Effect of combination endothelial nitric oxide synthase gene therapy and sildenafil on erectile function in diabetic rats

Erectile dysfunction associated with diabetes mellitus is caused in part by disordered endothelial smooth muscle relaxation, neuropathy, and a decrease in cavernosal nitric oxide synthase (NOS) activity. The purpose of this study was to determine whether a combination of sildenafil and adenoviral gene transfer of endothelial NOS (eNOS) could enhance the erectile response in diabetic rats. Five groups of animals were utilized: (1) age-matched control rats, (2) streptozotocin (STZ)-induced diabetic rats (60 mg/kg i.p.), (3) STZ-rats + sildenafil (2 mg/kg i.v.), (4) STZ-rats transfected with AdCMVbetagal or AdCMVeNOS, and (5) STZ-rats transfected with AdCMVeNOS +sildenafil (2 mg/kg i.v.). At 2 months after i.p. injection of STZ, groups 4 and 5 were transfected with the adenoviruses and 1-2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Cyclic 3',5'-guanosine monophosphate (cGMP) levels were assessed in the cavernosal tissue. STZ-diabetic rats had a significant decrease in erectile function as determined by the peak intracavernosal pressure (ICP) and total ICP (area under the erectile curve; AUC) after CNS when compared to control rats. STZ-diabetic rats+AdCMVeNOS had a peak ICP and AUC, which were similar to control animals. STZ-diabetic rats administered sildenafil demonstrated a significant increase in peak ICP at the 5 and 7.5 V settings, while the AUC was significantly increased at all voltage (V) settings. The increase in both ICP and AUC of STZ-diabetic rats transfected with AdCMVeNOS at all V settings was greater than STZ-diabetic rats transfected with AdCMVbetagal. STZ-diabetic rats transfected with AdCMVeNOS and administered sildenafil had a significant increase in total ICP that was greater than eNOS gene therapy alone. Cavernosal cGMP levels were significantly decreased in STZ-diabetic rats, but were increased after transfection with AdCMVeNOS to values greater than control animals. In conclusion, overexpression of eNOS and cGMP in combination with sildenafil significantly increased both the peak ICP and total ICP to CNS in the STZ-diabetic rat, which was similar to the response observed in control rats. Moreover, the total erectile response was greater in STZ-diabetic rats receiving eNOS gene therapy plus sildenafil than STZ-rats receiving sildenafil or eNOS gene therapy alone.     

Effects of diabetes on nitric oxide synthase and growth factor genes and protein expression in an animal model.

Erectile dysfunction occurs frequently in humans with diabetes mellitus; the molecular basis of this phenomenon is not known. We investigated the effects of diabetes on penile erection, nitric oxide synthase and growth factors expression in an animal model. Forty male rats were divided into two groups: the experimental group (n = 30) received intraperitoneal injection of Streptozotocin (STZ) dissolved in citrate buffer to induce diabetes; ten age-matched control rats received injection of citrate buffer vehicle only. Before euthanization at eight weeks, erectile function was assessed by electrostimulation of the cavernous nerves. NADPH diaphorase staining was used to identify NOS and immunostaining technique was used to identify nNOS in the penile nerve fibers. RT-PCR was used to identify mRNA expression of nNOS, eNOS, iNOS, ER-beta, ER-alpha, NGF, IGF-I, TGF-beta 1, and AR. Western blot was used to identify nNOS, IGF-I, NGF, and TFG-beta protein expressions. In the diabetic group, there was: (1) a significant decrease in NOS containing nerve fibers in the dorsal and intracavernosal nerves; (2) a significant lower maximal intracavernosal pressure. RT-PCR showed down-regulation of nNOS (large form), iNOS and ER-beta mRNA expression, Immunoblot showed down-regulation of nNOS protein expression and nNOS immunostaining showed less positive staining in the dorsal and intracavernous nerves in the diabetic group. These molecular changes may provide the basis for further studies to explore the association between diabetes and impotence.     

