Damage To Human Skin Research Articles

The protective role of DJ-1 in ultraviolet-induced damage of human skin: DJ-1 levels in the stratum corneum as an indicator of antioxidative defense.

DJ-1 is a multifunctional protein associated with Parkinson's disease and plays a significant role in protecting nerve cells from oxidative stress. DJ-1 is expressed in the skin, although its function there is unknown. In this study, we investigated DJ-1 function in keratinocytes. DJ-1 was induced by H2O2 exposure and UV irradiation in keratinocytes. DJ-1 knockdown with small interfering RNA (siRNA) increased reactive oxygen species (ROS) and lactate dehydrogenase (LDH) release after UVB irradiation, suggesting that DJ-1 reduces ROS and might protect skin cells from UV damage in vitro. To investigate the in vivo role of DJ-1 in the skin, we determined DJ-1 levels in human stratum corneum samples obtained by the tape-stripping method. DJ-1 levels in the stratum corneum (scDJ-1) correlated with total antioxidant capacity. We also examined the effect of scDJ-1 on changes in skin after UVB irradiation. DJ-1 was elevated in SC from the upper arm 1 to 2 weeks after UVB irradiation. One day after UVB irradiation, L* (brightness) and a* (redness) values, indicators of skin color, were altered regardless of scDJ-1 expression. However, these values recovered more quickly in subjects with high scDJ-1 expression than in those with low scDJ-1 expression. These data suggest that DJ-1 in skin plays a significant role in protection against UV radiation and oxidative stress, and that DJ-1 levels in the SC might be an indicator of antioxidative defense against UV-induced damage.

Determination of the Action Spectrum of UVR-Induced Mitochondrial DNA Damage in Human Skin Cells

Biological responses of human skin to UVR including cancer and aging are largely wavelength-dependent, as shown by the action spectra of UVR-induced erythema and nuclear DNA (nDNA) damage. A molecular dosimeter of UVR exposure is therefore required. Although mitochondrial DNA (mtDNA) damage has been shown to be a reliable and sensitive biomarker of UVR exposure in human skin, its wavelength dependency is unknown. The current study solves this problem by determining the action spectrum of UVR-induced mtDNA damage in human skin. Human neonatal dermal fibroblasts and primary human adult keratinocyte cells were irradiated with increasing doses of UVR. Dose-response curves of mtDNA damage were produced for each of the UVR sources and cell types, and an action spectrum for each cell type was determined by mathematical induction. Similarities between these mtDNA damage action spectra and previously determined nDNA damage were observed, with the most detrimental effects occurring over the shorter UVR wavelengths. Notably, a statistically significant (P<0.0001) greater sensitivity to mtDNA damage was observed in dermal fibroblasts compared with keratinocytes at wavelengths >300 nm, possibly indicating a wider picture of depth dependence in sensitivity. This finding has implications for disease/photodamage mechanisms and interventions.

An in vitro human skin test for assessing sensitization potential.

Sensitization to chemicals resulting in an allergy is an important health issue. The current gold-standard method for identification and characterization of skin-sensitizing chemicals was the mouse local lymph node assay (LLNA). However, for a number of reasons there has been an increasing imperative to develop alternative approaches to hazard identification that do not require the use of animals. Here we describe a human in-vitro skin explant test for identification of sensitization hazards and the assessment of relative skin sensitizing potency. This method measures histological damage in human skin as a readout of the immune response induced by the test material. Using this approach we have measured responses to 44 chemicals including skin sensitizers, pre/pro-haptens, respiratory sensitizers, non-sensitizing chemicals (including skin-irritants) and previously misclassified compounds. Based on comparisons with the LLNA, the skin explant test gave 95% specificity, 95% sensitivity, 95% concordance with a correlation coefficient of 0.9. The same specificity and sensitivity were achieved for comparison of results with published human sensitization data with a correlation coefficient of 0.91. The test also successfully identified nickel sulphate as a human skin sensitizer, which was misclassified as negative in the LLNA. In addition, sensitizers and non-sensitizers identified as positive or negative by the skin explant test have induced high/low T cell proliferation and IFNγ production, respectively. Collectively, the data suggests the human in-vitro skin explant test could provide the basis for a novel approach for characterization of the sensitizing activity as a first step in the risk assessment process.

