Biomedical subjects

Bruce A Buchholz

Publications and source records attributed to Bruce A Buchholz.

15 recordsLinked to original sources

PubMed2006

Neocortical neurogenesis in humans is restricted to development.

Stem cells generate neurons in discrete regions in the postnatal mammalian brain. However, the extent of neurogenesis in the adult human brain has been difficult to establish. We have taken advantage of the integration of (14)C, generated by nuclear bomb tests during the Cold War, in DNA to establish the age of neurons in the major areas of the human cerebral neocortex. Together with the analysis of the neocortex from patients who received BrdU, which integrates in the DNA of dividing cells, our results demonstrate that, whereas nonneuronal cells turn over, neurons in the human cerebral neocortex are not generated in adulthood at detectable levels but are generated perinatally.

Aged↗

PubMed2006

Human vitamin B12 absorption measurement by accelerator mass spectrometry using specifically labeled (14)C-cobalamin.

There is a need for an improved test of human ability to assimilate dietary vitamin B(12). Assaying and understanding absorption and uptake of B(12) is important because defects can lead to hematological and neurological complications. Accelerator mass spectrometry is uniquely suited for assessing absorption and kinetics of carbon-14 ((14)C)-labeled substances after oral ingestion because it is more sensitive than decay counting and can measure levels of (14)C in microliter volumes of biological samples with negligible exposure of subjects to radioactivity. The test we describe employs amounts of B(12) in the range of normal dietary intake. The B(12) used was quantitatively labeled with (14)C at one particular atom of the dimethylbenzimidazole (DMB) moiety by exploiting idiosyncrasies of Salmonella metabolism. To grow aerobically on ethanolamine, Salmonella enterica must be provided with either preformed B(12) or two of its precursors, cobinamide and DMB. When provided with (14)C-DMB specifically labeled in the C2 position, cells produced (14)C-B(12) of high specific activity (2.1 GBq/mmol, 58 mCi/mmol) (1 Ci = 37 GBq) and no detectable dilution of label from endogenous DMB synthesis. In a human kinetic study, a physiological dose (1.5 microg, 2.2 kBq/59 nCi) of purified (14)C-B(12) was administered and showed plasma appearance and clearance curves consistent with the predicted behavior of the pure vitamin. This method opens new avenues for study of B(12) assimilation.

Carbon Radioisotopes↗

PubMed2006

Analysis of artificial radiocarbon in different skeletal and dental tissue types to evaluate date of death.

Radiocarbon dating, with special reference to the modern bomb-curve, can provide useful information to elucidate the date of death of skeletonized human remains. Interpretation can be enhanced with analysis of different types of tissues within a single skeleton because of the known variability of formation times and remodeling rates. Analysis of radiocarbon content of teeth, especially the enamel in tooth crowns, provides information about the date of formation in the childhood years and in consideration of the known timing of tooth formation can be used to estimate the birth date after 1950 ad. Radiocarbon analysis of modern cortical and trabecular bone samples from the same skeleton may allow proper placement on the pre-1963 or post-1963 sides of the bomb-curve as most trabecular bone generally undergoes more rapid remodeling than does most cortical bone. Pre-1963 bone formation would produce higher radiocarbon values for most trabecular bone than for most cortical bone. This relationship is reversed for formation after 1963. Radiocarbon analysis was conducted in this study on dental, cortical, and trabecular bone samples from two adult individuals of known birth (1925 and 1926) and death dates (1995 and 1959). As expected, the dental results correspond to prebomb-curve values reflecting conditions during the childhoods of the individuals. The radiocarbon content of most bone samples reflected the higher modern bomb-curve values. Within the bone sample analyses, the values of the trabecular bone were higher than those of cortical bone and supported the known placement on the pre-1963 side of the bomb-curve.

Adult↗

PubMed2005

Forensics: age written in teeth by nuclear tests.

Establishing the age at death of individuals is an important step in their identification and can be done with high precision up to adolescence by analysis of dentition, but it is more difficult in adults. Here we show that the amount of radiocarbon present in tooth enamel as a result of nuclear bomb testing during 1955-63 is a remarkably accurate indicator of when a person was born. Age is determined to within 1.6 years, whereas the commonly used morphological evaluation of skeletal remains and tooth wear is sensitive to within 5-10 years in adults.

Age Determination by Teeth↗

PubMed2005

Retrospective birth dating of cells in humans.

