Expression of apoptosis-regulating genes in the rat prostate following botulinum toxin type A injection

Abstract

Background: Onabotulinumtoxin A (OnabotA) injection has been investigated as a novel treatment for benign prostatic enlargement caused by benign prostatic hyperplasia. An OnabotA-induced volume reduction caused by sympathetic fibers impairment has been proposed as a potential mechanism of action. Our aim was to investigate the expression of apoptosis-regulating proteins in the rat prostate following OnabotA intraprostatic injection.

Methods: Adult Wistar rats were injected in the ventral lobes of the prostate with 10 U of OnabotA or saline. A set of OnabotA-injected animals was further treated with 0.5 mg/kg of phenylephrine (PHE) subcutaneously daily. All animals were sacrificed after 1 week and had their prostates harvested. Immunohistochemical staining was performed for Bax, Bcl-xL and caspase-3 proteins and visualized by the avidin-biotin method. The optical density of the glandular cells was also determined, with measurement of differences between average optical densities for each group.

Results: Saline-treated animals showed intense epithelial staining for Bcl-xL and a faint labelling for both Bax and Caspase-3. OnabotA-treated rats showed a reduced epithelial staining of Bcl-xL and a consistently increased Bax and Caspase-3 staining when compared with saline-treated animals. PHE-treated animals showed a stronger Bcl-xL staining and reduced staining of both Bax and Caspase-3 when compared to the OnabotA group. Mean signal intensity measurements for each immunoreaction confirmed a significant decrease of the signal intensity for Bcl-xL and a significant increase of the signal intensity for Bax and Caspase 3 in OnabotA-injected animals when compared with the control group. In OnabotA+PHE treated animals mean signal intensity for Bcl-xL, Bax and Caspase 3 immunoreactions was identical to that of the control animals.

Conclusions: These results support the hypothesis that OnabotA activates apoptotic pathways in the rat prostate through a mechanism that involves sympathetic outflow impairment.

Figure 1

immunohistochemical expression of Bcl-xL (A), Caspase-3 (B) and Bax (C) in glands with tall epithelial lining in the control group (1), OnaBotA group (2) and OnaBotA+PHE group (3). Scale bar indicates 100 μm.

Figure 2

immunohistochemical expression of Bcl-xL (A), Caspase-3 (B) and Bax (C) in glands with short epithelial lining in the control group (1), OnaBotA group (2) and OnaBotA + PHE group (3). Scale bar indicates 100 μm.

Figure 3

mean signal intensity measurements for Bcl-xL, Caspase 3 and Bax in control, OnabotA and OnabotA + PHE groups (* indicates p < 0.05; ** indicates p < 0.01; *** indicates p < 0.001).