Carotid plaque composition differs between ethno-racial groups: an MRI pilot study comparing mainland Chinese and American Caucasian patients

OBJECTIVE

Ethnicity-based research may identify new clues to the pathogenesis of atherosclerotic disease. Therefore, we sought to determine whether carotid lesions differ between 20 Chinese and 20 Caucasian Americans by MRI.

METHODS AND RESULTS

Inclusion criteria were >50% stenosis as measured by duplex ultrasound and recent symptoms attributed to carotid artery disease. The patients were imaged in 2 centers (Beijing, China and Seattle, Wash) using a standardized protocol. Both carotid arteries were reviewed quantitatively (lumen, wall, outer wall, tissue components) and morphologically (lesion types, fibrous cap status). Significant differences between the Chinese and Americans were found for the mean size of the lipid/necrotic core (13.6 versus 7.8 mm2; P=0.002), percentage of slices with calcified type VII lesions (1.6 versus 12.4%; P=0.03), and percentage of slices with early type III lesions (19.3 versus 9.3%; P=0.02). Furthermore, the mean outer wall area in the common carotid artery was larger in the Chinese population (P=0.007).

CONCLUSIONS

This pilot study suggests that composition and morphology of atherosclerotic lesions in symptomatic carotid disease differ between ethno-racial groups. Quantitative MRI-based review of carotid atherosclerosis comparing plaque morphology and composition between ethno-racial groups is feasible, and future MRI studies may improve our understanding of the pathophysiology of this disease.

Differentiation of Intraplaque Versus Juxtaluminal Hemorrhage/Thrombus in Advanced Human Carotid Atherosclerotic Lesions by In Vivo Magnetic Resonance Imaging

Background— Intraplaque hemorrhage and juxtaluminal hemorrhage/thrombus may differ in cause and clinical implications. This study tested the hypothesis that MRI can distinguish between intraplaque hemorrhage and juxtaluminal hemorrhage/thrombus and investigated the association between hemorrhage and underlying lesion types.

Methods and Results— Twenty-six patients scheduled for carotid endarterectomy were imaged with a 1.5-T GE scanner by a multicontrast-weighted MRI technique. Hemorrhages were identified with previously established MRI criteria, and differentiations were made between intraplaque and juxtaluminal hemorrhage/thrombus. Corresponding histology was used to confirm the magnetic resonance findings. Tissues underlying areas of hemorrhage/thrombus were histologically categorized according to modified American Heart Association criteria. Of 190 matched sections, 140 contained areas of hemorrhage by histology, of which MRI correctly detected 134. The sensitivity and specificity for MRI to correctly identify cross sections that contained hemorrhage were 96% and 82%, respectively. Furthermore, MRI was able to distinguish juxtaluminal hemorrhage/thrombus from intraplaque hemorrhage with an accuracy of 96%. The distribution of lesion types underlying hemorrhages differed significantly ( P =0.004). Intraplaque hemorrhage had an underlying lipid-rich type IV/V lesion in 55% of histological sections, whereas juxtaluminal hemorrhage/thrombus had an underlying calcified lesion type VII in 70% of sections.

Conclusions— In vivo high-resolution MRI can detect and differentiate intraplaque hemorrhage from juxtaluminal hemorrhage/thrombus with good accuracy. The association of hemorrhage and lesion types suggests potential differences in origin. Noninvasive MRI therefore provides a possible tool for prospectively studying differences in origin of plaque hemorrhage and the association of plaque progression and instability.

Quantitative evaluation of carotid plaque composition by in vivo MRI

OBJECTIVE

This study evaluates the ability of MRI to quantify all major carotid atherosclerotic plaque components in vivo.

