Mechanism of action of phosphodiesterase type 5 inhibition in metabolic syndrome-associated prostate alterations: an experimental study in the rabbit

Tadalafil effect on metabolic syndrome-associated bladder alterations: an experimental study in a rabbit model

INTRODUCTION

Metabolic syndrome (MetS) and lower urinary tract symptoms (LUTS) are often associated. Bladder detrusor hyper-contractility-a major LUTS determinant-is characterized by increased Ras homolog gene family, member A/Rho-associated protein kinase (RhoA/ROCK) signaling, which is often upregulated in MetS.

AIM

This study investigated the effects of tadalafil dosing on RhoA/ROCK signaling in bladder, in a rabbit model of high-fat diet (HFD)-induced MetS.

METHODS

Adult male rabbits feeding a HFD for 12 weeks. A subset of HFD animals was treated with tadalafil (2 mg/kg/day, 1 week: the last of the 12 weeks) and compared with HFD and control (feeding a regular diet) rabbits.

MAIN OUTCOME MEASURES

In vitro contractility studies to evaluate the relaxant effect of the selective ROCK inhibitor, Y-27632, in carbachol precontracted bladder strips. Evaluation of RhoA activation by its membrane translocation. Immunohistochemistry for ROCK expression has been performed to evaluate ROCK expression in bladder from the different experimental groups. mRNA expression of inflammation, pro-fibrotic markers by quantitative RT-PCR has been performed to evaluate the effect of tadalafil on MetS-induced inflammation and fibrosis within the bladder. The in vitro effect of tadalafil on RhoA/ROCK signaling in bladder smooth muscle cells was evaluated by using chemotaxis assay.

RESULTS

Bladder strips from HFD rabbits showed hyper-responsiveness to Y-27632, indicating RhoA/ROCK overactivity in HFD bladder compared with matched controls. Accordingly, the fraction of activated (translocated to the membrane) RhoA as well as ROCK expression are increased in HFD bladder. Tadalafil dosing normalized HFD-induced bladder hypersensitivity to Y-27632, by reducing RhoA membrane translocation and ROCK overexpression. Tadalafil dosing reduced mRNA expression of inflammatory, pro-fibrotic, and hypoxia markers. A direct inhibitory effect of tadalafil on RhoA/ROCK signaling in bladder smooth muscle cell was demonstrated by using chemotaxis assay. Pre-treatment with tadalafil inhibited both basal and PDGF-induced migration of bladder smooth muscle cells.

CONCLUSIONS

Tadalafil dosing reduced RhoA/ROCK signaling and smooth muscle overactivity in an animal model of MetS-associated bladder alterations. Our findings suggest a novel mechanism of action of tadalafil in alleviating LUTS in MetS patients.

Metabolic syndrome induces inflammation and impairs gonadotropin-releasing hormone neurons in the preoptic area of the hypothalamus in rabbits

Rabbits with high fat diet (HFD)-induced metabolic syndrome (MetS) developed hypogonadotropic hypogonadism (HH) and showed a reduced gonadotropin-releasing hormone (GnRH) immunopositivity in the hypothalamus. This study investigated the relationship between MetS and hypothalamic alterations in HFD-rabbits. Gonadotropin levels decreased as a function of MetS severity, hypothalamic gene expression of glucose transporter 4 (GLUT4) and interleukin-6 (IL-6). HFD determined a low-grade inflammation in the hypothalamus, significantly inducing microglial activation, expression and immunopositivity of IL-6, as well as GLUT4 and reduced immunopositivity for KISS1 receptor, whose mRNA expression was negatively correlated to glucose intolerance. Correcting glucose metabolism with obetcholic acid improved hypothalamic alterations, reducing GLUT4 and IL-6 immunopositivity and significantly increasing GnRH mRNA, without, however, preventing HFD-related HH. No significant effects at the hypothalamic level were observed after systemic anti-inflammatory treatment (infliximab). Our results suggest that HFD-induced metabolic derangements negatively affect GnRH neuron function through an inflammatory injury at the hypothalamic level.

