Inflammatory change of fatty liver induced by intraportal low-dose lipopolysaccharide infusion deteriorates pancreatic insulin secretion in fructose-induced insulin-resistant rats

Glycine protects against high sucrose and high fat-induced non-alcoholic steatohepatitis in rats

We set out to explore the hypothesis that glycine attenuates non-alcoholic steatohepatitis (NASH) in rats and the possible mechanism by which is it does. Male Sprague-Dawley (SD) rats were fed a diet containing high fat and high sucrose (HSHF) for 24 weeks to induce NASH. Blood and liver tissues were sampled at selected time points throughout the study. Compared with control animals, the content of alanine transaminase (ALT), triglycerides (TGs), and free fatty acids (FFAs) in plasma and the TG and FFA content in the liver was increased from week 4 to 24. The level of TNFα and MCP-1 in plasma, the content of TNFα in the liver, the insulin resistance index, inflammatory cell infiltration, hepatocyte apoptosis, reactive oxygen species (ROS) generation, and endoplasmic stress-associated protein expression were unaltered at 4 weeks. However, these levels were significantly elevated in HSHF fed rats at 12 weeks. At the same time, the level of endotoxin progressively increased from 0.08 ± 0.02 endotoxin EU/ml at week 4 to 0.7 ± 0.19 EU/ml at week 24. Moreover, these rats had elevated blood endotoxin levels, which were positively associated with their NASH indexes. Liver histology progressively worsened over the course of the study. However, we found that with concomitant treatment with glycine, the level of endotoxin decreased, while NASH indexes significantly decreased and liver status markedly improved,. These data support the hypothesis that glycine protects against NASH in rats by decreasing the levels of intestinal endotoxin, alleviating endoplasmic reticulum and oxidative stress.

Cytosolic and Calcium-Independent Phospholipases A2 Activation and Prostaglandins E2 Are Associated with Escherichia coli-Induced Reduction of Insulin Secretion in INS-1E Cells

It is suspected that microbial infections take part in the pathogenesis of diabetes mellitus type 1 (T1DM). Glucose-induced insulin secretion is accompanied by the release of free arachidonic acid (AA) mainly by cytosolic- and calcium independent phospholipases A₂ (cPLA₂ and iPLA₂). Insulinoma cell line (INS-1E) was infected with E. coli isolated from the blood culture of a patient with sepsis. Invasion assay, Scanning Electron Microscopy and Transmission Electron Microscopy demonstrated the capacity of E. coli to enter cells, which was reduced by PLA₂ inhibitors. Glucose-induced insulin secretion was significantly increased after acute infection (8h) but significantly decreased after chronic infection (72h). PLA₂ activities, cPLA₂, iPLA₂, phospho-cPLA₂, and COX-2 expressions were increased after acute and, even more, after chronic E. coli infection. The silencing of the two isoforms of PLA₂s, with specific cPLA₂- or iPLA₂-siRNAs, reduced insulin secretion after acute infection and determined a rise in insulin release after chronic infection. Prostaglandins E₂ (PGE₂) production was significantly elevated in INS-1E after long-term E. coli infection and the restored insulin secretion in presence of L798106, a specific EP3 antagonist, and NS-398, a COX-2 inhibitor, and the reduction of insulin secretion in presence of sulprostone, a specific EP3 agonist, revealed their involvement in the effects triggered by bacterial infection. The results obtained demonstrated that cPLA₂ and iPLA₂ play a key role in insulin secretion process after E. coli infection. The high concentration of AA released is transformed into PGE₂, which could be responsible for the reduced insulin secretion.

Rutaecarpine ameliorates hyperlipidemia and hyperglycemia in fat-fed, streptozotocin-treated rats via regulating the IRS-1/PI3K/Akt and AMPK/ACC2 signaling pathways

AIM

We have shown that rutaecarpine extracted from the dried fruit of Chinese herb Evodia rutaecarpa (Juss) Benth (Wu Zhu Yu) promotes glucose consumption and anti-inflammatory cytokine expression in insulin-resistant primary skeletal muscle cells. In this study we investigated whether rutaecarpine ameliorated the obesity profiles, lipid abnormality, glucose metabolism and insulin resistance in rat model of hyperlipidemia and hyperglycemia.

METHODS

Rats fed on a high-fat diet for 8 weeks, followed by injection of streptozotocin (30 mg/kg, ip) to induce hyperlipidemia and hyperglycemia. One week after streptozotocin injection, the fat-fed, streptozotocin-treated rats were orally treated with rutaecarpine (25 mg·kg(-1)·d(-1)) or a positive control drug metformin (250 mg·kg(-1)·d(-1)) for 7 weeks. The body weight, visceral fat, blood lipid profiles and glucose levels, insulin sensitivity were measured. Serum levels of inflammatory cytokines were analyzed. IRS-1 and Akt/PKB phosphorylation, PI3K and NF-κB protein levels in liver tissues were assessed; pathological changes of livers and pancreases were examined. Glucose uptake and AMPK/ACC2 phosphorylation were studied in cultured rat skeletal muscle cells in vitro.

