Airborne polycyclic aromatic hydrocarbons trigger human skin cells aging through aryl hydrocarbon receptor

Evidence that the aryl hydrocarbon receptor orchestrates oxinflammatory responses and contributes to airborne particulate matter-induced skin aging

Exposure to airborne particulate matter (PM) is a substantial threat to public health, contributing to respiratory, cardiovascular, and skin-related diseases. Population-based studies strongly indicate that chronic exposure to airborne PM, especially combustion-derived PM2.5, accelerates skin aging and thus reduces the quality of life of those affected. There is increasing evidence that especially PM-bound polycyclic aromatic hydrocarbons (PAHs) critically contribute to the clinical manifestation of skin aging, i.e. the development of lentigines/pigment spots and coarse wrinkles. PAHs harm human skin primarily by activating the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor amongst others involved in orchestrating xenobiotic metabolism and immune responses. In this review, we summarize the available population-based data linking particulate air pollution exposure to skin aging. We explain in detail how PAH-rich PM induces the formation of oxidative stress, the release of pro-inflammatory mediators, the expression extracellular matrix degrading metalloproteases, and melanin synthesis, in an AHR-dependent manner, and how these events may culminate in the development of pigment spots and wrinkles, respectively. We also review the current data on the interaction of airborne PM with another factor of the skin aging exposome that exerts its deleterious effects in part through AHR-dependent signaling pathways, namely solar ultraviolet radiation.

Air Pollution and Skin Diseases

Air pollution is a widespread environmental issue, with substantial global implications for human health. Recent epidemiological studies have shown that exposure to air pollution exacerbates various inflammatory skin conditions, including atopic dermatitis, psoriasis, or acne. Furthermore, air pollutants are associated with accelerated skin aging, hair loss, and skin cancer. The aim of this review is to elucidate the current understanding of the impact of air pollution on skin health, emphasizing the underlying mechanisms involved and existing therapeutic and cosmetic interventions available to prevent or mitigate these effects. A pivotal factor in the harmful effects of air pollution is the formation of reactive oxygen species and the resulting oxidative stress. The aryl hydrocarbon receptor signaling pathway also substantially contributes to mediating the effects of air pollutants on various skin conditions. Moreover, air pollutants can disrupt the skin barrier function and trigger inflammation. Consequently, antioxidant and anti-inflammatory therapies, along with treatments designed to restore the skin barrier function, have the potential to mitigate the adverse effects of air pollutants on skin health.

A new mechanism involved in cardiovascular senescence induced by environmentally relevant dose of 16 priority-controlled PAHs

Polycyclic aromatic hydrocarbons (PAHs) are closely related to the occurrence of cardiovascular diseases, nevertheless the toxicological mechanism remains ambiguous. To verify whether PAHs exposure leads to cardiovascular senescence, 8-week-old male sprague-dawley rats and primary human umbilical vein endothelial cells were exposed to different concentrations of 16 priority-controlled PAHs for 90 d and 48 h respectively. In in vitro study, PAHs exposure promoted aryl hydrocarbon receptor (AhR) activation, and then directly or indirectly inhibited SIRT6 expression leading to telomere dysfunction, which further caused DNA damage and subsequently promoted endothelial cells senescence. But the treatment of CH-223191 (an AhR inhibitor) rescued the aging phenotypes induced by PAHs, suggesting that AhR plays an important role in PAHs-induced endothelial cells senescence. In in vivo study, PAHs exposure raised AhR expression, affected SIRT6-related aging signaling pathway, and induced myocardial and vascular remodeling in rats. Molecular dynamics simulations demonstrated that, in addition to benzo[a]pyrene-7,8-diol-9,10-epoxide (the mediate metabolite of benzo[a]pyrene), typical parent PAHs (phenanthrene, benzo[a]pyrene) can directly bind to known DNA strand binding sites of SIRT6 through hydrophobic force, which was further validated by electrophoretic mobility shift assay. All above indicates for the first time that in addition to classical AhR dependent pathway, parent PAHs may affect DNA damage response and telomere maintenance function of SIRT6, which is a new mechanism of PAHs induced cardiovascular senescence.

Role of microbiota in the GUT-SKIN AXIS responses to outdoor stressors

Beside the respiratory tract, the skin and the gut represent the first defensive lines of our body against the external insults displaying many important biochemical features able to maintain the epithelial barrier integrity and to regulate the tissue immune responses. The human microbiome is essential in maintaining the tissue homeostasis and its dysregulation may lead to tissue conditions including inflammatory pathologies. Among all external insults, air pollutants have been shown to cause oxidative stress damage within the target tissues via an OxInflammatory response. Dysregulation of the gut microbiome (dysbiosis) by outdoor stressors, including air pollutants, may promote the exacerbation of the skin tissue damage via the interplay between the gut-skin axis. The intent of this review is to highlight the ability of exogenous stressors to modulate the human gut-skin axis via a redox regulated mechanism affecting the microbiome and therefore contributing to the development and aggravation of gut and skin conditions.

