Antifolates inhibit Cryptococcus biofilms and enhance susceptibility of planktonic cells to amphotericin B

Naphthylthiazoles: a class of broad-spectrum antifungals

Cryptococcal infections remain a major cause of mortality worldwide due to the ability of Cryptococci to pass through the blood-brain barrier (BBB) causing lethal meningitis. The limited number of available therapeutics, which exhibit limited availability, severe toxicity and low tolerability, necessitates the development of new therapeutics. Investigating the antifungal activity of a novel series of naphthylthiazoles provided trans-diaminocyclohexyl derivative 18 with many advantageous attributes as a potential therapeutic for cryptococcal meningitis. Briefly, the antimycotic activity of 18 against cryptococcal strains was highly comparable to that of amphotericin-B and fluconazole with MIC values as low as 1 μg mL-1. Moreover, compound 18 possessed additional advantages over fluconazole; it significantly reduced the intracellular burden of Cryptococci and markedly inhibited cryptococcal biofilm formation. Initial PK assessment of 18 indicated its ability to reach the CNS after oral administration with high permeability, and it maintained therapeutic plasma concentrations for 18 h. Its antifungal activity extended to other clinically relevant strains, such as fluconazole-resistant C. auris.

Combating increased antifungal drug resistance in Cryptococcus, what should we do in the future?

Few therapeutic drugs and increased drug resistance have aggravated the current treatment difficulties of Cryptococcus in recent years. To better understand the antifungal drug resistance mechanism and treatment strategy of cryptococcosis. In this review, by combining the fundamental features of Cryptococcus reproduction leading to changes in its genome, we review recent research into the mechanism of four current anti-cryptococcal agents, coupled with new therapeutic strategies and the application of advanced technologies WGS and CRISPR-Cas9 in this field, hoping to provide a broad idea for the future clinical therapy of cryptococcosis.

The positive effect of malaria IPTp-SP on birthweight is mediated by gestational weight gain but modifiable by maternal carriage of enteric pathogens

BACKGROUND

Poor pregnancy and birth outcomes are common in sub-Saharan Africa and have complex aetiologies. Sulfadoxine-pyrimethamine (SP), given for intermittent preventive therapy of malaria in pregnancy (IPTp), is one of few existing interventions that improves outcomes of both mother and baby despite widespread SP-resistant malaria. Compelling evidence exists that malaria-independent pathways contribute to this protective effect, but the exact sources of non anti-malarial protection remained unknown. We hypothesized that the beneficial effect of SP on birthweight is mediated by SP activity on maternal factors, including increased gestational weight gain and antibiotic activity on pathogens in the maternal gut.

METHODS

Expectant mothers from a larger randomized control trial comparing the efficacy of IPTp-SP to IPTp with dihydroartemisinin-piperaquine (DP) were also enrolled in this sub-study study at their first antenatal care visit before commencement of IPTp (n = 105). Participants were followed monthly until delivery. Weights and mid-to-upper-arm circumferences (MUAC) were recorded. Monthly stool samples were collected and screened for five Escherichia coli pathotypes, Shigella spp., Vibrio cholerae, Salmonella, Campylobacter coli/jejuni, and three protozoa (Giardia spp., Entameba histolytica, and Cryptosporidium spp.) using previously validated molecular assays.

FINDINGS

IPTp-SP vs. IPTP-DP was associated with higher maternal gestational weight gain (GWG) and nutritional indicators (MUAC and body-mass index, BMI). GWG was found to be a mediator of the birthweight and IPTp-SP relationship, as the birthweight of SP infants, but not DP infants, varied according to maternal GWG. The burden of maternal enteric infections was high. The three most commonly observed pathogens were enteroaggregative E. coli (EAEC), atypical enteropathogenic E.coli/enterohaemorrhagic E. coli (aEPEC/EHEC), and typical enteropathogenic E.coli (tEPEC). We found that SP reduced the prevalence of EAEC in a dose-dependent manner. After 3 or more doses, SP-recipients were 90% less likely to be infected with EAEC compared to DP-recipients (ORadj = 0.07, CI95 = 0.12, 0.39, p = 0.002). Compared to DP, this coincided with higher maternal gestational weight gain (GWG) and nutritional indicators (MUAC and body-mass index, BMI). The beneficial effect of SP on maternal GWG, MUAC and BMI, was lower if SP mothers had detectable EAEC, aEPEC/EHEC, tEPEC, and LT-ETEC at baseline. Maternal EAEC and tEPEC at baseline associated with lower birthweight for babies of both SP mothers and DP mothers. When comparing IPTp regimens, the positive effect of SP on birthweight compared to DP was only observed for infants of women who did not test positive for EAEC at baseline (adjusted mean birthweight difference SP vs. DP = 156.0 g, CI95 = -18.0 g, 336.9 g, p = 0.087), though confidence intervals crossed the null.

