IMMUNOHISTOCHEMICAL LOCALIZATION OF ENDOTHELIAL ISOFORM (eNOS) IN HUMAN CEREBRAL ARTERIES AND THE AORTA

Fetal Cerebrovascular Maturation: Effects of Hypoxia

The human cerebral vasculature originates in the fourth week of gestation and continues to expand and diversify well into the first few years of postnatal life. A key feature of this growth is smooth muscle differentiation, whereby smooth muscle cells within cerebral arteries transform from migratory to proliferative to synthetic and finally to contractile phenotypes. These phenotypic transformations can be reversed by pathophysiological perturbations such as hypoxia, which causes loss of contractile capacity in immature cerebral arteries. In turn, loss of contractility affects all whole-brain cerebrovascular responses, including those involved in flow-metabolism coupling, vasodilatory responses to acute hypoxia and hypercapnia, cerebral autoregulation, and reactivity to activation of perivascular nerves. Future strategies to minimize cerebral injury following hypoxia-ischemic insults in the immature brain might benefit by targeting treatments to preserve and promote contractile differentiation in the fetal cerebrovasculature. This could potentially be achieved through inhibition of receptor tyrosine kinase-mediated growth factors, such as vascular endothelial growth factor and platelet-derived growth factor, which are mobilized by hypoxic and ischemic injury and which facilitate contractile dedifferentiation. Interruption of the effects of other vascular mitogens, such as endothelin and angiotensin-II, and even some miRNA species, also could be beneficial. Future experimental work that addresses these possibilities offers promise to improve current clinical management of neonates who have suffered and survived hypoxic, ischemic, asphyxic, or inflammatory cerebrovascular insults.

Calcimimetic R-568 vasodilatory effect on mesenteric vascular beds from normotensive (WKY) and spontaneously hypertensive (SHR) rats. Potential involvement of vascular smooth muscle cells (vSMCs)

The potential role of calcimimetics as vasculotropic agents has been suggested since the discovery that calcium sensing receptors (CaSRs) are expressed in cardiovascular tissues. However, whether this effect is CaSR-dependent or -independent is still unclear. In the present study the vascular activity of calcimimetic R-568 was investigated in mesenteric vascular beds (MVBs) isolated from Spontaneously Hypertensive rats (SHR) and the relative age-matched Wistar-Kyoto (WKY) control rats. Pre-constricted MBVs were perfused with increasing concentrations of R-568 (10 nM– 30 μM) resulting in a rapid dose-dependent vasodilatation. However, in MVBs from SHR this was preceded by a small but significant vasoconstriction at lowest nanomolar concentrations used (10–300 nM). Pre-treatment with pharmacological inhibitors of nitric oxide (NO) synthase (NOS, L-NAME), K_Ca channels (CTX), cyclo-oxygenase (INDO) and CaSR (Calhex) or the endothelium removal suggest that NO, CaSR and the endothelium itself contribute to the R-568 vasodilatory/vasoconstrictor effects observed respectively in WKY/SHR MVBs. Conversely, the vasodilatory effects resulted by highest R-568 concentration were independent of these factors. Then, the ability of lower R-568 doses (0.1–1 μM) to activate endothelial-NOS (eNOS) pathway in MVBs homogenates was evaluated. The Akt and eNOS phosphorylation levels resulted increased in WKY homogenates and Calhex significantly blocked this effect. Notably, this did not occur in the SHR. Similarly, vascular smooth muscle cells (vSMCs) stimulation with lower R-568 doses resulted in Akt activation and increased NO production in WKY but not in SHR cells. Interestingly, in these cells this was associated with the absence of the biologically active dimeric form of the CaSR thus potentially contributing to explain the impaired vasorelaxant effect observed in response to R-568 in MVB from SHR compared to WKY. Overall, these findings provide new insight on the mechanisms of action of the calcimimetic R-568 in modulating vascular tone both in physiological and pathological conditions such as hypertension.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

The effect of sumatriptan on nitric oxide synthase enzyme production after iatrogenic inflammation in the brain stem of adolescent rats: A randomized, controlled, experimental study

BACKGROUND

Migraine is a common disabling disorder of childhood and adolescence. Despite advances in the understanding of migraine pathophysiology, treatment remains a challenge.

OBJECTIVES

The aims of this study were to investigate the production of nitric oxide synthase (NOS) enzymes in the brain stem of adolescent rats, using an experimental model of migraine, and the effect of sumatriptan pretreatment on the production of the NOS enzymes.

METHODS

Male adolescent (aged ~2 months) Wistar rats were used in the study. The animals were anesthetized using pentobarbital. The trigeminovascular system was stimulated by injecting a proinflammatory molecule, carrageenan, into the cis-terna magna of the anesthetized rats. The animals were divided into 3 groups of equal size: (1) the study group, in which the rats were treated with sumatriptan succinate 2 hours before intracisternal carrageenan injection; (2) the sham group, in which the rats were not administered intracisternal carrageenan injection or sumatriptan pretreatment; and (3) the control group, in which the rats were administered intracisternal carrageenan injection but were not pretreated with sumatriptan. In the control and study groups, the rats were euthanized using ether anesthesia 1 hour after intracisternal carrageenan injection. Rats in the sham group were euthanized 1 hour after intracisternal catheterization. Brain tissue was removed and endothelial NOS (eNOS), neuronal NOS (nNOS), and inducible NOS (iNOS) immunohistochemistry was performed.

