Lower respiratory tract single-cell RNA sequencing and neutrophil extracellular trap profiling of COVID-19-associated pulmonary aspergillosis: a single centre, retrospective, observational study.

BACKGROUND: COVID-19-associated pulmonary aspergillosis (CAPA) is a severe superinfection with the fungus Aspergillus affecting patients who are critically ill with COVID-19. The pathophysiology and the role of neutrophil extracellular traps (NETs) in this infection are largely unknown. We aimed to characterise the immune profile, with a focus on neutrophils and NET concentrations, of critically ill patients with COVID-19, with or without CAPA. METHODS: We conducted a single-centre, retrospective, observational study in two patient cohorts, both recruited at University Hospitals Leuven, Belgium. We included adults aged 18 years or older who were admitted to the intensive care unit because of COVID-19 between March 31, 2020, and May 18, 2021, and who were included in the previous Contagious trial (NCT04327570). We investigated the immune cellular landscape of CAPA versus COVID-19 only by performing single-cell RNA sequencing (scRNA-seq) on bronchoalveolar lavage fluid. Bronchoalveolar lavage immune cell fractions were compared between patients with CAPA and patients with COVID-19 only. Additionally, we determined lower respiratory tract NET concentrations using biochemical assays in patients aged 18 years and older who were admitted to the intensive care unit because of severe COVID-19 between March 15, 2020, and Dec 31, 2021, for whom bronchoalveolar lavage was available in the hospital biobank. Bronchoalveolar lavage NET concentrations were compared between patients with CAPA and patients with COVID-19 only and integrated with existing data on immune mediators in bronchoalveolar lavage and 90-day mortality. FINDINGS: We performed scRNA-seq of bronchoalveolar lavage on 43 samples from 39 patients, of whom 36 patients (30 male and six female; 14 with CAPA) were included in downstream analyses. We performed bronchoalveolar lavage NET analyses in 59 patients (46 male and 13 female), of whom 26 had CAPA. By scRNA-seq, patients with CAPA had significantly lower neutrophil fractions than patients with COVID-19 only (16% vs 33%; p=0·0020). The remaining neutrophils in patients with CAPA preferentially followed a hybrid maturation trajectory characterised by expression of genes linked to antigen presentation, with enhanced transcription of antifungal effector pathways. Patients with CAPA also showed depletion of mucosal-associated invariant T cells, reduced T helper 1 and T helper 17 differentiation, and transcriptional defects in specific aspects of antifungal immunity in macrophages and monocytes. We observed increased formation of NETs in patients with CAPA compared with patients with COVID-19 only (DNA complexed with citrullinated histone H3 median 15 898 ng/mL [IQR 4588-86 419] vs 7062 ng/mL [775-14 088]; p=0·042), thereby explaining decreased neutrophil fractions by scRNA-seq. Low bronchoalveolar lavage NET concentrations were associated with increased 90-day mortality in patients with CAPA. INTERPRETATION: Qualitative and quantitative disturbances in monocyte, macrophage, B-cell, and T-cell populations could predispose patients with severe COVID-19 to develop CAPA. Hybrid neutrophils form a specialised response to CAPA, and an adequate neutrophil response to CAPA is a major determinant for survival in these patients. Therefore, measuring bronchoalveolar lavage NETs could have diagnostic and prognostic value in patients with CAPA. Clinicians should be wary of aspergillosis when using immunomodulatory therapy that might inhibit NETosis to treat patients with severe COVID-19. FUNDING: Research Foundation Flanders, KU Leuven, UZ Leuven, VIB, the Fundação para a Ciência e a Tecnologia, the European Regional Development Fund, la Caixa Foundation, the Flemish Government, and Horizon 2020.

FLUIDOT: A Modular Microfluidic Platform for Single-Cell Study and Retrieval, with Applications in Drug Tolerance Screening and Antibody Mining.

