Effects of metronidazole and tinidazole on NTPDase1 and ecto-5'-nucleotidase from intact cells of Trichomonas vaginalis

E-NTPDases: Possible Roles on Host-Parasite Interactions and Therapeutic Opportunities

Belonging to the GDA1/CD39 protein superfamily, nucleoside triphosphate diphosphohydrolases (NTPDases) catalyze the hydrolysis of ATP and ADP to the monophosphate form (AMP) and inorganic phosphate (Pi). Several NTPDase isoforms have been described in different cells, from pathogenic organisms to animals and plants. Biochemical characterization of nucleotidases/NTPDases has revealed the existence of isoforms with different specificities regarding divalent cations (such as calcium and magnesium) and substrates. In mammals, NTPDases have been implicated in the regulation of thrombosis and inflammation. In parasites, such as Trichomonas vaginalis, Trypanosoma spp., Leishmania spp., Schistosoma spp. and Toxoplasma gondii, NTPDases were found on the surface of the cell, and important processes like growth, infectivity, and virulence seem to depend on their activity. For instance, experimental evidence has indicated that parasite NTPDases can regulate the levels of ATP and Adenosine (Ado) of the host cell, leading to the modulation of the host immune response. In this work, we provide a comprehensive review showing the involvement of the nucleotidases/NTPDases in parasites infectivity and virulence, and how inhibition of NTPDases contributes to parasite clearance and the development of new antiparasitic drugs.

The Role of Purinergic Signaling in Trichomonas vaginalis Infection

Trichomoniasis, one of the most common non-viral sexually transmitted infections worldwide, is caused by the parasite Trichomonas vaginalis. The pathogen colonizes the human urogenital tract, and the infection is associated with complications such as adverse pregnancy outcomes, cervical cancer, and an increase in HIV transmission. The mechanisms of pathogenicity are multifactorial, and controlling immune responses is essential for infection maintenance. Extracellular purine nucleotides are released by cells in physiological and pathological conditions, and they are hydrolyzed by enzymes called ecto-nucleotidases. The cellular effects of nucleotides and nucleosides occur via binding to purinoceptors, or through the uptake by nucleoside transporters. Altogether, enzymes, receptors and transporters constitute the purinergic signaling, a cellular network that regulates several effects in practically all systems including mammals, helminths, protozoa, bacteria, and fungi. In this context, this review updates the data on purinergic signaling involved in T. vaginalis biology and interaction with host cells, focusing on the characterization of ecto-nucleotidases and on purine salvage pathways. The implications of the final products, the nucleosides adenosine and guanosine, for human neutrophil response and vaginal epithelial cell damage reveal the purinergic signaling as a potential new mechanism for alternative drug targets.

The Synergistic Effect of Mud Crab Antimicrobial Peptides Sphistin and Sph12-38 With Antibiotics Azithromycin and Rifampicin Enhances Bactericidal Activity Against Pseudomonas Aeruginosa

Overuse or abuse of antibiotics has undoubtedly accelerated the increasing prevalence of global antibiotic resistance crisis, and thus, people have been trying to explore approaches to decrease dosage of antibiotics or find new antibacterial agents for many years. Antimicrobial peptides (AMPs) are the ideal candidates that could kill pathogens and multidrug-resistant bacteria either alone or in combination with conventional antibiotics. In the study, the antimicrobial efficacy of mud crab Scylla paramamosain AMPs Sphistin and Sph₁₂₋₃₈ in combination with eight selected antibiotics was evaluated using a clinical pathogen, Pseudomonas aeruginosa. It was interesting to note that the in vitro combination of rifampicin and azithromycin with Sphistin and Sph₁₂₋₃₈ showed significant synergistic activity against P. aeruginosa. Moreover, an in vivo study was carried out using a mouse model challenged with P. aeruginosa, and the result showed that the combination of Sph₁₂₋₃₈ with either rifampicin or azithromycin could significantly promote the healing of wounds and had the healing time shortened to 4–5 days compared with 7–8 days in control. The underlying mechanism might be due to the binding of Sphistin and Sph₁₂₋₃₈ with P. aeruginosa lipopolysaccharides (LPS) and subsequent promotion of the intracellular uptake of rifampicin and azithromycin. Taken together, the significant synergistic antibacterial effect on P. aeruginosa in vitro and in vivo conferred by the combination of low dose of Sphistin and Sph₁₂₋₃₈ with low dose of rifampicin and azithromycin would be beneficial for the control of antibiotic resistance and effective treatment of P. aeruginosa-infected diseases in the future.

