Interindividual Differences In Metabolism Research Articles

A genome-wide association study of 24-hour urinary excretion of endocrine disrupting chemicals

Ubiquitous exposure to environmental endocrine disrupting chemicals (EDCs) instigates a major public health problem, but much remains unknown on the inter-individual differences in metabolism and excretion of EDCs. To examine this we performed a two-stage genome-wide association study (GWAS) for 24-hour urinary excretions of four parabens, two bisphenols, and nine phthalate metabolites. Results showed five genome-wide significant (p-value < 5x10-8) and replicated single nucleotide polymorphisms (SNPs) representing four independent signals that associated with mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) and mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP). Three of the four signals were located on chromosome 10 in a locus harboring the cytochrome P450 (CYP) genes CYP2C9, CYP2C58P, and CYP2C19 (rs117529685, pMECPP = 5.38x10-25; rs117033379, pMECPP = 1.96x10-19; rs4918798, pMECPP = 4.01x10-71; rs7895726, pMEHHP = 1.37x10-15, r2 with rs4918798 = 0.93). The other signal was on chromosome 6 close to the solute carrier (SLC) genes SLC17A1, SLC17A3, SLC17A4, and SCGN (rs1359232, pMECPP = 7.6x10-16). These four SNPs explained a substantial part (8.3 % - 9.2 %) of the variance in MECPP in the replication cohort. Bioinformatics analyses supported a likely causal role of CYP2C9 and SLC17A1 in metabolism and excretion of MECPP and MEHHP. Our results provide biological insights into mechanisms of phthalate metabolism and excretion with a likely causal role for CYP2C9 and SLC17A1.

Metabolites of dietary atractyligenin glucoside in coffee drinkers' urine

Arabica roast coffee contains a substantial amount of water soluble atractyligenin-2-O-β-d-glucoside, which is ingested by consumption of coffee brew. Metabolomics data suggest this coffee compound is excreted as glucuronides, but the structures of conjugates have not been elucidated so far. We collected coffee drinkers’ urine and isolated four metabolites by MS-guided liquid chromatographic fractionation. The structures were investigated by nuclear magnetic resonance (NMR) and time-of-flight mass spectrometry (ToF-MS) and identified as atractyligenin-19-O-β-d-glucuronide (M1), 2β-hydroxy-15-oxoatractylan-4α-carboxy-19-O-β-d-glucuronide (M2), and 2β-hydroxy-15-oxoatractylan-4α-carboxylic acid-2-O-β-d-glucuronide (M3). An unconjugated metabolite (M4) was confirmed as atractyligenin. We analyzed spot urines from n = 6 coffee drinking individuals and detected the metabolites M1, M2 and M4 in every sample, and M3 in four out of six samples, suggesting interindividual differences in metabolism.

Influence of Glutathione-S-Transferase A1*B Allele on the Metabolism of the Aromatase Inhibitor, Exemestane, in Human Liver Cytosols and in Patients Treated With Exemestane.

