Alterations of NOS, arginase, and DDAH protein expression in rabbit cavernous tissue after administration of cigarette smoke extract

Arginine, Transsulfuration, and Folic Acid Pathway Metabolomics in Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-Analysis

There is an increasing interest in biomarkers of nitric oxide dysregulation and oxidative stress to guide management and identify new therapeutic targets in patients with chronic obstructive pulmonary disease (COPD). We conducted a systematic review and meta-analysis of the association between circulating metabolites within the arginine (arginine, citrulline, ornithine, asymmetric, ADMA, and symmetric, SDMA dimethylarginine), transsulfuration (methionine, homocysteine, and cysteine) and folic acid (folic acid, vitamin B6, and vitamin B12) metabolic pathways and COPD. We searched electronic databases from inception to 30 June 2023 and assessed the risk of bias and the certainty of evidence. In 21 eligible studies, compared to healthy controls, patients with stable COPD had significantly lower methionine (standardized mean difference, SMD = -0.50, 95% CI -0.95 to -0.05, p = 0.029) and folic acid (SMD = -0.37, 95% CI -0.65 to -0.09, p = 0.009), and higher homocysteine (SMD = 0.78, 95% CI 0.48 to 1.07, p < 0.001) and cysteine concentrations (SMD = 0.34, 95% CI 0.02 to 0.66, p = 0.038). Additionally, COPD was associated with significantly higher ADMA (SMD = 1.27, 95% CI 0.08 to 2.46, p = 0.037), SDMA (SMD = 3.94, 95% CI 0.79 to 7.08, p = 0.014), and ornithine concentrations (SMD = 0.67, 95% CI 0.13 to 1.22, p = 0.015). In subgroup analysis, the SMD of homocysteine was significantly associated with the biological matrix assessed and the forced expiratory volume in the first second to forced vital capacity ratio, but not with age, study location, or analytical method used. Our study suggests that the presence of significant alterations in metabolites within the arginine, transsulfuration, and folic acid pathways can be useful for assessing nitric oxide dysregulation and oxidative stress and identifying novel treatment targets in COPD. (PROSPERO registration number: CRD42023448036.).

The Effects of Immediate vs Gradual Reduction in Nicotine Content of Cigarettes on Smoking Behavior: An Ecological Momentary Assessment Study

BACKGROUND

In recent years, much research has examined the effects of various interventions and treatments for smoking cessation. The results suggest that interventions targeting changes of nicotine content can help smokers reduce tobacco use or quit smoking. A number of clinical studies show that smokers who received an immediate reduction in nicotine content to very low levels have significantly greater reductions in the number of cigarettes smoked and toxic substance exposure compared to those with gradual reductions. However, from the perspective of smoking craving, whether the immediate and gradual reduction in nicotine content reduce smoking by reducing cravings needs further investigation.

METHODS

74 eligible Participants were randomly allocated to one of the two experimental conditions: (1) immediate reduction to 0.1 mg of nicotine per cigarette (n = 40); (2) gradual reduction from 1.0 (0.8 g ~ 1.2 mg) to 0.1 mg of nicotine per cigarette (n = 34). All participants completed 1-week baseline period during which they smoked their usual cigarette, followed by 16-week of interventions. The primary outcomes included cigarette cravings and number of cigarettes smoked per day (CPD); secondary outcomes included the number of cigarette-free day and emotional states.

RESULTS

Among the 52 participants [51 (98.1%) men; mean (SD) age, 33.44 (6.71) years; mean (SD) CPD, 16.83 (9.94)] who completed the trial, significantly lower cravings for cigarettes were observed in the immediate (n = 25) vs. gradual nicotine reduction group (n = 27) in the morning (t = -2.072, p = 0.039) and after dinner (t = -2.056, p = 0.041). Compared with the baseline daily smoking, the number of cigarettes smoked per day was significantly reduced at the beginning of week 12 in the immediate nicotine reduction group (p = 0.001) and at week 16 in the gradual nicotine reduction group (p < 0.001). The number of participants with any cigarette-free day was not significantly different between the groups (p = 0.198). The number of cigarette-free days was significantly more in the immediate vs. gradual nicotine reduction group (p = 0.027).

CONCLUSIONS

The significantly lower cravings were observed in the immediate vs. gradual nicotine reduction group, and led to faster reduction in the number of CPD, and a significant increase in the number of cigarette-free days. These findings add to the evidence base for reduced nicotine content in cigarettes.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier: ChiCTR2100048216.

