In vitro dermal penetration of nickel nanoparticles

Current research on ecotoxicity of metal-based nanoparticles: from exposure pathways, ecotoxicological effects to toxicity mechanisms

Metal-based nanoparticles have garnered significant usage across industries, spanning catalysis, optoelectronics, and drug delivery, owing to their diverse applications. However, their potential ecological toxicity remains a crucial area of research interest. This paper offers a comprehensive review of recent advancements in studying the ecotoxicity of these nanoparticles, encompassing exposure pathways, toxic effects, and toxicity mechanisms. Furthermore, it delves into the challenges and future prospects in this research domain. While some progress has been made in addressing this issue, there is still a need for more comprehensive assessments to fully understand the implications of metal-based nanoparticles on the environment and human well-being.

Bioaccessibility of Metallic Nickel and Nickel Oxide Nanoparticles in Four Simulated Biological Fluids

Bioaccessibility of metals from substances and alloys is increasingly used as part of the assessment to predict potential toxicity. However, data are sparse on the metal bioaccessibility from nanoparticle (NP) size metal substances. This study examines nickel ion release from metallic nickel and nickel oxide micron particles (MPs) and NPs in simulated biological fluids at various timepoints including those relevant for specific routes of exposure. The results suggest that MPs of both metallic nickel and nickel oxide generally released more nickel ions in acidic simulated biological fluids (gastric and lysosomal) than NPs of the same substance, with the largest differences being for nickel oxide. In more neutral pH fluids (interstitial and perspiration), nickel metal NPs released more nickel ions than MPs, with nickel oxide results showing a higher release for MPs in interstitial fluid yet a lower release in perspiration fluid. Various experimental factors related to the particle, fluid, and extraction duration were identified that can have an impact on the particle dissolution and release of nickel ions. Overall, the results suggest that based on nickel release alone, nickel NPs are not inherently more hazardous than nickel MPs. Moreover, analyses should be performed on a case-by-case basis with consideration of various experimental factors and correlation with in vivo data.

The pulmonary effects of nickel-containing nanoparticles: Cytotoxicity, genotoxicity, carcinogenicity, and their underlying mechanisms

With the exponential growth of the nanotechnology field, the global nanotechnology market is on an upward track with fast-growing jobs. Nickel (Ni)-containing nanoparticles (NPs), an important class of transition metal nanoparticles, have been extensively used in industrial and biomedical fields due to their unique nanostructural, physical, and chemical properties. Millions of people have been/are going to be exposed to Ni-containing NPs in occupational and non-occupational settings. Therefore, there are increasing concerns over the hazardous effects of Ni-containing NPs on health and the environment. The respiratory tract is a major portal of entry for Ni-containing NPs; thus, the adverse effects of Ni-containing NPs on the respiratory system, especially the lungs, have been a focus of scientific study. This review summarized previous studies, published before December 1, 2023, on cytotoxic, genotoxic, and carcinogenic effects of Ni-containing NPs on humans, lung cells in vitro, and rodent lungs in vivo, and the potential underlying mechanisms were also included. In addition, whether these adverse effects were induced by NPs themselves or Ni ions released from the NPs was also discussed. The extra-pulmonary effects of Ni-containing NPs were briefly mentioned. This review will provide us with a comprehensive view of the pulmonary effects of Ni-containing NPs and their underlying mechanisms, which will shed light on our future studies, including the urgency and necessity to produce engineering Ni-containing NPs with controlled and reduced toxicity, and also provide the scientific basis for developing nanoparticle exposure limits and policies.

Probing the effectiveness of barrier creams against human skin penetration of nickel powder

OBJECTIVE

Barrier creams (BCs) are marketed as locally applied medical devices or cosmetic products to protect the skin from exposure to chemicals and irritants. Generally, the mechanism of action of such products is mainly due to the formation of a superficial thin film between the skin and the irritant or sensitizer, thus reducing or totally blocking the cutaneous penetration of such agents. Specifically, studies focusing on the effectiveness of commercial protective creams to prevent nickel cutaneous penetration are extremely scarce. The aim of the current work, therefore, is to evaluate the protective role of a commercially available barrier cream for nickel and compare the results with a simple moisturizing, following exposure to Ni powder.