RESULTS

Twenty-one rats were randomized into 3 groups of 7. The mean values of the immunolabeling intensities for eNOS, nNOS, and iNOS enzymes in the brain stem were significantly lower in the sham group compared with the control group (P = 0.001, P = 0.002, and P = 0.001, respectively). The mean values of the immunolabeling intensities of eNOS, nNOS, and iNOS in the brain stem were significantly lower in the study group compared with the control group (P = 0.001, P = 0.025, and P = 0.005, respectively).

CONCLUSIONS

In this experimental model of migraine in adolescent rats, intracisternal injection of carrageenan was associated with a significant increase in the production of NOS enzymes in the brain stem. Pretreatment with sumatriptan was associated with a decrease in NOS production.

Cigarette smoke and LDL cooperate in reducing nitric oxide bioavailability in endothelial cells via effects on both eNOS and NADPH oxidase

The ubiquitous free radical nitric oxide (NO) plays an important role in many biological processes, including the regulation of both vascular tone and inflammatory response; however, its role in the effects of cigarette smoke exposure on atherosclerosis remains unclear. Our aim was to study the mechanisms of NO regulation in endothelial cells in response to cigarette smoke exposure in vitro. Using human umbilical vein endothelial cells (HUVEC), we have demonstrated that combining non-toxic concentrations of cigarette smoke bubbled through PBS (smoke-bubbled PBS [sbPBS]) with native LDL (nLDL) significantly reduces the amount of bioavailable NO. The effect is comparable to that seen with oxidized LDL (oxLDL), but has not been seen with sbPBS or nLDL alone. Mechanistic investigations showed that the combination of sbPBS+nLDL did not reduce the amount of endothelial nitric oxide synthase (eNOS), but did inhibit its enzymatic activity. Concomitantly, both sbPBS+nLDL and oxLDL significantly increased the production of reactive oxygen species (ROS) in the form of superoxide anions ((·)O(2)(-)) and peroxynitrite (ONOO(-)) in HUVEC. Selective inhibition of NADPH oxidase prevented this response. Incubation of sbPBS+nLDL revealed the formation of 7-ketocholesterol (7-KC) and 7-hydroxycholesterol, which are indicators for oxidative modification of LDL. This could explain the reported increase in circulatory levels of oxLDL in smokers. Our results suggest that reduction of functional NO in response to a combination of sbPBS+nLDL is secondary to both reduction of eNOS activity and stimulation of NADPH oxidase activity. Because sbPBS alone showed no effect on eNOS activity or ROS formation, nLDL should be included in cigarette-smoke-related mechanistic in vitro experiments on endothelial cells to be more reflective of the clinical situation.

Endothelial dysfunction in mice with streptozotocin-induced type 1 diabetes is opposed by compensatory overexpression of cyclooxygenase-2 in the vasculature

Cardiovascular complications of diabetes result from endothelial dysfunction secondary to persistent hyperglycemia. We investigated potential compensatory mechanisms in the vasculature that oppose endothelial dysfunction in diabetes. BALB/c mice were treated with streptozotocin (STZ) to induce type 1 diabetes (T1D). In mesenteric vascular beds (MVBs), isolated ex vivo from mice treated with STZ for 1 wk, dose-dependent vasorelaxation to acetylcholine (ACh) or sodium nitroprusside was comparable with that in age-matched control mice (CTRL). By contrast, MVBs from mice treated with STZ for 8 wk had severely impaired vasodilator responses to ACh consistent with endothelial dysfunction. Pretreatment of MVBs from CTRL mice with nitric oxide synthase inhibitor nearly abolished vasodilation to ACh. In MVB from 1-wk STZ-treated mice, vasodilation to ACh was only partially impaired by L-N(omega)-arginine methyl ester. Thus, vasculature of mice with T1D may have compensatory nitric oxide-independent mechanisms to augment vasodilation to ACh and oppose endothelial dysfunction. Indeed, pretreatment of MVBs isolated from 1-wk STZ-treated mice with NS-398 [selective cyclooxygenase (COX)-2 inhibitor] unmasked endothelial dysfunction not evident in CTRL mice pretreated without or with NS-398. Expression of COX-2 in MVBs, aortic endothelial cells, and aortic vascular smooth muscle cells from STZ-treated mice was significantly increased (vs. CTRL). Moreover, concentrations of the COX-2-dependent vasodilator 6-keto-prostaglandin F-1alpha was elevated in conditioned media from aorta of STZ-treated mice. We conclude that endothelial dysfunction in a mouse model of T1D is opposed by compensatory up-regulation of COX-2 expression and activity in the vasculature that may be relevant to developing novel therapeutic strategies for diabetes and its cardiovascular complications.

Investigation of the immunoreactivities of NOS enzymes and the effect of sumatriptan in adolescent rats using an experimental model of migraine

The aim was to investigate the immunoreactivities for NOS enzymes in frontal cortex and meningeal vessels after chemical stimulation of the subarachnoid space of adolescent rats and the effect of sumatriptan pre-treatment on the immunoreactivities of the NOS enzymes. Male adolescent Wistar rats were used. Rats in group 1 did not taken intracisternal injection. Rats in group 2 were taken intracisternal autologous blood injection, but no sumatriptan pre-treatment. Rats in group 3 were taken intracisternal autologous blood injection, but they were taken sumatriptan pre-treatment. Tissue samples were investigated for the presence of NOS immunoreactivity. The mean values of immunolabeling intensities for NOS enzymes in frontal cortex and meningeal vessels were significantly increased in group 2 compared to group 1. The mean values of immunolabeling intensities for NOS enzymes in frontal cortex and meningeal vessels were significantly reduced in group 3 compared to group 2. These results suggest that, chemical stimulation of the subarachnoid space increased the immunoreactivities of NOS enzymes in the brain of adolescent rats. The increased NOS immunoreactivities could be antagonized by pre-treatment with sumatriptan.