Apoptosis and hormonal milieu in ductal system of normal prostate and benign prostatic hyperplasia 

Shu-Jie XIA¹, Chun-Xiao XU¹,  Xiao-Da TANG²,  Wan-Zhong WANG³,  De-Li  DU³

¹Department of Urology, ³Department of Pathology, Shandong Provincial Hospital, Jinan, 250021, China
²University Department of Urology, Shanghai First People's Hospital, Shanghai, 200080, China

Asian J Androl  2001 Jun; 3:  131-134

Keywords: prostate; ductal system; hormonal milieu; androgen; estrogen; apoptosis

Abstract

Aim: To study the apoptotic rate (AR) and the androgen and estrogen milieu in the proximal and distal ductal systems of prostate, in order to help exploring the effects of these factors on prostatic growth and the pathogenesis of benign prostatic hypertrophy (BPH). Methods: The proximal and distal ends of the ductal system were incised from 20 normal prostate as well as the hypertrophic prostate tissue from 20 patients with BPH. The AR was determined by the DNA end-labeling method and dihydrotestosterone (DHT) and estrodiol (E₂), by radioimmunoassay. Results: There was no significant difference in DHT and E₂ density between the proximal and distal ends of the ductal systems in normal prostate. E₂ appeared to be higher in BPH than in normal prostatic tissues, but the difference was statistically insignificant. In normal prostatic tissue, the AR was significantly higher in the distal than in the proximal ends of the ductal system (P<0.05), while the AR of the proximal ends was significantly higher (P<0.01) than that in the BPH tissue. No significant correlation was noted between the DHT and E₂ density and the AR both in the normal prostate and BPH tissues. Conclusion: The paper is the first time describing a difference in AR in different regions of the ductal system of normal prostate, while the hormonal milieu is similar, indicating a functional inhomogeneity of these regions. A low AR in the proximal duct, where BPH originates, and an even lower AR in the BPH tissue, suggesting the participation of apoptosis in the BPH pathogenesis.

1 Introduction

2 Materials and methods

2.1 Tissue handling

2.1.1 Subjects and sample collection

Twenty normal prostate specimens were obtained from men (aged 20 to 30 years, without a history of chronic diseases and urogenital disorders) died from an acute accident with the permission from their family members, the local authority and the Hospital Ethical Committee. Every sample was divided inuo three parts each containing the distal and proximal ductal regions; one portion was snap frozen in liquid nitrogen for the determination of apoptosis study and the other two for hormonal determination and histological examination, respectively. The dissection was made according to the prostatic anatomy described by McNeal^[1] and Lee et al^[2]. The hypertrophic tissue of the prostate was obtained from 20 BPH patients (aged 57 to 80 years) undergoing suprapubic prostatectomy for lower urinary obstruction. These patients were otherwise apparently healthy.

2.1.2 Histological examination

Serial sections of the tissue were prepared, and the slides stained with hematoxylin-eosin for histological examination.

2.1.3 Hormonal determination

The tissue was sliced and homogenized using a polytron homogeniser in glycerol phosphate buffer (10% glycerol, 10 mmol/L phosphate, 1.5 mmol/L EDTA, 5 mmol/L monothioglycerol, pH 7.4) containing l ng/mL of each of the protease inhibitors, aprotinin and soybean trypsin inhibitor (both from Sigma, USA). The homogenate was centrifuged for l0 min at 800g and the supernatant centrifuged for another 60 min at 100,000g. The final supernatant was used for DHT and E₂ determination using the DSL9600 DHT kits (Webster Medical Center, Texas, USA) and E₂ kits (Jiu Ding Company, Tianjin, China). All tissue processing was performed at 4.

2.1.4 In situ determination of apoptosis

Cell apoptosis was determined according to the in situ labeling method described by Gavrieli et al^[3] with kits supplied by Boehringer Mannheim (Product MK1020); the kits provide the methodology specifications and the following reagents: labeling Buffer 400 L, TdT 20 L, DIGdUTP 20 L, blocking reagent 2000 L, SABC 20 L, proteinase K 20 L, and biotinylated antidigoxin antibody 20 L. The AR was determined by counting the numbers of the total cells (glandular and interstitial) and the positive cells in 5 fields under light microscope at 400magnification.

