Inactivation of lipoxygenase and cyclooxygenase by natural betalains and semi-synthetic analogues

Betalains are natural pigments characteristic of plants of the order Caryophyllales. In this work, the role of betalains in the anti-inflammatory activity described for plant extracts is analysed in terms of the inactivation of the enzymes involved in the biochemical response (lipoxygenase and cyclooxygenase). Pure natural betalains and semi-synthetic analogues are demonstrated to promote a significant reduction of the enzymes activity. Reactions were followed spectrophotometrically and by HPLC-DAD. Phenethylamine-betaxanthin was the most potent in the inactivation of cyclooxygenase, with a reduction of 32% of the control activity at 125 μM, while the natural pigment betanidin and a betalain analogue derived from indoline resulted as the most potent inactivators of lipoxygenase, with IC50 values of 41.4 and 40.1 μM, respectively. Molecular docking studies revealed that betalains interact with the lipoxygenase amino acids involved in substrate binding and with Tyr-385 and Ser-530 close to the cyclooxygenase active site, interfering in enzyme catalysis.