Causal association between antidiabetic drugs and erectile dysfunction: evidence from Mendelian randomization

Background

Antidiabetic drugs are widely used in clinical practice as essential drugs for the treatment of diabetes. The effect of hypoglycemic drugs on erectile dysfunction has not been fully proven due to the presence of multiple confounding factors.

Methods

Two-sample Mendelian randomization (TSMR) was used to examine the causal effect of antidiabetic drugs (including metformin, insulin and gliclazide) on erectile dysfunction. We used five robust analytic methods, of which the inverse variance weighting (IVW) method was the primary method, and also assessed factors such as sensitivity, pleiotropy, and heterogeneity. Effect statistics for exposures and outcomes were downloaded from publicly available data sets, including open Genome-Wide Association Studies (GWAS) and the UK Biobank (UKB).

Results

In some of the hypoglycemic drug use, there was a significant causal relationship between metformin use and erectile dysfunction [Beta: 4.9386; OR:1.396E+02 (95% CI:9.13-2135); p-value: 0.0004), suggesting that metformin increased the risk of erectile dysfunction development. Also, we saw that gliclazide use also increased the risk of erectile dysfunction [Beta: 11.7187; OR:0.0125 (95% CI:12.44-1.21E+09); P value: 0.0125). There was no significant causal relationship between insulin use and erectile dysfunction [Beta: 3.0730; OR:21.6071 (95% CI:0.24-1942.38); p-value: 0.1806).Leave-one-out, MR-Egger, and MR-PRESSO analyses produced consistent results.

Conclusion

The use of metformin and gliclazide have the potential to increase the risk of erectile dysfunction. There is no causal relationship between the use of insulin and erectile dysfunction.

Trigonella foenum-graecum L. and Psoralea corylifolia L. Improve Erectile Dysfunction in Streptozotocin-Induced Diabetic Rats through Suppression of Oxidative Stress

Background

Diabetes mellitus-induced erectile dysfunction (DMED) is one of the most common complications of diabetes and is mainly attributed to oxidative stress. Hu-Lu-Ba-Wan (HLBW) is a classic Chinese formulation consisting of Trigonella foenum-graecum L. (TFG) and Psoralea corylifolia L. (PC). HLBW has been used not only for the treatment of diabetes but also for the treatment of erectile dysfunction in clinics. This study aimed to explore the efficacy and underlying mechanism of HLBW in ameliorating erectile function in streptozotocin-induced diabetic rats.

Methods

The diabetic model was established by tail vein injection of streptozotocin (26 mg/kg), and then DMED rats screened by the apomorphine test were randomly divided into two groups: the model group and the HLBW group. The rats in the HLBW group were administered HLBW granules daily for 12 weeks. Fasting blood glucose and fasting insulin were tested by a commercial kit. Intracavernous pressure (ICP) and mean arterial pressure (MAP) were measured by cavernous nerve electrostimulation before the rats were killed. Erectile function was evaluated with ICP/MAP. The markers of oxidative stress in the corpus cavernosum (CC) were assayed by assay kits. Apoptosis in cavernosal tissue was detected by Western blotting (WB). The expression levels of vascular endothelial marker (vWF), α-smooth muscle actin (α-SMA), endothelial nitric oxide synthase (eNOS), and NADPH oxidase subunit P47^phox were determined by WB and PCR. Furthermore, the structure of the CC was further confirmed by Masson's trichrome staining.

Results

The results showed that HLBW significantly reduced blood glucose and increased insulin sensitivity. HLBW reduced oxidative stress and apoptosis. In addition, we observed that the expression levels of vWF, α-SMA, and eNOS as well as the ratio of smooth muscle to collagen increased in the HLBW group.

Conclusions

Our results demonstrated that HLBW could reduce oxidative stress damage in CC to improve diabetes mellitus-induced erectile dysfunction in rats by inhibiting NADPH oxidase.

