Keiko Kobayashi

Neutral sphingomyelinase-induced ceramide accumulation by oxidative stress during carbon tetrachloride intoxication

Ceramide is a biologically active lipid causing apoptosis in a variety of cells. In this study, we examined the effect of CCl4 on the ceramide metabolism and indicators of oxidative stress. After 12 h of oral administration of CCl4 (4 ml/kg body weight as a 1:1 mixture of CCl4 and mineral oil) to rats, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were increased. Antioxidants such as vitamins C and E were decreased in the liver and kidney. In addition, the ratio of GSH/GSSG in the liver, plasma, kidney, and brain decreased at 2h. The total ceramide in the liver significantly increased as early as 2h after CCl4 administration. After 24 and 36 h, the total ceramide in plasma and the kidney was also augmented. In the brain, the total ceramide dramatically increased at 36 h. These results suggested that the increased ceramide in plasma was transferred to the kidney and the brain. The activity of neutral sphingomyelinase (SMase), which was reported to be enhanced by the decrease of GSH, was significantly increased after CCl4 treatment in the liver, kidney, and brain. However, acid SMase activities were not increased in the liver and kidney. Thus, the activation of neutral SMase via oxidative stress induced the increase of ceramide during CCl4 intoxication in not only the liver but also other tissues. These results suggested that the excess accumulation of ceramide causes damage in other organs including the kidney and brain during fulminant hepatic failure.

PI3K/AKT/PTEN pathway as a target for Crohn's disease therapy (Review)

The pathogenesis of inflammatory bowel disease (IBD), including Crohns disease, is a subject of increasing interest. Loss-of-function mutations in nucleotide-binding oligomerization domain-containing protein 2 (NOD2) are strong genetic factors linked to Crohns disease, which eventually leads to an excessive mucosal inflammatory response directed against components of normal gut microbiota. Reactive oxygen species (ROS) play an important role in inflammation processes, as well as in transduction of signals from receptors for several cytokines, such as tumor necrosis factor α (TNFα). ROS activate nuclear factor-κB (NF-κB) via IκB kinase (IKK) through the PI3K/AKT/PTEN pathway. Therefore, this pathway is recognized to play a key role in Crohns disease. Loss of function has been demonstrated to occur as an early event in a wide variety of diseases. Given this prevalent involvement in a number of diseases, the molecular development that modulates this pathway has been the subject of several studies. In addition, it has been the focus of extensive research and drug discovery activities. A better understanding of the molecular assemblies may reveal novel targets for the therapeutic development against Crohns disease.

Racemization of the Aspartic Acid Residue of Amyloid-β Peptide by a Radical Reaction

Human amyloid-β peptide 1-42 (Aβ) was subjected to a radical reaction by using ascorbic acid and CuCl(2). The percentage of D-aspartic acid (D-Asp) after 24 h had increased to 6.69 ± 0.09%, this being comparable with the reported D-Asp concentration of purified core amyloids in Alzheimers disease patients. This racemization was significantly inhibited by radical scavengers. L-Alanine was also racemized during the same reaction.

Atherosclerosis and tumor suppressor molecules (review).

Atherosclerosis, the major cause of heart attack and stroke, is a chronic inflammatory disease characterized by the formation of atherosclerotic plaque. Oxidized low-density lipoprotein through increased oxidative stress has been identified as one of the primary factors responsible for atherogenesis. Cell proliferation and death are key processes in the progression of atherosclerosis. The oxidative environment in areas of lipid accumulation is mainly created by the production of reactive oxygen species, which are assumed to mediate vascular tissue injury. Oxidative DNA damage and levels of DNA repair are reduced during dietary lipid lowering. The tumor suppressor molecules play a pivotal role in regulating cell proliferation, DNA repair and cell death, which are important processes in regulating the composition of atherosclerotic plaque. Accordingly, in this review, we discuss the fundamental role of tumor suppressor molecules in regulating atherogenesis. In particular, we discuss how tumor suppressor molecules are activated in the complex environment of atherosclerotic plaque, and regulate growth arrest, cell senescence and the apoptosis of vascular smooth muscle cells, which may protect against the progression of atherosclerosis. In addition, we discuss promising alternatives to the use of medications (such as statin) against atherosclerosis, namely diet, with the use of plant-derived supplements to modulate the expression and/or activity of tumor suppressor molecules. We also summarize the progress of research made on herbs with a focus on the modulatory roles of tumor suppressors, and on the molecular mechanisms underlying the prevention if atherosclerosis, supporting designs for further research in this field.

Increase in plasma ceramide levels via secretory sphingomyelinase activity in streptozotocin-induced diabetic rats

Ceramide mediates apoptosis and is upregulated by oxidative stress. To reveal the causative agent of diabetes-induced complications, we examined the changes in ceramide metabolism during diabetes. Two and 8 weeks after intraperitoneal injection of streptozotocin (STZ: 40 mg kg−1 body weight) to rats, tissue ceramide levels were analyzed by liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS). Blood glucose was significantly increased 2 weeks after STZ administration. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and blood urea nitrogen (BUN) levels were also increased in the diabetic rats, suggesting that hepatic and renal damage was induced by STZ administration. Vitamin C, an indicator of oxidative stress, was significantly decreased in the plasma, liver, and kidney of rats 2 weeks after STZ administration. Although no differences in hepatic ceramide levels were observed between the control and diabetic rats, plasma and renal ceramide levels were significantly increased 8 weeks after STZ administration. In the liver and kidney, acid and neutral sphingomyelinase (SMase) activities were not increased, while secretory sphingomyelinase (sSMase) activity was increased in the plasma of diabetic rats after STZ administration. These data indicated that STZ administration induced the increase in plasma ceramide levels via the increase in sSMase activity. It was suggested that increased plasma ceramide levels were involved in the renal damage induced by STZ in diabetic rats accompanied with the enhancement of oxidative stress.