An in vivo model of Postinflammatory Hyperpigmentation and Erythema: Clinical, Colorimetric, and Molecular Characteristics.

BACKGROUND Post-inflammatory hyperpigmentation (PIH) is a common, acquired pigmentary disorder of the skin associated with significant quality of life impairment, especially in skin of color individuals. Current treatment for PIH is limited, largely due to a poor understanding of disease pathogenesis and the lack of a representative disease model. OBJECTIVES This study is intended to further develop, update, and validate our previously designed in vivo model of acne-induced PIH/post-inflammatory erythema (PIE) using different concentrations of trichloroacetic acid (TCA), a medium-depth chemical peel. METHODS 29 patients with skin types I-VI and clinician-confirmed presence of two or more truncal acne pustules and PIH/PIE were included. On the basis of IGA, CPP, colorimetry, and skindex, we (2) experimentally determine an optimum TCA-concentration and assess our model's ability to exhibit a dose-response relationship between degree of inciting insult and severity of resulting pigmentation. We also (3) perform differential microRNA profiling and pathway analysis to explore the potential of microRNAs as molecular adjuncts to our model. RESULTS Application of 30% TCA produced lesions indistinguishable from acne-induced PIH and PIE lesions on the basis of colorimetry data without causing epidermal necrosis. Application of progressively increasing TCA doses from 20%-30% resulted in concentration-dependent increases in CPP, IGA, and colorimetry scores at all time points during the study. miRNA-31 and miRNA-23b may play a role in PIH pathogenesis, though further validation is required. CONCLUSIONS Our TCA-based in vivo model, using TCA concentrations between 20-30% with an optimum of 30%, enables the quantitative assessment of the pigmentary response to varying degrees of cutaneous inflammation in a fashion that mirrors natural acne-induced PIH and PIE.