Permeation of platinum and rhodium nanoparticles through intact and damaged human skin

The aim of the study was to evaluate percutaneous penetration of platinum and rhodium nanoparticles (PtNPs: 5.8 ± 0.9 nm, RhNPs: 5.3 ± 1.9 nm) through human skin. Salts compounds of these metals are sensitizers and some also carcinogenic agents. In vitro permeation experiments were performed using Franz diffusion cells with intact and damaged skin. PtNPs and RhNPs, stabilized with polyvinylpyrrolidone, were synthesized by reduction of Na2PtCl6 and RhCl3·3H2O respectively. Suspensions with a concentration of 2.0 g/L of PtNPs and RhNPs were dispersed separately in synthetic sweat at pH 4.5 and applied as donor phases to the outer surface of the skin for 24 h. Measurements of the content of the metals in the receiving solution and in the skin were performed subsequently. Rhodium skin permeation was demonstrated through damaged skin, with a permeation flux of 0.04 ± 0.04 μg cm−2 h−1 and a lag time of 7.9 ± 1.1 h, while no traces of platinum were found in receiving solutions. Platinum and rhodium skin-analysis showed significantly higher concentrations of the metals in damaged skin. Rh and Pt applied as NPs can penetrate the skin barrier and Rh can be found in receiving solutions. These experiments pointed out the need for skin contamination prevention, since even a minor injury to the skin barrier can significantly increase penetration.

Human skin permeation of emerging mycotoxins (beauvericin and enniatins).

Currently, dermal exposure data of cyclic depsipeptide mycotoxins are completely absent. There is a lack of understanding about the local skin and systemic kinetics and effects, despite their widespread skin contact and intrinsic hazard. Therefore, we provide a quantitative characterisation of their dermal kinetics. The emerging mycotoxins enniatins (ENNs) and beauvericin (BEA) were used as model compounds and their transdermal kinetics were quantitatively evaluated, using intact and damaged human skin in an in vitro Franz diffusion cell set-up and ultra high-performance liquid chromatography (UHPLC)-MS analytics. We demonstrated that all investigated mycotoxins are able to penetrate through the skin. ENN B showed the highest permeation (kp,v=9.44 × 10(-6) cm/h), whereas BEA showed the lowest (kp,v=2.35 × 10(-6) cm/h) and the other ENNs ranging in between. Combining these values with experimentally determined solubility data, Jmax values ranging from 0.02 to 0.35 μg/(cm(2) h) for intact skin and from 0.07 to 1.11 μg/(cm(2) h) for damaged skin were obtained. These were used to determine the daily dermal exposure (DDE) in a worst-case scenario. On the other hand, DDE's for a typical occupational scenario were calculated based on real-life mycotoxin concentrations for the industrial exposure of food-related workers. In the latter case, for contact with intact human skin, DDE's up to 0.0870 ng/(kg BW × day) for ENN A were calculated, whereas for impaired skin barrier this can even rise up to 0.3209 ng/(kg BW × day) for ENN B1. This knowledge is needed for the risk assessment after skin exposure of contaminated food, feed, indoor surfaces and airborne particles with mycotoxins.

Astragaloside IV controls collagen reduction in photoaging skin by improving transforming growth factor-β/Smad signaling suppression and inhibiting matrix metalloproteinase-1.

