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1.  Mathematical Modeling of Corticosteroid Pharmacogenomics in Rat Muscle following Acute and Chronic Methylprednisolone Dosing 
Molecular pharmaceutics  2008;5(2):328-339.
The pharmacogenomic effects of a corticosteroid (CS) were assessed in rat skeletal muscle using microarrays. Adrenalectomized (ADX) rats were treated with methylprednisolone (MPL) by either 50 mg/kg intravenous injection or 7-day 0.3 mg/kg/h infusion through subcutaneously implanted pumps. RNAs extracted from individual rat muscles were hybridized to Affymetrix Rat Genome Genechips. Data mining yielded 653 and 2316 CS-responsive probe sets following MPL bolus and infusion treatments. Of these, 196 genes were controlled by MPL under both dosing conditions. Cluster analysis revealed that 124 probe sets exhibited three typical expression dynamic profiles following acute dosing. Cluster A consisted of up-regulated probe sets which were grouped into five subclusters each exhibiting unique temporal patterns during the infusion. Cluster B comprised down-regulated probe sets which were divided into two subclusters with distinct dynamics during the infusion. Cluster C probe sets exhibited delayed down-regulation under both bolus and infusion conditions. Among those, 104 probe sets were further grouped into subclusters based on their profiles following chronic MPL dosing. Several mathematical models were proposed and adequately captured the temporal patterns for each subcluster. Multiple types of dosing regimens are needed to resolve common determinants of gene regulation as chronic exposure results in unexpected differences in gene expression compared to acute dosing. Pharmacokinetic/pharmacodynamic (PK/PD) modeling provides a quantitative tool for elucidating the complexities of CS pharmacogenomics in skeletal muscle.
PMCID: PMC4196382  PMID: 18271548
Microarray studies; pharmacokinetics; pharmacodynamics; mathematical models; computational biology
2.  Pharmacodynamics of Glucose Regulation by Methylprednisolone. I. Adrenalectomized Rats 
Mechanisms related to the adverse effects of corticosteroids on glucose homeostasis were studied. Five groups of adrenalectomized (ADX) rats were given methylprednisolone (MPL) intravenously at 10 and 50 mg/kg, or a continuous 7 day infusion at rates of 0, 0.1, 0.3 mg/kg/h via subcutaneously implanted Alzet mini-pumps. Plasma concentrations of MPL, glucose and insulin were determined at various time points up to 72 h after injection or 336 h after infusion. The pharmacokinetics of MPL was captured with a two-compartment model. The Adapt II software was used in modeling. Injection of MPL caused a temporary glucose increase over 6 h by stimulating gluconeogenesis. The glucose changes stimulated pancreatic β-cell secretion yielding a later insulin peak at around 10 h. In turn, insulin can stimulate glucose disposition. However, long-term MPL treatment caused continuous hyperglycemia during and after infusion. Insulin was increased during infusion, and immediately returned to baseline after the infusion was terminated, despite the almost doubled glucose concentration. A disease progression model incorporating the reduced endogenous glucose disposition was included to capture glucose homeostasis under different treatments. The results exemplify the importance of the steroid dosing regimen in mediating pharmacological and adverse metabolic effects. This mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model quantitatively describes the induction of hyperglycemia and provides additional insights into metabolic disorders such as diabetes.
PMCID: PMC3712292  PMID: 19156931
corticosteroids; methylprednisolone; pharmacodynamics; pharmacokinetics; glucose; insulin
3.  Meta-Modeling of Methylprednisolone Effects on Glucose Regulation in Rats 
PLoS ONE  2013;8(12):e81679.
A retrospective meta-modeling analysis was performed to integrate previously reported data of glucocorticoid (GC) effects on glucose regulation following a single intramuscular dose (50 mg/kg), single intravenous doses (10, 50 mg/kg), and intravenous infusions (0.1, 0.2, 0.3 and 0.4 mg/kg/h) of methylprednisolone (MPL) in normal and adrenalectomized (ADX) male Wistar rats. A mechanistic pharmacodynamic (PD) model was developed based on the receptor/gene/protein-mediated GC effects on glucose regulation. Three major target organs (liver, white adipose tissue and skeletal muscle) together with some selected intermediate controlling factors were designated as important regulators involved in the pathogenesis of GC-induced glucose dysregulation. Assessed were dynamic changes of food intake and systemic factors (plasma glucose, insulin, free fatty acids (FFA) and leptin) and tissue-specific biomarkers (cAMP, phosphoenolpyruvate carboxykinase (PEPCK) mRNA and enzyme activity, leptin mRNA, interleukin 6 receptor type 1 (IL6R1) mRNA and Insulin receptor substrate-1 (IRS-1) mRNA) after acute and chronic dosing with MPL along with the GC receptor (GR) dynamics in each target organ. Upon binding to GR in liver, MPL dosing caused increased glucose production by stimulating hepatic cAMP and PEPCK activity. In adipose tissue, the rise in leptin mRNA and plasma leptin caused reduction of food intake, the exogenous source of glucose input. Down-regulation of IRS-1 mRNA expression in skeletal muscle inhibited the stimulatory effect of insulin on glucose utilization further contributing to hyperglycemia. The nuclear drug-receptor complex served as the driving force for stimulation or inhibition of downstream target gene expression within different tissues. Incorporating information such as receptor dynamics, as well as the gene and protein induction, allowed us to describe the receptor-mediated effects of MPL on glucose regulation in each important tissue. This advanced mechanistic model provides unique insights into the contributions of major tissues and quantitative hypotheses for the multi-factor control of a complex metabolic system.
