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Tea is an interesting source of antioxidants capable of counteracting the oxidative stress implicated in liver diseases. We investigated the impact of antioxidant molecules provided by a mixture of teas' leaves (green, oolong, pu-erh) after different infusion durations in the prevention of oxidative stress in isolated rat hepatocytes, by comparison with pure epigallocatechin-3-gallate (EGCG), the main representative of tea catechins. Dried aqueous tea extracts (ATE) obtained after 5, 15 and 30 min infusion time were characterized for total polyphenols (gallic acid equivalent), catechins, gallic acid and caffeine (HPLC-DAD/ESI-MS) contents, and for scavenging ability against 2,2-diphenyl-1-picrylhydrazyl free radical. Hepatoprotection was evaluated through hepatocyte viability tests using tert-butyl hydroperoxide as a stress inducer, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, neutral red uptake, real-time cellular impedance) and mitochondrial function tests. We showed that a 5-min incubation time is sufficient for an optimal bioaccessibility of tea compounds with the highest antioxidative ability, which decreases for longer durations. A 4-h pretreatment of cells with ATE significantly prevented cell death by regulating reactive oxygen species production and maintaining mitochondrial integrity. Pure EGCG, at doses similar in ATE (5–12 μM), was inefficient, suggesting a plausible synergy of several water-soluble tea compounds to explain the ATE beneficial effects. [ABSTRACT FROM AUTHOR]

Background. Sodium palmitate causes apoptosis of β-cells, and the anti-apoptotic protein Bcl-2 has been shown to counteract this event. However, the exact mechanisms that underlie palmitate-induced pancreatic β-cell apoptosis and through which pathway Bcl-2 executes the protective effect are still unclear. Methods. A stable Bcl-2-overexpressing RINm5F cell clone (BMG) and its negative control (B45) were exposed to palmitate for up to 8 h, and cell viability, mitochondrial membrane potential (Δψm), reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, and NF-κB activation were studied in time course experiments. Results. Palmitate exposure for 8 h resulted in increased cell death rates, and this event was partially counteracted by Bcl-2. Bcl-2 overexpression promoted in parallel also a delayed induction of GADD153/CHOP and a weaker phosphorylation of BimEL in palmitate-exposed cells. At earlier time points (2-4 h) palmitate exposure resulted in increased generation of ROS, a decrease in mitochondrial membrane potential (Δψm), and a modest increase in the phosphorylation of eIF2α and IRE1α. BMG cells produced similar amounts of ROS and displayed the same eIF2α and IRE1α phosphorylation rates as B45 cells. However, the palmitate-induced dissipation of Δψm was partially counteracted by Bcl-2. In addition, basal NF-κB activity was increased in BMG cells. Conclusions. Our results indicate that Bcl-2 counteracts palmitate-induced β-cell death by maintaining mitochondrial membrane integrity and augmenting NF-κB activity, but not by affecting ROS production and ER stress. [ABSTRACT FROM AUTHOR]