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A Parkinson

Publications and source records attributed to A Parkinson.

At least 19 recordsLinked to original sources
PubMed2005

Ethnic differences between Japanese and Caucasians in the expression levels of mRNAs for CYP3A4, CYP3A5 and CYP3A7: lack of co-regulation of the expression of CYP3A in Japanese livers.

Using a newly developed real-time reverse transcriptase-polymerase chain reaction method, mRNAs were quantitated for CYP3A4, CYP3A5 and CYP3A7 in adult livers from 24 Japanese and 24 Caucasian subjects to elucidate the potential ethnic differences in the expression levels of human cytochrome P450 (CYP) 3As. The expression level of CYP3A4 mRNA in Japanese livers (n = 24) was approximately three times higher than that in Caucasian livers (n = 24, p < 0.001). The mean level of CYP3A5 mRNA was approximately twice higher in Japanese (n = 9) than in Caucasians (n = 5) heterozygous for the CYP3A5 *1 allele (p = 0.057). The CYP3A7 mRNA level was twice higher in Japanese (n = 24) than in Caucasians (n = 22) carrying the CYP3A7 *1A/ *1A genotype (p = 0.042). The level of CYP3A4 mRNA did not correlate with those of CYP3A5 (r = 0.044, n = 24) or CYP3A7 (r = 0.21, n = 24) mRNAs in Japanese livers in contrast to co-regulatory expression of CYP3A4, CYP3A5 and CYP3A7 in Caucasian livers. The results indicate that there are ethnic differences in the expression levels of adult liver CYP3A mRNAs between Japanese and Caucasians, and that the mechanism(s) regulating the hepatic CYP3A expression may be different between these ethnic groups.

Aryl Hydrocarbon Hydroxylases↗
PubMed2002

Evaluation of angiography performed by radiographers and nurses.

AIM: To evaluate out-patient angiography performed by nurses and radiographers. MATERIALS AND METHODS: A protocol for out-patient angiography performed by nurses and radiographers was drawn up and approved by the Trust's Risk Management Committee. Following training, two experienced radiographers and one nurse undertook elective peripheral or renal angiography according to the protocol on 187 patients. Angiograms were performed using a 3F catheter introduced into the abdominal aorta from a femoral approach. Patients were discharged after 2 hours and contacted by telephone the following morning. RESULTS: No patient refused consent for the procedure. One hundred and seventy-two patients underwent successful catheterization without assistance from a radiologist. Radiologist assistance was required with femoral puncture or catheter/guidewire manipulation in 15 cases (8%). Images were considered diagnostic by the reporting radiologist in all but one case. This patient was recalled for further aortogram and pressure measurements. There was a single puncture site complication due to transient stenosis of the common femoral artery at the puncture site. This is thought to have been the result of subintimal injection of local anaesthetic, and it resolved spontaneously over 30 minutes. There were no delayed complications. CONCLUSION: Experienced nurses and radiographers can rapidly acquire the skills to perform diagnostic angiography safely and efficiently.

Allied Health Personnel↗
PubMed2001

Preliminary toxicity assessment of water after treatment with UV-irradiation and UVC/H2O2.

Photooxidation (UV radiation) and enhanced photooxidation (UVC/H2O2) are water treatment technologies which remove aquatic natural organic matter (NOM) by photodegradation, producing lower molecular weight components and CO2. Since these technologies are being investigated for the treatment of drinking water, knowledge of the potential toxicity of the photooxidation by-products is vital. The potential toxicity of UVA-, UVB-, UVC-irradiated, and UVC/H2O2-treated aquatic NOM in two spot samples from two Australian reservoirs was analysed in two spot samples using Vibriofischeri in the Microtox test, African green monkey kidney cells (AS/NZS 4020:1999), and Daphnia carinata in an acute immobilisation test. Toxicity was not apparent for both the Microtox procedure and cytotoxicity analyses for the UVC-irradiated and UVC/H2O2-treated NOM samples, while UVA- and UVB-irradiated water samples were non-toxic to D. carinata. In contrast, acute toxicity was observed for UVC- and UVC/H2O2-treated water samples. The observed toxicity was attributed to photooxidative degradation of NOM-metal binding sites, which resulted in the release of bioavailable copper ions, as evidenced by higher concentrations of free copper ions in photooxidised water. As the total copper concentrations of the two raw water samples were well below the Australian Water Quality Guidelines for metals in domestic supplies, the release of copper from photooxidised NOM is unlikely to cause health concerns in these samples.

