Arve Dahl

Increased Expression of Visfatin in Macrophages of Human Unstable Carotid and Coronary Atherosclerosis Possible Role in Inflammation and Plaque Destabilization

Background— Although the participation of inflammation in atherogenesis is widely recognized, the identification of the different components has not been clarified. In particular, the role of inflammation in plaque destabilization is not fully understood. Methods and Results— Our main findings were as follows: (1) In a microarray experiment, we identified visfatin, one of the most recently identified adipokines, as a gene that was markedly enhanced in carotid plaques from symptomatic compared with plaques from asymptomatic individuals. This finding was confirmed when carotid plaques from 7 patients with asymptomatic and 14 patients with symptomatic lesions were examined with real-time reverse transcription polymerase chain reaction. (2) Immunohistochemistry showed that visfatin was localized in areas that were rich in lipid-loaded macrophages. (3) The relationship between visfatin and unstable lesions was also found in patients with coronary artery disease, demonstrating a strong visfatin immunostaining in lipid-rich regions within the material obtained at the site of plaque rupture in patients with acute myocardial infarction. (4) Both oxidized low-density lipoprotein and tumor necrosis factor-&agr; increased visfatin expression in THP-1 monocytes, with a particularly enhancing effect when these stimuli were combined. (5) Visfatin increased matrix metalloproteinase-9 activity in THP-1 monocytes and tumor necrosis factor-&agr; and interleukin-8 levels in peripheral blood mononuclear cells. Both of these effects were abolished when insulin receptor signaling was blocked. Conclusions— Our findings suggest that visfatin should be regarded as an inflammatory mediator, localized to foam cell macrophages within unstable atherosclerotic lesions, that potentially plays a role in plaque destabilization.

A comparison of transcranial Doppler and cerebral blood flow studies to assess cerebral vasoreactivity.

Background and Purpose The aim of this study was to determine the ability of transcranial Doppler ultrasonography when used to assess cerebral vasoreactivity. The results of this method were compared with regional cerebral blood flow measurements. Methods Forty-three patients with symptoms suggesting cerebrovascular disease took part Transcranial Doppler findings in the middle cerebral arteries were compared with regional cerebral blood flow in the corresponding perfusion territories before and after acetazolamide administration. Results There was a significant positive correlation between the absolute increase in cerebral blood flow in milliliters per 100 g per minute and the percent increase in velocity (r=0.63). The right-left, side-to-side difference of the acetazolamide response obtained by the two methods also showed a positive correlation (r=0.80). Control limits obtained from healthy subjects were used for both the blood flow increase (absolute values and asymmetry in absolute values) and the velocity increase (percent increase and asymmetry in percent increase). The two methods then agreed in their evaluation of vasoreactivity in 74 (86%) of the 86 middle cerebral artery perfusion territories; 20 (23%) were assessed by both methods as having a reduced vasodilatory reserve. Eleven hemispheres with a slightly reduced regional cerebral blood flow response to acetazolamide were not detected by transcranial Doppler, whereas all territories with a marked reduction were identified by Doppler. Only one hemisphere with a normal cerebral blood flow increase after acetazolamide administration was assessed by Doppler as having reduced vasoreactivity. Conclusions Transcranial Doppler and the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.

Effect of nitroglycerin on cerebral circulation measured by transcranial Doppler and SPECT.

We used a combination of transcranial Doppler ultrasonography and single-photon emission computed tomography to noninvasively assess changes in the diameter of the middle cerebral artery induced by sublingual nitroglycerin in 10 healthy subjects. Nitroglycerin reduced mean blood flow velocities without concurrently changing regional cerebral blood flow in the perfusion territory of this vessel. Our results strongly suggest that nitroglycerin causes vasodilatation of the basal intracranial arteries.

Effect of acetazolamide on cerebral artery blood velocity and regional cerebral blood flow in normal subjects.