METHODS AND RESULTS

Thirty-one subjects scheduled for carotid endarterectomy were imaged with a 1.5T scanner using time-of-flight-, T1-, proton density-, and T2-weighted images. A total of 214 MR imaging locations were matched to corresponding histology sections. For MRI and histology, area measurements of the major plaque components such as lipid-rich/necrotic core (LR/NC), calcification, loose matrix, and dense (fibrous) tissue were recorded as percentages of the total wall area. Intraclass correlation coefficients (ICCs) were computed to determine intrareader and inter-reader reproducibility. MRI measurements of plaque composition were statistically equivalent to those of histology for the LR/NC (23.7 versus 20.3%; P=0.1), loose matrix (5.1 versus 6.3%; P=0.1), and dense (fibrous) tissue (66.3% versus 64%; P=0.4). Calcification differed significantly when measured as a percentage of wall area (9.4 versus 5%; P<0.001). Intrareader and inter-reader reproducibility was good to excellent for all tissue components, with ICCs ranging from 0.73 to 0.95.

CONCLUSIONS

MRI-based tissue quantification is accurate and reproducible. This application can be used in therapeutic clinical trials and in prospective longitudinal studies to examine carotid atherosclerotic plaque progression and regression.

Wedelolactone suppresses LPS-induced caspase-11 expression by directly inhibiting the IKK Complex

Caspase-11 is a key regulator of proinflammatory cytokine IL-1beta maturation and pathological apoptosis. Caspase-11 is not expressed in most tissues under normal condition, but highly inducible upon pathological stimulation such as in the presence of lipopolysaccharide (LPS). Here, we describe the identification and characterization of wedelolactone, a natural compound that inhibits LPS-induced caspase-11 expression in cultured cells by inhibiting NF-kappaB-mediated transcription. We demonstrate that wedelolactone is an inhibitor of IKK, a kinase critical for activation of NF-kappaB by mediating phosphorylation and degradation of IkappaBalpha.

Noise and motion correction in dynamic contrast-enhanced MRI for analysis of atherosclerotic lesions

Dynamic contrast-enhanced MRI of atherosclerotic vessels after contrast agent injection may provide unique information regarding lesion structure and vulnerability. The high-resolution images necessary for viewing lesion substructures, however, are often corrupted by patient motion and low signal-to-noise ratios, making pixel-level analyses difficult. This article presents a postprocessing method that enables pixel-level analysis of dynamic images by eliminating motion and enhancing image quality. Noise and motion correction are performed using optimal statistical methods under the assumption that noise and contrast agent dynamics are random processes. The method is demonstrated and validated on dynamic images of atherosclerotic plaques in human carotid arteries.

Phase evolution in cholesterol/DPPC monolayers: atomic force microscopy and near field scanning optical microscopy studies

A combination of atomic force microscopy (AFM) and near field scanning optical microscopy has been used to study domain formation in dipalmitoylphosphatidylcholine (DPPC)/cholesterol monolayers with cholesterol concentrations ranging from 0 to 50%. The results show a clear evolution from a mixture of liquid expanded and liquid condensed phases for cholesterol concentrations < 10% to a mixture of liquid expanded and two cholesterol-containing phases at intermediate concentrations, and finally to a single homogeneous liquid ordered phase for 33% cholesterol. Mixtures of the various phases are clearly identified by height differences in AFM and in some cases by fluorescence imaging for samples containing 0.5% BODIPY dye, which localizes preferentially in the more fluid phase. Note that fluorescence imaging, at least with the dye used here, is unable to distinguish between the cholesterol-rich and cholesterol-poor phases detected at intermediate cholesterol concentrations. The combination of fluorescence and AFM imaging provides a more complete picture of the phase evolution for cholesterol/DPPC monolayers than could be obtained by either technique alone, and presents substantial advantages over conventional fluorescence microscopy in that submicrometre-sized domains can be readily detected.

