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Negli ultimi anni numerose pubblicazioni hanno descritto un aumento nella frequenza delle malformazioni ed un declino nelle popolazioni di anfibi. Tra le possibili cause, viene riportata l’esposizione a prodotti fitosanitari usati in agricoltura. E’ noto infatti che gli organofosfati, tra cui chlorpyrifos (CPF), provochino effetti tossici negli organismi non bersaglio come per esempio l’inibizione dell’attività enzimatica dell’acetilcolinesterasi (AChE) che causa una continua stimolazione dei recettori colinergici con conseguente alterazione della contrazione muscolare. La valutazione del bioaccumulo e della capacità detossificante, in termini di clearance, negli stadi larvali di Xenopus laevis esposti a CPF, è uno degli scopi del progetto di ricerca attualmente in corso. I risultati ottenuti dai saggi ecotossicologici effettuati hanno permesso di evidenziare tre fasi distinte nella cinetica di uptake e clearance, ciascuna delle quali caratterizzata da una peculiare cinetica di reazione. Queste risultano essere tutte correlate alle proprietà chimico-fisiche della molecola in studio e alle proprietà biologiche dell’organismo saggiato. Le differenze delle reazioni individuate nei vari stadi di sviluppo hanno una grande rilevanza ecologica nell’ambito di una stima del rischio ecotossicologico per anfibi in seguito ad esposizione a xenobiotici

The effect of organophosphate pesticide chlorpyrifos (CPF) on acetylcholinesterase (AChE) activity and on skeletal muscle development in Xenopus laevis larvae was studied. To achieve our purpose embryos were exposed to 100, 250 and 3000 microg/l CPF concentrations from late blastula stage (8 h postfertilization, p.f.) to stage 47 (120 h p.f.) and the appearance of AChE activity was monitored every 24 h. Compared with control, CPF treated larvae showed a dose dependent AChE inhibition during the early stages (beginning from 24 h until 120 h p.f.) that are crucial for neuromuscular development. The amount of AChE activity that can still be measured in treated larvae at stage 47 relative to that of the control, ranged from 28% in CPFs 100 microg/l to 4% in CPFs 3000 microg/l. These low AChE activities were associated with muscular damages such as reduced myotome size and hypertrophies coupled with extensive vacuolated regions in myocytes. The occurrence of this tissue-specific injury was related to CPF concentrations and was most pronounced in CPFs 3000 microg/l which revealed a very severe AChE inhibition during the exposure. Since AChE is the major neurotransmitter of the neuromuscular system, this initial descriptive study will be an useful starting-point to ongoing and future subcellular/molecular studies that correlate the morphological damage with changes in AChE activity.

The embryotoxic potential of chlorpyrifos (CPF) and malathion (MTN), two organophosphorus insecticides (OPs), was evaluated by modified Frog Embryo Teratogenesis Assay- Xenopus (FETAX). CPF and MTN were not embryolethal even at the highest concentration tested (6000 g/l), but both exhibited a powerful teratogenicity. The probit analysis of malformed larva percentages showed a TC50 of 161.54g/l for CPF, and a TC50 of 2394.01g/l for MTN. Therefore, CPF teratogenicity was about 15 times higher than MTN. Larvae of both exposed groups were mainly affected by ventral and/or lateral tail flexure coupled with abnormal gut coiling. Histopathological diagnosis displayed abnormal myotomes and myocytes with marked hypertrophies localized at the cell extremity, probably due to a break away of myofibril extremities at the intersomitic junction level. We speculate that this muscular damage was related to inhibition of acetylcholinesterase that showed a clear concentration-response in CPF and MTN exposed larvae. The teratogenic effects of these anti-cholinesterase compounds on Xenopus laevismyogenesis suggest a possible role played by OPs on induction of congenital muscular dystrophy. © 2004 Elsevier B.V. All rights reserved.