Increased SS bonds in chronic solar elastosis: a study with N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM) stain

Chemical consequences of cutaneous photoageing

Human skin, in common with other organs, ages as a consequence of the passage of time, but in areas exposed to solar ultraviolet radiation, the effects of this intrinsic ageing process are exacerbated. In particular, both the severity and speed of onset of age-related changes, such as wrinkle formation and loss of elasticity, are enhanced in photoaged (also termed extrinsically aged) as compared with aged, photoprotected, skin. The anatomy of skin is characterised by two major layers: an outer, avascular, yet highly cellular and dynamic epidermis and an underlying vascularised, comparatively static and cell-poor, dermis. The structural consequences of photoageing are mainly evident in the extracellular matrix-rich but cell-poor dermis where key extracellular matrix proteins are particularly susceptible to photodamage. Most investigations to date have concentrated on the cell as both a target for and mediator of, ultraviolet radiation-induced photoageing. As the main effectors of dermal remodelling produced by cells (extracellular proteases) generally have low substrate specificity, we recently suggested that the differential susceptibility of key extracellular matrix proteins to the processes of photoageing may be due to direct, as opposed to cell-mediated, photodamage.

In this review, we discuss the experimental evidence for ultraviolet radiation (and related reactive oxygen species)-mediated differential degradation of normally long lived dermal proteins including the fibrillar collagens, elastic fibre components, glycoproteins and proteoglycans. Whilst these components exhibit highly diverse primary and hence macro- and supra-molecular structures, we present evidence that amino acid composition alone may be a useful predictor of age-related protein degradation in both photoexposed and, as a consequence of differential oxidation sensitivity, photoprotected, tissues.

P53 expression in altered limbal basal cells of pingueculae, pterygia, and limbal tumors

PURPOSE

We previously discovered that the pathogenesis of pterygia was due to a vimentin-expressing, altered limbal epithelial basal cell, the pterygium cell. Since UV radiation epidemiologically correlates as the etiologic agent for pterygia and limbal tumors and is mutagenic for the p53 gene, our goal was to search for p53 gene mutations immunohistochemically in the altered limbal basal cells of these growths and of pingueculae from which they seem to originate.

METHODS

Longitudinal serial sections through six pingueculae, 14 primary and five recurrent pterygia, and five limbal tumors were studied immunohistochemically with p53 monoclonal antibody DO-1 and, in some specimens, with antivimentin antibody.

RESULTS

P53 expression was found in the limbal cells of all pterygia, limbal tumors, and Stage II pingueculae, but not in normal limbal-corneal epithelial cells. However, when the same specimens were examined with a TUNEL assay, few if any apoptotic cells were found. A finding of increased nuclear p53 gene product with little or no apoptosis is consistent with an activating mutation of the p53 gene, resulting in increased steady-state levels of the protein.

CONCLUSIONS

The finding of increased nuclear p53 in the limbal epithelium of pterygia, limbal tumors, and most pingueculae indicates the probable existence of p53 mutations in these cells as an early event in their development, which is consistent with their causation by UV radiation causation. In addition, due to a damaged p53-dependent programmed cell death mechanism, mutations in other genes are progressively acquired which allows the multi-step development of pterygia and limbal tumor cells from p53 positive cells overlying a Stage II pinguecula. Similarly, a pterygium dysplasia could arise from a pterygium cell. A classification for limbal basal cell tumors is proposed, and the different stromal changes in pingueculae, pterygia, and limbal tumors are identified. Two cell types were also identified: a p53-positive pinguecula limbal epithelial cell (a pinguecula II cell) and a p53-positive pterygium dysplasia cell (pterygium dysplasia cell).

Photoaging from an oxidative standpoint

The free radical theory proposes that photoaging, which is both qualitatively and quantitatively different from chronological aging, may result from imperfect protection against cumulative stress of free radicals produced by chronic and repeated ultraviolet irradiation. Since the skin is always in contact with oxygen and is occasionally exposed to ultraviolet light, skin is one of the best target organs of environmental photo-oxidative stress. A growing body of evidence suggests that reactive oxygen species are generated by ultraviolet irradiation resulting in the structural and functional alteration of cutaneous components which should affect the photoaging process over a long period. The age-related alteration of cutaneous antioxidant defense capacity against cumulative effects of continual photo-oxidative stress to the skin may also affect the photoaging. Thus the possible use of antioxidants that attenuate photo-oxidative toxicity is believed to be an important strategy modulating photoaging. Several antioxidants have readily been proved to work in the experimental conditions. This paper reviews photoaging from a photo-oxidative standpoint and discusses the possible regulation of photoaging by antioxidants that is an important issue in the photodermatological field.