The effect of skin diffusion kinetics of isopropyl ester permeation enhancers on drug permeation: Role of lateral spread and penetration characteristics

The purpose of present work was to study the effects of permeation enhancers' two kinetic behaviors of simultaneous lateral diffusion and vertical penetration in the skin on its enhancing effect. The skin diffusion kinetics of isopropyl ester permeation enhancers were characterized by the innovative concentric tape peeling study and Raman imaging, which were quantitatively assessed through innovative parameters, namely, lateral-to-vertical penetration amount (CL-V) and lateral-to-vertical penetration distance (DL-V). The enhancement effect of permeation enhancers on drug flurbiprofen (FLU) was assessed by in vitro skin permeation tests, which were confirmed by transdermal water loss and skin resistance study. The relationship between kinetic parameters of permeation enhancers and permeation parameters of FLU was carried out by correlation analysis. The molecular mechanisms of effect of skin diffusion kinetics of permeation enhancers on drug permeation were characterized by molecular docking, modulated-temperature differential scanning calorimetry (MTDSC), Raman spectra, solid-state NMR and molecular dynamic simulation. The results indicated skin diffusion kinetics of short-chain (C8-C12) isopropyl ester permeation enhancers were governed by vertical penetration, while long-chain (C14-C18) ones were characterized by lateral spread. Quadratic correlation between CL-V and enhancement ratio of permeation-retention ratio of FLU (ERQ/R) (R2 = 0.95), DL-V and enhancement ratio of permeation area (ERA) of FLU (R2 = 0.98) indicating that varied skin diffusion kinetics of permeation enhancers directly influenced the barrier function of stratum corneum (SC) and further enhancing drug permeation. In terms of molecular mechanism, long-chain isopropyl ester enhancers had good miscibility with SC, leading to their high CL-V and DL-V, and causing strong interaction strength with SC and resulting in weaker skin barrier function for drug permeation. In summary, in comparison to short-chain isopropyl ester enhancers that relied on penetration, long-chain ones that depended on lateral spread exhibited greater enhancement efficacy, which guided the application of enhancers in transdermal formulations.

Microplastics Distribution within Western Arctic Seawater and Sea Ice

Microplastic pollution has emerged as a global environmental concern, exhibiting wide distribution within marine ecosystems, including the Arctic Ocean. Limited Arctic microplastic data exist from beached plastics, seabed sediments, floating plastics, and sea ice. However, no studies have examined microplastics in the sea ice of the Canadian Arctic Archipelago and Tallurutiup Imanga National Marine Conservation Area, and few have explored Arctic marginal seas' water column. The majority of the microplastic data originates from the Eurasian Arctic, with limited data available from other regions of the Arctic Ocean. This study presents data from two distinct campaigns in the Canadian Arctic Archipelago and Western Arctic marginal seas in 2019 and 2020. These campaigns involved sampling from different regions and matrices, making direct comparisons inappropriate. The study's primary objective is to provide insights into the spatial and vertical distribution of microplastics. The results reveal elevated microplastic concentrations within the upper 50 m of the water column and significant accumulation in the sea ice, providing evidence to support the designation of sea ice as a microplastic sink. Surface seawater exhibits a gradient of microplastic counts, decreasing from the Chukchi Sea towards the Beaufort Sea. Polyvinyl chloride polymer (~60%) dominated microplastic composition in both sea ice and seawater. This study highlights the need for further investigations in this region to enhance our understanding of microplastic sources, distribution, and transport.

Measurement of chemical penetration in skin using Stimulated Raman scattering microscopy and multivariate curve resolution - alternating least squares

The mechanistic understanding of skin penetration underpins the design, efficacy and risk assessment of many high-value products including functional personal care products, topical and transdermal drugs. Stimulated Raman scattering (SRS) microscopy, a label free chemical imaging tool, combines molecular spectroscopy with submicron spatial information to map the distribution of chemicals as they penetrate the skin. However, the quantification of penetration is hampered by significant interference from Raman signals of skin constituents. This study reports a method for disentangling exogeneous contributions and measuring their permeation profile through human skin combining SRS measurements with chemometrics. We investigated the spectral decomposition capability of multivariate curve resolution - alternating least squares (MCR-ALS) using hyperspectral SRS images of skin dosed with 4-cyanophenol. By performing MCR-ALS on the fingerprint region spectral data, the distribution of 4-cyanophenol in skin was estimated in an attempt to quantify the amount permeated at different depths. The reconstructed distribution was compared with the experimental mapping of CN, a strong vibrational peak in 4-cyanophenol where the skin is spectroscopically silent. The similarity between MCR-ALS resolved and experimental distribution in skin dosed for 4 h was 0.79 which improved to 0.91 for skin dosed for 1 h. The correlation was observed to be lower for deeper layers of skin where SRS signal intensity is low which is an indication of low sensitivity of SRS. This work is the first demonstration, to the best of our knowledge, of combining SRS imaging technique with spectral unmixing methods for direct observation and mapping of the chemical penetration and distribution in biological tissues.

