Possible Pathophysiological Roles of Neurotransmitter Systems in Men With Lifelong Premature Ejaculation: Protocol for a Scoping Review

BACKGROUND

Lifelong premature ejaculation (LPE) is a rare sexual condition believed to be caused by genetic neurobiological disorders. In the field of LPE, 2 main types of research have been conducted: direct genetic research and pharmacotherapeutic interference of neurotransmitter systems that can relieve the symptoms of LPE in male patients.

OBJECTIVE

We aim to provide an overview of studies on neurotransmitter systems as the pathophysiological cause of LPE by investigating direct genetic research or pharmacotherapeutic interference that relieves the main symptom of LPE in male patients.

METHODS

This scoping review will use the PRISMA-ScR tool (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews). In addition, this study will use a peer-reviewed search strategy. Systematic searches will be conducted using 5 scientific databases (Cochrane Database of Systematic Reviews, PubMed or MEDLINE, Cumulative Index to Nursing and Allied Health Literature [CINAHL], EMBASE, and Epistemonikos). Additionally, pragmatic searches for relevant information in gray literature databases will be performed. Two reviewers will independently include relevant studies in a 2-stage selection strategy. Finally, data will be extracted from the studies and charted to summarize relevant study characteristics and key findings.

RESULTS

As of July 2022, we completed the preliminary searches according to the PRESS 2015 guidelines and started to determine the final search terms that we will use in all selected 5 scientific databases.

CONCLUSIONS

This scoping review protocol is the first to focus on neurotransmitter pathways in LPE by combining the results from the genetic and pharmacotherapy studies. The results could help identify potential research gaps or target candidate proteins and neurotransmitter pathways in LPE for further genetic research.

TRIAL REGISTRATION

Open Science Framework 10.17605/OSF.IO/JUQSD; https://osf.io/juqsd.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/41301.

A comprehensive assessment of genetic variation in serotonin transporter gene (5-HTTLPR+rs25531) and the response to dapoxetine in Chinese patients with premature ejaculation

This study was to explore whether serotonin transporter gene-linked polymorphic region polymorphisms (5-HTTLPR+rs25531) influence the response to dapoxetine treatment in a Chinese population with premature ejaculation (PE). 112 patients with PE re-enrolled from our previous study received dapoxetine monotherapy. At the endpoint, patients with S'S' had a significant increased risk of nonresponse compared with L' carriers (p < .001). The improvement in S'S' genotype was significantly lower in premature ejaculation profile (PEP) items of 'control over ejaculation' (p = .035) and 'distress related to ejaculation' (p = .017) than that in L' carriers. As to clinical global impression of change (CGIC), results in S'S' subjects showed significantly lower scores (p = .008) and a less satisfaction rate reporting at least 'better' (p = .020) compared with L' carriers. Moreover, our findings suggested that patients with S'S' were more likely to develop adverse effects (AEs) compared with L' carriers (p = .040). This study suggests that PE patients bearing the S'S' genotype have an inferior comprehensive efficacy and safety of dapoxetine treatment, which consist of poorer response in IELTs, less improvement in patient-reported outcome (PRO) measures and greater incidence of AEs, than L' carriers. Variants of triallelic 5-HTTLPR may play a major role as a predictor of treatment response to dapoxetine.

Abnormal Thalamic Metabolism in Patients With Lifelong Premature Ejaculation

BACKGROUND

Although some recent neuroimaging studies have indicated the abnormal brain structure or function in patients with lifelong premature ejaculation (LPE), whether and how the abnormal thalamic function participates in processing sexual behavioral information are still unclear in patients with LPE.

AIM

The aim of this study was to assess the changes in the thalamus metabolism and structural integrity in patients with LPE.

METHODS

We performed a multimodal magnetic resonance approach in a 3.0 T system, including proton magnetic resonance spectroscopy (¹H-MRS), diffusion tensor imaging, and volumetric analysis to detect the differences in thalamic metabolism and structure between 20 patients with LPE and 15 healthy controls.

