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PubMed2002

An aspartate ring at the TolC tunnel entrance determines ion selectivity and presents a target for blocking by large cations.

The TolC protein of Escherichia coli comprises an outer membrane beta-barrel channel and a contiguous alpha-helical tunnel spanning the periplasm, providing an exit duct for protein export and multidrug efflux. It forms a single transmembrane pore that is open to the outside of the cell but constricted at the peri-plasmic tunnel entrance. This sole constriction is lined by a ring of six aspartate residues, two in each of the three identical monomers. When these were replaced by alanines, the resulting TolC(DADA) protein reconstituted normally in black lipid membranes but showed altered electrophysiological characteristics. In particular, it had lost the strong pH dependence of the wild type and had switched ion selectivity from cations to anions. The function of wild-type TolC as a membrane pore was severely inhibited by divalent and trivalent cations entering the channel tunnel from the channel ("extracurricular") side. Divalent cations bound reversibly to effect complete blocking of the transmembrane ion flux. Trivalent cations were more potent. Hexamminecobalt bound at nanomolar concentrations allowed visualization of single blocking events, whereas the smaller Cr(3+) cation bound irreversibly and could also access the cation binding site via the tunnel entrance. The inhibitory cations had no effect on the mutant TolC(DADA), supporting the view that the aspartate ring is the cation binding site. The electronegative entrance is widely conserved throughout the TolC family, which is essential for efflux and export my Gram-negative bacteria, suggesting that it could present a general target for drugs.

Aspartic Acid↗
PubMed2003

The rat as a model animal for the growing pig in determining ileal amino acid digestibility in soya and milk proteins.

The growing pig is an established model animal for humans to determine protein digestibility to the end of the small intestine. An ileal amino acid digestibility assay based on the laboratory rat offers an alternative. True ileal amino acid digestibility in high quality refined protein sources was determined and compared between the laboratory rat and the growing pig. Both species of animals were fed their daily ration in nine separate meals. Ileal digesta were collected at slaughter and chromic oxide was used as an indigestible marker. For several of the amino acids examined, there were no significant (p < 0.05) differences between the two species for true ileal amino acid digestibility, but for aspartic acid, serine, cysteine, methionine, tyrosine, phenylalanine and histidine, significant (p < 0.05) interspecies differences were found. The overall average amino acid digestibility, for all amino acids and all diets, was 95.8% for the pig and 96.1% for the rat. Cysteine digestibility was highly variable between individual animals fed the same diet. The extent of amino acid digestion and absorption appears to be broadly similar across the two species, but some important differences in digestibility were recorded.

Amino Acids↗
PubMed1990

An evaluation of the method used in digestibility estimations of a dietary ingredient and comparisons on external and internal markers, and time of faeces collection in digestibility studies in the fish Oreochromis aureus (Steindachner).

Results of experiments carried out on the tilapiine fish Oreochromis aureus (Steindachner) to evaluate the method used in the determination of the apparent dry matter and nutrient digestibilities of an ingredient, together with validity of estimations based on day and night collection of faeces, and internal and external markers, are presented. The apparent dry matter and protein digestibilities of the test diets were linearly correlated to the percent substitution of the test ingredient, percent fibre and ash in the test diets (P less than 0.05); the correlation coefficient for the individual relationships decreased in that order. Dry matter or protein digestibilities were not correlated to the dietary protein content (P greater than 0.05). Similarly there were no statistical differences between digestibility estimations based on faecal material, voided in the day or the night; and estimated using different markers viz crude fibre and Cr2O3. The apparent dry matter and protein digestibilities of the test ingredients, leaf meal, were curvilinearly related to the percent substitution of the ingredient in the test diets. The ingredient digestibilities estimated, using crude fibre as the marker, were consistently higher than those estimated with Cr2O3 (P less than 0.05). The present study suggests that, for ingredient digestibility estimations, test diets prepared by mixing 15-20% of the ingredient to a reference diet would be more desirable.

Animals↗
PubMed2004

Anti-diabetic activity and mechanism of action of chromium chloride.

Though supplementation of chromium has been found to improve deranged carbohydrate and lipid metabolism associated with suboptimal chromium intake in patients, its usefulness in the treatment of diabetes mellitus of variable etiology remains questionable. In the present investigation, the effect of 6 wk oral administration of chromium chloride (CC) on the glucose and lipid metabolism was studied in streptozotocin (STZ) diabetic and neonatal-STZ (nSTZ) diabetic rats. Further, its cellular mechanism was studied using 3T3-L1 adipocyte and C2C12 myoblast cell lines. Treatment with CC significantly improved the impaired glucose tolerance and insulin sensitivity of both STZ diabetic and nSTZ diabetic rats without any change in basal or glucose stimulated insulin response indicating insulin-sensitizing action of chromium. CC treatment also significantly improved deranged lipid metabolism. CC per se did not produce any effect in vitro, however, significantly increased insulin stimulated glucose uptake in C2C12 myoblasts and differentiation of 3T3-L1 preadipocytes into mature adipocytes supporting the in vivo insulin-sensitizing action of chromium. This study shows that CC exhibited significant anti-diabetic potential in chemically-induced diabetes in rats, the mechanism of which appears to be potentiation of insulin actions at the target tissues leading to improved peripheral insulin sensitivity.

