Hypoxia-reduced nitric oxide synthase activity is partially explained by higher arginase-2 activity and cellular redistribution in human umbilical vein endothelium

Adipose organ dysfunction and type 2 diabetes: Role of nitric oxide

Adipose organ, historically known as specialized lipid-handling tissue serving as the long-term fat depot, is now appreciated as the largest endocrine organ composed of two main compartments, i.e., subcutaneous and visceral adipose tissue (AT), madding up white and beige/brown adipocytes. Adipose organ dysfunction manifested as maldistribution of the compartments, hypertrophic, hypoxic, inflamed, and insulin-resistant AT, contributes to the development of type 2 diabetes (T2D). Here, we highlight the role of nitric oxide (NO·) in AT (dys)function in relation to developing T2D. The key aspects determining lipid and glucose homeostasis in AT depend on the physiological levels of the NO· produced via endothelial NO· synthases (eNOS). In addition to decreased NO· bioavailability (via decreased expression/activity of eNOS or scavenging NO·), excessive NO· produced by inducible NOS (iNOS) in response to hypoxia and AT inflammation may be a critical interfering factor diverting NO· signaling to the formation of reactive oxygen and nitrogen species, resulting in AT and whole-body metabolic dysfunction. Pharmacological approaches boosting AT-NO· availability at physiological levels (by increasing NO· production and its stability), as well as suppression of iNOS-NO· synthesis, are potential candidates for developing NO·-based therapeutics in T2D.

Endothelial dysfunction due to eNOS uncoupling: molecular mechanisms as potential therapeutic targets

Nitric oxide (NO) is one of the most important molecules released by endothelial cells, and its antiatherogenic properties support cardiovascular homeostasis. Diminished NO bioavailability is a common hallmark of endothelial dysfunction underlying the pathogenesis of the cardiovascular disease. Vascular NO is synthesized by endothelial nitric oxide synthase (eNOS) from the substrate L-arginine (L-Arg), with tetrahydrobiopterin (BH₄) as an essential cofactor. Cardiovascular risk factors such as diabetes, dyslipidemia, hypertension, aging, or smoking increase vascular oxidative stress that strongly affects eNOS activity and leads to eNOS uncoupling. Uncoupled eNOS produces superoxide anion (O₂^-) instead of NO, thus becoming a source of harmful free radicals exacerbating the oxidative stress further. eNOS uncoupling is thought to be one of the major underlying causes of endothelial dysfunction observed in the pathogenesis of vascular diseases. Here, we discuss the main mechanisms of eNOS uncoupling, including oxidative depletion of the critical eNOS cofactor BH₄, deficiency of eNOS substrate L-Arg, or accumulation of its analog asymmetrical dimethylarginine (ADMA), and eNOS S-glutathionylation. Moreover, potential therapeutic approaches that prevent eNOS uncoupling by improving cofactor availability, restoration of L-Arg/ADMA ratio, or modulation of eNOS S-glutathionylation are briefly outlined.

Paracrine Effects of Renal Proximal Tubular Epithelial Cells on Podocyte Injury under Hypoxic Conditions Are Mediated by Arginase-II and TGF-β1

Hypoxia is an important risk for renal disease. The mitochondrial enzyme arginase-II (Arg-II) is expressed and/or induced by hypoxia in proximal tubular epithelial cells (PTECs) and in podocytes, leading to cellular damage. Because PTECs are vulnerable to hypoxia and located in proximity to podocytes, we examined the role of Arg-II in the crosstalk of PTECs under hypoxic conditions with podocytes. A human PTEC cell line (HK2) and a human podocyte cell line (AB8/13) were cultured. Arg-ii gene was ablated by CRISPR/Case9 in both cell types. HK2 cells were exposed to normoxia (21% O₂) or hypoxia (1% O₂) for 48 h. Conditioned medium (CM) was collected and transferred to the podocytes. Podocyte injuries were then analyzed. Hypoxic (not normoxic) HK2-CM caused cytoskeletal derangement, cell apoptosis, and increased Arg-II levels in differentiated podocytes. These effects were absent when arg-ii in HK2 was ablated. The detrimental effects of the hypoxic HK2-CM were prevented by TGF-β1 type-I receptor blocker SB431542. Indeed, TGF-β1 levels in hypoxic HK2-CM (but not arg-ii^-/--HK2-CM) were increased. Furthermore, the detrimental effects of TGF-β1 on podocytes were prevented in arg-ii^-/--podocytes. This study demonstrates crosstalk between PTECs and podocytes through the Arg-II-TGF-β1 cascade, which may contribute to hypoxia-induced podocyte damage.

Vanillic Acid Attenuates Monocrotaline-Induced Pulmonary Arterial Hypertension by Enhancing NO Signaling Pathways

Pulmonary arterial hypertension (PAH) is a severe progressive disease characterized by elevated mean pulmonary arterial pressure, right ventricular hypertrophy, and eventual progression to right heart failure and death. This study aimed to examine the effect of the natural product vanillic acid (VA) on monocrotaline (MCT)-induced PAH in rats. The arginase inhibitory activity and enzyme kinetic reaction of VA were also investigated. The results showed that VA could improve pulmonary arterial pressure, pulmonary artery vascular remodeling, and right ventricular remodeling induced by MCT in rats and reduce the degree of pulmonary tissue fibrosis. Moreover, VA downregulated the gene and protein expression levels of Hif-2α, Hif-1β, and Arg2 and increased the P-eNOS/eNOS levels, thus increasing nitric oxide (NO) levels in PAH rats. Furthermore, VA was determined to be a mixed competitive arginase inhibitor with an IC50 of 26.1 μM. In conclusion, the arginase inhibitor VA exerted protective effects on MCT-induced PAH and pulmonary vascular remodeling by enhancing NO signaling pathways.

Role of Arginase-II in Podocyte Injury under Hypoxic Conditions

Hypoxia plays a crucial role in acute and chronic renal injury, which is attributable to renal tubular and glomerular cell damage. Some studies provide evidence that hypoxia-dependent upregulation of the mitochondrial enzyme arginase type-II (Arg-II) in tubular cells promotes renal tubular injury. It is, however, not known whether Arg-II is also expressed in glomerular cells, particularly podocytes under hypoxic conditions, contributing to hypoxia-induced podocyte injury. The effects of hypoxia on human podocyte cells (AB8/13) in cultures and on isolated kidneys from wild-type (wt) and arg-ii gene-deficient (arg-ii−/−) mice ex vivo, as well as on mice of the two genotypes in vivo, were investigated, respectively. We found that the Arg-II levels were enhanced in cultured podocytes in a time-dependent manner over 48 h, which was dependent on the stabilization of hypoxia-inducible factor 1α (HIF1α). Moreover, a hypoxia-induced derangement of cellular actin cytoskeletal fibers, a decrease in podocin, and an increase in mitochondrial ROS (mtROS) generation—as measured by MitoSOX—were inhibited by adenoviral-mediated arg-ii gene silencing. These effects of hypoxia on podocyte injury were mimicked by the HIFα stabilizing drug DMOG, which inhibits prolyl hydroxylases (PHD), the enzymes involved in HIFα degradation. The silencing of arg-ii prevented the detrimental effects of DMOG on podocytes. Furthermore, the inhibition of mtROS generation by rotenone—the inhibitor of respiration chain complex-I—recapitulated the protective effects of arg-ii silencing on podocytes under hypoxic conditions. Moreover, the ex vivo experiments with isolated kidney tissues and the in vivo experiments with mice exposed to hypoxic conditions showed increased Arg-II levels in podocytes and decreased podocyte markers regarding synaptopodin in wt mice but not in arg-ii−/− mice. While age-associated albuminuria was reduced in the arg-ii−/− mice, the hypoxia-induced increase in albuminuria was, however, not significantly affected in the arg-ii−/−. Our study demonstrates that Arg-II in podocytes promotes cell injury. Arg-ii ablation seems insufficient to protect mice in vivo against a hypoxia-induced increase in albuminuria, but it does reduce albuminuria in aging.

