Measurement of the complex between prostate-specific antigen and alpha1-protease inhibitor in serum

BACKGROUND

Prostate-specific antigen (PSA) occurs in serum both free and in complex with protease inhibitors. The complex with alpha1-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 alpha1-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 microgram/L. In patients with 4-20 microgram/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.

Salivary carbonic anhydrase isoenzyme VI is located in the human enamel pellicle

Salivary carbonic anhydrase (CA VI) appears to protect teeth from caries via mechanisms other than direct regulation of salivary pH and buffering capacity. To elucidate whether CA VI acts in the local microenvironment of the tooth surface, we studied the location and activity of the enzyme in the human enamel pellicle. The study was performed using a specific rabbit antiserum to human CA VI in conjunction with immunostaining and immunoblot techniques. CA activity was demonstrated using a histochemical staining method. CA VI immunostaining of extracted teeth having in vivo formed pellicle showed that the enzyme is present in the enamel pellicle. Immunostaining for salivary alpha-amylase, which is known to be present in the pellicle, showed a similar staining pattern. The presence of CA VI in the enamel pellicle was confirmed by immunoblotting of in vivo formed pellicle proteins. In vitro studies showed that CA VI binds to polished enamel surfaces from both saliva and solutions of purified enzyme. The intensity of the CA VI immunostaining on the enamel surface was dependent on the concentration of the applied enzyme. The histochemical staining of in vitro formed enamel pellicle confirmed that the bound enzyme retains its enzymatic activity. The presence of active CA VI in the human enamel pellicle suggests that it may accelerate the removal of acid by functioning locally in the pellicle layer on dental surfaces.

Prostate-specific antigen

Prostate specific antigen (PSA) is serine protease produced at high concentrations by normal and malignant prostatic epithelium. It is mainly secreted into seminal fluid, where it digests the gel forming after ejaculation. Only minor amounts of PSA leak out into circulation from the normal prostate, but the release of PSA is increased in prostatic disease. Thus PSA is a sensitive serum marker for prostate cancer but its specificity is limited by a high frequency of falsely elevated values in men with benign prostatic hyperplasia (BPH). Approximately two-thirds of all elevated values (>4 microg/l) in men over 50 years of age are due to BPH. In serum, most of the PSA immunoreactivity consists of a complex between PSA and alpha1-antichymotrypsin (PSA-ACT) whereas approximately 5-40% are free. The proportion of PSA-ACT is larger and the free fraction is smaller in prostate cancer than in benign prostatic hyperplasia (BPH). Determination of the proportion of free PSA has become widely used to improve the cancer specificity of PSA especially in men with PSA values in the 'grey zone' (4-10 microg/l). PSA also occurs in complexes with other protease inhibitors and determination of these and other markers may further improve the diagnostic accuracy for prostate cancer. Interpretation of the results for many different markers is complicated, but this can be simplified by using statistical methods. The diagnostic accuracy can be further improved by using logistic regression or neural networks to estimate the combined impact of marker results and other findings like digital rectal examination (DRE), transrectal ultrasound (TRUS) and heredity.

Characterization of monoclonal antibodies for prostate-specific antigen and development of highly sensitive free prostate-specific antigen assays

BACKGROUND

The recent elucidation of the importance of serological free prostate-specific antigen (PSA) in the diagnosis of prostate cancer has created a demand for immunoassays specific for free PSA.

METHODS

We developed and characterized 11 monoclonal antibodies with high affinities for PSA (Ka values from 1.1 x 10(8) to 1.8 x 10(10)L/mol), only 3 of which cross-react with human glandular kallikrein (hK2). Using these antibodies and PSA antibodies developed by others, in conjunction with time-resolved fluorometry, we developed ultrasensitive sandwich immunoassays specific for the free form of PSA.

RESULTS

The analytical detection limit of these immunoassays is 0.001 microg/L. To our knowledge, this is the most sensitive free PSA assay reported to date. The free PSA immunoassays exhibit <1% cross-reactivity with PSA-alpha1-antichymotrypsin, show no cross-reactivity with hK2, and correlate well with established free PSA kits. The 11 antibodies developed by our group, in conjunction with 4 commercially available antibodies, were used to generate a putative epitope map of the PSA molecule.

