The molar ratio of serum retinol-binding protein (RBP) to transthyretin (TTR) is not useful to assess vitamin A status during infection in hospitalised children.
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OBJECTIVE: To assess the usefulness of the molar ratio of serum retinol-binding protein (RBP) to transthyretin (TTR) to determine vitamin A (VA) status during infection. DESIGN: We took advantage of previously collected data during a randomised double-blind, placebo-controlled clinical trial to conduct a secondary analysis of the RBP/TTR ratio and its relationship to infection and VA status. In this clinical trial, children were randomly assigned to one of three groups and received either one single oral high dose of VA (200 000 IU) on the day of admission and subsequently a placebo daily until discharge or daily oral low doses of VA (5000 IU) from admission until discharge or a placebo daily from admission until discharge. SETTING: Lwiro pediatric hospital, Province of South Kivu, Democratic Republic of Congo. SUBJECTS: A total of 900 children aged 0-72 months hospitalised consecutively between March 1994 and March 1996. MAIN OUTCOME MEASURES: RBP/TTR molar ratio after 7 days hospitalisation. RESULTS: After 7 days hospitalisation, molar RBP:TTR ratio (mean+/-s.d.) of infected children (C-reactive proteins>10 mg/l) was 0.67+/-0.31 in the high-dose group (n=81), 0.74+/-0.44 in the low dose group (n=71) and 0.73+/-0.39 in the placebo group (n=81). These values did not differ significantly (one-way ANOVA P=0.472). In patients with baseline serum retinol concentrations<0.70 micromol/l, changes in RBP:TTR ratio between admission and day 7 were not statistically different in the three groups (one-way ANOVA P=0.548). CONCLUSIONS: In this population of malnourished hospitalised children, molar RBP:TTR ratio does not appear to be useful to assess VA status during infection. SPONSORSHIP: Our research was partially supported by a grant from the Fonds de la Recherche Scientifique et Medicale (contract 3.4505.94) and the David and Alice Van Buuren Foundation. (+info)
The transfer of transthyretin and receptor-binding properties from the plasma retinol-binding protein to the epididymal retinoic acid-binding protein.
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Members of the lipocalin superfamily share a common structural fold, but differ from each other with respect to the molecules with which they interact. They all contain eight beta-strands (A-H) that fold to form a well-defined beta-barrel, which harbours a binding pocket for hydrophobic ligands. These strands are connected by loops that vary in size and structure and make up the closed and open ends of the pocket. In addition to binding ligands, some members of the family interact with other macromolecules, the specificity of which is thought to be associated with the variable loop regions. Here, we have investigated whether the macromolecular-recognition properties can be transferred from one member of the family to another. For this, we chose the prototypical lipocalin, the plasma retinol-binding protein (RBP) and its close structural homologue the epididymal retinoic acid-binding protein (ERABP). RBP exhibits three molecular-recognition properties: it binds to retinol, to transthyretin (TTR) and to a cell-surface receptor. ERABP binds retinoic acid, but whether it interacts with other macromolecules is not known. Here, we show that ERABP does not bind to TTR and the RBP receptor, but when the loops of RBP near the open end of the pocket (L-1, L-2 and L-3, connecting beta-strands A-B, C-D and E-F, respectively) were substituted into the corresponding regions of ERABP, the resulting chimaera acquired the ability to bind TTR and the receptor. L-2 and L-3 were found to be the major determinants of the receptor- and TTR-binding specificities respectively. Thus we demonstrate that lipocalins serve as excellent scaffolds for engineering novel biological functions. (+info)
Phylogenetic relationships, ecological correlates, and molecular evolution within the cavioidea (mammalia, rodentia).
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A molecular phylogeny of the rodent superfamily Cavioidea was derived using two nuclear sequences (exon #10 of the growth hormone receptor gene and intron #1 of the transthyretin gene) and one mitochondrial gene (12S rRNA). A combined analysis produced a highly derived and well-supported phylogenetic hypothesis that differed from traditional taxonomy primarily in the placement of two taxa. Kerodon, traditionally included within the subfamily Caviinae with guinea pigs and its relatives, is placed sister to the family Hydrochaeridae and closely aligned with the subfamily Dolichotinae. Inclusion of Hydrochaeris within the Caviidae renders the familial classification paraphyletic. Our data further support the taxonomic separation of the families Agoutidae and Dasyproctidae. Both the molecular and traditional morphological interpretations are assessed in testing an ecological constraints hypothesis regarding social behaviors. Whereas traditional taxonomy is consistent with an environmental constraints explanation for social behavior, the molecular data suggest that phylogenetic effects may be a more important factor in the evolution of social behavior in this group. Although lineage-specific rate heterogeneity was identified in all three molecular data sets, no significant support was obtained for the metabolic rate hypothesis. However, both nuclear genes displayed patterns in accordance with the generation time hypothesis. (+info)
Severe iron deficiency anemia in transgenic mice expressing liver hepcidin.