PMCID: PMC3847111  PMID: 24312573
4.  Assessing the Dynamics of Nuclear Glucocorticoid-Receptor Complex: Adding Flexibility to Gene Expression Modeling1 
A retrospective analysis was performed to modify our fourth-generation pharmacodynamic model for glucocorticoid receptor (GR) dynamics with incorporation of more physiological features. This modified model was developed by integrating previously reported free cytosolic GR and GR mRNA data following single (10, 50 mg/kg) and dual (50 mg/kg at 0 and 24 hr) intravenous doses of methylprednisolone (MPL) in adrenalectomized (ADX) male Wistar rats with several in vitro studies describing real-time kinetics of the transfer of rat steroid-receptor complex from the cell cytosol to the nucleus. Additionally, free hepatic cytosolic GR and its mRNA data from a chronic infusion dosing study of MPL (0.1 and 0.3 mg/kg/hr) in male ADX Wistar rats were used to verify the predictability of the model. Incorporation of information regarding in vitro receptor kinetics allowed us to describe the receptor-mediated pharmacogenomic effects of MPL for a larger variety of genes in rat liver from microarray studies. These included early responsive gene like CCAAT/enhancer binding protein-β (CEBP-β), a transcription factor, as well as the later responsive gene for tyrosine aminotransferase (TAT), a classical biomarker of glucocorticoid (GC) genomic effects. This more mechanistic model of GR dynamics can be applied to characterize profiles for a greater number of genes in liver.
PMCID: PMC4184272  PMID: 17285360
glucocorticoids; glucocorticoid receptor; nuclear localization; pharmacodynamics; methylprednisolone; pharmacogenomics
5.  Pharmacokinetics of Methylprednisolone after Intravenous and Intramuscular Administration in Rats 
Methylprednisolone (MPL) pharmacokinetics was examined in adrenalectomized (ADX) and normal rats to assess the feasibility of intramuscular (i.m.) dosing for use in pharmacodynamic studies. Several study phases were pursued. Parallel group studies were performed in normal and ADX rats given 50 mg/kg MPL (i.v. or i.m.) and blood samples were collected up to 6 h. Data from studies where normal rats were dosed with 50 mg/kg MPL i.m. and killed over either 6 or 96 h were combined to determine muscle site and plasma MPL concentrations. Lastly, ADX rats were dosed with 50 mg/kg MPL i.m. and killed over 18 h to assess hepatic tyrosine aminotransferase (TAT) dynamics. MPL exhibited bi-exponential kinetics after i.v. dosing with a terminal slope of 2.1 h−1. The i.m. drug was absorbed slowly with two first-order absorption rate constants, 1.26 and 0.219 h−1 indicating flip-flop kinetics with overall 50% bioavailability. The kinetics of MPL at the injection site exhibited slow, dual absorption rates. Although i.m. MPL showed lower bioavailability compared with other corticosteroids in rats, TAT dynamics revealed similar i.m. and i.v. response profiles. The more convenient intramuscular dosing can replace the i.v. route without causing marked differences in pharmacodynamics.
PMCID: PMC4181331  PMID: 17569107
methylprednisolone; corticosteroids; pharmacokinetics; intramuscular injection; tyrosine aminotransferase
6.  Pharmacodynamic Modeling of Acute and Chronic Effects of Methylprednisolone on Hepatic Urea Cycle Genes in Rats* 
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.
PMCID: PMC2733100  PMID: 19787073
urea cycle; corticosteroids; methylprednisolone; pharmacodynamics; genomics
7.  Fifth-Generation Model for Corticosteroid Pharmacodynamics: Application to Steady-State Receptor Down-Regulation and Enzyme Induction Patterns during Seven-Day Continuous Infusion of Methylprednisolone in Rats 
A fifth-generation model for receptor/gene-mediated corticosteroid effects was proposed based on results from a 50 mg/kg IV bolus dose of methylprednisolone (MPL) in male adrenalectomized rats, and confirmed using data from other acute dosage regimens. Steady-state equations for receptor down-regulation and tyrosine aminotransferase (TAT) enzyme induction patterns were derived. Five groups of male Wistar rats (n=5/group) were subcutaneously implanted with Alzet mini-pumps primed to release saline or 0.05, 0.1, 0.2, and 0.3 mg/kg/hr of MPL for 7 days. Rats were sacrificed at the end of the infusion. Plasma MPL concentrations, blood lymphocyte counts, and hepatic cytosolic free receptor density, receptor mRNA, TAT mRNA, and TAT enzyme levels were quantitated. The pronounced steroid effects were evidenced by marked losses in body weights and changes in organ weights. All four treatments caused a dose-dependent reduction in hepatic receptor levels, which correlated with the induction of TAT mRNA and TAT enzyme levels. The 7 day receptor mRNA and free receptor density correlated well with the model predicted steady-state levels. However, the extent of enzyme induction was markedly higher than that predicted by the model suggesting that the usual receptor/gene-mediated effects observed upon single/intermittent dosing of MPL may be countered by alterations in other aspects of the system. A mean IC50 of 6.1 ng/mL was estimated for the immunosuppressive effects of methylprednisolone on blood lymphocytes. The extent and duration of steroid exposure play a critical role in mediating steroid effects and advanced PK/PD models provide unique insights into controlling factors.
