Consuming dietary protein stimulates whole-body and muscle protein synthesis, the latter of which is typically measured using invasive primed constant infusions of stable isotopes with concurrent muscle biopsies. Alternative non-invasive methodologies have been developed (namely the indicator amino acid oxidation (IAAO) technique) to estimate the impact of protein ingestion on whole-body protein synthesis as a proxy for determining dietary protein requirements. Given that the IAAO technique is based on principles of protein metabolism which occur in the liver, it is unclear how representative the IAAO outcomes of whole-body protein synthesis is to skeletal muscle protein synthesis. Validation of the IAAO technique against gold-standard, biopsy-derived measures of muscle metabolism (i.e., muscle protein synthesis) would assist in mitigating the invasiveness of muscle physiology and nutrition research.
Study Type
INTERVENTIONAL
Allocation
NA
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
8
Participants will consume 12 half-hourly (6 hours) isoenergetic, isonitrogenous beverages containing 0.9g/kg fat-free mass/day protein. Drinks will be enriched with stable isotopes \[2H5\]Phenylalanine and \[1-13C\]Phenylalanine, which will respectively allow for determination of muscle protein synthesis and whole-body protein synthesis over the subsequent 6 hours of feeding
Kinesiology & Physical Education
Toronto, Ontario, Canada
RECRUITINGPhenylalanine excretion (umol/kg/h)
Rate of whole-body phenylalanine excretion following orally ingested amino acid tracer \[1-13C\]Phenylalanine determined from the product of breath 13CO2 enrichment and carbon dioxide production rate (VCO2).
Time frame: 6.5 hours
Phenylalanine oxidation (umol/kg/h)
Rate of whole-body phenylalanine oxidation following orally ingested amino acid tracer \[1-13C\]Phenylalanine determined from the correction of phenylalanine excretion by the phenylalanine precursor enrichment via urine enrichment.
Time frame: 6.5 hours
Myofibrillar protein synthesis (%/hr)
Rate of myofibrillar fractional synthesis is determined by rate of incorporation of orally ingested tracer \[2H5\]Phenylalanine into myofibrillar proteins (isolated from skeletal muscle biopsies) and the enrichment of \[2H5\]Phenylalanine in plasma collected over the 6 hours protein consumption period. Enrichment will be quantified via tandem LC-MS/MS to derive a rate of incorporation over the 6-hour period.
Time frame: 6.5 hours
Sarcoplasmic protein synthesis (%/hr)
Rate of sarcoplasmic fractional synthesis is determined by rate incorporation of orally ingested tracer \[2H5\]Phenylalanine into sarcoplasmic (ie., soluble) proteins (isolated from skeletal muscle biopsies) and the enrichment of \[2H5\]Phenylalanine in plasma collected over the 6 hours protein consumption period. Enrichment will be quantified via tandem LC-MS/MS to derive a rate of incorporation over the 6-hour period.
Time frame: 6.5 hours
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