Tyrosine kinase inhibitors potentiate the induction of low density lipoprotein receptor gene expression by hepatocyte growth factor

Isoflavones in Animals: Metabolism and Effects in Livestock and Occurrence in Feed

Soybeans are a common ingredient of animal feed. They contain isoflavones, which are known to act as phytoestrogens in animals. Isoflavones were described to have beneficial effects on farm animals. However, there are also reports of negative outcomes after the consumption of isoflavones. This review summarizes the current knowledge of metabolization of isoflavones (including the influence of the microbiome, phase I and phase II metabolism), as well as the distribution of isoflavones and their metabolites in tissues. Furthermore, published studies on effects of isoflavones in livestock species (pigs, poultry, ruminants, fish) are reviewed. Moreover, published studies on occurrence of isoflavones in feed materials and co-occurrence with zearalenone are presented and are supplemented with our own survey data.

Inhibition of low density lipoprotein receptor expression by long-term exposure to phorbol ester via p38 mitogen-activated protein kinase pathway

The proximal region -234 to (+58 bp) of low-density lipoprotein receptor (LDLR) is responsible for its up-regulation by sterol regulatory element binding protein (SREBP). However, the mechanism of sterol-independent repression of LDLR has not been determined yet. In this study, we observed that there was an early induction and a later repression of LDLR by phorbol ester (PMA) in SK-Hep1 hepatocarcinoma cells and investigated the mechanisms through which PMA repressed LDLR transcription. SK-Hep1 cells were exposed to PMA and LDLR mRNA was evaluated by RT-PCR and Northern blot analysis. The effect of phorbol ester on LDLR transcriptional activity was studied using transient transfection of LDLR promoter-luciferase constructs. Overexpression of N-SREBP-2, a dominant positive SREBP2, did not reverse the PMA-repressed LDLR promoter activity. Serial deletion of LDLR promoter revealed that the region between -1,563 and -1,326 was responsible for the repression. The pretreatment with SB202190, an inhibitor for p38 mitogen-activated protein kinase pathway (p38-MAPK), but not other signaling inhibitors, reversed the PMA-induced repression. The 24 h-treatment with PMA efficiently arrested the SK-Hep1 cell cycle at G0/G1 as demonstrated by FACS analysis and decreased the 3H-thymidine incorporation. The PMA-induced repression of LDLR transcription may be exerted by the factor(s), not SREBP2, induced or modified by p38-MAPK-mediated signaling pathway and associated with cell cycle blockage.

Antioxidant activities and lipid lowering effects of isoflavone in male rabbits

Dietary flavonoids appear to play a role in the prevention of a number of chronic diseases such as cancer and cardiovascular disease and the soy isoflavones have been the focus of particular. Consumption of soy isoflavones may reduce the risk of cardiovascular disease both through reduction in serum lipids and by the antioxidant properties. We have therefore investigate the effects of either 2.5 or 5 mg/kg B.W. doses of isoflavones on the levels of free radicals, lipids and lipoproteins in male New Zealand White rabbits. Animals were orally given 2.5 or 5 mg/kg B.W. doses of isoflavones. The tested doses were given to rabbits every other day for 13 weeks. Treatment with isoflavones caused significant (P<0.05) decrease in the concentrations of free radicals in plasma by 33% and 35%, liver by 18% and 27%, brain by 12% and 33%, testes by 40% and 21%, and kidney by 38% and 20% for 2.5 or 5 mg/kg B.W. doses, respectively, as compared to the control. On the other hand, the activity of glutathione S-transferase (GST) did not change in treated animals as compared to control. Also, results showed that isoflavones caused a significant decrease (P<0.05) in the levels of plasma total lipids (TL) by 16% and 19%, total cholesterol by 20% and 20%, triglyceride (TG) by 18% and 23%, low density lipoprotein (LDL) by 19%, 22%, very low density lipoprotein (VLDL) by 18% and 23%, and LDL:HDL ratio by 36% and 39% for 2.5 or 5 mg/kg B.W. doses, respectively, as compared to the control. While the level of high density lipoprotein (HDL) increased by 29% and 32%. The present results showed that the 5 mg/kg dose of isoflavone seemed to be related to a better plasma lipid and lipoprotein profiles and antioxidant activity.