METHODS

Marketed BCs were evaluated and tested. Human skin absorption of Ni was studied in vitro using static Franz diffusion cells.

RESULTS

Our results demonstrate that the application of both formulations caused a reduction of Ni inside the skin (8.00 ± 3.35 μg cm-2 for the barrier cream and 22.6 ± 12.6 μg cm-2 for the general moisturizing product), with the specialized barrier cream being statistically (p = 0.015) more efficient on forming a protective barrier, thus evidencing the importance of some ingredients in such formulations on the nickel dermal accumulation.

CONCLUSIONS

The composition of the formulations based on film-forming or chelating agents may play an imperative role in reducing the cutaneous penetration of Ni.

A State-of-the-Science Review on Metal Biomarkers

PURPOSE OF REVIEW

Biomarkers are commonly used in epidemiological studies to assess metals and metalloid exposure and estimate internal dose, as they integrate multiple sources and routes of exposure. Researchers are increasingly using multi-metal panels and innovative statistical methods to understand how exposure to real-world metal mixtures affects human health. Metals have both common and unique sources and routes of exposure, as well as biotransformation and elimination pathways. The development of multi-element analytical technology allows researchers to examine a broad spectrum of metals in their studies; however, their interpretation is complex as they can reflect different windows of exposure and several biomarkers have critical limitations. This review elaborates on more than 500 scientific publications to discuss major sources of exposure, biotransformation and elimination, and biomarkers of exposure and internal dose for 12 metals/metalloids, including 8 non-essential elements (arsenic, barium, cadmium, lead, mercury, nickel, tin, uranium) and 4 essential elements (manganese, molybdenum, selenium, and zinc) commonly used in multi-element analyses.

RECENT FINDINGS

We conclude that not all metal biomarkers are adequate measures of exposure and that understanding the metabolic biotransformation and elimination of metals is key to metal biomarker interpretation. For example, whole blood is a good biomarker of exposure to arsenic, cadmium, lead, mercury, and tin, but it is not a good indicator for barium, nickel, and uranium. For some essential metals, the interpretation of whole blood biomarkers is unclear. Urine is the most commonly used biomarker of exposure across metals but it should not be used to assess lead exposure. Essential metals such as zinc and manganese are tightly regulated by homeostatic processes; thus, elevated levels in urine may reflect body loss and metabolic processes rather than excess exposure. Total urinary arsenic may reflect exposure to both organic and inorganic arsenic, thus, arsenic speciation and adjustment for arsebonetaine are needed in populations with dietary seafood consumption. Hair and nails primarily reflect exposure to organic mercury, except in populations exposed to high levels of inorganic mercury such as in occupational and environmental settings. When selecting biomarkers, it is also critical to consider the exposure window of interest. Most populations are chronically exposed to metals in the low-to-moderate range, yet many biomarkers reflect recent exposures. Toenails are emerging biomarkers in this regard. They are reliable biomarkers of long-term exposure for arsenic, mercury, manganese, and selenium. However, more research is needed to understand the role of nails as a biomarker of exposure to other metals. Similarly, teeth are increasingly used to assess lifelong exposures to several essential and non-essential metals such as lead, including during the prenatal window. As metals epidemiology moves towards embracing a multi-metal/mixtures approach and expanding metal panels to include less commonly studied metals, it is important for researchers to have a strong knowledge base about the metal biomarkers included in their research. This review aims to aid metals researchers in their analysis planning, facilitate sound analytical decision-making, as well as appropriate understanding and interpretation of results.

