Neuroimmunophilin Ligands Protect Cavernous Nerves after Crush Injury in the Rat: New Experimental Paradigms

Penile Rehabilitation and Treatment Options for Erectile Dysfunction Following Radical Prostatectomy and Radiotherapy: A Systematic Review

After radical prostatectomy (RP) or radiotherapy (RT) for prostate cancer, erectile dysfunction (ED) is the main complication next to urinary incontinence, affecting quality of life. The pathophysiology of ED after these treatments is believed to include neuropraxia causing reduced oxygenation and structural changes of the tissue in the corpora cavernosa. Next to the option of sparing the nerves during RP, research has been focusing on methods for penile rehabilitation after RP and RT, since it occurs often, even after nerve-sparing techniques were used. In animal studies, the use of phosphodiesterase type 5 inhibitors (PDE5i) after cavernous nerve damage is supported, but results in human studies are contradictory. Non-medical treatment options such as vacuum device therapy, hyperbaric oxygen therapy, yoga, aerobic, or pelvic floor training may be helpful, but evidence is scarce. Clear guidelines for penile rehabilitation are not yet available. However, care and support for ED after RP and RT is highly demanded by a large group of patients, so measures have to be taken even though the evidence is not strong yet. In this systematic review, an overview of the literature for penile rehabilitation and treatment options for ED after RP and RT is provided, using only randomized controlled trials (RCT).

A Randomized, Double-Blind, Placebo-Controlled Trial to Assess the Utility of Tacrolimus (FK506) for the Prevention of Erectile Dysfunction Following Bilateral Nerve-Sparing Radical Prostatectomy

INTRODUCTION

Radical prostatectomy (RP) is associated with erectile dysfunction, largely mediated through cavernous nerve injury. There are robust pre-clinical data supporting a potential role for neuromodulatory agents in this patient population. This study assessed tacrolimus in improving erectile function recovery rates after RP (ClinicalTrials.gov number, NCT00106392).

AIM

To define the utility of oral tacrolimus in improving erectile function recovery after nerve sparing radical prostatectomy.

METHODS

A randomized, double-blind trial compared tacrolimus 2-3 mg daily and placebo in men undergoing RP. Patients had localized prostate cancer and excellent baseline erectile function, underwent bilateral nerve-sparing RP, and were followed up for at least 18 months after RP. Patients received study drug for 27 weeks and completed the International Index of Erectile Function erectile function domain (EFD) questionnaire at baseline and serially after surgery.

MAIN OUTCOME MEASURES

International Index of Erectile Function erectile function domain score.

RESULTS

Data were available for 124 patients (59 tacrolimus, 65 placebo); mean age was 54.6 ± 6.2 years. No patient experienced permanent creatinine or potassium elevation. At baseline, mean EFD scores were 28.6 ± 2.1 (tacrolimus group) and 29 ± 1.5 (placebo group). By week 5, mean EFD scores had dropped to 8 ± 9.4 (tacrolimus) and 9 ± 10.7 (placebo). At 18 months, mean EFD scores were 16.0 ± 11.3 (tacrolimus) and 20.2 ± 9.0 (placebo) (P = .09). Tacrolimus failed to meet significance (hazard ratio = 0.83; P = .50), with no difference in: (i) percentage of patients achieving normal spontaneous erectile function (EFD score ≥24), (ii) time to normalization of EFD score (≥24), (iii) percentage of patients capable of intercourse in response to phosphieserase type 5 inhibitor (PDE5i), and (iv) time to achieve response to PDE5i.

CLINICAL IMPLICATIONS

Despite positive animal data, oral tacrolimus as used in this trial failed to improve erectile function after nerve sparing radical prostatectomy.

STRENGTHS & LIMITATIONS

The study is limited by a high attrition rate. The strengths include a randomized, placebo controlled design, extensive patient monitoring, use of medication diaries and a validated instrument as the primary outcome measure.

CONCLUSION

Despite supportive animal data, tacrolimus used in this fashion in the RP population failed to demonstrate any superiority over placebo. Mulhall JP, Klein EA, Slawin K, et al. A Randomized, Double-Blind, Placebo-Controlled Trial to Assess the Utility of Tacrolimus (FK506) for the Prevention of Erectile Dysfunction Following Bilateral Nerve-Sparing Radical Prostatectomy. J Sex Med 2018;15:1293-1299.

Increased expression of nestin in the major pelvic ganglion following cavernous nerve injury

In an effort to identify neuronal repair mechanisms of the major pelvic ganglion (MPG), we evaluated changes in the expression of nestin, an intermediate filament protein and neural stem cell marker following cavernous nerve crush injury (CNI). We utilized two groups of Sprague Dawley rats: (i) sham and (ii) bilateral CNI. Erectile responses to cavernous nerve stimulation (CNS) were determined at 48 h in a subset of rats. The MPG was isolated and removed at 48 h after CNI, and nestin immunolocalization, protein levels and RNA expression were evaluated. At 48 h, erectile responses to CNS in CNI rats were substantially reduced (P<0.05; ∼70% decrease in intracavernous pressure/mean arterial pressure) compared with sham surgery controls. This coincided with a dramatic 10-fold increase (P<0.05) in nestin messenger RNA expression and protein levels in the MPG of rats with CNI. Immunoflourescence microscopy demonstrated that nestin upregulation after CNI occurred within the ganglion cell bodies and nerve fibers of the MPG. In conclusion, CNI induces nestin in the MPG. These data suggest that nestin may be involved in the regenerative process of the cavernous nerve following crush injury.

