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Technical Briefs |
1
Ist. Istol. & Anal. Lab., Facoltà Sci. MFN Università, Via E. Zeppi, 61029 Urbino, Italia;
2
Div. Med. and
3
Lab. Anal. Ospedale Civile, Urbino, Italia;
a author for correspondence: fax +39-722-322370, e-mail mannello{at}bio.uniurb.it
Although previously thought to be produced almost exclusively by the epithelial cells of the prostate (1), prostate-specific antigen (PSA) is produced and secreted by several extraprostatic sources (2)(3). Considering the high degree of homology of PSA with the human glandular kallikrein (hKGK1) (4)(5) and the activation of the kallikrein–kinin system in peritoneal effusions (6)(7), we undertook the study of PSA distribution and expression in ascitic fluids. Between May 1996 and January 1997 we collected ascitic fluids from 44 consecutive women of ages 29–61 years (mean 49 ± 7) undergoing ultrasound examination and a diagnostic paracentesis. After collection (~10 mL), ascitic fluids were centrifuged at 20 120g for 20 min at +4 °C and the supernatants stored at -30 °C until processed. Blood samples were also taken, and after clotting were centrifuged at 360g for 5 min at +4 °C and stored at -30 °C until assay. In 24 patients (ages 28–81 years), the ascites was associated with malignancies (ovarian, pancreatic, breast, gastrointestinal, and lung). In the other 20 patients (18–75 years), ascites arose from chronic liver diseases, bacterial peritonitis, congestive heart failure, thrombosis, and other nonmalignant diseases. Albumin, serum–ascites albumin concentration gradients, total protein, lactate dehydrogenase, and cholesterol concentrations were also measured in the fluids (data not shown) (8). PSA was measured by two methods (9)(10)(11): a solid-phase two-site IRMA (PSA-RIACTTM) from CIS Bio International (Gif-sur-Yvette, France) and a microparticle capture enzyme immunoassay (MEIA) (IMx®) from Abbott Labs, Abbott Park, IL. Patients with malignant ascites had not yet received cytotoxic drugs and (or) chemotherapeutic agents before sample collection. Results are expressed as means ± SE. Statistical analyses were performed through the StatView v.4.1 package (Abacus Concepts, Berkeley, CA) on Macintosh Power PC (Apple Computer, Cupertino, CA).
The work was carried out in accordance with the Helsinki Declaration of 1975, as revised in 1983.
Among the 44 patients examined, 41% of ascitic fluids contained
detectable amounts of PSA, tested with both assay methods (mean ±
SE 0.278 ± 0.045 µg/L, range 0.06–0.78 µg/L, n = 18).
Matrix effects of ascitic fluid constituents in the PSA assays were
excluded by performing dilutions of samples having high PSA content. A
good linearity (r = 0.973) between PSA content and
dilution was obtained with the IMx method. The PSA-RIACT (y)
and IMx-PSA (x) agreed (n = 15, y =
0.019 + 0.863x, means ± SE of y =
0.251 ± 0.068 and of x= 0.268 ± 0.077,
r2 = 0.958, P <0.0001). In agreement
with others (12)(13), we found a plasma PSA
content 
0.05 µg/L in ~91% (40 of 44) of the women examined. The
PSA mean concentration in our series of ascitic fluid samples did not
show a significant difference between malignant-related and
nonmalignant ascitic fluids (0.262 ± 0.074 µg/L, 0.297 ±
0.047 µg/L, respectively; t = -0.317271,
P = 0.761). The total PSA content in ascitic fluids was
significantly greater than in plasma (0.278 ± 0.045 µg/L and
0.032 ± 0.011 µg/L, respectively; n = 18, P
<0.0001). PSA was not statistically significantly correlated with
patient's age.
A major 33-kDa immunoreactive band (due to the free form of this serine
protease) was seen on Western blots with an anti-human PSA monoclonal
antibody (Dako, Milan, Italy). The 100-kDa immunoreactive protein due
to the 
1-antichymotrypsin-bound form was not
detected, nor were other bands (Fig. 1
).
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Several sources could be suggested for PSA expression in ascitic fluids: (a) plasma ultrafiltration and accumulation, at an increased rate in the peritoneal space through a vascular hyperpermeability of the inflamed peritoneal tissue. Previous data have shown the liberation, accumulation, and activation of the kallikrein–kininogens–kinin system (6)(7) and the role of a vascular permeability factor in the pathogenesis of ascitic fluid accumulation (14). (b) Local secretion mainly due to the enhanced protease synthesis by the neoplastic ascitic cells. Several reports have documented the activity of proteolytic enzymes in peritoneal fluid (6)(15)(16) as well as in an experimental animal model (17). (c) Enhanced PSA expression modulated throughout the steroid receptors. Previous studies have revealed the presence of steroid hormones and their receptors in peritoneal fluid and mesothelium (18)(19).
The present report is the first evidence of PSA in ascitic fluids at measurable concentrations with commercial methods, even though it does not contribute to the discrimination of malignant-related and nonmalignant ascites. The detectable amounts of PSA in peritoneal effusions give further evidence of the distinctiveness of this widespread serine protease, even though the biological effects and the mechanism causing its increase still remain unexplained. Several hypotheses have been previously suggested for the new functions of PSA in nonprostatic sources (2)(3)(20): The presence in ascitic fluids of several mitogens and growth factors could be related to the enhanced expression of PSA in peritoneal effusions (21)(22)(23)(24).
We are currently investigating the potential role of PSA in nonprostatic tissues and in other biological fluids as a possible sensitive molecular marker implicated in hormone responsiveness and (or) in the inflammatory/neoplastic processes, which could, in part, be responsible for ascitic fluid proteolytic activities (15)(16).
References
The following articles in journals at HighWire Press have cited this article:
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  F. Mannello, M. Malatesta, F. Luchetti, S. Papa, S. Battistelli, and G. Gazzanelli Immunoreactivity, Ultrastructural Localization, and Transcript Expression of Prostate-specific Antigen in Human Neuroblastoma Cell Lines Clin. Chem., January 1, 1999; 45(1): 78 - 84. [Abstract] [Full Text] [PDF]
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F. Mannello, F. Luchetti, D. Lancioli, S. Battistelli, S. Papa, and G. Gazzanelli Prostate-specific Antigen Expression in Neoplastic Human Myeloid Cell Lines Clin. Chem., September 1, 1998; 44(9): 1991 - 1993. [Full Text] [PDF]
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