Physiology of skin aging.
Skin is the most voluminous organ of the body. It assumes several important physiological functions and represents also a "social interface" between an individual and other members of society. This is the main reason its age-dependent modifications are in the forefront of dermatological research and of the "anti-aging" cosmetic industry. Here we concentrate on some aspects only of skin aging, as far as the cellular and extracellular matrix components of skin are concerned. Most well studied mechanisms of skin aging can be situated at the postgenetic level, both epigenetic and post-translational mechanisms being involved. Some of these mechanisms will be reviewed as well as the capacity of fucose- and rhamnose-rich oligo- and polysaccharides (FROP and RROP) to counteract several of the mechanisms involved in skin aging.
Pathol Biol (Paris). 2009 Jun;57(4):336-41
Skin aging and dry skin.
Skin aging appears to be the result of both scheduled and continuous "wear and tear" processes that damage cellular DNA and proteins. Two types of aging, chronological skin aging and photoaging, have distinct clinical and histological features. Chronological skin aging is a universal and inevitable process characterized primarily by physiologic alterations in skin function. In this case, keratinocytes are unable to properly terminally differentiate to form a functional stratum corneum, and the rate of formation of neutral lipids that contribute to the barrier function slows, causing dry, pale skin with fine wrinkles. In contrast, photoaging results from the UVR of sunlight and the damage thus becomes apparent in sun-exposed skin. Characteristics of this aging type are dry and sallow skin displaying fine wrinkles as well as deep furrows, resulting from the disorganization of epidermal and dermal components associated with elastosis and heliodermatitis. Understanding of the functions of the skin and the basic principles of moisturizer use and application is important for the prevention of skin aging. Successful treatment of dry skin with appropriate skin care products gives the impression of eternal youth.
J Dermatol. 2004 Aug;31(8):603-9
Age-related changes in cellular protection, purification, and inflammation-related gene expression: role of dietary phytonutrients.
Oxidative injury and inflammation are intimately involved in the aging process and the development of age-related diseases. To date, most nutritional antiaging strategies have focused solely on the delivery of exogenous antioxidants to combat the negative effects of aging. A promising new strategy is to identify nutrients and phytochemicals that can directly target intrinsic cytoprotective mechanisms, including modulation of the expression of (1) genes involved in the detoxification of xenobiotics, (2) genes involved in the synthesis and regulation of intrinsic antioxidants and antioxidant enzymes, (3) genes involved in the regulation of inflammation, and (4) vitagenes. The purpose of this review is to provide an overview of the age-related changes in gene expression related to oxidative stress, detoxification, and inflammatory processes, and to discuss natural compounds with the potential to oppose age-related changes in gene expression related to these processes, which therefore may be suitable for use in human antiaging research.
Ann N Y Acad Sci. 2012 Jul;1259:112-20
Interaction between elastin and elastases and its role in the aging of the arterial wall, skin and other connective tissues. A review.
Elastic fibers are progressively lysed during maturation and aging and in an accelerated fashion in several aging diseases such as diabetes, arteriosclerosis, emphysema and several skin diseases. Several enzymes (elastase-type proteases) were isolated in recent years in our laboratory which appear to be involved in these processes. A cell membrane bound serine protease was isolated from arterial smooth muscle cells and was shown to increase with in vitro aging of the cells. A metallo-protease was isolated from skin fibroblasts and was shown to be capable of attacking the constituents of elastic fibers, mainly the microfibrillar glycoproteins and also the desmosine cross linked elastin in vivo. This partially purified fibroblast enzyme was shown to attack these elastic fibers when injected into the dermis. A new selective staining procedure was used to visualise and quantitate, by computerized image analysis, the skin elastic fibers in normal and pathological human or animal skin biopsies. This method, combined with the injection of elastase in rabbit skins, alone or together with inhibitors, enables the ex vivo/in vivo study of elastase action (and of its inhibition).
