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Biomedical subjects

J Lademann

Publications and source records attributed to J Lademann.

33 records · Page 2Linked to original sources
PubMed2001

The role of follicular penetration. A differential view.

Textbooks describe percutaneous absorption through normal skin as diffusion through the stratum corneum barrier, i.e., in a simplified view, as a physiochemical interaction of a penetrating compound with the horizontal multilayer lipid structures and the underlying corneocytes within the horny layer. Hair follicles and sweat glands are vertical structures and are considered of little importance since 'they represent a small and insignificant percentage of the skin surface'. To this integral view, a differentiated hypothesis is proposed: the more perfect the barrier function of the horny layer, the greater the relative role of the imperfections within the skin as a defence organ. Three kinds of imperfections should be taken into account: (1) the follicular apparatus of hair follicles; (2) the sweat glands, and (3) microlesions in the interfollicular horny layer. Each of these can theoretically represent a vertical pathway for percutaneous absorption, i.e. a 'shunt'.

Animals↗
PubMed2001

Correlation of the local distribution of topically applied substances inside the stratum corneum determined by tape-stripping to differences in bioavailability.

Tape-stripping and optical spectroscopy are used as a suitable combined method to determine the horny layer profile. Firstly, typical ultraviolet filter substances are used as active substances which are fixed inside the horny layer. Secondly, clobetasol propionate was applied topically in two formulations, Temovate Cream and Temovate and Emollient. The measured changes in the local distribution of the drug inside stratum corneum reflect the observed differences in the biological response visualized as blanching. The concentration of the drug in deeper parts of the horny layer proposes the existence of a small channel available for the percutaneous absorption. The observed low intensity blanching is correlated to the follicle orifices of the skin. After application of Temovate and Emollient, a lateral spreading of the drug must be taken into account.

Administration, Topical↗
PubMed1997

A spark counter as a control unit of a radio frequency surgery device.

A new approach in radio frequency (rf) electrosurgery, used for tissue treatment, is achieved by using a new process control method. An external control unit allows a commonly available rf-generator to automatically supply the appropriate power for differing tissue types, thus ensuring best cutting quality. The sparks, generated during the scalpel electrode interaction with the tissue, appear statistically distributed. The spark rate depends on various factors and is monotonic with the supplied electrical power. This allows it to be used as the controlled variable in the cutting process. The ac current passing through the tissue is evaluated by an external control unit using an analyzation algorithm to determine the number of sparks. The external unit is comprised of a system, which measures the spark rate, and a subsequent proportional integral (P.I.) controller. The functionality of the control method as well as the electrical circuitry is verified through cuts with different degrees of carbonization and cuts through tissue heterojunctions.

Adipose Tissue↗
PubMedDate not supplied

Synergy effects between organic and inorganic UV filters in sunscreens.

The influence of the synergy effects between organic and inorganic UV filter substances on the sun protection factor (SPF) of topically applied sunscreen formulations is investigated. The medium is considered to have reflection, absorption, and scattering properties. The distribution of photons in this medium is investigated by Monte Carlo calculation. Typical optical parameters of the skin and substances are used to characterize the synergy effect. The results of the model calculation are checked by in vitro and in vivo measurements investigating the influence of different types of scattering microparticles on the absorption efficacy of topically applied formulations. It is found that the inorganic filter substances act as scattering microparticles in the upper skin layers. They increase the optical pathway of the photons in the topically applied absorbing formulation also localized there. In this way, more photons are absorbed, increasing the SPF. The results obtained are important for the optimization of the SPF of sunscreen formulation containing organic and inorganic UV-filter components.

Administration, Cutaneous↗
PubMedDate not supplied

Penetration studies of topically applied substances: Optical determination of the amount of stratum corneum removed by tape stripping.

