VEGF causes vasodilation and stimulates endogenous NO formation [47–49]. Therefore, it is reasonable to suggest that VEGF affects arterial BP regulation [50].

Plasma nitrite and nitrate (NOx, products of NO oxidation) levels are circulating markers which may reflect endogenous NO formation. Lower VEGF and NOx levels are described in hypertensive patients than in healthy subjects, and these biomarkers correlate positively in healthy subjects, but not in hypertensives [51]. Indeed, NO is a major physiologic vasodilator [52], and impaired NO bioavailability apparently contributes to clinical hypertension [53]. Therefore, it is possible that SNPs in the VEGF gene contribute to cardiovascular disease susceptibility, in particular to hypertension [50].

We studied whether SNPs in the VEGF gene (C-2578A, G-1154A, and G-634C) and their haplotypes affect the susceptibility to hypertension and assessed plasma NOx levels to study whether these VEGF SNPs affect NO formation in hypertensive and normotensive subjects [50]. We found that the “C-A-G” haplotype was more common in normotensive than in hypertensive subjects, and the same haplotype was more common in subjects with higher than with lower NOx levels (Table 33.1). Therefore, VEGF haplotypes may affect hypertension susceptibility, and the haplotype associated with normotension was more common in subjects with increased NO formation, which supports that impaired NO bioavailability contributes to hypertension [50].

Interestingly, the same “C-A-G” haplotype was recently found marginally associated with the group of normotensive subjects when compared to a different group of hypertensive patients [54] (Table 33.1).

Hypertensive disorders of pregnancy, including gestational hypertension (GH) and preeclampsia (PE), complicate 3–10 % of pregnancies and are major contributors to maternal mortality [55]. PE is characterized by hypertension and proteinuria after 20 weeks of gestation and is associated with maternal and fetal complications [56]. Moreover, women with a history of PE are at increased risk of future cardiovascular disease [57, 58].

The mechanisms responsible for PE are not fully elucidated, but reduced placental perfusion is postulated as an initiating mechanism, which leads to widespread dysfunction of the maternal vascular endothelium and hypertension [59, 60]. One major hypothesis is based on abnormal cytotrophoblast differentiation leading to hypoperfusion of placenta and then hypoxia and release of some soluble factors to the maternal circulation, thereby causing systemic endothelial dysfunction [61, 62].

VEGF is induced by hypoxia as it initiates vasculogenesis in the placenta in coordination with other angiogenic factors [63]. PE is associated with modified cytotrophoblast expression of VEGF family ligands and receptors, and increased expression of sFlt-1, which captures VEGF and prevents its interaction with ligands and downregulates its biological effects [19, 47, 64, 65].

Since abnormalities in VEGF functions are possibly associated with PE, we studied whether SNPs in the VEGF gene (C-2578A, G-1154A, and G-634C) and their haplotypes affect the susceptibility to GH and PE [66]. We found that the haplotype “C-G-C” was more common in healthy pregnant than in PE (Table 33.1). Interestingly, this haplotype was associated with higher VEGF gene expression [67, 68], suggesting a protective effect for this haplotype against the development of PE [66].

Normal pregnancy is accompanied by increased blood volume and vasodilation, which involves increased NO formation, thus decreasing peripheral vascular resistance [69]. Conversely, deficient NO formation has been implicated in PE [70, 71].

Abnormal cytotrophoblast differentiation leads to hypoperfusion of placenta and then hypoxia and release of soluble factors, including the antiangiogenic factors sFlt-1 and soluble endoglin (sEng) produced in the placenta, which gain access to the maternal circulation and are involved in the pathogenesis of PE [72, 73]. The circulating sFlt-1 captures VEGF and downregulates its biological effects, such as angiogenesis [74] and stimulation of NO synthesis by endothelial cells [47, 75]. Concentrations of sEng are increased in PE. sEng is highly expressed in vascular endothelial cells and may inhibit transforming growth factor (TGF)-β1 signaling in the vasculature [76, 77]. Interestingly, endoglin enhances Smad2 protein levels potentiating TGF-β signaling and leading to an increased eNOS expression in endothelial cells [78].

