Biomedical subjects

Martin F Fromm

Publications and source records attributed to Martin F Fromm.

At least 37 records · Page 2Linked to original sources

PubMed2004

Genetic polymorphisms in the multidrug resistance-associated protein 3 (ABCC3, MRP3) gene and relationship to its mRNA and protein expression in human liver.

AIMS: To determine the genetic variability of multidrug resistance protein 3 (MRP3). METHODS: Genomic DNA samples from 103 Caucasians were systematically screened for genetic variations to find a potential relationship with hepatic MRP3 expression. Sequencing comprised all 31 exons, approximately 100 bp of the flanking intronic regions and 2 kb of the 5' UTR. RESULTS: In total, 51 mutations were identified. Fifteen SNPs were located in the coding exons of MRP3, six of which are nonsynonymous mutations. SNPs 39G>C (allele frequency: 0.5%, located in exon 1), 202C>T (1.6%, exon 2), 1037C>T (0.5%, exon 9), 1537C>A (0.5%, exon 12), 3890G>A (5.2%, exon 27) and 4267G>A (0.6%, exon 29) resulted in Lys13Asn, His68Tyr, Ser346Phe, Gln513Lys, Arg1297His and Gly1423Arg amino acid substitutions, respectively. A splice site mutation (1339-1G>T) was found at the intron 10-exon 11 boundary. To evaluate, whether mutations in the MRP3 gene correlate with human hepatic MRP3 expression, we analyzed the genetic variants in Caucasian liver samples, whose MRP3 mRNA (n = 84) and protein (n = 50) expression has been determined by real time quantitative PCR and Western Blot, respectively. We found a significant correlation of a polymorphism in the 5' promoter region (-211C>T) of MRP3 with mRNA expression. Individuals homozygous and heterozygous for the -211C>T promoter polymorphism had significantly lower MRP3 transcript levels compared to wild-type individuals (P < 0.05). Accordingly, electrophoretic mobility shift assay demonstrated that -211C>T polymorphism affected the binding of nuclear factors. CONCLUSIONS: Multiple genetic polymorphisms of MRP3 exist in Caucasians. The -211C>T promoter polymorphism appears to be associated with altered hepatic MRP3 mRNA expression.

Alternative Splicing↗

PubMed2004

Variable expression of P-glycoprotein in the human placenta and its association with mutations of the multidrug resistance 1 gene (MDR1, ABCB1).

The MDR1 gene product P-glycoprotein in the human placenta is important for protecting the fetus from unintended, harmful drug exposure, but also for limiting the access of therapeutic drugs to the fetus after maternal drug intake. A polymorphism in exon 26 of the MDR1 gene (C3435T) has previously been shown to be associated with reduced P-glycoprotein expression in the small intestine, kidney and lymphocytes. In the present study, we examined systematically whether MDR1 polymorphisms also have an impact on P-glycoprotein expression in the human placenta. MDR1 mRNA and P-glycoprotein were analysed in 73 full-term human placentas of Caucasians, as well as respective MDR1 genotypes/haplotypes, for the C3435T and G2677T/A polymorphisms of mothers and infants. MDR1 mRNA levels were not different between these genotype groups. However, P-glycoprotein expression was significantly lower when both mother and infant were homozygous for the 3435T allele (TT/tt) compared to maternal and fetal homozygotes for the C-allele (0.40 +/- 0.18 a.u. for TT/tt versus 0.66 +/- 0.30 a.u. for CC/cc, P = 0.01). Moreover, placentas from mothers carrying both polymorphisms (3435T and 2677T; TT/TT) also had a significantly lower P-glycoprotein expression (0.31 +/- 0.12 a.u.) compared to placentas of wild-type individuals (CC/GG, 0.71 +/- 0.31 a.u., P = 0.02). Taken together, the MDR1 polymorphisms C3435T and G2677T are associated with altered P-glycoprotein expression in the human placenta, and may have clinical consequences due to genetically determined, variable drug exposure of the fetus.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2004

Identification of budesonide and prednisone as substrates of the intestinal drug efflux pump P-glycoprotein.

