Quercetin – Part I: Anti-Allergic Action

March is the month of spring, a season characterized by the flowering of various plants whose pollen, in predisposed subjects, causes the onset of pathologies of allergic origin. Help for the treatment of allergies comes from nature and in particular from quercetin, a flavonoid contained in various types of fruit, which shows particular anti-inflammatory and anti-allergic effects.

To better understand how quercetin can help us in the treatment of allergic symptoms, let's take a brief overview of the immune mechanism underlying allergic diseases.

In the presence of an allergen, our immune system reacts by recruiting leukocytes and producing Th2 lymphocytes to the detriment of Th1 lymphocytes. In fact, it is said that the Th1/Th2 balance in allergies shifts toward the Th2 phenotype. Th2 lymphocytes release particular types of cytokines, including IL-3, IL-4, IL-5 and IL-13, which promote the production of IgE by plasma cells, thus triggering the allergic-inflammatory reaction. IgE, which due to exposure to allergens are bound to the external membrane of mast cells, trigger the release of mediators, by the mast cells themselves, such as histamine and leukotrienes, responsible for the typical allergic symptoms such as:

• Dilation of arterioles;
• Increased vascular permeability;
• Itching;
• Rhinorrhea;
• Mucus secretion;
• Contraction of smooth muscle in the lung.

Mediators and cytokines released during the initial phase of an immune response to a triggering allergen trigger a further cellular inflammatory response over the next 4 to 8 hours (late-phase inflammatory response) resulting in recurrent symptoms (usually nasal congestion) that often persist for a long time.

The antiallergic action of quercetin is linked to its action on the immune system, in particular quercetin is able to act on the recruitment of leukocytes and on the regulation of the balance between Th1/Th2 lymphocytes. It has also been reported that quercetin inhibits the secretion of harmful chemical mediators, including histamine, leukotrienes, major basic protein and eosinophil cationic protein from mast cells and eosinophils in vitro and in vivo. Furthermore, quercetin, according to some studies such as the one carried out by Moon et al., is able to reduce histamine levels when taken by inhalation. 

Quercetin can therefore be used to treat various allergic-based pathologies, such as asthma.

A study by Jung et al. evaluated the effects of quercetin on immune responses related to the early and late phases of asthma. It was seen that quercetin was able to inhibit specific airway resistance, in a dose-dependent manner, both in the early and late phase, as well as the recruitment of leukocytes, particularly eosinophils and neutrophils.

These combined actions significantly reduce allergic symptoms, with an anti-asthmatic activity similar to that of dexamethasone. The anti-allergic activity of quercetin is particularly useful in the treatment of allergic rhinitis, a chronic IgE-mediated inflammatory disease in the nasal wall, which is mainly mediated by Th2-type cytokines such as IL-4, IL-5 and IL-13.

Current therapeutic agents for allergic rhinitis are limited to antihistamines, antileukotrienes and nasal glucocorticoids that can mitigate allergic symptoms but fail to modulate allergic reactions and lead to adverse side effects such as throat irritation and dry mouth. The use of quercetin for the treatment of allergic rhinitis is effective in inhibiting the production of inflammatory cytokines and chemokines released by eosinophils and mast cells after immunological stimulation in vitro and in vivo.

It is therefore evident that the use of quercetin, especially if taken topically - inhaled, can be useful to treat the symptoms of allergies without necessarily resorting to antihistamines and corticosteroids. In the next article we will see how quercetin can also be useful to treat inflammation related to allergies.

References

• Jafarinia M, Sadat Hosseini M, Kasiri N, Fazel N, Fathi F, Ganjalikhani Hakemi M, Eskandari N. Quercetin with the potential effect on allergic diseases. Allergy Asthma Clin Immunol. 2020 May 14;16:36.
• Tanaka Y, Furuta A, Asano K, Kobayashi H. Modulation of Th1/Th2 Cytokine Balance by Quercetin In Vitro. Medicines (Basel). 2020 Jul 30;7(8):46.
• Jung CH, et al. Anti-asthmatic action of quercetin and rutin in conscious guinea-pigs challenged with aerosolized ovalbumin. Arch Pharmacal Res. 2007;30(12):1599.
• Moon H, et al. Quercetin inhalation inhibits the asthmatic responses by exposure to aerosolized-ovalbumin in conscious guinea-pigs. Arch Pharmacal Res. 2008;31(6):771.