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Evolution and Distribution of Saxitoxin Biosynthesis in Dinoflagellates  [PDF]
Russell J. S. Orr,Anke Stüken,Shauna A. Murray,Kjetill S. Jakobsen
Marine Drugs , 2013, DOI: 10.3390/md11082814
Abstract: Numerous species of marine dinoflagellates synthesize the potent environmental neurotoxic alkaloid, saxitoxin, the agent of the human illness, paralytic shellfish poisoning. In addition, certain freshwater species of cyanobacteria also synthesize the same toxic compound, with the biosynthetic pathway and genes responsible being recently reported. Three theories have been postulated to explain the origin of saxitoxin in dinoflagellates: The production of saxitoxin by co-cultured bacteria rather than the dinoflagellates themselves, convergent evolution within both dinoflagellates and bacteria and horizontal gene transfer between dinoflagellates and bacteria. The discovery of cyanobacterial saxitoxin homologs in dinoflagellates has enabled us for the first time to evaluate these theories. Here, we review the distribution of saxitoxin within the dinoflagellates and our knowledge of its genetic basis to determine the likely evolutionary origins of this potent neurotoxin.
A Putative Gene Cluster from a Lyngbya wollei Bloom that Encodes Paralytic Shellfish Toxin Biosynthesis  [PDF]
Troco K. Mihali,Wayne W. Carmichael,Brett A. Neilan
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0014657
Abstract: Saxitoxin and its analogs cause the paralytic shellfish-poisoning syndrome, adversely affecting human health and coastal shellfish industries worldwide. Here we report the isolation, sequencing, annotation, and predicted pathway of the saxitoxin biosynthetic gene cluster in the cyanobacterium Lyngbya wollei. The gene cluster spans 36 kb and encodes enzymes for the biosynthesis and export of the toxins. The Lyngbya wollei saxitoxin gene cluster differs from previously identified saxitoxin clusters as it contains genes that are unique to this cluster, whereby the carbamoyltransferase is truncated and replaced by an acyltransferase, explaining the unique toxin profile presented by Lyngbya wollei. These findings will enable the creation of toxin probes, for water monitoring purposes, as well as proof-of-concept for the combinatorial biosynthesis of these natural occurring alkaloids for the production of novel, biologically active compounds.
Origin of Saxitoxin Biosynthetic Genes in Cyanobacteria  [PDF]
Ahmed Moustafa, Jeannette E. Loram, Jeremiah D. Hackett, Donald M. Anderson, F. Gerald Plumley, Debashish Bhattacharya
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005758
Abstract: Background Paralytic shellfish poisoning (PSP) is a potentially fatal syndrome associated with the consumption of shellfish that have accumulated saxitoxin (STX). STX is produced by microscopic marine dinoflagellate algae. Little is known about the origin and spread of saxitoxin genes in these under-studied eukaryotes. Fortuitously, some freshwater cyanobacteria also produce STX, providing an ideal model for studying its biosynthesis. Here we focus on saxitoxin-producing cyanobacteria and their non-toxic sisters to elucidate the origin of genes involved in the putative STX biosynthetic pathway. Methodology/Principal Findings We generated a draft genome assembly of the saxitoxin-producing (STX+) cyanobacterium Anabaena circinalis ACBU02 and searched for 26 candidate saxitoxin-genes (named sxtA to sxtZ) that were recently identified in the toxic strain Cylindrospermopsis raciborskii T3. We also generated a draft assembly of the non-toxic (STX?) sister Anabaena circinalis ACFR02 to aid the identification of saxitoxin-specific genes. Comparative phylogenomic analyses revealed that nine putative STX genes were horizontally transferred from non-cyanobacterial sources, whereas one key gene (sxtA) originated in STX+ cyanobacteria via two independent horizontal transfers followed by fusion. In total, of the 26 candidate saxitoxin-genes, 13 are of cyanobacterial provenance and are monophyletic among the STX+ taxa, four are shared amongst STX+ and STX-cyanobacteria, and the remaining nine genes are specific to STX+ cyanobacteria. Conclusions/Significance Our results provide evidence that the assembly of STX genes in ACBU02 involved multiple HGT events from different sources followed presumably by coordination of the expression of foreign and native genes in the common ancestor of STX+ cyanobacteria. The ability to produce saxitoxin was subsequently lost multiple independent times resulting in a nested relationship of STX+ and STX? strains among Anabaena circinalis strains.
