Platelet responsiveness to L-arginine in hypertensive disorders of pregnancy

Platelet function in preeclampsia - a systematic review and meta-analysis

Preeclampsia is a serious pregnancy-related complication. Platelets are potentially important in the pathogenesis of preeclampsia, and platelet function analyses may prove as sensitive preeclampsia biomarkers. This study aimed to systematically review and summarise the literature on platelet function markers in preeclampsia. This systematic review was conducted according to PRISMA and registered in PROSPERO. Relevant studies were identified through PubMed and Embase on 15/08/17. As platelet function markers platelet activation, platelet aggregation and platelet adhesion markers were included. If possible, relevant data were extracted for each marker to perform a meta-analysis of the mean difference between women with and without preeclampsia. All 69 included articles underwent quality rating. Some platelet activation markers, especially p-selectin and mean platelet volume (MPV), were significantly increased comparing the two groups of women, while others were not. The meta-analysis demonstrated that, overall, women with preeclampsia had significantly higher MPV than in women without preeclampsia. No significant difference was found regarding platelet aggreg`ation comparing the two groups. Platelet adhesion was investigated in noneof the included studies. In conclusion, further studies are warranted to investigate platelet activation markers future role as predictive markers in preeclampsia. MPV is suggested as the most promising biomarker for evaluating platelet function in preeclampsia.

The role of L-arginine in the prevention and treatment of pre-eclampsia: a systematic review of randomised trials

Pre-eclampsia is a significant health issue in pregnancy, complicating between 2-8% of pregnancies. L-arginine is an important mediator of vasodilation with a potential preventative role in pregnancy related hypertensive diseases. We aimed to systematically review randomised trials in the literature assessing the role of L-arginine in prevention and treatment of pre-eclampsia. We searched the Cochrane Controlled Trials Register, PUBMED, and the Australian and International Clinical Trials Registry, to identify randomised trials involving pregnant women where L-arginine was administered for pre-eclampsia to improve maternal and infant health outcomes. We identified eight randomised trials, seven of which were included. The methodological quality was fair, with a combined sample size of 884 women. For women at risk of pre-eclampsia, L-arginine was associated with a reduction in pre-eclampsia (RR: 0.34, 95% CI: 0.21-0.55), when compared with placebo and a reduction in risk of preterm birth (RR: 0.48 and 95% CI: 0.28 to 0.81). For women with established hypertensive disease, L-arginine was associated with a reduction in pre-eclampsia (RR: 0.21; 95% CI: 0.05-0.98). L-arginine may have a role in the prevention and/or treatment of pre-eclampsia. Further well-designed and adequately powered trials are warranted, both in women at risk of pre-eclampsia and in women with established disease.

L-arginine-nitric oxide pathway and oxidative stress in plasma and platelets of patients with pre-eclampsia

Pre-eclampsia (PE), a syndrome of pregnancy-induced hypertension, continues to be a leading cause of maternal and fetal morbidity and mortality. The aim of this study was to investigate whether changes in oxidative status are correlated with alterations in the L-arginine-nitric oxide pathway and platelet aggregation in PE. Plasma and platelets from women with PE (n=24) or normotensive pregnancy (NP, n=27) recruited in the third trimester of gestation were used to measure oxidative damage assessed by protein carbonyl content, antioxidant activities of superoxide dismutase (SOD), catalase (CAT) and nitrite levels. Transport of L-[(3)H]-arginine, as well as the activities of the nitric oxide (NO) synthase (eNOS and inducible NO synthase (iNOS)) and platelet aggregation, were also evaluated. Plasma nitrite levels and the activities of SOD and CAT were reduced in PE (5.2±2.7, 3.4±0.8, 0.3±0.4, respectively, P<0.05) compared with NP (8.7±2.3, 6.7±3.1, 1.0±0.5, respectively), whereas protein carbonyl content and L-arginine levels were not significantly different between PE and NP groups. In platelets, L-arginine transport was reduced in PE (19.2±10.5, P<0.05) compared with NP (62.0±31.1), whereas the NOS activity, eNOS and iNOS expression, nitrite levels and platelet aggregation were unaffected. Protein carbonyl content was increased, and CAT activity was reduced in platelets from PE (0.03±0.02, 0.55±0.30, respectively, P<0.05), compared with NP (0.005±0.005, 1.01±0.36, respectively). The data suggest that a systemic impairment of antioxidant defense mechanisms is associated with decreased plasma nitrite levels, which may contribute to hypertension in PE. Oxidative stress may contribute to the reduced influx of L-arginine in platelets. Compensatory mechanisms may contribute to the maintenance of NO production and its modulatory role on platelet function.

