Disruption of glucose homeostasis and induction of insulin resistance by elevated free fatty acids in human L02 hepatocytes

Wan, Xue-Dong; Yang, Wu-Biao; Xia, Yi; Wang, J. F.; Lu, Tao; Wang, Xue Min

doi:10.1007/bf03346485

Cited by 10 publications

(7 citation statements)

References 22 publications

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“…A growing number of studies suggest that an important mechanism underlying this response is an increase in transcription of key gluconeogenic genes, particularly PCK1 and G6PC [26]. Increasing plasma FFA in rats increase hepatic G6PC mRNA abundance [28], and exposing primary hepatocytes to elevated FFA enhances mRNA abundance and the promoter activity of both PCK1 and G6PC [26,29], as well as PCK1 activity [30]. We found that exposing HepG2 and HuH7 cells to various concentrations of palmitate for 24 h significantly increased PCK1 and G6PC mRNA abundance in a dose-dependent manner; PCK1 promoter activity in HepG2 cells was increased twofold after a 24-h incubation in the presence of 1000 μM palmitate.…”

Section: Discussionmentioning

confidence: 99%

Toll-like receptor 4 signaling is required for induction of gluconeogenic gene expression by palmitate in human hepatic carcinoma cells

Mamedova

Yuan

Laudick

et al. 2013

The Journal of Nutritional Biochemistry

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Saturated free fatty acids (FFA) can activate inflammatory cascades including the toll-like receptor 4 (TLR4) pathway. TLR4 is expressed by hepatocytes and may help link FFA to altered hepatic gluconeogenesis in type 2 diabetes mellitus. This study examined the role of TLR4 in mediating palmitate effects on the expression of phosphoenolpyruvate carboxykinase (PCK1) and the catalytic subunit of glucose-6-phosphatase (G6PC), rate-determining gluconeogenic enzymes. Human hepatocellular carcinoma cells (HepG2 and HuH7) were incubated in media including 2% bovine serum albumin and 250 to 1000 μM palmitate for 24 h. Signaling mediated by TLR4 was blocked by a TLR4 decoy peptide or small interfering RNA knockdown of TLR4. Palmitate induced dose-dependent increases in PCK1 and G6PC mRNA abundance, which were prevented by the TLR4 decoy peptide. Palmitate doubled PCK1 promoter activity, and TLR4 knockdown ablated this response. Lipopolysaccharide and monophosphoryl lipid A also up-regulated G6PC and PCK1 transcript abundance in a TLR4-dependent manner. Addition of oleate attenuated palmitate-induced increases in G6PC and PCK1 mRNA abundance. Palmitate increased nuclear factor κ-light-chain-enhancer of activated B cells reporter gene activity, which was unaffected by TLR4 blockade, but increased mRNA abundance of hepatocyte-specific cyclic AMP response element binding protein, a transcriptional regulator of PCK1, in a TLR4-dependent manner. Finally, TLR4 activation by palmitate increased subsequent cellular uptake of palmitate, and inhibiting ceramide synthesis ablated palmitate effects on PCK1 mRNA abundance and promoter activity. These results suggest that TLR4 signaling could play a critical role in linking elevated saturated FFA to increased transcription of gluconeogenic genes.

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Section: Discussionmentioning

confidence: 99%

Toll-like receptor 4 signaling is required for induction of gluconeogenic gene expression by palmitate in human hepatic carcinoma cells

Mamedova

Yuan

Laudick

et al. 2013

The Journal of Nutritional Biochemistry

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“…Failure of insulin to inhibit hepatic gluconeogenesis is to a large extent responsible for the disruption of glucose homeostasis and development of fasting hyperglycaemia [41]. PKB is a key molecule mediating the metabolic effect of insulin in the liver.…”

Section: Discussionmentioning

confidence: 99%

Long-term melatonin administration improves glucose homeostasis and insulin resistance state in high-fat-diet fed rats