Gustatory Detection of Tetrodotoxin and Saxitoxin, and Its Competitive Inhibition by Quinine and Strychnine in Freshwater Fishes  [PDF]
Toshiaki J. Hara
Marine Drugs , 2011, DOI: 10.3390/md9112283
Abstract: Fish detect extremely low levels of marine toxins tetrodotoxin (TTX) and saxitoxin (STX) via the specialized gustatory receptor(s). Physiological and pharmacological studies show that receptor(s) for TTX and STX are distinct from those which detect feeding stimulant amino acids and bile acids, and that TTX and STX do not share the same receptor populations, while interacting with quinine and strychnine in a competitive fashion suggestive of an antidotal relationship.
Genotoxic, neurotoxic and neuroprotective activities of apomorphine and its oxidized derivative 8-oxo-apomorphine
Picada, J.N.;Roesler, R.;Henriques, J.A.P.;
Brazilian Journal of Medical and Biological Research , 2005, DOI: 10.1590/S0100-879X2005000400001
Abstract: apomorphine is a dopamine receptor agonist proposed to be a neuroprotective agent in the treatment of patients with parkinson's disease. both in vivo and in vitro studies have shown that apomorphine displays both antioxidant and pro-oxidant actions, and might have either neuroprotective or neurotoxic effects on the central nervous system. some of the neurotoxic effects of apomorphine are mediated by its oxidation derivatives. in the present review, we discuss recent studies from our laboratory in which the molecular, cellular and neurobehavioral effects of apomorphine and its oxidized derivative, 8-oxo-apomorphine-semiquinone (8-oasq), were evaluated in different experimental models, i.e., in vitro genotoxicity in salmonella/microsome assay and wp2 mutoxitest, sensitivity assay in saccharomyces cerevisiae, neurobehavioral procedures (inhibition avoidance task, open field behavior, and habituation) in rats, stereotyped behavior in mice, and comet assay and oxidative stress analyses in mouse brain. our results show that apomorphine and 8-oasq induce differential mutagenic, neurochemical and neurobehavioral effects. 8-oasq displays cytotoxic effects and oxidative and frameshift mutagenic activities, while apomorphine shows antimutagenic and antioxidant effects in vitro. 8-oasq induces a significant increase of dna damage in mouse brain tissue. both apomorphine and 8-oasq impair memory for aversive training in rats, although the two drugs showed a different dose-response pattern. 8-oasq fails to induce stereotyped behaviors in mice. the implications of these findings are discussed in the light of evidence from studies by other groups. we propose that the neuroprotective and neurotoxic effects of dopamine agonists might be mediated, in part, by their oxidized metabolites.
Genotoxic, neurotoxic and neuroprotective activities of apomorphine and its oxidized derivative 8-oxo-apomorphine  [cached]
Picada J.N.,Roesler R.,Henriques J.A.P.
Brazilian Journal of Medical and Biological Research , 2005,
Abstract: Apomorphine is a dopamine receptor agonist proposed to be a neuroprotective agent in the treatment of patients with Parkinson's disease. Both in vivo and in vitro studies have shown that apomorphine displays both antioxidant and pro-oxidant actions, and might have either neuroprotective or neurotoxic effects on the central nervous system. Some of the neurotoxic effects of apomorphine are mediated by its oxidation derivatives. In the present review, we discuss recent studies from our laboratory in which the molecular, cellular and neurobehavioral effects of apomorphine and its oxidized derivative, 8-oxo-apomorphine-semiquinone (8-OASQ), were evaluated in different experimental models, i.e., in vitro genotoxicity in Salmonella/microsome assay and WP2 Mutoxitest, sensitivity assay in Saccharomyces cerevisiae, neurobehavioral procedures (inhibition avoidance task, open field behavior, and habituation) in rats, stereotyped behavior in mice, and Comet assay and oxidative stress analyses in mouse brain. Our results show that apomorphine and 8-OASQ induce differential mutagenic, neurochemical and neurobehavioral effects. 8-OASQ displays cytotoxic effects and oxidative and frameshift mutagenic activities, while apomorphine shows antimutagenic and antioxidant effects in vitro. 8-OASQ induces a significant increase of DNA damage in mouse brain tissue. Both apomorphine and 8-OASQ impair memory for aversive training in rats, although the two drugs showed a different dose-response pattern. 8-OASQ fails to induce stereotyped behaviors in mice. The implications of these findings are discussed in the light of evidence from studies by other groups. We propose that the neuroprotective and neurotoxic effects of dopamine agonists might be mediated, in part, by their oxidized metabolites.
Surface Plasmon Spectroscopic Detection of Saxitoxin  [PDF]
Hongxia Chen,Youn Sook Kim,Sam-Rok Keum,Sung-Hoon Kim,Heung-Jin Choi,Jaebeom Lee,Won Gun An,Kwangnak Koh
Sensors , 2007, DOI: 10.3390/s7071216
Abstract: For the surface-optoelectronic study of Saxitoxin sensing, we fabricated self-assembled calix[4]arene derivative monolayers as the recognition-functional interfaces ona gold surface. An interaction study between Saxitoxin and calix[4]arene derivativemonolayers were performed using surface plasmon resonance (SPR) spectroscopy. Amongthree calix[4]arene derivatives, calix[4]arene crown ether SAM showed the highestsensitivity to Saxitoxin. The detection limit of this system is three orders of magnitudelower than that of the mouse bioassay which is the current benchmark for Saxitoxindetection.
