Estado epiléptico refractario en UCIP. Experiencia en un hospital de la Provincia de Buenos Aires / Refractory status epilepticus in the PICU. Experience at a hospital in the Province of Buenos Aires

Introducción: El estado epiléptico (EE) es la emergencia neurológica más frecuente en pediatría. Los pacientes que no responden al tratamiento estándar con dosis adecuadas de benzodiacepinas seguido de una droga antiepiléptica aceptable son definidos como Estado epiléptico Refractario (ER). Objetivo: caracterizar la población de niños con EE que ingresan a UCIP y determinar qué factores son predictores de refractariedad en esta población. Métodos: Estudio de casos y controles, retrospectivo. Población: niños con EE internados en UCIP desde Febrero 2015 a Febrero 2017. Casos: Estado epiléptico Refractario (ER). Controles: Estado epiléptico No Refractario (ENR). Se calculó el Odds Ratio (OR) individual para las distintas variables en Med Calc. Resultados: Se internaron 35 pacientes de los cuales 12 fueron casos y 23 controles. Hubo fiebre en 77% de los pacientes. En el total de niños estudiados hubo 11% con antecedente de convulsión febril, 11% con antecedente de epilepsia y 9% con antecedente de malformación del SNC. Los niños con antecedente de convulsión febril tuvieron 2,5 veces mayor riesgo de ER (OR: 2,58; IC 95%: 1,17-5,68). Los niños con EE que tenían antecedentes de enfermedad neurológica previa presentaron riesgo de ER 2,6 veces mayor que el grupo control (OR 2,60; IC 95%: 1,24-5,42). Discusión: Dado el aumento en la mortalidad de los pacientes con ER sería importante disponer de más herramientas para predecir este desenlace e iniciar tratamiento oportuno. Resultaría útil entrenar a los padres de niños con antecedente de convulsión febril en la aplicación de medicación antiepiléptica prehospitalaria, esto podría prevenir la farmacorresistencia, el daño neurológico y las complicaciones que acarrea el ingreso a UCIP. (AU)

Introduction: Status epilepticus (SE) is the most common neurologic emergency in children. Patients that do not respond to standard treatment with adequate doses of benzodiazepines followed by an acceptable antiepileptic drug are defined as having refractory status epilepticus (RSE). Objective: To characterize the population of children with SE admitted to the PICU and to determine predictive factors for refractoriness in this population. Methods: A retrospective case-control study was conducted. Population: Children with SE admitted to the PICU between February 2015 and February 2017. Cases: Refractory status pilepticus (RSE). Controls: Non-refractory status epilepticus (NRSE). Individual Odds Ratio (OR) was calculated for different variables using Med Calc. Results: 35 patients were admitted of whom 12 were cases and 23 controls. Overall, 77% of the patients had fever. Of all the children, 11% had a history of febrile seizures, 11% had history of epilepsy and 9% had a CNS malformation. Children with a history of febrile seizures had a 2.5-fold higher risk of developing RSE (OR: 2.58; 95% CI: 1.17-5.68). Children with SE that had a history of neurologic disease had a 2.6-fold higher risk of developing RSE than controls (OR 2.60; 95% CI: 1.24-5.42). Discussion: Given the increased mortality in children with RSE, availability of tools to predict this outcome in order to initiate early treatment is important. It would be useful to train the parents of children with a history of febrile seizures in the prehospital administration of antiepileptic drugs as this may prevent pharmaco-resistance, neurologic damage, and complication related to PICU admission (AU)

Evaluación de reactantes de fase aguda como predictores de bacteriemia en niños con fiebre, leucemia aguda y linfoma / Evaluation of acute-phase reactants as predictors of bacteremia in children with fever, acute leukemia, and lymphoma

