Correlations of PDE-4 inhibition between enzymes of smooth muscle and inflammatory cell sources

NOVEL THERAPEUTIC APPROACHES FOR ALLERGIC RHINITIS

The last 2 decades have witnessed enormous changes in our understanding of allergic rhinitis. As we have begun to unravel the complex underlying immunologic and inflammatory pathophysiology of the disease, new therapeutic strategies as well as specific molecular and cellular constituents have emerged as potential targets for clinical intervention. These efforts also have shed light on the mechanisms by which current antiallergy medications act—or sometimes fail to be effective.7, 31, 51, 89 The similar pathophysiologic basis for allergic rhinitis and the often comorbid condition, asthma, was underscored in the recently published American Thoracic Society Workshop Summary on the Immunobiology of Asthma and Rhinitis: Pathogenic Factors and Therapeutic Options.¹⁸ In his conclusion, workshop chair, Thomas Casale,¹⁸ counsels readers to consider that “…allergic asthma and rhinitis represent a systemic disease affecting two organs, the lung and the nose. Asthma and allergic rhinitis share many of the same pathogenic factors, but they operate in different parts of the airway. Inflammatory cells and mediators are often the same, and there may be common alterations that occur in the immune system.” Thus, therapeutic strategies and potential therapeutic agents found to be beneficial in the treatment of one airway target may show similar effects in the other. For this reason, and because many of the therapies now being developed are at early stages in their evolution, physicians interested in rhinitis therapy also must examine what is known about these agents in asthma.

One avenue of active research has been the role of leukotrienes and other mediators in the pathophysiology of asthma and rhinitis. Three leukotriene modifiers now have been approved for the treatment of asthma in the United States; their potential use in the treatment of rhinitis has been a focus of considerable speculation and investigation. An early “day in the park” study showed that with antileukotriene therapy, patients with rhinitis had demonstrable improvements in their rhinitic symptoms.²⁹ Roquet et al⁸³ reported that in the treatment of asthma, there was a synergistic effect when an antileukotriene agent and an antihistamine were used, compared with either drug alone. A product combining an antileukotriene with an antihistamine is currently under development.

The most exciting developments, however, may be in the immunology arena. As described by Baraniuk elsewhere in this issue, the pathophysiology of allergic rhinitis is highly complex. Multiple interacting, interdependent, and redundant pathways and molecular and cellular constituents are involved in the pathogenesis of allergic rhinitis.

Briefly, exposure of the nasal mucosa to allergen in a sensitized individual leads to the release and further production of inflammatory mediators and the release of cytokines.⁵ These released cytokines activate endothelial cells, thereby inducing expression of adhesion receptors on the cell surface and initiating a cascade of events that facilitates transendothelial migration of inflammatory cells. T lymphocytes also are activated by these cytokines. Within a given tissue, specific patterns of cytokines are released, dependent on the dominant subset of local T lymphocytes. These, in turn, lead to the preferential activation and recruitment of specific inflammatory cells and the characteristic cellular inflammation observed in allergic rhinitis.