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Biomedical subjects

J C Hoyt

Publications and source records attributed to J C Hoyt.

15 recordsLinked to original sources
PubMed2001

Macrolide antibiotics and pulmonary inflammation.

Many clinically effective therapeutic agents can exhibit localized and systemic effects that are manifestly different from their intended primary pharmacological mode of action. Macrolide antibiotics such as erythromycin and its derivatives are no exception. In addition to their antibacterial action, this class of antibiotics exhibits anti-inflammatory activity in a variety of airway diseases such as asthma and diffuse panbronchiolitis that is separate and distinct from a direct antibacterial action. A variety of erythromycin derivatives have been shown to be clinically beneficial in these airway diseases. The anti-inflammatory activities of these macrolide antibiotics are becoming a research topic of intense interest. Recent work in this field has led to the understanding of the various physiological, cellular and molecular processes of the inflammatory response that are inhibited or suppressed by these compounds. This review presents a brief summary of the fascinating recent work in this active research area.

Anti-Bacterial Agents↗
PubMed2001

Peroxynitrite inhibits inducible (type 2) nitric oxide synthase in murine lung epithelial cells in vitro.

Peroxynitrite, formed by nitric oxide (NO) and superoxide, can alter protein function by nitrating amino acids such as tyrosine, cysteine, trytophan, or methionine. Inducible nitric oxide synthase (Type 2 NOS or iNOS) converts arginine to citrulline, releasing NO. We hypothesized that peroxynitrite could function as a negative feedback modulator of NO production by nitration of iNOS. Confluent cultures of the murine lung epithelial cell line, LA-4 were stimulated with cytokines to express iNOS, peroxynitrite was added, and the flasks sealed. After 3 h, NO in the headspace above the culture was sampled. Peroxynitrite caused a concentration-dependent decrease in NO. Similar results were obtained when 3-morpholinosydnonimine (SIN-1), a peroxynitrite generator, was added to the flasks. PAPA-NONOate, the NO generator, did not affect the headspace NO. Nitration of the iNOS was confirmed by detection of 3-nitrotyrosine by Western blotting. These data suggest a mechanism for inhibition of NO synthesis at inflammatory sites where iNOS, NO, and superoxide would be expected.

Animals↗
PubMed2001

Inflammatory cytokines modulate eotaxin release by human lung fibroblast cell line.

Eotaxin, a potent eosinophil-specific chemotactic factor, is increased in the lower respiratory tract of asthma patients. Recently, lung fibroblasts have been reported to produce eotaxin and their activation can be modulated by inflammatory cytokines. To test the hypothesis that inflammatory cytokines modulate the eotaxin release from lung fibroblasts, we investigated the potential of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), or interferon-gamma (IFN-gamma) to induce the release of eotaxin and eotaxin mRNA by the human fetal lung fibroblast cell line, HFL-1, was evaluated. HFL-1 released eotaxin constitutively without stimulation, but IL-1beta or TNF-alpha stimulated eotaxin release in a dose- and time-dependent manner. IL-1beta or TNF-alpha treatment of HFL-1 also resulted in the augmented expression of eotaxin mRNA. Although IFN-gamma alone had negligible effect on eotaxin release and mRNA expression, IFN-gamma induced a significant, concentration-dependent attenuation of eotaxin release and eotaxin mRNA expression from HFL-1 stimulated with IL-1beta or TNF-alpha. These findings are consistent with the concept that lung fibroblast-derived eotaxin may in part be responsible for the eosinophil infiltration observed in the airways of asthmatic patients and that network of cytokines may modulate the eosinophil recruitment to the airways by stimulation of fibroblasts to release eotaxin.

Cell Line↗
PubMed2001

Erythromycin modulates eosinophil chemotactic cytokine production by human lung fibroblasts in vitro.

Recent studies suggest that erythromycin can suppress the production of some cytokines and may be an effective treatment for asthma. Eosinophil chemotactic cytokines have been suggested to contribute to the pathogenesis of asthma by the recruitment of eosinophils. We hypothesized that erythromycin modulates eosinophil chemotactic cytokine production. To test the hypothesis, we evaluated the potential of erythromycin to modulate the release of eosinophil chemoattractants from the human lung fibroblast cell line HFL-1. HFL-1 released eotaxin, granulocyte-macrophage colony-stimulating factor, and regulated and normal T-cell expressed and presumably secreted (RANTES) in response to interleukin-1beta or tumor necrosis factor alpha. Erythromycin attenuated the release of these cytokines and eosinophil chemotactic activity by the HFL-1. The suppressive effect on eotaxin was the most marked of these cytokines. Erythromycin therapy also suppressed eotaxin mRNA significantly. These results suggest a mechanism that may account for the apparent beneficial action of macrolide antibiotics in the treatment of allergic airway disorders.

Anti-Bacterial Agents↗
PubMed2000

Bradykinin stimulates eotaxin production by a human lung fibroblast cell line.

