Breadboard RL10-2B low-thrust operating mode (second iteration) test report

Cryogenic rocket engines requiring a cooling process to thermally condition the engine to operating temperature can be made more efficient if cooling propellants can be burned. Tank head idle and pumped idle modes can be used to burn propellants employed for cooling, thereby providing useful thrust. Such idle modes required the use of a heat exchanger to vaporize oxygen prior to injection into the combustion chamber. During December 1988, Pratt and Whitney conducted a series of engine hot firing demonstrating the operation of two new, previously untested oxidizer heat exchanger designs. The program was a second iteration of previous low thrust testing conducted in 1984, during which a first-generation heat exchanger design was used. Although operation was demonstrated at tank head idle and pumped idle, the engine experienced instability when propellants could not be supplied to the heat exchanger at design conditions

The transformation in biomarker detection and management of drug-induced liver injury

Drug-induced liver injury (DILI) is a major concern for patients, care givers and the pharmaceutical industry. Interpretation of the serum biomarkers routinely used to detect and monitor DILI, which have not changed in almost 50 years, can be improved with recently proposed models employing quantitative systems pharmacology. In addition, several newer serum biomarkers are showing great promise. Studies in rodents indicate that the ratio of the caspase cleaved fragment of cytokeratin 18 to total K18 in serum (termed the “apoptotic index”) estimates the relative proportions of apoptosis vs necrosis during drug-induced liver injury. Glutamate dehydrogenase can reliably differentiate liver from muscle injury and, when serum is properly prepared, may also detect mitochondrial toxicity as a mechanism of liver injury. MicroRNA-122 is liver-specific, but recent data suggests it can be actively released from hepatocytes in the absence of overt toxicity limiting enthusiasm for it as a DILI biomarker. Finally, damage associated molecular patterns, particularly high mobility group box 1 and its various modified forms, are promising biomarkers of innate immune activation, which may be useful in distinguishing benign elevations in aminotransferases from those that portend clinically important liver injury. These new biomarkers are already being measured in early clinical trials, but broad acceptance will require widespread archiving of serum from diverse clinical trials and probably pre-competitive analysis efforts. We believe that utilization of a panel of traditional and newer biomarkers in conjunction with quantitative systems pharmacology modeling approaches will transform DILI detection and risk management

cyclosporine and liver transplantation: Will the midazolam test make blood level monitoring obsolete?

Immunosuppression therapy with cyclosporine is often hampered by significant interindividual variability in the metabolic clearance of the drug. It has been suggested that much of the variability in cyclosporine clearance is due to differences in the cytochrome P450 3A4 (CYP3A4) content in the liver and intestinal mucosa. A study was conducted in liver transplant recipients to characterize hepatic CYP3A4 variability during the first 10 days after surgery. The formation of 1′-hydroxymidazolam (1′-OH MDZ) was followed in the plasma after i.v. midazolam (MDZ) administration to 21 multiple-organ donors and to recipients of 10 of the 21 donor livers. Liver biopsy tissue was obtained from donors and recipients after the in vivo pharmacokinetic test. For liver donors, the plasma 1′-OH MDZ/MDZ concentration ratio 30 min after the i.v. MDZ dose was well correlated with the hepatic CYP3A4 content (r = 0.87, P < .001). Much of the variability in the two parameters was attributed to the administration of enzyme-inducing drugs before organ procurement. The mean hepatic CYP3A4 content and plasma 1′-OH MDZ/MDZ concentration ratio in six inducer-treated donors was 4.7-fold and 2.3-fold higher than the respective mean value for all other donors. The hepatic CYP3A4 content and plasma 1′-OH MDZ/MDZ ratio for liver recipients, studied on postoperative day 10, was negatively correlated with the respective parameter measured in donors on day 0 (r = −0.60 for CYP3A4 and r = −0.79 for 1′-OH MDZ/MDZ; P < .05 and P < .01). The dynamic changes in hepatic CYP3A4 expression during the perioperative period, some of which appear to be due to the effect of enzyme-inducing drugs, help explain the difficulties often encountered in the achievement and maintenance of therapeutic cyclosporine blood levels after liver transplantation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38412/1/1840220342_ftp.pd

Antimicrosomal antibodies: What are they telling us?

