Dietary fructo-oligosaccharides dose-dependently increase translocation of salmonella in rats

Prebiotics, such as fructo-oligosaccharides (FOS), stimulate the protective gut microflora, resulting in an increased production of organic acids. This may result in increased luminal killing of acid-sensitive pathogens. However, host defense against invasive pathogens, like salmonella, also depends on the barrier function of the intestinal mucosa. Rapid fermentation of prebiotics leading to high concentrations of organic acids may impair the barrier function. Therefore, we determined the dose-dependent effect of dietary FOS on the resistance of rats to Salmonella enteritidis. Male Wistar rats were fed restricted quantities of a "humanized" purified diet supplemented with 0, 3 or 6 g/100 g of FOS (n = 7 in the 6% FOS group and n = 8 in the other diet groups). After an adaptation period of 2 wk, rats were orally infected with 1.7 x 10(10) colony-forming units of S. enteritidis. Supplement-induced changes in the intestinal microflora and fecal cation excretion were determined before and after infection. Cytotoxicity of fecal water was determined with an in vitro bioassay, and fecal mucins were quantified fluorimetrically. Colonization of S. enteritidis was determined by quantification of salmonella in cecal contents and mucosa. Translocation of S. enteritidis was quantified by analysis of urinary nitric oxide metabolites in time. Before infection, FOS decreased cecal and fecal pH, increased fecal lactic acid concentration and increased bifidobacteria and enterobacteria. FOS also increased cytotoxicity of fecal water and fecal mucin excretion, indicating mucosal irritation. Remarkably, FOS dose-dependently increased salmonella numbers in cecal contents and mucosa and caused a major increase in infection-induced diarrhea. In addition, FOS enhanced translocation of salmonella. Thus, in contrast to most expectations, FOS dose-dependently impairs the resistance to salmonella infection in rats. These results await verification by other controlled animal and human studies.     

Interaction of calcium and phosphate decreases ileal magnesium solubility and apparent magnesium absorption in rats.

We tested the hypothesis that increased intakes of calcium and phosphate lower magnesium solubility in the intestinal lumen, causing a decreased magnesium absorption. In in vitro experiments at a constant magnesium concentration, increasing calcium concentrations reduced magnesium solubility. This effect did not occur in the absence of phosphate. Increasing phosphate concentrations decreased the solubility of magnesium in the presence, but not in the absence, of calcium. These results suggest that the formation of an insoluble calcium-magnesium-phosphate complex determines magnesium solubility. To extend this concept to in vivo conditions, rats were fed purified diets containing a constant concentration of magnesium (16.4 mumol/g) but different concentrations of calcium (25, 100 or 175 mumol/g) and phosphate (58, 103 or 161 mumol/g). Increased intakes of calcium decreased magnesium solubility in the ileal lumen and lowered magnesium absorption. The latter result occurred only if the dietary phosphate concentration was at least 103 mumol/g. Increasing dietary phosphate concentrations reduced both magnesium solubility in the ileum and magnesium absorption, but only if the dietary calcium concentration was at least 100 mumol/g. These results support those obtained in vitro. We conclude that increased intakes of calcium and phosphate decrease magnesium absorption by the formation of an insoluble calcium-magnesium-phosphate complex in the intestinal lumen.     

Oxalic acid decreases calcium absorption in rats

Calcium absorption from salts and foods intrinsically labeled with 45Ca was determined in the rat model. Calcium bioavailability was nearly 10 times greater for low oxalate kale, CaCO3 and CaCl2 than from CaC2O4 (calcium oxalate) and spinach (high in oxalates). Extrinsic and intrinsic labeling techniques gave a similar assessment of calcium bioavailability from kale but not from spinach.     

