Biology Reference
In-Depth Information
periods whereas pup viability and weight on postnatal day remained unaffected. GD8 mouse embryos
exposed to 0.1-0.25 µg anatoxin-a for 26-28 h showed no embryonic dysmorphology but there were
perturbations in mouse yolk sac vasculature. Synergistic toxicity of MC-LR and anatoxin-a has been
studied by orally administering MC-LR fi rst (500, 1000 µg kg
-1
body weight) followed by anatoxin-a
(500, 1000 or 2500 µg kg
-1
body weight). Neither death nor defi nite signs of intoxication were noted
even at high concentrations. However, in amphibian toxicity assays involving exposure of toad
embryos (stages 17 and 25 of
Bufo arenarum
) to anatoxin-a (0.3 to 30 mg L
-1
for 10 days) resulted in
100% lethality at high dose in groups 6-13 days post-exposure (Rogers
et al
., 2005).
The effects of anatoxin-a on non-neurone cells have been studied. In this connection, the studies
of Rao
et al
. (2002) on anatoxin-a induced apopotosis in cultured rat thymocytes and African green
monkey kidney cells are signifi cant. Plasma membrane blebbing, condensed chromatin, nuclear
fragmentation and formation of apoptotic bodies are the characteristics of anatoxin-a-induced
apoptosis. The involvement of capsases (capsase-3 activity) and reactive oxygen species in apoptosis
was also indicated.
Homoanatoxin-a (mol wt. 179 D) is structurally similar to anatoxin-a and is produced by an
Oscillatoria formosa
(
P
.
formosum)
strain (Fig. 13). Méjean
et al
. (2009) reported the production of
anatoxin-a and homoanatoxin-a by
Oscillatoria
PCC 6506. A propinyl group at C-2 is characteristic
instead of the acetyl group in anatoxin-a (Skulberg
et al
., 1992). The LD
50
of homoanatoxin-a was
288-578 µg kg
-1
body weight. The LD
50
value of homoanatoxin-a (i.p.) was 250 µg kg
-1
body weight.
Toxicity due to lethal doses leads to body paralysis, convulsions and death by respiratory arrest
in 7-12 minutes (Kupier-Goodman
et al
., 1999). The physiological effects of homoanatoxin-a are
shown to be due to d-tubocurarine (Skulberg
et al
., 1992). It also enhances the infl ux of Ca
2+
ions in
cholinergic nerve terminals (Aas
et al
., 1996).
In an attempt to detect toxins from health food supplements (tablets and capsulses of
Spirulina
)
marketed in Rome (Italy), Draisci
et al.
(2001) reported the existence of epoxyanatoxin-a and its
analogues (18 to 19 µg g
-1
in only two of the fi ve samples tested) and dihydrohomoanatoxin-a (10
µg g
-1
in three of the fi ve samples). Thus these authors suggested that a potential human health
hazard could be associated with the consumption of such food supplements. It is interesting to note
that anatoxin-a and homoanatoxin-a have been isolated from
Oscillatoria
sp. strain 193 PCC 9240
and
O
.
formosa
NIVA CYA-92 PCC 10111, respectively. Other strains of
Oscillatoria
such as PCC 6407,
PCC 6412 and PCC 9107 produced exclusively anatoxin-a where as strains PCC 9029 and PCC 6506
synthesized both anatoxin-a and homoanatoxin-a (Aráoz
et al
., 2005).
O
H
2
+
N
CH
3
Figure 13:
Structure of homoanatoxin-a.
