Casein-fed Rats Research Articles

Low-Protein Diets Composed of Protein Recovered from Food Processing Supported Growth, but Induced Mild Hepatic Steatosis Compared with a No-Protein Diet in Young Female Rats

BackgroundLiving in low-income countries often restricts the consumption of adequate protein and animal protein. ObjectivesThis study aimed to investigate the effects of feeding low-protein diets on growth and liver health using proteins recovered from animal processing. MethodsFemale Sprague–Dawley rats (aged 28 d) were randomly assigned (n = 8 rats/group) to be fed standard purified diets with 0% or 10% kcal protein that was comprised of either carp, whey, or casein. ResultsRats that were fed low-protein diets showed higher growth but developed mild hepatic steatosis compared to rats that were fed a no-protein diet, regardless of the protein source. Real-time quantitative polymerase chain reactions targeting the expression of genes involved in liver lipid homeostasis were not significantly different among groups. Global RNA-sequencing technology identified 9 differentially expressed genes linked to folate-mediated 1–carbon metabolism, endoplasmic reticulum (ER) stress, and metabolic diseases. Canonical pathway analysis revealed that mechanisms differed depending on the protein source. ER stress and dysregulated energy metabolism were implicated in hepatic steatosis in carp- and whey-fed rats. In contrast, impaired liver one-carbon methylations, lipoprotein assembly, and lipid export were implicated in casein-fed rats. ConclusionsCarp sarcoplasmic protein showed comparable results to commercially available casein and whey protein. A better understanding of the molecular mechanisms in hepatic steatosis development can assist formulation of proteins recovered from food processing into a sustainable source of high-quality protein.

Dairy Proteins Protect against Dimethylhydrazine-Induced Intestinal Cancers in Rats

The impact of different dietary protein sources (whey, casein, soybean, red meat) on the incidence, burden and mass index of intestinal tumors induced by dimethylhydrazine in male Sprague-Dawley rats was assessed. A purified diet (based on AIN-76A) with a fat concentration of 20 g/100 g and other proteins substituted for casein (20 g/100 g) was used. Whey and casein diets were more protective against the development of intestinal tumors than were the red meat or soybean diets, as evidenced by a reduced incidence of rats affected (P = 0.15), fewer tumors per treatment group (burden, P < 0.005), and a reduced pooled area of tumors (tumor mass index) that formed (P = 0.39). Intracellular concentration of glutathione, an antioxidant and anticarcinogenic tripeptide, measured in liver, was greatest in whey protein- and casein-fed rats and lowest in soybean-fed animals (P < 0.001). For other tissues (spleen, colon, tumor) the differences were not significant, although the whey-fed animals had the highest concentrations of glutathione (P = 0.8). Whey is a source of precursors (cysteine-rich proteins) for glutathione synthesis and may be important in providing protection to the host by stimulating glutathione synthesis. A positive correlation was observed between mean fecal fat concentrations for rats in each treatment group and large intestinal tumor burden (r2 = 0.898, P = 0.05). Fecal fat could be involved in aiding initiation and/or promotion of carcinogenesis. Whatever the mechanism(s), dairy proteins, and whey proteins in particular, offer considerable protection to the host against dimethylhydrazine-induced tumors relative to the other protein sources examined.

