Vein adaptation to arterialization in an experimental model.
OBJECTIVE
The events preceding myointimal thickening in vein grafts after vascular reconstructions are not well characterized. Indeed, the injury response associated with vein graft arterialization may be different than that observed in the balloon angioplasty model. Therefore, we used a rat model to study the early cellular response after arterialization of vein grafts.


METHODS
Epigastric veins were placed as femoral artery interposition grafts in 37 male Lewis rats (weight range, 350-400 g). Vein grafts and contralateral epigastric veins were harvested at different time points (6 hours, 1 day, 2 days, 3 days, 7 days, 14 days, 21 days, 30 days, and 70 days). Tissue specimens were processed for histology and immunohistochemistry with antibodies for the proliferating cell nuclear antigen (PCNA) and for different cell types. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay was used as a means of determining the presence of apoptosis. Electron microscopy was used as means of assessing the integrity of the endothelial cell surface (SEM) and confirming the presence of apoptosis (TEM). Specimens were also snap frozen in liquid nitrogen for RNA isolation and molecular analysis.


RESULTS
At 1 day, endothelial denudation with platelet deposition on the surface was shown by means of SEM. Both apoptosis and necrosis of smooth muscle cells (SMCs) were present in the media, along with monocyte infiltration. Cellular proliferation and apoptosis were most intense within the first week of implantation. PCNA staining was first seen in the adventitial fibroblasts and microvessels, then in the medial SMCs at 3 days. With reverse transcriptase polymerase chain reaction, upregulation of vascular endothelial growth factor (VEGF) messenger RNA (mRNA) was noted at 1 day. Myointimal thickening progressively developed, with no apparent diminution of the luminal area as long as 70 days after implantation. By means of the analysis of the transforming growth factor beta1, mRNA showed expression during intimal thickening and accumulation of extracellular matrix. Reendothelialization was complete at 30 days.


CONCLUSIONS
These observations indicate that the cellular composition in our vein graft model is similar to human stenotic explants. Endothelial denudation is observed in rat vein grafts with complete regeneration by 30 days. VEGF mRNA is upregulated at 1 day, followed by proliferation of microvessel endothelial cells in the adventitia. Cellular proliferation and apoptosis are minimal after 21 days, with progressive intimal thickening likely to be the result of matrix accumulation.
Section of Vascular Surgery, and the Department of Pathology, University of Arizona Health Sciences Center and Southern Arizona VA Health Care System, Tucson, AZ, USA. halex94@aol.com
A
A
Westerband
D
D
Crouse
L C
LC
Richter
M L
ML
Aguirre
C C
CC
Wixon
D C
DC
James
J L
JL
Mills
G C
GC
Hunter
R L
RL
Heimark
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D016228:Endothelial Growth Factors / Q000032:analysis; D004730:Endothelium, Vascular / Q000473:pathology; D005263:Femoral Artery / Q000473:pathology / Q000601:surgery*; D005352:Fibromuscular Dysplasia / Q000473:pathology*; D006083:Graft Occlusion, Vascular / Q000473:pathology*; D020287:In Situ Nick-End Labeling; D008222:Lymphokines / Q000032:analysis; D008297:Male; D008854:Microscopy, Electron; D009131:Muscle, Smooth, Vascular / Q000473:pathology; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D051381:Rats; D011917:Rats, Inbred Lew; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016212:Transforming Growth Factor beta / Q000032:analysis; D053773:Transforming Growth Factor beta1; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D014680:Veins / Q000473:pathology / Q000637:transplantation*
D016228:Endothelial Growth Factors; D008222:Lymphokines; D018809:Proliferating Cell Nuclear Antigen; C508960:TGFB1 protein, human; C508962:Tgfb1 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors