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.

Phytochemistry, antifungal and antioxidant activity, and cytotoxicity of byrsonima gardneriana (A. Juss) extract

OBJECTIVE

To determine the phytochemical composition of Byrsonima gardneriana (A. Juss) leaf extract (BGE) and its antifungal activity against Candida spp., antioxidant potential and in vitro cytotoxicity.

MATERIAL AND METHODS

BGE was obtained and submitted to Gas Chromatography Coupled to Mass Spectrometry for phytochemical analysis. The ethanolic extract was tested for its antifungal activity against C. albicans and non-albicans reference strains and clinical isolates in addition to inhibition of C. albicans growth kinetics. It was also tested for antioxidant potential in the presence of phenylhydrazine and reactive oxygen species (ROS). And cytoxicity in human erythrocytes. The data were analyzed by one-way Analysis of Variance (ANOVA) followed by Tukey's or Dunnett's post-hoc test, with α = 0.05.

RESULTS

Pyroglutamic acid (90.77 %), eucalyptol (89.61 %) and octanoic acid (76.22 %) were the major compounds detected in BGE, P (%) is the percent probability of compound identification, according to the mass spectra library. The extract showed fungistatic activity, with MIC of 125 μg/mL against most tested strains. While BGE showed low hemolytic activity on all blood types tested herein, it could not prevent osmotic stress in human erythrocytes. The extract did not have oxidizing effects in the presence of phenylhydrazine, but it showed antioxidant potential against ROS when tested at 31 μg/mL and 62 μg/mL.

CONCLUSION

B. gardneriana extract showed antifungal activity against Candida spp., demonstrated low hemolytic potential, no oxidant activity in human erythrocytes and antioxidant activity against ROS. This study opens avenues for the study of BGE as a promising biocompatible antifungal agent.

Fusogenic Liposomes Increase the Antimicrobial Activity of Vancomycin Against Staphylococcus aureus Biofilm

Objective: The aim of the present study was to encapsulate vancomycin in different liposomal formulations and compare the in vitro antimicrobial activity against Staphylococcus aureus biofilms.

Methods: Large unilamellar vesicles of conventional (LUV VAN), fusogenic (LUV_fuso VAN), and cationic (LUV_cat VAN) liposomes encapsulating VAN were characterized in terms of size, polydispersity index, zeta potential, morphology, encapsulation efficiency (%EE) and in vitro release kinetics. The formulations were tested for their Minimum Inhibitory Concentration (MIC) and inhibitory activity on biofilm formation and viability, using methicillin-susceptible S. aureus ATCC 29213 and methicillin-resistant S. aureus ATCC 43300 strains.

Key Findings: LUV VAN showed better %EE (32.5%) and sustained release than LUV_fuso VAN, LUV_cat VAN, and free VAN. The formulations were stable over 180 days at 4°C, except for LUV VAN, which was stable up to 120 days. The MIC values for liposomal formulations and free VAN ranged from 0.78 to 1.56 µg/ml against both tested strains, with no difference in the inhibition of biofilm formation as compared to free VAN. However, when treating mature biofilm, encapsulated LUV_fuso VAN increased the antimicrobial efficacy as compared to the other liposomal formulations and to free VAN, demonstrating a better ability to penetrate the biofilm.

Conclusion: Vancomycin encapsulated in fusogenic liposomes demonstrated enhanced antimicrobial activity against mature S. aureus biofilms.

Antifungal Activity, Mode of Action, Docking Prediction and Anti-biofilm Effects of (+)-β-pinene Enantiomers against Candida spp

AIMS

The objective of this study was to investigate the effectiveness of (+)-β-pinene inhibition on Candida spp. growth, aiming at elucidation of the mechanism of action; to determine fungal cell enzyme binding activity (through molecular docking simulations) and its effects on biofilm reduction.

METHODS

Candida strains (n=25) from referenced and clinical origins, either susceptible or resistant to standard clinical antifungals, were tested for determination of Minimum Inhibitory Concentration (MIC); Minimum Fungicidal Concentration (MFC); and microbial death curves upon treatment with (+)-β-pinene; the effects of (+)-β-pinene on the cell wall (sorbitol assay), membrane ergosterol binding, and effects on biofilm were evaluated by microdilution techniques. We also evaluated the interactions between (+)-β-pinene and cell wall and membrane enzymes of interest.