Exemestane (EXE) is used to treat postmenopausal women diagnosed with estrogen receptor positive (ER+) breast cancer. A major mode of metabolism of EXE and its active metabolite, 17β-dihydroexemestane, is via glutathionylation by glutathione-S-transferase (GST) enzymes. The goal of the present study was to investigate the effects of genetic variation in EXE-metabolizing GST enzymes on overall EXE metabolism. Ex vivo assays examining human liver cytosols from 75 subjects revealed the GSTA1 *B*B genotype was associated with significant decreases in S-(androsta-1,4-diene-3,17-dion-6α-ylmethyl)-L-glutathione (P = 0.034) and S-(androsta-1,4-diene-17β-ol-3-on-6α-ylmethyl)-L-gutathione (P = 0.014) formation. In the plasma of 68 ER+ breast cancer patients treated with EXE, the GSTA1 *B*B genotype was associated with significant decreases in both EXE-cysteine (cys) (29%, P = 0.0056) and 17β-DHE-cys (34%, P = 0.032) as compared with patients with the GSTA1*A*A genotype, with significant decreases in EXE-cys (Ptrend = 0.0067) and 17β-DHE-cys (Ptrend = 0.028) observed in patients with increasing numbers of the GSTA1*B allele. A near-significant (Ptrend = 0.060) trend was also observed for urinary EXE-cys levels from the same patients. In contrast, plasma and urinary 17β-DHE-Gluc levels were significantly increased (36%, P = 0.00097 and 52%, P = 0.0089; respectively) in patients with the GSTA1 *B*B genotype. No significant correlations were observed between the GSTM1 null genotype and EXE metabolite levels. These data suggest that the GSTA1*B allele is associated with interindividual differences in EXE metabolism and may play a role in interindividual variability in overall response to EXE.SIGNIFICANCE STATEMENTThe present study is the first comprehensive pharmacogenomic investigation examining the role of genetic variability in GST enzymes on exemestane metabolism. The GSTA1 *B*B genotype was found to contribute to interindividual differences in the metabolism of EXE both ex vivo and in clinical samples from patients taking EXE for the treatment of ER+ breast cancer. Since GSTA1 is a major hepatic phase II metabolizing enzyme in EXE metabolism, the GSTA1*B allele may be an important biomarker for treatment outcomes and toxicities.

Potential health risks of maternal phthalate exposure during the first trimester - The Saudi Early Autism and Environment Study (SEAES)

Phthalates are the most ubiquitous contaminants that we are exposed to daily due to their wide use as plasticizers in various consumer products. A few studies have suggested that in utero exposure to phthalates can disturb fetal growth and development in humans, because phthalates can interfere with endocrine function. We collected spot urine samples from 291 pregnant women in their first trimester (9.8 ± 2.3 gestational weeks) recruited in an ongoing prospective cohort study in Saudi Arabia. A second urine sample was collected within 1–7 d after enrollment. The aims of this study were to: (1) assess the extent of exposure to phthalates during the first trimester and (2) estimate the risk from single and cumulative exposures to phthalates. Most phthalate metabolites' urinary levels were high, several-fold higher than those reported in relevant studies from other countries. The highest median levels of monoethyl phthalate, mono-n-butyl phthalate (MnBP), mono-iso-butyl phthalate (MiBP), and mono-(2-ethylhexyl) phthalate (MEHP) in μg/l (μg/g creatinine) were 245.62 (197.23), 114.26 (99.45), 39.59 (34.02), and 23.51 (19.92), respectively. The MEHP levels were highest among three di (2-ethylhexyl) phthalate (DEHP) metabolites. %MEHP4, the ratio of MEHP to four di (2-ethylhexyl) phthalate metabolites (∑4DEHP), was 44%, indicating interindividual differences in metabolism and excretion. The hazard quotient (HQ) of individual phthalates estimated based on the reference dose (RfD) of the U.S. Environmental Protection Agency indicated that 58% (volume-based) and 37% (creatinine-based) of the women were at risk of exposure to ∑4DEHP (HQ > 1). Based on the tolerable daily intake (TDI) from the European Food Safety Authority, 35/12% (volume-/creatinine-based data) of the women were at risk of exposure to two dibutyl phthalate (∑DBP) metabolites (MiBP and MnBP). The cumulative risk was assessed using the hazard index (HI), the sum of HQs of all phthalates. The percentages of women (volume-/creatinine-based data) at health risks with an HI > 1 were 64/40% and 42/22% based on RfD and TDI, respectively. In view of these indices for assessing risk, our results for the anti-androgenic effects of exposing pregnant women to ∑4DEHP and ∑DBP early during pregnancy are alarming.

Effect of CYP2C19, UGT1A8, and UGT2B7 on valproic acid clearance in children with epilepsy: a population pharmacokinetic model.

