Quantitative immunoassay for complexes of prostate-specific antigen with alpha2-macroglobulin

We have developed two ELISAs for quantifying complexes of prostate-specific antigen (PSA) with alpha2-macroglobulin (alpha2M), using partially purified PSA:alpha2M complex as the calibrator. One ELISA was designed to evaluate )SA:alpha2M complex in fluids containing a huge excess of PSA over the amount of complex (semen-derived fluids), the other for use in fluids containing an excess of alpha2M over PSA (blood plasma). The range of the assays was 2-1000 micrograms/L for PSA complexed to alpha2M; the detection limit was 3 micrograms/: Intra- and interassay CVs were 7-13% and 11-17%, respectively, at complexed PSA concentrations of 6-500 micrograms/L. Seminal fluid from healthy men (n = 60) contained 5.2 +/- 2.6 micrograms/L PSA complexed with alpha2M. Prostatic and seminal vesicle fluids contained 6.5 +/- 2.9 ad 0.3 +/- 0.2 mg/L PSA complexed to alpha2M, respectively. When purified PSA was incubated with citrated plasma, between 45% and 65% of the added PSA was recovered as free PSA, whereas approximately 25% formed complexes with alpha2M, 10% complexed with alpha1-antichymotrypsin, and only 0.1-6% was complexed with protein C inhibitor. Of 30 patients with prostate disease, 20 showed detectable plasma PSA:alpha2M complexes; however, the potential diagnostic significance of this complex requires further investigation.

Inhibition of 2,3-oxidosqualene-lanosterol cyclase in Candida albicans by pyridinium ion-based inhibitors

The N-(4E,8E)-5,9,13-trimethyl-4,8,12-tetradecatrien-1- ylpyridinium and N-(4E,8E)-5,9,13-trimethyl-4,8,12-tetradecatrien-1- ylpicolinium cations were evaluated for their ability to inhibit 2,3-oxidosqualene-lanosterol cyclase activity in Candida albicans. Both compounds inhibited fungal growth, were fungicidal, and resulted in the accumulation of squalene epoxide concurrent with a decrease in ergosterol, monomethyl sterols, and lanosterol, as was expected for the specific inhibition of 2,3-oxidosqualene-lanosterol cyclase activity. These compounds are electron-poor aromatic mimics of a monocyclized transition state or high-energy intermediate formed from oxidosqualene, which may explain their selective action.

Quantitative immunoassay for complexes of prostate-specific antigen with alpha2-macroglobulin

We have developed two ELISAs for quantifying complexes of prostate-specific antigen (PSA) with alpha2-macroglobulin (alpha2M), using partially purified PSA:alpha2M complex as the calibrator. One ELISA was designed to evaluate )SA:alpha2M complex in fluids containing a huge excess of PSA over the amount of complex (semen-derived fluids), the other for use in fluids containing an excess of alpha2M over PSA (blood plasma). The range of the assays was 2-1000 micrograms/L for PSA complexed to alpha2M; the detection limit was 3 micrograms/: Intra- and interassay CVs were 7-13% and 11-17%, respectively, at complexed PSA concentrations of 6-500 micrograms/L. Seminal fluid from healthy men (n = 60) contained 5.2 +/- 2.6 micrograms/L PSA complexed with alpha2M. Prostatic and seminal vesicle fluids contained 6.5 +/- 2.9 ad 0.3 +/- 0.2 mg/L PSA complexed to alpha2M, respectively. When purified PSA was incubated with citrated plasma, between 45% and 65% of the added PSA was recovered as free PSA, whereas approximately 25% formed complexes with alpha2M, 10% complexed with alpha1-antichymotrypsin, and only 0.1-6% was complexed with protein C inhibitor. Of 30 patients with prostate disease, 20 showed detectable plasma PSA:alpha2M complexes; however, the potential diagnostic significance of this complex requires further investigation.

Nephron-sparing surgery for renal cell carcinoma

There are multiple surgical approaches or techniques for nephron-sparing surgery. These include simple nucleation, segmental polar nephrectomy, wedge resection, major transverse resection, and extracorporeal partial nephrectomy with autotransplant. This article discusses the indications and follow-up for nephron-sparing surgery, focusing specifically on the surgical techniques for wedge resection and segmental polar nephrectomy.

