Free and complexed prostate-specific antigen (PSA): in vitro stability, epitope map, and development of immunofluorometric assays for specific and sensitive detection of free PSA and PSA-alpha 1-antichymotrypsin complex

1995 ◽  
Vol 41 (10) ◽  
pp. 1480-1488 ◽  
Author(s):  
K Pettersson ◽  
T Piironen ◽  
M Seppälä ◽  
L Liukkonen ◽  
A Christensson ◽  
...  
Keyword(s):  
Prostate Specific Antigen ◽  
Solid Phase ◽  
Specific Antigen ◽  
Close Correlation ◽  
Cathepsin G ◽  
Free Psa ◽  
Total Psa ◽  
The Stability ◽  
Storage Buffer

Abstract Generation of 15 monoclonal antibodies (MAbs) allowed construction of epitope maps and specific two-site immunofluorometric assays for free prostate-specific antigen (PSA) and PSA complexed with alpha 1-antichymotrypsin (ACT). Close correlation of PSA concentrations obtained with the use of different assays of free PSA suggested extensive similarity in immunodetection of free PSA in serum. Assays of the PSA-ACT complex overestimated the concentration of PSA-ACT in serum because of nonspecific adsorbance of ACT or cathepsin G-complexed ACT to the solid phase. This interference was substantially decreased in the presence of heparin. In studying the stability of purified PSA and PSA-ACT complexes formed in vitro, we found that the free PSA was stable during storage for 4 weeks at 35 degrees C, whereas PSA-ACT complexes largely dissociated in these conditions. The instability of PSA-ACT complexes was counteracted by storage at low temperatures, by adjusting the pH of the storage buffer between 6.8 and 7.4, and through addition of 100-1000-fold molar excess of native ACT. The ease of calibration and the accuracy of free PSA assays in comparison with assays of the PSA-ACT complex suggest that measurements of free to total PSA most accurately reflect the inverse of the proportion of PSA complexed to ACT in serum.

Dual-label one-step immunoassay for simultaneous measurement of free and total prostate-specific antigen concentrations and ratios in serum

1995 ◽  
Vol 41 (8) ◽  
pp. 1115-1120 ◽  
Author(s):  
K Mitrunen ◽  
K Pettersson ◽  
T Piironen ◽  
T Björk ◽  
H Lilja ◽  
...  
Keyword(s):  
Prostate Specific Antigen ◽  
Simultaneous Measurement ◽  
Solid Phase ◽  
Characteristic Curve ◽  
Specific Antigen ◽  
Sample Volume ◽  
Free Psa ◽  
One Step ◽  
Total Psa ◽  
Dual Label

Abstract We developed a simple one-step dual-label immunoassay for simultaneous measurement of the free, noncomplexed form of prostate-specific antigen (PSA) and total PSA. The assay is based on time-resolved fluorescence and includes a stable fluorescent chelate of Eu to label a monoclonal antibody (mAb) that detects only free PSA, whereas a second mAb labeled with a fluorescent chelate of Tb provides equimolar detection of both free PSA and PSA complexed to alpha 1-antichymotrypsin. A third mAb on a solid phase captures the free and complexed forms of PSA in an equimolar fashion. The simultaneous measurement of the free-to-total PSA ratio (F/T) with the one-step dual assay is not sensitive to variations in the sample volume. The discrimination between benign prostatic hyperplasia and prostate cancer patients, i.e., the area under the receiver-operating characteristic curve, increased from 0.64 (total PSA assay) to 0.78 and 0.81 when the F/T ratio was measured with single and dual assays, respectively.

scholarly journals Measurement of the Complex between Prostate-specific Antigen and α1-Protease Inhibitor in Serum

1999 ◽  
Vol 45 (6) ◽  
pp. 814-821 ◽  
Author(s):  
Wan-Ming Zhang ◽  
Patrik Finne ◽  
Jari Leinonen ◽  
Satu Vesalainen ◽  
Stig Nordling ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Protease Inhibitor ◽  
Prostate Specific Antigen ◽  
Specific Antigen ◽  
Serum Samples ◽  
Free Psa ◽  
Total Psa ◽  
Healthy Females

