Pathology of the penis in long-term diabetic rats

The effects of new herbal formula (KBMSI-2) on penile erection and expression of nitric oxide synthase isoforms in streptozotocin-induced diabetic rat model

OBJECTIVE

To investigate the effects of new herbal formula (KBMSI-2) on erectile dysfunction in streptozotocin (STZ)-induced diabetic rat model.

METHODS

Twenty four Sprague-Dawley male rats were randomly divided into three groups; control (n=8), diabetes model (n=8), diabetes + KBMSI-2 200 mg/kg treatment (n=8) groups. The diabetes induced groups received a single intraperitoneal injection of STZ. Distilled water was administered in the control and model groups. To investigate the penile erection, intracavernosal pressure (ICP) and intracavernosal pressure/mean arterial pressure (ICP/MAP) were recorded in all groups. Serial sections of the penis were used to perform Masson's trichrome stain. The expression of neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and cyclic guanosine monophosphate (cGMP) concentration in the isolated corpus cavernosum were analyzed by Western blotting.

RESULTS

Peak ICP/MAP ratio was increased in the KBMSI-2 treatment group compared with the model group (P<0.05). Masson's trichrome staining confirmed that the smooth muscle component was increased in the KBMSI-2 treatment group compared with the model group (P<0.05). The nNOS, eNOS and cGMP expression of KBMSI-2 200 mg/kg treatment group was increased compared with the model group (P<0.05).

CONCLUSION

This study showed that herbal formula of KBMSI-2 improved the erectile function by preserving the smooth muscle content and inhibiting the fibrosis of the corpus cavernosum in STZ-induced diabetic rat model.

Molecular targets for diabetes mellitus-associated erectile dysfunction

Protein expression profiles in rat corporal smooth muscle tissue were compared between animal models of streptozotocin-induced diabetes mellitus (STZ-DM) and age-matched controls (AMCs) at 1 week and 2 months after induction of hyperglycemia with STZ treatment. At each time point, protein samples from four STZ-DM and four AMC rat corpora tissues were prepared independently and analyzed together across multiple quantitative two-dimensional gels using a pooled internal standard sample to quantify expression changes with statistical confidence. A total of 170 spots were differential expressed among the four experimental groups. A subsequent mass spectrometry analysis of the 170 spots identified a total of 57 unique proteins. Network analysis of these proteins using MetaCore suggested altered activity of transcriptional factors that are of too low abundance to be detected by the two-dimensional gel method. The proteins that were down-regulated with diabetes include isoforms of collagen that are precursors to fibril-forming collagen type 1; Hsp47, which assists and mediates the proper folding of procollagen; and several proteins whose abundance is controlled by sex hormones (e.g. CRP1 and A2U). On the other hand, proteins seen or predicted to be up-regulated include proteins involved in cell apoptosis (e.g. p53, 14-3-3-gamma, Serpinf1, Cct4, Cct5, and Sepina3n), proteins that neutralize the biological activity of nerve growth factor (e.g. anti-NGF 30), and proteins involved in lipid metabolism (e.g. apoA-I and apoA-IV). Subsequent Western blot validation analysis of p53, 14-3-3-gamma, and Hsp47 confirmed increased p53 and 14-3-3-gamma and decreased Hsp47 levels in separate samples. According to the results from the Western blot analysis, Hsp47 protein showed a approximately 3-fold decrease at 1 week and was virtually undetectable at 2 months in diabetic versus control. Taken together, our results identify novel candidate proteins playing a role in erectile dysfunction in diabetes resulting from STZ treatment.

Chronic administration of phosphodiesterase 5 inhibitor improves erectile and endothelial function in a rat model of diabetes