PMCID: PMC4207287  PMID: 12194533
pharmacodynamics; pharmacogenomics; methylprednisolone; tyrosine amino-transferase
8.  Glycerol-3-Phosphate Acyltransferase 1 Deficiency in ob/ob Mice Diminishes Hepatic Steatosis but Does Not Protect Against Insulin Resistance or Obesity 
Diabetes  2010;59(6):1321-1329.
Hepatic steatosis is strongly associated with insulin resistance, but a causal role has not been established. In ob/ob mice, sterol regulatory element binding protein 1 (SREBP1) mediates the induction of steatosis by upregulating target genes, including glycerol-3-phosphate acyltransferase-1 (Gpat1), which catalyzes the first and committed step in the pathway of glycerolipid synthesis. We asked whether ob/ob mice lacking Gpat1 would have reduced hepatic steatosis and improved insulin sensitivity.
Hepatic lipids, insulin sensitivity, and hepatic insulin signaling were compared in lean (Lep+/?), lean-Gpat1−/−, ob/ob (Lepob/ob), and ob/ob-Gpat1−/− mice.
Compared with ob/ob mice, the lack of Gpat1 in ob/ob mice reduced hepatic triacylglycerol (TAG) and diacylglycerol (DAG) content 59 and 74%, respectively, but increased acyl-CoA levels. Despite the reduction in hepatic lipids, fasting glucose and insulin concentrations did not improve, and insulin tolerance remained impaired. In both ob/ob and ob/ob-Gpat1−/− mice, insulin resistance was accompanied by elevated hepatic protein kinase C-ε activation and blunted insulin-stimulated Akt activation.
These results suggest that decreasing hepatic steatosis alone does not improve insulin resistance, and that factors other than increased hepatic DAG and TAG contribute to hepatic insulin resistance in this genetically obese model. They also show that the SREBP1-mediated induction of hepatic steatosis in ob/ob mice requires Gpat1.
PMCID: PMC2874692  PMID: 20200319
9.  A Microarray Analysis of the Temporal Response of Liver to Methylprednisolone: A Comparative Analysis of Two Dosing Regimens 
Endocrinology  2007;148(5):2209-2225.
Microarray analyses were performed on livers from adrenalectomized male Wistar rats chronically infused with methylprednisolone (MPL) (0.3 mg/kg·h) using Alzet mini-osmotic pumps for periods ranging from 6 h to 7 d. Four control and 40 drug-treated animals were killed at 10 different times during drug infusion. Total RNA preparations from the livers of these animals were hybridized to 44 individual Affymetrix REA230A gene chips, generating data for 15,967 different probe sets for each chip. A series of three filters were applied sequentially. These filters were designed to eliminate probe sets that were not expressed in the tissue, were not regulated by the drug, or did not meet defined quality control standards. These filters eliminated 13,978 probe sets (87.5%) leaving a remainder of 1989 probe sets for further consideration. We previously described a similar dataset obtained from animals after administration of a single dose of MPL (50 mg/kg given iv). That study involved 16 time points over a 72-h period. A similar filtering schema applied to the single-bolus-dose data-set identified 1519 probe sets as being regulated by MPL. A comparison of datasets from the two different dosing regimens identified 358 genes that were regulated by MPL in response to both dosing regimens. Regulated genes were grouped into 13 categories, mainly on gene product function. The temporal profiles of these common genes were subjected to detailed scrutiny. Examination of temporal profiles demonstrates that current perspectives on the mechanism of glucocorticoid action cannot entirely explain the temporal profiles of these regulated genes.
PMCID: PMC4183266  PMID: 17303664
10.  Tissue-Specific Gene Expression and Regulation in Liver and Muscle Following Chronic Corticosteroid Administration 
Although corticosteroids (CSs) affect gene expression in multiple tissues, the array of genes that are regulated by these catabolic steroids is diverse, highly tissue specific, and depends on their functions in the tissue. Liver has many important functions in performing and regulating diverse metabolic processes. Muscle, in addition to its mechanical role, is critical in maintaining systemic energy homeostasis and accounts for about 80% of insulin-directed glucose disposal. Consequently, a better understanding of CS pharmacogenomic effects in these tissues would provide valuable information regarding the tissue-specificity of transcriptional dynamics, and would provide insights into the underlying molecular mechanisms of action for both beneficial and detrimental effects.
We performed an integrated analysis of transcriptional data from liver and muscle in response to methylprednisolone (MPL) infusion, which included clustering and functional annotation of clustered gene groups, promoter extraction and putative transcription factor (TF) identification, and finally, regulatory closeness (RC) identification.
This analysis allowed the identification of critical transcriptional responses and CS-responsive functions in liver and muscle during chronic MPL administration, the prediction of putative transcriptional regulators relevant to transcriptional responses of CS-affected genes which are also potential secondary bio-signals altering expression levels of target-genes, and the exploration of the tissue-specificity and biological significance of gene expression patterns, CS-responsive functions, and transcriptional regulation.
The analysis provided an integrated description of the genomic and functional effects of chronic MPL infusion in liver and muscle.
