Volunteers with normal glucose tolerance.

type 2 diabetic patients without microvascular (retinopathy, nephropathy or neuropathy) or macrovascular (coronary, cerebrovascular or lower extremity arterial disease) complications.

type 2 diabetic patients with lower extremity artery disease diagnosed through the measurement of ABI (the ratio of ankle-to-brachial systolic blood pressure).

Metabolomics is a rapidly evolving high-throughput technology that allows the measurement of the entire complement of metabolites generated by biochemical reactions under certain conditions in biological fluids or tissues. This technology has been used extensively to identify biomarkers in various cancers, nervous system diseases, cardiovascular diseases, pituitary diseases, and other diseases. The identification of biomarkers can be clinically useful for a more accurate diagnosis, prognosis, and treatment choice as well as disease monitoring. Among mass spectrometry (MS) methods, liquid chromatography-mass spectrometry (LC-MS) has been recognized as a robust metabolomics tool and has been widely applied in metabolite identification and quantification due to its high sensitivity, peak resolution, and repro- ducibility.

LC-MS analysis will be performed using a Q ExactiveTM HF-X liqiud chromatograph system coupled with a Thermo ScientificTM OrbitrapTM mass spectrometer according to a previously published procedure to detect the peak, identify the metabolites and perform the PCA and OPLS-DA analyses to better visualize the subtle similarities and differences among the complex datasets.

Screening for potential biomarkers will be performed according to the VIP value (VIP > 1.0) and significance test (P < 0.05) from the OPLS-DA model.