Metabolites of the
pyrrolizidine alkaloid monocrotaline cause progressive development of
pulmonary hypertension in rats. The putative reactive intermediate
monocrotaline pyrrole (
MCTP) has been shown to cause cytotoxicity,
hypertrophy, decreased proliferation, and altered synthetic capability in cultured pulmonary endothelial cells. We compared effects of
monocrotaline (MCT) at 60 micrograms/ml (0.185 mM) with previously identified metabolites,
MCTP 10 micrograms/ml (0.031 mM) and
glutathione-conjugated dihydropyrrolizine (GSH-DHP) 60 micrograms/ml (0.135 mM), in cultured bovine pulmonary artery endothelial cells (BPAECs). To determine whether endothelial metabolism might contribute to the mechanism of this toxicity, we used markers of cytotoxicity (LDH release), synthetic activity (PGI2 synthesis),
hypertrophy (planimetry), cell density (cell count/area), and
Evans blue albumin (EBA) transudation as a marker for loss of fluid barrier integrity. We found changes in all endothelial markers with
MCTP only.
MCTP caused increased LDH release by 48 hr, augmented PGI2 synthesis by 96 hr, and resulted in
hypertrophy and decreased cell density by 48 hr that persisted at least 21 days. There was increased EBA transudation at 24 hr posttreatment. We concluded that, based on markers of endothelial damage, BPAECs showed no apparent ability to metabolize MCT to a reactive intermediate nor to further metabolize GSH-DHP to a toxic species. We also concluded that
MCTP can cause a direct effect on fluid barrier integrity of endothelial cell monolayers in the absence of
inflammation.