Immunohistochemical demonstration of beta-naphthoflavone-inducible cytochrome P450 1A1/1A2 in rat intrahepatic biliary epithelial cells

Although intrahepatic biliary epithelial cells are targets for certain hepatotoxic chemicals, including some procarcinogens, their ability to monooxygenate, and thereby bioactivate and inactivate xenobiotics, remains to be established. Thus, the present study was undertaken to immunohistochemically determine if cytochrome P450 (CYP) 1A1/1A2 is present and can be induced within these nonparenchymal liver cells. Immunoperoxidase and immunofluorescent staining for CYP1A1/1A2 was detected within intrahepatic biliary epithelial cells as well as hepatocytes of control rats and was markedly enhanced in both cell types by beta-naphthoflavone (BNF). Color confocal laser microscopic analyses of dual immunofluorescent staining for CYP1A1/1A2 and cytokeratins 6 and 9 (56 and 64 kd, respectively) provided unequivocal evidence for the presence and induction of CYP1A1/1A2 within intrahepatic bile duct epithelia. Moreover, microdensitometric analyses of immunoperoxidase staining intensities for CYP1A1/1A2 revealed that intrahepatic biliary epithelial cells of control rats contain 44%, 56%, and 58% as much CYP1A1/1A2 as do centrilobular, midzonal, and periportal hepatocytes, respectively. These analyses further revealed that BNF increased the content of CYP1A1/1A2 in biliary epithelial cells by approximately 120%, while CYP1A1/1A2 levels in centrilobular, midzonal, and periportal hepatocytes were increased by 82%, 159%, and 160%, respectively. The results of this study represent the first in situ demonstration that mammalian intrahepatic biliary epithelial cells contain a CYP isoform, and further that CYP1A1/1A2 can be induced in these cells by BNF. These findings therefore indicate that intrahepatic biliary epithelial cells can oxidatively metabolize xenobiotics in situ and that their ability to bioactivate and inactivate xenobiotics can be significantly enhanced by CYP1A1/1A2 induction.

Glucuronidation of amines and other xenobiotics catalyzed by expressed human UDP-glucuronosyltransferase 1A3

Glucuronide conjugation of xenobiotics containing a tertiary amine moiety represents a unique and important metabolic pathway for these compounds in humans. Previously, human UDP-glucuronosyltransferase (UGT) 1A4 was shown to be an important enzyme for the formation of quaternary ammonium-linked glucuronides. UGT1A3 is 93% identical to UGT1A4 in primary amino acid sequence. We show that human UGT1A3, transiently expressed in human embryonic kidney 293 cells, also catalyzes the N-glucuronidation of primary, secondary, and tertiary amine substrates, such as 4-aminobiphenyl, diphenylamine, and cyproheptadine. In contrast to expressed human UGT1A4, which catalyzes the glucuronidation of amines with high efficiency, glucuronidation of amines catalyzed by UGT1A3 exhibited low efficiency, suggesting that UGT1A3 makes only a limited contribution to the metabolic elimination of these compounds. The reactivity of expressed human UGT1A3 toward hydroxylated and carboxylic acid-containing compounds was also examined. In addition to amines, expressed human UGT1A3 catalyzed the glucuronidation of opioids (e.g. morphine and buprenorphine), coumarins, flavonoids (e.g. naringenin and quercetin), anthraquinones, and small phenolic compounds (e.g. 4-nitrophenol). Drugs containing a carboxylic acid moiety, such as nonsteroidal anti-inflammatory agents (e.g. naproxen and ibuprofen) and fibrates (e.g. ciprofibrate), were substrates for human UGT1A3. In contrast, compounds containing an aliphatic hydroxyl group, such as sapogenins, monoterpenoid alcohols (e.g. menthol and borneol), and androgens, were not conjugated by expressed human UGT1A3. Of the compounds tested, scopoletin, naringenin, and norbuprenorphine appeared to be the best xenobiotic substrates for human UGT1A3.

Rapid hematopoietic recovery after multicycle high-dose chemotherapy: enhancement of filgrastim-induced progenitor-cell mobilization by recombinant human stem-cell factor

PURPOSE

To assess the mobilization potential and safety of recombinant human stem-cell factor (SCF) when coadministered with filgrastim to untreated women with poor-prognosis breast cancer.

