Utility of Galleria mellonella larvae for evaluating nanoparticle toxicology

Multimodal evaluation of drug antibacterial activity reveals cinnamaldehyde analog anti-biofilm effects against Haemophilus influenzae

Biofilm formation by the pathobiont Haemophilus influenzae is associated with human nasopharynx colonization, otitis media in children, and chronic respiratory infections in adults suffering from chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD). β-lactam and quinolone antibiotics are commonly used to treat these infections. However, considering the resistance of biofilm-resident bacteria to antibiotic-mediated killing, the use of antibiotics may be insufficient and require being replaced or complemented with novel strategies. Moreover, unlike the standard minimal inhibitory concentration assay used to assess antibacterial activity against planktonic cells, standardization of methods to evaluate anti-biofilm drug activity is limited. In this work, we detail a panel of protocols for systematic analysis of drug antimicrobial effect on bacterial biofilms, customized to evaluate drug effects against H. influenzae biofilms. Testing of two cinnamaldehyde analogs, (E)-trans-2-nonenal and (E)-3-decen-2-one, demonstrated their effectiveness in both H. influenzae inhibition of biofilm formation and eradication or preformed biofilms. Assay complementarity allowed quantifying the dynamics and extent of the inhibitory effects, also observed for ampicillin resistant clinical strains forming biofilms refractory to this antibiotic. Moreover, cinnamaldehyde analog encapsulation into poly(lactic-co-glycolic acid) (PLGA) polymeric nanoparticles allowed drug vehiculization while maintaining efficacy. Overall, we demonstrate the usefulness of cinnamaldehyde analogs against H. influenzae biofilms, present a test panel that can be easily adapted to a wide range of pathogens and drugs, and highlight the benefits of drug nanoencapsulation towards safe controlled release.

Development and characterization of potential larvicidal nanoemulsions against Aedes aegypti

Plant-based insecticides offer advantages such as negligible residual effects, reduced risks to both humans and the environment, and immunity to resistance issues that plague conventional chemicals. However, the practical use of monoterpenes in insect control has been hampered by challenges including their poor solubility and stability in aqueous environments. In recent years, the application of nanotechnology-based formulations, specifically nanoemulsions, has emerged as a prospective strategy to surmount these obstacles. In this study, we developed and characterized nanoemulsions based on cymene and myrcene and assessed their toxicity both in vitro using human keratinocytes (HaCAT) cells and in an in vivo model involving Galleria mellonella larvae. Additionally, we investigated the insecticidal efficacy of monoterpenes against the mosquito Aedes aegypti, the primary dengue vector, via larval bioassay. Employing a low-energy approach, we successfully generated nanoemulsions. The cymene-based nanoemulsion exhibited a hydrodynamic diameter of approximately 98 nm and a zeta potential of -25 mV. The myrcene-based nanoemulsion displayed a hydrodynamic diameter of 118 nm and a zeta potential of -20 mV. Notably, both nanoemulsions demonstrated stability over 60 days, accompanied by controlled release properties and low toxicity towards HaCAT cells and Galleria mellonella larvae. Moreover, the nanoemulsions exhibited significant lethality against third-instar Aedes aegypti larvae at a concentration of 50 mg/L. In conclusion, the utilization of nanoemulsions encapsulating cymene and myrcene presents a promising avenue for overcoming the limitations associated with poor solubility and stability of monoterpenes. This study sheds light on the potential of the nanoemulsions as effective and environmentally friendly insecticides in the ongoing battle against mosquito-borne diseases.

Nanomedicine against biofilm infections: A roadmap of challenges and limitations

Microbial biofilms are complex three-dimensional structures where sessile microbes are embedded in a polymeric extracellular matrix. Their resistance toward the host immune system as well as to a diverse range of antimicrobial treatments poses a serious health and development threat, being in the top 10 global public health threats declared by the World Health Organization. In an effort to combat biofilm-related microbial infections, several strategies have been developed to independently eliminate biofilms or to complement conventional antibiotic therapies. However, their limitations leave room for other treatment alternatives, where the application of nanotechnology to biofilm eradication has gained significant relevance in recent years. Their small size, penetration efficiency, and the design flexibility that they present makes them a promising alternative for biofilm infection treatment, although they also present set-backs. This review aims to describe the main possibilities and limitations of nanomedicine against biofilms, while covering the main aspects of biofilm formation and study, and the current therapies for biofilm treatment. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Culture media influences Candida parapsilosis growth, susceptibility, and virulence

Introduction

Candida parapsilosis, a pathogenic yeast associated with systemic infections, exhibits metabolic adaptability in response to nutrient availability.

