Skin model cultivation under static conditions limits the observation of the toxicity to this single organ. Biology-inspired microphysiological systems associating skin with a liver in the same circulating medium provide a more comprehensive insight into systemic substance toxicity; however, its advantages or limitations for topical substance toxicity remain unknown. Herein, we performed topical (OECD test guideline no. 439) and systemic administration of terbinafine in reconstructed human skin (RHS) vs. a RHS plus liver model cultured in TissUse' HUMIMIC Chip2 (Chip2). Aiming for a more detailed insight into the cutaneous substance irritancy/toxicity, we assessed more than the MTT cell viability: lactate dehydrogenase (LDH), lactate and glucose levels, as well as inherent gene expressions. Sodium dodecyl sulfate (SDS) was the topical irritant positive control. We confirmed SDS irritancy in both static RHS and Chip2 culture by the damage in the morphology, reduction in the lactate production and lower glucose consumption. In the static RHS, the SDS-treated tissues also released significantly high LDH (82%; p < 0.05) and significantly lower IL-6 release (p < 0.05), corroborating with the other metabolic levels. In both static RHS and Chip2 conditions, we confirmed absence of irritancy or systemic toxicity by LDH, glucose or lactate levels for topical 1% and 5% terbinafine and systemic 0.1% terbinafine treatment. However, topical 5% terbinafine treatment in the Chip2 upregulated IL-1α in the RHS, unbalanced apoptotic and proliferative cell ratios in the liver and significantly increased its expression of CYP1A2 and 3A4 enzymes (p < 0.05), proving that it has passed the RHS barrier promoting a liver impact. Systemic 0.1% terbinafine treatment in the Chip2 increased RHS expression of EGFR, increased apoptotic cells in the liver, downregulated liver albumin expression and upregulated CYP2C9 significantly (p < 0.05), acting as an effective hepatotoxic terbinafine control. The combination of the RHS and liver model in the Chip2 allowed a more sensitive assessment of skin and hepatic effects caused by chemicals able to pass the skin (5% terbinafine and SDS) and after systemic 0.1% terbinafine application. The present study opens up a more complex approach based on the microphysiological system to assess more than a skin irritation process.

Highly hydrophilic, responsive nanogels are attractive as potential systems for the topical delivery of bioactives encapsulated in their three-dimensional polymeric scaffold. Yet, these drug carrier systems suffer from drawbacks for efficient delivery of hydrophobic drugs. Addressing this, β-cyclodextrin (βCD) could be successfully introduced into the drug carrier systems by exploiting its unique affinity toward dexamethasone (DXM) as well as its role as topical penetration enhancer. The properties of βCD could be combined with those of thermoresponsive nanogels (tNGs) based on dendritic polyglycerol (dPG) as a crosslinker and linear thermoresponsive polyglycerol (tPG) inducing responsiveness to temperature changes. Electron paramagnetic resonance (EPR) studies localized the drug within the hydrophobic cavity of βCD by differences in its mobility and environmental polarity. In fact, the fabricated carriers combining a particulate delivery system with a conventional penetration enhancer, resulted in an efficient delivery of DXM to the epidermis and the dermis of human skin ex vivo (enhancement compared to commercial DXM cream: ∼2.5 fold in epidermis, ∼30 fold in dermis). Furthermore, DXM encapsulated in βCD tNGs applied to skin equivalents downregulated the expression of proinflammatory thymic stromal lymphopoietin (TSLP) and outperformed a commercially available DXM cream.

