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Biomedical subjects

C Nathan

Publications and source records attributed to C Nathan.

At least 19 recordsLinked to original sources
PubMed2002

Metabolic enzymes of mycobacteria linked to antioxidant defense by a thioredoxin-like protein.

Mycobacterium tuberculosis (Mtb) mounts a stubborn defense against oxidative and nitrosative components of the immune response. Dihydrolipoamide dehydrogenase (Lpd) and dihydrolipoamide succinyltransferase (SucB) are components of alpha-ketoacid dehydrogenase complexes that are central to intermediary metabolism. We find that Lpd and SucB support Mtb's antioxidant defense. The peroxiredoxin alkyl hydroperoxide reductase (AhpC) is linked to Lpd and SucB by an adaptor protein, AhpD. The 2.0 angstrom AhpD crystal structure reveals a thioredoxin-like active site that is responsive to lipoamide. We propose that Lpd, SucB (the only lipoyl protein detected in Mtb), AhpD, and AhpC together constitute a nicotinamide adenine dinucleotide (reduced)-dependent peroxidase and peroxynitrite reductase. AhpD thus represents a class of thioredoxin-like molecules that enables an antioxidant defense.

Acyltransferases↗
PubMed2001

Reprogramming of the macrophage transcriptome in response to interferon-gamma and Mycobacterium tuberculosis: signaling roles of nitric oxide synthase-2 and phagocyte oxidase.

Macrophage activation determines the outcome of infection by Mycobacterium tuberculosis (Mtb). Interferon-gamma (IFN-gamma) activates macrophages by driving Janus tyrosine kinase (JAK)/signal transducer and activator of transcription-dependent induction of transcription and PKR-dependent suppression of translation. Microarray-based experiments reported here enlarge this picture. Exposure to IFN-gamma and/or Mtb led to altered expression of 25% of the monitored genome in macrophages. The number of genes suppressed by IFN-gamma exceeded the number of genes induced, and much of the suppression was transcriptional. Five times as many genes related to immunity and inflammation were induced than suppressed. Mtb mimicked or synergized with IFN-gamma more than antagonized its actions. Phagocytosis of nonviable Mtb or polystyrene beads affected many genes, but the transcriptional signature of macrophages infected with viable Mtb was distinct. Studies involving macrophages deficient in inducible nitric oxide synthase and/or phagocyte oxidase revealed that these two antimicrobial enzymes help orchestrate the profound transcriptional remodeling that underlies macrophage activation.

Animals↗
PubMed2001

Peptide methionine sulfoxide reductase from Escherichia coli and Mycobacterium tuberculosis protects bacteria against oxidative damage from reactive nitrogen intermediates.

Inducible nitric oxide synthase (iNOS) plays an important role in host defense. Macrophages expressing iNOS release the reactive nitrogen intermediates (RNI) nitrite and S-nitrosoglutathione (GSNO), which are bactericidal in vitro at a pH characteristic of the phagosome of activated macrophages. We sought to characterize the active intrabacterial forms of these RNI and their molecular targets. Peptide methionine sulfoxide reductase (MsrA; EC ) catalyzes the reduction of methionine sulfoxide (Met-O) in proteins to methionine (Met). E. coli lacking MsrA were hypersensitive to killing not only by hydrogen peroxide, but also by nitrite and GSNO. The wild-type phenotype was restored by transformation with plasmids encoding msrA from E. coli or M. tuberculosis, but not by an enzymatically inactive mutant msrA, indicating that Met oxidation was involved in the death of these cells. It seemed paradoxical that nitrite and GSNO kill bacteria by oxidizing Met residues when these RNI cannot themselves oxidize Met. However, under anaerobic conditions, neither nitrite nor GSNO was bactericidal. Nitrite and GSNO can both give rise to NO, which may react with superoxide produced by bacteria during aerobic metabolism, forming peroxynitrite, a known oxidant of Met to Met-O. Thus, the findings are consistent with the hypotheses that nitrite and GSNO kill E. coli by intracellular conversion to peroxynitrite, that intracellular Met residues in proteins constitute a critical target for peroxynitrite, and that MsrA can be essential for the repair of peroxynitrite-mediated intracellular damage.

