Inhibition of inducible nitric oxide synthase improved erectile dysfunction in rats with type 1 diabetes

Diabetes mellitus (DM), which is closely related to microvascular dysfunction, is a risk factor for erectile dysfunction (ED). Furthermore, the upregulation of inducible nitric oxide synthase (iNOS) is associated with systemic vascular dysfunction in rats with diabetes. The purpose of this study was to investigate the role of iNOS in diabetes mellitus erectile dysfunction (DMED). First, we developed a type 1 DM rat model using streptozotocin and selected those that developed DMED. Then, we injected these rats with the 1400W, an iNOS inhibitor, for 10 weeks and subsequently assessed their ED. Lastly, we performed various molecular studies and histopathological analyses of penile tissues collected from these rats after the experiments. Through the histopathological studies, we also found that the treatment restored the ratios of the smooth muscle to collagen fibres, delayed the development of microvascular injury and alleviated the oxidative stress caused by hyperglycaemia. Based on these results, we confirmed that upregulation of iNOS leads to microvascular dysfunction in patients with ED. Overall, we found that inhibition of iNOS displayed beneficial effects in the treatment of ED, suggesting that its mechanism should be further explored.     

New therapies for erectile dysfunction

The quest for improving and maintaining sexual function has been going on since time immemorial. The advent of an effective oral drug, sildenafil, has brought about unprecedented open discussion on male erectile dysfunction, and gas accelerated the pace of development of new therapies for erectile dysfunction. New knowledge in the physiology of sexual function has enabled researchers to target drug treatment at the whole network of the central nervous system and the numerous cascadic enzymatic reactions leading to relaxation of the corporal smooth muscle. One of the brightest potential applications of future molecular technology in the study of erectile dysfuction is in the utilization of gene therapy.     

Association of the T-786C, G894T and 4a/4b polymorphisms of the endothelial nitric oxide synthase gene with vasculogenic erectile dysfunction in Iranian subjects

What's known on the subject? and What does the study add? We know that nitric oxide (NO) plays a significant role in penile tumescence. NO is produced during enzymatic conversion of L‐arginine to L‐citrulline by three distinct isoforms of NO synthase (NOS), namely, inducible (iNOS), endothelial (eNOS) and neural (nNOS). The endothelial isoform of NOS (eNOS), encoded by the NOS3 gene, is the main source of NO. We determined all three eNOS gene polymorphisms in men with vasculogenic erectile dysfunction. There was a significant difference between the group of men with vasculogenic erectile dysfunction and normal healthy men when compared by genotype distribution.

OBJECTIVE

? To investigate the association of the T‐786C, G894T and variable number of tandem repeats (VNTRs) in intron 4 (a/b) polymorphisms of the eNOS gene in Iranian subjects with vasculogenic erectile dysfunction (ED).

PATIENTS AND METHODS

? A total of 322 consecutive patients with vasculogenic ED were recruited. Patients with concomitant risk factors for ED were excluded. ? Patients with ED were identified based on history‐taking, detailed physical examination, serum biochemistry, sex hormone measurements, application of the International Index of Erectile Function (IIEF) questionnaire, and penile duplex Doppler ultrasonography after intracavernosal injection of 20 µg prostaglandin E₁. The control group comprised 318 age‐matched healthy male volunteers. ? Genotyping was performed by polymerase chain reaction–restriction fragment length polymorphism and the T‐786C, G894T and VNTR intron 4 polymorphisms of the eNOS gene were determined.

RESULTS

? After multivariate regression analysis, significant differences were seen in the frequencies of genotypes and alleles of the two T‐786C and G894T polymorphisms when patients with ED and normal controls were compared. ? In a multiple logistic regression analysis, the odds ratio (OR) of increased ED was strongly associated with the ‐786C allele [adjusted OR = 3.12, 95% confidence interval (CI) = 2.28–4.25; P= 0.001] and the 894T allele (adjusted OR = 3.87, 95% CI = 2.53–4.87; P= 0.001). ? The data showed a higher prevalence of the T‐786C CC genotype (adjusted OR = 2.72, 95% CI = 1.88–3.65; P= 0.006), and the G894T GT (adjusted OR = 1.72, 95% CI 1.24–2.83; P= 0.037) and G894T TT genotypes (adjusted OR = 3.42, 95% CI 2.42–4.26; P= 0.001) in patients with ED than in the controls.

