Atomistic simulation of voids effect on nanoindentation

In this paper, spherical voids effect on the first dislocation emission of single-crystal Cu in nanoindentation is investigated by means of the atomistic simulation. The results show that there are two opposite effects on dislocation emission resulting from the stable voids in matrix. The existence of voids can lower or heighten the load needed to nucleate the first dislocation. The relative distance between the void and the indenter, and the void size play an important role in the yield load of the first dislocation emission in nanoindentation.

Structural analysis of anti-tumor heteropolysaccharide GFPS1b from the cultured mycelia of Grifola frondosa GF9801

A 21-kDa heteropolysaccharide, coded as GFPS1b, was obtained from the cultured mycelia of Grifola frondosa GF9801 by hot-water extraction, ethanol precipitation, and fractioned by DEAE Sepharose Fast-flow, followed by the purification with Sephadex G-100 column chromatography using an AKTA purifier. It exhibited more potent anti-proliferative activity on MCF-7 cells than other polysaccharide fractions. GFPS1b was an acidic polysaccharide with approximately 16.60% protein and 4.3% uronic acid. Gas chromatography of absolute acid hydrolysate of GFPS1b suggested that it was composed of D-glucose, D-galactose, and L-arabinose with a molar ratio of 4:2:1. Periodate oxidation, Smith degradation, partial acid hydrolyzation, methylation analysis, FT-IR, and (1)H, (13)C NMR spectroscopy analysis revealed that GFPS1b had a backbone consisting of alpha-(1-->4)-linked D-galacopyranosyl and alpha-(1-->3)-linked D-glucopyranosyl residues substituted at O-6 with glycosyl residues composed of alpha-L-arabinose-(1-->4)-alpha-D-glucose (1--> linked residues.

Optimization of the medium composition for production of mycelial biomass and exo-polymer by Grifola frondosa GF9801 using response surface methodology

In this work, a three-level Box-Behnken factorial design was employed combining with response surface methodology (RSM) to optimize the medium composition for the production of the mycelial biomass and exo-polymer in submerged cultures by Grifola frondosa GF9801. A mathematical model was then developed to show the effect of each medium composition and their interactions on the production of mycelial biomass and exo-polymer. The model estimated that, a maximal yield of mycelial biomass (17.61 g/l) could be obtained when the concentrations of glucose, KH2PO4, peptone were set at 45.2 g/l, 2.97 g/l, 6.58 g/l, respectively; while a maximal exo-polymer yield (1.326 g/l) could be achieved when setting concentrations of glucose, KH2PO4, peptone at 58.6 g/l, 4.06 g/l and 3.79 g/l, respectively. These predicted values were also verified by validation experiments. Compared with the values obtained by other runs in the experimental design, the optimized medium resulted in a significant increase in the yields of mycelial biomass and exo-polymer. Maximum mycelial biomass yield of 22.50 g/l was achieved in a 15-l fermenter using the optimized medium.

Branchlet nutrient concentration in hoop pine (Araucaria cunninghamii) relative to family, stable carbon and oxygen isotope ratios and growth rate in contrasting environments