Dietary fructooligosaccharides increase intestinal permeability in rats

We showed previously that fructooligosaccharides (FOS) decrease the resistance to salmonella infection in rats. However, the mechanism responsible for this effect is unclear. Therefore, we examined whether dietary FOS affects intestinal permeability before and after infection with Salmonella enterica serovar Enteritidis. Male Wistar rats were fed restricted quantities of a purified diet that mimicked the composition of a Western human diet. The diet was supplemented with 60 g/kg cellulose (control) or 60 g/kg FOS and with 4 mmol/kg of the intestinal permeability marker chromium EDTA (CrEDTA) (n = 8 or 10). After an adaptation period of 2 wk, rats were orally infected with 10(8) colony-forming units (cfu) of S. enteritidis. Mucin concentrations in intestinal contents and mucosa were measured fluorimetrically, as markers of mucosal irritation. Intestinal permeability was determined by measuring urinary CrEDTA excretion. Translocation of salmonella was quantified by analysis of urinary nitric oxide metabolites with time. Before infection, FOS increased mucosal lactobacilli and enterobacteria in cecum and colon, but not in the ileum. However, FOS increased cytotoxicity of fecal water and intestinal permeability. Moreover, FOS increased fecal mucin excretion and mucin concentrations in cecal and colonic contents, and in cecal mucosa before infection. After infection, mucin excretion and intestinal permeability in the FOS groups increased even further in contrast to the control group. In addition, FOS increased translocation of salmonella to extraintestinal sites. Thus, FOS impairs the intestinal barrier in rats, as indicated by higher intestinal permeability. Whether these results can be extrapolated to humans requires further investigation.     

濮阳市鼠类肠道寄生虫及沙门菌感染状况调查

鼠类与人类的关系极为密切,多种疾病人鼠共患,可严重影响人群身体健康。为了解濮阳市鼠类肠道寄生虫及沙门菌感染状况,2008年5月,组织专业技术人员分赴濮阳市5县2区（濮阳县、清丰县、南乐县、范县、台前县、濮阳市区和开发区）,在县（区）级疾病预防控制中心的大力配合下,开展了调查工作。     

Dietary alpha-tocopherol decreases alpha-tocotrienol but not gamma-tocotrienol concentration in rats

We previously showed that alpha- and gamma-tocotrienols accumulate in adipose tissue and skin but not in plasma or other tissues of rats fed a tocotrienol-rich fraction extracted from palm oil containing alpha-tocopherol and alpha- and gamma-tocotrienols. To clarify the nature of tocotrienol metabolism, we studied the distribution of alpha- or gamma-tocotrienol in rats fed alpha- or gamma-tocotrienol without alpha-tocopherol, and the effect of alpha-tocopherol on their distribution. Wistar rats (4-wk-old) were fed a diet with 50 mg alpha-tocotrienol/kg alone or with 50 mg alpha-tocopherol/kg in expt. 1, and a diet with 50 mg gamma-tocotrienol/kg alone or with 50 mg alpha-tocopherol/kg in expt. 2, for 8 wk. alpha-Tocotrienol was detected in various tissues and plasma of the rats fed alpha-tocotrienol alone, and the alpha-tocotrienol concentrations in those tissues and plasma decreased (P < 0.05) by the dietary alpha-tocopherol in the rats fed alpha-tocotrienol with alpha-tocopherol. However, gamma-tocotrienol preferentially accumulated in the adipose tissue and skin of the rats fed gamma-tocotrienol alone, and the dietary alpha-tocopherol failed either to decrease (P >/= 0.05) gamma-tocotrienol concentrations in the adipose tissue and skin or to increase (P >/= 0.05) in the urinary excretion of 2,7,8-trimethyl-2(2'-carboxymethyl)-6-hydroxycroman, a metabolite of gamma-tocotrienol, in the rats fed gamma-tocotrienol with alpha-tocopherol. These data suggest that alpha-tocopherol enhances the alpha-tocotrienol metabolism but not the gamma-tocotrienol metabolism in rats.     