Hyperglycemia-impaired aortic vasorelaxation mediated through arginase elevation: Role of stress kinase pathways

Diabetes-induced vascular endothelial dysfunction has been reported to involve hyperglycemia-induced increases in arginase activity. However, upstream mediators of this effect are not clear. Here, we have tested involvement of Rho kinase, ERK1/2 and p38 MAPK pathways in this process. Studies were performed with aortas isolated from wild type or hemizygous arginase 1 knockout (Arg1^+/-) mice and bovine aortic endothelial cells exposed to high glucose (HG, 25 mmol/l) or normal glucose (NG, 5.5 mmol/l) conditions for different times. Effects of inhibitors of arginase, p38 MAPK, ERK1/2 or ROCK and ex vivo adenoviral delivery of active Arg1 and inactive (D128-Arg1) cDNA were also determined. Exposure in wild type aorta or endothelial cells to HG significantly increased arginase activity and Arg1 expression and impaired aortic relaxation. Transduction of wild type aorta with active Arg1 cDNA impaired vascular relaxation, whereas inactive Arg1 had no effect. The HG-induced vascular endothelial dysfunction was associated with increased phosphorylation (activation) of ERK1/2 and p38 MAPK. Pretreatment with inhibitors of ERK1/2, p38 MAPK, ROCK or arginase blocked HG-induced elevation of arginase activity and Arg1 expression and prevented the vascular dysfunction. Inhibition of ROCK blunted the HG-induced activation of ERK1/2 and p38 MAPK. In summary, activated ROCK and subsequent activation of ERK1/2 or p38 MAPK elevates arginase activity and Arg1 expression in hyperglycemic states. Targeting this pathway may provide an effective means for preventing diabetes/hyperglycemia-induced vascular endothelial dysfunction.

Cerebroprotective effects of hydrogen sulfide in homocysteine-induced neurovascular permeability: Involvement of oxidative stress, arginase, and matrix metalloproteinase-9

An elevated level of homocysteine (Hcy) leads to hyperhomocysteinemia (HHcy), which results in vascular dysfunction and pathological conditions identical to stroke symptoms. Hcy increases oxidative stress and leads to increase in blood-brain barrier permeability and leakage. Hydrogen sulfide (H₂ S) production during the metabolism of Hcy has a cerebroprotective effect, although its effectiveness in Hcy-induced neurodegeneration and neurovascular permeability is less explored. Therefore, the current study was designed to perceive the neuroprotective effect of exogenous H ₂ S against HHcy, a cause of neurodegeneration. To test this hypothesis, we used four groups of mice: control, Hcy, control + sodium hydrosulfide hydrate (NaHS), and Hcy + NaHS, and an HHcy mice model in Swiss albino mice by giving a dose of 1.8 g of dl-Hcy/L in drinking for 8-10 weeks. Mice that have 30 µmol/L Hcy were taken for the study, and a H ₂ S supplementation of 20 μmol/L was given for 8 weeks to all groups of mice. HHcy results in the rise of the levels of superoxide and nitrite, although a concomitant decrease in the level of superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, and arginase in oxidative stress and a concomitant decrease in the endogenous level of H ₂ S. Although H ₂ S supplementation ameliorated, the effect of HHcy and the levels of H ₂ S returned to the average level in HHcy animals supplemented with H ₂ S. Interestingly, H ₂ S supplementation ameliorated neurovascular remodeling and neurodegeneration. Thus, our study suggested that H ₂ S could be a beneficial therapeutic candidate for the treatment of Hcy-associated neurodegeneration, such as stroke and neurovascular disorders.

Epigallocatechin-3-gallate ameliorates erectile function in aged rats via regulation of PRMT1/DDAH/ADMA/NOS metabolism pathway

Aging-related ED is predominantly attributed to neurovascular dysfunction mediated by NO suppression and increased oxidative stress in penis. The alterations of protein arginine methyltransferases 1 (PRMT1)/dimethylarginine dimethylaminohydrolase (DDAH)/asymmetrical dimethylarginine (ADMA)/NO synthase (NOS) pathway regulate NO production in the vascular endothelium. Epigallocatechin-3-gallate (EGCG) is one of the most abundant and antioxidative ingredients isolated from green tea. In the present study, 40 Sprague-Dawley rats were randomly distributed into four groups: one young rat group and three aged rat groups treated with daily gavage feedings of EGCG at doses of 0, 10 mg kg⁻¹, and 100 mg kg⁻¹ for 12 weeks, respectively. Erectile function was assessed by electrical stimulation of the cavernous nerves with intracavernous pressure (ICP) measurement. After euthanasia, penile tissue was investigated using Western blot and ELISA to assess the PRMT1/DDAH/ADMA/NOS metabolism pathway. Superoxide dismutase (SOD) and malondialdehyde (MDA) levels were detected by colorimetry. We also evaluated smooth muscle contents. The ratio of maximal ICP and mean systemic arterial pressure (MAP) was markedly higher in EGCG-treated aged rats than in untreated aged rats. We found that DDAH1 and DDAH2 were expressed in cavernosal tissue, and they were downregulated in corpora of aged rats. The administration of EGCG upregulated the expression and activity of DDAH. In contrast, EGCG treatment downregulated the expression of PRMT1 and ADMA content. Moreover, EGCG-treated rats showed an improvement in smooth muscle expression, the ratio of smooth muscle cell/collagen fibril, SOD activity, and MDA levels when compared with untreated aged rats.