A systematic review of the literature on mechanisms of 5-nitroimidazole resistance in Trichomonas vaginalis

BACKGROUND

Trichomonas vaginalis is the most common non-viral sexually transmitted infection. 5-Nitroimidazoles [metronidazole (MTZ) and tinidazole (TDZ)] are FDA-approved treatments. To better understand treatment failure, we conducted a systematic review on mechanisms of 5-nitroimidazole resistance.

METHODS

PubMed, ScienceDirect and EMBASE databases were searched using keywords Trichomonas vaginalis, trichomoniasis, 5-nitroimidazole, metronidazole, tinidazole and drug resistance. Non-English language articles and articles on other treatments were excluded.

RESULTS

The search yielded 606 articles, of which 550 were excluded, leaving 58 articles. Trichomonas vaginalis resistance varies and is higher with MTZ (2.2-9.6%) than TDZ (0-2%). Resistance can be aerobic or anaerobic and is relative rather than absolute. Differential expression of enzymes involved in trichomonad energy production and antioxidant defenses affects 5-nitroimidazole drug activation; reduced expression of pyruvate:ferredoxin oxidoreductase, ferredoxin, nitroreductase, hydrogenase, thioredoxin reductase and flavin reductase are implicated in drug resistance. Trichomonas vaginalis infection with Mycoplasma hominis or T. vaginalis virus has also been associated with resistance. Trichomonas vaginalis has two genotypes, with greater resistance seen in type 2 (vs type 1) populations.

DISCUSSION

5-Nitroimidazole resistance results from differential expression of enzymes involved in energy production or antioxidant defenses, along with genetic mutations in the T. vaginalis genome. Alternative treatments outside of the 5-nitroimidazole class are needed.

Modified Field stain - rapid viability test for Trichomonas vaginalis

AIMS

We previously reported that Modified Field Stain (MF) can be used as a rapid stain for diagnosis. In the present study we extend the observation to include the stain as an alternative method to assess viability of the cells.

METHODS AND RESULTS

Six isolates of Trichomonas vaginalis were used to assess the utility of the Modified Field stain as a rapid viability test for T. vaginalis and to compare with 0·4% Trypan Blue dye exclusion test in three conditions; normal in vitro culture growth using Hollander medium, lysed in distilled water and treated with metronidazole. MF stain showed similar growth profile pattern as Trypan Blue dye exclusion for identifying viable cells of T. vaginalis. Although, Trypan Blue dye exclusion test is ready made, rapid and widely used in laboratory as reliable viability assay, however, the limitation using Trypan Blue is the dye was unable to show internal morphological changes during the parasite's transition from being viable to non-viable. On day 3 where cultures peaked the correlation factor of both assays done to assess the viability of parasites harvested from the controls, metronidazole and distilled water treated parasites were more than 0·9 respectively.

CONCLUSIONS

This confirms that MF staining does not only record permanently the morphological changes and retain internal structural details but also provides a reliable and rapid viability assay for the parasites.

SIGNIFICANCE AND IMPACT OF THE STUDY

Therefore, in our study, Modified Field's stain may offer the researchers and laboratory technologists the opportunity to get the result on the same day and the most important thing is the ability to differentiate between viable and non-viable of T. vaginalis under three different conditions (normal culture, drug and distilled water condition). Modified Field's staining method enhanced the morphological identification of T. vaginalis compared to Trypan Blue dye exclusion.

Tinidazole: a nitroimidazole antiprotozoal agent

BACKGROUND

Tinidazole, a structural analogue of metrondazole, is an antiprotozoal agent that has been widely used in Europe and developing countries for >2 decades with established efficacy and acceptable tolerability. It was recently approved by the US Food and Drug Administration for the treatment of trichomoniasis, giardiasis, amebiasis, and amebic liver abscess.

OBJECTIVE

This article reviews the pharmacologic and pharmacokinetic properties and clinical usefulness of tinidazole.

METHODS

Relevant information was identified through a search of MEDLINE (1966-August 2005), Iowa Drug Information Service (1966-August 2005), and International Pharmaceutical Abstracts (1970-August 2005) using the terms tinidazole, Fasigyn, and nitroimidazole.

