[ADMAdda5]-microcystins in Planktothrix agardhii strain PH-123 (cyanobacteria)--importance for monitoring of microcystins in the environment

Two major and two minor microcystins (MCYST) were isolated from a hepatotoxic Danish strain of Planktothrix agardhii (Gomont) Anagnostidis et Komárek by reversed-phase high-performance liquid chromatography. The microcystins were characterized by UV spectroscopy, amino acid analysis, fast atom bombardment mass spectrometry (FABMS), and high-resolution FABMS. The major microcystins were further analysed by collisionally induced tandem electrospray ionization MS. The microcystins were found to be demethylated variants of MCYST-HtyR (homotyrosine-arginine) and MCYST-LR (leucine-arginine). The two major microcystins contained an acetyl-demethyl variant (ADMAdda) of 3-amino-9-acetoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (Adda). This is the first report of [ADMAdda5]-microcystins in Planktothrix. The two [ADMAdda5]-microcystins inhibited protein phosphatase activity but showed low cross-reactivity with antibodies of an enzyme-linked immunosorbent assay (ELISA), emphasizing the potential underestimation of the toxicity of natural blooms dominated by Planktothrix when microcystin content is quantified using only an ELISA.

Human fatalities from cyanobacteria: chemical and biological evidence for cyanotoxins

An outbreak of acute liver failure occurred at a dialysis center in Caruaru, Brazil (8 degrees 17' S, 35 degrees 58' W), 134 km from Recife, the state capital of Pernambuco. At the clinic, 116 (89%) of 131 patients experienced visual disturbances, nausea, and vomiting after routine hemodialysis treatment on 13-20 February 1996. Subsequently, 100 patients developed acute liver failure, and of these 76 died. As of December 1996, 52 of the deaths could be attributed to a common syndrome now called Caruaru syndrome. Examination of phytoplankton from the dialysis clinic's water source, analyses of the clinic's water treatment system, plus serum and liver tissue of clinic patients led to the identification of two groups of cyanobacterial toxins, the hepatotoxic cyclic peptide microcystins and the hepatotoxic alkaloid cylindrospermopsin. Comparison of victims' symptoms and pathology using animal studies of these two cyanotoxins leads us to conclude that the major contributing factor to death of the dialyses patients was intravenous exposure to microcystins, specifically microcystin-YR, -LR, and -AR. From liver concentrations and exposure volumes, it was estimated that 19.5 microg/L microcystin was in the water used for dialysis treatments. This is 19.5 times the level set as a guideline for safe drinking water supplies by the World Health Organization.

Isolation and characterization of microcystins from a river nile strain of Oscillatoria tenuis Agardh ex Gomont

The River Nile is the major source of drinking water in Egypt, however, increased eutrophication due to agricultural, municipal and industrial runoff has contributed to the growth of toxin producing cyanobacteria. This study describes the isolation and characterization of microcystins (MCYSTs), cyclic heptapeptide hepatotoxins, from a rare strain of Oscillatoria tenuis, isolated from the River Nile at Sohag province in July 1995. The MCYST concentration of laboratory-cultured O. tenuis strain E6 was found to be 0.3 mg/g freeze-dried weight determined by enzyme-linked immunosorbent assay (ELISA). Two microcystins, 1 and 2, were isolated from lyophilized cells using solid phase extraction and reversed-phase high performance liquid chromatography (HPLC). Structures were assigned based upon their amino acid analyses, electrospray ionization mass spectrometry (ESIMS, ESIMS-CID-MS), high resolution fast atom bombardment mass spectrometry, and nuclear magnetic resonance data ((1)H and (1)H COSY NMR). Toxin 1 was identified as MCYST-LR, and toxin 2, a new MCYST, as MCYST-LHArg ([L-homoarginine(4)]). Previous studies indicate that Oscillatoria agardhii strains produce demethylated MCYSTs (containing D-Asp and/or dehydroalanine). This is the first report of a toxic O. tenuis, strain E6, one which produces a fully methylated MCYST, MCYST-LR and a new L-homoarginine containing MCYST, MCYST-LHArg.

Enantiospecific synthesis of N-Boc-Adda: a linear approach

[structure: see text] Synthesis of the unusual amino acid (2S,3S,8S, 9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid (Adda), a unit of numerous cyanobacterial toxins, is described. Construction of the target molecule was achieved in 13 steps with an overall yield of 40%. The work is highlighted by a novel one-pot transformation from isoxazolidin-5-one intermediate 6 to the final product, a step that can also be used to form beta-amino acids.

