Effects of soy protein diet on digestive lumenal polyamines and colonic cell proliferation in pigs.

This study was performed to determine whether erythrocyte and digestive lumenal polyamine concentrations are affected by a soy protein diet when compared to a casein diet. We also determined the effects of these diets on colonic cell proliferation. Sixteen pigs received either a 16% soy protein or casein diet for 25 days. The erythrocyte putrescine was higher in pigs fed the soy protein diet. Significant levels of polyamines were observed in the digestive lumen on both diets. Lumenal putrescine and cadaverine were higher in the proximal colon in the casein group. Lumenal spermidine was higher in the caecum and colon in the soy protein group. No significant differences in the ornithine decarboxylase activity nor in the proliferative cell nuclear antigen labelling index were observed in the colonic mucosa regardless of the regimen. These results indicate that the dietary source of protein induces significant changes in lumenal polyamines in the colon. The physiological effects of these changes need to be further investigated.     

Effects of dietary polyamines and clofibrate on metabolism of polyamines in the rat

The activities of catalase, polyamine oxidase, diamine oxidase, ornithine decarboxylase, and peroxisomal β-oxidation were assayed in homogenates from liver and small intestinal mucosa of rats which had been fed either a diet very low in polyamines or a diet containing five times the levels of dietary polyamines (putrescine, spermine, and spermidine) found in a standard rat diet. In rats fed the high polyamine diet, hepatic activities of catalase and polyamine oxidase were significantly decreased. Levels of the other activities were unchanged, except that intestinal ornithine decarboxylase was decreased. In rats treated simultaneously with clofibrate, the high polyamine diet restored activities of catalase, ornithine decarboxylase, and polyamine oxidase back to levels found in rats fed the low polyamine diet. The expected increase in activity of peroxisomal β-oxidation was observed, although this was somewhat diminished in rats fed the high polyamine diet. Intestinal diamine oxidase activity was stimulated by clofibrate, particularly in rats fed the high polyamine diet. For the duration of the experiment (20 days), levels of putrescine, spermine, and spermidine in blood remained remarkably constant irrespective of treatment, suggesting that polyamine homeostasis is essentially independent of dietary supply of polyamines. It is suggested that intestinal absorption/metabolism of polyamines is of significance in this respect. Treatment with clofibrate appeared to alter polyamine homeostasis.     

Soy protein,casein, and zein regulate histidase gene expression by modulating serum glucagon

Glucagon has been postulated as an important physiological regulator of histidase (Hal) gene expression; however, it has not been demonstrated whether serum glucagon concentration is associated with the type and amount of protein ingested. The purpose of the present work was to study the association between hepatic Hal activity and mRNA concentration in rats fed 18 or 50% casein, isolated soy protein, or zein diets in a restricted schedule of 6 h for 10 days, and plasma glucagon and insulin concentrations. On day 10, five rats of each group were killed at 0900 (fasting), and then five rats were killed after being given the experimental diet for 1 h (1000). Rats fed 50% casein or soy diets showed higher Hal activity than the other groups studied. Rats fed 50% zein diets had higher Hal activity than rats fed 18% casein, soy, or zein diets, but lower activity than rats fed 50% casein or soy diets. Hal mRNA concentration followed a similar pattern. Hal activity showed a significant association with serum concentrations of glucagon. Serum glucagon concentration was significantly correlated with protein intake. Thus the type and amount of protein consumed affect Hal activity and expression through changes in serum glucagon concentrations.     

Proinflammatory gene expression and renal lipogenesis are modulated by dietary protein content in obese Zucker fa/fa rats

Obesity is a risk factor for the development of chronic kidney disease (CKD) and end-stage renal disease. It is not clear whether the adoption of a high-protein diet in obese patients affects renal lipid metabolism or kidney function. Thus the aims of this study were to assess in obese Zuckerfa/fa rats the effects of different types and amounts of dietary protein on the expression of lipogenic and inflammatory genes, as well as renal lipid concentration and biochemical parameters of kidney function. Rats were fed different concentrations of soy protein or casein (20, 30, 45%) for 2 mo. Independent of the type of protein ingested, higher dietary protein intake led to higher serum triglycerides (TG) than rats fed adequate concentrations of protein. Additionally, the soy protein diet significantly increased serum TG compared with the casein diet. However, rats fed soy protein had significantly decreased serum cholesterol concentrations compared with those fed a casein diet. No significant differences in renal TG and cholesterol concentrations were observed between rats fed with either protein diets. Renal expression of sterol-regulatory element binding protein 2 (SREBP-2) and its target gene HMG-CoA reductase was significantly increased as the concentration of dietary protein increased. The highest protein diets were associated with greater expression of proinflammatory cytokines in the kidney, independent of the type of dietary protein. These results indicate that high soy or casein protein diets upregulate the expression of lipogenic and proinflammatory genes in the kidney.     