Engineered nanogels are of high value for a targeted and controlled transport of compounds due to the ability to change their chemical properties by external stimuli. As it has been indicated that nanogels possess a high ability to penetrate the stratum corneum, it cannot be excluded that nanogels interact with dermal dendritic cells, especially in diseased skin. In this study the potential crosstalk of the thermoresponsive nanogels (tNGs) with the dendritic cells of the skin was investigated with the aim to determine the immunotoxicological properties of the nanogels. The investigated tNGs were made of dendritic polyglycerol (dPG) and poly(glycidyl methyl ether-co-ethyl glycidyl ether) (p(GME-co-EGE)), as polymer conferring thermoresponsive properties. Although the tNGs were taken up, they displayed neither cytotoxic and genotoxic effects nor any induction of reactive oxygen species in the tested cells. Interestingly, specific uptake mechanisms of the tNGs by the dendritic cells were depending on the nanogels cloud point temperature (Tcp), which determines the phase transition of the nanoparticle. The study points to caveolae-mediated endocytosis as being the major tNGs uptake mechanism at 37°C, which is above the Tcp of the tNGs. Remarkably, an additional uptake mechanism, beside caveolae-mediated endocytosis, was observed at 29°C, which is the Tcp of the tNGs. At this temperature, which is characterized by two different states of the tNGs, macropinocytosis was involved as well. In summary, our study highlights the impact of thermoresponsivity on the cellular uptake mechanisms which has to be taken into account if the tNGs are used as a drug delivery system.

Dermal absorption is a critical part in the risk assessment of complex mixtures such as agrochemical formulations. To reduce the number of in vivo or in vitro absorption experiments, the present study aimed to develop an in silico prediction model that considers mixture-related effects. Therefore, an experimental 'real-world' dataset derived from regulatory in vitro studies with human and rat skin was processed. Overall, 56 test substances applied in more than 150 mixtures were used. Descriptors for the substances as well as the mixtures were generated and used for multiple linear regression analysis. Considering the heterogeneity of the underlying data set, the final model provides a good fit (r² = 0.75) and is able to estimate the influence of a newly composed formulation on dermal absorption of a well-known substance (predictivity Q²Ext = 0.73). Application of this model would reduce animal and non-animal testings when used for the optimization of formulations in early developmental stages, or would simplify the registration process, if accepted for read-across.

Actinic keratosis, a frequent carcinoma in situ of non-melanoma skin cancer (NMSC), can transform into life-threatening cutaneous squamous cell carcinoma. Current treatment is limited due to low complete clearance rates and asks for novel therapeutic concepts; the novel purine nucleotide analogue OxBu may be an option. In order to enhance skin penetration, solid lipid nanoparticles (SLN, 136-156 nm) were produced with an OxBu entrapment efficiency of 96.5 ± 0.1%. For improved preclinical evaluation, we combined tissue engineering with clinically used keratin-18 quantification. Three doses of 10-3 mol/l OxBu, dissolved in phosphate-buffered saline as well as loaded to SLN, were effective on reconstructed NMSC. Tumour response and apoptosis induction were evaluated by an increase in caspase-cleaved fragment of keratin-18, caspase-7 activation as well as by reduced expression of matrix metallopeptidase-2 and Ki-67. OxBu efficacy was superior to equimolar 5-fluorouracil solution, and thus the drug should be subjected to the next step in preclinical evaluation.

The measurement of acoustic attenuation in small samples of low-loss solids in the range 50 kc/s to 10 Mc/s has, up till now, proved difficult. When the pulse method is applied below 10 Mc/s it is not easy to perform satisfactory corrections for diffraction and mode-conversion errors. These considerations apart, however, the realization of resolution of successive pulse echoes requires the use of embarrassingly long specimens. On the other hand the resonance method, in the form most frequently used, is suitable for elastic constant and attenuation measurements over the lower part of the kilocycle range, i.e. 1–20 kc/s. The frequency-modulation modification devised by Bordoni permits measurements up to 10 Mc/s but is restricted to the investigation of elastic constants. In either form, however, a decreasing output signal and deteriorating signal/noise ratio are obtained as the frequency is raised, whether by using a shorter bar or by raising the order of the harmonic employed. This paper is an account of various modifications in the experimental set-up of the resonance method of attenuation measurements, whereby good signal/noise ratios have been realized up to 700 kc/s, attenuation measured from 20 kc/s to 600 kc/s, and output signals generated from 0.5 V down to 10μV.