Advancements in lab-on-a-chip technologies have revolutionized the single-cell analysis field. However, an accessible platform for in-depth screening and specific retrieval of single cells, which moreover enables studying diverse cell types and performing various downstream analyses, is still lacking. As a solution, FLUIDOT is introduced, a versatile microfluidic platform incorporating customizable microwells, optical tweezers and an interchangeable cell-retrieval system. Thanks to its smart microfluidic design, FLUIDOT is straightforward to fabricate and operate, rendering the technology widely accessible. The performance of FLUIDOT is validated and its versatility is subsequently demonstrated in two applications. First, drug tolerance in yeast cells is studied, resulting in the discovery of two treatment-tolerant populations. Second, B cells from convalescent COVID-19 patients are screened, leading to the discovery of highly affine, in vitro neutralizing monoclonal antibodies against SARS-CoV-2. Owing to its performance, flexibility, and accessibility, it is foreseen that FLUIDOT will enable phenotypic and genotypic analysis of diverse cell samples and thus elucidate unexplored biological questions.

Lung epithelial and myeloid innate immunity in influenza-associated or COVID-19-associated pulmonary aspergillosis: an observational study.

BACKGROUND: Influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) affect about 15% of critically ill patients with influenza or COVID-19, respectively. These viral-fungal coinfections are difficult to diagnose and are associated with increased mortality, but data on their pathophysiology are scarce. We aimed to explore the role of lung epithelial and myeloid innate immunity in patients with IAPA or CAPA. METHODS: In this observational study, we retrospectively recruited patients who had been admitted to the intensive care unit (ICU) of University Hospitals Leuven, Belgium, requiring non-invasive or invasive ventilation because of severe influenza or COVID-19, with or without aspergillosis, between Jan 1, 2011, and March 31, 2021, whose bronchoalveolar lavage samples were available at the hospital biobank. Additionally, biobanked in vivo tracheobronchial biopsy samples from patients with IAPA or CAPA and invasive Aspergillus tracheobronchitis admitted to ICUs requiring invasive ventilation between the same dates were collected from University Hospitals Leuven, Hospital Network Antwerp (Belgium), and Amiens-Picardie University Hospital (France). We did nCounter gene expression analysis of 755 genes linked to myeloid innate immunity and protein analysis of 47 cytokines, chemokines, and growth factors on the bronchoalveolar lavage samples. Gene expression data were used to infer cell fractions by use of CIBERSORTx, to perform hypergeometric enrichment pathway analysis and gene set enrichment analysis, and to calculate pathway module scores for the IL-1ß, TNF-α, type I IFN, and type II IFN (IFNγ) pathways. We did RNAScope targeting influenza virus or SARS-CoV-2 RNA and GeoMx spatial transcriptomics on the tracheobronchial biopsy samples. FINDINGS: Biobanked bronchoalveolar lavage samples were retrieved from 166 eligible patients, of whom 40 had IAPA, 52 had influenza without aspergillosis, 33 had CAPA, and 41 had COVID-19 without aspergillosis. We did nCounter gene expression analysis on bronchoalveolar lavage samples from 134 patients, protein analysis on samples from 162 patients, and both types of analysis on samples from 130 patients. We performed RNAScope and spatial transcriptomics on the tracheobronchial biopsy samples from two patients with IAPA plus invasive Aspergillus tracheobronchitis and two patients with CAPA plus invasive Aspergillus tracheobronchitis. We observed a downregulation of genes associated with antifungal effector functions in patients with IAPA and, to a lesser extent, in patients with CAPA. We found a downregulated expression of several genes encoding proteins with functions in the opsonisation, recognition, and killing of conidia in patients with IAPA versus influenza only and in patients with CAPA versus COVID-19 only. Several genes related to LC3-associated phagocytosis, autophagy, or both were differentially expressed. Patients with CAPA had significantly lower neutrophil cell fractions than did patients with COVID-19 only. Patients with IAPA or CAPA had downregulated IFNγ signalling compared with patients with influenza only or COVID-19 only, respectively. The concentrations of several fibrosis-related growth factors were significantly elevated in the bronchoalveolar lavage fluid from patients with IAPA versus influenza only and from patients with CAPA versus COVID-19 only. In one patient with CAPA, we visualised an active or very recent SARS-CoV-2 infection disrupting the epithelial barrier, facilitating tissue-invasive aspergillosis. INTERPRETATION: Our results reveal a three-level breach in antifungal immunity in IAPA and CAPA, affecting the integrity of the epithelial barrier, the capacity to phagocytise and kill Aspergillus spores, and the ability to destroy Aspergillus hyphae, which is mainly mediated by neutrophils. The potential of adjuvant IFNγ in the treatment of IAPA and CAPA should be investigated. FUNDING: Research Foundation Flanders, Coronafonds, the Max Planck Society, the Fundação para a Ciência e a Tecnologia, the European Regional Development Fund, "la Caixa" Foundation, and Horizon 2020.

