Ammonium decreases human polymorphonuclear leukocyte cytoskeletal actin

Amniotic fluid neutrophils can phagocytize bacteria: A mechanism for microbial killing in the amniotic cavity

PROBLEM

Neutrophils are capable of performing phagocytosis, a primary mechanism for microbial killing. Intra-amniotic infection is characterized by an influx of neutrophils into the amniotic cavity. Herein, we investigated whether amniotic fluid neutrophils could phagocytize bacteria found in the amniotic cavity of women with intra-amniotic infection.

METHODS

Amniotic fluid neutrophils from women with intra-amniotic infection were visualized by transmission electron microscopy (n=6). The phagocytic activity of amniotic fluid neutrophils from women with intra-amniotic infection and/or inflammation (n=10) or peripheral neutrophils from healthy individuals (controls, n=3) was tested using ex vivo phagocytosis assays coupled with live imaging. Phagocytosis by amniotic fluid neutrophils was also visualized by confocal microscopy (n=10) as well as scanning and transmission electron microscopy (n=5).

RESULTS

(i) Intra-amniotic infection-related bacteria including cocci (eg Streptococcus agalactiae), bacilli (eg Bacteriodes fragilis and Prevotella spp.), and small bacteria without a cell wall (eg Ureaplasma urealyticum) were found inside of amniotic fluid neutrophils; (ii) peripheral neutrophils (controls) rapidly phagocytized S. agalactiae, U. urealyticum, Gardnerella vaginalis, and Escherichia coli; (iii) amniotic fluid neutrophils rapidly phagocytized S. agalactiae and G. vaginalis; and (iv) amniotic fluid neutrophils slowly phagocytized U. urealyticum and E. coli; yet, the process of phagocytosis of the genital mycoplasma was lengthier.

CONCLUSION

Amniotic fluid neutrophils can phagocytize bacteria found in the amniotic cavity of women with intra-amniotic infection, namely S. agalactiae, U. urealyticum, G. vaginalis, and E. coli. Yet, differences in the rapidity of phagocytosis were observed among the studied microorganisms. These findings provide a host defense mechanism whereby amniotic fluid neutrophils can kill microbes invading the amniotic cavity.

Cytochalasin D can improve heterologous protein productivity in adherent Chinese hamster ovary cells

We generated a series of adherent gene-amplified CHO clones expressing human secreted alkaline phosphatase (SEAP) as a model for heterologous protein production. Clones demonstrate a 26- to 52-fold increase in productivity compared to controls after dhfr/methotrexate-mediated gene amplification and clone selection. SEAP is stably expressed in these clones over at least a 6-week period without significant productivity loss. Two-dimensional protein electrophoresis identified 21 proteins that exhibited altered expression in clones of increasing SEAP productivity. Based on MALDI TOF/TOF mass spectrometry of relevant protein spots, changes in translation, energy pathways, chaperones, regulatory proteins, and cytoskeletal proteins were observed, including a 4-fold expression increase in actin capping protein. We hypothesized that an alteration of the actin cytoskeleton using cytochalasin D as a mimic for actin-capping protein could have a beneficial effect on heterologous protein secretion. Treatment with 0.5 mug/mL cytochalasin D increased SEAP productivity 2- to 3-fold compared to an amplified control which resulted in an increase in productivity from 52- to 150-fold compared to a nonamplified parent.

Ammonium affects tight junctions and the cytoskeleton in MDCK cells

In the kidney medulla, tubule cells are exposed not only to elevated NaCl but also to high NH(4)Cl concentrations. Although it is well known that long-term exposure to high NaCl concentrations leads to reorganization of the actin-based cytoskeleton and to altered transport properties of renal epithelial cells, there have been no comparable studies on the effects of elevated extracellular NH(4)Cl concentrations. We therefore examined the effect of prolonged (up to 72 h) exposure of Madin-Darby canine kidney (MDCK) cells to increased NH(4)Cl concentrations on the actin-based cytoskeleton, the transepithelial electrical resistance (TER) and the expression and intracellular distribution of the tight junction protein occludin. NH(4)Cl exposure resulted in rarefaction of cytoplasmic stress fibres, formation of intense peripheral actin bands and reduced abundance of both F- and G-actin. While under control conditions occludin staining was restricted to the tight junction region, ample dot-like intracellular staining was apparent after NH(4)Cl exposure. These changes in cell structure were associated with an increase in TER and the enhanced expression of an additional putative, 40-kDa occludin isoform. Exposure to elevated extracellular NH(4)Cl concentrations thus leads to distinct alterations in the architecture and transepithelial transport properties of MDCK cells that may also be relevant for the tubule cells of the renal inner medulla.