Changes in some hematological and biochemical indices of rabbits induced by isoflavones and cypermethrin

Protective effect of isoflavones on cypermethrin-induced changes in blood hematology, and plasma lipids, lipoproteins, glucose, urea, creatinine, total bilirubin and protein concentrations of male New Zealand White rabbits was studied. Rabbits were orally given sublethal dose of cypermethrin (24 mg/kg BW; 1/100 LD50), while isoflavones (2 mg/kg BW) was given alone or in combination with cypermethrin. The tested doses were given to rabbits every other day for 12 weeks. Results showed that cypermethrin caused a significant (P<0.05) increase in the levels of plasma total lipids (TL), cholesterol, triglyceride (TG), low density lipoprotein (LDL) and very low density lipoprotein (VLDL), while the level of high density lipoprotein (HDL) decreased. Isoflavones alone significantly (P<0.05) decreased the levels of TL, cholesterol, TG, LDL and VLDL, and increased HDL, and alleviated the harmful effects of cypermethrin on lipid profiles. Cypermethrin caused a significant (P<0.05) increase in glucose, urea, creatinine and total bilirubin. The concentrations of plasma total protein (TP) and albumin (A) were significantly (P<0.05) decreased in plasma of rabbits treated with cypermethrin, while globulin concentration and A/G ratio were not affected. Results showed that cypermethrin significantly (P<0.05) decreased hemoglobin (Hb), total erythrocytic count (TEC) and packed cell volume (PCV), while total leukocyte count (TLC) increased. Isoflavones alone did not cause any significant change in these parameters, but minimized the toxic effect of cypermethrin. Results demonstrated the beneficial influences of isoflavones in reducing the negative effects of cypermethrin on blood hematology and biochemical parameters of male rabbits.

Effects of supplementation with purified red clover (Trifolium pratense) isoflavones on plasma lipids and insulin resistance in healthy premenopausal women

Consumption of isoflavone-rich soyabean protein is reported to reduce total and LDL-cholesterol, but the specific components responsible are undetermined. In a previous crossover trial we showed that purified isoflavones, derived from red clover (Trifolium pratense), raised HDL3-cholesterol in premenopausal women; however, these findings were inconclusive due to period and carryover effects. In an attempt to overcome this problem, we utilised a parallel study designed to re-examine the effects of purified isoflavones on plasma lipoproteins and markers of insulin resistance in premenopausal women. Twenty-five healthy premenopausal women participated in a double-blind, randomised, parallel study. The treatment group (n 12) consumed a placebo for the first menstrual cycle and an isoflavone supplement (86 mg/d, derived from red clover) for three cycles, while the placebo group (n 13) consumed a placebo supplement for four menstrual cycles. Blood samples were collected weekly during cycles 1, 3 and 4. Supplementation with isoflavones resulted in a 15-fold increase in urinary isoflavone excretion (P<0.0001). There were no significant effects on total cholesterol, LDL- and HDL-cholesterol, HDL subfractions, triacylglycerol, lipoprotein(a), glucose or insulin concentrations. Our present results indicate that purified isoflavones derived from red clover have no effect on cholesterol homeostasis or insulin resistance in premenopausal women, a group which is at low risk of CHD.

Transfer of soy isoflavone into the egg yolk of chickens

A diet containing a high concentration of soy isoflavone was administered to laying hens and the contents of the isoflavones transferred to the plasma and egg yolk were measured. A method for quantitatively measuring the concentration of isoflavone in the yolk was first established, before a high concentration of soy isoflavone was administered to the laying hens over an 18-day period. The concentrations of isoflavone in the plasma and egg yolk reached their highest on the 12th day of the feeding period, the values being 3,167 nmol/l and 65.29 microg/100 g, respectively. The concentration of cholesterol in the yolk was slightly affected during the early stages of the feeding period. These findings clearly demonstrate that soy isoflavone was transferred into the yolk from the feed and that the cholesterol concentration in the yolk was affected by administering the soy isoflavone-enriched feed.