Hypoxia Induces Renal Epithelial Injury and Activates Fibrotic Signaling Through Up-Regulation of Arginase-II

The ureohydrolase, type-II arginase (Arg-II), is a mitochondrial enzyme metabolizing L-arginine into urea and L-ornithine and is highly expressed in renal proximal tubular cells (PTC) and upregulated by renal ischemia. Recent studies reported contradictory results on the role of Arg-II in renal injury. The aim of our study is to investigate the function of Arg-II in renal epithelial cell damage under hypoxic conditions. Human renal epithelial cell line HK2 was cultured under hypoxic conditions for 12–48 h. Moreover, ex vivo experiments with isolated kidneys from wild-type (WT) and genetic Arg-II deficient mice (Arg-II^–/–) were conducted under normoxic and hypoxic conditions. The results show that hypoxia upregulates Arg-II expression in HK2 cells, which is inhibited by silencing both hypoxia-inducible factors (HIFs) HIF1α and HIF2α. Treatment of the cells with dimethyloxaloylglycine (DMOG) to stabilize HIFα also enhances Arg-II. Interestingly, hypoxia or DMOG upregulates transforming growth factor β1 (TGFβ1) levels and collagens Iα1, which is prevented by Arg-II silencing, while TGFβ1-induced collagen Iα1 expression is not affected by Arg-II silencing. Inhibition of mitochondrial complex-I by rotenone abolishes hypoxia-induced reactive oxygen species (mtROS) and TGFβ1 elevation in the cells. Ex vivo experiments show elevated Arg-II and TGFβ1 expression and the injury marker NGAL in the WT mouse kidneys under hypoxic conditions, which is prevented in the Arg-II^–/– mice. Taking together, the results demonstrate that hypoxia activates renal epithelial HIFs-Arg-II-mtROS-TGFβ1-cascade, participating in hypoxia-associated renal injury and fibrosis.

Endothelial Colony-Forming Cells Dysfunctions Are Associated with Arterial Hypertension in a Rat Model of Intrauterine Growth Restriction

Infants born after intrauterine growth restriction (IUGR) are at risk of developing arterial hypertension at adulthood. The endothelium plays a major role in the pathogenesis of hypertension. Endothelial colony-forming cells (ECFCs), critical circulating components of the endothelium, are involved in vasculo-and angiogenesis and in endothelium repair. We previously described impaired functionality of ECFCs in cord blood of low-birth-weight newborns. However, whether early ECFC alterations persist thereafter and could be associated with hypertension in individuals born after IUGR remains unknown. A rat model of IUGR was induced by a maternal low-protein diet during gestation versus a control (CTRL) diet. In six-month-old offspring, only IUGR males have increased systolic blood pressure (tail-cuff plethysmography) and microvascular rarefaction (immunofluorescence). ECFCs isolated from bone marrow of IUGR versus CTRL males displayed a decreased proportion of CD31+ versus CD146+ staining on CD45- cells, CD34 expression (flow cytometry, immunofluorescence), reduced proliferation (BrdU incorporation), and an impaired capacity to form capillary-like structures (Matrigel test), associated with an impaired angiogenic profile (immunofluorescence). These dysfunctions were associated with oxidative stress (increased superoxide anion levels (fluorescent dye), decreased superoxide dismutase protein expression, increased DNA damage (immunofluorescence), and stress-induced premature senescence (SIPS; increased beta-galactosidase activity, increased p16INK4a, and decreased sirtuin-1 protein expression). This study demonstrated an impaired functionality of ECFCs at adulthood associated with arterial hypertension in individuals born after IUGR.

The deleterious effects of acute hypoxia on microvascular and large vessel endothelial function

NEW FINDINGS

What is the central question of this study? The aim was primarily to determine the effect of hypoxia on microvascular function and secondarily whether superior cardiorespiratory fitness is protective against hypoxia-induced impairment in vascular function. What is the main finding and its importance? Hypoxia reduced endothelium-dependent but not endothelium-independent microvascular function. The extent of impairment was twofold higher in the microcirculation compared with the large blood vessels. This study suggests that individuals with superior cardiorespiratory fitness might preserve microvascular function in hypoxia. These findings highlight the sensitivity of the microvascular circulation to hypoxia.

ABSTRACT

Hypoxia is associated with diminished bioavailability of the endothelium-derived vasodilator, nitric oxide (NO). Diminished NO bioavailability can have deleterious effects on endothelial function. The endothelium is a heterogeneous tissue; therefore, a comprehensive assessment of endothelial function is crucial to understand the significance of hypoxia-induced endothelial dysfunction. We hypothesized that acute hypoxia would have a deleterious effect on microvascular and large vessel endothelial function. Twenty-nine healthy adults [24 (SD = 4 ) years of age] completed normoxic and hypoxic [inspired O₂  fraction = 0.209] trials in this double-blinded, counterbalanced crossover study. After 30 min, we assessed the laser Doppler imaging-determined perfusion response to iontophoresis of ACh as a measure of endothelium-dependent microvascular function and iontophoresis of sodium nitroprusside as a measure of endothelium-independent microvascular function. After 60 min, we assessed brachial flow-mediated dilatation as a measure of large vessel endothelial function. Thirty minutes of hypoxia reduced endothelium-dependent microvascular function determined by the perfusion response to ACh (median difference (x̃∆) = -109% {interquartile range: 542.7}, P < 0.05), but not endothelium-independent microvascular function determined by the perfusion response to sodium nitroprusside (x̃∆ = 69% {interquartile range: 453.7}, P = 0.6). In addition, 60 min of hypoxia reduced allometrically scaled flow-mediated dilatation compared with normoxia ( x ¯ Δ = - 1.19 [95% CI = -1.80, -0.58 (Confidence Intervals)]%, P < 0.001). The decrease in microvascular endothelial function was associated with cardiorespiratory fitness (r  = 0.45, P = 0.02). In conclusion, acute exposure to normobaric hypoxia significantly reduced endothelium-dependent vasodilatory capacity in small and large vessels. Collectively, these findings highlight the sensitivity of the microvascular circulation to hypoxic insult, particularly in those with poor cardiorespiratory fitness.

