1 Introduction

Omega-3 polyunsaturated fatty acids (PUFAs), especially docosahexaenoic acid (22:6, DHA), are well known for a range of documented health benefits such as decreasing the risk of sudden cardiac death (Harris et al.,2008; Saravanan et al., 2010), inhibiting hypertriglyceridemia (Hedengran et al., 2015; Nagao et al., 2014), and significant antithrombotic effects (Robinson and Stone,2006). The role of DHA has been verified in the brain,semen, and retina, and it is assumed to play an important physiological and pharmacological role in the central nervous system. Based on these findings, an increased intake of DHA and eicosapentaenoic acid (EPA) has been recommended (Kris-Etherton, 2009), which represents the current mean intake for EPA and DHA in the United States (E100 mg d−1). Omega-3 PUFAs exist as triglyceride (TG) or phospholipids (PL) in marine aquaculture raw materials. Increasing evidences indicate that DHA-bound phospholipids (PL-DHA) have superior functions such as anti-inflammatory activity (Awada et al., 2013),improvement of brain function (Hiratsuka et al., 2009),and hypolipidemic activity (Fukunaga et al., 2016). Since PL-DHA consists of PL and DHA, it could have the functions of both components. Moreover, the beneficial effects of PL-DHA perhaps are due to the amphiphilic character of PL. The adult mammalian brain contains approximately 50%–60% lipids of its dry weight, and the majority are composed of PL. These PL are largely made up of long-chain PUFAs, particularly DHA and arachidonic acid (Yavin et al., 2002), and ingestion of PL-DHA might increase the bioavailability of DHA. Although PL-DHA has important functions, it exists primarily in marine sources such as fish roe and krill (Maki et al.,2009; Takahashi and Inoue, 2012). TG-DHA, egg-phosphatidylcholine (Egg-PC), and soybean-phosphatidylcholine can be obtained from a wide range of raw materials. Till date, there is a lack of a comparative study on the effects of PL-DHA and the combination of TG-DHA with Egg-PL on lipid metabolism.

Currently available data provide strong concordant evidence that DHA could improve lipid metabolism(Masoodi et al., 2015). Our previous reports have compared the short-term effects of TG, ethyl ester (EE), free fatty acid (FFA), and PL forms of low-dose DHA supplementation (0.7%) on lipid metabolism and absorption of DHA in mice fed with a low-fat diet (5%) or a high-fat diet (22.5%). In those studies, PL-DHA demonstrated effective bioactivity in decreasing hepatic and serum total cholesterol (TC) and TG levels and in increasing omega-3 concentrations in mice organs (Ding et al., 2013; Tang et al., 2012).

那天，黑暗中，他迫不及待地抱住她，就像一个溺水的人的挣扎。花洒下两个人凝固了。像黑夜里淋雨的一组雕塑。

PPP投资型项目投资管理中，要深入施工现场调查，详细掌握项目工程建设基本情况。然后制定健全的投资管理制度，明确管理目标和要求，推动投资管理活动顺利进行。要制定合理的投资预算，对资金使用作出科学安排，防止资金浪费现象发生。要提高施工图纸设计水平，加强图纸审核，对存在的问题及时采取优化措施，从而有效指导PPP投资型项目建设，防止延误工期。要明确施工的重点环节，对施工现场拍照，加强现场清单管理，保证现场秩序良好，施工资金得到合理利用[3]。总之，从多个方面入手，提升投资管理水平，有利于促进项目效益提升。

To date, however, the effects of supplementation with a low dose of DHA on lipid metabolism have not been reported. Therefore, in the present study, mice were fed low amounts of dietary DHA (0.5%) under high-fat condition(22.5%) for 6 weeks. Serum, hepatic, and cerebral lipid concentrations and the fatty acid composition of the liver and brain were determined. The effects of PL-DHA and the combination of TG-DHA and Egg-PL on lipid metabolism were also compared.

