Role of intestinal P-glycoprotein (mdr1) in interpatient variation in the oral bioavailability of cyclosporine

Interpatient differences in the oral clearance of cyclosporine (INN, ciclosporin) have been partially attributed to variation in the activity of a single liver enzyme termed CYP3A4. Recently it has been shown that small bowel also contains CYP3A4, as well as P-glycoprotein, a protein able to transport cyclosporine. To assess the importance of these intestinal proteins, the oral pharmacokinetics of cyclosporine were measured in 25 kidney transplant recipients who each had their liver CYP3A4 activity quantitated by the intravenous [14C-N-methyl]-erythromycin breath test and who underwent small bowel biopsy for measurement of CYP3A4 and P-glycoprotein. Forward multiple regression revealed that 56% (i.e., r2 = 0.56) and 17% of the variability in apparent oral clearance [log (dose/area under the curve)] were accounted for by variation in liver CYP3A4 activity (p < 0.0001) and intestinal P-glycoprotein concentration (p = 0.0059), respectively. For peak blood concentration, liver CYP3A4 activity accounted for 32% (p = 0.0002) and P-glycoprotein accounted for an additional 30% (p = 0.0024) of the variability. Intestinal levels of CYP3A4, which varied tenfold, did not appear to influence any cyclosporine pharmacokinetic parameter examined. We conclude that intestinal P-glycoprotein plays a significant role in the first-pass elimination of cyclosporine, presumably by being a rate-limiting step in absorption. Drug interactions with cyclosporine previously ascribed to intestinal CYP3A4 may instead be mediated by interactions with intestinal P-glycoprotein.

Genetic polymorphisms in the 5'-flanking region change transcriptional regulation of the human cytochrome P450IIE1 gene

We identified genetic polymorphisms in the 5'-flanking region of the human cytochrome P450IIE1 gene and investigated the effect of these polymorphisms on the transcriptional regulation of the gene. PCR direct sequencing of the two homozygous alleles [types A (c1/c1) and C (c2/c2)] revealed the existence of several point mutations in the distal 5'-flanking region of the gene, but no differences in the proximal promoter region. The DNA segment (-1372 to -960) placed upstream of SV40 promoter and the chloramphenicol acetyltransferase (CAT) gene enhanced the expression of the gene, and the enhancement of expression by type C DNA was about 10 times that by its type A counterpart. DNase I footprinting analysis showed at least one protected region in which one of the polymorphic loci (RsaI polymorphism) was located. The DNase I sensitivities and protection profiles of the two genotypes were different. The protected region had high homology to the consensus sequence of the binding region of liver specific transcription factor HNF1 (LF-B1), and this was confirmed by gel retardation assay. These results indicate that genetic polymorphisms in the 5'-flanking region of the human P450IIE1 gene affect its binding of trans-acting factor and change its transcriptional regulation. This may lead to inter-individual differences of microsomal drug oxidation activity.

Possible involvement of pregnane X receptor-enhanced CYP24 expression in drug-induced osteomalacia

Vitamin D controls calcium homeostasis and the development and maintenance of bones through vitamin D receptor activation. Prolonged therapy with rifampicin or phenobarbital has been shown to cause vitamin D deficiency or osteomalacia, particularly in patients with marginal vitamin D stores. However, the molecular mechanism of this process is unknown. Here we show that these drugs lead to the upregulation of 25-hydroxyvitamin D(3)-24-hydroxylase (CYP24) gene expression through the activation of the nuclear receptor pregnane X receptor (PXR; NR1I2). CYP24 is a mitochondrial enzyme responsible for inactivating vitamin D metabolites. CYP24 mRNA is upregulated in vivo in mice by pregnenolone 16alpha-carbonitrile and dexamethasone, 2 murine PXR agonists, and in vitro in human hepatocytes by rifampicin and hyperforin, 2 human PXR agonists. Moreover, rifampicin increased 24-hydroxylase activity in these cells, while, in vivo in mice, pregnenolone 16alpha-carbonitrile increased the plasma concentration of 24,25-dihydroxyvitamin D(3). Transfection of PXR in human embryonic kidney cells resulted in rifampicin-mediated induction of CYP24 mRNA. Analysis of the human CYP24 promoter showed that PXR transactivates the sequence between -326 and -142. We demonstrated that PXR binds to and transactivates the 2 proximal vitamin D-responsive elements of the human CYP24 promoter. These data suggest that xenobiotics and drugs can modulate CYP24 gene expression and alter vitamin D(3) hormonal activity and calcium homeostasis through the activation of PXR.

Novel detection assay by PCR-RFLP and frequency of the CYP3A5 SNPs, CYP3A5*3 and *6, in a Japanese population

In this study, we established useful and reliable methods for the direct detection of the variants of CYP3A5 gene by polymerase chain reaction (PCR) and DdeI restriction analysis. The frequency of CYP3A5 related SNPs in 200 healthy Japanese male subjects was determined. The homozygous wild-type (*1/*1) frequency was 7.0% (14/200), the heterozygous (*1/*3) frequency was 32.5% (65/200) and the homozygous mutant-type (*3/*3) frequency was 60.5% (121/200). The *6 allele was not detected in any of the Japanese individuals. This result suggests that an estimated 40% of the Japanese express relatively high levels of metabolically active CYP3A5 protein. The proposed detection assays are useful for screening the CYP3A5 related SNPs in pharmacogenetic research.

