Pharmacokinetics, pharmacodynamics, safety, and tolerability of single-dose fingolimod (FTY720) in adolescents with stable renal transplants.

Oral fingolimod signals the sphingosine 1-phosphate receptor and this in turn mediates immunomodulatory activity. No data of fingolimod in any pediatric population existed before this study. We put our study results in perspective against data from adult renal transplant patients. We investigated pharmacokinetics and pharmacodynamics of single-dose fingolimod (0.07 mg/kg) and its effects on lymphocytes and heart rate in seven adolescents (14.1 ± 1.6 yr) with stable renal transplants. Blood samples for pharmacokinetics and lymphocytes were collected at screening, baseline, and up to 28 days post-dosing. Cardiac monitoring included 12-lead ECG, 24-h Holter monitoring, and echocardiography. A fingolimod dose of 0.07 mg/kg resulted in mean AUC of 731 ± 240 ng·h/mL and C(max) of 3.6 ± 0.6 ng/mL. Drug exposure was nearly identical to adults receiving the same dose. Absolute lymphocyte count decreased 85% from baseline; average nadir occurred by six h post-dose. Heart rate decreased from 74 bpm (predose mean) to 53 bpm (nadir) three h post-dose. Mean heart rates recovered by Day 14 (75 bpm). Weight-adjusted doses of fingolimod in adolescents resulted in drug exposure similar to adults. Adolescents and adults shared comparable negative chronotropic effects and decreased lymphocyte count. Recovery trajectories of these parameters back to baseline were similar between age groups.

Mycophenolic acid metabolite profile in renal transplant patients receiving enteric-coated mycophenolate sodium or mycophenolate mofetil.

Mycophenolate mofetil (MMF), a prodrug of mycophenolic acid (MPA), is an effective immunosuppressive treatment in renal transplant recipients but is known to have gastrointestinal side effects. Enteric-coated mycophenolate sodium (EC-MPS; myfortic) is a new formulation for delivering MPA. This open-label, two-period, cross-over study was carried out to characterize the time course of MPA and its metabolites, mycophenolic acid glucuronide (MPAG) and acyl mycophenolic acid glucuronide (AcMPAG) in stable renal transplant patients (n = 40) after 28-day chronic dosing with EC-MPS (720 mg bid) or MMF (1000 mg bid). The relative abundance and exposure of all three compounds was also assessed. EC-MPS demonstrated the typical pharmacokinetic profile of an enteric-coated formulation with a delayed release of MPA compared with MMF (Tmax 2.5 versus 1.0 hours, respectively). Consistent with a similar disposition of MPA, both EC-MPS and MMF treatments resulted in the same ratio of MPAG to MPA exposure, 23:1. Furthermore, comparison of the AUC of MPAG and AcMPAG for both treatments indicated that steady state MPAG exposure was 75 to 90 times that of AcMPAG, confirming MPAG as the predominant metabolite of MPA. AcMPAG has been identified as a possible active metabolite of MPA; the present study indicates that AcMPAG may contribute around 14% of the exposure to active drug after administration of MPA. Both EC-MPS and MMF treatments were well tolerated over the 1-month period of chronic treatment. In summary, consistent with its enteric-coated design, EC-MPS delays delivery of MPA, but results in similar exposure to that provided by MMF.

Differential alteration of cytochrome P450 isoenzymes in two experimental models of cirrhosis.

Liver diseases are associated with a decrease in hepatic drug elimination, but there is evidence that cirrhosis does not result in uniform changes of cytochrome P450 (CYP) isoenzymes. The objective of this study was to determine the content and activity of four CYP isoenzymes in the bile duct ligation and carbon tetrachloride (CCl4)-induced models of cirrhosis. The hepatic content of CYP1A, CYP2C, CYP2E1, and CYP3A was measured by Western blot analysis. CYP activity in vivo was evaluated with breath tests using substrates specific for different isoenzymes: caffeine (CYP1A2), aminopyrine (CYP2C11), nitrosodimethylamine (CYP2E1), and erythromycin (CYP3A). Bile duct ligation resulted in biliary cirrhosis; CYP1A, CYP2C and CYP3A content was decreased and the caffeine, aminopyrine, and erythromycin breath tests were reduced whereas CYP2E1 content and the nitrosodimethylamine breath test were unchanged compared with controls. CCl4 treatment resulted in cirrhosis of varying severity as assessed from the decrease in liver weight and serum albumin. In rats with mild cirrhosis, CYP content was comparable with controls except for a decrease in CYP2C. The activity of CYPs was also unchanged except for an increase in CYP2E1 activity. In rats with more severe cirrhosis, the content of all four CYP isoenzymes and the caffeine, aminopyrine, and erythromycin breath tests were reduced whereas the nitrosodimethylamine breath test was unchanged. In both models of cirrhosis, there was a significant correlation between the breath tests results and the severity of cirrhosis as assessed from serum albumin levels. These results indicate that content and the catalytic activity of individual CYP enzymes are differentially altered by cirrhosis in the rat and also suggest that drug probes could be useful to assess hepatic functional reserve.

Ras-dependent and -independent regulation of reactive oxygen species by mitogenic growth factors and TGF-beta1.

