Testosterone Partially Ameliorates Metabolic Profile and Erectile Responsiveness to PDE5 Inhibitors in an Animal Model of Male Metabolic Syndrome

Hypogonadism and metabolic syndrome

BACKGROUND

The relationship between metabolic syndrome (MetS), male hypogonadism and their possible interaction in cardiovascular (CV) risk stratification are not completely understood.

AIM

We reviewed relationships between testosterone (T) and MetS emphasizing their possible interaction in the pathogenesis of CV diseases.

MATERIALS AND METHODS

A systematic search of published evidence was performed using Medline (1969 to January 2011).

RESULTS

Cross-sectional data have shown that subjects with MetS have lower levels of total T (TT) (about 3 nmol/l), as hypogonadism is more evident in subjects with than in those without erectile dysfunction (ED) than in those without. Longitudinal evidence shows that low T is allocated with a higher risk of subsequent development of MetS, although the reverse condition is also possible. Which are the factors in MetS responsible for the low T is not completely clarified. In clinical studies, increased waist circumference is the major determinant of MetS-associated hypogonadism. Our experiments in rabbits do not support the idea that visceral fat is the main determinant of MetS-associated male hypogonadism. Only few randomized clinical trials have evaluated the impact of T replacement therapy (TRT) in patients with MetS. Available evidence suggests that TRT decreases visceral fat accumulation and ameliorates insulin sensitivity, whereas androgen deprivation increases abdominal adiposity.

CONCLUSIONS

The clinical significance of the MetS-associated hypogonadism needs further clarifications. In particular, it has not been completely clarified if low T might be considered a cause or a consequence of MetS. The benefit of TRT in term of the reduction of CV risk needs to be confirmed in larger and longer studies.

Spermatogenic and sperm quality differences in an experimental model of metabolic syndrome and hypogonadal hypogonadism

The synergistic effect of the co-morbidities that comprise metabolic syndrome (MetS) is increasingly being recognised as an important contributor in the pathology of a broad spectrum of seemingly disparate conditions. However, in terms of male reproductive function, beyond erectile dysfunction, little is known about the influence of this cohort (collectively or separately) on spermatogenesis and sperm quality. The aims of this study were to assess the reproductive tract of a MetS animal model for detrimental changes, to determine whether a group of compounds (advanced glycation end products and their receptor) known to cause cell dysfunction and DNA damage was present and assess whether hypogonadotropic hypogonadism was the main contributing factor for the changes seen. Animals fed a high-fat diet were found to have significantly increased cholesterol, triglycerides, blood glucose, mean arterial pressure and visceral fat levels. Although serum testosterone was decreased, no changes were seen in either testicular or epididymal histology. Immunolocalisation ofNϵ-carboxymethyl-lysine and the receptor for advanced glycation end products was found in the testes, epididymides and sperm of the two treated groups of animals; however, ELISA did not show any difference in protein levels. Similarly, assessment of sperm nuclear DNA (nDNA) fragmentation by acridine orange test did not find significant differences in nDNA integrity. We conclude that the minimal effect on spermatogenesis and sperm quality seen in our model is probably due to the moderate increase of blood glucose rather than the hypogonadism.

Hypogonadal men nonresponders to the PDE5 inhibitor tadalafil benefit from normalization of testosterone levels with a 1% hydroalcoholic testosterone gel in the treatment of erectile dysfunction (TADTEST study)

INTRODUCTION

Addition of testosterone (T) may improve the action of phosphodiesterase type 5 inhibitors (PDE5-Is) in patients with erectile dysfunction not responding to PDE5-Is with low or low-normal T levels.

AIMS

To confirm this add-on effect of T in men optimally treated with PDE5-Is and to specify the baseline T levels at which such an effect becomes significant.