2 Materials and Methods

2.1 Preparation of Different Forms of DHA

Omega-3 PUFAs have several biological activities (Riediger et al., 2009; Yates et al., 2014). The bioavailability of DHA is related to the chemical form of omega-3 PUFAs. A series of experiments have demonstrated the effects of different omega-3 fatty acid formulations on lipid metabolism (Hung et al., 2000; Tandy et al., 2009).However, there are no reports describing the effects of low dietary DHA (＜ 0.5%) supplementation on lipid metabolism. In the present study, the effects of PL-DHA and the combination of TG-DHA and Egg-PL on lipid metabolism were also compared.

Table 1 Primary fatty acid compositions of three different lipid forms

Notes: The results were expressed as mean ± SEM (n = 8). n.d. =not detected.

FA composition (%) TG-DHA PL-DHA Egg-PL C14:0 4.09 ± 0.02 2.28 ± 0.12 0.13 ± 0.01 C16:0 20.5 ± 0.43 26.6 ± 0.60 29.3 ± 0.52 C16:1 5.67 ± 0.03 0.57 ± 0.02 1.68 ± 0.01 C17:0 0.74 ± 0.02 1.52 ± 0.07 0.12 ± 0.01 C17:1 1.21 ± 0.01 0.41 ± 0.01 0.17 ± 0.00 C18:0 2.37 ± 0.02 8.44 ± 0.03 22.2 ± 0.14 C18:1 10.1 ± 0.09 6.08 ± 0.03 24.0 ± 0.22 C18:2 10.8 ± 0.11 n.d. 14.2 ± 0.12 C18:3n-6 0.43 ± 0.01 0.18 ± 0.01 0.16 ± 0.01 C18:3n-3 0.53 ± 0.01 0.26 ± 0.02 0.11 ± 0.00 C20:1 0.82 ± 0.01 10.7 ± 0.05 0.18 ± 0.00 C20:4(AA) n.d. 2.09 ± 0.02 5.05 ± 0.08 C20:5(EPA) 10.0 ± 0.13 9.80 ± 0.32 0.32 ± 0.01 C22:6(DHA) 31.5 ± 0.21 30.0 ± 0.25 1.55 ± 0.01

2.2 Animals and Diets

Male C57BL/6J mice were provided by Vital River Laboratories (Beijing, China). The mice were housed individually at the Laboratory Animal Facility in the Ocean University of China in metal cages under a 12-h light/dark cycle, a constant temperature of 24℃ ± 1℃,and a relative humidity of 65% ± 15% with free access to water and food for 7 days. The mice were randomly assigned to the following five groups: low-fat (LF) group with 5% dietary fat levels, high-fat (HF) group with dietary fat levels at 22.5%, TG-DHA group, PL-DHA group,and the combination of TG-DHA and Egg-PL group with HF diet (22.5%). Each group consisted of eight mice. The diets were modified according to the recommendation of the AIN76, as shown in Table 2. To make omega-3 PUFA concentrations equal in all the diets, all omega-3 supplementation groups contained 0.5% DHA + EPA, and the ratio of DHA to EPA was approximately 3:1, as shown in Table 3. All animals were handled according to the guidelines of the ethical committee of experimental animal care of the Ocean University of China.

Blood samples were collected by removing the eyeball after the mice were fasted for 10 h. The livers, brains, and epididymal white adipose tissue were excised. The epididymal white adipose tissues were weighed immediately,frozen in liquid nitrogen, and then stored at −80℃ until analysis. Serum was extracted by centrifuging the blood sample at 5100 × g for 15 min.

2.3 Determination of Lipids in Serum, Liver,and Brain

四是学生的能力有偏差.传统教学模式下培养的学生与应用型人才培养目标有偏差，学生在课堂上感觉“学会了”，但不会把所学知识应用到自己开发的网站上.传统的课程教学模式会导致学生实践操作时完全模仿教师上课演示的网页案例，不能独立完成一个真实的有创意的网站.

Table 2 Formulation of the experimental diets

Notes: The results were expressed as mean ± SEM (n =8). n.d. =not detected.

