How to assess endothelial function in human blood vessels

Pathophysiology of Atherosclerosis

Atherosclerosis is the main risk factor for cardiovascular disease (CVD), which is the leading cause of mortality worldwide. Atherosclerosis is initiated by endothelium activation and, followed by a cascade of events (accumulation of lipids, fibrous elements, and calcification), triggers the vessel narrowing and activation of inflammatory pathways. The resultant atheroma plaque, along with these processes, results in cardiovascular complications. This review focuses on the different stages of atherosclerosis development, ranging from endothelial dysfunction to plaque rupture. In addition, the post-transcriptional regulation and modulation of atheroma plaque by microRNAs and lncRNAs, the role of microbiota, and the importance of sex as a crucial risk factor in atherosclerosis are covered here in order to provide a global view of the disease.

Uric acid, as a double-edged sword, affects the activity of epidermal growth factor (EGF) on human umbilical vein endothelial cells by regulating aging process

Uric acid (UA) is the main metabolite of the human body. Although UA is only a product of metabolism, it is important biological regulator. Epidermal growth factor (EGF) has important biological functions. However, so far, the effect of UA on EGF’s activity has not been revealed. For this, in the current study, we systematically studied the effect of OA on the biological activity of EGF. Human Umbilical Vein Endothelial Cells (HUVECs) were used as an in vitro model, and Western-blot, RT-PCR, laser scanning confocal microscopy (CLSM) and co-localization analyses were carried out. The results showed that high concentration of UA (10 mg/dl) severely affected the biological activity of EGF. High concentration of UA suppressed the activity of EGF, and inhibited the biological effect of EGF on the HUVECs. However, it is interesting that EGF-mediated intracellular signaling was significantly down-regulated in the H₂O₂-induced senescent HUVEC, and physiological concentration of UA could at least partially restore the EGF-mediated signaling. Further work showed that physiological concentration of UA (5 mg/dl) shows the anti-aging effect. Taken together, current research indicates that UA may be a ‘double-edged sword’, physiological concentration of UA may be beneficial, but high concentrations of uric acid (UA) are harmful.

Identification of the vasodilatory endothelial cannabinoid receptor in the human pulmonary artery

BACKGROUND

The endocannabinoid anandamide is implicated in the pathogenesis of hypotension in haemorrhagic, endotoxic, and cardiogenic shock. It has been demonstrated in animal, but not in human, vessels that the vasodilatory effects of anandamide and abnormal cannabidiol are partially mediated by an as yet unidentified endothelial cannabinoid receptor. Our study was performed to examine the influence of abnormal cannabidiol on the human pulmonary artery.

METHODS

Isolated human pulmonary arteries were obtained from patients without clinical evidence of pulmonary hypertension during resection of lung carcinoma. Vasodilatory effects of abnormal cannabidiol were examined on endothelium-intact vessels preconstricted with serotonin or potassium chloride.

RESULTS

Anandamide and abnormal cannabidiol relaxed serotonin-preconstricted vessels concentration-dependently. The effect of abnormal cannabidiol was reduced by endothelium denudation, pertussis toxin and two antagonists of the novel endothelial receptor, cannabidiol and O-1918, but not by the nitric oxide synthase inhibitor L-NAME given together with the cyclooxygenase inhibitor indomethacin. It was also diminished by blockade of calcium-activated potassium channels by the nonselective blocker tetraethylammonium or by combination of selective blockers of small (apamin) and intermediate and large (charybdotoxin) conductance calcium-activated potassium channels. The potency of abnormal cannabidiol to relax vessels was lower in potassium chloride than in serotonin-preconstriced preparations.

CONCLUSIONS

Abnormal cannabidiol relaxes human pulmonary arteries in an endothelium-independent and endothelium-dependent manner. The latter component is probably mediated via the putative endothelial cannabinoid receptor, activation of which may release endothelium-derived hyperpolarizing factor, which in turn acts via calcium-activated potassium channels. Abnormal cannabidiol is behaviourally inactive; it may have a therapeutic implication in vascular diseases, especially in the treatment of pulmonary hypertension.

The vascular effects of metabolic impairment clusters in subjects of different ethnicities

BACKGROUND

Although metabolic syndrome affects vascular function, the impact of individual impairments and their clustering is unclear.

OBJECTIVE

To assess the vascular impact of metabolic impairments before they reach treatment thresholds in different ethnic groups.

METHODS

Metabolic variables, inflammatory markers, endothelium dependent vasodilatation (EDV) and carotid intima media thickness (CIMT) were measured in population samples of 82 Caucasians and 78 matched Afro-Caribbeans with no vascular disease. Insulin resistance was assessed using homeostasis model assessment (HOMA-IR). EDV was measured as the change in the height of the inflection point of the digital volume pulse following intravenous infusion of 5 mcg/min of albuterol (DeltaRIDeltaLB). Regression models were used to investigate the independent effects of metabolic impairment clusters and their interaction with ethnicity on EDV and CIMT.

RESULTS

HOMA-IR (2.4-3.8, p < 0.0001), IL-6 levels (1.1-2.8 pg/mL, p = 0.02) and CIMT (0.71-0.83 mm, p = 0.009) increased whereas in DeltaRIBASELINE (77.6-72.9 percentage points, p < 0.0001) and DeltaRIDeltaLB (15.5-7.1 percentage points, p < 0.0001) decreased with the number of metabolic impairments present. DeltaRIDeltaLB decreased by 1.6 (95% CI 0.2-3.7) percentage points and CIMT increased by 0.06 (95% CI 0.02-0.10) mm for each metabolic impairment present after adjusting for age, gender, ethnicity and HOMA-IR. There were significant interactions between Afro-Caribbean ethnicity and metabolic impairments for IL-6 (p = 0.037) and DeltaRIDeltaLB (p = 0.002).

CONCLUSIONS

Clustering of metabolic impairments is associated with inflammatory activation, impaired EDV and increased CIMT even before reaching treatment thresholds for individual impairments. This effect was more marked in Afro-Caribbean subjects.

