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Unilever Health Institute, Unilever R & D, Vlaardingen, The Netherlands
2To whom correspondence should be addressed. E-mail: Yuguang.Lin{at}unilever.com.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • cholesterol • hamsters • isoflavones • plant sterol esters • soy protein
An elevated plasma total cholesterol concentration and especially, LDL cholesterol, increases the risk of coronary heart disease (CHD)3 (1). Lowering plasma cholesterol concentration by medication has been shown to reduce CHD events and mortality from CHD (2). In addition to medication, plasma cholesterol concentration can also be reduced by naturally occurring dietary components, e.g., plant sterols and soy protein (3–6). The U.S. FDA recently endorsed health claims that food products containing adequate amounts of plant sterols/stanols (7) or soy protein (8) may reduce CHD risk. However, it is unclear whether a combination of plant sterols and soy protein would have an additive, synergistic or negative effect on their individual cholesterol-lowering abilities. These data are crucial in guiding the treatment of hyperlipemia via dietary approaches.
Plant sterols have molecular structures similar to that of cholesterol. Compared with cholesterol, plant sterols have an extra methyl or ethyl group and a double bond in the side chain. It is hypothesized that plant sterols inhibit intestinal cholesterol absorption through competition with cholesterol for incorporation into micelles formed in the intestinal lumen (9) and interference with the uptake of cholesterol into enterocytes, although the exact mechanisms of action remain to be fully elucidated (10). Compared with plant sterols, soy protein may lower plasma cholesterol via other mechanisms. Several possible mechanisms proposed for soy protein include a decrease in the intestinal absorption of cholesterol and/or bile acids (11,12), increased plasma cholesterol clearance through enhancing hepatic LDL-receptor activity (13,14) and changes in hepatic biotransformation of cholesterol (15). Because plant sterols and soy protein have different biological actions, the combination of these two dietary ingredients may lead to a more powerful cholesterol-lowering effect.
The present study examined the hypocholesterolemic effect of the combination of plant sterols and soy protein. Compared with unesterified plant sterols, plant sterol ester (PSE) are more fat soluble and thus easier to incorporate into food products, e.g., margarine (3). PSE have a similar or even stronger cholesterol-lowering effect compared with unesterified plant sterols (16). Therefore, PSE were used in the present study. Additionally, the component(s) responsible for the cholesterol-lowering effect of soy protein are unclear. Several studies demonstrated that soy protein itself (including soy peptides) has cholesterol-lowering activity (17). In contrast, other studies (18–20), but not all (21,22) demonstrated that soy isoflavones, i.e., genistein and daidzein, may cause the beneficial effect of soy protein. Because soy isoflavones might be the bioactive components in soy protein, we also investigated the combined effect of PSE and soy isoflavones. This study was conducted in Syrian golden hamsters, an established animal model based on their similarities in cholesterol and bile acid metabolism to humans (23,24).
