FormalPara Key Summary Points

Why carry out this study?

Glucagon-like peptide-1 receptor agonist therapy (GLP-1RA) has been recently reported to considerably ameliorate atherosclerotic cardiovascular disease.

Oxidative stress, a surrogate marker of cardiovascular risk, is linked to glucose variability.

This is the first study to compare the effects of semaglutide therapy with another GLP-1RA (dulaglutide) on oxidative stress and glucose variability.

What was learned from the study?

Injectable semaglutide therapy is better than dulaglutide therapy for reducing oxidative stress and improving glucose variability.

Patients reported higher treatment satisfaction with dulaglutide therapy than with semaglutide therapy.

Introduction

Type 2 diabetes mellitus (T2DM) is a major risk factor for atherosclerosis. Atherosclerotic cardiovascular disease (CVD) is a leading cause of death in patients with T2DM [1, 2]. The United Kingdom Prospective Diabetes Study (UKPDS) 80 reported that intensive treatment of hyperglycemia considerably reduced the risk of myocardial infarction and death in patients with early diagnosed T2DM followed up during a 10-year post-trial period [3]. However, the Action to Control Cardiovascular Risk in Diabetes Study and Veterans Affairs Diabetes Trial revealed the limited beneficial effects of relatively short-term strict blood glucose control on cardiovascular events in patients with long-lasting T2DM with CVD history or multiple cardiovascular risk factors [4, 5]. Therefore, how and when hyperglycemia has been treated may be two important factors in preventing atherosclerotic CVD in patients with T2DM.

Recently, the Semaglutide Unabated Sustainability in Treatment of Type 2 Diabetes (SUSTAIN) 6 and Researching Cardiovascular Events with a Weekly Incretin in Diabetes trials have shown that therapy with glucagon-like peptide-1 receptor agonists (GLP-1RAs) decreases the risk of cardiovascular events in high-risk patients with T2DM [6, 7]. Based on the positive results of these clinical trials, the American Diabetes Association and European Association for the Study of Diabetes Consensus Report recommend the use of GLP-1RAs for treating patients with T2DM with atherosclerotic CVD and/or multiple coronary risk factors [8].

However, accumulating evidence shows that glucose variability is associated with endothelial dysfunction in patients with T2DM, an initial step for progression to atherosclerosis through oxidative stress generation, which reportedly plays a pivotal role in the development and progression of atherosclerotic CVD [9, 10]. Indeed, we have previously demonstrated that diacron-reactive oxygen metabolites (d-ROMs), a surrogate marker of oxidative stress, are correlated with glucose variability, as evaluated through continuous glucose monitoring (CGM) in patients with T2DM [11]. Furthermore, endothelial dysfunction and the presence and severity of coronary artery disease are positively associated with glucose variability in patients with T2DM. These observations suggest that increased oxidative stress and glucose variability may be therapeutic targets for atherosclerotic CVD in patients with T2DM [12, 13].

In the SUSTAIN 7 trial, injectable semaglutide therapy was more effective than dulaglutide therapy in reducing glycated hemoglobin (HbA1c) levels and body weight (BW) in patients with T2DM [14]. However, to the best of our knowledge, no clinical study has compared the effects of injectable semaglutide and dulaglutide therapies on oxidative stress and glucose variability in patients with T2DM. Additionally, we are unsure whether once-weekly dulaglutide therapy can further improve patient satisfaction in T2DM compared with once-daily liraglutide therapy [15, 16]. Therefore, the aim of this study was to compare the effects of injectable semaglutide and dulaglutide therapies on oxidative stress evaluated via d-ROMs, glucose variability assessed through CGM, and treatment satisfaction according to the Diabetes Treatment Satisfaction Questionnaire (DTSQ) scores in patients with T2DM.

Methods

Patients

Outpatients with T2DM (age ≥ 20 years) who had been treated with dulaglutide for at least 12 weeks at Showa University Hospital and Tokatsu Hospital in Japan and whose HbA1c levels were ≥ 6.5% (47 mmol/mol) were enrolled in the present study. The following patients were excluded: (1) those with an estimated glomerular filtration rate (eGFR) of ≤ 30 mL/min/1.73 m2 according to the Cockcroft–Gault formula; (2) those who were undergoing steroid and/or anti-inflammatory drug treatment, including vitamin C supplementation; (3) those with severe infection and trauma and/or perioperative period; (4) those with diabetic ketosis or those who were in coma within the 3 preceding months of entering into the study; (5) pregnant women; (6) those with malignancy; and (7) those who were deemed inappropriate for inclusion as assessed by their respective physician.