RESULTS

The MIC values of (+)-β-pinene ranged from <56.25 to 1800 µmol/L. The MIC of (+)-β-pinene did not increase when ergosterol was added to the medium, however it did increase in the presence of sorbitol, leading to a doubled MIC for C. tropicalis and C. krusei. The results of the molecular docking simulations indicated better interaction with delta-14-sterol reductase (-51 kcal/mol). (+)-β-pinene presents anti-biofilm activity against multiples species of Candida.

CONCLUSION

(+)-β-pinene has antifungal activity and most likely acts through interference with the cell wall; through molecular interaction with Delta-14-sterol reductase and, to a lesser extent, with the 1,3-β- glucan synthase. This molecule was also found to effectively reduce Candida biofilm adhesion.

Anadenanthera Colubrina vell Brenan: anti-Candida and antibiofilm activities, toxicity and therapeutical action

We evaluated the antifungal and antibiofilm potential of the hydroalcoholic extract of bark from Anadenanthera colubrina (vell.) Brenan, known as Angico, against Candida spp. Antifungal activity was evaluated using the microdilution technique through the Minimum Inhibitory and Fungicide Concentrations (MIC and MFC). The antibiofilm potential was tested in mature biofilms formed by Candida species and analyzed through the counting of CFU/mL and scanning electron micrograph (SEM). In vivo toxicity and therapeutic action was evaluated in the Galleria mellonella model. The treatment with the extract, in low doses, was able to reduce the growth of planktonic cells of Candida species. MIC values range between 19.5 and 39 µg/mL and MFC values range between 79 and 625 µg/mL. In addition was able to reduce the number of CFU/mL in biofilms and to cause structural alteration and cellular destruction, observed via SEM. A. colubrina showed low toxicity in the in vivo assay, having not affected the viability of the larvae at doses below 100mg/kg and high potential in the treatment of C. albicans infection. Considering its high antifungal potential, its low toxicity and potential to treatment of infections in in vivo model, A. colubrina extract is a strong candidate for development of a new agent for the treatment of oral candidiasis.

Diacetylcurcumin: a new photosensitizer for antimicrobial photodynamic therapy in Streptococcus mutans biofilms

This study evaluated the effect of antimicrobial photodynamic therapy (aPDT) on S. mutans using diacetylcurcumin (DAC) and verified DAC toxicity. In vitro, S. mutans biofilms were exposed to curcumin (CUR) and DAC and were light-irradiated. Biofilms were collected, plated and incubated for colony counts. DAC and CUR toxicity assays were conducted with Human Gingival Fibroblast cells (HGF). In vivo, G. mellonella larvae were injected with S. mutans and treated with DAC, CUR and aPDT. The hemolymph was plated and incubated for colony counts. Significant reductions were observed when DAC and CUR alone were used and when aPDT was applied. HGF assays demonstrated no differences in cell viability for most groups. DAC and CUR reduced the S. mutans load in G. mellonella larvae both alone and with aPDT. Systematic toxicity assays on G. mellonella demonstrated no effect of DAC and CUR or aPDT on the survival curve.

The Biology of Streptococcus mutans

As a major etiological agent of human dental caries, Streptococcus mutans resides primarily in biofilms that form on the tooth surfaces, also known as dental plaque. In addition to caries, S. mutans is responsible for cases of infective endocarditis with a subset of strains being indirectly implicated with the onset of additional extraoral pathologies. During the past 4 decades, functional studies of S. mutans have focused on understanding the molecular mechanisms the organism employs to form robust biofilms on tooth surfaces, to rapidly metabolize a wide variety of carbohydrates obtained from the host diet, and to survive numerous (and frequent) environmental challenges encountered in oral biofilms. In these areas of research, S. mutans has served as a model organism for ground-breaking new discoveries that have, at times, challenged long-standing dogmas based on bacterial paradigms such as Escherichia coli and Bacillus subtilis. In addition to sections dedicated to carbohydrate metabolism, biofilm formation, and stress responses, this article discusses newer developments in S. mutans biology research, namely, how S. mutans interspecies and cross-kingdom interactions dictate the development and pathogenic potential of oral biofilms and how next-generation sequencing technologies have led to a much better understanding of the physiology and diversity of S. mutans as a species.

