Chemotherapy-induced gut toxicity and pain: involvement of TLRs

Purpose: Chemotherapy-induced gut toxicity is associated with significant pain, and pain influences gut function. Toll-like receptors (TLRs) that regulate gut homeostasis are activated by tissue damage and microbes, and their altered expression following chemotherapy may change cellular responses. This study examined the interaction between chemotherapy-induced gut toxicity and pain and related these to gut TLR and glial fibrillary acidic protein (GFAP) expression. Methods: Female tumor bearing Dark Agouti rats received irinotecan (175 mg/kg, n = 34) or vehicle (n = 5) and were assessed over 120 h for gut toxicity (diarrhea, weight loss), pain (facial), and GFAP, TLR2, 4, 5, and 9 gut expression. Results: Irinotecan caused diarrhea (72 % of animals grade ≥ 1), weight loss (11.1 ± 6.6 %, P < 0.0001), and pain (5 (0–5), P < 0.0001) all peaking at 72 h. Higher pain scores were observed in rats with diarrhea versus those without: median (range) of 2.0 (0–5) versus 0 (0–5), P = 0.01. Irinotecan also caused a decrease in TLR4 and 5, and an increase in GFAP expression in jejuna crypt at 96 and 120 h (all P < 0.05); with lower TLR4 expression associated with lower pain (P = 0.012). Conclusions: The association between gut toxicity and pain suggests these toxicities are linked, possibly via TLR-mediated inflammatory pathways. Further, as TLR4 and 5 expression was absent during recovery in the jejuna and GFAP expression was increased in the jejuna, this implies expression of these may be critical in the healing phase following chemotherapy. Detailed studies of gut TLRs and GFAP are now warranted.