Rick D. Plumb

Functional consequences of endothelial nitric oxide synthase uncoupling in congestive cardiac failure.

Background—Impaired endothelium-mediated vasodilatation (EMVD) in congestive cardiac failure (CCF) has been linked to decreased nitric oxide (NO) bioavailability because of its interaction with vascular superoxide (O2·−), derived predominantly from NAD(P)H-dependent oxidases. When uncoupled from essential cofactors, endothelial nitric oxide synthase (eNOS) produces O2·−. We studied the functional consequences of eNOS uncoupling in relation to EMVD in patients with CCF. Methods and Results—We employed the platelet as a compartmentalized ex-vivo model to examine O2·− and NO production. When eNOS is functioning normally, incorporation of N&ohgr;-Nitro-l-Arginine methyl ester (L-NAME, 1 mmol/L), results in increased O2·− detection, as inhibition of NO production prevents NO scavenging of O2·−. This was observed in controls and 9 of the CCF patients, in whom O2·− detection increased by 63% and 101%, respectively. In the remaining 9 CCF patients, incorporation of L-NAME reduced O2·− production by 39%, indicating O2·− production by eNOS uncoupling. Detection of platelet-derived NO was significantly greater in eNOS-coupled platelets compared with the uncoupled group (2.8±1.4 versus 0.9±0.4 pmol/108 platelets, P =0.04). Endothelium-dependent and -independent vasodilator responses to acetylcholine and sodium nitroprusside recorded using venous occlusion plethysmography were significantly impaired in patients exhibiting eNOS uncoupling. Conclusions—This study provides first evidence that platelet eNOS can become uncoupled in human CCF. Impaired endothelium-dependent and -independent vasodilator responses and diminished platelet-derived NO production occurred in association with enzyme uncoupling.

Microcirculatory hemodynamics and endothelial dysfunction in systemic lupus erythematosus.

Objective—Impaired flow-mediated dilation (FMD) occurs in disease states associated with atherosclerosis, including SLE. The primary hemodynamic determinant of FMD is wall shear stress, which is critically dependent on the forearm microcirculation. We explored the relationship between FMD, diastolic shear stress (DSS), and the forearm microcirculation in 32 patients with SLE and 19 controls. Methods and Results—DSS was calculated using (mean diastolic velocity×8×blood viscosity)/baseline brachial artery diameter. Doppler velocity envelopes from the first 15 seconds of reactive hyperemia were analyzed for resistive index (RI), and interrogated in the frequency domain to assess forearm microvascular hemodynamics. FMD was significantly impaired in SLE patients (median, 2.4%; range, −2.1% to 10.7% versus median 5.8%; range, 1.9% to 14%; P<0.001). DSS (dyne/cm2) was significantly reduced in SLE patients (median, 18.5; range, 3.9 to 34.0 versus median 21.8; range, 14.1 to 58.7; P=0.037). A strong correlation between FMD and DSS, rs=0.65, P=0.01 was found. Postischemic RI was not significantly different between the 2 groups; however, there were significant differences in the power-frequency spectrums of the Doppler velocity envelopes (P<0.05). Conclusions—These data suggest that in SLE, altered structure and function of the forearm microcirculation contributes to impaired FMD through a reduction in shear stress stimulus.

Nitric oxide modulation of ophthalmic artery blood flow velocity waveform morphology in healthy volunteers.

Quantitative analysis of the arterial pressure pulse waveform recorded by applanation tonometry of the radial artery can track NO (nitric oxide)-mediated modulation of arterial smooth muscle tone. The changes in pressure pulse waveform morphology result from pulse wave reflection arising predominantly from smaller arteries and arterioles. Employing Doppler ultrasound to record the spectral flow velocity waveform in the ophthalmic artery, we studied the effects of NO modulation on waveforms recorded in the proximity of the terminal ocular microcirculatory bed. In healthy young men (n=10; age 18-26 years), recordings were made at baseline, following 300 mug of sublingual GTN (glyceryl trinitrate) and during the intravenous infusion of 0.25 and 0.5 mg/kg of L-NAME (N(G)-nitro-L-arginine methyl ester). Peaks (P1, P2 and P3) and nodes (N1, N2 and N3) on the arterial flow velocity waveform were identified during the cardiac cycle and employed to quantify wave shape change in response to the haemodynamic actions of the pharmacological interventions. The administration of GTN resulted in a significant (P<0.05) increase in heart rate without significant alteration in blood pressure. At the doses employed, L-NAME did not significantly alter systemic haemodynamics. With the exception of peak Doppler systolic velocity, all other peaks and nodes decreased significantly in response to GTN (P<0.05 for all points compared with baseline). In response to the administration of L-NAME, all peaks and nodes decreased significantly (P<0.05 for all points compared with baseline). The resistive index, a ratio calculated from the peak and trough flow velocities employed to assess change in flow resistance, increased significantly in response to GTN (0.77 at baseline compared with 0.85; P<0.05). Quantification of changes in the flow velocity spectral waveform during the cardiac cycle sensitively identified NO modulation of smooth muscle tone prior to alteration in systemic haemodynamics. Focusing on the resistive index, which identifies isolated points on the waveform describing the excursions of flow, may provide misleading information in relation to the haemodynamic effects of drug interventions.

