In vivo and in vitro skin absorption of lipophilic compounds, dibutyl phthalate, farnesol and geraniol in the hairless guinea pig

Endocrine adverse effects of mono(2-ethylhexyl) phthalate and monobutyl phthalate in male pubertal rats

Considering that research of adverse effects of mono(2-ethylhexyl) phthalate (MEHP) and monobutyl phthalate (MBP), two key metabolites of the most common phthalates used as plasticisers in various daily-life products, has been scattered and limited, the aim of our study was to provide a more comprehensive analysis by focusing on major organ systems, including blood, liver, kidney, and pancreas in 66 male pubertal rats randomised into eleven groups of six. The animals were receiving either metabolite at doses of 25, 50, 100, 200, or 400 mg/kg bw a day by gavage for 28 days. The control group was receiving corn oil. At the end of the experiment, blood samples were collected for biochemical, haematological, and immunological analyses. Samples of kidney, liver, and pancreas were dissected for histopathological analyses. Exposure to either compound resulted in increased liver and decreased pancreas weight, especially at the highest doses. Exposed rats had increased ALT, AST, glucose, and triglyceride levels and decreased total protein and albumin levels. Both compounds increased MCV and decreased haemoglobin levels compared to control. Although they also lowered the insulin level, exposed rats had negative islet cell and insulin antibodies, same as control. Treatment-related histopathological changes included sinusoidal degeneration in the liver, glomerular degeneration in the kidney, and degeneration of pancreatic islets. Our findings document toxic outcomes of MEHP and MBP on endocrine organs in male pubertal rats but also suggest the need for additional studies to better understand the mechanisms behind adverse effects in chronic exposure.

Pharmacokinetics and the Dermal Absorption of Bromochlorophene, a Cosmetic Preservative Ingredient, in Rats

The cosmetic industry has flourished in recent years. Accordingly, the safety of cosmetic ingredients is increasing. Bromochlorophene (BCP) is a commonly used cosmetic preservative. To evaluate the effects of BCP exposure, in vitro dermal absorption and in vivo pharmacokinetic (PK) studies were conducted using gel and cream formulations. The Franz diffusion cell system and rat dorsal skin were used for tests according to the Korea Ministry of Food and Drug Safety guidelines for in vitro skin absorption methods. After the dermal application (1.13 mg/cm²) of BCP in the gel and cream formulations, liquid chromatography–mass spectrometry (LC–MS/MS) was used to evaluate the amount of BCP that remained unabsorbed on the skin (WASH), and that was present in the receptor fluid (RF), stratum corneum (SC), and (epi)dermis (SKIN). The total dermal absorption rate of BCP was 7.42 ± 0.74% for the gel formulation and 1.5 ± 0.9% for the cream formulation. Total recovery in an in vitro dermal absorption study was 109.12 ± 8.79% and 105.43 ± 11.07% for the gel and cream formulations, respectively. In vivo PK and dermal absorption studies of BCP were performed following the Organization for Economic Cooperation and Development guidelines 417 and 427, respectively. When intravenous (i.v.) pharmacokinetics was performed, BCP was dissolved in glycerol formal and injected into the tail vein (n = 3) of the rats at doses of 1 and 0.2 mg/kg. Dermal PK parameters were estimated by the application of the gel and cream formulations (2.34 mg/kg of BCP as an active ingredient) to the dorsal skin of the rats. Intravenous and dermal PK parameters were analyzed using a non-compartmental method. The dermal bioavailability of BCP was determined as 12.20 ± 2.63% and 4.65 ± 0.60% for the gel and cream formulations, respectively. The representative dermal absorption of BCP was evaluated to be 12.20 ± 2.63% based on the results of the in vivo PK study.

Skin models for dermal exposure assessment of phthalates

Phthalates are a class of compounds that have found widespread use in industrial applications, in particular in the polymer, cosmetics and pharmaceutical industries. While ingestion, and to a lesser degree inhalation, have been considered as the major exposure routes, especially for higher molecular weight phthalates, dermal exposure is an important route for lower weight phthalates such as diethyl phthalate (DEP). Assessing the dermal permeability of such compounds is of great importance for evaluating the impact and toxicity of such compounds in humans. While human skin is still the best model for studying dermal permeation, availability, cost and ethical concerns may preclude or restrict its use. A range of alternative models has been developed over time to substitute for human skin, especially in the early phases of research. These include ex vivo animal skin, human reconstructed skin and artificial skin models. While the results obtained using such alternative models correlate to a lesser or greater degree with those from in vivo human studies, the use of such models is nevertheless vital in dermal permeation research. This review discusses the alternative skin models that are available, their use in phthalate permeation studies and possible new avenues of phthalate research using skin models that have not been used so far.

