A review on metronidazole: an old warhorse in antimicrobial chemotherapy

In Vitro and In Vivo Drug Release from a Nano-Hydroxyapatite Reinforced Resorbable Nanofibrous Scaffold for Treating Female Pelvic Organ Prolapse

Pelvic prolapse stands as a substantial medical concern, notably impacting a significant segment of the population, predominantly women. This condition, characterized by the descent of pelvic organs, such as the uterus, bladder, or rectum, from their normal positions, can lead to a range of distressing symptoms, including pelvic pressure, urinary incontinence, and discomfort during intercourse. Clinical challenges abound in the treatment landscape of pelvic prolapse, stemming from its multifactorial etiology and the diverse array of symptoms experienced by affected individuals. Current treatment options, while offering relief to some extent, often fall short in addressing the full spectrum of symptoms and may pose risks of complications or recurrence. Consequently, there exists a palpable need for innovative solutions that can provide more effective, durable, and patient-tailored interventions for pelvic prolapse. We manufactured an integrated polycaprolactone (PCL) mesh, reinforced with nano-hydroxyapatite (nHA), along with drug-eluting poly(lactic-co-glycolic acid) (PLGA) nanofibers for a prolapse scaffold. This aims to offer a promising avenue for enhanced treatment outcomes and improved quality of life for individuals grappling with pelvic prolapse. Solution extrusion additive manufacturing and electrospinning methods were utilized to prepare the nHA filled PCL mesh and drug-incorporated PLGA nanofibers, respectively. The pharmaceuticals employed included metronidazole, ketorolac, bleomycin, and estrone. Properties of fabricated resorbable scaffolds were assessed. The in vitro release characteristics of various pharmaceuticals from the meshes/nanofibers were evaluated. Furthermore, the in vivo drug elution pattern was also estimated on a rat model. The empirical data show that nHA reinforced PCL mesh exhibited superior mechanical strength to virgin PCL mesh. Electrospun resorbable nanofibers possessed diameters ranging from 85 to 540 nm, and released effective metronidazole, ketorolac, bleomycin, and estradiol, respectively, for 9, 30, 3, and over 30 days in vitro. Further, the mesh/nanofiber scaffolds also liberated high drug levels at the target site for more than 28 days in vivo, while the drug concentrations in blood remained low. This discovery suggests that resorbable scaffold can serve as a viable option for treating female pelvic organ prolapse.

Small molecule MarR modulators potentiate metronidazole antibiotic activity in aerobic E. coli by inducing activation by the nitroreductase NfsA

Antibiotic-resistant Enterobacterales pose a major threat to healthcare systems worldwide, necessitating the development of novel strategies to fight such hard-to-kill bacteria. One potential approach is to develop molecules that force bacteria to hyper-activate prodrug antibiotics, thus rendering them more effective. In the present work, we aimed to obtain proof-of-concept data to support that small molecules targeting transcriptional regulators can potentiate the antibiotic activity of the prodrug metronidazole (MTZ) against Escherichia coli under aerobic conditions. By screening a chemical library of small molecules, a series of structurally related molecules were identified that had little inherent antibiotic activity but showed substantial activity in combination with ineffective concentrations of MTZ. Transcriptome analyses, functional genetics, thermal shift assays, and electrophoretic mobility shift assays were then used to demonstrate that these MTZ boosters target the transcriptional repressor MarR, resulting in the upregulation of the marRAB operon and its downstream MarA regulon. The associated upregulation of the flavin-containing nitroreductase, NfsA, was then shown to be critical for the booster-mediated potentiation of MTZ antibiotic activity. Transcriptomic studies, biochemical assays, and electron paramagnetic resonance measurements were then used to show that under aerobic conditions, NfsA catalyzed 1-electron reduction of MTZ to the MTZ radical anion which in turn induced lethal DNA damage in E. coli. This work reports the first example of prodrug boosting in Enterobacterales by transcriptional modulators and highlights that MTZ antibiotic activity can be chemically induced under anaerobic growth conditions.

Exploring novel pyrazole-nitroimidazole hybrids: Synthesis and antiprotozoal activity against the human pathogen trichomonas vaginalis

Trichomoniasis, a prevalent sexually transmitted infection (STI) caused by the protozoan Trichomonas vaginalis, has gained increased significance globally. Its relevance has grown in recent years due to its association with a heightened risk of acquiring and transmitting the human immunodeficiency virus (HIV) and other STIs. In addition, many publications have revealed a potential link between trichomoniasis and certain cancers. Metronidazole (MTZ), a nitroimidazole compound developed over 50 years ago, remains the first-choice drug for treatment. However, reports of genotoxicity and side effects underscore the necessity for new compounds to address this pressing global health concern. In this study, we synthesized ten pyrazole-nitroimidazoles 1(a-j) and 4-nitro-1-(hydroxyethyl)-1H-imidazole 2, an analog of metronidazole (MTZ), and assessed their trichomonacidal and cytotoxic effects. All compounds 1(a-j) and 2 exhibited IC50 values ≤ 20 μM and ≤ 41 μM, after 24 h and 48 h, respectively. Compounds 1d (IC50 5.3 μM), 1e (IC50 4.8 μM), and 1i (IC50 5.2 μM) exhibited potencies equivalent to MTZ (IC50 4.9 μM), the reference drug, after 24 h. Notably, compound 1i showed high anti-trichomonas activity after 24 h (IC50 5.2 μM) and 48 h (IC50 2.1 μM). Additionally, all compounds demonstrated either non-cytotoxic to HeLa cells (CC50 > 100 μM) or low cytotoxicity (CC50 between 69 and 100 μM). These findings suggest that pyrazole-nitroimidazole derivatives represent a promising heterocyclic system, serving as a potential lead for further optimization in trichomoniasis chemotherapy.

A Comparison of Bottom-Up Proteomic Sample Preparation Methods for the Human Parasite Trichomonas vaginalis

Bottom-up proteomic approaches depend on the efficient digestion of proteins into peptides for mass spectrometric analysis. Sample preparation strategies, based on magnetic beads, filter-aided systems, or in-solution digests, are commonly used for proteomic analysis. Time-intensive methods like filter-aided sample preparation (FASP) have led to the development of new, more time-efficient filter-based strategies like suspension trappings (S-Traps) or magnetic bead-based strategies like SP3. S-Traps have been reported as an alternative proteomic sample preparation method as they allow for high sodium dodecyl sulfate (SDS) concentrations to be present in the sample. In this study, we compare the efficiency of different protocols for FASP, SP3, and S-Trap-based digestion of proteins after extraction from Trichomonas vaginalis. Overall, we found a high number of protein IDs for all tested methods and a high degree of reproducibility within each method type. However, FASP with a 3 kDa cutoff filter unit outperformed the other methods analyzed, referring to the number of protein IDs. This is the first work providing the direct comparison of four different bottom-up proteomic approaches regarding the most efficient proteomic sample preparation protocol for the human parasite T. vaginalis.