Animals↗
PubMed2001

Channel weights for speech recognition in cochlear implant users.

The purpose of this study was to develop and validate a method of estimating the relative "weight" that a multichannel cochlear implant user places on individual channels, indicating its contribution to overall speech recognition. The correlational method as applied to speech recognition was used both with normal-hearing listeners and with cochlear implant users fitted with six-channel speech processors. Speech was divided into frequency bands corresponding to the bands of the processor and a randomly chosen level of corresponding filtered noise was added to each channel on each trial. Channels in which the signal-to-noise ratio was more highly correlated with performance have higher weights, and conversely, channels in which the correlations were smaller have lower weights. Normal-hearing listeners showed approximately equal weights across frequency bands. In contrast, cochlear implant users showed unequal weighting across bands, and varied from individual to individual with some channels apparently not contributing significantly to speech recognition. To validate these channel weights, individual channels were removed and speech recognition in quiet was tested. A strong correlation was found between the relative weight of the channel removed and the decrease in speech recognition, thus providing support for use of the correlational method for cochlear implant users.

Adult↗
PubMed2000

Endotoxin pretreatment protects against the hepatotoxicity of acetaminophen and carbon tetrachloride: role of cytochrome P450 suppression.

Bacterial endotoxin (lipopolysaccharide, LPS) is known to potentiate the toxicity of many hepatotoxicants. However, exposure to a sublethal dose of LPS renders animals tolerant to a lethal dose of LPS, and protects against the toxicity of some chemicals. This study was designed to examine the effects of LPS pretreatment on acetaminophen- and carbon tetrachloride (CCl(4))-induced liver injury in LPS-sensitive C3H/OuJ and LPS-resistant C3H/HeJ mice. Pretreatment of male C3H/OuJ mice with a single injection of LPS (0. 1 mg/kg, ip, for 24 h) protected against the hepatotoxic effects of acetaminophen (400 mg/kg) and carbon tetrachloride (CCl(4), 30 mg/kg), as indicated by serum alanine aminotransferase activity. In contrast, pretreatment of C3H/HeJ mice with 0.1 or 10 mg/kg LPS afforded no protection against the hepatotoxic effects of acetaminophen and CCl(4). In an attempt to determine the mechanism of LPS-induced protection against acetaminophen- and CCl(4)-induced hepatotoxicity in C3H/OuJ mice, liver cytochrome P450 was determined 24 h after LPS injection. LPS treatment caused a 26% decrease in total P450 content in C3H/OuJ but not in C3H/HeJ mice. CYP3A-catalized testosterone 6 beta-, 2 beta-, and 15 beta-hydroxylation was decreased 40% by LPS only in C3H/OuJ mice. To determine whether the differences to LPS-response in the two stains of mice is mediated by a strain-related difference in the release of cytokines, mice were pretreated with interleukin-1 (IL-1 alpha, 5 x 10(5) U/mouse), and the hepatoprotection and hepatic P450 enzymes were examined. IL-1 alpha pretreatment equally protected against the hepatotoxicity of acetaminophen and CCl(4) in both strains, and suppressed the total microsomal P450 and P450 enzyme-catalyzed testosterone hydroxylation to a similar extent. In conclusion, LPS pretreatment suppressed hepatic cytochrome P450 enzymes and protected against the hepatotoxicity of acetaminophen and CCl(4) in LPS-sensitive C3H/OuJ mice, but not in LPS-refractory C3H/HeJ mice. This protective effect of LPS appears to be mediated through the release of cytokines such as IL-1 alpha, which in turn suppresses the cytochrome P450 responsible for the activation of acetaminophen and CCl(4) to reactive metabolites.