PATIENTS AND METHODS

Eligible women had breast cancer with 10 or more positive axillary nodes, or estrogen receptor-negative tumor with 4 positive nodes, or stage III disease. Patients were randomized to receive SCF plus filgrastim or filgrastim alone. Filgrastim 12 microg/kg daily was administered for 6 days by continuous subcutaneous infusion. SCF was administered by daily subcutaneous injection at 5, 10, or 15 microg/kg concurrent with filgrastim for 7 days, or 10 microg/kg daily starting 3 days before filgrastim for a total of 10 days (SCF pretreatment). Apheresis was performed on days 5, 6, and 7 of filgrastim administration. Patients then had three cycles of epirubicin 200 mg/m2 and cyclophosphamide 4 g/m2 every 28 days, each supported by one third of the apheresis product.

RESULTS

Sixty-two women were treated. Greater yields occurred in patients who received SCF 10 microg/kg daily plus filgastim than those who received filgrastim alone (P=.013 for CD34+ cells; P=.07 for granulocyte-macrophage colony-forming cells [GM-CFCs]). The difference was more marked with SCF-pretreatment than concurrent SCF. Fewer aphereses were required to reach the predetermined target of peripheral-blood progenitor/stem cells (PBPCs) in women who received SCF. SCF was generally well tolerated. Hematologic recovery was rapid after each of the three cycles of chemotherapy. There was no difference in recovery between the different treatment groups.

CONCLUSION

Mobilization of PBPCs by filgrastim is significantly enhanced by coadministration of SCF, and commencing SCF before filgrastim can optimize this effect. SCF has the potential to reduce the number of aphereses required to collect a target number of PBPCs.

Effect of filgrastim on the pharmacokinetics of MX2 hydrochloride in patients with advanced malignant disease

PURPOSE

To investigate the effect of granulocyte colony-stimulating factor (G-CSF) on the pharmacokinetics and pharmacodynamics of the new morpholino anthracycline drug MX2.

METHODS

A total of 25 patients with advanced malignant disease participated in a dose-escalation study in the first cycle of treatment given i.v. at doses of 50-80 mg/m2 (74-152 mg) with concomitant filgrastim (G-CSF, 5 microg/kg) given daily beginning at 24 h after the dose of MX2.

RESULTS

The mean fast distribution half-life (1.5 +/- 1.0 min) and the mean plasma clearance (2.18 +/- 0.95 l/min) were significantly lower than the respective mean values found in a previous study in which 27 patients had received MX2 (16.8-107.5 mg) alone (3.3 +/- 2.2 min and 2.98 +/- 1.68 l/min, respectively; P < 0.05). There was no correlation between plasma clearance and the delivered dose for the combined MX2-alone and MX2-filgrastim groups, indicating that the lower clearance observed in the G-CSF group was probably not due to the higher dose. Elimination half-lives of the metabolites M1 and M4 were significantly greater in the filgrastim group (19.8 +/- 14.7 and 11.8 +/- 5.0 h for M1 and 14.8 +/- 4.1 and 12.3 +/- 6.3 h for M2, respectively). Unlike the MX2-alone group, there was no relationship in the MX2-filgrastim group between the relative nadir neutrophil count and the dose or between the duration of grade IV neutropenia and the dose of MX2.

CONCLUSIONS

This study shows that filgrastim decreased the plasma clearance of MX2 by approximately 25%, possibly by inhibition of metabolism.

A streptococcal score card revisited

OBJECTIVE

To evaluate the utility of a simple scoring system as a predictor of obtaining a positive throat culture for group A streptococci (GAS).

DESIGN

Prospective descriptive study. Scores were assigned prior to the availability of the results of throat cultures.

SETTING

Emergency department and walk-in clinic of the Children's Hospital of Pittsburgh.

PATIENTS

Patients were 365 children between the ages of two and 16 years with acute onset of sore throat and a history of or documentation of fever within the preceding 24 hours.

INTERVENTIONS

A streptococcal score was assigned on the basis of a 6-point schema in which the features were 1) age; 2) season; 3) temperature of at least 38.3 degrees C; 4) adenopathy; 5) pharyngeal erythema, edema, or exudate; and 6) no symptoms of a viral upper respiratory infection (conjunctivitis, rhinorrhea, or cough). A throat culture was performed for the isolation of GAS.

MAIN OUTCOME MEASURE

Positive predictive value of the streptococcal score in identifying children with a positive throat culture for GAS.

RESULTS

A score of 5 or 6 predicted a positive culture for GAS in 59 and 75% of children, respectively. In patients with evidence of acute pharyngitis, the combination of age between five and 15 years, fever and absence of upper respiratory symptoms predicted a positive culture for GAS in 72% of patients.

CONCLUSIONS

The score can be used to predict the likelihood that a throat culture will be positive for GAS.

