The ingestion of seafood contaminated with the marine biotoxin okadaic acid (OA) can lead to diarrhetic shellfish poisoning with symptoms like nausea, vomiting and abdominal cramps. Both rat and the human hepatic cytochrome P450 monooxygenases (CYP) metabolize OA. However, liver cell toxicity of metabolized OA is mainly unclear. The aim of our study was to detect the cellular effects in HepG2 cells exposed to OA in the presence of recombinant CYP enzymes of both rat and human for the investigation of species differences. The results should be set in correlation with a CYP-specific metabolite pattern. Comparative metabolite profiles of OA after incubation in rat and human recombinant CYP enzymes were established by using LC-MS/MS technique. Results demonstrated that metabolism of OA to oxygenated metabolites correlates with detoxification which was mainly catalyzed by human CYP3A4 and CYP3A5. Detoxification by rat Cyp3a1 was lower compared to human CYP3A enzymes and activation of OA by Cyp3a2 was observed, coincident with minor overall conversion capacity of OA. By contrast human and rat CYP1A2 seem to activate OA into cytotoxic intermediates. In conclusion, different mechanisms of OA metabolism may occur in the liver. At low OA doses, the human liver is likely well protected against cytotoxic OA, but for high shellfish consumers a potential risk cannot be excluded.
Four metabolites of okadaic acid were generated by incubation with human recombinant cytochrome P450 3A4. The structures of two of the four metabolites have been determined by MS/MS experiments and 1D and 2D NMR methods using 94 and 133 ug of each metabolite. The structure of a third metabolite was determined by oxidation to a metabolite of known structure. Like okadaic acid, the metabolites are inhibitors of protein phosphatase PP2A. Although one of the metabolites does have an alpha,beta unsaturated carbonyl with the potential to form adducts with an active site cysteine, all of the metabolites are reversible inhibitors of PP2A.
来源:Hazardous Substances Data Bank (HSDB)
毒理性
毒性总结
识别和使用:岗田酸(OA)是一种固体。OA 是最常见且全球分布的海洋毒素之一。它容易被贝类动物积累,主要是双壳类软体动物和鱼类,随后可能被人类食用,导致食物中毒。OA 作为一种生化工具,用作肿瘤促进剂和细胞调控探针。人体研究:OA 是主要的腹泻性贝类中毒(DSP)毒素,其摄入会导致胃肠道症状,尽管它并不被认为是致命的。在分子水平上,OA 是几种丝氨酸/苏氨酸蛋白磷酸酶的特异性抑制剂。OA 在人角质形成细胞和人支气管上皮细胞中诱导 DNA 加合物。动物研究:在小鼠口服 1 毫克/千克/天的 OA 7 天后,引起了腹泻、体重减轻、食物摄入量减少和死亡。OA 在小鼠皮肤的二阶段实验中是一种肿瘤促进剂。OA 可导致细胞骨架结构和细胞间接触的紊乱,引起染色体丢失、凋亡、DNA 损伤并抑制磷酸酶,这表明其潜在的胚胎毒性。OA 在不同物种中用作阿尔茨海默病的药理学诱导模型。在大鼠海马内双侧微注射 OA 导致空间记忆受损。与对照相比,从暴露于 OA 的小组贻贝 Perna perna 中观察到的微核频率显著较高。OA 在仓鼠肾(BHK)细胞中诱导 DNA 加合物的形成,也在斑马鱼胚胎中证明了 DNA 加合物的诱导。生态毒性研究:蓝贻贝 Mytilus edulis 和太平洋牡蛎 Crassostrea gigas 在体内暴露于 OA,并测量了对 DNA 断裂的影响。与对照组相比,两种细胞类型的两种物种都观察到了显著的 DNA 断裂增加。在较高的毒素浓度下,这种增加在太平洋牡蛎中更为显著。在贻贝 Mytilus galloprovincialis 中,贻贝鳃细胞对 OA 介导的早期遗传毒性比血细胞更敏感。在玉米细胞中,OA 导致细胞周期在前期停滞,导致幼苗生长抑制。
IDENTIFICATION AND USE: Okadaic acid (OA) is a solid. OA is one of the most frequent and worldwide distributed marine toxins. It is easily accumulated by shellfish, mainly bivalve mollusks and fish, and, subsequently, can be consumed by humans causing alimentary intoxications. OA is used as a biochemical tool as tumor promoter and probe of cellular regulation. HUMAN STUDIES: OA is the main representative diarrheic shellfish poisoning (DSP) toxin and its ingestion induces gastrointestinal symptoms, although it is not considered lethal. At the molecular level, OA is a specific inhibitor of several types of serine/threonine protein phosphatases. Induction of DNA adducts by OA was shown in human keratinocytes and human bronchial epithelial cells. ANIMAL STUDIES: In mice after 7 days of oral