Wei-Jian Zhang

α-Lipoic acid inhibits TNF-α-induced NF-κB activation and adhesion molecule expression in human aortic endothelial cells

Endothelial activation and monocyte adhesion are initiating steps in atherogenesis thought to be caused in part by oxidative stress. The metabolic thiol antioxidant a‐lipoic acid has been suggested to be of therapeutic value in pathologies associated with redox imbalances. We investigated the role of (R)‐a‐lipoic acid (LA) vs. glutathione and ascorbic acid in tumor necrosis factor a (TNF‐a) ‐induced adhesion molecule expression and nuclear factor KB (NF‐κB) signaling in human aortic endothelial cells (HAEC). Preincubation of HAEC for 48 h with LA (0.05–1 mmol/l) dose‐dependently inhibited TNF‐a (10 U/ml) ‐induced adhesion of human monocytic THP‐1 cells, as well as mRNA and protein expression of E‐selectin, vascular cell adhesion molecule 1 and intercellular adhesion molecule 1. LA also strongly inhibited TNF‐a‐induced mRNA expression of monocyte chemoat‐tractant protein‐1 but did not affect expression of TNF‐a receptor 1. Furthermore, LA dose‐dependently inhibited TNF‐a‐induced IκB kinase activation, subsequent degradation of IκB, the cytoplasmic NF‐κB inhibitor, and nuclear translocation of NF‐κB. In contrast, TNF‐a‐induced NF‐κB activation and adhesion molecule expression were not affected by ascorbic acid or by manipulating cellular glutathione status with L‐2‐oxo‐4‐thiazolidinecarboxylic acid, N‐acetyl‐L‐cys‐teine, or D,L‐buthionine‐S,R‐sulfoximine. Our data show that clinically relevant concentrations of LA, but neither vitamin C nor glutathione, inhibit adhesion molecule expression in HAEC and monocyte adhesion by inhibiting the IκB/NF‐κB signaling pathway at the level, or upstream, of IκB kinase.—Zhang, W.‐J., Frei, B. α‐Lipoic acid inhibits TNF‐α‐induced NF‐κB activation and adhesion molecule expression in human aortic endothelial cells. FASEB J. 15, 2423–2432 (2001)

α-Lipoic acid attenuates LPS-induced inflammatory responses by activating the phosphoinositide 3-kinase/Akt signaling pathway

The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway was recently shown to negatively regulate LPS-induced acute inflammatory responses. We previously observed that the metabolic thiol antioxidant α-lipoic acid (LA) inhibits LPS-induced expression of cellular adhesion molecules and adherence of monocytes to human aortic endothelial cells. Here we investigated the mechanism by which LA attenuates LPS-induced monocyte activation in vitro and acute inflammatory responses in vivo. Incubation of human monocytic THP-1 cells with LA induced phosphorylation of Akt in a time- and dose-dependent manner. In cells pretreated with LA followed by LPS, Akt phosphorylation was elevated initially and further increased during incubation with LPS. This LA-dependent increase in Akt phosphorylation was accompanied by inhibition of LPS-induced NF-κB DNA binding activity and up-regulation of TNFα and monocyte chemoattractant protein 1. Lipoic acid-dependent Akt phosphorylation and inhibition of NF-κB activity were abolished by the PI3K inhibitors LY294002 and wortmannin. Furthermore, LA treatment of LPS-exposed C57BL/6N mice strongly enhanced phosphorylation of Akt and glycogen synthase kinase 3β in blood cells; inhibited the LPS-induced increase in serum concentrations and/or tissue expression of adhesion molecules, monocyte chemoattractant protein 1, and TNFα; and attenuated NF-κB activation in lung, heart, and aorta. Lipoic acid also improved survival of endotoxemic mice. All of these antiinflammatory effects of LA were abolished by treatment of the animals with wortmannin. We conclude that LA inhibits LPS-induced monocyte activation and acute inflammatory responses in vitro and in vivo by activating the PI3K/Akt pathway. Lipoic acid may be useful in the prevention of sepsis and inflammatory vascular diseases.