Antitumor compounds from tunicates

Of the six marine-derived compounds that have reached clinical trials as antitumor agents three-didemnin B, Aplidine, and ecteinascidin 743-are derived from tunicates. Di-demnin B (DB), a cyclic depsipeptide from the compound tunicate Trididemnum solidum, was the first marine-derived compound to enter Phases I and II clinical trials. The Phase II studies, sponsored by the U. S. National Cancer Institute, indicated complete or partial remissions with non-Hodgkins lymphoma, but cardiotoxicity caused didemnin B to be dropped from further study. The closely related dehydrodidemnin B (DDB, Aplidine) was isolated in 1988 from a second colonial tunicate, Aplidium albicans, and spectroscopic studies assigned a structural formula in which a pyruvyl group in DDB replaced the lactyl group in DB and syntheses of DDB have been achieved. Aplidine is more active than DB and lacks DB's cardiotoxicity. It was introduced by PharmaMar into Phase I clinical trials in January 1999. The second family of tunicate-derived antitumor agents are the ecteinascidins (ETs), from the mangrove tunicate Ecteinascidia turbinata. The antitumor extracts of E. turbinata were first described in 1969, but the small amount of ETs in E. turbinata prevented their isolation for over a decade. The structures of ETs have been assigned mainly by spectroscopy. Phase II clinical trials with ET 743 are underway. Future supplies of ET's should be available from aquaculture or synthesis.

Antitumor compounds from tunicates

Of the six marine-derived compounds that have reached clinical trials as antitumor agents three-didemnin B, Aplidine, and ecteinascidin 743-are derived from tunicates. Di-demnin B (DB), a cyclic depsipeptide from the compound tunicate Trididemnum solidum, was the first marine-derived compound to enter Phases I and II clinical trials. The Phase II studies, sponsored by the U. S. National Cancer Institute, indicated complete or partial remissions with non-Hodgkins lymphoma, but cardiotoxicity caused didemnin B to be dropped from further study. The closely related dehydrodidemnin B (DDB, Aplidine) was isolated in 1988 from a second colonial tunicate, Aplidium albicans, and spectroscopic studies assigned a structural formula in which a pyruvyl group in DDB replaced the lactyl group in DB and syntheses of DDB have been achieved. Aplidine is more active than DB and lacks DB's cardiotoxicity. It was introduced by PharmaMar into Phase I clinical trials in January 1999. The second family of tunicate-derived antitumor agents are the ecteinascidins (ETs), from the mangrove tunicate Ecteinascidia turbinata. The antitumor extracts of E. turbinata were first described in 1969, but the small amount of ETs in E. turbinata prevented their isolation for over a decade. The structures of ETs have been assigned mainly by spectroscopy. Phase II clinical trials with ET 743 are underway. Future supplies of ET's should be available from aquaculture or synthesis.

Electrospray ionization mass spectrometric analysis of microcystins, cyclic heptapeptide hepatotoxins: modulation of charge states and [M + H]+ to [M + Na]+ ratio

Electrospray ionization mass spectrometry was used to develop a rapid, sensitive, and accurate method for determination and identification of hepatotoxic microcystins, cyanobacterial cyclic heptapeptides. To optimize the electrospray ionization conditions, factors affecting charge state distribution, such as amino acid components of sample, proton affinity of the additives, and additive concentration, were investigated in detail and a method for controlling charge states was developed to provide molecular-related ions for assignment of molecular weight and reasonably abundant precursor ions for MS/MS analysis. A procedure for identification of microcystins consisting of known amino acids was proposed: for microcystins giving abundant [M + 2H]2+ ions, the addition of nitrogen-containing bases to the aqueous sample solution is effective to obtain an increased intensity of [M + H]+ ions, whereas the addition of Lewis acids containing nitrogen can produce increased abundances of [M + 2H]2+ ions for microcystins giving weak [M + 2H]2+ ions. Microcystins possessing no arginine residue always give sodium adduct ions [M + Na]+ as the base peak, and these are difficult to fragment via low energy collision-induced dissociation to yield structurally informative products; the addition of oxalic acid increases [M + H]+ ion abundances, and these fragment readily.

