Evolving role of leukotrienes in the pathogenesis of viral infections, including otitis media

Lysophospholipid acyltransferases and leukotriene biosynthesis: intersection of the Lands cycle and the arachidonate PI cycle

Leukotrienes (LTs) are autacoids derived from the precursor arachidonic acid (AA) via the action of five-lipoxygenase (5-LO). When inflammatory cells are activated, 5-LO translocates to the nuclear membrane to initiate oxygenation of AA released by cytosolic phospholipase A2 (cPLA2) into leukotriene A₄ (LTA₄). LTA₄ can also be exported from an activated donor cell into an acceptor cell by the process of transcellular biosynthesis. When thimerosal is added to cells, the level of free AA increases by inhibition of lysophospholipid acyltransferases of the Lands pathway of phospholipid remodeling. Another arachidonate phospholipid cycle involves phosphatidylinositol (PI) in the plasma membrane that undoubtedly intersects with the Lands pathway of phospholipid remodeling. The highest abundance of PI occurs between the ER and the plasma membrane and is probably a result of the importance of the PI signaling cascade in cellular biochemistry. Because transport proteins mediate the rapid intracellular movement of phospholipids, largely as result of physical membrane contact, 5-LO-dependent production of LTA₄ could be mediated by the disappearance of free AA from the nuclear membrane, transfer to the ER for Lands cycle reesterification into PI, and population of PI(18:0/20:4) for cell membrane signaling.

RCT of montelukast as prophylaxis for upper respiratory tract infections in children

BACKGROUND

Infections with viruses causing upper respiratory tract infection (URI) are associated with increased leukotriene levels in the upper airways. Montelukast, a selective leukotriene-receptor antagonist, is an effective treatment of asthma and allergic rhinitis.

OBJECTIVE

To determine whether prophylactic treatment with montelukast reduces the incidence and severity of URI in children.

METHODS

A randomized, double-blind, placebo-controlled study was performed in 3 primary care pediatric ambulatory clinics in Israel. Healthy children aged 1 to 5 years were randomly assigned in a 1:1 ratio to receive 12-week treatment with 4 mg oral montelukast or look-alike placebo. Patients were excluded if they had a previous history of reactive airway disease. A study coordinator contacted the parents by phone once a week to obtain information regarding the occurrence of acute respiratory episodes. The parents received a diary card to record any acute symptoms of URI. The primary outcome measure was the number of URI episodes.

RESULTS

Three hundred children were recruited and randomly assigned into montelukast (n = 153) or placebo (n = 147) groups. One hundred thirty-one (85.6%) of the children treated with montelukast and 129 (87.7%) of the children treated with placebo completed 12 weeks of treatment. The number of weeks in which URI was reported was 30.4% in children treated with montelukast and 30.7% in children treated with placebo. There was no significant difference in any of the secondary variables between the groups.

CONCLUSIONS

In preschool-aged children, 12-week treatment with montelukast, compared with placebo, did not reduce the incidence of URI.

Otitis Media and Sinusitis

Otitis media (OM) and sinusitis are common and costly maladies that are often preceded by the development of a viral upper respiratory infection (vURI). Although antibiotics have been shown to be somewhat effective in the treatment of these disorders, increasing concern over the emergence of pathogen resistence to these agents underscores the need for the development of other treatment options, including agents to treat and/or prevent vURIs. Earlier research implicated roles for cytopathology, cellular infiltration, and inflammatory mediators such as bradykinin, in the pathogenesis of vURIs and its complications, including OM and sinusitis, but these factors are now recognized as late events with specific and limited contributions to disease expression. Current therapies are relatively ineffective and aimed at reducing symptoms rather than moderating underlying mechanisms. Nasal elevations of proinflammatory cytokines and leukotrienes track symptom expression during vURIs, and it is hypothesized that these chemicals orchestrate a common response to infection with many different viruses causing vURIs. Moreover, recent evidence demonstrates that specific cytokine gene polymorphisms may modulate the severity of illness and incidence of complications during episodes of vURI. Additionally, other evidence supports a role for neurogenic inflammation in the development of complications. Future studies should dissect the role of proinflammatory cytokines, leukotrienes, and neuropeptides in the expression of symptoms, signs, pathophysiologies, and complications of vURIs.