Complement receptor 3 is required for maximum in vitro trogocytic killing of the parasite Trichomonas vaginalis by human neutrophil-like cells

Trichomonas vaginalis (Tv) is a parasite that causes trichomoniasis, a prevalent sexually-transmitted infection. Neutrophils are found at the site of infection, and can rapidly kill the parasite in vitro, using trogocytosis. However, the specific molecular players in neutrophil killing of Tv are unknown. Here, we show that complement proteins play a role in Tv killing by human neutrophil-like cells (NLCs). Using CRISPR/Cas9, we generated NLCs deficient in each of three complement receptors (CRs) known to be expressed on human neutrophils: CR1, CR3, and CR4. Using in vitro trogocytosis assays, we found that CR3, but not CR1 or CR4 is required for maximum trogocytosis of the parasite by NLCs, with NLCs lacking CR3 demonstrating ~40% reduction in trogocytosis, on average. We also observed a reduction in NLC killing of Tv in CR3 knockout, but not CR1 or CR4 knockout NLCs. On average, NLCs lacking CR3 had ~50% reduction in killing activity. We also used a parallel approach of pre-incubating NLCs with blocking antibodies against CR3, which similarly reduced NLC killing of parasites. These data support a model in which Tv is opsonized by the complement protein iC3b, and bound by neutrophil CR3 receptor, to facilitate trogocytic killing of the parasite.

Characterization of Lophomonas spp. Infection in a Population of Critical Care Patients

Lophomonas are flagellated protozoa that have been increasingly associated with upper and lower airway infection in humans. The prevalence and characterization of this disease in the critically ill remains poorly understood. We present a series of eleven ICU patients with confirmed Lophomonas spp. identification in respiratory samples.

Metronidazole Induced Cutaneous Adverse Drug Reaction- A Systematic Review of Descriptive Studies

BACKGROUND

A substantial number of research studies on metronidazole-related cutaneous symptoms have recently been published. Our objective was to identify and evaluate descriptive studies that described metronidazole-related skin manifestations, therapeutic interventions, and consequences.

METHODS

A comprehensive literature search was carried out in the PubMed, Scopus, and grey literature databases from inception to April 2022 without any constraints, as well as a snowball search in Google and a search in Google Scholar. Descriptive articles describing metronidazole-related cutaneous manifestations were considered for the review. Two distinct reviewers carried out the research selection, data extraction, and quality assessment; any discrepancies were resolved by consensus with the third reviewer.

RESULTS

About 24 out of 4648 descriptive studies, including 26 patients (20 Female patients and 6 male patients), were included in this review. The included studies comprised a range of ages from 16 to 78 years old. Metronidazole was indicated for the treatment of bacterial vaginosis, trichomoniasis, sepsis, anti-infection therapy, perforated appendicitis, rosacea, vaginal discharge, dysentery, acne rosacea, trichomonal vaginitis, lichen planus, liver abscess, facial rosacea, intestinal amoebiasis, and gingivitis. Fixed drug eruption was the most common skin manifestation which was reported in 7 cases included in this review. Cutaneous manifestations were ameliorated by cessation of the offending drug and by apportioning antihistamines, topical steroids, parenteral corticosteroids, emollients, and topical moisturizers.

CONCLUSION

Clinicians and healthcare professionals should be cognizant of the potential cutaneous adverse drug reactions (CADRs) induced by metronidazole to mitigate fatal circumstances. The management of the CADRs appears to respond effectively with immediate drug discontinuation and supportive therapy.

[Feline and canine giardiosis: An Update]

Giardia duodenalis is a facultative pathogenic intestinal parasite. Giardiosis in dogs and cats may appear with or without clinical signs. Typical signs include diarrhea with or without vomiting. The prevalence in young animals is high and may amount to up to 50%. There are 8 different genotypes (A - H), which are called assemblages. Assemblages C and D are most common in dogs and assemblage F most frequent in cats. However, animals may also be infected with the zoonotically effective assemblages A and B or exhibit mixed infections. The immunofluorescence test (IFA), the enzyme-linked immunosorbent assay (ELISA) and fecal centrifugation using zinc sulphate solution are currently recommended as diagnostic methods. Polymerase chain reaction (PCR) may be used to determine the corresponding assemblage. Approved treatments for giardiosis include fenbendazole and metronidazole. In addition, undertaking specific hygiene measures is warranted. Only animals showing clinical signs or those living in the same household with high-risk patients (e. g. immunosuppressed humans) are recommended to receive medication. The aim of treatment is clinical improvement of the diseased dogs and cats. Frequently, complete elimination of Giardia is not attained.

Metronidazole prescribing practices in Australian hospitals: Measuring guideline compliance and appropriateness to support antimicrobial stewardship

BACKGROUND

Metronidazole is a commonly prescribed antimicrobial in Australian hospitals. Inappropriate use may increase risks to patient care, such as toxicities and antimicrobial resistance. To date, there is limited information on the quality of metronidazole prescriptions to inform antimicrobial stewardship and quality improvement initiatives. This study aims to describe the quality of metronidazole prescribing practices in Australian hospitals.

METHODS

Retrospective data analysis of the Hospital National Antimicrobial Prescribing Survey (Hospital NAPS). Data were collected by auditors at each participating hospital using a standardised auditing tool. All data from 2013 to 2021 were de-identified and analysed descriptively. Variables included were antimicrobial prescribed, indication, guideline compliance and appropriateness.

RESULTS

Metronidazole was the fifth most prescribed antimicrobial in the Hospital NAPS dataset (2013-2021), accounting for 5.7 % (n = 14,197) of all antimicrobial prescriptions (n = 250,863). The proportion of metronidazole prescriptions declined by 2 % from 2013 to 2021 (p < 0.001). The most common indications were surgical prophylaxis (15.3 %), diverticulitis (9.4 %), aspiration pneumonia (7.3 %). Over half (53.5 %) of metronidazole prescriptions were deemed compliant with prescribing guidelines and 67.8 % were deemed appropriate. These rates were comparatively lower than the overall results of all antimicrobials. The primary documented reason for inappropriateness was that the spectrum was too broad (34.2 %). Surgical prophylaxis had the lowest rates of guideline compliance (53.8 %) and appropriateness (54.3 %).

CONCLUSIONS

Metronidazole remains widely used in Australian hospitals with suboptimal rates of guideline compliance and appropriateness. A noted area for improvement that we identified was using metronidazole when its spectrum was too broad, possibly when anaerobic therapy is unnecessary. With increasing international adoption of the Hospital NAPS programme, future comparative studies will be critical to identify global trends of antimicrobial prescribing quality. Antimicrobial stewardship (AMS) programmes have proven to be effective in improving prescribing quality and should be considered to specifically target improvements in metronidazole prescribing.

Antimicrobial potential of quaternary phosphonium salt compounds: a review

Given that mitochondrial dysregulation is a biomarker of many cancers, cationic quaternary phosphonium salt (QPS) conjugation is a widely utilized strategy for anticancer drug design. QPS-conjugated compounds exhibit greater cell permeation and accumulation in negatively charged mitochondria, and thus, show enhanced activity. Phylogenetic similarities between mitochondria and bacteria have provided a rationale for exploring the antibacterial properties of mitochondria-targeted compounds. Additionally, due to the importance of mitochondria in the survival of pathogenic microbes, including fungi and parasites, this strategy can be extended to these organisms as well. This review examines recent literature on the antimicrobial activities of various QPS-conjugated compounds and provides future directions for exploring the medicinal chemistry of these compounds.