Dry Beans Inhibit Azoxymethane-Induced Colon Carcinogenesis in F344 Rats

Epidemiological studies show a low incidence of colon cancer in many Latin American countries where the consumption of dry beans (e.g., pinto) is high. The purpose of this study was to use rats as an animal model to obtain experimental data on the inhibition of colon carcinogenesis by dry beans. Fifty-three 5-wk-old weanling male F344 rats were randomly assigned by weight to the following groups: control (11 rats), casein diet (21 rats), and bean diet (21 rats). Animals fed the casein and bean diets were treated with the carcinogen azoxymethane (AOM) once weekly for 2 wk. Rats in the control group also consumed the casein diet but were not exposed to AOM. All diets were isocaloric. The protein concentration of the diets was adjusted to 18 g/100 g with casein, and the fat concentration was adjusted to 5 g/100 g with corn oil. Rats fed the bean diet had significantly fewer colon adenocarcinomas (P< 0.05) than rats fed the casein diet (5 vs. 22 tumors), and significantly fewer rats fed the bean diet (P< 0.05) had colonic tumors than did casein-fed rats (24 vs. 50%). Tumor multiplicity was also significantly lower for the bean-fed rats, and significantly fewer (P< 0.05) tumors per tumor-bearing rat were observed in bean-fed rats than in casein-fed rats (1.0 ± 0.0 vs. 2.5 ± 0.6). This study demonstrates that dry beans contain anticarcinogenic compounds capable of inhibiting AOM-induced colon cancer in rats. However, the specific anticarcinogenic components within dry beans have not been identified, and it is unclear whether dietary fiber, phytochemicals or other components within dry beans are primarily responsible for the anticarcinogenic properties of beans.

Protein quality and safety evaluation of sarcoplasmic protein derived from silver carp (Hypophthalmichthys molitrix) using a rat model.

Consisting of 25 to 30% of protein in carp, water-soluble sarcoplasmic proteins lost in wash water, have been recovered and freeze-dried into a protein-rich powder. Study objectives were to evaluate protein quality and safety of a silver carp sarcoplasm derived protein powder (CSP) compared to commercial protein supplements, casein, and whey. In vivo protein quality assessment of CSP showed a lower (P<0.05) protein digestibility corrected amino acid score compared to the commercial protein sources. Despite greater (P<0.05) fecal amino acid excretion in casein-fed rats, there were no significant differences in liver and muscle amino acid profiles. All low (10%kcal) protein diets supported growth with the normal range. However, whey protein supplementation resulted in greater (P<0.05) adiposity. CSP, casein, or whey-fed rats showed no differences in major organ weights, renal damage biomarkers, or bone indices. Collectively, results indicated CSP was safe with protein quality comparable to casein. PRACTICAL APPLICATION: As much as 40 percent of protein in fish can be lost due to sarcoplasmic protein solubilization in processing wash water. Silver carp sarcoplasm protein powder may have similar commercial potential as a sustainable and nutritious alternative to whey and casein proteins. This project aimed to verify the protein quality and safety of this economical protein source.

Short-Term Soy Protein Isolate Feeding Prevents Liver Steatosis and Reduces Serum ALT and AST Levels in Obese Female Zucker Rats.

Non-alcoholic fatty liver disease is a common liver disorder worldwide and is associated with obesity. We investigated effects of obesity and short-term intake of soy protein with isoflavones (SPI) on body weight change, energy intake, liver steatosis, and serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and leptin levels. Seventeen lean and seventeen obese (fa/fa) female Zucker rats were randomly assigned to either casein or SPI diet for 8 weeks. Body weight was recorded twice weekly; feed intake was measured weekly. Livers were examined histologically, and serum AST, ALT, and leptin levels were measured. Obese soy-fed (OS) rats gained more weight but had lower liver steatosis than obese casein-fed (OC) rats. Energy intake for OS versus OC rats were only different at weeks 2 and 3. Serum AST and ALT levels were lower in OS versus OC rats. Obesity increased serum leptin levels for both diets. In summary, short-term SPI intake reduced liver steatosis, and the only time points at which the mean energy intakes of OS and OC rats differed were at weeks 2 and 3, where OS rats had a higher mean energy intake, which may have accounted for the increased body weight in OS rats.