Mech Ageing Dev. 1984 Dec;28(2-3):155-66
Ultraviolet radiation and skin aging: roles of reactive oxygen species, inflammation and protease activation, and strategies for prevention of inflammation-induced matrix degradation - a review.
Inflammation and the resulting accumulation of reactive oxygen species (ROS) play an important role in the intrinsic and photoaging of human skin in vivo. Environmental insults such as ultraviolet (UV) rays from sun, cigarette smoke exposure and pollutants, and the natural process of aging contribute to the generation of free radicals and ROS that stimulate the inflammatory process in the skin. UV irradiation initiates and activates a complex cascade of biochemical reactions in human skin. In short, UV causes depletion of cellular antioxidants and antioxidant enzymes (SOD, catalase), initiates DNA damage leading to the formation of thymidine dimmers, activates the neuroendocrine system leading to immunosuppression and release of neuroendocrine mediators, and causes increased synthesis and release of pro-inflammatory mediators from a variety of skin cells. The pro-inflammatory mediators increase the permeability of capillaries leading to infiltration and activation of neutrophils and other phagocytic cells into the skin. The net result of all these effects is inflammation and free radical generation (both reactive oxygen and nitrogen species). Furthermore, elastsases and other proteases (cathepsin G) released from neutrophils cause further inflammation, and activation of matrix metalloproteases. The inflammation further activates the transcription of various matrixes degrading metalloproteases, leading to abnormal matrix degradation and accumulation of non-functional matrix components. In addition, the inflammation and ROS cause oxidative damage to cellular proteins, lipids and carbohydrates, which accumulates in the dermal and epidermal compartments, contributing to the aetiology of photoaging. Strategies to prevent photodamage caused by this cascade of reactions initiated by UV include: prevention of UV penetration into skin by physical and chemical sunscreens, prevention/reduction of inflammation using anti-inflammatory compounds (e.g. cyclooxygenase inhibitors, inhibitors of cytokine generation); scavenging and quenching of ROS by antioxidants; inhibition of neutrophil elastase activity to prevent extracellular matrix damage and activation of matrix metalloproteases (MMPs), and inhibition of MMP expression (e.g. by retinoids) and activity (e.g. by natural and synthetic inhibitors).
Int J Cosmet Sci. 2005 Feb;27(1):17-34
Recent advances in characterizing biological mechanisms underlying UV-induced wrinkles: a pivotal role of fibrobrast-derived elastase.
In clinical studies, the formation of facial wrinkles has been closely linked to the loss of elastic properties of the skin. Cumulative irradiation with ultraviolet (UV) B at suberythemal doses significantly reduces the elastic properties of the skin, resulting in the formation of wrinkles. In in vitro studies, we identified a paracrine pathway between keratinocytes and fibroblasts, which leads to wrinkle formation via the up-regulation of fibroblast elastases that degrade elastic fibers. UVB irradiation stimulates the activity of fibroblast elastases in animal skin. Scanning electron microscopy revealed that cumulative UVB irradiation elicits a marked alteration in the three-dimensional structure of elastic fibers, which is closely associated with the subsequent reduction in the elastic properties of the skin, resulting in wrinkle formation. Studies using anti-wrinkle treatments suggest a close relationship between the recovery of wrinkles and an improvement in the linearity of elastic fibers. Those studies also suggest a close correlation between the recovery in the linearity of elastic fibers and the improvement in skin elasticity. In a study using ovariectomized animals, we characterized the important role of elastase in their high vulnerability to UV-induced wrinkle formation. A synthetic inhibitor specific for fibroblast elastases significantly prevents wrinkle formation without reducing the elastic properties of the skin, accompanied by minor damage in elastic fibers. Finally, we identified an effective extract of Zingiber officinale (L.) Rose from a screen of many herb extracts, which has a safe and potent inhibitory activity against fibroblast elastases. Animal studies using the L. Rose extract revealed that it has significant preventive effects against UVB-induced wrinkle formation, which occur in concert with beneficial effects on skin elasticity. A 1-year clinical study on human facial skin to determine the efficacy of the L. Rose extract demonstrated that it inhibits the UV-induced decrease in skin elasticity and prevents or improves wrinkle formation in skin around the corner of the eye without changing the water content of the stratum corneum. Our long-term studies support our hypothesis for a mechanism of wrinkle formation in which cytokine expression is activated by UV irradiation and triggers dermal fibroblasts to increase the expression of elastase. That increase in elastase results in the deterioration of the three-dimensional architecture of elastic fibers, reducing skin elasticity and finally leading to the formation of wrinkles.