Valproic acid (VPA) is an important drug in seizure control with great inter-individual differences in metabolism and treatment effect. This study aims to identify the effects of genetic variants on VPA clearance in a population pharmacokinetic (popPK) model in children with epilepsy. A total of 325 VPA plasma concentrations from 290 children with epilepsy were used to develop the popPK model by using the nonlinear mixed-effects modeling method. The one-compartment model was established to describe the pharmacokinetics of VPA. Twelve single nucleotide polymorphisms involved in the pharmacokinetics of VPA were identified by MassARRAY system and their effects on VPA clearance were evaluated. In the two final popPK models, inclusion of a combined genotype of four variants (rs1042597, rs28365062, rs4986893, and rs4244285), total daily dose (TDD), and body surface area (BSA) significantly reduced inter-individual variability for clearance over the base model. The inter-individual clearance equals to 0.73 × (TDD/628.92)0.59 × eUGT-CYP for TDD included model and 0.70 × (BSA/0.99)0.57 × eUGT-CYP for BSA included model. The precision of all parameters were acceptable (relative standard error < 32.81%). Bootstrap and visual predictive check results indicated that both two final popPK models were stable with acceptable predictive ability. TDD, BSA, and genotype might affect VPA clearance in children. The popPK models may be useful for dosing adjustment in children on VPA therapy.

O7: Evaluation of hair analysis with socio-demographic profile of crack users in Brazil

A study of 1383 drug users was undertaken in Brazil focusing on crack cocaine users. Detailed interviews were undertaken about their personal life history and psychoactive substance use and hair samples were taken to corroborate the interview data. The main objective of this paper is to evaluate hair drug testing as a biomarker capable of corroborating the interview data and history of drug use. Head hair samples were collected from 333 known drug users, 298 males and 35 females, from various parts of Brazil, prior to their voluntary detoxification treatment. The samples were sent to ChromaTox for analysis. Head hair sections (N=327) measured from 0.5 to 4 cm. Body hair samples (N=6) were not sectioned and measured from 1.5 to 3 cm. The samples were extracted and analysed by LC-MS/MS using methods accredited to ISO/IEC 17025 standards. A cutoff of 0.5 ng/mg was used for cocaine and 0.2 ng/mg for AEME, cocaethylene, and norcocaine. The limit of quantitation (LOQ) was 0.1 ng/mg for all analytes (cocaine, benzoylecgonine, norcocaine, AEME, crack cocaine). Cocaine was detected above cutoff in 272 samples of hair with levels ranging from 0.5 ng/mg to 385.2 ng/mg. AEME was detected in 200 samples with levels from 0.3 to 16.6 ng/mg; benzoylecgonine was detected in 70 samples with levels from 0.2 to 242.8 ng/mg and norcocaine was detected in 207 samples with levels from 0.2 ng/mg to 8.2 ng/mg. Where current cocaine use was not detected (N=13) or was below cutoff but above LOQ (N=48), the period covered by the sample length corresponded with the period when crack and/or cocaine use ceased for the majority of the cases. Alprazolam, diazepam, nordiazepam and THC were also detected in various combinations in 89 samples. Levels detected in hair were not correlated with other data collected in the interviews such as type of abode, education, race, religion, income or parental drug use nor with the age people started using crack cocaine. The results of the analysis of hair samples confirmed the usefulness of the detection of drugs in hair to assess drug consumption over a long period of time, and in this case to corroborate interview data. Samples where use of cocaine was not detected correlated with individuals who declared at their interviews that they had stopped using crack cocaine prior to the period covered by the sample. The results also showed no correlation between the declared amounts used of crack cocaine and/or of cocaine with the levels detected in hair. This is expected, since, whilst the hair results can be compared with the results previously analysed by the laboratory, it is well established that there are many factors that affect levels of drugs in hair and therefore it is not possible to infer from the levels detected in hair the amount of drug used. These factors are for example, inter-individual differences in metabolism, hair types and cosmetic treatments. Hair drug testing is an excellent tool for showing whether people used drugs or not over a long period of time. It is not possible therefore to establish the amount of drug used from the levels detected in hair. It is possible, however to compare the results with the results previously analysed by the laboratory and to use the levels of drugs in hair as a guide to the changes in pattern of use over time in the same individual.