METHODS

A multicenter, multinational, double-blind, placebo-controlled study of 173 men, 45-80 years, nonresponders to treatment with different PDE5-Is, with baseline total T levels ≤ 4 ng/mL or bioavailable T ≤ 1 ng/mL. Men were first treated with tadalafil 10 mg once a day (OAD) for 4 weeks; if not successful, they were randomized in a double-blind, placebo-controlled design to receive placebo or a 1% hydroalcoholic T gel (50 mg/5 g gel), to be increased to 10 mg T if results were clinically unsatisfactory. Main Outcomes Measures.  Mean change from baseline in the Erectile Function Domain Score of the International Index of Erectile Function and rate of successful intercourses (Sexual Encounter Profile 3 question).

RESULTS

Erectile function progressively improved over a period of at least 12 weeks in both the placebo and T treatment groups. In the overall population with a mean baseline T level of 3.37 ± 1.48 ng/mL, no additional effect of T administration to men optimally treated with PDE5-Is was encountered. The differences between the T and placebo groups were significant for both criteria only in the men with baseline T ≤ 3 ng/mL.

CONCLUSIONS

The maximal beneficial effects of OAD dosing with 10 mg tadalafil may occur only after as many as 12 weeks. Furthermore, addition of T to this PDE5-I regimen is beneficial, but only in hypogonadal men with baseline T levels ≤ 3 ng/mL.

Effects of testosterone undecanoate on cardiovascular risk factors and atherosclerosis in middle-aged men with late-onset hypogonadism and metabolic syndrome: results from a 24-month, randomized, double-blind, placebo-controlled study

INTRODUCTION

Longitudinal studies have demonstrated that male hypogonadism could be considered a surrogate marker of incident cardiovascular disease.

AIM

To evaluate the effects of parenteral testosterone undecanoate (TU) in outclinic patients with metabolic syndrome (MS) and late-onset hypogonadism (total testosterone (T) at or below 11nmol/L or free T at or below 250pmol/L).

METHODS

This is a randomized, double-blind, double-dummy, placebo-controlled, parallel group, single-center study. Fifty patients (mean age 57±8) were randomized (4:1) to receive TU 1,000mg (every 12 weeks) or placebo (PLB) gel (3-6 g/daily) for 24 months.

MAIN OUTCOME MEASURES

Homeostasis model assessment index of insulin resistance (HOMA-IR), carotid intima media thickness (CIMT), and high-sensitivity C-reactive protein (hsCRP).

RESULTS

At baseline, all patients fulfilled the National Cholesterol Education Program-Third Adult Treatment Panel (NCEP-ATPIII) and International Diabetes Federation (IDF) criteria for the definition of MS. An interim analysis conducted at 12 months showed that TU markedly improved HOMA-IR (P < 0.001), CIMT (P < 0.0001), and hsCRP (P<0.001) compared with PLB; thus, all patients were shifted to TU treatment. After 24 months, 35% (P < 0.0001) and 58% (P < 0.001) of patients still presented MS as defined by NCEP-ATPIII and IDF criteria, respectively. Main determinants of changes were reduction in waist circumference (P<0.0001), visceral fat mass (P<0.0001), and improvement in HOMA-IR without changes in body mass index (BMI).

CONCLUSIONS

TU reduced fasting glucose, waist circumference, and improved surrogate markers of atherosclerosis in hypogonadal men with MS. Resumption and maintenance of T levels in the normal range of young adults determines a remarkable reduction in cardiovascular risk factors clustered in MS without significant hematological and prostate adverse events.

Update on corpus cavernosum smooth muscle contractile pathways in erectile function: a role for testosterone?

INTRODUCTION

Normal erectile function (EF) involves a coordinated relaxation of the arteries that supply the penis and the corpus cavernosum smooth muscle (CCSM), resulting in expansion of the sinusoids and increased intracavernous pressure. But the CCSM spends the majority of its time in the contracted state which is mediated by norepinephrine released from nerve endings and other vasoconstrictors like endothelins released from the endothelium. These agents cause smooth muscle myosin (SMM) phosphorylation by elevating intracellular calcium. When calcium returns to basal levels, the calcium sensitivity increases and prevents myosin dephosphorylation, which involves the RhoA/Rho-kinase (ROK) mechanism, thus maintaining force. Although mounting evidences demonstrate that androgens have a major influence on EF that is not just centrally mediated, this notion remains quite controversial.

