How Vitamin D Prevent Skin Aging

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In addition to its effect on maintaining bone health and normal calcium metabolism, Vitamin D influences a much broader array of physiological processes and is associated with a host of age-related health conditions (see post “Vitamin D Deficiency And Healthy Aging”). Vitamin D Deficiency has been linked to some skin conditions as well. These include psoriasis, eczema, acne, skin aging. Optimal level of vitamin D in the skin helps boost skin elasticity, stimulate collagen production, enhance radiance, and lessen wrinkles and fine lines, reduce dark spot.

Vitamin D is primarily synthesized in skin exposed to UV light, if not obtained by diet or supplements. Vitamin D metabolism in the epidermis begins with 7- dehydrocholesterol, which produces both cholesterol and previtamin D3. This generates calcitriol – the hormonally active form of vitamin D later in the liver and transported to various parts of the body. Skin has the ability to manufacture as much as 10,000 IU of vitamin D after 20–30 minutes of sun exposure. The following factors can limit or influence the amount of internal vitamin D synthesis through sun exposure alone: age, skin color, geographic latitude, seasonal variation in sunlight intensity and the widespread (but necessary) use of sunscreen. Calcitriol has been found to be able to regulate or activate over 2,000 genes and therefore contribute to a broad spectrum of impact on various health problems (see post “Vitamin D Deficiency And Healthy Aging”).

How does vitamin D maintain skin health and prevent (premature) skin aging?

One mechanism is through its ability in regulating genes and molecules involved in the immune system function and inflammation process. Vitamin D deficiency weakens immune system function and increase the adverse effect of chronic or excess inflammation on healthy skin (see article “Chronic or Excess Inflammation” from the skin aging theory section). Active vitamin D has its role in immune health and stimulates factors important for suppressing inflammation of the skin.

Another mechanism that vitamin D can prevent skin aging is through the regulation of skin cell (Keratinocytes) growth, differentiation and renewal for replenishment and rejuvenation of skin’s surface. Vitamin D promote skin cell renewal by regulating (epidermal) growth factors and other molecules involved in the skin cell division and differentiation. This is why vitamin D is absolutely essential to the maintenance of healthy-looking skin.

Moreover, Vitamin D was also implicated in its role to neutralize free radicals – one of the main causes of skin aging – including the skin damaging free radicals (reactive oxygen species) induced by too much sun exposure. (see article “free radical theory of skin aging”;  photo skin aging:  “UV Radiation And Skin Aging”). True, together with other well known antioxidant vitamins (Vitamin A, C, and E), vitamin D is a cell membrane antioxidant that can combat reactive oxygen species (inhibit cell membrane lipid peroxidation). The fact is vitamin D has been found to be more effective in reducing lipid peroxidation and increasing enzymes that protect against oxidation than vitamin E.

Vitamin D can also activate genes coding for antimicrobial receptors and the antimicrobial peptide, cathelicidin. This is why vitamin D is also known to combat acne and prevent skin infection at the site of injury and accelerate skin healing by stimulating the angiogenesis.

The general skin aging process also lead to a decreased ability in skin to synthesis vitamin D induced by sun exposure. When this intrinsic route of vitamin D synthesis is impaired by aging process (reduce by about 75%), external sources of vitamin D from diet and supplement may become even more crucial, because bulk of the vitamin D produced by sunlight is used by many other systems in the body. Heliotherapy – the controlled therapeutic exposure to sunlight may increase deficient vitamin D levels while also treating skin problems. In addition, topical Vitamin D skin care products is definitely an option to be be combined with supplements and outdoor activity in protecting and rejuvenating the aging skin.

Your Anti-Aging Shopping Center

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Looking for a way to slow-down aging? Good nutrition should be the key to that. Of course, medicine has advanced quite a bit and there are many products to help you with just that.

Anti-Aging Skin Care Beauty is a place where you can look at and compare many products. They are all made by different certified brands and you will be able to find many reviews that approach each product with authority.

If you are looking for a great choice of anti-aging products, this marketplace seems like the best choice online.

Bildergebnis für slow-down aging

Professional Reviews

Anti-Aging Skin Care Beauty provides visitors not only with many excellent options when it comes down to actual products, but there are also many professional reviews, which seem to look into the chemical composition of each individual good sold on the portal as well as recommend creams and other cosmetics based on the type of skin you have. The website is focused on educating the buyer and is above all else a portal where you can examine products in detail and familiarise with how cosmetics work and why you might need a certain product.

There are multiple categories covered in the reviews such as creams, regimens, dermal fillers, lift home devices, LED home, Ultrasonic Home Device and more. The website is very convenient when it comes to navigation. You will find each separate tab to contain comprehensive information about the individual products listed.

Skin Aging is dug deep into, including an overview of the condition, causes, and how the process changes the skin. Thankfully, there are many skin care tips, which will allow you to keep your skin fresh and young without having to commit too much to expensive cosmetics.

Each section will provide you with extensive information about each individual procedure and product you can find. There is an additional side menu where you will find extra information about various aging problems that pertain to the skin.

There is an extensive blog section that runs a series of educatory materials, which will help you understand how skin aging occurs and what the results thereof are. The website is dedicated to selling products as much as it is to writing science-pop articles that help readers leave the page a little more educated about the effects of skin aging. To know from where to buy, we recommend to visit a list that provides in-depth comparison of online pharmacies in Germany.

