Modeling interactions between adrenal suppression and T-helper lymphocyte trafficking during multiple dosing of methylprednisolone

Unintended Consequences: Risk of Opportunistic Infections Associated With Long-term Glucocorticoid Therapies in Adults

Glucocorticoids are widespread anti-inflammatory medications used in medical practice. The immunosuppressive effects of systemic glucocorticoids and increased susceptibility to infections are widely appreciated. However, the dose-dependent model frequently used may not accurately predict the risk of infection in all patients treated with long-term glucocorticoids. In this review, we examine the risks of opportunistic infections (OIs) in patients requiring glucocorticoid therapy by evaluating the influence of the glucocorticoid dose, duration, and potency, combined with biological and host clinical factors and concomitant immunosuppressive therapy. We propose strategies to prevent OIs, which involve screening, antimicrobial prophylaxis, and immunizations. While this review focuses on patients with autoimmune, inflammatory, or neoplastic diseases, the potential risks and preventative strategies are likely applicable to other populations. Clinicians should actively assess the benefit-harm ratios of systemic glucocorticoids and implement preventive efforts to decrease their associated infections complications.

Fifty Years of Unraveling the Clinical Pharmacology of Corticosteroids

This review will highlight portions of Dr. William Jusko's and colleagues' work that affected the clinical use and study of corticosteroids in acute and chronic disease management. Selected publications related to corticosteroid pharmacokinetics and pharmacodynamics from the 1970s through today were included in this review, with a focus on the foundational human-based studies conducted in the 1970s-1990s. Dr. Jusko contributed significantly to early corticosteroid pharmacology across several domains including: 1) foundational corticosteroid pharmacokinetic methods and parameter development, 2) disease state-variation in corticosteroid pharmacokinetics, 3) drug interaction effects on corticosteroid pharmacokinetics, and 4) early corticosteroid pharmacodynamic studies. In an era where little was known about the pharmacokinetics and pharmacodynamics of corticosteroids, Dr. Jusko's work opened the eyes of researchers and clinicians to the potential for disease and drug interactions that could reduce or enhance the effects of corticosteroids. This significant body of work paved the way for alternative routes of administration that would be useful in concentrating the activity at the site of action and markedly reduced systemic drug exposure, minimizing the risk of adverse effects through application of the dose-sparing pharmacokinetic and pharmacodynamic principles.

Transitioning from Basic toward Systems Pharmacodynamic Models: Lessons from Corticosteroids

Technology in bioanalysis, -omics, and computation have evolved over the past half century to allow for comprehensive assessments of the molecular to whole body pharmacology of diverse corticosteroids. Such studies have advanced pharmacokinetic and pharmacodynamic (PK/PD) concepts and models that often generalize across various classes of drugs. These models encompass the "pillars" of pharmacology, namely PK and target drug exposure, the mass-law interactions of drugs with receptors/targets, and the consequent turnover and homeostatic control of genes, biomarkers, physiologic responses, and disease symptoms. Pharmacokinetic methodology utilizes noncompartmental, compartmental, reversible, physiologic [full physiologically based pharmacokinetic (PBPK) and minimal PBPK], and target-mediated drug disposition models using a growing array of pharmacometric considerations and software. Basic PK/PD models have emerged (simple direct, biophase, slow receptor binding, indirect response, irreversible, turnover with inactivation, and transduction models) that place emphasis on parsimony, are mechanistic in nature, and serve as highly useful "top-down" methods of quantitating the actions of diverse drugs. These are often components of more complex quantitative systems pharmacology (QSP) models that explain the array of responses to various drugs, including corticosteroids. Progressively deeper mechanistic appreciation of PBPK, drug-target interactions, and systems physiology from the molecular (genomic, proteomic, metabolomic) to cellular to whole body levels provides the foundation for enhanced PK/PD to comprehensive QSP models. Our research based on cell, animal, clinical, and theoretical studies with corticosteroids have provided ideas and quantitative methods that have broadly advanced the fields of PK/PD and QSP modeling and illustrates the transition toward a global, systems understanding of actions of diverse drugs. SIGNIFICANCE STATEMENT: Over the past half century, pharmacokinetics (PK) and pharmacokinetics/pharmacodynamics (PK/PD) have evolved to provide an array of mechanism-based models that help quantitate the disposition and actions of most drugs. We describe how many basic PK and PK/PD model components were identified and often applied to the diverse properties of corticosteroids (CS). The CS have complications in disposition and a wide array of simple receptor-to complex gene-mediated actions in multiple organs. Continued assessments of such complexities have offered opportunities to develop models ranging from simple PK to enhanced PK/PD to quantitative systems pharmacology (QSP) that help explain therapeutic and adverse CS effects. Concurrent development of state-of-the-art PK, PK/PD, and QSP models are described alongside experimental studies that revealed diverse CS actions.

