Soyasaponins lowered plasma cholesterol and increased fecal bile acids in female golden Syrian hamsters

A study was conducted in hamsters to determine if group B soyasaponins improve plasma cholesterol status by increasing the excretion of fecal bile acids and neutral sterols, to identify group B soyasaponin metabolites, and to investigate the relationship between a fecal group B soyasaponin metabolite and plasma lipids. Twenty female golden Syrian hamsters, 11-12 weeks old and 85-125 g, were randomly assigned to a control diet or a similar diet containing group B soyasaponins (containing no isoflavones), 2.2 mmol/kg, for 4 weeks. Hamsters fed group B soyasaponins had significantly lower plasma total cholesterol (by 20%), non-high-density lipoprotein (HDL) cholesterol (by 33%), and triglycerides (by 18%) compared with those fed casein (P < 0.05). The ratio of total cholesterol to HDL cholesterol was significantly lower (by 13%) in hamsters fed group B soyasaponins than in those fed casein (P < 0.05). The excretion of fecal bile acids and neutral sterols was significantly greater (by 105% and 85%, respectively) in soyasaponin-fed hamsters compared with those fed casein (P < 0.05). Compared with casein, group B soyasaponins lowered plasma total cholesterol levels and non-HDL cholesterol levels by a mechanism involving greater excretion of fecal bile acids and neutral sterols. Hamsters fed group B soyasaponins statistically clustered into two fecal soyasaponin metabolite-excretion phenotypes: high excreters (n = 3) and low excreters (n = 7). When high and low producers of this soyasaponin metabolite were compared for plasma cholesterol status, the high producers showed a significantly lower total-cholesterol-to-HDL-cholesterol ratio compared with the low producers (1.38 +/- 0.7 vs. 1.59 +/- 0.13; P < 0.03). Greater production of group B soyasaponin metabolite in hamsters was associated with better plasma cholesterol status, suggesting that gut microbial variation in soyasaponin metabolism may influence the health effects of group B soyasaponins.     

Anacetrapib promotes reverse cholesterol transport and bulk cholesterol excretion in Syrian golden hamsters

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester (CE) and triglyceride between HDL and apoB-containing lipoproteins. Anacetrapib (ANA), a reversible inhibitor of CETP, raises HDL cholesterol (HDL-C) and lowers LDL cholesterol in dyslipidemic patients; however, the effects of ANA on cholesterol/lipoprotein metabolism in a dyslipidemic hamster model have not been demonstrated. To test whether ANA (60 mg/kg/day, 2 weeks) promoted reverse cholesterol transport (RCT), 3H-cholesterol-loaded macrophages were injected and (3)H-tracer levels were measured in HDL, liver, and feces. Compared to controls, ANA inhibited CETP (94%) and increased HDL-C (47%). 3H-tracer in HDL increased by 69% in hamsters treated with ANA, suggesting increased cholesterol efflux from macrophages to HDL. 3H-tracer in fecal cholesterol and bile acids increased by 90% and 57%, respectively, indicating increased macrophage-to-feces RCT. Mass spectrometry analysis of HDL from ANA-treated hamsters revealed an increase in free unlabeled cholesterol and CE. Furthermore, bulk cholesterol and cholic acid were increased in feces from ANA-treated hamsters. Using two independent approaches to assess cholesterol metabolism, the current study demonstrates that CETP inhibition with ANA promotes macrophage-to-feces RCT and results in increased fecal cholesterol/bile acid excretion, further supporting its development as a novel lipid therapy for the treatment of dyslipidemia and atherosclerotic vascular disease.     

Pharmacokinetics of isoflavones,daidzein and genistein,after ingestion of soy beverage compared with soy extract capsules in postmenopausal Thai women

Background  

Isoflavones from soybeans may provide some beneficial impacts on postmenopausal health. The purpose of this study was to compare the pharmacokinetics and bioavailability of plasma isoflavones (daidzein and genistein) after a single dose of orally administered soy beverage and soy extract capsules in postmenopausal Thai women.     