Environmental and genetic determinants of aflatoxin-albumin adducts in the Gambia

Aflatoxins together with chronic hepatitis B virus (HBV) infection contribute to the high incidence of hepatocellular carcinoma in developing countries. An understanding of the mechanism of interaction between these factors would provide a strong rationale for developing effective prevention strategies. In this study in The Gambia we examined the effect of environmental (place of residence and timing of sample collection) and host factors (age, sex, HBV status and interindividual variations in carcinogen metabolising enzymes) in determining blood aflatoxin-albumin adduct levels in 357 individuals of whom 181 were chronic HBV carriers. Samples were analysed for aflatoxin-albumin adducts, HBV status and genotypes of glutathione S-transferase (GST) M1, GSTT1, GSTP1 and epoxide hydrolase (EPXH). Urine samples were analysed for 6beta-hydroxycortisol:cortisol ratio as a marker of cytochrome P450 (CYP) 3A4 activity. Adduct levels were significantly higher in subjects resident in rural [geometric mean adduct level 34.9 pg aflatoxin B1-lysine equivalent (28.5-42.8; 95%CI)/mg albumin] than in periurban areas [22.2 pg (14.9-33.4)/mg] and were approximately twice as high in the dry season [mid-February to March; 83.2 pg (53.3-130.8)/mg] than the wet [July to August; 34.9 pg (28.5-42.8)/mg]. In contrast, HBV status, CYP3A4 phenotype, GSTT1, GSTP1 and EPXH genotypes were not associated with aflatoxin-albumin adduct level. However, mean adduct levels were significantly higher in non-HBV infected subjects with GSTM1 null genotype. The main factors which affect aflatoxin-albumin adduct levels in this population are environmental, notably place of residence and timing of sample collection. This study further emphasises the priority to reduce aflatoxin exposure in these communities by primary prevention measures.

Effect of topiramate or carbamazepine on the pharmacokinetics of an oral contraceptive containing norethindrone and ethinyl estradiol in healthy obese and nonobese female subjects

PURPOSE

To study the pharmacokinetics of a combination oral contraceptive (OC) containing norethindrone and ethinyl estradiol during OC monotherapy, concomitant OC and topiramate (TPM) therapy, and concomitant OC and carbamazepine (CBZ) therapy in order to comparatively evaluate the pharmacokinetic interaction, which may cause contraceptive failure.

METHODS

This randomized, open-label, five-group study included two 28-day cycles. Five groups of female subjects received oral doses of ORTHO-NOVUM 1/35 alone (cycle 1) and then concomitant with TPM or CBZ (cycle 2). The treatment groups were group 1, TPM, 50 mg/day; group 2, TPM, 100 mg/day; group 3, TPM, 200 mg/day; group 4, TPM, 200 mg/day (obese women); and group 5, CBZ, 600 mg/day. Group 4 comprised obese women whose body mass index (BMI) was between 30 and 35 kg/m(2). The BMI of the remaining four groups was < or =27 kg/m2.

RESULTS

Coadministration of TPM at daily doses of 50, 100, and 200 mg (nonobese) and 200 mg (obese) nonsignificantly (p > 0.05) changed the mean area under the curve (AUC) of ethinyl estradiol by -12%, +5%, -11%, and -9%, respectively, compared with OC monotherapy. A similar nonsignificant difference was observed with the plasma levels and AUC values of norethindrone (p > 0.05). CBZ (600 mg/day) significantly (p < 0.05) decreased the AUC values of norethindrone and ethinyl estradiol by 58% and 42%, respectively, and increased their respective oral clearance by 69% and 127% (p < 0.05). Because CBZ induces CYP 3A-mediated and glucuronide conjugation metabolic pathways, the significant increase in the oral clearance of ethinyl estradiol and norethindrone was anticipated.

CONCLUSIONS

TPM, at daily doses of 50-200 mg, does not interact with an OC containing norethindrone and ethinyl estradiol. The lack of the TPM-OC interaction is notable when it is compared with the CBZ-OC interaction.

St John's wort induces both cytochrome P450 3A4-catalyzed sulfoxidation and 2C19-dependent hydroxylation of omeprazole

OBJECTIVE

St John's wort, an extract of the medicinal plant Hypericum perforatum, is widely used as an herbal antidepressant. Although the ability of St John's wort to induce cytochrome P450 (CYP) 3A4-mediated reaction has been well established, the effect on CYP2C19 is still not determined. Thus the objective of this study was to determine the impact of St John's wort on the pharmacokinetic profiles of omeprazole and its metabolites.