Greener and Whiter Analytical Chemistry Using Cyrene as a More Sustainable and Eco-Friendlier Mobile Phase Constituent in Chromatography

Cyrene (dihydrolevoglucosenone) was evaluated for the first time as a potential sustainable mobile phase solvent in reversed-phase chromatography. As a benign biodegradable solvent, Cyrene is an attractive replacement to classical non-green organic chromatographic solvents such as acetonitrile and a modifier, co-eluent to known green solvents such as ethanol. Compared to ethanol, Cyrene is less toxic, non-flammable, biobased, biodegradable, and a cheaper solvent. A fire safety spider chart was generated to compare the properties of Cyrene to ethanol and show its superiority as a greener solvent. Cyrene's behavior, advantages, and drawbacks in reversed-phase chromatography, including the cut-off value of 350 nm, elution power, selectivity, and effect on the column, were investigated using a model drug mixture of moxifloxacin and metronidazole. A monolithic C18 (100 × 4.6 mm) column was used as a stationary phase. Different ratios of Cyrene: ethanol with an aqueous portion of sodium acetate buffer mobile phases were tested. A mobile phase consisting of Cyrene: ethanol: 0.1 M sodium acetate buffer pH 4.25 (8:13:79, v/v/v) was selected as the most suitable mobile phase system for separating and simultaneously determining metronidazole and moxifloxacin. The greenness and whiteness of the method were evaluated using the qualitative green assessment tool AGREE and the white analytical chemistry assessment tool RGB12. Further potentials of Cyrene as a solvent or modifier in normal phase chromatography, liquid chromatography-mass spectrometry, and supercritical fluid chromatography are discussed.

Digestive exophagy of biofilms by intestinal amoeba and its impact on stress tolerance and cytotoxicity

The human protozoan parasite Entamoeba histolytica is responsible for amebiasis, a disease endemic to developing countries. E. histolytica trophozoites colonize the large intestine, primarily feeding on bacteria. However, in the gastrointestinal tract, bacterial cells form aggregates or structured communities called biofilms too large for phagocytosis. Remarkably, trophozoites are still able to invade and degrade established biofilms, utilizing a mechanism that mimics digestive exophagy. Digestive exophagy refers to the secretion of digestive enzymes that promote the digestion of objects too large for direct phagocytosis by phagocytes. E. histolytica cysteine proteinases (CPs) play a crucial role in the degradation process of Bacillus subtilis biofilm. These proteinases target TasA, a major component of the B. subtilis biofilm matrix, also contributing to the adhesion of the parasite to the biofilm. In addition, they are also involved in the degradation of biofilms formed by Gram-negative and Gram-positive enteric pathogens. Furthermore, biofilms also play an important role in protecting trophozoites against oxidative stress. This specific mechanism suggests that the amoeba has adapted to prey on biofilms, potentially serving as an untapped reservoir for novel therapeutic approaches to treat biofilms. Consistently, products derived from the amoeba have been shown to restore antibiotic sensitivity to biofilm cells. In addition, our findings reveal that probiotic biofilms can act as a protective shield for mammalian cells, hindering the progression of the parasite towards them.

Development and Optimization of a Novel Lozenge Containing a Metronidazole-Peppermint Oil-Tranexamic Acid Self-Nanoemulsified Delivery System to Be Used after Dental Extraction: In Vitro Evaluation and In Vivo Appraisal

In-depth studies on essential oil-based nanoemulsions (NEs) have centered on a variety of oral health issues. NEs improve the delivery of nonpolar active agents to sites and thereby boost the dissolution and distribution of the agents. Metronidazole-peppermint oil-tranexamic acid self-nanoemulsifying drug delivery systems (MZ-PO-TX-SNEDDS) were created and loaded into novel lozenges to act as antifungal, hemostatic, antimicrobial, and analgesic dosage forms after dental extractions. The design-of-experiments approach was used in creating them. To generate the NEs, different concentrations of MZ-PO (240, 180, and 120 mg), 2% TX (600, 450, and 300 mg), and Smix1:1 (600, 400, and 200 mg) were used. The ideal formulation had serum levels of 1530 U/mL of interleukin-6, a minimal inhibitory concentration against bacteria of 1.5 µg/mL, a droplet size of 96 nm, and a blood coagulation time of 16.5 min. Moreover, the produced NE offered better MZ release. The adopted design was used to produce the ideal formulation; it contained 240 mg of MZ-PO, 600 mg of 2% TX, and 600 mg of Smix1:1. It was incorporated into lozenges with acceptable characteristics and an improved capability for drug release. These lozenges had reasonable coagulation times, IL-6 serum levels, and MIC values. All of these characteristics are desirable for managing symptoms following tooth extractions. Therefore, these lozenges loaded with MZ-PO-TX-SNEDDs might be considered a beneficial paradigm for relieving complications encountered after tooth extractions.

The use of metronidazole in acute diarrhea in dogs: a narrative review

Acute diarrhea is a common reason for non-wellness veterinary visits in dogs. Treatment for acute diarrhea usually consists of supportive care with nutritional intervention, fluid therapy, anthelmintics, and often an antibiotic - commonly metronidazole in North America. The empirical use of metronidazole for acute diarrhea in dogs has been a common practice in veterinary medicine for many decades; however, recent studies evaluating its use suggest it may be inappropriately utilized in many cases. Herein, we review the evidence evaluating the use of metronidazole and other antibiotics in acute diarrhea in the human and veterinary literature. Recommendations on the use of metronidazole and other antibiotics as well as other therapeutic considerations in the treatment of acute diarrhea are also provided.

Mycoplasma hominis and Candidatus Mycoplasma girerdii in Trichomonas vaginalis: Peaceful Cohabitants or Contentious Roommates?

Trichomonas vaginalis is a pathogenic protozoan diffused worldwide capable of infecting the urogenital tract in humans, causing trichomoniasis. One of its most intriguing aspects is the ability to establish a close relationship with endosymbiotic microorganisms: the unique association of T. vaginalis with the bacterium Mycoplasma hominis represents, to date, the only example of an endosymbiosis involving two true human pathogens. Since its discovery, several aspects of the symbiosis between T. vaginalis and M. hominis have been characterized, demonstrating that the presence of the intracellular guest strongly influences the pathogenic characteristics of the protozoon, making it more aggressive towards host cells and capable of stimulating a stronger proinflammatory response. The recent description of a further symbiont of the protozoon, the newly discovered non-cultivable mycoplasma Candidatus Mycoplasma girerdii, makes the picture even more complex. This review provides an overview of the main aspects of this complex microbial consortium, with particular emphasis on its effect on protozoan pathobiology and on the interplays among the symbionts.

Genome-Wide Libraries for Protozoan Pathogen Drug Target Screening Using Yeast Surface Display

The lack of genetic tools to manipulate protozoan pathogens has limited the use of genome-wide approaches to identify drug or vaccine targets and understand these organisms' biology. We have developed an efficient method to construct genome-wide libraries for yeast surface display (YSD) and developed a YSD fitness screen (YSD-FS) to identify drug targets. We show the efficacy of our method by generating genome-wide libraries for Trypanosoma brucei, Trypanosoma cruzi, and Giardia lamblia parasites. Each library has a diversity of ∼105 to 106 clones, representing ∼6- to 30-fold of the parasite's genome. Nanopore sequencing confirmed the libraries' genome coverage with multiple clones for each parasite gene. Western blot and imaging analysis confirmed surface expression of the G. lamblia library proteins in yeast. Using the YSD-FS assay, we identified bonafide interactors of metronidazole, a drug used to treat protozoan and bacterial infections. We also found enrichment in nucleotide-binding domain sequences associated with yeast increased fitness to metronidazole, indicating that this drug might target multiple enzymes containing nucleotide-binding domains. The libraries are valuable biological resources for discovering drug or vaccine targets, ligand receptors, protein-protein interactions, and pathogen-host interactions. The library assembly approach can be applied to other organisms or expression systems, and the YSD-FS assay might help identify new drug targets in protozoan pathogens.