CONCLUSION

The highly sensitive free PSA immunoassays may be used for measuring PSA subfractions in female serum, an application currently impossible with other reported free PSA immunoassays.

Characterization and immunological determination of the complex between prostate-specific antigen and alpha2-macroglobulin

Prostate-specific antigen (PSA) rapidly forms a complex with alpha2-macroglobulin (A2M) in vitro; however, PSA complexed with A2M (PSA-A2M) is not detected by conventional immunoassays for PSA because it is encapsulated by the A2M. In this study, we show that denaturation of PSA-A2M at high pH renders PSA immunoreactive. Part of the complexed PSA is released in free form and part remains bound to denatured A2M. These forms can be measured by a conventional immunoassay for PSA. This finding enabled us to design a dissociation assay for the detection of PSA-A2M, which was based on the removal of immunoreactive PSA in serum by immunoadsorption, denaturation of PSA-A2M at high pH, and measurement of the released PSA immunoreactivity by a conventional PSA immunoassay. This PSA-A2M assay was calibrated with PSA-A2M formed in vitro. The detection limit of the assay was 0.14 microg/L. Inter- and intraassay coefficients variation were 4-9% and 8-14%, respectively. When purified PSA was incubated with A2M, the loss of PSA immunoreactivity was highly correlated with the PSA-A2M formed, as measured by the dissociation assay for PSA-A2M (r = 0.99; P <0.0001). The concentration of PSA-A2M in serum correlated with that of total PSA both in prostate cancer (PCa) and benign prostatic hyperplasia (BPH); however, the ratio of PSA-A2M in relation to total PSA was significantly higher in BPH than in PCa (P <0.0003). ROC curve analysis suggested that measurement of the ratio of PSA-A2M to total PSA in serum improves the diagnostic accuracy for PCa compared with assays for total PSA only.

The association between the total antioxidant potential of plasma and the presence of coronary heart disease and renal dysfunction in patients with NIDDM

Oxidative stress may be an important pathogenetic factor in the development of diabetic vascular complications. The total antioxidative potential of plasma reflects the ability of an individual to resist oxidative stress. We measured the plasma total peroxyl radical-trapping potential (TRAP) and the concentrations of four plasma chain-breaking antioxidants in 81 patients with non-insulin-dependent diabetes mellitus (NIDDM) nine years after diagnosis and in 102 well-matched non-diabetic control subjects. The association between the total antioxidative potential and the presence of coronary heart disease (CHD) and diabetic kidney disease were also studied. There were no significant differences in plasma TRAP between NIDDM patients and control subjects (1250+/-199 vs. 1224+/-198 microM). Nor were there any significant differences in the concentrations of plasma uric acid, ascorbic acid, alpha-tocopherol, and protein thiols between NIDDM patients and control subjects. Patients with a low glomerular filtration rate and/or high urinary albumin excretion had elevated plasma uric acid. Plasma TRAP was not, however, associated with renal dysfunction. The plasma of NIDDM patients with CHD had a significantly higher value of unidentified antioxidative potential than that of patients without CHD. This relation was strongly dependent upon smoking. In conclusion, these data demonstrate that there are no major defects in the antioxidative potential of plasma caused by NIDDM per se. CHD and diabetic renal dysfunction were not associated with changes in plasma TRAP.

The clinical importance of free prostate‐specific antigen (PSA)

The proportion of free prostate-specific antigen (PSA) in serum relative to total PSA (F/T) is lower in patients with prostate cancer than in those with elevated levels of PSA due to benign prostatic disease. When applied to early diagnosis and screening for prostate cancer, the proportion of free PSA can be used to reduce the number of false-positive results by 20-40%. The utility of F/T is better in men with a small prostate volume, i.e. in relatively young men, who are most likely to benefit from early diagnosis and treatment of prostate cancer. The concentrations of PSA and especially free PSA are affected by considerable intra-individual variation and sample stability. Assay standardization is variable and it is therefore important to establish reference values for the methods used. Better control of these factors is likely to improve the diagnostic accuracy. The utility of determining free PSA can be improved by evaluating the combined impact of free and total PSA by logistic regression analysis or neural networks.