Dietary sesame seed decreases urinary excretion of alpha- and gamma-tocopherol metabolites in rats

We previously showed that dietary sesame seed and its lignan inhibited gamma-tocopherol metabolism to 2,7,8-trimethyl-2(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), a gamma-tocopherol metabolite, and markedly elevated tissue gamma-tocopherol concentration in rats. The aim of this study was to clarify the effect of dietary sesame seed on alpha-tocopherol metabolism. Vitamin E-deficient rats fed a vitamin E-free diet for 4 wk were fed a diet containing alpha-tocopherol, alpha- and gamma-tocopherol, or alpha-tocopherol with sesame seed for 7 d. Urinary excretion of 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), a alpha-tocopherol metabolite, in rats fed alpha-tocopherol with sesame seed was inhibited (p<0.05) as compared with that in rats fed alpha-tocopherol alone, or alpha- and gamma-tocopherol. The gamma-CEHC excretion was also less (p<0.05) in rats fed alpha-tocopherol with sesame seed than that in rats fed alpha- and gamma-tocopherol. The inhibition of alpha- and gamma-CEHC excretion by sesame seed was accompanied by elevation (p<0.05) of the alpha- and gamma-tocopherol concentration in the liver. These results suggest that dietary sesame seed inhibits not only gamma-tocopherol metabolism to gamma-CEHC but also alpha-tocopherol metabolism to alpha-CEHC in rats.     

Dietary calcium phosphate promotes Listeria monocytogenes colonization and translocation in rats fed diets containing corn oil but not milk fat

Most Gram-positive bacteria are susceptible to the bactericidal action of fatty acids and bile acids. Because dietary calcium phosphate (CaP(i)) lowers the intestinal concentration of these antimicrobial agents, high CaP(i) intake may enhance intestinal colonization of Gram-positive pathogens and the subsequent pathogenesis. In this study, we tested this hypothesis in a rat model using Listeria monocytogenes. Rats were fed diets containing low (20 micromol/g diet) or high (160 micromol/g diet) amounts of CaP(i). Dietary fat was provided as corn oil or milk fat. Rats were orally inoculated with L. monocytogenes. When rats consumed diets containing corn oil, high CaP(i) intake indeed stimulated colonization of L. monocytogenes and increased L. monocytogenes translocation and diarrhea. In addition, supplemental CaP(i) enhanced ex vivo growth of L. monocytogenes in fecal extracts of rats fed corn oil diets, suggesting that high CaP(i) intake decreased a luminal inhibitory factor. The concentrations of bile salts and fatty acids, which were highly listericidal in vitro, were indeed considerably decreased in fecal water of rats in the high calcium corn oil group. Surprisingly, dietary CaP(i) did not affect colonization and translocation of L. monocytogenes in rats fed the milk fat diet, nor did CaP(i) enhance ex vivo growth in fecal extracts. This absence of Listeria stimulation was associated with a lack of effect of dietary CaP(i) on fecal soluble fatty acids. In addition, residual soluble bile salts were higher in rats fed the high CaP(i) milk fat diet compared with the high CaP(i) corn oil diet. These results suggest that the stimulating effect of CaP(i) on L. monocytogenes infection depends on the type of dietary fat consumed.     

Dietary calcium supplementation suppresses bone formation in magnesium-deficient rats

The purpose of this study was to clarify the effects of dietary calcium (Ca) supplementation on bone metabolism of magnesium (Mg)-deficient rats. Male Wistar rats were randomized by weight into three groups, and fed a control diet (control group), a Mg-deficient diet (Mg- group) or a Mg-deficient diet having twice the control Ca concentrations (Mg-2Ca group) for 14 days. Trabecular bone volume was significantly lower in the Mg- and Mg-2Ca groups than in the control group. Trabecular number was also significantly lower in the Mg- and Mg-2Ca groups than in the control group. Mineralizing bone surface, mineral apposition rate (MAR), and surface referent bone formation rate (BFR/BS) were significantly lower in the Mg- and Mg-2Ca groups than in the control group. Furthermore, MAR and BFR/BS were significantly lower in the Mg-2Ca group than in the Mg- group. These results suggest that dietary Ca supplementation suppresses bone formation in Mg-deficient rats.     

