21,739 research outputs found

    Hooray for Hypoxia?

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    The mortality of critically ill patients rises steadily as the partial pressure of arterial oxygen falls below about 11 kPa (80 mm Hg). A new animal study in the May 2005 issue of PLoS Biology showing a potential benefit for hypoxia is thus a challenge to current thinking

    Oxygenation inhibits the physiological tissue-protecting mechanism and thereby exacerbates acute inflammatory lung injury

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    Acute respiratory distress syndrome (ARDS) usually requires symptomatic supportive therapy by intubation and mechanical ventilation with the supplemental use of high oxygen concentrations. Although oxygen therapy represents a life-saving measure, the recent discovery of a critical tissue-protecting mechanism predicts that administration of oxygen to ARDS patients with uncontrolled pulmonary inflammation also may have dangerous side effects. Oxygenation may weaken the local tissue hypoxia-driven and adenosine A2A receptor (A2AR)-mediated anti-inflammatory mechanism and thereby further exacerbate lung injury. Here we report experiments with wild-type and adenosine A2AR-deficient mice that confirm the predicted effects of oxygen. These results also suggest the possibility of iatrogenic exacerbation of acute lung injury upon oxygen administration due to the oxygenation-associated elimination of A2AR-mediated lung tissue-protecting pathway. We show that this potential complication of clinically widely used oxygenation procedures could be completely prevented by intratracheal injection of a selective A2AR agonist to compensate for the oxygenation-related loss of the lung tissue-protecting endogenous adenosine. The identification of a major iatrogenic complication of oxygen therapy in conditions of acute lung inflammation attracts attention to the need for clinical and epidemiological studies of ARDS patients who require oxygen therapy. It is proposed that oxygen therapy in patients with ARDS and other causes of lung inflammation should be combined with anti-inflammatory measures, e.g., with inhalative application of A2AR agonists. The reported observations may also answer the long-standing question as to why the lungs are the most susceptible to inflammatory injury and why lung failure usually precedes multiple organ failure

    HIF1A reduces acute lung injury by optimizing carbohydrate metabolism in the alveolar epithelium

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    Background: While acute lung injury (ALI) contributes significantly to critical illness, it resolves spontaneously in many instances. The majority of patients experiencing ALI require mechanical ventilation. Therefore, we hypothesized that mechanical ventilation and concomitant stretch-exposure of pulmonary epithelia could activate endogenous pathways important in lung protection. Methods and Findings: To examine transcriptional responses during ALI, we exposed pulmonary epithelia to cyclic mechanical stretch conditions—an in vitro model resembling mechanical ventilation. A genome-wide screen revealed a transcriptional response similar to hypoxia signaling. Surprisingly, we found that stabilization of hypoxia-inducible factor 1A (HIF1A) during stretch conditions in vitro or during ventilator-induced ALI in vivo occurs under normoxic conditions. Extension of these findings identified a functional role for stretch-induced inhibition of succinate dehydrogenase (SDH) in mediating normoxic HIF1A stabilization, concomitant increases in glycolytic capacity, and improved tricarboxylic acid (TCA) cycle function. Pharmacologic studies with HIF activator or inhibitor treatment implicated HIF1A-stabilization in attenuating pulmonary edema and lung inflammation during ALI in vivo. Systematic deletion of HIF1A in the lungs, endothelia, myeloid cells, or pulmonary epithelia linked these findings to alveolar-epithelial HIF1A. In vivo analysis of 13C-glucose metabolites utilizing liquid-chromatography tandem mass-spectrometry demonstrated that increases in glycolytic capacity, improvement of mitochondrial respiration, and concomitant attenuation of lung inflammation during ALI were specific for alveolar-epithelial expressed HIF1A. Conclusions: These studies reveal a surprising role for HIF1A in lung protection during ALI, where normoxic HIF1A stabilization and HIF-dependent control of alveolar-epithelial glucose metabolism function as an endogenous feedback loop to dampen lung inflammation

    Attenuation of ischemic liver injury by prostaglandin E<inf>1</inf> analogue, misoprostol, and prostaglandin I<inf>2</inf> analogue, OP-41483

