Aged skin: a study by light, transmission electron, and scanning electron microscopy

Age-related changes in oxidative damage to lipids and DNA in rat skin

Skin is a tissue exposed most frequently to oxidative stress from the environment in daily life. Age-related changes of oxidative damage and antioxidant enzyme activity in the skin were examined in male Fischer 344 rats aged 6 to 30 months. The contents of phosphatidylcholine hydroperoxide (PCOOH) and thiobarbituric acid-reacting substances (TBARS) increased linearly with age. The content of cholesterol hydroperoxide increased until 24 months of age and then decreased. The content of 8-oxo-2'-deoxyguanosine (8-oxodG) increased gradually with age, and was significantly higher at 30 months of age than at 6 months of age. Superoxide dismutase activity tended to decrease with age. The activities of catalase and glutathione peroxidase showed no changes with age. We examined the effect of dietary restriction on the accumulation of oxidative damage in rat skin. The increase in PCOOH content in the skin of dietary-restricted rats was suppressed until 30 months of age. The TBARS and cholesterol hydroperoxide contents in the skin of dietary-restricted rats were significantly lower than in the skin of ad libitum-fed rats, while the 8-oxodG content was somewhat lower in the dietary-restricted rats than the ad libitum-fed rats. These results indicate that oxidative damage to the lipids and DNA in rat skin increases with age and that dietary restriction delays the accumulation of oxidative damage in skin.

Age-related changes in the proteoglycans of human skin

Skin undergoes dramatic age-related changes in its mechanical properties, including changes in tissue hydration and resiliency. Proteoglycans are macromolecular conjugates of protein and carbohydrate (glycosaminoglycan) which are involved in these tissue properties. In order to examine whether age-related changes in skin proteoglycans may contribute to the age-related changes in the mechanical properties of skin, proteoglycans from human skin of various ages were extracted and analyzed. Samples were obtained from two different fetal ages, from mature skin, and from senescent skin. As a function of age, there is a decrease in the proportion of large chondroitin sulfate proteoglycans (versican) and a concomitant increase in the proportion of small dermatan sulfate proteoglycans (decorin). Based on reactivity with antibodies to various chondroitin sulfate epitopes, fetal versican differs from the versican found in older skin with respect to the chondroitin sulfate chains. Also, the decorin of fetal skin is slightly larger, while the decorin of older skin shows greater polydispersity in both its size and its charge to mass ratio. There are also age-related differences in the size and polydispersity of the core proteins of decorin. The most pronounced change in skin proteoglycans is the appearance in mature skin of a proteoglycan which is smaller than decorin, but which has the same amino terminal amino acid sequence as decorin. This small proteoglycan is abundant in mature skin and may be a catabolic fragment of decorin or an alternatively spliced form of decorin. In light of the known ability of decorin to influence collagen fibrillogenesis and fibril diameter, the appearance of this small decorin-related proteoglycan may have a significant effect on skin elasticity. The observation that proteoglycans in skin show dramatic age-related differences suggests that these changes may be involved in the age-related changes in the physical properties of skin.

Topical retinoids in the treatment of aging of the skin

Aging of the skin is a complex phenomenon resulting from the interaction of several intrinsic and extrinsic factors [1]. Due to the cosmetic disfigurement it produces and its psychological impact, especially to women, aging of the skin has become an issue of great social significance and concern. Intrinsic aging is an inevitable, genetically programmed process, the underlying mechanisms of which remain largely unknown. No prevention or effective treatment is currently available [1]. Among extrinsic influences (wind, heat, cigarette smoke, chemicals, etc.), ultraviolet radiation appears to be the single most important factor associated with aging of the skin [2]. Photoaging refers to gross and microscopic cutaneous changes induced by cumulative exposure to ultraviolet radiation (UVR). These changes are superimposed on the background of intrinsic aging [2]. Increased recreational sun exposure, including excessive sunbathing, the depletion of stratospheric ozone, the use of UVR in the treatment of various skin diseases, are some of the causes that have led to increased prevalence of photoaging during the last decades. The clinical importance of photoaging lies mostly on the potential for the development of precancerous lesions or skin cancer [3]. In contrast to intrinsic aging, photodamage can be prevented by sun avoidance and proper sun protection [2]. Furthermore, overwhelming clinical and histological evidence indicate that skin changes of photoaging can be reversed by the use of topical retinoids [4].