Ingredients(g kg−1) LF HFTG-DHA PL-DHATG-DHA +Egg-PL Soybean oil 25 50 47.3 47.5 44.8 Lard 25 175 165.6 166.3 156.9 Cornstarch 25075 75 69.5 69.5 Sucrose 400400 400 400 400 Casein 200200 200 200 200 Fiber 50 50 50 50 50 Mineral 35 35 35 35 35 Vitamin 10 10 10 10 10 Choline bitartrate2 2 2 2 2 DL-meth 3 3 3 3 3 DHA-TG n.d.n.d. 12.1 n.d. 12.1 DHA-PL n.d.n.d. n.d. 16.7 n.d.Egg-PL n.d.n.d. n.d. n.d. 16.7

Table 3 Fatty acid compositions of experimental diets

Notes: The results were expressed as mean ± SEM of eight mice. n.d. = not detected.

Composition(g kg−1) LF HF TG-DHA PL-DHA TG-DHA +Egg-PL C14:0 0.34 ± 0.03 2.27 ± 0.04 2.70 ± 0.12 2.50 ± 0.03 2.63 ± 0.03 C16:0 7.85 ± 0.35 43.2 ± 0.25 43.9 ± 0.47 44.8±0.45 42.1 ± 0.52 C16:1 0.70 ± 0.24 4.89 ± 0.36 5.44 ± 0.67 4.83 ± 0.64 5.31 ± 0.13 C18:0 5.47 ± 0.07 38.3 ± 0.17 37.5 ± 0.85 38.3 ± 0.45 36.4 ± 0.34 C18:1 15.6 ± 0.14 74.2 ± 0.83 71.7 ± 0.92 71.4 ± 0.74 67.8 ± 0.47 C18:2 18.0 ± 0.28 58.3 ± 0.47 54.8 ± 0.39 53.8 ± 0.82 49.8 ± 0.56 C18:3 1.87 ± 0.6 3.73 ± 0.06 3.24 ± 0.05 3.25 ± 0.04 2.67 ± 0.03 C20:0 0.09 ± 0.01 0.17 ± 0.02 0.15 ± 0.04 0.15 ± 0.05 0.12 ± 0.05 C20:1 n.d. n.d. 0.06 ± 0.01 1.34 ± 0.03 0.06 ± 0.01 C20:4n-6(AA) n.d. n.d. 0.10 ± 0.01 0.26 ± 0.04 0.10 ± 0.01 C20:5n-3(EPA) n.d. n.d. 1.20 ± 0.02 1.21 ± 0.05 1.20 ± 0.09 C22:6n-3(DHA) n.d. n.d. 3.80 ± 0.04 3.79 ± 0.07 3.80 ± 0.06

2.4 Fatty Acid Composition of Liver and Brain

式（1）中：R-扩散半径，m；γg-浆液比重，kg/L；β-有效充填系数；n-品地层孔隙率，%；C-单位耗灰量，g。将吃浆量不大的地层去除，如果单位注浆量＞500kg/m，就可以满足相应的防渗要求了。

2.5 Statistical Analysis

The results were expressed as mean ± SEM. All data were subjected to the analysis of variance using the SPSS software (version 18.0; SPSS Inc., Chicago, IL, USA).Differences between the LF and HF groups were evaluated by Student’s t-test. Differences between the mean values were tested by one-way ANOVA. The level of significance was represented by P ＜ 0.05.

3 Results

3.1 General Observation

In fish oil, DHA and EPA primarily exist in the TG form. Interestingly, the majority of n-3 PUFAs are present in the PL form in fish roe and krill (Higuchi et al., 2006;Burri et al., 2012). Dietary supplementation with n-3 PUFAs in the form of PL has superior functions such as antiinflammatory effects (Awada et al., 2013) and improvement of learning ability and memory (Hiratsuka et al.,2009).

Table 4 Growth parameters of C57BL/6J mice fed experimental diets

Notes: The results were expressed as mean ± SEM (n = 8). *P ＜ 0.05, significant difference compared with the LF group. Different superscript letters indicate significant differences at P ＜ 0.05.