Demethylation treatment restores erectile function in a rat model of hyperhomocysteinemia

Methylation modification is an important cellular mechanism of gene expression regulation. Dimethylarginine dimethylaminohydrolase-2 (DDAH-2) protein is a pivotal molecular for endothelium function. To explore the effects of 5-aza-deoxycytidine (5-aza), a demethylation agent, in hyperhomocysteinemia (hhcy)-related erectile dysfunction (ED) rats, 5-aza (1 mg kg⁻¹) was administrated to Sprague-Dawley hhcy-rats induced by supplemented methionine chow diet. Erectile function, nitric oxide-cyclic guanosine monophosphate (NO-cGMP) levels, expression of DDAH-2 protein and promoter methylation status of DDAH-2 were studied in the corpora cavernosa. We found that supplemented methionine diet induced a high homocysteine level after 6 weeks of treatment. DDAH-2 protein was down-regulated in the corpora cavernosa while the administration of 5-aza up-regulated DDAH-2 expression and restored erectile function. The methionine-fed rats showed high methylation levels of DDAH-2 promoter region while the group treated with 5-aza demonstrated lower-methylation levels when compared to the methionine-fed group. Besides, the administration of 5-aza improved NO and cGMP levels in methionine-fed rats. Therefore, the methylation mechanism involves in ED pathogenesis, and demethylation offers a potential new strategy for ED treatment.

The Effects of Adipose-Derived Stem Cells in a Rat Model of Tobacco-Associated Erectile Dysfunction

Tobacco use is associated with erectile dysfunction (ED) via a number of mechanisms including vascular injury and oxidative stress in corporal tissue. Adipose derived stem cells (ADSC) have been shown to ameliorate vascular/corporal injury and oxidative stress by releasing cytokines, growth factors and antioxidants. We assessed the therapeutic effects of intracavernous injection of ADSC in a rat model of tobacco-associated ED. Thirty male rats were used in this study. Ten rats exposed to room air only served as negative controls. The remaining 20 rats were passively exposed to cigarette smoke (CS) for 12 weeks. At the 12-week time point, ADSC were isolated from paragonadal fat in all rats. Amongst the 20 CS exposed rats, 10 each were assigned to one of the two following conditions: (i) injection of phosphate buffered saline (PBS) into the corpora cavernosa (CS+PBS); or (ii) injection of autologous ADSC in PBS into the corpora cavernosa (CS+ADSC). Negative control animals received PBS injection into the corpora cavernosa (normal rats [NR] + PBS). After injections all rats were returned to their previous air versus CS exposure state. Twenty-eight days after injection, all rats were placed in a metabolic cage for 24-hour urine collection to be testing for markers of oxidative stress. After 24-hour urine collection all 30 rats also underwent erectile function testing via intracavernous pressure (ICP) testing and were then sacrificed. Corporal tissues were obtained for histological assessment and Western blotting. Mean body weight was significantly lower in CS-exposed rats than in control animals. Mean ICP, ICP /mean arterial pressure ratio, serum nitric oxide level were significantly lower in the CS+PBS group compared to the NR+PBS and CS+ADSC groups. Urine markers for oxidative stress were significantly higher in the CS+PBS group compared to the NR+PBS and CS+ADSC groups. Mean expression of corporal nNOS and histological markers for endothelial and smooth muscle cells was significantly lower, and tissue apoptotic index significantly higher, in the CS+PBS group compared to the NR+PBS and CS+ADSC groups. Our findings confirm that chronic tobacco exposure causes ultrastructural damage to the corporal tissue and increases systemic oxidative stress states. Treatment with ADSC ameliorates these adverse effects and holds promise as a potential therapy for tobacco-related ED.

