Magdalena Korecka

Biomarkers of neurodegeneration for diagnosis and monitoring therapeutics

Rapid progress towards understanding the molecular underpinnings of neurodegenerative disorders such as Alzheimers disease is revolutionizing drug discovery for these conditions. Furthermore, the development of models for these disorders is accelerating efforts to translate insights related to neurodegenerative mechanisms into disease-modifying therapies. However, there is an urgent need for biomarkers to diagnose neurodegenerative disorders early in their course, when therapy is likely to be most effective, and to monitor responses of patients to new therapies. As research related to this need is currently most advanced for Alzheimers disease, this Review focuses on progress in the development and validation of biomarkers to improve the diagnosis and treatment of Alzheimers disease and related disorders.

Update on the biomarker core of the Alzheimer's Disease Neuroimaging Initiative subjects

Here, we review progress by the Penn Biomarker Core in the Alzheimers Disease Neuroimaging Initiative (ADNI) toward developing a pathological cerebrospinal fluid (CSF) and plasma biomarker signature for mild Alzheimers disease (AD) as well as a biomarker profile that predicts conversion of mild cognitive impairment (MCI) and/or normal control subjects to AD. The Penn Biomarker Core also collaborated with other ADNI Cores to integrate data across ADNI to temporally order changes in clinical measures, imaging data, and chemical biomarkers that serve as mileposts and predictors of the conversion of normal control to MCI as well as MCI to AD, and the progression of AD. Initial CSF studies by the ADNI Biomarker Core revealed a pathological CSF biomarker signature of AD defined by the combination of Aβ1‐42 and total tau (T‐tau) that effectively delineates mild AD in the large multisite prospective clinical investigation conducted in ADNI. This signature appears to predict conversion from MCI to AD. Data fusion efforts across ADNI Cores generated a model for the temporal ordering of AD biomarkers which suggests that Aβ amyloid biomarkers become abnormal first, followed by changes in neurodegenerative biomarkers (CSF tau, F‐18 fluorodeoxyglucose‐positron emission tomography, magnetic resonance imaging) with the onset of clinical symptoms. The timing of these changes varies in individual patients due to genetic and environmental factors that increase or decrease an individuals resilience in response to progressive accumulations of AD pathologies. Further studies in ADNI will refine this model and render the biomarkers studied in ADNI more applicable to routine diagnosis and to clinical trials of disease modifying therapies.

Mycophenolic acid pharmacodynamics and pharmacokinetics provide a basis for rational monitoring strategies.

Mycophenolic acid (MPA), the active immunosuppressant form of the pro-drug mycophenolate mofetil (MMF), is a widely used component of immunosuppressive regimens in organ transplantation. This immunosuppressant is commonly administered in combination with a calcineurin inhibitor (CIN)+ corticosteroid with or without induction therapy in the form of a polyclonal anti-T lymphocyte preparation or one of the available humanized monoclonal interleukin 2 inhibitors. There is strong evidence that maintenance CIN-MMFsteroid-based triple therapy, initiated in the early posttransplant period significantly reduces the risk of acute rejection in the first post-transplant year, when compared to double therapy regimens comprising CIN and steroids alone. After the initial phase of graft stabilization, there are several therapeuticapproachescurrentlyemployed in transplantpractice, including: (1) maintenance of a three-drug regimen, at reduced doses compared to the early post-transplant period; (2) elimination of corticosteroid; (3) reduction or elimination of CIN; (4) replacement of CIN with sirolimus in patients who are especially sensitive to the nephrotoxic effects of these agents; or (5) reduction or discontinuation of MMF, while retaining full-dose CIN or sirolimus and maintenance corticosteroids are among the other therapeutic options under investigation. Dose individualization of CIN is facilitated by target drug concentration monitoring, whereas for MMF, empiric dosing is most commonly practiced.