Nickel ions influence the transepithelial sodium transport in the trachea, intestine and skin

Measurements of transepithelial potential and resistance in tissue and organ model systems enable the evaluation of the Ni2+ effect on the epithelial sodium channels, aquaporin 3, and the sodium-potassium pump in the epithelial cells. The aim of the presented study was to assess the immediate and prolonged effect of nickel ions on the transport of sodium ions in tissues exposed to direct contact with nickel, including airways, digestive tract and the skin. The influence of 0.1 mM nickel solution was performed on the trachea (n = 34), intestine (n = 44), and skin (n = 51) samples descended from 16 New Zealand albino rabbits. The electrophysiological parameters were measured in a modified Ussing chamber in stationary conditions and during a 15-s mechanical-chemical stimulation. A statistically significant decrease in the electric resistance values and the smallest range of the measured potential were observed for the Ni-treated trachea specimens. The use of nickel solution did not affect the sodium transport in the intestine epithelium. The skin fragments showed altered sodium ion transport, as demonstrated by the lower range and intensity of the measured potential. The gastrointestinal tract seems to be an organ best adapted to contact with nickel ions. In airways, nickel ions most likely enter epithelial cells and the space between them, modifying proteins and the airway surface liquid. The skin turned out to be the most sensitive tissue to the intensification of sodium ion transport through nickel ions.

Evaluating the role of protective creams on the cutaneous penetration of Ni nanoparticles

There is an increase of application of Nickel in the form of nanoparticles (NiNPs) in several fields including modern metallurgy, bioengineering, and medicine. Such growth of the areas of application is actually accompanied with an increase of exposure to Nickel, thus an intensification of the negative effects, the most frequent being the allergic contact dermatitis. Indeed, due to their smaller size, and therefore their higher surface area, NiNPs can release more Ni ions compared to bulk material, that can penetrate and permeate through the skin. To reduce the Ni cutaneous penetration, barrier creams (BC) are applied on the skin surface. There is little information, however, on the efficiency of such commercial protective creams on decreasing Ni cutaneous penetration. For this reason, the objective of the current study was to investigate the protective role of one commercially available formulation for Ni (Nik-L-Block™ containing a chelating agent) and one moisturizing cream (Ceramol 311 basic cream without chelating agent), following exposure to NiNPs, using in vitro Franz cells, as well as the cytotoxicity of NiNPs in primary human dermal fibroblasts was studied. Our results demonstrated that although both tested formulations can decrease Ni accumulation in the skin (4.13 ± 1.74 μg/cm² for Nik-L-Block™ and 7.14 ± 1.46 μg/cm² for Ceramol 311 basic cream); there are significant differences between the two creams (p = 0.004). Based on the experimental evidence, we therefore conclude that the composition of such formulations has an imperative role for dermal uptake of Ni. Finally, NiNPs showed no cytotoxic effect on cultured human dermal fibroblasts after 24 and 72 h.

Skin absorption of inorganic nanoparticles and their toxicity: A review

The role of inorganic nanoparticles in our society is increasing every day, from its use in sunscreens to their introduction in analytical laboratories, pharmacy, medicine, agricultural and other uses. Therefore, in order to establish precautions as well as correct handling of this type of material by operators, it is important to determine the ability of these compounds to travel through the different layers of the skin and to study their possible toxicological effects. In this sense, several authors have studied the ability of inorganic nanoparticles to penetrate the skin barrier by diverse methodologies in in vivo and in vitro modes. In the first case, most of the studies have been performed with animal skins that can imitate the human one (porcine, mouse and guinea pigs, among others), although human skin from surgery have been also explored. However, the use of animals is a common model that should be avoided in the following years due to ethical issues. In this sense, the use of in vitro methodologies is also usually selected to study the dermal absorption of nanoparticles through the skin. Nevertheless, most of the studies are performed with authentic animal skins, instead of the use of synthetic skins that imitate the permeability of our skin system, which has been scarcely studied. In addition, most of the literature is focused in achieving high-transdermal uptake to use nanoparticles (not only inorganic) as carriers for drugs, but little efforts have been done in the study of their inherent percutaneous absorption and toxicity. For these reasons, this review covers the current state-of-the-art of dermal absorption of inorganic nanoparticles in skin and their possible toxicity taking into account that people can be in contact with these nanomaterials in daily life, work or other places. In this sense, the observed results showed that the nanoparticles rarely reach the blood circulatory system, and no big toxicological effects were commonly found when in vivo and actual skin was used. In addition, similar results were found when synthetic skins were used, demonstrating the possibility of avoiding animals in these studies. In any case, more studies covering the dermal absorption of nanoparticles should be performed to have a better understanding of how nanoparticles can affect our health.

