Analysis of complex mixtures of flavonoids and polyphenols by high-performance liquid chromatography electrochemical detection methods.
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Chromatography, High Pressure Liquid↗
Biomedical subjects
P E Milbury
Publications and source records attributed to P E Milbury.
Characterization of diet-dependent metabolic serotypes: analytical and biological variability issues in rats.
This report, the first in a series on diet-dependent changes in the serum metabolome (metabolic serotype), describes validation of the use of high performance liquid chromatography (HPLC) separations coupled with Coulometric array detectors to characterize changes in the metabolome. The long-term aim of these studies is to improve understanding of the effects of significant variation in nutritive status on physiology and on disease processes. Initial studies focus on identifying the effects of dietary (or caloric) restriction on the redox-active components of rat serum. Identification of compounds of interest is being carried out using HPLC separations coupled with coulometric array analysis, an approach allowing simultaneous examination of nearly 1200 serum compounds. The technical and practical issues discussed in this report are related to both analytical validity (HPLC running conditions, computer-automated peak identification, mathematical compensation for chromatographic drift, etc.) and biological variability (individual variability, cohort-cohort variability, outliers). Attention to these issues suggests approximately 250 compounds in serum are sufficiently reliable, both analytically and biologically, for potential use in building mathematical models of serotype.
Animals↗
Influence of repeated levodopa administration on rabbit striatal serotonin metabolism, and comparison between striatal and CSF alterations.
Parkinson's disease (PD) is characterized by decreased striatal dopamine, but serotonin (5-HT) is also reduced. Because 5-HT decreases following a single levodopa injection, levodopa has been suggested to contribute to PD's serotonergic deficits. However, in a recent study, rat striatal serotonin levels were reported to increase following 15-day levodopa administration. To address this issue, we administered levodopa (50 mg/kg) to rabbits for 5 days, then measured serotonin, its precursors tryptophan and 5-hydroxytryptophan (5-HTP), and its major metabolite 5-hydroxyindole-acetic acid (5-HIAA) in striatum and CSF. Striatal serotonin and tryptophan were unchanged, while 5-HTP and 5-HIAA increased 4- and 7-fold, respectively. CSF 5-HTP and 5-HIAA were also significantly increased. In levodopa-treated animals, 5-HTP concentrations were moderately correlated (r = 0.679) between striatum and CSF, while weak correlations were present between striatal and CSF concentrations of both serotonin and 5-HIAA. These results suggest that repeated levodopa treatment increases striatal serotonin turnover without changing serotonin content. However, levodopa-induced alterations in striatal serotonin metabolism may not be accurately reflected by measurement of serotonin and 5-HIAA in CSF.
5-Hydroxytryptophan↗
A comparative bear model for immobility-induced osteopenia.
The National Institutes of Health (NIH) and the National Aeronautics and Space Administration (NASA) are seeking solutions to the human problem of osteopenia, or immobility-induced bone loss. Bears, during winter dormancy, appear uniquely exempted from the debilitating effects of immobility osteopenia. NIH and ESA, Inc. are creating a large database of metabolic information on human ambulatory and bedrest plasma samples for comparison with metabolic data obtained from bear plasma samples collected in different seasons. The database generated from NASA's HR113 human bedrest study showed a clear difference between plasma samples of ambulatory and immobile subjects through cluster analysis using compounds determined by high performance liquid chromatography with coulometric electrochemical array detection (HPLC-EC). We collected plasma samples from black bears (Ursus americanus) across 4 seasons and from 3 areas and subjected them to similar analysis, with particular attention to compounds that changed significantly in the NASA human study. We found seasonal differences in 28 known compounds and 33 unknown compounds. A final database contained 40 known and 120 unknown peaks that were reliably assayed in all bear and human samples; these were the primary data set for interspecies comparison. Six unidentified compounds changed significantly but differentially in wintering bears and immobile humans. The data are discussed in light of current theories regarding dormancy, starvation, and anabolic metabolism. Work is in progress by ESA Laboratories on a larger database to confirm these findings prior to a chemical isolation and identification effort. This research could lead to new pharmaceuticals or dietary interventions for the treatment of immobility osteopenia.
