Effects Of Conjugated Linoleic Acid On Lipid Metabolism, Immunity, Flesh Quality And PPAR Gene Expression In Large Yellow Croaker

Conjugated linoletic acid (CLA) is one of natural unsaturated fatty acids with many physiological functions. It has been testified by experiments on human beings and animals that CLA are characterized for a variety of special functions, including lowing fat content, increasing muscle, anticancer, antiatherosclerosis, enhancing immunity, and improving metabolism of bony tissue. In the study, different levels of CLA were added to diet of large yellow croaker. Effects of various levels of CLA (0, 1, 2, or 4%) on the growth, lipid metabolism, immunity, and muscular properties of large yellow croaker were investigated. Moreover, PPARa and PPARγin liver of large yellow croaker were cloned and expressed, which demonstrated the action mechanism of CLA on lipid metabolism of large yellow croaker in molecular level. The main content and results were listed as follows:1. Effects of dietary CLA on growth and lipid metaboliam in large yellow croakerThe study was conducted to investigate the effects of dietary conjugated linoleic acid (CLA) on growth, body composition, lipid content, lipogenic enzyme and fatty acid composition of large yellow croaker (Pseudosciaena crocea, R). Four dietary treatments were formulated to contain 0%, 1%, 2% or 4% CLA (instead of fish oil) in diets, respectively. The fish were fed for 10 weeks with ad libitum twice daily. Ten weeks later, as is shown by the results, the specific growth rate (SGR) and condition factor (CF) of large yellow croaker were increased with addition of 1% CLA, but SGR was decreased while high content of CLA (2% & 4%) was added. Meanwhile, little difference was found among the four dietary treatments (P<0.05). Feed conversion ratio (FCR) were not significantly affected by dietary CLA (P>0.05). Hepato-somatic indices (HSI) and viscero-somatic indices (VSI) were both slightly increased in fish fed dietary CLA, but the difference was not significant (P>0.05). With an increasing of CLA concentration, protein, moisture and ash in whole body increased gradually, but the difference was not significant between groups (P>0.05). The dissimilar result was observed in lipid content of liver and flesh. Dietary CLA had no significant effects on lipid content, although there were trends of decreasing in fish fed high CLA levels.Compared with the control group (D1), the triglyceride (TG) content were significantly decreased, whereas the free fatty acid (FFA) content were significantly increased (P<0.05) in both serum and liver. The TG contents were decreased with the increasing of dietary CLA levels. In serum, notable difference were observed between D3, D4 and D2 (P<0.05). In liver, however, no significant difference was found between treatment groups (D2-D4) (P<0.05). In serum and liver, the contents of FFA in D4 was highest and the difference was marked between D1, D2 and D4 (P<0.05). The content of cholesterol (CHO) and low density lipoprotein - cholesterol (LDL-C) in serum were much lower than D1 (P<0.05), and high density lipoprotein -cholesterol (HDL-C) content in serum was rather higher than D1 (P<0.05). However, no significant difference was observed between treatment groups (P>0.05).Lipogenic activities in liver of large yellow croaker during the experiment were detected in the study. The activities of hepatic lipase (HL) and lipoprotein lipase (LPL) were decreased significantly by CLA incorporation levels. In both serum and liver, the difference was significant between control and treatment groups, and apparent difference was also found between D3, D4 and D2 (P<0.05). Besides, dietary CLA had diverse influence on the activities of glucose-6-phosphate dehydrogenase (G6PD), fatty acid synthetase (FAS) and malic enzyme (ME). There were no strong effects on G6PD activities both in serum and liver in fish fed with diets containing 1% CLA. However, the activities of G6PD were reduced in fish fed with high CLA levels (2% and 4%), and the difference was significant between D2, D4 and D1 (P<0.05). CLA seemed to decrease the activities of FAS in serum. The FAS activity in serum of D4 was about 16% lower than that of D1, and the difference between D1 and D4 was significant (P<0.05). Similar results were observed in liver, but the difference between four groups was not significant (P>0.05). There was a downward trend for the activities of ME both on serum and liver in fish fed CLA. In serum, the difference between D3, D4 and D1 was significant (P<0.05), and there was no statistically significant between four groups in liver (P>0.05).Dietary CLA had great influence on fatty acid composition in both muscle and liver (P<0.05). The main fatty acids were C16:0 of saturated fatty acids (SFA), and C18:l n-7 of monounsaturated fatty acids (MUFA). MUFA decreased significantly whereas SFA and polyunsaturated fatty acids (PUFA) showed a clear increase (P<0.05). Concerning the PUFA fraction, a gradual increase of EPA (65% of PUFA) and DHA (63% of PUFA) were observed in both tissues with increasing CLA levels. The fatty acid compositions of muscle and liver reflected the fatty acid composition of the diets. Dietary CLA resulted in the deposition of the cis-9, trans-11 and trans-10, cis-12 CLA isomer in both tissues.2. Effects of dietary CLA on immunity and antioxidation in large yellow croakerEffects of dietary CLA supplementation on immune parameters of large yellow croaker were investigated. With the increasing of CLA concentration, the spleen body index (SBI) were increased remarkably (P<0.05), but the difference of D3 and D4 was not significant. Compared with D1, the activities of lysozyme and immunoglobulin M (IgM) were increased significantly (P<0.05). Dietary CLA had great affect on activities of complement components C3, C4 (P<0.05). The activities in D3 were the highest than the other groups (P<0.05), increased by 59% and 65% respectively, compared with D1. The activities of SOD in both serum and tissues were augmented in fish fed CLA supplementation. The SOD activities in liver had reached 202.89 U/ml, about 1.7 fold of that in serum and muscle. In both serum and liver, the SOD activities in treatment groups were higher than control group significantly (P<0.05), and no significant difference were found between treatment groups.3. Effects of dietary CLA on flesh quality in large yellow croakerEffects of dietary CLA on amino acid (AA), inosine monphosphate (IMP) and volatile flavor components of large yellow croaker were investigated. With the increasing levels of dietary CLA, essential amino acids and flavour amino acids contents in fillets of large yellow croaker increased, and the difference of flavour AA contents was significantly (P<0.05). IMP content in fillets of large yellow croaker was remarkably increased by supplementing CLA into basal diets (P<0.05).Volatile flavour compounds from muscle of large yellow croaker were extracted by microwave distillation and solid phase microextraction. The technique of gas chromatography-mass spectrometry was employed to analyze the components, and 54 compounds which mainly contain alcohols, aldehydes and ketones, were identified. By comparing the results of all groups, the percentage profiles of components were not affected by dietary CLA levels, but the contents of aldehydes and ketones with special odor were increased slightly.4. Effects of dietary CLA on expression of PPAR gene in liver of large yellow croakerThe DNA sequence of PPARa and PPARγgene in liver of large yellow croaker were identified by cloning the two genes. The expression levels of PPARa and PPARγwere analyzed by using the real-time quantitative PCR method. The results showed that dietary CLA had significant influence on PPARa and PPARγexpression (P<0.05). PPARa and PPARγexpression levels were significantly increased compared with D1 (P<0.05).