Role of Glucose-Lowering Medications in Erectile Dysfunction

Erectile dysfunction (ED) is a long-term complication of type 2 diabetes (T2D) widely known to affect the quality of life. Several aspects of altered metabolism in individuals with T2D may help to compromise the penile vasculature structure and functions, thus exacerbating the imbalance between smooth muscle contractility and relaxation. Among these, advanced glycation end-products and reactive oxygen species derived from a hyperglycaemic state are known to accelerate endothelial dysfunction by lowering nitric oxide bioavailability, the essential stimulus of relaxation. Although several studies have explained the pathogenetic mechanisms involved in the generation of erectile failure, few studies to date have described the efficacy of glucose-lowering medications in the restoration of normal sexual activity. Herein, we will present current knowledge about the main starters of the pathophysiology of diabetic ED and explore the role of different anti-diabetes therapies in the potential remission of ED, highlighting specific pathways whose activation or inhibition could be fundamental for sexual care in a diabetes setting.

Erectile Dysfunction Is a Hallmark of Cardiovascular Disease: Unavoidable Matter of Fact or Opportunity to Improve Men's Health?

Erectile dysfunction (ED) is an early manifestation of cardiovascular (CV) disease. For this reason, men with ED should be carefully assessed for CV risk factors in order to prevent future major adverse CV events (MACE). Traditional risk factors are not found in all subjects at high CV risk. In fact, a relevant proportion of MACE occurs in men who are apparently risk factor free. In men with ED, it is important to take into account not only traditional risk factors but also unconventional ones. Several parameters that derive from good clinical assessment of subjects with ED have proven to be valuable predictors of MACE. These include family history of cardiometabolic events, alcohol abuse, fatherhood, decreased partner’s sexual interest, severe impairment in erection during intercourse or during masturbation, impaired fasting glucose, increased triglycerides, obesity even without metabolic complications, decreased penile blood flows or impaired response to an intra-cavernosal injection test. Recognizing these risk factors may help in identifying, among subjects with ED, those who merit stricter lifestyle or pharmacological interventions to minimize their CV risk. Effective correction of risk factors in ED men considered as high risk, besides reducing CV risk, is also able to improve erectile function.

Conflict processing networks: A directional analysis of stimulus-response compatibilities using MEG

The suppression of distracting information in order to focus on an actual cognitive goal is a key feature of executive functions. The use of brain imaging methods to investigate the underlying neurobiological brain activations that occur during conflict processing have demonstrated a strong involvement of the fronto-parietal attention network (FPAN). Surprisingly, the directional interconnections, their time courses and activations at different frequency bands remain to be elucidated, and thus, this constitutes the focus of this study. The shared information flow between brain areas of the FPAN is provided for frequency bands ranging from the theta to the lower gamma band (4–40 Hz). We employed an adaptation of the Simon task utilizing Magnetoencephalography (MEG). Granger causality was applied to investigate interconnections between the active brain regions, as well as their directionality. Following stimulus onset, the middle frontal precentral cortex and superior parietal cortex were significantly activated during conflict processing in a time window of between 300 to 600ms. Important differences in causality were found across frequency bands between processing of conflicting stimuli in the left as compared to the right visual hemifield. The exchange of information from and to the FPAN was most prominent in the beta band. Moreover, the anterior cingulate cortex and the anterior insula represented key areas for conflict monitoring, either by receiving input from other areas of the FPAN or by generating output themselves. This indicates that the salience network is at least partly involved in processing conflict information. The present study provides detailed insights into the underlying neural mechanisms of the FPAN, especially regarding its temporal characteristics and directional interconnections.

Comparison of Improving Effects for Diabetic Erectile Dysfunction according to the Anti-Glycemic Agents: Phlorizin and Insulin

Purpose

To compare the improving effects of diabetic erectile dysfunction with two anti-glycemic agents; phlorizin and insulin.

Materials and Methods

Sixty Sprague-Dawley rats were divided into four groups (n=15 in each group): normal control (C), untreated diabetic rats (D), and diabetic rats treated by phlorizin (P) or insulin (I). Ten weeks after the diabetic induction using an injection of streptozotocin (55 mg/kg), four weeks of diabetic control was conducted. Erectile response, Western blot, and immunohistochemistry were assessed.