Progress in management of acute myeloid leukaemia (AML) in Australia since 1980: a single institution retrospective study

BACKGROUND

Much research has been conducted into the pathobiology, diagnosis, and management of acute myeloid leukaemia (AML) since 1980, with major contributions from Australian studies in this period.

AIMS

To determine whether advances in basic and clinical research into AML have translated into improved survival for patients in the community.

METHODS

A retrospective survey of records of all patients with AML presenting to the Royal Melbourne Hospital (RMH) over a 16 year period, analysed according to induction therapy and established prognostic factors. Between 1980 and December 1996 223 (98%) of 227 patients were evaluable.

RESULTS

The probability of survival at five years for patients treated since 1990 has improved significantly compared to the cohort treated between 1980-89 (34 +/- 5% vs 4 +/- 2%; mean +/- standard error). This benefit is most evident in patients less than 60 years of age (50 +/- 7% vs 11 +/- 4%). Successive induction protocols in the context of clinical trials conducted since 1985 contributed to improved outcomes. The selective application of bone marrow transplantation, and use of retinoic acid as induction therapy for acute promyelocytic leukaemia has also improved survival. Despite increases in dose-intensity, early death rates for patients undergoing induction therapy fell during the study period.

CONCLUSIONS

Participation in clinical and basic research with the development of more intense and specific treatments for patients with AML has contributed to better outcomes, underpinned by improvements in supportive care.

Genetic predisposition to the metabolism of irinotecan (CPT-11). Role of uridine diphosphate glucuronosyltransferase isoform 1A1 in the glucuronidation of its active metabolite (SN-38) in human liver microsomes

Irinotecan (CPT-11) is a promising antitumor agent, recently approved for use in patients with metastatic colorectal cancer. Its active metabolite, SN-38, is glucuronidated by hepatic uridine diphosphate glucuronosyltransferases (UGTs). The major dose-limiting toxicity of irinotecan therapy is diarrhea, which is believed to be secondary to the biliary excretion of SN-38, the extent of which is determined by SN-38 glucuronidation. The purpose of this study was to identify the specific isoform of UGT involved in SN-38 glucuronidation. In vitro glucuronidation of SN-38 was screened in hepatic microsomes from normal rats (n = 4), normal humans (n = 25), Gunn rats (n = 3), and patients (n = 4) with Crigler-Najjar type I (CN-I) syndrome. A wide intersubject variability in in vitro SN-38 glucuronide formation rates was found in humans. Gunn rats and CN-I patients lacked SN-38 glucuronidating activity, indicating the role of UGT1 isoform in SN-38 glucuronidation. A significant correlation was observed between SN-38 and bilirubin glucuronidation (r = 0.89; P = 0.001), whereas there was a poor relationship between para-nitrophenol and SN-38 glucuronidation (r = 0.08; P = 0.703). Intact SN-38 glucuronidation was observed only in HK293 cells transfected with the UGT1A1 isozyme. These results demonstrate that UGT1A1 is the isoform responsible for SN-38 glucuronidation. These findings indicate a genetic predisposition to the metabolism of irinotecan, suggesting that patients with low UGT1A1 activity, such as those with Gilbert's syndrome, may be at an increased risk for irinotecan toxicity.

Glucuronidation of opioids, carboxylic acid-containing drugs, and hydroxylated xenobiotics catalyzed by expressed monkey UDP-glucuronosyltransferase 2B9 protein

UDP-glucuronosyltransferase (UGT) 2B9, isolated from a cynomolgus monkey liver cDNA library, is 89% identical to human UGT2B7 in primary amino acid sequence, and the two expressed enzymes were previously shown to catalyze the glucuronidation of many common endogenous substrates. The purpose of the present study was to characterize the reactivity of expressed UGT2B9 with important therapeutic agents and other xenobiotics. UGT2B9, stably expressed in human embryonic kidney 293 cells, catalyzes the 3-O- and 6-O-glucuronidation of morphine and the 6-O-glucuronidation of codeine. A number of other morphinan (e.g. naloxone, naltrexone, and nalorphine) and oripavine (e.g. buprenorphine) derivatives are substrates for this enzyme. In general, morphinan derivatives are glucuronidated at higher rates, compared with oripavines; however, glucuronidation efficiency values (Vmax/KM) for the compounds are similar. Stably expressed UGT2B9 also catalyzes the glucuronidation of profen nonsteroidal anti-inflammatory drugs, fibrate hypolipidemic agents, and straight-chain fatty acids at the carboxylic acid moiety. Monoterpenoid alcohols and propanolol are glucuronidated at aliphatic hydroxyl positions. Expressed UGT2B9 exhibits enantioselective glucuronidation for (R/S)-ibuprofen, (R/S)-propanolol, and (+)/(-)-menthol. The data suggest that monkey UGT2B9 and human UGT2B7 are functionally similar.

