ORIGINAL RESEARCH—BASIC SCIENCE: Intracavernosal Basic Fibroblast Growth Factor Improves Vasoreactivity in the Hypercholesterolemic Rabbit

Stem cell therapy for erectile dysfunction of cavernous nerve injury rats: a systematic review and meta-analysis

INTRODUCTION

Stem cell treatment is a novel therapeutic strategy for erectile dysfunction (ED) patients with bilateral cavernous nerve injury (CNI). The relative animal studies provide important clues to design pre-clinical studies and clinical studies further in the future.

PURPOSE

This study aims to evaluate the effects and influential factors of stem cell transplantation on ED rats with CNI.

MATERIALS AND METHODS

We searched PubMed and EBSCO databases published before April 30, 2014 for pre-clinical studies to evaluate the efficacy of stem cell transplantation in the treatment of ED rats with CNI. A systematic review and a planned subgroup analysis were performed to identify whether or not some certain influential factors could bring significant effects on stem cell treatment.

RESULTS

12 studies with 319 rats were enrolled in this meta-analysis. Pooled analysis results confirmed the efficacy of stem cell transplantation. Subgroup analysis results showed that treatment effects were not related to CNI models, follow-up time, stem cell species, stem cell sources, markers and delivery approaches in the transplantation. Uncultured stem cells were poorly effective compared with cultured stem cells. Periprostatic implantation (PPI) with acellular scaffolds could promote cavernous nerve regeneration, but was less effective for smooth muscle cell recovery. Stem cells modified by NGF or BDNF combined with udenafil/bFGF seemed to be more effective than those modified by BDNF alone.

CONCLUSION

This meta-analysis shows that stem cell therapy can be performed to recover erectile function. Future studies should focus on nerve restoration and vascular cell recovery. The synergistic actions of multiple growth factors following stem cell transplantation should also be considered as beneficial strategies to obtain preferable effects.

Effects of insulin-like growth factor-1 on the relaxation responses of the cavernous smooth muscle from aged rats

OBJECTIVE

The aim of this study was determine whether intracavernosal injection (ICI) of insulin-like growth factor-1 (IGF-1) protein can improve corpus cavernosal smooth muscle relaxation in aging rats.

MATERIALS AND METHODS

Ten young (4-month-old) and 30 old (24-month-old) Sprague-Dawley male rats were enrolled in the study. The old rats were divided into three groups: vehicle-only (n = 10), IGF-1 1 µg/kg (n = 10) and IGF-1 10 µg/kg treatment groups (n = 10). After 4 weeks of single IGF-1 injection treatment, strips of corporal tissue were precontracted with phenylephrine, and dose-response curves were generated to evaluate endothelial-dependent [acetylcholine (ACh)], endothelial-independent [sodium nitroprusside (SNP)] and electrical field stimulation (EFS) vasoreactivity. The changes in percentage of cavernosal smooth muscle and the concentration of nitric oxide (NO) in penile tissue were also evaluated.

RESULTS

After IGF-1 treatment, the vasoreactivity was significantly improved in both the 1 µg/kg and the 10 µg/kg treatment groups compared with the vehicle-only group at 4 weeks in response to ACh, SNP and EFS (all p < 0.05). The percentage of cavernosal smooth muscle was increased in the IGF-1 treatment groups. The NO concentrations were increased after IGF-1 treatment.

CONCLUSIONS

These data demonstrate that ICI of IGF-1 can improve vasoreactivity via endothelium-dependent and endothelial-independent mechanisms in the corpus cavernosum of the aging rat.

