TNF-alpha infusion impairs corpora cavernosa reactivity

The pathogenic role of the immune system in erectile dysfunction and Peyronie's disease: focusing on immunopathophysiology and potential therapeutic strategies

INTRODUCTION

Erectile dysfunction (ED) represents the major cause of male sexual dysfunction, which is often associated with obesity, diabetes mellitus, atherosclerotic cardiovascular disease, and cigarette smoking. Peyronie's disease is a chronic disorder associated with irreversible fibrotic damage of the tunica albuginea leading to ED, painful erection, coital disturbance, and physical and social complaints. Both conditions are characterized by chronic inflammation, oxidative stress, and significant changes in intracavernous hydrodynamics. In this scenario, oxidized lipoproteins, M1-polarized macrophages, proinflammatory cytokines (such as the tumor necrosis factor α), endothelial nitric oxide synthase, penile smooth muscle cells, and toll-like receptors represent the main triggers of the inflammatory process in ED. Phosphodiesterase-5 inhibitors are the most common treatment for ED. This treatment is used intermittently, as it is conceived as a symptomatic and not curative therapy. Moreover, not all patients respond to phosphodiesterase-5 inhibitors (35%-85%), particularly those with dysmetabolic phenotypes. Additional or alternative treatments are therefore desirable, mostly in refractory cases.

OBJECTIVES

In this review, we describe the immune-mediated pathogenesis of ED and Peyronie's disease (PD). In our literature search we placed particular emphasis on potentially practical therapeutic approaches, including natural products (such as polyphenols), due to their anti-inflammatory and antioxidant activities, stem cell therapy, and platelet-derived preparations.

METHODS

We searched PubMed/MEDLINE, Web of Science, Scopus, Cochrane Library, Google Scholar, and institutional websites. Original studies, narrative reviews, systematic reviews, and meta-analyses written in English were searched, screened, and selected.

RESULTS

In animal models of ED and PD, therapeutic approaches, including anti-inflammatory and antioxidant agents, stem cell therapy, and platelet-derived preparations, have provided positive results, including improved penile function, reduced inflammation and oxidative stress, and promotion of tissue repair. However, clinical evidence of improvement in human patients is still insufficient.

CONCLUSION

Promising results for treating ED and PD have been shown in preclinical and pilot clinical studies, but specific clinical trials are needed to validate the efficacy of these therapeutic approaches in men with ED.

Macrophage-Specific Toll Like Receptor 9 (TLR9) Causes Corpus Cavernosum Dysfunction in Mice Fed a High Fat Diet

BACKGROUND

Erectile dysfunction (ED) has been shown to be related with inflammatory markers in humans. Chronic infusion of TNF-α caused ED in mice while TNF-α knockout mice exhibited improvement in the relaxation of the corpus cavernosum (CC).

AIM

Since obesity triggers an inflammatory process, we aimed to investigate the hypothesis that in obesity, Toll-like receptor 9 (TLR9) activation leads to increased TNF-α levels and impairment in CC reactivity.

METHODS

Four-week old male C57BL6 (WT) and TLR9 mutant (TLR9_MUT) mice were fed a standard chow or high fat diet (HFD) for 12 weeks. Body weight and nonfasting blood glucose were analyzed. Contractile and relaxation responses of the CC were evaluated by electrical field stimulation and concentration response curves to phenylephrine and acetylcholine. Protein expression of nNOS, TNF-α, TNF-R1, TLR9 and MyD88 were measured by western blot. Plasma levels of TNF-α were measured by ELISA.

OUTCOME

In obesity, impaired cavernosal relaxation is associated with the activation of the innate immune system, by increasing the production of TNF-α through the activation of TLR9 in the macrophages.

RESULTS

After 12 weeks of HFD both WT and TLR9_MUT mice had increased body weight and nonfasting blood glucose compared to standard chow. In the CC, acetylcholine-induced relaxation was not changed. A trend to increased contraction to phenylephrine and KCl was seen in WT HFD only. electrical field stimulation-induced relaxation of the CC was decreased in WT HFD as well as nNOS expression in the CC of WT HFD, but not in TLR9_MUT HFD. In the CC, protein expression of TLR9 and MyD88 was similar in all groups. While circulating levels of TNF-α presented only a trend to increase in mice fed HFD, the CC expression of TNF-α was increased only in WT HFD mice.

CLINICAL TRANSLATION

The innate immune system can be a target for the treatment of erectile complications in obesity.

STRENGTHS AND LIMITATIONS

This is the first study demonstrating that activation of TLR9 expressed in macrophages leads to impaired cavernosal relaxation. The main limitation of the study is the lack of understanding about the source/expression of the macrophages in the cavernous tissue. Further, herein, the experiments were performed only in isolated cavernous tissue (in vitro), thus the lack of knowledge on how the TLR9 modulates the in vivo response of the erectile tissue is another limitation of this study.