The oestrogen receptor beta contributes to sex related differences in endothelial function of murine small arteries via EDHF

Sex related differences in cardiovascular function have been reported in oestrogen receptor beta knockout (ERbetaKO) mice. In this study we examined the role of endothelium-derived hyperpolarizing factor (EDHF) in differences in small artery endothelial function between ERbetaKO and wild-type (WT) mice. Small femoral arteries were isolated from ERbetaKO and WT mice and mounted on a wire myograph. Concentration-response curves to ACh were compared before and after incubation with inhibitors of nitric oxide (NO) and prostacyclin (PGI2) synthesis. Comparison of the expression of the principal vascular connexins (Cx37, 40 and 43), implicated in EDHF-mediated dilatation were undertaken by immunohistochemistry. Vascular ultrastructure was studied by transmission and scanning electron microscopy. ACh-induced relaxation of arteries (< 200 microm internal diameter) was greater in WT females versus males and was attributable to a greater EDHF component of relaxation. This sex difference was absent in ERbetaKO mice. Arteries from ERbetaKO males (but not females) were more sensitive to ACh compared to WT. The pharmacological evidence and morphological prerequisite for involvement of gap junctions in EDHF-mediated responses was confirmed in male arteries. The absence of ERbeta had no influence on expression of main Cx subtypes within vascular wall or on ultrastructure and morphology of the endothelium. The data suggest that in WT male mice, ERbeta reduces EDHF-mediated relaxation through gap junction communication.

Impact of endothelial dysfunction on left ventricular remodeling after successful primary coronary angioplasty for acute myocardial infarction--analysis by quantitative ECG-gated SPECT--

BACKGROUND

We hypothesized that endothelial cell integrity in the risk area would influence left ventricular remodeling after acute myocardial infarction.

PATIENTS AND METHODS

Twenty patients (61 +/- 8 y.o.) with acute myocardial infarction underwent 99mTc-tetrofosmin imaging in the subacute phase and three months after successful primary angioplasty due to myocardial infarction. All patients were administered angiotensin-converting enzyme inhibitor after revascularization. Cardiac scintigraphies with quantitative gated SPECT were performed at the sub-acute stage and again 3 months after revascularization to evaluate left ventricular (LV) remodeling. The left ventricular ejection fraction (EF) and end-systolic and end-diastolic volume (ESV, EDV) were determined using a quantitative gated SPECT (QGS) program. Three months after myocardial infarction, all patients underwent cardiac catheterization examination with coronary endothelial function testing. Bradykinin (BK) (0.2, 0.6, 2.0 microg/min) was administered via the left coronary artery in a stepwise manner. Coronary blood flow was evaluated by Doppler flow velocity measurement. Patients were divided into two groups by BK-response: a preserved endothelial function group (n = 10) and endothelial dysfunction group (n = 10).

RESULTS

At baseline, both global function and LV systolic and diastolic volumes were similar in both groups. However, LV ejection fraction was significantly improved in the preserved-endothelial function group, compared with that in the endothelial dysfunction group (42 +/- 10% to 48 +/- 9%, versus 41 +/- 4% to 42 +/- 13%, p < 0.05). LV volumes progressively increased in the endothelial dysfunction group compared to the preserved-endothelial, function group (123 +/- 45 ml to 128 +/- 43 ml, versus 111 +/- 47 ml to 109 +/- 49 ml, p < 0.05).

CONCLUSION

In re-perfused acute myocardial infarction, endothelial function within the risk area plays an important role with left ventricular remodeling after myocardial infarction.

Renal endothelial dysfunction and impaired autoregulation after ischemia-reperfusion injury result from excess nitric oxide

Endothelial dysfunction in ischemic acute renal failure (IARF) has been attributed to both direct endothelial injury and to altered endothelial nitric oxide synthase (eNOS) activity, with either maximal upregulation of eNOS or inhibition of eNOS by excess nitric oxide (NO) derived from iNOS. We investigated renal endothelial dysfunction in kidneys from Sprague-Dawley rats by assessing autoregulation and endothelium-dependent vasorelaxation 24 h after unilateral (U) or bilateral (B) renal artery occlusion for 30 (U30, B30) or 60 min (U60, B60) and in sham-operated controls. Although renal failure was induced in all degrees of ischemia, neither endothelial dysfunction nor altered facilitation of autoregulation by 75 pM angiotensin II was detected in U30, U60, or B30 kidneys. Baseline and angiotensin II-facilitated autoregulation were impaired, methacholine EC(50) was increased, and endothelium-derived hyperpolarizing factor (EDHF) activity was preserved in B60 kidneys. Increasing angiotensin II concentration restored autoregulation and increased renal vascular resistance (RVR) in B60 kidneys; this facilitated autoregulation, and the increase in RVR was abolished by 100 microM furosemide. Autoregulation was enhanced by N(omega)-nitro-l-arginine methyl ester. Peri-ischemic inhibition of inducible NOS ameliorated renal failure but did not prevent endothelial dysfunction or impaired autoregulation. There was no significant structural injury to the afferent arterioles with ischemia. These results suggest that tubuloglomerular feedback is preserved in IARF but that excess NO and probably EDHF produce endothelial dysfunction and antagonize autoregulation. The threshold for injury-producing, detectable endothelial dysfunction was higher than for the loss of glomerular filtration rate. Arteriolar endothelial dysfunction after prolonged IARF is predominantly functional rather than structural.

Intracellular smooth muscle [Ca2+] in acetylcholine and nitric oxide-mediated relaxation of human small arteries

In human resistance arteries the role of intracellular calcium during receptor agonist and nitric oxide (NO)-mediated vasorelaxation is almost unknown. We examined changes in smooth muscle calcium concentration ([Ca2+]i) caused by acetylcholine and the NO donor S-nitroso-N-acetylpenicillamine (SNAP) in isolated human subcutaneous small arteries. In arteries constricted with 50 mM KCl, acetylcholine and SNAP induced relaxation without any change in [Ca2+]i, whereas in noradrenaline constricted vessels, both acetylcholine and to a lesser degree also SNAP-mediated relaxation were associated with a decrease in [Ca2+]i. Furthermore incubation with SNAP (1 microM) induced a rightward shift in the [Ca2+]i-force relationship. These results suggest that relaxation mediated by endothelium derived hyperpolarizing factors (EDHF) is associated with reduction in [Ca2+]i, whereas NO-mediated relaxation can take place without changes in [Ca2+]i. This finding seems to be, at least partly, due to NO-mediated desensitization of the contractile apparatus to calcium.

