Stable Isotope Research Applications

Stable Isotope Assays for Muscle Protein Turnover

We quantify muscle protein synthesis, turnover, and half-life using deuterium oxide (D₂O) and amino acid tracer methods. Our assays deliver dynamic, reproducible endpoints that help researchers understand muscle remodeling and metabolic responses with regulatory-ready precision.

Trusted by Pharma and Biotech to Validate Mechanism of Action

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35+ Years exclusively in stable isotope tracer studies

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Experimental protocol designs and results delivered weeks faster than CROs
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GLP-compliant, CLIA-certified, 21 CFR Part 11 validated

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Consultative approach, with over 1,000+ studies guided from design to submission

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Understanding Muscle Protein Turnover

Muscle protein turnover reflects the continuous remodeling of muscle tissue through the simultaneous processes of protein synthesis and protein breakdown. Traditional nitrogen-balance approaches overlook this dynamic exchange.

Stable isotope tracer methods—particularly D₂O labeling—enable direct, in vivo measurement of muscle protein synthesis rates and turnover kinetics over days or weeks. These assays capture subtle changes in metabolism and provide mechanism-level insights that support therapeutic evaluation, nutrition studies, and metabolic physiology research.

Endpoints & Readouts

Tracer Protocols for Muscle Protein Turnover Studies

Our assays enable researchers to quantify:

  • Fractional synthesis rates (FSR) of muscle proteins
  • Muscle protein turnover rate constants
  • Amino acid isotopomer enrichment (GC–MS)
  • Individual protein half-lives
  • Incorporation of deuterium into alanine during protein synthesis

These dynamic endpoints exceed the capabilities of static protein concentration measurements.
Below are protocols used to quantify muscle protein synthesis and turnover using stable isotope tracers.

D₂O Labeling for Muscle Protein Synthesis (MPS)

Quantifies muscle protein synthesis and half-life in vivo.

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Muscle protein turnover and half-life can be quantified in vivo by dosing with deuterium oxide (D₂O), where deuterium is incorporated into amino acids during de novo synthesis and subsequently into newly made muscle proteins during protein synthesis.

Here’s how it works:

  1. Subjects consume oral doses of D₂O.
  2. Deuterium is incorporated into the α-hydrogen of alanine during amino acid synthesis.
  3. Newly made muscle proteins contain predictable isotopic signatures.
  4. These can be analyzed by:
    • Liquid chromatography–high-resolution mass spectrometry to quantify peptide isotopomers, or
    • Gas chromatography–mass spectrometry (GC–MS) to quantify amino acid enrichment.

  5. By modeling mass isotopomer shifts over time—such as M0 depletion or enrichment plateaus—researchers can calculate:
    • Fractional synthesis rates
    • Rate constants
    • Half-lives of individual muscle proteins or the muscle tissue pool

This approach has been demonstrated in humans (Previs et al., Am J Physiol 286:E665–E672, 2004).

Peptide Isotopomer Analysis

High-resolution measurement of newly synthesized muscle proteins.

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Peptides derived from newly synthesized muscle proteins exhibit predictable isotope content shifts after D₂O labeling.

Our instruments provide high sensitivity for detecting these isotopomer distributions, enabling precise quantification of muscle protein fractional synthesis rates at the peptide level.

Amino Acid–Based Measurements (GC–MS)

Tissue-level turnover analysis via labeled alanine.

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Individual amino acids derived from newly made muscle proteins can be analyzed by GC–MS.

By quantifying alanine enrichment, researchers can derive tissue-level muscle protein synthesis rates and turnover kinetics.

How Researchers Use These Assays in Muscle Protein Turnover Programs

Our tracer methods support research across different programs, and provide dynamic, mechanism-focused endpoints that complement traditional nitrogen balance or static protein concentration measurements.

  • Muscle remodeling and metabolic adaptation
  • Nutritional interventions
  • Pharmacologic modulation of muscle protein synthesis
  • Metabolic physiology and exercise research
  • Longitudinal evaluation of muscle turnover over days to weeks

All Analyses Are Performed In Our Certified Laboratory Environment

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Trusted by Leaders in Metabolic Research

They’ve been very consistent… the sample analysis and data has always been timely and high quality.

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Dan Tardiff CAMP4

There are academic labs that do it as well, but they’re much harder to engage and contract with.

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Scott Turner Arda Therapeutics

I think they’re extremely organized and very on top of sample management. All the interactions that I’ve had with them have been great.

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Morganne A. Ultragenyx
Looking for Answers?

Frequently Asked Questions

Is D₂O safe for muscle protein turnover studies?

Yes. Deuterium oxide is a stable (non-radioactive) isotope and is safe for repeated measures.

What muscle protein turnover metrics can be quantified?

Fractional synthesis rates and protein half-lives can be determined based on quantified protein specific isotope enrichment.

Are your assays GLP/CLIA compliant?

Yes. All analyses are conducted in our GLP-compliant, CLIA-certified laboratory under 21 CFR Part 11–validated workflows.

