Methods for measuring tissue protein breakdown rate in vivo.
OBJECTIVE
To describe the latest innovations in measuring protein breakdown in vivo, particularly in muscle.


RESULTS
The traditional method of using 3-methylhistidine excretion to measure muscle protein breakdown has been updated to include arteriovenous or microdialysis measurements, which address the concern that there are alternative sources of 3-methylhistidine in the body other than muscle. Several variations of a precursor-product method to measure fractional breakdown rate of tissues have been developed that are analogous to fractional synthesis rate of tissues. These methods are more generally applicable than the 3-methylhistidine methods and are less invasive than arteriovenous methods. The various precursor-product methods are distinguished by whether they require an isotopic steady state or multiple tracers and by how many biopsies are required.


CONCLUSIONS
The new precursor-product methods have enabled assessment in clinical trials of protein breakdown for proteins other than myofibrillar proteins and in circumstances in which arteriovenous sampling is not feasible.
Chinkes
David L
DL
Department of Surgery, University of Texas Medical Branch and Shriners Hospitals for Children, Galveston, Texas 77550, USA. dlchinke@utmb.edu
D015415:Biomarkers / Q000097:blood; D003285:Contractile Proteins / Q000378:metabolism; D006801:Humans; D008762:Methylhistidines / Q000378:metabolism*; D017551:Microdialysis; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D014176:Protein Biosynthesis; D012039:Regional Blood Flow
D015415:Biomarkers; D003285:Contractile Proteins; D008762:Methylhistidines; D009124:Muscle Proteins; C028118:3-methylhistidine