Maintenance Immunosuppression in Solid Organ Transplantation: Integrating Novel Pharmacodynamic Biomarkers to Inform Calcineurin Inhibitor Dose Selection

Calcineurin inhibitors, the primary immunosuppressive therapy used to prevent alloreactivity of transplanted organs, have a narrow therapeutic index. Currently, treatment is individualized based on clinical assessment of the risk of rejection or toxicity guided by trough concentration monitoring. Advances in immune monitoring have identified potential markers that may have value in understanding calcineurin inhibitor pharmacodynamics. Integration of these markers has the potential to complement therapeutic drug monitoring. Existing pharmacokinetic-pharmacodynamic (PK-PD) data is largely limited to correlation between the biomarker and trough concentrations at single time points. Immune related gene expression currently has the most evidence supporting PK-PD integration. Novel biomarker-based approaches to pharmacodynamic monitoring including development of enhanced PK-PD models are proposed to realize the full clinical benefit.

Effects of cyclosporine and dexamethasone on canine T cell expression of interleukin-2 and interferon-gamma

Cyclosporine and glucocorticoids are powerful immunosuppressive agents used to treat many inflammatory diseases in dogs. Cyclosporine inhibits calcineurin-dependent pathways of T cell activation and resultant T cell cytokine production, and glucocorticoids directly inhibit genes coding for cytokines. Little work has been done comparing the effects of these agents on T cell cytokine production in dogs. Our study measured T cell interleukin-2 (IL-2) and interferon-gamma (IFN-γ) production using flow cytometry and T cell IL-2 and IFN-γ gene expression using quantitative reverse transcription polymerase chain reaction (qRT-PCR) in activated canine T cells incubated with cyclosporine and dexamethasone in vitro. For flow cytometric assays, diluted whole blood was cultured for 7 h in the presence of cyclosporine (10, 100, 500, and 1000 ng/mL) or dexamethasone (10 ng/mL, 100 ng/mL, 1 μg/mL, and 10 μg/mL). For qRT-PCR, whole blood was cultured for 5 h with the same drugs at the same concentrations, and RNA was then extracted from leukocytes. Flow cytometry and qRT-PCR both demonstrated inhibition of IL-2 and IFN-γ that was concentration-dependent in response to cyclosporine, and was more variable for dexamethasone. Quantitative RT-PCR but not flow cytometry documented significant reduction of IL-2 expression after dexamethasone treatment, while both methods showed concentration-dependent suppression of IFN-γ. Quantitative RT-PCR also revealed additional cytokine suppression at higher cyclosporine concentrations, an effect not found using flow cytometry, and may therefore be the preferred method for cytokine determination in dogs. Suppression of IL-2 and IFN-γ in activated T cells may have potential as an indicator of the efficacy of cyclosporine and glucocorticoids in suppressing canine T cell function in vivo, and may therefore be of value for characterizing the immunosuppression induced by these drugs in clinical patients.

Pharmacokinetics, Pharmacodynamics and Pharmacogenomics of Immunosuppressants in Allogeneic Haematopoietic Cell Transplantation: Part I

Although immunosuppressive treatments and target concentration intervention (TCI) have significantly contributed to the success of allogeneic haematopoietic cell transplantation (alloHCT), there is currently no consensus on the best immunosuppressive strategies. Compared with solid organ transplantation, alloHCT is unique because of the potential for bidirectional reactions (i.e. host-versus-graft and graft-versus-host). Postgraft immunosuppression typically includes a calcineurin inhibitor (cyclosporine or tacrolimus) and a short course of methotrexate after high-dose myeloablative conditioning, or a calcineurin inhibitor and mycophenolate mofetil after reduced-intensity conditioning. There are evolving roles for the antithymyocyte globulins (ATGs) and sirolimus as postgraft immunosuppression. A review of the pharmacokinetics and TCI of the main postgraft immunosuppressants is presented in this two-part review. All immunosuppressants are characterized by large intra- and interindividual pharmacokinetic variability and by narrow therapeutic indices. It is essential to understand immunosuppressants' pharmacokinetic properties and how to use them for individualized treatment incorporating TCI to improve outcomes. TCI, which is mandatory for the calcineurin inhibitors and sirolimus, has become an integral part of postgraft immunosuppression. TCI is usually based on trough concentration monitoring, but other approaches include measurement of the area under the concentration-time curve (AUC) over the dosing interval or limited sampling schedules with maximum a posteriori Bayesian personalization approaches. Interpretation of pharmacodynamic results is hindered by the prevalence of studies enrolling only a small number of patients, variability in the allogeneic graft source and variability in postgraft immunosuppression. Given the curative potential of alloHCT, the pharmacodynamics of these immunosuppressants deserves to be explored in depth. Development of sophisticated systems pharmacology models and improved TCI tools are needed to accurately evaluate patients' exposure to drugs in general and to immunosuppressants in particular. Sequential studies, first without and then with TCI, should be conducted to validate the clinical benefit of TCI in homogenous populations; randomized trials are not feasible, because there are higher-priority research questions in alloHCT. In Part I of this article, we review the alloHCT process to facilitate optimal design of pharmacokinetic and pharmacodynamics studies. We also review the pharmacokinetics and TCI of calcineurin inhibitors and methotrexate.