Multiplex Analysis to Unravel the Mode of Antifungal Activity of the Plant Defensin HsAFP1 in Single Yeast Cells.

Single cell analyses have gained increasing interest over bulk approaches because of considerable cell-to-cell variability within isogenic populations. Herein, flow cytometry remains golden standard due to its high-throughput efficiency and versatility, although it does not allow to investigate the interdependency of cellular events over time. Starting from our microfluidic platform that enables to trap and retain individual cells on a fixed location over time, here, we focused on unraveling kinetic responses of single Saccharomyces cerevisiae yeast cells upon treatment with the antifungal plant defensin HsAFP1. We monitored the time between production of reactive oxygen species (ROS) and membrane permeabilization (MP) in single yeast cells for different HsAFP1 doses using two fluorescent dyes with non-overlapping spectra. Within a time frame of 2 min, only <0.3% cells displayed time between the induction of ROS and MP. Reducing the time frame to 30 s did not result in increased numbers of cells with time between these events, pointing to ROS and MP induction as highly dynamic and correlated processes. In conclusion, using an in-house developed continuous microfluidic platform, we investigated the mode of action of HsAFP1 at single cell level, thereby uncovering the close interdependency between ROS induction and MP in yeast.

Posaconazole for prevention of invasive pulmonary aspergillosis in critically ill influenza patients (POSA-FLU): a randomised, open-label, proof-of-concept trial.

PURPOSE: Influenza-associated pulmonary aspergillosis (IAPA) is a frequent complication in critically ill influenza patients, associated with significant mortality. We investigated whether antifungal prophylaxis reduces the incidence of IAPA. METHODS: We compared 7 days of intravenous posaconazole (POS) prophylaxis with no prophylaxis (standard-of-care only, SOC) in a randomised, open-label, proof-of-concept trial in patients admitted to an intensive care unit (ICU) with respiratory failure due to influenza (ClinicalTrials.gov, NCT03378479). Adult patients with PCR-confirmed influenza were block randomised (1:1) within 10 days of symptoms onset and 48 h of ICU admission. The primary endpoint was the incidence of IAPA during ICU stay in patients who did not have IAPA within 48 h of ICU admission (modified intention-to-treat (MITT) population). RESULTS: Eighty-eight critically ill influenza patients were randomly allocated to POS or SOC. IAPA occurred in 21 cases (24%), the majority of which (71%, 15/21) were diagnosed within 48 h of ICU admission, excluding them from the MITT population. The incidence of IAPA was not significantly reduced in the POS arm (5.4%, 2/37) compared with SOC (11.1%, 4/36; between-group difference 5.7%; 95% CI - 10.8 to 21.7; p = 0.32). ICU mortality of early IAPA was high (53%), despite rapid antifungal treatment. CONCLUSION: The higher than expected incidence of early IAPA precludes any definite conclusion on POS prophylaxis. High mortality of early IAPA, despite timely antifungal therapy, indicates that alternative management strategies are required. After 48 h, still 11% of patients developed IAPA. As these could benefit from prophylaxis, differentiated strategies are likely needed to manage IAPA in the ICU.