PMCID: PMC3956809  PMID: 24653645
liver; muscle; glucocorticoids; corticosteroids; gene expression; gene regulation; promoter analysis
11.  Hepatic Overexpression of Glycerol-sn-3-phosphate Acyltransferase 1 in Rats Causes Insulin Resistance* 
Fatty liver is commonly associated with insulin resistance and type 2 diabetes, but it is unclear whether triacylglycerol accumulation or an excess flux of lipid intermediates in the pathway of triacyglycerol synthesis are sufficient to cause insulin resistance in the absence of genetic or diet-induced obesity. To determine whether increased glycerolipid flux can, by itself, cause hepatic insulin resistance, we used an adenoviral construct to overexpress glycerol-sn-3-phosphate acyltransferase-1 (Ad-GPAT1), the committed step in de novo triacylglycerol synthesis. After 5–7 days, food intake, body weight, and fat pad weight did not differ between Ad-GPAT1 and Ad-enhanced green fluorescent protein control rats, but the chow-fed Ad-GPAT1 rats developed fatty liver, hyperlipidemia, and insulin resistance. Liver was the predominant site of insulin resistance; Ad-GPAT1 rats had 2.5-fold higher hepatic glucose output than controls during a hyperinsulinemic-euglycemic clamp. Hepatic diacylglycerol and lysophosphatidate were elevated in Ad-GPAT1 rats, suggesting a role for these lipid metabolites in the development of hepatic insulin resistance, and hepatic protein kinase Cε was activated, providing a potential mechanism for insulin resistance. Ad-GPAT1-treated rats had 50% lower hepatic NF-κB activity and no difference in expression of tumor necrosis factor-α and interleukin-β, consistent with hepatic insulin resistance in the absence of increased hepatic inflammation. Glycogen synthesis and uptake of 2-deoxyglucose were reduced in skeletal muscle, suggesting mild peripheral insulin resistance associated with a higher content of skeletal muscle triacylglycerol. These results indicate that increased flux through the pathway of hepatic de novo triacylglycerol synthesis can cause hepatic and systemic insulin resistance in the absence of obesity or a lipogenic diet.
PMCID: PMC2819346  PMID: 17389595
12.  Microarray analysis of the temporal response of skeletal muscle to methylprednisolone: comparative analysis of two dosing regimens 
Physiological genomics  2007;30(3):282-299.
The transcriptional response of skeletal muscle to chronic corticosteroid exposure was examined over 168 h and compared with the response profiles observed following a single dose of corticosteroid. Male adrenalectomized Wistar rats were given a constant-rate infusion of 0.3 mg•kg−1•h−1 methylprednisolone for up to 7 days via subcutaneously implanted minipumps. Four control and forty drug-treated animals were killed at ten different time points during infusion. Liver total RNAs were hybridized to 44 individual Affymetrix REA230A gene chips. Previously, we described a filtration approach for identifying genes of interest in microarray data sets developed from tissues of rats treated with methylprednisolone (MPL) following acute dosing. Here, a similar approach involving a series of three filters was applied sequentially to identify genes of interest. These filters were designed to eliminate probe sets that were not expressed in the tissue, not regulated by the drug, or did not meet defined quality control standards. Filtering eliminated 86% of probe sets, leaving a remainder of 2,316 for further consideration. In a previous study, 653 probe sets were identified as MPL regulated following administration of a single (acute) dose of the drug. Comparison of the two data sets yielded 196 genes identified as regulated by MPL in both dosing regimens. Because of receptor downregulation, it was predicted that genes regulated by receptor-glucocorticoid response element interactions would exhibit tolerance in chronic profiles. However, many genes did not exhibit steroid tolerance, indicating that present perspectives on the mechanism of glucocorticoid action cannot entirely explain all temporal profiles.
PMCID: PMC4186702  PMID: 17473217
glucocorticoids; corticosteroids; Affymetrix gene chips; gene expression; time series
13.  Dynamic modeling of methylprednisolone effects on body weight and glucose regulation in rats 
Influences of methylprednisolone (MPL) and food consumption on body weight (BW), and the effects of MPL on glycemic control including food consumption and the dynamic interactions among glucose, insulin, and free fatty acids (FFA) were evaluated in normal male Wistar rats. Six groups of animals received either saline or MPL via subcutaneous infusions at the rate of 0.03, 0.1, 0.2, 0.3 and 0.4 mg/kg/h for different treatment periods. BW and food consumption were measured twice a week. Plasma concentrations of MPL and corticosterone (CST) were determined at animal sacrifice. Plasma glucose, insulin, and FFA were measured at various times after infusion. Plasma MPL concentrations were simulated by a two-compartment model and used as the driving force in the pharmacodynamic (PD) analysis. All data were modeled using ADAPT 5. The MPL treatments caused reduction of food consumption and body weights in all dosing groups. The steroid also caused changes in plasma glucose, insulin, and FFA concentrations. Hyper-insulinemia was achieved rapidly at the first sampling time of 6 h; significant elevations of FFA were observed in all drug treatment groups; whereas only modest increases in plasma glucose were observed in the low dosing groups (0.03 and 0.1 mg/kg/h). Body weight changes were modeled by dual actions of MPL: inhibition of food consumption and stimulation of weight loss, with food consumption accounting for the input of energy for body weight. Dynamic models of glucose and insulin feedback interactions were extended to capture the major metabolic effects of FFA: stimulation of insulin secretion and inhibition of insulin-stimulated glucose utilization. These models of body weight and glucose regulation adequately captured the experimental data and reflect significant physiological interactions among glucose, insulin, and FFA. These mechanism-based PD models provide further insights into the multi-factor control of this essential metabolic system.