Albumin selectively inhibits TNFα-induced expression of vascular cell adhesion molecule-1 in human aortic endothelial cells

OBJECTIVE Leukocyte adhesion to, and transmigration across, the vascular endothelium are critical initiating steps in inflammation and atherosclerosis. We hypothesized that albumin, the major plasma protein, acts as an anti-inflammatory agent towards endothelial cells. METHODS AND RESULTS To test the hypothesis, we studied the effects of bovine serum albumin (BSA) on TNF alpha-induced expression of adhesion molecules in cultured human aortic endothelial cells (HAEC). We found that incubation of HAEC for 16 h with BSA (0.5-5%, w/v) dose-dependently inhibited TNF alpha-induced mRNA and protein expression of vascular cell adhesion molecule-1 (VCAM-1), but not intercellular adhesion molecule-1 nor E-selectin. Yeast recombinant human serum albumin exerted similar inhibitory effects on VCAM-1 expression, whereas gamma-globulin was ineffective. BSA also significantly inhibited TNF alpha-induced adhesion of monocytic THP-1 cells to HAEC in a dose-dependent manner. Furthermore, BSA strongly inhibited activation and nuclear translocation of the transcription factor, nuclear factor-kappa B (NF-kappa B). For example, the physiologically relevant concentration of 5% BSA inhibited NF-kappa B activation by 90+/-7%, VCAM-1 mRNA and protein expression by 81+/-4 and 80+/-13%, respectively, and THP-1 adhesion by 73+/-9% (n=3). The inhibitory effect of BSA on TNF alpha-induced VCAM-1 expression was not attenuated by inhibition of intracellular GSH synthesis. CONCLUSIONS Our data show that physiological concentrations of albumin selectively inhibit TNF alpha-induced upregulation of VCAM-1 expression and monocyte adhesion, most likely by inhibiting NF-kappa B activation in a GSH-independent manner.

Intracellular metal ion chelators inhibit TNFα-induced SP-1 activation and adhesion molecule expression in human aortic endothelial cells

Endothelial adhesion molecule expression and monocyte recruitment are causal events in human atherosclerosis, and are believed to be caused, in part, by oxidative stress. Because redox-active transition metal ions, such as iron and copper, play an essential role in the generation of free radicals and the initiation and propagation of lipid peroxidation, we hypothesized that transition metal ions may also be involved in endothelial activation. Therefore, we investigated the effects of the intracellular iron-chelator, desferrioxamine (DFO), and the intracellular copper-chelator, neocuproine (NC), on TNFalpha-induced expression of adhesion molecules in human aortic endothelial cells (HAEC). Treatment of HAEC with DFO (0.01-0.1 mM) or NC (0.1 and 0.5 mM) time- and dose-dependently inhibited TNFalpha-induced protein expression of E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1). In contrast, iron-saturated DFO and the extracellular copper chelator, bathocuproinedisulfonic acid, had no effect on adhesion molecule expression. DFO and NC also dose-dependently inhibited TNFalpha-induced upregulation of adhesion molecule mRNA levels. Furthermore, treatment of HAEC with 0.5 mM DFO or NC completely inhibited TNFalpha-induced activation of the transcription factor, specificity protein-1 (SP-1), but only partially inhibited or did not affect activation of other transcription factors known to regulate adhesion molecule expression, i.e., nuclear factor kappaB (NFkappaB), activator protein-1 (AP-1), and interferon regulatory factor-1 (IRF-1). Finally, inhibition of endothelial nitric oxide synthase with N-nitro-L-arginine methylester (0.5 mM) did not attenuate the inhibitory effects of the metal ion chelators on adhesion molecule expression. Our data suggest that intracellular, but not extracellular, transition metal ions mediate inflammatory cytokine-induced SP-1 activation and adhesion molecule expression in endothelial cells.

Genetic deficiency of NADPH oxidase does not diminish, but rather enhances, LPS-induced acute inflammatory responses in vivo

