Interactions between non-phospholipid liposomes containing cetylpyridinium chloride and biofilms of Streptococcus mutans: modulation of the adhesion and of the biodistribution

Intestinal biofilms: pathophysiological relevance, host defense, and therapeutic opportunities

SUMMARYThe human intestinal tract harbors a profound variety of microorganisms that live in symbiosis with the host and each other. It is a complex and highly dynamic environment whose homeostasis directly relates to human health. Dysbiosis of the gut microbiota and polymicrobial biofilms have been associated with gastrointestinal diseases, including irritable bowel syndrome, inflammatory bowel diseases, and colorectal cancers. This review covers the molecular composition and organization of intestinal biofilms, mechanistic aspects of biofilm signaling networks for bacterial communication and behavior, and synergistic effects in polymicrobial biofilms. It further describes the clinical relevance and diseases associated with gut biofilms, the role of biofilms in antimicrobial resistance, and the intestinal host defense system and therapeutic strategies counteracting biofilms. Taken together, this review summarizes the latest knowledge and research on intestinal biofilms and their role in gut disorders and provides directions toward the development of biofilm-specific treatments.

Development of "Intelligent particles" for the treatment of dental caries

Dental caries is one of the most prevalent non-communicable diseases worldwide, mediated by a multispecies biofilm that consists of high levels of acidogenic bacteria which ferment sugar to acid and cause teeth demineralization. Current treatment practice remains insufficient in addressing 1) rapid clearance of therapeutic agents from the oral environment 2) destroying bacteria that contribute to the healthy oral microbiome. In addition, increasing concerns over antibiotic resistance calls for innovative alternatives. In this study, we developed a pH responsive nano-carrier for delivery of polycationic silver nanoparticles. Branched-PEI capped silver nanoparticles (BPEI-AgNPs) were encapsulated in a tannic acid - Fe (III) complex-modified poly(D,L-lactic-co-glycolic acid) (PLGA) particle (Fe(III)-TA/PLGA@BPEI-AgNPs) to enhance binding to the plaque biofilm and demonstrate "intelligence" by releasing BPEI-AgNPs under acidic conditions that promote dental caries The constructed Fe(III)-TA/PLGA@BPEI-AgNPs (intelligent particles - IPs) exhibited significant binding to an axenic S. mutans biofilm grown on hydroxyapatite. Ag+ ions were released faster from the IPs at pH 4.0 (cariogenic pH) compared to pH 7.4. The antibiofilm results indicated that IPs can significantly reduce S. mutans biofilm volume and viability under acidic conditions. Cytotoxicity on differentiated Caco-2 cells and human gingival fibroblasts indicated that IPs were not cytotoxic. These findings demonstrate great potential of IPs in the treatment of dental caries.

A facile and smart strategy to enhance bone regeneration with efficient vitamin D3 delivery through sterosome technology

The spontaneous healing of critical-sized bone defects is often limited, posing an increased risk of complications and suboptimal outcomes. Osteogenesis, a complex process central to bone formation, relies significantly on the pivotal role of osteoblasts. Despite the well-established osteogenic properties of vitamin D3 (VD3), its lipophilic nature confines administration to oral or muscle injection routes. Therefore, a strategic therapeutic approach involves designing a multifunctional carrier to enhance efficacy, potentially incorporating it into the delivery system. Here, we introduce an innovative sterosome-based delivery system, utilizing palmitic acid (PA) and VD3, aimed at promoting osteogenic differentiation and facilitating post-defect bone regeneration. The delivery system exhibited robust physical characteristics, including excellent stability, loading efficiency, sustained drug release and high cellular uptake efficiency. Furthermore, comprehensive investigations demonstrated outstanding biocompatibility and osteogenic potential in both 2D and 3D in vitro settings. A critical-sized calvarial defect model in mice recapitulated the notable osteogenic effects of the sterosomes in vivo. Collectively, our research proposes a clinically applicable strategy for bone healing, leveraging PA/VD3 sterosomes as an efficient carrier to deliver VD3 and enhance bone regenerative effects.

