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Biomedical subjects

R Albert

Publications and source records attributed to R Albert.

At least 73 records · Page 4Linked to original sources
PubMed1983

Approach to risk assessment for genotoxic carcinogens based on data from the mouse skin initiation-promotion model.

Tumor induction data in the mouse skin initiation-promotion system were found to be consistent with a quadratic function where the coefficient of the linear term depended on the dose of the promoter. The model implies that the existence of promoters may be more important at low doses of the carcinogen than at high doses where most testing is performed. Experiments are described showing that the initiating effect of carcinogenic chemicals, such as benzo(a)pyrene, 7,12-dimethyl-benz(a)anthracene, nitroquinoline oxide and beta-propiolactone, accumulates in a linear, irreversible manner at low doses. Even when 7,12-dimethylbenz(a)anthracene was applied intragastrically to pregnant females, initiating activity was found in the skins of exposed offspring about in proportion to dose applied and number of cells at risk. The initiated cells essentially represent a potential for cancer that has a high probability for expression in the presence of a promoter. Risk then can be interpreted in terms of the accumulated dose of initiator which alone presents a small risk of cancer. However, a promoter may substantially expand the overall risk, possibly by clonally expanding the initiated cells. Promotion needs to be sustained since there is a reduction of cancer risk if promotion is ended early. Some tissues, such as mouse bladder, may be intrinsically promoted more than others so that comparisons between tissues and between species are best made when the combination of intrinsic promotion and response to extrinsic promotion are comparable.

Animals↗
PubMed1981

Dose-dependent size increases of aortic lesions following chronic exposure to 7,12-dimethylbenz(a)anthracene.

The prevalence, size, and patterns of distribution of arterial lesions (plaques) were investigated in cockerels exposed chronically to 7,12-dimethylbenz(a)anthracene (DMBA). Animals, from 5 to 20 weeks of age, received weekly i.m. injections of 5, 10, or 20 mg of DMBA per kg, dissolved in dimethyl sulfoxide. Control animals received weekly injections of dimethyl sulfoxide. All animals were sacrificed at 21 weeks of age. The entire aorta from each animal was cut transversely into 5-mm segments starting at the iliac trifurcation. The cross-sectional area of plaques was determined by light microscopic analysis of sections taken from the face of each segment. Plaque frequency was similar in DMBA-treated and control groups. However, mean plaque cross-sectional area was 7- to 11-fold higher for the treatment groups than for the controls. The distribution of plaque areas in both treated animals and controls was consistent with a log normal distribution. Median cross-sectional area and plaque volume index each increased in a linear fashion with DMBA dose. Small plaques were present in all groups. Large plaques were present only in DMBA-treated animals. Labeling indices of plaques, although low, were 2.3- to 26-fold higher than for underlying medial smooth muscle cells. The data indicate that the primary response to chronic DMBA exposure is a dose-dependent size increase of spontaneous aortic lesions and not the induction of new lesions.

9,10-Dimethyl-1,2-benzanthracene↗
PubMedDate not supplied

Performance characteristics of methods of analysis used for regulatory purposes. Part II. Pesticide formulations.

The precision parameters of the method-performance (collaborative) studies published in the AOAC Journal from 1915 through 1990 for pesticide formulations have been recalculated on a uniform basis by the International Union of Pure and Applied Chemistry 1987 protocol. About 93% of the 953 accepted assays, which are predominantly gravimetric (G), volumetric (V), and gas (GC) and liquid (LC) chromatographic methods, exhibit relative standard deviations among laboratories (RSDR) that are generally less than 2 times the values predicted from the Horwitz equation: RSDR (%) = 2 exp (1-0.5 log C), where C is the concentration expressed as a decimal fraction. UV, VIS, and IR spectrophotometric (S) methods are somewhat poorer, with about 80% of the reported RSDR values less than twice the predicted RSDR value. The precision parameters of pesticide formulations analyzed by the older methods (G, V, GC) are equivalent to those previously found for drug preparations in the same concentration range; the precision parameters of pesticide formulations analyzed by LC and S are somewhat poorer. Overall, however, the precision parameters of pesticide formulations are generally independent of analyte, method, and matrix, and are primarily a function of concentration. The method-acceptability decisions of the AOAC for pesticide formulations during the past 75 years can be approximated retrospectively by using a criterion for RSDR that is less than 2 times the RSDR calculated from the Horwitz equation.