Steroid resistance is a major problem in the management of patients with inflammatory bowel disease. In Crohn disease, poor response to corticosteroids has been related to increased expression of the drug efflux pump, P-glycoprotein. However, it has not been investigated thoroughly whether corticosteroids commonly used for drug therapy in inflammatory bowel disease are substrates of P-glycoprotein. We tested the hypothesis that budesonide and prednisone are substrates of P-glycoprotein thereby possibly contributing to variable therapeutic effects. Polarized, basal to apical transport of [3H]budesonide and [3H]prednisone was studied in monolayers of L-MDR1 cells (LLC-PK1 cells stably transfected with human MDR1 cDNA) and Caco-2 cells, both of which express P-glycoprotein in their apical membrane. Drug transport was measured during 4 hours at substrate concentrations of 5 microM. Net transport rates and permeability coefficients were calculated. Inhibition of P-glycoprotein-mediated transport across Caco-2 monolayers was determined after addition of the P-glycoprotein inhibitor PSC-833. The net transport rate from the basolateral to the apical side was significantly higher in L-MDR1 than in LLC-PK1 cells for both budesonide and prednisone. Apparent permeability coefficients of budesonide and prednisone reflected polarized transport from basal to apical. PSC-833 inhibited the polarized transport of both corticosteroids. In conclusion, budesonide and prednisone were identified as substrates of the intestinal drug efflux pump, P-glycoprotein. Therefore, drug secretion via P-glyco-protein into gut lumen might play a more important role in pharmacokinetics and pharmacodynamics of these corticosteroids than currently appreciated in gastroenterological practice.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2004

High plasma pravastatin concentrations are associated with single nucleotide polymorphisms and haplotypes of organic anion transporting polypeptide-C (OATP-C, SLCO1B1).

This study aimed to characterize possible relationships between polymorphisms in the drug transporter genes organic anion transporting polypeptide-C (OATP-C, SLCO1B1), OATP-B (SLCO2B1), multidrug resistance-associated protein 2 (MRP2, ABCC2) and multidrug resistance transporter (MDR1, ABCB1) and the pharmacokinetics of pravastatin. We studied 41 healthy Caucasian volunteers who had previously participated in pharmacokinetic studies with pravastatin. Six volunteers had a very high pravastatin AUC value and were defined as outliers according to statistical criteria. The OATP-C gene was sequenced completely in all subjects, and they were also genotyped for selected single nucleotide polymorphisms (SNP) in the OATP-B, MDR1 and MRP2 genes. Of the six outliers, five were heterozygous for the OATP-C 521T>C (Val174Ala) SNP (allele frequency 42%) and three were heterozygous for a new SNP in the promoter region of OATP-C (-11187G>A, allele frequency 25%). Among the remaining 35 subjects, two were homozygous and six were heterozygous carriers of the 521T>C SNP (allele frequency 14%, P = 0.0384 versus outliers) and three were heterozygous carriers of the -11187G>A SNP (allele frequency 4%, P = 0.0380 versus outliers). In subjects with the -11187GA or 521TC genotype, the mean pravastatin AUC0-12 was 98% (P = 0.0061) or 106% (P = 0.0034) higher, respectively, compared to subjects with the reference genotype. These results were substantiated by haplotype analysis. In heterozygous carriers of *15B (containing the 388A>G and 521T>C variants), the mean pravastatin AUC0-12 was 93% (P = 0.024) higher compared to non-carriers and, in heterozygous carriers of *17 (containing the -11187G>A, 388A>G and 521T>C variants), it was 130% (P = 0.0053) higher compared to non-carriers. No significant associations were found between OATP-B, MRP2 or MDR1 polymorphisms and the pharmacokinetics of pravastatin. These results suggest that haplotypes are more informative in predicting the OATP-C phenotype than single SNPs.

Adult↗

PubMed2004

Lipid-lowering response to statins is affected by CYP3A5 polymorphism.

