Non-antibiotic properties of tetracyclines as anti-allergy and asthma drugs

Abstract

All available therapies for human allergic disease target IgE mediated pathologic responses after IgE has been produced. We are developing tetracyclines as anti-allergy drugs to prevent IgE production, based on our findings that minocycline or doxycycline treatment of allergic asthmatic humans significantly improves their asthma symptoms, reduces their oral steroid requirements, and strongly suppresses their ongoing IgE responses (ELISA, mast cell mediated cutaneous late phase responses); the tetracyclines also strongly suppress peak IgE responses of BPO-KLH sensitized mice (ELISPOT assay, ELISA, skin tests). The antibiotic activity of the tetracyclines is not required for suppression of IgE responses; inclusion of minocycline or doxycycline in sterile culture prevents anti-CD40/IL-4 mediated induction of memory IgE responses by PBMC of allergic asthmatic patients (ELISA), and induction of specific memory IgE responses by spleen cells of BPO-KLH sensitized mice (ELISPOT assay, ELISA). The tetracyclines affect an epsilon specific pathway because IgM, IgG and IgA responses did not decrease. Further, in humans, DTH responses to recall antigens did not decrease. In related studies, we found that two distinct T cell subsets: CD4+CD60 negative and CD8+CD60+ (CD60 is a ganglioside) (humans) and CD4+ Asialo GM1 ganglioside negative and CD8+Asialo GM1 ganglioside+ (mice), both are required for induction of memory IgE responses. Phosphorylated (phos) p38 MAP kinase, but not phos ERK or phos JNK expression by CD4+ and CD8+, including CD8+CD60+, T cells is increased in allergic asthmatic humans, as is IL-4 and IL-10 production. The tetracyclines appear to target T cell pathways to induce suppression of IgE responses because they suppress phos p38 MAP kinase expression by both CD4+ and CD8+, including CD8+CD60+, T cell subsets, and IL-4 and IL-10, while upregulating IL-2 and IFN gamma, and suppressing IgE responses. Our finding that tetracyclines do not require antibiotic activity to suppress IgE responses opens the door to development of new tetracycline-based and other therapeutics for human allergic disease.

Introduction

Allergic disorders including asthma, rhinoconjunctivitis, food allergy, and atopic dermatitis affect a substantial proportion of the general population [1]. The therapeutic armamentarium to treat these conditions has been limited for many years. Recent studies of the effects of tetracyclines on allergic responses have opened a new door to the potential treatment of allergy and asthma.

The prevalence of allergic disorders has doubled in ten to fifteen years and now affects 10–15% of Western populations [1]. A current explanation for the increase in allergic disease is offered by the hygiene hypothesis [2]. Western societies have, for the most part, successfully limited major infectious diseases (through sanitary measures and vaccinations) with a possible inadvertent adverse effect [3]. Such decrease in stimulation of the Th1 arm of the immune system due to decrease in infectious stimuli, either bacterial or viral, may have led to skewing of immune responses towards the allergen-specific IgE producing Th2 arm of the immune system. Allergic disorders such as allergic rhinitis and asthma result, in part, when allergen-specific IgE binds to its receptors on the surfaces of mast cells and basophils [4]. Subsequent exposure to allergens in the airways results in the release of histamine and other mediators that are involved in the eosinophilic inflammation and airway hyperreactivity thought to be characteristic of asthma [4].

State University of New York Downstate Medical Center, located in Brooklyn, serves a large population of racial and ethnic minorities of low socioeconomic status residing in an urban environment, a population that is disproportionately at high risk for asthma morbidity and mortality [5], [6]. Epidemiologic studies suggest that key risk factors contributing to asthma morbidity within the inner city include social demography, the physical environment (indoor and outdoor), and health care access and quality [7]. Death from asthma is two to six times more likely to occur among African Americans and Hispanics than among whites [8], [9]. Rates of hospitalization for asthma demonstrate similar variations; rates for African Americans hospitalized are almost triple those for whites [8], [9]. For children living in the inner city, asthma tends to be more frequent and severe. Although the number of deaths annually from asthma is low compared to other chronic diseases, the death rate for children aged 5–14 years and young adults aged 15–34 years doubled from 1979–80 to 1993–95 [8], [9].

Recent studies at our institution [10], [11] have shown a high prevalence of self-reported food allergy. Adult and pediatric patients seen at our institution for non-allergy reasons report that 12.9% and 20.5%, respectively, have food allergy symptoms. Both adult and pediatric groups show a strong correlation between food allergy symptoms and asthma [10], [11]. This cohort of asthma patients, vulnerable to increased morbidity and mortality from asthma, has been understudied with respect to new treatments for asthma.

The mainstay of treatment of asthma at present is inhaled corticosteroid therapy [12]. While inhaled corticosteroids are effective, rates of adherence are low and they do not seem to modify the course of the disease. All inhaled corticosteroids are absorbed in the lung and might have systemic effects [12]. Ciclesonide is a recently introduced inhaled steroid that is a pro-drug activated by esterases and may be safer with fewer systemic effects [13]. While it has been approved for treatment of allergic rhinitis and asthma, its long term effects are not known.

The only currently available treatment approved specifically for allergic asthma is omalizumab, an anti-IgE monoclonal antibody injected once or twice per month. It is a useful adjunct for allergic asthma [14]. However, omalizumab is an expensive treatment that is not easily obtainable for many patients.

While investigation of inflammatory mediator antagonists is an active area of research, the only ones currently approved and available are the anti-leukotriene agents. As a group these are considered weakly effective and may not contribute much to treatment of severe asthma [15]. Studies of treatment of asthma with anti-TNF biologic agents such as etanercept and infliximab have demonstrated benefit, but are not approved for asthma, are expensive, and may only be beneficial in the treatment of severe asthma [15]. Experimental agents that inhibit phosphodiesterase dampen inflammatory responses in a wide range of cells involved in airway inflammation. In studies done by Bousquet et al. [16], there was decrease in allergen induced responses in asthma after treatment with roflumilast. However, the side effect profile of this class of drugs is limiting and includes both upper and lower gastrointestinal effects and headaches [15].

Current therapies, including omalizumab (anti-IgE monoclonal antibody), target cellular and clinical sequelae of IgE after it has been produced and binds to its cellular receptors [15]—i.e. a post-factum approach rather than decreasing IgE responses at the level of IgE production.

While IgE is central to the immune processes resulting in allergic disease such as asthma [17], [18], [19], [20], [21], there is, at present, no commercially available drug that decreases human IgE responses at the level of IgE production. As reviewed by Blaser and colleagues [22], there has been an ongoing effort in this area. Promising approaches to decreasing IgE responses include blockage of IL-4 and IL-13, and targeting of GATA-3, the major transcription factor controlling Th2 associated cytokines, with antisense message [22]. Strategies for augmenting natural CD4+CD25+ FoxP3+ regulatory T cells may result in suppression of allergen specific Th2 responses [22].