Population toxicokinetics of tetrachloroethylene

 In assessing the distribution and metabolism of toxic compounds in the body, measurements are not always feasible for ethical or technical reasons. Computer modeling offers a reasonable alternative, but the variability and complexity of biological systems pose unique challenges in model building and adjustment. Recent tools from population pharmacokinetics, Bayesian statistical inference, and physiological modeling can be brought together to solve these problems. As an example, we modeled the distribution and metabolism of tetrachloroethylene (PERC) in humans. We derive statistical distributions for the parameters of a physiological model of PERC, on the basis of data from Monster et al. (1979). The model adequately fits both prior physiological information and experimental data. An estimate of the relationship between PERC exposure and fraction metabolized is obtained. Our median population estimate for the fraction of inhaled tetrachloroethylene that is metabolized, at exposure levels exceeding current occupational standards, is 1.5% [95% confidence interval (0.52%, 4.1%)]. At levels approaching ambient inhalation exposure (0.001 ppm), the median estimate of the fraction metabolized is much higher, at 36% [95% confidence interval (15%, 58%)]. This disproportionality should be taken into account when deriving safe exposure limits for tetrachloroethylene and deserves to be verified by further experiments. Received: 20 April 1995/Accepted: 24 August 1995     

Lead in finger-bone analysed in vivo in active and retired lead workers

In 75 active lead workers the median lead level in finger-bone (bone-Pb), as determined in vivo by an X-ray fluorescence method, was 43 micrograms/g (range less than 20-122). In 32 retired workers the median level was even higher, 59 micrograms/g (range less than 20-135), which indicates a slow turnover rate of lead in finger-bone. This was confirmed in 18 of the "active" workers, in whom bone-Pb was studied in connection with an exposure-free period. In spite of a significant decrease in blood-lead levels (B-Pb), no systematic change of bone-Pb occurred. There was an increase of bone-Pb with time of employment, but with a large interindividual variation. No association was found between bone-Pb and present B-Pb in the active lead workers. However, in the retired ones, B-Pb rose with increasing bone-Pb. The bone-lead pool thus causes an "internal" lead exposure.     

混配农药中氰戊菊酯在小鼠体内的代谢和分布

目的　了解混配农药中氰戊菊酯在小鼠体内的代谢和分布。方法　以14 C -氰戊菊酯为示踪剂 ,静脉注射给药。给药后 0 .5～ 12 0min之间采 9次血样 ,8～ 96 0min之间分别对脑、心脏、肝脏和肺脏采 8次样品。样品用 β闪烁计数仪测量 ,并换算成化学浓度。用残数法计算毒代动力学参数。结果　混配农药中的氰戊菊酯的代谢符合二室开放模型。分布相T1/ 2 α为 2 .7min ,消除相T1/ 2 β为 10 6 .6min ,表观分布容积为 2 .9L/kg ,正向扩散系数k12 (0 .17min-1)大于逆向扩散系数k2 1(0 .0 77min-1)。分布浓度肺脏中最高 ,其次为肝脏、心脏、脑。结论　肺脏优势参与了氰戊菊酯的代谢过程 ,应重视此类农药的肺脏毒性。     

Characterization of AUCs from Sparsely Sampled Populations in Toxicology Studies

Purpose. The objective of this work was to develop and validate blood sampling schemes for accurate AUC determination from a few samples (sparse sampling). This will enable AUC determination directly in toxicology studies, without the need to utilize a large number of animals. Methods. Sparse sampling schemes were developed using plasma concentration-time (Cp-t) data in rats from toxicokinetic (TK) studies with the antiepileptic felbamate (F) and the antihistamine loratadine (L); Cp-t data at 13–16 time-points (N = 4 or 5 rats/time-point) were available for F, L and its active circulating metabolite descarboethoxyloratadine (DCL). AUCs were determined using the full profile and from 5 investigator designated time-points termed critical time-points. Using the bootstrap (re-sampling) technique, 1000 AUCs were computed by sampling (N = 2 rats/point, with replacement) from the 4 or 5 rats at each critical point. The data were subsequently modeled using PCNONLIN, and the parameters (k_a, k_e, and V_d) were perturbed by different degrees to simulate pharmacokinetic (PK) changes that may occur during a toxicology study due to enzyme induction/inhibition, etc. Finally, Monte Carlo simulations were performed with random noise (10 to 40%) applied to Cp-t and/or PK parameters to examine its impact on AUCs from sparse sampling. Results. The 5 time-points with 2 rats/point accurately and precisely estimated the AUC for F, L and DCL; the deviation from the full profile was ~10%, with a precision (%CV) of ~15%. Further, altered kinetics and random noise had minimal impact on AUCs from sparse sampling. Conclusions. Sparse sampling can accurately estimate AUCs and can be implemented in rodent toxicology studies to significantly reduce the number of animals for TK evaluations. The same principle is applicable to sparse sampling designs in other species used in safety assessments.     

