An in vitro evaluation of epigallocatechin gallate (eGCG) as a biocompatible inhibitor of ricin toxin

Publication date: July 2016
Source:Biochimica et Biophysica Acta (BBA) - General Subjects, Volume 1860, Issue 7
Author(s): Paul D.R. Dyer, Arun K. Kotha, Alex S. Gollings, Susan A. Shorter, Thomas R. Shepherd, Marie W. Pettit, Bruce D. Alexander, Giulia T.M. Getti, Samer El-Daher, Les Baillie, Simon C.W. Richardson
The catechin, epigallocatechin gallate (eGCG), found in green tea, has inhibitory activity against a number of protein toxins and was investigated in relation to its impact upon ricin toxin (RT) in vitro. The IC50 for RT was 0.08±0.004ng/mL whereas the IC50 for RT+100μM eGCG was 3.02±0.572ng/mL, indicating that eGCG mediated a significant (p<0.0001) reduction in ricin toxicity. This experiment was repeated in the human macrophage cell line THP-1 and IC50 values were obtained for RT (0.54±0.024ng/mL) and RT+100μM eGCG (0.68±0.235ng/mL) again using 100μM eGCG and was significant (p=0.0013). The documented reduction in ricin toxicity mediated by eGCG was found to be eGCG concentration dependent, with 80 and 100μg/mL (i.e. 178 and 223μM respectively) of eGCG mediating a significant (p=0.0472 and 0.0232) reduction in ricin toxicity at 20 and 4ng/ml of RT in Vero and THP-1 cells (respectively). When viability was measured in THP-1 cells by propidium iodide exclusion (as opposed to the MTT assays used previously) 10ng/mL and 5ng/mL of RT was used. The addition of 1000μM and 100μM eGCG mediated a significant (p=0.0015 and <0.0001 respectively) reduction in ricin toxicity relative to an identical concentration of ricin with 1μg eGCG. Further, eGCG (100μM) was found to reduce the binding of RT B chain to lactose-conjugated Sepharose as well as significantly (p=0.0039) reduce the uptake of RT B chain in Vero cells. This data suggests that eGCG may provide a starting point to refine biocompatible substances that can reduce the lethality of ricin.



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