Zebra finches in poor condition produce more and consume more food in a producer–scrounger game

When they forage in groups, animals can search for their own food (producer tactic) or exploit the discoveries of others (scrounger tactic). Previous experimental inquiries have demonstrated that individuals vary in their tendency to play either tactic but the extent to which individual factors influence variation in foraging behavior are little studied. In the present study, we have assessed the influence of natural variation in body condition on the differential use of social foraging tactics and their resulting payoffs in zebra finches (Taeniopygia guttata). The producer tactic was found to yield more consistent and predictable rewards across trials than the scrounger tactic. The use of producer was related to reduced variation in food intake and an increased amount of food consumed. We found that poor-condition birds were more likely to produce and so consumed more seeds than good-condition birds. The results are consistent with theoretical models of variance-sensitive social foraging but suggest that scrounging may not represent a variance-averse option in all situations. We propose that in a producer‐scrounger context, the variance-averse option may depend on group size and food clumping. Finally, we discuss our results in relation to interindividual differences in metabolism and behavior. Key words: bootstrap, decision rules, food intake, residual body mass, scramble competition, variance-sensitive foraging. [Behav Ecol]

Androgen Sulfation in Healthy UDP-Glucuronosyl Transferase 2B17 Enzyme-Deficient Men

The conspicuous interindividual differences in metabolism and urinary excretion of testosterone and its metabolites make it challenging to reveal testosterone doping. The variation in testosterone glucuronide excretion is strongly associated with a deletion polymorphism in the uridine diphosphate-glucuronosyltranferase (UGT) 2B17 gene. The objective of the study was to identify additional biomarkers to detect testosterone abuse and to elucidate alternative pathways for testosterone elimination in individuals devoid of the UGT2B17 enzyme. For this purpose a new ultraperformance liquid chromatographic tandem mass spectrometric method for simultaneous determination of 10 different sulfo- and glucuronide-conjugated steroids was developed. Fifty-four healthy male volunteers with two, one, or no allele (ins/ins, ins/del, or del/del) of the UGT2B17 gene participated in the study. Intervention included a single im dose of 500 mg testosterone enanthate. Urinary sulfo- and glucuronide-conjugated steroids were measured. Testosterone sulfate levels decreased in all individuals after the dose. The individual differences in the excretion of all sulfated metabolites were large. Thus, these metabolites will not serve as appropriate biomarkers for testosterone abuse. However, androsterone glucuronide excretion increased in all of our study subjects after the testosterone dose. Etiocholanolone sulfate was excreted at significantly higher levels in UGT2B17 del/del individuals. We propose that the androsterone glucuronide to epitestosterone glucuronide ratio may serve as a complementary biomarker to reveal testosterone abuse.

Systemic Bioavailability and Pharmacokinetics of the Doxylamine–Pyridoxine Delayed-Release Combination (Diclectin)