AIM

To summarize the current knowledge on CCSM contractile pathways, the role they play in modulating EF, and the influence of androgens.

METHODS

The article reviews the literature and contains some previously unpublished data on CCSM contraction signaling including the role that androgens are known to play in modulating these pathways.

MAIN OUTCOME MEASURES

Data from peer-reviewed publications and previously unpublished observations.

RESULTS

In addition to downregulation of many pro-erectile molecular mechanisms, decreased testosterone (T) levels upregulate CCSM contractility, including hyperresponsiveness to α-adrenergic agonists, increased SMM phosphorylation, alteration of SMM isoform composition, activation of RhoA/ROK signaling and modulation of sphingosine-1-phosphate regulation of CCSM tone.

CONCLUSIONS

Decreased T levels upregulate CCSM contractile signaling. Meanwhile, it downregulates CCSM relaxation pathways synergizing to produce erectile dysfunction (ED). Although some urologists and researchers are still skeptical of the influence of androgens on penile erection, understanding these molecular control mechanisms as well as the influence that androgens have on these pathways should provide new evidence supporting the roles of androgens in EF and enhance the discovery of novel targets for drug development to treat ED.

Farnesoid X receptor activation improves erectile dysfunction in models of metabolic syndrome and diabetes

The metabolic syndrome (MetS) is an insulin-resistant state characterized by a cluster of cardiovascular risk factors, including abdominal obesity, hyperglycemia, elevated blood pressure and combined dyslipidemia. In this review, we discuss the potential of farnesoid X receptor (FXR) agonists in the treatment of erectile dysfunction (ED), a multifactorial disorder often comorbid with MetS. FXR not only regulates lipid and glucose homeostasis but also influences endothelial function and atherosclerosis, suggesting a regulatory role for this hormone nuclear receptor in the cardiovascular complications associated with the MetS, including ED. MetS induces ED via several mechanisms, and in particular through endothelial dysfunction in penile vessels. In a high-fat diet rabbit model of MetS, a 3-month treatment with the potent and selective FXR agonist INT-747 restores endothelium-dependent relaxation in isolated cavernous tissue, normalizing responsiveness to acetylcholine and to electrical field stimulation. Accordingly, eNOS expression in the penis is greatly up-regulated by INT-747 treatment. Experiments in a rat model of chemically-induced type 1 diabetes further demonstrate that INT-747 treatment preserves erectile function induced by electrical stimulation of the cavernous nerve. These results add a new facet to the pleiotropic activities mediated by FXR, and reveal novel beneficial effects of FXR activation with potential clinical relevance. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Type 2 diabetes mellitus and testosterone: a meta-analysis study

Several studies suggest that type 2 diabetes mellitus (T2DM) is often associated with male hypogonadism. Despite the well-known link, the role of testosterone replacement therapy (TRT) in T2DM has not been completely clarified. The aim of the present study was to analyse systematically the relationship between androgen levels and T2DM by reviewing and meta-analysing available prospective and cross-sectional studies. In addition, a specific meta-analysis on the metabolic effects of TRT in available randomized clinical trials (RCTs) was performed. An extensive Medline search was performed including the following words: 'testosterone', 'type 2 diabetes mellitus' and 'males'. Of 742 retrieved articles, 37 were included in the study. In particular 28, 5 and 3 were cross-sectional, longitudinal and interventional studies, respectively. A further unpublished RCT was retrieved from http://www.clinicaltrials.gov. T2DM patients showed significantly lower testosterone plasma levels in comparison with non-diabetic individuals. Similar results were obtained when T2DM subjects with and without erectile dysfunction were analysed separately. Meta-regression analysis demonstrated that ageing reduced, while obesity increased, these differences. However, in a multiple regression model, after adjusting for age and body mass index (BMI), T2DM was still associated with lower total testosterone (TT) levels (adjusted r = -0.568; p < 0.0001). Analysis of longitudinal studies demonstrated that baseline TT was significantly lower among patients with incident diabetes in comparison with controls (HR = -2.08[-3.57;-0.59]; p < 0.001). Combining the results of RCTs, TRT was associated with a significant reduction in fasting plasma glucose, HbA1c, fat mass and triglycerides. Conversely, no significant difference was observed for total and high-density lipoprotein cholesterol, blood pressure and BMI. The meta-analysis of the available cross-sectional data suggests that T2DM can be considered independently associated with male hypogonadism. Although only few RCTs have been reported, TRT seems to improve glycometabolic control as well as fat mass in T2DM subjects.