Introducción: Para predecir una infección en estadios tempranos en niños con cáncer se han evaluado marcadores como ESD, PCR y PCT. Objetivo: evaluar la precisión diagnóstica para bacteriemia de estos marcadores al ingreso en niños con fiebre y leucemia aguda (LA) o linfoma (L) internados entre 2013-2016. Métodos: estudio analítico retrospectivo. Revisión de historias clínicas. Se calcularon sensibilidad, especificidad, valor predictivo positivo, valor predictivo negativo y área bajo la curva ROC para cada marcador en MedCalc® V16.8.4. Se obtuvo autorización del Comité de Ética. Resultados:en total se internaron 31 niños con diagnóstico de LA y L, 19 presentaron fiebre y 12 no. Hubo 40 episodios de fiebre clasificados en 4 grupos: bacteriemia 14 (35%), infección documentada microbiológicamente 5 (12.5%), infección documentada clínicamente 2 (5%) y fiebre de origen desconocido 19 (47.5%). Los niveles de PCT fueron mayores en el grupo de bacteriemia registrando un valor promedio de 1,17ng/ mL (p: 0.045). El área bajo la curva ROC entre el grupo con y sin bacteriemia fue de 0.50 para ESD, 0.65 para PCR y 0.83 para PCT con S de 77.78%, E de 66.67%, VPP de 50% y VPN de 92.86%. Discusión: la PCT mostró ser el más eficaz que ESD y PCR para predecir bacteriemia. se deben realizar investigaciones con biomarcadores con el objeto de disminuir el uso inadecuado de antibióticos en pacientes con fiebre secundaria a enfermedad y acortar los tiempos de tratamiento en pacientes con infecciones adecuadamente resueltas mejorando ampliamente la calidad de vida en niños con cáncer (AU)

Introduction: To predict infection in early stages in children with cancer, markers such as ESR, CRP, and PCT have been evaluated. Objective: To evaluate the diagnostic precision for bacteremia of these markers on admission of children with fever and acute leukemia (AL) or lymphoma (L) admitted between 2013- 2016. Methods: A retrospective analytical study. Review of the clinical records. Sensitivity, specificity, positive predictive value, negative predictive value, and area under the ROC curve were calculated for each marker in MedCalc® V16.8.4. The study was approved by the Ethics Committee. Results: Overall, 31 children with AL and L were admitted, 19 of whom presented with fever and 12 did not. There were 40 episodes of fever classified into 4 groups: bacteremia 14 (35%), microbiologically documented infection 5 (12.5%), clinically documented infection 2 (5%), and fever of unknown etiology 19 (47.5%). PCT levels were higher in the group with bacteremia with a mean value of 1.17ng/mL (p:0.045). The area under the ROC curve between the groups with and without bacteremia was 0.50 for ESR, 0.65 for CRP, and 0.83 for PCT with a sensitivity of 77.78%, specificity of 66.67%, PPV of 50%, and NPV of 92.86%. Discussion: PCT showed a greater efficacy than ESD and CRP to predict bacteremia. Research on biomarkers should be conducted to reduce the inadequate use of antibiotics in patients with fever secondary to disease and to shorten treatment times in patients with adequately resolved infections, thereby improving quality of life in children with cancer (AU)

Factores asociados con falla en el diagnóstico y tratamiento de sífilis materna / Factors associated with misdiagnosis and treatment failure of maternal syphilis

Introducción: La sífilis materna inadecuadamente tratada constituye un problema de salud pública ya que puede producir gran morbimortalidad fetal y neonatal. Objetivo: describir factores relacionados con falla en el diagnóstico y tratamiento de sífilis materna. Población y métodos: Estudio analítico de casos y controles en el Hospital Materno infantil de Malvinas Argentinas, 2014 y 2015. Casos: mujeres puérperas con sífilis sin tratamiento o inadecuado e hijos con sífilis congénita. Controles: mujeres puérperas e hijos recién nacidos vivos sanos. Se realizó revisión de historias clínicas. Estadística: Caracterización de grupos a través del test de Fisher y t-Student. Se estimó el OR individual y ajustado de "falla en el diagnóstico" y "falla en el tratamiento" fijando IC 95% (p<0,05) para cada variable estudiada en SPSS 24.0. Resultados: Hubo 106 casos de sífilis congénita y 100 controles. Recién nacidos de madres con ≤ 5 controles prenatales (CPN) tuvieron 4 veces más riesgo de presentar falla en el diagnóstico de sífilis materna respecto del grupo control (OR: 4,83; IC 95%: 1,79-12,98) patrón igualmente observado para baja escolaridad materna. Las madres ≤18 años y aquellas con número insuficiente de CPN constituyeron un factor de riesgo significativo para falla en el tratamiento (individual OR ajustado: 4,07; IC 95%: 1,43-11,57 y OR ajustado: 2,85; IC 95%: 1,29-6,28, respectivamente). Conclusiones: Resulta necesario implementar estrategias institucionales orientadas a mejorar el número de controles obstétricos, el índice de escolaridad materna y la tasa de embarazo en adolescentes, con el objeto de reducir fallas en el proceso de diagnóstico y tratamiento de la sífilis materna y por consiguiente disminuir la incidencia de sífilis congénita en nuestra población (AU)

Introduction: Inadequately treated maternal syphilis poses a public health problem as it may cause significant fetal and neonatal morbidity and mortality. Aim: To describe factors related to the misdiagnosis and failure of treatment of maternal syphilis. Population and methods: An analytical case-control study conducted at the Hospital Materno infantil de Malvinas Argentinas, from 2014 to 2015. Cases: post-partum women with syphilis without or with inadequate treatment and children with congenital syphilis. Controls: post-partum women and liveborn healthy neonates. Clinical charts were reviewed. Statistical analysis: The groups were evaluated using Fisher's test and the Student's t test. Individual and adjusted ORs were estimated for "misdiagnosis" and "treatment failure" setting a 95% CI (p<0.05) for each study variable using SPSS 24.0. Results: 106 cases of congenital syphilis and 100 controls were included in the study. Infants born to mothers with ≤ 5 prenatal controls (PNC) had a four-fold risk of presenting with a missed diagnosis of maternal syphilis compared to the control group (OR: 4.83; 95% CI: 1.79-12.98). A similar pattern was observed for maternal educational level. Mothers ≤18 years of age and those with an insufficient number of PNC were significant risk factors for treatment failure (individual OR: 4.07; 95% CI: 1.43-11.57 and adjusted OR: 2.85; 95% CI: 1.29-6.28, respectively). Conclusions: It would be necessary to implement institutional strategies developed to improve the number of pregnancy controls, maternal educational level, and teen pregnancy rates aimed at reducing failures in the diagnostic process and treatment of maternal syphilis thereby diminishing the incidence of maternal syphilis in our population (AU)

Imaging of cerebral α4ß2* nicotinic acetylcholine receptors with (-)-[(18)F]Flubatine PET: Implementation of bolus plus constant infusion and sensitivity to acetylcholine in human brain.

The positron emission tomography (PET) radioligand (-)-[(18)F]flubatine is specific to α4ß2(⁎) nicotinic acetylcholine receptors (nAChRs) and has promise for future investigation of the acetylcholine system in neuropathologies such as Alzheimer's disease, schizophrenia, and substance use disorders. The two goals of this work were to develop a simplified method for α4ß2(⁎) nAChR quantification with bolus plus constant infusion (B/I) (-)-[(18)F]flubatine administration, and to assess the radioligand's sensitivity to acetylcholine fluctuations in humans. Healthy human subjects were imaged following either bolus injection (n=8) or B/I (n=4) administration of (-)-[(18)F]flubatine. The metabolite-corrected input function in arterial blood was measured. Free-fraction corrected distribution volumes (VT/fP) were estimated with modeling and graphical analysis techniques. Next, sensitivity to acetylcholine was assessed in two ways: 1. A bolus injection paradigm with two scans (n=6), baseline (scan 1) and physostigmine challenge (scan 2; 1.5mg over 60min beginning 5min prior to radiotracer injection); 2. A single scan B/I paradigm (n=7) lasting up to 240min with 1.5mg physostigmine administered over 60min beginning at 125min of radiotracer infusion. Changes in VT/fP were measured. Baseline VT/fP values were 33.8±3.3mL/cm(3) in thalamus, 12.9±1.6mL/cm(3) in cerebellum, and ranged from 9.8 to 12.5mL/cm(3) in other gray matter regions. The B/I paradigm with equilibrium analysis at 120min yielded comparable VT/fP values with compartment modeling analysis of bolus data in extrathalamic gray matter regions (regional means <4% different). Changes in VT/fP following physostigmine administration were small and most pronounced in cortical regions, ranging from 0.8 to 4.6% in the two-scan paradigm and 2.8 to 6.5% with the B/I paradigm. These results demonstrate the use of B/I administration for accurate quantification of (-)-[(18)F]flubatine VT/fP in 120min, and suggest possible sensitivity of (-)-[(18)F]flubatine binding to physostigmine-induced changes in acetylcholine levels.