Nutritional Quality of Weaning Foods Formulated from Yam (&amp;lt;i&amp;gt;Dioscorea alata&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Dioscorea cayenensis&amp;lt;/i&amp;gt;) Composite Flours

Some potential weaning diets formulated from yam species <i>Dioscorea alata</i> variety <i>Bètè bètè</i> and <i>Dioscorea cayenensis</i> variety <i>Lokpa, soybean</i> and cassava have previously been evaluated. In this study, four different diets (unfermented flour made of <i>Dioscorea alata</i>, fermented flour made of <i>Dioscorea alata</i>, unfermented flour made of <i>Dioscorea cayenensis</i>, fermented flour made of <i>Dioscorea cayenensis</i>) were prepared and fed to weaning rats for a period of 28 days. The study aimed to find out the <i>in vivo</i> impact of these yam composite flours. The performance characteristics of the developed products were investigated and compared with those of <i>Cérélac</i> (a commercial weaning food).The body weight change (BWC) of rats fed the different diets was highest in the rats fed <i>Cérélac</i> (3.39 g) followed by rats fed the fermented composite flours (FBBF and FLOF; 1.97 and 2.00 g, respectively) and casein-based diets (2.48 g) and least in rats fed the unfermented composite flour diets (FBBNF and FLONF; 1.60 and 1.51 g, respectively). A similar trend was observed in the total feed and protein intakes of the experimental animals. Moreover, the rat fed fermented composite flours showed high Protein Efficiency Ratio (2.25 – 2.37), Biological Value (78.94 – 79.46), True Digestibility (80.11 – 92.28) and Net Protein Utilization (60.91 – 76.34), comparable to those obtained with the casein-fed rats. The present study have shown that the values obtained with the test diet, especially for the fermented composite flours compared favourably with the reference diets (<i>Cérélac</i> and casein) in all the parameters investigated and should be considered a good weaning diet from a nutritional point of view.

Dietary Casein and Soy Protein Isolate Modulate the Effects of Raffinose and Fructooligosaccharides on the Composition and Fermentation of Gut Microbiota in Rats.

Although diet has an important influence on the composition of gut microbiota, the impact of dietary protein sources has only been studied to a minor extent. In this study, we examined the influence of different dietary protein sources regarding the effects of prebiotic oligosaccharides on the composition and metabolic activity of gut microbiota. Thirty female rats were fed casein and soy protein isolate with cellulose, raffinose (RAF), and fructooligosaccharides (FOS). Microbiota composition was examined by real-time qPCR and denaturing gradient gel electrophoresis. Dietary protein source affected cecum microbiota; acetic acid concentration and Lactobacillus spp. populations were greater with soy protein than with casein. Prebiotic oligosaccharides had distinctive effects on gut microbiota; RAF increased the acetic acid concentration and Bifidobacterium spp. populations, and FOS increased the butyric acid concentration regardless of the dietary protein. Likewise, Bifidobacterium sp., Collinsella sp., and Lactobacillus sp. were detected in microbiota of the rats fed RAF, and Bacteroides sp., Roseburia sp., and Blautia sp. were seen in microbiota of the rats fed FOS. Interactions between dietary proteins and prebiotic oligosaccharides were observed with Clostridium perfringens group populations and cecum IgA concentration. RAF and FOS decreased C. perfringens group populations in casein-fed rats, and the combination of soy protein and RAF substantially increased cecum IgA concentration. These results indicate that dietary proteins can differentially modulate the effects of prebiotic oligosaccharides on gut fermentation and microbiota, depending on the type of carbohydrate polymers involved.

Soy β-conglycinin improves glucose uptake in skeletal muscle and ameliorates hepatic insulin resistance in Goto-Kakizaki rats

Although the underlying mechanism is unclear, β-conglycinin (βCG), the major component of soy proteins, regulates blood glucose levels. Here, we hypothesized that consumption of βCG would normalize blood glucose levels by ameliorating insulin resistance and stimulating glucose uptake in skeletal muscles. To test our hypothesis, we investigated the antidiabetic action of βCG in spontaneously diabetic Goto-Kakizaki (GK) rats. Our results revealed that plasma adiponectin levels and adiponectin receptor 1 messenger RNA expression in skeletal muscle were higher in βCG-fed rats than in casein-fed rats. Phosphorylation of adenosine monophosphate–activated protein kinase (AMP kinase) but not phosphatidylinositol-3 kinase was activated in βCG-fed GK rats. Subsequently, βCG increased translocation of glucose transporter 4 to the plasma membrane. Unlike the results in skeletal muscle, the increase in adiponectin receptor 1 did not lead to AMP kinase activation in the liver of βCG-fed rats. The down-regulation of sterol regulatory element-binding factor 1, which is induced by low insulin levels, promoted the increase in hepatic insulin receptor substrate 2 expression. Based on these findings, we concluded that consumption of soy βCG improves glucose uptake in skeletal muscle via AMP kinase activation and ameliorates hepatic insulin resistance and that these actions may help normalize blood glucose levels in GK rats.

