Efficient and simple quantification of stratum corneum proteins on tape strippings by infrared densitometry

Background: The analysis of stratum corneum (SC) components is a widely accepted method to determine 'skin health' status or to follow the effects of topical treatments. These analytes are normally corrected to the amount of SC removed which can be determined gravimetrically or by extraction of SC proteins and their subsequent analysis. Unfortunately, this is a time consuming procedure and usually requires a laboratory. As a result there is a need for equipment that can be used in a clinical setting. Equally, a concurrent determination of total SC protein content and enzyme activity or any other analyte on the same tape stripping is difficult and also time consuming. Therefore a compact infrared densitometer was developed allowing a convenient and user friendly indirect measurement of SC protein content on tape strippings by optical absorption. As this is a non-destructive technique, the tape strippings can subsequently be utilized for any other bioassay. Methods: Using tape strippings from human subjects the SC optical absorption was determined densitometrically and after extraction of the tape strippings, their protein content was measured. A comparison between SC optical absorption and protein content was made between samples from different body sites, differing hydration and pH levels, different age groups and between the genders. Results: The progression of absorption and protein curves was similar irrespective of tape strip number. The overall coefficient of determination (n=238) between absorption and protein content of forearm measurements was R-2=0.852 and the corresponding overall linear regression 0.623x+2.703. Although the data distribution in the different subject groups varied, the regression was always quite similar and independent of gender, age, skin hydration rate, skin pH and varying skin areas. The correlations reached were statistically significant. Conclusion: Infrared densitometry is an easy to use and non-destructive technique for the convenient measurement of the optical absorption of SC tape strippings which was shown to be linearly proportional to their protein content. Thus the corresponding SC densitometric-protein content calibration curves can be used for a fast indirect protein evaluation of tape strippings. As this is a non-destructive method, the unmodified tapes can be used for further investigations.