CONCLUSION

Our findings indicate that CC dysfunction observed in obesity is at least in part mediated by the production of TNF-α upon activation of TLR9 expressed in the macrophages. Priviero F, Calmasini F, Dela Justina V, et al. Macrophage-Specific Toll Like Receptor 9 (TLR9) Causes Corpus Cavernosum Dysfunction in Mice Fed a High Fat Diet. J Sex Med 2021;18:723-731.

Hypertension and Erectile Dysfunction: Breaking Down the Challenges

A diagnostic of hypertension increases the risk of erectile dysfunction (ED); likewise, ED can be an early sign of hypertension. In both cases, there is evidence that endothelial dysfunction is a common link between the 2 conditions. During hypertension, the sustained and widespread release of procontractile factors (e.g., angiotensin II, endothelin 1, and aldosterone) impairs the balance between vasoconstrictors and vasodilators and, in turn, detrimentally impacts vascular and erectile structures. This prohypertensive state associates with an enhancement in the generation of reactive oxygen species, which is not compensated by internal antioxidant mechanisms. Recently, the innate immune system, mainly via Toll-like receptor 4, has also been shown to actively contribute to the pathophysiology of hypertension and ED not only by inducing oxidative stress but also by sustaining a low-grade inflammatory state. Furthermore, some drugs used to treat hypertension can cause ED and, consequently, reduce compliance with the prescribed pharmacotherapy. To break down these challenges, in this review, we focus on discussing the well-established as well as the emerging mechanisms linking hypertension and ED with an emphasis on the signaling network of the vasculature and corpora cavernosa, the vascular-like structure of the penis.

The Inflammation Network in the Pathogenesis of Erectile Dysfunction: Attractive Potential Therapeutic Targets

BACKGROUND

Erectile dysfunction (ED) is an evolving health problem in the aging male population. Chronic low-grade inflammation is a critical component of ED pathogenesis and a probable intermediate stage of endothelial dysfunction, especially in metabolic diseases, with the inclusion of obesity, metabolic syndrome, and diabetes.

OBJECTIVE

This review will present an overview of preclinical and clinical data regarding common inflammatory mechanisms involved in the pathogenesis of ED associated with metabolic diseases and the effect of antiinflammatory drugs on ED.

METHODS

A literature search of existing pre-clinical and clinical studies was performed on databases [Pubmed (MEDLINE), Scopus, and Embase] from January 2000 to October 2019.

RESULTS

Low-grade inflammation is a possible pathological role in endothelial dysfunction as a consequence of ED and other related metabolic diseases. Increased inflammation and endothelial/prothrombotic markers can be associated with the presence and degree of ED. Pharmacological therapy and modification of lifestyle and risk factors may have a significant role in the recovery of erectile response through reduction of inflammatory marker levels.

CONCLUSION

Inflammation is the least common denominator in the pathology of ED and metabolic disorders. The inflammatory process of ED includes a shift in the complex interactions of cytokines, chemokines, and adhesion molecules. These data have established that anti-inflammatory agents could be used as a therapeutic opportunity in the prevention and treatment of ED. Further research on inflammation-related mechanisms underlying ED and the effect of therapeutic strategies aimed at reducing inflammation is required for a better understanding of the pathogenesis and successful management of ED.

Interactions between inflammation and female sexual desire and arousal function

PURPOSE OF REVIEW

To describe the current state of research on interactions between inflammation and female sexual function.

RECENT FINDINGS

Inflammation may interfere with female sexual desire and arousal via direct (neural) and indirect (endocrine, vascular, social/behavioral) pathways. There are significant sex differences in the effect of inflammation on sexual function, arising from different evolutionary selection pressures on regulation of reproduction. A variety of inflammation-related conditions are associated with risk of female sexual dysfunction, including cardiovascular disease, metabolic syndrome, and chronic pain.

SUMMARY

Clinical implications include the need for routine assessment for sexual dysfunction in patients with inflammation-related conditions, the potential for anti-inflammatory diets to improve sexual desire and arousal function, and consideration of chronic inflammation as moderator of sexual effects of hormonal treatments. Although the evidence points to a role for inflammation in the development and maintenance of female sexual dysfunction, the precise nature of these associations remains unclear.