Benign prostatic hyperplasia: a new metabolic disease of the aging male and its correlation with sexual dysfunctions

Metabolic syndrome (MetS) is a well-recognized cluster of cardiovascular (CV) risk factors including obesity, hypertension, dyslipidemia, and hyperglycaemia, closely associated with an increased risk of forthcoming cardiovascular disease and type 2 diabetes mellitus. Emerging evidence indicates that benign prostate hyperplasia (BPH) and its related lower urinary tract symptoms (LUTS) represent other clinical conditions frequently observed in subjects with MetS. Several modifiable factors involved in MetS determinism, such as inadequate diet, lack of physical exercise, and smoking and drinking behaviours are emerging as main contributors to the development of BPH. The pathogenetic mechanisms underlying the connection between MetS and BPH have not been completely clarified. MetS and its components, hypogonadism, and prostate inflammation probably play an important role in inducing BPH/LUTS. Although historically considered as a "normal" consequence of the aging process, BPH/LUTS should now be faced proactively, as a preventable disorder of the elderly. Type of diet and level of physical activity are now considered important factors affecting prostate health in the aging male. However, whether physical exercise, weight loss, and modifications of dietary habit can really alter the natural history of BPH/LUTS remains to be determined. Further research is advisable to better clarify these points.

Opposite effects of tamoxifen on metabolic syndrome-induced bladder and prostate alterations: a role for GPR30/GPER?

BACKGROUND

BPH and LUTS have been associated to obesity, hypogonadism, and metabolic syndrome (MetS). MetS-induced prostate and bladder alterations, including inflammation and tissue remodeling, have been related to a low-testosterone and high-estrogen milieu. In addition to ERs, GPR30/GPER is able to mediate several estrogenic non-genomic actions.

METHODS

Supplementing a subgroup of MetS rabbits with tamoxifen, we analyzed the in vivo effects on MetS-induced prostate and bladder alterations. The effects of selective ER/GPER ligands and GPER silencing on prostate inflammation were also studied in vitro using hBPH cells.

RESULTS

ERα, ERβ, and PR expression was upregulated in MetS bladder, where tamoxifen decreased ERα and PR expression, further stimulating ERβ. In addition, tamoxifen-dosing decreased MetS-induced overexpression of inflammatory and tissue remodeling genes. In prostate, sex steroid receptors, pro-inflammatory and pro-fibrotic genes were upregulated in MetS. However, tamoxifen did not affect them and even increased COX-2. In hBPH cells, 17β-estradiol increased IL-8 secretion, an effect blunted by co-treatment with GPER antagonist G15 but not by ER antagonist ICI 182,780, which further increased it. GPER agonist G1 dose-dependently (IC50  = 1.6 nM) induced IL-8 secretion. In vitro analysis demonstrated that GPER silencing reverted these stimulatory effects.

CONCLUSIONS

GPER can be considered the main mediator of estrogen action in prostate, whereas in bladder the mechanism appears to rely on ERα, as indicated by in vivo experiments with tamoxifen dosing. Limiting the effects of the MetS-induced estrogen action via GPER could offer new perspectives in the management of BPH/LUTS, whereas tamoxifen dosing showed potential benefits in bladder.

PDE5 inhibitors blunt inflammation in human BPH: a potential mechanism of action for PDE5 inhibitors in LUTS

BACKGROUND

Metabolic syndrome (MetS) and benign prostate hyperplasia (BPH)/low urinary tract symptoms (LUTS) are often comorbid. Chronic inflammation is one of the putative links between these diseases. Phosphodiesterase type 5 inhibitors (PDE5i) are recognized as an effective treatment of BPH-related LUTS. One proposed mechanism of action of PDE5 is the inhibition of intraprostatic inflammation. In this study we investigate whether PDE5i could blunt inflammation in the human prostate.

METHODS

Evaluation of the effect of tadalafil and vardenafil on secretion of interleukin 8 (IL-8, a surrogate marker of prostate inflammation) by human myofibroblast prostatic cells (hBPH) exposed to different inflammatory stimuli. We preliminary evaluate histological features of prostatic inflammatory infiltrates in BPH patients enrolled in a randomized, double bind, placebo controlled study aimed at investigating the efficacy of vardenafil (10 mg/day, for 12 weeks) on BPH/LUTS.

RESULTS

In vitro treatment with tadalafil or vardenafil on hBPH reduced IL-8 secretion induced by either TNFα or metabolic factors, including oxidized low-density lipoprotein, oxLDL, to the same extent as a PDE5-insensitive PKG agonist Sp-8-Br-PET-cGMP. These effects were reverted by the PKG inhibitor KT5823, suggesting a cGMP/PKG-dependency. Treatment with tadalafil or vardenafil significantly suppressed oxLDL receptor (LOX-1) expression. Histological evaluation of anti-CD45 staining (CD45 score) in prostatectomy specimens of BPH patients showed a positive association with MetS severity. Reduced HDL-cholesterol and elevated triglycerides were the only MetS factors significantly associated with CD45 score. In the MetS cohort there was a significant lower CD45 score in the vardenafil-arm versus the placebo-one.

