Lethal ostreocin

O. siamensis was first characterized as a toxin producer by Nakajima et al. (1981). Some years later, Yasumoto et al. (1987) and Holmes et al. (1988) reported the lethafity and haemolytic activity of the O. siamensis toxins. Usami et al. (1995) were the first to elucidate the structure of the major ostreocin produced by O. siamensis (strain SOA 1 from Aka island, Okinawa, Japan) and point out its structural and chemical properties resemblance to palytoxin. This major constituent was named ostreocin-D and accounted for 90% of total toxicity of extracts. None of the other (more than 10) minor ostreocins present in the O. siamensis extracts were identical to palytoxin, as initially indicated by ESl-MS (Ukena et al. 2001, 2002). New Zealand O. siamensis isolates have also been reported to produce toxins exhibiting strong haemolytic activity and mouse lethality (Rhodes et al. 2000, 2002). Recently, Penna et al. (2005) have reported the presence of toxins with strong delayed haemolytic activity in Ostreopsis cf siamensis from the NW Mediterranean Sea. This haemolytic activity was inhibited by the palytoxin antagonist ouabain, indicating the palytoxin-like nature of these toxins. 

The MS profiles of McTx-A and McTx-B were both very similar to the respective profile of reference palytoxin, but the estimated molecular masses (between 2500-2535 Da) were lower than that of reference palytoxin (2680 Da) or other palytoxins and ostreocin-D. Nevertheless, the MS profile and fragmentation patterns of McTx-A and McTx-B together with mouse bioassay symptomatology and delayed haemolytic activity confirm the palytoxin-like character of these compounds. Quantitative differences in the hemolytic action and mouse lethality, as well as minor deviations in the MS spectra and retention times, could be attributed to structural variations between mascarenotoxins and the reference palytoxin (Lenoir et al. 2004). This is also supported by Usami et al. (1995), who showed that small changes in the structure of palytoxin analogues can have an impact on mouse toxicity, haemolytic potency, and cytotoxicity. 

Nakajima et al. [67] were the first to characterize 0. siamensis as a toxin producer. The lethality and hemolytic activity of the O. siamensis toxins was reported some years later [80,84]. Usami et al. [23] first elucidated the structme of the major ostreocin produced by 0. siamensis (strain SOA 1 from Aka island, Okinawa, Japan) and pointed out its structural and chemical properties resemblance to palytoxin. This major constituent, accounting for 90% of the total extracts toxicity. 

The small structural changes barely affected the mice lethality of ostreocin D (5). The LD50 value of 5 was 0.75 pg/kg (i.p. injection). Ostreocin D also exhibited potent cytotoxicity against P388 cells and hemolytic potency against mouse blood cell suspension in the same order concentrations as PTX (1). 

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