Since both sFlt-1 and sEng interfere with eNOS activity, we assessed the correlations between these antiangiogenic factors and plasma and whole blood nitrite levels (circulating markers of NO formation) in GH and PE [20]. Nitrite levels are lower in GH and PE patients than in healthy pregnant (both P < 0.05). As expected, we found higher circulating sFlt-1 and sEng levels in PE than in GH or healthy pregnant (both P < 0.05) [20]. Therefore, NO formation is inversely related to sFlt-1 and sEng levels in PE [20], which suggests a possible inhibitory effect caused by these antiangiogenic factors produced in the placenta on the endogenous formation of NO in patients with PE. It is possible that therapeutic approaches focusing on upregulating NO bioavailability may be useful targets in patients with gestational disorders of pregnancy [20].

Antihypertensive therapy for PE includes methyldopa, nifedipine, hydralazine, and labetalol, which allow the prolongation of gestation, thereby decreasing fetal and maternal adverse outcomes [79] (Chap.​ 61). Several calcium channel blockers, including nifedipine, may improve endothelial function and restore NO bioavailability [80, 81]. In addition, hydralazine enhanced cyclic guanosine 3′, 5′ monophosphate levels in PE, thus suggesting that hydralazine produces its effects by activating NO synthesis [82]. Although there is no evidence that methyldopa produces antihypertensive effects by mechanisms involving NO production, it is possible that some drugs used to treat hypertensive disorders of pregnancy produce their effects by enhancing NO bioavailability, thus counteracting the impaired NO formation that has been reported in these hypertensive conditions [19, 20] (Chap.​ 39).

However, according to the responsiveness criteria presented by our group, 42 % of preeclamptic women do not respond to antihypertensive therapy, and this subgroup of pregnant women is associated with the worst clinical outcomes [83]. These findings suggest the need for the development of new therapies, which may be guided by pharmacogenomic approaches [84]. In addition, they suggest that the use of biomarkers may benefit a subgroup of pregnant women through a more individualized treatment [85].

Pathophysiological mechanisms previously recognized in PE may be further explored in an attempt to identify potential therapeutic targets, and the NO system is a notable example. Endothelial dysfunction is associated with the hypertension and proteinuria in PE, and NO plays an important role in regulating endothelial function [85]. Reduced expression of eNOS consequently results in reduced NO bioavailability, which plays a significant role in the endothelial dysfunction associated with PE [20]. We have shown that haplotypes of the eNOS gene are associated with PE [86, 87] and that eNOS haplotypes affect the responsiveness to antihypertensive therapy in PE [83]. However, both eNOS and other candidate genes have not been totally accepted as causal for PE [85].

These findings highlight the importance of considering the interaction among different candidate genes [84, 85, 88]. We studied the interactions among SNPs in the eNOS, MMP-9 (matrix metalloproteinase-9), and VEGF genes in PE and found specific combinations of MMP-9 and VEGF genotypes which may affect susceptibility to PE [89]. We hypothesized that the VEGF effects on angiogenesis and vascular homeostasis may be compromised not only to VEGF binding to the sFlt-1 but also to the degradation of the VEGFR-2 extracellular domain by MMP-9 in PE. Both mechanisms may involve diminished NO bioavailability as a result of impaired eNOS phosphorylation by Akt. Additional studies are required to confirm the hypothesis regarding the molecular mechanisms underlying these interactions [89].

Preeclampsia is characterized by hypertension and proteinuria, and NO formation is inversely related to the antiangiogenic factors soluble VEGF receptor-1 (sFlt-1) and soluble endoglin levels in patients with PE. Antihypertensive therapy may produce their effects by enhancing NO bioavailability, thus counteracting the impaired NO formation reported in PE. Further interaction studies among candidate genes coupled with functional studies focused on clarifying the underlying molecular mechanisms may help to identify novel biomarkers of PE. In addition, further studies with focus on the mechanisms linking VEGF and NO bioavailability may reveal potential specific targets for gestational hypertension and PE antihypertensive therapy.