Immunosuppressive tor kinase inhibitor everolimus (RAD) suppresses growth of cells derived from posttransplant lymphoproliferative disorder at allograft-protecting doses

Background. Posttransplant lymphoproliferative disorders (PTLDs) represent a life-threatening complication of standard immunosuppressive therapy. The impact of novel, rapamycin-related immunosuppressive drugs on the pathogenesis of PTLDs remains undefined. Methods. We tested the effect of everolimus (RAD, Novartis Pharma AG, Basel, Switzerland) on human PTLD-derived cells using in vitro assays and an in vivo severe combined immunodeficiency disease mouse xenotransplant model. Results. Everolimus profoundly inhibited the proliferation, cell-cycle progression, and survival of the PTLD-1 cell line established from a pulmonary PTLD. Equally profound inhibition of PTLD-1 growth was achieved in vivo at well-tolerated everolimus doses of 0.5 to 5 mg/kg per day. Five mg/kg per day of everolimus, given once per day, inhibited PTLD-1 tumor volume gain by more than 10-fold in treated mice compared with untreated mice. Because the subsequent pharmacokinetic analysis indicated rapid everolimus absorption, distribution, and clearance in mice (with a half-life of 3 to 6 hr and maximum drug blood concentration reached after 0.5 to 1 hr), treatment was changed to a twice-daily regimen. Everolimus given twice daily at 0.5 mg/kg per dose inhibited tumor-volume gain by more than 60-fold and at 0.25 mg/kg per dose by more than 10-fold. Similar everolimus doses were required to prevent graft rejection in a mouse heart allotransplantation model; the highest dose tested (1.5 mg/kg twice daily) resulted in long-term graft survival in all mice that underwent transplantation. Conclusions. Everolimus displays a potent inhibitory effect on PTLD-derived cells in vitro and in vivo in a dose range leading to prevention of allograft rejection and may prove effective in both the prevention and treatment of PTLDs in transplant patients.

Pharmacokinetics of Mycophenolic Acid in Renal Transplant Patients with Delayed Graft Function

The pharmacokinetics of mycophenolic acid (MPA), the immunosuppressant form of the prodrug mycophenolate mofetil (MMF), and the primary glucuronide metabolite, MPAG, were characterized in renal transplant patients with delayed graft function using random effects piecewise linear models. Eight patients were evaluated after receiving their first and subsequent daily oral doses of 1.5 g mycophenolate mofetil twice daily on study days 1 (n = 8), 7 (n = 8), 14 (n = 5), 21 (n = 2), and 28 (n = 7). The area under the concentration—time curve from zero to 12 hours (AUC0–12) for MPA, MPAG, MPA free fraction, and free MPA were analyzed in serial plasma samples using validated high‐performance liquid chromatography and ultrafiltration procedures. Random effects piecewise linear models, fit by maximum likelihood methods, were applied to AUC0–12 of MPA and MPAG, MPA free fraction, AUC0–12 of free MPA, and serum creatinine concentration, the index of renal function used in this study. Two hemodialysis sessions did not lower MPA plasma concentration, although some MPAG was removed. The AUC0–12 of MPA increased as a function of time, although it was not possible to fit a statistical model to the data due to considerable among‐patient variation in the pattern of increase with time. The AUC0–12 of MPAG, MPA free fraction, and AUC0–12 of free MPA reached maximal values on day 7; each of these parameters had unique day 1 to 7 positive slope values and unique day 7 to 28 negative slope values. The average creatinine concentration was maximal at day 1 and a unique negative slope was obtained between days 7 and 28. Thus, this study provides statistical models for the alteration of AUC0–12 of MPAG, MPA free fraction, AUC0–12 of free MPA, and serum creatinine in renal transplant patients with delayed graft function. These results provide evidence that renal dysfunction is associated with altered pharmacokinetics of MPA, particularly increased AUC0–12 of MPAG, MPA free fraction, and AUC0–12 of free MPA. The perturbed pharmacokinetics normalized with improving renal function.