Enhanced levels and enhanced clonogenic capacity of blood progenitor cells following administration of stem cell factor plus granulocyte colony-stimulating factor to humans

Administration of hematopoietic growth factors is being used increasingly to obtain populations of blood progenitor/stem cells (PBPC) for clinical transplantation. Here we examined the effect of combining stem cell factor (SCF ) and granulocyte colony-stimulating factor (G-CSF ) versus G-CSF alone in a randomized clinical study involving 62 women with early-stage breast cancer. In the first patient cohorts, escalating doses of SCF were administered for 7 days with concurrent G-CSF administration. At baseline, levels of progenitor cells in the bone marrow or blood were comparable in the different patient groups. As with administration of G-CSF alone, the combination of SCF plus G-CSF did not alter the wide variation in levels of PBPC observed between individuals and did not alter the selective nature of PBPC release, with preferential release of day-14 granulocyte-macrophage colony-stimulating factor (GM-CFC) versus day-7 GM-CFC. However, SCF acted to sustain the levels of PBPC after cessation of growth factor treatment; levels of PBPC were elevated 100-fold at later timepoints compared with G-CSF alone. In addition, the maximum levels of PBPC observed were increased approximately fivefold at day 5 of growth-factor administration. The increased levels of PBPC resulted in significantly increased levels of PBPC obtained by leukapheresis. In a subsequent patient cohort, 3-days pretreatment with SCF was introduced and followed by 7 days concurrent SCF plus G-CSF. The 3-days pretreatment with SCF resulted in an earlier wave of PBPC release in response to commencement of G-CSF. In addition, maximum PBPC levels in blood and PBPC yield in leukapheresis products were further increased. Unexpectedly however, SCF pretreatment resulted in progenitor cells with enhanced self-generation potential. Recloning assays documented the ability of approximately 30% of primary granulocyte-macrophage (GM) colonies from control cell populations to generate secondary GM colonies (n = 1,106 primary colonies examined). In contrast approximately 90% of GM colonies from PBPC after SCF pretreatment generated secondary clones and 65% generated secondary colonies. The action of SCF was not explicable in terms of altered SCF, GM-CSF, or G-CSF responsiveness, but SCF pretreatment was associated with maximum serum SCF levels at the time G-CSF was commenced. These results show that PBPC populations mobilized by different growth factor regimens can differ in their functional properties and caution against solely considering number of harvested progenitor cells without regard to their function.

Comparison of whole blood and serum levels of mefloquine and its carboxylic acid metabolite

Because of the widespread presence of chloroquine-resistant Plasmodium falciparum malaria, mefloquine is now the recommended drug of choice for long-term malaria prophylaxis in these areas. Although several studies have compared plasma and whole blood concentrations of either mefloquine or its carboxylic acid metabolite, we report the first comparison of serum and whole blood levels in 86 Dutch marines taking 250 mg of mefloquine weekly for 18 weeks while deployed in western Cambodia. All samples were taken during steady-state and at 42-48 hr after the most recent dose. The concentration of mefloquine in serum (mean = 979 ng/ml) was significantly greater than in whole blood (mean = 788 ng/ml) (P < 0.00001, by paired t-test) with an overall mean ratio of 1.28. The concentration of the metabolite in serum (mean = 3,039 ng/ml) was also significantly greater than in whole blood (mean = 1,390 ng/ml) (P < 0.00001, by paired t-test) with an overall mean ratio of 2.25. These findings are similar to previous reports of plasma-to-whole blood levels. Furthermore, we report that the within-individual ratios of the metabolite concentration to the mefloquine concentration were also found to be significantly different in serum (3.79; P < 0.00001, by paired t-test) and in whole blood (2.02; P < 0.00001, by paired t-test). Appropriate attention must be given to these differences when comparing serum and whole blood concentrations of either mefloquine or its metabolite to avoid misinterpretation of their respective levels. Also, the determination of the relative mefloquine ratios in various blood fluids, as well as the documentation of the metabolite levels and their ratios, is critical to the appropriate interpretation of both chemoprophylaxis and chemotherapy, especially in the presence of resistant strains.

Chest wall and lung mechanics during acute hemorrhage in anesthetized dogs

OBJECTIVES

In trauma and in surgical patients, respiratory mechanics may change because of many factors, including the hypotension induced by hemorrhage. The effects of acute hemorrhage on elastic and resistive characteristics of the respiratory system were studied.

