all-trans Retinoic acid is a metabolite of vitamin A and a ligand for retinoic acid receptors (RARs) with IC50 values of 9, 3, and 10 nM for RARα, RARβ, and RARγ, respectively, in radioligand binding assays.¹ It induces expression of a luciferase reporter in COS-7 cells expressing RARα, RARβ, or RARγ (EC50s = 169, 9, and 2 nM, respectively). all-trans Retinoic acid (17 nmol) reduces papilloma formation induced by phorbol 12-myristate 13-acetate (TPA) in mice.² It reduces bile duct proliferation, hydroxyproline levels, and liver inflammation in a rat model of α-naphthylisothiocyanate-induced chronic cholestasis and reduces plasma levels of alkaline phosphatase and bile salts in the Mdr2-/- mouse model of cholestasis.³ all-trans Retinoic acid also reduces hepatic fat accumulation, triglycerides, body weight, and serum glucose levels in mice with Western diet-induced obesity.⁴