METHODS

Twelve healthy adult men (6 CYP2C19*1/CYP2C19*1, 4 CYP2C19*2/CYP2C19*2 and 2 CYP2C19*2/CYP2C19*3) were enrolled in a 2-phase randomized crossover design. In each phase the volunteers received placebo or a 300-mg St John's wort tablet 3 times daily for 14 days. Then all subjects took a 20-mg omeprazole capsule orally. Blood samples were collected up to 12 hours after omeprazole administration. Omeprazole and its metabolites were quantified by use of HPLC with ultraviolet detection.

RESULTS

Omeprazole and its metabolites all exhibit CYP2C19 genotype-dependent pharmacokinetic profiles. After a 14-day treatment with St John's wort, substantial decreases in plasma concentrations of omeprazole were observed. The peak plasma concentration (C(max)) significantly decreased by 37.5% +/- 13.3% (P =.001) in CYP2C19*2/CYP2C19*2 or *3 and by 49.6% +/- 20.7% (P =.017) in CYP2C19*1/CYP2C19*1; the area under the concentration-time curve extrapolated to infinity [AUC(0- infinity )] decreased by 37.9% +/- 21.3% (P =.014) and 43.9% +/- 23.7% (P =.011) in CYP2C19 mutant and wild genotypes, respectively. Moreover, the C(max) and AUC(0- infinity ) of omeprazole sulfone increased by 160.3% +/- 45.5% (P =.001) and by 136.6% +/- 84.6% (P =.014), 155.5% +/- 58.8% (P =.001), and 158.7% +/- 101.4% (P =.017) in mutant and wild genotypes, respectively. St John's wort increased the C(max) of 5-hydroxyomeprazole by 38.1% +/- 30.5% (P =.028) and the AUC(0- infinity ) by 37.2% +/- 26% (P =.005) in CYP2C19 wild-type subjects, whereas it did not produce any significant alterations to the corresponding pharmacokinetic parameters in subjects with variant genotypes.

CONCLUSION

St John's wort induces both CYP3A4-catalyzed sulfoxidation and CYP2C19-dependent hydroxylation of omeprazole and enormously decreases the plasma concentrations of omeprazole. Clinically relevant interactions with other drugs may occur and must be taken into account when St John's wort is being taken.

Effects of serum from patients with chronic renal failure on rat hepatic cytochrome P450

1. In humans, chronic renal failure (CRF) is associated with decreased hepatic drug metabolism, particularly that mediated by the cytochrome P450 (P450). The mechanisms remain poorly understood. The present study aimed to investigate the effects of the serum of patients with CRF on liver P450, and to evaluate whether renal replacement therapies (dialysis or transplantation) impede the inhibition of CRF serum on P450. 2. Rat hepatocytes were incubated for 24 h with serum from patients with severe CRF and from controls to measure (1) P450 level, (2) protein expression and mRNA levels of P450 isoforms and (3) metabolic activities of CYP3A and CYP1A. Similar experiments were performed with serum of patients once on chronic hemodialysis and after kidney transplantation. 3. In rat hepatocytes incubated for 24 h with serum from patients with CRF, P450 level and protein expression, as well as mRNA levels of P450 isoforms (CYP1A2, 2C6, 2C11, 2D1/2D2, 3A2 and 4A1/4A3), were decreased by more than 45% (P<0.001) compared to control serum, while the levels of CYP2E1 were not modified. CYP3A and CYP1A activities were decreased by 51 and 59% (P<0.001), respectively. The inhibitory effect of serum obtained from patients before first dialysis was similar after 1 or 6 months on chronic hemodialysis but was lost after successful kidney transplantation. In CRF serum, the fraction containing proteins between 10 and 15 kDa decreases P450. 4. Human uremic serum contains mediator(s) that decreases rat hepatic P450 activity and expression secondary to reduced gene expression. The inhibitory effect of serum persists even after initiation of dialysis, but disappears after normalization of renal function following kidney transplantation.

Novel substituted pyridinyl imidazoles as potent anticytokine agents with low activity against hepatic cytochrome P450 enzymes

A series of polysubstituted pyridin-4-yl imidazole inhibitors of p38 MAP (mitogen-activated protein) kinase was prepared as small molecular anticytokine agents and drug candidates for the treatment of chronic inflammatory diseases. The contribution of substituents at the pyridinyl and imidazole moiety to selective inhibition of p38 without concomitant cytochrome P450 interaction was evaluated. Placement of a 1-phenylethyl (7e, p38: IC(50) 0.38 microM) or acetyl substituent at the exocyclic nitrogen of several 2-aminopyridine imidazoles led to the identification of potent p38 inhibitors which exceeded the starting lead ML 3375 (p38: IC(50) 0.63 microM) in potency. A preliminary modeling study related the enhanced bioactivity of 7e to a novel interaction between its 1-phenylethylamino side chain and a hydrophobic pocket close to the linker region of p38. The most active p38 inhibitors in this series maintained their efficacy in functional PBMC (peripheral blood mononuclear cells) and whole blood assays. Moreover, cytochrome P450 interaction, which has been linked to the liver toxicity observed for model p38 inhibitors, was very efficiently reduced through introduction of a tetramethylpiperidine substituent at the 1 position of the imidazole nucleus. Combination of both structural features provided 14c (p38: 0.34 microM, inhibition of CYP1A2 0%, 2C9 2.6%, 2C19 7.6% at 10 microM), which was selected for further development.

