Correlation between catechin content and NF-κB inhibition by infusions of green and black tea.

This study investigates whether infusions of green and black tea inhibit the NF-κB driven transcription in human epithelial gastric AGS cells. Water extracts were prepared from different brands of green and black tea available on the Italian market. Teas with or without caffeine were studied. An industrially prepared freeze-dried water extract of green tea was also tested. Catechin and caffeine contents were measured by HPLC analysis. The decrease in phenol and catechin content three months after the expiry date was also investigated. The NF-κB driven transcription and the free radical scavenger activity were inhibited, and this effect was related to catechin levels. The potency of epigallocatechin 3-gallate in inhibiting NF-κB driven transcription is so great that tea extracts low in epigallocatechin 3-gallate are still highly active. In one decaffeinated sample of green tea, the phenol and catechin content was very low, probably as a consequence of caffeine removal. The decrease in catechin levels after 3 months did not reduce the inhibition of NF-κB driven transcription by tea infusions. This is the first paper reporting the inhibitory effect of NF-κB of commercial green and black infusions at the gastric level, evaluating their stability as well.