Toshi Tsuzuki

Cytoprotection against ischemia-induced DNA cleavages and cell injuries in the rat liver by pro-vitamin C via hydrolytic conversion into ascorbate

To search a regimen for prevention of post-ischemic reperfusional (I/R) injuries, I/R in the liver was induced by 30-min clamping and subsequent unfastening of the portal vein of a rat, which underwent previous intravenous administration with ascorbic acid (Asc) of 1 mg/kg or the autooxidation-resistant pro-vitamin C, 2-O-alpha-D-glucosylated Asc (Asc2G) or 2-O-phosphorylated Asc (Asc2P) of 1 mg Asc equivalent/kg from the viewpoint of utilization of antioxidants that can promptly scavenge I/R-derived reactive oxygen species. The administration with Asc, Asc2P or Asc2G prevented some features of hepatic I/R injuries such as release of hepatic marker enzymes GOT and GPT into the blood vessel, cellular degenerative symptoms including vacuolation and cell fragmentation, and nuclear DNA strand cleavage as detected by TUNEL staining. The preventive effects on I/R injuries were in the order: Asc2G > Asc2P >> Asc. This order of preventive degrees of three anti-oxidants is partly attributable to proper efficiency of conversion to vitamin C and stability in blood stream; Asc2P was moderately converted to a free monoanion form of Asc in human serum, but, in rat serum, so efficiently converted to Asc as to undergo the resultant oxidative decomposition before reaching the liver, whereas Asc2G underwent scarce conversion to Asc in human serum but moderate conversion in rat serum, suggesting that Asc2P might be less cytoprotective against I/R injury than Asc2G in the rat liver in a way different from the human liver. In contrast Asc was so susceptible to autooxidation as to be rapidly decomposed in either rat or human serum. The concentrations of ascorbyl radicals (AscR) in serum were unchanged during I/R for sham-operated rats, but appreciably diminished time-dependently for I/R-operated rats as shown by ESR spectra. A marked increase in serum AscR occurred in rats receiving Asc, Asc2G or Asc2P, but it was time-dependently restored down to the pre-ischemic level of AscR in I/R-operated rats more rapidly than in sham-operated rats. Thus, hepatic I/R injuries were shown to be prevented more markedly by Asc2G or Asc2P than by Asc, which is attributable to efficiencies of both vitamin C conversion and subsequent AscR retention.

Topical Application of a Novel, Water-soluble γ-Tocopherol Derivative Prevents UV-induced Skin Damage in Mice¶

Abstract We investigated whether the topical application of a novel, water-soluble γ-tocopherol (γ-Toc) derivative, γ-tocopherol-N,N-dimethylglycinate hydrochloride (γ-TDMG), could protect against UV-induced skin damage in hairless mice. Topical pre- or post-application of a 5% (93 mM) γ-TDMG solution in water/propylene glycol/ethanol (2:1:2) significantly prevented sunburn cell formation, lipid peroxidation and edema/inflammation that were induced by exposure to a single dose of UV irradiation of 5 kJ/m2 (290–380 nm, maximum 312 nm). This effect was greater than that seen with two α-Toc derivatives, α-tocopherol acetate (α-TA) and α-tocopherol-N,N-dimethylglycinate (α-TDMG). When a 5% solution of γ-TDMG was applied to mouse skin for 1 h, cutaneous γ-Toc increased by 25-fold after 24 h; levels of cutaneous α-Toc increased by only two- and eight-fold in α-TDMG and α-TA treated skins, respectively. These findings indicated that γ-TDMG immediately converted to γ-Toc in the skin and suggest that ability of γ-TDMG to protect the skin from the damaging effects of irradiation was due to its conversion to γ-Toc. When a 5% solution of γ-Toc was applied to mouse skin for 1 h, cutaneous γ-Toc rapidly increased by 25-fold, but fell to baseline levels by 24 h. In contrast, the concentration of γ-Toc in skin that was treated with γ-TDMG similarly increased, but these high levels were maintained after 24 h. These results suggest that γ-TDMG may be a more effective source of γ-Toc in skin. Thus, the topical application of γ-TDMG may be efficacious for the prevention of UV-B-induced skin damage.

Anti-transforming nature of ascorbic acid and its derivatives examined by two-stage cell transformation using BALB/c 3T3 cells

The anti-transforming effects of sodium ascorbate and its stable derivatives were examined in the two-stage transformation assay. When BALB/c 3T3 cells were treated with 0.2 microg/ml 20-methylcholanthrene as an initiator, and 100 ng/ml 12-O-tetradecanoylphorbol-13-acetate as a promoter, the addition at the promotion stage of L-ascorbic acid-2-phosphate ester magnesium (APM) was most marked in the inhibition of transformation. The inhibitory effects of sodium ascorbate and ascorbic acid-2-glucoside (AG) were comparable, but weaker than those of APM; L (+)-ascorbic acid-2-sulfate ester disodium 2H(2)O showed little effect. When phorbol 12, 13-didecanoate or tumor necrosis factor alpha (TNF-alpha) were used as promoters, APM also effectively suppressed transformation.