Begona Lavin Plaza1, Alkystis Phinikaridou1, Marcelo Andia2, Silvia Lorrio Gonzalez1, and Rene Botnar1
1King's College London, London, United Kingdom, 2Pontificia Universidad Catolica de Chile, Santiago de Chile, Chile
Synopsis
Atherothrombosis is a systemic arterial disease
mainly involving the intima of large- and medium-sized arteries including the
carotid, aorta, coronary, and peripheral arteries. Although it has long been known that
atherosclerosis is a systemic disease, the effects of vascular
alteration distally from the site of injury and the underlying mechanisms
responsible for the systemic response have not been elucidated. In this study, we used an
albumin-binding contrast agent to assess whether (1) vascular injury in the
abdominal aorta triggers plaque progression in the brachiocephalic artery
located distally to the site of injury and (2) whether neutrophils can be the
link involved in this systemic response. INTRODUCTION
Although it is known
that atherosclerosis is a systemic disease, the systemic effects of vascular injury
have not been elucidated. Vascular
permeability and inflammation are major players in the pathophysiology of
atherosclerosis. Vascular permeability
regulates recruitment and infiltration of immune cells to the site of injury,
and therefore, controls disease progression. While
the contribution of monocytes in plaque progression and destabilization has
been extensively studied, the role of neutrophils, the most abundant white
blood cell type, remains poorly understood. Few studies suggest that neutrophils
may increase vascular permeability and promote plaque destabilization.1,2 Here, we used an
albumin-binding contrast agent to assess whether (1) aortic wall injury triggers plaque progression in the
brachiocephalic artery located distally to the site of injury and (2) whether neutrophils could be the
link involved in this systemic response.
METHODS
Three
groups of male ApoE-/- mice were imaged at 4, 8 and 12 weeks after
commencement of the experimental protocol. (1)
Mice were fed a high fat diet (HFD) to induce atherosclerosis (n=6); (2) Injured mice underwent endothelial
denudation surgery3 followed by HFD (n=9); (3) Treated mice underwent vascular injury followed by HFD and
pravastatin treatment (40mg/kg/day) (n=6). Control mice were imaged before HFD ± injury (n=6). In-vivo MRI:
A 3T Philips Achieva system and a 23mm single-loop microscopy surface coil were
used. Images were acquired 30min after gadofosveset administration (0.03mmol/kg).
Acquisition parameters are summarized in Table
1. Flow
cytometry: Neutrophil characterization
was performed by using CD11b and Ly6G markers.
RESULTS
DE-MRI
using gadofosveset (Fig. 1) showed a significant enhancement of the brachiocephalic
artery in mice that underwent vascular injury in the abdominal aorta (Fig. 1E-G) compared to the HFD group (Fig. 1B-D) suggesting that vascular
injury may trigger a systemic response that accelerates lesion progression
distally. Importantly, injured mice treated with statins showed decreased
uptake, demonstrating the beneficial systemic effects of statins on lesion
progression (Fig. 1H). Control mice
showed little uptake (Fig. 1A).
Histology revealed larger and advanced lesions after 12 weeks in the injury
group with a surprisingly thick fibrous cap (Fig. 1J) as compared to the HFD (Fig. 1K) and statin-treatment groups (Fig. 1I), suggesting a more stable phenotype in the injury group.
Quantitative analysis of vessel wall enhancement (Fig. 2A) and relaxation rate R1 (Fig. 2B) showed increased vascular permeability in the injury group
12 weeks after denudation as compared to other groups. The luminal area of the
BCA was significantly decreased in the injury group as compared to the other groups
(Fig. 2C). Quantitative analysis by flow
cytometry revealed monocytosis and increased T-cell content under
hyperlipidemic conditions. However, no significant differences were found
between the HFD and injury group (data not shown). Interestingly, a significant
increase of neutrophils was detected in the BCA of the injury group compared to
other groups (Fig. 3A). In addition
a significant correlation was detected between R1 values and neutrophil content
in the BCA (Fig. 3B). These results
suggest that neutrophils may be the systemic link between focal vascular injury
and distal progression of atherosclerosis.
CONCLUSIONS
Increased
albumin leakage into the BCA vessel wall was observed in the aortic injury
group demonstrating that vascular injury aggravates disease progression at a
vascular segment located distally from the site of injury. BCA plaques in the
injury group were characterised by larger and more stenotic atherosclerotic
lesions with surprisingly thick fibrous cap. We also demonstrate that the
systemic effects of vascular injury may be mediated by the mobilization of
neutrophils that may represent a link between focal vascular injury and distal
disease progression.
Acknowledgements
British Heart Foundation (RG/12/1/29262)References
(1) Gautam N., et al. Nat Med. 2001. (2) DiStasi MR., et al. Trends Immunol. 2009. (3) Lavin B., et
al. Circulation: Cardiovasc Imag. 2015.