Pentoxifylline inhibits PDGF-induced proliferation of and TGF-beta-stimulated collagen synthesis by vascular smooth muscle cells

There is growing evidence that pentoxifylline (PTX) may have potential Valu e as an antiproliferative and antifibrogenic agent. To assess whether this drug may be of use in the prevention of atherosclerosis or restenosis after angioplasty, we investigated the ability of PTX to inhibit proliferation a nd collagen synthesis in rat vascular smooth muscle cells (VSMCs) under bot h basal and platelet-derived growth factor (PDGF)- or transforming growth f actor-beta (TGF-beta)-stimulated conditions, Intracellular cyclic AMP (cAMP ) and cyclic GMP (cGMP) levels were measured in confluent cells using enzym e immunoassay kits. Cell proliferation was measured by methyltetrazolium as say. Cell cycle distribution was determined by flow cytometry. Total collag en synthesis was measured by H-3-proline incorporation assay, Expression of collagen alpha 1(I) and collagen alpha 1(III) mRNAs was detected by northe rn blotting. Addition of PTX to VSMC cultures suppressed both basal and PDG F-AB (25 ng/ml)-driven cell proliferation, in conjunction with a cell cycle blockade at the G1/S phase at 24h. This effect was predominantly cAMP-depe ndent, as PTX increased cAMP in a dose-dependent manner (0.03 to 0.33 mg/ml ) but not cGMP level, and the addition of dibutyryl-cAMP (0.2 to 2 mM) clos ely mimicked the effect of PTX. Furthermore, co-incubation with a selective inhibitor of cAMP-dependent protein kinase (PKA), H-89 (2.0 mu M), or an N -myristoylated PKA pseudosubstrate nonapeptide, m-psi PKA (10 mu M), preven ted the antimitogenic effect of PTX. PTX also suppressed both basal and TGF -beta 1-augmented collagen alpha 1(I) and collagen alpha 1(III) mRNA levels beginning at 24 h, and attenuated both basal and TGF-beta 1 (5 ng/ml)-stim ulated total collagen synthesis at 48 h, Go-incubation with H-89 or m-psi P KA reversed PTX-attenuated collagen alpha 1(I) and collagen alpha 1(III) mR NA levels at 24 h. These data suggest that the antimotigenic and anticollag en effects of PTX were mediated predominantly through a cAMP-PKA effector p athway, The dual effect of PTX on VSMC proliferation and collagen synthesis may form the rationale for animal or clinical trials for the treatment of vascular occlusion due to atherosclerosis and restenosis following angiopla sty. (C) 1999 Academic Press.