大蒜化合物之類似物烯丙基硒半胱胺酸對於DMBA/TPA誘導皮膚腫瘤形成之影響

Abstract

烯丙基硒半胱胺酸 (Se-allylselenocysteine, ASC) 為有機硫化物之結構相似物，先前研究證實其在體外和體內實驗中能抑制乳腺癌之發生。然而，ASC對抗發炎之功效仍是未知。有越來越多的證據顯示，慢性發炎與部分腫瘤生成有很大的相關性，因此調節發炎過程之中間產物例如：誘導型一氧化氮合成酶 (Inducible nitric oxide synthase, iNOS) 和環氧化酵素2 (Cyclooxygenase-2, COX-2) 可降低癌症發生之可能性。本研究以體外細胞實驗探討ASC對於脂多醣 (Lipopolysaccharide, LPS) 誘導RAW 264.7細胞發炎之功效，進一步以ICR female mice進行7, 12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) 誘導皮膚致癌模式，探討ASC對腫瘤生成之功效。細胞實驗結果顯示，ASC在50M下抑制LPS誘導RAW 264.7的NF-B活性，進而抑制一氧化氮 (Nitric oxide ,NO) 產量和iNOS蛋白質表現量；另一方面，觀察到COX-2蛋白質和基因表現增加。在動物實驗過程中，Positive control組在第十一週時腫瘤發生率達百分之百，而ASC 5 mol/200 L實驗組則在第九週時腫瘤發生率已達百分之百；Positive control組實驗二十週結束後，每隻小鼠之腫瘤數平均約有22顆，ASC 5 mol/200 L實驗組約為35顆。小鼠之腫瘤大小分布方面，處理ASC實驗組與Positive control組比較起來有較多的趨勢。因此ASC在DMBA/TPA誘導動物致癌模式下，可能會加速乳突瘤之形成、增加腫瘤數量和腫瘤大小。同時表現ASC可促進DMBA/TPA所誘導之COX-2蛋白質表現量。綜合目前結果，推測ASC在DMBA/TPA誘導的皮膚致癌模式中，COX-2的上調對腫瘤促進扮演重要的角色，至於其詳細之作用機轉仍需進一步的探討。

Se-allylselenocysteine (ASC), an analogue of garlic compound, has been shown to inhibit mammary carcinogenesis in vivo and cell growth in vitro. However, the function of ASC on anti-inflammatory effect remains largely unknown. Therefore, we investigated whether ASC has anti-inflammatory on LPS-induced inflammation in vitro or anti-tumor promoting on 7, 12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin tumorigenesis in vivo and tried to elucidate the mechanisms involved. In in vitro study, the result showed that ASC inhibited lipopolysaccharide (LPS)-induced production of nitric oxide (NO) with decreased protein level of inducible nitric oxide synthase (iNOS) in RAW 264.7 cells. ASC also reduced nuclear factor-B (NF-B) luciferase activity. On the other hand, ASC can enhance LPS-induced COX-2 protein level and mRNA expression in RAW 264.7 cells. In in vivo study, topical application of ASC on the dorsal skin of DMBA-initiated and TPA-promoted mice could significantly accelerate skin tumorigenesis and raise tumor multiplicity than positive control group (DMBA+TPA). The number of tumors that were 1–3 mm, 3–5 mm and >5 mm in size per mouse was increased in a dose-dependent manner in the ASC-pretreated groups. Pretreatment with ASC showed significant increment on the expression of COX-2 compared with positive control group. In summary, the present results speculate that COX-2 played a crucial role in tumor-promoting effect of ASC on DMBA/TPA-induced skin cancer in mice.