The Anti-Platelet Agent, Ticlopidine, Upregulates Interleukin-1-Beta-Stimulated Nitric Oxide Production in Cultured Rat Vascular Smooth Muscle Cells

Abstract

Background: Hemodialysis patients who had been treated with anti-platelet aggregation drugs, including ticlopidine, sometimes developed hypotension. The mechanism by which ticlopidine lowers the blood pressure in hemodialysis patients is unclear. To elucidate the mechanism of the action of this drug, we investigated cytokine-stimulated nitric oxide (NO) metabolism by ticlopidine in cultured rat vascular smooth muscle cells (VSMC). Methods: Nitrite, a stable metabolite of NO, and intracellular cAMP and cGMP contents were assayed by the Griess method and enzyme immunoassay, respectively. iNOS mRNA and protein expressions were analyzed by Northern blotting and Western blotting. Results: Ticlopidine enhanced interleukin-1β (IL-1β)-induced nitrite production in a dose- and time-dependent manner. The mRNA and protein expressions of inducible NO synthase were upregulated by ticlopidine in a dose- and time-dependent manner. IL-1β alone stimulated both intracellular cAMP and cGMP contents, and the addition of ticlopidine further enhanced their contents. KT 5720, a selective inhibitor of protein kinase A, but not KT 5823, a selective inhibitor of protein kinase G, abolished the enhancement of IL-1β-induced nitrite production by ticlopidine. In addition, a phosphodiesterase inhibitor, isobutylmethylxanthine, enhanced IL-1β and ticlopidine induced nitrite production. Conclusion: We concluded that ticlopidine enhanced the IL-1β-induced NO production via cAMP and subsequent activation of protein kinase A in cultured rat VSMC.

Endothelium-independent vasorelaxation by ticlopidine and clopidogrel in rat caudal artery

“…reported an immediate and direct endothelial action of thienopyridines in the isolated guinea‐pig heart, independent of antiplatelet activity [20] . Also, it has been suggested that ticlopidine enhances the interleukin 1 β ‐stimulated nitric oxide release in cultured rat smooth muscle cells via cAMP‐ and protein kinase A‐dependent mechanisms [35,36] . In cultured endothelium, thienopyridines also directly stimulated the release of PGI 2 [37] .…”

Invited Lectures

“…The effects induced by clopidogrel were not affected by the presence of 50 µM ADP or 0.1 µM 2-MethioADP; as for ticlopidine, no inhibition between adenine nucleotides and clopidogrel on the VSMC proliferation was evidenced. It has been shown that clopidogrel significantly inhibits intimal proliferation after arterial injury in rabbit by unknown mechanisms ( 1 ) and it has been suggested that ticlopidine enhances the interleukin 1β-stimulated NO release in cultured rat smooth muscle cells via cAMP- and pKA-dependent mechanism ( 2 ). Our experimental data indicate that thienopyridines, without hepatic biotrasformation, can directly influence vascular cell growth in culture, since both ticlopidine and clopidogrel at micromolar concentrations inhibit VSMC proliferation, whereas at higher concentrations stimulate it.…”