Intact dietary soy protein, but not adding an isoflavone-rich soy extract to casein, improves plasma lipids in ovariectomized cynomolgus monkeys.

The dietary consumption of soy protein has been linked to a reduction in coronary heart disease and improvements in a number of related risk factors. Recent investigations have focused on isoflavone components of soy protein. The purpose of this study was to examine plasma lipids and lipoproteins, particularly LDL, with the intake of intact soy protein or casein-lactalbumin diets with and without a semipurified extract of soy, rich in isoflavones. Sixty ovariectomized cynomolgus monkeys were assigned to one of three groups fed diets containing the following: 1) casein-lactalbumin as the protein source (CAS; n = 20); 2) CAS plus a semipurified extract of soy, rich in isoflavones (ISO; n = 20); or 3) intact soy protein (SOY; n = 20) for 12 wk. Lipoproteins were fractionated by combined ultracentrifugation and HPLC. Isolated LDL particles were further subfractionated by dividing the LDL peak into three fractions for compositional analyses. The SOY group had significantly lower plasma total cholesterol, VLDL plus IDL cholesterol and LDL cholesterol, and significantly less HDL cholesterol than the CAS group. LDL particles from the SOY group had a significantly less cholesteryl ester than the CAS group. The semipurified extract of soy, rich in isoflavones, added to casein-lactalbumin protein did not have the same effects as intact soy protein on plasma lipids and lipoproteins. Other components of soy protein, either alone or in combination with isoflavones, may be involved in the effects seen in this study.     

Effects of soy isoflavone and/or estrogen treatments on bone metabolism in ovariectomized rats

This study investigated whether soy isoflavone intake, with or without estrogen treatment, can reduce postmenopausal bone loss, and whether soy isoflavones can be an alternative for estrogen replacement therapy using a postmenopausal osteoporotic rat model in which ovariectomized female rats were fed a low calcium, high fat diet. Nine-week-old female Sprague-Dawley rats were ovariectomized and then fed low (0.1%) calcium diets with or without soy isoflavone supplementation (80 or 160 ppm) for 6 weeks. Some ovariectomized rats were fed the same diets but also injected with estrogen (10 microg/kg of body weight) subcutaneously. Serum calcium and phosphate levels were normal in all rats. Serum alkaline phosphatase activities were not affected by the treatments. Serum tartrate-resistant acid phosphatase activities and urinary hydroxyproline levels were not different between experimental groups. Bone mineral (calcium and phosphorus) contents were increased in the rats supplemented with 80 ppm soy isoflavone or the rats treated with only estrogen without soy isoflavone. Therefore, the effect of 80 ppm soy isoflavone supplementation was the same as estrogen injection, but there was no beneficial effect from combining soy isoflavones and estrogen injections. When 160 ppm soy isoflavone was used, the benefits were lessened or disappeared altogether. These results suggest that appropriate soy isoflavone supplementation prevents postmenopausal bone loss without estrogen injection and may have efficacy as an alternative to estrogen therapy.     

Effects of feeding rats low protein diets containing casein or soy protein isolate supplemented with methionine or oligo-L-methionine

The effects of supplementing 8% casein or 10% soy protein isolate (SPI) diets with graded levels of oligo-L-methionine (a mixture of hexa- and heptapeptides, OM) or L-methionine (Met) were studied in rats to determine the reason for the difference in nutritional quality between proteins and corresponding amino acid mixtures. As the OM concentration of the casein-based diet was increased from 0.02% to 0.6%, maximum weight gain was attained at 0.2%, and the growth-promoting activity of OM was comparable to Met at all the corresponding levels tested. Liver fat began to accumulate when supplemental Met reached a level of 0.08% of the casein diet, but OM addition did not produce a fatty liver at dietary levels of less than 0.3%. When SPI was used as the dietary protein source, the effect of supplemental OM was significantly less than that of Met. Digestibility of OM (assessed by incremental portal plasma Met concentration) was measured 30 min after feeding the casein or SPI diet supplemented with 3% OM using rats fasted for 24 h. Plasma Met concentration was greatly increased in rats fed the casein plus OM diet compared with that of rats fed the SPI + OM diet. Similarly, the 30-min portal Met concentration significantly increased in response to the casein + OM diet compared with the SPI + OM diet regardless of the prefed proteins (25% casein and 25% SPI for 2 wk).(ABSTRACT TRUNCATED AT 250 WORDS)     