Chronic Cigarette Smoking Impairs Erectile Function through Increased Oxidative Stress and Apoptosis, Decreased nNOS, Endothelial and Smooth Muscle Contents in a Rat Model

Cigarette use is an independent risk factor for the development of erectile dysfunction (ED). While the association between chronic smoking and ED is well established, the fundamental mechanism(s) of cigarette-related ED are incompletely understood, partly due to no reliable animal model of smoking-induced ED. The present study was designed to validate an in vivo rat model of chronic cigarette-induced ED. Forty 12-week old male Sprague-Dawley rats were divided into 4 groups. Ten rats served as control group and were exposed only to room air. The remaining 30 rats were passively exposed to cigarette smoke (CS) for 4 weeks (n = 10), 12 weeks (n = 10), and 24 weeks (n = 10). At the 24-week time point all rats were assessed with intracavernous pressure (ICP) during cavernous nerve electrostimulation. Blood and urine were collected to measure serum testosterone and oxidative stress, respectively. Corporal tissue was assessed by Western blot for neuronal nitric oxide synthase (nNOS). Penile tissues were subjected to immunohistochemistry for endothelial, smooth muscle, and apoptotic content. Mean arterial pressure (MAP) was significantly higher in 24-week cigarette exposed animals compared to the control animals. Mean ICP/MAP ratio and cavernosal smooth muscle/endothelial contents were significantly lower in the 12- and 24-week rats compared to control animals. Oxidative stress was significantly higher in the 24-week cigarette exposed group compared to control animals. Mean nNOS expression was significantly lower, and apoptotic index significantly higher, in CS-exposed animals compared to control animals. These findings indicate that the rat model exposure to CS increases apoptosis and oxidative stress and decreases nNOS, endothelial and smooth muscle contents, and ICP in a dose dependent fashion. The rat model is a useful tool for further study of the molecular and cellular mechanisms of CS-related ED.

Effect of DDAH/ADMA/NOS regulation pathway on cavernae corporum cavernosorum rat penis of different age

The effect of DDAH/ADMA/NOS pathway in penile tissue of rats of different age was investigated to better understand the mechanism of age-related erectile dysfunction (ED). The Sprague Dawley male rats were assigned as the young group (3 month old, n = 10) and the old group (18 month old, n = 10) respectively. Intracavernous pressure (ICP) was measured before and after papaverine intracavernous injection. Pathology structure of penile tissue was evaluated under transmission electron microscope. The expression amounts of asymmetric dimethylarginine (ADMA) and cyclic guanosine monophosphate (cGMP) in penile tissue were detected by ELISA; the expression levels of isoform-specific DDAH and NOS were assessed via Western blot. Compared with the young group, the ICP in the old group rat decreased significantly (33.46 ± 5.37 versus 39.71 ± 3.67 mmHg, P = 0.02) after papaverine injection. Diffused fibrosis and impairment of endothelial cell were observed in corpus cavernosum in the old group rats. Higher level of ADMA (10.83 ± 0.96 versus 7.51 ± 1.39 μmol per gpro, P = 3.14 × 10(-4) ) and lower level of cGMP (29.42 ± 3.84 versus 47.09 ± 6.07 nmol per gpro, P = 1.57 × 10(-6) ) were detected in penile tissue of the old group compared with those of the young group. Expression of DDAH1, DDAH2, endothelial NOS (eNOS) and neuronal NOS(nNOS) all decreased significantly in penile tissue of the old group rat. The DDAH/ADMA/NOS regulation pathway changes dramatically accompanying with lower ICP in old group rat compared with those of the young group. Such findings in rats are suggestive in understanding the mechanism of age-related ED in humans.

Association of the AGXT2 V140I polymorphism with risk for coronary heart disease in a Chinese population

AIM

Asymmetric dimethylarginine (ADMA) is a nitric oxide synthase (NOS) inhibitor that decreases NO production and promotes the development of cardiovascular diseases. Alanine-glyoxylate aminotransferase 2 (AGXT2) plays an important role in ADMA metabolism. This study was designed to explore the association of the AGXT2 V140I (rs37369 G＞A) polymorphism with risk for coronary heart disease (CHD) in a Chinese population.

METHODS

A case-control study including 1103 controls and 942 CHD patients was performed. The patients were genotyped for rs37369 using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Plasma ADMA concentration in healthy controls was measured by an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The rs37369 GG genotype was significantly overrepresented in CHD patients compared to the controls (18.5% versus 14.8%, p=0.025), and it was significantly associated with increased risk for CHD in smokers (OR=2.21, 95% CI: 1.24-3.92, p=0.007) and marginally increased CHD risk for individuals with diabetes mellitus (OR=1.92; 95% CI: 0.94-3.91, p=0.074). The association between rs37369 and CHD risk was further increased in smokers with diabetes mellitus (OR=3.32, 95% CI:1.14-9.67, p=0.028). Patients who smoked and were rs37369 GG homozygous showed significantly higher plasma ADMA levels than carriers of the rs37369 A allele (p=0.004). However, in non-smokers, patients homozygous for rs37369 GG showed significantly lower plasma ADMA concentrations than carriers of the rs37369 A allele (p=0.003). Furthermore, smokers homozygous for rs37369 GG showed significantly higher plasma ADMA concentrations than non-smokers with the same genotype (p=0.012).