Study Design

This was an open-label, multicenter, randomized, prospective study conducted at Showa University Hospital, a private university hospital responsible for tertiary care, and Tokatsu Hospital, a general hospital providing secondary care, in Japan between April 2021 and May 2022. Figure 1 summarizes the study protocol. We randomly assigned patients to two groups using an Excel (Microsoft Corp., Redmond, WA, USA)-based allocation system with stratification and 1:1 allocation via permuted-block randomization; one group received a continuous dose of 0.75 mg/week dulaglutide therapy and the other group switched to injectable semaglutide therapy (0.25 mg/week) after dulaglutide therapy. After 4 weeks, the semaglutide dose was increased to 0.5 mg/week. At baseline and 24 weeks following the intervention, we measured the following clinical and laboratory parameters before breakfast on day 1 of CGM [17]: BW, low-density lipoprotein cholesterol (LDL-C) levels, high-density lipoprotein cholesterol (HDL-C) levels, triglyceride (TG) levels, eGFR, blood pressure, fasting plasma glucose (FPG) levels, and HbA1c levels. All clinical data, such as diabetes duration and smoking habit, were retrieved from the medical records of the patients. The patients were instructed to maintain their lifestyle and continue receiving the same dose of any concomitant drugs. Additionally, they were instructed to follow a weight-maintaining diet (25–30 kcal/kg ideal BW; 50–60% carbohydrates, 20% proteins, and the rest fat) during the study period.

All procedures were followed according to the ethical standards of the responsible committee on human experimentation (institutional and national) and/or the Helsinki Declaration of 1964 and its later versions. Informed consent or an acceptable alternative was obtained from all patients included in the study. The study was approved by the Ethics Committee of Showa University (Approval number 3292; date of approval, 19 November 2020), and was registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR ID: UMIN000042670). The treatment costs were covered by insurance.

Fig. 1
figure 1

Study protocol. Outpatients with T2DM were treated with dulaglutide for at least 12 weeks, then randomized into a maintenance therapy group receiving dulaglutide therapy or a group switched to semaglutide therapy. CGM Continuous glucose monitoring, T2DM type 2 diabetes mellitus

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Procedures and Measurements

A FreeStyle Libre Pro CGM device (Abbott Japan, Tokyo, Japan) was subcutaneously inserted into each patient on day 1 of the study and subsequently removed from the patient on day 14. We calculated glucose variability from day 3 to day 12 to exclude inaccurate data. The coefficient of variation (%CV) was measured by dividing the standard deviation (SD) of the glucose level by the mean glucose level (MGL) and multiplying it by 100 [18]. To assess daily glucose variability, we calculated the mean amplitude of glucose excursion (MAGE) [19]. The mean of the absolute difference between the corresponding glucose values indicated the mean daily difference in blood glucose levels [20]. We also calculated the time above range (TAR), defined as the percentage of time spent at > 180 mg/dL (> 10.0 mmol/L), the time in range (TIR), defined as the percentage of time spent within the target range of 70–180 mg/dL (3.9–10.0 mmol/L) during a 24-h period, and the time below range, defined as the percentage of time spent at < 70 mg/dL (< 3.9 mmol/L) [21].

Laboratory Measurements

Oxidative stress was measured using the d-ROMs test, which evaluates free radical activity by measuring the serum levels of hydroperoxides according to previous reports [22, 23]. The results of the d-ROMs test are expressed in arbitrary units (i.e., as Caratelli Units [U.CARR], where 1 U.CARR = the oxidant capacity of 0.08 mg/dL H2O2 solution and the normal range was 250–300 U.CARR). Moreover, clinical variables were measured using an automated analyzer (model BM6070; Japan Electron Optics Laboratory, Tokyo, Japan). The plasma glucose levels were measured using the glucose oxidase method, and HbA1c levels were determined by high-performance liquid chromatography [24].

Diabetes Treatment Satisfaction and Eating Behavior

To assess treatment satisfaction, we used the DTSQ, which is a validated self-administered questionnaire, and calculated its scores at baseline and 24 weeks after the intervention [25, 26]. The DTSQ comprises eight items scored on a 7-point Likert scale ranging from 0 (very dissatisfied) to 6 (very satisfied). The scores of six satisfaction items, namely “Current treatment,” “Convenience,” “Flexibility,” “Understanding,” “Recommend,” and “Continue,” were summed up, with 36 as the highest possible total score. The two remaining items, “Perceived frequency of hyperglycemia” and “Perceived frequency of hypoglycemia,” were evaluated individually.