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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75 g were obtained from Charles River Laboratories, Wilmington, MA. After 1 wk of acclimation, 120 hamsters were allocated to 6 similar groups (n = 20 per group) on the basis of their body weight. The hamsters were housed individually in Makrolon II cages with a layer of sawdust as bedding. Hamsters were kept in an environmentally controlled room (temperature 22–25°C and relative humidity 55%) with a 12-h light:dark cycle (lights on 0700–1900h). Throughout the study, the hamsters had free access to food and drinking water. Clinical observation and body weight measurement were conducted once a week. Food consumption was measured during two consecutive days every 2 wk. Experimental protocols and procedures were approved by the Animal Care Committee of Unilever, the Netherlands. Test compounds. PSE were prepared by esterifying soy plant sterols with fatty acids from rapeseed oil (esterification degree of >92%) (Unilever Research, Vlaardingen, NL). The fatty acid composition of rapeseed oil (g/100 g) was 16:0, 6.7; 18:0, 3.4; 18:1, 23.3; 18:2, 62.4; 18:3, 0.5 and others (<16:0 and >18:0), 3.9. The composition of PSE, as expressed in the unesterified form (g/100g), was ß-sitosterol 46.7; ß-sitostanol, 1; campesterol, 26.9; stigmasterol, 18.3; brassicasterol, 2.7; and other plant sterols, 4.4. The soy protein was a Supro soy protein isolate which contained (per 100 g) 87 g protein, 5.7 g moisture, 98 mg isoflavones (expressed as aglycones, genistein, 62 mg; daidzein, 31 mg; and glycitein, 7 mg); the remainder (7.2 g) was made up of carbohydrates, fat and ash (PTI Technologies, St. Louis, MO). The commercial soy isoflavone product Novasoy-400 was used as the isoflavone concentrate (Novasoy, Archer Daniels Midland Company, Decatur, IL). One gram of Novasoy-400 contains 352 mg isoflavones (the remainder was moisture, carbohydrate, protein, fat and ash). The composition of Novasoy-400 soy isoflavones (g/100 g) was genistein, 53; daidzein, 39; and glycitein, 8. Although isoflavones in both Novasoy-400 and soy protein were mainly in the glucosylated form, they are expressed in aglycone units in this study.
Diets. During the adaptation period, hamsters were fed a semipurified diet based on the AIN-93 rodent diet (25). During the experimental period, hamsters were fed six different diets for 5 wk. Fat contributed 30% to the total dietary energy, in which SFA, monounsaturated fatty acids and PUFA contributed 16.8, 8.5 and 4.7% of total dietary energy, respectively. The composition of the dietary fat resembled that in a typical Western diet. The composition of the mineral mix and the vitamin mix were described in detail previously (25). The experimental diets (g/100 g) contained cholesterol, 0.08 and dietary protein, 20. Soy protein isolate (20 g) contributed only 2.6 mg of plant sterols to each 100 g of diet; this was a negligible amount compared with the quantity of PSE (0.24 g) added to the same amount of diet. The detailed compositions of the experimental diets are shown in Table 1. These diets were designed to be identical in composition except for protein type and isoflavone or PSE contents. To ensure homogenous mixing of the diets, cholesterol and PSE were incorporated into the fat blend at 60°C in a water bath. The warmed fat was mixed with other dietary ingredients which were prewarmed to 60°C in an oven. Soy isoflavones (Novasoy-400) were premixed with small amounts of starch before they were mixed with other diet components.
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16 h) and then exsanguinated under anesthesia using a gaseous mixture of N2O, O2 and halothane. Orbital blood samples were collected in EDTA tubes/4 mL and centrifuged at 3000 x g for 10 min to obtain plasma. The liver was excised and gallbladder bile was aspirated through puncture. Aliquots of the liver were used for determination of hepatic cholesterol and LDL-receptor abundance. Plasma lipid and lipoprotein analysis. Plasma total cholesterol (TC) and triacylglycerol (TG) concentrations were determined enzymatically with commercial assay kits (CHOD-PAP and GPO-PAP method, Roche Diagnostics, Basel, Switzerland) using a COBAS Mira S automated analyzer (Roche Diagnostics). The assay procedures were according to the manufacturers’ instructions. Lipoprotein fractions were isolated from 0.6 mL plasma by sequential ultracentrifugation at 627,000 x g for 90 min based on the following densities: VLDL (d < 1.006 kg/L), LDL (1.006 < d <1.055 kg/L), HDL (1.055 < d < 1.021 kg/L). TC in all the lipoprotein fractions and TG in VLDL were measured as described above.
Hepatic cholesterol analysis.
Lipids in liver samples (250 mg) were extracted according to the modified method of Bligh and Dyer (26), in which chloroform was substituted by dichloromethane. TC was determined as described above and free cholesterol (FC) was analyzed by HPLC. The concentration of cholesterol esters (CE) was calculated as the difference between TC and FC.
