Fatty acids augment endothelium-dependent dilation in hand veins by a cyclooxygenase-dependent mechanism

Small lipid-binding proteins in regulating endothelial and vascular functions: focusing on adipocyte fatty acid binding protein and lipocalin-2

Dysregulated production of adipokines from adipose tissue plays a critical role in the development of obesity-associated cardiovascular abnormalities. A group of adipokines, including adipocyte fatty acid binding protein (A-FABP) and lipocalin-2, possess specific lipid-binding activity and are up-regulated in obese human subjects and animal models. They act as lipid chaperones to promote lipotoxicity in endothelial cells and cause endothelial dysfunction under obese conditions. However, different small lipid-binding proteins modulate the development of vascular complications in distinctive manners, which are partly attributed to their specialized structural features and functionalities. By focusing on A-FABP and lipocalin-2, this review summarizes recent advances demonstrating the causative roles of these newly identified adipose tissue-derived lipid chaperones in obesity-related endothelial dysfunction and cardiovascular complications. The specific lipid-signalling mechanisms mediated by these two proteins are highlighted to support their specialized functions. In summary, A-FABP and lipocalin-2 represent potential therapeutic targets to design drugs for preventing vascular diseases associated with obesity.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Acute effects of elevated NEFA on vascular function: a comparison of SFA and MUFA

There is emerging evidence to show that high levels of NEFA contribute to endothelial dysfunction and impaired insulin sensitivity. However, the impact of NEFA composition remains unclear. A total of ten healthy men consumed test drinks containing 50 g of palm stearin (rich in SFA) or high-oleic sunflower oil (rich in MUFA) on separate occasions; a third day included no fat as a control. The fats were emulsified into chocolate drinks and given as a bolus (approximately 10 g fat) at baseline followed by smaller amounts (approximately 3 g fat) every 30 min throughout the 6 h study day. An intravenous heparin infusion was initiated 2 h after the bolus, which resulted in a three- to fourfold increase in circulating NEFA level from baseline. Mean arterial stiffness as measured by digital volume pulse was higher during the consumption of SFA (P < 0·001) but not MUFA (P = 0·089) compared with the control. Overall insulin and gastric inhibitory peptide response was greater during the consumption of both fats compared with the control (P < 0·001); there was a second insulin peak in response to MUFA unlike SFA. Consumption of SFA resulted in higher levels of soluble intercellular adhesion molecule-1 (sI-CAM) at 330 min than that of MUFA or control (P ≤ 0·048). There was no effect of the test drinks on glucose, total nitrite, plasminogen activator inhibitor-1 or endothelin-1 concentrations. The present study indicates a potential negative impact of elevated NEFA derived from the consumption of SFA on arterial stiffness and sI-CAM levels. More studies are needed to fully investigate the impact of NEFA composition on risk factors for CVD.

Non-esterified fatty acids increase arterial pressure via central sympathetic activation in humans

Previous studies have shown that acute increases in plasma NEFAs (non-esterified fatty acids) raise SVR (systemic vascular resistance) and BP (blood pressure). However, these studies have failed to distinguish between CNS (central nervous system) mechanisms that raise sympathetic activity and paracrine mechanisms that increase SVR directly, independent of CNS involvement. The aim of the present study was to directly determine whether the sympathetic nervous system contributes to the pressor response to NEFAs. On 2 days separated by at least 2 weeks, 17 lean healthy volunteers (ten male/seven female; age, 22±1 years; body mass index, 23±1 kg/m2; values are means±S.E.M.) received a 4-h intravenous infusion of 20% Intralipid® or placebo (in a single-blind randomized balanced order). MSNA (muscle sympathetic nerve activity), HR (heart rate), BP (oscillometric brachial measurement) and (cardiac output; acetylene rebreathing) were measured before and throughout infusion. The change in HR (+8.2±1.0 and +2.4±1.2 beats/min), systolic BP (+14.0±1.6 and +3.2±2.5 mmHg) and diastolic BP (+8.2±1.0 and −0.1±1.7 mmHg) were significantly greater after the 4-h infusion of Intralipid® compared with placebo (P<0.001). The change in BP with Intralipid® resulted from an increase in SVR (/mean arterial pressure; P<0.001) compared with baseline, without a change in . MSNA burst frequency increased during Intralipid® infusion compared with baseline (+4.9±1.3 bursts/min; P<0.05), and total MSNA (frequency×amplitude) was augmented 65% (P<0.001), with no change during placebo infusion. Lipid infusion increased insulin, aldosterone and F2-isoprostane, but not leptin, concentrations. On the basis of the concomitant increase in BP, MSNA and SVR, we conclude that central sympathetic activation contributes to the pressor response to NEFAs.

Are patients after Kawasaki disease at increased risk for accelerated atherosclerosis?

OBJECTIVE

To assess whether patients after Kawasaki disease (KD) have increased risk factors and abnormalities suggestive of early atherosclerosis in systemic arteries.