A toxicokinetic model of malathion and its metabolites as a tool to assess human exposure and risk through measurements of urinary biomarkers.

A toxicokinetic model is proposed to predict the time evolution of malathion and its metabolites, mono- and dicarboxylic acids (MCA, DCA) and phosphoric derivatives (dimethyl dithiophosphate [DMDTP], dimethyl thiophosphate [DMTP], and dimethyl phosphate [DMP]) in the human body and excreta, under a variety of exposure routes and scenarios. The biological determinants of the kinetics were established from published data on the in vivo time profiles of malathion and its metabolites in the blood and urine of human volunteers exposed by intravenous, oral, or dermal routes. In the model, body and excreta compartments were used to represent the time varying amounts of each of the following: malathion, MCA, DCA, DMDTP, DMTP, and DMP. The dynamic of intercompartment exchanges was described mathematically by a differential equation system that ensured conservation of mass at all times. The model parameters were determined by statistically adjusting the explicit solution of the differential equations to the experimental human data. Simulations provide a close approximation to kinetic data available in the published literature. When simulating a dermal exposure to malathion, the main route of entry for workers, the model predicts that it takes an average of 11.8 h to recover half of the absorbed dose of malathion eventually excreted in urine as metabolites, compared to 3.2 h following an intravenous injection and 4.0 h after oral administration. This shows that following a dermal exposure, the absorption rate governs the urinary excretion rate of malathion metabolites because the dermal absorption rate is much slower than biotransformation and renal clearance processes. The model served to establish biological reference values for malathion metabolites in urine since it allows links to be made between the absorbed dose of malathion and the time course of cumulative amounts of metabolites excreted in urine. From the no-observed-effect level (NOEL) of 0.61 micromol/kg/day derived from the data of Moeller and Rider (1962), the model predicts corresponding biological reference values for MCA, DCA, and phosphoric derivatives of 44, 13, and 62 nmol/kg, respectively, in 24-h urine samples. The latter were used to assess the health risk of workers exposed to malathion in botanical greenhouses, starting from urinary measurements of MCA and DCA metabolites.     

The refinement of uncertainty/safety factors in risk assessment by the incorporation of data on toxicokinetic variability in humans.

The derivation of safe levels of exposure in humans for compounds that are assumed to cause threshold toxicity has relied on the application of a 100-fold uncertainty factor to a measure for the threshold, such as the no observed adverse effect level (NOAEL) or the benchmark dose (BMD). This 100-fold safety factor consists of the product of two 10-fold factors allowing for human variability and interspecies differences. The International Programme on Chemical Safety has suggested the subdivision of these 10-fold factors to allow for variability in toxicokinetics and toxicodynamics. This subdivision allows the replacement of the default uncertainty factors with a chemical-specific adjustment factor (CSAF) when suitable data are available. This short review describes potential options to refine safety factors used in risk assessment, with particular emphasis on pathway-related uncertainty factors associated with variability in kinetics. These pathway-related factors were derived from a database that quantified interspecies differences and human variability in phase I metabolism, phase II metabolism, and renal excretion. This approach allows metabolism and pharmacokinetic data in healthy adults and subgroups of the population to be incorporated in the risk-assessment process and constitutes an intermediate approach between simple default factors and chemical-specific adjustment factors.     

Uptake and disposition of inhaled methanol vapor in humans.

Methanol is a widely used solvent and a potential fuel for motor vehicles. Human kinetic data of methanol are sparse. As a basis for biological exposure monitoring and risk assessment, we studied the inhalation toxicokinetics of methanol vapor in four female and four male human volunteers during light physical exercise (50 W) in an exposure chamber. The relative uptake of methanol was about 50% (range 47-53%). Methanol in blood increased from a background level of about 20 to 116 and 244 microM after 2 h exposure at 0, 100 ppm (131 mg/m3) and 200 ppm (262 mg/m3), respectively. Saliva showed substantially higher levels than blood immediately after exposure. This difference disappeared in a few minutes; thereafter the concentrations and time courses in blood, urine, and saliva were similar, with half times of 1.4, 1.7, and 1.3 h, respectively. The postexposure decrease of methanol in exhaled air was faster, with a half time of 0.8 h. The methanol concentrations were approximately twice as high in all four types of biological samples at 200 compared to 100 ppm. No increase in urinary formic acid was seen in exposed subjects. Our study indicates non-saturated, dose-proportional kinetics of methanol up to 200 ppm for 2 h. No gender differences were detected. Similar, parallel patterns were seen with regard to the methanol time courses in blood, urine, and saliva, whereas the concentration in exhaled air decreased markedly faster. Thus, apart from blood and urine, saliva also seems suitable for biomonitoring of methanol exposure.     