Adenoviral gene transfer of endothelial nitric oxide synthase (eNOS) to the penis improves age-related erectile dysfunction in the rat

Nitric oxide (NO) is the principal mediator of penile erection. NO is synthesized by a variety of nitric oxide synthases (NOS). It has been demonstrated that a decrease in NOS activity, as observed in aging, is associated with a diminished erectile response. The objective of this study was to determine if adenoviral-mediated gene transfer of eNOS could reverse age-related erectile dysfunction in the rat. Two groups of animals were transfected with adenoviruses: (1) aged rats (60 weeks) with AdRSVbetagal; and (2) aged rats (60 weeks) with AdRSVeNOS. Five days after transfection, these study animals underwent cavernosal nerve stimulation (CNS) to assess erectile function and their responses were compared with young (20 weeks) control rats. Cross-sections of the rat penises transfected with AdRSVeNOS were examined after trichrome staining. Adenoviral transduction efficiency of beta-galactosidase reporter gene was measured by a galacto-light chemiluminescent reporter gene assay in cavernosal tissues of rats administered AdRSVbetagal. The transgene expression of eNOS was examined by RT-PCR in rats transfected with AdRSVbetagal and AdRSVeNOS. eNOS and iNOS protein levels were measured by Western blot analysis, and cGMP levels were assessed in cavernosal tissue by enzyme immunoassay. Adenoviral expression of the beta-galactosidase reporter gene was observed in cavernosal tissue for up to 30 days, with peak expression registered at 5 days after intracavernosal administration of AdRSVbetagal. Cross-sections of the rat penises transfected with the AdRSVeNOS revealed no pathological (morphological or histological) changes. Five days after administration of AdRSVeNOS, eNOS protein, mRNA and cGMP levels in the corpora cavernosa were significantly increased (P<0. 05), while iNOS protein levels remained unchanged (P>0.05). In conclusion, enhanced expression of eNOS employing an adenoviral vector significantly increased the erectile response to cavernosal nerve stimulation in the aged rat, similar to the response observed in younger rats. These data suggest that in vivo adenoviral gene transfer of eNOS can physiologically improve erectile function in the aged rat.     

胰岛素对糖尿病大鼠阴茎内nNOS神经纤维的影响

目的探讨糖尿病性阴茎勃起功能障碍（ED）的发病机制及胰岛素的治疗作用。方法注射链脲佐菌素建立糖尿病（DM）大鼠模型，胰岛素治疗组于成模后注射胰岛素。7周和12周后注射阿扑吗啡（APO）进行大鼠阴茎勃起功能实验，取大鼠阴茎和血浆，用ABC免疫组织化学法观察nNOS神经纤维的变化。测定血浆NOS活性。结果（1）与对照组相比，DM组大鼠阴茎勃起次数明显减少;胰岛素治疗后症状缓解;（2）与对照组相比，DM组血浆NOS活性明显增高;DM组血浆NOS活性与病程延长呈负相关;与DM组比较，胰岛素治疗组血浆NOS活性明显降低;（3）与对照组相比，DM组阴茎内nNOS阳性神经纤维明显减少;与DM组比较，胰岛素治疗组nNOS阳性神经纤维表达增加。结论糖尿病性ED阴茎内nNOS阳性纤维的数量及光密度随DM病程的延长而下降;早期给予胰岛素治疗可预防糖尿病大鼠ED的出现及阴茎内nNOS含量的下降。     

Effect of basic fibroblast growth factor incorporating gelatin microspheres on erectile function in the diabetic rat

PURPOSE: We report the potential of basic fibroblast growth factor (bFGF) incorporating gelatin microspheres to preserve erectile function in a diabetic rat model. MATERIALS AND METHODS: A total of 48 adult male rats were divided into 3 groups, namely control (nondiabetic rats), diabetes mellitus (DM) (diabetic rats that received gelatin microspheres with saline) and bFGF (diabetic rats that received gelatin microspheres with bFGF). After 4 and 8 weeks we examined intracavernous pressure responses with electrical stimulation to the cavernous nerve. For histological examination of the penis we performed Azan-Mallory staining for smooth muscle and collagen, and immunohistochemistry for endothelial nitric oxide synthase (NOS) in endothelium and neuronal NOS in cavernous nerve fiber. RESULTS: Although the intracavernous pressure response was significantly lower in the DM group than in the control group, pressure in the bFGF group was maintained at the normal level found in controls. Azan-Mallory staining showed a mass decrease in smooth muscle in cavernous tissue in the DM group. However, that in the bFGF group was maintained. There was no significant difference in endothelial NOS positive areas and the distribution of the diameter of neuronal NOS positive nerve fibers in cavernous tissue among the 3 groups. CONCLUSIONS: We report the maintenance of erectile function with bFGF incorporating gelatin microspheres in diabetic rats. The rationale of this maneuver is smooth muscle preservation by the long-term release of bFGF. This is a novel therapeutic option that is clinically applicable for diabetes induced erectile dysfunction.     