RESULTS

Administration of rutaecarpine or metformin significantly decreased obesity, visceral fat accumulation, water consumption, and serum TC, TG and LDL-cholesterol levels in fat-fed, streptozotocin-treated rats. The two drugs also attenuated hyperglycemia and enhanced insulin sensitivity. Moreover, the two drugs significantly decreased NF-κB protein levels in liver tissues and plasma TNF-α, IL-6, CRP and MCP-1 levels, and ameliorated the pathological changes in livers and pancreases. In addition, the two drugs increased PI3K p85 subunit levels and Akt/PKB phosphorylation, but decreased IRS-1 phosphorylation in liver tissues. Treatment of cultured skeletal muscle cells with rutaecarpine (20-180 μmol/L) or metformin (20 μmol/L) promoted the phosphorylation of AMPK and ACC2, and increased glucose uptake.

CONCLUSION

Rutaecarpine ameliorates hyperlipidemia and hyperglycemia in fat-fed, streptozotocin-treated rats via regulating IRS-1/PI3K/Akt signaling pathway in liver and AMPK/ACC2 signaling pathway in skeletal muscles.

The chemical chaperon 4-phenylbutyric acid ameliorates hepatic steatosis through inhibition of de novo lipogenesis in high-fructose-fed rats

Non-alcoholic fatty liver disease caused by dietary factors such as a high fructose intake is a growing global concern. The aim of this study was to investigate the intervention effects of an endoplasmic reticulum stress (ERS) inhibitor 4-phenylbutyric acid (PBA) on liver steatosis induced by high-fructose feeding in rats and the possible underlying mechanisms. Wistar rats were divided into the control, high-fructose group (HFru) and PBA intervention (HFru-PBA) groups. PBA intervention was initiated following 4 weeks of high-fructose feeding. After 8 weeks of feeding, the ERS markers p-PERK, p-eIF2α, p-IRE-1, spliced XBP-1, ATF-6 were measured by western blotting. Liver triglyceride contents and morphological changes were examined. The protein expression of lipogenic key enzymes (ACC, FAS and SCD-1) and upstream transcriptional factors (SREBP-1c and ChREBP) were measured. The ERS-related cell events, oxidative stress and apoptosis, were evaluated by standard methods. Results demonstrated that PBA intervention significantly resolved hepatic ERS and improved liver steatosis induced by high-fructose feeding in rats. The protein expression of ACC, FAS, SCD-1 and SREBP-1c was upregulated in high-fructose-fed rats, whereas it decreased following PBA intervention. Oxidative stress and apoptosis were observed in livers of high-fructose-fed rats, but were alleviated by PBA intervention. ERS is involved in the development of fatty liver induced by a high fructose intake. ERS inhibition by PBA can therefore ameliorate liver steatosis through inhibition of hepatic lipogenesis.

Lipoic acid suppresses portal endotoxemia-induced steatohepatitis and pancreatic inflammation in rats

AIM: To examine the effect of α-lipoic acid (LA) on mild portal endotoxemia-induced steatohepatitis and associated pancreatic abnormalities in fructose-fed rats.

METHODS: Rats were randomly assigned into two groups with a regular or 60% fructose-enriched diet for 8 wk. After fructose feeding for 4 wk, rats were further divided into four subgroups: with intraportal saline (F_PV), with intraportal saline plus administration of LA (F_{PV + LA}), with lipopolysaccharide (LPS) infusion (F_PLPS), and with LPS infusion plus administration of LA (F_{PLPS + LA}). Rats were treated with LPS using intraportal infusion while LA was administered orally. Metabolite levels, superoxide levels, inflammatory markers, malondialdehyde content, glutathione content and toll-like receptor 4 (TLR4) gene expression were all measured using standard biochemical techniques. Pancreatic insulin secretion was evaluated by a hyperglycemic clamp technique. Histology of liver and pancreas tissues were evaluated using hematoxylin and eosin staining and immunohistochemistry.

RESULTS: Fructose-induced elevation in plasma C-reactive protein, amylase, superoxide, white blood cell count as well as in hepatic and pancreatic contents of malondialdehyde, tumor necrosis factor alpha and interleukin-6 were increased in animals treated with LPS and reversed with LA administration. The augmented hepatic gene expression of TLR4 in fructose-fed rats was further increased in those with intraportal LPS infusion, which was partially reversed by LA administration. Pathological examination showed inflammatory changes and leukocyte infiltration in hepatic and pancreatic islets of animals treated with LPS but were rarely observed in those with LA treatment. In addition to affects on the liver, impaired pancreatic insulin secretion seen in fructose-fed rats was deteriorated in with LPS treatment and partially reversed with LA administration.