Lipofuscin: mechanisms of formation and increase with age

Lipofuscin (age pigment) is a brown-yellow, electron-dense, autofluorescent material that accumulates progressively over time in lysosomes of postmitotic cells, such as neurons and cardiac myocytes. The exact mechanisms behind this accumulation are still unclear. This review outlines the present knowledge of age pigment formation, and considers possible mechanisms responsible for the increase of lipofuscin with age. Numerous studies indicate that the formation of lipofuscin is due to the oxidative alteration of macromolecules by oxygen-derived free radicals generated in reactions catalyzed by redox-active iron of low molecular weight. Two principal explanations for the increase of lipofuscin with age have been suggested. The first one is based on the notion that lipofuscin is not totally eliminated (either by degradation or exocytosis) even at young age, and, thus, accumulates in postmitotic cells as a function of time. Since oxidative reactions are obligatory for life, they would act as age-independent enhancers of lipofuscin accumulation, as well as of many other manifestations of senescence. The second explanation is that the increase of lipofuscin is an effect of aging, caused by an age-related enhancement of autophagocytosis, a decline in intralysosomal degradation, and/or a decrease in exocytosis.

Pressure ulcers in SCI: does tension stimulate wound healing?

Pressure ulcers are an immense problem among older and disabled populations. Although there are many studies in the literature about the etiology, interface pressures, natural history, and epidemiology of skin breakdown, there is relatively little information about factors that stimulate the repair of body wall tissues after breakdown. Specifically, there is a paucity of information about the effects of mechanical stress on healing. This is a particularly important consideration for those areas, such as the perineal tissues, that bear large mechanical forces. The purpose of this paper is to discuss the research that addresses skin and tissue repair in response to tension. Two case studies that support the hypothesis that tension stimulates wound healing are presented from the Spinal Cord Injury Center at the Seattle VAMC. After weeks of nonhealing, each of these cases healed within 2 weeks of initiating a range of motion program that applied tension to the nonhealing portion of a myocutaneous flap.

Cumulative effects from repeated exposures to suberythemal doses of UVB and UVA in human skin

BACKGROUND

The skin is repeatedly exposed to solar UV radiation. Long-term photodamage is a consequence of cumulative UV radiation injury. Hence an examination of the repetitive effects of UV exposure is more likely to yield clues to the early alterations that lead to photoaged skin than a single exposure.

OBJECTIVE

We examined the effects of repetitive low-dose UV irradiation on human skin with the aim of identifying UVA-induced effects that may have a different wavelength dependence than acute erythema.

METHODS

Areas on the lower part of the back were each exposed to a suberythemal dose (0.5 minimal erythema dose [MED]) of solar simulated radiation (290 to 400 nm) and of UVA (320 to 400 nm) once daily, 5 days a week, for 28 doses. One site was also treated daily with a sunscreen having a sun protection factor of 22 and then exposed to 11 MEDs of solar simulated radiation for the same duration. Epidermal and dermal changes were analyzed and quantified by histochemical stains in combination with computer-assisted image analysis of tissue sections.

RESULTS

At equal 0.5 MED doses, UVA induced greater cumulative changes than solar simulated radiation, as assessed by development of a greater cumulative erythema response in the first week of treatment, the presence of epidermal hyperplasia and stratum corneum thickening, depletion of Langerhans cells, dermal inflammatory infiltrates, and deposition of lysozyme on elastin fibers. These changes were not prevented by the sunscreen. A single short-term dose of UVA did not elicit these changes.

CONCLUSION

These findings suggest that UVA may contribute significantly to long-term actinic damage and that the spectral dependence for cumulative damage does not parallel the action spectrum for acute injury (erythema) in human beings.

Analysis of the age-related composition of human skin collagen and collagens synthesized by fibroblast culture

Age-related differences in the composition and the post-translational modifications of human skin collagens were examined in the present study. The data were compared with results of collagen synthesis from in vivo-aged fibroblasts in culture. Skin extracts and newly synthesized collagen from fibroblast cultures derived from both old and young donor groups showed the same ratio of collagen III to collagen I. Furthermore, no difference was noted in the degree of prolyl and lysyl hydroxylation of collagen I and collagen III Young and old fibroblasts synthesized a similar quantity of collagen in vitro. The data suggest that fibroblasts maintain a uniform level of collagen production, composition and modification independent of the age of the donor.