LF HF TG-DHA PL-DHA TG-DHA + Egg-PL Food intake (g d−1) 3.29 ± 0.22 2.82 ± 0.12*a 2.83 ± 0.09a 2.79 ± 0.07a 2.78 ± 0.07a Energy intake (kcal d−1) 12.7 ± 0.52 13.3 ± 0.30a 13.4 ± 0.22a 13.2 ± 0.20a 13.1 ± 0.18a Initial body weight (g) 19.6 ± 0.27 19.6 ± 0.23a 19.7 ± 0.23a 19.6 ± 0.36a 19.7 ± 0.32a Body weight gain (g) 6.21 ± 0.42 9.31 ± 0.51*a 8.22 ± 0.60ab 7.29 ± 0.49b 8.20 ± 0.62ab Epididymal white adipose tissue weight(g (100 g body weight)−1) 1.93 ± 0.15 2.88 ± 0.20*a 2.23 ± 0.16b 2.11 ± 0.10b 2.69 ± 0.10a

3.2 Serum Lipid Concentrations

2.1.1 种实采集 粗糠树果实成熟期7—8月[2]，有些9月中下旬成熟[7]，7月中旬开始有果实自然脱落，从7月中旬起开始捡拾；9月中下旬用高枝剪剪下带果枝条，手工采下果实。本试验种子来源于洛阳市西苑公园、河南省林科院、南阳内乡宝天曼，共采集种实156 kg。

Lipids extracted from the liver and brain were prepared by transmethylation with HCL/methanol, and the fatty acid composition was analyzed by gas chromatography.An Agilent 7820 gas chromatograph equipped with a flame ionization detector was used to analyze the composition of cerebral and hepatic fatty acids and the fatty acid composition of the diet in each group. The chromatograph consisted of an HP-INNOWAX capillary column (30 m ×0.32 mm × 0.25 μm, Agilent Technologies Inc., Beijing,China). The temperatures of the detector and the injector were kept constant at 300℃ and 240℃, respectively, and the column temperature was increased from 170℃ to 240℃ at the rate of 3℃ min−1 and held at 210℃ for 30 min. Nitrogen was used as a carrier gas at the flow rate of 1.19 mL min−1. The relative content of each peak was detected by normalization of the peak area. Absolute concentrations of fatty acids were calculated using the pentadecanoic acid (C15:0).

Fig.1 Effects of DHA diet on serum lipid concentrations. A, Serum triglyceride levels; B, Serum TC concentrations; C,HDL-c concentrations; D, Atherogenic index. The results are expressed as mean ± SEM (n = 8). *P ＜ 0.05; significantly different compared with the LF group. Different letters indicate significant differences at P ＜ 0.05.

3.3 Hepatic Lipid Concentrations

Fig.2 shows that the hepatic TG concentrations in the HF group were significantly increased compared with those in the LF group (P ＜ 0.05). After 6 weeks of DHA diet intervention, the hepatic TG concentrations in the PL-DHA group and the combination of TG-DHA and Egg-PL group were significantly decreased compared with those in the HF group (P ＜ 0.05); however, no statistically significant difference was observed between the HF group and the TG-DHA group (P ＞ 0.05). The TC concentrations in the DHA diet groups showed a decreasing trend compared with those in the HF group, especially in the combination of DHA and Egg-PL group (P ＜ 0.05).

The results of serum lipid concentrations are shown in Fig.1. After 6 weeks of HF diet feeding, the serum TG levels and the AI in the HF group were significantly increased compared with those in the LF group (P ＜ 0.05).However, after 6 weeks of DHA diet feeding, serum TG and TC concentrations and HDL-c levels were significantly lower than those in the HF group (P ＜ 0.05), with no significant difference among the DHA diet groups (P ＞0.05). PL-DHA diet dramatically decreased the AI in the DHA diet groups compared with that in the HF group (P ＜0.05). Moreover, PL-DHA diet was more efficient in de-creasing the AI than TG-DHA diet and the combination diet of TG-DHA and Egg-PL (P ＜ 0.055).