Determination of hepatic LDL-receptor abundance. Hepatic microsomes were isolated by ultracentrifugation at 100,000 x g for 60 min as previously described (27) and stored at –80°C. Microsomal protein was determined using a modified Lowry procedure (28). Hepatic LDL-receptor abundance was determined by ELISA as described by May at al (29). Polyclonal rabbit anti-rat hepatic LDL-receptor antibody was a gift from Dr. Roach (CSIRO Health Sciences and Nutrition, Adelaide, Australia). This antibody had been demonstrated in our laboratory to cross against hamster hepatic LDL-receptor. Goat anti-rabbit IgG antibody conjugated with peroxidase was provided by Sigma-Aldrich (Zwijndrecht, the Netherlands). The amount of anti-LDL-receptor antibody specifically bound to the hepatic membrane was determined by measuring absorbance. The LDL-receptor abundance/mg liver cell-membrane protein was expressed as arbitrary units, which were the values of the absorbance measured by ELISA.
Analysis of fecal sterols and bile acids.
Fecal sterols and total bile acids were first extracted from dried feces according to the following procedures. An aliquot of dried feces (10 mg) was used for the extraction of fecal sterols. After the addition of 5
-cholestane (Sigma-Aldrich), the sample was hydrolyzed with sodium hydroxide in methanol for 2 h at 80°C. After cooling down to ambient temperature, the saponified sample was extracted using hexane. Before GC, the sample was derivatized using bis(trimethylsilyl)trifluoroacetamide (Pierce, Rockford, IL). GC analyses were carried out using a CP-SIL 5CB column (50 m, 0.25 mm i.d., 0.12-µm film thickness, Varian-Chrompack, Middelburg, the Netherlands). An on-column injector and hydrogen gas as carrier were used. The temperature program started at 90°C. After an initial hold of 1 min, the oven was programmed to 285°C (30 min) at a rate of 15°C/min. Finally, the oven was programmed to 345°C (8 min) at a rate of 15°C/min. Detection was with a flame ionization detector. Sterol peak identification was based on retention times using model components and confirmed by MS identification. The MS identification was performed in the full-scan electron ionization mode (70 eV) using a scan window of 50–600 amu (HP5973 mass selective detector, Hewlett-Packard, Waldborn, Germany). Characteristic peaks are the molecular ions of the silylated compounds and the characteristic M-15 ion.
Fecal bile acid concentration was determined by TNO, Leiden, The Netherlands (30). An aliquot of dried feces (5 mg) was used for the extraction of bile acids. The methodology for the extraction of bile acids and hydrolysis of conjugated bile acids was reported previously (30). Bile acids were derivatized by incubation with 50 µL trifluoroacetic anhydride and 30 µL 1,1,1,3,3,3-hexafluoro-2-propanol for 1 h at 60°C. The bile acid derivatives were separated on a 25 m x 0.25 mm capillary GC column (CP Sil 5B, Chrompack International) in a 3800 GC gas chromatograph (Varian) equipped with a flame ionization detector. The injector and the flame ionization detector were kept at 300°C. The column temperature was programmed from 230 to 280°C. Bile acid derivatives were introduced by split injection (split ratio, 20:1). Quantification was based on the area ratio of the individual bile acid to the internal standard.
Statistical analysis.
