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Biomedical subjects

E J Sampson

Publications and source records attributed to E J Sampson.

At least 19 recordsLinked to original sources
PubMed1995

Using biological monitoring to assess human exposure to priority toxicants.

Scientifically valid exposure assessment is crucial to risk assessment, risk management, and prevention of environmental disease. Scientists have used three tools to assess exposure: exposure history/questionnaire, environmental monitoring (including personal monitoring), and biological monitoring. Combinations of these tools usually provide the exposure information needed to meet objectives of human studies evaluating the exposure-health effect relationship. Biological monitoring is a capable exposure assessment tool that has provided important information used in public health decisions. We briefly describe how risk assessment and risk management decisions for lead, dioxin, and volatile organic compounds have substantially benefited from exposure information obtained from biological monitoring.

Dioxins↗
PubMed1995

The priority toxicant reference range study: interim report.

The relationship between human exposure to environmental toxicants and health effects is of utmost interest to public health scientists. To define this relationship, these scientists need accurate and precise methods for assessing human exposure and effects. One of the most accurate and precise means of assessing exposure is to measure the level of the toxicant or its primary metabolite in a biologic specimen; this has been defined as measuring the internal dose. This measurement must be quantitative to best study the dose-response relationship. Pertinent questions asked during an exposure assessment include "How do the levels of a given toxicant in a particular population compare with the levels of that toxicant in other populations?" and "What is the prevalence of exposure to that toxicant in other populations?" To answer these questions for two chemical classes of environmental toxicants, we developed state-of-the-art analytic methods and then applied them to measure the levels of 44 environmental toxicants in biologic specimens from 1000 United States residents who participated in the Third National Health and Nutrition Examination Survey (NHANES III). These 1000 people are a cross-sectional subset of the NHANES III population and were selected from urban and rural communities in four regions of the United States; all were between 20 and 59 years of age. This subset is not a probability-based sample.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Traditional lipoprotein profile: clinical utility, performance requirement, and standardization.

The lipid and lipoprotein parameters which are predominantly measured and effectively comprise the traditional lipoprotein profile include total cholesterol, high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglyceride. Total cholesterol is accepted as the initial entry point in a case finding approach such as that recommended by the National Cholesterol Education Program (NCEP). HDL cholesterol, known to be a strong inverse predicator of risk, is an additional measurement to total cholesterol to improve risk assessments. The evidence for triglyceride association remains mixed: although strong associations are found in some studies, the evidence as an independent risk factor is still incomplete. Triglyceride is therefore measured primarily for LDL estimation. Final classification and potential intervention is ultimately based on the measurement of LDL cholesterol. Reliability in the measurement of total cholesterol, HDL, LDL, and triglyceride is especially important if the uniform decision points established by the NCEP are to be properly implemented. Attention must be placed on controlling preanalytical sources of variation, which can account for as much as 60% of the total measurement variability. The major analytical source of error comes from matrix effects, which results in problems of proper analytical calibration. Instrument system calibration should be verified by a comparison with an accuracy base using fresh patient specimens. CDC has established a network of reference method laboratories to provide access to these lipid and lipoprotein accuracy bases.

Coronary Disease↗
PubMed1994

Technical and scientific developments in exposure marker methodology.

Recent advances in techniques to measure markers of exposure to environmental toxicants in humans are changing the ways in which environmental scientists, epidemiologists, and policymakers characterize and interpret such exposure. In this article we review some major technical and scientific developments in exposure marker methodology for estimating internal dose, with special reference to studies conducted at the US Centers for Disease Control and Prevention. We consider important characteristics of laboratory methods, advances in laboratory technology, analytical standards, and quality assurance of laboratory measurements; comparisons with indirect methods for estimating exposures, such as exposure indices and questionnaires; human pharmacokinetic data; sampling problems; surveillance of human exposures to toxicants; and interpretation of measurements. With a view to increasing the reliability of exposure assessment, we make recommendations for obtaining more data on human exposure to toxicants.

Biomarkers↗
PubMed1991

Factors influencing the accuracy of the national reference system total cholesterol reference method.

Previous comparisons between the Reference and Definitive Methods for measuring serum cholesterol have demonstrated a small but persistent positive bias in the Reference Method, averaging about +1.6%. Here we describe the results of further investigations designed to better characterize the nature of this bias. Analysis of a well-characterized model serum sample (SRM 909) suggests that more than half of the difference in cholesterol values determined by the two methods is the result of small contributions from cholesterol precursor sterols and phytosterols, which are also measured for the Reference Method. An additional significant contribution may be from cholesterol oxidation products, particularly 7-hydroxycholesterol isomers, which are active in the Liebermann-Burchard reaction. The 7-hydroxycholesterol in SRM 909, most of which appeared to be already present in the serum rather than formed during saponification, may account for as much as 20% of the observed difference between the methods. Contributions from other possible sources, including impurities in the cholesterol standard and incomplete saponification of cholesteryl esters, are very small. Because the observed bias is both quite small and consistent among samples, the cholesterol Reference Method continues to meet all of the requirements generally expected for a dependable and effective Reference Method.

