Clinical significance of small airway obstruction markers in patients with asthma.

BACKGROUND: The role of small airway obstruction in the clinical expression of asthma is incompletely understood. OBJECTIVE: We tested the hypotheses that markers of small airway obstruction are associated with (i) increased asthma severity, (ii) impaired asthma control and quality of life and (iii) frequent exacerbations. METHODS: Seventy-four adults with asthma and 18 healthy control subjects underwent impulse oscillometry (IOS), multiple breath inert gas washout (MBW), body plethysmography, single-breath determination of carbon monoxide uptake and spirometry. Patients completed the six-point Asthma Control Questionnaire (ACQ-6) and standardized Asthma Quality of Life Questionnaire [AQLQ(S)]. Asthma severity was classified according to the Global Initiative for Asthma (GINA) treatment steps. RESULTS: The putative small airway obstruction markers Sacin , resistance at 5 Hz minus resistance at 20 Hz (R5-R20) and reactance area (AX) were not independently associated with asthma severity, control, quality of life or exacerbations. In contrast, markers of total (R5) and mean airway resistance of large and small airways (R20) were significantly higher in the severe asthma group compared with the mild-moderate group (0.47 vs. 0.37, P < 0.05 for R5; 0.39 vs. 0.31, P < 0.01 for R20). The strongest independent contributors to ACQ-6 score were R20 and forced expiratory volume in one second (% pred.), and the strongest independent contributors to AQLQ(S) score were R20 and forced vital capacity (% pred.). A history of one or more exacerbations within the previous year was independently associated with R20. CONCLUSIONS AND CLINICAL RELEVANCE: Previously reported markers of small airway obstruction do not appear to be independently associated with asthma disease expression. In contrast, the IOS parameter R20, a marker of mean airway resistance of both large and small airways, appears to have independent clinical significance. These observations require confirmation in prospective longitudinal studies.

TL1A/TNFSF15 directly induces proinflammatory cytokines, including TNFα, from CD3+CD161+ T cells to exacerbate gut inflammation.

Tumor necrosis factor (TNF)-like cytokine 1A (TL1A)/TNF superfamily member 15 (TNFSF15) is a proinflammatory cytokine and TNFα superfamily member that is linked preclinically and clinically to inflammatory bowel disease (IBD). By homology and function, TNFα is its closest family member. In this study, we investigated the mechanism of TL1A-induced inflammation in CD4+ T cells and compared it with the TNFα pathway. We found that TL1A induces proinflammatory cytokines, including TNFα, from isolated human CD4+CD161+ T cells, whereas these cells were resistant to TNFα treatment. Anti-TNFα failed to block TL1A-induced cytokine production, indicating that the effects of TL1A are direct. Lastly, CD161 and TL1A expression were significantly and selectively increased in gut tissue biopsies, but not in the peripheral blood, from IBD patients. Thus, TLIA not only functions upstream of TNFα, driving its expression from CD161+ T cells, but is also independent of TNFα. These findings may have therapeutic IBD implications.

The integrative membrane properties of human bronchial parasympathetic Ganglia neurons.

Parasympathetic ganglia neurons in the lower airway of laboratory animals have membrane properties associated with integration of signals from the central nervous system. In this study, intracellular recordings were made from parasympathetic ganglia located on bronchi from human lungs in order to determine the level of integration provided by human neurons. Ganglion neurons were characterized as either tonic or phasic: tonic neurons responded with repetitive action potentials sustained throughout a depolarizing current step whereas phasic neurons generated one action potential and accommodated. Phasic neurons could be further differentiated as having either short or long duration after hyperpolarizing potentials following single action potentials. In phasic neurons, stimulation of preganglionic nerves elicited one or two populations of nicotinic fast excitatory postsynaptic potentials (fEPSPs) that were graded in amplitude, subthreshold for action potential generation, and decreased in amplitude during higher frequency stimulation. In tonic neurons, single preganglionic stimuli evoked two to five populations of fEPSPs, one to three of which were at threshold for action potential generation. Dye injection into the neurons revealed multiple, branching dendrites. These results provide evidence that human bronchial ganglion neurons have unique membrane properties and anatomical characteristics associated with integrating presynaptic stimuli. Changes in these properties may thus affect output from these ganglia and, consequently, autonomic tone in the lower airways.

Neural integration and allergic disease.

Changes in neural activity play a key role in many symptoms of allergic disease, including sneezing, coughing, itching, and ocular irritation, among others. The mechanisms underlying allergen-induced changes in neural activity (reflexes) are largely unknown and under active investigation. Allergic inflammation can affect neural activity on a variety of levels, including at the primary afferent sensory nerve, integrative centers of the central nervous system, autonomic ganglia, and autonomic neuroeffector junction. At the level of the afferent sensory nerve, mediators released after allergen exposure either directly or indirectly increase neuronal firing. At the level of sensory ganglia, which contain cell bodies that innervate a variety of organs, changes in neuronal excitability may lead to a generalization of allergic symptoms. In the central nervous system, where afferent inputs from throughout the body converge, allergic inflammation may be associated with central sensitization, leading to the modulation of the neural reflexes. Finally, at the autonomic ganglia and neuroeffector junction, allergic inflammation appears to be associated with enhanced ganglionic transmission and neurotransmitter release, respectively. Mechanisms by which allergen challenge affects neuronal activity at various levels of the nervous system are reviewed, with a primary emphasis on studies of airway physiologic factors.