Genetic variation in branchlet nutrient (N, P, K, Na, Ca, Mg, Mn and Fe) concentrations and mineral concentration (sum of branchlet P, K, Na, Ca, Mg, Mn and Fe concentrations) of 8-9-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) half-sib families was assessed for four canopy positions at a wet site (23 families) and two canopy positions at an N- and water-limiting dry site (22 families) in relation to tree growth and associated branchlet carbon (delta13C) and oxygen (delta18O) isotope composition in southeast Queensland, Australia. Branchlet nutrient and mineral concentrations varied significantly among families and with canopy position and site. Depending on the canopy position sampled, the hoop pine family effect accounted for 0 to 13.8% of the total variation in branchlet N concentration, and for 0 to 30.3% of the total variation in branchlet mineral concentration at the wet site. The corresponding values for the family effect at the dry site were 0-13.3% for branchlet N concentration and 0-25.7% for branchlet mineral concentration. There were significant variations in branchlet P, K, Ca and Mg concentrations at both sites, and these variations differed with canopy position. Relationships between family means of branchlet N concentration and tree growth or delta13C or delta18O varied with canopy position at both sites. At the wet site, there were significant positive correlations between branchlet mineral concentration in the upper-outer or upper-inner canopy and tree height (r = 0.26 and 0.37, P < 0.01) and between branchlet mineral concentration and delta13C (r = 0.24, P < 0.01) in the upper-inner canopy, and a significant negative correlation between branchlet mineral concentration and delta13C (r = -0.21, P < 0.05) in the upper-outer canopy. At the dry site, branchlet mineral concentrations in the upper-inner and upper-outer canopy were significantly correlated with branchlet delta13C (r = -0.28 and -0.51, P < 0.01), and branchlet N concentration in the upper-inner canopy was significantly correlated with tree growth (r = 0.29, P < 0.01). A significant correlation between branchlet delta18O (an index of stomatal conductance) and branchlet mineral concentration at the dry site (r = 0.39, P = 0.020) indicated that stomatal conductance might be a factor regulating the variation in branchlet mineral concentration of the hoop pine families. Both branchlet N concentration and mineral concentration at particular canopy positions assist in selecting hoop pine families with improved tree growth and N- and water-use efficiency in environments where both N deficiency and a limited water supply are major factors affecting plantation productivity.

Auxin distribution and transport during embryogenesis and seed germination of Arabidopsis

Auxin distribution during embryogenesis and seed germination were studied with transgenic Arabidopsis plants expressing GUS gene driven by a synthetic DR5 promoter, an auxin responsive promoter. The results showed that GUS activity is higher in ends of hypophysis and cotyledon primordia of heart-, torpedo- and cotyledon-stage embryos, leaf tip area, lateral root primordia, root apex and cotyledon of young seedlings. And GUS accumulated in root apex of the seedlings grown on auxin transport inhibitor containing media. All these suggested that above-mentioned part of the organs and tissues have a higher level of auxin, and auxin polar transport inhibitor could cause the accumulation of auxin in root apex. And auxin transport inhibitor also resulted in aberration of Arabidopsis leaf pattern formation, root gravitropism and elongation.

Existence of homologous sequences corresponding to cDNA of the ver gene in diverse higher plant species

The presence of DNA homologues corresponding to verc203 (vernalization-related cDNA clone) was investigated by molecular hybridization techniques. The genes were detected in 16 plant species that cover 12 subclasses of the Takhtajan system of angiosperms classification including diverse model species. The results of Southern blot analysis showed a low copy number of this gene existed in rice, wheat, barley and Arabidopsis. The hybridization result of PCR products demonstrated the conservation of the gene corresponding to ver203 in diverse plants. The phylogenetic tree of the ver203 gene in tested plants was supported by evolution relationship of species. The ver203 gene expressed in a vernalized plumule winter wheat, instead of the root. And the endosperm before the treatment was essential for the ver203 expression during vernalization in wheat. In Arabidopsis thaliana, the pattern of expression showed that the gene corresponding to ver203 was expressed at low temperature for 14 days. Gibberellin (GA3) may accelerate the expression of ver203 gene in Arabidopsis exposed to low temperature. However, it could not replace vernalization treatment to initiate the gene expression.

[Raman and infrared spectral studies of tungsten organometallic carbyne complex at high external pressure]

The Raman and infrared spectra of complex: [Cl(CO)2 (DPPE) W identical to CC6H4C identical to CC6H4NC]2 Re Cl(CO)3 (DPPE = bis (diphenylphosphino) ethane, (Ph)2PCH2CH2P(Ph)2) were measured at high external pressure (up to about 50 kbar). The pressure induced phase transition was observed near 30 kbar. The pressure dependence d nu/dp of nu (W identical to C) at the low-pressure phase is a little high (0.59 cm-1.(kbar)-1) and is very low (0.04 cm-1.(kbar)-1) at the high-pressure phase. It shows that the pi-backbonding from W to pi*--orbital of CO is strengthened at the high external pressure in fragment Cl(CO)2 (DPPE) W identical to C; The bond intensity and the force constant of W identical to C and nu (W identical to C) are decreasing; This effect compete with the normal increasing nu (W identical to C) on compression.