Methods

We investigated the impact of RPMI glucose supplemented (RPMId), TSB, BHI and YPD media on C. parapsilosis growth, morphology, susceptibility (caspofungin and amphotericin B), and in vivo virulence (Galleria mellonella) in planktonic and biofilm states.

Results

High-glucose media favors growth but hinders metabolic activity and filamentation. Media promoting carbohydrate production reduces biofilm susceptibility. Virulence differences between planktonic cells and biofilm suspensions from the same media shows that biofilm-related factors influence infection outcome depending on nutrient availability. Pseudohyphal growth occurred in biofilms under low oxygen and shear stress, but its presence is not exclusively correlated with virulence.

Discussion

This study provides valuable insights into the intricate interplay between nutrient availability and C. parapsilosis pathogenicity. It emphasizes the importance of considering pathogen behavior in diverse conditions when designing research protocols and therapeutic strategies.

Antifungal Activity of Nontoxic Nanocomposite Based on Silver and Reduced Graphene Oxide against Dermatophytes and Candida spp

Dermatomycoses are typical hair, skin, or nail infections caused mainly by dermatophytes and nondermatophytes: Trichophyton, Microsporum, Epidermophyton, and Candida. In addition to the esthetical impact, pain, and nail deformity, these mycoses can be a source of severe disease. The high cost of treatment, toxicity, and the emergence of resistant infectious agents justifies research into new drugs. This work evaluates the fungicidal activity of nanocomposites (NCs) based on reduced graphene oxide (rGO) loaded with silver (Ag) nanoparticles (rGO/Ag) against clinical isolates of dermatophytes and Candida species. This is an unprecedented study in which, for the first time, hybrid nanocompounds based on Ag/rGO were tested against Epidermophytom, Microsporum, and Trichophyton species (dermatophytes agents). In this paper, we synthesize rGO using different concentrations of Ag by hydrolysis of metal salt AgNO3 and follow the growth of nanocrystals on sheets of rGO provided by the NaBH4. The NCs were analyzed by X-ray diffraction analysis, and the NC morphology, silver distribution on the rGO surface, and crystalline information were investigated by transmission electron microscopy. Antifungal susceptibility assay was performed by the microdilution method based on modified Clinical and Laboratory Standards Institute (CLSI) protocol. Time-kill kinetics was conducted to monitor the effect of the composite to inhibit fungal cells or promote structural changes, avoiding germination. The toxicological evaluation of the NCs was born in an in vivo model based on Galleria mellonella (G. mellonella). Minimum inhibitory concentration (MIC) values of the rGO/Ag NCs ranged from 1.9 to 125 μg/mL. The best inhibitory activity was obtained for rGO/Ag12%, mainly against Candida spp. and Epidermophyton floccosum. In the presence of sorbitol, MIC values of rGO/Ag NCs were higher (ranging from 15.6 to 250 μg/mL), indicating the action mechanism on the cell wall. Both yeast and dermatophytes clinical isolates were inhibited at a minimum of 6 and 24 h, respectively, but after 2 and 12 h, they had initial antifungal interference. All hybrid formulations of rGO/Ag NCs were not toxic for G. mellonella. This study provides insights into an alternative therapeutic strategy for controlling dermatomycoses.

A potential strategy against clinical carbapenem-resistant Enterobacteriaceae: antimicrobial activity study of sweetener-decorated gold nanoparticles in vitro and in vivo

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) present substantial challenges to clinical intervention, necessitating the formulation of novel antimicrobial strategies to counteract them. Nanomaterials offer a distinctive avenue for eradicating bacteria by employing mechanisms divergent from traditional antibiotic resistance pathways and exhibiting reduced susceptibility to drug resistance development. Non-caloric artificial sweeteners, commonly utilized in the food sector, such as saccharin, sucralose, acesulfame, and aspartame, possess structures amenable to nanomaterial formation. In this investigation, we synthesized gold nanoparticles decorated with non-caloric artificial sweeteners and evaluated their antimicrobial efficacy against clinical CRE strains.