CONCLUSION

The AGXT2 rs37369 polymorphism is associated with increased risk for CHD in smokers and in diabetes mellitus patients. This increased risk may be due to increased plasma ADMA levels.

Arginase inhibition prevents inflammation and remodeling in a guinea pig model of chronic obstructive pulmonary disease

Airway inflammation and remodeling are major features of chronic obstructive pulmonary disease (COPD), whereas pulmonary hypertension is a common comorbidity associated with a poor disease prognosis. Recent studies in animal models have indicated that increased arginase activity contributes to features of asthma, including allergen-induced airway eosinophilia and mucus hypersecretion. Although cigarette smoke and lipopolysaccharide (LPS), major risk factors for COPD, may increase arginase expression, the role of arginase in COPD is unknown. This study aimed to investigate the role of arginase in pulmonary inflammation and remodeling using an animal model of COPD. Guinea pigs were instilled intranasally with LPS or saline twice weekly for 12 weeks and pretreated by inhalation of the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) or vehicle. Repeated LPS exposure increased lung arginase activity, resulting in increased l-ornithine/l-arginine and l-ornithine/l-citrulline ratios. Both ratios were reversed by ABH. ABH inhibited the LPS-induced increases in pulmonary IL-8, neutrophils, and goblet cells as well as airway fibrosis. Remarkably, LPS-induced right ventricular hypertrophy, indicative of pulmonary hypertension, was prevented by ABH. Strong correlations were found between arginase activity and inflammation, airway remodeling, and right ventricular hypertrophy. Increased arginase activity contributes to pulmonary inflammation, airway remodeling, and right ventricular hypertrophy in a guinea pig model of COPD, indicating therapeutic potential for arginase inhibitors in this disease.

Chronic oral administration of the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) improves erectile function in aged rats

Arginase expression and activity have been noted to be heightened in conditions associated with erectile dysfunction, including aging. Previously, arginase inhibition by chronic administration of the arginase inhibitor 2-(S)-amino-6-boronohexanoic acid (ABH) has been shown to improve endothelial dysfunction in aged rats. The objective of this study was to assess whether chronic oral ABH administration affects cavernosal erectile function. Rats were divided into 4 groups: young control, young treated with arginase inhibitor, aged control, and aged treated with arginase inhibitor. Arginase activity was measured and presented as a proportion of young untreated rats. In vivo erectile responses to cavernous nerve stimulation were measured in all cohorts. The cavernous nerve was stimulated with a graded electrical stimulus, and the intracavernosal/mean arterial pressure ratios and total intracavernosal pressure were recorded. Arginase activity was elevated in the aged rats compared with young controls; however, arginase activity was significantly decreased in aged rats treated with ABH. With the addition of ABH, erectile responses improved in the aged rats (P < .05). Oral inhibition of arginase with ABH results in improved erectile function in aged rats, resulting in erectile hemodynamics similar to young rats. This represents the first documentation of systemic arginase inhibition positively affecting corporal cavernosal function.

Phosphodiesterase type 5 (PDE5) inhibitors in erectile dysfunction: the proper drug for the proper patient

INTRODUCTION

Erectile dysfunction (ED) is a very common multidimensional disorder affecting men worldwide. Physical illness, reaction to life stresses, or an unhappy couple relationship influence clinical outcome. Phosphodiesterase type 5 (PDE5) inhibitors are recognized as efficacious and well tolerated, and are the first-line treatment for ED. Sildenafil, tadalafil, and vardenafil are the most widely used and studied PDE5 inhibitors. Data acquired during a routine diagnostic workup for ED should be taken into account when choosing the best PDE5 inhibitor for the individual patient, creating an individualized treatment plan, and going beyond "experience-based" subjective opinion and unfounded ideas and prejudice regarding currently available drugs.

AIM

As the process of matching a given patient's profile to any selected PDE5 inhibitor often relies more on physician's personal convictions than on solid evidence, the aim of this review is to identify the main clinical, demographic, and relational factors influencing the choice of the PDE5 inhibitor to be used for the treatment of ED.

METHODS

A systematic literature search and current treatment guidelines were evaluated in a systematic manner.

MAIN OUTCOME MEASURES

The main clinical, cultural, and demographical factors to be considered for the treatment of ED have been identified.

RESULTS

Main factors influencing the choice of the treatment for ED have been described. A short list of items that may help in choosing the right PDE5 inhibitor for the treatment of different patients in daily clinical practice has been prepared.

CONCLUSIONS

The simple algorithms prepared should be a useful tool to be used in daily practice, which may help in choosing the right treatment for each subject affected by ED.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Anatomy, physiology, and pathophysiology of erectile dysfunction

INTRODUCTION

Significant scientific advances during the past 3 decades have deepened our understanding of the physiology and pathophysiology of penile erection. A critical evaluation of the current state of knowledge is essential to provide perspective for future research and development of new therapies.