Diclectin, composed of 10 mg doxylamine succinate (DOX) and 10 mg pyridoxine hydrochloride, is the drug combination of choice for the management of nausea and vomiting during pregnancy in Canada. However, there is large variability in its onset and duration of action among women. To understand and improve its effectiveness, the variability in the pharmacokinetics of the ingredients in this doxylamine succinate/pyridoxine hydrochloride combination must be studied. To determine the pharmacokinetics of DOX and pyridoxine after oral administration of two tablets of this drug combination in the form of Diclectin and to calculate their respective relative bioavailability by comparison with intravenous administration in another population. Eighteen nonpregnant, nonlactating, healthy females between 18 and 45 years of age were administered two tablets of Diclectin with 240 mL of water under empty stomach conditions. Blood samples were analyzed for DOX and pyridoxine along with its four active metabolites: pyridoxal, pyridoxal-5'-phosphate (PLP), pyridoxamine, and pyridoxamine-5'-phosphate using tandem mass spectrometry. For the purpose of this study, pharmacokinetic values for DOX and PLP were adjusted for body weight. The mean DOX-AUC0→∞ was calculated to be 3137.22 ± 633.57 ng·hr/mL (range, 2056.59-4376.06 ng·hr/mL). The mean PLP-AUC0→∞ was calculated to be 5513.10 ± 2362.35 ng·hr/mL (range, 1572.56-10,153.77 ng·hr/mL). Based on literature values of the PLP-AUC0→∞ after intravenous administration and data from the current study, the relative bioavailability of pyridoxine in Diclectin was calculated at 100%. There was a 2.1-fold variability in the DOX-AUC0→∞ and 6.5-fold variability in the PLP-AUC0→∞ after oral administration of 20 mg Diclectin. Using literature values and data from the current study, we estimated the oral bioavailability of pyridoxine to be 100%. Therefore, interindividual differences in metabolism, and not in bioavailability, may be important sources of variability that need to be addressed in dosing guidelines.

Development of a high-throughput LC/APCI-MS method for the determination of thirteen phytoestrogens including gut microbial metabolites in human urine and serum

The investigation into the potential usefulness of phytoestrogens in the treatment of menopausal symptoms requires large-scale clinical trials that involve rapid, validated assays for the characterization and quantification of the phytoestrogenic precursors and their metabolites in biological matrices, as large interindividual differences in metabolism and bioavailability have been reported. Consequently, a new sensitive high-performance liquid chromatography-mass spectrometry method (HPLC–MS) for the quantitative determination of thirteen phytoestrogens including their most important gut microbial metabolites (genistein, daidzein, equol, dihydrodaidzein, O-desmethylangolensin, coumestrol, secoisolariciresinol, matairesinol, enterodiol, enterolactone, isoxanthohumol, xanthohumol and 8-prenylnaringenin) in human urine and serum within one single analytical run was developed. The method uses a simple sample preparation procedure consisting of enzymatic deconjugation followed by liquid–liquid extraction (LLE) or solid-phase extraction (SPE) for urine or serum, respectively. The phytoestrogens and their metabolites are detected with a single quadrupole mass spectrometer using atmospheric pressure chemical ionization (APCI), operating both in the positive and the negative mode. This bioanalytical method has been fully validated and proved to allow an accurate and precise quantification of the targeted phytoestrogens and their metabolites covering the lower parts-per-billion range for the measurement of relevant urine and serum levels following ingestion of phytoestrogen-rich dietary supplements.

MRP2 and GSTP1 polymorphisms and chemotherapy response in advanced non-small cell lung cancer

PurposeThe level of drug metabolism and drug transport is correlated with the sensitivity of cancer cells towards platinum-based chemotherapy. We hypothesize that genetic polymorphisms in metabolising enzymes gene GSTP1 (glutathione S-transferase P1), and MRP2 (multidrug resistance-associated protein 2) (ABCC2), which result in inter-individual differences in metabolism and drug disposition, may predict clinical response to platinum agents in advanced non-small cell lung cancer (NSCLC) patients.MethodsTotally 113 patients with advanced NSCLC were routinely treated with platinum-based chemotherapy, and clinical response was evaluated after four cycles. MRP2 C-24T (−24C>T), MRP2 Val417Ile (1249G>A), MRP2 Ile1324Ile (3972C>T), and GSTP1 Ile105Val (342A>G) genotype were determined by gene-chip method (a 3-D (three dimensions) polyacrylamide gel-based DNA microarray method) using DNA samples isolated from peripheral blood collected before treatment. Pearson Chi-square test and Fisher’s exact test were performed to measure the differences of the chemotherapeutic efficacy among variant genotype. The odds ratios and 95% confidence intervals were computed by logistic regression.ResultsThe C→T change of MRP2 C-24T and the A→G change of GSTP1 Ile105Val polymorphism significantly increased platinum-based chemotherapy response.ConclusionThe polymorphic status of MRP2 C-24T and GSTP1 Ile105Val might be the predictive markers for the treatment response of advanced NSCLC patients. The DNA microarray-based method is accurate, high throughput and inexpensive, suitable for single-nucleotide polymorphism genotyping in a large number of individuals.

