Gamma-Tocotrienol Protects the Intestine from Radiation Potentially by Accelerating Mesenchymal Immune Cell Recovery

Abstract

Natural antioxidant gamma-tocotrienol (GT3), a vitamin E family member, provides intestinal radiation protection. We seek to understand whether this protection is mediated via mucosal epithelial stem cells or sub-mucosal mesenchymal immune cells. Vehicle- or GT3-treated male CD2F1 mice were exposed to total body irradiation (TBI). Cell death was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Villus height and crypt depth were measured with computer-assisted software in tissue sections. Functional activity was determined with an intestinal permeability assay. Immune cell recovery was measured with immunohistochemistry and Western blot, and the regeneration of intestinal crypts was assessed with ex vivo organoid culture. A single dose of GT3 (200 mg/kg body weight (bwt)) administered 24 h before TBI suppressed cell death, prevented a decrease in villus height, increased crypt depth, attenuated intestinal permeability, and upregulated occludin level in the intestine compared to the vehicle treated group. GT3 accelerated mesenchymal immune cell recovery after irradiation, but it did not promote ex vivo organoid formation and failed to enhance the expression of stem cell markers. Finally, GT3 significantly upregulated protein kinase B or AKT phosphorylation after TBI. Pretreatment with GT3 attenuates TBI-induced structural and functional damage to the intestine, potentially by facilitating intestinal immune cell recovery. Thus, GT3 could be used as an intestinal radioprotector.

Nuclear and Radiological Emergencies: Biological Effects, Countermeasures and Biodosimetry

“…Recent preclinical studies evidenced that GT3 may be a potential countermeasure against late degenerative tissue effects of high-LET radiation in the heart [ 190 ] and lung radiation injury [ 191 ]. Tocotrienols accumulate in the intestine to a greater level than tocopherols, and this can be involved in its greater ability to attenuate GIS [ 192 ]. γ-tocotrienols seem to have a greater efficacy as radioprotectors attributed [ 189 ] to their: (a) higher antioxidant potential [ 191 ], (b) capacity to downregulate proapoptotic/antiapoptotic ratio [ 193 ], (c) ability to accumulate in endothelial cells and intestinal epithelium which facilitates the recovery of mesenchymal immune cells [ 192 ], and (d) ability to inhibit HMG-CoA reductase, helping to avoid chronic inflammatory responses associated to radio-induced vascular and intestinal damage [ 185 ].…”

“…Tocotrienols accumulate in the intestine to a greater level than tocopherols, and this can be involved in its greater ability to attenuate GIS [ 192 ]. γ-tocotrienols seem to have a greater efficacy as radioprotectors attributed [ 189 ] to their: (a) higher antioxidant potential [ 191 ], (b) capacity to downregulate proapoptotic/antiapoptotic ratio [ 193 ], (c) ability to accumulate in endothelial cells and intestinal epithelium which facilitates the recovery of mesenchymal immune cells [ 192 ], and (d) ability to inhibit HMG-CoA reductase, helping to avoid chronic inflammatory responses associated to radio-induced vascular and intestinal damage [ 185 ]. Moreover, recent studies have also evidenced the anti-cancer properties of γ-tocotrienols [ 179 ] and, although their low bioavailability is an important limiting factor [ 177 ], new formulations may help to overcome this pitfall.…”

Fractionated radiation suppresses Kruppel-like factor 2 pathway to a greater extent than by single exposure to the same total dose

“…We tested the efficacy of inhibitors of the mevalonate pathway, specifically, HMG-CoA reductase inhibitors (i.e., atorvastatin and GT3) and GGTi, in attenuating KLF2 suppression after fractionated radiation. We and others have shown HMG-CoA reductase inhibitors enhanced the expression of KLF2 and its downstream target molecules, such as TM and eNOS and provided radiation protection 28,30,38,39,41 . Treatment with atorvastatin, GT3, and GGTi significantly prevented fractionated radiation-induced suppression of not only KLF2 but also its downstream target molecules TM and eNOS (Fig.…”

“…Appropriate positive and negative controls were included. Immunohistochemical staining for KLF2 and ICAM-1 was performed as described elsewhere 39 . Briefly, tissue sections were incubated with rabbit anti-KLF2 (1:100, LSBio, Seattle, WA, USA) or rabbit anti-ICAM-1 (1:250, Novus Biologicals, Centennial, CO, USA) antibodies for 2 hours.…”

JAC4 Protects from X-ray Radiation-Induced Intestinal Injury by JWA-Mediated Anti-Oxidation/Inflammation Signaling

“…Intestinal epithelial cells exposed to radiation will lead to cell death due to oxidative stress, DNA fragmentation, apoptosis, etc., resulting in a radiation damage subsequent reaction [ 5 ]. The damage of epithelial cells not only affects the villus–crypt structural integrity, but also compromises the barrier integrity and enhances intestinal permeability, allowing enteric bacteria to invade the damaged tissue and cause intestinal inflammation [ 6 ].…”