Intrinsic antibacterial and osteoinductive sterosomes promote infected bone healing

Open fractures and internal fixation implants are often accompanied by bacterial infection, leading to osteomyelitis, characterized by intractable bone infection and sequestrum formation, and can result in lifelong disability or fatal sepsis. As common clinical treatment strategies, high-dose antibiotic application and autologous bone transplantation face the risk of recurrence and donor site injury. Herein, we designed and prepared a novel drug delivery system by rational selection of the antibacterial single-chain amphiphile (cetylpyridinium chloride, CPC) and osteoinductive sterol (20S-hydroxycholesterol, Oxy) to formulate CPC/Oxy sterosomes. We demonstrate their excellent biocompatibility and antibacterial ability through 2D and 3D settings in vitro. In addition, the osteogenic differentiation of bone marrow mesenchymal stem cells was investigated in cell monolayers and a hydrogel environment. Moreover, a rat infected critical-sized calvarial defect model was employed to illustrate the effects of antibacterial and osteogenic CPC/Oxy sterosomes in vivo. Our results showed that CPC/Oxy sterosomes not only exterminated bacterial infections, but also enhanced calvarial healing without additional antibiotics, bone formation promoters or exogenous cells. This research provides a promising and effective multifunctional sterosomal platform for the treatment of infected bone defects, with the potential to be combined with therapeutic genes, and small molecule drugs.

Evaluation of the transdentinal capability of the intrinsic antibacterial cetylpyridinium chloride/cholesterol sterosomes in vitro and in vivo

AIM

Dentinal tubules serve as disease-causing channels for infiltration and penetration of bacteria and their by-products; which are regarded as the major driver of pathogenesis in pulpal inflammation and infection. In this study, we aimed to evaluate the transdentinal potential of nanoscale cetylpyridinium chloride/cholesterol (CPC/Chol) sterosomes, which are a recently developed type of cationic non-phospholipid liposomal nanocarrier; as well as their intrinsic and universal antibacterial activity.

METHODOLOGY

Cetylpyridinium chloride/cholesterol sterosomes were formulated, with a hydrodynamic diameter of 134 ± 4 nm, a low polydisperse index of 0.161 ± 0.007, and a positive zeta potential of 41 ± 3 mV at pH 7.4. Transdentinal diffusion ability of sterosomes was evaluated using human dentine blocks in vitro, and Wistar rat molar teeth in vivo. The intrinsic antibacterial activities of CPC/Chol sterosomes against Enterococcus faecalis, Streptococcus mutans, Fusobacterium nucleatum, and Porphyromonas gingivalis were further examined.

RESULTS

Cetylpyridinium chloride/cholesterol sterosomes successfully penetrated through the dentinal tubules, and diffused into the pulp, which could be internalized by dental pulp cells with a high efficiency. In addition, they exhibited substantial levels of intrinsic antibacterial activity against these Gram-positive and Gram-negative endodontic bacteria and their biofilms.

CONCLUSIONS

Given its high penetration and diffusion ability through the dentine and pulp, great potential for multi-drug delivery, and distinct intrinsic antibacterial activity; sterosome-based nanocarriers might serve as a promising therapeutic strategy aimed at targeting various specific pathways associated with pulpal diseases. This will help determine and characterize the most appropriate prophylactic and therapeutic targets for early intervention in our future dentistry practice.

Formation of Oxidation- and Acid-Sensitive Assemblies from Sterols and a Quaternary Ammonium Ferrocene Derivative: Quatsome- and Onion-like Vesicles and Extended Nanoribbons

Quatsomes are a class of nonphospholipid vesicles in which bilayers are formed from mixtures of quaternary ammonium (QA) amphiphiles and sterols. We describe the formation of oxidation and acid-sensitive quatsome-like vesicles and other bilayer assemblies from mixtures of a ferrocenylated QA amphiphile (FTDMA) and several cholesterol derivatives. The influence of the sterol and the preparation method (extrusion or probe sonication) on the stability and morphology of the resulting vesicles is explored; a variety of structures can be obtained from small (ca. 30 nm) spherical unilamellar and oligolamellar quatsome-like vesicles to large (ca. 200 nm) multilamellar onion-like vesicles to extended nanoribbons many micrometers long. FTDMA-sterol vesicles undergo drastic shifts in vesicle and membrane structure when treated with a chemical oxidant (Frémy's salt), a feature previously observed in liposomes containing FTDMA and now confirmed in nonphospholipid vesicles. Size distributions of spherical quatsome-like vesicles obtained from cryo-TEM are examined to estimate the membrane bending rigidity, and a hypothesis is presented to explain the underlying mechanism of the profound membrane alterations observed as a consequence of ferrocene oxidation.