Acetaminophen↗
PubMed2000

Expression and regulation of cytochrome P450 enzymes in primary cultures of human hepatocytes.

The aim of this study was to test suitable culture conditions for maintaining normal cellular cytoarchitecture and inducibility of P450 enzymes in primary cultures of human hepatocytes by prototypical inducers. The selectivity and sensitivity of a sandwich culture system were determined by treating cultures with a number of clinically relevant drugs that are known to be inducers of either rodent and/or human P450 enzymes. The results showed that considerable induction of CYP3A4 activity is observed at DMSO concentrations greater than 0.1% (v/v). No differences in P450 induction response were observed between cultures maintained under different matrix conditions. However, the matrix condition considered to be optimal for maintaining cellular integrity, protein yields, and P450 enzyme induction was a sandwich configuration in combination with modified Chee's medium containing insulin (6.25 microg/mL) and dexamethasone (< or =0.1 microM). Under these conditions, induction of CYP3A4 occurred at clinically relevant drug concentrations, and maximal activities were achieved after 3 days of exposure. Overall, the response of human hepatocyte cultures to treatment with both positive and negative modulators was found to reflect that observed in vivo with respect to both enzyme specificity and potency of enzyme induction, although considerable sample-to-sample variability was observed in the magnitude of induction.

Cells, Cultured↗
PubMed2000

DNA structure control by polycationic species: polyamine, cobalt ammines, and di-metallo transition metal chelates.

Many polycationic species bind to DNA and induce structural changes. The work reported here is the first phase of a program whose long-term aim is to create a class of simple and inexpensive sequence-selective compounds that will enable enhanced DNA structure control for a wide range of applications. Three classes of molecule have been included in this work: the polyamine spermine (charge: 4(+)) and spermidine (charge: 3(+)) (which are known to induce a wide range of DNA conformational changes but whose binding modes are still not well understood); cobalt (III) amine transition metal complexes as potential polyamine mimics and [Fe(H(2)O)(6)](3+); and the first member of a new class of di-metallo tris-chelated cylinders of helical structure (charge 4(+)). Temperature-dependent absorption, circular dichroism, linear dichroism, gel electrophoresis, and molecular modeling data are presented. The cobalt amines prove to be effective polyamine mimics, although their binding appears to be restricted to backbone and major groove. All the ligands stabilize the DNA, but the 4(+) di-iron tris-chelate does so comparatively weakly and seems to have a preference for single-stranded DNA. All the molecules studied bend the DNA, with the di-iron tris-chelate having a particularly dramatic effect even at very low drug load.

Chelating Agents↗
PubMed2000

Regulation of glutathione S-transferase enzymes in primary cultures of rat hepatocytes maintained under various matrix configurations.

Primary rat hepatocytes were cultured under various matrix and media conditions and examined after 1 week for the expression and regulation of cytosolic glutathione S-transferase (GST) enzymes. Striking effects on cell morphology were observed in relation to the different matrix conditions, whereas media effects were less prominent. Hepatocytes cultured in serum-free Dulbecco's modified Eagle's medium (DMEM) or modified Chee's medium (MCM) maintained similar levels of total GST protein regardless of the matrix configuration or corresponding cell integrity. However, HPLC analysis showed a differential expression pattern of individual GST subunits in both a time- and medium-dependent fashion. A variable, but pronounced, matrix and medium effect was observed on the induction of total GST expression by various prototypical inducers. Dexamethasone (10 microM) induced subunits A2, M1 and M2 in a medium- and matrix-dependent fashion, whereas phenobarbital (100 microM) induced significantly only subunit A2. beta-Naphthoflavone (50 microM) suppressed all GST subunit expression except subunit P1, which was induced in a matrix- and medium-dependent fashion. These studies show that total basal level expression of GSTs in vitro is reflective of a concomitant increase in mu and pi class subunits and a decrease in alpha class subunits. Moreover, the matrix and medium conditions influence both the basal and inducible expression of GST subunits in cultured rat hepatocytes.

