Abstract: Objective To explore the expression and significance of peripheral blood omentin-1 (Omentin-1) level, lipid metabolism and oxidative stress in peripheral blood of diabetic patients with different bone density levels. 
Methods A total of 120 patients with type 2 diabetes mellitus (T2DM) admitted were retrospectively included. According to the level of bone mineral density, they were divided into normal bone mass group (n=38), osteopenia group (n=45), and osteoporosis group (n=37), and another 80 physical examinees with normal bone mass during the same period were selected as the control group. The peripheral blood Omentin-1 levels and lipid metabolism indexes ［total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C)］ and oxidative stress indicators ［superoxide dismutase (SOD), malondialdehyde (MDA), glutathione catalase (GSH-Px)］ levels were measured respectively. Pearson correlation was used to analyze the correlation of Omentin-1, lipid metabolism, and expression of oxidative stress indicators in T2DM patients. Ordered multi-class Logistic regression was used to analyze the influencing factors of bone metabolism in T2DM patients. 
Results Pearson correlation analysis showed that peripheral blood Omentin-1 levels in T2DM patients were significantly and negatively correlated with TC, TG, LDL-C, and MDA (r=-0.407, -0.437, -0.440, -0.460, P＜0.01), while peripheral blood Omentin-1 levels in T2DM patients were significantly and positively correlated with HDL-C, SOD, and GSH-Px (r=0.602, 0.578, 0.650, P＜0.01). There was no difference in gender, age, BMI, WHR, FBG, TC, TG, HDL-C and LDL-C levels in different bone density subgroups of T2DM patients (P＞0.05). The course of disease, HOMA-IR and MDA levels in osteoporosis group and osteopenia group were significantly higher than those in normal bone mass group, and higher in osteoporosis group than in the osteopenia group (P＜0.05). SOD, GSH-Px, and Omentin-1 levels in osteoporosis group and osteopenia group were significantly lower than those in normal bone mass group, and lower in osteoporosis group than in osteopenia group (P＜0.05). The glycated hemoglobin （HbA1c） levels in osteoporosis and osteopenia groups were significantly higher than those in normal bone mass group (P＜0.05), but there was no difference between osteoporosis group and osteopenia group (P＞0.05). The FINS level of osteoporosis group was significantly higher than that of the normal bone group (P＜0.05), but was not significantly different from that in osteopenia group (P＞0.05). Ordered multi-class Logistic regression analysis showed that the course of disease and HOMA-IR were independent risk factors affecting the bone metabolism status of T2DM patients (P＜0.05), while GSH-Px and Omentin-1 were independent protective factors affecting the bone metabolism status of T2DM patients (P＜0.05); However, HbA1c, FINS, SOD, and MDA were not related to the bone metabolism status of patients with T2DM (P＞0.05). 
Conclusion The level of Omentin-1 in peripheral blood of T2DM patients decreases with the decrease of bone density, and is related to abnormal lipid metabolism and oxidative stress. It may play a key role in the progression of T2DM and abnormal bone metabolism. Therefore, increasing the level of Omentin-1 may be one of the approaches to prevention and treatment of diabetic osteoporosis.

Key words: diabetes mellitus, bone density, lipid metabolism