Abstract 480: NaCl-Independent Dietary Effects are Associated with Altered DNA Methylation in Dahl Salt-Sensitive (SS) Hypertension

Salt-sensitive hypertension and renal damage were compared in colonies of SS rats fed casein-and grain-based diets. When 6 week old rats were fed a low NaCl diet (n=7-11/group), mean arterial pressure (MAP) and urinary albumin (UAlb) excretion were not significantly different in grain-fed rats compared to values in casein-fed rats (107±2 mmHg and 6±2 mg/day). Increasing dietary NaCl intake to 4.0% for three weeks led to a significantly greater increase in MAP (171±7 vs 119±7 mmHg), UAlb (164±19 vs 24±6 mg/day) and renal histological damage in SS rats fed the casein diet (p&lt;.05). To assess mechanisms of this NaCl independent effect, an RNA-Seq analysis of renal outer medullary tissue of rats (n=4/group) fed the grain- or casein-based diets was performed. Over 1500 known genes were differentially expressed between the casein- and grain-fed rats on low salt; over 2100 were different between the groups fed the 4.0% chow (FDR&lt;0.05); and 897 genes were common to these two data sets. The differentially expressed genes were significantly enriched for genes related to hematopoietic cell lineage, the complement and coagulation cascade, B-cell signaling, NK cell-mediated cytotoxicity, and primary immunodeficiency. To understand potential mechanisms of the regulation of gene expression, a genome-wide DNA methylation analysis of the renal outer medulla at single-base resolution was performed. Of nearly 3,000 methylated CpG islands identified, 534 and 650 were differentially methylated between the casein and grain fed groups when comparing effects of low to high salt diets, respectively (FDR&lt;0.05). Approximately 200 differentially methylated CpG islands were located in the proximity of transcriptional start sites. We first focused our attention on several genes which exhibited a reciprocal pattern of DNA methylation and RNA abundance. These include Klotho (an aging-related gene), and Cyp39a1 (a cytochrome P450) which exhibited significantly more 5-methylcytosine modifications in the transcription start site and reduced mRNA expression in rats fed the casein-based diet with low salt. These data provide evidence that epigenetic modifications due to NaCl-independent dietary effects may alter salt-sensitive blood pressure and renal disease phenotypes.

Whey protein hydrolysate enhances the exercise-induced heat shock protein (HSP70) response in rats

Whey protein has been suggested to be potential protective agent against various forms of stress. The heat shock protein HSP70 confers greater cellular tolerance against stressors. The present study evaluated the effects of whey protein intake on HSP70 expression. Forty-eight male Wistar rats were divided into sedentary and exercised groups, and each group was fed as a protein source casein (CAS), whey protein (WP) or whey protein hydrolysate (WPH) for 3weeks. Exercise on a treadmill was used as the source of stress in the animals from the exercised group. The results showed a larger increase in HSP70 expression in the soleus, gastrocnemius and lung of the WPH-fed rats than WP or casein-fed rats. HSP70 expression in the sedentary rats was very low, independent of the diet or tissue. Protein carbonyls were lower in the group that consumed WPH. These data suggest that the consumption of WPH enhances HSP70 expression.