Soy protein peptides regulate cholesterol homeostasis in Hep G2 cells

The activation of LDL receptors was described recently in a human hepatoma cell line (Hep G2) exposed both to alpha + alpha' subunits from 7S soy globulin and to Croksoy(R)70, a commercial isoflavone-poor soy concentrate. To assess the final identity of the peptide(s) putatively responsible for the biochemical effect, experiments were performed in Hep G2 cells, exposed either to synthetic peptides corresponding to specific sequences of 7S soy globulin or to peptides from the in vitro digestion of Croksoy(R)70. Moreover, the ability of the whole 7S globulin, its subunits and whole Croksoy(R)70 to interfere in the apolipoprotein B (apo B) secretion in the medium as well as in sterol biosynthesis was evaluated in the same model. Increased (125)I-LDL uptake and degradation vs. controls were shown after Hep G2 incubation with a synthetic peptide (10(-)(4) mol/L, MW 2271 Da) corresponding to positions 127-150 of the 7S globulin. Cells exposed to Croksoy(R)70 enzyme digestion products showed a more marked up-regulation of LDL receptors vs. controls, compared with vs. Hep G2 cells incubated with undigested Croksoy(R)70. Among soy-derived products, only the 7S globulin inhibited apo B secretion and (14)C-acetate incorporation when tested in Hep G2 cells at a concentration of 1.0 g/L. These findings support the hypothesis that if one or more peptides can reach the liver after intestinal digestion, they may elicit a cholesterol-lowering effect. Moreover, the protein moiety, devoid of isoflavone components, is likely to be responsible for this major biochemical effect of soy protein.

A cooperative interaction between soy protein and its isoflavone-enriched fraction lowers hepatic lipids in male obese Zucker rats and reduces blood platelet sensitivity in male Sprague-Dawley rats

Soy protein diets lower plasma cholesterol in hyperlipoproteinemic human subjects, as well as in animal models. We fed 7-wk-old male obese (fa/fa) and lean Zucker rats a modified AIN-76 diet (20 g protein/kg diet) containing casein (C), low isoflavone soy protein (38 mg isoflavones/kg diet; LI), or high isoflavone soy protein (578 mg isoflavones/kg diet; HI) for 70 d. In obese rats, plasma total cholesterol was 21 and 29% lower in the LI and HI groups, respectively, than in the C group (P: </= 0.004). Liver weight and liver triglyceride and cholesteryl ester concentrations were 27, 33 and 46% lower, respectively, in the LI group than in the C group (P: < 0.003). These liver measurements were 23, 24 and 57% lower, respectively, in the HI group than in the LI group (P: < 0.05). In a complementary study, 5-wk-old male Sprague-Dawley rats were fed the same C, LI and HI diets for 42 d. Thrombin-mediated platelet serotonin release in vitro was 13% lower in the HI group than in the C group (P: = 0.003). In a third study, 7-wk-old male Sprague-Dawley rats were fed either a modified AIN-76 control diet or a high fat casein-based atherogenic diet (140 g fat, 12 g cholesterol, and 2 g cholic acid/kg diet) with or without a soy isoflavones extract (983 mg isoflavones/kg diet) for 63 d. Addition of the isoflavones extract to the atherogenic diet lowered the liver triglyceride concentration by 33% relative to the atherogenic diet without isoflavones (P: = 0.0001). Our studies suggest that the hypocholesterolemic mechanism of dietary soy protein involves a cooperative interaction between the protein and isoflavone-enriched fraction that lowers hepatic lipid concentrations. We speculate that modulation of liver and plasma lipid homeostasis can also lower blood platelet sensitivity.

Antiproliferative efficacy of lipophilic soy isoflavone phytoestrogens delivered by low density lipoprotein particles into cultured U937 cells

Some fat-soluble bioactive substances incorporated into low density lipoprotein (LDL) may be delivered into cells via LDL receptor pathway influencing cellular functions. In this study, we synthesized a number of fat-soluble isoflavone esters and investigated their incorporation into LDL as well as their delivery into U937 cells. Using an artificial transfer system (Celite dispersion), genistein and daidzein oleates and daidzein dilinoleate were efficiently incorporated into LDL with concentrations ranging between 2.7 to 16.9 isoflavone molecules/LDL particle, while much smaller amounts of unesterified isoflavones and genistein stearates were transferred into LDL. LDL containing 7-oleates or 4',7-dioleates of genistein and daidzein significantly reduced U937 cell proliferation by 36-43%. The strongest inhibitory effect was shown by daidzein 4',7-dilinoleate with 93% reduction of cell proliferation. Neither of the 4'-oleates of genistein and daidzein contained in LDLs exhibited antiproliferative effects although they were incorporated into LDL. In summary, we demonstrated that isoflavones made fat-soluble by esterification can be incorporated into LDL in vitro and delivered into cultured U937 cells via the LDL-receptor pathway, reducing the cell proliferation.

