Biosynthesis of tunicamycin and metabolic origin of the 11-carbon dialdose sugar, tunicamine

Tunicamycin is a reversible inhibitor of polyprenol-phosphate: N-acetylhexosamine-1-phosphate translocases and is produced by several Streptomyces species. We have examined tunicamycin biosynthesis, an important but poorly characterized biosynthetic pathway. Biosynthetic precursors have been identified by incorporating radioactive and stable isotopes, and by determining the labeling pattern using electrospray ionization-collision induced dissociation-mass spectrometry (ESI-CID-MS), and proton, deuterium, and C-13 nuclear magnetic resonance (NMR) spectroscopy. Preparation and analysis of [uracil-5-(2)H]-labeled tunicamycin established the complete ESI-CID-MS fragmentation pathway for the major components of the tunicamycin complex. Competitive metabolic experiments indicate that 7 deuteriums incorporate into tunicamycin from [6,6'-(2)H,(2)H]-labeled D-glucose, 6 of which arise from D-GlcNAc and 1 from uridine and/or D-ribose. Inverse correlation NMR experiments (heteronuclear single-quantum coherence (HSQC)) of (13)C-labeled tunicamycin enriched from D-[1-(13)C]glucose suggest that the unique tunicamine 11-carbon dialdose sugar backbone arises from a 5-carbon furanose precursor derived from uridine and a 6-carbon N-acetylamino-pyranose precursor derived from UDP-D-N-acetylglucosamine. The equivalent incorporation of (13)C into both the alpha-1" and beta-11' anomeric carbons of tunicamycin supports a direct biosynthesis via 6-carbon metabolism. It also indicates that the tunicamine motif and the alpha-1"-linked GlcNAc residue are both derived from the same metabolic pool of UDP-GlcNAc, without significant differential metabolic processing. A biosynthetic pathway is therefore proposed for tunicamycin for the first time: an initial formation of the 11-carbon tunicamine sugar motif from uridine and UDP-GlcNAc via uridine-5'-aldehyde and UDP-4-keto-6-ene-N-acetylhexosamine, respectively, and subsequent formation of the anomeric-to-anomeric alpha, beta-1",11'-glycosidic bond.

Bacterial peptidoglycan-associated lipoprotein is released into the bloodstream in gram-negative sepsis and causes inflammation and death in mice

Gram-negative bacterial sepsis commonly causes organ dysfunction and death in humans. Although circulating bacterial toxins trigger inflammation in sepsis, little is known about the composition of bacterial products released into the blood during sepsis or the contribution of various bacterial components to the pathogenesis of sepsis. We have shown that diverse Gram-negative bacteria release bacterial peptidoglycan-associated lipoprotein (PAL) into serum. The present studies explored release of PAL into the blood during sepsis and tested the hypothesis that PAL contributes to bacterial virulence and inflammation in Gram-negative sepsis. Released PAL was detected in the blood of 94% of mice following cecal ligation and puncture. Picomolar to nanomolar levels of PAL stimulated macrophages and splenocytes from lipopolysaccharide-hyporesponsive (C3H/HeJ) mice. Injection of PAL into C3H/HeJ mice stimulated production of serum cytokines and increased pulmonary and myocardial expression of inflammatory markers. PAL caused death in sensitized C3H/HeJ mice. Mutant Escherichia coli bacteria with reduced levels of PAL or truncated PAL were less virulent than wild-type bacteria, as indicated by higher survival rates and lower circulating levels of interleukin 6 and bacteria in a model of peritonitis in lipopolysaccharide-responsive mice. The studies suggest that PAL may be an important bacterial mediator of Gram-negative sepsis.

