Soy isoflavones prevent ovariectomy-induced atherosclerotic lesions in Golden Syrian hamster model of postmenopausal hyperlipidemia

Tetrahydropalmatine Prevents High-Fat Diet-Induced Hyperlipidemia in Golden Hamsters (Mesocricetus Auratus)

Background

Hyperlipidemia is a major cause of atherosclerotic cardiovascular disease. Tetrahydropalmatine (THP) can exhibit hepatoprotective, anti-arrhythmic, and anti-inflammatory activities. The mechanism of THP on the hyperlipidemia remains unknown; therefore, the present study explored the role of THP in hyperlipidemia.

Material/Methods

We established an animal model of hyperlipidemia by high-fat diet (HFD) feeding. Blood samples were obtained for determination of serum cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c), pro-inflammatory cytokines, and CYP7A1 expression. Histology was performed and inflammation was detected in the liver using hematoxylin-eosin (HE) staining and enzyme-linked immunosorbent assay (ELISA), respectively. The mRNA and protein levels of TLR4 and TRAF-6 were determined by quantitative real-time PCR (qPCR) and Western blot, respectively.

Results

THP suppressed hepatic lipid accumulation and reduced serum levels of TC, TG, LDL-c, and HDL-c in HFD-fed golden hamsters. THP increased cholesterol 7 α-hydroxylase (CYP7A1) expression and prevented inflammation by the limited reduction in interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expressions in serum and liver. THP slightly increased the ratio of the body/liver weight. THP inhibited the mRNA and protein levels of Toll-like receptor 4 (TLR4) and TNF-receptor associated factor-6 (TRAF-6).

Conclusions

These results suggest that THP attenuates hyperlipidemia by multiple effects, including hepatoprotective and anti-inflammatory effects. Moreover, THP also suppressed the expressions of TLR4 and TRAF-6 in golden hamsters.

Endocannabinoid Signaling at Hypothalamic Steroidogenic Factor-1/Proopiomelanocortin Synapses Is Sex- and Diet-Sensitive

We tested the hypotheses that steroidogenic factor (SF)-1 neurons in the hypothalamic ventromedial nucleus (VMN) provide sexually disparate, endocannabinoid (EC)- and diet-sensitive glutamatergic input onto proopiomelanocortin (POMC) neurons. Electrophysiological recordings were performed in hypothalamic slices from intact and castrated guinea pigs, along with in vitro optogenetic experiments in intact male as well as cycling and ovariectomized female NR5A1-Cre mice. In slices from castrated male and female guinea pigs, depolarized-induced suppression of excitation (DSE) time-dependently reduced the amplitude of evoked excitatory postsynaptic currents (eEPSCs) in POMC neurons generated by electrically stimulating the dorsomedial VMN. Androgen stimulation rapidly enhanced this DSE, which was also found in insulin-resistant, high-fat diet (HFD)-fed males. By contrast, retrograde signaling at VMN/ARC POMC synapses was markedly attenuated in periovulatory females. HFD potentiated central cannabinoid-induced hyperphagia in both males and females, but exerted differential influences on cannabinoid-induced increases in energy expenditure. In NR5A1-Cre mice, the reduction in light-evoked EPSC amplitude caused by postsynaptic depolarization in cycling females was modest in comparison to that seen in intact males. Estradiol attenuated the DSE in light-evoked EPSC amplitude in slices from ovariectomized females. Moreover, the retrograde inhibition of transmission was further accentuated in HFD-fed males. Chemogenetic activation of SF-1 neurons suppressed appetite and increased energy expenditure in males, effects which were attenuated by HFD. Conversely, energy expenditure was increased in estradiol- but not vehicle-treated ovariectomized females. Together with our previous studies indicating that DSE in POMC neurons is EC-mediated, these findings indicate that VMN SF-1/ARC POMC synapses represent a sexually differentiated, EC- and diet-sensitive anorexigenic component within the hypothalamic energy balance circuitry.

The α' subunit of β-conglycinin and the A1-5 subunits of glycinin are not essential for many hypolipidemic actions of dietary soy proteins in rats

PURPOSE

This study examined the effects of dietary soy protein (SP) lacking different storage protein subunits and isoflavones (ISF) on the abdominal fat, blood lipids, thyroid hormones, and enzymatic activities in rats.

METHODS

Weanling Sprague-Dawley rats (8 males and 8 females/group) were fed diets containing either 20 % casein without or with supplemental isoflavones or alcohol-washed SP isolate or SP concentrates (SPC) prepared from 6 different soy bean lines for 8 weeks.

