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

Abstract

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 IC(50) for RT was 0.08±0.004 ng/mL whereas the IC(50) for RT+100 μM eGCG was 3.02±0.572 ng/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 IC(50) values were obtained for RT (0.54±0.024 ng/mL) and RT+100 μM eGCG (0.68±0.235 ng/mL) again using 100 μM 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 100 μg/mL (i.e. 178 and 223 μM respectively) of eGCG mediating a significant (p=0.0472 and 0.0232) reduction in ricin toxicity at 20 and 4 ng/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) 10 ng/mL and 5 ng/mL of RT was used. The addition of 1000 μM and 100 μM eGCG mediated a significant (p=0.0015 and <0.0001 respectively) reduction in ricin toxicity relative to an identical concentration of ricin with 1 μg eGCG. Further, eGCG (100 μM) 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.

Does Green Tea Induce Hormesis?

“…(-)-Epigallocatechin-3-gallate was also found to protect the human macrophage cell line THP-1 against the highly toxic agent ricin in a hormetic fashion ( Figure S21). 47 While EGCG induced hormesis in all cases, the low-dose positive response for the RPE cells was an undesirable effect since it could lead to enhanced tissue vascularization. However, in all other cases reported, the dose stimulation was considered to be protective.…”

The Delivery of Personalised, Precision MedicinesviaSynthetic Proteins

“…This was due to the navigation of the endomembrane system afforded by the RT b-chain (RTBC). This example highlights the need for the active navigation of the endomembrane system if the translocation of large membrane non-permeable molecules is required [4,17].…”

“…Ricin toxin (RT) depurinates ribosomal RNA at the ricin/sarcin loop, inhibiting protein synthesis. To exert this effect RT a-chain (RTAC) needs to access the cytosol and to then interact with ribosomes [17]. When ricin holotoxin's (i.e.…”

Treatments for Pulmonary Ricin Intoxication: Current Aspects and Future Prospects

“…There are many antioxidants used clinically, including N-acetylcysteine (NAC)—a widely used mucus-dissolving over-the-counter medication—which was shown to suppress the release of IL-1β from bone marrow-derived macrophages incubated with ricin [ 21 ]. Epigallocatechin gallate (EGCG), an antioxidant found in green tea, diminished ricin-induced cytotoxicity in cell cultures [ 106 , 107 ]. Several antioxidants, such as butylated hydroxyanisole (BHA) and vitamin E succinate, were also shown to provide protective effects in vivo against systemic ricin intoxication [ 58 ].…”

“…Additional studies were performed with the closely related protein Ricinus communis agglutinin (RCA), demonstrating potent binding to Galβ1-4GlcNAc, with specificity for highly branched glycans containing this structure [ 168 ]. EGCG, a potent antioxidant possessing anti-inflammatory properties [ 109 , 110 ], was also suggested to interfere with the binding of RTB to lactose-conjugated sepharose [ 107 ].…”