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Hypolipidemic study of xylanase-modified corn bran fibre in rats
Food Chemistry 123 (2010) 563–567
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Hypolipidemic study of xylanase-modified corn bran fibre in rats Ye-Bi Hu a,b, Xiang-Jin Fu a,b, Feng-Xiang Zhang b, Fu-Min Ma b, Zhang Wang b,*, Shi-Ying Xu b a b
School of Food Science and Engineering, Central South University of Forestry and Technology, No. 498 Shaoshan Road, Changsha 410000, PR China State Key Laboratory of Food Science and Technology, Jiangnan University, Box 98, No.1800 Lihu Road, Wuxi 214036, PR China
a r t i c l e
i n f o
Article history: Received 9 July 2009 Received in revised form 25 January 2010 Accepted 31 March 2010
Keywords: Xylanase modification Corn bran fibre Serum lipids Liver lipids Lipids excretion Hypolipidemic study
a b s t r a c t In order to understand the regulatory effect of xylanase-modified corn bran fibre (XMF) on lipid homeostasis, detailed influences, following the ingestion of XMF and its original form (corn bran dietary fibre, CDF), on serum, liver and faecal lipids were studied in Sprague–Dawley rats. In both CDF and XMF groups, serum total cholesterol (TC), triacylglycerol (TG) and low-density lipoprotein cholesterol (LDL-C) were significantly lowered after 4 weeks (p < 0.05). By the end of week 6, data in the XMF group showed that serum LDL-C was lowered further and high-density lipoprotein cholesterol (HDL-C) was significantly increased (p < 0.05); liver TC, TG and fat were significantly lower (p < 0.05), while the excretions of faecal fat, TC and bile acids were significantly higher (p < 0.05). The decrease of liver and serum lipids in the XMF group was consistent with the improved excretion of faecal lipids and bile acids. Other related mechanisms are also considered. Ó 2010 Published by Elsevier Ltd.
1. Introduction Hyperlipidemia is a risk factor for coronary heart disease (CHD) which is a leading cause of death in the world. In China, CHD has become the second leading cause of cardiovascular death. Elevated levels of blood cholesterol are believed to be a major contributing factor for heart disease (Thongngam & McClements, 2005; Zhang, Lu, & Liu, 2008). Within TC, low-density lipoprotein cholesterol (LDL-C) and very low-density lipoprotein cholesterol (VLDL-C) are the most important actors for coronary heart disease. Highdensity lipoprotein cholesterol (HDL-C) suppresses the ingestion of LDL-C by body cells and transports excessive cholesterol out of cells in the ester form. Thus it prevents the accumulation of cholesterol in the cells (Barter, 2005). However, hyperlipidemia is closely connected with dietary factors. Greater consumption of fruits, vegetables and cereals has been encouraged to reduce the risk of heart disease, partly because these foods contain relatively high levels of dietary fibres, which are believed to help reduce blood cholesterol levels (Kritchevsky & Tepper, 2005; Sanchez-Alonso, Haji-Maleki, & Borderias, 2007; Sudha, Vetrimani, & Leelavathi, 2007). Adding certain dietary fibre sources to mixed test meals, at the level of 4–10 g/meal, can reduce the postprandial triacylglycerol (TG) and total cholesterol (TC) generated by a mixed meal (Lairon, Play, & Jourdheuil-Rahmani, 2007).
* Corresponding author. Tel./fax: +86 510 85884496. E-mail address: [email protected] (Z. Wang). 0308-8146/$ - see front matter Ó 2010 Published by Elsevier Ltd. doi:10.1016/j.foodchem.2010.03.131
Corn bran has a higher dietary fibre content than have wheat and rice brans (Wang & Liu, 2000), in which about 40% is heteroxylan (Saulnier, Marot, Chanliaud, & Thibault, 1995). Shane and Walker (1995) reported that corn fibre supplementation of controlled low-fat diet in men with hypercholesterolemia resulted in lowering of serum TC, TG and VLDL-C, while serum LDL-C and high-density lipoprotein cholesterol (HDL-C) concentrations were not significantly altered. Corn bran fibre, hydrolysed by a-amylase, was also found to lower plasma and liver cholesterol concentrations significantly in rats (Ebihara & Nakamoto, 2001). The addition of a corn dietary fibre prepared by a-amylase and alkali proteinase hydrolysis, lowered the levels of serum TC and TG, and increased the HDL-C (Zhang & Wang, 2005). However, the hypolipidemic mechanism of corn bran fibre is still unclear. In our previous study, corn bran fibre, modified by xylanase (XMF), positively regulated the mRNA expression of several genes involved in lipid catabolism in rats, e.g. the farnesoid X receptor (FXR), cholesterol 7 alpha-hydroxylase (CYP7A1), lipoprotein lipase (Lpl), hepatic lipase (Lipc), peroxisome proliferatoractivated receptors (PPARa and PPARc) and intestine-bile acidbinding protein (I-BABP) (Hu, Wang, & Xu, 2008a). Furthermore, XMF could bind bile acids more than could CDF in vitro (Hu, Wang, & Xu, 2008b). In order to understand the hypolipidemic mechanisms of XMF, it is necessary to investigate the changes of serum and liver lipids and the excretion of faecal lipids after the ingestion of XMF. Therefore, the purpose of this study was to explore detailed effects of XMF in rats with atherogenic diet-induced hyperlipidemia on the changes of serum, liver and faecal lipids after
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feeding; and then explore the hypolipidemic mechanisms of XMF on the basis of the present and our previous results. 2. Methods and materials 2.1. Chemicals Corn bran was provided by Dancheng Caixin Group Co. Ltd. (Henan, PR China) and was milled through a 250 lm screen (Ebihara & Nakamoto, 2001); then CDF was processed as we reported previously (Hu et al., 2008b). Xylanase (NCB 77, 8000 IU/g, from Bacillus subtilis, main enzyme activity EC 3.2.1.8) was supplied by Hunan New Century Biochemical Co. Ltd., Hunan, PR China. TG, TC, and high-density lipoprotein cholesterol (HDL-C) kits were purchased from Zhejiang Dongou Bioengineering Co. Ltd., Ningbo, China. 2.2. Xylanase-modified corn bran fibre (XMF) According to the results by Ebihara and Nakamoto (2001), corn bran fibre of particle size 250 lm is enough for the benefits of corn bran fibre on lipid metabolism and intestinal functions; therefore, a particle size of 250 lm was chosen for the preparation of CDF and XMF in this study. Xylanase was added at a rate of 7 g/kg of CDF to a container with 8 l of 50 mM phosphate buffer (pH 5.3). Eight hundred grammes CDF were added to the freshly prepared xylanase enzyme solution. The reaction mixture was incubated in a super water bath thermostatic vibrator (Model 501, Shanghai Experimental instrument Co., Shanghai, PR China) at 50 °C with 145 rpm agitation for 105 min, and the reactants worked up to obtain XMF as reported earlier (Hu et al., 2008b).
Table 1 Components of animal diets (%).