Endothelial Dysfunction Driven by Hypoxia-The Influence of Oxygen Deficiency on NO Bioavailability

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. The initial stage of CVDs is characterized by endothelial dysfunction, defined as the limited bioavailability of nitric oxide (NO). Thus, any factors that interfere with the synthesis or metabolism of NO in endothelial cells are involved in CVD pathogenesis. It is well established that hypoxia is both the triggering factor as well as the accompanying factor in cardiovascular disease, and diminished tissue oxygen levels have been reported to influence endothelial NO bioavailability. In endothelial cells, NO is produced by endothelial nitric oxide synthase (eNOS) from L-Arg, with tetrahydrobiopterin (BH₄) as an essential cofactor. Here, we discuss the mechanisms by which hypoxia affects NO bioavailability, including regulation of eNOS expression and activity. What is particularly important is the fact that hypoxia contributes to the depletion of cofactor BH₄ and deficiency of substrate L-Arg, and thus elicits eNOS uncoupling-a state in which the enzyme produces superoxide instead of NO. eNOS uncoupling and the resulting oxidative stress is the major driver of endothelial dysfunction and atherogenesis. Moreover, hypoxia induces impairment in mitochondrial respiration and endothelial cell activation; thus, oxidative stress and inflammation, along with the hypoxic response, contribute to the development of endothelial dysfunction.

Arginase II polymorphisms modify the hypotensive responses to propofol by affecting nitric oxide bioavailability

PURPOSE

Propofol anesthesia is usually accompanied by hypotensive responses, which are at least in part mediated by nitric oxide (NO). Arginase I (ARG1) and arginase II (ARG2) compete with NO synthases for their common substrate L-arginine, therefore influencing the NO formation. We examined here whether ARG1 and ARG2 genotypes and haplotypes affect the changes in blood pressure and NO bioavailability in response to propofol.

METHODS

Venous blood samples were collected from 167 patients at baseline and after 10 min of anesthesia with propofol. Genotypes were determined by polymerase chain reaction. Nitrite concentrations were measured by using an ozone-based chemiluminescence assay, while NO_x (nitrites + nitrates) levels were determined by using the Griess reaction.

RESULTS

We found that patients carrying the AG + GG genotypes for the rs3742879 polymorphism in ARG2 gene and the ARG2 GC haplotype show lower increases in nitrite levels and lower decreases in blood pressure after propofol anesthesia. On the other hand, subjects carrying the variant genotypes for the rs10483801 polymorphism in ARG2 gene show more intense decreases in blood pressure (CA genotype) and/or higher increases in nitrite levels (CA and AA genotypes) in response to propofol.

CONCLUSION

Our results suggest that ARG2 variants affect the hypotensive responses to propofol, possibly by modifying NO bioavailability.

TRIAL REGISTRATION

NCT02442232.

The role of arginase in the microcirculation in cardiovascular disease

In the microcirculation, the exchange of nutrients, water, gas, hormones, and waste takes place, and it is divided into the three main sections arterioles, capillaries, and venules. Disturbances in the microcirculation can be measured using surrogate parameters or be visualized either indirectly or directly.Arginase is a manganese metalloenzyme hydrolyzing L-arginine to urea and L-ornithine. It is located in different cell types, including vascular cells, but also in circulating cells such as red blood cells. A variety of pro-inflammatory factors, as well as interleukins, stimulate increased arginase expression. An increase in arginase activity consequently leads to a consumption of L-arginine needed for nitric oxide (NO) production by endothelial NO synthase. A vast body of evidence convincingly showed that increased arginase activity is associated with endothelial dysfunction in larger vessels of the vascular tree. Of note, arginase also influences the microcirculation. Arginase inhibition leads to an increase in the bioavailability of NO and reduces superoxide levels, resulting in improved endothelial function. Arginase inhibition might, therefore, be a potent treatment strategy in cardiovascular medicine. Recently, red blood cells emerged as an influential player in the development from increased arginase activity to endothelial dysfunction. As red blood cells directly interact with the microcirculation in gas exchange, this could constitute a potential link between arginase activity, endothelial dysfunction and microcirculatory disturbances.The aim of this review is to summarize recent findings revealing the role of arginase in regulating vascular function with particular emphasis on the microcirculation.

Improvement in endothelial function in cardiovascular disease - Is arginase the target?

Endothelial dysfunction represents an early change in the vascular wall in areas prone to atherosclerotic plaque formation and is present in association with several risk factors for cardiovascular disease. The underlying mechanisms behind endothelial dysfunction are multifactorial and complex. Arginase has emerged as a key player in the regulation of endothelial integrity by the ability of reciprocally inhibits nitric oxide formation and promoting oxidative stress. A chain of evidence suggest that arginase is implicated in the pathogenesis underlying endothelial dysfunction induced by several cardiovascular risk factors and established cardiovascular disease including diabetes, hypercholesteremia, ischemia/reperfusion, atherosclerosis, obesity, ageing and hypertension. Recent data has unveiled a key role of arginase as one of the key mechanisms underlying endothelial dysfunction in diabetes and may serve as a potential therapeutic target in previously overlooked compartments including red blood cells. The current review is devoted to discuss arginase as a key mediator in endothelial dysfunction and the potential for therapeutic possibilities to target this enzyme in various diseases, especially type 2 diabetes, atherosclerosis and ischemia/reperfusion with focus on translational and clinical aspects. Moreover, approaches of how and in which patient group(s) arginase may be targeted in future clinical trials are discussed.

Hypoxia Enhances Endothelial Intercellular Adhesion Molecule 1 Protein Level Through Upregulation of Arginase Type II and Mitochondrial Oxidative Stress

Hypoxia plays a crucial role in the pathogenesis of cardiovascular diseases. Mitochondrial enzyme arginase type II (Arg-II) is reported to lead to endothelial dysfunction and enhance the expression of endothelial inflammatory adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). In this study, we investigate the role of Arg-II in hypoxia-induced endothelial activation and the potential underlying mechanisms. Exposure of the human endothelial cells to hypoxia induced a time-dependent increase in Arg-II, HIF1α, HIF2α, and ICAM-1 protein level, whereas no change in the protein level of VCAM-1 and E-selectin was observed. Similar effects were obtained in cells treated with a hypoxia mimetic Dimethyloxaloylglycine (DMOG). Silencing HIF1α, but not HIF2α, reversed hypoxia-induced upregulation of Arg-II. Moreover, silencing Arg-II prevented the ICAM-1 upregulation induced by hypoxia or DMOG. Furthermore, the endothelial cells incubated under hypoxic condition or treated with DMOG or hypoxia enhanced monocyte adhesion, which was inhibited by silencing Arg-II. Lastly, silencing Arg-II prevented hypoxia-induced mitochondrial superoxide production in endothelial cells, and hypoxia-induced ICAM-1 upregulation was reversed by mitochondrial electron transport inhibitor rotenone. These data demonstrate that hypoxia enhances ICAM-1 protein level and monocyte-endothelial interaction through HIF1α-mediated increase in Arg-II protein level on leading to increased mitochondrial reactive oxygen species production. These effects of hypoxia on endothelial cells may play a key role in cardiovascular diseases. Our results suggest that Arg-II could be a promising therapeutic target to prevent hypoxia-induced vascular damage/dysfunction.