This study was conducted to determine if the long-term administration of the phosphodiesterase type 5 (PDE 5) inhibitor, DA-8159, to diabetic rats can ameliorate the development of erectile dysfunction (ED) and endothelial dysfunction. After inducing diabetes with streptozotocin, DA-8159 was orally administered at a dose of 3 mg/kg or 10 mg/kg for 8 weeks. To examine the effect on erectile response, electrostimulation of the cavernous nerve with the parameters of 3 V, 5 ms, 5 Hz or 10 Hz, was performed to measure the intracavernous pressure (ICP) and mean arterial pressure (MAP). Thoracic aorta relaxation in vitro was evaluated by adding acetylcholine (Ach) cumulatively to the bathing medium. In addition, the plasma endothelin-1 (ET-1) levels were measured in order to investigate the effect of DA-8159 on endothelial dysfunction. The area under the curve (AUC) from the ICP/MAP ratio in the 10 Hz stimulation showed a significantly increased AUC after the 10 mg/kg treatment compared with the diabetic group (8891 +/- 619 vs. 6316 +/- 1016, respectively, p < 0.05). At the 5 Hz frequency, DA-8159 10 mg/kg also induced a significant increase in the AUC compared with the diabetic control. The maximum ICP/MAP ratio (%) of the 10 mg/kg treatment group was significantly higher in both the 10 Hz and 5 Hz frequency groups (p < 0.05). A treatment of 3 mg/kg tended to increase the AUC and peak ICP/MAP but was not statistically significant. The Ach EC50 value of the diabetic group was significantly higher than in the normal control (120.50 +/- 22.90 nm vs. 86.80 +/- 9.30 nm, respectively), and 10 mg/kg treatment group showed a significantly lower EC(50) value (88.38 +/- 19.7 nm). The ET-1 level was lower in groups treated with DA-8159, 3 mg/kg and 10 mg/kg treatment induced a statistical difference compared with the diabetic control (1.15 +/- 0.34 fmol/mL vs. 2.51 +/- 0.55 fmol/mL, respectively, p < 0.05). These results demonstrate that chronic administration of DA-8159 could attenuate the development of the ED in diabetes and its effect is associated with an improvement in the endothelial function.

Microarray analysis reveals novel gene expression changes associated with erectile dysfunction in diabetic rats

To investigate the full range of molecular changes associated with erectile dysfunction (ED) in Type 1 diabetes, we examined alterations in penile gene expression in streptozotocin-induced diabetic rats and littermate controls. With the use of Affymetrix GeneChip arrays and statistical filtering, 529 genes/transcripts were considered to be differentially expressed in the diabetic rat cavernosum compared with control. Gene Ontology (GO) classification indicated that there was a decrease in numerous extracellular matrix genes (e.g., collagen and elastin related) and an increase in oxidative stress-associated genes in the diabetic rat cavernosum. In addition, PubMatrix literature mining identified differentially expressed genes previously shown to mediate vascular dysfunction [e.g., ceruloplasmin (Cp), lipoprotein lipase, and Cd36] as well as genes involved in the modulation of the smooth muscle phenotype (e.g., Kruppel-like factor 5 and chemokine C-X3-C motif ligand 1). Real-time PCR was used to confirm changes in expression for 23 relevant genes. Further validation of Cp expression in the diabetic rat cavernosum demonstrated increased mRNA levels of the secreted and anchored splice variants of Cp. CP protein levels showed a 1.9-fold increase in tissues from diabetic rats versus controls. Immunohistochemistry demonstrated localization of CP protein in cavernosal sinusoids of control and diabetic animals, including endothelial and smooth muscle layers. Overall, this study broadens the scope of candidate genes and pathways that may be relevant to the pathophysiology of diabetes-induced ED as well as highlights the potential complexity of this disorder.

Endothelin and erectile dysfunction: a target for pharmacological intervention?

Although erectile dysfunction (ED) is not life threatening, this common problem can significantly affect the quality of life and psychological and social well-being. The Massachusetts male ageing study (1,290 men aged 40 - 70 years) showed that 52% of men reported some degree of ED (17.1% mild, 25.2% moderate, 9.6% total). In the UK, an estimated 17 - 19% of men are thought to suffer from ED. This problem is more common with advancing age and since this proportion of the population is increasing, the prevalence of ED is expected to rise. Endothelin-1 (ET-1) belongs to a family of potent vasoconstrictor peptides consisting of 21 amino acids. We review the evidence showing that ET-1 plays a role via (ET(A) and ET(B) receptors) in the regulation of cavernosal smooth muscle tone. We also consider the various risk factors that are involved in the pathogenesis of ED and how these relate to the action of ET-1. In particular, the role of diabetes, hypertension, smoking and dyslipidaemia are discussed. The pharmaceutical industry has declared an interest in the development of ET antagonists for use in the treatment of various diseases including ED. We briefly comment on experimental ET-1 antagonists that may be of therapeutic benefit in ED.

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.

