The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 21

I answered the 107 questions I have been asked most in the last four years. No jargon. No terminology. Just answers.

30. Why does my skin get red and itchy?
• Flushing is one of the hallmark signs of mast cell disease. It is sometimes the symptom that drives providers to look at mast cell disease as a potential diagnosis.
• Mast cells make and release many chemicals. These chemicals are commonly called mediators because they mediate many reactions in the body that affect the body in many different ways.
• Some mast cell mediators make blood vessels relax. The vessels get a little wider. When the vessels get bigger, the ones under the skin get closer to the skin. Because those vessels show red from the blood in them, the blood is closer to the skin so the skin looks red.
• Flushing is often asymmetrical. There isn’t a hard and fast reason for why this happens but is likely caused by local mast cell mediator release. Essentially, if the mast cells on the right side of your face get irritated, the right side is more likely to flush than the left side.
Flushing is mostly mediated by prostaglandin D2. Aspirin is often prescribed for mast cell patients that tolerate it because aspirin blocks cells from making prostaglandins. This is because aspirin interferes with the molecule that manufactures them. Many other substances can also interfere with this, including other NSAIDs. Another class of drug, 5-lipoxygenase inhibitors, can also stop production of prostaglandins in a different way.
• To a lesser extent, histamine contributes flushing and antihistamines sometimes help.
What exactly causes itching is still not entirely clear. There are special little places in your body called itch receptors. When they notice something itchy, it’s their job to raise the alarm. We think that mast cells carry the message from those places to the nervous system that then spread the itch signal. It’s like carrying the flame of one candle from the itch receptor to the nervous system, which sets the forest on fire.
• Hydroxyzine and other antihistamines are often used for itching. Corticosteroids like prednisone, either oral or topical, may help. Also, medications that interfere with prostaglandin production, like an NSAID or a 5-lipoxygenase inhibitor, sometimes help.

For more detailed reading, please visit these posts:
The Provider Primer Series: Management of mast cell mediator symptoms and release
Prostaglandins and leukotrienes
Mast cell mediators: Prostaglandin D2 (PGD2)

Symptoms, mediators and mechanisms: A general review (Part 1 of 2)

Skin symptoms    
Symptom Mediators Mechanism
Flushing Histamine (H1), PGD2 Increased vasodilation and permeability of blood vessels

Blood is closer to the skin and redness is seen

Itching Histamine (H1), leukotrienes LTC4, LTD4, LTE4, PAF Possibly stimulation of itch receptors or interaction with local neurotransmitters
Urticaria Histamine (H1), PAF, heparin, bradykinin Increased vasodilation and permeability of blood vessels and lymphatic vessels

Fluid is trapped inappropriately between layers of skin

Angioedema Histamine (H1), heparin, bradykinin, PAF Increased vasodilation and permeability of blood vessels and lymphatic vessels

Fluid is trapped inappropriately between layers of tissue

 

Respiratory symptoms    
Symptom Mediators Mechanism
Nasal congestion Histamine (H1), histamine (H2), leukotrienes LTC4, LTD4, LTE4 Increased mucus production

Smooth muscle constriction

Sneezing Histamine (H1), histamine (H2), leukotrienes LTC4, LTD4, LTE4 Increased mucus production

Smooth muscle constriction

Airway constriction/ difficulty breathing Histamine (H1), leukotrienes LTC4, LTD4, LTE4, PAF Increased mucus production

Smooth muscle constriction

 

Cardiovascular symptoms    
Symptom Mediators Mechanism
Low blood pressure Histamine (H1), PAF,  PGD2, bradykinin Decreased force of heart contraction

Increased vasodilation and permeability of blood vessels

Impact on norepinephrine signaling

Change in heart rate

Presyncope/syncope (fainting) Histamine (H1), histamine (H3), PAF, bradykinin Increased vasodilation and permeability of blood vessels

Decrease in blood pressure

Dysfunctional release of neurotransmitters

High blood pressure Chymase,  9a,11b-PGF2, renin, thromboxane A, carboxypeptidase A Impact on renin-angiotensin pathway

Impact on norepinephrine signaling

Tightening and decreased permeability of blood vessels

Tachycardia Histamine (H2), PGD2 Increasing heart rate

Increasing force of heart contraction

Impact on norepinephrine signaling

Arrhythmias Chymase, PAF, renin Impact on renin-angiotensin pathway

Impact on norepinephrine signaling

 

Gastrointestinal symptoms    
Symptom Mediators Mechanism
Diarrhea Histamine (H1), histamine (H2), bradykinin, serotonin Smooth muscle constriction

