Mechanisms behind the synergistic effect of sirolimus and imatinib in preventing restenosis after intimal injury.
BACKGROUND
We have shown that the combination of sirolimus and imatinib synergistically inhibits denudation-induced neointimal hyperplasia in rats. We have now dissected the mechanisms behind this synergy and evaluated its long-term efficacy.


METHODS
After aortic denudation injury, rats received established submaximal doses of sirolimus (1.0 mg/kg/day), imatinib (10.0 mg/kg/day), the combination of these, or vehicle per os from 3 days before the operation until 14 days after injury. Vessel histology and complete blood counts were monitored until 90 days after injury. Neointimal cell outgrowth, migration and proliferation were evaluated in ex vivo vessel cultures. Quantitative real-time polymerase chain reaction and immunohistochemistry were used for gene and protein expression analysis.


RESULTS
The combination therapy caused a synergistic decrease in the number of neointimal nuclei and area throughout the observation period. It also prevented postinjury thrombocytosis and leukocytosis, and almost abolished neointimal cell outgrowth and migration. Furthermore, the combination therapy resulted in upregulation of smooth muscle cell (SMC) markers SM22alpha and cysteine and glycine-rich protein 2, and of the anti-apoptotic BCL2 mRNA.


CONCLUSIONS
Combination therapy confers superior long-term vasculoprotection, possibly by inhibition of postoperative thrombocytosis and leukocytosis, inhibition of neointimal cell migration to the injury site and maintenance of cell integrity by inhibition of apoptosis and SMC dedifferentiation.
Tigerstedt
Nina-Maria
NM
Transplantation Laboratory, University of Helsinki and Helsinki University Central Hospital, Haartmaninkatu 3, Helsinki, Finland. nina-maria.tigerstedt@helsinki.fi
Aavik
Einari
E
Lehti
Satu
S
Hayry
Pekka
P
Savolainen-Peltonen
Hanna
H
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000473:pathology; D001549:Benzamides; D001772:Blood Cell Count; D004357:Drug Synergism; D006965:Hyperplasia; D000068877:Imatinib Mesylate; D060588:LIM Domain Proteins; D008297:Male; D008840:Microfilament Proteins / Q000235:genetics; D009124:Muscle Proteins / Q000235:genetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics; D010879:Piperazines / Q000008:administration & dosage* / Q000633:toxicity; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D011743:Pyrimidines / Q000008:administration & dosage* / Q000633:toxicity; D051381:Rats; D017208:Rats, Wistar; D020123:Sirolimus / Q000008:administration & dosage* / Q000633:toxicity; D017539:Tunica Intima / Q000187:drug effects* / Q000473:pathology; D014841:von Willebrand Factor / Q000235:genetics
D001549:Benzamides; C098930:CSRP2 protein, human; D060588:LIM Domain Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D009687:Nuclear Proteins; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D011743:Pyrimidines; C051615:transgelin; D014841:von Willebrand Factor; D000068877:Imatinib Mesylate; D020123:Sirolimus