Patients with dihydralazine hepatotoxicity have been found to have circulating autoantibodies that react with liver microsomes (anti-liver microsome antibodies) and that are clearly distinct from anti-liver and kidney microsomal antibodies observed in patients with tienilic acid-induced hepatitis and in some patients with autoimmune hepatitis. The authors show that anti-liver microsome antibodies present in the sera of five patients with dihydralazine-induced hepatitis specifically react on immunoblots with a 53 kD protein. They further conclude that this target antigen is the phase I drug metabolizing enzyme termed P-450IA2 based on the following observations: (a) immunoblots of a battery of human liver microsomes produced the identical pattern of relative staining whether the blots were developed with anti-rat P-450IA2 IgG, anti-human P-450IA2 IgG or each of the five patients' sera; (b) P-450IA2 catalytic activity was selectively inhibited when human liver microsomes were preincubated with anti-liver microsome-positive sera; (c) anti-liver microsome-positive sera identified purified human P-450IA2 on immunoblots. Anti-liver microsome antibodies appeared to be specific for dihydralazine hepatitis because they were not present in sera obtained from 28 other patients including patients receiving dihydralazine without a toxic response and patients with other significant liver diseases. Finally, the authors demonstrated that dihydralazine could competitively inhibit catalytic activity characteristic of P-450IA2 in human liver microsomes, suggesting that P-450IA2 may be involved in the metabolism of dihydralazine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38348/1/1840130231_ftp.pd

Use of a systems model of drug-induced liver injury (DILIsym®) to elucidate the mechanistic differences between acetaminophen and its less-toxic isomer, AMAP, in mice

AbstractAcetaminophen (APAP) has been used as a probe drug to investigate drug-induced liver injury (DILI). In mice, 3′-hydroxyacetanilide (AMAP), a less-toxic isomer of APAP, has also been studied as a negative control. Various mechanisms for the divergence in toxicological response between the two isomers have been proposed. This work utilized a mechanistic, mathematical model of DILI to test the plausibility of four mechanistic hypotheses. Simulation results were compared to an array of measured endpoints in mice treated with APAP or AMAP. The four hypotheses included: (1) quantitative differences in drug metabolism profiles as a result of different affinities for the relevant enzymes; (2) differences in the amount of reactive metabolites produced due to cytochrome P450 (CYP450) inhibition by the AMAP reactive metabolites; (3) differences in the rate of conjugation between the reactive metabolites and proteins; (4) differences in the downstream effects or potencies of the reactive metabolites on vital components within hepatocytes. The simulations did not support hypotheses 3 or 4 as the most likely hypotheses underlying the difference in hepatoxic potential of APAP and AMAP. Rather, the simulations supported hypotheses 1 and 2 (less reactive metabolite produced per mole of AMAP relative to APAP). Within the simulations, the difference in reactive metabolite formation was equally likely to have occurred from differential affinities for the relevant drug metabolism enzymes or from direct CYP450 inhibition by the AMAP reactive metabolite. The demonstrated method of using simulation tools to probe the importance of possible contributors to toxicological observations is generally applicable across species

Seville orange juice‐felodipine interaction: Comparison with dilute grapefruit juice and involvement of furocoumarins

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109875/1/cptclpt20013.pd

Cytochrome P450 3A4 and P‐glycoprotein mediate the interaction between an oral erythromycin breath test and rifampin