Nickel penetration into stratum corneum in FLG null carriers - a human experimental study

Background

The filaggrin gene (FLG) plays a role in skin diseases, with the skin barrier function being impaired in FLG null carriers. The role of FLG status in relation to nickel penetration into the skin remains unclear.

Objectives

To elucidate the association between FLG status and nickel penetration into stratum corneum (SC) in individuals without self‐reported history of nickel allergy.

Methods

Forty participants (23 FLG wt and 17 FLG null) were exposed to a nickel solution (80 μg/cm²) which was applied onto 2 × 2 cm on their left forearm. After 4 h, the area was tape‐stripped with 10 consecutive tapes. Nickel in each tape was quantified using inductively coupled plasma mass spectrometry.

Results

The average recovered nickel dose was 35%–48%. A tendency towards lower recovery was seen in FLG null carriers compared to FLG wt carriers, and lower recovery in those with history of skin and/or respiratory symptoms compared to those without such history. This was however not statistically significant.

Conclusion

FLG null carriers had less nickel recovered by tape strips compared with FLG wt carriers and, compared with individuals without a history of skin and/or respiratory symptoms, indicating higher nickel penetration into SC for FLG null carriers, but further studies are needed.

Percutaneous metals absorption following exposure to road dust powder

The skin constitutes a protective barrier to external physical and chemical aggressions. Although it is constantly exposed to various xenobiotics, it is generally considered poorly permeable to them, as for example metal ions, becoming unfortunately an entry route of such substances. Metals may penetrate inside the skin inducing more or less local effects such as skin sensitization and potential metals diffusion into the bloodstream. The objective of the study was to investigate the percutaneous penetration of metals in vitro - ex vivo in Franz cell with intact as well damaged skin applying a road dust powder. Moreover, porcine and human skins were compared. This study demonstrated that, after the application of a road dust powder on the skin, metals can penetrate and permeate this cutaneous membrane. From this experimental analysis, in intact skin lead (Pb) achieved the highest skin absorption in both human and porcine skin, while skin absorption profile of cobalt (Co) was the lowest in human skin than the one in porcine model. The concentrations of Ni present in receiving solution were higher compared to other metals in all experiments performed. The present work, definitely shows that metals permeation through damaged skin is accelerated than intact skin, as a result of the weaker cutaneous barrier function. According to published data, pig skin appeared as a suitable model for human skin. Our results confirmed that skin absorption of metals can be relevant in environmental exposures.

Skin permeation of nickel, cobalt and chromium salts in ex vivo human skin, visualized using mass spectrometry imaging

Skin permeation and distribution of three of the most common skin sensitizers was investigated using a previously developed animal-free exposure method combined with imaging mass spectrometry. Nickel, cobalt, and chromium (III) salts were dissolved in a buffer and exposed to human skin ex vivo, to be analyzed using time of flight secondary ion mass spectrometry (ToF-SIMS). Our findings demonstrate that metal haptens mainly accumulated in the stratum corneum, however all three metal sensitizers could also be detected in the epidermis. Cobalt and chromium (III) species penetrated into the epidermis to a larger extent than nickel species. The degree of penetration into the epidermis is suggested to be affected by the sensitization potency of the metal salts, as well as their speciation, i.e. the amount of the respective metal present in the solution as bioaccessible and solubilised ions. Our method provided permeation profiles in human skin for known sensitizers, on a level of detail that is not possible to achieve by other means. The findings show that the permeation profiles are different, despite these sensitizers being all metal ions and common causes of contact allergy. Studying skin uptake by only considering penetration through the skin might therefore not give accurate results.