Growth factor therapy and neuronal nitric oxide synthase

Trauma to the cavernous nerve is a known cause of erectile dysfunction, with lengthy and often incomplete recovery. Using rat models, we have previously shown that injury to the cavernous nerves or ligation of pudendal arteries causes a significant decrease of neuronal nitric oxide synthase (nNOS) in the dorsal nerve of the penis and intracavernosal tissue as well as loss of erectile response to neurostimulation. Intracavernous injection of vascular endothelial growth factor or brain-derived neurotrophic factor facilitates the recovery of nNOS and erectile function. Studies are underway to elucidate the molecular mechanism of cavernous nerve regeneration and the potential of using growth factors to enhance the recovery of erectile function in patients after radical pelvic surgery. International Journal of Impotence Research (2004) 16, S38-S39. doi:10.1038/sj.ijir.3901214     

褪黑素抗氧化治疗糖尿病大鼠阴茎勃起功能障碍的研究

目的 观察褪黑素对糖尿病大鼠阴茎勃起功能的影响,探讨氧化应激在糖尿病性勃起功能障碍发病机制中的作用.方法 一次性腹腔注射STZ建立糖尿病大鼠模型,随机分为糖尿病组、褪黑素(MT)治疗组以及对照组.8周后通过电刺激各组大鼠勃起神经来检测海绵体内压,评价勃起功能;采用硫代芭比妥酸法检测阴茎海绵体组织中丙二醛(MDA)含量,黄嘌呤氧化酶法测超氧化物氧化酶(SOD)活性;免疫组化染色半定量分析各组大鼠阴茎海绵体中平滑肌及内皮的含量.结果 与正常对照组相比,阴茎海绵体组织中MDA含量显著增加(P＜0.01),SOD活性降低(P＜0.05),最大海绵体内压(ICP)亦显著降低(P＜0.05);与糖尿病组相比,MT组大鼠海绵体MDA含量明显降低(P＜0.05),其SOD活性和ICP显著升高(P＜0.05);且其海绵体平滑肌及海绵窦内皮细胞含量明显提高.结论 MT可通过改善组织中氧化应激水平,促进阴茎海绵体平滑肌和内皮组织修复,提高勃起功能;抗氧化治疗可能为糖尿病性勃起功能障碍的防治提供新的策略.     

Dysregulation of cGMP-dependent protein kinase 1 (PKG-1) impairs erectile function in diabetic rats: influence of in vivo gene therapy of PKG1alpha

OBJECTIVES: To investigate the expression of cGMP-dependent protein kinase 1 (PKG1)alpha and PKG1beta in the corpus cavernosum, and to evaluate the effect of adenoviral gene transfer of PKG1alpha to the erectile compartment on erectile function in a rat model of diabetes. MATERIALS AND METHODS: Diabetic (DM; induced by streptozotocin) male Sprague Dawley rats were transfected with adenoviruses (AdCMVbetagal or AdCMVPKG1alpha, in 10 rats each) 2 months after the induction of DM. Intracavernosal pressure (ICP) during stimulation of the cavernosal nerve (CN) was assessed, and compared with mean arterial pressure (MAP). Erectile tissue was harvested for Western blot analysis, immunohistochemistry and total PKG activity. Ten age-matched rats without DM served as the control. RESULTS: Compared to controls, AdCMVbetagal-transfected DM rats had significantly lower peak ICP responses, ICP/MAP ratios, and filling rates during CN stimulation. In DM rats transfected with AdCMVPKG1alpha, peak ICP, ICP/MAP ratios and filling rates were significantly better than in DM rats transfected with the reporter gene. As assessed by Western blot and immunohistochemistry, expression of PKG1alpha and PKG1beta was lower in corporal tissue from DM AdCMVbetagal-transfected rats than in controls. PKG1alpha expression was improved after AdCMVPKG1alpha gene therapy. Total PKG activity was lower in DM rat corporal tissue than in controls, and PKG1alpha gene transfer significantly improved DM corporal PKG activity to a value greater than in the control. CONCLUSION: PKG1alpha and PKG1beta activities are reduced in the erectile tissue of the diabetic rat, and gene transfer of PKG1alpha to the penis restored PKG activity and erectile function in vivo in diabetic rats. Gene therapy procedures targeting PKG1alpha might be an interesting future therapeutic approach to overcome diabetic erectile dysfunction resistant to oral pharmacotherapy.     