Farnesoid X receptor activation improves erectile function in animal models of metabolic syndrome and diabetes

INTRODUCTION

The farnesoid X receptor (FXR) is critically involved in the regulation of the hepato-biliary system. Recent data suggest a role for FXR in modulating other metabolic pathways and vascular function.

AIM

To investigate whether long-term administration of the selective FXR agonist INT-747 ameliorates erectile function, we tested it in two animal models of metabolic derangements: a rabbit model of high-fat diet (HFD)-induced metabolic syndrome (MetS) and a rat model of streptozotocin (STZ)-induced type 1 diabetes.

METHODS

HFD rabbit or STZ rats with or without chronic INT-747 dosing (10 mg/kg/day for 12 weeks). INT-747 addition to rabbit penile smooth muscle cells (rpSMCs).

MAIN OUTCOME MEASURE

Effects of INT-747 on metabolic features and erectile function in animal models and clarification of mechanism of action in isolated cells.

RESULTS

INT-747 dosing normalized visceral adiposity and glucose intolerance in HFD rabbits. INT-747 increased penile FXR expression and partially restored endothelial nitric oxide synthase and dimethylarginine dimethylaminohydrolase 1 expression as well as impaired nitric oxide (NO)-dependent relaxation (improved responsiveness to acetylcholine and electrical field stimulation). INT-747 was also effective in regulating NO downstream events, as shown by increased sodium nitroprusside-induced relaxation. Because phosphodiesterase type 5 and protein kinase G (PKG) were unaltered by INT-747, we analyzed the calcium-sensitizing RhoA/ROCK pathway. HFD increased, and INT-747 normalized, RhoA membrane translocation/activation. RhoA/ROCK signaling inhibition by INT-747 was confirmed in rpSMCs by confocal microscopy, MYPT1-phosphorylation, cytoskeleton remodeling, cell migration, and smooth muscle-related genes expression. In STZ rats, FXR penile expression was not altered but was significantly upregulated by INT-747 dosing. In this model, INT-747 improved penile erection induced by electrical stimulation of cavernous nerve and hypersensitivity to intracavernous injection of a ROCK-inhibitor, Y-27632, without improving hyperglycemia.

CONCLUSION

In HFD rabbits, INT-747 dosing improved glucose sensitivity and MetS-associated erectile dysfunction, via upregulation of NO transmission and inhibition of RhoA/ROCK pathway. In STZ rats, INT-747 restored in vivo penile erection and sensitivity to ROCK inhibition, independently of effects on glycemia.

Testosterone and metabolic syndrome: a meta-analysis study

INTRODUCTION

Metabolic syndrome (MetS) is often associated with male hypogonadism. Despite the well-known link, the role of testosterone replacement therapy (TRT) in MetS has not been completely clarified.

AIM

To systematically analyse the relationship between androgen levels and MetS we performed a review and meta-analyses of available prospective and cross-sectional studies. In addition, a specific meta-analysis on the metabolic effects of TRT in available randomized clinical trials (RCTs) was also performed.

METHODS

An extensive Medline search was performed including the following words "testosterone,""metabolic syndrome," and "males".

