VASCULAR ENDOTHELIAL GROWTH FACTOR RESTORES CORPOREAL SMOOTH MUSCLE FUNCTION IN VITRO

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.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Transplantation of endothelial progenitor cells transfected with VEGF165 to restore erectile function in diabetic rats

The present study investigated the effect of transplanting endothelial progenitor cells (EPCs) transfected with the vascular endothelial growth factor gene (VEGF165) into the corpora cavernosa of rats with diabetic erectile dysfunction (ED). A rat model of diabetic ED was constructed via intraperitoneal injection of streptozotocin. After streptozotocin treatment, pre-treated EPCs from each of three groups of rats were transplanted into their corpora cavernosa. Our results, following intracavernosal pressure (ICP) monitoring, showed that ICP increased significantly among rats in the trial group when compared to the results from rats in the blank-plasmid and control groups during basal conditions and electrical stimulation (P<0.01 for both comparisons). Histological examination revealed extensive neovascularisation in the corpora cavernosa of rats in the trial group. Fluorescence microscopy indicated that many of the transplanted EPCs in the trial group survived, differentiated into endothelial cells and integrated into the sites of neovascularisation. Based on the results of this study, we conclude that transplantation of VEGF165-transfected EPCs into the corpora cavernosa of rats with diabetic ED restores erectile function.

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.

High cholesterol feeding in C57/Blc6 mice alters expression within the VEGF receptor-ligand family in corporal tissue

INTRODUCTION

Angiogenesis, the growth and proliferation of blood vessels from existing vascular structures, is mediated by many cytokine growth factors and receptors, among the most important are the vascular endothelial growth factor (VEGF) family.

AIM

Decreases in VEGF receptor signaling have been linked to abnormalities in vasoreactivity in corporal tissue, but it is unknown if alterations in the VEGF ligands and/or receptors contribute to this process.

MAIN OUTCOME MEASURES

We sought to determine changes in vasoreactivity and the expression of the family of VEGF ligands and receptors in corporal tissue with cholesterol feeding in C57BL6 mice. Methods. Twenty-four mice (N = 8/group) were fed a normal diet (Group 1) or a 1.25% high cholesterol diet for 4 (Group 2) or 12 (Group 3) weeks. Isometric tension studies were performed on corporal strips and dose response curves were generated to evaluate endothelium-dependent and endothelium-independent vasoreactivities. Levels of VEGF-A, B, C, D, VEGF receptors (VEGFRs) were detected by PCR (polymerase chain reaction) and/or western blot/enzyme-linked immunosorbent assay (ELISA). Endothelial and smooth muscle cell contents were determined by immunohistochemistry.

RESULTS

At 4 weeks there was a small but significant decrease in endothelium-dependent vasoreactivity. Both mRNA and protein levels of VEGFR-1 were decreased, while VEGF-B was increased in Group 2 vs. Group 1, with no change in VEGF-A or endothelial cell content. By 12 weeks, decreases in both endothelium-dependent and endothelium-independent vasoreactivity were evident with decrease in most VEGF ligands (except VEGF-B), receptors, and receptor signaling.

CONCLUSIONS

Cholesterol feeding in C57BL6 mice results in alterations in the VEGF receptor-ligand family that may initially serve to limit the degree of vascular injury but these adaptations fail with the continuation of cholesterol feeding.

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.

The role of nitric oxide in erectile dysfunction: implications for medical therapy

