Amino acids stimulate Akt phosphorylation,and reduce IL‐8 production and NF‐κB activity in HepG2 liver cells

Hepatic insulin resistance and inflammatory cytokine production contribute to the manifestation of the metabolic syndrome. As amino acids have been implicated in modulating insulin signaling and inflammation, we have investigated the effects of glutamine, leucine and proline on markers of inflammation and insulin sensitivity in HepG2 liver cells. Cells were incubated with IL‐1β (5 ng/mL) to stimulate IL‐8 production. After 24 h, glutamine inhibited IL‐8 production significantly (p<0.05) at 2, 5 and 10 mM (to 82, 73 and 72% of control), whereas leucine reduced IL‐8 production significantly only at 10 mM (66%) and proline at 5 and 10 mM (71 and 52%). Glutamine, leucine and proline all reduced NF‐κB activity after 3 h of IL‐1β stimulation at 2, 5 and 10 mM (p<0.001). Insulin‐induced (1 nM) Akt phosphorylation was reduced in cells treated with tumour necrosis factor‐α (10 ng/mL) for 24 h, but was partly restored by simultaneous incubation with glutamine, leucine and proline (25 mM). Phosphorylation of glycogen synthase kinase‐3β was unaffected by insulin stimulation and amino acid treatment. Our results indicate that glutamine, leucine and proline attenuate IL‐8 production, probably through inhibition of NF‐κB, and that they increase Akt phosphorylation in HepG2 cells.     

Resveratrol Regulates Activated Hepatic Stellate Cells by Modulating NF‐κB and the PI3K/Akt Signaling Pathway

In the present study, we investigated whether resveratrol could suppress the hepatic fibrogenesis in activated hepatic stellate cells. The immortalized rat hepatic stellate cells, t‐HSC/Cl‐6, were treated with resveratrol 1 h prior to lipopolysaccharide (LPS, 1 μg/mL). Resveratrol decreased t‐HSC/Cl‐6 cell viability at much lower concentrations within 24 h. Resveratrol pretreatment also decreased the LPS‐induced protein expression of α‐SMA and collagen I. In addition, resveratrol significantly reduced the protein expression of Toll‐like receptor 4 (TLR4) and myeloid differentiation primary response gene 88 (MyD88), and the expression of phosphorylated phosphatidylinositol 3‐kinase (PI3K) and phosphorylated serine/threonine kinase B (Akt). Moreover, resveratrol markedly blocked the translocation of nuclear factor (NF)‐κB in LPS‐activated HSCs. Furthermore, resveratrol inhibited HSCs activation through stimulating LXRβ, but did not influence LXRα. Overall, we conclude that the antifibrotic effect of resveratrol is the result of blocking NF‐κB activation and PI3K/Akt phosphorylation, which inhibits HSC activation to obstruct liver fibrosis. Thus, resveratrol may be a natural agent for preventing hepatic fibrosis.     

Myricetin attenuates lipopolysaccharide‐stimulated activation of mouse bone marrow‐derived dendritic cells through suppression of IKK/NF‐κB and MAPK signalling pathways

BACKGROUND: Myricetin is a naturally occurring flavonoid that is found in many fruits, vegetables, teas and medicinal herbs. It has been demonstrated to have anti‐inflammatory properties, but, to date, no studies have described the immunomodulatory effects of myricetin on the functions of dendritic cells (DCs). The aim of this study was to evaluate the potential for myricetin to modulate lipopolysaccharide (LPS)‐stimulated activation of mouse bone marrow‐derived DCs. RESULTS: Our experimental data showed that treatment with myricetin up to 10 µg mL⁻¹ does not cause cytotoxicity in cells. Myricetin significantly decreased the secretion of tumour necrosis factor‐α, interleukin‐6 and interleukin‐12p70 by LPS‐stimulated DCs. The expression of LPS‐induced major histocompatibility class II, CD40 and CD86 on DCs was also inhibited by myricetin, and the endocytic and migratory capacity of LPS‐stimulated DCs was blocked by myricentin. In addition, LPS‐stimulated DC‐elicited allogeneic T‐cell proliferation was reduced by myricetin. Moreover, our results confirmed that myricetin attenuates the responses of LPS‐stimulated activation of DCs via suppression of IκB kinase/nuclear factor‐κB and mitogen‐activated protein kinase‐dependent pathways. CONCLUSION: Myricetin has novel immunopharmacological activity, and modulation of DCs by myricetin may be an attractive strategy for the treatment of inflammatory and autoimmune disorders, and for transplantation. Copyright © 2012 Society of Chemical Industry