Chronopharmacology of glucocorticoids

Glucocorticoids influence a wide array of metabolic, anti-inflammatory, immunosuppressive, and cognitive signaling processes, playing an important role in homeostasis and preservation of normal organ function. Synthesis is regulated by the hypothalamic-pituitary-adrenal (HPA) axis of which cortisol is the primary glucocorticoid in humans. Synthetic glucocorticoids are important pharmacological agents that augment the anti-inflammatory and immunosuppressive properties of endogenous cortisol and are widely used for the treatment of asthma, Crohn's disease, and rheumatoid arthritis, amongst other chronic conditions. The homeostatic activity of cortisol is disrupted by the administration of synthetic glucocorticoids and so there is interest in developing treatment options that minimize HPA axis disturbance while maintaining the pharmacological effects. Studies suggest that optimizing drug administration time can achieve this goal. The present review provides an overview of endogenous glucocorticoid activity and recent advances in treatment options that have further improved patient safety and efficacy with an emphasis on chronopharmacology.

Dose Equivalency Evaluation of Major Corticosteroids: Pharmacokinetics and Cell Trafficking and Cortisol Dynamics

The integrity of current corticosteroid dose equivalency tables, as assessed by mechanistic models for cell trafficking and cortisol dynamics, was investigated in this study. Single, presumably equivalent, doses of intravenous hydrocortisone, methylprednisolone, dexamethasone, and oral prednisolone were given to 5 white men, according to total body weight, in a 5-way crossover, placebo-controlled study. Pharmacodynamic (PD) response-time profiles for T helper cells, T suppressor cells, neutrophils, and adrenal suppression were evaluated by extended indirect response models. For adrenal suppression, prednisolone appears to be less potent than methylprednisolone or dexamethasone. A good correlation was found between the estimated in vivo EC50 values and relative receptor affinity (equilibrium dissociation constants normalized to dexamethasone). Area under the effect curves of all PD responses was calculated using a linear-trapezoidal method. Although T helper cell trafficking and adrenal suppression achieved significant differences by repeated-measures ANOVA (p = 0.014 and 0.022), post hoc analysis using the Bonferroni method revealed no difference between treatments. Although limited by the use of single doses and a relatively small sample size, this study applies mechanistic models for several biomarkers showing that currently used dosing tables reflect reasonable dose equivalency relationships for four corticosteroids.

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.

Pharmacokinetics of methylprednisolone acetate after intra-articular administration and its effect on endogenous hydrocortisone and cortisone secretion in horses

OBJECTIVE

To determine the pharmacokinetics of methylprednisolone (MP) and develop a pharmacokinetic-pharmacodynamic model of the related changes in plasma concentrations of endogenous hydrocortisone (HYD) and cortisone (COR) following intra-articular administration of methylprednisolone acetate (MPA) in horses.

ANIMALS

6 Thoroughbreds.

PROCEDURES

In each horse, 200 mg of MPA was injected intrasynovially into a carpal joint, and plasma MP, HYD, and COR concentrations were determined via liquid chromatography-mass spectrometry.

