H2O2 Accumulation by Catalase Reduction Changes MAP Kinase Signaling in Aged Human Skin In Vivo

Enzymes for dermatological use

Skin is the ultimate barrier between body and environment and prevents water loss and penetration of pathogens and toxins. Internal and external stressors, such as ultraviolet radiation (UVR), can damage skin integrity and lead to disorders. Therefore, skin health and skin ageing are important concerns and increased research from cosmetic and pharmaceutical sectors aims to improve skin conditions and provide new anti-ageing treatments. Biomolecules, compared to low molecular weight drugs and cosmetic ingredients, can offer high levels of specificity. Topically applied enzymes have been investigated to treat the adverse effects of sunlight, pollution and other external agents. Enzymes, with a diverse range of targets, present potential for dermatological use such as antioxidant enzymes, proteases and repairing enzymes. In this review, we discuss enzymes for dermatological applications and the challenges associated in this growing field.

Acetyl Zingerone: A Photostable Multifunctional Skincare Ingredient That Combats Features of Intrinsic and Extrinsic Skin Aging

The cumulative damage skin sustains from exposure to environmental stressors throughout life exerts significant effects on skin aging and cancer development. One of the main ways by which environmental stressors mediate their effects within skin is through induction of reactive oxygen species (ROS). In this review, we chronicle the multiple properties by which acetyl zingerone (AZ) as a skincare ingredient can benefit skin (1) by helping manage overproduction of ROS through multiple routes as an antioxidant, physical quencher and selective chelator, (2) by fortifying protection after UV exposure ends to prevent the type of epidermal DNA damage that correlates with development of skin cancer, (3) by modulating matrisome activity and nurturing the integrity of the extracellular matrix (ECM) within the dermis and (4) through its proficient ability to neutralize singlet oxygen, by stabilizing the ascorbic acid precursor tetrahexyldecyl ascorbate (THDC) in the dermal microenvironment. This activity improves THDC bioavailability and may blunt pro-inflammatory effects of THDC, such as activation of type I interferon signaling. Moreover, AZ is photostable and can sustain its properties during UV exposure, in contrast to α-tocopherol. All these properties of AZ translate into measurable clinical benefits to improve the visual appearance of photoaged facial skin and to strengthen the skin's own defenses against sun damage.

Ultraviolet Light Protection: Is It Really Enough?

Our current understanding of the pathogenesis of skin aging includes the role of ultraviolet light, visible light, infrared, pollution, cigarette smoke and other environmental exposures. The mechanism of action common to these exposures is the disruption of the cellular redox balance by the directly or indirectly increased formation of reactive oxygen species that overwhelm the intrinsic antioxidant defense system, resulting in an oxidative stress condition. Altered redox homeostasis triggers downstream pathways that contribute to tissue oxinflammation (cross-talk between inflammation and altered redox status) and accelerate skin aging. In addition, both ultraviolet light and pollution increase intracellular free iron that catalyzes reactive oxygen species generation via the Fenton reaction. This disruption of iron homeostasis within the cell further promotes oxidative stress and contributes to extrinsic skin aging. More recent studies have demonstrated that iron chelators can be used topically and can enhance the benefits of topically applied antioxidants. Thus, an updated, more comprehensive approach to environmental or atmospheric aging protection should include sun protective measures, broad spectrum sunscreens, antioxidants, chelating agents, and DNA repair enzymes.

Reactive Species in Progeroid Syndromes and Aging-Related Processes

Significance: Reactive species have been classically considered causative of age-related degenerative processes, but the scenario appears considerably more complex and to some extent counterintuitive than originally anticipated. The impact of reactive species in precocious aging syndromes is revealing new clues to understand and perhaps challenge the resulting degenerative processes. Recent Advances: Our understanding of reactive species has considerably evolved, including their hormetic effect (beneficial at a certain level, harmful beyond this level), the occurrence of diverse hormetic peaks in different cell types and organisms, and the extended type of reactive species that are relevant in biological processes. Our understanding of the impact of reactive species has also expanded from the dichotomic damaging/signaling role to modulation of gene expression. Critical Issues: These new concepts are affecting the study of aging and diseases where aging is greatly accelerated. We discuss how notions arising from the study of the underlying mechanisms of a progeroid disease, Cockayne syndrome, represent a paradigm shift that may shed a new light in understanding the role of reactive species in age-related degenerative processes. Future Issues: Future investigations urge to explore established and emerging notions to elucidate the multiple contributions of reactive species in degenerative processes linked to pathophysiological aging and their possible amelioration. Antioxid. Redox Signal. 37, 208-228.

Focus on the Contribution of Oxidative Stress in Skin Aging

Skin aging is one of the most evident signs of human aging. Modification of the skin during the life span is characterized by fine lines and wrinkling, loss of elasticity and volume, laxity, rough-textured appearance, and pallor. In contrast, photoaged skin is associated with uneven pigmentation (age spot) and is markedly wrinkled. At the cellular and molecular level, it consists of multiple interconnected processes based on biochemical reactions, genetic programs, and occurrence of external stimulation. The principal cellular perturbation in the skin driving senescence is the alteration of oxidative balance. In chronological aging, reactive oxygen species (ROS) are produced mainly through cellular oxidative metabolism during adenosine triphosphate (ATP) generation from glucose and mitochondrial dysfunction, whereas in extrinsic aging, loss of redox equilibrium is caused by environmental factors, such as ultraviolet radiation, pollution, cigarette smoking, and inadequate nutrition. During the aging process, oxidative stress is attributed to both augmented ROS production and reduced levels of enzymatic and non-enzymatic protectors. Apart from the evident appearance of structural change, throughout aging, the skin gradually loses its natural functional characteristics and regenerative potential. With aging, the skin immune system also undergoes functional senescence manifested as a reduced ability to counteract infections and augmented frequency of autoimmune and neoplastic diseases. This review proposes an update on the role of oxidative stress in the appearance of the clinical manifestation of skin aging, as well as of the molecular mechanisms that underline this natural phenomenon sometimes accelerated by external factors.

