Collagen loss in photoaged human skin is overestimated by histochemistry

Multidirectional activity of bakuchiol against cellular mechanisms of facial aging - Experimental evidence for a holistic treatment approach

Objective

Skin ageing is a multifactorial process involving formation of reactive oxygen species, consecutive inflammation with reduced epidermal and dermal cell viability and resulting damage to the extracellular matrix. Effective dermocosmetic treatment modalities should ideally address these hallmarks in a holistic approach. Here, we determined the corresponding activity profile of bakuchiol, a plant‐derived meroterpene, in an array of in vitro, ex vivo and in vivo studies and compared it to retinol, currently considered as gold standard in topical antiageing cosmetics.

Methods

The antioxidative capacity and power of bakuchiol and retinol were analysed by measuring 2,2′‐diphenyl‐1‐picrylhydrazyl (DPPH) reduction via its absorption decay and electron spin resonance spectroscopy, respectively. Effects on prostaglandin E2 (PGE2), macrophage migration inhibitory factor (MIF), fibroblast growth factor 7 (FGF7), collagen type I and VII (COL1A1, COL7A1), fibronectin (FN) levels as well as the metabolization of water‐soluble tetrazolium 1 (WST‐1) were determined in human dermal fibroblasts. Epidermal regeneration was assessed utilizing an in vitro wound healing model. FN protein levels were analysed ex vivo after treatment with a formulation containing bakuchiol, retinol or vehicle using suction blister fluid. Skin condition improvement was determined in vivo in a split‐face comparison study after application of bakuchiol or vehicle.

Results

In contrast to retinol, bakuchiol demonstrated high antioxidative efficacy. Levels of PGE2 and MIF were significantly decreased by both bakuchiol and retinol. Bakuchiol but not retinol significantly increased FGF7 protein levels. WST‐1 metabolization levels were significantly augmented by bakuchiol and retinol. Bakuchiol and retinol application led to a significant augmentation of COL1A1, COL7A1 and FN protein levels. Wounds supplemented with bakuchiol but not retinol displayed a significant increase in epidermis regeneration. Clinically, areas treated with a bakuchiol‐containing formulation showed a statistically significant increase in FN protein values after a 4‐week application compared to untreated areas and areas treated with vehicle.

Conclusion

These data provide evidence for the multidirectional efficacy of bakuchiol against cellular hallmarks of skin ageing. Its activity profile shares some common features with retinol but demonstrates several hitherto unknown biopositive effects in our studies, namely stimulation of the critical extracellular matrix component FN, and accelerated epidermal regeneration and wound healing.

The effects of Origanum hypericifolium essential oil application and ultraviolet B irradiation on mouse skin: An ultrastructural study

Exposure to UV radiation can cause histopathological and ultrastructural changes in the skin. Origanum hypericifolium, an endemic Turkish plant,essential oil is mainly composed of monoterpenes. The effects of undiluted O. hypericifolium oil on the ultrastructural characteristics of the UVB-irradiated dorsal skin of mice were investigated using transmission electron microscopy. The BALB/c mice were shaved of dorsal hair and randomly housed into 4 groups: 1: control; 2: UVB-irradiated; 3: oil applied; and 4: oil applied and UVB-irradiated. The oil was applied topically to the dorsal skins of the mice on alternate days for 1week prior to UVB exposure. The skins were irradiated for a total dose of 3.5J/cm(2). The sections were stained with hematoxylin and eosin, semithin sections were stained with toluidine blue and ultrathin sections were contrasted with uranyl acetate/lead citrate. There were histopathological changes such as parakeratosis and squamous hyperplasia in the epidermal cell layers (Groups 3 and 4). There were also ultrastructural changes including lacunae formations throughout the stratum corneum layer (Groups 2, 3, and 4), enlargement of intercellular spaces (Groups 2 and 3), reduced desmosomes, narrow and elongated interdigitations, shortened, relatively indistinct and electron dense intermediate keratin filament bundles (Group 3). There were various sizes of cytoplasmic and perinucleolar vacuoles (Groups 3 and 4) and apoptotic bodies phagocytized by keratinocytes (Group 4). I conclude that undiluted oil has side-effects and the potential to inflict injury to the skin. The oil does not ameliorate the negative effects of UVB on epidermal skin cells.

