Biomedical subjects

Livia Pica-Mattoccia

Publications and source records attributed to Livia Pica-Mattoccia.

8 recordsLinked to original sources

PubMed2006

Cytochalasin D abolishes the schistosomicidal activity of praziquantel.

To test the hypothesis that calcium channels of schistosomes are the targets for the action of praziquantel, we subjected schistosomes in vitro to pharmacological agents capable of interfering with the functioning of calcium channels. After 1-h exposure to these agents, praziquantel was added and incubation continued overnight. Worms were then washed, resuspended in drug-free medium and observed during the following 7-10 days. About 50% of schistosomes pre-exposed to the calcium channel blockers nicardipine and nifedipine were able to survive a praziquantel concentration (3 microM) that normally killed the majority of adult male worms. Since the organization of the actin cytoskeleton controls the activity of calcium channels in a number of different systems, we also pre-exposed schistosomes to the actin depolymerizing agent cytochalasin D. This treatment rendered the parasites completely refractory to the effects of very high praziquantel levels (up to 36 microM). These results are consistent with the hypothesis that schistosome calcium channels are involved in the mechanism of action of praziquantel.

Actins↗

PubMed2006

Praziquantel for the treatment of schistosomiasis: its use for control in areas with endemic disease and prospects for drug resistance.

Praziquantel became available for the treatment of schistosomiasis and other trematode-inflicted diseases in the 1970s. It was revolutionary because it could be administered orally and had very few unwanted side effects. As a result of marked reductions in the price of praziquantel, the rate at which it is used has accelerated greatly in recent years. For the foreseeable future it will be the mainstay of programs designed to control schistosome-induced morbidity, particularly in sub-Saharan Africa where schistosomiasis is heavily endemic. There is currently no evidence to suggest that any schistosomes have developed resistance to praziquantel as a result of its widespread use. Nevertheless, while resistance may not pose an obvious or immediate threat to the usefulness of praziquantel, complacency and a failure to monitor developments may have serious consequences in the longer term since it will be the only drug that is readily available for large-scale treatment of schistosomiasis.

Animals↗

PubMed2005

Effect of praziquantel on the immature stages of Schistosoma haematobium.

Schistosoma mansoni is known to be refractory to praziquantel treatment in the pre-patent period of infection. Since Schistosoma haematobium has a much longer pre-patent period (10-12 weeks vs. 5-6 for the former species), we asked the question whether a correspondingly longer period of insusceptibility exists in urinary schistosomiasis. In hamsters treated at different times after infection, S. haematobium was partially refractory to praziquantel when treatment was given at week 5, but showed practically full sensitivity at 7-8 weeks and later times. Schistosoma haematobium worms obtained at different times after infection and exposed in vitro to praziquantel were refractory to low drug concentrations between 4 and 6 weeks, but were clearly affected at higher concentrations and at later time points. We conclude that S. haematobium does not have a praziquantel-insensitive window longer than in S. manson, in spite of its much longer maturation period. In addition, refractoriness of immature stages can be overcome at higher drug concentrations.

Animals↗

PubMed2004

Sex- and stage-related sensitivity of Schistosoma mansoni to in vivo and in vitro praziquantel treatment.

The efficacy of praziquantel against a Puerto Rican strain of Schistosoma mansoni was assessed using both in vivo and in vitro approach. The drug effective dose (50%) in the infected mouse model was about 30 times higher when determined against 28-day-old infections than against 7-week-old parasites. Single-sex female infections were also largely refractory to treatment and single-sex male infections moderately refractory, in comparison with bisexual infections. The in vitro approach consisted of overnight exposure of parasite cultures to various drug concentrations, followed by several days of culture in drug-free medium. In vitro results confirmed in vivo data and allowed for the observation of schistosome morphological phenomena after praziquantel exposure. Early worm contraction was observed in all cases, even after exposure to sub-lethal concentrations of praziquantel or upon exposure of the largely refractory 28-day-old schistosomes. In these instances, however, worms resumed movements and normal shape upon drug removal and were able to survive. The inference of these observations on the clinical use of praziquantel and on its mechanism of action is discussed.

Animals↗

PubMed2004

Determination of ED50 values for praziquantel in praziquantel-resistant and -susceptible Schistosoma mansoni isolates.

