The EMPYREAN study is an ongoing multicenter, randomized, open-label (empagliflozin vs. sitagliptin), assessor-blinded, active controlled using sitagliptin, parallel-group clinical trial planned to test the hypothesis that empagliflozin improves autonomic disturbance in patients with T2DM during 24 weeks of treatment. Before patient enrollment, the study protocol was approved by the certified review board of Shinshu University School of Medicine. This study is being conducted in accordance with the Declaration of Helsinki. Written informed consent is obtained from each patient before enrollment. Personal information about potential and enrolled participants is kept confidential, and subject data are de-identified using participant numbers.
Inclusion and exclusion criteria
We aim to recruit a total of 134 participants across approximately 20 sites in Japan. Recruitment for the trial began in December 2017 and will end in April 2020. Eligible participants for the trial are patients with T2DM aged 20 to 74 years who meet the enrollment criteria detailed in Table 1. Briefly, eligible patients include those with a diagnosis of T2DM, HbA1c ranging from 6.5% to 10.0% (7.0% to 10.0% for patients treated with sulfonylurea or glinide), no anti-diabetic therapy with SGLT2 inhibitors or dipeptidyl peptidase 4 inhibitor (DPP4-I) agents for ≥12 weeks prior to randomization, and body mass index ≥18.5 kg/m2 and ≤40 kg/m2 at screening.
Trial design and follow-up
Eligible patients undergo a 4-week screening period (Figure 1), during which time background glucose-lowering therapy is continued unchanged. The purpose of the screening period is to evaluate participants’ willingness and ability to adhere to the treatment and follow-up planned in the trial and evaluate baseline clinical characteristics. Blood/urine sampling (on-site and central measurement), electrocardiogram (ECG) recording, the Schellong test, and 24-hour Holter ECG are also performed. Details of the blood/urine sampling for on-site monitoring and central measurement are listed in Table 2. HbA1c is evaluated by on-site management of diabetes and by central measurement as an exploratory outcome. Following the screening period, patients still meeting the inclusion/exclusion criteria are randomized (1:1) to receive either empagliflozin 10 mg or sitagliptin 50 mg once daily in addition to their background therapy. Treatment allocation is centrally performed with a minimization algorithm implementing a random component by the data management group of the data center. Baseline heart rate (<75 count/min or ≥75 count/min), age (<50 years or ≥50 years), HbA1c (<8% or ≥8%), and treatment center are considered as balancing factors. Background glucose-lowering therapy is to remain unchanged for the 24 weeks after randomization if possible, although rescue therapy can be initiated. During this period, empagliflozin (10-25 mg/day) or sitagliptin (50-100 mg/day) can be adjusted to achieve desired glycemic control at the investigator’s discretion for the best standard of care according to local guidelines (18). Twenty-four hour Holter ECG and blood sampling (on-site/central measurement) are performed at 12 and 24 weeks of treatment (Table 3). HRV is analyzed in the time-frequency domain as shown in Table 4.
Endpoints
The primary outcome of this study is the change in the LF/HF ratio from the baseline to the end of the study (24 weeks). The key secondary outcomes include the changes in LF, HF, and LF/HF ratio from baseline to 12 weeks and changes in LF and HF from baseline to 24 weeks. The following variables are evaluated for changes from baseline to 12 and 24 weeks: average of all N-N intervals, standard deviation of N-N intervals (SDNN), standard deviation of the averages of N-N intervals for all 5-minute segments of a 24-hour recording, mean of the standard deviations of N-N intervals for all 5-minute segments of a 24-hour recording, root mean square of successive differences between adjacent N-N intervals (rMSSD), percentage of differences between adjacent N-N intervals that are greater than 50 ms, incidence of premature heartbeat and arrhythmia events, body weight and body mass index, and HbA1c. The changes from baseline to 12 and 24 weeks in waist circumference, serum catecholamines, thyroid-stimulating hormone, fT4, fT3, brain natriuretic peptide (BNP), N-terminal-pro-BNP, pro-BNP, and atrial natriuretic peptide (ANP) are investigated as exploratory outcomes. Details of the outcomes are described in Table 5.