A histochemical study of ultraviolet B irradiation and Origanum hypericifolium oil applied to the skin of mice

Ultraviolet (UV) rays cause skin damage. Chronic exposure to UV irradiation causes decreased collagen synthesis, degenerative changes in collagen bundles, accumulation of elastotic material and increased epidermal thickness. Origanum hypericifolium, an endemic Turkish plant, belongs to Lamiaceae family. The main constituents of its oil are monoterpenes including cymene, carvacrol, thymol and γ-terpinene. The effects of undiluted O. hypericifolium oil on UVB irradiated skin of mice were investigated histochemically. Four groups of female BALB/c mice, whose dorsal hair was shaved, were allocated as follows: non-UVB irradiated (Group 1), UVB-irradiated (Group 2), O. hypericifolium oil treated (Group 3), and O. hypericifolium oil treated and UVB irradiated (Group 4). Sections of dorsal skin samples were stained with Mallory's phosphotungstic acid hematoxylin for collagen fibers and Taenzer-Unna orcein for elastic fibers. Sections also were stained with hematoxylin and eosin to measure epidermal thickness. We observed intense staining of collagen and homogeneous, scattered thin elastic fibers in Group 1; scattered and weakly stained collagen and curled, amorphous, accumulate elastic fibers in Group 2; and intense staining of collagen in Groups 3 and 4. Accumulation of elastic fibers in the dermis was unremarkable in Groups 3 and 4. In Groups 3 and 4, O. hypericifolium oil treatment thickened the epidermis. Epidermal thickness was greatest in Group 4. We suggest that O. hypericifolium oil may block UVB induced alterations of collagen and elastic fibers, and increase epidermal thickness.

Impaired keratinocyte function on matrix metalloproteinase-1 (MMP-1) damaged collagen

Healing of superficial skin wounds depends on the proliferation and migration of keratinocytes at the wound margin. When human epidermal keratinocytes were incubated on polymerized type I collagen, they rapidly attached and spread. The cells underwent a proliferative response and, over the subsequent 6-day period, covered the collagen surface with a monolayer of cells. When keratinocytes were plated on collagen that had been fragmented by exposure to matrix metalloproteinase-1 (MMP-1, collagenase-1), the cells attached as readily as to intact collagen but spread more slowly and less completely. Growth was reduced by approximately 50%. Instead of covering the collagen surface, the keratinocytes remained localized to the site of attachment. Keratinocytes on fragmented collagen expressed a more differentiated phenotype as indicated by a higher level of surface E-cadherin. Based on these findings, we suggest that damage to the underlying collagenous matrix may impede efficient keratinocyte function and retard wound closure.

Ex vivo and in vivo second-harmonic-generation imaging of dermal collagen fiber in skin: comparison of imaging characteristics between mode-locked Cr:forsterite and Ti:sapphire lasers

Second-harmonic-generation (SHG) microscopy is an interesting new tool for observing dermal collagen fiber in skin. However, conventional SHG microscopy using a mode-locked Ti:sapphire laser suffers from low penetration depth and a slow image acquisition rate caused by scattering and absorption in tissue, making it difficult to use for in vivo applications on human skin. We develop an SHG microscope equipped with a mode-locked Cr:forsterite laser with a long wavelength and compare its imaging characteristics with that of a Ti:sapphire-laser-based SHG microscope for the measurement of dermal collagen fiber in animal and human skins. The results indicate the suitability of the Cr:forsterite laser-based SHG microscope for in vivo imaging of human skin.