Response of hormones modulating plasma cholesterol to dietary casein or soy protein in minipigs

To elucidate the mechanism mediating the effect of dietary casein or soy protein on serum cholesterol concentrations we followed the endocrine response to the intake of these dietary proteins. The hormones analyzed were those known to modulate serum cholesterol concentration. A 7-wk crossover nutrition study was performed with six adult G?ttingen minipigs consuming semisynthetic diets based on either 20 wt% casein or soy isolate. At d 42 and 49, concentrations of six hormones were determined in 22 blood samples taken over the whole day. There were no significant differences in insulin, glucagon, the insulin/glucagon ratio, hydrocortisone or triiodothyronine among dietary groups. In the late postprandial phase (5 h after the meal and later) there were significantly higher growth hormone concentrations in soy-fed animals. At all times of the day, total and free thyroxine concentrations were higher after soy feeding than after casein feeding. On average, total and free thyroxine concentrations were 34 and 26% higher with soy protein feeding than with casein feeding. Our data agree with other reports of protein-dependent changes of thyroid hormones and may explain why different dietary proteins have different effects on serum cholesterol levels in sensitive species.     

Plasma amino acids and cholesterol following consumption of dietary casein or soy protein in minipigs

Numerous investigators have claimed that protein-induced differences in plasma cholesterol are mediated by differences in amino acid composition. We have explored whether the venous postprandial amino acid profile reflects differences in the amino acid composition of the protein consumed. Six adult G?ttingen miniature pigs were fed a semisynthetic diet based on either casein or soy protein isolate. Frequent blood sampling was performed over a whole day after consumption of each diet for 6 wk. Postprandial plasma amino acid concentrations reached their maxima within the first 3 h. A group of eight protein amino acids (Met, Arg, Tyr, Val, Trp, Leu, Lys and Cys) exhibited the most marked and significant protein-dependent differences during this early postprandial phase, whereas Thr and His showed less marked differences. With one exception (Ser) all protein amino acids exhibited venous plasma concentration changes in qualitative accordance with their content in the dietary protein consumed. In quantitative terms, however, venous plasma amino acid changes were less marked than expected from the amino acid composition of the dietary proteins. We conclude that neither the considerable number of amino acids showing differences as reported herein nor the multitude of contradictory reported by others concerning single amino acids affecting serum cholesterol favor the hypothesis that one or several amino acid(s) cause protein-induced hypercholesterolemia.     

Effect of cholesterol supplementation on plasma and liver cholesteryl ester fatty acids in rats fed casein or soy protein

The effect of supplementation with cholesterol on plasma and liver cholesteryl ester fatty acids was examined in rats fed diets containing different protein sources. Weanling male rats were fed a semi-purified diet containing 20% casein or 20% soy protein for seven weeks and then 1% (by weight) of cholesterol was added for three more weeks. Rats fed soy protein grew consistently slower than those fed casein. The plasma and liver cholesterol contents were not significantly different between the two protein groups in the unsupplemented rats; however, they were significantly increased in cholesterol-fed animals, particularly in casein-fed rats. Analysis of the cholesteryl ester fatty acid composition in plasma and liver demonstrated that cholesterol-feeding significantly increased the levels of saturated fatty acids, monounsaturated fatty acids and linoleic acid in casein-fed rats as compared to those fed soy protein. The level of cholesteryl arachidonate in liver, which was low initially, increased slightly in the liver of casein-fed rats but did not significantly change in the plasma of either protein group.     

Pancreatic response to long-term feeding of soy protein isolate, casein or egg white in rats

Rats were fed purified diets which provided 24% protein from casein (C), soy protein isolate (SPI), or egg white (EW) for 18 mo. Groups of rats were killed at 3, 6, 12 and 18 mo; the pancreata were removed and examined histologically for occurrence of atypical nodules. The weight, protein, DNA, trypsin and chymotrypsin concentrations of the pancreas at each period were measured. Over the entire experimental period, body weight did not differ among groups. Pancreatic weight, protein and trypsin activity were highest in the EW group, followed by the SPI group, and lowest in the C group. Chymotrypsin activity was significantly higher in the EW and SPI groups than the C group. DNA content did not differ significantly among groups over the entire experimental period, although it was elevated in the SPI or EW groups compared to the C groups at some of the time periods. Only one microscopic nodule was observed in all of the animals; it was found at 3 mo in the pancreas from an animal fed EW. Overall, the results suggest that the elevation in enzyme activity and pancreatic weight associated with long-term consumption of EW and SPI did not result in development of pancreatic lesions in rats.     