Three-fold induction of renal 25-hydroxyvitamin D3-24-hydroxylase activity and increased serum 24,25-dihydroxyvitamin D3 levels are correlated with the healing process after chick tibial fracture

To investigate the possible biological actions of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3), a tibial fracture-healing model was established in White Leghorn chicks. Three-week-old White Leghorn chicks fed a vitamin D3-replete diet were divided into four groups (control, anesthetized, sham, and fractured). On varying days after tibial fracture (F) or sham manipulation (S), renal 25(OH)D3-1 alpha-hydroxylase and 25(OH)D3-24-hydroxylase (24-hydroxylase) activities and serum Ca2+ concentrations were measured. Metofane anesthesia was found to have no effect on the activity of either of the hydroxylases; the activities of the hydroxylases in the control, anesthetized, and sham-operated birds were similar. By 10 days after tibial fracture, the renal 24-hydroxylase activity increased more than 3-fold in F (1.33 +/- 0.07 pmol/mg of protein) as compared with S (0.42 +/- 0.03 pmol/mg of protein) (p < 0.0001). A time-dependent study of the renal 24-hydroxylase activity during the fracture repair process revealed a slow increase from the first day after fracture, a higher activity at 8 days, which peaked at 10-11 days, which is consistent with the formation of the callus. The 24-hydroxylase activity then returned to the same level as the sham group 14 days after fracture. There was no significant difference in serum Ca2+ levels between the F and S groups over the 3-week postfracture period. Serum levels of vitamin D3 metabolites were also measured during the fracture healing process: a 3.4x increase of the 24,25(OH)2D3 level in the fractured group (3.64 +/- 1.16 nM) was observed as compared with the control groups (1.08 +/- 0.49 nM) at 10 days after fracture (p = 0.068). No significant differences were observed in the plasma levels of 25(OH)D3 or 1 alpha, 25(OH)2D3 between the group with a fracture and the controls. Exposure of primary chick kidney cells in culture to serum obtained from chicks with a tibial fracture for 20 h resulted in an approximately 40% increase in the activity of the 24-hydroxylase as compared with cells exposed to serum from control birds. These results suggest that 24,25(OH)2D3 is involved in the early process of fracture repair and that there is some form of physiological communication between the fractured bone and the kidney so as to increase the renal 24-hydroxylase and the circulating concentration of this metabolite.

Characterization of deltamethrin metabolism by rat plasma and liver microsomes

Deltamethrin, a widely used type II pyrethroid insecticide, is a relatively potent neurotoxicant. While the toxicity has been extensively examined, toxicokinetic studies of deltamethrin and most other pyrethroids are very limited. The aims of this study were to identify, characterize, and assess the relative contributions of esterases and cytochrome P450s (CYP450s) responsible for deltamethrin metabolism by measuring deltamethrin disappearance following incubation of various concentrations (2 to 400 microM) in plasma (esterases) and liver microsomes (esterases and CYP450s) prepared from adult male rats. While the carboxylesterase metabolism in plasma and liver was characterized using an inhibitor, tetra isopropyl pyrophosphoramide (isoOMPA), CYP450 metabolism was characterized using the cofactor, NADPH. Michaelis-Menten rate constants were calculated using linear and nonlinear regression as applicable. The metabolic efficiency of these pathways was estimated by calculating intrinsic clearance (Vmax/Km). In plasma, isoOMPA completely inhibited deltamethrin biotransformation at concentrations (2 and 20 microM of deltamethrin) that are 2- to 10-fold higher than previously reported peak blood levels in deltamethrin-poisoned rats. For carboxylesterase-mediated deltamethrin metabolism in plasma, Vmax=325.3+/-53.4 nmol/h/ml and Km=165.4+/-41.9 microM. Calcium chelation by EGTA did not inhibit deltamethrin metabolism in plasma or liver microsomes, indicating that A-esterases do not metabolize deltamethrin. In liver microsomes, esterase-mediated deltamethrin metabolism was completely inhibited by isoOMPA, confirming the role of carboxylesterases. The rate constants for liver carboxylesterases were Vmax=1981.8+/-132.3 nmol/h/g liver and Km=172.5+/-22.5 microM. Liver microsomal CYP450-mediated biotransformation of deltamethrin was a higher capacity (Vmax=2611.3+/-134.1 nmol/h/g liver) and higher affinity (Km=74.9+/-5.9 microM) process than carboxylesterase (plasma or liver) detoxification. Genetically engineered individual rat CYP450s (Supersomes) were used to identify specific CYP450 isozyme(s) involved in the deltamethrin metabolism. CYP1A2, CYP1A1, and CYP2C11 in decreasing order of importance quantitatively, metabolized deltamethrin. Intrinsic clearance by liver CYP450s (35.5) was more efficient than that by liver (12.0) or plasma carboxylesterases (2.4).