A critical analysis of the role of testosterone in erectile function: from pathophysiology to treatment-a systematic review

CONTEXT

Androgen modulation of erectile function (EF) is widely accepted. However, the use of testosterone replacement therapy (TRT) in men with erectile dysfunction (ED) has generated an unprecedented debate.

OBJECTIVE

To summarize the relevant data on the incidence, diagnosis, and management of ED coexisting with hypogonadism and to develop a pathophysiology-based treatment algorithm.

EVIDENCE ACQUISITION

We reviewed the relevant medical literature, with a particular emphasis on original molecular studies, prospective observational data, and randomized controlled trials performed in the past 20 yr.

EVIDENCE SYNTHESIS

Testosterone modulates nearly every component involved in EF, from pelvic ganglions to smooth muscle and the endothelial cells of the corpora cavernosa. It also regulates the timing of the erectile process as a function of sexual desire, coordinating penile erection with sex. Epidemiologic studies confirm the significant overlap of hypogonadism and ED; however, most guidelines do not consider the differential diagnosis of hypogonadism or the relevance of subclinical disease. Various clinical tools can help the physician to assess and restore androgen levels in men with ED. Special attention is given to fertility-sparing treatments, due to the increasing number of older men desiring fatherhood. The simultaneous use of phosphodiesterase type 5 inhibitors (PDE5-Is) and TRT has recently been questioned. Originally proposed as a salvage therapy for nonresponders to PDE5-Is, this approach has been inappropriately transformed into a combination therapy. Clinical data are consistent when reinterpreted in the proper framework, whereas molecular evidence remains controversial.

CONCLUSIONS

A body of molecular and clinical evidence supports the use of TRT in hypogonadal patients with ED, although the benefit-risk ratio is uncertain in advanced age. Critical appraisal of this evidence enabled the development of a pathophysiology-oriented algorithm designed to avoid inappropriate treatments and support whether to start with TRT, PDE5-I only, or both. Apparently divergent findings are reconciled when TRT is correctly indicated. An improved diagnosis and individualized management is desirable in light of the many available options.

Risks and benefits of late onset hypogonadism treatment: an expert opinion

Late-onset hypogonadism (LOH) is a syndromic condition that has a well-recognized association with sexual and reproductive failure. LOH is frequently associated with chronic conditions including cardiovascular diseases (CVD), obesity, osteoporosis, HIV infection, renal failure, and obstructive pulmonary diseases. Despite this evidence, in patients with these conditions, LOH is still only rarely investigated and testosterone replacement therapy (TRT) rarely considered. In this paper, we critically reviewed the available evidence on LOH treatment focusing on possible risks and benefits. Medical therapy of LOH should be individualized depending on the etiology of the disease and the patient's expectations. The fear of prostate cancer and the risk of erythrocytosis probably represent the main limitations of TRT in aging men. However, TRT in healthy older men in near physiological doses does not appear to incur serious adverse events, although regular monitoring of prostate-specific antigen and hematocrit levels is required. Available evidence also suggests that TRT might ameliorate central obesity and glycometabolic control in patients with metabolic syndrome and type 2 diabetes. In addition, TRT has been associated with an increase in bone mineral density in men with osteoporosis, with an improvement in lean body mass in subjects with human immunodeficiency virus infection or chronic obstructive pulmonary disease, as well as with peripheral oxygenation in patients with chronic kidney diseases. Despite this evidence, however, it should be recognized that the results of these trials were heterogeneous and limited by small sample sizes. Hence, further research is required regarding the long-term benefits and adverse effects of TRT in LOH.

Effects of tadalafil on lower urinary tract symptoms secondary to benign prostatic hyperplasia and on erectile dysfunction in sexually active men with both conditions: analyses of pooled data from four randomized, placebo-controlled tadalafil clinical studies

INTRODUCTION

Erectile dysfunction (ED) and lower urinary tract symptoms suggestive of benign prostatic hyperplasia (LUTS/BPH) are common in aging males and frequently occur together. Tadalafil has demonstrated efficacy in treating both conditions.

AIM

The study aims to evaluate the efficacy and safety of tadalafil 5 mg once daily vs. placebo over 12 weeks in treating both LUTS/BPH and ED in sexually active men. We also assessed relationships of baseline disease severity and prostate specific antigen (PSA) to outcomes.