Replacing 40% of dietary animal fat with vegetable oil is associated with lower HDL cholesterol and higher cholesterol ester transfer protein in cynomolgus monkeys fed sufficient linoleic acid

This study was designed to evaluate whether replacing approximately 40 g/100 g dietary animal fat with vegetable oil would improve plasma lipids and lipoproteins when diets contained prudent levels of total saturated acid (SFA), monounsaturated acid (MUFA) and PUFA. Using a cross-over design, male Cynomolgus monkeys (n = 10) were fed purified diets containing a mixture of fats. For the diet based on animal fat (AF-diet), approximately 85 g/100 g of the total fat was derived from pork fat, and approximately 40 g/100 g of this was replaced with olive oil for the vegetable oil-based diet (VO-diet). Thus, the fat content of the VO diet comprised 50% pork fat and 35% olive oil. The remaining 15% of the total fat (for both diets) was safflower oil. Both diets provided approximately 30% of total energy (%en) from fat, <10%en SFA and approximately 6-7%en from PUFA. Monkeys were rotated through two 7-wk feeding periods, during which time plasma lipids and lipoproteins were evaluated. Compared with the AF diet, plasma total cholesterol (TC) concentrations tended to be lower ( approximately 10%) after monkeys consumed the VO diet (3.18 +/- 0.83 vs. 3.52 +/- 0.93 mmol/L, P = 0.099), and this was due entirely to a significant 12% reduction in HDL cholesterol (1.53 +/- 0.41 vs. 1.73 +/- 0.47, mmol/L, P = 0.0009). Although plasma lipoprotein compositional analyses revealed no significant differences in either lipoprotein composition or the estimated particle diameters, the measurement of cholesterol ester transfer protein (CETP) using (3)H-cholesterol ester-labeled HDL revealed that the lower HDL cholesterol (HDL-C) when monkeys consumed the VO diet was associated with a 31% increase in transfer (P = 0.04). However, despite the changes in HDL-C, the TC/HDL-C ratio did not differ between monkeys after the two diet treatments. Regression analyses of data from these monkeys revealed a significant correlation between the dietary 16:0/18:2 ratio and plasma HDL-C. These data suggest that within the context of currently recommended prudent diets, it may be possible to manipulate HDL-C beneficially. Whether a similar effect would occur in humans warrants investigation.     

The effect of soy protein with or without isoflavones relative to milk protein on plasma lipids in hypercholesterolemic postmenopausal women

BACKGROUND: Clinical trial data and the results of a meta-analysis suggest a hypocholesterolemic effect of soy protein. The effect may be partially attributable to the isoflavones in soy. Few studies have examined the separate effects of soy protein and isoflavones. OBJECTIVE: The objective of this study was to determine the effect of soy protein and isoflavones on plasma lipid concentrations in postmenopausal, moderately hypercholesterolemic women. DESIGN: This was a randomized, double-blind, placebo-controlled clinical trial with 3 treatment groups. After a 4-wk run-in phase during which the women consumed a milk protein supplement, the subjects were randomly assigned to 12 wk of dietary protein supplementation (42 g/d) with either a milk protein (Milk group) or 1 of 2 soy proteins containing either trace amounts of isoflavones (Soy- group) or 80 mg aglycone isoflavones (Soy+ group). RESULTS: LDL-cholesterol concentrations decreased more in the Soy+ group (n = 31) than in the Soy- group (n = 33) (0.38 compared with 0.09 mmol/L; P = 0.005), but neither of these changes was significantly different from the 0.26-mmol/L decrease observed in the Milk group (n = 30). The results for total cholesterol were similar to those for LDL cholesterol. There were no significant differences in HDL-cholesterol or triacylglycerol concentrations between the 3 groups. CONCLUSIONS: The difference in total- and LDL-cholesterol lowering between the 2 soy-protein supplements suggests an effect attributable to the isoflavone-containing fraction. However, the unexpected LDL-cholesterol lowering observed in the Milk group, and the fact that there was no significant difference between either soy group and the Milk group, suggests that changes may have been due to other factors related to participation in the study.     

Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy

BACKGROUND: Phytoestrogens, which are abundant in flaxseed and soy, have chemical structures resembling those of endogenous estrogens and have been shown to exert hormonal effects, thereby affecting chronic diseases. OBJECTIVE: We compared the effects of consuming equal amounts of flaxseed or soy on estrogen metabolism and biochemical markers of bone metabolism in postmenopausal women. DESIGN: In a parallel design, the diet of postmenopausal women (n = 46) was supplemented with either a placebo, soy (25 g soy flour), or flaxseed (25 g ground flaxseed) muffin for 16 wk. Blood and 24-h urine samples were collected at baseline and at the endpoint. Urine samples were analyzed for phytoestrogens, estrogen metabolites (2-hydroxyestrone, 16alpha-hydroxyestrone), and serum hormones (estradiol, estrone, estrone sulfate). Serum and urine samples were also analyzed for biochemical markers of bone metabolism. RESULTS: Urinary concentrations of 2-hydroxyestrone, but not of 16alpha-hydroxyestrone, increased significantly in the flaxseed group (P = 0.05). In the flaxseed group, the ratio of 2-hydroxyestrone to 16alpha-hydroxyestrone was positively correlated with urinary lignan excretion (r = 0.579, P = 0.02). In the soy and placebo groups, no significant correlation was observed. No significant change in serum hormones or biochemical markers of bone metabolism was observed within or between the treatment groups. CONCLUSIONS: Supplementation with flaxseed modifies urinary estrogen metabolite excretion to a greater extent than does supplementation with an equal amount of soy. This modification by flaxseed is associated with an increase in urinary lignan excretion. Despite the shift in estrogen metabolism to favor the less biologically active estrogens, a negative effect on bone cell metabolism was not observed.     

Inducibility of hepatic CYP1A enzymes by 3-methylcholanthrene and isosafrole differs in male rats fed diets containing casein, soy protein isolate or whey from conception to adulthood

Hepatic cytochrome P450 (CYP)1A1 and 1A2 enzymes were studied in male Sprague-Dawley rats derived from 5-7 litters fed diets in which the protein source was casein, soy protein isolate or whey. At age 65 d, rats were gavaged with corn oil (vehicle), 40 mg/kg 3-methylcholanthrene (3-MC) or 75 mg/kg isosafrole (ISO). Hepatic expression of CYP1A1 and CYP1A2 mRNA, apoprotein and associated monooxygenase activities were measured 17 h later. No significant dietary effects were observed on basal expression of either enzyme. However, interactions between diet and the two inducers (3-MC and ISO) were observed in soy-fed rats for ethoxy- and methoxyresorufin O-dealkylase activity, CYP1A1 and CYP1A2 apoprotein and mRNA (P < 0.05). The level of induction of CYP1A1 mRNA and apoprotein was lower in rats fed soy diets than in rats fed casein diets (P < 0.05), and the level of induced CYP1A2 mRNA was lower in rats fed soy or whey (P < 0.05) after treatment with the aryl hydrocarbon (Ah) receptor-dependent inducer 3-MC. This was accompanied by a 50% reduction in constitutive levels of the Ah receptor in liver cytosol of soy-fed, relative to casein-fed rats, and a slightly smaller reduction in whey-fed rats. Expression of the Ah receptor correlated with 3-MC-inducibility of CYP1A1 mRNA in rats fed the three diets. In contrast, in rats induced with ISO, which does not bind to the Ah receptor and induces CYP1As via different mechanisms than 3-MC, ethoxyresorufin O-deethylase activity and levels of CYP1A1 apoprotein and mRNA were elevated to a greater degree in soy-fed than in casein- or whey-fed rats (P < 0.05). Moreover, after ISO treatment, induction of methoxyresorufin O-demethylase activity, CYP1A2 apoprotein and mRNA levels was observed only in rats fed soy (P < 0.05). These data suggest potential effects of dietary protein source on metabolism of a wide variety of CYP1A substrates, including environmental and dietary carcinogens, many of which induce their own metabolism.     

Substrate oxidation and control of food intake in men after a fat-substitute meal compared with meals supplemented with an isoenergetic load of carbohydrate, long-chain triacylglycerols, or medium-chain triacylglycerols.