Tape stripping is a standard measuring method for the investigation of the dermatopharmacokinetics of topically applied substances using adhesive films. These tape strips are successively applied and removed from the skin after application and penetration of topically applied substances. Thus, layers of corneocytes and some amount of topical applied substances are removed. The amount of substances and the amount of stratum corneum removed with a single tape strip has to be determined for the calculation of the penetration profile. The topically applied substances removed from the skin can be determined by classical analytical methods like high-pressure liquid chromatography, mass spectroscopy, and spectroscopic measurements. The amount of corneocytes on the tape strips can be easily detected by their pseudoabsorption. In the present paper, an easy and cheap corneocyte density analyzer is presented that is based on a slide projector. Comparing the results of the measurements obtained by the corneocyte density analyzer and by uv-visible spectrometry, identical results were obtained.

Administration, Topical↗
PubMedDate not supplied

Determination of the horny layer profile by tape stripping in combination with optical spectroscopy in the visible range as a prerequisite to quantify percutaneous absorption.

A new method was developed to determine the horny layer profile of volunteers using tape stripping in combination with UV/visible spectroscopy. The optical absorbance and the weight of corneocyte aggregates were compared as parameters for the determination of the mass of the horny layer particles fixed to the individual tapes. It was shown that the potential disturbances influencing both parameters must be considered critically before calculating the correlation factor, found as R2mean = 0.93 +/- 0.05. It was proven that the absorbance in the visible range is better suited than the weight to quantify the amount of corneocyte aggregates removed by a single strip. The new method allows an exact anatomical localization of the individual tapes and all data obtained within the depth profile of the stratum corneum. This was exemplified by the determination of the penetration of chemical and physical UV filters into the horny layer.

Adult↗
PubMedDate not supplied

Bioavailability of clobetasol propionate-quantification of drug concentrations in the stratum corneum by dermatopharmacokinetics using tape stripping.

The concentration of clobetasol propionate in the stratum corneum after application of three different formulations was determined, quantifying the influence of the formulations on the bioavailability of the drug. The stratum corneum was sampled by tape stripping. The concentrations of clobetasol propionate were determined quantitatively by HPLC. After application of Clobetasol Propionate Cream USP, 0.05%, and Temovate Cream, 0.05%, identical amounts of the drug were found in the stratum corneum, whereas after application of Temovate epsilon Emollient, 0.05%, the quantity was clearly decreased. From results obtained measuring the drug concentration in the adjacent sites of the skin where the creams had not been applied, it became clear that clobetasol propionate in Temovate epsilon Emollient, migrated to a large extent in the lateral direction. This explains the lower concentration measured for this formulation in the skin areas where the cream had been applied. In general, a lateral distribution of the applied drug must be taken into account when positioning the application areas on the forearm.

Administration, Cutaneous↗
PubMedDate not supplied

Investigation of the stability of coated titanium microparticles used in sunscreens.

Due to its UV-light-absorbing properties, titanium dioxide is used in many sunscreen products. However, concern has been raised about a possible photocatalytic activity of titanium dioxide on living tissues. To reduce potential adverse effects, titanium dioxide used in cosmetic preparations is often coated. The coating should be stable under conditions of use. In order to verify the coating stability, sunscreen-grade-coated titanium microparticles were investigated by laser-induced plasma spectroscopy. No changes in the mechanical stability of the coated microparticles could be detected during the manufacturing and penetration of the sunscreen. Applying strong forces on the microparticles by centrifugation, exceeding by far in use conditions, resulted only in small changes in the coating.

Aluminum↗
PubMedDate not supplied

Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice.

Coated titanium dioxide (TiO2) microparticles are commonly used as UV filter substances in commercial sunscreen products. The penetration of these microparticles into the horny layer and the orifice of the hair follicle was investigated. The distribution of the microparticles in the horny layer was analyzed using the method of tape stripping in combination with spectroscopic measurements. Deeper layers of the stratum corneum were devoid of TiO(2) even after repetitive application of sunscreen preparation when analyzing interfollicular areas. Only in the areas of the pilosebaceous orifices could microparticles be identified. The penetration of TiO(2) was investigated in histological skin sections. A biopsy was taken from a skin area from which the horny layer had been removed by tape stripping. In isolated areas, a penetration of coated TiO2 into the open part of the follicle was observed. The amount of TiO2 found in a given follicle was less than 1% of the applied total amount of sunscreens. A penetration of microparticles into viable skin tissue could not be detected.

