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Division of Maternal-Fetal Medicine, 1 Department of Obstetrics and Gynecology, 2 Department of Pediatrics, and 3 Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0526
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Oxidative stress may increase
production of superoxide and nitric oxide, leading to formation of
prooxidant peroxynitrite to cause vascular dysfunction. Having found
nitrotyrosine residues, a marker of peroxynitrite action, in placental
vessels of preeclamptic and diabetic pregnancies, we determined whether
vasoreactivity is altered in these placentas and treatment with
peroxynitrite produces vascular dysfunction. The responses of diabetic,
preeclamptic, and normal placentas to increasing concentrations of the
vasoconstrictors U-46619
(10
9-107
M) and ANG II
(109-107
M) and the vasodilators glyceryl trinitrate
(109-107
M) and prostacyclin (PGI2;
108-106
M) were compared as were responses to these agents in normal placentas
before and after treatment with 3.16 × 104 M peroxynitrite for 30 min.
Responses to both vasoconstrictors and vasodilators were significantly
attenuated in diabetic and preeclamptic placentas compared with
controls. Similarly, responses to U-46619, nitroglycerin, and
PGI2, but not ANG II, were significantly attenuated
following peroxynitrite treatment. The presence of nitrotyrosine
residues confirmed peroxynitrite interaction with placental vessels.
Overall, our data suggest that peroxynitrite formation is capable of
attenuating vascular responses in the human placenta.
reactive oxygen species; nitric oxide; superoxide; oxidative injury
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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PREECLAMPSIA IS CONSIDERED one of the most significant health problems in human pregnancy (12), complicating ~5-7% of pregnancies, and is a leading cause of fetal growth restriction, indicated premature delivery, and maternal death. The disorder is characterized by maternal hypertension, proteinuria, and edema with accompanying platelet aggregation, vasoconstriction of the maternal vascular bed, and increased resistance of the fetal-placental circulation, with characteristic reduced uteroplacental and fetal-placental blood flows. Increasingly, preeclampsia is recognized to be a syndrome characterized by profound dysfunction of the vascular endothelium (31), perhaps secondary to oxidative stress (32).
In the United States, 16 million people are afflicted by diabetes mellitus, and pregestational diabetes mellitus complicates 2-5% of pregnancies. Despite improved perinatal morbidity over the last several decades, considerable morbidity related to growth aberrations, including a wide range of structural and biological abnormalities, still exists in infants of insulin-dependent diabetic mothers. A number of placental lesions have been described, particularly in cases of poorly controlled glucose homeostasis, including plethora, chorangiosis, edema, hypo- and hyperramification of the terminal villi, infarcts, fetal-placental sclerosis, fibrotic villi, and villous basement membrane changes (6). Such changes are likely to affect placental vascular resistance and vascular volume and therefore may lead to chronic disturbances in fetal-placental blood flow. In addition, diabetes mellitus in pregnancy is accompanied by an increased incidence of preeclampsia and pregnancy-induced hypertension (9), which like diabetes are characterized as being states of endothelial dysfunction (33).
Recently, evidence has accumulated which suggests that reactive oxygen
species play an important role in both diabetes- and preeclampsia-related complications. In diabetes, oxygen free radicals are thought to be produced as a result of prolonged periods of exposure
to hyperglycemia, which is known to cause nonenzymatic glycation of
plasma proteins (39). The glycated products undergo further spontaneous
reactions leading to the production and release of free radicals,
including superoxide (O2·) (35).
Gillery et al. (14) have demonstrated that glycated protein prepared
from diabetic serum is able to generate
O2· at physiological pH, which in
the absence of appropriate levels of scavengers may lead to an
imbalance between prooxidants and antioxidants and produce a state of
oxidative stress. Pregnancies complicated by preeclampsia are
associated with elevated blood and tissue levels of lipid peroxidation
products (21, 25), thus implicating increased oxidative stress in the
etiology of preeclampsia. Increased lipid peroxide levels in
preeclampsia may also be the result of decreased antioxidant
activities, such as superoxide dismutase, glutathione peroxidase, and
vitamin E, which have been shown to be decreased in placental tissues
from preeclamptic pregnancies (41).
