Chromous siloxides of variable nuclearity and magnetism.

Treatment of Cr[N(SiMe3)2]2(thf)2 with HOSiR3 (R = Et, iPr) in THF afforded the bridged CrII siloxide complexes Cr3(OSiEt3)2(µ-OSiEt3)4(thf)2 and Cr2(OSiiPr3)2(µ-OSiiPr3)2(thf)2 in high yield. Exposure of these compounds to vacuum in aliphatic solvents led to the loss of coordinated THF and to the formation of the homoleptic chromous siloxides Cr4(µ-OSiEt3)8 and Cr3(OSiiPr3)2(µ-OSiiPr3)4, respectively, in moderate to high yield. Use of TMEDA as a potentially bidentate donor molecule gave the monomeric cis-coordinated siloxide Cr(OSiiPr3)2(tmeda) (tmeda = N,N,N',N'-tetramethylethane-1,2-diamine). Oxidation of Cr2(OSiiPr3)2(µ-OSiiPr3)2(thf)2 with CHI3 and C2Cl6 produced the trigonal bipyramidal chromic compound CrIII(OSiiPr)3(thf)2 and asymmetrically coordinated Cr2Cl3(OSiiPr3)3(thf)3, respectively. Magnetic measurements (Evans and SQUID) hinted at (a) antiferromagnetic interactions between the CrII centres, (b) revealed higher effective magnetic moments (µeff) for cis-coordinated monomeric heteroleptic complexes compared to trans-coordinated ones, and (c) pointed out the highest (µeff) for the tetranuclear complex Cr4(µ-OSiEt3)8 (6.26µB, SQUID, 300 K; Cr⋯Cradjacent avg. 2.535 A).

Salmonella typhimurium translocates flagellin across intestinal epithelia, inducing a proinflammatory response.

This study investigated whether soluble paracrine factors mediated Salmonella-induced IL-8 expression in polarized model intestinal epithelia. We found that the basolateral media of model epithelia that had been apically infected with Salmonella typhimurium for a short period (10 minutes) could activate IL-8 secretion in virgin model epithelia, demonstrating that a proinflammatory factor (PIF) was indeed present. Initial characterization found that PIF was a heat-stable protein with a molecular mass of about 50 kDa that acts on the basolateral, but not apical, surface of model intestinal epithelia to elicit IL-8 secretion. PIF was not present in the media of model epithelia stimulated with other inducers of IL-8 secretion (TNF-alpha or carbachol) but was present in S. typhimurium supernatants, indicating PIF is of bacterial origin. PIF was purified from bacterial culture supernatants by anion/cation exchange chromatography and SDS-PAGE and found by using microsequencing to be the protein flagellin. In support of this finding, flagellin-deficient S. typhimurium mutants did not secrete detectable levels of PIF (i.e., a bioactivity that induced IL-8 secretion when placed basolaterally on model epithelia). Furthermore, viable flagellin-deficient mutant organisms (fliC/fljB and flhD) failed to elicit IL-8 secretion when added apically to model intestinal epithelia. These findings indicate that translocation of flagellin across epithelia, subsequent to apical epithelial-S. typhimurium interaction, is likely a major means of activating a mucosal inflammatory response.

Salmonella typhimurium induces epithelial IL-8 expression via Ca(2+)-mediated activation of the NF-kappaB pathway.

Interactions between the enteric pathogen Salmonella typhimurium and the luminal surface of the intestine provoke an acute inflammatory response, mediated in part by epithelial cell secretion of the chemokine IL-8 and other proinflammatory molecules. This study investigated the mechanism by which this pathogen induces IL-8 secretion in physiologically polarized model intestinal epithelia. IL-8 secretion induced by both the prototypical proinflammatory cytokine TNF-alpha and S. typhimurium was NF-kappaB dependent. However, NF-kappaB activation and IL-8 secretion induced by S. typhimurium, but not by TNF-alpha, was preceded by and required an increase in intracellular [Ca(2+)]. Additionally, agonists that increased intracellular [Ca(2+)] by receptor-dependent (carbachol) or independent (thapsigargin, ionomycin) means also induced IL-8 secretion. Furthermore, the ability of S. typhimurium mutants to induce IkappaB-alpha degradation, NF-kappaB translocation, and IL-8 transcription and secretion correlated precisely with their ability to induce an intracellular [Ca(2+)] increase in model intestinal epithelia, but not with their ability to invade these cells. Finally, S. typhimurium, but not TNF-alpha, induced a Ca(2+)-dependent phosphorylation of IkappaB-alpha. These results indicate that S. typhimurium-induced activation of NF-kappaB-dependent epithelial inflammatory responses proceeds by a Ca(2+)-mediated activation of an IkappaB-alpha kinase. These observations raise the possibility that pharmacologic intervention of the acute inflammatory response can be selectively matched to the specific class of initiating event.