RESULTS

Among these, gold nanoparticles decorated with aspartame (ASP_Au NPs) exhibited the most potent antimicrobial effect, displaying minimum inhibitory concentrations ranging from 4 to 16 µg/mL. As a result, ASP_Au NPs were chosen for further experimentation. Elucidation of the antimicrobial mechanism unveiled that ASP_Au NPs substantially elevated bacterial reactive oxygen species (ROS) levels, which dissipated upon ROS scavenger treatment, indicating ROS accumulation within bacteria as the fundamental antimicrobial modality. Furthermore, findings from membrane permeability assessments suggested that ASP_Au NPs may represent a secondary antimicrobial modality via enhancing inner membrane permeability. In addition, experiments involving crystal violet and confocal live/dead staining demonstrated effective suppression of bacterial biofilm formation by ASP_Au NPs. Moreover, ASP_Au NPs demonstrated notable efficacy in the treatment of Galleria mellonella bacterial infection and acute abdominal infection in mice, concurrently mitigating the organism's inflammatory response. Crucially, evaluation of in vivo safety and biocompatibility established that ASP_Au NPs exhibited negligible toxicity at bactericidal concentrations.

CONCLUSIONS

Our results demonstrated that ASP_Au NPs exhibit promise as innovative antimicrobial agents against clinical CRE.

Progress and promise of alternative animal and non-animal methods in biomedical research

Cell culture and invertebrate animal models reflect a significant evolution in scientific research by providing reliable evidence on the physiopathology of diseases, screening for new drugs, and toxicological tests while reducing the need for mammals. In this review, we discuss the progress and promise of alternative animal and non-animal methods in biomedical research, with a special focus on drug toxicity.

Pseudomonas aeruginosa Nonphosphorylated AlgR Induces Ribonucleotide Reductase Expression under Oxidative Stress Infectious Conditions

Ribonucleotide reductases (RNRs) are key enzymes which catalyze the synthesis of deoxyribonucleotides, the monomers needed for DNA replication and repair. RNRs are classified into three classes (I, II, and III) depending on their overall structure and metal cofactors. Pseudomonas aeruginosa is an opportunistic pathogen which harbors all three RNR classes, increasing its metabolic versatility. During an infection, P. aeruginosa can form a biofilm to be protected from host immune defenses, such as the production of reactive oxygen species by macrophages. One of the essential transcription factors needed to regulate biofilm growth and other important metabolic pathways is AlgR. AlgR is part of a two-component system with FimS, a kinase that catalyzes its phosphorylation in response to external signals. Additionally, AlgR is part of the regulatory network of cell RNR regulation. In this study, we investigated the regulation of RNRs through AlgR under oxidative stress conditions. We determined that the nonphosphorylated form of AlgR is responsible for class I and II RNR induction after an H₂O₂ addition in planktonic culture and during flow biofilm growth. We observed similar RNR induction patterns upon comparing the P. aeruginosa laboratory strain PAO1 with different P. aeruginosa clinical isolates. Finally, we showed that during Galleria mellonella infection, when oxidative stress is high, AlgR is crucial for transcriptional induction of a class II RNR gene (nrdJ). Therefore, we show that the nonphosphorylated form of AlgR, in addition to being crucial for infection chronicity, regulates the RNR network in response to oxidative stress during infection and biofilm formation. IMPORTANCE The emergence of multidrug-resistant bacteria is a serious problem worldwide. Pseudomonas aeruginosa is a pathogen that causes severe infections because it can form a biofilm that protects it from immune system mechanisms such as the production of oxidative stress. Ribonucleotide reductases are essential enzymes which synthesize deoxyribonucleotides used in the replication of DNA. RNRs are classified into three classes (I, II, and III), and P. aeruginosa harbors all three of these classes, increasing its metabolic versatility. Transcription factors, such as AlgR, regulate the expression of RNRs. AlgR is involved in the RNR regulation network and regulates biofilm growth and other metabolic pathways. We determined that AlgR induces class I and II RNRs after an H₂O₂ addition in planktonic culture and biofilm growth. Additionally, we showed that a class II RNR is essential during Galleria mellonella infection and that AlgR regulates its induction. Class II RNRs could be considered excellent antibacterial targets to be explored to combat P. aeruginosa infections.

Lycopene, Mesoporous Silica Nanoparticles and Their Association: A Possible Alternative against Vulvovaginal Candidiasis?

Commonly found colonizing the human microbiota, Candida albicans is a microorganism known for its ability to cause infections, mainly in the vulvovaginal region known as vulvovaginal candidiasis (VVC). This pathology is, in fact, one of the main C. albicans clinical manifestations, changing from a colonizer to a pathogen. The increase in VVC cases and limited antifungal therapy make C. albicans an increasingly frequent risk in women's lives, especially in immunocompromised patients, pregnant women and the elderly. Therefore, it is necessary to develop new therapeutic options, especially those involving natural products associated with nanotechnology, such as lycopene and mesoporous silica nanoparticles. From this perspective, this study sought to assess whether lycopene, mesoporous silica nanoparticles and their combination would be an attractive product for the treatment of this serious disease through microbiological in vitro tests and acute toxicity tests in an alternative in vivo model of Galleria mellonella. Although they did not show desirable antifungal activity for VVC therapy, the present study strongly encourages the use of mesoporous silica nanoparticles impregnated with lycopene for the treatment of other human pathologies, since the products evaluated here did not show toxicity in the in vivo test performed, being therefore, a topic to be further explored.

