Artifacts and limitations of enzyme immunoassay.
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Antigen-Antibody Reactions↗
Biomedical subjects
A J Pesce
Publications and source records attributed to A J Pesce.
Pharmacokinetics of zidovudine phosphorylation in patients infected with the human immunodeficiency virus.
The relationship between zidovudine phosphorylation inside mononuclear cells and plasma zidovudine pharmacokinetic was assessed in six subjects. Plasma and intracellular concentrations were measured by radioimmunoassay over an 8-h period after administration of 100 or 200 mg of zidovudine. Plasma pharmacokinetics followed expected patterns, with considerable interpatient variability in area under the concentration-versus-time curve (AUC), and a terminal half-life of 1.5 h. Intracellular AUC was even more variable than plasma AUC, but the data suggested a crude linear relationship between these parameters. The intracellular half-life of 3.5 h was consistently longer than the plasma half-life, and varied little between patients. The prolonged intracellular half-life suggested that total phosphorylated zidovudine, as measured by the method described, is not greatly dominated by the 5'-monophosphate as predicted from the in vitro studies reported in the literature. Plasma concentrations of zidovudine have shown little correlation with clinical effect. Study of the relationship between phosphorylated zidovudine and clinical outcome could lead to a more effective management of therapy.
Extracellular Space↗
Monoethylglycinexylide formation in assessing pediatric donor liver function.
Lidocaine metabolism to monoethylglycinexylide (MEGX) has been described as a novel method to assess liver function in adult transplant donors and recipients. While this assay appears to offer a number of advantages over existing liver function tests, limited work has been done to evaluate its potential in the pediatric population. This study evaluated MEGX formation in potential pediatric liver donors (n = 35) and a control group of children (n = 16). The mean MEGX formation was significantly higher in pediatric donors than in the control group (156 +/- 62 vs 106 +/- 33 ng/ml, p < 0.05). No correlation with age, total bilirubin, liver transaminases, or alkaline phosphatase could be made within each group. Significant differences in MEGX levels were noted when each group was compared to its adult counterpart. Both pediatric donors and controls had greater mean MEGX formation than has been reported for adult donors and controls (156 +/- 62 vs 127 +/- 61 ng/ml, p < 0.05 and 106 +/- 33 vs 72 +/- 36 ng/ml, p < 0.05, respectively). Drugs that alter lidocaine pharmacokinetics and their potential influence on MEGX formation were evaluated in the pediatric donor group. Donors exposed to hepatic enzyme-inducing drugs had a higher mean MEGX formation (187 +/- 60 vs 146 +/- 63 ng/ml). No significant differences were noted between donors receiving and not receiving vasopressors. In conclusion, the significant differences between pediatric and adult MEGX formation should be noted when establishing reference or normal ranges for this diagnostic test. Furthermore, concomitant drug therapy may significantly alter MEGX formation.
Adult↗
Selection criteria for liver transplant donors.
As the number of successful liver transplants has increased, the demand for donors has outpaced the supply. Approximately 25% of patients die awaiting an appropriate donor. Current criteria for assessing potential donors need to be closely examined. Fifty-six potential donors were evaluated by our transplant team by utilizing standard liver function tests (LFT's)-SGOT, SGPT, bilirubin. Additionally, a lidocaine metabolism test was performed by giving a 1 mg/kg IV dose of lidocaine over 1 minute and measuring the accumulation of the major metabolite monoethylglycinxylidide (MEGX) at 15 minutes by fluorescent polarization immunoassay (Abbott Diagnostics, Abbott Park, IL). Previous work has suggested that a MEGX less than 50 ng/mL is associated with initial non-function. Thirty-four donors were transplanted (group I) and all had initial function (all MEGX values were greater than 50). Twenty-two donors (39%) were judged unacceptable (group II) by our transplant team and by outside centers based upon one of the following criteria: II A) elevated LFT's--8, 11 B) donor age--5, II C) donor instability--4, II D) no available recipient--3, II E) miscellaneous--2. Standard LFT's were not statistically different in the donors used and in those not used when excluding category II A. Six of seven donors excluded in group I had acceptable MEGX values indicating they may have been transplantable. Ten of 12 patients excluded in groups II B-D had normal LFT's and nine of 12 had acceptable MEGX values indicating they may have been transplantable also. In this era of organ shortage, a reevaluation of donor selection criteria utilizing new tests like MEGX may be necessary to meet the increased need.