Wan

et al. 2013

Open Life Sciences

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Emerging evidence support an important role of reactive oxygen species in various forms of insulin resistance. It is identified that melatonin has antioxidant properties and prevents toxic effects of reactive oxygen species. In this study, we sought to assess the involvement of melatonin in the progression of insulin resistance in response to a high-fat diet (HFD) and to investigate the underlying mechanisms. Male rats were fed with a control diet, a high-fat diet, or a high-fat diet supplemented with melatonin (5 mg kg−1, i.p.) for 10 weeks. Glucose homeostasis, insulin sensitivity, antioxidative potency, and metabolic profiles in the rats were evaluated. Our results showed that a HFD led to increasing body mass, adipose tissue weight, plasma insulin, total cholesterol (TC), triglycerides (TG), free fatty acids (FFA), and decreased HDL-cholesterol (HDL-C) in rats. There was also a significant increase in the level of malondialdehyde (MDA) and decrease in superoxide dismutase (SOD) activity, oxidative stress markers both in the plasma and liver. An enhanced hepatic phosphoenolpyruvate carboxy-kinase (PEPCK) activity and RNA expression were observed. Impaired insulin signaling was evidenced by reducing insulin receptor substrate 2 (IRS2) tyrosine phosphorylation and protein kinase B (PKB) serine phosphorylation in response to insulin. Overactivation of stress-activated protein kinases JNK was also observed in the liver of HFD rats. However, simultaneous administration of melatonin to HFD rats significantly reduced oxidative stress in the system and liver, markedly improved impaired glucose homeostasis, insulin sensitivity, antioxidative potency, metabolic profiles and all the aforesaid adverse changes in HFD rats. Our results demonstrated that anti-oxidative property of melatonin is sufficient to ameliorate the insulin resistance condition, leading to the improvement of glucose homeostasis and the restoration of hepatic insulin signaling in a rat model of HFD-induced insulin resistance.

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“…In vitro IR models are mainly generated in hepatocytes, fat cells, and skeletal muscle cells using high concentrations of insulin; medium containing high levels of sugar and fat; dexamethasone; palmitic acid; and tunicamycin [26][27][28][29], although a high insulin concentration is most frequently used [30]. Dexamethasone, a kind of glucocorticoid, is easily confused with dexmedetomidine (owing to similar abbreviations), which induces IR by inhibiting the binding of insulin to the insulin receptor.…”

Section: Discussionmentioning

confidence: 99%

Dexmedetomidine alleviates insulin resistance in hepatocytes by reducing endoplasmic reticulum stress

Liu

Zhu

et al. 2019

Endocrine

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Purpose Dexmedetomidine (DEX) stabilizes intraoperative blood glucose levels and reduces insulin resistance (IR), a common perioperative complication. However, the molecular mechanisms underlying these effects remain unclear. Since endoplasmic reticulum stress (ERS) is a mechanism of IR, this study sought to examine whether DEX can effectively alleviate IR by reducing ERS. Methods HepG2 and LO2 cells were treated with different concentrations of insulin. The glucose content assay and Cell Counting Kit-8 (CCK-8) were then employed to determine the optimal insulin concentration capable of inducing IR without affecting cell viability. Insulin-resistant hepatocytes were cultured with different concentrations of DEX for 24 h, and the glucose concentration in the supernatant was measured. ERS was assessed by qPCR and western blotting. The latter was also used to quantify the expression of phosphorylated protein kinase B (p-AKT), phosphoenolpyruvate carboxykinase (PEPCK), and glucose 6 phosphatase (G6Pase), which are key proteins involved in the action of insulin. Results After 48-h of culturing with 10 μg/mL insulin, glucose consumption in hepatocytes was found to be reduced. IR hepatocytes cultured with 10, 100, or 1000 ng/ml DEX for 24 h showed a concentration-dependent increase in glucose consumption. Elevated mRNA and protein levels of ERS markers binding immunoglobulin protein (BIP) and ER protein 29 (ERp29), were reversed by DEX treatment. Moreover, reduced p-AKT and increased PEPCK and G6Pase protein levels in IR hepatocytes were also restored following DEX treatment. Conclusion DEX may alleviate IR in hepatocytes by reducing ERS serving to restore insulin action via the IRS-1/PI3K/AKT pathway.

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Disruption of glucose homeostasis and induction of insulin resistance by elevated free fatty acids in human L02 hepatocytes

Cited by 10 publications

References 22 publications

Toll-like receptor 4 signaling is required for induction of gluconeogenic gene expression by palmitate in human hepatic carcinoma cells

Toll-like receptor 4 signaling is required for induction of gluconeogenic gene expression by palmitate in human hepatic carcinoma cells

Long-term melatonin administration improves glucose homeostasis and insulin resistance state in high-fat-diet fed rats

Dexmedetomidine alleviates insulin resistance in hepatocytes by reducing endoplasmic reticulum stress

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