Helicobacter pylori lipopolysaccharide hinders polymorphonuclear leucocyte apoptosis

A prominent histologic feature of Helicobacter pylori infection is a dense infiltration of polymorphonuclear leukocytes (PMNL) in gastric mucosa. H. pylori lipopolysaccharide (LPS) has been recognized as a primary virulence factor evoking acute mucosal inflammatory reaction. Previous works have shown that H. pylori LPS immunologic activities are lower than those of enterobacterial LPS. However, the effect of H. pylori LPS on spontaneous PMNL apoptosis, and mechanisms by which this H. pylori LPS may promote PMNL survival remain to be established. In this study, we investigated, by both morphologic and biochemical approaches, the action of H. pylori LPS on PMNL apoptosis in vitro, using broth culture filtrates (BCF) of H. pylori strains with different genotypes. We found that BCF from H. pylori caused a significant delay in spontaneous PMNL apoptosis and this delay was independent of the VacA, cag pathogenicity island and urease status. We demonstrated that LPS in BCF is responsible for this effect because it was abrogated by the LPS antagonist B287 (a synthetic analog of Rhodobactersphaeroides lipid A). Moreover, BCF from H. pylori induced P42/44MAP kinase activation in PMNL. Similar results were obtained with BCF of an Escherichia coli strain. Taken together these data suggest that longer survival of PMNL induced by H. pylori LPS may increase gastric epithelium injury in H. pylori-associated diseases.

Intracellular alkalinisation in Vero cells parasitised by Trypanosoma cruzi

We studied the intracellular pH of Vero cells parasitised by Trypanosoma cruzi, using different methods: fluorimetric measurement after labelling the cells with the pH-sensitive intracellular fluorescent dye 2',7',-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester; flow cytometry; and image analysis after staining the cells with neutral-red vital stain. The results show that the intracellular pH of the parasitised cells rose in comparison with that of the uninfected control cells. A study of the population of parasitised cells made by flow cytometry allowed us to subdivide the cells from the infected cultures into two populations according to their pH as obtained by fluorimetric measurements. Image analysis showed that the cell cytoplasm was more alkaline in the vicinity of the sites containing parasites. Treatment of the parasitised cells with amiloride, ouabain, or with 4.4'-diisothiocyano-2,2'-stilbene disulphate consistently lowered the pH values of the parasitised cells, but not sufficiently to return to the values of the non-parasitised control cells. When the control cells were subject to similar treatments with the inhibitors, only amiloride acidified the cytoplasm to any extent. The basification undergone by the parasitised cells was independent of the transport systems and may be a consequence of the release of NH4+ by the intracellular amastigotes.

A comparison of changes in nucleotide-protein interactions in the striatal, hippocampus and paramedian cortex after cerebral ischemia and reperfusion: correlations to regional vulnerability

[32P]Azido-purine analogs of ATP and GTP were used to detect changes in phosphorylation and nucleotide binding induced by ischemia and subsequent reperfusion in rat brain striatum, hippocampus and paramedian cortex (PM cortex) tissues. Major changes in phosphorylation were observed for a 130-kDa protein, tentatively identified as the Ca2+ transport ATPase, and calcium/calmodulin-dependent protein kinase II (CaM Kinase II) in all tissues. However, recovery of the phosphorylation of the 130-kDa protein occurred only in the PM cortex on reperfusion. A 200-300% increase in [32P]8N3ATP photoinsertions was observed in the striatum and hippocampus regions for a 43-kDa protein with an isoelectric point of 6.8. This protein was identified as glutamine synthetase (GS) and the increase in binding was found to be due to both increased copy number and activation by Mn2+. An increase in [32P]8N3GTP photoinsertion into a 55-kDa protein, identified as the beta-subunit of tubulin, was found only in the striatum and hippocampus. This indicates the depolymerization of microtubulin in these tissues. These changes correlate to the vulnerability of the striatum and hippocampus to ischemia-induced neuronal death.

NH4Cl activates AE2 anion exchanger in Xenopus oocytes at acidic pHi

In the course of experiments to define regulation by intracellular pH (pHi) of the AE2 anion exchanger expressed in Xenopus oocytes, we discovered an unexpected regulation of AE2 by NH4+. Intracellular acidification produced by extracellular acidification or produced by equimolar substitution of NaCl with sodium acetate each inhibited AE2 activity. In contrast, intracellular acidification by equimolar substitution of NaCl with NH4Cl activated AE2-associated, trans-anion-dependent, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive 36Cl- influx and efflux. Regulation by NH4+ was isoform specific, since neither erythroid nor kidney AE1 was activated. AE2 activation was maximal at <5 mM NH4Cl; was not mimicked by extracellular KCl, chloroquine, or polyamines; and was insensitive to amiloride, bumetanide, barium, and gadolinium. Whether NH4Cl acts directly on AE2 or on another target remains to be determined. Activation of AE2 by NH4+ may serve to sustain Cl-/HCO3- exchange activity in the presence of acidic pH in renal medulla, colon, abscesses, and other AE2-expressing acidic locales exposed to elevated NH4+ concentration.