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    Background: Prostaglandin has been reported to have protective effects against liver injury. Use of this agent in clinical settings, however, is limited because of drugrelated side effects. This study investigated whether misoprostol, prostaglandin E1 analogue, and OP-41483, prostaglandin I2 analogue, which have fewer adverse effects with a longer half-life, attenuate ischemic liver damage. Study Design: Thirty beagle dogs underwent 2 hours of hepatic vascular exclusion using venovenous bypass. Misoprostol was administered intravenously for 30 minutes before ischemia and for 3 hours after reperfusion. OP-41483 was administered intraportally for 30 minutes before ischemia (2 μg/kg/min) and for 3 hours after reperfusion (0.5 μg/kg/min). Animals were divided into five groups: untreated control group (n = 10); high-dose misoprostol (total 100 μg/kg) group (MP-H, n = 5); middle-dose misoprostol (50 μg/kg) group (MP-M, n = 5); low-dose misoprostol (25 μg/kg) group (MP-L, n = 5); and OP-41483 group (OP, n = 5). Animal survival, hepatic tissue blood flow (HTBF), liver function, and histology were analyzed. Results: Two-week animal survival rates were 30% in control, 60% in MP-H, 100% in MP-M, 80% in MP-L, and 100% in OP. The treatments with prostaglandin analogues improved HTBF, and attenuated liver enzyme release, adenine nucleotrides degradation, and histologic abnormalities. In contrast to the MP-H animals that exhibited unstable cardiovascular systems, the MP- M, MP-L, and OP animals experienced only transient hypotension. Conclusions: These results indicate that misoprostol and OP-41483 prevent ischemic liver damage, although careful dose adjustment of misoprostol is required to obtain the best protection with minimal side effects

    Regulation of peripheral inflammation by spinal p38 MAP kinase in rats.

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    BackgroundSomatic afferent input to the spinal cord from a peripheral inflammatory site can modulate the peripheral response. However, the intracellular signaling mechanisms in the spinal cord that regulate this linkage have not been defined. Previous studies suggest spinal cord p38 mitogen-activated protein (MAP) kinase and cytokines participate in nociceptive behavior. We therefore determined whether these pathways also regulate peripheral inflammation in rat adjuvant arthritis, which is a model of rheumatoid arthritis.Methods and findingsSelective blockade of spinal cord p38 MAP kinase by administering the p38 inhibitor SB203580 via intrathecal (IT) catheters in rats with adjuvant arthritis markedly suppressed paw swelling, inhibited synovial inflammation, and decreased radiographic evidence of joint destruction. The same dose of SB203580 delivered systemically had no effect, indicating that the effect was mediated by local concentrations in the neural compartment. Evaluation of articular gene expression by quantitative real-time PCR showed that spinal p38 inhibition markedly decreased synovial interleukin-1 and -6 and matrix metalloproteinase (MMP3) gene expression. Activation of p38 required tumor necrosis factor alpha (TNFalpha) in the nervous system because IT etanercept (a TNF inhibitor) given during adjuvant arthritis blocked spinal p38 phosphorylation and reduced clinical signs of adjuvant arthritis.ConclusionsThese data suggest that peripheral inflammation is sensed by the central nervous system (CNS), which subsequently activates stress-induced kinases in the spinal cord via a TNFalpha-dependent mechanism. Intracellular p38 MAP kinase signaling processes this information and profoundly modulates somatic inflammatory responses. Characterization of this mechanism could have clinical and basic research implications by supporting development of new treatments for arthritis and clarifying how the CNS regulates peripheral immune responses

    Nucleotide-, chemotactic peptide- and phorbol ester-induced exocytosis in HL-60 leukemic cells