Adolescent↗
Electrochemical determination of azidothymidine in human whole blood.
An electrochemical method based on differential pulse voltammetry is presented for the determination of AZT in whole blood of fasted subjects. A protein-free supernatant of whole blood is prepared using HClO4 precipitation followed by neutralization with phosphate buffer. The AZT is reduced at a hanging mercury drop electrode. The linear dynamic range of standards in buffer is from the detection limit of 4.1 nM to 206.5 microM (1.1 to 55,200 ng/ml). However, in spiked blood samples the linear dynamic range is from 0.029 to 0.29 microM (7.75 to 77.5 ng/ml). The whole blood assay yields a recovery of 92.30 +/- 5.92% compared to the standard solution assay. After a 30-min preparation time, each sample can be analyzed in 10 min by a manual procedure.
Chemical Precipitation↗
Concentrations of phosphorylated zidovudine (ZDV) in patient leukocytes do not correlate with ZDV dose or plasma concentrations.
Zidovudine (ZDV) elicits its antiviral effect through intracellular metabolism to the 5'-triphosphate, which interferes with viral replication. Monitoring of the active metabolites of ZDV in cells could lead to an intracellular therapeutic range. This study was performed to determine whether a radioimmunoassay, previously used for in vitro quantitation of total phosphorylated ZDV inside peripheral blood leukocytes, could be used for similar determinations in patient samples. The relationship between ZDV dose, plasma concentrations, and intracellular metabolite concentrations was also examined. Ten-milliliter blood samples were drawn from each of 13 human immunodeficiency virus-infected patients and were assayed. Intracellular concentrations of phosphorylated ZDV ranged from 0.33 to 3.54 pmol/10(6) cells, similar to those observed in vitro. Phosphorylated ZDV was independent of dose, and did not correlate with plasma concentrations. Intracellular concentration in the patient population as a whole did not change during the 4-h dosing interval, while plasma concentration decayed normally. Later determinations in the same patients gave intracellular values within 31% of earlier values. Intraassay variability was less than 10%. Thus, the method is valid for measurement of phosphorylated ZDV in patient cells. Although individual concentrations showed no clear change during the 3-month study period, intracellular concentrations decreased with increasing length of therapy (up to 3 years) in the population as a whole. This suggests a decreased cellular ability to phosphorylate ZDV after prolonged exposure to drug. The lack of intracellular decay implies a half-life longer than the 1-h half-life of plasma ZDV. These data suggest that smaller doses or longer dosing intervals might maintain intracellular concentrations once steady state is achieved.(ABSTRACT TRUNCATED AT 250 WORDS)
Administration, Oral↗
Cyclosporine dose reduction by ketoconazole administration in renal transplant recipients.
Cyclosporine metabolism occurs in the liver via hepatic cytochrome P-450 microsomal enzymes. Ketoconazole, an imidazole derivative, has been shown to inhibit the cytochrome P-450 enzyme system. Thirty-six renal transplant recipients receiving cyclosporine as part of a triple immunosuppressive drug regimen were started on 200 mg/day of oral ketoconazole. The dose of cyclosporine was reduced by 70% at the start of ketoconazole; this dose reduction was based on our previous experience with concomitant cyclosporine-ketoconazole therapy. Ketoconazole was started in patients who had been on cyclosporine for between 10 days and 74 months. The mean cyclosporine dose was 420 mg/day (5.9 mg/kg/day) before starting ketoconazole and 66 mg/day (0.9 mg/kg/day) one year after the addition of ketoconazole; this represents a cyclosporine dose reduction of 84.7% (P less than 0.0001). The mean trough whole-blood cyclosporine concentrations measured by HPLC, were 130 ng/mL preketoconazole and 149 ng/mL after 1 year of combination therapy. Mean serum creatinine and BUN levels were unchanged before and during ketoconazole administration, and no changes in liver function tests were noted. Cyclosporine pharmacokinetics were performed before and after at least three weeks of ketoconazole. Hourly whole-blood samples were measured by HPLC (parent cyclosporine only) and TDX (parent + metabolites). Combination therapy resulted in decreases in the maximum blood concentration and the steady-state volume of distribution divided by the fractional absorption, and increases in mean residence time and the parent-to-parent plus metabolite ratio (calculated by dividing the HPLC by the TDX value). The addition of ketoconazole to cyclosporine-treated patients resulted in a significant inhibition of cyclosporine metabolism and decrease in the dosage. There was minimal nephrotoxicity, and only four rejection episodes occurred on combined therapy. The concomitant administration of the two drugs was well tolerated, and there was no deleterious effect on the immunosuppressive activity of cyclosporine. This drug interaction provides a significant reduction in the costs associated with organ transplantation.