Adult↗
PubMedDate not supplied

UV/VIS absorbance allows rapid, accurate, and reproducible mass determination of corneocytes removed by tape stripping.

The accurate determination of the mass of the horny layer removed by tape stripping is a decisive prerequisite for the application of this technique in penetration studies. A novel method using optical spectroscopy to determine the amount of stratum corneum (SC) is presented. We could show that the absorbance measured in the visible spectral range accurately reflects the mass of the SC fixed on individual tapes. Furthermore, absorbance measurement allows determination of the absolute mass of corneocyte aggregates on the removed tape strips. Topically applied substances do not disturb the spectroscopic measurements in contrast to the conventionally employed weight determination. Identical results were obtained when performing spectroscopic horny layer quantification independently in two separate institutions. Taken together, this new method is rapid, sensitive, reproducible, and accurate. We anticipate a wide application in penetration studies as well as in dermatopharmacokinetics.

Adult↗
PubMedDate not supplied

Evaluation of the pseudo-absorption method to quantify human stratum corneum removed by tape stripping using protein absorption.

Tape stripping is a well-known method to study the barrier function of the stratum corneum (SC) and penetration processes of topically applied substances into the horny layer. The quantification of the removed corneocytes for each tape strip is the prerequisite for these studies. The pseudo-absorption of the corneocytes was proposed as a measure for the quantification of the removed corneocyte aggregates. In this study, the pseudo-absorption of the corneocytes in the visible range (430 nm) is compared with the protein absorption in the UV range (278 nm) and an absorption at 652 nm obtained after staining of the SC proteins with Trypan blue. Both the protein absorption and the absorption measured after staining correlate well with the pseudo-absorption measured at 430 nm (R(2) = 0.92 +/- 0.04 and R(2) = 0.95 +/- 0.04, respectively).

Adult↗
PubMedDate not supplied

Lateral spreading of topically applied UV filter substances investigated by tape stripping.

The lateral spreading of topically applied substances is a competitive process to the penetration into the stratum corneum (SC). The penetration of topically applied UV filter substances into the human SC and the lateral spreading were investigated in vivo. Tape stripping in combination with spectroscopic measurements was used to study both processes of two UV filter substances. The concentration of both UV filters was determined inside and outside the application area by varying the application and tape stripping protocol. A spreading of the topically applied substances from the treated to the untreated areas was observed, which caused a concentration gradient. This lateral spreading depends on the time between application and tape stripping and the size of the treated skin area. Significant amounts of topically applied substances were found adjoining the application area, due to the lateral spreading which takes place on the skin surface. In general, the lateral spreading must be considered to be a competitive process when studying penetration processes of topically applied substances. It has to be considered during drug treatment of small limited skin areas and for the interpretation of recovery rates obtained in penetration studies.

Administration, Cutaneous↗
PubMedDate not supplied

Reservoir function of the stratum corneum: development of an in vivo method to quantitatively determine the stratum corneum reservoir for topically applied substances.

Investigations on the stratum corneum (SC) reservoir for topically applied substances are of importance in dermatologic science in order to assess the pharmacokinetics of these substances. In the present study, an in vivo method was developed to determine the SC reservoir quantitatively and to investigate the temporal behavior of this reservoir. Therefore, increasing amounts of an oil-in-water emulsion (o/w emulsion) containing 4% of a chemical UV filter were topically applied onto the flexor forearms of 5 healthy volunteers. The saturation of the SC reservoir was determined utilizing the tape stripping technique 1 and 6 h after application. The capacity of the SC reservoir for the o/w emulsion was found to be approximately 2.7 mg/cm(2). Furthermore, a correlation of the capacity of the SC with transepidermal water loss was observed. Extending the time between the topical application and SC removal did not affect the distribution or the recovery rate of the UV filter in the SC. The results indicate that the reservoir of the SC is limited. This is reflected by the saturation level, which depends on the individual volunteer and, presumably, the topically applied substances and formulations used. The results show that the method developed is suited to quantitatively determine in vivo the SC reservoir for topically applied substances.

Administration, Topical↗