Mast Cell Activation and Antihistamine Therapies

1 Hardcastle et al. 2016 — Mast Cell Phenotype Abnormalities in ME/CFS

Full Citation:: Hardcastle SL, Brenu EW, Johnston S, et al. Novel characterisation of mast cell phenotypes from peripheral blood mononuclear cells in chronic fatigue syndrome/myalgic encephalomyelitis patients. BMC Immunology. 2016;17(1):30. DOI:: 10.1186/s12865-016-0167-z PMID:: 27362406 PMCID:: PMC4928291 Published:: June 29, 2016 Study Design:: Cross-sectional immunophenotyping study Sample Size:: 18 ME/CFS patients (12 moderate, 6 severe), 13 matched healthy controls Key Findings::

- Significant increase in naïve mast cells (CD117^+^CD34^+^Fc$\varepsilon$RI^-^chymase^-^) in moderate and severe ME/CFS ($p\\<0.05$)
- Elevated CD40 ligand and MHC-II receptors on differentiated mast cells in severe ME/CFS
- Demonstrates measurable mast cell abnormalities at cellular level
- Supports hypothesis that mast cells may be involved in ME/CFS pathophysiology

Certainty:: High (well-designed study, statistically significant findings) Clinical Relevance:: Provides biological basis for mast cell involvement in ME/CFS; supports rationale for mast cell-targeted therapies

Full Citation:: Wirth K, Scheibenbogen C. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Comorbidities: Linked by Vascular Pathomechanisms and Vasoactive Mediators? Healthcare. 2023;11(7):978. DOI:: 10.3390/healthcare11070978 PMID:: 37046903 PMCID:: PMC10224216 Published:: March 27, 2023 Study Type:: Review and hypothesis paper Key Mechanisms::

- Mast cell activation shares pathogenic mechanisms with ME/CFS through excessive histamine, heparin, prostaglandins, leukotrienes, and protease release
- Spillover of vasoactive mediators into systemic circulation worsens orthostatic intolerance via histamine's vascular effects
- $\beta_2$-adrenergic receptor dysfunction amplifies symptoms
- ME/CFS patients with MCAS and orthostatic intolerance reported symptom alleviation significantly more often following mast cell-targeted treatment ($p\\<0.0001$)

Certainty:: Medium (mechanistic hypothesis with clinical correlation) Clinical Relevance:: Links mast cell activation to orthostatic intolerance; suggests mast cell-targeted therapies may benefit subset of ME/CFS patients with vascular/autonomic symptoms

2 Novak et al. 2022 — Mast Cell Disorders, Cerebral Hypoperfusion, and Small Fiber Neuropathy

Full Citation:: Novak P, Giannetti MP, Weller E, Hamilton MJ, Castells M. Mast cell disorders are associated with decreased cerebral blood flow and small fiber neuropathy. Ann Allergy Asthma Immunol. 2022;128(3):299–306.e1. DOI:: 10.1016/j.anai.2021.10.006 PMID:: 34648976 Published:: March 2022 Study Design:: Case-control study with objective neurological measurements Sample Size:: 15 hereditary alpha tryptasemia (H\(\alpha\)T), 16 mast cell activation syndrome (MCAS), 14 matched controls Key Findings::

- *Small fiber neuropathy highly prevalent*: 80% of H$\alpha$T and 81% of MCAS patients (vs controls, $p\\<0.001$)
- *Cerebral hypoperfusion during orthostatic stress*: CBFv reduced $-24.2 \pm 14.3%$ in H$\alpha$T, $-20.8 \pm 5.5%$ in MCAS (vs controls $+2.3 \pm 8.1%$, $p\\<0.001$)
- *Universal dysautonomia*: All patients showed abnormalities when sympathetic, parasympathetic, and sudomotor tests combined
- Similar outcomes despite different tryptase levels (H$\alpha$T: $ 14.3 \pm 2.5$ ng/mL vs MCAS: $ 3.8 \pm 1.8$ ng/mL) — suggests common final pathway

Certainty:: High (objective measurements, rigorous protocols, appropriate controls) Clinical Relevance:: Critical for ME/CFS — provides objective biomarkers for mast cell-mediated neurological dysfunction. The 80% SFN prevalence, cerebral hypoperfusion, and dysautonomia mirror ME/CFS findings, suggesting MCAS screening in ME/CFS patients with severe orthostatic intolerance. Testable via autonomic testing battery, transcranial Doppler, and skin biopsy.

