Impaired erectile function in CD73-deficient mice with reduced endogenous penile adenosine production

Date (Phoenix dactylifera L. Mill) fruit enhances sexual performance via modulation of oxido-inflammatory mediators and purinergic signaling in hypertensive male rats

INTRODUCTION

The present study aimed at investigating the effect of dietary supplementation of Phoenix dactylifera, an important component of aphrodisiac supplements, on sexual performance, oxido-inflammatory mediators and purinergic signaling system in hypertensive rats.

MATERIAL AND METHODS

Hypertension was induced via oral administration of 40 mg/kg L-NAME. Thereafter, the sexual performance of the experimental animals was determined and the hypertensive rats with impaired sexual activities were placed on P. dactylifera-supplemented diet for 21 days, and the effects of the treatment on the overall sexual behavior, antioxidant status, oxido-inflammatory biomarkers, and enzyme activity of the purinergic system were assessed.

RESULTS

Hypertensive rats showed a significant (p < 0.05) decrease in sexual performance, elevated level of oxido-inflammatory mediators, and altered purinergic enzymes activity when compared with the control. However, sub-chronic feeding with P. dactylifera-supplemented diet improved sexual performance, significantly lowered oxido-inflammatory biomarkers, and enhanced the activity of purinergic enzymes in hypertensive rats.

CONCLUSION

Findings presented in this study suggest that dietary inclusion of P. dactylifera could be useful in managing erectile dysfunction (ED) commonly observed in subjects with hypertension. Findings highlighted in this study thus provide the scientific basis supporting the folkloric use of P. dactylifera as a key ingredient in aphrodisiac supplements.

Effect of Antioxidants Supplementation on Erectile Dysfunction: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

INTRODUCTION

In Erectile dysfunction (ED) patients, phosphodiesterase type 5 (PDE5) inhibitors are considered as the first-line therapy. However, 30-50% of ED patients fail to follow this therapeutic option because of adverse events, lack of efficacy, or drug costs. Antioxidant supplementation is widely applied in clinical practice and viewed as a potential therapeutic option for ED. Therefore, it is attractive to assess the effect of antioxidants supplementation on ED patients.

OBJECTIVES

To evaluate the effects of antioxidants supplementation on ED.

METHODS

Published randomized controlled trials of antioxidants in ED were searched in the PubMed, Embase, and Cochrane Library databases from inception to October 3, 2021. Meta-analyses were carried out using a random-effects model. The results were presented as standard mean differences (SMDs) with their 95% confidence intervals (CIs).

RESULTS

Eighteen studies with 1,331 ED patients were included in the study. Compared with placebo, antioxidants alone treatment showed a statistical increase in International Index of Erectile Function (IIEF) score (SMD = 1.93; 95% CI: 0.15, 3.72; P = .034). Compared with placebo, antioxidants compound treatment elicited a significant increase in IIEF score (SMD = 2.74; 95% CI: 1.67, 3.81; P < .001) as well as sexual satisfaction score (SMD = 1.61; 95% CI: 0.63, 2.59; P = .001). Compared with the PDE5 inhibitors alone, combination of PDE5 inhibitors and antioxidants showed a significant increase in IIEF score (SMD = 1.1; 95% CI: 0.51, 1.68; P < .001) and sexual satisfaction score (SMD = 1.28; 95% CI: 0.06, 2.51; P = .04).

CONCLUSION

This study found that the effect of antioxidant alone treatment on ED may be limited. However, antioxidant compound treatment, as well as combination of PDE5 inhibitors and antioxidants, were associated with improved ED, and can be considered as an accessary therapeutic option for ED. Su L, Yang Z, Qu H, et al. Effect of Antioxidants Supplementation on Erectile Dysfunction: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Sex Med Rev 2021;XX:XXX-XXX.

