Figure 4. Irinotecan causes tight junction defects in the colon of DA rats. ZO-1 protein expression was significantly decreased in the apical crypt epithelium 96 h following chemotherapy. Irinotecan caused significant downregulation in claudin-1 protein expression in the apical crypt epithelium 24 h following treatment, while a significant decrease was observed 96 h following irinotecan in the crypt crypt epithelium of the colon. Significant downregulation in occludin protein expression was observed at 24 and 48 h following irinotecan administration in the apical and basal crypt epithelium. ZO-1, claudin-1, and occludin protein expression was analyzed in the basal and apical crypt epithelium of the colon. Staining intensity was analyzed in a blinded fashion (HR Wardill and RJ Gibson) using a validated semi-quantitative grading system.55 A Kruskall–Wallis with a Dunn multiple comparison was performed to determine significance. Data presented as median values (n = 39); ■□ P < 0.05 vs. control.