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Maca extracts regulate glucose and lipid metabolism in insulin-resistant HepG2 cells via the PI3K/AKT signalling pathway.

ABSTRACT: This work focused on the separation of the active ingredients of maca (Lepidium meyenii Walpers) and evaluated the antioxidative capability of these components with effects on improving glucose and lipid metabolism in insulin-resistant HepG2 cells. DPPH free radical scavenging and reducing power assays were used to evaluate the antioxidant activity of maca extracts. An insulin-resistant HepG2 cell model induced by glucose, fructose, oleic acid, and palmitic acid was adopted to investigate the effects of maca extracts on regulating glucose and lipid metabolism in this study. LC-MS/MS was then used for determination of the maca n-butanol (NBT) subfraction. The results showed that maca ethanol extract and subfractions of this extract exhibited certain antioxidant capacity. Furthermore, the NBT subfraction reversed the disorders in glucose and lipid metabolism in insulin-resistant HepG2 cells and significantly increased the mRNA expression of phosphoinositide 3-kinases (PI3K) and AKT in insulin-resistant HepG2 cells in a dose-dependent manner. In addition, the LC-MS/MS results showed that the NBT subfraction contained many active ingredients. Overall, this study suggests that the NBT subfraction of the ethanol extract rich in glucosinolates modulates insulin resistance via PI3K/AKT activation in insulin-resistant HepG2 cells and might exert potentially beneficial effects in improving or treating glucose and lipid metabolic disorders.

SUBMITTER: Li A

PROVIDER: S-EPMC8194906 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Impaired insulin-mediated glucose uptake characterizes cardiac muscle in humans and animals with insulin resistance and diabetes, despite preserved or enhanced phosphatidylinositol 3-kinase (PI3K) and the serine-threonine kinase, Akt-signaling, via mechanisms that are incompletely understood. One potential mechanism is PI3K- and Akt-mediated activation of mechanistic target of rapamycin (mTOR) and ribosomal protein S6 kinase (S6K), which may impair insulin-mediated activation of insulin receptor substrate (IRS)1/2 via inhibitory serine phosphorylation or proteasomal degradation. To gain mechanistic insights by which constitutive activation of PI3K or Akt may desensitize insulin-mediated glucose uptake in cardiomyocytes, we examined mice with cardiomyocyte-restricted, constitutive or inducible overexpression of a constitutively activated PI3K or a myristoylated Akt1 (myrAkt1) transgene that also expressed a myc-epitope-tagged glucose transporter type 4 protein (GLUT4). Although short-term activation of PI3K and myrAkt1 increased mTOR and S6 signaling, there was no impairment in insulin-mediated activation of IRS1/2. However, insulin-mediated glucose uptake was reduced by 50-80%. Although longer-term activation of Akt reduced IRS2 protein content via an mTORC1-mediated mechanism, treatment of transgenic mice with rapamycin failed to restore insulin-mediated glucose uptake, despite restoring IRS2. Transgenic activation of Akt and insulin-stimulation of myrAkt1 transgenic cardiomyocytes increased sarcolemmal insertion of myc-GLUT4 to levels equivalent to that observed in insulin-stimulated wild-type controls. Despite preserved GLUT4 translocation, glucose uptake was not elevated by the presence of constitutive activation of PI3K and Akt. Hexokinase II activity was preserved in myrAkt1 hearts. Thus, constitutive activation of PI3K and Akt in cardiomyocytes impairs GLUT4-mediated glucose uptake via mechanisms that impair the function of GLUT4 after its plasma-membrane insertion.

Project description:Background: Little is known about the impact of nutrients on cellular transcriptional responses, especially in face of environmental stressors such as oxygen deprivation. Hypoxia-inducible factors (HIF) coordinate the expression of genes essential for adaptation to oxygen-deprived environments. A second family of oxygen-sensing genes known as the alpha-ketoglutarate-dependent dioxygenases are also implicated in oxygen homeostasis and epigenetic regulation. The relationship between nutritional status and cellular response to hypoxia is understudied. In vitro cell culture systems frequently propagate cells in media that contains excess nutrients, and this may directly influence transcriptional response in hypoxia. Methods: We studied the effect of glucose and glutamine concentration on HepG2 hepatoma transcriptional response to low oxygen and expression of hypoxia inducible factor-1α (HIF-1α). Mass spectrometry confirmed low oxygen perturbation of dioxygenase transcripts resulted in changes in DNA methylation. Results: Under normoxic conditions, we observed a significant upregulation of both HIF-target genes and oxygen-dependent dioxygenases in HepG2 cells cultured with physiological levels of glucose or glutamine relative to regular DMEM media, demonstrating that excess glutamine/glucose can mask changes in gene expression. Under hypoxic conditions, CA9 was the most upregulated gene in physiological glutamine media while TETs and FTO dioxygenases were downregulated in physiological glucose. Hypoxic regulation of these transcripts did not associate with changes in HIF-1α protein expression. Downregulation of TETs suggests a potential for epigenetic modulation. Mass-spectrometry quantification of modified DNA bases confirmed our transcript data. Hypoxia resulted in decreased DNA hydroxymethylation, which correlated with TETs downregulation. Additionally, we observed that TET2 expression was significantly downregulated in patients with hepatocellular carcinoma, suggesting that tumour hypoxia may deregulate TET2 expression resulting in global changes in DNA hydroxymethylation. Conclusion: Given the dramatic effects of nutrient availability on gene expression, future in vitro experiments should be aware of how excess levels of glutamine and glucose may perturb transcriptional responses.

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Maca extracts regulate glucose and lipid metabolism in insulin-resistant HepG2 cells via the PI3K/AKT signalling pathway.

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