PMCID: PMC3407886  PMID: 21394487
Glucocorticoids; Methylprednisolone; Pharmacodynamics; Food intake; Body weight; Glucose; Insulin; Free fatty acids
14.  Corticosteroids modulate Seoul virus infection, regulatory T cell responses, and MMP-9 expression in male, but not female, Norway rats 
The Journal of general virology  2008;89(0 11):2723-2730.
Human hantaviral disease is mediated by excessive proinflammatory and CD8+ T cell responses, which can be alleviated by administration of corticosteroids. In contrast to humans, male rats that are infected with their species-specific hantavirus, Seoul virus (SEOV), have reduced proinflammatory and elevated regulatory T cell responses in tissues where virus persists. To determine the effects of glucocorticoids on SEOV persistence and immune responses during infection, male and female Norway rats received sham surgeries (sham) or were adrenalectomized (ADX0), in some of which corticosterone was replaced at low (ADX10) or high (ADX80) doses. Rats were inoculated with SEOV and serum corticosterone, SEOV RNA, gene expression, and protein production were measured at different timepoints post-inoculation (p.i.). We observed that SEOV infection suppressed corticosterone in sham males to concentrations seen in ADX0 males. Furthermore, males with low corticosterone had more SEOV RNA in the lungs than either females or males with high corticosterone concentrations during peak infection. Although high concentrations of corticosterone suppressed the expression of innate antiviral and proinflammatory mediators to a greater extent in females than males, these immunomodulatory effects did not correlate with SEOV load. Males with low corticosterone concentrations and high viral load had elevated regulatory T cell responses and expression of matrix metalloprotease (Mmp)9. MMP-9 is a glycogenase that disrupts cellular matrices and may facilitate extravasation of SEOV-infected cells from circulation into lung tissue. Suppression of glucocorticoids may, thus, contribute to more efficient dissemination of SEOV in male than female rats.
PMCID: PMC4152707  PMID: 18931068
corticosterone; hantavirus; host-pathogen co-evolution; HFRS; IFN-β; TGF-β; TNF-α
15.  Pharmacodynamics of Glucose Regulation by Methylprednisolone. II. Normal Rats 
A physiologic pharmacodynamic model was developed to jointly describe the effects of methylprednisolone (MPL) on adrenal suppression and glycemic control in normal rats. Six groups of animals were given MPL intravenously at 0, 10 and 50 mg/kg, or by subcutaneous 7 day infusion at rates of 0, 0.1 and 0.3 mg/kg/h. Plasma concentrations of MPL, corticosterone (CST), glucose and insulin were determined at various times up to 72 h after injection and 336 h after infusion. The pharmacokinetics of MPL was described by a two-compartment model. A circadian rhythm for CST was found in untreated rats with a stress-altered baseline caused by handling, which was captured by a circadian harmonic secretion rate with an increasing mesor. All drug treatments caused CST suppression. Injection of MPL caused temporary increases in glucose over 4 h. Insulin secretion was thereby stimulated yielding a later peak around 6 h. In turn, insulin can normalize glucose. However, long-term dosing caused continuous hyperglycemia during and after infusion. Hyperinsulinemia was achieved during infusion, but diminished immediately after dosing despite the high glucose concentration. The effects of CST and MPL on glucose production were described with a competitive stimulation function. A disease progression model incorporating reduced endogenous glucose uptake/utilization was used to describe glucose metabolism under different treatments. The results exemplify the roles of endogenous and exogenous hormones in mediating glucose dynamics. The pharmacokinetic/pharmacodynamic model is valuable for quantitating diabetogenic effects of corticosteroid treatments and provides mechanistic insights into the hormonal control of the metabolic system.
PMCID: PMC3712293  PMID: 19156669
corticosterone; methylprednisolone; pharmacodynamics; pharmacokinetics; glucose; insulin
16.  The effects of chronic AMPK activation on hepatic triglyceride accumulation and glycerol 3-phosphate acyltransferase activity with high fat feeding 
High fat feeding increases hepatic fat accumulation and is associated with hepatic insulin resistance. AMP Activated Protein Kinase (AMPK) is thought to inhibit lipid synthesis by the acute inhibition of glycerol-3-phosphate acyltransferase (GPAT) activity and transcriptional regulation via sterol regulatory element binding protein-1c (SREBP-1c).
The purpose of this study was to determine if chronic activation of AMPK prevented an increase in GPAT1 activity in rats fed a high fat diet. Rats were fed a control (C), or a high fat (HF) diet (60% fat) for 6 weeks and injected with saline or a daily aminoimidazole carboxamide ribnucleotide (AICAR) dose of 0.5 mg/g body weight.