Benzo[b]fluoranthene damages coronary artery and affects atherosclerosis markers in mice and umbilical vein endothelial cells

Polycyclic aromatic hydrocarbons (PAHs) exposure is associated with cardiovascular diseases. Toxic effects of PAHs are diverse, while cardiovascular consequences of benzo[b]fluoranthene (B[b]F) are unclear. Here, we reported the impacts of B[b]F on coronary artery and atherosclerosis markers both in mice and umbilical vein endothelial EAhy.926 cells. In mice, we found that B[b]F decreases heart-to-body weight ratio, affects aortic physiology, elevates serum low-density lipoprotein and total cholesterol, increases aortic levels of collagen fiber and atherosclerotic marker vascular cell adhesion molecule-1 (VCAM-1), and downregulates oxidative stress related nuclear factor erythroid 2-related factor 2 (Nrf2). In EAhy.926 cells, we showed that B[b]F inhibits cell proliferation and migration in a dose-dependent manner, induces cell cycle arrest and apoptosis, increases reactive oxygen species, upregulates VCAM-1 level, and suppresses expression of Nrf2. Taken together, our findings reveal that B[b]F exposure may contribute to coronary artery damage and potentially induce atherosclerosis, possibly via the Nrf2-related signaling pathways.

Particulate Matter and Its Molecular Effects on Skin: Implications for Various Skin Diseases

Particulate matter (PM) is a harmful air pollutant composed of chemicals and metals which affects human health by penetrating both the respiratory system and skin, causing oxidative stress and inflammation. This review investigates the association between PM and skin disease, focusing on the underlying molecular mechanisms and specific disease pathways involved. Studies have shown that PM exposure is positively associated with skin diseases such as atopic dermatitis, psoriasis, acne, and skin aging. PM-induced oxidative stress damages lipids, proteins, and DNA, impairing cellular functions and triggering inflammatory responses through pathways like aryl hydrocarbon receptor (AhR), NF-κB, and MAPK. This leads to increased production of inflammatory cytokines and exacerbates skin conditions. PM exposure exacerbates AD by triggering inflammation and barrier disruption. It disrupts keratinocyte differentiation and increases pro-inflammatory cytokines in psoriasis. In acne, it increases sebum production and inflammatory biomarkers. It accelerates skin aging by degrading ECM proteins and increasing MMP-1 and COX2. In conclusion, PM compromises skin health by penetrating skin barriers, inducing oxidative stress and inflammation through mechanisms like ROS generation and activation of key pathways, leading to cellular damage, apoptosis, and autophagy. This highlights the need for protective measures and targeted treatments to mitigate PM-induced skin damage.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

Assessment of comprehensive PAH index in roasted Tan lamb by two-dimensional correlation spectroscopy combined with hyperspectral imaging

Thermally processed meat may contain harmful compounds, including polycyclic aromatic hydrocarbons (PAHs). This study constructed, for the first time, the comprehensive PAH index (CPI) concentration (phenanthrene [26.47%], acenaphthene [21.83%], pyrene [18.64%], fluoranthene [17.11%], fluorene [8.49%], and anthracene [7.46%]). A visible near-infrared (Vis-NIR) hyperspectral image (HSI) system was employed to detect CPI in 150 roasted Tan lamb samples. Furthermore, two-dimensional correlation spectra were used to identify spectral features and reveal the order of chemical bond changes under the characteristic peaks at 579-737-631-449 nm. The results indicated that competitive adaptive reweighted sampling-multiple linear regression quantitative prediction model worked the best with calibration set coefficient of determination of 0.9161, calibration set coefficient of root mean square error of 2.3426 µg/kg, R-squared prediction of 0.8469, and root mean square error of prediction of 2.4119 µg/kg. Finally, PAH content distributions were visualized using the best prediction model. This study aimed to propose a feasible method for CPI in roasted Tan lamb detection based on Vis-NIR HSI coupled with multivariate analysis methods.

Environmental Air Pollutants Affecting Skin Functions with Systemic Implications

The increase in air pollution worldwide represents an environmental risk factor that has global implications for the health of humans worldwide. The skin of billions of people is exposed to a mixture of harmful air pollutants, which can affect its physiology and are responsible for cutaneous damage. Some polycyclic aromatic hydrocarbons are photoreactive and could be activated by ultraviolet radiation (UVR). Therefore, such UVR exposure would enhance their deleterious effects on the skin. Air pollution also affects vitamin D synthesis by reducing UVB radiation, which is essential for the production of vitamin D3, tachysterol, and lumisterol derivatives. Ambient air pollutants, photopollution, blue-light pollution, and cigarette smoke compromise cutaneous structural integrity, can interact with human skin microbiota, and trigger or exacerbate a range of skin diseases through various mechanisms. Generally, air pollution elicits an oxidative stress response on the skin that can activate the inflammatory responses. The aryl hydrocarbon receptor (AhR) can act as a sensor for small molecules such as air pollutants and plays a crucial role in responses to (photo)pollution. On the other hand, targeting AhR/Nrf2 is emerging as a novel treatment option for air pollutants that induce or exacerbate inflammatory skin diseases. Therefore, AhR with downstream regulatory pathways would represent a crucial signaling system regulating the skin phenotype in a Yin and Yang fashion defined by the chemical nature of the activating factor and the cellular and tissue context.