Redox modulation of Ca2+ signaling in human endothelial and smooth muscle cells in pre-eclampsia

Pre-eclampsia (PE) is a leading cause of maternal hypertension in pregnancy and is associated with fetal growth restriction, premature birth, and fetal and maternal mortality. Activation and dysfunction of the maternal and fetal endothelium in PE appears to be a consequence of increased oxidative stress, resulting from elevated levels of circulating lipid peroxides. Accumulating evidence implicates reactive oxygen species (ROS) in the pathogenesis of vascular dysfunction in PE, perhaps involving a disturbance in intracellular Ca(2+) signaling. Several ion-transport pathways are highly sensitive to oxidative stress, and the resulting modulation of ion transport by ROS will affect intracellular Ca(2+) homeostasis. We review the evidence that changes in ion transport induced by ROS may be linked with abnormalities in Ca(2+)-mediated signal transduction, leading to endothelial and smooth muscle dysfunction in maternal and fetal circulations in PE. As dysregulation of Ca(2+) signaling in fetal umbilical endothelial cells is maintained in culture and embryonic, fetal, and postnatal development is affected by the cellular redox state, we hypothesize that impaired redox signaling in PE may influence "programming" of the fetal cardiovascular system and endothelial function in adulthood.

The role of the L-arginine-nitric oxide pathway in preeclampsia

Preeclampsia (PE) is a major cause of maternal and perinatal mortality, especially in developing countries. Its etiology involves multiple factors, but no specific cause has been identified. Evidence suggests that clinical manifestations are caused by endothelial dysfunction. Nitric oxide (NO), which is synthesized from L-arginine in endothelial cells by the endothelial nitric oxide synthase (eNOS), provides a tonic dilator tone and regulates the adhesion of white blood cells and platelet aggregation. Alterations in the L-arginine-NO pathway have been associated with the development of PE. Various studies, reporting decreased, elevated or unchanged levels of nitrite (NO(2)) and nitrate (NO(3)), two end products of NO metabolism, have been published. Our group contributed to those contradictory reports describing cases of PE with both elevated and decreased levels of NO(2) and NO(3). Apparently, diminished levels of NO could be related to deficiencies in the ingestion of dietary calcium associated to low levels of plasma ionic calcium, which is crucial to the eNOS' activity. Also, low levels of NO could be associated with the presence of eNOS polymorphisms or the presence of increased levels of ADMA, the endogenous inhibitor of NO. High levels of NO associated to low levels of cGMP suggest a decreased bioactivity of NO, which is probably related to an increased degradation of NO caused by a high production of superoxide in states of infection and inflammation. The present article analyses and reviews the reported paradoxical roles of the L-arginine-NO pathway in PE and gives a possible explanation for these results.

L-arginine supplementation in patients with gestational hypertension: a pilot study

OBJECTIVE

To evaluate the effects of L-arginine (L-Arg) supplementation on clinical outcomes and blood pressure (BP) changes in patients with gestational hypertension.

METHODS

Patients with gestational hypertension and proteinuria (n = 28, >300 mg/24 h) and those without proteinuria (n = 46) were randomized in a double-blind design to receive either L-Arg (20g/500 mL intravenously daily, for 5 days followed by 4 g/day orally for 2 weeks) or placebo (PL). The primary outcome variable was time from randomization to delivery (Latency). Automated BP readings were obtained every 2 hours, between 8.00 am and 8.00 pm daily, untill the sixth day after treatment.

RESULTS

At inclusion, gestational age and proportions of patients with proteinuria did not differ significantly between the PL and L-Arg group. Latency was significantly longer in the L-Arg group compared with the PL group (19.5 +/- 16.9 vs. 31.7 +/- 25.2 days; p = 0.008). Compared with baseline, both systolic and diastolic BP 6 days after treatment were significantly reduced in the L-Arg group but not in the PL group. The subgroup of patients without proteinuria randomized to the group receiving L-Arg showed a trend to prolong pregnancy, to attenuate the evolution to PE, and to reduce the rate of low birth weight.