Identifiability of sorption parameters in stirred flow-through reactor experiments and their identification with a Bayesian approach.

This paper addresses the methodological conditions -particularly experimental design and statistical inference- ensuring the identifiability of sorption parameters from breakthrough curves measured during stirred flow-through reactor experiments also known as continuous flow stirred-tank reactor (CSTR) experiments. The equilibrium-kinetic (EK) sorption model was selected as nonequilibrium parameterization embedding the Kd approach. Parameter identifiability was studied formally on the equations governing outlet concentrations. It was also studied numerically on 6 simulated CSTR experiments on a soil with known equilibrium-kinetic sorption parameters. EK sorption parameters can not be identified from a single breakthrough curve of a CSTR experiment, because Kd,1 and k- were diagnosed collinear. For pairs of CSTR experiments, Bayesian inference allowed to select the correct models of sorption and error among sorption alternatives. Bayesian inference was conducted with SAMCAT software (Sensitivity Analysis and Markov Chain simulations Applied to Transfer models) which launched the simulations through the embedded simulation engine GNU-MCSim, and automated their configuration and post-processing. Experimental designs consisting in varying flow rates between experiments reaching equilibrium at contamination stage were found optimal, because they simultaneously gave accurate sorption parameters and predictions. Bayesian results were comparable to maximum likehood method but they avoided convergence problems, the marginal likelihood allowed to compare all models, and credible interval gave directly the uncertainty of sorption parameters θ. Although these findings are limited to the specific conditions studied here, in particular the considered sorption model, the chosen parameter values and error structure, they help in the conception and analysis of future CSTR experiments with radionuclides whose kinetic behaviour is suspected.

Kinetics and dynamics of cyclosporine A in three hepatic cell culture systems.

In vitro experiments have a high potential to improve current chemical safety assessment and reduce the number of animals used. However, most studies conduct hazard assessment alone, largely ignoring exposure and kinetic parameters. Therefore, in this study the kinetics of cyclosporine A (CsA) and the dynamics of CsA-induced cyclophilin B (Cyp-B) secretion were investigated in three widely used hepatic in vitro models: primary rat hepatocytes (PRH), primary human hepatocytes (PHH) and HepaRG cells. Cells were exposed daily to CsA for up to 14 days. CsA in cells and culture media was quantified by LC-MS/MS and used for pharmacokinetic modeling. Cyp-B was quantified by western blot analysis in cells and media. All cell systems took up CsA rapidly from the medium after initial exposure and all showed a time- and concentration-dependent Cyp-B cellular depletion and extracellular secretion. Only in PRH an accumulation of CsA over 14 days repeated exposure was observed. Donor-specific effects in CsA clearance were observed in the PHH model and both PHH and HepaRG cells significantly metabolized CsA, with no bioaccumulation being observed after repeated exposure. The developed kinetic models are described in detail and show that all models under-predict the in vivo hepatic clearance of CsA, but to different extents with 27-, 24- and 2-fold for PRH, PHH and HepaRG cells, respectively. This study highlights the need for more attention to kinetics in in vitro studies.

Intratracheal instillation of cytoplasmic granules from Phleum pratense pollen induces IgE- and cell-mediated responses in the Brown Norway rat.

BACKGROUND: Release of cytoplasmic granules from grass pollen upon contact with water is thought to be an important source of airborne allergens. OBJECTIVES: To investigate the humoral and cellular responses to intratracheal instillation of Phleum pratense (timothy grass) pollen cytoplasmic granules (PCG) in the Brown Norway rat. METHODS: PCG were purified from timothy grass pollen by filtration through 5-microm-mesh filters. Rats were sensitized (day 0) and challenged (day 21) intratracheally with purified PCG suspended in saline (6 x 10(6) PCG/rat). Rats were then challenged 4 weeks later (1.5 x 10(6) PCG/rat). Blood samples, bronchial lymph nodes and lungs were collected from the rats 4 days after the second challenge. PCG-specific IgE and IgG1 levels and specificity were determined by ELISA and Western blotting. Pollen, pollen extract and PCG-induced proliferation of lymph node cells were monitored by [(3)H]-thymidine incorporation in a lymph node assay. Histopathological examination was carried out on the lungs. RESULTS: Specific IgE and IgG1 were present in the sera. Cultured lymph node cells proliferated in the presence of pollen, pollen extract and PCG. Western blots showed that all major pollen allergens are recognized by IgE and IgG1 from PCG-treated rats. Histopathological examination revealed features of a mild allergic reaction. CONCLUSIONS: In our rat model of allergy, purified timothy grass PCG instillation induced specific antibodies and lymph node cell responses, comparable to those obtained with intact pollen.