Study on the photocatalytic degradation of metronidazole antibiotic in aqueous media with TiO2 under lab and pilot scale

Nowadays, the increased consumption of antibiotics, such as metronidazole (MTZ), leads to their introduction in wastewater as well as in the receiving surface waters due to their incomplete removal by conventional wastewater treatment plants. Heterogeneous photocatalysis is a versatile technology that can efficiently degrade such organic contaminants. In the present research, the photocatalytic degradation of MTZ with TiO₂ P25 was studied under lab and pilot (CPC reactor) conditions. The antibiotic was efficiently removed at high rates in both cases (100 % and 91 %) following pseudo-first order kinetics with rate constants equal to 0.0452 min^-1 (±RSD% = 0.68 % - 2.57 %) and 0.0462 L KJ^-1 (±RSD% = 8.94 % - 21.64 %) respectively. Also, by scavenging lab scale experiments, the contribution of the generated reactive species was investigated and hydroxy radicals (HO^•) were proposed as the predominant species. By applying high resolution mass spectrometry techniques, the transformation products (TPs) were identified and possible transformation pathways were proposed. The ecotoxicity of the TPs was assessed in silico using the ECOSAR software with the results revealing that most of them were less toxic than the parent compound. Similarly, the mutagenicity, developmental toxicity and bioconcentration factors of the TPs were predicted by utilizing the T.E.S.T. software and in their majority, were found to be less mutagenic and developmentally toxic than MTZ. The ecotoxicity monitoring with the Vibrio fischeri bioassay in both laboratory and pilot scale experiments indicated that through heterogeneous photocatalysis it is possible to reduce the toxicity of wastewater containing MTZ. Finally, the stability and reusability of the photocatalyst was investigated through three consecutive catalytic cycles with the results showing that the performance of TiO₂ decreased after each use. For the heterogeneous photocatalysis with TiO₂ to be a "real life" applicable technique, further studies focusing on catalyst regeneration and optimization of the catalytic conditions must be conducted.

Anaerobic energy metabolism in human microaerophile parasites

Mucosal-associated parasites, such as Giardia intestinalis, Entamoeba histolytica, and Trichomonas vaginalis, have significant clinical relevance. The pathologies associated with infection by these parasites are among those with the highest incidence of gastroenteritis (giardiasis and amoebiasis) and sexually transmitted infections (trichomoniasis). The treatment of these diseases is based on drugs that act on the anaerobic metabolism of these parasites, such as nitroimidazole and benzimidazole derivatives. One interesting feature of parasites is their ability to produce ATP under anaerobic conditions. Due to the absence of enzymes capable of producing ATP under anaerobic conditions in the vertebrate host, they have become interesting therapeutic targets. This review discusses anaerobic energy metabolism in mucosal-associated parasites, focusing on the anaerobic metabolism of pyruvate, the importance of these enzymes as therapeutic targets, and the importance of treating their infections.

Proteomic analysis of metronidazole resistance in the human facultative pathogen Bacteroides fragilis

The anaerobic gut bacteria and opportunistic pathogen Bacteroides fragilis can cause life-threatening infections when leaving its niche and reaching body sites outside of the gut. The antimicrobial metronidazole is a mainstay in the treatment of anaerobic infections and also highly effective against Bacteroides spp. Although resistance rates have remained low in general, metronidazole resistance does occur in B. fragilis and can favor fatal disease outcomes. Most metronidazole-resistant Bacteroides isolates harbor nim genes, commonly believed to encode for nitroreductases which deactivate metronidazole. Recent research, however, suggests that the mode of resistance mediated by Nim proteins might be more complex than anticipated because they affect the cellular metabolism, e.g., by increasing the activity of pyruvate:ferredoxin oxidoreductase (PFOR). Moreover, although nim genes confer only low-level metronidazole resistance to Bacteroides, high-level resistance can be much easier induced in the laboratory in the presence of a nim gene than without. Due to these observations, we hypothesized that nim genes might induce changes in the B. fragilis proteome and performed comparative mass-spectrometric analyses with B. fragilis 638R, either with or without the nimA gene. Further, we compared protein expression profiles in both strains after induction of high-level metronidazole resistance. Interestingly, only few proteins were repeatedly found to be differentially expressed in strain 638R with the nimA gene, one of them being the flavodiiron protein FprA, an enzyme involved in oxygen scavenging. After induction of metronidazole resistance, a far higher number of proteins were found to be differentially expressed in 638R without nimA than in 638R with nimA. In the former, factors for the import of hemin were strongly downregulated, indicating impaired iron import, whereas in the latter, the observed changes were not only less numerous but also less specific. Both resistant strains, however, displayed a reduced capability of scavenging oxygen. Susceptibility to metronidazole could be widely restored in resistant 638R without nimA by supplementing growth media with ferrous iron sulfate, but not so in resistant 638R with the nimA gene. Finally, based on the results of this study, we present a novel hypothetic model of metronidazole resistance and NimA function.

Nitroimidazoles Part 10. Synthesis, crystal structure, molecular docking, and anticancer evaluation of 4-nitroimidazole derivatives combined with piperazine moiety

Piperazine-tagged imidazole derivatives 3a (symmetrical di-substituted piperazine) and 5-11 were synthesized through the combination of 4-nitroimidazole derivatives with piperazine moiety. The structural characterization was done by different physical and spectral techniques like NMR (¹H and ¹³C) and mass spectrometry. The constituency of compound 3a was confirmed by X-ray structural analyses. All compounds were assessed for their antiproliferative inhibition potency against five human cancer cell lines namely MCF-7, PC3, MDA-231, A549 and Fibro dental. Compound 5 was found to be the most potent anticancer agents against MCF-7 cell line with IC₅₀ values of (1.0 ± 0 µm) and against PC3 with IC₅₀ value of (9.00 ± 0.028 µm). The molecular docking of compound 5 had been studied, and the results revealed that the newly designed 4-nitroimidazole combined with piperazine moiety derivatives bond to the hydrophobic pocket and polar contacts with high affinity.

RdxA Diversity and Mutations Associated with Metronidazole Resistance of Helicobacter pylori

Metronidazole (MNZ) is administered as first-line antibiotic for Helicobacter pylori eradication therapy; however, increasing resistance to MNZ impaired the efficacy. Increasing the dose of MNZ was recommended to overcome low-level resistance, but it was difficult to determine MNZ resistance level simply based on the rdxA gene mutation. In this study, the rdxA sequences of 511 clinical H. pylori strains were analyzed to assess the genotypes associated with MNZ resistance. We observed that the prevalences of rdxA sequences with missense, nonsense, and frameshift mutations were 70.25, 11.35, and 17.03%, respectively. Regarding the amino acid substitutions, T31E, H53R, D59N, L62V, S88P, G98S/N, R131K, and V172I were present in most strains regardless of the resistance phenotype. The correlation analysis showed R16H/C, Y47C, A67V/T, and V204I substitutions were associated with MNZ resistance. The mutation resulting in RdxA truncation was observed in 36.29% of the resistant strains, and 83.45% of these strains displayed high-level MNZ resistance (MIC > 256 μg/mL). Moreover, all strains with truncated mutation positions before amino acid 70 expressed high-level MNZ resistance. Our results indicated that most amino acid mutations probably contributed to the sequence diversity of RdxA, while R16H/C, Y47C, A67V/T, and V204I were potentially helpful to identify resistant strains. Although it was difficult to determine the mutations associated with MNZ resistance, the prediction of high-level resistance based on truncated characteristics of RdxA might be an important approach, which can effectively avoid H. pylori eradication therapy with unreasonable of MNZ dose increases for patients with high-level drug resistance. IMPORTANCE The increasing resistance to metronidazole impaired the efficacy of Helicobacter pylori eradication, and increasing the dose of metronidazole was recommended to overcome low-level resistance. For patients infected with highly resistant strains, the current empirical treatments, which generally used metronidazole in double doses or more, appeared impossibly to overcome the resistance and would only increase the incidence of adverse effects. Our results indicated that high-level metronidazole resistance was predominant, and almost half of the patients with high-level drug resistance could avoid usage of metronidazole based on the truncated mutations of RdxA sequences, which can effectively avoid H. pylori eradication therapy with unreasonable increases in the metronidazole dose.