Effects of oral cyclosporine on canine T-cell expression of IL-2 and IFN-gamma across a 12-h dosing interval

The duration of immunosuppressive effects following oral cyclosporine in dogs is unknown. This study used flow cytometry and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) to evaluate the effects of high-dose oral cyclosporine across a 12-h dosing interval. Expression of interleukin-2 (IL-2) and interferon-gamma (IFN-γ) was compared before and after 8 days of cyclosporine at 10 mg/kg every 12 h in six healthy dogs. Samples were collected at 0, 2, 4, and 8 h postdosing for analysis of unactivated and activated T-cell and whole blood cytokine expression using flow cytometry and qRT-PCR, respectively, and at 0, 2, 4, 6, 8, and 10 h postdosing for measurement of cyclosporine concentrations. Flow cytometry and qRT-PCR both demonstrated significant marked reductions in IL-2 and IFN-γ levels at 0, 2, 4, and 8 h after dosing compared to pretreatment levels (P < 0.05) for activated samples, with less consistent effects observed for unactivated samples. Both flow cytometry and qRT-PCR are viable techniques for measuring cyclosporine pharmacodynamics in dogs, yielding comparable results with activated samples. Two hours postdrug administration is the preferred time for concurrent assessment of peak drug concentration and cytokine expression, and T-cell activation is needed for optimal results.

Relationship between pharmacokinetics and pharmacodynamics of calcineurin inhibitors in renal transplant patients

The calcineurin inhibitors (CNIs) cyclosporine A (CsA) and tacrolimus (Tac) are immunosuppressive drugs, which are typically employed in the field of organ transplantation. Both drugs have narrow therapeutic indices, highly variable pharmacokinetics, and are associated with severe adverse effects. In current clinical routine, the dose finding of CNIs is based on the measurement of their blood concentrations. However, this method is limited in its ability to determine the biological impact of the drug. Alternative monitoring strategies, focusing on the pharmacodynamics of CNIs, could help to personalize drug dosing and optimize the treatment with CNIs. Therefore, we analyzed the relationship between pharmacokinetic and pharmacodynamic of the CNIs CsA (n = 9) and Tac (n = 8) in stable renal transplant patients during a 12-h dosing period. We observed a significant decrease in the drug-blood concentration during the course of the day and in parallel a significant recovery of T cell function. In addition, our data document that analysis of intracellular interleukin (IL)-2 production and determination of the IL-2 release are accurate parameters for monitoring the pharmacodynamics of CNIs.

Analytical validation of a quantitative reverse transcriptase polymerase chain reaction assay for evaluation of T-cell targeted immunosuppressive therapy in the dog

Cyclosporine is an immunosuppressive agent that inhibits T-cell function by decreasing production of cytokines such as interleukin-2 (IL-2) and interferon-γ(IFN-γ). In dogs, there is currently no reliable analytical method for determining effective cyclosporine dosages in individual patients. Our laboratory has developed a quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) assay that measures IL-2 and IFN-γ gene expression, with the goal of quantifying immunosuppression in dogs treated with cyclosporine. This study focuses on analytical validation of our assay, and on the effects of sample storage conditions on cyclosporine-exposed samples. Heparinized whole blood collected from healthy adult dogs was exposed to a typical post-treatment blood concentration for cyclosporine(500 ng/mL) for 1 h, and then stored for 0, 24, and 48 h at both room temperature and 4 ◦C.The study was then repeated using a cyclosporine concentration of 75 ng/mL, with sample storage for 0, 24, and 48 h at 4 ◦C. Cytokine gene expression was measured using RT-qPCR,and assay efficiency and inter- and intra-assay variability were determined. Storage for upto 24 h at room temperature, and up to 48 h at 4 ◦C, did not significantly alter results compared to samples that were processed immediately. Validation studies showed our assay to be highly efficient and reproducible and robust enough to be feasible under standard practice submission conditions.

Pharmacokinetic evaluation of oral dantrolene in the dog

The pharmacokinetics of dantrolene and its active metabolite, 5-hydroxydantrolene, after a single oral dose of either 5 or 10 mg/kg of dantrolene was determined. The effects of exposure to dantrolene and 5-hydroxydantrolene on activated whole-blood gene expression of the cytokines interleukin-2 (IL-2) and interferon-γ (IFN-γ) were also investigated. When dantrolene was administered at a 5 mg/kg dose, peak plasma concentration (Cmax ) was 0.43 μg/mL, terminal half-life (t1/2 ) was 1.26 h, and area under the time-concentration curve (AUC) was 3.87 μg·h/mL. For the 10 mg/kg dose, Cmax was 0.65 μg/mL, t1/2 was 1.21 h, and AUC was 5.94 μg·h/mL. For all calculated parameters, however, there were large standard deviations and wide ranges noted between and within individual dogs: t1/2 , for example, ranged from 0.43 to 6.93 h, Cmax ratios ranged from 1.05 to 3.39, and relative bioavailability (rF) values ranged from 0.02 to 1.56. While activated whole-blood expression of IL-2 and IFN-γ as measured by qRT-PCR was markedly suppressed following exposure to very high concentrations (30 and 50 μg/mL, respectively) of both dantrolene and 5-hydroxydantrolene, biologically and therapeutically relevant suppression of cytokine expression did not occur at the much lower drug concentrations achieved with oral dantrolene dosing.

Inflammatory bowel disease and pregnancy: overlapping pathways

Several studies have reported on the association between inflammatory bowel disease (IBD) and adverse pregnancy outcomes, such as preterm birth. The exact mechanisms of action are unclear; however, several pathways and processes are involved in both IBD and pregnancy that may help explain this. In this review, we discuss the immune system's T helper cells and human leukocyte antigens, inflammation, its function, and the role of Toll-like receptors (TLRs), NOD-like receptors (NLRs), and prostaglandins in the inflammatory response. For each of these topics, we consider their involvement in IBD and pregnancy, and we speculate as to how they can lead to preterm birth. Finally, we review briefly corticosteroids, biologic therapies, and immunosuppressants for the treatment of IBD, as well as their safety in use during pregnancy, with special focus on preterm birth.