Solution structures of two FHA1-phosphothreonine peptide complexes provide insight into the structural basis of the ligand specificity of FHA1 from yeast Rad53

Rad53, a yeast checkpoint protein involved in regulating the repair of DNA damage, contains two forkhead-associated domains, FHA1 and FHA2. Previous combinatorial library screening has shown that FHA1 strongly selects peptides containing a pTXXD motif. Subsequent location of this motif within the sequence of Rad9, the target protein, coupled with spectroscopic analysis has led to identification of a tight binding sequence that is likely the binding site of FHA1: (188)SLEV(pT)EADATFVQ(200). We present solution structures of FHA1 in complex with this pT-peptide and with another Rad9-derived pT-peptide that has ca 30-fold lower affinity, (148)KKMTFQ(pT)PTDPLE(160). Both complexes showed intermolecular NOEs predominantly between three peptide residues (pT, +1, and +2 residues) and five FHA1 residues (S82, R83, S85, T106, and N107). Furthermore, the following interactions were implicated on the basis of chemical shift perturbations and structural analysis: the phosphate group of the pT residue with the side-chain amide group of N86 and the guanidino group of R70, and the carboxylate group of Asp (at the +3 position) with the guanidino group of R83. The generated structures revealed a similar binding mode adopted by these two peptides, suggesting that pT and the +3 residue Asp are the major contributors to binding affinity and specificity, while +1 and +2 residues could provide additional fine-tuning. It was also shown that FHA1 does not bind to the corresponding pS-peptides or a related pY-peptide. We suggest that differentiation between pT and pS-peptides by FHA1 can be attributed to hydrophobic interactions between the methyl group of the pT residue and the aliphatic protons of R83, S85, and T106 from FHA1.

Carotid atherosclerotic plaque: noninvasive MR characterization and identification of vulnerable lesions

Measurement of vessel stenosis by using ultrasonography or angiography remains the principal method for determining the severity of carotid atherosclerosis and the need for endarterectomy. The ipsilateral stroke rate, however--even in patients with severely stenotic vessels--is relatively low, which suggests that the amount of luminal narrowing may not represent the optimal means of assessing clinical risk. As a result, some patients may undergo unnecessary surgery. Improved imaging techniques are, therefore, needed to enable reliable identification of high-risk plaques that lead to cerebrovascular events. High-spatial-resolution magnetic resonance (MR) imaging has been described as one promising modality for this purpose, because the technique allows direct visualization of diseased vessel wall and can be used to characterize the morphology of individual atherosclerotic carotid plaques. The purpose of this report is to review the current state of carotid plaque MR imaging and the use of carotid MR to evaluate plaque morphology and composition.

High-Resolution magnetic resonance imaging of normal and atherosclerotic human coronary arteries ex vivo: discrimination of plaque tissue components

BACKGROUND

Noninvasive detection of plaque lipid and calcium in human atherosclerosis may have clinical utility, because the presence of each may be associated with increased risk of plaque disruption. Magnetic resonance imaging (MRI) has the potential to detect both plaque lipid and calcium. However, no previous studies have: 1) used an MR coil with sufficient resolution to image the components of human coronary arteries, 2) evaluated the utility of a combination of different MR contrast weightings in discriminating plaque components in human coronary arteries, or 3) used sensitive and specific histological stains for lipid and calcium to determine their MR image characteristics in human atherosclerosis.

METHODS

Using a custom-made surface coil on a whole-body, 1.5T MRI scanner, high resolution MR images were obtained from 22 nonatherosclerotic and atherosclerotic human coronary artery segments and then compared with histological sections stained for neutral lipid, calcium, and ribrous and cellular components.

RESULTS

With a multicontrast protocol using T1-, proton density-, and T2-weighted images, statistically significant differences were found among MR image contrast values for regions identified by histological stains as containing lipid only, calcium only, mixed lipid and calcium, or fibrous tissue. All four of these histologically defined region types could be differentiated from one another by a multicontrast MRI protocol. Of the 22 segments, 10 (45%) contained areas with combined plaque lipid and calcium; calcium would not have been recognized histologically in these regions without the use of a specific calcium stain.

CONCLUSIONS

These results demonstrate that multicontrast MRI can produce remarkably high-resolution images and can discriminate between clinically relevant components of the atherosclerotic vessel wall.