The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited. Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope 14C in the atmosphere, followed by an exponential decrease after 1963. We show that the level of 14C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region. Retrospective birth dating is a generally applicable strategy that can be used to measure cell turnover in man under physiological and pathological conditions.

Adult↗

PubMed2005

Neuroscience and accelerator mass spectrometry.

Accelerator mass spectrometry (AMS) is a mass spectrometric method for quantifying rare isotopes. It has had a great impact in geochronology and archaeology and is now being applied in biomedicine. AMS measures radioisotopes such as 3H, 14C, 26Al, 36Cl and 41Ca, with zepto- or attomole sensitivity and high precision and throughput, allowing safe human pharmacokinetic studies involving microgram doses, agents having low bioavailability or toxicology studies where administered doses must be kept low (<1 microg kg(-1)). It is used to study long-term pharmacokinetics, to identify biomolecular interactions, to determine chronic and low-dose effects or molecular targets of neurotoxic substances, to quantify transport across the blood-brain barrier and to resolve molecular turnover rates in the human brain on the time-scale of decades. We review here how AMS is applied in neurotoxicology and neuroscience.

Age Factors↗

PubMed2004

Quantitation of in vivo human folate metabolism.

BACKGROUND: A quantitative understanding of human folate metabolism is needed. OBJECTIVE: The objective was to quantify and interpret human folate metabolism as it might occur in vivo. DESIGN: Adults (n = 13) received 0.5 nmol [(14)C]pteroylmonoglutamate (100 nCi radioactivity) plus 79.5 nmol pteroylmonoglutamate in water orally. (14)C was measured in plasma, erythrocytes, urine, and feces for >/=40 d. Kinetic modeling was used to analyze and interpret the data. RESULTS: According to the data, the population was healthy and had a mean dietary folate intake of 1046 nmol/d, and the apparent dose absorption of (14)C was 79%. The model predictions showed that only 0.25% of plasma folate was destined for marrow, mean bile folate flux was 5351 nmol/d, and the digestibility of the mix (1046 + 5351 nmol/d) was 92%. About 33% of visceral pteroylmonoglutamate was converted to the polyglutamate form, most of the body folate was visceral (>99%), most of the visceral folate was pteroylpolyglutamate (>98%), total body folate was 225 micromol, and pteroylpolyglutamate synthesis, recycling, and catabolism were 1985, 1429, and 556 nmol/d, respectively. Mean residence times were 0.525 d as visceral pteroylmonoglutamate, 119 d as visceral pteroylpolyglutamate, 0.0086 d as plasma folate, and 0.1 d as gastrointestinal folate. CONCLUSIONS: Across subjects, folate absorption, bile folate flux, and body folate stores were larger than prior estimates. Marrow folate uptake and pteroylpolyglutamate synthesis, recycling, and catabolism are saturable processes. Visceral pteroylpolyglutamate was an immediate precursor of plasma p-aminobenzoylglutamate. The model is a working hypothesis with derived features that are explicitly model-dependent. It successfully quantitated folate metabolism, encouraging further rigorous testing.

Adult↗

PubMed2004

Phytochemical research using accelerator mass spectrometry.

Vegetables and fruits provide an array of microchemicals in the form of vitamins and secondary metabolites (phytochemicals) that may lower the risk of chronic disease. Tracing these phytochemicals at physiologic concentrations has been hindered by a lack of quantitative sensitivity for chemically equivalent tracers that could be used safely in healthy people. Accelerator mass spectrometry is a relatively new technique that provides the necessary sensitivity (in attomoles) and measurement precision (<3%) towards 14C-labeled phytochemicals for detailed kinetic studies in humans at dietary levels.

Food Analysis↗

PubMed2003

Absorption and retinol equivalence of beta-carotene in humans is influenced by dietary vitamin A intake.