Arch Dermatol Res. 2008 Apr;300 Suppl 1:S7-20
Mechanism of UVB-induced wrinkling of the skin: paracrine cytokine linkage between keratinocytes and fibroblasts leading to the stimulation of elastase.
In clinical studies, the formation of facial wrinkles has been closely linked to the loss of elastic properties of the skin. Repetitive irradiation of animal skin with UVB radiation at suberythemal doses significantly reduces its elastic properties, resulting in the formation of wrinkles. Repetitive UVB irradiation elicits a marked alteration in the three-dimensional structure of elastic fibers, which is closely associated with a subsequent reduction in the elastic properties of the skin. Although UVB irradiation stimulates the activity of fibroblast elastases in the dermis, a synthetic inhibitor specific for fibroblast elastases prevents wrinkle formation. The close interrelationships among wrinkle formation, elastic properties, and elastic fiber linearity are revealed by the effects of different concentrations of the elastase inhibitor (R(2)>0.9), suggesting that enhanced elastase activity by dermal fibroblasts plays a pivotal role in the UVB wrinkling mechanism. In in vitro studies we identified a paracrine linkage between keratinocytes and fibroblasts that leads to wrinkle formation through the upregulation of fibroblast elastases. These studies support our hypothesis for a mechanism of wrinkle formation by which cytokine expression is activated in epidermal keratinocytes by UVB radiation and triggers dermal fibroblasts to increase their expression of elastase.
J Investig Dermatol Symp Proc. 2009 Aug;14(1):36-43
Effect of moisturizers on epidermal barrier function.
A daily moisturizing routine is a vital part of the management of patients with atopic dermatitis and other dry skin conditions. The composition of the moisturizer determines whether the treatment strengthens or deteriorates the skin barrier function, which may have consequences for the outcome of the dermatitis. One might expect that a patient's impaired skin barrier function should improve in association with a reduction in the clinical signs of dryness. Despite visible relief of the dryness symptoms, however, the abnormal transepidermal water loss has been reported to remain high, or even to increase under certain regimens, whereas other moisturizers improve skin barrier function. Differing outcomes have also been reported in healthy skin: some moisturizers produce deterioration in skin barrier function and others improve the skin. Possible targets for barrier-influencing moisturizing creams include the intercellular lipid bilayers, where the fraction of lipids forming a fluid phase might be changed due to compositional or organizational changes. Other targets are the projected size of the corneocytes or the thickness of the stratum corneum. Moisturizers with barrier-improving properties may delay relapse of dermatitis in patients with atopic dermatitis. In a worst-case scenario, treatment with moisturizing creams could increase the risks of dermatitis and asthma.
Clin Dermatol. 2012 May-Jun;30(3):286-96
The moisturizing effect of a wheat extract food supplement on women's skin: a randomized, double-blind placebo- controlled trial.
