Allergic contact dermatitis (ACD) in domestic pigs is frequently used as a dermatitis model to evaluate anti‐ inflammatory activity of topically applied test articles. Pharmacological effects so far have been quantified by subjective clinical examination alone. The present study for the first time aimed at the biophysical characterization of acute and subchronic ACD lesions in order to identify objective, reliable and non invasive measures of inflammation. Six weaned domestic pigs (Landrasse x Deutsches Edelschwein) were epicutaneously sensitized with 10% 2,4‐dinitrofluorobenzene (DNFB) on day 1 and challenged at distant test sites on the dorsolateral back with 1,0% DNFB on day 12 to elicit acute ACD. Similarly, 6 pigs were challenged 5 times, on days 12, 14, 16, 18 and 20 with 0,2% DNFB for induction of subchronic ACD. The examinations were performed before challenge (baseline findings) and 6, 24 and 48 hrs after the first (acute ACD) and last challenge (subchronic ACD). In addition to semiquantitative clinical examinations (scoring) the following parameters were measured: skin color by reflectometry (Chroma Meter CR‐400/410), dermal vascular microperfusion (Periflux System 5000), transepidermal water loss (Tewameter TM 210), skin hydration (Corneometer CM 820), skin pH (Skin pH Meter PH 900), sebum production (Sebumeter SM 810) and skin thickness with ultrasonography (DUB 20).
In acute ACD clinical examination revealed earliest signs 6 hrs after challenge, which culminated at 24 hrs and decreased thereafter. Reflectometry indicated a slight increase in red colour values after 6 hrs. Microvascular blood flow was already significantly and moderately increased after 6 hrs and peaked after 24 hrs. TEWL measurements did not show a pronounced increase. Corneometry exhibited maximal changes at 6 hrs. Skin pH was also a sensitive parameter. Significantly decreased values were measured after 6 and 24 hrs, but values had normalized after 48 hrs. Measurement of skin thickness revealed the same kinetic profile as clinical examination. Sebumetry, however, proved to be useless, since sebum production was always below the detection limit of the sebumeter.
In contrast to acute ACD, clinical lesions of subchronic ACD were most pronounced already 6 hrs after the last challenge. This clinical observation was confirmed with the seven different measurement methods whereby sebumetry resulted probably in a false positive finding due to superficial residues of olive oil used as vehicle of DNFB.
In summary, results of all applied biophysical measurements, except sebumetry, agreed with scoring of clinical findings. The most appropriate measurements proved to be reflectometry, corneometry, TEWL measurement, skin pH and ultrasonography. These biophysical techniques result in reliable and reproducible results which are not subjected to inter‐individual variations as subjective scorning. Therefore these measurements are very useful to quantify inflammatory skin changes and to assess anti‐inflammatory activities of test articles.