Results

During the experiment, the C-group showed continuous weight gain, while the other groups suffered from weight loss. After start of diabetic control, the body weight of I-group was increased; whereas, there was no meaningful change in the P-group. Meanwhile, comparable blood glucose levels were achieved in the P- and I-groups. The erectile response was markedly decreased in the D-group, whereas the P- and I-groups were similar as good as the C-group. In addition, D-group showed the significant decrease in the cavernosal smooth muscle content and increased apoptosis. Platelet endothelial cell adhesion molecule-1 protein expression, phosphorylation of endothelial nitric oxide synthase and myosin phosphatase target subunit 1 were significantly distorted in the D-group, while the P- and I-groups were comparable with the C-group.

Conclusions

Phlorizin treatment resulted in the improvement of erectile function as same as insulin despite the lack of anabolic weight gains. These results suggest that control of blood glucose level rather than a type of anti-glycemic agents is more important for the prevention and treatment of diabetic erectile dysfunction

Islet transplantation improved penile tissue fibrosis in a rat model of type 1 diabetes

BACKGROUND

Glycaemic control is one of the most effective strategies for the treatment of diabetes-related erectile dysfunction (DMED). Compared to conventional anti-diabetic drugs and insulin, islet transplantation is more effective in the treatment of diabetic complications. The aim of this study was to investigate the efficacy of islet transplantation for reversing advanced-stage DMED in rats and to observe its influence on corpus cavernosum fibrosis.

METHODS

Wistar rats were intraperitoneally injected with streptozotocin to establish a diabetes model. After 12 weeks, the rats were divided into 4 groups: diabetic, insulin, islet transplantation, and normal control. Following supplementation, the changes in blood glucose and weight were determined sequentially. Penile erectile function was evaluated by apomorphine experiments in the fourth week, and the penile corpus cavernosum was also collected for assessment by Masson staining, immunohistochemistry and Western blot to observe the spongy tissue and the related cellular changes at the molecular level.

RESULTS

Islet transplantation significantly ameliorated penile erectile function in advanced-stage diabetic rats. The ratio of corpus cavernosum smooth muscle cells to fibroblasts and the expression level of α-SMA in the islet transplantation group were significantly higher than those in the diabetic and insulin groups. In addition, the expression levels of TGF-β1, p-Samd2, and connective tissue growth factor (CTGF) in the islet transplantation and insulin groups were much lower than those in the diabetic group, while those in the islet transplantation group were significantly lower than those in the insulin group.

CONCLUSIONS

Our findings strongly suggest that islet transplantation can promote the regeneration of smooth muscle cells and ameliorate corpus cavernosum fibrosis to restore its normal structure in advanced-stage diabetic rats. The possible mechanism of ameliorating corpus cavernosum fibrosis by islet transplantation may be associated with improvement of the hyperglycaemic status in diabetic rats, thereby inhibiting the TGF-β1/Samd2/CTGF pathway.

Penile alterations at early stage of type 1 diabetes in rats

Objective

Diabetes affects the erectile function significantly. However, the penile alterations in the early stage of diabetes in experimental animal models have not been well studied. We examined the changes of the penis and its main erectile components in diabetic rats.

Materials and methods

Male Sprague-Dawley rats were divided into 2 groups: streptozotocin (STZ)-induced diabetics and age-matched controls. Three or nine weeks after diabetes induction, the penis was removed for immunohistochemical staining of smooth muscle and neuronal nitric oxide synthase (nNOS) in midshaft penile tissues. The cross-sectional areas of the whole midshaft penis and the corpora cavernosa were quantified. The smooth muscle in the corpora cavernosa and nNOS in the dorsal nerves were quantified.

Results

The weight, but not the length, of the penis was lower in diabetics. The cross-sectional areas of the total midshaft penis and the corpora cavernosa were lower in diabetic rats compared with controls 9 weeks, but not 3 weeks after diabetes induction. The cross-sectional area of smooth muscle in the corpora cavernosa as percentage of the overall area of the corpora cavernosa was lower in diabetic rats than in controls 9 weeks, but not 3 weeks after diabetes induction. Percentage change of nNOS in dorsal nerves was similar at 3 weeks, and has a decreased trend at 9 weeks in diabetic rats compared with controls.

