A phenolic antioxidant from the freshwater orchid, Habenaria repens

Recently, an unusual compound named habenariol was isolated from the freshw ater orchid, Habenaria repens. Its phenolic structure suggested that habena riol should have substantial antioxidant activity. This possibility was inv estigated by evaluating the capacity of habenariol to inhibit copper-induce d lipid peroxidation of human low density lipoprotein (LDL), a popular expe rimental model. LDL was incubated with 5 mu M cupric chloride in the presen ce and absence of habenariol or a positive control, viz., alpha-tocopherol. Both kinetic and end-point spectrophotometric assays were used to determin e extent of lipid peroxidation of LDL. In the kinetic assay, the time elaps ing before the onset of rapid formation of conjugated lipid hydroperoxides in LDL (marked by a sharp increase in UV absorbance) was prolonged by haben ariol, indicative of an antioxidant effect. In the end-point assay, direct colorimetric measurement confirmed habenariol's ability to inhibit formatio n of lipid hydroperoxides. However, in both assays, habenariol was less pot ent than a-tocopherol in inhibiting lipid peroxidation of LDL. (C) 1999 Els evier Science Inc. All rights reserved.