Endothelial dysfunction: a comprehensive appraisal

The endothelium is a thin monocelular layer that covers all the inner surface of the blood vessels, separating the circulating blood from the tissues. It is not an inactive organ, quite the opposite. It works as a receptor-efector organ and responds to each physical or chemical stimulus with the release of the correct substance with which it may maintain vasomotor balance and vascular-tissue homeostasis. It has the property of producing, independently, both agonistic and antagonistic substances that help to keep homeostasis and its function is not only autocrine, but also paracrine and endocrine. In this way it modulates the vascular smooth muscle cells producing relaxation or contraction, and therefore vasodilatation or vasoconstriction. The endothelium regulating homeostasis by controlling the production of prothrombotic and antithrombotic components, and fibrynolitics and antifibrynolitics. Also intervenes in cell proliferation and migration, in leukocyte adhesion and activation and in immunological and inflammatory processes. Cardiovascular risk factors cause oxidative stress that alters the endothelial cells capacity and leads to the so called endothelial "dysfunction" reducing its capacity to maintain homeostasis and leads to the development of pathological inflammatory processes and vascular disease.

There are different techniques to evaluate the endothelium functional capacity, that depend on the amount of NO produced and the vasodilatation effect. The percentage of vasodilatation with respect to the basal value represents the endothelial functional capacity. Taking into account that shear stress is one of the most important stimulants for the synthesis and release of NO, the non-invasive technique most often used is the transient flow-modulate "endothelium-dependent" post-ischemic vasodilatation, performed on conductance arteries such as the brachial, radial or femoral arteries. This vasodilatation is compared with the vasodilatation produced by drugs that are NO donors, such as nitroglycerine, called "endothelium independent". The vasodilatation is quantified by measuring the arterial diameter with high resolution ultrasonography. Laser-Doppler techniques are now starting to be used that also consider tissue perfusion.

There is so much proof about endothelial dysfunction that it is reasonable to believe that there is diagnostic and prognostic value in its evaluation for the late outcome. There is no doubt that endothelial dysfunction contributes to the initiation and progression of atherosclerotic disease and could be considered an independent vascular risk factor. Although prolonged randomized clinical trials are needed for unequivocal evidence, the data already obtained allows the methods of evaluation of endothelial dysfunction to be considered useful in clinical practice and have overcome the experimental step, being non-invasive increases its value making it use full for follow-up of the progression of the disease and the effects of different treatments.

Effect of telmisartan/hydrochlorothiazide vs lisinopril/hydrochlorothiazide combination on ambulatory blood pressure and cognitive function in elderly hypertensive patients

The aim of this study was to compare the effects of telmisartan/hydrochlorothiazide (HCTZ) vs lisinopril/HCTZ combination on ambulatory blood pressure and cognitive function in elderly hypertensive patients. A total of 160 patients, 76 men and 84 women, aged 61-75 years, with sitting diastolic blood pressure (DBP)>90 mmHg and <110 mmHg and systolic blood pressure (SBP)>140 mmHg were randomized to receive temisartan 80 mg/HCTZ 12.5 mg o.d. or lisinopril 20 mg/HCTZ 12.5 mg o.d. for 24 weeks, according to a prospective, open-label, blinded end point, parallel-group design. At the end of a 2-week wash-out period and after 12 and 24 weeks of active treatment, 24-h noninvasive ambulatory BP monitoring (ABPM) was performed and cognitive function was evaluated through six different tests (verbal fluency, Boston naming test, word-list memory, word-list recall, word-list recognition and Trails B). Both treatments significantly reduced ambulatory BP. However, the telmisartan/HCTZ combination produced a greater reduction in 24-h, day-time and night time ABPM values. Lisinopril/HCTZ did not induce significant changes in any of the cognitive function test scores at any time of the study, whereas at both 12 and 24 weeks telmisartan/HCTZ significantly improved the word-list memory score (+17.1 and +15.7%, respectively, P<0.05 vs baseline), the word-list recall score (+13.5 and +16.9%, P<0.05) and the Trails B score (-33 and -30.5%, P<0.05). These results suggest that in elderly hypertensive patients treatment with telmisartan/HCTZ produces a slightly greater reduction in ambulatory BP than lisinopril/HCTZ combination and, unlike this latter, improves some of the components of cognitive function, particularly episodic memory and visuospatial abilities.

Wild blueberry-rich diets affect the contractile machinery of the vascular smooth muscle in the Sprague-Dawley rat

Weanling male Sprague-Dawley rats were randomly fed a control diet (AIN-93) (C) or a blueberry diet (B) for 13 weeks, or a reverse diet (R) (C diet for 13 weeks, switched to the B diet for 8 weeks). Aortas were excised, and two intact and two endothelium-denuded rings were immersed in tissue baths containing physiological salt solution at 37 degrees C and aerated with 95% O(2) and 5% CO(2) (pH 7.4). Following equilibration and preconditioning under 1.5-g preload, cumulative dose-response curves were generated with six doses of the alpha1-adrenergic receptor-selective agonist L-phenylephrine (L-Phe, 10(8)-3 x 10(-6) M) and relaxed with one dose of acetylcholine (3 x 10(-6) M) to assess intact endothelium. The maximum force of contraction (Fmax) and vessel sensitivity (pD(2)) were determined in intact and endothelium-denuded rings. A two-way analysis of variance test revealed that blueberry-fed animals (B and R diets) developed a significantly lower F (max) (0.873 +/- 0.0463 and 0.9266 +/- 0.0463 g, respectively) when contracted with L-Phe, compared with the animals on the C diet (1.109 +/- 0.0463 g) (P < .05). The pD(2) of the intact rings was not significantly different among diet groups. Additionally, diet did not significantly affect the mean F (max) or pD(2) of endothelium-denuded rings. Our results indicate for the first time that wild blueberries incorporated into the diet affect the vascular smooth muscle contractile machinery by suppressing the alpha1-adrenergic receptor agonist-mediated contraction while having no effect on membrane sensitivity of the endothelial or vascular smooth muscle cell layer. Furthermore, their mechanism of action seems to be accomplished through an endothelium-dependent pathway.