Soy protein with and without isoflavones fails to substantially increase postprandial antioxidant capacity

Five methods for the assessment of antioxidant capacity [whole plasma conjugated diene formation, low-density lipoprotein oxidation susceptibility, ferric-reducing ability of plasma, oxygen radical absorbance capacity and perchloric-acid-treated oxygen radical absorbance capacity (PCA-ORAC)] were used in a randomized, double blind, crossover study to determine the acute postprandial antioxidant protection imparted by the isoflavone component of soy. On separate days, 16 subjects consumed one of three isocaloric shakes containing 25 g of protein in the form of soy, with 107 mg of total aglycone units of isoflavones, soy with trace isoflavones (<4 mg) or total milk protein. Blood was collected at baseline, 4 h, 6 h and 8 h after consumption. Antioxidant capacity, serum isoflavone levels, fat-soluble antioxidants and plasma vitamin C levels were evaluated. Repeated measures analysis of variance showed no significant differences (P=.05) within treatments over time in four of five antioxidant capacity measurements. Significant differences over time between the soy with trace isoflavones and the total milk protein group were observed using the PCA-ORAC assay. It can be concluded that, on an acute basis, a significant increase in serum antioxidant capacity is not detectable following consumption of soy protein.     

Corn fiber oil lowers plasma cholesterol levels and increases cholesterol excretion greater than corn oil and similar to diets containing soy sterols and soy stanols in hamsters

The aims of this study were to compare the cholesterol-lowering properties of corn fiber oil (CFO) to corn oil (CO), whether the addition of soy stanols or soy sterols to CO at similar levels in CFO would increase CO's cholesterol-lowering properties, and the mechanism(s) of action of these dietary ingredients. Fifty male Golden Syrian hamsters were divided into 5 groups of 10 hamsters each, based on similar plasma total cholesterol (TC) levels. The first group of hamsters was fed a chow-based hypercholesterolemic diet containing either 5% coconut oil + 0.24% cholesterol (coconut oil), 5% CO, 5% CFO, 5% CO + 0.6% soy sterols (sterol), or 5% CO + 0.6% soy stanols (stanol) in place of the coconut oil for 4 weeks. The stanol diet significantly inhibited the elevation of plasma TC compared to all other dietary treatments. Also, the CFO and sterol diets significantly inhibited the elevation of plasma TC compared to the CO and coconut oil diets. The CFO, sterol, and stanol diets significantly inhibited the elevation of plasma non-high density lipoprotein cholesterol compared to the CO and coconut oil diets. The stanol diet significantly inhibited the elevation of plasma high density lipoprotein cholesterol (HDL-C) compared to all other dietary treatments. The sterol diet significantly inhibited the elevation of plasma HDL-C compared to the CO and coconut oil diets, whereas the CFO diet significantly inhibited the elevation of plasma HDL-C compared to the coconut oil diet only. No differences were observed between the CFO and CO for plasma HDL-C. There were no differences observed between groups for plasma triglycerides. The CO and CFO diets had significantly less hepatic TC compared to the coconut oil, sterol, and stanol diets. The CO and CFO diets had significantly less hepatic free cholesterol compared to the sterol and stanol diets but not compared to the coconut oil diet; whereas the coconut oil and sterol diets had significantly less hepatic free cholesterol compared to the stanol diet. The CFO, sterol, and stanol diets excreted significantly more fecal cholesterol compared to the coconut oil and CO diets. In summary, CFO reduces plasma and hepatic cholesterol concentrations and increases fecal cholesterol excretion greater than CO through some other mechanism(s) in addition to increase dietary sterols and stanols-possibly oryzanols.     

Soy protein hydrolyzate with bound phospholipids reduces serum cholesterol levels in hypercholesterolemic adult male volunteers

This study was done to evaluate the effects of soy protein hydrolyzate with bound phospholipids (c-SPHP), on the serum cholesterol levels in hypercholesterolemic subjects over a three-month period. Subjects were Taiwanese adult male volunteers whose serum total cholesterol levels were above 220 mg/dl. Twenty-one subjects were divided into three groups randomly, and each group was given c-SPHP zero, 3, or 6 g per day. Test diets were orally administered in a powdered drink form that contained c-SPHP or casein hydrolyzate (placebo). The subjects were given the test diet four times daily. The study consisted of a two-week pre-feeding period, a three-month feeding period, followed by a two-week post-feeding period. After 3 months of c-SPHP administration, 3 g per day, serum total cholesterol decreased significantly from the initial level (15.0%, p<0.01) and compared with the placebo group (p<0.05). Furthermore, LDL-cholesterol decreased significantly (27.7%, p<0.01) and the LDL/HDL ratio also decreased significantly (47.4%, p<0.01) from the initial levels. These effects of c-SPHP were dose-dependent. This study suggests that c-SPHP has remarkable improving effects on the serum cholesterol levels in hypercholesterolemic subjects.     