SummaryThe effect of intravenous acetazolamide L g on cerebral artery blood velocity and regional blood flow (rCBF) was investigated in eight normal subjects. Blood velocity was measured with 2 MHz pulsed Doppler in the proximal segments of the middle, anterior and posterior cerebral artery (MCA, ACA, and PCA) and in the distal extracranial internal carotid artery (ICA). The rCBF in the regions of interest tentatively corresponding to the perfusion territories of these vessels was estimated using133Xe inhalation and a rapidly rotating single photon emission computer tomograph.Both blood velocity and rCBF increased after acetazolamide. There was no significant difference between the percentage ICA blood velocity increase (22 ± 12%) and the percentage rCBF increase in the ICA region of interest (25 ± 9%). In the MCA, ACA, and PCA, however, blood velocity increased more (mean increase 36–42%) than the rCBF in the corresponding regions of interest (mean increase 24–26%). These differences were highly significant suggesting a direct and site specific effect of acetazolamide in narrowing the lumen of the proximal MCA, ACA, and PCA, but not of the extracranial ICA. We also propose that the effect of acetazolamide induces reciprocal changes in the extent of adjacent perfusion territories in individual brain hemispheres.Data compiled from all subjects investigated at two very different perfusion levels (before and after acetazolamide) revealed a significant positive correlation between blood velocity and rCBF.

Blood velocity and regional blood flow in defined cerebral artery systems

SummaryCerebral artery blood velocity and regional blood flow (rCBF) were investigated in 17 normal subjects. Blood velocity was measured with 2 MHz pulsed Doppler ultrasound in the proximal segments of the middle, anterior and posterior cerebral artery (MCA, ACA, and PCA) and in the distal extracranial internal carotid artery (ICA). The rCBF in the regions of interest tentatively corresponding to the perfusion territories of these vessels was estimated using133Xe inhalation and a rapidly rotating single photon emission computer tomograph.Concomitant capnograph recordings showed that the end-expiratory pCO2 was higher during the rCBF than during the blood velocity examinations. This difference was highly significant. While there was no significant correlation between blood velocity and rCBF when these clear differences in pCO2 were disregarded, we did find significant positive correlations when the data were normalized to a standard pCO2 (5.3 kPa) using accepted formulas. The best correlation was found for the MCA (r=0.630, p<0.001) and the PCA (r=0.73, p < 0.001), with a lower correlation in the ACA (r=0.49, p<0.01) and the ICA (r=0.41, p<0.05). The estimated blood velocity (V) given rCBF=0 was not significantly different from 0.The results support the validity of expressing the relationship between blood velocity (V) and rCBF in defined cerebral artery systems as: V=1/60(rCBF) T (A)−1, where A represents the area of the lumen of the vessel segment where the velocity is being measured, and T denotes the size of the brain region being perfused from this artery.

Cerebral Vasoreactivity Assessed With Transcranial Doppler and Regional Cerebral Blood Flow Measurements: Dose, Serum Concentration, and Time Course of the Response to Acetazolamide

BACKGROUND AND PURPOSE To improve the assessment of cerebral vasoreactivity using acetazolamide (ACZ), we studied the time course of the response and the relationship between dose, response, and serum concentration. METHODS Blood flow velocities were measured with the use of transcranial Doppler ultrasonography in one of the middle cerebral arteries of 48 healthy subjects after the intravenous administration of 1 to 1.6 g ACZ. In 34 subjects (group 1), velocities were measured every second minute to detect the maximum middle cerebral artery velocity increase. We also measured regional cerebral blood flow using single-photon emission computed tomography in 27 of the subjects in group 1 before and approximately 15 to 20 minutes after the ACZ injection. The serum concentration of ACZ was measured in 15 subjects. In the remaining 14 subjects (group 2), middle cerebral artery velocity measurements were made 10, 25, 30, and 45 minutes after ACZ administration to obtain information regarding the late time course of the response. RESULTS In group 1 the plateau phase of the velocity response was reached 8 to 15 minutes after ACZ administration. A large range of velocity increase was observed, and a significant correlation was found between the maximum velocity increase and the dose and serum concentration of ACZ. In group 2 subjects, maximum velocities were maintained 30 minutes after the injection, but after 45 minutes velocities had decreased to 68% of their highest level. No significant relationship was found between dose or serum concentration of ACZ and the regional cerebral blood flow increase. The velocity increase after ACZ was similar in both older and younger subjects. CONCLUSIONS This study shows that cerebral vasoreactivity is best assessed 10 to 30 minutes after ACZ administration and that the dose should probably exceed 15 mg/kg if a maximum vasodilatory response in the cerebral circulation is to be obtained.

