Poster Board I-554
Placental Growth Factor (PlGF) is a functional cytokine in the vascular endothelial growth factor (VEGF) family that generally promotes angiogenesis, depending on the specific context, and can also promote atherogenesis. Produced in erythroid cells, its level in patients with sickle cell disease (SCD) has been previously related to the rate of erythropoiesis. We evaluated PlGF plasma levels in SCD patients by ELISA, and related it to biomarkers of pulmonary hypertension (PH), an emerging and serious complication of SCD linked to early mortality. We find that PlGF levels are significantly higher in SCD (n=95) than healthy African American control subjects (n=19) (median 16.6 vs. 2.1 pg/mL, p<0.001). PlGF levels were higher in SCD patients with elevated pulmonary pressure (normal pulmonary pressure vs. mildly elevated vs. highly elevated: medians 13.7 vs. 16.7 vs. 19.8 pg/mL, p<0.0001). Supporting a linkage to rate of hemolysis, PlGF correlated with LDH (p=0.001) and inversely with hemoglobin level (p<0.0001). Suggesting a link to inflammation, PlGF correlated significantly with C-reactive protein (p=0.001) and erythrocyte sedimentation rate (p<0.001). PlGF correlated with markers of iron overload, including ferritin, transferrin saturation and inversely with transferrin (all p<0.001). Finally, PlGF correlated with markers of hepatic dysfunction, including low albumin and high direct bilirubin (p<0.001).
We found significantly higher PlGF levels in SCD patients taking hydroxyurea compared to those not taking it (median 17.4 vs. 14.0 pg/ml, p<0.01). Confirming that hydroxyurea increases PlGF levels, in a separate cohort of seven patients, PlGF levels rose significantly from their baseline values after initiating hydroxyurea (median approx 22 vs. 27, p<0.05). Our data suggest that elevated PlGF level is associated with PH in patients with SCD, and PlGF is correlated with severity of hemolysis, inflammation, iron overload and hepatic dysfunction. Considering the variable evidence in the literature for either stimulating or inhibiting angiogenesis, it is not clear whether pathologic elevation of PlGF may be mediating pulmonary hypertension, or perhaps conversely providing an adaptive response to vascular damage. It has been suggested by Perelman et al. that PlGF may mediate leukocyte activation that might promote disease severity in SCD. However, hydroxyurea, which tends to ameliorate SCD complications, stimulates PlGF level in an unexpected manner, possibly related to the ability of hydroxyurea to stimulate erythropoietin production, which might in turn induce PlGF. Further research is needed to reconcile the role of PlGF in PH in SCD.
Asterisk with author names denotes non-ASH members.