Corn powder Soy bean pomace Lard Fish powder Cellulose Flour CaHPO4 CaCO3 Lysine Methionine Choline Mineral mixtureb Vitamin mixturec NaCl Cholesterol Sodium cholate Yolk powder CDF XMF
NFa
HF
CDF
XMF
35.5 21.6 2 2 10 26 1 1.3 0.12 0.13 0.1 0.03 0.02 0.2 – – – – –
30 20 15 4 3 13.8 1 1.1 0.12 0.13 0.1 0.03 0.02 0.2 2 0.5 9 – –
25 20 15 4 – 11.8 1 1.1 0.12 0.13 0.1 0.03 0.02 0.2 2 0.5 9 10 –
25 20 15 4 – 11.8 1 1.1 0.12 0.13 0.1 0.03 0.02 0.2 2 0.5 9 – 10
a NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF (corn bran fibre), treatment of CDF; XMF, HF diet with an addition of 10% of XMF (xylanase-modified corn bran fibre), treatment of XMF. b AIN-76 mineral mixture contained (in g/kg of mixture): calcium phosphate, dibasic 500.0; sodium chloride, 74.0; potassium citrate, monohydrate, 220.0; potassium sulphate, 52.0; magnesium oxide, 24.0; manganous carbonate, 3.5; ferric citrate, 6.0; zinc carbonate, 1.6; cupric carbonate, 0.3; potassium iodate, 0.01; sodium selenite, 0.01; chromium potassium sulphate, 0.55; sucrose, finely powdered, 118.03. c AIN-76A vitamin mixture contained (in g/kg of mixture): thiamine HCl, 0.6; riboflavin, 0.6; pyridoxine HCl, 0.7: niacin, 3.0; calcium-D pantothenate, 1.6; folic acid, 0.2: D-biotin, 0.02; cyanocobalamin (vitamin B12), 1.0; dry vitamin A palmitate (500,000 U/g), 0.8; dry vitamin E acetate (500 U/g), 10.0; vitamin D3 trituration (400,000 U/g), 0.25; menadione sodium bisulphite complex, 0.15; sucrose, fine powder, 981.08.
2.3. Animals and diets The Jiangnan University (Jiangsu, China) Animal Care and Use Committee approved all rat studies. All rats, weighing 100 ± 10 g (male Sprague–Dawley, from Shanghai Slac Laboratory Animal Co. Ltd., Shanghai, PR China) were placed individually in stainless steel wire mesh cages in a room maintained at 23 ± 2.0 °C, with relative humidity of 55 ± 10%, and a daily photoperiod from 7:00 am to 7:00 pm. Rats consumed food and water ad libitum and were acclimatised to the conditions for 1 week. All were then randomly assigned to NF (negative control), HF (positive control), CDF (treatment of CDF) or XMF (treatment of XMF) groups with eight rats per group. Rats in the NF and HF groups were fed with basic feed (NF diet) and an atherogenic diet (HF diet), respectively, for 6 weeks. The rats of CDF or XMF groups were fed HF diet, for 2 weeks first, and then changed to the CDF or XMF diet, respectively, for 4 weeks. The components of diets were as shown in Table 1. HF diet was an atherogenic diet. Cholesterol, sodium cholate, yolk powder and basic feed were purchased from Shanghai Slac Laboratory Animal Co. Ltd., Shanghai, PR China. Lard was purchased from a local market in Wuxi, PR China. Food intake was recorded daily, while body weight was recorded weekly.
Arteriosclerosis index (AI) was calculated as described by Queiroz-Monici, Costa, da Silva, Reis, and de Oliveira (2005):
AI ¼
TC ðHDL-CÞ HDL-C
in which, TC is serum total cholesterol; HDL-C is high-density lipoprotein cholesterol. Aliquots of liver were extracted with chloroform–methanol 2:1 and the lipid extract was analysed for TC, TG and fat (Kritchevsky & Tepper, 2005). Faeces were collected on day 42 and vacuum-dried. Extraction of lipids and the analysis of fat in faeces were done according to Hsu et al. (2006). TC and bile acids in faeces were determined using appropriate commercially available kits. 2.5. Statistical analysis The statistical analyses were done using SPSS 13.0 for Windows software (SPSS Institute Inc., Cary NC). Comparison of the means was done by one-way ANOVA using the honestly significant difference (HSD) of Tukey’s ad hoc test. Significance level was 0.05. 3. Results
2.4. Sampling and analytical procedures 3.1. Food intake, growth and body fat On days 0, 14 and 28, blood samples were drawn from the tail vein. Serum was analysed for TC, TG and HDL-C using appropriate commercially available kits. LDL-C was calculated according to the Friedwald equation (Anna, Riitta, Marjukka, Kirsi, & Oksman, 2003). On day 42, rats were weighed and sedated by barbiturate injection. They were exsanguinated, and the livers were removed and weighed. Serum was analysed for TC, TG, HDL-C and LDL-C.
All groups started with similar mean body weights of 150 ± 10 g (Table 2). All rats gained weight during the study. The body weight gain in rats fed the XMF diet was significantly lower than that in rats fed the HF diet (p < 0.05, Table 2), but close to that in the NF group (p > 0.05). The difference of body weight gains between the CDF and the HF group did not reach statistical significance
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Y.-B. Hu et al. / Food Chemistry 123 (2010) 563–567 Table 2 Necropsy data on rats (eight per group) fed NF or HF or test fibre diets for 42 days (mean ± SD). NFf Food intake (g/rat day) Body weight gain (BW) (g/rat day) Liver weight (g/100 g BW) Epididymal fat (g/100 g BW) AIe Liver lipids TC (lmol/g) TG (lmol/g) Fat (%)
HF
CDF
XMF
a
23.65 ± 0.95 5.48 ± 0.48a 4.08 ± 0.34a 1.16 ± 0.11a 0.89 ± 0.41a
a
a
23.67 ± 0.49 6.23 ± 0.52b 6.24 ± 0.26c 1.89 ± 0.14c 8.27 ± 1.36d
25.24 ± 3.76 5.98 ± 0.90ab 5.79 ± 0.40bc 1.52 ± 0.24b 5.82 ± 1.28c
26.04 ± 3.36a 5.30 ± 0.83a 5.41 ± 0.58b 1.47 ± 0.28b 2.54 ± 0.48b
8.37 ± 0.58a 5.75 ± 0.98a 5.27 ± 0.03a
87.4 ± 7.02c 50.2 ± 5.17c 25.7 ± 0.29d
81.2 ± 12.19c 44.0 ± 4.04c 19.1 ± 0.41c
47.2 ± 2.30b 33.1 ± 2.06b 17.6 ± 0.29b
a,b,c,d
Same superscript letters in a row show values that do not differ significantly (p > 0.05, n = 8). AI, arteriosclerosis index; TC, total cholesterol; TG, total triacylglycerol. f NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF treatment of CDF; XMF, HF diet with an addition of 10% of XMF treatment of XMF. e
(p > 0.05). The food intake in the HF group was similar to that in the NF group. As compared with the NF group, the food intake ratio in the groups to which CDF and XMF were added was increased by 6.7% and 10.1%, respectively (Table 2). The HF diet significantly elevated the weight of epididymal fat by 63% as compared with the NF diet (p < 0.05, Table 2). The epididymal fat in rats fed the CDF and XMF diet was significantly lower than in those fed the HF diet (p < 0.05, Table 2). The liver weight of rats in the XMF group was significantly lower than that of rats in the HF group (p < 0.05), and that in the CDF group was also somewhat lower, however, insignificantly (p > 0.05, Table 2). 3.2. Time course of serum lipids At the start, TC was almost the same in all groups of rats (Fig. 1a). TC level in rats fed the NF diet did not change apparently
TC (mM)
NF HF C DF CDF XM F XMF
d c
NF HF C DF CDF XM F XMF
c
b
b
a
b
b
b
a
a
TG (mM)
a
from week 1 to week 6. By contrast, TC in rats fed the HF diet increased nearly linearly during the whole experiment for 42 days. After 2 weeks of CDF and XMF feeding, TC values in the CDF and XMF groups were significantly lower than those in the HF group (p < 0.05, Fig. 1a). At the end of the 6th week, there was no increase in TC for rats fed the XMF diet, while TC in rats fed the CDF diet increased further as compared with the end of the 4th week. For serum TG, there were no significant differences on week 0 in the four groups (p > 0.05, Fig. 1b), and there were no apparent changes in rats fed the NF diet throughout the 6 weeks programme. However, TG in rats fed the HF diet was highly elevated within 2 weeks of feeding time. In rats fed the CDF and XMF diets, serum TG was always higher than in rats fed the NF diet after the end of the 2nd week but was significantly lower than that in rats fed the HF diet (p < 0.05), and there was no prominent increase from weeks 2 to 6 (Fig. 1b).
