Possible Long-Term Efficacy of Sitagliptin, a Dipeptidyl Peptidase-4 Inhibitor, for Slowly Progressive Type 1 Diabetes (SPIDDM) in the Stage of Non-Insulin-Dependency: An Open-Label Randomized Controlled Pilot Trial (SPAN-S)

This study was conducted in accordance with the International Conference on Harmonization Guidelines for Good Clinical Practice and the Declaration of Helsinki. The Saitama Medical University Ethics Committee approved this study, and the protocol was approved by the institutional review boards of the collaborating hospitals or the directors of the clinics. All of the procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1964, as revised in 2013. Written informed consent was obtained from all patients for being included in the study.

This was an open-label, prospective, randomized, controlled trial (Fig. 1). The protocol of this trial and supporting CONSORT checklist are available as Protocol S1 (original language), S2 (English translation) and Checklist S1. Participants were recruited from 10 June 2010, and follow-up data were collected until 23 February 2017. Fourteen SPIDDM patients were enrolled, and 11 of them were followed for at least 12 months (Fig. 1b). The inclusion criteria were as follows: (1) diabetes diagnosis and HbA1c level between 6.9% and 8.4%, (2) GADAb-positive, (3) fasting serum C-peptide level ≥1.0 ng/ml, (4) age 20–79 years of age, (5) no treatment with oral glucose-lowering drugs except metformin within 2 months before enrollment and (6) no history of insulin or GLP-1 receptor antagonist treatment. The exclusion criteria were: (1) women who were pregnant or planning on becoming pregnant, (2) renal dysfunction with serum creatinine ≥1.5 mg/dl for males and ≥1.3 mg/dl for females, or creatinine clearance ≤50 ml/min, and (3) patients who were deemed unsuitable for participation by their attending physician because of associated disease, complications or any other reasons. All subjects included in the study were Japanese.

The eligible patients, who were recruited from the collaborating hospitals or clinics, were all randomly assigned using a centralized internet web system to receive either sitagliptin or pioglitazone based on minimization adjusting for age, sex, HbA1c level, GADAb titer and metformin use before entry. Because the inferiority of SU compared to insulin treatment had been revealed in the Tokyo study, pioglitazone, a thiazolidinedione (TZD) approved in Japan, was selected as the comparator. The efficacy of TZD on SPIDDM/LADA has been evaluated in several studies with conflicting results [23, 24]. In addition, from an ethical point of view, patients under treatment with metformin were allowed to be enrolled because a possible favorable effect of metformin on SPIDDM/LADA was suggested in our previous study [23].

Patients were scheduled for visits at 2-month intervals for at least 12 months of follow-up. The dosage for the sitagliptin group was started at 50 mg once per day and that for the pioglitazone group was 15 mg once per day; if metformin was used at enrollment, the dosage was not changed. The target for glycemic control was set at an HbA1c level <7.0%. If glycemic control was not achieved during each visit, the regimens were intensified by either (1) increasing the dosage of sitagliptin or pioglitazone to 100 or 30 mg, respectively, and/or (2) adding metformin at 250–2250 mg or increasing the dosage up to 2250 mg and/or adding an alpha-glucosidase inhibitor (acarbose, voglibose or miglitol). Notably, SU agents were never used. The patients in both groups were switched to an insulin injection regimen when the HbA1c levels became ≥9.4% despite the above protocol of medication.

The patients’ body weight, blood pressure, plasma glucose (PG) and HbA1c levels were measured every 2 months. All of the patients received an annual 75-g oral glucose tolerance test (OGTT) without receiving their morning dose of medication, and their islet antibodies (GADAb, IA-2Ab and IAA) were determined annually. The primary endpoints were the HbA1c values, the proportion of patients whose HbA1c values increased to ≥9.4%, and the period from enrollment in which their HbA1c values increased to ≥9.4%. The secondary endpoints included the sum of the serum C-peptide levels at 0, 30, 60, 90 and 120 min during the OGTT (∑C-peptide), body mass index (BMI) and islet autoantibodies.

