The central mechanism of tadalafil vs Chaihu-Shugan-San capsule for psychogenic erectile dysfunction: a magnetic resonance imaging study protocol of a randomized placebo-controlled trial

Background: Erectile dysfunction (ED) affects many adult men worldwide. Many studies on the brain of psychogenic ED have shown significant cerebral functional changes and reduced volume of gray matter and white matter microstructural alterations in widespread brain regions. We design this study to provide both an enhanced level of evidence of central mechanism research and an evidence-based treatment option for patients suffering from psychogenic ED. Furthermore, we also aim to provide a new evidence as well as an innovation of the clinical treatment in psychogenic ED. Methods: This study is designed as a multi-center, three-arms, randomized trial. From the perspective of psychogenic ED, we will divide patients into three groups, which are placebo group, tadalafil group and CHSGS group. 135 patients will be randomly allocated to receive placebo, CHSGS capsule or tadalafil oral pharmacotherapy. After the period of 4-week treatment, the outcome of primary assessment changes in the IIEF-5, EHS and QEQ total scores from baseline. Secondary assessments include the SEAR, HAMA-14, HAMD-17 scores, response rate of the patients and their partners. Apart from brain MRI from baseline, we will also attach great importance to other changes in the follow-up four weeks. Discussion: We expect that the results of this trial can provide both an enhanced level of evidence for central mechanism research and an evidence-based treatment option for patients suffering from ED, as well as to provide an innovation of the clinical treatment in psychogenic ED.


KEYWORDS
Erectile dysfunction, psychogenic ED, MRI, Randomized controlled trial believes that CHSGS could regulated the mental disorders. Despite significant progress, the mechanism aiming at CNS targets treated by tadalafil or CHSGS capsule is still unknown.
Normal erectile function is a result of the harmonious regulation and control of the central nervous system (CNS), which includes the supraspinal centres, the spinal cord and peripheral nerves. In the last two decades, exploring the role of CNS in sexual arousal by functional and structural neuro-imaging studies, the magnetic resonance imaging (MRI) [20] such as diffusion tensor imaging (DTI) [21,[23][24][25], functional MRI (fMRI) and restingstate fMRI attracted many researchers [23][24][25]. Since 2002, compared with healthy subjects (HS), much researchers have found that psychological ED patients showed significant changes in cerebral functions. What is more, reduced volume of gray matter and white matter microstructural alterations in widespread brain regions mediating controlled and regulated the processes of erection have also been found in many regions of the human brain of the psychogenic ED [21][22][23][24][25][26][27][28]33]. MRI techniques are widely used to study the central mechanism and show positive result with premature ejaculation [34], rheumatoid arthritis [35], functional dyspepsia [36], fibromyalgia [37], addictive disorders [38]and especially in depressive patients treated with paroxetine [39]. Therefore, we hypothesized that compared with the tadalafil or CHSGS or placebo alone, to treat psychogenic ED with the CHSGS or tadalafil will be more effective due to its specific brain function modulation.

Study design
This is a multi-center, three-arms, randomized trial which was designed following the guidelines [40][41][42].
This study will be carried out in the Hospital of Chengdu University of Traditional Chinese Medicine and Sichuan Integrative Medicine Hospital. During the 4-week treatment, patients in three interventions will receive a continuous oral medication with tadalafil, or CHSGS or placebo. Both the MRI scan and outcome assessment will be fulfilled at two time points, including the baseline and the end of the intervention treatments ( Figs. 1 and 2).
This trial is reported in accordance with the Standard Protocol Items: Recommendations for Intervention Trials (SPIRIT) guidelines [40,42]. All of the participants will be asked to sign an informed consent before the trial that will contain an introduction of pED and ED, the inclusion and exclusion criteria, and a detailed introduction to the interventions.

Sample size
Due to the lack of reference on the expected effect size of using CHSGS to treat erectile dysfunction evaluated in this study, we did not estimate the sample size based on a power calculation. According to previous studies, International Index of Erectile Function 5 (IIEF-5) scores of ED patients increased 6.0-7.1 after tadalafil [13,15]. Therefore, we predicted ascension of IIEF-5 score by 6.5 points after oral tadalafil or CHSGS capsule, a reduction by 2.5 points after placebo. According to the calculation with PASS software (Version 11.0, NCSS, LLC. Kaysville, UT, USA) in a 1:1:1 ratio, when α=0.05, 1-β=0.8 with the standard deviation to be 3.8, the effect size is 0.2550 of 41 participants in each group. Considering a dropout rate of 10% and according to our previous study, a sample size of 135 patients at baseline will be planned in this study.
According to the sample size of previous BOLD-fMRI [23], TDI [21], and fMRI studies, 12-15 subjects is the very reasonable sample size with stable statistical effect [29,30].
Considering the dropout rate and loss of data as to head motion during MRI scans, 15 participants from each group will undergo MRI scans in this study.

