Pterostilbene reverses palmitic acid mediated insulin resistance in HepG2 cells by reducing oxidative stress and triglyceride accumulation

Abstract

Insulin resistance (IR) is known to precede onset of type 2 diabetes and increased oxidative stress appears to be a deleterious factor leading to IR. In this study, we evaluated ability of pterostilbene (PTS), a methoxylated analogue of resveratrol and a known antioxidant, to reverse palmitic acid (PA)-mediated IR in HepG2 cells. PTS prevented reactive oxygen species (ROS) formation and subsequent oxidative lipid damage by reducing the expression of NADPH oxidase 3 (NOX3) in PA treated HepG2 cells. Hepatic glucose production was used as a measure of IR and PTS reversed PA-mediated increase in hepatic glucose production by reducing expression of genes coding for gluconeogenic enzymes namely glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), and pyruvate carboxylase (PC); and their transcription factors cAMP response element binding protein (CREB) and fork head class Box O (FOXO1) along with its coactivator peroxisome proliferator-activated receptor gamma co-activator-1 α (PGC1α). PTS reversed PA-mediated activation of c-Jun N-terminal kinase (JNK), which in turn altered insulin signalling pathway by phosphorylating IRS-1 at Ser 307, leading to inhibition of phosphorylation of Akt and GSK-3β. PTS also reduced PA-mediated lipid accumulation by reducing expression of transcription factors SREBP1c and PPARα. SREBP1c activates genes involved in fatty acid and triglyceride synthesis while PPARα activates CPT1, a rate limiting enzyme for controlling entry and oxidation of fatty acids into mitochondria. PTS, however, did not influence PA uptake confirmed by using BODIPY-labelled fluorescent C16 fatty acid analogue. Thus, our data provides a possible mechanistic explanation for reversal of PA-mediated IR in HepG2 cells.

Keywords:

• Gluconeogenesis
• insulin resistance
• oxidative stress
• palmitic acid
• pterostilbene
• reactive oxygen species

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

SSG is thankful to Council of Scientific and Industrial Research (CSIR) (37 (1590)113-EMR-II) and Department of Biotechnology (DBT) (BT/PR7625/BRB/10/1176/2013), Government of India, for financial assistance. Financial support by University Grants Commission (UGC) and Department of Science and Technology, Government of India (DST-PURSE) to Department of Zoology, Savitribai Phule Pune University, Pune-411007 is also acknowledged. SSK is thankful to a Wellcome Trust DBT India Alliance Intermediate fellowship and a DST-SERB Early Career Award in Life Sciences for financial support. A DST-FIST Infrastructure Development Grant to the Biology Department, IISER Pune is also thanked towards setting up the lipidomics facility. JDA acknowledges funds from Start-up research grant (SB/YS/LS-23/2014), Science and Engineering Research Board, India. NKM is supported by a research fellowship from the Department of Biotechnology (DBT), Government of India. SAM is supported by Research Assistantship under the DST-PURSE scheme of Department of Zoology, Savitribai Phule Pune University, India.