Phleum pratense pollen starch granules induce humoral and cell-mediated immune responses in a rat model of allergy.

BACKGROUND: Timothy grass (Phleum pratense) pollen allergens are an important cause of allergic symptoms. However, pollen grains are too large to penetrate the deeper airways. Grass pollen is known to release allergen-bearing starch granules (SG) upon contact with water. These granules can create an inhalable allergenic aerosol capable of triggering an early asthmatic response and are implicated in thunderstorm-associated asthma. OBJECTIVE: We studied the humoral (IgE) and bronchial lymph node cells reactivities to SG from timothy grass pollen in pollen-sensitized rats. METHODS: Brown-Norway rats were sensitized (day 0) and challenged (day 21) intratracheally with intact pollen and kept immunized by pollen intranasal instillation by 4 weeks intervals during 3 months. Blood and bronchial lymph nodes were collected 7 days after the last intranasal challenge. SG were purified from fresh timothy grass pollen using 5 microm mesh filters. To determine the humoral response (IgE) to SG, we developed an original ELISA inhibition test, based on competition between pollen allergens and purified SG. The cell-mediated response to SG in the bronchial lymph node cells was determined by measuring the uptake of [3H]thymidine in a proliferation assay. RESULTS: An antibody response to SG was induced, and purified SG were able to inhibit the IgE ELISA absorbance by 45%. Pollen extract and intact pollen gave inhibitions of 55% and 52%, respectively. A cell-mediated response was also found, as pollen extract, intact pollen and SG triggered proliferation of bronchial lymph node cells. CONCLUSIONS: It was confirmed that timothy grass pollen contains allergen-loaded SG, which are released upon contact with water. These granules were shown to be recognized by pollen-sensitized rats sera and to trigger lymph node cell proliferation in these rats. These data provide new arguments supporting the implication of grass pollen SG in allergic asthma.

Decrease in ovalbumin-induced pulmonary allergic response by benzaldehyde but not acetaldehyde exposure in a Guinea pig model.

The pulmonary effects of two environmentally relevant aldehydes were investigated in nonsensitized or ovalbumin (OA)-sensitized guineapigs (GPs). Four-week-old male Hartley GPs, weighing about 400 g, were intraperitoneally injected with 1 ml of an NaCl solution containing 100 microg OA and 100 mg Al(OH)(3). They were then exposed to either acetaldehyde (200 ppb) or benzaldehyde (500 ppb) for 4 wk (6 h/d, 5 d/wk). At the end of exposure, GPs were challenged with an OA aerosol (0.1% in NaCl) and pulmonary functions were measured. The day after, guinea pigs were anesthetized and several endpoints related to inflammatory and allergic responses were assessed in blood, whole-lung histology, and bronchoalveolar lavage (BAL). Sensitized nonexposed GPs showed bronchial hyperresponsiveness to OA and an increased number of eosinophils in blood and BAL, together with a rise in total protein and leukotrienes (LTB(4) and LTC(4)/D(4)/E(4)) in BAL. In nonsensitized GPs, exposure to acetaldehyde or benzaldehyde did not induce any change in the tested parameters, with the exception of irritation of the respiratory tract as detected by histology and an increased number of alveolar macrophages in animals exposed to acetaldehyde. In sensitized GPs, exposure to acetaldehyde induced a moderate irritation of the respiratory tract but no change in biological parameters linked to the inflammatory and allergic responses. In contrast, exposure to benzaldehyde induced a decrease both in OA-induced bronchoconstriction and in eosinophil and neutrophil numbers in BAL, an increase in the bronchodilatator mediator prostaglandin E(2) (PGE(2)), and a decrease in the bronchoconstrictor mediators LTC(4)/D(4)/E(4). Further investigations are needed to determine if the attenuated response observed in sensitized GPs exposed to benzaldehyde is due to an alteration of the mechanism of sensitization or to a more direct effect on various mechanisms of the allergic response.