Endothelial nitric oxide synthase protein expression, localization, and activity in the penis of the alloxan-induced diabetic rat

PURPOSE

To explore the possible relevance of endothelial nitric oxide synthase (eNOS) in the pathophysiology of erectile dysfunction (ED) associated with diabetes mellitus, we compared the catalytic activity, protein expression, and cellular localization of eNOS with those of neuronal nitric oxide synthase (nNOS) in the penis of rats with alloxan-induced diabetes.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were given alloxan or vehicle only and monitored weekly by Dextrostix for confirmation of glucosuria. Tail-flick immersion and penile reflex testing were used to evaluate sensory neuropathy and ED, respectively. At 4 to 5 weeks (early) and 10 to 11 weeks (late), animals were sacrificed, and their penes were subjected to nNOS and eNOS catalytic activity assay, Western immunoblotting, and immunohistochemistry examination. Masson's trichrome staining of penile tissue and serum testosterone measurements were performed for light microscopy and sex steroidogenic analysis, respectively.

RESULTS

Confirmed diabetic rats showed significant reductions in penile nNOS expression and eNOS activity and expression early, prior to observed ED, and nNOS and eNOS activities and expressions late, synchronous with ED. Decreased intensities of both nNOS staining, localized to the dorsal and cavernosal nerves distributing to the penis, and eNOS staining, localized to penile vascular and sinusoidal endothelium, were assessed in diabetic animals. Penile vascular and cavernosal tissue appeared intact in diabetic rats. Testosterone levels were equivalent in nondiabetic and diabetic rats.

CONCLUSIONS

In the penis of the alloxan-induced diabetic rat, eNOS protein expression and synthetic activity were reduced compared with the normal rat penis, independent of testosterone influence and in the absence of significant erectile tissue degenerative changes. These eNOS effects apparently preceded nNOS effects. Full elucidation of the possible mechanisms affecting eNOS function in the diabetic rat penis requires further investigation.

The effect of superoxide dismutase on nitric oxide-mediated and electrical field-stimulated diabetic rabbit cavernosal smooth muscle relaxation

OBJECTIVE

To investigate the effect of superoxide dismutase (SOD, the enzyme that accelerates the breakdown of the superoxide anion, O2- to H2O) on nitric oxide (NO)-mediated and electrical field stimulated (EFS) relaxation in diabetic rabbit cavernosal smooth muscle. Materials and methods Diabetes was induced with alloxan (65 mg/kg) in six adult New Zealand White rabbits. After 6 months, cavernosal smooth muscle strips from age-matched controls and diabetic animals were mounted in organ baths. After precontraction with phenylephrine (10 micromol/L) in the presence of atropine (1 micromol/L), guanethidine (5 micromol/L) and indomethacin (10 micromol/L), relaxation responses to EFS (1-20 Hz), carbachol (10(-8)-10(-4) mol/L) and sodium nitroprusside (SNP, 10(-9)-10(-4) mol/L) were assessed in the presence and absence of SOD (100 IU/mL).

RESULTS

SNP- and carbachol-mediated (endothelium-independent and -dependent, respectively) relaxations were impaired in the diabetic cavernosal smooth muscle strips compared with controls (concentration required for 50% inhibition, 1.4 micromol/L for diabetic and 0.75 micromol/L for control with SNP, and 44 micromol/L for diabetic and 0.4 micromol/L for control with carbachol). SOD significantly enhanced both SNP- and carbachol-mediated diabetic cavernosal smooth muscle relaxations (both P < 0.05). EFS-mediated relaxations were also significantly (P < 0.05) impaired in the diabetic cavernosal smooth muscle strips; these relaxations were also significantly (P < 0.05) enhanced by SOD.

CONCLUSION

NO- and EFS-mediated cavernosal smooth muscle relaxation is impaired in a rabbit model of diabetes but SOD significantly reversed the impaired relaxation. Therefore, in diabetes, the generation of reactive oxygen species may play an important role in the development of erectile dysfunction.

Sildenafil: a urologist's view

Erectile dysfunction (ED) is a common problem with a multifactorial aetiology. The treatment of ED has been revolutionised by the introduction of intracavernosal injections some two decades ago. However, the recent development of the orally-administered drug sildenafil (Viagra) has had a major impact on the treatment of ED. We discuss the trials with sildenafil with special reference to cardiovascular risk factors associated with ED.

Diabetic sexual dysfunction

Although the overall incidence of erectile dysfunction in the general population between the ages of 40 and 70 years is 52%, men with diabetes mellitus have impotence at an earlier age and with a significantly higher prevalence, ranging as high as 75%. Numerous advances have been made in understanding the physiologic and biochemical mechanisms controlling penile erection. Improved clinical techniques for the diagnosis and treatment of impotence, including dynamic vascular testing, intracavernosal pharmacotherapy, and microsurgical revascularization, have allowed us to enter a new and exciting era in the quest for a more complete understanding of erectile dysfunction.