3 Magadmi et al. 2019 — CADM1-Mediated Mast Cell-Nerve Adhesion Amplifies Inflammation

Full Citation:: Magadmi R, Meszaros J, Damanhouri ZA, Seward EP. CADM1-dependent adhesion between mast cells and sensory neurons enhances mast cell inflammatory responses. Front Cell Neurosci. 2019;13:262. DOI:: 10.3389/fncel.2019.00262 Published:: 2019 Study Design:: In vitro mechanistic study (mouse cells) Key Findings::

- CADM1 protein mediates physical adhesion between mast cells and sensory neurons
- Neuronal contact amplifies mast cell degranulation ( 2-fold) and IL-6 secretion ( 3-fold)
- Blocking CADM1 abolished enhancement — demonstrates adhesion requirement
- Effect is neuron-specific (HEK 293 cells expressing CADM1 did not replicate) — suggests additional neuronal signals
- TNF$\alpha$ unchanged — indicates selective pathway modulation

Certainty:: Medium (well-controlled in vitro study, but mouse cells; awaits human and in vivo validation) Clinical Relevance:: Provides mechanistic support for “signal amplifier hypothesis” of mast cell-nerve interactions in ME/CFS. Could explain pain amplification disproportionate to tissue damage and the connection between mast cell activation and small fiber neuropathy documented in Novak et al. 2022.

4 Nakamura et al. 2014 — Circadian Clock Regulates Mast Cell Function

Full Citation:: Nakamura Y, Nakano N, Ishimaru K, et al. Circadian regulation of allergic reactions by the mast cell clock in mice. J Allergy Clin Immunol. 2014;133(2):568–575. DOI:: 10.1016/j.jaci.2013.07.040 PMID:: 24060274 Published:: February 2014 Study Design:: Genetic mouse model with circadian clock manipulation Key Findings::

- Mast cells possess intrinsic circadian clocks that drive time-of-day variation in degranulation
- *Clock* gene mutation abolished temporal variation in IgE-mediated responses (both in vivo and in vitro)
- Fc$\varepsilon$RI receptor expression and signaling show circadian rhythms in wild-type cells, lost in *Clock*-mutant
- Adrenalectomy disrupts mast cell clock rhythms — demonstrates adrenal hormones entrain mast cell clocks

Certainty:: High for mechanism (elegant genetics, replicated); Low-Medium for ME/CFS relevance (extrapolation from mouse allergy model) Clinical Relevance:: Provides basis for “temporal priming hypothesis” — HPA axis dysfunction in ME/CFS could disrupt mast cell circadian regulation, leading to inappropriate activation timing. May explain symptom timing patterns, sleep-symptom interactions, and potential for chronotherapy (timing mast cell treatments to peak reactivity periods).

5 Steinberg et al. 1996 — Terfenadine Trial (Negative)

Full Citation:: Steinberg P, McNutt BE, Marshall P, et al. A double-blind placebo-controlled study of the efficacy of oral terfenadine in the chronic fatigue syndrome. J Allergy Clin Immunol. 1996;97(1 Pt 1):119–126. DOI:: 10.1016/S0091-6749(96)80212-6 PMID:: 8568124 Published:: January 1996 Study Design:: Double-blind, placebo-controlled RCT Sample Size:: 30 CFS patients enrolled, 28 completed Intervention:: Terfenadine 60 mg twice daily for 8 weeks (H1 antihistamine only) Results::

- *NO therapeutic benefit detected*
- No improvement in symptom amelioration
- No improvement in physical or social functioning
- No improvement in health perceptions or mental health
- Additional finding: 73% had atopy, 53% had positive immediate skin test results

Conclusion:: “Terfenadine is unlikely to be of clinical benefit in treating CFS symptoms” Certainty:: High (well-designed RCT with negative results) Clinical Implications:: H1 antihistamine alone insufficient; suggests combination therapy (H1+H2 or H1+mast cell stabilizer) may be necessary