Erectile dysfunction is a common, multifactorial disorder that is associated with aging and a range of organic and psychogenic conditions, including hypertension, hypercholesterolemia, diabetes mellitus, cardiovascular disease, and depression. Penile erection is a complex process involving psychogenic and hormonal input, and a neurovascular nonadrenergic, noncholinergic mechanism. Nitric oxide (NO) is believed to be the main vasoactive nonadrenergic, noncholinergic neurotransmitter and chemical mediator of penile erection. Released by nerve and endothelial cells in the corpora cavernosa of the penis, NO activates soluble guanylyl cyclase, which increases 3',5'-cyclic guanosine monophosphate (cGMP) levels. Acting as a second messenger molecule, cGMP regulates the activity of calcium channels as well as intracellular contractile proteins that affect the relaxation of corpus cavernosum smooth muscle. Impaired NO bioactivity is a major pathogenic mechanism of erectile dysfunction. Treatment of erectile dysfunction often requires combinations of psychogenic and medical therapies, many of which have been only moderately successful in the past. The advent of oral phosphodiesterase type 5 (PDE-5) inhibitors, however, has greatly enhanced erectile dysfunction treatment; patients have demonstrated high tolerability and success rates for improved erectile function. The efficacy of the PDE-5 inhibitors also serves to illustrate the importance of the NO-cGMP pathway in erectile function since these agents counteract the degradation of NO-generated cGMP. Because not all patients respond to PDE-5 inhibitors, additional therapies are being investigated, such as soluble guanylyl cyclase activators and NO donors, which act on NO-independent and NO-dependent pathways, respectively.

Gene Therapy for Erectile Dysfunction: Fact or Fiction?

OBJECTIVES

Erectile dysfunction (ED) is a major health problem that seriously affects the quality of life of patients and their partners. Although all three selective phosphodiesterase type 5 inhibitors (PDE5-Is) are effective in the majority of ED cases, PDE5-I therapy is less efficacious in some hard-to-treat populations (diabetics, men after radical prostatectomy), prompting the development of new approaches, including gene therapy strategies for ED.

METHODS

Gene therapy approaches are discussed in terms of the possible role of gene therapy for the treatment of ED, potential targets for gene transfer, vectors to carry targeted genes, and gene strategies for ED in certain disease states, such as diabetes, ageing, arterial and venogenic insufficiency, and cavernous nerve injury.

RESULTS

The penis is a convenient tissue target for gene therapy because of its external location and accessibility, the ubiquity of endothelial-lined spaces, and low level of blood flow, especially in the flaccid state. Gene therapy approaches have focused on a number of signaling pathways that are crucial for penile erection, such as nitric oxide/cyclic guanosine monophosphate, RhoA/Rho-kinase, growth factors, ion channels, peptides, and control of oxidative stress.

CONCLUSIONS

The need for effective ED therapies in difficult-to-treat patients has encouraged investigators to seek novel modalities for the treatment of ED. Recent preclinical and clinical trials have demonstrated that gene therapy strategies may be feasible for these purposes.

Nitric oxide/redox-based signalling as a therapeutic target for penile disorders

Oxidative and/or nitrosative stress is implicated in the pathogeneses of assorted penile disorders of clinical significance, notably erectile dysfunction, priapism and penile fibrosis. It is becoming increasingly recognised that the generation and activity of reactive oxygen and nitrogen species in the penis influence vascular homeostasis of this organ, with adverse effects exerted at cellular and molecular levels. Furthermore, these elements may interact with molecular signalling pathways operating in the penis, modulating their functional roles. This interaction in particular suggests that by accessing molecular targets associated with oxidative/nitrosative stress in the penis, new pharmacotherapeutic approaches may be developed to promote normal erectile ability and preserve erectile tissue health. This notion pertains to, but also extends beyond, interventions which predictably target components of the nitric oxide-based signal transduction pathway for the on-demand treatment of erectile dysfunction. The next line of pharmaceuticals for disorders of the penis, in general, may well spawn from an integrative understanding of the complex regulatory interactions influenced by, as well as influencing nitric oxide signalling in this organ.

Combined Angiopoietin-1 and vascular endothelial growth factor gene transfer restores cavernous angiogenesis and erectile function in a rat model of hypercholesterolemia