Abstract Background: Prostate-specific antigen (PSA) occurs in serum both free and in complex with protease inhibitors. The complex with α1-antichymotrypsin (ACT) is the major form in serum, and the proportion of PSA-ACT is higher in prostate cancer (PCa) than in benign prostatic hyperplasia (BPH). PSA also forms a complex with α1-protease inhibitor (API) in vitro, and the PSA-ACT complex has been detected in serum from patients with prostate cancer. The aim of the present study was to develop a quantitative method for the determination of PSA-API and to determine the serum concentrations in patients with PCa and BPH. Methods: The assay for PSA-API utilizes a monoclonal antibody to PSA as capture and a polyclonal antibody to API labeled with a Eu-chelate as a tracer. For calibrators, PSA-API formed in vitro was used. Serum samples were obtained before treatment from 82 patients with PCa, from 66 patients with BPH, and from 22 healthy females. Results: The concentrations of PSA-API are proportional to the concentrations of total PSA. PSA-API comprises 1.0–7.9% (median, 2.4%) of total immunoreactive PSA in PCa and 1.3–12.2% (median, 3.6%) in BPH patients with serum PSA concentrations >4 μg/L. In patients with 4–20 μg/L total PSA, the proportion of PSA-API serum is significantly higher in BPH (median, 4.1%) than in PCa (median, 3.2%; P = 0.02). Conclusions: The proportion of PSA-API in serum is lower in patients with PCa than in those with BPH. These results suggest that PSA-API is a potential adjunct to total and free PSA in the diagnosis of prostate cancer.

scholarly journals Dual-Label Immunoassay for Simultaneous Measurement of Prostate-specific Antigen (PSA)-α1-Antichymotrypsin Complex Together with Free or Total PSA

2003 ◽  
Vol 49 (1) ◽  
pp. 97-103 ◽  
Author(s):  
Lei Zhu ◽  
Jari Leinonen ◽  
Wan-Ming Zhang ◽  
Patrik Finne ◽  
Ulf-Håkan Stenman
Keyword(s):  
Detection Limit ◽  
Prostate Specific Antigen ◽  
Simultaneous Measurement ◽  
Solid Phase ◽  
Specific Antigen ◽  
Cathepsin G ◽  
Serum Samples ◽  
Total Psa ◽  
Dual Label

Abstract Background: A major portion of prostate-specific antigen exists in circulation as a complex with α1-antichymotrypsin (PSA-ACT), whereas a minor part is free (fPSA). The proportion of PSA-ACT is increased in prostate cancer (PCa), but immunologic determination of PSA-ACT is hampered by a background produced by nonspecific adsorption of ACT to the solid phase. To reduce the nonspecific interference, we produced an antibody specific for complexed ACT and developed immunofluorometric assays (IFMAs) for simultaneous measurement of fPSA + PSA-ACT (fPSA/PSA-ACT) and PSA-ACT + total PSA (tPSA, PSA-ACT/tPSA). Methods: Monoclonal antibodies (MAbs) were produced by immunization with PSA-ACT. The dual-label time-resolved IFMAs for fPSA/PSA-ACT and PSA-ACT/tPSA used a capture MAb to tPSA, an Eu3+-labeled MAb to fPSA or complexed ACT, and an Sm3+-labeled MAb to complexed ACT or to tPSA as tracer antibodies. The clinical utility was evaluated using serum samples from individuals with or without PCa with PSA concentrations of 2.0–20.0 μg/L. Results: One MAb (1D10) showed low cross-reactivity with free ACT and cathepsin G-ACT. A sandwich assay for PSA-ACT with 1D10 as tracer had a detection limit of 0.05 μg/L, and with this assay, PSA-ACT was undetectable in female sera. The detection limit for fPSA was 0.004 μg/L. Determinations of the ratio of fPSA to PSA-ACT and the proportions of fPSA/tPSA and PSA-ACT/tPSA provided the same clinical specificity for PCa and provided significantly better clinical specificity than did tPSA. Conclusions: Background problems observed in earlier PSA-ACT assays are eliminated by the use of a MAb specific for complexed ACT as a tracer. The same clinical validity can be obtained by determination of fPSA or PSA-ACT together or in combination with tPSA.