As the human fetal-placental vasculature lacks autonomic innervation,
autocrine and/or paracrine agents such as nitric oxide radical
(NO ·) play an important role in the regulation of
fetal-placental blood flows, being shown to maintain low-basal tone and
attenuate the vasoconstrictive effects of thromboxane and endothelin
(27). However, NO · is inactivated by superoxide
anion (O2·), therefore limiting
its activity, but this interaction yields peroxynitrite anion
(ONOO), a powerful oxidant of a variety of
biomolecules (2). Peroxynitrite is known to cause lipid peroxidation,
inhibit the mitochondrial electron transport system and nitrate
tyrosine residues, and oxidize sulfhydryl groups on proteins, hence
altering their activity or disrupting signal transduction pathways
(20). Administration of ONOO impairs relaxation of
the isolated perfused rat heart (40) and causes vascular dysfunction in
rats via selection impairment of adrenoreceptors when given
systemically (5). We have recently observed increased expression of
nitrotyrosine residues, formed from the interaction of
ONOO with tyrosine moieties, in the fetal
vasculature and villous stroma of preeclamptic and diabetic placentas
(22, 28). These findings suggest involvement of ONOO
in the pathological processes of diabetic and preeclamptic placental injury.
However, the functional significance associated with the presence of
altered tyrosine residues on proteins in the fetal-placental vasculature remains unknown. The present study was therefore undertaken to determine whether the responsiveness to vasoactive agents of the
fetal-placental vasculature of pregnancies affected by diabetes or
preeclampsia is compromised. In addition, we sought to directly determine whether ONOO causes functional deficit in
this vascular bed by perfusing the fetal-placental vasculature with
authentic ONOO and determining its effects on
vascular reactivity.
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MATERIALS AND METHODS |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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List of chemicals. Polyvinylpyrrolidone K30 was purchased from
Acros (Geel, Belgium). Peroxynitrite was obtained from Alexis (San
Diego, CA) and stored at 
80°C until used for experiments. The exact concentration of the peroxynitrite was determined
spectrophotometrically before use at 302 nm using a molar absorptivity
of E302 = 1.67 × 103
M1 · cm1
and was infused directly into the inflow line of the perfused placenta
to give a final concentration of 3.16 × 104 M. All other chemicals
were obtained from Sigma Chemical (St. Louis, MO).
Tissue procurement. Placentas from uncomplicated pregnancies
and those affected by either pregestational insulin-dependent diabetes
mellitus or by preeclampsia were obtained after vaginal delivery or
cesarean section at term in the labor and delivery service at
University Hospital under a protocol approved by the Institutional
Review Board. For the purpose of our study, preeclampsia was defined as
occurrence of hypertension (sustained blood pressure greater than 140 mmHg systolic and 90 mmHg diastolic), edema, and proteinuria
(
1+ protein on dip stick) after 20 wk gestation in a
previously normotensive woman. Placentas from multifetal pregnancies
and pregnancies affected by drug abuse or with coexisting medical
conditions other than insulin-dependent diabetes mellitus or
preeclampsia were excluded from the study.
Placentas were transported to the laboratory immediately following
delivery and processed for perfusion. Samples of placental villous
tissue were flash frozen in isopentane-cooled liquid nitrogen within 15 min after delivery or immediately following perfusion experiments and
stored at 80°C until further processed for immunohistochemistry.