Adipocytes↗
PubMed1985

Gastric emptying of barley-soya-bean diets in the pig: effects of feeding level, supplementary maize oil, sucrose or cellulose, and water intake.

A technique for measuring gastric emptying in growing pigs by complete removal of digesta through a gastric cannula is described. Four pigs were fitted with gastric cannulas and each was used in three trials. The effects of level of feeding (trial 1), cellulose (C), maize-oil (MO) or sucrose (SU) supplementation (trial 2) and the level of water intake (trial 3) on gastric emptying of digesta, dry matter (DM) and nitrogen from a barley-weatings-soya-bean (B) diet were measured during 4 h after the morning feed. In trial 1, pigs were given 0.66, 0.83, 1.00 or 1.17 times their standard level of feeding. As the level of feeding rose, so the weight of digesta, DM and N emptied in the first hour after feeding increased. This trend continued to some extent in the second hour, but no effects of level of feeding were seen in the third and fourth hours. In trial 2, maize-oil addition to the diet significantly reduced the gastric-emptying rate of DM in the second hour after feeding, compared with the rates for diet C. The rate of N emptying was significantly slower for diets MO and SU than for diet C. In trial 3 there were no significant effects of water intake level (1.75, 2.50 and 3.25 times the weight of diet) on the rate of DM or N emptying from the stomach. The rate of digesta (and thus of water) emptying in the first hour after feeding increased significantly as the water intake rose. It was concluded that because the pattern of gastric emptying was very similar despite large differences in nutritional inputs, an important property of the process appeared to be resilience.

Animals↗
PubMed1996

Apparent ileal dry matter and crude protein digestibility of rations fed to pigs and determined with the use of chromic oxide (Cr2O3) and acid-insoluble ash as digestive markers.

Two experiments were conducted to determine apparent ileal DM and crude-protein (CP) digestibilities in rations fed to pigs. An evaluation was made of Cr2O3 and HCl-insoluble ash as digestive markers. In addition, the effects of body weight (BW) on apparent ileal DM and CP (N x 6.25) digestibilities were studied. In Expt 1, thirteen barrows averaging 35 kg BW were fitted with post-valve T-caecum (PVTC) cannulas to determine the apparent ileal DM and CP digestibilities of a wheat gluten-bran ration (B2) and a soyabean-meal ration (E1). Immediately after morning feeding ileal digesta samples were collected on an hourly basis for a total of 12 h. Subsequently. N and marker contents were determined in the samples. The postprandial patterns of N and Cr passage were more similar than those of N and HCl-insoluble ash. Therefore Cr2O3 is more suitable as a marker than HCl-insoluble ash. The apparent ileal CP digestibility coefficient of ration B2 derived using Cr2O3 as a marker was significantly (P < 0.05) higher by 0.018 compared with the value obtained using HCl-insoluble ash. The corresponding values for ration E2 obtained using Cr2O3 and HCl-insoluble ash were both 0.825. In Expt 2, apparent ileal DM and CP digestibilities were determined in eighteen rations using twelve barrows also fitted with PVTC cannulas (BW from 40 to 100 kg). The protein sources for these rations were from different groups of feedstuffs. In four and three of the rations apparent ileal DM and CP digestibilities respectively were significantly different (P < 0.05) when assessed using the two markers. The digestibility coefficients were not systematically higher or lower for either marker. Absolute differences were < 0.049 on average. Significant effects of live weight on apparent ileal CP digestibilities were found.

Animal Feed↗
PubMedDate not supplied

Occupational exposure to chemical and biological agents in the nonproduction departments of pulp, paper, and paper product mills: an international study.

As part of an international epidemiological study of workers in the pulp and paper industry, previously unpublished exposure measurements were assembled in a database. This article describes 7293 measurements in nonproduction departments from 147 mills in 11 countries. The greatest variety of agents was measured in the maintenance, construction, and cleaning department, where high exposures to asbestos, chromium [VI] compounds, copper, mercury in urine, nitrogen dioxide, ozone, styrene, sulfur dioxide, trichloroethylene, and welding fumes were observed. Measurements in the storage, yard, loading, and shipping department indicated high exposures to asbestos, carbon monoxide, fungal spores, nitrogen oxides, sulfur dioxide, and total dust. The steam and power generation department had high exposures to methyl mercaptan, silica, and total dust. Measurements in process and effluent water treatment, laboratory and research, engineering, and office, administration, and cafeteria areas had few elevated exposures. Throughout the nonproduction departments, measurements of pulp-production chemicals such as chlorine and sulfur compounds tended to be low, with many below detection limits. There were some problems with the available data; in particular, detection limits were often not specified, and the data tended to be clustered in such a way that sources of exposure variability could not be distinguished. Despite these problems, the data provide new insight into the exposures of nonproduction pulp and paper industry personnel.