The inflammasome NLRP3 plays a dual role on mouse corpora cavernosa relaxation

NLRP3 plays a role in vascular diseases. Corpora cavernosa (CC) is an extension of the vasculature. We hypothesize that NLRP3 plays a deleterious role in CC relaxation. Male C57BL/6 (WT) and NLRP3 deficient (NLRP3^−/−) mice were used. Intracavernosal pressure (ICP/MAP) measurement was performed. Functional responses were obtained from CC strips of WT and NLRP3^−/− mice before and after MCC950 (NLRP3 inhibitor) or LPS + ATP (NLRP3 stimulation). NLRP3, caspase-1, IL-1β, eNOS, nNOS, guanylyl cyclase-β1 (GCβ1) and PKG1 protein expressions were determined. ICP/MAP and sodium nitroprusside (SNP)-induced relaxation in CC were decreased in NLRP3^−/− mice. Caspase-1, IL-1β and eNOS activity were increased, but PKG1 was reduced in CC of NLRP3^−/−. MCC950 decreased non-adrenergic non-cholinergic (NANC), acetylcholine (ACh), and SNP-induced relaxation in WT mice. MCC950 did not alter NLRP3, caspase-1 and IL-1β, but reduced GCβ1 expression. Although LPS + ATP decreased ACh- and SNP-, it increased NANC-induced relaxation in CC from WT, but not from NLRP3^−/− mice. LPS + ATP increased NLRP3, caspase-1 and interleukin-1β (IL-1β). Conversely, it reduced eNOS activity and GCβ1 expression. NLRP3 plays a dual role in CC relaxation, with its inhibition leading to impairment of nitric oxide-mediated relaxation, while its activation by LPS + ATP causes decreased CC sensitivity to NO and endothelium-dependent relaxation.

Impact of Immune System Activation and Vascular Impairment on Male and Female Sexual Dysfunction

INTRODUCTION

Male and female sexual dysfunction (SD) is considered a multifactorial condition. Numerous studies have shown the involvement of inflammatory processes in this pathological condition. Sexual intercourse requires healthy and functioning vessels to supply the pelvic region in both males and females, generating penile erection and clitoral and vaginal lubrication, respectively. Cardiovascular diseases and associated risk factors may contribute negatively to pelvic blood flow, possibly through immune system activation.

AIM

The study aimed to address the correlation between vascular inflammation driven by immune system activation and SD in males and females.

METHODS

A literature review was performed to identify articles addressing male and female SD and vascular inflammation. Key words included "male and female sexual dysfunction," "vascular inflammation," "iliac and pudendal arteries dysfunction," "genitourinary tract," and "blood flow."

MAIN OUTCOME MEASURES

Management of systemic and local inflammation may be a useful alternative to improve SD and reduce the risk of cardiovascular diseases in the future.

RESULTS

Increased levels of cytokines and chemokines have been detected in humans and animals with hypertension, obesity, and diabetic conditions. Chronic activation of the innate immune system, especially by pathogen- or damage-associated molecular patterns, and metabolic-related disorders may act as triggers further contributing to an increased inflammatory condition. Due to the reduced size of vessels, SD and retinal vascular impairments have been shown to be predictive factors for cardiovascular diseases. Therefore, considering that blood flow to the genitalia is essential for sexual function, endothelial dysfunction and vascular remodeling, secondary to chronic immune system activation, may be implicated in male and female vasculogenic SD.

CONCLUSIONS

Several conditions appear to play a role in SD. In the present review, we have identified a role for the immune system in generating vascular and tissue impairments contributing to erectile dysfunction and female SD. Calmasini FB, Klee N, Webb RC, et al. Impact of Immune System Activation and Vascular Impairment on Male and Female Sexual Dysfunction. Sex Med Rev 2019;7:604-613.

Decreased expression of pigment epithelium-derived factor within the penile tissues contributes to erectile dysfunction in diabetic rats

Increased production of reactive oxygen species (ROS) and inflammation are major contributors to the development and progression of diabetes-associated erectile dysfunction (DMED). As an endogenous antioxidant and anti-inflammatory factor, the potential implication of pigment epithelium-derived factor (PEDF) in DMED has not been revealed. To assess the potential antioxidant and anti-inflammatory functions of PEDF in DMED, we first demonstrated that PEDF was significantly decreased at the levels of the mRNA and protein in the penis of diabetic rats compared with normal controls. To test the hypothesis that decreased the penile levels of PEDF are associated with oxidative stress and inflammation in DMED, an adenovirus expressing PEDF (Ad-PEDF) or the same titer of control virus (Ad-GFP) was intracavernously administered at 2 weeks after diabetic onset. After 6 weeks of treatment, we found that administration of Ad-PEDF could significantly increase erectile response to cavernosal nerve stimulation in the diabetic rats by restoring the endothelial NO synthase (eNOS), P-eNOS, and neuronal NO synthase (nNOS) protein levels to the standard levels represented in normal rats and by suppressing the levels of tumor necrosis factor-α (TNF-α) and oxidative stress. In conclusion, the present data indicated that the antioxidant and anti-inflammatory potential of PEDF plays important role in restoring erectile function by the inhibition of oxidative stress and TNF-α production.