Interindividual difference in expression of human Ah receptor and related P450 genes

The genomic clones of human aryl hydrocarbon receptor (Ahr) and Ahr nuclear translocator (Arnt) were isolated, and the structures of exon-intron junctions of these genes were partially determined. Based on the sequence information, a quantitative RT-PCR analysis was developed, and the expression of these genes was studied in various human tissues. mRNAs for Ahr and Arnt were widely expressed in human tissues and abundantly in lung. Individual difference in expression levels of Ahr and Arnt mRNA was observed in liver, lung and blood. In order to examine whether expression levels of Ahr and Arnt were associated with those of CYP1A1, we studied the expression of these mRNAs in blood among 20 healthy subjects, taking account of individuals' cigarette smoking habits. We found that the expression levels of CYP1A1 appeared to associate with those of Ahr and Arnt mRNAs (P < 0.06), and also that the expression of Ahr and Arnt was influenced by cigarette smoking. The expression of human Ahr and Arnt is reported here for the first time, providing a quantitative RT-PCR analysis as a useful tool for further studies.

Studies on the mechanism of omega-hydroxylation of platelet 12-hydroxyeicosatetraenoic acid (12-HETE) by unstimulated neutrophils

Stimulated platelets, in the presence or absence of aspirin, synthesize significant quantities of 12-hydroxyeicosatetraenoic acid (12-HETE), which is chemotactic and chemokinetic, and enhances mononuclear cell procoagulant activity. During a cell-cell interaction between stimulated platelets and unstimulated neutrophils, platelet 12-HETE is metabolized to 12,20-dihydroxyeicosatetraenoic acid (12,20-DiHETE) by neutrophils. Characteristics of the enzyme system in unstimulated neutrophils responsible for this omega-hydroxylation were investigated. A broad range of cytochrome P-450 inhibitors, as well as leukotriene B4, blocked formation of 12,20-DiHETE. Owing largely to released proteases, neutrophil homogenization abolished activity. Pretreatment with diisopropylfluorophosphate preserved activity in neutrophil homogenates. omega-Hydroxylation of 12-HETE was confined solely to the microsomal fraction. Specific activity increased 6.6-fold compared with neutrophil sonicates. The electron donor NADPH was a required cofactor. These results indicate that the enzyme in unstimulated human neutrophils, which metabolizes 12-HETE from stimulated platelets to 12,20-DiHETE in this cell-cell interaction, is a cytochrome P-450 monooxygenase.

Characterization of human neutrophil leukotriene B4 omega-hydroxylase as a system involving a unique cytochrome P-450 and NADPH-cytochrome P-450 reductase

Leukotriene B4 (LTB4), a potent chemotactic agent, was catabolized to 20-hydroxyleukotriene B4 (20-OH-LTB4) by the 150,000 x g pellet (microsomal fraction) of human neutrophil sonicate. The reaction required molecular oxygen and NADPH, and was significantly inhibited by carbon monoxide, suggesting that a cytochrome P-450 is involved. The neutrophil microsomal fraction showed a carbon monoxide difference spectrum with a peak at 450 nm in the presence of NADPH or dithionite, indicating the presence of a cytochrome P-450. The addition of LTB4 to the microsomal fraction gave a type-I spectral change with a peak at around 390 nm and a trough at 422 nm, indicating a direct interaction of LTB4 with the cytochrome P-450. The dissociation constant of LTB4, determined from the difference spectra, is 0.40 microM, in agreement with the kinetically determined apparent Km value for LTB4 (0.30 microM). Such a spectral change was not observed with prostaglandins A1, E1 and F2 alpha or lauric acid, none of which inhibited the LTB4 omega-hydroxylation. The inhibition of the LTB4 omega-hydroxylation by carbon monoxide was effectively reversed by irradiation with monochromatic light of 450 nm wavelength. The photochemical action spectrum of the light reversal of the inhibition corresponded remarkably well with the carbon monoxide difference spectrum. These observations provide direct evidence that the oxygen-activating component of the LTB4 omega-hydroxylase system is a cytochrome P-450. Ferricytochrome c inhibited the hydroxylation of LTB4 and the inhibition was fortified by cytochrome oxidase. An antibody raised against rat liver NADPH-cytochrome-P-450 reductase inhibited both LTB4 omega-hydroxylase activity and the NADPH-cytochrome-c reductase activity of human neutrophil microsomal fraction. These observations indicate that NADPH-cytochrome-P-450 reductase acts as an electron carrier in LTB4 omega-hydroxylase. On the other hand, an antibody raised against rat liver microsomal cytochrome b5 inhibited the NADH-cytochrome-c reductase activity but not the LTB4 omega-hydroxylase activity of human neutrophil microsomal fraction, suggesting that cytochrome b5 does not participate in the LTB4-hydroxylating system. These characteristics indicate that the isoenzyme of cytochrome P-450 in human neutrophils, LTB4 omega-hydroxylase, is different from the ones reported to be involved in omega-hydroxylation reactions of prostaglandins and fatty acids.