Dietary manganese suppresses α1 adrenergic receptor-mediated vascular contraction

We examined the effect of dietary manganese (Mn) on the vascular contractile machinery in rat thoracic aortas. Weanling male Sprague-Dawley rats were fed either an Mn-deficient (MnD), Mn-adequate (MnA) or Mn-supplemented (MnS) diet (<1, 10-15 and 45-50 ppm Mn, respectively). After 15 weeks on the diets the rats were sacrificed and 3-mm aortic rings were contracted in six cumulative doses of the alpha(1) adrenergic receptor agonist L-phenylephrine (l-Phe, 10(-8) to 3 x 10(-6) M) under 1.5-g preload and relaxed with one dose of acetylcholine (3 x 10(-6) M) to assess intact endothelium. The maximal force (F(max)) of contraction and relaxation, as well as the vessel sensitivity (pD(2)) were determined. Manganese deficiency, assessed by hepatic Mn content, significantly lowered the rate of animal growth. A two-way analysis of variance revealed that MnS animals developed lower F(max) when contracted with L-Phe compared with the MnD and MnA animals (P</=.001). Thus, dietary Mn at levels of 45-50 ppm affects the contractile machinery by reducing maximal vessel contraction to an alpha(1) adrenergic agonist. The observed pD(2) was significantly greater in the MnD group compared with the MnA and MnS animals (P</=.001). Thus, restriction of dietary Mn affects vascular sensitivity to the alpha(1) adrenergic receptor. Our results demonstrate for the first time that dietary Mn influences the receptor signaling pathways and contractile machinery of vascular smooth muscle cells in response to an alpha(1) adrenergic receptor.

Interactions between autonomic nervous system activity and endothelial function: a model for the development of cardiovascular disease

OBJECTIVES

Endothelial dysfunction is a new pathway in cardiovascular disease (CVD) development. Psychosocial factors have been little studied in relation to endothelial function, although they may interact via associations with the autonomic nervous system (ANS). The purpose of this review is to propose a model by which psychosocial factors are related to CVD development through interactions between the ANS and vascular endothelium.

METHODS

The literature supporting an interaction between the ANS and endothelium in healthy and disease states is reviewed. Potential mechanisms linking the two systems are explored as a pathway for CVD development.

RESULTS

Endothelial dysfunction and impaired cardiovascular ANS regulation are both markers for increased CVD risk. Sympathetic nerves and vascular endothelial cells share a functional antagonism in healthy states to maintain appropriate blood vessel tone. Alterations in sympathetic activity and endothelial cell function are both observed early in the development of CVD and may result from an inability to maintain the functional antagonism. Impairments in either ANS regulation or endothelial function may contribute to further disease development by evoking maladaptive changes in the opposing system.

CONCLUSIONS

Although interactions between cardiovascular ANS regulation and endothelial function are likely involved in CVD development, further research is needed to determine whether ANS and endothelium interactions are a plausible pathway linking psychosocial factors with increased CVD risk.

Effects of valsartan compared with enalapril on blood pressure and cognitive function in elderly patients with essential hypertension

OBJECTIVE

This prospective, randomised, open-label, blinded-endpoint study was to compare the effects of the angiotensin II (Ang II) AT1 receptor antagonist valsartan with those of the ACE inhibitor enalapril on blood pressure (BP) and cognitive functions in elderly hypertensive patients.

METHODS

One hundred and forty-four patients aged 61-80 years with mild to moderate essential hypertension (DBP > or =95 mmHg and < or =110 mmHg at the end of a 2-week placebo run-in period) were randomly assigned to once daily (o.d.) treatment with valsartan 160 mg ( n=73) or enalapril 20 mg ( n=71) for 16 weeks. The patients were examined every 4 weeks during the study, with pre-dose BP (standard mercury sphygmomanometer, Korotkoff I and V) and heart rate (pulse palpation) being recorded at each visit. Cognitive function was evaluated at the end of the wash-out period and after 16 weeks of active treatment by means of five tests (verbal fluency, the Boston naming test, word list memory, word list recall and word list recognition).

RESULTS

Both valsartan and enalapril had a clear antihypertensive effect, but the former led to a slightly greater reduction in SBP/DBP at 16 weeks (18.6+/-4.6/13.7+/-4.0 mmHg vs 15.6+/-5.1/10.9+/-3.9 mmHg; P<0.01). Enalapril did not induce any significant changes in any of the cognitive function test scores; valsartan significantly increased the word list memory score (+11.8%; P<0.05 vs baseline and P<0.01 vs enalapril) and the word list recall score (+18.7%; P<0.05 vs baseline and P<0.01 vs enalapril), but not those of the other tests.

CONCLUSION

These findings indicate that, in elderly hypertensive patients, 16 weeks of treatment with valsartan 160 mg o.d. is more effective than enalapril 20 mg o.d. in reducing BP, and (unlike enalapril) improves some of the components of cognitive function, particularly episodic memory.

Role of Endothelium-Derived Hyperpolarizing Factor in Human Forearm Circulation

Endothelium-derived hyperpolarizing factor (EDHF) contributes to endothelium-dependent relaxation of isolated arteries, but it is not known whether this also occurs in the case of humans in vivo. The present study examined the role of EDHF in human forearm circulation. Forearm blood flow (FBF) was measured by strain-gauge plethysmography in 31 healthy, normal subjects (mean±SE age, 23±2 years; 24 men and 7 women). After oral administration of aspirin (486 mg), we infused N G -monomethyl- l -arginine (8 μmol/min for 5 minutes) into the brachial artery. We used tetraethylammonium chloride (TEA, 1 mg/min for 20 minutes), a K Ca channel blocker, as an EDHF inhibitor, and nicorandil as a direct K + channel opener. TEA significantly reduced FBF ( P <0.05) but did not change systemic arterial blood pressure. Furthermore, TEA significantly inhibited the FBF increase in response to substance P (0.8, 1.6, 3.2, and 6.4 ng/min, n=8) and bradykinin (12.5, 25, 50, and 100 ng/min, n=8; both P <0.001), whereas it did not affect the FBF increase in response to acetylcholine (4, 8, 16, and 32 μg/min, n=8), sodium nitroprusside (0.4, 0.8, 1.6, and 3.2 μg/min, n=8), or nicorandil (0.128, 0.256, 0.512, and 1.024 mg/min, n=8). These results suggest that EDHF contributes substantially to basal forearm vascular resistance, as well as to forearm vasodilatation evoked by substance P and bradykinin in humans in vivo.