Several polylactosamine-modifying glycosyltransferases also use internal GalNAcbeta1-4GlcNAc units of synthetic saccharides as acceptors

The GalNAcbeta1-4GlcNAc determinant (LdN) occurs in some human and bovine glycoconjugates and also in lower vertebrates and invertebrates. It has been found in unsubstituted as well as terminally substituted forms at the distal end of conjugated glycans, but it has not been reported previously at truly internal positions of polylactosamine chains. Here, we describe enzyme-assisted conversion of LdNbeta1-OR oligosaccharides into GlcNAcbeta1-3GalNAcbeta1-4GlcNAcbeta1-OR. The extension reactions, catalyzed by human serum, were modeled after analogous beta3-GlcNAc transfer processes that generate GlcNAcbeta1-3Galbeta1-4GlcNAcbeta1-OR. The newly synthesized GlcNAcbeta1-3GalNAc linkages were unambiguously identified by nuclear magnetic resonance data, including the appropriate long-range correlations in heteronuclear multiple bond correlation spectra. The novel GlcNAcbeta1-3'LdN determinant proved to be a functional acceptor for several mammalian glycosyltransferases, suggesting that human polylactosamines may contain internal LdN units in many distinct forms. The GlcNAcbeta1-3'LdN determinant was unusually resistant toward jackbean beta-N-acetylhexosaminidase; the slow degradation should lead to a convenient method for the search of putative internal LdN determinants in natural polylactosamine chains.

The role of progenitor cells in repair of liver injury and in liver transplantation

There are three levels of cells in the hepatic lineage that respond to injury or carcinogenesis: the mature hepatocyte, the ductular "bipolar" progenitor cell, and a putative periductular stem cell. Hepatocytes are numerous, and respond rapidly to liver cell loss by one or two cell cycles but can only produce other hepatocytes. The ductular progenitor cells are less numerous, may proliferate for more cycles than hepatocytes, and are generally considered "bipolar," i.e., they can give rise to biliary cells or hepatocytes. Periductular stem cells are rare in the liver, have a very long proliferation potential, and may be multipotent. Extrahepatic (bone marrow) origin of the periductular stem cells is supported by recent data showing that hepatocytes may express genetic markers of donor hematopoietic cells after bone marrow transplantation. These different regenerative cells with variations in potential for proliferation and differentiation may provide different sources of cells for liver transplantation: hepatocytes for treatment of acute liver damage, liver progenitor cell lines for liver-directed gene therapy, and bone marrow-derived cells for chronic long-term liver replacement. A limiting factor in the success of liver cell transplantation is the condition of the hepatic microenvironment in which the cells must proliferate and set up housekeeping.

[Quantitative assay of metabolic rate of para-aminobenzoic acid combining glycine for the assessment of rabbit liver function]

OBJECTIVE

To evaluate liver function by the assessment of the capacity of glycine combining para-aminobenzoic acid (PABA) to form hippuric acid in rabbits with acute liver injury.

METHODS

Thirty rabbits were randomly divided into two groups: experiment group (n=20) received D-galactosamine to be subject to acute liver necrosis, and control group (n=10) received saline as placebo. Serum concentrations of PABA, para-aminohippuric acid (PAHA), para-acetamidobenzoic acid (PAABA), and para-acetamidohippuric acid (PAAHA) were measured by high pressure liquid chromatography (HPLC).

RESULTS

Compared with control group, the serum concentrations of PAHA and PAAHA were significantly reduced in experimental group, which were correlated with the degree of liver injury.

CONCLUSIONS

The metabolic rate of glycine combining PABA is a sensitive index for quantitative test of liver function and assessment of acute liver necrosis.

In vitro gene delivery mediated by chitosan. effect of pH, serum, and molecular mass of chitosan on the transfection efficiency

Aminopolysaccharides such as chitosan and polygalactosamine (pGalN) were used to transfer luciferase plasmid into tumor cells. Chitosan largely enhanced the transfection efficiency of luciferase plasmid (pGL3), while pGalN did not at all. Transfection efficiencies of the pGL3/chitosan complexes were dependent on pH of culture medium, stoicheometry of pGL3:chitosan, serum, and molecular mass of chitosan. Transfection efficiency at pH 6.9 was higher than that at pH7.6. Optimum charge ratio of the pGL3:chitosan was 1:5. Chitosan polymer of 15 and 52 kDa largely promoted luciferase activities. Transfection efficiency mediated by chitosan of > 100 kDa was less than that by chitosan of 15 and 52 kDa. Heptamer (1.3 kDa) did not show any gene expression. Cationic liposome (lipofectin)-associated gene expression was inhibited by serum, while chitosan showed resistance to serum.

