Participants
A total of 28 Chinese subjects were recruited in this study. After excluding 5 subjects with IGT and 4 subjects with DM based on the WHO 1997 criteria[16]. There were 19 participants with NGT and normal fasting blood glucose (8 males and 11 females) were included in the study.
This study was approved by the Peking Union Medical College Hospital (PUMCH) Ethics Committee and followed the ethical standards of the responsible committee on human experimentation (institution and national) and with the Helsinki Declaration of 1964, as revised in 2013. All participants signed written informed consent.
Anthropometric measurements
Anthropometric measurements were collected by well-trained examiners at study entry, including age, weight, height, waist circumference, thigh circumference and blood pressure. Blood pressure was measured three times after five minutes' rest and was recorded as the mean value of three times measurements. Body mass index (BMI) was calculated as weight (kg) divided by the square of the height in meters (m2). Chinese visceral adiposity index (CAVI) was calculated according to the formula in previous article[17] to evaluate visceral fat distribution.
General laboratory measurements
General laboratory measurements were collected after fasting for 8 to 12 hours, including common blood counts, fasting blood glucose, SUA, blood urea nitrogen, serum creatinine (Cr), total serum cholesterol (TC), high- and low-density lipoprotein cholesterols (HDL-c and LDL-c), triglyceride (TG) and glycosylated hemoglobin A1c (HbA1c). Blood samples were collected in 3-hour OGTT from forearms to assay serum glucose, insulin and C-peptide at fasting (0-minute), 30-minute, 60-minute, 120-minute and 180-minute after 75g anhydrous glucose load by oral. Those data were measured by Beckman automatic biochemical analyzer AU5800.
QUICKI[8], ISIMatsuda[10], IAI, AUCGlu/AUCIns[12] and HOMA-IR[11] were calculated as simple indices to evaluate insulin resistance.
Hyperinsulinemic euglycemic clamp technique
Three days before the test, the subject was asked to take a normal calorie balanced diet (1806kcal/day, carbohydrate accounted for 55%, protein accounted for 15% and fat accounted for 30% of the total calories). The day before the clamp test, the subject should avoid severe activities after dinner, not drink alcohol and take drugs, and start fasting at 20:00pm. At 8:00am on the day of the clamp test, the subject took a supine position with one cubital vein set with a double channel trocar, one channel was connected with an injection pump, insulin was continuously infused at the speed of 40 mIU · m-2 · min-1 to obtain a certain concentration of serum insulin platform and to inhibit the output of hepatic glucose and gluconeogenesis; the other channel was connected with a three-way pipe. Among them, two infusion pumps were connected at each end with one pump was used to infuse 20% glucose injection intravenously, the other was infused with potassium chloride (1.5g) plus saline (0.9% 500ml) at a constant rate. A trocar was placed in the vein of the forearm on the opposite side of the infusion side and sealed with heparin for blood sampling. The arm for collecting blood samples was placed in a constant temperature device to maintain the temperature around 55 ° C, so as to achieve the arterialization of venous blood.
Fasting blood glucose was set as the target normal blood glucose level (5±0.5mmol/ L). During the clamp test, the arterialized venous blood was measured every 5 minutes, and the glucose infusion rate was adjusted according to the equation described by Defronzoto to maintain the blood glucose in a satisfactory range, that was target blood glucose value±10%, so as to inhibit the secretion of endogenous insulin.
The classical Defronzo equation: Si = [(Gd-Gi) × 10 × (0.25 × body weight) × PF] / (glucose concentration × 15) + [SMi-2 -(Gd / Gi)] × FMi-l (SMi = SMi-2 × FMi× FMi -2, FMi= (Gd / Gi). (Si is the drop rate of glucose to be adjusted at any time; Gd is the target blood glucose level; PF is the adjustment coefficient of different infusion pumps.)
The blood samples were taken every 20 minutes in 2 hours for the measurements of serum insulin and C-peptide, all those blood samples were sent to the laboratory on the same day. ADVIA Centaur XP immunoassay system was used to analyze insulin and C peptide concentrations. The unit of glucose disposal rate value (M value) was mg·kg-1· min -1, the calculation formula was the glucose infusion per kilogram of body weight per minute in the last 40 minutes of clamp test + (G80-G120) ×0.0625 (where G80 and G120 were the blood glucose values at the time of 80 and 120 minutes respectively, the unit is g/L).
Standardized questionnaire
Detailed in-person interviews were administered using a standardized questionnaire to collect information on demographic characteristics, past medical history, family history, alcohol intake, smoking and exercise habits. Drinking habits were classified as never drinking and currently drinking. Smoking habits were classified as never, former or currently smoking. Regular exercise was evaluated as any kind of physical activity except for walking for work or daily life performed at least 30 minutes for no less than 3 days per week.
Statistical Analysis
Continuous variables were expressed as mean ± standard deviation and percentages were as categorical variables. Differences between continuous variables were analyzed by the ANCOVA analysis, and the variables that failed the normality test were logarithmically transformed before analysis. Differences between categorical variables were analyzed by the chi-square test. Pearson linear regression analysis was performed to evaluate correlations between SUA and other clinical parameters. A stepwise multiple linear regression analysis was carried out to evaluate the independent associations of variables and SUA. P-value less than 0.05 was considered significant. All statistical analyses were carried out using the statistical program SPSS (version 25, SPSS, Chicago, IL).