Animals↗
PubMed2000

Experience with the prevention of invasive Haemophilus influenzae type b disease by vaccination in Alaska: the impact of persistent oropharyngeal carriage.

OBJECTIVES: To report the epidemiology of invasive Haemophilus influenzae type b (Hib) disease in high-risk Alaska Native infants before and after universal infant Hib vaccination and evaluate an increase in invasive Hib disease in 1996 after changing Hib vaccine type. STUDY DESIGN: Statewide laboratory surveillance for invasive Hib disease has been conducted since 1980. Three cross-sectional Hib carriage studies were conducted in 1997 and 1998. RESULTS: The invasive Hib disease rate in Alaska Natives decreased from 332 cases per 100,000 children <5 years old in 1980-1991 to 17:100,000 in 1992-1995 but increased primarily in rural areas to 57.9:100,000 after a switch in Hib vaccine types. Carriage studies in 5 rural Alaska Native villages showed oropharyngeal Hib carriage as high as 9.3% in children aged 1 to 5 years; in contrast, carriage in urban Alaska Native children was <1%. CONCLUSIONS: Although Hib disease has decreased in Alaska, the rate of Hib disease and carriage in rural Alaska Natives did not decrease to the same extent as in non-Natives and urban Alaska Natives. Use of polyribosylribitol phosphate-outer-membrane protein conjugate vaccine for the first vaccine dose is critical to disease control in this population with continued transmission in infants <6 months of age. The ability to eliminate Hib carriage and disease may be affected by population characteristics, vaccination coverage, and Hib vaccine type used. This may pose a challenge to global elimination of Hib.

Adolescent↗
PubMed2000

In vitro inhibition and induction of human hepatic cytochrome P450 enzymes by modafinil.

The ability of modafinil to affect human hepatic cytochrome P450 (CYP) activities was examined in vitro. The potential for inhibition of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4/5, and CYP4A9/11 by modafinil (5-250 microM) was evaluated with pooled human liver microsomes. Modafinil exhibited minimal capacity to inhibit any CYP enzyme, except CYP2C19. Modafinil inhibited the 4'-hydroxylation of S-mephenytoin, a marker substrate for CYP2C19, reversibly and competitively with a K(i) value of 39 microM, which approximates the steady-state C(max) value of modafinil in human plasma at a dosage of 400 mg/day. No irreversible inhibition of any CYP enzyme was observed, and there was no evidence of metabolism-dependent inhibition. The potential for induction of CYP activity was evaluated by exposing primary cultures of human hepatocytes to modafinil (10-300 microM). Microsomes were then prepared and assayed for CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5 activities. The mean activities of microsomal CYP1A2, CYP2B6, and CYP3A4/5 from modafinil-treated hepatocytes were higher (up to 2-fold) than those in the solvent-treated controls but were less than those produced by reference inducers of these enzymes. At high concentrations of modafinil (>/=100 microM), the mean activity of CYP2C9 was decreased (up to 60%) relative to that in the solvent controls. Overall, modafinil was shown to have effects on human hepatic CYP1A2, CYP2B6, CYP2C9, CYP2C19, and CYP3A4/5 activities in vitro. Although effects obtained in vitro are not always predictive of effects in vivo, such results provide a rational basis for understanding drug-drug interactions that are observed clinically and for planning subsequent investigations.

Benzhydryl Compounds↗
PubMed2000

Biotransformation of the anti-angiogenic compound SU5416.