Chronic exposure to short photoperiod inhibits free thyroxine index and plasma levels of TSH, T4, triiodothyronine (T3) and cholesterol in female Syrian hamsters

1. Chronic exposure of female Syrian hamsters (Mesocricetus auratus) for 9 weeks to a short photoperiod (10L:14D) depressed the pituitary-thyroid axis as indicated by a drop in circulating titers of thyroid stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3) and the free thyroxine index (FT4I) compared to animals maintained under long photoperiodic conditions (14L:10D). 2. Short day treatment also reduced plasma cholesterol levels. 3. Neither plasma triglycerides, glucose nor growth hormone (GH) levels differed between hamsters exposed to short or long daily photoperiods.     

The influence of natural short photoperiodic and temperature conditions on plasma thyroid hormones and cholesterol in male Syrian hamsters

Adult male Syrian hamsters were subjected to 1, 3, 5, 7 or 11 weeks of either natural winter conditions or rigorously controlled laboratory conditions (LD 1014; 22 ± 2C). Although both groups of hamsters gained weight over the course of the experiment, hamsters housed indoors were significantly heavier after 5 weeks of treatment compared to their outdoors counterparts. Animals housed under natural conditions exhibited a significant decrease in circulating levels of thyroxine (T₄) and a rapid rise in triiodothyronine (T₃) levels; the free T₄ and free T₃ index (FT₄I and FT₃I) mirrored the changes in circulating levels of the respective hormones. Laboratory-housed animals had a slight rise in T₄ and FT₄I at 3 weeks followed by a slow steady decline in these values; T₃ and FT₃I values did not change remarkably in these animals. Plasma cholesterol declined steadily over the course of the experiment in laboratory-maintained animals but increased slightly during the first 5 weeks in animals under natural conditions. Since the photoperiodic conditions were approximately of the same duration in these 2 groups, it is concluded that the major differences in body weight, thyroid hormone values and plasma cholesterol are due to some component (possibly temperature) in the natural environment.     

Ultrastructural and immunohistochemical analysis of cholangiocarcinoma in immunized Syrian golden hamsters infected with Opisthorchis viverrini and administered with dimethylnitrosamine.

Utilizing the experimental model in Syrian golden hamsters, we explored the role of immunization in carcinogenesis. The animals, which were infected with liver flukes (Opisthorchis viverrini), and administered a subcarcinogenic dose of dimethylnitrosamine, developed cancer. Pre-immunizing with a crude somatic antigen did not reduce cancer development, but accelerated carcinogenesis. Histopathological analysis of the cancer tissues was done once at week 30 and again at week 39 using H and E staining, immunostaining for the p53 tumor suppressor phosphoprotein, and electron microscopy. Thirty weeks after immunization, the immunized hamsters developed tubular adenocarcinoma at a higher rate (71.43%) than the non-immunized group (20.00%). This rate (20.00%) increased to 63.64% by week 39. The small foci cancer in the non-immunized group decreased in frequency from 80.00% (at week 30) to 36.36% (by week 39), suggesting the small foci cancer progressed to tubular adenocarcinoma during the 9-week interval. Most of the observed tubular adenocarcinoma was well differentiated. Nearly all hamsters that tested positive for cancer also tested positive for p53 immunostaining in the epithelia of the small bile ducts. The positive reaction for p53-immunostaining was localized in the rough endoplasmic reticulum, Golgi apparatus and perinuclear membranes. The electron micrographs of these positive p53-immunostained cells showed characteristics of early cancer. The detection of p53 in early cancer development makes it a candidate as a tumor marker.     