Preferential incorporation of glucosamine into the galactosamine moieties of chondroitin sulfates in articular cartilage explants

OBJECTIVE

To determine the metabolic fate of glucosamine (GlcN) in intact articular cartilage tissue.

METHODS

Intact articular cartilage explants were cultured for up to 13 days in Dulbecco's modified Eagle's medium supplemented with 1) 1-13C-labeled GlcN, 2) 1-13C-labeled glucose (Glc), or 3) no labeling. Every 3-4 days, samples were removed and frozen in liquid nitrogen for carbon-13 magnetic resonance spectroscopic (MRS) analysis. The metabolic products of the labeled precursors were determined from the MRS data based on resonance positions and comparison with known standards and published values.

RESULTS

GlcN was taken up by the chondrocytes and incorporated selectively into the hexosamine, but not the hexuronic acid, components of the glycosaminoglycan chains of articular cartilage proteoglycan. The data also demonstrated that GlcN is the substrate of choice for the galactosamine moieties of the chondroitin sulfates, incorporating at levels 300% higher than with an equivalent amount of labeled Glc.

CONCLUSION

The results indicate that GlcN facilitates the production of proteoglycan components that are synthesized through the hexosamine biochemical pathway.

1-O-galloyl-6-O-(4-hydroxy-3,5-dimethoxy)benzoyl-beta-D-glucose, a new hepatoprotective constituent from Combretum quadrangulare

A new gallic acid derivative, 1-O-galloyl-6-O-(4-hydroxy-3,5-dimethoxy)benzoyl-beta-D-glucose (1) has been isolated from an H2O-fraction of MeOH extract of Combretum quadrangulare seeds. Compound 1 exhibited potent hepatoprotective activity against D-GalN/TNF-alpha-induced cell death in primary cultured mouse hepatocytes with an IC50 of 3.3 microM.

α- and β-Homogalactonojirimycins (α- and β-Homogalactostatins) synthesis and further biological evaluation

The homoiminosugars alpha- and beta-homogalactonojirimycins were prepared from a common intermediate, tetra-O-benzyl-D-galacto-heptenitol 6, by way of highly stereoselective reaction sequences involving, as the key steps, an internal amidomercuration (alpha-epimer) and a double reductive amination (beta-epimer). alpha-Homogalactonojirimycin retains a large part of the potent activity of the parent galactonojirimycin and 1-deoxygalactonojirimycin as an inhibitor of alpha-galactosidases. However, by contrast with the parent iminosugars, it does not inhibit beta-galactosidases, with the exception of the Jack beans enzyme. beta-Homogalactonojirimycin is a weak alpha-galactosidase inhibitor and is completely devoid of activity towards beta-galactosidases. Thus, a marked selectivity toward one family of enzymes has been achieved by the addition of an alpha-CH(2)OH group in the structure of the parent iminosugars.

Kinetics of expression of connective tissue growth factor gene during liver regeneration after partial hepatectomy and D-galactosamine-induced liver injury in rats

Connective tissue growth factor (CTGF) is up-regulated by TGF-beta1 during wound healing. The present study examined the expression of CTGF during regeneration after 70% partial hepatectomy (PH) or d-galactosamine (GalN)-injured liver in rats. CTGF, TGF-beta1, and type I collagen mRNAs were semiquantified by a ribonuclease protection assay. After PH, TGF-beta1 and type I collagen were increased at 2-6 h and at 12-48 h. CTGF increased at 6 h and returned to the control level thereafter. The ribonuclease protection assay of cultured hepatic stellate cells (HSC) and in situ hybridization suggest that the cells express CTGF along sinusoid might be HSCs. After GalN administration, CTGF increased at 2-96 h with a shoulder peak at 6-12 h followed by a main peak at 24 h. TGF-beta1 and type I collagen were up-regulated with kinetics similar to those of CTGF. The different kinetics between PH and GalN regenerations indicate that regulation of CTGF in the two processes is different. Higher TGF-beta1 expression after inflammatory/necrotic process in the GalN regeneration may caused the prolonged CTGF expression.

