Cognitive decline in thrombotic thrombocytopenic purpura survivors: The role of white matter health as assessed by MRI.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare condition caused by severe ADAMTS13 deficiency, leading to platelet aggregation and thrombosis. Despite treatment, patients are prone to cognitive impairment and depression. We investigated brain changes in iTTP patients during remission using advanced magnetic resonance imaging (MRI) techniques, correlating these changes with mood and neurocognitive tests. Twenty iTTP patients in remission (30 days post-haematological remission) were compared with six healthy controls. MRI scans, including standard and specialized sequences, were conducted to assess white matter health. Increased T1 relaxation times were found in the cingulate cortex (p < 0.05), and elevated T2 relaxation times were observed in the cingulate cortex, frontal, parietal and temporal lobes (p < 0.05). Pathological changes in these areas are correlated with impaired cognitive and depressive scores in concentration, short-term memory and verbal memory. This study highlights persistent white matter damage in iTTP patients, potentially contributing to depression and cognitive impairment. Key regions affected include the frontal lobe and cingulate cortex. These findings have significant implications for the acute and long-term management of iTTP, suggesting a need for re-evaluation of treatment approaches during both active phases and remission. Further research is warranted to enhance our understanding of these complexities.

Simultaneous measurements of myocardial glucose metabolism and extracellular volumes with hybrid PET/MRI using concurrent injections of Gd-DTPA and [18F]FDG.

BACKGROUND: The aims of this study were to investigate the application of a constant infusion (CI) to mitigate the issue of constantly changing Gd-DTPA contrast levels in a bolus injection for extracellular volume (ECV) measurements by (a) comparing a CI alone to a bolus alone and a bolus followed by CI in healthy myocardium, (b) evaluating the impact of glucose suppression using heparin on ECV. METHODS: Five healthy canine subjects were imaged to compare three different protocols for injecting Gd-DTPA and FDG: bolus alone, CI alone, bolus followed by CI. Suppression of myocardial glucose uptake was induced using a continuous infusion of 20% lipid at a rate of 0.25 mL·min-1·kg-1 as well as 2000 units of intravenous heparin injected 20 minutes prior to FDG/Gd-DTPA injection. RESULTS: There was no significant effect on ECV measurement when heparin was used for glucose suppression at equilibrium irrespective of infusion protocol). Measurements of ECV in myocardium, regardless of infusion protocol showed no significant difference at all time points (P = 0.21) prior to washout. CONCLUSIONS: The suppression of myocardial uptake of [18F]FDG with heparin did not alter the determination of myocardial ECV though a larger sample size may show differences. Further, the infusion protocol (bolus or constant infusion) had no effect on the calculated ECV.

Tracking the progress of inflammation with PET/MRI in a canine model of myocardial infarction.

BACKGROUND: Following myocardial infarction, tissue undergoes pathophysiological changes involving inflammation and scar tissue formation. However, little is known about the pathophysiology and prognostic significance of any corresponding changes in remote myocardium. The aim of this study was to investigate the potential application of a combined constant infusion of 18F-FDG and Gd-DTPA to quantitate inflammation and extracellular volume (ECV) from 3 to 40 days after myocardial infarction. METHODS: Eight canine subjects were imaged at multiple time points following induction of an MI with a 60-minute concurrent constant infusion of Gd-DTPA and 18F-FDG using a hybrid PET/MRI scanner. RESULTS: There was a significant increase in ECV in remote myocardium on day 14 post-MI (P = .034) and day 21 (P = .021) compared to the baseline. ECV was significantly elevated in the infarcted myocardium compared to remote myocardium at all time points post-MI (days 3, 7, 14, 21, and 40) (P < .001) while glucose uptake was also increased within the infarct on days 3, 7, 14, and 21 but not 40. CONCLUSIONS: The significant increase in ECV in remote tissue may be due to an ongoing inflammatory process in the early weeks post-infarct.

Same day comparison of PET/CT and PET/MR in patients with cardiac sarcoidosis.

