Phospholipase C-dependent hydrolysis of phosphatidylcholine hydroperoxides to diacylglycerol hydroperoxides and its reduction by phospholipid hydroperoxide glutathione peroxidase

Protective Effect of Ebselen on Ischemia-reperfusion Injury in Epigastric Skin Flaps in Rats

The purpose of this study was to determine the role of oxidized diacylglycerol (DAG) and the molecular mechanism underlying ischemia-reperfusion (I/R) injury in rat skin flaps. The protective effect of ebselen on the viability of rat skin flaps with I/R injury was investigated. Flaps were designed and raised in the left inguinal region. Then, a microvascular clamp was applied to the vascular pedicle and reperfused after 6 hr. After 7 days of I/R (I/R group), the skin flap survival area ratio was significantly reduced compared to the normal skin. The administration of ebselen significantly improved the ratio compared to the I/R group. The flap survival area ratio of the I/R + ebselen group was significantly improved compared to the I/R + vehicle group. In the I/R + ebselen group, the oxidized DAG content and intensity of phosphorylated PKCα and PKCδ were significantly lower compared to the I/R + vehicle group. Furthermore, the inflammatory response was suppressed in the I/R + ebselen group compared to the I/R + vehicle group. These results indicate that ebselen is useful as a preventive and therapeutic agent for skin flap necrosis caused by I/R, because of reduction and elimination of oxidized DAG.

Roles of Oxidized Diacylglycerol for Carbon Tetrachloride-induced Liver Injury and Fibrosis in Mouse

Since there is a report that an inhibitor of protein kinase C (PKC) effectively suppresses the development of hepatic fibrosis, it is suggested that the PKC signaling pathway plays an important role in the pathogenesis of hepatic fibrosis. We reported that oxidized diacylglycerol (DAG), which is an activator of PKC, had a remarkably stronger PKC-activating action than un-oxidized DAG. In the present study, we explored the roles of oxidized DAG in hepatic fibrogenesis using mice, the livers of which developed fibrosis by long-term administration of carbon tetrachloride (CCl₄). Liver fibrosis models were created by 4- or 8-week repetitive subcutaneous injections of CCl₄ to the backs of C57BL/6J mice. The amount of oxidized DAG was significantly increased in the CCl₄-treated group. Moreover, it was found that PKCα, βI, βII and δ were activated. In the CCl₄-treated group, phosphorylation of ERK and JNK, which are downstream signal transmitters in the PKC pathway, was increased. It was also found in this group that there was an increase in TIMP-1, which is a fibrogenesis-promoting factor whose expression is enhanced by activated JNK, and of TNF-α, an inflammatory cytokine. Analysis by quantitative real-time RT-PCR showed that expressions of αSMA, collagen I, TNF-α and IL-10 were remarkably increased in the 8-week CCl₄-treated group. The above results strongly suggested that oxidized DAG, which is increased by augmented oxidative stress, activated PKCα, βI, βII and δ molecular species and that these molecular species in turn stimulated the phosphorylation of MAP kinases including ERK and JNK, resulting in enhancement of hepatic fibrogenesis.

Carbon tetrachloride-induced hepatic injury through formation of oxidized diacylglycerol and activation of the PKC/NF-κB pathway

Protein kinase C (PKC) participates in signal transduction, and its overactivation is involved in various types of cell injury. PKC depends on diacylglycerol (DAG) for its activation in vivo We have previously reported that DAG peroxides (DAG-O(O)H) activate PKC in vitro more strongly than unoxidized DAG, suggesting that DAG-O(O)H, if generated in vivo under oxidative stress, would act as an aberrant signal transducer. The present study examined whether DAG-O(O)H are formed in carbon tetrachloride (CCl(4))-induced acute rat liver injury in association with activation of the PKC/nuclear factor (NF)-κB pathway. A single subcutaneous injection of CCl(4) resulted in a marked increase in hepatic DAG-O(O)H content. At the molecular level, immunohistochemistry and subcellular fractionation combined with immunoblotting localized PKCα, βI, βII and δ isoforms to cell membranes, while immunoblotting showed phosphorylation of the p65 subunit of NF-κB, and immunoprecipitation using isoform-specific anti-PKC antibodies revealed specific association of PKCα and p65. In addition, expression of tumor necrosis factor α (TNFα) and neutrophil invasion increased in the CCl(4)-treated rats. Furthermore, we demonstrated that Vitamin E, one of the most important natural antioxidants that suppresses peroxidation of membrane lipids, significantly inhibited the CCl(4)-induced increase in hepatic DAG-O(O)H content and TNFα expression as well as phosphorylation of PKCα and p65. These data demonstrate for the first time that DAG-O(O)H are generated in the process of CCl(4)-induced liver injury, resulting in activation of the PKC/NF-κB pathway and TNFα-mediated aggravation of liver injury.

Various Molecular Species of Diacylglycerol Hydroperoxide Activate Human Neutrophils via PKC Activation

We have proposed that diacylglycerol hydroperoxide-induced unregulated signal transduction causes oxidative stress-related diseases. In this study, we investigated which molecular species of diacylglycerol hydroperoxide activated human peripheral neutrophils. All diacylglycerol hydroperoxides, diacylglycerol hydroxides, and diacyglycerols tested in the present study induced superoxide production by neutrophils. The ability to activate neutrophils among molecular species containing the same fatty acid composition was as follows; diacylglycerol hydroperoxide>diacylglycerol hydroxide>/=diacylglycerol. The diacylglycerol hydroperoxide composed of linoleate was a stronger activator for neutrophils than that composed of arachidonate. 1-Palmitoyl-2-linoleoylglycerol hydroperoxide (PLG-OOH) was the strongest stimulator for neutrophils. We reconfirmed that PLG-OOH activated protein kinase C (PKC) in neutrophils. PLG-OOH induced the phosphorylation of p47(phox), a substrate of PKC and a cytosolic component of NADPH oxidase, in neutrophils, as did N-formyl-methionyl-leucyl-phenylalanine or 4beta-phorbol-12beta-myristate-13alpha-acetate. Moreover, the time course of p47(phox) phosphorylation was comparable to that of superoxide production. These results suggest that PLG-OOH activated intracellular protein kinase C. PLG-OOH, produced via an uncontrolled process, can act as a biological second messenger to cause inflammatory disease from oxidative stress.