Colon Barrier Breakdown in the Elderly
Principal Investigator: J M Mullin
Abstract: Although cancers of the lower gastrointestinal tract have a pronounced dependence on age, very few studies have been performed on changes of gastrointestinal epithelial cell biology as a function of age. Our group has focused intensely over fifteen years on changes in the barrier function of epithelial layers as an early event in epithelial neoplasia. We have published numerous evidence that increased permeability in specifically epithelial tight junctions (a major parameter of epithelial barriers) is a promotional event in epithelial cancers. We intend in this proposal to now advance a related hypothesis: tight junction permeability in the lower gastrointestinal tract increases as a function of age. Our proposal is to first validate this phenomenon in a patient-based study in the broadest way possible, by using oral probes of paracellular permeability (Aim 1). We will simultaneously pursue two potential molecular mechanisms for this increased permeability (Aims 2 and 3) by using biopsies of colonic mucosa taking during routine cancer screen colonoscopies. We wish to focus attention on the phenomenon of increased tight junction permeability as a significant means of morbidity and cancer risk in the aging population. Aim 1: We will administer to consenting healthy patients undergoing colonoscopy cancer screening, a solution of either marmitol/lactulose or rbamuose/cellobiose to consume at bedtime. The group of probes will be selected at randon. We will instruct patients to collect an overnight urine sample. These probes' appearance in urine is quantitatively reflective of their paracellular diffusion out of the lumen of the lower gastrointestinal tract. They are reflective specifically of paracellular diffusion across the lower GI tract because of the probes lacking affinity for any membrane transport proteins anywhere in the GI tract, and their transit time through the length of the GI tract. The age range of patients will be 30 to 80 years of age. We will statistically compare two age blocks, 30 - 50 and 60 - 80 years of age. Aim 2: These same patient volunteers will be contributing biopsies of the ascending colon, descending colon and sigmoid colon during their colonoscopy. We will analyze these biopsies for age-related changes in the expression level, subcellular localization and phosphorylation state of the tight junction proteins occludin and claudius 1 - 3. Aim 3: These same biopsy samples will also be analyzed for age-related changes in plasma membrane lipid composition of colonocytes. Changes in membrane composition/fluidity are known to affect paracellular permeability in general, and tight junction proteins specifically.
Funding Period: 2004-09-01 - 2006-07-31
more information: NIH RePORT
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