Gallotannin Improves the Photoaged-Related Proteins by Extracellular Signal-Regulated Kinases/c-Jun N-Terminal Kinases Signaling Pathway in Human Epidermal Keratinocyte Cells.

Tannins are a type of polyphenols found in several fruits such as grapes and berries, and nuts such as aronias and acorns. Both hydrolyzable tannins and condensed tannins are referred to as tannins. Among the hydrolyzable tannins, gallotannin has a strong antioxidative property and is known to protect the skin by inhibiting the precursors of elastolytic enzymes. However, its mechanism of protection against ultraviolet B (UVB) damage in human fibroblasts and keratinocytes has not yet been elucidated. In this study, we investigate the antioxidant and antiaging effect of gallotannin on UVB-irradiated human cells by studying its effect on extracellular signal-regulated kinases/c-Jun N-terminal kinases (EKRs/JNKs) signaling related to cell growth and differentiation/stress apoptosis. The results showed that gallotannin improved collagen synthesis, reduced metalloproteinase-1 (MMP-1) expression in a dose-dependent manner, and downregulated MMP-1 levels through the ERK/JNK signaling pathway in UVB-irradiated human cells. Gallotannin also increased glutathione but did not increase transforming growth factor beta 1, which induces fibrosis. We propose that gallotannin is a novel agent for protection against UVB, and acts as an antiaging agent that can be used in food, pharmaceuticals, and cosmetics.

Growth retardation of Escherichia coli by artificial increase of intracellular ATP.

Overexpression of phosphoenolpyruvate carboxykinase (PCK) was reported to cause the harboring of higher intracellular ATP concentration in Escherichia coli, accompanied with a slower growth rate. For systematic determination of the relationship between the artificial increase of ATP and growth retardation, PCKWT enzyme was directly evolved in vitro and further overexpressed. The evolved PCK67 showed a 60% greater catalytic efficiency than that of PCKWT. Consequently, the PCK67-overexpressing E. coli showed the highest ATP concentration at the log phase of 1.45 µmol/gcell, with the slowest growth rate of 0.66 h(-1), while the PCKWT-overexpressing cells displayed 1.00 µmol/gcell ATP concentration with the growth rate of 0.84 h(-1) and the control had 0.28 µmol/gcell with 1.03 h(-1). To find a plausible reason, PCK-overexpressing cells in a steady state during chemostat growth were applied to monitor intracellular reactive oxygen species (ROS). Higher amount of intracellular ROS were observed as the ATP levels increased. To confirm the hypothesis of slower growth rate without perturbation of the carbon flux by PCK-overexpression, phototrophic Gloeobacter rhodopsin (GR) was expressed. The GR-expressing strain under illumination harbored 81% more ATP concentration along with 82% higher ROS, with a 54% slower maximum growth rate than the control, while both the GR-expressing strain under dark and dicarboxylate transporter (a control membrane protein)-expressing strain showed a lower ATP and increased ROS, and slower growth rate. Regardless of carbon flux changes, the artificial ATP increase was related to the ROS increase and it was reciprocally correlated to the maximum growth rate. To verify that the accumulated intracellular ROS were responsible for the growth retardation, glutathione was added to the medium to reduce the ROS. As a result, the growth retardation was restored by the addition of 0.1 mM glutathione. Anaerobic culture even enabled the artificial ATP-increased E. coli to grow faster than control. Collectively, it was concluded that artificial ATP increases inhibit the growth of E. coli due to the overproduction of ROS.