BACKGROUND: Inflammatory cardiac disorders, in particular, sarcoidosis, play an important role in left ventricular dysfunction, conduction abnormalities, and arrhythmias. In this study, we compared the imaging characteristics and diagnostic information obtained when patients were imaged sequentially with PET/CT and then with hybrid PET/MRI on the same day following a single 18F-FDG injection. METHODS: Ten patients with known or suspected sarcoidosis underwent imaging in sequence of (a) 99mTc-MIBI, (b) 18F-FDG with PET/CT, and (c) 18F-FDG with 3T PET/MRI. Images were compared quantitatively by determination of SUVmax and SUV on a voxel by voxel basis, and qualitatively by two experienced observers. RESULTS: When both platforms were compared quantitatively, similar data for the evaluation of enhanced 18F-FDG uptake were obtained. Qualitatively, there were (1) several instances of normal perfusion with delayed enhancement and/or focal 18F-FDG uptake, (2) comparable enhanced 18F-FDG uptake on PET/CT vs. PET/MRI, and (3) diversity in disease patterns with delayed enhancement only, increased 18F-FDG uptake only, or both. CONCLUSION: In this limited patient study, PET/CT and PET/MR provided similar diagnostic data for 18F-FDG uptake, and the concurrent acquisition of MR images provided further insight into the disease process.

Hybrid PET/MR imaging in myocardial inflammation post-myocardial infarction.

Hybrid PET/MR imaging is an emerging imaging modality combining positron emission tomography (PET) and magnetic resonance imaging (MRI) in the same system. Since the introduction of clinical PET/MRI in 2011, it has had some impact (e.g., imaging the components of inflammation in myocardial infarction), but its role could be much greater. Many opportunities remain unexplored and will be highlighted in this review. The inflammatory process post-myocardial infarction has many facets at a cellular level which may affect the outcome of the patient, specifically the effects on adverse left ventricular remodeling, and ultimately prognosis. The goal of inflammation imaging is to track the process non-invasively and quantitatively to determine the best therapeutic options for intervention and to monitor those therapies. While PET and MRI, acquired separately, can image aspects of inflammation, hybrid PET/MRI has the potential to advance imaging of myocardial inflammation. This review contains a description of hybrid PET/MRI, its application to inflammation imaging in myocardial infarction and the challenges, constraints, and opportunities in designing data collection protocols. Finally, this review explores opportunities in PET/MRI: improved registration, partial volume correction, machine learning, new approaches in the development of PET and MRI pulse sequences, and the use of novel injection strategies.

Building nursing and midwifery leadership capacity in the Pacific.

AIM: The Australian Award Fellowship Program aimed to strengthen nursing and midwifery leadership and capacity in developing countries in the Pacific. BACKGROUND: It is necessary to build an optimal global health workforce, and leadership and mentorship are central to this need. This is especially important in small island states such as the Pacific who have limited capacity and resources. INTRODUCTION: This health system strengthening program addressed quality improvement in education, through the mentorship of potential nursing and midwifery leaders in the South Pacific Region. METHODS: Program participants between 2013 and 2015 were interviewed. Data were audio-taped, transcribed and analysed thematically using an inductive process. RESULTS: Thirty-four nurses and midwives from 12 countries participated. There were four main themes arising from the data which were: having a country-wide objective, learning how to be a leader, negotiating barriers and having effective mentorship. DISCUSSION: Our study showed that participants deemed their mentorship from country leaders highly valuable in relation to completing their projects, networking and role modelling. Similar projects are described. LIMITATIONS: The limitation of this study was its small size. There is a need to continue to build the momentum of the program and Fellows in each country in order to build regional networks. CONCLUSIONS AND IMPLICATIONS FOR NURSING AND MIDWIFERY: The Program has provided beneficial leadership education and mentorship for nurses and midwives from Pacific countries. It has provided a platform to develop quality improvement projects in line with national priorities. IMPLICATIONS FOR HEALTH POLICY: Global aid programs and the recipients of the program would benefit from comparable health strengthening approaches to nursing and midwifery in similar developing countries.

Ulysses radio and plasma wave observations in the jupiter environment.

The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of aurorallike hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the lo plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the lo torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.

Rigid-body motion correction in hybrid PET/MRI using spherical navigator echoes.

