The Theoharis Theoharides Lab
Mast Cells and Disease Processes
Mast cells play a critical role in the pathogenesis of allergies, asthma and atopic dermatitis, but also in chronic fatigue syndrome, fibromyalgia, mastocytosis and mast cell activation syndrome (Fig. 2), coronary artery disease and possibly autism (Figure 1). Mast cells are capable of participating in the pathogenesis of many different diseases because unlike pro-inflammatory molecules without degranulation (Figure 1). Despite their importance, no clinically effective inhibitor of mast cell secretion exists with the exception of antihistamines and leukotrienes, which target only two of numerous inflammatory mediators secreted by mast cells A major roadblock in the development of MC therapies is the lack of understanding of the molecular mechanisms regulating the early steps of MC stimulus-secretion coupling regardless of the type of trigger.
Figure 1. Different pathways of mast cell secretion of allergic and inflammatory mediators.
Our laboratory investigates the regulation of secretion from mast cells, especially the mechanism of selective secretion of cytokines and other pro-inflammatory molecules and their role in neuro-inflammation, as well as the ability of innate molecules such as chondroitin sulfate and natural flavonoids such as luteolin, to inhibit secretion. We have shown for the first time that mast cells can be activated by corticotropin-releasing hormone (CRH), the first molecule generated under stress, and by other peptides such as neurotensin and substance p; these have synergistic effects with the pro-inflammatory cytokine IL-33. Stimulated mast cells lead to disruption of the gut-blood and blood-brain barriers permitting circulating and environmental toxins to activate microglia leading to focal inflammation of the brain
Mast cells are known for their involvement in allergic reactions, but we were among the first to show that they are also necessary in inflammation, especially inflammatory diseases that worsen by stress. Mast cells can be triggered by numerous allergic, immune, pathogenic and peptide triggers (Figure 2). We have developed in vivo and in vitro models for these diseases and we are studying neurohormonal activation of mast cells. The only plausible way to explain how mast cells can participate in so many diverse processes is their ability to secrete distinct chemicals relative for different pathophysiological settings.
Figure 2.Mast Cell Activation and Mediator Release. Mast cells can be triggered to secrete either through immediate degranulation IgE, neuropeptides) of slow (cytokines, pathogens) newly synthesized pro-inflammatory mediators.
In allergic patients, mast cells are stimulated by specific allergens acting through the specific surface receptors for IgE. In mastocytosis and mast cell activation syndrome, patients are “allergic to life” with mast cells responding to triggers for which there are not know surface receptors, such as odors, heat, and stress (Figure 3). As a result, many organs are affected and patients present with multiple symptoms making their diagnosis and management very difficult.
Figure 3.Mast cells can participate in allergies, mastocytosis, mast cell activation syndrome and other related diseases. Depending what mediators are being secreted, every and all organs of the body can be affected making it very difficult for the patient and the physician to find the correct diagnosis and treatment
Our laboratory also investigates the ability of the cytokine IL-33, either alone or when administered together with the peptide Substance P, to stimulate cytokine and chemokine secretion from mast cells.
Neonatal Mast Cell Activation in the Pathogenesis of Autism
We first reported that the prevalence of autism is ten times higher (1/10 children) in patients with mastocytosis than the general population (1/100 children). What makes this finding even more impressive is that mastocytosis is a rare disease occurring in 1/4000 children and is characterized by many hypersensitive mast cells in many tissues; once would, therefore, expect that the combined prevalence would have been 1/100x1/4,000=1/400,000 and not 1/10 children! We also found that the neuropeptide neurotensin, which is a potent mast cell trigger, is statistically much higher in the serum of autistic patients. We also showed that neurotensin can stimulate human cultured microglia to secrete pro-inflammatory mediators leading to focal inflammation in brain areas regulating behavior (Figure 4).
Figure 4. Mast cells can stimulate microglia, which then secrete pro-inflammatory molecules leading to focal inflammation in the brain and disrupt neuronal connectivity.
Once mast cells are stimulated, they disrupt the protective gut-blood and blood-brain-barriers and allow circulating and environmental toxins, as well as immune cells, to enter the brain activating microglia and leading to local inflammation and disrupted neuronal connectivity (Figure 5). Drugs inhibiting mast cell and microglia activation could be an effective treatment for autism.
Figure 5. Schematic depiction of the proposed role of mast cell activation in brain inflammation and ASD. Allergic and non-allergic triggers could derive from the GI tract and stimulate the release of mast cell-derived vasoactive, inflammatory and neurotoxic mediators, which could increase gut-blood-brain-barrier permeability. These substances could disrupt the blood–brain-barrier and stimulate brain mast cells to further release molecules that increase BBB permeability and contribute to brain inflammation, and autism.
Anti-allergic and Anti-inflammatory Actions of Some Natural Compounds
Secretion of numerous mediators from mast cells play a critical role in the pathogenesis of allergies, asthma and atopic dermatitis, but also in chronic fatigue syndrome, fibromyalgia, mastocytosis, coronary artery disease and possibly autism. Despite the importance of these mediators in disease, no clinically effective inhibitor of mast cell secretion exists with the exception of antihistamines and anti-leukotrienes that target only two of numerous inflammatory mediators secreted by mast cells. A major roadblock in the development of mast cell inhibitors is the lack of understanding of the molecular mechanisms regulating the early steps of mast cell secretion regardless of the type of trigger.
We are investigating the mechanism of the inhibitory action of the natural flavonoids luteolin and methoxyluteolin, their formulation in ways that increases their absorption, as well as their blood concentrations in order to achieve maximal effective levels for anti-allergic and anti-inflammatory effects. We then showed that tetramethoxyluteolin is more potent than luteolin in inhibiting both human mast cells and microglia.
Figure 6. Structures of luteolin and methoxyluteolin.
We have been investigating the presence of objective biomarkers in the serum of patients with inflammatory conditions, including fibromyalgia and autism. We showed that the peptide neurotensin is increased in the serum of children with autism and so are the inflammatory cytokines IL-6 and TNF. We also showed that these cytokines are significantly reduced after treatment with a luteolin-containing formulation that also improved symptoms in those children.
We are presently investigating the presence of extracellular microvesicles (exosomes) in the serum of children with autism and their effects on human cultured microglia, as well as in the serum of patients with psoriasis and their effect on human cultured keratinocyte activation.
Inhibitory Effect of Mast Cell Secretory Granule Components
Even though we have shown that methoxyluteolin inhibits TNF-induced human keratinocyte activation, we are investigating the ability of mast cell secretory granule molecules, chondroitin sulfate and spermine, to inhibit mast cell and keratinocyte activation.