Exposure to ultraviolet (UV) light reduces levels of type I collagen in the dermis and results in human skin damage and premature skin aging (photoaging). This leads to a wrinkled appearance through the inhibition of transforming growth factor-β (TGF-β)/Smad signaling. UV irradiation increases type I collagen degradation through upregulating matrix metalloproteinase (MMP) expression. Astragaloside IV (AST) is one of the major active components extracted from Astragalus membranaceus. However, its multiple anti-photoaging effects remain to be elucidated. In the present study, the effects of AST against collagen reduction in UV-induced skin aging in human skin fibroblasts were investigated. The expression of type I procollagen (COL1), MMP-1, TGF-βRII and Smad7 were determined using reverse transcription-polymerase chain reaction, western blotting and ELISA, respectively. UV irradiation inhibits type I collagen production by suppressing the TGF-β/Smad signaling pathway and increasing COL1 degradation by inducing MMP-1 expression. Transforming growth factor-β type II protein and COL1 mRNA decreased but MMP-1 and Smad7 levels increased in the photoaging model group, which was reversed by topical application of AST. AST prevents collagen reduction from UV irradiation in photoaging skin by improving TGF-β/Smad signaling suppression and inhibiting MMP-1, thus AST may be a potential agent against skin photoaging.

A Review of the Photodynamic Application of 5-Aminolevulinic acid, Hypericin and Phthalocyanines in dermatology

Ultraviolet radiation can damage human skin leading to photo-aging and cancer. Treatment options for skin cancers are available. Amongst them, there is photodynamic therapy (PDT), the treatment modality that involves a photochemical reaction between a light sensitive compound, visible light and tissue oxygen. In PDT, a photosensitive compound also called photosensitizer (PS) is administered and allowed to accumulate in the cancerous tissue then irradiated with light corresponding to absorption wavelength of the PS, in the presence of molecular oxygen, to produce cytotoxic species that kill the cancerous tissue. PDT is increasingly used and studied globally for the treatment of different classes of cancers because of its selective destruction of diseased tissue or cancer. Newly developed non-invasive imaging technologies including photodynamic diagnosis, may assist with early identification of skin cancer to reduce the rates of morbidity and mortality following treatment. Photodynamic diagnosis (PDD) is a diagnostic modality defined from the PDT principle. It utilizes light and fluorescent PS to highlight tumour cells from normal cells. Excitation of PS by appropriate light source causes them to fluoresce over well-defined spectral regions. Therefore, the fluorescent properties of PSs can serve as an important diagnostic tool to highlight cancer at an early stage of development. In this review, our knowledge about PDT and PDD of skin cancers using 5-aminolevulinic acid (ALA), Hypericin and phthalocyanines as photosensitizers is presented.

Fucosterol Inhibits Matrix Metalloproteinase Expression and Promotes Type‐1 Procollagen Production in UVB‐induced HaCaT Cells

Ultraviolet (UV) radiation damages human skin and causes skin diseases such as epidermal hyperplasia, sunburn, inflammatory responses and photoaging. Photoaging is associated with upregulated matrix metalloproteinase (MMP) expression and downregulated collagen synthesis. Fucosterol, which is isolated from marine brown algae, has been reported to possess antioxidant and anticancer activities; however, its effects on photoaging are unknown. This study assessed the effects of fucosterol on photoaging and investigated its mechanisms of action in UV-irradiated immortalized human keratinocytes (HaCaT) by enzyme-linked immunosorbent assay, semi-quantitative reverse transcription-polymerase chain reaction, Western blot analysis and 2',7'-dichlorofluorescein diacetate assay. Our results showed that fucosterol attenuated UV-induced MMP and inflammatory cytokine expression by deactivating mitogen-activated protein kinases (MAPKs) induced by reactive oxygen species. Fucosterol also increased type-I procollagen and antioxidant enzyme expression. Taken together, fucosterol regulates the expression of MMPs and type-I procollagen in UV-irradiated HaCaT by modulating MAPK, suggesting it as a potential candidate for prevention and treatment of skin aging.

Stressed out mitochondria: The role of mitochondria in ageing and cancer focussing on strategies and opportunities in human skin

Mitochondrial DNA damage has been used as a successful and unique biomarker of tissue stress. A valuable example of this is sun damage in human skin which leads to ageing and skin cancer. The skin is constantly exposed to the harmful effects of sunlight, such as ultraviolet radiation, which causes it to age with observable characteristic features as well as clinical precancerous lesions and skin cancer. Formation of free radicals by the sun's harmful rays which contribute to oxidative stress has been linked to the induction of deletions and mutations in the mitochondrial DNA. These markers of mitochondrial DNA damage have been proposed to contribute to the mechanisms of ageing in many tissues including skin and are associated with many diseases including cancer. In this article we highlight the role of this important organelle in ageing and cancer with particular emphasis on experimental strategies in the skin.