Translational paradigms in cerebrovascular gene transfer

Gene transfer involves the use of an engineered biologic vehicle known as a vector to introduce a gene encoding a protein of interest into a particular tissue. In diseases with known defects at a genetic level, gene transfer offers a potential means of restoring a normal molecular environment via vector-mediated entry (transduction) and expression of genes encoding potentially therapeutic proteins selectively in diseased tissues. The technology of gene transfer therefore underlies the concept of gene therapy and falls under the umbrella of the current genomics revolution. Particularly since 1995, numerous attempts have been made to introduce genes into intracranial blood vessels to demonstrate and characterize viable transduction. More recently, in attempting to translate cerebrovascular gene transfer technology closer to the clinical arena, successful transductions of normal human cerebral arteries ex vivo and diseased animal cerebral arteries in vivo have been reported using vasomodulatory vectors. Considering the emerging importance of gene-based strategies for the treatment of the spectrum of human disease, the goals of the present report are to overview the fundamentals of gene transfer and review experimental studies germane to the clinical translation of a technology that can facilitate genetic modification of cerebral blood vessels.

Potential mechanisms of impaired endothelial function in arterial hypertension and hypercholesterolemia

This review focuses on the role of impaired endothelial function for the development of atherosclerosis in human arterial hypertension and hypercholesterolemia in vivo. Potential mechanisms underlying impaired endothelial function and decreased bioavailability of nitric oxide under these clinical conditions are discussed. It further addresses therapeutic strategies aimed at improving the bioavailability of nitric oxide in these patients. The overall conclusion is that the bioavailability of nitric oxide is probably impaired, not by a single defect, but by various mechanisms affecting nitric oxide synthesis as well as nitric oxide breakdown. In both diseases increased superoxide anion production and oxidative stress represent a major mechanism. Decreased bioavailability of nitric oxide not only impairs endothelium-dependent vasodilation, but also activates other mechanisms that play an important role in the pathogenesis of atherosclerosis. Thus, therapeutic strategies should aim to restore bioavailability of nitric oxide, which has been demonstrated for lipid-lowering therapy in hypercholesterolemia and blood pressure control in hypertension. In addition, antioxidative strategies will represent a major therapeutic tool against atherosclerotic diseases in the future. Statins and blockers of the renin-angiotensin system seem to have such antioxidative effects independent from their effects on lipid profiles or blood pressure control.

Endothelium-dependent vasodilation in the skin microcirculation of patients with septic shock

The evidence for endothelial dysfunction in sepsis is mostly restricted to animal models. We investigated endothelial function in the skin microcirculation of eight patients hospitalized for septic shock in an intensive care unit (ICU). All patients required adrenergic support. Twelve hemodynamically stable ICU patients without sepsis who did not receive any vasoactive medication were used as controls. The two groups were of similar age and sex ratio. For additional reference, 16 healthy, nonsmoking subjects matched for age and sex to the first two groups were also studied. The evaluation of endothelial function was based on the comparison of skin blood flow responses to iontophoretically applied acetylcholine (Ach, an endothelium-dependent vasodilator) and sodium nitroprusside (SNP, an endothelium-independent vasodilator). Skin blood flow was measured on the volar face of the forearm using laser Doppler imaging. Before application of Ach or SNP, the mean baseline skin blood flow was below 100 perfusion units (PU) in all subjects and did not differ between groups. The maximal increase in blood flow elicited by both agents was significantly depressed in the patients with sepsis (Ach: 167 +/- 63 PU; SNP: 138 +/- 34 PU, mean +/- SD) compared with the ICU control patients (Ach: 291 +/- 135 PU, P < 0.05; SNP: 261 +/- 121 PU, P < 0.01) and the healthy, nonsmoking groups (Ach: 336 +/- 98 PU, P < 0.01; SNP: 304 +/- 81 PU, P < 0.01). The ratio of responses to Ach and SNP did not significantly differ between groups (septic: 1.22 +/- 0.40; ICU control 1.18 +/- 0.46, healthy, nonsmoking 1.12 +/- 0.24, P = 0.86). Thus, sepsis was not associated with a selective depression of the endothelium-dependent response. These results suggest that the capacity of the endothelium to produce signals for vasorelaxation remains intact in the skin microcirculation of patients with septic shock.

Effects of severe hypertension on endothelial and platelet microparticles

The molecular mechanisms by which extreme blood pressure elevation leads to vascular injury are not defined. To explore the hypothesis that activation of endothelium and platelets as manifested by increased concentrations of circulating endothelial microparticles and platelet microparticles could play a role in this target organ injury, we conducted a cross-sectional study of these markers in 3 groups: (1) untreated patients referred specifically for treatment of severe uncontrolled hypertension; (2) untreated patients with established mild hypertension; and (3) normotensive volunteer subjects. By ANOVA, endothelial (P=0.002) and platelet (P=0.01) microparticles were greatest in the severely hypertensive group. There was a significant correlation between both of these markers and blood pressure, even in the setting of multiple risk factors. Our results suggest that these markers may be useful and specific for pressure-induced endothelial and platelet activation in hypertension. Furthermore, because of the combined effects of endothelial and platelet microparticles on coagulation, leukocytes, and endothelium, it is possible that they may play a pathogenic role in mediating target organ injury in severe hypertension.