Hyaluronic acid in cutaneous intrinsic aging

BACKGROUND

In elderly individuals all components of the skin and subcutaneous tissue undergo histologic and ultrastructural changes. The turgidity of the dermis appears decreased, presumably due to altered patterns and levels of glycosaminoglycans (GAGS), especially hyaluronic acid and dermatan sulfate that are the most common. A linear, age-related decrease in the content of GAGS (mainly hyaluronic acid) has been hypothesized in human aged skin.

METHODS

We used the cationic dye Alcain Blue to selectively stain hyaluronic acid within the dermis in old and young subjects to compare ultrastructurally its topography and variations with age.

RESULTS

We demonstrated a progressive reduction in the number of electron-dense granules of hyaluronic acid and of their filaments until they were completely absent in subjects aged 60.

CONCLUSIONS

We propose that the variations of the levels of hyaluronic acid in the dermis in aging could account for some of the most striking alterations of the aged skin, including decreased turgidity, less support for microvessels, wrinkling, and altered elasticity.

Stereological analysis of collagen and elastic fibers in the normal human dermis: variability with age, sex, and body region

Normal human dermis has been analyzed using stereological methods to estimate the quantitative modifications of collagen and elastic fibers in relation to age, sex, and body region. Forty-five skin biopsies from the trunk or the limbs of 26 males and 19 females of different age were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin. The relative volumes of collagen and elastic fibers were calculated by the point counting method on 1 micron semithin sections. Photographic sampling was performed on four consecutive dermis layers: the papillary layer and three consecutive layers of reticular dermis. The data were subjected to analysis of variance which showed that all the factors studied exert a significant influence on the relative amounts of collagen and elastic fibers. The fractional volume of collagen fibers is constant throughout all dermis layers analyzed and is always higher in females than in males, except for the second and third decades of life. Collagen fiber density increases with age in both sexes up to 30-40 years, when it starts decreasing. Both the relative volumes and the diameters of elastic fibers increase from papillary to deep reticular dermis. In reticular dermis of both sexes there is an increment of elastic fiber density in the first decade of life, followed by a drop particularly marked in males. After 20 years, the relative volume of elastic fibers displays a decreasing trend in females, whereas it increases in males, attaining the highest values beyond the 40s.

Effects of skin thickness, age, body fat, and sunlight on serum 25-hydroxyvitamin D

We tested the hypothesis that the age-related decline in skin thickness may contribute to the age-related decline in serum 25-hydroxyvitamin D [25(OH)D]. We measured skinfold thickness on the back of the hand, serum 25(OH)D, height, and weight in 433 normal postmenopausal women. We also noted the average daily hours of sunlight in the month in which the observations were made and in the preceding 2 mo. Serum 25(OH)D was positively related to hours of sunlight (with a time lag of 2 mo) and to skin thickness, and negatively to body mass index (wt/ht2). Serum 25(OH)D fell significantly after age 69 y. Seasonal variation of serum 25(OH)D was greater in lean than in fat subjects, which we attributed to the larger fat mass and consequent larger pool size in the latter group. The results suggest that the tendency for serum 25(OH)D to fall with age is due in part to the age-related decline in skin thickness.

Lateral growth and terminal differentiation during repeated epidermal regeneration in vitro

By incubating multilayered primary cultures of human epidermal keratinocytes in a low calcium medium, the suprabasal layers can be stripped off leaving a basal cell monolayer. When this monolayer is refed normal calcium medium a reproducible series of cell kinetic, morphological and biochemical changes take place resulting in the regeneration of a multilayered tissue. The stripping procedure seems to induce the selective proliferation of a cohort of basal cells that is committed to vertical migration and rapid terminal differentiation. In contrast, when the basal cells are allowed to regenerate in the presence of the strong mitogen, cholera toxin, lateral growth and continued proliferation are favoured at the expense of the capacity of the cells to differentiate. Repeated stripping of the same cultures disclosed a considerable heterogeneity in the capacity of the basal cells to regenerate the suprabasal layers. The number of times the basal cells could restore the suprabasal layers after repeated stripping varied from four to nine times. A negative correlation between donor age and regenerative capacity was observed. The experiments with repeated stripping of the same cultures also showed that the capacity to proliferate and to restore the multilayering was fully retained for at least four cycles of stripping-regeneration, whereas the capacity to terminally differentiate was rapidly lost. It is suggested that the present system of regenerating epidermal tissue cultures may serve as an experimental model for the study of epidermal tissue homeostasis and cellular aging.