STUDY DESIGN

In a case-control study, we compared 52 patients after typical Kawasaki disease with varying coronary artery involvement (67% males; mean time from illness episode 11.2 +/- 3.7 years) studied between 10 and 20 years of age with 60 healthy control subjects (50% males). Brachial artery reactivity (BAR) was assessed using vascular ultrasonography, and atherosclerosis risk assessment was performed. Differences between cases and controls and factors associated with endothelial function in cases were determined.

RESULTS

Case patients had lower resting systolic blood pressure (P < .001), lower apolipoprotein AI levels (P < .05), and higher levels of glycosylated hemoglobin (P = .007). There were no significant differences in BAR between case patients and control subjects in response to increased flow (P = .60) and nitroglycerine (P = .93). For case patients, significant factors in multivariable analysis for lower flow-mediated BAR included higher fasting triglyceride levels (P = .04) and lower free fatty acid levels (P < .001). No significant relationship was noted with past or current coronary artery involvement.

CONCLUSION

Patients with KD have some abnormalities for risk factors for atherosclerosis, but systemic arterial endothelial dysfunction is not present in the long term.

Effect of a low-dose oral contraceptive on venous endothelial function in healthy young women: preliminary results

BACKGROUND

A possible increase in the incidence of venous thromboembolic events has been reported among users of third generation oral contraceptives. The objective of this study was to evaluate the effect of a low dose oral contraceptive (15 microg ethinyl estradiol/60 microg gestodene) on the venous endothelial function of healthy young women.

METHODS

Prospective case control study using the dorsal hand vein technique. Venous endothelial function was evaluated at baseline and after 4 months in the oral contraceptive users group (11 women) and in a control group (9 women). After preconstriction of the vein with phenylephrine, dose-response curves for acetylcholine and sodium nitroprusside were constructed.

RESULTS

In the contraceptive users group, a reduction occurred in the maximum venodilation response to acetylcholine and sodium nitroprusside after 4 months of oral contraceptive use, but this difference was not statistically significant (P > 0.05). No significant changes were detected in maximum venodilation responses to acetylcholine and sodium nitroprusside at the 4-month time point in the control group.

CONCLUSION

This study found no significant impairment of endothelium-dependent or independent venodilation in healthy young women following oral contraceptive use. Further studies are necessary using the same methodology in a larger sample over a longer follow-up period.

Effects of Intralipid infusion on hemorheology and peripheral resistance in neonates and children

Deleterious microcirculatory effects of Intralipid (IL) infusion may be caused by hemorheological or vascular effects. The aim of this investigation was to study vascular and hemorheological effects of IL in preterm and fullterm neonates and children. Ten preterm newborns, 10 fullterm neonates, and 10 children received an initial infusion of IL (0.6 g/kg) over 4 h. Calf blood flow (venous occlusion plethysmography), blood pressure (Dinamap), whole blood and plasma viscosity (capillary viscometer), red blood cell deformability (rheoscope), and erythrocyte aggregation (aggregometer) were measured before and after administration of IL. Plasma triglyceride levels showed the greatest increase in preterm infants. Whole blood viscosity decreased by about 10% in all three groups because of a similar reduction in hematocrit. Red blood cell aggregation decreased by about 20% after IL infusion. Blood pressure rose by 10%, and peripheral blood flow declined by about 10% in the three groups. Vascular hindrance, a calculation of blood pressure divided by blood flow and viscosity, was raised by about 20%, suggesting marked vasoconstriction of peripheral arteries. Vasoconstriction rather than hemorheological changes during infusion of IL may play a crucial role in the pathogenesis of circulatory alterations in parenterally-fed neonates.

Direct effects of propofol on myocardial and vascular tissue from mature and immature rats

OBJECTIVE

To determine the effect of age on the direct myocardial and vascular effects of propofol in rats.

DESIGN

Randomized, prospective with repeated measures.

SETTING

University research laboratory.

PARTICIPANTS

Myocardial and aortic tissue from 12 immature (4-week-old) and 12 mature (16-week-old) male Sprague-Dawley rats.

INTERVENTIONS

Change in force of contraction was measured in isolated myocardial strips or in isolated descending thoracic aorta rings during exposure to propofol or intralipid.

MEASUREMENTS AND MAIN RESULTS

Propofol produced a dose-dependent decrease in vascular tone (p < 0.05). This effect was similar for intralipid. Propofol was more potent in the younger animals (EC(50), 5.3 microg/mL [confidence interval, 2.5 to 11.1] for 4-week-old and 26.6 microg/mL [confidence interval, 6.8 to 103.7] for 16-week-old rats; p < 0.05). In contrast, propofol produced a dose-dependent decrease in contractility (p = 0.001), whereas intralipid produced no decrease in contractility.

CONCLUSIONS

Although propofol does produce a dose-dependent decrease in contractility, this effect is similar at different ages. Propofol produces more direct vascular relaxation in the immature tissue. Propofol's direct cardiovascular effect and its indirect cardiovascular effects should be considered in the young and old, especially when cardiovascular reserve is limited.

