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The Prostate 29:65-66 ( 1996)
LETTER TO THE EDITOR
Isoforms of Prostate-Specific Antigen in Serum:
A Result of the Glycosylation Process in
Dysplastic Prostatic Cells?
Klaus Jung, Michael Lein, Wolfgang Henke, Dietmar Schnorr, and
Stefan A. Loening
Department of Urology, University Hospital Charite, Humboldt University Berlin,
Berlin, Germany
In two recent papers published in The Prostate
[1,2], the authors presented data on the fractionation
of the free and complexed serum prostate specific antigen (PSA) isoforms. The authors are in doubt about
the concept of PSA isoforms as a diagnostic tool to
improve the discrimination between patients with
prostate cancer (PCa) and benign prostatic hyperplasia (BPH) [2]. Moreover, they suggest further intensive investigation of the biochemical properties of the
isoforms and conclude from their results that PSA
released from BPH tissue was otherwise glycosylated
as PSA released from prostate cancer cells [l].The
authors point out that it is not known whether there
are different carbohydrate moieties in the PSA molecule from PCa patients. Since we have carried out
experiments in this direction similarly using lectins,
we will soon report on them to complement the data
and conclusions of Huber et al. [1,2].
There are numerous histochemical evidences [3-81
that the pattern of lectin bindings in dysplastic prostatic cells differs from that in cells of normal prostatic
epithelium. Lectins are glycoproteins that exhibit selective binding to specific carbohydrate moieties.
Thus, changes in the N-glycosylation of proteins can
be recognized by different lectins and can perhaps
provide the basis for more discriminative clinical tests
[8,9]. However, few experiments were performed to
use lectins as diagnostic tool for differentiating possible N-glycosylation variants of PSA. Barak et al. [lo]
were able to distinctly separate BPH and PCa patients
on the basis of percentages of serum PSA bound to
concanavalin A-sepharose. However, further experiments could not verify such differentiation and
showed analytical pitfalls [ll].Thus, we applied, in
addition to concanavalin A, various other lectins to
demonstrate these N-glycosylation variants (Table I).
0 1996 Wiley-Liss, Inc.
For that purpose, we incubated 150 pl of pooled serum of 10 patients with prostate cancer and of 10
patients with benign prostatic hyperplasia according
to a standard procedure of Lorentz et al. [12] with 50
pl solutions of different lectins (Sigma Chemical Co.,
St. Louis, MO) dissolved in 200 mM Tris-acetate (pH
7.2), 1 mM CaCl,, 1mM MgCl,, and 20 mM MnCl, for
2 hr at room temperature, centrifuged at 12,OOOg for 2
min, and determined PSA in the supernatants and
the original serum pools. Mean percentages of PSA in
the supernatants related to the PSA in the original
serum were calculated as nonreactive percentage PSA
(TableI). The effects of lectin concentrations at 10-250
pM were investigated. Because lectins, except those
from Concanavalia ensiformis and Triticum vulgare,
showed a limited solubility, only data obtained with
40 pM and, for the last mentioned two lectins, with
250 pM were presented (Table I). The data show that
(1) the precipitation of serum PSA by different lectins
is of negligible quantity, so that differences observed
on the basis of histochemical stainings are not caused
by glycosylation variants of PSA in the cells; and (2) a
differentiation of serum PSA from prostate cancer
and BPH based on the assumption of the occurrence
of differently glycosylated PSA variants is not possible. This goes to prove at least that lectins are not
suited to demonstrate glycosylation variants of serum
PSA as suggested by chromatofocusingtechnique [ 11.
Address reprint requests to Doz. Dr. Klaus Jung, Department of
Urology, University Hospital Charit& Humboldt University Berlin,
SchumannstraBe 20121, D-10098 Berlin, Germany.
66
Letter to the Editor
TABLE 1. Effect of Various Leains on PSA in Serum of Patients
With Prostate Cancer or Benign Prostatic Hyperplasia*
Nonreactive PSA (%)
Lectins
Aruchis hypogueu (peanut)
40 PM
Concanuvalia ensiformis (jack bean)
40 PM
250 PM
Glycine maximum (soybean)
40 PM
Phuseolus vulgaris (red kidney bean)
40 PM
Phytolacca americana (rhizome)
40 PM
Triticum uulgure (wheat germ)
40 PM
250 KM
Ulex europueus (gorse)
40 KM
Prostate cancer
BPH
99.6
96.6
94.6
43.5
99.8
46.7
96.6
101.6
88.5
92.7
98.3
102.1
99.6
91.6
96.1
91.2
99.6
98.4
'Pooled serum of 10 patients with prostate cancer and 10 patients with benign
prostatic hyperplasia was incubated with lectins (final concentrationsindicated),
centrifuged, and the PSA determined. Mean percentages of PSA in the supernatants related to the PSA in the original serum were calculated as nonreactive
percentage PSA. Values are means of three separate measurements.
REFERENCES
1. Huber PR, Schmid HP, Mattarelli G, Strittmatter B,
Vansteenbrugge GJ, Maurer A: Serum free prostate
specific antigen: Isoenzymes in benign hyperplasia and
cancer of the prostate. Prostate 27:212-219, 1995.
2. Huber PR, Mattarelli G, Strittmatter 8, Vansteenbrugge
GJ, Schmid HP, Maurer A: In vivo and in vitro complex
formation of prostate specific antigen with a,-anti-chymotrypsin. Prostate 27:166-175, 1995.
3. Lad PM, Learn DB, Olson CV: Identification of structural and secretory lectin-binding glycoproteins of normal and cancerous human prostate. Biochim Biophys
Acta 791:186-197, 1984.
4. Abel PD, Leathem A, Aylott A, Marsh C, Henderson
D, Williams G: Carbohydrate residues in non-malignant prostatic epithelium as revealed by lectins. Urol
Res 15:173-176, 1987.
5. Siiderstrom KO: Lectin binding to prostatic adenocarcinoma. Cancer 60:1823-1831, 1987.
6. McNeal JE, Leav I, Alroy J, Skutelsky E: Differential
lectin staining of central and peripheral zones of the
prostate and alterations in dysplasia. Am J Clin Pathol
89:41-48, 1988.
7. McNeal JE, Alroy J, Leav I, Redwine EA, Freiha FS,
Stamey TA: Immunohistochemical evidence for impaired cell differentiation in the premalignant phase of
prostate carcinogenesis. Am J Clin Pathol 90:23-32,
1988.
8. Drachenberg CB, Papadimitriou JC: Aberrant pattern
of lectin binding in low and high grade prostatic intraepithelial neoplasia. Cancer 75:2539-2544, 1995.
9. Turner GA: N-Glycosylation of serum proteins in disease and its investigation using lectins. Clin Chim Acta
208:149-171, 1992.
10. Barak M, Mecz Y, Lurie A, Gruener N: Binding of serum prostate antigen to concanavalin A in patients with
cancer or hyperplasia of the prostate. Oncology 46:375377, 1989.
11. Van Dieiijen-Visser MP, Van Pelt J, Delaere KF'J: Pitfalls
in the differentiation of N-glycosylation variants of
prostate-specific antigen using concanvalin A. Eur J
Clin Chem Clin Biochem 32:473-478, 1994.
12. Lorentz K, Flatter B, Kolle FW: Lectine als Reagentien
zur Differenzierung von Enzymen im Serum. Lectine
als Reagentien, I. Mitteilung. J Clin Chem Clin Biochem
17757-765, 1979.
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