Mass Spectrometry-Based Metabolomics Revealed Effects of Metronidazole on Giardia duodenalis

Giardia duodenalis is a significant protozoan that affects humans and animals. An estimated 280 million G. duodenalis diarrheal cases are recorded annually. Pharmacological therapy is crucial for controlling giardiasis. Metronidazole is the first-line therapy for treating giardiasis. Several metronidazole targets have been proposed. However, the downstream signaling pathways of these targets with respect to their antigiardial action are unclear. In addition, several giardiasis cases have demonstrated treatment failures and drug resistance. Therefore, the development of novel drugs is an urgent need. In this study, we performed a mass spectrometry-based metabolomics study to understand the systemic effects of metronidazole in G. duodenalis. A thorough analysis of metronidazole processes helps identify potential molecular pathways essential for parasite survival. The results demonstrated 350 altered metabolites after exposure to metronidazole. Squamosinin A and N-(2-hydroxyethyl)hexacosanamide were the most up-regulated and down-regulated metabolites, respectively. Proteasome and glycerophospholipid metabolisms demonstrated significant differential pathways. Comparing glycerophospholipid metabolisms of G. duodenalis and humans, the parasite glycerophosphodiester phosphodiesterase was distinct from humans. This protein is considered a potential drug target for treating giardiasis. This study improved our understanding of the effects of metronidazole and identified new potential therapeutic targets for future drug development.

Toxicological parameters of the drug based on Ornidazole and Levamisole hydrochloride

The purpose of the research is the study of pharmaco-toxicological properties of the Ornidazole- and Levamisole hydrochloride-based drug.Materials and methods. The pharmaco-toxicological properties of the Ornidazole- and Levamisole hydrochloride-based drug were studied in the premises of the Laboratory of Preclinical Studies, Faculty of Veterinary Medicine, Stavropol State Agrarian University. Acute and chronic toxicity, and irritant effect of the drug was studied under the Guidelines for Preclinical Studies of Drugs (2012). Hematological studies of laboratory animals were performed with an automatic hematological analyzer, and biochemical studies of the blood serum were done with an automatic biochemical analyzer.Results and discussion. It has been found that the Ornidazole- and Levamisole hydrochloride-based drug belongs to the Hazard Class 3 for the median lethal oral dose in accordance with GOST 12.1.007–76 as moderately hazardous substances; it does not have a pronounced subchronic toxicity or irritant effect. Multiple use of the active substance for 14 days does not cause significant changes in the clinical condition, or in hematological and biochemical profile of laboratory animals.

Genetic diversity in the metronidazole metabolism genes nitroreductases and pyruvate ferredoxin oxidoreductases in susceptible and refractory clinical samples of Giardia lamblia

The effectiveness of metronidazole against the tetraploid intestinal parasite Giardia lamblia is dependent on its activation/inactivation within the cytoplasm. There are several activating enzymes, including pyruvate ferredoxin reductase (PFOR) and nitroreductase (NR) 1 which metabolize metronidazole into toxic forms, while NR2 on the other hand inactivates it. Metronidazole treatment failures have been increasing rapidly over the last decade, indicating genetic resistance mechanisms. Analyzing genetic variation in the PFOR and NR genes in susceptible and refractory Giardia isolates may help identify potential markers of resistance. Full length PFOR1, PFOR2, NR1 and NR2 genes from clinical culturable isolates and non-cultured clinical Giardia assemblage B samples were cloned, sequenced and single nucleotide variants (SNVs) were analyzed to assess genetic diversity and alleles. A similar ratio of amino acid changing SNVs per gene length was found for the NRs; 4.2% for NR1 and 6.4% for NR2, while the PFOR1 and PFOR2 genes had less variability with a ratio of 1.1% and 1.6%, respectively. One of the samples from a refractory case had a nonsense mutation which caused a truncated NR1 gene in one out of six alleles. Further, we found three NR2 alleles with frameshift mutations, possibly causing a truncated protein in two susceptible isolates. One of these isolates was homozygous for the affected NR2 allele. Three nsSNVs with potential for affecting protein function were found in the ferredoxin domain of the PFOR2 gene. The considerable variation and discovery of mutations possibly causing dysfunctional NR proteins in clinical Giardia assemblage B isolates, reveal a potential for genetic link to metronidazole susceptibility and resistance.

Bone-Muscle Crosstalk: Musculoskeletal Complications of Chemotherapy

PURPOSE OF REVIEW

Chemotherapy drugs combat tumor cells and reduce metastasis. However, a significant side effect of some chemotherapy strategies is loss of skeletal muscle and bone. In cancer patients, maintenance of lean tissue is a positive prognostic indicator of outcomes and helps to minimize the toxicity associated with chemotherapy. Bone-muscle crosstalk plays an important role in the function of the musculoskeletal system and this review will focus on recent findings in preclinical and clinical studies that shed light on chemotherapy-induced bone-muscle crosstalk.

RECENT FINDINGS

Chemotherapy-induced loss of bone and skeletal muscle are important clinical problems. Bone antiresorptive drugs prevent skeletal muscle weakness in preclinical models. Chemotherapy-induced loss of bone can cause muscle weakness through both changes in endocrine signaling and mechanical loading between muscle and bone. Chemotherapy-induced changes to bone-muscle crosstalk have implications for treatment strategies and patient quality of life. Recent findings have begun to determine the role of chemotherapy in bone-muscle crosstalk and this review summarizes the most relevant clinical and preclinical studies.

Antileishmanial Activities of ( Z )-2-(Nitroimidazolylmethylene)-3( 2H )-Benzofuranones: Synthesis, In Vitro Assessment, and Bioactivation by NTR 1 and 2

The antileishmanial activity of a series of ( Z )-2-(heteroarylmethylene)-3(2 H )-benzofuranone derivatives, possessing 5-nitroimidazole or 4-nitroimidazole moieties, was investigated against Leishmania major promastigotes and some analogues exhibited prominent activities. Compounds with IC 50 values lower than 20 μM were further examined against L. donovani axenic amastigotes.

Application of Fourier transform-based algorithms to resolve spectral overlapping for UV spectrophotometric co-assay of spiramycin and metronidazole in tablets

Fourier transform-based algorithms were investigated to resolve UV spectral overlapping of spiramycin and metronidazole in binary mixtures. UV spectra and ratio spectra were both subjected to fast Fourier transform-based first-order differentiation and discrete Fourier transform {i.e. using trigonometric functions such as sin x_i - sin (x_i + 45⁰), cos x_i + cos (x_i + 45⁰), sin 2x_i - sin 2(x_i + 45⁰), cos 2x_i + cos 2(x_i + 45⁰), sin x_i - sin (x_i + 60⁰), cos x_i + cos (x_i + 60⁰)} that followed by 3 passes of 17-point triangular smooth. Such signal transforms generated linear calibration graphs for either drug in the concentration range of 6.25 - 25 mg/L with R² > 0.990. In comparison with the RP-HPLC reference method, the developed UV spectrophotometric methods had no significant difference in terms of accuracy and precision (p > 0.05) when quantifying spiramycin and metronidazole in their coated tablets. They are suggested as analytical quality control methods for their being environmentally friendly, technically simple, quick and economic.