Adult↗
Regulation of the human immune response to ragweed pollen by immunotherapy. A controlled trial comparing the effect of immunosuppressive peptic fragments of short ragweed with standard treatment.
A new allergenic preparation consisting of peptic fragments of short ragweed has been tested for its clinical effectiveness. Such enzymatically derived fragments have been shown in prior murine studies to retain the T epitopes of the original allergen but to have a severe reduction in the number of B epitopes. Three groups of ragweed hayfever patients were placed on pre-seasonal immunotherapy. One group received a conventional ragweed preparation that had been enriched for antigen E (Amb a I), designated as Pool 2. The second group was given fragments of Pool 2 (fSRW) prepared by peptic digestion and the third group was injected with histamine as a placebo. Groups treated with the fSRW and Pool 2 had significantly reduced symptom-medication scores compared with the placebo-treatment group. However, fSRW-treated patients fared significantly better than Pool 2 patients (P less than 0.02). fSRW injections caused a significant rise in preseasonal specific IgG, antibodies as well as suppression of the seasonal anamnestic specific IgE increase. Similar, but not quite as marked changes occurred with Pool 2 treatment. fSRW was well tolerated and non-toxic. Thus, allergen modification by enzymatic degradation, as demonstrated here, appears to be a promising new approach for allergen immunotherapy.
Adult↗
Critical ketoconazole dosage range for ciclosporin clearance inhibition in the dog.
Ciclosporin (CsA) is metabolized exclusively by the hepatic cytochrome P-450 mixed function oxidase system. Ketoconazole (KC) is a potent inhibitor of this enzyme system. CsA was administered alone and in combination with five different doses of KC (1.25, 2.5, 5.0, 10.0, 20.0 mg/kg/day) under steady-state conditions to 7 adult mongrel dogs. KC produced a highly significant (p = 0.0001), dose-dependent decrease in CsA total body clearance [Cl(T)]. The critical KC dosage range for this to occur was found to be between 2.5 and 10 mg/kg/day. The reduction of CsA CL(T) was insignificant (p greater than 0.05) at a KC dose of less than 2.5 mg/kg/day, and the 92% reduction observed using 20 mg/kg/day KC was not significantly greater than the 85% reduction occurring after only 10 mg/kg/day KC (p greater than 0.05). The dose of concomitant KC was also highly correlated with a reduction in the whole blood CsA parent/parent + metabolite ratio as determined using high-performance liquid chromatography and polyclonal fluorescent polarization immunoassay for CsA measurement (r = 0.998, p less than 0.0001). The absolute oral bioavailability of CsA as well as the time required to reach its maximum concentration in the blood following oral administration did not change significantly over the course of the study (p greater than 0.05). We conclude from these new observations that the KC-induced decrease in CsA Cl(T) in the dog in vivo is dose-dependent and maximized within the KC dosage range of 2.5-10 mg/kg/day. The effect does not appear to involve a decrease in the rate of CsA oral absorption, and may be compensated for by an appropriate reduction in the concomitantly administered dose of CsA.
Administration, Oral↗
Cationization of protein antigens. V. Effect of the degree of cationization on patterns of immune responsiveness.
Preparations of bovine serum albumin (BSA) were cationized by substituting anionic side chain carboxyl groups with polycationic aminoethylamide groups. Different degrees of substitution were obtained by varying the reaction time. Mice immunized with partially cationized proteins produced early increased levels of antibody over those made by mice immunized with nBSA, followed by a period of decreased response before returning to a second period of enhanced and prolonged antibody synthesis. In contrast, fully substituted BSA gave rise to a significantly enhanced response which was delayed in its onset. Differences in isotype or in antibody specificity during the early and late periods of enhanced responsiveness could not be demonstrated. Cell transfer experiments showed that T cells harvested from mice immunized with the less cationized cBSA preparations could, in contrast to T cells from mice immunized with the fully cationized preparations, suppress antibody responses to both nBSA and cBSA in normal mice. These data are consistent with the possibility that the partially cationized proteins, in contrast to the fully cationized antigen, yield a unique pattern of responsiveness due to retention of determinants necessary for the induction of Ts while exhibiting the enhanced immunogenicity characteristic of cationized molecules.