Combined effects of brain-derived neurotrophic factor immobilized poly-lactic-co-glycolic acid membrane with human adipose-derived stem cells and basic fibroblast growth factor hydrogel on recovery of erectile dysfunction

Erectile dysfunction (ED) is the most frequent long-term problem after radical prostatectomy. We aimed to evaluate whether the use of combination therapy with basic fibroblast growth factor (bFGF)-hydrogel on corpus cavernosum and with adipose-derived stem cells (ADSCs) and brain-derived neurotrophic factor (BDNF)-immobilized poly-lactic-co-glycolic acid (PLGA) membrane on the cavernous nerve (CN) could improve erectile function in a rat model of bilateral cavernous nerve crush injury (BCNI). Rats were randomly divided into five groups (n=15 per group): a normal group (N group), a group receiving saline application after bilateral cavernous nerve crush injury (BCNI), a group undergoing bFGF-hydrogel injection in the corpus cavernosum after BCNI (bFGF), a group receiving ADSC application covered with BDNF-membrane after BCNI (ADSC/BDNF), and a group undergoing coadministration of bFGF-hydrogel injection and BDNF-membrane with ADSCs after BDNF (bFGF+ADSC/BDNF). Four weeks postoperatively, the erectile function was assessed by detecting the ratio of intracavernous pressure (ICP) to mean arterial pressure (MAP). Smooth muscle and collagen contents were measured using Masson's trichrome staining. Neuronal nitric oxide synthase (nNOS) expression in the dorsal penile nerve was detected by immunostaining. The protein expression of the α-smooth muscle actin (α-SMA) and the cyclic guanosine monophosphate (cGMP) level of the corpus cavernosum were quantified by western blot and cGMP assay, respectively. In the bFGF+ADSC/BDNF group, the erectile function was significantly elevated compared with the BCNI and other treated groups and showed a significantly increased smooth muscle/collagen ratio, nNOS content, α-SMA expression, and cGMP level. In particular, there were no statistical differences in the ICP/MAP ratio, smooth muscle/collagen ratio, and α-SMA and cGMP levels between the bFGF+ADSC/BDNF group and normal group. Application of the BDNF-immobilized PLGA membrane with human ADSC into the CN and bFGF-incorporated hydrogel into the corpus carvernosum improved nearly normal erectile function in a rat model of postprostatectomy ED. This result suggests that a combined application of bFGF+ADSC/BDNF might be a promising treatment for postprostatectomy ED.

Intracavernous administration of bone marrow mononuclear cells: a new method of treating erectile dysfunction?

While PDE5 inhibitors have revolutionized treatment of ED, approximately 30% of patients are non-responsive. A significant cause of this is vascular and smooth muscle dysfunction, as well as nerve atrophy. Autologous administration of bone marrow mononuclear cells (BMMC) has been performed in over 2000 cardiac patients without adverse effects, for stimulation of angiogenesis/regeneration. Despite its ease of access, and dependence on effective vasculature for function, comparatively little has been perform in terms of BMMC therapy for ED. Here we outline the rationale for use of autologous BMMC in patients with ED, as well as provide early safety data on the first use of this procedure clinically.

Animal models of erectile dysfunction (ED): potential utility of non-human primates as a model of atherosclerosis-induced vascular ED

Erectile dysfunction (ED) is a prevalent medical condition affecting 18 million men and their sexual partners in the United States alone. In the majority of patients, ED is related to alterations in the flow of blood to or from the penis. Undeniably, significant progress has been made in understanding the multifactorial mechanisms that modulate erectile capacity and predispose one to ED, and this, in turn, has led to the availability of more effective treatment options. Nonetheless, all current therapies have untoward side effects, and moreover, there are still no satisfactory treatments for many patients with ED. Further enhancements in the treatment of ED would logically result from both early intervention and more detailed mechanistic insight into the characteristics of the disease process per se. This fact underscores the importance of improved understanding of the initiation, development and progression of ED. However, to do so requires longitudinal studies on animal models that more closely approximate the corresponding clinical features and time course of human disease. The goal of this report is twofold. First, to provide a brief general overview of the applicability of commonly used animal models for the study of ED. The second and primary goal is to highlight the scientific rationale for using non-human primates to evaluate the impact of atherosclerosis-induced vascular disease on the penile and systemic circulatory systems. This latter goal seems especially relevant in light of the recent literature documenting a link between ED and systemic vascular disease, a finding that has major implications in an aging US male population consuming a high fat diet.