Relationship between skin color and skin response to ultraviolet light

Relationship between skin color and skin response to ultraviolet light

Melatonin enhances antioxidative enzyme gene expression (CAT, GPx, SOD), prevents their UVR‐induced depletion, and protects against the formation of DNA damage (8‐hydroxy‐2'‐deoxyguanosine) in ex vivo human skin

UV radiation (UVR) induces serious structural and functional alterations in human skin leading to skin aging and carcinogenesis. Reactive oxygen species are key players in UVR-mediated photodamage and induce the DNA-base-oxidized, intermediate 8-hydroxy-2'-deoxyguanosine (8-OHdG). Herein, we report the protective action of melatonin against UVR-induced 8-OHdG formation and depletion of antioxidative enzymes using ex vivo human full-thickness skin exposed to UVR in a dose (0, 100, 300 mJ/cm(2))- and time-dependent manner (0, 24, 48 hr post-UVR). Dynamics of depletion of antioxidative enzymes including catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD), or 8-OHdG formation were studied by real-time PCR and immunofluorescence/immunohistochemical staining. UVR-treated skin revealed significant and immediate (0 hr 300 mJ/cm(2)) reduction of gene expression, and this effect intensified within 24 hr post-UVR. Simultaneous increase in 8-OHdG-positive keratinocytes occurred already after 0 hr post-UVR reaching 71% and 99% up-regulation at 100 and 300 mJ/cm(2), respectively (P < 0.001). Preincubation with melatonin (10(-3) M) led to 32% and 29% significant reductions in 8-OHdG-positive cells and the prevention of antioxidative enzyme gene and protein suppression. Thus, melatonin was shown to play a crucial role as a potent antioxidant and DNA protectant against UVR-induced oxidative damage in human skin.

Coriandrum sativum L. Protects Human Keratinocytes from Oxidative Stress by Regulating Oxidative Defense Systems

Background: Oxidative radicals are major environmental causes of human skin damage. Oxidative defense factors, including nuclear factor erythroid-derived 2-related factor 2 (Nrf2), are centrally involved in repairing skin cells or protecting them from oxidative damage. Coriandrum sativum L. (coriander; CS) is a commonly consumed food and a traditional phytomedicine in Asia and Europe. In this study, we examined the protective effects of a standardized CS leaf extract against oxidative stress in human HaCaT keratinocytes. Methods and Results: CS significantly and dose-dependently protected cells against reduced cell viability caused by H₂O₂-induced damage, as assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Other assays demonstrated that CS protected HaCaT cells by increasing the levels of glutathione and activities of oxidative defense enzymes, such as superoxide dismutase and catalase. Moreover, it increased the expression of activated Nrf2, which plays a crucial role in protecting skin cells against oxidative stress. Conclusion: These results suggest that CS protects human keratinocytes from H₂O₂-induced oxidative stress through antioxidant effects.

Preventive Effects of β-Thujaplicin Against UVB-Induced MMP-1 and MMP-3 mRNA Expressions in Skin Fibroblasts