Nuclear magnetic resonance–based metabonomics reveals strong sex effect on plasma metabolism in 17-year–old Scandinavians and correlation to retrospective infant plasma parameters

Nuclear magnetic resonance (NMR)–based metabonomics was carried out on plasma samples from a total of seventy-five 17-year–old Danes to investigate the impact of key parameters such as sex, height, weight, and body mass index on the plasma metabolite profile in a normal, healthy population. Principal component analysis identified sex to have a large impact on the NMR plasma metabolome, whereas no apparent effects of height, weight, and body mass index were found. Partial least square regression discriminant analysis and quantification of relative metabolite concentrations by integration of NMR signals revealed that the sex effect included differences in plasma lipoproteins (mainly high-density lipoprotein), glucose, choline, and amino acid content. Accordingly, the present study suggests a higher lipid synthesis in young women than young men and a higher protein turnover in young men compared with women. Data on plasma content of triglyceride, lipoprotein fractions, and cholesterol at an age of 9 months were available for selected individuals (n = 40); and partial least square regressions revealed correlations between these infant parameters and the NMR plasma metabolome at an age of 17 years. In conclusion, the present study demonstrates the feasibility of NMR-based metabonomics for obtaining a deeper insight into interindividual differences in metabolism and for exploring relationships between parameters measured early in life and metabolic status at a later stage.

Prevalence of Daidzein-Metabolizing Phenotypes Differs between Caucasian and Korean American Women and Girls

Interindividual differences in metabolism of the soy isoflavone, daidzein, to equol and O-desmethylangolensin (ODMA) by human gut bacteria, have been associated with altered risk of cancer and other chronic diseases, according to some studies. Differences have been reported in the prevalence of the equol-producer phenotype among populations, with a higher prevalence in soy-consuming Asian populations than in Western populations. To date, prevalence of the daidzein-metabolizing phenotypes in Asians, compared with Caucasians, has not been evaluated in the context of a standardized phenotyping method. We assessed the prevalence of equol- and ODMA-producer phenotypes in 91 Korean American (KA) women and girls living in the Seattle, Washington area and compared this with previous similarly collected prevalence data in Caucasian American (CA) women and girls (n = 222). We also compared the dietary habits of the 2 groups. Isoflavonoid concentrations in first-void morning urines, collected after a 3-d soy challenge, were used to establish equol-, and ODMA-producer phenotypes (>44 microg/L). The prevalence of the equol-producer phenotype was higher (51 vs. 36%; P = 0.015) and the ODMA-producer phenotype was lower (84 vs. 92%, P = 0.03) in KA than in CA women and girls. KAs consumed approximately 3 times more soy foods than the CAs, but no significant associations were found between the consumption of soy foods and equol-producer phenotype. Our findings support the reports that, compared with Western populations, Asian populations have a higher equol-producer prevalence. The additional observation that the prevalence of the ODMA-producer phenotype is lower in KAs suggests that daidzein-metabolizing patterns in general may differ between KAs and CAs.

Experience with CYP2D6 Genotyping in Psychiatry

Background: Inter-individual differences in metabolism of psychotropic drugs have a major impact on clinical outcome. Important discoveries about polymorphic cytochrome P450 enzymes (CYP) raise expectations that pharmacogenetic testing might become a routine tool to identify patients at risk of adverse drug reactions (ADR) or therapeutic failures.