AIM

To develop an evidence-based, state-of-the-art consensus report on the anatomy, physiology, and pathophysiology of erectile dysfunction (ED).

METHODS

Consensus process over a period of 16 months, representing the opinions of 12 experts from seven countries.

MAIN OUTCOME MEASURE

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

RESULTS

ED occurs from multifaceted, complex mechanisms that can involve disruptions in neural, vascular, and hormonal signaling. Research on central neural regulation of penile erection is progressing rapidly with the identification of key neurotransmitters and the association of neural structures with both spinal and supraspinal pathways that regulate sexual function. In parallel to advances in cardiovascular physiology, the most extensive efforts in the physiology of penile erection have focused on elucidating mechanisms that regulate the functions of the endothelium and vascular smooth muscle of the corpus cavernosum. Major health concerns such as atherosclerosis, hyperlipidemia, hypertension, diabetes, and metabolic syndrome (MetS) have become well integrated into the investigation of ED.

CONCLUSIONS

Despite the efficacy of current therapies, they remain insufficient to address growing patient populations, such as those with diabetes and MetS. In addition, increasing awareness of the adverse side effects of commonly prescribed medications on sexual function provides a rationale for developing new treatment strategies that minimize the likelihood of causing sexual dysfunction. Many basic questions with regard to erectile function remain unanswered and further laboratory and clinical studies are necessary.

Inhibition of L-arginine metabolizing enzymes by L-arginine-derived advanced glycation end products

N^ω-Carboxymethyl-arginine (CMA), N^ω-carboxyethyl-arginine (CEA) and N^δ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) have been identified as L-arginine-derived advanced glycation end products (AGEs) formed by non-enzymatic reactions between reducing sugars such as glucose and amino groups in proteins. These AGEs are structurally analogous to endogenous inhibitors of nitric oxide synthases (NOS) including N^G-monomethyl-L-arginine (L-NMMA) and asymmetric N^G,N^G-dimethyl-L-arginine (ADMA). Increased plasma levels of these NOS inhibitors, and thus impaired generation of NO in vivo has been associated with the pathogenesis of vascular complications such as kidney failure and atherosclerosis. For these reasons we examined whether L-arginine-derived AGEs inhibit the activities of three L-arginine metabolizing enzymes including three isoforms of NOS (endothelium, neuronal and inducible NOS), dimethylarginine dimethylaminohydrolase (DDAH) that catalyzes the hydrolytic degradation of L-NMMA and ADMA to L-citrulline, and arginase that modulates intracellular L-arginine bioavailability. We found that AGEs inhibited the in vitro activities of endothelium type NOS weakly (IC₅₀ values of CMA, CEA and MG-H1 were 830, 3870 and 1280 µM, respectively) and were also potential endogenous inhibitors for arginase (IC₅₀ values of CMA and CML were 1470 and 1060 µM), but were poor inhibitors for DDAH. These results suggest that the tested L-arginine- and L-lysine-derived AGEs appear not to impair NO biosynthesis directly.

Dimethylarginine dimethylaminohydrolase in rat penile tissue: reduced enzyme activity is responsible for erectile dysfunction in a rat model of atherosclerosis

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is mainly metabolized by N(G),N(G)-dimethylarginine dimethylaminohydrolase (DDAH). We investigated whether altered cavernosal ADMA-DDAH metabolism might cause impairment of erection in rat model of atherosclerosis (AS). Male Sprague-Dawley rats (3 months old) were divided into an AS group and a normal control (Con) group (n=20 in each group). The AS rats received AS-prone treatment (6 weeks of 1% cholesterol diet plus early 2 weeks of N(G)-nitro-L-arginine methyl ester (3 mg ml(-1) per day) treatment). After 6 weeks, rats underwent cavernosometry measuring the maximal intracavernosal pressure/mean arterial pressure (ICP/MAP) ratios as a surrogate marker of erectile function. The amount of cavernosal ADMA was assessed by immunoblot analysis and correlated with the ICP/MAP. Isoform-specific DDAH expression was compared by immunohistochemistry. Cavernosal DDAH and NOS activity were measured. Cavernosal malondialdehyde levels were assayed to determine the degree of lipid peroxidation. Compared to the controls, the AS rats had signs of impaired erectile function. Higher cavernosal ADMA was observed in the AS rats. The cavernosal ADMA had a moderately negative correlation with the ICP/MAP. Immunohistochemistry revealed the expression of both isoforms was not affected by the presence of AS. However, significantly diminished DDAH as well as NOS activity was observed in the AS group. In addition, elevated cavernosal malondialdehyde levels were noted in the AS rats. Our study showed that decreased cavernosal DDAH activity is the cause of cavernosal ADMA accumulation leading to reduced cavernosal NOS activity and impairment of erectile function.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.