The Arginase Pathway in Neonatal Brain Hypoxia-Ischemia

Brain damage after hypoxia-ischemia (HI) occurs in an age-dependent manner. Neuroprotective strategies assumed to be effective in adults might have deleterious effects in the immature brain. In order to create effective therapies, the complex pathophysiology of HI in the developing brain requires exploring new mechanisms. Critical determinants of neuronal survival after HI are the extent of vascular dysfunction, inflammation, and oxidative stress, followed later by tissue repair. The key enzyme of these processes in the human body is arginase (ARG) that acts via the bioavailability of nitric oxide, and the synthesis of polyamines and proline. ARG is expressed throughout the brain in different cells. However, little is known about the effect of ARG in pathophysiological states of the brain, especially hypoxia-ischemia. Here, we summarize the role of ARG during neurodevelopment as well as in various brain pathologies.

Altered methylation and expression patterns of genes regulating placental nitric oxide pathway in patients with severe preeclampsia

Pre-eclampsia is a common pregnancy disorder syndrome whose molecular mechanism is not clear. Nitric oxide (NO) is a key regulator of placentation. Reduction of NO has previously been associated with endothelial dysfunction in pre-eclamptic women. Therefore, we measured expression and methylation of some placental genes that were involved in NO pathway like named ARG II, PRMT1 and DDAH2 in pre-eclampsia and normal pregnancies in order to determine whether impairment of expression of these genes in the pre-eclamptic placenta could contribute to development of disease. ARG II, PRMT1 expressions as well as DDAH2 expression and methylation, in placentas collected from 59 patients with preeclampsia and 40 normotensive pregnancies were measured using real-time PCR and methylation specific PCR, respectively. The relationship among ARG II, PRMT1 and DDAH2 expressions was analyzed statistically. ARG II expression was increased, PRMT1 expression was not significantly changed. DDAH2 expression was decreased and qualitative methylation patterns were 32/59 and 21/40 in placentas from patients with pre-eclampsia compared with control group, respectively. The alterations in ARG II and DDAH2 expressions in pre-eclampsia patients maybe correlated with decreased eNOS expression. These findings indicate that ARG II and DDAH2 may be involved in pre-eclampsia pathogenesis and could be potential therapeutic targets for this disease.

Pre-pregnancy maternal obesity associates with endoplasmic reticulum stress in human umbilical vein endothelium

Obesity associates with the endoplasmic reticulum (ER) stress-induced endothelial dysfunction. Pregnant women with pre-pregnancy maternal obesity (PGMO) may transfer this potential risk to their offspring; however, whether ER stress occurs and associates with foetoplacental endothelial dysfunction in PGMO is unknown. We studied the l-arginine transport and nitric oxide (NO) synthesis in human umbilical vein endothelial cells (HUVECs) from women with PGMO or with a normal pre-pregnancy weight. We analysed the expression and activation of the ER stress sensors protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6). PGMO associated with lower endothelial NO synthase activity due to increased Thr⁴⁹⁵-inhibitor and decreased Ser¹¹⁷⁷-stimulator phosphorylation. However, higher expression and activity of the human cationic amino acid transporter 1 was found. PGMO caused activation of PERK and its downstream targets eukaryotic initiation factor 2 (eIF2α), C/EBP homologous protein 10 (CHOP), and tribbles-like protein 3 (TRB3). Increased IRE1α protein abundance (but not its phosphorylation or X-box binding protein 1-mRNA splicing) and increased c-Jun N-terminal kinase 1 phosphorylation was seen in PGMO. A preferential nuclear location of the activating transcription factor 6 (ATF6) was found in HUVECs from PGMO. All the changes seen in PGMO were blocked by TUDCA but unaltered by tunicamycin. Thus, PGMO may determine a state of ER stress via upregulation of the PERK-eIF2α-CHOP-TRB3 axis signalling in HUVECs. This phenomenon results in foetoplacental vascular endothelial dysfunction at birth.

Maternal supraphysiological hypercholesterolemia associates with endothelial dysfunction of the placental microvasculature

Maternal physiological or supraphysiological hypercholesterolemia (MPH, MSPH) occurs during pregnancy. MSPH is associated with foetal endothelial dysfunction and atherosclerosis. However, the potential effects of MSPH on placental microvasculature are unknown. The aim of this study was to determine whether MSPH alters endothelial function in the placental microvasculature both ex vivo in venules and arterioles from the placental villi and in vitro in primary cultures of placental microvascular endothelial cells (hPMEC). Total cholesterol < 280 mg/dL indicated MPH, and total cholesterol ≥280 mg/dL indicated MSPH. The maximal relaxation to histamine, calcitonin gene-related peptide and adenosine was reduced in MSPH venule and arteriole rings. In hPMEC from MSPH placentas, nitric oxide synthase (NOS) activity and L-arginine transport were reduced without changes in arginase activity or the protein levels of endothelial NOS (eNOS), human cationic amino acid 1 (hCAT-1), hCAT-2A/B or arginase II compared with hPMEC from MPH placentas. In addition, it was shown that adenosine acts as a vasodilator of the placental microvasculature and that NOS is active in hPMEC. We conclude that MSPH alters placental microvascular endothelial function via a NOS/L-arginine imbalance. This work also reinforces the concept that placental endothelial cells from the macro- and microvasculature respond differentially to the same pathological condition.

Mechanisms of the effect of magnesium salts in preeclampsia

Preeclampsia is a heterogeneous pregnancy-specific syndrome associated with abnormal trophoblast invasion and endothelial dysfunction. Magnesium (Mg²⁺) level may be normal or decreased in women with preeclampsia. However, the use of Mg²⁺ salts, such as Mg²⁺ sulphate, are useful in reducing the pathophysiological consequences of preeclampsia with severe features and eclampsia. Although the mechanism of action of this Mg²⁺ salt is not well understood, the available evidence suggests a beneficial effect of Mg²⁺ for the mother and foetus. The mechanisms include a lower level of soluble fms-like tyrosine kinase 1 and endoglin, blockage of brain N-methyl-D-aspartate receptors, decreased inflammation mediators, activation of nitric oxide synthases, blockage of arginases, and reduced free radicals level. The maintenance of Mg²⁺ homeostasis in pregnancy is crucial for an appropriate pregnancy progression. Oral Mg²⁺ salts can be used for this purpose which could result in mitigating the deleterious consequences of this syndrome to the mother, foetus, and newborn.