Individuals expressing the polymorphic CYP3A5 enzyme might show a more than average efficiency in the metabolism of lovastatin, simvastatin and atorvastatin. We studied whether the expression of CYP3A5 is associated with an impaired lipid-lowering response to statins in 69 Caucasian patients. Lovastatin, simvastatin and atorvastatin were significantly less effective in CYP3A5 expressors than in non-expressors. The mean serum total cholesterol concentration at 1 year was 23% higher (P = 0.0014) and the mean serum low-density lipoprotein cholesterol concentration was 24% higher (P = 0.036) in subjects possessing the CYP3A5*1 allele (CYP3A5 expressors, n = 7) than in subjects homozygous for the CYP3A5*3 allele (non-expressors, n = 39). The mean percentage reduction in serum total cholesterol from baseline was significantly smaller in CYP3A5 expressors than in non-expressors (17% versus 31%, P = 0.026). No association between hypolipidemic efficacy and CYP3A5 polymorphism was observed among 23 subjects taking statins that are not dependent on CYP3A5 (fluvastatin, pravastatin). These findings suggest that CYP3A5 may be a genetic determinant of interindividual differences in response to certain statins.

Aged↗

PubMed2004

Functional interaction of intestinal CYP3A4 and P-glycoprotein.

Intestinal CYP3A4-mediated biotransformation and active efflux of absorbed drug by P-glycoprotein are major determinants of bioavailability of orally administered drugs. The hypothesis that CYP3A4 and P-glycoprotein may act in concert to limit oral drug bioavailability is attractive from a theoretical point of view. Evidence in support of such an interplay between CYP3A4 and P-glycoprotein comes mainly from a limited number of in vitro and animal studies. Obviously, it is a challenging task to demonstrate in vivo in humans that the function of CYP3A4 and P-glycoprotein in enterocytes is complementary, and results to directly support this concept remain elusive. However, CYP3A4 and P-glycoprotein are clearly an integral part of an intestinal defence system to protect the body against harmful xenobiotics, and drugs that are substrates of both proteins often have a low bioavailability after oral administration. The functional interaction of intestinal CYP3A4 and P-glycoprotein warrants additional study. Further understanding this interplay would be potentially useful during drug development to solve bioavailability problems of new drug entities.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Celecoxib inhibits metabolism of cytochrome P450 2D6 substrate metoprolol in humans.

OBJECTIVE: In vitro data have shown that celecoxib inhibits the metabolism of cytochrome P450 (CYP) 2D6 substrates. However, very limited data are available on the influence of cyclooxygenase 2 inhibitors on the disposition of CYP2D6 substrates in humans. Therefore the objective of this study was to examine the effect of celecoxib and rofecoxib on the pharmacokinetics of the clinically relevant CYP2D6 substrate metoprolol. METHODS: An open, randomized, 3-period crossover study was performed in 12 healthy male volunteers. Metoprolol (50 mg) was given in all 3 periods without or after 7 days of pretreatment with celecoxib (200 mg twice daily) or rofecoxib (25 mg daily) to achieve steady-state conditions of cyclooxygenase 2 inhibitors in periods 2 and 3. RESULTS: Celecoxib significantly increased the area under the plasma concentration-time curve of metoprolol from 271 to 414 micro g. h/L (64% +/- 57%, P <.001) and by more than 200% in 1 volunteer. The extent of this drug interaction was more pronounced in volunteers with 2 fully functional alleles compared with volunteers with 1 fully functional allele (103% +/- 75% versus 36% +/- 23%, P <.05). After administration of celecoxib, the area under the plasma concentration-time curve from 0 to 24 hours of alpha-hydroxymetoprolol decreased significantly from 474 to 387 micro g. h/L (P <.01). Rofecoxib caused no significant effects on the pharmacokinetics of metoprolol. CONCLUSION: We conclude that celecoxib inhibits the metabolism of the CYP2D6 substrate metoprolol but that rofecoxib does not. Clinically relevant drug interaction may occur between celecoxib and CYP2D6 substrates, particularly those with a narrow therapeutic index.

Adrenergic beta-Antagonists↗

PubMed2003

Association between the C3435T MDR1 gene polymorphism and susceptibility for ulcerative colitis.