负压吸引对糖尿病性ED大鼠阴茎海绵体组织一氧化氮合酶表达的影响

目的研究负压吸引对糖尿病性勃起功能障碍（ED）大鼠阴茎组织一氧化氮合酶（NOS）表达水平的影响。方法25只实验鼠中随机选取5只为正常对照组（A组）,其余火鼠用链脲左菌素和阿朴吗啡诱导建立Ⅰ型糖尿病性ED大鼠模型。之后把造模成功的糖尿病性ED大鼠随机分成糖尿病ED吸引组（B组）和糖尿病ED非吸引组（C组）。在B组大鼠负压吸引治疗结束后将A、B、C3组大鼠处死并取阴茎组织进行石蜡包埋。采用免疫组织化学方法检测各组大鼠阴茎组织中三种一氧化氮合酶亚型（nNOS、eNOS、iNOS）的表达情况。结果A组大鼠阴茎组织中nNOS蛋白表达水平高于B组和C组（均P〈0.001）;A组和B组大鼠阴茎组织中eNOS蛋白表达水平高于C组（均P〈0.01）;A组iNOS蛋白表达水平低于B组和C组（P〈0.01,P〈0.001）,同时B组iNOS蛋白表达水平低于C组（P〈0.01）;剩余其他各组间的比较差异无统计学意义（P〉0.05）。结论负压吸引可以通过升高阴茎组织中的eNOS和降低iNOS的表达来改善勃起功能。     

Novel nitric oxide signaling mechanisms regulate the erectile response

Nitric oxide (NO) is a physiologic signal essential to penile erection, and disorders that reduce NO synthesis or release in the erectile tissue are commonly associated with erectile dysfunction. NO synthase (NOS) catalyzes production of NO from L-arginine. While both constitutively expressed neuronal NOS (nNOS) and endothelial NOS (eNOS) isoforms mediate penile erection, nNOS is widely perceived to predominate in this role. Demonstration that blood-flow-dependent generation of NO involves phosphorylative activation of penile eNOS challenges conventional understanding of NO-dependent erectile mechanisms. Regulation of erectile function may not be mediated exclusively by neurally derived NO: Blood-flow-induced fluid shear stress in the penile vasculature stimulates phosphatidyl-inositol 3-kinase to phosphorylate protein kinase B, which in turn phosphorylates eNOS to generate NO. Thus, nNOS may initiate cavernosal tissue relaxation, while activated eNOS may facilitate attainment and maintenance of full erection.     

Immunocytochemical distribution of nitric oxide synthase in the human corpus cavernosum: an electron microscopical study using the tyramide signal amplification technique

Nitric oxide has proven to be an important mediator in the relaxation of human cavernosal smooth muscle. Nevertheless, there are many inconsistencies in the literature regarding the cellular and subcellular distribution of endothelial nitric oxide synthase in the human penis. The purpose of this study was to reexamine the localization of eNOS and nNOS in the cellular anatomy of the human cavernous body by means of electron microscopical immunocytochemistry in combination with the tyramide signal amplification technique (TSA). Using specific antibodies against eNOS and nNOS, the NAPDH-diaphorase reaction and advanced protocols for fixation and staining procederes, the occurrence of NOS isoenzymes eNOS and nNOS were examined in cavernosal specimens of ten male patients who were subjected to surgery for penile deviation. eNOS immunoreactivity and NADPH-d staining was seen to be significantly present in the endothelial cells covering the cavernous spaces and in the endothelium of helicine arteries. In endothelial cells, the NADPH-d reaction product BSPT-formazan was abundantly detectable attached to membranes of the endoplasmatic reticulum and the mitochondria whereas posititve eNOS immunostaining was seen in the endothelial cells throughout their cytoplasm without any particular relation to organelles. No considerable eNOS immunoreactivity was detectable in the trabecular smooth muscle cells. nNOS staining was found in nerve fibers innervating the cavernous body and cavernosal arteries. Our results counteract the hypothesis of the cavernous smooth muscle as a local source of NO and underline the importance of an intact endothelial function for penile erection and the contribution of eNOS to this process. Received: 14 September 2000 / Accepted: 9 February 2001     