Prevalence of late-onset hypogonadism in men with type 2 diabetes mellitus

Late-onset hypogonadism (LOH) or age-associated testosterone deficiency syndrome is defined as a clinical and biochemical syndrome associated with advancing age and characterised by symptoms and a deficiency in serum testosterone levels. This condition may result in significant detriment in the quality of life and adversely affect the function of multiple organ systems. It has been suggested that sex steroid hormones may play a causal role in the development of insulin resistance and type II diabetes. This comparative study was aimed at determining the prevalence of LOH in diabetic men with erectile dysfunction and investigating the effect of testosterone replacement therapy on erectile function and on glycaemic control.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

Anatomy, physiology, and pathophysiology of erectile dysfunction

INTRODUCTION

Significant scientific advances during the past 3 decades have deepened our understanding of the physiology and pathophysiology of penile erection. A critical evaluation of the current state of knowledge is essential to provide perspective for future research and development of new therapies.

AIM

To develop an evidence-based, state-of-the-art consensus report on the anatomy, physiology, and pathophysiology of erectile dysfunction (ED).

METHODS

Consensus process over a period of 16 months, representing the opinions of 12 experts from seven countries.

MAIN OUTCOME MEASURE

Expert opinion was based on the grading of scientific and evidence-based medical literature, internal committee discussion, public presentation, and debate.

RESULTS

ED occurs from multifaceted, complex mechanisms that can involve disruptions in neural, vascular, and hormonal signaling. Research on central neural regulation of penile erection is progressing rapidly with the identification of key neurotransmitters and the association of neural structures with both spinal and supraspinal pathways that regulate sexual function. In parallel to advances in cardiovascular physiology, the most extensive efforts in the physiology of penile erection have focused on elucidating mechanisms that regulate the functions of the endothelium and vascular smooth muscle of the corpus cavernosum. Major health concerns such as atherosclerosis, hyperlipidemia, hypertension, diabetes, and metabolic syndrome (MetS) have become well integrated into the investigation of ED.

CONCLUSIONS

Despite the efficacy of current therapies, they remain insufficient to address growing patient populations, such as those with diabetes and MetS. In addition, increasing awareness of the adverse side effects of commonly prescribed medications on sexual function provides a rationale for developing new treatment strategies that minimize the likelihood of causing sexual dysfunction. Many basic questions with regard to erectile function remain unanswered and further laboratory and clinical studies are necessary.

The effect of intracavernous injection of adipose tissue-derived stem cells on hyperlipidemia-associated erectile dysfunction in a rat model

INTRODUCTION

Hyperlipidemia has been associated with erectile dysfunction (ED) via damage to the cavernous endothelium and nerves. Adipose tissue-derived stem cells (ADSC) have been shown to differentiate into endothelial cells and secrete vasculotrophic and neurotrophic factors.

AIM

To assess whether ADSC have therapeutic effects on hyperlipidemia-associated ED.

METHODS

Twenty-eight male rats were induced to develop hyperlipidemia with a high-fat diet (hyperlipidemic rats, HR). Ten additional male rats were fed a normal diet to serve as controls (normal rats, NR). Five months later, all rats were subjected to ADSC isolation from paragonadal fat. The cells were cultured for 1 week, labeled with 5-ethynyl-2'-deoxyuridine (EdU), and then injected autologously into the corpus cavernosum of 18 HR. The remaining 10 HR rats were injected with phosphate buffered saline (PBS). At 2 and 14 days post-transplantation, four rats in the HR + ADSC group were sacrificed for tracking of the transplanted cells. At 28 days post-transplantation, all remaining rats were analyzed for serum biochemistry, erectile function, and penile histology.

MAIN OUTCOME MEASURES

Erectile function was assessed by intracavernous pressure (ICP) measurement during electrostimulation of the cavernous nerve. Cavernous nerves, endothelium, and smooth muscle were assessed by immunohistochemistry.

