Title : Taraxasterol augments 4-phenylbutyric acid inhibition of glucose-induced inflammation, cellular stress and mitochondrial dysfunction in HepG2 cellsTaraxasterol augments 4-phenylbutyric acid inhibition of glucose-induced inflammation, cellular stress and mitochondrial dysfunction in HepG2 cells
Abstract:
Type 2 diabetes is characterized by hyperglycemia with associated mitochondrial dysfunction and cellular stress. 4-phenylbutyric acid (4PBA) is a chemical chaperone that ameliorates endoplasmic reticulum stress, while taraxasterol (TAX) is a pentacyclic triterpene whose antidiabetic potential is still being elucidated. The aims of this study are to evaluate the in vitro antidiabetic potentials in HepG2 cells, representing the liver, which is a glucose-utilizing organ. HepG2 cells were treated with high glucose concentration (40 mM), low TAX (25 μM), high TAX (50 μM), and 4PBA (2.5 mmol/L), for 24, 48 and 72 hours. Other groups contained glucose-treated cells that were also exposed to 4PBA, low TAX, high TAX, low TAX + 4PBA and high TAX + 4PBA. Colorimetric methods were used to determine the protein levels of antioxidant enzymes viz. superoxide dismutase (SOD) and catalase; inflammatory markers (interleukin-1β, and tumor necrosis factor alpha) and malondialdehyde. Real time polymerase chain reaction (RT-PCR) was used to estimate the mRNA levels of nuclear factor erythroid 2–related factor-2 (Nrf2) as well as endoplasmic reticulum (ER) stress markers - glucose regulated protein 78 (GRP78), activating transcription factor-4 (Atf4) and C/EBP homologous protein (CHOP). Mitochondrial dysfunction was evaluated by means of change in mitochondrial membrane potential. Results obtained from this study showed that both concentrations of TAX significantly (P < 0.05) increased the levels of antioxidant enzymes with a corresponding reduction of level of inflammatory proteins. Moreover, expression of ER stress markers was also significantly attenuated, while glucose-induced reduction of mitochondrial membrane potential was reversed. It was also observed that a synergy exists between TAX and 4PBA. It could be concluded that a synergistic effect between taraxasterol and 4-phenylbutyric acid inhibited glucose-induced cellular stress, inflammation and mitochondrial dysfunction in HepG2 cells.