c
c
b
b
b
a
0
2
6
4
0
d
2
4
6
1.8
b
1.6 1.4
c
c
b
b
b a
a
2
d
4
Time (weeks)
6
HDL-C (mM)
LDL-C (mM)
NF HF CDF CDF XM F XMF
0
a
a
Time (weeks)
Time (weeks)
c
b
b
1.2
a
1
a
0.8 0.6 0.4
CDF XM F
0.2 0
0
2
NF HF CDF XMF 4
a
6
Time (weeks)
Fig. 1. Time course of serum lipids expressed as a function of (a) cholesterol (TC), (b) triacylglycerol (TG), (c) low-density cholesterol (LDL-C), (d) high-density cholesterol (HDL-C). NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF treatment of CDF; XMF, HF diet with an addition of 10% of XMF treatment of XMF. Rats in the NF group were fed NF diet all the time; rats in the HF group were fed HF diet all the time. Rats in the CDF and XMF groups were fed HF diet in the first 2 weeks, then changed to CDF and XMF diets, respectively, and fed for 4 weeks. Each point is the mean ± SD of eight rats; values at each time point with different letters are significantly different (p < 0.05).
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Table 3 Excretion of fat, TC and bile acids in faeces (mean ± SD, mg/rat day). NFe Fat TC Bile acids
HF a
0.115 ± 0.02 1.41 ± 0.17a 45.5 ± 3.11a
CDF b
0.299 ± 0.04 19.9 ± 1.89b 47.0 ± 6.71a
XMF b
0.424 ± 0.04 53.8 ± 6.32c 82.6 ± 8.53c
0.697 ± 0.06c 76.3 ± 6.45d 114 ± 14.3d
a,b,c,d
Same superscript letters in a row show values that do not differ significantly (p > 0.05, n = 8). e NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF treatment of CDF; XMF, HF diet with an addition of 10% of XMF treatment of XMF.
LDL-C was stable in rats fed the NF diet, but increased rapidly over time in rats fed the HF diet (Fig. 1c). As compared with the HF diet, the addition of CDF and XMF effectively decreased serum LDL-C level at the end of week 4 (Fig. 1c). XMF was more efficient than was CDF because the LDL-C in rats fed the XMF diet was lowered further at the end of week 6 (Fig. 1c). There was a slight decrease of HDL-C in rats fed the HF and CDF diets at the end of week 6, but this was insignificant when compared with that in rats fed the NF diet (p > 0.05, Fig. 1d). While HDL-C level increased significantly in rats fed with the XMF diet (p < 0.05, Fig. 1d), AI in the HF group was 9.3-fold to that in the NF group. The addition of CDF and XMF decreased AI to 70.4% and 30.7% of that in the HF group with a significance of p < 0.05, respectively (Table 2). 3.3. Liver lipids There was a tendency for the CDF diet to suppress the increase of liver TG and TC, while the level of liver fat in rats fed the CDF diet was significantly lower than that in rats fed the HF diet (p < 0.05, Table 2). On the other hand, the levels of liver TG, TC and fat in the rats fed the XMF diet were all significantly lower than those in the rats fed the CDF diet (p < 0.05). 3.4. Excretion of fat, TC and bile acids The content of faecal lipids indicated the excretion levels of these lipids by animals. Fat excretions in the CDF and XMF groups were 1.42 and 2.33 times those of the HF group, respectively (Table 3). The excretion of fat was significantly increased in rats fed the XMF diet (p < 0.05). The excretion of TC in rats fed the XMF diet was significantly higher than that in rats fed the CDF diet (p < 0.05); the amount of the former was 1.4 times that of the latter. Bile acids excretion in the XMF group was also 1.4 times that in CDF group with a significance of p < 0.05. 4. Discussion Supplementing a low-fat diet with corn bran was effective in reducing the serum lipid concentration in men with hypercholesterolemia (Shane & Walker, 1995). In type II diabetes patients, consumption of corn bran lowered the plasma VLDL-C level. On the other hand, consumption of corn bran did not reduce the plasma cholesterol concentration in 10 healthy men (Ebihara & Nakamoto, 2001). A fibre supplement containing corn bran provided significant and sustained reductions in LDL-C without reducing HDL-C or increasing TG in subjects with mild to moderate hypercholesterolemia (Knopp et al., 1999). In this study, CDF and XMF could enhance the catabolism of energy or suppress the absorption of energy, and XMF is more efficient than is CDF, suppressing the accumulation of fat in rats, even though rats fed these diets consumed more food. Dong et al. (2000) also reported lowered TC and TG by use of corn bran fibre extracted by amylase on male Wister rats at a 100 g/kg addition for 3 weeks.