Posttranslational modification of constitutive nitric oxide synthase in the penis

Erectile dysfunction (ED) is a common men's health problem characterized by the consistent inability to sustain an erection sufficient for sexual intercourse. Basic science research on erectile physiology has been devoted to investigating the pathogenesis of ED and has led to the conclusion that ED is predominately a disease of vascular origin, neurogenic dysfunction, or both. The constitutive forms of nitric oxide synthase (NOS, endothelial [eNOS] and neuronal [nNOS]) are important enzymes involved in the production of nitric oxide (NO) and thus regulate penile vascular homeostasis. Given the effect of endothelial- and neuronal-derived NO in penile vascular biology, a great deal of research over the past decade has focused on the role of NO synthesis from the endothelium and nitrergic nerve terminal in normal erectile physiology, as well as in disease states. Loss of the functional integrity of the endothelium and subsequent endothelial dysfunction plays an integral role in the occurrence of ED. Therefore, molecular mechanisms involved in dysregulation of these NOS isoforms in the development of ED are essential to discovering the pathogenesis of ED in various disease states. This communication reviews the role of eNOS and nNOS in erectile physiology and discusses the alterations in eNOS and nNOS via posttranslation modification in various vascular diseases of the penis.

Sildenafil inhibits superoxide formation and prevents endothelial dysfunction in a mouse model of secondhand smoke induced erectile dysfunction

PURPOSE

We determined the effect of passive secondhand cigarette smoke on 1) erectile function in vivo, 2) molecular mechanisms involved in penile vascular function, and 3) erectile function and penile molecular signaling in the presence of phosphodiesterase type 5 inhibitor therapy.

MATERIALS AND METHODS

Four groups of mice were used, including group 1--controls, group 2--mice exposed to 3 weeks of secondhand smoke (5 hours per day for 5 days per week), group 3--control plus sildenafil (100 mg/kg per day) and group 4--smoke exposed plus sildenafil (100 mg/kg per day). Cavernous nerve electrical stimulation and intracavernous injection of acetylcholine were done to assess erectile function. Constitutive and inducible nitric oxide synthase activity, reactive oxygen species generation, nitrotyrosine formation and superoxide anion levels were assessed.

RESULTS

Decreased erectile responses to cavernous nerve electrical stimulation and impaired endothelium dependent erectile responses to ACh in mice exposed to secondhand smoke were observed. Superoxide anion was increased in endothelial and corporeal smooth muscle cells of smoking mouse penises. In mice exposed to secondhand smoke constitutive nitric oxide synthase activity was decreased, and inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation increased. Sildenafil therapy restored constitutive nitric oxide synthase activity in the penis of smoking mice, decreased inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation, and improved erectile responses to cavernous nerve electrical stimulation and acetylcholine.

CONCLUSIONS

Short-term exposure to secondhand smoke impairs erectile function through excessive penile reactive oxygen species signaling and inducible nitric oxide synthase activity. Decreased penile constitutive nitric oxide synthase activity may be attributable to the decreased endothelial nitric oxide synthase activity resulting from increased oxidative stress. Sildenafil therapy restored nitric oxide synthase activity and decreased reactive oxygen species signaling, resulting in improved erectile function.

Nitric oxide upregulates dimethylarginine dimethylaminohydrolase-2 via cyclic GMP induction in endothelial cells

Dimethylarginine dimethylaminohydrolase (DDAH) is an enzyme that metabolizes asymmetrical N(G),N(G)-dimethyl-L-arginine (ADMA) and N(G)-monomethyl-L-arginine (MMA), which are competitive endogenous inhibitors of NO synthase. However, it remains unknown whether NO itself influences DDAH activity and/or ADMA/MMA contents to regulate NO generation via a biofeedback mechanism. The present study was designed to examine the effects of NO on intracellular ADMA and MMA contents and DDAH gene expression levels and enzymatic activities in cultured rat aortic endothelial cells. The NO donors SNAP and NOR3 did not influence DDAH-1 expression but increased DDAH-2 mRNA and protein levels in concentration-dependent manners. SNAP upregulated DDAH enzymatic activity and reduced the MMA and ADMA contents but did not affect the symmetrical N(G),N'(G)-dimethyl-L-arginine and L-arginine levels, thereby negating a mediatory role for system y(+) in ADMA/MMA downregulation. The cGMP agonists 8-bromo-cGMP and C-type natriuretic peptide also stimulated DDAH-2 gene and protein expression levels and DDAH activity and increased the amount of nitrite/nitrate released into the culture supernatants. SNAP-induced DDAH-2 gene expression and DDAH activity were significantly inhibited by a protein kinase G inhibitor, KT5823, and a soluble guanylate cyclase inhibitor, ODQ, suggesting a mediatory role for cGMP in NO-induced DDAH-2 expression. Suppression of DDAH-2 mRNA using small interfering RNA technology abrogated NO-induced DDAH-2 expression. These data demonstrate that NO acts on endothelial cells to induce DDAH-2 expression via a cGMP-mediated process to reduce ADMA/MMA. Thus, the DDAH-2-ADMA/MMA-endothelial NO synthase regulatory pathway and NO-induced cGMP constitute a positive feedback loop that ultimately serves to maintain NO levels in the endothelial environment.