New biomarker evidence of oxidative DNA damage in patients with non-insulin-dependent diabetes mellitus

Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been reported to serve as a sensitive biomarker of oxidative DNA damage and also of oxidative stress. We have investigated oxidative DNA damage in patients with non-insulin-dependent diabetes mellitus (NIDDM) by urinary 8-OHdG assessments. We determined the total urinary excretion of 8-OHdG from 24 h urine samples of 81 NIDDM patients 9 years after the initial diagnosis and of 100 non-diabetic control subjects matched for age and gender. The total 24 h urinary excretion of 8-OHdG was markedly higher in NIDDM patients than in control subjects (68.2 +/- 39.4 microg vs. 49.6 +/- 37.7 microg, P = 0.001). High glycosylated hemoglobin was associated with a high level of urinary 8-OHdG. The increased excretion of urinary 8-OHdG is seen as indicating an increased systemic level of oxidative DNA damage in NIDDM patients.

Prostate-specific antigen forms a complex with and cleaves alpha 1-protease inhibitor in vitro

BACKGROUND

Complexes between prostate-specific antigen (PSA) and alpha 1-protease inhibitor (API) occur in serum and they are of potential interest in the diagnosis of prostate cancer. Pure PSA-API complexes are needed for development of specific assays, but complex formation has not earlier been achieved in vitro.

METHODS

PSA was incubated with an excess of API at 37 degrees C. Complexes formed were quantitated by an immunofluorometric assay using antibodies to PSA and API. The products were further characterized by SDS-PAGE, immunoblotting and amino-acid sequencing. PSA-API was purified by gel filtration and immunoaffinity chromatography.

RESULTS

PSA formed an SDS-stable 80-kDa one-to-one complex with API. The rate of formation of PSA-API was slow compared to that of PSA-alpha 2-macroglobulin (A2M) or PSA-alpha 1-antichymotrypsin (ACT), and only about 15% of PSA complexed with a 5-fold molar excess of API at 37 degrees C in 7 days. A major part of API was cleaved between 358-Met and 359-Ser, causing loss of inhibitory activity. PSA-API formed in vitro was purified by gel filtration and immunoaffinity chromatography with anti-PSA antibody. After incubation for 7 days at 37 degrees C, 30-40% of the complex had dissociated causing release of active PSA and proteolytically cleaved inactive API. The dissociation was accelerated in the presence of serum, and released PSA complexed with A2M and ACT.

CONCLUSIONS

PSA forms a complex with API in vitro, but the reaction is slow and part of the API is cleaved. Complex formation is reversible and released PSA is enzymatically active, whereas API is inactivated. Purified PSA-API will facilitate development of quantitative immunoassays for this complex.

Activation of type IV procollagenases by human tumor-associated trypsin-2

Increased production of proteinases, such as matrix metalloproteinases (MMPs), is a characteristic feature of malignant tumors. Some human cancers and cell lines derived from them also express trypsinogen, but the function of the extrapancreatic trypsin has remained unclear. In this study we cloned and sequenced trypsinogen-2 cDNA from human COLO 205 colon carcinoma cells and characterized the ability of the enzyme to activate latent human type IV procollagenases (proMMP-2 and proMMP-9). As shown by cloning and N-terminal amino acid sequencing, the amino acid sequence of tumor-associated trypsin-2 is identical to that of pancreatic trypsin-2. We found that both pancreatic trypsin-2 and tumor cell-derived trypsin-2 are efficient activators of proMMP-9 and are capable of activating proMMP-9 at a molar ratio of 1:1000, the lowest reported so far. Human trypsin-2 was a more efficient activator than widely used bovine trypsin and converted the 92-kDa proMMP-9 to a single 77-kDa product that was not fragmented further. The single peptide bond cleaved by trypsin-2 in proMMP-9 was Arg87-Phe88. The generation of the 77-kDa species coincided with the increase in specific activity of MMP-9. In contrast, trypsin-2 only partially activated proMMP-2. Trypsin-2 cleaved the Arg99-Lys100 peptide bond of proMMP-2 generating 62-65-kDa MMP-2 species. Trypsin-2-induced proMMP-2 and -9 conversions were inhibited by tumor-associated trypsin inhibitor added either prior to or during activation indicating that proMMPs were not activated autocatalytically. Trypsin-2 also activated proMMPs associated with tissue inhibitor of matrix metalloproteinases, the complexes of which are thought to be the major MMP forms in vivo. The ability of human tumor cell-derived trypsin-2 to activate latent MMPs suggests a role for trypsin-2 in initiating the proteinase cascade that mediates tumor invasion and metastasis formation.