Chemokine expression in human 3-dimensional cultured epidermis exposed to PM2.5 collected by cyclonic separation

Fine particulate matter (PM2.5) exposure has a risk of inducing several health problems, especially in the respiratory tract. The skin is the largest organ of the human body and is therefore the primary target of PM2.5. In this study, we examined the effects of PM2.5 on the skin using a human 3-dimensional cultured epidermis model. PM2.5 was collected by cyclonic separation in Yokohama, Japan. Global analysis of 34 proteins released from the epidermis revealed that the chemokines, chemokine C-X-C motif ligand 1 (CXCL1) and interleukin 8 (IL-8), were significantly increased in response to PM2.5 exposure. These chemokines stimulated neutrophil chemotaxis in a C-X-C motif chemokine receptor 2-dependent manner. The oxidative stress and signal transducer and activator of transcription 3 pathways may be involved in the increased expression of CXCL1 and IL-8 in the human epidermis model. Interestingly, in the HaCaT human keratinocyte cell line, PM2.5 did not affect chemokine expression but did induce IL-6 expression, suggesting a different effect of PM2.5 between the epidermis model and HaCaT cells. Overall, PM2.5 could induce the epidermis to release chemokines, followed by neutrophil activation, which might cause an unregulated inflammatory reaction in the skin.

Commentary: Facial Aesthetic Dermatological Procedures and Photoprotection in Chinese Populations

The medical literature on aesthetic dermatology has primarily focused on a light-skinned patient population, yet patients of darker skin types have different needs and priorities. In Chinese individuals, key concerns include altered pigmentation, which is perceived to age the individual, and also relates to the Chinese cultural standard of beauty of fair skin; many seek aesthetic treatment for this. Non-invasive cosmetic procedures such as lasers and injections are also gaining in popularity in the Chinese market, but this population is prone to hyperpigmentation as an adverse effect of such procedures. Considered and tailored approaches, both to primary concerns of photoaging and the side effects of cosmetic treatments, are warranted.

Aging in the sebaceous gland

Sebaceous glands (SGs) originate from hair follicular stem cells and secrete lipids to lubricate the skin. The coordinated effects of intrinsic and extrinsic aging factors generate degradation of SGs at a late age. Senescence of SGs could be a mirror of the late aging of both the human body and skin. The procedure of SG aging goes over an initial SG hyperplasia at light-exposed skin areas to end with SG atrophy, decreased sebum secretion, and altered sebum composition, which is related to skin dryness, lack of brightness, xerosis, roughness, desquamation, and pruritus. During differentiation and aging of SGs, many signaling pathways, such as Wnt/β-catenin, c-Myc, aryl hydrocarbon receptor (AhR), and p53 pathways, are involved. Random processes lead to random cell and DNA damage due to the production of free radicals during the lifespan and neuroendocrine system alterations. Extrinsic factors include sunlight exposure (photoaging), environmental pollution, and cigarette smoking, which can directly activate signaling pathways, such as Wnt/β-catenin, Notch, AhR, and p53 pathways, and are probably associated with the de-differentiation and hyperplasia of SGs, or indirectly activate the abovementioned signaling pathways by elevating the inflammation level. The production of ROS during intrinsic SG aging is less, the signaling pathways are activated slowly and mildly, and sebocytes are still differentiated, yet terminal differentiation is not completed. With extrinsic factors, relevant signaling pathways are activated rapidly and fiercely, thus inhibiting the differentiation of progenitor sebocytes and even inducing the differentiation of progenitor sebocytes into keratinocytes. The management of SG aging is also mentioned.

Aryl hydrocarbon receptor: From pathogenesis to therapeutic targets in aging-related tissue fibrosis

Aging promotes chronic inflammation, which contributes to fibrosis and decreases organ function. Fibrosis, the excessive synthesis and deposition of extracellular matrix components, is the main cause of most chronic diseases including aging-related organ failure. Organ fibrosis in the heart, liver, and kidneys is the final manifestation of many chronic diseases. The aryl hydrocarbon receptor (AHR) is a cytoplasmic receptor and highly conserved transcription factor that is activated by a variety of small-molecule ligands to affect a wide array of tissue homeostasis functions. In recent years, mounting evidence has revealed that AHR plays an important role in multi-organ fibrosis initiation, progression, and therapy. In this review, we summarise the relationship between AHR and the pathogenesis of aging-related tissue fibrosis, and further discuss how AHR modulates tissue fibrosis by regulating transforming growth factor-β signalling, immune response, and mitochondrial function, which may offer novel targets for the prevention and treatment of this condition.

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.

Does healthy lifestyle attenuate the detrimental effects of urinary polycyclic aromatic hydrocarbons on phenotypic aging? An analysis from NHANES 2001-2010