Membrane-Interacting Antifungal Peptides.

The incidence of invasive fungal infections is increasing worldwide, resulting in more than 1.6 million deaths every year. Due to growing antifungal drug resistance and the limited number of currently used antimycotics, there is a clear need for novel antifungal strategies. In this context, great potential is attributed to antimicrobial peptides (AMPs) that are part of the innate immune system of organisms. These peptides are known for their broad-spectrum activity that can be directed toward bacteria, fungi, viruses, and/or even cancer cells. Some AMPs act via rapid physical disruption of microbial cell membranes at high concentrations causing cell leakage and cell death. However, more complex mechanisms are also observed, such as interaction with specific lipids, production of reactive oxygen species, programmed cell death, and autophagy. This review summarizes the structure and mode of action of antifungal AMPs, thereby focusing on their interaction with fungal membranes.

Tuning the Surface Interactions between Single Cells and an OSTE+ Microwell Array for Enhanced Single Cell Manipulation.

Retrieving single cells of interest from an array of microwells for further off-chip analysis is crucial in numerous biological applications. To this end, several single cell manipulation strategies have been developed, including optical tweezers (OT). OT represent a unique approach for contactless cell retrieval, but their performance is often suboptimal due to nonspecific cell adhesion to the microwell surface. In this study, we focused on improving the surface chemistry of microwell arrays to ensure efficient single cell manipulation using OT. For this purpose, the surface of an off-stoichiometry thiol-ene-epoxy (OSTE+) microwell array was grafted with polyethylene glycol (PEG) molecules with different molecular weights: PEG 360, PEG 500, PEG 2000, and a PEG Mix (an equimolar ratio of PEG 500 and PEG 2000). Contact angle measurements showed that the PEG grafting process resulted in an increased surface energy, which was stable for at least 16 weeks. Next, cell adhesion of two cell types, baker's yeast (Saccharomyces cerevisiae) and human B cells, to surfaces treated with different PEGs was evaluated by registering the presence of cellular motion inside microwells and the efficiency of optical lifting of cells that display motion. Optimal results were obtained for surfaces grafted with PEG 2000 and PEG Mix, reaching an average fraction of cells with motion of over 93% and an average lifting efficiency of over 96% for both cell types. Upon the integration of this microwell array with a polydimethylsiloxane (PDMS) microfluidic channel, PEG Mix resulted in proper washing of non-seeded cells. We further demonstrated the wide applicability of the platform by manipulating non-responding yeast cells to antifungal treatment and B cells expressing surface IgG antibodies. The combination of the optimized microwell surface with continuous microfluidics results in a powerful and versatile platform, allowing high-throughput single cell studies and retrieval of target cells for off-chip analysis.

Repurposing the Antidepressant Sertraline as SHMT Inhibitor to Suppress Serine/Glycine Synthesis-Addicted Breast Tumor Growth.

