Quantification and monitoring of inflammation in murine inflammatory bowel disease with targeted contrast-enhanced US

Purpose: To evaluate ultrasonography (US) by using contrast agent microbubbles (MBs) targeted to P-selectin (MB _P-selectin) to quantify P-selectin expression levels in inflamed tissue and to monitor response to therapy in a murine model of chemically induced inflammatory bowel disease (IBD). Materials and Methods: All procedures in which laboratory animals were used were approved by the institutional administrative panel on laboratory animal care. Binding affinity and specificity of MB _P-selectin were tested in cell culture experiments under flow shear stress conditions and compared with control MBs (MB _Control). In vivo binding specificity of MB _P-selectin to P-selectin was tested in mice with trinitrobenzenesulfonic acid-induced colitis (n = 22) and control mice (n = 10). Monitoring of anti-tumor necrosis factor a antibody therapy was performed over 5 days in an additional 30 mice with colitis by using P-selectin-targeted US imaging, by measuring bowel wall thickness and perfusion, and by using a clinical disease activity index score. In vivo targeted contrast material-enhanced US signal was quantitatively correlated with ex vivo expression levels of P-selectin as assessed by quantitative immunofluorescence. Results: Attachment of MB _P-selectin to endothelial cells was significantly (P = .0001) higher than attachment of MB _Control and significantly (ρ = 0.83, P = .04) correlated with expression levels of P-selectin on endothelial cells. In vivo US signal in mice with colitis was significantly higher (P = .0001) with MB _P-selectin than with MB _Control. In treated mice, in vivo US signal decreased significantly (P = .0001) compared with that in nontreated mice and correlated well with ex vivo P-selectin expression levels (ρ = 0.69; P = .04). Colonic wall thickness (P ≥ .06), bowel wall perfusion (P ≥ .85), and clinical disease activity scoring (P ≥ .06) were not significantly different between treated and nontreated mice at any time. Conclusion: Targeted contrast-enhanced US imaging enables noninvasive in vivo quantification and monitoring of P-selectin expression in inflammation in murine IBD.