In a randomized , cross-over , placebo-controlled trial of 44 healthy men and women , homozygous for UGT1A6 * 1 or UGT1A6 * 2 , we explored differences between global epithelial and stromal expression , using Affymetrix U133 +2.0 microarrays and tested effects of 60-day aspirin supplementation ( 325 mg/d ) on epithelial and stromal gene expression and colon prostaglandin E2 ( PGE2 ) levels .