[Show abstract][Hide abstract] ABSTRACT: Epigallocatechin-3-gallate (EGCG), a bioactive component of green tea, has been reported to exert anti-inflammatory effects on immune cells. EGCG is also shown to activate the metabolic regulator, adenosine 5'-monophosphate-activated protein kinase (AMPK). Reports have also indicated that EGCG inhibits the immune-stimulated phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. The PI3K/Akt/mTOR pathway has been implicated in mesangial cell activation in lupus. Mesangial cells from MRL/lpr lupus-like mice are hyper-responsive to immune stimulation and overproduce nitric oxide (NO) and other inflammatory mediators when stimulated. In our current studies, we sought to determine the mechanism by which EGCG attenuates immune-induced expression of pro-inflammatory mediators. Cultured mesangial cells from MRL/lpr mice were pre-treated with various concentrations of EGCG and stimulated with lipopolysaccharide (LPS)/interferon (IFN)-gamma. EGCG activated AMPK and blocked LPS/IFN-gamma-induced inflammatory mediator production (iNOS expression, supernatant NO and interleukin-6). Interestingly, EGCG attenuated inflammation during AMPK inhibition indicating that the anti-inflammatory effect of EGCG may be partially independent of AMPK activation. Furthermore, we found that EGCG effectively inhibited the immune-stimulated PI3K/Akt/mTOR pathway independently of AMPK, by decreasing phosphorylation of Akt, suggesting an alternate mechanism for EGCG-mediated anti-inflammatory action in mesangial cells. Taken together, these studies show that EGCG attenuated inflammation in MRL/lpr mouse mesangial cells via the PI3K/Akt/mTOR pathway. Our findings suggest a potential therapeutic role for the use of EGCG to regulate inflammation and control autoimmune disease.
[Show abstract][Hide abstract] ABSTRACT: Recent reports show that 5-amino-4-imidazole carboxamide riboside (AICAR), a pharmacological activator of AMP-activated protein kinase (AMPK), inhibits the lipopolysaccharide (LPS)-induced production of proinflammatory cytokines. MRL/MPJ-Fas(lpr) (MRL/lpr) mice show an intrinsic decreased threshold for the production of inflammatory mediators when stimulated. In our current studies, we sought to determine if AMPK activation would inhibit inflammatory mediator production in stimulated kidney mesangial cells. Cultured mesangial cells from MRL/lpr mice were treated with AICAR and stimulated with LPS/interferon (IFN)-gamma. AICAR decreased dose-dependently inducible nitric oxide synthase (iNOS), cyclooxygenase-2 and interleukin-6 production in LPS/IFN-gamma-stimulated mesangial cells. Mechanistically, AICAR inhibited the LPS/IFN-gamma-stimulated PI3K/Akt signalling inflammatory cascade but did not affect LPS/IFN-gamma-mediated inhibitory kappa B phosphorylation or nuclear factor (NF)-kappaB (p65) nuclear translocation. Treatment with the adenosine kinase inhibitor 5'-iodotubercidin blocked the ability of AICAR to activate AMPK and prevented AICAR from inhibiting the LPS/IFN-gamma-stimulated PI3K/Akt pathway and attenuating iNOS expression. Taken together, these observations suggest that AICAR inhibits LPS/IFN-gamma-induced Akt phosphorylation through AMPK activation and may serve as a potential therapeutic target in inflammatory diseases.
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to test the hypothesis that the inflammatory response to a high-fat, low-carbohydrate weight loss diet (HF) we previously observed was due to oxidative stress. Nineteen overweight subjects (BMI>27 kg/m(2)) were randomly assigned to either an antioxidant supplement (AS) (1 g vitamin C/800 IU vitamin E) or a placebo (P) group and provided with a HF for 7 days. Fasted pre- and post serum samples were measured for markers of inflammation (C-reactive protein (CRP), interleukin-6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1)), oxygen radical absorbance capacity (ORAC), and glucose, whereas urine was measured for oxidative stress (8-epi-prostaglandin-F(2alpha) (8-epi)). HF resulted in significant reductions in weight (-3.2%), glucose (-18.7%), and MCP-1 (-15%) (all P<0.01), with no difference between groups. There was a trend for a differential effect between groups for CRP as it decreased 32% in the AS group but increased 50% for P (P=0.076). Inverse correlations were noted between initial values and changes in several inflammatory and oxidative stress markers, including CRP (r= -0.501), 8-epi (r= -0.863), and ORAC (r= -0.546) (all P<0.05). It was concluded that weight loss on a short-term HF caused reduction of some but not all markers of inflammation. A role for oxidative stress in causing inflammation was not confirmed; however, longer term diet-controlled studies are necessary to further explore the trend for a differential response in CRP with antioxidant supplementation.