Influence of microcystine-YR and nodularin on the activity of some glucosidases in mouse liver

Microcystine-YR (20 ug/kg bodyweight) and 8 ug/kg bodyweight of nodularin were intraperitoneally injected to 90 female Swiss mice. After 15, 30, 60 min and 24 h the changes were observed in the activity of some glucosidases in the complete cell homogenate and in the lysosomal, microsomal and cytosol fraction. Significant differences were connected with the time after administration of poison and with the cellular fraction. Nodularin induces the activity of beta-D-glucuronidase, alpha-glucosidase, lysosomal esterase and N-acetyl-glucosaminidase and influenced on the labilization of endoplasmatic reticulum membranes. Microcystine-YR inhibited the biosynthesis of glucosidases and revealed a destructive effect on membranes of lysosomes and endoplasmatic reticulum.     

Protective effect of melatonin against nodularin-induced oxidative stress in mouse liver

Nodularin is a hepatotoxin from a cyanobacterium, Nodularia spumigena, that inhibits protein phosphatases 1 and 2 and posseses tumor-promoting activity. The aim of this paper was to examine whether nodularin is able to induce oxidative stress in mouse liver tissue and whether melatonin (protective compound against oxidative damage) could supress the activity of nodularin.We studied the effect of nodularin (1, 5, and 10 microg/kg body weight) and melatonin (5, 10, and 15 mg/kg body weight) administration on the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) in mouse liver. Intraperitoneal treatment of mice with nodularin per 7 days decreased the activities of all estimated enzymes in a dose-dependent manner. Intraperitoneal treatment of animals with melatonin per 7 days increased the activities of SOD, CAT, and GSH-Px and this effect was concentration-dependent. Co-treatment (nodularin 5 microg/kg body weight + melatonin 5, 10, and 15 mg/kg body weight per 7 days) and post-treatment with melatonin (nodularin 5 microg/kg body weight per 7 days + melatonin 5, 10, and 15 mg/kg body weight per next 7 days) increased the activities of SOD, CAT, and GSH-Px in comparison to the nodularin group. No significant differences from the nodularin group were noted in the group after pre-treatment with melatonin. In conclusion, these findings suggest that oxidative damage may be involved in the toxicity of nodularin. Moreover, co-treatment and post-treatment with 10 and 15 mg/kg body weight of melatonin may protect against nodularin-induced oxidative stress. There was no protective effect of pre-treatment with melatonin.     

Effects of Four Local Anaesthetics on the Membrane Stability of Isolated Rat Liver Lysosomes

Abstract The effects of the local anaesthetics bupivacaine, lidocaine, mepivacaine and prilocaine on lysosomal membrane stability have been studied on isolated rat liver lysosomes. The lysosomal membranes were stabilized by the local anaesthetics only within a very narrow range of concentration (around 0.001 M). In lower concentrations there was no effect of the substances while in higher concentrations there was a marked labilizing effect on the lysosomal membranes. The phlogistic effect of an injected suspension of lysosomes in the rat paw was increased by mepivacaine in concentrations of 1 % (0.04 M) and higher. The labilizing effects of local anaesthetics on lysosomes were probably due to precipitation of lysosomal membrane proteins by the local anaesthetics.     

Nodularin-induced genotoxicity following oxidative DNA damage and aneuploidy in HepG2 cells

The problem of toxicity of Nodularia spumigena to animals and people is of increasing concern, as the incidence of such blooms grows. It was shown that nodularin is a liver carcinogen possessing both initiating and tumor-promoting activities. However, the mechanisms by which this toxin damages the DNA and induces liver cancer are not well understood. The aim of the present study was to investigate the DNA damaging properties of nodularin. The effect of different doses of nodularin (1-10 microg/ml) on DNA damage was determined in HepG2 cells after 6, 12, 24 and 48 h of the treatment. The modified comet assay in conjunction with Fpg (ROS-induced DNA damage) and FISH-micronucleus assay (clastogenic and/or aneugenic activities of nodularin) were applied. In addition the occurrence of apoptosis was estimated by the morphological analysis of chromatin condensation and the annexin method using flow cytometry. We found that nodularin induces oxidative DNA damage by oxidation of purines and increases the formation of centromere positive micronuclei due to aneugenic activity. In addition to genotoxic properties, nodularin exerts a cytotoxic activity by inducing apoptosis in HepG2 cells. These results suggest a causative role for nodularin in the process leading to the accumulation of genetic alterations which may be implicated in carcinogenesis.     