Different Anti-Aging Skin Procedures to Consider

Bildergebnis für slow-down aging

Looking to learn every procedure there is about skin aging and preventing the downsides of this process? Well, the website will assist you with quite a few of those. Of course, you need to be a little better informed before you subject yourself to any of these procedures. There are various ones to consider, including:

  • Skin Needling
  • Dermal Filler
  • Microcurrent Face Lift
  • Nonablative Light Therapy
  • Radio Frequency Treatment
  • Ultrasonic Treatment
  • Ablative Laser Resurfacing
  • Chemical Peel
  • Plasma Resurfacing
  • Plastic Surgery

Some of these methods are more invasive than others. Usually, people – and mostly women – who are committed to maintaining their youthful look for as long as possible don’t stop before anything to guarantee themselves the coveted reward.

Anti-Aging Skin Care Beauty will help you approach a skin care specialist prepared and knowing much of what they will be able to provide you as information. There is even an eBook which is a very interesting read and provides you with details.

Buying the Proper Medicine

Anti-Aging Skin Care Beauty offers extensive information about all products in the catalogue and just general buying guides. In each article, you will find information about the active ingredient of a product as well as the ingredients and what is being treated.

There are usually a few shortlisted products of each category, which will help you get a quick snippet of the best skin care products without having to dive deep into websites that you are ill familiar with.

This portal is equipped with the tools to provide you with a quick breakdown of the main characteristic of an excellent product and then recommend suitable products that have shown promising results in other users.

Of course, certain creams can affect your skin differently and it may take you a while to get the best possible combination of products you will want to use or your own skin. Retaining your youthful look is not at all too difficult these days. All it takes is picking the right cosmetic products and you will be able to keep your skin healthy and well-nourished for years to come.

 

UV-Induced Neutrophil Infiltration and Increased MMP Secretion in Photo Skin Aging

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The primary mechanism of photo skin aging is mediated by UV induced reactive oxygen species (ROS). ROS damages biomacromolecules and function as intracellular signal to activate transcription factors AP-1 and NF-kB . AP-1 And NF-kB are known to regulate a wide varieties of genes that are essential components of chronological and photo skin aging processes. One group of effector protein in skin aging of AP-1 signal transduction pathway is the induction of matrix metalloproteinases (MMP) – the extracellular matrix enzyme synthesized mainly by dermal fibroblast whose function is to degrade extra cellular matrix protein – collagen and elastin – the structural protein fiber network in the dermis connective tissue that account for skin’s strength and elasticity. Both chronologic and photo skin aging is associated with increased MMP and increased degradation of matrix collagen and elastic fiber.

UV irradiation induces MMP-1. MMP-3, MMP-9 significantly, each belong to one of the three main functional subgroups of MMP – the collagenases, stromelysins, and gelatinases. MMP-1 (collagenase 1) is synthesized by keratinocytes and fibroblasts and degrades the Collagens I, II, III, VII and X. Collagen I and III is the major collagen type forming dermis fiber network of the skin, collagen VII is the component in skin’s base membrane at the dermal-epidermal junction (DEJ). Stromelysin (MMP-3) degrades collagen types II, III, IV, IX, and X, proteoglycans, fibronectin, laminin, and elastin. Collagen IV and laminin is the main components in the basal lamina of the base membrane. Gelatinase (MMP-9) degrades type IV and V collagens. Together, these three MMPs can fully degrade skin collagen. Initially, MMP-1 cleaves the triple-helical collagen molecule into three-quarter and one-quarter length fragments which are further degraded by MMP-3 and MMP-9.

UV irradication induces infiltration of neutrophils in the skin and is involved in the UV-induced inflammaging mechanism of skin aging. They are packed with proteolytic enzymes, including MMP and neutrophil elastase. Furthermore, activated neutrophils generate and release ROS. Infiltrating neutrophils can thus damage collagen fibers and elastic fibers. Research data suggests that neutrophils, rather than keratinocytes and fibroblasts, may be the major sources of proteolytic enzymes (particular MMPs and neutrophil elastase) in photo skin aging in vivo. Similar to other cells including fibroblasts, these proteolytic enzymes are normally stored in vesicles in an inactive form. The probable mechanism by which neutrophil-derived proteolytic enzymes are activated (and/or prevented from being inactivated by antiproteinases) is through proteolytic or oxidative mechanisms. ProMMPs can be activated by proteolytic mechanism (by active MMPs or other serine proteases) while antiproteinases can be inactivated by certain oxygen metabolites.

MMP-8 or neutrophil collagenase is a collagenase mainly synthesized by neutrophils. MMP-8 cleaves type I collagen faster than type III collagen, whereas MMP-1 has more specificity to type III collagen relative to type I collagen. Both MMP-1 and MMP-8 are synthesized as latent proenzymes that require proteolytic processing to become catalytically active. Whereas MMP-1 is synthesized and released from cells into the extracellular matrix, however, MMP-8 is synthesized and stored in specific granules in neutrophil. MMP-8 activity is therefore regulated by factors such as surface-bound ligands (IgG or complement components) that release it through degranulation. Once released and activated through proteolytic or oxidative mechanisms, MMP-8 has a major role in the connective tissue turnover. Research has shown that UV irradiation increases MMP-8 activity in vivo in the skin. Proenzyme form of MMP-8 increased significantly within 8 h post UV irradiation. Increased MMP-8 protein was associated with infiltration into the skin of neutrophils.