INTERPRETATION

Our findings indicate that in pregnant Malawian women, IPTp-SP vs. IPTp-DP is consistently associated with higher MUAC, BMI, and GWG following the WHO-recommended regimen of at least 3 doses, but carriage of maternal gut pathogens before initiation of IPTp lessens this effect. Because GWG was a mediator of the association between birthweight and SP, we show that SP's previously proven positive effect on birthweight is by promoting maternal weight gain. Overall, our results present one plausible pathway SP exerts malaria-independent protection against poor birth outcomes in the context of its waning antimalarial activity and warrants further investigation.

FUNDING

A full list of funding bodies that contributed to this study can be found in the Acknowledgements section.

The role of Cryptococcus neoformans histone deacetylase genes in the response to antifungal drugs, epigenetic modulators and to photodynamic therapy mediated by an aluminium phthalocyanine chloride nanoemulsion in vitro

Cryptococcus is a globally distributed fungal pathogen that primarily afflicts immunocompromised individuals. The therapeutic options are limited and include mostly amphotericin B or fluconazole, alone or in combination. The extensive usage of antifungals allowed the selection of resistant pathogens posing threats to global public health. Histone deacetylase genes are involved in Cryptococcus virulence, and in pathogenicity and resistance to azoles in Candida albicans. Aiming to assess whether histone deacetylase genes are involved in antifungal response and in synergistic drug interactions, we evaluated the activity of amphotericin B, fluconazole, sulfamethoxazole, sodium butyrate or trichostatin A (histone deacetylase inhibitors), and hydralazine or 5- aza-2'-deoxycytidine (DNA methyl-transferase inhibitors) against different Cryptococcus neoformans strains, C. neoformans histone deacetylase null mutants and Cryptococcus gattii NIH198. The drugs were employed alone or in different combinations. Fungal growth after photodynamic therapy mediated by an aluminium phthalocyanine chloride nanoemulsion, alone or in combination with the aforementioned drugs, was assessed for the C. neoformans HDAC null mutant strains. Our results showed that fluconazole was synergistic with sodium butyrate or with trichostatin A for the hda1Δ/hos2Δ double mutant strain. Sulfamethoxazole was synergistic with sodium butyrate or with hydralazine also for hda1Δ/hos2Δ. These results clearly indicate a link between HDAC impairment and drug sensitivity. Photodynamic therapy efficacy on controlling the growth of the HDAC mutant strains was increased by amphotericin B, fluconazole, sodium butyrate or hydralazine. This is the first study in Cryptococcus highlighting the combined effects of antifungal drugs, histone deacetylase or DNA methyltransferase inhibitors and photodynamic therapy in vitro.

Alternative treatment of fungal infections: Synergy with non-antifungal agents

Fungal infections are responsible for high mortality rates in immunocompromised and high-risk surgical patients. Therapy failures during the last decades due to increasing multidrug resistance demand innovative strategies for novel and effective antifungal drugs. Synergistic combinations of antifungals with non-antifungal agents highlight a pragmatic strategy to reduce the development of drug resistance and potentially repurpose known compounds with other functions to bypass costly and time-consuming novel drug development.

Metabolomic analysis of low and high biofilm-forming Helicobacter pylori strains

The biofilm-forming-capability of Helicobacter pylori has been suggested to be among factors influencing treatment outcome. However, H. pylori exhibit strain-to-strain differences in biofilm-forming-capability. Metabolomics enables the inference of spatial and temporal changes of metabolic activities during biofilm formation. Our study seeks to examine the differences in metabolome of low and high biofilm-formers using the metabolomic approach. Eight H. pylori clinical strains with different biofilm-forming-capability were chosen for metabolomic analysis. Bacterial metabolites were extracted using Bligh and Dyer method and analyzed by Liquid Chromatography/Quadrupole Time-of-Flight mass spectrometry. The data was processed and analyzed using the MassHunter Qualitative Analysis and the Mass Profiler Professional programs. Based on global metabolomic profiles, low and high biofilm-formers presented as two distinctly different groups. Interestingly, low-biofilm-formers produced more metabolites than high-biofilm-formers. Further analysis was performed to identify metabolites that differed significantly (p-value < 0.005) between low and high biofilm-formers. These metabolites include major categories of lipids and metabolites involve in prostaglandin and folate metabolism. Our findings suggest that biofilm formation in H. pylori is complex and probably driven by the bacterium’ endogenous metabolism. Understanding the underlying metabolic differences between low and high biofilm-formers may enhance our current understanding of pathogenesis, extragastric survival and transmission of H. pylori infections.

