Elastin and calcium rather than collagen or lipid content are associated with echogenicity of human carotid plaques.
OBJECTIVE
Echolucent carotid plaques have been associated with increased risk for stroke. Histological studies suggested that echolucent plaques are hemorrhage- and lipid-rich, whereas echogenic plaques are characterized by fibrosis and calcification. This is the first study to relate echogenicity to plaque composition analyzed biochemically.


METHODS
Echogenicity of human carotid plaques was analyzed by standardized high-definition ultrasound and classified into echolucent, with gray-scale median (GSM) <32 and echogenic with GSM > or =32. The biochemical composition of the plaques was assessed by fast-performance liquid chromotography and high-performance thin-layer chromotography.


RESULTS
As assessed biochemically (milligrams per gram [mg/g]), echolucent plaques contained less hydroxyapatite (43.8 [SD 41.2] mg/g versus 121.6 [SD 106.2] mg/g; P=0.018), more total elastin (1.7 [SD 0.4] mg/g versus 1.2 [SD 0.4] mg/g; P=0.008), and more intermediate-size elastin forms (1.2 [SD 0.3] mg/g versus 0.8 [SD 0.4] mg/g; P=0.018). There was no difference in collagen amount between echogenic and echolucent plaques, neither biochemically (15.3 [SD 3.7] mg/g versus 14.4 [SD 3.4] mg/g) nor histologically (13.4 [SD 4.9] % versus 13.0 [SD 5.6] %). Cholesterol esters, unesterified cholesterol, and triglycerides were increased in plaques associated with symptoms (22.5 [SD 23.3] mg/g versus 13.3 [SD 3.2]; P=0.04), but no differences were detected between echolucent and echogenic plaques (13.5 [SD 4.0] versus 20.2 [SD 21.5] mg/g). Similar results were obtained by Oil Red O staining (symptomatic 7.6 [SD 4.7] % versus asymptomatic 4.2 [SD 3.6] %; P=0.03; echolucent 5.9 [SD 4.1] % versus echogenic 5.0 [SD 4.0] % of area).


CONCLUSIONS
Echogenicity of carotid plaques is mainly determined by their elastin and calcium but not collagen or lipid content. In addition, echolucency is associated to higher elastin content.
Gonçalves
Isabel
I
Department of Medicine, Wallenberg Laboratory, University of Lund, Entrance 46, 1st Floor, Malmö University Hospital, SE-20502 Malmö, Sweden. isabel.goncalves@medforsk.mas.lu.se
Lindholm
Marie W
MW
Pedro
Luís M
LM
Dias
Nuno
N
Fernandes e Fernandes
José
J
Fredrikson
Gunilla Nordin
GN
Nilsson
Jan
J
Moses
Jonatan
J
Ares
Mikko P S
MP
D000368:Aged; D002118:Calcium / Q000032:analysis; D016893:Carotid Stenosis / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D002853:Chromatography, Liquid; D003094:Collagen / Q000032:analysis; D004549:Elastin / Q000032:analysis; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D006801:Humans; D008055:Lipids / Q000097:blood; D008297:Male; D014463:Ultrasonography
D008055:Lipids; D003094:Collagen; D004549:Elastin; D002118:Calcium