A phenolic antioxidant from the freshwater orchid, Habenaria repens.

Recently, an unusual compound named habenariol was isolated from the freshwater orchid, Habenaria repens. Its phenolic structure suggested that habenariol should have substantial antioxidant activity. This possibility was investigated by evaluating the capacity of habenariol to inhibit copper-induced lipid peroxidation of human low density lipoprotein (LDL), a popular experimental model. LDL was incubated with 5 microM cupric chloride in the presence and absence of habenariol or a positive control, viz., alpha-tocopherol. Both kinetic and end-point spectrophotometric assays were used to determine extent of lipid peroxidation of LDL. In the kinetic assay, the time elapsing before the onset of rapid formation of conjugated lipid hydroperoxides in LDL (marked by a sharp increase in UV absorbance) was prolonged by habenariol, indicative of an antioxidant effect. In the end-point assay, direct colorimetric measurement confirmed habenariol's ability to inhibit formation of lipid hydroperoxides. However, in both assays, habenariol was less potent than alpha-tocopherol in inhibiting lipid peroxidation of LDL.