Targeting of vascular adhesion protein-1 by positron emission tomography visualizes sites of inflammation in Borrelia burgdorferi-infected mice

BACKGROUND In the present study, we sought to evaluate the feasibility of targeting vascular adhesion protein-1 (VAP-1) by positron emission tomography (PET) for the longitudinal quantitative assessment of Borrelia burgdorferi infection-induced inflammation in mice. METHODS Mice with B. burgdorferi infection-induced arthritis were studied. During a 7-week follow-up period, the progression of arthritis was monitored weekly with 68Ga-DOTA-Siglec-9 PET/computed tomography (CT) and measurement of tibiotarsal joint swellings. A subgroup of infected mice was treated with ceftriaxone. Finally, histopathological assessment of joint inflammation was performed and VAP-1 expression in joints were determined. RESULTS Explicit joint swelling and 68Ga-DOTA-Siglec-9 uptake could be demonstrated in the affected joints from B. burgdorferi-infected mice. By contrast, no obvious accumulation of 68Ga-DOTA-Siglec-9 was detected in joints of uninfected mice. The maximum swelling and highest uptake in the affected joints were observed 4 weeks after the infection. 68Ga-DOTA-Siglec-9 uptake in joints correlated with joint swelling (P < 0.0001) and histopathological scoring of inflammation (P = 0.020). Despite short-term antibiotic treatment, the arthritis persisted, and the PET signal remained as high as in nontreated mice. Immunohistochemistry revealed strong-to-moderate expression of VAP-1 in the synovium of B. burgdorferi-infected mice, while only weak expression of VAP-1 was detected in uninfected mice. CONCLUSIONS The present study showed that 68Ga-DOTA-Siglec-9 can detect B. burgdorferi infection-induced arthritis in mice. Furthermore, longitudinal PET/CT imaging allowed monitoring of arthritis development over time.