2.3. Measurements
INSULIN RESISTANCE
The BMI was calculated by dividing the subject’s weight (kg) by their height squared (mHbA1c levels were measured at SNUBH, a National Glycohemoglobin Standardization Program Level II-certified laboratory, using the Bio-Rad Variant II Turbo Hemoglobin Testing System (Bio-Rad Laboratories, Hercules, CA, USA) on a high-performance liquid chromatography analyzer. Fasting plasma and postprandial 2 h glucose concentrations (FPG and PP2, respectively) were analyzed using the hexokinase method. Fasting plasma insulin levels were measured by radioimmunoassay (Linco, St. Louis, MO, USA). The plasma concentration of C-peptide was measured by radioimmunoassay (Izotop, HoilBioMed, Seoul, Republic of Korea). Triglyceride levels were measured using the glycerol-3-phosphate oxidase peroxide method, and high-density lipoprotein and low-density lipoprotein cholesterol levels were measured by relevant enzymatic assays. Aspartate and alanine aminotransferase (AST and ALT, respectively) levels were measured using the reduced nicotinamide adenine dinucleotide ultraviolet method, and serum creatinine (Cr) was measured by Jaffe’s kinetic method using a Hitachi 747 chemistry analyzer (Hitachi, Tokyo, Japan).All subjects underwent a standardized 75 g oral glucose tolerance test (OGTT) with overnight fasting for 10 h at the baseline and after 6 months. The levels of plasma glucose, insulin, and C-peptide were measured at the baseline and at 30 min, 60 min, and 2 h after the OGTT. The area under the OGTT curve of glucose concentration (AUCglucose) was derived using trapezoidal integration. The homeostasis models of assessment of insulin resistance (HOMA-IR) and pancreatic β-cell function (HOMA-β) were calculated as: (glucose (mg/dL)) × insulin (mg/dL)/405) and (360 × insulin (μIU/mL))/(glucose (mg/dL) − 63), respectively.Serum high-sensitivity C-reactive protein (hsCRP) was measured using a high-sensitivity automated immunoturbidimetric method (Roche, Basel, Switzerland). Plasminogen activator inhibitor-1 (PAI-1) level was measured using an ELISA kit (RayBiotech, Peachtree Corners, GA, USA).Amino acid levels were calculated using the Cliquid Software (SCIEX, Framingham, MA, USA) from the plasma peak area ratio analyzed by liquid chromatography–tandem mass spectrometry using the aTRAQ reagent (SCIEX, Framingham, MA, USA) with internal standards. Branched-chain amino acids (BCAAs) were defined as the sum of leucine, isoleucine, and valine, whereas aromatic amino acids (AAAs) were defined as the sum of phenylalanine, tryptophan, and tyrosine.While the subjects were in a fasting state, body composition was assessed using multifrequency bioelectrical impedance analytical machines (Inbody720, InBody, Seoul, Republic of Korea), followed by validation by dual-energy X-ray absorptiometry or computed tomography [