Chronic AMPK activation by AICAR injections resulted in a significant reduction in hepatic triglyceride accumulation in both the C and HF fed animals (C, 5.5±0.7; C+AICAR, 2.7 ±0.3; HF, 21.8±3.3; and HF+AICAR, 8.0±1.8 mg/g liver). HF feeding caused an increase in total GPAT and GPAT1 activity, which was not affected by chronic AMPK activation (GPAT1 activity vs. C, C+AICAR, 92±19%; HF, 186±43%; HF+AICAR, 234±62%). Markers of oxidative capacity, including citrate synthase activity and cytochrome c abundance, were not affected by chronic AICAR treatment. Interestingly, HF feeding caused a significant increase in long chain acyl-CoA dehydrogenase or LCAD (up 66% from C), a marker of fatty acid oxidation capacity.
These results suggest that chronic AMPK activation limits hepatic triglyceride accumulation independent of a reduction in total GPAT1 activity.
PMCID: PMC3679947  PMID: 23725555
17.  Gene arrays and temporal patterns of drug response: corticosteroid effects on rat liver 
It was hypothesized that expression profiling using gene arrays can be used to distinguish temporal patterns of changes in gene expression in response to a drug in vivo, and that these patterns can be used to identify groups of genes regulated by common mechanisms. A corticosteroid, methylprednisolone (MPL), was administered intravenously to a group of 47 rats (Rattus rattus) that were sacrificed at 17 timepoints over 72 h after MPL administration. Plasma drug concentrations and hepatic glucocorticoid receptors were measured from each animal. In addition, RNAs prepared from individual livers were used to query Affymetrix genechips for mRNA expression patterns. Statistical analyses using Affymetrix and GeneSpring software were applied to the results. Cluster analysis revealed six major temporal patterns containing 196 corticosteroid-responsive probe sets representing 153 different genes. Four clusters showed increased expression with differences in lag-time, onset rate, and/or duration of transcriptional effect. A fifth cluster showed rapid reduction persisting for 18 h. The final cluster identified showed decreased expression followed by an extended period of increased expression. These results lend new insights into the diverse hepatic genes involved in the physiologic, therapeutic, and adverse effects of corticosteroids and suggest that a limited array of control processes account for the dynamics of their pharmacogenomic effects.
PMCID: PMC4207265  PMID: 12928814
Corticosteroids; Glucocorticoids; Expression profiling; Cluster analysis
18.  Modeling receptor/gene-mediated effects of corticosteroids on hepatic tyrosine aminotransferase dynamics in rats: dual regulation by endogenous and exogenous corticosteroids 
Receptor/gene-mediated effects of corticosteroids on hepatic tyrosine aminotransferase (TAT) were evaluated in normal rats. A group of normal male Wistar rats were injected with 50 mg/kg methylprednisolone (MPL) intramuscularly at the nadir of their plasma corticosterone (CST) rhythm (early light cycle) and sacrificed at various time points up to 96 h post-treatment. Blood and livers were collected to measure plasma MPL, CST, hepatic glucocorticoid receptor (GR) mRNA, cytosolic GR density, TAT mRNA, and TAT activity. The pharmacokinetics of MPL showed bi-exponential disposition with two first-order absorption components from the injection site and bioavailability was 21%. Plasma CST was reduced after MPL dosing, but resumed its daily circadian pattern within 36 h. Cytosolic receptor density was significantly suppressed (90%) and returned to baseline by 72 h resuming its biphasic pattern. Hepatic GR mRNA follows a circadian pattern which was disrupted by MPL and did not return during the study. MPL caused significant down-regulation (50%) in GR mRNA which was followed by a delayed rebound phase (60–70 h). Hepatic TAT mRNA and activity showed up-regulation as a consequence of MPL, and returned to their circadian baseline within 72 and 24 h of treatment. A mechanistic receptor/gene-mediated pharmacokinetic/pharmacodynamic model was able to satisfactorily describe the complex interplay of exogenous and endogenous corticosteroid effects on hepatic GR mRNA, cytosolic free GR, TAT mRNA, and TAT activity in normal rats.
PMCID: PMC4180077  PMID: 17593325
Methylprednisolone; Corticosteroids; Pharmacokinetics; Pharmacodynamics; Tyrosine aminotransferase; Glucocorticoid receptors
19.  Oxytocin projections to the nucleus of the solitary tract contribute to the increased meal-related satiety responses in primary adrenal insufficiency 
Experimental physiology  2013;98(10):1495-1504.
Anorexia is a common clinical manifestation of primary adrenal gland failure. Adrenalectomy (ADX)-induced hypophagia is reversed by oxytocin (OT) receptor antagonist and is associated with increased activation of satiety-related responses in the nucleus of the solitary tract (NTS). This study evaluated OT projections from the paraventricular nucleus of the hypothalamus (PVN) to NTS after ADX and the effect of pretreatment with intracerebroventricular injection of OT receptor antagonist ([d(CH2)5,Tyr(Me)2,Orn8]-vasotocin, OVT) on the activation of NTS neurons induced by feeding in adrenalectomized rats. Adrenalectomized animals showed higher OT labeling in the NTS than sham and ADX with corticosterone replacement (ADX+B) groups. Adrenalectomized animals exhibited co-localization of the anterograde tracer Phaseolus vulgaris-leucoagglutinin and OT in axons in the NTS as well as OT fibers apposing NTS neurons activated by refeeding. After vehicle pretreatment, compared to fasting, refeeding increased the numbers of Fos− and Fos+TH-immunoreactive neurons in the NTS in sham, ADX and ADX+B groups, with a higher number of these immunolabeled neurons in adrenalectomized animals. Compared to fasting condition, refeeding also increased the activation of NTS neurons in OVT pretreated sham, ADX and ADX+B groups, however there was no difference among the three experimental groups. These data demonstrate that OT is up-regulated in projections to the NTS following ADX and that OT receptor antagonist reverses the greater activation of NTS neurons induced by feeding after ADX. The data indicate that OT pathways to the NTS contribute to higher satiety-related responses and, thus, to reduce meal size in primary adrenal insufficiency.