Highly water-soluble dapsone nanocrystals: Towards innovative preparations for an undermined drug

Dapsone (DAP)is a dual-function drug substance; however, its limited water solubility may impair its bioavailability. Drug nanocrystals are an alternative to overcome this limitation. Herein, a DAP nanosuspension was prepared using adesign space approach aiming to investigate the influence of raw material properties and process parameters on the critical quality attributes of the drugnanocrystals. Optimized nanocrystals with 206.3 ± 6.7 nm using povacoat™ as stabilizer were made. The nanoparticles were characterized by dynamic light scattering, laser diffraction, scanning electron microscopy, differential scanning calorimetry, X-ray powder diffraction, and saturation solubility. Compared to the raw material, the nanocrystals were 250-times smaller. Meanwhile, its crystalline state remained basically unchanged even after milling and drying. The nanosuspension successfully maintained its physical stability inlong-termandaccelerated stability studiesover, 4 and 3 months. Furthermore, toxicity studiesshowed low a toxicity at a20 mg/kg. As expected for nanocrystals, the size reduction improvedsaturation solubility3.78 times in water. An attempt to scale up from lab to pilot scale resulted nanocrystals of potential commercial quality. In conclusion, the present study describes the development of dapsone nanocrystals for treating infectious and inflammatory diseases. The nanocrystal formuation can be scaled up for commercial use.

Development of a ternary cyclodextrin–arginine–ciprofloxacin antimicrobial complex with enhanced stability

Designing useful functionalities in clinically validated, old antibiotics holds promise to provide the most economical solution for the global lack of effective antibiotics, as undoubtedly a serious health threat. Here we show that using the surface chemistry of the cyclodextrin (βCD) cycle and arginine (arg) as a linker, provides more stable ternary antibiotic complex (βCD-arg-cpx). In contrast to classical less stable inclusion complexes, which only modify antibiotic solubility, here-presented ternary complex is more stable and controls drug release. The components of the complex intensify interactions with bacterial membranes and increase the drug’s availability inside bacterial cells, thereby improving its antimicrobial efficacy and safety profile. Multifunctional antibiotics, formulated as drug delivery systems per se, that take the drug to the site of action, maximize its efficacy, and provide optical detectability are envisaged as the future in fighting against infections. Their role as a tool against multiresistant strains remains as interesting challenge open for further research.

Antimicrobial Efficacy of Green Synthesized Nanosilver with Entrapped Cinnamaldehyde against Multi-Drug-Resistant Enteroaggregative Escherichia coli in Galleria mellonella

The global emergence of antimicrobial resistance (AMR) needs no emphasis. In this study, the in vitro stability, safety, and antimicrobial efficacy of nanosilver-entrapped cinnamaldehyde (AgC) against multi-drug-resistant (MDR) strains of enteroaggregative Escherichia coli (EAEC) were investigated. Further, the in vivo antibacterial efficacy of AgC against MDR-EAEC was also assessed in Galleria mellonella larval model. In brief, UV-Vis and Fourier transform infrared (FTIR) spectroscopy confirmed effective entrapment of cinnamaldehyde with nanosilver, and the loading efficiency was estimated to be 29.50 ± 0.56%. The AgC was of crystalline form as determined by the X-ray diffractogram with a mono-dispersed spherical morphology of 9.243 ± 1.83 nm in electron microscopy. AgC exhibited a minimum inhibitory concentration (MIC) of 0.008−0.016 mg/mL and a minimum bactericidal concentration (MBC) of 0.008−0.032 mg/mL against MDR- EAEC strains. Furthermore, AgC was stable (high-end temperatures, proteases, cationic salts, pH, and host sera) and tested safe for sheep erythrocytes as well as secondary cell lines (RAW 264.7 and HEp-2) with no negative effects on the commensal gut lactobacilli. in vitro, time-kill assays revealed that MBC levels of AgC could eliminate MDR-EAEC infection in 120 min. In G. mellonella larvae, AgC (MBC values) increased survival, decreased MDR-EAEC counts (p < 0.001), had an enhanced immunomodulatory effect, and was tested safe to the host. These findings infer that entrapment enhanced the efficacy of cinnamaldehyde and AgNPs, overcoming their limitations when used individually, indicating AgC as a promising alternative antimicrobial candidate. However, further investigation in appropriate animal models is required to declare its application against MDR pathogens.