For assessing eating behavior, we used the questionnaire of the Guideline for Obesity issued by the Japan Society for the Study of Obesity at baseline and 24 weeks after the start of the study. This questionnaire consists of 55 items with seven major scales [27, 28].

Endpoints and Assessments

The primary endpoints were changes in d-ROMs and glucose variability from baseline after completing the 24-week treatment intervention. The secondary endpoint was changes in the DTSQ score.

Sample Size Calculation

As mentioned above, to our knowledge, no clinical studies have yet compared the effects of dulaglutide and injectable semaglutide therapies on glucose variability and oxidative stress. Therefore, we determined the sample size after reviewing the studies that have investigated the effects of incretin modulators, including GLP-1RAs, on glucose variability and oxidative stress [16, 29]. Furthermore, considering the possibility of a 20% dropout rate, we calculated the sample size as 20 individuals per group.

Statistical Analysis

All normally distributed continuous data, as determined via the Shapiro–Wilk test, are expressed as the mean ± SD. Differences in continuous variables between the semaglutide and dulaglutide therapy groups at baseline and after treatment were evaluated using independent samples t-test or Mann–Whitney U-test, as appropriate. To compare categorical variables, we used the Chi-square test. A p value of < 0.05 was to be considered statistically significant. All the statistical data were analyzed using SPSS version 22 for Windows (IBM Corp., Armonk, NY, USA).

Results

Patient Sample and Characteristics

Figure 2 shows the flowchart of patient inclusion. We screened 42 patients, of whom one declined to participate and two did not meet the inclusion criteria. Of the 39 remaining patients, 19 were randomized to the semaglutide therapy group and 20 to the dulaglutide therapy group. However, one patient from each group was removed because they experienced pain from injection and were lost to follow-up, ultimately leaving 18 and 19 patients in the semaglutide and dulaglutide therapy groups, respectively, for analysis (Fig. 2). Table 1 lists the baseline clinical characteristics. The mean age, diabetes duration, and HbA1c levels of the semaglutide and dulaglutide therapy groups were 72.2 ± 9.7 and 71.8 ± 11.3 years, 18.2 ± 11.1 and 20.3 ± 10.7 years, and 7.7% ± 0.7% and 7.4% ± 0.6%, respectively. The clinical characteristics and biochemical parameters at baseline were not significantly different between the two groups.

Fig. 2
figure 2

Flow-chart of participant inclusion during the trial

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Table 1 Baseline clinical characteristics of study participants
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Effects of Semaglutide and Dulaglutide Therapies on Clinical and Biochemical Parameters

Table 2 summarizes the clinical and biochemical parameters. After 24 weeks of treatment, changes in clinical and biochemical parameters from baseline were not significantly different between the two groups, except for oxidative stress and glucose metabolism. Compared to the dulaglutide group, the semaglutide therapy group exhibited better changes in d-ROMs (mean ± SD, 4.4 ± 60.5 vs. − 36.1 ± 57.6 U.CARR, respectively; p = 0.045) and HbA1c levels (0.2% ± 0.6% vs. − 0.4% ± 0.5%, respectively; p = 0.006). Figure 3 shows the 24-h blood glucose profiles as assessed by CGM. The mean (± SD) changes in SD, MAGE, %CV, TAR, and TIR were also better in the semaglutide therapy group than in the dulaglutide therapy group (SD: − 4.3 ± 10.1 vs. 5.3 ± 9.3 mg/dL, p = 0.005; MAGE: − 6.7 ± 21.1 vs. 12.2 ± 22.8 mg/dL, p = 0.013; %CV: − 2.8% ± 4.6% vs. 0.1% ± 3.3%, p = 0.038; TAR: − 4.0 ± 22.5 vs. 11.3 ± 20.8 mg/dL, p = 0.039; TIR;4.7 ± 22.2 vs. − 10.4 ± 18.6 mg/dL, p = 0.031). Clinical and biochemical parameters, including MGL, MAGE, and TAR, were unaffected by the switch to semaglutide therapy, whereas they worsened significantly by continuous dulaglutide therapy for 24 weeks (from 140.2 ± 20.9 to 158.0 ± 28.6 mg/dL, p = 0.035; from 95.4 ± 15.7 to 107.6 ± 20.1 mg/dL, p = 0.045; from 18.6% ± 13.8% to 30.3% ± 19.4%, p = 0.045, respectively).