 

The Endogenous Photoprotective Mechanisms In The Skin

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UV-induced photo skin aging is primarily mediated via generation of reactive oxygen species/free radicals. Free radical theory of aging and skin aging is one of the most common causes of chronological and photo skin aging. UV irradiation not only activate aging process in the skin, but also activate the endogenous protective mechanisms to prevent UV-induced skin alterations including counteract or slow down photo aging process and/or to prevent skin cancer.

UV induced apoptosis is the internal mechanisms for protecting and preventing skin cancer. UV induced apoptosis mechanism is mainly transduced and activated via p53 signaling. p53 is a tumor suppressor protein functions as a tumor suppressor and is a transcription factor that is involved in cancer prevention. p53 has been described as “the guardian of the genome” because of its role in conserving stability by preventing genome mutation. In skin, p53 is activated when epidermal skin cells are damaged by UV radiation. p53 signaling activates mechanism of protection for skin cancer via cell cycle regulation and apoptosis. Upon DNA damage by acute UV radiation, p53 is induced and transcriptionally activated. Posttranscriptional activation of p53 is by phosphorylation of various serine residues. Various protein kinase including kinases in MAPK signal transduction pathway are involved in the phosphorylation of various p53 serine residues in response to UV radiation. The accumulation of the activated p53 protein result in the observation that G1 phase of cell cycle is prolonged; cell cycle regulatory proteins such as CDKs and cyclins are increased; and cyclin-dependent kinases inhibitors (CDKIs) are decreased. These changes in cell cycle regulation may provide mechanism for the cell to trigger and enter apoptosis with extensive DNA damage. If the DNA damage caused by UV radiation is very severe and the repair mechanism in response to UV induced DNA damage will not function to proceed to the DNA replication S phase of the cell cycle, apoptotic pathways are activated to eliminate damaged cells. Protein p53 as a transactivator of transcription can induce apoptosis by activating pro-apoptotic genes such as Bax and Fas and deregulating the anti-apoptotic gene bcl-2. Fas ligand is a type-II transmembrane protein that belongs to the tumor necrosis factor (TNF) family. Its binding with its receptor induces apoptosis. The cytoplasmic redistribution of apoptotic receptor Fas to the cell surface and Fas-Fas ligand interaction results in the cleavage and activation of procaspase-3,8,9, a group of proteases essential for the degradation of proteins and cellular components of the apoptotic cell. There are two types of apoptotic caspases: initiator (apical) caspases and effector (executioner) caspases. Initiator caspases (e.g., CASP2, CASP8, CASP9, and CASP10) cleave inactive pro-forms of effector caspases, thereby activating them. Effector caspases (e.g., CASP3, CASP6, CASP7) in turn cleave other protein substrates within the cell in the apoptotic process.

The skin consists of a network of natural antioxidants which include antioxidants enzymes such as superoxide dismutase, catalase and glutathione peroxidase and nonenzymatic antioxidants (e.g. vitamin E, coenzyme Q10, ascorbate, carotenoids). (see post “The Antioxidant Enzymes Network of The Skin” and “The Nonenzymatic Antioxidant Systems In Aging Skin”). These antioxidants provide protection from ROS produced during cellular metabolism and in photo skin aging. A number of antioxidant enzymes may be induced in response to UV irradiation initially. There is now ample evidence that after UV exposure a rapid cellular antioxidant response is induced, since Cu–Zn-dependent superoxide dismutase (SOD1), manganese-dependent superoxide dismutase (SOD2), glutathione peroxidase and catalase, hemeoxygenase-1 (HO-1), ferritin are induced after solar irradiation in vitro and in vivo.

Superoxide dismutase (SOD) belongs to major antioxidant enzymes that contribute to the homeostasis of oxygen radicals in the skin. It exists in isozymes , cytosolic CuZnSOD and mitochondrial MnSOD. UVA exposure to human dermal fibroblasts in vitro resulted in a significant increase in MnSOD on both mRNA and protein levels. UVB irradiation of human keratinocytes was shown to induce a significant increase in SOD activity and protein level. This increase in SOD was attributed to CuZnSOD. UVB irradiation of the epidermal keratinocytes induced release of IL-1α, IL-1β, and TNF-α that amplified MnSOD activity in dermal fibroblasts. Although the increase of SOD can remove superoxide anion, the product of the reaction – hydrogen peroxide itself can be easily converted to other ROS. The antioxidant enzyme which remove hydrogen peroxide – glutathione peroxidase (GPx) and catalase (CAT) has not been observed to be induced upon UV irradiation. Glutathione peroxidase (GPx) is a selenoprotein, that catalyzes the conversion of UV-induced H2O2 into water and molecular oxygen using GSH as a substrate. The activity is not strongly affected by UV and is considered to be the most important antioxidant defense system in the skin. Catalase (CAT) catalyzes the conversion of H2O2 into water and molecular oxygen thus reduces the damaging effects of H2O2. CAT activity in the skin is strongly reduced after UVA and UVB exposure. Therefore, the overall antioxidant enzyme functionality appear to be reduced by chronic UV exposure.

