Chromatographic and spectral behaviour and detection of hepatotoxic nodularin in fish, clam, mussel and mouse tissues using HPLC analysis

Comprehensive insights into the occurrence and toxicological issues of nodularins

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

Effect of crude extracts from Nodularia spumigena on round goby (Neogobius melanostomus)

Nodularia spumigena is a nitrogen-fixing filamentous cyanobacteria in the Baltic Sea. Nodularin (NOD), the hepatotoxic peptide produced by this cyanobacterium, accumulates in the organisms from different trophic levels. In this paper, the effects of N. spumigena cell extract on the round goby (Neogobius melanostomus) was investigated under laboratory conditions. This benthic fish species feed on mussels in which nodularin accumulation was well documented. In current study a sharp increase in the NOD concentration in analyzed organs was observed after 24 h (PPIA) after 72 h of exposure (LC/MS). To determine the direction and strength of the changes induced in the fish by the toxin, several biochemical markers of exposure such as concentration of glutathione and activities of catalase, guaiacol peroxidase and glutathione S-transferase were used. In analyzed organs (liver, gills and muscle) of the round goby, the activity of these enzymes were suppressed. Higher GSH/protein amount and CAT and POD activity in gills than in liver reflects the importance of gills in NOD entering into analyzed fish body when exposed to toxin. The results indicate that the round goby (Neogobius melanostomus) exposed to extracts from N. spumigena cells triggered a defense system in a time-dependent manner. The obtained results contribute to a better understanding of fish response to the presence of compounds produced by N. spumigena.

Combination of CDNF and Deep Brain Stimulation Decreases Neurological Deficits in Late-stage Model Parkinson's Disease

Several neurotrophic factors (NTF) are shown to be neuroprotective and neurorestorative in pre-clinical animal models for Parkinson's disease (PD), particularly in models where striatal dopamine neuron innervation partially exists. The results of clinical trials on late-stage patients have been modest. Subthalamic deep brain stimulation (STN DBS) is a proven treatment for a selected group of advanced PD patients. The cerebral dopamine neurotrophic factor (CDNF) is a promising therapeutic protein, but its effects in animal models of late-stage PD have remained under-researched. The interactions of NTF and STN DBS treatments have not been studied before. We found that a nigral CDNF protein alone had only a marginal effect on the behavioral deficits in a late-stage hemiparkinsonian rat model (6-OHDA MFB). However, CDNF improved the effect of acute STN DBS on front limb use asymmetry at 2 and 3 weeks after CDNF injection. STN lesion-modeling chronic stimulation-had an additive effect in reducing front limb use in the cylinder test and apomorphine-induced rotation. The combination of CDNF and acute STN DBS had a favorable effect on striatal tyrosine hydroxylase. This study presents a novel additive beneficial effect of NTF and STN DBS, which might be explained by the interaction of DBS-induced endogenous NTFs and exogenously injected CDNF. SNpc can be reached via similar trajectories used in clinical STN DBS, and this interaction is an important area for future studies.

Detection of free microcystins in the liver and muscle of freshwater fish by liquid chromatography-tandem mass spectrometry

MC analysis of biological tissue is considered to be very difficult due to the lack of validated methods. This is the primary limiting factor for monitoring potential risks in both the flesh of aquatic organisms and the aquatic ecosystem. In this study, an effective method to determine free MCs (MC-LR and MC-RR) in the muscle and liver tissues of freshwater cultured fish was developed using solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC/MS-MS). The extraction solvent, time of extraction, eluent and purification of the extract were optimized. Various SPE cartridges were also investigated. In this optimized analytical procedure, an 85% methanol/water solution (v/v) was selected as the extraction solvent, after which the extracts were purified by removing fats and proteins; a HLB cartridge was chosen for MCs enrichment; and 90% methanol containing 0.02% formic acid/water solution (v/v) was used as the eluent. Under the optimized pretreatment conditions and instrument parameters, good recoveries of MC-LR and MC-RR were obtained at three concentrations (0.5, 1.0 and 2.0 µg g^-1 dry weight (DW)), with values ranging from 92.5 to 98.3% and 92.1 to 98.6%, respectively. The method detection limit (MDL) for muscle samples was 0.5 µg kg^-1 and 0.4 µg kg^-1 (DW) for MC-LR and MC-RR, respectively. The MDL for the liver samples was 0.8 µg kg^-1 (DW) for both MC-LR and MC-RR. The developed procedure was successfully applied to analyze MCs in the muscle and liver of fish samples collected from a Chinese freshwater aquaculture pond during bloom seasons. The MC-LR concentrations ranged from below the MDL to 4.17 µg kg^-1 and the MC-RR concentrations ranged from below the MDL to 2.64 µg kg^-1.