BACKGROUND & AIMS: The human multidrug resistance 1 (MDR1) gene product P-glycoprotein is highly expressed in intestinal epithelial cells, where it constitutes a barrier against xenobiotics. The finding that mdr1a knockout mice develop a form of colitis that is similar to ulcerative colitis, which can be prevented by antibiotics, indicates a barrier function for P-glycoprotein against the invasion of bacteria or toxins. Because the MDR1 single nucleotide polymorphism C3435T is associated with lower intestinal P-glycoprotein expression, we tested whether this polymorphism predisposes to development of ulcerative colitis. METHODS: Allele frequencies and genotype distributions of the C3435T single nucleotide polymorphism were investigated in 149 patients with ulcerative colitis, 126 patients with Crohn's disease, and sex-matched healthy controls. RESULTS: Significantly increased frequencies of the 3435T allele and the 3435TT genotype were observed in patients with ulcerative colitis compared with controls (3435T: P = 0.049; odds ratio, 1.4; 95% confidence interval, 1.02-1.94; 3435TT: P = 0.045; odds ratio, 2.03; 95% confidence interval, 1.04-3.95). In contrast, frequencies of the T allele and the TT genotype were the same in patients with Crohn's disease as in controls (P = 0.66 and P = 0.59, respectively). In comparison to 998 non-sex-matched controls, the effect for the TT genotype in ulcerative colitis patients was more pronounced (P = 0.0055; odds ratio, 2.1). CONCLUSIONS: The higher frequency of the 3435TT genotype in patients with ulcerative colitis corroborates the findings from the mdr1a knockout mice. The results support the notion that P-glycoprotein plays a major role in the defense against intestinal bacteria or toxins. Impairment of barrier function in 3435TT subjects could render this genotype more susceptible to the development of ulcerative colitis.

Adolescent↗

PubMed2003

P-glycoprotein-mediated intestinal and biliary digoxin transport in humans.

BACKGROUND AND AIMS: Intestinal transport by P-glycoprotein is a recently recognized determinant of drug disposition. However, direct measurements of transporter-mediated drug elimination into isolated segments of human small intestine are lacking. METHODS: Using a recently developed intestinal perfusion catheter, we perfused in healthy volunteers two 20-cm jejunal segments with and without the P-glycoprotein inhibitor quinidine before and during administration of the P-glycoprotein inducer rifampin (INN, rifampicin). RESULTS: Within 3 hours after intravenous administration of digoxin (1 mg), perfusate samples were collected. We found that 0.45% +/- 0.24% and 0.83% +/- 0.60% of the digoxin dose were eliminated into a jejunal segment and into bile, respectively. Perfusion of the isolated segment with quinidine reduced intestinal digoxin elimination (0.23% +/- 0.08%, P =.031). During rifampin, intestinal digoxin elimination was 0.80 +/- 0.59 (P =.383). Enterocyte P-glycoprotein content correlated with the area under the plasma concentration-time curve of digoxin (Spearman nonparametric correlation coefficient [r(S)] = -0.73, P =.003) and digoxin nonrenal clearance (r(S) = 0.52, P =.056), as well as with intraluminal and plasma concentrations of quinidine (r(S) = 0.55, P =.041 and r(S) = -0.67, P =.009, respectively). CONCLUSION: Using segmental intestinal perfusion, we provide direct evidence that intestinal P-glycoprotein mediates substantial drug elimination after intravenous administration from the systemic circulation into the gut lumen and prevents entry of luminally administered P-glycoprotein substrates into the enterocytes. These data also highlight the relative importance of direct intestinal drug secretion in comparison with drug elimination through bile.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Differential expression and function of CYP2C isoforms in human intestine and liver.