[Positional hypoxaemia complicating a Bochdalek hernia in an adult]. / Hypoxémie positionnelle compliquant une hernie de Bochdalek chez l'adulte.

Bochdalek hernias are the result of a congenital defect of the postero-lateral part of the diaphragm, usually discovered in the neonatal period. The diagnosis is rare in adult life and usually follows an acute gastro-intestinal complication. We report the case of a 63 year old man presenting with positional hypoxaemia that could have been related to a left sided Bochdalek hernia.

Assessing the reliability of PBPK models using data from methyl chloride-exposed, non-conjugating human subjects.

Physiologically based pharmacokinetic (PBPK) models are often optimized by adjusting metabolic parameters so as to fit experimental toxicokinetic data. The estimates of the metabolic parameters are then conditional on the assumed values for all other parameters. Meanwhile, the reliability of other parameters, or the structural model, is usually not questioned. Inhalation exposures with human volunteers in our laboratory show that non-conjugators lack metabolic capacity for methyl chloride entirely, and that elimination in these subjects takes place via exhalation only. Therefore, data from these methyl chloride exposures provide an excellent opportunity to assess the general reliability of standard inhalation PBPK models for humans. A hierarchical population PBPK model for methyl chloride was developed. The model was fit to the experimental data in a Bayesian framework using Markov chain Monte Carlo (MCMC) simulation. In a Bayesian analysis, it is possible to merge a priori knowledge of the physiological, anatomical and physicochemical parameters with the information embedded in the experimental toxicokinetic data obtained in vivo. The resulting estimates are both statistically and physiologically plausible. Model deviations suggest that a pulmonary sub-compartment may be needed in order to describe the inhalation and exhalation of volatile adequately. The results also indicate that there may be significant intra-individual variability in the model parameters. To our knowledge, this is the first time that the toxicokinetics of a non-metabolized chemical is used to assess population PBPK parameters. This approach holds promise for more elaborate experiments in order to assess the reliability of PBPK models in general.

Two dimerization domains in the trans-activation response RNA-binding protein (TRBP) individually reverse the protein kinase R inhibition of HIV-1 long terminal repeat expression.

Trans-activation response (TAR) RNA-binding protein (TRBP) is a cellular protein that binds to the human immunodeficiency virus-1 (HIV-1) TAR element RNA. It has two double-stranded RNA binding domains (dsRBDs), but only one is functional for TAR binding. TRBP interacts with the interferon-induced protein kinase R (PKR) and inhibits its activity. We used the yeast two-hybrid assay to map the interaction sites between the two proteins. We show that TRBP and PKR-N (178 first amino acids of PKR) interact with PKR wild type and inhibit the PKR-induced yeast growth defect in this assay. We characterized two independent PKR-binding sites in TRBP. These sites are located in each dsRBD in TRBP, indicating that PKR-TRBP interaction does not require the RNA binding activity present only in dsRBD2. TRBP and its fragments that interact with PKR reverse the PKR-induced suppression of HIV-1 long terminal repeat expression. In addition, TRBP activates the HIV-1 long terminal repeat expression to a larger extent than the addition of each domain. These data suggest that TRBP activates gene expression in PKR-dependent and PKR-independent manners.

Genetic and dietary factors affecting human metabolism of 1,3-butadiene.