A2B Adenosine Receptor Agonist Improves Erectile Function in Diabetic Rats

Diabetes is an important risk factor for erectile dysfunction (ED). Recent studies have indicated that A2B adenosine receptor (ADORA2B) signaling is essential for penile erection. Thus, we hypothesize that diabetic ED may be attributed to impaired A2B adenosine signaling. To test this hypothesis, we generated diabetic rats by injecting streptozocin as animal model. After 12 weeks, immunohistochemistry staining was used to localize the expression of ADORA2B. Western Blot and quantitative PCR were employed to determine ADORA2B expression level. Intracavernosal pressure (ICP) measurement was used to evaluate erectile function. Diabetic rats received a single intravenous injection of BAY 60-6583, an ADORA2B agonist, or vehicle solution, at 60 min before the ICP measurement. The results showed that ADORA2B expressed in the nerve bundle, smooth muscle, and endothelium in penile tissue of control mice. Western Blot and quantitative PCR results indicated that the expression levels of ADORA2B protein and mRNA were significantly reduced in penile tissues of diabetic rats. Functional studies showed that the erectile response induced by electrical stimulation was remarkably decreased in diabetic rats, compared with age-matched control rats. However, at 60 min after BAY 60-6583 treatment, the erectile function was improved in diabetic rats, suggesting that enhancement of ADORA2B signaling may improve erectile function in diabetic ED. This preclinical study has revealed a previously unrecognized therapeutic possibility of BAY 60-6583 as an effective and mechanism-based drug to treat diabetic ED. In conclusion, we propose that impaired A2B adenosine signaling is one of the pathological mechanisms of diabetic ED.

Role of Adenosine Receptor(s) in the Control of Vascular Tone in the Mouse Pudendal Artery

Activation of adenosine receptors (ARs) has been implicated in the modulation of renal and cardiovascular systems, as well as erectile functions. Recent studies suggest that adenosine-mediated regulation of erectile function is mainly mediated through A2BAR activation. However, no studies have been conducted to determine the contribution of AR subtype in the regulation of the vascular tone of the pudendal artery (PA), the major artery supplying and controlling blood flow to the penis. Our aim was to characterize the contribution of AR subtypes and identify signaling mechanisms involved in adenosine-mediated vascular tone regulation in the PA. We used a DMT wire myograph for muscle tension measurements in isolated PAs from wild-type, A2AAR knockout, A2BAR knockout, and A2A/A2BAR double-knockout mice. Real-time reverse transcription-polymerase chain reaction was used to determine the expression of the AR subtypes. Data from our pharmacologic and genetic approaches suggest that AR activation-mediated vasodilation in the PA is mediated by both the A2AAR and A2BAR, whereas neither the A1AR nor A3AR play a role in vascular tone regulation of the PA. In addition, we showed that A2AAR- and A2BAR-mediated vasorelaxation requires activation of nitric oxide and potassium channels; however, only the A2AAR-mediated response requires protein kinase A activation. Our data are complemented by mRNA expression showing the expression of all AR subtypes with the exception of the A3AR. AR signaling in the PA may play an important role in mediating erection and represent a promising therapeutic option for the treatment of erectile dysfunction.

Beneficial and detrimental role of adenosine signaling in diseases and therapy

Adenosine is a major signaling nucleoside that orchestrates cellular and tissue adaptation under energy depletion and ischemic/hypoxic conditions by activation of four G protein-coupled receptors (GPCR). The regulation and generation of extracellular adenosine in response to stress are critical in tissue protection. Both mouse and human studies reported that extracellular adenosine signaling plays a beneficial role during acute states. However, prolonged excess extracellular adenosine is detrimental and contributes to the development and progression of various chronic diseases. In recent years, substantial progress has been made to understand the role of adenosine signaling in different conditions and to clarify its significance during the course of disease progression in various organs. These efforts have and will identify potential therapeutic possibilities for protection of tissue injury at acute stage by upregulation of adenosine signaling or attenuation of chronic disease progression by downregulation of adenosine signaling. This review is to summarize current progress and the importance of adenosine signaling in different disease stages and its potential therapeutic effects.

