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Mechanisms of Tape Stripping and Protein Quantification
By: Ali Alikhan, MD, and Howard I. Maibach, MD
Posted: February 26, 2010, from the March 2010 issue of Cosmetics & Toiletries.
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In the second bioassay using this technique, SA, benzoyl peroxide (BPO) and retinoic acid were examined.23 The test preparations were: 0.05% all-trans retinoic acid; 2% salicylic acid at pH 6.95; 2% BPO; vehicle; untreated skin; and occluded but untreated skin.23 After 3 hr of treatment, only the BPO treatment removed significantly more SC on 25 strips than untreated skin, while the other treatments did not achieve statistical significance.23 At 3 hr, SA had greater SC amounts removed in the first 10 (superficial) strips, while deeper strips (11–25) demonstrated BPO to have the greatest SC removal.23 Statistically significant masses of SC were removed after 6 hr and 25 tape strips in all three experimental groups, when compared with the vehicle, untreated and occluded groups.23 At 6 hr, the first 10 tape strips from the SA group removed more protein than the other groups. At 10–15 strips, all treatments were comparable, and at 16–25 strips, BPO removed the most protein.23
These in vivo human results indicate that all treatments tested are effective keratolytics, which may account for their effectiveness against Acne vulgaris. Furthermore, it appears that SA may be a more suitable treatment for mild, superficial acne while BPO may be optimal for deeper, inflammatory acne. The ability of BPO to loosen the SC at deeper levels complements its antimicrobial/anti-inflammatory properties, resulting in an effective anti-inflammatory agent for papulo-pustular acne. Additionally, BPO appears to be effective even with short-term administration. RA had inferior SC disruption at 3 hr but significant disruption at 6 hr, indicating time-dependent keratolytic effects, consistent with its complex nuclear receptor interactions and alteration of gene transcription.
The SC is a an efficient indicator of the percutaneous penetration of an active agent and/or excipient, based upon the work of Rougier et al.24 These researchers demonstrated the close relationship between what is present in the SC after 30 min of application, and what ultimately penetrates into the body in both hairless rats and humans. This provides a facile assay for Galenic formulation variables. Further, the SC integrity to water loss (TEWL) appears to mirror the ability of a chemical to penetrate inwardly. Therefore, individuals with high TEWL also have increased percutaneous penetration.25
Lastly, the importance of the approximate 15 SC layers in relation to cutaneous health is impressive. The stripping method provides insight into how this thin membrane functions, and this method should become an important part of cutaneous investigative biology. As previously mentioned, Waller et al. demonstrated the robust evaluation of keratolytics in vivo in man using tape stripping with a colorimetric protein assay.23 The SC is beginning to reveal some of its secrets but much remains to be done.
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