Depression induced by chronic stress leads to penile cavernosal dysfunction: protective effect of anti-TNF-α treatment

Psychological stress may lead to erectile dysfunction (ED), and inflammation has been evaluated as a major contributing factor. The goal of this study was to investigate the effects of etanercept (ETN), an anti-tumor necrosis factor α (TNF-α) protein, on cavernosal function in the unpredictable chronic mild stress (UCMS) rat model of depression. Animals were divided into 4 groups: animals not exposed to UCMS, animals not exposed to UCMS and treated with ETN, animals exposed to UCMS, and animals treated with ETN while exposed to UCMS. UCMS significantly impaired the neurogenic and endothelium-dependent relaxation responses; reduced cavernosal endothelial nitric oxide (NO) synthase (eNOS) and neuronal NO synthase (nNOS) expressions; decreased testosterone levels; enhanced systemic levels of corticosterone, TNF-α, interleukin 1β (IL-1β), interleukin 6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and intercellular adhesion molecule 1 (ICAM-1); and also increased cavernosal levels of TNF-α, IL-1β, and IL-6 in rats. ETN administration restored NO-mediated neurogenic and endothelium-dependent relaxation responses of the corpus cavernosum, increased cavernosal eNOS and nNOS expressions, enhanced testosterone levels, and decreased corticosterone levels in UCMS-exposed rats. Also, systemic inflammatory markers and cavernosal proinflammatory cytokine levels were reduced by ETN. Our results demonstrate the role of TNF-α-mediated inflammation in the development of depression and ED in rats exposed to chronic stress.

Obesity and Erectile Dysfunction: From Bench to Clinical Implication

Obesity is a major public health issue worldwide and is frequently associated with erectile dysfunction (ED). Both conditions may share an internal pathologic environment, also known as common soil. Their main pathophysiologic processes are oxidative stress, inflammation, and resultant insulin and leptin resistance. Moreover, the severity of ED is correlated with comorbid medical conditions, including obesity. Therefore, amelioration of these comorbidities may increase the efficacy of ED treatment with phosphodiesterase 5 inhibitors, the first-line medication for patients with ED. Although metformin was originally developed as an insulin sensitizer six decades ago, it has also been shown to improve leptin resistance. In addition, metformin has been reported to reduce oxidative stress, inflammatory response, and body weight, as well as improve ED, in animal and human studies. Moreover, administration of a combination of metformin and phosphodiesterase 5 inhibitors improves erectile function in patients with ED who have a poor response to sildenafil and are insulin resistant. Thus, concomitant treatment of metabolic derangements associated with obesity in patients with ED who are obese would improve the efficacy and reduce the refractory response to penile vasodilators. In this review, we discuss the connecting factors between obesity and ED and the possible combined treatment modalities.

Aldosterone induces inflammatory cytokines in penile corpus cavernosum by activating the NF-κB pathway

Emerging evidence indicates that aldosterone and mineralocorticoid receptors (MRs) are associated with the pathogenesis of erectile dysfunction. However, the molecular mechanisms remain largely unknown. In this study, freshly isolated penile corpus cavernosum tissue from rats was treated with aldosterone, with or without MRs inhibitors. Nuclear factor (NF)-kappa B (NF-κB) activity was evaluated by real-time quantitative PCR, luciferase assay, and immunoblot. The results demonstrated that mRNA levels of the NF-κB target genes, including inhibitor of NF-κB alpha (IκB-α), NF-κB1, tumor necrosis factor-alpha (TNF-α), and interleukin 6 (IL-6), were higher after aldosterone treatment. Accordingly, phosphorylation of p65/RelA, IκB-α, and inhibitor of NF-κB kinase-β was markedly increased by aldosterone. Furthermore, knockdown of MRs prevented activation of the NF-κB canonical pathway by aldosterone. Consistent with this finding, ectopic overexpression of MRs enhanced the transcriptional activation of NF-κB by aldosterone. More importantly, the MRs antagonist, spironolactone blocked aldosterone-mediated activation of the canonical NF-κB pathway. In conclusion, aldosterone has an inflammatory effect in the corpus cavernosum penis, inducing NF-κB activation via an MRs-dependent pathway, which may be prevented by selective MRs antagonists. These data reveal the possible role of aldosterone in erectile dysfunction as well as its potential as a novel pharmacologic target for treatment.