Effect of bradykinin on membrane properties of guinea pig bronchial parasympathetic ganglion neurons.

The effect of bradykinin on membrane properties of parasympathetic ganglion neurons in isolated guinea pig bronchial tissue was studied using intracellular recording techniques. Bradykinin (1-100 nM) caused a reversible membrane potential depolarization of ganglion neurons that was not associated with a change in input resistance. The selective bradykinin B(2) receptor antagonist HOE-140 inhibited bradykinin-induced membrane depolarizations. Furthermore, the cyclooxygenase inhibitor indomethacin attenuated bradykinin-induced membrane depolarizations to a similar magnitude ( approximately 70%) as HOE-140. However, neurokinin-1 and -3 receptor antagonists did not have similar inhibitory effects. The ability of bradykinin to directly alter active properties of parasympathetic ganglion neurons was also examined. Bradykinin (100 nM) significantly reduced the duration of the afterhyperpolarization (AHP) that followed four consecutive action potentials. The inhibitory effect of bradykinin on the AHP response was reversed by HOE-140 but not by indomethacin. These results indicate that bradykinin can stimulate airway parasympathetic ganglion neurons independent of sensory nerve activation and provide an alternative mechanism for regulating airway parasympathetic tone.

Characterization of vagal afferent subtypes stimulated by bradykinin in guinea pig trachea.

In vitro electrophysiological techniques were used to examine the effect of bradykinin on guinea pig trachea and bronchus afferent nerve endings arising from the nodose or jugular ganglia. The data reveal that bradykinin activates nerve terminals of jugular C and Adelta fibers. Although the fibers were too few in number to study rigorously, bradykinin also stimulated nodose C fibers innervating the trachea and bronchus. In contrast, Adelta fibers arising from the nodose ganglion were unresponsive to bradykinin challenge. The responses in both jugular C and Adelta fiber types were blocked by a selective bradykinin B2 receptor antagonist and were not dependent on the efferent release of sensory neuropeptides. These data indicate that the sensitivity of guinea pig airway afferent fibers to bradykinin is dependent more on the ganglionic origin of the cell body than on the conduction velocity of its axon.

Modulation of the release and activity of neuropeptides in the microcirculation.

Electrical stimulation of the sensory saphenous nerve leads to neurogenic edema formation in the innervated area of the paw of the anesthetized rat. Evidence suggests that the edema formation is the result of increased microvascular permeability mediated via neurokinin NK1 receptors and increased blood flow mediated via calcitonin gene related peptide CGRP1 receptors. Results indicate that selective receptor antagonists will only inhibit the response mediated by the specific receptor they antagonise. In the case of neurogenic inflammation, where it is common for more than one biologically active neuropeptide to be released concomitantly, it may be more sensible to develop agents that inhibit neuropeptide release. The effects of some agents suggested to affect neurogenic responses are presented. The anti-inflammatory steroid dexamethasone (1 mg/kg subcutaneously, -4 h) significantly (p < 0.01) inhibited edema formation, but the mechanism of action is likely to be related to the general anti-edema effect of dexamethasone. In contrast the anti-asthma agent nedocromil sodium (up to 10 mg/kg intravenously, -15 min) and the histamine H3 agonist (R)-alpha-methyl histamine (1-10 mg/kg intravenously, -5 min) both failed to inhibit saphenous nerve induced edema formation, despite positive results in other sensory nerve systems. The results are discussed in the context of evidence obtained using other agents in skin.

Effect of a 5-HT1 receptor agonist, CP-122,288, on oedema formation induced by stimulation of the rat saphenous nerve.

Neurogenic oedema formation in the rat hind paw skin induced by electrical stimulation of the saphenous nerve and measured by extravasation of [125I]-albumin, was inhibited by the 5-HT1B receptor agonist, CP-93,129, and the novel tryptamine analogue, CP-122,288. Significant inhibition of up to 66% of control was observed with CP-122,288 (2 x 10(-14) - 2 x 10(-7) mol kg-1) and CP-93,129 (5 x 10(-7) - 5 x 10(-6) mol kg-1), with the minimum effective dose for CP-122,288 being about 10(7) fold less than that for CP-93,129. Oedema formation induced by the intradermal administration of exogenous mediators (substance P and histamine) in rat dorsal skin was not inhibited by CP-122,288 (2 x 10(-10) mol kg-1). These results suggest that CP-122,288 is a potent inhibitor of neurogenic inflammation in rat skin and that the effect may be due to a prejunctional inhibition of neuropeptide release.

Essential role for nitric oxide in neurogenic inflammation in rat cutaneous microcirculation. Evidence for an endothelium-independent mechanism.