New biflavanones and bioactive compounds from Stellera chamaejasme L

AIM

To study the chemical constituents of the root of Stellera chamaejasme L.

METHODS

Various column chromatographies on silica gel and RP-18 were employed for isolation and purification. Structures of compounds were elucidated by spectral analysis.

RESULTS

Eight lignans and three biflavonoids possessing a C-3/C-3" linkage were isolated. They are ruixianglangdusu A (1) and B (2), 4',4'",5,5",7,7"-hexahydroxy-3,3"-biflavone (3), (+)-kusunokinin (4), lirioresinol-B (5), magnolenin C (6), (-)-pinoresinol monomethyl ether (7), (-)-pinoresinol (8), (+)-matairesinol (9), isohinokinin (10) and (-)-eudesmin (11).

CONCLUSION

Compounds 1 and 2 are new biflavanones, 1 is enantiomeric to known chamaejasmenin C, 4, 6, 8, 9, 10 and 11 were isolated from this plant for the first time, and 7 was isolated from natural resources for the first time. In vitro bioassays showed that 3 and 8 exhibited antibacterial activity, and 1, 2, 9 and 11 exhibited immunomodulatory activity.

[Studies on chemical constituents of Stellera chamejasma L]

OBJECTIVE

Isolate and identify the bioactive compounds from the root of Stellera chamejasma.

METHOD

The compounds were extracted with solvents, isolated by column chromatography and identified by spectroscopic methods.

RESULT

Seven compounds were isolated and identified as umbelliferone(1); daphnoretin (2); 2,6-dimethoxyl p-benzoquinone(3); (-)-eudesmin(4); (+)-matairesinol(5); lirioresinol B(6) and daucosterol(7).

CONCLUSION

Compounds 3, 4 and 5 were isolated from the plant for the first time.

[Response of lithium fluoride detector to charged particle LET]

Response of LiF thermoluminescence (TL) detector to charged particle is dependent on particles' LET. High LET can cause reduction of detector response and underestimation of radiation dose. This paper summarized the response of LiF detector to charged particles' LET, and suggested a new approach to solve the dose contribution of high LET charged particles.

A new bicoumarin from Stellera chamaejasme L

Thirteen compounds were isolated from roots of Stellera chamaejasme L. (Thymelaeaceae). They are 3-sitosterol (2), simplexin (3), pimelea factor P2 (4), daucosterol (5), (+)-3-hydroxy-1,5-diphenyl-1-pentanone (6), 4-ethoxy-benzoic acid (7), 2,4,6-Trimethoxy-benzoic acid (8), (+)-afzelechin (9), fumaric acid (10), N,N-dimethyl-L-aspartic acid (11), umbelliferone (12), daphniretin (13) and a novel bicoumarin named bicoumastechamin (1). Among the known compounds, 7, 8, 9, 10 and 11 were first isolated from this plant, and 6 was first isolated from the natural resources. Their structures have been elucidated on the basis of spectral data. In vitro bioassays showed that 4 inhibited cancer cell growth, 13 exhibited immunomodulatory activity, and 6 exhibited both immunomodulatory and anti-tumor activity.

5-hydroxylation of omeprazole by human liver microsomal fractions from Chinese populations related to CYP2C19 gene dose and individual ethnicity

