Oil- and waterbased formulations containing
The dermal behaviour after topical application under in-vitro conditions (BUS-Model)
Wolfgang Pittermann 1, Olaf Lammerschop 1, Marcel Roth 1, Michael Schmitt 1 and
1 Henkel KGaA, 40191 Duesseldorf,
2 Institute for Pharmacology, Toxicology and Pharmacy, Veterinary School Hannover
Oil- and water-based formulations were frequently used for cosmetic and
dermatological treatments or as process chemicals. It is well known that
the specific behaviour concerning the dermal penetration and irritation
potential will be modified during and after the course of application
due to supersaturated solutions by evaporization of water and other volatile
components (1). It can also be influenced by ingredients of which the
distribution coefficient is not known before.
The aim of this in-vitro skin study was to learn the dermal behaviour of newly developed ferrofluides (nanoparticles) dispersed in water- and oil-based formulations under different application conditions.
|Material and Methods|
Ferrofluids are nanoparticles either magnetic or non-magnetic dis-persed in solvent (Fig. 1, Fig. 2). Two water-based products (product 1, 3) contain magnetite-particles coated by polyacrylic acid and lauric acid (product 3*) respectively. The other two samples (magnetite or zinc-ferrit) are based on the emollient dicaprylyl ether as vehicle and isostearic acid (Cognis Deutschland) as coating material. The product 4 contains zinc-ferrit instead of magnetite.
To achieve long-term stability in water and organic solvents respectively, the particle size has been adjusted to 5 - 20 nm and the particle surface has been modified to adapt the polarity of the particles to the dispersing agent. The core of the nanoparticles consists of non-toxic iron oxide and was synthesised by precipitation of ferric salt precursors. A suspension of these particles is long-term stable especially by applying a magnetic field. The surface modification consists of fatty acids which shows a good adhesion to iron oxide.
The isolated perfused bovine udder skin (BUS) is regarded as a viable
in-vitro model (Fig. 3). Using unimpaired natural
skin it takes into account active skin barrier properties and cutaneous
metabolic processes, so that it be used to study for both, penetration
and irritation induced by ingredients or formulations (2, 3, 4, 5).
The open application (2 - 4 g / 100 cm2) was performed in four independent studies (Fig. 4) either by the means of glass spatula (conventional) or a intensive finger massage (1 minute) of the skin. After the exposure periods of 1.0 h and 5.0 h the repeated horny layer stripping method (10 times) was used (Tesa 4204, BDF, Hamburg, 19 mm × 100 mm) for studying the penetration of Fe. For the irritation assays a short term exposure period of 0.5 h was added to the periods of 1.0 h and 5.0 h. Whole skin biopsies were prepared for the MTT-assay (cytotoxicity) and the determination of the PGE2-tissue concentration (irritancy) compared to untreated sites.
Additionally a new technique for a precise histochemical determination
of six different layers of the skin was introduced (Fig.
4). In contrast to the standard preparation of the whole skin biopsies
this procedure (V-max-technique, HistoServe GmbH, Münster, Germany)
allows to assay the activities of certain intracellular enzymes in freely
selected regions of epidermal or dermal layers.
|Results and Discussion|
Penetration Calculated up-take (%)
The percentual up-take was at the maximum approx. 10 % - 12 % (Fig.
5). As expected the 1st strips of all groups exhibited more Fe-content
(> 1.0 %) than each of the following nine strips at both exposure periods.
Irritation (cytotoxicity / irritancy)
For the irritation assay a very short exposure period of 0.5 h was included into the study design additionally. The degree of irritation is demonstrated by the score value combined from the relative MTT-result (cytoxicity, irreversible) and the PGE2-concentration (irritancy, reversible) (6, 7). All columns in Fig. 6 consist of both, the singular score for irritancy on the basis and for the cytotoxicity on the top.
Only after the very short exposure period of 0.5 h a difference between
the water- or oil-based formulations could be observed. The score value
of the oil-based formulations (product 2, 4) was more than twofold compared
to the value of the water-based formulations.
As expected intensive massage application induces an increased score level compared to the conventional application due the intensified release of PGE2. Under massage conditions the change from the formulation-related profile at the exposure period of 0.5 h to the individual product profile after additional 30 minutes was very similar to the results obtained after the conventional application.
Generally the massage procedure also altered the relationship between cytotoxic and irritant action of all products independently from the type. The mechanical skin treatment by the massage induced an increase of the PGE2-tissue concentration by about 70 %, whereas simultaneously the cytotoxic activity of the formulations was decreased by approx. 50 %.
Although the tape stripping did not result in the complete removal of
all of the stratum corneum and contents of the hair follicles the material
recovered should be treated as representative fraction of that present
in the horny layer due to the extra large size of the strips.
The results shown in the Figures 5 and 6 are combined in Fig. 8 for direct comparison. Clearly the penetration potential (up-take) into the horny layer is differently profiled than the irritation potential (score).
The results (Fig. 9, relative units) of the V-max-technique showed no altered activity for the enzyme SDH with its main activity in SB. However, the massage treatment induced a slight decrease of activity of LDH in SB, SS and SG, but not in the horny and dermal layers.
1. Th. Förster, W. Pittermann, M. Schmitt and M. Kietzmann; Skin
penetration properties of cosmetic formulations using a perfused bovine
udder model; J. Cosmet. Sci. 50, 147-157 (1999)
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