Non-conventional therapeutics for oral infections

As our knowledge of host-microbial interactions within the oral cavity increases, future treatments are likely to be more targeted. For example, efforts to target a single species or key virulence factors that they produce, while maintaining the natural balance of the resident oral microbiota that acts to modulate the host immune response would be an advantage. Targeted approaches may be directed at the black-pigmented anaerobes, Porphyromonas gingivalis and Prevotella intermedia, associated with periodontitis. Such pigments provide an opportunity for targeted phototherapy with high-intensity monochromatic light. Functional inhibition approaches, including the use of enzyme inhibitors, are also being explored to control periodontitis. More general disruption of dental plaque through the use of enzymes and detergents, alone and in combination, shows much promise. The use of probiotics and prebiotics to improve gastrointestinal health has now led to an interest in using these approaches to control oral disease. More recently the potential of antimicrobial peptides and nanotechnology, through the application of nanoparticles with biocidal, anti-adhesive and delivery capabilities, has been explored. The aim of this review is to consider the current status as regards non-conventional treatment approaches for oral infections with particular emphasis on the plaque-related diseases.

Nanoparticles vs. biofilms: a battle against another paradigm of antibiotic resistance

Microbes form surface-adherent community structures called biofilms and these biofilms play a critical role in infection.

Characterization and optimization of pH-responsive polymer nanoparticles for drug delivery to oral biofilms

We previously reported on cationic, pH-responsive p(DMAEMA)-b-p(DMAEMA-co-BMA-co-PAA) block copolymer micelles with high affinity for dental and biofilm surfaces and efficient anti-bacterial drug release in response to acidic pH, characteristic of cariogenic (tooth-decay causing) biofilm microenvironments. Here, we show that micelle pH-responsive behaviors can be enhanced through alterations in corona:core molecular weight ratios (CCR). Although similarly stable at physiological pH, upon exposure to acidic pH, micelles with CCR of 4.1 were less stable than other CCR examined. Specifically, a ~1.5-fold increase in critical micelle concentration (CMC) and ~50% decrease in micelle diameters were observed for micelles with CCR of 4.1, compared to no changes in micelles with CCR of 0.8. While high CCR was shown to enhance pH-responsive drug release, it did not alter drug loading and dental surface binding of micelles. Diblocks were shown to encapsulate the antibacterial drug, farnesol, at maximal loading capacities of up to ~27 wt% and at >94% efficiencies, independent of CCR or core size, resulting in micelle diameter increases due to contributions of drug volume. Additionally, micelles with small diameters (~17 nm) show high binding capacity to hydroxyapatite and dental pellicle emulating surfaces based on Langmuir fit analyses of binding data. Finally, micelles with high CCR that have enhanced pH-responsive drug release and binding were shown to exhibit greater antibiofilm efficacy in situ. Overall, these data demonstrate how factors essential for nanoparticle carrier (NPC)-mediated drug deliverycan be enhanced via modification of diblock characteristics, resulting in greater antibiofilm efficacy in situ.

Distribution and Inhibition of Liposomes on Staphylococcus aureus and Pseudomonas aeruginosa Biofilm

BACKGROUND

Staphylococcus aureus and Pseudomonas aeruginosa are major pathogens in chronic rhinosinusitis (CRS) and their biofilms have been associated with poorer postsurgical outcomes. This study investigated the distribution and anti-biofilm effect of cationic (+) and anionic (-) phospholipid liposomes with different sizes (unilamellar and multilamellar vesicle, ULV and MLV respectively) on S. aureus and P. aeruginosa biofilms.

METHOD

Specific biofilm models for S. aureus ATCC 25923 and P. aeruginosa ATCC 15692 were established. Liposomal distribution was determined by observing SYTO9 stained biofilm exposed to DiI labeled liposomes using confocal scanning laser microscopy, followed by quantitative image analysis. The anti-biofilm efficacy study was carried out by using the alamarBlue assay to test the relative viability of biofilm treated with various liposomes for 24 hours and five minutes.

RESULTS

The smaller ULVs penetrated better than larger MLVs in both S. aureus and P. aeruginosa biofilm. Except that +ULV and -ULV displayed similar distribution in S. aureus biofilm, the cationic liposomes adhered better than their anionic counterparts. Biofilm growth was inhibited at 24-hour and five-minute exposure time, although the decrease of viability for P. aeruginosa biofilm after liposomal treatment did not reach statistical significance.

