Transplacental exposure to methylene blue initiates teratogenesis in the mouse: preliminary evidence for a mechanistic implication of cyclic GMP pathway disruption.
BACKGROUND
The vital dye methylene blue (MB) has been shown to be teratogenic when injected into the amnion in the second trimester. On the other hand, the teratogenic potential of transplacental exposure to MB has not been determined.


METHODS
MB was administered subcutaneously to ICR (CD-1) mice at 0, 35, 50, 60, or 70 mg/kg on gestation day 8 (plug day = day 0). Teratological assessments were carried out at term gestation, on gestation day 18. Since MB inhibits soluble guanylate cyclase enzyme activity, zaprinast (ZPN), a selective cGMP-phosphodiesterase type V inhibitor, was administered to prevent developmental disorders initiated by MB at 50 mg/kg.


RESULTS
There was a dose-dependent increment of embryolethality. MB treatment also produced axial skeleton and neural tube defects. Coadministration of ZPN (20 mg/kg per three times) abolished completely MB-induced neural tube defects and reduced by one-half the incidence of fetuses exhibiting axial skeletal defects. ZPN did not provide protection against the embryocidal effects of MB.


CONCLUSIONS
This study showed that transplacental exposure to MB is teratogenic in the mouse. Coadministration of ZPN prevented partly MB-induced teratogenesis, which supports the hypothesis that imbalance of cGMP pathway accounts, in part, for the teratogenicity of MB.
Tiboni
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Sezione di Ostetricia e Ginecologia, Dipartimento di Medicina e Scienze dell'Invecchiamento, Facoltà di Medicina e Chirurgia, Università "G. d'Annunzio," Ospedale Clinicizzato "SS. Annunziata," 66013-Chieti, Italy. tiboni@unich.it
Lamonaca
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D000818:Animals; D001842:Bone and Bones / Q000002:abnormalities; D006152:Cyclic GMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000009:adverse effects*; D005260:Female; D018811:Maternal Exposure; D008751:Methylene Blue / Q000009:adverse effects*; D051379:Mice; D008813:Mice, Inbred ICR; D009436:Neural Tube Defects / Q000139:chemically induced; D010726:Phosphodiesterase Inhibitors / Q000009:adverse effects; D010920:Placenta / Q000187:drug effects*; D011688:Purinones / Q000009:adverse effects; D013723:Teratogens; D013997:Time Factors
D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D011688:Purinones; D013723:Teratogens; C011145:zaprinast; D006152:Cyclic GMP; D008751:Methylene Blue