CDF was more efficient in suppressing the increase of serum TG than of TC, while XMF suppressed the serum TG and TC efficiently at the same time. When feeding time was continued for 6 weeks, the serum TC in the XMF group was stable and LDL-C was lowered further, as compared with the end of week 4. However, the serum TC and LDL-C values in the CDF group were increased apparently from the end of week 4 to week 6. Furthermore, ingestion of XMF for 6 weeks increased the HDL-C level and, as a result, decreased AI under the HF diet. Therefore, the hypolipidemic effect of XMF was significantly better than that of CDF. Within the total cholesterol, LDL-C and VLDL-C are the most important mediators for coronary heart disease (Barter, 2005). The changes of LDL-C in each group were similar to that of TC, this might indicate that the main cause of hypercholesterolemia was the high level of LDL-C in this study. During the 6 week feeding period, the studied dietary fibre CDF and XMF lowered TC, mainly by decreasing the LDL-C level. However, in this study, the high lipid diet did not lower HDL-C in rats significantly, as reported elsewhere, and only the HDL-C in rats fed the XMF diet was increased significantly (p < 0.05) (Dong et al., 2000). XMF could bind more bile acids than CDF in vitro (Hu et al., 2008b). Significantly increased excretion of faecal fat and TC indicated that XMF prevented the absorption of fat and TC in the intestine, enhanced their decomposition more efficiently, and then decreased the levels of liver and serum TC and TG. The homeostasis of TC and LDL-C is regulated by several genes, such as FXR, I-BABP, CYP7A1 and PPARs (Makishima et al., 1999; Mezei et al., 2003). Up-regulation of ileum FXR and hepatic CYP7A1 expression and down-regulation of I-BABP and hepatic FXR enhance the catabolism of cholesterols by depressing the enterohepatic transport of bile acids (Li, Hou, Tang, & Ling, 2004; Makishima et al., 1999). Up-regulation of the transcription of PPARa, PPARc, Lpl and Lpic improve the catabolism of triacylglycerols by reducing the rates of lipogenesis and enhancing lipid hydrolysis (Takahashi et al., 2002; Anonymous, 2007-01-03 20:00). It was reported that XMF up-regulated the transcription of CYP7A1, PPARa, PPARc, Lpl, Lipc and, down-regulated the transcription of I-BABP more efficiently than did CDF (Hu et al., 2008a). Such results were consistent with the increased faecal excretion of lipids and bile acids, decreased serum and liver TC and TG in this study. Therefore, the hypolipidemic effects of XMF were associated with the efficient regulation of certain genes and increased excretion of lipids and bile acids. The hypolipidemic mechanisms of XMF can be partly elucidated as follows: first, XMF binds bile salts and lipids more efficiently in the intestine; as a result, it decreases the absorption of these chemicals, and then enhances their excretion in faeces more efficiently than does CDF; second, XMF effectively regulates the transcription of certain genes involved in lipid catabolism, positively, such as FXR, I-BABP, CYP7A1, PPARa, PPARc, Lpl and Lpic.
5. Conclusions From this study, it can be concluded that the hypolipidemic effect of XMF was significantly better than that of CDF. XMF displayed potential (to be developed) as a supplementary agent in treatment of hyperlipidemia, with proposed consumption of more than 6 weeks. CDF and XMF lowered TC, mainly by decreasing the LDL-C level. Integrating this with our previous studies (Hu et al., 2008a, 2008b), the hypolipidemic mechanisms of XMF can be elucidated partly as follows: first, XMF binds bile salts and lipids more efficiently in the intestine, and as a result, decreases the absorption of these chemicals, and then enhances their excretion in faeces; second, XMF effectively regulates the transcription of certain genes involved in lipid catabolism, positively.
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References Anna, M. N., Riitta, P. P., Marjukka, A., Kirsi, M., & Oksman, C. (2003). Comparison of antioxidant activities of onion and garlic extracts by inhibition of lipid peroxidation and radical scavenging activity. Food Chemistry, 81, 485–493. Barter, P. (2005). The role of HDL-cholesterol in preventing atherosclerotic disease. European Heart Journal Supplements(Suppl. F), F4–F8. Dong, W.-Y., Zhang, D.-P., Wu, L.-J., Jin, L., Li, P., & Wang, J.-B. (2000). A comparison of study among three dietary fibres on their influences upon serum lipid, excretion and obesity in rats. Journal of the Chinese Cereals and Oils Association, 15, 40–44. Ebihara, K., & Nakamoto, Y. (2001). Effect of the particle size of corn bran on the plasma cholesterol concentration, fecal output and cecal fermentation in rats. Nutrition Research, 21, 1509–1518. Hu, Y.-B., Wang, Z., & Xu, S.-Y. (2008a). Corn bran dietary fibre modified by xylanase improves the mRNA expression of genes involved in lipids metabolism in rats. Food Chemistry, 109, 499–505. Hu, Y.-B., Wang, Z., & Xu, S.-Y. (2008b). Treatment of corn bran dietary fiber with xylanase increases its ability to bind bile salts, in vitro. Food Chemistry, 106, 113–121. Knopp, R. H., Superko, R., Davidson, M., Insull, W., Dujovne, C. A., Kwiterovich, P. O., et al. (1999). Long-term blood cholesterol-lowering effects of a dietary fiber supplement. American Journal of Preventive Medicine, 17, 18–23. Kritchevsky, D., & Tepper, S. A. (2005). Influence of a fiber mixture on serum and liver lipids and on fecal fat excretion in rats. Nutrition Research, 25, 485–489. Lairon, D., Play, B., & Jourdheuil-Rahmani, D. (2007). Digestible and indigestible carbohydrates: Interactions with postprandial lipid metabolism. Journal of Nutritional Biochemistry, 18, 217–227. Li, Y., Hou, M.-J., Tang, Z.-H., & Ling, W.-H. (2004). Effects of dietary fats on cholesterol homeostasis in mice. Chinese Journal of Public Health, 20, 1299–1301.
567
Makishima, M., Okamoto, A. Y., Repa, J. J., Tu, H., Learned, R. M., Luk, A., et al. (1999). Identification of a nuclear receptor for bile acids. Science, 284, 1362–1365. Mezei, O., Banz, W. J., Steger, R. W., Peluso, M. R., Winters, T. A., & Shay, N. (2003). Soy isoflavones exert antidiabetic and hypolipidemic effects through the PPAR Pathways in obese Zucker rats and murine Raw 264.7 cells. Journal of Nutrition, 133, 1238–1243. Queiroz-Monici, K. d. S., Costa, G. E. A., da Silva, N., Reis, S. M. P. M., & de Oliveira, A. C. (2005). Bifidogenic effect of dietary fiber and resistant starch from leguminous on the intestinal microbiota of rats. Nutrition, 21, 602–608. Sanchez-Alonso, I., Haji-Maleki, R., & Borderias, A. J. (2007). Wheat fiber as a functional ingredient in restructured fish products. Food Chemistry, 100, 1037–1043. Saulnier, L., Marot, C., Chanliaud, E., & Thibault, J.-F. (1995). Cell wall polysaccharide interactions in maize bran. Carbohydrate Polymers, 26, 279–287. Shane, J. M., & Walker, P. M. (1995). Corn bran supplementation of a low-fat controlled diet lowers serum lipids in men with hypercholesterolemia. Journal of the American Dietetic Association, 95, 40–45. Sudha, M. L., Vetrimani, R., & Leelavathi, K. (2007). Influence of fibre from different cereals on the rheological characteristics of wheat flour dough and on biscuit quality. Food Chemistry, 100, 1365–1370. Takahashi, N., Kawada, T., Goto, T., Yamamoto, T., Taimatsu, A., Matsui, N., et al. (2002). Dual action of isoprenols from herbal medicines on both PPAR[gamma] and PPAR[alpha] in 3T3-L1 adipocytes and HepG2 hepatocytes. FEBS Letters, 514, 315–322. Thongngam, M., & McClements, D. J. (2005). Isothermal titration calorimetry study of the interactions between chitosan and a bile salt (sodium taurocholate). Food Hydrocolloids, 19, 813–819. Zhang, X. H., Lu, Z. L., & Liu, L. (2008). Coronary heart disease in China. Heart, 94, 1126–1131. Zhang, Z., & Wang, D.-S. (2005). Corn dietary fibre effective on depressing blood lipid for experimental hyperlipaemia mice. Journal of the Chinese Cereals and Oils Association, 20, 120–123.
