Excised Porcine Skin Research Articles

The Outermost Stratum Corneum Layer is an Effective Barrier Against Dermal Uptake of Topically Applied Micronized Titanium Dioxide

In order to help clarify the controversially discussed dermal uptake properties of micronized titanium dioxide (TiO _ 2), we conducted extensive in vitro dermal absorption studies with 'Franz-type' diffusion cells on excised porcine skin. After biopsies and chemical fixation, the overall localization of TiO _ 2 in the skin was analyzed by means of transmission electron microscopy (TEM). The lateral and vertical distribution of TiO _ 2 within the stratum corneum (SC) was investigated by tape stripping and subsequent scanning electron microscopy (SEM) in combination with energy dispersive X-ray analysis (EDXA). TiO _ 2 was found exclusively on the outermost SC layer. The surface deposit, as displayed by TEM, featured clearly distinguishable agglomerates as well as single particles with a characteristic cubic shape and a primary particle size of about 20-50 nm. Concurrently, SEM/EDXA micrographs first showed an even distribution of TiO _ 2 on the skin surface. After 10-fold stripping, however, TiO _ 2 was found to be localized only in the furrows and not on the partially removed ridges of the skin surface. SEM/EDXA micrographs of the adhesive tape strips revealed a characteristic pattern of stripped material and free regions. This pattern was an imprint of the skin's topography. Hence, tape stripping initially removed TiO _ 2 and SC layers only from the ridges and not from the deeper furrows. Continued stripping increasingly yielded material from the deeper contours of the SC surface. TiO _ 2 was found only in traces in the upper part of the follicle without any evidence of uptake into the follicular epithelium. This indicates that there is not any relevant penetration via the follicular route. We conclude that due to the microtopography of the skin, the strip number normally does not reflect the SC layer number. Accordingly, tape stripping results should always be interpreted with care, especially in the case of topically applied particles, as even higher numbers of subsequent strips may still sample material from the outermost SC layer of the deeper furrows, which could be interpreted falsely as penetrated material. Our results clearly demonstrate that TiO _ 2 homogeneously and completely covers the outermost SC layer. It is neither delivered to the SC nor to the underlying skin layers when applied topically to porcine skin in vitro in the cosmetic vehicle used here. These findings underscore the safety of this micronized inorganic UV filter.

Therapeutic Effect and Pharmacokinetics of Ketotifen Transdermal Delivery System

Ketotifen transdermal delivery systems were prepared using polyisobutylene, liquid paraffin, and fatty acid. In vitro skin penetration studies were conducted in Franz diffusion cells using excised porcine skin to determine the skin permeation rates of ketotifen patches. A trend of increased skin penetration of ketotifen was observed as the amount of liquid paraffin in the patch was increased. In addition, we found that lauric acid was a suitable enhancer for percutaneous absorption of ketotifen. Challenge tests were performed in guinea pigs to determine the therapeutic effect of the delivery systems for the inhibition of anaphylactic shock using varied concentrations of chicken ovum albumin as sensitizer. Our results showed that compared with the treatment of intramuscular administration, the skin patch was more effective and produced higher survival rates. The pharmacokinetics of the ketotifen-patch were determined by applying the skin patch to the dorsal skin of rabbits. The plasma levels were maintained constant (42.5–36.4 ng/ml) from 9 to 30 hr. From our study, the prepared ketotifen patch may further be developed for the treatment or prevention of allergic asthma.

Transdermal ion migration

This chapter will focus on the influence of ion composition on the transdermal delivery of drug species through mammalian skin, due to an applied electric field. The pH of the drug-containing medium is shown to affect drug transport by altering the fraction of charged drug and the permselectivity of skin. The competitive transport of ions having the same charge as the drug ion (co-ions) and those having a charge opposite that of the drug ion (counter-ions), is discussed in detail. A model is derived to predict drug ion flux through a homogeneous non-ionic membrane at constant current, in the presence of one type of co-ion and counter-ion. Model values are compared to experimental data for ion migration through a synthetic aqueous membrane and through excised porcine skin. This comparison suggests that ion transport through pig skin occurs primarily along an aqueous pathway. In addition, a comparison of in vitro and in vivo data for several drug ions as well as comparison of in vivo results for transdermal sodium influx and efflux, suggests that the apparent sodium chloride concentration of the viable epidermis is hypotonic, having a value of about 0.09 M.

Percutaneous absorption of parathion in vitro in porcine skin: Effects of dose, temperature, humidity, and perfusate composition on absorptive flux

The effect of environmental factors on the percutaneous absorption of parathion in excised porcine skin was assessed in a flow-through diffusion cell system by varying the temperature ( T), relative humidity (%RH), perfusate flow rate ( F), and composition (porcine serum) at three parathion doses (4, 40, and 400 μg/cm 2) compared to standard conditions (air temperature = 37°C, perfusate temperature = 37°C, %RH = 60, flow rate = 4 ml/hr, and standard bovine serum albumin medium). Parathion absorption was assessed by monitoring total radiolabeled activity appearing in the perfusate over time. High relative humidity significantly increased parathion penetration, as did two elevated temperature conditions. The effects of flow rate and perfusate composition were variable and dose dependent. In the present studies, lower applied doses appeared to be more sensitive to changes in the environmental conditions studied. These results suggest that these parameters have independent and different degrees of effect on parathion percutaneous absorption. Experimental conditions should be strictly controlled and dose-response studies need to be conducted when evaluating transdermal studies. Finally, if similar effects occur in vivo, the risk assessment calculations on percutaneous absorption should take these parameters into consideration.

Percutaneous Absorption of Alkanoic Acids I: A Study of Operational Conditions

The rate of penetration of propionic and butyric acids through excised porcine skin was determined in vitro in specific apparatus allowing optimal control of operational conditions. In one technique, the rate was followed by continuous pH-stat titration of acid appearing in the perfusate, in another, by periodic monitoring of [14C]propionic acid in the perfusate. With the assumption that Fick's equation applies to the process of penetration, it was found that the permeability coefficient, Kp, increases with increasing mass of neat penetrant applied per unit area to the donor side, increases with increasing concentration of penetrant in n-heptane as vehicle, increases with increasing temperature, Ea =11.4 kcal/mol, and decreases with decreasing perfusion rate of the acceptor side when this rate is smaller than 60 mL/h.

The role of Willebrand factor in platelet - blood vessel interaction, including a discussion of resistance to atherosclerosis in pigs with von Willebrand's disease.

Von Willebrand pigs have all the manifestations of the severe human disease. The role of Willebrand antigen (VIII R:AG) and ristocetin cofactor (VIII: RWF) was assessed in these pigs by (1) transfusion and (2) "in vitro" bleeding time assay. The skin bleeding time became normal when the level of transfused Willebrand factor (VIII R:AG/RWF) was raised in the plasma above 30 U/dl. After single or repeated transfusions, skin capillary endothelium and platelets were still distinguished from normal by VIII R:AG deficiency. When incisions in excised porcine skin ("in vitro" bleeding time) were perfused with blood and plasma fractions, haemostasis occurred when plasmatic Willebrand factor exceeded 30 U/dl whether the skin or platelets came from normal or from von Willebrand pigs. The platelet plug occluding the skin incision contained VIII R:AG by immunofluorescence. Willebrand factor appears to coat surfaces and to serve as a platelet attachment protein. These bleeder pigs are resistant to atherosclerosis. If platelets are involved in early atherosclerotic lesions, the role of Willebrand factor in platelet - blood vessel interaction may be important.