Pharmacodynamic Modeling of Acute and Chronic Effects of Methylprednisolone on Hepatic Urea Cycle Genes in Rats

Abstract

Corticosteroids (CS) regulate many enzymes at both mRNA and protein levels. This study used microarrays to broadly assess regulation of various genes related to the greater urea cycle and employs pharmacokinetic/pharmacodynamic (PK/PD) modeling to quantitatively analyze and compare the temporal profiles of these genes during acute and chronic exposure to methylprednisolone (MPL). One group of adrenalectomized male Wistar rats received an intravenous bolus dose (50 mg/kg) of MPL, whereas a second group received MPL by a subcutaneous infusion (Alzet osmotic pumps) at a rate of 0.3 mg/kg/hr for seven days. The rats were sacrificed at various time points over 72 hours (acute) or 168 hours (chronic) and livers were harvested. Total RNA was extracted and Affymetrix® gene chips (RG_U34A for acute and RAE 230A for chronic) were used to identify genes regulated by CS. Besides five primary urea cycle enzymes, many other genes related to the urea cycle showed substantial changes in mRNA expression. Some genes that were simply up- or down-regulated after acute MPL showed complex biphasic patterns upon chronic infusion indicating involvement of secondary regulation. For the simplest patterns, indirect response models were used to describe the nuclear steroid-bound receptor mediated increase or decrease in gene transcription (e.g. tyrosine aminotransferase, glucocorticoid receptor). For the biphasic profiles, involvement of a secondary biosignal was assumed (e.g. ornithine decarboxylase, CCAAT/enhancer binding protein) and more complex models were derived. Microarrays were used successfully to explore CS effects on various urea cycle enzyme genes. PD models presented in this report describe testable hypotheses regarding molecular mechanisms and quantitatively characterize the direct or indirect regulation of various genes by CS.

Meta-Modeling of Methylprednisolone Effects on Glucose Regulation in Rats

“…The dynamic profiles were consistent with our measurements in liver, skeletal muscle and adipose tissue [19], [24], [35], [38]. However, during chronic MPL infusion, similar to previous studies [39], [40], the receptor mRNA decreased first and then rose to a new steady-state (Fig. 3B), indicating a tolerance phenomenon.…”

Functional proteomic analysis of corticosteroid pharmacodynamics in rat liver: Relationship to hepatic stress, signaling, energy regulation, and drug metabolism

“…For over a decade, our laboratories have utilized genomic microarray data in conjunction with mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) modeling [117] to better understand the receptor/gene-mediated effects of steroids in multiple organ systems [7, 118, 119]. In order to identify common mechanisms underlying MPL-induced mRNA expression of genes, unifying mathematical models were developed to describe temporally-clustered groups of genes.…”

The activity of the carbamoyl phosphate synthase 1 promoter in human liver‐derived cells is dependent on hepatocyte nuclear factor 3‐beta

“…CREB stimulates the transcription of CPS1 and ASS based on glucagon signals . The transcription of partial enzymes in the urea cycle is also regulated by glucocorticoid and the glucagon signalling pathway, but the regulation mechanism is different .…”