Benjamin Pulli MD, Presenter: Nothing to Disclose

Cuihua Wang PhD, Abstract Co-Author: Nothing to Disclose

Gregory R. Wojtkiewicz MSc, Abstract Co-Author: Nothing to Disclose

Anning Li MD, Abstract Co-Author: Nothing to Disclose

Yue Wu, Abstract Co-Author: Nothing to Disclose

John Chen MD, PhD, Abstract Co-Author: Research Grant, Pfizer Inc

Myeloperoxidase (MPO) is an important oxidative enzyme stored in neutrophil granules. It is crucial for defense against pathogens but also contributes to tissue damage in inflammation. We sought to develop a molecular imaging probe sensitive and specific for MPO that is suitable for fluorescence imaging applications.

Ten female C57BL/6J (wildtype) mice and 3 MPO-knockout mice were either treated topically with 0.08 μmoles phorbol 12-myristate 13-acetate (PMA) on one hindpaw and with vehicle on the other to induce irritant contact dermatitis, or injected subcutaneously with 108 colony forming units of streptococcus pneumonia (SPn) to induce bacterial cellulitis. 6 hours after induction, mice were injected with the MPO sensor or a non-specific control sensor. Extracellular DNA in cellulitis was visualized with Sytox Green. Mice were imaged using a fluorescence reflectance imaging system (Olympus OV-110).

Sensitivity to MPO was tested first in vitro by embedding the MPO sensor together with and without MPO in matrigel. A linear increase in signal is seen only in the presence of MPO (figure, A). In vivo, increased fluorescent signal was detected with dermatitis on the hindpaws of wildtype mice injected with MPO sensor (130.5±8.2 for PMA vs. 34.4±14.9 relative fluorescent units (RFUs) for vehicle, P<0.01, figure, B+C). In MPO-knockout mice injected with MPO sensor, and in wildtype mice injected with control sensor, no signal increase was detectable (36.9±13.8 and 50.13±10.0 for PMA vs. 43.9±15.2 and 28.4±9.4 RFUs for vehicle, P>0.05, figure, B+C). In wildtype mice induced with bacterial cellulitis, increased MPO specific signal was found in the hindlimb (212.5±22.9 for SPn vs. 49.4±15.5 RFUs for vehicle, P<0.001, figure, D). Sytox green signal revealed extracellular DNA in the inflamed area consistent with neutrophil extracellular trap formation, and MPO and DNA co-localized (figure, D).

The results of this proof-of-concept study reveal that our novel fluorescent MPO sensor can specifically detect MPO activity in vivo at relevant biological concentrations. This was validated in two murine disease models. Neutrophil extracellular trap formation can be imaged by co-injection of MPO-sensor and Sytox Green. 

Upon translation, MPO fluorescence molecular imaging could be used in perioperative as well as endoscopic settings (e.g., assessment of activity of inflammatory bowel disease). 

Pulli, B, Wang, C, Wojtkiewicz, G, Li, A, Wu, Y, Chen, J, Fluorescence Molecular Imaging of Myeloperoxidase in Irritant Contact Dermatitis and Bacterial Cellulitis.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14009659.html