6 Davis et al. 2023 — Long COVID Case with H1/H2 Combination Success

Full Citation:: Davis HE, McCorkell L, Vogel JM, Topol EJ. Case Study of ME/CFS Care Applied to Long COVID: Hypothesis Regarding Exercise Intolerance, Orthostatic Intolerance, Mast Cell Activation, Sleep Dysfunction, Neuropathy, and Viral Persistence. Healthcare. 2023;11(6):896. DOI:: 10.3390/healthcare11060896 PMID:: 36981567 PMCID:: PMC10048325 Published:: March 21, 2023 Study Type:: Single case report (n=1) Patient:: Long COVID patient meeting ME/CFS criteria Interventions and Outcomes::

- *H1 blockers* (loratadine 10 mg OR fexofenadine 180 mg): “helpful with energy and cognitive dysfunction”
- *H2 blocker* (famotidine 40 mg BID): “helpful with energy and cognitive dysfunction”
- *Discontinuation test*: Stopping fexofenadine and famotidine → “increased fatigue and increased cognitive dysfunction, both of which improved rapidly upon resumption”
- *Cromolyn* (400 mg QID): Peak heart rate during walking fell from 130–140 bpm to 100–105 bpm
- *Quercetin* (1000 mg BID): “Improvement in fatigue and allergic symptoms”

Certainty:: Low (n=1 case report, but dramatic response with discontinuation-rechallenge confirmation) Clinical Relevance:: Demonstrates potential for H1+H2 combination therapy; suggests mast cell-targeted approach may benefit post-viral fatigue syndromes

7 Theoharides et al. 2012 — Quercetin Superior to Cromolyn

Full Citation:: Theoharides TC, Asadi S, Panagiotidou S. Quercetin in combination with IL-6 inhibits histamine and TNF release from mast cells through interaction with the IL-6 receptor. PLOS ONE. 2012;7(3):e33805. DOI:: 10.1371/journal.pone.0033805 PMID:: 22470478 PMCID:: PMC3314669 Published:: March 29, 2012 Study Design:: In vitro comparison + clinical pilot trials Concentration:: Quercetin 100 \(\mu\)M (approximated by 2 g/day oral dosing) Key Findings::

- *IgE/Anti-IgE stimulation*: Quercetin inhibited histamine (82% vs 67%), PGD~2~ (77% vs 75%), leukotrienes (99% vs 88%) comparably to cromolyn
- *Substance P stimulation*: Quercetin dramatically outperformed cromolyn — IL-8 reduced from 437.2 to 115.4 pg/mL (quercetin) vs 362.9 pg/mL (cromolyn)
- *Mechanism*: Quercetin worked prophylactically (30 min pre-stimulus); cromolyn required simultaneous addition
- *Clinical trial — Contact dermatitis*: Quercetin 2 g/day for 3 days reduced nickel patch reactions $>$ 50% in 8 of 10 patients; pruritus eliminated completely
- *Clinical trial — Photosensitivity*: Quercetin 1 g increased minimal erythema dose in all patients ($p$=0.002)

Certainty:: Medium-High (strong in vitro data, pilot clinical success) Clinical Relevance:: Quercetin may be superior to prescription cromolyn for mast cell stabilization; available over-the-counter; well-tolerated

8 Clemons et al. 2011 — Amitriptyline Mast Cell Inhibition

Full Citation:: Clemons A, Vasiadi M, Kempuraj D, et al. Amitriptyline and prochlorperazine inhibit proinflammatory mediator release from human mast cells: possible relevance to chronic fatigue syndrome. J Clin Psychopharmacol. 2011;31(3):385–387. DOI:: 10.1097/JCP.0b013e3182196e50 PMID:: 21532369 PMCID:: PMC3498825 Published:: June 2011 Study Design:: In vitro study on human mast cells Key Findings::

- Amitriptyline (AMI) and prochlorperazine (PRO) at 25 $\mu$M significantly reduced IL-8, VEGF, and IL-6 release from stimulated human mast cells
- Bupropion, citalopram, and atomoxetine did NOT inhibit mast cells
- Mechanism involves modulation of intracellular calcium (FURA2 AM calcium indicator assays)
- AMI inhibits histamine release while permitting serotonin release