CONCLUSIONS

? The findings of the present study suggest that the eNOS T‐786C and G894T polymorphisms are strong predictors of the predisposition to ED in addition to traditional risk factors, signifying a genetic influence for this multifactorial disease. ? Further studies in different ethnic populations are needed to better elucidate the role of eNOS gene polymorphism in the pathogenesis of ED.     

Growth factors for therapeutic angiogenesis in hypercholesterolemic erectile dysfunction

The past decade has seen an explosion of new information on the physiology of penile erection, and pathophysiology of erectile dysfunction （ED）. Hypercholesterolemia is a chronic condition that can lead to degeneration in the vasculature bed and can result in ED if the penile vasculature is involved. Angiogenesis is the growth of new blood vessels from preexisting vasculature. Therapeutic angiogenesis seeks to harness the mechanisms of vascular growth to treat disorders of inadequate tissue perfusion, such as coronary artery disease and ED. There have been tremendous changes in the field of therapeutic angiogenesis over the past decade, and there is much promise for the future. Initial preclinical work with cytokine growth factor delivery resulted in a great deal of enthusiasm for the treatment of ischemic heart and/or peripheral vascular disease, though clinical studies have not achieved similar success. With an increased understanding of the complex mechanisms involved in angiogenesis, novel therapies which target multiple different angiogenic pathways are also being developed and tested. 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. Therapeutic angiogenesis is an exciting field that continues to evolve. This review will focus on the development of growth factors for hypercholesterolemic ED, the use of various growth factors for ED therapy, their routes of delivery, and the results in animal studies.     

Endothelium-specific gene and stem cell-based therapy for erectile dysfunction

Erectile dysfunction （ED） commonly results from endothelial dysfunction of the systemic vasculature. Although phosphodiesterase type 5 （PDE-5） inhibitors are effective at treating most cases of ED, they must be taken routinely and are ineffectual for a meaningful number of men. In recent years gene and stem cell-based therapies targeted at the penile endothelium have been gaining momentum in preclinical studies. These early studies reveal that gene and stem cell-based therapies may be both enduring and efficacious, and may eventually lead to a cure for ED. The following review will highlight our current understanding of endothelial-specific gene and stem cell-based therapies performed to date in a number of experimental animal models.     

Significance of nitric oxide and its modulation mechanisms by endogenous nitric oxide synthase inhibitors and arginase in the micturition disorders and erectile dysfunction

Abstract:   Evidence indicates that nitric oxide (NO) deficiency contributes to micturition disorders, especially in the afferent pathway and erectile dysfunction (ED). Two possible causes of NO deficiency are substrate ( l -arginine) limitation and increased levels of endogenous inhibitors of NO synthase (particularly asymmetric dimethylarginine: ADMA) in plasma and tissues. Elevated tissues of ADMA and N^G-monomethyl-L-arginine (L-NMMA) have been reported to be associated with impaired NO-mediated urethral, trigonal and cavernosal relaxations by pelvic ischemia. Also, plasma ADMA may help to identify underlying cardiovascular disease in men with ED. Decreased l -arginine availability to NO synthase is due to the shunting of l -arginine into other pathways such as arginase. Interaction between NO synthase and arginase has been reported to be involved in NO-mediated urethral and prostatic relaxations. Also, increased arginase activity in cavernosal tissues likely contributes to the ED that accompanies diabetes mellitus and aging. Therefore, arginase inhibition has been reported to enhance the NO-dependent physiological process for erectile function.     

