Effect of lipopolysaccharide and lipid A on mouse liver pyruvate kinase activity

Leishmania infantum modulates host macrophage mitochondrial metabolism by hijacking the SIRT1-AMPK axis

Metabolic manipulation of host cells by intracellular pathogens is currently recognized to play an important role in the pathology of infection. Nevertheless, little information is available regarding mitochondrial energy metabolism in Leishmania infected macrophages. Here, we demonstrate that during L. infantum infection, macrophages switch from an early glycolytic metabolism to an oxidative phosphorylation, and this metabolic deviation requires SIRT1 and LKB1/AMPK. SIRT1 or LBK1 deficient macrophages infected with L. infantum failed to activate AMPK and up-regulate its targets such as Slc2a4 and Ppargc1a, which are essential for parasite growth. As a result, impairment of metabolic switch caused by SIRT1 or AMPK deficiency reduces parasite load in vitro and in vivo. Overall, our work demonstrates the importance of SIRT1 and AMPK energetic sensors for parasite intracellular survival and proliferation, highlighting the modulation of these proteins as potential therapeutic targets for the treatment of leishmaniasis.

Lycium barbarum polysaccharide LBPF4-OL may be a new Toll-like receptor 4/MD2-MAPK signaling pathway activator and inducer

Recognition of the utility of the traditional Chinese medicine Lycium barbarum L. has been gradually increasing in Europe and the Americas. Many immunoregulation and antitumor effects of L. barbarum polysaccharides (LBP) have been reported, but its molecular mechanism is not yet clear. In this study, we reported that the activity of the polysaccharide LBPF4-OL, which was purified from LBP, is closely associated with the TLR4-MAPK signaling pathway. We found that LBPF4-OL can significantly induce TNF-α and IL-1β production in peritoneal macrophages isolated from wild-type (C3H/HeN) but not TLR4-deficient mice (C3H/HeJ). We also determined that the proliferation of LBPF4-OL-stimulated lymphocytes from C3H/HeJ mice is significantly weaker than that of lymphocytes from C3H/HeN mice. Furthermore, through a bio-layer interferometry assay, we found that LPS but not LBPF4-OL can directly associate with the TLR4/MD2 molecular complex. Flow cytometry analysis indicated that LBPF4-OL markedly upregulates TLR4/MD2 expression in both peritoneal macrophages and Raw264.7 cells. As its mechanism of action, LBPF4-OL increases the phosphorylation of p38-MAPK and inhibits the phosphorylation of JNK and ERK1/2, as was observed through Western blot analysis. These data suggest that the L. barbarum polysaccharide LBPF4-OL is a new Toll-like receptor 4/MD2-MAPK signaling pathway activator and inducer.

Inverse gene expression patterns for macrophage activating hepatotoxicants and peroxisome proliferators in rat liver

Macrophage activation contributes to adverse effects produced by a number of hepatotoxic compounds. Transcriptional profiles elicited by two macrophage activators, LPS and zymosan A, were compared to those produced by 100 paradigm compounds (mostly hepatotoxicants) using cDNA microarrays. Several hepatotoxicants previously reported to activate liver macrophages produced transcriptional responses similar to LPS and zymosan, and these were used to construct a gene signature profile for macrophage activators in the liver. Measurement of cytokine mRNAs in the same liver samples by RT-PCR independently confirmed that these compounds are associated with macrophage activation. In addition to expected effects on acute phase proteins and metabolic pathways that are regulated by LPS and inflammation, a strong induction was observed for many endoplasmic reticulum-associated stress/chaperone proteins. Additionally, many genes in our macrophage activator signature profile were well-characterized PPARalpha-induced genes which were repressed by macrophage activators. A shared gene signature profile for peroxisome proliferators was determined using a training set of clofibrate, WY 14643, diethylhexylphthalate, diisononylphthalate, perfluorodecanoic acid, perfluoroheptanoic acid, and perfluorooctanoic acid. The signature profile included macrophage activator-induced genes that were repressed by peroxisome proliferators. NSAIDs comprised an interesting pharmacological class in that some compounds, notably diflunisal, co-clustered with peroxisome proliferators whereas several others co-clustered with macrophage activators, possibly due to endotoxin exposure secondary to their adverse effects on the gastrointestinal system. While much of these data confirmed findings from the literature, the transcriptional patterns detected using this toxicogenomics approach showed relationships between genes and biological pathways requiring complex analysis to be discerned.