OUTCOMES

We analyzed and correlated the clinical symptoms of the subjects with significant ¹H-MRS-based features. Peak areas of N-acetylaspartate, choline, creatine (Cr), and glutamate/glutamine (Glu) were calculated with the LCModel software.

RESULTS

Diffusion tensor imaging and volumetric analysis of thalami showed no differences between the 2 groups. On the contrary, ¹H-MRS study disclosed that both Glu concentrations and Glu/Cr ratio values in the thalami of patients with LPE were remarkably increased when compared with healthy controls (P < .01 for both variables). In addition, both the intravaginal ejaculatory latency time score and Chinese Index of Sexual Function for Premature Ejaculation-5 score were negatively related to increased Glu concentrations and Glu/Cr ratio values.

CLINICAL IMPLICATIONS

Glutamatergic activity changes of thalamus may be an underlying indicator for evaluating sensory conduction efficiency in patients with LPE.

STRENGTHS & LIMITATIONS

The present study first found the abnormal thalamic metabolism in patients with LPE and contributed to a better understanding of the LPE etiology. Limitations include a cross-sectional study design with small samples and no examination of other brain areas.

CONCLUSION

Our findings show that the increase in glutamatergic activity of thalamus is related to LPE, suggesting that the increased Glu neurotransmission in the thalamus may contribute to the development of premature ejaculation. Xia J-D, Chen F, Zhang Q-J, et al. Abnormal Thalamic Metabolism in Patients With Lifelong Premature Ejaculation. J Sex Med 2021;18:275-283.

Network Pharmacology-Based Strategy to Investigate Pharmacological Mechanisms of Qiaoshao Formula for Treatment of Premature Ejaculation

Background

Qiaoshao (QS) formula, a traditional Chinese medicine (TCM) comprising seven herbs, has been clinically proven to have a favorable treatment effect on premature ejaculation (PE). However, its underlying pharmacological mechanisms in the treatment of PE need to be further clarified.

Methods

In the present study, a network pharmacology-based strategy was adopted. The active compounds of QS formula were obtained from the Chinese medicine database, and the potential targets of these compounds were collected from the DrugBank database to construct compound-compound targets network. PE-related targets were identified from human disease databases and used to construct the protein-protein interaction (PPI) networks. Compound-disease target PPI network was constructed by merging the PPI network of disease-targets and compound-targets. Cluster and enrichment analyses were performed on the PPI network of disease targets and compound-disease targets. The influence of QS formula on serum 5-HT, NO, oxytocin, and thyroid hormones of PE patients was verified.

Results

Four primary pharmacological networks of QS formula were constructed, including the compound-compound targets network, PPI network of PE-related targets and compound-disease targets, and the QS-PE mechanism network. The module and pathway enrichment analyses revealed that the QS formula had the potential to affect varieties of biological process and pathways, such as nitric oxide biosynthetic process, oxytocin, thyroid hormone, TNF, PI3K-Akt, and the HIF-1 signaling pathway, that play an important role in the pathogenesis of PE. Meanwhile, the QS formula has been clinically confirmed to regulate the serum level of 5-HT, NO, oxytocin, and TT in PE patients.

Conclusion

This study preliminarily discovered the potential targets and pathways of QS formula in the treatment of PE, which laid a good foundation for further experimental research.

Gene Variants in Premature Ejaculation: Systematic Review and Future Directions

INTRODUCTION

A growing number of genetic association studies have been performed to investigate the association between the genetic susceptibility alleles and the risk of premature ejaculation (PE); however, the results remain inconclusive.

OBJECTIVES

This systematic review aimed: (i) to determine whether an association exists between gene(s) or allelic variant(s) and PE; (ii) to assess whether the associations are consistent across studies in magnitude and direction, and (iii) to identify any limitation, gap, or shortcoming in the included studies.

METHODS

The literature search was conducted in PubMed, MEDLINE, Scopus, Cochrane Library, EMBASE, Academic Search Complete, Google Scholar, and CINAHL databases.