Dietary whey protein modulates liver glycogen level and glycoregulatory enzyme activities in exercise-trained rats

This study compared the effects of dietary whey protein with dietary casein or soy protein on glycogen storage and glycoregulatory enzyme activities in the liver of sedentary and exercise-trained rats. Male Sprague-Dawley rats (ca. 130 g) were divided into one sedentary and three exercise-trained groups, with eight animals in each group. Casein was provided as the source of dietary protein in the sedentary group while the exercise-trained groups were fed casein, whey, or soy protein. Rats in the exercise-trained groups ran for 30 mins/day, 4 days/week on a motor-driven treadmill. In the exercise-trained rats, animals fed whey protein had higher liver glycogen content than animals in the other two diet groups. Glucokinase activity was significantly higher in rats fed whey protein compared to that in rats fed soy protein, while glucose 6-phosphatase activity was significantly decreased in animals on the whey protein diet compared with those the other two diets. Although 6-phospho-fructokinase activity was significantly lower in the whey protein group than in the soy protein group, we found that fructose 1,6-bisphosphatase activity was significantly higher in the whey group compared with either the casein or soy groups. Pyruvate kinase activity in rats fed the casein diet was significantly higher than in rats fed either the whey or soy protein diets. In addition, hepatic alanine aminotransferase activity and serum alanine level were also increased in the whey protein group compared with the casein or soy protein groups. Taken together, these results demonstrate that the whey protein diet in exercise-trained rats results in significantly higher levels of liver glycogen, because of the combined effects of regulation of rate limiting glycolytic and gluconeogenic enzyme activities and activation of glycogenesis from alanine via alanine amino-transferase.     

Regulation of polyamine synthesis by dietary alpha-aminoisobutyric acid and ornithine

An experiment was conducted to determine the effect of feeding ornithine in combination with alpha-aminoisobutyric acid (AIB), an inhibitor of arginase, on the regulation of polyamine synthesis in chicks. A total of 48 chicks with genetically elevated renal arginase activity was fed diets containing crystalline amino acids and 1% AIB with or without 2% ornithine. Feeding AIB reduced renal arginase activity, while renal and hepatic ornithine decarboxylase (ODC) activity increased. Feeding AIB plus ornithine caused no further reduction in renal arginase activity compared with that in chicks fed the AIB-supplemented diet. Renal and hepatic ODC activities, however, fell to below control levels. Renal, hepatic, and breast muscle ornithine concentrations increased substantially when ornithine was fed. AIB plus ornithine increased renal putrescine and spermidine concentrations. It was concluded that AIB could partially overcome the ornithine-induced inhibition of ODC activity. These findings support the hypothesis that dietary manipulation of precursor amino acids of polyamines in the presence of metabolites that induce ODC activity can influence tissue polyamine concentrations.     

Role of soy isoflavones in the hypotriglyceridemic effect of soy protein in the rat