Bacterial Proteins↗
PubMed2001

The effect of glucagon-like peptide 2 on intestinal permeability and bacterial translocation in acute necrotizing pancreatitis.

BACKGROUND: Acute pancreatitis (AP) initiates a generalized inflammatory response that increases intestinal permeability and promotes bacterial translocation (BT). Impairment of the intestinal epithelial barrier is known to promote BT. Glucagon-like peptide 2 (GLP-2), a 33 residue peptide hormone, is a key regulator of the intestinal mucosa by stimulating epithelial growth. The purpose of this study was to determine whether GLP-2 decreases intestinal permeability and BT in AP. METHODS: To examine whether GLP-2 can decrease intestinal permeability and thereby decrease BT in acute necrotizing pancreatitis, 34 male Sprague-Dawley rats (200 to 300 g) were studied. AP was induced in group I and group II by pressure injection of 3% taurocholate and trypsin into the common biliopancreatic duct (1 mg/kg of body weight). The potent analog to GLP-2 called ALX-0600 was utilized. Group I rats received GLP-2 analog (0.1 mg/kg, SQ, BID) and group II rats received a similar volume of normal saline as a placebo postoperatively for 3 days. Group III and group IV received GLP-2 analog and placebo, respectively. At 72 hours postoperatively, blood was drawn for culture of gram-negative organisms. Specimens from mesenteric lymph nodes (MLN), pancreas and peritoneum were harvested for culture of gram-negative bacteria. Intestinal resistance as defined by Ohm's law was determined using a modified Ussing chamber to measure transepithelial current at a fixed voltage. A point scoring system for five histologic features that include intestinal edema, inflammatory cellular infiltration, fat necrosis, parenchymal necrosis, and hemorrhage was used to evaluate the severity of pancreatitis. Specimens from MLN, pancreas, jejunum, and ileum were taken for pathology. RESULTS: All group I and group II rats had AP. The average transepithelial resistance in group I was 82.8 Omega/cm(2) compared with 55.9 Omega/cm(2) in group II (P <0.01). Gram-negative BT to MLN, pancreas, and peritoneum was 80%, 0%, and 0%, respectively in group I compared with 100%, 30%, and 20% translocation in group II. CONCLUSION: GLP-2 treatment significantly decreases intestinal permeability in acute pancreatitis.

Analysis of Variance↗
PubMed2001

Colonization of skilled-care facility residents with antimicrobial-resistant pathogens.

OBJECTIVES: To determine the frequency of and risk factors for colonization of skilled-care unit residents by several antimicrobial-resistant bacterial species, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococcus (VRE), or extended-spectrum-beta-lactamase-producing (ESBL-producing) (ceftazidime resistant) Klebsiella pneumoniae or Escherichia coli. DESIGN: Point-prevalence survey and medical record review. SETTING: The skilled-care units in one healthcare facility. PARTICIPANTS: 120 skilled-care unit residents. MEASUREMENTS: Colonization by each of the four antimicrobial-resistant pathogens during a point-prevalence survey, using rectal, nasal, gastrostomy-tube site, wound, and axillary cultures, June 1-3, 1998; 117 (98%) had at least one swab collected and 114 (95%) had a rectal swab collected. Demographic and clinical characteristics were evaluated as risk factors for colonization. All isolates were strain typed by pulsed-field gel electrophoresis of total genomic deoxyribonucleic acid. RESULTS: Of 117 participants, 50 (43%) were culture positive for > or =1 antimicrobial-resistant pathogen: MRSA (24%), ESBL-producing K. pneumoniae (18%) or E. coli (15%), and VRE (3.5%). Of 50 residents culture positive for any of these four antimicrobial-resistant species, 13 (26%) were colonized by more than one resistant species; only three (6%) were on contact-isolation precautions at the time of the prevalence survey. Risk factors for colonization varied by pathogen: total dependence on healthcare workers (HCWs) for activities of daily living (ADLs) and antimicrobial receipt for MRSA, total dependence on HCWs for ADLs for ESBL-producing K. pneumoniae, and antimicrobial receipt for VRE. No significant risk factors were identified for colonization by ESBL-producing E. coli. Among colonized patients, there was a limited number of strain types for MRSA (24 patients, 4 strain types) and ESBL-producing K. pneumoniae (21 patients, 3 strain types), and a high proportion of unique strain types for VRE (4 patients, 4 strain types) and FSBL-producing E. coli (17 patients, 10 strain types). CONCLUSION: A large unrecognized reservoir of skilled-care-unit residents was colonized by antimicrobial-resistant pathogens, and co-colonization by more than one target species was common. To prevent transmission of antimicrobial-resistant pathogens in long-term care facilities in which residents have high rates of colonization, infection-control strategies may need to be modified. Potential modifications include enhanced infection-control strategies, such as universal gloving for all or high-risk residents, or screening of high-risk residents, such as those with total dependence on HCWs for ADLs or recent antimicrobial receipt, and initiation of contact-isolation precautions for colonized residents.