Trophic transfer of cyanobacterial toxins from zooplankton to planktivores: consequences for pike larvae and mysid shrimps

The aim of this study was to evaluate the potentially harmful effects of zooplankton preexposed to cyanobacteria on two planktivorous animals: a fish larva (pike, Esox lucius) and a mysid shrimp (Neomysis integer). The planktivores were fed zooplankton from a natural community that had been preexposed to cell-free extract or to purified toxin (nodularin) of the cyanobacterium Nodularia spumigena, and the growth, feeding, and pellet production of the planktivores, as well as the toxin content of the pellets, were measured. In addition, radiolabeled nodularin ((3)H-dihydronodularin) was used in separate experiments to measure the vector transfer of nodularin from zooplankton to their predators. During 11-day exposures, dissolved nodularin was transferred to pike larvae and N. integer via zooplankton at very low rates of accumulation. Treatment with N. spumigena extract decreased the ingestion and feces production rates of pike larvae. With purified nodularin alone, no such effect could be observed. No effect on molting cycle length, fecal pellet production, C:N ratio, or growth of N. integer was detected. The results suggest that dissolved cyanobacterial toxins released during bloom decay can have a negative impact on feeding and, hence, on the growth of fish larvae via zooplankton, even without direct contact between cyanobacteria and the fish.     

The potential role of lysosomes in tissue distribution of weak bases

The potential importance of lysosomes as a site of accumulation of weak bases in tissues is discussed. A simple mathematical treatment predicts the quantitative significance of lysosomal trapping for monoacidic and diacidic weak bases. The features which are characteristics of lysosomal trapping are discussed, particularly in comparison with active transport and intracellular binding mechanisms. These features include: linear accumulation at low concentrations; nonlinearity at higher concentrations; dependence on structural integrity of tissue; energy dependence and competition with other weak bases. Subcellular distribution studies have previously shown that weak bases accumulate extensively in membranes; however, the dependence of accumulation on the structural integrity of tissue suggests that this is not the only significant mechanism of accumulation. The results of a range of studies of tissue distribution of weak bases are discussed to illustrate that these findings are consistent with accumulation in lung and liver being attributable to a combination of lysosomal trapping and accumulation in membranes whereas, in muscle, accumulation in membranes is the predominant mechanism of accumulation. The possible pharmacokinetic significance of lysosomal trapping of weak bases is also discussed.     

Induction of Fas receptor and Fas ligand by nodularin is mediated by NF-κB in HepG2 cells

Nodularin is a natural toxin with multiple features, including inhibitor of protein phosphatases 1 and 2A as well as tumor initiator and promoter. One unique feature of nodularin is that this chemical is a hepatotoxin. It can accumulate into the liver after contact and lead to severe damage to hepatocyte, such as apoptosis. Fas receptor (Fas) and Fas ligand (FasL) system is a critical signaling network triggering apoptosis. In current study, we investigated whether nodularin can induce Fas and FasL expression in HepG2 cell, a well used in vitro model for the study of human hepatocytes. Our data showed nodularin induced Fas and FasL expression, at both mRNA and protein level, in a time- and dose-dependent manner. We also found nodularin induced apoptosis at the concentration and incubation time that Fas and FasL were significantly induced. Neutralizing antibody to FasL reduced nodularin-induced apoptosis. Further studies demonstrated that nodularin promoted nuclear translocation and activation of p65 subunit of NF-κB. By applying siRNA targeting p65, which knocked down p65 in HepG2 cells, we successfully impaired the activation of NF-κB by nodularin. In these p65 knockdown cells, we observed that Fas and FasL expression and apoptosis induced by nodularin were significantly reduced. These findings suggest the induction of Fas and FasL expression and thus cell apoptosis in HepG2 cells by nodularin is mediated through NF-κB pathway.     

Different methods for toxin analysis in the cyanobacterium Nodularia spumigena (Cyanophyceae).