Hypercholesterolemia-related endothelial cell dysfunction and decreased endothelium-derived nitric oxide formation may account for impaired angiogenesis and subsequent erectile dysfunction. Angiopoietin-1 (Ang1) is a critical angiogenic factor for vascular maturation and enhances vascular endothelial growth factor (VEGF)-induced angiogenesis in a complementary manner. We hypothesized that combined adenovirus-delivered human Ang1 (ad-Ang1) and VEGF165 (ad-VEGF165) gene transfer might promote angiogenesis cooperatively in a rat model of hypercholesterolemic erectile dysfunction and result in a recovery of erectile function. Ad-Ang1 and ad-VEGF165 were injected either alone or in combination into the corpus cavernosum of the penis. Combined gene transfer of both ad-Ang1 and ad-VEGF165 significantly increased cavernous angiogenesis, eNOS phosphorylation, and cGMP expression compared with that in the groups treated with either therapy alone. Erectile function, as evaluated by electrical stimulation of the cavernous nerve 2 and 8 weeks after treatment, was completely restored in the combined treatment group, whereas intracavernous injection of either ad-Ang1 or ad-VEGF165 alone elicited partial improvement. The results indicate that combined application of angiogenic factors may enhance cavernous angiogenesis cooperatively by reinforcing the endothelium both structurally and functionally, which results in an additive effect on erectile function in hypercholesterolemic rats.

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

PURPOSE

We determined the effects of intracavernosal injection (ICI) of recombinant basic fibroblast growth factor (rbFGF) on corporal tissue in hypercholesterolemic rabbits.

METHODS

Twenty New Zealand White rabbits were fed a 1% cholesterol diet for 6 weeks and were randomly divided into four groups. Group 1 (N = 5) received an ICI of phosphate buffered saline solution (PBS) once and again 3 weeks later. Group 2 (N = 4) received an ICI of 2.5 microg rbFGF once and PBS 3 weeks later. Group 3 (N = 6) received an ICI of 2.5 microg rbFGF once and again 3 weeks later. Group 4 (N = 5) received an ICI of 2.5 microg rbFGF once. All animals were maintained on the high cholesterol diet until sacrifice, 3 weeks after last injection. Strips of corporal tissue were submaximally contracted with norepinephrine, and dose-response curves were generated to evaluate endothelial-dependent (acetylcholine, ACH) and endothelial-independent (sodium nitroprusside, SNP) vasoreactivity. Protein levels of bFGF and vascular endothelial growth factor (VEGF) were assessed by enzyme-linked immunosorbent assay. Neuronal nitric oxide synthase (nNOS) protein and mRNA were detected by Western blot and semi-quantitative polymerase chain reaction, respectively.

RESULTS

Vasoreactivity was improved by bFGF treatment as shown by higher ED50[-log(M)] of ACH and SNP in Groups 2, 3, and 4. The expression of bFGF protein, VEGF protein, nNOS protein, and mRNA were all increased after bFGF treatment.

CONCLUSIONS

ICI of bFGF improved vasoreactivity in hypercholesterolemic rabbit corporal tissue, offering a new direction to explore for the treatment of erectile dysfunction.

Characterization of hypertriglyceridemia-induced erectile dysfunction

OBJECTIVES

To characterize the effects of experimental hypertriglyceridemia on erectile function.

METHODS

The daily water intake of 40 sexually mature male rats (groups II to V) was supplemented for 12 weeks with 10% fructose solution to induce hypertriglyceridemia. In addition, animals from three groups (III, IV, and V) were given through daily oral gavage metformin (group III), fenofibrate (group IV), and fish oil (group V) to estimate their therapeutic effects on fructose-induced metabolic alterations. Another group (I) of 10 rats served as controls. At 12 weeks, changes in sexual behavior and cavernous pressure response to nerve stimulation were correlated with serum triglyceride levels and response to preventive measures.

RESULTS

After administration of 10% fructose, triglyceride levels increased fourfold to 1.79 +/- 0.31 mmol/L (mean +/- standard deviation) (group II). Coinciding with this elevation was a significant impairment of the copulatory pattern, with prolongation of mount (3.70 +/- 3.44 minutes), intromission (7.09 +/- 4.49 minutes), and ejaculatory latencies and reduced intracavernous pressure (27.56 +/- 2.04 mm Hg) response to nerve electrical stimulation. Whereas similar significant impairment was seen in group III, the other two groups (IV and V) showed beneficial effects of triglyceride reduction on these parameters.

CONCLUSIONS

Our results provide the first evidence for an impact of triglycerides on erectile function. This detrimental effect is likely to be due to functional vascular and neuronal deficits related to hypertriglyceridemia.

