Development of PBPK model for intra-articular injection in human: methotrexate solution and rheumatoid arthritis case study.

A physiologically based model describing the dissolution, diffusion, and transfer of drug from the intra-articular (IA) space to the plasma, was developed for GastroPlus® v9.8. The model is subdivided into compartments representing the synovial fluid, synovium, and cartilage. The synovium is broken up into two sublayers. The intimal layer acts as a diffusion barrier between the synovial fluid and the subintimal layer. The subintimal layer of the synovium has fenestrated capillaries that allow the free drug to be transported into systemic circulation. The articular cartilage is broken up into 10 diffusion sublayers as it is much thicker than the synovium. The cartilage acts as a depot tissue for the drug to diffuse into from synovial fluid. At later times, the drug will diffuse from the cartilage back into synovial fluid once a portion of the dose enters systemic circulation. In this study, a listing of all relevant details and equations for the model is presented. Methotrexate was chosen as a case study to show the application and utility of the model, based on the availability of intravenous (IV), oral (PO) and IA administration data in patients presenting rheumatoid arthritis (RA) symptoms. Systemic disposition of methotrexate in RA patients was described by compartmental pharmacokinetic (PK) model with PK parameters extracted using the PKPlus™ module in GastroPlus®. The systemic PK parameters were validated by simulating PO administration of methotrexate before being used for simulation of IA administration. For methotrexate, the concentrations of drug in the synovial fluid and plasma were well described after adjustments of physiological parameters to account for RA disease state, and with certain assumptions about binding and diffusion. The results indicate that the model can correctly describe PK profiles resulting from administration in the IA space, however, additional cases studies will be required to evaluate ability of the model to scale between species and/or doses.

Physiologically Based Pharmacokinetic Absorption Model for Pexidartinib to Evaluate the Impact of Meal Contents and Intake Timing on Drug Exposure.

Pexidartinib is a systemic treatment for patients with tenosynovial giant cell tumor not amenable to surgery. Oral absorption of pexidartinib is affected by food; administration with a high-fat meal (HFM) or low-fat meal (LFM) increases absorption by approximately 100% and approximately 60%, respectively, compared with the fasted state. Pexidartinib is currently dosed 250 mg orally twice daily with an LFM (approximately 11-14 g of total fat). We developed a physiologically based pharmacokinetic model to determine the impact on drug exposure of dose timing with respect to meals, meal type, and caloric content. A 15%-16% increase in plasma exposure was predicted when consuming an HFM 1 hour after dosing with an LFM, but almost no effect on pharmacokinetics was predicted when an HFM was consumed 3 hours or more before or after pexidartinib dosing with an LFM. Exposure was not significantly affected when pexidartinib was taken with a 500-kcal LFM over the range of fat (approximately 11-14 g of total fat; 20%-25% calories from fat) for an LFM. These findings on timing of pexidartinib dose with respect to meals should be considered by patients and physicians to reduce the potential for side effects.

Assessing the risk of pH-dependent absorption for new molecular entities: a novel in vitro dissolution test, physicochemical analysis, and risk assessment strategy.

Weak base therapeutic agents can show reduced absorption or large pharmacokinetic variability when coadministered with pH-modifying agents, or in achlorhydria disease states, due to reduced dissolution rate and/or solubility at high gastric pH. This is often referred to as pH-effect. The goal of this study was to understand why some drugs exhibit a stronger pH-effect than others. To study this, an API-sparing, two-stage, in vitro microdissolution test was developed to generate drug dissolution, supersaturation, and precipitation kinetic data under conditions that mimic the dynamic pH changes in the gastrointestinal tract. In vitro dissolution was assessed for a chemically diverse set of compounds under high pH and low pH, analogous to elevated and normal gastric pH conditions observed in pH-modifier cotreated and untreated subjects, respectively. Represented as a ratio between the conditions, the in vitro pH-effect correlated linearly with clinical pH-effect based on the Cmax ratio and in a non-linear relationship based on AUC ratio. Additionally, several in silico approaches that use the in vitro dissolution data were found to be reasonably predictive of the clinical pH-effect. To explore the hypothesis that physicochemical properties are predictors of clinical pH-effect, statistical correlation analyses were conducted using linear sequential feature selection and partial least-squares regression. Physicochemical parameters did not show statistically significant linear correlations to clinical pH-effect for this data set, which highlights the complexity and poorly understood nature of the interplay between parameters. Finally, a strategy is proposed for implementation early in clinical development, to systematically assess the risk of clinical pH-effect for new molecular entities that integrates physicochemical analysis and in vitro, in vivo and in silico methods.

