| Several trials of animals and clinic showed that hyperlipemia is familiar with many chronic metabolic diseases.The essential fatty acids have important effects on human health. It is well documented that polyunsaturated fatty acids (PUFA), especially for n-3 and n-6 PUFA, have various benefits on lipid metabolism and glucose metabolism, and are able to induce lipolysis as well. However, ingesting only one type of PUFA cannot simultaneously meet the nutritional requirements and improve the lipid metabolism and fat accumulation. At present, the FAO recommends that the optimal ratios of n-3 to n-6 ranges from 1:10~1:5. Currently, n-6 PUFA intake is excessive in general, while for n-3 PUFA is severely inadequate although controversy about the ratio remains within the academic community.PUFA perform all these above-mentioned functions, maybe by affecting AMP-activated protein kinase (AMPK). The substrates of AMPK are HMGR, ACC, hormone sensitive lipoidase (HSL), glycogen synthatase and so on. AMPK is the key component of a protein kinase cascade that plays a very important role in regulating energy control. Though the molecular mechanisms underlying the divergent regulation for AMPK are unknown, the effect of AMPK by affecting NPY and AgRP at least. Our experiment employs different dietary structures in order to find out the optimal n-3 to n-6 PUFA ratios. The n-3 PUFA being used are derived from linolenic acid oil, which contains 60%α-linolenic acid. Plenty of experiments indicate thatγ-linolenic acid is capable of improving hyperlipemia more significantly than linoleic acid. So the n-6 PUFA come from borage oil, which contains 20%γ-linolenic acid and 40% linoleic acid. Furthermore, our experiment would explore whether PUFA regulate the body energy metabolism by affecting AMPK in the periphery and central nervous system and ascertain whether AMPK influences food intake by affecting the expression of NPY, which may provide scientific support for the prevention and treatment of hyperlipemia and metabolism disorder in human being.MethodsAccording to their serum total cholesterol level, 58 male Sprague-Dawley rats were randomly divided into 6 groups, and were fed common feed diet, high fat diet, high fat with n-3/n-6 1:1 PUFA diet, high fat with n-3/n-6 1:5 PUFA diet, common feed with n-3/n-6 1:1 PUFA diet, and common feed with n-3/n-6 1:5 PUFA diet, respectively. We collected the blood sample at 15, 30, 45 days and measured the triglycerides (TG), total cholesterol (TC), HDL cholesterol (HDL-C), and LDL cholesterol (LDL-C) level in the plasma were using kits. After 45days, the rats were sacrificed, and adipose tissues (subcutaneous, mesenteric, retroperitoneal, epididymal), were removed, weighed and compute the ratio of fat/body.Also, we measured the mRNA expression of peroxisome proliferator-activated receptorγ(PPARγ) and AMPK-α2 in the liver. RT-PCR was used for measuring the expression of neuropepide Y (NPY) and AMPK-α2 mRNA in the hypothalamus. Western blotting was used for measuring the expression of AMPK-αand phosphorylation AMPK-αprotein level in liver and hypothalamus, respectively.Results(1) Effect of different ratios of n-3/n-6 PUFA diet on the lipid level of SD ratsFour diets with any ratio of n-3/n-6 PUFA resulted in significant restraint of TG,TC and LDL-C level compared with the high fat group in the plasma(P <0.05). These results indicate that dietary PUFA can improve lipid metabolism(2) Effect of different ratios of n-3/n-6 PUFA diet on the body weight and body fat weight of SD ratsAfter feeding with different ratios of n-3/n-6 PUFA diets for 45 days, the rats'weights increased visibly. All the PUFA groups reduced in mesenteric, retroperitoneal, epididymal adipose tissue, body weight and the ratio of fat/body weight compared with that of the high-fat group(P<0.05),and both 1:5 PUFA groups decreased in subcutaneous adipose tissue compared with that of the high-fat group. These data indicated that PUFA diets can reduce the body weight and body fat weight, especially the n-3/n-6 1:1 PUFA diet.(3) Effect of different ratios of n-3/n-6 PUFA diet on the food intake of SD ratsFed with different PUFA ratios diets for 45 days, the food intake of the four PUFA groups were suppressed compared with that of the high-fat group and control group(P<0.05)(Fig.1.B). The results suggested that n-3/n-6 1:1 and 1:5 PUFA were able to cut down the food intake. (4) Effect of different ratios of n-3/n-6 PUFA diet on the expression of NPY, AMPK-α2 and PPARγmRNA in liver of SD ratsThe expression of AMPK-α2 mRNA of the four PUFA groups decreased in livers compared with that of the control group (P<0.05), while the expression increased compared with that of the high-fat group (P<0.05). Moreover, the expression of PPARγmRNA in livers of the four PUFA groups was lower than that of the control group except the low-fat 1:1 group and was higher than that of the high-fat group (P<0.05).While the expression of AMPK-α2 and NPY mRNA in hypothalamus of the four PUFA groups decreased compared with that of the control and high-fat groups (P<0.05), and that expression of the high-fat PUFA groups was higher than the low-fat PUFA groups.(5) Effect of different ratios of n-3/n-6 PUFA diets on the protein abundance and phosphorylation of AMPK-αprotein level of SD ratsIn livers, the protein abundance and phosphorylation of AMPK-α(P-AMPK) of the four PUFA groups increased significantly compared with that of the high-fat group and the protein abundance of AMPK-αof the four PUFA groups increased compared with that of the control group. The P-AMPK of the two high fat PUFA groups and the high fat group decreased compared with that of control group and no significant difference among the control group and low fat PUFA groups was found. However, in hypothalamus, the protein abundance and P-AMPK of the four PUFA groups were lower than that of the control group and high fat group. The protein abundance and P-AMPK of the two low fat PUFA groups decreased considerably compared with that of the two high fat PUFA groups. ConclusionsIn conclusion, PUFA are able to improve lipid metabolism by reducing the expression of NPY in CNS and enhance PPARγin periphery by altering AMPK. However, the precise mechanism of how dietary PUFA affecting AMPK activation remains to be determined. |
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