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Food Chemistry journal homepage: www.elsevier.com/locate/foodchem
Hypolipidemic study of xylanase-modified corn bran fibre in rats Ye-Bi Hu a,b, Xiang-Jin Fu a,b, Feng-Xiang Zhang b, Fu-Min Ma b, Zhang Wang b,*, Shi-Ying Xu b a b
School of Food Science and Engineering, Central South University of Forestry and Technology, No. 498 Shaoshan Road, Changsha 410000, PR China State Key Laboratory of Food Science and Technology, Jiangnan University, Box 98, No.1800 Lihu Road, Wuxi 214036, PR China
a r t i c l e
i n f o
Article history: Received 9 July 2009 Received in revised form 25 January 2010 Accepted 31 March 2010
Keywords: Xylanase modification Corn bran fibre Serum lipids Liver lipids Lipids excretion Hypolipidemic study
a b s t r a c t In order to understand the regulatory effect of xylanase-modified corn bran fibre (XMF) on lipid homeostasis, detailed influences, following the ingestion of XMF and its original form (corn bran dietary fibre, CDF), on serum, liver and faecal lipids were studied in Sprague–Dawley rats. In both CDF and XMF groups, serum total cholesterol (TC), triacylglycerol (TG) and low-density lipoprotein cholesterol (LDL-C) were significantly lowered after 4 weeks (p < 0.05). By the end of week 6, data in the XMF group showed that serum LDL-C was lowered further and high-density lipoprotein cholesterol (HDL-C) was significantly increased (p < 0.05); liver TC, TG and fat were significantly lower (p < 0.05), while the excretions of faecal fat, TC and bile acids were significantly higher (p < 0.05). The decrease of liver and serum lipids in the XMF group was consistent with the improved excretion of faecal lipids and bile acids. Other related mechanisms are also considered. Ó 2010 Published by Elsevier Ltd.
1. Introduction Hyperlipidemia is a risk factor for coronary heart disease (CHD) which is a leading cause of death in the world. In China, CHD has become the second leading cause of cardiovascular death. Elevated levels of blood cholesterol are believed to be a major contributing factor for heart disease (Thongngam & McClements, 2005; Zhang, Lu, & Liu, 2008). Within TC, low-density lipoprotein cholesterol (LDL-C) and very low-density lipoprotein cholesterol (VLDL-C) are the most important actors for coronary heart disease. Highdensity lipoprotein cholesterol (HDL-C) suppresses the ingestion of LDL-C by body cells and transports excessive cholesterol out of cells in the ester form. Thus it prevents the accumulation of cholesterol in the cells (Barter, 2005). However, hyperlipidemia is closely connected with dietary factors. Greater consumption of fruits, vegetables and cereals has been encouraged to reduce the risk of heart disease, partly because these foods contain relatively high levels of dietary fibres, which are believed to help reduce blood cholesterol levels (Kritchevsky & Tepper, 2005; Sanchez-Alonso, Haji-Maleki, & Borderias, 2007; Sudha, Vetrimani, & Leelavathi, 2007). Adding certain dietary fibre sources to mixed test meals, at the level of 4–10 g/meal, can reduce the postprandial triacylglycerol (TG) and total cholesterol (TC) generated by a mixed meal (Lairon, Play, & Jourdheuil-Rahmani, 2007).
* Corresponding author. Tel./fax: +86 510 85884496. E-mail address: [email protected] (Z. Wang). 0308-8146/$ - see front matter Ó 2010 Published by Elsevier Ltd. doi:10.1016/j.foodchem.2010.03.131
Corn bran has a higher dietary fibre content than have wheat and rice brans (Wang & Liu, 2000), in which about 40% is heteroxylan (Saulnier, Marot, Chanliaud, & Thibault, 1995). Shane and Walker (1995) reported that corn fibre supplementation of controlled low-fat diet in men with hypercholesterolemia resulted in lowering of serum TC, TG and VLDL-C, while serum LDL-C and high-density lipoprotein cholesterol (HDL-C) concentrations were not significantly altered. Corn bran fibre, hydrolysed by a-amylase, was also found to lower plasma and liver cholesterol concentrations significantly in rats (Ebihara & Nakamoto, 2001). The addition of a corn dietary fibre prepared by a-amylase and alkali proteinase hydrolysis, lowered the levels of serum TC and TG, and increased the HDL-C (Zhang & Wang, 2005). However, the hypolipidemic mechanism of corn bran fibre is still unclear. In our previous study, corn bran fibre, modified by xylanase (XMF), positively regulated the mRNA expression of several genes involved in lipid catabolism in rats, e.g. the farnesoid X receptor (FXR), cholesterol 7 alpha-hydroxylase (CYP7A1), lipoprotein lipase (Lpl), hepatic lipase (Lipc), peroxisome proliferatoractivated receptors (PPARa and PPARc) and intestine-bile acidbinding protein (I-BABP) (Hu, Wang, & Xu, 2008a). Furthermore, XMF could bind bile acids more than could CDF in vitro (Hu, Wang, & Xu, 2008b). In order to understand the hypolipidemic mechanisms of XMF, it is necessary to investigate the changes of serum and liver lipids and the excretion of faecal lipids after the ingestion of XMF. Therefore, the purpose of this study was to explore detailed effects of XMF in rats with atherogenic diet-induced hyperlipidemia on the changes of serum, liver and faecal lipids after
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feeding; and then explore the hypolipidemic mechanisms of XMF on the basis of the present and our previous results. 2. Methods and materials 2.1. Chemicals Corn bran was provided by Dancheng Caixin Group Co. Ltd. (Henan, PR China) and was milled through a 250 lm screen (Ebihara & Nakamoto, 2001); then CDF was processed as we reported previously (Hu et al., 2008b). Xylanase (NCB 77, 8000 IU/g, from Bacillus subtilis, main enzyme activity EC 3.2.1.8) was supplied by Hunan New Century Biochemical Co. Ltd., Hunan, PR China. TG, TC, and high-density lipoprotein cholesterol (HDL-C) kits were purchased from Zhejiang Dongou Bioengineering Co. Ltd., Ningbo, China. 2.2. Xylanase-modified corn bran fibre (XMF) According to the results by Ebihara and Nakamoto (2001), corn bran fibre of particle size 250 lm is enough for the benefits of corn bran fibre on lipid metabolism and intestinal functions; therefore, a particle size of 250 lm was chosen for the preparation of CDF and XMF in this study. Xylanase was added at a rate of 7 g/kg of CDF to a container with 8 l of 50 mM phosphate buffer (pH 5.3). Eight hundred grammes CDF were added to the freshly prepared xylanase enzyme solution. The reaction mixture was incubated in a super water bath thermostatic vibrator (Model 501, Shanghai Experimental instrument Co., Shanghai, PR China) at 50 °C with 145 rpm agitation for 105 min, and the reactants worked up to obtain XMF as reported earlier (Hu et al., 2008b).
Table 1 Components of animal diets (%).