Databases, Factual↗
PubMed2003

Apparent ileal digestibility of amino acids and the digestible and metabolizable energy content of high-oil corn varieties and its effects on growth performance of pigs.

Two experiments were conducted to compare the nutritional value of normal and high-oil corn for pigs. The normal corn and the two varieties (high-oil corns A and B) of high-oil corn contained 4.41, 7.35 and 8.86% ether extract, on DM basis, respectively. In experiment 1, six non-littermate crossbred barrows (37.8 +/- 1.3 kg BW) were fitted with ileal T-cannulas and used in a double replicated Latin Square digestion trial. Three diets were formulated containing 96.6% of one of the three varieties of corn as the only protein source. Chromic oxide (0.4%) was added as a digestibility marker. Additional vitamins and minerals were added to meet requirements. The digestible energy concentrations for normal corn and high-oil corn A and B were 16.53, 16.99 and 17.07 MJ/kg while the metabolizable energy values were 15.82, 16.32 and 16.36 MJ/kg, on DM basis, respectively. The ileal amino acid digestibility of high-oil corn was generally higher than that of normal corn with significant differences being observed for the essential amino acids isoleucine and phenylalanine. In experiment 2, 96 pigs (8.01 +/- 0.14 kg BW) were used to evaluate four diets in a 2 x 2 factorial design conducted over a 35-day period. Corn variety (high-oil vs. normal corn) and nutrient density (high content of protein and ME vs. low content of protein and ME) were set as the two main effects. During the first 14 days, pigs fed high-oil corn diets consumed more feed and tended to get higher daily gain than pigs fed normal corn. Over the entire 35-day experiment, increasing dietary nutrient density increased daily gain and tended to increase feed conversion, while variety of corn had no significant effects on performance. Overall, the present results indicate that the energy concentration and ileal amino acid digestibility of high-oil corn varieties were equal or superior to those in normal corn and therefore they should be able to be effectively utilized in diets fed to swine.

Amino Acids↗
PubMed2002

Ileal amino acid digestibility assay for the growing meat chicken--comparison of ileal and excreta amino acid digestibility in the chicken.

1. The apparent and true amino acid digestibilities in sorghum, wheat, soyabean meal, meat-and-bone meal, fish meal and blood meal for growing meat chickens were determined using an assay based on the collection of digesta from the terminal ileum and comparison was made with digestibility values determined using an excreta-based assay. 2. Five-week-old meat chickens were given maize-soyabean meal basal diet or mixtures of the basal diet and test diets containing the 6 ingredients as the sole source of dietary protein (50:50 on weight basis). Apparent amino acid digestibility values of assay diets at ileal and excreta levels were calculated using chromic oxide as the indigestible marker. True digestibility values were calculated using endogenous outputs determined by feeding a protein-free diet. Amino acid digestibilities of the ingredients were calculated by difference. 3. The site of measurement had no influence on endogenous amino acid output, the exceptions being aspartic acid and glutamic acid. The output of these two amino acids was higher in the excreta. 4. Significant differences were found between ileal and excreta-based digestibility of certain amino acids in some ingredients, with excreta values being usually higher than the ileal values, indicating a net catabolism of amino acids in the large intestine. The degree of net amino acid disappearance was found to be variable among amino acids and ingredients. In general, threonine had the lowest digestibility at the ileal level and, compared with other amino acids, the highest degredation during passage through the hindgut. 5. The results showed that digestibility determination based on excreta collection will overestimate the uptake for some amino acids in some feeds. The degree of overestimation was often considerable, ranging from 8.9% (apparent digestibility of threonine in soyabean meal) to 56% (apparent digestibility of aspartic acid in wheat). It is concluded that digestibility values measured at the terminal ileum provide a more reliable measure of amino acid availability than those measured in the excreta.

Amino Acids↗
PubMed2002

The effect of microbial phytase on ileal phosphorus and amino acid digestibility in the broiler chicken.