RESULTS

Feeding of diets containing SPC regardless of their subunit compositions significantly lowered relative liver weights, blood total, free, and LDL cholesterol in both genders (P < 0.05) and also reduced serum free fatty acids (FFA) and abdominal fat in females (P < 0.05) compared to the casein or casein + ISF diets. Dietary SPC significantly elevated the plasma free triiodothyronine (T3) in both genders and total T3 in females compared to the casein diet (P < 0.05). The SPC lacking β-conglycinin α' and either the glycinin A1-3 or A1-5 subunits increased total T3 in males and reduced plasma enzymatic activities of creatine kinase and lactate dehydrogenase compared to casein or casein + ISF diet (P < 0.05).

CONCLUSIONS

Soy isoflavones were mainly responsible for the hypocholesterolemic effects and increased plasma free T3, whereas reduction in FFA, abdominal fat, liver weight and increased plasma total T3 were the effects of the soy proteins. Neither the α' subunit of β-conglycinin nor the A1-5 subunits of glycinin are essential for the hypolipidemic properties of soy proteins.

The Experimental Use of Syrian Hamsters

The Syrian hamster (Mesocricetus auratus) is a widely used experimental animal model. This chapter focuses primarily on the most current research uses of the hamster. More classical uses are covered only as they pertain to these current uses. Hamsters possess unique anatomical and physiological features, which make them desirable research models. Unlike other commonly used laboratory rodents, hamsters possess a cheek pouch, which can be easily everted and examined at both the gross and microscopic level. The hamster's relative size also allows for better visualization of certain biological systems including the respiratory and reproductive systems when compared to the mouse. Further, laboratory hamsters develop a variety of inherited diseases, which display similarities to human conditions. Hamsters possessing some of these inherited traits are commercially available. They are susceptible to a variety of carcinogens and develop tumors that other research animals less commonly develop. Also they are susceptible to the induction of a variety of metabolic disorders through the use of dietary manipulations. The antagonistic nature of hamsters is used to study the effect of treatment on male aggressive and defensive behaviors. Syrian hamsters display several unique characteristics that make them desired models for carcinogenesis studies.

Soyasaponin Ab ameliorates colitis by inhibiting the binding of lipopolysaccharide (LPS) to Toll-like receptor (TLR)4 on macrophages

Many clinical studies have shown that daily intake of soybean [ Glycine max (L.) Merr., Fabacease] or its foods may reduce the risk of osteoporosis, heart attack, hyperlipidemia, coronary heart disease, cardiovascular and chronic renal diseases, and cancers, including prostate, colon, and breast cancers. Of the soy constituents, soyasaponins exhibit anti-aging, antioxidant, apoptotic, and anti-inflammatory effects. However, the anti-inflammatory effect of soyasaponin Ab has not been thoroughly studied. Therefore, we investigated its anti-inflammatory effects in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitic mice and lipopolysaccharide (LPS)-stimulated peritoneal macrophages. Soyasaponin Ab inhibited colon shortening, myeloperoxidase activity, the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), and activation of the transcription factor nuclear factor-κB (NF-κB). Soyasaponin Ab (1, 2, 5, and 10 μM) inhibited the production of NO (IC(50) = 1.6 ± 0.1 μM) and prostaglandin E(2) (IC(50) = 2.0 ± 0.1 ng/mL), the expression of tumor necrosis factor (TNF)-α (IC(50) = 1.3 ± 0.1 ng/mL), interleukin (IL)-1β (IC(50) = 1.5 ± 0.1 pg/mL), and toll-like receptor (TLR)4, and the phosphorylation of interleukin-1 receptor-associated kinase (IRAK)-1 in LPS-stimulated peritoneal macrophages. Soyasaponin Ab weakly inhibited the phosphorylation of ERK, JNK, and p38. Soyasaponin Ab significantly reduced the binding of Alexa-Fluor-594-conjugated LPS to peritoneal macrophages. Soyasaponin Ab did not affect TLR4 expression or LPS-induced NF-κB activation in TLR4 siRNA-treated peritoneal macrophages (knockdown efficiency of TLR4 > 94%). On the basis of these findings, soyasaponin Ab may ameliorate colitis by inhibiting the binding of LPS to TLR4 on macrophages.