Intrinsic And Extrinsic Causes of Wrinkles: An Overview

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Many factors cause wrinkle formation. They are generally classified as intrinsic causes and extrinsic causes:

Intrinsic causes of wrinkle include:

  • reactive oxygen species and free radicals – free radical theory of skin aging
  • crosslinking of biomacromolecules
    • by glycation
    • by ROS/free radicals
  • collagen and elastin fiber damage
  • DNA damage and mutation
    • nuclear DNA damage
    • mitochondria DNA damage
  • mitochondria damage and reduced cellular energy production
  • genetics
  • telomere length shortening and cellular senescence
  • chronic inflammaging
  • reduced dermal stem cell function and activity – the stem cell theory of skin aging
  • dehydration
    • extracellular matrix ground substance – decreased proteoglycan and glycosaminoglycan
    • epidermal-dermal junction structural changes – reduced barrier function
  • reduced epidermal cell renewal and skin homeostasis functionality
  • decreased functionality of the natural antioxidant system of the skin
  • hormone theory of skin aging
  • mechanical causes
    • facial muscle movement
    • gravity
  • facial bone aging

Extrinsic causes of wrinkle include:

  • sun exposure
  • smoking
  • diet (deficiency in antioxidants and anti-inflammatory diet)
  • pollutions
  • stress
  • drug

Age-Related Morphological, Histological, Structural, And Molecular Changes In Skin Fibroblast In Vitro

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The study of age-related changes in the physiology, biochemistry, and molecular biology of isolated skin cell populations in culture has expanded and provide the basis for the understanding of the fundamental aspects of skin aging. In the field of molecular and cellular biology of aging and skin aging the terminology and theory about ‘‘cellular aging,’’ ‘‘cell senescence,’’ or ‘‘replicative senescence’’ is most commonly derived from the study of normal diploid cells (e.g. dermal fibroblast) in vitro through serial subcultivation. This process of cellular senescence, or replicative senescence in vitro is generally known as the Hayflick phenomenon, and the limited division potential of cells (dermal fibroblast) is called the Hayflick limit. After a limited number of serial passaging, fibroblast enter into the period of slowing-down of cell proliferation rate, followed the cessation of cell division known as “replicative senescence’’. After fibroblasts reaches replicative senescence, some cells can still stay alive and be metabolically active at a minimal level for sometime and generally resist undergoing apoptosis. For fibroblasts the range of cumulative population doublings (CPD, i.e. the total number of cell divisions) for the cell strains originating from embryonic tissues is between 50 and 70, whereas for those originating from adult biopsies it is generally less than 50 CPD. Additionally, gaseous composition, especially oxygen levels, and the quality of the nutritional serum and growth factors of the culture medium as well as the type of skin biopsy (sun-exposed vs sun-protected skin biopsy), can significantly affect the proliferative lifespan of fibroblasts in vitro. The in vitro system of fibroblast cellular aging provide the model for studying structural and functional aspects of skin aging.

There is a progressive and accumulative occurrence of a wide variety of phenotype changes during the whole serial passaging of fibroblasts before cessation of cell replication occurs. The emerging senescent phenotype of serially passaged fibroblasts can be categorized into the structural, physiological, and biochemical and molecular phenotypes. There are more than 200 such structural, physiological, biochemical, and molecular characteristics that have been studied during cellular aging of fibroblast that appear progressively in cell cultures.

The structural changes occur progressively during in vitro fibroblast senescence include: the increase in cell size, changed cellular morphology (from thin, long, and spindle-like to flattened and irregular cell shape), rod-like polymerization of the cytoskeletal actin filaments and disorganized microtubules, increased membrane rigidity, increased multinucleation, increased number of vacuoles and dense lysosomal autophagous bodies. In addition to the gross structural alterations, there are several ultrastructural changes by electron microscopic studies.

The physiological changes occur progressively during fibroblast in vitro serial subcultivation include: altered calcium flux, pH, viscosity, and membrane potential, reduced activity of ionic pumps, reduced mobility, reduced respiration and energy production, reduced response to growth factors and other mitogens, increased sensitivity to drugs, irradiation, and other stresses.

A large amount of data documented a plethora of changes of fibroblast during cellular senescence at the biochemical and molecular level which form the mechanistic bases of structural and physiological alterations. The biochemical and molecular changes of fibroblast occur progressively during fibroblast cellular aging include: cell cycle pause at the G1 phase near the S phase boundary (cessation of cell division), increased mRNA and protein levels of cell cycle inhibitors, increased mRNA and protein levels of inhibitors of proteases (decreased damaged protein degradation), decreased amount and activities of numerous house-keeping enzymes, decreased activities of macromolecular turnover pathways, reduced levels of DNA methylation, reduced length of telomeres, increased nuclear and mitochondria DNA damage, increased protein damage, increased macromolecular cross-linking, increased accumulation of reactive oxygen species (ROS).

The correlation between cellular aging in vitro and in vivo is often based on the evidence gathered from studies of fibroblast derived from aging skin biopsies and from premature aging syndromes on cellular proliferative capacity in vitro. These studies indicate that the genetic and intrinsic Hayflick limit of fibroblast in vitro subcultivation is a true reflection of what is going on during aging and skin aging.