Placental perfusion. Perfusion of the placentas was performed as previously described by Glance et al. (15). To establish perfusion of the fetal-placental circulation, a suitable third- or fourth-order artery and corresponding vein were cannulated at a site immediately before passage through the chorionic plate. For perfusion of the maternal intervillous space, two remnants of the spiral arteries were cannulated in the basal plate. The effluent from the intervillous space was collected by gravity into a Plexiglas funnel, over which the cotyledon was placed basal plate downward. The perfusion medium for both fetal and maternal circulation consisted of Hanks' balanced salt solution containing polyvinylpyrrolidone 40 (25 mg/ml), 0.1% BSA, heparin (20 IU/ml), and gentamicin (48 µg/ml). The pH of the perfusion buffer was adjusted to 7.3-7.5 with sodium bicarbonate, and the medium was gassed with 95% O2-5% CO2 and maintained at 37°C. The perfusion rates were 4 ml/min for the fetal and 10 ml/min for the maternal circulations. Lateral pressure readings were taken in the fetal and maternal inflow lines close to the points of cannulation. Data on perfusion pressure and inflow and outflow PO2 were sampled every second and stored using a computer system with Windaq 200 software (Dataq Instruments; Akron, OH).
Vascular reactivity in diabetic or preeclamptic placentas.
Fetal-placental vascular reactivity in control, diabetic, or
preeclamptic placentas was studied in vitro. Placentas were first
equilibrated for a period of at least 30 min, after which changes in
perfusion pressure were recorded following the administration of 2-ml
bolus injections into the fetal-placental vasculature of vehicle
followed by the vasoconstrictors U-46619 (a thromboxane mimetic,
109-107
M) or ANG II
(109-107
M), or by the vasodilators glyceryl trinitrate (GTN,
109-107
M) or prostacyclin (PGI2;
108-106
M). When dose responses to the vasodilators were being studied, the
placental cotyledons were first preconstricted with constant infusion
of 1 × 108 to 5 × 108 M U-46619 to the same range of
perfusion pressures (between 80 and 120 mmHg) in each group. Each
experiment was repeated in five or six separate placentas from each group.
Immunohistochemical staining. Immunohistochemical staining was
performed as previously described (28). Placental villous tissues were
obtained before or following perfusion with ONOO or
vehicle, frozen in liquid nitrogen-cooled isopentane, and cryosectioned
at 6-8 µm. Tissue sections were blocked with 1.5% goat serum
for 30 min and immunostained with rabbit polyclonal anti-nitrotyrosine
antibody (10 µg/ml; Upstate Biotechnology; Lake Placid, NY), which
had been preabsorbed in human normal serum using the Vectastain Elite
ABC Kit, and aminoethylcarbazole as peroxidase substrate. Sections were
rinsed in PBS and coverslipped, and localization pattern and intensity
of immunostaining for nitrotyrosine were assessed subjectively. Images
were captured using Image Pro-Plus software (Media Cybernetics; Silver
Springs, MD). Sections treated with pooled rabbit IgG instead of the
primary antibody served as negative immunological controls.
Effect of peroxynitrite on placental vascular reactivity. Two
protocols were used to test the reactivity of placentas to either vasoconstrictors or vasodilators before and after
ONOO treatment. To study the effect on
vasoconstrictors, placentas were first equilibrated for a period of at
least 30 min, after which they were treated with bolus administrations
of either solvent solution or U-46619 or ANG II
(109-107
M) and perfusion pressure was recorded. Then, after infusion of
ONOO [3.16 × 104 M, based on work by Villa et al.
(40)] into the fetal-placental vasculature for 30 min, the
injections of solvent solution and the two vasoconstrictors were
repeated and again changes in perfusion pressure were recorded. The
stock ONOO solution was infused into the perfusion
inflow line immediately proximal to the placental tissue at a dilution
of 1:538 to yield a final concentration at the site of infusion of 3.16 × 104 M. pH was maintained between
7.3 and 7.5. A separate series of control experiments following the
same protocol was performed where vehicle for the stock
ONOO solution (5.5 × 104 M NaOH) was infused at the
appropriate dilution for 30 min. To study the effect of
ONOO on vasodilators, placentas were again
equilibrated for at least 30 min. Then the fetal placental vasculature
was preconstricted to between 80 and 120 mmHg with constant infusion of
U-46619. In the continued presence of U-46619, dose-response curves to solvent solution and GTN
(109-107
M) or PGI2
(108- 106
M) were performed. After a 30-min infusion of 3.16 × 104 M ONOO,
administration of vasodilators was then repeated in the same placentas
ensuring that they were preconstricted with U-46619 to the same
perfusion pressure as prior to ONOO treatment. Again
for control purposes, a separate series of experiments following the
same protocol was conducted where the vehicle for the
ONOO solution was infused for 30 min. For each
protocol six or seven placentas were studied in each group.