Impact of inter‐individual differences in drug metabolism and pharmacokinetics on safety evaluation

Safety evaluation aims to assess the dose-response relationship to determine a dose/level of exposure for food contaminants below which no deleterious effect is measurable that is 'without appreciable health risk' when consumed daily over a lifetime. These safe levels, such as the acceptable daily intake (ADI) have been derived from animal studies using surrogates for the threshold such as the no-observed-adverse-effect-level (NOAEL). The extrapolation from the NOAEL to the human safe intake uses a 100-fold uncertainty factor, defined as the product of two 10-fold factors allowing for human variability and interspecies differences. The 10-fold factor for human variability has been further subdivided into two factors of 10(0.5) (3.16) to cover toxicokinetics and toxicodynamics and this subdivsion allows for the replacement of an uncertainty factor with a chemical-specific adjustment factor (CSAF) when compound-specific data are available. Recently, an analysis of human variability in pharmacokinetics for phase I metabolism (CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, hydrolysis, alcohol dehydrogenase), phase II metabolism (N-acetyltransferase, glucuronidation, glycine conjugation, sulphation) and renal excretion was used to derive pathway-related uncertainty factors in subgroups of the human population (healthy adults, effects of ethnicity and age). Overall, the pathway-related uncertainty factors (99th centile) were above the toxicokinetic uncertainty factor for healthy adults exposed to xenobiotics handled by polymorphic metabolic pathways (and assuming the parent compound was the proximate toxicant) such as CYP2D6 poor metabolizers (26), CYP2C19 poor metabolizers (52) and NAT-2 slow acetylators (5.2). Neonates were the most susceptible subgroup of the population for pathways with available data [CYP1A2 and glucuronidation (12), CYP3A4 (14), glycine conjugation (28)]. Data for polymorphic pathways were not available in neonates but uncertainty factors of up to 45 and 9 would allow for the variability observed in children for CYP2D6 and CYP2C19 metabolism, respectively. This review presents an overview on the history of uncertainty factors, the main conclusions drawn from the analysis of inter-individual differences in metabolism and pharmacokinetics, the development of pathway-related uncertainty factors and their use in chemical risk assessment.

Exocyclic DNA adducts as secondary markers for oxidative stress: applications in human cancer etiology and risk assessment.

DNA-bound carcinogen adducts reflect the amount of an exogenous chemical or its metabolite that covalently interacted with nucleic acid bases at the target site (biologically effective dose) or in surrogate tissues. DNA adducts are mechanistically more relevant to carcinogenesis than internal doses of genotoxins, since they take into account interindividual differences in metabolism and of DNA repair capacity. The rationale for measuring DNA adducts as relevant dosimeters of biological effects and predictor of cancer risk is derived from extensive experimental and human data, supporting their role in the initiation and probably the progression of cancer. Several hundreds of DNA adducts, many with miscoding properties, are known to be produced by some 20 classes of carcinogens and through endogenous processes including oxidized DNA bases (Hemminki et al., 1994). These lesions provide powerful tools for studying disease pathogenesis, etiology and for verifying preventive measures in human cancer or other chronic degenerative diseases.

Prediction of interindividual variation in drug plasma levels in vivo from individual enzyme kinetic data and physiologically based pharmacokinetic modeling

A strategy is presented to predict interindividual variation in drug plasma levels in vivo by the use of physiologically based pharmacokinetic modeling and human in vitro metabolic parameters, obtained through the combined use of microsomes containing single cytochrome P450 enzymes and a human liver microsome bank. The strategy, applied to the pharmaceutical compound ( N-[2-(7-methoxy-1-naphtyl)-ethyl]acetamide), consists of the following steps: (1) estimation of enzyme kinetic parameters K m and V max for the key cytochrome P450 enzymes using microsomes containing individual P450 enzymes; (2) scaling-up of the V max values for each individual cytochrome P450 involved using the ratio between marker substrate activities obtained from the same microsomes containing single P450 enzymes and a human liver microsome bank; (3) incorporation into a physiologically based pharmacokinetic model. For validation, predicted blood plasma levels and pharmacokinetic parameters were compared to those found in human volunteers: both the absolute plasma levels as well as the range in plasma levels were well predicted. Therefore, the presented strategy appears to be promising with respect to the integration of interindividual differences in metabolism and prediction of the possible impact on plasma and tissue concentrations of drugs in humans.