Evaluation of Anti-Candida Potential of Piper nigrum Extract in Inhibiting Growth, Yeast-Hyphal Transition, Virulent Enzymes, and Biofilm Formation

Due to the increased incidence of fungal infections and the emergence of antifungal resistance mainly by Candida species, the need for safe and effective novel therapies is imperative. Consequently, plants and herbs are a powerful source to combat infections. Here, we evaluated the anti-Candida potential of an ethanolic extract from Piper nigrum. The phytochemical analysis of P. nigrum revealed bioactive compounds such as alkaloids, terpenoids, and tannis. Our results showed that P. nigrum extract suppressed the virulence factors of C. albicans strains, including hyphae formation in both liquid and solid media, reduced secretion of phospholipases/proteinases, and affected biofilm formation. Furthermore, the P. nigrum extract showed no hemolytic effect in vitro and exhibited reduced cytotoxicity on Vero cells and G. mellonella larvae at concentrations that inhibited hyphae and biofilm in C. albicans. Moreover, the extract demonstrated antifungal activity against C. auris strains. In conclusion, the P. nigrum extract affected the growth and morphogenesis of Candida (even in resistant strains), demonstrating that this plant has an anti-candida activity and represents a promising resource for discovering novel antifungal compounds.

Evaluation of the Antimicrobial Activity in Host-Mimicking Media and In Vivo Toxicity of Antimicrobial Polymers as Functional Mimics of AMPs

Activity tests for synthetic antimicrobial compounds are often limited to the minimal inhibitory concentration assay using standard media and bacterial strains. In this study, a family of acrylamide copolymers that act as synthetic mimics of antimicrobial peptides were synthesized and shown to have a disruptive effect on bacterial membranes and structural integrity through microscopy techniques and membrane polarization experiments. The polymers were tested for their antimicrobial properties using media that mimic clinically relevant conditions. Additionally, their activity was compared in two different strains of the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Pseudomonas aeruginosa. We showed that the medium composition can have an important influence on the polymer activity as there was a considerable reduction in minimal inhibitory concentrations against S. aureus grown in synthetic wound fluid (SWF), and against P. aeruginosa grown in synthetic cystic fibrosis sputum media (SCFM), compared to the concentrations in standard testing media. In contrast, we observed a complete loss of activity against P. aeruginosa in the serum-containing SWF. Finally, we made use of an emerging invertebrate in vivo model, using Galleria mellonella larvae, to assess toxicity of the polymeric antimicrobials, showing a good correlation with cell line toxicity measurements and demonstrating its potential in the evaluation of novel antimicrobial materials.

Musca domestica (Diptera: Muscidae) as a biological model for the assessment of magnetite nanoparticles toxicity

The use of nanoparticles (NPs) is rapidly expanding; there is a critical need for efficient assays to first determine the potential toxicity of NPs before their use in human applications. Magnetite nanoparticles (Fe₃O₄ NPs) have tremendous applications which include cell separation, arsenic removal from water and DNA separation. Spherically shaped Fe₃O₄ NPs with sizes ranging from 23 to 30 nm were used in this study. The housefly, Musca domestica is the most common fly species. It is present worldwide and considered to be an important medical insect which can carry and transmit over 100 human pathogens and zoonotic agents. It has been used in this study to assess Fe₃O₄NPs toxicity and give us an overview of their impact. The larvicidal activity of Fe₃O₄NPs was tested against the third instar larvae of M. domestica. We investigated the effects of six varying concentrations (15, 30, 45, 60, 75 and 90 μg/mL) used under laboratory conditions in two differential application assays: contact and feeding. The LC₅₀ value for Fe₃O₄ NPs was 60 and 75 μg/mL by feeding and contact, respectively. To investigate the toxicity effects of Fe₃O₄ NPs on houseflies, morphological and histoarchitectural changes in larvae, pupae and adult flies were analyzed. NP exposure caused morphological abnormalities of larvae and pupae as well as larval pupal intermediates, and deformed adult with crumpled wings. Also, some adults couldn't emerge and remained in their puparia. The histological examinations showed that Fe₃O₄ NPs caused severe tissue damage especially in the cuticle and the digestive system. Thus, besides affecting the organ of first contact (digestive system), remote organs such as the integument are also targeted by Fe₃O₄ NPs suggesting a systemic impact on fly development and physiology.