Analysis of midazolam and metabolites in plasma by high-performance liquid chromatography: probe of CYP3A

Hydroxylation of midazolam (MDZ) is mediated almost exclusively by CYP3A isoforms. The authors describe a high-performance liquid chromatography assay involving MDZ, 1'-hydroxymidazolam, and 4-hydroxymidazolam in plasma. The compounds were eluted on an Ultrasphere ODS, 3-microm particle size, 7.5 cm x 4.6 mm reversed-phase column and monitored by ultraviolet absorbance at 254 nm. The composition of the mobile phase was 35.2% acetonitrile:4.8% methanol:60% buffer acetate (vol/vol/vol), 0.1 M, pH 4.7; the flow rate was 1 ml/minute. Calibration curves were linear (coefficients of correlation > 0.99) within the range of concentrations established (20 to 640 nM). Within- and between-day coefficients of variation were consistently better than 8%. The overall recovery was >90% and the lowest detectable concentration was 8 nM. This approach provides a simple, rapid, and sensitive assessment of MDZ and metabolites in plasma, with a very good accuracy and precision, which enables it as an in vivo marker of CYP3A activity in humans.

Specific packaging and circulation of cytochromes P450, especially 2E1 isozyme, in human plasma exosomes and their implications in cellular communications

Cytochrome P450 (CYP) enzymes metabolize the majority of xenobiotics and are mainly found in hepatic and some extra-hepatic cells. However, their presence and functional role in exosomes, small extracellular vesicles that are secreted from various cells into extracellular fluids including plasma, is unknown. In this study, we analyzed the expression and biological activity of CYP enzymes in human plasma exosomes. First, we optimized isolation of plasma exosomes and characterized them for their physical properties and quality. The results showed that the purity of exosomes (<200 nm) improved upon prior filtration of plasma using a 0.22 micron filter. We then analyzed the relative level of exosomal CYP mRNAs, proteins, and enzyme activity. The results showed that the relative level of CYP enzymes in exosomes is higher than in plasma, suggesting their specific packaging in exosomes. Of the seven CYP enzymes tested, the mRNA of CYP1B1, CYP2A6, CYP2E1, and CYP3A4 were detectable in exosomes. Interestingly, the relative level of CYP2E1 mRNA was >500-fold higher than the other CYPs. The results from the Western blot showed detectable levels of CYP1A1, CYP1B1, CYP2A6, CYP2E1, and CYP3A4. Our results also demonstrated that exosomal CYP2E1 and CYP3A4 show appreciable activity relative to their respective positive controls (CYP-induced baculosomes). Our results also showed that CYP2E1 is expressed relatively higher in plasma exosomes than hepatic and monocytic cells and exosomes derived from these cells. In conclusion, this is the first evidence of the specific packaging and circulation of CYP enzymes, especially CYP2E1, in human plasma exosomes. The findings have biological and clinical significance in terms of their implications in cellular communications and potential use of plasma exosomal CYPs as biomarkers.

In vivo function tests of hepatic drug-oxidizing capacity in patients with liver disease

Aminopyrine, antipyrine and trimethadione have been widely used for some time as probe drugs to assess non-selective P450 liver function. They have proved useful in evaluating pre- and post-operative liver function when performing surgery, transplantations, etc., in addition to a general evaluation of liver function and drug interactions. Progress has recently been made both in these non-selective P450 function tests and in the analysis of drug-metabolizing enzymes at a molecular level, which has resulted in more selective P450 function tests. The caffeine (CYP1 A2), chlorzoxazone (CYP2E1), lidocaine (CYP3 A) and midazolam (CYP3 A) function tests and the erythromycin breath test (CYP3 A) are currently being used as specific probes. The future use of these tests needs to be discussed in terms of potential clinical implications.

Carbon monoxide inhibits omega-oxidation of leukotriene B4 by human polymorphonuclear leukocytes: evidence that catabolism of leukotriene B4 is mediated by a cytochrome P-450 enzyme

Carbon monoxide significantly inhibits omega-oxidation of exogenous leukotriene B4 to 20-OH-leukotriene B4 and 20-COOH-leukotriene B4 by unstimulated polymorphonuclear leukocytes as well as omega-oxidation of leukotriene B4 that is generated when cells are stimulated with the calcium ionophore, A23187. Inhibition of omega-oxidation by carbon monoxide is concentration-dependent, completely reversible, and specific. Carbon monoxide does not affect synthesis of leukotriene B4 by stimulated polymorphonuclear leukocytes or other cell functions (i.e., degranulation, superoxide anion generation). These findings suggest that a cytochrome P-450 enzyme in human polymorphonuclear leukocytes is responsible for catabolizing leukotriene B4 by omega-oxidation.

Cord blood Per- and polyfluoroalkyl substances, placental steroidogenic enzyme, and cord blood reproductive hormone

BACKGROUND

Per- and polyfluoroalkyl substances (PFASs) are widely used in China, but little is known about the association between prenatal PFASs exposure and fetal reproductive development as well as its potential mechanism.

OBJECTIVE

We investigated the effects of cord blood PFASs on fetal reproductive hormones and its potential mechanism in relation to steroidogenic enzymes.