Spontaneous recovery of cavernous nerve crush injury

Purpose

To investigate pathophysiological consequences and spontaneous recovery after cavernous nerve crush injury (CNCI) in a rat model.

Materials and Methods

Twenty 4-week-old male Sprague-Dawley rats were divided into the following groups: sham-operated group (n=10) and bilateral CNCI groups (n=10) for two different durations (12 and 24 weeks). At both time points, CN electrical stimulation was used to assess erectile function by measuring the intracavernous pressure. The expression of hypoxia inducible factor (HIF)-1α and sonic hedgehog (SHH) was examined in penile tissue. Immunohistochemical staining was performed for nerve growth factor (NGF), endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and smooth muscle α-actin.

Results

CNCI significantly decreased erectile function at 12 weeks (51.7% vs. 71.9%, mean ICP/BP ratio, p<0.05) and increased the expression of HIF-1α and decreased the expression of eNOS, nNOS, and SHH. At 24 weeks, erectile function in the CNCI group was improved with no significant difference versus the sham group (70.5% vs. 63.3%, mean ICP/BP ratio, p<0.05) or the CN group at 12 weeks (51.7% vs. 63.3%, mean ICP/BP ratio, p<0.05). By RT-PCR, the increase in HIF-1α and decrease in SHH mRNA was restored at 24 weeks. By immunohistochemistry, the expression of eNOS and nNOS was increased at 24 weeks.

Conclusions

CN injury induces significantly impaired erectile function and altered gene and protein expression, which suggests that local hypoxic and inflammatory processes may contribute to this change. Significant spontaneous recovery of erectile function was observed at 6 months after CN crush injury.

Activated RhoA/Rho kinase impairs erectile function after cavernous nerve injury in rats

PURPOSE

RhoA and rho kinase serve as key regulators of penile vascular homeostasis. The role of RhoA/rho kinase signaling in the penis after cavernous nerve injury has not been fully investigated. We characterized the molecular expression profiles of RhoA/rho kinase signaling that occur in the penis after cavernous nerve injury. We hypothesized that erectile dysfunction after bilateral cavernous nerve injury is accompanied by up-regulation of RhoA/rho kinase activity in the rat penis.

MATERIAL AND METHODS

We used 2 groups, including sham operation and bilateral cavernous nerve injury. At 14 days after nerve injury each group underwent cavernous nerve stimulation to determine erectile function at baseline and after intracavernous injection of the rho kinase inhibitor Y-27632 (Tocris Bioscience, Ellisville, Missouri). Penes were assessed at baseline for protein expression of neuronal nitric oxide synthase, RhoA, and rho kinase 1 and 2 by Western blot, immunoreactivity of neuronal nitric oxide synthase, rho kinase 1 and 2, RhoA-guanosine triphosphatase and rho kinase activity.

RESULTS

Erectile function was decreased in nerve injured rats. Neuronal nitric oxide synthase protein was significantly decreased while RhoA and rho kinase 2 protein levels were significantly increased in rat penes with nerve injury. Rho kinase 1 protein expression was equivalent. Rho kinase immunoreactivity was qualitatively increased in the corporeal smooth muscle of nerve injured rats. RhoA-guanosine triphosphatase and rho kinase activity was significantly increased in injured rat penes compared to that in sham operated penes. Intracavernous injection of Y-27632 caused a significantly greater increase in intracavernous pressure in nerve injured rats compared to that in sham operated rats, suggesting increased rho kinase activity.

CONCLUSIONS

Data suggest that RhoA/rho kinase up-regulation in response to cavernous nerve injury contributes to penile vasculature dysfunction after cavernous nerve injury. Thus, the RhoA/rho kinase pathway may be a suitable target for treating post-radical prostatectomy erectile dysfunction.

Emerging neuromodulatory molecules for the treatment of neurogenic erectile dysfunction caused by cavernous nerve injury

Advances in the neurobiology of growth factors, neural development, and prevention of cell death have resulted in a heightened clinical interest for the development of protective and regenerative neuromodulatory strategies for the cavernous nerves (CNs), as therapies for prostate cancer and other pelvic malignancies often result in neuronal damage and debilitating loss of sexual function. Nitric oxide released from the axonal end plates of these nerves within the corpora cavernosa causes relaxation of smooth muscle, initiating the haemodynamic changes of penile erection as well as contributing to maintained tumescence; the loss of CN function is primarily responsible for the development of erectile dysfunction (ED) after pelvic surgery and serves as the primary target for potential neuroprotective or regenerative strategies. Evidence from pre-clinical studies for select neuromodulatory approaches is reviewed, including neurotrophins, glial cell line-derived neurotrophic factors (GDNF), bone morphogenic proteins, immunophilin ligands, erythropoetin (EPO), and stem cells.