FK506 binding protein 12 is expressed in rat penile innervation and upregulated after cavernous nerve injury

An update on the current status and future prospects of erectile dysfunction following radical prostatectomy

BACKGROUND

Radical prostatectomy (RP) and radiation treatment are standard options for localized prostate cancer. Even though nerve-sparing techniques have been increasingly utilized in RP, erectile dysfunction (ED) due to neuropraxia remains a frequent complication. Erectile function recovery rates after RP remain unsatisfactory, and many men still suffer despite the availability of various therapies.

OBJECTIVE

This systematic review aims to summarize the current treatments for post-RP-ED, assess the underlying pathological mechanisms, and emphasize promising therapeutic strategies based on the evidence from basic research.

METHOD

Evaluation and review of articles on the relevant topic published between 2010 and 2021, which are indexed and listed in the PubMed database.

RESULTS

Phosphodiesterase type 5 inhibitors, intracavernosal and intraurethral injections, vacuum erection devices, pelvic muscle training, and surgical procedures are utilized for penile rehabilitation. Clinical trials evaluating the efficacy of erectogenic drugs in this setting are conflicting and far from being conclusive. The use of androgen deprivation therapy in certain scenarios after RP further exacerbates the already problematic situation and emphasizes the need for effective treatment strategies.

CONCLUSION

This article is a detailed overview focusing on the pathophysiology and mechanism of the nerve injury developed during RP and a compilation of various strategies to induce cavernous nerve regeneration to improve erectile function (EF). These strategies include stem cell therapy, gene therapy, growth factors, low-intensity extracorporeal shockwave therapy, immunophilins, and various pharmacological approaches that have induced improvements in EF in experimental models of cavernous nerve injury. Many of the mentioned strategies can improve EF following RP if transformed into clinically applicable safe, and effective techniques with reproducible outcomes.

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.

Dipyridamole reduces penile apoptosis in a rat model of post-prostatectomy erectile dysfunction

Purpose:

Despite the nerve-sparing technique, many patients suffer from erectile dysfunction after radical prostatectomy (RP) due to cavernous nerve injury. The aim of this study was to evaluate dipyridamole as a potential treatment agent of post-radical prostatectomy erectile dysfunction.

Material and methods:

A total of 18 male Sprague-Dawley rats were randomized into three experimental Groups (SHAM+DMSO, BCNI+DMSO and BCNI+DIP). An animal model of bilateral cavernous nerve crush injury (BCNI) was established to mimic the partial nerve damage during nerve-sparing RP. After creating of BCNI, dimethyl sulphoxide (DMSO) was administered transperitoneally as a vehicle to SHAM+DMSO and BCNI+DMSO Groups. BCNI+DIP Group received dipyiridamole (10mg/kg/day) as a solution in DMSO for 15 days. Afterwards, rats were evaluated for in vivo erectile response to cavernous nerve stimulation. Penile tissues were also analyzed biochemically for transforming growth factor-β1 (TGF-β1) level. Penile corporal apoptosis was determined by TUNEL method.

Results:

Erectile response was decreased in rats with BCNI and there was no significant improvement with dipyridamole treatment. TGF-β1 levels were increased in rats with BCNI and decreased with dipyridamole treatment. Dipyridamole led to reduced penile apoptosis in rats with BCNI and there was no significant difference when compared to sham operated rats.

Conclusions:

Although fifteen-day dipyridamole treatment has failed to improve erectile function in rats with BCNI, the decline in both TGF-β1 levels and apoptotic indices with treatment may be helpful in protecting penile morphology after cavernous nerve injury.

Use of low-dose tacrolimus and associated hypomagnesemia in the prevention of erectile dysfunction following prostatectomy for prostate cancer

BACKGROUND

Hypomagnesemia with urinary magnesium wasting is a well described adverse event with calcineurin inhibitor therapy. Prostate cancer is the most prevalent cancer in men in the United States. Injury to the cavernous nerves during radical prostatectomy frequently results in erectile dysfunction. Tacrolimus has been shown to be neuroprotective in the rat cavernous nerve injury model, an animal model representative of the neural injury that occurs in humans at the time of radical prostatectomy.

METHODS

In a randomized, double-blind, placebo-controlled trial, the utility of tacrolimus was assessed for prevention of erectile dysfunction following bilateral nerve-sparing radical prostatectomy.