Integrated positron emission tomography and magnetic resonance imaging (PET/MRI) is an imaging technology that provides complementary anatomical and functional information for medical diagnostics. Both PET and MRI are highly susceptible to motion artifacts due, in part, to long acquisition times. The simultaneous acquisition of the two modalities presents the opportunity to use MRI navigator techniques for motion correction of both PET and MRI data. For this task, we propose spherical navigator echoes (SNAVs)-3D k-space navigators that can accurately and rapidly measure rigid body motion in all six degrees of freedom. SNAVs were incorporated into turbo FLASH (tfl)-a product fast gradient echo sequence-to create the tfl-SNAV pulse sequence. Acquiring in vivo brain images from a healthy volunteer with both sequences first compared the tfl-SNAV and product tfl sequences. It was observed that incorporation of the SNAVs into the image sequence did not have any detrimental impact on the image quality. The SNAV motion correction technique was evaluated using an anthropomorphic brain phantom. Following a stationary reference image where the tfl-SNAV sequence was acquired along with simultaneous list-mode PET, three identical PET/MRI scans were performed where the phantom was moved several times throughout each acquisition. This motion-up to 11° and 14 mm-resulted in motion artifacts in both PET and MR images. Following SNAV motion correction of the MRI and PET list-mode data, artifact reduction was achieved for both the PET and MR images in all three motion trials. The corrected images have improved image quality and are quantitatively more similar to the ground truth reference images.

Phase I pharmacokinetic study of cyclosporin A combined with doxorubicin.

We performed a phase I trial of cyclosporin A (CsA) in combination with doxorubicin (dox) to determine the maximally tolerated dose (MTD) of the combination in man, to define the quantitative and qualitative toxicities of the combination, and to determine the pharmacokinetics of the two drugs when used together. CsA was administered as a continuous infusion for 6 days, and dox was administered as a single 10-min infusion 24 h after the initiation of CsA. The starting CsA infusion rate was 5 micrograms/kg/min, and the dox starting dose was 30 mg/m2. Courses were administered every 4 weeks with first CsA and then dox being escalated in consecutive cohorts of patients until the MTD was determined. Twenty-three patients and 40 courses were evaluable for toxicity. Pharmacokinetic analysis was performed in 23 patients on the first course for whole blood CsA and plasma dox and doxorubicinol. The MTD of CsA was 6 micrograms/kg/min, and for dox it was 45 mg/m2. Dose-limiting toxicity was neutropenia. Serum creatinine and creatinine clearance did not change over the infusion period. Bilirubin increased from a median of 10 mumol/liter at the initiation of the infusion to a median of 40.4 mumol/liter at the end of the infusion but returned to normal before the next cycle of therapy. Nausea and vomiting were common and marked, whereas thrombocytopenia was mild. Two patients, one with small cell lung cancer and one with breast cancer, had stable disease while receiving treatment for 5 and 6 months, respectively. Mean whole blood steady state concentrations of CsA were 2210 ng/ml during the infusion with total body clearance of 0.177 liter/h/kg. The area under the concentration x time curve (AUC) increased linearly with dose of dox, and total body clearance was independent of dose. The mean total body clearance was 2.46 liters/h/m2, and terminal half-life was 49.6 h. The AUC for dox was greater and clearance was less than has been previously reported at the doses administered in this study. The ratio of AUC for doxorubicinol to AUC for dox was less than expected, suggesting that the metabolism and/or excretion of dox was decreased when administered with CsA. We conclude that dox can be combined with infusioned CsA but at a lower dose than when given alone. This may be due to altered metabolism and/or excretion of dox or increased bone marrow stem cell sensitivity to dox.

MR-compatibility of a high-resolution small animal PET insert operating inside a 7 T MRI.

A full-ring PET insert consisting of 16 PET detector modules was designed and constructed to fit within the 114 mm diameter gradient bore of a Bruker 7 T MRI. The individual detector modules contain two silicon photomultiplier (SiPM) arrays, dual-layer offset LYSO crystal arrays, and high-definition multimedia interface (HDMI) cables for both signal and power transmission. Several different RF shielding configurations were assessed prior to construction of a fully assembled PET insert using a combination of carbon fibre and copper foil for RF shielding. MR-compatibility measurements included field mapping of the static magnetic field (B 0) and the time-varying excitation field (B 1) as well as acquisitions with multiple pulse sequences: spin echo (SE), rapid imaging with refocused echoes (RARE), fast low angle shot (FLASH) gradient echo, and echo planar imaging (EPI). B 0 field maps revealed a small degradation in the mean homogeneity (+0.1 ppm) when the PET insert was installed and operating. No significant change was observed in the B 1 field maps or the image homogeneity of various MR images, with a 9% decrease in the signal-to-noise ratio (SNR) observed only in EPI images acquired with the PET insert installed and operating. PET detector flood histograms, photopeak amplitudes, and energy resolutions were unchanged in individual PET detector modules when acquired during MRI operation. There was a small baseline shift on the PET detector signals due to the switching amplifiers used to power MRI gradient pulses. This baseline shift was observable when measured with an oscilloscope and varied as a function of the gradient duty cycle, but had no noticeable effect on the performance of the PET detector modules. Compact front-end electronics and effective RF shielding led to minimal cross-interference between the PET and MRI systems. Both PET detector and MRI performance was excellent, whether operating as a standalone system or a hybrid PET/MRI.