The present study was undertaken to determine whether isoflavones present in soy protein isolate contribute to the triglyceride-lowering effect of the protein relative to casein. Plasma triglyceride concentrations, their secretion rate into blood circulation, and post-heparin plasma lipoprotein lipase activity (a major determinant of intravascular catabolism of triglycerides) were measured in the fasted state in male Sprague-Dawley rats fed for 21 days one of three experimental diets varying in protein source (20% weight/weight): soy protein isolate, casein or casein to which 1.82 mg/g isoflavones (genistein and daidzein) were added to match the isoflavone content of soy protein isolate. Body weight gain was slightly lower in soy protein fed rats than in casein fed rats, but this effect was not statistically significant (P = 0.22). Casein plus isoflavones diet induced intermediary weight gain. A decrease in plasma total triglycerides was observed in rats fed soy protein and casein plus isoflavones compared with casein (P < 0.05), and there was a tendency to a positive correlation between weight gain and plasma triglyceride concentrations (r = 0.35, P = 0.06). However, no significant effect was observed on hepatic triglyceride concentrations, triglyceride secretion rate by the liver and post-heparin plasma lipoprotein lipase activity. These results show that soy protein isolate, in comparison with casein, has a hypotriglyceridemic effect in the rat and suggest that isoflavones may be responsible, at least in part, for this effect. The lowering effect of soy protein isolate and isoflavones on plasma triglyceride concentrations may be mediated by an alteration in energy balance, and possibly by the hepatic production of lipoproteins more susceptible to intravascular hydrolysis. Subtle but sustained changes in triglyceride secretion and post-heparin plasma lipoprotein lipase activity may also be implicated.     

Effect of phytate in soy protein on the serum and liver cholesterol levels and liver fatty acid profile in rats

Dietary soy protein, in comparison with casein, generally lowers the serum cholesterol concentration in rats fed on a cholesterol-enriched diet, while mixed results were observed in rats fed on a diet free of cholesterol. Soy protein also suppresses the conversion of linoleic acid to arachidonic acid in the rat liver. The present study examines whether phytate, a minor component of a soy protein isolate, is responsible for these beneficial effects of soy protein. Weanling male rats were fed for 4 weeks on a purified diet containing a 20% level of protein (either casein (CAS), soy protein (SOY), phytate-depleted SOY (PDSOY) or phytate-replenished PDSOY (PRSOY)) and cholesterol (0 or 0.5%). The dietary protein source and phytate level only affected the serum and liver cholesterol concentrations when the animals were fed on the cholesterol-enriched diet, being significantly lower in those rats fed on the SOY and PRSOY diets than in those fed on the CAS diet, while the concentrations in the rats fed on the PDSOY diet were intermediate. When the animals were fed on the cholesterol-free diet, the ratio of (20:3n-6 + 20:4n-6)/18:2n-6 in liver phosphatidylcholine, a delta6 desaturation index, was significantly lower in the SOY diet group than in the CAS, PDSOY and PRSOY diet groups. Dietary cholesterol significantly depressed the ratio, but neither depletion nor replenishment of phytate affected the ratio. These results suggest that phytate in soy protein played a limited role in the cholesterol-lowering effect of soy protein and was not involved in the metabolism of linoleic acid.     

Supplementation of orotic acid to the casein, but not to egg protein, soy protein, or wheat gluten diets, increases serum ornithine carbamoyltransferase activity

Effects of dietary supplementation of orotic acid to a diet containing the casein protein were compared with diets containing egg protein, soy protein, or wheat gluten on lipid levels in the liver and serum and activities of ornithine carbamoyltransferase (OCT) and alanine aminotransferase in the serum of rats. We found that supplementation of orotic acid to each diet increased the contents of the liver total lipids, triacylglycerol, and phospholipids compared with those not supplemented. The contents of liver total lipids, triacylglycerol, cholesterol, and phospholipids in rats fed the casein diet were significantly higher than those of rats fed the other three diets when orotic acid was supplemented. The levels of triacylglycerol, cholesterol, and phospholipids in the serum of rats fed the casein diet were markedly decreased by addition of orotic acid. The supplementation of orotic acid significantly increased the activities of both serum OCT and alanine aminotransferase in rats fed the casein diet, but not in rats fed the other diets. In conclusion, liver lipid accumulation induced by dietary orotic acid depends on the type of dietary protein. The enhancement of serum OCT activity may result from liver lipid accumulation in rats fed the casein diet supplemented with orotic acid, demonstrating hepatic damage.     