Aged↗
PubMed2001

Lung surfactant and reactive oxygen-nitrogen species: antimicrobial activity and host-pathogen interactions.

Surfactant protein (SP) A and SP-D are members of the collectin superfamily. They are widely distributed within the lung, are capable of antigen recognition, and can discern self versus nonself. SPs recognize bacteria, fungi, and viruses by binding mannose and N-acetylglucosamine residues on microbial cell walls. SP-A has been shown to stimulate the respiratory burst as well as nitric oxide synthase expression by alveolar macrophages. Although nitric oxide (NO.) is a well-recognized microbicidal product of macrophages, the mechanism(s) by which NO. contributes to host defense remains undefined. The purpose of this symposium was to present current research pertaining to the specific role of SPs and reactive oxygen-nitrogen species in innate immunity. The symposium focused on the mechanisms of NO*-mediated toxicity for bacterial, human, and animal models of SP-A- and NO.-mediated pathogen killing, microbial defense mechanisms against reactive oxygen-nitrogen species, specific examples and signaling pathways involved in the SP-A-mediated killing of pulmonary pathogens, the structure and binding of SP-A and SP-D to bacterial targets, and the immunoregulatory functions of SP-A.

Animals↗
PubMed2000

Peroxynitrite reductase activity of bacterial peroxiredoxins.

Nitric oxide (NO) is present in soil and air, and is produced by bacteria, animals and plants. Superoxide (O2-) arises in all organisms inhabiting aerobic environments. Thus, many organisms are likely to encounter peroxynitrite (OONO-), a product of NO and O2- that forms at near diffusion-limited rates, and rapidly decomposes upon protonation through isomerization to nitrate (NO3-; ref. 1) while generating hydroxyl radical (*OH) and nitrogen dioxide radical (*NO2) (refs 2, 3), both more reactive than peroxynitrite's precursors. The oxidative, inflammatory, mutagenic and cytotoxic potential (ref. 4) of peroxynitrite contrasts with the antioxidant, anti-inflammatory and tissue-protective properties ascribed to NO itself. Thus, the ability of cells to cope with peroxynitrite is central in determining the biological consequences of NO production. We considered whether cells might be equipped with enzymes to detoxify peroxynitrite. Peroxiredoxins have been identified in most genomes sequenced, but their functions are only partly understood. Here we show that the peroxiredoxin alkylhydroperoxide reductase subunit C (AhpC) from Salmonella typhimurium catalytically detoxifies peroxynitrite to nitrite fast enough to forestall the oxidation of bystander molecules such as DNA. Results are similar with peroxiredoxins from Mycobacterium tuberculosis and Helicobacter pylori. Thus, peroxynitrite reductase activity may be widespread among bacterial genera.

Catalysis↗
PubMed2000

Reactive oxygen and nitrogen intermediates in the relationship between mammalian hosts and microbial pathogens.