Shedding a New Light on Skin Aging, Iron- and Redox-Homeostasis and Emerging Natural Antioxidants

Reactive oxygen species (ROS) are necessary for normal cell signaling and the antimicrobial defense of the skin. However excess production of ROS can disrupt the cellular redox balance and overwhelm the cellular antioxidant (AO) capacity, leading to oxidative stress. In the skin, oxidative stress plays a key role in driving both extrinsic and intrinsic aging. Sunlight exposure has also been a major contributor to extrinsic photoaging of the skin as its oxidising components disrupt both redox- and iron-homeostasis, promoting oxidative damage to skin cells and tissue constituents. Upon oxidative insults, the interplay between excess accumulation of ROS and redox-active labile iron (LI) and its detrimental consequences to the skin are often overlooked. In this review we have revisited the oxidative mechanisms underlying skin damage and aging by focussing on the concerted action of ROS and redox-active LI in the initiation and progression of intrinsic and extrinsic skin aging processes. Based on these, we propose to redefine the selection criteria for skin antiaging and photoprotective ingredients to include natural antioxidants (AOs) exhibiting robust redox-balancing and/or iron-chelating properties. This would promote the concept of natural-based or bio-inspired bifunctional anti-aging and photoprotective ingredients for skincare and sunscreen formulations with both AO and iron-chelating properties.

What Are Reactive Oxygen Species, Free Radicals, and Oxidative Stress in Skin Diseases?

Oxygen in the atmosphere is a crucial component for life-sustaining aerobic respiration in humans. Approximately 95% of oxygen is consumed as energy and ultimately becomes water; however, the remaining 5% produces metabolites called activated oxygen or reactive oxygen species (ROS), which are extremely reactive. Skin, the largest organ in the human body, is exposed to air pollutants, including diesel exhaust fumes, ultraviolet rays, food, xenobiotics, drugs, and cosmetics, which promote the production of ROS. ROS exacerbate skin aging and inflammation, but also function as regulators of homeostasis in the human body, including epidermal keratinocyte proliferation. Although ROS have been implicated in various skin diseases, the underlying mechanisms have not yet been elucidated. Current knowledge on ROS-related and oxidative stress-related skin diseases from basic research to clinical treatment strategies are discussed herein. This information may be applied to the future treatment of skin diseases through the individual targeting of the ROS generated in each case via their inhibition, capture, or regulation.

Persistent JunB activation in fibroblasts disrupts stem cell niche interactions enforcing skin aging

Fibroblasts residing in the connective tissues constitute the stem cell niche, particularly in organs such as skin. Although the effect of fibroblasts on stem cell niches and organ aging is an emerging concept, the underlying mechanisms are largely unresolved. We report a mechanism of redox-dependent activation of transcription factor JunB, which, through concomitant upregulation of p16INK4A and repression of insulin growth factor-1 (IGF-1), initiates the installment of fibroblast senescence. Fibroblast senescence profoundly disrupts the metabolic and structural niche, and its essential interactions with different stem cells thus enforces depletion of stem cells pools and skin tissue decline. In fact, silencing of JunB in a fibroblast-niche-specific manner-by reinstatement of IGF-1 and p16 levels-restores skin stem cell pools and overall skin tissue integrity. Here, we report a role of JunB in the control of connective tissue niche and identified targets to combat skin aging and associated pathologies.

Alpha-Tocopherol Protects Human Dermal Fibroblasts by Modulating Nitric Oxide Release, Mitochondrial Function, Redox Status, and Inflammation

BACKGROUND

The altered balance between oxidants/antioxidants and inflammation, changes in nitric oxide (NO) release, and mitochondrial function have a role in skin aging through fibroblast modulation. Tocopherol is promising in counteracting the abovementioned events, but the effective mechanism of action needs to be clarified.

OBJECTIVE

The aim of this study was to examine the effects of α-tocopherol on cell viability/proliferation, NO release, mitochondrial function, oxidants/antioxidants, and inflammation in human dermal fibroblasts (HDF) subjected to oxidative stress.

METHODS

HDF were treated with H2O2 in the presence or absence of 1-10 μM α-tocopherol. Cell viability, reactive oxygen species (ROS), NO release, and mitochondrial membrane potential were measured; glutathione (GSH), superoxide dismutase (SOD)-1 and -2, glutathione peroxidase-1 (GPX-1), inducible NO synthase (iNOS), and Ki-67 were evaluated by RT-PCR and immunofluorescence; cell cycle was analyzed using FACS. Pro- and anti-inflammatory cytokine gene expression was analyzed through qRT-PCR.

RESULTS

α-Tocopherol counteracts H2O2, although it remains unclear whether this effect is dose dependent. Improvement of cell viability, mitochondrial membrane potential, Ki-67 expression, and G0/G1 and G2/M phases of the cell cycle was observed. These effects were accompanied by the increase of GSH content and the reduction of SOD-1 and -2, GPX-1, and ROS release. Also, iNOS expression and NO release were inhibited, and pro-inflammatory cytokine gene expression was decreased, confirming the putative role of α-tocopherol against inflammation.

CONCLUSION

α-Tocopherol exerts protective effects in HDF which underwent oxidative stress by modulating the redox status, inflammation, iNOS-dependent NO release, and mitochondrial function. These observations have a potential role in the prevention and treatment of photoaging-related skin cancers.

NMDA Receptor Hypofunction in the Aging-Associated Malfunction of Peripheral Tissue

Glutamatergic transmission through NMDA receptors (NMDARs) is important for the function of peripheral tissues. In the bone, NMDARs and its co-agonist, D-serine participate in all the phases of the remodeling. In the vasculature, NMDARs exerts a tonic vasodilation decreasing blood perfusion in the corpus cavernosum and the filtration rate in the renal glomerulus. NMDARs are relevant for the skin turnover regulating the proliferation and differentiation of keratinocytes and the formation of the cornified envelope (CE). The interference with NMDAR function in the skin leads to a slow turnover and repair. As occurs with the brain and cognitive functions, the manifestations of a hypofunction of NMDARs resembles those observed during aging. This raises the question if the deterioration of the glomerular vasculature, the bone remodeling and the skin turnover associated with age could be related with a hypofunction of NMDARs. Furthermore, the interference of D-serine and the effects of its supplementation on these tissues, suggest that a decrease of D-serine could account for this hypofunction pointing out D-serine as a potential therapeutic target to reduce or even prevent the detriment of the peripheral tissue associated with aging.