Cholesterol Feeding Reduces Vascular Endothelial Growth Factor Signaling in Rabbit Corporal Tissues

PURPOSE

Hypercholesterolemia is a major risk factor for erectile dysfunction (ED), but the mechanisms are not completely understood. Vascular endothelial growth factor (VEGF) is reduced in rabbit corporal tissue with cholesterol feeding. VEGF signaling leads to the phosphorylation of Akt and endothelial nitric oxide synthase (p-Akt and p-eNOS).

MATERIAL AND METHODS

New Zealand White rabbits (n = 50) were fed a 1% cholesterol (n = 8, 8, 8, 4) or normal (n = 6, 6, 6, 4) diet for 2, 4.5, 7.5, and 12 weeks. Akt, p-Akt, and p-Akt/Akt were measured by enzyme-linked immunosorbent assay. Levels of eNOS, p-eNOS, and neuronal and inducible nitric oxide synthase (nNOS and iNOS) mRNA and protein were assessed by polymerase chain reaction and Western analysis.

RESULTS

Cholesterol feeding was associated with a significant decrease in p-Akt/Akt 2.16-fold (P < 0.05), 3.28-fold (P < 0.02), and 3.42-fold (P < 0.02) at 4.5, 7.5, and 12 weeks, respectively. The reduction in p-Akt/Akt with the cholesterol diet at 2 weeks was not significantly different, but the correlation between the duration of cholesterol feeding and the reduction in p-Akt/Akt was high (r( 2) = 0.858). eNOS protein or mRNA did not change with cholesterol feeding, but p-eNOS was significantly decreased at 4.5 weeks and all subsequent time points. nNOS mRNA and protein levels were decreased at 4.5 weeks and all subsequent time points, while iNOS was not different between groups.

CONCLUSIONS

Hypercholesterolemia results in decreased VEGF signaling and decreased levels of the active form of eNOS in corporal tissue. Levels of nNOS were reduced by a different mechanism. VEGF signaling may provide a target to modulate ED.

Application of angiogenic factors for therapy of erectile dysfunction: Protein and DNA transfer of VEGF 165 into the rat penis

OBJECTIVES

To establish a laboratory animal model for vascular endothelial growth factor (VEGF) transfer in the rat penis to invent a curative therapy for erectile dysfunction (ED). Vascular insufficiency is a common pathomechanism of ED. Previous investigations have shown neovascularization of ischemic organs after gene transfer of VEGF.

METHODS

For VEGF-protein transfer, osmotic pumps were connected to the renal arteries of rats. The pumps were filled with human VEGF 165 protein (n = 20) or sterile saline (n = 20). After 28 days, a VEGF serum immunoassay was performed to document successful delivery. For VEGF-DNA transfer, liposome complexes containing VEGF 165 expression vectors were injected into rat corpora cavernosa. After immunostaining, computerized image analysis was performed to quantify the percentage of area (within the corpora cavernosa) covered by smooth muscle or endothelial cells.

RESULTS

The immunoassay of the VEGF-protein transfer showed a 10-fold greater VEGF concentration in the serum of rats carrying VEGF pumps than in the control group. In the VEGF-DNA transfer, the penes transfected with VEGF 165 vectors showed a 283-bp polymerase chain reaction product according to specific primers for human VEGF. Although statistical trends were measured in the VEGF protein-treated group, no statistically significant difference in smooth muscle or endothelial cell content was found between the control and VEGF-treated rats.

CONCLUSIONS

Our findings have established proof of principle for successful delivery of VEGF protein and VEGF-DNA transfer in the rat penis. This study was a prelude to attempt to manipulate genetically expression of angiogenic factors in insufficient erectile tissue as a curative therapy for ED.

Age‐Related Changes in Phosphorylation of Endothelial Nitric Oxide Synthase in the Rat Penis

AIM

Aging is associated with erectile dysfunction (ED) attributed to reduced nitric oxide synthase (NOS) activity and nitric oxide bioavailability. However, the mechanism for this effect has not been fully investigated. We evaluated (i) whether age-related ED involves dysregulation of endothelial NOS (eNOS) phosphorylation; and (ii) whether vascular endothelial growth factor (VEGF) exerts erectile effects and operates via eNOS phosphorylation in aged rats.