Percutaneous Penetration and Metabolism of Plasticizers by Skin Cells and Its Implication in Dermal Exposure to Plasticizers by Skin Wipes

Numerous studies focused on the human exposure to plasticizers via dermal contact; however, the percutaneous penetration of plasticizers was seldom considered in exposure assessment. In the present study, skin wipes of palms, back-of-hands, and forehead were collected from 114 participants (ages: 18-27). There was no significant difference between the levels of phthalates from palms and back-of-hand, while all phthalates collected from the forehead were significantly higher than those from palms and back-of-hand (p < 0.001); di(2-ethylhexyl)phthalate levels were substantially higher than other detected phthalates followed by di(n-butyl)phthalate and di(isobutyl)phthalate (DiBP), and for alternative plasticizers, bis-2-ethylhexyl terephthalate levels were substantially higher than acetyltributyl citrate and bis-2-ethylhexyladipate. Skin permeation and metabolism of phthalates was assessed using human skin equivalent models. The permeability coefficient (k_p) values of phthalates were significantly negatively correlated with their log octanol-water partition coefficient (log K_ow), while a significantly positive correlation was found between the log K_ow and the cumulative amounts of phthalates in the cells. The proportion of phthalate intake via dermal exposure to skin wipes ranges from 1.3% (for dimethyl phthalate) to 8.6% (for DiBP) and suggests that dermal absorption is a significant route for adult phthalate exposure.

Antiaging and smoothness-improving properties of farnesol-based facial masks on rat skin exposed to ultraviolet B

BACKGROUND

Farnesol is an acyclic sesquiterpene presents in various natural sources including fruits, vegetables, and herbs. In this study, we successfully prepared a farnesol-containing gel with ultraviolet B-screening and skin-repairing capabilities. Furthermore, the advantageous potential of farnesol-containing facial masks for UVB-caused sunburnt skin was evaluated.

AIMS

Thus, the objectives of this study are to design and prepare optimal facial masks possessing collagen production and smoothness-enhancing capabilities for the skin.

METHODS

A series of formulations consisting of hydroxypropyl methylcellulose, hyaluronan, and farnesol were used to prepare the facial masks. The effects of the facial masks on collagen production by skin fibroblasts in vitro were examined. The effects of the prepared masks on collagen synthesis, smoothness, and inflammation of the skin were further evaluated in vivo using two modes (mask administration interspersed with UVB exposure and mask administration after UVB exposure) of a rat model.

RESULTS

Facial masks containing both 0.3 and 0.8 mM farnesol improved skin smoothness and enhanced collagen content and arrangement in the skin of rats with mask administration interspersed with and after UVB exposure. The masks containing 0.8 mM farnesol exerted the greatest effects on collagen production/arrangement and smoothness improvement in vivo model. Histopathologically observed inflammation was alleviated, and interleukin (IL)-6 was decreased in the 0.8 mM farnesol-containing facial mask-covered skin compared with that without facial masks.

CONCLUSIONS

The farnesol-containing facial masks prepared in this study may have collagen production-increasing, smoothness-improving, and anti-inflammatory properties for UVB-caused sunburn; thus, farnesol is potentially a beneficial component in facial masks.

Sanitary pads and diapers contain higher phthalate contents than those in common commercial plastic products

Sanitary pads and diapers are made of synthetic plastic materials that can potentially be released while being used. This study measured the amounts of volatile organic compounds (VOCs) (methylene chloride, toluene, and xylene) and phthalates (DBP, DEHP, DEP, and BBP) contained in sanitary pads and diapers. In sanitary pads, 5,900- and 130-fold differences of VOC and phthalate concentrations were seen among the brands. In the diapers, 3- and 63-fold differences of VOC and phthalate concentrations were detected among the brands. VOC concentrations from the sanitary pads and diapers were similar to that of the residential air. However, phthalate concentrations of sanitary pads and diapers were significantly higher than those found in common commercial plastic products. As sanitary pads and diapers are in direct contact with external genitalia for an extended period, there is a probability that a considerable amount of VOCs or phthalates could be absorbed into the reproductive system.

Percutaneous permeability of 1-phenoxy-2-propanol, a preservative in cosmetics

1-Phenoxy-2-propanol (PP) is used as a preservative in cosmetics. PP is currently permitted to be used to up to 1% in cosmetic formulations in Korea and Europe. For risk assessment, percutaneous absorption is a crucial factor, but dermal absorption of PP has not yet been reported. In this study, Franz diffusion method was used to determine the percutaneous penetration of PP using the dorsal skin of rats. Each formulation of shampoo or cream, 113.6 mg/cm², was applied to a donor compartment of Franz diffusion cell for 24 h. Receptor fluid was collected at 0, 1, 2, 4, 8, 12, and 24 h following dermal application. Remaining formulation was removed with a cotton swab after last sampling. Using tape stripping method, stratum corneum was removed. PP in epidermis and dermis was extracted in PBS for 24 h. The concentration of PP from the swab, stratum corneum, and epidermis and dermis samples was determined using high performance liquid chromatography. Total percutaneous absorption rates of PP for shampoo and cream were 50.0 ± 6.0% and 33.0 ± 3.2%, respectively. In vitro skin permeability was calculated as 1,377.2 ± 240.1 mg/cm² for shampoo and 1,038.0 ± 72.2 mg/cm² for cream for 24 h.

