Modulatory effect of curcumin on survival of irradiated human intestinal microvascular endothelial cells: role of Akt/mTOR and NF-κB

Abstract

Radiation therapy is an essential modality in the treatment of colorectal cancers. Radiation exerts an antiangiogenic effect on tumors, inhibiting endothelial proliferation and survival in the tumor microvasculature. However, damage from low levels of irradiation can induce a paradoxical effect, stimulating survival in endothelial cells. We used human intestinal microvascular endothelial cells (HIMEC) to define effects of radiation on these gut-specific endothelial cells. Low-level irradiation (1-5 Gy) activates NF-kappaB and the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, which is involved in cell cycle reentry and cell survival in HIMEC. A downstream target of PI3K/Akt is mammalian target of rapamycin (mTOR), which contributes to endothelial proliferation and angiogenesis. The aim of this study was to investigate the signaling molecules involved in the radiosensitizing effects of curcumin on HIMEC subjected to low levels of irradiation. We have demonstrated that exposure of HIMEC to low levels of irradiation induced Akt and mTOR phosphorylation, which was attenuated by curcumin, rapamycin, LY294002, and mTOR small interference RNA (siRNA). Activation of NF-kappaB by low levels of irradiation was inhibited by curcumin, SN-50, and mTOR siRNA. Curcumin also induced apoptosis by induction of caspase-3 cleavage in irradiated HIMEC. In conclusion, curcumin significantly inhibited NF-kappaB and attenuated the effect of irradiation-induced prosurvival signaling through the PI3K/Akt/mTOR and NF-kappaB pathways in these gut-specific endothelial cells. Curcumin may be a potential radiosensitizing agent for enhanced antiangiogenic effect in colorectal cancer radiation therapy.

Anti inflammatory and anti angiogenic effect of black raspberry extract on human esophageal and intestinal microvascular endothelial cells

“…Reverse transcription was done with 1 μg of RNA using Bio-Rad’s iScript cDNA synthesis kit for RT-PCR. Real-time PCR was done using Bio-Rad’s SYBR Green Master Mix, 2 μl of cDNA, and 250 nM primers in 25 μl reactions as previously described (Rafiee et al, 2010a). Real-time data was analyzed with Bio-Rad’s iQ5 software.…”

“…Adhesion assays were performed as previously described (Rafiee et al, 2010a) (Binion et al, 2009). Briefly, ECs were seeded onto fibronectin-coated 24-well plate (0.5 × 10 5 cells/well).…”

“…Using a modified Wright’s stain (Diff-Quik Stain; Baxter Scientific, McGraw, IL) adhered cells were fixed, stained and counted in 10 high-power fields (X20). Data was expressed as number of adherent leukocytes/mm 2 (Rafiee et al, 2010a) (Binion et al, 2009). …”

“…SDS-PAGE and Western blot analysis were performed using specific antibodies to COX2, NFkB (p65), Akt and MAPK as described previously (Rafiee et al, 2010a) (Binion et al, 2009). …”

Contemporary Radiation Countermeasure

“…Mice that were given a 5 per cent solution of curcumin versus those that were given a controlled diet showed not only improved survival, but also decreased radiation-induced lung fibrosis. As a chemopreventive agent, curcumin has both known antioxidant and tumor cell radiosensitising properties 35 . Thus, dietary curcumin ameliorates radiation-induced pulmonary fibrosis and increases mouse survival while not impairing pulmonary tumor cell killing by radiation 34 .…”