SU5416 [3-(3,5-dimethyl-1H-pyrrol-2-ylmethylene)-1, 3-dihydro-indol-2-one], an inhibitor of VEGF (vascular endothelial growth factor) receptor tyrosine kinase, Flk-1/KDR (fetal liver kinase 1/kinase insert domain-containing receptor), also known as VEGF receptor 2 (VEGFR2) is in advanced clinical trials for treatment of AIDS-related Kaposi's sarcoma and colorectal and nonsmall cell lung cancers. Since this chemical class has not been studied previously with therapeutic intent, the present study was designed to investigate the in vitro metabolism of SU5416 by mouse, rat, dog, monkey, and human liver microsomes and to identify the major metabolites of SU5416. An HPLC procedure was developed and validated to resolve and quantify SU5416 and its metabolites. To evaluate the in vitro metabolism of SU5416, pooled liver microsomes from mice, rats, dogs, monkeys, and humans were incubated with SU5416 (25 microM) in the presence of an NADPH-generating system. In the presence of NADPH, mouse, rat, dog, monkey, and human liver microsomes converted SU5416 to at least 12, 9, 9, 7, and 6 polar metabolites, respectively. Microsomal metabolism of SU5416 showed marked species differences in the levels of different metabolites formed. The overall rate of SU5416 metabolism by liver microsomes from the species examined followed the rank order: monkey > or = mouse approximately rat > dog > human. Two major metabolites of SU5416 were identified, a hydroxymethyl derivative of SU5416 (M12) and a carboxylic acid derivative of SU5416 (M6), by spectroscopic methods and comparison with authentic compounds. Both of these oxidative metabolites were further metabolized in vivo through glucuronidation. The metabolic fate of SU5416 in microsomes from various species as well as data from in vivo biotransformation in the rat are discussed.

Angiogenesis Inhibitors↗
PubMed1999

Effects of musk xylene and musk ketone on rat hepatic cytochrome P450 enzymes.

The purpose of the present work was to characterize the effect of musk xylene (MX) and musk ketone (MK) treatment on rat hepatic cytochrome P450 enzymes. Male F344 rats were dosed orally with MX (10, 50 or 200 mg/kg) or MK (20, 100 or 200 mg/kg) for 7 days, after which CYP1A, 2B and 3A enzyme activities and protein levels were determined. MX treatment resulted in a two- to four-fold increase in the activity of CYP1A, 2B and 3A enzymes. For CYP1A and 3A, these changes were consistent with small increases in immunoreactive proteins. However, for CYP2B, despite only a three-fold increase in enzyme activity, protein levels were increased nearly 50-fold relative to control. This induction occurred by transcriptional activation of the CYP2B1 gene as evidenced by increased steady state CYP2B1 mRNA levels. In contrast to MX, MK treatment increased CYP2B activity, protein and mRNA levels. However MK treatment also increased CYP1A enzyme activity nearly 30-fold higher than control rats, a profile that was markedly different from MX, and very different from its effects in mice (Stuard, S.B., Caudill, D., Lehman-Mc-Keeman, L.D., 1997. Characterization of the effects of musk ketone on mouse cytochrome P450 enzymes. Fund. Appl. Toxicol. 40, 264-271). These results indicate that in rats, MX is an inducer of CYP2B enzymes, but these enzymes are not functionally active. In contrast, MK also induces CYP2B enzymes, with no concurrent inactivation. MK also exhibits a unique pattern of cytochrome P450 induction by increasing both CYP1A and CYP2B in rats.

Animals↗
PubMed1999

Reemergence of invasive Haemophilus influenzae type b disease in a well-vaccinated population in remote Alaska.

Before vaccination, Alaska Natives experienced very high rates of invasive Haemophilus influenzae type b (Hib) disease and carriage. Vaccination with Hib conjugate vaccine PRP-OMP (polyribosylribitol phosphate Neisseria meningitidis outer membrane protein) began in 1991 and resulted in a sharp decline in cases. In 1996, after switching to a different Hib conjugate vaccine, DTP-HbOC (which combines diphtheria-tetanus-whole cell pertussis vaccines with HbOC [Hib oligosaccharide CRM197]), cases of invasive Hib disease increased, suggesting ongoing Hib transmission despite widespread vaccination. To determine the prevalence of and risk factors for carriage, a cross-sectional study of oropharyngeal Hib carriage was conducted among Alaska Native children aged 1-5 years in remote southwestern Alaska. Of 496 children with swabs taken, 46 (9.3%) were colonized with Hib. Carriage rates varied by village from 2.2% to 13.2% and by age from 6.1% in 1-year-olds to 14.7% in 5-year-olds. Crowding was associated with Hib carriage. Widespread vaccination with PRP-OMP Hib conjugate vaccine did not eliminate carriage in this population of Alaska Natives, and ongoing carriage contributed to disease resurgence.