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We recently reported the hemochromatosis-like phenotype observed in our Usf2 knockout mice. In these mice, as in murine models of hemochromatosis and patients with hereditary hemochromatosis, iron accumulates in parenchymal cells (in particular, liver and pancreas), whereas the reticuloendothelial system is spared from this iron loading. We suggested that this phenotypic trait could be attributed to the absence, in the Usf2 knockout mice, of a secreted liver-specific peptide, hepcidin. We conjectured that the reverse situation, namely overexpression of hepcidin, might result in phenotypic traits of iron deficiency. This question was addressed by generating transgenic mice expressing hepcidin under the control of the liver-specific transthyretin promoter. We found that the majority of the transgenic mice were born with a pale skin and died within a few hours after birth. These transgenic animals had decreased body iron levels and presented severe microcytic hypochromic anemia. So far, three mosaic transgenic animals have survived. They were unequivocally identified by physical features, including reduced body size, pallor, hairless and crumpled skin. These pleiotropic effects were found to be associated with erythrocyte abnormalities, with marked anisocytosis, poikylocytosis and hypochromia, which are features characteristic of iron-deficiency anemia. These results strongly support the proposed role of hepcidin as a putative iron-regulatory hormone. The animal models devoid of hepcidin (the Usf2 knockout mice) or overexpressing the peptide (the transgenic mice presented in this paper) represent valuable tools for investigating iron homeostasis in vivo and for deciphering the molecular mechanisms of hepcidin action. (+info)
Prealbumin: a marker for nutritional evaluation.
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Determining the level of prealbumin, a hepatic protein, is a sensitive and cost-effective method of assessing the severity of illness resulting from malnutrition in patients who are critically ill or have a chronic disease. Prealbumin levels have been shown to correlate with patient outcomes and are an accurate predictor of patient recovery. In high-risk patients, prealbumin levels determined twice weekly during hospitalization can alert the physician to declining nutritional status, improve patient outcome, and shorten hospitalization in an increasingly cost-conscious economy. (+info)
Structural basis of negative cooperativity in transthyretin.
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A comparison of the AC and BD binding sites of transthyretin (TTR) was made in terms of the interatomic distances between the Ca atoms of equivalent amino acids, measured across the tetramer channel in each binding site. The comparison of the channel diameter for apo TTR from different sources revealed that in the unliganded transthyretin tetramers the distances between the A, D and H beta-strands are consistently larger, while the distances between the G beta-strands are smaller in one site than in the other. These differences might be described to have a 'wave' character. An analogous analysis performed for transthyretin complexes reveals that the shape of the plot is similar, although the amplitudes of the changes are smaller. The analysis leads us to a model of the changes in the binding sites caused by ligand binding. The sequence of events includes ligand binding in the first site, followed by a slight collapse of this site and concomitant opening of the second site, binding of the second molecule and collapse of the second site. The following opening of the first, already occupied site upon ligand binding in the second site is smaller because of the bridging interactions already formed by the first ligand. This explains the negative cooperativity (NC) effect observed for many ligands in transthyretin. (+info)
Complex of rat transthyretin with tetraiodothyroacetic acid refined at 2.1 and 1.8 A resolution.
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The crystal structure of rat transthyretin (rTTR) complex with 3,5,3',5'-tetraiodothyroacetic acid (T4Ac) was determined at 1.8 A resolution with low temperature synchrotron data collected at CHESS. The structure was refined to R = 0.207 and Rfree = 0.24 with the use of 8-1.8 A data. The additional 8000 reflections from the incomplete 2.1-1.8 data shell, included in the refinement, reduced the Rfree index by 1.3%. Structure comparison with the model refined against the complete 8-2.1 A data revealed no differences in the ligand orientation and the conformation of the polypeptide chain in the core regions. However, the high-resolution data included in the refinement improved the model in the flexible regions poorly defined with the lower resolution data. Also additional sixteen water molecules were found in the difference map calculated with the extended data. The structure revealed both forward and reverse binding of tetraiodothyroacetic acid in one binding site and two modes of forward ligand binding in the second site, with the phenolic iodine atoms occupying different sets of the halogen binding pockets. (+info)
Comparison of binding interactions of dibromoflavonoids with transthyretin.
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The crystal structure of rat transthyretin (rTTR) complex with the dibromoflavone EMD21388 was determined to 2.3 A resolution and refined to R = 0.203 and Rfree = 0.288. Two different orientations of EMD21388, which differ in the channel penetration by 1.6 A, were found in the A/C binding site of rTTR. The single ligand position observed in the BID site is intermediate between the two positions found in the A/C site. The position of the dibromoflavone in the B/D site is similar to that reported for dibromoaurone in human TTR. The bromine atoms of EMD21388 form strong interactions in the P3 and P3' pockets of rTTR. Due to the different molecular architectures of both ligands, dibromoflavone forms only one interaction with Lys-15 near the channel entrance, while direct interactions with the pair of Lys-15 were reported for dibromoaurone. The C3* methyl group of EMD21388 mediates the bridging interactions between two TTR subunits in the P2 pockets. The interactions of the O2* hydroxyl group of dibromoaurone with the Thr-119 side chain in the P3 pockets are not matched by similar interactions in EMD21388. Both these alternative interactions can explain the competitive binding of 3',5'-dibromoflavonoids to transthyretin. (+info)