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

A Pea (Pisum sativum L.) Seed Vicilins Hydrolysate Exhibits PPARγ Ligand Activity and Modulates Adipocyte Differentiation in a 3T3-L1 Cell Culture Model

Legume consumption has been reported to induce beneficial effects on obesity-associated metabolic disorders, but the underlying mechanisms have not been fully clarified. In the current work, pea (Pisum sativum L.) seed meal proteins (albumins, legumins and vicilins) were isolated, submitted to a simulated gastrointestinal digestion, and the effects of their hydrolysates (pea albumins hydrolysates (PAH), pea legumins hydrolysates (PLH) and pea vicilin hydrolysates (PVH), respectively) on 3T3-L1 murine pre-adipocytes were investigated. The pea vicilin hydrolysate (PVH), but not native pea vicilins, increased lipid accumulation during adipocyte differentiation. PVH also increased the mRNA expression levels of the adipocyte fatty acid-binding protein (aP2) and decreased that of pre-adipocyte factor-1 (Pref-1) (a pre-adipocyte marker gene), suggesting that PVH promotes adipocyte differentiation. Moreover, PVH induced adiponectin and insulin-responsive glucose transporter 4 (GLUT4) and stimulated glucose uptake. The expression levels of peroxisome proliferator-activated receptor γ (PPARγ), a key regulator of adipocyte differentiation, were up-regulated in 3T3-L1 cells treated with PVH during adipocyte differentiation. Finally, PVH exhibited PPARγ ligand activity. Lactalbumin or other pea hydrolysates (PAH, PLH) did not exhibit such effects. These findings show that PVH stimulates adipocyte differentiation via, at least in part, the up-regulation of PPARγ expression levels and ligand activity. These effects of PVH might be relevant in the context of the beneficial health effects of legume consumption in obesity-associated metabolic disorders.

A critical review of food-associated factors proposed in the etiology of feline hyperthyroidism

Since the first description of feline hyperthyroidism (HT) in 1979, several studies have been undertaken to define the etiology of the disease. Epidemiologic studies, after investigating non-food- and food-associated factors, suggest a multifactorial etiology. However, in the absence of prospective cohort studies that can confirm a cause-and-effect relationship between HT and associated risk factors, no causative factor for HT has been identified to date. Feline HT resembles toxic nodular goiter in humans, with autonomously functioning upregulated iodide uptake systems. Contribution of the diet to HT development remains controversial. The purpose of this paper is to review critically the reported food-associated risk factors for HT.

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.

Effect of supplementation of probiotics and phytosterols alone or in combination on serum and hepatic lipid profiles and thyroid hormones of hypercholesterolemic rats

Probiotic bacteria and phytosterols are natural hypocholesterolemic agents with potential cardiovascular benefits. Accordingly, the present study was conducted to evaluate the effect of supplementation of probiotics and phytosterols alone or in combination on serum and hepatic lipid profiles and thyroid hormones of hypercholesterolemic rats. Mixed probiotics treatment consisted of 8 probiotic strains: 2 strains of each of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus gasseri, and Lactobacillus reuteri. The rats were fed for 8 wk with the given treatments in addition to a high-fat-high-cholesterol basal diet to induce hypercholesterolemia. Results showed that supplementation significantly reduced serum total cholesterol, low-density-lipoprotein cholesterol (LDL-C), high-density-lipoprotein cholesterol, and triglycerides compared with the controls. The symbiotic treatment was more effective in lowering LDL-C, whereas mixed probiotics treatment more effectively lowered serum total cholesterol and LDL-C than the phytosterol-containing treatment. The phytosterol-containing treatments induced the increased activity of thyroid glands, as evident by elevated levels of serum total thyroxine, total triiodothyronine, and free triiodothyronine. In conclusion, the lipid profile can effectively be reduced to lower the incidence of cardiovascular disease using combinations of Lactobacillus-based probiotics and phytosterols in functional foods.