Animals↗
In vitro measurement of phosphorylated zidovudine in peripheral blood leucocytes.
A method has been developed to measure the concentration of total phosphorylated zidovudine (ZDV) inside peripheral blood leucocytes (PBLs) using a modified commercial radioimmunoassay (RIA) specific for ZDV. ZDV 5'-monophosphate was readily synthesized and used as a procedural control for RIA modification. PBLs were isolated from healthy volunteers and incubated with ZDV for 24 h to allow metabolic phosphorylation. Viable cells were counted, washed, and extracted overnight with 60% methanol. After evaporation, the extract was reconstituted in Tris buffer, pH 9.5. Because of minimal RIA antibody cross reactivity with phosphorylated ZDV, samples were split into two fractions, one of which was treated with alkaline phosphatase (AP) to liberate phosphate groups. Each fraction was then assayed for ZDV. Concentrations of phosphorylated ZDV were determined by subtracting the concentration of the non-AP-treated fraction from that of the treated fraction. Recovery of phosphorylated ZDV from cell extracts was approximately 90%, and reproducibility was acceptable (coefficients of variation less than 15% for concentrations greater than or equal to 0.25 ng/ml). Intracellular concentrations (0.1-1.4 pmoles/10(6) cells) followed a nonlinear dose-response relationship over the range 0-50 microM extracellular ZDV, with concentration-dependent saturation. These results demonstrate the feasibility of determining concentrations of phosphorylated ZDV in HIV-infected patients, a potentially key step in establishing a therapeutic range and optimal dosing regimen for these patients.
Alkaline Phosphatase↗
Modulation of the immune response to allergens: phospholipase A degradation products suppress IgG and IgE response in mice.
Degradation products of phospholipase A2 (PLA2), the major allergen of honeybee venom, were prepared by peptic digestion of the enzyme and fractionated by molecular exclusion chromatography. The largest of the isolated products, P-1, was found to be a centrally nicked PLA2 molecule with a loss of several amino acids. It was examined for its antigenic, immunogenic and immunosuppressive properties. This peptic product was unable to block antigen-antibody reactions between PLA2 and anti-PLA2 antibodies and was incapable of inducing passive cutaneous anaphylaxis in rat skin sensitized with mouse anti-PLA2 IgE antibodies. BDF1 female mice injected intravenously with P-1 exhibited suppressed IgG and IgE anti-PLA2 responses to a subsequent PLA2 immunization. Intravenous administration of P-1 to mice with ongoing immune response to PLA2 resulted in decline of antigen-specific IgE titers. Transfer of splenic T cells from mice injected with P-1 into naive recipients caused profound suppression of the response to subsequent immunization with PLA2 indicating presence of PLA2-specific T suppressor cells. These results indicate that a degradation product of PLA2 prepared by peptic digestion lost antigenic and immunogenic properties of the intact enzyme but retained immunosuppressive properties, thus offering a novel approach to allergen immunotherapy.
Allergens↗
An evaluation of cyclosporine monitoring by nonselective fluorescence polarization immunoassay.
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Bone Marrow Transplantation↗
Clinical correlations of cyclosporine HPLC and FPIA levels in renal transplant recipients.
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Adolescent↗
Concomitant administration of cyclosporin and ketoconazole in renal transplant recipients.
18 renal transplant recipients receiving cyclosporin, prednisone, and azathioprine were given ketoconazole, a potent inhibitor of the cytochrome P-450 enzyme system. Within a month ketoconazole-induced blockade of cyclosporin metabolism allowed a significant reduction (451 vs 106 mg/day; 77%) of the mean dose of cyclosporin without altering cyclosporin whole blood trough levels, although maximum blood levels were almost halved. This dose reduction was maintained in patients followed up for up to 13 months. Renal and hepatic function were unchanged after the addition of ketoconazole. This drug interaction has the potential to reduce dramatically expenditure on cyclosporin in transplant recipients.
Administration, Oral↗
Hemoglobin determination in plasma or serum by first-derivative recording spectrophotometry. Evaluation of the procedure of Soloni, Cunningham, and Amazon.
