A non-toxic hydrolytically fast-degradable antibacterial hydrogel is herein presented to preemptively treat surgical site infections during the first crucial 24 h period without relying on conventional antibiotics. The approach capitalizes on a two-component system that form antibacterial hydrogels within 1 min and consist of i) an amine functional linear-dendritic hybrid based on linear poly(ethylene glycol) and dendritic 2,2-bis(hydroxymethyl)propionic acid, and ii) a di-N-hydroxysuccinimide functional poly(ethylene glycol) cross-linker. Broad spectrum antibacterial effect is achieved by multivalent representation of catatonically charged β-alanine on the dendritic periphery of the linear dendritic component. The hydrogels can be applied readily in an in vivo setting using a two-component syringe delivery system and the mechanical properties can accurately be tuned in the range equivalent to fat tissue and cartilage (G' = 0.5-8 kPa). The antibacterial effect is demonstrated both in vitro toward a range of relevant bacterial strains and in an in vivo mouse model of surgical site infection.

The rapid emergence of antibiotic-resistant microbes worldwide and the urgent need of new antimicrobial agents have stimulated interest in antimicrobial peptides (AMPs) as new therapeutics for treatment of infectious diseases. AMPs are present in all living species and constitute an important part of the innate immune system in multicellular organisms, including humans. AMPs display a remarkably broad spectrum of antimicrobial activity covering both Gram-positive and Gram-negative bacteria, including many antibiotic-resistant strains, as well as fungi, viruses, and protozoa. Further, in contrast to many conventional antibiotics, AMPs rapidly kill bacteria instead of just inhibiting bacterial growth. In addition, AMPs act as modulators of the innate immune system and, importantly, bacteria seem less efficient in developing resistance towards AMPs than towards conventional antibiotics. Together these properties make AMPs highly attractive as a new class of antimicrobials, with clinical potential also extending to diseases where inflammation is part of the pathology. The aim of this thesis was to study novel AMPs with respect to their mechanism of action (MOA), antimicrobial spectrum, propensity to select for resistance, and in vivo efficacy and safety. To achieve this, we used a number of in vitro and in vivo assays, together generating a comprehensive preclinical evaluation of the peptides. The hypothesis was that the AMPs in this thesis have potential to be developed as therapeutic agents for several infectious and inflammatory conditions, including treatment of skin and soft tissue infections and prevention of postsurgical adhesion formation. The results showed that all AMPs tested (i.e. PXL03, PXL150, HLR1r, and five variants of CEN1 HC-Br) had broad antimicrobial spectra in vitro with varying sensitivity to salt and serum. Furthermore, PXL150 caused a rapid permeabilization of bacterial membrane in vitro, indicating that this is at least one part of the MOA of this peptide. Under selection pressure in vitro, bacteria did not develop resistance to the peptides tested, i.e. PXL150 and CEN1 HC. Interestingly, all peptides showed anti-inflammatory activity by inhibiting the secretion of proinflammatory mediators from stimulated human cell lines. In addition, PXL01, PXL150, and HLR1r demonstrated fibrinolytic ability in vitro by suppressing the release of plasminogen activator inhibitor-1 (PAI-1). In ex vivo and in vivo skin/wound infection models, the peptides reduced the number of viable bacteria and yeast cells. Further, PXL01 decreased postsurgical adhesion formation in vivo. Notably, nonclinical safety studies showed that PXL150 was safe and well tolerated. In conclusion, several of the peptides evaluated in this thesis demonstrated a promising preclinical efficacy and safety profile motivating further development as drug candidates for local treatment of infectious and inflammatory conditions.

Bacterial resistance against antibiotic treatment has become a major threat to public health. Antimicrobial peptides (AMPs) have emerged as promising alternative agents for treatment of infectious diseases. This study characterizes novel synthetic peptides sequentially derived from the AMP centrocin 1, isolated from the green sea urchin, for their applicability as anti-infective agents. The microbicidal effect of centrocin 1 heavy chain (CEN1 HC-Br), its debrominated analogue (CEN1 HC), the C-terminal truncated variants of both peptides, i.e. CEN1 HC-Br (1–20) and CEN1 HC (1–20), as well as the cysteine to serine substituted equivalent CEN1 HC (Ser) was evaluated using minimal microbicidal concentration assay. The anti-inflammatory properties were assessed by measuring the inhibition of secretion of pro-inflammatory cytokines. All the peptides tested exhibited marked microbicidal and anti-inflammatory properties. No difference in efficacy was seen comparing CEN1 HC-Br and CEN1 HC, while the brominated variant had higher cytotoxicity. C-terminal truncation of both peptides reduced salt-tolerability of the microbicidal effect as well as anti-inflammatory actions. Also, serine substitution of cysteine residue decreased the microbicidal effect. Thus, from the peptide variants tested, CEN1 HC showed the best efficacy and safety profile. Further, CEN1 HC significantly reduced bacterial counts in two different animal models of infected wounds, while Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) failed to develop resistance against this peptide under continued selection pressure. In summary, CEN1 HC appears a promising new antimicrobial agent, and clinical studies are warranted to evaluate the applicability of this AMP for local treatment of infections in man.