In silico approaches for screening molecular targets in Candida albicans: A proteomic insight into drug discovery and development

Candida species are opportunistic pathogens which can cause conditions ranging from simple mucocutaneous infections to fungemia and death in immunosuppressed and hospitalized patients. Candida albicans is considered to be the species mostly associated with fungal infections in humans and, therefore, the mostly studied yeast. This microorganism has survival and virulence factors which, allied to a decreased host immunity response, make infection more difficult to control. Today, the current limited antifungal arsenal and a dramatic increase in fungal resistance have driven the need for the synthesis of drugs with novel mechanisms of action. However, the development of a new drug from discovery to marketing takes a long time and is highly costly. The objective of this review is to show that with advances in biotechnology and biofinformatics, in silico tools such as molecular docking can optimize such a timeline and reduce costs, while contributing to the design and development of targeted drugs. Here we highlight the most promising protein targets in Candida albicans for the development of drugs with new mechanisms of action.

Whole genome sequence and phenotypic characterization of a Cbm+ serotype e strain of Streptococcus mutans

We report the whole genome sequence of the serotype e Cbm⁺ strain LAR01 of Streptococcus mutans, a dental pathogen frequently associated with extra-oral infections. The LAR01 genome is a single circular chromosome of 2.1 Mb with a GC content of 36.96%. The genome contains 15 phosphotransferase system gene clusters, seven cell wall-anchored (LPxTG) proteins, all genes required for the development of natural competence and genes coding for mutacins VI and K8. Interestingly, the cbm gene is genetically linked to a putative type VII secretion system that has been found in Mycobacteria and few other Gram-positive bacteria. When compared with the UA159 type strain, phenotypic characterization of LAR01 revealed increased biofilm formation in the presence of either glucose or sucrose but similar abilities to withstand acid and oxidative stresses. LAR01 was unable to inhibit the growth of Strpetococcus gordonii, which is consistent with the genomic data that indicate absence of mutacins that can kill mitis streptococci. On the other hand, LAR01 effectively inhibited growth of other S. mutans strains, suggesting that it may be specialized to outcompete strains from its own species. In vitro and in vivo studies using mutational and heterologous expression approaches revealed that Cbm is a virulence factor of S. mutans by mediating binding to extracellular matrix proteins and intracellular invasion. Collectively, the whole genome sequence analysis and phenotypic characterization of LAR01 provides new insights on the virulence properties of S. mutans and grants further opportunities to understand the genomic fluidity of this important human pathogen.

Isoflavonoids from Brazilian red propolis down-regulate the expression of cancer-related target proteins: A pharmacogenomic analysis

Vestitol and neovestitol are bioactive isoflavonoids isolated from Brazilian red propolis, a unique Apis melifera type of propolis botanically originated from Dalbergia ecastophyllum. Although these molecules have relevant biological effects, including anticancer and immunomodulatory activities, their mechanism(s) of action and the affected pathways remain largely unknown. Here, we carried out a pharmacogenomic analysis to investigate the effects of vestitol and neovestitol on the whole-genome expression in human tumor cells, particularly cancer-related target proteins. HeLa cells were exposed to the compounds at IC₂₀ and genomic information of treated cells was analyzed using the Illumina transcriptome system and GeneGo MetaCore software. Our results showed that vestitol (IC₂₀  = 214.7 μM) reduced the expression of genes enrolled with the alpha tubulin (fold -3.7), tubulin in microtubules (fold -3.7), and histone h3 (fold = -3.03), and that treatment with neovestitol (IC₂₀  = 102.91 μM) downregulated prostaglandin E synthase gene (fold = -3.12), which are considered ideal targets for anticancer therapy. These data open avenues for the study of vestitol and neovestitol as potential promising candidates for anticancer therapy. Toxicological, non-clinical, and clinical validation of the findings presented herein is needed.