Problems in the determination of prostate specific antigen

Accurate determination of prostate specific antigen is important because of the increasing use of prostate specific antigen for diagnosis, follow-up and screening of prostate cancer. Standardization of this assay is complicated by the occurrence in serum of two major molecular forms of prostate specific antigen, free prostate specific antigen and a complex between prostate specific antigen and alpha 1-antichymotrypsin. These two forms of prostate specific antigen are recognized differently by many but not all antibodies. Thus, it is possible and desirable to develop methods that measure each form equally. To achieve better comparability, it is also necessary to prepare international standards for prostate specific antigen and its complex with alpha 1-antichymotrypsin. Furthermore, reference methods should be established which use these standards and carefully selected reference antibodies.

Serum complex of trypsin 2 and alpha 1 antitrypsin as diagnostic and prognostic marker of acute pancreatitis: clinical study in consecutive patients

OBJECTIVE

To estimate the usefulness of serum concentrations of the complex of trypsin 2 and alpha 1 antitrypsin in diagnosing and assessing the severity of acute pancreatitis in comparison with serum C reactive protein, amylase, and trypsinogen 2 concentrations (reference markers).

DESIGN

Markers were measured in consecutive patients admitted with acute abdominal pain that was either due to pancreatitis or to other disease unrelated to the pancreas (controls).

SETTING

Department of surgery of a teaching hospital in Helsinki.

SUBJECTS

110 patients with acute pancreatitis and 66 with acute abdominal diseases of extrapancreatic origin. On the basis of the clinical course, acute pancreatitis was classified as mild (82 patients) or severe (28 patients).

MAIN OUTCOME MEASURES

Clinical diagnosis of acute pancreatitis and severity of the disease.

RESULTS

At admission all patients with acute pancreatitis had clearly raised concentrations of trypsin 2-alpha 1 antitrypsin complex (32 micrograms/l), whereas only three of the controls had such values. Of the markers studied, trypsin 2-alpha 1 antitrypsin complex had the largest area under the receiver operating curve, both in differentiating acute pancreatitis from extrapancreatic disease and in differentiating mild from severe disease.

CONCLUSIONS

Of the markers studied, trypsin 2-alpha 1 antitrypsin complex was the most accurate in differentiating between acute pancreatitis and extrapancreatic disease and in predicting a severe course for acute pancreatitis.

Screening for prostate cancer using serum prostate-specific antigen: a randomised, population-based pilot study in Finland

The possibility of screening the general population for prostate cancer using serum prostate-specific antigen (PSA) level (alone or in combination with other tests) as screening test has recently been discussed. A number of studies are on the way, but the published reports have almost exclusively been based on men volunteering for screening. We assessed the feasibility of a screening study based on men identified from a central population registry. A random sample of 600 men in the age groups 55, 60 and 65 years was identified from the Finnish Population Registry as the study population. Half of them were randomised to the intervention group and an invitation to participate was sent to them. The participation rate was 77% (230 out of 300). Twenty-five men had a serum PSA concentration of 4.0 micrograms l-1 or above and were invited for further examination including digital rectal examination, transrectal ultrasound and transrectal Tru-cut biopsies (directed and/or random). Six cases of cancer were detected among the 230 participating men, which corresponds to a detection rate of 2.6% and a positive predictive value of 24%. The number of cases detected is equivalent to the expected number of prostate cancer cases during a 10 year follow-up in this population. The ratio of free to total PSA was also measured and a cut-off level of 0.20 was chosen. Its use as an additional criterion of the screening test would have decreased the prevalence of false-positive screening tests from 8% (19 of 230) to 3% (7 of 230) at a cost of missing one of the six cancers compared with serum total PSA concentration alone. Of the six cancers, five were clinically regarded as localised and locally confined disease was confirmed pathologically in four of them. In conclusion, a population-based study in Finland seems feasible and the properties of the PSA test can be regarded as suitable for a randomised screening study. Thus, all prerequisites for a multicentre study, which is planned, seem to exist.