Resistance to activated protein C: a common inherited cause of venous thrombosis

Resistance to activated protein C (RAPC) is a newly recognized hypercoagulable state that was first described in 1993. It has become apparent that RAPC is even more common than deficiencies in protein C, protein S, or antithrombin III (AT-III) and affects an estimated 5% of the general population. The majority of patients with RAPC have an abnormality in factor V (Arg506Gln), which renders factor Va resistant to degradation by activated protein C. Studies in 75 patients referred to the Hematology Laboratory at Walter Reed Army Institute of Research (WRAIR) over a 14-month period for evaluation of venous thromboembolism were reviewed to determine the percentage of those with RAPC. Of the 75 patients in the study, one was deficient in protein S, one was deficient in protein C, and none was deficient in AT-III. In contrast, 27 (36%) patients tested positive for RAPC. Blood was available for DNA analysis in 15 patients with RAPC. Of these 15 patients, nine (60%) tested positive for the Arg506Gln mutation in factor V. Six other patients with RAPC did not have the factor V mutation. Additional risk factors for thrombosis were immobility, obesity, use of oral contraceptives, and pregnancy. The majority of patients had deep venous thrombosis of the lower extremities; 71% had a recurrence if not placed on chronic anticoagulation therapy. Thus RAPC is a significant risk factor for venous thrombosis. Evaluation for inherited hypercoagulable states should include testing for this newly described condition.

Thrombosis in otherwise well children with the factor V Leiden mutation

OBJECTIVE

To determine whether resistance to activated protein C caused by the factor V Leiden mutation (Arg506 to Gln) is associated with thrombosis occurring during childhood.

STUDY DESIGN

Children with thrombosis were screened for activated protein C resistance. Children found resistant to activated protein C had DNA analysis for the factor V Leiden mutation. Family members of the children with activated protein C resistance were similarly studied.

RESULTS

Three of fourteen children examined had abnormal normalized activated protein C sensitivity ratios. One child had protein S deficiency. The children had hyperlipidemia. Molecular confirmation of the factor V Leiden mutation was obtained for all three children. Family members of each of the three children were affected.

CONCLUSIONS

Children have thromboses in association with the factor V Leiden mutation, as do adults. This mutation may be identified as an isolated risk factor or in association with other risk factors for thrombosis.

A two-allele polymorphism in protein C inhibitor with varying frequencies in different ethnic populations

cDNAs for protein C inhibitor (PCI), prepared from human liver RNA, contained two forms of PCI, designated PCI*A and PCI*B. While PCI*A is identical to the published PCI sequence, PCI*B differs in 4 of 1221 bp and two amino acids, A36V and K86E. Frequencies for the PCI*B allele, determined from genomic DNA, differed among ethnic groups. Frequency distribution and historical migration of modern man suggest that PCI*A arose from the PCI*B allele. Antigen levels in plasma homozygous for PCI*A or PCI*B equalled that of pooled normal plasma. K86E in PCI*B causes a charge alteration in helix D which is likely involved in heparin binding in antithrombin III but not likely involved in glycosaminoglycan binding in PCI. Kinetic studies showed that plasmas homozygous for PCI*A and PCI*B are similar in their APC inhibiting properties and in their heparin sensitivity, consistent with the idea that helix D in PCI is not involved in heparin binding.

Design, synthesis and in vitro evaluation of pyridinium ion based cyclase inhibitors and antifungal agents

The design, synthesis and in vitro biological evaluation of pyridinium ion based inhibitors of oxidosqualene cyclase enzymes are reported. N-Alkyl- and N-prenylpyridinium ions have been found to be potent and specific inhibitors of Candida albicans oxidosqualene-lanosterol cyclase and to exhibit antifungal activity. The ability of pyridinium ions to inhibit the C. albicans cyclase increases with increasing structural resemblance to a putative monocyclized species formed during the course of the cyclization process. The N-(4E,8E)-5,9,13-trimethyl-4,8,12-tetradecatrien-1- ylpyridinium cation 1 inhibits the C. albicans enzyme at concentrations more than 100-fold lower than does the directly analogous piperidinium derivative 4.