The effect of vitamin A supplements on metabolic behavior of an oral tracer dose of [14C]beta-carotene was investigated in a longitudinal test-retest design in two adults. For the test, each subject ingested 1 nmol of [14C]beta-carotene (100 nCi) in an emulsified olive oil-banana drink. Total urine and stool were collected for up to 30 days; concentration-time patterns of [14C]beta-carotene, [14C]retinyl esters, and [14C]retinol were determined for 46 days. On Day 53, the subjects were placed on a daily vitamin A supplement (10000 IU/day), and a second dose of [14C]beta-carotene (retest) was given on Day 74. All 14C determinations were made using accelerator mass spectrometry. In both subjects, the vitamin A supplementation was associated with three main effects: 1). increased apparent absorption: test versus retest values rose from 57% to 74% (Subject 1) and from 52% to 75% (Subject 2); 2). an approximately 10-fold reduction in urinary excretion; and 3). a lower ratio of labeled retinyl ester/beta-carotene concentrations in the absorptive phase. The molar vitamin A value of the dose for the test was 0.62 mol (Subject 1) and 0.54 mol (Subject 2) vitamin A to 1 mol beta-carotene. Respective values for the retest were 0.85 and 0.74. These results show that while less cleavage of beta-carotene occurred due to vitamin A supplementation, higher absorption resulted in larger molar vitamin A values.

Absorption↗

PubMed2003

Shrinkage estimation for functional principal component scores with application to the population kinetics of plasma folate.

We present the application of a nonparametric method to performing functional principal component analysis for functional curve data that consist of measurements of a random trajectory for a sample of subjects. This design typically consists of an irregular grid of time points on which repeated measurements are taken for a number of subjects. We introduce shrinkage estimates for the functional principal component scores that serve as the random effects in the model. Scatterplot smoothing methods are used to estimate the mean function and covariance surface of this model. We propose improved estimation in the neighborhood of and at the diagonal of the covariance surface, where the measurement errors are reflected. The presence of additive measurement errors motivates shrinkage estimates for the functional principal component scores. Shrinkage estimates are developed through best linear prediction and in a generalized version, aiming at minimizing one-curve-leave-out prediction error. The estimation of individual trajectories combines data obtained from that individual as well as all other individuals. We apply our methods to new data regarding the analysis of the level of 14C-folate in plasma as a function of time since dosing of healthy adults with a small tracer dose of 14C-folic acid. A time transformation was incorporated to handle design irregularity concerning the time points on which the measurements were taken. The proposed methodology, incorporating shrinkage and data-adaptive features, is seen to be well suited for describing population kinetics of 14C-folate-specific activity and random effects, and can also be applied to other functional data analysis problems.

Adult↗

PubMed2002

Mass spectrometric immunoassay for parathyroid hormone-related protein.

This paper describes a novel two-site peptide immunoassay using the isotope 14C as the label and accelerator mass spectrometry as the detection system. A mouse monoclonal antibody (1A5) against the amino terminal region of human parathyroid hormone-related protein (PTHrP) was labeled with 14C by growing the hybridoma cells in a miniPERM bioreactor in the presence of [U-14C]L-leucine and [U-14C]D-glucose. The antibody was purified from the culture media using protein G affinity chromatography. The purified 14C-labeled antibody (14C-1A5) fractions showed excellent correlation between the levels of radioactivity and binding activity for PTHrP. Using 14C-1A5 as the detection antibody in a two-site immunoassay format for PTHrP1-141, a 16-kDa polypeptide, an analytic sensitivity of 10 pmol/L was achieved with a linear measurement range up to 1.3 nmol/L. Only approximately 17 pCi/ well (or 1.6 nCi/96-well microtiter plate) 14C-1A5 was used, which is far below the limit (50 nCi/g) for disposal as nonradioactive waste. This study may serve as a model for the development of sensitive and "nonradioactive" immunoassays for peptides, including polypeptide tumor markers.

Animals↗

PubMed2002

Dual isotope test for assessing beta-carotene cleavage to vitamin A in humans.