Existing evidence has showed that exposure to polycyclic aromatic hydrocarbons (PAHs) increases the risk of many chronic diseases. Given the close connection between aging (a major risk factor) and chronic diseases, however, very few studies have evaluated the association between PAHs and aging. Furthermore, whether modifiable healthy lifestyle could attenuate the detrimental effect of PAHs on aging remains unknown. Therefore, we conducted this study, aiming to: (1) examine the associations of urinary monohydroxy polycyclic aromatic hydrocarbons (OH-PAHs) and lifestyle with Phenotypic Age Acceleration (PhenoAge.Accel), a novel aging measure that captures morbidity and mortality risk; and (2) evaluate the potential interaction effects of OH-PAHs and lifestyle on PhenoAge.Accel. Cross-sectional data of 2,579 participants (aged 20-84 years, n = 1,292 females) from the National Health and Nutrition Examination Survey for years 2001-2010 were analyzed. A lifestyle index was constructed based on five components (drinking, smoking, body mass index, physical activity, and diet), ranging from 0 to 5. We calculated PhenoAge.Accel using algorithms developed previously. General linear regression models were used to examine the associations. We observed strong associations of OH-PAHs and lifestyle with PhenoAge.Accel. For instance, one unit increase in ∑NAP (sum of 1- and 2-hydroxynaphthalene) was associated with 0.37 year (95% confidence interval [CI]: 0.26, 0.48) increase in PhenoAge.Accel. We did not observe statistically significant interaction effects between OH-PAHs and lifestyle on PhenoAge.Accel. After stratified by sex, we observed strong associations as well as statistically significant interactions of OH-PAHs and lifestyle with PhenoAge.Accel among females. In conclusion, both OH-PAHs and lifestyle were independently associated with phenotypic aging and there were statistically significant interactions between OH-PAHs and lifestyle on phenotypic aging among females. The findings highlight the importance of adherence to a healthy lifestyle to attenuate the detrimental effects of exposures to PAHs on phenotypic aging among females.

Pterostilbene Attenuates Particulate Matter-Induced Oxidative Stress, Inflammation and Aging in Keratinocytes

Particulate matter (PM) is the main indicator of air pollutants, and it may increase the level of reactive oxygen species (ROS) in keratinocytes, leading to skin inflammation, aging, and decreased moisturizing ability. Pterostilbene (PTS) is a dimethylated analog of resveratrol that has antioxidant effects. However, the molecular mechanisms of PTS in preventing PM-induced keratinocyte inflammation and aging have not been investigated yet. Therefore, we used PM-induced human keratinocytes to investigate the protective mechanisms of PTS. The results showed that 20 μM PTS had no toxicity to HaCaT keratinocytes and significantly reduced PM-induced intracellular ROS production. In addition, nuclear translocation of the aryl hydrocarbon receptor (AHR) was inhibited by PTS, leading to reduced expression of its downstream CYP1A1. PTS further inhibited PM-induced MAPKs, inflammation (COX-2), and aging (MMP-9) protein cascades, and rescued moisturizing (AQP-3) protein expression. We analyzed the PTS content in cells at different time points and compared the concentration required for PTS to inhibit the target proteins. Finally, we used the skin penetration assay to show that the PTS essence mainly exists in the epidermal layer and did not enter the system circulation. In conclusion, PTS could protect HaCaT keratinocytes from PM-induced damage and has the potential to become a cosmetic ingredient.

Inflammasome Activation in Pollution-Induced Skin Conditions

SUMMARY

Exposure to air pollutants has been now associated with detrimental effects on a variety of organs, including the heart, lungs, GI tract, and brain. However, recently it has become clear that pollutant exposure can also promote the development/exacerbation of a variety of skin conditions, including premature aging, psoriasis, acne, and atopic dermatitis. Although the molecular mechanisms by which pollutant exposure results in these cutaneous pathological manifestations, it has been noticed that an inflammatory status is a common denominator of all those skin conditions. For this reason, recently, the activation of a cytosolic multiprotein complex involved in inflammatory responses (the inflammasome) that could promote the maturation of proinflammatory cytokines interleukin-1β and interleukin-18 has been hypothesized to play a key role in pollution-induced skin damage. In this review, we summarize and propose the cutaneous inflammasome as a novel target of pollutant exposure and the eventual usage of inflammasome inhibitor as new technologies to counteract pollution-induced skin damage. Possibly, the ability to inhibit the inflammasome activation could prevent cutaneous inflammaging and ameliorate the health and appearance of the skin.

Natural compounds protect the skin from airborne particulate matter by attenuating oxidative stress

Particulate matter (PM) is a common indirect indicator of air pollution and threatens public health upon prolonged exposure, leading to oxidative stress, increasing the risk of develop respiratory and cardiovascular, as well as several autoimmune diseases and cancer. Nowadays, as a first line defense against PM, skin health attracted much attention. Our review summarized the skin damage mechanism induced by PM, including damage skin barrier directly, reactive oxygen species (ROS) accumulation, autophagy, and two canonical signaling pathways. Furthermore, ROS and oxidative stress have been considered pathogenesis centers, with essential skin damage roles. Extracts from plants and natural compounds which present high antioxidant capacity could be used to treat or protect against air pollution-related skin damage. We conclude the extracts reported in recent studies with protective effects on PM-mediated skin damage. Besides, the mechanism of extracts' positive effects has been revealed partially.

Environmentally-Induced (Extrinsic) Skin Aging: Exposomal Factors and Underlying Mechanisms

As a barrier organ, the skin is an ideal model to study environmentally-induced (extrinsic) aging. In this review, we explain the development of extrinsic skin aging as a consequence of skin exposure to specific exposomal factors, their interaction with each other, and the modification of their effects on the skin by genetic factors. We also review the evidence that exposure to these exposomal factors causes extrinsic skin aging by mechanisms that critically involve the accumulation of macromolecular damage and the subsequent development of functionally altered and/or senescent fibroblasts in the dermal compartment of the skin.