Statistical analysis. Data were expressed as means ± SE.
Statistical significance was tested using repeated measures ANOVA for
studies evaluating the vasoreactivity to the different agonists in
control vs. diabetic or preeclamptic placentas, in diabetic vs.
preeclamptic placentas, and between ONOO-treated and
vehicle-treated placentas. P < 0.05 was considered significant.
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Table 1 shows the maternal characteristics
and pregnancy outcomes for the control, diabetic, and preeclamptic
groups studied. Although mean fetal and placental weights were greater
in the diabetic group, the difference from the control group did not reach statistical significance. Delivery mode, gestational age, birth
weight, placental weight, ratio of placenta weight to birth weight, and
Apgar scores were similar between control and preeclamptic pregnant
women. As expected, blood pressures of preeclamptics were significantly
higher compared with control patients. In addition, we found a
statistically significant difference in maternal age between
preeclamptic and control groups, which may simply reflect increased
incidence of preeclampsia in first pregnancies. All women in the
preeclamptic group received MgSO4 as a routine course of
treatment. Four of the five preeclamptic women had urinary protein
levels of 4+ and one of 1+ on dipstick. The
diabetic group consisted of two women in White classification C, two in
class D, one in class R, and one in class R+F. The two White class D
were proteinuric with levels of 2+ and 3+, and
the White class R+F patient had urinary protein of 4+. The
third trimester hemoglobin A1C level of five of the six women in this group fell within the normal range of 5.8-6.4% in our population, suggesting they had good glycemic control, with the
remaining woman having a hemoglobin A1C level of 6.8%.
None of the women in the diabetic or control groups was treated with MgSO4. All patients in the preeclamptic and diabetic groups
were gravida 1/parity 0 (G1/P0) except for one G3/P0 in each of these two groups. The normal control group consisted of patients who were
G8/P6, G4/P1, G2/P1, G4/P1, G6/P3, and G4/P2.
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Figure 1, A-D, illustrates fetal
vascular reactivity of diabetic, preeclamptic, and control placentas.
Significant concentration-dependent responses were observed in each
group to increasing concentrations of the vasoconstrictors U-46619
(Fig. 1A) and ANG II (Fig. 1B) and the vasodilators GTN
(Fig. 1C) and PGI2 (Fig. 1D), respectively. However, the responses to each of the four vasoactive agents were significantly attenuated in the diabetic (P < 0.01, P < 0.05, P < 0.0005, and P < 0.0001 for U-46619,
ANG II, GTN, and PGI2, respectively) and preeclamptic
groups (P < 0.01, P < 0.001, P < 0.05, and P < 0.01, respectively) compared with
controls. The responses to the highest concentration of
the vasoactive agents used were only 31, 41, 36, and 23% of control
values in the diabetic placentas and 39, 43, 78, and 51% of controls
in preeclamptic placentas for U-46619, ANG II, GTN, and
PGI2, respectively. Differences in responses to
vasodilators were not due to differences in the extent of
preconstriction to U-46619 between the three groups of placentas
(P > 0.05, ANOVA). The decreases in vasoactive responses to
U-46619 and ANG II from controls were similar (P > 0.05, repeated measures ANOVA) in the diabetic and preeclamptic placentas,
whereas the decrease in responses to GTN from control and
PGI2 was greater in diabetic than preeclamptic placentas
(P < 0.05, repeated measures ANOVA). Thus the responses to
vasodilators were more affected in the placentas from diabetic
individuals, whereas the responses to vasoconstrictors were equally
affected in the diabetic and preeclamptic groups.
