The purpose of this study is to evaluate the safety, tolerability, and PK (Pharmacokinetics) of single oral doses of JTT-251 in healthy and type 2 diabetes mellitus subjects and to evaluate the effect of food on the PK of JTT-251 in healthy subjects.

Inclusion Criteria:

Healthy Subject Cohorts:

• Healthy male or female subjects
• 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 diagnosed for at least 3 months
• BMI between 25 and 40 kg/m2 (inclusive)
• Have a glycosylated hemoglobin (HbA1c) of >6.5% to ≤10.9% (inclusive) if treatment naïve with respect to hypoglycemic agents OR >6.5% to ≤10.0% (inclusive) if treated with metformin

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 >150 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 >160 mmHg and/or diastolic blood pressure >95 mmHg with documented ongoing treatment)