Comparative modeling of the three CP modules of the beta-chain of C4BP and evaluation of potential sites of interaction with protein S

A computer model of the beta-chain of C4b-binding protein (C4BP) was constructed, using the backbone fold of the NMR structures of the sixteenth CP module of factor H (H16) and of a pair of modules consisting of the fifteenth and sixteenth CPs of factor H (H15-16). The characteristic hydrophobic core responsible for dictating the three-dimensional structure of the CP family is conserved in the amino acid sequence of C4BP beta 1, beta 2 and beta 3. The distribution of the electrostatic potential shows that the model is mainly covered by a negative contour. Interestingly, a positive area is observed in the C-terminal region of the first CP module, enclosing peptide 31-45, known to be a binding site for protein S. This observation suggests that electrostatic interactions can be of importance for the interaction of C4BP to protein S. A solvent-accessible hydrophobic patch, located nearby and involving the peptide 31-45, was also found in the model, further confirming that this area is involved in the interaction with protein S. The contribution of beta-chain residues 31-45 to the affinity for protein S was studied further by means of synthetic mutant peptides. The results suggest that both electrostatic and hydrophobic interactions are important for the binding to protein S.

Prostate specific antigen-alpha 2-macroglobulin complexes in prostate cancer patient sera

Quantitative immunoblotting of prostate cancer patient sera revealed that most prostate specific antigen was in complexes with alpha 1-antichymotrypsin or alpha 2-macroglobulin with little of it being free antigen. Complexes of prostate specific antigen with these protease inhibitors in patient sera comigrated during electrophoresis with the respective purified complexes. Each complex was selectively removed from patient sera by absorption with specific antibodies. When prostate specific antigen was added to normal plasma, complexes with alpha 2-macroglobulin appeared first and after 1 hr, the distribution was approximately 40% free antigen, approximately 40% complexes with alpha 2-macroglobulin, and approximately 20% complexes with alpha 1-antichymotrypsin. These data show that prostate specific antigen reacts more readily with alpha 2-macroglobulin than with any other protease inhibitor in plasma and that the antigen complexes with alpha 2-macroglobulin in vivo in cancer patients.

Two mutations in the promoter region of the human protein C gene both cause type I protein C deficiency by disruption of two HNF-3 binding sites

Protein C is a vitamin K-dependent zymogen of a serine protease that inhibits blood coagulation by the proteolytic inactivation of factors Va and VIIIa. Individuals affected with protein C deficiency are at risk for thrombosis. Genetic analyses of affected individuals, to determine the cause of the protein C deficiency, revealed a large variety of mutations in the protein C gene, including several in the promoter region of this gene. Comparison of the region around two of these mutations, A-32-->G and T-27-->A, with transcription factor consensus sequences suggested the presence of two overlapping and inversely oriented HNF-3 binding sites. Direct evidence for the presence of the two HNF-3 binding sites in the protein C promoter was obtained using electrophoretic mobility shift assays and UV cross-linking experiments. These experiments revealed that HNF-3 can bind specifically to both putative HNF-3 sites in the wild-type protein C promoter. Due to the T-27-->A mutation, one binding site is completely lost, while the other site still binds HNF-3, but with strongly reduced affinity. As a consequence of the A-32-->G mutation, the protein C promoter loses all its HNF-3 binding capacity. Transient transfection experiments demonstrated that the binding of HNF-3 to the protein C promoter is of physiological significance. This followed from experiments in which the introduction of the A-32-->G or T-27-->A mutation resulted in a 4-5-fold reduced promoter activity in HepG2 cells. Furthermore, transactivation of the wild-type protein C promoter construct with HNF-3 showed a 4-5-fold increased promoter activity in HepG2 cells. In HeLa cells, significant wild-type promoter activity was only observed after transactivation with HNF-3. When a promoter construct containing the T-->A mutation at position -27 was used, the transactivation potential of HNF-3 was 2-fold reduced in HepG2 cells, whereas in HeLa cells no transactivation was observed. With the promoter construct containing the A-32-->G mutation, no transactivation by HNF-3 was found either in HepG2 or in HeLa cells.