Table 2 Comparison of clinical and biochemical parameters at baseline and 24 weeks
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Fig. 3
figure 3

Continuous glucose monitoring data at baseline (a) and 24 weeks after intervention (b)

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Table 3 shows the correlations between the changes in d-ROMs and glucose metabolism parameters. In the dulaglutide therapy group, no statistically significant relationship was observed between changes in d-ROMs and glucose metabolism parameters. In the semaglutide therapy group, changes in d-ROMs tended to be associated with changes in SD (r = 0.420, p = 0.083) and TIR (r = − 0.401, p = 0.099). When the data of both the groups were combined, changes in d-ROMs were significantly correlated with HbA1c (r = 0.338, p = 0.040), MGL (r = 0.349, p = 0.034), SD (r = 0.430, p = 0.008), MAGE (r = 0.333, p = 0.044), CV (r = 0.325, p = 0.050), TAR (r = 0.373, p = 0.023), and TIR (r = − 0.404, p = 0.013) values in the univariate analysis. In the multivariate stepwise regression analysis, only SD appeared to be correlated with d-ROMs (β = 0.430, p = 0.008) (adjusted multiple R2 = 0.162).

Table 3 Correlations between the changes in diacron-reactive oxygen metabolites and glucose variability
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Effects of Semaglutide and Dulaglutide on DTSQ Scores

Table 4 summarizes the self-reported patient treatment satisfaction as evaluated via the DTSQ scores and eating behavior at baseline and 24 weeks following the treatment. Although DTSQ scores did not significantly improve with either of the treatments, changes in “Convenience” and “Recommend” from baseline significantly differed between the dulaglutide and semaglutide therapy groups (“Convenience”: − 0.5 ± 1.3 vs. 0.7 ± 1.4, p = 0.005; “Recommend”: − 0.2 ± 1.1 vs. 1.1 ± 2.1, p = 0.045). After 24 weeks of treatment, there were no changes in either group regarding the eating behavior scores.

Table 4 Effect of semaglutide and dulaglutide on Diabetes Treatment Satisfaction Questionnaire and eating behavior
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Discussion

To the best of our knowledge, this clinical study is the first to compare the effects of injectable semaglutide and dulaglutide therapies on oxidative stress and glucose metabolism as measured via CGM, patient satisfaction, and eating behavior. The results of this study demonstrated that switching to injectable semaglutide therapy was more effective than continuous dulaglutide therapy in reducing an oxidative stress marker, d-ROMs, and glucose variability in patients with T2DM, whereas continuous dulaglutide therapy demonstrated higher treatment satisfaction than its counterpart.

In studies on patients with T2DM who were on diet and exercise therapy, dulaglutide and liraglutide therapies reportedly improved the daily glucose variability [30, 31]. However, we have previously reported that once-weekly dulaglutide therapy is better than once-daily liraglutide therapy in terms of controlling the daily glucose variability [16]. In the present study, we compared the effects of therapy with another once-weekly GLP-1 RA, i.e., semaglutide, with those of dulaglutide therapy and showed that semaglutide therapy was more effective than dulaglutide therapy in reducing the daily glucose variability following a 24-week treatment. Although there was no statistically significant difference in the FPG levels of patients treated with 0.5 mg/week semaglutide and 0.75 mg/week dulaglutide, semaglutide therapy demonstrated more favorable effects on HbA1c levels. Furthermore, while changes in HbA1c levels were not correlated with FPG (r = 0.258, p = 0.301), they were correlated with the other glucose metabolism parameters, such as MGL (r = 0.537, p = 0.021), SD (r = 0.500, p = 0.034), MAGE (r = 0.533, p = 0.023), TAR (r = 0.595, p = 0.009), and TIR (r = − 0.599, p = 0.009). In the SUSTAIN 7 trial, 0.5 mg/week semaglutide therapy considerably reduced the mean blood glucose levels, postprandial hyperglycemia across all meals, and mean 7-point self-measured blood glucose levels compared with the 0.75 mg/week dulaglutide therapy [14]. Therefore, semaglutide therapy may improve glucose variability with greater efficiency than dulaglutide therapy by reducing postprandial hyperglycemia in patients with T2DM.