Dietary soy protein induces hepatic lipogenic enzyme gene expression while suppressing hepatosteatosis in obese female Zucker rats bearing DMBA-initiated mammary tumors

Fatty liver is associated with obesity and breast cancer. We used an obese rat model of mammary cancer to examine whether hepatosteatosis is modifiable by diet and associated with altered expression of hepatic lipogenic enzyme genes, thyroid hormone system genes and cholesterol metabolism-related genes. Beginning at the age of 5weeks, lean and obese female Zucker rats were fed high-isoflavone soy protein- or casein (control protein)-containing diets. Rats were euthanized at 200days of age [corresponding to 147days after administration of carcinogen to induce mammary tumors; (Hakkak et al. in, Oncol Lett 2:29-36, 2011)]. Obese rats had a greater degree of liver steatosis than lean rats. Obese casein-fed rats had marked steatosis with small foci of mononuclear infiltration, whereas obese soy protein-fed rats had a significantly lower steatosis index. Comparisons between lean and obese casein-fed rats showed that obesity was associated with significant reductions in hepatic mRNA abundance for Glucose 6-Phosphate Dehydrogenase (G6PD), 6-Phosphogluconate Dehydrogenase (6PGD), Thyroid Receptor Alpha 1 (TRα1), Thyroid Receptor Beta 1 (TRβ1) and Iodothyronine Deiodinase 1 (DIO1). The soy protein diet was associated with increased expression of Fatty Acid Synthase (FASN), Malic Enzyme 1 (ME1), 6PGD, Sterol Regulatory Element Binding Protein-1c (SREBP-1c) and SREBP-2 genes in the livers of obese but not lean rats. Western blot analysis showed a significant induction of ME1 protein expression in the livers of obese, soy protein-fed rats, which paralleled the increased serum insulin level in this group. Long-term soy protein consumption can counter hepatic steatosis while coincidently promoting hepatic lipogenic gene expression, the latter likely a consequence of elevated serum insulin. We suggest that elevations in serum insulin, hepatic lipogenesis and cholesterol synthesis all contributed to the increased tumorigenesis previously observed for the obese, soy protein-fed rats.

Beneficial effects of cod protein on skeletal muscle repair following injury

This study examined the effect of peanut and cod proteins on post-damage skeletal muscle repair, compared with casein. We hypothesized that because of their high arginine content, these proteins would improve the resolution of inflammation and muscle mass recovery following injury. One hundred and twenty-eight male Wistar rats were assigned to isoenergetic diets composed of casein and peanut (experiment 1) or cod protein (experiment 2). After 21 days of feeding, one tibialis anterior muscle (TA) was injured with bupivacaine, while the contralateral TA was injected with saline (sham muscle). Measurements were taken at days 0, 3, 14, and 24 post-injury. Compared with casein, peanut protein reduced muscle mass at days 0 (-12%, p = 0.005) and 14 post-injury in the injured muscle (-13%, p = 0.04), and lowered myofiber cross-sectional area in both the sham (-21%, p = 0.008) and injured muscles (-26%, p = 0.05) at day 24 post-injury, showing that peanut protein has a weak potential to support muscle growth. At day 14 post-injury, muscle mass in the sham (13%, p = 0.02) and injured muscles (12%, p = 0.01) was higher in cod-protein-fed rats, indicating better muscle mass recovery, than in casein-fed rats. Cod protein tended (p = 0.06) to decrease the density of neutrophils (-24%) at day 14 post-injury in the injured muscle, and to decrease the density of ED1(+) macrophages at day 24 post-injury in both sham (-29%, p = 0.03) and injured (-40%, p = 0.01) muscles. No effects were observed for peanut protein. These data indicate that cod protein is better for promoting growth and regeneration of skeletal muscle after trauma, partly because of the improved resolution of inflammation.

In vivo Evaluation of the Proteins in the Cultivated Mushrooms

Chemical and biological assays were performed with freeze-dried samples of the cultivated mushroom A. brunnescens. Dried fruitbodies were subjected to proximate analysis and protein, carbohydrates, fat, moisture, ash, and amino acid contents were determined. The mushroom fruitbodies were found to contain 39.5% protein, 2.0% fat, 39.2% carbohydrates and 9.5% ash, on dry weight basis. Furthermore, the amino acid analysis showed that mushroom contains all the essential amino acids, and the limiting amino acid is methionine, with an amino acid score of 51.2. Diets containing 10% mushroom protein resulted in Protein Efficiency Ratio (PER) of 1.5 and Net Protein Ratio (NPR) of 0.74, compared with values for casein of 2.7% and 2.4%, respectively. No significant differences were observed between the weights of the pancreas, spleen and livers of the mushroom protein-fed rats and caseinfed rats. In addition, mushroom was found to be a good source of protein, iron, magnesium, phosphorus, thiamin, riboflavin, niacin, and vitamin C.

