Mutation at the HPRT locus in patients with neurocysticercosis treated with praziquantel

Effectiveness of hyperbaric oxygen for experimental treatment of schistosomiasis mansoni using praziquantel-free and encapsulated into liposomes: assay in adult worms and oviposition

The treatment of schistosomiasis depends on a single drug: praziquantel (PZQ). However, this treatment presents limitations such as low and/or erratic bioavailability that can contribute to cases of tolerance. Improvements to the available drug are urgently needed and studies with a controlled system of drug release, like liposomes, have been gaining prominence. The present study evaluated the activity and synergy between liposomal-praziquantel (lip.PZQ) and hyperbaric oxygen therapy (HBO). Mice received doses of 60 or 100mg/kg PZQ or lip.PZQ, 50 days post-infection, and after the treatment, were exposed to HBO (3 atmosphere absolute - ATA) for 1h. The viability of adult worms and oviposition were analyzed, by necropsy and Kato-Katz examination performed after 15 days of treatment. A concentration of 100mg/kg of lip.PZQ+HBO was more effective (48.0% reduction of worms, 83.3% reduction of eggs/gram of feces) and 100% of the mice had altered of oograms (indicating interruption of oviposition) compared to other treatments and to the Control group (infected and untreated). It is known that PZQ requires participation of the host immune system to complete its antischistosomal activity and that HBO is able to stimulate the immune system. The drug became more available in the body when incorporated into liposomes and, used with HBO, the HBO worked as an adjuvant. This explains the decreases of oviposition and worms recovered form hepatic portal system.

Oral cysticercosis: a collaborative study of 16 cases

Cysticercosis is a potentially fatal parasitic disease that rarely involves the oral region in humans. This study includes 21 lesions seen in 16 Latin American patients. There were 8 men and 8 women, with an age range from 6 to 67 years (mean 33.6 years). Most cases appeared as asymptomatic submucosal nodules that resembled mucous cysts or benign mesenchymal neoplasms. Most were found in the tongue (11 cases), followed by buccal mucosa and the lower lip (4 cases each) and upper lip (2 cases). These were well circumscribed, and ranged in size from 1 to 2.5 cm in diameter. Typical histologic features of viable cysticerci were observed in 15 cases, and the presence of colloid degeneration and granular mineralization were detected in only 1 case. In all cases, simple surgical excision was sufficient to ensure complete removal of the lesions without postoperative complications. It is important to carry out a detailed study in every case, in order to exclude the presence of the parasite in other sites.

Induction of DNA damage in human lymphocytes treated with a soluble factor secreted by Taenia solium metacestodes

We have previously reported that a factor secreted by the metacestode of Taenia solium (MF) is able to transform Syrian hamster embryo cells. The aim of this study was to analyze the genotoxicity of MF in cultured human lymphocytes using the micronucleus assay. Results show a significantly high frequency of micronucleated cells in lymphocyte cultures treated with MF. Although further experiments are needed to determine whether this factor is also secreted by T. solium metacestodes in humans, analysis of the frequency of micronucleus induced in cultured human lymphocytes indicates that DNA instability induced by MF could represent a risk for malignant transformation.

Micronuclei and chromatid buds are the result of related genotoxic events

Chromatin buds (CHB), broken eggs, or budding cell nuclei are structures similar to micronuclei (MN) in shape, structure, and size, which are linked to the main nuclei of cells by a thread or stalks of chromatin. They have been observed in numerous cell types and there are reports of their existence relating them with MN or with genotoxic events. However, there is no systematic study reporting their frequency and no experiment has been done to ascertain whether they are really induced by genotoxins. Furthermore, they have been discarded as genotoxic events with the argument that they are not formed in dividing cells. Studies are presented here that indicate that CHB can be considered as genotoxic events and that their origin is comparable to that of MN. Bromodeoxyuridine (BrdU) was used to label proliferating lymphocytes, which were later identified by means of an immunohistochemical method, using the H2O2-DAB stain. The results show that CHB are consistently formed where MN are seen. CHB were induced by the clastogen mitomycin C (MMC) as well as by the aneuploidogen colcemid, with frequencies similar to MN in both cases, and to multinucleated cells in the case of colcemid. CHB occur in lymphocytes of smokers with frequencies similar to those of MN, and we found that the infection with Taenia solium metacestodes induced a comparable increase of both MN and CHB frequency in lymphocytes from pigs.