Soy protein isolate in the presence of cornstarch reduces body fat gain in rats

The objective of the present study was to determine the combined effects of dietary protein and carbohydrate sources on total body energy and protein and fat gains as well as on plasma insulin and glucose and tissue lipoprotein lipase activity in male Sprague-Dawley rats fed semipurified diets for 28 days. The diets varied in both protein and carbohydrate sources, namely, casein-cornstarch, casein-sucrose, soy protein isolate (SPI)-cornstarch, SPI-sucrose, cod protein-cornstarch, and cod protein-sucrose. When SPI was combined with cornstarch, lower total body energy and fat gains were observed compared with the combination of either casein and sucrose, casein and cornstarch, or SPI and sucrose. Plasma glucose and insulin concentrations in addition to total and metabolizable energy intake and body weight gain were lower in rats fed the SPI-cornstarch diet than in those fed the casein-sucrose diet. Feeding the SPI-cornstarch diet compared with feeding either the casein-cornstarch or the SPI-sucrose diet also caused lower plasma glucose concentrations and a concomitant trend (p = 0.06) to reduced energy intake and body weight gain. Therefore, the reducing effects of the SPI-cornstarch diet compared with the casein-cornstarch, the casein-sucrose, and the SPI-sucrose diets on body energy and fat gains may result from reductions in energy intake and in plasma glucose concentrations.     

Soy protein diet ameliorates renal nitrotyrosine formation and chronic nephropathy induced by puromycin aminonucleoside

It has been shown that reactive oxygen species are involved in chronic puromycin aminonucleoside (PAN) induced nephrotic syndrome (NS) and that a 20% soy protein diet reduces renal damage in this experimental model. The purpose of the present work was to investigate if a 20% soy protein diet is able to modulate kidney nitrotyrosine formation and the activity of renal antioxidant enzymes (catalase, glutathione peroxidase, Cu,Zn- or Mn-superoxide dismutase) which could explain, at least in part, the protective effect of the soy protein diet in rats with chronic NS induced by PAN. Four groups of rats were studied: (1) Control rats fed 20% casein diet, (2) Nephrotic rats fed 20% casein diet, (3) Control rats fed 20% soy protein diet, and (4) Nephrotic rats fed 20% soy protein diet. Chronic NS was induced by repeated injections of PAN and rats were sacrificed at week nine. The soy protein diet ameliorated proteinuria, hypercholesterolemia, and the increase in serum creatinine and blood urea nitrogen observed in nephrotic rats fed 20% casein diet. Kidney nitrotyrosine formation increased in nephrotic rats fed 20% casein diet and this increase was ameliorated in nephrotic rats fed 20% soy protein diet. However, the soy protein diet was unable to modulate the antioxidant enzymes activities in control and nephrotic rats fed 20% soy protein diet. Food intake was similar in the two diet groups. The protective effect of a 20% soy protein diet on renal damage in chronic nephropathy induced by PAN was associated with the amelioration in the renal nitrotyrosine formation but not with the modulation of antioxidant enzymes.     

54Mn absorption and excretion in rats fed soy protein and casein diets

Rats were fed diets containing either soy protein or casein and different levels of manganese, methionine, phytic acid, or arginine for 7 days and then fed test meals labeled with 2 microCi of 54Mn after an overnight fast. Retention of 54Mn in each rat was measured every other day for 21 days using a whole-body counter. Liver manganese was higher (P less than 0.0001) in soy protein-fed rats (8.8 micrograms/g) than in casein-fed rats (5.2 micrograms/g); manganese superoxide dismutase activity also was higher in soy protein-fed rats than in casein-fed rats (P less than 0.01). There was a significant interaction between manganese and protein which affected manganese absorption and biologic half-life of 54Mn. In a second experiment, rats fed soy protein-test meals retained more 54Mn (P less than 0.001) than casein-fed rats. Liver manganese (8.3 micrograms/g) in the soy protein group was also higher than that (5.7 micrograms/g) in the casein group (P less than 0.0001), but manganese superoxide dismutase activity was unaffected by protein. Supplementation with methionine increased 54Mn retention from both soy and casein diets (P less than 0.06); activity of manganese superoxide dismutase increased (P less than 0.05) but liver manganese did not change. The addition of arginine to casein diets had little effect on manganese bioavailability. Phytic acid affected neither manganese absorption nor biologic half-life in two experiments, but it depressed liver manganese in one experiment. These results suggest that neither arginine nor phytic acid was the component in soy protein which made manganese more available from soy protein diets than casein diets.     

