Journal of cellular physiology
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Suppression of inducible nitric oxide generation by agmatine aldehyde: beneficial effects in sepsis.
The induction of inducible nitric oxide synthase (iNOS) serves an important immuno-protective function in inflammatory states, but ungoverned nitric oxide (NO) generation can contribute to a number of pathologic consequences. Delineation of the mechanisms that can downregulate iNOS-generated NO in inflammation could have therapeutic relevance. Here we show that agmatine, a metabolite of arginine, inhibits iNOS mediated nitric oxide generation in cytokine stimulated cell culture preparations. ⋯ Agmatine treatment also increased the survival of LPS treated mice. Our data demonstrate the capacity of agmatine aldehyde to suppress iNOS mediated NO generation, and indicate a protective function of agmatine in a model of endotoxic shock. How agmatine may aid in coordinating the early NO phase and the later repair phase responses in models of inflammation is discussed.
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A mutant Escherichia coli lipopolysaccharide (LPS) lacking myristoyl fatty acid markedly stimulates the activity of manganese superoxide dismutase (MnSOD) without inducing tumor necrosis factor alpha (TNFalpha) production by human monocytes (Tian et al., 1998, Am J Physiol 275:C740.), suggesting that induction of MnSOD and TNFalpha by LPS are regulated through different signal transduction pathways. The protein tyrosine kinase (PTK)/mitogen-activated protein kinase (MAPK) pathway plays an important role in the LPS-induced TNFalpha production. In the current study, we determined the effects of PTK inhibitors, genistein and herbimycin A, on the induction of MnSOD and TNFalpha in human monocytes. ⋯ In contrast, at similar concentrations, genistein and herbimycin A had no effect on the LPS-induced activation of nuclear factor kappaB (NFkappaB) and induction of MnSOD (mRNA and enzyme activity) in human monocytes. In addition, inhibition of NFkappaB activation by gliotoxin and pyrrodiline dithiocarbamate, inhibited LPS induction of TNFalpha and MnSOD mRNAs. These results suggest that (1) while PTK and MAPK are essential for the production of TNFalpha, they are not necessary for the induction of MnSOD by LPS, and (2) while activation of NFkappaB alone is insufficient for the induction of TNFalpha mRNA by LPS, it is necessary for the induction of TNFalpha as well as MnSOD mRNAs.
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Mucosal tissues, such as the lung and intestine, are primary targets for ischemic damage. Under these conditions, neutrophil (polymorphonuclear leukocyte; PMN) infiltration into the protective epithelium has been implicated as a pathophysiologic mediator. Because PMN transepithelial migration results in increased paracellular permeability, and because our previous data revealed that epithelial hypoxia enhances PMN transmigration, we hypothesized that macromolecular permeability may be altered in epithelium exposed to hypoxia and reoxygenation (H/R) in the presence of PMNs. ⋯ Because intracellular cyclic AMP (cAMP) has been demonstrated to regulate epithelial permeability, and because PMN-derived compound(s), (i.e., 5'-adenosine monophosphate; AMP) elevate epithelial cAMP, we examined the impact of hypoxia on epithelial cAMP responses. These experiments revealed that hypoxic epithelia were diminished in their ability to generate cAMP, and pharmacologic elevation (8-bromo-cAMP) of intracellular cAMP in hypoxic cells normalized both PMN-induced permeability changes and restoration of barrier function. These results support a role for PMN in increased intestinal permeability associated with reperfusion injury and imply a substantial role for cAMP signaling in maintenance of permeability during PMN transmigration.
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To clarify the manner by which erythropoietin (EP), stem cell factor (SCF), or insulin-like growth factor I (IGF-I) regulate erythropoiesis, apoptosis of human erythroid progenitor cells was investigated. Human burst-forming units-erythroid (BFU-E) partially purified from peripheral blood were cultured for 6 days to generate erythroid colony-forming cells (ECFC), which consist mainly of colony-forming units-erythroid (CFU-E). The cells were labeled with [3H]thymidine, incubated in serum-free liquid media, at 37 degrees C, for 16 h, and the pattern of DNA breakdown was analyzed by agarose gel electrophoresis. ⋯ Dose-response experiments with SCF and IGF-I showed a dose-dependent reduction in DNA fragmentation at concentrations that stimulate colony formation in serum-free semisolid cultures. Finally, assays of ECFC performed by the plasma clot method, after serum-free liquid culture, at 37 degrees C, for 16 h, demonstrated marked protection of erythroid colony-forming capacity by SCF or IGF-I in the absence of EP, as well as by EP itself. These data indicate that human erythroid progenitor cells undergo apoptosis which is reduced by SCF and IGF-I as well as EP and suggest that the control of apoptosis by each of these factors has a prominent role in the regulation of erythropoiesis.
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Regulation of polyamine transport in murine L1210 leukemia cells was characterized in order to better understand its relationship to specific intracellular polyamines and their analogs and to quantitate the sensitivity by which it is controlled. Up-regulation of polyamine uptake was evaluated following a 48-hr treatment with a combination of biosynthetic enzyme inhibitors to deplete intracellular polyamine pools. The latter declined gradually over 48 hr and was accompanied by a steady increase in spermidine (SPD) and spermine (SPM) transport as indicated by rises in Vmax to levels approximately 4.5 times higher than control values. ⋯ A dose response with BESPM at 48 hr revealed a biphasic effect on uptake whereby concentrations of analog < 3 microM produced an increase in SPD and SPM Vmax values, whereas concentrations 3 microM and higher produced a marked suppression of these values. Cells treated with 3 microM BESPM for 2 hr and placed in analog-free medium recovered transport capability in only 3 hr. Thus, whereas stimulation of polyamine transport is a relatively insensitive and slowly responsive process that tends to parallel polyamine depletion, down-regulation of polyamine transport by exogenous polyamines and analogs and its reversal are rapidly responsive events that correlate with relatively small (i.e., 15-20%) changes in intracellular polyamine pools.