Inhibitory effects of tranilast on expression of transforming growth factor-β isoforms and receptors in injured arteries Original Research Article

Tranilast (N(3,4-dimethoxycinnamoyl)anthranilic acid), an agent which in cell culture inhibits transforming growth factor-β (TGF-β) secretion and antagonises the effects of TGF-β and platelet-derived growth factor (PDGF) on cell migration and proliferation, has been reported to reduce the incidence of restenosis after angioplasty in angiographically validated human clinical trials. We investigated in a rat model of balloon angioplasty whether tranilastʹs effects in vivo could be attributed to inhibition of expression of TGF-β and/or its receptor types. Using a standardised reverse transcriptase-polymerase chain reaction (RT-PCR) assay, we examined the effects of three doses of tranilast (25, 50 and 100 mg/kg) on the expression of two TGF-β isoforms, the types I and II TGF-β receptors and two putative TGF-β responses, induction of integrins αv and β3 mRNA, 2 h after oral administration and 26 h after vessel injury. Tranilast attenuated in a dose-dependent and reversible manner the injury-induced increases in mRNA levels encoding TGF-β1, TGF-β3, two type I TGF-β receptors ALK-5 and ALK-2, and the type II receptor TβRII. At the highest dose mRNA levels encoding TGF-β1 and TβRII were attenuated to levels approaching or below those observed in uninjured vessels. Messenger RNAs encoding TGF-β3, ALK-5 and ALK-2 were all attenuated by between 70 and 74% (all P<0.05). Tranilast also attenuated in a reversible manner the elevations in mRNA levels for integrins αv and β3 observed after vessel injury, by 90 and 72%, respectively. We also investigated, in cultured smooth muscle cells derived from injured carotid arteries, the extent to which tranilast (300 mg/l) attenuated any increases in expression of type I and type II receptors stimulated by PDGF-BB and TGF-β1, growth factors implicated in smooth muscle cell migration and proliferation in injured vessels. Increases in mRNA levels of the type I receptors ALK-5 and ALK-2 induced by PDGF-BB and TGF-β1 were almost completely prevented by tranilast. Tranilast also prevented the PDGF-BB induced increases in TβRII but only partially inhibited the TGF-β1 induced upregulation of TβRII. We conclude that tranilast can inhibit transcriptional mechanisms associated with the upregulation of TGF-β and its receptor types in balloon catheter injured vessels. It is possible that these mechanisms contribute to its ability to reduce the frequency of restenosis after angioplasty.