Initial expression levels of nimA are decisive for protection against metronidazole in Bacteroides fragilis

OBJECTIVES

In the genus Bacteroides, the nim genes are resistance determinants for metronidazole, a nitroimidazole drug widely used against anaerobic pathogens. The Nim proteins are considered to act as nitroreductases. However, data from several studies suggest that the expression levels of Nim do not increase with increasing resistance which is conflicting with this notion. The impact of Nim protein levels on low-level metronidazole resistance, however, representing the early stage of induced resistance in the laboratory, has not been assessed as yet.

METHODS

The nimA gene was cloned into two different plasmids and introduced into B. fragilis strain 638R. Expression levels of nimA mRNA were measured by RT-qPCR and compared to those in strain 638R harbouring plasmid pI417, the original clinical plasmid harbouring IS element IS1168 with the nimA gene. Further, metronidazole susceptibility was assessed by Etest and the activity of pyruvate:ferredoxin oxidoreductase (PFOR) was measured in all strains after induction of high-level metronidazole resistance.

RESULTS

The level of protection against metronidazole by nimA correleated with the level of expression of nimA mRNA. Further, the activity of PFOR in highly-resistant B. fragilis 638R was only preserved when expression levels of nimA were high.

CONCLUSIONS

Although the development of high-level metronidazole resistance in B. fragilis strains with a nimA gene is not caused by an increase of nimA expression as compared to the less resistant parent strains, nimA expression levels might be of decisive importance in the early stage of resistance development. This has potential implications for metronidazole resistance in clinical isolates.

Activity of Apo-Lactoferrin on Pathogenic Protozoa

Parasites and other eventually pathogenic organisms require the ability to adapt to different environmental conditions inside the host to assure survival. Some host proteins have evolved as defense constituents, such as lactoferrin (Lf), which is part of the innate immune system. Lf in its iron-free form (apo-Lf) and its peptides obtained by cleavage with pepsin are microbicides. Parasites confront Lf in mucosae and blood. In this work, the activity of Lf against pathogenic and opportunistic parasites such as Cryptosporidium spp., Eimeria spp., Entamoeba histolytica, Giardia duodenalis, Leishmania spp., Trypanosoma spp., Plasmodium spp., Babesia spp., Toxoplasma gondii, Trichomonas spp., and the free-living but opportunistic pathogens Naegleria fowleri and Acanthamoeba castellani were reviewed. The major effects of Lf could be the inhibition produced by sequestering the iron needed for their survival and the production of oxygen-free radicals to more complicated mechanisms, such as the activation of macrophages to phagocytes with the posterior death of those parasites. Due to the great interest in Lf in the fight against pathogens, it is necessary to understand the exact mechanisms used by this protein to affect their virulence factors and to kill them.

Modulation of Iron Import and Metronidazole Resistance in Bacteroides fragilis Harboring a nimA Gene

Bacteroides fragilis is a commensal of the human gut but can also cause severe infections when reaching other body sites, especially after surgery or intestinal trauma. Bacteroides fragilis is an anaerobe innately susceptible to metronidazole, a 5-nitroimidazole drug that is prescribed against the majority of infections caused by anaerobic bacteria. In most of the cases, metronidazole treatment is effective but a fraction of B. fragilis is resistant to even very high doses of metronidazole. Metronidazole resistance is still poorly understood, but the so-called nim genes have been described as resistance determinants. They have been suggested to encode nitroreductases which reduce the nitro group of metronidazole to a non-toxic aminoimidazole. More recent research, however, showed that expression levels of nim genes are widely independent of the degree of resistance observed. In the search for an alternative model for nim-mediated metronidazole resistance, we screened a strain carrying an episomal nimA gene and its parental strain 638R without a nim gene for physiological differences. Indeed, the 638R daughter strain with the nimA gene had a far higher pyruvate-ferredoxin oxidoreductase (PFOR) activity than the parental strain. High PFOR activity was also observed in metronidazole-resistant clinical isolates, either with or without a nim gene. Moreover, the strain carrying a nimA gene fully retained PFOR activity and other enzyme activities such as thioredoxin reductase (TrxR) after resistance had been induced. In the parental strain 638R, these were lost or very strongly downregulated during the development of resistance. Further, after induction of high-level metronidazole resistance, parental strain 638R was highly susceptible to oxygen whereas the daughter strain with a nimA gene was hardly affected. Ensuing RT-qPCR measurements showed that a pathway for iron import via hemin uptake is downregulated in 638R with induced resistance but not in the resistant nimA daughter strain. We propose that nimA primes B. fragilis toward an alternative pathway of metronidazole resistance by enabling the preservation of normal iron levels in the cell.

Multicomponent Assembly of Trisubstituted Imidazoles and Their Photochemical Cyclization into Fused Polyheterocyclic Scaffolds

A straightforward route to a large and diverse library of trisubstituted imidazoles was established via a three-component reaction of 2-oxoaldehydes, 1,3-dicarbonyl compounds, and acyclic nitrogen bis-nucleophiles. The obtained products were subsequently explored in a photochemical cyclization yielding a variety of imidazole-fused polycyclic compounds.

Effect of the Symbiosis with Mycoplasma hominis and Candidatus Mycoplasma Girerdii on Trichomonas vaginalis Metronidazole Susceptibility

Trichomoniasis, the most common non-viral sexually transmitted infection worldwide, is caused by the protozoon Trichomonas vaginalis. The 5- nitroimidazole drugs, of which metronidazole is the most prescribed, are the only effective drugs to treat trichomoniasis. Resistance against metronidazole is increasingly reported among T. vaginalis isolates. T. vaginalis can establish an endosymbiosis with two Mycoplasma species, Mycoplasma hominis and Candidatus Mycoplasma girerdii, whose presence has been demonstrated to influence several aspects of the protozoan pathobiology. The role of M. hominis in T. vaginalis resistance to metronidazole is controversial, while the influence of Ca. M. girerdii has never been investigated. In this work, we investigate the possible correlation between the presence of Ca. M. girerdii and/or M. hominis and the in vitro drug susceptibility in a large group of T. vaginalis isolated in Italy and in Vietnam. We also evaluated, via RNA-seq analysis, the expression of protozoan genes involved in metronidazole resistance in a set of syngenic T. vaginalis strains, differing only for the presence/absence of the two Mycoplasmas. Our results show that the presence of M. hominis significantly increases the sensitivity to metronidazole in T. vaginalis and affects gene expression. On the contrary, the symbiosis with Candidatus Mycoplasma girerdii seems to have no effect on metronidazole resistance in T. vaginalis.

Low-Energy Electron Induced Reactions in Metronidazole at Different Solvation Conditions

Metronidazole belongs to the class of nitroimidazole molecules and has been considered as a potential radiosensitizer for radiation therapy. During the irradiation of biological tissue, secondary electrons are released that may interact with molecules of the surrounding environment. Here, we present a study of electron attachment to metronidazole that aims to investigate possible reactions in the molecule upon anion formation. Another purpose is to elucidate the effect of microhydration on electron-induced reactions in metronidazole. We use two crossed electron/molecular beam devices with the mass-spectrometric analysis of formed anions. The experiments are supported by quantum chemical calculations on thermodynamic properties such as electron affinities and thresholds of anion formation. For the single molecule, as well as the microhydrated condition, we observe the parent radical anion as the most abundant product anion upon electron attachment. A variety of fragment anions are observed for the isolated molecule, with NO₂^- as the most abundant fragment species. NO₂^- and all other fragment anions except weakly abundant OH^- are quenched upon microhydration. The relative abundances suggest the parent radical anion of metronidazole as a biologically relevant species after the physicochemical stage of radiation damage. We also conclude from the present results that metronidazole is highly susceptible to low-energy electrons.