Testosterone and Its Analogs as a Male Contraceptive  [PDF]
Abdul S. Ansari, Chandra Shekhar Yadav, Nirmal K. Lohiya
Advances in Sexual Medicine (ASM) , 2013, DOI: 10.4236/asm.2013.33A002
Abstract: Male contraception by means of hormonal approach was initiated more than 60 years ago when men became azoospermic with administration of testosterone. The basic principle of male hormonal contraception is suppression of spermatogenesis. Exogenous testosterone/testosterone analogs alone or in combination with progestin have been tested for contraceptive efficacy by inhibiting gonadotropins release from pituitary gland. In this review article, advancement in different testosterone preparation tested alone or in combination for contraceptive efficacy has been focused. Administration of testosterone or testosterone analogs alone failed to provide uniform azoospermia or severe oligospermia (<1 million/ml sperm count) at lower doses regimens whereas higher doses causes side effects. Newer, androgen-progestin combination has proved better contraceptive efficacy than testosterone alone. Further, long term studies with hormonal regimens and other alternative approaches are required with fewer side effects for development of safe and reversible contraceptive.
An Overview on the Marine Neurotoxin, Saxitoxin: Genetics, Molecular Targets, Methods of Detection and Ecological Functions  [PDF]
Kathleen D. Cusick,Gary S. Sayler
Marine Drugs , 2013, DOI: 10.3390/md11040991
Abstract: Marine neurotoxins are natural products produced by phytoplankton and select species of invertebrates and fish. These compounds interact with voltage-gated sodium, potassium and calcium channels and modulate the flux of these ions into various cell types. This review provides a summary of marine neurotoxins, including their structures, molecular targets and pharmacologies. Saxitoxin and its derivatives, collectively referred to as paralytic shellfish toxins (PSTs), are unique among neurotoxins in that they are found in both marine and freshwater environments by organisms inhabiting two kingdoms of life. Prokaryotic cyanobacteria are responsible for PST production in freshwater systems, while eukaryotic dinoflagellates are the main producers in marine waters. Bioaccumulation by filter-feeding bivalves and fish and subsequent transfer through the food web results in the potentially fatal human illnesses, paralytic shellfish poisoning and saxitoxin pufferfish poisoning. These illnesses are a result of saxitoxin’s ability to bind to the voltage-gated sodium channel, blocking the passage of nerve impulses and leading to death via respiratory paralysis. Recent advances in saxitoxin research are discussed, including the molecular biology of toxin synthesis, new protein targets, association with metal-binding motifs and methods of detection. The eco-evolutionary role(s) PSTs may serve for phytoplankton species that produce them are also discussed.
Growth and Saxitoxin Production by Cylindrospermopsis raciborskii (Cyanobacteria) Correlate with Water Hardness  [PDF]
Ronaldo Leal Carneiro,Ana Beatriz Furlanetto Pacheco,Sandra Maria Feliciano de Oliveira e Azevedo
Marine Drugs , 2013, DOI: 10.3390/md11082949
Abstract: The cosmopolitan and increasing distribution of Cylindrospermopsis raciborskii can be attributed to its ecophysiological plasticity and tolerance to changing environmental factors in water bodies. In reservoirs in the semi-arid region of Brazil, the presence and common dominance of C. raciborskii have been described in waters that are considered hard. We investigated the response of a Brazilian C. raciborskii strain to water hardness by evaluating its growth and saxitoxin production. Based on environmental data, a concentration of 5 mM of different carbonate salts was tested. These conditions affected growth either positively (MgCO 3) or negatively (CaCO 3 and Na 2CO 3). As a control for the addition of cations, MgCl 2, CaCl 2 and NaCl were tested at 5 or 10 mM, and MgCl 2 stimulated growth, NaCl slowed but sustained growth, and CaCl 2 inhibited growth. Most of the tested treatments increased the saxitoxin (STX) cell quota after six days of exposure. After 12 days, STX production returned to concentrations similar to that of the control, indicating an adaptation to the altered water conditions. In the short term, cell exposure to most of the tested conditions favored STX production over neoSTX production. These results support the noted plasticity of C. raciborskii and highlight its potential to thrive in hard waters. Additionally, the observed relationship between saxitoxin production and water ion concentrations characteristic of the natural environments can be important for understanding toxin content variation in other harmful algae that produce STX.
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