It has been previously reported that omeprazole (OP) oxidation is mediated by CYP2C19 and CYP3A4 in human livers. In this study, we assessed their relative contributions with human liver microsomal fractions from Chinese populations that were genotyped by CYP2C19 and recruited from two ethnic groups, Han and Zhuang. The kinetics of 5-hydroxyomeprazole (5-OH-OP) formation was best described by the two-enzyme and single-enzyme Michaelis-Menten equations for liver microsomes from CYP2C19 extensive (EMs) and poor metabolizers, respectively. At a low substrate concentration that may be encountered in vivo, the monoclonal antibody to CYP2C8/9/19 strongly inhibited 5-OH-OP formation in EM microsomes, whereas troleandomycin (TAO) eliminated most of the formation at a high substrate concentration. In poor metabolizer microsomes, either TAO or anti-CYP3A4 could alone abolish 5-OH-OP formation. Furthermore, there were differences between homozygous and heterozygous EMs in the percentage of inhibition by TAO and the antibodies. At the low substrate concentration, OP 5-hydroxyaltion was correlated well with S-mephenytoin 4'-hydroxylation and CYP2C19 contents in liver microsomes of 34 Chinese individuals. Moreover, in these individuals, obviously genetic and somewhat ethnic differences in OP 5-hydroxylation were observed between different CYP2C19 genotypes (wt/wt > wt/m1 > m1/m1) and between Han and Zhuang (Han > Zhuang), respectively. The results indicate that CYP2C19 is a high-affinity enzyme for OP 5-hydroxylation by liver microsomes from Chinese individuals and that its contribution is CYP2C19 gene dependent and ethnically related. Similar studies indicate that OP sulfoxidation is mediated mainly by CYP3A4 and independent of CYP2C19 genotype status.

Variation in branchlet delta13C in relation to branchlet nitrogen concentration and growth in 8-year-old hoop pine families (Araucaria cunninghamii) in subtropical Australia

Carbon isotope composition (delta13C) of branchlet tissue at nine canopy positions, and nitrogen concentration (N(mass)) at four canopy positions, were assessed in 8-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) trees from 23 half-sib families, grown in six blocks of a progeny test in southeastern Queensland, Australia. There was considerable variation among sampling positions, families and blocks in both delta13C and N(mass). The delta13C was positively related to N(mass) only for samples from the upper outer crown (P < 0.005). Phenotypic correlations existed between tree growth and canopy delta13C. Branchlet delta13C of the inner and lower outer crown was positively related (P < 0.037) to tree height, but delta13C in branchlets of the upper outer crown was not related to tree height, or was related negatively (P < 0.045). There were significant differences in delta13C between hoop pine families for six canopy positions (upper canopy positions as well as lower canopy positions on the northern side), with heritabilities greater than 0.40. The significance of these findings is discussed in relation to water and light competition within the tree canopy of hoop pine.

[Factors on somatic embryogenesis of soybean elite cultivars and plant regeneration]

Factors on in vitro somatic embryogenesis of soybean (three elite cultivars) were studied using cotyledons of 3.0-6.0 mm immature seed as explants. Not only the kinds, concentrations and combinations of plant growth regulatory substances but also immature embryo length and inoculum density have main effects on the approaches of embryogenesis. The results of two-factors analysis of variance experiments showed that immature embryo length, plant growth substance concentration and basic medium type have very significant effects on the frequency of embryogenic response, furthermore, interactions exist between the former two factors and are just very significant(at 1% level). The best combinations between 2,4-D concentration and cotyledon length are 10 mg/L 2,4-D & 4.0 mm immature embryos, 20-40 mg/L 2,4-D & 5.0 mm immature embryo. Under these combinations, the salt composition of E1 are very significantly better than that of MS. In conclusion, in the regeneration system established by us the frequency of somatic embryogenesis from the soybean immature cotyledons is greater than 50% and the frequency of conversion of normal (not fused) somatic embryos is about 52.9%-62.6%.

Human 3'-phosphoadenosine 5'-phosphosulfate synthetase 1 (PAPSS1) and PAPSS2: gene cloning, characterization and chromosomal localization