DESIGN

Prospective study.

SETTING

Anesthesia research laboratory.

INTERVENTIONS

Acute hemorrhagic shock was induced in 24 supine anesthetized/paralyzed, mechanically ventilated dogs by blood withdrawal over a 12-minute period to decrease systolic arterial pressure to 50 mmHg; additional blood was subsequently withdrawn to maintain this pressure for 2 hours. Total respiratory system dynamic compliance and resistance and lung and chest wall compliances and resistances were measured.

MEASUREMENTS AND MAIN RESULTS

Total respiratory system dynamic compliance decreased from control (0.03 +/- 0.002 L/cmH2O) by the first 10 minutes of shock (p < 0.05) and was 9.8 +/- 2% lower than control 2 hours after the induction of shock because of decreases in both lung (9.6 +/- 3%) and chest wall (7.7 +/- 3%) compliances. Total respiratory resistance increased 12.8 +/- 3% from control (3.08 +/- 0.19 cmH2O/L/s) after 2 hours of shock (p < 0.05) because of an increase in chest wall resistance (21.6 +/- 8%, p < 0.05). Pulmonary resistance was not significantly increased (p > 0.05). In six control dogs, prepared similarly but not hemorrhaged, chest wall compliance and resistance did not change, but lung compliance gradually decreased by 17.8% during 150 minutes of anesthesia/paralysis. Lung resistance increased only after 100 minutes (p < 0.05).

CONCLUSIONS

(1) Hemorrhagic shock caused slight changes in the chest wall, but effects on lung mechanics were a consequence of prolonged mechanical ventilation during anesthesia/paralysis, and (2) changes in respiratory mechanics caused by hemorrhagic shock are small and, unless other deleterious factors are present, would probably have little clinical significance.

Isolation and characterization of UGT2B15(Y85): a UDP-glucuronosyltransferase encoded by a polymorphic gene

Genetic polymorphisms occur in many of the drug metabolizing enzymes. However, the effect of polymorphisms in the genes encoding phase II drug metabolizing UDP-glucuronosyltransferases is still undescribed, despite the many reported cases of variations in glucuronidation activities. Characterization of the UGT2B15(Y85) cDNA, which was isolated from human prostate and LNCaP cell cDNA libraries, revealed 20 nucleotide differences between UGT2B15(Y85) and the previously characterized UGT2B15 protein UGT2B15(D85). However, only one of the two variations in the coding region leads to an amino acid change from aspartic acid to a tyrosine residue at position 85. The genomic DNA of 27 subjects were analysed by direct sequencing of polymerase chain reaction (PCR) products and demonstrated that UGT2B15(D85) and UGT2B15(Y85) are encoded by variant alleles prevalent in the Caucasian population. Expression of UGT2B15(D85) and UGT2B15(Y85) in HK293 cells demonstrated similar substrate specificities. Of the 65 potential substrates tested for activity, the proteins were active on phenolic compounds, coumarins, flavonoids, drugs and steroid hormones. Both proteins displayed similar Km values of 2.2 and 2.4 microM for androstane-3alpha,17beta-diol and dihydrotestosterone, respectively. However, results suggest that UGT2B15(Y85) has a higher Vmax than UGT2B15(D85). Specific reverse transcriptase (RT)-PCR analysis revealed expression of the UGT2B15 gene in a wide range of extrahepatic tissues including the human liver, kidney, testis, mammary gland, placenta, adipose, skin, uterus, prostate and lung. The wide expression of UGT2B15 in many tissues indicates that it is a major glucuronidation enzyme in humans.

Glucuronidation of retinoids by rat recombinant UDP: glucuronosyltransferase 1.1 (bilirubin UGT)

Rat liver recombinant BR1UGT1.1 was found to have significant activity toward retinoid substrates. UGT1.1 glucuronidation activity was 91 +/- 18 pmol/mg x min for atRA and 113 +/- 19 pmol/mg x min for 5,6-epoxy-atRA. The apparent K(M) and V(max) of atRA acid glucuronidation by UGT1.1 were 59.1 +/- 5.4 microM and 158 +/- 43 pmol/mg x min, respectively. SDS-PAGE and Western blot analysis of UGT1.1-transfected HK293 membrane proteins photolabeled with [11,12-3H]atRA revealed a protein of approximately 56 kDa that was labeled by [3H]atRA, detected by anti-pNP UGT antibody and not present in membranes from nontransfected HK293 cells. Liver microsomes from Gunn rats, which lack UGT1.1, had significant activity toward atRA (111 +/- 28 pmol/mg x min).

