Phenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation

From the European plant Ballota nigra L. various polyphenols including phen ylpropanoid derivatives were isolated. There is increasing evidence that ox idized low-density lipoproteins (Ox-LDL) might be involved in the pathogene sis of atherosclerosis and it has been reported that polyphenols inhibit LD L peroxidation and atherogenesis. The goal of this study was to test whethe r the major polyphenolic compounds extracted from Ballota nigra, four pheny lpropanoid glycosides, verbascoside, forsythoside B, arenarioside, and ball otetroside and one non-glycosidic phenylpropanoid, caffeoyl-L-malic acid, i nhibit Cu2+-induced LDL peroxidation. The effectiveness of these compounds was compared to the activity of quercetin, a well-known polyphenol inhibito r of Cu2+-induced LDL oxidation, Antioxidant efficacious doses (ED 50) of a renarioside and ballotetroside were 1.8 mu M and 7.5 mu M respectively, whi le in the same conditions, the ED 50 of forsythoside B and verbascoside wer e similar (1 mu M) and those of quercetin and of caffeoyl-L-malic acid were 2.3 mu M and 9.5 mu M respectively. Spectrophotometric studies show that quercetin is a Cu2+ chelator while phe nylpropanoid glycosides and caffeoyl-L-malic acid are not Cu2+ chelators, T herefore, phenylpropanoid glycosides are strong inhibitors of Cu2+-induced LDL oxidation, independent of any capacity to act as Cu2+ chelators, Copyri ght (C) 2000 John Whey & Sons, Ltd.