Characterization of a cDNA for rhesus monkey protein C inhibitor--evidence for N-terminal involvement in heparin stimulation

cDNAs for protein C inhibitor (PCI) were cloned from human and rhesus monkey liver RNAs by reverse transcription and polymerase chain reaction (PCR) amplification. Sequencing showed that rhesus monkey and human PCI cDNAs were 93% identical. Predicted amino acid sequences differed at 26 of 387 residues. Four of these differences (T352M, N359S, R362K, L363I) were in the reactive center loop that is important for inhibitory specificity, and two were in the N-terminal helix (M8T, E13K) that is implicated in glycosaminoglycan binding. PCI in human or rhesus monkey plasma showed comparable inhibitory activity towards human activated protein C in the presence of 10 U/ml heparin. However, maximal acceleration of the inhibition of activated protein C required 5-fold lower heparin concentration for rhesus monkey than for human plasma, consistent with the interpretation that the additional positive charge (E13K) in a putative-heparin binding region increased the affinity for heparin.

Incidence of activated protein C resistance caused by the ARG 506 GLN mutation in factor V in 113 unrelated symptomatic protein C-deficient patients. The French Network on the behalf of INSERM

Because multiple risk factors in one patient may increase the clinical expression of thrombophilia, we assessed the presence in protein C-deficient patients of the factor V Arg 506 Gln mutation responsible for activated protein C resistance. Using a strategy allowing rapid screening of factor V exon 10, we studied 113 patients with protein C deficiency and 104 healthy volunteers. We detected the Arg 506 Gln mutation in 15 patients (14%) and in one healthy subject (1%). We identified a previously unpublished sequence variation leading to an Arg 485 Lys substitution in three normal subjects and seven protein C-deficient patients. A significant difference in the allelic frequency of the Arg 506 Gln factor V mutation was found between protein C-deficient patients heterozygous for an identified protein C mutation (n = 84; allelic frequency, 4.8%) and protein C-deficient patients with no identified mutation in the protein C gene coding regions (n = 25; allelic frequency, 14%). The results demonstrate that a significant subset of thrombophilic patients has multiple genetic risk factors although additional secondary genetic risk factors remain to be identified for the majority of symptomatic protein C-deficient patients.

Activated protein C resistance: molecular mechanisms

Activated protein C (APC) resistance is usually associated with a single DNA mutation predicting replacement of Arg506 by Gln in factor V (FV). Studies using synthetic peptides suggest that FV residues 493-506 provide factor Xa (FXa) and protein S binding sites. Biochemical studies were performed to test the hypothesis that the Arg506Gln FV mutation causes APC resistance and to define the nature of the resistance of Gln506-FVa to APC. Purified Gln506-FV conveyed APC resistance to FV-deficient plasma in APTT and FXa-1-stage assays. Purified Gln506-FVa, generated either by thrombin or by FXa, was resistant to APC. Nonetheless, Gln506-FVa was not completely resistant to APC since it was inactivated by APC approximately 10-fold slower than normal Arg506-FVa, probably due to cleavage at Arg306. This reduced but significant susceptibility of Gln506-FVa to APC inactivation may help explain why APC resistance, especially for heterozygotes, is a relatively moderate risk factor for venous thrombosis. Cardiolipin promotes APC anticoagulant activity better than FXa coagulant activity, and antibodies from some antiphospholipid antibody syndrome patients downregulate APC activity. Thus, acquired APC resistance may contribute to pathogenesis of thrombosis in the antiphospholipid antibody syndrome.