The release of contaminants from steel slags and natural aggregates: Evaluation of toxicity and genotoxicity

Steel slags (SS) are the major waste produced by iron and steel industry. Slags may be reused as recycled materials, instead of natural aggregates (NA), to reduce the final disposal in a landfill and the exploitation of raw materials. However, the reuse of SS may generate a potential release of toxic compounds for the environment and humans. The purpose of this study was to evaluate the toxicity and genotoxicity of SS, in comparison with NA, by using an integrated chemical-biological approach to enable their safe reuse in engineering applications. Leaching solutions from samples were obtained by using short-term leaching tests (CEN EN 12457-2, 2004) usually adopted for the evaluation of waste recovery and final disposal. Chemical analyses of leachates were performed according to the Italian legislation on waste recovery (Ministerial Decree 186/2006). The leaching solutions were assayed by using toxicity test on Daphnia magna. Moreover, mutagenicity/genotoxicity tests on Salmonella typhimurium, Allium cepa, and human leucocytes and fibroblasts were carried out. The releases of pollutants from all samples were within the limits of the Italian legislation for waste recovery. Despite the effects that SS and NA could have on different cells, in terms of toxicity and genotoxicity, globally, SS do not seem to be any more hazardous than NA. This ecotoxicological assessment, never studied before, is important for promoting further studies that may support the decision-making process regarding the use of such types of materials.

The absorption of polycyclic aromatic hydrocarbons into the skin to elicit cutaneous inflammation: The establishment of structure-permeation and in silico-in vitro-in vivo relationships

Polycyclic aromatic hydrocarbons (PAHs) can induce skin toxicity. Although some investigations have been conducted to assess the skin toxicity of different PAHs, few comparisons using a series of PAHs with different ring numbers and arrangements have been done. We aimed to explore the skin absorption of 6 PAH compounds and their effect on cutaneous inflammation. In vitro skin permeation was rated by Franz cell with pig skin. Molecular docking was employed to compute the PAH interaction with stratum corneum (SC) lipids. Cultured keratinocytes were exposed to PAHs for analyzing cytotoxicity, cyclooxygenase (COX)-2, prostaglandin E₂ (PGE₂), chemokines, and differentiation proteins. The in vivo topical PAH exposure in mice was characterized by skin absorption, transepidermal water loss (TEWL), PGE₂ level, and histology. The skin deposition from the aqueous vehicle increased following the increase of PAH lipophilicity and molecular size, with benzo[a]pyrene (5-ring PAH) showing the greatest absorption. Pyrene was the compound showing the highest penetration across the skin (flux). Although the PAHs fluoranthene, pyrene, chrysene, and 1,2-benzanthracene all had 4 rings, the skin permeation was quite different. 1,2-Benzanthracene showed the greatest absorption among the 4-ring compounds. The PAHs with higher absorption exhibited stronger interaction with SC lipids according to the in silico modeling. Chrysene and 1,2-benzanthracene generally showed the highest COX-2 and PGE₂ expression, followed by benzo[a]pyrene. The lowest COX-2 and PGE₂ upregulation was observed for naphthalene (2-ring PAH). A contrary tendency was detected for the upregulation of chemokines. Filaggrin and integrin β1 in keratinocytes were suppressed at a comparable level by all PAHs. The skin's absorption of PAHs showed strong in vivo-in vitro correlation. 1,2-Benzanthracene and benzo[a]pyrene highly disrupted the skin barrier and elevated the inflammation in vivo. The tendency toward in vivo inflammation caused by various PAHs could be well predicted by the combined estimation using in vitro skin absorption and a keratinocyte bioassay. This study also established the structure-permeation relationship (SPR) of PAHs.

Impact of airborne particulate matter on skin: a systematic review from epidemiology to in vitro studies

BACKGROUND

Air pollution is killing close to 5 million people a year, and harming billions more. Air pollution levels remain extremely high in many parts of the world, and air pollution-associated premature deaths have been reported for urbanized areas, particularly linked to the presence of airborne nano-sized and ultrafine particles.

MAIN TEXT

To date, most of the research studies did focus on the adverse effects of air pollution on the human cardiovascular and respiratory systems. Although the skin is in direct contact with air pollutants, their damaging effects on the skin are still under investigation. Epidemiological data suggested a correlation between exposure to air pollutants and aggravation of symptoms of chronic immunological skin diseases. In this study, a systematic literature review was conducted to understand the current knowledge on the effects of airborne particulate matter on human skin. It aims at providing a deeper understanding of the interactions between air pollutants and skin to further assess their potential risks for human health.

CONCLUSION

Particulate matter was shown to induce a skin barrier dysfunction and provoke the formation of reactive oxygen species through direct and indirect mechanisms, leading to oxidative stress and induced activation of the inflammatory cascade in human skin. Moreover, a positive correlation was reported between extrinsic aging and atopic eczema relative risk with increasing particulate matter exposure.

Cancer risk among career male and female Florida firefighters: Evidence from the Florida Firefighter Cancer Registry (1981-2014)

BACKGROUND

Firefighters are at increased risk for select cancers. However, many studies are limited by relatively small samples, with virtually no data on the cancer experience of female firefighters. This study examines cancer risk in over 100,000 career Florida firefighters including 5000 + females assessed over a 34-year period.

METHODS

Florida firefighter employment records (n = 109 009) were linked with Florida Cancer Data System registry data (1981-2014; ~3.3 million records), identifying 3760 male and 168 female-linked primary cancers. Gender-specific age and calendar year-adjusted odds ratios (aOR) and 95% confidence intervals for firefighters vs non-firefighters were calculated.