Induction of pancreatic trypsin by dietary amino acids in rats: four trypsinogen isozymes and cholecystokinin messenger RNA

We previously demonstrated that feeding a diet containing a high level of amino acid mixture simulating casein (AA) induced an increase in pancreatic protease activities in rats. In the present study, this effect of dietary AA was further characterized with three separate experiments. These experiments (1) examined periodic changes in pancreatic and small intestinal trypsin activities after switching from a 20% (a normal nitrogen level) AA diet to a 60% AA (a high nitrogen level) diet; (2) measured the abundance of mRNA for four trypsinogen isozymes and for intestinal cholecystokinin (CCK) and secretin in rats fed 20% and 60% AA diets for 10 days compared with rats fed 20% and 60% casein diets; and (3) measured the abundance of mRNA for four trypsinogen isozymes after chronic administration of CCK. Trypsin activities were gradually increased in both the pancreas and the small intestinal lumen and reached maximum at 5 days after the switch to the 60% AA diet (Exp. 1). This result is evidence that the increase in the protease activity in the pancreas is due to enhancement of pancreatic trypsin production. In experiment 2, pancreatic trypsinogen isozymes I, II, III, and IV mRNA abundance were evaluated by the Northern blotting method using cDNA probes specific for each isozyme mRNA. Abundance of trypsinogen mRNA without trypsinogen I tended to increase in the rats fed the 60% casein diet but tended to decrease in the rats fed the 60% AA diet compared with the respective normal nitrogen level diet groups without significant difference. CCK mRNA abundance in the jejunal mucosa increased as a result of feeding the 60% casein diet, but not the 60% AA diet. Subcutaneous CCK injections (3.5 nmole/kg body weight/day, twice daily, at 8:30 am and 7:30 pm) for 10 days resulted in increased pancreatic trypsin activity, whereas the changes in mRNA of the four trypsinogen isozymes was similar between the 20% and 60% casein groups but differed between the 20% and 60% AA groups (Exp. 3). These results suggest that CCK is not involved in the induction of pancreatic trypsin that occurs with feeding of a high AA diet and that the mechanism of protease induction by dietary AA is different from that in the case of dietary protein.     

Effect of the Supplementation of Sulfur Amino Acids to a Diet Containing Soy Protein Isolate on Lipid Metabolism in Rats

The effect of the supplementation of sulfur amino acids to a low casein or soy protein isolate diet on tissue lipid metabolism was investigated. Supplementation of methionine to a 8% casein diet produced a fatty liver in rats, however, supplementation of methionine to a 8.8% soy protein diet (corresponding to a 8% casein diet as to sulfur amino acids content) did not produce a fatty liver. At the level of 8% or less of soy protein in the diet, the accumulation of liver lipids and serum triglyceride was observed. An amino acid mixture simulating the composition of soy protein isolate caused significant accumulation of liver lipids, but serum triglyceride was not changed. Serum cholesterol in rats fed the soy protein diet was lower than that in rats fed the casein diet, but on feeding the amino acid mixtures simulating these protein diets, there was no difference between the two groups. The small differences between soy protein isolate and casein as to lipid metabolism might be due to the small differences in the contents of sulfur amino acids or the specific nature of the soy protein or casein. The supplemental effect of methionine and cystine was also studied. About 60% of total sulfur amino acids could be substituted by cystine for maximum growth.     

Regulation of intestinal mucosal growth by amino acids

Amino acids, especially glutamine (GLN) have been known for many years to stimulate the growth of small intestinal mucosa. Polyamines are also required for optimal mucosal growth, and the inhibition of ornithine decarboxylase (ODC), the first rate-limiting enzyme in polyamine synthesis, blocks growth. Certain amino acids, primarily asparagine (ASN) and GLN stimulate ODC activity in a solution of physiological salts. More importantly, their presence is also required before growth factors and hormones such as epidermal growth factor and insulin are able to increase ODC activity. ODC activity is inhibited by antizyme-1 (AZ) whose synthesis is stimulated by polyamines, thus, providing a negative feedback regulation of the enzyme. In the absence of amino acids mammalian target of rapamycin complex 1 (mTORC1) is inhibited, whereas, mTORC2 is stimulated leading to the inhibition of global protein synthesis but increasing the synthesis of AZ via a cap-independent mechanism. These data, therefore, explain why ASN or GLN is essential for the activation of ODC. Interestingly, in a number of papers, AZ has been shown to inhibit cell proliferation, stimulate apoptosis, or increase autophagy. Each of these activities results in decreased cellular growth. AZ binds to and accelerates the degradation of ODC and other proteins shown to regulate proliferation and cell death, such as Aurora-A, Cyclin D1, and Smad1. The correlation between the stimulation of ODC activity and the absence of AZ as influenced by amino acids is high. Not only do amino acids such as ASN and GLN stimulate ODC while inhibiting AZ synthesis, but also amino acids such as lysine, valine, and ornithine, which inhibit ODC activity, increase the synthesis of AZ. The question remaining to be answered is whether AZ inhibits growth directly or whether it acts by decreasing the availability of polyamines to the dividing cells. In either case, evidence strongly suggests that the regulation of AZ synthesis is the mechanism through which amino acids influence the growth of intestinal mucosa. This brief article reviews the experiments leading to the information presented above. We also present evidence from the literature that AZ acts directly to inhibit cell proliferation and increase the rate of apoptosis. Finally, we discuss future experiments that will determine the role of AZ in the regulation of intestinal mucosal growth by amino acids.     