Glucocorticosteroid-induced osteoporosis in adult primiparous Göttingen miniature pigs: effects on bone mineral and mineral metabolism

Information on the pathophysiology of glucocorticoid-induced osteoporosis (GIO) is limited, since its clinical picture often reflects a combined effect of glucocorticoids (GC) and the treated systemic disease (i.e., inflammation and immobility). In 50 healthy adult (30-mo-old) primiparous Göttingen minipigs, we studied the short-term (8 mo, n = 30) and long-term (15 mo, n = 10) effect of GC on bone and mineral metabolism longitudinally and cross-sectionally compared with a control group (n = 10). All animals on GC treatment received prednisolone orally at a dose of 1.0 mg x kg body wt(-1) x day(-1) for 8 wk and thereafter at 0.5 mg/kg body wt(-1) x day(-1). In the short term, GC reduced bone mineral density (BMD) at the lumbar spine by -47.5 +/- 5.1 mg/cm(3) from baseline (P < 0.001), which was greater (P < 0.05) than the loss [not significant (NS)] in the control group of -11.8 +/- 12.6 mg/cm(3). Calcium absorption decreased from baseline by -2,488 +/- 688 mg/7 days (P < 0.001) compared with -1,380 +/- 1,297 mg/7 days (NS) in the control group. Plasma bone alkaline phosphatase (BAP) decreased from baseline by -17.8 +/- 2.2 U/l (P < 0.000), which was significantly different (P < 0.05) from the value of the control group of -1.43 +/- 4.8 U/l. In the long term, the loss of BMD became more pronounced and bone mineral content (BMC), trabecular thickness, mechanical stability, calcium absorption, 25-hydroxyvitamin D(3), 1,25-dihydroxyvitamin D(3), and parathyroid hormone tended to be lower compared with the control group. There was a negative association between the cumulative dose of GC and BMD, which was associated with impaired osteoblastogenesis. In conclusion, the main outcomes after GC treatment are comparable to symptoms of GC-induced osteoporosis in human subjects. Thus the adult Göttingen miniature pig appears to be a valuable animal model for GC-induced osteoporosis.

Effects of soybean isoflavones, probiotics, and their interactions on lipid metabolism and endocrine system in an animal model of obesity and diabetes

The effects of soybean isoflavones with or without probiotics on tissue fat deposition, plasma cholesterol, and steroid and thyroid hormones were studied in SHR/N-cp rats, an animal model of obesity, and were compared to lean phenotype. We tested the hypothesis that probiotics by promoting the conversion of isoflavone glycosides to their metabolically active aglycone form will have a synergistic effect on body fat, cholesterol metabolism, and the endocrine system. Obese and lean SHR/N-cp rats were fed AIN-93 diets containing 0.1% soy isoflavone mixture, 0.1% probiotic mixture, or both together. Different fat tissues were teased and weighed. Plasma was analyzed for cholesterol and steroid and thyroid hormones. In both phenotypes, isoflavones lowered fat deposition in several fat depots. Probiotics alone had no significant effect on fat depots. Isoflavones lowered total, LDL, and HDL cholesterol in lean rats, but in obese rats isoflavones lowered only total and LDL cholesterol. Isoflavones also lowered many of the steroid hormones involved in lipid metabolism but had no significant effect on thyroid hormones. Probiotics had no significant effect on cholesterol or hormones. Thus, our data show that soy isoflavones also lower plasma cholesterol and that this hypocholesterolemic effect appears to be due in part to the modulation of steroid hormones. Probiotics do not seem to enhance the effect of isoflavones.

Effect of dietary soy on serum thyroid hormone concentrations in healthy adult cats

OBJECTIVE

To compare effects of short-term administration of a soy diet with those of a soy-free diet on serum thyroid hormone concentrations in healthy adult cats.

ANIMALS

18 healthy adult cats.

PROCEDURE

Cats were randomly assigned to receive either a soy or soy-free diet for 3 months each in a crossover design. Assays included CBC, serum biochemical profile, thyroid hormone analysis, and measurement of urinary isoflavone concentrations.

RESULTS

Genistein, a major soy isoflavone, was identified in the urine of 10 of 18 cats prior to dietary intervention. Compared with the soy-free diet, cats that received the soy diet had significantly higher total thyroxine (T4) and free T4 (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations. The T3/fT4 ratio was also significantly lower in cats that received the soy diet. Although the magnitudes of the increases were small (8% for T4 and 14% for fT4), these changes resulted in an increased proportion of cats (from 1/18 to 4/18) that had fT4 values greater than the upper limit of the laboratory reference range. There was no significant effect of diet on any other measured parameter.