Mechanism of UV Induced ROS Generation: Photosensitization

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The primary mechanism of UV induced skin aging is the production and generation of reactive oxygen species (ROS). ROS/free radicals is one of the main causes of chronologic and photo skin aging. ROS damages and oxidizes biomacromolecules and cellular components. ROS also are intracellular signals which activate and regulate transcriptions factors and genes involved in the molecular mechanism of the skin aging process. One mechanism of UV induced ROS generation is via photosensitization. The molecular mechanism linking the photon absorption and ROS generation has been elucidated while the detailed mechanism seems to be elusive. Photosensitization is the process that the absorption of photon by the chromophores in the molecule cause the chromophore to change to the photoexcited state from the electronic ground state. When there is no subsequent energy dissipation or photon emission after the photon absorption. The absorbed energy will initiate chemical reactions leading to the formation of reactive intermediates and photoproduct where the absorbed photon energy is converted to chemical energy and the chromophores return to the electronic ground state. The Photoreactive intermediate react with substrate molecules including DNA bases (type I photosensitization reaction) or molecular oxygen (type II photosensitization reaction) leading to ROS formation. Both Type I and Type II mechanism can cause the formation of superoxide anion which will produce H2O2 (hydrogen peroxide) by spontaneous or enzyme catalyzed dismutation. Thus, it is the physical nature of the incident solar photons and the chemical nature of the absorbing chromophore in skin that determine the biological effects of the ROS generation. Most of the solar UV energy incident on the skin is from the UVA region which is a deep penetrating UV in the skin. Photosensitization by endogenous non-DNA chromophores of skin appears to be a key primary mechanism of light driven ROS production in skin although UV irradiation may also cause the electron leakage at the mitochondria respiratory chain and thereby increase the production of ROS byproduct in the aerobic metabolism or by activating existing NADPH oxidase activity through UV induced intracellular calcium influx (see post “Mechanism of UV Induced ROS Generation: NADPH Oxidase Activation”).

The endogenous photosensitizers in the skin are primary intermediates for the ROS formation in the photo oxidative stress mechanism of skin aging. Human skin is an abundant source of numerous chromophores with strong absorption particularly in the UVA region. The endogenous photosensitizers include a multitude of chemical structures, pathways of formation, skin localization and photochemical mechanisms of action. Photosensitizers in the skin exists both as constitutive structural and functional intra- and extracellular molecules and as dynamically generated accumulated molecules as a result of posttranslational modification and crosslinking of skin structural proteins and as a result of photooxidative and carbonyl stress by spontaneous chemical modification of intra- and extracellular molecules. A 3-step model of skin photosensitization process has been proposed to illustrate general UV-induced ROS formation mechanism in photo skin aging. Step I is the formation of photosensitizer by enzymatic and spontaneous reaction pathways leading to the accumulation of photosensitizer chromophores, particularly on skin structural proteins of the extracellular matrix. Step II is the photosensitizer activation via generation of the photoexcited state of the sensitizer upon absorption of photons. Photochemical reaction cascades available to the particular photosensitizer are initiated depending on the local pH, solute concentrations, water activity, oxygen
partial pressure, and surrounding target molecules. Photoactivation of endogenous sensitizers occurs throughout skin, ranges from nuclear to extracellular compartments. Step III is the execution of photosensitization which is the process of ROS/free radical induced aging and skin aging and the accumulation of photoproducts formed by photooxidation of target molecules

The Effect of UV-Induced Gene Activation On Photo Skin Aging

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The primary mechanism of UV-induced skin aging is mediated by the generation and accumulation of free radicals including reactive oxygen species (ROS) and reactive nitrogen species (RNS). ROS or free radicals not only can damage proteins, DNA, cellular membrane and cellular organelles, it also function as an intracellular signals to initiate different signal transduction pathways which regulate and activate genes that are either involved in the skin aging process or to further regulate other signaling pathways for cellular aging process. Levels of MMP (MMP1, 2, 3. 9), COX-2, HO-1, iNOS, ODC, p53, bcl2, bax, c-jun, c-fos, AP-1, NF-kB, TNF-alpha, IL-1, IL-6, are increased in response to UV irradiation.

1. genes that cause the photo skin aging phenotypes

MMP, the matrix metalloproteinase, are a group of extra cellular matrix degradation enzymes that degrade skin connective tissue fiber networks, primarily the collagen and elastin fibers. MMPs is the effector molecules for phenotypes of skin aging and its activities and amount is increased in both chronologic and photo skin aging. Collagenase (MMP1) degrades the Collagens I, II, III, VII and X, collagen I and III is the major collagen type forming dermis fiber network of the skin, collagen VII is the component in skin’s base membrane at the dermal-epidermal junction (DEJ). MMP-2 degrades degrades type IV collagen. Stromelysin (MMP-3) degrades collagen types II, III, IV, IX, and X, proteoglycans, fibronectin, laminin, and elastin. Collagen IV and laminin is the main components in the basal lamina of the base membrane. Elastin is the other main skin structural proteins found in the dermis connective tissue. The damage of the ECM of the dermis and DEJ is causatively related to the observed skin aging signs. Gelatinase (MMP-9) degrades type IV and V collagens.

COX-2 (cyclooxygenase-2) is one of the mediators in inflammaging and ROS generation as a result of inflammaging.

iNOS (inducible Nitric oxide synthase) produces NO from L-arginine. iNOS was found to reduce the proliferative activity of dermal fibroblast and may be related to fibroblast senescence. iNOS is increased in chronological skin aging as well.