RESULTS

A 5-compartment pharmacokinetic-pharmacodynamic model was used to describe the concatenated changes in the plasma concentrations of MP, HYD, and COR and to estimate the instantaneous rate of endogenous HYD production. The median transfer half-life (t(1/2t)) of methylprednisolone from the joint to plasma and elimination half-life (t(1/2e)) from plasma were 1.7 and 19.2 hours, respectively. Maximum plasma concentration of methylprednisolone was 7.26 +/- 3.3 ng/mL at 8 hours, which decreased to 0.11 +/- 0.08 ng/mL at 144 hours after injection. At 3 hours after MPA administration, plasma COR and HYD concentrations were significantly decreased from baseline values (from 2.9 +/- 0.28 ng/mL to 2.10 +/- 1.0 ng/mL and from 61.1 +/- 18.9 ng/mL to 25.7 +/- 12.1 ng/mL, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The sensitivity of the analytic method used allowed complete description of the related kinetics of MP, HYD, and COR following intra-articular administration of MPA. A single intra-articular administration of MPA profoundly affected the secretion of HYD and COR in horses; secretion of endogenous corticosteroids remained suppressed for as long as 240 hours after injection.

Intraepithelial but not lamina propria lymphocytes in the porcine gut are affected by dexamethasone treatment

It is well established that glucocorticoids are key regulators of the immune system and act as immunosuppressive agents in high concentrations. In the pig, effects on the gut immune system and trafficking of lymphocytes between tissues and blood plasma were not investigated so far. Twelve pigs of 70 kg were fed 0.4 mg portions of dexamethasone (Dexa) twice daily for 9 days or remained untreated (controls) and were sacrificed for tissue collection at the end of Dexa treatment. Another six pigs with jugular vein catheters were left untreated for 7 days (control period) and then received Dexa for 9 days. Blood was drawn twice during the control period and at days 3, 6 and 9 of the Dexa period for characterization of peripheral blood leukocytes. Cells were obtained from thymus, mesenteric lymph nodes, jejunal mucosa and Peyer's patches. Lymphoid cells from gut tissue were isolated from two fractions: the EDTA-fraction, containing the intraepithelial lymphocytes (IEL), and the Collagenase-fraction, containing the lamina propria lymphocytes (LPL). In all samples, cell counts and phenotypic characterization of cells by flow cytometry (FCM) were performed. In thymus, Dexa led to a more than 90% reduction of the absolute cell number, which was mainly found in the CD4+CD8+ subpopulation. Dexa effects on lymphocytes from mesenteric lymph nodes were less severe (50%) and led mainly to a decrease (71%) of B-lymphocytes. The number of lymphocytes in the EDTA-fraction (IEL) of the jejunal mucosa decreased significantly by 56% in the Dexa-treated animals compared to the controls, whereas the number of lymphocytes in the Collagenase-fraction (LPL) decreased only moderately. In the Peyer's patches, a decreasing tendency in the number of lymphocytes in the EDTA-fraction was observed which, however, was not significant. In blood, monocytes and granulocytes were significantly increased in an order of 60%. The data show that supraphysiological amounts of Dexa remarkably reduce cell numbers in thymus and also in the intraepithelial compartment of the jejunal mucosa and ileal Peyer's patches. In blood, a notable homeostasis was observed for several leukocyte populations whereas both monocytes and granulocytes increased.

Pharmacokinetics and pharmacodynamics of systemically administered glucocorticoids

Glucocorticoids have pleiotropic effects that are used to treat diverse diseases such as asthma, rheumatoid arthritis, systemic lupus erythematosus and acute kidney transplant rejection. The most commonly used systemic glucocorticoids are hydrocortisone, prednisolone, methylprednisolone and dexamethasone. These glucocorticoids have good oral bioavailability and are eliminated mainly by hepatic metabolism and renal excretion of the metabolites. Plasma concentrations follow a biexponential pattern. Two-compartment models are used after intravenous administration, but one-compartment models are sufficient after oral administration.The effects of glucocorticoids are mediated by genomic and possibly nongenomic mechanisms. Genomic mechanisms include activation of the cytosolic glucocorticoid receptor that leads to activation or repression of protein synthesis, including cytokines, chemokines, inflammatory enzymes and adhesion molecules. Thus, inflammation and immune response mechanisms may be modified. Nongenomic mechanisms might play an additional role in glucocorticoid pulse therapy. Clinical efficacy depends on glucocorticoid pharmacokinetics and pharmacodynamics. Pharmacokinetic parameters such as the elimination half-life, and pharmacodynamic parameters such as the concentration producing the half-maximal effect, determine the duration and intensity of glucocorticoid effects. The special contribution of either of these can be distinguished with pharmacokinetic/pharmacodynamic analysis. We performed simulations with a pharmacokinetic/pharmacodynamic model using T helper cell counts and endogenous cortisol as biomarkers for the effects of methylprednisolone. These simulations suggest that the clinical efficacy of low-dose glucocorticoid regimens might be increased with twice-daily glucocorticoid administration.