RESULTS

Low dose tacrolimus, associated with low trough levels, resulted in mild hypomagnesemia, which was an early and persistent finding. As early as one week after institution of therapy, mean and median serum magnesium levels were significantly lower in the tacrolimus arm as compared to the placebo arm (p<0.001 for both). While the mean and median levels were within the normal range at Week 1, 10.9% of tacrolimus-treated patients had levels <1.8mg/dL, compared to none in the placebo arm (p=0.017). Median and mean levels remained significantly different at Week 5, Month 3 and Month 6. No clinical manifestations of hypomagnesemia were noted and no subject required treatment with magnesium. Changes in serum magnesium occurred earlier than other potential metabolic adverse events described with tacrolimus (changes in serum glucose, creatinine or potassium).

CONCLUSIONS

These data indicate that mild hypomagnesemia is an early and sensitive biomarker for the effect of tacrolimus on the kidney.

Peptidomics and Secretomics of the Mammalian Peripheral Sensory-Motor System

The dorsal root ganglion (DRG) and its anatomically and functionally associated spinal nerve and ventral and dorsal roots are important components of the peripheral sensory-motor system in mammals. The cells within these structures use a number of peptides as intercellular signaling molecules. We performed a variety of mass spectrometry (MS)-based characterizations of peptides contained within and secreted from these structures, and from isolated and cultured DRG cells. Liquid chromatography-Fourier transform MS was utilized in DRG and nerve peptidome analysis. In total, 2724 peptides from 296 proteins were identified in tissue extracts. Neuropeptides are among those detected, including calcitonin gene-related peptide I, little SAAS, and known hemoglobin-derived peptides. Solid phase extraction combined with direct matrix-assisted laser desorption/ionization time-of-flight MS was employed to investigate the secretome of these structures. A number of peptides were detected in the releasate from semi-intact preparations of DRGs and associated nerves, including neurofilament- and myelin basic protein-related peptides. A smaller set of analytes was observed in releasates from cultured DRG neurons. The peptide signals observed in the releasates have been mass-matched to those characterized and identified in homogenates of entire DRGs and associated nerves. This data aids our understanding of the chemical composition of the mammalian peripheral sensory-motor system, which is involved in key physiological functions such as nociception, thermoreception, itch sensation, and proprioception.

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.

GPI-1046 increases presenilin-1 expression and restores NMDA channel activity

BACKGROUND

Previously we showed that 6-hydroxydopamine lesions of the substantia nigra eliminate corticostriatal LTP and that the neuroimmunolophilin ligand (NIL), GPI-1046, restores LTP.

METHODS

We used cDNA microarrays to determine what mRNAs may be over- or under-expressed in response to lesioning and/or GPI-1046 treatment. Patch clamp recordings were performed to investigate changes in NMDA channel function before and after treatments.

RESULTS

We found that 51 gene products were differentially expressed. Among these we found that GPI-1046 treatment up-regulated presenilin-1 (PS-1) mRNA abundance. This finding was confirmed using QPCR. PS-1 protein was also shown to be over-expressed in the striatum of lesioned/GPI-1046-treated rats. As PS-1 has been implicated in controlling NMDA-receptor function and LTP is reduced by lesioning we assayed NMDA mediated synaptic activity in striatal brain slices. The lesion-induced reduction of dopaminergic innervation was accompanied by the near complete loss of NDMA receptor-mediated synaptic transmission between the cortex and striatum. GPI-1046 treatment of the lesioned rats restored NMDA-mediated synaptic transmission but not the dopaminergic innervation. Restoration of NDMA channel function was apparently specific as the sodium channel current density was also reduced due to lesioning but GPI-1046 did not reverse this effect. We also found that restoration of NMDA receptor function was also not associated with either an increase in NMDA receptor mRNA or protein expression.

CONCLUSION

As it has been previously shown that PS-1 is critical for normal NMDA receptor function, our data suggest that the improvement of excitatory neurotransmission occurs through the GPI-1046-induced up-regulation of PS-1.

Using gene chips to identify organ-specific, smooth muscle responses to experimental diabetes: potential applications to urological diseases

OBJECTIVE

To identify early diabetes-related alterations in gene expression in bladder and erectile tissue that would provide novel diagnostic and therapeutic treatment targets to prevent, delay or ameliorate the ensuing bladder and erectile dysfunction.

MATERIALS AND METHODS

The RG-U34A rat GeneChip (Affymetrix Inc., Sunnyvale, CA, USA) oligonucleotide microarray (containing approximately 8799 genes) was used to evaluate gene expression in corporal and male bladder tissue excised from rats 1 week after confirmation of a diabetic state, but before demonstrable changes in organ function in vivo. A conservative analytical approach was used to detect alterations in gene expression, and gene ontology (GO) classifications were used to identify biological themes/pathways involved in the aetiology of the organ dysfunction.

