γ-Tocotrienol Inhibits TGF-β1-Induced Contractile Phenotype Expression of Human Airway Smooth Muscle Cells

Background: Tocotrienols, members of the vitamin E family, exist in four different isoforms (α, β, γ and δ tocotrienol) that have can be protective against brain damage, as well as having anticancer effects in vivo and in vitro. We have shown that γ-tocotrienol inhibits human airway smooth muscle cell proliferation and migration induced by platelet-derived growth factor (PDGF)-BB by suppressing RhoA activation. In this study, we tested whether γ-tocotrienol modulates transforming growth factor (TGF) -β-induced induction of human airway smooth muscle (ASM) into a contractile phenotype and concomitant synthesis of extracellular matrix proteins.

Methods: ASM cells were stimulated with TGF-β1 (2 ng/mL) for 48 hours and the effect of γ-tocotrienol (50 μM) on α-smooth muscle actin, fibronectin and collagen I expression was assessed using Western blotting. The signaling pathways involved in TGF-β1 stimulation were also investigated.

Results: TGF-β1 increased α-smooth muscle actin, fibronectin and collagen Ⅰ abundance by 3- to 5-fold. This response was inhibited significantly by γ-tocotrienol. Furthermore, γ-tocotrienol suppressed RhoA activation, but did not affect Smad2 or Smad3 phosphorylation.

Conclusion: These results indicate that γ-tocotrienol has potential for benefit in modulating on airway remodeling in asthma, likely via a mechanism involving the suppression of TGF-β activation of RhoA.