Databases, Factual↗
PubMedDate not supplied

Precision parameters of methods of analysis required for nutrition labeling. Part I. Major nutrients.

Major components of foods and feeds are fat, protein, and carbohydrates. Fat and protein are determined by direct measurements that are interpreted as the quantity of the constituent. Carbohydrates are usually calculated by difference. For this calculation, values for moisture/solids, ash, and "fiber" are also needed. The readily available collaborative studies for the determination of these major components are reviewed in an attempt to assign precision parameters to validated methods of analysis. When a number of studies for the same analyte, in the same food, by the same method are available, it is seen that the precision parameters among laboratories (standard deviations, SR; relative standard deviations, RSDR) and the ISO maximum tolerable difference functions (repeatability value, r; reproducibility value, R) are not characterized by any conventional distribution. The precision data are best summarized as a median or average parameter and the interval containing the centermost 90% of reported values. Typically, the precision of methods of analysis can be expressed as a function of concentration only, independent of analyte, matrix, and method. The average RSDR value from each collaborative data set can then be used as the numerator in a ratio containing, as the denominator, the value calculated from the Horwitz equation: RSDR = 2 exp (1 - 0.5 log C) where C is the concentration as a decimal fraction. A series of ratios consistently above 1, and especially above 2, probably indicates that a method is unacceptable with respect to precision. By this criterion, only the protein (Kjeldahl) determination is unqualifiedly acceptable with a 90% interval for RSDR of 1 to 3% at C values above about 0.01 (1 g/100 g). Fat, moisture/solids, and ash are acceptable down to limiting concentrations in the region of 1 to 5 g/100 g, if a test portion large enough to provide at least 50 mg of weighable residue or volatiles is specified. Measurements of individual carbohydrates and fiber-related analytes have unexpectedly poor precisions among laboratories. The variability, although high, may still be suitable for nutrition labeling. Reliability of analyses for the control of labeling of the primary nutrients must be achieved through quality assurance programs that require strict adherence to the directions of empirical methods and the use of suitable reference materials for absolute methods.

Databases, Bibliographic↗
PubMedDate not supplied

Precision parameters of standard methods of analysis for dairy products.

The available collaborative studies for standard methods of analysis for various constituents of milk and milk products were examined in an attempt to assign specific repeatability and reproducibility precision parameters to these methods. The different collaborative assays for the primary constituents (moisture/solids, fat, protein), the nutritionally important elements (calcium, sodium, potassium, phosphorus), and miscellaneous analytes/physical constants (ash, lactose, salt, freezing point) produced different estimates of the precision parameters for the same method. A suitable summary of the precision estimates from collaborative studies is given by the reproducibility relative standard deviation, RSDg, which is relatively constant within a product and permits comparisons across products. An estimate of the variation of RSDR for an analyte from a number of collaborative studies is presented in terms of the median and 90% interval (the range of the centermost 90% of values). These estimates are only informative when a substantial number of independent studies are available for pooling the independent estimates to form a distribution of RSDR values. The RSDR for the determination of the primary constituents of milk and milk products is characterized by a median RSDR of 1% and a 90% interval of 0.3-3%, with RSDR estimates occasionally occurring below 0.3% and above 4%. These overall estimates appear to be independent of analyte, matrix, and method and apply to concentrations of primary constituents that range from about 2 to 80%. The repeatability relative standard deviation, RSDr, is unstable, although it tends to converge to about 0.5-0.7 X RSDR. Too few collaborative assays are available to characterize RSDR for the determination of certain other constituents (acidity, ash, lactose, salt, and the nutritionally important elements) unless RSDR values for different analytes, methods, and matrixes are pooled on the basis of similar analyte concentrations. When pooled, the RSDR values are generally better than predicted from the Horwitz equation, RSDR (%) = 2 exp (1-0.5 log10C), where C is the concentration expressed as a decimal fraction; all but one of 661 RSDR values are within the upper empirical limit of twice this curve.

