C Y Li1, C L Zimmerman, T S Wiedmann. 1. Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis 55455, USA.
Abstract
PURPOSE: The capacity and specificity of bile salt (BS)/ phosphatidylcholine (PC) mixed lipid aggregated systems in solubilizing four structurally related retinoids, etretinate, motretinid, fenretinide and N-ethyl retinamide, were determined. METHODS: Excess solid drug was dispersed into sodium taurocholate (NaTC)/egg PC systems at lipid ratios of 10:0, 10:2 and 10 mM:10 mM in isotonic HEPES buffer, pH 6.5. A sensitive HPLC method was used to quantify the amount solubilized. The melting point and associated enthalpy change as well as the aqueous solubilities were also measured. RESULTS: The retinoids had aqueous solubilities of less than 25 nM. The predicted aqueous solubility was less than 0.01 nM. The amount of retinoid in 10 mM NaTC was increased from three to four orders of magnitude relative to the aqueous solubility. Further increases in the amount solubilized were observed in the 10:10 mixed micelle dispersion. Fenretinide and N-ethyl retinamide were particularly well solubilized by BS and BS/PC aggregated systems which may be related to the presence of a cyclohexenyl ring. CONCLUSIONS: The discrepancy between the observed and predicted aqueous solubility may be due to self-association of the retinoids. Micellar/aqueous distribution ratios appear to be dominated by the hydrophobic effect, although specific interactions also are important. In considering intestinal absorption, the large increase in solubilization with BS/PC micelles would be capable of dramatically increasing the bioavailability in spite of the smaller effective diffusivity of the solubilized retinoid.
PURPOSE: The capacity and specificity of bile salt (BS)/ phosphatidylcholine (PC) mixed lipid aggregated systems in solubilizing four structurally related retinoids, etretinate, motretinid, fenretinide and N-ethyl retinamide, were determined. METHODS: Excess solid drug was dispersed into sodium taurocholate (NaTC)/egg PC systems at lipid ratios of 10:0, 10:2 and 10 mM:10 mM in isotonic HEPES buffer, pH 6.5. A sensitive HPLC method was used to quantify the amount solubilized. The melting point and associated enthalpy change as well as the aqueous solubilities were also measured. RESULTS: The retinoids had aqueous solubilities of less than 25 nM. The predicted aqueous solubility was less than 0.01 nM. The amount of retinoid in 10 mM NaTC was increased from three to four orders of magnitude relative to the aqueous solubility. Further increases in the amount solubilized were observed in the 10:10 mixed micelle dispersion. Fenretinide and N-ethyl retinamide were particularly well solubilized by BS and BS/PC aggregated systems which may be related to the presence of a cyclohexenyl ring. CONCLUSIONS: The discrepancy between the observed and predicted aqueous solubility may be due to self-association of the retinoids. Micellar/aqueous distribution ratios appear to be dominated by the hydrophobic effect, although specific interactions also are important. In considering intestinal absorption, the large increase in solubilization with BS/PC micelles would be capable of dramatically increasing the bioavailability in spite of the smaller effective diffusivity of the solubilized retinoid.
Authors: Grace A Ledet; Richard A Graves; Elena Y Glotser; Tarun K Mandal; Levon A Bostanian Journal: Int J Pharm Date: 2014-12-24 Impact factor: 5.875
Authors: Yoshikazu Imanishi; Matthew L Batten; David W Piston; Wolfgang Baehr; Krzysztof Palczewski Journal: J Cell Biol Date: 2004-01-26 Impact factor: 10.539