RESULTS

Serum total cholesterol and low-density lipoprotein levels were significantly higher in HR than in NR. High-density lipoprotein level was significantly lower in HR than in NR. Mean ICP/mean arterial pressure ratio was significantly lower in HR + PBS than in NR + PBS or HR + ADSC. Neuronal nitric oxide synthase (nNOS)-positive nerve fibers and endothelial cells were fewer in HR + PBS than in HR + ADSC. Smooth muscle content was significantly higher in both HR groups than in NR.

CONCLUSIONS

Hyperlipidemia is associated with abnormalities in both the nerves and endothelium. Treatment with ADSC ameliorates these adverse effects and holds promise as a potential new therapy for ED.

The endothelial-erectile dysfunction connection: an essential update

INTRODUCTION

The endothelial monolayer plays a crucial role in the vasodilation and hemodynamic events involved in erection physiology. Due to its relevant functions, a close link has been established between endothelial integrity and erectile dysfunction (ED). Endothelial dysfunction is induced by the detrimental actions of vascular risk factors (VRFs), identified as common correlates for the development of cardiovascular disease and ED. It is currently recognized that ED is the early harbinger of a more generalized vascular systemic disorder, and, therefore, an evaluation of endothelial health in ED patients should be of prime relevance. Several noninvasive methods for endothelial function assessment have been proposed, including the Penile Nitric Oxide Release Test (PNORT).

AIM

To highlight the most recent gathered knowledge on basic and clinical mechanisms underlying loss of cavernosal endothelial function promoted by VRFs and to discuss local and systemic methods for endothelial function assessment in ED individuals, focusing on the PNORT.

MAIN OUTCOME MEASURES

A complete revision on the novel basic and clinical links between endothelial and ED.

METHODS

A systematic review of the literature regarding the aforementioned issues.

RESULTS

Risk factor-associated cavernosal endothelial dysfunction is mostly induced by unifying mechanisms, including oxidative stress and impaired endothelial nitric oxide functional activities, which present clinically as ED. Several techniques to evaluate endothelial dysfunction were revised, with advantages and limitations debated, focusing on our detailed expertise using the PNORT method.

CONCLUSIONS

The established endothelial-erectile dysfunction connection was thoroughly revised, from basic mechanisms to the clinical importance of endothelial dysfunction assessment as diagnosis for generalized vascular disease. Further studies are required to disclose efficient approaches to repair disabled endothelium and both restore and prevent endothelial dysfunction.

Nitric oxide synthesis leads to vascular endothelial growth factor synthesis via the NO/cyclic guanosine 3',5'-monophosphate (cGMP) pathway in human corpus cavernosal smooth muscle cells

INTRODUCTION

Vascular smooth muscle cells express endothelial nitric oxide synthase (eNOS) and produce nitric oxide (NO). Recently, increased NO production has been reported to induce the synthesis and secretion of vascular endothelial growth factor (VEGF) via the NO/cyclic guanosine 3',5'-monophosphate (cGMP) pathway. L-arginine (L-arg), the precursor of NO, and selective phosphodiesterase type 5 (PDE-5) inhibitors that increase levels of intracellular cGMP may complementarily enhance VEGF synthesis in corpus cavernosal smooth muscle cells (CCSMCs), and may consequently restore impaired endothelial function. Expression of eNOS in corpus cavernosal smooth muscle has also been reported. However, it is unclear whether CCSMCs can generate NO.

AIM

To elucidate whether CCSMCs can synthesize NO and whether NO synthesis enhances VEGF synthesis via the NO/cGMP pathway.

METHODS

Corpus cavernosal cells were cultured and characterized by immunocytochemistry and immunoblotting. CCSMCs were treated with L-arg. CCSMCs were also incubated with L-arg and with vardenafil, an inhibitor of PDE-5.

MAIN OUTCOME MEASURES

Release of NO from cells was confirmed by assay of NO metabolites (NOx). Intracellular cGMP concentration and VEGF concentration in the medium were measured.