The altered balance between sympathetic nervous system and nitric oxide in salt hypertensive Dahl rats: ontogenetic and F2 hybrid studies

OBJECTIVE

We have demonstrated earlier that the nitric oxide (NO) system is not able to counterbalance effectively the hyperactivity of the sympathetic nervous system (SNS) in salt hypertension of young Dahl rats in which augmented superoxide anion formation lowers NO bioavailability. The aim of the present study was to determine whether SNS hyperactivity and/or relative NO deficiency are also present in salt hypertension elicited in adult Dahl rats, and whether they are associated with blood pressure (BP) in the F2 population of Dahl rats.

DESIGN AND METHODS

The contribution of major vasoactive systems [renin-angiotensin system (RAS), SNS and NO] and superoxide anions to BP maintenance was studied in SS/Jr rats in which salt hypertension was induced either in adulthood or in youth (8% NaCl diet from the age of 12 or 4 weeks). The contribution of particular vasoactive systems was also investigated in 122 young salt-loaded F2hybrids [derived from salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) Dahl rats] which were fed a high-salt diet (8% NaCl) for 6 weeks after weaning. Mean arterial pressure (MAP) was measured in conscious animals subjected to acute consecutive blockade of RAS (captopril 10 mg/kg i.v.), SNS (pentolinium 5 mg/kg i.v.) and NO synthase (l-NAME 30 mg/kg i.v.).

RESULTS

Dahl rats with salt hypertension induced in adulthood were also characterized by enhanced pentolinium-induced BP fall (DeltaMAPpento), but their residual BP (recorded after the blockade of both RAS and SNS) was unaltered, in contrast to its elevation seen in young salt-hypertensive rats. The BP rise after NO synthase inhibition by l-NAME (DeltaMAPL-NAME), which was substantially greater in adult than in young hypertensive rats, was not enhanced by superoxide scavenging with tempol in adult hypertensive animals, in which this drug elicited a moderate BP reduction only. Basal MAP of young salt-loaded F2 hybrids was positively associated not only with DeltaMAPpento (P < 0.0001) and residual BP (P < 0.001) but also with DeltaMAPL-NAME (P < 0.001). The slope of the relationship between basal BP and pentolinium-induced BP changes was steeper than that between basal BP and BP changes elicited by l-NAME. The positive correlation of basal BP with DeltaMAPpento/DeltaMAPL-NAME ratio (P < 0.01) indicates that an altered balance between sympathetic vasoconstriction and NO-dependent vasodilation was associated with high blood pressure, even in the F2 population of Dahl rats.

CONCLUSIONS

A comparison of young and adult salt-hypertensive Dahl rats stressed the importance of increased residual BP and relative NO deficiency for the severity of hypertension, because these two alterations were absent in a less-pronounced form of salt hypertension elicited in adulthood. The findings obtained in our young salt-loaded F2 population also confirm the major importance of both sympathetic hyperactivity and relative NO deficiency for the maintenance of salt hypertension in Dahl rats.

Effects of severe, uncontrolled hypertension on endothelial activation: soluble vascular cell adhesion molecule-1, soluble intercellular adhesion molecule-1 and von Willebrand factor

OBJECTIVES

The molecular mechanisms whereby severe, uncontrolled hypertension (SHT) is translated into acute vascular target organ dysfunction have not been completely defined. We sought to determine whether SHT is associated with pressure-dependent endothelial activation as assessed by soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble intercellular adhesion molecule-1 (sICAM-1) and von Willebrand Factor (vWF).

METHODS

We determined sVCAM-1, sICAM-1 and vWF in three groups: (i) untreated patients referred specifically for treatment of SHT [diastolic blood pressure (DBP) > or = 120 mm Hg; n = 24]; (ii) untreated patients with established mild hypertension (MHT; DBP 95-100 mmHg; n = 19); and (iii) normotensive volunteers (DBP < or = 90; n = 16).

RESULTS

By analysis of variance, sVCAM-1 (P = 0.002), sICAM-1 (P = 0.02) and vWF (P = 0.009) were greater in SHT and MHT than in normotensives but did not differ between SHT and MHT. We observed a significant positive correlation between blood pressure and soluble activation markers at lower blood pressures (normotensives and MHT considered together) that was not present in SHT.

CONCLUSIONS

Even mild elevation of blood pressure may be sufficient to activate the expression of adhesion molecules. Mechanisms other than the endothelial expression of adhesion molecules may be important in mediating the accelerated target organ injury produced by SHT in humans. Concentrations of soluble adhesion molecules and vWF may depend more strongly upon factors in the hypertensive microenvironment other than the absolute level of blood pressure.

Endothelial adrenoceptors

alpha2 -Adrenergic agonists cause endothelium-dependent relaxation in a number of isolated blood vessels. This effect is explained by the activation of endothelial alpha 2 -adrenoceptors linked to nitric oxide synthase by G i -coupling proteins. The endothelial response to alpha 2 -adrenergic agonists is blunted considerably after regeneration of the endothelium and in atherosclerotic arteries. The relaxation of isolated arteries caused by beta-adrenergic agonists is reduced by removal of the endothelium and, in most cases, by inhibitors of the l -arginine nitric oxide pathway. Likewise, in the intact animal and in the human forearm the vasodilatation to beta 2 -adrenergic agonists is blunted by inhibitors of nitric oxide synthase. Whether these findings reflect the presence of functional beta-adrenoceptors on the endothelium remains controversial. Several beta-adrenergic blockers cause endothelium-dependent relaxation in vitro or augment the production of nitric oxide in vivo. However, these responses cannot be attributed to interactions with endothelial beta-adrenoceptors.

Comparison of endothelium-dependent vasoactivity of internal mammary arteries from hypertensive, hypercholesterolemic, and diabetic patients

BACKGROUND

Endothelium-dependent relaxation is abnormal in a variety of diseased states. Despite the widespread use of the internal mammary artery (IMA) in coronary artery bypass grafting, there is a lack of comparative studies on IMA endothelial-dependent function in patients with major cardiovascular risk factors.