Clinical reliability of multi-drug intracavernous vasoactive pharmacotherapy for diabetic impotence

The aim of this study was to assess the effectiveness and safety of intracavernous injections of a four-drug vasoactive mixture in diabetic patients with organic impotence. A group of 60 diabetic patients with either pure neurogenic, pure vasculogenic or mixed neurovasculogenic impotence were treated with intracavernous injections of a combination of 12.1 mg/ml papaverine hydrochloride, 1.01 mg/ml phentolamine mesylate, 10.1 micrograms/ml prostaglandin E1 and 0.15 mg/ml atropine sulphate ('full-dose' mixture). A mixture of the same drugs but at one-third concentrations ('reduced-dose' mixture) was also used. The mean (+/- SEM) volumes of the full-dose and reduced-dose mixtures used were 0.21 +/- 0.03 ml and 0.31 +/- 0.02 ml, respectively. All the patients were able to sustain a rigid erection at the end of the titration phase of the study. At a mean follow-up of 18 months, 48 patients (80%) were successfully using the mixture, 6 patients (10%) were using the mixture at a dose lower than the initial dose and 6 patients (10%) had dropped out from the injection therapy. No major complications were seen. The association of multiple vasoactive drugs which use different mechanisms of action, thus exerting a pharmacological synergism, is an effective and safe procedure in intracavernous pharmacotherapy for diabetic patients with organic impotence.

Pathophysiology of erectile dysfunction

During the past decade, our knowledge of the hemodynamics, functional anatomy, neurophysiology, and neuropharmacology of erectile function has evolved substantially. The change of smooth muscle tone has emerged as a key factor in erection and detumescence. However, future studies are needed to elucidate the cellular and molecular basis of erectile physiology. With insight into normal physiology we will understand the pathologic process and be able to treat it.

Diabetes mellitus impairs neurogenic and endothelium-dependent relaxation of rabbit corpus cavernosum smooth muscle

The effect of alloxan-induced diabetes on the reactivity of corporeal nerves, endothelium and smooth muscle was studied in the New Zealand white rabbit. Fifteen rabbits were randomly divided into treated (n = 6) and control (n = 9) groups. The treated group was maintained for 6 weeks. Two control groups were studied. One control group (n = 3) was maintained for 6 weeks as littermate controls for diabetic group. The second control group (n = 6) was not maintained but was weight matched with the 6 week diabetic group. The reactivity of corpus cavernosum tissue from the diabetic animals and the control animals was studied in organ chambers. When tissue contraction was produced with phenylephrine for the study of relaxation to various stimuli, the tension induced was similar in the diabetic and the control groups. Relaxation of corpus cavernosum tissue to electrical stimulation of autonomic nerves as well as relaxation to the endothelium-dependent vasodilator acetylcholine were comparably unaffected in the weight matched and littermate control groups while significantly inhibited in the diabetic group. Treatment of the corporeal tissue with the cyclooxgenase inhibitor indomethacin enhanced the relaxation to electrical stimulation and to acetylcholine in the control and in the diabetic groups but did not improve the significant difference in relaxation between the two groups. Relaxation of corporeal tissue to endothelium-independent vasodilators, papaverine and nitroprusside was similar in the control groups and the diabetic groups. It is concluded that diabetes impairs neurogenic and endothelium-mediated relaxation of rabbit corpus cavernosum smooth muscle. These findings are comparable to those described in corpus cavernosum tissue from diabetic men, showing the validity of this experimental animal model. The mechanism for the nerve or endothelial dysfunction does not appear to involve alteration in cyclooxygenase products of arachidonate or the ability of the corporeal smooth muscle to relax via a cGMP-dependent mechanism. Since nitric oxide has been shown to act as the nonadrenergic noncholinergic neurotransmitter as well as endothelium-derived relaxing factor (EDRF) of the trabecular smooth muscle, it is possible that impairment of neurogenic and endothelium-dependent relaxation due to diabetes is mediated by alteration in the synthesis or availability of nitric oxide in corporeal tissue.

Fine structure of the human corpus cavernosum

This paper demonstrates the ultrastructure of the human corpus cavernosum from eight male transexuals (aged 20 to 30 years) undergoing penectomy. The presence of collagen, smooth muscle, endothelial cells lining cavernous spaces, mast cells, and different types of nerve terminals, including those of a nonadrenergic and noncholinergic type, are illustrated.