METHODS

Male Fischer 344 "young" (4-month-old) and "aged" (19-month-old) rats were used. Electrical stimulation of the cavernous nerve (CNS) was performed to generate penile erection. Erectile response in the presence of rhVEGF165 was evaluated by intracavernosal pressure monitoring 25 minutes after intracavernosal injection of VEGF. Penes were excised at baseline, with or without rhVEGF treatment, and after CNS for Western immunoblot of phospho-eNOS (Ser-1177 and Thr-495), phospho-Akt, and eNOS.

RESULTS

Erectile response was significantly reduced in aged rats compared with young rats. Phospho-eNOS (Ser-1177) and phospho-Akt were significantly reduced, while phospho-eNOS (Thr-495) was significantly increased, in the aged penis at baseline and after CNS. rhVEGF significantly improved erection and reversed downregulated Ser-1177, but not upregulated Thr-495 phosphorylation, on eNOS in aged penes. eNOS protein was significantly increased in aged penes.

CONCLUSIONS

Age-related ED is associated with eNOS inactivation through a decrease in phosphorylation of its positive regulatory site (Ser-1177) and an increase in phosphorylation of its negative regulatory site (Thr-495) in the penis. Altered phosphorylation/constitutive activation of eNOS by fluid shear stress may be a major determinant of compromised vascular homeostasis of the aged penis. The finding that VEGF rapidly induces erection and partly corrects alterations in eNOS phosphorylation in the aged rat penis suggests impaired eNOS activation by deficient endogenous VEGF and supports the potential for growth factor therapy in the treatment of age-related ED.

DECREASES IN CORPOREAL VASCULAR ENDOTHELIAL GROWTH FACTOR EXPRESSION PRECEDE VASOREACTIVITY CHANGES IN CHOLESTEROL FED RABBITS

PURPOSE

We determined temporal changes in vasoreactivity and angiogenic growth factor levels in corporeal tissue at varying time points after the induction of hypercholesterolemia in rabbits.

MATERIALS AND METHODS

A total of 42 New Zealand White rabbits were fed a 1% cholesterol (8 per group) or normal (6 per group) diet for 2, 4.5 or 7.5 weeks. Vascular endothelial growth factor (VEGF) mRNA expression in corpus cavernosum was assessed by real-time polymerase chain reaction analyses for the 3 isoforms VEGF121, VEGF165 and VEGF189. Isometric tension studies were performed and dose response curves were generated to evaluate endothelial dependent and endothelial independent vasoreactivity.

RESULTS

Real-time polymerase chain reaction analysis showed 2.2 to 2.5 and 1.5 to 2.7-fold decreases in VEGF121 and VEGF165, respectively, in the corporeal tissues of the high cholesterol group vs the normal diet group at the 2 week time point. At 2 weeks VEGF189 was unchanged but it was decreased 1.5 to 2-fold at 4.5 weeks. Acetylcholine isometric tension studies revealed no difference in mean ED50 (-log [M]) +/- SD until 7.5 weeks of high cholesterol diet (5.10 +/- 0.64 vs 3.95 +/- 1.35, p = 0.0269). The response to sodium nitroprusside was not statistically different at any time point. Endothelial cell and smooth muscle content were decreased for the high cholesterol vs normal diet at 4.5 weeks (endothelial only) and 7.5 weeks (each cell).

CONCLUSIONS

Alterations in corporeal tissue levels of VEGF occur before abnormalities in vasoreactivity. The results suggest that VEGF has a role in normal vasoreactivity in corporeal tissue and, thereby, in normal erectile function.

Understanding erectile dysfunction medication preference studies

PURPOSE OF REVIEW

The existence of three phosphodiesterase 5 inhibitors has resulted in an increase in the marketing of the drugs. This has led to a shift in focus from scientifically rigorous endpoints such as efficacy and adverse event profiles to patient preference.

RECENT FINDINGS

Although no consensus currently exists as to the correct methodology for preference studies, some basic guidelines should be adhered to, including: (1) the double-blinding of drug administration; (2) non-biased drug administration instructions; (3) an adequately conducted crossover study; (4) comparison of equivalent doses; (5) standardized preference assessment; (6) declaration of patient demographics; and (7) rigorous statistical analysis. These factors are discussed in the light of the three published preference studies.