Fig.2 Effect of DHA diet on hepatic lipids. (A) Hepatic triglyceride levels, (B) Hepatic TC levels. The results were expressed as mean ± SEM (n =8). *P ＜ 0.05; significantly different compared with the LF group. Different letters indicate significant differences at P ＜ 0.05.

3.4 FA Composition of Hepatic Phospholipids

As shown in Table 5, after 6 weeks of feeding, AA levels in the HF group were significantly higher than those in the LF group (P ＜ 0.05). After 6 weeks of DHA diet feeding, the DHA levels in the TG-DHA, PL-DHA, and TG-DHA and Egg-PL combination groups were significantly increased by 10.9%, 10.2% and 11.6%, respectively, compared with those in the HF group. However, no significant difference was observed in the DHA levels among all the types of DHA diet groups. Moreover, the AA levels in the DHA diet groups obviously declined by 12.3%, 14.1% and 13.5%, respectively, compared with those in the HF group.

Serum TG, TC, and high-density lipoprotein cholesterol(HDL-c) levels were determined using the corresponding diagnostic kits (Biosino, Beijing, China) according to the manufacturer’s instructions. The atherosclerotic index (AI)was calculated as (TC-HDL-c)/HDL-c. Lipids in the liver and brain were extracted using a 2:1 solution of chloro-form:methanol, as described by Folch et al. (1957), and then dissolved with Triton X-100.

Table 5 FA composition of hepatic phospholipids in mice

Notes: n.d. = not detected. The results were expressed as mean ± SEM (n =8). * P ＜ 0.05, ** P ＜ 0.01 significantly different compared with the LF group. Different superscript letters indicate significant differences at P ＜ 0.05.

Composition (%) LF HF TG-DHA PL-DHA TG-DHA + Egg-PL C14:0 0.21 ± 0.03 0.14 ± 0.04a 0.23 ± 0.03a 0.14 ± 0.02a 0.15 ± 0.04a C16:0 25.9 ± 1.27 25.1 ± 1.73a 26.4 ± 2.51b 26.2 ± 2.53b 27.6 ± 2.34b C18:0 18.9 ± 0.39 21.5 ± 2.48*a 20.4 ± 1.36a 19.7 ± 0.36bc 18.8 ± 1.30c C18:1 17.1 ± 1.43 11.3 ± 0.37**a 11.2 ± 0.24a 10.7 ± 0.22a 10.9 ± 0.04a C18:2 14.2 ± 0.65 16.6 ± 0.72*a 16.9 ± 0.07a 17.9 ± 1.26b 16.1 ± 1.20a C18:3 0.19 ± 0.02 0.37 ± 0.07 0.27 ± 0.05 0.18 ± 0.03 0.32 ± 0.02 C20:4 (AA) 17.0 ± 1.73 18.3 ± 0.32*a 12.3 ± 1.2b 14.1 ± 0.53b 13.5 ± 0.47b C20:5 (EPA) n.d. n.d. 1.10 ± 0.13a 0.82 ± 0.04a 0.94 ± 0.06a C22:6 (DHA) 6.36 ± 0.47 6.74 ± 0.62a 10.9 ± 0.26c 10.2 ± 1.23c 11.6 ± 0.35c

3.5 FA Composition of Hepatic Triglycerides

Table 6 shows the results of FA composition of hepatic triglycerides. After 6 weeks of feeding, the AA and DHA levels in the HF group were significantly higher than those in the LF group (P ＜ 0.05). The DHA levels in the TG-DHA, PL-DHA, TG-DHA and Egg-PL combination groups were significantly increased by 10.9%, 10.2%,and 11.6%, respectively, compared with those in the HF group (P ＜ 0.05). However, no significant difference was observed in the DHA levels among all types of DHA diet groups (P ＜ 0.05). Moreover, the AA levels in the TGDHA, PL-DHA, and TG-DHA and Egg-PL combination groups were obviously declined by 12.3%, 14.1%, and 13.5%, respectively, compared with those in the HF group(P ＞ 0.05).