Double-label time-resolved immunofluorometric assay of prostate-specific antigen and of its complex with alpha 1-antichymotrypsin

1993 ◽  
Vol 39 (10) ◽  
pp. 2098-2103 ◽  
Author(s):  
J Leinonen ◽  
T Lövgren ◽  
T Vornanen ◽  
U H Stenman
Keyword(s):  
Prostate Specific Antigen ◽  
Solid Phase ◽  
Specific Antigen ◽  
Time Resolved ◽  
Free Psa ◽  
Double Label ◽  
Total Psa ◽  
Positive Results ◽  
As Solid Phase ◽  
Label Time

Abstract We have developed a procedure for simultaneous immunofluorometric assay (IFMA) of prostate-specific antigen (PSA) and its complex with alpha 1-antichymotrypsin (ACT). A PSA-specific monoclonal antibody, which captures both free PSA and the PSA-ACT complex, was used as solid-phase antibody. Total PSA immunoreactivity was measured with a Eu(3+)-labeled PSA antibody that reacted with both free PSA and PSA-ACT. PSA-ACT was assayed simultaneously with a Sm(3+)-labeled polyclonal ACT antibody as a tracer. As standard we used pooled serum in which most of the PSA occurred as the PSA-ACT complex. The assay range was 0.03-500 micrograms/L for total PSA and 0.16-450 micrograms/L for PSA-ACT. In comparison with the assay for total PSA, assay of the PSA-ACT/PSA ratio improved the clinical specificity for cancer by reducing the number of false-positive results in prostatic hyperplasia.

Effect of Marathon Running on Total and Free Serum Prostate-Specific Antigen Concentrations

2003 ◽  
Vol 127 (3) ◽  
pp. 345-348 ◽  
Author(s):  
Alexander Kratz ◽  
Kent B. Lewandrowski ◽  
Arthur J. Siegel ◽  
Patrick M. Sluss ◽  
Kelly Y. Chun ◽  
...  
Keyword(s):  
Prostate Specific Antigen ◽  
Specific Antigen ◽  
Physical Exertion ◽  
The United States ◽  
Marathon Running ◽  
Reliable Determination ◽  
Free Psa ◽  
Sporting Event ◽  
Exercise Induced ◽  
Total Psa

Abstract Context.—Prostate-specific antigen (PSA) is an important tumor marker for the most frequently diagnosed cancer in the United States. A major limitation of this marker is falsely elevated results in patients who are found not to have prostate cancer. The effects of vigorous physical exertion on PSA concentrations are controversial. Objective.—To determine the effects of marathon running on PSA levels. Design.—Measurement of total and free PSA levels in the sera of participants in a marathon before and within 4 and 24 hours after the race. Results.—None of the participants had elevated total PSA levels before the race. Although we found no statistically significant changes in average total or free PSA concentrations at either time point, after the marathon, 2 (11%) of 18 runners had total PSA concentrations outside the standard reference range. Changes in total PSA levels did not correlate with age or prerace PSA concentrations. Free PSA levels were not statistically significantly changed after the race and did not allow a reliable determination of exercise-induced PSA elevations. Conclusions.—Although it may not be necessary for men to abstain from exercise involving running before blood draws for PSA analysis, elevated PSA concentrations may be observed in some individuals after participation in a major sporting event. In these cases, repeat measurements should be considered at a time significantly removed from such exercise.