CONCLUSION: These data suggest LA could significantly suppress mild portal-endotoxemia but not fructose-induced liver and pancreatic abnormalities in a rodent model for metabolic syndrome.

α-Lipoic acid prevents mild portal endotoxaemia-induced hepatic inflammation and β cell dysfunction

BACKGROUND

This study was undertaken to evaluate the preventive effect of α-lipoic acid (LA) on chronic mild portal endotoxaemia-mediated subacute hepatic inflammation and pancreatic β cell dysfunction in rats.

MATERIALS AND METHODS

Male Sprague-Dawley rats were randomly assigned into four groups: those with intraportal vehicle (saline) or low-dose lipopolysaccharide (LPS) (0·42 ng/kg/min) infusion, combined with oral administration of vehicle or LA, a potent antioxidant (60 mg/kg/day) for 4 weeks. The hyperglycaemic clamp and euglycaemic clamp techniques were used to access the glucose-stimulated insulin secretion and systemic insulin sensitivity in vivo.

RESULTS

Body weight, fasting plasma glucose and insulin were not different among groups. In rats with chronic intraportal LPS infusion, plasma C-reactive protein, amylase, superoxide levels, the contents of thiobarbituric acid-reactive substance, tumour necrosis factor α and interleukin 6 in liver and pancreas and also the gene expression of Toll-like receptor 4 in liver were significantly increased as compared with those with LA cotreatment. The histopathological examination showed that inflammatory changes were clearly visible in liver and pancreatic islets of LPS-infused rats and rarely observed in those cotreated with LA. In addition, low-dose intraportal LPS infusion also significantly impaired glucose-stimulated insulin secretion but not affect the systemic insulin sensitivity and metabolic clearance rate of insulin. LA administration markedly reversed LPS-induced β cell dysfunction.

CONCLUSIONS

α-Lipoic acid cotreatment could significantly prevent mild portal endotoxaemia-induced chronic hepatic inflammation and impaired pancreatic insulin secretion in absence of changing systemic insulin resistance.

Impact of liver diseases on the development of type 2 diabetes mellitus

The prevalence of type 2 diabetes mellitus (T2DM) is higher in patients who have liver diseases such as nonalcoholic fatty liver disease, chronic viral hepatitis, hemochromatosis, alcoholic liver disease and cirrhosis. It is suggested that there is a pathogenic link between the presence of T2DM and the severity of liver injury. However, evidence related to the impact of hepatic inflammation on the development of T2DM has not yet emerged. This article provides an overview of the evidence for an increased prevalence of diabetes in a range of liver diseases, the impact of liver diseases on insulin resistance and β cell dysfunction, and the potential mechanisms whereby coexistent liver diseases exacerbate the development of T2DM.

Cyanidin-3-O-beta-glucoside inhibits LPS-induced expression of inflammatory mediators through decreasing IkappaBalpha phosphorylation in THP-1 cells

OBJECTIVE AND DESIGN

As a common phytochemical, cyanidin 3-O-beta-glucoside (C3G) has a role in inhibiting inflammatory mediators; however, its mechanism of action remains unclear. The purpose of this study was to explore the effect of C3G on lipopolysaccharide (LPS)-stimulated TNFalpha and IL-6 expression in the human monocyte/macrophage cell line THP-1, and to explore the mechanisms involved.

METHODS

Differentiated THP-1 cells were treated with different concentrations of C3G (0.005, 0.05, 0.5,10 microM) in the absence or presence of 1 ng/mL LPS. mRNA expression levels were detected by real time PCR, and secretion of TNFalpha and IL-6, phosphorylated IkappaBalpha, and nuclear factor-kappa B (NF-kappaB) P65 were monitored by ELISA or Western blotting analysis. The role of an inhibitor of IkappaBalpha phosphorylation, BAY 11-7082, in C3G inhibition of LPS-induced cytokines expression was investigated.

RESULTS

C3G (0.05-0.5 microM) treatment significantly inhibited LPS-stimulated TNFalpha and IL-6 mRNA expression and secretion of these proteins by THP-1 cells. Phosphorylation of IkappaBalpha and NF-kappaB nuclear translocation could be blocked by 0.5 microM C3G. BAY 11-7082 treatment abolished C3G-induced reduction of TNFalpha and IL-6.

CONCLUSION

Our results suggest that C3G exerts its anti-inflammatory effect through inhibiting IkappaBalpha phosphorylation, thereby suppressing NF-kappaB activity in THP-1 cells.