Activity of 3'-hydroxychalcone against Cryptococcus gattii and toxicity, and efficacy in alternative animal models

AIM

This work aimed to evaluate the activity of 3'-hydroxychalcone against Cryptococcus gattii in planktonic and biofilm forms and their toxicity using alternative animal models.

MATERIALS & METHODS

Minimum inhibitory concentration and minimum fungicide concentration were determined. Biofilm formation and the susceptibility tests were performed by the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-5-[carbonyl(phenylamino)]-2H-tetrazolium hydroxide assay. Toxicity and efficacy were checked in Danio rerio and Galleria mellonella models.

RESULTS

The compound 3'-hydroxychalcone showed fungicidal activity against C. gattii in both planktonic and biofilm forms. The toxicity in zebrafish embryos revealed a low lethal concentration. In G. mellonella, the compound did not show antifungal activity and larvae toxicity.

CONCLUSION

Because of the activity of 3'-hydroxychalcone against C. gattii in vitro, molecular modifications should be made to improve efficacy and to reduce toxicity in vivo. [Formula: see text].

Biofilm Formation by Cryptococcus neoformans

The fungus Cryptococcus neoformans possesses a polysaccharide capsule and can form biofilms on medical devices. The increasing use of ventriculoperitoneal shunts to manage intracranial hypertension associated with cryptococcal meningoencephalitis highlights the importance of investigating the biofilm-forming properties of this organism. Like other microbe-forming biofilms, C. neoformans biofilms are resistant to antimicrobial agents and host defense mechanisms, causing significant morbidity and mortality. This chapter discusses the recent advances in the understanding of cryptococcal biofilms, including the role of its polysaccharide capsule in adherence, gene expression, and quorum sensing in biofilm formation. We describe novel strategies for the prevention or eradication of cryptococcal colonization of medical prosthetic devices. Finally, we provide fresh thoughts on the diverse but interesting directions of research in this field that may result in new insights into C. neoformans biology.

Inhibitory activity of isoniazid and ethionamide against Cryptococcus biofilms

In recent years, the search for drugs to treat systemic and opportunistic mycoses has attracted great interest from the scientific community. This study evaluated the in vitro inhibitory effect of the antituberculosis drugs isoniazid and ethionamide alone and combined with itraconazole and fluconazole against biofilms of Cryptococcus neoformans and Cryptococcus gattii. Antimicrobials were tested at defined concentrations after susceptibility assays with Cryptococcus planktonic cells. In addition, we investigated the synergistic interaction of antituberculosis drugs and azole derivatives against Cryptococcus planktonic cells, as well as the influence of isoniazid and ethionamide on ergosterol content and cell membrane permeability. Isoniazid and ethionamide inhibited both biofilm formation and viability of mature biofilms. Combinations formed by antituberculosis drugs and azoles proved synergic against both planktonic and sessile cells, showing an ability to reduce Cryptococcus biofilms by approximately 50%. Furthermore, isoniazid and ethionamide reduced the content of ergosterol in Cryptococcus spp. planktonic cells and destabilized or permeabilized the fungal cell membrane, leading to leakage of macromolecules. Owing to the paucity of drugs able to inhibit Cryptococcus biofilms, we believe that the results presented here might be of interest in the designing of new antifungal compounds.

Enhancement of the antibiofilm activity of amphotericin B by polyamine biosynthesis inhibitors

The aim of this study was to investigate the effect of polyamine biosynthesis inhibitors on the activity of amphotericin B (AmB) against Candida albicans biofilms and to clarify the underlying mechanisms. The antibiofilm activity of AmB was significantly enhanced when used in combination with the polyamine biosynthesis inhibitors 1,4-diamino-2-butanone (DAB) and α-difluoromethylornithine (DFMO). Further study showed that DAB and DFMO also enhanced the antibiofilm activity of several other antifungal agents. Moreover, the combination of AmB and polyamine biosynthesis inhibitors resulted in an increase in intracellular levels of reactive oxygen species. In addition, caspase activity and transcription of the caspase-encoding gene CaMCA1 were greatly increased upon combined treatment with polyamine biosynthesis inhibitors and AmB. Consistently, the biofilm formed by a Δcamca1 mutant exhibited greater viability and lower caspase activity than that of the wild-type strain upon combined treatment. These data provide useful information for the development of new strategies to enhance the antibiofilm activities of antifungal agents.