Solar UV radiation damages human skin by affecting skin tone and resiliency and leads to premature aging (photoaging). The skin damage is caused by the activation of the AP-1 transcription factor, which increases matrix metalloproteinase (MMP) expression and collagen degradation. An increase of interleukin (IL)-6 is also correlated with the activation of MMP-1 expression. β-thujaplicin has shown both acaricidal and antimicrobial activities. Also, β-thujaplicin has been shown to be protective against apoptosis due to the oxidative effects of UV irradiation. However, the effect of β-thujaplicin on UVB-induced MMPs had not been investigated. In this study, after UVB exposure, MMP-1 and IL-6 production in human skin fibroblasts was examined in the presence of β-thujaplicin, vitamin C, and vitamin E. The expression of MMP-1, MMP-3, tissue inhibitor of metalloproteinase (TIMP-1, TIMP-3) and procollagen mRNA was also investigated. Results showed that UVB-induced MMP-1 production was suppressed by the β-thujaplicin treatment in a dose-dependent manner, but not by vitamin C and vitamin E. β-thujaplicin also prevented the up-regulation of MMP-1 and MMP-3 mRNA. Moreover, the UVB-suppressed procollagen gene expression was restored to normal by β-thujaplicin. Neither UVB nor β-thujaplicin affected the mRNA expression of TIMP-1 and TIMP-3. The IL-6 production induced by UVB was lower in β-thujaplicin treated fibroblasts than in the controls. In conclusion, this study shows the capability of β-thujaplicin in preventing MMP-1 production due to UVB irradiation via inhibition of MMP gene expression. Importantly, the UVB-suppressed procollagen gene expression can be restored to normal by β-thujaplicin. These findings indicate that β-thujaplicin is a promising and potent agent to inhibit UVB-induced MMP-1 and MMP-3 gene expression in skin fibroblasts.

Phototoxicity and Environmental Transformation of Polycyclic Aromatic Hydrocarbons (PAHs)—Light-Induced Reactive Oxygen Species, Lipid Peroxidation, and DNA Damage

Polycyclic aromatic hydrocarbons (PAHs) are a class of mutagenic and tumorigenic environmental contaminants. Although the mechanisms by which PAHs induce cancer in experimental animals have been extensively studied and the metabolic activation pathways have been determined, the environmental fate of PAHs and the phototoxicity exerted by PAHs, as well as their photoreaction products formed in the environment, have received much less attention. In this review, the formation of oxygenated PAHs, PAH quinones, nitro-PAHs, and halogenated PAHs from photoreaction of environmental PAHs are addressed. Upon light irradiation, PAHs and all PAH photoreaction products can absorb light energy to reach photo-excited states, which react with molecular oxygen, medium, and coexisting chemicals to produce reactive oxygen species (ROS) and other reactive intermediates, such as oxygenated PAHs and free radicals. These intermediates, including ROS, induce lipid peroxidation, and DNA damage including DNA strand breakage, oxidation to 8-oxo-2′-deoxyguanosine, and DNA-adducts. Since these toxicological endpoints are associated with age-related diseases, including cancer, environmental PAHs concomitantly exposed to sunlight may potentially promote human skin damage, leading to ageing and skin cancers. Thus, we suggest that (i) in addition to the widely recognized metabolic pathways, more attention must be paid to photoreaction as an important activation pathway for PAHs, (ii) risk assessment of environmental PAHs should take into consideration the complex photochemical reactions leading to mixtures of products that are also phototoxic; and (iii) the study of structure-toxicity relationships should be expanded to cover the complex photoreactions and extrinsic factors that affect phototoxicity endpoints.

Human skin penetration of gold nanoparticles through intact and damaged skin

Gold nanoparticles (AuNPs) are produced for many applications but there is a lack of available data on their skin absorption. Experiments were performed using the Franz diffusion cell method with intact and damaged human skin. A physiological solution was used as receiving phase and 0.5 mL (1st exp) and 1.5 mL (2nd exp) of a solution containing 100 mgL-1 of AuNPs (15 and 45 μg cm-2, respectively) was applied as donor phase to the outer surface of the skin for 24 h. Skin absorption was dose dependent. Mean gold content of 214.0 ± 43.7 ng cm-2 and 187.7 ± 50.2 ng cm-2 were found in the receiving solutions of cells where the AuNPs solution was applied in higher concentration on intact skin (8 Franz cells) and on damaged skin (8 Franz cells), respectively. Twenty-four hours gold flux permeation was 7.8 ± 2.0 ng cm-2 h-1 and 7.1 ± 2.5 ng cm-2 h-1 in intact and damaged skin, respectively, with a lag time less than 1 hour. Transmission Electron Microscope analysis on skin samples and chemical analysis using Inductively Coupled Plasma-Mass Spectrometry demonstrated the presence of AuNPs into epidermis and dermis. This study showed that AuNPs are able to penetrate the human skin in an in vitro diffusion cell system.