Randomized, blinded, placebo-controlled phase I trial of pegylated recombinant human megakaryocyte growth and development factor with filgrastim after dose-intensive chemotherapy in patients with advanced cancer

Thrombocytopenia caused by chemotherapy is an important cause of morbidity and mortality in the treatment of malignant disease. Recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) is a potent stimulator of megakaryocytopoiesis and prevents chemotherapy-induced thrombocytopenia in preclinical studies. We administered PEG-rHuMGDF with filgrastim after dose-intensive chemotherapy to 41 patients with advanced cancers to determine its safety and effects on hematologic recovery. Carboplatin 600 mg/m2 and cyclophosphamide 1,200 mg/m2 were administered to patients with advanced cancer. Patients were randomly assigned to receive blinded study drug, either PEG-rHuMGDF or placebo (3-to-1 ratio), commencing the day after chemotherapy. PEG-rHuMGDF was given at doses of 0.03, 0.1, 0.3, 1.0, 3.0, and 5.0 microg per kilogram body weight by daily subcutaneous injection for between 7 and 20 days. All patients received concurrent filgrastim 5 microg per kilogram body weight per day until neutrophil recovery. Fifteen patients had received PEG-rHuMGDF alone in a previous phase I study. Platelet function and peripheral blood progenitor cells (PBPC) were assessed. PEG-rHuMGDF enhanced platelet recovery in a dose-related manner when compared with placebo. The platelet nadir occurred earlier in patients given PEG-rHuMGDF (P = .002) but there was no difference in the depth of the nadir. Recovery to baseline platelet count was achieved significantly earlier following PEG-rHuMGDF administration compared with placebo (median, 17 days for PEG-rHuMGDF 0.3 to 5.0 microg/kg versus 22 days for placebo, P = .014). In addition, platelet recovery was faster in patients who had previously received PEG-rHuMGDF, suggesting that pretreatment might be beneficial. Platelet function did not change during or after administration of PEG-rHuMGDF. Levels of PBPC on day 15 after chemotherapy were significantly greater in patients administered PEG-rHuMGDF 0.3 to 5.0 microg/kg and filgrastim compared with those given placebo plus filgrastim. PEG-rHuMGDF was well tolerated at all doses. Two patients given PEG-rHuMGDF had a thrombotic episode. PEG-rHuMGDF accelerates platelet recovery after moderately dose-intensive carboplatin and cyclophosphamide, and is likely to be clinically useful in treatment of chemotherapy-induced thrombocytopenia. Because it enhances mobilization of PBPC by filgrastim, PEG-rHuMGDF might also allow more efficient collection of stem cells for autologous or allogeneic transplantation.

Comparison of stably expressed rat UGT1.1 and UGT2B1 in the glucuronidation of opioid compounds

Opioids are important drugs used as analgesics, antitussives, antidiarrheals, and in the therapy of myocardial infarctions, and as antagonists of opioid intoxication. The glucuronidation of these compounds, catalyzed by UDP-glucuronosyltransferases (UGTs), is well known to be a primary step in their metabolism to hydrophilic products and in their ultimate excretion. The present study was designed to compare the reactivity and relative glucuronidation efficiencies of opioid agonists, antagonists, and partial agonists with two rat UGT isoforms; UGT1.1, which is generally considered the "bilirubin UGT," and UGT2B1, which has previously been shown to catalyze the glucuronidation of testosterone, chloramphenicol, and (-)-morphine. Rat UGT2B1, stably expressed in HK293 cells, exhibited high glucuronidation rates and catalytic efficiencies for many opioids, although values for (-)-morphine and nalorphine were the highest. In contrast, these compounds were very poor substrates for expressed rat UGT1.1. Comparably high glucuronidation rates and efficiencies were found for buprenorphine and diprenorphine with both UGT isoforms. These results suggest that opioids with morphinan-based chemical structures similar to (-)-morphine interact with UGTs differently than those with oripavine-based chemical structures similar to buprenorphine. To investigate the contribution of rat UGT1.1 and UGT2B1 in the overall rate of glucuronidation of buprenorphine in the rat liver, hepatic microsomes from Gunn rats (where UGT1.1 activity is absent) and Wistar rats (where UGT1.1 activity is present) were studied. Buprenorphine glucuronidation activity in Gunn rat liver microsomes exhibit approximately 25% of rates observed in Wistar rat liver microsomes, whereas (-)-morphine, naloxone, and naltrexone glucuronidation rates were not significantly different in microsomal preparations from Gunn and Wistar rats. These data suggest that UGT2B1 is the major hepatic enzyme involved in the glucuronidation of (-)-morphine and naloxone in livers from untreated rats, whereas buprenorphine glucuronidation is preferentially catalyzed by rat UGT1.1.