Mitogenic growth factors and transforming growth factor beta1 (TGF-beta1) induce the generation of reactive oxygen species (ROS) in nonphagocytic cells, but their enzymatic source(s) and regulatory mechanisms are largely unknown. We previously reported on the ability of TGF-beta1 to activate a cell surface-associated NADH:flavin:O(2) oxidoreductase (NADH oxidase) that generates extracellular H(2)O(2). In this study, we compared the ROS-generating enzymatic systems activated by mitogenic growth factors and TGF-beta1 with respect to the primary reactive species produced (O(2)(.-) vs. H(2)O(2)), the site of generation (intracellular vs. extracellular) and regulation by Ras. We find that the mitogenic growth factors PDGF-BB, FGF-2, and TGF-alpha (an EGF receptor ligand) are able to rapidly (within 5 min) induce the generation of intracellular O(2)(.-) without detectable NADH oxidase activity or extracellular H(2)O(2) release. In contrast, TGF-beta1 does not stimulate intracellular O(2)(.-) production and the delayed induction of extracellular H(2)O(2) release is not associated with O(2)(.-) production. Expression of dominant-negative Ras (N17Ras) protein by herpes simplex virus-mediated gene transfer blocks mitogen-stimulated intracellular O(2)(.-) generation but has no effect on TGF-beta1-induced NADH oxidase activation/H(2)O(2) production. These results demonstrate that there are at least two distinctly different ROS-generating enzymatic systems in lung fibroblasts regulated by mitogenic growth factors and TGF-beta1 via Ras-dependent and -independent mechanisms, respectively. In addition, these findings suggest that endogenous production of ROS by growth factors/cytokines may have different biological effects depending on the primary reactive species generated and site of production.

Effect of cyclosporine A on cytochrome P-450-mediated drug metabolism in the partially hepatectomized rat.

Despite its hepatotoxic potential, cyclosporine A (CsA) has been reported to positively influence compensatory liver growth. To probe the physiological consequences of CsA on the recovery of liver function, studies were initiated in the 2/3 partially hepatectomized (PHx) rat, taking the recovery of cytochromes P-450-dependent drug metabolism as primary outcome. CsA was administered at a dose of 3. 33 mg/kg/day for 10 days. Drug metabolism was evaluated by the recovery of 14CO2 after administration of isotopically labeled model drugs and by studying the expression of the P-450 transcripts involved in their biotransformation before and 24 to 96 h after PHx. Before PHx, neither the steady-state mRNA nor the in vivo disposition of caffeine (CYP1A2), erythromycin (CYP3A2 and 3A1), or aminopyrine (CYP2B1 and 2C11) were influenced by CsA. Studies 24 h after PHx revealed a 29 to 39% reduction in the elimination of [14C]aminopyrine and [14C]erythromycin, which was unaffected by CsA. Their metabolism at 48 to 96 h after PHx also remained unaffected by CsA. By contrast, postPHx, [14C]caffeine elimination decreased to a level closely proportional to the loss in liver mass. In addition, CsA accelerated the recovery and/or prevented the decrease of caffeine elimination 24 h after PHx but not at later time points, indicating an early, but unsustained, beneficial effect of CsA on the recovery of CYP1A2-mediated activities. These data show that at the critical time of greatest loss in liver mass, CsA has only a selective influence on the biotransformation of cytochrome P-450 protein-dependent activities and that its effect on the regeneration process does not translate into an overall accelerated recovery of the hepatic drug-metabolizing function.

Identification and characterization of a protein destruction signal in the encephalomyocarditis virus 3C protease.

The amino acid sequence LLVRGRTLVV, which is probably located in a strand-turn-strand structure, has been identified as a protein destruction signal in the rapidly degraded encephalomyocarditis virus 3C protease. Mutations within this sequence reduced the susceptibility of the 3C protease toward ubiquitination and degradation in rabbit reticulocyte lysate. This signal is transferable, since poliovirus 3C protease, which is a poor ubiquitin-mediated proteolytic system substrate, was found to be ubiquitinated and degraded when the signal sequence was either generated at an internal location in the protein or fused to the N terminus. An evaluation of the behavior of 3C protease proteins containing mutations in the signal region indicates that considerable variability in the primary structure is tolerated, although the conservation of certain features appears to be required for signal function. Two E3 ubiquitin-protein ligases that recognize the encephalomyocarditis virus 3C protease as a substrate were also partially purified. One of these was identified as the previously described E3alpha, and this was shown to require the destruction signal sequence to catalyze efficiently the ubiquitination of the 3C protease. The other is a Ubc5-dependent E3 that appears to recognize a different, unidentified feature of the 3C protease.

Characterization of cytochrome P450 2E1 activity by the [14C]nitrosodimethylamine breath test.

The objective of this study was to measure the rate of demethylation of nitrosodimethylamine in vivo in the rat and determine its value to assess CYP2E1 activity in intact animals. Nitrosodimethylamine labeled with 14C on both methyl groups was administered to rats and exhaled 14CO2 was collected during 2-3 h. The nitrosodimethylamine breath test was increased by inducers of CYP2E1, such as ethanol (+139%) and 4-methylpyrazole (+115%), and decreased by the inhibitor diallyl sulfide (-53%). In addition, the nitrosodimethylamine breath test was not changed significantly by inducers specific for other cytochrome P450 such as beta-naphthoflavone, dexamethasone, and phenobarbital. The specificity of the induction by 4-methylpyrazole and of the inhibition by diallyl sulfide for CYP2E1 was determined using the [14C]caffeine (CYP1A2), [14C]aminopyrine (CYP2C11), and [14C]erythromycin (CYP3A2) breath tests. 4-Methylpyrazole treatment caused a small increase of the caffeine (+33%) and aminopyrine (+9%) breath tests and no change of the erythromycin breath test. Diallyl sulfide treatment led to a small decrease of the caffeine breath test (-33%) and of the aminopyrine breath test (-13%) but a 23% increase of the erythromycin breath test. It is concluded that the [14C]nitrosodimethylamine breath test is useful to assess CYP2E1 activity in vivo in the rat.