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Biomedical subjects

J C Loo

Publications and source records attributed to J C Loo.

At least 19 recordsLinked to original sources
PubMed1995

A chemiluminescence enzyme immunoassay (CLEIA) for the determination of medroxyprogesterone acetate in human serum.

An enzyme immunoassay with chemiluminescence detection (CLEIA) for measuring serum levels of medroxyprogesterone acetate (MPA), a synthetic progestational agent currently used in fertility control and hormonal cancer, is reported. The polyclonal antiserum was obtained by immunizing rabbits with the synthetized 17-hemisuccinate derivative of medroxyprogesterone (MPS) coupled to serum albumin. This antiserum does not display any cross reactivity with extracted metabolites or with corticosteroid analogs with modifications at positions 11 and 16. The same MPS coupled to alkaline phosphatase is used as tracer. For the chemiluminescent detection system, adamantyl-1,2-dioxetane phosphate is selected as substrate. The typical standard curve ranges from 18.5 to 1182 pg per well and displays a slope factor of 0.74, with an ED50 of 143.8 pg of MPA per well and a minimum detectable and maximal level of 0.83 and 12,400 pg per well respectively. The assay has been validated on spiked serum samples in terms of precision (intra- and interassay coefficient variations of less than 8% and 13%, respectively), and of accuracy (mean recovery 105%). The validation on clinical samples demonstrates a good correlation of MPA serum values obtained both by radioimmunoassay and CLEIA. This specific and sensitive CLEIA, which requires less than 100 microliters of serum sample, appears to be an interesting alternative for the monitoring of serum levels of MPA in humans.

Administration, Oral↗
PubMed1991

Isolation of cross-reacting compounds to Incstar Cyclo-Trac SP RIA in blood samples obtained from cardiac allograft patients on cyclosporine therapy.

To examine the specificity of the Incstar Cyclo-Trac SP RIA kit, individual blood samples from 28 cardiac allograft patients on cyclosporine A (CsA) therapy were extracted and chromatographed by HPLC. Initially, eluates from a pool of the above samples were collected at regular intervals and measured by RIA to locate possible cross-reacting compounds. Unknown cross-reacting materials were detected in a fraction (UNK) that was collected before elution of CsA. For each patient's sample, fraction UNK and the fraction containing CsA were then collected and measured by RIA. In 9 of 28 samples, cross-reactivity was detected in fraction UNK; range 11 to 36%, mean 22 +/- 7.5%. Cross-reactivity was not apparent in fraction UNK of CsA-free blood samples from normal volunteers.

Antibody Specificity↗
PubMed1991

Monitoring of blood levels of cyclosporine in renal and cardiac transplant recipients--comparison of HPLC to Incstar CYCLO-Trac SP RIA.

Cyclosporine in whole blood samples from renal and cardiac transplant recipients was measured by high-performance liquid chromatography (HPLC) and by CYCLO-Trac SP specific radioimmunoassay (RIA). The fresh samples assayed by RIA were remeasured in a second laboratory after storage at -20 degrees C for two to six months and good interlaboratory agreement was obtained on the 59 samples assayed (y = 0.926x + 14.8 micrograms/L, r = 0.982). The calibration curve for RIA was not influenced by fresh whole blood, hemolyzed whole blood or serum matrix from normal volunteers. However, comparison of the RIA results from patient samples with those from an HPLC procedure showed that RIA values averaged about double those measured by HPLC. The difference is attributable to differences between the blood matrix of transplant and nontransplant subjects, rather than exclusively to the apparent nonspecific nature of the antibody.

Calibration↗
PubMed1991

Effect of chronic exposure of PCB (Aroclor 1254) on specific and nonspecific immune parameters in the rhesus (Macaca mulatta) monkey.