Development of intestinal bifidobacteria and lactobacilli in breast-fed neonates

BACKGROUND & AIMS: Neonates are subject to numerous factors that affect normal intestinal colonization. This study was to quantify bifidobacteria and lactobacilli in the faeces of breast-fed neonates using quantitative real-time PCR assay, and to investigate the effects of different delivery on the development of bifidobacteria or lactobacilli. METHODS: The faecal bifidobacteria and lactobacilli of 40 healthy breast-fed neonates were studied prospectively. Twenty infants were vaginally delivered (VD), and 20 by caesarean delivery (CD) with prophylactically 4 g intravenous cefradine administered to their mothers three times. The faecal bifidobacteria and lactobacilli of neonates were consecutively quantified by SYBR Green I-based real-time PCR assay in the first 7 days after birth. RESULTS: The mean levels of bifidobacteria increased from 5.1 to 9.3 in the VD group vs from less than 4.6 to 8.7 in the CD group. The bifidobacteria colonization levels in six samples in the CD group were lower than the limit of detection on day 2. The mean levels of bifidobacteria in the VD group were significantly higher than in the CD group (p<0.05). The mean levels of lactobacilli increased from 4.9 to 7.2 in the VD group vs from 4.9 to 6.9 in the CD group. There was no statistical difference between two groups during the first week (p>0.05). The development of bifidobacteria and lactobacilli showed significant interindividual differences in all infants studied. CONCLUSIONS: Primary intestinal bifidobacteria in neonates by caesarean may be disturbed more significantly than lactobacilli.     

The rhamnogalacturonan-II dimer decreases intestinal absorption and tissue accumulation of lead in rats

The rhamnogalacturonan-II dimer (dRG-II) forms strong complexes in vitro with lead (Pb) and other selected cations. We examined the in vivo bioavailability of Pb complexed with dRG-II and the effect of unleaded dRG-II on the intestinal absorption and tissue retention of Pb in rats. Forty male Wistar rats were divided into four groups. Each group consumed a purified control diet for 3 wk or the same diet supplemented with: i) 3 mg of Pb/kg, ii) 0.5 g of leaded dRG-II/kg, or iii) 0.5 g of leaded dRG-II/kg and 4.5 g of unleaded dRG-II/kg. The leaded dRG-II provided approximately 3 mg of Pb/kg of diet. A chemical balance study was conducted during the last 5 d of the 3-wk study, and blood and organs were sampled for Pb and mineral analyses. The apparent intestinal absorptions of Pb were 62.3, 15.2, 11.8 and -0.1%, and Pb balances were 1.9, 9.6, 5.6 and -0.2 microg/d for the control and the three experimental groups, respectively. The Pb complexed with dRG-II was less available than Pb acetate, as reflected by significantly lower blood and tissue Pb levels. The addition of unleaded dRG-II decreased the intestinal absorption and the tissue retention of Pb significantly. We further found that the apparent absorption and status of magnesium, zinc and iron were unaffected by Pb treatment or dRG-II addition. We conclude that dRG-II may be useful in decreasing toxicity related to chronic Pb exposure. Human studies will be necessary however, to further evaluate the clinical utility of this beneficial effect.     

Dietary phosphate deprivation increases renal synthesis and decreases renal catabolism of 1,25-dihydroxycholecalciferol in guinea pigs.

In guinea pigs, dietary phosphate deprivation decreases plasma phosphate concentration, increases plasma 1.25-dihydroxycholecalciferol [1,25-(OH)2D3] concentration and causes hypercalcemia concurrent with the maximal increase in plasma 1,25-(OH)2D3 levels. Our objective was to determine whether increased synthesis or decreased catabolism contributed to the elevation in plasma 1,25-(OH)2D3. Preliminary experiments using renal mitochondria from guinea pigs fed a control diet revealed that 23,25-dihydroxycholecalciferol [23,25-(OH)2D3], not 24,25-dihydroxycholecalciferol [24,25-(OH)2D3], was the reciprocal side-chain metabolite to 1,25-(OH)2D3 in this species. An assay employing guinea pig renal mitochondria was used to measure the renal synthesis of 1,25-(OH)2D3 and 23,25-(OH)2D3 from [3H]25-OH-D3. These metabolites were unequivocally identified by combinations of HPLC, ultraviolet spectrophotometry and mass spectrometry. This renal mitochondrial assay was subsequently used to investigate the effect of dietary phosphate deprivation on guinea pig vitamin D metabolism. Within 1 wk the rate of synthesis of 1,25-(OH)2D3 was maximal in phosphate-deprived guinea pigs. This rate was significantly (P less than 0.005) higher than that achieved in same-day control guinea pigs. Conversely, within 1 d the synthesis of 23,25-(OH)2D3 was significantly (P less than 0.005) decreased in phosphate-deprived guinea pigs. Similarly, the rate of 1,25-(OH)2D3 metabolism was decreased within 1 d of dietary phosphate deprivation and was at a minimum within 1 wk. This rate was significantly (P less than 0.005) less than that attained in same-day control guinea pigs. These results suggest that both increased synthesis and decreased metabolism of 1,25-(OH)2D3 contribute to the plasma 1,25-(OH)2D3 elevation that occurs in response to dietary phosphate deprivation.     