Colour Doppler ultrasound of the ocular circulation in patients with systemic lupus erythematosus identifies altered microcirculatory haemodynamics

We assessed whether quantitative analysis of Doppler flow velocity waveforms is able to identify subclinical microvascular abnormalities in SLE and whether eigenvector analysis can detect changes not detectable using the resistive index (RI). Fifty-four SLE patients with no conventional cardiovascular risk factors, major organ involvement or retinopathy were compared to 32 controls. Flow velocity waveforms were obtained from the ophthalmic artery (OA), central retinal artery (CRA) and common carotid artery (CA). The waveforms were analysed using eigenvector decomposition and compared between groups at each arterial site. The RI was also determined. The RI was comparable between groups. In the OA and CRA, there were significant differences in the lower frequency sinusoidal components (P < 0.05 for each component). No differences were apparent in the CA between groups. Eigenvector analysis of Doppler flow waveforms, recorded in proximity of the terminal vascular bed, identified altered ocular microvascular haemodynamics in SLE. Altered waveform structure could not be identified by changes in RI, the traditional measure of downstream vascular resistance. This analytical approach to waveform analysis is more sensitive in detecting preclinical microvascular abnormalities in SLE. It may hold potential as a useful tool for assessing disease activity, response to treatment, and predicting future vascular complications.

Statins have beneficial effects on platelet free radical activity and intracellular distribution of GTPases in hyperlipidaemia

In addition to lowering cholesterol, statins may alter endothelial release of the vasodilator NO and harmful superoxide free radicals. Statins also reduce cholesterol intermediates including isoprenoids. These are important for post-translational modification of substances including the GTPases Rho and Rac. By altering the membrane association of these molecules, statins affect intracellular positioning and hence activity of a multitude of substances. These include eNOS(endothelial NO synthase), which produces NO (inhibited by Rho), and NADPH oxidase, which produces superoxide (dependent on Rac). Statins may improve endothelial function by enhancing production of NO while decreasing superoxide production. A total of 40 hypercholesterolaemic patients were randomized to treatment with either atorvastatin or placebo; 20 normolipidaemic patients were also studied. Platelet nitrite, NO and superoxide were examined as was the cellular distribution of the GTPases Rho and Rac at baseline and after 8 weeks of treatment.Following atorvastatin therapy, platelet NO was increased (3.2 pmol/10(8) platelets) and superoxide output was attenuated [-3.4 pmol min(-1) (10(8) platelets)(-1)] when compared with placebo. The detection of both Rho and Rac was significantly reduced in the membranes of platelets, implying reduced activity. In conclusion, the results of the present study show altered NO/superoxide production following statin therapy. A potential mechanism for this is the change in the distribution of intracellular GTPases, which was considered to be secondary to decreases in isoprenoid intermediates, suggesting that the activity of the former had been affected by atorvastatin.

Wave reflection signatures: identifying early microvascular abnormalities in type 2 diabetes

Microvascular changes occur early in diabetes mellitus. Doppler ultrasound enables non-invasive identification of ocular microvascular haemodynamics through interrogation of blood flow velocity waveforms. Wave decomposition permits the spectrum of sinusoidal components comprising flow velocity waveforms to be quantified. We hypothesised that comprehensive interrogation of waveforms would be more sensitive in identifying microvascular abnormalities than traditional analysis employing the resistive index. Thirty-four subjects with type 2 diabetes and 20 healthy controls between 30 and 70 years old were recruited. Doppler flow velocity waveform signals were captured from the ophthalmic and carotid arteries under standardised conditions. The signals were analysed using a wave decomposition algorithm and the sinusoidal components of average waveforms were compared between groups at both arterial sites. The diabetes group displayed significant differences in the lower frequency sinusoidal components of both the ophthalmic artery (p<0.001) and, to a lesser extent, the carotid artery (p<0.05) waveforms compared with controls, with no difference noted in the resistive index at either site. We conclude that wave decomposition analysis of Doppler flow velocity waveforms, recorded in proximity of the terminal vascular bed of interest, can identify subtle microvascular haemodynamic abnormalities not detected by traditional methods of analysis. Br J Diabetes Vasc Dis 2011;11:243-248