Neurocysticercosis and oncogenesis

Recent studies suggest that neurocysticercosis may be a risk factor for human cancer. Pathogenetic mechanisms explaining possible oncogenic effects of cysticerci include the following: (a) parasite-induced modulation of the host immune response that may be associated with loss of regulatory mechanisms implicated in the immunological surveillance against cancer; (b) transfer of genetic material from the parasite to the host, causing DNA damage and malignant transformation of host cells, and (c) chronic inflammation with liberation of nitric oxide and inhibition of tumor suppressor genes. Further research is needed to confirm the potential role of cysticercosis in the development of cancer. These studies should determine the presence of cysticercotic factors responsible for the transfer of genetic material and potential mutations in the tumor suppressor genes in proliferating astrocytes surrounding cysticercotic lesions. Additionally, the complex interaction between the immune state of the host with variable cytokine release and the presence of inflammatory cells releasing nitric oxide that cause DNA damage and impair tumor suppressive mechanisms needs to be investigated.

Possible relationship between neurocysticercosis and hematological malignancies

BACKGROUND

Previous studies have shown an increased frequency of chromosomal abnormalities in lymphocytes from animals and humans with cysticercosis. Some reports have suggested an association between cancer and cysticercosis. The aim of this study was to investigate the possible association between neurocysticercosis and cancer.

METHODS

We designed a mortality rate study from the autopsy files of the Department of Pathology at the General Hospital of Mexico. A total of 1,271 autopsy files were reviewed. All files in which a malignant neoplasia was found during autopsy were selected as cases. Autopsies in which no malignant disease was found were used as controls. The odds ratio was determined between the frequency of neurocysticercosis in patients with any malignant neoplasia and that of the controls.

RESULTS

Neurocysticercosis was more frequent in cases with malignant hematological diseases (MHD) than in controls (p = 0.01). The odds ratio for this association was 3.54, with 95% confidence interval from 1.17-9.79.

CONCLUSIONS

Most human cancers arise from the interaction of a multiplicity of factors, including xenobiotics and endogenous constituents. Therefore, while it will be difficult to demonstrate that neurocysticercosis is a causal agent of malignant hematological diseases (MHD), it should be considered as a potential risk factor for cancer induction in countries where cysticercosis remains a public health problem.

Genotoxic activity of praziquantel

Praziquantel is a synthetic drug with a remarkable activity against parasites, particularly treamatodes and cestodes. Initial genotoxicity tests used a spectrum of endpoints including tests in bacteria, yeasts, mammalian cells and Drosophila and each one gave negative results. Effects on reproductive cells of mice were negative as well. However, host mediated studies in mice and humans were contradictory and a comutagenic effect with several mutagens and carcinogens was found. Later studies, including monitoring in humans and pigs have shown that Praziquantel induces a greater frequency of hyperploid lymphocytes as well as structural chromosomal aberrations, but not in all the individuals treated. In vitro studies have demonstrated that Praziquantel can induce micronuclei in syrian hamster embryonic (SHE) cells and in lymphocytes of some individuals. The same was found about structural chromosomal aberrations. Fetal death and fetal resorption were found when Praziquantel was administered in high doses to pregnant rats between the 6th and 10th day of gestation. Due to its efficiency as a parasiticide, Praziquantel is in use in Latin-American, Asiatic, African and East-European countries where infections by trematodes and cestodes are frequent. However, the extensive use of Praziquantel in multiple reinfections, in non-infected and non-diagnosed individuals for prevention, in higher doses or repeated doses for cysticercosis treatment and in individuals exposed to environmental mutagens, in conjunction with new findings about its metabolism and genotoxic properties, make it necessary to further evaluate the potential of this drug not only to be mutagenic per se, but to contribute in the development of neoplasm.

Antischistosomal drugs: past, present ... and future?

The major antischistosomal drugs that have been or still are in use against infections with schistosomes are considered here together with some compounds that have not been in clinical use, but show interesting characteristics. Each individual compound presents aspects that may be enlightening about parasite biochemistry, parasite biology, and host-parasite relationships. Special attention is given to the mechanisms of action, an understanding of which is seen here as a major factor of progress in chemotherapy. Three compounds are currently in use, i.e., metrifonate, oxamniquine, and praziquantel, and all three are included in the World Health Organization list of essential drugs. They are analyzed in some detail, as each one presents advantages and disadvantages in antischistosomal therapy. The reported occurrence of drug-resistant schistosomes after treatment with oxamniquine and praziquantel suggests strict monitoring of such phenomena and encourages renewed efforts toward the development of multiple drugs against this human parasite.