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Sunlight is vital for several biochemical processes of the skin organ. However, acute or chronic exposure to ultraviolet radiation (UVR) has several harmful effects on the skin structure and function, especially in the case of the failing function of antioxidative enzymes, which may lead to substantial tissue damage due to the increased presence of reactive oxygen species (ROS). The aim of this work was to investigate the combined effect of ultraviolet B (UVB) irradiation and oxidative stress on the skin barrier integrity. For this, we employed electrical impedance spectroscopy (EIS) to characterize changes of the electrical properties of excised pig skin membranes after various exposure conditions of UVB irradiation, oxidative stress, and the inhibition of antioxidative enzymatic processes. The oxidative stress was regulated by adding hydrogen peroxide (H2O2) as a source of ROS, while sodium azide (NaN3) was used as an inhibitor of the antioxidative enzyme catalase, which is naturally present throughout the epidermis. By screening for the combined effect of UVB and oxidative stress on the skin membrane electrical properties, we developed a new protocol for evaluating these parameters in a simple in vitro setup. Strikingly, the results show that exposure to extreme UVB irradiation does not affect the skin membrane resistance, implying that the skin barrier remains macroscopically intact. Likewise, exposure to only oxidative stress conditions, without UVB irradiation, does not affect the skin membrane resistance. In contrast to these observations, the combination of UVB irradiation and oxidative stress conditions results in a drastic decrease of the skin membrane resistance, indicating that the integrity of the skin barrier is compromised. Further, the skin membrane effective capacitance remained more or less unaffected by UVB exposure, irrespective of simultaneous exposure of oxidative stress. The EIS results were concluded to be associated with clear signs of macroscopic tissue damage of the epidermis as visualized with microscopy after exposure to UVB irradiation under oxidative stress conditions. Finally, the novel methodology was tested by performing an assessment of cosmetic sunscreen formulations with varying sun protection factor (SPF), with an overall successful outcome, showing good correlation between SPF value and protection capacity in terms of skin resistance change. The results from this study allow for the development of new skin sensors based on EIS for the detection of skin tissue damage from exposure to UVB irradiation and oxidative stress and provide a new, more comprehensive methodology, taking into account both the influence of UVB irradiation and oxidative stress, for in vitro determination of SPF in cosmetic formulations.

The development of formulation concepts for improved skin tissue oxygenation, including methods for measuring oxygen (O2) transport across biological barriers, are important research topics with respect to all processes that are affected by the O2 concentration, such as radiation therapy in oncology treatments, wound healing, and the general health status of skin. In this work we approach this topic by a novel strategy based on the antioxidative enzyme catalase, which is naturally present in the skin organ where it enables conversion of the reactive oxygen species hydrogen peroxide (H2O2) into O2. We introduce various applications of the skin covered oxygen electrode (SCOE) as an in-vitro tool for studies of catalase activity and function. The SCOE is constructed by placing an excised skin membrane directly on an O2 electrode and the methodology is based on measurements of the electrical current generated by reduction of O2 as a function of time (i.e. chronoamperometry). The results confirm that a high amount of native catalase is present in the skin organ, even in the outermost stratum corneum (SC) barrier, and we conclude that excised pig skin (irrespective of freeze-thaw treatment) represents a valid model for ex vivo human skin for studying catalase function by the SCOE setup. The activity of native catalase in skin is sufficient to generate considerable amounts of O2 by conversion from H2O2 and proof-of-concept is presented for catalase-based transdermal O2 delivery from topical formulations containing H2O2. In addition, we show that this concept can be further improved by topical application of external catalase on the skin surface, which enables transdermal O2 delivery from 50 times lower concentrations of H2O2. These important results are promising for development of novel topical or transdermal formulations containing low and safe concentrations of H2O2 for skin tissue oxygenation. Further, our results indicate that the O2 production by catalase, derived from topically applied S. epidermidis (a simple model for skin microbiota) is relatively low as compared to the O2 produced by the catalase naturally present in skin. Still, the catalase activity derived from S. epidermidis is measurable. Taken together, this work illustrates the benefits and versatility of the SCOE as an in vitro skin research tool and introduces new and promising strategies for transdermal oxygen delivery, with simultaneous detoxification of H2O2, based on native or topically applied catalase.