Ex vivo Model of Human Aortic Valve Bacterial Colonization

The interaction of pathogens with host tissues is a key step towards successful colonization and establishment of an infection. During bacteremia, pathogens can virtually reach all organs in the human body (e.g., heart, kidney, spleen) but host immunity, blood flow and tissue integrity generally prevents bacterial colonization. Yet, patients with cardiac conditions (e.g., congenital heart disease, atherosclerosis, calcific aortic stenosis, prosthetic valve recipients) are at a higher risk of bacterial infection. This protocol was adapted from an established ex vivo porcine heart adhesion model and takes advantage of the availability of heart tissues obtained from patients that underwent aortic valve replacement surgery. In this protocol, fresh tissues are used to assess the direct interaction of bacterial pathogens associated with cardiovascular infections, such as the oral bacterium Streptococcus mutans, with human aortic valve tissues.

Alternative Animal and Non-Animal Models for Drug Discovery and Development: Bonus or Burden?

Mammalian models have served as a basis for R&D over the past decades. Nevertheless, these models are expensive, laborious, may yield results that cannot always be translated into the human in vivo situation and, more recently, have reverberated great social and ethical dilemmas. Hence, the prospect of changes in the global scientific scenario and the Three Rs principle (Reduction, Replacement and Refinement) have encouraged the development of alternative methods to the use of mammals. Despite the efforts, suitable alternative tests are not available in all areas of biomedical research, as regulatory acceptance requires time, prior validation and robust financial and scientific investment. In this perspective, we aim to shed light on the concepts, challenges and perspectives for implementation of innovative alternative animal and non-animal methods in scientific research. The applicability and meaningfulness of invertebrate animal models, in silico analysis and reverse pharmacology are discussed, among other aspects of relevance in today's scenario. Overall, the use of alternative models, including Artemia salina (brine shrimp), Caenorhabditis elegans (roundworm), Danio rerio (zebra fish), Drosophila melanogaster (fruit fly), Galleria mellonella (greater waxmoth) and in silico modelling, increased 909% from 1990 to 2015, as compared to 154% of conventional mammals in the same period. Thus, technological and scientific advancements in the fields of toxicology and drug development seem to have diminished the need for mammalian models. Today, however, mammals still remain critically indispensable to provide - in most cases -reliable data subsidizing and validating translation into the clinical setting.

Antifungal activity, mode of action and anti-biofilm effects of Laurus nobilis Linnaeus essential oil against Candida spp

OBJECTIVE

The present study demonstrated the antifungal potential of the chemically characterized essential oil (EO) of Laurus nobilis L. (bay laurel) against Candida spp. biofilm adhesion and formation, and further established its mode of action on C. albicans.

METHODS

L. nobilis EO was obtained and tested for its minimum inhibitory and fungicidal concentrations (MIC/MFC) against Candida spp., as well as for interaction with cell wall biosynthesis and membrane ionic permeability. Then we evaluated its effects on the adhesion, formation, and reduction of 48hC. albicans biofilms. The EO phytochemical profile was determined by gas chromatography coupled to mass spectrometry (GC/MS).

RESULTS

The MIC and MFC values of the EO ranged from (250 to 500) μg/mL. The MIC values increased in the presence of sorbitol (osmotic protector) and ergosterol, which indicates that the EO may affect cell wall biosynthesis and membrane ionic permeability, respectively. At 2 MIC the EO disrupted initial adhesion of C. albicans biofilms (p<0.05) and affected biofilm formation with no difference compared to nystatin (p>0.05). When applied for 1min, every 8h, for 24h and 48h, the EO reduced the amount of C. albicans mature biofilm with no difference in relation to nystatin (p>0.05). The phytochemical analysis identified isoeugenol as the major compound (53.49%) in the sample.

CONCLUSIONS

L. nobilis EO has antifungal activity probably due to monoterpenes and sesquiterpenes in its composition. This EO may affect cell wall biosynthesis and membrane permeability, and showed deleterious effects against C. albicans biofilms.