NF-kB is a transcription factor that regulate and activate genes in immune response and is involved in inflammaging mechanism in intrinsic aging and photo skin aging. UV induced ROS signaling activates NF-kB. NF-kB activity is further amplified by many of its signaling pathway effectors – the proinflammatory cytokines (e.g. IL-1, IL-6) are themselves activators of NF-kB.

see “Is NF-kB the Secret to Skin Aging?”

AP-1 is transcription factor complex composed of c-Jun and c-Fos. AP-1 is induced by ROS-triggered signaling pathways. AP-1 regulate and activate genes that result in the increased extracellular matrix fiber network degradation (collagen breakdown) and decreases the production of new collagen. see “AP-1 Signaling Activates MMP in Chronological and Photo Skin Aging” and “NF-kB and AP-1 Molecular Signaling Mechanisms of Intrinsic And Extrinsic Skin Aging” for detail.

c-Jun is a transcription factor activated by JNK (c-Jun N-terminal kinases) pathway. JNK is activated by MAP kinase pathways which also mediate ROS-induced AP-1 and NF-kB activation. UV induced c-Jun interferes with the type I and type III procollagen transcription, thus block partly the procollagen synthesis in dermal fibroblast. c-Fos is a cellular proto-oncogene belonging to the immediate early gene family of transcription factors.

TNF-alpha (tumor necrosis factor-alpha) has the primary role in regulation of immune cells. TNF-alpha may be related to the age-related decrease of cutaneous immunity. TNF-alpha signaling pathway also activate transcription factor AP-1 and NF-kB.

IL-1 (Interleukin-1) is a proinflammatory cytokine that has several effects in the immune and inflammatory response and inflammaging process. UV induced ROS activate IL-1 via NF-kB pathway. ROS also activate IL-1 receptor. When IL-1 binds to its cell-surface receptor, IL-1 initiates a signaling cascade that leads to activation of the transcription factor NF-kB and AP-1 in fibroblast. Both IL-1α and IL-1β are produced by macrophage and fibroblasts of the dermis. IL-1α is constitutively produced by epithelial cells. It is found in substantial amounts in epidermis. The essential role of IL-1α in maintenance of skin barrier function is due to the constitutive production of large amounts of IL-1α precursor by healthy epidermal keratinocytes. A wide variety of other cells only upon stimulation can be induced to transcribe the IL-1α genes and produce the precursor form of IL-1α such as dermal fibroblasts. IL-1 signaling in infiltrated immune cells produce more free radicals and oxidative stress which resulting in skin aging.

IL-6 (Interleukin-6) is an interleukin that acts as both a pro-inflammatory cytokine and anti-inflammatory cytokine after the acute immune response. It is secreted by T cells and macrophages to stimulate immune response. Increasing amounts of measurable serum IL-6 is associated with aging. IL-6 is is mainly modulated by NF-KB. IL-6 signaling activates JAK pathway – the transducer and activator of STAT transcription factor and SHP2/ERK/MAP kinase pathway. There is also trans signaling pathway by IL-6 which may be related to the chronic inflammation mechanism of aging.

2. genes that are the UV-induced endogenous protective mechanism

HO-1 (Heme oxygenase) is a redox regulated enzyme that have antioxidant and anti-inflammatory activities and its level is affected by cellular redox state such as the level of glutathione (GSH, a natural antioxidant) and/or GSSH to GSH ratio. Increased HO-1 in response to UV irradiation appears to be part of the natural photoprotective mechanism.

ODC (Ornithine decarboxylase) is an enzyme in the polyamine-biosynthesis pathway and has a role in the in the regulation of DNA synthesis and cell proliferation. The polyamine produced has the function to stabilize DNA structure and as antioxidants . UV-induced ODC response decreases with age, suggesting the photoprotective role of ODC induction.

p53 is a tumor suppressor protein functions as a tumor suppressor and is a transcription factor that is involved in preventing cancer. p53 has been described as “the guardian of the genome” because of its role in conserving stability by preventing genome mutation. p53 becomes activated in response to a myriad of stress types (e.g. UV induced DNA damage, oxidative stress). In skin, p53 is activated when epidermal skin cells are damaged by UV radiation. p53 signaling activate mechanism of protection for skin cancer – the DNA repair mechanism or apoptosis mechanism when excess DNA damage/mutation is accumulated.

Bcl2 (B-cell lymphoma 2) is an apoptosis regulator proteins an apoptosis suppressor. UVB irradiation induces apoptosis of keratinocytes by sequential activation of caspase 8, 3 and 1 in keratinocytes. In vitro and in vivo transfer of bcl-2 gene into keratinocytes suppresses UV-induced apoptosis. Decreased bcl-2 level is observed in UV irradiated skin in vivo and in vitro via p53 regulation. Bax (Bcl-2–associated X protein) is pro-apoptotic member of the Bcl-2 protein family. Bax is activated by p53 signaling.