Activated protein C resistance: molecular mechanisms based on studies using purified Gln506-factor V

Gln506-factor V (FV) was purified from plasma of an individual homozygous for an Arg506Gln mutation in FV that is associated with activated protein C (APC) resistance. Purified Gln506-FV, as well as Gln506-FVa generated by either thrombin or FXa, conveyed APC resistance to FV-deficient plasma in coagulation assays. Clotting assay studies also suggested that APC resistance does not involve any abnormality in FV-APC-cofactor activity. In purified reaction mixtures, Gln506-FVa in comparison to normal FVa showed reduced susceptibility to APC, because it was inactivated approximately 10-fold slower than normal Arg506-FVa. It was previously reported that inactivation of normal FVa by APC involves an initial cleavage at Arg506 followed by phospholipid-dependent cleavage at Arg306. Immunoblot and amino acid sequence analyses showed that the 102-kD heavy chain of Gln506-FVa was cleaved at Arg306 during inactivation by APC in a phospholipid-dependent reaction. This reduced but measurable susceptibility of Gln506-FVa to APC inactivation may help explain why APC resistance is a mild risk factor for thrombosis because APC can inactivate both normal FVa and variant Gln506-FVa. In summary, this study shows that purified Gln506-FV can account for APC resistance of plasma because Gln506-FVa, whether generated by thrombin or FXa, is relatively resistant to APC.

Use of a generally applicable tissue factor--dependent factor V assay to detect activated protein C-resistant factor Va in patients receiving warfarin and in patients with a lupus anticoagulant

The original activated partial thromboplastin time-based assay for activated protein C (APC)-resistant factor Va (FVa) requires carefully prepared fresh plasma and cannot be used in patients receiving warfarin or in patients with antiphospholipid antibodies. A new test is described here that circumvents these limitations and distinguishes without overlap heterozygotes for APC-resistant FVa from persons with normal FV. A diluted test plasma is incubated with an FV-deficient substrate plasma and tissue factor and then clotted with Ca2+ or Ca2+ plus APC. Test results are independent of the FV level or the dilution of the test plasma used. Of 39 controls, 37 gave normal results. Two controls (5%) gave results indicative of APC resistant FVa and on DNA analysis were found to be heterozygous for FV R506Q. Twenty of 21 randomly selected patients receiving warfarin gave normal results. In the single patient with abnormal results, heterozygous FV R506Q was confirmed by DNA analysis. Two of 15 patients with protein S deficiency and 5 of 29 patients with a lupus anticoagulant had abnormal results. APC resistance caused by FV R506Q was confirmed in the five of these seven patients available for DNA analysis. APC-resistant FVa was also detected in 10 of 21 (46%) stored plasma from unrelated patients with venous thrombosis and negative earlier evaluation for a lupus anticoagulant or a deficiency of protein C, protein S, or antithrombin, which confirms a high incidence of this defect among patients with venous thrombosis.

Identification of candidate residues for interaction of protein S with C4b binding protein and activated protein C

Protein S is a plasma factor essential for prevention of thrombosis, partly due to its activity as a cofactor for the plasma anticoagulant protease-activated protein C. To expand knowledge about structure-function relationships in homologous protein S molecules, studies of protein S from different species have been performed. Protein S anti-coagulant activity in human, monkey, bovine, and porcine plasma has been inactivated by purified human C4b binding protein (C4BP) with dose-dependence, suggesting that each protein S can bind human C4BP and that only the free form of each is anti-coagulantly active. Purified porcine protein S has a 10-fold higher Kd for human C4BP than has human protein S. Protein S residues 420-434 provide an essential binding site for the negative regulator C4BP. cDNA sequences show that protein S residues 420-434 are highly conserved in all four species with the notable exception of Lys-429-Ile in porcine protein S. Differences between porcine and human protein S, e.g. Lys-429-Ile, Lys-43-Ala, Ser-197-Leu, Ser 199-Phe, Glu-463-Gly, Lys-571-Glu, Asn-602-Ile, Gln-607-Pro, may contribute to the decreased affinity of porcine protein S for human C4BP. Moreover, the species specificity of cofactor activities of various species of protein S is determined for human versus bovine-activated protein C, and these results, combined with sequence comparisons, agree with previous evidence that the thrombin-sensitive region and the first epidermal growth factor domain of protein S, i.e. residues 47-116, are responsible for recognition of activated protein C.

