Gali-Muhtasib H U, Perchellet J P, Khatib S H
American University of Beirut, Division of Biology, Lebanon.
Photochem Photobiol. 1998 Jun;67(6):663-8.
Naturally occurring hydrolyzable (HT) and condensed (CT) tannins and their monomeric units were tested for their ability to inhibit the stimulation of DNA synthesis by UVB radiation. Hairless mice were irradiated with either single (200 mJ/cm2) or multiple (150 mJ/cm2) doses of UVB applied at 24 h intervals and epidermal DNA synthesis was measured at different times after the last of these treatments. The peak of DNA synthesis that is observed 48-56 h after a single UVB irradiation shifts to an earlier time of 16-24 h after multiple UVB treatments. Interestingly, the early inhibitory period of DNA synthesis observed 8 h after a single UVB treatment is not detected following multiple UVB treatments. Rather, DNA synthesis is stimulated six-fold 24 h after multiple UVB treatment, a response that is higher than the peak occurring 48-56 h after a single UVB irradiation. The disappearance of the early period of inhibition when the peak of DNA synthesis shifts to an earlier time may be linked to reactive oxygen species brought to the epidermis by infiltrating leukocytes, which, in turn, act as second messengers to stimulate growth signals in cells. Topical applications of HT or CT remarkably inhibit the DNA responses to single and multiple UVB treatments, an effect that is dependent on the dose and time of administration. Indeed, the peak stimulation of DNA synthesis is maximally inhibited when 17 mg of Tarapod tannic acid (TA), an HT, are applied topically 20 min before a single UVB treatment. The polymeric tannins inhibited DNA synthesis to a greater degree than equal doses of their monomeric units, gallic acid and catechin. These results suggest that various oligomeric HT and CT may be useful against tumor-promoting responses associated with the exposure of skin to physical carcinogens.
对天然存在的可水解（HT）和缩合（CT）单宁及其单体单元抑制紫外线B（UVB）辐射刺激DNA合成的能力进行了测试。无毛小鼠接受单次（200 mJ/cm²）或多次（150 mJ/cm²）剂量的UVB照射，照射间隔为24小时，并在最后一次照射后的不同时间测量表皮DNA合成。单次UVB照射后48 - 56小时观察到的DNA合成峰值在多次UVB处理后提前至16 - 24小时。有趣的是，单次UVB处理后8小时观察到的DNA合成早期抑制期在多次UVB处理后未被检测到。相反，多次UVB处理后24小时DNA合成被刺激了6倍，这一反应高于单次UVB照射后48 - 56小时出现的峰值。当DNA合成峰值提前时早期抑制期的消失可能与浸润白细胞带到表皮的活性氧有关，这些活性氧反过来作为第二信使刺激细胞中的生长信号。HT或CT的局部应用显著抑制对单次和多次UVB处理的DNA反应，这种作用取决于给药剂量和时间。实际上，在单次UVB处理前20分钟局部应用17毫克塔拉波德单宁酸（TA，一种HT）时，DNA合成的峰值刺激被最大程度地抑制。聚合单宁比等量的单体单元没食子酸和儿茶素更能抑制DNA合成。这些结果表明，各种低聚HT和CT可能对与皮肤暴露于物理致癌物相关的肿瘤促进反应有用。