Effects of isoflavones containing soy protein isolate compared with fish protein on serum lipids and susceptibility of low density lipoprotein and liver lipids to in vitro oxidation in hamsters

The effects of dietary soy protein isolate (SPI), ethanol-extracted SPI (E-SPI) low in isoflavones, and fish protein (FP) on the concentration of blood lipids and the susceptibility of low density lipoprotein (LDL) to copper-induced oxidation were compared in male golden Syrian hamsters fed a moderate hypercholesterolemic semi-purified diet for 10 weeks. SPI, E-SPI, and FP were incorporated into the isonitrogenous experimental diets as protein sources. The SPI group exhibited significantly lower serum total cholesterol concentration compared with the E-SPI group (P < 0.05) and the FP group (P < 0.01). Both the SPI and E-SPI groups showed lower LDL cholesterol (P < 0.001 and P < 0.05, respectively) and less LDL apolipoprotein B (P < 0.01) compared with the FP group. The distribution pattern of serum lipoprotein cholesterol fractions of the SPI and E-SPI groups were similar to each other, but different from that of the FP group. The lysine/arginine ratio of the three diets was significantly correlated with serum total cholesterol concentration (r = 0.462, P = 0.023). The resistance of LDL to copper-induced oxidation was greater in the SPI group than in the E-SPI and FP groups as assessed by the lower concentrations of thiobarbituric acid-reactive substances (TBARS) and the longer lag time required for the formation of conjugated dienes (P < 0.01). Livers of hamsters fed the FP diet had a higher amount of TBARS than those of hamsters fed SPI (P < 0.01) and E-SPI (P < 0.05) diets. The SPI diet showed sparing effects on alpha-tocopherol contents in both serum and liver. It seems likely that soy isoflavones protect the circulating and membrane lipids by sparing alpha-tocopherol and endogenous antioxidants.     

Metabolism of the soy isoflavones daidzein, genistein and glycitein in human subjects. Identification of new metabolites having an intact isoflavonoid skeleton

Epidemiological studies have associated high soy intake with a lowered risk for certain hormone-dependent diseases. Soy and soy foods are rich sources of isoflavones, which have been shown to possess several biological activities. In this study, the metabolism of soy isoflavones daidzein, genistein and glycitein was investigated in human subjects. The aim was to find and identify urinary phase I metabolites of isoflavones, which have an intact isoflavonoid skeleton, and which might possess some bioactivity. Six volunteers included three soy bars per day into their normal western diet for a 2-week period. Daily urine samples were collected before, and after the supplementation period. Urine samples were hydrolyzed with Helix pomatia, extracted with diethyl ether, purified with Sephadex LH-20 chromatography, and analyzed as trimethylsilyl derivatives using gas chromatography–mass spectrometry (GC–MS). The structures of the isoflavone metabolites were identified using authentic reference compounds. The metabolites, for which authentic reference compounds were not available, were identified by the interpretation of mass spectra. Several new isoflavone metabolites were identified, and the presence of previously reported metabolites confirmed. The metabolic pathways of daidzein, genistein and glycitein are presented on the basis of the identification of the metabolites in human urine after soy supplementation.     

Effects of food deprivation on locomotor activity, plasma glucose, and circadian clock resetting in Syrian hamsters

Circadian rhythms in Syrian hamsters can be phase advanced by activity or arousal stimulated during the daily rest phase ("subjective day"). A widely used method for stimulating activity is confinement to a novel wheel. Some hamsters decline to run, and some procedures may reduce the probability of running. The authors evaluated food deprivation (FD) as a method to promote running. Given evidence that perturbations of cell metabolism or glucose availability may affect circadian clock function in some tissues or species, they also assessed the effects of FD on free-running circadian phase, resetting responses to photic and nonphotic stimuli and plasma glucose. In constant light, a 27-h fast significantly increased running in a novel wheel and marginally increased the average size of resulting phase shifts. FD, without novel wheel confinement, was associated with some very large phase shifts or disruption of rhythmicity in hamsters that spontaneously ran in their home wheels during the subjective day. Hamsters that ran only during the usual active phase (subjective night) or that were prevented from running did not exhibit phase shifts, despite refeeding in the mid-subjective day. Using an Aschoff Type II design for measuring shifts, a 27-h fast significantly increased the number of hamsters that ran continuously when confined to a novel wheel but did not affect the dose-response relation between the amount of running and the size of the resulting shift. A day of fasting also did not affect the size of phase delay or advance shifts to 30-min light pulses in the subjective night. Plasma glucose was markedly reduced by wheel running in combination with fasting but was increased by running in nonfasted hamsters. These results establish FD as a useful tool for stimulating activity in home cage or novel wheels and indicate that in Syrian hamsters, significant alterations in glucose availability, associated with running, fasting, and refeeding, have surprisingly little effect on circadian pacemaker function.     