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The responses of the human placentas to bolus infusions of U-46619, ANG
II, GTN, and PGI2 before and after treatment with ONOO are shown in Fig.
2, A-D, respectively. Again, the
vasoconstrictor and vasodilator responses increased in a significant
concentration-dependent manner with increasing amounts of vasoactive
agent infused into the fetal-placental circulation both before and
after ONOO treatment. However, the responses were
significantly altered for U-46619, GTN, and PGI2 after the
30-min ONOO infusion compared with responses before
ONOO infusion, being diminished by 65% (P < 0.001), 80% (P < 0.05), and 65% (P < 0.001)
at the highest concentration of vasoactive agent used. The
concentration of U-46619 used was varied so that the extent of
preconstriction to U-46619 in the vasodilator experiments was not
different before and after ONOO treatment (P > 0.05, paired t-test). The apparent decreased
vasoconstriction of the fetal-placental vasculature to ANG II caused by
ONOO did not reach statistical significance.
Experiments carried out in a separate series of placentas employing the
vehicle for ONOO to control for a potential temporal
effect on vasoreactive responses to agonist showed no effect of time on
responses to repeated infusion of vasoactive agents.
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Representative photomicrographs of placental villous tissue
immunostained for nitrotyrosine are shown in Fig.
3. No positive immunostaining for
nitrotyrosine was observed in nonperfused placental villous tissue
(Fig. 3A), ONOO-perfused placental tissue
stained with control preimmune IgG instead of the primary
anti-nitrotyrosine antibody (Fig. 3B), or villous tissue
perfused with vehicle for the ONOO solution (Fig.
3C). In contrast, however, as is seen in Fig. 3D,
villous tissue perfused with authentic peroxynitrite showed intense
immunostaining for nitrotyrosine. Nitrotyrosine residues were evident
in the vascular endothelium, which in some places had become detached
from the underlying basement membrane, and also in the vascular smooth
muscle and the surrounding mesenchyme.
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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The human placenta lacks local autonomic vascular control, and thus circulating autocrine-paracrine or humoral factors are essential for placental hemodynamic control. In pregnancies complicated by insulin-dependent diabetes mellitus or preeclampsia, both of which are characterized by endothelial cell injury, compromised perfusion of organ systems, including the placenta, is seen and can lead to significant morbidity and mortality in both mothers and neonates.
Ample evidence has accumulated indicating that oxidative stress plays a
role in the pathogenesis of diabetic and preeclamptic complications in
the placenta. Oxidative stress is produced by either an increase in
reactive oxygen species (ROS) formation and/or a decrease in ROS
scavenging ability. The diabetic state leads to increased
production of O2· (11, 24, 35)
and/or increased NO · formation via increased enzymatic activity of endothelial (11) or inducible (38) isoforms of nitric oxide
synthase. In addition, changes in total radical-trapping antioxidant
capacity, such as reduction in scavenger activity of superoxide
dismutase and catalase, glutathione metabolism, and/or vitamin E levels
as well as increases in lipid peroxides have been observed in
preeclamptic and diabetic patients (23, 25, 37, 41). Preeclampsia is
also characterized by an increased presence of reactive oxygen species
as suggested by significantly elevated levels of fetal lipid peroxides
in pregnancies complicated by preeclampsia (21, 25). Administration of
antioxidative vitamins C and E has been shown to reduce placental lipid
peroxidation in perfused human preeclamptic placentas (29). However,
vitamin C-oxidizing activity, and thus ascorbate radical formation, is increased in preeclamptic plasma and may therefore contribute to
vascular dysfunction in this disorder (18).
When O2· and NO · coexist in close proximity, ONOO is formed at a rate
of 6.7 × 109 ms1 (19).