The brackish water cyanobacterium Nodularia spumigena produce the hepatotoxic cyclic pentapeptide nodularin. Intoxications for both human as well as animal may arise when water reservoirs are contaminated with potentially toxic Nodularia species. Here, results of three independent methods for the determination of nodularin in different strains of N. spumigena are presented. The results obtained with a protein phosphatase assay and a HPLC/UV/MS method are compared with the results obtained with a bioluminescence assay, which is successfully introduced here for nodularin determination. Statistical evaluation of the three applied methods revealed a good comparability towards the detected toxin content. The methods were evaluated taking into consideration the parameters: handling, efficiency, sensitivity and selectivity. The detection limit in the protein phosphatase assay is highest (0.05ng nodularin) and lowest (250ng nodularin) in the bioluminescence assay- it was determined with 5ng (MS) and 25ng (UV) for the HPLC/UV/MS methods. The different selectivities and sensitivities are critically discussed and an analytical pathway for the determination of the biotoxin nodularin from Nodularia samples is proposed.     

Detection of nodularin in flounders and cod from the Baltic Sea

The brackish water cyanobacterium Nodularia spumigena regularly forms waterblooms in the Baltic Sea. Many N. spumigena strains can produce nodularin, a hepatotoxic penta-peptide, which has caused several animal poisonings in the Baltic Sea area. To improve our understanding of nodularin bioaccumulation in aquatic organisms this study measured nodularin in flounder and cod caught from the Baltic Sea. Flounders were collected from the western Gulf of Finland in July 1996, September 1997, and September 1998, and from the Gulf of Bothnia in August 1997 and September 1998. Flounders were also collected from the coastal areas of Sweden in the Baltic Proper during September 1998. Cod were caught from the southern Baltic Sea in August 1998. Livers and muscles of the 1997 fish were isolated, extracted, and analysed for nodularin using high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA) and protein phosphatase 1 (PP1) inhibition assay. Approximately 30-70 ng of nodularin/g dry weight (maximum value 140 ng/g) were found in the liver tissue samples by ELISA and PP1 inhibition. These concentrations were below the detection limit of HPLC. PP1 assay showed inhibition also in muscle samples, but this may due to other compounds present in the muscle extracts rather than NODLN or due to matrix interference. The recovery of nodularin from liver tissue with ELISA and PP1 assays was about 30%. Nodularin concentrations in samples are not corrected for recovery. Although the concentrations of nodularin found in this study are low further studies of nodularin are needed to assess possible bioaccumulation in brackish water food webs.     

Action of nonachlazine on the creatine phosphokinase and acid phosphatase activity and on the lysosomal membrane stability of the ischemic myocardium in rats after preliminary reserpinization

Experiments on the ischemic myocardial tissue of the rat in vitro showed that despite the fact that reserpine-induced depletion of the tissue catecholamine storage failed to affect the stability of lysosomal membranes, a combination of reserpine pretreatment of the animals with subsequent administration of nonachlazine at the low dose yielded stabilization of lysosomal membranes to a greater extent than administration of nonachlazine alone. The effects of nonachlazine (0.25 mg/kg) on the activity of creatine phosphokinase and total activity of acid phosphatase with and without reserpine pretreatment were similar.     

Estimating the accumulation and transfer of Nodularia spumigena toxins by the blue mussel Mytilus edulis: an appraisal from culture and mesocosm experiments.

Accumulation of Nodularia spumigena toxins by Mytilus edulis was studied during laboratory and mesocosm experiments in order to investigate the possible pathways of nodularin in mussels and calculate toxin budgets. Mussels were exposed to 0.2-15.6 microg nodularin l(-1), fed for up to 5 days with Nodularia cells from culture, or blooming in different nutrient-treated seawater. Toxin concentration was monitored with LC-ESI-MS. During different exposures, the amount of nodularin detected in mussels increased linearly with increasing toxin concentration in food and attained 0.28-13.8 microg of nodularin g dw(-1) of the mussel whole body tissue after 12 h. The digestive gland was found to be the tissue with the highest toxin concentration. Nodularin concentration in faeces was not proportional to faeces production or to toxin concentration in food; however, it seemed to be mostly related to food quality as well as to food availability. The percentage of nodularin taken up by the mussels, relative to the amount contained in the offered food, varied from 10% to 20%, depending on food quality. During a 5-day toxin accumulation experiment, the acute reduction of the toxin in mussel tissues the second day and the following stabilization, showed that probably mussels maintain low toxin levels via efficient elimination and/or toxin metabolism. After a 72 h depuration period, mussels showed 75% reduction in their toxin content.     