Conclusions

Diabetes causes temporal alterations in the penis, and the significant changes in STZ rat model begin 3-9 weeks after induction. Further studies on the reversibility of the observed changes are warranted.

Translational Perspective on the Role of Testosterone in Sexual Function and Dysfunction

INTRODUCTION

The biological importance of testosterone is generally accepted by the medical community; however, controversy focuses on its relevance to sexual function and the sexual response, and our understanding of the extent of its role in this area is evolving.

AIM

To provide scientific evidence examining the role of testosterone at the cellular and molecular levels as it pertains to normal erectile physiology and the development of erectile dysfunction and to assist in guiding successful therapeutic interventions for androgen-dependent sexual dysfunction.

METHODS

In this White Paper, the Basic Science Committee of the Sexual Medicine Society of North America assessed the current basic science literature examining the role of testosterone in sexual function and dysfunction.

RESULTS

Testosterone plays an important role in sexual function through multiple processes: physiologic (stimulates activity of nitric oxide synthase), developmental (establishes and maintains the structural and functional integrity of the penis), neural (development, maintenance, function, and plasticity of the cavernous nerve and pelvic ganglia), therapeutically for dysfunctional regulation (beneficial effect on aging, diabetes, and prostatectomy), and phosphodiesterase type 5 inhibition (testosterone supplement to counteract phosphodiesterase type 5 inhibitor resistance).

CONCLUSION

Despite controversies concerning testosterone with regard to sexual function, basic science studies provide incontrovertible evidence for a significant role of testosterone in sexual function and suggest that properly administered testosterone therapy is potentially advantageous for treating male sexual dysfunction.

Chronic administration of atorvastatin could partially ameliorate erectile function in streptozotocin-induced diabetic rats

The efficacy of statins is related to the ‘common soil’ hypothesis, which proposes oxidative stress and inflammation as main pathophysiologic processes in the disease group of diabetes and endothelial dysfunction. This study evaluated the recovery of erectile function after administration of chronic statin alone in streptozotocin (STZ)-induced diabetes mellitus (DM) rats, focusing on the anti-oxidative effects and consequentially recuperated endothelial function. A total of 45 male Sprague-Dawley rats (8 weeks old) were divided into three groups (n = 15 each): an age-matched normal control group (Control group), an uncontrolled DM group (DM group), and a statin-treated group (Statin group). The rats in the DM and Statin group received an injection of STZ (60 mg/kg). Beginning 10 weeks after the establishment of DM, the Statin group received daily treatment with atorvastatin (10 mg/kg) via oral gavage for four weeks. After 14 weeks, the results of the experiment were evaluated. The ratios of intracavernosal pressure (ICP) to mean arterial pressure (MAP) were recorded with cavernosometry (20 Hz, 3 V, 0.2 msec for 30 seconds) before and after the intravenous administration of udenafil (1 mg/kg). Expression of alpha-smooth muscle actin (α-SMA) was evaluated using cavernosal tissue. In addition, changes in RhoA translocation ratio and myosin phosphatase target subunit 1 (MYPT1) phosphorylation were evaluated with western blot. Superoxide dismutase (SOD) and malondialdehyde (MDA) levels were also analyzed as measurements of oxidative stress levels. The ICP/MAP and area under the curve (AUC)/MAP ratios of the Statin group were obviously superior to the DM group, but were not comparable to the Control group (P<0.001). The level of oxidative stress, namely SOD activity, was also significantly lower in the Statin group than in the DM group (P = 0.015), and was comparable to the Control group. In contrast, MDA levels were not considerably different among the groups (P = 0.217). The RhoA translocation ratio was not significantly different among the groups (P = 0.668), whereas MYPT1 phosphorylation in the Statin group was significantly lower than in the DM group (P = 0.030), and similar to the Control group. Expression of α-SMA in the Statin group was higher than in the DM group (P<0.001), and comparable to the Control group. Chronic statin treatment alone showed anti-oxidative effects and helped to restore the erectile mechanism, but did not lead to the full recovery of erectile function in STZ-induced DM rats. Therefore, combination therapy rather than a single agent should be the preferred treatment strategy for DM-associated erectile dysfunction, especially in the setting of severe diabetes.