Effectiveness of arginase inhibitors against experimentally induced stroke

Stroke is a lethal disease, but it disables more than it kills. Stroke is the second leading cause of death and the most frequent cause of permanent disability in adults worldwide, with 90% of survivors having residual deficits. The pathophysiology of stroke is complex and involves a strong inflammatory response associated with oxidative stress and activation of several proteolytic enzymes. The current study was designed to investigate the effect of arginase inhibitors (L-citruline and L-ornithine) against ischemic stroke induced in rats by middle cerebral artery occlusion (MCAO). MCAO resulted in alteration in rat behavior, brain infarct, and edema associated with disruption of the blood-brain barrier (BBB). This was mediated through overexpression of arginase I and II, inducible NOS (iNOS), malondialdehyde (MDA), advanced glycation end products (AGEs), TNF-α, and IL-1β and downregulation of endothelial nitric oxide synthase (eNOS). Treatment with L-citruline and L-ornithine and the standard neuroprotective drug cerebrolysin ameliorated all the deleterious effects of stroke. These results indicate the possible use of arginase inhibitors in the treatment of stroke after suitable clinical trials are done.

Hypoxia in Obesity and Diabetes: Potential Therapeutic Effects of Hyperoxia and Nitrate

The prevalence of obesity and diabetes is increasing worldwide. Obesity and diabetes are associated with oxidative stress, inflammation, endothelial dysfunction, insulin resistance, and glucose intolerance. Obesity, a chronic hypoxic state that is associated with decreased nitric oxide (NO) bioavailability, is one of the main causes of type 2 diabetes. The hypoxia-inducible factor-1α (HIF-1α) is involved in the regulation of several genes of the metabolic pathways including proinflammatory adipokines, endothelial NO synthase (eNOS), and insulin signaling components. It seems that adipose tissue hypoxia and NO-dependent vascular and cellular dysfunctions are responsible for other consequences linked to obesity-related disorders. Although hyperoxia could reverse hypoxic-related disorders, it increases the production of reactive oxygen species (ROS) and decreases the production of NO. Nitrate can restore NO depletion and has antioxidant properties, and recent data support the beneficial effects of nitrate therapy in obesity and diabetes. Although it seems reasonable to combine hyperoxia and nitrate treatments for managing obesity/diabetes, the combined effects have not been investigated yet. This review discusses some aspects of tissue oxygenation and the potential effects of hyperoxia and nitrate interventions on obesity/diabetes management. It can be proposed that concomitant use of hyperoxia and nitrate is justified for managing obesity and diabetes.

Netrin-1 acts as a non-canonical angiogenic factor produced by human Wharton's jelly mesenchymal stem cells (WJ-MSC)

BACKGROUND

Angiogenesis, the process in which new blood vessels are formed from preexisting ones, is highly dependent on the presence of classical angiogenic factors. Recent evidence suggests that axonal guidance proteins and their receptors can also act as angiogenic regulators. Netrin, a family of laminin-like proteins, specifically Netrin-1 and 4, act via DCC/Neogenin-1 and UNC5 class of receptors to promote or inhibit angiogenesis, depending on the physiological context.

METHODS

Mesenchymal stem cells secrete a broad set of classical angiogenic factors. However, little is known about the expression of non-canonical angiogenic factors such as Netrin-1. The aim was to characterize the possible secretion of Netrin ligands by Wharton's jelly-derived mesenchymal stem cells (WJ-MSC). We evaluated if Netrin-1 presence in the conditioned media from these cells was capable of inducing angiogenesis both in vitro and in vivo, using human umbilical vein endothelial cells (HUVEC) and chicken chorioallantoic membrane (CAM), respectively. In addition, we investigated if the RhoA/ROCK pathway is responsible for the integration of Netrin signaling to control vessel formation.

RESULTS

The paracrine angiogenic effect of the WJ-MSC-conditioned media is mediated at least in part by Netrin-1 given that pharmacological blockage of Netrin-1 in WJ-MSC resulted in diminished angiogenesis on HUVEC. When HUVEC were stimulated with exogenous Netrin-1 assayed at physiological concentrations (10-200 ng/mL), endothelial vascular migration occurred in a concentration-dependent manner. In line with our determination of Netrin-1 present in WJ-MSC-conditioned media we were able to obtain endothelial tubule formation even in the pg/mL range. Through CAM assays we validated that WJ-MSC-secreted Netrin-1 promotes an increased angiogenesis in vivo. Netrin-1, secreted by WJ-MSC, might mediate its angiogenic effect through specific cell surface receptors on the endothelium, such as UNC5b and/or integrin α6β1, expressed in HUVEC. However, the angiogenic response of Netrin-1 seems not to be mediated through the RhoA/ROCK pathway.

CONCLUSIONS

Thus, here we show that stromal production of Netrin-1 is a critical component of the vascular regulatory machinery. This signaling event may have deep implications in the modulation of several processes related to a number of diseases where angiogenesis plays a key role in vascular homeostasis.

Nitric oxide synthase and changes in oxidative stress levels in embryonic kidney observed in a rabbit model of intrauterine growth restriction

OBJECTIVE

This work aimed to study the effect of uteroplacental circulation restriction on endothelial kidney damage in a fetal rabbit model.

METHODS

New Zealand rabbits were subjected to 40% to 50% of uteroplacental artery ligation at day 25 of pregnancy. After 5 days, surviving fetuses were harvested by cesarean section. The gene and protein expressions of selected enzymes associated with nitric oxide production and oxidative stress were analyzed in fetal kidney homogenates.

RESULTS

The placenta weight (6.06 ± 0.27, p < 0.0319) and fetal body (19.90 ± 1.03, p < 0.0001) were significantly reduced in the uteroplacental circulation restriction group. The kidneys from restricted fetuses presented a mild vascular congestion and glomerular capillary congestion, without inflammation or hypertrophy. We found endothelial nitric oxide synthase phosphorylation inhibition (0.23 ± 0.13, p < 0.012) and arginase-2 (0.29 ± 0.14, p < 0.023) protein induction in fetal kidneys of the circulation restriction group. Finally, the kidneys from circulation-restricted fetuses showed increased inducible nitric oxide synthase messenger RNA (mRNA) (2.68 ± 0.24, p < 0.01) and reduced heme oxygenase-1 mRNA (23 ± 1.3, p < 0.003), with increased reactive oxygen species (1.69 ± 0.09, p < 0.001) and nitrotyrosine protein (1.74 ± 0.28, p < 0.003) levels, without changes in Nox mRNA.

CONCLUSION

We describe significant deregulation of vascular activity and oxidative damage in kidneys of fetal rabbits that have been exposed to restriction of the uterine circulation. © 2016 John Wiley & Sons, Ltd.

Arginase-endothelial nitric oxide synthase imbalance contributes to endothelial dysfunction during chronic intermittent hypoxia

OBJECTIVE

Chronic intermittent hypoxia (CIH), the main feature of obstructive sleep apnoea, is associated with impaired vascular function despite unaltered response to nitric oxide donors. This study addressed whether arginase contributes to the endothelial dysfunction in CIH rats.