Previous data showed that the SD of plasma cholesterol concentration in hamsters was 0.2 mmol/L. Based on a power calculation, 20 hamsters/group will provide 80% power with = 0.05 to detect a significant difference of 10% in TC concentrations between the treatment and control groups. Data are presented as the means ± SEM. Differences were assessed for statistical significance using two-way ANOVA. Student-Newman-Keuls test was used to assess the differences between the groups of treatments. This statistical analysis was conducted by using software SAS (version 6.12). Significant difference was based on a two-sided P-value < 0.05.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Plasma lipid concentrations. After 5 wk of feeding, the PSE and soy protein diets reduced plasma TC by 13 and 9%, respectively, compared with the control diet, whereas the isoflavone-diet had no effect (Table 2). The combination of PSE and soy protein in the diet resulted in a 26% decrease in plasma TC. The treatment-induced decrease in plasma cholesterol occurred mainly in the VLDL + LDL (non-HDL) fractions (Table 2). PSE plus isoflavones did not lower plasma cholesterol more than did PSE alone. The plasma TG concentrations were not influenced by the diets containing PSE, soy protein or isoflavones alone, whereas the combination of PSE and soy protein in the diet significantly reduced plasma TG by 37% compared to the control diet (Table 2).
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Liver weight, hepatic cholesterol and LDL-receptor abundance. In hamsters fed PSE, soy protein and the combination of these two components, hepatic TC was significantly lower than in controls (Table 3). Only in hamsters fed diets containing both PSE and soy protein was the relative hepatic CE concentration significantly decreased, whereas the relative hepatic CE concentrations in hamsters fed the other diets, including the control diet did not differ. In addition, the relative liver weight of hamsters fed the diet containing PSE plus soy protein was significantly lower than those of the control and other treatment groups. These data indicate that less fat was accumulated in the liver of hamsters fed PSE + soy protein. The hepatic LDL-receptor abundance did not differ between groups.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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An unexpected finding was that the combination of PSE and soy protein had such a strong lipid-lowering effect. First, PSE at the dose of 0.24 g/100 g diet was reported to reach a maximal cholesterol-lowering effect of 15% in hamsters (31), similar to the value in our study. The combination of PSE with soy protein lowered plasma total cholesterol concentration by 26%, which is greater than the combined effect of these two ingredients given individually (8% + 13%, respectively). Second, the combination of PSE and soy protein significantly lowered plasma TG concentration by 37%, whereas PSE and soy protein alone had no effect. Because an increase in plasma TG concentration is considered to be an independent risk factor for the development of CHD (32), the combination of PSE with soy protein may have an extra benefit in reducing the risk of heart disease. Third, only the combination of PSE and soy protein significantly decreased the relative hepatic CE concentration (36% of TC), whereas the other treatments did not affect CE concentration compared with casein (60% of TC). Hepatic CE, the storage form of cholesterol in the liver, was lower because less fat accumulated in the livers of hamsters fed the diet containing both PSE and soy protein. Fourth, the combination of PSE and soy protein increased fecal total sterol excretion by 270% compared with control, whereas PSE and soy protein individually increased total sterol excretions only by 140 and 73%, respectively. These data strongly support an additional benefit of the dietary combination of PSE and soy protein in lowering plasma lipids.
PSE selectively increased fecal neutral sterol excretion (189%), indicating that intestinal cholesterol absorption was suppressed. Similar results were reported in human studies (33). This "selective" action of plant sterols indicates that the inhibitory mechanism is a competitive process. Because their molecular structures are similar to that of cholesterol, plant sterols may compete with cholesterol for the incorporation into micelles in the intestinal lumen and/or inhibit the sterol-transporter(s) possibly located on the enterocyte membrane (34,35).
In contrast to PSE, soy protein mainly increased fecal bile acid excretion (123%) and only moderately increased fecal neutral sterol excretion (66%). This finding is in agreement with findings reported by Potter and Nestel (36) showing that substitution of cow’s milk with soy milk in infants decreased plasma cholesterol concentration and increased excretion of fecal bile acids. Similarly, a study in swine (37) showed that soy protein increased bile acid and neutral sterol excretions. However, other studies in rats (38) and monkeys (39) showed that soy protein significantly reduced cholesterol absorption, but not bile acid absorption, compared with casein. The reason for these conflicting results concerning the ability of soy protein to increase fecal neutral sterol excretion or bile acid excretion, or both, is unclear. It might be due to species differences. However, it seems more likely related to differences in diet compositions, e.g., cholesterol contents of the diets. The highly selective action of PSE (increasing excretion of neutral sterols) and less selective action of soy protein (increasing excretion of both bile acids and neutral sterols) clearly indicates that different mechanisms must be involved in the cholesterol lowering action of plant sterols and soy protein.