SUMMARY

In the final analysis, it is unclear to this author how preference studies impact upon clinician decision-making when confronted by a patient with erectile dysfunction.

Intracavernosal Injection of Vascular Endothelial Growth Factor Improves Erectile Function in Aged Rats

OBJECTIVES

To investigate whether intracavernosal injection of vascular endothelial growth factor (VEGF) can restore erectile function in the aging rat.

MATERIALS AND METHODS

Ten young (4-5 months) and 30 old (24 months) Sprague-Dawley male rats were used. The old rats were divided into 3 groups: vehicle-only (phosphate buffered saline plus 0.1% bovine serum albumin; n = 10), VEGF 1 microg/kg (n = 10), and VEGF 10 microg/kg (n = 10). At 2 and 4 weeks after treatment, erectile function and histology were evaluated by hemodynamic study, histomorphometric analysis, and immunohistochemistry.

RESULTS

After 4 weeks of treatment, the ratio of peak intracavernosal pressure to systemic arterial blood pressure in response to neurostimulation was significantly higher in both the VEGF 1 microg/kg (79.9 +/- 7.7%) and the VEGF 10 microg/kg group (76.8 +/- 5.8%) compared to the vehicle-only group (63.1 +/- 8.5%; p < 0.05). The percentage of cavernosal smooth muscle was significantly higher in the VEGF 10 microg/kg group (16.1 +/- 1.4%) compared to the vehicle-only group (12.8 +/- 2.2%; p = 0.047). VEGF treatment in old rats increased e-NOS and VEGF expression in both treatment groups.

CONCLUSION

Intracavernosal injection of VEGF appears to restore smooth muscle integrity and improve erectile function in aged rats.

Alterations in angiogenic growth factors and neuronal nitric oxide synthase expression in chronic cavernosal ischemia

Our aim was to study anatomical and molecular changes at varying time points after the induction of cavernosal ischemia (CI) in a rabbit model of arteriogenic erectile dysfunction. Tissue structure and the expression of angiogenic and neurogenic genes were examined using immunostaining and reverse transcription-polymerase chain reaction (RT-PCR) analyses. We found a progressive increase of erectile connective tissue together with a decrease in smooth muscle cell content as the duration of CI increased. Immunohistochemical staining showed an increase in vascular endothelial growth factor (VEGF) levels at the early stages and a decrease at the later stages of ischemia. RT-PCR analysis of VEGF and neuronal nitric oxide synthase (nNOS) confirmed these results and showed nearly a two-fold increase in VEGF and nNOS mRNA levels in the early stages of CI with a decrease at the later stages of CI. On the other hand, mRNA levels of VEGF receptor, KDR, decreased approximately by 50% over the course of CI. Our studies showed that the cellular and molecular responses of the erectile tissue to short-term ischemia are different than those seen after long-term ischemia. The dramatic reduction in KDR expression suggests that the cavernosal endothelium is very sensitive to ischemia. The similar changes in VEGF and nNOS expression over the course of CI suggest a tissue-defensive mechanism to CI via the VEGF and NO pathways. Taken together, this study suggests that supplementation of VEGF at earlier stages of ischemia may restore the damaged endothelial cells of the corpus cavernosum and support tissue perfusion.

Phosphorylated Endothelial Nitric Oxide Synthase Mediates Vascular Endothelial Growth Factor-Induced Penile Erection1