METHODS

Adult male Sprague-Dawley rats were exposed for 21 days to CIH (5% oxygen, 12 times/h, 8 h/day). The internal carotid arteries were isolated to study endothelial nitric oxide synthase (eNOS) and arginase-1 levels by western blot and immunohistochemistry, and their vasoactive responses using wire myography. Relaxation to sodium nitroprusside (SNP; nitric oxide donor) in the presence or absence of soluble guanylyl cyclase inhibitor, and acetylcholine with and without a NOS inhibitor [N(G)-nitro-L-arginine (L-NA)] and the arginase inhibitor BEC were determined.

RESULTS

Arteries from the CIH rats presented higher active contraction induced by KCl (3.5 ± 0.4 vs. 2.3 ± 0.2 N/m2), augmented media-to-lumen ratio (∼40%), decreased relaxation to acetylcholine (12.8 ± 1.5 vs. 30.5 ± 4.6%) and increased sensitivity to SNP (pD2 7.3 ± 0.1 vs. 6.7 ± 0.1). Arginase inhibition reversed the impaired acetylcholine-induced relaxation in CIH arteries (49.5 ± 7.4%), an effect completely blocked by L-NA. In the carotid arteries, arginase-1 protein level was increased, whereas eNOS levels decreased in the CIH arteries.

CONCLUSION

The current results suggest that endothelial dysfunction in CIH-induced hypertension may result from imbalanced arginase-1 to eNOS expression, vascular remodelling and increased contractile capacity, rather than decreased vascular response to nitric oxide.

Folic Acid Promotes Recycling of Tetrahydrobiopterin and Protects Against Hypoxia-Induced Pulmonary Hypertension by Recoupling Endothelial Nitric Oxide Synthase

AIMS

Nitric oxide (NO) derived from endothelial NO synthase (eNOS) has been implicated in the adaptive response to hypoxia. An imbalance between 5,6,7,8-tetrahydrobiopterin (BH4) and 7,8-dihydrobiopterin (BH2) can result in eNOS uncoupling and the generation of superoxide instead of NO. Dihydrofolate reductase (DHFR) can recycle BH2 to BH4, leading to eNOS recoupling. However, the role of DHFR and eNOS recoupling in the response to hypoxia is not well understood. We hypothesized that increasing the capacity to recycle BH4 from BH2 would improve NO bioavailability as well as pulmonary vascular remodeling (PVR) and right ventricular hypertrophy (RVH) as indicators of pulmonary hypertension (PH) under hypoxic conditions.

RESULTS

In human pulmonary artery endothelial cells and murine pulmonary arteries exposed to hypoxia, eNOS was uncoupled as indicated by reduced superoxide production in the presence of the nitric oxide synthase inhibitor, L-(G)-nitro-L-arginine methyl ester (L-NAME). Concomitantly, NO levels, BH4 availability, and expression of DHFR were diminished under hypoxia. Application of folic acid (FA) restored DHFR levels, NO bioavailability, and BH4 levels under hypoxia. Importantly, FA prevented the development of hypoxia-induced PVR, right ventricular pressure increase, and RVH.

INNOVATION

FA-induced upregulation of DHFR recouples eNOS under hypoxia by improving BH4 recycling, thus preventing hypoxia-induced PH.

CONCLUSION

FA might serve as a novel therapeutic option combating PH.

Nitrergic system and plasmatic methylarginines: Evidence of their role in the perinatal programming of cardiovascular diseases

Atherosclerosis, in turn preceded by endothelial dysfunction, underlies a series of important cardiovascular diseases. Reduced bioavailability of endothelial nitric oxide, by increasing vascular tone and promoting platelet aggregation, leukocyte adhesion, and smooth muscle cell proliferation, plays a key role in the onset of the majority of cardiovascular diseases. In addition, high blood levels of asymmetric dimethylarginine, a potent inhibitor of nitric oxide synthesis, are associated with future development of adverse cardiovascular events and cardiac death. Recent reports have demonstrated that another methylarginine, i.e., symmetric dimethylarginine, is also involved in the onset of endothelial dysfunction and hypertension. Almost a decade ago, prematurity at birth and intrauterine growth retardation were first associated with a potential negative influence on the cardiovascular apparatus, thus constituting risk factors or leading to early onset of cardiovascular diseases. This condition is referred to as cardiovascular perinatal programming. Accordingly, cardiovascular morbidity and mortality are higher among former preterm adults than in those born at term. The aim of this paper was to undertake a comprehensive literature review focusing on cellular and biochemical mechanisms resulting in both reduced nitric oxide bioavailability and increased methylarginine levels in subjects born preterm. Evidence of the involvement of these compounds in the perinatal programming of cardiovascular risk are also discussed.

Arginase as a Critical Prooxidant Mediator in the Binomial Endothelial Dysfunction-Atherosclerosis

Arginase is a metalloenzyme which hydrolyzes L-arginine to L-ornithine and urea. Since its discovery, in the early 1900s, this enzyme has gained increasing attention, as literature reports have progressively pointed to its critical participation in regulating nitric oxide bioavailability. Indeed, accumulating evidence in the following years would picture arginase as a key player in vascular health. Recent studies have highlighted the arginase regulatory role in the progression of atherosclerosis, the latter an essentially prooxidant state. Apart from the fact that arginase has been proven to impair different metabolic pathways, and also as a consequence of this, the repercussions of the actions of such enzyme go further than first thought. In fact, such metalloenzyme exhibits direct implications in multiple cardiometabolic diseases, among which are hypertension, type 2 diabetes, and hypercholesterolemia. Considering the epidemiological repercussions of these clinical conditions, arginase is currently seen under the spotlights of the search for developing specific inhibitors, in order to mitigate its deleterious effects. That said, the present review focuses on the role of arginase in endothelial function and its participation in the establishment of atherosclerotic lesions, discussing the main regulatory mechanisms of the enzyme, also highlighting the potential development of pharmacological strategies in related cardiovascular diseases.

Arginase inhibition enhances angiogenesis in endothelial cells exposed to hypoxia

Hypoxia-induced arginase elevation plays an essential role in several vascular diseases but influence of arginase on hypoxia-mediated angiogenesis is completely unknown. In this study, in vitro network formation in bovine aortic endothelial cells (BAEC) was examined after exposure to hypoxia for 24h with or without arginase inhibition. Arginase activity, protein levels of the two arginase isoforms, eNOS, and VEGF as well as production of NO and ROS were examined to determine the involvement of arginase in hypoxia-mediated angiogenesis. Hypoxia elevated arginase activity and arginase 2 expression but reduced active p-eNOS(Ser1177) and NO levels in BAEC. In addition, both VEGF protein levels and endothelial elongation and network formation were reduced with continued hypoxia, whereas ROS levels increased and NO levels decreased. Arginase inhibition limited ROS, restored NO formation and VEGF expression, and prevented the reduction of angiogenesis. These results suggest a fundamental role of arginase activity in regulating angiogenic function.