Sulfae conjugation is an important pathway in the metabolism of a large number of exogenous and endogenous compounds. These reactions are catalyzed by sulfotransferase (SULT) enzymes that utilize 3'-phosphoadenosine 5'-phosphosulfate (PAPS) as a sulfate donor. PAPS is synthesized from ATP and inorganic sulfate by PAPS synthetase (PAPSS). Two separate PAPSS cDNAs, PAPSS1 and PAPSS2, have been identified in human tissues. We have cloned and characterized the genes for human PAPSS1 and PAPSS2 to make it possible to study the pharmacogenomics of these enzymes. Both genes consisted of 12 exons with virtually identical exon-intron splice junction locations. All splice junctions conformed to the "GT-AG" rule. The total length of PAPSS1 was approximately 108 kb, while that of PAPSS2 was greater than 37 kb. The 5'-flanking region of PAPSS1 did not include a TATA box sequence near the site of transcription initiation, but PAPSS2 had a TATA motif located 21 bp upstream from the site of transcription initiation. Northern blot analysis showed that the major PAPSS1 and PAPSS2 transcripts were approximately 2.7 and 4.2 kb in length, respectively. PAPSS1 mapped to human chromosome band 4q24 while PAPSS2 mapped to 10q22-23 by fluorescence in situ hybridization analysis. Cloning and structural characterization of PAPSS1 and PAPSS2 will make it possible to perform molecular genetic and pharmacogenomic studies of these important enzymes in humans.

Phenotypic polymorphism and gender-related differences of CYP1A2 activity in a Chinese population

AIMS

To investigate the distribution characteristics of CYP1A2 in a Chinese population, and to examine gender-related differences in CYP1A2 activity.

METHODS

Two hundred and twenty-nine healthy subjects, 120 men and 109 women, were enrolled in this study. CYP1A2 activity was measured by plasma paraxanthine/caffeine (1,7X/1,3,7X) ratio 6 h after administration of 300 mg caffeine. The concentrations of paraxanthine and caffeine in plasma were detected by h.p.l.c.

RESULTS

A 16-fold variation of CYP1A2 activity (range 0. 09 to 1.46) was shown in this study. The coefficient of variation (CV %) of CYP1A2 activity was 62.9%. Non-normal distribution of CYP1A2 activity was indicated by the Shapiro-Wilk test (P<0.001). Probit plots of CYP1A2 activity revealed a bimodal distribution with breakpoint of 1,7X/1,3,7X ratio of 0.12. The percentage of poor metabolizers (PMs) was 5.24% (95% CI: 2.35% approximately 8.13%) in this Chinese population. Residual analysis of the data also supported bimodality (P<0.01). The CYP1A2 activity of men was higher than that of women (median: 0.33 vs 0.23, P<0.001). A probit plot of CYP1A2 activity in men was shifted to the left compared with that in women. Based on phenotype, the gender-related difference was observed in extensive metabolizers (EMs) (P<0.001), but not in PMs (P >0.1). In addition, there was no sex-related difference in the incidence of PMs (P >0.1).

CONCLUSIONS

There is a phenotypic polymorphism in CYP1A2 activity in this Chinese population, and CYP1A2 activity is higher in men than that in women.

An isopimarane diterpene from Euphorbia ebracteolata Hayata

From the ethanolic extract of the roots of Euphorbia ebracteolata Hayata four compounds were isolated. They are 24-methylenecycloartanone, tirucallol, procesterol and a new isopimarane diterpene, namely yuexiandajisu C. The structure of yuexiandajisu C was elucidated by spectral analysis. The bioassay in vitro showed yuexiandajisu C exhibited immunomodulatory activity.

Effect of the gene dosage of CgammaP2C19 on diazepam metabolism in Chinese subjects

OBJECTIVE

To determine whether the gene dosage of CYP2C19 affects the metabolism of diazepam and desmethyldiazepam in healthy Chinese subjects.

SUBJECTS AND METHODS

Eighteen unrelated adult men were recruited for the study from a total of 101 healthy Chinese volunteers who had been screened for CYP2C19 phenotype and genotype. All subjects received a single oral dose (5 mg) of diazepam, and the pharmacokinetics of diazepam and desmethyldiazepam were compared in six ml homozygotes (ml/ml), six ml heterozygotes (wt/ml), and six wild-type homozygotes (wt/wt).