Corn powder Soy bean pomace Lard Fish powder Cellulose Flour CaHPO4 CaCO3 Lysine Methionine Choline Mineral mixtureb Vitamin mixturec NaCl Cholesterol Sodium cholate Yolk powder CDF XMF
NFa
HF
CDF
XMF
35.5 21.6 2 2 10 26 1 1.3 0.12 0.13 0.1 0.03 0.02 0.2 – – – – –
30 20 15 4 3 13.8 1 1.1 0.12 0.13 0.1 0.03 0.02 0.2 2 0.5 9 – –
25 20 15 4 – 11.8 1 1.1 0.12 0.13 0.1 0.03 0.02 0.2 2 0.5 9 10 –
25 20 15 4 – 11.8 1 1.1 0.12 0.13 0.1 0.03 0.02 0.2 2 0.5 9 – 10
a NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF (corn bran fibre), treatment of CDF; XMF, HF diet with an addition of 10% of XMF (xylanase-modified corn bran fibre), treatment of XMF. b AIN-76 mineral mixture contained (in g/kg of mixture): calcium phosphate, dibasic 500.0; sodium chloride, 74.0; potassium citrate, monohydrate, 220.0; potassium sulphate, 52.0; magnesium oxide, 24.0; manganous carbonate, 3.5; ferric citrate, 6.0; zinc carbonate, 1.6; cupric carbonate, 0.3; potassium iodate, 0.01; sodium selenite, 0.01; chromium potassium sulphate, 0.55; sucrose, finely powdered, 118.03. c AIN-76A vitamin mixture contained (in g/kg of mixture): thiamine HCl, 0.6; riboflavin, 0.6; pyridoxine HCl, 0.7: niacin, 3.0; calcium-D pantothenate, 1.6; folic acid, 0.2: D-biotin, 0.02; cyanocobalamin (vitamin B12), 1.0; dry vitamin A palmitate (500,000 U/g), 0.8; dry vitamin E acetate (500 U/g), 10.0; vitamin D3 trituration (400,000 U/g), 0.25; menadione sodium bisulphite complex, 0.15; sucrose, fine powder, 981.08.
2.3. Animals and diets The Jiangnan University (Jiangsu, China) Animal Care and Use Committee approved all rat studies. All rats, weighing 100 ± 10 g (male Sprague–Dawley, from Shanghai Slac Laboratory Animal Co. Ltd., Shanghai, PR China) were placed individually in stainless steel wire mesh cages in a room maintained at 23 ± 2.0 °C, with relative humidity of 55 ± 10%, and a daily photoperiod from 7:00 am to 7:00 pm. Rats consumed food and water ad libitum and were acclimatised to the conditions for 1 week. All were then randomly assigned to NF (negative control), HF (positive control), CDF (treatment of CDF) or XMF (treatment of XMF) groups with eight rats per group. Rats in the NF and HF groups were fed with basic feed (NF diet) and an atherogenic diet (HF diet), respectively, for 6 weeks. The rats of CDF or XMF groups were fed HF diet, for 2 weeks first, and then changed to the CDF or XMF diet, respectively, for 4 weeks. The components of diets were as shown in Table 1. HF diet was an atherogenic diet. Cholesterol, sodium cholate, yolk powder and basic feed were purchased from Shanghai Slac Laboratory Animal Co. Ltd., Shanghai, PR China. Lard was purchased from a local market in Wuxi, PR China. Food intake was recorded daily, while body weight was recorded weekly.
Arteriosclerosis index (AI) was calculated as described by Queiroz-Monici, Costa, da Silva, Reis, and de Oliveira (2005):
AI ¼
TC ðHDL-CÞ HDL-C
in which, TC is serum total cholesterol; HDL-C is high-density lipoprotein cholesterol. Aliquots of liver were extracted with chloroform–methanol 2:1 and the lipid extract was analysed for TC, TG and fat (Kritchevsky & Tepper, 2005). Faeces were collected on day 42 and vacuum-dried. Extraction of lipids and the analysis of fat in faeces were done according to Hsu et al. (2006). TC and bile acids in faeces were determined using appropriate commercially available kits. 2.5. Statistical analysis The statistical analyses were done using SPSS 13.0 for Windows software (SPSS Institute Inc., Cary NC). Comparison of the means was done by one-way ANOVA using the honestly significant difference (HSD) of Tukey’s ad hoc test. Significance level was 0.05. 3. Results
2.4. Sampling and analytical procedures 3.1. Food intake, growth and body fat On days 0, 14 and 28, blood samples were drawn from the tail vein. Serum was analysed for TC, TG and HDL-C using appropriate commercially available kits. LDL-C was calculated according to the Friedwald equation (Anna, Riitta, Marjukka, Kirsi, & Oksman, 2003). On day 42, rats were weighed and sedated by barbiturate injection. They were exsanguinated, and the livers were removed and weighed. Serum was analysed for TC, TG, HDL-C and LDL-C.
All groups started with similar mean body weights of 150 ± 10 g (Table 2). All rats gained weight during the study. The body weight gain in rats fed the XMF diet was significantly lower than that in rats fed the HF diet (p < 0.05, Table 2), but close to that in the NF group (p > 0.05). The difference of body weight gains between the CDF and the HF group did not reach statistical significance
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Y.-B. Hu et al. / Food Chemistry 123 (2010) 563–567 Table 2 Necropsy data on rats (eight per group) fed NF or HF or test fibre diets for 42 days (mean ± SD). NFf Food intake (g/rat day) Body weight gain (BW) (g/rat day) Liver weight (g/100 g BW) Epididymal fat (g/100 g BW) AIe Liver lipids TC (lmol/g) TG (lmol/g) Fat (%)
HF
CDF
XMF
a
23.65 ± 0.95 5.48 ± 0.48a 4.08 ± 0.34a 1.16 ± 0.11a 0.89 ± 0.41a
a
a
23.67 ± 0.49 6.23 ± 0.52b 6.24 ± 0.26c 1.89 ± 0.14c 8.27 ± 1.36d
25.24 ± 3.76 5.98 ± 0.90ab 5.79 ± 0.40bc 1.52 ± 0.24b 5.82 ± 1.28c
26.04 ± 3.36a 5.30 ± 0.83a 5.41 ± 0.58b 1.47 ± 0.28b 2.54 ± 0.48b
8.37 ± 0.58a 5.75 ± 0.98a 5.27 ± 0.03a
87.4 ± 7.02c 50.2 ± 5.17c 25.7 ± 0.29d
81.2 ± 12.19c 44.0 ± 4.04c 19.1 ± 0.41c
47.2 ± 2.30b 33.1 ± 2.06b 17.6 ± 0.29b
a,b,c,d
Same superscript letters in a row show values that do not differ significantly (p > 0.05, n = 8). AI, arteriosclerosis index; TC, total cholesterol; TG, total triacylglycerol. f NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF treatment of CDF; XMF, HF diet with an addition of 10% of XMF treatment of XMF. e
(p > 0.05). The food intake in the HF group was similar to that in the NF group. As compared with the NF group, the food intake ratio in the groups to which CDF and XMF were added was increased by 6.7% and 10.1%, respectively (Table 2). The HF diet significantly elevated the weight of epididymal fat by 63% as compared with the NF diet (p < 0.05, Table 2). The epididymal fat in rats fed the CDF and XMF diet was significantly lower than in those fed the HF diet (p < 0.05, Table 2). The liver weight of rats in the XMF group was significantly lower than that of rats in the HF group (p < 0.05), and that in the CDF group was also somewhat lower, however, insignificantly (p > 0.05, Table 2). 3.2. Time course of serum lipids At the start, TC was almost the same in all groups of rats (Fig. 1a). TC level in rats fed the NF diet did not change apparently
TC (mM)
NF HF C DF CDF XM F XMF
d c
NF HF C DF CDF XM F XMF
c
b
b
a
b
b
b
a
a
TG (mM)
a
from week 1 to week 6. By contrast, TC in rats fed the HF diet increased nearly linearly during the whole experiment for 42 days. After 2 weeks of CDF and XMF feeding, TC values in the CDF and XMF groups were significantly lower than those in the HF group (p < 0.05, Fig. 1a). At the end of the 6th week, there was no increase in TC for rats fed the XMF diet, while TC in rats fed the CDF diet increased further as compared with the end of the 4th week. For serum TG, there were no significant differences on week 0 in the four groups (p > 0.05, Fig. 1b), and there were no apparent changes in rats fed the NF diet throughout the 6 weeks programme. However, TG in rats fed the HF diet was highly elevated within 2 weeks of feeding time. In rats fed the CDF and XMF diets, serum TG was always higher than in rats fed the NF diet after the end of the 2nd week but was significantly lower than that in rats fed the HF diet (p < 0.05), and there was no prominent increase from weeks 2 to 6 (Fig. 1b).
