| Obesity can bring about many metabolic disorders, such as hyperlipidemia, hyperinsulinemia and abnormal glucose tolerance. So it becomes a main risk factor of hypertension, type 2 diabetes, cardiovascular disease and stroke. At present, the prevalence of obesity is increasing, which is a serious disease threatening human health. Leptin resistance is the main pathological mechanism in the occurrence and development of obesity, and it has increasingly been attracting peoples’ attention. Therefore, it is necessary to explore the mechanisms of leptin resistance, and how to eliminate leptin resistance of obesity has attracts many countries’attentions.Lithocarpus polystachyus Rehd (ST) is derived from the leaflets of Lithocarpus polystachyus Rehd of Quercus L. It is a Traditional Chinese Herb, which has been widely used in South China. It contains substantial flavonoids and polyphenolic compounds. It can be used for treatment of diseases, such as syndrome of dampness-heat of dysentery, pruritus cutanea, swelling and malignant sore. Besides, it has special effects on diabetes, hypertension, hyperlipidemia and coronary heart disease. Phloridzin is a kind of flavonoids, which is extracted from ST. It is also the active ingredient of ST. Our previous studies also showed that they can reduce the levels of blood glucose, lipids, leptin and insulin, so we speculated that they may also be effective for treatment of diet-induced-obesity rats with leptin resistance. So far, there were no related literatures about the effect of ST and phloridzin on obesity or leptin resistance at home and abroad. Therefore, the aim of this study is to verify the efficacy of ST and phloridzin to losing weight, then observe their intervention and molecular biological mechanisms on obese rats with leptin resistance, so as to lay a reliable basis for their clinical applications in preventing and curing obesity and its complications.1. ObjectiveTo establish obesity rat model with leptin resistance by feeding on high fat and sugar diet, then treating the rats with Lithocarpus polystachyus Rehd and phloridzin, and with sibutramine hydrochloride as a positive control medicine. In the meantime, observe the effects of ST and phloridzin on rats’weight, food-intake, blood glucose, lipids, leptin, insulin resistance, adipocytokines, and oxidative stress, as well as UCP2, C/EBP-α, PPARγ, OB-Rb and PTP1B mRNA expressions in white adipose tissue, to explore the improvement and mechanisms of ST and phloridzin on obese rats with leptin resistance. Then select STAT3 and p38MAPK pathways as our two primary research objectives, to observe the effects of Lithocarpus polystachyus Rehd and phloridzin on the expression of STAT3 and p38MAPK protein and their phosphorylations, to explore the signal transduction mechanisms of ST and phloridzin on obese rats with leptin resistance. 2. MethodsMale SPF Sprague-Dawley rats, weighed 80-120g, were randomly chosen 8 as normal control group, which were fed with normal standard diet, the rest were fed with high fat and sugar diet. After 14 weeks, selected the obese rats, then divided into obese model group, sibutramine hydrochloride (3mg/kg) group, high, middle and low dose (300,150,75mg/kg) of ST groups, high and low dose (80,40mg/kg) of phloridzin groups in line with their average weights. All rats were treated for 8 weeks. Their body weights and food intake were recorded once a week. At the end of week 8, the rats were fasted for 12 hours, blood glucose was measured by tail clip. The serum TG, TC, HDL-C and LDL-C levels were measured by automatic biochemical analyzer; the SOD activity and MDA content were measured by UV spectrophotometer; FFA, leptin, insulin, adiponectin, resistin, CRP and NPY by ELISA Reader. After animals’execution, abdominal white adipose tissue was collected and weighed, then the visceral fat mass and its index were calculated. The expression of UCP2, C/EBP-α, PPARγ, OB-Rb and PTP1B mRNA in adipose tissue were measured by real time RT-PCR. STAT3, p38MAPK protein and their phosphorylations levels were measured by western blotting.3. Results(1) The effects of ST and Phloridzin on leptin resistance in obese ratsST and phloridzin can reduce the body weights, serum TG, TC and leptin levels in obese rats; ST can also reduce blood glucose and LDL-C, improve HDL-C levels; phloridzin can reduce visceral fat mass and its index, food intake, as well as serum NPY levels.(2) The effects of ST and Phloridzin on insulin resistance, adipocytokines, and oxidative stress in obese ratsST and phloridzin can reduce serum insulin levels and HOMA-IR, as well as serum resistin, CRP and FFA levels, improve adiponectin levels. Besides, they can improve SOD activity, reduce MDA content.(3) The effects of ST and Phloridzin on UCP2, C/EBP-α, PPARγmRNA expression in adipose tissue of obese ratsST and phloridzin can reduce PPARy mRNA expression; phloridzin can also up-regulate UCP2 mRNA expression, and ST can reduce C/EBP-amRNA expression.(4) The effects of ST and Phloridzin on OB-Rb and PTP1B mRNA expression in adipose tissue of obese ratsST and phloridzin can up-regulate OB-Rb mRNA expression, ST can also up-regulate PTP1B mRNA expression.(5) The effects of ST and Phloridzin on STAT3 and p38 MAPK signaling pathways in adipose tissue of obese ratsST and phloridzin can up-regulate p-STAT3 and p-p38 MAPK protein levels, but didn’t affect STAT3 and p38 MAPK protein levels.4. ConclusionST and phloridzin can effectively reduce body weights, redress disturbance of glucose and lipid metabolism, improve leptin and insulin resistance, alleviate chronic inflammation, reduce dangerous factors of obesity, increase the capability of oxidation and stress resistance, accelerate energy metabolism, restrain transcription activity of adipogenesis genes, suppress adipogenesis and apoptosis of adipocyte, up-regulate OB-Rb expression, improve leptin sensitivity, activate STAT3 and p38MAPK pathways in adipose tissue, and eventually ameliorate leptin resistance in obese rats. |