RESULTS

In all, 320 and 313 genes were differentially expressed in bladder and corporal tissue, respectively. GO analysis in bladder tissue showed prominent increases in biological pathways involved in cell proliferation, metabolism, actin cytoskeleton and myosin, as well as decreases in cell motility, and regulation of muscle contraction. GO analysis in corpora showed increases in pathways related to ion channel transport and ion channel activity, while there were decreases in collagen I and actin genes.

CONCLUSIONS

The changes in gene expression in these initial experiments are consistent with the pathophysiological characteristics of the bladder and erectile dysfunction seen later in the diabetic disease process. Thus, the observed changes in gene expression might be harbingers or biomarkers of impending organ dysfunction, and could provide useful diagnostic and therapeutic targets for a variety of progressive urological diseases/conditions (i.e. lower urinary tract symptoms related to benign prostatic hyperplasia, erectile dysfunction, etc.).

FK1706 Enhances the Recovery of Erectile Function Following Bilateral Cavernous Nerve Crush Injury in the Rat

INTRODUCTION

Advances in neurobiology have led to a surge of clinical interest in the development of protective and regenerative neuromodulatory strategies, as surgical therapies for prostate cancer often result in neuronal damage and debilitating loss of sexual function.

AIM

To investigate the dose-dependent efficacy of FK1706, a nonimmunosuppressant immunophilin ligand, for the recovery of erectile function following bilateral cavernous nerve crush injury in the rat.

MAIN OUTCOME MEASURES

Recovery of erectile function was assessed by cavernous nerve electrostimulation and reported as maximal increase of intracavernous pressure (ICP) and area under the curve (AUC). Changes in animal weights, percentage completion of treatment course, and survival were compared between groups. METHODS; Thirty-five Sprague-Dawley male rats were randomly divided into five equal groups: seven animals received a sham operation, whereas 28 animals underwent bilateral cavernous nerve crush injury, followed by subcutaneous injection of vehicle alone (1.0 mL/kg), or low (0.1 mg/kg), medium (0.32 mg/kg), or high dose (1.0 mg/kg) FK1706 5 days per week for 8 weeks.

RESULTS

Erectile dysfunction did not occur in the sham group (mean maximal ICP increase of 100.8 +/- 6.3 cmH(2)O), whereas nerve injury and vehicle treatment produced a significant reduction in ICP response to 34.4 +/- 12.8 cmH(2)O. The mean ICP increase for high-dose FK106 treatment was 73.9 +/- 6.3 cmH(2)O (P < 0.01 vs. vehicle) compared with 58.3 +/- 7.4 cmH(2)O and 56.9 +/- 8.3 for low and medium doses (P > 0.05). Similar stepwise findings were observed using AUC data. No significant maximal aortic blood pressure or weight differences occurred between groups and all animals completed treatment.

CONCLUSION

High-dose subcutaneous FK1706 therapy promoted recovery of erectile function following bilateral cavernous nerve crush injury in the rat. No significant differences between groups were observed for changes in weight, and the 8-week treatment course was completed for all animals.

Neuroimmunophilin ligands protect cavernous nerves after crush injury in the rat: new experimental paradigms

OBJECTIVES

We investigated the effects of the orally bioavailable non-immunosuppressive immunophilin ligand GPI 1046 (GPI) on erectile function and cavernous nerve (CN) histology following unilateral or bilateral crush injury (UCI, BCI, respectively) of the CNs.

METHODS

Adult male Sprague-Dawley rats were administered GPI 15 mg/kg intraperitoneally (ip) or 30 mg/kg orally (po), FK506 1 mg/kg, ip, or vehicle controls for each route of administration just prior to UCI or BCI and daily up to 7 d following injury. At day 1 or 7 of treatment, erectile function induced by CN electrical stimulation was measured, and electron microscopic analysis of the injured CN was performed.

RESULTS

Intraperitoneal administration of GPI to rats with injured CN protected erectile function, in a fashion similar to the prototypic immunophilin ligand FK506, compared with vehicle-treated animals (93%+/-9% vs. 70%+/-5% vs. 45%+/-1%, p<0.01, respectively). Oral administration of GPI elicited the same level of significant protection from CN injury. GPI administered po at 30 mg/kg/d, dosing either once daily or four times daily with 7.5 mg/kg, provided nearly complete protection of erectile function. In a more severe BCI model, po administration of GPI maintained erectile function at 24 h after CN injury. Ultrastructural analysis of injured CNs indicated that GPI administered at the time of CN injury prevents degeneration of about 83% of the unmyelinated axons at 7 d after CN injury.