Potential Use of Amla (Phyllanthus emblica L.) Fruit Extract to Protect Skin Keratinocytes from Inflammation and Apoptosis after UVB Irradiation

Ultraviolet B (UVB) exposure is the primary risk factor for the deadliest type of skin cancer—melanoma. Incorporating natural antioxidants in skin protection products is currently a favored research theme. For this study, we selected Phyllanthus emblica L. fruit extract (PE) to assess its potential use in dermal protection against UVB-induced keratinocyte inflammation and apoptosis. High-performance liquid chromatography (HPLC) was used to investigate PE’s phytochemical constituents (ascorbic acid, ellagic acid, gallic acid, chlorogenic acid, and quercetin), while ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), total ROS, OH^•, O₂^•−, and H₂O₂-scavenging activities were used to determine the antioxidant properties. PE significantly increased the cell viability (MTT assay) and reduced apoptosis (Hoechst staining) in HaCaT cells exposed to UVB (40 mJ/cm²). PE abolished oxidative stress by reducing the production of intracellular ROS, O₂^•− and H₂O₂ production. Catalase activity (but not superoxide dismutase or glutathione peroxidase activity) was enhanced in keratinocytes incubated with PE prior to UVB exposure. Western blot analysis suggested that PE inhibited cytochrome c release and inhibited the dysregulation of PI3K/Akt without any impact on p38 activation. PE attenuated the inflammatory response to UVB irradiation by inhibiting AP-1, NF-κB, and the mediator PGE₂. Thus, PE is a candidate with great potential for use as an active ingredient in skin care products.

Copper/Zinc Superoxide Dismutase in Human Skin: Current Knowledge

Superoxide dismutase is widespread in the human body, including skin and its appendages. Here, we focus on human skin copper/zinc superoxide dismutase, the enzyme that protects skin and its appendages against reactive oxygen species. Human skin copper/zinc superoxide dismutase resides in the cytoplasm of keratinocytes, where up to 90% of cellular reactive oxygen species is produced. Factors other than cell type, such as gender, age and diseased state influence its location in skin tissues. We review current knowledge of skin copper/zinc superoxide dismutase including recent studies in an attempt to contribute to solving the question of its remaining unexplained functions. The research described here may be applicable to pathologies associated with oxidative stress. However, recent studies on copper/zinc superoxide dismutase in yeast reveal that its predominant function may be in signaling pathways rather than in scavenging superoxide ions. If confirmed in the skin, novel approaches might be developed to unravel the enzyme's remaining mysteries.

Skin Health from the Inside Out

The skin is the main interface between the body and the environment, providing a biological barrier against an array of chemical and physical pollutants (e.g., ultraviolet light, ozone, etc.). Exposure of the skin to these outdoor stressors generates reactive oxygen species (ROS), which can overwhelm the skin's endogenous defense systems (e.g., catalase, vitamins C and E, etc.), resulting in premature skin aging due to the induction of DNA damage, mitochondrial damage, lipid peroxidation, activation of inflammatory signaling pathways, and formation of protein adducts. In this review, we discuss how topical application of antioxidants, including vitamins C and E, carotenoids, resveratrol, and pycnogenol, can be combined with dietary supplementation of these antioxidant compounds in addition to probiotics and essential minerals to protect against outdoor stressor-induced skin damage, including the damage associated with aging.

A Potato Peel Extract Stimulates Type I Collagen Synthesis via Akt and ERK Signaling in Normal Human Dermal Fibroblasts

The ability of dermal fibroblasts to synthesize collagen decreases with ages. The integrity of collagen fibers severely decreases in aged skin, causing its characteristic morphological changes such as wrinkles and sagging. To prevent and improve skin aging, the stimulation of collagen synthesis in dermal fibroblasts is important. Potato peels contain many biofunctional compounds, but not much is known about their effects on human skin physiology. To characterize the potential effects of a potato peel extract (PPE) against skin aging, we examined its effects on the synthesis of type I collagen by normal human dermal fibroblasts (NHDFs). Treatment with the PPE significantly increased the expression of type I collagen mRNA in NHDFs and their secretion of type I collagen. To elucidate the mechanism involved, we examined the signaling pathway controlled by transforming growth factor-β (TGF-β), which regulates the synthesis of type I collagen. Treatment of NHDFs with the PPE significantly increased the expression of TGF-β receptor mRNA. TGF-β signaling involves Smad-dependent and Smad-independent pathways, like phosphatidylinositol-3 kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK). The PPE did not activate Smad, but significantly activated Akt and ERK. These results demonstrate that the PPE activates PI3K/Akt and MAPK/ERK signals via TGF-β receptors, which stimulate the synthesis of type I collagen in NHDFs. These results suggest that the PPE could be a novel and effective antiaging material.

DNA damage in human skin and the capacities of natural compounds to modulate the bystander signalling

Human skin is a stratified organ frequently exposed to sun-generated ultraviolet radiation (UVR), which is considered one of the major factors responsible for DNA damage. Such damage can be direct, through interactions of DNA with UV photons, or indirect, mainly through enhanced production of reactive oxygen species that introduce oxidative changes to the DNA. Oxidative stress and DNA damage also associate with profound changes at the cellular and molecular level involving several cell cycle and signal transduction factors responsible for DNA repair or irreversible changes linked to ageing. Crucially, some of these factors constitute part of the signalling known for the induction of biological changes in non-irradiated, neighbouring cells and defined as the bystander effect. Network interactions with a number of natural compounds, based on their known activity towards these biomarkers in the skin, reveal the capacity to inhibit both the bystander signalling and cell cycle/DNA damage molecules while increasing expression of the anti-oxidant enzymes. Based on this information, we discuss the likely polypharmacology applications of the natural compounds and next-generation screening technologies in improving the anti-oxidant and DNA repair capacities of the skin.

Establishment of Photoaging In Vitro by Repetitive UVA Irradiation: Induction of Characteristic Markers of Senescence and its Prevention by PAPLAL with Potent Catalase Activity

To understand a role of UVA radiation in photoaging of the skin, we established a model of photoaging cells using cultured human dermal fibroblasts. Repeated low-dose UVA radiation for 10 consecutive days induced senescence in fibroblasts, characterized with (1) increased level of senescence-associated β-galactosidase, (2) flattened large cell shape, (3) accumulation of reactive oxygen species, (4) yellowish coloration and (5) expression of p16. These were also observed in chronologically aged fibroblasts (doubling times >20), whereas none of these were detected in young cells (doubling times <10). Collectively, we propose that fibroblasts exposed to repetitive UVA radiation may be a good model of aged cells to study the mechanism of aging and photoaging and further to search for novel agents preventing cellular senescence. In addition, H₂ O₂ was produced in the culture medium by a single low dose of UVA irradiation. Further, PAPLAL, a nanoparticle of platinum and palladium having potent catalase-like activity, significantly delayed the onset of H₂ O₂ -induced cell senescence. The present study strongly indicates that repetitive short-term UVA irradiation induces aging of cells possibly via H₂ O₂ and may be suppressed by potent anti-H₂ O₂ agents.