CONCLUSIONS

The treatment with L-Arg seems promising in prolonging pregnancy and reducing blood pressure, particularly in patients with gestational hypertension and without proteinuria. This benefit should be confirmed in larger studies with the power to evaluate the effectiveness of L-Arg in preventing the development to preeclampsia.

Nitric oxide for preventing pre-eclampsia and its complications

BACKGROUND

Pre-eclampsia, a multisystem disorder of pregnancy characterised by high blood pressure and protein in the urine, is associated with endothelial dysfunction. Nitric oxide mediates many functions of the endothelium, including vasodilatation and inhibition of platelet aggregation. Pre-eclampsia may be associated with nitric oxide deficiency, but the evidence to support this suggestion is contradictory. Nevertheless, it has been hypothesised that agents which increase nitric oxide may prevent pre-eclampsia.

OBJECTIVES

To assess the effectiveness and safety of nitric oxide donors and precursors for preventing pre-eclampsia and its complications.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (November 2006), CENTRAL (The Cochrane Library 2006, Issue 3), and EMBASE (2002 to December 2004).

SELECTION CRITERIA

Studies were included if they were randomised trials evaluating nitric oxide donors or precursors for preventing pre-eclampsia and its complications.

DATA COLLECTION AND ANALYSIS

Both review authors independently assessed studies for inclusion. Data were extracted and double checked for accuracy.

MAIN RESULTS

Six trials (310 women) were included. Four were of good quality and two were of uncertain quality. Four trials (170 women) compared nitric oxide donors (glyceryl trinitrate) or precursors (L-arginine) with either placebo or no intervention. There are insufficient data for reliable conclusions about the effects on pre-eclampsia (four trials, 170 women; relative risk (RR) 0.83, 95% confidence interval (CI) 0.49 to 1.41) or its complications. One trial (36 women) compared a nitric oxide donor with nifedipine, and another (76 women) compared it with antiplatelet agents. Both were too small for reliable conclusions about possible differential effects. Glyceryl trinitrate was associated with an increased risk of headache (two trials, 56 women; RR 6.85, 95% CI 1.42 to 33.04), and of stopping treatment (two trials, 56 women; RR 4.02, 95% CI 1.15 to 14.09) compared to placebo. However, the increase for both outcomes was due to an extreme result in one small trial (7/7 versus 0/9 for both outcomes).

AUTHORS' CONCLUSIONS

There is insufficient evidence to draw reliable conclusions about whether nitric oxide donors and precursors prevent pre-eclampsia or its complications.

Cooperative type of platelet hypersensitivity to ADP

We found that gestosis is associated with platelet hypersensitivity to ADP. Cell P2X1 receptors exhibited a positive cooperative response to ADP (EC(50)=10.88+/-3.70 nM, Hill constant n=2.59+/-0.50 rel. units). Cooperative binding of ADP to platelet P2X1 receptors was also observed during incubation of cells from pregnant women with isosorbide dinitrate.

System y+ arginine transport and NO production in peripheral blood mononuclear cells in pregnancy and preeclampsia

Systemic inflammation and oxidative stress are features of normal pregnancy and, in excess, contribute to the pathogenesis of preeclampsia. Inflammatory cell activation stimulates uptake of arginine (the precursor for nitric oxide) by transport system y+, expression of one of its genes (CAT-2) together with inducible nitric oxide synthase, leading to nitric oxide production. We investigated whether these changes occur in peripheral blood mononuclear cells in normal pregnancy and are exaggerated in preeclampsia. Samples from matched trios of nonpregnant, normal pregnant, and preeclamptic women were studied. Arginine transport was characterized, and the expression of inducible nitric oxide synthase and cell-specific nitric oxide production were measured. Arginine uptake by system y+ was significantly increased (P<0.001) in peripheral blood mononuclear cells in normal pregnancy but not in preeclampsia. CAT-2 mRNA was not detected in cells from nonpregnant women but was detected in 3 of 10 normal pregnant and 8 of 10 of preeclamptic women (P<0.001). Inducible nitric oxide synthase protein expression was significantly increased in normal pregnant women (P<0.05) but not preeclamptic women. No significant differences in cell-specific nitric oxide production were observed. These changes confirm the predictions for normal pregnancy but not for preeclampsia in which, despite increases in CAT-2 expression, arginine uptake is not additionally increased. This may create a relative deficiency of arginine in PBMCs favoring superoxide and peroxynitrite production and contribute to oxidative and nitrosative stress in preeclampsia.