Cyanobacterial nodularin is a potent inhibitor of type 1 and type 2A protein phosphatases.

The present study characterizes the inhibitory effects of nodularin, a recently isolated hepatotoxic compound from the cyanobacterium Nodularia spumigena, on type 1 (PP1), type 2A, (PP2A), type 2B (PP2B), and type 2C (PP2C) protein phosphatases. Both PP2A and PP1 were potently inhibited (IC50 = 0.026 and 1.8 nM, respectively) by nodularin, whereas PP2B was inhibited to a lesser extent (IC50 = 8.7 microM). Nodularin had no apparent effect on PP2C, alkaline phosphatase, acid phosphatase, insulin receptor tyrosine kinase, protein kinase A, phosphorylase kinase, or protein kinase C. In a whole-cell extract of T51B liver cells, nodularin inhibited PP1 and PP2A activity with a potency similar to that seen with their purified catalytic subunits. Thus, due to the high specificity of nodularin for PP2A and PP1, this hepatotoxin may prove to be useful as a probe for distinguishing the activity of these protein phosphatases in cell extracts.     

Nucleotide excision repair impairment by nodularin in CHO cell lines due to ERCC1/XPF inactivation

The problem of toxicity of cyanobacterial toxins is of increasing concern, as the incidence of such blooms grows. Among the toxins, the most abundant in the environment are hepatotoxins known as nodularins and microcystins. These toxins are responsible for almost all known cases of fresh and brackish water intoxication and are responsible for recurrent episodes of human and animal illness and death. Moreover, they are believed to be potent tumor promoters and initiators. However, the mechanisms by which these toxins induce liver cancer are not well understood. The aim of the present study was to determine the effect of nodularin on the kinetics of nucleotide excision repair (NER) in Chinese hamster ovary (CHO) cells exposed to UV radiation. The first set of experiments was performed to define the optimal treatment conditions for nodularin to avoid the possibility of encountering false positive signals in the comet assay due to the apoptogenic activity of nodularin. Based on the analysis of apoptosis, the 6-h treatment time of cells with nodularin (1mug/ml, 10mug/ml and 20mug/ml) was chosen for the alkaline comet assay. The kinetics of NER was determined in CHO cell lines: AA8 (wild-type) and mutant cell lines: UV135 (XPG(-)), UV41 (XPF(-)) and UV20 (ERCC1(-)) exposed to 20J/m(2) UV radiation. The micronucleus assay was performed to determine a residual DNA damage in four cell lines treated with nodularin (10mug/ml) and exposed to equitoxic doses UV radiation. Radiation doses of UV producing 50% of survival for AA8, UV135, UV20 and UV41 cell lines were calculated from UV survival curves. The results show that nodularin impairs the incision/excision step of NER in CHO cells by the ERCC1/XPF inactivation and leads to an increased level of UV-induced cytogenetic DNA damage.     

Further studies on the in vivo effect of cephaloridine on the stability of rat kidney lysosomes

The stabilizing effect of cephaloridine, an antibiotic, on rat kidney lysosomal membranes was tested by a single subcutaneous injection. The release of two lyososomal enzymes, acid phosphatase and muramidase, was used as an index of lysosome membrane integrity. The levels of these enzymes in the kidney extracts as well as in the isolated kidney lysosome fractions were found to be raised considerably, compared to the controls. In rats treated with cephaloridine, the supernatant fraction obtained from the kidney homogenates, after centrifugation at 15,000 g_av, contained lower enzyme activities than were found in the control animals. It is suggested that cephaloridine may inhibit the release of acid phosphatase and muramidase from rat kidney lysosomes and, therefore, may exert a stabilizing effect on the lysosomal membrane system. The possible mechanism of interaction of this antibiotic with rat kidney lysosomal membranes is proposed.     