CONCLUSIONS AND CLINICAL RELEVANCE

Short-term administration of dietary soy has a measurable although modest effect on thyroid hormone homeostasis in cats. Increase in T4 concentration relative to T3 concentration may result from inhibition of 5'-iodothyronine deiodinase or enhanced T3 clearance. Soy is a common dietary component that increases serum T4 concentration in cats.

Beneficial role of dietary phytoestrogens in obesity and diabetes

Evidence is emerging that dietary phytoestrogens play a beneficial role in obesity and diabetes. Nutritional intervention studies performed in animals and humans suggest that the ingestion of soy protein associated with isoflavones and flaxseed rich in lignans improves glucose control and insulin resistance. In animal models of obesity and diabetes, soy protein has been shown to reduce serum insulin and insulin resistance. In studies of human subjects with or without diabetes, soy protein also appears to moderate hyperglycemia and reduce body weight, hyperlipidemia, and hyperinsulinemia, supporting its beneficial effects on obesity and diabetes. However, most of these clinical trials were relatively short and involved a small number of patients. Furthermore, it is not clear whether the beneficial effects of soy protein and flaxseed are due to isoflavones (daidzein and genistein), lignans (matairesinol and secoisolariciresinol), or some other component. Isoflavones and lignans appear to act through various mechanisms that modulate pancreatic insulin secretion or through antioxidative actions. They may also act via estrogen receptor-mediated mechanisms. Some of these actions have been shown in vitro, but the relevance of these studies to in vivo disease is not known. The diversity of cellular actions of isoflavones and lignans supports their possible beneficial effects on various chronic diseases. Further investigations are needed to evaluate the long-term effects of phytoestrogens on obesity and diabetes mellitus and their associated possible complications.

Effect of soy protein on endogenous hormones in postmenopausal women

BACKGROUND

The long-term clinical effects of soy protein containing various concentrations of isoflavones on endogenous hormones are unknown.

OBJECTIVE

We examined the effects of ingestion of soy protein containing various concentrations of isoflavones on hormone values in postmenopausal women.

DESIGN

Seventy-three hypercholesterolemic, free-living, postmenopausal women participated in a 6-mo double-blind trial in which 40 g protein as part of a National Cholesterol Education Program Step I diet was provided as casein from nonfat dry milk (control), isolated soy protein (ISP) containing 56 mg isoflavones (ISP56), or ISP containing 90 mg isoflavones (ISP90). Endogenous hormone concentrations were measured at baseline and at 3 and 6 mo.

RESULTS

The concentration of thyroxine and the free thyroxine index were higher in the ISP56 group, and the concentration of thyroid-stimulating hormone was higher in the ISP90 group than in the control group at 3 and 6 mo (P < 0.05). Triiodothyronine was significantly higher in the ISP90 group only at 6 mo. Thyroxine, free thyroxine index, and thyroid-stimulating hormone at 6 mo were inversely associated with measures of baseline estrogenicity. No significant differences were found for endogenous estrogens, cortisol, dehydroepiandrosterone sulfate, insulin, glucagon, or follicle-stimulating hormone after baseline hormone values were controlled for.

CONCLUSIONS

This study does not provide evidence that long-term ingestion of soy protein alters steroid hormone values, but it suggests that soy protein may have small effects on thyroid hormone values that are unlikely to be clinically important. The thyroid effects are, however, consistent with previous findings in animals and highlight the need for future research investigating possible mechanisms of action.

Lack of effect of soy isoflavone on thyroid hyperplasia in rats receiving an iodine-deficient diet

We have reported a dramatic synergism between soy intake and iodine deficiency regarding induction of thyroid hyperplasia in rats. Because isoflavones are active constituents of soybeans, in the present study, their possible contribution was examined. Female F344 rats were divided into 8 groups, exposed to diet containing a 0.2% soy isoflavone mixture (SI), 0.2% SI + iodine deficiency (ID), 0.04% SI, 0.04% SI + ID, 20% defatted soybean (DS) alone, 20% DS + ID, ID alone or basal diet alone for 5 weeks. Thyroid weight was not influenced by SI, but was increased by the ID and DS diets with a further significant increment in the DS + ID group (P < 0.01). Compared to the control value, serum T(4) was significantly (P < 0.01) increased by 20% DS alone and decreased in all groups given the ID treatment (P < 0.001). Serum thyroid stimulating hormone (TSH) level was increased by ID, and further enhanced by DS (P < 0.01) but not SI. Histopathologically, diffuse hypertrophy and / or hyperplasia of thyroid follicles were observed in the ID-treated groups, the severity being enhanced by DS but not SI. Proliferating cell nuclear antigen labeling indices (%) were elevated in the ID diet groups and again enhanced by DS, but not SI. These results thus suggest that isoflavones may not be involved in the mechanisms underlying the synergistic goitrogenic effect of soybean with iodine deficiency.