Complex formation between PSA isoenzymes and protease inhibitors

PURPOSE

We have studied complex formation between the isoenzymes of prostate specific antigen (PSA) and protease inhibitors in vitro.

MATERIALS AND METHODS

Ion exchange chromatography and hydrophobic interaction chromatography (HIC) were used for rapid separation of PSA isoenzymes from inhibitors and for characterization of the complex formation. Immunofluorometric assays (IFMA) specific for free PSA, the PSA-alpha 1-antichymotrypsin (PSA-ACT) complex and for both of these (total PSA) were used to measure various forms of PSA. Loss of free PSA immunoreactivity was used to estimate complex formation with alpha 2-macroglobulin (A2M) and ACT, which also was measured by PSA-ACT IFMA.

RESULTS

Complex formation between PSA and A2M was more rapid than with ACT. After extended incubation, about 75% of PSA reacted with ACT and 85% with A2M. When added to a mixture of ACT and A2M at concentrations corresponding to those in plasma, only 17% of PSA formed a complex with ACT while 17% remained free and 66% was undetectable, indicating complex formation with A2M. After extended incubation of PSA-ACT at 37C, a significant proportion of PSA was released as free active PSA. When A2M was included in the reaction mixture, the loss of PSA-ACT was not accompanied by appearance of free PSA, an indication that it complexed with A2M. Five to 18% of nicked PSA complexed with ACT whereas 54 to 67% reacted with A2M.

CONCLUSIONS

alpha 2-macroglobulin is the major inhibitor of PSA when it reached the circulation. Contrary to earlier assumptions, nicked PSA can bind to A2M rendering it inaccessible to antibodies.

Purification and characterization of different molecular forms of prostate-specific antigen in human seminal fluid

We have developed a new procedure for purifying prostate-specific antigen (PSA) from human seminal fluid. The method is based on ammonium sulfate precipitation, hydrophobic interaction chromatography, gel filtration, and anion-exchange chromatography. It can be completed within 2 days with a recovery of intact PSA of 30%. By anion-exchange chromatography, five isoforms of PSA (A, B, C, D, and E) can be separated. The major form (PSA-B) consists of the intact enzyme, as shown by the occurrence of only one band of 33 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing or nonreducing conditions, and by amino acid sequencing, which reveals only one amino-terminal sequence corresponding to the reported amino-terminal sequence of intact PSA. The specific absorbance of 1 g/L PSA-B at 280 nm was 1.61, and 80% of the PSA-B formed a complex with alpha 1-antichymotrypsin, indicating that it is enzymatically active. Three cleaved forms of PSA with different nicking sites and low enzymatic activity were separated from intact PSA by ion-exchange chromatography. In addition, we isolated a glycosylation variant, PSA-A, which showed a higher isoelectric point (pI = 7.2) than PSA-B (pI = 6.9) but similar enzymatic activity; this form accounts for 5-10% of total PSA. After treatment with sialidase, PSA-A and B had the same isoelectric point value (pI = 7.7).