Antimicrobial peptides (AMPs) have emerged as a new class of drug candidates for the treatment of infectious diseases. Here we describe a novel AMP, HLR1r, which is structurally derived from the human milk protein lactoferrin and demonstrates a broad spectrum microbicidal action in vitro. The minimum concentration of HLR1r needed for killing ≥99% of microorganisms in vitro, was in the range of 3-50 μg/ml for common Gram-negative and Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), and for the yeast Candida albicans, when assessed in diluted brain-heart infusion medium. We found that HLR1r also possesses anti-inflammatory properties as evidenced by inhibition of tumor necrosis factor alpha (TNF-α) secretion from human monocyte-derived macrophages and by repression of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) secretion from human mesothelial cells, without any cytotoxic effect observed at the concentration range tested (up to 400 μg/ml). HLR1r demonstrated pronounced anti-infectious effect in in vivo experimental models of cutaneous candidiasis in mice and of excision wounds infected with MRSA in rats as well as in an ex vivo model of pig skin infected with S. aureus. In conclusion, HLR1r may constitute a new therapeutic alternative for local treatment of skin infections.

The urgent need to develop novel antimicrobial therapies has stimulated interest in antimicrobial peptides as therapeutic candidates for the treatment of infectious diseases. The aim of this study was to evaluate the anti-infectious effect of the synthetic antimicrobial peptide PXL150, formulated in hydroxypropyl cellulose (HPC) gel, on Pseudomonas aeruginosa in vitro and in an in vivo mouse model of infected burn wounds as well as to assess the in vivo safety profile of PXL150 in rats and rabbits. Minimal microbicidal concentration analysis showed prominent efficacy of PXL150 against P. aeruginosa in vitro, which was further enhanced in formulating the peptide in HPC gel. Application of 1.25, 2.5, 5, 10 and 20 mg/g PXL150 in HPC gel twice daily for four consecutive days significantly reduced bacterial counts in the burn wounds compared with non-treated or placebo-treated controls. Continuous bioluminescence measurements of the bacteria revealed a pronounced anti-infective effect already at the first day post infection by PXL150 in concentrations of ≥2.5 mg/g. In the non-clinical safety studies, PXL150 showed a favourable safety profile following repeated administration systemically and locally in rats and rabbits, respectively. In conclusion, these data support that PXL150 has the potential to be an effective and safe drug candidate for the treatment of infected burn wounds. The findings encourage the progression of PXL150 as a novel topical treatment of microbial infections.

Cellulose nanofibrils (CNFs) were obtained by applying a chemical pretreatment consisting of autoclaving the pulp fibers in sodium hydroxide, combined with 2,2,6,6-tetramethylpiperidinyl-1-oxyl-mediated oxidation. Three levels of sodium hypochlorite were applied (2.5, 3.8, and 6.0 mmol/g) to obtain CNF qualities (CNF_2.5, CNF_3.8, and CNF_6.0) with varying content of carboxyl groups, that is, 1036, 1285, and 1593 μmol/g cellulose. The cytotoxicity and skin irritation potential (indirect tests) of the CNFs were determined according to standardized in vitro testing for medical devices. We here demonstrate that autoclaving (121 °C, 20 min), which was used to sterilize the gels, caused a modification of the CNF characteristics. This was confirmed by a reduction in the viscosity of the gels, a morphological change of the nanofibrils, by an increase of the ultraviolet-visible absorbance maxima at 250 nm, reduction of the absolute zeta potential, and by an increase in aldehyde content and reducing sugars after autoclaving. Fourier-transform infrared spectroscopy and wide-angle X-ray scattering complemented an extensive characterization of the CNF gels, before and after autoclaving. The antibacterial properties of autoclaved carboxylated CNFs were demonstrated in vitro (bacterial survival and swimming assays) on Pseudomonas aeruginosa and Staphylococcus aureus. Importantly, a mouse in vivo surgical-site infection model on S. aureus revealed that CNF_3.8 showed pronounced antibacterial effect and performed as good as the antiseptic Prontosan wound gel.