Metabolic rewiring is a hallmark of cancer that supports tumor growth, survival, and chemotherapy resistance. Although normal cells often rely on extracellular serine and glycine supply, a significant subset of cancers becomes addicted to intracellular serine/glycine synthesis, offering an attractive drug target. Previously developed inhibitors of serine/glycine synthesis enzymes did not reach clinical trials due to unfavorable pharmacokinetic profiles, implying that further efforts to identify clinically applicable drugs targeting this pathway are required. In this study, we aimed to develop therapies that can rapidly enter the clinical practice by focusing on drug repurposing, as their safety and cost-effectiveness have been optimized before. Using a yeast model system, we repurposed two compounds, sertraline and thimerosal, for their selective toxicity against serine/glycine synthesis-addicted breast cancer and T-cell acute lymphoblastic leukemia cell lines. Isotope tracer metabolomics, computational docking, enzymatic assays, and drug-target interaction studies revealed that sertraline and thimerosal inhibit serine/glycine synthesis enzymes serine hydroxymethyltransferase and phosphoglycerate dehydrogenase, respectively. In addition, we demonstrated that sertraline's antiproliferative activity was further aggravated by mitochondrial inhibitors, such as the antimalarial artemether, by causing G1-S cell-cycle arrest. Most notably, this combination also resulted in serine-selective antitumor activity in breast cancer mouse xenografts. Collectively, this study provides molecular insights into the repurposed mode-of-action of the antidepressant sertraline and allows to delineate a hitherto unidentified group of cancers being particularly sensitive to treatment with sertraline. Furthermore, we highlight the simultaneous inhibition of serine/glycine synthesis and mitochondrial metabolism as a novel treatment strategy for serine/glycine synthesis-addicted cancers.

Implant functionalization with mesoporous silica: A promising antibacterial strategy, but does such an implant osseointegrate?

OBJECTIVES: New strategies for implant surface functionalization in the prevention of peri-implantitis while not compromising osseointegration are currently explored. The aim of this in vivo study was to assess the osseointegration of a titanium-silica composite implant, previously shown to enable controlled release of therapeutic concentrations of chlorhexidine, in the Göttingen mini-pig oral model. MATERIAL AND METHODS: Three implant groups were designed: macroporous titanium implants (Ti-Porous); macroporous titanium implants infiltrated with mesoporous silica (Ti-Porous + SiO2 ); and conventional titanium implants (Ti-control). Mandibular last premolar and first molar teeth were extracted bilaterally and implants were installed. After 1 month healing, the bone in contact with the implant and the bone regeneration in the peri-implant gap was evaluated histomorphometrically. RESULTS: Bone-to-implant contact and peri-implant bone volume for Ti-Porous versus Ti-Porous + SiO2 implants did not differ significantly, but were significantly higher in the Ti-Control group compared with Ti-Porous + SiO2 implants. Functionalization of titanium implants via infiltration of a SiO2 phase into the titanium macropores does not seem to inhibit implant osseointegration. Yet, the importance of the implant macro-design, in particular the screw thread design in a marginal gap implant surgery set-up, was emphasized by the outstanding results of the Ti-Control implant. CONCLUSIONS: Next-generation implants made of macroporous Ti infiltrated with mesoporous SiO2 do not seem to compromise the osseointegration process. Such implant functionalization may be promising for the prevention and treatment of peri-implantitis given the evidenced potential of mesoporous SiO2 for controlled drug release.

Combining Biocontrol Agents with Chemical Fungicides for Integrated Plant Fungal Disease Control.

Feeding a rising population of currently 7.8 billion people globally requires efficient agriculture, which is preferably sustainable. Today, farmers are largely dependent on synthetic fungicides to avoid food losses caused by fungal diseases. However, the extensive use of these has resulted in the emergence of fungicide-resistant pathogens and concerns have been raised over the residual effects on the environment and human health. In this regard, biocontrol agents (BCAs) have been proposed as an alternative to standard fungicides but their disease management capacity is usually incomplete and heavily relies on uncontrollable environmental conditions. An integrated approach combining BCAs with fungicides, which is the focus of this review, is put forward as a way to reduce the fungicide doses to manage plant diseases and thereby their residue on harvested crops. In addition, such a strategy of combining antifungal treatments with different modes of action reduces the selection pressure on pathogens and thereby the chances of resistance development. However, to allow its large-scale implementation, further knowledge is needed, comprising timing, number and interval of repeated BCA applications and their compatibility with fungicides. The compatibility of BCAs with fungicides might differ when applied in a mixture or when used in alternation.

Combination Therapy to Treat Fungal Biofilm-Based Infections.

