Interactions Between Leptin And Lipoprotein Lipase, Hepatic Lipase In Lipid Metabolism Disorders In Gestational Diabetes

Background and objective:Gestational Diabetes Mellitus (GDM) is the endocrine disease of abnormal glucosemetabolism which occurs in pregnancy and is one of the common complications ofpregnancy. The incidence of GDM has been increasing every year, it has an impact on theworld’s3-5%women during pregnancy, seriously endangers the health of mother and childand has become a hot issue of international concern.Leptin is an important factor that regulates energy and fat metabolism, and insulin is thekey substance of glucose and lipid metabolism. Several domestic and foreign studies haveshown that leptin and insulin exist bidirectional regulation. when gestational diabetes happens,the bidirectional regulation changed, result in hyperleptinemia and hyperinsulinemia. Highlevel of insulin cannot play a normal physiological function as usual, causing unbalancedtriglyceride (TG) synthesis and catabolism and thus elevated TG levels in serum of patientswith GDM. However, it cannot reasonably explain why TG level is still abnormal in pregnantwomen with GDM who get diet and insulin therapy and get well blood sugar controlled. Thissuggests some other reason may responsible for abnormal lipid metabolism.Lipoprotein lipase (LPL) and hepatic lipase (HL) is key enzymes regulating lipidmetabolism, they catalytic chylomicron (CM), very low density lipoprotein (VLDL) and highdensity lipoprotein (HDL) into TG, respectively. Studies have demonstrated that decrease ofLPL and HL levels or activity can reduce the ability of lipid metabolism, resulting in elevatedTG in blood and metabolic disorders. Now, the correlation between leptin and LPL、HL andwhether they play roles in lipid metabolism disorders occurrence and development in GDM,has not yet been elucidated in and abroad.This study aims to explore the correlationships between LPL, HL, lipid metabolismand leptin, and understand whether high concentrations of leptin improves TG metabolismdisorder by changing LPL, HL level or activity in GDM, hoping to have a further understanding in pathophysiological changes and new therapies of GDM.Methods:1. Cell experiments:Insulin resistance (Insulin Resistance, IR) liver cell model (LO2-I) was constructedby1×10-6mol/L insulin treating LO2cells for48hours. The cell model was identified byusing glucose oxidase-peroxidase method (GOD-POD). After the cell model was identifiedsuccessfully, the LO2and LO2-I cells were gathered. Then western blot and RT-PCR wereused to evaluate the relative expression of intracellular LPL, HL mRNA and protein, and oilred staining was used to observe intracellular fat content. The two kinds of cells weregrouped and treated with0,50,100or250μg/L leptin medium respectively for24hours.After culturing, the LPL, HL mRNA and protein’s relative expression and accumulation offat were detected by methods aforementioned. The LO2-I cells cultured by concentration of100μg/L leptin were divided into in three groups, with a group added culture mediumalone, a group added culture medium with100μg/L Leptin concentration only, and a groupadded culture medium containing100μg/L medium leptin concentration and2μmol/Lleptin antagonist (Leptin-A), and cultivated24hours respectively. Samingly, to understandthe effects of leptin to lipid metabolism of cultured hepatocytes in vitro, the LPL, HLmRNA and protein’s relative expression in three groups were detected by RT-PCR and WB,and the accumulation of body fat inside cells in three groups were observed by oil redstaining.2. Animal experiments:C57BL/KSJ (as group A) and heterozygous (Lepr db/+) female mice (as group B) wereboth raised with wild-type (Lepr+/+) male mice. Orbital blood was collected followed byserum isolation by centrifugation. The serum levels of leptin, insulin, LPL, HL and FFA weredetected in two groups before and during pregnancy using ELISA assay. The enzymeactivities of LPL and HL were evaluated by enzyme activity assay kit. In addition,5mg/kgper day of leptin was intravenously injected into the mice of both groups before and duringpregnancy for continuous three days, followed by serum collection on the next day after everyinjection. ELISA and enzyme activity assay kit was used to evaluate the LPL, HL level andactivity, to understand the influence of leptin on lipid metabolism of Lepr+/+mice and Leprdb/+mice. Results:1. Results of cell studies:①Glucose tolerance of LO2-I cells was much lower thanLO2cells, indicating the successfully formation of IR cell model.②The LPL, HL mRNAand protein’s relative expression were significantly lower in LO2-I cells than in the normalLO2cells, while the oil red staining was much higher in LO2-I cells.③The LPL, HLmRNA and protein’s relative expression all increased and the accumulation of fat decreasedto different extent in the LO2-I cells treated by different levels of leptin, especially in thecells treated by leptin at a concentration of100μg/L.④In cells treated by both leptin andleptin antagonist, the LPL, HL mRNA and protein’s relative expression and theaccumulation of fat showed no significant increase.2. Results of animal studies:①The serum leptin level in Lepr db/+mice (GDM mice)was obviously higher than Lepr+/+mice (normal mice) both before and during pregnancy.However, Lepr db/+mice presented GDM only during pregnancy, with conditions such ashyperinsulinism, reduced glucose tolerance, elevated TG, and significantly reduced LPL, HLenzyme activity.②After the injection of5mg/kg per day of leptin into the mice of bothgroups, we found that both LPL and HL enzyme activity increased. Before pregnancy, theenzyme activity of GDM mice showed no difference with the normal ones, while duringpregnancy, the incrcease of LPL and HL enzyme activity was not that high in GDM mice thanin normal mice (P＜0.01).Conclusions:1.In insulin resistant liver cells, the activity of LPL and HL is decreased, fatdecomposition is reduced, fat accumulation in cells.2. A certain concentration of leptin can increase the expression of LPL and HL ininsulin resistant liver cells, and reduce fat accumulation in cells.3. In pregnant GDM mice, the activity of LPL and HL is decreased, fat decompositionis reduced, and lipid metabolism disorder is caused.4. Leptin can increase the activity of LPL and HL of GDM mice, thus improve lipidmetabolism disorder and offer a new way for the treatment of GDM.