Observation of dermal collagen fiber in wrinkled skin using polarization-resolved second-harmonic-generation microscopy

Optical probe methods for in vivo assessments of cutaneous photoaging are necessary in fields such as anti-aging dermatology and skin cosmetic development. We investigated the relation between wrinkle direction and collagen orientation in ultraviolet-B-exposed (UVB-exposed) skin using polarization-resolved second-harmonic-generation (SHG) microscopy. A polarization anisotropic image of the SHG light indicated that wrinkle direction in UVB-exposed skin is predominantly parallel to the orientation of dermal collagen fibers. Furthermore, collagen orientation in post-UVB-exposed skin with few wrinkles changed from that of UVB-exposed wrinkled skin to that of no-UVB-exposed skin. The method proposed has the potential to become a powerful non-invasive tool for assessment of cutaneous photoaging.

Modulation of cutaneous aging with calorie restriction in Fischer 344 rats: a histological study

OBJECTIVE

To examine whether histological changes in skin owing to intrinsic aging in a laboratory rodent model are modulated by caloric restriction (CR).

METHODS

The abdominal skin from colony-raised ad libitum-fed Fischer 344 rats and age-matched rats subjected to CR was studied in the light microscope using histological morphometric methods. Animals 4, 12, and 24 months or older were used in this study. We studied the skin to obtain (1) quantitative data on the depth of the epidermis, dermis, and fat layer, the epidermal cellular density, the percentage fraction of dermal collagen, elastic fibers, pilosebaceous units, and capillaries, and the fibroblast density; and (2) qualitative assessment of histological staining for dermal glycosaminoglycans. We analyzed data by means of general linear model 2-way analysis of variance to obtain significance for the effects of age, diet, and age-diet interaction.

RESULTS

The ad libitum-fed rats showed age-related increase in the depth of the epidermis, dermis, and fat layer. Calorie restriction prevented these changes, but epidermal nuclear density appeared to be stimulated. A trend toward increased values for collagen and elastic fibers, fibroblasts, and capillaries in skin samples from CR rats was observed. Pilosebaceous units were not modified. Moderately reduced staining for the dermal glycosaminoglycans in the skin of CR rats was noticed.

CONCLUSIONS

Histomorphological changes resulting from intrinsic aging affected some of the studied variables in the rat skin, and these changes were delayed or prevented by CR. Some stimulatory effects, such as increased densities of fibroblasts and capillary profiles and higher values of connective tissue fibers resulting from CR, were also observed. Cutaneous morphological changes due to natural aging in this rat model seem to be modified by physiological or metabolic alterations imposed by CR.

Skin aging and natural photoprotection

Aging of skin is a continuous process that may be enhanced by sun exposure. Photoaging may provoke changes different from aging. Epidermal changes involve thinning of stratum spinosum and flattening of the dermo-epidermal junction. The senescent keratinocytes becomes resistant to apoptosis and may survive for a long time giving time for DNA and protein damage to accumulate with possible implication for carcinogenesis. The numbers of melanocytes decrease with age with dysregulation of melanocyte density resulting in freckles, guttate hypo-melanosis, lentigines and nevi. The number of dendritic Langerhans cells also decreases with age and the cells get less dendrites and have reduced antigen-trapping capacity. Aging involves dermal changes such as damage to elastic and collagen fibers giving thickened, tangled, and degraded non-functional fibers. Collagen intermolecular cross-links are stable and essential for stability and tensile strength. Cross-links increase with age converting divalent cross-links into mature trivalent cross-links of, e.g. histidinohydroxylysinonorleucine. Two mechanisms are involved; an enzyme-controlled process of maturation and a non-enzymatic glycosylation, the Maillard reaction leading to cross-links in proteins such as in collagen between arginine and lysine. Such may be seen with age and in diabetes mellitus. However, autofluorescence studies have shown that UVR reduces collagen cross-links. Natural photoprotection involves thickening of stratum corneum by sunlight and increased pigmentation. This leads to a factor 2 increase in photoprotection from spring until after-summer. The constitutive pigmentation is independent of age and thickness of stratum corneum is likewise independent of age. The minimal erythema dose is thus the same through life, when corrected for pigmentation or measured in areas with constitutive pigmentation.