ARS | Publication request: CHRONIC PROTEIN DEFICIENCY DIFFERENTIALLY AFFECTS THE KINETICS OF PLASMA PROTEINS IN YOUNG PIGS

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 1996
Publication Date: N/A

Interpretive Summary: It is standard for scientists to use plasma (blood) protein concentrations to measure a person's protein nutritional status. These plasma proteins include transthyretin, retinol binding protein, and others. The question: Is it appropriate to use them to measure protein nutrition when we know that their concentration levels and behavior are affected by factors besides protein intake--for example, infection? To answer this question, we fed a group of healthy pigs a diet of insufficient protein (protein-deprived pigs) and compared them to a group that got enough protein. We used an intravenous isotope to trace what happened. We found that protein deficiency did not produce lower concentrations of all proteins. Two of them, transthyretin, did not change and one was higher. We also measured synthesis rates and found these varied as well. Our results show that it is not valid to predict protein nutritional status from the concentrations of all plasma proteins; that chronic protein deficiency only affects the synthesis rate of some plasma proteins; and that plasma concentrations cannot be used to predict the kinetic (activity) response of plasma proteins to protein restriction.

Technical Abstract: The use of plasma protein concentrations to assess protein nutritional status has been questioned because concentrations and kinetics are affected by factors besides protein intake. To determine the effect of protein deficiency on plasma protein concentrations and synthesis, two groups of four piglets consumed diets containing either 20% or 3% protein. After 8 wk, 2H3-leucine was infused intravenously to measure the fractional and absolute synthesis rates (FSR and ASR) of albumin, transferin, retinol binding protein (RBP), transthyretin (TTR), a new peptide called TTR2, the high density apolipoprotein (HDL-apoA-1), fibrinogen, and haptaglobin. Compared to controls, protein-deficient pigs had decreased plasma albumin, RBP and TTR2 concentrations, slower FSRs of fibrinogen, HDL-apoA-1, transferrin, and TTR2 lower ASRs of albumin, fibrinogen, transferrin, and TTR2, and a higher ASR of TTR. Fibrinogen and transferrin concentrations did not differ between groups, but TTR concentration was higher in protein-deficient pigs. These results suggest that 1) protein-nutritional status cannot be predicted from the concentrations of all plasma proteins; 2) chronic protein deficiency only affects the rate of synthesis of some plasma proteins; 3) the kinetic response of plasma proteins to protein resriction cannot be predicted from measurements of plasma concentrations.