RESULTS

Different gene variants associated with PE were assessed. 25 genetic association studies met the inclusion criteria that investigated 11 genes, 2,624 men with PE compared with 9,346 men as controls, twins, and siblings. 19 studies demonstrated a significant association with PE, whereas 4 studies denied such a relationship. SLC6A4 gene polymorphism was investigated in 11 studies (7 studies demonstrated a significant relationship with PE, and 4 studies denied such a relationship). Dopamine transporter gene (DAT1) polymorphism was investigated in 4 studies exhibiting a significant relationship. Androgen receptor gene polymorphisms were investigated in 2 studies, 1 with a significant relationship and the other with a non-significant relationship. Oxytocin gene polymorphisms and tryptophan hydroxylase 2 gene polymorphisms were investigated in 2 studies with a significant relationship.

CONCLUSION

While this review has highlighted several genes that may be potentially associated with PE such as SLC6A4, limitations such as variance in study methods, lack of robust findings, small sample sizes, lack of reproducibility, quality of reporting, and quality of assessment remain a major concern. Further efforts such as standardizing reporting, exploring complementary designs, and the use of genome-wide association studies technology are warranted to test the reproducibility of these early findings. Mostafa T, Abdel-Hamid IA, Taymour M, et al. Gene Variants in Premature Ejaculation: Systematic Review and Future Directions. Sex Med Rev 2020;8:586-602.

Association between 5-hydroxytryptamine transporter gene-linked promoter region polymorphism and the susceptibility of lifelong premature ejaculation: a meta-analysis involving 1,604 subjects

The relationship between 5-hydroxytryptamine transporter-linked promoter region (5-HTTLPR) gene and lifelong premature ejaculation (LPE) risk was discussed widely for the last few years, which was still controversial and remained to be explored. We performed the meta-analysis with 8 reliable research, which were searched in the following databases: PubMed, Embase and Cochrane Library. We also performed random and fixed effects models to evaluate the odds ratios (ORs) and 95% confidence intervals respectively. By pooling all included studies, we found that SS genotype of 5-HTTLPR polymorphism was linked with significantly higher PE risk in Caucasian population (OR =0.635, 95% CI: 0.417–0.958, I²=0.311, P=0.035), and S-allele of 5-HTTLPR polymorphism increased the risk of LPE significantly in Asian population (OR =0.656, 95% CI: 0.539–0.799, I²=0.435, P<0.001). However, no significant was observed between 5-HTTLPR gene polymorphism and LPE risk in overall studies. Further studies were anticipated to be done.

Testosterone Replacement Therapy for Sexual Symptoms

BACKGROUND

Several data have clearly shown that the endocrine system-and androgens in particular-play a pivotal role in regulating all the steps involved in the male sexual response cycle. Accordingly, testosterone (T) replacement therapy (TRT) represents a cornerstone of pharmacologic management of hypogonadal subjects with erectile dysfunction.

AIM

The aim of this review is to summarize all the available evidence supporting the role of T in the regulation of male sexual function and to provide a comprehensive summary regarding the sexual outcomes of TRT in patients complaining of sexual dysfunction.

METHODS

A comprehensive PubMed literature search was performed.

MAIN OUTCOME MEASURE

Specific analysis of preclinical and clinical evidence on the role of T in regulating male sexual function was performed. In addition, available evidence supporting the role of TRT on several sexual outcomes was separately investigated.

RESULTS

T represents an important modulator of male sexual response function. However, the role of T in sexual functioning is less evident in epidemiologic studies because other factors, including organic, relational, and intrapsychic determinants, can orchestrate their effect independently from the state of androgens. Nonetheless, it is clear that TRT can ameliorate several aspects of sexual functioning, including libido, erectile function, and overall sexual satisfaction. Conversely, data on the role of TRT in improving orgasmic function are more conflicting. Finally, further controlled studies are needed to investigate the combination of TRT and PDE5 inhibitors.

CONCLUSION

Positive effects of TRT are observed only in the presence of a hypogonadal status (ie, total T < 12 nmol/L). In addition, TRT alone can be effective in restoring only milder forms of erectile dysfunction, whereas the combined therapy with other drugs is required when more severe vascular damage is present. Rastrelli G, Guaraldi F, Reismann Y, et al. Testosterone Replacement Therapy for Sexual Symptoms. Sex Med Rev 2019;7:464-475.