Ceramides, specific lipid components of the skin, represent 35-40% of the intercellular cement binding cells together and contributing to skin hydration. A wheat extract rich in ceramides and digalactosyl-diglycerides was developed by Hitex in two forms: wheat extract oil (WEO) and wheat extract powder (WEP). In vitro tests and two clinical studies demonstrated promising efficacy results with WEP on skin hydration. To confirm these early results, a double-blind, randomized, placebo-controlled study was carried out on 51 women aged 20-63 years with dry to very dry skin who received either 350 mg of WEO or placebo for 3 months. Evaluation of skin hydration on legs, arms and face, assessed at baseline (D0) and at study end (D84) was performed by the dermatologist using dermatological scores (dryness, roughness, erythema), skin hydration measurement (corneometry) and self-assessment scores (Visual Analogue Scale: VAS). Perceived efficacy was noted by participants throughout the study; tolerability and overall acceptability of the study products were evaluated by the dermatologist and the participants at the end of study. Skin hydration was significantly increased between D0 and D84 on the arms (P < 0.001) and legs (P = 0.012) in the WEO group compared with placebo. Even if no significant statistical differences between groups were observed for the dermatological evaluation, skin dryness and redness tended to be reduced in the WEO group. Moreover, from D0 to D84, the VAS index had a tendency to increase in favour of WEO for the overall skin hydration (P = 0.084) indicating that participants perceived an improvement. The WEO capsules were perceived by participants as being more effective than placebo on all skin dryness signs. In conclusion, WEO capsules were well tolerated and appreciated. After 3 months' treatment, a significant increase in skin hydration and an improvement in associated clinical signs were observed in women with dry skin.
Int J Cosmet Sci. 2011 Apr;33(2):138-43
The skin barrier in healthy and diseased state.
The primary function of the skin is to protect the body for unwanted influences from the environment. The main barrier of the skin is located in the outermost layer of the skin, the stratum corneum. The stratum corneum consists of corneocytes surrounded by lipid regions. As most drugs applied onto the skin permeate along the lipid domains, the lipid organization is considered to be very important for the skin barrier function. It is for this reason that the lipid organization has been investigated quite extensively. Due to the exceptional stratum corneum lipid composition, with long chain ceramides, free fatty acids and cholesterol as main lipid classes, the lipid organization is different from that of other biological membranes. In stratum corneum, two lamellar phases are present with repeat distances of approximately 6 and 13 nm. Moreover the lipids in the lamellar phases form predominantly crystalline lateral phases, but most probably a subpopulation of lipids forms a liquid phase. Diseased skin is often characterized by a reduced barrier function and an altered lipid composition and organization. In order to understand the aberrant lipid organization in diseased skin, information on the relation between lipid composition and organization is crucial. However, due to its complexity and inter-individual variability, the use of native stratum corneum does not allow detailed systematic studies. To circumvent this problem, mixtures prepared with stratum corneum lipids can be used. In this paper first the lipid organization in stratum corneum of normal and diseased skin is described. Then the role the various lipid classes play in stratum corneum lipid organization and barrier function has been discussed. Finally, the information on the role various lipid classes play in lipid phase behavior has been used to interpret the changes in lipid organization and barrier properties of diseased skin.
Biochim Biophys Acta. 2006 Dec;1758(12):2080-95
Dietary phytochemicals and cancer prevention: Nrf2 signaling, epigenetics, and cell death mechanisms in blocking cancer initiation and progression.
Reactive metabolites from carcinogens and oxidative stress can drive genetic mutations, genomic instability, neoplastic transformation, and ultimately carcinogenesis. Numerous dietary phytochemicals in vegetables/fruits have been shown to possess cancer chemopreventive effects in both preclinical animal models and human epidemiological studies. These phytochemicals could prevent the initiation of carcinogenesis via either direct scavenging of reactive oxygen species/reactive nitrogen species (ROS/RNS) or, more importantly, the induction of cellular defense detoxifying/antioxidant enzymes. These defense enzymes mediated by Nrf2-antioxidative stress and anti-inflammatory signaling pathways can contribute to cellular protection against ROS/RNS and reactive metabolites of carcinogens. In addition, these compounds would kill initiated/transformed cancer cells in vitro and in in vivo xenografts via diverse anti-cancer mechanisms. These mechanisms include the activation of signaling kinases (e.g., JNK), caspases and the mitochondria damage/cytochrome c pathways. Phytochemicals may also have anti-cancer effects by inhibiting the IKK/NF-κB pathway, inhibiting STAT3, and causing cell cycle arrest. In addition, other mechanisms may include epigenetic alterations (e.g., inhibition of HDACs, miRNAs, and the modification of the CpG methylation of cancer-related genes). In this review, we will discuss: the current advances in the study of Nrf2 signaling; Nrf2-deficient tumor mouse models; the epigenetic control of Nrf2 in tumorigenesis and chemoprevention; Nrf2-mediated cancer chemoprevention by naturally occurring dietary phytochemicals; and the mutation or hyper-expression of the Nrf2-Keap1 signaling pathway in advanced tumor cells. The future development of dietary phytochemicals for chemoprevention must integrate in vitro signaling mechanisms, relevant biomarkers of human diseases, and combinations of different phytochemicals and/or non-toxic therapeutic drugs, including NSAIDs.