生长因子与勃起功能障碍的基因治疗

生长因子具有广泛的生物学作用。勃起功能障碍(ED)的基因治疗是ED治疗的新探索,本文就生长因子,尤其是血管内皮生长因子(VEGF)和胰岛素样生长因子1(IGF-1)在ED基因治疗中的作用和价值作一综述。     

Nerve injury-related erectile dysfunction following nerve-sparing radical prostatectomy: A novel experimental dissection model

Objectives:   To establish a new experimental rat model in order to define the mechanisms of erectile dysfunction (ED) and to evaluate the changes of neuronal nitric oxide synthase (nNOS) in the pelvic ganglia following nerve-sparing radical prostatectomy.
Methods:   Sprague-Dawley rats were randomized to sham operation, bilateral cavernous nerve dissection (BCND) and bilateral cavernous nerve resection (BCNR) groups. In the BCND group, the cavernous nerves were only dissected bilaterally from the major pelvic ganglion (MPG) to the apex of the prostate without crushing or cutting. At 1, 2, 4 and 8 weeks after surgery, we examined intracavernous pressure along with arterial pressure (ICP/AP), retrograde dye tracing using Fluorogold (FG) and expression of nNOS in the MPG.
Results:   Intracavernous pressure and arterial pressure in the BCND group was significantly decreased at 2 and 4 weeks after surgery compared with the sham group, and improved at 8 weeks. The number of FG-positive cells in the MPG also recovered at 8 weeks. ICP/AP and FG-positive cells in the BCNR group were greatly decreased until 8 weeks. The percentage of nNOS-positive cells per total cells was not different between the sham and BCND groups during the experimental period, whereas that in the BCNR group gradually decreased with time.
Conclusions:   We established a novel rat model, in which cavernous nerve dissection alone caused nerve injury-related ED. We believe that this cavernous nerve dissection model might help clarify the mechanism of nerve injury-related ED and the recovery from ED after nerve-sparing radical prostatectomy.     

Effects of icariin on erectile function and expression of nitric oxide synthase isoforms in castrated rats

Aim： To investigate the effect of icariin on erectile function and the expression of nitric oxide synthase （NOS） isoforms in castrated rats. Methods： Thirty-two adult male Wistar rats were randomly divided into one shamoperated group （A） and three castrated groups （B, C and D）. One week after surgery, rats were treated with normal saline （groups A and B） or oral icariin （1 mg/[kg·day] for group C and 5 mg/[kg·day] for group D） for 4 weeks. One week after treatment, the erectile function of the rats was assessed by measuring intracavernosal pressure （ICP） during electrostimulation of the cavernosal nerve. The serum testosterone （ST） levels, the percent of smooth muscle （PSM） in trabecular tissue, and the expression of mRNA and proteins of neuronal nitric oxide synthase （nNOS）, inducible nitric oxide synthase （iNOS）, endothelial nitric oxide synthase （eNOS） and phosphodiesterase V （PDES） in corpus cavernosum （CC） were also evaluated. Results： ICP, PSM, ST and the expression of nNOS, iNOS, eNOS and PDE5 were significantly decreased in group B compared with those in group A （P 〈 0.01）. However, ICE PSM and the expression of nNOS and iNOS were increased in groups C and D compared with those in group B （P 〈 0.05）. Changes in ST and the expression of eNOS and PDE5 were not significant （P 〉 0.05） in groups C and D compared with those in group B. Conclusion： Oral treatment with icariin （〉 98.6 % purity） for 4 weeks potentially improves erectile function. This effect is correlated with an increase in PSM and the expression of certain NOS in the CC of castrated rats. These results suggest that icariin may have a therapeutic effect on erectile dysfunction.     

糖尿病性阴茎勃起功能障碍大鼠阴茎海绵体一氧化氮合酶活性的测定

目的　探讨糖尿病 (DM )性阴茎勃起功能障碍 (ED)的发病机理。　方法　SD大鼠注射链脲佐菌素建立DM动物模型后 ,注射阿朴吗啡观察 6周、8周及 12周大鼠阻茎勃起情况 ,筛选DM性ED大鼠模型 ,测定其阴茎海绵体组织一氧化氮合酶 (NOS)的活性。　结果　DM性ED大鼠阴茎海绵体组织NOS活性与对照组相比显著降低 (P <0 0 0 1或P <0 0 1) ,随DM病程延长 ,NOS活性明显下降 (P <0 0 1)。　结论　DM严重影响阴茎勃起功能 ,海绵体组织NOS活性降低可能是其发病机理之一。     