METHODS

Data were pooled from four multinational, randomized studies of men ≥45 years with LUTS/BPH, with analyses restricted to sexually active men with ED. Randomization (baseline) followed a 4-week placebo run-in; changes from baseline were assessed vs. placebo using analysis of covariance.

MAIN OUTCOME MEASURES

International Prostate Symptom Score (IPSS), IPSS subscores, Quality-of-Life Index (IPSS-QoL), BPH Impact Index (BII), and International Index of Erectile Function-Erectile Function (IIEF-EF) Domain score were used in this study.

RESULTS

Tadalafil (N = 505) significantly improved total IPSS vs. placebo (N = 521); mean changes from baseline were -6.0 and -3.6, respectively (P < 0.001). Improvements in IIEF-EF Domain score (tadalafil, 6.4; placebo, 1.4) were also significant vs. placebo, as were the IPSS storage and voiding subscores, IPSS-QoL, and BII (all P < 0.001). No significant impact of baseline ED severity or PSA category on IPSS response was observed (interaction P values, 0.463 and 0.149, respectively). Similarly, improvement in IIEF-EF Domain score was not significantly impacted by baseline LUTS/BPH severity or PSA category (interaction P values, 0.926 and 0.230, respectively). Improvements in IPSS and IIEF-EF Domain score during treatment were weakly correlated (r = -0.229). Treatment-emergent adverse events were consistent with previous reports.

CONCLUSIONS

Tadalafil was efficacious and well tolerated in treating ED and LUTS/BPH in sexually active men with both conditions. Improvements in both conditions were significant regardless of baseline severity. Improvements in the total IPSS and the IIEF-EF Domain score were weakly correlated.

The use of a single daily dose of tadalafil to treat signs and symptoms of benign prostatic hyperplasia and erectile dysfunction

A strong and independent association between lower urinary tract symptoms suggestive of benign prostatic hyperplasia (LUTS/BPH) and erectile dysfunction (ED) has been widely evidenced in several clinical epidemiologic studies. Preclinical animal models have provided a great deal of information on potential common pathogenic mechanisms underlying these two clinical identities. Although the efficacy of the most commonly used treatments for LUTS/BPH is well defined, the negative impact of these treatments on sexual function – in particular, on ED – has triggered the search for new treatment options. In this regard, a new role for phosphodiesterase type 5 inhibitors in the treatment of LUTS/BPH and ED has been claimed. Tadalafil is one of the most extensively investigated phosphodiesterase type 5 inhibitors for this new indication. All evidence reported to date suggests that tadalafil 5 mg once daily is a safe and effective treatment option for both LUTS/BPH and ED.

FXR activation normalizes insulin sensitivity in visceral preadipocytes of a rabbit model of MetS

Insulin resistance is the putative key underlying mechanism linking adipose tissue (AT) dysfunction with liver inflammation and steatosis in metabolic syndrome (MetS). We have recently demonstrated that the selective farnesoid X receptor (FXR) agonist obeticholic acid (OCA) ameliorates insulin resistance and the metabolic profile with a marked reduction in the amount of visceral AT (VAT) in a high-fat diet (HFD)-induced rabbit model of MetS. These effects were mediated by the activation of FXR, since treatment with the selective TGR5 agonist INT-777 was not able to ameliorate the metabolic parameters evaluated. Herein, we report the effects of in vivo OCA dosing on the liver, the VAT, and the adipogenic capacity of VAT preadipocytes (rPADs) isolated from rabbits on a HFD compared with those on a control diet. VAT and liver were studied by immunohistochemistry, Western blot analysis, and RT-PCR. rPADs were exposed to a differentiating mixture to evaluate adipogenesis. Adipocyte size, hypoxia, and the expression of perilipin and cytosolic insulin-regulated glucose transporter GLUT4 (SLC2A4) were significantly increased in VAT isolated from the HFD rabbits, and normalized by OCA. The expression of steatosis and inflammation markers was increased in the liver of the HFD rabbits and normalized by OCA. rPADs isolated from the HFD rabbits were less sensitive to insulin, as demonstrated by the decreased insulin-induced glucose uptake, triglyceride synthesis, and adipogenic capacity, as well as by the impaired fusion of lipid droplets. OCA treatment preserved all the aforementioned metabolic functions. In conclusion, OCA dosing in a MetS rabbit model ameliorates liver and VAT functions. This could reflect the ability of OCA to restore insulin sensitivity in AT unable to finalize its storage function, counteracting MetS-induced metabolic alterations and pathological AT deposition.