Tumor promoters--microcystin-LR, nodularin and TNF-α and human cancer development

Microcystin-LR and nodularin, along with okadaic acid, are potent inhibitors of protein phosphatases 1 and 2A (PP1 and PP2A). The mechanisms of action of microcystin-LR and nodularin in the liver and that of okadaic acid, a potent tumor promoter on mouse skin, have attracted the attention of the scientists. This paper reviews several topics: new inhibitors of PP1 and PP2A with new chemical structures, structure-function relationships for both receptor binding and inhibition of protein phosphatases, the crystal structure of PP1 or PP2A-toxin complex, induction of gene expression and apoptosis. These subjects were studied by using in vitro and in vivo experimental systems. Two-stage carcinogenesis experiments with microcystin-LR and nodularin for the first time demonstrated that microcystin-LR is a new tumor promoter in rat liver initiated with diethylnitrosamine (DEN), and that nodularin is a potent tumor promoter associated with weak initiating activity in rat liver initiated with DEN. A working group of WHO (IARC) concluded that microcystin-LR is "possibly carcinogenic to humans" and that nodularin is "not classifiable as to carcinogenicity". Our studies revealed that chemical tumor promoters are inducers of TNF-α in the cells of target tissues and that TNF-α is an endogenous tumor promoter. This advance in carcinogenesis made it possible to look for the link between chemical tumor promoters and endogenous tumor promoters, such as TNF-α and IL-1. The carcinogenic features of TNF-α are described in this review, and the TNF-α inducing protein (Tipα) of Helicobacter pylori genome is presented as an example of a tumor promoter of human stomach cancer development.     

An ultrasensitive competitive binding assay for the detection of toxins affecting protein phosphatases.

An ultrasensitive assay is described for microcystin-LR and other substances (microcystins, nodularin, okadaic acid, calyculin A, tautomycin) which block the active site of protein phosphatases (PP) 1 and 2A. The assay is based on competition between the unknown sample and [125I]microcystin-YR for binding to the catalytic subunit of PP2A. The PP2A-bound [125I]microcystin-YR was stable (half-time of dissociation = 1.8 h), allowing non-bound [125I]microcystin-YR to be removed by Sephadex G-50 size-exclusion chromatography. Compared to current assays based on inhibition of protein phosphatase activity the present assay was more robust against interference (from fluoride, ATP, histone, and casein), and had an even better sensitivity. The detection limit was below 50 pM (2.5 fmol) for nodularin and microcystin-LR, and below 200 pM (10 fmol) for okadaic acid. The method was used successfully to detect extremely low concentrations of either microcystin or nodularin in drinking water or seawater, and okadaic acid in shellfish extract.     

Effect of aflatoxin on rat liver lysosomes

The effect of aflatoxin on the activities of 5 rat liver lysosomal enzymes (acid deoxyribonuclease, arylsulfatases A and B, β-glucuronidase, β-glucosidase and β-galactosidase) has been investigated in vivo and in vitro. Three hours after the administration of aflatoxin, activities of most of the enzymes increased significantly reaching maximal levels at 48 hr. The activity of acid DNase increased the most (276 per cent of the control level). At the same period (48 hr) the activity of the soluble lysosomal enzymes greatly increased. Aflatoxin had a labilizing effect on lysosomal membranes, causing the release of lysosomal enzymes into the supernatant. The data are discussed in connection with the biochemical mechanism of aflatoxin intoxication.     

Impulse control disorder,lysosomal malfunction and ATP13A2 insufficiency in Parkinsonism

Lysosomal transport of cargos in neurons is essential for neuronal proteostasis, transmission and functional motors and behaviours. Lysosomal malfunction including storage disorders is involved in the pathogenesis of Parkinson's disease (PD). Given the unclear molecular mechanisms of diverse defects in PD phenotypes, especially behavioural deficits, this mini review explores the cellular contexts of PD impulse control disorders and the molecular aspects of lysosomal cross‐membrane transports. Focuses are paid to trace metal involvements in α‐synuclein assembly in Lewy bodies, the functions and molecular interactions of ATP13A2 as ATPase transporters in lysosomal membranes for cross‐membrane trafficking and lysosomal homeostasis, and our current understandings of the neural circuits in ICD. Erroneously polarized distributions of cargos such as metals and lipids on each side of lysosomal membranes triggered by gene mutations and deregulated expression of ATP13A2 may thus instigate sensing protein structural changes such as aggregations, organelle degeneration, and specific neuronal ageing and death in Parkinsonism.