Hemodynamic effects of lipids in humans

Evidence suggests lipid abnormalities may contribute to elevated blood pressure, increased vascular resistance, and reduced arterial compliance among insulin-resistant subjects. In a study of 11 normal volunteers undergoing 4-h-long infusions of Intralipid and heparin to raise plasma nonesterified fatty acids (NEFAs), we observed increases of blood pressure. In contrast, blood pressure did not change in these same volunteers during a 4-h infusion of saline and heparin. To better characterize the hemodynamic responses to Intralipid and heparin, another group of 21 individuals, including both lean and obese volunteers, was studied after 3 wk on a controlled diet with 180 mmol sodium/day. Two and four hours after starting the infusions, plasma NEFAs increased by 134 and 111% in those receiving Intralipid and heparin, P < 0.01, whereas plasma NEFAs did not change in the first group of normal volunteers who received saline and heparin. The hemodynamic changes in lean and obese subjects in the second study were similar, and the results were combined. The infusion of Intralipid and heparin induced a significant increase in systolic (13.5 +/- 2.1 mmHg) and diastolic (8.0 +/- 1.5 mmHg) blood pressure as well as heart rate (9.4 +/- 1.4 beats/min). Small and large artery compliance decreased, and systemic vascular resistance rose. These data raise the possibility that lipid abnormalities associated with insulin resistance contribute to the elevated blood pressure and heart rate as well as the reduced vascular compliance observed in subjects with the cardiovascular risk factor cluster.

Heterogeneity in hand veins responses to acetylcholine is not associated with polymorphisms in the G-protein beta3-subunit (C825T) and endothelial nitric oxide synthase (G894T) genes but with serum low density lipoprotein cholesterol

Vascular responses to acetylcholine (ACh) are notoriously variable, the reason for this phenomenon is unknown. We tested the hypothesis that the variability in venous response to acetylcholine may be associated with two recently identified genetic polymorphisms for proteins involved in the signal transduction pathway, i.e. the G-protein beta3-subunit (GNB3) and endothelial nitric oxide synthase (eNOS). The dorsal hand vein technique was used in 37 healthy subjects. Hand veins were preconstricted with the alpha1-adrenoceptor agonist phenylephrine and the venodilator response to local ACh infusion was measured with and without comedication of acetylsalicylic acid or co-infusion of N(G)-monomethyl-L-arginine (L-NMMA). In addition, all subjects received routine laboratory tests and 26 of them were genotyped for the C825T polymorphism of the GNB3 gene and for the G894T polymorphism of the eNOS gene. A striking variability in venous response to ACh was found with dilation observed in the low ACh concentration range and reduced dilation or even constriction at high concentrations. ACh-induced venodilation was mediated by muscarinic receptors and abolished in the presence of both acetylsalicylic acid and L-NMMA suggesting dependence on endothelium. We did not find any association of the variability in ACh response with GNB3 or eNOS allele status. On the other hand, a significant positive correlation between ACh responsiveness and low density lipoprotein-cholesterol status was detected. Two recently discovered gene polymorphisms are not responsible for the profound heterogeneity in venodilator response to ACh. Surprisingly, this variability appears to relate to the lipid status of the subjects. The exact nature of this new finding requires further study.

Free fatty acids/triglycerides increase ocular and subcutaneous blood flow

Elevated plasma free fatty acids (FFA) induce skeletal muscle insulin resistance and impair endothelial function. The aim of this study was to characterize the acute hemodynamic effects of FFA in the eye and skin. A triglyceride (Intralipid 20%, 1.5 ml/min)/heparin (bolus: 200 IU; constant infusion rate: 0.2 IU. kg(-1). min(-1)) emulsion or placebo was administered to 10 healthy subjects. Measurements of pulsatile choroidal blood flow with laser interferometry, retinal blood flow with the blue field entoptic technique, peak systolic and end diastolic blood velocity (PSV, EDV) in the ophthalmic artery with Doppler sonography, and subcutaneous blood flow with laser Doppler flowmetry were performed during an euglycemic somatostatin-insulin clamp over 405 min. Plasma FFA/triglyceride elevation induced a rise in pulsatile choroidal blood flow by 25 +/- 3% (P < 0.001) and in retinal blood flow by 60 +/- 23% (P = 0.0125). PSV increased by 27 +/- 8% (P = 0.001), whereas EDV was not affected. Skin blood flow increased by 149 +/- 38% (P = 0.001). Mean blood pressure and pulse rate remained unchanged, whereas pulse pressure amplitude increased by 17 +/- 5% (P = 0.019). Infusion of heparin alone had no hemodynamic effect in the eye or skin. In conclusion, FFA/triglyceride elevation increases subcutaneous and ocular blood flow with a more pronounced effect in the retina than in the choroid, which may play a role for early changes of ocular perfusion in the insulin resistance syndrome.

How to assess endothelial function in human blood vessels

This brief review discusses the ways, if and when available, to examine endothelium-dependent changes diameter in human blood vessels. It stresses the problems in ensuring proper matching between arteries (and veins) from different human sources. It briefly considers the evidence in vitro supporting the role of endothelium-derived nitric oxide, hyperpolarizing factor and contracting factors (including metabolites of arachidonic acid and endothelin). It emphasizes the difficulty in extrapolating observations obtained in isolated arteries (and veins) to the intact human circulation. The overall conclusion is that the interpretations derived from animal work apply to the human vasculature.