Interactions between panax quinquefoliumsaponis and vitamin C are observedin vitro

Inasmuch as the oxidation of low-density lipoprotein (Ox-LDL) may play a ke y role in the initiation and progression of atherosclerosis, it has become increasingly important to identify potential antioxidants. Panax quinquefol ium saponins (PQS) are extracted from the stems and leaves of the North Ame rican form of ginseng,Panax quinquefolium. Our previous studies have indica ted that PQS (0.25-1 mg/ml) can protect against oxidation of LDLin vitro. T he purpose of the current work was to investigate the potential interaction of lower concentrations of PQS (1-100 mu g/ml) with vitamin C on the reduc tion of LDL oxidation. LDL was isolated from the plasma of healthy human do nors by sequential ultracentrifugation. Native LDL (0.05 or 0.2 mg/ml) was incubated with PQS and/or vitamin C for 30 min at 20 degrees C. Oxidative m odification was initiated with 2 mu M or 5 mu M CuSO4 at 37 degrees C for 0 -24 h. Pretreatment with PQS (100 mu g/ml) reduced alterations in phospholi pids, lipid peroxide levels and relative electrophoretic mobility of Ox-LDL . The presence of vitamin C (1-10 mu M) significantly enhanced the protecti ve effects of PQS. Pretreatment with PQS (1-100 mu g/ml) resulted in concen tration-dependent inhibition of LDL oxidation and prolongation of lag time as determined from measurements of conjugated lipid hydroperoxide content i n Ox-LDL samples. Interestingly, the inhibitory actions of lower amounts of PQS (1 and 10 mu g/ml) on the formation of conjugated dienes were signific antly increased when vitamin C (0.1 or 1 mu M) was present. In conclusion, our results suggest that PQS not only have direct antioxidant property but at low concentrations, their actions can be enhanced by vitamin C.