Use of Monoclonal Antibodies in the Sensitive Detection and Neutralization of Botulinum Neurotoxin Serotype B

Botulinum neurotoxins (BoNT) are some of nature’s most potent toxins. Due to potential food contamination, and bioterrorism concerns, the development of detection reagents, therapeutics and countermeasures are of urgent interest. Recently, we have developed a sensitive electrochemiluminescent (ECL) immunoassay for BoNT/B, using monoclonal antibodies (mAbs) MCS6-27 and anti-BoNT/B rabbit polyclonal antibodies as the capture and detector. The ECL assay detected as little as 1 pg/mL BoNT/B in the buffer matrix, surpassing the detection sensitivities of the gold standard mouse bioassays. The ECL assay also allowed detection of BoNT/B in sera matrices of up to 100% sera with negligible matrix effects. This highly-sensitive assay allowed the determination of the biological half-lives of BoNT/B holotoxin in vivo. We further tested the toxin neutralization potential of our monoclonal antibodies using the mouse systemic and oral intoxication models. A combination of mAbs protected mice in both pre- and post-exposure models to lethal doses of BoNT/B. MAbs were capable of increasing survival of animals when administered even 10 h post-intoxication in an oral model, suggesting a likely time for BoNT/B complexes to reach the blood stream. More sensitive detection assays and treatments against BoNT intoxication will greatly enhance efforts to combat botulism.     

UPLC-MS/MS测定大鼠血浆多柔比星浓度方法的建立及毒代动力学应用

目的 建立一种简便、快速、灵敏的测定大鼠多柔比星血药浓度的超高效液相-质谱联用（UPLC-MS/MS）法,并将其应用于注射用盐酸多柔比星大鼠体内毒代动力学实验。方法 采用ACQUITY UPLC^® BEH C₁₈（50 mm×2.1 mm,1.7 μm）色谱柱,流动相为0.1%甲酸（含2 mmol/L甲酸铵）水溶液-乙腈,梯度洗脱。体积流量为0.4 mL/min,进样量为10 μL。采用电喷雾离子源（ESI）,多反应监测（MRM）方式扫描,以正离子方式进行检测,蛋白沉淀法提取样品。用于定量分析的离子对分别为多柔比星m/z 544.43→m/z 397.08,内标地西泮m/z 285.02→154.40。SD大鼠30只,按体质量随机分为3组,分别单次iv 52.2、61.4、72.3 mg/m²盐酸多柔比星后测定血药浓度,并用DAS 3.1.4软件计算毒代参数。结果 血浆中内源性物质不干扰待测物和内标的测定,多柔比星在0.5～100 ng/mL范围内线性关系良好,定量下限为0.5 ng/mL。多柔比星在0.5、1、20、80 ng/mL 4个浓度的批内批间精密度RSD值为3.21%～12.79%。多柔比星在1、80 ng/mL的提取回收率和基质效应分别为102.00%～103.75%和79.27%～89.34%。SD大鼠分别单次iv给予注射用盐酸多柔比星52.2、61.4、72.3 mg/m²后,多柔比星在大鼠体内的AUC_0-t分别为（2 318.78±282.65）、（3 203.11±829.41）和（3 326.96±546.04） ng·h/mL,C_0.083h分别为（1 720.50±851.19）、（3 363.00±1 458.84）和（2 156.50±919.90）ng/mL。结论 建立的UPLC-MS/MS分析方法灵敏度高、样品处理方法简单、样品分析时间短,可以应用于大鼠多柔比星毒代动力学试验中。     

Chronic Exposure to Deoxynivalenol Has No Influence on the Oral Bioavailability of Fumonisin B1 in Broiler Chickens

Both deoxynivalenol (DON) and fumonisin B₁ (FB₁) are common contaminants of feed. Fumonisins (FBs) in general have a very limited oral bioavailability in healthy animals. Previous studies have demonstrated that chronic exposure to DON impairs the intestinal barrier function and integrity, by affecting the intestinal surface area and function of the tight junctions. This might influence the oral bioavailability of FB₁, and possibly lead to altered toxicity of this mycotoxin. A toxicokinetic study was performed with two groups of 6 broiler chickens, which were all administered an oral bolus of 2.5 mg FBs/kg BW after three-week exposure to either uncontaminated feed (group 1) or feed contaminated with 3.12 mg DON/kg feed (group 2). No significant differences in toxicokinetic parameters of FB₁ could be demonstrated between the groups. Also, no increased or decreased body exposure to FB₁ was observed, since the relative oral bioavailability of FB₁ after chronic DON exposure was 92.2%.