Pathways for the utilization of N-acetyl-galactosamine and galactosamine in Escherichia coli

Among enteric bacteria, the ability to grow on N-acetyl-galactosamine (GalNAc or Aga) and on D-galactosamine (GalN or Gam) differs. Thus, strains B, C and EC3132 of Escherichia coli are Aga+ Gam+ whereas E. coli K-12 is Aga- Gam-, similarly to Klebsiella pneumoniae KAY2026, Klebsiella oxytoca M5a1 and Salmonella typhimurium LT2. The former strains carry a complete aga/kba gene cluster at 70.5 min of their gene map. These genes encode an Aga-specific phosphotransferase system (PTS) or IIAga (agaVWE) and a GalN-specific PTS or IIGam (agaBCD). Both PTSs belong to the mannose-sorbose family, i.e. the IIB, IIC and IID domains are encoded by different genes, and they share a IIA domain (agaF). Furthermore, the genes encode an Aga6P-deacetylase (agaA), a GalN6P deaminase (agaI), a tagatose-bisphosphate aldolase comprising two different peptides (kbaYZ) and a putative isomerase (agaS), i.e. complete pathways for the transport and degradation of both amino sugars. The genes are organized in two adjacent operons (kbaZagaVWEFA and agaS kbaYagaBCDI) and controlled by a repressor AgaR. Its gene agaR is located upstream of kbaZ, and AgaR responds to GalNAc and GalN in the medium. All Aga- Gam- strains, however, carry a deletion covering genes agaW' EF 'A; consequently they lack active IIAga and IIGam PTSs, thus explaining their inability to grow on the two amino sugars. Remnants of a putative recombination site flank the deleted DNA in the various Aga- Gam- enteric bacteria. Derivatives with an Aga+ Gam- phenotype can be isolated from E. coli K-12. These retain the DeltaagaW' EF 'A deletion and carry suppressor mutations in the gat and nag genes for galactitol and N-acetyl-glucosamine metabolism, respectively, that allow growth on Aga but not on GalN.

Comparable endotoxic properties of lipopolysaccharides are manifest in diverse clinical isolates of gram-negative bacteria

In general there is a poor correlation between serum lipopolysaccharide (LPS; the biologically active constituent of endotoxin) levels and mortality in septic patients. The objective of this study was to determine if chemical, structural, or biological differences among LPS from different clinical isolates of gram-negative bacteria might explain this discrepancy. LPS preparations were made using the hot phenol-water extraction method from eight clinical isolates of gram-negative bacteria. As a percentage of the total weight of the LPS, the phosphate content ranged from 3.0 to 13.8% (average, 6.7 +/- 3.6%), and the 2-keto-3-deoxyoctonate content ranged from 1.9 to 27.4% (average, 8.9 +/- 8.5%). These values were not dissimilar to those obtained for a reference endotoxin. In a standard measure of LPS activity, the Limulus amoebocyte lysate assay, there was approximately a twofold difference between the least and most active preparations. The two preparations with the greatest difference in their ability to elicit the secretion of tumor necrosis factor alpha from a mouse peritoneal macrophage cell line were similar in lethality when administered to mice sensitized to the effects of LPS by D(+)-galactosamine. These relatively minor differences in LPS activity seem unlikely to explain the generally observed discrepancy between serum endotoxin levels and mortality in patients with gram-negative sepsis.