L-arginine transport in the human coronary and peripheral circulation.

BACKGROUND: Nitric oxide synthase (NOS) uses arginine for the production of nitric oxide (NO). High intracellular concentrations of arginine suggest that NOS activity should be independent of plasma arginine supply. However, under certain conditions, increased plasma arginine concentrations appear to be associated with increased NOS activity. The purpose of this study was to explore arginine transport within the human coronary and peripheral circulation METHODS AND RESULTS: Mass-labeled 15N2-arginine was infused to steady state before cardiac catheterization in 31 patients. After diagnostic angiography, a catheter was placed in the coronary sinus. The transcardiac concentration gradient (aorta-coronary sinus) of 15N2-arginine was used as a measure of arginine transport at baseline and during infusions of acetylcholine and N(G)-monomethyl-L-arginine (L-NMMA). No gradient was detected at rest. During the infusion of acetylcholine, a significant gradient was detected (2.5+/-1.2 micromol/L, P=0.01) corresponding to a fractional extraction of 11.7+/-7.5%. This is consistent with in vitro studies that suggest that stimulation of NOS induces arginine transport. During the infusion of L-NMMA, the concentration of 15N2-arginine increased in the coronary sinus, producing a gradient of -3.9+/-1.3 micromol/L (P=0.0002), corresponding to a fractional production of 20.5+/-5.0%. This is consistent with in vitro studies that suggest that L-NMMA induces the efflux of arginine from the cell to the extracellular space via transporter-mediated transstimulation. CONCLUSIONS: The use of steady-state 15N2-arginine to examine transorgan L-arginine gradients represents a novel tool for the study of L-arginine transport and the mechanisms of endothelial and NOS dysfunction.

Phase I and pharmacologic study of 9-aminocamptothecin colloidal dispersion formulation given as a 24-hour continuous infusion weekly times four every 5 weeks.

PURPOSE: 9-Aminocamptothecin (9-AC) is a water-insoluble camptothecin (CMP) derivative that inhibits normal topoisomerase I function. Schedule dependency was noted, with the greatest activity seen in the setting of greater than 24 hours exposure to lactone (L) concentrations > or = 10 nmol/L. In this phase I study, 9-AC was given by a continuous intravenous infusion over 24 hours once weekly times four every 5 weeks. PATIENTS AND METHODS: Twenty patients, of whom 16 had fluorouracil-refractory colorectal cancer (CRC), entered the study. Dose levels were 0.7 mg/m2 (n = 4), 1.4 mg/m2 (n = 3), 1.9 mg/m2 (n = 6), and 1.65 mg/m2 (n = 7). Detailed pharmacokinetic (PK) measurements of 9-AC L and carboxylate (C) were performed on day 1 of cycles 1 and 2. RESULTS: At 1.9 mg/m2, dose-limiting toxicity (DLT) was reached, with three of six patients having grade 4 neutropenia. At 1.65 mg/m2, one of seven patients had grade 4 neutropenia. Nonhematologic toxicity was modest, with diarrhea > or = grade 3 in two patients and lethargy > or = grade 3 in eight. PK/pharmacodynamic (PD) analyses showed marked interpatient variability. Steady-state concentrations (Css) of 9-AC L > or = 10 nmol/L (3.6 microg/L) were seen in five of seven patients at 1.65 mg/m2 and five of six patients at 1.9 mg/m2. Using the sigmoidal maximal effect (Emax) model, 9-AC L area under the concentration-time curve (AUC) and Css correlated with day 15 decrease in neutrophils (R2 = .47), but not platelets. CONCLUSION: The recommended phase II dose of 9-AC colloidal dispersion (CD) given as a 24-hour continuous infusion weekly for 4 of every 5 weeks is 1.65 mg/m2.

