The biotoxin okadaic acid (OA) is a lipophilic secondary metabolite of marine microalgae. Therefore, OA accumulates in the fatty tissue of various shellfish and may thus enter the food chain. The ingestion of OA via contaminated marine species can lead to the diarrhetic shellfish poisoning syndrome characterized by the occurrence of a series of acute gastrointestinal symptoms in humans. In addition, genotoxicity and tumor-promoting properties of OA might constitute a long-term threat to human health. In order to deepen our understanding of the molecular effects of OA, we compared long-term (14 d) and short-term (24 h and 48 h) apoptotic effects of the compound on human HepaRG hepatocarcinoma cells. Cells were treated either with single doses for 24 and 48 h, respectively, or seven times over a period of 14 d, so that the cumulated quantities of OA in the long-term approach were equal to the single doses upon short-term treatment. Both short-term treatment scenarios led to the induction of apoptosis. Specific caspase activation assays and transcriptional analysis of mRNAs encoding proteins involved in the regulation of apoptosis suggest that OA-induced apoptosis occurs presumably by activation of the intrinsic apoptotic pathway. In contrast, effects were much less pronounced in case of long-term treatment. This is possibly linked to cellular protective mechanisms against low amounts of toxins, e.g. transporter-mediated efflux. In conclusion, our results show a clear concentration- and time-dependency of OA-mediated apoptotic effects in HepaRG cells and contribute to the elucidation of molecular effects of OA.

中文翻译：

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冈田酸对人HepaRG细胞凋亡状态的长期和短期影响的比较。

冈田生物毒素（OA）是海洋微藻的亲脂性次级代谢产物。因此，OA积聚在各种贝类的脂肪组织中，因此可能进入食物链。通过受污染的海洋物种摄入OA可导致腹泻性贝类中毒综合征，其特征是在人体内出现一系列急性胃肠道症状。另外，OA的遗传毒性和促进肿瘤的性质可能对人类健康构成长期威胁。为了加深我们对OA分子作用的了解，我们比较了该化合物对人HepaRG肝癌细胞的长期（14 d）和短期（24 h和48 h）凋亡作用。将细胞分别以单剂量处理24 h和48 h，或在14 d内处理7次，因此，长期治疗中的OA累积量等于短期治疗后的单剂量。两种短期治疗方案均导致细胞凋亡的诱导。特定的半胱天冬酶激活分析和编码涉及凋亡调控蛋白的mRNA的转录分析表明，OA诱导的凋亡可能是通过激活内在的凋亡途径而发生的。相反，在长期治疗的情况下效果并不明显。这可能与针对少量毒素（例如转运蛋白介导的外排）的细胞保护机制有关。总之，我们的结果表明，OA细胞介导的凋亡作用在HepaRG细胞中具有明显的浓度和时间依赖性，并有助于阐明OA的分子作用。