1. The study aimed to assess the effect of a commercially available microbial phytase on phytate phosphorus and total phosphorus content at the terminal ileum as well as true ileal amino acid digestibility. 2. Five diets, each containing a different plant-based feedstuff, were supplemented with microbial phytase and fed, along with a non-supplemented corresponding diet, to 28-d-old broiler chickens, Chromic oxide was used as an indigestible marker. Ileal contents were collected and analysed, along with the diets, for total phosphorus, phytate phosphorus and amino acids. 3. Endogenous phosphorus determined at the terminal ileum was 272 +/- 108 mg/kg food dry matter (mean +/- SE). Endogenous ileal amino acid flows ranged from 58 +/- 10 mg/kg food dry matter for methionine to 568 +/- 47 mg/kg food dry matter for glutamic acid. 4. Supplementation with microbial phytase resulted in a significantly greater phytate P disappearance from the terminal ileum for rice bran (17% units), but not for soyabean meal, maize, wheat or rapeseed meal. Similarly total phosphorus digestibility was significantly (P < 0.05) higher when microbial phytase was added to the rice-bran-based diet but not for any of the other feedstuffs. 5. Amino acid digestibility was significantly greater in the presence of microbial phytase for all the amino acids examined in wheat, for several of the amino acids each in maize and rapeseed meal and for one amino acid in rice bran and soyabean meal. The average increase in amino acid digestibility for those amino acids affected, was 13, 6, 10, 7 and 12% units for wheat, maize, rapeseed meal, rice bran and soyabean meal, respectively. 6. It appears that microbial phytase improves phosphorus digestibility and amino acid digestibility for certain plant-based feedstuffs.

6-Phytase↗
PubMed1997

Development of an ileal amino acid digestibility assay for the growing chicken--effects of time after feeding and site of sampling.

1. The study aimed to establish the optimum time after ingestion and optimum sampling site for the development of an ileal amino acid digestibility assay for broiler chickens. 2. To establish the optimal sampling time, 4-week-old broiler chickens were given one of 6 protein sources (meat-and-bone, soyabean, cottonseed, fish, maize and wheat meals) as the sole source of protein in a test diet. The diets contained chromic oxide as an indigestible marker. The birds were starved for 24 h, fed and subsequently killed for sampling of ileal digesta (terminal 15 cm) at 2, 3, 4, 5 and 6 h after the start of feeding. 3. For the soyabean, fish, wheat and maize meal diets, sampling time had no significant effect on apparent ileal nitrogen digestibility, whereas for the meat-and-bone and cottonseed meal diets there was a significant quadratic effect of sampling time. The amount of digesta collected was maximised and the mean apparent ileal nitrogen digestibility had the lowest variation around the 4 h sampling time. 4. To establish the optimum sampling site, 4-week-old chickens were given either a meat-and-bone, a soyabean or a wheat bran meal-based diet. The birds were killed 4 h after the start of feeding, and digesta were sampled from 0-10, 0-15, 0-20 or 0-25 cm of terminal ileum. 5. There was no significant effect of sampling site on the apparent ileal digestibility of dietary nitrogen. The terminal 15 cm of ileum was considered a preferred site for sampling ileal digesta from broiler chickens.

Amino Acids↗
PubMed1996

Urinary chromium concentrations in humans following ingestion of safe doses of hexavalent and trivalent chromium: implications for biomonitoring.

In this study, we evaluate the significance of increased urinary chromium concentrations as a marker of chromium exposure and potential health risk. Six human volunteers ingested trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] at doses that are known to be safe but are much higher than typical dietary levels. The following dosing regimen was used: d 1-7, 200 micrograms/d chromium picolinate (a dietary supplement); d 8-10, Cr(VI) ingestion at the U.S. Environmental Protection Agency (EPA) reference dose (RfD) of 0.005 mg/kg/d; d 11-13, no dose; d 14-16, Cr(III) ingestion at the U.S. EPA RfD of 1.0 mg/ kg/d; and d 17-18, postdose. Urine voids were collected throughout the dosing periods and analyzed for chromium. Our findings are as follows: (1) ingestion of 200 micrograms/d of chromium picolinate yielded significantly elevated urine concentrations such that each participant routinely exceeded background, (2) ingestion of the Cr(VI) RfD (0.005 mg/kg/d) yielded individual mean urinary chromium levels (1.2-23 micrograms/L) and a pooled mean urinary chromium level (2.4 micrograms/L) that significantly exceeded background, and (3) ingestion of the Cr(III) RfD yielded no significant increase in urinary chromium concentrations, indicating that little, if any, absorption occurred. Our work identified three critical issues that need to be accounted for in any future studies that will use urinary chromium as a marker of exposure. First, a minimum urinary chromium concentration of approximately 2 micrograms/L should be used as a screening level to critically identify individuals who may have experienced elevated exposures to chromium. Second, if Cr(III) levels in soils are known to be less than 80,000 ppm and the Cr(III) is insoluble, urinary chromium concentrations are not an appropriate marker of exposure. Third, newer forms of chromium supplements that contain organic forms of Cr(III) must be considered potential confounders and their contribution to residential chromium uptake must be carefully evaluated.

Administration, Oral↗