Division of Pathology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Toxicology. 2013 Sep 15;311(3):216-24. doi: 10.1016/j.tox.2013.07.003. Epub 2013 Jul 12.
Citrinin (CTN) is a food-contaminating mycotoxin that efficiently induces renal tumors in rats. However, the modes of carcinogenic action are still unknown, preventing assessment of the risks of CTN in humans. In the present study, the proliferative effects of CTN and its causal factors were investigated in the kidneys of gpt delta rats. In addition, three in vivo genotoxicity assays (reporter gene mutation using gpt delta rats and comet and micronucleus assays using F344 rats) were performed to clarify whether CTN was genotoxic in vivo. CTN was administrated at 20 and 40mg/kg/day, the higher dose being the maximal tolerated dose and a nearly carcinogenic dose. In the kidney cortex of gpt delta rats, significant increases in the labeling indices of proliferating cell nuclear antigen (PCNA)-positive cells were observed at all doses of CTN. Increases in the mRNA expression levels of Ccna2, Ccnb1, Ccne1, and its transcription factor E2f1 were also detected, suggesting induction of cell cycle progression at all tested doses of CTN. However, histopathological changes were found only in rats treated with the higher dose of CTN, which was consistent with increases in the mRNA expression levels of mitogenic factors associated with tissue damage/regeneration, such as Hgf and Lcn2, at the same dose. Thus, the proliferative effects of CTN may result not only from compensatory reactions, but also from direct mitogenic action. Western blot analysis showed that ERK phosphorylation was increased at all doses, implying that cell cycle progression may be mediated by activation of the ERK pathway. On the other hand, in vivo genotoxicity analyses were negative, implying that CTN did not have the potential for inducing DNA damage, gene mutations, or chromosomal aberrations. The overall data clearly demonstrated the molecular events underlying CTN-induced cell cycle progression, which could be helpful to understand CTN-induced renal carcinogenesis.
桔青霉素（CTN）是一种污染食物的真菌毒素，能有效地在大鼠中诱导肾肿瘤。然而，其致癌作用模式仍不清楚，这阻碍了对 CTN 在人类中风险的评估。在本研究中，研究了 CTN 及其因果因素在 gpt delta 大鼠肾脏中的增殖作用。此外，还进行了三项体内遗传毒性检测（使用 gpt delta 大鼠的报告基因突变和彗星试验和微核试验检测 F344 大鼠），以明确 CTN 在体内是否具有遗传毒性。CTN 以 20 和 40mg/kg/天的剂量给药，高剂量是最大耐受剂量和接近致癌剂量。在 gpt delta 大鼠的肾皮质中，所有 CTN 剂量均观察到增殖细胞核抗原（PCNA）阳性细胞标记指数的显著增加。还检测到 Ccna2、Ccnb1、Ccne1 及其转录因子 E2f1 的 mRNA 表达水平增加，表明所有测试剂量的 CTN 诱导细胞周期进程。然而，只有在高剂量 CTN 处理的大鼠中才发现组织学变化，这与同一剂量下与组织损伤/再生相关的有丝分裂因子 Hgf 和 Lcn2 的 mRNA 表达水平增加一致。因此，CTN 的增殖作用可能不仅来自代偿反应，而且来自直接的有丝分裂作用。Western blot 分析表明，所有剂量的 ERK 磷酸化均增加，表明细胞周期进程可能通过激活 ERK 途径介导。另一方面，体内遗传毒性分析为阴性，表明 CTN 没有诱导 DNA 损伤、基因突变或染色体畸变的潜力。总体数据清楚地表明了 CTN 诱导细胞周期进程的分子事件，这有助于理解 CTN 诱导的肾致癌作用。