METHODS

An IMA segment from 48 selected patients undergoing coronary artery bypass grafting was harvested intraoperatively and assigned to one of four groups (n = 12): diabetics requiring therapy, hypertensives, hypercholesterolemic, and nondiabetic-normotensive-normocholesterolemic patients. Internal mammary artery specimens were cut into rings and suspended in organ bath chambers, and the isometric tension of vascular tissues was recorded. The IMA rings were (1) precontracted with norepinephrine, and the endothelium-derived relaxation was evaluated by cumulative addition of acetylcholine, (2) contracted with cumulative concentrations of endothelin-1, and (3) contracted with the nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine. Furthermore, the release of prostacyclin by the IMA rings was directly measured during basal tone conditions and at the end of the various pharmacologic interventions. Histology of IMA rings was randomly performed.

RESULTS

The results obtained in these experiments showed that IMA rings harvested from hypertensive patients have the greatest impairment of endothelium-dependent response to relaxant and contracting stimuli (p < 0.01 versus nondiabetic-normotensive-normocholesterolemic tissues; p < 0.05 versus hypercholesterolemic and diabetic tissues) and prostacyclin release in normal and stimulated conditions. To a lesser extent, hypercholesterolemic and diabetic tissues show similar depression (diabetic > hypercholesterolemic) both of relaxation and prostacyclin production, with respect to nondiabetic-normotensive-normocholesterolemic specimens (p < 0.05). Histology findings (scanning electron microscopy) did not differ in multiple sections from vessel studies.

CONCLUSIONS

Major cardiovascular risk factors affect the endothelium-dependent vasoactive homeostasis of human IMA differently. Depression of relaxation is highest in patients with a history of hypertension. These findings may be pertinent to early and long-term treatment of patients undergoing coronary artery bypass grafting.

Pathophysiology of sickle cell disease: role of cellular and genetic modifiers

Sickle hemoglobin (HbS), caused by a point mutation in the beta-globin gene of hemoglobin, polymerizes when deoxygenated. The pathophysiology of sickle cell disease results from cellular defects caused directly by the hemoglobin mutation interacting with the environment and many other gene products--a few known, but most yet unidentified--a typical example of epistasis. How normal tissue perfusion is interrupted is complex and why the phenotype of sickle cell disease differs from patient to patient is poorly understood. We review the "classic" aspects of the pathophysiology of sickle cell disease and focus on known and potential modulators of the phenotype of this disorder.

Free radical production in aortic rings from rats fed a fish oil-rich diet

To study the effect of the degree of unsaturation of dietary fatty acids on the production of free radicals and on the vascular smooth muscle tone in rings of the aorta, Sprague-Dawley rats were fed a semipurified diet containing 5% lipids from either corn oil (CO) or menhaden oil (MO) for 8 wk. The MO diet did not change the basal or NADPH-dependent superoxide anion (O[Formula: see text]·) release. There were no significant differences in phenylephrine-induced contractions between the two groups in intact rings. However, these contractions increased in endothelium-intact aortic rings from the MO group after addition of the nitric oxide (·NO) synthase inhibitor N G-nitro-l-arginine and in endothelium-denuded rings, both indicating a greater endothelial basal ·NO production in rats fed with the MO diet. Endothelium-dependent relaxations in response to acetylcholine were more prominent in rings from the MO group. These differences were not due to an increased smooth muscle response to ·NO, because relaxations were the same using an exogenous ·NO donor. Our results indicate that dietary MO did not modify O[Formula: see text]· release by the vessel wall or relaxation due to the cyclooxygenase pathway, but it potentiated endothelial production of ·NO.

Role of sex differences and effects of endothelial NO synthase deficiency in responses of carotid arteries to serotonin

We examined the hypothesis that contraction of the carotid arteries to serotonin is normally inhibited by endothelial NO synthase (eNOS) and is enhanced in mice lacking the gene for eNOS. Because the influence of eNOS may vary with the sex of the mouse, we also tested whether responses to serotonin were dependent on sex. We studied carotid arteries in vitro from littermate control (eNOS(+/+)) mice, heterozygous (eNOS(+/-)) mice, and homozygous eNOS-deficient (eNOS(-/-)) mice (male and female). Contraction to serotonin was greater in male eNOS(+/+) mice than in female eNOS(+/+) mice. In male mice, contraction to serotonin increased by approximately 40% and 2.5-fold in male eNOS(+/-) and eNOS(-/-) mice, respectively. Contraction to serotonin was more than doubled in female eNOS(+/-) mice and increased >5-fold in arteries from eNOS(-/-) mice. In contrast, maximum vasoconstriction to U46619 was similar in male and female eNOS(+/+), eNOS(+/-), and eNOS(-/-) mice. Relaxation to acetylcholine was not different in male and female eNOS(+/+) or eNOS(+/-) mice but was absent in eNOS(-/-) mice. These findings suggest that the contraction of carotid arteries to serotonin is influenced by the sex of the animal. eNOS deficiency in gene-targeted mice is associated with enhanced contraction to serotonin, particularly in female mice, providing direct evidence that eNOS is a major determinant of vascular effects of serotonin. The results with eNOS(+/-) mice suggest a "gene-dosing" effect for vascular responses to serotonin.

Gene transfer for cerebrovascular disease

Gene transfer is a powerful, evolving technique that uses a biologic vehicle (eg, an engineered adenovirus) to introduce a specific gene of interest (ie, a recombinant gene) into a target tissue. This approach, which has considerable therapeutic potential, underlies the concept of gene therapy. Several studies have characterized the morphologic, biochemical, and functional effects of recombinant gene expression in animal and human cerebral arteries, and support the possibility of gene therapy for cerebrovascular disease. However, for successful integration into future clinical practice, key issues concerning vector safety, delivery methods, and transduction specificity need to be addressed. Alongside completion of the Human Genome Project, transfer of novel genes into the central nervous system is likely to impact greatly on our ability to favorably modify diseased human tissue. Knowledge of the fundamental concepts of cerebrovascular gene transfer is therefore useful to understanding both its molecular basis and potential clinical utility.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Factors influencing efficacy of nitrate therapy for stable angina pectoris: a multiple linear regression analysis