MAIN OUTCOME MEASURES

Out of 323 retrieved articles, 302 articles were excluded for different reasons. Among the 20 published studies included, 13, 3, and 4 were cross-sectional, longitudinal, and RCTs, respectively. Another unpublished RCT was retrieved on http://www.clinicaltrials.gov.

RESULTS

MetS patients showed significantly lower T plasma levels, as compared with healthy individuals. Similar results were obtained when MetS subjects with and without erectile dysfunction were analyzed separately or when NCEP-ATPIII MetS criteria were compared with other definitions. Meta-regression analysis demonstrated that type 2 diabetes (T2DM) increased the MetS-associated T fall. In a multiple regression model, after adjusting for age and BMI, both T2DM and MetS independently predicted low testosterone (adj. r = -0.752; P < 0.001 and -0.271; P < 0.05, respectively). Analysis of longitudinal studies demonstrated that baseline testosterone was significantly lower among patients with incident MetS in comparison with controls (2.17 [-2.41;-1.94] nmol/L; P < 0.0001). Combining the results of RCTs, TRT was associated with a significant reduction of fasting plasma glucose, homeostatic model assessment index, triglycerides, and waist circumference. In addition, an increase of high-density lipoprotein cholesterol was also observed.

CONCLUSIONS

The meta-analysis of the available cross-sectional data suggests that MetS can be considered an independent association of male hypogonadism. Although only few RCTs have been reported, TRT seems to improve metabolic control, as well as central obesity.

Treatment of 161 men with symptomatic late onset hypogonadism with long-acting parenteral testosterone undecanoate: effects on body composition, lipids, and psychosexual complaints

INTRODUCTION

Elderly men may suffer from late-onset hypogonadism (LOH). The long-term effects of long-acting testosterone undecanoate (TU) in a large number of LOH men have not yet been reported. Aims.  We analyzed the effects of normalization of plasma testosterone (T) in LOH men.

METHODS

The records of 161 men with LOH (baseline T<300 ng/dL) were reviewed and 100 men had used parenteral TU for >12 months. The mean duration of treatment was 90.6 weeks (54 to 150 weeks).

MAIN OUTCOME MEASURES

Body mass index (BMI), waist circumference, percentage body fat, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, prostate-specific antigen (PSA), and hematocrit were measured. Further the Aging Male Symptoms' scale (AMS) and the International Index of Erectile Function (IIEF-5 and 15) were scored.

RESULTS

T therapy was associated with a significant decline in waist circumference (P=0.028) and percentage body fat (P<0.001), but no change of BMI. Total cholesterol and LDL cholesterol declined significantly (P=0.005 and P=0.024, respectively), with no significant changes of HDL cholesterol and triglycerides. The scores of sub-scales of AMS (psychological, somotovegetative and sexual factors) decreased (P=0.044, P=0.200 and P=0.071, respectively). The mean IIEF-5 (P=0.011) and IIEF-15 scores (P=0.021) improved significantly. Erectile function domain, orgasmic function domain, sexual desire domain, intercourse satisfaction domain, and overall satisfaction domain improved. Median PSA rose from 0.95 (0.640; 1.558) ng/mL to 1.480 (1.015; 2.275) ng/mL (P<0.001), with 11 patients >4 ng/mL (4.01-13.21). On biopsy there was no evidence for malignancy. The mean hematocrit level increased significantly from 42.3±3.4% to 47.1±3.8%.

CONCLUSIONS

Normalizing serum T in men with LOH resulted in improvement of the metabolic syndrome, mood and sexual functions and appeared acceptably safe.

A new perfusion model for studying erectile function

INTRODUCTION

The present study introduces a newly devised in vitro penile perfusion model, which allows the measurement of changes in intracavernosum pressure (ICP), tension, and cyclic nucleotides in penile tissue in a one-step procedure.

AIMS

We compared the penile perfusion model with the classical penile strip chamber model to develop the new model.