An increasing number of people is affected by fungal biofilm-based infections, which are resistant to the majority of currently-used antifungal drugs. Such infections are often caused by species from the genera Candida, Aspergillus or Cryptococcus. Only a few antifungal drugs, including echinocandins and liposomal formulations of amphotericin B, are available to treat such biofilm-based fungal infections. This review discusses combination therapy as a novel antibiofilm strategy. More specifically, in vitro methods to discover new antibiofilm combinations will be discussed. Furthermore, an overview of the main modes of action of promising antibiofilm combination treatments will be provided as this knowledge may facilitate the optimization of existing antibiofilm combinations or the development of new ones with a similar mode of action.

Combination of Miconazole and Domiphen Bromide Is Fungicidal against Biofilms of Resistant Candida spp.

The occurrence and recurrence of mucosal biofilm-related Candida infections, such as oral and vulvovaginal candidiasis, are serious clinical issues. Vaginal infections caused by Candida spp., for example, affect 70 to 75% of women at least once during their lives. Miconazole (MCZ) is the preferred topical treatment against these fungal infections, yet it has only moderate antibiofilm activity. Through screening of a drug-repurposing library, we identified the quaternary ammonium compound domiphen bromide (DB) as an MCZ potentiator against Candida biofilms. DB displayed synergistic anti-Candida albicans biofilm activity with MCZ, reducing the number of viable biofilm cells 1,000-fold. In addition, the MCZ-DB combination also resulted in significant killing of biofilm cells of azole-resistant C. albicans, C. glabrata, and C. auris isolates. In vivo, the MCZ-DB combination had significantly improved activity in a vulvovaginal candidiasis rat model compared to that of single-compound treatments. Data from an artificial evolution experiment indicated that the development of resistance against the combination did not occur, highlighting the potential of MCZ-DB combination therapy to treat Candida biofilm-related infections.

Correction to: International survey on influenza-associated pulmonary aspergillosis (IAPA) in intensive care units: responses suggest low awareness and potential underdiagnosis outside Europe.

In the publication of this article [1], there was an error in Fig. 1 which caused that the a, b were switched and 'b' was missing as a caption on Fig. 1b.

The antifungal plant defensin HsAFP1 induces autophagy, vacuolar dysfunction and cell cycle impairment in yeast.

The plant defensin HsAFP1 is characterized by broad-spectrum antifungal activity and induces apoptosis in Candida albicans. In this study, we performed a transcriptome analysis on C. albicans cultures treated with HsAFP1 to gain further insight in the antifungal mode of action of HsAFP1. Various genes coding for cell surface proteins, like glycosylphosphatidylinositol (GPI)-anchored proteins, and proteins involved in cation homeostasis, autophagy and in cell cycle were differentially expressed upon HsAFP1 treatment. The biological validation of these findings was performed in the model yeast Saccharomyces cerevisiae. To discriminate between events linked to HsAFP1's antifungal activity and those that are not, we additionally used an inactive HsAFP1 mutant. We demonstrated that (i) HsAFP1-resistent S. cerevisiae mutants that are characterized by a defect in processing GPI-anchors are unable to internalize HsAFP1, and (ii) moderate doses (FC50, fungicidal concentration resulting in 50% killing) of HsAFP1 induce autophagy in S. cerevisiae, while high HsAFP1 doses result in vacuolar dysfunction. Vacuolar function is an important determinant of replicative lifespan (RLS) under dietary restriction (DR). In line, HsAFP1 specifically reduces RLS under DR. Lastly, (iii) HsAFP1 affects S. cerevisiae cell cycle in the G2/M phase. However, the latter HsAFP1-induced event is not linked to its antifungal activity, as the inactive HsAFP1 mutant also impairs the G2/M phase. In conclusion, we demonstrated that GPI-anchored proteins are involved in HsAFP1's internalization, and that HsAFP1 induces autophagy, vacuolar dysfunction and impairment of the cell cycle. Collectively, all these data provide novel insights in the mode of action of HsAFP1 as well as in S. cerevisiae tolerance mechanisms against this peptide.