PMCID: PMC3786458  PMID: 23813803
Adrenalectomy; oxytocin; nucleus of the solitary tract
20.  Modeling of Corticosteroid Effects on Hepatic Low-Density Lipoprotein Receptors and Plasma Lipid Dynamics in Rats 
Pharmaceutical research  2007;25(4):769-780.
This study examines methylprednisolone (MPL) effects on the dynamics of hepatic low-density lipoprotein receptor (LDLR) mRNA and plasma lipids associated with increased risks for atherosclerosis.
Materials and methods
Normal male Wistar rats were given 50 mg/kg MPL intramuscularly (IM) and sacrificed at various times. Measurements included plasma MPL and CST, hepatic glucocorticoid receptor (GR) mRNA, cytosolic GR density and hepatic LDLR mRNA, and plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), high density lipoprotein cholesterol (HDLC), and triglycerides (TG).
MPL showed bi-exponential disposition with two first-order absorption components. Hepatic GR and LDLR mRNA exhibited circadian patterns which were disrupted by MPL. Down-regulation in GR mRNA (40–50%) was followed by a delayed rebound phase. LDLR mRNA exhibited transient down-regulation (60–70%). Cytosolic GR density was significantly suppressed but returned to baseline by 72 h. Plasma TC and LDLC showed increases (55 and 142%) at 12 h. A mechanistic receptor/gene pharmacokinetic/pharmacodynamic model was developed to describe CS effects on hepatic LDLR mRNA and plasma cholesterols.
Our PK/PD model was able to satisfactorily capture the MPL effects on hepatic LDLR, its relationship to various plasma cholesterols, and builds the foundation to explore this area in the future.
PMCID: PMC4196440  PMID: 17674160
cholesterol; corticosteroids; glucocorticoid receptors; LDL receptors; lipids; pharmacodynamics
21.  Cancer cachexia is associated with a decrease in skeletal muscle mitochondrial oxidative capacities without alteration of ATP production efficiency 
Cancer cachexia is a complex syndrome related to a negative energy balance resulting in muscle wasting. Implication of muscle mitochondrial bioenergetics alterations during cancer cachexia was suggested. Therefore, the aim of this study was to explore the efficiency of oxidative phosphorylation in skeletal muscle mitochondria in a preclinical model of cancer cachexia.
Berlin–Druckrey IX rats with peritoneal carcinosis (PC) were used as a model of cancer cachexia with healthy pair-fed rats (PF) as control. Hindlimb muscle morphology and fibre type composition were analysed in parallel with ubiquitin ligases and UCP gene expression. Oxidative phosphorylation was investigated in isolated muscle mitochondria by measuring oxygen consumption and ATP synthesis rate.
PC rats underwent significant muscle wasting affecting fast glycolytic muscles due to a reduction in fibre cross-sectional area. MuRF1 and MAFbx gene expression were significantly increased (9- and 3.5-fold, respectively) in the muscle of PC compared to PF rats. Oxygen consumption in non-phosphorylating state and the ATP/O were similar in both groups. Muscle UCP2 gene was overexpressed in PC rats. State III and the uncoupled state were significantly lower in muscle mitochondria from PC rats with a parallel reduction in complex IV activity (−30 %).
This study demonstrated that there was neither alteration in ATP synthesis efficiency nor mitochondrial uncoupling in skeletal muscle of cachectic rats despite UCP2 gene overexpression. Muscle mitochondrial oxidative capacities were reduced due to a decrease in complex IV activity. This mitochondrial bioenergetics alteration could participate to insulin resistance, lipid droplet accumulation and lactate production.
PMCID: PMC3505576  PMID: 22648737
Muscle atrophy; PROb-BDIX model; Energy wasting; Cardiolipin; UCP; COX IV
22.  Differential glucocorticoid effects on stress-induced gene expression in the paraventricular nucleus of the hypothalamus and ACTH secretion in the rat 
Stress (Amsterdam, Netherlands)  2009;12(5):400-411.