腺病毒介导的激活大鼠阴茎海绵体平滑肌细胞中NO／cGMP通路的实验研究

目的：探讨靶向大鼠iNOS基因的shRNA重组腺病毒载体对大鼠阴茎海绵体平滑肌细胞iN0s基因的激活作用,为阴茎勃起功能障碍（ED）的基因治疗提供实验依据。方法：将前期构建的重组腺病毒AdS—iN—OSrshRNA-EGFP（AdU6／shiNOS）和对照病毒AdU6／shControl,分别转染大鼠阴茎海绵体平滑肌细胞,分别在不同病毒MOI（25,50,75）值下72小时后采样检测。采用realtimeRT-PCR半定量检测AdU6／shiNOS对细胞iNOS基因mRNA表达影响;Western—blot法检测海绵体平滑肌细胞iNOS蛋白表达变化。然后培养基中加L—Arg（10mmol／L）,用酶联免疫法检测病毒转染72小时后海绵体平滑肌细胞内cGMP的浓度变化,记录AdU6／shiNOS对平滑肌细胞内cGMP的影响。结果：AdU6／shiNOS转染大鼠阴茎海绵体平滑肌细胞72小时后,和空白对照组、阴性对照组相比iN0s基因在mRNA和蛋白表达水平均显著上调（P〈O．05）,呈剂量依赖性,MOI一75时RNAa效果最好。而且转染72小时后,实验组原代平滑肌细胞内cGMP水平显著高于对照组及空白组（Pd0．05）。结论：利用腺病毒介导的RNAa技术,提高海绵体平滑肌细胞iN0s基因表达获得成功,可以增加阴茎海绵体平滑肌细胞cGMP水平,激活了NO／cGMP通路,这为勃起功能障碍的基因治疗研究开辟了新的方向。     

Gene therapy and erectile dysfunction： the current status

Current available treatment options for erectile dysfunction （ED） are effective but not without failure and/or side effects. Although the development of phosphodiesterase type 5 （PDE5） inhibitors （i.e. sildenafil, tadalafil and vardenafil） has revolutionized the treatment of ED, these oral medications require on-demand access and are not as effective in treating ED related to diabetic, post-prostatectomy and severe veno-occlusive disease states. Improvement in the treatment of ED is dependent on understanding the regulation of human corporal smooth muscle tone and on the identification of relevant molecular targets. Future ED therapies might consider the application of molecular technologies such as gene therapy. As a potential therapeutic tool, gene therapy might provide an effective and specific means for altering intracavernous pressure ＂on demand＂ without affecting resting penile function. However, the safety of gene therapy remains a major hurdle to overcome before being accepted as a mainstream treatment for ED. Gene therapy aims to cure the underlying conditions in ED, including fibrosis. Furthermore, gene therapy might help prolong the efficacy of the PDE5 inhibitors by improving penile nitric oxide bioactivity. It is feasible to apply gene therapy to the penis because of its location and accessibility, low penile circulatory flow in the flaccid state and the presence of endothelial lined （lacunar） spaces. This review provides a brief insight of the current role of gene therapy in the management of ED.     

阴茎勃起功能障碍的基因治疗进展

50～70岁男性中50%以上患有勃起功能障碍(ED),40岁的男性中有40%的患有不同程度的ED,全球范围内ED患者已超过1亿人,ED已成为困扰全球男性的重要疾病之一。在过去的20年里,对于ED发生机制及治疗有了很大的进展,现有的PDE5抑制剂对大部分ED患者疗效较好,但是对糖尿病性ED、前列腺癌根治术后ED及严重的心血管病变导致的ED疗效欠佳。人们正在寻找更好的治疗ED的方法——基因治疗。本文总结了近年来临床前期基因治疗ED的新进展,即糖尿病ED、老年性ED、神经损伤性ED及血管病变导致的ED的基因治疗。     

NADPH oxidase： recent evidence for its role in erectile dysfunction

Important roles for reactive oxygen species （ROS） in physiology and pathophysiology have been increasingly recognized. Under normal conditions, ROS serve as signaling molecules in the regulation of cellular functions. However, enhanced ROS production as a result of the activation of nicotinamide adenine dinucleotide phosphate （NADPH） oxidase contributes significantly to the pathogeneses of vascular diseases. Although it has become evident that increased ROS is associated with erectile dysfunction （ED）, the sources of ROS in the penis remain largely unknown. In recent years, emergent evidence suggests the possible role of NADPH oxidase in inducing ED. In this review, we examine the relationship between ROS and ED in different disease models and discuss the current evidence basis for NADPH oxidase-derive＇d ROS in ED.     