Proteins isolated from lucerne roots by affinity chromatography with sugars analogous to Nod factor moieties

Nod factors are important elicitors in legume-bacterium symbiosis. Any candidate plant receptor(s) for these lipo-oligosaccharides can be expected to show some lectin-like properties. A novel protein (P60), a native tetramer with 60 kDa monomers, has been isolated from a membrane fraction of Medicago sativa (lucerne, alfalfa) roots by using affinity chromatography with either GlcNAc or N,N', N"-triacetyl-(1-->4)-beta-d-chitotriose [(GlcNAc)(3)] grafted to agarose beads as the matrix and, in a second step, Sephadex G-200 gel filtration. With (GlcNAc)(3)-agarose an additional protein of 78 kDa was isolated. P60 showed haemagglutination activity with specificity for GalNAc, GalN, GlcNAc and GlcN. Binding experiments with radioactive GlcNAc gave a K(d) of 95 nM and one binding site per monomer of P60; Nod factor competed strongly for this binding. In native PAGE, protein incubated with O-sulphated Nod factors had a higher electrophoretic mobility as a consequence of binding. However, the largest modification was observed with a natural mixture of Nod factors, containing the O-acetylated and O-sulphated tetrasaccharidic NodRm-IV(Ac,S) (in which Ac stands for an O-acetylated group at the non-reducing end and S for O-sulphation at the reducing end) in addition to the non-O-acetylated NodRm-IV(S) (which alone had little effect) and NodRm-V(S). The native PAGE study was also performed with known lectins from other sources, but only the 34 kDa lectin of Phytolacca americana (pokeweed) showed any such interaction, although without discrimination between Nod factors. Finally, one peptide of each isolated protein was sequenced; the peptide from P60 showed some similarity with dihydrolipoamide dehydrogenase and ferric leghaemoglobin reductase, whereas the peptide from P78 was identical with an analogous region of 70 kDa heat shock protein.

Co-production of staphylococcal enterotoxin A with toxic shock syndrome toxin-1 (TSST-1) enhances TSST-1 mediated mortality in a D-galactosamine sensitized mouse model of lethal shock

It has previously been reported that staphylococcal enterotoxin A (SEA) is frequently co-expressed with toxic shock syndrome toxin-1 (TSST-1) in menstrual Toxic Shock Syndrome (MTSS)-associated Staphylococcus aureus. It was hypothesized that co-production of SEA and TSST-1 might yield a more virulent strain than one that produced TSST-1 but not SEA. To test this hypothesis, a TSST-1+/SEA- derivative of S. aureus RN3984 (TSST-1+/SEA+) was constructed by plasmid integration, and the isogenic pair were introduced into a D-galactosamine sensitized mouse model of lethal shock. At 72 h, 27 out of 30 (90%) mice inoculated with the parental strain died, as compared to 21 out of 30 (70%) mice inoculated with the isogenic derivative (P=0.05, Fisher's exact test; 1-tailed; 95% confidence limits, 0.80-20.80). Our results suggest that co-production of SEA with TSST-1 does enhance the ability of this strain of S. aureus to induce lethal shock in vivo. This enhanced virulence could be due to an additive or synergistic activity of the toxin combination on T cell proliferation and cytokine production in the animal model.

Induction of lethal shock and tolerance by Porphyromonas gingivalis lipopolysaccharide in D-galactosamine-sensitized C3H/HeJ mice

Lipopolysaccharide (LPS) obtained from Porphyromonas gingivalis was found to exhibit marked lethal toxicity in galactosamine-sensitized C3H/HeJ mice. Although no lethality was observed in mice intraperitoneally challenged with 1 mg of P. gingivalis LPS without galactosamine, when they were sensitized with 30 mg of galactosamine, challenge with 1 and 10 micrograms of LPS resulted in 67 and 100% lethality, respectively. The lethal dose of LPS was almost the same in LPS-responsive C57BL/6 mice and non-LPS-responsive C3H/HeJ mice. Furthermore, when 1 microgram of P. gingivalis LPS was administered to each mouse 90 min before the challenge with the same LPS with galactosamine, tolerance to the lethal action of LPS was induced, and the mice were completely protected from death, even at a dose 100-fold greater than the lethal dose of LPS. Neither a lethal effect nor induction of tolerance to the lethality of P. gingivalis LPS was exhibited by Salmonella LPS in galactosamine-sensitized C3H/HeJ mice. A protein-LPS complex derived from Pseudomonas aeruginosa, which exhibited strong lethality and induced tolerance to a subsequent challenge with a lethal dose of LPS in galactosamine-sensitized LPS-responsive mice, did not exhibit lethal toxicity in galactosamine-sensitized C3H/HeJ mice and failed to induce tolerance in these mice to the lethality of P. gingivalis LPS. These results indicate that P. gingivalis LPS plays the central role in the activation of non-LPS-responsive C3H/HeJ mice.

