Measurement of plasma protein synthesis rate in infant pig: an investigation of alternative tracer approaches

1994 ◽  
Vol 267 (1) ◽  
pp. R221-R227 ◽  
Author(s):  
F. Jahoor ◽  
D. G. Burrin ◽  
P. J. Reeds ◽  
M. Frazer
Keyword(s):  
Protein Synthesis ◽  
Plasma Protein ◽  
Apolipoprotein B ◽  
Plasma Proteins ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Isotopic Equilibrium ◽  
Fractional Synthesis

To devise a new method to measure plasma protein synthesis, we tested the hypothesis that, when [U-13C]glucose is used to produce [U-13C]alanine, plasma pyruvate and alanine will be in isotopic equilibrium with the alanine used to synthesize plasma proteins. The incorporation of labeled leucine, lysine, and alanine into very-low-density lipoprotein (VLDL) apolipoprotein B (apoB)-100, albumin, and fibrinogen was measured in seven infant pigs by infusing [U-13C]glucose, [2H3]leucine, and [2H4]lysine. The plateau enrichments of plasma alanine (2.29 +/- 0.29), pyruvate (2.5 +/- 0.33), and apoB-alanine (2.33 +/- 0.25) were not different. The fractional synthesis rates of fibrinogen and albumin calculated using the isotopic enrichments of apoB-bound lysine, leucine, and alanine as the precursor were similar to those based on plasma alanine. These results suggest that the intrahepatic precursor alanine pool and plasma alanine were in isotopic equilibrium. Thus plasma protein synthesis can be measured by infusing [U-13C]glucose and using plasma alanine as precursor.

Protein kinetics in stable heart failure patients

2003 ◽  
Vol 94 (1) ◽  
pp. 295-300 ◽  
Author(s):  
Charles W. Cortes ◽  
Paul D. Thompson ◽  
Niall M. Moyna ◽  
Margaret D. Schluter ◽  
Maria J. Leskiw ◽  
...  
Keyword(s):  
Protein Metabolism ◽  
Protein Turnover ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Bed Rest ◽  
Whole Body ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Body Protein ◽  
Fractional Synthesis

Heart failure (HF) is a slow progressive syndrome characterized by low cardiac output and peripheral metabolic, biochemical, and histological alterations. Protein loss and reduced protein turnover occur with aging, but the consequences of congestive HF (CHF) superimposed on the normal aging response are unknown. This study has two objectives: 1) to determine whether there was a difference between older age-matched controls and those with stable HF (i.e., ischemic pathology) in whole body protein turnover and 2) to determine whether protein metabolism in liver and skeletal muscle protein turnover is impacted by CHF. We measured the whole body protein synthesis rate with a U-15N-labeled algal protein hydrolysate in 10 patients with CHF and in 10 age-matched controls. Muscle fractional synthesis rate of lateral vastus muscle was determined with [U-13C]alanine on muscle biopsies obtained by a standard percutaneous needle biopsy technique. Fractional synthesis rates of five plasma proteins of hepatic origin (fibrinogen, complement C-3, ceruloplasmin, transferrin, and very low-density lipoprotein apoliprotein B-100) were determined by using2H5-labeled l-phenylalanine as tracer. Results showed that whole body protein synthesis rate was reduced in CHF patients (3.09 ± 0.19 vs. 2.25 ± 0.71 g protein · kg−1 · day−1, P < 0.05) as was muscle fractional synthesis rate (3.02 ± 0.58 vs. 1.33 ± 0.71%/day, P < 0.05) and very low-density lipoprotein apoliprotein B-100 (265 ± 25 vs. 197 ± 16%/day, P < 0.05). CHF patients were hyperinsulinemic (9.6 ± 3.1 vs. 47.0 ± 7.8 μU/ml, P < 0.01). The results were compared with those found with bed rest patients. In conclusion, protein turnover is depressed in CHF patients, and both skeletal muscle and liver are impacted. These results are similar to those found with bed rest, which suggests that inactivity is a factor in depressed protein metabolism.

Assessment of the mathematical issues involved in measuring the fractional synthesis rate of protein using the flooding dose technique

1993 ◽  
Vol 84 (2) ◽  
pp. 177-183 ◽  
Author(s):  
David L. Chinkes ◽  
Judah Rosenblatt ◽  
Robert R. Wolfe
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Intracellular Concentration ◽  
Upper And Lower Bounds ◽  
Constant Infusion ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Underlying Assumption ◽  
Fractional Synthesis Rate ◽  
Fractional Synthesis