Metformin restores the penile expression of nitric oxide synthase in high-fat-fed obese rats

Obesity is a well-known risk factor for erectile dysfunction, which is associated with reduced penile nitric oxide synthase (NOS) expression. Recently it was reported that metformin activates AMP-activated protein kinase (AMPK), which increases the expression of neuronal (n) NOS and endothelial (e) NOS. Thus, to evaluate whether metformin restores NOS expression in penile tissue, we measured penile expression of nNOS and eNOS after 4 weeks of metformin treatment (300 mg/kg/d) in 5-month-old high-fat-fed obese (HFO) rats. HFO rats have increased fat accumulation in visceral areas and marked suppression of nNOS and eNOS expression in penile tissue. However, metformin treatment decreased visceral fat deposition and restored nNOS and eNOS expression in penile tissue. The levels of AMPK and phosphorylated AMPK were also decreased in HFO rats but were subsequently elevated by metformin treatment. These results suggest that expression of NOS was suppressed by the high-fat diet but restored by metformin treatment. The effect of metformin on the expression of NOS may be associated with its activation of AMPK.     

Neuronal and endothelial nitric oxide synthase isoforms: quantification of protein and mRNA in the normal rat penis

Nitric oxide synthase (NOS) is an important enzyme for erection. We evaluated the content of neuronal (nNOS) and endothelial (eNOS) isoforms and their mRNA in the penis and major pelvic ganglion (MPG) of adult male rats by Western and Northern blot analysis. The cerebellum was evaluated as a control. nNOS protein and its mRNA were detected in abundance in the MPG, cerebellum, pelvic urethra and within the crura of the penis. In contrast, the penile urethra, neurovascular bundle and the shaft of penis contained smaller amounts of this protein. eNOS protein was most abundant in the penile and pelvic parts of the urethra, whereas a moderate level was found in the penile shaft, crura, neurovascular bundle, MPG and cerebellum. Similarly eNOS mRNA was abundant in the penile and pelvic parts of the urethra, MPG and cerebellum. Penile shaft, crura and neurovascular bundle showed moderate amounts of eNOS mRNA. In conclusion, nNOS and its mRNA are most abundant in the MPG and crura of penis whereas eNOS is most abundant in the urethra and to a lesser extent present in the penis. Importantly eNOS protein and mRNA were demonstrated in the MPG, where eNOS function has to be studied.     

糖尿病性勃起功能障碍大鼠阴茎海绵体组织中神经生长因子的表达及其治疗作用的研究

目的:本研究通过检测糖尿病性勃起功能障碍(ED)大鼠阴茎组织中神经生长因子(NGF)表达,并使用hNGF进行治疗,以探讨糖尿病性ED发病机制及NGF治疗作用的机制。方法:成年雄性SD大鼠60只,随机取50只大鼠用于制作糖尿病模型,饲养8周后,取正常组和糖尿病组大鼠阴茎海绵体组织,采用RT-PCR和W estern印迹法检测NGF的mRNA及蛋白水平。从造模成功的糖尿病大鼠中筛选出有ED大鼠,把所有大鼠分为5组:正常组、糖尿病性ED组、糖尿病性ED单用NGF组(NGF组)、糖尿病性ED单用胰岛素组(R I组)、糖尿病性ED联合应用NGF和胰岛素组(NGF+R I组,胰岛素通过颈部皮下注射给药,NGF通过腹腔内注射给药),8周后测海绵体内压(ICP),并取所有大鼠阴茎海绵体组织用免疫组化法观察nNOS神经纤维的变化。结果:与正常组相比,糖尿病性ED组大鼠阴茎海绵体组织中NGF的mRNA表达增加,蛋白含量增加。与糖尿病性ED组相比,NGF组、R I组、NGF+R I组ICP水平显著升高(P<0.05);NGF组、R I组、NGF+R I组阴茎组织中nNOS神经纤维水平显著升高(P<0.05)。结论:糖尿病晚期勃起神经出现损伤并发生ED,推测可能与NGF分泌增加的幅度小于高血糖状态对勃起神经的损伤程度有关,也可能与NGF与其相应受体结合转运能力损害有关,给予外源性NGF可能有助于糖尿病性ED局部神经病变减轻和勃起功能改善。提示NGF的异常在糖尿病性ED的发病及治疗中可能具有重要作用。     

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.