Objective: To investigate the beneficial effects of Anaxagorea luzonensis (AL) extract on homocysteine thiolactone (HTL)-
induced impairment of endothelium-dependent relaxation in rat aortic rings. The mechanisms involved in the effects of AL on
endothelial dysfunctions by HTL are also examined.
Material and Method: Aortic rings from male Wistar rats were co-incubated for 90 minutes with L-arginine (3 mM), a precursor of nitric oxide (NO); superoxide dismutase (SOD, 200 U/mL), a scavenger of superoxide anion; indomethacin (10 μM), a cyclooxygenase (COX) inhibitor; SC560 (10 μM), a COX-1 inhibitor; NS398 (10 μM), a COX-2 inhibitor; or SQ29548 (1 μM), a thromboxane A2 receptor antagonist in the presence of HTL (1 mM). After 90 minutes of incubation period, the rings were pre-contracted with methoxamine, and then carbachol was cumulatively added to the bath. AL (1 and 3 μg/mL) was co-incubated with 1 mM HTL in the presence of NG-nitro-L-arginine methyl ester (L-NAME, 300 μM), a NO synthase inhibitor, and p-hydroxymercurybenzoate (PHMB, 10 μM), a sulfhydryl group blocking agent. Changes in tension were measured using an isometric force transducer and recorded on the PowerLab.
Results: Endothelium-dependent vasorelaxation to carbachol was impaired after exposure of aortic rings to HTL (0.3 and 1
mM). The inhibitory effects of HTL (1 mM) on relaxant responses to carbachol were restored by L-arginine, SOD, indomethacin,
SC560 and SQ29548, but not NS398. Interestingly, AL reduced impairment of vasorelaxation induced by HTL (1 mM). However, L-NAME and PHMB largely inhibited the protective effects of AL.
Conclusion: These results suggest that HTL-induced impairment of endothelium-dependent vasorelaxation may occur via decreased NO release, and generation of oxygen free radical. This study first shows that enhancement of TxA2 production via
COX-1 pathway is involved in HTL-induced endothelial dysfunctions. The protective effects of AL on impairment of relaxation by HTL may be related to increasing NO production and sulfhydryl-dependent.

Keywords: Anaxagorea luzonensis, Homocysteine thiolactone, Thromboxane A2,Oxygen free radicals, Nitric oxide