It has been suggested that the soy protein–induced decrease in plasma cholesterol was through enhanced removal of LDL from plasma by increasing LDL-receptor activity (40,41). However, the present study showed that the hepatic LDL-receptor abundance was not influenced by soy protein feeding. These data indicate that the increase in fecal bile acid and neutral sterol excretion was the primary effect of soy protein, which was independent of an effect on hepatic LDL-receptors. It has been demonstrated that the hepatic LDL-receptor abundance in hamsters is regulated by dietary cholesterol (42). Thus, the previously reported effect of soy protein on LDL-receptor up-regulation may possibly be a secondary effect via decreasing plasma cholesterol and preventing a dietary cholesterol–induced decrease in hepatic LDL-receptor abundance (13). Such a secondary LDL-receptor up-regulating effect was not observed in our study. Assuming that the dietary cholesterol–induced hypercholesterolemia suppressed hepatic LDL-receptor expression, PSE and soy protein may not have been powerful enough to reverse this suppression under the present study conditions.
Isoflavones as part of soy protein have been postulated to account for the hypocholesterolemic effect of soy protein (18). The present study shows that isolated soy isoflavones added to a casein diet did not affect plasma cholesterol. The addition of soy isoflavones to the PSE diet also did not increase cholesterol lowering. These data do not support the hypothesis that soy isoflavones are responsible for the cholesterol-lowering action of soy protein. Our results are in agreement with studies in humans in which isoflavones alone did not affect plasma lipid and lipoprotein concentrations (21,22). These data suggest that soy protein itself may account for the beneficial effect. A recent study by Nagaoka et al. (11) reported that a peptic hydrolysate of soy protein had a cholesterol-lowering effect similar to that of intact soy protein. Not all soy peptides may be fully degraded by digestive enzymes such as trypsin and peptidase in the intestinal lumen. These enzyme-resistant soy peptides may have properties similar to those of dietary fibers in their ability to bind to bile acids and cholesterol and thus increase their fecal excretion. Further studies are required to discover how enzyme-resistant soy peptides affect intestinal sterol absorption.
In conclusion, the combination of PSE with soy protein is superior to PSE or soy protein alone for its ability to lower plasma non-HDL cholesterol and TG as well as decrease hepatic cholesterol accumulation in hamsters. PSE decreased plasma TC through selectively inhibiting intestinal cholesterol absorption, whereas soy protein exerted its beneficial effect mainly via suppressing the intestinal absorption of bile acids. The combination of these two components resulted in an additional fecal excretion of total sterols compared with the treatments of PSE or soy protein individually.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Present address: Unilever-Bestfoods, Rotterdam, The Netherlands.
4 Abbreviations used: CE, cholesterol esters; CHD, coronary heart disease; FC, free cholesterol; PSE, plant sterol esters; TC, total cholesterol; TG, triacylglycerol.
Manuscript received 14 July 2003. Initial review completed 29 August 2003. Revision accepted 20 October 2003.
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LITERATURE CITED |
|---|
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
1. LRCP (1984) The Lipid Research Clinics Coronary Primary Prevention Trial results.II. The relationship of reduction in incidence of coronary heart disease to cholesterol lowering. J. Am. Med. Assoc. 251:365-374.
2. Downs, J. R., Clearfield, M., Weis, S., Whitney, E., Shapiro, D. R., Beere, P. A., Langendorfer, A., Stein, E. A., Kruyer, W. & Gotto, A. M., Jr (1998) Primary prevention of acute coronary events with lovastatin in men and women with average cholesterol levels: results of AFCAPS/TexCAPS.Air Force/Texas Coronary Atherosclerosis Prevention Study. J. Am. Med. Assoc. 279:1615-1622.
