

AbstractPurpose. Assess the feasibility ofin vivo topical drug delivery in humans with a single photomechanical wave. Methods. Photomechanical waves were generated with a 23 nsec Q-switched ruby laser. In vivo fluorescence spectroscopy was used as an elegant non-invasive assay of transport of 5-aminolevulinic acid into the skin following the application of a single photomechanical wave. Results. The barrier function of the human stratum corneum in vivo may be modulated by a single (110 nsec) photomechanical compression wave without adversely affecting the viability and structure of the epidermis and dermis. Furthermore, the stratum corneum barrier always recovers within minutes following a photomechanical wave. The application of the photomechanical wave did not cause any pain. The dose delivered across the stratum corneum depends on the peak pressure and has a threshold at ∼350 bar. A 30% increase in peak pressure, produced a 680% increase in the amount delivered. Conclusions. Photomechanical waves may have important implications for transcutaneous drug delivery.

Determination of UVA protection factors using the persistent pigment darkening (PPD) as the end point (part 1) calibration of the method

Background/Aims: The accuracy and reliability of any method to assess the UVA protection effectiveness of sunscreens needs to be demonstrated. The aim of the present study was to calibrate the effectiveness of a biological end point (Persistent Pigment Darkening, PPD) to assess UVA photoprotection.

UVA protection efficacy of sunscreens can be determined by the persistent pigment darkening (PPD) method. (Part 2).

Background: The UVA‐induced Persistent Pigment Darkening (PPD) in vivo has been proposed as an end point for the evaluation of UVA protection.

Erythema and melanogenesis action spectra in heavily pigmented individuals as compared to fair-skinned Caucasians

The protective role of epidermal melanin pigmentation against chronic exposure to ultraviolet radiation is widely accepted, although its photoprotective effect against acute exposure is less certain. In this study, the action spectra of erythema and melanogenesis in heavily pigmented individuals (skin type V) were determined at 295, 305, 315, and 365 nm, and compared with those of skin types I and II. When the erythema and melanogenesis action spectra for skin type V were normalized to 295 nm, they were identical to the corresponding action spectra for fair‐skinned individuals, indicating that the photoprotection of epidermal melanin pigmentation is essentially independent of wavelength. The ratio of values for the minimum erythema dose (MED) between skin type V and skin types I and II was 2.29, which is close to the ratio of pigment in these skin types, as measured by diffuse reflectance spectroscopy in the visible range. The minimum immediate pigment darkening dose (IPD) and the minimum melanogenic dose (MMD) at 365 nm, and the MED and MMD at 315 nm were the same for all skin types, while the variation of MED for every skin type was maximum at 305 and 365 nm. The results provide circumstantial evidence that erythema and melanogenesis have the same mechanism at short‐wavelength UVB (295 and 305 nm), and different mechanisms in UVA (365 nm). Furthermore, the 24 h MED at 305 nm appears to be a sensitive indicator of skin type.

Polarized light photography in the evaluation of photoaging

BACKGROUND The clinical characteristics of photodamaged skin, such as coarse and fine wrinkling, sallowness, hyperpigmentation, tactile roughness, laxity, and erythema, are not accurately evaluable from photographic records. OBJECTIVE The purpose of this study was to develop accurate and reproducible photographic techniques that generate an evaluable record of the characteristics of photodamaged skin. METHODS The method used involved illumination and photography through polarizing filters (polarized light photography). RESULTS Polarized light photography generates images that selectively enhance either the surface features or the subsurface features of the skin, providing an accurate and evaluable record for evaluation of photodamaged skin. CONCLUSION Polarized light photography, when coupled with precise framing and mapping, yields an accurate and evaluable record of photodamaged skin.