Bioanalysis of aplidine, a new marine antitumoral depsipeptide, in plasma by high-performance liquid chromatography after derivatization with trans-4-hydrazino-2-stilbazole

A sensitive bio-analytical assay in plasma of the depsipeptide aplidine is reported, based on reversed-phase liquid chromatography and fluorescence detection of the trans-4'-hydrazino-2-stilbazole (4'H2S) derivative of the analyte. At ambient temperature, two conformations of the depsipeptide are observed in solution due to cis-trans isomerism at the proline-pyruvoyl peptide bond. Aplidine is isolated from the matrix by solid-phase extraction on an octadecyl modified silica stationary phase. After evaporation of the acetone eluate, a derivatization with 4'H2S is performed in a water-acetonitrile mixture at pH 4. The reaction mixture is injected directly into the chromatograph and the analyte is quantified by fluorescence detection at 410 and 560 nm for excitation and emission, respectively. The method has been validated in the 2-100 ng/ml-range, 2 ng/ml being the lower limit of quantification. Precision and accuracy both meet the current requirements for a bioanalytical assay. The identity of the 4'H2S reaction products of aplidine have been confirmed by mass spectrometric analysis. Finally, the method has been employed for a pilot pharmacokinetic study of aplidine in mice which demonstrated its usefulness for pharmacological research.

Low-energy collisionally activated decomposition and structural characterization of cyclic heptapeptide microcystins by electrospray ionization mass spectrometry

Characteristics of electrospray ionization mass spectrometry/collision-induced dissociation (ESIMS/CID) mass spectra of microcystins, cyanobacterial cyclic heptapeptide hepatoxins, were examined. The collision conditions showed remarkable effects on the quality of the CID mass spectra, which were divided into three patterns according to the number of Arg residues. A characteristic cleavage reaction and neutral losses of MeOH, NH3 and guanidine group(s) from the (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4 E,6E-dienoic acid (Adda) and Arg residues were observed in the ESI and ESIMS/CID mass spectra, suggesting the most probable protonation sites in [M + H]+ and [M + 2H]2+ ions of microcystins. Microcystins with no Arg residue showed only [M + H]+ ions with a proton reacting at the methoxyl group in the Adda residue, and the ESIMS/CID/MS data revealed their structures unambiguously. The protonation site in [M + H]+ ions of microcystins with Arg residue(s) was the guanidine group. The [M + 2H]2+ ions of microcystins possessing one Arg residue had one proton on the Arg residue and probably another proton on the Adda residue, while the [M + 2H]2+ ions of microcystins having two Arg residues showed protonation at both Arg residues and the ESIMS/CID/MS data assigned their sequences. Structures of microcystins possessing one Arg residue can be assigned by ESIMS/CID/MS of [M + H]+ ions combined with those of [M + 2H]2+ ions.

Seven new microcystins possessing two L-glutamic acid units, isolated from Anabaena sp. strain 186

Electrospray ionization mass spectrometry has been applied to the structure assignment of seven new microcystins (1-7), obtained from cultured Anabaena sp. strain 186. The seven new microcystins contain the dehydroalanine (Dha) or L-Ser unit instead of the N-methyldehydroalanine unit and the L-Glu and/or its delta-methyl ester [E(OMe)] units at the two variable L-amino acid units, and the structures were assigned as [Dha7]microcystin-E(OMe)E(OMe) (1), [D-Asp3,Dha7]microcystin-E(OMe)E(OMe) (2), [L-Ser7]microcystin-E(OMe)E(OMe) (3), [D-Asp3,L-Ser7]microcystin-E(OMe)E(OMe) (4), [Dha7]microcystin-EE(OMe) (5), [D-Asp3,Dha7]microcystin-EE(OMe) (6), and [L-Ser7]microcystin-EE(OMe) (7). These microcystins are the first examples containing dicarboxylic amino acids at the two variable L-amino acid units in microcystins.

Isolation of three novel neuropeptides, the Cyanea-RFamides I-III, from Scyphomedusae

Cnidarians are the lowest animal group having a nervous system. Using a radioimmunoassay for the C-terminal sequence Arg-Phe-NH2 (RFamide), we have isolated three novel neuropeptides from the jellyfish Cyanea lamarckii (belonging to the class Scyphozoa): (Glu-Trp-Leu-Arg-Gly-Arg-Phe-NH2 (Cyanea-RFamide I), (Glu-Pro-Leu-Trp-Ser-Gly-Arg-Phe-NH2 (Cyanea-RFamide II) and Gly-Arg-Phe-NH2 (Cyanea-RFamide III). The Cyanea-RFamides are neuropeptides and form a peptide family with other known neuropeptides isolated from Hydra and hydromedusae (belonging to the class Hydrozoa), and various sea anemones and sea pansies (belonging to the class Anthozoa). The presence of RFamide neuropeptides in all major cnidarian classes suggests that this type of substance was among the first neurotransmitters used in evolution.