BACKGROUND: The ability of beta-carotene to deliver bioactive retinoids to tissues is highly variable. A clearer understanding of the environmental and genetic factors that modulate the vitamin A potential of beta-carotene is needed. AIM OF STUDY: Assess the vitamin A value of orally administered beta-carotene relative to a co-administered reference dose of preformed vitamin A. METHODS: Equimolar doses (30 micromol) of hexadeuterated D6 beta-carotene and D6 retinyl acetate were orally co-administered in an emulsified formulation to a male subject. The plasma concentration time courses of D6 retinol (derived from D6 retinyl acetate) and bioderived D3 retinol (from D(6) beta-carotene) were determined for 554 h postdosing using gas chromatography/mass spectrometry. Intact D6 beta-carotene plasma concentrations were determined by high-pressure liquid chromatography. The ratio of the two forms of vitamin A, D6 retinol/D3 retinol, at any single time point is postulated to reflect the quantity of vitamin A derived from beta-carotene relative to preformed vitamin A. Additionally, a minute amount of 14C beta-carotene (50 nCi; 0.27 microg) was included in the oral dose and cumulative 24-h stool and urine samples were collected for two weeks to follow absorption and excretion of the b-carotene. The 14C nuclide was detected using accelerator mass spectrometry (AMS). Results During the absorption/distribution phase (3-11 h) the D6/D3 ratio of the two retinols was not stable and ranged between a value of 3 and 16. Between 11 and 98 h postdosing the ratio was relatively stable with a mean value of 8.5 (95 % CI: 7.5, 8.7). These data suggest that in this subject and under these conditions, 8.5 moles of beta-carotene would provide a vitamin A quantity equivalent to 1 mole of preformed vitamin A. On a mass basis, 15.9 microg of beta-carotene was equivalent to 1 microg of retinol. The total administered beta-carotene was found to be 55 % absorbed by AMS analysis of cumulative stool. CONCLUSION: The co-administration of D6 beta-carotene and D6 retinyl acetate provides a technique for assessing individual ability to process beta-carotene to vitamin A. The results indicate that a single time point taken between 11-98 h after dose administration may provide a reliable value for the relative ratio of the two forms of vitamin A. However, results from more subjects are needed to assess the general utility of this method.

Adult↗

PubMed2002

Semiparametric modeling of labeled-cell kinetics, with application to isotope labeling of erythrocytes.

We propose a stochastic model for the kinetics of cells that have been tagged with a chemical label. The proposed model consists of two components: a parametrically specified distribution for the time to incorporation of the label into the cells and a nonparametric survival function reflecting the survival time of the label-cell combination. The target quantity of this modeling approach is the fraction of labeled cells among all cells, viewed as a function of time. Longitudinal measurements of this labeled-cell fraction are available from a recent experiment with folate-labeled red blood cells. The proposed semiparametric model is fitted to these data and some of the implications are explored. The proposed method also includes bootstrap-based inference.

Carbon Radioisotopes↗

PubMed2002

Protein binding of isofluorophate in vivo after coexposure to multiple chemicals.

Full toxicologic profiles of chemical mixtures, including dose-response extrapolations to realistic exposures, is a prohibitive analytical problem, even for a restricted class of chemicals. We present an approach to probing in vivo interactions of pesticide mixtures at relevant low doses using a monitor compound to report the response of biochemical pathways shared by mixture components. We use accelerator mass spectrometry (AMS) to quantify [14C]-diisopropylfluorophosphate as a tracer at attomole levels with 1-5% precision after coexposures to parathion (PTN), permethrin (PER), and pyridostigmine bromide separately and in conjunction. Pyridostigmine shows an overall protective effect against tracer binding in plasma, red blood cells, muscle, and brain that is not explained as competitive protein binding. PTN and PER induce a significant 25-30% increase in the amount of tracer reaching the brain with or without pyridostigmine. The sensitivity of AMS for isotope-labeled tracer compounds can be used to probe the physiologic responses of specific biochemical pathways to multiple compound exposures.

Animals↗

PubMedDate not supplied

Use of bomb pulse carbon-14 to age senile plaques and neurofibrillary tangles in Alzheimer's disease.

The time course of formation of neurofibrillary tangles (NFT) and senile plaques (SP) in Alzheimer's disease (AD) brain is unknown. Above ground nuclear weapons testing in the late 1950s and early 1960s led to significantly increased levels of 14C in the atmosphere and carbon cycle. Because the amyloid beta peptide of SP and paired helical filaments of NFT, once formed, are relatively resistant to degradation, 14C levels observed in SP and NFT should reflect their year of formation. The purpose of this study was to develop a method to determine whether 14C levels could be used to define NFT and SP ages. Using accelerator mass spectrometry to measure bomb-pulse 14C levels, we determined the average age of formation of isolated SP and NFT fractions in bulk brain samples of 6 AD subjects. Although preliminary, the results demonstrate that it is possible to use bomb pulse 14C to determine the average year of formation of NFT and SP in the brain in AD. In addition, the data show that these structures, once formed, have a much slower carbon turnover rate than normal brain and are not in a formation/enzymatic degradation equilibrium.

Aged↗