The objective of the present study was to evaluate whether vascular endothelial growth factor (VEGF)-induced penile erection is mediated by activation of endothelial nitric oxide synthase (eNOS) through its phosphorylation. We assessed the role of constitutively activated eNOS in VEGF-induced penile erection using wild-type (WT) and eNOS-knockout (eNOS(-/-)) mice with and without vasculogenic erectile dysfunction. Adult WT and eNOS(-/-) mice were subjected to sham operation or bilateral castration to induce vasculogenic erectile dysfunction. At the time of surgery, animals were injected intracavernosally with a replication-deficient adenovirus expressing human VEGF145 (10(9) particle units) or with empty virus (Ad.Null). After 7 days, erectile function was assessed in response to cavernous nerve electrical stimulation. Total and phosphorylated protein kinase B (Akt) as well as total and phosphorylated eNOS were quantitatively assessed in mice penes using Western immunoblot and immunohistochemistry. In intact WT mice, VEGF145 significantly increased erectile responses, and in WT mice after castration, it completely recovered penile erection. However, VEGF145 failed to increase erectile responses in intact eNOS(-/-) mice and only partially recovered erectile function in castrated eNOS(-/-) mice. In addition, VEGF145 significantly increased phosphorylation of eNOS at Serine 1177 by approximately 2-fold in penes of both intact and castrated WT mice. The data provide a molecular explanation for VEGF stimulatory effect on penile erection, which involves phosphorylated eNOS (Serine 1177) mediation.

Vasculogenic erectile dysfunction: newer therapeutic strategies

PURPOSE

Despite recent advances in therapy, reversal of vasculogenic erectile dysfunction (ED) is rarely possible. A review of vasculogenic ED may further our understanding of the underlying pathophysiology and help develop more effective curative therapy.

MATERIALS AND METHODS

We reviewed the mechanisms of vasculogenic erectile dysfunction and discuss the therapies currently available or being developed for possible future use.

RESULTS

Penile erection is a complex neurovascular phenomenon that may be affected by hypercholesterolemia, atherosclerotic vascular occlusive disease, veno-occlusive dysfunction and cavernosal fibrosis. Animal models of diffuse pelvic atherosclerosis can be maintained by feeding oral cholesterol and injuring the arterial endothelium. Impaired inflow may be addressed by penile revascularization but this strategy is applicable only in select cases. Neovascularization using vascular growth factors has recently been demonstrated to be feasible in animal models. Permanent reversal of impaired cavernosal relaxation requires control of hypercholesterolemia and lifestyle changes, such as smoking cessation. Cavernosal fibrosis may be reversible via some of the same approaches used in treating Peyronie's disease but to date little clinical success has been reported. Venous ligation appears to have a limited role in treating veno-occlusive dysfunction only in highly selected men with minimal cavernosal smooth muscle dysfunction. Hypoxemia, sleep apnea and respiratory failure may also affect erectile dysfunction. However, little attention has been paid to oxygen as therapy for ED.

CONCLUSIONS

Current therapy, while effective in circumventing vasculogenic ED, is relatively ineffective in permanently reversing the condition. Further research aimed at long-term treatment strategies in vasculogenic ED is needed.

Systemic basic fibroblast growth factor induces favorable histological changes in the corpus cavernosum of hypercholesterolemic rabbits

PURPOSE

Hypercholesterolemia causes erectile dysfunction that is associated with abnormalities in vascular smooth muscle and endothelial cells. We determined the effects of basic fibroblast growth factor (bFGF) on corporeal tissue in hypercholesterolemic rabbits.

MATERIALS AND METHODS

A total of 16 New Zealand White rabbits were fed a 1% cholesterol diet for 6 weeks and were randomly divided into 3 groups. Group 1 (5 rabbits) received 2.5 microg recombinant bFGF intravenously once and again 3 weeks later. Group 2 (6 rabbits) received 2.5 microg bFGF intravenously once and placebo 3 weeks later. Group 3 (5 rabbits) received placebo intravenously each time. Rabbits were continuously fed a 1% cholesterol diet and sacrificed 3 weeks after the last treatment. Smooth muscle, endothelial cell and collagen content were assessed by immunohistochemistry and histochemical staining of corporeal tissue. Vascular endothelial growth factor (VEGF) protein and mRNA expression were assessed by enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction.

RESULTS

Corporeal smooth muscle content was greater in groups 1 and 2 (35.24% +/- 4.25% and 24.79% +/- 3.39%, p <0.01) vs group 3 (19.68% +/- 2.94%, vs groups 1 and 2 p <0.001 and <0.05, respectively). Endothelial cell and collagen content were similar among the groups. VEGF protein was increased in group 1 vs group 2 (97.90 +/- 26.00 vs 57.03 +/- 14.99 pg/ml, p <0.01) and vs group 3 (39.93 +/- 15.08, p <0.01). There was no statistical difference between groups 2 and 3. VEGF mRNA expression was similar among the groups.