Detecting and characterizing N-acyl-homoserine lactone signal molecules by thin-layer chromatography

Many Gram-negative bacteria regulate gene expression in response to their population size by sensing the level of acyl-homoserine lactone signal molecules which they produce and liberate to the environment. We have developed an assay for these signals that couples separation by thin-layer chromatography with detection using Agrobacterium tumefaciens harboring lacZ fused to a gene that is regulated by autoinduction. With the exception of N-butanoyl-L-homoserine lactone, the reporter detected acyl-homoserine lactones with 3-oxo-, 3-hydroxy-, and 3-unsubstituted side chains of all lengths tested. The intensity of the response was proportional to the amount of the signal molecule chromatographed. Each of the 3-oxo- and the 3-unsubstituted derivatives migrated with a unique mobility. Using the assay, we showed that some bacteria produce as many as five detectable signal molecules. Structures could be assigned tentatively on the basis of mobility and spot shape. The dominant species produced by Pseudomonas syringae pv. tabaci chromatographed with the properties of N-(3-oxohexanoyl)-L-homoserine lactone, a structure that was confirmed by mass spectrometry. An isolate of Pseudomonas fluorescens produced five detectable species, three of which had novel chromatographic properties. These were identified as the 3-hydroxy- forms of N-hexanoyl-, N-octanoyl-, and N-decanoyl-L-homoserine lactone. The assay can be used to screen cultures of bacteria for acyl-homoserine lactones, for quantifying the amounts of these molecules produced, and as an analytical and preparative aid in determining the structures of these signal molecules.

Distribution of tritiated dihydromicrocystin in swine

The distribution of tritiated dihydromicrocystin [3H]2H-MCLR was studied in anesthetized specific-pathogen-free pigs. Two doses were administered i.m. and one dose was given via an isolated ileal loop. At 4 hr after i.v. administration of the toxin at 25 micrograms/kg, 64.6% of the total dose (%TD) was located in the liver, with smaller amounts distributed to the kidneys (1.2% TD), lungs (1.75% TD), heart (0.22% TD), ileum (0.13% TD) and spleen (0.04% TD). A similar distribution was found at 4 hr postdosing in pigs given 75 micrograms/kg, although the liver contained a lower fraction of the total dose, at 46.99% TD, and the kidneys had somewhat more, at 2.19% TD, than the low dose. At the high dose, the fractions of the amount given accounted for by the lungs (0.55% TD), heart (0.23% TD), ileum (0.20% TD) and spleen (0.07% TD) were similar to those at the low dose. The livers of the pigs given 75 micrograms/kg via the ileal loop, at 5 hr postdosing, contained 49.5% TD and the ileum had 33.94% TD. Smaller amounts were distributed to kidneys (1.04% TD), lungs (0.65% TD), heart (0.81% TD) and spleen (0.16% TD). The livers of both groups dosed at 75 micrograms/kg contained higher concentrations of toxin, but lower percentages of the total dose, than the livers of pigs dosed at 25 micrograms/kg. Larger increases in serum arginase in the two 75 micrograms/kg groups were associated with histological evidence of more severe liver damage than at the 25 micrograms/kg dose. Analysis of radiolabeled compounds from hepatic tissue using fast atom bombardment mass spectrometry determined that the primary constituent was [3H]2H-MCLR, but two minor radioactive components were also isolated. These findings indicate that [3H]2H-MCLR is rapidly concentrated in the liver of swine, whether given i.v. or via an isolated ileal loop, that at extremely toxic doses uptake is slowed, and that it is as toxicologically active as the parent compound.

Isolation of four novel neuropeptides, the hydra-RFamides I-IV, from Hydra magnipapillata

Using a radioimmunoassay for the sequence Arg-Phe-NH2 (RFamide), we have isolated four novel peptides from extracts of Hydra magnipapillata: <Glu-Trp-Leu-Gly-Gly-Arg-Phe-NH2 (Hydra-RFamide I), <Glu-Trp-Phe-Asn-Gly-Arg-Phe-NH2 (Hydra-RFamide II), Lys-Pro-His-Leu-Arg-Gly-Arg-Phe-NH2 (Hydra-RFamide III) and His-Leu-Arg-Gly-Arg-Phe-NH2 (Hydra-RFamide IV). The Hydra-RFamides I-IV are neuropeptides. They form a peptide family with other known neuropeptides from hydromedusae, sea anemones and sea pansies.