The immunomodulatory effects of low-level, chronic polychlorinated biphenyl PCB; (Aroclor 1254) exposure were investigated in female rhesus (Macaca mulatta) monkeys. Five groups of monkeys (initially 16 monkeys/group) were orally administered PCB at levels of 0, 5, 20, 40 or 80 micrograms/kg body wt/day. Tests for immunomodulation were initiated after 55 months of exposure to PCBs. Statistically significant observed immune changes included a dose-related decrease in the anamnestic (IgM and IgG) response to sheep red blood cells. Conversely, the antibody response to pneumococcus antigen did not differ significantly across the test groups. A statistically significant dose-related decrease in lymphoproliferation was noted with increasing doses of PCBs when phytohemagglutinin and Concanavalin A, but not when pokeweed mitogen, were used as mitogens. A trend toward reduced peak chemiluminescence (mV/min) was observed in zymosan-activated peripheral blood monocytes. The time to peak chemiluminescence of phorbol myristate acetate activation was statistically increased in a dose-response fashion. Flow cytometric analysis results of peripheral blood lymphocytes using the markers CD4, CD8, and CD20 were similar across the test groups. The mean percentage levels for the CD2 marker in the treated groups were statistically lower than the mean in the control, while absolute numbers for CD2 were similar across the test groups. Serum hydrocortisone levels did not differ among the test groups. Taken together these results indicate that low-level, chronic PCB exposure alters a number of rhesus monkey immune system components and that these effects may be due to altered T-cell and/or macrophage function. These data may be of use in extrapolating potential human health effects following chronic PCB exposure.

Animals↗
PubMed1989

Immunotoxicity studies of PCB (Aroclor 1254) in the adult rhesus (Macaca mulatta) monkey--preliminary report.

The effects of PCB (Aroclor 1254) on the immune system of adult female rhesus monkeys were investigated in a chronic study wherein five groups of monkeys (16/group) were administered (orally) PCB at levels of 0.0, 5.0, 20.0, 40.0 or 80.0 micrograms/kg body wt daily. Tests for immunotoxicity were initiated at 23 months of exposure to PCB, at which time the monkeys had achieved an apparent pharmacokinetic steady state based on the PCB concentration in fat and/or blood. A statistically significant (P less than 0.05) dose response reduction in antibody levels (IgG and IgM) to sheep red blood cells (SRBC) was observed following i.v. administration of three immunizing doses of SRBC at weekly intervals. A statistically significant decrease in the percent TH and an increase in the percent and absolute TS lymphocyte levels was found in the 80 micrograms/kg body wt group compared to the control. The TH/TS ratio was also significantly lower in the 80 micrograms/kg body wt group compared to the control. Other parameters investigated including percent of B-lymphocytes and total T-lymphocytes, total serum immunoglobulin levels (IgG, IgM and IgA), other serum proteins, glucocorticosteroid levels and lymphocyte transformation results following stimulation with the mitogens PHA-P and Con A were not affected significantly by PCB treatment. Additional immunologic parameters are currently being investigated to further elucidate the mechanism by which PCB induces immunotoxicity.

Animals↗
PubMed1988

Application of HPLC with a metal-free column to the analysis of cyclosporin in whole blood samples from cardiac transplant patients.

A simplified, reverse-phase HPLC method utilizing a metal-free column was developed for the analysis of cyclosporin (CYA) in whole blood in humans. The average intra and inter assay variation at the low end of the therapeutic range are less than or equal to 4.5 and 8.8% respectively. The procedure was successfully applied to the measuring of CYA in whole blood collected from cardiac transplant patients over a one year period.

Chromatography, High Pressure Liquid↗
PubMed1987

Characterization of digoxin and related cardiac glycosides by fast atom bombardment mass spectrometry.

The potential of using fast atom bombardment mass spectrometry for the detection and the characterization of digoxin and a series of related cardenolide analogues was investigated. The spectra were dependent upon the type of support-matrix in which they were recorded; thioglycerol proved to be satisfactory for the characterization of digoxin and allowed for its detection in human urine extract spiked with ca 11 ng ml(-1).

Journal Article↗
PubMed1984

Digoxin biotransformation.

