98 Biochimica et Biophysica Acta, 1055 (1990) 98-101 Elsevier BBAMCR 12802 In vitro interactions of the aromatic retinoids Ro 10-9359 (etretinate) and Ro 10-1670 (acitretin), its main metabolite, with human serum lipoproteins and albumin V6ronique Carillet 1, Patrice Morli~re 1, Jean-Claude Mazi6re 2,3, Gabriele Hiippe 1, Ren6 Santus 3 and Louis Dubertret 1 1 Laboratoire de Dermatologie, I N S E R M U. 312, H@ital Henri Mondor, CrOteil, : Laboratoire de Biochimie, Facult~ de Medicine Saint Antoine, Paris and 3 Laboratoire de Physico-Chimie de l'Adaptation Biologique, 1NSERM U. 312, Mus~urn National d'Histoire Naturelle, Paris (France) (Received 29 January 1990) Key words: Retinoid; Carrier; Serum protein Serum lipoproteins are good carriers for the aromatic retinoid Ro 10-9359 (etretinate) and to a lesser extent for its main metabolite in human Ro 10-1670 (acitretin). Up to about 200 and 130 etretinate molecules and 200 and 70 acitretin molecules can bind to one LDL and one HDL, respectively. In contrast human serum albumin only binds about 10 etretinate or 30 acitretin molecules. In whole human serum loaded with the retinoids, lipoproteins carry approx. 67% of total etretinate or approx. 37% of total acitretin. In the particular case of etretinate, low density lipoproteins account for about 30% of the lipoprotein-carried etretinate. Introduction Etretinate (Ro 10-9359, Tegison in U.S.A., Tigason in Europe, see molecular structure in Fig. 1) is a syn- thetic retinoid used in the treatment of some skin dis- eases [1,2]. Its main metabolite in human (Ro 10-1670, see molecular structure in Fig. 1) is also efficient in skin diseases such as psoriasis [3]. It is eliminated faster than the ester parent compound [4]. Among side effects of etretinate or acitretin [5,6], teratogenic properties and increase in transaminases, triacylglycerols and cholesterol have been mentioned. Significant elevations of low density lipoprotein (LDL) cholesterol plasma levels, concomitant with a decrease in high density lipoprotein (HDL) cholesterol concentration were re- ported [7-10]. These effects might be related to the deregulation of the LDL catabolism. Since the compa- nion paper [11] is devoted to the uptake of etretinate and acitretin by cultured human fibroblasts using LDL, Abbreviations: E, etretinate; E*, [a4C]etretinate; A, acitretin; A*, [14C]acitretin; DMSO, dimethylsulfoxide; VLDL, very low density lipoprotein; LDL, low density lipoprotein; HDL, high density lipo- protein; HSA, human serum albumin; IF, intermediate fractions; BF, bottom fraction. Tris, Tris-buffered saline. Correspondence: P. Morlirre, Laboratoire de Dermatologie, INSERM U. 312, Hrpital Henri Mondor, 94010 Cr&eil, France. high density lipoprotein and human serum albumin (HSA) as carriers, this introductory paper deals with the interaction of etretinate and acitretin with LDL, HDL and HSA. Materials and Methods Materials. Water was obtained with a Milli Ro 4 filtering system equipped with a Milli Q unit (Millipore). Dimethylsulfoxide (DMSO) was purchased from Merck, while tris(hydroxymethyl)aminomethane and non-de- lipidated HSA (used without further purification) were obtained from Sigma. Etretinate, 14C9-radiolabelled etretinate ([14C]etretinate), acitretin, and 14C9-radio- labelled acitretin ([14C]acitretin) were kindly provided by Hoffmann-La Roche. Low density lipoproteins and HDL were isolated from human serum by sequential ultracentrifugation [12]. Absorption spectra were re- corded with a Varian DMS 100 spectrophotometer and fluorescence spectra were obtained from a Spex Fl12 fluorometer. Saturation assays. Radiolabelled etretinate (8.5 mM, 43 mCi/mmol) and acitretin (8.5 mM, 13 mCi/mmol) stock solutions were prepared in DMSO from powdered material and stored at -20°C under argon atmosphere. Stock solutions of radiolabelled etretinate and acitretin were diluted in DMSO to a 0.2 mM final concentration. The LDL, HDL, and HSA solutions were prepared in 0167-4889/90//$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)