Carbon Isotopes↗
PubMed1988

Standardization of lipid, lipoprotein, and apolipoprotein measurements.

Accurate laboratory measurement of serum cholesterol has become a national public health priority. National proficiency testing surveys indicate that laboratory inaccuracy in cholesterol testing is more of a problem than precision. Like precision, accuracy is a function of multiple pre-analytical and analytical sources of variation. Controlling pre-analytical sources of variation helps minimize such sources of variation as intraperson biological, behavioral, and clinical differences, and variations caused by sample collection, handling, and shipping. Standardization of analytical sources of variation helps to achieve and maintain desirable analytical performance, accurate reporting, and correct interpretation of a reported cholesterol result. The intraperson total variation in lipoproteins and their constituents is of primary interest when one is interpreting a single result or a series of results from a single person. The mean of multiple specimens from the same person is required if one is to obtain an accurate value for intraperson total cholesterol and minimize pre-analytical sources of variation. Standardizing analytical sources of variation in some instrument systems requires standardizing results by using "fresh" patients' specimens.

Apolipoproteins↗
PubMed1986

2,3,7,8-Tetrachlorodibenzo-p-dioxin levels in adipose tissue of exposed and control persons in Missouri. An interim report.

The compound 2,3,7,8-tetrachlorodibenzo-p-dioxin, commonly known as dioxin, was measured in the adipose tissue of 39 persons with a history of residential, recreational, or occupational exposure in Missouri and in 57 persons in a control group. All participants had detectable levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in their adipose tissue, but the exposed group had significantly higher levels. Levels of six of the exposed persons were more than five times greater than the level of the highest control. Measuring 2,3,7,8-tetrachlorodibenzo-p-dioxin in adipose tissue provides a much improved index of exposure, an important advance for research studies evaluating the possible health effects of this compound.

Adipose Tissue↗
PubMed1984

Determination of steroid hormones in a human-serum reference material by isotope dilution--mass spectrometry: a candidate definitive method for cortisol.

We report a method, based on isotope dilution--mass spectrometry, for determining cortisol in a pooled specimen of human serum. Isotopically labeled cortisol is added to 5.0 mL of serum so that the molar concentrations of labeled cortisol and unlabeled cortisol are approximately equal. The specimen and two calibration standards are extracted with dichloromethane, and the extracted cortisol is converted to the methoxime-trimethylsilyl ether derivative. Samples and standards are analyzed by gas chromatography--mass spectrometry by monitoring the peak areas for m/z 605 and 608. The cortisol concentration is calculated by linear interpolation between the two bracketing standards. Variances of data collected during six weeks showed that the overall coefficient of variation (CV) was 0.69% (n = 32); the within-vial CV, 0.63%; the among-vial CV, 0.22%; and the among-day CV, 0.15% (means = 3.973 nmol/vial). Method specificity was demonstrated by liquid chromatographic as well as C8 mini-column cleanup of samples before derivation, by alternative ion monitoring at m/z 636 and 639, and by negative-ion chemical ionization at m/z 459 and 462. Derivatives of all observed degradation products of cortisol under basic, neutral, and acidic conditions did not interfere.

Chromatography, High Pressure Liquid↗
PubMed1984

Multivariate examination of response surfaces around the reaction conditions for the Scandinavian Society's recommended method for creatine kinase determinations.

We examined the reaction surfaces around five variables (imidazole, ADP, creatine phosphate, magnesium, and pH) in the Scandinavian method for determining creatine kinase, using factorial experimentation (five level, five factor) at reaction temperatures of 30 and 37 degrees C. Theoretical response surfaces were computed by fitting a quadratic polynomial equation to the experimental data by least-squares regression. Essentially no differences were apparent in the theoretical curves among the five specimens we analyzed, or between reaction temperatures. Our response-surface data showed the following: for pH and imidazole, activity optima in the region of the Scandinavian conditions; for creatine phosphate, a broad plateau over the concentration range investigated (10 to 50 mmol/L); and for magnesium and ADP, gently increasing contours with maximal creatine kinase activity at concentrations greater than those investigated in our study (magnesium 15 mmol/L, ADP 3.5 mmol/L).

Adenosine Diphosphate↗
PubMed1983

Creatine kinase response surfaces explored by use of factorial experiments and simplex maximization.

