Testosterone and erectile function: from basic research to a new clinical paradigm for managing men with androgen insufficiency and erectile dysfunction

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.

The effect of regular exercise on penile nitric oxide synthase expression in rats

Erectile dysfunction (ED) is a major public health problem that seriously affects the quality of life of patients and their partners and its prevalence increases significantly with ageing. In this study, we tested the hypothesis that age-associated decrease in penile endothelial (eNOS) and neuronal nitric oxide synthase (nNOS) activity in aged rats may be increased by regular exercise. A total of 28 young (4 m) and aged (24 m) male rats were divided into four equal groups: group 1 - young control; group 2 - young trained; group 3 - old control and group 4 - old trained group. Groups 2 and 4 rats were trained to swim for 30 min a day and 5 days a week, which lasted 8 weeks. At the end of 8 weeks, rats were sacrificed and penile tissues evaluated for eNOS and nNOS activities. eNOS and nNOS activities were evaluated by immunohistochemistry in paraffinized penile tissues and results assessed semiquantitatively. Results also were compared with healthy age-matched and adult (4 m) controls. Serum level of testosterone (T) was determined using ELISA kits (Beckman Coulter, Fullerton, CA, USA). In penile tissues of aged control rats, eNOS and nNOS staining were weakly positive; however in trained groups, eNOS and nNOS immunoreactivity were increased. In young control group, eNOS and nNOS activities were more intense than aged control. eNOS and nNOS activities were higher in adult trained group than control. Serum T concentrations were significantly higher in young and aged trained group than in control groups. We can suggest that regular exercise upregulates eNOS and nNOS expressions in the aged and young rat penis. Regular exercise may improve penile erection by increasing penile neurotransmitter in both young and aged rats.

Ginsenoside Rg1 improves male copulatory behavior via nitric oxide/cyclic guanosine monophosphate pathway

INTRODUCTION

Ginsenoside Rg1 is the purified ingredient from ginseng, there has been little research on the effect of Rg1 on male copulatory behavior and its mechanism of action.

AIM

The purpose of this study was to investigate the effect of ginsenoside Rg1 on copulatory behavior of male mice and the mechanism of its action.

METHODS

Male mice were treated with Rg1 intraperitoneally; three elements of copulatory behavior (mounting, intromission, pelvic thrusting) were assessed. After final treatment and behavior determination, nitric oxide (NO) concentration were determined by spectrophotometry method. Plasma testosterone, cyclic guanosine monophosphate (cGMP) in corpus cavernosum both in vivo and in vitro were measured by radioimmunoassay. Rabbit corpus cavernosum segments were incubated with Rg1 (0.05, 0.5 and 5 microM) in the presence of exogenous NO donor sodium nitroprusside (SNP) (10 microM), and the cGMP level was measured. The half maximal inhibitory concentration (IC50) of Rg1 for phosphodiesterase type 5 (PDE5) inhibitors was determined by measuring the conversion of cGMP to 5'-mononucleotides. Sildenafil was set as a positive control. MAIN COME OUT MEASURES: Mounting and intromission frequency, pelvic thrusts, serum testosterone, NO level, cGMP accumulation, IC50 for PDE5.

RESULTS

Rg1 (10 mg/kg) significantly increased mounting and pelvic thrusting frequency and numbers of intromission of male mice from d16 to d20. Rg1 increased serum testosterone concentration, enhanced NO release, and cGMP accumulation in corpus cavernosum both in vivo and in vitro. The IC50 of sildenafil and Rg1 for PDE5 were 4.24 +/- 0.78 and 12.47 +/- 2.31 nmol/L.

CONCLUSIONS

Ginsenoside Rg1 improved copulatory behavior of male mice and this may attribute to its actions at both testosterone level and signal transduction pathway in corpus cavernosum. NO/cGMP pathway appeared to play a key role in mediating the effect of Rg1 on male sexual function. These experimental data provide evidence that Rg1 could be a promising new drug for erectile dysfunction and low libido.

