Kathryn L. Gilliland

Systemic Isotretinoin Therapy Normalizes Exaggerated TLR-2-Mediated Innate Immune Responses in Acne Patients

Retinoids are used in the treatment of inflammatory skin diseases and malignancies, but studies characterizing the in vivo actions of these drugs in humans are lacking. Isotretinoin is a pro-drug for all-trans retinoic acid that can induce long-term remissions of acne; however, its complete mechanism of action is unknown. We hypothesized that isotretinoin induces remission of acne by normalizing the innate immune response to the commensal bacterium P. acnes. Compared to normal subjects, peripheral blood monocytes from acne patients expressed significantly higher levels of TLR-2 and exhibited significantly greater induction of TLR-2 expression following P. acnes stimulation. Treatment of patients with isotretinoin significantly decreased monocyte TLR-2 expression and subsequent inflammatory cytokine response to P. acnes by one week of therapy. This effect was sustained six months following cessation of therapy, indicating that TLR-2 modulation may be involved in the durable therapeutic response to isotretinoin. This study demonstrates that isotretinoin exerts immunomodulatory effects in patients and sheds light on a potential mechanism for its long-term effects in acne. The modulation of TLR-2 expression on monocytes has important implications in other inflammatory disorders characterized by TLR-2 dysregulation.

Temporal changes in gene expression in the skin of patients treated with isotretinoin provide insight into its mechanism of action

Isotretinoin (13-cis RA) is the most potent agent in the treatment of acne. Insights into its mechanism of action can lead to drug discovery of alternative compounds with comparable efficacy but improved safety. The goal of this study is to compare the temporal changes in gene expression in the skin of acne patients after 1 week and 8 weeks of treatment with isotretinoin. Microarray analysis was performed on skin biopsies taken from 8 acne patients prior to and at 8 weeks of treatment with isotretinoin. Results were compared with data obtained from 7 acne patients biopsied at one week of treatment in a prior study. Distinctly different patterns of gene expression were noted. At 8 weeks, genes encoding extracellular matrix proteins were up-regulated and numerous genes encoding lipid metabolizing enzymes were down-regulated. At one week, genes encoding differentiation markers, tumor suppressors and serine proteases were up-regulated. Only three genes were commonly down-regulated. The temporal changes in gene expression in patient skin noted with isotretinoin substantiate many previously reported effects of isotretinoin and other retinoids, suggesting a model wherein isotretinoin induces apoptosis leading to reduced sebaceous gland size, decreased expression of lipid metabolizing enzymes and increased matrix remodeling during acne resolution.

Isotretinoin Temporally Regulates Distinct Sets of Genes in Patient Skin

TO THE EDITOR The goal of this study is to gain insight into putative pathways by which 13-cis retinoic acid (13-cisRA) improves acne by comparing the temporal changes in gene expression in the skin of acne patients. Gene array analysis and immunohistochemistry were performed on skin biopsies from patients at baseline and after 8 weeks of isotretinoin therapy and compared to data obtained at 1 week (Nelson et al., 2008). As 13-cisRA drastically decreases sebaceous gland size after 16 weeks (Goldstein et al., 1982); we chose an 8week time point to examine changes in skin histology and gene expression. All protocols were approved by the Institutional Review Board of The Pennsylvania State University College of Medicine and were conducted according to the principles outlined in the Declaration of Helsinki. Eight patients who were prescribed isotretinoin for their severe acne enrolled in the study after giving informed consent and 5-mm punch biopsies of uninvolved skin were taken from their upper backs at baseline and 8 weeks of treatment. Demographic data are presented in Figure 1a. After 8 weeks, sebaceous gland size was reduced by 76% (4.17fold) compared to baseline (P1⁄40.009) (Figure 1b and d). At 1 week, glands were decreased by approximately 49% (not significant; Figure 1c and d). Gene array expression analysis was performed on biopsies at baseline and after 8 weeks of therapy. Using a false discovery rate of 0.05 corresponding to Abbreviation: 13-cisRA, 13-cis retinoic acid

Isotretinoin Increases Skin Surface Levels of Neutrophil Gelatinase-Associated Lipocalin in Patients Treated for Severe Acne

Background  A clear‐cut need exists for safe and effective alternatives to the use of isotretinoin in severe acne. Lack of data regarding the specifics of isotretinoin’s mechanism of action has hampered progress in this area. Recently, the protein neutrophil gelatinase‐associated lipocalin (NGAL) has been identified as a mediator of the apoptotic effect of isotretinoin on sebocytes.

Early gene changes induced by isotretinoin in the skin provide clues to its mechanism of action

Gene expression analysis of patient skin at one-week of oral isotretinoin therapy for severe acne illustrates the initial changes caused by 13-cis RA. Focus on the function of these significantly changed genes provides clues to its mechanism of action in skin. Significant gene changes included the up-regulation of lipocalin 2, which encodes the protein neutrophil gelatinase associated lipocalin (NGAL). Detailed studies of NGAL’s localization and function within the sebaceous gland demonstrated that NGAL mediates the apoptotic action of 13-cis RA on sebaceous glands, thereby suggesting that agents which selectively induce NGAL expression in sebaceous glands might represent therapeutic alternatives to the use of 13-cis RA for the treatment of acne