Purification and characterization of different molecular forms of prostate-specific antigen in human seminal fluid

We have developed a new procedure for purifying prostate-specific antigen (PSA) from human seminal fluid. The method is based on ammonium sulfate precipitation, hydrophobic interaction chromatography, gel filtration, and anion-exchange chromatography. It can be completed within 2 days with a recovery of intact PSA of 30%. By anion-exchange chromatography, five isoforms of PSA (A, B, C, D, and E) can be separated. The major form (PSA-B) consists of the intact enzyme, as shown by the occurrence of only one band of 33 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing or nonreducing conditions, and by amino acid sequencing, which reveals only one amino-terminal sequence corresponding to the reported amino-terminal sequence of intact PSA. The specific absorbance of 1 g/L PSA-B at 280 nm was 1.61, and 80% of the PSA-B formed a complex with alpha 1-antichymotrypsin, indicating that it is enzymatically active. Three cleaved forms of PSA with different nicking sites and low enzymatic activity were separated from intact PSA by ion-exchange chromatography. In addition, we isolated a glycosylation variant, PSA-A, which showed a higher isoelectric point (pI = 7.2) than PSA-B (pI = 6.9) but similar enzymatic activity; this form accounts for 5-10% of total PSA. After treatment with sialidase, PSA-A and B had the same isoelectric point value (pI = 7.7).

Detection of prostatic cells in peripheral blood: correlation with serum concentrations of prostate-specific antigen

We have studied the expression of prostate-specific antigen (PSA) mRNA by reverse transcriptase-polymerase chain reaction in peripheral blood of 25 patients with cancer of the prostate (CAP), four with benign prostatic hyperplasia (BPH), two with renal stones, three with other types of cancer, and six healthy male and three female controls. Expression of mRNA specific for a certain tissue in peripheral blood is thought to indicate the presence of circulating cancer cells and metastatic spread of a tumor originating from this tissue. We detected PSA mRNA in 9 of 18 CAP patients with metastatic disease but in none of 7 patients without metastases. Negative results in patients with metastatic disease were associated with successful endocrine therapy and low concentrations of serum PSA, and the correlation between serum concentrations of PSA and the presence of PSA mRNA in peripheral blood was statistically significant. PSA mRNA was not found in patients with BPH, other types of cancer, or in healthy controls. Thus the occurrence of PSA mRNA in peripheral blood is associated with metastatic CAP.

Detection of prostatic cells in peripheral blood: correlation with serum concentrations of prostate-specific antigen

We have studied the expression of prostate-specific antigen (PSA) mRNA by reverse transcriptase-polymerase chain reaction in peripheral blood of 25 patients with cancer of the prostate (CAP), four with benign prostatic hyperplasia (BPH), two with renal stones, three with other types of cancer, and six healthy male and three female controls. Expression of mRNA specific for a certain tissue in peripheral blood is thought to indicate the presence of circulating cancer cells and metastatic spread of a tumor originating from this tissue. We detected PSA mRNA in 9 of 18 CAP patients with metastatic disease but in none of 7 patients without metastases. Negative results in patients with metastatic disease were associated with successful endocrine therapy and low concentrations of serum PSA, and the correlation between serum concentrations of PSA and the presence of PSA mRNA in peripheral blood was statistically significant. PSA mRNA was not found in patients with BPH, other types of cancer, or in healthy controls. Thus the occurrence of PSA mRNA in peripheral blood is associated with metastatic CAP.

Standardization of PSA determinations

Standardization of determinations for prostate specific antigen (PSA) has become an important issue due to the widespread use of these determinations for prostate cancer screening. Standardization of this assay is complicated due to the occurrence of two major forms of PSA in serum, the free antigen and a complex between PSA and alpha 1-antichymotrypsin (PSA-ACT). These two forms of PSA are recognized differently by different antibodies, but by careful selection of antibodies, it is possible to design methods that measure each form equally. It is suggested, that standards for PSA and PSA-ACT should be prepared and established as international standards. Furthermore, reference methods should be established on the basis that these standards and carefully selected reference antibodies.