RESULTS

The plasma elimination half-life values of diazepam (84.0 +/- 13.7 hours) and desmethyldiazepam (176.0 +/- 28.9 hours) in subjects of ml/ml were significantly longer than those (62.9 +/- 9.8 hours for diazepam; 132.1 +/- 24.9 hours for desmethyldiazepam; both P < .01) in subjects of wt/ml or those (20.0 +/- 10.8 hours for diazepam; 99.2.+/- 21.7 hours for desmethyldiazepam; both P < .01) in subjects of wt/wt. A significant difference in the corresponding half-life values existed between the wt/ml and wt/wt subjects (P < .01). As expected, the slowest mean clearance of diazepam was observed in the ml/ml subjects (2.8 +/- 0.9 mL/min) and the fastest in the wt/wt subjects (19.5 +/- 9.8 mL/min), with the wt/ml heterozygotes having an intermediate value (7.2 +/- 2.6 mL/min).

CONCLUSION

The presence of a single-nucleotide polymorphism (G681A) of the CYP2C19 gene cosegregates with the impaired metabolism of diazepam and desmethyldiazepam among Chinese subjects in a gene-dosage effect manner.

Evidence for involvement of polymorphic CYP2C19 and 2C9 in the N-demethylation of sertraline in human liver microsomes

AIMS

The present study was designed to define the kinetic behaviour of sertraline N-demethylation in human liver microsomes and to identify the isoforms of cytochrome P450 involved in this metabolic pathway.

METHODS

The kinetics of the formation of N-demethylsertraline were determined in human liver microsomes from six genotyped CYP2C19 extensive (EM) and three poor metabolisers (PM). Selective inhibitors of and specific monoclonal antibodies to various cytochrome P450 isoforms were also employed.

RESULTS

The kinetics of N-demethylsertraline formation in all EM liver microsomes were fitted by a two-enzyme Michaelis-Menten equation, whereas the kinetics in all PM liver microsomes were best described by a single-enzyme Michaelis-Menten equation similar to the low-affinity component found in EM microsomes. Mean apparent Km values for the high-and low-affinity components were 1.9 and 88 microm and V max values were 33 and 554 pmol min-1 mg-1 protein, respectively, in the EM liver microsomes. Omeprazole (a CYP2C19 substrate) at high concentrations and sulphaphenazole (a selective inhibitor of CYP2C9) substantially inhibited N-demethylsertraline formation. Of five monoclonal antibodies to various cytochrome P450 forms tested, only anti-CYP2C8/9/19 had any inhibitory effect on this reaction. The inhibition of sertraline N-demethylation by anti-CYP2C8/9/19 was greater in EM livers than in PM livers at both low and high substrate concentrations. However, anti-CYP2C8/9/19 did not abolish the formation of N-demethylsertraline in the microsomes from any of the livers.

CONCLUSIONS

The polymorphic enzyme CYP2C19 catalyses the high-affinity N-demethylation of sertraline, while CYP2C9 is one of the low-affinity components of this metabolic pathway.

[Vascular bundle specific expression of iaaL gene affects the generation frequencies of transgenic tobacco]

A vascular bundles specific expressing vector pBAL1 with a promoter AQ630 from rice phenylalanine ammonialyase gene and a gene encoding indoleacetic-lysine synthytase from Pseudomonas syringae subsp. savastanoi was constructed. Affirmed by Southern blotting and RTPCR analysis, the AQ630-iaaL transgenic plants show increasing shoots-regeneration frequency of young stem explants on hormone-free 1/2 MS medium and lower sensibility to IAA when roots were induced from the root explants on the media containing different concentrations of IAA compared to untransformed plants.

Foliar modifications induced by inhibition of polar transport of auxin

The effects of auxin polar transport inhibitors, 9-hydroxy-fluorene-9-carboxylic acid (HFCA); 2, 3, 5-triiodobenzoic acid (TIBA) and trans-cinnamic acid (CA) on leaf pattern formation were investigated with shoots formed from cultured leaf explants of tobacco and cultured pedicel explants of Orychophragmus violaceus, and the seedlings of tobacco and Brassica chinensis. Although the effective concentration varies with the inhibitors used, all of the inhibitors induced the formation of trumpet-shaped and/or fused leaves. The frequency of trumpet-shaped leaf formation was related to the concentration of inhibitors in the medium. Histological observation of tobacco seedlings showed that there was only one main vascular bundle and several minor vascular bundles in normal leaves of the control, but there were several vascular bundles of more or less the same size in the trumpet-shaped leaves of treated ones. These results indicated that auxin polar transport played an important role on bilateral symmetry of leaf growth.