The authors tested the plasma hemoglobin measurement procedure of Soloni, Cunningham, and Amazon (Am J Clin Pathol 1986;85:342-347), which uses recording derivative spectrophotometry. By this technique, the authors were able to measure plasma or serum hemoglobin down to a level of 10 mg/L (1 mg/dL). The method was found to be quantitative and not affected by bilirubin or lipemia. Methemoglobin did not interfere with the assay. The observed first derivative maxima and minima were reproducible but instrument dependent. The authors applied this technique to the measurement of serum hemoglobin in 100 healthy human subjects. They observed a geometric mean value of 68 mg/L (6.8 mg/dL) with the actual range 21-189 mg/L (2.1-18.9 mg/dL). The authors confirm that this technique is a simple, rapid, and reproducible method for determining plasma or serum hemoglobin.
Bilirubin↗
A comparison of the clinical utility of the radioimmunoassay, high-performance liquid chromatography, and TDx cyclosporine assays in outpatient renal transplant recipients.
Rapid and precise cyclosporine measurements are necessary to maximize immunosuppression and minimize toxicity. The new cyclosporine and metabolites TDx fluorescent polarization immunoassay was studied to determine its precision, sensitivity, and stability. Further, it was compared with the existing radioimmunoassay and high-performance liquid chromatography assays for clinical utility. The TDx procedure utilizes 50 microliter of serum or blood. The range of the assay is 0-1000 ng/ml for serum and 0-2000 ng/ml for whole blood. Precision studies of three control levels provided coefficients of variation of 2.1-5.8% for both assays. The sensitivities of the assays were less than 25 ng/ml for serum and less than 50 ng/ml for whole blood. In order to compare the TDx with the currently used RIA and HPLC methods, 362 simultaneous whole blood and serum samples were obtained from 122 renal transplant recipients over a 4-month period. The serum and whole blood TDx assays excluded fewer patients than either the RIA or HPLC assays with regard to sensitivity. The mean serum cyclosporine concentration for samples above the sensitivity was as follows: TDx 120 +/- 5 ng/ml, RIA 116 +/- 4 ng/ml, and HPLC 100 +/- 5 ng/ml. The mean whole-blood cyclosporine concentration for samples above the sensitivity was as follows: TDx 585 +/- 19 ng/ml, RIA 543 +/- 14 ng/ml, and HPLC 178 +/- 5 ng/ml. Serum and blood TDx levels correlated well with RIA levels, with regression coefficients of r = 0.813 and r = 0.897, respectively. Serum and blood TDx levels did not correlate strongly with HPLC levels, with regression coefficients of 0.332 and 0.781, respectively. Seventeen patients were diagnosed as having acute cyclosporine nephrotoxicity. The serum and whole-blood cyclosporine concentrations in these patients were at the upper end of the therapeutic range for all analytical methods. Five patients had acute cellular rejection; serum and whole-blood cyclosporine levels in these patients did not differ significantly from the stable patients when measured by each of the analytical methods. In conclusion, the TDx cyclosporine and metabolites assay provides reliable blood and serum concentrations that correlate well with RIA measurements in renal transplant recipients. This assay offers rapid sample turn-around times making possible same-day results for all patients without putting great demands upon the laboratory.
Ambulatory Care↗
Co-trimoxazole (sulphamethoxazole plus trimethoprim) peritoneal barrier transfer pharmacokinetics.
The pharmacokinetics of co-trimoxazole (sulphamethoxazole plus trimethoprim) were studied in end-stage renal disease in patients undergoing treatment with continuous ambulatory peritoneal dialysis (CAPD) and free of peritonitis. Plasma and dialysate concentrations were monitored for 1 exchange after administration of a single oral or intraperitoneal dose of co-trimoxazole, and were fitted by a pharmacokinetic model that took into account the equilibrium nature of CAPD by including return from the peritoneum in oral studies and from the plasma in intraperitoneal studies. Clearances were calculated and compared by analysis of variance. There was a significant effect of direction of flow (p less than 0.01), plasma-peritoneal clearances being larger than peritoneal-plasma clearances for both drugs. In addition, there was a significant difference (p less than 0.0001) between sulphamethoxazole clearances and trimethoprim clearances, with the latter being greater in both directions.
Administration, Oral↗