CONCLUSION

The distribution and anti-biofilm effects of cationic and anionic liposomes of different sizes differed in S. aureus and P. aeruginosa biofilms. Reducing the liposome size and formulating liposomes as positively charged enhanced the penetration and inhibition of S. aureus and P. aeruginosa biofilms.

pH-activated nanoparticles for controlled topical delivery of farnesol to disrupt oral biofilm virulence

Development of effective therapies to control oral biofilms is challenging, as topically introduced agents must avoid rapid clearance from biofilm-tooth interfaces while targeting biofilm microenvironments. Additionally, exopolysaccharides-matrix and acidification of biofilm microenvironments are associated with cariogenic (caries-producing) biofilm virulence. Thus, nanoparticle carriers capable of binding to hydroxyapatite (HA), saliva-coated HA (sHA), and exopolysaccharides with enhanced drug release at acidic pH were developed. Nanoparticles are formed from diblock copolymers composed of 2-(dimethylamino)ethyl methacrylate (DMAEMA), butyl methacrylate (BMA), and 2-propylacrylic acid (PAA) (p(DMAEMA)-b-p(DMAEMA-co-BMA-co-PAA)) that self-assemble into ∼21 nm cationic nanoparticles. Nanoparticles exhibit outstanding adsorption affinities (∼244 L-mmol(-1)) to negatively charged HA, sHA, and exopolysaccharide-coated sHA due to strong electrostatic interactions via multivalent tertiary amines of p(DMAEMA). Owing to hydrophobic cores, nanoparticles load farnesol, a hydrophobic antibacterial drug, at ∼22 wt %. Farnesol release is pH-dependent with t1/2 = 7 and 15 h for release at pH 4.5 and 7.2, as nanoparticles undergo core destabilization at acidic pH, characteristic of cariogenic biofilm microenvironments. Importantly, topical applications of farnesol-loaded nanoparticles disrupted Streptococcus mutans biofilms 4-fold more effectively than free farnesol. Mechanical stability of biofilms treated with drug-loaded nanoparticles was compromised, resulting in >2-fold enhancement in biofilm removal under shear stress compared to free farnesol and controls. Farnesol-loaded nanoparticles effectively attenuated biofilm virulence in vivo using a clinically relevant topical treatment regimen (2×/day) in a rodent dental caries disease model. Strikingly, treatment with farnesol-loaded nanoparticles reduced both the number and severity of carious lesions, while free farnesol had no effect. Nanoparticle carriers have great potential to enhance the efficacy of antibiofilm agents through multitargeted binding and pH-responsive drug release due to microenvironmental triggers.

Quatsomes for the treatment of Staphylococcus aureus biofilm

The anti-biofilm effect of drug delivery systems composed of the antiseptic quaternary ammonium compound cetylpyridinium chloride (CPC) and cholesterol was evaluated in Staphylococcus aureus biofilm. Self-assembly of CPC/cholesterol to approximately 100 nm CPC-quatsomes was successfully accomplished by a simple sonication/dispersion method over a broad concentration range from 0.5 to 10 mg ml^-1 CPC. CPC-quatsomes showed a dose-dependent anti-biofilm effect, killing >99% of biofilm-associated S. aureus from 5% mg ml^-1 after 10 minutes exposure. Cell toxicity studies with CPC-quatsomes in Nuli-1 cells revealed no adverse effects at all tested CPC concentrations. CPC-quatsomes, therefore, have a promising potential as novel drug delivery systems with "built-in" anti-biofilm activity.

Formation, stability, and pH sensitivity of free-floating, giant unilamellar vesicles using palmitic acid-cholesterol mixtures

Despite the fact that palmitic acid (PA) and cholesterol (Chol) do not form fluid bilayers once hydrated individually, giant unilamellar vesicles (GUVs) were formed from a mixture of palmitic acid and cholesterol, 30/70 mol/mol. These free-floating GUVs were stable over weeks, did not aggregate and were shown to be highly stable in alkaline pH compared to conventional phospholipid-based GUVs. Acidic pH-triggered payload release from the GUVs was associated with the protonation state of palmitic acid that dictated the mixing lipid properties, thus affecting the stability of the fluid lamellar phase. The successful formation of PA-Chol GUVs reveals the possibility to create monoalkylated amphiphile-based GUVs with distinct pH stability/sensitivity.