Conclusion:: “The ability of amitriptyline, but not other antidepressants, to inhibit human mast cell release of pro-inflammatory cytokines may be relevant to their apparent benefit in CFS” Certainty:: Medium (mechanistic in vitro study, explains clinical observations) Clinical Relevance:: Amitriptyline’s benefit in ME/CFS may involve mast cell inhibition beyond pain/sleep effects; specific pharmacological mechanism

9 Rupatadine — Dual H1/PAF Antagonist with Mast Cell Stabilization

Full Citations::

- Piñero-González J, et al.\ Rupatadine inhibits proinflammatory mediator secretion from human mast cells triggered by different stimuli. *J Investig Allergol Clin Immunol*. 2017;27(3):161–168. PMID: 19672095; PMCID: PMC7065400.
- Mullol J, Bousquet J, Bachert C, et al.\ Rupatadine in allergic rhinitis and chronic urticaria. *Allergy*. 2008;63(Suppl 87):5–28. PMID: 18339040.

Mechanism:: Triple action — (1) H1 receptor antagonist, (2) PAF (platelet-activating factor) antagonist, (3) Direct mast cell stabilizer Mast Cell Effects::

- Rupatadine (10–50 $\mu$M) inhibited IL-8 (80%), VEGF (73%), histamine (88%) release from LAD2 mast cell line
- Also inhibited IL-6, IL-8, IL-10, IL-13, and TNF release from human cord blood-derived cultured mast cells
- More effective than levocetirizine and desloratadine at PAF-induced mast cell inhibition

PAF Antagonism Potency::

- Rupatadine IC~50~ = 4.6 $\mu$M (most potent)
- Loratadine IC~50~ = 142 $\mu$M ($\sim$ 31$\\times$ less potent)
- Cetirizine IC~50~ $>$ 200 $\mu$M ($>$ 43$\\times$ less potent)
- Fexofenadine IC~50~ $>$ 200 $\mu$M ($>$ 43$\\times$ less potent)

Efficacy Ranking:: Network meta-analysis for allergic rhinitis (SUCRA scores):

- Rupatadine 20 mg: 99.7% (highest rank)
- Rupatadine 10 mg: 76.3%
- Fexofenadine, cetirizine: moderate
- Loratadine 10 mg: lowest (inferior to all others)

Certainty:: High (multiple RCTs, network meta-analysis, in vitro mechanistic data) Clinical Relevance:: Superior to standard H1 antihistamines; unique PAF antagonism may benefit ME/CFS patients with mast cell activation and vascular/orthostatic symptoms Note:: PAF is a key inflammatory mediator in ME/CFS contributing to vascular leakage, brain fog, and orthostatic issues

10 Moldofsky et al. 2015 — Ketotifen in Fibromyalgia (Negative)

Full Citation:: Moldofsky H, Harris HW, Archambault WT, Kwong T, Lederman S. A randomized, double-blind, placebo-controlled Phase 1 trial of ketotifen in fibromyalgia. J Rheumatol. 2015;42(12):2505–2513. DOI:: 10.3899/jrheum.150460 PMID:: 26472411 PMCID:: PMC4417653 Published:: December 2015 Study Design:: Phase 1 RCT, double-blind, placebo-controlled Sample Size:: 51 fibromyalgia patients (24 ketotifen, 27 placebo) Intervention:: Ketotifen 2 mg BID for 8 weeks (after 1-week titration) Results:: NO significant differences in primary outcomes:

- Pain intensity: ketotifen $-1.3$ vs placebo $-1.5$ ($p$=0.7)
- FIQR scores: $-12.1$ vs $-12.2$ ($p$=0.9)
- Side effect: Transient sedation 28.6% vs 4%

Certainty:: High (well-designed RCT showing no benefit) Clinical Relevance:: Mast cell stabilization alone may not address core pathophysiology in central pain syndromes like fibromyalgia; relevance to ME/CFS unclear Note:: Despite this negative finding, retrospective ME/CFS study (not included here) showed 77% of continuers had significant PEM reduction with ketotifen