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

Effects of Dietary Protein on Thyroid Axis Activity

Thyroid hormones (TH) are essential for the normal development and function of every vertebrate. The hypothalamic-pituitary-thyroid (HPT) axis is regulated to maintain euthyroid status. One of the most influential environmental factors that determines HPT axis activity is nutrition. Both food availability and substrate diversity affect thyroid hormone economy. The present paper aims to summarize literature data concerning the influence of the amount and the type of protein on thyroid axis activity. This review sheds light on the contribution of a low-protein diet or insufficient intake of essential amino acids to TH abnormalities. We believe that the knowledge of these dependencies could improve the results of nutritional interventions in thyroid axis disorders and enhance the efficiency of animal breeding.

What Effect, if any, does Soy Protein have on Breast Tissue?

Differences in breast tissue can be determined using breast-enhanced scintigraphy test (BEST) imaging. Minimal work in vivo has been done previously to determine the effects of soy protein on breast tissue. The authors' earlier work demonstrated reduction in inflammatory changes in breast tissue. This work was conducted to examine the effect of daily soy protein consumption on a larger group of women over the course of 1 year. Sixty-four premenopausal women were studied after initial BEST imaging evaluation revealed fibrocystic changes of the breast. Women were asked to consume a medical-grade soy protein on a daily basis, making no other dietary or lifestyle changes during that time. Each woman underwent BEST imaging 1 year later with the results compared to the initial findings. Women and their physicians reported a subjective reduction in both breast tenderness and fibrocystic disease (FCD). There was a nonstatistical reduction in both the average and maximal count breast activity following 1 year of daily soy consumption. There was a statistically significant reduction ( P< .01) in variability of tissue activity following 1 year of soy protein treatment. This is the first in vivo study looking at the effect of soy protein on breast tissue health. The findings are promising and showed both objective and subjective findings consistent with a reduction in fibrocystic disease of the breast. Further research is needed to confirm these findings in a greater number of women and to determine if soy protein has the same beneficial effect in atypia and breast cancer.

Soy extracts suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes

Soy consumption is associated with thyroid disorders such as hypothyroidism, goiter, and autoimmune thyroid disease (ATD) as well as increased iodine requirement in certain cases. However, the anti-thyroid component(s) in soy are yet to be identified and the molecular mechanism(s) involved remain unclear. This study examined the effects of soy isoflavones (ISF) on iodide uptake and expression of thyroglobulin (Tg) and sodium/iodide symporter (NIS) in thyrocytes. Fischer rat thyroid cells (FRTL) were treated with Novasoy (a soy alcohol extract containing 30% ISF) or major ISF aglycones or glycosides for 24 h. Iodide uptake was measured by a colorimetric assay. The protein level of Tg and NIS was measured by Western blotting. Cytotoxicity of tested compounds was determined by the MTT cell proliferation assay. Iodide uptake in FRTL cells was dose-dependently suppressed by Novasoy added into the cell culture (10, 25, or 50 µg/mL, P < 0.05). However, neither the major ISF aglycones nor glycosides alone or in combination had similar effects. Novasoy (up to 200 µg/mL) had no cytotoxic effect. Novasoy (1, 10, and 50 µg/mL) and genistein (1 and 10 µM) markedly increased the protein content of a 40 kDa Tg fragment (P40, a known autoimmunogen) and non-glycosylated NIS in the FRTL cells (P < 0.05). Overall, this study demonstrated that the alcohol soluble component(s) other than the major ISF in soy remarkably inhibited iodide uptake in the FRTL cells. Soy ISF, particularly genistein, induced the production of P40, which might be responsible for the higher incidence of ATD reported in soy infant formula-fed children.

Effect of different levels of supplemental yeast on body weight, thyroid hormone metabolism and lipid profile of broiler chickens

In poultry, the benefits of probiotic supplementation on broiler performance and health have been reported. The present study examined the effect of supplemental yeast probiotic preparations on body weight, thyroid hormone metabolism and serum lipid profile in broilers. The experiment was carried out on hybrid Marshall broiler chickens (n=200). Two hundred 1-day-old chicks were randomly selected and distributed into 4 groups of 50 1-day-old chicks each (control, C; E10.5%, E21.5% and E32.0%, experimental groups). The birds were housed in an environmentally controlled poultry house with the floor covered with wood shavings. Chicks were fed commercial broiler starter diet for the first 28 days of age, followed by pelleted finisher diet from 29-42 days. Feed and water were provided ad libitum. Chickens fed 2.0% probiotic had a significantly (P<0.05) higher body weight when compared with the control group. The blood glucose concentration was significantly (P<0.05) different in the E31.5% probiotic supplemented group when compared with the control. There was highly significant (P<0.05) difference in T4 level in the E32.0% probiotic group when compared with the control. However, there was a significant difference in cholesterol concentrations observed in the experimental group supplemented with E10.5% probiotic. The concentration of triglycerides was not affected by the probiotic supplementation. Significant differences (P<0.01) were observed in HDL concentrations in all experimental groups supplemented with the probiotic when compared with the control group. In conclusion, supplementing broiler feeds with a yeast probiotic increased body weight, enhanced thyroid hormone metabolism, and decreased cholesterol and lipoproteins in broiler chickens.

