Short Communication: Identification of equine corticotropin-like intermediate lobe peptide (CLIP) binding to an adrenocortipcotrophic hormone (ACTH) assay capture antibody.

The research article focuses on the exploration of adrenocorticotrophic hormone (ACTH) concentration measurement methods that aid in diagnosing pituitary pars intermedia dysfunction in horses. The study specifically evaluates how the hormone equine corticotropin-like intermediate lobe peptide (CLIP) interacts with the commonly used chemiluminescent immunoassay.

Background

• ACTH is a hormone produced and released by the pituitary gland, playing a critical role in the stress response and regulation of blood cortisol levels.
• In horses, accurate measurement of ACTH concentration is essential in diagnosing pituitary pars intermedia dysfunction, a common equine endocrine disorder.
• The diagnosis process typically uses a chemiluminescent immunoassay, a test that measures specific proteins in the blood.
• A previous study suggested that ACTH measurements might be seasonally influenced by the cross-reactivity of the immunoassay with endogenous equine CLIP, a portion of the ACTH molecule.

Aim of the Study

• This research aimed to demonstrate if and how the endogenous equine CLIP binds to the capture antibody in the ACTH chemiluminescent immunoassay.

Methodology

• The research used liquid chromatography-mass spectrometry (LCMS) methods to identify specific ions from synthetic versions of human ACTH, α-melanocyte-stimulating hormone (α-MSH), and CLIP.
• These synthetic molecules were then tested to assess their binding to the capture antibody in the ACTH chemiluminescent immunoassay.
• Furthermore, the research studied plasma samples from ponies taken in autumn to evaluate the occurrence and interaction of endogenous equine CLIP with the immunoassay.

Findings

• The study found that synthetic ACTH and CLIP bind to the capture antibody of the chemiluminescent ACTH immunoassay, but α-MSH does not.
• Moreover, endogenous equine CLIP was identified in the pony plasma collected in autumn, and it could be eluted from the assay’s capture antibody.

Conclusion and Further Research

• The findings suggested that equine CLIP may influence the measured ACTH concentrations in vivo, potentially affecting the accuracy of pituitary pars intermedia dysfunction diagnosis.
• However, the study concluded that more research is needed to quantify CLIP and further evaluate its impact on ACTH measurements in the diagnosis process.