Two microcystins, MC-LR and [D-Leu1]MC-LR, present in La Plata Basin blooms, are differentiated by substitution of D-Alanine for D-Leucine at position 1. Our objective was to evaluate acute toxicity of [D-Leu1]MC-LR and MC-LR in mice (N:NIH Swiss) and beans (Phaseolus vulgaris). We observed variations in [D-Leu1]MC-LR lethal doses with respect to those reported for MC-LR (100 μg/kg), with an increased liver/body weight ratio and intrahepatic hemorrhages in mice exposed to 50–200 μg [D-Leu1]MC-LR/kg and slight steatosis after a single 25 μg [D-Leu1]MC-LR/kg i.p. dose. Our study in the plant model showed alterations in germination, development, morphology and TBARs levels after a single contact with the toxins during imbibition (3.5 and 15 µg/mL), those treated with [D-Leu1]MC-LR being more affected than those treated with the same concentration of MC-LR. Protein phosphatase 1 (PP1) IC50 values were 40.6 nM and 5.3 nM for [D-Leu1]MC-LR and MC-LR, respectively. However, the total phosphatase activity test in root homogenate showed 60% inhibition for [D-Leu1]MC-LR and 12% for MC-LR. In mouse liver homogenate, 50% inhibition was observed for [D-Leu1]MC-LR and 40% for MC-LR. Our findings indicate the need for further research into [D-Leu1]MC-LR toxicity since together with oxidative stress, the possible inhibition of other phosphatases could explain the differences detected in the potency of the two toxins.Centro de Investigaciones del MedioambienteFacultad de Ciencias Médica