Pharmacokinetics and pharmacodynamics of MX2 hydrochloride in patients with advanced malignant disease

The purpose of the present study was to investigate the pharmacokinetics and pharmacodynamics of the new morpholino anthracycline drug MX2. A total of 27 patients with advanced cancer participated in a dose-escalation study in the first cycle of treatment with drug given i.v. at doses of 10-50 mg/m2 (total dose 16.8-107.5 mg). The mean total systemic plasma clearance (CL) of MX2 was 2.98 +/- 1.68 l/min, the mean volume of distribution at steady state was 1460 +/- 749 l and mean elimination half-life was 10.8 +/- 5.1 h. The area under the plasma concentration-time curve (AUC) of MX2 was linearly related to the dose per kilogram and the dose per body surface area (r2 = 0.43, P < 0.01 and r2 = 0.44, P < 0.01, respectively). CL did not correlate with total body weight, lean body mass or body surface area. The mean elimination half-lives of the metabolites M1, M2, M3 and M4 were 11.8 +/- 5.0, 21.9 +/- 11.8, 19.0 +/- 11.3 and 12.3 +/- 6.3 h, respectively. The fractional Emax model produced a much better fit to the relative nadir neutrophil count versus dose data (r2 = 0.42) than to the relative nadir neutrophil count versus AUC or peak concentration (Cmax) data (r2 = 0.15 and 0.09, respectively). There seemed to be a threshold dose of about 65 mg of MX2 at or above which a large proportion of patients had a nadir neutrophil count of less than 0.5 x 10(9)/l. This study shows that the pharmacokinetics of MX2 are similar to those of other anthracyclines. With other anthracyclines the degree of myelosuppression seems to depend more on the AUC and Cmax than on the delivered dose; however, with MX2 the degree of myelosuppression depends more on the dose given than on drug exposure expressed as the AUC or Cmax.

Formation of hydroxyeicosatetraenoic acids from hemozoin-catalyzed oxidation of arachidonic acid

Hemozoin, a heme byproduct of hemoglobin digestion by malaria parasites, is released into the blood stream of the host upon lysing of infected erythrocytes. Since heme-compounds are potent catalysts of lipid peroxidation, we evaluated the catalytic ability of Plasmodium falciparum-derived hemozoin to oxidize arachidonic acid to hydroxyeicosatetraenoic acids (HETEs). Hemozoin, beta-hematin, and hematin all catalyzed the formation of 15-, 12- and 5-HETE as major products. Although there were no significant differences in total amounts of HETEs generated by hemozoin relative to hematin or beta-hematin, there were significant differences in the proportions of certain isomers. 15-HETE was the predominant isomer generated by hemozoin catalysis while 5-HETE was the major product formed by hematin catalysis. Since HETEs are important vasoactive mediators, the non-enzymatic oxidation of arachidonic acid by hemozoin catalysis may contribute to some of the pathophysiology associated with severe and cerebral malaria.

Folate and 10-formyltetrahydrofolate dehydrogenase in human and rat retina: relation to methanol toxicity

Ocular toxicity, a well-recognized outcome of methanol poisoning in humans, correlates with formate accumulation in blood following the ingestion of methanol. Rodents, however, are a species known to be resistant to the toxicity of formate. The present study was designed to determine whether components of folate-dependent formate oxidation, e.g., folate and 10-CHO-H4-folate dehydrogenase (10-FDH), exist in retina and whether differences in these components might explain species-determined susceptibility to methanol intoxication. Total folate levels were determined in human and rat retinal tissues and were found to be much lower than the levels in liver. However, folate levels in human retina were only 14% of those determined in rat retina. Western blot analysis was used to quantify the amount of cytosolic and mitochondrial 10-FDH in retinal tissues. Results of these studies showed that comparable amounts of this enzyme were present in both cellular compartments in each species. However, the amount of 10-FDH in human retina was approximately three times the amount found in rat retina. In order to determine the cell type(s) within the retina that contained 10-FDH, immunohistochemical staining for 10-FDH was carried out. Confocal microscopic image analysis of human and rat retinae showed colocalization of 10-FDH primarily with Muller cell protein markers [glial fibrillary acidic protein (GFAP), vimentin, and carbonic anhydrase]. Therefore, 10-FDH was found to be preferentially localized in this cell type. Since Müller cells appear to represent the target for formate-induced ocular toxicity, our data suggest that formate oxidation reactions might serve two roles, first a protective role and then a role in methanol-induced toxicity in Müller cells.