In an open-label self-controlled study of 1,350 patients with stable angina pectoris (SAP), we previously demonstrated that 50 mg of isosorbide mononitrate (ISMN) slow release formulation once daily not only provided a better antianginal effect but also a better quality of life (QOL) than did the daily administration of multiple small doses of the compound. It is unknown whether certain patient characteristics contribute to this benefit. The objective of this article was to determine what independent factors contribute to this benefit. Multiple linear regression analysis was performed on the data from these 1,350 patients. Quality of life was assessed by the Marquis QOL-questionnaire for patients with angina and included the domains of immobility, pain, and psychological distress. For the purpose of this study, overall QOL was calculated as the pooled sums of the domain scores and expressed as mean scores on an ordinal scale of 10. Age did not influence the beneficial effect of nitrate therapy on QOL. Neither did gender, rhythmic disturbances, peripheral artery disease, or the concomitant use of calcium channel blockers or beta blockers. New York Heart Association (NYHA) angina classification was an independent variable: patients with a NYHA class I or II benefited less than did patients with NYHA III or IV (p = 0.02). Obese patients as well as hypertensive patients benefited less (p = 0.04 and 0.02), and smokers tended to benefit less also (p = 0.08). In contrast, hypercholesterolemia and diabetes mellitus improved the beneficial effect of nitrates on QOL (p = 0.03 and 0.05). The authors conclude that patients with coronary artery disease (CAD) and concomitant diabetes mellitus or hypercholesterolemia, a category particularly prone to early endothelial dysfunction and thus dysfunctional endogenous nitric oxide (NO) production, may benefit more from NO-donor therapy than patients without such concomitant conditions.

Vasodilator mechanisms in the coronary circulation of endothelial nitric oxide synthase-deficient mice

Previous studies have demonstrated that responses to endothelium-dependent vasodilators are absent in the aortas from mice deficient in expression of endothelial nitric oxide synthase (eNOS -/- mice), whereas responses in the cerebral microcirculation are preserved. We tested the hypothesis that in the absence of eNOS, other vasodilator pathways compensate to preserve endothelium-dependent relaxation in the coronary circulation. Diameters of isolated, pressurized coronary arteries from eNOS -/-, eNOS heterozygous (+/-), and wild-type mice (eNOS +/+ and C57BL/6J) were measured by video microscopy. ACh (an endothelium-dependent agonist) produced vasodilation in wild-type mice. This response was normal in eNOS +/- mice and was largely preserved in eNOS -/- mice. Responses to nitroprusside were also similar in arteries from eNOS +/+, eNOS +/-, and eNOS -/- mice. Dilation to ACh was inhibited by N(G)-nitro-L-arginine, an inhibitor of NOS in control and eNOS -/- mice. In contrast, trifluoromethylphenylimidazole, an inhibitor of neuronal NOS (nNOS), decreased ACh-induced dilation in arteries from eNOS-deficient mice but had no effect on responses in wild-type mice. Indomethacin, an inhibitor of cyclooxygenase, decreased vasodilation to ACh in eNOS-deficient, but not wild-type, mice. Thus, in the absence of eNOS, dilation of coronary arteries to ACh is preserved by other vasodilator mechanisms.

Contractile effects of arginine analogues on human internal thoracic and radial arteries

OBJECTIVES

Plasma levels of endogenous guanidino-substituted analogues of L -arginine are increased in various pathologic conditions. In the present study we determined the effects of some of these compounds on basal and stimulated release of nitric oxide in human internal thoracic and radial arteries.

METHODS

Rings of human internal thoracic and radial arteries were obtained from 16 multiorgan donors. The rings were suspended in organ baths for isometric recording of tension.

RESULTS

N(G)-monomethyl L -arginine (10(-6) to 10(-3) mol/L) and N(G),N(G)-dimethyl L -arginine (10(-6) to 10(-3) mol/L) caused concentration- and endothelium-dependent contractions. Maximal force of contractions for N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine in the internal thoracic artery were 18.0% +/- 4.3% and 17.8% +/- 3.8%, respectively, of the contraction to 100 mmol/L KCl, and those found in the radial artery were 9.6% +/- 2.5% and 9.1% +/- 2.4%, respectively. Aminoguanidine (10(-5) to 3 x 10(-3) mol/L) and methylguanidine (10(-5) to 3 x 10(-3) mol/L) produced endothelium-independent contractions. L -Arginine (10(-3) mol/L) prevented the contractions by N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine but did not change contractions induced by aminoguanidine and methylguanidine. N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine inhibited, in a concentration-dependent manner, the endothelium-dependent relaxation to acetylcholine in the internal thoracic artery and had little attenuating effect in the radial artery; aminoguanidine and methylguanidine were without effect.

CONCLUSIONS

The results suggest that the contractions induced by N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine are due to inhibition of both basal and stimulated nitric oxide production, whereas aminoguanidine and methylguanidine do not affect the synthesis of nitric oxide. An increase in the plasma concentration of N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine is likely to represent a risk factor for abnormal vasomotor tone in conduit arteries used as coronary grafts.

Impaired endothelial function in arterial hypertension and hypercholesterolemia: potential mechanisms and differences

This review focuses on the role of impaired endothelial function for the development of atherosclerosis in human arterial hypertension and hypercholesterolemia in vivo. Potential mechanisms underlying impaired endothelial function and decreased bioavailability of nitric oxide under these clinical conditions are discussed and potential differences in these mechanisms between arterial hypertension and hypercholesterolemia are outlined. It further addresses therapeutic strategies aiming to improve the bioavailability of nitric oxide in these patients. The overall conclusion is that the bioavailability of nitric oxide is probably impaired not by a single defect, but by various mechanisms affecting nitric oxide synthesis as well as nitric oxide breakdown. In both diseases, increased superoxide anion production and oxidative stress represents a major mechanism. However, potential differences in the underlying mechanisms of superoxide production or nitric oxide synthesis are evident between arterial hypertension and hypercholesterolemia. Decreased bioavailability of nitric oxide does not only impair endothelium-dependent vasodilation, but also activates other mechanisms that play an important role in the pathogenesis of atherosclerosis. Thus, therapeutic strategies should aim to restore bioavailability of nitric oxide, which has been demonstrated for lipid-lowering therapy in hypercholesterolemia. The mechanisms by which nitric oxide bioavailability can be improved by any drug therapy remain to be elucidated and may provide further insights into the mechanisms that are involved in impaired endothelial function and atherogenesis.