Mechanism of UV Induced ROS Generation: NADPH Oxidase Activation

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The primary mechanism of UV induced skin aging is the production and generation of reactive oxygen species (ROS). ROS/free radicals is one of the main causes of chronologic and photo skin aging . ROS exerts aging effect via damaging and oxidizing biomacromolecules and cellular components. ROS also are intracellular signals which activate and regulate transcriptions factors and genes involved in the molecular mechanism of the aging process. One mechanism of UV induced ROS generation is via NADPH oxidase activation. NADPH oxidase (NOX) is an enzyme that catalyzes the production of superoxide from oxygen and NADPH. The superoxide produced is quantitatively converted to hydrogen peroxide which in turn can be further converted to other ROS. Several oxidoreductases have been identified to generate superoxide. These include cyclooxygenase, cytochrome P450 enzymes, nitric-oxide synthase, mitochondrial NADH:ubiquinone oxidoreductase, and NADPH oxidase. Differ from the other oxidoreductases that produce superoxide, NADPH oxidase only catalyzes the production of superoxide from oxygen and NADPH. Whereas the other enzymes produce ROS only as byproducts along with their specific catalytic pathways at mitochondria aerobic oxygen metabolism or from other sources. There are seven isoforms of NOX being identified thus far. Different isoforms of NADPH oxidase seems to be tissue or cell type specific. The NADPH oxidase paradigm was largely derived from studies in immune cells such as neutrophils and macrophages.

Skin also contain NADPH oxidase subunits. UV-induced NADPH oxidase activity has been studied in skin keratinocytes in vitro. NADPH oxidase activity is induced following UV exposure. In keratinocytes, NADPH oxidase activity is induced 2-fold within 20 minutes following UV exposure. Block of NADPH oxidase activity using small interfering RNA (siRNA) and/or inhibitor of NADPH oxidase completely blocked UV-induced hydrogen peroxide generation, indicating that UV induced ROS produced by mitochondria or other sources are due to NADPH oxidase activation. Thus, NADPH oxidase is a major enzymatic source of hydrogen peroxide production following UV irradiation in keratinocytes.

Many stress stimuli can acutely activate NOX enzyme activity before the transcriptional and/or post transcriptional activation of NOX genes. The mechanism for activation of NOX is mediated by an increase in intracellular calcium concentration and protein kinase C (PKC) mediated phosphorylation. NOX phosphorylation by PKC is essential for NADPH oxidase activation. As with PKC, increased intracellular Ca2+ has been observed in cells exposed to various stress. The binding of calcium to the NOX calcium binding domain also activates NADPH oxidase and this mechanism of UV induced NADPH oxidase activation was observed in skin keratinocytes. An increase in intracellular Ca2+ can be a secondary response after PKC activation and vice versa. Activation of conventional PKC isoforms α, β, and γ is Ca2+-dependent; thus, Ca2+ influx and PKC activation is inter-related. NADPH oxidase-generated ROS may further increase intracellular Ca2+ by enhancing the membrane ion channel activity and/or Ca2+ release from intracellular stores. NADPH oxidase gene may also be activated subsequently via yet unclear signal tranduction pathway/mechanism. AP-1 – a transcription factor activated by ROS signal which regulate a number of genes (e.g matrix metalloproteinase) in aging process – binding sequence has been identified in some NOX isoforms, suggesting AP-1 signaling may regulate and increase NADPH oxidase.

The Nonenzymatic Antioxidant Systems In Aging Skin

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The free radical theory of aging established the role of oxidative stress as one of the main causes of aging and skin aging. Reactive oxygen species (ROS) – produced as byproduct of oxidative energy metabolism and induced by external factors – are known to damage protein, DNA, cellular membrane and are known to be the intracellular signal to activate the signal transduction pathways, leading to the activation of transcription factors NF-kB and AP-1 which regulate various genes involved in skin aging. Body has an internal natural antioxidant system to prevent and protect skin cells and extracellular matrix from ROS damage. Endogenous antioxidant system is composed of a network of enzymatic antioxidants or antioxidant enzymes such as glutathione peroxidase, superoxide dismutase, and catalase, and nonenzymatic low-molecular-weight antioxidants such as vitamin E isoforms, vitamin C, Coenzyme 10, glutathione (GSH), Alpha Lipoid Acid, NADPH, thioredoxin. Antioxidant enzymes system of the skin not only removes detrimental ROS and free radicals, some of the redox antioxidant enzyme system such as gluthathion reductase also capable of regenerating active antioxidant (reduced form) from antioxidant radicals (inactive oxidized form). Once an antioxidant removes ROS, itself become oxidized. In living systems, however, antioxidants can be regenerated, often with the help of other antioxidants. For example, glutathione can regenerate a number of other antioxidants such as vitamin C and vitamin E

Vitamin C is the most abundant antioxidant in both the dermis and epidermis. Epidermis contain more vitamin C than that of dermis. Vitamin C concentrations in both layers are approximately equal to that of glutathione. L-ascorbic acid is the active form of vitamin C and is water soluble as the major aqueous phase antioxidant. The body can not synthesize vitamin C. Vitamin C in the skin is normally transported from the bloodstream. Transport proteins specific for ascorbic acid are found on cells in all layers of the skin. Keratinocytes is more efficient in vitamin C transport, possibly due to the limited vascularization of the epidermis. When plasma vitamin C levels are saturated, skin vitamin C concentrations can no longer increase. Aging, however, causes a decline in vitamin C content in both the epidermis and dermis. Excessive exposures to UV light may also lower vitamin C content, primarily in the epidermis. Besides having antioxidant properties, Vitamin C also stimulate the collagen synthesis and is one of the major exogenous topical ingredient in skin care products. Vitamin C is a cofactor for enzymes involved in several collagen synthesis reactions.