This study aimed to characterize the intestinal and hepatic expression and function of CYP2C enzymes in the same set of subjects. CYP2C isoform-specific quantitative reverse transcription-polymerase chain reaction assays, Western immunoblotting and marker reactions of CYP2C8, CYP2C9 and CYP2C19 activities were employed to investigate expression and activity of the CYP2C isoforms in samples of small intestine and liver obtained from 15 patients undergoing gastrectomy or pancreatoduodenectomy. The rank order for CYP2C mRNA expression in the intestine was CYP2C9 = CYP2C18 > CYP2C19 > CYP2C8, whereas that in the liver was CYP2C9 > CYP2C8 > CYP2C18 > CYP2C19. The rank order for expression of CYP2C protein in the intestine was CYP2C9 > CYP2C19 > CYP2C8 (content below limit of quantification) > CYP2C18 (not detected) and that in the liver was CYP2C9 > CYP2C8 > CYP2C19 > CYP2C18 (not detected). The CYP2C9 protein content was approximately 10-fold higher in the liver than in the intestine (P < 0.001). The CLint for the formation of D-703 from verapamil (marker of CYP2C8 activity) was 7.6-fold higher (P < 0.001) and that for the diclofenac 4'-hydroxylation (marker of CYP2C9 activity) was 6.1-fold higher (P < 0.001) in the liver than in the intestine. Apart from a borderline positive correlation (r = 0.58, P = 0.0504) between the intestinal and hepatic CLint for the diclofenac 4'-hydroxylation, no intra-individual relationships between these tissues with respect to expression or activity of different CYP2C isoforms were found. Collectively, these results show that CYP2C8, CYP2C9 and CYP2C19 are expressed as functional enzymes in the human small intestine, and further suggest that CYP2C genes are independently regulated in human intestine and liver. Although, overall, the expression and activity of CYP2C enzymes is lower in the gut than in the liver, the surface area of the proximal small intestine is large and intestinal CYP2C9 and CYP2C19 may well contribute to the first-pass metabolism of their substrate drugs.

Adult↗

PubMed2003

Influence of omeprazole on multidrug resistance protein 3 expression in human liver.

Multidrug resistance protein (MRP) 3 transports bile salts and conjugated xenobiotics from cells (hepatocytes and enterocytes) into the blood. Hepatic MRP3 expression is low under normal conditions but is markedly up-regulated during cholestasis. Since little is known about additional factors increasing human hepatic MRP3 expression, we investigated the variability of MRP3 expression in a large collection of human livers and factors contributing to variable MRP3 expression in liver and HepG2 cells. MRP3 was measured in 62 human livers from patients with and without omeprazole treatment and in HepG2 cells with and without omeprazole or beta-naphthoflavone treatment. Livers of patients treated with omeprazole showed 4.8-fold (P < 0.0001) higher MRP3 protein expression compared with the remainder of the population. Accordingly, MRP3 mRNA and protein were induced 2.4- and 1.8-fold, respectively (P < 0.01 and P < 0.05), in HepG2 cells treated with omeprazole. Finally, MRP3 was induced in HepG2 cells by beta-naphthoflavone. In summary, treatment with omeprazole and beta-naphthoflavone is a determinant of variable human hepatic MRP3 expression.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2003

Pharmacokinetic interactions with rifampicin : clinical relevance.

The antituberculosis drug rifampicin (rifampin) induces a number of drug-metabolising enzymes, having the greatest effects on the expression of cytochrome P450 (CYP) 3A4 in the liver and in the small intestine. In addition, rifampicin induces some drug transporter proteins, such as intestinal and hepatic P-glycoprotein. Full induction of drug-metabolising enzymes is reached in about 1 week after starting rifampicin treatment and the induction dissipates in roughly 2 weeks after discontinuing rifampicin. Rifampicin has its greatest effects on the pharmacokinetics of orally administered drugs that are metabolised by CYP3A4 and/or are transported by P-glycoprotein. Thus, for example, oral midazolam, triazolam, simvastatin, verapamil and most dihydropyridine calcium channel antagonists are ineffective during rifampicin treatment. The plasma concentrations of several anti-infectives, such as the antimycotics itraconazole and ketoconazole and the HIV protease inhibitors indinavir, nelfinavir and saquinavir, are also greatly reduced by rifampicin. The use of rifampicin with these HIV protease inhibitors is contraindicated to avoid treatment failures. Rifampicin can cause acute transplant rejection in patients treated with immunosuppressive drugs, such as cyclosporin. In addition, rifampicin reduces the plasma concentrations of methadone, leading to symptoms of opioid withdrawal in most patients. Rifampicin also induces CYP2C-mediated metabolism and thus reduces the plasma concentrations of, for example, the CYP2C9 substrate (S)-warfarin and the sulfonylurea antidiabetic drugs. In addition, rifampicin can reduce the plasma concentrations of drugs that are not metabolised (e.g. digoxin) by inducing drug transporters such as P-glycoprotein. Thus, the effects of rifampicin on drug metabolism and transport are broad and of established clinical significance. Potential drug interactions should be considered whenever beginning or discontinuing rifampicin treatment. It is particularly important to remember that the concentrations of many of the other drugs used by the patient will increase when rifampicin is discontinued as the induction starts to wear off.