Differential effects of melatonin as a broad range UV-damage preventive dermato-endocrine regulator

Melatonin or N-acetyl-5-methoxytryptamine, is a compound derived from tryptophan that is found in all organisms from single cells to vertebrates and the human. It is one of the most evolutionarily conserved and pleiotropic hormone still active in humans and has been implicated in vital skin functions such as hair growth, fur pigmentation as well as melanoma control. Being a main secretory product of the pineal gland, melatonin regulates seasonal biorhythms, reproductive mechanisms or mammary gland metabolism. Due to its wide range endocrine properties it is also recognized to modulate numerous additional functions ranging from scavenging free radicals, immunomodulation-mediated DNA repair, wound healing, involvement in gene expression connected with circadian clocks and modulation of secondary endocrine signaling including prolactin release. Recently, apart from above mentioned entities, it was shown that melatonin suppresses ultraviolet (UV)-induced damage in human skin and human derived cell lines (e.g., keratinocytes, fibroblasts). The magnitude of UV-induced damage is mediated apparently by various molecular mechanisms related to generation of reactive oxygen species (ROS), apoptosis and mitochondrial-mediated cell death which are all counteracted or modulated by melatonin. We provide here an update of the relevant protective effects and molecular mechanisms of action of melatonin in the skin.

Skin cell protection against UVA by Sideroxyl, a new antioxidant complementary to sunscreens

Oxidative stress resulting from photosensitized ROS production in skin is widely accepted as the main contributor to the deleterious effects of UVA exposure. Among the mechanisms known to be involved in UVA-induced oxidative damage, iron plays a central role. UVA radiation of skin cells induces an immediate release of iron, which can then act as a catalyst for uncontrolled oxidation reactions of cell components. Such site-specific damage can scarcely be counteracted by classical antioxidants. In contrast, iron chelators potentially offer an effective way to protect skin against UVA insults. However, iron chelation is very difficult to achieve without disturbing iron homeostasis or inducing iron depletion. A novel compound was developed to avoid these potentially harmful side effects. Sideroxyl was designed to acquire its strong chelating capability only during oxidative stress according to an original process of intramolecular hydroxylation. Herein, we describe in vitro results demonstrating the protective efficiency of Sideroxyl against deleterious effects of UVA at the molecular, cellular, and tissular levels. First, the Sideroxyl diacid form protects a model protein against UVA-induced photosensitized carbonylation. Second, intracellular ROS are dose-dependently decreased in the presence of Sideroxyl in both human cultured fibroblasts and human keratinocytes. Third, Sideroxyl protects normal human fibroblasts against UVA-induced DNA damage as measured by the comet assay and MMP-1 production. Finally, Sideroxyl provides protection against UVA-induced alterations in human reconstructed skin. These results suggest that Sideroxyl may prevent UVA-induced damage in human skin as a complement to sunscreens, especially in the long-wavelength UVA range.

Differential Effects of Low-Dose and High-Dose Beta-Carotene Supplementation on the Signs of Photoaging and Type I Procollagen Gene Expression in Human Skin in vivo

Background: Although the photoprotective effects of β-carotene are thought to originate from its antioxidant properties, some studies documented pro-oxidant effects of β-carotene. Objective: Our purpose was to determine the effects of 2 different doses of dietary β-carotene on wrinkles and elasticity, procollagen gene expression and ultraviolet (UV)-induced DNA damage in human skin. Methods: Thirty healthy female subjects over the age of 50 years were randomized and received 2 different doses (30 and 90 mg/day) of β-carotene for 90 days. The baseline status was used as control. At baseline and completion of the study, facial wrinkles and elasticity were measured objectively. Buttock skin was taken to determine the type I procollagen, matrix metalloproteinase-1 and fibrillin-1 mRNA levels, and UV-induced thymine dimer and 8-hydroxy-2′-deoxyguanosine formation. Results: β-Carotene improved facial wrinkles and elasticity significantly only in the low-dose group. The minimal erythema dose decreased significantly only in the high-dose group. Type I procollagen mRNA levels were significantly increased to 4.4 ± 1.6 times the baseline level only in the low-dose group, and procollagen immunostaining increased accordingly. UV-induced thymine dimer staining was reduced in the low-dose group but tended to increase in the high-dose group. 8-hydroxy-2′-deoxyguanosine staining was significantly reduced in the low-dose group. Conclusions: 30 mg/day of β-carotene supplementation is demonstrated to prevent and repair photoaging.