RESULTS

Isolated cells were determined to be CCSMCs. The expression of eNOS by CCSMCs was also identified. NOx and cGMP levels in the L-arg-treated group were significantly greater than those in the control group. VEGF and cGMP levels in the L-arg-treated group were also significantly greater than those in the control group. VEGF and cGMP levels in the L-arg + vardenafil-treated group were significantly greater than those in the L-arg-treated group and the control group.

CONCLUSIONS

CCSMCs express eNOS and synthesize NO. NO synthesis leads to enhancement of VEGF synthesis via the NO/cGMP pathway. Combined L-arg and vardenafil treatment, which can enhance VEGF production, may provide a novel therapeutic strategy for the treatment of erectile dysfunction as well as endothelial dysfunction in general.

Insulin-like growth factor-1 restores erectile function in aged rats: modulation the integrity of smooth muscle and nitric oxide-cyclic guanosine monophosphate signaling activity

INTRODUCTION

Insulin-like growth factor-1 (IGF-1) is one of the growth factors that have a wide range of biologic effects. We have confirmed that gene transfer of IGF-1 to the penis could improve erectile capacity. However, there are some limitations in gene therapies, such as toxicity or a risk of insertional mutagenesis. Protein treatment may be another choice for decreasing these risks.

AIM

To investigate whether intracavernosal injection of IGF-1 protein can restore erectile function in the aging rat.

MAIN OUTCOME MEASURES

Erectile responses, morphological changes, and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) signaling pathways-related marker were determined.

METHODS

Ten young (4 months) and 30 old (24 months) Sprague-Dawley male rats were enrolled in this study. The old rats were divided into three groups: vehicle-only (N = 10), IGF-1 1 microg/kg (N = 10) and IGF-1 10 microg/kg treatment group (N = 10). After 4 and 8 weeks of single IGF-1 injection treatment, intracavernous pressure (ICP) responses with electrical stimulation to the cavernous nerve were evaluated. The percent of smooth muscle in corpus cavernosum tissue, the expression of mRNA and protein of endothelial nitric oxide synthase (eNOS) were also evaluated. The activity of nitric oxide synthase (NOS) and concentration of guanosine 3',5'-cyclic-monophosphate (cGMP) that act upon the major NO-cGMP signaling pathways in penile tissue were also analyzed.

RESULTS

After IGF-1 treatment, the ICP responses was significantly increased as the young control group in both the IGF-1 1 microg/kg and the IGF-1 10 microg/kg group compared with the vehicle-only group at 4 and 8 weeks (P < 0.05). Masson's trichrom staining showed the percentage of cavernosal smooth muscle was increased in IGF-1 treatment group. IGF-1 increased e-NOS expression. NOS activities and cGMP concentrations were also significantly increased in IGF-1 treatment rats.

CONCLUSIONS

IGF-1 improved erectile function in aged rats via restoration the integrity of smooth muscle of corpus cavernosum and modulation of NO-cGMP pathways.

Efficient gene expression system using the RTP801 promoter in the corpus cavernosum of high-cholesterol diet-induced erectile dysfunction rats for gene therapy

INTRODUCTION

The application of gene therapy for a nonlife-threatening disease, such as erectile dysfunction (ED), requires a higher safety level and more efficacious systems for gene transfer.

AIM

To establish a novel technique for gene expression in a rat model of hypercholesterolemic ED that uses the RTP801 promoter, a hypoxia-inducible promoter.

METHODS

Two-month-old male Sprague-Dawley rats were fed a diet containing 4% cholesterol and 1% cholic acid, and age-matched control animals were fed a normal diet, for 3 months.

MAIN OUTCOME MEASURES

Cavernous expression of hypoxia-inducible factor (HIF)-1alpha was evaluated by Western blot. After intracavernous injection of pSV-Luc or pRTP801-Luc, gene expression was evaluated by luciferase assay, and the gene expression area was evaluated by immunohistochemistry.