This rate is three times faster than the interaction of
O2· with superoxide dismutase, an
endogenous scavenger of O2·. Thus
at elevated concentrations of NO · or
O2·, NO · outcompetes
superoxide dismutase for O2· with
resultant ONOO formation. Peroxynitrite has been
shown to nitrosylate substrates such as tyrosine moieties within
proteins, and although other reactive nitrogen species have the
potential to nitrate tyrosine (17), the formation of nitrotyrosine in
vivo is thought to be specific for ONOO interaction
with tissue. Our laboratory has recently shown increased expression of
nitrotyrosine residues in the fetal vasculature and villous placental
stroma of pregnancies complicated by preeclampsia (28) and type 1 insulin-dependent diabetes mellitus (22). In addition, Roggensack et
al. (34) have observed increased endothelial nitric oxide synthase,
decreased superoxide dismutase, and increased nitrotyrosine
immunostaining in the maternal vasculature of women with preeclampsia.
These findings thus suggest increased ONOO formation
as a result of oxidative stress during the pathological processes of
preeclamptic and diabetic injury.
Our current study provides evidence that ONOO
synthesis and action in placentas of pregnancies complicated by
preeclampsia or diabetes mellitus may lead to dysfunction of the
fetal-placental vasculature. The responses of the fetal-placental
circulation to both the vasoconstrictors U-46619, a thromboxane
mimetic, and ANG II, and to the vasodilators GTN and PGI2
are attenuated in these conditions compared with control placentas. In
addition, we found an attenuation in fetal-placental vascular
reactivity to these vasoactive agents following treatment of the
fetal-placental vasculature from noncomplicated pregnancies with
authentic ONOO. Both ONOO-treated
placental villous tissue and placental villous tissue from preeclamptic
and diabetic pregnancies show nitrotyrosine residues in fetal and cord
vessels, indicating ONOO interaction with placental
tissue. Taken together, these findings suggest that
ONOO may be at least in part responsible for changes
in altered vascular reactivity seen in placentas affected by diabetes
or preeclampsia.
The actual concentration of ONOO reaching the
resistance vessels of the fetal-placental circulation in our
preparation is unknown. Because the cotyledon vascular volume is ~4
ml, we estimate it takes the perfusion medium about 15 s to begin to
reach the capillary bed of the placental cotyledon from the chorionic
plate at an infusion rate of 4 ml/min, i.e., equivalent to 14 half-lives with a half-life of 1.08 s for ONOO (3).
The ONOO concentration at this point is then
~2 × 108 M, which may
be an overestimate because it presumes that none of the infused
ONOO reacts with any of the numerous biological
targets present in the placental villous vasculature. We recognize that
in CO2-containing solutions as here ONOO
may interact with CO2 to give a
ONO2-CO2 complex, which can
give rise to secondary oxidizing intermediates of different
reactivities from ONOO (13).
Our observations are supported by recent findings of other groups. Although preeclampsia is principally associated with an increase in maternal vascular sensitivity to pressor agents (26), Read et al. (31) reported significant attenuation of vasoconstrictor responses to U-46619 in the fetal-placental vasculature of women with preeclampsia, although no effect was seen on vasodilator responses to PGI2. Similarly, Wilkes et al. (42) found responses to U-46619 to be attenuated in the fetal-placental vasculature of diabetic placentas accompanied by a reduction in the affinity of thromboxane receptors. Gonzales et al. (16) showed that both human placental chorionic plate arteries and veins obtained from preeclamptic pregnancies were significantly less sensitive to S-nitroso-N-acetyl-penicillamine, which spontaneously releases NO ·, than the respective vessels from control placentas. Markedly reduced endothelium-dependent relaxation was found in the myometrial arteries from preeclamptic women when compared with nonpregnant or normotensive pregnant women (1), and flow-induced shear stress resulted in less vasodilation in arteries of preeclamptic women than in normal pregnant women (10). Thus diminished vascular responses to vasoactive agents may be observed in resistance vessels of diabetic and preeclamptic patients. In addition, in diabetic placentas, vascular responses to vasoactive agents may also be affected by other pathophysiological processes, such as progressive glycation and cross-linking of connective tissue proteins of the fetal-placental vasculature, which can produce vascular stiffness as shown in other vascular beds (7).
