Half of 27 protected bioactive peptides degraded in horse plasma, and identifying their breakdown products could improve doping detection.
14 peptidesdegraded in plasma with identifiable breakdown products that can serve as new doping markers
What the researchers found
Of 27 bioactive peptides with chemical protection at both ends (to resist degradation), 13 remained stable after 72 hours at body temperature in horse plasma. The other 14 broke down to varying degrees.
The researchers identified specific breakdown products (catabolites) for all 14 unstable peptides, including novel catabolites never previously reported for chemotactic peptide, DALDA, dmtDALDA, deltorphins I and II, and several dermorphin analogs.
Key stability rules emerged: a D-amino acid (mirror image of normal) at position 2 or position 1 of a peptide, or next to its C-terminus, protected that end from degradation. But a D-amino acid at position 3 did not help. N-terminal modifications like pyroglutamic acid or N-methylation did not protect the N-terminal end. A C-terminal ethylamide group did protect against carboxypeptidase attack. The C-terminal lysine amide in DALDA, dmtDALDA, and Lys7-dermorphin was unexpectedly vulnerable to plasma enzymes.
Why it matters
Peptide doping in horse racing is hard to detect because peptides break down quickly in blood. If testing labs only look for the intact peptide, they will miss it. Knowing the specific breakdown products means labs can test for those instead, catching cheaters who use peptides that would otherwise disappear before testing.
The numbers in context
27 peptides; 13 stable at 72h; 14 degraded; novel catabolites for 8 peptide types; D-amino acid position rules established
How the study worked
Researchers incubated 27 peptides in horse plasma under different conditions (temperature, time) and analyzed breakdown products using HILIC (a type of liquid chromatography) coupled with HRMS (high-resolution mass spectrometry). They predicted theoretical breakdown masses computationally, then confirmed them experimentally by their appearance over time and their fragmentation patterns.
Who was studied
27 bioactive peptides tested in equine plasma samples
What this study cannot tell us
This tested peptide stability in horse plasma specifically, and degradation patterns may differ in human plasma or in vivo. The ex vivo (in a tube) conditions do not perfectly replicate what happens inside a living horse, where additional enzymes and clearance mechanisms are present. Only peptides with terminal protection were tested.
How to read the evidence
Moderate evidence. Rigorous analytical chemistry with validated methods, though tested only in horse plasma under ex vivo conditions.
When this study was published
Published in 2020. Anti-doping analytical methods continue to evolve with improved detection limits.
The bigger picture
Peptide doping is a growing challenge in equine and human sports. Traditional testing looks for the intact drug, but peptides break down quickly. This study enables detection of breakdown products, closing a significant gap in anti-doping testing capabilities.
Questions still open
- Do these peptides break down similarly in human plasma?
- Can the breakdown product signatures be used to estimate when the peptide was administered?
- Are there additional undiscovered peptide doping agents not covered in this study?
Common questions
Why is peptide doping hard to detect?
Does this apply to human doping too?
Read the original research
Identification of ex vivo catabolites of peptides with doping potential in equine plasma by HILIC-HRMS.
Drug testing and analysis, 12(6), 771-784
Citation
Guan, Fuyu; Fay, Savannah; Li, Xiaoqing; You, Youwen; Robinson, Mary A. (2020). Identification of ex vivo catabolites of peptides with doping potential in equine plasma by HILIC-HRMS.. Drug testing and analysis, 12(6), 771-784. https://doi.org/10.1002/dta.2781