3. Weststrate, J. A. & Meijer, G. W. (1998) Plant sterol-enriched margarines and reduction of plasma total- and LDL-cholesterol concentrations in normocholesterolaemic and mildly hypercholesterolaemic subjects. Eur. J. Clin. Nutr. 52:334-343.[Medline]
4. Moghadasian, M. H. & Frohlich, J. J. (1999) Effects of dietary phytosterols on cholesterol metabolism and atherosclerosis: clinical and experimental evidence. Am. J. Med. 107:588-594.[Medline]
5. Cassidy, A., Bingham, S. & Setchell, K. D. (1994) Biological effects of a diet of soy protein rich in isoflavones on the menstrual cycle of premenopausal women. Am. J. Clin. Nutr. 60:333-340.
6. Teixeira, S. R., Potter, S. M., Weigel, R., Hannum, S., Erdman, J.W.J. & Hasler, C. M. (2000) Effects of feeding 4 levels of soy protein for 3 and 6 wk on blood lipids and apolipoproteins in moderately hypercholesterolemic men. Am. J. Clin. Nutr. 71:1077-1084.
7. U.S. Food and Drug Administration (2000) FDA authorizes new coronary heart disease health claim for plant sterol and plant stanol esters 2000 U.S. FDA Washington, DC.
8. U.S. Food and Drug Administration (1999) FDA final rule for food labeling: heath claims; soy protein and coronary heart disease. Fed. Regist. 64:57699-57733.
9. Armstrong, M. J. & Carey, M. C. (1987) Thermodynamic and molecular determinants of sterol solubilities in bile salt micelles. J. Lipid Res. 28:1144-1155.[Abstract]
10. Trautwein, E. A., Duchateau, G.S.M.J.E., Lin, Y., Mel’nikov, S. M., Molhuizen, H.O.F. & Ntanios, F. Y. (2003) Proposed mechanisms of cholesterol-lowering action of plant sterols. Eur. J. Lipid Sci. Technol. 105:171-185.
11. Nagaoka, S., Miwa, K., Eto, M., Kuzuya, Y., Hori, G. & Yamamoto, K. (1999) Soy protein peptic hydrolysate with bound phospholipids decreases micellar solubility and cholesterol absorption in rats and Caco-2 cells. J. Nutr. 129:1725-1730.
12. Anderson, J. W., Johnstone, B. M. & Cook-Newell, M. E. (1995) Meta-analysis of the effects of soy protein intake on serum lipids. N. Engl. J. Med. 333:276-282.
13. Lovati, M. R., Manzoni, C., Canavesi, A., Sirtori, M., Vaccarino, V., Marchi, M., Gaddi, G. & Sirtori, C. R. (1987) Soybean protein diet increases low density lipoprotein receptor activity in mononuclear cells from hypercholesterolemic patients. J Clin. Investig. 80:1498-1502.
14. Baum, J. A., Teng, H., Erdman, J.W.J., Weigel, R. M., Klein, B. P., Persky, V. W., Freels, S., Surya, P., Bakhit, R. M., Ramos, E., Shay, N. F. & Potter, S. M. (1998) Long-term intake of soy protein improves blood lipid profiles and increases mononuclear cell low-density-lipoprotein receptor messenger RNA in hypercholesterolemic, postmenopausal women. Am. J. Clin. Nutr. 68:545-551.[Abstract]
15. Potter, S. M. (1995) Overview of proposed mechanisms for the hypocholesterolemic effect of soy. J. Nutr. 125:606S-611S.
16. Ikeda, I. & Sugano, M. (1998) Inhibition of cholesterol absorption by plant sterols for mass intervention. Curr. Opin. Lipidol. 9:527-531.[Medline]
17. Greaves, K. A., Wilson, M. D., Rudel, L. L., Williams, J. K. & Wagner, J. D. (2000) Consumption of soy protein reduces cholesterol absorption compared to casein protein alone or supplemented with an isoflavone extract or conjugated equine estrogen in ovariectomized cynomolgus monkeys. J. Nutr. 130:820-826.