Differential effects of dietary flaxseed protein and soy protein on plasma triglyceride and uric acid levels in animal models

The effect of dietary soy protein and flaxseed meal on metabolic parameters was studied in two animal models, F344 rats with normal lipid levels and obese SHR/N-cp rats with elevated levels of cholesterol and triglyceride. The rats were fed AIN 93 diet differing only in the source of protein. The rats were fed either 20% casein, 20% soy protein or 20% flaxseed meal. Plasma was analyzed for cholesterol, triglyceride, uric acid, blood urea nitrogen (BUN), creatinine and total protein. In both strains of rats, flaxseed meal significantly decreased plasma cholesterol and triglyceride concentrations. The effect of soy protein on lipids was not as striking as that of flaxseed meal. Flaxseed meal also lowered uric acid in F344 rats and BUN in SHR/N-cp rats. Since cholesterol, triglyceride and uric acid are independent risk factors for cardiovascular disorders, our data show that both flaxseed meal and soy protein may have beneficial effects. Which chemical constituent(s) of flaxseed meal or soybean is (are) responsible for the beneficial effects need to be identified.     

Effect of fasting, phenobarbital, or hydrocortisone on serum creatine-phosphokinase and aldolase activity in myopathic Syrian hamsters.

The hereditary polymyopathy and cardiomyopathy of inbred Syrian hamsters (UM X 7.1) are associated with a marked elevation of serum creatine phosphokinase (CPK) and aldolase levels. Fasting (overnight) further increases (+100-500%) the serum concentration of these enzymes in myopathic hamsters; however, no such effect is demonstrable in normal hamsters, or in first generation offspring produced by crossbreeding the two strains (myopathic and normal). The changes are reversible, and the enzyme values return to previous levels within 72 hr. Neither phenobarbital nor hydrocortisone prevents the rises, as shown by CPK determinations; on the contrary, hydrocortisone elicits even greater serum enzyme increases.     

Effect of phytate in soy protein on the serum and liver cholesterol levels and liver fatty acid profile in rats

Dietary soy protein, in comparison with casein, generally lowers the serum cholesterol concentration in rats fed on a cholesterol-enriched diet, while mixed results were observed in rats fed on a diet free of cholesterol. Soy protein also suppresses the conversion of linoleic acid to arachidonic acid in the rat liver. The present study examines whether phytate, a minor component of a soy protein isolate, is responsible for these beneficial effects of soy protein. Weanling male rats were fed for 4 weeks on a purified diet containing a 20% level of protein (either casein (CAS), soy protein (SOY), phytate-depleted SOY (PDSOY) or phytate-replenished PDSOY (PRSOY)) and cholesterol (0 or 0.5%). The dietary protein source and phytate level only affected the serum and liver cholesterol concentrations when the animals were fed on the cholesterol-enriched diet, being significantly lower in those rats fed on the SOY and PRSOY diets than in those fed on the CAS diet, while the concentrations in the rats fed on the PDSOY diet were intermediate. When the animals were fed on the cholesterol-free diet, the ratio of (20:3n-6 + 20:4n-6)/18:2n-6 in liver phosphatidylcholine, a delta6 desaturation index, was significantly lower in the SOY diet group than in the CAS, PDSOY and PRSOY diet groups. Dietary cholesterol significantly depressed the ratio, but neither depletion nor replenishment of phytate affected the ratio. These results suggest that phytate in soy protein played a limited role in the cholesterol-lowering effect of soy protein and was not involved in the metabolism of linoleic acid.