Although previous studies have examined the extent to which adrenocorticotropic hormone (ACTH) secretion depends on endogenous glucocorticoid levels, few have examined the parallel glucocorticoid dependency of gene expression within the corticotropin releasing hormone (CRH) neuron containing subregion of the hypothalamic paraventricular nucleus (PVN). This study examined resting and stress-induced expression of three immediate early genes (c-fos, zif268, and NGFI-B mRNAs) and two phenotypic restricted immediate early genes that code for ACTH secretagogues (CRH and arginine vasopressin [AVP] hnRNAs) in the PVN of adrenalectomized (ADX) rats given either 0.9% saline to drink for 5 days or saline with corticosterone (CORT; 25 µg/ml). CORT-containing saline was replaced with saline 18 h before testing to ensure clearance of CORT at the time of testing. Dependent measures were examined 0, 15, 30, 60, or 120 min after 30 min restraint. Compared to sham surgery, ADX produced a large upregulation of basal ACTH secretion but only a trend for an increase in basal PVN CRH and parvocellular (mp) PVN AVP hnRNA expression, and a marked augmentation of restraint-induced ACTH secretion and the expression of all five genes examined. CORT containing saline partially normalized basal and restraint-induced ACTH secretion and restraint-induced AVP hnRNA, c-fos mRNA, and zif268 mRNA in the PVN in ADX rats. In contrast, expression patterns of restraint-induced PVN CRH hnRNA and NGFI-B mRNA were not different between ADX rats with or without CORT replacement. Given that there was no circulating CORT present at the time of restraint challenge in either group of ADX rats, the differential impact of CORT replacement on restraint-induced PVN gene expression must reflect differential dependency of the expression of these genes in the PVN on the prior presence of CORT.
PMCID: PMC2787849  PMID: 19065454
AVP; CRH; glucocorticoid negative feedback; HPA axis; immediate early gene; PVN
We have recently identified two promoters, distal and proximal for rat mitochondrial glycerophosphate acyltransferase (mtGPAT). Here we are reporting further characterization of the promoters. Insulin and epidermal growth factor (EGF) stimulated while leptin and glucagon inhibited the luciferase activity of the distal promoter and the amounts of the distal transcript. Conversely, luciferase activity of the proximal promoter and proximal transcript remained unchanged due to these treatments. Only the distal promoter has binding sites for carbohydrate response element binding protein (ChREBP) and sterol regulatory element binding protein-1 (SREBP-1). Electromobility shift assays and chromatin immunoprecipitation assays demonstrated that ChREBP and SREBP-1 bind to the mtGPAT distal promoter. Insulin and EGF increased while glucagon and leptin decreased the binding of SREBP-1 and ChREBP to the distal promoter. Thus, the distal promoter is the regulatory promoter while the proximal promoter acts constitutively for rat mtGPAT gene under the influence of hormones and growth factor.
PMCID: PMC2761506  PMID: 19682972
24.  The importance of corticosterone in mediating restraint-induced weight loss in rats 
Physiology & behavior  2010;102(2):225-233.
Rats restrained for 3 hours/day for 3 days (RR) lose weight and do not return to the weight of non-restrained controls once restraint has ended. This study tested the importance of restraint-induced corticosterone release in mediating the change in body weight by injecting ADX rats with 2.0 mg corticosterone/kg before each restraint to replicate the restraint-induced surge in circulating corticosterone. Restrained adrenalectomized (ADX) rats injected with corticosterone had the same initial weight loss as intact restrained rats, whereas corticosterone injection in non-restrained ADX rats and restraint of ADX rats injected with saline each produced only half as much initial weight loss. Sustained weight loss, measured for 14 days after the end of RR, was the same for restrained intact rats and restrained ADX rats injected with corticosterone whereas restrained ADX rats injected with saline achieved the same weight gain as their controls. Corticosterone injections had no effect on weight gain of non-restrained intact rats. In situ hybridization showed that corticotropin releasing factor (CRF) mRNA expression in the paraventricular nucleus of the hypothalamus (PVN) was increased by the same degree in ADX rats and restrained intact rats and was not modified by corticosterone injections. There was no significant effect of restraint, ADX or corticosterone injection on PVN arginine vasopressin (AVP) mRNA expression. These data indicate that a surge in corticosterone causes sustained weight loss in ADX rats through a mechanism that can be compensated for in intact rats and is independent of changes in PVN CRF or AVP mRNA expression.
PMCID: PMC3010503  PMID: 21092743
Adrenalectomy; in situ hybridization; corticotrophin releasing factor; arginine vasopressin; paraventricular nucleus
25.  Mechanistic population modeling of diabetes disease progression in Goto-Kakizaki rat muscle 
Pyruvate dehydrogenase kinase 4 (PDK4) is a lipid status responsive gene involved in muscle fuel selection. Evidence is mounting in support of the therapeutic potential of PDK4 inhibitors to treat diabetes. Factors that regulate PDK4 mRNA expression include plasma corticosterone, insulin and free fatty acids. Our objective was to determine the impact of those plasma factors on PDK4 mRNA and to develop and validate a population mathematical model to differentiate aging, diet and disease effects on muscle PDK4 expression. The Goto-Kakizaki (GK) rat, a polygenic non-obese model of type 2 diabetes, was used as the diabetic animal model. We examined muscle PDK4 mRNA expression by real-time QRTPCR. Groups of GK rats along with controls fed with either a normal or high fat diet were sacrificed at 4, 8, 12, 16, and 20 weeks of age. Plasma corticosterone, insulin and free fatty acid were measured. The proposed mechanism-based model successfully described the age, disease and diet effects and the relative contribution of these plasma regulators on PDK4 mRNA expression. Muscle growth reduced the PDK4 mRNA production rate by 14% per gram increase. High fat diet increased the initial production rate constant in GK rats by 2.19-fold. The model indicated that corticosterone had a moderate effect and PDK4 was more sensitive to free fatty acid than insulin fluxes, which was in good agreement with the literature data.
PMCID: PMC3080028  PMID: 21162119
population model; type 2 diabetes; disease progression; PDK4; Goto-Kakizaki rats

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