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

Christiane Bumke-Vogt,Valentina Guzman-Perez,Andreas F H Pfeiffer,Volker Bähr,Martin A Osterhoff,Andreas L Birkenfeld,Zeinab Sarem,Andrea Borchert,Juergen Eckel

doi:10.1371/journal.pone.0104321

Christiane Bumke-Vogt, Valentina Guzman-Perez + Show 7 more

Open Access

https://doi.org/10.1371/journal.pone.0104321

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Abstract

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.

Highlights

The prevalence of type 2 diabetes (T2DM) and associated comorbidities is rising worldwide [1]
With FOXO1 as the endpoint of IGF signaling and of insulin signaling via the phosphatidylinositol 39-kinase (PI3K)-AKT pathway, we focused our investigations on the metabolic effects of apigenin and luteolin to analyze their roles in modulating insulin signal transduction which is disturbed in insulin resistance and T2D
In analyses of micronutrients screened in concentrations of 1, 10 and 100 mM with our FOXO1 translocation assay, we calculated

Summary

Introduction

The prevalence of type 2 diabetes (T2DM) and associated comorbidities is rising worldwide [1]. The prevention of type 2 diabetes by life style intervention including diet and exercise was successful [4]. Consumption of higher quantities of vegetable and a variety of fruits and vegetables containing bioactive phytochemicals were associated with a reduced risk of T2D in a case cohort study of EPIC-Norfolk [6]. Micronutrients such as the polyphenol resveratrol (3,5,49-trihydroxystilbene) showed controversial outcomes in different studies from improvement of insulin sensitivity [7,8,9] to absence of any evidence of metabolic effects [10]. Mediterranean diets rich in polyphenols were shown to prevent T2DM [11]

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