Anticoagulant response to activated protein C: method validation and assay comparison

Poor anticoagulant response to activated protein C (APC), present in 20-60% of thrombophilic patients, is most often caused by abnormal factor Va due to the mutation of Arg506 to Gln, and DNA sequencing confirms this finding. At Scripps Reference Laboratory (SRL), we have validated an in-house assay to detect APC resistance. A study of 80 normal subjects (40 males and 40 females, 21-60 years old) showed that adult males and females have statistically significant differences in their anticoagulant response to APC. Furthermore, APC response is increased in older individuals. APC responses of the same 80 normal samples determined using the SRL assay were compared to a commercial kit (Chromogenix, Coatest). Although both procedures are similar, the SRL assay gave a greater difference between male and female normal ranges. Eight of 18 (44%) thrombophilic patients were identified as APC-resistant. Samples from individuals having the factor V Arg506Gln mutation yielded low responses to APC in both assays. Determination of APC resistance assists physicians in determining the cause of thrombotic disorders and may eventually help in predicting the risk of familial thrombosis.

Possible structural implications of 20 mutations in the protein C protease domain

Analysis of naturally occurring protein mutations yields valuable insights into functionally important sequences. Characterizing mutations responsible for protein C deficiency at the molecular level has been the subject of intensive investigation. In a previous study, a three-dimensional model of the serine protease domain of protein C was used to analyze the set of protease domain mutations previously available. The mutations were largely found to fall into a limited number of categories. A recently updated protein C mutation data base has provided a number of new mutations which have been analyzed for structural predictions.

Protein C inhibitor is expressed in tubular cells of human kidney

Protein C inhibitor (PCI) is a serpin that inhibits a number of proteases. PCI is found in urine and binds to kidney epithelial cells. To determine if kidney is a source of PCI, cDNA was produced from human kidney total RNA. Sequencing and restriction mapping showed identity between kidney and liver PCI cDNA sequences. Similar cDNAs were obtained from rhesus monkey kidney and liver RNAs. Conditioned medium from the rhesus monkey kidney cell line CCL7.1 was analyzed on immunoblots, showing a 57,000-D protein band that comigrated with human plasma PCI. Immunohistochemical staining and in situ hybridization of human kidney tissue sections showed that kidney PCI antigen and RNA were confined to tubular cells. The findings are consistent with the idea that PCI is synthesized and localized in kidney tissue where it may provide protease inhibitory activity and suggest that complexes of PCI with urokinase found in human urine may be produced locally in the kidney.

A structural model for the prostate disease marker, human prostate-specific antigen

Prostate-specific antigen (PSA) provides an excellent serum marker for prostate cancer, the most frequent form of cancer in American males. PSA is a 237-residue protease based on sequence homology to kallikrein-like enzymes. To predict the 3-dimensional structure of PSA, homology modeling studies were performed based on sequence and structural alignments with tonin, pancreatic kallikrein, chymotrypsin, and trypsin. The structurally conserved regions of the 4 reference X-ray proteins provided the core structure of PSA, whereas the loop structures were modeled on the loops of tonin and kallikrein. The unique "kallikrein loop" insert, between Ser 95b and Pro 95k of kallikrein, was constructed using molecular mechanics, dynamics, and electrostatics calculations. In the resulting PSA structure, the catalytic triad, involving residues His 57, Asp 102, and Ser 195, and hydrophobic and electrostatic interactions typical of serine proteases were extremely well conserved. Similarly, the 5-disulfide bonds of kallikrein were also conserved in PSA. These results, together with the fact that no major steric clashes arose during the modeling process, provide strong evidence for the validity of the PSA model. Calculation of the electrostatic potential contours of kallikrein and PSA was carried out using the finite difference Poisson-Boltzmann method. The calculations revealed matching areas of negative potential near the catalytic triad, but differences in the positive potential surrounding the active site. The PSA glycosylation site, Asn 61, is fully accessible to the solvent and is enclosed in a positive region of the isopotential map. The bottom of the substrate specificity pocket, residue S1, is a serine (Ser 189) as in chymotrypsin, rather than aspartate (Asp 189) as in tonin, kallikrein, and trypsin. This fact, plus other features of the S1 binding-pocket region, suggest that PSA would prefer substrates with hydrophobic residues at the P1 position. The location of a potential zinc ion binding site involving the side chain of histidines 91, 101, and 233 is also suggested. This PSA model should facilitate the understanding and prediction of structural and functional properties of this important cancer marker.