Caspase-1 is not involved in experimental hepatitis in mouse

Experimental hepatitis induced by tumor necrosis factor in D-(+)-galactosamine-sensitized mice or by an agonistic anti-Fas antibody in normal mice is accompanied by dramatic apoptosis of hepatocytes. Apoptosis is the final result of activation of a cascade of caspases. We used caspase-1-/- mice, generated by gene targeting, to study the role of this protease in TNF- and anti-Fas-induced lethal hepatitis. We found that mutant mice exhibited the typical caspase-1-/- phenotype, since they resisted to a lethal injection of LPS and released no interleukin-1beta in the circulation, in contrast to wild-type littermates. When caspase-1-/- mice were challenged with different doses of tumor necrosis factor/D-(+)-galactosamine or with anti-Fas, no increased survival was observed compared with control mice. Furthermore, apoptosis in the livers of these mice and serum levels of alanine aminotransferase were not reduced. These data indicate that caspase-1 deficiency does not lead to reduced apoptosis in these models, either because caspase-1 is irrelevant in this model or because of functional redundancy.

Effects of various kinds of dietary amino acids on the hepatotoxic action of D-galactosamine in rats

The protective effects of various kinds of dietary amino acids against the hepatotoxic action of D-galactosamine (GalN) were examined. Male Wistar rats fed with 20% casein diets containing 10% or 5% amino acid for one week were injected with GalN (800 mg/kg body weight), and the serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) activities, the hepatic glycogen concentration, and the serum glucose-level were examined 20 hours after the injection. In the groups with the 10% amino acid diets, activities of AST, ALT, and LDH in serum of 10% L-glutamine (Gln), 10% L-asparagine (Asn), and 10% L-serine (Ser) groups were significantly lower than those of the control group, and in the groups with the 5% amino acid diets, those activities of 5% L-histidine (His), 5% L-tyrosine (Tyr), 5% L-lysine (Lys), and 5% L-glycine (Gly) groups were also lower than those of the control group. The concentration of liver glycogen of 10% Gln-, 10% Asn-, and 10% Ser- groups and those levels of 5% His-, 5% Tyr-, 5% Lys-, and 5% Gly-groups were also significantly higher than that of the control group. As a result, it was found that some kinds of dietary amino acid such as L-Ser, L-Asn, L-His, L-Lys, L-Tyr, and L-Gly, in addition to L-Gln were effective to protect the rats from GalN-induced injury.

Structural basis for the recognition of carbohydrates by human galectin-7

Knowledge about carbohydrate recognition domains of galectins, formerly known as S-type animal lectins, is important in understanding their role(s) in cell-cell interactions. Here we report the crystal structure of human galectin-7 (hGal-7), in free form and in the presence of galactose, galactosamine, lactose, and N-acetyl-lactosamine at high resolution. This is the first structure of a galectin determined in both free and carbohydrate-bound forms. The structure shows a fold similar to that of the prototype galectins -1 and -2, but has greater similarity to a related galectin molecule, Gal-10. Even though the carbohydrate-binding residues are conserved, there are significant changes in this pocket due to shortening of a loop structure. The monomeric hGal-7 molecule exists as a dimer in the crystals, but adopts a packing arrangement considerably different from that of Gal-1 and Gal-2, which has implications for carbohydrate recognition.

Monoclonal antibodies directed against extracellular matrix proteins reduce the adherence of Candida albicans to HEp-2 cells

The presence of the extracellular matrix (ECM) proteins collagen types I and IV, laminin and fibronectin on the surface of HEp-2 cells was confirmed by flow cytometry using monoclonal antibodies. Monoclonal antibodies directed against these ECM proteins reduced the adherence of C. albicans ATCC 44990 to HEp-2 cells, the greatest reductions being evident in assays which incorporated anti-collagen type IV monoclonal antibody. The ability of sugaramines to inhibit the adherence of C. albicans to a variety of cell types has been demonstrated previously and the most significant reduction in C. albicans-HEp-2 adherence was in assays which incorporated 0.2M galactosamine. The combination of anti-collagen IV monoclonal antibody and galactosamine reduced the adherence of C. albicans to HEp-2 cells by approximately 70% (p < 0.05).