Combining cyclosporin with chemotherapy controls intraocular retinoblastoma without requiring radiation.

Chemotherapy without radiation has not controlled most intraocular retinoblastoma, perhaps because of the common high expression of multidrug resistance P-glycoprotein that we found in retinoblastoma. Cyclosporin blocks P-glycoprotein-induced efflux of vincristine and teniposide in vitro, and possibly modulates responses to carboplatin. To avoid eye irradiation in bilateral retinoblastoma patients with RB1 germline mutations, which incurs a high second malignancy rate, we added cyclosporin A to a vincristine-teniposide-carboplatin protocol and consolidated chemotherapy responses with focal therapy. We scored patients requiring irradiation, enucleation, or focal ablation of central vision as failures. In 21 study patients, the overall relapse-free rate at a median follow-up of 3.3 years was 76%, with a rate of 92% for newly diagnosed and 50% for previously treated, relapsed retinoblastoma. Our results for the most unfavorable tumors with vitreous seeds (86% at 3.5 years) are better than published success rates of irradiation for similar tumors, or irradiation with the same chemotherapy without cyclosporin (45% at 2. 6 years). These results also exceeded our historic success rate with similar chemotherapy without cyclosporin, focal therapy, and/or radiation in 19 equivalently poor-risk patients (relapse-free rate 37% at a median follow-up of 5.6 years, P = 0.032), 16 of whom were previously untreated (relapse-free rate also 37%, P = 0.012). A better outcome occurred with higher cyclosporin blood levels and projected tissue exposure. Cyclosporin did not enhance the usual chemotoxicity. This clinical study suggests that cyclosporin improves the long-term response of retinoblastoma to chemotherapy, possibly by more than one mechanism.

Metoprolol kinetics and dose response in hypertensive patients.

The kinetics and dose-response characteristics of metoprolol were examined in a series of hypertensive patients. In 14 the elimination half-life of metoprolol after single 100-mg doses (4.1 +/- 0.6 hr) was prolonged (p less than 0.05) after 6 to 12 wk of therapy (5.6 +/- 0.7 hr). In 5 patients receiving 100 mg twice daily evidence of nonlinear metoprolol kinetics emerged, because the area under the concentration-time curve at steady state was 86.8% more (p less than 0.02) than predicted from a single dose. Kinetic data from single doses of metoprolol appear to be a poor predictor of steady-state kinetics. Single metoprolol dosage also induced a fall (p less than 0.01) in blood pressure with pretreatment levels (163/108), reaching a minimum at 5 hr (133/189). During long-term therapy incremented doses of metoprolol between 100 and 600 mg/day in 34 hypertensive patients resulted in a relatively horizontal dose-response curve at doses above 200 mg/day.

Cystic fibrosis: enhanced theophylline metabolism may be linked to the disease.

Theophylline disposition (5.5 mg/kg administered intravenously) was studied in 12 patients with cystic fibrosis (CF) and 16 healthy control volunteers. Dietary controls and logs were used to minimize the influence of food on theophylline metabolism. Control subjects were restudied in random order on two subsequent occasions after 2 weeks of either pancreatic enzymes or placebo. Theophylline and its three main metabolites, 1-methyluric acid, 3-methylxanthine, and 1,3-dimethyluric acid, were analyzed in serum and urine by HPLC. The total body clearance, renal clearance, nonrenal clearance, and volume of distribution of theophylline were significantly greater (p less than 0.05) in patients with CF than in control subjects. The increased nonrenal clearance was the result of increased biotransformation to each of the three main metabolites. Patients with CF exhibited enhanced N-demethylation and 8-hydroxylation of theophylline, pathways that appear to be mediated by two different families of P-450 enzymes. Theophylline clearance after 2 weeks of pancreatic enzyme administration in the control subjects was the same as with placebo. Possible reasons for enhanced theophylline biotransformation in CF are discussed.

Rapid development of enhanced clearance after high-dose cyclophosphamide.