Mycophenolic Acid Area under the Curve Values in African American and Caucasian Renal Transplant Patients Are Comparable

The possibility of an effect of ethnicity on the pharmacokinetics of mycophenolic acid, the immunosuppressive metabolite of the prodrug mycophenolate mofetil, was studied over 90 days following renal transplantation in African American (n = 13) and Caucasian patients (n = 20). Since renal dysfunction and time after transplant surgery are two factors known to alter mycophenolic acid pharmacokinetics, two‐way analysis of variance of the data at each time point with ethnicity and renal function status as covariates was used to evaluate the possibility of an ethnicity effect on the pharmacokinetic parameters. No statistically significant difference based on ethnicity was detected for the primary pharmacokinetic parameters, abbreviated mycophenolic acid area under the concentration‐time curve (MPA AUC), or the predose trough concentration on study days 4,7,14,28, or 90. A statistically significant decrease in MPA AUC and increase in oral apparent clearance were observed in renally impaired patients regardless of ethnicity on days 4, and 4 and 7, respectively. The suggested mechanism for these differences is uremia‐induced increased MPA free fraction, leading to a temporary increased clearance for this restrictively cleared drug.

Pharmacokinetic, pharmacodynamic, and outcome investigations as the basis for mycophenolic acid therapeutic drug monitoring in renal and heart transplant patients

Mycophenolate mofetil is widely used in combination with either cyclosporine or tacrolimus for rejection prophylaxis in renal and heart transplant patients. Although not monitored routinely nearly to the degree that other agents such as cyclosporine or tacrolimus, there is an expanding body of experimental evidence for the utility of monitoring mycophenolic acid, the primary active metabolite of mycophenolate mofetil, plasma concentration as an index of risk for the development of acute rejection. The following are important experimentally-based reasons for recommending the incorporation of target therapeutic concentration monitoring of mycophenolic acid: (1) the MPA dose-interval area-under-the-concentration-time curve, and less precisely, MPA predose concentrations predict the risk for development of acute rejection; (2) the strong correlation between mycophenolic acid plasma concentrations and expression of important cell surface activation antigens, whole blood pharmacodynamic assays of lymphocyte proliferation and median graft rejection scores in a heart transplant animal model; (3) the greater than 10-fold interindividual variation of MPA area under the concentration time curve values in heart and renal transplant patients receiving a fixed dose of the parent drug; (4) drug-drug interactions involving other immunosuppressives are such that when switching from one to another (eg, from cyclosporine to tacrolimus or vice-versa) substantial changes in MPA concentrations can occur in patients receiving a fixed dose of the parent drug; (5) significant effects of liver and kidney diseases on the steady-state total and free mycophenolic acid area under the concentration time curve values; (6) the need to closely monitor mycophenolic acid when a major change in immunosuppression is planned such as steroid withdrawal. Current investigations are focused on determination of the most optimal sampling time and for mycophenolic acid target therapeutic concentration monitoring. Further investigations are needed to evaluate the pharmacologic activity of the newly described acyl glucuronide metabolite of mycophenolic acid which has been shown to inhibit, in vitro, inosine monophosphate dehydrogenase.

Clinical Utility and Analytical Challenges in Measurement of Cerebrospinal Fluid Amyloid-β1–42 and τ Proteins as Alzheimer Disease Biomarkers

BACKGROUND Over the past 2 decades, clinical studies have provided evidence that cerebrospinal fluid (CSF) amyloid β(1-42) (Aβ(1-42)), total τ (t-τ), and τ phosphorylated at Thr181 (p-τ(181)) are reliable biochemical markers of Alzheimer disease (AD) neuropathology. CONTENT In this review, we summarize the clinical performance and describe the major challenges for the analytical performance of the most widely used immunoassay platforms [based on ELISA or microbead-based multianalyte profiling (xMAP) technology] for the measurement of CSF AD biomarkers (Aβ(1-42), t-τ, and p-τ(181)). With foundational immunoassay data providing the diagnostic and prognostic values of CSF AD biomarkers, the newly revised criteria for the diagnosis of AD include CSF AD biomarkers for use in research settings. In addition, it has been suggested that the selection of AD patients at the predementia stage by use of CSF AD biomarkers can improve the statistical power of clinical trial design. Owing to the lack of a replenishable and commutable human CSF-based standardized reference material (SRM) and significant differences across different immunoassay platforms, the diagnostic-prognostic cutpoints of CSF AD biomarker concentrations are not universal at this time. These challenges can be effectively met in the future, however, through collaborative ongoing standardization efforts to minimize the sources of analytical variability and to develop reference methods and SRMs. SUMMARY Measurements of CSF Aβ(1-42), t-τ, and p-τ(181) with analytically qualified immunoassays reliably reflect the neuropathologic hallmarks of AD in patients at the early predementia stage of the disease and even in presymptomatic patients. Thus these CSF biomarker tests are useful for early diagnosis of AD, prediction of disease progression, and efficient design of drug intervention clinical trials.

