L-arginine depletion in preeclampsia orients nitric oxide synthase toward oxidant species.
Less nitric oxide (NO)-dependent vasodilation and excess formation of reactive oxygen species could explain poor placenta perfusion in preeclampsia, but the pathways involved are unknown. We tested the hypothesis that reduced NO activity and increased oxidative stress in preeclamptic placenta is related to a low bioavailability of l-arginine. Placental endothelial NO synthase (ecNOS) expression (by immunoperoxidase) and activity (by diaphorase and [(3)H]L-citrulline formation) were comparable in normotensive pregnancy and in preeclampsia, whereas nitrotyrosine staining, a marker of peroxynitrite, was stronger in preeclamptic villi, confirming previously reported data. Oxidative tissue damage was documented in preeclamptic villi by strong 4-hydroxynonenal-lysine staining (by immunoperoxidase), which closely colocalized with nitrotyrosine. Concentration of the NO precursor l-arginine (by HPLC) in umbilical blood and in villous tissue was lower in preeclampsia than in normotensive pregnancy. This was not caused by a defective l-arginine transport, because gene expression of the CAT-1, 4F2hc, and LAT-1 cationic amino acid transporters (by real-time reverse-transcription polymerase chain reaction [RT-PCR]) was normal. Instead, gene expression (by real-time RT-PCR) and protein tissue content (by immunoperoxidase and Western blot) of arginase II-the enzyme that degrades arginine to ornithine-were higher in preeclamptic villi than in normotensive pregnancy. These results provide a biochemical explanation for defective NO activity and increased oxidative stress in preeclamptic placenta. In normal placenta, adequate concentration of l-arginine orients ecNOS toward NO. In preeclampsia, a lower than normal l-arginine concentration caused by arginase II overexpression redirects ecNOS toward peroxynitrite.
Noris
Marina
M
Mario Negri Institute for Pharmacological Research, Via Gavazzeni, 11, 24125 Bergamo, Italy. noris@marionegri.it
Todeschini
Marta
M
Cassis
Paola
P
Pasta
Fabio
F
Cappellini
Anna
A
Bonazzola
Samantha
S
Macconi
Daniela
D
Maucci
Raffaella
R
Porrati
Francesca
F
Benigni
Ariela
A
Picciolo
Claudio
C
Remuzzi
Giuseppe
G
D000328:Adult; D026923:Amino Acid Transport Systems, Basic / Q000378:metabolism; D001119:Arginase / Q000378:metabolism; D001120:Arginine / Q000378:metabolism*; D005260:Female; D006801:Humans; D015227:Lipid Peroxidation; D008431:Maternal-Fetal Exchange; D009252:NADPH Dehydrogenase / Q000032:analysis; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III; D018384:Oxidative Stress; D030421:Peroxynitrous Acid / Q000096:biosynthesis*; D010920:Placenta / Q000201:enzymology / Q000378:metabolism; D011225:Pre-Eclampsia / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D011247:Pregnancy; D026361:Reactive Nitrogen Species / Q000378:metabolism
D026923:Amino Acid Transport Systems, Basic; D026361:Reactive Nitrogen Species; D030421:Peroxynitrous Acid; D001120:Arginine; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D009252:NADPH Dehydrogenase; C477631:ARG2 protein, human; D001119:Arginase