Three measures of skin barrier function (ER, TEWL and TWF) were utilised in this study using methods and previously established cut-off values for the rejection of abnormal samples (Davies et al., 2004, Heylings et al., 2001 and Imhof et al., 2009). For ER, this was measured using a PRISM Electronics AIM6401 LCR data bridge connected to two stainless steel electrodes using a setting of 100 kHz and ER was expressed
as kΩ for the exposed skin surface area (2.54 cm2). Further details on the equipment used can be found in our previous publication (Davies et al., 2004). The Dinaciclib clinical trial diffusion chambers were allowed to equilibrate in a water bath at 32 °C for approximately 30 min. One electrode was inserted into the saline in the receptor chamber underneath the skin via the side arm and the other electrode immersed in 2 ml of
saline in the donor chamber above the skin. When the resistance across the skin sample had stabilised, the ER reading was recorded. TWF was determined by firstly allowing the membranes to equilibrate in a water bath at 32 °C for approximately 30 min after which a 2 ml aliquot of tritiated water (T2O), containing a AZD1208 concentration known amount of radioactivity, was applied to the surface of the membranes. Contact between the T2O and the skin membrane was deemed to be the start of the experiment (time zero). Samples of the receptor fluid were taken 3, 4, 5 and 6 h after application and analysed for radioactivity content by LSC. The receptor fluid removed was not replaced. However, the receptor fluid and skin membranes were in good contact throughout the T2O permeability measurement.
A permeability coefficient (Kp) was calculated by dividing the steady state absorption rate by the radioactivity concentration of the T2O applied to the membranes. TEWL was measured by firstly placing the diffusion cells containing skin membranes in a humidity (40–60%) and temperature-controlled incubator at 32 °C. The cells tetracosactide were allowed to equilibrate for at least 30 min before taking a measurement using a calibrated, ServoMed EP-2 Evaporimeter (ServoMed, Varberg, Sweden) by placing the probe directly on to the dry skin surface. Once the TEWL value had stabilised the reading was recorded. Part of the pre-selection criteria of the membranes was a conventional ER skin integrity test which was used to identify any damaged pig skin samples. Any skin sample, in our static diffusion cells, that did not meet the cut-off value of 3 kΩ was discarded and not used in these investigations. The criteria for barrier damage in dermatomed pig skin was as described previously (Davies et al., 2004). Normal skin samples from five different animals were then randomly assigned to groups to be left unstripped (control membranes) or to groups to be subjected to tape stripping 5, 10, 15 or 20 times, in order to remove different proportions of the stratum corneum.