Table 6 FA composition of hepatic triglycerides in mice

Notes: The results were expressed as mean ± SEM (n = 8). *P ＜ 0.05, **P ＜ 0.01, significantly different compared with the LF group. Different superscript letters indicate significant differences at P ＜ 0.05.

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3.6 FA Composition of Cerebral Lipids

As shown in Table 7, no significant change was observed in the cerebral DHA proportions in the mice of all groups; however, the AA concentrations in the mice fed with DHA diets were significantly decreased compared with those in the mice fed with HF diets (P ＜ 0.05). No significant changes in the DHA levels were observed between the DHA diet groups and the LF diet groups (P ＞0.05).

Table 7 Fatty acid composition of mice brain

Notes: Data were expressed as mean ± SEM (n = 8). *P ＜ 0.05, **P ＜ 0.01, significantly different compared with the LF group. Different superscript letters indicate significant differences at P ＜ 0.05.

Composition (%) LF HF TG-DHA PL-DHA TG-DHA+Egg-PL C16:0 24.7 ± 1.4 23.7 ± 1.32a 24.0 ± 2.46a 24.5 ± 2.63a 24.3 ± 2.35a C18:0 25.6 ± 0.87 25.9 ± 0.04a 26.2 ± 1.47a 26.0 ± 3.15a 26.4 ± 1.58a C18:1 22.2 ± 0.32 22.4 ± 1.30a 22.3 ± 0.48a 22.5 ± 1.28a 22.5 ± 3.27a C18:2 0.60 ± 0.02 0.69 ± 0.04a 0.74 ± 0.03a 1.07 ± 0.16a 0.80 ± 0.05a C20:4 (AA) 10.1 ± 0.12 10.4 ± 0.18a 9.40 ± 0.06b 9.29 ± 0.06b 9.30 ± 1.30b C22:6 (DHA) 16.9 ± 0.08 17.0 ± 1.29 17.3 ± 0.42 16.7 ± 0.04 16.7 ± 0.48

4 Discussion

In this study, two different forms of omega-3 PUFAs were prepared, including TG-DHA and PL-DHA. TGDHA was provided by the College of Food Science and Engineering, Ocean University of China. Dietary PLDHA was extracted from squid roe using the method described by Folch et al. (1957) and purified by silica gel chromatography. The ratio of DHA to EPA, determined by Agilent 7820 gas chromatography, was 3:1, and the purity of Egg-PL, purchased from Tianjin Bodi BiotechCo., Ltd., was 90%. The primary fatty acid compositions are shown in Table 1.

As shown in Table 4, compared with the mice in the LF group, the HF group mice consumed significantly less food (P ＜ 0.05). No differences were observed in daily food and energy intake between the HF group and the three DHA diet groups. Compared with the HF diet, only the DHA-PL diet was able to significantly suppress body weight gain by 22%. After 6 weeks of HF diet feeding,the epididymal adipose tissue weight in the HF group mice was significantly increased compared with that inthe LF group mice. However, in the DHA diet groups,particularly in the TG-DHA and PL-DHA groups, the epididymal adipose tissue weight was significantly lower than that in the HF group. There was no significant difference in the epididymal adipose tissue weight between the HF group and the combination of TG-DHA and Egg-PL group.

PL-DHA possesses the biological activities of both PL and DHA. The present study showed that the epididymal adipose tissue weight of the PL-DHA group was significantly lower than that in the combination group (TGDHA + Egg-PL), as shown in Table 4. This finding suggests that the biological activity of PL-DHA was different from that of the combination of DHA and non-DHA-PL.Epididymal adipose tissue weights of mice in the PLDHA and TG-DHA groups were significantly lower than that in the HF group; however, no significant difference was observed between PL-DHA group and TG-DHA group. In our previous study, we observed that supplementation with an HF diet containing PL-DHA (2%) significantly decreased the epididymal adipose tissue weight(Liu et al., 2014). Tang et al. (2012) reported that PLDHA rather than TG-DHA could decrease the epididymal adipose tissue weight of mice fed with the diets containing 0.7% omega-3 fatty acid supplementation. However,Tandy et al. (2009) reported that supplementation of an HF diet with krill oil did not show any obvious effect in decreasing the adipose tissue weight.