Purification and characterization of prostate-specific antigen (PSA) complexed to alpha 1-antichymotrypsin: potential reference material for international standardization of PSA immunoassays

1995 ◽  
Vol 41 (9) ◽  
pp. 1273-1282 ◽  
Author(s):  
Z Chen ◽  
A Prestigiacomo ◽  
T A Stamey
Keyword(s):  
Molecular Mass ◽  
Prostate Specific Antigen ◽  
Specific Antigen ◽  
Gel Filtration ◽  
Exchange Chromatography ◽  
Molar Ratio ◽  
Free Psa ◽  
Apparent Homogeneity ◽  
International Standardization

Abstract We describe for the first time a protocol to purify to apparent homogeneity an in vitro-prepared complex of prostate-specific antigen (PSA) and alpha 1-antichymotrypsin (ACT) by using a combination of gel filtration and ion-exchange chromatography. The purity of the PSA-ACT complex was confirmed by gel electrophoresis and Western blot. The PSA-ACT complex was stable in the pH range 6.0 to 7.8; it was also stable in various matrices, temperatures, and high concentrations of salt. Purification of the PSA-ACT complex was highly reproducible. An absorptivity of 0.99 L x g-1 x cm-1 at 280 nm was assigned to the PSA-ACT complex, based on amino acid analysis. Because PSA and ACT bind in a 1:1 molar ratio, we determined the molecular mass of the PSA-ACT complex as the mass encoded by the cDNA of ACT (plus 26% carbohydrate) plus the molecular mass of PSA (28,430 Da), which totals 89,280 Da. Using this material, we made two common calibrators, one of 100% PSA-ACT complex and one of 90% PSA-ACT complex plus 10% free PSA by volume (90:10 calibrator). Substitution of these calibrators for the manufacturers' calibrators in nine commercial immunoassays substantially reduced differences between immunoassays, especially for serum PSA values between 4 and 10 micrograms/L. The 90:10 calibrator is recommended as a universal calibrator for international standardization of PSA immunoassays.

scholarly journals The Combination of Human Glandular Kallikrein and Free Prostate-specific Antigen (PSA) Enhances Discrimination Between Prostate Cancer and Benign Prostatic Hyperplasia in Patients with Moderately Increased Total PSA

1999 ◽  
Vol 45 (11) ◽  
pp. 1960-1966 ◽  
Author(s):  
Angeliki Magklara ◽  
Andreas Scorilas ◽  
William J Catalona ◽  
Eleftherios P Diamandis
Keyword(s):  
Prostate Cancer ◽  
Benign Prostatic Hyperplasia ◽  
Prostate Specific Antigen ◽  
Prostatic Carcinoma ◽  
Specific Antigen ◽  
Area Under The Curve ◽  
Prostatic Hyperplasia ◽  
Free Psa ◽  
Glandular Kallikrein ◽  
Total Psa

Abstract Background: Prostate-specific antigen (PSA) is the most reliable tumor marker available and is widely used for the diagnosis and management of prostate cancer. Unfortunately, PSA cannot distinguish efficiently between benign and malignant disease of the prostate, especially within the range of 4–10 μg/L. Among the refinements developed to enhance PSA specificity is the free/total PSA ratio, which is useful in discriminating between the two diseases within the diagnostic “gray zone”. Recent data indicate that human glandular kallikrein (hK2), a protein with high homology to PSA, may be an additional serum marker for the diagnosis and monitoring of prostate cancer. Methods: We analyzed 206 serum samples (all before treatment was initiated) from men with histologically confirmed benign prostatic hyperplasia (n = 100) or prostatic carcinoma (n = 106) with total PSA in the range of 2.5–10 μg/L. Total and free PSA and hK2 were measured with noncompetitive immunological procedures. Statistical analysis was performed to investigate the potential utility of the various markers or their combinations in discriminating between benign prostatic hyperplasia and prostatic carcinoma. Results: hK2 concentrations were not statistically different between the two groups of patients. There was a strong positive correlation between hK2 and free PSA in the whole patient population. hK2/free PSA ratio (area under the curve = 0.69) was stronger predictor of prostate cancer than the free/total PSA ratio (area under the curve = 0.64). At 95% specificity, the hK2/free PSA ratio identified 30% of patients with total PSA between 2.5–10 μg/L who had cancer. At 95% specificity, the hK2/free PSA ratio identified 25% of patients with total PSA between 2.5 and 4.5 μg/L who had cancer. Conclusions: Our data suggest that hK2 in combination with free and total PSA can enhance the biochemical detection of prostate cancer in patients with moderately increased total PSA concentrations. More specifically, the hK2/free PSA ratio appears to be valuable in identifying a subset of patients with total PSA between 2.5 and 4.5 μg/L who have high probability of cancer and who should be considered for biopsy.