Holter ECG
All data from 24-hour Holter ECG are sent to the Core Laboratory for analysis by an unrelated physician in a blinded manner (MemCalc/CHIRAM, Suwa Trust GMS, Tokyo, Japan) to obtain the LF (0.04–0.15 Hz) and HF (0.15–0.4 Hz) components of HRV (measured in absolute units; i.e., ms2). The total power of HRV is also calculated for regression analysis as a global marker of cardiac autonomic function. From the electrocardiographic recordings, the statistical and geometric time domain indices are calculated from the N-N intervals noted above (Table 5). Frequency domain variables including the total, LF, and HF powers as well as the LF/HF ratio are derived from spectral analysis of successive N-N intervals.
Safety
Throughout the study, safety information is collected by recording such serious adverse events as all-cause mortality, fatal events, and adverse conditions requiring admission or prolongation of admission regardless of the causal relationship with the trial drugs or protocol, in addition to pre-defined adverse events of special interest including hepatic injury, decreased renal function, metabolic acidosis, ketoacidosis, diabetic ketoacidosis, and events involving lower limb amputation. When investigators identify any adverse event, its severity or grade, procedures conducted, outcomes, and relationship to the study drug are recorded and assessed. Investigators promptly report the occurrence of adverse events to the secretariat who then immediately informs the principal investigator for relay to Nippon Boehringer Ingelheim and the Data and Safety Monitoring Board (DSMB). The DSMB consists of an authorized endocrinologist and clinical epidemiologists with relevant expertise. Blinded to treatment allocation, the DSMB independently evaluates safety during the trial, assesses the necessity for any revisions to the trial design, and validates any decisions to continue the trial. If needed, the DSMB makes recommendations on safety issues to the principal investigator.
Study monitoring
Risk-based monitoring of the study sites is implemented to ensure that this study is properly conducted. A monitoring protocol has been separately created for the detailed monitoring-related plan. Auditing by an independent third party is also conducted to ensure the reliability of study results. Auditing is performed according to a separately specified, documented procedure. Records and medical information identifying the patients are kept confidential during monitoring and auditing. When new safety information-related issues arise, the Protocol Steering Committee or the DSMB discuss the issue, including study discontinuation or continuation, and the ethical review committee at each study site confirms each patient’s intention to continue participation in the study.
Statistical considerations
Sample size estimation
To date, no data are available on the impact of SGLT-2 inhibitors on cardiac autonomic nerve activity. Thus, we referred to a previous study which evaluated the LF/HF ratio of patients treated with amlodipine or verapamil. The mean difference and standard deviation of the LF/HF ratio was 0.15±0.25; thus, the effect size was 0.6 (19) in the study. Accordingly, we considered a conservative effect size of 0.5, alpha error of 5%, and power of 80%. To allow for approximately 10% drop-out, 67 patients are required per group, i.e., 134 participants in total.
Statistical analysis plan
The primary efficacy population has been defined as a full analysis set (patients who were randomly assigned to a group and received Holter ECG at least once). The change in the LF/HF ratio at 24 weeks is examined via mixed model repeated measures analysis for comparisons between the efficacy of the treatments (empagliflozin and sitagliptin). Inter-group comparisons of the least squares means at 24 weeks are performed as well. Missing data are not imputed. The covariates included in the model are: treatment group, time point, interaction between treatment group and time point, baseline heart rate, age, and HbA1c. Additionally, unstructured correlation is assigned via the restricted maximum likelihood concerning the correlation structure, and the Kenward-Roger method is used to calculate the degree of freedom (20). When difficulties (e.g., convergence is not attained) arise, first-order autoregressive covariance is used followed by compound symmetry. Similar analytical methods are applied to the secondary endpoints. The safety population has been defined as a safety analysis set (patients who were randomly assigned to a group and received at least one dose of the study treatment). Descriptive analysis is performed for the frequency of adverse events. A two-sided P-value of <0.05 is considered statistically significant. All statistical analyses are performed using SAS Version 9.4 software (SAS Institute, Cary, NC).