BACKGROUND: It has been suggested that hunger may be delayed and food intake reduced under metabolic conditions that spare carbohydrate oxidation. OBJECTIVE: Our objective was to examine the role of glucose metabolism in the control of food intake in men by using medium-chain triacylglycerols (MCTs) to spare carbohydrate oxidation. DESIGN: In 10 male volunteers, isolated and deprived of any time cues, we studied the effects of 4 lunches on hunger ratings, the duration of satiety, the amount of food ingested at dinner, energy expenditure, substrate oxidation, and plasma variables until the time of the dinner request. One lunch was a basic 2310-kJ meal containing 40 kJ fat substitute (Sub lunch). The 3 other lunches consisted of the same basic meal supplemented with either 1200 kJ long-chain triacylglycerols (LCT lunch), 1200 kJ MCTs (MCT lunch), or 900 kJ carbohydrate plus 300 kJ LCTs (Cho lunch). RESULTS: Energy expenditure was not significantly different after the different lunches, but carbohydrate oxidation was lower after the MCT and LCT lunches than after the Cho lunch. Fat oxidation was greater after the MCT and LCT lunches. The time of the dinner request was significantly delayed after the Cho lunch. Food intake at dinner was significantly lower after the MCT lunch than after the Sub and Cho lunches, but the dinner meal request was not delayed. CONCLUSION: Carbohydrate may have a greater role in the duration of satiety than does fat, but MCTs may play an active role in other aspects of the control of food intake, especially in satiation at the next meal.     

Evaluation of the safety and immunogenicity of Plasmodium falciparum apical membrane antigen 1, merozoite surface protein 1 or RTS,S vaccines with adjuvant system AS02A administered alone or concurrently in rhesus monkeys

In an effort to broaden the immune response induced by the RTS,S/AS02_A,vaccine, we have evaluated the immunogenicity of the RTS,S antigen when combined with MSP1₄₂ and with AMA1, antigens derived from the asexual blood stage. The objectives of this study were (i) to determine whether MSP1₄₂ and AMA1 vaccines formulated with the AS02_A Adjuvant System were safe and immunogenic in the rhesus monkey model; (ii) to investigate whether MSP1₄₂ or AMA1 induced immune interference to each other, or to RTS,S, when added singly or in combinations at a single injection site; (iii) in the event of immune interference, to determine if this could be reduced when antigens were administered at separate sites. We found that MSP1₄₂ and AMA1 were safe and immunogenic, eliciting antibodies, and Th1 and Th2 responses using IFN-γ and IL-5 as markers. When malaria antigens were delivered together in one formulation, MSP1₄₂ and RTS,S reduced AMA1-specific antibody responses as measured by ELISA however, only MSP1₄₂ lowered parasite growth inhibitory activity of anti-AMA1 antibodies as measured by in vitro growth inhibition assay. Unlike RTS,S, MSP1₄₂ significantly reduced AMA1 IFN-γ and IL-5 responses. MSP1₄₂ suppression of AMA1 IFN-γ responses was not seen in animals receiving RTS,S + AMA1 + MSP1₄₂ suggesting that RTS,S restored IFN-γ responses. Conversely, AMA1 had no effect on MSP1₄₂ antibody and IFN-γ and IL-5 responses. Neither AMA1 alone or combined with MSP1₄₂ affected RTS,S antibody or IFN-γ and IL-5 responses. Immune interference by MSP1₄₂ on AMA1 antibody responses was also evident when AMA1, MSP1₄₂ and RTS,S were administered concurrently at separate sites. These results suggest that immune interference may be complex and should be considered for the design of multi-antigen, multi-stage vaccines against malaria.     

Double-blind study to assess the efficacy of chlorproguanil given alone or in combination with chloroquine for malaria chemoprophylaxis in an area with Plasmodium falciparum resistance to chloroquine, pyrimethamine and cycloguanil

In this study the efficacy of chlorproguanil (20 mg base weekly) was compared in schoolchildren with that of chloroquine (200 mg base weekly) and that of both drugs combined (20 mg base + 200 mg base weekly). The double blind trial was performed in the rice field area of the Ruzizi valley in Burundi, where Plasmodium falciparum is widely resistant to chloroquine, and where pyrimethamine resistance with cycloguanil cross-resistance had been demonstrated. After 17 weeks, when the trial was ended, 60% breakthroughs had been observed among the children taking chloroquine, 72% among those under chlorproguanil and 61% among those under chlorproguanil and chloroquine. In children weighing between 15 and 24 kg, the failure rate was significantly higher in those treated with chlorproguanil than in the group treated with chloroquine. No difference in efficacy was observed in children weighing 25 to 39 kg. There was no significant increase of efficacy when chlorproguanil was given in association with chloroquine. The mean titre of fluorescent antibodies was the same in each treated group on week 5 and week 15. The comparison of these data with the infection rates in non-protected children suggests that malaria could not be prevented with any of the drug regimens utilized in the study.