Kinetics and pH dependence of light-induced deprotonation of the Schiff base of rhodopsin: possible coupling to proton uptake and formation of the active form of Meta II

In this paper we first review what is known about the kinetics of Meta II formation, the role and stoichiometry of protons in Meta II formation, the kinetics of the light-induced changes of proton concentration, and the site of proton uptake. We then go on to compare the processes that lead to the deprotonation of the Schiff base in bacteriorhodopsin with rhodopsin. We point out that the similarity of the signs of the light-induced electrical signals from the two kinds of oriented pigment molecules could be explained by bacteriorhodopsin releasing a proton from its extracellular side while rhodopsin taking up a proton on its cytoplasmic side. We then examined the pH dependence of both the absorption spectrum of the unphotolyzed state and the amplitude and kinetics of Meta II formation in bovine rhodopsin. We also measured the effect of deuteration and azide on Meta II formation. We concluded that the pKa of the counter-ion to the Schiff base of bovine rhodopsin and of a surface residue that takes up a proton upon photolysis are both less than 4 in the unphotolyzed state. The data on pH dependence of Meta II formation indicated that the mechanisms involved are more complicated than just two sequential, isospectral forms of Meta II in the bleaching sequence. Finally we examined the evidence that, like in bacteriorhodopsin, the protonation of the Schiff bases's counter-ion (Glu113) is coupled to the changing of the pKa of a protonatable surface group, called Z for rhodopsin and tentatively assigned to Glu134. We conclude that there probably is such a coupling, leading to the formation of the active form of Meta II.

In vivo accuracy of multispectral magnetic resonance imaging for identifying lipid-rich necrotic cores and intraplaque hemorrhage in advanced human carotid plaques

BACKGROUND

High-resolution MRI has been shown to be capable of identifying plaque constituents, such as the necrotic core and intraplaque hemorrhage, in human carotid atherosclerosis. The purpose of this study was to evaluate differential contrast-weighted images, specifically a multispectral MR technique, to improve the accuracy of identifying the lipid-rich necrotic core and acute intraplaque hemorrhage in vivo.

METHODS AND RESULTS

Eighteen patients scheduled for carotid endarterectomy underwent a preoperative carotid MRI examination in a 1.5-T GE Signa scanner using a protocol that generated 4 contrast weightings (T1, T2, proton density, and 3D time of flight). MR images of the vessel wall were examined for the presence of a lipid-rich necrotic core and/or intraplaque hemorrhage. Ninety cross sections were compared with matched histological sections of the excised specimen in a double-blinded fashion. Overall accuracy (95% CI) of multispectral MRI was 87% (80% to 94%), sensitivity was 85% (78% to 92%), and specificity was 92% (86% to 98%). There was good agreement between MRI and histological findings, with a value of kappa=0.69 (0.53 to 0.85).

CONCLUSIONS

Multispectral MRI can identify the lipid-rich necrotic core in human carotid atherosclerosis in vivo with high sensitivity and specificity. This MRI technique provides a noninvasive tool to study the pathogenesis and natural history of carotid atherosclerosis. Furthermore, it will permit a direct assessment of the effect of pharmacological therapy, such as aggressive lipid lowering, on plaque lipid composition.

Effects of prolonged intensive lipid-lowering therapy on the characteristics of carotid atherosclerotic plaques in vivo by MRI: a case-control study