Age Factors↗
PubMed1999

Severe respiratory syncytial virus disease in Alaska native children. RSV Alaska Study Group.

Hospitalization rates for respiratory syncytial virus (RSV) infection range from 1 to 20/1000 infants. To determine the rate and severity of RSV infections requiring hospitalization for infants in the Yukon-Kuskokwim (YK) Delta of Alaska, a 3-year prospective surveillance study was conducted. The annual rate of RSV hospitalization for YK Delta infants <1 year of age was 53-249/1000. RSV infection was the most frequent cause of infant hospitalization. RSV disease severity did not differ among non-high-risk infants in the YK Delta and at Johns Hopkins Hospital (JHH). On average, 1/125 infants born in the YK Delta required mechanical ventilation for RSV infection. During the peak season, approximately $1034/child <3 years of age was spent on RSV hospitalization in the YK Delta. In YK Delta infants </=6 months old, RSV microneutralizing antibody titers <1200 were associated with severe disease (odds ratio=6.2, P=.03). In the YK Delta and at JHH, newborns may be at greater risk for severe RSV illness than previously thought.

Age Factors↗
PubMed1999

Induction of hepatic xenobiotic metabolizing enzymes in female Fischer-344 rats following repeated inhalation exposure to decamethylcyclopentasiloxane (D5).

Decamethylcyclopentasiloxane (D5) is a cyclic siloxane with a wide range of commercial applications. The present study was designed to investigate the effects of D5 on the expression and activity of selected rat hepatic phase I and phase II metabolizing enzymes. Female Fischer-344 rats were exposed to 160 ppm D5 vapors (6 h/day, 7 days/week, for 28 days) by whole-body inhalation. Changes in the activity and relative abundance of hepatic microsomal cytochromes P450 (CYP1A, CYP2B, CYP3A, and CYP4A), epoxide hydrolase, and UDP-glucuronosyltransferase (UDPGT) were measured. Repeated inhalation exposure of rats to D5 increased liver size by 16% relative to controls by day 28. During a 14-day post-exposure period, liver size in D5-exposed animals showed significant recovery. Exposure to D5 did not change total hepatic P450, but increased the activity of hepatic NADPH-cytochrome c reductase by 1.4-fold. An evaluation of cytochrome P450 (CYP) enzymes in hepatic microsomes prepared from D5-exposed rats revealed a slight (1.8-fold) increase in 7-ethoxyresorufin O-deethylase (EROD) activity, but no change in immunoreactive CYP1A1/2 protein. A moderate increase (4.2-fold) in both 7-pentoxyresorufin O-depentylase (PROD) activity and immunoreactive CYP2B1/2 protein (3.3-fold) was observed. Testosterone 6beta-hydroxylase activity was also increased (2.4-fold) as was CYP3A1/2 immunoreactive protein. Although a small increase in 11- and 12-hydroxylation of lauric acid was detected, no change in immunoreactive CYP4A levels was measured. Liver microsomal epoxide hydrolase activity and immunoreactive protein increased 1.7- and 1.4-fold, respectively, in the D5-exposed group. UDPGT activity toward chloramphenicol was induced 1.8-fold, while no change in UDPGT activity toward 4-nitrophenol was seen. These results suggest that the profile for enzyme induction following inhalation exposure of female Fischer-344 rats to D5 vapors is similar to that reported for phenobarbital, and therefore D5 may be described as a weak "phenobarbital-like" inducer.

