[Nasal allergy and leukotriene. 2. Kinetics of peptide leukotrienes and inflammatory cells in nasal lavage fluid after antigen challenge]

Leukotriene D4 increases the excitability of capsaicin-sensitive nasal sensory nerves to electrical and chemical stimuli

BACKGROUND AND PURPOSE

Clinical studies have demonstrated significant reductions in allergen-induced nasal symptoms of atopic rhinitis subjects by CysLT1 antagonists, including neuronally mediated symptoms such as sneeze, itch and reflex hypersecretion. Here, we test the hypothesis that cysteinyl leukotrienes activate and/or alter the activity of nasal nociceptive (capsaicin-sensitive) sensory neurones.

EXPERIMENTAL APPROACH

Using retrograde tracer (DiI), we labelled guinea-pig trigeminal sensory neurones that projected fibres to the nasal mucosa. Single-neurone reverse transcriptase (RT)-PCR was used to evaluate CysLT receptor gene expression. The effect of cysteinyl leukotrienes on individual nasal sensory nerve activity was assessed in Ca2+ assays and whole-cell gramicidin-perforated patch-clamp studies.

KEY RESULTS

Nasal C-fibre neurones express CysLT1 but not CysLT2 mRNA. LTD4 and LTC4 increased intracellular [Ca2+]free in a population of capsaicin-sensitive trigeminal nerves, an effect blocked by the CysLT1 antagonist ICI198615. In current clamp mode, LTD4 had no effect on resting membrane potential. However, LTD4 significantly increased electrical excitability (action potential discharge during current pulses) threefold in capsaicin-sensitive nasal neurones, which was inhibited by CysLT1 antagonists ICI198615 and montelukast. LTD4 had no effect on electrical excitability in capsaicin-insensitive neurones. Finally, LTD4 significantly augmented histamine-induced responses in capsaicin-sensitive neurones as measured by increased action potential discharge, peak frequency and membrane depolarization.

CONCLUSIONS AND IMPLICATIONS

LTD4, likely through CysLT1 receptors, directly increases the excitability of capsaicin-sensitive guinea-pig nasal trigeminal neurones, demonstrating a novel mechanism for the actions of cysteinyl leukotrienes and potentially explains the effectiveness of CysLT1 antagonists in treating nasal allergen-induced neuronal symptoms.

Cysteinyl leukotrienes: multi-functional mediators in allergic rhinitis

Cysteinyl leukotrienes (CysLTs) are a family of inflammatory lipid mediators synthesized from arachidonic acid by a variety of cells, including mast cells, eosinophils, basophils, and macrophages. This article reviews the data for the role of CysLTs as multi-functional mediators in allergic rhinitis (AR). We review the evidence that: (1) CysLTs are released from inflammatory cells that participate in AR, (2) receptors for CysLTs are located in nasal tissue, (3) CysLTs are increased in patients with AR and are released following allergen exposure, (4) administration of CysLTs reproduces the symptoms of AR, (5) CysLTs play roles in the maturation, as well as tissue recruitment, of inflammatory cells, and (6) a complex inter-regulation between CysLTs and a variety of other inflammatory mediators exists.