ANTIOXIDANT ACTIVITY AND PHENOLIC CONTENT OF FLOUR AND PROTEIN CONCENTRATE OF AMARANTHUS CRUENTUS SEEDS

The aim of this work was to investigate bioactive compounds and antioxidant activity in flour (FAc) and protein concentrate (PCAc) from Amaranthus cruentus seeds (Ac), and to study their effect on the liver histoarchitecture of Wistar rats. Total phenols (mg gallic acid eq/100 g dry weight) content was 73.78 ± 1.70 for FAc, and 190.23 ± 1.50 for PCAc. The antioxidant activity was estimated by: 1,1-diphenyl-2-picrylhydrazyl (DPPH), nitric oxide scavenging activity (NO) and β-carotene bleaching method (β-carotene). The values expressed as percentage correspond to FAc and PCAc, respectively. DPPH: 86.30 ± 1.1 and 88.83 ± 1.2; NO: 29.38 ± 1.9 and 48.75 ± 1.7; andβ-carotene: 83.00 ± 1.8 and 44.60 ± 1.5. The histopathological diagnosis indicates that casein-fed rats present moderate fat infiltration in the liver, whereas in PCAc-fed rats, the liver has structural integrity. The presence of phenols would provoke an increase of the antioxidant defenses and would produce a protective role in liver. It is suggested that Ac could be a good antioxidant source. PRACTICAL APPLICATIONS A number of epidemiological studies initially indicated the utility of antioxidants in disease prevention, particularly for cardiovascular disease and cancer. This association is often attributed to different antioxidant components, such as polyphenols, vitamin C, vitamin E, carotenoids and other phytochemicals. Amaranth species are receiving special attention in developing countries as an alternative to tackle protein deficiencies in diets. At present, some studies have been conducted on amaranth antioxidant activity (AA). Furthermore, protein concentrates, as nutritional sources, also exhibit physiological effects. In order to understand the protective effect of natural compounds, in vitro studies of antioxidant components must be conducted, followed by an assessment of their antioxidant function. Our results are a contribution to research into new sources of natural antioxidants in this and other related species, and we hope that they will enhance the national food composition database.

Extrusion decreases the negative effects of kidney bean on enzyme and transport activities of the rat small intestine

The objective of the present study was to evaluate the influence of raw and extruded kidney bean (Phaseolus vulgaris L. var. Pinto) consumption on the gut physiology of young growing rats. The intestinal enzyme activity (sucrase, maltase, Na(+) /K(+) ATPase, aminopeptidase N, dipeptidylpeptidase IV, alkaline phosphatase) and the uptake of sugar (d-galactose) and amino acids (l-leucine) were measured in brush border membrane vesicles. Five groups of growing male Wistar rats were fed ad libitum for 15 days on five different 10% protein diets: one containing casein as the main source of protein (Control, C), and four containing raw (RKB1, RKB6) or extruded kidney bean (EKB1, EKB6) at 1% and 6% of total protein content respectively. Extrusion treatment significantly reduced the content of bioactive factors (phytates, tannins) and abolished lectins, trypsin, chymotrypsin, and α-amylase inhibitory activities. Rats fed raw beans (especially RKB6) showed lower growth rate and food intake as compared to those fed extruded legumes, probably due to the high levels of lectins and other anti-nutritive factors in the raw beans. Gut enzymatic activities and uptake of d-galactose and l-leucine were lower in RKB6 and RKB1-fed animals, although they significantly improved in the groups fed extruded beans. Enzymatic activity and uptake in EKB1 were similar to those of casein-fed rats, whereas the uptake and growth rate of EKB6 were different to the control. This is attributable to the higher non-thermolabile biofactor content in the EKB6 diet, especially phytates and tannins, than in EKB1. This article shows the dose-dependent toxicological effects of bioactive factors contained in kidney beans on gut function. The extrusion process reduced their adverse impact on gut physiology and growth rate.