Opiorphin-dependent upregulation of CD73 (a key enzyme in the adenosine signaling pathway) in corporal smooth muscle cells exposed to hypoxic conditions and in corporal tissue in pre-priapic sickle cell mice

The precise molecular mechanisms underlying priapism associated with sickle cell disease remain to be defined. However, there is increasing evidence that up-regulated activity of the opiorphin and adenosine pathways in corporal tissue, resulting in heighted relaxation of smooth muscle, play an important role in development of priapism. A key enzyme in the adenosine pathway is CD73, an ecto-5-prime-nucleotidase (5-prime-ribonucleotide phosphohydrolase; EC 3.1.3.5) which catalyzes the conversion of adenosine mononucleotides to adenosine. In the present study we investigated how sickle cell disease and hypoxia regulate the interplay between opiorphin and CD73. In the corpora of sickle cell mice we observed significantly elevated expression of both the mouse opiorphin homologue mSmr3a (14-fold) and CD73 (2.2-fold) relative to non-sickle cell controls at a life-stage prior to the exhibition of priapism. Sickle cell disease has a pronounced hypoxic component, therefore we determined if CD73 was also modulated in in vitro corporal smooth muscle (CSM) models of hypoxia. Hypoxia significantly increased CD73 protein and mRNA expression by 1.5-fold and 2-fold, respectively. We previously demonstrated that expression of another component of the adenosine signaling pathway, the adensosine 2B receptor, can be regulated by sialorphin (the rat opiorphin homolologue), and we demonstrate that sialorphin also regulates CD73 expression in a dose and time dependent fashion. Using siRNA to knock-down sialorphin mRNA expression in CSM cells in vitro, we demonstrate that the hypoxic up-regulation of CD73 is dependent on the up-regulation of sialorphin. Overall our data provides further evidence to support a role for opiorphin in CSM in regulating the cellular response regulating response to hypoxia or sickle cell disease by activating smooth muscle relaxant pathways.

Purinergic signalling in the reproductive system in health and disease

There are multiple roles for purinergic signalling in both male and female reproductive organs. ATP, released as a cotransmitter with noradrenaline from sympathetic nerves, contracts smooth muscle via P2X1 receptors in vas deferens, seminal vesicles, prostate and uterus, as well as in blood vessels. Male infertility occurs in P2X1 receptor knockout mice. Both short- and long-term trophic purinergic signalling occurs in reproductive organs. Purinergic signalling is involved in hormone secretion, penile erection, sperm motility and capacitation, and mucous production. Changes in purinoceptor expression occur in pathophysiological conditions, including pre-eclampsia, cancer and pain.

Isolation and characterization of novel, highly proliferative human CD34/CD73-double-positive testis-derived stem cells for cell therapy

Human adult stem cells are a readily available multipotent cell source that can be used in regenerative medicine. Despite many advantages, including low tumorigenicity, their rapid senescence and limited plasticity have curtailed their use in cell-based therapies. In this study, we isolated CD34/CD73-double-positive (CD34(+)/CD73(+)) testicular stromal cells (HTSCs) and found that the expression of CD34 was closely related to the cells' stemness and proliferation. The CD34(+)/CD73(+) cells grew in vitro for an extended period of time, yielding a multitude of cells (5.6×10(16) cells) without forming tumors in vivo. They also differentiated into all three germ layer lineages both in vitro and in vivo, produced cartilage more efficiently compared to bone marrow stem cells and, importantly, restored erectile function in a cavernous nerve crush injury rat model. Thus, these HTSCs may represent a promising new autologous cell source for clinical use.

Adenosine signaling: good or bad in erectile function?

The erectile status of penile tissue is governed largely by the tone of cavernosal smooth muscle cells, which is determined by the balance of vascular relaxants and constrictors. Vascular relaxants play a key role in regulating the tone of cavernosal smooth muscle and thus the initiation and maintenance of penile erection. Early studies drew attention to the potential role of adenosine signaling in this process. However, the serendipitous discovery of the effect of sildenafil on erectile physiology drew more attention toward nitric oxide (NO) as a vasodilator in the process of penile erection, and a recently discovered, unexpected erectile phenotype of adenosine deaminase-deficient mice reemphasizes the importance of adenosine as a key regulatory of erectile status. Adenosine, like NO, is a potent and short-lived vasorelaxant that functions via cyclic nucleotide second messenger signaling to promote smooth muscle relaxation. Recent studies reviewed here show that adenosine functions to relax the corpus cavernosum and promote penile erection. Excess adenosine in penile tissue contributes to the disorder called priapism, and impaired adenosine signaling is associated with erectile dysfunction. More recent research summarized in this review reveals that adenosine functions as a key endogenous vasodilator in the initiation and maintenance of normal penile erection. This new insight highlights adenosine signaling pathways operating in penile tissue as significant therapeutic targets for the treatment of erectile disorders.