Methods
Study Populations
We conducted a randomized prospective multicenter study in patients with type 2 diabetes who did not achieve the treatment goal with diet, exercise, sulfonylurea, metformin or pioglitazone treatment. We recruited 66 patients (men and women) who were from 20 to 85 years of age. Thirty-one patients received the sitagliptin (50 mg/day) treatment and 35 patients, the voglibose (0.6 mg/day) treatment. The doses of the two drugs used in this study are recommended therapeutic doses for Japanese and the doses are covered by the Japanese National Health Insurance. The exclusion criteria were as follows: treatment with insulin, alpha GI or glinide, type 1 diabetes, HbA1c ≥ 9.0%, systolic blood pressure ≥ 160 mmHg and serum creatinine ≥ 1.5 mg/dL at baseline. The study protocol was approved by the Ethics Committee of Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, and written informed consent was obtained from all patients before any study procedure was undertaken.
Study Protocol
The patients were followed for at least 8 weeks to confirm that they did not achieve the treatment goal with diet, exercise, sulfonylurea, metformin or pioglitazone treatment. The patients were prospectively randomly assigned to additional treatment with either sitagliptin (50 mg/day) or voglibose (0.6 mg/day) for 12 weeks (Figure 1). The flow-mediated dilatation (FMD) of the brachial artery was measured in the fasting state at baseline and after 12 weeks of the treatment. Blood and urine tests were also performed at baseline and at the end of the study. The patients' antihypertensive, antihyperlipidemic and antidiabetic drugs were not changed and anti-oxidant drugs, including vitamin C and E, were not added throughout the study period.
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Figure 1.
Study protocol. The patients were followed for at least 8 weeks to confirm that they did not achieve the treatment goal. The patients were prospectively, randomly assigned to additional treatment with either sitagliptin (50 mg/day) or voglibose (0.6 mg/day) for 12 weeks. Measurements of flow-mediated dilatation (FMD) of the brachial artery and blood and urine tests were performed in the fasting state at baseline and after 12 weeks of treatment.
Measurements of Biochemical Parameters
The following parameters were measured at baseline and after 12 weeks of treatment: complete blood count, liver function test including measurement of AST, ALT and LDH, renal function test including measurement of BUN, creatinine, Na, K and Cl, HbA1c, gastric inhibitory peptide (GIP), GLP-1, C-peptide, CD34, lipid profile including total cholesterol, triglyceride, and high-density lipoprotein (HDL-C), adiponectin, oxidative stress markers including MDA-LDL and urine 8-OHdG, inflammatory markers including hs-CRP and PTX-3, and estimated glomerular filtration rate (eGFR). HbA1c levels were measured using high-performance liquid chromatography. The number of CD34+ cells was determined by flow cytometry using FITC-labeled CD45 and phycoerythrin (PE)-labeled CD34 antibodies (BD Biosciences). eGFR (mL/min/1.73 m) was determined by the modified Modification of Diet and Renal Disease study formula (MDRD) for Japanese: eGFR = 194 × (age) × (serum creatinine) × (0.739 if female). These measurements were performed by SRL Company, Ltd. (Tokyo, Japan).
Flow-mediated Dilation (FMD)
Endothelium-dependent dilation was assessed as a parameter of vasodilation according to the guidelines for ultrasound assessment of FMD of the brachial artery in the fasting state. Using a 10-MHz linear-array transducer probe (Unex Company Ltd., Nagoya, Japan), longitudinal images of the brachial artery at baseline were recorded with a stereotactic arm, and measurements of the artery diameter were made after supine rest for ≥5 min as previously described. The diameter of the artery was measured from clear anterior (media-adventitia) and posterior (intima-media) interfaces, which were manually determined. Then, suprasystolic compression (50 mmHg higher than systolic blood pressure) was performed at the right forearm for 5 min, and measurements of the artery diameter were made continuously from 30 sec before to ≥2 min after cuff release. Maximum vasodilation was then evaluated from the change in artery diameter after the release of occlusion (%FMD). FMD is known to be affected by a wide range of biological, environmental, and methodological factors. To quantify inter- and intra-observer reproducibility, baseline brachial diameter and FMD were measured by three individuals in Okayama University Hospital. Inter- and intra-observer coefficients were high (r > 0.90).
Statistical Analysis
The results are expressed as mean ± SD. We assumed that FMD increased by 2% in sitagliptin group and decreased by 0.5% in voglibose group with a standard deviation of 3%. A minimum sample size of 24 participants in each group was required to detect statistical differences in FMD with a power of 80% and α error of 5%. The effects of sitagliptin and voglibose on FMD were assessed by ANCOVA after adjustment for the baseline FMD, age, sex, current smoking, diabetes duration and body mass index (BMI). Differences in age, sex, BMI and abdominal girth were compared using Student's t-test. The duration of diabetes was compared using the Wilcoxon rank sum test and categorical variables, using Fisher's exact test. Differences in secondary efficacy measures between baseline and 12 weeks were compared using the paired Student's t-test. Values of P < 0.05 were considered to be statistically significant.