Antimicrobial peptides have recently emerged as a promising new group to be evaluated in the therapeutic intervention of infectious diseases. This study evaluated the anti-infectious effect of the short, synthetic, broad-spectrum antimicrobial peptide PXL150 in a mouse model of staphylococcal surgical site infections. We found that administration of PXL150, formulated in an aqueous solution or in a hydroxypropyl cellulose gel, significantly reduced the bacterial counts in the wound compared with placebo treatment, warranting further investigations of the potential of this peptide as a novel local treatment of microbial infections.

Antimicrobial peptides, also known as host defense peptides, have recently emerged as a promising new category of therapeutic agents for the treatment of infectious diseases. This study evaluated the preclinical in vitro, ex vivo, and in vivo antimicrobial activity, as well as the potential to cause skin irritation, of human kininogen-derived antimicrobial peptide DPK-060 in different formulations designed for topical delivery. We found that DPK-060 formulated in acetate buffer or poloxamer gel caused a marked reduction of bacterial counts of Staphylococcus aureus in vitro (minimum microbicidal concentration <5 μg/ml). We also found that DPK-060 in poloxamer gel significantly suppressed microbial survival in an ex vivo wound infection model using pig skin and in an in vivo mouse model of surgical site infection (≥99 or ≥94% reduction in bacterial counts was achieved with 1% DPK-060 at 4 h post-treatment, respectively). Encapsulation of DPK-060 in different types of lipid nanocapsules or cubosomes did not improve the bactericidal potential of the peptide under the applied test conditions. No reduction in cell viability was observed in response to administration of DPK-060 in any of the formulations tested. In conclusion, the present study confirms that DPK-060 has the potential to be an effective and safe drug candidate for the topical treatment of microbial infections; however, adsorption of the peptide to nanocarriers failed to show any additional benefits.

The rapid development of microbial resistance to conventional antibiotics has accelerated efforts to find anti-infectives with a novel mode-of-action, which are less prone to bacterial resistance. Intense nonclinical and clinical research is today ongoing to evaluate antimicrobial peptides (AMPs) as potential next-generation antibiotics. Currently, multiple AMPs are assessed in late-stage clinical trials, not only as novel anti-infective drugs, but also as innovative product candidates for immunomodulation, promotion of wound healing, and prevention of post-operative scars. The efforts to translate AMP-based research findings into pharmaceutical product candidates are expected to accelerate in coming years due to technological advancements in multiple areas, including an improved understanding of the mechanism-of-action of AMPs, smart formulation strategies, and advanced chemical synthesis protocols. At the same time, it is recognized that cytotoxicity, low metabolic stability due to sensitivity to proteolytic degradation, and limited oral bioavailability are some of the key weaknesses of AMPs. Furthermore, the pricing and reimbursement environment for new antimicrobial products remains as a major barrier to the commercialization of AMPs.

Antimicrobial peptides (AMPs), also known as host defense peptides, are short and generally positively charged peptides found in a wide variety of life forms from microorganisms to humans. Most AMPs have the ability to kill microbial pathogens directly, whereas others act indirectly by modulating the host defense systems. Against a background of rapidly increasing resistance development to conventional antibiotics all over the world, efforts to bring AMPs into clinical use are accelerating. Several AMPs are currently being evaluated in clinical trials as novel anti-infectives, but also as new pharmacological agents to modulate the immune response, promote wound healing, and prevent post-surgical adhesions. In this review, we provide an overview of the biological role, classification, and mode of action of AMPs, discuss the opportunities and challenges to develop these peptides for clinical applications, and review the innovative formulation strategies for application of AMPs.

Background: Bacterial airborne contamination in the operating room during surgery indicates an increased risk for surgical site infection. The conventional surveillance method for bacteria in the air is by air sampling, plating, and counting of colony-forming units (CFU). Particle counting measures particles in the air, typically in sizes of 1-20 µm, and has been suggested as an alternative to CFU measurements. The primary aim was to investigate the correlation between the number of airborne CFU and particles during surgery. The secondary aim was to explore whether different ventilation settings influence the correlation between CFU and particles. Methods: The databases Cochrane, Embase, and Medline were searched for relevant publications. Due to the heterogeneity of the data, meta-analysis was not possible and a narrative analysis was performed instead. Results: The review included 11 studies. Two of the studies (n = 2) reported strong correlation between particles and CFU (Rp = 0.76 and Rc = 0.74). The remaining studies observed moderate correlation (n = 3), low correlation (n = 3), or no correlation (n = 3). Based on the primary results from this study, ventilation attribution to distinguish the correlation between particles and CFU had no or little contribution. Conclusions: Due to the lack of convincing evidence of correlation and lack of high-quality studies performing measurements in a standardized way, the studies could not provide the necessary evidence that show that particle counting could be used as a substitution for conventional air bacterial assessment. Further studies are warranted to strengthen the conclusion. © 2023 The Authors