Actinomyces naeslundii displays variant fimP and fimA fimbrial subunit genes corresponding to different types of acidic proline-rich protein and beta-linked galactosamine binding specificity

Actinomyces naeslundii genospecies 1 and 2 bind to acidic proline-rich proteins (APRPs) and statherin via type 1 fimbriae and to beta-linked galactosamine (GalNAcbeta) structures via type 2 fimbriae. In addition, A. naeslundii displays two types of binding specificity for both APRPs-statherin and GalNAcbeta, while Actinomyces odontolyticus binds to unknown structures. To study the molecular basis for these binding specificities, DNA fragments spanning the entire or central portions of fimP (type 1) and fimA (type 2) fimbrial subunit genes were amplified by PCR from strains of genospecies 1 and 2 and hybridized with DNA from two independent collections of oral Actinomyces isolates. Isolates of genospecies 1 and 2 and A. odontolyticus, but no other Actinomyces species, were positive for hybridization with fimP and fimA full-length probes irrespective of binding to APRPs and statherin, GalNAcbeta, or unknown structures. Isolates of genospecies 1 and 2, with deviating patterns of GalNAcbeta1-3Galalpha-O-ethyl-inhibitable coaggregation with Streptococcus oralis Ss34 and MPB1, were distinguished by a fimA central probe from genospecies 1 and 2, respectively. Furthermore, isolates of genospecies 1 and 2 displaying preferential binding to APRPs over statherin were positive with a fimP central probe, while a genospecies 2 strain with the opposite binding preference was not. The sequences of fimP and fimA central gene segments were highly conserved among isolates with the same, but diversified between those with a variant, binding specificity. In conclusion, A. naeslundii exhibits variant fimP and fimA genes corresponding to diverse APRP and GalNAcbeta specificities, respectively, while A. odontolyticus has a genetically related but distinct adhesin binding specificity.

Upregulation of endothelin-1 and adrenomedullin gene expression in the mouse endotoxin shock model

Septic shock is a life-threatening disorder caused by lipopolysaccharide (LPS) and other bacterial products. Accumulating evidence indicates a role for vasoactive substances and cytokines in this disease process. In this study we examined the effect of LPS on the gene expression of endothelin-1 (ET-1) and adrenomedullin (AM), two major vasoactive peptides predominantly produced by vascular endothelial cells, to investigate their role in the pathophysiology of septic shock. LPS induced ET-1 and AM gene expression in the heart, lung, kidney, liver, and aorta within 6 h. In the liver, whereas basal ET-1 and AM mRNA were hardly detectable, ET-1 and AM gene expression and peptide production were markedly increased by LPS. This LPS-induced upregulation of ET-1 and AM expression is greatly potentiated by D-galactosamine (D-GalN), although D-GalN alone could not induce ET-1 and AM gene expression. These results, together with the previous findings that liver injury induced by LPS and D-GalN is mainly mediated by tumor necrosis factor-alpha (TNF-alpha), suggest that the LPS-cytokine pathway may cause upregulation of ET-1 and AM production, leading to dysregulation of systemic and regional vascular tone.

Targetable HPMA copolymer-adriamycin conjugates. Recognition, internalization, and subcellular fate