Prevalence of Sexual Dysfunction and Associated Risk Factors in Middle-Aged and Elderly Korean Men in Primary Care

Although several studies have individually investigated the risk factors for erectile dysfunction (ED), premature ejaculation (PE), and late-onset hypogonadism (LOH), few studies have considered ED, PE, and LOH as categories of sexual dysfunction (SD) within the same population. We therefore aimed to investigate the prevalence of SD and its associated risk factors among men in primary care. Study participants were enrolled by 18 family physicians from 15 hospital-based family practices in Korea between August 2010 and May 2011. Participants answered a questionnaire regarding their demographic characteristics and lifestyle factors as well as the Korean versions of the Androgen Deficiency in the Aging Male, the International Index of Erectile Function, and the Premature Ejaculation Diagnostic Tool questionnaires. SD prevalence was 64.9% among study participants who were ≥ 40 years of age. ED prevalence was 43.7%, PE prevalence was 38.6%, and LOH prevalence was 16.8%. SD prevalence was significantly associated with increased age, overweight, hypertension, diabetes, and depression. These findings highlight the importance of screening questions for SD in primary care, especially among older male patients with the identified risk factors.

Effects of the start time of glycemic control on erectile function in streptozotocin-induced diabetic rats

Diabetes-induced ED correlates with diabetes duration and glycemic control. This study evaluated the effect of glycemic control start time on erectile function in streptozotocin-induced diabetic rats. Rats were divided into normal controls (C); untreated diabetic rats (DM); and rats treated after 7 weeks (7W), and 10 weeks (10W) from DM. Treated diabetic rats received a timed daily injection of insulin. After 14 weeks of lab-controlled diabetes, experiments were performed. Group DM showed the ratio of intracavernosal pressure, significantly lower than other groups (10W vs DM; P<0.001). Groups 7W and 10W responded similarly, but did not recover to normal level (group C vs 7W; P<0.001). The percentage of α-smooth muscle actin increased more with earlier start times, and group DM's percentages decreased significantly (group 10W vs DM; P<0.001). Apoptosis recovered significantly only in group 7W, comparable to group C. As start times became earlier, for all molecules (eNOS, Akt, MYPT1 and PECAM-1), treatment groups' results neared those of group C. In conclusion, erectile function of diabetic rats recovered closer to normal controls if diabetic treatment started earlier. And the level of glycemic control was expected to be more important than the start time of diabetic treatment.

Improvement of erectile dysfunction by the active pepide from Urechis unicinctus by high temperature/pressure and ultra - wave assisted lysis in Streptozotocin Induced Diabetic Rats

Introduction:

We investigate the effect of active peptide from Urechis unicinctus (UU) by high temperature/pressure and ultra-wave assisted lysis on erectile dysfunction in streptozotocin-induced diabetic rats.

Materials and Methods:

Forty 12-week-old Sprague-Dawley rats were used in this study. Diabetes was induced by a one-time intraperitoneal injection of streptozotocin (50mg/kg). One week later, the diabetic rats were randomly divided into four groups: normal control, untreated diabetes control, and groups treated with 100 or 500mg/kg/d UU peptide. Rats were fed with UU peptide by intragastric administration for 8 weeks. After 8 weeks, penile hemodynamic function was evaluated in all groups by measuring the intracavernosal pressure after electrostimulating the cavernous nerve. Nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) activities were measured and endothelial nitric oxide synthase (eNOS) and neuronal NOS (nNOS) protein expression was determined by Western blot.