Studies on persisting effects of soy-based compared with amino acid-supplemented casein-based diet on protein metabolism and oxidative stress in juvenile pigs

Juvenile growing pigs were studied to explore whether a soy-based diet can induce persistent physiological alterations, especially in protein and energy metabolism, nutrient oxidation and redox homeostasis. In former studies we have shown that in juvenile pigs chronically fed protein diets based on either casein (CAS) or soy protein isolate (SPI), the SPI diet significantly decreases growth rate and increases oxidative stress responsiveness as compared to CAS. In addition, here we show that chronic feeding of SPI vs. CAS diet decreases whole body protein synthesis (WBPS) (p = 0.007) and hepatic gene expression associated with protein synthesis. To study persistent SPI effects, a three-period feeding experiment was designed: In the test group 18 pigs received the CAS diet for 24 days (period 1), followed by 31 days on the SPI diet (period 2) and further 31 days on the CAS diet (period 3). In the control group 18 pigs were fed the CAS diet throughout the three periods (86 days). Temporary consumption of SPI diet results in persistent changes of protein metabolism and oxidative stress responsiveness. After switching back from SPI to CAS diet the decrease of WBPS of the test group vs. control group was of borderline significance (p = 0.061), transcript levels of hepatic gene expressions of leucine aminopeptidase, endopeptidase 24.16, glutathione-S-transferase and peptide methionine sulfoxide reductase were increased. In liver tissue, total glutathione was increased and thiobarbituric acid reactive substances were decreased in the test vs. control group. In conclusion, results suggest that SPI-induced changes in protein and amino acid metabolism as well as in redox homeostasis and antioxidative potential in growing pigs persist 4 weeks after the cessation of SPI feeding.

Expression of genes participating in regulation of fatty acid and glucose utilization and energy metabolism in developing rat hearts

The heart is a unique organ that can use several fuels for energy production. During development, the heart undergoes changes in fuel supply, and it must be able to respond to these changes. We have examined changes in the expression of several genes that regulate fuel transport and metabolism in rat hearts during early development. At birth, there was increased expression of fatty acid transporters and enzymes of fatty acid metabolism that allow fatty acids to become the major source of energy for cardiac muscle during the first 2 wk of life. At the same time, expression of genes that control glucose transport and oxidation was downregulated. After 2 wk, expression of genes for glucose uptake and oxidation was increased, and expression of genes for fatty acid uptake and utilization was decreased. Expression of carnitine palmitoyltransferase I (CPT I) isoforms during development was different from published data obtained from rabbit hearts. CPT Iα and Iβ isoforms were both highly expressed in hearts before birth, and both increased further at birth. Only after the second week did CPT Iα expression decrease appreciably below the level of CPT Iβ expression. These results represent another example of different expression patterns of CPT I isoforms among various mammalian species. In rats, changes in gene expression followed nutrient availability during development and may render cardiac fatty acid oxidation less sensitive to factors that influence malonyl-CoA content (e.g., fluctuations in glucose concentration) and thereby favor fatty acid oxidation as an energy source for cardiomyocytes in early development.

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.

Effects of dietary soy and estrous cycle on adrenal cytochrome P450 1B1 expression and DMBA metabolism in adrenal glands and livers in female Sprague–Dawley rats

Cytochrome p450 1B1 (CYP1B1) has been shown to be important in the bioactivation of 7,12-dimethylbenz[a]anthracene (DMBA) to an adrenal toxin in rats. We investigated the effects of diet and stage of estrous cycle on CYP1B1 expression in rat adrenal glands and on DMBA metabolism by rat adrenal and hepatic microsomes. Female Sprague-Dawley (SD) rats were placed on either standard soy-containing NIH-31 rat chow or soy- and alfalfa-free 5K96 diet from postnatal day (PND) 21 until sacrifice at PND50+/-5. Stage of estrous at sacrifice was assessed by vaginal cytology and confirmed by histological examination of the vagina. Dietary soy at the level present in NIH-31 diet did not affect serum estrogen and progesterone levels. Immunohistochemical analysis confirmed that CYP1B1 was exclusively expressed in the zona fasciculata and zona reticularis in adrenal cortex, which are the regions vulnerable to DMBA-induced adrenal necrosis. Adrenal CYP1B1 protein expression, 3H-DMBA depletion, and formation of DMBA-3,4-, and -8,9-dihydrodiols by adrenal microsomes were greater in animals fed 5K96 diet, and the stage of the estrous cycle affected these parameters only in the soy-free 5K96 diet. In hepatic microsomes, the formation of DMBA-3,4-dihydrodiol, 7-hydroxy- and 12-hydroxy-DMBA were lower in animals fed NIH-31 diet than in those fed 5K96 diet. Thus, dietary soy and the estrous cycle appear to regulate adrenal CYP1B1 expression and DMBA metabolism by both adrenal and hepatic microsomes. The use of different basal diets containing variable levels of soy components may affect certain toxicity assessments.