The dose of praziquantel required to kill 50% of adult worms in vivo (i.e. the ED50) was estimated for nine different isolates of Schistosoma mansoni in infected mice. Four of the isolates were selected because they had not knowingly been in contact with the drug (i.e. they were putatively praziquantel-susceptible). Five putatively praziquantel-resistant isolates were chosen because they had been selectively bred for drug-resistance in the laboratory and/or had previously been shown to be relatively resistant to praziquantel in the field. The work was performed in three laboratories in different countries using pre-agreed and comparable experimental protocols. All four praziquantel-susceptible isolates had ED50s estimated to be <100 mg/kg (mean=70+/-7 SD; median=68), while all five putatively praziquantel-resistant isolates had estimated ED50s >100 mg/kg (mean=209+/-48 SD; median=192). Thus, the five praziquantel-resistant isolates, including two that had been subjected to drug pressure during more than 20 passages in mice, had drug ED50s that were approximately three times as great as those of the praziquantel-susceptible isolates. Two of the five isolates in the putatively resistant group had previously been passaged 15 or more times in mice without administration of drug-pressure, but had ED50s consistent with the other three isolates in the group, indicating that the trait of praziquantel-resistance did not necessarily impair biological fitness during laboratory passage. The protocols used here to estimate the praziquantel ED50s of S. mansoni isolates should be useful for establishing and monitoring the drug susceptibility/resistance profiles of parasite isolates freshly obtained from endemic areas, particularly those in which increased usage of the drug is likely to occur.

Adolescent↗

PubMed2003

Sequence and level of endogenous expression of calcium channel beta subunits in Schistosoma mansoni displaying different susceptibilities to praziquantel.

Kohn et al. [J. Biol. Chem. 276 (2001) 36873] demonstrated that cells expressing the structurally unusual schistosome beta subunit SmCavbeta1 in their voltage-operated calcium channels, exhibit an increased current amplitude in the presence of praziquantel (PZQ). This suggests that the beta subunit is involved in PZQ activity and is consistent with the known pharmacological effects of the drug. If this is so, the low susceptibility to PZQ noted in some Schistosoma mansoni strains could be due to some mutation(s) in the gene coding for this protein. We have sequenced the cDNAs coding for the SmCavbeta1 and SmCavbeta2 subunits of different sensitive and resistant strains and we have not been able to detect any meaningful differences. As an alternative hypothesis, the different sensitivity of schistosomes to PZQ action could be due to the expression of different beta subunits in the parasite. This interpretation could also explain the low PZQ susceptibility of immature worms (28 days). We analyzed Northern blots of various strains and various developmental stages, but we were unable to demonstrate major quantitative differences in the expression of the beta subunits.

Animals↗

PubMed2002

Praziquantel.

Praziquantel is the drug of choice for the treatment of all forms of schistosomiasis. This review summarizes the main features of the drug, with special attention being given to those aspects that may be of interest to the practicing physician. After a brief mention of the history, the chemistry, the major available brands and their costs, doses and administration schedules are reviewed. Pharmacokinetics and drug interactions are analyzed and the low toxicity and mild side effects are stressed. A major weakness of praziquantel is its relative inefficacy against recent infections, a factor that may occasionally result in low cure rates in hyperendemic areas. Recent findings of schistosome isolates with a decreased sensitivity to praziquantel are discussed in the broader context of a possible emergence of drug resistance.

Animals↗

PubMedDate not supplied

Rapamycin insensitivity in Schistosoma mansoni is not due to FKBP12 functionality.

Rapamycin (RAPA) is a well-known immunosuppressant, the action of which is mediated by the immunophilin FKBP12. Upon RAPA binding, FKBP12 forms ternary complexes with phosphatidyl inositol related kinases known as the target of RAPA (TOR), which can lead to a mitotic block at the G1-S phase transition. Such an antiproliferative effect makes RAPA an attractive anticancer, antifungal or antiparasitic compound. In this study, we found the helminth parasite Schistosoma mansoni to be insensitive to the drug. In order to elucidate the mechanism underlying RAPA resistance, the S. mansoni drug receptor FKBP12 (SmFKBP12) was cloned for functional analysis. Western blot experiments showed that the protein is constitutively expressed in all life cycle stages and in both male and female parasites. The Escherichia coli-synthesised recombinant protein possessed enzymatic activity, which was inhibitable by RAPA. Moreover, SmFKBP12 was able to complement mutant Saccharomyces cerevisiae cells lacking FKBP12 in their RAPA sensitivity phenotype, leading us to conclude that SmFKBP12 is expressed in yeast in a functional form and capable of interacting with the drug and yeast TOR kinase. Even though the wild type SmFKBP12 appeared to restore a large part of RAPA sensitivity, a mutation of Asp(89)-Lys(90) to Pro(89)-Gly(90) in the schistosome protein was found to be more effective and restored drug sensitivity to the same level as the endogenous yeast protein. Despite ternary complex formation, our results suggest that additional unknown factors other than a functional drug receptor are implicated in drug resistance mechanisms.

Amino Acid Sequence↗