Serum concentrations of prostate specific antigen and its complex with alpha 1-antichymotrypsin before diagnosis of prostate cancer

Prostate cancer can be detected at an early, potentially curable stage by screening based on digital rectal examination and serum prostate specific antigen (PSA). The value of screening appears doubtful, based on high 10-year survival rates in selected cases of early prostate cancer, but this follow-up time may be insufficient. By linking the information on 21172 men who took part in a screening examination in Finland, 1968-73, with data from the Finnish Cancer Registry, 44 cases of prostate cancer diagnosed up to 1980 were identified. Serum samples from cancer cases and from 74 controls matched for age and time of sampling were assayed for PSA and its complex with alpha 1-antichymotrypsin (PSA-ACT). With a cut-off for PSA of 2.5 micrograms/L giving 92% specificity, 95% of the cancers developing within the first 5 years, and 52% developing in 6-10 years tested positive. As a potential screening test with a 5-year interval for men under 65, the sensitivity would be 92% and specificity 97%. The ratio of PSA-ACT to total PSA was lower in controls than in patients with cancer. Using this ratio, we could eliminate half of the false-positive results in the range 2.5-25 micrograms/L without loss of sensitivity. Cancer was typically diagnosed 5-10 years after PSA exceeded 2.5 micrograms/L, and the median survival after diagnosis was 3.6 years. 10-year survival after drawing the sample was 71% in cancer cases with a PSA concentration less than 4 micrograms/L and 48% in those with higher concentrations. The corresponding figures at 15 years were 53% and 27%, and at 20 years 43% and 18%, respectively. These results suggest it is advisable to confine screening for prostate cancer to men with a life expectancy of clearly more than 10 years--ie, younger men, who have the greatest chance to benefit from early detection.

Time-resolved immunofluorometric assay of trypsin-2 complexed with alpha 1-antitrypsin in serum

We developed a sensitive time-resolved immunofluorometric assay (IFMA) for trypsin-2 complexed with alpha 1-antitrypsin (AAT). We used a trypsin-2-specific monoclonal antibody on the solid phase and a europium-labeled polyclonal antibody to AAT as tracer. The detection limit is 0.05 microgram/L and the range of linearity extends to 100 micrograms/L. We compared the clinical utility of the trypsin-2-AAT assay with that of free trypsinogen-2 and amylase in serum by studying 120 healthy subjects, 29 patients with acute pancreatitis, 11 with extrahepatic biliary obstruction, and 34 with acute abdominal disorders of extrapancreatic origin. In patients with acute pancreatitis the median concentration of trypsin-2-AAT in serum was 59-fold that in healthy controls, 42-fold that in patients with biliary obstruction, and 33-fold that in patients with acute abdominal disorders of extrapancreatic origin. These differences are greater than those for trypsinogen-2 (19-, 20-, and 28-fold, respectively) and amylase (5.4-, 6.5-, and 5.4-fold, respectively). Compared with the assays of free trypsinogen-2 and amylase, our assay of trypsin-2-AAT improved the clinical specificity for acute pancreatitis by eliminating false-positive results in our control groups. Increased concentrations of trypsin-2-AAT and trypsinogen-2 were also observed in patients with chronic renal failure undergoing dialysis.

Time-resolved immunofluorometric assay of trypsin-2 complexed with alpha 1-antitrypsin in serum

We developed a sensitive time-resolved immunofluorometric assay (IFMA) for trypsin-2 complexed with alpha 1-antitrypsin (AAT). We used a trypsin-2-specific monoclonal antibody on the solid phase and a europium-labeled polyclonal antibody to AAT as tracer. The detection limit is 0.05 microgram/L and the range of linearity extends to 100 micrograms/L. We compared the clinical utility of the trypsin-2-AAT assay with that of free trypsinogen-2 and amylase in serum by studying 120 healthy subjects, 29 patients with acute pancreatitis, 11 with extrahepatic biliary obstruction, and 34 with acute abdominal disorders of extrapancreatic origin. In patients with acute pancreatitis the median concentration of trypsin-2-AAT in serum was 59-fold that in healthy controls, 42-fold that in patients with biliary obstruction, and 33-fold that in patients with acute abdominal disorders of extrapancreatic origin. These differences are greater than those for trypsinogen-2 (19-, 20-, and 28-fold, respectively) and amylase (5.4-, 6.5-, and 5.4-fold, respectively). Compared with the assays of free trypsinogen-2 and amylase, our assay of trypsin-2-AAT improved the clinical specificity for acute pancreatitis by eliminating false-positive results in our control groups. Increased concentrations of trypsin-2-AAT and trypsinogen-2 were also observed in patients with chronic renal failure undergoing dialysis.