RESULTS

In vitro, tinidazole exhibits activity against pathogenic protozoa (eg, Tricbomonas vaginalis, Entamoeba bistolytica, Giardia duodenalis), a wide range of clinically significant anaerobic bacteria (eg, Bacteroides fragilis, Clostridium difficile), and the microaerophilic bacterium Helicobacter pylori. In susceptible protozoal and bacterial cells, tinidazole is reduced to cytotoxic intermediates that covalently bind to DNA, causing irreversible damage. In human adults, tinidazole had a bioavailability of 100% and a V(d) of 50.7 L, was minimally bound to plasma protein (12%), had a plasma elimination t((1/2)) of 12.3 hours, and was eliminated primarily by hepatic metabolism (approximately 63%). Dose adjustment does not appear to be necessary on the basis of race, sex, or renal function. No data were found on the disposition of tinidazole in patients with hepatic insufficiency; therefore, use of tinidazole in patients with severe hepatic impairment (Child-Pugh class C) is not recommended. Clinical cure rates in patients with trichomoniasis, giardiasis, amebiasis, and amebic liver abscess were generally >90%. In comparative trials, tinidazole was as effective as metronidazole in the treatment of trichomoniasis and was significantly more effective than metronidazole in the treatment of giardiasis (P < 0.05) and amebiasis (P < 0.05). The most commonly reported (>1%) adverse effects included bitter taste, nausea, abdominal discomfort, anorexia, vomiting, and fatigue. The recommended dosage of tinidazole is a single dose of 2 g for trichomoniasis and giardiasis, and 2 g/d for 3 to 5 days for amebiasis.

CONCLUSIONS

Tinidazole appears to be a promising agent for the treatment of trichomoniasis, giardiasis, amebiasis, and amebic liver abscess. Clinical studies are needed to evaluate the use of tinidazole against anaerobic bacteria and H pylori.

Heterogeneity in extracellular nucleotide hydrolysis among clinical isolates of Trichomonas vaginalis

Trichomonas vaginalis is a parasitic protozoan that causes trichomonosis, a sexually-transmitted disease, with serious sequelae to women and men. As the host-parasite relationship is complex, it is important to investigate biochemical aspects of the parasite that contribute to our understanding of trichomonal biology and pathogenesis. Nucleoside triphosphate diphosphohydrolase 1 (NTPDase 1), which hydrolyses extracellular ATP and ADP, and ecto-5'-nucleotidase, which hyrolyses AMP, have been characterized in laboratory isolates of T. vaginalis. Here we show that the extracellular ATP: ADP hydrolysis ratio varies among fresh clinical isolates, which presented higher ATPase and ADPase activities than long-term-grown isolates. Growth of parasites in iron-replete and iron-depleted medium resulted in different, albeit minor, patterns in extracellular ATP and ADP hydrolysis among isolates. Importantly, some isolates had low or absent ecto-5'-nucleotidase activity, regardless of environmental conditions tested. For isolates with ecto-5'-nucleotidase activity, high- and low-iron trichomonads had increased and decreased levels of activity, respectively, compared to organisms grown in normal TYM-serum medium. This suggests a regulation in expression of either the enzyme amounts and/or activity under the control of iron. Finally, we found no correlation between the presence or absence of dsRNA virus infection among trichomonad isolates and NTPDase and ecto-5'-nucleotidase activities.

Trichomonas vaginalis: cytochemical localization of a NTPDase1 and an ecto-5'-nucleotidase and effects of adenine nucleotides on cellular viability

Nucleoside triphosphate diphosphohydrolase 1 (NTPDase1), which hydrolyzes extracellular ATP and ADP, and ecto-5'-nucleotidase, which hydrolyzes AMP, are characterized for Trichomonas vaginalis. Ultrastructural cytochemical microscopy showed NTPDase1 and ecto-5'-nucleotidase activities on the surface of the parasites. High levels of extracellular adenine nucleotides and adenosine did not exert cytolytic effects in intact cells of T. vaginalis. Our results suggest that these enzymes are relevant for the survival of the parasite during exposure to extracellular nucleotides. Since the ecto-localization of these enzymes is essential for the maintenance of adenosine extracellular levels, this nucleoside could be important for the purine salvage pathway in the parasite.