Contact Us

Quantify Muscle Protein Turnover With Confidence

Our D₂O-based tracer methods provide mechanistic insight into muscle protein remodeling. Let’s design the right protocol for your study.
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Metabolic Solutions, LLC.
460 Amherst St., Nashua,
NH 03063, USA

Hours of Operation
Monday – Friday
7:30 am – 6:00 pm EST 

Published Protein Turnover Studies Analyzed By Metabolic Solutions

  1. Pasiakos SM, Margolis LM, McClung JP, Cao JJ, Whigham LD, Combs GF, and Young AJ. Whole-body protein turnover response to short-term high-protein diets during weight loss: a randomized controlled trial. Int J Obes Epub ahead of print, Oct 29, 2013.“Whole-body protein turnover responses to high-protein diets during weight loss were investigated using 1-13C-leucine infusion.”

  2. Wagner AL, Urschel KL, Betancourt A, Adams AA, and Horohov DW. Effects of advanced age on whole-body protein synthesis and skeletal muscle mechanistic target of rapamycin signaling in horses.“Whole-body protein synthesis was measured with a 4-hour primed constant infusion of 1-13C-phenylalanine in horses. After the infusions, a gluteus medius muscle biopsy was collected for determination of muscle protein synthesis rates.”

  3. Yang Y, Breen L, Burd NA, Hector AJ, Churchward-Venne TA, Josse AR, Tarnopolsky MA, and Phillips SM. Resistance exercise enhances myofibrillar protein synthesis with graded intakes of whey protein in older men. Br J Nutr. 108(10):1780-8, 2012.“Infusion of 1-13C-leucine and ring-13C6-phenylalanine and collection of muscle biopsies were used to ascertain whole-body leucine oxidation and muscle protein synthesis.”

  4. Niemczyk S, Sikorska H, Wiecek A, Zukowska-Szczechowska E, Zalecka K, Gorczynska J, Kubik M, Czerwienska B, Gosek K, Veldhuis JD, Wagner DA, Gaudreau P, Hakonen T, Kay SW, Jouhikainen T, and Schaefer F. A super-agonist of growth hormone-releasing hormone causes rapid improvement of nutritional status in patients with chronic kidney disease. Kidney Int. 77(5):450-8, 2009.
    “In this study, a new GH-releasing hormone super-agonist (AKL-0707) was evaluated for improved anabolism and nutritional status of nondialyzed patients with stage 4-5 chronic kidney disease.”

  5. Mehrotra R, Bross R, Wang H, Appell M, Tso L, and Kopple JP. Effect of high-normal compared with low-normal arterial pH on protein balances in automated peritoneal dialysis patients. Am J Clin Nutr. 90(6):1532-40, 2009.
    “Tested the hypothesis that in peritoneal dialysis patients with an arterial pH of 7.43-7.45 are associated with more-positive nitrogen balance. Used a primed, continuous infusion of 1-13C-leucine to determine leucine flux and whole-body protein turnover.”

  6. Miller SL, Gaine PC, Maresh CM, Armstrong LE, Ebbeling CB, Lamont LS, and Rodriguez NR. The effects of nutritional supplementation throughout an endurance run on leucine kinetics during recovery.“Determined the effect of nutritional supplementation on whole body leucine kinetics using a primed, continuous infusion of 1-13C-leucine.”

  7. Shankaran, M., King, C. L., Angel, T. E., Holmes, W. E., Li, K. W., Colangelo, M., ... & Hellerstein, M. K. (2016). Circulating protein synthesis rates reveal skeletal muscle proteome dynamics. The Journal of Clinical Investigation, 126(1), 288-302.

  8. Naylor, B. C., Anderson, C. N., Hadfield, M., Parkinson, D. H., Ahlstrom, A., Hannemann, A., ... & Price, J. C. (2022). Utilizing nonequilibrium isotope enrichments to dramatically increase turnover measurement ranges in single biopsy samples from humans. Journal of Proteome Research, 21(11), 2703-2714.

  9. Angel, T. E., Naylor, B. C., Price, J. C., Evans, C., & Szapacs, M. (2019). Improved sensitivity for protein turnover quantification by monitoring immonium ion isotopologue abundance. Analytical Chemistry, 91(15), 9732-9740.

  10. Loomba, R., Decaris, M., Li, K. W., Shankaran, M., Mohammed, H., Matthews, M., ... & Hellerstein, M. K. (2019). Discovery of half-life of circulating hepatitis B surface antigen in patients with chronic hepatitis B infection using heavy water labeling. Clinical Infectious Diseases, 69(3), 542-545.

  11. Angel, T. E., Chen, Z., Moghieb, A., Ng, S. L., Beal, A. M., Capriotti, C., ... & Pesiridis, G. S. (2025). Implications of tissue specific STING protein flux and abundance on inflammation and the development of targeted therapeutics. PloS One, 20(2), e0319216.

  12. Holmes, W. E., Angel, T. E., Li, K. W., & Hellerstein, M. K. (2015). Dynamic proteomics: in vivo proteome-wide measurement of protein kinetics using metabolic labeling. Methods in Enzymology, 561, 219-276.

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Metabolic Solutions, LLC.
460 Amherst St., Nashua, NH 03063, USA

(603) 598-6960

(603) 598-6973

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Research: info@metsol.com

Hours of Operation
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7:30 am – 6:00 pm EST

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