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    Undifferentiated and differentiated HL-60 leukemic cells possess nucleotide receptors which functionally couple to phospholipase C via pertussis toxin-sensitive guanine nucleotide-binding proteins (G-proteins). We investigated the role of extracellular nucleotides in the regulation of beta-glucuronidase release in HL-60 cells. In dibutyryl cyclic AMP (Bt2cAMP)-differentiated HL-60 cells, the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe), the phosphorothioate analogue of ATP, adenosine 5'-O-[3-thio]triphosphate (ATP[gamma S]), and UTP increased cytosolic Ca2+ from 100 nM up to 1.2 microM with EC50 values of 4 nM, 1 microM and 100 nM, respectively. In these cells, ATP[gamma S] induced exocytosis with an EC50 of 4 microM and an effectiveness amounting to 50-70% of that of fMet-Leu-Phe. ATP, ITP, UTP, CTP, and uridine 5'-O-[2-thio]diphosphate activated exocytosis as well. Phorbol myristate acetate (PMA) induced exocytosis with an EC50 of 115 ng/ml and an effectiveness similar to that of ATP[gamma S]. Cytochalasin B (CB) differently potentiated exocytosis induced by ATP[gamma S], fMet-Leu-Phe and PMA. Treatment of Bt2cAMP-differentiated HL-60 cells with pertussis toxin (500 ng/ml) for 24 h resulted in ADP-ribosylation of more than 97.5% of the G-proteins. Under these conditions, pertussis toxin almost completely inhibited the increase in cytosolic Ca2+ and beta-glucuronidase release induced by fMet-Leu-Phe but only partially inhibited the effects of ATP[gamma S] and UTP. fMet-Leu-Phe at a non-stimulatory concentration (1 nM) potentiated ATP[gamma S]-induced beta-glucuronidase release in the presence but not in the absence of CB. In contrast, ATP[gamma S] and fMet-Leu-Phe synergistically activated superoxide formation in the absence of CB. PMA potentiated superoxide formation induced by ATP[gamma S] or fMet-Leu-Phe and did not affect exocytosis induced by ATP[gamma S] or fMet-Leu-Phe. In undifferentiated HL-60 cells, fMet-Leu-Phe, ATP[gamma S], UTP and PMA did not induce beta-glucuronidase release. fMet-Leu-Phe did not increase cytosolic Ca2+ in undifferentiated HL-60 cells, whereas ATP[gamma S] and UTP were similarly potent and effective as in Bt2cAMP-differentiated cells. In differentiated HL-60 cells, fMet-Leu-Phe induced aggregation, and ATP[gamma S] induced a transient shape change. Our results show (I) that exocytosis in HL-60 cells does not obligatorily depend on CB. (II) Purine and pyrimidine nucleotides activate exocytosis via pertussis toxin-sensitive and -insensitive signal transduction pathways.(ABSTRACT TRUNCATED AT 400 WORDS

    Evidence for coordinated induction and repression of ecto-5'-nucleotidase (CD73) and the A2a adenosine receptor in a human B cell line

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    In the human B cell line P493-6 two mitogenic signals, the EpsteinBarr virus nuclear antigen 2 (EBNA2) and myc, can be independently regulated by means of an estrogen receptor fusion construct or an inducible expression vector, respectively. Shut off of EBNA2, either in the presence or absence of myc, leads to a significant increase in enzymatic activity and surface expression of ecto-5nucleotidase (CD73) as well as an increased adenosine receptor response in cyclic AMP formation. Shut off of myc expression has a small additional positive effect on CD73 activity. Among the four different subtypes of adenosine receptors, the A2a receptor exclusively is subject to regulation in this system, which is substantiated by pharmacologic data (specific agonists and inhibitors), as well as on the mRNA level. With upregulated CD73 and A2a, cells also respond to 5AMP with increased cyclic AMP formation. Turn on of EBNA2 has the reverse effect of repression of CD73 and A2a expression. The time course of both induction and repression of CD73 and A2a is rather slow

    Physiological roles for ecto-5’-nucleotidase (CD73)

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    Nucleotides and nucleosides influence nearly every aspect of physiology and pathophysiology. Extracellular nucleotides are metabolized through regulated phosphohydrolysis by a series of ecto-nucleotidases. The formation of extracellular adenosine from adenosine 5’-monophosphate is accomplished primarily through ecto-5’-nucleotidase (CD73), a glycosyl phosphatidylinositol-linked membrane protein found on the surface of a variety of cell types. Recent in vivo studies implicating CD73 in a number of tissue protective mechanisms have provided new insight into its regulation and function and have generated considerable interest. Here, we review contributions of CD73 to cell and tissue stress responses, with a particular emphasis on physiologic responses to regulated CD73 expression and function, as well as new findings utilizing Cd73-deficient animals

    Bacillus anthracis edema factor substrate specificity: evidence for new modes of action

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    Since the isolation of Bacillus anthracis exotoxins in the 1960s, the detrimental activity of edema factor (EF) was considered as adenylyl cyclase activity only. Yet the catalytic site of EF was recently shown to accomplish cyclization of cytidine 5'-triphosphate, uridine 5'-triphosphate and inosine 5'-triphosphate, in addition to adenosine 5'-triphosphate. This review discusses the broad EF substrate specificity and possible implications of intracellular accumulation of cyclic cytidine 3':5'-monophosphate, cyclic uridine 3':5'-monophosphate and cyclic inosine 3':5'-monophosphate on cellular functions vital for host defense. In particular, cAMP-independent mechanisms of action of EF on host cell signaling via protein kinase A, protein kinase G, phosphodiesterases and CNG channels are discussed
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