RESULTS

Male firefighters were at increased risk of melanoma (aOR = 1.56; 1.39-1.76), prostate (1.36; 1.27-1.46), testicular (1.66; 1.34-2.06), thyroid (2.17; 1.78-2.66) and late-stage colon cancer (1.19;1.00-1.41). Female firefighters showed significantly elevated risk of brain (2.54; 1.19-5.42) and thyroid (2.42; 1.56-3.74) cancers and an elevated risk of melanoma that approached statistical significance (1.68; 0.97-2.90). Among male firefighters there was additional evidence of increased cancer risk younger than the age of 50 vs 50 years and older for thyroid (2.55; 1.96-3.31 vs 1.69; 1.22-2.34), prostate (1.88; 1.49-2.36 vs 1.36; 1.26-1.47), testicular (1.60; 1.28-2.01 vs 1.47; 0.73-2.94), and melanoma (1.87; 1.55-2.26 vs 1.42; 1.22-1.66) cancers.

CONCLUSION

Male career firefighters in Florida are at increased risk for five cancers with typically stronger associations in those diagnosed younger than the age of 50, while there was evidence for increased thyroid and brain cancer, and possibly melanoma risk in female firefighters. Larger cohorts with adequate female representation, along with the collection of well-characterized exposure histories, are needed to more precisely examine cancer risk in this occupational group.

Symurban Nanocrystals for Advanced Anti-Pollution Skincare

Several of most common dermatoses worldwide, e.g., psoriasis and atopic dermatitis, are worsened in their clinical picture when the skin is regularly exposed to an increased air pollution level, e.g., particulate matter. This is explainable by the activation of the aryl hydrocarbon receptor (AhR) in the skin, which results in an increased release of proinflammatory cytokines and matrix metalloproteinases. Symurban is a competitive AhR antagonist and thus allows the effective protection of skin. In order to improve its dermal bioavailability as a poorly soluble active agent (0.25 µg/mL), nanocrystals were prepared and evaluated. Nanocrystals are pure active crystals reduced in particle size to the submicron range of 100 to 1000 nm. They feature the properties of nanocrystals, such as increased saturation solubility and dissolution velocity, without having to be declared as nanomaterial. Production methods and parameters were systematically investigated. Wet bead milling at 2000 rpm for 30 min yielded the best results. A z-average of 280 nm was achieved for a 10% Symurban suspension with a polydispersity index of 0.20, indicating a narrow size distribution. For the long-term stabilization of the nanocrystal suspension, the performance of 15 surfactants of different categories and HLB values were investigated and evaluated. It was found that non-ionic surfactants in general were better able to stabilize the system than anionic or amphoteric surfactants. Highest stability of over 12 months at 25 °C was achieved with 2% Plantacare 810 UP, an ECOCERT surfactant with high skin tolerance. The suspension was also chemically long-term stable with >97% of remaining Symurban over 12 months. The saturation solubility of Symurban as nanocrystals was significantly increased from 0.25 to 2.9 μg/mL, which corresponds to a factor of >11. In a case study of one male volunteer with healthy skin conditions, penetration profiles of Symurban nanocrystal hydrogel and commercial anti-pollution serum containing an identical amount of Symurban were determined and compared. After 20 min of exposure, the relative Symurban concentration in the deeper skin layers (tape 19-30) was more than two times higher for nanocrystal hydrogel (16%) than the commercial serum (7%). These results suggest that nanocrystals are a promising delivery system for the poorly soluble anti-pollution agent Symurban.

The Aryl Hydrocarbon Receptor (AhR) in the Aging Process: Another Puzzling Role for This Highly Conserved Transcription Factor

Aging is the most important risk factor for the development of major life-threatening diseases such as cardiovascular disorders, cancer, and neurodegenerative disorders. The aging process is characterized by the accumulation of damage to intracellular macromolecules and it is concurrently shaped by genetic, environmental and nutritional factors. These factors influence the functionality of mitochondria, which play a central role in the aging process. Mitochondrial dysfunction is one of the hallmarks of aging and is associated with increased fluxes of ROS leading to damage of mitochondrial components, impaired metabolism of fatty acids, dysregulated glucose metabolism, and damage of adjacent organelles. Interestingly, many of the environmental (e.g., pollutants and other toxicants) and nutritional (e.g., flavonoids, carotenoids) factors influencing aging and mitochondrial function also directly or indirectly affect the activity of a highly conserved transcription factor, the Aryl hydrocarbon Receptor (AhR). Therefore, it is not surprising that many studies have already indicated a role of this versatile transcription factor in the aging process. We also recently found that the AhR promotes aging phenotypes across species. In this manuscript, we systematically review the existing literature on the contradictory studies indicating either pro- or anti-aging effects of the AhR and try to reconcile the seemingly conflicting data considering a possible dependency on the animal model, tissue, as well as level of AhR expression and activation. Moreover, given the crucial role of mitochondria in the aging process, we summarize the growing body of evidence pointing toward the influence of AhR on mitochondria, which can be of potential relevance for aging.