Animals↗
PubMedDate not supplied

Performance characteristics of methods of analysis used for regulatory purposes. I. Drug dosage forms. F. Gravimetric and titrimetric methods.

The original gravimetric and titrimetric methods approved by AOAC for the analysis of pharmaceutical preparations, particularly during the period 1915-1950, show precision, recovery, and outlier parameters approximately the same as those exhibited by the previously reviewed instrumental methods that are currently used. Fifty-nine published collaborative studies utilized gravimetric methods and 85 used titrimetric. The studies of the gravimetric methods encompassed 47 analytes, 95 dosage forms, and 136 assays; the corresponding figures for the titrimetric studies are 72, 112, and 152. An average of approximately 7 laboratories participated per study. The line of best fit of the relative standard deviation between-laboratories (RSDR) plotted against the negative logarithm of the fractional concentration, C, extends from 1.2 and 1.0% for the gravimetric and titrimetric methods, respectively, at 100% concentration to 2.2 and 2.8% at 1.0% concentration. Below this concentration the precision of the titrimetric methods degenerates faster than that of the gravimetric methods. Above about 0.1% concentration the gravimetric and titrimetric methods are somewhat more precise than the instrumental methods in current use for drug analysis. The difference, however, is not statistically significant and the general equation, RSDR = 2 exp(1-0.5 log C), is also applicable to gravimetric and titrimetric methods above a concentration level of about C = 0.001 (0.1%).

Chemical Phenomena↗
PubMedDate not supplied

Performance characteristics of methods of analysis used for regulatory purposes. I. Drug dosage forms. C. Automated methods.

For analysis of drug dosage forms, precision measures of AOAC approved automated methods, usually containing a spectrophotometric or fluorometric measurement step, were recalculated on a consistent statistical basis, using a computer program "FDACHEMIST." Ten collaborative studies of 14 compounds in 38 materials, consisting of various dosage forms, usually in 10 replications by an average of 7 laboratories, with a total of 2461 determinations, were reviewed. The average relative standard deviations within-laboratory (RSDo) and among-laboratories (RSDx) were 1.1 and 1.9%, respectively, and the ratio of RSDo/RSDx was 0.57, with an average outlier rate of 0.57% of the reported values. The line of best fit for RSDx plotted against - log concentration increases slightly with decreasing concentration, extending from an RSDx of about 1.6% at 100% concentration to an RSDx of 2.2% at 0.1% concentration, a change in RSDx of about 0.2% for a 10-fold decrease in concentration, independent of analyte and matrix.

Autoanalysis↗
PubMedDate not supplied

Performance characteristics of methods of analysis used for regulatory purposes. I. Drug dosage forms. E. miscellaneous methods.

Precision parameters of miscellaneous methods for the analysis of drug dosage forms approved by AOAC since 1972, and not previously reviewed in this series, were recalculated on a consistent statistical basis by using the computer program FDACHEMIST. Seventeen published collaborative studies were reviewed; the studies encompassed 19 analytes in 80 different materials (dosage forms), 102 collaborative assays, approximately 10 laboratories per study, and principally direct spectrophotometric, polarographic, and spectroscopic methods, for a total of 1451 determinations. The average repeatability relative standard deviation (within-laboratories, RSDo) for the instrumental methods was 1.5%; the reproducibility relative standard deviation (among-laboratories, including within-, RSDx) was 2.6%; the ratio RSDo/RSDx of the averages was 0.57, with an average outlier rate of 2.7% of the reported determinations. The line of best fit of RSDx for the instrumental methods plotted against the negative logarithm of the concentration increases slightly with decreasing concentration, extending from an RSDx of approximately 2.0% at 100% concentration to an RSDx of 3.4% at 0.001% (10 ppm) concentration; this represents an RSDx change of approximately 0.3% (absolute) for each 10-fold decrease in concentration, independent of analyte, matrix, and method. A method for determining precipitated allergenic protein by the micro-Kjeldahl technique appeared to be outside this general relation, showing an RSDx of about 13% at a concentration of 0.015% (150 ppm) nitrogen.

Allergens↗