Effects of metal nanoparticles on tight junction-associated proteins via HIF-1α/miR-29b/MMPs pathway in human epidermal keratinocytes

Background

The increasing use of metal nanoparticles in industry and biomedicine raises the risk for unintentional exposure. The ability of metal nanoparticles to penetrate the skin ranges from stopping at the stratum corneum to passing below the dermis and entering the systemic circulation. Despite the potential health risks associated with skin exposure to metal nanoparticles, the mechanisms underlying the toxicity of metal nanoparticles on skin keratinocytes remain unclear. In this study, we proposed that exposure of human epidermal keratinocytes (HaCaT) to metal nanoparticles, such as nickel nanoparticles, dysregulates tight-junction associated proteins by interacting with the HIF-1α/miR-29b/MMPs axis.

Methods

We performed dose-response and time-response studies in HaCaT cells to observe the effects of Nano-Ni or Nano-TiO₂ on the expression and activity of MMP-2 and MMP-9, and on the expression of tight junction-associated proteins, TIMP-1, TIMP-2, miR-29b, and HIF-1α. In the dose-response studies, cells were exposed to 0, 10, or 20 μg/mL of Nano-Ni or Nano-TiO₂ for 24 h. In the time-response studies, cells were exposed to 20 μg/mL of Nano-Ni for 12, 24, 48, or 72 h. After treatment, cells were collected to either assess the expression of mRNAs and miR-29b by real-time PCR or to determine the expression of tight junction-associated proteins and HIF-1α nuclear accumulation by Western blot and/or immunofluorescent staining; the conditioned media were collected to evaluate the MMP-2 and MMP-9 activities by gelatin zymography assay. To further investigate the mechanisms underlying Nano-Ni-induced dysregulation of tight junction-associated proteins, we employed a HIF-1α inhibitor, CAY10585, to perturb HIF-1α accumulation in one experiment, and transfected a miR-29b-3p mimic into the HaCaT cells before Nano-Ni exposure in another experiment. Cells and conditioned media were collected, and the expression and activities of MMPs and the expression of tight junction-associated proteins were determined as described above.

Results

Exposure of HaCaT cells to Nano-Ni resulted in a dose-dependent increase in the expression of MMP-2, MMP-9, TIMP-1, and TIMP-2 and the activities of MMP-2 and MMP-9. However, exposure of cells to Nano-TiO₂ did not cause these effects. Nano-Ni caused a dose-dependent decrease in the expression of miR-29b and tight junction-associated proteins, such as ZO-1, occludin, and claudin-1, while Nano-TiO₂ did not. Nano-Ni also caused a dose-dependent increase in HIF-1α nuclear accumulation. The time-response studies showed that Nano-Ni caused significantly increased expressions of MMP-2 at 24 h, MMP-9 at 12, 24, and 48 h, TIMP-1 from 24 to 72 h, and TIMP-2 from 12 to 72 h post-exposure. The expression of miR-29b and tight junction-associated proteins such as ZO-1, occludin, and claudin-1 decreased as early as 12 h post-exposure, and their levels declined gradually over time. Pretreatment of cells with a HIF-1α inhibitor, CAY10585, abolished Nano-Ni-induced miR-29b down-regulation and MMP-2/9 up-regulation. Introduction of a miR-29b-3p mimic into HaCaT cells by transfection before Nano-Ni exposure ameliorated Nano-Ni-induced increased expression and activity of MMP-2 and MMP-9 and restored Nano-Ni-induced down-regulation of tight junction-associated proteins.