Kynurenine, a Tryptophan Metabolite That Increases with Age, Induces Muscle Atrophy and Lipid Peroxidation

The cellular and molecular mechanisms underlying loss of muscle mass with age (sarcopenia) are not well-understood; however, heterochronic parabiosis experiments show that circulating factors are likely to play a role. Kynurenine (KYN) is a circulating tryptophan metabolite that is known to increase with age and is a ligand of the aryl hydrocarbon receptor (Ahr). Here, we tested the hypothesis that KYN activation of Ahr plays a role in muscle loss with aging. Results indicate that KYN treatment of mouse and human myoblasts increased levels of reactive oxygen species (ROS) 2-fold and KYN treatment in vivo reduced muscle size and strength and increased muscle lipid peroxidation in young mice. PCR array data indicate that muscle fiber size reduction with KYN treatment reduces protein synthesis markers whereas ubiquitin ligase gene expression is not significantly increased. KYN is generated by the enzyme indoleamine 2,3-dioxygenase (IDO), and aged mice treated with the IDO inhibitor 1-methyl-D-tryptophan showed an increase in muscle fiber size and muscle strength. Small-molecule inhibition of Ahr in vitro, and Ahr knockout in vivo, did not prevent KYN-induced increases in ROS, suggesting that KYN can directly increase ROS independent of Ahr activation. Protein analysis identified very long-chain acyl-CoA dehydrogenase as a factor activated by KYN that may increase ROS and lipid peroxidation. Our data suggest that IDO inhibition may represent a novel therapeutic approach for the prevention of sarcopenia and possibly other age-associated conditions associated with KYN accumulation such as bone loss and neurodegeneration.

Particulate matter-induced senescence of skin keratinocytes involves oxidative stress-dependent epigenetic modifications

Ambient air particulate matter (PM) induces senescence in human skin cells. However, the underlying mechanisms remain largely unknown. We investigated how epigenetic regulatory mechanisms participate in cellular senescence induced by PM with a diameter <2.5 (PM2.5) in human keratinocytes and mouse skin tissues. PM2.5-treated cells exhibited characteristics of cellular senescence. PM2.5 induced a decrease in DNA methyltransferase (DNMT) expression and an increase in DNA demethylase (ten-eleven translocation; TET) expression, leading to hypomethylation of the p16INK4A promoter region. In addition, PM2.5 led to a decrease in polycomb EZH2 histone methyltransferase expression, whereas the expression of the epigenetic transcriptional activator MLL1 increased. Furthermore, binding of DNMT1, DNMT3B, and EZH2 to the promoter region of p16INK4A decreased in PM2.5-treated keratinocytes, whereas TET1 and MLL1 binding increased, leading to decreased histone H3 lysine 27 trimethylation (H3K27Me3) and increased H3K4Me3 in the promoter of p16INK4A. PM2.5-induced senescence involved aryl hydrocarbon receptor (AhR)-induced reactive oxygen species (ROS) production. ROS scavenging dampened PM2.5-induced cellular senescence through regulation of DNA and histone methylation. Altogether, our work shows that skin senescence induced by environmental PM2.5 occurs through ROS-dependent the epigenetic modification of senescence-associated gene expression. Our findings provide information for the design of preventive and therapeutic strategies against skin senescence, particularly in light of the increasing problem of PM2.5 exposure due to air pollution.

Skin inflammation induced by ambient particulate matter in China

Most published studies on particulate matter (PM) concerning PM_2.5 and PM₁₀ have focused on PM-induced effects on the respiratory system (particularly lung) and cardiovascular system effects. However, epidemiological and mechanistic studies suggest that PM_2.5 and PM₁₀ also affects the skin, which is a key health issue. In this study, we first reviewed the current status of PM_2.5 and PM₁₀ in China, including relevant regulations, concentration levels, chemical components, and emission sources. Next, we summarized the association between PM_2.5 and PM₁₀ or its representative components, in relation to skin inflammation as well as inflammatory skin diseases, such as atopic dermatitis, acne, eczema, and skin aging. Finally, we determined the mechanism of oxidative stress or programmed cell death induced through PM, which can provide useful information for future research on PM-induced skin inflammation.

Environmental Stressors on Skin Aging. Mechanistic Insights

The skin is the main barrier that protects us against environmental stressors (physical, chemical, and biological). These stressors, combined with internal factors, are responsible for cutaneous aging. Furthermore, they negatively affect the skin and increase the risk of cutaneous diseases, particularly skin cancer. This review addresses the impact of environmental stressors on skin aging, especially those related to general and specific external factors (lifestyle, occupation, pollutants, and light exposure). More specifically, we have evaluated ambient air pollution, household air pollutants from non-combustion sources, and exposure to light (ultraviolet radiation and blue and red light). We approach the molecular pathways involved in skin aging and pathology as a result of exposure to these external environmental stressors. Finally, we reflect on how components of environmental stress can interact with ultraviolet radiation to cause cell damage and the critical importance of knowing the mechanisms to develop new therapies to maintain the skin without damage in old age and to repair its diseases.

Protective effects of Camellia japonica flower extract against urban air pollutants

Background

Exposure of skin to urban air pollutants is closely related to skin aging and inflammatory responses such as wrinkles formation, pigmentation spot, atopic dermatitis, and acne. Thus, a great deal of interest has been focused on the development of natural resources that can provide a protective effect to skin from pollutants.

Methods

The antioxidative activity of Camellia japonica flower extract (CJFE) was evaluated by 1,2-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) assay, and the inhibitory effect of CJFE by urban air pollutants-induced reactive oxygen species (ROS) production was determined in cultured normal human dermal fibroblasts (NHDFs). We additionally investigated the protective effects of CJFE against urban air pollutant using in vitro and ex vivo model.

