Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P43026 (lipopolysaccharide)
 62,215 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Histamine is inactivated by the histamine-metabolizing enzyme histamine N-methyltransferase (HNMT) in bronchus, kidney, and the central nervous system. HNMT seems to be localized in the cytoplasm, but histamine is unable to easily enter the intracellular space. Therefore, two hypotheses can be elicited: one is the plasma membrane hypothesis that HNMT can be translocated to the plasma membrane and function at the cell surface under growth factor stimulation and the other is the transporter hypothesis that organic cation transporter (OCT)-2 and -3 can function as a histamine transporter as well. To investigate the involvement of OCT2, HEK293 cells stably double transfected with C-terminal hemagglutinin (HA)-tagged HNMT cDNA and/or C-terminal myc-tagged rat OCT2 were prepared for analysis of HNMT activity associated with OCT2 function. After 60-min incubation of these cells with PBS including HA (100 microM), N(tau)-methylhistamine (MHA) concentration of the supernatants was determined by the HPLC-fluorometry method. MHA from cells with HNMT plus OCT-2 was produced at about 3-fold higher level than that from cells with HNMT alone, suggesting that OCT-2 could function as a histamine transporter as well and that HNMT function could partly depend on OCT-2 transporter activity. Using OCT-3 knockout (OCT-3-/-) mice, histamine content and survival rates were investigated in lipopolysaccharide (LPS)-induced endotoxemia model. Without LPS stimulation, histamine content was compared between OCT-3-/- and wild mice. Histamine content in the spleen of OCT-3-/- mice was higher than that f wild mice. With LPS stimulation, the survival rate of OCT-3-/- mice was significantly decreased 12 h after LPS (20 mg/kg) stimulation, suggesting that before immunological stimulation, a higher content of histamine in spleen could stimulate histamine receptors in mast cells, macrophages, dendritic cells, as well as T lymphocytes and explaining the decreased survival rate in OCT-3-/- mice possibly due to the functional changes of immunological cells.
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PMID:Recent advances in molecular pharmacology of the histamine systems: organic cation transporters as a histamine transporter and histamine metabolism. 1664 65

We examined whether treatment with amodiaquine, a potent inhibitor of histamine N-methyltransferase protects mice from Propionibacterium acnes (P. acnes)-primed and lipopolysaccharide (LPS)-induced hepatitis. The subcutaneous injection of amodiaquine (2 and 5 mg/kg) significantly increased the histamine levels in the liver in comparison to saline treated mice. Pretreatment with amodiaquine also improved the survival rate of the hepatitis mice, and this improvement was partially associated with the decrease in serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Amodiaquine partially suppressed increases of tumor necrosis factor (TNF)-alpha in the serum and TNF-alpha mRNA expression in the liver, whereas the expression of interleukin (IL)-18, interferon (IFN)-gamma and IL-12 in the liver was not changed by amodiaquine treatment. In conclusion, the present findings suggested that the elevation of endogenous histamine by amodiaquine may thus play a protective role through the regulation of TNF-alpha production in endotoxin-induced hepatic injury mice.
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PMID:Effect of amodiaquine, a histamine N-methyltransferase inhibitor, on, Propionibacterium acnes and lipopolysaccharide-induced hepatitis in mice. 1722 19

Histamine is a physiological amine which initiates a multitude of physiological responses by binding to four known G-protein coupled histamine receptor subtypes as follows: histamine H1 receptor (H1 R), H2 R, H3 R, and H4 R. Brain histamine elicits neuronal excitation and regulates a variety of physiological processes such as learning and memory, sleep-awake cycle and appetite regulation. Microglia, the resident macrophages in the brain, express histamine receptors; however, the effects of histamine on critical microglial functions such as chemotaxis, phagocytosis, and cytokine secretion have not been examined in primary cells. We demonstrated that mouse primary microglia express H2 R, H3 R, histidine decarboxylase, a histamine synthase, and histamine N-methyltransferase, a histamine metabolizing enzyme. Both forskolin-induced cAMP accumulation and ATP-induced intracellular Ca(2+) transients were reduced by the H3 R agonist imetit but not the H2 R agonist amthamine. H3 R activation on two ubiquitous second messenger signalling pathways suggests that H3 R can regulate various microglial functions. In fact, histamine and imetit dose-dependently inhibited microglial chemotaxis, phagocytosis, and lipopolysaccharide (LPS)-induced cytokine production. Furthermore, we confirmed that microglia produced histamine in the presence of LPS, suggesting that H3 R activation regulate microglial function by autocrine and/or paracrine signalling. In conclusion, we demonstrate the involvement of histamine in primary microglial functions, providing the novel insight into physiological roles of brain histamine.
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PMID:Histamine H3 receptor in primary mouse microglia inhibits chemotaxis, phagocytosis, and cytokine secretion. 2575 56