2.2 Data analysis

3 Results

Table 1.  DHT and E₂ density and apoptotic rate in prostatic tissues. ^bP<0.05, ^cP<0.001,  compared with the proximal end.

4 Discussion

In rats, the morphology and the function of the cells in the prostatic ductal system are different in different sections of the system^[4].  Ce1l death is not evident in either the intermediate or distal regions, while in the proximal region immediately adjacent to the urethra, cells are actively undergoing apoptosis^[1]. In the human prostate, the difference in AR in different regions of the ductal system is unknown.

This study is the first to examine the AR and its androgen and estrogen milieu in prostatic ductal system in the normal prostate and the BPH tissues in man. The authors showed that in the normal human prostate, the AR was significantly lower in the proximal ends of the ductal system (P<0.05), where the BPH originated. Moreover, it was shown that the AR in the BPH tissue was still lower. The finding was in coincidence with the results of Krprianou^[5], who indicated that after balancing the apoptosis versus the proliferation activities, there was a net decrease (fourfold) in the total number of cells dying via apoptosis in both the glandular and basal epithelial cells of the BPH tissue when compared with the normal gland.

The conventiona1 concept of androgen action on the prostate was that the maintenance of the structural and functional activity of the prostate required the support of an adequate amount of androgen^[6]. Depletion of this androgenic support leads to prostatic cell death, as confirmed by animal experiments and clinical experience with BPH and prostatic cancer treatment^[7]. Although in the present study, it was indicated that cells in different regions of the ductal system were exposed to a similar 1evel of androgen density, they responded in a different way: the cell apoptosis was much less in the proximal ends. The results may suggest that that the morphological and functional characteristics of the proximal and the distal ends of the ductal system are also different in human prostate. The identification of a lower apoptotic rate in the proximal region of the normal prostate offers a train of thoughts to the exploration of the mechanism of cell dynamics both in the normal prostate and the BPH tissue. Our observations maintain the view that the initiation of BPH probably begins in man in the transitional zone (corresponding to the proximal end) before 30 years of age^[8].

The prostate is an androgen-dependent organ, but it is most likely that other factors also contribute to its growth after adolescence. It is known that the role of stromal cells on epithelia1 cell activity is mediated through specific paracrine growth factors (EGF, KGF, TGF-, etc). The regiona1 heterogeneity in cellular activity along the prostatic ductal system brings forward the postulation that there may be a regional specificity in the production of the types of growth factors by the stromal cells in response to androgen stimulation.

Estrogen has been assumed to be implicated in the pathogenesis of BPH, since the estrogen receptors predominantly localized in the stromal elements^[9,10]. In studies on canine and rat prostate, a combination of estrogen and androgen treatment has a synergistic effect on prostatic growth as compared with androgen treatment alone^[11].  Recent studies indicated that estrogen, acting in association with steroid hormone binding globulin (SHBG), produced an 8-fold increase in the intracellular levels of cyclic adenosine monophosphate (cAMP) in human BPH tissues, which has been considered an important step in the signal transudation pathways^[12]. This SHBG -cAMP mediated process has been localized primarily in the stroma. Estrogen may also stimulate epithelial cell proliferation through insulin-like growth factor-I^[13]. Prostatic hyperplasia in dogs may be accelerated by estrogens, which increase the level of androgen receptors in the prostate. Although there is only a low concentration of the classical high-affinity estrogen receptor in human BPH, the amount may be already sufficient for a biological activity. From experimental studies with aromatase inhibitors in animal models it appears that decreases in intra-prostatic estrogen may reduce estrogen-induced stromal hyperplasia^[14]. In this study, we found that E₂ density was somewhat increased in BPH tissues.

Acknowledgements

References

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Correspondence to: Dr. Shu-Jie XIA, University Department of Urology, Shanghai First People's Hospital, 85 Wu Jin Rd., Shanghai 200080, China.
Tel: +86-21-6324 0090 Ext. 5511   Fax: +86-21-6324 0825
E-mail: xiashujie@yahoo.com
Received 2001-05-16     Accepted 2001-05-28