CONCLUSIONS

The orally administered immunophilin ligand GPI neuroprotects CNs and maintains erectile function in rats under various conditions of CN crush injury.

Neuromodulatory Therapy to Improve Erectile Function Recovery Outcomes After Pelvic Surgery

PURPOSE

Erectile dysfunction is a recognized, common adverse consequence of radical prostatectomy as well as various other pelvic surgeries. While a host of management options have been considered to decrease this complication, neuromodulatory therapy has recently been advanced as an intervention that may be applied for this purpose. We evaluated concepts regarding the neuropathic basis for erectile dysfunction following pelvic surgery, principles for establishing neuromodulatory therapy in this clinical context, evidence from preclinical studies supporting neuromodulatory approaches as a therapeutic strategy and the progress of early clinical developments in this field.

MATERIALS AND METHODS

The exercise principally consisted of a current literature search using the National Library of Medicine PubMed Services, a survey of recent abstract proceedings from national meetings relevant to the topic and an Internet online search for current information on federally and privately supported clinical trials specific to this topic. References were made to such key words as neuroprotection, nerve regeneration, nerve growth factors, neurotrophic factors, cavernous nerves, nerve guides and penile erection.

RESULTS

Basic science research and clinical studies support the concept that erectile loss after pelvic surgery is frequently related to neuropathic effects, resulting in penile vascular impairment. An assortment of neurobiological studies using rodent models of cavernous nerve injury have shown nerve reconstitutive actions for a host of neurotrophic substances, including classic neurotrophins, growth hormone, cytokines and atypical neurotrophic mediators. Clinical trials of several proposed neuroprotective and neurotrophic applications have been done or are in progress.

CONCLUSIONS

Erectile dysfunction is a well recognized and yet ineffectively averted complication of pelvic surgery. Neuromodulatory therapy offers a therapeutic approach for addressing the neuropathic changes of the penis that occurs in this context with the goal of maximally preserving erectile function postoperatively. While several specific neuromodulatory applications have gained interest for their potential benefit with pelvic surgery, determining their actual roles awaits the completion of controlled clinical trials.

Sexual dysfunction after pelvic surgery

Pelvic surgeries are among the most common causes of organic sexual dysfunction in men and women. The impact of nerve-sparing surgery on potency has been well documented in radical prostatectomy. However, its impact on potency needs to be evaluated in other pelvic surgeries. Sexual dysfunction is highly prevalent even after multiple technical advances in the field of oncological surgeries. The prevalence varies from 8 to 82%, depending on the type of pelvic surgery. In females, sexual dysfunction has not been evaluated adequately using validated questionnaires. However, in subspecialized circles, treatment for female sexual dysfunction is becoming routine. Currently, physicians have several options for the treatment of erectile dysfunction (ED) in men. Since the introduction of oral PDE-5 inhibitors, oral therapy has become the first-line treatment option for ED, irrespective of etiology. Currently available treatment options for the female sexual dysfunction include estrogens, androgens, phosphodiesterase inhibitors, and dopamine receptor antagonists. Initial reports regarding the role of early rehabilitation are encouraging and may become the part of routine practice in the management of ED after pelvic surgery. In this article, we summarize the sexual dysfunction following pelvic surgeries and their management.

Nonimmunosuppressant immunophilin ligand GPI-1046 does not promote in vitro growth of prostate cancer cells

OBJECTIVES

Nonimmunosuppressant immunophilin ligands such as GPI-1046 have gained interest recently for their clinical potential to reduce the extent of injury sustained by penile innervation during radical prostatectomy for prostate cancer treatment and thereby improve erectile function recovery postoperatively. Preclinical studies in rat animal models of cavernous nerve injury have demonstrated that immunophilin ligands exert both neuroprotective and neuroregenerative effects on physiologic erection and on the morphology of erectile tissue and penile innervation. Before establishing their clinical roles, however, it would be useful to evaluate whether they exert mitogenic effects on malignant prostate cells.

METHODS

Human prostate cancer cell lines (LAPC-4, CWR22Rv1, LNCaP, and PC-3) were treated in vitro with 0 to 10 microM of the prototypical nonimmunosuppressant ligand GPI-1046 in 1% fetal bovine serum (FBS)-containing (ie, low growth) media, and their growth was assayed during a 7-day period using spectrophotometric cell counting. The results were normalized for comparison to the maximal growth produced in 10% FBS-containing media.