scholarly journals Reference Reagents for Prostate-specific Antigen (PSA): Establishment of the First International Standards for Free PSA and PSA (90:10)

2000 ◽  
Vol 46 (9) ◽  
pp. 1310-1317 ◽  
Author(s):  
Brian Rafferty ◽  
Peter Rigsby ◽  
Matthew Rose ◽  
Thomas Stamey ◽  
Rose Gaines Das
Keyword(s):  
Confidence Interval ◽  
Prostate Specific Antigen ◽  
Recombinant Dna ◽  
Collaborative Study ◽  
Specific Antigen ◽  
International Standards ◽  
Serum Samples ◽  
International Standard ◽  
Free Psa ◽  
Total Psa

Abstract Background: Prostate-specific antigen (PSA) measurements in serum by immunoassay are widely used in the screening, diagnosis, and monitoring of patients with prostate cancer although the lack of common reference reagents has led in the past to wide differences in estimates. We report here the results of a WHO international collaborative study in which two preparations of PSA representative of the main immunoreactive components in serum, free PSA and PSA 90:10, and a preparation of recombinant DNA-derived PSA were assessed as potential standards for the calibration of diagnostic immunoassays for PSA. Methods: Coded vials of the candidate materials and serum preparations containing PSA in the clinically important range were provided to the 10 laboratories in the study, and participants were asked to perform PSA assays currently in use in their laboratories. Data from 89 immunoassays by 26 different method-laboratory combinations were contributed to the study and analyzed centrally at the National Institute for Biological Standards and Control. Results: Potency estimates of the preparations relative to the in-house calibrators were in good agreement with the target value of 1 μg of total PSA/vial, the preparation of free PSA giving 1.10 μg/vial (95% confidence interval, 0.99–1.21 μg/vial) and PSA 90:10, 1.11 μg/vial (95% confidence interval, 1.04–1.18 μg/vial). No immunoreactivity was detected in ampoules containing the recombinant material. Use of a common standard of PSA 90:10 significantly reduced the between-laboratory geometric coefficients of variation for serum samples included in the study and gave a much narrower range of potency estimates. Conclusions: The preparation of free PSA was established by WHO as the First International Standard for PSA (free) with an assigned content of 1 μg of total PSA per vial. In addition, the preparation of bound PSA was established as the First International Standard for PSA (90:10) with an assigned content of 1 μg of total PSA per vial.

scholarly journals Determination of Non-α1-Antichymotrypsin-complexed Prostate-specific Antigen as an Indirect Measurement of Free Prostate-specific Antigen: Analytical Performance and Diagnostic Accuracy

2003 ◽  
Vol 49 (6) ◽  
pp. 887-894 ◽  
Author(s):  
Sebastian Wesseling ◽  
Carsten Stephan ◽  
Axel Semjonow ◽  
Michael Lein ◽  
Brigitte Brux ◽  
...  
Keyword(s):  
Prostate Specific Antigen ◽  
Sensitivity And Specificity ◽  
Specific Antigen ◽  
Roc Curves ◽  
Indirect Measurement ◽  
Free Psa ◽  
Specificity And Sensitivity ◽  
Diagnostic Sensitivity And Specificity ◽  
Total Psa