TNF-α antagonism with etanercept enhances penile NOS expression, cavernosal reactivity, and testosterone levels in aged rats

Erectile dysfunction (ED) has been reported to be associated with inflammation. This study investigated the effects of tumor necrosis factor alpha (TNF-α) inhibitor etanercept on penile neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS) expressions, testosterone concentrations, neurogenic and endothelium-dependent relaxations of corpus cavernosum (CC), and circulating and cavernosal levels of inflammatory markers in aged rats. Animals were separated into control, aged, and etanercept-treated aged groups. Aged rats displayed significantly increased serum and cavernosal TNF-α, C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule (ICAM-1) levels, and decreased penile nNOS and eNOS expressions and serum testosterone levels compared with controls. In etanercept-treated aged group, NOS expressions were similar to that of the control group. The circulating and cavernosal concentrations of TNF-α, CRP, MCP-1, ICAM-1, and testosterone were also normalized by etanercept. Neurogenic and endothelium-dependent relaxant responses significantly decreased in aged rats and etanercept treatment markedly improved these relaxation responses. Our findings indicate that aging decreases penile NOS expression, neurogenic and endothelium-dependent relaxations of CC, and also suppresses serum testosterone levels by inducing inflammatory response that may contribute to the development of ED. TNF-α antagonism may be a novel strategy to treat aging-associated ED.

Effects of TNF-α on penile structure alteration in rats with hyperprolactinemia

This study aimed to investigate the effects of anti-tumor necrosis factor (TNF)-α antibody (Ab) on alteration of penile structure in the hyperprolactinemia (hyperPRL) rat model. HyperPRL was induced in 8-week-old male Sprague-Dawley rats by allografting anterior pituitary (AP) glands under the renal capsule (+AP rats). Rats implanted with cerebral cortex (CX) were used as sham control (+CX rats). At 6 weeks post implantation, rats received either a single intra-testicular dose of TNF-α Ab (12.5 μg/kg) or testosterone replacement (2 doses of testosterone enanthate [TE], 3 mg/kg), and they were sacrificed 1 week later. Blood and penile tissue was collected for analysis. Compared to +CX rats, the +AP group had lower serum testosterone concentration and neuronal nitric oxide synthase (nNOS) expression, but exhibited a higher ratio of collagen III/I in the corpus cavernosum. Smooth muscle content exhibited no significant changes. At 1 week post TNF-α Ab injection, the collagen III/I ratio in the +AP group was decreased, and the smooth muscle content and nNOS expression increased significantly. These findings were comparable to those observed in +AP rats receiving TE. Testicular TNF-α suppresses testosterone release, which in turn results in the erectile dysfunction (ED) seen in hyperPRL. Intra-testicular TNF-α Ab treatment is as effective as testosterone supplementation on penile structure normalization in the hyperPRL model.

Effects of Fine Particulate Matter on Erectile Function and Its Potential Mechanism in Rats

OBJECTIVE

To investigate whether the exposure to fine particulate matter (PM_2.5) in a rat model can impair erectile function and the possible mechanism.

MATERIALS AND METHODS

Sprague-Dawley rats were distributed into 4 groups (n = 9 each): 1 control group and 3 groups exposed to different levels of PM_2.5. Rats were exposed to PM_2.5 (0.0 [saline control], 0.8, 1.6, and 3.2 mg/rat). After exposure period, the ratio of maximum intracavernosal pressure to mean arterial pressure, molecular-biological indicators in corpus cavernosum tissue and plasma, and the pathologic changes of the lung tissue and penile tissue were detected and compared between the control group and the 3 exposure groups.

RESULTS

The ratio of maximum intracavernosal pressure to mean arterial pressure in 2 groups exposed to PM_2.5 was significantly lower than that of the control group only (P <.05). Exposure to PM_2.5 could trigger the significant increase of plasma malondialdehyde, vascular endothelial growth factor, C-reactive protein, and tumor necrosis factor-α in experimental groups than that of the control group (P <.05). Expression of endothelial nitric oxide synthase (NOS), neuronal NOS, cyclic guanosine monophosphate, NOS activity, and content of reactive oxygen species in penile tissue were higher than that of the control group in a dose-response way (P <.05).

CONCLUSION

The function of penile erection is impaired by exposure to PM_2.5. The decrease in the expression of endothelial NOS and NOS activity in penile cavernous tissue caused by systemic inflammatory and oxidative stress status induced by exposure to PM_2.5 may be one of the important risk factors of erectile dysfunction.

A Toll-Like Receptor 1/2 Agonist Augments Contractility in Rat Corpus Cavernosum

INTRODUCTION

Activation of the innate immune Toll-like receptor 2 (TLR2) initiates inflammation and has been implicated in vascular dysfunction. Increased contraction and decreased relaxation responses in the penile vasculature lead to erectile dysfunction, a condition associated with inflammation. However, whether TLR2 activation plays a role in penile vascular function has not been established.

AIM

We hypothesized that activation of the TLR 1/2 heterodimer (TLR1/2) augments contractile and impairs relaxation responses of corpus cavernosum and that these perturbations of vascular function are mediated by low nitric oxide (NO) availability and enhanced activity of the RhoA/Rho-kinase pathway.