Animals↗
Markers of dopamine depletion and compensatory response in striatum and cerebrospinal fluid.
Though depletion of CSF homovanillic acid (HVA) concentration has often been regarded as a direct indicator of dopamine (DA) deficiency in Parkinson's Disease (PD), CSF HVA is normal in mildly affected patients. To explore why, we measured DA and its metabolites in striatum and CSF in rabbits receiving reserpine for 5 days. Reserpine, which depletes striatal DA by disrupting vesicular storage of the neurotransmitter, results in a compensatory increase of DA turnover. In response to a 96% depletion of striatal DA, its catabolic intermediates 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) decreased 64% and 92% in striatum, although the endproduct, HVA, was unchanged. In contrast, CSF concentrations of HVA and DOPAC increased significantly, though 3-MT and levodopa (LD) were unaltered. A 5-fold rise in striatal LD concentration after reserpine-induced DA depletion provided evidence for enhanced DA synthesis. As in PD, the compensatory increase of DA synthesis after reserpine administration confounds the ability of CSF HVA to reflect DA depletion.
3,4-Dihydroxyphenylacetic Acid↗
Direct adrenergic stimulation of the release of thyrotropin and its subunits from the thyrotrope in vitro.
Adrenergic effects on TSH and subunit secretion were investigated in bovine anterior pituitary monolayer cultures. Epinephrine (E) (10(-6) M) caused a significant increase in TSH, alpha-subunit, and TSH beta release into the medium (P less than 0.001, P less than 0.001, and P less than 0.01, respectively). E, norepinephrine, and phenylephrine, all alpha-adrenergic agonists, caused significant increases in TSH release, with half-maximal effects at 4.3 X 10(-7), 6.8 X 10(-7), and 8.2 X 10(-7) M, respectively. However, isoproterenol, a beta-adrenergic agonist (10(-7)-10(-4) M), did not alter TSH or subunit release. Clonidine, an alpha 2-adrenergic agonist (10(-7)-10(-4) M), had no effect on TSH or subunit secretion; however, coincubation of clonidine (5 X 10(-7) M) with a submaximal concentration of phenylephrine (5 X 10(-7) M) caused a rise in TSH release greater (P less than 0.02) than that seen with P alone. The alpha-adrenergic antagonists phentolamine and fluphenazine completely inhibited (P less than 0.001) the E-induced rise in TSH and subunits. In contrast, the beta-adrenergic antagonists propranolol and metoprolol did not significantly inhibit the stimulation of TSH by E. TSH and subunit secretion is stimulated by adrenergic agonists acting directly on the pituitary, and this is probably mediated via an alpha-adrenergic receptor.
Adrenergic alpha-Agonists↗
A possible role for elastin ligands in the proteolytic degradation of arterial elastic lamellae in the rabbit.
Thoracic aortae of normal rabbits were perfused with pancreatic elastase in vitro at 37 degrees C and 70 mm Hg pressure in the presence or absence of elastin ligands previously shown to stimulate or inhibit the enzymatic degradation of elastin. Perfusion with elastase results in an average of 3.6 lamellae degraded, whereas addition of sodium linoleate before and during the perfusion with elastase increases this value to 7.9 (P less than 0.001). Conversely, perfusion with the cationic detergent, dodecyltrimethylammonium chloride, completely prevents the degradation of elastic lamellae by elastase. These effects do not reflect alterations of the intrinsic catalytic activity of elastase, but apparently indicate the formation of complexes between the elastin ligands and arterial elastic lamellae, as is consistent with prior studies indicating such interactions between fatty acids or detergents and purified elastin. These studies suggest that agents such as fatty acids may significantly alter the metabolic susceptibility of elastin in vivo and possibly contribute to the degradation of elastic lamellae seen in arteries with advanced atherosclerosis.
Animals↗