Assessment of penetration and permeation of caffeine by confocal Raman spectroscopy in vivo and ex vivo by tape stripping

OBJECTIVE

Tape stripping is an often-used non-invasive destructive method to investigate the skin penetration of a substance. In recent years, however, the suitability of confocal Raman spectroscopy (CRS) as a non-invasive method of non-destructive examination of the skin has become increasingly apparent. In this study, we compared invasion and depletion penetration and permeation kinetics of a 2% caffeine solution with and without 1,2-pentanediol as a penetration enhancer measured with CRS and tape stripping.

METHODS

Porcine skin was used for tape stripping and human skin for CRS. 2% caffeine solution was applied to the skin for different incubation times. Human skin was then examined by CRS while caffeine was extracted from porcine skin and quantified via reverse-phase HPLC. Fluxes were also measured and calculated by sum of the total amounts of caffeine penetrated into the skin.

RESULTS

Without penetration enhancers, there is hardly any difference between the penetration profiles of the two measurement methods for invasion, but the curves for depletion are different. Furthermore, the calculated flux values for the invasion are almost identical, but for the depletion the tape stripping values are about twice as high as the CRS values.

CONCLUSION

The relevance of conducting invasion and depletion studies became clear and was able to show the still existing problems in the comparability of CRS and tape stripping.

Impact of Alkanediols on Stratum Corneum Lipids and Triamcinolone Acetonide Skin Penetration

Alkanediols are widely used as multifunctional ingredients in dermal formulations. In addition to their preservative effect, considering their possible impact on drug penetration is also essential for their use. In the present study, the influence of 2-methyl-2,4-pentanediol, 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol on the skin penetration of triamcinolone acetonide from four different semisolid formulations was investigated. Furthermore, confocal Raman spectroscopy measurements were performed to examine the influence of the alkanediols on stratum corneum lipid content and order. Alkanediols were found to increase the penetration of triamcinolone acetonide. However, the extent depends strongly on the formulation used. In certain formulations, 1,2-pentanediol showed the highest effect, while in others the penetration-enhancing effect increased with the alkyl chain length of the alkanediol used. None of the tested alkanediols extracted lipids from the stratum corneum nor reduced its thickness. Notwithstanding the above, the longer-chained alkanediols cause the lipids to be converted to a more disordered state, which favors drug penetration. This behavior could not be detected for the shorter-chained alkanediols. Therefore, their penetration-enhancing effect is supposed to be related to an interaction with the hydrophilic regions of the stratum corneum.

Optimal configuration of confocal Raman spectroscopy for precisely determining stratum corneum thickness: Evaluation of the effects of polyoxyethylene stearyl ethers on skin

Properties regarding stratum corneum (SC), the outermost membrane of the skin, remain an active area in dermatologic and cosmetic research. The reduced thickness of SC is associated with varied adverse statuses such as skin lipid deficiency, skin barrier dysfunctions and skin deceases, etc. Emulsifiers with existing irritative effects on skin components also face the risk of decreasing SC thickness. We have been focusing on the effects of PEGylated emulsifiers on the skin and have an interest in finding the role of their polyethylene glycol (PEG)-chain length in tuning skin irritations. With this aim, PEG-stearyl ethers with different numbers of hydrophilic chains were applied on the skin, and their influence on skin thickness was discovered to determine their skin barrier effect. Confocal Raman spectroscopy (CRS) with extensive application in skin research was used here. To obtain the precise determination of skin thickness, our secondary aim was to find the optimal CRS configuration referring to varied objectives and pinhole sizes where further study is still in demand. Therefore, SC thickness measured via eddy current approach served as reference. The applied PEG-stearyl ethers formed the system to achieve varied thicknesses. Results confirmed that the skin interactions rose with increasing PEG-chain length, however only up to a certain limit, with decreasing effects recorded from PEG-40 stearyl ether and no effects observed from PEG-100 stearyl ether. Simultaneously, CRS combined with water immersion objective and 50 μm pinhole presented the most consistent values to the references and exhibited better spectral intensity and signal-to-noise ratio. Correlation plots involving different cases of configurations were calculated for error corrections. Taken together, this work helps to identify the potential mechanisms governing the interactions between PEG-stearyl ethers and skin and offers powerful evidence of using CRS as a reliable alternative to obtain accurate thickness values.

Tracking heavy-water-incorporated confocal Raman spectroscopy for evaluating the effects of PEGylated emulsifiers on skin barrier

The class of PEGylated emulsifiers finds broad application in the pharmaceutical and cosmetic industry. We target on one of the categories of polyethylene glycol (PEG) alkyl ethers with different lipophilic and hydrophilic chain length and aim to examine their effects on the skin comprehensively. In this study, we employed confocal Raman spectroscopy for skin depth profiling and imaging. A unique probe of heavy water (D₂ O) was incorporated, which can be tracked percutaneously and simultaneously monitor the effects caused by emulsifiers. According to the results, most of the PEGylated emulsifiers caused changes in skin lipid content/organization and induced the alteration in relative water content/hydrogen bonding structure. The results obtained from the depth profiling analysis provided the possibility to estimate the least penetration depth of emulsifiers. Among them, PEG-20 ethers displayed the most penetration ability. Meanwhile, it is interesting to find that the treatment of emulsifiers also affected the spatial distribution of D₂ O whose differences were in line with the molecular skin variations. In particular, the isotopic H/D substitution in the skin was highlighted in detail. This result supports the possibility to use D₂ O as an excellent and cost-effective probe to evaluate the skin barrier function.