Effect of Gold Nanostars Plus Amikacin against Carbapenem-Resistant Klebsiella pneumoniae Biofilms

Simple Summary

Carbapenem-resistant Klebsiella pneumoniae (CR-KP) infection rates represent a challenging treatment since the pipeline for effective antibiotics against this pathogen, such as beta-lactams among others, is practically nil. This study aims to evaluate the antibacterial effect of gold nanostars (GNS) alone or associated with some of the most widely used antibiotics for the treatment of CR-KP strains, i.e., meropenem or amikacin, on both planktonic or free-living and sessile forms. GNS were able to inhibit the planktonic growth of CR-KP at 80 µM, to eradicate the bacterial viability at 160 µM, and were unable to inhibit or eradicate the biofilm growth of this bacterium. GNS gave rise to filamentous bacteria through mechanisms mediated by the inhibition of energy-dependent cytoplasmic proteases. The combination of GNS and amikacin was able to inhibit or even eradicate the CR-KP biofilm. This combination was administered to greater wax moth larvae (Galleria mellonella), and this treatment was found to be tolerated well and to prevent the CR-KP infection. Thus, GNS in combination with amikacin represent a promising anti-CR-KP nanomaterial.

Abstract

(1) Background: Carbapenem-resistant Klesiella pneumoniae (CR-KP) infection rates depict an almost pre-antibiotic scenario since the pipeline for effective antibiotics against this pathogen has been almost entirely depleted. This study aims to evaluate the antibacterial effect of gold nanostars (GNS) alone or associated with some of the most widely used antibiotics for the treatment of CR-KP strains, i.e., meropenem or amikacin, on both planktonic and sessile forms. Additionally, we measured the effect of GNS on cell proliferation and biocompatibility in invertebrate in vivo models. (2) Materials and methods: GNS were made from gold seeds grown using a seeded-growth surfactant-free method assisted by silver ions and functionalized with mercapto-poly(ethylene glycol)amino by ligand exchange. The antimicrobial capacity, effect on cell proliferation, and biocompatibility of the most effective combination was evaluated in a Galleria mellonella model. (3) Results: The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were 80 and 160 µM of GNS for all strains, respectively. The minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC) were >320 µM of GNS for both. A synergy was found between GNS and amikacin. Larvae administered GNS plus amikacin were found to tolerate the treatment well, which prevented infection. (4) Conclusions: GNS are a promising anti-CR-KP nanomaterial.

Comparative Investigation of Cellular Effects of Polyethylene Glycol (PEG) Derivatives

Nowadays, polyethylene glycols referred to as PEGs are widely used in cosmetics, consumer care products, and the pharmaceutical industry. Their advantageous properties such as chemical stability, low immunogenicity, and high tolerability explain why PEGs are applied in many fields of pharmaceutical formulations including parenteral, topical, ophthalmic, oral, and rectal preparations and also in modern drug delivery systems. Given their extensive use, they are considered a well-known group of chemicals. However, the number of large-scale comparative studies involving multiple PEGs of wide molecular weight range is low, as in most cases biological effects are estimated upon molecular weight. The aim of this publication was to study the action of PEGs on Caco-2 cells and G. mellonella larvae and to calculate the correlation of these effects with molecular weight and osmolality. Eleven PEGs of different molecular weight were used in our experiments: PEG 200, PEG 300, PEG 400, PEG 600, PEG 1000, PEG 1500, PEG 4000, PEG 8000, PEG 10,000, 12,000, and PEG 20,000. The investigated cellular effects included cytotoxicity (MTT and Neutral Red assays, flow cytometry with propidium iodide and annexin V) and autophagy. The osmolality of different molecular weight PEGs with various concentrations was measured by a vapor pressure osmometer OSMOMAT 070 and G. mellonella larvae were injected with the solutions of PEGs. Sorbitol was used as controls of the same osmolality. Statistical correlation was calculated to describe the average molecular weight dependence of the different measured effects. Osmolality, the cytotoxicity assays, flow cytometry data, and larvae mortality had significant correlation with the structure of the PEGs, while autophagosome formation and the proportion of early apoptotic cells showed no statistical correlation. Overall, it must be noted that PEGs must be tested individually for biological effects as not all effects can be estimated by the average molecular weight.

