Messenger RNA levels of plasma proteins following fasting

Plasma transferrin concentration as a nutritional marker in malnourished dogs with nutritional treatment

Rapid turnover proteins, such as transferrin (Tf), are used as dynamic nutritional assessment proteins in human medicine. However, nutritional status in veterinary medicine is mostly assessed on the basis of classical static factors, such as body weight, body condition score and plasma albumin level. This study evaluated the clinical usefulness of Tf as a nutritional assessment marker by measuring plasma Tf concentrations in malnourished dogs before and after nutritional treatment. Posttreatment plasma Tf concentrations were significantly higher than the pretreatment concentrations, although the albumin concentration did not change significantly. The numbers of dogs that exhibited increases in plasma Tf concentrations were significantly related to weight gain. Furthermore, the survival rates at day 60 after treatment initiation were significantly higher in dogs with plasma Tf concentrations above the reference value (180 mg/dl) after the nutritional treatment than in those with a plasma Tf concentration<180 mg/dl. In conclusion, the plasma Tf concentration is related to nutritional condition and would be a candidate for a novel nutritional assessment marker in dogs.

Structural modifications of serum transthyretin in rats during protein-energy malnutrition

Transthyretin (TTR) is a sensitive marker of protein-energy malnutrition and changes in serum and expression levels during protein and energy deficiency are well described. However, little is known about structural modifications of TTR during protein and/or energy deprivation. Therefore, the aim of this study was to determine the effects of protein inadequacies on post-translational modifications of TTR. For this purpose, male Wistar rats were fed a diet with either casein or gelatine as sole protein source subsequent to a protein wash-out period. Changes in TTR serum levels as well as other markers of nutritional status as body weight, food consumption, total serum protein and serum RBP4 levels as well as antioxidative capacity were determined. Post-translational modifications of TTR were examined by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) analysis. The rats from the gelatine group revealed a marked change in the post-translational modification pattern of TTR which was reflected by a significant elevation of sulfonated TTR and which was inversely correlated to the antioxidative capacity. Additionally, the elevation of sulfonated TTR was accompanied by a decrease in body weight and food consumption, low antioxidative capacity as well as a deprivation of serum TTR, RBP4 and total serum protein levels in the animals of the gelatine group. Protein-energy malnutrition leads therefore next to changes in TTR serum concentration, also to changes in the post-translational modification pattern of TTR. Such changes are probably induced by protein-energy malnutrition-driven oxidative stress and might be linked to alterations in protein function and stability.

Nutritional regulation of visceral markers in rat liver and cultured hepatoma cells

Protein malnutrition in humans and other animals is consistently associated with a decreased concentration of circulating serum albumin, transthyretin (TTR), and insulin-like growth factor-I (IGF-I). The molecular mechanisms for regulation of the three polypeptides by dietary protein remain to be completely elucidated. The abundance of albumin, TTR and IGF-I mRNA is decreased in liver of juvenile rats consuming insufficient amounts of protein. Moreover, protein restriction specifically decreases the abundance of albumin and TTR nuclear transcripts, indicating that the reduction in mRNA levels for these two genes is caused at least partly by a decrease in gene transcription. Expression of several other genes transcribed at a high level in the liver is also decreased under conditions of dietary protein restriction, suggesting that the level/functional activity of liver-enriched transcription factor(s) might be decreased under these conditions. Limitation of cultured hepatoma cells for a single amino acid also selectively decreases the mRNA levels of several genes with liver-enriched expression, including albumin and TTR. The decrease in albumin mRNA is caused partly by decreased albumin gene transcription and partly by destabilization of albumin mRNA.

Significance of transthyretin in protein metabolism

Total body nitrogen (TBN) is mainly sequestered within the metabolically active lean body mass, in close relationship with total body potassium (TBK). TBN and TBK of growing children manifest superimposed accretion rates, display a sexual difference at the onset of adolescence and during adulthood, thereafter decreasing in elderly subjects. Plasma transthyretin (TTR) follows a comparable profile from birth to death in healthy individuals. Uncomplicated protein-energy malnutrition primarily affects the activity of nitrogen metabolic pool, reducing protein syntheses to levels compatible with survival. This adaptive response is well identified by declining TTR concentrations. In various stressful conditions, in vivo responses are characterized by upregulation in injured regions and with muscle proteolysis exceeding protein synthesis, resulting in a net body negative nitrogen balance. Again, this evolutionary pattern mirrors that of plasma TTR. Attenuation of stress and/or introduction of nutritional rehabilitation allows restoration to normal of both TBN and TTR values that follow parallel slopes. Despite distinct etiopathogenic mechanisms, TTR concentrations appear to reflect the loss or gain of TBN in body pools and they predict later outcome in malnutrition and in conditions of acute and/or chronic inflammation.

Changes of liver-enriched nuclear transcription factors for albumin gene in starvation in rats

The regulatory mechanism of albumin gene transcription was examined using male Donryu rats (7 wk old) starved for 1 or 3 d. At the designated times, the rats were sacrificed to harvest the liver and to measure the serum albumin level. Neither the serum albumin nor the albumin messenger RNA (mRNA) level showed a significant change for these starvation periods. Among nuclear factors binding to the D site of albumin gene promoter, the CCAAT/enhancer binding protein alpha (C/EBP alpha) mRNA level showed a decrease and the D site binding protein (DBP) mRNA level tended to decrease after 3 d of starvation. In contrast, the C/EBP beta mRNA level showed a significant increase at day 1. As a B site binding nuclear factor, the hepatocyte nuclear factor 1 (HNF-1) mRNA level significantly increased at day 1. Gel mobility-shift analysis combined with Western immunoblotting confirmed the presence of D site binding proteins composed of DBP and C/EBP alpha and beta in both groups subjected to oral feeding and to 3-d starvation, though quantitative analysis could not be done. In conclusion, the nuclear transcription factors binding to the albumin gene promoter undergo regulatory changes during 3 d of starvation, whereas there is no significant decrease in the albumin mRNA level.

Transferrin kinetics are altered in children with severe protein-energy malnutrition

This study was undertaken to determine the following: 1) the kinetic changes responsible for the depletion and repletion of plasma transferrin (Tr) concentration in children with protein-energy malnutrition (PEM); 2) the role of infection in mediating these changes; and 3) whether plasma Tr concentration is related to body protein status. We measured plasma Tr concentration, and fractional (FSR) and absolute (ASR) Tr synthesis rates with the use of a constant intragastric infusion of 2H3-leucine in 14 children with PEM, at 2 d postadmission (study 1), 8 d postadmission when infections were under control (study 2), and at recovery (study 3). In studies 1 and 2, the children synthesized less Tr and had lower Tr concentrations compared with values at recovery. When infections were controlled, plasma Tr concentration rose, but Tr synthesis was unchanged. There were only fair correlations (P < 0. 05) between plasma Tr concentrations and indices of wasting. Concerning malnourished children, we reached the following conclusions: 1) changes in the Tr pool size are achieved mainly through changes in synthesis rate; 2) infections play a minor role in reducing the Tr pool through either changes in the rate of catabolism or loss from the intravascular space; and 3) Tr concentration is not a very good indicator of protein nutritional status.