The acute oral toxicity of a new palytoxin congener, 42-hydroxy-palytoxin (42-OH-PLTX), was investigated in female CD-1 mice. The toxin (300-1697 μg/kg), administered by gavage, induced scratching, jumping, respiratory distress, cyanosis, paralysis and death of mice, with an LD₅₀ of 651 μg/kg (95% confidence limits: 384-1018 μg/kg) within 24 h. Hematoclinical analyses showed increased plasma levels of lactate dehydrogenase and aspartate-aminotransferase at doses of 600 μg/kg and above, as well as of alanine-aminotransferase, creatine phosphokinase and potassium ions at ≥ 848 μg/kg. Histology revealed inflammatory lesions in the non-glandular area of the stomach of mice that survived up to 24 h after gavage (424-1200 μg/kg). Although no histological alterations were seen in skeletal and cardiac muscles, changes in some plasma biomarkers (creatine phosphokinase, lactate dehydrogenase) suggested involvement of these tissues in 42-OH-PLTX oral toxicity, in agreement with epidemiological data on seafood poisonings ascribed to palytoxins. Complete recovery of the tissue and hematological changes was observed two weeks post-exposure. Furthermore, 42-OH-PLTX induced in vitro delayed erythrocyte hemolysis at concentrations similar to those of PLTX (EC₅₀ = 7.6 and 13.2 x 10⁻¹² M, respectively). This hemolysis could be completely neutralized by a monoclonal anti-PLTX antibody. The in vivo data, together with the in vitro data recorded for 42-OH-PLTX, seem to indicate Na+/K+-ATPase as one of the key cellular targets of this toxin.
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