BACKGROUND: Bradykinin, a potent inflammatory peptide, is increased in the airways of allergic patients. Accompanying the elevated bradykinin levels are increases in both eosinophils and fibroblasts. Eotaxin, a potent eosinophil-specific chemotactic factor, is released by fibroblasts and increased in the lower respiratory tract of allergic patients. OBJECTIVE: We sought to test the hypothesis that lung fibro-blasts release eotaxin in response to bradykinin. METHODS: The potential of bradykinin to induce the release of eotaxin from the human lung fibroblast cell line HFL-1 was tested by cell culture and evaluation of the culture supernatant fluids and RNA for immunoreactive eotaxin and eotaxin messenger RNA. RESULTS: HFL-1 cells released eotaxin constitutively without stimulation, but bradykinin stimulated eotaxin release in a dose- and time-dependent manner and resulted in augmented expression of eotaxin messenger RNA. The release of eotaxin was sensitive to the action of glucocorticoids. Eosinophil chemotactic activity by HFL-1 supernatant fluids was inhibited by anti-human eotaxin-neutralizing antibody. Consistent with these results, inhibitors of bradykinin B2 receptors, but not bradykinin B1 receptors, inhibited bradykinin-induced eotaxin release. CONCLUSION: These data demonstrate that bradykinin may stimulate lung fibroblasts to release eotaxin and suggest the potential for this mechanism to be important in modulation of lung inflammation.

Bradykinin↗
PubMed1997

Purification and preliminary characterization of (E)-3-(2,4-dioxo-6-methyl-5-pyrimidinyl)acrylic acid synthase, an enzyme involved in biosynthesis of the antitumor agent sparsomycin.

Sparsomycin is an antitumor antibiotic produced by Streptomyces sparsogenes. Biosynthetic experiments have previously demonstrated that one component of sparsomycin is derived from L-tryptophan via the intermediacy of (E)-3-(4-oxo-6-methyl-5-pyrimidinyl)acrylic acid and (E)-3-(2,4-dioxo-6-methyl-5-pyrimidinyl)acrylic acid. An enzyme which catalyzes the conversion of (E)-3-(4-oxo-6-methyl-5-pyrimidinyl)acrylic acid to (E)-3-(2,4-dioxo-6-methyl-5-pyrimidinyl)acrylic acid has been purified 740-fold to homogeneity from S. sparsogenes. The molecular mass of the native and denatured enzyme was 87 kDa, indicating that the native enzyme is monomeric. The enzyme required NAD+ for activity but lacked rigid substrate specificity, since analogs of both NAD+ and 3-(4-oxo-6-methyl-5-pyrimidinyl)acrylic acid could serve as substrates. The enzyme was very weakly inhibited by mycophenolic acid. Monovalent cations were required for activity, with potassium ions being the most effective. The enzyme exhibited sensitivity toward diethylpyrocarbonate and some thiol-directed reagents, and it was irreversibly inhibited by 6-chloropurine. The properties of the enzyme suggest it is mechanistically related to inosine-5'-monophosphate dehydrogenase.

Acrylates↗
PubMed1996

Carbocyclic analogues of D-ribose-5-phosphate: synthesis and behavior with 5-phosphoribosyl alpha-1-pyrophosphate synthetases.

The synthesis of cyclopentyl and cyclopentenyl analogues of the alpha-anomer of D-ribose-5-phosphate from D-ribonolactone and D-ribose is described. These analogues, which have the same absolute configuration as D-ribose-5-phosphate, were incubated with PRPP synthetases in an attempt to prepare the corresponding carbocyclic PRPP analogues. The carbocyclic ribose-5-phosphate analogues were found to be inhibitors, rather than substrates, for 5-phosphoribosyl alpha-1-pyrophosphate synthetases of both bacterial and human origin. The inhibitory behaviour of the analogues is described.

Humans↗
PubMed1992

Phosphorylation of Acinetobacter isocitrate lyase.

During growth on succinate, Acinetobacter calcoaceticus contains two forms of the enzyme isocitrate dehydrogenase. Addition of acetate to a lag-phase culture grown on succinate causes a dramatic increase in activity of form II of isocitrate dehydrogenase and in isocitrate lyase. Form II of isocitrate dehydrogenase may be responsible for the partition of isocitrate between the TCA cycle and the glyoxylate by-pass. This report describes the phosphorylation of the enzyme isocitrate lyase from A. calcoaceticus. This phosphorylation may be a regulatory mechanism for the glyoxylate by-pass.

Acinetobacter calcoaceticus↗
PubMed1991

Purification and characterization of Acinetobacter calcoaceticus isocitrate lyase.