Dietary sucrose enhances intestinal lactase gene expression in euthyroid rats

It is postulated that dietary carbohydrates and thyroid hormones are major regulators for expression of the lactase/phlorizin hydrolase (LPH) gene in rat jejunum. In this study, we investigated the effects of thyroid hormones and dietary sucrose on LPH gene expression and lactase activity in starved rats. Firstly, animals at 8 wk of age were fed a low-starch diet (5.5% energy as cornstarch) or high-starch diet (71% energy as cornstarch) for 7 d (experiment 1). The mRNA level of LPH as well as lactase activity significantly decreased in rats fed the low-starch diet as compared to those fed the high-starch diet. To investigate the effects of thyroid hormone status, the animals previously fed the low-starch diet were starved for 3 d, and half of the animals were given intraperitoneal (i.p.) injections of 20 microg/ 100 g body weight triiodothyronine (T3) twice daily (experiment 2). The LPH mRNA level and lactase activity were elevated by starvation for 3 d, but they were repressed by the injection of T3 during starvation. To investigate the effects of dietary sucrose in starved rats, they were force-fed a sucrose diet for 6 h (experiment 3). The LPH gene expression and lactase activity were up-regulated by force-feeding a sucrose diet, only when the animals were kept in euthyroid status by daily T3 administrations. In contrast, the sucrase-isomaltase mRNA levels and sucrase activity were unaffected by force-feeding the sucrose diet for both T3-treated and untreated starved rats. Our work suggests that dietary sucrose is capable of enhancing lactase gene expression in starved rats when they have a sustainable thyroid hormone level.     

Dietary fiber-rich barley products beneficially affect the intestinal tract of rats

The objective of this study was to investigate the effects of barley-rich diets in the intestinal tract of rats. Four test groups (A-D) of 10 young male Wistar rats were fed diets containing 50 g/100 g barley extrudates (A, B and D) or mixtures (C) for 6 wk; the control diet contained no barley. The barley-containing supplements in the test diets were: A = cultivar "HiAmi"; B = "HiAmi" and "Prowashonupana" (50:50); C = "Prowashonupana" and Novelose (50:50); D = "Prowashonupana" and amylose from maize (60:40). These supplements contained 7-12 g/100 g beta-glucan and 7-24 g/100 g resistant starch. Additionally, 5 g microcrystalline cellulose/100 g was present in all diets. Carbohydrate utilization (indirect calorimetry) was lower (P < 0.05) in rats fed the barley-containing diets C or D than in the controls. In the test groups, the following differences from the controls were found: greater food intake in the last 2 wk (P < 0.05); increased weight gain in wk 6 (P < 0.05); greater mass of the ceca (groups B-D; P < 0.05) and colons (P < 0.001) as well as masses of cecal (groups C and D; P < 0.01) and colon contents (P < 0.001); greater concentrations of resistant starch in cecal and most of the colon contents (P < 0.05); and more beta-glucan in the small intestine, cecum and colon (P < 0.05). The numbers of coliforms and Bacteroides were lower than in the controls in groups B-D and those of Lactobacillus were greater in all test groups (P < 0.05). Short-chain fatty acids (SCFA) were higher in the cecal contents of the test groups (> or = 800 micro mol/g DM; P < 0.001) compared with the controls ( approximately 200 micro mol/g DM). Similarly, SCFA were higher in colon and feces of the test groups. The concentrations of excreted bile acids increased up to 30% during the feeding period. The proportions of secondary bile acids were lower and the amounts of neutral sterols (P < 0.001) were greater in feces of rats fed the barley-containing diets for 6 wk than in the controls. Diets containing more soluble macromolecular dietary fibers such as beta-glucans affected the excretion of bile acids and neutral sterols the most, whereas the fermentation of dietary fiber, including resistant starch, influenced the steroids in feces. These results suggest that dietary fiber-rich barley-containing diets have beneficial physiologic effects.     

