Expression of the apelin-APJ pathway and effects on erectile function in a mouse model of vasculogenic erectile dysfunction

Regenerative therapies as a potential treatment of erectile dysfunction

Erectile dysfunction (ED) is the most common sexual dysfunction disease in adult males. ED can be caused by many factors, such as vascular disease, neuropathy, metabolic disturbances, psychosocial causes, and side effects of medications. Although current oral phosphodiesterase type 5 inhibitors can achieve a certain effect, they cause temporary dilatation of blood vessels with no curative treatment effects. Emerging targeted technologies, such as stem cell therapy, protein therapy, and low-intensity extracorporeal shock wave therapy (Li-ESWT), are being used to achieve more natural and long-lasting effects in treating ED. However, the development and application of these therapeutic methods are still in their infancy, and their pharmacological pathways and specific mechanisms have not been fully discovered. This article reviews the preclinical basic research progress of stem cells, proteins, and Li-ESWT therapy, as well as the current status of clinical application of Li-ESWT therapy.

Biomarkers of Oxidative Stress Tethered to Cardiovascular Diseases

Cardiovascular disease (CVD) is a broad term that incorporated a group of conditions that affect the blood vessels and the heart. CVD is a foremost cause of fatalities around the world. Multiple pathophysiological mechanisms are involved in CVD; however, oxidative stress plays a vital role in generating reactive oxygen species (ROS). Oxidative stress occurs when the concentration of oxidants exceeds the potency of antioxidants within the body while producing reactive nitrogen species (RNS). ROS generated by oxidative stress disrupts cell signaling, DNA damage, lipids, and proteins, thereby resulting in inflammation and apoptosis. Mitochondria is the primary source of ROS production within cells. Increased ROS production reduces nitric oxide (NO) bioavailability, which elevates vasoconstriction within the arteries and contributes to the development of hypertension. ROS production has also been linked to the development of atherosclerotic plaque. Antioxidants can decrease oxidative stress in the body; however, various therapeutic drugs have been designed to treat oxidative stress damage due to CVD. The present review provides a detailed narrative of the oxidative stress and ROS generation with a primary focus on the oxidative stress biomarker and its association with CVD. We have also discussed the complex relationship between inflammation and endothelial dysfunction in CVD as well as oxidative stress-induced obesity in CVD. Finally, we discussed the role of antioxidants in reducing oxidative stress in CVD.

Apelin pathway in cardiovascular, kidney, and metabolic diseases: Therapeutic role of apelin analogs and apelin receptor agonists

The apelin/apelin receptor (ApelinR) signal transduction pathway exerts essential biological roles, particularly in the cardiovascular system. Disturbances in the apelin/ApelinR axis are linked to vascular, heart, kidney, and metabolic disorders. Therefore, the apelinergic system has surfaced as a critical therapeutic strategy for cardiovascular diseases (including pulmonary arterial hypertension), kidney disease, insulin resistance, hyponatremia, preeclampsia, and erectile dysfunction. However, apelin peptides are susceptible to rapid degradation through endogenous peptidases, limiting their use as therapeutic tools and translational potential. These proteases include angiotensin converting enzyme 2, neutral endopeptidase, and kallikrein thereby linking the apelin pathway with other peptide systems. In this context, apelin analogs with enhanced proteolytic stability and synthetic ApelinR agonists emerged as promising pharmacological alternatives. In this review, we focus on discussing the putative roles of the apelin pathway in various physiological systems from function to dysfunction, and emphasizing the therapeutic potential of newly generated metabolically stable apelin analogs and non-peptide ApelinR agonists.

Apelin-13 Protects Corpus Cavernosum Against Fibrosis Induced by High-Fat Diet in an MMP-Dependent Mechanism

BACKGROUND

An increased fibrosis of the corpora cavernosa is a prevalent process that underlies most cases of erectile dysfunction. Apelin, an endogenous circulating peptide, has been documented as an important effector on cardiovascular homeostasis, controlling vascular function and reducing fibrosis in multiple pathological conditions. Recently, initial studies have shown that Apelin, acting through the APJ receptor, also modulates penile erection, however, the role of this system on penile structure and intracorporal collagen remodeling has not been investigated yet.