Synthesis and antifungal activity in vitro of isoniazid derivatives against histoplasma capsulatum var. capsulatum

Histoplasmosis is a severe infection that affects millions of patients worldwide and is endemic in the Americas. Amphotericin B (AMB) and itraconazole are highly effective for the treatment of severe and milder forms of the disease, but AMB is toxic, and the bioavailability of itraconazole is erratic. Therefore, it is important to investigate new classes of drugs for histoplasmosis treatment. In this study, a series of nine isoniazid hydrazone derivatives were synthesized and evaluated for their antifungal activities in vitro against the dimorphic fungus Histoplasma capsulatum var. capsulatum. The drugs were tested by microdilution in accordance with CLSI guidelines. The compound N'-(1-phenylethylidene)isonicotinohydrazide had the lowest MIC range of all the compounds for the yeast and filamentous forms of H. capsulatum. The in vitro synergy of this compound with AMB against the planktonic and biofilm forms of H. capsulatum cells was assessed by the checkerboard method. The effects of this hydrazone on cellular ergosterol content and membrane integrity were also investigated. The study showed that the compound alone is able to reduce the ergosterol content of planktonic cells and can alter the membrane permeability of the fungus. Furthermore, the compound alone or in combination with AMB showed inhibitory effects against mature biofilms of H. capsulatum. N'-(1-Phenylethylidene)isonicotinohydrazide alone or combined with AMB might be of interest in the management of histoplasmosis.

Anti-Candida albicans biofilm effect of novel heterocyclic compounds

OBJECTIVES

The aims of this study were to develop new anti-biofilm drugs, examine their activity against Candida albicans biofilm and investigate their structure-activity relationship and mechanism of action.

METHODS

A series of thiazolidinedione and succinimide derivatives were synthesized and their ability to inhibit C. albicans biofilm formation and destroy pre-formed biofilm was tested. The biofilms' structure, metabolic activity and viability were determined by XTT assay and propidium iodide and SYTO 9 live/dead stains combined with confocal microscopic analysis. The effect of the most active compounds on cell morphology, sterol distribution and cell wall morphology and composition was then determined by specific fluorescent stains and transmission electron microscopy.

RESULTS

Most of the compounds were active at sub-MICs. Elongation of the aliphatic side chain resulted in reduced anti-biofilm activity and the sulphur atom contributed to biofilm killing, indicating a structure-activity relationship. The compounds differed in their effects on biofilm viability, yeast-to-hyphal form transition, hyphal morphology, cell wall morphology and composition, and sterol distribution. The most effective anti-biofilm compounds were the thiazolidinedione S8H and the succinimide NA8.

CONCLUSIONS

We developed novel anti-biofilm agents that both inhibited and destroyed C. albicans biofilm. With some further development, these agents might be suitable for therapeutic purposes.

Cryptococcosis: epidemiology, fungal resistance, and new alternatives for treatment

Cryptococcosis is an important systemic mycosis and the third most prevalent disease in human immunodeficiency virus (HIV)-positive individuals. The incidence of cryptococcosis is high among the 25 million people with HIV/acquired immunodeficiency syndrome (AIDS), with recent estimates indicating that there are one million cases of cryptococcal meningitis globally per year in AIDS patients. In Cryptococcus neoformans, resistance to azoles may be associated with alterations in the target enzyme encoded by the gene ERG11, lanosterol 14α-demethylase. These alterations are obtained through mutations, or by overexpressing the gene encoding. In addition, C. gattii and C. neoformans present a heteroresistance phenotype, which may be related to increased virulence. Other species beyond C. neoformans and C. gattii, such as C. laurentii, have been diagnosed mainly in patients with immunosuppression. Infections of C. albidus have been isolated in cats and marine mammals. Recent evidence suggests that the majority of infections produced by this pathogen are associated with biofilm growth, which is also related with increased resistance to antifungal agents. Therefore, there is a great need to search for alternative antifungal agents for these fungi. The search for new molecules is currently occurring from nanoparticle drugs of plant peptide origin. This article presents a brief review of the literature regarding the epidemiology of cryptococcosis, as well as fungal resistance and new alternatives for treatment.