Drug Interactions↗

PubMed2002

Genetically determined differences in P-glycoprotein function: implications for disease risk.

The MDR1 gene product P-glycoprotein does not only contribute to drug resistance during chemotherapy of tumors but it is also expressed in healthy tissues with excretory function (intestine, liver and kidney). It transports a wide range of structurally unrelated compounds out of cells. Intestinal expression of this transporter has been shown to determine bioavailability of orally administered P-glycoprotein substrates such as digoxin. Recently, several mutations were found in the MDR1 gene. Subjects homozygous for the C3435T mutation (24% of Caucasians) have low intestinal P-glycoprotein levels, high plasma concentrations after oral digoxin and a reduced P-glycoprotein function in peripheral blood cells in comparison to the remainder of the population. Potential implications of this reduced mechanism of detoxification will be shown for three selected diseases: (1) association of low intestinal P-glycoprotein expression with development of inflammatory bowel disease; (2) implications for disease risk and therapeutic outcome of HIV; and (3) consequences of this mutation for renal P-glycoprotein expression and risk of renal cell carcinoma.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2002

The influence of MDR1 polymorphisms on P-glycoprotein expression and function in humans.

The MDR1 (ABCB1) gene product P-glycoprotein is a membrane protein, which functions as an ATP-dependent exporter of xenobiotics from cells. Its importance was first recognized because of its role in the development of multidrug resistance (MDR) of cultured tumor cells against various anticancer agents. It is now, however, well established that this transporter is not only expressed in tumor cells, but also in normal tissues with excretory function (intestine, liver, kidney). Since P-glycoprotein has a very broad substrate specificity, it determines disposition of a broad variety of drugs. Moreover, induction and inhibition of P-glycoprotein are new mechanisms for drug interactions in humans. Very recently, systematic screens of the MDR1 gene have identified multiple single nucleotide polymorphisms. Some of those appear to be associated with altered transporter function and expression. This review discusses the currently available data on the influence of MDR1 polymorphisms on P-glycoprotein tissue expression, drug disposition, treatment outcome and disease risk.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2002

Pharmacokinetics of intravenous etoposide in patients with breast cancer: influence of dose escalation and cyclophosphamide and doxorubicin coadministration.

This study investigates the impact of dose escalation and of doxorubicin and cyclophosphamide coadministration on the pharmacokinetics of etoposide (ETO). Pharmacokinetics of ETO were analyzed in seven patients with breast cancer receiving 3-4 cycles of conventional-dose (CD) and one final course of high-dose (HD) chemotherapy including ETO (450 mg/m(2) and 2100 mg/m(2), respectively, fractionated over 3 consecutive days). ETO was given as monoinfusion apart from day 1 of CD, where cyclophosphamide and doxorubicin were coadministered. Plasma samples obtained on day 1 and day 2 of CD- and HD-therapy, respectively, were analyzed for ETO by HPLC. Data from a total of 25 cycles of CD- and 7 cycles of HD-therapy are given as means +/- SD for CD-day 1, CD-day 2, HD-day 1 and HD-day 2, respectively. Following administration of 210+/-29, 278+/-41, 1143+/-79 and 1143+/-79 mg ETO, the AUC (0-24 h, normalized to 150 mg/m(2)) was 123+/-23, 113+/-22, 92+/-11 and 100+/-22 microgxh/ml. The AUC and CL of single-agent ETO were not significantly different between CD (day 2) and both days of HD ETO. However, we observed a modest but significant difference for AUC and CL between day 1 of CD (coadministration of doxorubicin and cyclophosphamide) and day 2 of CD (ETO monoinfusion), the AUC and CL being 9% higher (see above) and 10% lower (21.1 vs. 23.3 ml/minxm(2)) ( P<0.05), respectively, on day 1. The fraction of unbound ETO was similar on all occasions (range: 5.5%-6.6%). Interpatient variability for AUC and CL during CD-therapy was moderate with coefficients of variation (CV) of 17%-20%, while intraindividual variability was comparatively high and almost in the same range (CV of 13%-16%). Pharmacokinetics of etoposide were not significantly altered following fivefold dose escalation in the same patients. A 10% decrease in systemic clearance of etoposide was observed during doxorubicin and cyclophosphamide coadministration, which could result from drug interactions affecting renal and/or metabolic elimination of etoposide. The magnitude of the decrease, however, is unlikely to be of clinical significance.