A stochastic version of corticosteriod pharmacogenomic model

The purpose of this study was to develop a stochastic version of corticosteriod fifth generation pharmacogenomic model. The Gillespie algorithm was used to generate the independent time courses of the receptor messenger RNA (mRNA). Initial parameters for the stochastic simulation were adapted from the study by Jin et al. The result obtained from the proposed stochastic model showed an overall agreement with the deterministic fifth generation model. This study suggested that because the stochastic model takes into account the "noise" nature of gene regulation, it would have potential application in pharmacogenomic modeling.

Modeling of corticosteroid pharmacogenomics in rat liver using gene microarrays

Corticosteroid (CS) pharmacogenomics was studied using gene microarrays in rat liver. Methylprednisolone (MPL) was administered intravenously at 50 mg/kg. Rats were sacrificed and liver excised at 17 time points over 72 h. RNAs from individual livers were used to query Affymetrix GeneChips that contain sequences for 8000 genes. Cluster analysis revealed six temporal patterns consisting of 197 CS-responsive probes representing 143 genes. Based on our fifth-generation model of CS pharmacokinetics/pharmacodynamics (PK/PD), mechanistic models were developed to describe the time pattern for each CS-responsive gene. Two clusters showed increased expression with different effect duration. PK/PD models assuming CS stimulation of mRNA synthesis were applied. Another two clusters showed an initial decline followed by delayed increase, suggesting two mechanisms might be involved jointly. The initial suppression was captured by CS inhibition of mRNA synthesis or stimulation of degradation. CS may also stimulate the production of a biosignal (transcription factors or other hormones), which can cause secondary induction of the target mRNA. One cluster showed a very abrupt increase in message followed by rapid decrease. These genes were lymphocytic in origin and were modeled combining the fast gene induction effect of CS in lymphoid cells and its direct lymphocyte trafficking effect. Another cluster showed reduction persisting for 18 h, which was described by CS inhibition of mRNA synthesis. Our results reveal the marked diversity of genes regulated by CS via a limited array of mechanisms. These PK/PD models provide quantitation of CS pharmacogenomics and new hypotheses regarding understanding of diverse mechanisms of CS receptor-gene mediated action.

Pharmacokinetics and pharmacodynamics of methylprednisolone after one bolus dose compared with two dose fractions

OBJECTIVE

Although the elimination half-life of most glucocorticoids is short, they are usually administered once daily, or even on alternate days. Our hypothesis was that this practice might compromise the immunosuppressive effect of those drugs during the second part of the administration interval.

METHODS

Eight healthy male volunteers were randomly assigned to receive intravenous methylprednisolone either 32 mg in the morning, or 16 mg in the morning and 16 mg in the evening in a cross-over design. Methylprednisolone concentrations were determined in plasma by high-pressure liquid chromatography. The total number of CD3+ lymphocytes, and CD4+ and CD8+ T-cell subpopulations was measured in blood. The suppression of these cells was used as a surrogate parameter for the immunosuppressive response, and expressed as reduction of the area under the effect time curve (AUETC). Possible adverse effects on blood pressure, glucose, insulin, and endogenous cortisol levels were monitored.