[Enhanced resistance of transgenic tobacco expressing Shiva A gene against bacterial wilt disease (Pseudomonas solanacearum pv tabaci)]

Shiva A gene was introduced into tobacco mediated by Agrobacterium tumefaciens. Transgenic plants show enhanced resistance against bacterial wilt disease (Pseudomonas solanacearum pv tabaci). Compared with control plants, the disease indexes of transgenic tobacco plants Sc-2 and Sc-6 drop about 42.1% and 60.6%.

Determination of S/R ratio of mephenytoin in human urine by chiral HPLC and ultraviolet detection and its comparison with gas chromatography

AIM

To improve HPLC method for rapid determination of urinary S/R-ratio of mephenytoin, a widely used metabolic index for cytochrome P-450 2C19 (CYP2C19) activity.

METHODS

Aliquots of 0-8-h urine sample after dosing racemic mephenytoin 100 mg underwent one-step extraction with dichloromethane. Analysis was performed on a chiral column (250 mm x 4 mm, 5 microns) at lambda = 207 nm. The eluent was a mixture of acetronitrile and water containing both 0.1% glacial acetic acid and 0.2% triethylamine (14:86, vol/vol) at a flow-rate of 0.9 mL.min-1.

RESULTS

The enatiomers of mephenytoin in urine were well separated within 9 min. A linear correlation was observed between 50-5000 micrograms.L-1 with the detection limit of 12.5 micrograms.L-1 for both enantiomers of mephenytoin. This HPLC analysis was comparable to gas chromatography in accuracy and sensitivity, but with much shorter retention time and better resolution.

CONCLUSION

The present HPLC method is good for rapid determination of the ability of subjects to hydroxylate S-mephenytoin after oral administration of the racemic drug.

Clomipramine N-demethylation metabolism in human liver microsomes

AIM

To study the effect of cytochrome P-450 (CYP450) inhibitors on clomipramine (Clo) N-demethylation in vitro.

METHODS

The kinetic parameters of Clo N-demethylation in human liver microsomes were obtained by the Michaelis-Menten equation. The parameters after pretreatment with putative inhibitors of various CYP450 isoforms were compared with controls.

RESULTS

K(m1), K(m2), Vmax1, Vmax2, Vmax1/K(m1), and Vmax2/K(m2) were (0.11 +/- 0.06), (24 +/- 14) mumol.L-1, (114 +/- 47), (428 +/- 188) nmol.g-1.min-1, (1.8 +/- 1.6), and (0.019 +/- 0.005) L.g-1.min-1, respectively. The interindividual variations for the last 4 parameters reached up to 2.5-, 7.3-, 3.4-, and 1.8-fold. At 5 mumol.L-1 of Clo, troleandomycin (Tro), furafylline (Fur), ditiocarb sodium (Dit), and S-mephenytoin (Mep) produced a marked inhibition on Clo N-demethylation while sulfaphenazole (Sul) and quinidine (Qui) had only slight effects. The inhibitory rates by Dit 30, Mep 500, Fur 10, Tro 10, Fur 80, Tro 200 and Fur 80 + Tro 200 mumol.L-1 were 27.0%, 32.9%, 42.8%, 40.5%, 63.9%, 66.4%, and 78.3%, respectively. The IC50 (95% confidence limits) for Fur and Tro were 27.7 (19.1-36.3) and 42.1 (20.9-63.3) mumol.L-1, respectively.

CONCLUSIONS

The N-demethylation of Clo exhibited a biphasic behavior. This reaction was mediated mainly by both CYP1A2 and CYP3A4, to a minor extent by CYP2C19 at the low concentration of Clo in vitro.