PBPK Modeling as a Tool for Predicting and Understanding Intestinal Metabolism of Uridine 5'-Diphospho-glucuronosyltransferase Substrates.

Uridine 5'-diphospho-glucuronosyltransferases (UGTs) are expressed in the small intestines, but prediction of first-pass extraction from the related metabolism is not well studied. This work assesses physiologically based pharmacokinetic (PBPK) modeling as a tool for predicting intestinal metabolism due to UGTs in the human gastrointestinal tract. Available data for intestinal UGT expression levels and in vitro approaches that can be used to predict intestinal metabolism of UGT substrates are reviewed. Human PBPK models for UGT substrates with varying extents of UGT-mediated intestinal metabolism (lorazepam, oxazepam, naloxone, zidovudine, cabotegravir, raltegravir, and dolutegravir) have demonstrated utility for predicting the extent of intestinal metabolism. Drug-drug interactions (DDIs) of UGT1A1 substrates dolutegravir and raltegravir with UGT1A1 inhibitor atazanavir have been simulated, and the role of intestinal metabolism in these clinical DDIs examined. Utility of an in silico tool for predicting substrate specificity for UGTs is discussed. Improved in vitro tools to study metabolism for UGT compounds, such as coculture models for low clearance compounds and better understanding of optimal conditions for in vitro studies, may provide an opportunity for improved in vitro-in vivo extrapolation (IVIVE) and prospective predictions. PBPK modeling shows promise as a useful tool for predicting intestinal metabolism for UGT substrates.

In ovo non-invasive quantification of the myocardial function and mass of chick embryos using magnetic resonance imaging.

Magnetic resonance imaging (MRI) has evolved as one of the major non-invasive tools to study healthy and diseased hearts in animal models, especially rodent models. Even though, the chick embryo has long been used as a model for cardiovascular research, MRI has not yet been used for in vivo cardiac studies. Part of the reason for this is the difficulty in monitoring the ECG and respiration of the chick embryo in the magnet for gating purposes. To overcome this complication, this paper presents the use of retrospective Cine MRI to measure the cardiac function of chick embryos in ovo for the first time, without the need for respiratory or cardiac gating. The resulting left ventricular functional parameters, from six chick embryos at 20 days of incubation, were (mean +/- SD) EDV 69 +/- 15 microL, ESV 31 +/- 7 microL, SV 38 +/- 9 microL and EF 54.5 +/- 2%. The use of retrospective Cine MRI at earlier stages of development is also discussed and difficulties have been highlighted.

Effects of magnesium treatment in a model of internal capsule lesion in spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: The study aim was to assess the effects of magnesium sulfate (MgSO(4)) administration on white matter damage in vivo in spontaneously hypertensive rats. METHODS: The left internal capsule was lesioned by a local injection of endothelin-1 (ET-1; 200 pmol) in adult spontaneously hypertensive rats. MgSO(4) was administered (300 mg/kg SC) 30 minutes before injection of ET-1, plus 200 mg/kg every hour thereafter for 4 hours. Infarct size was measured by T2-weighted magnetic resonance imaging (day 2) and histology (day 11), and functional recovery was assessed on days 3 and 10 by the cylinder and walking-ladder tests. RESULTS: ET-1 application induced a small, localized lesion within the internal capsule. Despite reducing blood pressure, MgSO(4) did not significantly influence infarct volume (by magnetic resonance imaging: median, 2.1 mm(3); interquartile range, 1.3 to 3.8, vs 1.6 mm(3) and 1.2 to 2.1, for the vehicle-treated group; by histology: 0.3 mm(3) and 0.2 to 0.9 vs 0.3 mm(3) and 0.2 to 0.5, respectively). Significant forelimb and hindlimb motor deficits were evident in the vehicle-treated group as late as day 10. These impairments were significantly ameliorated by MgSO(4) in both cylinder (left forelimb use, P<0.01 and both-forelimb use, P<0.03 vs vehicle) and walking-ladder (right hindlimb score, P<0.02 vs vehicle) tests. CONCLUSIONS: ET-1-induced internal capsule ischemia in spontaneously hypertensive rats represents a good model of lacunar infarct with small lesion size, minimal adverse effects, and a measurable motor deficit. Despite inducing mild hypotension, MgSO(4) did not significantly influence infarct size but reduced motor deficits, supporting its potential utility for the treatment of lacunar infarct.