RESULTS

There were no significant differences in methylprednisolone half-life (2.2 +/- 0.4 h), clearance (575 +/- 113 mL/min), volume of distribution (106 +/- 22 l), concentration producing the half-maximum effect on CD4+ T-cells (1.5 +/- 0.7 ng/mL), and Hill-coefficient (1.2 +/- 0.1), after single or divided dose. However, the total 24 h effect area (AUETC) of lymphocytes, and mainly CD4+ T-cells was significantly more suppressed (P = 0.008) with the divided dosage regimen than after the single dose (8422 +/- 2163 vs. 11,545 +/- 3020 h cells/microL). The surrogate markers for adverse events were not different, except for cortisol.

CONCLUSION

Within a 24-h interval, two dose fractions of methylprednisolone produce a stronger and more sustained immunosuppressive response than one single bolus dose.

Pharmacokinetic/pharmacodynamic model for prednisolone inhibition of whole blood lymphocyte proliferation

AIMS

Mitogen-induced ex vivo whole blood lymphocyte proliferation (WBLP) is a widely used method to assess lymphocyte responsiveness to immunosuppressive therapy. A three-component complex model was developed to characterize effects of prednisolone on cell trafficking, transduction, and lymphocyte suppression.

METHODS

An oral dose (0.27 mg kg-1) of prednisone was given to 32 subjects. The study consisted of baseline and prednisone phases each with 32 h of sampling. Measurements included plasma prednisolone concentrations, in vitro and ex vivo WBLP, and lymphocyte cell counts during baseline and prednisone phases.

RESULTS

The final model consists of a precursor-dependent indirect response model with a first-order periodic influx rate for lymphocyte trafficking. This accounts for the rebound phenomenon and the circadian rhythm seen in all individual ex vivo WBLP effect-time profiles. Prednisolone was modelled as inhibiting lymphocyte influx from the precursor to the blood pools. The direct suppressive effect of prednisolone on WBLP was modelled with the simple Imax model. A transduction step with rate constant kt was introduced to the simple Imax model to account for the delay ( approximately 4 h) in reaching the maximum inhibition. The IC50 values obtained ex vivo were circa 10 times lower than in vitro values (3.76 vs 38.8 ng ml-1), suggesting additional in vivo factors may have enhanced lymphocyte response to the inhibitory effect of prednisolone.

CONCLUSIONS

This integrated PK/PD model enables evaluation of multicomponent direct and indirect inhibition of ex vivo WBLP by steroids and other immunosuppressants in relation to sex and race.

Pharmacodynamics and pharmacogenomics of methylprednisolone during 7-day infusions in rats

An array of adverse steroid effects was examined on a whole body, tissue, and molecular level. Groups of male adrenalectomized Wistar rats were subcutaneously implanted with Alzet mini-pumps giving zero-order release rates of 0, 0.1, and 0.3 mg/kg/h methylprednisolone for 7 days. The rats were sacrificed at various times during the 7-day infusion period. A two-compartment model with a zero order input could adequately describe the kinetics of methylprednisolone upon infusion. Blood lymphocyte counts dropped to a minimum by 6 h and were well characterized by the cell trafficking model. The time course of changes in body and organ (liver, spleen, thymus, gastrocnemius muscle, and lungs) weights was described using indirect response models. Markers of gene-mediated steroid effects included hepatic cytosolic free receptor density, receptor mRNA, tyrosine aminotransferase (TAT) mRNA, and TAT levels. Our fifth-generation model of acute corticosteroid pharmacodynamics was used to predict the time course of receptor/gene-mediated effects. An excellent agreement between the expected and observed receptor dynamics suggested that receptor events and mRNA autoregulation are not altered upon 7-day methylprednisolone dosing. However, the model indicated a decoupling between the receptor and TAT dynamics with this infusion. The strong tolerance seen in TAT mRNA induction could be partly accounted for by receptor down-regulation. An amplification of translation of TAT mRNA to TAT and/or a reduction in the enzyme degradation rate could account for the observed exaggerated TAT activity. Our results exemplify the importance of biological signal transduction variables in controlling receptor/gene-mediated steroid responses during chronic dosing.