Effects Of Pregnancy And Gestational Fructose Diet On Hepatic Lipid Metabolism In Mice

Objective To investigate the features of hepatic lipid metabolism in late pregnant mice and the effects of gestational high fructose diet on them. To further explore the effects of pregnancy on the expression of genes and nuclear involved with fatty acid synthesis,uptake and oxidation.Methods Experiment 1: To investigate the changes of hepatic lipid metabolism in late pregnant mice, the mice were divided into two groups: pregnant mice and virgin mice. Mice had free access to the food. The mice were sacrificed after 9 hours fasting at gestation day 17. Fasting blood-glucose, serum and hepatic triglyceride(TG), cholesterol(TCH), very low density lipoprotein(VLDL) are tested. Liver lipid is measured by oil red O staining. Liver tissue was collected for histological examination. To further explore the effects of pregnancy on the expression of genes and nuclear involved with fatty acid synthesis,uptake and oxidation, q PCR and Western bloting were used to measure the m RNA level of related genes and nucleoprotein level of related nuclear receptors. Experiment 2: To investigate the effects of gestational high fructose diet on hepatic lipid metabolism in late pregnant mice, the mice were divided into two groups: FP group and CP group. The FP group were given double distilled water containing 30% fructose and the CP group were given plain tap water since gestation day 3. The mice were sacrificed at gestation day18. Fasting blood-glucose, serum triglyceride(TG), cholesterol(TCH),and hepatic serum triglyceride(TG), cholesterol(TCH), high density lipoprotein(HDL), very low density lipoprotein(VLDL) are tested. Liver lipid is measured by oil red O staining. To further explore the effects of high fructose diet on the expression of genes and nuclear involved with fatty acid synthesis,uptake and oxidation, q PCR and Westernbloting were used to measure the m RNA level of related genes and nucleoprotein level of related nuclear receptors.Results Experiment 1: The serum TG and VLDL level of the pregnant mice was 2.30±0.84mmol/l and 0.85±0.31 mmol/l, respectively. The virgin mice was 1.04±0.38mmol/l, 0.38±0.14mmol/l. Compared with the virgin mice, the pregnant mice show a significant higher level of TG and VLDL. The hepatic TG and VLDL level of the pregnant mice was 156.67±27.06mmol/l and 6.77±1.00 mmol/l, respectively. The virgin mice was 108.31±50.20mmol/l, 4.98±1.86mmol/l. Compared with the virgin mice, the pregnant mice show a significant higher level of TG and VLDL. Oil red O staining show an obvious hepatic lipid accumulation and histological examination show an obvious morphology change in pregnant mice. The levels of hepatic pregnane X receptor(PXR) and its target gene fatty acid transloc ase cd36 m RNA were significantly increased in pregnant mice. The sterol regulated el ement-binding protein-1c(SREBP-1c) of pregnant mice is activated compared with vi rgin mice, parallel with its target gene fas and acc. Furthermore, the levels of hepatic peroxisome proliferator-activated receptorsα(PPARα) in pregnant mice are significant ly down-regulated and its target genes carnitine palmitoyltransferase 1α(cpt1α), cytoc hrome P450 enzymes 4A10(cyp4a10) and cytochrome P450 enzymes 4A14(cyp4a14) m RNA. Experiment 2: The serum fasting blood-glucose was 2.21±0.77mmol/l of the FP group, the TG and TCH level were 2.75±1.10mmol/l and 1.99±0.48 mmol/l, respectively. The serum fasting blood-glucose was 1.99±0.95mmol/l of the CP group, the TG and TCH level were 2.31±0.52mmol/l and 2.07±0.43mmol/l, respectively. Compared with the CP group, the FP group show a higher level of fasting blood-glucose and TG, but there was no statistically significant difference. The hepatic TG and VLDL level of the FP group was 100.40±19.41mmol/l and 1.88±0.31mmol/l, respectively. The CP group was 72.25±12.83mmol/l, 1.47±0.03mmol/l. Compared with the CP group, the FP group show a significant higher level of TG, the level of VLDL had a slightly increase. Oil red O staining show an obvious hepatic lipid accumulation. The q PCR and Western bloting show no statistically significantdifference of the genes and nuclear involved with fatty acid synthesis,uptake and oxidation expect the SREBP-1c. Both of the m RNA and nucleoprotein level of SREBP-1c had increased, the nucleoprotein level show a significant increase.Conclusion Experiment 1: Pregnancy could up-regulate the key enzymes of fatty acid uptake through the activation of PXR, up-regulate the key enzymes of de novo fatty acid synthesis through the activation of SREBP-1c, and down-regulate the key enzymes of fatty acid oxidation through the suppression of PPARα, result in the hepatic lipid synthesis and accumulation in late-pregnant mice. Experiment 2: The high fructose diet can make the hepatic TG level of pregnant mice rise further, this may result from the increase of SREBP-1c.