Microbial phenolic metabolites improve glucose-stimulated insulin secretion and protect pancreatic beta cells against tert-butyl hydroperoxide-induced toxicity via ERKs and PKC pathways Elisa Fernández-Millán a , Sonia Ramos b , Carmen Alvarez a,c , Laura Bravo b , Luis Goya b , María Ángeles Martín a,b,⇑ a Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Instituto de Salud Carlos III (ISCIII), Madrid, Spain b Departamento de Metabolismo y Nutrición, Instituto de Ciencia y Tecnología de los Alimentos y Nutrición (ICTAN), Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain c Departamento de Bioquímica y Biología Molecular II, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain article info Article history: Received 8 January 2014 Accepted 27 January 2014 Available online 31 January 2014 Keywords: Dietary polyphenols INS-1E beta cells Oxidative stress Type 2 diabetes mellitus abstract Oxidative stress is accepted as one of the causes of beta cell failure in type 2 diabetes. Therefore, identi- fication of natural antioxidant agents that preserve beta cell mass and function is considered an interest- ing strategy to prevent or treat diabetes. Recent evidences indicated that colonic metabolites derived from flavonoids could possess beneficial effects on various tissues. The aim of this work was to establish the potential anti-diabetic properties of the microbial-derived flavonoid metabolites 3,4-dihydroxyphen- ylacetic acid (DHPAA), 2,3-dihydroxybenzoic acid (DHBA) and 3-hydroxyphenylpropionic acid (HPPA). To this end, we tested their ability to influence beta cell function and to protect against tert-butyl hydroper- oxide-induced beta cell toxicity. DHPAA and HPPA were able to potentiate glucose-stimulated insulin secretion (GSIS) in a beta cell line INS-1E and in rat pancreatic islets. Moreover, pre-treatment of cells with both compounds protected against beta cell dysfunction and death induced by the pro-oxidant. Finally, experiments with pharmacological inhibitors indicate that these effects were mediated by the activation of protein kinase C and the extracellular regulated kinases pathways. Altogether, these findings strongly suggest that the microbial-derived flavonoid metabolites DHPAA and HPPA may have anti-dia- betic potential by promoting survival and function of pancreatic beta cells. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Type 2 diabetes (T2D) is a complex metabolic disorder consid- ered a major health problem because of its high frequency and its associated complications resulting in blindness, kidney failure, heart disease, stroke and amputations (Chaturvedi, 2007). There are currently 366 million people worldwide with diabetes and the incidence of the disease is projected to be more than double by 2030 (Whiting et al., 2011) T2D results from a combination of genetic and acquired factors that impair beta cell function and tissue insulin sensitivity but there is growing evidence that beta cell dysfunction is crucial for the development and progression of the disease (Marchetti et al., 2008). Indeed, the inability of beta cells to secrete adequate amounts of insulin results in chronic hypergly- cemia and excessive oxidative stress which has been largely impli- cated in the pathogenesis of pancreatic beta cell failure (Bensellam et al., 2012). This scenario leads to a vicious circle that contributes to the decline of the functional beta cell mass and the consequent progression of T2D (Poitout and Robertson, 2008) Therefore, treat- ments aimed at enhancing beta cell mass and function are consid- ered key to prevent or treat diabetes and retard the onset of http://dx.doi.org/10.1016/j.fct.2014.01.044 0278-6915/Ó 2014 Elsevier Ltd. All rights reserved. Abbreviations: AKT/PKB, protein kinase B; DCF, dichorofluorescein; DHBA, 2,3- dihydroxybenzoic acid; DHPAA, 3,4-dihydroxyphenylacetic acid; ERK, extra cellular regulated kinase; GSIS, glucose-stimulated insulin secretion; HPPA, 3-hydroxy- phenylpropionic acid; KRB, Krebs–Ringer bicarbonate buffer; PKA, protein kinase A; PKC, protein kinase C; T2D, type 2 diabetes; t-BOOH, tert-butyl hydroperoxide; PI3K, phosphatidylinositol-3-kinase. ⇑ Corresponding author. Address: Departamento de Metabolismo y Nutrición, Instituto de Ciencia y Tecnología de los Alimentos y Nutrición (ICTAN), Consejo Superior de Investigaciones Científicas (CSIC), José Antonio Novais 10, Ciudad Universitaria, 28040 Madrid, Spain. Tel.: +34 91 544 56 07; fax: +34 91 549 36 27. E-mail address: amartina@ictan.csic.es (M.Ángeles Martín). Food and Chemical Toxicology 66 (2014) 245–253 Contents lists available at ScienceDirect Food and Chemical Toxicology journal homepage: www.elsevier.com/locate/foodchemtox