Chronic inhibition of nitric‐oxide synthase induces hypertension and erectile dysfunction in the rat that is not reversed by sildenafil

Study Type – Aetiology (case control)
Level of Evidence 3b

OBJECTIVE

To evaluate the effect of N(G)‐nitro‐l ‐arginine methyl ester (L‐NAME)‐induced hypertension (HT) on erectile function in the rat and determine if the phosphodiesterase (PDE)‐5 inhibitor, sildenafil, can reverse the effects of nitric oxide (NO) deficiency, as HT is a risk factor for erectile dysfunction (ED) and the NO synthase (NOS) inhibitor L‐NAME induces NO‐deficient HT.

MATERIALS AND METHODS

Thirty‐six adult Sprague‐Dawley male rats were divided into three groups, i.e. a control, L‐NAME‐HT (40 mg/rat/day in the drinking water for 4 weeks), and sildenafil‐treated L‐NAME‐HT (1.5 mg/rat/day sildenafil, by oral gavage concomitantly with L‐NAME). The erectile response expressed as a ratio of intracavernosal pressure (ICP)/mean arterial pressure (MAP), evaluated after electrical stimulation of the right cavernous nerve. The isometric tension of corpus cavernosum smooth muscle (CCSM) was measured in organ‐bath experiments. NOS expression was determined immunohistochemically for neuronal (n)NOS and by Western blot analysis for endothelial (e) and inducible (i) NOS protein. cGMP levels were evaluated by enzyme‐linked immunosorbent assay.

RESULTS

The erectile response was diminished in the HT group. Nitrergic and endothelium‐dependent relaxation was reduced, while the relaxation response to sodium nitroprusside and contractile response to phenylephrine were not altered in CCSM from L‐NAME‐treated rats. HT rats showed decreased expression of nNOS, whereas eNOS and iNOS protein expression was increased. Sildenafil partly restored endothelial and molecular changes in CCSM from HT rats, but did not reverse the decreased erectile response, even as cGMP levels returned to normal levels.

CONCLUSIONS

Sildenafil treatment did not correct the ED in L‐NAME‐treated HT rats. Under sustained high blood pressure, up‐regulation of PDE5 expression failed to reverse the depletion of neuronal NO and/or impaired nNOS activity. However, endothelium‐dependent relaxation was restored. Drug targeting of neuronal dysfunction might delay the onset of ED in HT.     

Endothelial dysfunction and erectile dysfunction in the aging man

Penile erection is a vascular event that requires an intact endothelium to occur. A dysfunctional endothelium is an early marker for the development of atherosclerotic changes and can also contribute to the occurrence of acute cardiovascular events. The pathogenesis of both endothelial and erectile dysfunction (ED) is intimately linked through decreased expression and activation of endothelial nitric oxide (NO) synthase, and the subsequent blunted physiological actions of NO naturally occurring with aging. It is now well-understood that ED is a symptom of underlying disease rather than a disease itself; for this reason in the near future both general practitioners, internal medicine practitioners and many specialists will have to interplay with sexual medicine. Aging in the man is also associated with several changes in arterial structure and function, part of them related to the decline of circulating levels of steroids, that is, testosterone and estradiol. These changes may be responsible, in part, for the lack of efficacy of ED treatments. The recent discovery that chronic administration of phosphodiesterase type 5 inhibitors may improve erectile and endothelial responsiveness of men previously non-responsive to on-demand regimes, and the knowledge that testosterone is one of the main modulators of the expression of penile phosphodiesterase type 5 isoenzyme, opens a new scenario in the treatment of men with ED and co-morbidities. The aim of this review is to discuss the pathophysiology of endothelial dysfunction and its relationship with ED in the aging male, and to suggest possible strategies to improve arterial function with regard to sexual dysfunctions.     