Soyasaponin I attenuates TNBS-Induced colitis in mice by inhibiting NF-κB pathway

Soybean, which contains soyasaponins and isoflavones as representative constituents, exhibits anti-inflammatory and antioxidant effects. To understand the anti-inflammatory effects of soyasaponins, we isolated soyasaponin I, a major constituent of soybean, and investigated the inhibitory effects on inflammatory markers in LPS-stimulated mouse peritoneal macrophages and 3,4,5-trinitrobenzenosulfonic acid (TNBS)-induced colitic mice. Soyasaponin I, which exhibited lipid peroxidation-inhibitory effects in vitro, inhibited the production of proinflammatory cytokines (TNF-α and IL-1β), inflammatory mediators (NO and PGE2), and inflammatory enzymes (COX-2 and iNOS) in LPS-stimulated peritoneal macrophages. Soyasaponin I also suppressed the phosphorylation of IκB-α and the nuclear translocation of NF-κB. However, these soyasaponins barely inhibited mitogen-activated protein kinases. Oral administration of soyasaponin I (10 and 20 mg/kg) to TNBS-treated colitic mice significantly reduced inflammatory markers, colon length, myeloperoxidase, lipid peroxide (malondialdehyde and 4-hydroxy-2-nonenal), proinflammatory cytokines and NF-κB activation in the colon, as well as increased glutathione content, superoxide dismutase, and catalase activity. Based on these findings, soyasaponin I may attenuate colitis by inhibiting the NF-κB pathway.

One-year soy protein supplementation does not improve lipid profile in postmenopausal women

OBJECTIVE

The risk of heart disease increases significantly in women after menopause mostly because of estrogen deficiency. Soy protein, a good source of isoflavones that are known to bind estrogen receptors, has also been promoted as a dietary means for reducing the risk of heart disease. The aim of this study was to examine the effects of soy protein consumption on heart disease risk in postmenopausal women.

METHODS

Moderately hypercholesterolemic postmenopausal women were randomly assigned to consume soy or control foods daily for 1 year. Serum samples were analyzed for total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, apolipoprotein (Apo) A, and Apo B. Sixty-two women completed the study.

RESULTS

There was a trend for total cholesterol and high-density lipoprotein cholesterol levels to increase after 1 year of soy protein supplementation (230.04 +/- 6.1 vs 242.57 +/- 6.2 mg/dL, P < 0.1, and 56.87 +/- 2.5 vs 60.33 +/- 2.5 mg/dL, P < 0.1, respectively). There were no significant differences in low-density lipoprotein cholesterol or triglyceride levels; however, a significant increase in Apo B levels (105.5 +/- 5.9 vs 120.21 +/- 5.9 mg/dL; P = 0.002) and a significant decrease in Apo A levels (189.36 +/- 10 vs 173.21 +/- 10 mg/dL; P = 0.009) were seen.

CONCLUSIONS

Our data indicate that 1-year soy protein supplementation did not confer cardiovascular benefits, in terms of favorable alterations in the lipid profile, in this cohort of postmenopausal women. These findings, as well as those from other studies, lend credence to the decision of the Food and Drug Administration to reevaluate the soy protein health claim issued a decade ago.

Isoflavone glycitein diminished plasma cholesterol in female golden Syrian hamsters

The soybean isoflavones, daidzein, genistein, and glycitein, were hypothesized to act as cholesterol-lowering components, separate from soy protein. Pure synthetic daidzein, genistein, or glycitein (0.9 mmol/kg diet) or a casein-based control diet was fed to groups of 10 female Golden Syrian hamsters for 4 weeks. Hamsters fed glycitein had significantly lower plasma total (by 15%) and non-HDL (by 24%) cholesterol compared with those fed casein (P<0.05). Daidzein and genistein's effects on these lipids did not differ from the effects of either casein or glycitein. Plasma HDL cholesterol and triglyceride concentrations were not significantly affected by dietary treatments. The percentage of urinary recovery of the ingested dose of each isoflavone was glycitein>daidzein>genistein (33.2%, 4.6%, 2.2%, respectively), with the apparent absorption of glycitein significantly greater than that of the other isoflavones. These data suggest that glycitein's greater cholesterol-lowering effect was due to its greater bioavailability, as reflected in its urinary recovery compared with that of the other isoflavones.