High-dose squalene ingestion increases type I procollagen and decreases ultraviolet-induced DNA damage in human skinin vivobut is associated with transient adverse effects

Evidence for beneficial effects of squalene on ultraviolet (UV)-induced photoageing of the skin is lacking. To investigate whether squalene supplementation improves signs and molecular markers of photoageing in human skin in vivo. In total, 40 female volunteers aged > 50 years received two different doses [13.5 g/day (low-dose group) and 27 g/day (high-dose group)] of squalene for 90 days. At baseline and at the completion of the study, facial wrinkles were measured using skin replicas. Skin samples were taken to compare type I procollagen and matrix metalloproteinase 1 mRNA levels by real-time reverse-transcriptase PCR, and for type I procollagen immunostaining. Skin samples were also taken 24 h after 2 x minimal erythema dose (MED) of UV irradiation before and after squalene intake to assess UV-induced thymine dimer formation and keratinocytic apoptosis. In total, 37 subjects completed the trial. Transient loose stool was experienced by 35% of volunteers in the low-dose group and 55% in the high-dose group. Facial wrinkles decreased significantly (P < 0.05) in the high-dose group, while procollagen type I mRNA levels and MED increased significantly in the low-dose group. Procollagen immunostaining tended to increase in both groups. Facial erythema decreased and pigmentation increased significantly in both groups. UV-induced keratinocytic apoptosis and thymine dimer staining were substantially reduced in both groups. Daily ingestion of 13.5 or 27 g of squalene per day resulted in antiageing effects in photoaged skin. However, in view of the frequent incidence of loose stool experienced by the subjects, the risk-benefit ratio of high-dose squalene supplementation is too high to recommend it for treating skin ageing.

In vitro absorption of metal powders through intact and damaged human skin

The bioavailability of metals, which are known as important contact allergens, is decisive for the development and the maintenance of contact dermatitis. The aim of this study was to evaluate the percutaneous penetration of metal powders of cobalt (Co), nickel (Ni) and chromium (Cr) and the effect of skin lesions on skin absorption. In vitro permeation experiments were performed using the Franz diffusion cells with intact and damaged human skin. Physiological solution was used as receiving phase and metal powders (Co, Ni and Cr) dispersed in synthetic sweat at pH 4.5 were applied as donor phase to the outer surface of the skin for 24 h. The amount of each metal permeating the skin was analysed by electro-thermal atomic absorption spectroscopy (ETAAS). Donor solution analysis demonstrated that metals were present as ions. Measurements of metals skin content were also exploited. Median Co and Ni concentrations found in the receiving phase were significantly higher when Co and Ni powders were applied on the abraded skin than after application on the intact skin (3566 and 2631 ngcm −2 vs. 8.4 and 31 ngcm −2, respectively). No significant difference was found in Cr permeation through intact and damaged skin. The measurement of metals skin content showed that Co, Ni and Cr concentrations were significantly higher in the damaged skin than in the intact skin. Co and Ni ions concentrations increased significantly when the donor solutions were applied on the damaged skin, while Cr ions concentrations did not increase. This study demonstrated that Co and Ni powders can permeate through damaged skin more easily than Cr powder, which has probably a stronger skin proteins binding capacity. Therefore, our results suggest that is necessary to prevent skin contamination when using toxic substances because a small injury to the skin barrier can significantly increase skin absorption.