Energy metabolism and thyroid hormone levels of growing rats in response to different dietary proteins--soy protein or casein

Energy balances were measured by indirect calorimetry in four experiments on male growing rats, fed restrictively on isoenergetic and isonitrogenous (10% CP) diets based on either casein supplemented with methionine, or soy protein isolate (experiments 1, 2 and 3) and soy protein isolate supplemented with methionine (experiment 0), respectively. At the end of experiments the rats were killed for body analysis and determination of thyroid hormones and lipids in blood as well as mitochondrial respiration in liver and heart. Feeding of non-supplemented soy protein resulted in a lower efficiency of energy utilisation as well as a lower protein utilisation compared to casein-fed and supplemented soy protein-fed rats. Chemical body composition was not markedly different between the dietary groups. After long-term feeding of soy protein (experiment 3) mass and mitochondrial protein content of the interscapular brown adipose tissue were increased compared to casein-fed rats. Serum thyroid hormone levels were not changed (T3 and free T3) or were significantly lowered (T4 and free T4) following soy protein feeding in comparison with casein feeding (except for experiment 2). Cholesterol and triglycerides were decreased on an average in response to soy protein or supplemented soy protein feeding. In two of three experiments a significant lower efficiency of hepatic mitochondrial respiration with succinate as substrate, expressed by the ratio of added ADP to oxygen consumed, was observed in soy protein-fed rats compared to casein-fed rats.

Dietary phytoestrogens

Broadly defined, phytoestrogens include isoflavones, coumestans, and lignans. A number of these compounds have been identified in fruits, vegetables, and whole grains commonly consumed by humans. Soybeans, clover and alfalfa sprouts, and oilseeds (such as flaxseed) are the most significant dietary sources of isoflavones, coumestans, and lignans, respectively. Studies in humans, animals, and cell culture systems suggest that dietary phytoestrogens play an important role in prevention of menopausal symptoms, osteoporosis, cancer, and heart disease. Proposed mechanisms include estrogenic and antiestrogenic effects, induction of cancer cell differentiation, inhibition of tyrosine kinase and DNA topoisomerase activities, suppression of angiogenesis, and antioxidant effects. Although there currently are no dietary recommendations for individual phytoestrogens, there may be great benefit in increased consumption of plant foods.

Intake of 25 g of soybean protein with or without soybean fiber alters plasma lipids in men with elevated cholesterol concentrations

Twenty-one mildly hypercholesterolemic men consumed a diet that was low in fat (< 30% of energy) and cholesterol (300 mg/d) and were given muffins containing 25 g protein + 20 g dietary fiber daily from either isolated soybean protein + soybean cotyledon fiber, isolated soybean protein + cellulose, casein + soybean cotyledon fiber or casein + cellulose. All subjects progressed through the low fat, low cholesterol baseline period, lasting 2 wk, and then through all four dietary treatments, lasting 4 wk each, according to a Latin square design. Plasma concentrations of total, LDL, HDL and VLDL cholesterol, total and VLDL triacylglycerols, and apolipoprotein A-I and B were measured at the end of each period. When data from all subjects were analyzed, dietary treatments did not influence lipemia; however, in subjects with initial total cholesterol concentrations > 5.7 mmol/L, both isolated soybean protein treatments resulted in significantly lower total cholesterol compared with the two casein treatments (P < 0.05). In addition, a negative linear relationship was observed when a subject's total or LDL cholesterol change after each of the soybean treatments was regressed against the subject's baseline cholesterol concentration (P < 0.05). Apolipoprotein A-I varied dependent on baseline cholesterol with no apparent pattern, whereas apolipoprotein B levels were not affected. Results indicate that consumption of 25 g soybean protein/d is associated with lower total cholesterol concentrations in individuals with initial cholesterol concentrations > 5.7 mmol/L.

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 Göttingen 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.