Clinical pharmacokinetics of sedatives in neonates.

Sedation is currently administered to neonates experiencing pain and stress during intensive care for medical diseases, as well as postoperatively. Drugs commonly used for sedation in neonates include benzodiazepines (midazolam and lorazepam), chloral hydrate and opioids (fentanyl and morphine). Sedation protocols and dosage schedules are, in most cases, adapted from those which have been developed in children and even adults. The effectiveness and safety of the sedative agents remain underevaluated, however, due to the difficulties of quantifying pain and stress in neonates, and because of the limited use of validated scoring methods by practitioners. Among the benzodiazepines, midazolam is probably the drug of choice for continuous sedation. However, its elimination is delayed in the neonatal period and hypotension may occur when given as a bolus injection or when taken with opioids. Lorazepam requires further evaluation to exclude severe neurotoxicity. Chloral hydrate is administered orally, but because of its delayed elimination and risk of accumulation, a single administration for short term sedation is recommended. Among opioids, fentanyl (which was initially administered for postoperative analgesia) is now prescribed for sedation during mechanical ventilation. Tolerance and dependence may develop rapidly, limiting its usefulness for prolonged sedation. Although extensively studied in neonates, the efficacy and safety of morphine are not clearly determined, because of the limited number of patients included in individual studies. In addition, important interindividual differences in metabolism render dosage recommendations difficult. Alfentanil and sufentanil need further investigations to define their pharmacokinetic-pharmacodynamic properties in neonates. Although the choice of drug is important, the way the drug is used and monitored is equally important. All the drugs used for the sedation of neonates have large inter- and intraindividual differences in disposition, justifying specific pharmacological knowledge and individual dosage adjustments based on clinical evaluation of the patient and the monitoring of drug concentrations.

Exposure factors that contribute to variability in toxic responses in man

The route of exposure is an important determinant of the internal dose of a chemical in man and the expression of toxicity. Routes of exposure are inhalation via the lung and dermal penetration, and the degree of absorption and first pass metabolism vary between chemicals. Inter-individual differences in metabolism of both genetic and environmental cause contribute to variability in metabolic fate and toxic response.

A note on individual differences in the urinary excretion of optical enantiomers of styrene metabolites and of styrene-derived mercapturic acids in humans.

Urine samples from 20 male workers in the polyester industry exposed by inhalation to styrene concentrations ranging from 29 to 41 ppm were investigated. Excretion products of styrene metabolism, mandelic acid and mercapturic acids, were purified from the urine over an extraction column packed with Porapak Q, with subsequent ether elution. The optical enantiomers R- and S-mandelic acid were then determined by thin layer chromatography (TLC) using chiral plate material and selective staining with vanadium pentoxide. Quantitative analysis of these compounds was performed using commercial reference substances. Styrene-specific mercapturic acids were analyzed by a modified TLC method, using synthesized reference substances. The concentration of racemic mandelic acid in the individual urine samples ranged from 80 to 1610 mg/l, and the ratio of the R- and S-enantiomers ranged from 0.7 to 2.2. These individual variations are not explained by differences in individual styrene exposure levels, or by differences in the concentration of the urine samples (in relation to creatinine excretion). Styrene-specific mercapturic acids were detected in the urine of only 1 of the 20 workers, at a concentration much lower than expected from previous investigations by others in humans and laboratory animals, in which less specific analytical methods had been used. The results point to marked interindividual differences in metabolism of styrene, probably related to enzyme polymorphisms.