Polyamine metabolism in enterocytes isolated from newborn pigs.

In the pig, the growth of intestinal mucosa is very intense after birth. Since the polyamines are key elements affecting cell proliferation and differentiation, the present work was undertaken in order to know whether this hypertrophy is associated with an adaptation of polyamine metabolism. Villus enterocytes isolated from pig immediately after birth or 2 days later were found to contain similar amounts of putrescine, spermidine and spermine, i.e., 0.23; 0.41 and 1.24 nmol/10(6) cells, respectively. At birth, despite a relatively high ODC activity, putrescine synthesis from 1 mM L-arginine or 2 mM L-glutamine was very low in isolated enterocytes (6.4 +/- 3.8 pmol/10(6) cells per 30 min), while spermidine and spermine production were not detectable. This could be explained by a very low L-ornithine generation from both amino acids and to an inhibitory effect of polyamines on ODC activity. Two days later, polyamine synthesis from L-arginine remained undetectable despite a higher L-ornithine generation. This was concomitant with a dramatic fall in ODC activity. At both stages, enterocytes were able to take up polyamines from the extracellular medium in a temperature-dependent manner. It is concluded that de-novo synthesis of polyamines from L-arginine or L-glutamine does not play a significant role in the control of polyamine content of pig enterocytes during the postnatal period. In contrast, polyamine uptake by enterocytes would contribute to maintain a steady-state polyamine content during this period.     

Isoflavone-poor soy protein alters the lipid metabolism of rats by SREBP-mediated down-regulation of hepatic genes

Soy intake acts hypolipidemically. Besides isoflavones, soy protein itself is suggested to influence plasma lipid concentrations. We investigated the effects of an alcohol-washed isoflavone-poor soy protein isolate on plasma and liver lipids and the hepatic expression of genes encoding proteins involved in cholesterol and fatty acid metabolism. Therefore, rats were fed diets containing 200 g/kg of either ethanol-extracted soy protein isolate or casein over 22 days. Rats fed soy protein isolate had markedly lower concentrations of liver cholesterol and lower concentrations of triglycerides in the liver and in plasma than rats fed casein (P<.05). Rats fed soy protein isolate had lower relative mRNA concentrations of sterol-regulatory element-binding protein (SREBP)-2, 3-hydroxy-3-methylglutaryl coenzyme A reductase, low-density lipoprotein receptor, cholesterol 7alpha-hydroxylase, apolipoprotein B, Delta9-desaturase and glucose-6-phosphate dehydrogenase in the liver than rats fed casein (P<.05). Hepatic mRNA concentration of SREBP-1c tended to be lower in rats fed soy protein isolate (P<.10). Hepatic mRNA concentrations of insulin-induced gene (Insig) 1 and Insig-2 and of microsomal triglyceride transfer protein, as well as plasma concentrations of free fatty acids, insulin and glucagon, were not different between the two groups. In conclusion, this study suggests that isoflavone-poor soy protein isolate affects cellular lipid homeostasis by the down-regulation of SREBPs and its target genes in the liver, which are involved in the synthesis of cholesterol and triglycerides.     