c
c
b
b
b
a
0
2
6
4
0
d
2
4
6
1.8
b
1.6 1.4
c
c
b
b
b a
a
2
d
4
Time (weeks)
6
HDL-C (mM)
LDL-C (mM)
NF HF CDF CDF XM F XMF
0
a
a
Time (weeks)
Time (weeks)
c
b
b
1.2
a
1
a
0.8 0.6 0.4
CDF XM F
0.2 0
0
2
NF HF CDF XMF 4
a
6
Time (weeks)
Fig. 1. Time course of serum lipids expressed as a function of (a) cholesterol (TC), (b) triacylglycerol (TG), (c) low-density cholesterol (LDL-C), (d) high-density cholesterol (HDL-C). NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF treatment of CDF; XMF, HF diet with an addition of 10% of XMF treatment of XMF. Rats in the NF group were fed NF diet all the time; rats in the HF group were fed HF diet all the time. Rats in the CDF and XMF groups were fed HF diet in the first 2 weeks, then changed to CDF and XMF diets, respectively, and fed for 4 weeks. Each point is the mean ± SD of eight rats; values at each time point with different letters are significantly different (p < 0.05).
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Table 3 Excretion of fat, TC and bile acids in faeces (mean ± SD, mg/rat day). NFe Fat TC Bile acids
HF a
0.115 ± 0.02 1.41 ± 0.17a 45.5 ± 3.11a
CDF b
0.299 ± 0.04 19.9 ± 1.89b 47.0 ± 6.71a
XMF b
0.424 ± 0.04 53.8 ± 6.32c 82.6 ± 8.53c
0.697 ± 0.06c 76.3 ± 6.45d 114 ± 14.3d
a,b,c,d
Same superscript letters in a row show values that do not differ significantly (p > 0.05, n = 8). e NF, basic diet, negative control; HF, atherogenic diet, positive control; CDF, HF diet with an addition of 10% of CDF treatment of CDF; XMF, HF diet with an addition of 10% of XMF treatment of XMF.
LDL-C was stable in rats fed the NF diet, but increased rapidly over time in rats fed the HF diet (Fig. 1c). As compared with the HF diet, the addition of CDF and XMF effectively decreased serum LDL-C level at the end of week 4 (Fig. 1c). XMF was more efficient than was CDF because the LDL-C in rats fed the XMF diet was lowered further at the end of week 6 (Fig. 1c). There was a slight decrease of HDL-C in rats fed the HF and CDF diets at the end of week 6, but this was insignificant when compared with that in rats fed the NF diet (p > 0.05, Fig. 1d). While HDL-C level increased significantly in rats fed with the XMF diet (p < 0.05, Fig. 1d), AI in the HF group was 9.3-fold to that in the NF group. The addition of CDF and XMF decreased AI to 70.4% and 30.7% of that in the HF group with a significance of p < 0.05, respectively (Table 2). 3.3. Liver lipids There was a tendency for the CDF diet to suppress the increase of liver TG and TC, while the level of liver fat in rats fed the CDF diet was significantly lower than that in rats fed the HF diet (p < 0.05, Table 2). On the other hand, the levels of liver TG, TC and fat in the rats fed the XMF diet were all significantly lower than those in the rats fed the CDF diet (p < 0.05). 3.4. Excretion of fat, TC and bile acids The content of faecal lipids indicated the excretion levels of these lipids by animals. Fat excretions in the CDF and XMF groups were 1.42 and 2.33 times those of the HF group, respectively (Table 3). The excretion of fat was significantly increased in rats fed the XMF diet (p < 0.05). The excretion of TC in rats fed the XMF diet was significantly higher than that in rats fed the CDF diet (p < 0.05); the amount of the former was 1.4 times that of the latter. Bile acids excretion in the XMF group was also 1.4 times that in CDF group with a significance of p < 0.05. 4. Discussion Supplementing a low-fat diet with corn bran was effective in reducing the serum lipid concentration in men with hypercholesterolemia (Shane & Walker, 1995). In type II diabetes patients, consumption of corn bran lowered the plasma VLDL-C level. On the other hand, consumption of corn bran did not reduce the plasma cholesterol concentration in 10 healthy men (Ebihara & Nakamoto, 2001). A fibre supplement containing corn bran provided significant and sustained reductions in LDL-C without reducing HDL-C or increasing TG in subjects with mild to moderate hypercholesterolemia (Knopp et al., 1999). In this study, CDF and XMF could enhance the catabolism of energy or suppress the absorption of energy, and XMF is more efficient than is CDF, suppressing the accumulation of fat in rats, even though rats fed these diets consumed more food. Dong et al. (2000) also reported lowered TC and TG by use of corn bran fibre extracted by amylase on male Wister rats at a 100 g/kg addition for 3 weeks.
