Phenolic composition and in vitro antiproliferative activity of Borago spp. seed extracts on HT-29 cancer cells

Borage oil contains γ-linolenic acid (GLA, 18:3n-6), and significant amounts of tocopherols, sterols and squalene. However, data on phenolics are absent for most Borago species, while such compounds are relevant for improving human health. In this work, seeds of all endemic-wild Borago species and wild and farmed B. officinalis were surveyed for phenolic compound composition and in vitro antiproliferative activities. Phenolic analyses were conducted by HPLC-DAD and LC-MS, and antiproliferative activity were checked by the MTT assay. Besides a flavonol (kaemferol), 13 phenolic acids were identified and quantified. Among B. officinalis samples, the highest amounts of total phenolics and rosmarinic acid were found in the warmest and southernmost localities. Rosmarinic acid ranged from 12.21 (B. officinalis ‘Alba’ B2) to 105.06 mg/100 g seed (B. longifolia). Ferulic acid was also found in all Borago species, ranging from 1.38 in wild B. officinalis to 55.98 mg/100 g seed in B. longifolia. The MTT assay showed dose- and time-dependent inhibitory effects of Borago extracts on HT-29 cancer cells, with GI50 values within the 250–300 μg/mL range after 72 h of cell exposure to seeds extracts. Due to the occurrence of some compounds lacking antiproliferative activity in the crude phenolic extract, as evidenced by 1H NMR spectrum, the antiproliferative activity of the phenolics-containing extracts was lower than that obtained due to pure phenolics. This work constitutes the first approach to evaluate the phenolic composition of all Borago species and provides arguments for using endemic-wild Borago taxa by the pharmaceutical, cosmetic and food industries.