Adult↗

PubMed2002

Molecular mechanisms of polymorphic CYP3A7 expression in adult human liver and intestine.

Human CYP3A enzymes play a pivotal role in the metabolism of many drugs, and the variability of their expression among individuals may have a strong impact on the efficacy of drug treatment. However, the individual contributions of the four CYP3A genes to total CYP3A activity remain unclear. To elucidate the role of CYP3A7, we have studied its expression in human liver and intestine. In both organs, expression of CYP3A7 mRNA was polymorphic. The recently identified CYP3A7*1C allele was a consistent marker of increased CYP3A7 expression both in liver and intestine, whereas the CYP3A7*1B allele was associated with increased CYP3A7 expression only in liver. Because of the replacement of part of the CYP3A7 promoter by the corresponding region of CYP3A4, the CYP3A7*1C allele contains the proximal ER6 motif of CYP3A4. The pregnane X and constitutively activated receptors were shown to bind with higher affinity to CYP3A4-ER6 than to CYP3A7-ER6 motifs and transactivated only promoter constructs containing CYP3A4-ER6. Furthermore, we identified mutations in CYP3A7*1C in addition to the ER6 motif that were necessary only for activation by the constitutively activated receptor. We conclude that the presence of the ER6 motif of CYP3A4 mediates the high expression of CYP3A7 in subjects carrying CYP3A7*1C.

Adult↗

PubMed2002

Determination of fexofenadine in human plasma and urine by liquid chromatography-mass spectrometry.

A sensitive method was developed to determine fexofenadine in human plasma and urine by HPLC-electrospray mass spectrometry with MDL 026042 as internal standard. Extraction was carried out on C18 solid-phase extraction cartridges. The mobile phases used for HPLC were: (A) 12 mM ammonium acetate in water and (B) acetonitrile. Chromatographic separation was achieved on a LUNA CN column (10 cm x 2.0 mm I.D., particle size 3 microm) using a linear gradient from 40% B to 60% B in 10 min. The mass spectrometer was operated in the selected ion monitoring mode using the respective MH+ ions, m/z 502.3 for fexofenadine and m/z 530.3 for the internal standard. The limit of quantification achieved with this method was 0.5 ng/ml in plasma and 1.0 ng in 50 microl of urine. The method described was successfully applied to the determination of fexofenadine in human plasma and urine in pharmacokinetic studies.

Chromatography, High Pressure Liquid↗

PubMed2002

Genetic polymorphisms of the human MDR1 drug transporter.

P-glycoprotein is an ATP-dependent efflux pump that contributes to the protection of the body from environmental toxins. It transports a huge variety of structurally diverse compounds. P-glycoprotein is involved in limiting absorption of xenobiotics from the gut lumen, in protection of sensitive tissues (brain, fetus, testis), and in biliary and urinary excretion of its substrates. P-glycoprotein can be inhibited or induced by xenobiotics, thereby contributing to variable drug disposition and drug interactions. Recently, several SNPs have been identified in the MDR1 gene, some of which can affect P-glycoprotein expression and function. Potential implications of MDR1 polymorphisms for drug disposition, drug effects, and disease risk are discussed.

ATP Binding Cassette Transporter, Subfamily B, Mem↗