Cigarette smoking increases aortic dilatation without affecting matrix metalloproteinase-9 and -12 expression in a modified mouse model of aneurysm formation.
OBJECTIVE
The development of abdominal aortic aneurysms (AAA) is presumed to result from multiple genetic and environmental factors, with exposure to tobacco smoke the single largest known factor predisposing to aneurysm growth. We have attempted to adapt the elastase-perfused animal model to determine whether tobacco exposure can lower the threshold of aortic injury necessary for AAA development.


METHODS
Adult C57BL/6 mice underwent transient perfusion of the infrarenal aorta with an active solution of elastase: high-dose (HDE, 0.19 U/mL, n=9), standard-dose (SDE, 0.16 U/mL, n=21) or low-dose (LDE, 0.07 U/mL, n=24). Control animals (n=24) were treated with heat inactivated elastase (HIE). Twenty LDE perfused mice were exposed to cigarette smoke (LDE-S) beginning 2 weeks before perfusion and continuing until aortic harvest. Aortic diameter (AD) was measured preperfusion, postperfusion, and at harvest on day 14. AAA was defined as %DeltaAD>or=100% between preperfusion and harvest. Aortas from each group (except HDE) were analyzed for matrix metalloproteinase-9 (MMP-9) and MMP-12 expression by real-time polymerase chain reaction normalized to glyceraldehyde-3-phosphate dehydrogenase.


RESULTS
All SDE mice developed large AAA by %DeltaAD (189.3%+/-16.9%, mean+/-standard error of the mean), but control mice had only a small dilatation (69.7%+/-3.7%, P<.01). Higher doses of elastase did not produce larger aneurysms in HDE mice. In contrast, only 63% of LDE mice showed aneurysmal dilatation, and these were significantly smaller (104.3%+/-4.2%, P<.01). When exposed to cigarette smoke, LDE animals developed significantly larger aneurysms (%DeltaAD, 134.5%+/-7.9%, P=.0021). There was no difference in normalized aortic MMP-9 and MMP-12 expression between elastase doses or between smoke-exposed and unexposed animals. Histologic analysis revealed that smoking increased the extent of aortic elastin degradation when compared with LDE-S animals.


CONCLUSIONS
Aneurysm development in the elastase model is dependent on the quantity of active elastase infused. Exposure of animals to tobacco smoke after a relatively minor aortic elastase injury produces increases in elastin degradation and aneurysm size without affecting MMP-9 or MMP-12 expression. To our knowledge, this is the first demonstration in an animal model that smoking can act as a synergistic factor in AAA development. Further understanding of the relationship between smoking and AAA in this model may help unveil the pathophysiologic pathways involved between cigarette smoke and AAAs.
Bergoeing
Michel P
MP
Department of Surgery (Section of Vascular Surgery), Washington University School of Medicine, St. Louis, MO 63110, USA.
Arif
Batool
B
Hackmann
Amy E
AE
Ennis
Terri L
TL
Thompson
Robert W
RW
Curci
John A
JA
D000818:Animals; D001012:Aorta, Abdominal / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D017544:Aortic Aneurysm, Abdominal / Q000139:chemically induced / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D001794:Blood Pressure / Q000187:drug effects; D003367:Cotinine / Q000652:urine; D004108:Dilatation, Pathologic; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D008297:Male; D053508:Matrix Metalloproteinase 12 / Q000032:analysis* / Q000235:genetics; D020780:Matrix Metalloproteinase 9 / Q000032:analysis* / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D010196:Pancreatic Elastase; D012333:RNA, Messenger / Q000032:analysis; D012307:Risk Factors; D012906:Smoke / Q000009:adverse effects*; D013997:Time Factors; D014026:Nicotiana
D012333:RNA, Messenger; D012906:Smoke; D010196:Pancreatic Elastase; D020780:Matrix Metalloproteinase 9; D053508:Matrix Metalloproteinase 12; D003367:Cotinine