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 an- tigen (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 hyperpla- sia (BPH) [2]. Moreover, they suggest further inten- sive 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 mole- cule 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 pros- tatic cells differs from that in cells of normal prostatic epithelium. Lectins are glycoproteins that exhibit se- lective 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 pos- sible 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 experi- ments 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).

For that purpose, we incubated 150 pl of pooled se- rum 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,, 1 mM 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 (Table I). 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 possi- ble. This goes to prove at least that lectins are not suited to demonstrate glycosylation variants of serum PSA as suggested by chromatofocusing technique [ 11.

Address reprint requests to Doz. Dr. Klaus Jung, Department of Urology, University Hospital Charit& Humboldt University Berlin, SchumannstraBe 20121, D-10098 Berlin, Germany.

0 1996 Wiley-Liss, Inc.

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 Prostate cancer BPH

Aruchis hypogueu (peanut)

Concanuvalia ensiformis (jack bean) 40 PM 99.6 96.6

40 PM 94.6 99.8 250 PM 43.5 46.7

Glycine maximum (soybean)

Phuseolus vulgaris (red kidney bean)

Phytolacca americana (rhizome)

Triticum uulgure (wheat germ)

40 PM 96.6 101.6

40 PM 88.5 92.7

40 PM 98.3 102.1

40 PM 99.6 96.1 250 KM 91.6 91.2

40 KM 99.6 98.4 Ulex europueus (gorse)

'Pooled serum of 10 patients with prostate cancer and 10 patients with benign prostatic hyperplasia was incubated with lectins (final concentrations indicated), centrifuged, and the PSA determined. Mean percentages of PSA in the super- natants related to the PSA in the original serum were calculated as nonreactive percentage PSA. Values are means of three separate measurements.

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