Black rice (Oryza sativa L.) extract modulates ultraviolet-induced expression of matrix metalloproteinases and procollagen in a skin cell model

Exposure of the skin to ultraviolet (UV) radiation causes extracellular matrix (ECM) collapse in the dermis, owing to an increase in matrix metalloproteinase (MMP) production in both the epidermis and dermis, and a decrease in type I collagen expression in the dermis. Recently, black rice (Oryza sativa L.) was reported to have a wide range of pharmacological effects in various settings. However, the effects of black rice extract (BRE) on UV‑irradiated skin cells have not yet been characterized. BRE treatment did not affect cell morphology and viability of HaCaT and human dermal fibroblasts (HDF). We demonstrated that BRE downregulated basal and UV‑induced MMP‑1 expression in HaCaT cells. Furthermore, BRE significantly increased type I procollagen expression, and decreased MMP‑1 and MMP‑3 expression in UV‑irradiated HDF. The underlying mechanisms of these results involve a decrease in p38 and c‑Jun N‑terminal kinase activity, and suppression of UV‑induced activation of activator protein‑1 (AP‑1). BRE reduced UV‑induced reactive oxygen species production in HaCaT cells in a dose‑dependent manner. Indeed, mass spectrometry revealed that BRE contained antioxidative flavonoid components such as cyanidin‑3‑O‑β‑D‑glycoside and taxifolin‑7‑O‑glucoside. These findings suggest that BRE attenuates UV‑induced ECM damage by modulating mitogen‑activated protein kinase and AP‑1 signaling, and could be used as an active ingredient for preventing photoaging of the skin.

Bryostatin and its synthetic analog, picolog rescue dermal fibroblasts from prolonged stress and contribute to survival and rejuvenation of human skin equivalents

Skin health is associated with the day-to-day activity of fibroblasts. The primary function of fibroblasts is to synthesize structural proteins, such as collagen, extracellular matrix proteins, and other proteins that support the structural integrity of the skin and are associated with younger, firmer, and more elastic skin that is better able to resist and recover from injury. At sub-nanomolar concentrations (0.03-0.3 nM), bryostatin-1 and its synthetic analog, picolog (0.1-10 nM) sustained the survival and activation of human dermal fibroblasts cultured under the stressful condition of prolonged serum deprivation. Bryostatin-1 treatment stabilized human skin equivalents (HSEs), a bioengineered combination of primary human skin cells (keratinocytes and dermal fibroblasts) on an extracellular matrix composed of mainly collagen. Fibroblasts activated by bryostatin-1 protected the structural integrity of HSEs. Bryostatin-1 and picolog prolonged activation of Erk in fibroblasts to promote cell survival. Chronic stress promotes the progression of apoptosis. Dermal fibroblasts constitutively express all components of Fas associated apoptosis, including caspase-8, an initiator enzyme of apoptosis. Prolong bryostatin-1 treatment reduced apoptosis by decreasing caspase-8 and protected dermal fibroblasts. Our data suggest that bryostatin-1 and picolog could be useful in anti-aging skincare, and could have applications in tissue engineering and regenerative medicine.

Protective effects of rosmarinic acid against hydrogen peroxide‑induced cellular senescence and the inflammatory response in normal human dermal fibroblasts

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) that induces numerous cellular events, including cellular senescence and inflammatory responses. Therefore, the aim of this study was to investigate the protective effect of Rosmarinic acid (RA) in H2O2‑induced oxidative stress in normal human dermal fibroblasts (NHDFs). Cytotoxicity assays were performed using a water‑soluble tetrazolium salt, and senescence‑associated β‑galactosidase activity was determined to investigate the proportion of senescent cells. Antioxidant capacities were evaluated via H2O2‑scavenging activity, reverse transcription‑quantitative polymerase chain reaction, NRF2 luciferase reporter gene activity and intracellular ROS scavenging assays. Cytokine‑coded gene expression analysis and nuclear factor‑κB luciferase activity were determined to verify the anti‑inflammatory effect of RA. As a result, the present study demonstrated that rosmarinic acid inhibited H2O2‑induced oxidative stress and inflammatory responses in normal human dermal fibroblasts. Initially, the doses of RA that exerted minimal cytotoxic effects in NHDFs were determined using a cytotoxicity assay. Subsequently, pretreatment with the appropriate doses of RA significantly reversed the H2O2‑induced decrease in NHDF cell viability and decreased cellular senescence of NHDFs. In addition, RA inhibited H2O2‑induced ROS production in NHDFs, as determined by a ROS scavenging assay. The protective effects of RA were mediated by the inhibition of nuclear factor erythroid‑derived 2‑like 2, a transcription factor that functions as a key regulator of redox sensitivity. Furthermore, RA suppressed H2O2‑induced inflammation in NHDFs and significantly rescued H2O2‑induced downregulation of sirtuin 1. RA also inhibited nuclear factor (NF)‑κB transcriptional activity and the expression of NF‑κB target genes, including tumor necrosis factor‑α and interleukin‑6, in H2O2‑exposed NHDFs. Taken together, these data indicate that RA inhibits H2O2‑induced cellular damage in NHDFs.

Age-related reduction of dermal fibroblast size upregulates multiple matrix metalloproteinases as observed in aged human skin in vivo

BACKGROUND

Fragmentation of collagen fibrils, the major structure protein in skin, is a hallmark of dermal ageing. Matrix metalloproteinases (MMPs) are largely responsible for the fragmentation of collagen fibrils.

OBJECTIVES

To quantify gene expression of all 23 known mammalian MMPs in sun-protected young and aged human skin in vivo and to investigate the potential mechanism underlying age-related alteration of multiple MMPs.

METHODS

MMP mRNA expression levels and MMP activity in sun-protected young and aged human skin in vivo were determined by real-time reverse transcription polymerase chain reaction (RT-PCR) and in situ zymography, respectively. The relative contributions to elevated MMPs in epidermis and dermis were quantified by laser capture microdissection coupled real-time RT-PCR. Dermal fibroblast morphology and collagen fibril fragmentation in human skin in vivo were assessed by second-harmonic generation microscopy and atomic force microscopy, respectively. In vitro cell morphology was assessed by CellTracker® fluorescent dye (Molecular Probes, Eugene, OR, U.S.A.) and phalloidin staining. Protein levels were determined by ProteinSimple capillary electrophoresis immunoassay (ProteinSimple, Santa Clare, CA, U.S.A.).