Administration, Inhalation↗
PubMed1999

Effect of cryopreservation on cytochrome P-450 enzyme induction in cultured rat hepatocytes.

In the present study, we evaluated the inducibility of cytochrome P-450 (CYP) CYP1A, CYP2B, CYP3A, and CYP4A by beta-naphthoflavone, phenobarbital, dexamethasone, and clofibric acid, respectively, in primary hepatocyte cultures prepared from both fresh and cryopreserved rat hepatocytes. Rat hepatocytes were successfully thawed and cultured after cryopreservation in liquid nitrogen for up to 1 month. Percentage of total recovery, viable cell recovery, and final viability of the cells were 68%, 72%, and 85%, respectively. Regardless of whether they were cryopreserved or not, cultured hepatocytes exhibited near-normal morphology. Treatment of cryopreserved hepatocytes with beta-naphthoflavone caused an 8-fold increase in 7-ethoxyresorufin O-dealkylase (CYP1A1/2) activity, with an EC50 of 1.5 microM; treatment with phenobarbital caused a 26-fold increase in 7-pentoxyresorufin O-dealkylase (CYP2B1/2) activity, with an EC50 of 10 microM; treatment with dexamethasone caused a 10-fold increase in testosterone 6beta-hydroxylase (CYP3A1/2) activity, with an EC50 of 1.3 microM, whereas treatment with clofibric acid caused a 3-fold increase in lauric acid 12-hydroxylase (CYP4A1-3) activity, with an EC50 of 170 microM. The induction of CYP1A, CYP2B, CYP3A, and CYP4A enzymes by these inducers was confirmed by Western immunoblotting. The patterns of P-450 induction in cryopreserved rat hepatocytes, in terms of concentration response, reproducibility, magnitude, and specificity of response, were similar to those observed in freshly isolated hepatocytes. Additionally, the magnitude and specificity of induction was similar to that observed in vivo in rats. In conclusion, under the conditions examined, cryopreserved rat hepatocytes appear to be a suitable in vitro system for evaluating xenobiotics as inducers of P-450 enzymes.

Animals↗
PubMed1999

Role of CYP2B6 and CYP3A4 in the in vitro N-dechloroethylation of (R)- and (S)-ifosfamide in human liver microsomes.

The central nervous system toxicity of ifosfamide (IFF), a chiral antineoplastic agent, is thought to be dependent on its N-dechloroethylation by hepatic cytochrome P-450 (CYP) enzymes. The purpose of this study was to identify the human CYPs responsible for IFF-N-dechloroethylation and their corresponding regio- and enantioselectivities. IFF exists in two enantiomeric forms, (R) - and (S)-IFF, which can be dechloroethylated at either the N2 or N3 positions, producing the corresponding (R,S)-2-dechloroethyl-IFF [(R, S)-2-DCE-IFF] and (R,S)-3-dechloroethyl-IFF [(R,S)-3-DCE-IFF]. The results of the present study suggest that the production of (R)-2-DCE-IFF and (S)-3-DCE-IFF from (R)-IFF is catalyzed by different CYPs as is the production of (S)-2-DCE-IFF and (R)-3-DCE-IFF from (S)-IFF. In vitro studies with a bank of human liver microsomes revealed that the sample-to-sample variation in the production of (S)-3-DCE-IFF from (R)-IFF and (S)-2-DCE-IFF from (S)-IFF was highly correlated with the levels of (S)-mephenytoin N-demethylation (CYP2B6), whereas (R)-2-DCE-IFF production from (R)-IFF and (R)-3-DCE-IFF production from (S)-IFF were both correlated with the activity of testosterone 6beta-hydroxylation (CYP3A4/5). Experiments with cDNA-expressed P-450 and antibody and chemical inhibition studies supported the conclusion that the formation of (S)-3-DCE-IFF and (S)-2-DCE-IFF is catalyzed primarily by CYP2B6, whereas (R)-2-DCE-IFF and (R)-3-DCE-IFF are primarily the result of CYP3A4/5 activity.

Animals↗