Dietary isoflavones reduce plasma cholesterol and atherosclerosis in C57BL/6 mice but not LDL receptor-deficient mice

Susceptibility to atherosclerosis is determined by a combination of genetic and environmental factors, including diet. Consumption of diets rich in soy protein has been claimed to protect against the development of atherosclerosis. Potential mechanisms include cholesterol lowering, inhibition of lipoprotein oxidation and inhibition of cell proliferation by soy proteins or isoflavones, such as genistein, that are present in soy. This study was designed to determine whether soy isoflavones confer protection against atherosclerosis in mice and whether they reduce serum cholesterol levels and lipoprotein oxidation. C57BL/6 and LDL receptor-deficient (LDLr-null) mice were fed soy protein-based, high fat diets with isoflavones present (IF+, 20.85 g/100 g protein, 0.027 g/100 g genistein, 0.009 g/100 g daidzein) or diets from which isoflavones, and possibly other components, had been extracted (IF-, 20.0 g/100 g protein, 0.002 g/100 g genistein, 0.001 g/100 g daidzein). Because LDLr-null mice develop extensive atherosclerosis and hypercholesterolemia after minimal time on a high fat diet, they were fed the diets for 6 wk, whereas C57BL/6 mice were fed the diets for 10 wk. Plasma cholesterol levels did not differ between LDLr-null mice fed IF- and those fed IF+, but were 30% lower in C57BL/6 mice fed the IF+ diet than in those fed the IF- diet. Susceptibility of LDL to oxidative modification, measured as the lag phase of conjugated diene formation in LDLr-null mice, was not altered by isoflavone consumption. All LDLr-null mice developed atherosclerosis, and the presence or deficiency of dietary isoflavones did not influence atherosclerotic lesion area. In contrast, atherosclerotic lesion area was significantly reduced in C57BL/6 mice fed IF+ compared with those fed IF-. Thus, this study demonstrates that although the isoflavone-containing diet resulted in a reduction in cholesterol levels in C57BL/6 mice, it had no effect on cholesterol levels or on susceptibility of LDL to oxidative modification in LDLr-null mice. Further, dietary isoflavones did not protect against the development of atherosclerosis in LDLr-null mice but did decrease atherosclerosis in C57BL/6 mice. These findings suggest that soy isoflavones might lower cholesterol levels by increasing LDL receptor activity, and the reduction in cholesterol may offer some protection against atherosclerosis.

The uptake of LDL-IC by human macrophages: predominant involvement of the Fc gamma RI receptor

The incubation of human macrophages with antigen antibody complexes prepared with rabbit anti-LDL and human LDL (LDL-IC) is followed by ingestion of those immune complexes (IC), massive cholesterol ester accumulation, cytokine release and overexpression of the LDL receptor. The massive accumulation of cholesterol esters and overexpression of the native LDL receptor are specifically induced by immune complexes containing native or modified LDL, but not by any other type of IC. We report the results of a series of experiments aimed at defining the receptor preferentially involved in LDL-IC uptake. Flow cytometry studies using CD16, CD32 and CD64 monoclonal antibodies showed a sharp reduction on the expression of CD64 (Fc gamma RI) both by human monocyte-derived macrophages and THP-1 cells after incubation with LDL-IC, suggesting preferential engagement of this type of Fc receptor. Blocking experiments with aggregate-free IgG1 and CD32 monoclonal antibody confirmed that blocking Fc gamma RI prevented both LDL-IC uptake and the upregulation of LDL receptors on THP-1 cells. In contrast, blocking Fc gamma RII did not affect either the uptake of LDL-IC or the expression of LDL receptors on the same cells. The preferential engagement of Fc gamma R-I by LDL-IC suggests a biological difference of LDL-IC relative to other types of IC and opsonized particles. The precise molecular mechanism(s) responsible for the paradoxical upregulation of LDL receptor after the uptake of LDL-IC remain to be elucidated.