Morphological and functional changes in p-glycoprotein during dexamethasone-induced hepatomegaly.
1. The effect of dexamethasone on hepatic and renal P-glycoprotein (P-gp) expression, localization and activity was investigated in rats after 4 days oral administration of two dose regimens (1 or 25 mg/kg per day). Simultaneous increases in liver weight were evaluated by quantitative histological examination. 2. In the liver, dexamethasone pretreatment produced hepatomegaly as a consequence of extensive periportal fat accumulation, which was quantified by densitometry of oil red O-stained liver sections. Quantitative immunohistochemical analysis revealed preferential periportal zonation of P-gp in control animals. Dexamethasone pretreatment resulted in spatially disproportional induction of P-gp protein expression within the liver acinus characterized by preferential increase in pericentral areas, with consequent uniform panlobular distribution. Western blot analysis confirmed these results, showing increases in P-gp protein. Quantitative reverse transcription-polymerase chain reaction analysis revealed no statistically significant change in liver mdr1b mRNA expression after either dexamethasone treatment regimen. The expression of mdr1a mRNA was significantly decreased by 85-87%. 3. In the kidney, dexamethasone reduced mdr1a mRNA expression by 69-89%, whereas mdr1b mRNA expression was increased in a dose-dependent manner. However, despite tendencies, no significant increases in P-gp expression were observed at the protein level. 4. The in vivo function of P-gp was evaluated by measuring renal and biliary secretion of rhodamine-123 (Rho123) under a steady state plasma concentration. The biliary, renal and tubular secretory clearance of Rho123 was significantly increased only after high-dose dexamethasone. 5. In conclusion, the present study suggests that drug interactions observed during corticosteroid therapy may be mediated, at least in part, through increased biliary, and also renal, excretion of P-gp substrates. Expression of P-gp in the liver showed primary periportal zonation with differential changes during induction. Accompanying hepatomegaly may be explained by severe microvesicular steatosis selectively localized to the periportal areas.
Micuda
Stanislav
S
Department of Pharmacology, Charles University in Prague, Faculty of Medicine in Hradec Kralove, Simkova 870, 500-38 Hradec Kralove, The Czech Republic. micuda@lfhk.cuni.cz
Fuksa
Leos
L
Mundlova
Lucie
L
Osterreicher
Jan
J
Mokry
Jaroslav
J
Cermanova
Jolana
J
Brcakova
Eva
E
Staud
Frantisek
F
Pokorna
Pavla
P
Martinkova
Jirina
J
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000032:analysis* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D003907:Dexamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005234:Fatty Liver / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D005938:Glucocorticoids / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity; D006529:Hepatomegaly / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D007120:Immunochemistry / Q000379:methods; D007441:Intubation, Gastrointestinal; D007668:Kidney / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008657:Metabolic Clearance Rate; D008859:Microscopy, Polarization / Q000379:methods; D009929:Organ Size / Q000187:drug effects; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020112:Rhodamine 123 / Q000008:administration & dosage / Q000493:pharmacokinetics; D015431:Weight Loss / Q000187:drug effects; D000097202:ATP-Binding Cassette Sub-Family B Member 4
D018435:ATP Binding Cassette Transporter, Subfamily B; D018528:ATP-Binding Cassette Transporters; D003907:Dexamethasone; D005938:Glucocorticoids; D012333:RNA, Messenger; D020112:Rhodamine 123; D000097202:ATP-Binding Cassette Sub-Family B Member 4; C095122:multidrug resistance protein 3