1. The fractional synthesis rate of protein is commonly measured by either the constant infusion method or the flooding dose method. The two methods often give different results. 2. An underlying assumption of the traditional flooding dose formula is that the protein synthesis rate is not stimulated by the flooding dose. A new formula for calculation of the fractional synthesis rate is derived with the alternative assumption that the protein synthesis rate is stimulated by an amount proportional to the change in the intracellular concentration of the infused amino acid. The alternative formula is: where EB and EF are the enrichments of bound and free amino acid, respectively (atom per cent excess), and C=1-(EF/EI), where EI is the enrichment of the infusate. This approach defines the lowest possible value for the fractional synthesis rate. The traditional equation gives a maximal value for the fractional synthesis rate. 3. When data from the literature are considered, the fractional synthesis rate of muscle protein as calculated by the constant infusion technique falls between the values of fractional synthesis rate calculated by the two flooding dose formulae when leucine is the tracer, suggesting that a flooding dose of leucine exerts a stimulatory effect on the rate of protein synthesis, but that the increase is not as great as the increase in the intracellular concentration of leucine. 4. The precision of the formula for the calculation of fractional synthesis rate is limited by the accuracy of the underlying assumptions regarding the effect of the flooding dose on the fractional synthesis rate. At present, the best approach would appear to be the use of both equations to calculate the upper and lower bounds of the true fractional synthesis rate.

scholarly journals The ubiquitin ligase Nedd4 mediates oxidized low-density lipoprotein-induced downregulation of insulin-like growth factor-1 receptor

2008 ◽  
Vol 295 (4) ◽  
pp. H1684-H1689 ◽  
Author(s):  
Yusuke Higashi ◽  
Sergiy Sukhanov ◽  
Sampath Parthasarathy ◽  
Patrice Delafontaine
Keyword(s):  
Smooth Muscle ◽  
Growth Factor ◽  
Oxidized Ldl ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Receptor Protein ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Mrna Levels ◽  
Insulin Like Growth Factor

Oxidized low-density lipoprotein (LDL) is proatherogenic and induces smooth muscle cell apoptosis, which contributes to atherosclerotic plaque destabilization. We showed previously that oxidized LDL downregulates insulin-like growth factor-1 receptor in human smooth muscle cells and that this is critical for induction of apoptosis. To identify mechanisms, we exposed smooth muscle cells to 60 μg/ml oxidized LDL or native LDL and assessed insulin-like growth factor-1 receptor mRNA levels, protein synthesis rate, and receptor protein stability. Oxidized LDL decreased insulin-like growth factor-1 receptor mRNA levels by 30% at 8 h compared with native LDL, and this decrease was maintained for up to 20 h. However, insulin-like growth factor-1 receptor protein synthesis rate was not altered by oxidized LDL. Pulse-chase labeling experiments revealed that oxidized LDL reduced insulin-like growth factor-1 receptor protein half-life to 12.2 ± 1.7 h from 24.4 ± 4.7 h with native LDL. This destabilization of insulin-like growth factor-1 receptor protein was accompanied by enhanced receptor ubiquitination. Overexpression of dominant-negative Nedd4 prevented oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor, suggesting that Nedd4 was the ubiquitin ligase that mediated receptor downregulation. However, the proteasome inhibitors lactacystin, MG-132, and proteasome inhibitor-1 failed to block oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor. Thus oxidized LDL downregulates insulin-like growth factor-1 receptor by destabilizing the protein via Nedd4-enhanced ubiquitination, leading to degradation via a proteasome-independent pathway. This finding provides novel insights into oxidized LDL-triggered oxidant signaling and mechanisms of smooth muscle cell depletion that contribute to plaque destabilization and coronary events.

scholarly journals Interaction of 4-hydroxynonenal-modified low-density lipoproteins with the fibroblast apolipoprotein B/E receptor

1986 ◽  
Vol 234 (1) ◽  
pp. 245-248 ◽  
Author(s):  
W Jessup ◽  
G Jurgens ◽  
J Lang ◽  
H Esterbauer ◽  
R T Dean
Keyword(s):  
Apolipoprotein B ◽  
Negative Charge ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Low Density ◽  
Lipid Peroxidation Product ◽  
Modified Low Density Lipoproteins ◽  
Peroxidation Product

The incorporation of the lipid peroxidation product 4-hydroxynonenal into low-density lipoprotein (LDL) increases the negative charge of the particle, and decreases its affinity for the fibroblast LDL receptor. It is suggested that this modification may occur in vivo, and might promote atherogenesis.

scholarly journals Apolipoprotein B mediates the capacity of low density lipoprotein to suppress neutrophil stimulation by particulates.

1986 ◽  
Vol 261 (33) ◽  
pp. 15662-15667
Author(s):  
R Terkeltaub ◽  
J Martin ◽  
L K Curtiss ◽  
M H Ginsberg
Keyword(s):  
Apolipoprotein B ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density
Sign in / Sign up

Export Citation Format

Share Document