老福站起来对姐弟俩说：“你们放心，我从不诬陷谁，也不会放走罪犯。最近请你们配合我们调查，不要离开本市。”说完，三个人离开了罗家。

On the other hand, the combination of TG-DHA and Egg-PL was able to significantly decrease the serum lipid levels (Fig.1). However, PL-DHA was more effective in decreasing serum TG and TC concentrations than TGDHA and the combination of TG-DHA and Egg-PL. In particular, PL-DHA was much more efficient in decreasing the AI than TG-DHA and the combination of TGDHA and Egg-PL. Shirouchi et al. (2007) reported that omega-3 phosphatidylcholine, derived from fish roe,showed a tendency to decrease serum TG and cholesterol levels compared with that by the Egg-PC diet. The present study showed that the combination of TG-DHA and Egg-PL was not superior to TG-DHA. Hiratsuka et al.(2009) reported that TG-DHA and PL-DHA could significantly decrease serum TC levels, but no significant effect was observed in decreasing the serum TG concentrations. In our previous studies, PL-DHA rather than TGDHA was shown to significantly decrease serum TG and TC levels in mice fed with an LF diet with 0.7% DHA +EPA supplementation, but both PL-DHA and TG-DHA could not decrease serum TG and TC levels in an HF diet(Ding et al., 2013; Tang et al., 2012). The effects of DHA diets on hepatic TG and TC levels corresponded with their effects on serum lipids, which suggests that serum lipids might be regulated by hepatic lipids.

Tanaka et al. (2003) supplemented LF diets of mice with TG, EE, FFA, and PL forms of DHA to assess the long-term effects of molecular lipid forms on the distribution of omega-3 fatty acids in different organs. In the present study, the long-term effects of low-dose dietary supplementation with DHA + EPA (0.5%) on fatty acid composition in the liver and brain were investigated in mice fed with HF diet (22.5%). The intake of all DHA diets significantly increased the hepatic DHA content in mice. However, no significant changes were observed in the proportion of DHA in the brain among all the DHA diet-fed groups. We presume that the low-dose DHA supplementation (0.5%) was not sufficient to improve the DHA proportion in the brain. Moreover, the brain regulates fatty acid absorption to protect against drastic changes in dietary fatty acid composition. A previous study suggested that supplementation with low amounts of fish oil could not obviously improve cerebral DHA proportions (Bourre et al., 1990). In addition, our previous study found no significant changes in the cerebral DHA content when an LF diet was supplemented with FFA-DHA, EE-DHA, TG-DHA, and PL-DHA, respectively. However, FFA-DHA, EE-DHA, and PL-DHA significantly increased the cerebral DHA concentration when HF diet was supplemented with 0.7% dietary DHA + EPA supplementation (Ding et al., 2013). Although the exact dietary supplementation dose that could improve the cerebral DHA proportion is unclear, we presume that it might range from 0.5% to 0.7%. It has been reported previously that high fat content could increase the bioavailability of DHA (Lawson and Hughes, 1988). However, it is still unknown whether 0.5% DHA + EPA could improve the cerebral DHA proportion under LF or non-HF conditions.

5 Conclusions

The results of the present study suggest that PL-DHA was superior to the combination of TG-DHA and Egg-PL in decreasing the AI. In addition, long-term dietary supplementation with low amount of DHA (0.5%) could improve lipid metabolism and significantly increase hepatic DHA levels, although it is less efficient in improving cerebral DHA levels.

Acknowledgements

This work was supported by the grants from the project supported by the State Key Program of National Natural Science of China (No. 31330060), the National Natural Science Foundation of China (Nos. 31301446, 31371757),and the Program for New Century Excellent Talents in University (No. NCET-13-0534).

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