The placental pursuit for an adequate oxidant balance between the mother and the fetus

The placenta is the exchange organ that regulates metabolic processes between the mother and her developing fetus. The adequate function of this organ is clearly vital for a physiologic gestational process and a healthy baby as final outcome. The umbilico-placental vasculature has the capacity to respond to variations in the materno-fetal milieu. Depending on the intensity and the extensity of the insult, these responses may be immediate-, mediate-, and long-lasting, deriving in potential morphostructural and functional changes later in life. These adjustments usually compensate the initial insults, but occasionally may switch to long-lasting remodeling and dysfunctional processes, arising maladaptation. One of the most challenging conditions in modern perinatology is hypoxia and oxidative stress during development, both disorders occurring in high-altitude and in low-altitude placental insufficiency. Hypoxia and oxidative stress may induce endothelial dysfunction and thus, reduction in the perfusion of the placenta and restriction in the fetal growth and development. This Review will focus on placental responses to hypoxic conditions, usually related with high-altitude and placental insufficiency, deriving in oxidative stress and vascular disorders, altering fetal and maternal health. Although day-to-day clinical practice, basic and clinical research are clearly providing evidence of the severe impact of oxygen deficiency and oxidative stress establishment during pregnancy, further research on umbilical and placental vascular function under these conditions is badly needed to clarify the myriad of questions still unsettled.

The implications of hyponitroxia in cancer

Tumors are spatially heterogeneous, with regions of relative hypoxia and normoxia. The tumor microenvironment is an important determinant of both tumor growth and response to a variety of cytotoxic and targeted therapies. In the tumor microenvironment, reactive oxygen species and nitric oxide (NO) are important mediators of the level of expression of many transcription factors and signaling cascades that affect tumor growth and responses to therapy. The primary objective of this review is to explore and discuss the seemingly dichotomous actions of NO in cancer biology as both a tumor promoter and suppressor with an emphasis on understanding the role of persistently low NO concentrations or hyponitroxia as a key mediator in tumor progression. This review will also discuss the potential role of hyponitroxia as a novel therapeutic target to treat cancer and outline an approach that provides new opportunities for pharmacological intervention.

Hypobaric hypoxia induced arginase expression limits nitric oxide availability and signaling in rodent heart

BACKGROUND

This study was aimed to evaluate regulation of cardiac arginase expression during hypobaric hypoxia and subsequent effect on nitric oxide availability and signaling.

METHODS

Rats were exposed to hypobaric hypoxia (282mmHg for 3h) and ARG1 expression was monitored. The expression levels of eNOS and eNOS(Ser1177) were determined by Western blotting, cGMP levels were measured by ELISA and amino acid concentrations were measured by HPLC analysis. Transcription regulation of arginase was monitored by chromatin immunoprecipitation (ChIP) assay with anti-c-Jun antibody for AP-1 consensus binding site on ARG1 promoter. Arginase activity was inhibited by intra-venous dose of N-(ω)-hydroxy-nor-l-arginine (nor-NOHA) prior to hypoxia exposure and subsequent effect on NO availability and oxidative stress were evaluated.

RESULTS

Hypobaric hypoxia induced cardiac arginase expression by recruiting c-Jun to AP-1 binding site on ARG1 promoter. This increased expression redirected l-arginine towards arginase and resulted in limited endothelial nitric oxide synthase (eNOS) activity, nitric oxide (NO) availability and cGMP mediated signaling. Inhibition of arginase restored the eNOS activity, promoted cardiac NO availability and ameliorated peroxynitrite formation during hypoxia.

CONCLUSIONS

Hypoxic induced arginase under transcription control of AP-1 reciprocally regulates eNOS activity and NO availability in the heart. This also results in cardiac oxidative stress.

GENERAL SIGNIFICANCE

This study provides understanding of hypoxia-mediated transcriptional regulation of arginase expression in the heart and its subsequent effect on eNOS activity, NO availability and signaling as well as cardiac oxidative stress. This information will support the use of arginase inhibitors as therapeutics for pathological hypoxia.

Maternal Hypercholesterolemia in Pregnancy Associates With Umbilical Vein Endothelial Dysfunction

Objective—

Human pregnancy that courses with maternal supraphysiological hypercholesterolemia (MSPH) correlates with atherosclerotic lesions in fetal arteries. It is known that hypercholesterolemia associates with endothelial dysfunction in adults, a phenomenon where nitric oxide (NO) and arginase are involved. However, nothing is reported on potential alterations in the fetoplacental endothelial function in MSPH. The aim of this study was to determine whether MSPH alters fetal vascular reactivity via endothelial arginase/urea and l -arginine transport/NO signaling pathways.

Approach and Results—

Total cholesterol <280 mg/dL was considered as maternal physiological hypercholesterolemia (n=46 women) and ≥280 mg/dL as MSPH (n=28 women). Maternal but not fetal total cholesterol and low-density lipoprotein-cholesterol levels were elevated in MSPH. Umbilical veins were used for vascular reactivity assays (wire myography), and primary cultures of umbilical vein endothelial cells to determine arginase, endothelial NO synthase (eNOS), and human cationic amino acid transporter 1 and human cationic amino acid transporter 2A/B expression and activity. MSPH reduced calcitonine gene–related peptide-umbilical vein relaxation and increased intima/media ratio (histochemistry), as well as reduced eNOS activity ( l -citrulline synthesis from l -arginine, eNOS phosphorylation/dephosphorylation), but increased arginase activity and arginase II protein abundance. Arginase inhibition increased eNOS activity and l -arginine transport capacity without altering human cationic amino acid transporter 1 or human cationic amino acid transporter 2A/B protein abundance in maternal physiological hypercholesterolemia and MSPH.

Conclusions—

MSPH is a pathophysiological condition altering umbilical vein reactivity because of fetal endothelial dysfunction associated with arginase and eNOS signaling imbalance. We speculate that elevated maternal circulating cholesterol is a factor leading to fetal endothelial dysfunction, which could have serious consequences to the growing fetus.

Regulation of cardiac nitric oxide signaling by nuclear β-adrenergic and endothelin receptors

At the cell surface, βARs and endothelin receptors can regulate nitric oxide (NO) production. β-adrenergic receptors (βARs) and type B endothelin receptors (ETB) are present in cardiac nuclear membranes and regulate transcription. The present study investigated the role of the NO pathway in the regulation of gene transcription by these nuclear G protein-coupled receptors. Nitric oxide production and transcription initiation were measured in nuclei isolated from the adult rat heart. The cell-permeable fluorescent dye 4,5-diaminofluorescein diacetate (DAF2 DA) was used to provide a direct assessment of nitric oxide release. Both isoproterenol and endothelin increased NO production in isolated nuclei. Furthermore, a β3AR-selective agonist, BRL 37344, increased NO synthesis whereas the β1AR-selective agonist xamoterol did not. Isoproterenol increased, whereas ET-1 reduced, de novo transcription. The NO synthase inhibitor l-NAME prevented isoproterenol from increasing either NO production or de novo transcription. l-NAME also blocked ET-1-induced NO-production but did not alter the suppression of transcription initiation by ET-1. Inhibition of the cGMP-dependent protein kinase (PKG) using KT5823 also blocked the ability of isoproterenol to increase transcription initiation. Furthermore, immunoblotting revealed eNOS, but not nNOS, in isolated nuclei. Finally, caged, cell-permeable isoproterenol and endothelin-1 analogs were used to selectively activate intracellular β-adrenergic and endothelin receptors in intact adult cardiomyocytes. Intracellular release of caged ET-1 or isoproterenol analogs increased NO production in intact adult cardiomyocytes. Hence, activation of the NO synthase/guanylyl cyclase/PKG pathway is necessary for nuclear β3ARs to increase de novo transcription. Furthermore, we have demonstrated the potential utility of caged receptor ligands in selectively modulating signaling via endogenous intracellular G protein-coupled receptors.

