The combination of analytical-scale HPLC separation with a TR-FRET assay to investigate JAK2 inhibitory compounds in a Boysenberry drink.

We report the detection of JAK2 inhibitory activity in a Boysenberry (Rubus loganbaccus x R. baileyanus Britt.) drink using a combination of analytical-scale high performance liquid chromatography (HPLC) with a high-sensitivity time-resolved fluorescence coupled with fluorescence resonance energy transfer (TR-FRET) method. Phytochemical components of a Boysenberry drink were separated by reversed phase HPLC , and 84 separate fractions were collected. HPLC fractions corresponding to the ellagitannin and ellagic acid peaks observed in the chromatogram inhibited JAK2 activity. Anthocyanins, while they were the major phytochemical components of the Boysenberry drink, had no JAK2 inhibitory activity even though anthocyanins have previously been shown to be anti-inflammatory. This study demonstrates the usefulness of combining rapid analytical-scale HPLC separation with a highly sensitive fluorescence bioassay for characterising bioactivity in complex plant extracts. Ellagic acid was found to have an IC(50) of 92 nM against JAK2 and complete inhibition of JAK2 activity was observed in HPLC fractions of Boysenberry extract which had been diluted several hundred fold. To the best of our knowledge, this is the first demonstration that ellagitannins and other natural ellagic acid analogues are potent inhibitors of JAK2. Thus a drink containing Boysenberry juice concentrate may have anti-inflammatory properties.