Simultaneous Assessment of Vasoreactivity Using Transcranial Doppler Ultrasound and Cerebral Blood Flow in Healthy Subjects

Blood flow velocities in both middle cerebral arteries and regional cerebral blood flow in their perfusion territories were measured simultaneously in 36 healthy subjects. In 20 subjects, the measurements were first performed under basal conditions and then repeated 15–20 min after an intravenous injection of 1 g of acetazolamide. Reproducibility of simultaneous blood flow and velocity measurements was tested by examining 16 subjects on two occasions under basal conditions with an interval of 20 min. Relatively good reproducibility was found for repeated measurements of velocity and blood flow, being best when side-to-side asymmetry was assessed. The increase in blood flow velocities after acetazolamide was symmetrical (right side, 34.2%; and left side, 35.5%), and the velocity increase was significantly correlated with basal values. The increase in cerebral blood flow was also symmetrical (right side, 29.8%; left side, 30.1%) but not correlated with basal flow values. No significant relationship was found between velocity increase and increase in regional cerebral blood flow. This finding is probably not only due to methodological inaccuracies but may suggest that acetazolamide has an effect on the diameter of the middle cerebral artery or on the magnitude of this arterys perfusion territory. This study supports the use of acetazolamide for assessing cerebral vasoreactivity following the definition of lower limits for velocity and flow increase and for asymmetry of the response.

A comparison of regional cerebral blood flow and middle cerebral artery blood flow velocities : simultaneous measurements in healthy subjects

Blood flow velocities were measured in both middle cerebral arteries (MCAs) of 36 healthy subjects using transcranial Doppler ultrasound. Measurements were first made using a hand-held probe. Velocities were then studied bilaterally with fixed probes under resting conditions and during simultaneous regional CBF (rCBF) measurements. A significant (p < 0.05) positive correlation was found between MCA flow velocities and rCBF in the estimated perfusion territory of this artery. The correlation coefficient was highest when the measurements were performed simultaneously (p < 0.001) or when velocities recorded with a hand-held probe were adjusted to take into account the significant velocity increase induced by the CBF study situation. The increased velocities during CBF measurements cannot be fully explained by the moderate but significant Pco2 increase. Other possible mechanisms are increased blood flow due to mental activation or MCA vasoconstriction secondary to stimulation of the sympathetic nervous system. The effect of mental activation and Pco2 differences should therefore be considered when comparing the results of repeated velocity and CBF measurements.

Cluster Headache: Transcranial Doppler Ultrasound and rCBF Studies

Transcranial Doppler and rCBF examinations were carried out in 25 cluster headache patients. Spontaneous and glyceryl trinitrate (nitroglycerin) provoked attacks were accompanied by a bilateral decrease in middle cerebral artery blood flow velocities. This decrease was more pronounced on the symptomatic side but the difference did not reach statistical significance. Mean hemispheric blood flow and rCBF were within normal limits during provoked attacks and similar to those found when patients were attack-free. During cluster periods middle cerebral artery velocities were significantly higher on the symptomatic side. Glyceryl trinitrate caused a bilateral middle cerebral artery velocity decrease which was significantly greater on the symptomatic side. Attacks provoked by glyceryl trinitrate appeared to begin when the vasodilatory effect of this substance was receding.

Soluble CD36 in Plasma Is Increased in Patients With Symptomatic Atherosclerotic Carotid Plaques and Is Related to Plaque Instability

Background and Purpose— The risk for cardiovascular events is related to the composition and stability of an atherosclerotic plaque driven by inflammation and deposition of lipids. Scavenger receptors are a family of cell surface receptors involved in lipid uptake and inflammation. Recently, we found that soluble CD36 is increased in plasma from patients with diabetes strongly correlated with insulin resistance. Methods— We tested whether soluble CD36 is a marker of plaque stability in patients with high-grade internal carotid stenoses (n=62). The patients were classified according to plaque symptomatology and plaque echogenicity on ultrasound examination. Results— When patients were divided into 3 groups according to the latest clinical symptoms from plaques (ie, symptoms within the last 2 months [n=16], symptoms within the last 2 to 6 months [n=15], or asymptomatic [n=31]), the former group had significantly raised plasma levels of soluble CD36 as compared with the other 2 groups. In contrast, we found no differences in plasma levels of C-reactive protein, β-thromboglobulin, lipid parameters, or HbA1C between these groups. The patients with echolucent carotid plaques (n=20) tended to have higher soluble CD36 levels in plasma compared with those with echogenic/heterogenic plaque (n=39; P=0.087). By immunohistochemistry, CD36 was localized to macrophages-rich area of intima within the atherosclerotic lesion. Conclusion— We propose that sCD36 may be a marker of plaque instability and symptomatic carotid atherosclerosis, possibly at least partly as a result of CD36 release to the circulation from the foam cells within the atherosclerotic lesion.