GADAb, IA-2Ab and IAA levels were determined in this study via radioimmunoassay (RSR Ltd., Cardiff, UK). With regard to the thyroid autoantibodies (TAb), thyroid peroxidase autoantibodies (TPOAb) and thyroglobulin autoantibodies (TGAb) were determined by an electrochemiluminescence immunoassay (Roche Diagnostics GmbH, Mannheim, Germany). Regarding the present GADAb assay, 10 U/ml corresponded to 180 U/ml (WHO units), the cutoff value that predicted further progression of β-cell dysfunction in the Tokyo study [25].

Any adverse events associated with the medications used in this study were evaluated and treated properly by physicians. Hypoglycemia was defined as a blood glucose level <70 mg/dl (3.9 mmol/l), irrespective of hypoglycemic symptoms.

Based on our previous intervention trial (Tokyo Study) [15], in which 60 SPIDDM patients (30 each in the insulin and SU groups) were followed and the primary endpoint was the time at which the patient reached an insulin-dependent state (i.e., ∑C-peptide <4 ng/ml), and on the more preserved β-cell function in the inclusion criteria of this trial, which would show deleterious progression of the function more clearly, we anticipated that a total of 40 patients (20 each in the S and P groups) would be a sufficient population in our initial plan for the SPAN-S. Although the primary endpoint in the present study was defined by HbA1c values, worsening of HbA1c values was expected to correspond well to worsening of ∑C-peptide levels.

Continuous data at baseline (n = 11) were first checked for their normality by the D’Agostino and Pearson test, revealing that the age, GADAb titer and change ratio of the GADAb titer from baseline significantly deviated from a normal distribution. Thus, the Mann-Whitney U test and Wilcoxon signed rank test were applied to these data for comparisons between groups and comparison from the baseline within the same group, respectively. An unpaired t test and paired t-test were used for duration, BMI, HbA1c, ∑PG, ∑C-peptide and change ratio of ∑C-peptide from baseline, respectively. Categorical variables were compared using Fisher’s exact test. To evaluate the difference in the longitudinal ∑C-peptide data or their change ratios between the treatment groups, the interaction between time and treatment assignment at entry was examined using a repeated measures analysis of variance (ANOVA). The correlation between the change ratio of the GADAb titers and that of the ∑C-peptide values was assessed using a nonparametric Spearman’s correlation coefficient. Statistical significance was defined as p < 0.05. The GraphPad Prism software program ver. 6 (GraphPad Software, Inc., La Jolla, CA, USA) was used for these tests.

As shown in Fig. 1b, 14 patients were allocated: 7 were assigned sitagliptin (S group) and 7 pioglitazone (P group). Among them, six patients in the S group and five patients in the P group were followed for more than 1 year and analyzed.

The baseline characteristics of these 11 patients are shown in Table 1. There were no significant differences between the two groups in age, sex, duration, metformin use before entry, BMI, HbA1c levels, GADAb titers or positivity of other autoantibodies (IA2Ab, IAA and TAb).

Six and five patients in the S group were followed for 24 and 48 months, respectively, while five, four and two patients in the P group were followed for 12, 24 and 48 months, respectively (Table S1). The intensification of the regimens after entry is shown in Table S2. Briefly, the sitagliptin dosage was not increased in any patients, and the pioglitazone dosage was increased in three patients (cases P2, P4 and P5). Metformin was added to two patients (case S5 and P5) among those who had not been treated by metformin at entry (cases S5, P1 and P5), and an alpha-glucosidase inhibitor (voglibose) was added to one patient (case S4). The metformin dosage was changed in four patients (cases S2, S4, P3 and P4).

The BMI (or body weight) of the S group did not significantly differ from that at baseline; the BMI (or body weight) of the P group showed an increasing trend from the value at enrollment, but the change was not significant (Table S1). The blood pressure of both groups did not significantly differ from that at baseline (data not shown). The HbA1c levels were decreased in both groups, and significant reductions from baseline were observed at several points in the S group: at 12 months in the patients with both 24 and 48 months of follow-up (n = 6 and n = 5, respectively) and at 36 months in those with 48 months of follow-up (Table S1). The worst HbA1c levels in the S and P groups were 8.2% and 8.2%, respectively (Table S2). The values of BMI (or body weight), blood pressure and HbA1c did not significantly differ between the two groups during the study.