RESULTS

Multiple MMPs are elevated in aged human skin dermis. Increased MMP activity and collagen fibril fragmentation were observed in aged skin dermis. As dermal fibroblasts are the major MMP-producing cells in the dermis, reduction of dermal fibroblast size, which is observed in aged human skin, contributes to the elevation of age-related multiple MMPs. Reduction of fibroblast size upregulates c-Jun/c-Fos and activates AP-1.

CONCLUSIONS

Combined actions of the wide variety of MMPs that are constitutively elevated in aged dermis may be involved in the progressive degradation of dermal collagen fibrils. Age-related elevations of multiple MMPs are likely to be a result of the reduction of fibroblast size via activation of AP-1.

Cell-size-dependent upregulation of HGF expression in dermal fibroblasts: Impact on human skin connective tissue aging

BACKGROUND

Aged human skin is primarily attributable to loss of collagen, the main structural component of skin. Hepatocyte growth factor (HGF) acts as an anti-fibrotic factor by suppression of collagen production. It is not known whether HGF is involved in age-related collagen deficit in human skin.

OBJECTIVE

The objective of this study was to investigate the expression of HGF in human skin, and the underlying mechanisms of age-related elevation of HGF expression.

METHODS

The expression of HGF in young (25±5years, six subjects) and aged (75±6years, six subjects) human skin was determined by laser capture microdissection (LCM) coupled real-time PCR and immunohistology. The underlying mechanisms of age-related elevation of HGF were investigated by reducing dermal fibroblast size, which is a prominent feature of aged skin fibroblast in vivo.

RESULTS

HGF is predominantly expressed in human skin dermal fibroblasts, the major cells responsible for collagen production, and is significantly elevated in aged human skin in vivo. Mechanistically, reduced fibroblast size, which is a prominent feature of aged skin fibroblasts in vivo, is responsible for age-related elevation of HGF expression. Cell-size-dependent upregulation of HGF expression is driven by increased c-Jun and impaired TGF-β signaling. Restoration of fibroblast size normalizes increased c-Jun expression and impaired TGF-β signaling, and thus reversed the elevated HGF expression. Finally, we confirmed that application of retinoid (ROL), which has been shown to improve aged human skin, significantly reduced elevated HGF mRNA expression in aged human skin in vivo (78±4years, six subjects).

CONCLUSION

These data reveal a novel mechanism by which reduction of fibroblast size upregulates HGF expression, which in turn contributes to loss of collagen, a prominent feature of aged skin.

Featured Article: Nanoenhanced matrix metalloproteinase-responsive delivery vehicles for disease resolution and imaging

The wide array of proteases, including matrix metalloproteinases, produced in response to many pathogenic insults, confers a unique proteolytic signature which is often disease specific and provides a potential therapeutic target for drug delivery. Here we propose the use of collagen-based nanoenhanced matrix metalloproteinase-responsive delivery vehicles that display matrix metalloproteinase-specific degradation in diverse in vitro models of proteolysis. We demonstrate that collagen particles comprised of protease substrates (primarily collagen) can be made of uniform size and loaded efficiently with assorted cargo including fluorescently labeled mesoporous silica, magnetic nanoparticles, proteins and antioxidants. We also demonstrate that pathologic concentrations of proteases produced in situ or in vitro display protease-specific cargo release. Additionally, we show that the collagen-based particles display bright fluorescence when loaded with a fluorophore, and have the potential to be used as vehicles for targeted delivery of drugs or imaging agents to regions of high proteolytic activity.

Adenophora remotiflora protects human skin keratinocytes against UVB-induced photo-damage by regulating antioxidative activity and MMP-1 expression

BACKGROUND/OBJECTIVES

Chronic ultraviolet (UV) exposure-induced reactive oxygen species (ROS) are commonly involved in the pathogenesis of skin damage by activating the metalloproteinases (MMP) that break down type I collagen. Adenophora remotiflora (AR) is a perennial wild plant that inhabits Korea, China, and Japan. The present study investigated the protective effects of AR against UVB-induced photo-damage in keratinocytes.

MATERIALS/METHODS

An in vitro cell-free system was used to examine the scavenging activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical and nitric oxide (NO). The effect of AR on ROS formation, antioxidant enzymes, elastase, MMP-1 level, and mRNA expression of MMP-1 were determined in UVB-irradiated human keratinocyte HaCaT cells.

RESULTS

AR demonstrated strong DPPH free radical and NO scavenging activity in a cell-free system exhibiting IC₅₀ values of 1.88 mg/mL and 6.77 mg/mL, respectively. AR pretreatment dose-dependently attenuated the production of UVB-induced intracellular ROS, and antioxidant enzymes (catalase and superoxide dismutase) were enhanced in HaCaT cells. Furthermore, pretreatment of AR prevented UVB-induced elastase and collagen degradation by inhibiting the MMP-1 protein level and mRNA expression. Accordingly, AR treatment elevated collagen content in UVB-irradiated HaCaT cells.

CONCLUSION

The present study provides the first evidence of AR inhibiting UVB-induced ROS production and induction of MMP-1 as a result of augmentation of antioxidative activity in HaCaT human keratinocytes. These results suggest that AR might act as an effective inhibitor of UVB-modulated signaling pathways and might serve as a photo-protective agent.

Polysaccharide Extracted from Laminaria japonica Delays Intrinsic Skin Aging in Mice

This study aimed to determine the effect of topically applied Laminaria polysaccharide (LP) on skin aging. We applied ointment containing LP (10, 25, and 50 μg/g) or vitamin E (10 μg/g) to the dorsal skin of aging mice for 12 months and young control mice for 4 weeks. Electron microscopy analysis of skin samples revealed that LP increased dermal thickness and skin collagen content. Tissue inhibitor of metalloprotease- (TIMP-) 1 expression was upregulated while that of matrix metalloproteinase- (MMP-) 1 was downregulated in skin tissue of LP-treated as compared to untreated aging mice. Additionally, phosphorylation of c-Jun N-terminal kinase (JNK) and p38 was higher in aging skin than in young skin, while LP treatment suppressed phospho-JNK expression. LP application also enhanced the expression of antioxidative enzymes in skin tissue, causing a decrease in malondialdehyde levels and increases in superoxide dismutase, catalase, and glutathione peroxidase levels relative to those in untreated aging mice. These results indicate that LP inhibits MMP-1 expression by preventing oxidative stress and JNK phosphorylation, thereby delaying skin collagen breakdown during aging.