Combining Miconazole and Domiphen Bromide Results in Excess of Reactive Oxygen Species and Killing of Biofilm Cells.

Fungal biofilm-related infections are increasingly occurring. We previously identified a fungicidal antibiofilm combination, consisting of miconazole (MCZ) and the quaternary ammonium compound domiphen bromide (DB). DB eliminates tolerance rather than altering the susceptibility to MCZ of various Candida spp. Here we studied the mode of action of the MCZ-DB combination in more detail. We found that DB's action increases the permeability of the plasma membrane as well as that of the vacuolar membrane of Candida spp. Furthermore, the addition of DB affects the intracellular azole distribution. MCZ is a fungicidal azole that, apart from its well-known inhibition of ergosterol biosynthesis, also induces accumulation of reactive oxygen species (ROS). Interestingly, the MCZ-DB combination induced significantly more ROS in C. albicans biofilms as compared to single compound treatment. Co-administration of the antioxidant ascorbic acid resulted in abolishment of the ROS generated by MCZ-DB combination as well as its fungicidal action. In conclusion, increased intracellular MCZ availability due to DB's action results in excess of ROS and enhanced fungal cell killing.

An antibiofilm coating of 5-aryl-2-aminoimidazole covalently attached to a titanium surface.

Biofilms, especially those formed by Staphylococcus aureus, play a key role in the development of orthopedic implant infections. Eradication of these infections is challenging due to the elevated tolerance of biofilm cells against antimicrobial agents. In this study, we developed an antibiofilm coating consisting of 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine, designated as LC0024, covalently bound to a titanium implant surface (LC0024-Ti). We showed in vitro that the LC0024-Ti surface reduces biofilm formation of S. aureus in a specific manner without reducing the planktonic cells above the biofilm, as evaluated by plate counting and fluorescence microscopy. The advantage of compounds that only inhibit biofilm formation without affecting the viability of the planktonic cells, is that reduced development of bacterial resistance is expected. To determine the antibiofilm activity of LC0024-Ti surfaces in vivo, a biomaterial-associated murine infection model was used. The results indicated a significant reduction in S. aureus biofilm formation (up to 96%) on the LC0024-Ti substrates compared to pristine titanium controls. Additionally, we found that the LC0024-Ti substrates did not affect the attachment and proliferation of human cells involved in osseointegration and bone repair. In summary, our results emphasize the clinical potential of covalent coatings of LC0024 on titanium implant surfaces to reduce the risk of orthopedic implant infections. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1908-1919, 2019.

Structure-activity relationship study of the antimicrobial CRAMP-derived peptide CRAMP20-33.

We report here on the structure-activity relationship study of a 14 amino acid fragment of the cathelicidin-related antimicrobial peptide (CRAMP), CRAMP20-33 (KKIGQKIKNFFQKL). It showed activity against Escherichia coli and filamentous fungi with IC50 values below 30 µM and 10 µM, respectively. CRAMP20-33 variants with glycine at position 23 substituted by phenylalanine, leucine or tryptophan showed 2- to 4-fold improved activity against E. coli but not against filamentous fungi. Furthermore, the most active single-substituted peptide, CRAMP20-33 G23 W (IC50 = 2.3 µM against E. coli), showed broad-spectrum activity against Candida albicans, Staphylococcus epidermidis and Salmonella Typhimurium. Introduction of additional arginine substitutions in CRAMP20-33 G23 W, more specifically in CRAMP20-33 G23 W N28R or CRAMP20-33 G23 W Q31R, resulted in 3-fold increased activity against S. epidermidis (IC50 = 4 µM and 4.8 µM, respectively) as compared to CRAMP20-33 G23 W (IC50 = 15.1 µM) but not against the other pathogens tested. In general, double-substituted variants were non-toxic for human HepG2 cells, pointing to their therapeutic potential.