A Silent Operon of Photorhabdus luminescens Encodes a Prodrug Mimic of GTP

With the overmining of actinomycetes for compounds acting against Gram-negative pathogens, recent efforts to discover novel antibiotics have been focused on other groups of bacteria. Teixobactin, the first antibiotic without detectable resistance that binds lipid II, comes from an uncultured Eleftheria terra, a betaproteobacterium; odilorhabdins, from Xenorhabdus, are broad-spectrum inhibitors of protein synthesis, and darobactins from Photorhabdus target BamA, the essential chaperone of the outer membrane of Gram-negative bacteria. Xenorhabdus and Photorhabdus are symbionts of the nematode gut microbiome and attractive producers of secondary metabolites. Only small portions of their biosynthetic gene clusters (BGC) are expressed in vitro. To access their silent operons, we first separated extracts from a small library of isolates into fractions, resulting in 200-fold concentrated material, and then screened them for antimicrobial activity. This resulted in a hit with selective activity against Escherichia coli, which we identified as a novel natural product antibiotic, 3′-amino 3′-deoxyguanosine (ADG). Mutants resistant to ADG mapped to gsk and gmk, kinases of guanosine. Biochemical analysis shows that ADG is a prodrug that is converted into an active ADG triphosphate (ADG-TP), a mimic of GTP. ADG incorporates into a growing RNA chain, interrupting transcription, and inhibits cell division, apparently by interfering with the GTPase activity of FtsZ. Gsk of the purine salvage pathway, which is the first kinase in the sequential phosphorylation of ADG, is restricted to E. coli and closely related species, explaining the selectivity of the compound. There are probably numerous targets of ADG-TP among GTP-dependent proteins. The discovery of ADG expands our knowledge of prodrugs, which are rare among natural compounds.

Biomarker Characterization and Prediction of Virulence and Antibiotic Resistance from Helicobacter pylori Next Generation Sequencing Data

The Gram-negative bacterium Helicobacter pylori colonizes c.a. 50% of human stomachs worldwide and is the major risk factor for gastric adenocarcinoma. Its high genetic variability makes it difficult to identify biomarkers of early stages of infection that can reliably predict its outcome. Moreover, the increasing antibiotic resistance found in H. pylori defies therapy, constituting a major human health problem. Here, we review H. pylori virulence factors and genes involved in antibiotic resistance, as well as the technologies currently used for their detection. Furthermore, we show that next generation sequencing may lead to faster characterization of virulence factors and prediction of the antibiotic resistance profile, thus contributing to personalized treatment and management of H. pylori-associated infections. With this new approach, more and permanent data will be generated at a lower cost, opening the future to new applications for H. pylori biomarker identification and antibiotic resistance prediction.

Functionalized Nitroimidazole Scaffold Construction and Their Pharmaceutical Applications: A 1950–2021 Comprehensive Overview

Nitroimidazole represents one of the most essential and unique scaffolds in drug discovery since its discovery in the 1950s. It was K. Maeda in Japan who reported in 1953 the first nitroimidazole as a natural product from Nocardia mesenterica with antibacterial activity, which was later identified as Azomycin 1 (2-nitroimidazole) and remained in focus until now. This natural antibiotic was the starting point for synthesizing numerous analogs and regio-isomers, leading to several life-saving drugs and clinical candidates against a number of diseases, including infections (bacterial, viral, parasitic) and cancers, as well as imaging agents in medicine/diagnosis. In the present decade, the nitroimidazole scaffold has again been given two life-saving drugs (Delamanid and Pretomanid) used to treat MDR (multi-drug resistant) tuberculosis. Keeping in view the highly successful track-record of the nitroimidazole scaffold in providing breakthrough therapeutic drugs, this comprehensive review focuses explicitly on presenting the activity profile and synthetic chemistry of functionalized nitroimidazole (2-, 4- and 5-nitroimidazoles as well as the fused nitroimidazoles) based drugs and leads published from 1950 to 2021. The present review also presents the miscellaneous examples in each class. In addition, the mutagenic profile of nitroimidazole-based drugs and leads and derivatives is also discussed.

An Overview of Mucosa-Associated Protozoa: Challenges in Chemotherapy and Future Perspectives

Parasitic infections caused by protozoans that infect the mucosal surfaces are widely neglected worldwide. Collectively, Entamoeba histolytica, Giardia lamblia, Cryptosporidium spp. and Trichomonas vaginalis infect more than a billion people in the world, being a public health problem mainly in developing countries. However, the exact incidence and prevalence data depend on the population examined. These parasites ultimately cause pathologies that culminate in liver abscesses, malabsorption syndrome, vaginitis, and urethritis, respectively. Despite this, the antimicrobial agents currently used to treat these diseases are limited and often associated with adverse side effects and refractory cases due to the development of resistant parasites. The paucity of drug treatments, absence of vaccines and increasing problems of drug resistance are major concerns for their control and eradication. Herein, potential candidates are reviewed with the overall aim of determining the knowledge gaps and suggest future perspectives for research. This review focuses on this public health problem and focuses on the progress of drug repositioning as a potential strategy for the treatment of mucosal parasites.

Discovery of Benzopyrrolizidines as Promising Antigiardiasic Agents

Current treatments for giardiasis include drugs with undesirable side effects, which increase the levels of therapeutic desertion and promote drug resistance in the parasites. Herein, we describe the antigiardiasic evaluation on Giardia lamblia trophozoites of a structurally diverse collection of 74 molecules. Among these scaffolds, we discovered a benzopyrrolizidine derivative with higher antigiardiasic activity (IC₅₀ = 11 µM) and lower cytotoxicity in human cell cultures (IC₅₀ = 130 µM) than those displayed by the current gold-standard drugs (metronidazole and tinidazole). Furthermore, this compound produced morphologic modifications of trophozoites, with occasional loss of one of the nuclei, among other changes not observed with standard giardicidal drugs, suggesting that it might act through a novel mechanism of action.

Haemin deprivation renders Bacteroides fragilis hypersusceptible to metronidazole and cancels high-level metronidazole resistance

BACKGROUND

Infections with Bacteroides fragilis are routinely treated with metronidazole, a 5-nitroimidazole antibiotic that is active against most anaerobic microorganisms. Metronidazole has remained a reliable treatment option, but resistance does occur, including in B. fragilis.

OBJECTIVES

In this study we tested whether haemin, a growth supplement for B. fragilis in vivo and in vitro, had an influence on the susceptibility of resistant B. fragilis strains to metronidazole. We further tested whether haemin-deprived B. fragilis would be more susceptible to oxygen and oxidative stress. Metronidazole has been described to cause oxidative stress, which we argued would be exacerbated in haemin-deprived B. fragilis because the bacteria harness haemin, and the iron released from it, in antioxidant enzymes such as catalase and superoxide dismutase.

METHODS

Haemin was omitted from growth media and the effect on metronidazole susceptibility was monitored in susceptible and resistant B. fragilis strains. Further, haemin-deprived B. fragilis were tested for resistance to aeration and hydrogen peroxide and the capacity for the removal of oxygen.