Methylation and Esterification of Magnolol for Ameliorating Cutaneous Targeting and Therapeutic Index by Topical Application

PURPOSE

As a continuing effort to elucidate the impact of structure modification upon cutaneous absorption behavior, we attempted to assess the skin permeation of magnolol by methylation and acetylation.

METHODS

Diacetylmagnolol and 2-O-acetyl-2'-O-methylmagnolol (AMM) were designed and synthesized in this study. The anti-inflammatory activity against stimulated neutrophils and keratinocytes was evaluated to check the bioactivity of the analogues. In vitro skin absorption was investigated using nude mouse and pig skin models at both equimolar and saturated doses.

RESULTS

Magnolol generally showed the strongest anti-inflammatory potential, followed by diacetylmagnolol and AMM. The antibacterial activity was observed for magnolol and diacetylmagnolol but not AMM. Diacetylmagnolol and AMM could be partly hydrolyzed to magnolol and 2-O-methylmagnolol after entering the skin. The hydrolysis rate of diacetylmagnolol was faster than that of AMM. The lipophilicity played a crucial role in cutaneous absorption, with AMM exhibiting the highest skin deposition. AMM accumulation within nude mouse skin was about 2.5-fold greater than that of magnolol and diacetylmagnolol. On the other hand, the transdermal penetration across the skin was lessened by methylation and esterification. This led to a superior skin targeting of AMM. Although the pharmacological activity of AMM was low, the high skin uptake and bioconversion into 2-O-methylmagnolol in the skin contributed to a greater therapeutic index (TI, skin deposition x inflammatory inhibition percentage) compared to the others. The accumulation of AMM in the hair follicles was 77.12 nmol/cm(2), which was significantly greater than that with magnolol (44.84 nmol/cm(2)) and diacetylmagnolol (26.96 nmol/cm(2)). The synthetic analogues were tolerable to the nude mouse skin.

CONCLUSIONS

Based on the experimental results, we may suggest topically applied AMM as a potent and safe candidate for the treatment of cutaneous inflammation.

Skin absorption and human exposure estimation of three widely discussed UV filters in sunscreens--In vitro study mimicking real-life consumer habits

Due to health concerns about safety, three UV-filters (Benzophenone-3, BP3, 10%; Ethylhexyl Methoxycinnamate, EHMC, 10%; Butyl Methoxydibenzoylmethane, BMDBM; 5%) were examined in vitro for absorption on full-thickness pig-ear skin, mimicking human in-use conditions. Kinetic profiles confirmed the rapid permeation of BP3; after the first hour of skin (frozen-stored) exposure to 2 mg/cm(2) (W/O sunscreen; recommended but unrealistic amount), about 0.5% of the applied dose passed into the receptor fluid. The absorption rate of filters was higher from W/O than from O/W emulsions. The fresh/frozen-stored skin permeability coefficient (0.83-0.54) for each UV filter was taken into account. Systemic Exposure Dosage of BP3, EHMC, BMDBM for humans as a consequence of (i) whole-body and (ii) face treatment with 0.5 mg/cm(2) of W/O sunscreen for 6-h skin exposure followed by washing and subsequent 18-h permeation (a realistic scenario) were estimated to be (i) 4744, 1032 and 1036 μg/kg-bw/day, and (ii) 153, 33 and 34 μg/kg-bw/day, respectively. From Margin of Safety for BP3, EHMC and BMDBM (i) 42, 485 and 192 as well as (ii) 1307; 15,151 and 5882, respectively, only the value of 42 (<100) for BP3 indicated a possible health risk. Escalation of a phobia towards all organic UV filters is undesirable.

