Hapalindoles from the cyanobacterium fischerella: potential sodium channel modulators.

Hapalindoles make up a large group of bioactive metabolites of the cyanobacterial order Stigonematales. 12-epi-Hapalindole E isonitrile, 12-epi-hapalindole C isonitrile, 12-epi-hapalindole J isonitrile, and hapalindole L from Fischerella are acutely toxic for insect larvae; however, the biochemical targets responsible for the biological activities of hapalindoles are not understood. We describe here the electron impact mass spectra of these four hapalindole congeners; their structures were confirmed by nuclear magnetic resonance spectroscopy. In combination with the presented mass spectra of (15)N-labeled species and their retention times on a gas chromatography capillary column, a rapid and reliable determination should be possible in future research. The bioactivity of these hapalindoles was tested on mammalian cells focusing on their effects in the BE(2)-M17 excitable human neuroblastoma cell line. The fluorescent dye Alamar Blue was applied to monitor cytotoxicity, fura-2 to evaluate changes in the cytosolic calcium concentrations, and bis-oxonol to detect effects on membrane potential. Data showed that the hapalindoles did not affect cell viability of the neuroblastoma cells, even when they were incubated for 72 h. Neither depolarization nor initiation of calcium influx was observed in the cells upon hapalindole treatment. However, the data provide evidence that hapalindoles are sodium channel-modulating neurotoxins. They inhibited veratridine-induced depolarization in a manner similar to that of neosaxitoxin. Our data suggest hapalindoles should be added to the growing number of neurotoxic secondary metabolites, such as saxitoxins and anatoxins, already known in freshwater cyanobacteria. As stable congeners, hapalindoles may be a risk in freshwater ecosystems or agricultural water usage and should therefore be considered in water quality assessment.

Novel bioassay demonstrates attraction of the white potato cyst nematode Globodera pallida (Stone) to non-volatile and volatile host plant cues.

Potato cyst nematodes (PCNs) are a major pest of solanaceous crops such as potatoes, tomatoes, and eggplants and have been widely studied over the last 30 years, with the majority of earlier studies focusing on the identification of natural hatching factors. As a novel approach, we focused instead on chemicals involved in nematode orientation towards its host plant. A new dual choice sand bioassay was designed to study nematode responses to potato root exudates (PRE). This bioassay, conducted together with a traditional hatching bioassay, showed that biologically active compounds that induce both hatching and attraction of PCNs can be collected by water extraction of incised potato roots. Furthermore, our results demonstrated that PCN also were attracted by potato root volatiles. Further work is needed to fully understand how PCNs use host plant chemical cues to orientate towards hosts. Nevertheless, the simple attraction assay used in this study provides an important tool for the identification of host-emitted attractants.