Reactive oxygen species (ROS) and oxidative stress are thought to play a central role in the etiology of cell dysfunction and tissue damage in sepsis. However, there is limited and controversial evidence from in vivo studies that ROS mediate cell signaling processes that elicit acute inflammatory responses during sepsis. Because NADPH oxidase is one of the main cellular sources of ROS, we investigated the role of this enzyme in lipopolysaccharide (LPS)-induced acute inflammation in vivo, utilizing mice deficient in the gp91(phox) or p47(phox) subunits of NADPH oxidase. Age-and body weight-matched C57BL/6J wild-type (WT) and gp91(phox-/-) and p47(phox-/-) mice were injected ip with 50 microg LPS or saline vehicle and sacrificed at various time points up to 24 h. We found that LPS-induced acute inflammatory responses in serum and tissues were not significantly diminished in gp91(phox-/-) and p47(phox-/-) mice compared to WT mice. Rather, genetic deficiency of NADPH oxidase was associated with enhanced gene expression of inflammatory mediators and increased neutrophil recruitment to lung and heart. Furthermore, no protection from LPS-induced septic death was observed in either knockout strain. Our findings suggest that NADPH oxidase-mediated ROS production and cellular redox signaling do not promote, but instead limit, LPS-induced acute inflammatory responses in vivo.

The iron chelator, desferrioxamine, reduces inflammation and atherosclerotic lesion development in experimental mice

Vascular inflammation and monocyte recruitment are initiating events in atherosclerosis that have been suggested to be caused, in part, by iron-mediated oxidative stress and shifts in the intracellular redox environment of vascular cells. Therefore, the objective of this study was to investigate whether the intracellular iron chelator, desferrioxamine (DFO), reduces inflammation and atherosclerosis in experimental mice. Treatment of C57BL/6J mice with DFO (daily intraperitoneal injection of 100 mg/kg body weight for two weeks) strongly inhibited lipopolysaccharide-induced increases of soluble cellular adhesion molecules and monocyte chemoattractant protein-1 (MCP-1) in the serum and activation of the redox-sensitive transcription factors, nuclear factor-κB and activator protein-1, in the aorta. Furthermore, treatment of apolipoprotein E-deficient (apoE−/−) mice with DFO (100 mg/kg, intraperitoneal, daily for 10 weeks) attenuated aortic atherosclerotic lesion development by 26% (P < 0.05). DFO treatment of apoE−/− mice also lowered serum levels of MCP-1 and gene expression of proinflammatory and macrophage markers in the aorta and heart, in parallel with increased protein expression of the transferrin receptor in the heart and liver. In contrast, DFO treatment had no effect on serum cholesterol and triglyceride levels. These data show that DFO inhibits inflammation and atherosclerosis in experimental mice, providing the proof-of-concept for an important role of iron in atherogenesis. Whether eliminating excess iron is a useful adjunct for the prevention or treatment of atherosclerosis in humans remains to be investigated.

Lipoic acid and vitamin C potentiate nitric oxide synthesis in human aortic endothelial cells independently of cellular glutathione status

Abstract Vitamin C and thiol agents improve vasomotor function. To determine whether these compounds directly affect endothelial function, nitric oxide (NO) synthesis was measured in human aortic endothelial cells treated with ascorbic acid or the thiol modulating agents lipoic acid or L-2-oxothiazolidine-4-carboxylic acid (OTC). A dose-dependent increase in A23187-stimulated NO synthesis and elevated cGMP levels were observed in all cases except for OTC. Cellular GSH levels were not significantly increased, and the GSH/GSSG ratio was not significantly affected by treatment of the cells with lipoic acid, OTC, or ascorbic acid. Thus, vitamin C and lipoic acid potentiate endothelial NO synthesis and bioactivity by mechanisms that appear to be independent of cellular GSH levels and redox environment.

Genetic ablation of phagocytic NADPH oxidase in mice limits TNFα-induced inflammation in the lungs but not other tissues

In vitro and limited in vivo evidence suggests that reactive oxygen species derived from NADPH oxidases (NOX-ROS) play an important role in inflammatory responses by enhancing the activity of redox-sensitive cell signaling pathways and transcription factors. Here, we investigated the role of NOX-ROS in TNFα-induced acute inflammatory responses in vivo, using mice deficient in the gp91(phox) (NOX2) or p47(phox) subunits of NADPH oxidase. Age- and body weight-matched C57BL/6J wild-type (WT) and gp91(phox) or p47(phox) knockout mice were injected intraperitoneally with 50 μg TNFα/kg bw or saline vehicle control and sacrificed at various time points up to 24 h. Compared to WT mice, gp91(phox -/-) mice exhibited significantly diminished (P<0.05) TNFα-induced acute inflammatory responses in the lungs but not other tissues, including heart, liver, and kidney, as evidenced by decreased activation of the redox-sensitive transcription factor NF-κB, and decreased gene expression of interleukin (IL)-1β, IL-6, TNFα, E-selectin, and other cellular adhesion molecules. Similar results were observed in p47(phox -/-) mice. Interestingly, decreased lung inflammation in knockout mice was accompanied by increased leukocyte infiltration into the lungs compared to other tissues. Our data suggest that phagocytic NOX-ROS signaling plays a critical role in promoting TNFα-induced, NF-κB-dependent acute inflammatory responses and tissue injury specifically in the lungs, which is effected by preferential leukocyte infiltration.