Randomization
Qualified participants will be randomly assigned to either the tadalafil group, the placebo group or the CHSGS capsule group in a ratio of 1: 1:1. Random numbers will be generated by a random number generator in the SPSS statistical software package (Version 22.0, SAS Institute Inc.), which will be operated by a third party who is uninvolved with the treatment and data collection. The drawn letters (A or B or C) will be placed into opaque envelopes labeled with sequential numbers. The envelopes will be sealed and remain in numerical order in a safe place till the completion of this study. The same researcher (not involved in the study) will prepare the envelopes.

Blinding
The medicine will be specially handled and labeled by the Pharmacy Department in the Hospital of Chengdu University of TCM to guarantee that the patients and the practitioners included in the study will maintain completely blinded as to the identity of the treatment administered. Besides, the all practitioner will be prohibited to communicate with participants about the information of this trail.

Recruitment requirement
All psychogenic ED patients are recruited at the outpatient department in the Hospital of (HAMD-17). All of the above must be by checked before being enrolled in this study.

Inclusion criteria
Patients must meet the following diagnostic criteria from the current guidelines, including: (i)men be right-handed and the age ranged from 20 to 40, (ii) men be diagnosed as psychogenic ED (DSM-5), (iii) men must be in a stable heterosexual relationship for at least 1 year with his regular sexual partner, (iv) penile erection can occur in the circumstance of masturbation or audiovisual stimulation, (v) men who meet the TCM diagnosis of stagnation of liver-qi", (vi) men who agree to complete all demand during the study period, (vii) sign an informed consent form.

Exclusion criteria
Exclusion criteria for the forthcoming study are as follows: (i) be diagnosed as organic ED rather than psychogenic disorder, (ii) a current diagnosis or history of drug or alcohol dependence; (iii) use of any medication that might impact sexual function during the previous 30 days before enrolled in this study; (iv) any physical illness as assessed by personal history and laboratory analysis finding any history of serious psychiatric, neurological, cardiovascular, respiratory, gastrointestinal or renal diseases or hepatic disorders or significant physical disorders; (v) participated in any other current clinical trials; (vi) had any contraindications for MRI scan.

Tadalafil group
Patients will be provided a once-daily treatment with 5 mg tadalafil added to the capsule until 4 weeks.
According to the current guidelines, the therapeutic interventions for ED are basic  43,44].Therefore, we selected tadalafil as the positive control group as well as the treatment group. Smashed tadalafil will be mixed with starch powder and stir well into a container in order to be made into capsule.

CHSGS group
Patients will be provided three-daily treatment with 5g CHSGS added to the 5 capsule each time until 4 weeks.
The CHSGS preparation contained the gathering of the following components: 6g Bupleurum Chinese root, 4.5g Rhizoma Chuanxiong, 4.5g Fructus Aurantii, 6g Pericarpium CitriReticulatae, 4.5g Paeonia, 1.5g Glycyrrhizaeuralensis root and 5g Cyperusrotundus. CHSGS and its components were individually decocted in boiling water for 30 min, concentrated and vacuum-dried to form a paste, and were subsequently combined into a paste containing 8g crude extracts per gram. Starch powder was mixed into a container.
Stir it well and make it into capsule.

Placebo group
Patients will be provided three-daily treatment with the 5g mixed starch powder added to the 5 capsule each time until 4 weeks.
It is known that placebos are the best comparison between clinical controlled trials.
Therefore, we adopted this placebo and standardized its performance. The placebo components were obtained from the Hospital of Chengdu University of TCM. The standard operating procedures (SOP) are listed as follows: (i) the materials are starch, (ii) add the liquid base: place the mixed starch powder into a container, add honey and stir well to make it into capsule. The above materials made shared the same character with the CHSGS capsule in terms of appearance, weight and taste.

Outcome assessment
The following outcomes will be assessed by independent assessors, who had been trained before participating in this study and blinded to the randomization. All outcome data for participants whether completed or withdrawn during the study will be collected and recorded in the case report form (CRF).

Symptom assessment
Based on various clinical studies, the primary symptoms of the ED patients will be assessed on mean changes from baseline to end of observation in the International Index of Erectile Function 5 (IIEF-5) total scores [45,46], which has been widely used and recommended as a primary outcome for clinical trials of ED. Furthermore, the quality of erection questionnaire (QEQ) [47][48][49] and the erection hardness score (EHS) total scores will also be included in this study [47,50]. In terms of the assessment of symptom severity of erectile function for all the participants in this study, the secondary outcome will be based on the self-esteem and relationship (SEAR) questionnaire [51]. As to the level of anxiety and depression of all the participants in this study, it will be evaluated by two independent psychologists within the questionnaires of the 14-item Hamilton Anxiety Rating Scale (HAMA-14) and the 17-item Hamilton Depression Rating Scale (HAMD-17) [52,53].

MRI scan
The MRI scanning of the brain will be executed on T1-weighted structure images in 3D Magnetization-Prepared Rapid-Gradient-Echo (MPRAGE) Images will be firstly collected before resting-state scanning with the following sequence parameters: field of view (FOV)= 240ⅹ240 mm 2 , repetition time (TR)=1900 ms, echo time (TE) =2.26ms, and matrix = 256ⅹ256.