The accepted methodology by regulatory agencies to determine the efficacy of sunscreen products makes use of healthy human volunteers who are exposed to radiation. In order to find an alternative to these types of evaluations, the effect of exposure to UV radiation was investigated in an ex vivo pig skin model on the bioelectrical signals of the tissue in terms of energy and impedance. A system was implemented using the measurements configuration of 4 electrodes (Two electrostimulation electrodes and two electrodes for the signals acquisition all of them were silver cup electrodes) and a mathematical model was established in relation to electrical change as a function of exposure time. As a result, an attenuation of the energy response signal relative to the non-irradiated tissue was obtained, as well as impedance values after irradiation. This behavior is directly related to damage in the tissue structure. The results allow to conclude that the device can quantify the effect caused by radiation on the electrical properties of an ex vivo tissue and are promising in the understanding of the phenomena associated with the electrical response of a tissue to ultraviolet radiation.

6-Methylcoumarin (6MC) is a semisynthetic coumarin with important in vitro and in vivo anti-inflammatory activity. In order to continue the pre-clinical characterization of this molecule, in vitro intestinal permeability, plasma profile and tissue distribution after oral administration in rats were studied. The permeability of 6MC was evaluated by the Caco-2 cellular model in both the apical-basal (A-B) and basal-apical (B-A) directions. The pharmacokinetics and biodistribution were evaluated in rats after oral and intraperitoneal administration at doses of 200 mg/kg. Transport experiments with Caco-2 cells showed that 6MC presented high permeability at all concentrations evaluated. This finding suggested that 6MC could be transported across the gut wall by passive diffusion. The plasma concentration-time curve showed that the maximum concentration (Cmax) was 17.13 ± 2.90 µg/mL at maximum time (Tmax) of 30 min for the oral route and Cmax 26.18 ± 2.47 µg/mL at 6.0 min for the intraperitoneal administration, with elimination constant of (Ke) 0.0070 min-1 and a short life half time of (T1/2) lower that 120 min. The distribution study showed that 6MC has high accumulation in the liver, and widespread distribution in all the organs evaluated. Fil: Cárdenas, Paola Andrea. Universidad Nacional de Colombia. Departamento de Farmacia. Grupo Sistemas de Liberación Modificada de Moléculas Biológicamente Activas; Colombia Fil: Kratz, Jadel Müller. Universidade Federal de Santa Catarina. Departamento de Ciências Farmacêuticas. Grupo de Análise e Desenvolvimento de Fármacos de Origem Natural; Brasil Fil: Hernández, Aura. Universidad Nacional de Colombia. Departamento de Farmacia.Grupo Sistemas de Liberación Modificada de Moléculas Biológicamente Activas; Colombia Fil: Costa, Geison Modesti. Universidad Nacional de Colombia. Departamento de Química. Grupo de Estudio y Aprovechamiento de Productos Naturales Marinos y Frutas de Colombia ; Colombia Fil: Ospina, Luis Fernando. Universidad Nacional de Colombia. Departamento de Farmacia.Grupo de Principios Bioactivos de Plantas Medicinales; Colombia Fil: Baena, Yolima. Universidad Nacional de Colombia. Departamento de Farmacia.Grupo Sistemas de Liberación Modificada de Moléculas Biológicamente Activas; Colombia Fil: Simões, Cláudia Maria Oliveira. Universidade Federal de Santa Catarina. Departamento de Ciências Farmacêuticas. Grupo de Análise e Desenvolvimento de Fármacos de Origem Natural; Brasil Fil: Jimenez Kairuz, Alvaro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Ciencias Farmacéuticas; Argentina Fil: Aragón, Marcela. Universidad Nacional de Colombia. Departamento de Farmacia. Grupo Sistemas de Liberación Modificada de Moléculas Biológicamente Activas; Colombia

A sensitive, specific and reproducible HPLC method has been developed and validated for the quantitative determination of 6-methylcoumarin (6MC) in plasma and other tissues in Wistar rats. A C18 column was used with UV detection at 321 nm and a gradient system consisting of methanol-deionized water was used as mobile phase. The retention time for 6MC was 14.921 min and no interfering peaks were observed for any of the matrices. Linear relationships (r2 > 0.997) were obtained between the peak height ratios and the corresponding biological sample concentrations over the range 0.4–12.8 µg/mL. Precision and accuracy were evaluated; the coefficient of variation and the relative error for all of the organs were