Alfuzosin attenuates erectile dysfunction in rats with partial bladder outlet obstruction

OBJECTIVE

To determine how partial bladder outlet obstruction (PBOO) in a rat model affects erectile function, and whether an uroselective α1‐adrenoceptor antagonist, alfuzosin (Sanofi‐Aventis, Paris, France) attenuates any erectile dysfunction (ED).

MATERIALS AND METHODS

Adult male Sprague‐Dawley rats (120) were randomized into four groups: 1, sham‐operated; 2, alfuzosin‐treated; 3, PBOO; and 4, alfuzosin‐treated with PBOO. Groups 3 and 4 were subjected to PBOO for 6 weeks by ligation of the urethra, while groups 2 and 4 rats received daily oral alfuzosin (10 mg/day) for 6 weeks. In vivo erectile responses were monitored by evaluating ratios of intracavernosal pressure (ICP)/mean arterial pressure, and total ICP (area under the curve). Organ‐bath studies were performed on corpus cavernosum smooth muscle (CCSM) strips. Nitric oxide synthase (NOS) expression was determined immunohistochemically (IHC) for neuronal (n)NOS and by Western blot analysis for endothelial (e) and inducible (i) NOS protein.

RESULTS

Rats with PBOO showed lower erectile responses than controls. Maximum electrical field stimulation‐mediated and endothelium‐dependent acetylcholine‐induced relaxations and contractile responses to phenylephrine were significantly reduced in CCSM strips from the PBOO group. The NO donor sodium nitroprusside completely relaxed CCSM from rats in all groups. IHC analyses showed decreased expression of nNOS in PBOO groups compared with controls; by contrast, protein expression of eNOS and iNOS was increased. Alfuzosin‐treatment partially attenuated functional and molecular changes in penises of PBOO rats.

CONCLUSION

Rats with PBOO show ED, most likely due to altered NOS expression and NO bioavailability. The α‐adrenoreceptor antagonist alfuzosin reversed this ED by altering sympathetic tone, increasing NO‐induced relaxation and augmenting blood flow in the penis. This study suggests a rationale for further clinical trials using combinations of α‐adrenoceptor antagonists and phosphodiesterase‐5 inhibitors in patients with ED and lower urinary tract symptoms.     

Effect of aging on expression of nitric oxide synthase I and activity of nitric oxide synthase in rat penis

Aim: To investigate the effect of aging on the expression of nitric oxide synthase I (NOS I) and the activity of NOS in rat penis. Methods: Sixty male rats from 3 age groups (adult, old and senescent) were investigated. The expression of NOS I protein and mRNA in rat penis were detected by Western blot and RT-PCR respectively and the NOS activity, with ultraviolet spectrophotometry. Results: In the old and senescent group, NOS I protein expression was significantly decreased as compared with the adult. NOS I mRNA expression was well correlated with the protein expression. NOS activity was not statistically different between the adult and old groups, but it was significantly reduced in the senescent compared with the adult group (P<0.01). Conclusion: The aging-induced decreases in NOS I expression and NOS activity may be one of the main mechanisms leading to erectile dysfunction in the senescent rats.     

Venogenic erectile dysfunction in Klippel-Trenaunay syndrome

OBJECTIVE: To report the management of erectile dysfunction (ED) secondary to Klippel-Trenaunay syndrome (KTS), a rare congenital vascular disease. PATIENTS AND METHODS: Three men (mean age 33 years) with vasogenic ED secondary to KTS underwent venous ligation surgery of the affected veins. These men had tried various treatments for their ED, including phosphodiesterase type 5 inhibitors and intracavernosal injection therapy, with little success. RESULTS: There was abnormal penile venous drainage in all three men, probably associated with congenital vascular malformation from KTS. After venous ligation the men were followed for 5 years and all reported good quality erections satisfactory for sexual intercourse. CONCLUSION: ED in men with KTS may be due to venous drainage anomalies and if confirmed, venous ligation surgery should be performed as this gives the best chance of a complete resolution.