In order to compare the effects of TG, EE, FFA and PL forms of omega-3
s on lipid metabolism in mice, the ratio of DHA to EPA and their respective amount in diets were confirmed to be statistically equal in each DHA supplement group. Furthermore, fat level in diets was considered, for previous study has suggested that fat level in diets can significantly affect bioavailability of omega-3 fish oil [26
week feeding of omega-3
s, serum TC and TG levels in mice fed diets with DHA-PL, DHA-FFA and DHA-EE were significantly decreased at low fat compared to LF control, while no significant difference were observed among high fat fed mice (Table
). The result suggested that PL, FFA and EE forms of omega-3
s were effective in inhibiting serum lipids concentration compared with TG. Additionally, the results implied that high fat content in diets may restrain the therapeutic effect of omega-3
s on hyper-triglyceridemia compared with low fat content. This result was different from Lawson et al., who reported that high fat content could increase the bioavailability of DHA, other than low fat content [26
]. The difference implied that high fat content was effective in increasing the bioavailability of DHA but not the efficiency of DHA in lowering TC and TG concentrations in serum. The inefficiency of omega-3 supplement in high fat fed mice was probably based on its lower ratio in the total fat content, for the ratio of DHA
EPA in diet was 0.7% in both high fat and low fat groups, while the ratio of total fat content in diet increased a lot in high fat groups.
At low fat level, the decrease of TC and TG level in liver mainly existed in PL, TG and EE groups, and no significant difference was observed between TG and EE. Especially, hepatic PL concentration experienced a significant increase in PL group for high fat diet. These results suggested better effect of PL, TG and EE bound DHA in decreasing hepatic TC, TG levels compared with FFA, and equal efficiency of EE and TG in decreasing TC and TG level in liver. This was different from the previous study [31
], in which DHA-TG reduced liver TG level more effectively than DHA-EE after one-week feeding. The indifference between EE and TG forms in the present study was probably due to the lower dosage of DHA
EPA (0.7%) supplement. PL bound DHA is efficient in increasing PL level in liver. This could probably account for the increase of hepatic DHA level, because DHA-PL is a major form for DHA in liver.
] fed mice with TG, EE, FFA and PL forms of DHA supplement (1.5%) in the low-fat diet (6%) for 4
weeks to assess the effects of molecular form on distribution of omega-3 into organs. In the present study, short-term effect of low dosage of DHA
EPA (0.7%) on fatty acid composition in liver and brain of mice were investigated in high fat or low fat content. The ingestion of all the four forms of omega-3
s significantly increased hepatic DHA content. Furthermore, we found total fat content in diets a key factor in influencing the effect of different forms of omega-3
s on hepatic DHA concentration. When low dosage of DHA was fed to mice in low fat context, the effect of DHA-PL was more effective than TG, EE and FFA forms in increasing hepatic DHA contents.
Recent studies have shown possible therapeutic and preventive effects of cerebral DHA on many psychiatric diseases such as attention deficit hyperactivity disorder [32
], depression [34
], Alzheimer’s [35
], and, probably Parkinson’s disease [36
]. In the present study, cerebral DHA concentration of mice fed diets with low fat was found to have no significant change after 1
week feeding. However, cerebral DHA concentration increased significantly in mice fed diets with FFA, EE and PL at high fat by 9.1%, 9.1% and 11.0% respectively. There was no significant increase for cerebral DHA level in HF-TG group but with a 5.5% higher level compared to HF-control group. Results of this study suggested that in short-term feeding of omega-3
s, the increase of DHA level is much more significant in liver than in brain, and also, indicated that the efficiency of dietary DHA supplement on cerebral DHA content would be affected dramatically by co-ingested fat content, which implied a dietary suggestion when consuming omega-3
s. A series of behavioral experiment [37
] have shown that DHA intake could particularly increase cerebral DHA level, and as a consequence, improve learning and memory abilities of rats or mice. Most of those studies are carried out with a long period feeding of DHA. Our present study indicated that short-term feeding of omega-3 in high fat meals could also increase cerebral DHA level.
The present results indicated that DHA-PL could increase DHA concentration in liver and brain during a short period. The efficiency of PL bound omega-3
s is more significant than EE or FFA forms in increasing DHA concentration in tissues. This result was probably due to the difference in absorption and distribution of different omega-3 formulation. When dietary lipids are consumed, they are digested mainly in intestine, where the lipids are broken into free fatty acids and other remaining substances, such as monoglycerides, ethanol or lyso-phosphatidylcholine and they are absorbed by enterocytes of the intestinal wall. Afterwards those absorbed FFAs and other substances are reassembled into triglyceride and phospholipids. For EE form fatty acids, this is obviously a less efficient process than direct absorption of triglycerides [14
], which may lead to a worse bioavailability of EE form omega-3
s compared with TG form. In the present study, the superior bioavailability of PL bound DHA was probably due to its amphiphilic character, which might influence the surface composition of fat droplets thus facilitate the binding of hydrolyzing enzymes and hence the digestion [41
]. Otherwise, PL was one of the main forms for DHA in organs, especially in brains, for which the ingestion of DHA-PL might increase the efficiency in short-term incorporation of DHA into organs.
Up to date, TG and EE are two main forms of fish oil in the market. TG is the natural form of fish oil, while EE form of omega-3 is the most common form in industrial fish oil products because of convenience in synthesis and purification. However, results of the present study suggested that DHA-PL was also a bioactive form. Furthermore, as a natural form of fish oil, PL was much safer compared with EE or FFA form. Additionally, it has been reported in a 10-week oxidation study that the stability of DHA-EE decayed 33% more rapidly than DHA-PL [42
]. Thus, PL was suggested a better form for dietary omega-3 fatty acid.