Serum free prostate specific antigen: Isoenzymes in benign hyperplasia and cancer of the prostate

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Abstract
Prostate specific antigen (PSA) in serum of patients with benign prostatic hyperplasia (BPH) or prostate cancer (P‐CA) not bound to α‐1‐antichymotrypsin (ACT) was analyzed by chromatofocusing. The procedure allowed the simultaneous separation of complexed and free PSA and the fractionation of the free PSA fraction into several isoenzymes. The detection of the isoenzymes was strongly dependent on the combination of antibodies introduced in the applied commercially available immunoassays (Cobas® Core, Delfia®). Isoenzymes in sera of patients with benign prostatic hyperplasia were mainly situated in the pI range of 6.6 to 7.3. Isoenzymes in sera of prostate cancer patients or in PSA from LNCAP cells were mainly situated in the pI range 7.0 to 8.3. Neuraminidase treatment of the sera shifted the isoelectric points of all three sources towards more basic pHs. An irregular glycosylation process in the dysplastic cells of the prostate is suggested to be the cause for the shift of the isoelectric points. The difference of isoenzyme distribution along the pH axis is discussed as a diagnostic tool to differentiate between BPH and P‐CA.