Detection of free and covalently bound microcystins in different tissues (liver, intestines, gills, and muscles) of rainbow trout (Oncorhynchus mykiss) by liquid chromatography-tandem mass spectrometry: method characterization

So far only a few publications have explored the development of extraction methods of cyanotoxin extracted from complex matrices. With regard to cyanobacterial microcystins (MCs), the data on the contamination of the flesh of aquatic organisms is hard to compare and very limited due to the lack of validated methods. In recent years, evidence that both free and bound fractions of toxin are found in these tissues has highlighted the need to develop effective methods of quantification. Several techniques do exist, but only the Lemieux oxidation has so far been used to investigate complex tissue matrices. In this study, protocols based on the Lemieux approach were adapted for the quantitative chemical analysis of free MC-LR and MMPB derived from bound toxin in the tissues of juvenile trout gavaged with MC-LR. Afterwards, the NF V03 110 guideline was used to characterize the protocols elaborated and evaluate their effectiveness.

First report of a toxic Nodularia spumigena (Nostocales/ Cyanobacteria) bloom in sub-tropical Australia. II. Bioaccumulation of nodularin in isolated populations of mullet (Mugilidae)

Fish collected after a mass mortality at an artificial lake in south-east Queensland, Australia, were examined for the presence of nodularin as the lake had earlier been affected by a Nodularia bloom. Methanol extracts of muscle, liver, peritoneal and stomach contents were analysed by HPLC and tandem mass spectrometry; histological examination was conducted on livers from captured mullet. Livers of sea mullet (Mugil cephalus) involved in the fish kill contained high concentrations of nodularin (median 43.6 mg/kg, range 40.8-47.8 mg/kg dry weight; n = 3) and the toxin was also present in muscle tissue (median 44.0 μg/kg, range 32.3-56.8 μg/kg dry weight). Livers of fish occupying higher trophic levels accumulated much lower concentrations. Mullet captured from the lake 10 months later were also found to have high hepatic nodularin levels. DNA sequencing of mullet specimens revealed two species inhabiting the study lake: M. cephalus and an unidentified mugilid. The two mullet species appear to differ in their exposure and/or uptake of nodularin, with M. cephalus demonstrating higher tissue concentrations. The feeding ecology of mullet would appear to explain the unusual capacity of these fish to concentrate nodularin in their livers; these findings may have public health implications for mullet fisheries and aquaculture production where toxic cyanobacteria blooms affect source waters. This report incorporates a systematic review of the literature on nodularin measured in edible fish, shellfish and crustaceans.

Simple assay for analyzing five microcystins and nodularin in fish muscle tissue: hot water extraction followed by liquid chromatography-tandem mass spectrometry

A simple, specific, and sensitive procedure for determining six cyanotoxins, that is, microcystins RR, LR, YR, LA, and LW and nodularin, in fish muscle tissue is presented. This method is based on the matrix solid-phase dispersion technique with heated water as extractant followed by liquid chromatography (LC)-tandem mass spectrometry (MS) equipped with an electrospray ion source. Target compounds were extracted from tissue by 4 mL of water acidified to pH 2 and heated at 80 degrees C. After acidification and filtration, 0.2 mL of the aqueous extract was injected in the LC column. MS data acquisition was performed in the multireaction monitoring mode, with at least two precursor ion > product ion transitions selected for each target compound. Analyte recovery ranged between 61 and 82% and was not substantially affected by either the analyte concentrations or the type of fish. The nonexcellent recovery of some of the microcystins was traced to binding of these compounds to protein phosphatases in fish tissue occurring during sample treatment. The existence of covalently bound microcystins in fish has been evidenced by several studies. Compared to an older sample preparation procedure, this one extracted larger amounts of the analytes in a simpler and much more rapid way. On the basis of a signal-to-noise ratio of 10, limits of quantification were estimated to range between 1.6 and 4.0 ng/g. The effects of temperature and volume of the extractant on the analyte recovery were studied.