METHODS

We investigated the role of nitric oxide-cyclic guanosine monophosphate pathway in both systems activated by acetylcholine or electrical field stimulation (EFS). We measured cGMP (cyclic guanosine monophosphate) in the penile corpus cavernosum smooth muscle in both systems and perfusates in the penile perfusion model. We determined ICP, tension, and cGMP simultaneously in penile perfusion model during the experiments.

MAIN OUTCOME MEASURES

Changes of tension and cGMP in both models, and of cGMP in perfusates and of ICP in penile perfusion model.

RESULTS

In both systems, acetylcholine relaxed the phenylephrine-precontracted penile corpus cavernosum smooth muscle in a concentration-dependent manner. EFS decreased the tension in both models and ICP in the penile perfusion model in a frequency-dependent manner. Pretreatment with atropine, Nomega nitro-L-arginine-methyl ester (L-NAME), and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) blocked the acetylcholine-induced decrease in the tension in both models and ICP in penile perfusion model. Acetylcholine increased cGMP levels in the perfusate of penile perfusion model and the changes were attenuated by tetrodotoxin (TTX), atropine, L-NAME and ODQ. EFS increased cGMP levels of the penile corpus cavernosum smooth muscle of both models and the changes were attenuated by TTX, atropine, L-NAME, and ODQ.

CONCLUSION

The results indicated that the responses of penile strip and perfused penile tissue to acetylcholine and EFS were very similar in both models in terms of tension and cGMP levels. Furthermore, the new model has more advantages over the classical penile strip chamber model in measuring intracavernosum metabolic changes and ICP without interruption of the procedure.

Testosterone deficiency in the aging male and its relationship with sexual dysfunction and cardiovascular diseases

: The relationship between age-associated dec-line of testosterone (T), cardiovascular (CV) risk and sexual dysfunction in males is not completely clear. The aim of the present study was to report our experience in a large series of patients seeking medical care for sexual dysfunction and comparing our results with current evidence.

: Here, we review published data from our laboratory and reported data from a cross-sectional analysis on a consecutive series of 3149 patients seeking medical care at our Unit for sexual dysfunction (between 2000 and 2010). Among them, 1687 (studied between 2000 and 2007) patients were also longitudinally evaluated (mean follow-up 4.3±2.6 years) for forthcoming major cardiovascular events (MACEs). All major findings were discussed in comparison with data reported in the literature.

: T levels were associated with a wide array of biological and psychological factors, which substantially differ as a function of age. Some of these associations were more evident in the youngest patients (psychological symptoms), whereas sexual symptoms, including erectile function, sexual desire and the frequency of sexual intercourse, were associated with T levels only in the oldest patients. We did not find any association between T and MACEs, whereas we reported a close link between CV mortality and low T. Both these observations are in line with data obtained in community-dwelling men.

: T plays a crucial role in regulating different aspects of male sexual function. The effect of T on CV risk needs to be confirmed in larger epidemiological and interventional studies.

The role of testosterone in erectile dysfunction

Erectile dysfunction (ED) is a clinical disorder that results from a continuous spectrum of clinical factors, including physical illness (comprising the organic component of ED), reaction to stress (the intrapsychic component of ED) and relationship difficulties (the relationship component of ED). Testosterone clearly has a relevant role in all three causes of ED; the usefulness of this hormone in the treatment of ED has not, however, been completely clarified. The main physiological action of testosterone in the male sexual response is to regulate the timing of the erectile process as a function of sexual desire, thereby coordinating penile erection with sex. The link between ED, hypogonadism and underlying disorders (such as metabolic syndrome and type 2 diabetes mellitus) is nowadays well documented. The recognition of underlying disorders might be useful in motivating men with ED to improve their health-related lifestyle choices. Hence, patients with ED might be considered 'lucky', because their disorder offers the opportunity to undergo medical examinations to detect underlying disease. Both ED and hypogonadism are treatable conditions. A range of testosterone preparations are available for supplementation; their combination with phosphodiesterase 5 inhibitors might improve outcomes in some cases.