Laser Doppler measurements of cutaneous blood flow in ageing mice and rats

Laser Doppler velocimetry (LDV) is a non-invasive technique that measures capillary blood perfusion parameters (blood flow, volume and velocity) and can be used non-invasively to evaluate the effects of ageing on cutaneous blood perfusion. Male Fischer-344 rats (R) of 1, 2, 3, 8, 12, 16, 20 and 24 months and C57BL/6N mice (M) 1, 2, 3, 9, 15, 19 and 22 months (n = 6/mo) were used. Animals were anesthetized with ketamine/xylazine and LDV-measured blood flow was made on the backs of all animals. Five readings for each parameter were recorded in order to obtain a mean value of the individual. Skin biopsies (4 mm) were removed after LDV for assessing epidermal and dermal thickness and number of epidermal cell layers. The number of viable epidermal layers in M remained constant while in R it decreased with age. Epidermal thickness in both M and R decreased from 2-3 months and then remained constant. Dermal thickness decreased from 3 to 22 months in M, and increased in R from 1 to 2 months and remained constant. Blood flow of M increased between 1 and 2 months, remained constant to 19 months, then increased at 22 months; flow in R was constant except at 2 months. Thus age differences in epidermal and dermal thickness, and blood flow of M and R occur and should be considered when evaluating cutaneous toxicity studies in different-aged animals. These changes may potentially alter dermal absorption and/or distribution of xenobiotics.

Morphometric analysis of dermal collagen fibers in normal human skin as a function of age

A quantitative study of dermal collagen as a function of age was carried out by computerized digital image analysis. Fast Green-Syrius Red stained sections were obtained of skin biopsies taken from the upper inner arm of 33 healthy women and 38 healthy men. The Leitz texture Analysis System (Leitz-TAS) and mathematical morphology (Serra, 1982) were used for the evaluation of the data. Collagen was studied in the superficial dermis and also in the reticular dermis using the same program. There were significant correlations, firstly between the percentage of collagen measured by the morphometric method and the concentration of collagen analysed biochemically (microg/mm(2) of tissue section) (r = 0.79, p < 0.001) and secondly between the decreased concentration of collagen and age (r = 0.58, p < 0.05). The morphometrical measurements have shown that the relative percentage of collagen bundles (surface of collagen fibers as a function of the dermal area analyzed) was 93.35% in the superficial dermis and 89.2% in the reticular dermis. Although this value is higher than the chemically determined ratio of collagen to other proteins (over 70%), this may be due to the relatively uniform distribution pattern of (type I and III) collagen through the dermis covering most other components of the skin. As the collagen fiber density per unit dermal surface did not change with age, the decrease in collagen content of the skin may be ascribed to the loss of about 6% of dermal mass per decade (Branchet, 1990), although large individual variations exist. The histogram of the diameter distribution of collagen fiber bundles of the reticular dermis showed thinner diameters in persons between 20 and 40 years of age than in older persons. The histogram of the distribution of interfiber spaces did not show any variation with age in the superficial dermis, while in the reticular dermis there was a predominance of smaller interspaces in persons older than 50 years.

An in vitro model to test relative antioxidant potential: ultraviolet-induced lipid peroxidation in liposomes