Hydroxyl radical generation and membrane fluidity of erythrocytes treated with lipopolysaccharide

The effect of lipopolysaccharide (LPS) and/or bile acids on rat erythrocyte membranes was studied in vitro. Addition of LPS isolated from E. coli (J5 mutant) into the erythrocyte resulted in the decrease of membrane fluidity as determined by spin labelling using electron paramagnetic resonance (EPR). This was accompanied by membrane fragility. It was found that hydroxyl radicals were generated from erythrocytes treated with LPS by using DMPO spin trapping. However, pretreatment of erythrocytes with taurine-conjugated bile acids was found to modify the membrane response induced by LPS. Taurocholic acid (TCA) and tauroursodeoxycholic acid (TUDCA) prevented the decrease of membrane fluidity induced by LPS, and, as a result, the membrane integrity was maintained although no significant changes were observed in the amount of hydroxyl radicals produced by LPS addition. However, taurochenodeoxycholic acid (TCDCA) exhibited little beneficial effect on the dynamic properties and the function of the erythrocyte membranes, although the hydroxyl radical declined markedly in the erythrocytes. Therefore, it is suggested that TCA and TUDCA have a protective effect against LPS-induced membrane fragility by modulating membrane fluidity.

Altered transcriptional regulation of phosphoenolpyruvate carboxykinase in rats following endotoxin treatment

The molecular mechanism involved in altered regulation of the rate-limiting enzyme in hepatic gluconeogenesis, phosphoenolpyruvate carboxykinase (PEPCK), during endotoxemia is not completely understood. We examined, therefore, the effect of a nonlethal dose of Escherichia coli endotoxin on PEPCK gene expression in fasted rats. 5 h after endotoxin treatment, the PEPCK transcription rate and the amount of mRNA(PEPCK) were significantly decreased at a time when the insulin/glucagon (I/G) molar ratio and plasma corticosterone levels were significantly increased. Similar results were observed in a time course study, in which altered cAMP induction of PEPCK gene expression paralleled changes in the I/G molar ratio. In diabetic rats treated with endotoxin, PEPCK gene expression was decreased in the absence, however, of an increased I/G molar ratio. This finding indicates that other factors, such as inflammatory mediators or cytokines, alter PEPCK gene transcription during endotoxemia. IL-6, a putative mediator of endotoxin action in the liver, had no effect on PEPCK gene expression in fasted rats, but did decrease cAMP induction of PEPCK gene expression. These results indicate that, during endotoxemia, regulation of PEPCK gene expression is influenced by inflammatory mediators in addition to the classical endocrine hormones. IL-6, however, does not appear to be involved directly in the altered regulation of the PEPCK gene during endotoxemia.

The characteristics and site of inhibition of gluconeogenesis in rat liver cells by bacterial endotoxin. Stimulation of phosphofructokinase-1

The characteristics and site of inhibition of gluconeogenesis by endotoxin were investigated in liver cells isolated from control and endotoxin-treated rats. Endotoxin treatment was associated with inhibition (40-50%) of gluconeogenesis from lactate plus pyruvate over a range of concentrations of substrate and of oleate and with or without glucose or glucagon. Similar inhibition was observed with asparagine, proline, glutamine, alanine and a substrate mixture, but not with glycerol, glyceraldehyde, dihydroxyacetone or endogenous substrates. There was no change in cellular ATP content or in the rates of ketogenesis or ureogenesis from asparagine, proline or glutamine. Other effects on isotopic fluxes, metabolite contents, enzyme activities and control coefficients were consistent with the suggestion that the effects of endotoxin on gluconeogenesis are exerted at the level of phosphofructokinase-1, and not at phosphoenolpyruvate carboxykinase, pyruvate kinase, pyruvate carboxylase or glucokinase.