High-resolution magnetic resonance imaging (MRI) with flow suppression not only provides useful information on luminal and wall areas of the carotid artery but also can identify the principal tissue components of the carotid atherosclerotic plaque. The effects of intensive lipid-lowering therapy on these MRI tissue characteristics were examined in patients with coronary disease (CAD). Eight CAD patients who have been receiving intensive lipid-lowering treatment (niacin 2.5 g/d, lovastatin 40 mg/d, and colestipol 20 g/d) for 10 years in the Familial Atherosclerosis Treatment Study (FATS) follow-up were randomly selected from among 60 such treated patients. Eight CAD patients who were matched to the treated patients for age (+/-3 years), baseline low density lipoprotein (+/-5 mg/dL), and triglycerides (+/-50 mg/dL) but who had never been treated with lipid-lowering drugs were selected as controls. For each of these 32 carotid arteries, luminal and plaque areas were measured by planimetry, in a blinded protocol, from the magnetic resonance image that showed most plaque. Fibrous tissue, calcium, and lipid deposits were identified on the basis of established criteria. Plaque composition was estimated as a fraction of total planimetered area. Patients treated with 10-year intensive lipid-lowering therapy, compared with control subjects, had significantly lower low density lipoprotein cholesterol levels (84 versus 158 mg/dL, respectively; P<0.001) and higher high density lipoprotein cholesterol levels (51 versus 37 mg/dL, respectively; P<0.001). As a group, treated patients, compared with untreated control subjects, had a smaller core lipid area (0.7 versus 10.2 mm(2), respectively; P=0.01) and lipid composition (1% versus 17%, respectively). Group differences in luminal area (55 [treated] versus 44 [control] mm(2), P=NS) and plaque area (58 [treated] versus 64 [control] mm(2), P=NS) tended to favor treatment. MRI appears useful for estimating carotid plaque size and composition. Hyperlipidemic CAD patients frequently (97%) have at least moderate (>/=40% area stenosis) carotid plaque. In this case-control study, prolonged intensive lipid-lowering therapy is associated with a markedly decreased lipid content, a characteristic of clinically stable plaques.

[Rat keratinocyte primary cultures based on conductive polypyrrole primary cell culture technique]

Orthogonal experimental design has been applied to study the suitable cell culture medium and condition of conductive polypyrrole on rat keratinocyte cell cultures. The results showed that one thousand milliliters of complete minimum essential medium(CMEM) which contained 900 ml minimum essential medium(MEM), 10% fetal bovine serum(FBS), 1% NEAA, 6 ml insulin and 10 mg hydrocortisone was fit for keratinocyte cell culture. And the conductive polypyrrole obtained with 10 mA current density for 100 second switching times, given 100 mV electrical stimulation voltage for 2 hours, would stimulate the growth of rat keratinocyte cell in vitro cultures. The cell density under culture conditions described above was 1.30 times as high as that under routine culture conditions.

Atomic force microscopy studies of ganglioside GM1 domains in phosphatidylcholine and phosphatidylcholine/cholesterol bilayers

The distribution of ganglioside in supported lipid bilayers has been studied by atomic force microscopy. Hybrid dipalmitoylphosphatidylcholine (DPPC)/dipalmitoylphosphatidylethanolamine (DPPE) and (2:1 DPPC/cholesterol)/DPPE bilayers were prepared using the Langmuir Blodgett technique. Egg PC and DPPC bilayers were prepared by vesicle fusion. Addition of ganglioside GM1 to each of the lipid bilayers resulted in the formation of heterogeneous surfaces that had numerous small raised domains (30--200 nm in diameter). Incubation of these bilayers with cholera toxin B subunit resulted in the detection of small protein aggregates, indicating specific binding of the protein to the GM1-rich microdomains. Similar results were obtained for DPPC, DPPC/cholesterol, and egg PC, demonstrating that the overall bilayer morphology was not dependent on the method of bilayer preparation or the fluidity of the lipid mixture. However, bilayers produced by vesicle fusion provided evidence for asymmetrically distributed GM1 domains that probably reflect the presence of ganglioside in both inner and outer monolayers of the initial vesicle. The results are discussed in relation to recent inconsistencies in the estimation of sizes of lipid rafts in model and natural membranes. It is hypothesized that small ganglioside-rich microdomains may exist within larger ordered domains in both natural and model membranes.