RESULTS

All four prostate cancer cell lines grew maximally in 10% FBS-containing media, and this growth was reduced by more than twofold (P <0.05) when the cells were maintained in 1% FBS-containing media. The addition of 10 microM or less GPI-1046 to the cells in 1% FBS-containing media did not exert statistically significant mitogenic effects on human prostate cancer cells in vitro.

CONCLUSIONS

These data contribute toward allaying concerns that the use of nonimmunosuppressant immunophilin ligand therapy for the improvement of erectile function recovery after radical prostatectomy will promote recurrent prostate cancer.

Neuroprotective strategies in radical prostatectomy

In this section, authors from New York give their views on the various neuroprotective strategies for patients having a radical prostatectomy, such as the use of nerve grafts and other approaches. A joint study from Korea, the USA, Canada and the UK is presented in a paper on the importance of patient perception in the clinical assessment and management of BPH. There is also a review of robotic urological surgery. Finally, authors from New York give a review on the life of Isaac Newton. This is a new historical review in the journal, but one that will be of general interest.

Current concepts in the management of erectile dysfunction in men with prostate cancer

Development in the management of prostate cancer has placed increased attention on patient quality of life after treatment, particularly sexual function. The incidence of erectile dysfunction (ED) in men following radical prostatectomy has been estimated to range from 16% to 82%. Several factors determine the postoperative incidence of erectile difficulties; these include patient age, degree of cavernosal nerve sparing during surgery, cancer stage, and associated comorbidities. Early initiation of available treatments after radical prostatectomy, such as phosphodiesterase-5 (PDE-5) inhibitors and intracavernosal alprostadil, may improve the speed and degree of recovery of erectile function. Oral PDE-5 inhibitors are recognized as the first line of therapy for men with ED after radical prostatectomy, with reasonable success rates reported for all commercially available PDE-5 inhibitors. In recognition of the neurogenic basis for erectile dysfunction after radical prostatectomy, new strategies have been devised, such as cavernous nerve graft interposition procedures, perioperative neuroprotection measures, and postoperative neurotrophic treatments. Hopefully, these efforts will improve quality of life for patients with prostate cancer. The aim of this article is to review the current modalities of ED management for men with prostate cancer.

Specific binding to intracellular proteins determines arterial transport properties for rapamycin and paclitaxel

Endovascular drug-eluting stents have changed the practice of medicine, and yet it is unclear how they so dramatically reduce restenosis and how to distinguish between the different formulations available. Biological drug potency is not the sole determinant of biological effect. Physicochemical drug properties also play important roles. Historically, two classes of therapeutic compounds emerged: hydrophobic drugs, which are retained within tissue and have dramatic effects, and hydrophilic drugs, which are rapidly cleared and ineffective. Researchers are now questioning whether individual properties of different drugs beyond lipid avidity can further distinguish arterial transport and distribution. In bovine internal carotid segments, tissue-loading profiles for hydrophobic paclitaxel and rapamycin are indistinguishable, reaching load steady state after 2 days. Hydrophilic dextran reaches equilibrium in several hours at levels no higher than surrounding solution concentrations. Both paclitaxel and rapamycin bind to the artery at 30-40 times bulk concentration. Competitive binding assays confirm binding to specific tissue elements. Most importantly, transmural drug distribution profiles are markedly different for the two compounds, reflecting, perhaps, different modes of binding. Rapamycin, which binds specifically to FKBP12 binding protein, distributes evenly through the artery, whereas paclitaxel, which binds specifically to microtubules, remains primarily in the subintimal space. The data demonstrate that binding of rapamycin and paclitaxel to specific intracellular proteins plays an essential role in determining arterial transport and distribution and in distinguishing one compound from another. These results offer further insight into the mechanism of local drug delivery and the specific use of existing drug-eluting stent formulations.

Current and Future Strategies for Preventing and Managing Erectile Dysfunction Following Radical Prostatectomy

INTRODUCTION AND OBJECTIVES

As radical prostatectomy remains a commonly used procedure in the treatment of clinically localized prostate cancer, we critically analyzed current and future strategies for preventing and managing postoperative erectile dysfunction.

METHODS

Systematic literature review using Medline and CancerLit from January 1997 to June 2003. Abstracts published in the journals European Urology, The Journal of Urology and the International Journal of Impotence Research as official proceedings of internationally known scientific societies held in the same time period were also assessed.