Vitamin E is the most abundant endogenous antioxidant of the lipid phase cellular membranes with alpha-tocopherol being the most biologically active form. Vitamin E act as a peroxyl radical scavenger and terminates lipid peroxide radicals (LOOs) chain propagation on cell surface or cellular lipid/membrane. Lipid peroxyl radicals are the oxidation product resulting from the ROS damage.The antioxidant activities of alpha-tocopherol are heavily relied on the regeneration of reduced form by other antioxidants such as glutathione, vitamin C and Coenzyme 10. Glutathione and vitamin C are the major cofactors for Vitamin E antioxidant activity. UV irradiation has been shown to deplete this effective antioxidant.

Coenzyme 10 also known as ubiquinone is present in most cells, primarily in the mitochondria. It is a component of the electron transport chain and participates in cellular respiration, generating energy in the form of ATP. There are three redox states of coenzyme Q10: fully oxidized (ubiquinone), semiquinone (ubisemiquinone), and fully reduced (ubiquinol). The capacity of this molecule to exist in a completely oxidized form and a completely reduced form enables it to perform its functions in the electron transport chain and as an antioxidant. CoQ10 prevents lipid peroxidation by removing lipid peroxyl radicals (LOO), perferryl radical and oxygen radical. CoQ efficiently prevents the oxidation of DNA bases, particularly mitochondrial DNA by neutralizing hydroxyl radicals. In addition, it also regenerates other antioxidants such as vitamin E. The reduced form of CoQ effectively regenerates active vitamin E from the a-tocopheroxyl radical (the oxidized form of Vitamin E). Besides having antioxidant properties, Vitamin E also has anti-inflammatory effect through interfering the eicosanoid pathway.

Glutathione (GSH), most abundant tissue thiol, is a tripeptide antioxidant. Thiol groups of cysteine are reducing agents that can neutralize ROS and other free radicals after which itself is oxidized, forming glutathione disulfide (GSSG). The active/reduced Glutathione is regenerated from its oxidized form – glutathione disulfide (GSSG) – by glutathione reductase. In healthy cells and tissue, more than 90% glutathione is in the reduced form (GSH) and less than 10% exists in the disulfide form (GSSG). An increased GSSG-to-GSH ratio is considered indicative of oxidative stress. Glutathione acts synergistically with the other endogenous antioxidants to scavenge free radicals and is vital in maintaining and regenerating the ascorbates of vitamin C and the tocopherols of vitamin E in their reduced form. Glutathione works with the enzyme glutathione peroxidase to break down hydrogen peroxide and lipid hydroperoxides. Redox status is an parameter for assessing the in vivo prooxidant environment. Several indicators of in vivo redox status (oxidative stress) are available, including the ratios of GSH to GSSG, NADPH to NAPD+, and NADH to NAD+, as well as ratio of reduced and oxidized thioredoxin. Among these redox pairs, the GSH-to-GSSG ratio is one of most abundant redox indicator. The effect of aging on the glutathione redox system has been studied. A progressively decrease of GSH-GSSH ratio (increased oxidative stress) has been observed.

Alpha lipoic acid (ALA) is an endogenous dithiol antioxidant that is both hydrophilic and hydrophobic, making it an antioxidant to combat free radicals in aqueous and lipid phase of cell. Endogenous ALA is essential cofactors of several mitochondria enzyme complex for the aerobic metabolism, similar in function to many of the vitamins B . Alpha lipoic acid (ALA) has an essential role in mitochondrial dehydrogenase reactions. Its reduced form, Dihydrolipoic acid (DHLA), neutralize reactive oxygen species such as superoxide radicals, hydroxyl radicals, oxygen radical, hypochlorous acid. Two cytosolic enzymes, glutathione reductase (GR) and thioredoxin reductase (Trx1), and two mitochondrial enzymes, lipoamide dehydrogenase and thioredoxin reductase (Trx2), reduce ALA to DHLA. In addition to its antioxidant activities, Dihydrolipoic acid (DHLA), may exert prooxidant actions through reduction of iron. It may also exert antioxidant effects in biological systems through transitional metal chelation. Dihydrolipoic acid has been shown to have antioxidant but also pro-oxidant properties in systems in which hydroxyl radical was generated. Alpha lipoic acid also regenerates active forms of other antioxidants such as vitamin C and glutathione. ALA increases intracellular glutathione and coenzyme 10 levels.

A comprehensive in vivo study of the changes in major antioxidant enzymes and antioxidant molecules during intrinsic aging and photoaging processes in the epidermis and dermis of skin suggest that the components of the antioxidant defense system in human skin are probably regulated in a complex manner during the intrinsic aging and photoaging processes. The data showed that the activities of superoxide dismutase and glutathione peroxidase are not changed while the activity of catalase was significantly increased in the epidermis of photoaged (163%) and naturally aged (118%) skin, but it was significantly lower in the dermis of photoaged (67%) and naturally aged (55%) skin. The activity of glutathione reductase was significantly higher (121%) in naturally aged epidermis. The concentration of alpha-tocopherol was significantly lower in the epidermis of photoaged (56%) and aged (61%) skin, but this was not found to be the case in the dermis. Ascorbic acid levels were lower in both epidermis (69% and 61%) and dermis (63% and 70%) of photoaged and naturally aged skin. Glutathione concentrations were also lower.