This review summarizes recent evidence from knock-out mice on the role of reactive oxygen intermediates and reactive nitrogen intermediates (RNI) in mammalian immunity. Reflections on redundancy in immunity help explain an apparent paradox: the phagocyte oxidase and inducible nitric oxide synthase are each nonredundant, and yet also mutually redundant, in host defense. In combination, the contribution of these two enzymes appears to be greater than previously appreciated. The remainder of this review focuses on a relatively new field, the basis of microbial resistance to RNI. Experimental tuberculosis provides an important example of an extended, dynamic balance between host and pathogen in which RNI play a major role. In diseases such as tuberculosis, a molecular understanding of host-pathogen interactions requires characterization of the defenses used by microbes against RNI, analogous to our understanding of defenses against reactive oxygen intermediates. Genetic and biochemical approaches have identified candidates for RNI-resistance genes in Mycobacterium tuberculosis and other pathogens.

Animals↗
PubMed2000

Embryos with high implantation potential after intracytoplasmic sperm injection can be recognized by a simple, non-invasive examination of pronuclear morphology.

Embryos are conventionally selected for transfer based on the evaluation of the cleavage speed and extent of blastomere fragmentation. Here we examined whether the predictive value of these criteria, as indicators of the chance of embryo implantation, can be further potentiated by adding previously described criteria reflecting the regularity of pronuclear development. In a group of embryos selected for transfer in 380 fresh embryo transfer cycles according to the conventional criteria, the transfer of only those embryos that developed from zygotes judged normal at the pronuclear stage (pattern 0) gave significantly higher pregnancy (44.8%) and implantation (30.2%) rates compared with the pregnancy (22.1%; P < 0. 05) and implantation rates (11.2%; P < 0.001) for the transfers of only those embryos that developed from zygotes judged abnormal (non-pattern 0). The transfer of only one pattern 0 embryo was sufficient for the optimal chance of pregnancy (no differences in pregnancy rates after transfer of one, two or three pattern 0 embryos), whereas the transfer of two pattern 0 embryos mostly resulted in a twin pregnancy. The inclusion of the criteria based on pronuclear morphology can thus lead to the application of a single embryo transfer policy and optimize the selection of embryos for transfer and cryopreservation.

Cell Nucleus↗
PubMed2000

The effect of interleukin-6 on bacterial translocation in acute canine pancreatitis.

BACKGROUND: Bacterial translocation from the gut to mesenteric lymph nodes and other extraintestinal sites is an important source of infection in acute pancreatitis. Impaired host immunity is known to promote bacterial translocation. Interleukin-6 (IL-6) is a multifunctional cytokine that regulates the immune response, acute phase reaction, and hematopoiesis. METHODS: Twenty-four mongrel dogs (18-29 kg) were studied in four equal groups. In Groups I and II, acute pancreatitis was induced by direct pressure injection of 4% taurocholate and trypsin into the pancreatic duct at laparotomy. Groups III and IV had only laparotomy. Group I and III dogs were given IL-6 (50 microg/kg/d, sq) daily starting 24 h after operation and Group II and IV dogs received an equal volume of saline administered at similar time. All animals had blood drawn for culture, complete blood count (CBC), platelets, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and amylase on d 0, 1, 4, and 7. On d 7, mesenteric lymph nodes (MLN), spleen, liver, pancreas, and cecum were harvested for pathology study and for cultures of aerobic and anaerobic bacteria. Quantitative cecal cultures of aerobic and anaerobic bacteria were obtained. RESULTS: All Group I and Group II dogs had severe pancreatitis. The increase of plasma CRP in Group I was sustained throughout treatment (1.3+/-0.3 on d 0 vs 3.1+/-0.3*, 3.0+/-0.3*, and 2.9+/-0.3* on d 1,4, and 7, respectively). Plasma CRP was increased in Group II on d 1 and d 4 (1.3+/-0.3 mg/dL on d 0 vs 3.6+/-0.3* mg/dL on d 1, and 3.1+/-0.3* on d 4, *p < 0.05). There were no differences in white blood cell (WBC) count, differential, platelets, and ESR between Groups I and II. Bacterial translocation to MLN was lower in Group I (1/6) than in Group II (6/6) (p < 0.05). All 6 dogs in Group II had bacterial spread to distant sites compared to 2 of 6 dogs in Group I (p = 0.066). Both MLN and other distant organ cultures were negative in Group III and only 1 of 6 MLN cultures was positive in Group IV. CONCLUSIONS: IL-6 treatment decreases bacterial translocation to MLN and may be beneficial in reducing septic complications in acute pancreatitis.