We compared our present data with those in the Tokyo Study as a historical control. In the Tokyo Study [15], the GADAb-positive non-insulin-requiring diabetic patients (SPIDDM), the same target subjects as in the present SPAN-S trial, were randomly assigned to receive either insulin (I group) or SU (SU group) and were followed up for a maximum of 60 months. The longitudinal changes in the ∑C-peptide values of the S and P groups were compared with those of the I and SU groups in the Tokyo Study. Of note, no significant differences were observed between the S or P group in the present study and the I or SU group in the Tokyo Study in the baseline characteristics of age, sex, duration, BMI, HbA1c levels, GADAb titers and ∑C-peptide values. Although the I group demonstrated better preservation of ∑C-peptide values than the SU group, as reported previously, the preservation of ∑C-peptide values in the S group in the present study appeared to be even better. As shown in Fig. 2a, a repeated-measures ANOVA revealed a significant interaction between time and treatment assignment (sitagliptin or insulin) as well as between time and treatment assignment (sitagliptin or SU) in the patients with 48 months of follow-up (p = 0.030 and p = 0.00004, respectively), indicating that treatment by sitagliptin significantly influenced the longitudinal changes of the C-peptide responses to the OGTT with a more increased direction than insulin and SU. Differences between the S group and the I and SU groups were further assessed based on the change ratios of the ∑C-peptide values from baseline (Fig. 2b). The significant superiority of treatment by sitagliptin to that by insulin or SU in the preservation of the ∑C-peptide values appeared to be more evident in the patients with 48 months of follow-up (p = 0.014 and p = 0.007, respectively), although the significant superiority of sitagliptin to insulin or SU was also observed in the patients with 24 and 36 months of follow-up (data not shown). As for the P group, no significant superiority of pioglitazone compared to insulin or SU was observed in a repeated-measures ANOVA (data not shown).

We were able to observe the clinical course for 48 months in 5 patients of the S group (cases S1, S2, S3, S4 and S5 in Table S2). Individual longitudinal change ratios of their ∑C-peptide values, GADAb and IA-2Ab titers from baseline are shown in Fig. S1. Among these patients, four were heterozygous for the susceptible and neutral HLA haplotypes (S/N), and the other one (case S1) was homozygous for the neutral haplotype (N/N) [26]. Regarding TAb (TPOAb or TGAb), two patients (cases S3 and S5) were positive for TPOAb. The ∑C-peptide values of all five patients were preserved during the 48 months of follow-up. Except for cases S2 and S5 whose ∑C-peptide values remained almost the same throughout the study (S2) or slightly decreased from 24 to 48 months (S5), the values of the other three patients showed a tendency to increase from 12 to 24 months and then decreased from 36 to 48 months (Fig. S1). In comparison to cases S2, S3 and S5, who all had GADAb >10 U/ml and two of whom (S2 and S3) were IA2Ab-positive, the ∑C-peptide values of cases S1 and S4, who both showed GADAb <10 U/ml and were IA2Ab-negative, were increased to a greater degree from baseline, even at 48 months from entry. The relative increase from baseline was highest in case S1, who carried the HLA N/N genotype as well as both GADAb <10 U/ml and IA2Ab-negative status.

The titers of GADAb were not significantly different between the S and P groups at any time point in the present study (Table S1). However, as shown in Fig. 3, the change ratios of the GADAb titers from baseline were significantly inversely correlated with the change ratios of the ∑C-peptide values from baseline in the S group by a nonparametric analysis (Spearman’s rank correlation coefficient = −0.600, p = 0.003). In particular, when the change ratios of the GADAb titers from baseline were negative, those of the ∑C-peptide values were mostly positive, i.e., when the GADAb titers decreased from baseline, the ∑C-peptide values frequently increased. In contrast, when the change ratios of the GADAb titers from baseline were positive, those of the ∑C-peptide values tended to show values around zero (Fig. 3). In the P group, a nonsignificant inverse correlation was observed (Spearman’s rank correlation coefficient = −0.478, p = 0.101; Fig. S2).

No drug-related adverse events, including hypoglycemia, were observed.