Antifungal potential of Sideroxylon obtusifolium and Syzygium cumini and their mode of action against Candida albicans

Context The emergence of resistant pathogens and toxicity of antifungals have encouraged an active search for novel candidates to manage Candida biofilms. Objective In this study, the little known species Sideroxylon obtusifolium T.D. Penn (Sapotacea) and Syzygium cumini (L.) Skeels (Myrtaceae), from the Caatinga biome in Brazil were chemically characterized and explored for their antifungal potential against C. albicans. Materials and methods We determined the effects of hydroalcoholic extracts/fractions upon fungal growth (minimum inhibitory and fungicidal concentrations, MIC/MFC), biofilm morphology (scanning electron microscopy) and viability (confocal laser scanning microscopy), proposed their mode of action (sorbitol and ergosterol assays), and finally investigated their effects against macrophage and keratinocyte cells in a cell-based assay. Data were analysed using one-way analysis of variance with Tukey-Kramer post-test (α = 0.05). Results The n-butanol (Nb) fraction from S. obtusifolium and S. cumini extract (Sc) showed flavonoids (39.11 ± 6.62 mg/g) and saponins (820.35 ± 225.38 mg/g), respectively, in their chemical composition and demonstrated antifungal activity, with MICs of 62.5 and 125 μg/mL, respectively. Nb and Sc may complex with ergosterol as there was a 4-16-fold increase in MICs in the presence of exogenous ergosterol, leading to disrupted permeability of cell membrane. Deleterious effects were observed on morphology and viability of treated biofilms from concentrations as low as their MICs and higher. Sc was not toxic to macrophages and keratinocytes at these concentrations (p > 0.05), unlike Nb. Conclusions Nb and Sc demonstrated considerable antifungal activity and should be further investigated as potential alternative candidates to treat Candida biofilms.

Eugenia uniflora Dentifrice for Treating Gingivitis in Children: Antibacterial Assay and Randomized Clinical Trial

Abstract School-age children are frequently at high risk for the onset of biofilm-dependent conditions, including dental caries and periodontal diseases. The objective of this study was to evaluate the clinical efficacy of a dentifrice containing Eugenia uniflora Linn. (Surinam cherry) extract versus a triclosan-based comparator in treating gingivitis in children aged 10-12 years. The in vitro antibacterial potential of the dentifrice was tested against oral pathogens (Streptococcus mutans, Streptococcus oralis and Lactobacillus casei). Then a phase-II clinical trial was conducted with 50 subjects aged 10-12 years, with clinical signs of gingivitis. The subjects were randomly assigned to the experimental group (n=25) and control group (n=25), in which participants used the experimental dentifrice and a triclosan-based fluoridated dentifrice (Colgate Total 12(r)), respectively. Clinical examinations assessed the presence of gingivitis (primary outcome) and biofilm accumulation (secondary outcome) using the Gingival-Bleeding Index (GBI) and Simplified Oral Hygiene Index (OHI-S), respectively, at baseline and after seven days of tooth brushing 3x/day. The data were analyzed using paired and unpaired t-test (GBI) and Wilcoxon and Mann-Whitney (OHI-S), with p≤0.05. The experimental dentifrice showed efficient antibacterial activity in vitro. In the clinical trial, a significant reduction in gingival bleeding was observed in both experimental and control groups (p<0.0001), with no statistical difference between them (p=0.178), although a small size effect was observed. Biofilm accumulation was only reduced in the control group (p=0.0039). In conclusion, E. uniflora dentifrice showed anti-gingivitis properties in children aged 10-12 years. Thus, it may be a potentially efficient and safe product to be used alternatively in preventive dental practice

How Natural Product Research has Contributed to Oral Care Product Development? A Critical View

PURPOSES

Despite the high number of studies on the biological effects of natural products (NP) and molecules isolated therefrom, only a small part of them reach the clinical phase and become commercially available. In this perspective we make an analysis on how plant research has impacted oral health care over the last 15 years.