The possible modulatory role of nitric oxide (NO) in neurogenic edema formation in rat paw skin, induced by electrical stimulation of the saphenous nerve, was investigated by using two NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI). Both L-NAME (100 mg/kg IV, P < .05) and 7-NI (10 mg/kg IV, P < .05) caused an L-arginine (100 mg/kg IV, P < .01)-reversible inhibition of neurogenic edema as measured by 125I-albumin accumulation, whereas D-NAME (inactive enantiomer of L-NAME) and 6-aminoindazole (structurally similar to 7-NI) were without inhibitory effect. L-NAME produced the predicted vasopressor effect (before, 115 +/- 18 mm Hg; 5 minutes after, 174 +/- 18 mm Hg; n = 6; P < .05), whereas 7-NI showed no significant increase in blood pressure (before, 96 +/- 9 mm Hg; 5 minutes after, 102 +/- 10 mm Hg; n = 6), and neither L-NAME nor 7-NI had any effect on basal or vasodilator calcitonin gene-related peptide (CGRP, 10 pmol per site)-stimulated local blood flow in rat skin, as measured by laser Doppler flowmetry. Furthermore, systemic and local 7-NI had no effect on edema formation induced by local administration of substance P (with or without CGRP) and histamine (with or without CGRP) in rat skin. Since 7-NI blocks edema produced by stimulation of the saphenous nerve, it is suggested that release of NO is involved in neurogenic edema formation, but the vasodilator action of NO is unimportant in this context.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary adenylate cyclase activating polypeptide is a potent vasodilator in humans.

The vasodilator effect of the novel peptide pituitary adenylate cyclase activating polypeptide (PACAP) was investigated in humans. Forearm blood flow was measured in six healthy men by venous occlusion plethysmography. Infusion of PACAP into the brachial artery at 0.01, 0.1, 1, 3, and 10 pmol/min produced a dose-related increase in forearm blood flow in the cannulated arm from 2.8 +/- 0.6 to 8.6 +/- 2.4 ml/100 ml/min at the highest dose (mean +/- SEM, p less than 0.05). In a subsequent experiment, where the highest dose of PACAP was repeated after a 36 min interval, there was no tachyphylaxis of the forearm blood flow response, with the forearm blood flow increasing by 129 +/- 9% during the first infusion and 128 +/- 31% during the second infusion (N.S.). In further experiments, microvascular blood flow was measured by a laser-Doppler flow probe to compare the effects of intradermally injected PACAP, vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP). When injected into the skin of normal volunteers at 10(-12) to 10(-11) mol/site, each peptide caused a rapid flare lasting 2-3 min, which became erythematous after 5 min. At 10(-12) mol/site, intradermally injected PACAP and VIP caused a maximum increase in skin blood flow at 15 min of 379 +/- 96 and 307 +/- 121% (% increase above basal +/- SEM), respectively, and these responses were not significantly affected by oral aspirin (600 mg) taken 1.5 h beforehand. The vasodilation induced by PACAP at 10(-12) mol/site lasted approximately 6 h, whereas the effect of the same dose of CGRP and VIP lasted less than 2 h. These data suggest that PACAP is a potent and long-lasting vasodilator in humans.

Pituitary adenylate cyclase activating polypeptide is a potent vasodilator and oedema potentiator in rabbit skin in vivo.

1. The effects of pituitary adenylate cyclase activating polypeptide (PACAP) on microvascular blood flow and plasma protein leakage were investigated in rabbit skin in vivo. 2. Intradermal injection of PACAP38, the 38 amino acid form of the peptide, caused a dose-dependent increase in blood flow measured by a 133Xe clearance technique. An equivalent increase in blood flow was induced by 10(-12) mol per site of PACAP38, 10(-12) mol per site of human alpha-calcitonin gene-related peptide (CGRP) and 10(-10) mol per site of vasoactive intestinal polypeptide (VIP). 3. The vasodilator activity of PACAP38 was not significantly different from that of the 27 amino acid form of the peptide, PACAP27, when measured with a laser Doppler flow meter, causing a 104 +/- 14% compared with 110 +/- 18% increase above basal blood flow at 10(-12) mol per site respectively. 4. At 10(-12) mol per site the effect of PACAP38 was longer lasting than that of CGRP. Blood flow remained significantly increased above control at 2 h with PACAP38 (P less than 0.05) whereas blood flow after intradermal CGRP had returned to control values by this time. 5. PACAP38 injected alone had no significant effect on microvascular leakage of 125I-labelled albumin. However, PACAP38 significantly potentiated bradykinin-induced oedema where it was approximately 100 fold more potent than VIP. 6. Oedema potentiation induced by PACAP38 was not inhibited by indomethacin at a dose which did inhibit potentiation of bradykinin-induced oedema by arachidonic acid.7. PACAP38 is at least as potent as other peptides which have been postulated to be involved in the inflammatory response when tested in rabbit skin in vivo. PACAP may contribute to both the hyperaemia and oedema components of inflammation.