Since antioxidants have been shown to play a major role in preventing some of the effects of aging and photoaging in skin, it is important to study this phenomenon in a controlled manner. This was accomplished by developing a simple and reliable in vitro technique to assay antioxidant efficacy. Inhibition of peroxidation by antioxidants was used as a measure of relative antioxidant potential. Liposomes, high in polyunsaturated fatty acids (PUFA), were dispersed in buffer and irradiated with ultraviolet (UV) light. Irradiated liposomes exhibited a significantly higher amount of hydroperoxides than liposomes containing antioxidants in a dose- and concentration-dependent manner. Lipid peroxidation was determined spectrophotometrically by an increase in thiobarbituric acid reacting substances. To further substantiate the production of lipid peroxides, gas chromatography was used to measure a decrease in PUFA substrate. In order of decreasing antioxidant effectiveness, the following results were found among lipophilic antioxidants: BHA greater than catechin greater than BHT greater than alpha-tocopherol greater than chlorogenic acid. Among hydrophilic antioxidants, ascorbic acid and dithiothreitol were effective while glutathione was ineffective. In addition, ascorbic acid was observed to act synergistically with alpha-tocopherol, which is in agreement with other published reports on the interaction of these two antioxidants. Although peroxyl radical scavengers seem to be at a selective advantage in this liposomal/UV system, these results demonstrate the validity of this technique as an assay for measuring an antioxidant's potential to inhibit UV-induced peroxidation.

Histologic changes in skin associated with aging

This is a review of histologic changes noted in the skin of elderly individuals. Among the epidermal changes associated with skin aging are a flattened dermal-epidermal junction, giving the appearance of atrophy and cellular heterogeneity. The melanocyte density declines slowly, and the Langerhans cells decrease in number with advancing age. Among the dermal changes are attenuation in the number and diameter of elastic fibers in the papillary dermis, an increase in number and thickness of the same fibers in the reticular dermis, and a coarsening of collagen fibers with an increase in density of the collagen network. A decrease in the dermal cell population as well as a functional decline in glandular activity are also noted with intrinsic aging. A decline in hair number, rate of growth, and diameter, along with a slowing of the rate of growth of nails, have been well documented with progressive aging.

Mechanical properties of human forearm and vulvar skin

Using a newly developed suction device, the mechanical properties of forearm and vulvar skin were studied in 22 healthy women, 12 before and 10 after the menopause. The ratio between viscous deformation (Uv) and elastic deformation (Ue) and the biological elasticity, i.e. the ratio between immediate recovery (Ur) and total deformation (Uf), were both significantly lower in vulvar than in forearm skin. Ur/Uf decreased significantly with load in vulvar, but not in forearm skin, whereas Uv/Ue was not load-dependent in either site. Uv/Ue remained constant with age in both test sites, whereas Ur/Uf was significantly lower in post-menopausal women in both forearm and vulvar skin. In vulvar, but not in forearm skin, Uv/Ue was significantly correlated with body height which may be an indicator of mechanical connective tissue properties. Viscous deformation plays a lesser role and biological elasticity is decreased in vulvar compared to forearm skin. Despite differences in mechanical parameters at both sites, age-related changes seem to be similar.

Elastic fibers in normal human skin. variations with age: a morphometric analysis

A quantitative study of dermal elastic fibers was carried out by computerized digital image analysis. Sections of skin biopsies taken from the upper inner arm of 33 healthy women and 38 healthy men were stained by a selective procedure for elastic fibers. The Leitz texture analysis system (Leitz-Tas) and mathematical morphology were used for the evaluation of the data. Distinct programs were used for the vertical superficial elastic fibers and for the mature elastic fibers of the reticular dermis. For elastic fibers of the superficial dermis there was no significant variation with age or sex for total area occupied by the fibers or for the total number of fibers per unit skin area or total fiber length. The distribution of the relative fiber number as a function of their length showed that about 80% of the fibers had a length of 0-20 microm, with no detectable age- or sex-dependent variation. The distribution of fiber number frequency as a function of fiber diameter did not show any significant variation with sex or age, either. The relative area of mature elastic fibers increased significantly with age after the sixth decade of life. The total number (Nt) of these fibers did not show however any significant variation with age or sex: Nt per mm(2) of skin surface was 3220+/-660 (S.D.). We found for all age groups a significant increase of total fiber length by comparing persons between 20 and 30 years with those above 60 years. There was, however, no significant variations according to age or sex for the frequency distribution of mature elastic fiber length and diameter. As a significant decrease with age of the dermal thickness was also found in males and females, the loss of elastic fibers with age is mainly due to a loss of skin thickness (skin volume) with age. This loss is about 30% at 50 years and nearly 50% at 80 years. Loss of skin elasticity with age can be due to loss of cells (fibroblasts), to a decrease of their biosynthetic activity and to qualitative modifications of extracellular matrix macromolecules.