We have studied the disposition of cyclophosphamide, its major cytotoxic metabolite phosphoramide mustard, and the synthetic glucocorticoid dexamethasone in nine patients receiving high-dose cyclophosphamide daily for 2 days before bone marrow transplantation. The total body clearance of cyclophosphamide was observed to increase from 93 +/- 27 ml/min on the first day to 178 +/- 83 ml/min on the second day. This was associated with an increase in the clearance of dexamethasone from 369 +/- 104 ml/min to 526 +/- 123 ml/min. An increased rate of formation of phosphoramide mustard with higher peak concentrations was also seen. Simulation studies show that these changes are most likely the result of an increase in the hepatic metabolism of cyclophosphamide. These results show that high-dose cyclophosphamide causes an increase in its own clearance and that of dexamethasone through an apparent induction of hepatic-metabolizing enzymes detectable 24 hours after initial exposure to cyclophosphamide.

Effect of alcohol on propylthiouracil disposition.

We examined the effect of ethanol on propylthiouracil (PTU) disposition in normal subjects and a rabbit. The drug is metabolized by conjugation. In six normal subjects 19.2 gm oral ethanol, taken either with or two hr after 300 mg PTU, did not change maximum concentration, time to maximum concentration, or total or free AUC of PTU. Pretreatment with ethanol and supplementation to keep blood ethanol concentration above 800 mg/l for 8 hr also did not alter PTU disposition. In the rabbit, the infusion of ethanol (8.81 mg/min) 4 hr after the beginning of an intravenous infusion of PTU 0.05 mg/min did not alter the plasma concentration profile. These results indicate that short-term ethanol dosing does not affect PTU disposition and therefore dosage adjustment is not necessary in patients who drink alcohol.

Strain-specific 1.7 kilobase repetitive deoxyribonucleic acid sequence family in Trichinella spiralis.

Eco RI digestion of bulk DNA from Trichinella spiralis P1, an isolate from domestic pig, reveals the presence of families of repetitive sequences. One of the most prominent of these has a monomer size of 1.7 kb, which exists in minimally dispersed direct tandem arrays, with a copy number of about 2800, and represents 2% of the genome. Although there is evidence that the Eco RI site is missing in some of the family members and that a 1.9 kb variant of the sequence also occurs, the family is highly homogeneous. When bulk DNA from other pig isolates (P2, PB1) and two black bear isolates from Pennsylvania (UPB6, UPB8) is probed with a typical member of the 1.7 kb sequence family cloned into pUC9, hybridization is identical in pattern and intensity with self-hybridization, indicating that the 1.7 kb family exists equally in the repetitive fraction of all of these isolates. When blots of bulk DNA from wild carnivore isolates (MSIL, PF1, AF1, AF2, AF3, AF4, SL, TC) are probed with pPRA, no hybridization can be detected. Faint hybridization of the probe to DNA from T. spiralis var. pseudospiralis occurs at 1.7 kb on an Eco RI profile and indicates that the 1.7 kb sequence has been conserved in the course of strain evolution.

Methylphenidate hydrochloride given with or before breakfast: II. Effects on plasma concentration of methylphenidate and ritalinic acid.

Methylphenidate HCl (Ritalin) is often prescribed for the treatment of hyperactivity and is usually administered orally 30 minutes to 1 hour before meals, based on an assumption that meals may interfere with the absorption or metabolism of the drug. Seven boys who were taking methylphenidate regularly for the treatment of hyperactivity were hospitalized and given their established dose of the drug intravenously or orally, either with breakfast or in a fasted state. Blood samples were taken to determine the pharmacokinetics of the drug in each condition. Few differences between the "fed" and "fasted" states were noted, but the statistically significant differences indicated that meals accelerate rather than impede the absorption of methylphenidate.

Effect of PSC 833, a potent inhibitor of P-glycoprotein, on the growth of astrocytoma cells in vitro.

Malignant astrocytomas have been found to express P-glycoprotein (Pgp, mdr1 gene product). It was hypothesized that in addition to conferring multidrug resistance, Pgp is intimately associated with the development of astrocytomas. Accordingly, we studied the effect of PSC 833 (PSC, Novartis), a potent inhibitor of Pgp, on the growth of Pgp-expressing astrocytoma cells. The results showed that in all the cell lines tested, PSC (10-60 microM) inhibited the growth as well as induced cell death. Cells exposed to PSC exhibited DNA ladder characteristic of apoptosis. PSC-induced cell death could be reversed by Z-VAD-fmk, a general caspase inhibitor, indicating that PSC-induced cell death was characteristic of caspase-mediated apoptosis. These results suggest a novel therapeutic strategy in the treatment of malignant astrocytomas by inhibitors of Pgp.