CONCLUSIONS

Systemic bFGF increases smooth muscle content and VEGF protein in hypercholesterolemic rabbit corporeal tissue.

Intracavernosal vascular endothelial growth factor (VEGF) injection and adeno-associated virus-mediated VEGF gene therapy prevent and reverse venogenic erectile dysfunction in rats

Penile veno-occlusive dysfunction (venogenic erectile dysfunction) is a common cause of erectile dysfunction (ED). We investigated whether vascular endothelial growth factor (VEGF) can be used to prevent and reverse venogenic ED in a rat model. Pharmacological cavernosometry was developed and validated using adult male rats with either arteriogenic or venogenic ED. Castrated animals were treated with intracavernous VEGF as either a recombinant protein (C+VEGF) or adeno-associated virus (AAV)-mediated VEGF gene therapy (C+VEGF gene) in an attempt to prevent the development of venogenic ED. Other animal groups received testosterone replacement (C+testosterone) or intracavernous AAV-LacZ gene (C+LacZ). Animals with documented venogenic ED were treated with intracavernous VEGF in an attempt to reverse their ED. Functional analysis (pharmacological infusion cavernosometry) was performed following treatment. Penile specimens were harvested for immunohistochemistry and electron microscopic evaluation. Castrated rats showed a decrease in papaverine-induced intracavernous pressure and an increase in maintenance and drop rates during pharmacological cavernosometry. These changes were prevented by systemic testosterone and intracavernous VEGF or AAV-VEGF therapy. Moreover, intracavernous VEGF was able to reverse the venogenic ED produced by castration. The quantity of penile smooth muscle detected by alpha actin staining decreased after castration but not in the C+T, C+VEGF, or C+VEGF gene groups. Transmission electron microscopy revealed atrophy of penile smooth muscle cells and nerves in the castrated rats. In VEGF-treated rats, regeneration of smooth muscle and nerves as well as endothelial cell hypertrophy and hyperplasia were the prominent features. In our animal model, systemic testosterone replacement or intracavernous VEGF (protein and VEGF gene) prevented the veno-occlusive dysfunction in castrated animals. In rats with established venous leakage, VEGF treatment reversed the cavernosometric findings of leakage. Intracavernous injection of either VEGF protein or VEGF gene may be a preferred therapy to preserve erectile function in patients in whom testosterone therapy is contraindicated.

Recent advances in the treatment of erectile dysfunction in patients with diabetes mellitus

OBJECTIVE

To present current information on the pathogenesis of and available therapeutic options for erectile dysfunction (ED) in patients with diabetes.

METHODS

We provide a detailed review of the following topics: (1) peripheral and central neurotransmitter pathways involved in the penile erectile process (for example, nitric oxide, acetylcholine, vasoactive intestinal polypeptide, and prostaglandin E(1)), (2) pathogenesis of ED in patients with diabetes (vascular insufficiency, endothelial dysfunction, and autonomic neuropathy), (3) currently available treatment options for ED and their advantages and disadvantages, (4) potential new avenues for future research, and (5) the possibility of preventive treatment.

RESULTS

Clearly a need exists for effective treatment options for ED in patients with diabetes. Because the development of ED in patients with diabetes is often caused by several interrelated mechanisms, including vascular disease, endothelial dysfunction, autonomic neuropathy, hormone imbalance, and certain medications, a thorough understanding of the various pathways involved in penile erection and their modulation in diabetes is essential for physicians to design an effective treatment plan. Interventions that modulate the erectile pathway at different points include therapies that enhance the erectile mechanism (amplification of the nitric oxide pathway), inhibit the detumescence mechanism, or affect the final common pathway by augmenting smooth muscle relaxation. Oral therapy, intracavernosal injections, transurethral pellets, combination therapy, and surgical procedures are available treatment strategies.

CONCLUSION

Despite the availability of many treatment options for ED, early intervention and prevention (by such measures as improved glycemic control and general reduction of associated risk factors) should be emphasized because many of the diabetes-related complications leading to ED are irreversible.