METHODS

Contraction and relaxation responses were measured in rat cavernosal strips using a myograph after incubation with a TLR1/2-activating ligand Pam3 CSK4 (Pam3), the TLR1/2 inhibitor CuCPT 22 (CuCPT), and inhibitors of NO synthase (LNAME) and Rho-kinase (Y27632). TLR2 protein expression was assessed by immunohistochemistry.

MAIN OUTCOME MEASURES

Cumulative concentration response curves, sensitivity (pEC50), and maximal response (Emax ) of cavernosal strips to vasodilatory and vasocontractile agonists were compared between treatments.

RESULTS

Pam3-treated cavernosal strips exhibited greater pEC50 and higher Emax to phenylephrine (PE) than control tissues. Inhibition of NO synthase increased Emax to PE in Pam3-treated cavernosal strips. Pam3 treatment reduced relaxation to Y27632 compared with control tissues. Inhibition of TLR1/2 activation with CuCPT returned the augmented contraction to PE and the decreased relaxation to Y27632 of Pam3-treated cavernosal strips to control values.

CONCLUSIONS

The TLR1/2 heterodimer mediates augmented contraction and reduced relaxation in rat cavernosal strips. Thus, TLR1/2 activation antagonizes vascular responses crucial for normal erectile function and implicates immune activation in vasculogenic erectile dysfunction. Immune signaling via TLR2 may offer novel targets for treating inflammation-mediated vascular dysfunction in the penis.

Treatment of erectile dysfunction: new targets and strategies from recent research

In recent years, research on penile erection has increasingly been centered on the molecular mechanisms involved. Major progress has been made in the field and at present a whole number of neurotransmitters, chemical effectors, growth factors, second-messenger molecules, ions, intercellular proteins, and hormones have been characterized as components of the complex process of erection. This knowledge has led to the discovery of several new therapeutic targets and multiple medical approaches for the treatment of erectile dysfunction (ED). This review focuses on the progress made in this field within the last few years.

TNF-α, erectile dysfunction, and NADPH oxidase-mediated ROS generation in corpus cavernosum in high-fat diet/streptozotocin-induced diabetic rats

INTRODUCTION

Patients with diabetes-associated erectile dysfunction (ED) are characterized by an increase in circulating tumor necrosis factor-alpha (TNF-α). However, no study has indicated whether and how TNF-α plays a role in the pathogenesis of ED associated with diabetes.

AIM

We examined the effects and potential mechanism of infliximab (INF), a chimeric monoclonal antibody to TNF-α, on reactive oxygen species (ROS) generation in corpus cavernosum and ED in diabetic rats.

METHODS

Four groups of male rats were used: age-matched normal controls; diabetic rats induced by a high-fat diet (HFD) combined with a single streptozotocin (STZ) injection (35 mg/kg body weight, intraperitoneal [i.p.]); nondiabetic rats receiving INF (5 mg/kg body weight/week, i.p.), and diabetic rats receiving INF. Erectile function was assessed with electrical stimulation of the cavernous nerve after 8 weeks. The blood and penile tissues were harvested for plasma biochemical determinations, serum TNF-α measurement, penile ROS detection, and molecular assays of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, endothelial nitric oxide synthase (eNOS), phospho-eNOS, and neural nitric oxide synthase (nNOS) in the penis.

MAIN OUTCOME MEASURES

The effect of INF on HFD/STZ-induced diabetic ED and NADPH oxidase-mediated ROS generation was studied in diabetic corpus cavernosum.

RESULTS

Untreated diabetic rats displayed significantly decreased erectile parameters, and increased plasma TNF-α levels, penile ROS production, p47(phox) and gp91(phox) expression compared with nondiabetic controls. INF neutralized TNF-α and significantly reduced ED in diabetic rats, in which marked decreases in p47(phox) and gp91(phox) expression and ROS generation in corpus cavernosum were noted. The ratio of phospho-eNOS to eNOS and expression of nNOS in the penis were significantly increased in INF-treated vs. untreated diabetic rats.

CONCLUSIONS

Increased TNF-α expression associated with diabetes contributes to ED by promoting NAPDH oxidase-mediated ROS generation in corpus cavernosum. INF protects against diabetic ED by neutralizing TNF-α.

Is there a link between soft drinks and erectile dysfunction?

This review focuses on the potential role of soft drinks, particularly the sugar component, in the pathogenesis of erectile dysfunction (ED). We analyzed the hypothetical link between metabolic disorders, induced by sweetened soft drinks overconsumption, and ED. High caloric intake, high refined-carbohydrates, and high fructose corn syrup (HFCS) content and less satiety are main factors responsible for metabolic disorders contributing to ED development. Regular diet mistakes among human males, such as soft drink consumption, may lead to slow and asymptomatic progression of ED, finally resulting in full claimed manifestation of ED.