RESULTS

Omission of haemin from the growth medium rendered metronidazole-resistant B. fragilis strains, including an MDR isolate from the UK, highly susceptible to metronidazole. Haemin deprivation further rendered B. fragilis highly susceptible to oxygen, which was further exacerbated in resistant strains. B. fragilis was incapable of scavenging oxygen when haemin was omitted.

CONCLUSIONS

We propose that haemin deprivation overrules resistance mechanisms by rendering B. fragilis hypersusceptible to metronidazole due to a compromised antioxidant defence. Monitoring of haemin concentrations is imperative when conducting metronidazole susceptibility testing in B. fragilis.

Are Metabolites From the Gut Microbiota Capable of Regulating Epigenetic Mechanisms in the Human Parasite Entamoeba histolytica?

The unicellular parasite Entamoeba histolytica inhabits the human gut. It has to adapt to a complex environment that consists of the host microbiota, nutritional stress, oxidative stress, and nitrosative stress. Adaptation to this complex environment is vital for the survival of this parasite. Studies have shown that the host microbiota shapes virulence and stress adaptation in E. histolytica. Increasing evidence suggests that metabolites from the microbiota mediate communication between the parasite and microbiota. In this review, we discuss the bacterial metabolites that regulate epigenetic processes in E. histolytica and the implications that this knowledge may have for the development of new anti-amebic strategies.

In Vitro and In Vivo Antiamebic Activity of Iron-Targeting Polypyridine Compounds against Enteric Protozoan Parasite Entamoeba histolytica

The infectious protozoan parasite Entamoeba histolytica is responsible for amebiasis causing colitis and liver abscesses, which is an epidemic in developing countries. To develop a drug discovery strategy targeting the iron source required for the proliferation of E. histolytica, an untapped chemical group consisting of low-molecular-weight compounds with metal-binding affinity was investigated. Electrochemically neutral polypyridine compounds, PHN-R₂, that showed specific Fe(II)-binding affinity and growth inhibitory ability against E. histolytica were identified. Furthermore, the iron-dependent IC₅₀ values of PHN-R₂ and the spectrometric analytical data of their iron complexes clarified the relationship between the antiamebic activity and the iron-targeting specificity. Notably, when PHN-H₂ was administrated to E. histolytica-infected hamsters as an animal model of amebiasis, it exhibited a prominent therapeutic efficacy to completely cure liver abscesses without serious side effects. Deciphering the antiamebic activity of iron-targeting compounds in vitro and in vivo provides valuable insights into the development of a next-generation drug against amebiasis.

Characterization of Metronidazole-Resistant Giardia intestinalis Lines by Comparative Transcriptomics and Proteomics

Metronidazole (MTZ) is a clinically important antimicrobial agent that is active against both bacterial and protozoan organisms. MTZ has been used extensively for more than 60 years and until now resistance has been rare. However, a recent and dramatic increase in the number of MTZ resistant bacteria and protozoa is of great concern since there are few alternative drugs with a similarly broad activity spectrum. To identify key factors and mechanisms underlying MTZ resistance, we utilized the protozoan parasite Giardia intestinalis, which is commonly treated with MTZ. We characterized two in vitro selected, metronidazole resistant parasite lines, as well as one revertant, by analyzing fitness aspects associated with increased drug resistance and transcriptomes and proteomes. We also conducted a meta-analysis using already existing data from additional resistant G. intestinalis isolates. The combined data suggest that in vitro generated MTZ resistance has a substantial fitness cost to the parasite, which may partly explain why resistance is not widespread despite decades of heavy use. Mechanistically, MTZ resistance in Giardia is multifactorial and associated with complex changes, yet a core set of pathways involving oxidoreductases, oxidative stress responses and DNA repair proteins, is central to MTZ resistance in both bacteria and protozoa.

Capillary Zone Electrophoresis in Tandem with Flow Cytometry in Viability Study of Various ATCC Bacterial Strains under Antibiotic Treatment

The aim of this study was to develop an innovative method of examining bacterial survival using capillary zone electrophoresis (CZE) and flow cytometry (FC) as a reference method. For this purpose, standard strains of bacteria from the ATCC collection were used: Enterococcus faecalis ATCC 14506, Staphylococcus aureus ATCC 11632, Klebsiella pneumoniae ATCC 10031, Pseudomonas aeruginosa ATCC 27853, and Escherichia coli ATCC 25922, as well as seven antibiotics with different antimicrobial mechanisms of action. The ratio of live and dead cells in the tested sample in CZE measurements were calculated using our algorithm that takes into account the detection time. Results showed a high agreement between CZE and FC in the assessment of the percentage of live cells exposed to the stress factor in both antibiotic susceptibility and time-dependent assays. The applied measuring system to assess the effectiveness of antibiotic therapy in in vitro conditions is a method with great potential, and the data obtained with the use of CZE mostly correspond to the expected drug sensitivity according to EUCAST and CLSI guidelines.

Has Ferrocene Really Delivered Its Role in Accentuating the Bioactivity of Organic Scaffolds?

Ferrocene is an important structural core in bioorganometallic chemistry because of its inherent stability, excellent redox properties, and low toxicity. Ferroquine and ferrocifen are two of the most notable contributions of ferrocene to medicinal chemistry with remarkable antimalarial and anticancer properties. The improved medicinal properties of these drug candidates highlight the impact that ferrocene can have on the molecular and biological properties of the bioactive compounds. In this Perspective, we investigate the scope and limitations of ferrocene incorporation into organic compounds/natural products on their mode of action and biological activities. We have also discussed the detailed role of ferrocene modifications in influencing the anticancer, antimalarial, and antimicrobial properties of various bioactive moieties to design safer and promising ferrocene-based drugs.

Gut microbiome affects the metabolism of metronidazole in mice through regulation of hepatic cytochromes P450 expression

Microbiome is now considered as a significant metabolic organ with an immense potential to influence overall human health. A number of diseases that are associated with pharmacotherapy interventions was linked with altered gut microbiota. Moreover, it has been reported earlier that gut microbiome modulates the fate of more than 30 commonly used drugs and, vice versa, drugs have been shown to affect the composition of the gut microbiome. The molecular mechanisms of this mutual relationship, however, remain mostly elusive. Recent studies indicate an indirect effect of the gut microbiome through its metabolites on the expression of biotransformation enzymes in the liver. The aim of this study was to analyse the effect of gut microbiome on the fate of metronidazole in the mice through modulation of system of drug metabolizing enzymes, namely by alteration of the expression and activity of selected cytochromes P450 (CYPs). To assess the influence of gut microbiome, germ-free mice (GF) in comparison to control specific-pathogen-free (SPF) mice were used. First, it has been found that the absence of microbiota significantly affected plasma concentration of metronidazole, resulting in higher levels (by 30%) of the parent drug in murine plasma of GF mice. Further, the significant interaction between presence/absence of the gut microbiome and effect of metronidazole application, which together influence mRNA expression of CAR, PPARα, Cyp2b10 and Cyp2c38 was determined. Administration of metronidazole itself influenced significantly mRNA expression of Cyp1a2, Cyp2b10, Cyp2c38 and Cyp2d22. Finally, GF mice have shown lower level of enzyme activity of CYP2A and CYP3A than their SPF counterparts. The results hence have shown that, beside direct bacterial metabolism, different expression and enzyme activity of hepatic CYPs in the presence/absence of gut microbiota may be responsible for the altered metronidazole metabolism.