METHODS

Sixteen major clinical trial registry databases across the globe were searched for completed randomized clinical trials of herbal/natural product interventions (RCTHI) in theperiod 2000-2015.

RESULTS

There was a considerable increase in the number of RCTHI, which points out an interest of academia and industry in the development of novel NP-based therapeutics. There is a trendfor greater heterogeneity of targeted dental conditions, mostly oral mucositis, periodontitis and dental caries. Topical application rather than systemic use predominated in the dental scope as mouthwashes, toothpastes, oral patches and gels have been the most commonly tested pharmaceutical forms. Today, despite the high number of in vitro, in vivo and clinical studies testing NP and/or NP-isolated molecules, only 11% (n = 9) of them are phase IV clinical trials assessing commercially available herbal products. This may be a result of poorly designed, superficial basic research that does not provide evidence to support the clinical testing of NP and derived molecules.

CONCLUSION

As of now, plant research is promising although still accounts for a modest participation in the oral health care industry due to limited investment and incomplete or inconsistent information from preclinical and clinical testing.

Chemical composition and antifungal potential of Brazilian propolis against Candida spp

Propolis is known to have biological properties against numerous microorganisms of clinical interest. This study aimed to determine the chemical composition and antifungal activity of Brazilian propolis (types 3 and 13) against Candida spp. and their effects on the morphology of preformed and mature Candida biofilms. Samples of propolis (3 and 13) collected by Apis mellifera honeybees were obtained from different regions in Brazil. Ethanolic extracts of propolis (EEP) were prepared, fractionated and submitted to chemical analysis by GC/MS. The extracts and their hexane, dichloromethane and ethyl acetate fractions were tested for their ability to inhibit Candida spp. (C. albicans, C. dubliniensis, C. glabrata, C. kruzei, C. tropicalis and C. parapsilosis) by determination of the minimum inhibitory and fungicidal concentrations (MIC/MFC). Additionally, their effects on morphology of preformed and mature biofilms were observed by scanning electron microscopy. The phenolic compounds p-coumaric acid, caffeic acid phenethyl ester (CAPE), kaempferol and quercetin were identified in the EEP-3 and its bioactive dichloromethane fraction; and isoflavonoids such as medicarpin, vestitol and formononetin were found in the EEP-13, and triterpenes in its bioactive hexane fraction. The EEP-3 and EEP-13 and their bioactive fractions showed MIC values ranging from 0.2 to 125μg/mL and MFC values between 125 and 500μg/mL. The EEP and fractions were predominantly fungistatic agents. All extracts and fractions disrupted biofilm structures at 500μg/mL and amorphous areas with cell damage were clearly observed in preformed and mature biofilms. Propolis types 3 and 13 have strong anti-Candida activity and should be considered as promising candidates to treat oral and systemic candidiasis.

Antibacterial Activity of Essential Oils and Their Isolated Constituents against Cariogenic Bacteria: A Systematic Review

Dental caries remains the most prevalent and costly oral infectious disease worldwide. Several methods have been employed to prevent this biofilm-dependent disease, including the use of essential oils (EOs). In this systematic review, we discuss the antibacterial activity of EOs and their isolated constituents in view of a potential applicability in novel dental formulations. Seven databases were systematically searched for clinical trials, in situ, in vivo and in vitro studies addressing the topic published up to date. Most of the knowledge in the literature is based on in vitro studies assessing the effects of EOs on caries-related streptococci (mainly Streptococcus mutans) and lactobacilli, and on a limited number of clinical trials. The most promising species with antibacterial potential against cariogenic bacteria are: Achillea ligustica, Baccharis dracunculifolia, Croton cajucara, Cryptomeria japonica, Coriandrum sativum, Eugenia caryophyllata, Lippia sidoides, Ocimum americanum, and Rosmarinus officinalis. In some cases, the major phytochemical compounds determine the biological properties of EOs. Menthol and eugenol were considered outstanding compounds demonstrating an antibacterial potential. Only L. sidoides mouthwash (1%) has shown clinical antimicrobial effects against oral pathogens thus far. This review suggests avenues for further non-clinical and clinical studies with the most promising EOs and their isolated constituents bioprospected worldwide.