Characterization of erectile function in elastin haploinsufficicent mice

INTRODUCTION

Elastin fibers confer passive recoil to many tissues including the lung, skin, and arteries. In the penis, elastin is present in sinusoids, arterioles, and in the tunica albuginea. Although decreased penile elastin has been reported in men with erectile dysfunction, the exact role of elastin in physiologic processes integral to erection remains speculative.

AIM

The aim of this study was to characterize erectile function in elastin-deficient mice.

METHODS

Elastin haploinsufficient mice (Eln(+/-) ) and aged match Eln(+/+) (Wt) mice were used. Cavernosum was removed from some mice for quantification of elastin, collagen, and smooth muscle actin. Ex vivo assessment of contractile force generation was performed by myography. In vivo assessment of intracorporal pressure normalized to mean arterial pressure in response to electrical stimulation of the cavernosal nerve was measured. Veno-occlusive function was determined by cavernosography.

MAIN OUTCOME MEASURES

The main outcome measures of this study were the in vitro and in vivo assessment of cavernosal vasoreactivity, veno-occlusive function and erection in mice deficient in elastin.

RESULTS

Eln (+/-) mice exhibited ∼33% less penile elastin than Wt mice, with no change in collagen. Cavernosal tissue from Eln(+/-) mice has a significantly heightened contractile response, explained in part by increased smooth muscle cell content. Veno-occlusive function was significantly altered in Eln(+/-) mice. Interestingly, erectile function was impaired only at submaximal voltage (1 V) stimulation (there was no impairment during the higher 2-V stimulus).

CONCLUSIONS

Eln (+/-) mice display a cavernosal phenotype consistent with developmental changes attributable to the loss of elastin. These alterations confer a degree of altered erectile function that is able to be overridden by maximal stimulatory input. Altogether, these data suggest that elastin is important for erectile function.

Effect of periodontitis on erectile function and its possible mechanism

INTRODUCTION

Periodontitis is one of the important risk factors resulting in cardiovascular diseases. Erectile dysfunction (ED) is strongly correlated with cardiovascular diseases. The expression of endothelial nitric oxide synthase (eNOS) in penile tissue has an important role in the mechanism of erection.

AIM

To investigate the effect of periodontitis on erectile function and the possible mechanism.

METHODS

After induction of periodontitis in rat, the ratio of maximum intracavernosal pressure/mean arterial pressure (ICPmax /MAP)×100, the expression of eNOS in penile tissue, the level of serum C-reactive protein (CRP) and tumor necrosis factor-α (TNF-α), and the ultrastructural changes of the cavernous tissue were examined and compared between periodontitis rats (group A) and control rats (group B).

MAIN OUTCOME MEASURE

Periodontitis significantly decrease not only the ICPmax/MAP×100 and the expression of eNOS but also the activity of NOS and the level of cyclic guanosine monophosphate (cGMP) in cavernous tissue of rat.

RESULTS

After electrostimulation by 3 and 5 voltage, the ratio of ICPmax /MAP×100 in group A was significantly less than that in group B (19.54±6.16 vs. 30.45±3.12; 30.91±5.61 vs. 50.52±9.52, respectively; P<0.05).The level of serum CRP and TNF-α in group A is significantly higher in group B (P<0.05).The quantitative real-time reverse transcription polymerase chain reaction study demonstrated no statistically significant difference in the expression of mRNA of eNOS in cavernous tissue between the two groups (P>0.05). But there was significant decrease in eNOS protein of the cavernous tissue in group A than in group B (P<0.05). Total NOS activity and cGMP level in cavernosal tissue were significantly lower in group A than in group B (P<0.05). There was no significant alternation occurred in the ultrastructures of penile cavernous tissue.

CONCLUSIONS

The function of penile erection is impaired by periodontitis. The decreased in the expression of eNOS and NOS activity in penile cavernous tissue caused by mild systemic inflammatory status in periodontitis may be one of the important risk factors of ED.

Imbalanced low-grade inflammation and endothelial activation in patients with type 2 diabetes mellitus and erectile dysfunction

INTRODUCTION

Erectile dysfunction (ED) is highly prevalent among type 2 diabetes mellitus patients (T2DM). Although a link among systemic inflammation, endothelial dysfunction, and ED is described in clinical situations mainly related with coronary heart disease (CHD) risk, evidences of this link in T2DM patients are rather limited.

AIMS

To evaluate the association between endothelial dysfunction and balance of pro-/anti-inflammatory mediators with ED presence and severity in T2DM.