Serum digoxin and metabolites were assayed in plasma and urine by HPLC in 10 dialysis-dependent patients with end-stage renal failure (group I) and in five patients with comparatively normal renal function (group II) after ingestion of 150 muCi 3H-digoxin-12 alpha. Thirteen patients were on maintenance digoxin therapy and were at steady state. Metabolites found regularly but usually in small amounts, were 3 beta-digoxigenin and its mono- and bis-digitoxosides, and 3-keto and 3 alpha(epi)-digoxigenin. Quantitatively the most abundant metabolites were polar and averaged 26% (7 to 76) of the radioactivity in plasma 6 hr after drug, and 60% (11 to 88) for digoxin for all 15 patients. Neither values between group I and II for the polar metabolites nor digoxin differed significantly. The metabolites reacted with antibody to digoxin to varying degrees and may make up an important component of the serum digoxin concentration when determined by standard radioimmunoassay. In some patients, digoxin undergoes extensive biotransformation, mainly, we suggest by hydrolysis, oxidation, epimerization, and conjugation to polar end-metabolites.

Administration, Oral↗
PubMed1984

Quantitation of delta 4-reduced metabolite of norethindrone in human plasma by HPLC-RIA.

An HPLC-RIA method for the measurement of the delta 4-reduced metabolite of norethindrone is described. The sensitivity of the method was such as to permit the quantitation of pg amounts (30 pg with an inter-assay CV of less than 7%). Nineteen volunteers received a single oral dose of 1 mg of norethindrone and, blood samples withdrawn at timed intervals, were pooled for each time period and assayed. The plasma concentrations of the dihydro metabolite ranged from 460 pg/ml at 30 min to 20 pg/ml at 24h.

Biotransformation↗
PubMed1983

HPLC-RIA of a metabolite of norethindrone in human plasma, 17 alpha-ethinyl-5 beta-estrane-3 alpha, 17 beta-diol, following conjugate hydrolysis.

An HPLC-RIA method for the assay of a reduced metabolite of norethindrone, 17 alpha-ethinyl-5 beta-estrane-3 alpha, 17 beta-diol, is described. Conjugated metabolites were extracted from human plasma and subjected to hydrolysis prior to analysis. With a daily dose of 2 mg of norethindrone, the mean plasma level of the metabolite was 24.8 ng/ml with a range of 22.8 ng/ml to 33.9 ng/ml.

Chromatography, High Pressure Liquid↗
PubMed1983

Analysis of 25-hydroxy vitamin D3 in plasma by high-performance liquid chromatography.

A specific high-performance liquid chromatographic (HPLC) procedure for the determination of 25-(OH) vitamin D3 (25-OH-D) in plasma is described. The organic solvent extract from plasma is first purified on an HPLC silica column and then chromatographed on a reversed-phase column in a high-performance liquid chromatograph fitted with an ultraviolet detector (254 nm); quantitation from plasma samples containing as low as 2 ng/ml of 25-OH-D is reported. Endogenous substances do not interfere with the assay. The determination of vitamin 25-OH-D concentrations in plasma in normal subjects is described.

25-Hydroxyvitamin D 2↗
PubMed1983

Norethindrone antisera: anomalous cross-reactivities with use of 3H-tetrahydro-reduced norethindrone as radioligand.

Anomalous cross-reactions with the dihydro- and tetrahydro-reduced metabolites of norethindrone were observed utilizing antisera raised against norethindrone-3-bovine serum albumin. Whereas displacement of 3H-norethindrone from the antiserum by the metabolites was generally minimal, where one of the metabolites was used as radiotracer, displacement by the metabolites was equal to or greater than that achieved by norethindrone. This unexpected finding was examined for its usefulness in developing a radioimmunoassay system for norethindrone metabolites in plasma. The sensitivity of the resulting standard curve was such as to permit quantitation of pg amounts of the reduced metabolites.

Animals↗
PubMed1981

An investigation of the interaction between isoniazid and the contraceptive steroid norethindrone in vivo.

Isonicotinic acid hydrazide (isoniazid) was shown to react readily with 17 alpha-ethinyl-17 beta-hydroxyestr-4-en-3-one (norethindrone) to form the isonicotinyl hydrazone of the steroid under conditions likely to exist in the stomach. The hydrazone was detected in guinea-pig, but not rat, plasma following its oral administration. Rat liver tissue metabolized the compound more rapidly than guinea-pig liver in vitro which probably accounts for the failure to detect the hydrazone in rat plasma.

Animals↗