Results:

Maximum intracavernosal pressure in diabetic control rats decreased significantly compared to normal control rats, and was increased significantly compared to untreated diabetic rats after UU peptide supplementation. Treatment with the higher dose of UU peptide significantly increased the NO and cGMP levels compared with the diabetic control group. Decreased activity and expression eNOS and nNOS were found in the diabetic rats compared with the normal control group. Decreased eNOS and nNOS in diabetic rats were improved by UU peptide administration.

Conclusions:

Active peptide from UU ameliorates erectile function in a streptozotocin induced diabetic rat model of erectile dysfunction.

Penile Dimensions of Diabetic and Nondiabetic Men With Erectile Dysfunction: A Case-Control Study

This study aimed to report penile dimensions in diabetic and nondiabetic men with erectile dysfunction (ED) and correlate their dimensions with other study variables. A case-control study was designed through retrospective data analysis of diabetic and nondiabetic patients consulting for ED and a control group ( n = 105, each group). Study data retrieved included history, clinical evaluation, and penile dimensions (pendulous length [PL], total length [TL], and circumference [CF]) at flaccid and erect states. Results identified that patients had lower values (mean, cm) for almost all penile dimensions. The diabetic patients identified significant differences in most dimensions, whether in flaccid (PL: 7.46 vs. 7.51 and 7.81, p = .11; TL: 11.8 vs. 12.77 and 12.88, p = .000; CF: 8.84 vs. 9.1 and 9.14, p = .016) or erect state (PL: 9.66 vs. 9.61 and 10, p = .092; TL: 13.96 vs. 14.88 and 15.04, p = .000; CF: 11.56 vs. 12.06 and 11.92, p = .018) as compared with the nondiabetic patients and controls, respectively. No significant correlation was detected between the dimensions and age, durations of diabetes and ED, or erectile function scores. In conclusion, diabetic and nondiabetic patients with ED presented, in varying degrees, significant decline in their penile dimensions, and this was more prevalent in diabetic patients. As changes in penile size could be a silent corollary of comorbidities, monitoring the changes in penile dimensions should be an important component of the clinical checkup of any patient with ED, especially a diabetic patient.

Involvement of Rho-Kinase/LIM Kinase/Cofilin Signaling Pathway in Corporal Fibrosis after Cavernous Nerve Injury in Male Rats

INTRODUCTION

The molecular mechanism of corporal fibrosis leading to erectile dysfunction (ED) following cavernous nerve (CN) injury is poorly understood.

AIM

To determine whether the LIMK2/cofilin pathway, the downstream effectors of ROCK1, was involved in ED and corporal fibrosis following bilateral CN injury in male rats.

METHODS

Forty-eight 10-week-old male Sprague-Dawley rats were equally divided into three groups: sham surgery (S); bilateral CN crush injury (I); and bilateral CN resection (R). Within each groups, two subgroups were analyzed at 1 and 4 weeks postoperatively.

MAIN OUTCOME MEASURES

Electrostimulation was performed to assess erectile function by the ratio of maximal intracavernous pressure to mean arterial pressure (ICP/MAP) and areas under the ICP curve to MAP (AUC/MAP). Penile tissue was processed for Masson's trichrome staining, Western blot (ROCK1, total LIMK2, phospho-LIMK2, total cofilin, phospho-cofilin), immunohistochemistry (alpha-SM actin [α-SMA]), and double immunofluorescent staining (ROCK1, phospho-LIMK2, vimentin).

RESULTS

At each time point, both I and R groups showed a significantly lower percent of ICP/MAP and AUC, and decreased SM cell/collagen ratio and expression of α-SMA than S group. Densitometry revealed a significantly higher expression of ROCK1 in I and R groups compared with S group at all time points. The LIMK2 phosphorylation in I and R groups significantly increased at 1 week, but not at 4 weeks. The cofilin phosphorylation in R group significantly increased to that in S group starting at 1 week, while that in I group was increased significantly at 4 weeks. The double immunofluorescent staining noted that coexpression of vimentin with ROCK1 or phospho-LIMK2 in I and R groups was significantly increased mainly in the subtunical area at 1 week but not at 4 weeks.

CONCLUSIONS

The ROCK1/LIMK2/cofilin pathway may be involved in ED related to corporal fibrosis, and it appears to be functional particularly in the early period after CN injury.