Astragaloside IV Inhibits NF-κB Activation and Inflammatory Gene Expression in LPS-Treated Mice

In this study we investigated the role of astragaloside IV (AS-IV), one of the major active constituents purified from the Chinese medicinal herb Astragalus membranaceus, in LPS-induced acute inflammatory responses in mice in vivo and examined possible underlying mechanisms. Mice were assigned to four groups: vehicle-treated control animals; AS-IV-treated animals (10 mg/kg b.w. AS-IV daily i.p. injection for 6 days); LPS-treated animals; and AS-IV plus LPS-treated animals. We found that AS-IV treatment significantly inhibited LPS-induced increases in serum levels of MCP-1 and TNF by 82% and 49%, respectively. AS-IV also inhibited LPS-induced upregulation of inflammatory gene expression in different organs. Lung mRNA levels of cellular adhesion molecules, MCP-1, TNFα, IL-6, and TLR4 were significantly attenuated, and lung neutrophil infiltration and activation were strongly inhibited, as reflected by decreased myeloperoxidase content, when the mice were pretreated with AS-IV. Similar results were observed in heart, aorta, kidney, and liver. Furthermore, AS-IV significantly suppressed LPS-induced NF-κB and AP-1 DNA-binding activities in lung and heart. In conclusion, our data provide new in vivo evidence that AS-IV effectively inhibits LPS-induced acute inflammatory responses by modulating NF-κB and AP-1 signaling pathways. Our results suggest that AS-IV may be useful for the prevention or treatment of inflammatory diseases.

Copper chelation by tetrathiomolybdate inhibits lipopolysaccharide-induced inflammatory responses in vivo

Redox-active transition metal ions, such as iron and copper, may play an important role in vascular inflammation, which is an etiologic factor in atherosclerotic vascular diseases. In this study, we investigated whether tetrathiomolybdate (TTM), a highly specific copper chelator, can act as an anti-inflammatory agent, preventing lipopolysaccharide (LPS)-induced inflammatory responses in vivo. Female C57BL/6N mice were daily gavaged with TTM (30 mg/kg body wt) or vehicle control. After 3 wk, animals were injected intraperitoneally with 50 μg LPS or saline buffer and killed 3 h later. Treatment with TTM reduced serum ceruloplasmin activity by 43%, a surrogate marker of bioavailable copper, in the absence of detectable hepatotoxicity. The concentrations of both copper and molybdenum increased in various tissues, whereas the copper-to-molybdenum ratio decreased, consistent with reduced copper bioavailability. TTM treatment did not have a significant effect on superoxide dismutase activity in heart and liver. Furthermore, TTM significantly inhibited LPS-induced inflammatory gene transcription in aorta and heart, including vascular and intercellular adhesion molecule-1 (VCAM-1 and ICAM-1, respectively), monocyte chemotactic protein-1 (MCP-1), interleukin-6, and tumor necrosis factor (TNF)-α (ANOVA, P < 0.05); consistently, protein levels of VCAM-1, ICAM-1, and MCP-1 in heart were also significantly lower in TTM-treated animals. Similar inhibitory effects of TTM were observed on activation of nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) in heart and lungs. Finally, TTM significantly inhibited LPS-induced increases of serum levels of soluble ICAM-1, MCP-1, and TNF-α (ANOVA, P < 0.05). These data indicate that copper chelation with TTM inhibits LPS-induced inflammatory responses in aorta and other tissues of mice, most likely by inhibiting activation of the redox-sensitive transcription factors, NF-κB and AP-1. Therefore, copper appears to play an important role in vascular inflammation, and TTM may have value as an anti-inflammatory or anti-atherogenic agent.