Oxidative stress in aging human skin

Oxidative stress in skin plays a major role in the aging process. This is true for intrinsic aging and even more for extrinsic aging. Although the results are quite different in dermis and epidermis, extrinsic aging is driven to a large extent by oxidative stress caused by UV irradiation. In this review the overall effects of oxidative stress are discussed as well as the sources of ROS including the mitochondrial ETC, peroxisomal and ER localized proteins, the Fenton reaction, and such enzymes as cyclooxygenases, lipoxygenases, xanthine oxidases, and NADPH oxidases. Furthermore, the defense mechanisms against oxidative stress ranging from enzymes like superoxide dismutases, catalases, peroxiredoxins, and GSH peroxidases to organic compounds such as L-ascorbate, α-tocopherol, beta-carotene, uric acid, CoQ10, and glutathione are described in more detail. In addition the oxidative stress induced modifications caused to proteins, lipids and DNA are discussed. Finally age-related changes of the skin are also a topic of this review. They include a disruption of the epidermal calcium gradient in old skin with an accompanying change in the composition of the cornified envelope. This modified cornified envelope also leads to an altered anti-oxidative capacity and a reduced barrier function of the epidermis.

Age-associated reduction of cellular spreading/mechanical force up-regulates matrix metalloproteinase-1 expression and collagen fibril fragmentation via c-Jun/AP-1 in human dermal fibroblasts

The dermal compartment of human skin is largely composed of dense collagen-rich fibrils, which provide structural and mechanical support. Skin dermal fibroblasts, the major collagen-producing cells, are interact with collagen fibrils to maintain cell spreading and mechanical force for function. A characteristic feature of aged human skin is fragmentation of collagen fibrils, which is initiated by matrix metalloproteinase 1 (MMP-1). Fragmentation impairs fibroblast attachment and thereby reduces spreading. Here, we investigated the relationship among fibroblast spreading, mechanical force, MMP-1 expression, and collagen fibril fragmentation. Reduced fibroblast spreading due to cytoskeletal disruption was associated with reduced cellular mechanical force, as determined by atomic force microscopy. These reductions substantially induced MMP-1 expression, which led to collagen fibril fragmentation and disorganization in three-dimensional collagen lattices. Constraining fibroblast size by culturing on slides coated with collagen micropatterns also significantly induced MMP-1 expression. Reduced spreading/mechanical force induced transcription factor c-Jun and its binding to a canonical AP-1 binding site in the MMP-1 proximal promoter. Blocking c-Jun function with dominant negative mutant c-Jun significantly reduced induction of MMP-1 expression in response to reduced spreading/mechanical force. Furthermore, restoration of fibroblast spreading/mechanical force led to decline of c-Jun and MMP-1 levels and eliminated collagen fibril fragmentation and disorganization. These data reveal a novel mechanism by which alteration of fibroblast shape/mechanical force regulates c-Jun/AP-1-dependent expression of MMP-1 and consequent collagen fibril fragmentation. This mechanism provides a foundation for understanding the cellular and molecular basis of age-related collagen fragmentation in human skin.

Detoxifying effect of fermented black ginseng on H2O2-induced oxidative stress in HepG2 cells

Fermented black ginseng (FBG) is prepared by repeated steaming and drying processes with fresh ginseng followed by fermentation with Saccharomyces cerevisiae. It has recently been shown to have several bioactivities. FBG contains crude saponin (1,440 µg/ml), ginsenoside Rg2 (2.86 µg/ml), ginsenoside Rg3 (24.52 µg/ml), ginsenoside Rh1 (12.64 µg/ml), ginsenoside Rh2 (0.63 µg/ml) and ginsenoside Rf (1.32 µg/ml). The present study investigated the antioxidant defense properties of FBG against hydrogen peroxide (H2O2)-mediated oxidative stress in HepG2 human hepatocellular carcinoma cells. The increased production of reactive oxygen species (ROS) induced by H2O2 was attenuated in a dose-dependent manner when the cells were pre-treated with FBG (10-50 µg/ml). FBG induced both the expression and activity of antioxidant enzymes, such as superoxide dismutase, catalase and glutathione peroxidase in the H2O2-treated HepG2 cells. The inhibitory effects of FBG on the phosphorylation of upstream mitogen-activated protein kinases (MAPKs), such as c-Jun N-terminal kinase, extracellular signal-regulated kinase and p38 were also observed. Overall, our results demonstrate that FBG protects HepG2 cells from oxidative stress through the induction of antioxidant enzyme activity and the inhibition of MAPK pathways.

Modulation of PPARγ provides new insights in a stress induced premature senescence model

Peroxisome proliferator-activated receptor gamma (PPARγ) may be involved in a key mechanism of the skin aging process, influencing several aspects related to the age-related degeneration of skin cells, including antioxidant unbalance. Therefore, we investigated whether the up-modulation of this nuclear receptor exerts a protective effect in a stress-induced premature senescence (SIPS) model based on a single exposure of human dermal fibroblasts to 8-methoxypsoralen plus + ultraviolet-A-irradiation (PUVA). Among possible PPARγ modulators, we selected 2,4,6-octatrienoic acid (Octa), a member of the parrodiene family, previously reported to promote melanogenesis and antioxidant defense in normal human melanocytes through a mechanism involving PPARγ activation. Exposure to PUVA induced an early and significant decrease in PPARγ expression and activity. PPARγ up-modulation counteracted the antioxidant imbalance induced by PUVA and reduced the expression of stress response genes with a synergistic increase of different components of the cell antioxidant network, such as catalase and reduced glutathione. PUVA-treated fibroblasts grown in the presence of Octa are partially but significantly rescued from the features of the cellular senescence-like phenotype, such as cytoplasmic enlargement, the expression of senescence-associated-β-galactosidase, matrix-metalloproteinase-1, and cell cycle proteins. Moreover, the alterations in the cell membrane lipids, such as the decrease in the polyunsaturated fatty acid content of phospholipids and the increase in cholesterol levels, which are typical features of cell aging, were prevented. Our data suggest that PPARγ is one of the targets of PUVA-SIPS and that its pharmacological up-modulation may represent a novel therapeutic approach for the photooxidative skin damage.

