| Abstract: | Short-term fasting protects mice from lethal doses of chemotherapy through undetermined mechanisms. Herein, we demonstrate that fasting preserves small intestinal (SI) architecture by maintaining SI stem cell viability and SI barrier function following exposure to high-dose etoposide. Nearly all SI stem cells were lost in fed mice, whereas fasting promoted sufficient SI stem cell survival to preserve SI integrity after etoposide treatment. Lineage tracing demonstrated that multiple SI stem cell populations, marked by Lgr5, Bmi1, or HopX expression, contributed to fasting-induced survival. DNA repair and DNA damage response genes were elevated in SI stem/progenitor cells of fasted etoposide-treated mice, which importantly correlated with faster resolution of DNA double-strand breaks and less apoptosis. Thus, fasting preserved SI stem cell viability as well as SI architecture and barrier function suggesting that fasting may reduce host toxicity in patients undergoing dose intensive chemotherapy.Cancer patients undergoing chemotherapy experience high rates of morbidity, despite regimens that attempt to balance timing and dose intensity to mitigate off-target effects and dose-limiting toxicities (1–3). Interestingly, fasting has been shown to provide host-protective effects against high-dose chemotherapy-induced toxicity in preclinical and clinical studies. For example, etoposide, which forms a ternary complex with DNA and topoisomerase II causing DNA double-strand breaks (DSBs), is far less toxic if mice are fasted before treatment (4). Fasting has also been shown to protect normal, but not cancer cells, from the toxicity of chemotherapy, thereby extending the lifespan of tumor-bearing mice (4–8).Because of the rapid rate of epithelial cell proliferation in the small intestine (SI), gastrointestinal (GI) toxicity is one of the most common complications for a variety of chemotherapeutic treatments (9). Therefore, we investigated if fasting was capable of mitigating the GI toxicity normally associated with high-dose chemotherapy. Herein, we demonstrate that mice allowed to feed ad libitum before receiving high-dose chemotherapy showed marked histological changes to SI epithelium before death. These histological changes reflected loss of regenerative capacity as a result of stem cell depletion as well as structural damage from inflammatory cell infiltrates, similar to the SI response to high-dose ionizing radiation (10). In contrast, SI homeostasis was preserved in fasted mice by protection of stem cell viability and prevention of proinflammatory cell infiltrates. These results indicate that fasting mitigates GI side effects associated with chemotherapy by activating pathways that preserve SI stem cell integrity and by maintaining barrier function. |