administration of 1 mg/kg/day OA induced diarrhea, body weight loss, reduced food consumption, and death. OA was a tumor promoter in two-stage experiments on mouse skin. OA can induce disorganization in cytoskeletal architecture and cell-cell contact, cause chromosome loss, apoptosis, DNA damage and inhibit phosphatases, suggesting its potential embryotoxicity. OA is used as a pharmacologically induced model of Alzheimer's disease in different species. In rats intrahippocampal bilateral microinjection of OA led to a spatial memory impairment. A significantly higher frequency of micronuclei was observed in hemocytes from the OA-exposed group of the mussel Perna perna compared to control. Induction of DNA adducts by OA was shown in Baby Hamster Kidney (BHK) cells, also the induction of DNA adducts in zebra fish embryos was demonstrated. ECOTOXICITY STUDIES: The blue mussel, Mytilus edulis and the pacific oyster, Crassostrea gigas were exposed in vivo to OA and impacts on DNA fragmentation were measured. A significant increase in DNA fragmentation was observed in the two cell types from both species relative to the controls. This increase was greater in the pacific oyster at the higher toxin concentration. In mussel Mytilus galloprovincialis mussel gill cells display higher sensitivity to early OA-mediated genotoxicity than hemocytes. In maize cells, OA caused the cell cycle arrest at preprophase, leading to seedling growth inhibition.
/The authors/ generated a neuroblastoma (SH-SY5Y) cell system in which cytoskeletal proteins are abnormally phosphorylated resulting in microtubule disruption due to the marked inhibition of protein phosphatase activities by okadaic acid (OA). OA-induced declines in cell viability and mitochondrial metabolic activity were remarkably prevented by melatonin. In addition, the hyperphosphorylation/accumulation of neurofilament-(NF-) H/M subunits and the disruption of microtubules, induced by OA, were significantly inhibited by melatonin.
In awake rats the microinjection into the hippocampus of okadaic acid, a potent inhibitor of protein phosphatases 1 and 2A, induces in about 20 min intense electroencephalographic and behavioral limbic-type seizures, which are suppressed by the systemic administration of the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine hydrogen maleate and by the intrahippocampal administration of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine, an inhibitor of protein kinases.
Okadaic acid (OA) is a marine toxin, a tumor promoter and an inducer of apoptosis. It mainly inhibits protein-phosphatases, protein synthesis and enhances lipid peroxidation. Caco-2 cells were treated exclusively by OA (15 ng/mL) or cadmium (Cd) (0.625 and 5 ug/mL) for 24 hr, protein synthesis was inhibited (by 42 +/- 5%, 18 +/- 13%, and 90 +/- 4% respectively) while /malondialdehyde/ (MDA) production was 2,235 +/- 129, 1710 +/- 20, and 11,496 +/-1,624 pmol/mg protein respectively. In addition, each toxicant induced modified bases in DNA; increases in oxidised bases and methylated dC. The combination of OA and cadmium was more cytotoxic and caused more DNA base modifications; the ratio m(5)dC/(m(5)dC + dC) was increased from 3 +/- 0.15 to 9 +/- 0.15 and the ratio 8-(OH)-dG/10(5) dG also (from 36 +/- 2 to 76 +/- 6). The combination of OA and Cd also increased the level of MDA (1,6874 +/- 2,189 pmole/mg protein). The present results strongly suggest that DNA damage resulting from the oxidative stress induced by these two toxicants may significantly contribute to increasing their carcinogenicity via epigenetic processes.