RESULTS

HIF-1alpha was up-regulated in the corpus cavernosum of hypercholesterolemic rats. Although pSV-Luc did not induce gene expression in either the control or the cholesterol group, pRTP801-Luc significantly induced gene expression in the cholesterol group and resulted in higher luciferase activity than did pSV-Luc up to 14 days after injection. Immunohistochemistry showed that the gene expression area was also greater in the pRTP801-Luc group than in the pSV-Luc group, but the difference was not as great as that in luciferase activity. This suggests that pRTP801-Luc exerts its effect mainly by inducing promoter activity under hypoxia, not by increasing the number of transfected cells.

CONCLUSION

The RTP801 promoter-driven gene expression system increased gene expression in the corpus cavernosum tissue of rats with cholesterol-induced ED. This may be a useful system for the development of gene therapy in vasculogenic ED.

The Role of Penile Color-Duplex Ultrasound for the Evaluation of Erectile Dysfunction

INTRODUCTION

In the era of orally active agents, dynamic penile color-duplex ultrasound (D-PCDU) is not considered a necessary first screening for all patients with erectile dysfunction (ED). Various parameters, such as peak systolic flow velocity, end diastolic velocity, resistance index, acceleration time, and degree of arterial dilatation, have been suggested for the diagnosis of vascular ED by D-PCDU.

AIM

To highlight the clinical utility and evidence-based interpretation of D-PCDU criteria.

METHODS

Extensive, unsystematic PubMed literature search reviewing relevant data on D-PCDU in the evaluation of male ED.

RESULTS

The advantage of ultrasound is the minimally invasive nature of the procedure and the ability to screen patients to identify a normal arterial response of cavernous arteries. Men with sexual dysfunctions above 55 years of age and comorbidities are more likely to have multi-organ vascular dysfunction and may necessitate further testing because erectile failure may be the first presenting symptom requiring investigation and treatment even in the absence of cardiovascular risk factors. All patients affected with Peyronie's disease and younger men with persistent ED, a history of pelvic traumas, or fractures of the penile shaft should be offered ultrasonographic penile blood flow studies before referral to surgery or more invasive vascular investigations.

CONCLUSIONS

In the near future, D-PCDU may be used in preference to patients presenting with or without vascular risk factors, particularly those not responding to first-line orally active drugs and seeking an explanation as to why these agents failed.

A Mouse Model of Hypercholesterolemia-Induced Erectile Dysfunction

INTRODUCTION

Hypercholesterolemia is one of the most important risk factors for the development of erectile dysfunction (ED) in men.

AIM

We employed an established mouse model of hypercholesterolemia.

MAIN OUTCOME MEASURES

We test for abnormalities in vasoreactivity in corporal tissue and temporally correlated changes in vasoreactivity with alterations in histology and protein expression.

METHODS

A total of 150 mice were studied. A total of 100 apolipoprotein-E knockout (ApoE(-/-)) mice were fed a 1.25% cholesterol diet for 2, 4, 8, and 12 weeks (N = 25/group), while a group of ApoE(-/-) and wild-type Bl-6 mice were fed a normal diet. The study was terminated, and all mice were harvested at 22 weeks of age for vasoreactivity, histology, and protein studies from corporal tissues. Dose-response curves were generated to evaluate endothelium-dependent and endothelium-independent vasoreactivity, ex vivo. The contents of endothelial cells, smooth muscle cells, and smooth muscle/collagen ratio were assessed by immunohistochemistry staining or Masson staining. Level of cyclic guanosine monophosphate (cGMP) was detected by enzyme immunoassay assay. Levels of phosphorylated endothelial nitric oxide synthase (p-eNOS)/total eNOS, neuronal nitric oxide synthase (nNOS), and cyclic GMP-dependent kinase (cGK-1) protein were assessed by Western analysis.

RESULTS

Abnormalities in endothelium-dependent and endothelium-independent vasoreactivities, endothelial content, smooth muscle/collagen ratio, p-eNOS phosphorylation at Ser1177 only, nNOS, cGMP, and cGK-1 changed with the different durations of the high-cholesterol diet.

CONCLUSIONS

These data demonstrate that this mouse model is suitable for investigating aspects of hypercholesterolemic ED.