The liver was a constantly increasing and significant source of fluorescence attributed to its role in clearance. The other region contributing to enhancement in fluorescent signal was selleck chemical found below the liver attributed to the pancreas after necropsy (figure 2b). A fivefold enhancement in signal intensity was observed compared to the time point from before caerulein administration. Therefore, in vivo fluorescent imaging was further used to evaluate the role of trypsin inhibitors in the caerulein mechanistic pancreatitis model. Occasionally, there was signal enhancement in the duodenal region as well. We compared the mPEG-PL-Cy5.5 probe to a commercially available protease activatable probe Prosense (Perkin Elmer, Waltham, MA). When compared to the in-house trypsin activatable mPEG-PL-Cy5.

5 probe, Prosense was found to be unsuitable for use in the experimental pancreatitis model. We believe that due to its large size (~400 kD), Prosense was unable to extravasate in significant quantities in the pancreas in the given window of three hours. The signal enhancement in the pancreas was barely distinguishable over time in disease animals (data not shown). From the edema imaging study with Angiosense (~250 kD), it was known that a probe of up to 250 kD should be able to extravasate in the pancreas with caerulein insult. MPEG-PL-Cy5.5 probe (~200 kD), as expected, showed a fivefold signal enhancement suggesting that the size of the probe is also an important factor in optical imaging of pancreatitis in the rat model. To further characterize the mPEG-PL-Cy5.5 probe, pH sensitivity and intra- vs.

extracellular trypsin activation was investigated (see supplemental figure S1 and S2). 9.3 Functional vs. anatomical comparison Edema reduction is a prominent outcome of a trypsin inhibitor study in a caerulein model. However, edema reduction gives inadequate information about trypsin inhibition in the pancreas because it is a biomarker not specific to the target. We compared animals pretreated with Camostat (see Table 1 for protease selectivity) at a dose of 300 mg/kg orally to untreated animals. Both sets of animals received three subsequent caerulein doses SC. Animals that did not receive caerulein were used as baseline controls. When imaged using Angiosense 680, there was no signal enhancement as noticed by reduced intensity (figure 3a, b).

Healthy control animals did not show any increase in fluorescence in the region of the pancreas. In another study, the same group of animals was imaged using the mPEG-PL-Cy5.5 smart probe. Animals treated with Camostat showed reduced Cilengitide probe activation (figure 3c, d) in comparison to untreated caerulein animals (P<0.001). Camostat treated animals and control animals did not show any significant difference in probe activation after 3 subsequent caerulein administration. All animals indicated high signal intensity in the liver suggesting that the mPEG-PL-Cy5.