Plasma concentration of prolactin, testosterone might be associated with brain response to visual erotic stimuli in healthy heterosexual males

OBJECTIVE

Many studies have showed that excess or lack of sexual hormones, such as prolactin and testosterone, induced the sexual dysfunction in humans. Little, however, is known about the role of sexual hormones showing normal range in, especially, the basal state unexposed to any sexual stimulation. We hypothesized sexual hormones in the basal state may affect sexual behavior.

METHODS

We investigated the association of the sexual hormones level in the basal hormonal state before visual sexual stimulation with the sexual response-related brain activity during the stimulation. Twelve heterosexual men were recorded the functional MRI signals of their brain activation elicited by passive viewing erotic (ERO), happy-faced (HA) couple, food and nature pictures. Both plasma prolacitn and testosterone concentrations were measured before functional MR scanning. A voxel wise regression analyses were performed to investigate the relationship between the concentration of sexual hormones in basal state and brain activity elicited by ERO minus HA, not food minus nature, contrast.

RESULTS

The plasma concentration of prolactin in basal state showed positive association with the activity of the brain involving cognitive component of sexual behavior including the left middle frontal gyrus, paracingulate/superior frontal/anterior cingulate gyri, bilateral parietal lobule, right angular, bilateral precuneus and right cerebellum. Testosterone in basal state was positively associated with the brain activity of the bilateral supplementary motor area which related with motivational component of sexual behavior.

CONCLUSION

Our results suggested sexual hormones in basal state may have their specific target regions or network associated with sexual response.

Testosterone therapy in men

Androgens exert effects on virtually all bodily tissues, and have a multitude of physiological roles in health. Testosterone, the predominant androgen in men, when deficient (hypogonadism), leads to a multiplicity of symptoms and signs that are corrected with physiological substitution. The impact of hypogonadism depends on the age at which it occurs. In any case, when testosterone replacement is initiated close monitoring for efficacy and safety is advised. The relation of ageing, the metabolic syndrome, type 2 diabetes, obesity and survival with plasma testosterone has been closely examined in recent studies. However, the effect of testosterone replacement therapy on the above clinical states needs to be clarified in large long-term duration/outcome studies. Recent research has shed light on possible molecular testosterone targets. Based on those research outcomes, drugs targeting the androgen receptor, which spare androgenic effects and preserve anabolic tissue effects, called selective androgen receptor modulators (SARMS), are under clinical trials. The role of testosterone in regulating erectile function has been studied in animal models and critical tissue testosterone targets have been elucidated.

The relationship of serum and salivary cortisol levels to male sexual dysfunction as measured by the International Index of Erectile Function

To evaluate the biomarkers of sexual function, we investigated the relationship between questionnaire responses and biological hormones such as testosterone (T) and cortisol (F) in serum and saliva. The study population included 105 men aged 30-72 years (mean: 49+/-4.5, median: 49). Levels of all serum hormones (Total-T, Free-T, Bioavailable-T, Total-F and Bioavailable-F) and salivary hormones (Saliva-T and Saliva-F) were measured directly by liquid chromatography/tandem mass spectrometry. The International Index of Erectile Function (IIEF) was used as a questionnaire to evaluate sexual dysfunction. Free-T and Bioavailable-T showed significant inverse correlations with age (P<0.01). In the group not taking antidepressants, the levels of Bioavailable-F and Saliva-F showed significant inverse correlations with a portion of the IIEF score (P<0.05). However, reductions in Bioavailable-T and Saliva-T showed no association with the IIEF score. In the group taking antidepressants, these hormone levels showed no correlation with IIEF.

Testosterone regulates erectile function and Vcsa1 expression in the corpora of rats

Vcsa1 plays an important role in the erectile physiology of the rat. We conducted experiments to determine if erectile function, testosterone levels and Vcsa1 expression were correlated. In orchiectomized rats, total testosterone in blood fell from an average of 4 ng/ml to <0.04 ng/ml. Erectile function was significantly lower compared to controls and Vcsa1 expression was significantly (>6-fold) decreased. Injection of orchiectomized animals with testosterone (2 mg in 100ml sesame oil every 4 days for 2 weeks) restored average levels of testosterone to 2 ng/ml, increased erectile function and significantly increased Vcsa1 expression. In isolated corporal cells there was testosterone dependent Vcsa1 expression. However, intracorporal injection of orchiectomized animals with a plasmid expressing Vcsa1 or its gene product Sialorphin (previously demonstrated to improve erectile function in old animals) gave no significant improvement in erectile function. Also, the ability of Sialorphin to reduce tension in corporal smooth muscle strips isolated from orchiectomized animals was impaired compared to controls.

