Hydroxypropyl-beta-cyclodextrin as delivery system for thyroid hormones, regulating glutathione S-transferase expression in rat hepatocyte co-cultures

Thyroid hormones play a role in the regulation of glutathione S-transferase (GST) expression. Here, co-cultures of rat hepatocytes with bile duct epit helial cells have been used to study the direct effects of both triiodothyr onine (T3) and thyroxine (T4) on GST activities and proteins. Because T3 an d T4 are poorly water soluble and organic solvents used to dissolve them of ten interfere with biotransformation pathways, an alternative delivery syst em namely hydroxypropyl-beta -cyclodextrin (HPBC) has been applied. Appropr iate control cultures contained either 0.02 or 0.10% (w/v) HPBC, the concen trations necessary to supply T3 and T4 (10(-9) to 10(-5) M) to the cells, r espectively. No effect of the vehicle HPBC on the different GST isoenzyme a ctivities and proteins could be observed. On the contrary, after 10 days of co-culture, T3 and T4 decreased GST protein concentrations as well as GST activities measured by 1-chloro-2,4-dinitrobenzene (broad spectrum), 1,2-di chloro-4-nitrobenzene (Mu class M1/M2-specific) and 7-chloro-4-nitrobenzo-2 -oxa-1,3-diazole (Alpha class A1/2-specific) in a concentration-dependent m anner. The Alpha class subunits A1/2 and A3, and the Mu class subunit M2 we re mostly affected. No effect was observed on the Pi class enzyme. These fi ndings indicate that a combination of co-cultured hepatocytes with an HPBC- based delivery system for hydrophobic compounds represents a powerful in vi tro tool in drug development. (C) 2001 Elsevier Science Inc. All rights res erved.