RESULTS

Patient selection and surgical technique are the major determinants of postoperative erectile function. Apoptosis of corporeal smooth muscle cells plays a role in the development of cavernous veno-occlusive dysfunction following radical prostatectomy. Pharmacological prophylaxis and treatment of postoperative erectile dysfunction is effective and safe. The concepts of cavernous nerve reconstruction and neuroprotection have been associated to promising results.

CONCLUSIONS

In the hands of experienced surgeons, properly selected patients undergoing a nerve sparing radical prostatectomy should achieve unassisted or medically assisted erections postoperatively.

Neuroimmunophilins: A novel drug therapy for the reversal of neurodegenerative disease?

Neuroimmunophilin ligands (NILs) are drugs derived from the immunosuppressant FK506 (tacrolimus) that have been shown to have variable efficacy in reversing neuronal degeneration and preventing cell death. In a wide range of animal models mimicking Parkinson's disease, dementia and even surgical nerve damage they induce re-sprouting, are neurotrophic or prevent nerve damage. The neurotrophic mechanism of action of these compounds is not known and may be dependent on the type of damage and genetic variability at the species or cellular level. Some evidence suggests that NILs may act through a family of proteins called FK506 binding proteins, some of which may regulate steroid hormone receptors. Other evidence suggests that NILs may protect neurons by upregulating the antioxidant glutathione and stimulating nerve regrowth by inducing the production of neurotrophic factors. Initial clinical trials have had mixed success. In one, patients with moderately severe Parkinson's disease showed no overall improvement in fine motor skills following 6 months of treatment by the neuroimmunophilin GPI 1485. But these patients did exhibit decreased loss of dopaminergic nerve terminals with a low dose of GPI 1485 and in fact some increase in dopaminergic terminals within 6 months of the higher dose of GPI 1485 drug treatment. As a result, a second phase II clinical trial using a patient population with less severe degeneration has been initiated concurrent with an investigation of GPI 1485 and other neuroprotective therapies funded by the National Institute of Neurological Disorders and Stroke. Another clinical trial ongoing at this time is exploring the use of a neuroimmunophilin ligand to prevent nerve degeneration and erectile dysfunction resulting from prostatectomy. In summary, neuroimmunophilins show promise to reverse some forms of neurodegeneration but exact factors that predict outcome have not been identified.

Immunophilin Ligands Promote Penile Neurogenesis and Erection Recovery After Cavernous Nerve Injury

PURPOSE

We investigated the long-term effect of immunophilin ligands on erection physiology and cavernous tissue histology using rat models of unilateral and bilateral cavernous nerve (CN) injury.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were administered the immunophilin ligand FK506 (5 mg/kg subcutaneously daily for 5 days), the nonimmunosuppressant FK506 derivative GPI1046 (3 to 3-pyridyl)-1-propyl(2 seconds)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine carboxylate) (40 mg/kg subcutaneously daily for 5 or 28 days) or saline immediately upon induction of 2 paradigms of cavernous nerve injury, namely focal transection of the CN unilaterally, and a combination of focal transection of the CN unilaterally and excision of a 5 mm segment of contralateral CN (BIL treated). At 28 days following CN injury electrical stimulation of the transected CN and penile erection monitoring were performed. Whole penes were removed and evaluated immunohistochemically for the nitric oxide generator neuronal nitric oxide synthase, the neuronal marker synaptophysin, the endothelial marker CD31 and the smooth muscle marker alpha-actin.

RESULTS

In unilaterally treated groups erection recovery was significantly greater in FK506 treated than in saline treated animals ((83.5% +/- 9.2% vs 24.3% +/- 8.1%, p <0.001) and similarly greater in GPI1046 treated animals than in the respective saline treated controls for this group (57.9% +/- 12.6% vs 23.8% +/- 7.0%, p <0.05). In BIL treated groups erection recovery for FK506 and GPI1046 treated rats exceeded saline treated values by approximately 70% (p <0.05) and 40% (p = 0.14), respectively. After 28 days of continuous treatment in BIL treated groups erection recovery for GPI1046 treated rats exceeded saline treated values by 140% (p <0.05). Neuronal and endothelial staining was preserved after immunophilin ligand treatment.

CONCLUSIONS

Immunophilin ligands exert neurotrophic effects on the penile innervation that preserve cavernous tissue structure and promote erectile function recovery in rats after extensive CN injury.