Changes in the penile arteries of the rat after fractionated irradiation of the prostate: a pilot study

INTRODUCTION

External beam radiotherapy for prostate cancer leads to erectile dysfunction in 36%-43% of patients. The underlying mechanism is largely unknown, although some clinical studies suggest that the arterial supply to the corpora cavernosa is responsible. Two animal experimental studies reported on the effects of a single fraction of prostate irradiation on the penile structures. However, irradiation in multiple fractions is more representative of the actual clinical treatment.

AIM

The present prospective, controlled study was initiated to investigate the effect of fractionated prostate irradiation on the arteries of the corpora cavernosa.

MAIN OUTCOME MEASURES

Histological evaluation of the penile tissue in comparison with control rats at 2, 4, and 9 weeks after irradiation.

METHODS

The prostate of twelve rats was treated with external beam radiation in 5 daily fractions of 7.4 gray. Three control rats were treated with sham irradiation. Prostatic and penile tissue was evaluated for general histology (hematoxylin-eosin). The penile tissue was further evaluated after combined staining for collagen (resorcin fuchsin) and alpha-smooth muscle actin (SMA) (Biogenex).

RESULTS

The prostate showed adequate irradiation with fibrosis occurring at 9 weeks after irradiation. The corpora cavernosa showed arteries that had developed loss of smooth muscle cells expressing SMA, thickening of the intima, and occlusions. All the control rats maintained normal anatomy.

CONCLUSION

This is the first animal experimental study that demonstrates changes in the arteries of the corpora cavernosa after fractionated irradiation to the prostatic area. The preliminary data suggests that erectile dysfunction after radiotherapy might be caused by radiation damage to the arterial supply of the corpora cavernosa.

Does regular consumption of green tea influence expression of vascular endothelial growth factor and its receptor in aged rat erectile tissue? Possible implications for vasculogenic erectile dysfunction progression

Erectile dysfunction (ED) is a highly prevalent disease affecting millions of men worldwide with a tendency for widespread increase. ED is now considered an early manifestation of atherosclerosis and, consequently, a precursor of systemic vascular disease. Atherosclerosis and ED share potentially modifiable risk factors, as smoking or high-fat food intake, but it is unclear how regular consumption of anti-oxidant rich drinks, which exhibit recognised anti-atherosclerotic features, affects ED progression. The objective of this study was to evaluate the modulating effects of chronic consumption of catechin-rich beverages on the vascular structure of the rat corpus cavernosum, and how this could contribute to delay or prevention of the onset of ED. Male Wistar rats aged 12 months were treated with green tea (GT) or a green tea extract solution (GTE) as the only liquid source for 6 months. Consumption of GT and GTE led to decreased plasma androgen levels without any significant change in plasma lipid levels. A reduction in corpus cavernosum intracellular storage of lipids, associated with decreased expression of vascular endothelial growth factor (VEGF) and its receptor VEGFR2 in endothelial cells, was observed. Taken together, these results suggest diminished atherosclerotic progression in cavernous tissue. However, functional studies will be necessary to elucidate if catechin-rich beverages are useful compounds in the prevention of deleterious vascular events associated with ED. It was also demonstrated that regular consumption of catechins reduces atherosclerotic progression and mortality due to cardiovascular disease. The results reported here suggest diminished atherosclerotic progression in cavernous tissue in aged rats following chronic ingestion of catechin-rich beverages.

The effect of testosterone therapy on lower urinary tract symptoms/bladder and sexual functions in men with symptomatic late-onset hypogonadism

OBJECTIVE

To prospectively investigate the effect of testosterone therapy on lower urinary tract symptoms (LUTS)/bladder and sexual functions in men with symptomatic late-onset hypogonadism (SLOH).