AIMS

Here we sought to investigate the effect of chronic Apelin treatment on the corpus cavernosum structure of hyperchOlesterolemic mice.

METHODS

Apolipoprotein gene-deleted (ApoE^-/-) mice were fed with a Western diet for 11 weeks and received Apelin-13 (2 mg/kg/day) or vehicle during the last 3 weeks. Penile samples were obtained for histological and biochemical analyses to assess the intracorporal collagen content and key proteins expression. Furthermore, the effect of Apelin-13 was evaluated in cultured NIH3T3 mouse fibroblasts stimulated with TGF-β.

OUTCOME

Local expression of Apelin-13 in mouse corpus cavernosum and its protective effect against fibrosis.

RESULTS

Apelin and APJ receptor were expressed (gene and protein) within the corpus cavernosum of ApoE^-/- mice, indicating a local modulation of the Apelin system. Interestingly, 3 weeks of Apelin-13 treatment strongly reduced intracavernosal collagen content. In addition, Apelin-13 enhanced total matrix metalloproteinase (MMP) activity in the mice penis, which was associated with an increased protein expression of MMP-1, MMP-3, MMP-8, and MMP-9, while tissue inhibitor of metalloproteinase were unaltered. These beneficial actions were not associated with changes in nNOS or eNOS protein expression, intracavernosal reactive oxygen species content, or atherosclerotic plaque deposition. Additionally, in cultured fibroblast, Apelin-13 inhibited TGF-β-induced fibroblast to myofibroblast differentiation and collagen production, possibly through the activation of ERK1/2 kinase.

CLINICAL TRANSLATION

These results point out Apelin/APJ system as a potential target to treat intracavernosal fibrosis-related disorders.

STRENGTH & LIMITATIONS

These results provide the first evidence of the Apelin system's positive role on erectile tissue structure/remodeling. Nevertheless, additional functional study addressing erectile response would bring extended validation regarding the relevance of such effect.

CONCLUSION

These results suggest a local modulation of the Apelin system within the corpus cavernosum. Remarkably, Apelin-13 reduced intracavernosal fibrosis in hypercholesterolemic mice by: (i) enhancing MMPs expression and activity; and (ii) inhibiting fibroblast differentiation into myofibroblast. Altogether, these results suggest an essential protective role of Apelin, indicating Apelin/APJ system as a promising candidate for the development of fibrosis-associated erectile dysfunction treatments. Sturny M, Anguenot L Costa-Fraga FP, et al. Apelin-13 Protects Corpus Cavernosum Against Fibrosis Induced by High-Fat Diet in an MMP-Dependent Mechanism. J Sex Med 2021;18:875-888.

Molecular and Histologic Evidence of Novel Erectile Dysfunction Rat Model as an Aging Atherosclerosis Model: A Preliminary Study

Purpose

To validate a novel arteriogenic erectile dysfunction (ED) model with atherosclerosis (AS) based on molecular and histologic evidence induced by chronic pelvic ischemia (CPI) and determine effect of phosphodiesterase-5 inhibitor treatment.

Materials and Methods

Twenty 16-week-old male Sprague–Dawley rats were divided into three experimental groups (Group I, untreated sham-operated rats with regular diet; Group II, CPI with cholesterol diet; Group III, CPI model with cholesterol diet and mirodenafil). Erectile function was accessed using maximum intracavernous pressure (ICP) and ICP/mean arterial pressure (MAP). Molecular changes were examined by western blot analysis using hypoxia inducible factor 1-alpha (HIF-1α), endothelial nitric oxide synthase (eNOS), and transforming growth factor beta-1 (TGF-β1) antibodies. Collagen change was evaluated by Masson's trichrome staining.

Results

In vivo measurements of ICP and ICP/MAP in Group II were significantly lower than those in Group I (p<0.01). Smooth muscle/collagen ratio in Group II was significantly lower than that in Group I (p<0.05). After treatment with mirodenafil for four weeks, Group III showed significantly higher levels of ICP and ICP/MAP than Group II (p<0.05). Western blot analysis showed that HIF-1α and TGF-β1 levels were significantly higher in Group II whereas eNOS levels were significantly lower in Group II than those in Group I or III.