Involvement of altered arginase activity, arginase I expression and NO production in accelerated intimal hyperplasia following cigarette smoke extract

In the present experiments, we tried to elucidate whether changes in arginase activity, protein expression of arginase-I and -II, and NO production are involved in accelerating the intimal hyperplasia following administration of cigarette smoke extract (CSE). The intimal hyperplasia was caused by removing endothelial cells with the aid of balloon embolectomy catheter in the right carotid artery of the male rabbit. The left carotid artery underwent sham operation and served as control. CSE was prepared by bubbling a stream of cigarette smoke into phosphate buffered saline. Rabbits were given subcutaneously with CSE once a day for 5 weeks from 1 week before to 4 weeks after the surgery. The specimens were assessed histologically and the intima/media ratio (%) was evaluated as an index of the intimal hyperplasia. The accelerated intimal hyperplasia with CSE was accompanied by the augmentation of the impaired cyclic GMP production, enhanced overall arginase activity and up-regulation of arginase-I. Pearson's correlation coefficient analyses revealed the close relationships among the arginase activities in endothelial cells and smooth muscle layer, the intimal/media ratio and cyclic GMP production. These results suggest that the enhanced arginase activity together with facilitated up-regulation of arginase-I with CSE, which was associated with the augmented impairment of NO production, shed a new light on the processes associated with accelerating the intimal hyperplasia in rabbit carotid arteries following CSE.

Arginase and pulmonary diseases

Recent studies have indicated that arginase, which converts L-arginine into L-ornithine and urea, may play an important role in the pathogenesis of various pulmonary disorders. In asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis, increased arginase activity in the airways may contribute to obstruction and hyperresponsiveness of the airways by inducing a reduction in the production of bronchodilatory nitric oxide (NO) that results from its competition with constitutive (cNOS) and inducible (iNOS) NO synthases for their common substrate. In addition, reduced L-arginine availability to iNOS induced by arginase may result in the synthesis of both NO and the superoxide anion by this enzyme, thereby enhancing the production of peroxynitrite, which has procontractile and pro-inflammatory actions. Increased synthesis of L-ornithine by arginase may also contribute to airway remodelling in these diseases. L-Ornithine is a precursor of polyamines and L-proline, and these metabolic products may promote cell proliferation and collagen production, respectively. Increased arginase activity may also be involved in other fibrotic disorders of the lung, including idiopathic pulmonary fibrosis. Finally, through its action of inducing reduced levels of vasodilating NO, increased arginase activity has been associated with primary and secondary forms of pulmonary hypertension. Drugs targeting the arginase pathway could have therapeutic potential in these diseases.

Possible involvement of altered arginase activity, arginase type I and type II expressions, and nitric oxide production in occurrence of intimal hyperplasia in premenopausal human uterine arteries

In the present experiments, we tried to elucidate whether changes in arginase activity and protein expression of arginase I and II are involved in the occurrence of intimal hyperplasia in premenopausal human uterine arteries. They were obtained from thirty-four patients undergoing total abdominal hysterectomy with informed consent for the present study. All specimens were assessed histologically and the intima/media ratio (%) was evaluated as an index of the intimal hyperplasia. Thirteen patients out of 34 had histologically normal arteries (intima/media ratio = 18.1 +/- 0.7%), whereas the remaining 21 patients had various degrees of intimal hyperplasia (intima/media ratio = 32.7 +/- 2.3%), and these specimens were categorized as hyperplasic. Intimal hyperplasia was accompanied by impaired cyclic GMP production, enhanced overall arginase activity, and up-regulations of arginase I and II in endothelial cells and of arginase II in the smooth muscle layer. Pearson's correlation coefficient analyses revealed the close relationships among the arginase activities in endothelial cells and smooth muscle layer, the intimal/media ratio, and cyclic GMP production. These results suggest that the enhanced arginase activity and expressions of two arginase subtypes shed new light on the processes associated with the occurrence of intimal hyperplasia in premenopausal human uterine arteries.