Conclusion

Our study herein demonstrated that exposure of human epidermal keratinocytes to Nano-Ni caused increased HIF-1α nuclear accumulation and increased transcription and activity of MMP-2 and MMP-9 and down-regulation of miR-29b and tight junction-associated proteins. Nano-Ni-induced miR-29b down-regulation was through Nano-Ni-induced HIF-1α nuclear accumulation. Restoration of miR-29b level by miR-29b-3p mimic transfection abolished Nano-Ni-induced MMP-2 and MMP-9 activation and down-regulation of tight junction-associated proteins. In summary, our results demonstrated that Nano-Ni-induced dysregulation of tight junction-associated proteins in skin keratinocytes was via HIF-1α/miR-29b/MMPs pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00405-2.

Dermal absorption of gallium antimonide in vitro and pro-inflammatory effects on human dermal fibroblasts

Gallium antimonide (GaSb) is a group III-V compound semiconductor with a comparatively narrow band gap energy (0.73 eV at 300 K) that allows efficient operation in the near-infrared region. This property may be useful in developing new biomedical instruments such as epidermal optoelectronic devices. The present study investigated the absorption of GaSb in pig skin in vitro for 24 h using Franz cells. A donor solution was prepared by soaking GaSb thin films in synthetic sweat. The results showed that both gallium and antimony penetrated the skin, and permeation and resorption occurred for gallium. Histopathological findings showed no inflammatory responses in pig skin exposed to GaSb for 24 h. Cytotoxicity was significantly elevated after 3 and 7 days, and pro-inflammatory cytokines and IL-8 levels were low after 1 and 3 days but elevated 7 days following the direct culturing of human dermal fibroblasts (HDF) on GaSb thin films. These results demonstrate that the short-term cytotoxicity and pro-inflammatory effect of GaSb on HDF were relatively low.

A review to support the derivation of a worst-case dermal penetration value for nanoparticles

Data on dermal penetration of nanoparticles (NPs) was reviewed with the goal to establish a worst-case dermal penetration value for NPs. To this aim, the main focus was on studies providing quantitative dermal penetration data (29 studies). In vivo dermal penetration studies and ex vivo studies based on skin explants were included. These studies used NPs with different compositions, dimensions, and shapes. The overall results showed that skin is an efficient barrier for NPs, indistinctly of their properties. However, some studies reported that a small percentage of the applied NP dose penetrated the skin surface and reached deeper skin layers. The integrity of the skin layer and the product formulation were more critical determinants of dermal penetration than the NP properties. Most quantitative studies were based on elemental analysis such that it cannot be concluded if detected levels are attributable to a dissolved fraction or to the penetration of particles as such. Results of qualitative imaging studies suggest that at least a fraction of the levels reported in quantitative studies could be due to particle penetration. Altogether, based on the data compiled, we propose that 1% could be used as a worst-case dermal penetration value for nanoparticles within the boundaries of the properties of those included in our analysis.

Peptide bond cleavage in the presence of Ni-containing particles

NiO nanoparticles and non-stoichiometric black NiO were shown to be effective sources of Ni2+ ions causing sequence-selective peptide bond hydrolysis. NiO nanoparticles were as effective in this reaction as their molar equivalent of soluble Ni(ii) salt. These findings highlight the efficacy of delivery of toxic Ni2+ by these environmentally available particles.