The objective of this project was to determine the factors associated with differences in butadiene (BD) inhalation uptake and the rate of metabolism for BD to epoxy butene by monitoring exhaled breath during and after a brief exposure to BD in human volunteers. A total of 133 subjects (equal males and females; four racial groups) provided final data. Volunteers gave informed consent and completed a questionnaire including diet and alcohol use. A venous blood sample was collected for genotyping CYP2E1. Subjects received a 20 min exposure to 2.0 ppm of BD, followed by a 40 min washout period. The total administered dose was 0.6 ppm*h, which is in the range of everyday exposures. Ten, 1 or 2 min exhaled breath samples (five during and five after exposure) were collected using an optimized strategy. BD was determined by GC-FID analysis. Breathing activity (minute ventilation, breath frequency and tidal volume) was measured to estimate alveolar ventilation. After the washout period, 250 mg of chlorzoxazone were administered and urine samples collected for 6 h to measure 2E1 phenotype. The total BD uptake during exposure (inhaled BD minus exhaled) was estimated. A three-compartment PBPK model was fitted to each subject's breath measurements to estimate personal and population model parameters, including in-vivo BD metabolic rate. A hierarchical Bayesian PBPK model was fit by Monte Carlo simulations to estimate model parameters. Regression and ANOVA analyses were performed. Earlier data analysis showed wide ranges for both total uptake BD and metabolic rate. Both varied significantly by sex and age, and showed suggestive differences by race, with Asians having the highest rates. The analyses reported here found no correlation between total BD uptake and metabolic rate. No significant differences were found for oxidation rates by 2E1 genotype or phenotype, but the rates showed trends consistent with reported differences by genotype and phenotype for chlorzoxazone metabolism. No effects on metabolic rate were observed for long-term alcohol consumption, or consumption in the past 24 h. Overall, neither dietary factors nor genetic differences explained much of the wide variability in metabolic rates. Population characteristics, age, sex, and race, were the most important explanatory variables, but a large fraction of the total variability in metabolism remains to be explained.

Duplication of a truncated paralog of the family B DNA polymerase gene Aa-polB in the Agrocybe aegerita mitochondrial genome.

The Agrocybe aegerita mitochondrial genome contains a truncated family B DNA polymerase gene (Aa-polB P1) whose nucleotide sequence is 86% identical to the previously described and potentially functional Aa-polB gene. A tRNA(Met) gene occurs at the 3' end of the Aa-polB P1 gene. The Aa-polB P1 gene could result from reverse transcription of an Aa-polB mRNA primed by a tRNA(Met) followed by the integration of the cDNA after recombination at the mitochondrial tRNA locus. Two naturally occurring alleles of Aa-polB P1 carry one or two copies of the disrupted sequence. In strains with two copies of Aa-polB P1, these copies are inverted relative to one another and separated by a short sequence carrying the tRNA(Met) gene. Both A. aegerita mitochondrial family B DNA polymerases were found to be related to other family B DNA polymerases (36 to 53% amino acid similarity), including the three enzymes of the archaebacterium Sulfolobus solfataricus. If mitochondria originated from a fusion between a Clostridium-like eubacterium and a Sulfolobus-like archaebacterium, then the A. aegerita family B DNA polymerase genes could be remnants of the archaebacterial genes.

Applications of population approaches in toxicology.

Many experimental or observational studies in toxicology are best analysed in a population framework. Recent examples include investigations of the extent and origin of intra-individual variability in toxicity studies, incorporation of genotypic information to address intra-individual variability, optimal design of experiments, and extension of toxicokinetic modelling to the analysis of biomarker studies. Bayesian statistics provide powerful numerical methods for fitting population models, particularly when complex mechanistic models are involved. Challenges and limitations to the use of population models, in terms of basic structure, computational burden, ease of implementation and data accessibility, are identified and discussed.

Physiologically based pharmacokinetic modeling of inhalation exposure of humans to dichloromethane during moderate to heavy exercise.

Dichloromethane (methylene chloride, DCM) is metabolized via two pathways in humans: mixed-function oxidases (MFO) and glutathione-S:-transferase (GST). Most likely, the carcinogenicity for DCM is related to metabolic activation of DCM via the GST pathway. However, as the two pathways are competing, the metabolic capacity for the MFO pathway in vivo is also of interest in risk assessment for DCM. Past estimates of MFO metabolism are based on the in vitro activity of tissue samples. The aim of the present study was to develop a population model for DCM in order to gain more knowledge on the variability of DCM inhalation toxicokinetics in humans, with main emphasis on the MFO metabolic pathway. This was done by merging published in vitro data on DCM metabolism and partitioning with inhalation toxicokinetic data (Astrand et al., 1975, Scand. J. Work.Environ. Health 1, 78-94) from five human volunteers, using the MCMC technique within a population PBPK model. Our results indicate that the metabolic capacity for the MFO pathway in humans is slightly larger than previously estimated from four human liver samples. Furthermore, the interindividual variability of the MFO pathway in vivo is smaller among our five subjects than indicated by the in vitro samples. We also derive a Bayesian estimate of the population distribution of the MFO metabolism (median maximum metabolic rate 28, 95% confidence interval 12-66 micromol/min) that is a compromise between the information from the in vitro data and the toxicokinetic information present in the experimental data.