The use of polymyxin B and C3H/HeJ mouse spleen cells as criteria for endotoxin contamination

We have performed experiments designed to evaluate the potential contribution of endotoxin contamination to lymphocyte reponses. Saline and EDTA extracts of 4 different strains of gram negative bacteria were examined for their capacity to initiate mitogenic responses in murine spleen cells. As compared to phenol extracts of these bacteria which contain primarily lipopolysaccharide-LPS, these saline and EDTA extracts were significantly less active in this assay. The mitogenic activity which was present was also manifest in spleen cells from the C3H/HeJ mouse, whereas phenol-extracted LPS preparations were inactive. In addition, mitogenic activity of saline and EDTA extracts was not blocked by polymyxin B, an agent known to abrogate LPS mediated responses. We conclude that LPS contamination may not normally be as significant a problem as had earlier been assumed. However, when endotoxin contamination is present, neither the use of C3H/HeJ spleen cells nor polymyxin B is an appropriate test to evaluate this possibility.

Immunologic responsiveness of the C3H/HeJ mouse: differential ability of butanol-extracted lipopolysaccharide (LPS) to evoke LPS-mediated effects

The lipopolysaccharide (LPS)-protein complex extracted from the cell wall of Escherichia coli K235 by the butanol-water technique has been shown to evoke a mitogenic response in bone marrow-derived (B) lymphocytes from the C3H/HeJ mouse strain. These mice are resistant to the effects of LPS extracted with phenol. Therefore, the ability of butanol-extracted LPS to modulate a spectrum of C3H/HeJ B-cell functions was investigated. Both butanol-extracted (LPS-B) and phenol-extracted (LPS-P) LPS preparations activated responder C3H/St spleen cell cultures to polyclonal antibody production, while only LPS-B activated C3H/HeJ spleen cells. Both LPS-P and LPS-B acted as adjuvants when injected after aggregated human gamma globulin (HGG) in C3H/St mice, but neither preparation was effective as a adjuvant in C3H/HeJ mice. LPS-P injected with deaggregated HGG (tolerogen) into LPS-sensitive mice has been shown previously to inhibit the induction of tolerance HGG. In the present studies, it was shown that LPS-B, but not LPs-p, was able to inhibit tolerance induction to HGG in the C3H/HeJ, whereas both preparations were effective in the C3H/St. LPS has also been shown to bypass tolerant T cells in LPS-sensitive mice late in tolerance to HGG at a time when B cells are responsive. However, in the C3H/HeJ, neither LPS-B nor LPS-P was capable of this function. The responsiveness of these B cells to HGG was demonstrated in transfer experiments. Thus, in the C3H/HeJ, LPS-B stimulates mitogenesis, polyclonal B-cell activation, and inhibition of tolerance induction, but cannot act as an effective adjuvant or as a bypass mechanism to activate B cells in the presence of tolerant T cells. The explanation for this pattern of responses may be attributable to yet another cellular defect in the C3H/HeJ mouse.

Lipid A-induced tolerance and hyperreactivity to hypothermia in mice

Mice responded to lipopolysaccharide (LPS) with a dose-dependent, monophasic hypothermia reaching a maximum at 2 h postinjection. Degraded polysaccharide was not active; free lipid A, however, induced a similar pattern of hypothermia, indicating that the hypothermic principle of LPS was embedded within the lipid A component. The hypothermic response of mice to LPS was modified by prior exposure of the host to LPS. This altered reactivity was manifested by refractory periods (early and late tolerance), in which animals no longer responded with hypothermia, or a hyperreactive phase (hypersensitivity), in which hypothermic responses were greatly augmented upon LPS challenge. Thus, tolerance observed 24 h after a single injection of LPS (early tolerance) was followed, on further LPS challenge, by an enhanced hypothermic responses reaching a maximum on day 4. Further daily exposure of the animals to LPS eliminated hyperreactivity and led to the establishment of a late tolerance maximally expressed on day 8. Hyperreactivity could also be evoked on day 4 after a single injection of LPS. Mice pretreated with Salmonella S- and R-form LPS or free lipid A (Salmonella) demonstrated tolerance and hyperreactivity to both homologous and heterologous challenge. In addition, complete cross-tolerance was observed with S-form LPS derived from Shigella. It was concluded that the differential effects of LPS on host responses (tolerance and hyperreactivity) were due to lipid A.