An exploration of the methods to determine the protein-specific synthesis and breakdown rates in vivo in humans

TY - JOUR

T1 - An exploration of the methods to determine the protein-specific synthesis and breakdown rates in vivo in humans

AU - Holm, Lars

AU - Dideriksen, Kasper

AU - Nielsen, Rie H.

AU - Doessing, Simon

AU - Bechshoeft, Rasmus L.

AU - Hojfeldt, Grith

AU - Moberg, Marcus

AU - Blomstrand, Eva

AU - Reitelseder, Soren

AU - van Hall, Gerrit

PY - 2019/9/1

Y1 - 2019/9/1

N2 - The present study explores the methods to determine human in vivo protein-specific myofibrillar and collagenous connective tissue protein fractional synthesis and breakdown rates. We found that in human myofibrillar proteins, the protein-bound tracer disappearance method to determine the protein fractional breakdown rate (FBR) (via (H2O)-H-2 ingestion, endogenous labeling of H-2-alanine that is incorporated into proteins, and FBR quantified by its disappearance from these proteins) has a comparable intrasubject reproducibility (range: 0.09-53.5%) as the established direct-essential amino acid, here L-ring-C-13(6)-phenylalanine, incorporation method to determine the muscle protein fractional synthesis rate (FSR) (range: 2.8-56.2%). Further, the determination of the protein breakdown in a protein structure with complex post-translational processing and maturation, exemplified by human tendon tissue, was not achieved in this experimentation, but more investigation is encouraged to reveal the possibility. Finally, we found that muscle protein FBR measured with an essential amino acid tracer prelabeling is inappropriate presumably because of significant and prolonged intracellular recycling, which also may become a significant limitation for determination of the myofibrillar FSR when repeated infusion trials are completed in the same participants.

AB - The present study explores the methods to determine human in vivo protein-specific myofibrillar and collagenous connective tissue protein fractional synthesis and breakdown rates. We found that in human myofibrillar proteins, the protein-bound tracer disappearance method to determine the protein fractional breakdown rate (FBR) (via (H2O)-H-2 ingestion, endogenous labeling of H-2-alanine that is incorporated into proteins, and FBR quantified by its disappearance from these proteins) has a comparable intrasubject reproducibility (range: 0.09-53.5%) as the established direct-essential amino acid, here L-ring-C-13(6)-phenylalanine, incorporation method to determine the muscle protein fractional synthesis rate (FSR) (range: 2.8-56.2%). Further, the determination of the protein breakdown in a protein structure with complex post-translational processing and maturation, exemplified by human tendon tissue, was not achieved in this experimentation, but more investigation is encouraged to reveal the possibility. Finally, we found that muscle protein FBR measured with an essential amino acid tracer prelabeling is inappropriate presumably because of significant and prolonged intracellular recycling, which also may become a significant limitation for determination of the myofibrillar FSR when repeated infusion trials are completed in the same participants.

KW - Amino acid recycling

KW - deuterated alanine

KW - deuterated water

KW - fractional breakdown rate

KW - fractional synthesis rate

KW - protein turnover

KW - stable isotope

U2 - 10.14814/phy2.14143

DO - 10.14814/phy2.14143

M3 - Journal article

C2 - 31496135

SN - 2051-817X

VL - 7

JO - Physiological Reports

JF - Physiological Reports

IS - 17

M1 - e14143

ER -