Pharmacol Ther. 2012 Oct 3. pii: S0163-7258(12)00210-0
Selective depletion of mutant p53 by cancer chemopreventive isothiocyanates and their structure-activity relationships.
Isothiocyanates (ITCs) derived from cruciferous vegetables induce apoptosis in cancer cells. We demonstrate that certain naturally occurring ITCs selectively deplete mutant p53 but not the wild-type and do so via a transcription-independent mechanism. Direct p53 binding followed by conformational changes appears to be a mechanism by which mutant p53 is depleted. Structure-activity relationship studies (SARs) using naturally occurring and synthetic ITCs show that depletion is influenced by the ITC side-chain moiety. Furthermore, we show that cells with p53 mutations are more sensitive to cytotoxicity induced by phenethyl isothiocyanate (PEITC) than those with the wild-type protein. 2,2-Diphenylethyl ITC, a synthetic ITC, is one of the most potent depletors of mutant p53 studies and induces apoptosis to the greatest extent in mutant p53 breast cancer cells. Collectively, this study shows that mutant p53 depletion may be an important novel target for cancer chemoprevention and therapy by natural and synthetic ITCs
J Med Chem. 2011 Feb 10;54(3):809-16
Potent induction of phase 2 enzymes in human prostate cells by sulforaphane.
Two population-based, case-control studies have documented reduced risk of prostate cancer in men who consume cruciferous vegetables. Cruciferae contain high levels of the isothiocyanate sulforaphane. Sulforaphane is known to bolster the defenses of cells against carcinogens through up-regulation of enzymes of carcinogen defense (phase 2 enzymes). Prostate cancer is characterized by an early and near universal loss of expression of the phase 2 enzyme glutathione S-transferase (GST)-pi. We tested whether sulforaphane may act in prostatic cells by increasing phase 2 enzyme expression. The human prostate cancer cell lines LNCaP, MDA PCa 2a, MDA PCa 2b, PC-3, and TSU-Pr1 were treated with 0.1-15 microM sulforaphane in vitro. LNCaP was also treated with an aqueous extract of broccoli sprouts. Quinone reductase enzymatic activity, a surrogate of global phase 2 enzyme activity, was assayed by the menadione-coupled reduction of tetrazolium dye. Expression of NQO-1, GST-alpha, gamma-glutamylcysteine synthetase-heavy and -light chains, and microsomal GST was assessed by Northern blot analysis. Sulforaphane and broccoli sprout extract potently induce quinone reductase activity in cultured prostate cells, and this induction appears to be mediated by increased transcription of the NQO-1 gene. Sulforaphane also induces expression of gamma-glutamylcysteine synthetase light subunit but not the heavy subunit, and this induction is associated with moderate increases in intracellular glutathione levels. Microsomal and alpha-class glutathione transferases were also induced transcriptionally. Sulforaphane induces phase 2 enzyme expression and activity significantly in human prostatic cells. This induction is accompanied by, but not because of, increased intracellular glutathione synthesis. Our findings may help explain the observed inverse correlation between consumption of cruciferae and prostate cancer risk.
Cancer Epidemiol Biomarkers Prev. 2001 Sep;10(9):949-54