Acinetobacter calcoaceticus is capable of growing on acetate or compounds that are metabolized to acetate. During adaptation to growth on acetate, A. calcoaceticus B4 exhibits an increase in NADP(+)-isocitrate dehydrogenase and isocitrate lyase activities. In contrast, during adaptation to growth on acetate, Escherichia coli exhibits a decrease in NADP(+)-isocitrate dehydrogenase activity that is caused by reversible phosphorylation of specific serine residues on this enzyme. Also, in E. coli, isocitrate lyase is believed to be active only in the phosphorylated form. This phosphorylation of isocitrate lyase may regulate entry of isocitrate into the glyoxylate bypass. To understand the relationships between these two isocitrate-metabolizing enzymes and the metabolism of acetate in A. calcoaceticus B4 better, we have purified isocitrate lyase to homogeneity. Physical and kinetic characterization of the enzyme as well as the inhibitor specificity and divalent cation requirement have been examined.

Acinetobacter calcoaceticus↗
PubMed1989

Variceal transformation of the subendocardial microvasculature in regions of chronic myocardial ischemia.

The nature and cause of the striking regional dilatation of the microvasculature of the subendocardial myocardium seen in some patients with ischemic heart disease are unknown. To examine this question, we reviewed nine patients in whom regions of the left ventricular free wall had marked prominence of subendocardial vasculature on postmortem arteriography. All hearts had severe diffuse atherosclerosis of major epicardial coronary arteries. Histologic findings, including serial transmural sections, showed extreme dilatation of arterioles, capillaries, and venules of the subendocardial third of the myocardium. In this same region myocytes showed atrophy, vacuolization (a marker of chronic ischemia), and small foci of necrosis and fibrosis. The generalized small-vessel dilatation with adjacent ischemic myocytes makes it improbable that the vascular changes are caused by collateral flow. Previous anatomic studies have shown artery-vein arrangements in the myocardium providing for countercurrent regulation of regional blood flow. This mechanism, which produces vascular enlargement on the basis of metabolic need, may explain the regional variceal transformation of the subendocardial microvasculature seen with chronic ischemia.

Adult↗
PubMed1988

Escherichia coli isocitrate lyase: properties and comparisons.

The glyoxylate cycle was first discovered during studies on bacteria and fungi with the ability to grow on acetate or ethanol as the sole carbon source. Isocitrate lyase, the first enzyme unique to the glyoxylate cycle, has been studied in numerous prokaryotic and eukaryotic organisms. However, information on this enzyme from Escherichia coli is limited. We have recently reported the purification and in vitro phosphorylation of this enzyme. In the present study we have examined and characterized a variety of inhibitors, the divalent cation requirement and the amino acid composition of E. coli isocitrate lyase and compared these results to those obtained with other organisms.

Amino Acids↗
PubMed1988

In vivo phosphorylation of isocitrate lyase from Escherichia coli D5H3G7.

This report describes the in vivo phosphorylation of isocitrate lyase and examines the possible consequences to the control of the Kreb's cycle and glyoxylate bypass. NADP-specific isocitrate dehydrogenase from E. coli was the first bacterial protein whose enzymic activity was shown to be modulated by reversible phosphorylation. This enzyme has been thought to be solely responsible for the partitioning of isocitrate between the Kreb's cycle and glyoxylate bypass. No studies to date have examined the possible role of isocitrate lyase in controlling this flux.

Citric Acid Cycle↗
PubMed1988

Evidence of histidine phosphorylation in isocitrate lyase from Escherichia coli.

Escherichia coli isocitrate lyase (EC 4.1.3.1.) can be phosphorylated in vitro by an ATP-dependent reaction. The enzyme becomes phosphorylated by an endogenous kinase when partially purified sonic extracts are incubated with [gamma-32P]ATP. Treatment of isocitrate lyase with diethyl pyrocarbonate, a histidine-modifying reagent, blocked incorporation of [32P]phosphate from [gamma-32P]ATP. The isoelectric point of the enzyme was altered by treatment with phosphoramidate, a histidine phosphorylating agent, which suggests that isocitrate lyase can be phosphorylated at a histidine residue(s). Immunoprecipitated 32P-labeled isocitrate lyase was subjected to alkaline hydrolysis, mixed with chemically synthesized phosphohistidine standards, and analyzed by anion exchange chromatography. Characterization of the phosphoamino acid was based on the demonstration that the 32P-labeled product from alkali-hydrolyzed isocitrate lyase comigrated with synthetic 1-phosphohistidine. In addition, loss of catalytic activity after treatment with potato acid phosphatase indicates that catalytically active isocitrate lyase is the phosphorylated form of the enzyme.

Acid Phosphatase↗
PubMed1986

Angiomatous variant of so-called mesothelioma of the atrioventricular node.

A case is presented of an elderly woman found to have an angiomatous tumor involving the atrioventricular (AV) node. The entire AV node was not involved, which explains her lack of symptomatology during her life. The divergent histologic patterns observed in these tumors suggest that the term AV node tumor is preferable to the term mesothelioma.

Aged↗