Expression of hormone-/carcinogen-metabolising enzymes in the prostate : clues into peripheral-zone susceptability?

Abstract

INTRODUCTION & OBJECTIVES: The peripheral zone (PZ) of the prostate presents with a higher occurrence of adenocarcinoma (CaP) compared to transition zone (TZ). Environmental procarcinogens and endogenous hormones implicated in the aetiology, often requires bio-activation to DNA-binding species (that form DNA-carcinogen adducts) which are done by phase I cytochrome P-450 (CYP) isoenzymes (CYP1A1, CYP1A2 and CYP1B1) and, the phase II N-acetyl transferases (NAT1 and NAT2) and catechol-O-methyl transferase (COMT). The objective of this study is to assess intra- (PZ vs. TZ) and inter-individual variations in the gene expression of phase I and II enzymes using quantitative real-time RT-PCR in CaP-free tissues. MATERIAL & METHODS: With ethical approval, prostate tissue sets (PZ and TZ) (n=27) were obtained from patients (inclusion criteria - low PSA (<20 mg/l serum) and/or low volume disease ≤two/eight core biopsies positive for CaP)) undergoing radical prostatectomy, isolated from a lobe preoperatively identified as negative for CaP. Real-time RT-PCR was employed to quantitatively examine CYP1A1, CYP1A2, CYP1B1, NAT1, NAT2 and COMT. Immunohistochemistry (with polyclonal anti-CYP1B1 antibody) was employed to assess CYP1B1 protein and location in the prostate. In all cases, retrospective analysis (after H&E) of adjacent tissue by a pathologist was performed to determine the cancer-free nature of the tissue. RESULTS: CYP1B1, NAT1 and COMT gene expression was detected in both zones of all tissue sets (n=27) examined. CYP1A1 (23/27) and NAT2 (26/27) mRNA transcripts were also detected. CYP1A2 (14/27) transcripts, although detectable, were unquantifiable. Inter-individual variations (up to 10-fold) were noted in CYP1A1, CYP1B1, NAT1, NAT2 or COMT expression levels. In an intraindividual analysis, in cancer-free (n=19) tissue sets, CYP1B1 mRNA transcript levels (18/19) were 2- to 50-fold higher in the PZ compared to the TZ. Such a differential expression profile was not observed for other genes. In 13/27 tissue sets examined, intra-individual expression of these latter genes were equivalent or higher in the TZ. A retrospective finding of CaP was consistently associated with an altered expression profi le i.e. CYP1B1 was expressed was higher in the cancer zone, be it PZ or TZ (7/8). Immunohistochemistry (n=12) in the cancer-free tissues showed strong CYP1B1 staining (nuclear in nature) in the basal epithelial cells; some nuclear staining was also observed in the stroma. In CaP tissue, sheaths of cells exhibiting both nuclear staining and cytoplasmic staining were observed. CONCLUSIONS: Our study demonstrates the expression in the prostate of phase I and II enzymes. And CYP1B1 expression is particularly high in peripheral zone. Its role as a target either for chemoprevention/treatment strategies remains to be investigated.