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This is the second of three reviews of technical literature examining the facts and misconceptions about aging skin. Articles on cutaneous blood flow were reviewed in the July 2006 issue. Skin thickness will be reviewed in the November issue.
Age-related transformations in skin’s appearance inevitably inspire curiosity about internal structural changes. In addition to the generally accepted histological changes, recent technological advances have increased markedly the understanding of specific biochemical changes that occur in aging skin.
Based on a literature search of PubMed, Em-Base, Science Citation Index and the University of California at San Francisco dermatological library, this article reviews some of the structural modifications in skin that underlie the visible effects of aging. Where possible, the discussion addresses differences between intrinsic, physiologic aging and extrinsic aging due to photo-exposure, wind, relative humidity and other environmental factors, although the authors acknowledge that this distinction is not always easily made.
Techniques for Protein Study Raman spectroscopy: Raman spectroscopy is a nondestructive analytical method for determining the structure and conformation of molecular compounds such as proteins. It does not require sample preparation or pretreatment and thus eliminates much potential interference. Recently, nearinfrared Fourier transform Raman spectroscopy has emerged as being specially suited for investigations of biologic material. This method gives highly reproducible results with only minor differences seen in spectra of different skin types.
Another method of protein study involves measurement of racemized aspartic acid. Racemization represents one of the major types of nonenzymatic covalent modifications of proteins initially synthesized using only L-amino acids. Aspartic acid racemization (AAR) leads to an age-dependent accumulation of D-aspartic acid in more long-lived human proteins.
Racemization in collagen is slow because of conformational constraints of the triple helix, but occurs more quickly in elastin. Skin samples can be purified such that, if indicated, the AAR due to elastin alone can be studied and its longevity can be measured.2Studies of elastin in various tissues including the aorta and lungs reveal high levels of AAR.3 This indicates a lack of turnover and accumulation of elastin damage in diverse aging tissues, possibly as part of programmed aging.
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