Increased gastric acid secretion

Dysfunctional release of neurotransmitters

Gas Histamine (H1), histamine (H2), bradykinin Smooth muscle constriction

Increased gastric acid secretion

Abdominal pain Histamine (H1), histamine (H2), bradykinin, serotonin Smooth muscle constriction

Increased gastric acid secretion

Dysfunctional release of neurotransmitters

Nausea/vomiting Histamine (H3), serotonin Dysfunctional release of neurotransmitters
Constipation Histamine (H2), histamine (H3), serotonin (low) Dysfunctional release of neurotransmitters

 

Mast cell mediators: Prostaglandin D2 (PGD2)

Prostaglandin D2 (PGD2) is the predominant prostaglandin product released by mast cells. It is found prevalently in the central nervous system and peripheral tissues, where it performs both inflammatory and normal processes. In the brain, PGD2 helps to regulate sleep and pain perception. PGD2 can be further broken down into other prostaglandins, including PGF2a; 9a, 11b-PGF2a (a different shape of PGF2a), and forms of PGJ. 9a, 11b-PGF2a shares the same biological functions as PGD2. Both of these can be tested for in 24 hour urine test as markers of mast cell disease.

PGD2 is a strong bronchoconstrictor. It is 10.2x more potent in this capacity than histamine and 3.5x more potent than PGF2a. It has been associated with inflammatory and atopic conditions for many years. Presence of allergen activates PGD2 production in sensitized people. In asthmatics, bronchial samples can achieve over 150x the level of PGD2 compared to controls. Elevated PGD2 has been associated with chronic coughing.

PGD2 is a driver of inflammation in many settings. It acts on bronchial epithelium to cause production of chemokines and cytokines. It also brings lymphocytes and eosinophils to the airway, which induces airway inflammation and hyperreactivity in asthmatics. PGD2 may also inhibit eosinophil cell death, resulting in further inflammation.

An interesting facet of PGD2 is its role in nerve pain. It has been found that PGD2 is produced by microglia in the spine after a peripheral nerve injury. These cells make more COX-1, which then makes PGD2. Newer COX-2 inhibiting NSAIDs do not affect nerve pain in mouse models, but older NSAIDs that inhibit COX-1 and COX-2 reduce neuropathy.

PGD2 is found to inhibit inflammation in other settings. It can reduce eosinophilia in allergic inflammation in mouse models. Additionally, once the acute phase of inflammation is over and it is resolving, administering a COX-2 inhibitor actually makes the inflammation worse. This indicates that PGD2 may be important in resolving inflammation in some processes.

Aspirin is commonly used in mast cell patients to inhibit prostaglandin production. PGD2 is primarily manufactured by COX-2, but the pathway that evokes neuropathy uses COX-1. There are a number of COX-1 and COX-2 inhibitors available.

In mast cell patients, PGD2 is probably most well known for causing flushing. This happens due to dilation of blood vessels in the skin. Due to a well characterized response to aspirin, this is generally the first line medication choice. Some salicylate sensitive mast cell patients undergo aspirin desensitization to be able to use this medication.

 

References:

Emanuela Ricciotti, Garret A. FitzGerald. Prostaglandins and Inflammation. Arterioscler Thromb Vasc Biol. 2011; 31: 986-1000.

Matsuoka T, Hirata M, Tanaka H, Takahashi Y, Murata T, Kabashima K, Sugimoto Y, Kobayashi T, Ushikubi F, Aze Y, Eguchi N, Urade Y, Yoshida N, Kimura K, Mizoguchi A, Honda Y, Nagai H, Narumiya S. Prostaglandin D2 as a mediator of allergic asthma. Science. 2000;287: 2013–2017.

G Bochenek, E Nizankowska, A Gielicz, M Swierczynska, A Szczeklik. Plasma 9a,11b-PGF2, a PGD2 metabolite, as a sensitive marker of mast cell activation by allergen in bronchial asthma. Thorax 2004; 59: 459–464.

Victor Dishy, MD, Fang Liu, PhD, David L. Ebel, BS, RPh, George J. Atiee, MD, Jane Royalty, MD, Sandra Reilley, MD, John F. Paolini, MD, PhD, John A. Wagner, MD, PhD, and Eseng Lai, MD, PhD. Effects of Aspirin When Added to the Prostaglandin D2 Receptor Antagonist Laropiprant on Niacin-Induced Flushing Symptoms. Journal of Clinical Pharmacology, 2009; 49: 416-422