Pentoxifylline promotes recovery of erectile function in a rat model of postprostatectomy erectile dysfunction

Abstract

Background: Cavernous nerve (CN) injury during radical prostatectomy (RP) causes CN degeneration and secondary penile fibrosis and smooth muscle cell (SMC) apoptosis. Pentoxifylline (PTX) is a phosphodiesterase inhibitor that further inhibits multiple cytokine pathways involved in nerve degeneration, apoptosis, and fibrosis.

Objectives: To evaluate whether PTX enhances erectile function in a rat model of CN injury. DESIGN, SETTING AND INTERVENTIONS: Forty male Sprague-Dawley rats underwent CN crush injury and were randomized to oral gavage feeding of phosphate-buffered saline (vehicle) or PTX 25, PTX 50, or PTX 100 mg/kg per day. Ten animals underwent sham surgery and received vehicle treatment. Treatment continued for 28 d, followed by a wash-out period of 72 h. An additional eight rats underwent resection of the major pelvic ganglion (MPG) for tissue culture and examination of direct effects of PTX on neurite sprouting.

Measurements: Intracavernous pressure recording on CN electrostimulation, immunohistologic examination of the penis and the CN distal to the injury site, and length of neurite sprouts in MPG culture.

Results: Daily oral gavage feeding of PTX resulted in significant improvement of erectile function compared to vehicle treatment in all treated groups. After treatment with PTX 50 and PTX 100 mg/kg per day, the expression of neuronal nitric oxide synthase in the dorsal penile nerve was significantly higher than in vehicle-treated rats. Furthermore, PTX treatment prevented collagen deposition and SMC loss in the corpus cavernosum. In the CN, signs of Wallerian degeneration were ameliorated by PTX treatment. MPG culture in medium containing PTX resulted in a significant increase of neurite length.

Conclusions: PTX treatment following CN injury in rats improved erectile recovery, enhanced nerve regeneration, and preserved the corpus cavernosum microarchitecture. The clinical availability of this compound merits application in penile rehabilitation studies following RP in the near future.

Fig. 1

Electrostimulation of cavernous nerves at 4 wk. (a) Top: the effects of chronic treatment with pentoxifylline (PTX) in increasing dosages on the increase of intracavernous pressure (ICP) on electrical stimulation of the cavernous nerve. Bottom: ratio of ICP to mean arterial pressure (MAP). (b) Representative ICP recordings. The red bar represents an electrical stimulation of the cavernous nerve with a duration of 50 s. * p < 0.05 versus vehicle-treated rats. # p < 0.05.

Fig. 2

Neuronal nitric oxide synthase (nNOS) staining in a penile midshaft specimen. (a) Representative images in each treatment group of the dorsal penile nerves within the dorsal penile neurovascular bundle. Phalloidin staining for actin and immunostaining for nNOS. Original magnification: ×200. (b) High-power images of the helicine neurovascular bundles in the corpus cavernosum in each treatment group. Note the near-complete absence of small nerve fibers expressing nNOS surrounding the helicine arteries following cavernous nerve crush and the preservation of these in animals treated with pentoxifylline (PTX). Sections stained for nNOS, actin and DAPI. Original magnification: ×1000.

Fig. 3

Neurodegeneration in the cavernous nerve distal to the crush injury. Note microanatomic signs of Wallerian degeneration, including an overall distortion of normal nerve anatomy, axonal swelling and axonal vacuolization (arrows) in the vehicle treated group. Further note an increased number of small axons in the pentoxifylline (PTX) treated groups, indicative of nerve regeneration. Sections were immunostained for neurofilament. Original magnification: ×400, ×1000.

Fig. 4

Changes in the architecture of the corpus cavernosum: smooth muscle. Images showing detailed changes in the structure of cavernous smooth muscle surrounding sinusoids (asterisk). The left panel shows an overview of one side of the corpus cavernosum. The sinus indicated by the white box is depicted in high magnification in the right panel. Loss of smooth muscle structure was more pronounced in the longitudinal, or inner, layer of smooth muscle cells (closed arrows) rather than the circular, or outer, layer (closed arrowheads). Open arrowheads: Architectural changes in the such as a decrease in cell number in both layers were observed. Chronic pentoxifylline (PTX) treatment resulted in partial restoration of smooth muscle architecture (open arrows). Phalloidin staining for actin and nuclear staining with 4′,6-diamidino-2-phenylindole. Original magnification: ×40, ×400.

Fig. 5

Changes in the architecture of the corpus cavernosum: collagen. Overview of collagen content in the middle corpus cavernosum. Collagen is located mainly in the trabeculae and the tunica albuginea where it consists of thick, bright red bundles. Reticular collagen fibers further are visible as thin fibrils forming a subendothelial meshwork. Note the deposition of reticular collagen in the sinusoids following crush injury (black arrows); this was partially prevented by pentoxifylline (PTX) treatment. Sections were stained with picrosirius red stain. Original magnification: ×200.

Fig. 6

Culture of the major pelvic ganglion (MPG) and evaluation of neurite sprouting in vitro. (a) Representative images of inverted microscopy of the MPG following 48-h culture in medium supplemented with pentoxifylline (PTX) in increasing concentrations. White arrows indicate the longest neurite. The shaded area on the right is a fragment of the dorsocaudal region of the MPG. Note increased length of neurites in the MPG cultures treated with PTX. Original magnification: ×100. (b) Mean neurite length in cultured MPG fragments. * p < 0.05 versus control group.