Antioxidant icariside II combined with insulin restores erectile function in streptozotocin-induced type 1 diabetic rats

Erectile dysfunction (ED) worsens in patients with diabetes mellitus (DM) despite good control of blood glucose level with insulin. Recent studies imply that diabetic vascular stresses (e.g. oxidative stress) persist in spite of glucose normalization, which is defined as metabolic memory. Studies suggest that the interaction between advanced glycation end products (AGEs) and their receptor (RAGE) mediates the development of metabolic memory. To investigate the effects of the antioxidant icariside II plus insulin on erectile function in streptozotocin (STZ)- induced type 1 diabetic rats. Fifty 8-week-old Sprague-Dawley rats were randomly distributed into five groups: normal control, diabetic, insulin-treated diabetic, icariside II-treated diabetic, and insulin plus icariside II-treated diabetic. Diabetes was induced by a single intraperitoneal injection of STZ. Eight weeks after induction of diabetes, icariside II was administered by gastric lavage once a day (5 mg/kg) for 6 weeks; and 2-6 units of intermediate-acting insulin were given to maintain normal glycemia for 6 weeks. The main outcome measures were the ratio of intracavernous pressure (ICP) to mean arterial pressure (MAP); histology of penile endothelial cells and smooth muscle cells; neural nitric oxide synthase, AGEs and RAGE expression; malondialdehyde concentration; superoxide dismutase activity; and apoptosis index. Diabetic rats demonstrated a significantly lower ICP/MAP ratio, reduced penile endothelial cells, reduced smooth muscle cells, increased AGEs and RAGE, and increased apoptosis. Insulin and icariside II monotherapy partially restored erectile function and histological changes. However, the combination therapy group showed significantly better erectile parameters, cytological components and biochemistry, similar to those in the normal control group. These results suggest that, although insulin can effectively control glycemic levels, it does not completely alter the pathological changes in erectile tissues. Better efficacy could be expected with tight glycemic control plus the antioxidant icariside II. The proposed combination therapy might have the potential to eliminate metabolic memory by down-regulating the AGEs-RAGE-oxidative stress axis.

S-allyl cysteine restores erectile function through inhibition of reactive oxygen species generation in diabetic rats

Excessive production of reactive oxygen species (ROS) by an overactive nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system in penile tissue is an important mechanism of erectile dysfunction (ED). S-allyl cysteine (SAC), a bioactive component derived from garlic, was recently reported to exert versatile antioxidant properties. We hypothesized that SAC would be able to resolve diabetes-related ED by reducing ROS generation, and designed this study to investigate this possibility as well as to determine the related underlying mechanisms. A streptozotocin-induced diabetes rat model was established and used for comparative analysis of 4-week treatment regimens with insulin or SAC. The ratio of maximal intracavernous pressure (ICP) to mean arterial blood pressure (MAP) was measured to determine erectile function. Differential levels of ROS, NADPH oxidase subunits, nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signalling pathway, and apoptosis were evaluated in cavernous tissues. Max ICP/MAP was found to be markedly decreased in untreated diabetic rats; SAC, but not insulin, treatment restored the ratio to baseline (in non-diabetic untreated controls). The corpus cavernosum of untreated diabetic rats showed increased p47(phox) and p67(phox) expression, ROS production and penile apoptotic index, and decreased phospho-endothelial nitric oxide synthase (phospho-eNOS, Ser1177) expression, cGMP concentration, B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax) ratio and smooth muscle cell number. SAC treatment normalized all the diabetes-induced effects, whereas insulin treatment partially normalized the alterations, but produced no effects on P47(phox) expression, penile ROS level, apoptotic index, Bcl-2/Bax ratio and smooth muscle cell number. Collectively, these data indicate that SAC treatment can restore erectile function in diabetic rats by preventing ROS formation through modulation of NADPH oxidase subunit expression. Furthermore, the poor efficacy of conventional insulin treatment for diabetic ED may be associated with an elevated level of ROS in penile tissue.