Zinc Oxide Nanoparticles Prime a Protective Immune Response in Galleria mellonella to Defend Against Candida albicans

Purpose: Zinc oxide nanoparticles (ZnO-NPs) have exerted antimicrobial properties. However, there is insufficient evaluation regarding the in vivo antifungal activity of ZnO-NPs. This study aimed to investigate the efficacy and mechanism of ZnO-NPs in controlling Candida albicans in the invertebrate Galleria mellonella. Methods: Galleria mellonella larvae were injected with different doses of ZnO-NPs to determine their in vivo toxicity. Non-toxic doses of ZnO-NPs were chosen for prophylactic injection in G. mellonella followed by C. albicans infection. Then the direct in vitro antifungal effect of ZnO-NPs against C. albicans was evaluated. In addition, the mode of action of ZnO-NPs was assessed in larvae through different assays: quantification of hemocyte density, morphology observation of hemocytes, characterization of hemocyte aggregation and phagocytosis, and measurement of hemolymph phenoloxidase (PO) activity. Results: Zinc oxide nanoparticles were non-toxic to the larvae at relatively low concentrations (≤20 mg/kg). ZnO-NP pretreatment significantly prolonged the survival of C. albicans-infected larvae and decreased the fungal dissemination and burden in the C. albicans-infected larvae. This observation was more related to the activation of host defense rather than their fungicidal capacities. Specifically, ZnO-NP treatment increased hemocyte density, promoted hemocyte aggregation, enhanced hemocyte phagocytosis, and activated PO activity in larvae. Conclusion: Prophylactic treatment with lower concentrations of ZnO-NPs protects G. mellonella from C. albicans infection. The innate immune response primed by ZnO-NPs may be part of the reason for the protective effects. This study provides new evidence of the capacity of ZnO-NPs in enhancing host immunity and predicts that ZnO-NPs will be attractive for further anti-infection applications.

Antimicrobial Activity of Nanoconjugated Glycopeptide Antibiotics and Their Effect on Staphylococcus aureus Biofilm

In the era of antimicrobial resistance, the use of nanoconjugated antibiotics is regarded as a promising approach for preventing and fighting infections caused by resistant bacteria, including those exacerbated by the formation of difficult-to-treat bacterial biofilms. Thanks to their biocompatibility and magnetic properties, iron oxide nanoparticles (IONPs) are particularly attractive as antibiotic carriers for the targeting therapy. IONPs can direct conjugated antibiotics to infection sites by the use of an external magnet, facilitating tissue penetration and disturbing biofilm formation. As a consequence of antibiotic localization, a decrease in its administration dosage might be possible, reducing the side effects to non-targeted organs and the risk of antibiotic resistance spread in the commensal microbiota. Here, we prepared nanoformulations of the 'last-resort' glycopeptides teicoplanin and vancomycin by conjugating them to IONPs via surface functionalization with (3-aminopropyl) triethoxysilane (APTES). These superparamagnetic NP-TEICO and NP-VANCO were chemically stable and NP-TEICO (better than NP-VANCO) conserved the typical spectrum of antimicrobial activity of glycopeptide antibiotics, being effective against a panel of staphylococci and enterococci, including clinical isolates and resistant strains. By a combination of different methodological approaches, we proved that NP-TEICO and, although to a lesser extent, NP-VANCO were effective in reducing biofilm formation by three methicillin-sensitive or resistant Staphylococcus aureus strains. Moreover, when attracted and concentrated by the action of an external magnet, NP-TEICO exerted a localized inhibitory effect on S. aureus biofilm formation at low antibiotic concentration. Finally, we proved that the conjugation of glycopeptide antibiotics to IONPs reduced their intrinsic cytotoxicity toward a human cell line.

Galleria mellonella (greater wax moth) as an eco-friendly in vivo approach for the assessment of the acute toxicity of medicinal plants: Application to some plants from Cameroon

Background:

The evaluation of medicinal plants’ toxicity is a prerequisite prior to their usage. The vertebrate models used for this purpose are often the object of ethical consideration. Though invertebrate models including Galleria mellonella (GM) have demonstrated the ability to be used to assess the toxicity of various products. To the authors’ knowledge, GM has never been exploited to determine the toxicity of medicinal plants.

Aim:

The aim of this study was to demonstrate the potential of GM larvae as a simple, inexpensive, and rapid model for the evaluation of the toxicity of herbal medicines.

Method:

In this study, the toxicity of aqueous and ethanolic (80%, v/v) extracts of seven well known plants from Cameroon namely leaves of Cymbopogon citratus (DC.) Stapf, Moringa oleifera Lam and Vernonia amygdalina Delile; barks of Cinchona officinalis and Enantia chlorantha Oliv; barks and seeds of Garcinia lucida Vesque and leaves and seeds of Azadirachta indica (Neem) was evaluated using the larval form of GM. The median lethal doses (LD₅₀), 90% (LD₉₀), and 100% (LD₁₀₀) were determined using the spline cubic survival curves and equations from the data obtained on the survival rate of GM 24 hours after the injection with the extracts.

