Dorota Tomalik-Scharte

Should We Use N-Acetyltransferase Type 2 Genotyping To Personalize Isoniazid Doses?

ABSTRACT Isoniazid is metabolized by the genetically polymorphic arylamine N-acetyltransferase type 2 (NAT2). A greater number of high-activity alleles are related to increased acetylation capacity and in some reports to low efficacy and toxicity of isoniazid. The objective of this study was to assess individual isoniazid exposure based on NAT2 genotype to predict a personalized therapeutic dose. Isoniazid was administered to 18 healthy Caucasians (age 30 ± 6 years, body weight 74 ± 10 kg, five women) in random order as a 200-mg infusion, a 100-mg oral, and a 300-mg oral single dose. For the assessment of NAT2 genotype, common single nucleotide polymorphisms identifying 99.9% of variant alleles were characterized. Noncompartmental pharmacokinetics and compartmental population pharmacokinetics were estimated from isoniazid plasma concentrations until 24 h postdose by high-pressure liquid chromatography. The influence of NAT2 genotype, drug formulation, body weight, and sex on dose-normalized isoniazid pharmacokinetics was assessed by analysis of variance from noncompartmental data and confirmed by population pharmacokinetics. Eight high-activity NAT2*4 alleles were identified. Sex had no effect; the other factors explained 93% of the variability in apparent isoniazid clearance (analysis of variance). NAT2 genotype alone accounted for 88% of variability. Individual isoniazid clearance could be predicted as clearance (liters/hour) = 10 + 9 × (number of NAT2*4 alleles). To achieve similar isoniazid exposure, current standard doses presumably appropriate for patients with one high-activity NAT2 allele may be decreased or increased by approximately 50% for patients with no or two such alleles, respectively. Prospective clinical trials are required to assess the merits of this approach.

Pharmacokinetics and pharmacodynamics of rosiglitazone in relation to CYP2C8 genotype.

Rosiglitazone is metabolically inactivated predominantly via the cytochrome P450 (CYP) enzyme CYP2C8. The functional impact of the CYP2C8*3 allele coding for the Arg139Lys and Lys399Arg amino acid substitutions is controversial. The purpose of this was to clarify the role of this polymorphism with regard to the pharmacokinetics and clinical effects of rosiglitazone.

Toxicokinetics of Acrylamide in Humans after Ingestion of a Defined Dose in a Test Meal to Improve Risk Assessment for Acrylamide Carcinogenicity

High amounts of acrylamide in some foods result in an estimated daily mean intake of 50 μg for a western style diet. Animal studies have shown the carcinogenicity of acrylamide upon oral exposure. However, only sparse human toxicokinetic data is available for acrylamide, which is needed for the extrapolation of human cancer risk from animal data. We evaluated the toxicokinetics of acrylamide in six young healthy volunteers after the consumption of a meal containing 0.94 mg of acrylamide. Urine was collected up to 72 hours thereafter. Unchanged acrylamide, its mercapturic acid metabolite N-acetyl-S-(2-carbamoylethyl)cysteine (AAMA), its epoxy derivative glycidamide, and the respective metabolite of glycidamide, N-acetyl-S-(2-hydroxy-2-carbamoylethyl)cysteine (GAMA), were quantified in the urine by liquid chromatography-mass spectrometry. Toxicokinetic variables were obtained by noncompartmental methods. Overall, 60.3 ± 11.2% of the dose was recovered in the urine. Although no glycidamide was found, unchanged acrylamide, AAMA, and GAMA accounted for urinary excretion of (mean ± SD) 4.4 ± 1.5%, 50.0 ± 9.4%, and 5.9 ± 1.2% of the dose, respectively. Apparent terminal elimination half-lives for the substances were 2.4 ± 0.4, 17.4 ± 3.9, and 25.1 ± 6.4 hours. The ratio of GAMA/AAMA amounts excreted was 0.12 ± 0.02. In conclusion, most of the acrylamide ingested with food is absorbed in humans. Conjugation with glutathione exceeds the formation of the reactive metabolite glycidamide. The data suggests an at least 2-fold and 4-fold lower relative internal exposure for glycidamide from dietary acrylamide in humans compared with rats or mice, respectively. This should be considered for quantitative cancer risk assessment. (Cancer Epidemiol Biomarkers Prev 2006;15(2):266–71)

Absorption, Pharmacokinetics, and Safety of Triclosan after Dermal Administration

ABSTRACT We evaluated the pharmacokinetics and safety of the antimicrobial agent triclosan after dermal application of a 2% triclosan-containing cream to six volunteers. Percutaneous absorption calculated from urinary excretion was 5.9% ± 2.1% of the dose (mean ± standard deviation). The amount absorbed suggests that daily application of a standard adult dose would result in a systemic exposure 890 times lower than the relevant no-observed-adverse-effect level. Triclosan can be considered safe for use in hydrophobic creams.

