(528e) Pathway-Based Analysis of the Liver Response to Intravenous Methylprednisolone (MPL) Administration in Rats: Acute Versus Chronic Dosing

Pharmacological time-series data, from comparative dosing studies, is critical to characterizing tissue-specific drug effects during the drug development process. Reconciling the data from these multiple studies is inevitably difficult; multiple in vivo high-throughput -omics studies are necessary to capture the global and temporal effects of the drug, but these experiments, though analogous, differ in (microarray or other) platforms, time-scales, and dosing regimens and thus cannot be directly combined or compared [1]. Our investigation addresses this reconciliation issue with a meta-analysis technique applied to characterize the tissue-specific effects of Methylprednisolone (MPL), a widely used anti-inflammatory and immunosuppressive corticosteroid (CS) [2], within the liver.

Corticosteroids such as MPL are essential to treatment of a variety of inflammatory and auto-immune conditions. While short-term use is beneficial for reducing inflammation, long-term use is associated with serious consequences including hyperglycemia, negative nitrogen balance, and fat redistribution leading to complications including diabetes, muscle wasting, osteoporosis, etc. Adding to the complexity of the physiological and pharmacological effects of corticosteroids , different dosing regimens of CS administration induce different patterns of expression [1] further indicative of the drug’s dosing-dependent regulation. Our lab has previously focused on assessing tissue-specific transcriptional dynamics of MPL within the liver in order to (1) identify transcriptional modules of characteristic mRNA dynamic features across multiple dosing regimens; and (2) elaborate on their common regulatory controls [3]. However, a systemic characterization of the influence of MPL within the liver requires further analysis requiring the reconciliation of the data from multiple dosing studies.

In the present study, we apply a multivariate decomposition approach to analyze acute and chronic MPL dosing in male adrenalectomized rats and characterize the dosing-dependent differences in the dynamic response of MPL-responsive signaling and metabolic pathways. With this approach, we deconstruct signaling and metabolic pathways into their constituent pathway activities, activities which are then scored and compared across dosing studies [4]. The pathway scoring expresses the overall intrinsic dynamic of the pathway but does not rely on measuring a consistent set of transcriptional profiles across the various experimental conditions. To further elucidate, and consistently compare dosing-induced changes in the dynamics of pathway activities, we propose a novel model-based assessment of pathway dynamics, extending the principles of PKPD to describe pathway activities. The model-based approach enabled us to hypothesize on the likely emergence (or disappearance) of indirect dosing-dependent regulatory interactions, pointing to likely mechanistic implications of dosing of MPL transcriptional regulation. More specifically, both acute and chronic MPL administration induced a strong core of activity within pathway families including: lipid metabolism, amino acid metabolism, carbohydrate metabolism, metabolism of cofactors and vitamins, regulation of essential organelles, and xenobiotic metabolism pathway families. Some pathway families, such as all lipid metabolism pathways, exhibited activity strictly indicating a mechanism in which a MPL-receptor complex binds to a glucocorticoid response element (GRE) to regulate transcription. Chronic MPL administration elicited activity of greater complexity from these lipid metabolism pathways, indicating that the hypothesized mechanism of regulation is more complete when it includes both MPL-regulated drug-receptor GRE binding, and MPL-mediated intermediate biosignaling, as mechanisms transcriptional regulation. Other pathways, such as those within in the amino acid metabolism family, report a complex response to acute MPL administration, which changes in complexity in response to chronic MPL administration. Our investigation observes such changing activity and corresponding regulatory mechanism for all MPL-activated pathways, indicating that MPL response is both dose and regimen dependent. Further, because multiple pathway activities are dominant within a single pathway, we observe that pathways cannot be defined by a single response. Instead, pathways are defined by multiple, complex, and temporally related activities corresponding to different subgroups of genes within each pathway.

[1] Almon, R. R.; DuBois, D. C.; Jusko, W. J., Endocrinology 2007, 148 (5), 2209-25.

[2] Barnes, P. J., Clin Sci (Lond) 1998, 94 (6), 557-72.

[3] Nguyen, T. T.; Almon, R. R.; Dubois, D. C.; Jusko, W. J.; Androulakis, I. P., Bmc Bioinformatics 2010, 11, 515. DOI 10.1186/1471-2105-11-515.

[4] Ovacik, M. A.; Sen, B.; Euling, S. Y.; Gaido, K. W.; Ierapetritou, M. G.; Androulakis, I. P., Toxicol Appl Pharmacol 2013, 271 (3), 386-94. DOI 10.1016/j.taap.2010.09.008.