We conducted a five-component, five-level response-surface experiment to optimize the pH and the concentrations of magnesium, creatine phosphate, adenosine diphosphate, and buffer in an assay for creatine kinase. Under optimal conditions, creatine kinase activity was about 5% greater than that obtained with a previously reported assay (Clin Chem 23: 1569, 1977). We also applied a simplex maximization algorithm to the response-surface equation to locate areas of maximum sensitivity. Reaction conditions for two such areas were found, each yielding approximately 11% more activity than with the previously reported method.

Adenosine Diphosphate↗
PubMed1982

The development and evaluation of a homogeneous immunoassay for the isoenzymes of aspartate aminotransferase.

Purified isoenzymes of aspartate aminotransferase (AST) from human liver (mitochondrial) and erythrocytes (cytoplasmic) were used to elicit antisera in rabbits. Each antiserum was characterized for titer and specificity. Complexes formed upon addition of each isoenzyme to its specific antiserum were demonstrated to be catalytically inactive. Results obtained when either filtration or centrifugation was used for separating the complexes (heterogeneous assay) were comparable to those obtained when the complexes were not separated (homogeneous assay) from the mixture before assay. A quality control system was designed to monitor specificity in addition to the usual parameters. The precision for the inhibition of cytoplasmic (CV 4.8%) and mitochondrial (CV 3.5%) isoenzymes was within that of the enzymatic assay. Several parametric conditions of the enzyme-antibody reactions were examined, and the assay was adapted for semi-automation. The homogeneous assay was evaluated with a series of pseudo specimens containing known mixtures of pure isoenzymes to determine the extent of recovery (99.8%) for a particular isoenzyme in the presence of varying concentrations of the other isoenzyme. In addition, sera from patients having elevated AST concentrations were examined for isoenzyme contributions to total AST activity. A mean recovery of 96% was obtained for these specimens.

Antibody Specificity↗
PubMed1982

Stability of creatine kinase-3 in lyophilized materials.

We examined the stability of creatine kinase (EC 2.7.3.2) isoenzyme-3 (CK-3) in lyophilized bovine albumin matrices in the presence and absence of various sulfhydryl compounds and ADP. We initially purified CK-3 from human myocardium and skeletal muscle by the batch-chromatographic technique and by gradient elution column chromatography to specific activities of 293 and 93 kU/g, respectively. To assess stability, we subjected the lyophilized materials to storage studies at 4, 25, 37, 42, 56, and 65 degrees C and compared first-order rate constants for the decay of creatine kinase activity at 42 degrees C. Our most stable matrix contained, per liter, 2 mmol of ADP and 10 mmol of N-acetylcysteine, and had an extrapolated first-order half-life (Arrhenius plot) at -20 degrees C of approximately 60000 years.

Creatine Kinase↗
PubMed1982

Multivariate and univariate optimization studies of liquid-chromatographic separation of steroid mixtures.

We developed a high-performance liquid-chromatographic separation of five steroids (estriol, estradiol, cortisol, progesterone, and testosterone), eluting with a water-acetonitrile gradient from a reversed-phase (C18) column. By applying a simplex search algorithm to maximize a chromatographic-response function, we sought to optimize the original conditions of the chromatographic analysis, which did not separate two pairs of overlapping peaks. Our chromatographic-response function incorporated both peak separation and total time of analysis. Three factors were varied simultaneously to maximize this function: flow rate, column temperature, and gradient shape. From the simplex optimization, we selected a flow rate of 1.50 mL/min, a temperature of 52 degrees C, and a linear gradient for our analysis. Subsequent univariate studies of the initial mobile phase composition showed that acetonitrile/water (20/80 by vol) gave an adequate separation.

Analysis of Variance↗
PubMed1981

Characterization and intermethod relationships of materials containing purified human pancreatic and salivary amylase.

We describe the preparation and characterization of materials containing human pancreatic and salivary alpha-amylase (EC 3.2.1.1) and examine their relationship to endogenous amylase in human serum. Amylase was purified from human pancreas and saliva by solvent- and salt-fractionation and column chromatography to specific activities of 63 and 279 kU/g, respectively. Four liquid pools, differing only in activity, were prepared from each source of amylase, each in a matrix containing, per liter: 30 g of human albumin, 50 mmol of sodium chloride, 1 mmol of calcium chloride, and 50 mmol of Tris hydrochloride buffer, pH 7.4. Characterization of the pools showed that the amylase activity in the materials was stable for at least six months at 25 degrees C; among-vial variability of amylase activity was less than or equal to 0.5% (2 CV); and the pools were free from eight possible contaminating enzymes. Plots of salivary vs pancreatic amylase activity measure in our materials with eight commercially available methods showed least-squares slopes ranging from 0.51 to 1.0. The intermethod "commutability" of the materials (i.e., how closely they mimic endogenous serum amylase) was examined in relationship to approximately 100 human sera.

Amylases↗