Pharmacokinetics of mycophenolic acid in renal insufficiency

Mycophenolate mofetil (MMF) is now widely used in solid organ transplantation. MMF is rapidly converted to its active form, mycophenolic acid (MPA), upon reaching the systemic circulation. MPA is metabolized to its glucuronide metabolite, mycophenolic acid glucuronide (MPAG), by glucoronyl transferases in the liver and possibly elsewhere. MPAG is then excreted by the kidney. MPA is extensively and avidly bound to serum albumin. Previous studies have demonstrated that it is only the free (non-protein-bound) fraction of MPA that is available to exert its action. In vivo and in vitro studies demonstrate that renal insufficiency decreases the protein binding of MPA and increases free MPA concentrations. This decrease in protein binding seems to be caused both by the uremic state itself and by competition with the retained metabolite MPAG. The disposition of MPA in patients with severe renal impairment may be significantly affected by this change in protein binding.

Mycophenolic acid concentrations are associated with cardiac allograft rejection

BACKGROUND Mycophenolate mofetil (MMF) therapy decreases the incidence of allograft rejection following solid-organ transplantation. Current dosing strategies of MMF are not routinely adjusted based on mycophenolic acid (MPA) area under the concentration-time curve (AUC), MPA trough, or free MPA (fMPA) AUC values. METHODS To determine the clinical significance of MPA concentrations following orthotopic heart transplantation (OHT), we measured pre-dose MPA trough, MPA free fraction, an estimated MPA AUC using an abbreviated sampling schedule, and fMPA AUC in 38 consecutive patients. We measured MPA concentrations using a validated high-performance liquid chromatography method and graded endomyocardial biopsies based on the International Society for Heart and Lung Transplantation (ISHLT) grading system. RESULTS The MPA values for the study group were as follows: MPA trough of 1.2 +/- 0.6 microg/ml; MPA free fraction of 1.9 +/- 0.4%; MPA AUC of 44.5 +/- 16. 1 microg/hour/ml; and fMPA AUC of 0.83 +/- 0.30 microg/hour/ml. We compared patients with Grade 0 (n = 22), Grade 1 (n = 13), or Grade 2/3 (n = 3). The MPA AUC values were lower in patients with Grade 2/3 than in patients with Grade 0 (26.1 +/- 6.6 vs 42.8 +/- 14.0 microg/hour/ml, p < 0.08) or Grade 1 rejection (26.1 +/- 6.6 vs 51.7 +/- 17.5 microg/hour/ml, p < 0.05). The fMPA AUC values were lower in patients with Grade 2/3 than with patients with Grade 0 (0.49 +/- 0.11 vs 0.81 +/- 0.25 microg/hour/ml, p < 0.05) or Grade 1 (0.49 +/- 0.25 vs 0.95 +/- 0.34 microg/hour/ml, p < 0.05) rejection. We noted a trend in MPA trough concentrations between patients with Grade 2/3 vs 0 (0.65 +/- 0.15 vs 1.20 +/- 0.58 microg/ml, p = 0.15) and Grade 1 (0.65 +/- 0.15 vs 1.24 +/- 0.72 microg/ml, p = 0.14) rejection. CONCLUSION These preliminary results suggest that lower MPA AUC and fMPA AUC values are associated with cardiac allograft rejection in heart transplant recipients. Individualizing MMF dosing based on MPA determinations may minimize the risk of rejection following OHT.