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Mechanism of (−)-epigallocatechin gallate (EGCG) dimerization by low-temperature plasma

ABSTRACT: The efficient dimerization of (−)-Epigallocatechin gallate (EGCG), which is the major bioactive constituent isolated from the leaves of Camellia sinensis, was initially reported without changes in its stereochemistry using low-temperature plasma. The contribution of plasma during the dimerization of EGCG in a methanolic solution was quantified using a major factor, with the major factor demonstrated based on the contents of newly generated products, in this case the sum of oolonghomobisflavans A and B depending on the plasma treatment method. Samples were treated in three methods: plasma direct treatment, an indirect treatment using only reactive species, and an indirect treatment using effects other than those by reactive species. Ozone was identified as a major factor during the plasma treatment, and the operating ranges of the ozone concentration for regulated dimerization were evaluated. The mechanism by which EGCG synthesizes dimers A and B during the treatment process using low-temperature plasma was investigated using the derived major factor and prior literature. The ozone generated by the plasma reacted with methanol to form formaldehyde, and dimers A and B were synthesized by oligomers through a methylene-bridge by the formaldehyde. A plausible pathway of regulated dimerization was deduced based on these results, and the mechanism of EGCG dimerization by plasma is described using this pathway.

SUBMITTER: Park S

PROVIDER: S-EPMC9470551 | biostudies-literature | 2022 Jan

REPOSITORIES: biostudies-literature

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Project description:Background: Hepatocellular carcinoma (HCC) is increasing in incidence and treatment is often unsuccessful. Thus, prevention in high-risk patients with established cirrhosis has been proposed as an alternative strategy. It has been suggested that the increased inflammation and fibrogenesis observed during cirrhosis predisposes the liver to future malignant transformation to HCC through a “field effect”. A growing body of evidence indicates that the green tea polyphenol, (-)-epigallocatechin gallate (EGCG), can reduce inflammation and fibrogenesis during chronic liver injury. Here, we test the hypothesis that EGCG administered in the setting of cirrhosis can prevent future HCC development. Methods: A rat model of diethylnitrosamine (DEN)-induced cirrhosis was used to examine the efficacy of EGCG for inhibition of HCC formation in these cirrhotic livers. DEN (50 mg/kg) was administered weekly throughout the study while 0.02% EGCG was given in drinking water beginning at the onset of cirrhosis. At the end of the study, rats were sacrificed, livers were sectioned and stained to analyze disease progression and tumor nodules were counted. Liver function tests were performed to determine liver injury and overall liver function. Finally, genome-wide gene expression profiling on the surrounding, non-tumoral liver tissue was used to monitor the “field effect” in response to EGCG. Results: EGCG significantly (p < 0.01) prevented the development of HCC tumor nodules from on average 18.8 in vehicle controls to on average 9.1 in EGCG-treated animals. EGCG also reduced liver injury and improved liver function as assessed by serum chemistry tests. Finally, a gene expression signature predictive of poor survival and HCC development in human cirrhosis patients was reversed in response to EGCG. Conclusions: Our data are consistent with the growing body of evidence suggesting that EGCG has protective effects in liver disease. Further, our results suggest that EGCG is a potentially effective HCC prevention strategy that can be monitored using gene expression signatures.

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Mechanism of (−)-epigallocatechin gallate (EGCG) dimerization by low-temperature plasma

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