In vivo Role of Cytochrome P450 2E1 and Glutathione-S-Transferase Activity for Acrylamide Toxicokinetics in Humans

Acrylamide, a potential food carcinogen in humans, is biotransformed to the epoxide glycidamide in vivo. Both acrylamide and glycidamide are conjugated with glutathione, possibly via glutathione-S-transferases (GST), and bind covalently to proteins and nucleic acids. We investigated acrylamide toxicokinetics in 16 healthy volunteers in a four-period change-over trial and evaluated the respective role of cytochrome P450 2E1 (CYP2E1) and GSTs. Participants ingested self-prepared potato chips containing acrylamide (1 mg) without comedication, after CYP2E1 inhibition (500 mg disulfiram, single dose) or induction (48 g/d ethanol for 1 week), and were phenotyped for CYP2E1 with chlorzoxazone (250 mg, single dose). Unchanged acrylamide and the mercapturic acids N-acetyl-S-(2-carbamoylethyl)-cysteine (AAMA) and N-acetyl-S-(2-hydroxy-2-carbamoylethyl)-cysteine (GAMA) accounted for urinary excretion [geometric mean (percent coefficient of variation)] of 2.9% (42), 65% (23), and 1.7% (65) of the acrylamide dose in the reference period. Hemoglobin adducts increased clearly following the acrylamide test-meal. The cumulative amounts of acrylamide, AAMA, and GAMA excreted and increases in AA adducts changed significantly during CYP2E1 blockade [point estimate (90% confidence interval)] to the 1.34-fold (1.14-1.58), 1.18-fold (1.02-1.36), 0.44-fold (0.31-0.61), and 1.08-fold (1.02-1.15) of the reference period, respectively, but were not changed significantly during moderate CYP2E1 induction. Individual baseline CYP2E1 activity, CYP2E1*6, GSTP1 313A>G and 341T>C single nucleotide polymorphisms, and GSTM1-and GSTT1-null genotypes had no major effect on acrylamide disposition. The changes in acrylamide toxicokinetics upon CYP2E1 blockade provide evidence that CYP2E1 is a major but not the only enzyme mediating acrylamide epoxidation in vivo to glycidamide in humans. No obvious genetic risks or protective factors in xenobiotic-metabolizing enzymes could be determined for exposed subjects. (Cancer Epidemiol Biomarkers Prev 2009;18(2):433–43)

Plasma 4β-Hydroxycholesterol: An Endogenous CYP3A Metric?

We assessed the suitability of 4β‐hydroxycholesterol (4βOH‐C) as an endogenous cytochrome P450 3A (CYP3A) phenotyping metric. 4βOH‐C and its ratio to cholesterol (4βOH‐C/C) were determined in five cocktail phenotyping studies, with and without co‐medication with a potential CYP3A inhibitor. These parameters were compared with established midazolam‐based CYP3A metrics: clearance after intravenous (i.v.) administration (M‐Cl) and apparent clearance after oral administration (M‐Cl/F), reflecting hepatic and overall activity, respectively. In a common evaluation of periods without co‐medication, there was a slight positive correlation of 4βOH‐C and 4βOH‐C/C with midazolam metrics: M‐Cl (r = 0.239 and 0.348, respectively) and M‐Cl/F (r = 0.267 and 0.353, respectively); P (one‐sided) < 0.05. Co‐medication with lopinavir/ritonavir caused a strong decrease in midazolam metrics and a mild decrease in cholesterol metrics. However, the intake of propiverine resulted in opposite trends for midazolam‐based and cholesterol‐based metrics. The information currently available does not justify the use of 4βOH‐C for estimation of basal CYP3A activity. Further studies to address the temporal variations in local CYP3A activity are needed to assess its role as a biomarker during CYP3A inhibition.

Effect of propiverine on cytochrome P450 enzymes: a cocktail interaction study in healthy volunteers*

