Gene expression profiling of flaxseed in mouse lung tissues-modulation of toxicologically relevant genes

Flaxseed Consumption Inhibits Chemically Induced Lung Tumorigenesis and Modulates Expression of Phase II Enzymes and Inflammatory Cytokines in A/J Mice

Flaxseed consumption is associated with reduced oxidative stress and inflammation in lung injury models and has shown anticancer effects for breast and prostate tissues. However, the chemopreventive potential of flaxseed remains unexplored for lung cancer. In this study, we investigated the effect of flaxseed on tobacco smoke carcinogen (NNK)-induced lung tumorigenesis in an A/J mouse model. Mice exposed to NNK were fed a control diet or a 10% flaxseed-supplemented diet for 26 weeks. Flaxseed-fed mice showed reduced lung tumor incidence (78%) and multiplicity, with an average of 2.7 ± 2.3 surface lung tumor nodules and 1.0 ± 0.9 H&E cross-section nodules per lung compared with the control group, which had 100% tumor incidence and an average of 10.2 ± 5.7 surface lung tumor nodules and 3.9 ± 2.6 H&E cross-section nodules per lung. Furthermore, flaxseed-fed mice had a lower incidence of adenocarcinomas compared with control-fed mice. Western blotting performed on normal lung tissues showed flaxseed suppressed phosphorylation (activation) of p-AKT, p-ERK, and p-JNK kinases. RNA-Seq data obtained from normal lung and lung tumors of control and flaxseed-fed mice suggested that flaxseed intake resulted in differential expression of genes involved in inflammation-mediated cytokine signaling (IL1, 6, 8, 9, and 12α), xenobiotic metabolism (several CYPs, GSTs, and UGTs), and signaling pathways (AKT and MAPK) involved in tumor cell proliferation. Together, our results indicate that dietary flaxseed supplementation may be an effective chemoprevention strategy for chemically induced lung carcinogenesis by altering signaling pathways, inflammation, and oxidative stress. Cancer Prev Res; 11(1); 27-37. ©2017 AACR.

Enterolactone Induces G1-phase Cell Cycle Arrest in Nonsmall Cell Lung Cancer Cells by Downregulating Cyclins and Cyclin-dependent Kinases

Flaxseed is a rich source of the plant lignan secoisolariciresinol diglucoside (SDG), which is metabolized into mammalian lignans enterodiol (ED) and enterolactone (EL) in the digestive tract. The anticancer properties of these lignans have been demonstrated for various cancer types, but have not been studied for lung cancer. In this study, we investigated the anticancer effects of EL for several nonsmall cell lung cancer (NSCLC) cell lines of various genetic backgrounds. EL inhibited the growth of A549, H441, and H520 lung cancer cells in concentration- and time-dependent manners. The antiproliferative effects of EL for lung cancer cells were not due to enhanced cell death, but rather due to G1-phase cell cycle arrest. Molecular studies revealed that EL decreased mRNA or protein expression levels of the G1-phase promoters cyclin D1, cyclin E, cyclin-dependent kinases (CDK)-2, -4, and -6, and p-cdc25A; decreased phosphorylated retinoblastoma (p-pRb) protein levels; and simultaneously increased levels of p21WAF1/CIP1, a negative regulator of the G1 phase. The results suggest that EL inhibits the growth of NSCLC cell lines by downregulating G1-phase cyclins and CDKs, and upregulating p21WAF1/CIP1, which leads to G1-phase cell cycle arrest. Therefore, EL may hold promise as an adjuvant treatment for lung cancer therapy.

The Flaxseed-Derived Lignan Phenolic Secoisolariciresinol Diglucoside (SDG) Protects Non-Malignant Lung Cells from Radiation Damage

Plant phenolic compounds are common dietary antioxidants that possess antioxidant and anti-inflammatory properties. Flaxseed (FS) has been reported to be radioprotective in murine models of oxidative lung damage. Flaxseed’s protective properties are attributed to its main biphenolic lignan, secoisolariciresinol diglucoside (SDG). SDG is a free radical scavenger, shown in cell free systems to protect DNA from radiation-induced damage. The objective of this study was to investigate the in vitro radioprotective efficacy of SDG in murine lung cells. Protection against irradiation (IR)-induced DNA double and single strand breaks was assessed by γ-H2AX labeling and alkaline comet assay, respectively. The role of SDG in modulating the levels of cytoprotective enzymes was evaluated by qPCR and confirmed by Western blotting. Additionally, effects of SDG on clonogenic survival of irradiated cells were evaluated. SDG protected cells from IR-induced death and ameliorated DNA damage by reducing mean comet tail length and percentage of γ-H2AX positive cells. Importantly, SDG significantly increased gene and protein levels of antioxidant HO-1, GSTM1 and NQO1. Our results identify the potent radioprotective properties of the synthetic biphenolic SDG, preventing DNA damage and enhancing the antioxidant capacity of normal lung cells; thus, rendering SDG a potential radioprotector against radiation exposure.

