微囊藻毒素LR诱导细胞毒性机制研究的细胞模型建立

以18种细胞系为材料,研究微囊藻毒素LR(20μg/mL和50μg/mL)所诱导的细胞毒性。形态观察表明,在经过30h以上的微囊藻毒素处理后,PC-3,J82,786-0,5637,VERO-E6等5种细胞出现了明显的细胞形态改变,毒素浓度越高,形态改变越厉害。微囊藻毒素LR的细胞毒性用LDH泄漏来表示。结果显示,5种毒素处理细胞的LDH泄漏呈剂量依赖性增加,其中5637和PC-3的LDH泄漏在同样的处理后较为厉害;同对照比较,SOD活力在20μg/mL MCLR处理下呈增加趋势,但在50μg/mL浓度下则下降;GSH含量在两种浓度处理下呈总体下降趋势。鉴于对微囊藻毒素敏感性差异分析,作者选择以5637细胞为基础,建立微囊藻毒素的毒理机制研究模型。       

Molecular cloning and characterization of alpha-class glutathione S-transferase gene from the liver of silver carp, bighead carp, and other major Chinese freshwater fishes

Two full-length cDNAs encoding glutathione S-transferase (GST) were cloned and sequenced from the hepatopancreas of planktivorous silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis). The silver carp and bighead carp GST cDNA were 920 and 978 bp in length, respectively, and both contained an open reading frame that encoding 223 amino acids. Partial GST cDNA sequences were also obtained from the liver of grass carp (Ctenopharyngodon idellus), crucian carp (Carassius auratu), mud carp (Cirrhinus molitorella), and tilapia (Oreochromis nilotica). All these GSTs could be classified as alpha-class GSTs on the basis of their amino acid sequence identity with other species. The three-dimensional structure of the silver carp GST was predicted using a computer program, and was found to fit the classical two-domain GST structure. Using the genome walker method, a 875-bp 5'-flanking region of the silver carp GST gene was obtained, and several lipopolysaccharide (LPS) response elements were identified in the promoter region of the phytoplanktivorous fish GST gene, indicating that the GST gene expression of this fish might be regulated by LPS, released from the toxic blue-green algae producing microcystins. To compare the constitutive expression level of the liver GST gene among the six freshwater fishes with completely different tolerance to microcystins, beta-actin was used as control and the ratio GST/beta-actin mRNA (%) was determined as 130.7 +/- 6.6 (grass carp), 103.1 +/- 8.9 (bighead carp), 92.6 +/- 15.0 (crucian carp), 72.3 +/- 7.8 (mud carp), 58.8 +/- 11.5 (silver carp), and 33.6 +/- 13.7 (tilapia). The constitutive expression level of the liver GST gene clearly shows that all the six freshwater fishes had a negative relationship with their tolerance to microcystins: high-resistant fishes (phytoplanktivorous silver carp and tilapia) had the lowest tolerance to microcystins and the high-sensitive fish (herbivorous grass carp) had the highest tolerance to microcystins. Taken together with the reciprocal relationship of constitutive and inducible liver GST expression level in some of the tested fish species to microcystin exposure, a molecular mechanism for different microcystin detoxification abilities of the warm freshwater fishes was discussed.     

Potent toxins in Arctic environments – Presence of saxitoxins and an unusual microcystin variant in Arctic freshwater ecosystems

Cyanobacteria are the predominant phototrophs in freshwater ecosystems of the polar regions where they commonly form extensive benthic mats. Despite their major biological role in these ecosystems, little attention has been paid to their physiology and biochemistry. An important feature of cyanobacteria from the temperate and tropical regions is the production of a large variety of toxic secondary metabolites. In Antarctica, and more recently in the Arctic, the cyanobacterial toxins microcystin and nodularin (Antarctic only) have been detected in freshwater microbial mats. To date other cyanobacterial toxins have not been reported from these locations. Five Arctic cyanobacterial communities were screened for saxitoxin, another common cyanobacterial toxin, and microcystins using immunological, spectroscopic and molecular methods. Saxitoxin was detected for the first time in cyanobacteria from the Arctic. In addition, an unusual microcystin variant was identified using liquid chromatography–mass spectrometry. Gene expression analyses confirmed the analytical findings, whereby parts of the sxt and mcy operon involved in saxitoxin and microcystin synthesis, were detected and sequenced in one and five of the Arctic cyanobacterial samples, respectively. The detection of these compounds in the cryosphere improves the understanding of the biogeography and distribution of toxic cyanobacteria globally. The sequences of sxt and mcy genes provided from this habitat for the first time may help to clarify the evolutionary origin of toxin production in cyanobacteria.     

微囊藻毒素-LR对小鼠肠道消化酶的影响

微囊藻毒素-LR（MCLR）是一类对动物和人类健康影响很大的蓝藻毒素。已有调查认为MCLR能导致某些胃肠道疾病,相关实验室资料也证实MCLR能在肠道积累并引起肠道损伤。研究对小鼠连续腹腔染毒MCLR 28d,观察肠道病理水平及超微结构的变化,并测定肠黏膜刷状缘膜酶活性。结果显示,小肠绒毛受损较严重,绒毛数量减少、部分脱落至肠腔,固有层及黏膜下层水肿、充血;电镜观察发现肠细胞细胞质电子密度降低,伴有线粒体肿胀、细胞核变形现象;肠黏膜二糖酶（蔗糖酶、麦芽糖酶、乳糖酶）、碱性磷酸酶及-谷氨酰转移酶活性均呈下降趋势。在亚慢性MCLR染毒条件下,肠道的消化功能可能受到抑制,进而导致机体对营养物质吸收不良。研究对理解蓝藻毒素引起的胃肠道不适（如恶心、呕吐、腹痛、腹泻）提供了新的证据。       