14C radiolabeling of proteins to monitor biodistribution of ingested proteins

The economical preparation of microgram quantities of 14C-labeled proteins by in vacuo methylation with methyl iodide is described. The 14C radiolabeling was achieved by the covalent attachment of [ 14C]methyl groups onto amino and imidazole groups by reaction in vacuo with [ 14C]methyl iodide. The method was tested by investigating the biodistribution of 14C in rats that were fed 14C-labeled human soluble cluster of differentiation 14 (CD14) protein, a receptor for bacterial lipopolysaccharide. Two other control proteins, bovine serum albumin (BSA) and casein, were also labeled with 14C and used for comparative analysis to determine the following: (i) the efficacy and cost efficiency of the in vacuo radiolabeling procedure and (ii) the extent of incorporation of the 14C label into the organs of orogastrically fed 10-day-old Sprague–Dawley rats. [ 14C]BSA, [ 14C]casein, and [ 14C]CD14 were individually prepared with specific radioactivities of 34,400, 18,800, and 163,000 disintegrations per minute (dpm)/μg, respectively. It was found that the accumulation of 14C label in the organs of [ 14C]CD14-fed rats, most notably the persistence of 14C in the stomach 480 min postgavage, was temporally and spatially distinct from [ 14C]BSA and [ 14C]casein-fed rats.

Effects of high-isoflavone soy diet vs. casein protein diet and obesity on DMBA-induced mammary tumor development

Obesity and elevated serum insulin growth factor-1 (IGF-1) level are major risk factors in the development of breast cancer. We investigated the long-term effects of high-isoflavone soy intake and obesity on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumor development and on serum IGF-1 and binding protein (IGFBP-3) levels. Lean and obese female Zucker rats fed casein or high-isoflavone soy protein were orally gavaged at age 50 days with DMBA and sacrificed after 147 days. The majority of lean casein-fed rats (69%) developed mammary tumors compared to 50% in lean soy-fed rats (P=0.176). In the obese groups, 76% of soy-fed rats developed mammary tumors compared to 15% of obese casein-fed rats (P<0.001). At age 43 days, IGFBP-3 was increased in the lean soy-fed rats compared to the lean casein-fed rats (P<0.05). At age 99 days, soy- and obese casein-fed rats exhibited increased serum IGF-1 compared to the lean rats and this increase was maintained for the rest of the experiment (P<0.05). Obese rats fed casein exhibited increased IGFBP-3 levels (P<0.001). However, obese rats fed soy exhibited a significant decrease in IGFBP-3 levels compared to the lean soy-fed rats (P<0.001) and a significant decrease in IGFBP-3 levels compared to the obese casein-fed rats (P<0.001). At age 197 days, IGFBP-3 levels were increased in obese casein-and soy-fed rats (P<0.001). The results suggest that female Zucker rats fed casein diets are protected against DMBA-induced mammary tumors, which is not the case for those on high-isoflavone soy diet, and changes in the concentration of serum IGFBP-3 may contribute to the incidence of DMBA-induced mammary tumors.

Enhanced Mammary Progesterone Receptor-A Isoform Activity in the Promotion of Mammary Tumor Progression by Dietary Soy in Rats