A risk-benefit assessment of anthracycline antibiotics in antineoplastic therapy

The anthracycline antibiotics comprise a group of cytotoxic compounds with wide-ranging activity against human malignancies. They are used extensively for curative, adjuvant and palliative therapy, both as single agents and in combination regimens. They produce a number of adverse effects, some of which are shared by other cytotoxic drugs. The most important adverse effect is cardiotoxicity, which is unique to this class of compounds. Strategies have been devised to circumvent these adverse effects, including the development of less toxic analogues, alterations in scheduling, the addition of cardioprotectant agents and methods of monitoring for cardiac abnormalities.

Thrombopoietic effects of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) in patients with advanced cancer

BACKGROUND

Pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) is a potent stimulator of megakaryocyte colony formation and platelet production. It is likely to be useful in the management of severe thrombocytopenia. To determine its clinical activity and safety, we gave it to patients with advanced cancer before chemotherapy.

METHODS

Patients were randomly assigned to receive either PEG-rHuMGDF or placebo in a three to one ratio. PEG-rHuMGDF was given at a dose of 0.03, 0.1, 0.3, or 1.0 microgram/kg body weight. The study drug or placebo were administered daily by subcutaneous injection for up to 10 days or until a target platelet count was reached.

FINDINGS

17 patients, median age 59 years, received either PEG-rHuMGDF (13 patients) or placebo (four patients). PEG-rHuMGDF produced a dose-dependent increase in platelet counts. Patients given placebo. 0.03, and 0.1 microgram/kg of PEG-rHuMGDF had median increases in platelet counts of 16%, 12%, and 39%. Those receiving 0.3 and 1.0 microgram/kg of PEG-rHuMGDF had an increase in blood platelets of between 51% and 584%. Platelets rose from day 6 of PEG-rHuMGDF administration and continued to rise after stopping the drug. The platelet count peaked between days 12 and 18 and remained above 450 x 10(9)/L for up to 21 days. There were no alterations in white-blood-cell count or haematocrit, and low toxicity. Platelets taken from patients during PEG-rHuMGDF administration and at the time of peak platelet count were morphologically and functionally normal.

INTERPRETATION

The potency with which PEG-rHuMGDF stimulates platelet production and its low toxicity indicate that this is likely to be a useful agent for the management of thrombocytopenia.

Administration of pegylated recombinant human megakaryocyte growth and development factor to humans stimulates the production of functional platelets that show no evidence of in vivo activation

This report describes the effect of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) on platelet production and platelet function in humans. Subjects with advanced solid tumors received PEG-rHuMGDF daily for up to 10 days. There was no increase in circulating platelet count at doses of 0.03 or 0.1 microgram/kg/d by day 12 of study. At doses of 0.3 and 1.0 microgram/kg/d there was a threefold median increase (maximum 10-fold) in platelet count by day 16. The platelets produced in vivo in response to PEG-rHuMGDF showed unchanged aggregation and adenosine triphosphate (ATP)-release responses in in vitro assays. Tests included aggregation and release of ATP in response to adenosine diphosphate (ADP) (10, 5, 2.5, and 1.25 mumol/L), collagen (2 micrograms/mL), thrombin-receptor agonist peptide (TRAP, 10 mumol/L) and ristocetin (1.5 mg/mL). Administration of aspirin to an individual with platelet count of 1,771 x 10(3)/L resulted in the typical aspirin-induced ablation of the normal aggregation and ATP-release response to stimulation with arachidonic acid (0.5 mg/mL), collagen, and ADP (2.5 and 1.25 mumol/L). There was no change in the expression of the platelet-surface activation marker CD62P (P-selectin) nor induction of the fibrinogen binding site on glycoprotein IIb/IIIa as reported by the monoclonal antibody, D3GP3. An elevation of reticulated platelets was evident after 3 days of treatment with PEG-rHuMGDF and preceded the increase in circulating platelet count by 5 to 8 days; this reflected the production of new platelets in response to PEG-rHuMGDF. At later time points, the mean platelet volume (MPV) decreased in a manner inversely proportional to the platelet count. Levels of plasma glycocalicin, a measure of platelet turnover, rose 3 days after the initial increase in the peripheral platelet count. The level of plasma glycocalicin was proportional to the total platelet mass, suggesting that platelets generated in response to PEG-rHuMGDF were not more actively destroyed. Thus, the administration of PEG-rHuMGDF, to humans, increased the circulating platelet count and resulted in fully functional platelets, which showed no detectable increase in reactivity nor alteration in activation status.