Detection and characterization of DNA adducts of 3-methylindole

The pneumotoxin 3-methylindole is metabolized to the reactive intermediate 3-methyleneindolenine which has been shown to form adducts with glutathione and proteins. Reported here is the synthesis, detection, and characterization of nucleoside adducts of 3-methylindole. Adducted nucleoside standards were synthesized by the reaction of indole-3-carbinol with each of the four nucleosides under slightly acidic conditions, which catalyze the dehydration of indole-3-carbinol to 3-methyleneindolenine. Following solid phase extraction, the individual adducts were infused via an electrospray source into an ion trap mass spectrometer for molecular weight determination and characterization of the fragmentation patterns. The molecular ions and fragmentation of the dGuo, dAdo, and dCyd adducts were consistent with nucleophilic addition of the exocyclic primary amine of the nucleosides to the methylene carbon of 3-methyleneindolenine. The apparent chemical preference of this addition lead primarily to dAdo and dGuo adducts, with substantially less of the dCyd adduct formed. No adduct with dThd was detected. The adducts were purified by HPLC and subsequent NMR analysis of the dGuo and dCyd adducts confirmed the proposed structures. Mass spectral fragmentation of the three adducts produced primarily two ions which were the result of the loss of either the 3-methylindole moiety or the sugar. On a triple quadrupole electrospray mass spectrometer, the neutral loss of the sugar, [M + H - 116](+), was utilized for selected reaction monitoring of the calf thymus DNA adducts, formed by incubations of 3-methylindole with various microsomes (rat liver, goat lung, and human liver). All three adducts were detected from each of the microsomal incubations, following extraction and cleavage of the DNA to the nucleoside level. The dGuo adduct was the primary adduct formed, with smaller amounts of the dAdo and dCyd adducts. Rat hepatocytes incubated with 3-methylindole produced the same three adducts, in approximately the same proportions, while no adducts were detected in untreated hepatocytes. Microsomal incubations in the presence of ([3-(2)H(3)]-methyl)indole confirmed the formation and identification of the adducts as well as the fragmentation patterns. These results demonstrate that bioactivated 3-methylindole forms specific adducts with exogenous or intact cellular DNA, and indicates that 3-methylindole may be a potential mutagenic and/or carcinogenic chemical.

Comparison of carotid vessel wall area measurements using three different contrast-weighted black blood MR imaging techniques

Measuring carotid artery plaque burden from MRI is a reliable method for monitoring regression and progression of atherosclerosis. However, to measure all available images would be very time consuming, and in practice the image quality (IQ) of these images may be inconsistent, which can directly impact the quality of measurement. It is hypothesized that if IQ is comparable among different contrast weighted images, then carotid artery area measurements obtained from different contrast images of the same location will produce identical results. To test this, T1, proton density and T2 weighted images were acquired from ten patients (51 +/- 7 years old). Carotid lumen and vessel wall area was measured using a custom designed software program. The results showed strong agreement evidenced with only small differences on both lumen (mean: 40.5 mm(2)) and wall (mean: 52.6 mm(2)) area measurement among different weighted images. The maximum absolute mean differences are less than 2.7 mm(2) and 4.4 mm(2), and 90(th) percentile of the absolute differences are 5.6 mm(2) and 8.2 mm(2) respectively. In conclusion, different contrast weighted images with high and comparable IQ will yield similar results in lumen and vessel wall area measurement. At each matched location, it is recommended that the image with the highest IQ be used for area measurement.

A multi-scale method for automatic correction of intensity non-uniformity in MR images

In this paper, a novel multi-scale method for coil sensitivity profile correction is presented based on wavelet transform. A magnetic resonance (MR) image can be decomposed into two spaces by the wavelet transform: approximate space and residual space. The approximate templates in approximate space can be thought of as multi-scale sensitivity profiles of the surface coil for coil correction. When we choose a suitable filter for decomposition, one of the sensitivity profiles should be optimal among the multi-scale sensitivity profiles. The optimal sensitivity profile can be chosen automatically by an analysis of the contents of the two spaces. The multi-scale method does not rely on any data other than the image generated by the MR scanner. The experiment showed promising results based on one-dimensional simulation and images of phantom and human images.