Toxicity of binary mixtures of Al2O3 and ZnO nanoparticles toward fibroblast and bronchial epithelium cells

The objective of this study was to examine the cytotoxic effects of binary mixtures of Al₂O₃ and ZnO NPs using mouse fibroblast cells (L929) and human bronchial epithelial cells (BEAS-2B) as biological test systems. The synergistic, additive, or antagonistic behavior of the binary mixture was also investigated. In toxicity experiments, cellular morphology, mitochondrial function (MTT assay), apoptosis, nuclear size and shape, clonogenic assays, and damage based upon oxidative stress parameters were assessed under control and NPs exposure conditions. Although Abbott modeling results provided no clear evidence of the binary mixture of Al₂O₃ and ZnO NPs exhibiting synergistic toxicity, some specific assays such as apoptosis, nuclear size and shape, clonogenic assay, activities of antioxidant enzymatic enzymes catalase, superoxide dismutase, and levels of glutathione resulted in enhanced toxicity for the mixtures with 1 and 1.75 toxic units (TU) toward both cell types. Data demonstrated that co-presence of Al₂O₃ and ZnO NPs in the same environment might lead to more realistic environmental conditions. Our findings indicate cytotoxicity of binary mixtures of Al₂O₃ and ZnO NPs produced greater effects compared to toxicity of either individual compound.

Metal nanomaterials: Immune effects and implications of physicochemical properties on sensitization, elicitation, and exacerbation of allergic disease

The recent surge in incorporation of metallic and metal oxide nanomaterials into consumer products and their corresponding use in occupational settings have raised concerns over the potential for metals to induce size-specific adverse toxicological effects. Although nano-metals have been shown to induce greater lung injury and inflammation than their larger metal counterparts, their size-related effects on the immune system and allergic disease remain largely unknown. This knowledge gap is particularly concerning since metals are historically recognized as common inducers of allergic contact dermatitis, occupational asthma, and allergic adjuvancy. The investigation into the potential for adverse immune effects following exposure to metal nanomaterials is becoming an area of scientific interest since these characteristically lightweight materials are easily aerosolized and inhaled, and their small size may allow for penetration of the skin, which may promote unique size-specific immune effects with implications for allergic disease. Additionally, alterations in physicochemical properties of metals in the nano-scale greatly influence their interactions with components of biological systems, potentially leading to implications for inducing or exacerbating allergic disease. Although some research has been directed toward addressing these concerns, many aspects of metal nanomaterial-induced immune effects remain unclear. Overall, more scientific knowledge exists in regards to the potential for metal nanomaterials to exacerbate allergic disease than to their potential to induce allergic disease. Furthermore, effects of metal nanomaterial exposure on respiratory allergy have been more thoroughly-characterized than their potential influence on dermal allergy. Current knowledge regarding metal nanomaterials and their potential to induce/exacerbate dermal and respiratory allergy are summarized in this review. In addition, an examination of several remaining knowledge gaps and considerations for future studies is provided.

Cerium Oxide Nanoparticles Absorption through Intact and Damaged Human Skin

Cerium oxide (CeO2) nanoparticles (NPs) are used in polishing products and absorbents, as promoters in wound healing, and as organopesticide decontaminants. While systemic bioaccumulation and organ toxicity has been described after inhalation, data on CeO2 NPs' transdermal permeation are lacking. Our study was an in vitro investigation of the permeation of 17-nm CeO2 NPs dispersed in synthetic sweat (1 g L-1) using excised human skin on Franz cells. Experiments were performed using intact and needle-abraded skin, separately. The average amount of Ce into intact and damaged skin samples was 3.64 ± 0.15 and 7.07 ± 0.78 µg cm-2, respectively (mean ± SD, p = 0.04). Ce concentration in the receiving solution was 2.0 ± 0.4 and 3.3 ± 0.7 ng cm-2 after 24 h (p = 0.008). The Ce content was higher in dermal layers of damaged skin compared to intact skin (2.93 ± 0.71 µg cm-2 and 0.39 ± 0.16 µg cm-2, respectively; p = 0.004). Our data showed a very low dermal absorption and transdermal permeation of cerium, providing a first indication of Ce skin uptake due to contact with CeO2.

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.

CuO nanoparticle penetration through intact and damaged human skin

Trans-dermal in vitro study of CuO nanoparticles in contact with intact and damaged human skin using a Franz cell model.