Ammonia inhibits cAMP-regulated intestinal Cl- transport. Asymmetric effects of apical and basolateral exposure and implications for epithelial barrier function

The colon, unlike most organs, is normally exposed to high concentrations of ammonia, a weak base which exerts profound and diverse biological effects on mammalian cells. The impact of ammonia on intestinal cell function is largely unknown despite its concentration of 4-70 mM in the colonic lumen. The human intestinal epithelial cell line T84 was used to model electrogenic Cl- secretion, the transport event which hydrates mucosal surfaces and accounts for secretory diarrhea. Transepithelial transport and isotopic flux analysis indicated that physiologically-relevant concentrations of ammonia (as NH4Cl) markedly inhibit cyclic nucleotide-regulated Cl- secretion but not the response to the Ca2+ agonist carbachol. Inhibition by ammonia was 25-fold more potent with basolateral compared to apical exposure. Ion substitution indicated that the effect of NH4Cl was not due to altered cation composition or membrane potential. The site of action of ammonia is distal to cAMP generation and is not due simply to cytoplasmic alkalization. The results support a novel role for ammonia as an inhibitory modulator of intestinal epithelial Cl- secretion. Secretory responsiveness may be dampened in pathological conditions associated with increased mucosal permeability due to enhanced access of lumenal ammonia to the basolateral epithelial compartment.

Effect of cytochalasin D on the mechanical properties and morphology of passive human neutrophils

The actin-rich cortex plays a major role in neutrophil chemotaxis and phagocytosis. In passive neutrophils, 30-50% of the actin molecules are in the F (filamentous) form, and it is the shifting of equilibrium with its monomeric G (globular) form that controls cell motility and phagocytosis. Cytochalasins have been shown to inhibit cell phagocytosis and ruffling. In purified actin, cytochalasins have been shown to decrease the amount of F-actin by capping the fast-growth end of actin filaments. Recent studies with intact cells, however, reveal that the most potent cytochalasin, cytochalasin D (CD), actually increases F-actin content suggesting that CD disrupts the actin network so as to increase the number of actin-filament ends for further actin polymerization. In this paper, we report the effects of CD on the passive mechanical behavior and morphology of human neutrophils with 1, 2, 10, and 20 microM CD. At 1 and 2 microM CD, the cells remain spherical. However, in the presence of 10 and 20 microM CD, cells are severely deformed and "blebby" as shown by light and scanning electron microscopy. After 1 and 2 microM CD treatment, the cells show a decrease of 43 and 66%, respectively, in cortical tension when measured by static micropipet aspiration experiments. Similarly, the cytoplasmic viscosities of 1 and 2 microM CD-treated cells are decreased, but only by 17 and 24%, respectively. A proportionally greater effect on the cortical tension suggests that CD acts mainly on the actin-rich cortex by disrupting the filament network.

Propionate induces polymorphonuclear leukocyte activation and inhibits formylmethionyl-leucyl-phenylalanine-stimulated activation

Short-chain carboxylic acids (SCCA) are metabolic by-products of bacterial pathogens which can alter cytoplasmic pH and inhibit a variety of polymorphonuclear leukocyte (PMN) motile functions. Since cytoskeletal F-actin alterations are central to PMN mobility, in this study we examined the effects of SCCA on cytoskeletal F-actin. Initially, we tested nine SCCA (formate, acetate, propionate, butyrate, valerate, caproate, lactate, succinate, and isobutyrate). We document here that while eight altered cytoplasmic pH, only six altered cytoskeletal F-actin. We then selected one SCCA that altered both F-actin and cytoplasmic pH (propionate) and one SCCA that altered only cytoplasmic pH (lactate) for further study. Propionate, but not lactate, caused an irregular cell shape and F-actin distribution. Furthermore, propionate, but not lactate, inhibited formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated PMN polarization, F-actin localization, and cytoplasmic pH oscillation. Propionate-induced changes in cytoskeletal F-actin and cytoplasmic acidification were not affected by the fMLP receptor antagonist N-t-BOC-1-methionyl-1-leucyl-1-phenylalanine; however, alkalinization was affected. Pertussis toxin treatment completely inhibited propionate-induced changes in F-actin but had no effect on propionate-induced cytoplasmic pH oscillation. These results indicate that propionate (i) bypasses the fMLP receptor and G protein(s) to induce cytoplasmic pH oscillation, (ii) operates through G protein(s) to induce actin oscillation, cell shape changes (to irregular), and F-actin localization, and (iii) inhibits fMLP-stimulated cytoplasmic pH and actin oscillation, PMN polarization, and F-actin localization.

Cytochalasins induce actin polymerization in human leukocytes

We studied the effect of cytochalasins (B, D, and E) on the F-actin content in human neutrophils and lymphocytes using NBD-phallacidin labeling followed by flow cytometry. All three cytochalasins induced a concentration- and time-dependent increase in the F-actin content in both cell types. The order of potency was cytochalasin D greater than E greater than B. The increase in F-actin content was accompanied by a decrease in the G-actin content as measured by DNase I inhibition assay. These observations suggest that in intact cells cytochalasins may function differently compared to purified and semipurified systems, and their effects may be modified through other actin-binding or sequestering proteins. 2-deoxyglucose (20 mM) caused a decrease in the basal F-actin content and significantly reduced the change induced by the cytochalasins. These results suggest that the state of actin in intact cells is regulated by cytosolic ATP levels, primarily by the integrity of the glycolytic pathway. Based on these observations, we conclude that the mechanism of action of cytochalasins in intact cells is more complex than current models suggest.