Recovery of MC-LR in fish liver tissue

Cyanotoxins, particularly microcystins (MCs), have been shown to be a hazard to human health. MCs accumulate in aquatic organisms probably as a result of irreversible binding to liver protein phosphatases. The aim of this study was to describe the recovery of MC from fish liver using various detection methods, with MC-LR as the representative congener. These findings are discussed in conjunction with the current procedures and limit values used for human risk assessment. Following incubation of liver homogenates with various MC-LR concentrations, the homogenates were extracted by a water/methanol/butanol mixture via different treatments and subsequently analyzed via the colorimetric protein phosphatase inhibition assay (cPPA), HPLC, and anti-Adda ELISA. Detection via cPPA appeared to yield the highest recovery of MC-LR, although the presence of unspecific background may have resulted in overestimation of the true recovery. The recoveries determined via HPLC and anti-Adda ELISA were comparable to each other. The limits of detection were 0.01-2.4 microg MC-LR/g liver tissue, depending on the method used. Maximum MC-LR recovery from samples incubated with 10 and 100 microg MC-LR/g ranged between 44% and 101%. Recovery from samples incubated with 1 microg MC-LR/g liver tissue was below 3%. Lower recovery is assumed to result from irreversible, covalent MC protein binding, as confirmed by Western blotting of liver homogenates with anti-Adda immunoprobing. The results demonstrate that further investigation of and improvement in routinely applied MC methods for fish tissue and/or food analyses are needed for a reliable risk assessment.

Heterogeneity of nodularin bioaccumulation in northern Baltic Sea flounders in 2002

The cyanobacterial hepatotoxin nodularin is abundantly produced by the cyanobacterium Nodularia spumigena in the Baltic Sea during July-August. Nodularin is a potent hepatotoxin and a tumour promoter, distributed in various Baltic Sea environmental compartments, especially food webs involving mussels. Flounders receive nodularin through consumption of blue mussels. In this study nodularin concentrations in individual flounders (liver) were examined between July and September 2002 (six sample sets, four to 10 samples/set), providing information about contribution of sampling on estimates of bioaccumulation intensity. Toxin was determined using liquid chromatography/mass spectrometry (LC/MS) and enzyme-linked immunosorbent assay (ELISA). Additionally, liver histopathology was examined. Observed toxin concentrations were ND-390 microg kg(-1) dw (LC/MS) and 20-2230 microg kg(-1) dw (ELISA), with maximum concentrations in September (ELISA). The ELISA protocol generally resulted in higher, up to approximately 10-fold, toxin concentrations than LC/MS, with increasing difference toward September. This difference may have originated from different extraction solvents in LC/MS and ELISA, ion suppression in LC/MS, and temporal increase in nodularin metabolites detectable with ELISA. The differences in toxin concentrations between individual liver samples were considerable with relative standard deviation values of 20-154% (LC/MS) and 28-106% (ELISA). Since the precision of the ELISA method employed was <25% and that of LC/MS <10%, it can be concluded that the largest source of error in bioaccumulation estimates may be an inadequate number of samples. Although there were tissue lesions in several liver samples, occurrence of lesions was not related to toxin concentrations.

Cyanobacteria and prawn farming in northern New South Wales, Australia—a case study on cyanobacteria diversity and hepatotoxin bioaccumulation

