Centre for Free Radical Research, Department of Pathology, University of Otago Christchurch, Christchurch, New Zealand.
Centre for Free Radical Research, Department of Pathology, University of Otago Christchurch, Christchurch, New Zealand.
Free Radic Biol Med. 2014 Dec;77:331-9. doi: 10.1016/j.freeradbiomed.2014.09.025. Epub 2014 Oct 5.
The diterpenoid, adenanthin, represses tumor growth and prolongs survival in mouse promyelocytic leukemia models (Liu et al., Nat. Chem. Biol. 8, 486, 2012). It was proposed that this was done by inactivating peroxiredoxins (Prxs) 1 and 2 through the formation of an adduct specifically on the resolving Cys residue. We confirmed that adenanthin underwent Michael addition to isolated Prx2, thereby inhibiting oxidation to a disulfide-linked dimer. However, contrary to the original report, both the peroxidatic and the resolving Cys residues could be derivatized. Glutathione also formed an adenanthin adduct, reacting with a second-order rate constant of 25±5 M(-1) s(-1). With 50 µM adenanthin, the peroxidatic and resolving Cys of Prx2 reacted with half-times of 7 and 40 min, respectively, compared with 10 min for GSH. When erythrocytes or Jurkat T cells were treated with adenanthin, we saw no evidence for a reaction with Prxs 1 or 2. Instead, adenanthin caused time- and concentration-dependent loss of GSH followed by dimerization of the Prxs. Prxs undergo continuous oxidation in cells and are normally recycled by thioredoxin reductase and thioredoxin. Our results indicate that Prx reduction was inhibited. We observed rapid inhibition of purified thioredoxin reductase (half-time 5 min with 2 µM adenanthin) and in cells, thioredoxin reductase was much more sensitive than GSH and loss of both preceded accumulation of oxidized Prxs. Thus, adenanthin is not a specific Prx inhibitor, and its reported antitumor and anti-inflammatory effects are more likely to involve more general inhibition of thioredoxin and/or glutathione redox pathways.
二萜类化合物腺嘌呤通过形成特定于解析半胱氨酸残基的加合物来抑制过氧化物酶体增殖物激活受体（Prxs）1 和 2 的失活，从而抑制肿瘤生长并延长小鼠早幼粒细胞白血病模型的存活时间（Liu 等人，Nat. Chem. Biol. 8, 486, 2012）。我们证实腺嘌呤与分离的 Prx2 发生迈克尔加成反应，从而抑制其氧化为二硫键连接的二聚体。然而，与原始报道相反，过氧物酶和解析半胱氨酸残基都可以被修饰。谷胱甘肽也形成腺嘌呤加合物，反应的二级速率常数为 25±5 M(-1) s(-1)。用 50 µM 腺嘌呤处理 Prx2 的过氧物酶和解析半胱氨酸残基，反应的半衰期分别为 7 和 40 分钟，而 GSH 的半衰期为 10 分钟。当用腺嘌呤处理红细胞或 Jurkat T 细胞时，我们没有发现与 Prxs 1 或 2 反应的证据。相反，腺嘌呤导致 GSH 的时间和浓度依赖性损失，随后 Prxs 发生二聚化。Prxs 在细胞中不断被氧化，通常通过硫氧还蛋白还原酶和硫氧还蛋白进行循环利用。我们的结果表明 Prx 的还原被抑制。我们观察到纯化的硫氧还蛋白还原酶的快速抑制（用 2 µM 腺嘌呤处理的半衰期为 5 分钟），并且在细胞中，硫氧还蛋白还原酶比 GSH 更敏感，并且在氧化的 Prxs 积累之前，其消耗先于 GSH 的消耗。因此，腺嘌呤不是特定的 Prx 抑制剂，其报道的抗肿瘤和抗炎作用更可能涉及更普遍的硫氧还蛋白和/或谷胱甘肽氧化还原途径的抑制。
