The purpose of this study is to evaluate the safety, tolerability, and PK of single oral doses of JTT-252 and the effect of food on the PK of JTT-252 in healthy subjects, and to evaluate the safety, tolerability, PK and PD of single oral doses of JTT-252 in type 2 diabetes mellitus subjects.

Inclusion Criteria:

Healthy Subject Cohorts:

• Healthy male or female subjects
• Age 18 to 50 Years (inclusive)
• Body Mass Index (BMI) between 19.0 and 31.0 kg/m2 (inclusive)

Type 2 Diabetic Subject Cohorts:

• Male or female Type 2 diabetic subjects who are currently being treated with a stable dose of metformin
• Age 18 to 65 Years (inclusive)
• BMI between 25.0 and 40.0 kg/m2 (inclusive)
• Have a glycosylated hemoglobin (HbA1c) of >7.0% to ≤9.5%
• Have a fasting plasma glucose (FPG) <240 mg/dL

Exclusion Criteria:

Healthy Subject Cohorts:

• Known clinically relevant history or presence of significant respiratory, gastrointestinal, renal, hepatic, hematological, lymphatic, neurological, cardiovascular, psychiatric, musculoskeletal, genitourinary, immunological, metabolic and dermatological or connective tissue disease
• Subjects with a systolic blood pressure >140 mmHg and/or diastolic blood pressure >90 mmHg

Type 2 Diabetic Subject Cohorts:

• Subjects with a known medical history or presence of type 1 diabetes mellitus
• Subjects with known medical history of acute metabolic diabetic complications
• Subjects with uncontrolled hypertension (systolic blood pressure >150 mmHg and/or diastolic blood pressure >95 mmHg