18. Merz-Demlow, B. E., Duncan, A. M., Wangen, K. E., Xu, X., Carr, T. P., Phipps, W. R. & Kurzer, M. S. (2000) Soy isoflavones improve plasma lipids in normocholesterolemic, premenopausal women. Am. J. Clin. Nutr. 71:1462-1469.
19. Anthony, M. S., Clarkson, T. B. & Williams, J. K. (1998) Effects of soy isoflavones on atherosclerosis: potential mechanisms. Am. J. Clin. Nutr. 68:1390S-1393S.[Abstract]
20. Ni, W., Yoshida, S., Tsuda, Y., Nagao, K., Sato, M. & Imaizumi, K. (1999) Ethanol-extracted soy protein isolate results in elevation of serum cholesterol in exogenously hypercholesterolemic rats. Lipids 34:713-716.[Medline]
21. Hodgson, J. M., Puddey, I. B., Beilin, L. J., Mori, T. A. & Croft, K. D. (1998) Supplementation with isoflavonoid phytoestrogens does not alter serum lipid concentrations: a randomized controlled trial in humans. J. Nutr. 128:728-732.
22. Nestel, P. J., Yamashita, T., Sasahara, T., Pomeroy, S., Dart, A., Komesaroff, P., Owen, A. & Abbey, M. (1997) Soy isoflavones improve systemic arterial compliance but not plasma lipids in menopausal and perimenopausal women. Arterioscler. Thromb. Vasc. Biol. 17:3392-3398.
23. Spady, D. K., Stange, E. F., Bilhartz, L. E. & Dietschy, J. M. (1986) Bile acids regulate hepatic low density lipoprotein receptor activity in the hamster by altering cholesterol flux across the liver. Proc. Natl. Acad. Sci. U.S.A. 83:1916-1920.
24. Imray, C. H., Minoura, T., Davis, A., Radley, S., Newbold, K. M., Lavelle-Jones, M., Lawson, A. M., Baker, P. R. & Neoptolemos, J. P. (1992) Comparability of hamster with human faecal unconjugated bile acids in a model of colorectal cancer. Anticancer Res 12:553-558.[Medline]
25. Reeves, P. G., Nielsen, F. H. & Fahey, G. C., Jr (1993) AIN-93 purified diets for laboratory rodents: final report of the American Institute of Nutrition ad hoc writing committee on the reformulation of the AIN-76A rodent diet. J. Nutr. 123:1939-1951.
26. Bligh, E. G. & Dyer, W. J. (1959) A rapid method of total lipid extraction and purification. Can. J. Biochem. Biophys. 37:911-917.
27. Kovanen, P. T., Bilheimer, D. W., Goldstein, J. L., Jaramillo, J. J. & Brown, M. S. (1981) Regulatory role for hepatic low density lipoprotein receptors in vivo in the dog. Proc. Natl. Acad. Sci. U.S.A. 78:1194-1198.
28. Lowry, O. H., Rosebrough, N. J., Farr, A. L. & Randall, R. J. (1959) Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193:265-275.
29. May, K., Kraemer, F. B., Chen, J. & Cooper, A. D. (1990) ELISA measurement of LDL receptors. J. Lipid Res. 31:1683-1691.[Abstract]
30. Post, S. M., De Crom, R., Van Haperen, R., Van Tol, A. & Princen, H. M. (2003) Increased fecal bile acid excretion in transgenic mice with elevated expression of human phospholipid transfer protein. Arterioscler. Thromb. Vasc. Biol. 23:892-897.
