2-Oxoadenosine induces cytotoxicity through intracellular accumulation of 2-oxo-ATP and depletion of ATP but not via the p38 MAPK pathway.

2-Oxoadenosine (2-oxo-Ado), an oxidized form of adenosine, is cytotoxic and induces growth arrest and cell death, which has potential as an anti-cancer drug. However, it is not well understood how 2-oxo-Ado exerts its cytotoxicity. We examined the effects of 2-oxo-Ado on non-tumour cells, namely immortalized mouse embryonic fibroblast lines, and investigated mechanisms by which 2-oxo-Ado exerts its cytotoxicity. We found that cell death induced by 2-oxo-Ado is classical caspase-dependent apoptosis, and requires its sequential intracellular phosphorylation catalysed by adenosine kinase (ADK) and adenylate kinase 2, resulting in intracellular accumulation of 2-oxo-ATP accompanied by accumulation of 2-oxo-Ado in RNA and depletion of ATP. Moreover, we showed that overexpression of MTH1, an oxidized purine nucleoside triphosphatase, prevents 2-oxo-Ado-induced cytotoxicity accompanied by suppression of accumulation of both intracellular 2-oxo-ATP and 2-oxo-Ado in RNA and recovery of ATP levels. We also found that 2-oxo-Ado activates the p38 MAPK pathway. However, siRNAs against Mkk3 and Mkk6, or treatment with several p38 MAPK inhibitors, except SB203580, did not prevent the cytotoxicity. SB203580 prevented intracellular phosphorylation of 2-oxo-Ado to 2-oxo-AMP, and an in vitro ADK assay revealed that SB203580 directly inhibits ADK activity, suggesting that some of the effects of SB203580 may depend on ADK inhibition.

SCH23390, a dopamine D1 receptor antagonist, suppressed scratching behavior induced by compound 48/80 in mice.

To clarify the mechanisms by which compound 48/80 (C48/80) induces scratching behavior, the involvement of dopamine D(1) receptors was investigated. The intracisternal (i.t.) administration of SCH23390 (1.0 µg), a selective dopamine D(1) receptor antagonist, significantly decreased C48/80-induced scratching behavior in mice. These results suggest that dopamine D(1) receptors contribute to scratching behavior or the itch sensation induced by subcutaneous injection of C48/80 in mice. Co-administration of SCH23390 and C48/80 enhanced c-fos immunoreactivities in the peduncular part of the lateral hypothalamus (PLH), whereas the immunoreactivities in the other groups were unchanged. The dopaminergic system may be playing an important role in the suppression of C48/80-induced scratching behavior by SCH23390.

Dietary conjugated linoleic acid modifies the brain endocannabinoid system in mice.

Conjugated linoleic acid (CLA) has a role of biogenic regulation through modifying prostaglandin production. However, its effects on related metabolites of arachidonate remain unclear. Therefore, the effects of CLA on brain endocannabinoid content as well as its analogs were investigated. Mice (3-week-old), provided with diets containing 3% linoleic acid or 3% CLA for 4 weeks, were sacrificed and lipids were extracted from their cerebral cortex and hypothalamus. The amounts of N-arachidonoyl-ethanolamide, 2-arachidonoyl-glycerol (2-AG), oleoyl-ethanolamide and palmitoyl-ethanolamide were determined quantitatively by LC-MS. The 2-AG level in the cerebral cortex was significantly decreased by CLA treatment, but the other compounds were unaffected in the cerebral cortex and hypothalamus. The present study indicated that dietary CLA site-selectively decreases 2-AG in the cerebral cortex.

Arachidonic acid prevents fatty liver induced by conjugated linoleic acid in mice.

Conjugated linoleic acid (CLA) has anti-obesity effects, but induces fatty liver in mice. The present study investigated whether co-administration of arachidonic acid (ARA) attenuates fat accumulation in the mouse liver induced by CLA. Male mice (8 weeks old) were given diets with either no addition of dietary fat (control), 3 % linoleic acid (LA), 3 % CLA, 3 % CLA+1 % ARA, or 3 % CLA+2 % ARA for 4 weeks. The perirenal fat weight in ARA-treated groups decreased similarly as with CLA alone, when compared to control or LA. Plasma TAG concentration was significantly higher in the CLA group than in either CLA+ARA group, while plasma cholesterol and NEFA concentrations did not vary among the groups. In contrast to visceral fat, liver weight was significantly higher in the CLA group than in the control or LA groups, and the effects of CLA were attenuated by ARA. TAG and cholesterol were markedly accumulated in the liver with dietary CLA, whereas co-administration with ARA, at either concentration, suppressed CLA-induced lipid accumulation. Liver PGE(2) was enhanced by a combination of CLA and ARA when compared with CLA alone, but PGE(1) level was not significantly different among groups. In conclusion, fatty liver induced by CLA was attenuated by co-administration with ARA, furthermore, a combination of these fatty acids maintained the anti-obese effect of CLA.

mRNA expression of lysyl oxidase and matrix metalloproteinase-12 in mouse skin.

Elastic fibers in the dermis play an important role in skin elasticity. The desmosine crosslinking structure constructed of lysyl oxidase (LOX) in elastic fibers contributes to elasticity, while elastic fibers are primarily degraded by one of the matrix metalloproteinases (MMPs), MMP-12. We investigated the gender differences and diurnal variation of these enzymes. Gender-based differences in LOX mRNA expression were detected, and were significantly lower in females. In contrast, higher MMP-12 mRNA expression was observed in the light period, suggesting that elastic fibers might be degraded in the light rather than the dark period.