Cytotoxic Properties, Anthocyanin and Furanocoumarin Content of Red-Pigments Obtained from Callistemon citrinus (Curtis) Skeels Flowers

There is growing interest in introducing safe and bioactive natural red pigments to the pharmaceutical and cosmetic industries. This study was designed to determine the phytochemical content and potential cytotoxicity of red pigment from Callistemon citrinus (Curtis) Skeels (syn. Melaleuca citrina (Curtis) Dum.Cours.) flowers.

The flowers’ anthocyanin rich pigment was extracted with ethanol (70%, v/v) containing 0.5% formic acid. This extract was fractionated by a three-step process through a Sep-Pak C18 cartridge with water, ethyl acetate, and methanol, respectively. The anthocyanin and coumarin content of the red pigment was identified based on a reverse phase high performance liquid chromatography-electrospray ionization mass spectrometry (HPLC/ESI-MS/MS). The MTT assay was used to assess the cytotoxicity of red pigment evaluated on normal human foreskin fibroblasts as well as two malignant cell lines: human breast cancer (MCF-7) and human fibrosarcoma cells (HT1080) at 24, 48 and 72 hours.

The anthocyanin compounds in the red pigment fraction were cyanidin (1), cyanidin 3,5-O-diglucoside (2), cyanidin 3-O-glucoside (3), and cyanidin 3-O-glucoside-8-ethyl-catechin (4). Flowers’ pigment also contained two furanocoumarins, including 8-(but-2-en-2-yl)-8,9-dihydro-2H-furo[2,3-h] chromen-2-one (or 15-methyl angenomallin, (5)) and 9-methyl-7H-furo[3,2-g] chromen-7-one (or 8-methylpsoralen, (6)). According to the MTT assays, the highest cytotoxic effect was observed on human foreskin fibroblasts with an IC50 values of <12.5 (µg/ mL, 24 h) and 85.2 (µg/ mL, 48 h).

It might be assumed that application of the red pigment of C. citrinus in topical formulations and cosmetics should be done with caution due to the observed cytotoxicity on dermal fibroblasts.