Jennifer Kehlet Barton

We utilize a miniature, dual-modality endoscope that combines fluorescence-based surface magnifying chromoendoscopy (SMC) and optical coherence tomography (OCT) to follow the anatomical changes that occur during adenoma development in the mouse colon.

Optical coherence tomography (OCT) and laser-induced fluorescence (LIF) spectroscopy each have clinical potential in identifying human gastrointestinal (GI) pathologies, yet their diagnostic capability in mouse models is unknown. In this study, we combined the 2 modalities to survey the GI tract of a variety of mouse strains and ages and to sample dysplasias and inflammatory bowel disease (IBD) of the intestines. Segments (length, 2.5 cm) of duodenum and lower colon and the entire esophagus were imaged ex-vivo with combined OCT and LIE We evaluated 30 normal mice (A/J and 10- and 21-wk-old and retired breeder C57BL/6J) and 10 mice each of 2 strains modeling colon cancer and IBD (Apc(Min) and IL2-deficient mice, respectively). Histology was used to classify tissue regions as normal, Peyer patch, dysplasia, adenoma, or IBD. Features in corresponding OCT images were analyzed. Spectra from each category were averaged and compared via Student t tests. OCT provided structural information that led to identification of the imaging characteristics of healthy mouse GI. With histology as the 'gold standard,' we developed preliminary image criteria for early disease in the form of adenomas, dysplasias, and IBD. LIF characterized the endogenous fluorescence of mouse GI tract, with spectral features corresponding to collagen, NADH, and hemoglobin. In the IBD sample, LIF emission spectra displayed potentially diagnostic peaks at 635 and 670 nm, which we attributed to increased porphyrin production by bacteria associated with IBD. OCT and LIF appear to be useful and complementary modalities for ex vivo imaging of mouse GI tissues.

We successfully labeled colorectal cancer in vivo using quantum dots targeted to vascular endothelial growth factor receptor 2 (VEGFR2). Quantum dots with emission centered at 655 nm were bioconjugated to anti-VEGFR2 antibodies through streptavidin/biotin linking. The resulting QD655-VEGFR2 contrast agent was applied in vivo to the colon of azoxymethane (AOM) treated mice via lavage and allowed to incubate. The colons were then excised, cut longitudinally, opened to expose the lumen, and imaged en face using a fluorescence stereoscope. The QD655-VEGFR2 contrast agent produced a significant increase in contrast between diseased and undiseased tissues, allowing for fluorescence-based visualization of the diseased areas of the colon. Specificity was assessed by observing insignificant contrast increase when labeling colons of AOM-treated mice with quantum dots bioconjugated to isotype control antibodies, and by labeling the colons of saline-treated control mice. This contrast agent has a great potential for in vivo imaging of the colon through endoscopy.

The role of the endothelium in regulating transmural fluid filtration into the artery wall under pulsatile pressure and the effects of changes in pulsatile frequency on filtration have received little attention. Previous experiments (Alberding JP, Baldwin AL, Barton JK, and Wiley E. Am J Physiol Heart Circ Physiol 286: H1827-H1835, 2004) demonstrated significantly increased filtration after initial onset of pulsatile pressure compared with that predicted by using parameters measured under steady pressure. To determine the role of the endothelium in this phenomenon, the following experiments were performed on five New Zealand White rabbits (anesthetized with 30 mg/kg pentobarbital sodium). One of each pair of carotid arteries was deendothelialized, and filtration measurements under steady and pulsatile pressure were compared with those made in intact vessels (Alberding JP, Baldwin AL, Barton JK, and Wiley E. Am J Physiol Heart Circ Physiol 286: H1827-H1835, 2004). To determine the effect of increasing pulsatile frequency on arterial filtration, transmural filtration was measured by using pulsatile pressure frequencies of 1 Hz, followed by 2 Hz, in another set of intact arteries (6 arteries and 3 animals). For deendothelialized vessels, the initial increase in filtration after onset of pulsatility was similar to that observed in intact vessels, but the subsequent reduction in filtration was less abrupt. When pulsatile frequency was increased from 1 to 2 Hz in intact arteries, an initial increase in filtration was observed, similar to that obtained after onset of pulsatile pressure subsequent to a steady pressure. The observed responses of arteries to pulsatile pressure, with and without endothelium, or undergoing a frequency change, suggest a dynamic role for the endothelium in regulating transvascular transport in vivo.