LINOLEIC ACID METABOLISM AND COLON CARCINOGENESIS

候选人寻求发展他的职业生涯作为癌症化学预防领域的转化研究员，他现在正在一个非常有利于这种研究的环境中工作。该提案为候选人计划制定化学预防研究的多学科转化方法提供了框架。 需要更好的干预措施来预防结肠癌的高死亡率。 亚油酸（LA）是一种常见的膳食多不饱和脂肪酸，可转化为花生四烯酸（AA），花生四烯酸又可形成促有丝分裂代谢产物[如前列腺素E2（PGE 2）和白三烯B4（LTB 4）]。 LA也是15-脂氧合酶-1（15-lox-1）形成13-S-羟基十八碳二烯酸（13-S-HODE）的底物。 我们发现15- lox-1和13-S-HODE在人结肠癌中减少，并且13-S-HODE在转化的结肠细胞中诱导凋亡。 在正常细胞中，酶δ 6-去饱和酶（d-6-d）形成γ-亚麻酸（GLA）以开始LA向AA的转化。 许多肿瘤细胞缺乏d-6-d活性，并因GLA暴露而死亡。 一些证据表明肿瘤细胞通过需要δ 5-去饱和酶（d-5-d）的替代途径将LA转化为AA。 假设亚油酸代谢从产生促细胞凋亡产物[13-S-HODE和（GLA）]转变为形成花生四烯酸的促有丝分裂代谢物（例如PGE 2和LTB 4），显著促进结肠癌发生。 具体目的是：1）确定与体外结肠细胞转化和分化状态相关的旁路转化途径的活性; 2）使用临床观察研究模型评估LA代谢的转变与人类结肠癌发生的进展步骤之间的关联（通过测量LA旁路途径的活性和相关酶以及LA和AA的代谢物[例如13-S-HODE，PGE 2，LTB 4，d-6-d，和15-lox-1]）; 3）评估异位d-6-d表达对体外转化的结肠细胞中的凋亡、分化和LA代谢的影响; 4）评价选择性d-5-d抑制对LA代谢和转化结肠细胞体外存活的影响;和5）在大鼠中建立的短期测定中确定选择性D-5-D抑制对结肠癌发生的作用。 这项工作将为未来的动物和临床研究的LA替代途径调制结肠癌化学预防的手段。

The candidate seeks to develop his career as a translational researcher in the field of cancer chemoprevention and he is now working in an environment highly conducive to such research. This proposal provides the framework for the candidate's plans to develop a multidisciplinary translational approach to chemoprevention research. Better interventions are needed to prevent the high mortality of colon cancer. Linoleic acid (LA), a common dietary polyunsaturated fatty acid, can be convertted to arachidonic acid (AA) that can in turn form mitogenic metabolites [e.g. prostaglandin, E2 (PGE2) and leukotriene B4 (LTB4)]. LA is also the substrate for 15-lipoxygenase-1 (15-lox-1) in forming 13-S-hydroxyoctadecadienoic (13-S-HODE). We have found that 15- lox-1 and 13-S-HODE are reduced in human colon cancers and that 13-S-HODE induces apoptosis in transformed colonic cells. In normal cells, the enzyme delta 6-desaturase (d-6-d) forms gamma- linolenic acid (GLA) to start the conversion of LA to AA. Many tumor cells lack d-6-d activity and die by GLA exposure. Some evidence suggests tumor cells convert LA to AA by an alternative pathway that requires delta 5-desaturase (d-5-d). The hypothesis is that a shift in linoleic metabolism from producing pro- apoptosis products [13-S-HODE and (GLA)] to the formation of mitogenic metabolites of arachidonic acid (e.g. PGE2 and LTB4) significantly contributes to colonic carcinogenesis. The specific aims are 1) to determine the activity of the alternative conversion pathway in relation to the transformation and differentiation states of colonic cells in vitro; 2) to evaluate the association between the shift in LA metabolism and the progressive steps of human colonic carcinogenesis using a clinical observational study model(by measuring the activity of LA alternative pathway and levels of related enzymes and metabolites of LA and AA [e.g. 13-S-HODE, PGE2, LTB4, d-6-d, and 15-lox-1] in colonic tissues from 3 patient groups [normal, polyp, and colon cancers]); 3) to evaluate the effects of ectopic d-6-d expression on apoptosis, differentiation, and LA metabolism in transformed colonic cells in vitro; 4) to evaluate the impact of selective d-5-d inhibition on LA metabolism and the survival of transformed colonic cells in-vitro; and 5) to determine the effects of selective d-5-d inhibition on colon carcinogenesis in an established short-term assay in rats. This work will set the stage for future animals and clinical studies of LA alternative pathway modulation as means of colon cancer chemoprevention.