Results

CJFE with high phenolic concentration showed antioxidative activity on scavenging capacity of 1,2-diphenyl-2-picrylhydrazyl (DPPH) radicals and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical cation in a concentration dependent manner. CJFE inhibited urban air pollutants-induced ROS generation, matrixmetalloproteinase-1 (MMP-1) production and a xenobiotic response element (XRE)-luciferase activity indicating the aryl hydrocarbon receptor (AhR) transactivation. In addition, CJFE showed an excellent protective activity against pollutants-induced deteriorating effect in ex vivo model. CJFE reduced the level of pollutants-induced malondialdehyde (MDA), lipid peroxidation marker, inhibited MMP-1 expression and increased collagen synthesis. It also reduced the cell numbers with pyknotic nuclei (mainly occurring in apoptosis) and detachment of dermo-epidermal junction (DEJ) induced by pollutants.

Conclusions

Apparently, it is proposed that CJFE can be used as a protective material against pollutant-induced skin damages.

Electronic supplementary material

The online version of this article (10.1186/s12906-018-2405-4) contains supplementary material, which is available to authorized users.

Comparative Analysis of Zebrafish and Planarian Model Systems for Developmental Neurotoxicity Screens Using an 87-Compound Library

There is a clear need to establish and validate new methodologies to more quickly and efficiently screen chemicals for potential toxic effects, particularly on development. The emergence of alternative animal systems for rapid toxicology screens presents valuable opportunities to evaluate how systems complement each other. In this article, we compare a chemical library of 87-compounds in 2 such systems, developing zebrafish and freshwater planarians, by screening for developmental neurotoxic effects. We show that the systems' toxicological profiles are complementary to each other, with zebrafish yielding more detailed morphological endpoints and planarians more behavioral endpoints. Overall, zebrafish was more sensitive to this chemical library, yielding 86/87 hits, compared with 50/87 hits in planarians. The difference in sensitivity could not be attributed to molecular weight, log Kow, or the bioconcentration factor. Of the 87 chemicals, 28 had previously been evaluated in mammalian developmental neuro- (DNT), neuro-, or developmental toxicity studies. Of the 28, 20 were hits in the planarian, and 27 were hits in zebrafish. Eighteen of the 28 had previously been identified as DNT hits in mammals and were highly associated with activity in zebrafish and planarian behavioral assays in this study. Only 1 chemical (of 28) was a false negative in both zebrafish and planarian systems. The differences in endpoint coverage and system sensitivity illustrate the value of a dual systems approach to rapidly query a large chemical-bioactivity space and provide weight-of-evidence for prioritization of chemicals for further testing.

The increase of interfollicular epidermal stem cells and regulation of aryl hydrocarbon receptor and its repressors in the skin through hydroporation with anti-aging cocktail

BACKGROUNDS

Hydroporation is a procedure that involves a subsonic flow of air and microdroplets into the skin. We previously reported that hydroporation treatment with a cocktail solution containing copper-glycyl-L-histidyl-L-lysyl, oligo hyaluronic acid, rhodiola extract, tranexamic acid, and β-glucan yielded positive effects on skin aging.

OBJECTIVES

The aim of this study was to evaluate the effects of hydroporation with anti-aging cocktail on interfollicular epidermal stem cells (IFESCs) and expression of aryl hydrocarbon receptor (AhR)/AhR repressor (AhRR) in the skin.

METHODS

Skin samples from six volunteers who were treated with hydroporation were analyzed via confocal microscopic examination.

RESULTS

Markers for dermal matrix (procollagen type I and fibrillin-1) and basement membrane (type IV collagen and integrin α6) were increased after treatment. Moreover, there was a significant increase in the expression level of histone deacetylase 1-positive/p63-negative basal cells, which we previously reported as interfollicular epidermal stem cells. The expression level of AhR was significantly decreased, whereas that of AhRR was increased. This indicates an alteration in the interaction between the skin and environment posttreatment.

CONCLUSION

Anti-aging hydroporation treatment recovered the stem cell potential of basal cells. Moreover, this treatment decreased AhR and increased AhRR in the skin, which may protect the skin from the harmful environment.

PM2.5 induces autophagy-mediated cell death via NOS2 signaling in human bronchial epithelium cells

The biggest victim of ambient air pollution is the respiratory system. Mainly because of the harmful components, especially the particulate matters with an aerodynamic diameter of ≤ 2.5µm (PM2.5), can be directly inhaled and deeply penetrate into the lung alveoli, thus causing severe lung dysfunction, including chronic cough, bronchitis and asthma, even lung cancer. Unfortunately, the toxicological mechanisms of PM2.5 associations with these adverse respiratory outcomes have still not been clearly unveiled. Here, we found that PM2.5 rapidly induced inflammatory responses, oxidative injure and cell death in human bronchial epithelium cells through upregulation of IL-6 expression, ROS production and apoptosis. Furthermore, PM2.5 specifically induced nitric oxide synthase 2 (NOS2) expression and NO generation to elevate excessive autophagy. Finally, disruption of NOS2 signaling effectively blocked autophayosome formation and the subsequent cell death. Our novel findings systemically reveled the role of autophagy-mediated cell death in PM2.5-treated human bronchial epithelium cells and provided potential strategy for future clinic intervention.