METHODS

Ten selected PFASs (n = 351) including PFOS, PFOA, PFBS, PFDA, PFDoA, PFHpA, PFHxS, PFNA, PFOSA, and PFUA, and two reproductive hormones estradiol (E2) (n = 351) and testosterone (T) (n = 349) were measured in 351 cord blood serum samples from a Chinese birth cohort between 2010 and 2013. Three steroidogenic enzymes including P450arom (n = 125), 3β-HSD1 (n = 123), and 17β-HSD1 (n = 116) were measured in 125 placental tissue samples. Linear regression tested the associations between cord blood PFASs and reproductive hormones in cord blood. Mediation analysis assessed the role of placental steroidogenic enzymes between cord blood PFASs and reproductive hormones.

RESULTS

The positive associations between PFOA, PFHxS and E2 levels, PFOS, PFUA, PFNA and T levels, and PFOS, PFUA and T/E2 ratio were significant. PFUA, PFNA, PFDA, PFHxS, and ∑PFASs were associated with higher P450arom levels. PFHxS was also associated with increased 3β-HSD1 and 17β-HSD1 levels. These associations were more pronounced in females than males when stratified by gender. Furthermore, 17β-HSD1 demonstrated mediating effects in the positive association between cord blood PFHxS and E2 levels in females.

CONCLUSION

Our findings suggested the potential impacts of cord blood PFASs on fetal reproductive hormones, in which steroidogenic enzymes may play important roles. These associations were more pronounced in females than males.

Identification of the fenretinide metabolite 4-oxo-fenretinide present in human plasma and formed in human ovarian carcinoma cells through induction of cytochrome P450 26A1

PURPOSE

The synthetic retinoid fenretinide (4-HPR) exhibits preventive and therapeutic activity against ovarian tumors. An unidentified polar metabolite was previously found in 4-HPR-treated subjects and in A2780 human ovarian carcinoma cells continuously treated with 4-HPR (A2780/HPR). The metabolite and the enzyme involved in its formation in tumor cells are herein identified.

EXPERIMENTAL DESIGN

The metabolite was identified by mass spectrometry in A2780/HPR cell extracts and in plasma from 11 women participating in a phase III trial and treated with 200 mg/d 4-HPR for 5 years. The expression of proteins involved in retinoid metabolism and transport, cytochrome P450 26A1 (CYP26A1), cellular retinol-binding protein I (CRBP-I), and cellular retinoic acid-binding protein I and II (CRABP-I, CRABP-II) were evaluated in tumor cells by reverse transcription-PCR and Western blot analyses. Overexpression of CYP26A1 and retinoic acid receptors (RARs) in A2780 cells were obtained by cDNAs transfection.

RESULTS

The polar metabolite was 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) i.e., an oxidized form of 4-HPR with modification in position 4 of the cyclohexene ring. 4-oxo-4-HPR plasma levels were slightly lower (0.52 +/- 0.17 micromol/L) than those of the parent drug (0.84 +/- 0.53 micromol/L) and of the already identified metabolite N-(4-methoxyphenyl)retinamide (1.13 +/- 0.85 micromol/L). In A2780/HPR cells continuously treated with 4-HPR and producing 4-oxo-4-HPR, CYP26A1 and CRBP-I were markedly up-regulated compared with A2780 untreated cells. In A2780 cells, not producing 4-oxo-4-HPR, overexpression of CYP26A1 caused formation of 4-oxo-4-HPR, which was associated with no change in 4-HPR sensitivity. Moreover, the addition of 4-oxo-4-HPR to A2780 cells inhibited cell proliferation. Elevated levels of CYP26A1 protein and metabolism of 4-HPR to 4-oxo-4-HPR were found in A2780 cells transfected with RARbeta and to a lesser extent in those transfected with RARgamma.

CONCLUSIONS

A new metabolite of 4-HPR, 4-oxo-4-HPR, present in human plasma and in tumor cells, has been identified. The formation of this biologically active metabolite in tumor cells was due to CYP26A1 induction and was influenced by RAR expression. Moreover evidence was provided that 4-HPR up-modulates the expression of CRBP-I transcript, which is lost during ovarian carcinogenesis.

Cytochrome P450 epoxygenase CYP2J2 attenuates nephropathy in streptozotocin-induced diabetic mice

Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid into epoxyeicosatrienoic acids (EETs), which play important and diverse roles in the cardiovascular system. The anti-inflammatory, anti-apoptotic, pro-angiogenic, and anti-hypertensive properties of EETs in the cardiovascular system suggest a beneficial role for EETs in diabetic nephropathy. This study investigated the effects of endothelial specific overexpression of CYP2J2 epoxygenase on diabetic nephropathy in streptozotocin-induced diabetic mice. Endothelial CYP2J2 overexpression attenuated renal damage as measured by urinary microalbumin and glomerulosclerosis. These effects were associated with inhibition of TGF-β/Smad signaling in the kidney. Indeed, overexpression of CYP2J2 prevented TGF-β1-induced renal tubular epithelial-mesenchymal transition in vitro. These findings highlight the beneficial roles of the CYP epoxygenase-EET system in the pathogenesis of diabetic nephropathy.