METHODS

We conducted a cross-sectional study of 190 T2DM patients without symptomatic CHD, 150 out of them with ED and 40 without ED. Serum levels of E-selectin, intercellular adhesion molecule-1, tumor necrosis factor-α (TNF-α), and interleukin (IL)-10 were measured using specific enzyme-linked immunosorbent assays (ELISAs). ED presence and severity were tested by the five-item version of the International Index of Erectile Function questionnaire.

MAIN OUTCOME MEASURES

Differences in circulating levels of endothelial dysfunction (ICAM-1, E-selectin) and inflammatory/anti-inflammatory (TNF-α, IL-10, TNF-α : IL-10 ratio) markers between T2DM patients with and without ED, and assessment of biomarkers ED predictive value while adjusting for other known ED risk factors.

RESULTS

Patients with ED were older and had longer duration of diabetes than patients without ED. E-selectin serum levels were significantly increased, while IL-10 were lower in patients with ED; because TNF-α levels tend to be higher, TNF-α : IL-10 ratio was more elevated in ED patients. No significant differences of ICAM-1 levels were observed between study groups. Endothelial activation markers and TNF-α, as well as diabetes duration, were negatively correlated with erectile function. On multivariate analysis including age, duration of diabetes, insulin treatment, hypertension, insulin resistance, fair-to-poor glycemic control, and metabolic syndrome, increments in E-selectin levels and TNF-α : IL-10 ratio predicted independently ED presence, while IL-10 increases were associated with lower risk of ED in T2DM patients.

CONCLUSIONS

ED in T2DM patients without symptomatic CHD is associated with systemic endothelial dysfunction and a predominant, imbalanced low-grade inflammatory response.

Emerging role for TNF-α in erectile dysfunction

INTRODUCTION

A role for cytokines in the pathophysiology of erectile dysfunction (ED) has emerged. Cytokines induce genes that synthesize other peptides in the cytokine family and several mediators, such as prostanoids, leukotrienes, nitric oxide, bradykinin, reactive oxygen species, and platelet-activating factor, all of which can affect vascular function. Consistent with the fact that the cavernosal tissue is a complex extension of the vasculature, risk factors that affect the vasculature have been shown to affect cavernosal function as well. Accordingly, the penile tissue has been recognized as an early sentinel for atherosclerosis that underlies coronary artery disease and cardiovascular diseases (CVD).

AIM

To review the literature pertaining to the role of tumor necrosis factor-alpha (TNF-α) in ED.

METHODS

PubMed search for pertinent publications on the role of cytokines, particularly TNF-α, in CVD and ED.

MAIN OUTCOME MEASURES

Clinical and experimental evidence demonstrates that TNF-α may play a role in ED.

RESULTS

TNF-α has been shown to play an important role in CVD, mainly due to its direct effects on the vasculature. In addition, high levels of TNF-α were demonstrated in patients with ED. In this review, we present a short description of the physiology of erection and the cytokine network. We focus on vascular actions of TNF-α that support a role for this cytokine as a potential candidate in the pathophysiology of ED, particularly in the context of CVD. A brief overview of its discovery, mechanisms of synthesis, receptors, and its main actions on the systemic and penile vasculature is also presented.

CONCLUSIONS

Considering that ED results from a systemic arterial defect not only confined to the penile vasculature, implication of TNF-α in the pathophysiology of ED offers a humoral linking between CVD and ED.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

Diabetes, obesity and erectile dysfunction: field overview and research priorities

PURPOSE

We provide an overview of basic, clinical and epidemiological research in the field of erectile dysfunction and important research priorities presented at the 2009 National Institute of Diabetes and Digestive and Kidney Diseases symposium on Urological Complications of Diabetes and Obesity.

MATERIALS AND METHODS

Experts in molecular biology, physiology, pharmacology, clinical trials, epidemiology and urological surgery highlighted current knowledge on erectile dysfunction associated with diabetes mellitus and obesity.

RESULTS

Predictable associations between erectile dysfunction, and poor diabetic control and modifiable risk factors, including body mass index, have not yet been translated into randomized trials in the United States. The relationship between erectile dysfunction and metabolic syndrome, and surrogate markers for erectile dysfunction requires further investigation. Basic research aimed at discovering disease mechanisms and therapeutic targets has focused on autonomic neuropathy, vascular dysfunction, smooth muscle contractile function and matrix. However, significant gaps exist in regard to the integration of molecular, cellular and functional data. Animal models of type 2 diabetes and obesity associated erectile dysfunction require investigation because most basic science studies have used rodent models of type 1 diabetes.

CONCLUSIONS

Studies are needed to synthesize a systems biology understanding of erectile function/dysfunction, and characterize and disseminate rodent models of erectile dysfunction associated with type 2 diabetes and obesity. Clinical studies are needed of promising intervention and prevention strategies. Leveraging existing and future cohort phenotypes, and biological samples is needed for risk factor analysis, biomarker discovery and genome wide association studies.