Tiliroside and gnaphaliin inhibit human low density lipoprotein oxidation

Two flavonoids, gnaphaliin and tiliroside, isolated from Helichrysum italicum, were studied in vitro for their capacity to inhibit Cu2+-induced human low density lipoprotein (LDL) and diluted plasma oxidation. LDL oxidation was monitored by conjugated diene, thiobarbituric acid-reactive substances (TBARS) formation and electrophoretic mobility on agarose gel.Gnaphaliin and tiliroside increased the lag-phase for diene conjugate production in a dose-dependent manner. The reduction of TBARS production confirmed the antioxidant activity of gnaphaliin and tiliroside with 50% inhibitory concentration (IC50) values of 8.0 ± 3.9 μM and 7.0 ± 2.6 μM respectively. Furthermore, the flavonoids negated the Cu2+-induced increase in electrophoretic mobility of LDL. Antioxidant activity of gnaphaliin and tiliroside was significantly different when diluted plasma was oxidised by adding 1 mM CuSO4. Although both flavonoids again reduced the TBARS production, tiliroside showed higher activity than gnaphaliin (IC50 = 10.6 ± 2.5 μM vs. IC50 > 50 μM). In conclusion, tiliroside and gnaphaliin are antioxidants against in vitro Cu2+-induced LDL oxidation in the same order of magnitude compared to that of the reference drug, probucol.