leukotriene-b4 and Trichinellosis

Trichinella spiralis infection causes hyperexcitability in enteric after-hyperpolarising (AH) sensory neurons that is mimicked by neural, immune or inflammatory mediators known to stimulate adenylyl cyclase (AC)/cyclic 3',5'-adenosine monophosphate (cAMP) signaling. The hypothesis was tested that ongoing modulation and sustained amplification in the AC/cAMP/phosphorylated cAMP related element binding protrein (pCREB) signaling pathway contributes to hyperexcitability and neuronal plasticity in gut sensory neurons after nematode infection. Electrophysiological, immunological, molecular biological or immunochemical studies were done in T. spiralis-infected guinea-pigs (8000 larvae or saline) after acute-inflammation (7 days) or 35 days p.i., after intestinal clearance. Acute-inflammation caused AH-cell hyperexcitability and elevated mucosal and neural tissue levels of myeloperoxidase, mast cell tryptase, prostaglandin E2, leukotrine B4, lipid peroxidation, nitric oxide and gelatinase; lower level inflammation persisted 35 days p.i. Acute exposure to blockers of AC, histamine, cyclooxygenase or leukotriene pathways suppressed AH-cell hyperexcitability in a reversible manner. Basal cAMP responses or those evoked by forskolin (FSK), Ro-20-1724, histamine or substance P in isolated myenteric ganglia were augmented after T. spiralis infection; up-regulation also occurred in AC expression and AC-immunoreactivity in calbindin (AH) neurons. The cAMP-dependent slow excitatory synaptic transmission-like responses to histamine (mast cell mediator) or substance P (neurotransmitter) acting via G-protein coupled receptors (GPCR) in AH neurons were augmented by up to 2.5-fold after T. spiralis infection. FSK, histamine, substance P or T. spiralis acute infection caused a 5- to 30-fold increase in cAMP-dependent nuclear CREB phosphorylation in isolated ganglia or calbindin (AH) neurons. AC and CREB phosphorylation remained elevated 35 days p.i.. Ongoing immune activation, AC up-regulation, enhanced phosphodiesterase IV activity and facilitation of the GPCR-AC/cAMP/pCREB signaling pathway contributes to T. spiralis-induced neuronal plasticity and AH-cell hyperexcitability. This may be relevant in gut nematode infections and inflammatory bowel diseases, and is a potential therapeutic target.

Topics: Animals; Colforsin; Cyclic AMP; Cyclic AMP Response Element-Binding Protein; Dideoxyadenosine; Dinoprostone; Guinea Pigs; Histamine; Imidazoles; In Vitro Techniques; Intestinal Mucosa; Leukotriene B4; Lysine; Male; Membrane Potentials; Muscle, Smooth; Neuronal Plasticity; Neurons, Afferent; Nitric Oxide; Peroxidase; Signal Transduction; Substance P; Thiobarbituric Acid Reactive Substances; Trichinella spiralis; Trichinellosis; Tryptases

Rapid expulsion of the nematode Trichinella spiralis from immune rats is associated with an increase in volume of intestinal exudate and the presence of large numbers of tissue mucosal mast cells (MMC) and eosinophils. We have measured the concentrations of leukotrienes (LT) C4 (LTC4) and B4 (LTB4) in gut perfusates and mucosal homogenates at 30 min, 1, 3, 6 and 20 hr after challenge with larvae. Leukotrienes were identified by radioimmunoassay (RIA) combined with reverse-phase high-pressure liquid chromatography (RP-HPLC). There were significant elevations at 30 min and 1 hr in the concentrations of LTC4 in the perfusates from the gut of challenged immune rats compared to controls (infected unchallenged and uninfected naive rats). Similar increases in immunoreactive LTC4 and LTB4 were observed in mucosal homogenates from the gut of immune challenged animals. A second peak of LTB4 was also observed at 20 hr in both immune and naive challenged rats. There were also elevations in serum concentration of the MMC-associated specific serine protease, rat mast cell protease II (RMCPII). Since LTC4 causes smooth muscle contraction, increased vascular permeability and stimulation of mucus hypersecretion, and LTB4 recruits and activates inflammatory cells, leukotrienes may participate in the process of rapid expulsion of T. spiralis.

Topics: Animals; Chromatography, High Pressure Liquid; Chymases; Endopeptidases; Female; Immunity; Intestine, Small; Leukotriene B4; Mast Cells; Radioimmunoassay; Rats; Serine Endopeptidases; SRS-A; Trichinellosis