The Fat-Fed Apolipoprotein E Knockout Mouse

Chris JacksonBristol Heart Institute, University of Bristol, UK

Emerging Animal Models of Vulnerable Plaque

Animals• Closed outbred colony of

C57:129 homozygous apoE knockout mice

• Diet supplemented with 21% lard, 0.15% cholesterol

• Age at start of study was 6 to 8 weeks

Study Design

• 98 animals (51 male) were put on study

• 34 animals: scheduled termination• Pressure perfusion fixed (10% formalin) at

a constant pressure of 100mmHg

• 64 animals: sudden death• Not pressure perfusion fixed

Sudden Deaths

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10

20

30

40

50

60

70

80

90

100

Time (weeks)

Survival (%)

Brachiocephalic Artery

Parameters Measured• Presence or absence of rupture• Plaque cross-sectional area• Media cross-sectional area• Plaque/media area ratio• % Lumenal occlusion• Cap thickness• Number of previous ruptures• Lipid burden

Incidence of Rupture

• 64 sudden deaths• 35 ruptured brachiocephalics

• 34 scheduled terminations• 16 ruptured brachiocephalics

Time Course of Rupture

6055504540353025201510500

5

10

15

20

25

30

35

Time (Weeks)

Cumulative Ruptures

Plaque Characterisation

• Acutely ruptured (“ruptured”)• Visible tear or discontinuity in the cap• Blood-derived components within the

lesion

• Healed previous rupture (“intact”)• Buried fibrous cap

Vessel Dimensions

Intact Ruptured0

25000

50000

75000

100000

125000

150000

175000

200000

225000

Media AreaPlaque Area

Area (sq µm)

NS

p=0.0015

Expansive Remodelling

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50000

100000

150000

200000

250000

300000

350000

400000

450000

500000

550000

600000MediaPlaqueLumenTotal

Time (Weeks)

Area (sq µm)

Lumenal Occlusion

Intact Ruptured0

10

20

30

40

50

60Occlusion (%)

p<0.0001

Cap Thickness

Intact Ruptured0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Cap Thickness (um)

p=0.0004

Previous Healed Ruptures

Intact Ruptured0.0

0.5

1.0

1.5

2.0

2.5

3.0Buried Caps

p<0.0001

Lipid Burden

Intact Ruptured0

5

10

15

20

25

30

35

40

45

50

55Lipid Content (%)

p=0.0019

Summary

• Ruptured plaques:• Are 56% bigger

• Are 52% more occlusive

• Have caps that are 57% thinner

• Have 151% more previous ruptures

• Have a 36% greater lipid burden

Intervention Study Design

• To detect ∆(rupture, intact) with 80% power:

• Cap thickness: 17 mice

• Lipid content: 22 mice

• Lumenal occlusion: 24 mice

• Rupture frequency: 33 mice

• Plaque area: 53 mice

Late-Breaking News• Earliest ruptures are seen after 7 weeks

of high-fat diet• 75% of males have ruptures after 8 weeks

• Pravastatin significantly reduces the incidence of sudden death

• PAI-1-/-/apoE-/- double knockouts have significantly more plaque ruptures than apoE-/- single knockouts

Acknowledgments• Helen Williams, PhD• Jason Johnson, MSc• Kevin Carson, MB ChB• Ray Bush, PhD• Deb Watkins, BSc

• British Heart Foundation• Organon Laboratories• Pfizer• AstraZeneca