Dysfunctional penile cholinergic nerves in diabetic impotent men

Impotence in the diabetic man may be secondary to a neuropathic condition of the autonomic penile nerves. The relationship between autonomic neuropathy and impotence in diabetes was studied in human corporeal tissue obtained during implantation of a penile prosthesis in 19 impotent diabetic and 15 nondiabetic patients. The functional status of penile cholinergic nerves was assessed by determining their ability to accumulate tritiated choline (34), and synthesize (34) and release (19) tritiated-acetylcholine after incubation of corporeal tissue with tritiated-choline (34). Tritiated-choline accumulation, and tritiated-acetylcholine synthesis and release were significantly reduced in the corporeal tissue from diabetic patients compared to that from nondiabetic patients (p less than 0.05). The impairment in acetylcholine synthesis worsened with the duration of diabetes (p less than 0.025). No differences in the parameters measured were found between insulin-dependent (11) and noninsulin-dependent (8) diabetic patients. The ability of the cholinergic nerves to synthesize acetylcholine could not be predicted clinically with sensory vibration perception threshold testing. It is concluded that there is a functional penile neuropathic condition of the cholinergic nerves in the corpus cavernosum of diabetic impotent patients that may be responsible for the erectile dysfunction.

Correlation of altered penile ultrastructure with clinical arterial evaluation

We investigated the ultrastructural changes in the penile erectile tissue from 32 consecutive patients who underwent penile prosthesis implantation. Because most of the patients had undergone papaverine injection with or without duplex ultrasonography, we compared these results with the electron microscopic findings. In patients with a good arterial response and full erection after papaverine injection the ultrastructural findings were similar to those reported in normal men. In patients with moderate arterial disease a distinct increase in mitochondria with aggregation and cytoplasmic vacuolization in smooth muscle cells was noted. These findings could be interpreted as an active cellular attempt to respond to the altered environmental and nutritive situation. In patients with severe arterial insufficiency the cellular structure was markedly altered, the number of intracavernous smooth muscle cells was reduced and the density of the connective tissue separating individual cells was increased. These changes in the smooth muscle cells consisted of contour irregularity with fragmentation and loss of the basal lamina. The cytoplasm was largely devoid of contractile elements. The nuclei tended to be pleomorphic with unevenly distributed chromatin. The endothelium was also altered significantly in this group. A careful clinical evaluation of penile arterial function should be performed in all patients undergoing penile arterial or venous corrective surgery. If doubt remains, a penile biopsy may be indicated.

Impaired neurogenic and endothelium-mediated relaxation of penile smooth muscle from diabetic men with impotence

Relaxation of the smooth muscle of the corpora cavernosa of the penis is necessary for penile erection. To determine the relation of impaired relaxation to impotence in diabetic patients, we performed an in vitro examination of corpus cavernosum tissue obtained at the time of implantation of a penile prosthesis in 21 diabetic and 42 nondiabetic men with impotence. Contraction was induced in isolated strips of corporal smooth muscle by norepinephrine; then relaxation was assessed with electrical stimulation of autonomic nerves and with the administration of three agents: acetylcholine, which is known to be mediated by endothelium-derived relaxing factor; papaverine; and sodium nitroprusside. The latter two act directly on smooth muscle (i.e., they are endothelium-independent). Autonomically mediated relaxation with electrical stimulation was less pronounced in the smooth muscle from diabetic men (n = 18) than in the smooth muscle from nondiabetic men (n = 24; P = 0.001). The degree of impairment increased with the duration of diabetes (r = 0.61, P = 0.007). Endothelium-dependent relaxation was also impaired, as evidenced by a lower degree of muscle relaxation after the administration of acetylcholine in the tissue from diabetic men (n = 16) than in that from nondiabetic men (n = 22; P = 0.001). The adverse effects of diabetes persisted after we controlled for smoking and hypertension. Endothelium-independent relaxation after the administration of nitroprusside and papaverine was similar in tissue from the diabetic and nondiabetic men. We conclude that diabetic men with impotence have impairment in both the autonomic and the endothelium-dependent mechanisms that mediate the relaxation of the smooth muscle of the corpora cavernosa. These findings may provide a rationale for the treatment of diabetic men with impotence by intracavernosal injection of vasodilators to induce endothelium-independent relaxation of the smooth muscle.