The effects of grapefruit juice on sertraline metabolism: an in vitro and in vivo study

Grapefruit juice is an inhibitor of cytochrome P-450 3A4 (CYP3A4). This study was designed to assess the in vitro and in vivo effects of grapefruit juice on sertraline metabolism. The in vitro assay involved analysis of sertraline metabolism by CYP3A4 using CYP3A4-expressed human beta-lymphoblast microsomes. The in vivo study involved high-performance liquid chromatographic analysis of serum trough levels of sertraline and desmethylsertraline in 5 patients who had been taking their usual dose of sertraline for > or =6 weeks, followed by concurrent use of sertraline with grapefruit juice for 1 week. The in vitro assay demonstrated that grapefruit juice inhibited the formation of desmethylsertraline in a dose-dependent manner. In the in vivo study, mean serum sertraline levels were determined in 5 patients with a history of depression (4 males and 1 female). The mean age of the patients was 68.6 years, their mean weight was 69.6 kg, and their mean sertraline dosage was 55 mg/d. The results of the in vivo study appeared to be consistent with the in vitro findings, in that mean (+/- SD) serum sertraline trough levels increased significantly from 13.7+/-4.9 microg/L before to 20.2+/-4.4 microg/L (P = 0.047) after administration of grapefruit juice. Thus the in vitro study demonstrated that grapefruit juice can inhibit the metabolism of sertraline. A larger study is warranted to substantiate the clinical significance of the in vivo findings.

A protective lipidomic biosignature associated with a balanced omega-6/omega-3 ratio in fat-1 transgenic mice

A balanced omega-6/omega-3 polyunsaturated fatty acid (PUFA) ratio has been linked to health benefits and the prevention of many chronic diseases. Current dietary intervention studies with different sources of omega-3 fatty acids (omega-3) lack appropriate control diets and carry many other confounding factors derived from genetic and environmental variability. In our study, we used the fat-1 transgenic mouse model as a proxy for long-term omega-3 supplementation to determine, in a well-controlled manner, the molecular phenotype associated with a balanced omega-6/omega-3 ratio. The fat-1 mouse can convert omega-6 to omega-3 PUFAs, which protect against a wide variety of diseases including chronic inflammatory diseases and cancer. Both wild-type (WT) and fat-1 mice were subjected to an identical diet containing 10% corn oil, which has a high omega-6 content similar to that of the Western diet, for a six-month duration. We used a multi-platform lipidomic approach to compare the plasma lipidome between fat-1 and WT mice. In fat-1 mice, an unbiased profiling showed a significant increase in the levels of unesterified eicosapentaenoic acid (EPA), EPA-containing cholesteryl ester, and omega-3 lysophosphospholipids. The increase in omega-3 lipids is accompanied by a significant reduction in omega-6 unesterified docosapentaenoic acid (omega-6 DPA) and DPA-containing cholesteryl ester as well as omega-6 phospholipids and triacylglycerides. Targeted lipidomics profiling highlighted a remarkable increase in EPA-derived diols and epoxides formed via the cytochrome P450 (CYP450) pathway in the plasma of fat-1 mice compared with WT mice. Integration of the results of untargeted and targeted analyses has identified a lipidomic biosignature that may underlie the healthful phenotype associated with a balanced omega-6/omega-3 ratio, and can potentially be used as a circulating biomarker for monitoring the health status and the efficacy of omega-3 intervention in humans.

Selective expression of CYP3A5 and not CYP3A4 in human blood

There is a marked variation between people in the activity of CYP3A4 in liver and intestine. We reasoned that if CYP3A4 was expressed in peripheral blood cells, a simple blood based test of CYP3A4 phenotype might be feasible. We prepared peripheral blood smears from healthy volunteers and performed immunostaining with a rabbit polyclonal antibody that selectively reacts with enzymes within the CYP3A subfamily. Staining was observed only within the cytoplasm of neutrophils (PMNs). cDNA prepared from isolated PMNs and mononuclear cells was subjected the polymerase chain reaction using as primers synthetic oligonucleotides that selectively amplify fragments of each known CYP3A cDNAs (CYP3A3, CYP3A4, CYP3A5, and CYP3A7). Amplification was only obtained with the CYP3A5 specific oligonucleotides, predominantly in PMNs, and the identity of the amplified fragment was confirmed by sequencing. Next, whole white cell homogenate prepared from human blood was reacted on immunoblots with a monoclonal antibody that recognizes all CYP3A proteins or an absorbed polyclonal antibody that recognizes only CYP3A5. Both antibodies recognized a protein in the white cells that comigrated with purified CYP3A5. However, metabolism of midazolam, a substrate of CYP3A, could not be detected in homogenates of isolated granulocytes, in homogenates of the whole WBC fractions, or in incubations with unlysed WBC preparations. We conclude that CYP3A4 is not expressed in peripheral blood and hence a blood phenotyping test for this enzyme will not be feasible. Our discovery that CYP3A5 is present may be important since this enzyme is also present in the liver intestine and kidney of many people.