B-ring substituted 5,7-dihydroxyflavonols with high-affinity binding to P-glycoprotein responsible for cell multidrug resistance.

Starting from the interaction of galangin (3,5,7-trihydroxyflavone) with a cytosolic nucleotide-binding domain of P-glycoprotein, a series of flavonol derivatives was synthesized and tested for their binding affinity towards the same target. The 5,7-dihydroxy-4'-iodoflavonol and 5,7-dihydroxy-4'-n-octylflavonol derivatives displayed much higher binding affinities, with respective increases of 6- and 93-fold as compared to galangin.

Bayesian analysis of an epidemiologic model of Plasmodium falciparum malaria infection in Ndiop, Senegal.

Plasmodium falciparum has a complex transmission cycle. Public health planning and research would benefit from the ability of a calibrated model to predict the epidemiologic characteristics of populations living in areas of malaria endemicity. This paper describes the application of Bayesian calibration to a malaria transmission model using longitudinal data gathered from 176 subjects in Ndiop, Senegal, from July 1, 1993, to July 31, 1994. The model was able to adequately predict P. falciparum parasitemia prevalence in the study population. Further insight into the dynamics of malaria in Ndiop was provided. During the dry season, the estimated fraction of nonimmune subjects goes down to 20% and then increases up to 80%. The model-predicted time-weighted average incidences contributed by nonimmune and immune individuals are 0.52 cases per day and 0.47 cases per day, respectively. The median times needed to acquire infection (conversion delay) for nonimmune and immune individuals are estimated at 39 days and 285 days, respectively.

Statistical issues in toxicokinetic modeling: a bayesian perspective.

Determining the relationship between an exposure and the resulting target tissue dose is a critical issue encountered in quantitative risk assessment (QRA). Classical or physiologically based toxicokinetic (PBTK) models can be useful in performing that task. Interest in using these models to improve extrapolations between species, routes, and exposure levels in QRA has therefore grown considerably in recent years. In parallel, PBTK models have become increasingly sophisticated. However, development of a strong statistical foundation to support PBTK model calibration and use has received little attention. There is a critical need for methods that address the uncertainties inherent in toxicokinetic data and the variability in the human populations for which risk predictions are made and to take advantage of a priori information on parameters during the calibration process. Natural solutions to these problems can be found in a Bayesian statistical framework with the help of computational techniques such as Markov chain Monte Carlo methods. Within such a framework, we have developed an approach to toxicokinetic modeling that can be applied to heterogeneous human or animal populations. This approach also expands the possibilities for uncertainty analysis. We present a review of these efforts and other developments in these areas. Appropriate statistical treatment of uncertainty and variability within the modeling process will increase confidence in model results and ultimately contribute to an improved scientific basis for the estimation of occupational and environmental health risks.

Statistical analysis of Fisher et al. PBPK model of trichloroethylene kinetics.

Two physiologically based pharmacokinetic models for trichloroethylene (TCE) in mice and humans were calibrated with new toxicokinetic data sets. Calibration is an important step in model development, essential to a legitimate use of models for research or regulatory purposes. A Bayesian statistical framework was used to combine prior information about the model parameters with the data likelihood to yield posterior parameter distributions. For mice, these distributions represent uncertainty. For humans, the use of a population statistical model yielded estimates of both variability and uncertainty in human toxicokinetics of TCE. After adjustment of the models by Markov chain Monte Carlo sampling, the mouse model agreed with a large part of the data. Yet, some data on secondary metabolites were not fit well. The posterior parameter distributions obtained for mice were quite narrow (coefficient of variation [CV] of about 10 or 20%), but these CVs might be underestimated because of the incomplete fit of the model. The data fit, for humans, was better than for mice. Yet, some improvement of the model is needed to correctly describe trichloroethanol concentrations over long time periods. Posterior uncertainties about the population means corresponded to 10-20% CV. In terms of human population variability, volumes and flows varied across subject by approximately 20% CV. The variability was somewhat higher for partition coefficients (between 30 and 40%) and much higher for the metabolic parameters (standard deviations representing about a factor of 2). Finally, the analysis points to differences between human males and females in the toxicokinetics of TCE. The significance of these differences in terms of risk remains to be investigated.