Abstract 313 Poster Session I, Saturday, 5/1 (poster 146)

Background: Retinoic acid derivatives (retinoids) used for treatment of acne vulgaris exert their pleiotropic effects on cell development through specific nuclear receptors, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Because the role of these receptors in sebocyte growth and differentiation is unknown, we tested the effects of all-trans retinoic acid (ATRA), selective RAR and RXR agonists, and a RAR-β,γ antagonist in vitro.

Methods: Rat preputial sebocytes were grown in an epithelial cell culture system. Treatments were performed in triplicate in serum-free medium from days 3 to 9 at concentrations between 10-10 M and 10-6 M with ATRA and synthetic retinoids made in the laboratories of Galderma R&D: CD271 (RAR-β,γ agonist), CD2043 (RAR pan-agonist), CD2809 (RXR agonist), and CD2665 (RAR-β,γ antagonist) alone and in combination with ATRA or RAR agonists. Cell growth was determined by number of cells (n=4) and colonies (n=8), and differentiation by analysis of lipid-forming colonies (LFCs) defined as those colonies with greater than 5 Oil Red O-staining cells (n=8).

Results: ATRA, CD271, and CD2043 caused significant decreases in numbers of cells and colonies as well as numbers of LFCs. However, the differences among these retinoids at high dose (10-6 M) were noteworthy: with ATRA, only a few colonies grew but became twice as differentiated as controls (42.2 ± 11.2% vs. 22.6 ± 7.7% LFCs, p < 0.01); CD271 completely obliterated cell growth, and consequently differentiation; CD2043 showed no more inhibitory effects on cell growth and differentiation than at 10-8 M. Furthermore, CD2665 antagonized the inhibitory effects of these three retinoids on both cell growth and differentiation. In contrast, CD2809 increased both cell numbers and LFCs. The increase in cell number was only significant at 10-7 M (141.2 ± 13.2% control, p = 0.046) with no effect on colony number. However, LFCs increased in a clearly dose-related manner, with a maximum of 73.7 ± 19.0% at 10-6 M (p = 0.0001).

Conclusions: Our data suggest that RARs and RXRs differ in their roles in sebocyte growth and differentiation: 1) RARs, especially the β or γ subtypes, mediate both the anti-proliferative and anti-differentiative effects of retinoids, 2) RXRs mediate prominent differentiative and weak proliferative effects, 3) the anti-proliferative and anti-differentiative effects of ATRA are probably mediated by RARs, whereas its differentiative effect at high dose may be mediated by RXRs via ATRA metabolism to 9-cis retinoic acid (the natural ligand of RXRs).