Dietary threonine restriction specifically reduces intestinal mucin synthesis in rats

We determined whether the steady-state levels of intestinal mucins are more sensitive than total proteins to dietary threonine intake. For 14 d, male Sprague-Dawley rats (158 +/- 1 g, n = 32) were fed isonitrogenous diets (12.5% protein) containing 30% (group 30), 60% (group 60), 100% (control group), or 150% (group 150) of the theoretical threonine requirement for growth. All groups were pair-fed to the mean intake of group 30. The mucin and mucosal protein fractional synthesis rates (FSR) did not differ from controls in group 60. By contrast, the mucin FSR was significantly lower in the duodenum, ileum, and colon of group 30 compared with group 100, whereas the corresponding mucosal protein FSR did not differ. Because mucin mRNA levels did not differ between these 2 groups, mucin production in group 30 likely was impaired at the translational level. Our results clearly indicate that restriction of dietary threonine significantly and specifically impairs intestinal mucin synthesis. In clinical situations associated with increased threonine utilization, threonine availability may limit intestinal mucin synthesis and consequently reduce gut barrier function.     

钙对去势骨质疏松大鼠肠道菌群结构的影响

目的研究钙对去势骨质疏松大鼠肠道菌群结构的影响。方法30只SPF级雌性Wistar大鼠,按体重随机分为假手术组、模型组、碳酸钙补充组,去卵巢建立去势骨质疏松大鼠模型。造模1周后开始灌胃,碳酸钙补充组灌胃280mg/mL碳酸钙溶液10mL/kg,钙摄入量为1.34g/kg,其他两组灌胃等量无菌水,每日1次。连续灌胃12周后处死动物,取左侧股骨,用双能X射线骨密度仪测定骨密度;无菌提取粪便DNA,利用Illumina Miseq平台进行高通量测序。结果与假手术组相比,模型组大鼠体重增重显著增加,骨密度显著降低(P<0.05),肠道菌群多样性未见明显变化,厚壁菌门丰度降低,拟杆菌门丰度增加;与模型组相比,碳酸钙补充组大鼠体重增重显著降低,骨密度显著增加(P<0.05),肠道菌群多样性未见明显变化,厚壁菌门丰度增加,拟杆菌门丰度降低。结论实验周期内补钙能够升高大鼠骨密度,并抑制体重增加,其作用机制可能与调节肠道菌群结构有关。     

Dietary carbohydrate stimulates alcohol diet ingestion,promotes growth and prevents fatty liver in rats

When young male Sprague Dawley rats were fed ad libitum for 4 weeks a Lieber-DeCarli diet containing 36% of the total calories as ethanol, they consumed ca 50 ml of diet per day, gained 3–3.7 g/day and their livers contained ca 60 mg triglyceride/g. On the other hand, when rats were maintained on isocaloric diets containing 30%, 26% or 20% of calories as alcohol, the daily diet consumption (64, 67 and 88 ml respectively) and growth rate (4.2, 5.8 and 6.9 g respectively) increased markedly and their livers contained only 20–25 mg triglyceride/g. The amount of alcohol calories consumed per day or the alcohol consumption per 100 g body weight were comparable in the various diet groups. Since the reduction in alcohol calories was compensated for by including isocaloric amounts of maltose-dextrins, it is likely that the increased carbohydrate content stimulated diet ingestion, promoted growth and prevented the development of fatty liver despite chronic alcohol consumption.