Results:

We found that distilled water extracted a more important mass of phytochemical compounds (7.4%–21.2%) compared to ethanolic solution (5.8%–12.4%). LD varied depending on the plant materials and ethanolic extracts (hydroalcoholic extract, (HAE)) were more toxic to GM than aqueous ones. The LD₅₀ (mg/ml) of the tested extracts varied from 4.87 [3.90 g/kg body weight (bw)] to >200 (> 166.67 g/kg bw), the LD₉₀ (mg/ml) from 25.00 (18.52 g/kg bw) to >200 (> 181.82 g/kg bw) and LD₁₀₀ (mg/ml) from 45.00 (40.91 g/kg bw) to > 200 (>181.82 g/kg bw). The HAE of A. indica seed and C. officinalis bark exhibited the highest toxicity with LD₅₀ (g/kg bw) of 3.90 and 4.81, respectively.

Conclusion:

The results obtained in this study suggest that GM can be used as a sensitive, reliable, and robust eco-friendly model to gauge the toxicity of medicinal plants. Thus, avoid the sacrifice of vertebrate models often used for this purpose to limit ethical concerns.

Ecotoxicological effects of dietary titanium dioxide nanoparticles on metabolic and biochemical parameters of model organism Galleria mellonella (Lepidoptera: Pyralidae)

Nanoparticles (NPs) are now being used in many industrial activities, such as mining, paint and glass industries. The frequent industrial use of NPs contributes to environmental pollution and may cause cellular and oxidative damage in native organisms. In this study, the toxic effects of titanium dioxide nanoparticles (TiO₂ NPs) were investigated using Galleria mellonella larvae as a model insect species. Alterations in cell damage indicators, such as alanine transferase, aspartate transferase, lactate dehydrogenase, non-enzymatic antioxidants and biochemical parameters, were determined in the hemolymph of G. mellonella larvae exposed to TiO₂ NPs at different concentrations (5, 50, 250 and 1250 μg/mL) in their diets. TiO₂ NPs caused concentration-dependent cellular damage in the hemolymph of G. mellonella larvae and increased the levels of the non-enzymatic antioxidants uric acid and bilirubin. In addition, total protein in hemolymph significantly decreased at the highest concentration (1250 μg/mL) of TiO₂ NPs. Level of the urea increased at the highest concentration (1250 μg/mL) of TiO₂ NPs, whereas the amount of glucose was not affected. These findings demonstrated that TiO₂ NPs caused concentration-dependent toxic effects on G. mellonella larvae.

The diarrhetic shellfish-poisoning toxin, okadaic acid, provokes gastropathy, dysbiosis and susceptibility to bacterial infection in a non-rodent bioassay, Galleria mellonella

Diarrhetic shellfish-poisoning (DSP) toxins such as okadaic acid and dinophysistoxins harm the human gastrointestinal tract, and therefore, their levels are regulated to an upper limit of 160 μg per kg tissue to protect consumers. Rodents are used routinely for risk assessment and studies concerning mechanisms of toxicity, but there is a general move toward reducing and replacing vertebrates for these bioassays. We have adopted insect larvae of the wax moth Galleria mellonella as a surrogate toxicology model. We treated larvae with environmentally relevant doses of okadaic acid (80–400 μg/kg) via intrahaemocoelic injection or gavage to determine marine toxin-related health decline: (1) whether pre-exposure to a sub-lethal dose of toxin (80 μg/kg) enhances susceptibility to bacterial infection, or (2) alters tissue pathology and bacterial community (microbiome) composition of the midgut. A sub-lethal dose of okadaic acid (80 μg/kg) followed 24 h later by bacterial inoculation (2 × 10⁵Escherichia coli) reduced larval survival levels to 47%, when compared to toxin (90%) or microbial challenge (73%) alone. Histological analysis of the midgut depicted varying levels of tissue disruption, including nuclear aberrations associated with cell death (karyorrhexis, pyknosis), loss of organ architecture, and gross epithelial displacement into the lumen. Moreover, okadaic acid presence in the midgut coincided with a shift in the resident bacterial population over time in that substantial reductions in diversity (Shannon) and richness (Chao-1) indices were observed at 240 μg toxin per kg. Okadaic acid-induced deterioration of the insect alimentary canal resembles those changes reported for rodent bioassays.