High urinary isoflavone excretion phenotype decreases plasma cholesterol in golden Syrian hamsters fed soy protein

Apparent absorption of isoflavones varies greatly among individuals but is relatively stable within an individual. We hypothesized that high urinary isoflavone excreters would show less plasma non-HDL cholesterol (non-HDL-C) than low isoflavone excreters after soy protein feeding. Fifty Golden Syrian hamsters were fed a high-fat/casein diet (n = 10) or a high-fat/soy protein diet (n = 40) for 4 wk. We identified 2 distinct urinary isoflavone excretion phenotypes based upon HPLC analysis of urinary glycitein using a pairwise correlation plots analysis, or based upon total urinary isoflavone using a hierarchical cluster test. High isoflavone excreters showed greater urinary isoflavones (P < 0.05) than did low isoflavone excreters at wk 1 and 4. The low urinary glycitein excretion phenotype was more stable than the high urinary glycitein excretion phenotype by McNemar's test. High urinary isoflavone excreters had significantly less non-HDL-C than did the low isoflavone excreters or casein-fed controls (P < 0.05). Plasma total and non-HDL-C were negatively correlated with urinary daidzein, glycitein, and total isoflavone excretion (r = -0.45 to -0.58, P < 0.05). Urinary isoflavone excretion phenotypes predicted the cholesterol-lowering efficacy of soy protein. Isoflavone absorbability, probably due to gut microbial ecology, is an important controllable variable in studies of effects of soy protein on blood lipids.

Soy protein containing isoflavones favorably influences macrophage lipoprotein metabolism but not the development of atherosclerosis in CETP transgenic mice

The possibility that soy protein containing isoflavones influences the development of experimental atherosclerosis has been investigated in ovariectomized mice heterozygous for the human CETP transgene and for the LDL-receptor null allele (LDLr(+/-) CETP(+/-)). After ovariectomy at 8 wk of age they were fed a fat/cholesterol-rich diet for 19 wk and divided into three experimental groups: dietary unmodified soy protein containing isoflavones (mg/g of diet), either at low-dose (Iso Low, 0.272, n = 25), or at high-dose (Iso High, 0.535, n = 28); and the atherogenic diet containing an isoflavone-depleted alcohol-washed soy protein as a control group (n = 28). Aortic root lipid-stained lesion area (mean microm2 x 10(3) +/- SD) did not differ among Iso Low (12.3 +/- 9.9), Iso High (7.4 +/- 6.4), and controls (10.7 +/- 12.8). Autoantibody titers against plasma oxidized LDL did not differ among the experimental groups. Using the control mice as the reference value (100%), in vitro mouse peritoneal macrophage uptake of labeled acetylated LDL-cholesterol was lower in the Iso High (68%) than in the Iso Low (85%) group. The in vitro percent removal by exogenous HDL of labeled unesterified cholesterol from macrophages previously enriched with human [4- 14C]-cholesteryl oleate acetylated LDL was enhanced in the Iso High group (50%). In spite of these in vitro potentially antiatherogenic actions, soy protein containing isoflavones did not modify the average size of lipid-stained area in the aortic root.

Flaxseed reduces plasma cholesterol and atherosclerotic lesion formation in ovariectomized Golden Syrian hamsters

BACKGROUND

Dietary modification contributes significantly in reducing cardiovascular disease (CVD) risk factors including lowering cholesterol and atherosclerosis. The purpose of this study was to investigate the effects of flaxseed, a rich source of lignans, alpha-linolenic acid and soluble fiber mucilage, on the prevention of ovariectomy-induced rise in total cholesterol and atherosclerotic lesions.

METHODS

Seventy-two 6-month-old female Golden Syrian hamsters were either ovariectomized (ovx) or sham-operated (sham) and randomly assigned to six groups (n = 12): sham, ovx, or ovx plus either 17beta-estradiol (E(2), 10 microg/kg body weight) or semi-purified diet adjusted for macronutrients and fiber to contain one of the three doses of flaxseed (7.5, 15, or 22.5%) for 120 days.

RESULTS

Ovariectomy significantly elevated plasma total-, HDL-, and free-cholesterol concentrations. Similar to estrogen, all doses of flaxseed were effective in preventing the ovx-induced rise in plasma total cholesterol. Triglyceride concentrations were significantly higher in the flax-fed hamsters. There were no significant differences in plasma non-HDL- and esterified-cholesterol among the treatment groups. Ovariectomy also increased the number of hamsters with lesions and the aortic fatty streak area. All three doses of flaxseed reduced the fatty streak area and the incidence of lesions to levels similar to the sham group.

CONCLUSION

The findings of this study show that flaxseed is beneficial in reducing plasma cholesterol and plaque formation induced by ovarian hormone deficiency.