Immunochemical detection of 5 alpha-reductase in human serum

This study represents a continuing effort to find a new biomarker for the diagnosis and management of prostatic cancer. Polyclonal antibodies were prepared to a peptide (CAKP) representing amino acids 28 to 43 of the 5 alpha-reductase type 2 isozyme. Using immunoaffinity-purified antibodies, the sera of 62 patients were examined by Western blot following polyacrylamide gel electrophoresis. A positive band was detected in the sera of several patients at 42 kDa compatible with the purified native glycosylated 5 alpha-reductase type 2. These bands were nullified on coincubation of the antibody with the CAKP peptide. Analysis by high-performance liquid chromatography and amino acid sequencing by N-terminal Edman degradation of the immunoaffinity-purified antigen to the antipeptide antibodies of a patient with adenocarcinoma of the prostate suggests that the 5 alpha-reductase type 2 isozyme may be linked to an immunoglobulin. An identical immunoaffinity-purified antigen to the CAKP peptide was isolated from a section of prostatic tissue from a different patient showing benign prostatic hypertrophy with severe dysplasia. It is suggested that an immunological response to the 5 alpha-reductase type 2 isozyme was elicited in both instances.