Roles of nitric oxide and asymmetric dimethylarginine in pregnancy and fetal programming

Nitric oxide (NO) regulates placental blood flow and actively participates in trophoblast invasion and placental development. Asymmetric dimethylarginine (ADMA) can inhibit NO synthase, which generates NO. ADMA has been associated with uterine artery flow disturbances such as preeclampsia. Substantial experimental evidence has reliably supported the hypothesis that an adverse in utero environment plays a role in postnatal physiological and pathophysiological programming. Growing evidence suggests that the placental nitrergic system is involved in epigenetic fetal programming. In this review, we discuss the roles of NO and ADMA in normal and compromised pregnancies as well as the link between placental insufficiency and epigenetic fetal programming.

Endothelial eNOS/arginase imbalance contributes to vascular dysfunction in IUGR umbilical and placental vessels

Placental vascular tone is critically influenced by nitric oxide (NO) derived from endothelial NO synthase (eNOS) activity. Placental vessels from pregnancies complicated with intrauterine growth restriction present altered NOS-dependent vasodilation. Arginase-2 competes with eNOS for l-arginine and counteracts the NOS-dependent relaxation in umbilical vessels from normal pregnancies. However there is no data regarding the contribution of arginase activity on the impaired endothelial function in IUGR placenta. We studied whether arginase-2 participates in IUGR-related placental vascular dysfunction counteracting eNOS-dependent relaxation, and the regulation of arginase-2 and eNOS expression in endothelial cells from IUGR umbilical arteries (HUAEC) and veins (HUVEC). In IUGR-derived umbilical arteries (UA) and veins (UV), and chorionic arteries (CA), NOS-dependent vasoactive response in the presence and absence of BEC (arginase inhibitor) was studied. Protein levels of eNOS (total and Ser(1177)-P-eNOS), arginase-2 and arginase activity were determined in IUGR HUAEC and HUVEC. In IUGR vessels eNOS-dependent relaxation was reduced, being improved by BEC. This effect was higher in arteries than veins, and in chorionic compared with umbilical vessels. In cultured IUGR endothelial cells, arginase-2 protein expression and activity were increased in HUVEC, without changes in HUAEC. In IUGR-derived endothelium there was a generalized reduction in the in vitro eNOS activation (Ser(1177)-P-eNOS/eNOS), and therefore a decreased eNOS/arginase activity ratio. Here we provide ex vivo and in vitro evidence for a vascular role of arginase throughout placental vasculature, negatively controlling NOS activity. This effect seems to be crucial in the pathophysiology of endothelial dysfunction present in IUGR feto-placental vessels.

Effects of SAC on oxidative stress and NO availability in placenta: potential benefits to preeclampsia

Preeclampsia (PE) is a major cause of fetal growth restriction and perinatal mortality, which involves oxidative stress and vasodilator signaling disorder. S-allyl-L-cysteine (SAC) is one of the most abundant compounds in garlic extracts, and possesses several biological activities. This research was designed to investigate the protective effects of SAC against H(2)O(2)-induced oxidative insults, as well as the effects on NO/cGMP signaling pathway in placenta. We used TEV-1 cells and placental explants to detect the effects of SAC. TEV-1 cells and human placental explants were separately exposed to SAC, H(2)O(2), or a combination of H(2)O(2) and SAC. Intracellular ROS was detected by flow cytometry; the NO level was detected by an NO metabolites (NOx) assay; the cGMP level was simultaneously measured by the method of radioimmunoassay; the expression of eNOS in TEV-1 cells was measured by immunochemistry and Western blot. Our findings showed that H(2)O(2) treatment increased ROS productions in TEV-1 cells and significantly decreased cGMP and NO level either in TEV-1 cells or explants compared to the control groups (p < 0.05). The expression of eNOS in TEV-1 cells also significantly decreased in H(2)O(2) treated group compared to the control group (p < 0.05). Co-treatment of H(2)O(2) and SAC significantly decreased ROS productions, and increased NO, cGMP and eNOS level compared to the H(2)O(2) treated alone groups (p < 0.05), which were all reverted back to near control levels. Further more, SAC treatment increased NO and cGMP level of TEV-1 cells and explants in a dose-dependent manner even at non-oxidative stress status (p < 0.05). However, when the TEV-1 cells were cultured in the presence of NOS inhibitor (L-NAME) and NO donor (SNP), additional SAC treatment still significantly increased the NO level in comparison with SAC non-treated group (p < 0.05). In conclusion, these results demonstrate that ROS (H(2)O(2)-mediated) can induce insults to NO/cGMP pathway, while SAC could antagonize this insult. And SAC also possesses the ability to increase NO and cGMP level at non-oxidative stress status in TEV-1 cells and placenta explants. SAC is therefore hypothesized to be a potential drug for PE treatment.

Role of arginase-2 and eNOS in the differential vascular reactivity and hypoxia-induced endothelial response in umbilical arteries and veins

The main vasodilator in the placenta is nitric oxide (NO), which is synthesized by endothelial NO synthase (eNOS). Arginase-2 competes with eNOS for l-arginine, and its activity has been related with vascular dysfunction. Recently, we showed that hypoxia induces arginase-2, and decreases eNOS activity in human umbilical vein endothelial cells (HUVEC). However there is evidence that vascular responses to hypoxia are not similar throughout the placental vascular tree. We studied whether arginase-2 plays a role controlling vascular tone in human umbilical vessels, and the changes in the expression of arginase-2 and eNOS proteins by hypoxia in endothelial cells from umbilical arteries (HUAEC) and veins (HUVEC). In isolated umbilical vessels the presence of eNOS and arginase-2 was determined in the endothelium, and the NO-dependent vasoactive responses in the presence and absence of S-(2-boronoethyl)-L-cysteine (BEC, arginase inhibitor) were studied. Additionally, HUAEC and HUVEC were exposed (0-24 h) to hypoxia (2% O2) or normoxia (5% O2), and protein levels of eNOS (total and phosphorylated at serine-1177) and arginase-2 were determined. In umbilical arteries and veins arginase-2 and eNOS were detected mainly at the endothelium. BEC induced a higher concentration-dependent relaxation in umbilical arteries than veins, and these responses were NOS-dependent. In HUAEC exposed to hypoxia there were no changes in eNOS and arginase-2 levels, however there was a significant increase of p-eNOS. In contrast, HUVEC showed an increase in arginase-2 and a reduction of p-eNOS in response to hypoxia. These results show that arginases have a vascular role in placental vessels counteracting the NOS-dependent relaxation, which is differentially regulated in placental artery and vein endothelial cells.