Acute Disease↗
PubMed1999

Suppression of macrophage responses to bacterial lipopolysaccharide by a non-secretory form of secretory leukocyte protease inhibitor.

Expression of secretory leukocyte protease inhibitor (SLPI) suppresses the ability of macrophages to respond to bacterial lipopolysaccharide (LPS). Here, addition of recombinant or native SLPI to the extracellular medium was non-suppressive, while transfection with a non-secretory form of SLPI was fully suppressive, an effect overcome by treatment with interferon-gamma. A portion of the SLPI produced by untransfected macrophages was localized in the cytosol. Thus, SLPI can act intracellularly to block macrophage activation by LPS.

Animals↗
PubMed1999

Multiple antibiotic-resistant Klebsiella and Escherichia coli in nursing homes.

CONTEXT: Infections caused by ceftazidime sodium-resistant gram-negative bacteria that harbor extended-spectrum beta-lactamases (ESBLs) are increasing in frequency in hospitals in the United States. OBJECTIVES: To report a citywide nursing home-centered outbreak of infections caused by ESBL-producing gram-negative bacilli and to describe the clinical and molecular epidemiology of the outbreak. DESIGN: Hospital-based case-control study and a nursing home point-prevalence survey. Molecular epidemiological techniques were applied to resistant strains. SETTINGS: A 400-bed tertiary care hospital and a community nursing home. PATIENTS: Patients who were infected and/or colonized with ceftazidime-resistant Escherichia coli, Klebsiella pneumoniae, or both and controls who were admitted from nursing homes between November 1990 and July 1992. MAIN OUTCOME MEASURES: Clinical and epidemiological factors associated with colonization or infection by ceftazidime-resistant E coli or K pneumoniae; molecular genetic characteristics of plasmid-mediated ceftazidime resistance. RESULTS: Between November 1990 and October 1992, 55 hospital patients infected or colonized with ceftazidime-resistant E coli, K pneumoniae, or both were identified. Of the 35 admitted from 8 nursing homes, 31 harbored the resistant strain on admission. All strains were resistant to ceftazidime, gentamicin, and tobramycin; 96% were resistant to trimethoprim-sulfamethoxazole and 41% to ciprofloxacin hydrochloride. In a case-control study, 24 nursing home patients colonized with resistant strains on hospital admission were compared with 16 nursing home patients who were not colonized on hospital admission; independent risk factors for colonization included poor functional level, presence of a gastrostomy tube or decubitus ulcers, and prior receipt of ciprofloxacin and/or trimethoprim-sulfamethoxazole. In a nursing home point-prevalence survey, 18 of 39 patients were colonized with ceftazidime-resistant E coli; prior receipt of ciprofloxacin or trimethoprim-sulfamethoxazole and presence of a gastrostomy tube were independent predictors of resistance. Plasmid studies on isolates from 20 hospital and nursing home patients revealed that 17 had a common 54-kilobase plasmid, which conferred ceftazidime resistance via the ESBL TEM-10, and mediated resistance to trimethoprim-sulfamethoxazole, gentamicin, and tobramycin; all 20 isolates harbored this ESBL. Molecular fingerprinting showed 7 different strain types of resistant K pneumoniae and E coli distributed among the nursing homes. CONCLUSIONS: Nursing home patients may be an important reservoir of ESBL-containing multiple antibiotic-resistant E coli and K pneumoniae. Widespread dissemination of a predominant antibiotic resistance plasmid has occurred. Use of broad-spectrum oral antibiotics and probably poor infection control practices may facilitate spread of this plasmid-mediated resistance. Nursing homes should monitor and control antibiotic use and regularly survey antibiotic resistance patterns among pathogens.

Aged↗
PubMed1999

The effect of lexipafant on bacterial translocation in acute necrotizing pancreatitis in rats.

