One hundred and fifty normal patients, 150 patients with T2DM and 150 patients with T2DM + CHD were selected from Xi'an No. 5 Hospital (Xi'an, China). General data of the three groups of patients are given in Table I.

Inclusion criteria: Patients with T2DM: Diagnostic criteria for diabetes established by WHO in 1999 was taken as the reference of diagnosis; patients with T2DM + CHD: Patients that had diabetes mellitus complicated with CHD and the diagnostic criteria established by International Heart Association and WHO in 1979 were taken for the determination of CHD; normal group: Patients that were free from diabetes mellitus and CHD.

Exclusion criteria: i) Patients with type 1 diabetes mellitus or diabetes mellitus with complications; patients with resistant or primary hypertension or patients with hypertension with left ventricle hypertrophy; patients with peripheral vascular diseases; patients who were taking glucose-reducing, lipid-decreasing and antihypertensive drugs or using insulin for treatment. ii) Patients with hyperglycemia caused by other reasons or patients with acute or chronic inflammatory disease; patients with severe chronic complications such as heart failure and left ventricular ejection fraction <50%; patients who suffered from cerebrovascular accident. iii) Patients with endocrine diseases such as hyperthyroidism and gout; pregnant women; patients with autoimmune diseases; patients with family histories of infectious diseases and hereditary diseases. All the patients or their families signed the informed consent form and this study was approved by the Ethics Committee of Xi'an No. 5 Hospital.

The venous blood specimens were taken from the patients on an empty stomach in the morning. Sex, age, fasting plasma glucose (FPG), waist-to-hip ratio (WHR), body mass index (BMI), blood lipid, systolic blood pressure (SBP) and diastolic blood pressure (DBP), of all the subjects were measured or collected, in which, BMI = body mass (kg)/height (m²). Plasma glucose was measured by glucose oxidase method with Roche glucometer; blood lipid was measured by enzymatic method. The reagent was provided by Zhejiang Dongou Biochemical Co., Ltd., (Zhejiang, China) and the instrument used was 7170S fully-automatic biochemical analyzer provided by Hitachi, Ltd. (Tokyo, Japan); hemoglobin A1c (HbA1c) was measured by high-performance liquid chromatography (the kit was provided by Bio-Rad Laboratories, Inc., Hercules, CA, USA); fasting insulin (FINS) was measured by chemoluminescence immunoassay (the kit was provided by China Institute of Atomic Energy, Beijing, China and the instrument used was Abbotti 1000SR fully-automatic chemiluminescence analyzer provided by Abbott Pharmaceutical Co. Ltd., Lake Bluff, IL, USA); plasma leptin levels were determined by double-antibody sandwich method (plasma leptin kits were provided by Shenzhen Yinuojin Biotechnology Co., Ltd., and microplate reader was provided by Bio-Rad Laboratories, Inc.); high-sensitivity C-reactive protein (hs-CRP) was detected by turbidimetry (the kit was provided by DADE Corporation and the instrument used was BN ProSpec, a special Pr analyzer); von Willebrand factor (vWF), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were detected by double-antibody sandwich enzyme-linked immunosorbent assay. Endothelin (ET-1) kits were purchased from Nanjing Jiancheng Bioengineering Institute (Nanjing, China) and other kits were provided by Beijing United Bowei Biotechnology Co., Ltd., (Beijing, China). Homeostasis model assessment-insulin resistance (HOMA-IR) = FINS/22.5 (6) and insulin resistance index (IRI) = FPG (mmol/l)xFINS (mU/l)/22.5^[2] were used to evaluate IR.

All the data were processed using Statistical Product and Service Solutions (SPSS) version 22.0 (IBM Corp., Armonk, NY, USA) and the data that were in line with normal distribution are expressed as mean ± SD. The t-test was conducted for comparison between groups and the non-normally-distributed measurement data were expressed as median (interquartile range). Non-parametric rank sum test was conducted for the comparison between groups. The χ² test was adopted for comparison of rate, and variance analysis was used for comparison of the mean among multiple groups. One-way analysis of variance was used for comparison between two groups and the post-hoc test used was Tukey test. P<0.05 was considered to indicate a statistically significant difference. Pearson's correlation test was used for the analysis on the correlation of IR and leptin with inflammatory factors and vascular endothelial injury.

General data such as constituent ratio of age and sex had no statistical significance (P>0.05), and they were comparable. The differences of the comparison between the T2DM group (patients with T2DM) and the normal group in terms of biochemical indexes including FPG, DBP, FINS, HbA1c, HOMA-IR, low-density lipoprotein cholesterol (LDL-C), ET-1, TNF-α, IL-6 and vWF had statistical significance (P<0.05). The differences of the comparison between the T2DM and the normal groups and that between the T2DM+CHD and the T2DM groups in terms of BMI, FPG, SBP, DBP, HbA1c, HOMA-IR, high-density lipoprotein cholesterol (HDL-C), hs-CRP, leptin, ET-1, TNF-α, IL-6 and vWF had statistical significance (P<0.05). The difference of the comparison of WHR and FINS between the group of T2DM + CHD and the normal groups and that between the T2DM and the normal groups had statistical significance (P<0.05), while the difference of the comparison between the T2DM+CHD and the T2DM groups had no statistical significance (P>0.05). The differences of the comparison among the groups in terms of the remaining biochemical indexes had no statistical significance (P>0.05). Specific details are given in Table I.

Pearson correlation analysis of IRI with IL-6, TNF-α, hs-CRP and vascular endothelial function: IRI was positively correlated with IL-6, TNF-α and hs-CRP, and it had no direct correlation with vascular endothelial function (Table II).

Pearson correlation analysis of leptin with hs-CRP, IL-6, TNF-α and vascular endothelial function: Leptin revealed a positive correlation with hs-CRP, IL-6 and TNF-α, but was negatively correlated with vascular endothelial function (Table III).