The deleterious effects of reactive oxygen species have been studied in
many systems. Peroxynitrite, which can interact with and injure the
mitochondrial electron transport system, resulting in inhibition of
cellular respiration (30), is also thought to contribute to endothelial
dysfunction in septic shock (40) and initiates lipid peroxidation, a
mechanism that contributes to the pathogenesis of atherosclerosis,
where extensive nitrotyrosine residues have been localized to foamy
macrophages and endothelium in the atheromatous area (4). DNA breaks
have been shown to be caused by ONOO, which can lead
to initiation of a futile DNA repair cycle by activation of
poly(ADP-ribose)polymerase, resulting in depletion of cellular
NAD+ and ATP stores (43). The ischemia and
reperfusion tissue injury phenomenon may at least partially also be
exacerbated by ONOO-mediated oxidation of xanthine
dehydrogenase to xanthine oxidase, a ROS-generating system (36). Other
modifications of proteins include nitration of aromatic amino acids,
such as tyrosine, which has been demonstrated to affect signal
transduction pathways (20). The decrease in reactivity of the
fetal-placental vasculature observed in pregnancies affected by
insulin-dependent diabetes mellitus or preeclampsia may be the result
of ONOO-mediated alterations of signal transduction
pathways, including receptors and changes in the contractile apparatus
of the vascular smooth muscle. Recently, it has been shown that
ONOO may selectively inactivate the PGI2
receptor (44). If it is possible that different vascular receptors show
different sensitivity to ONOO, then this may explain
the apparent lack of effect on responses to ANG II with in vitro
treatment by ONOO.
Both preeclampsia and diabetes mellitus are associated with increased
fetal morbidity and mortality and may display abnormal placental blood
flow velocity waveforms, indicating increased vascular resistance. In
vitro the placental vasculature of these pregnancies displays altered
vascular reactivity despite apparently good fetal outcomes. However,
this dysfunctional vasculature may not allow the placenta to adequately
respond to increased demands for oxygen and nutrient transfer when the
fetus is stressed by severe insult. This perhaps explains the increased
morbidity and mortality and some of the unexpected fetal demises that
occur near term in diabetic pregnancies. Also, despite the apparent good glycemic control and good fetal outcomes seen in this and our
previous study (22), the placenta of diabetic pregnancies still
displays strong nitrotyrosine staining indicating
ONOO formation and action. Perhaps this illustrates
subclinical disease despite good glycemic control.
In conclusion, in well-controlled diabetes and preeclampsia,
alterations in fetal-placental vasoreactivity occur. Our finding suggests that these alterations may be linked by increased
ONOO production from NO · and
O2· and its subsequent interaction
with signal-transduction pathways linked to vasoactive agents. Further
investigations are necessary to determine whether ONOO is a participant in the pathogenesis of these
and other abnormalities observed in diabetic or preeclamptic placentas
or changes seen in maternal tissues affected by these conditions.
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ACKNOWLEDGEMENTS |
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We gratefully acknowledge the assistance of the residents and staff of the Labor and Delivery Ward at University Hospital of Cincinnati for their help in obtaining the placentas.
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FOOTNOTES |
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This research was sponsored by postdoctoral fellowship Grants SW-96-19-F and SW-97-21-F (W. Kossenjans), by the Ohio-West Virginia Affiliate of the American Heart Association, and by the National Heart, Lung, and Blood Institute Grant HL-57009-01 (L. Myatt).
The work was presented in part at the 45th and 46th annual scientific meetings of the Society of Gynecological Investigation on March 11-14, 1998, and March 10-13, 1999 (Atlanta GA).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: L. Myatt, Dept. of Obstetrics and Gynecology, Univ. of Cincinnati College of Medicine, 231 Bethesda Ave., Cincinnati, OH 45267-0526 (E-mail: leslie.myatt{at}uc.edu).
Received 14 July 1999; accepted in final form 19 October 1999.
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REFERENCES |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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