Intraplatelet cyclic guanosine-3',5'-monophosphate levels during pregnancy and preeclampsia

OBJECTIVE

To investigate the intraplatelet cyclic guanosine-3',5'-monophosphate (cGMP) levels during normal pregnancy and preeclampsia.

STUDY DESIGN

Pregnant women (n = 15), women with preeclampsia (n = 15), and nonpregnant, normotensive women (n = 15) were included. Intraplatelet cyclic guanosine-3',5'-monophosphate levels were measured by an enzyme-linked immunosorbent assay.

RESULTS

Intraplatelet cGMP levels were significantly different among all groups (p < 0.02). The values were higher in normal pregnant women (mean 19.8 SD 2.6 fmol/10(5) platelets) in comparison to nonpregnant women (mean 7.6 SD 0.3 fmol/10(5)platelets; p = 0.001) and women with preeclampsia (mean 11.3 SD 1.8 fmol/10(5) platelets; p = 0.05). Plasma nitric oxide levels did not reveal differences between all groups.

CONCLUSIONS

The results of this study in a high-risk Andean population demonstrated that intraplatelet cyclic guanosine-3',5'-monophosphate levels are decreased during preeclampsia compared to normal pregnancy, suggesting a lack in action of nitric oxide.

Increased NO-mediated and reduced TxA2-dependent responses in skeletal muscle arterioles in pregnancy

The contribution of skeletal muscle microvessels to pregnancy-induced decrease in peripheral vascular resistance and its underlying mechanisms are not fully understood. We aimed to test the hypothesis that pregnancy enhances arteriolar dilation and reduces constriction by increasing NO-mediation and decreasing reactivity to TxA2. Thus, changes in diameter of isolated, pressurized gracilis muscle arterioles (d: approximately 180 microm) of non-pregnant (NP) and pregnant (P) rabbits to vasoactive agents were measured by videomicroscopy. Acetylcholine (ACh) elicited significantly greater dilations in P than in NP arterioles that could be inhibited by L-NAME, a NO synthase blocker. Dilations to the NO donor SNP did not differ between P and NP arterioles. Constrictions to norepinephrine and the TxA2 receptor agonist U46619 were significantly attenuated in P as compared to NP arterioles. L-NAME increased norepinephrine-induced arteriolar constrictions eliminating the difference between responses of NP and P arterioles. L-NAME enhanced constrictions to U46619 in P and NP arterioles, but the constrictions were still greater in NP vessels. The number of vascular TxA2 receptors-characterized by the TxA2 analog [125I]-BOP in aortic membrane preparations-was significantly less in P as compared to NP rabbits (NP: 284 +/- 83, P: 62 +/- 14 fmol/mg protein, p<0.01). Thus, pregnancy up-regulates endothelial NO- and down regulates TxA2-mediation of responses of skeletal muscle arterioles. These changes in the local regulation of microvascular tone are likely to favor a dilated state of skeletal muscle arterioles, which may contribute to the decreased peripheral vascular resistance during normal pregnancy.

Plasma nitric oxide levels and the expression of P-selectin on platelets in preeclampsia

OBJECTIVE

The purpose of this study was to investigate the correlation of plasma nitric oxide levels with the expression of P-selectin on platelets in preeclampsia.

STUDY DESIGN

Plasma levels of nitrite and nitrate (the stable nitric oxide metabolites) and the expression of P-selectin on platelets (a platelet activation marker) were measured in 25 normal pregnant women and 25 women with preeclampsia. The effects of the inhibition of nitric oxide synthesis on the expression of P-selectin also was measured in vitro.

RESULTS

Plasma nitrate levels and the expression of P-selectin averaged 30.5 +/- 2.2 micromol/L and 8.9% +/- 1.1% (SEM), respectively, in preeclampsia, which was significantly higher than in normal pregnancy (P <.05). Nitric oxide synthesis inhibition in vitro significantly increased the expression of P-selectin in normal pregnancy by 284% (P <.05), which was significantly higher than in preeclampsia (156%, P <.05).

CONCLUSION

The inhibitory effects of increased nitric oxide on the expression of P-selectin is attenuated in preeclampsia, which may contribute partly to the pathogenesis of preeclampsia.