Bacterial translocation (BT) from the gastrointestinal tract to mesenteric lymph nodes (MLNs) and other extra intestinal organs is an important source of infection in acute pancreatitis (AP). Lexipafant (BB-882) is a potent platelet-activating factor receptor antagonist that has an anti-inflammatory effect. To examine whether BB-882 could affect BT in acute necrotizing pancreatitis, 48 male Sprague Dawley rats (250-350 g) were studied. AP was induced in Group I and Group II by pressure injection of 3% taurocholate and trypsin into the common biliopancreatic duct (1 mL/kg of body weight). Group I rats received BB-882 (10 mg/kg, i.p. qd) and Group II rats received a similar volume of normal saline as a placebo postoperatively for 2 days. Group III and Group IV received BB-882 and placebo, respectively, after an exploratory laparotomy. At 48 hours postoperatively, blood was drawn for culture, serum amylase, and tumor necrosis factor (TNF)-alpha determinations. Specimens from MLNs, spleen, liver, pancreas, and cecum were harvested for culture of gram-positive, gram-negative, and anaerobic bacteria. Quantitative cecal cultures of gram-positive, gram-negative, and anaerobic bacteria were obtained. A point scoring system for five histological features that include interstitial edema, inflammatory cellular infiltration, fat necrosis, parenchymal necrosis, and hemorrhage was used to evaluate the severity of pancreatitis. There was no difference in serum amylase levels (2415 +/- 127 IU/L versus 2476 +/- 170 IU/L), serum TNF-alpha levels (7820 +/- 1396 pg/mL versus 7318 +/- 681 pg/mL), and the mean pancreatic histology score (5.9 +/- 1.2 versus 6.5 +/- 1.1) between Group I and Group II, respectively (P > 0.05). Seven of 12 Group I rats had BT to MLNs, compared with 11 of 12 rats in Group II (P > 0.05). Five of 12 Group I rats had BT to distant sites such as pancreas, spleen, liver, and/or blood, compared with 11 of 12 rats in Group II (P < 0.05). BB-882 treatment decreases bacterial spread to distant sites, but does not reduce serum amylase levels and serum TNF-alpha levels or ameliorate pancreatic damage in rats with AP.

Amylases↗
PubMed1999

Phenotype of mice and macrophages deficient in both phagocyte oxidase and inducible nitric oxide synthase.

The two genetically established antimicrobial mechanisms of macrophages are production of reactive oxygen intermediates by phagocyte oxidase (phox) and reactive nitrogen intermediates by inducible nitric oxide synthase (NOS2). Mice doubly deficient in both enzymes (gp91(phox-/-)/NOS2(-/-)) formed massive abscesses containing commensal organisms, mostly enteric bacteria, even when reared under specific pathogen-free conditions with antibiotics. Neither parental strain showed such infections. Thus, phox and NOS2 appear to compensate for each other's deficiency in providing resistance to indigenous bacteria, and no other pathway does so fully. Macrophages from gp91(phox-/-)/NOS2(-/-) mice could not kill virulent Listeria. Their killing of S. typhimurium, E. coli, and attenuated Listeria was markedly diminished but demonstrable, establishing the existence of a mechanism of macrophage antibacterial activity independent of phox and NOS2.

Abscess↗
PubMed1999

noxR3, a novel gene from Mycobacterium tuberculosis, protects Salmonella typhimurium from nitrosative and oxidative stress.

Reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) produced by activated macrophages participate in host defense against the facultative intracellular pathogens Mycobacterium tuberculosis and Salmonella typhimurium. To survive within macrophages, such pathogens may have evolved ROI and RNI resistance mechanisms. ROI resistance pathways have been intensively studied. Much less is known about the mechanisms of resistance to RNI. To identify possible RNI resistance genes in M. tuberculosis, a mycobacterial library was expressed in S. typhimurium and subjected to selection by exposure to the NO donor S-nitrosoglutathione (GSNO) in concentrations sufficient to kill the vast majority of nontransformed salmonellae. Among the rare surviving recombinants was a clone expressing noxR3, a novel and previously anonymous M. tuberculosis gene predicted to encode a small, basic protein. Expression of noxR3 protected S. typhimurium not only from GSNO and acidified nitrite but also from H2O2. noxR3 is the third gene cloned from M. tuberculosis that has been shown to protect heterologous cells from both RNI and ROI. This suggests diversity in the repertoire of mechanisms that help pathogens resist the oxidative and nitrosative defenses of the host.

Amino Acid Sequence↗