METHODS

The study included 25 men (age range 38 to 73 years) presented with sexual dysfunction, having SLOH, at a single university hospital. All men received testosterone replacement therapy with transdermal testosterone 50-100 mg gel per day for one year. Urodynamic studies with pressure-flow analysis, measurement of prostate volume, prostate specific antigen (PSA) and free PSA level, International Prostate Symptom Score (IPSS), Aging Male Symptom (AMS) scale and International Index of Erectile Function (IIEF-5) score were recorded in all men before and after one year of the treatment.

RESULTS

The mean AMS score significantly decreased from 40.4 +/- 7.3 to 28.8 +/- 5.31 (p = 0.001), and mean IIEF-5 score significantly increased from 8.84 +/- 3.76 to 14.36 +/- 3.62 (p = 0.001). The mean maximal bladder capacity and compliance significantly increased (p = 0.007 and p = 0.032, respectively), and mean detrusor pressure at Qmax significantly decreased from pre-treatment to post-treatment (p = 0.017).

CONCLUSION

This study suggests that in addition to improvement in sexual functions, testosterone therapy may also improve LUTS/bladder functions by increasing bladder capacity and compliance and decreasing detrusor pressure at maximal flow in men with SLOH.

Hypogonadism and erectile dysfunction: an overview

In humans androgen decline is presented as a clinical picture which includes decreased sexual interest, diminished erectile capacity, delayed or absent orgasms and reduced sexual pleasure. Additionally, changes in mood, diminished well being, fatigue, depression and irritability are also associated with androgen insufficiency. The critical role of androgens on the development, growth, and maintenance of the penis has been widely accepted. Although, the exact effect of androgens on erectile physiology still remains undetermined, recent experimental studies have broaden our understanding about the relationship between androgens and erectile function. Preclinical studies showed that androgen deprivation leads to penile tissue atrophy and alterations in the nerve structures of the penis. Furthermore, androgen deprivation caused to accumulation of fat containing cells and decreased protein expression of endothelial and neuronal nitric oxide synthases (eNOS and nNOS), and phosphodiesterase type-5 (PDE-5), which play crucial role in normal erectile physiology. On the light of the recent literature, we aimed to present the direct effect of androgens on the structures, development and maintenance of penile tissue and erectile physiology as well. Furthermore, according to the clinical studies we conclude the aetiology, pathophysiology, prevalence, diagnosis and treatment options of hypogonadism in aging men.

The paradox dividing testosterone deficiency symptoms and androgen assays: a closer look at the cellular and molecular mechanisms of androgen action

INTRODUCTION

Central to the diagnosis and treatment of testosterone deficiency syndrome in the adult male is the remarkable paradox that there is a very poor correlation between the characteristic symptoms and levels of serum androgens.

AIM

Because androgen deficiency can be associated with severe symptomatology, as well as diverse conditions such as coronary heart disease, diabetes, and metabolic syndrome, the aim was to present an evidence-based working hypothesis to resolve this confusing clinical paradox.

METHODS

A review of the possible mechanisms in testosterone deficiency syndrome was carried out, and a hypothesis to explain this paradox and associated problems in the diagnosis and clinical management of androgen deficiency was established on the basis of a review of the literature.

MAIN OUTCOME MEASURES

The mechanisms by which androgen deficiency could arise were studied at five different levels: 1. Impaired androgen synthesis or regulation. 2. Increased androgen binding. 3. Reduced tissue responsiveness. 4. Decreased androgen receptor activity. 5. Impaired transcription and translation.

RESULTS

As with insulin in maturity onset diabetes mellitus, there can be both insufficient production and variable degrees of resistance to the action of androgens operating at several levels in the body simultaneously, with these factors becoming progressively worse with aging, adverse lifestyle, other disease processes, and a wide range of medications.

CONCLUSIONS

Using this model, androgen deficiency can be redefined as an absolute or relative deficiency of androgens or their metabolites according to the needs of that individual at that time in his life. There are important ways in which the considerations raised by this hypothesis affect the etiology, terminology, diagnosis, and treatment of androgen-deficient states.