The present study was conducted to assess a possible in vivo effect of propiverine, an anticholinergic drug to treat urinary incontinence and related disorders, on the activity of intestinal CYP3A4 and of hepatic CYP3A4, CYP2C9, CYP2C19, and CYP1A2. The activity of the respective cytochromes P450 was measured using the following metrics of selective substrates given as a tailored low-dose phenotyping cocktail: intestinal availability of midazolam (2 mg orally), clearance of midazolam (1 mg i.v.), apparent clearance of tolbutamide (125 mg orally), urinary excretion of 4′-hydroxymephenytoin 0 to 8 h postdose (50 mg of mephenytoin orally), and the paraxanthine/caffeine plasma ratio 6 h postdose (150 mg of caffeine orally). These metrics were determined in 16 healthy young men at the end of 7 days of treatment with 15 mg of propiverine (test) or placebo (reference) twice daily. All phenotyping drugs were quantified by liquid chromatography-tandem mass spectrometry. Chronic propiverine treatment reduced hepatic and intestinal CYP3A4 activity slightly to 0.89-fold and 0.80-fold, respectively [90% confidence interval (CI) for test/reference ratios 0.85–0.93 and 0.72–0.89], with the combined effect resulting in a 1.46-fold increase in area under the curve of oral midazolam (90% CI 1.36–1.57). Propiverine had no relevant effect on CYP2C9, CYP2C19, and CYP1A2 (90% CI for test/reference ratios 0.93–1.00, 0.84–0.96, and 0.97–1.07, respectively). All study drugs were well tolerated. In conclusion, propiverine has a minor potential to cause drug-drug interactions.

Pharmacokinetic/Pharmacodynamic Modeling of Biomarker Response to Sunitinib in Healthy Volunteers

A pharmacokinetic/pharmacodynamic (PK/PD) study of the tyrosine kinase inhibitor sunitinib was conducted in 12 healthy volunteers using blood pressure and circulating biomarker levels as PD markers. Blood pressure was measured, and plasma concentration–time courses of sunitinib, its major metabolite SU12662, vascular endothelial growth factors VEGF‐A and VEGF‐C, and soluble VEGF receptor‐2 (sVEGFR‐2) were studied in healthy subjects receiving 50 mg of sunitinib orally for 3–5 consecutive days. Using NONMEM, PK/PD models were established that predicted changes (expressed as multiples relative to baseline values) in systolic blood pressure, diastolic blood pressure, VEGF‐A level, and sVEGFR‐2 level, of 1.10, 1.18, 2.24, and 0.76, respectively, for a typical subject after 4 weeks of treatment with 50 mg/day. Simulated blood pressure–time courses compare excellently with published data in patients, whereas changes in circulating biomarkers were greater in patients than simulations suggest for healthy subjects. In conclusion, the tumor‐independent pharmacological response to sunitinib could be described by PK/PD models, thereby facilitating model‐based investigations with antiangiogenic drugs, using blood pressure and circulating proteins as biomarkers.

Assessment of Activity Levels for CYP2D6*1, CYP2D6*2, and CYP2D6*41 Genes by Population Pharmacokinetics of Dextromethorphan

The pharmacokinetics of dextromethorphan (DM) is markedly influenced by cytochrome P450 2D6 (CYP2D6) enzyme polymorphisms. The aim of this study was to quantify the effects of the CYP2D6*1, *2, and *41 variants on DM metabolism in vivo and to identify other sources of pharmacokinetic variability. Concentrations of DM and dextrorphan (DO) in plasma and urine were evaluated in 36 healthy Caucasian men. These volunteers participated in three clinical studies and received a single oral dose of 30 mg DM‐HBr. Data were modeled simultaneously using the population pharmacokinetics NONMEM software. A five‐compartment model adequately described the data. The activity levels of the alleles assessed differed significantly. The clearance attributable to an individual CYP2D6*1 copy was 2.5‐fold higher as compared with CYP2D6*2 (5,010 vs. 2,020 l/h), whereas the metabolic activity of CYP2D6*41 was very low (85 l/h). Urinary pH was confirmed as a significant covariate for DM renal clearance. These results refine genotype‐based predictions of pharmacokinetics for DM and presumably for other CYP2D6 substrates as well.

Profiling of mercapturic acids of acrolein and acrylamide in human urine after consumption of potato crisps.

SCOPE Acrolein (AC) and acrylamide (AA) are food contaminants generated by heat treatment. We studied human exposure after consumption of potato crisps by monitoring excretion of mercapturic acids (MAs) in urine. METHODS AND RESULTS MA excretion was monitored in human urine collected up to 72 h after ingestion of a test meal of experimental (study 1: 1 mg AA/150 g) or commercially available (study 2: 44 μg AA plus 4.6 μg AC/175 g) potato crisps. MA contents were analysed after purification via SPE using HPLC-ESI-MS/MS. On the basis of the area under the curve values of MAs excreted in urine, the total excretion of AC-related MAs exceeded that of AA-related MAs up to 12 times in study 1 and up to four times in study 2. Remarkably, AC content of potato crisps of study 2 was found to be only about 1/10 the AA content, as determined by isotope dilution headspace GC/MS. CONCLUSION Our results indicate substantially higher exposure to AC from potato crisps than to AA. Total AC in such foods may encompass bioavailable AC forms not detected by headspace GC/MS. Both findings may also apply to other heat processed foods.