Recognition, internalization, and subcellular trafficking of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates containing N-acylated galactosamine (GalN) or monoclonal OV-TL16 antibodies (Ab) have been investigated in human hepatocarcinoma HepG2 and ovarian carcinoma OVCAR-3 cells, respectively. The intrinsic fluorescence of fluorescein or adriamycin (ADR) attached to HPMA copolymers permitted us to follow the subcellular fate of HPMA copolymer conjugates by confocal fluorescence microscopy and fluorescence spectroscopy. The pattern of fluorescence during incubation of HPMA copolymer-ADR-GalN conjugate containing lysosomally degradable tetrapeptide (GFLG) side-chains with HepG2 cells was consistent with conjugate recognition, internalization, localization in lysosomes, followed by the release of ADR from the polymer chains and ultimately diffusion via the cytoplasm into the cell nuclei. A similar pattern was observed in OVCAR-3 cells for Ab targeted HPMA copolymer conjugates. To test our hypothesis that HPMA-copolymer-bound anticancer drugs will be inaccessible to the energy-driven P-glycoprotein efflux pump in multidrug resistant (MDR) cells, we have compared the internalization of the HPMA copolymer-ADR conjugates by sensitive (A2780) and ADR-resistant (A2780/AD) ovarian carcinoma cell lines. Preliminary data on relative retention of ADR in MDR (A2780/AD) cells indicate a higher intracellular ADR concentration after incubation with HPMA copolymer-ADR conjugate when compared to incubation with free (unbound) ADR.

M-cells in the rabbit tonsil exhibit distinctive glycoconjugates in their apical membranes

The tonsil crypt epithelium contains membranous (M)-cells that transport antigens from the lumen to underlying lymphoid cells, thereby initiating specific immune responses. Mechanisms mediating the adhesion of antigens to the M-cell surface are important for effective and selective uptake of potential pathogens but are still poorly understood. Therefore, the carbohydrates present on crypt epithelial cells of the rabbit palatine tonsil were studied by lectin histochemistry. Ultrathin LR White sections were incubated with a panel of eight lectins conjugated to colloidal gold or biotin. The glycocalyx of the apical membrane of M-cells was selectively labeled by UEA-I, LTA, HPA, and VVA, whereas that of the remaining squamous epithelial cells preferentially bound RCA-I and PNA. WGA and ConA showed only little binding, with no discernible preference for any of the cell types. Double labeling of UEA-1 together with anti-vimentin antibodies revealed that UEA-I-positive epithelial cells also contained the rabbit M-cell marker vimentin, and vice versa. The results show that a specific composition of glycoconjugates, which differs from that on squamous epithelial cells, is found on M-cells of the rabbit tonsil. The M-cell-specific glycoproteins and glycolipids could be selectively targeted by microorganisms that adhere to M-cells and enter the host along this pathway.

Mutational studies of the amino acid residues in the combining site of Erythrina corallodendron lectin

High-resolution X-ray crystallography of the complex of the Gal/GalNAc-specific Erythrina corallodendron lectin with lactose identified the amino acid side chains that form contacts with the galactose moiety of the disaccharide. The contribution of these amino acids to the binding of different monosaccharides and oligosaccharides by the lectin was examined by site-directed mutagenesis. Replacement of Phe131, on which the galactose is stacked, by tyrosine, gave a mutant with the same hemagglutinating activity and carbohydrate specificity as the parent lectin, but replacement by alanine or valine resulted in loss of activity. Mutations of Ala88, Asp89, and Asn133 produced mutants that were also inactive whereas those of the other combining site residues, Tyr106, Ala218, and Gln219, were biologically active. None of the active mutants interacted with mannose or glucose. Thus, contrary to an earlier assumption. Ala218 is not responsible for the inability of E. corallodendron lectin to bind these sugars. Our findings also demonstrate that Gln219 is not involved in galactose binding in solution, even though this is implicated by the crystal data. Instead, our data suggest that Gln219 assists in the ligation of N-acetyllactosamine to the lectin, by interacting with the acetamide group of the disaccharide. Comparison with other legume lectins specific for mannose/glucose, galactose, N-acetylgalactosamine, L-fucose or N-acetylglucosamine, shows that only three of the combining site residues of E. corallodendron lectin occupy invariant positions both in their primary and tertiary structures. These residues are an aspartic acid and an asparagine corresponding to positions 89 and 133, respectively, in E. corallodendron lectin, and an aromatic residue, either phenylalanine (as Phe131 in this lectin), tyrosine or tryptophan. We therefore postulate that these three residues are essential for ligand binding by all such lectins, irrespective of their specificity.