Inhibition of Src/STAT3 signaling-mediated angiogenesis is involved in the anti-melanoma effects of dioscin.

Angiogenesis plays an important role in the growth and metastasis of solid tumors including melanoma. Inhibiting tumor-associated angiogenesis is a tactic in treating melanoma. Dioscin restrains angiogenesis in colon tumor and has anti-melanoma effects in cell and animal models. In a previous study, we found that dioscin inhibits Src/STAT3 signaling in melanoma cells. Activation of the Src/STAT3 pathway has been shown to promote tumor angiogenesis. This study aimed to determine whether dioscin's anti-melanoma effects is related to inhibiting Src/STAT3 signaling-mediated angiogenesis. In a B16F10 allograft mouse model, we found that dioscin inhibited melanoma growth and angiogenesis. To exclude the impact of tumor growth on angiogenesis, a chicken chorioallantoic membrane (CAM) model was used to verify the anti-angiogenic effect of dioscin. Results showed that dioscin suppressed vessel formation in CAM. To determine if tumor secreted pro-angiogenic cytokines are involved in the anti-angiogenic effect of dioscin, conditioned media from dioscin-treated A375 melanoma cells were used to culture human umbilical vein endothelial cells (HUVECs), and tube formation was monitored. It was observed that the tube formation of HUVECs was inhibited. Mechanistic studies revealed that dioscin inhibited the activation of Src and STAT3, and lowered mRNA and protein levels of STAT3 transcriptionally-regulated genes, in B16F10 melanomas. ELISA assays showed that dioscin decreased the secretion of MMP-2, MMP-9 and VEGF from A375 cells. Over-activation of STAT3 lessened the effects of dioscin in decreasing the secretion of pro-angiogenic cytokines from melanoma cells, and in inhibiting tube formation of HUVECs cultured with conditioned media from melanoma cell cultures. In summary, we for the first time demonstrated that inhibiting Src/STAT3 signaling-mediated angiogenesis is involved in the anti-melanoma effects of dioscin. This study provides further pharmacological groundwork for developing dioscin as an anti-melanoma agent.

Molecular dynamics simulation of the processive endocellulase Cel48F from Clostridium cellulolyticum: a novel "water-control mechanism" in enzymatic hydrolysis of cellulose.

Glycoside hydrolase of Cel48F from Clostridium cellulolyticum is an important processive cellulose, which can hydrolyze cellulose into cellobiose. Molecular dynamics simulations were used to investigate the hydrolysis mechanism of cellulose. The two conformations of the Cel48F-cellotetrose complex in which the cellotetroses are bound at different sites (known as the sliding conformation and the hydrolyzing conformation) were simulated. By comparing these two conformations, a water-control mechanism is proposed, in which the hydrolysis proceeds by providing a water molecule for every other glucosidic linkage. The roles of certain key residues are determined: Glu55 and Asp230 are the most probable candidates for acid and base, respectively, in the mechanism of inverting anomeric carbon. Met414 and Trp417 constitute the water-control system. Glu44 might keep the substrate at a certain location within the active site or help the substrate chain to move from the sliding conformation to the hydrolyzing conformation. The other hydrophobic residues around the substrate can decrease the sliding energy barrier or provide a hydrophobic environment to resist entry of the surrounding water molecules into the active site, except for those coming from a specific water channel.

Inhibition of α-toxin production by subinhibitory concentrations of naringenin controls Staphylococcus aureus pneumonia.

Staphylococcal pneumonia provoked by methicillin-resistant Staphylococcus aureus (MRSA) is a life-threatening infection in which α-toxin is an essential virulence factor. In this study, we investigate the influence of naringenin on α-toxin production and further assess its therapeutic performance in the treatment of staphylococcal pneumonia. Remarkably, the expression of α-toxin was significantly inhibited when the organism was treated with 16 µg/ml of naringenin. When studied in a mouse model of S. aureus pneumonia, naringenin could attenuate the symptoms of lung injury and inflammation in infected mice. These results suggest that naringenin is a promising agent for treatment of S. aureus infection.

Allicin reduces the production of α-toxin by Staphylococcus aureus.

Staphylococcus aureus causes a broad range of life-threatening diseases in humans. The pathogenicity of this micro-organism is largely dependent upon its virulence factors. One of the most extensively studied virulence factors is the extracellular protein α-toxin. In this study, we show that allicin, an organosulfur compound, was active against S. aureus with MICs ranged from 32 to 64 µg/mL. Haemolysis, Western blot and real-time RT-PCR assays were used to evaluate the effects of allicin on S. aureus α-toxin production and on the levels of gene expression, respectively. The results of our study indicated that sub-inhibitory concentrations of allicin decreased the production of α-toxin in both methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in a dose-dependent manner. Furthermore, the transcriptional levels of agr (accessory gene regulator) in S. aureus were inhibited by allicin. Therefore, allicin may be useful in the treatment of α-toxin-producing S. aureus infections.