Yasuyoshi Torii

Anticarcinogenic antioxidants as inhibitors against intracellular oxidative stress

Oxidative stress has been implicated in the pathogenesis of numerous diseases, including cancer. In the present study, the protective effect of natural antioxidants, such as quercetin and tea polyphenols, on intracellular oxidative stress was studied. Here we report a novel function of quercetin and tea polyphenols, as potential inhibitors of 4-hydroxy-2-nonenal (HNE)-induced intracellular oxidative stress and cytotoxicity. In rat liver epithelial RL34 cells, a potent electrophile HNE dramatically induced the productions of reactive oxygen species (ROS), which correlated well with the reduction in cell viability. We found that quercetin and tea polyphenols, such as epigallocatechin gallate and theaflavins and their gallate esters, significantly inhibited the HNE-induced ROS production and cytotoxicity. In addition, HNE induced a transient decrease in the mitochondrial membrane potential (Δψ), which was also retarded by the antioxidants. These data suggest that the antioxidants, such as quercetin and tea polyphenols, are inhibitors against mitochondrial ROS production.

Sphingosine 1‐phosphate induces the production of glial cell line‐derived neurotrophic factor and cellular proliferation in astrocytes

Sphingosine 1‐phosphate (S1P) is a platelet‐derived bioactive sphingolipid that evokes a variety of biological responses. To understand the role of S1P in the central nervous system, we have examined the effect of S1P on the production of glial cell line‐derived neurotrophic factor (GDNF) and growth regulation of cortical astrocytes from rat embryo. Moreover, we examined the possibility that the expression of GDNF is regulated differently in cultured astrocytes from the stroke‐prone spontaneously hypertensive rat (SHRSP) than in those from Wistar kyoto rats (WKY). The mRNA expression was quantitated by RT‐PCR based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme‐linked immunosorbent assay. S1P induced the expression of GDNF mRNA and the production of GDNF protein in a dose‐dependent manner in WKY astrocytes. Moreover, S1P increased cell numbers and induced the proliferation of astrocytes. In addition, the level of mRNA expression and protein production of GDNF was significantly lower in SHRSP than WKY astrocytes following exposure to S1P. These findings revealed that S1P augments GDNF protein production and cellular growth in astrocytes. Also, our results indicate that production in SHRSP astrocytes was attenuated in response to S1P compared with that observed in WKY. We conclude that S1P specifically triggers a cascade of events that regulate the production of GDNF and cell growth in astrocytes. Our results also suggest that the reduced expression of GDNF caused by S1P is a factor in the stroke proneness of SHRSP. GLIA 41:199–206, 2003.

DEMONSTRATION OF ALKALINE PHOSPHATASE PARTICIPATION IN THE MINERALIZATION OF OSTEOBLASTS BY ANTISENSE RNA APPROACH

MC3T3‐E1 cells grown with ascorbic acid express sequentially osteoblastic marker proteins such as alkaline phosphatase (ALPase) and then form a mineralized extracellular matrix (ECM) as a consequence of osteoblastic differentiation. To explore the functional roles of ALPase in the process of osteoblastic maturation, an inducible expression vector for antisense ALPase RNA was constructed and stably transfected into MC3T3‐E1 cells. The expression of antisense ALPase RNA in the differentiated MC3T3‐E1 transfectants reduced markedly the ALPase activity, which resulted in a significant decrease in the deposition of minerals upon prolonged culture. These findings demonstrated directly that ALPase participated in the mineralizationof ECM.

Synergistic effect of BMP-2 and ascorbate on the phenotypic expression of osteoblastic MC3T3-E1 cells

Of TGF-β superfamily proteins, BMP-2 enhanced alkaline phosphatase (ALP) activity in cultured osteoblastic cells, MC3T3-E1, to the same level promoted by ascorbate, whereas TGF-βs (β1, β2, β3) reduced ALP activity and altered cell morphology under the same conditions. Activin appeared to have no distinct effect on ALP synthesis. Ascorbate dependent increase in ALP synthesis was markedly stimulated in the presence of BMP-2. The synergistic effect of ascorbate on ALP synthesis was replaced by type I collagen coated on the culture dish. However, BMP-2 appeared not to bind to type I collagen. These findings indicate that BMP-2 acts directly on osteoblastic cells through its receptors and collagenous matrix can neither recruit BMP-2 nor modulate directly the action of BMP-2 in the pericellular area. Treatment of cells grown in ascorbate media with TGF-βs decreased rapidly the cellular ALP activity indicating that TGF-βs direct cells to the differentiated stage.

Ascorbate-dependent elevation of mRNA levels for cytochrome P450s induced by polychlorinated biphenyls.

Trichlorobiphenyl induced only CYP1A2 mRNA, while pentachlorobiphenyl induced both CYP1A2 and CYP2B1 mRNAs in rat liver. The mRNA levels for these P450s were elevated when ascorbic acid-deficient ODS rats (mutant rats with a hereditary osteogenic disorder) were fed a diet supplemented with ascorbic acid. The amount of CYP2B1 mRNA increased rapidly and reached a maximum level of approximately double within 24 hr of injection of pentachlorobiphenyl. Thereafter, the amount of its mRNA decreased to a steady level. This pattern was roughly paralleled by changes in the amount of CYP1A2 mRNA.

Isolation of GnafC, a Polysaccharide Constituent of Gnaphalium affine, and Synergistic Effects of GnafC and Ascorbate on the Phenotypic Expression of Osteoblastic MC3T3-E1 Cells

After screening extensively factors in plant extracts that increase alkaline phosphatase activity, an osteoblastic differentiation marker protein in mouse calvarial osteoblast MC3T3-E1 cells, GnafC derived from Gnaphalium affine, was found to significantly enhance the alkaline phosphatase (ALPase) activity in a synergistic manner with ascorbate. GnafC was a polysaccharaide with an approximate molecular mass of 10,000 and comprised mannose, xylose, arabinose, galactose and glucose in a molar ratio of 1:2:4.3:2.5:2.7. Expression of the osteoblastic differentiation marker genes was examined by semiquantitative RT-PCR with RNAs prepared from cells at different developmental stages. With ascorbate in the culture, GnafC enhanced the expression of the ALPase and MMP13 genes from the early stage of differentiation, leading to maturation of the collagenous extracellular matrix (ECM), a prerequisite for mineralization.