Dietary contribution to breast cancer risk, recurrence, and progression remains incompletely understood. Increased consumption of soy and soy isoflavones is associated with reduced mammary cancer susceptibility in women and in rodent models of carcinogenesis. In rats treated with N-methyl-N-nitrosourea, dietary intake of soy protein isolate (SPI) reduced mammary tumor occurrence but increased incidence of more invasive tumors in tumored rats, relative to the control diet casein. Here we evaluated whether mammary tumor progression in tumor-bearing rats lifetime exposed to SPI is associated with deregulated progesterone receptor (PR) isoform expression. In histologically normal mammary glands of rats with invasive ductal carcinoma lesions, PR-A protein levels were higher for SPI- than casein-fed rats, whereas PR-B was undetectable for both groups. Increased mammary PR-A expression was associated with higher transforming growth factor-β1, stanniocalcin-1, and CD44 transcript levels; lower E-cadherin and estrogen receptor-α expression; and reduced apoptotic status in ductal epithelium. Serum progesterone (ng/ml) (CAS: 25.94 ± 3.81; SPI: 13.19 ± 2.32) and estradiol (pg/ml) (CAS: 27.9 ± 4.49; SPI: 68.48 ± 23.87) levels differed with diet. However, sera from rats of both diet groups displayed comparable mammosphere-forming efficiency in human MCF-7 cells. Thus, soy-rich diets may influence the development of more aggressive tumors by enhancing PR-A-dependent signaling in premalignant breast tissues.

β-Conglycinin Lowers Very-Low-Density Lipoprotein-Triglyceride Levels by Increasing Adiponectin and Insulin Sensitivity in Rats

The relationship between insulin sensitivity and the plasma triglyceride-lowering effect induced by beta-conglycinin was investigated. Male Wistar rats (19 weeks old) were fed diets containing casein, soy protein isolate, or beta-conglycinin for 4 weeks. In oral glucose administration, the beta-conglycinin-fed rats showed a significant decrease in the area under the glucose curve (0-60 min) as compared with the casein-fed rats. The hypoglycemic effect was significantly higher in the beta-conglycinin-fed rats than in the casein-fed rats at 30 min after intraperitoneal insulin injection. The liver sterol regulatory element-binding-protein-1 mRNA expression level was significantly lower and the plasma adiponectin concentration was significantly higher in the beta-conglycinin-fed rats than in the casein-fed rats. The hypotriglyceridemic effect of beta-conglycinin depended on a significant decrease in the concentration of very-low-density-lipoprotein triglycerides. These results indicate that beta-conglycinin increases adiponectin levels and improves glucose tolerance. The ability of beta-conglycinin to lower plasma lipid levels might be due to increased insulin sensitivity of the liver.

Effects of Obesity, short‐term soy vs casein protein diet and DMBA on Liver CYP 1A1 and CYP 1B1 Expression in Ovariectomized Obese Zucker Rats

Obesity is a risk factor for post‐menopausal breast cancer development. We have shown that obesity increases DMBA‐induced mammary tumor development in intact and ovariectomized Zucker rats. Several data suggest that DMBA requires metabolic activation to exert its carcinogenic effects. The objective of this study was to investigate the effect of obesity and high‐isoflavone soy (high‐isof soy) vs casein diet on hepatic expression of CYP1A1 and CYP1B1 following DMBA treatment in obese and lean ovariectomized Zucker rats. Forty day‐old, ovariectomized obese (n=40) and lean (n=40), Zucker rats were administered a diet containing either casein or high‐isof soy protein isolate and 10 days later were orally gavaged with either with sesame oil (control) or with 65 mg/kg DMBA in sesame oil. All rats were sacrificed 24 hrs post‐DMBA treatment. Liver microsomes were prepared and CYP1A1 and CYP 1B1 expression was measured by Western blotting using goat anti‐mouse CYP1A1 and CYP1B1 antibodies. DMBA treatment significantly (p&lt;0.001) increased expression of CYP1A1 in lean and obese ovariectomized rats in both casein and high‐isof soy‐fed group compared to the oil control groups. High‐isof soy diet decreased (p&lt;0.001) CYP1A1 expression in DMBA treated lean rats compared to lean casein‐fed rats but CYP1A1 expression was increased (p&lt;0.001) by DMBA in obese soy‐fed rats compared to high‐isof soy‐fed lean rats. CYP1B1 expression was not affected by diet, obesity or DMBA. These data suggest that obesity can increase the expression of enzymes that are responsible for DMBA metabolism in the ovariectomized Zucker rat model. (Supported by Susan G. Komen Foundation and ABI to RH).