Radioimmunoassay of prostatic acid phosphatase: Validation and clinical application

Abstract

A radioimmunoassay for prostatic acid phosphatase (PAP) has been established, using a purified preparation extracted from human seminal plasma. To obtain immunologically intact '%PAP as a tracer, the lactoperoxidase technique was used followed by double chromatography on Sephadex G-50 and G-200. The assay was sensitive, accurate and reproducible. Only leukocyte acid phosphatase cross-reacted completely whilst acid phosphatases from other tissues (skin, lymph nodes, lung, kidney, liver, testis, platelets) did not interfere in the assay. When this method was used, PAP levels in men over the age of 20 were greater than those of women and younger men. Patients with prostatitis, benign prostatic hypertrophy (BPH) and other prostatic disorders had normal levels in more than 95 K of cases. Patients who had prostatectomy for BPH had levels significantly lower than those of normal controls and those with unoperated BPH. This provides indirect evidence for the specificity of the PAP radioimmunoassay. In prostatic cancer, PAP levels measured by radioimmunoassay were more frequently and more greatly elevated with progression of the disease: 25 % at stages A and B,75 % at stage C and I00 % at stage D. Further, PAP measurement provided a quantitative marker to follow therapeutic response as PAP levels varied in parallel with clinical, radiologic and rintigraphic progression. Under our experimental conditions, the PAP radioimmunoassay proved to be more sensitive (percentage of increased levels in the serum of patients with prostatic cancer) and more specific (percentage of normal levels in the serum of patients with prostatic disorders other than cancer) than the enzymatic assay of these enzymes.Prostatic acid phosphatase (PAP) has been regarded as a marker for prostatic cancer for more than 40 years (Gutman et al., 1936). Until recently, the enzyme could be assayed only by spectrophotometry following the hydrolysis of various substrates by the phosphatases under acid conditions. However, these methods lacked specificity as none of the substrates used for hydrolysis nor the inhibition by L (+)-tartrate were specific for prostatic acid phosphatases (Yam, 1974 Mahan and Doctor, 1979). Having extracted the PAP in a purified form from human seminal plasma, we have established a radioimmunoassay for these enzymes, validated its reliability and applied it to various groups of normal subjects and patients with benign and malignant disorders of the prostate or of other organs. MATERIAL AND METHODS Purification of PAP from human seminal plasmaPAP was purified from human seminal plasma by a method previously described (Jaspar et al., 1981) associating the first phase of inhibin extraction (Franchimont et al., 1979) and the technique of Lee et al., (1978) who isolated PAP from prostatic tissue. The successive purification steps consisted of filtration of human seminal plasma on Sephadex G-100, selective precipitation with 75 % ammonium sulphate, affinity chromatography on concanavalin A followed by ion exchange chromatography on DE 52 ce...

Tissue Polypeptide Antigen (TPA) as a Prognostic Aid in Human Prostatic Carcinoma

“…It has long been hoped that serum determination of prostatic acid phosphatase (PAP) would become a specific diagnostic test especially after the elaboration of radioimmunoassays (RIA) [5,6]. However, the results have been controversial and the PAP-RIAs may have a limited specificity.…”