Estimating microcystin levels at recreational sites in western Lake Erie and Ohio

Cyanobacterial harmful algal blooms (cyanoHABs) and associated toxins, such as microcystin, are a major global water-quality issue. Water-resource managers need tools to quickly predict when and where toxin-producing cyanoHABs will occur. This could be done by using site-specific models that estimate the potential for elevated toxin concentrations that cause public health concerns. With this study, samples were collected at three Ohio lakes to identify environmental and water-quality factors to develop linear-regression models to estimate microcystin levels. Measures of the algal community (phycocyanin, cyanobacterial biovolume, and cyanobacterial gene concentrations) and pH were most strongly correlated with microcystin concentrations. Cyanobacterial genes were quantified for general cyanobacteria, general Microcystis and Dolichospermum, and for microcystin synthetase (mcyE) for Microcystis, Dolichospermum, and Planktothrix. For phycocyanin, the relations were different between sites and were different between hand-held measurements on-site and nearby continuous monitor measurements for the same site. Continuous measurements of parameters such as phycocyanin, pH, and temperature over multiple days showed the highest correlations to microcystin concentrations. The development of models with high R² values (0.81–0.90), sensitivities (92%), and specificities (100%) for estimating microcystin concentrations above or below the Ohio Recreational Public Health Advisory level of 6 μg L⁻¹ was demonstrated for one site; these statistics may change as more data are collected in subsequent years. This study showed that models could be developed for estimates of exceeding a microcystin threshold concentration at a recreational freshwater lake site, with potential to expand their use to provide relevant public health information to water resource managers and the public for both recreational and drinking waters.     

不同氮、磷浓度对铜绿微囊藻生长、光合及产毒的影响

对一株从野外分离得到的铜绿微囊藻产毒株进行分批培养,在不同的氮磷条件下研究其生长、光合荧光及毒素含量的变化。结果表明:正磷酸盐浓度不变时,铵氮浓度的改变对铜绿微囊藻的生长有明显影响。叶绿素a(Chl.a)含量在铵氮浓度为1.83-18.3mg/L时明显较大;微囊藻毒素(包括MC-LR和MC-RR)的含量在铵氮浓度为1.83mg/L时达到最大;当铵氮浓度为0-1.83mg/L时,随着铵氮浓度升高,可变荧光FV和MC的产量均增大,同时MC异构体的种类增多;铵氮浓度过大对M.aeruginosa的生长、生理和产毒均有抑制作用。在另一组实验中,即铵氮浓度不变而正磷酸盐浓度增大时,Chl.a含量呈总体下降的趋势,并且与FV/Fm呈显著正相关关系(P<0.01,r=0.97),MC(MC-LR和MC-RR)的含量在正磷酸盐浓度小于0.56mg/L时明显升高,MC-LR与FV/Fm呈显著正相关关系(P<0.01,r=0.967)。       

Immuno-crossreactivity and toxicity assessment of conjugation products of the cyanobacterial toxin, microcystin-LR

Immunoassays are increasingly used to investigate the production, properties and fates of the cyanobacterial hepatotoxic microcystins in vitro and in vivo. Responses of an ELISA immunoassay to microcystins have been determined using the authentic toxin antigen, microcystin-LR, and conjugation products between the toxin and glutathione, cysteine-glycine and cysteine. The antibodies against microcystin-LR crossreacted with the toxin conjugation products with similar affinities (96-112%) to that of microcystin-LR, when assayed at a concentration of 1 microg l(-1). Toxicity assessment of the conjugates, in comparison to microcystin-LR, indicated a reduction according to mouse bioassay. In vitro protein phosphatase inhibition assay indicated that the conjugates possessed approximately 3-9-fold lower toxicity than microcystin-LR.     

一种快速提取分析微囊藻毒素的方法

以五种群体和单细胞微囊藻及自然微囊藻水华为材料,在沸水浴中经不同时间处理,过滤后直接进行HPLC—UV检测,发现12min的沸水浴处理就足以达到抽提目的。研究中发现,去离子水比蒸馏水是更有效的抽提溶剂。传统的甲醇抽提结果与沸水浴处理的相对误差主要在0．2％—16．59％之间。结果还显示,群体微囊藻需要比单细胞微囊藻抽提更长时间。本研究提供了一种经过改进的高效、廉价和快速的微囊藻毒素抽提分析方法。     

Subchronic microcystin-LR exposure increased hepatic apoptosis and induced compensatory mechanisms in mice

Acute lethal cytotoxicity of microcystin-LR (MC-LR), a toxin produced by fresh-water cyanobacteria, has been attributed to protein phosphatases type 1 and type 2A (PP1/PP2A) inhibition and reactive oxygen species (ROS) generation. However, the effects and molecular mechanisms of prolonged, sublethal MC-LR exposure are less known. We studied mice intraperitonealy injected with saline or 25 μg MC-LR/kg for 28 days (every 2 days). MC-LR induced apoptosis in liver and not in kidneys or heart of treated animals. Liver also showed decreased α-tubulin levels (45.56% ± 7.65% of controls) and activation of p38-MAPK and CaMKII pathways (137.93% ± 11.64% and 419.35% ± 67.83% of the control group, respectively). PP1/PP2A activity decreased from 1.82 ± 0.23 (controls) to 0.91 ± 0.98 mU/mg (MC-LR-treated mice); however, no difference in total Ser/Thr phosphatase activity was found between both the groups. The results demonstrated that apoptosis and cytoskeleton disruption contributed to the hepatic cytotoxic effects of subchronic MC-LR administration. These effects occurred in association with sustained activation of signaling cascades and development of compensatory mechanisms to maintain total Ser/Thr phosphatase activity.