Effects of soy protein and isoflavone on hepatic fatty acid synthesis and oxidation and mRNA expression of uncoupling proteins and peroxisome proliferator-activated receptor gamma in adipose tissues of rats

Soy protein rich in isoflavones profoundly affects lipid metabolism in experimental animals. To distinguish the roles of the protein and isoflavone components of a soy protein preparation in regulating lipid metabolism, we compared the effects of diets containing methanol-washed soy protein low in isoflavone supplemented with a 0-, 0.5- and 4-g/kg isoflavone preparation on hepatic fatty acid metabolism and adipose tissue gene expression in rats. Diets containing soy protein irrespective of the isoflavone levels decreased the activities and mRNA expression of enzymes involved in hepatic fatty acid synthesis to similar levels. Methanol-washed soy protein compared to casein increased the mRNA expression of peroxisome proliferator-activated receptor (PPAR) alpha, and supplementing the soy protein diet with isoflavone further increased this parameter dose-dependently. However, methanol-washed soy protein compared to casein was totally ineffective in altering the activities and mRNA levels of enzymes involved in fatty acid oxidation. Supplementation of soy protein diets with isoflavone slightly increased these parameters. The mRNA level of uncoupling protein (UCP) 1 in brown adipose tissue was significantly increased and mRNA levels of UCP2 and 3, and PPARgamma2 tended to be higher in rats fed methanol-washed soy protein not supplemented with isoflavone than in the animals fed casein. Adding isoflavone to the soy protein diets dose-dependently increased these parameters. These results suggested that the protein rather than isoflavone component is primarily responsible for the physiological activity of soy protein rich in isoflavones in reducing hepatic lipogenesis. However, isoflavones may have a role in regulating heptic fatty acid oxidation and adipose tissue gene expression.     

A high-beef diet alters protein kinase C isozyme expression in rat colonic mucosa

We recently reported that a red meat (beef) diet relative to a casein-based diet increases protein kinase C (PKC) activity in rat colonic mucosa. The purpose of this study was to further elucidate the effects of a high-beef diet on colonic intracellular signal transduction by analyzing steady-state protein levels of different PKC isozymes as well as activities of the three types of sphingomyelinases. Male Wistar rats (n = 12/group) were fed AIN93G-based diets either high in beef or casein for 4 weeks. Rats fed the beef diet had significantly (P < 0.05) higher cytosolic PKC alpha and lower membrane PKC delta protein levels than rats fed the casein diet. The beef-fed rats also had alterations in subfractions of PKC zeta/lambda so that they had a significantly (P = 0.001) lower level of membrane 70 & 75 kDa fraction and a higher (P = 0.001) level of cytosolic 40 & 43 kDa fraction than rats fed the casein diet. Because protein levels analyzed with a PKC zeta-specific antibody were similar, these differences in PKC zeta/lambda were probably due to changes in PKC lambda expression. PKC beta2 levels did not differ between the dietary groups. Diet had no significant effect on the activity of acid, neutral, or alkaline sphingomyelinase. This study demonstrated that consumption of a high-beef diet is capable of modulating PKC isozyme levels in rat colon, which might be one of the mechanisms whereby red meat affects colon carcinogenesis.     

Caecal fermentation,putrefaction and microbiotas in rats fed milk casein,soy protein or fish meal

To clarify the effect of soy protein (SP) and fish meal (FM), compared to milk casein (MC), on the intestinal environment, we examined caecal environment of rats fed the test diets. Four-week-old rats were fed AIN-76-based diet containing 20 %, w/w MC, SP or FM for 16 days. Caecal organic acids were analysed by HPLC. Caecal putrefactive compounds (indole, phenol, H₂S and ammonia) were analysed by colorimetric assays. Caecal microflora was determined by 16S rRNA gene-DGGE and pyrosequencing with bar-coded primers targeting the bacterial 16S rRNA gene. n-Butyric and lactic acid levels were high in rats fed SP and FM, respectively. Butyrate-producing bacteria, such as Oscillibacter, and lactate-producing bacteria, such as Lactobacillus, were detected in each diet group. Also, the putrefactive compound contents were high in rats fed SP and FM. In this study, both DGGE and pyrosequencing analyses were able to evaluate the dynamics of the intestinal microbiota. The results indicate that dietary proteins can alter the intestinal environment, affecting fermentation by the intestinal microbiota and the generation of putrefactive compounds.