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109878/1/cptclpt2002114.pd

Pharmacogenetics and clinical gastroenterology

AbstractMany drugs exhibit variable efficacy and toxicity. Pharmacogenetics explores the genetic underpinnings of variable drug response. Pharmacogenetic testing is beginning to enter the clinic and will have a significant impact on the practice of clinical gastroenterology. Thiopurine S-methyltransferase screening, which will likely become routine for thiopurine recipients, illustrates the promise and limitations of pharmacogenetics. Testing for variation in other drug metabolism pathways may also become important. Pharmacogenetics will complement but not replace traditional methods for choosing drugs and for selecting dosing regimens for narrow-therapeutic-index drugs

Predicting drug interactions using cultured human hepatocytes

In previous papers we demonstrated that cyclosporin A (CsA) was specifically oxidized in rabbit and human liver by cytochrome P-450IIIA. We therefore anticipated that any drug that is an inducer or an inhibitor of this cytochrome should lead to interaction with CsA when given in association with it. In order to confirm this hypothesis, primary cultures of human hepatocytes and human liver microsomes were used to “reproduce” in vitro clinically significant interactions observed between CsA and drugs known either as specific inducers (i.e., rifampicin) or as specific inhibitors (i.e., erythromycin) of P-450IIIA. Our results were in close agreement with the clinical reports. Human hepatocytes maintained in primary cultures for 72 hr in the presence of 50 ΜM rifampicin exhibited increased levels of P-450IIIA, determined by Western blot using specific antibodies, and concomitant increase in CsA oxidase activity, determined by HPLC analysis of extra and intracellular media. Conversely, these cultures exhibited erythromycin concentrationdependent decreases in CsA oxidase activity when incubated in the presence of 5, 20, and 100 ΜM erythromycin. In addition, a Lineweaver-Burk analysis of the erythromycin-mediated inhibition of CsA oxidase activity in human liver microsomes revealed competitive inhibition (with K i of 75 ΜM) as expected, this macrolide being a specific substrate of P-450IIIA. Using this experimental approach, 59 molecules representative of 17 different therapeutic classes were screened for inducers and inhibitors of CsA oxidase activity. Our results allowed us to elucidate the molecular mechanism of previously observed, but unexplained, drug interactions involving CsA, and to detect drugs that should interfere with CsA metabolism as inducers or inhibitors. Drugs detected as potential inducers of CsA oxidase included: rifampicin, sulfadimidine, phenobarbital, phenytoin, phenylbutazone, dexamethasone, sulfinpyrazone, and carbamazepine. Drugs detected as potential competitive inhibitors included: triacetyloleandomycin, erythromycin, josamycin, midecamycin, ketoconazole, miconazole, midazolam, nifedipin, diltiazem, verapamil, nicardipine, ergotamine, dihydroergotamine, glibenclamide, bromocryptine, ethynylestradiol, progesterone, cortisol, prednisone, prednisolone, and methylprednisolone. Finally cefoperazone, cefotaxime, ceftazidime, isoniazide, doxycycline, spiramycin, sulfamethoxazole, norfloxacin, pefloxacin, vancocin, trimethoprime, amphotericine B, valproic acid, quinidine, cimetidine, ranitidine, omeprazole, diclofenac, aspirin, paracetamol, debrisoquine, guanoxan, captopril, furosemide, acetazolamide, sparteine, gliclazide, and imipramine were found not to interfere with the hepatic metabolism of CsA.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38363/1/1840140231_ftp.pd

In situ Rheo-GISANS of triblock copolymers : gelation and shear effects on quasi-crystalline structures at interfaces

The behaviour of polymeric systems at surfaces and under flow is extremely important in many applications, ranging from drug delivery to lubrication. We have studied a model triblock copolymer in deuterated water combining in situ rheology and grazing incidence small angle neutron scattering. Several thermotropic phases appear as a function of the temperature, including a bicontinuous phase not present in the bulk. Moreover, gelation can occur following a different route depending on the concentration. We show that shearing can be used to monitor the structural integrity of the micellar systems and in some cases as a tool for modifying the thermotropic phases: an fcc (face centred cubic) phase is sheared into a hcp (hexagonally close packed) phase, and is then recovered by cycling the temperature