31. Trautwein, E. A., Schulz, C., Rieckhoff, D., Kunath-Rau, A., Erbersdobler, H. F., de Groot, W. A. & Meijer, G. W. (2002) Effect of esterified 4-desmethylsterols and -stanols or 4,4'-dimethylsterols on cholesterol and bile acid metabolism in hamsters. Br. J. Nutr. 87:227-237.[Medline]
32. Davignon, J. & Cohn, J. S. (1996) Triglycerides: a risk factor for coronary heart disease. Atherosclerosis 124(suppl.):S57-S64.
33. Jones, P. J., MacDougall, D. E., Ntanios, F. & Vanstone, C. A. (1997) Dietary phytosterols as cholesterol-lowering agents in humans. Can. J. Physiol. Pharmacol. 75:217-227.[Medline]
34. Dawson, P. A. & Rudel, L. L. (1999) Intestinal cholesterol absorption. Curr. Opin. Lipidol. 10:315-320.[Medline]
35. Davis, H. R., Compton, D. S., Hoos, L. & Tetzloff, G. (2001) Ezetimibe, a potent cholesterol absorption inhibitor, inhibits the development of atherosclerosis in ApoE knockout mice. Arterioscler. Thromb. Vasc. Biol. 21:2032.
36. Potter, J. M. & Nestel, P. J. (1976) Greater bile acid excretion with soy bean than with cow milk in infants. Am. J. Clin. Nutr. 29:546-551.
37. Beynen, A. C., West, C. E., Spaaij, C. J., Huisman, J., Van Leeuwen, P., Schutte, J. B. & Hackeng, W. H. (1990) Cholesterol metabolism, digestion rates and postprandial changes in serum of swine fed purified diets containing either casein or soybean protein. J. Nutr. 120:422-430.
38. Nagata, Y., Ishiwaki, N. & Sugano, M. (1982) Studies on the mechanism of antihypercholesterolemic action of soy protein and soy protein-type amino acid mixtures in relation to the casein counterparts in rats. J. Nutr. 112:1614-1625.
39. Greaves, K. A., Wilson, M. D., Rudel, L. L., Williams, J. K. & Wagner, J. D. (2000) Consumption of soy protein reduces cholesterol absorption compared to casein protein alone or supplemented with an isoflavone extract or conjugated equine estrogen in ovariectomized cynomolgus monkeys. J. Nutr. 130:820-286.
40. Khosla, P., Samman, S., Carroll, K. K. & Huff, M. W. (1989) Turnover of 125I-VLDL and 131I-LDL apolipoprotein B in rabbits fed diets containing casein or soy protein. Biochim. Biophys. Acta 1002:157-163.[Medline]
41. Kirk, E. A., Sutherland, P., Wang, S. A., Chait, A. & LeBoeuf, R. C. (1998) Dietary isoflavones reduce plasma cholesterol and atherosclerosis in C57BL/6 mice but not LDL receptor-deficient mice. J. Nutr. 128:954-959.
42. Spady, D. K. & Dietschy, J. M. (1988) Interaction of dietary cholesterol and triglycerides in the regulation of hepatic low density lipoprotein transport in the hamster. J. Clin. Investig. 81:300-309.
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C. W. Xiao, J. Mei, W. Huang, C. Wood, M. R. L'Abbe, G. S. Gilani, G. M. Cooke, and I. H. Curran Dietary Soy Protein Isolate Modifies Hepatic Retinoic Acid Receptor-{beta} Proteins and Inhibits Their DNA Binding Activity in Rats J. Nutr., January 1, 2007; 137(1): 1 - 6. [Abstract] [Full Text] [PDF]
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 J. M. Martins, M. Riottot, M. C. de Abreu, A. M. Viegas-Crespo, M. J. Lanca, J. A. Almeida, J. B. Freire, and O. P. Bento Cholesterol-lowering effects of dietary blue lupin (Lupinus angustifolius L.) in intact and ileorectal anastomosed pigs J. Lipid Res., July 1, 2005; 46(7): 1539 - 1547. [Abstract] [Full Text] [PDF]
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