Itaconic Acid Increases the Efficacy of Tobramycin against Pseudomonas aeruginosa Biofilms

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Anti-Inflammatory Metabolites in the Pathogenesis of Bacterial Infection

Host and pathogen metabolism have a major impact on the outcome of infection. The microenvironment consisting of immune and stromal cells drives bacterial proliferation and adaptation, while also shaping the activity of the immune system. The abundant metabolites itaconate and adenosine are classified as anti-inflammatory, as they help to contain the local damage associated with inflammation, oxidants and proteases. A growing literature details the many roles of these immunometabolites in the pathogenesis of infection and their diverse functions in specific tissues. Some bacteria, notably P. aeruginosa, actively metabolize these compounds, others, such as S. aureus respond by altering their own metabolic programs selecting for optimal fitness. For most of the model systems studied to date, these immunometabolites promote a milieu of tolerance, limiting local immune clearance mechanisms, along with promoting bacterial adaptation. The generation of metabolites such as adenosine and itaconate can be host protective. In the setting of acute inflammation, these compounds also represent potential therapeutic targets to prevent infection.

Tobramycin-loaded complexes to prevent and disrupt Pseudomonas aeruginosa biofilms

Carbohydrate-based materials are increasingly investigated for a range of applications spanning from healthcare to advanced functional materials. Synthetic glycopolymers are particularly attractive as they possess low toxicity and immunogenicity and can be used as multivalent ligands to target sugar-binding proteins (lectins). Here, we utilised RAFT polymerisation to synthesize two families of novel diblock copolymers consisting of a glycopolymers block containing either mannopyranose or galactopyranose pendant units, which was elongated with sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) to generate a polyanionic block. The latter enabled complexation of cationic aminoglycoside antibiotic tobramycin through electrostatic interactions (loading efficiency in the 0.5-6.3 wt% range, depending on the copolymer). The resulting drug vectors were characterized by dynamic light scattering, zeta-potential, and transmission electron microscopy. Tobramycin-loaded complexes were tested for their ability to prevent clustering or disrupt biofilm of the Pseudomonas aeruginosa Gram-negative bacterium responsible for a large proportion of nosocomial infection, especially in immunocompromised patients. P. aeruginosa possesses two specific tetrameric carbohydrate-binding adhesins, LecA (PA-IL, galactose/N-acetyl-D-galactosamine-binding) and LecB (PA-IIL, fucose/mannose-binding), and the cell-associated and extracellular adhesin CdrA (Psl/mannose-binding) thus ideally suited for targeted drug delivery using sugar-decorated tobramycin-loaded complexes here developed. Both aliphatic and aromatic linkers were utilised to link the sugar pendant units to the polyacrylamide polymer backbone to assess the effect of the nature of such linkers on bactericidal/bacteriostatic properties of the complexes. Results showed that tobramycin-loaded complexes efficiently suppressed (40 to 60% of inhibition) in vitro biofilm formation in PAO1-L P. aeruginosa and that preferential targeting of PAO1-L biofilm can be achieved using mannosylated glycopolymer-b-AMPS_m.

Pseudomonas aeruginosa transcriptome adaptations from colonization to biofilm infection of skin wounds

In burn patients Pseudomonas aeruginosa infection is a major cause of morbidity. Analysis of the pathogen's gene expression as it transitions from colonization to acute and then biofilm wound infection may provide strategies for infection control. Toward this goal, we seeded log-phase P. aeruginosa (PAO1) into 3-day-old, full-thickness excision wounds (rabbit ear) and harvested the bacteria during colonization (Hrs 2 and 6), acute infection (Hr 24), and biofilm infection (Days 5 and 9) for transcriptome analysis (RNA-Seq). After 2-6 h in the wound, genes for metabolism and cell replication were down-regulated while wound-adaptation genes were up-regulated (vs. expression in log-phase culture). As the infection progressed from acute to biofilm infection, more genes became up-regulated than down-regulated, but the down-regulated genes enriched in more pathways, likely because the genes and pathways that bacteria already colonizing wounds up-regulate to establish biofilm infection are less known. Across the stages of infection, carbon-utilization pathways shifted. During acute infection, itaconate produced by myeloid cells appears to have been a carbon source because myeloid cell infiltration and the expression of the host gene, ACOD1, for itaconate production peaked coincidently with the expression of the PAO1 genes for itaconate transport and catabolism. Additionally, branched-chain amino acids are suggested to be a carbon source in acute infection and in biofilm infection. In biofilm infection, fatty acid degradation was also up-regulated. These carbon sources feed into the glyoxylate cycle that was coincidently up-regulated, suggesting it provided the precursors for P. aeruginosa to synthesize macromolecules in establishing wound infection.

The potential of using itaconate as treatment for inflammation-related heart diseases

Intracellular metabolites can cause critical changes in biological functions. Itaconate is perhaps the most fascinating substance in macrophages. Lipopolysaccharide can activate aconitate decarboxylase 1 and induces the generation of itaconate from the tricarboxylic acid cycle by decarboxylation of cis-aconitate. It has been reported that itaconate has beneficial effects on inflammation and oxidation. The mechanisms involved in these effects include the suppression of succinate dehydrogenase, the activation of nuclear factor E2-related factor 2 by alkylation of Kelch-like ECH-associated protein 1, suppression of aerobic glycolysis through regulation of glyceraldehyde-3-phosphate dehydrogenase and fructose-bisphosphate aldolase A, and suppression of IκBζ translation through activating transcription factor 3 activation. All of these findings elucidated the possible therapeutic implications of itaconate in inflammation-related diseases. In this review, we highlight that itaconate is a crucial molecule of the immunomodulatory response in macrophages and can regulate between immune response and cardiovascular metabolism. Furthermore, these discoveries suggest that itaconate is a very novel therapeutic molecule for the treatment of inflammation-related heart diseases.

Self-Assembled Amphiphilic Starch Based Drug Delivery Platform: Synthesis, Preparation, and Interactions with Biological Barriers

Core-shell structured nanoparticles (NPs) render the simultaneous coloading capacity of both hydrophobic and hydrophilic drugs and may eventually enhance therapeutic efficacy. In this study, we employed a facile squalenoylation technology to synthesize a new amphiphilic starch derivative from partially oxidized starch, which self-assembled into core-shell starch NPs (StNPs) only at a squalenyl degree of substitution (DoS) of ∼1%. The StNPs characteristics could be tuned as the functions of the polymer molecular weight, DoS, and NPs concentration. The biopharmaceutical features of the StNPs, including colloidal stability, carrier properties, and biocompatibility, were carefully investigated. The interaction study between StNPs and mucin glycoproteins, the main organic component of mucus, revealed a moderate mucin interacting profile. Furthermore, the StNPs also showed good penetration through Pseudomonas aeruginosa biofilms. These results nominate StNPs as a versatile drug delivery platform with potential applications for mucosal drug delivery and the treatment of persistent infections.