Abstract Background: A new assay measures prostate-specific antigen (PSA) not complexed to α1-antichymotrypsin (nACT-PSA) after removing PSA complexed to ACT by use of anti-ACT antibodies. We evaluated nACT-PSA and its ratio to total PSA (tPSA) as alternatives to free PSA (fPSA) and its ratio to tPSA in differentiating prostate cancer (PCa) and benign prostatic hyperplasia (BPH) in patients with tPSA of 2–20 μg/L. Methods: PSA in serum of 183 untreated patients with PCa and 132 patients with BPH was measured retrospectively on the chemiluminescence immunoassay analyzer LIAISON® (Byk-Sangtec Diagnostica) with the LIAISON tPSA and LIAISON fPSA assays. The nACT-PSA fraction was determined with a prototype assay measuring the residual PSA after precipitation of ACT-PSA with an ACT-precipitating reagent. Results:nACT-PSA was higher than fPSA in samples with fPSA concentrations <1 μg/L but lower in samples with >1 μg/L fPSA. The median ratios of fPSA/tPSA and of nACT-PSA/tPSA were significantly different between patients with BPH and PCa (19.4% vs 12.2% and 17.4% vs 13.0%, respectively). Within the tPSA ranges tested (2–20, 2–10, and 4–10 μg/L), areas under the ROC curves for the fPSA/tPSA ratios were significantly larger than those for nACT-PSA/tPSA. In the tPSA ranges <10 μg/L, the areas under the ROC curves for fPSA/tPSA were significantly larger than those for tPSA, whereas the areas for nACT-PSA/tPSA were not. At decision limits for 95% sensitivity and specificity, both ratios significantly increased specificity and sensitivity, respectively, compared with tPSA, but the fPSA/tPSA ratio showed higher values. Conclusions: nACT-PSA and its ratio to tPSA provide lower diagnostic sensitivity and specificity than fPSA/tPSA. The fPSA/tPSA ratio represents the state-of-the-art method for differentiating between PCa and BPH.

scholarly journals Effect of the Ratio of Free to Total Prostate-specific Antigen on Interassay Variability in Proficiency Test Samples

1999 ◽  
Vol 45 (8) ◽  
pp. 1181-1189 ◽  
Author(s):  
M Pat Fox ◽  
Andrew A Reilly ◽  
Erasmus Schneider
Keyword(s):  
Prostate Specific Antigen ◽  
Proficiency Test ◽  
Seminal Fluid ◽  
Specific Antigen ◽  
Free Form ◽  
Sample Mean ◽  
Substantial Impact ◽  
Free Psa ◽  
Total Prostate Specific Antigen ◽  
Total Psa

Abstract Background: Up to sevenfold differences were observed between total prostate-specific antigen (PSA) methods for New York State Proficiency Test samples prepared with seminal fluid PSA in human female serum. Because the PSA was mainly in its free form under these conditions, we wanted to determine whether a defined mixture of free and complexed PSA would reduce the interassay differences. Methods: We prepared a series of five solutions of 60 g/L bovine serum albumin with 10 μg/L total PSA consisting of varied proportions of free, noncomplexible PSA, and α1-antichymotrypsin (ACT)-complexed PSA from 0% to 100%. Two hundred seventy laboratories measured the total PSA in these samples, and 16 laboratories also analyzed the samples for free PSA. The results were used to calculate free/total PSA ratios. Results: Interassay CVs for total PSA measurements were ∼7% at 10–15% free PSA but became gradually larger as the free/total PSA ratio increased. Measured free-PSA concentrations were similar within each sample (mean CV, 12%), and the results were relatively independent of the proportion of free PSA in the samples. Twofold discrepancies between actual and expected ratios were observed with some methods at 100% free PSA and to a lesser degree at 30% free PSA. At 100% free PSA, the relatively higher total-PSA values measured by nonequimolar methods yielded low free/total PSA ratios of 50–60%. In contrast, the lower total PSA values obtained by equimolar methods yielded ratios close to the expected 100%. Conclusions: Preparing proficiency test samples with a 10:90 mixture of free, noncomplexible PSA:PSA-ACT is a viable alternative to the use of seminal fluid PSA. Furthermore, the method used to measure total PSA may have a substantial impact on the calculated proportion of free PSA and hence may have clinical relevance.

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