CDF was more efficient in suppressing the increase of serum TG than of TC, while XMF suppressed the serum TG and TC efficiently at the same time. When feeding time was continued for 6 weeks, the serum TC in the XMF group was stable and LDL-C was lowered further, as compared with the end of week 4. However, the serum TC and LDL-C values in the CDF group were increased apparently from the end of week 4 to week 6. Furthermore, ingestion of XMF for 6 weeks increased the HDL-C level and, as a result, decreased AI under the HF diet. Therefore, the hypolipidemic effect of XMF was significantly better than that of CDF. Within the total cholesterol, LDL-C and VLDL-C are the most important mediators for coronary heart disease (Barter, 2005). The changes of LDL-C in each group were similar to that of TC, this might indicate that the main cause of hypercholesterolemia was the high level of LDL-C in this study. During the 6 week feeding period, the studied dietary fibre CDF and XMF lowered TC, mainly by decreasing the LDL-C level. However, in this study, the high lipid diet did not lower HDL-C in rats significantly, as reported elsewhere, and only the HDL-C in rats fed the XMF diet was increased significantly (p < 0.05) (Dong et al., 2000). XMF could bind more bile acids than CDF in vitro (Hu et al., 2008b). Significantly increased excretion of faecal fat and TC indicated that XMF prevented the absorption of fat and TC in the intestine, enhanced their decomposition more efficiently, and then decreased the levels of liver and serum TC and TG. The homeostasis of TC and LDL-C is regulated by several genes, such as FXR, I-BABP, CYP7A1 and PPARs (Makishima et al., 1999; Mezei et al., 2003). Up-regulation of ileum FXR and hepatic CYP7A1 expression and down-regulation of I-BABP and hepatic FXR enhance the catabolism of cholesterols by depressing the enterohepatic transport of bile acids (Li, Hou, Tang, & Ling, 2004; Makishima et al., 1999). Up-regulation of the transcription of PPARa, PPARc, Lpl and Lpic improve the catabolism of triacylglycerols by reducing the rates of lipogenesis and enhancing lipid hydrolysis (Takahashi et al., 2002; Anonymous, 2007-01-03 20:00). It was reported that XMF up-regulated the transcription of CYP7A1, PPARa, PPARc, Lpl, Lipc and, down-regulated the transcription of I-BABP more efficiently than did CDF (Hu et al., 2008a). Such results were consistent with the increased faecal excretion of lipids and bile acids, decreased serum and liver TC and TG in this study. Therefore, the hypolipidemic effects of XMF were associated with the efficient regulation of certain genes and increased excretion of lipids and bile acids. The hypolipidemic mechanisms of XMF can be partly elucidated as follows: first, XMF binds bile salts and lipids more efficiently in the intestine; as a result, it decreases the absorption of these chemicals, and then enhances their excretion in faeces more efficiently than does CDF; second, XMF effectively regulates the transcription of certain genes involved in lipid catabolism, positively, such as FXR, I-BABP, CYP7A1, PPARa, PPARc, Lpl and Lpic.
5. Conclusions From this study, it can be concluded that the hypolipidemic effect of XMF was significantly better than that of CDF. XMF displayed potential (to be developed) as a supplementary agent in treatment of hyperlipidemia, with proposed consumption of more than 6 weeks. CDF and XMF lowered TC, mainly by decreasing the LDL-C level. Integrating this with our previous studies (Hu et al., 2008a, 2008b), the hypolipidemic mechanisms of XMF can be elucidated partly as follows: first, XMF binds bile salts and lipids more efficiently in the intestine, and as a result, decreases the absorption of these chemicals, and then enhances their excretion in faeces; second, XMF effectively regulates the transcription of certain genes involved in lipid catabolism, positively.
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References Anna, M. N., Riitta, P. P., Marjukka, A., Kirsi, M., & Oksman, C. (2003). Comparison of antioxidant activities of onion and garlic extracts by inhibition of lipid peroxidation and radical scavenging activity. Food Chemistry, 81, 485–493. Barter, P. (2005). The role of HDL-cholesterol in preventing atherosclerotic disease. European Heart Journal Supplements(Suppl. F), F4–F8. Dong, W.-Y., Zhang, D.-P., Wu, L.-J., Jin, L., Li, P., & Wang, J.-B. (2000). A comparison of study among three dietary fibres on their influences upon serum lipid, excretion and obesity in rats. Journal of the Chinese Cereals and Oils Association, 15, 40–44. Ebihara, K., & Nakamoto, Y. (2001). Effect of the particle size of corn bran on the plasma cholesterol concentration, fecal output and cecal fermentation in rats. Nutrition Research, 21, 1509–1518. Hu, Y.-B., Wang, Z., & Xu, S.-Y. (2008a). Corn bran dietary fibre modified by xylanase improves the mRNA expression of genes involved in lipids metabolism in rats. Food Chemistry, 109, 499–505. Hu, Y.-B., Wang, Z., & Xu, S.-Y. (2008b). Treatment of corn bran dietary fiber with xylanase increases its ability to bind bile salts, in vitro. Food Chemistry, 106, 113–121. Knopp, R. H., Superko, R., Davidson, M., Insull, W., Dujovne, C. A., Kwiterovich, P. O., et al. (1999). Long-term blood cholesterol-lowering effects of a dietary fiber supplement. American Journal of Preventive Medicine, 17, 18–23. Kritchevsky, D., & Tepper, S. A. (2005). Influence of a fiber mixture on serum and liver lipids and on fecal fat excretion in rats. Nutrition Research, 25, 485–489. Lairon, D., Play, B., & Jourdheuil-Rahmani, D. (2007). Digestible and indigestible carbohydrates: Interactions with postprandial lipid metabolism. Journal of Nutritional Biochemistry, 18, 217–227. Li, Y., Hou, M.-J., Tang, Z.-H., & Ling, W.-H. (2004). Effects of dietary fats on cholesterol homeostasis in mice. Chinese Journal of Public Health, 20, 1299–1301.
567
Makishima, M., Okamoto, A. Y., Repa, J. J., Tu, H., Learned, R. M., Luk, A., et al. (1999). Identification of a nuclear receptor for bile acids. Science, 284, 1362–1365. Mezei, O., Banz, W. J., Steger, R. W., Peluso, M. R., Winters, T. A., & Shay, N. (2003). Soy isoflavones exert antidiabetic and hypolipidemic effects through the PPAR Pathways in obese Zucker rats and murine Raw 264.7 cells. Journal of Nutrition, 133, 1238–1243. Queiroz-Monici, K. d. S., Costa, G. E. A., da Silva, N., Reis, S. M. P. M., & de Oliveira, A. C. (2005). Bifidogenic effect of dietary fiber and resistant starch from leguminous on the intestinal microbiota of rats. Nutrition, 21, 602–608. Sanchez-Alonso, I., Haji-Maleki, R., & Borderias, A. J. (2007). Wheat fiber as a functional ingredient in restructured fish products. Food Chemistry, 100, 1037–1043. Saulnier, L., Marot, C., Chanliaud, E., & Thibault, J.-F. (1995). Cell wall polysaccharide interactions in maize bran. Carbohydrate Polymers, 26, 279–287. Shane, J. M., & Walker, P. M. (1995). Corn bran supplementation of a low-fat controlled diet lowers serum lipids in men with hypercholesterolemia. Journal of the American Dietetic Association, 95, 40–45. Sudha, M. L., Vetrimani, R., & Leelavathi, K. (2007). Influence of fibre from different cereals on the rheological characteristics of wheat flour dough and on biscuit quality. Food Chemistry, 100, 1365–1370. Takahashi, N., Kawada, T., Goto, T., Yamamoto, T., Taimatsu, A., Matsui, N., et al. (2002). Dual action of isoprenols from herbal medicines on both PPAR[gamma] and PPAR[alpha] in 3T3-L1 adipocytes and HepG2 hepatocytes. FEBS Letters, 514, 315–322. Thongngam, M., & McClements, D. J. (2005). Isothermal titration calorimetry study of the interactions between chitosan and a bile salt (sodium taurocholate). Food Hydrocolloids, 19, 813–819. Zhang, X. H., Lu, Z. L., & Liu, L. (2008). Coronary heart disease in China. Heart, 94, 1126–1131. Zhang, Z., & Wang, D.-S. (2005). Corn dietary fibre effective on depressing blood lipid for experimental hyperlipaemia mice. Journal of the Chinese Cereals and Oils Association, 20, 120–123.