25 nM okadaic acid promotes DNA fragmentation in B16 melanoma, increasing cell detachment as well as pigmentation, a characteristic of melanocytic cell differentiation. At lower levels, okadaic acid synergizes with UV exposure to increase DNA fragmentation.
The results in this study show... that this marine toxin is able to cross the transplacental barrier. Fetal tissue contains more okadaic acid than the liver or kidney: 5.60% compared to 1.90 and 2.55% respectively as measured by HPLC and fluorescent detection after derivatization with 9-Anthryldiazomethane (ADAM).
This study concerns the distribution of 3H-okadaic acid (OA) in organs and biological fluids of Swiss mice having received a single dose per os of OA (50 ug/kg). The determination of the intestinal tissues and contents 24 hr after administration demonstrates a slow elimination of OA. When the dose of OA was increased from 50-90 ug/kg, the concentrations of the toxin in the intestinal content and feces increased proportionally. A good correlation was found between an increase of OA in the intestinal tissue and the diarrhea in animals given 90 ug/kg orally. Moreover OA was present in liver and bile and in all organs including skin and also fluids. Altogether these results confirmed an enterohepatic circulation of OA as previously shown.
The influence of nutritional regime and water temperature on depuration rates of OA-group toxins in the wedge shell Donax trunculus was examined by exposing naturally contaminated specimens to three nutritional regimes (microalgae, commercial paste of microalgae, and starvation) for 14 days at 16 °C and 20 °C. Total OA was quantified in the whole soft tissues of the individuals collected in days 2, 4, 6, 8, 10, 12 and 14. Mortality, dry weight, condition index, gross biochemical composition and gametogenic stages were surveyed. Low variation of glycogen and carbohydrates during the experiments suggest that wedge shells were under non-dramatic stress conditions. Wedge shells fed with non-toxic diets showed similar depuration rates being 15 and 38% higher than in starvation, at 16 and 20 °C, respectively. Depuration rates under non-toxic diets at 20 °C were 71% higher than at 16 °C. These results highlight the influence of water temperature on the depuration rate of total OA accumulated by D. trunculus, even when the increase is of only 4 °C, as commonly observed in week time scales in the southern Portuguese coastal waters. These results open the possibility of a faster release of OA in harvested wedge shells translocated to depuration systems when under a slight increase of water temperature.
... acidic toxins, include okadaic acid (OA) and its derivatives named dinophysistoxins (DTXs). OA and its derivatives (DTX1, DTX2 and DTX3) are lipophilic and accumulate in the fatty tissue of shellfish. These compounds are potent phosphatase inhibitors and this property is linked to inflammation of the intestinal tract and diarrhea in humans.
Okadaic acid is known as a diarrheal shellfish poison. It is thought that there is no specific target organ for okadaic acid after it has been absorbed into the body. However, the details of its pharmacokinetics are still unknown. In this study, we demonstrated that okadaic acid was more toxic to the hepatocyte-specific uptake transporter OATP1B1- or OATP1B3-expressing cells than control vector-transfected cells. In addition, PP2A activity, which is a target molecule of okadaic acid, was more potently inhibited by okadaic acid in OATP1B1- or OATP1B3-expressing cells compared with control vector-transfected cells. The cytotoxicity of okadaic acid in OATP1B1- or OATP1B3-expressing cells was attenuated by known substrates of OATP1B1- and OATP1B3, but not in control vector-transfected cells. Furthermore, after uptake inhibition study using OATP1B3-expressing cells, Dixon plot showed that okadaic acid inhibited the uptake of hepatotoxin microcystin-LR, which is a substrate for OATP1B1 and OATP1B3, in a competitive manner. These results strongly suggested that okadaic acid is a substrate for OATP1B3 and probably for OATP1B1, and could be involved in unknown caused liver failure and liver cancer. Since okadaic acid possesses cytotoxicity and cell proliferative activity by virtue of its known phosphatase inhibition activity.