Benzylglucosinolate Derived Isothiocyanate from Tropaeolum majus Reduces Gluconeogenic Gene and Protein Expression in Human Cells

Nasturtium (Tropaeolum majus L.) contains high concentrations of benzylglcosinolate. We found that a hydrolysis product of benzyl glucosinolate—the benzyl isothiocyanate (BITC)—modulates the intracellular localization of the transcription factor Forkhead box O 1 (FOXO1). FoxO transcription factors can antagonize insulin effects and trigger a variety of cellular processes involved in tumor suppression, longevity, development and metabolism. The current study evaluated the ability of BITC—extracted as intact glucosinolate from nasturtium and hydrolyzed with myrosinase—to modulate i) the insulin-signaling pathway, ii) the intracellular localization of FOXO1 and, iii) the expression of proteins involved in gluconeogenesis, antioxidant response and detoxification. Stably transfected human osteosarcoma cells (U-2 OS) with constitutive expression of FOXO1 protein labeled with GFP (green fluorescent protein) were used to evaluate the effect of BITC on FOXO1. Human hepatoma HepG2 cell cultures were selected to evaluate the effect on gluconeogenic, antioxidant and detoxification genes and protein expression. BITC reduced the phosphorylation of protein kinase B (AKT/PKB) and FOXO1; promoted FOXO1 translocation from cytoplasm into the nucleus antagonizing the insulin effect; was able to down-regulate the gene and protein expression of gluconeogenic enzymes; and induced the gene expression of antioxidant and detoxification enzymes. Knockdown analyses with specific siRNAs showed that the expression of gluconeogenic genes was dependent on nuclear factor (erythroid derived)-like2 (NRF2) and independent of FOXO1, AKT and NAD- dependent deacetylase sirtuin-1 (SIRT1). The current study provides evidence that BITC might have a role in type 2 diabetes T2D by reducing hepatic glucose production and increasing antioxidant resistance

第1090回千葉医学会例会・第7回環境生命医学研究会

<p>HepG2 cells were incubated with BITC 30 μM, insulin 100 nM and insulin + BITC for 30 min. PathScan Signaling Array Kit was used for the detection of the phosphorylated AKT (Thr308). Data shown as mean of fold phosphorylation normalized to untreated control + SEM (n = 3) *p<0.05(Unpaired Student’s t test).</p

Flavonoid Glycosides in <i>Brassica</i> Species Respond to UV-B Depending on Exposure Time and Adaptation Time

Recently, there have been efforts to use ultraviolet-B radiation (UV-B) as a biotechnological tool in greenhouses. Leafy Brassica species are mainly considered for their ability to synthesize glucosinolates and are valued as baby salads. They also have a remarkable concentration of chemically diverse flavonoid glycosides. In this study, the effect of short-term UV-B radiation at the end of the production cycle was investigated without affecting plant growth. The aim was to verify which exposure and adaptation time was suitable and needs to be further investigated to use UV as a biotechnological tool in greenhouse production of Brassica species. It is possible to modify the flavonoid glycoside profile of leafy Brassica species by increasing compounds that appear to have potentially high antioxidant activity. Exemplarily, the present experiment shows that kaempferol glycosides may be preferred over quercetin glycosides in response to UV-B in Brassica rapa ssp. chinensis, for example, whereas other species appear to prefer quercetin glycosides over kaempferol glycosides, such as Brassica oleracea var. sabellica or Brassica carinata. However, the response to short-term UV-B treatment is species-specific and conclusions on exposure and adaptation time cannot be unified but must be drawn separately for each species

The flavones apigenin and luteolin induce FOXO1 translocation but inhibit gluconeogenic and lipogenic gene expression in human cells.

The flavones apigenin (4',5,7,-trihydroxyflavone) and luteolin (3',4',5,7,-tetrahydroxyflavone) are plant secondary metabolites with antioxidant, antiinflammatory, and anticancer activities. We evaluated their impact on cell signaling pathways related to insulin-resistance and type 2 diabetes. Apigenin and luteolin were identified in our U-2 OS (human osteosarcoma) cell screening assay for micronutrients triggering rapid intracellular translocation of the forkhead box transcription factor O1 (FOXO1), an important mediator of insulin signal transduction. Insulin reversed the translocation of FOXO1 as shown by live cell imaging. The impact on the expression of target genes was evaluated in HepG2 (human hepatoma) cells. The mRNA-expression of the gluconeogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pc), the lipogenic enzymes fatty-acid synthase (FASN) and acetyl-CoA-carboxylase (ACC) were down-regulated by both flavones with smaller effective dosages of apigenin than for luteolin. PKB/AKT-, PRAS40-, p70S6K-, and S6-phosphorylation was reduced by apigenin and luteolin but not that of the insulin-like growth factor receptor IGF-1R by apigenin indicating a direct inhibition of the PKB/AKT-signaling pathway distal to the IGF-1 receptor. N-acetyl-L-cysteine did not prevent FOXO1 nuclear translocation induced by apigenin and luteolin, suggesting that these flavones do not act via oxidative stress. The roles of FOXO1, FOXO3a, AKT, sirtuin1 (SIRT1), and nuclear factor (erythroid-derived2)-like2 (NRF2), investigated by siRNA knockdown, showed differential patterns of signal pathways involved and a role of NRF2 in the inhibition of gluconeogenic enzyme expression. We conclude that these flavones show an antidiabetic potential due to reduction of gluconeogenic and lipogenic capacity despite inhibition of the PKB/AKT pathway which justifies detailed investigation in vivo

CAT gene expression in HepG2 cells modulated by BITC.

<p>Dose-dependency is shown for the antioxidant enzyme CAT. Results are presented as fold mRNA expression, normalized to the housekeeping gene RPL32 and the control. Data shown as mean value ± SEM *(p<0.05), **(p<0.01) and ***(p<0.001). (Oneway ANOVA and posthoc Bonferroni).</p

U-2 OS-FOXO1-GFP cells treated with BITC at selected concentrations.

<p>Nuclear accumulation was estimated by measuring the ratio of FOXO1 nuclear/FOXO1 cytosolic (FOXO1 Nuc/Cyt) after 1 h treatment normalized to untreated control cells. Ratios higher than 1 showed a nuclear accumulation of FOXO1. Results are presented as mean values + standard error (SEM) (n = 4). Significant differences vs control (0 μM) are labelled for *(p<i><</i>0.05) and **(p<i><</i>0.01) (Oneway ANOVA and posthoc Bonferroni multiple comparisons).</p

FOXO1 translocation in stably transfected U-2 OS (human osteosarcoma cells).

<p>Fig 1A–1D show FOXO1-GFP expressing cells and nuclear DAPI-staining (red) changing to orange-yellow in overlays with GFP after incubation with BITC at concentrations of 0 (1A-A’), 1 (1B-B’), 10 (1C-C’) and 100 μM (1D-D’), respectively. Following 1 h of starvation, stimulation of cells was performed with BITC for 1 h. Cells were fixed and stained with DAPI for identification of nuclear areas by fluorescence microscopic detection, for segmentation of cells and calculation of GFP-intensity ratios in nuclei and cytoplasm (Nuc/Cyt).</p