CopA3 peptide prevents ultraviolet-induced inhibition of type-I procollagen and induction of matrix metalloproteinase-1 in human skin fibroblasts

Ultraviolet (UV) exposure is well-known to induce premature aging, which is mediated by matrix metalloproteinase-1 (MMP-1) activity. A 9-mer peptide, CopA3 (CopA3) was synthesized from a natural peptide, coprisin, which is isolated from the dung beetle Copris tripartitus. As part of our continuing search for novel bioactive natural products, CopA3 was investigated for its in vitro anti-skin photoaging activity. UV-induced inhibition of type-I procollagen and induction of MMP-1 were partially prevented in human skin fibroblasts by CopA3 peptide in a dose-dependent manner. At a concentration of 25 μM, CopA3 nearly completely inhibited MMP-1 expression. These results suggest that CopA3, an insect peptide, is a potential candidate for the prevention and treatment of skin aging.

The relationship between skin aging and steady state ultraweak photon emission as an indicator of skin oxidative stress in vivo

BACKGROUND/PURPOSE

Ultraweak photon emission (UPE) is one potential method to evaluate the oxidative status of the skin in vivo. However, little is known about how the daily oxidative stress of the skin is related to skin aging-related alterations in vivo. We characterized the steady state UPE and performed a skin survey.

METHODS

We evaluated the skin oxidative status by UPE, skin elasticity, epidermal thickness and skin color on the inner upper arm, the outer forearm, and the buttock of 70 Japanese volunteers.

RESULTS

The steady state UPE at the three skin sites increased with age. Correlation analysis revealed that the steady state UPE only from the buttock was related to skin elasticity, which showed age-dependent changes. Moreover, analysis by age group indicated that b* values of the inner upper arm of subjects in their 20s were inversely correlated with UPE as occurred in buttock skin. In contrast, photoaged skin did not show a clear relationship with steady state UPE because the accumulation of sun-exposure might influence the sensitivity to oxidative stress.

CONCLUSION

These results suggest that steady state UPE reflects not only intrinsic skin aging and cutaneous color but also the current oxidative status independent of skin aging.

Redox Mechanisms of AVS022, an Oriental Polyherbal Formula, and Its Component Herbs in Protection against Induction of Matrix Metalloproteinase-1 in UVA-Irradiated Keratinocyte HaCaT Cells

Ayurved Siriraj HaRak (AVS022) formula has been used for topical remedy of dermatologic disorders. Oxidative stress induced by ultraviolet (UV) A irradiation could be implicated in photoaged skin through triggering matrix metalloproteinase-1 (MMP-1). We, therefore, explored the antioxidant mechanisms by which AVS022 formulation and its individual components protected against UVA-dependent MMP-1 upregulation in keratinocyte HaCaT cells. TLC analysis revealed the presence of multiple phenolics including gallic acid (GA) in the AVS022 extracts. We demonstrated that pretreatment with the whole formula and individual herbal components except T. triandra protected against increased MMP-1 activity in irradiated HaCaT cells. Moreover, all herbal extracts and GA, used as the reference compound, were able to reverse cytotoxicity, oxidant production, glutathione (GSH) loss, and inactivation of catalase and glutathione peroxidase (GPx). F. racemosa was observed to yield the strongest abilities to abolish UVA-mediated induction of MMP-1 and impairment of antioxidant defenses including GSH and catalase. Our observations suggest that upregulation of endogenous antioxidants could be the mechanisms by which AVS022 and its herbal components suppressed UVA-stimulated MMP-1 in HaCaT cells. In addition, pharmacological actions of AVS022 formula may be attributed to the antioxidant potential of its components, in particular F. racemosa, and several phenolics including GA.

Azelaic acid reduced senescence-like phenotype in photo-irradiated human dermal fibroblasts: possible implication of PPARγ

Azelaic acid (AzA) has been used for the treatment for inflammatory skin diseases, such as acne and rosacea. Interestingly, an improvement in skin texture has been observed after long-time treatment with AzA. We previously unrevealed that anti-inflammatory activity of AzA involves a specific activation of PPARγ, a nuclear receptor that plays a relevant role in inflammation and even in ageing processes. As rosacea has been considered as a photo-aggravated disease, we investigated the ability of AzA to counteract stress-induced premature cell senescence (SIPS). We employed a SIPS model based on single exposure of human dermal fibroblasts (HDFs) to UVA and 8-methoxypsoralen (PUVA), previously reported to activate a senescence-like phenotype, including long-term growth arrest, flattened morphology and increased synthesis of matrix metalloproteinases (MMPs) and senescence-associated β-galactosidase (SA-β-gal). We found that PUVA-treated HDFs grown in the presence of AzA maintained their morphology and reduced MMP-1 release and SA-β-galactosidase-positive cells. Moreover, AzA induced a reduction in ROS generation, an up-modulation of antioxidant enzymes and a decrease in cell membrane lipid damages in PUVA-treated HDFs. Further evidences of AzA anti-senescence effect were repression of p53 and p21, increase in type I pro-collagen and abrogation of the enhanced expression of growth factors, such as HGF and SCF. Interestingly, PUVA-SIPS showed a decreased activation of PPARγ and AzA counteracted this effect, suggesting that AzA effect involves PPARγ modulation. All together these data showed that AzA interferes with PUVA-induced senescence-like phenotype and its ability to activate PPAR-γ provides relevant insights into the anti-senescence mechanism.

Atomic hydrogen surrounded by water molecules, H(H2O)m, modulates basal and UV-induced gene expressions in human skin in vivo

Recently, there has been much effort to find effective ingredients which can prevent or retard cutaneous skin aging after topical or systemic use. Here, we investigated the effects of the atomic hydrogen surrounded by water molecules, H(H2O)m, on acute UV-induced responses and as well as skin aging. Interestingly, we observed that H(H2O)m application to human skin prevented UV-induced erythema and DNA damage. And H(H2O)m significantly prevented UV-induced MMP-1, COX-2, IL-6 and IL-1β mRNA expressions in human skin in vivo. We found that H(H2O)m prevented UV-induced ROS generation and inhibited UV-induced MMP-1, COX-2 and IL-6 expressions, and UV-induced JNK and c-Jun phosphorylation in HaCaT cells. Next, we investigated the effects of H(H2O)m on intrinsically aged or photoaged skin of elderly subjects. In intrinsically aged skin, H(H2O)m application significantly reduced constitutive expressions of MMP-1, IL-6, and IL-1β mRNA. Additionally, H(H2O)m significantly increased procollagen mRNA and also decreased MMP-1 and IL-6 mRNA expressions in photoaged facial skin. These results demonstrated that local application of H(H2O)m may prevent UV-induced skin inflammation and can modulate intrinsic skin aging and photoaging processes. Therefore, we suggest that modifying the atmospheric gas environment within a room may be a new way to regulate skin functions or skin aging.