Harmful cyanobacteria pose a hazard to aquatic ecosystems due to toxins (hepatotoxic microcystins, nodularins, and cylindrospermopsin) they produce. The microcystins and nodularins are potent toxins, which are also tumor promoters. The microcystins and nodularins may accumulate into aquatic organisms and be transferred to higher trophic levels, and eventually affect vector animals and consumers. Prawn farming is a rapidly growing industry in Australia. Because information regarding effects of cyanobacteria at prawn farms was lacking, we examined diversity of cyanobacteria and toxin production plus bioaccumulation into black tiger prawns (Penaeus monodon) under both field (northern New South Wales, Australia, December 2001-April 2002) and laboratory conditions. Samples were analyzed for hepatotoxins using enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC). The maximum density of cyanobacteria (1 x 10(6) to 4 x 10(6) cells/l) was reached in April. Cyanobacteria encountered were Oscillatoria sp. (up to 4 x 10(6) cells/l), Pseudanabaena sp. (up to 1.8 x 10(6) cells/l), Microcystis sp. (up to 3.5 x 10(4) cells/l), and Aphanocapsa sp. (up to 2 x 10(4) cells/l). An uncommon cyanobacterium, Romeria sp. (up to 2.2 x 10(6) cells/l), was also observed. Contrasting earlier indications, toxic Nodularia spumigena was absent. Despite that both Oscillatoria sp. and Microcystis sp. are potentially hepatotoxic, hepatotoxin levels in phytoplankton samples remained low (up to 0.5-1.2 mg/kg dw; ELISA) in 2001-2002. ELISA was found suitable not only for phytoplankton but prawn tissues as well. Enzymatic pretreatment improved extractability of hepatotoxin from cyanobacteria (nodularin from N. spumigena as an example), but did not generally increase toxin recovery from prawn hepatopancreas. There were slightly increasing hepatotoxin concentrations in prawn hepatopancreas (from 6-20 to 20-80 microg/kg dw; ELISA) during the study. Hepatotoxin concentrations in surface sediment remained low (<5 microg/kg dw; ELISA) throughout the study. Laboratory experiments indicated that prawn hepatopancreas, heart, and brain were primary organs for hepatotoxin bioaccumulation. Toxin concentration in other organs, including muscle, was less effective. Orally administered nodularin levels in hepatopancreas rapidly decreased from initial 830 to 250 microg/kg dw in 96 h. Similarly, concentration of microcystin-LR injected in prawns decreased from 130 to 30 microg/kg dw (hepatopancreas) in 2 h. These results demonstrate that potential risks caused by cyanobacteria in prawn farming (farmers, prawns, and consumers) were not substantial in 2001-2002. Although prawns may act as vectors for toxin transfer, they did not accumulate alerting amounts of hepatotoxins and were able to effectively detoxify them. Because bloom toxicity may vary, low-frequency toxin monitoring is recommended.

Mass spectrometric detection and quantification of nodularin-R in flounder livers

Livers of flounders caught during August 1995 from the western Gulf of Finland and the Archipelago Sea were analyzed for nodularin-R (NODLN) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and liquid chromatography-electrospray ionization-mass spectrometry (LC-MS). Results showed that NODLN was detected in samples by both MS techniques. NODLN content in samples varied between 0.082 and 0.637 microg g(-1) wet weight by LC-MS. Biotransformation products such as glutathione adduct were not found in the samples. The results showed that intact NODLN can be found in tissues after storage at -70 degrees C for several years.

Acute effects and bioaccumulation of nodularin in sea trout (Salmo trutta m. trutta L.) exposed orally to Nodularia spumigena under laboratory conditions

Nodularin (NODLN) is a cyclic pentapeptide hepatotoxin that is regularly produced in high amounts by the cyanobacterium Nodularia spumigena in the Baltic Sea, and can bioaccumulate in Baltic biota. Baltic sea trout (Salmo trutta m. trutta L.) were exposed orally to a single dose of food containing NODLN (125 mg/kg ww) from N. spumigena (strain AV1, from the Baltic Sea). The level of exposure was 210-620 (average 440) microg NODLN per kg bw. Based on an 8-day survey under laboratory conditions, NODLN-like compounds accumulated in trout liver, with increasing liver concentrations (from 19 microg/kg on day 1 up to 1200 microg/kg on day 8 as measured with the EnviroLogix ELISA kit) during the experiment. Thus, accumulation of NODLN-like compounds in liver increased from 0.05% of the total NODLN dose administered on day 1 to 0.53% on day 8. However, the ELISA test kit is also sensitive to metabolites of algal hepatotoxins. In the HPLC chromatograms, no NODLN peak was detected after 24 h that also suggested NODLN absorbed in trout was metabolized or bound rapidly. According to ELISA, NODLN-like compounds also accumulated in trout muscle in lower quantities (from 125 to 34 microg/kg dw). Histopathology revealed complete loss of liver architecture after 1-2 days of the single oral dose. From day 4 to 8, there was partial recovery of liver cells. NODLN did not affect thiamine levels or water content of trout liver. The results showed that NODLN rapidly induces severe but reversible liver damage. Apparently NODLN accumulated in trout liver from cyanobacteria in the intestine, but was detoxified rapidly. On the basis of discrepancies between the histopathology and ELISA, and on the other hand, between the HPLC and ELISA methods, analysis of NODLN and its metabolites in biological tissue needs to be improved.