Dietary flaxseed modulates the miRNA profile in irradiated and non-irradiated murine lungs: a novel mechanism of tissue radioprotection by flaxseed

INTRODUCTION

Dietary flaxseed (FS) displays antioxidant and anti-inflammatory properties in preclinical models of lung disease including radiation-induced pneumonopathy, however the mechanisms of lung radioprotection are incompletely understood. MicroRNAs (miRNAs) are short oligonucleotides that act as important posttranscriptional regulators of diverse networks including inflammatory response networks. Responses of miRNA profiles to diet and radiation exposure have been reported, but the potential contribution of miRNAs to diet-related radioprotection has never been tested.

METHODS

In this exploratory pilot study, mice were fed 10% FS or a 0% FS isocaloric control diet and exposed to a single-fraction 13.5 Gy thoracic X-ray radiation treatment (XRT). Lung RNA was extracted 48 h post-XRT and small RNAs profiled by OpenArray.

RESULTS

FS significantly modulated expression of multiple miRNAs, including 7 with P<0.001. miR-150 was downregulated approximately 2.9-fold in the FS groups and is disproportionately integrated into immune response-related networks. Although few miRNAs were significantly changed by radiation, interaction between diet and radiation was observed. For example, miR-29c was greatly downregulated in the FS/Control group (10- to 50-fold) but slightly upregulated in the FS/radiation group. Compared with FS/control, the FS/radiation group experienced a 50% decrease of the p53-responsive miR-34a, which regulates senescence- and apoptosis-related factors.

CONCLUSIONS

FS induced significant changes in lung miRNA profile suggesting that modulation of small RNA by dietary supplements may represent a novel strategy to prevent adverse side-effects of thoracic radiotherapy. This pilot study provides insight into a potential mechanism of flaxseed's radioprotection and provides a useful model-system to further explore and optimize such small RNA-based therapies.

Radioprotective role in lung of the flaxseed lignan complex enriched in the phenolic secoisolariciresinol diglucoside (SDG)

While dietary wholegrain Flaxseed (FS) has potent anti-inflammatory, anti-fibrotic and antioxidant properties in murine models of acute and chronic lung injury, the main bioactive ingredient that contributes to these protective effects remains unknown. This study evaluated the lignan complex of FS (FLC) enriched in secoisolariciresinol diglucoside with respect to lung radioprotective and tumor radiosensitizing efficacy using a mouse model of thoracic radiation-induced pneumonopathy. C57/Bl6 mice were fed 0% FS, 10% FS, 10% FLC or 20% FLC for 3 weeks, then irradiated with a single fraction (13.5 Gy) of X-ray radiation treatment (XRT). Mouse survival was monitored for 4 months after irradiation and inflammatory lung parameters were evaluated in bronchoalveolar lavage (BAL) fluid. Gene and protein levels of protective antioxidant and phase II enzymes were evaluated in lung tissue using qPCR and protein levels were verified by immunoblotting. Prolonged administration of the FLC diet was well tolerated and was not associated with any toxicity. Importantly, comparable to the whole grain 10% FS diet, irradiated mice fed 10% and 20% FLC diets displayed improved survival. Improved hemodynamic measurements were also recorded in irradiated mice fed 10% FS or 10% FLC diet compared to irradiated 0% FS fed mice. Flaxseed lignan complex diet also attenuated polymorphonuclear infiltration and overall lung inflammation to levels comparable to those in nonirradiated mice. Flaxseed lignan complex, similarly to FS, up-regulated gene expression as well as protein levels of protective antioxidant enzymes such as heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1). Dietary FLC induced radiosensitizing effects in our murine model of metastatic lung cancer. Importantly, protection of normal tissue does not thwart tumor cell death by radiation treatment. The dietary lignan complex of FS, mainly consisting of the phenolic secoisolariciresinol, is protective against radiation pneumonopathy in vivo while not hindering the tumoricidal effects of radiotherapy.