A proliferation of mast cells around the small pulmonary blood vessels and the alveolar septae has been noted in models of
pulmonary hypertension, and in plexiform lesions of
pulmonary arterial hypertension (PAH) in patients. Here, we hypothesize that total mast cell numbers and activation are increased in PAH and that they contribute to
vascular remodeling through cellular and soluble proangiogenic effectors. To test this, blood and urine were collected from patients with PAH (N=44),
asthma (N=18) and healthy controls (N=29) to quantitate
biomarkers of total body mast cell numbers and activation (total and mature
tryptase, N-methyl
histamine,
leukotriene LTE(4) and
prostaglandin PGD-M). Serum total
tryptase was higher in PAH than that in controls suggesting greater numbers of mast cells, but indicators of mast cell activation (mature
tryptase, LTE(4) and
PGD-M) were similar among PAH,
asthma, and controls. Immunohistochemistry of lung tissues identified mast cells as primarily perivascular and connective tissue
chymase(+) type in PAH, rather than mucosal phenotype. Intervention with mast cell inhibitors
cromolyn and
fexofenadine was performed in 9 patients for 12 weeks to identify the influence of mast cell products on the pathologic proangiogenic environment. Treatment decreased total
tryptase and LTE-4 levels over time of treatment. This occurred in parallel to a drop in
vascular endothelial growth factor (
VEGF) and circulating proangiogenic CD34+CD133+ progenitor cells, which suggests that mast cells may promote
vascular remodeling and dysfunction. In support of this, levels of exhaled
nitric oxide, a
vasodilator that is generally low in PAH, increased at the end of the 12-week mast cell blockade and
antihistamine. These results suggest that mast cells might contribute to the pulmonary vascular
pathologic processes underlying PAH. More studies are needed to confirm their potential contribution to the disease.