Coumarin derivatives, but not coumarin itself, cause skin irritation via topical delivery

Coumarin and its derivatives are widely employed as a fragrance in cosmetics and skin care products. The skin absorption level and possible disruption to the skin by topical application of coumarins were evaluated in this study. Percutaneous absorption of osthole, daphnoretin, coumarin, byakangelicin, and 7-hydroxycoumarin was assessed in vitro and in vivo. Skin physiology measurements and immunoblotting were utilized as methodologies for validating toxicity. The relationship between structures and permeation/toxicity of coumarins was elucidated. Both equimolar concentration and saturated solubility in 30% ethanol were used as the applied dose. Osthole with the most lipophilic characteristic demonstrated the greatest skin accumulation, followed by coumarin and 7-hydroxycoumarin. Coumarin was the permeant with the highest flux across the skin. The trend of in vivo deposition was consistent with that of the in vitro profiles. Skin uptake of osthole was 8-fold higher than that of coumarin. Hair follicles played a significant role as a pathway for transport of coumarin according to the examination of follicular accumulation. Osthole and 7-hydroxycoumarin slightly, but significantly, enhanced transepidermal water loss after a consecutive 5-day administration. The immunoblotting profiling verified the role of proliferation in skin damage induced by osthole, byakangelicin, and 7-hydroxycoumarin. The proliferation-related proteins examined in this work included glucose-regulated proteins, cytokeratin, and C-myc. Daphnoretin and coumarin showed a negligible alteration on protein biomarkers. The experimental results suggested that skin irritation caused by coumarins was mainly derived from the analogs but not from coumarin itself.

Dermal toxicity elicited by phthalates: evaluation of skin absorption, immunohistology, and functional proteomics

The toxicity of phthalates is an important concern in the fields of environmental health and toxicology. Dermal exposure via skin care products, soil, and dust is a main route for phthalate delivery. We had explored the effect of topically-applied phthalates on skin absorption and toxicity. Immunohistology, functional proteomics, and Western blotting were employed as methodologies for validating phthalate toxicity. Among 5 phthalates tested, di(2-ethylhexyl)phthalate (DEHP) showed the highest skin reservoir. Only diethyl phthalate (DEP) and dibutyl phthalate (DBP) could penetrate across skin. Strat-M(®) membrane could be used as permeation barrier for predicting phthalate penetration through skin. The accumulation of DEHP in hair follicles was ∼15nmol/cm(2), which was significantly greater than DBP and DEP. DBP induced apoptosis of keratinocytes and fibroblasts via caspase-3 activation. This result was confirmed by downregulation of 14-3-3 and immunohistology of TUNEL. On the other hand, the HSP60 overexpression and immunostaining of COX-2 suggested inflammatory response induced by DEP and DEHP. The proteomic profiling verified the role of calcium homeostasis on skin inflammation. Some proteins investigated in this study can be sensitive biomarkers for dermal toxicity of phthalates. These included HSPs, 14-3-3, and cytokeratin. This work provided novel platforms for examining phthalate toxicity on skin.

Design and performance of a spreadsheet-based model for estimating bioavailability of chemicals from dermal exposure

A comprehensive transient model of chemical penetration through the stratum corneum, viable epidermis and dermis formulated in terms of an Excel™ spreadsheet and associated add-in is presented. The model is a one-dimensional homogenization of underlying microscopic transport models for stratum corneum and dermis; viable epidermis is treated as unperfused dermis. The model's salient features are a detailed structural description of the skin layers, a combination of first-principles based transport equations and empirical partition and diffusion coefficients, and the capability of simulating a variety of exposure scenarios. Model predictions are compared with representative in vitro skin permeation data obtained from the literature using as summary parameters total absorption (Q(abs)), maximum flux (J(max)) and skin permeability coefficient (k(p)). The results of this evaluation demonstrate the current state-of-the-art in prediction of transient skin absorption and highlight areas in which further elaborations are needed to obtain satisfactory predictions.

Allergic contact dermatitis caused by farnesol: clinical relevance

CONTEXT

The fragrance material farnesol is cited as an infrequent but important cause of allergic contact dermatitis (ACD). It is included in the fragrance mix II patch series and requires labeling in the European Union if it is used in a consumer product.

OBJECTIVE

To review the existing literature to determine the causative role of farnesol in clinical contact allergy.

MATERIALS AND METHODS

Survey of the literature on farnesol studies; predictive and clinical elicitation tests in case reports, reviews, and abstracts.

RESULTS

Predictive animal studies demonstrated in most cases that farnesol was a nonsensitizer. However, 2 local lymph node assays (LLNAs) indicated strong sensitization potential. Predictive human test data indicated a low potential, if any, for sensitization in human tests with farnesol at 10% or 12%. A few clinical reports indicated low-level allergy or questionable reactions to farnesol, with 5% being the most commonly used. There were also reports in which no reactions were seen.

DISCUSSION

Predictive testing on farnesol in animals shows conflicting results depending on the study methodology used. Human predictive patch-test data also had gaps that prevented it from being definitive in pointing to a causative relationship between farnesol and contact dermatitis. The real sensitizing potential of a material can best be determined by evaluating the clinical and epidemiological data so as to help resolve the conflicting animal and human predictive test data.

CONCLUSIONS

This literature and scoring exercise showed that predictive and clinical elicitation data do not document a clear causative determination that farnesol is a frequent contact allergen. Detailed clinical relevance and patient studies should clarify the clinical problem farnesol represents.