Overgaard et al. reported that 0.5 mg/week semaglutide therapy resulted in higher circulating concentrations of GLP-1 than 0.75 mg/week dulaglutide therapy [32]. GLP-1RAs may have direct beneficial effects on oxidative stress because the cAMP–PKA pathway evoked by GLP-1RAs inhibited the NAD(P)H oxidase–derived oxidative stress generation [33, 34]. Furthermore, in experimental animal models, higher circulating concentrations of GLP-1 demonstrated more favorable effects on atherosclerotic lesion progression by suppressing oxidative stress [35, 36]. Owing to its favorable pharmacokinetic profile, switching to semaglutide therapy may reduce oxidative stress more efficiently than continuous dulaglutide therapy. Moreover, it is conceivable that GLP-1RAs decreased oxidative stress by improving glucose metabolism parameters, including glucose variability. Indeed, improvements in glucose variability were reportedly correlated with reduction in oxidative stress in patients with T2DM [37]. In the present study, a decrease in the oxidative stress marker d-ROMs was correlated with improvement in SD, one of the markers of daily glucose variability. Therefore, switching to semaglutide therapy may decrease oxidative stress more effectively by improving glucose variability compared to continuous dulaglutide therapy.

GLP-1 slows down gastric emptying and suppresses appetite by promoting satiety and inhibiting hunger through the central nervous system, thereby leading to BW loss [38, 39]. In the SUSTAIN 7 trial, injectable semaglutide therapy reduced BW more in comparison with dulaglutide therapy [14]. However, in the present study we found that BW loss did not show significant differences between the semaglutide and dulaglutide therapy groups. The discrepant results on BW between the SUSTAIN 7 trial and the present study could be ascribed partially to the differences in the study design; the former compared the effects of semaglutide and dulaglutide therapies in patients with GLP-1 RA–naïve T2DM, whereas we compared the effects of switching to semaglutide therapy and continuous dulaglutide therapy. Lucas et al. reported that injectable semaglutide therapy resulted in greater BW loss in patients with GLP-1 RA–naïve T2DM than in those who had already been treated with other GLP-1RAs and then switched to injectable semaglutide therapy [40]. In addition, switching from dulaglutide therapy to injectable semaglutide therapy has a weaker BW-reducing effect than switching from other GLP-1RAs [41].

In terms of the DTSQ scores for “Convenience” and “Recommend,” continuous dulaglutide therapy was better compared to switching to injectable semaglutide therapy. Additionally, the total scores of DTSQ, which reflect treatment satisfaction, tended to be higher in the dulaglutide therapy group than in the semaglutide therapy group. We used 29G needles for drug delivery in the semaglutide and dulaglutide therapy groups. A single-dose pen-injector (SPI) for semaglutide therapy is approved and used for patients with T2DM in Japan, whereas a multidose pen-injector (MPI) is used in other countries [42]. The mean visual analog scale score for pain intensity at the injection site has been reported to be higher with the SPI than with the MPI [42]. Furthermore, Matza et al. reported that patients with T2DM preferred an injection device for dulaglutide therapy to an MPI device for semaglutide therapy; more participants perceived that the device for dulaglutide therapy was easier to use than the device for semaglutide therapy [43]. These points may explain why DTSQ scores for “Convenience” and “Recommend” were higher in patients with T2DM who continued dulaglutide therapy than in those who received semaglutide therapy in place of dulaglutide therapy.

This study has several limitations. First, the sample size was small and not based on a statistical power calculation. The sample size was determined by reviewing previous studies that had investigated the effects of incretin modulators, including GLP-1RAs, on glucose variability and oxidative stress [16, 29]. Therefore, this limitation may result in potential changes in clinical and biochemical parameters being undetected. Second, the study period was relatively short (24 weeks); hence, we did not know the long-term effects of injectable semaglutide and dulaglutide therapies on oxidative stress and glucose variability in patients with T2DM. Third, the process of switching from dulaglutide therapy to another GLP-1RA may have induced a positive psychological change that could cause higher DTSQ scores in the semaglutide group. Therefore, to address these potential problems, a longitudinal observation study is required to clarify whether there are clinical differences in oxidative stress and glucose variability between patients with T2DM receiving injectable semaglutide and dulaglutide therapies. Fourth, although we did not justify the intervention dosage in this study, the standard dosage of injectable semaglutide therapy in Japan is 0.5 mg/week, and a dulaglutide therapy dosage of 0.75 mg/week is the only approved dosage for treating patients with T2DM in Japan.

Conclusion

We found that compared with dulaglutide therapy, injectable semaglutide therapy could exhibit better efficacy in ameliorating oxidative stress and glucose metabolism, including daily glucose variability, in patients with T2DM, while dulaglutide therapy may be better in improving treatment satisfaction as evaluated via DTSQ scoring.