Sodium-23 magnetic resonance imaging has potential for improving penumbra detection but not for estimating stroke onset time.

Tissue sodium concentration increases in irreversibly damaged (core) tissue following ischemic stroke and can potentially help to differentiate the core from the adjacent hypoperfused but viable penumbra. To test this, multinuclear hydrogen-1/sodium-23 magnetic resonance imaging (MRI) was used to measure the changing sodium signal and hydrogen-apparent diffusion coefficient (ADC) in the ischemic core and penumbra after rat middle cerebral artery occlusion (MCAO). Penumbra and core were defined from perfusion imaging and histologically defined irreversibly damaged tissue. The sodium signal in the core increased linearly with time, whereas the ADC rapidly decreased by >30% within 20 minutes of stroke onset, with very little change thereafter (0.5-6 hours after MCAO). Previous reports suggest that the time point at which tissue sodium signal starts to rise above normal (onset of elevated tissue sodium, OETS) represents stroke onset time (SOT). However, extrapolating core data back in time resulted in a delay of 72 ± 24 minutes in OETS compared with actual SOT. At the OETS in the core, penumbra sodium signal was significantly decreased (88 ± 6%, P=0.0008), whereas penumbra ADC was not significantly different (92 ± 18%, P=0.2) from contralateral tissue. In conclusion, reduced sodium-MRI signal may serve as a viability marker for penumbra detection and can complement hydrogen ADC and perfusion MRI in the time-independent assessment of tissue fate in acute stroke patients.

Serial postmortem relaxometry in the normal rat brain and following stroke.

PURPOSE: To investigate MRI for noninvasive autopsy by means of measurements of serial changes in relaxation parameters of the rat brain during the postmortem interval. MATERIALS AND METHODS: Postmortem relaxometry measurements were performed before and hourly after death for 24 h on five control rats and five rats that underwent middle cerebral artery occlusion. Analyses were performed on representative regions of gray, white, and mixed gray/white matter structures. RESULTS: Significant decreases in both T(1) and T(2) values were measured in all areas in the control group within 24 h of death. In the stroke animals, T(2) differences between normal and ischemic striatal tissue decreased by 11 +/- 4% (P < 0.01), with a complete convergence of T(2) values observed between ischemic striatal tissue and nonischemic cortical tissue. CONCLUSION: Lesion conspicuity and the ability to differentiate between different tissue compartments are significantly affected by postmortem interval, and alterations to pulse timing parameters will be necessary if the sensitivity of MRI to detect central nervous system diseases in postmortem tissue is to be maintained. Indeed in the case of stroke at least, convergence of T(2) values with normal tissue post mortem indicates that T(1)-weighted images may be more sensitive to the presence of such lesions.

17beta-Estradiol treatment following permanent focal ischemia does not influence recovery of sensorimotor function.

The development of therapy to aid poststroke recovery is essential. The female hormone 17beta-estradiol has been shown to promote synaptogenesis; the purpose of this study was to attempt to harness these mechanisms to promote repair and recovery in the peri-infarct zone. Rats were ovariectomized, tested for sensorimotor function, and the middle cerebral artery permanently occluded (MCAO). Infarct volumes were calculated using MRI, and damage was equivalent in all animals prior to implantation of either 17beta-estradiol or placebo pellets. Animals were tested for functional recovery for 28 days and tissue processed for synaptic marker syntaxin immunohistochemistry. The stroke induced a significant behavioral deficit, which persisted out to 28 days, and was not significantly different between 17beta-estradiol and placebo treatment groups. There was no difference in syntaxin immunostaining between groups in either the peri-infarct cortex or in the dendritic CA1 reference region. In conclusion, 17beta-estradiol treatment, delivered poststroke, did not influence recovery of function or synaptogenesis.