Chemical-induced contact allergy: from mechanistic understanding to risk prevention

Chemical allergens are small molecules able to form a sensitizing complex once they bound to proteins. One of the most frequent manifestations of chemical allergy is contact hypersensitivity, which can have serious impact on quality of life. Allergic contact dermatitis is a predominantly CD8 + T cell-mediated immune disease, resulting in erythema and eczema. Chemical allergy is of considerable importance to the toxicologist, who has the responsibility of identifying and characterizing the allergenic potential of chemicals, and estimating the risk they pose to human health. This review aimed at exploring the phenomena of chemical-induced contact allergy starting from a mechanistic understanding, immunoregulatory mechanisms, passing through the potency of contract allergen until the hazard identification, pointing out the in vitro models for assessing contact allergen-induced cell activation and the risk prevention.

Evaluation of immunoresponses and cytotoxicity from skin exposure to metallic nanoparticles

Nanotechnology is an interdisciplinary science that has developed rapidly in recent years. Metallic nanoparticles (NPs) are increasingly utilized in dermatology and cosmetology, because of their unique properties. However, skin exposure to NPs raises concerns regarding their transdermal toxicity. The tight junctions of epithelial cells form the skin barrier, which protects the host against external substances. Recent studies have found that NPs can pass through the skin barrier into deeper layers, indicating that skin exposure is a means for NPs to enter the body. The distribution and interaction of NPs with skin cells may cause toxic side effects. In this review, possible penetration pathways and related toxicity mechanisms are discussed. The limitations of current experimental methods on the penetration and toxic effects of metallic NPs are also described. This review contributes to a better understanding of the risks of topically applied metallic NPs and provides a foundation for future studies.

Isotope Tracers To Study the Environmental Fate and Bioaccumulation of Metal-Containing Engineered Nanoparticles: Techniques and Applications

The rapidly growing applicability of metal-containing engineered nanoparticles (MENPs) has made their environmental fate, biouptake, and transformation important research topics. However, considering the relatively low concentration of MENPs and the high concentration of background metals in the environment and in organisms, tracking the fate of MENPs in environment-related scenarios remains a challenge. Intrinsic labeling of MENPs with radioactive or stable isotopes is a useful tool for the highly sensitive and selective detection of MENPs in the environment and organisms, thus enabling tracing of their transformation, uptake, distribution, and clearance. In this review, we focus on radioactive/stable isotope labeling of MENPs for their environmental and biological tracing. We summarize the advantages of intrinsic radioactive/stable isotopes for MENP labeling and discuss the considerations in labeling isotope selection and preparation of labeled MENPs, as well as exposure routes and detection of labeled MENPs. In addition, current practice in the use of radioactive/stable isotope labeling of MENPs to study their environmental fate and bioaccumulation is reviewed. Future perspectives and potential applications are also discussed, including imaging techniques for radioactive- and stable-isotope-labeled MENPs, hyphenated multistable isotope tracers with speciation analysis, and isotope fractionation as a MENP tracer. It is expected that this critical review could provide the necessary background information to further advance the applications of isotope tracers to study the environmental fate and bioaccumulation of MENPs.

Recent advances in green nanoparticulate systems for drug delivery: efficient delivery and safety concern

Nanotechnology manipulates therapeutic agents at the nanoscale for the development of nanomedicines. However, there are current concerns over nanomedicines, mainly related to the possible toxicity of nanomaterials used for health medications. Due to their small size, they can enter the human body more readily than larger sized particles. Green chemistry encompasses the green synthesis of drug-loaded nanoparticles by reducing the use of hazardous materials in the synthesis process, thus reducing the adverse health impacts of pharmaceutics. This would greatly expand their potential in biomedical treatments. This review highlights the potential risks of nanomedicine formulations to health, delivery routes of green nanomedicines, recent advances in the development of green nanoscale systems for biomedical applications and future perspectives for the green development of nanomedicines.