Conclusions

A novel arteriogenic ED with AS model is successfully induced by CPI and validated based on molecular and histologic evidences.

Protective effect of apelin preconditioning in a rat model of hepatic ischemia reperfusion injury; possible interaction between the apelin/APJ system, Ang II/AT1R system and eNOS

Introduction

Hepatic ischemic reperfusion injury occurs in multiple clinical settings. Novel potential protective agents are still needed to attenuate this injury. Apelin preconditioning protects against ischemic reperfusion injury in different organs. However, the protective mechanism of apelin on hepatic ischemic reperfusion injury is not yet clear.

Aim

Evaluate the effect of apelin-13 preconditioning on hepatic ischemic reperfusion injury and clarify possible interactions between apelinergic, renin-angiotensin systems and endothelial nitric oxide synthase.

Methods

In total, 60 rats were assigned to four groups: control sham-operated, ischemic reperfusion, apelin-treated ischemic reperfusion and apelin + N-nitro-L-arginine methyl ester-treated ischemic reperfusion. Apelin 2 µg/kg/day and N-nitro-L-arginine methyl ester 10 mg/kg/day were injected intraperitoneally daily for 3 days and 2 weeks respectively before hepatic ischemic reperfusion. Serum aminotransferase, aspartate aminotransferase, hepatic malondialdehyde, apelin, gene expression of caspase-3, endothelial nitric oxide synthase and angiotensin type 1 receptor and liver histopathology were compared between groups.

Results

Apelin significantly reduced serum aminotransferase, aspartate aminotransferase, hepatic malondialdehyde, caspase-3 and angiotensin type 1 receptor expression, whereas hepatic apelin and endothelial nitric oxide synthase expression were significantly increased with improved hepatic histopathology. N-nitro-L-arginine methyl ester co-administration partially reversed this hepatoprotective effect.

Conclusion

Apelin-13 reduced hepatic ischemic reperfusion injury. This protection could be related to the suppression of hepatic angiotensin type 1 receptor expression and elevation of hepatic apelin level and endothelial nitric oxide synthase expression, which counteracts the pathologic effects of Ang II/angiotensin type 1 receptor. An interaction exists between apelinergic, renin-angiotensin systems and endothelial nitric oxide synthase in hepatic ischemic reperfusion pathophysiology.

Research in pharmacotherapy for erectile dysfunction

Although oral phosphodiesterase-5 (PDE5) inhibitors are generally accepted as an effective therapy for erectile dysfunction (ED), men with ED from diabetes or radical prostatectomy respond poorly to these drugs. Many researchers have tried to develop novel therapeutics that target alternative molecular pathways. A group of therapeutics belongs to centrally acting agents that target dopamine and melanocortin receptors. The other one is the peripherally acting agents that target soluble guanylate cyclase, Rho-kinase pathway, and Maxi-K channel, etc. Also, a variety of preclinical studies by the application of biotherapies in the concept of therapeutic angiogenesis or neural regeneration as well as anti-fibrosis to regenerate damaged erectile tissue have been reported. This article will address the current therapeutic targets for ED under clinical or preclinical development, including pharmacotherapy and biotherapy which comprises protein therapy and gene therapy. In spite of numerous clinical trials that target alternative pathways, these agents have yet to reach the market. The results from preclinical studies targeting therapeutic angiogenesis, neural regeneration, and anti-fibrosis are promising.

Treatment of erectile dysfunction: new targets and strategies from recent research

In recent years, research on penile erection has increasingly been centered on the molecular mechanisms involved. Major progress has been made in the field and at present a whole number of neurotransmitters, chemical effectors, growth factors, second-messenger molecules, ions, intercellular proteins, and hormones have been characterized as components of the complex process of erection. This knowledge has led to the discovery of several new therapeutic targets and multiple medical approaches for the treatment of erectile dysfunction (ED). This review focuses on the progress made in this field within the last few years.