The role of manganese superoxide dismutase in skin aging

The free radical theory of aging postulates that the production of mitochondrial reactive oxygen species is the major determinant of aging and lifespan. The skin represents an excellent and accessible model organ to study aging that is characterized by atrophy, wrinkle formation, reduced tensile strength and impaired wound healing. Oxidative stress as a consequence of an imbalance in prooxidants and antioxidants with increased ROS concentrations has been demonstrated in the aged skin in vitro and in vivo, suggesting the important role of the antioxidant balance. Here we will summarize recent data on the role of the mitochondrial superoxide dismutase 2 in skin aging.

Ageing skin: oestrogen receptor β agonists offer an approach to change the outcome

Oestrogen (17β estradiol) and the dietary antioxidants resveratrol, genistein and S-equol, an isoflavone produced from the gut biotransformation of soy daidzein, are effective agents to reduce ageing in skin. It is widely held that these antioxidants scavenge free radicals to prevent skin damage. However, the evidence to date suggests that the primary mechanism of action of these antioxidants is to activate oestrogen receptor β (ERβ), which in turn enhances the expression of antioxidant enzymes and inhibits the expression of snail, a transcription factor that regulates keratinocyte cell proliferation and migration. Based on their selectivity, ERβ agents provide a treatment option for ageing skin without the potential safety issues associated with oestrogen therapy.

Accelerated aging phenotype in mice with conditional deficiency for mitochondrial superoxide dismutase in the connective tissue

The free radical theory of aging postulates that the production of mitochondrial reactive oxygen species is the major determinant of aging and lifespan. Its role in aging of the connective tissue has not yet been established, even though the incidence of aging-related disorders in connective tissue-rich organs is high, causing major disability in the elderly. We have now addressed this question experimentally by creating mice with conditional deficiency of the mitochondrial manganese superoxide dismutase in fibroblasts and other mesenchyme-derived cells of connective tissues in all organs. Here, we have shown for the first time that the connective tissue-specific lack of superoxide anion detoxification in the mitochondria results in reduced lifespan and premature onset of aging-related phenotypes such as weight loss, skin atrophy, kyphosis (curvature of the spine), osteoporosis and muscle degeneration in mutant mice. Increase in p16(INK4a) , a robust in vivo marker for fibroblast aging, may contribute to the observed phenotype. This novel model is particularly suited to decipher the underlying mechanisms and to develop hopefully novel connective tissue-specific anti-aging strategies.

Protective effects of Chlorella-derived peptide on UVB-induced production of MMP-1 and degradation of procollagen genes in human skin fibroblasts

UV exposure is known to induce premature aging, which is mediated by matrix metalloproteinase-1 (MMP-1) activity. MMP-1 mRNA expression is up-regulated by elevated cysteine-rich 61 (CYR61) and monocyte chemoattractant protein-1 (MCP-1) via action of transcription factor AP-1. Collagen is degraded by MMP-1 activity but synthesized by transforming growth factor-β (TGF-β) signal. Chlorella has been shown to inhibit UVB-induced MMP-1 level, however its regulatory molecular mechanisms have not been studied. In this study, Chlorella derived peptide (CDP) was added to skin fibroblasts after UVB irradiation and the expression of MMP-1, CYR61, procollagen, c-fos, c-jun, and TGF-β receptor (TbRII) mRNA and MCP-1 production were investigated. CDP (10 or 5mg/ml) diminished UVB-induced MMP-1 and CYR61 mRNA expression and MCP-1 production, whereas, UVB-suppressed procollagen and TbRII mRNA was restored by CDP treatment. UVB-induced c-fos and c-jun expressions were also inhibited by the CDP treatment. Taken together, CDP inhibits UVB-induced MMP-1 expression in skin fibroblasts by suppressing expression of AP-1 and CYR61 and MCP-1 production.

Cholesterol, a Major Component of Caveolae, Down-regulates Matrix Metalloproteinase-1 Expression through ERK/JNK Pathway in Cultured Human Dermal Fibroblasts

BACKGROUND

Cholesterol is a major component of specialized membrane microdomains known as lipid rafts or caveolae, which modulate the fluidity of biological membranes. Membrane cholesterol therefore plays an important role in cell signaling and vesicular transport.

OBJECTIVE

In this study, we investigated the effects of cholesterol on matrix metalloproteinase-1 (MMP-1) expression in human dermal fibroblasts.

METHODS

MMP-1 mRNA and protein expression were determined by RT-PCR and Western blotting, respectively. AP-1 DNA binding activity was detected by electrophoretic mobility shift assays. The amount of cholesterol was analyzed by cholesterol assay kit.

RESULTS

We observed that MMP-1 mRNA and protein expression was dose-dependently decreased by cholesterol treatment. In contrast, cholesterol depletion by a cholesterol depletion agent, methyl-beta-cyclodextrin (MβCD) in human dermal fibroblasts, increased MMP-1 mRNA and protein expression in a dose-dependent manner. Also, we investigated the regulatory mechanism of MβCD-induced MMP-1 expression: cholesterol depletion by MβCD, activated ERK1/2 and JNK, but not p38 MAPK cascade, and it also significantly increased c-Jun phosphorylation, c-Fos expression and activator protein-1 binding activity. Furthermore, the inhibition of ERK or JNK with specific chemical inhibitors prevented MβCD-induced MMP-1 expression, which indicates that ERK and JNK play an important role in cholesterol depletion-mediated MMP-1 induction. In addition, MβCD-induced phosphorylation of ERK and JNK and MMP-1 expression were suppressed by cholesterol repletion.

CONCLUSION

Our results suggest that cholesterol regulates MMP-1 expression through the control of ERK and JNK activity in human dermal fibroblasts.

Squalene as a target molecule in skin hyperpigmentation caused by singlet oxygen

Based on our previous finding (Biochem. Biophys. Res. Commun., 223, 578-582, 1996) of singlet oxygen generation from coproporphyrin excreted on the skin surface from Propionibacterium acnes, we hypothesized that singlet oxygen formed in this way under UV exposure would promote peroxidation of skin surface lipids. We found that squalene was oxidized efficiently by singlet oxygen derived from coproporphyrin under UV exposure, and that the rate constant of squalene peroxidation by singlet oxygen was ten-fold higher than that of other skin surface lipids examined. The reaction was promoted more efficiently by UVA than by UVB. Furthermore, we found that topical application of squalene peroxide induced skin hyperpigmentation through increasing prostaglandin E(2) release from keratinocytes in guinea pigs. These results suggest that squalene peroxide formation by singlet oxygen plays a key role in photo-induced skin damage.