Safety assessment
Adverse events (AEs) related to tadalafil treatment such as myalgia, back pain and flushing will be appropriately estimated and recorded by the observers during the trial.
AEs will be managed by a specialized practitioner (do not participate in clinical data analysis) within 24 hours. The principal researcher (PH. Zhang) will make the final decision to terminate the trial if severe AEs occurs. All data for participants during the study and details of related and unexpected AEs (the time of occurrence, severity of AE, and suspected causes) will be collected and recorded in the case report form (CRF). Measures may vary from symptomatic treatment to case submission to the Research Ethics Committee within 48h depending on the severity of AEs.

Quality control and Data collection
Due to the fact that any nonstandard or bias input of clinical data can dominate the bias of results, two practitioners (to estimate the effect of treatment and the data authenticity) will independently gather the data with case report forms and original cerebrum MRI. The collected data will be input into a dedicated computer. The above process will maximize the reliability and safety of the all data. In order to guarantee the quality of the study, all practitioners will be required to have an official license for at least two years of protocol study and clinical experience.

Clinical variables
The clinical data will be analyzed with the help of SPSS22.0 (SPSS Inc., Chicago, IL, USA) by two blinded evaluators and the data analysis will be based on the intention-to-treat (ITT) principle regarding baseline characteristics. All the clinical data in this study will be presented as follows: (i) a continuous measurement data being presented as the mean ±standard deviation (SD), the mean, SD, median and interquartile range. (ii) a categorical data being presented as case and percentages. Analysis tools include: the Cochran-

Mantel-Haenszel (CMH) test or nonparametric test, an independent samples t-test, and a
two-sided test. Also, analysis of covariance, covariance analysis or generalized estimating equations, χ2 and Linear regression will be applied on all available and suitable data (p value < 0.05 is considered to be statistically significant).
Fig3 illustrates the data access and the analysis of the brain MRI data as well as the analysis methods of the primary and secondary outcomes.

Discussion
In this protocol study, the qualified participants are asked to maintain their current living habits and sexual performances, especially their diet, exercise and the quality of sleep.
Meanwhile, they are required to fill out relevant questionnaires throughout the full observational process. To satisfy the requirements of the Rule of Ethics and reduce the bias caused by performance, the rest of the all clinical procedures maintain the same.
Seen from the current records and recent RCT results, tadalafil has an enduring effect and was the best-marched choice between patients and their partner for treating psychogenic ED. However, its central mechanism remains unclear. Considering the importance of the brain for the psychogenic ED, we have designed the randomized controlled MRI trial to reveal the central mechanism of the psychogenic ED treated by tadalafil. In this study, we will compare the changes in brain function after administration of two interventions: the tadalafil and the CHSGS capsule.
Many regions of the human brain have been found to play a very important role in human sexual arousal as well as penile erection, emotion, and cognition. Over the last 15 years, MRI science has been widely used to disclose the cerebral mechanism of human sexual arousal especially the penile erection and investigate the brain function alteration in psychogenic ED and healthy subjects. Erection is known to be one of the most convincing and mischievous signs of the sexual response cycle. Relatively, ED not only can be conceptualized as an impairment in the arousal phase of sexual response [59], but also can be seen as a central and spinal center reflex, which can be sponsored by recruitment of penile afferents, both somatic and autonomic, and the changes of visual, imaginary stimuli, and olfactory. Several central transmitters [60] play a crucial role in erectile control and the main regions that control of male sexual arousal are summarized in Fig 4. Previous DTI studies showed that psychogenic ED had decreased or increased white matter microstructures in multiple brain regions [21]. Besides, brain networks neuroimaging studies also had showed that psychogenic ED had increased the small-worldness and modules in the left prefrontal cortex and limbic system including the right superior parietal gyrus, and the superior parietal gyrus [23][24][25].These brain networks were absolutely believed to be closely related to the brain sexual arousal of the psychogenic ED [60][61][62][63].
In order to guarantee the reliability of the result of this study, we adopt the quality key point control as follows: (i) patient in this study restricts the subjects to age between 20 to 40 and being right-handed for baseline homogeneity; (ii) sample size to obtain stable statistical power; 135 patients will be included in each group for clinical evaluation and 15 patients will be included in each group for the central mechanism study and receive MRI scans; and (iii) MRI scans; each scan will be performed in the afternoon with the same scanner and operator. During the scanning period, all participants will be asked to remain relaxed, keep their eyes closed and wear a birdcage head coil filled with sponge material and to stay still to reduce the effects of head movement. The scanning room maintains the noise less than 150 dB and the temperature between 18 and 22 °C, with humidity higher than 60%.
In conclusion, this study is conducted in the purpose of supporting the concept of brain MRI alteration in psychogenic ED with tadalafil or CHSGS capsule. We expect that the

Trial status
Participant recruitment is currently ongoing. 3 participants have been recruited. Its deadline would correspondingly be postponed to February 2019.

Consent for publication
Not applicable.

Availability of data and materials
Not applicable.

Competing interests
The authors declare that they have no competing interests.

Funding
The trial is financially supported by the National Natural Science Foundation of China (NO. 81774137). The role of the funding in the design is to collect and analysis the data.    Figure 1 The Flowchart of the study protocol.  The central transmitters in brain regions.

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