Lipid and polymer nanoparticles for drug delivery to bacterial biofilms
Summary (2 min read)
1. Introduction
- This allows the biofilm to respond cooperatively to environmental changes and threats.
- The reason why these infections are hard to eradicate is twofold.
- It is now estimated that over 60% of bacterial infections in humans involve biofilm formation. [17].
- Furthermore, by targeting of the nanoparticles to the biofilm, a high dose of antimicrobial agents can be delivered in the direct proximity of the bacterial cells, thereby maximizing therapeutic benefit while reducing unwanted side effects.
2.1 Lipid nanoparticles
- Due to their versatility and biocompatibility, liposomes are attractive candidates for nanoparticle mediated drug delivery in biofilms.
- Fusion of these liposomes with the bacteria was also proven by a combination of flow cytometry, lipid mixing, TEM and immunochemistry techniques as mentioned above. [36, 37].
- It is worth noting that co‐encapsulation of other antimicrobial substances together with an antibiotic into liposomes could improve the antimicrobial efficacy.
- Also, longer contact times between the antibiotic and the biofilm bacteria have been suggested to be responsible for the increased antimicrobial effect. [51, 52] DPPC:Chol:SA DPPC:Chol:DD AB DPPC:DC‐chol / Vancomycin / 0.12 Cationi c Yes ND ND Yes ND Targeting and sustained release S. aureus [79].
2.2 Polymer and lipid‐polymer hybrid nanoparticles
- In contrast to the various beneficial traits described above, the use of liposomes can also have several disadvantages.
- The polymeric particles already described in literature are typically formed from poly(lactic‐co‐ glycolic) acid (PLGA) or chitosan or a mixture of PLGA and lipids to form so called lipid‐polymer hybrid nanoparticles (LPH). [89, 90] PLGA is a biocompatible and biodegradable copolymer of lactic and glycolic acid and is FDA approved in various drug delivery systems. [91].
- It was therefore concluded that PLGA encapsulated ciprofloxacin is more promising for the treatment of E. coli biofilms.
- Chitosan itself has antimicrobial activity by adsorption onto the bacteria, causing aggregation and leakage of their intracellular content.
- 2.3 Encapsulation efficiency Similar as for liposomes, the encapsulation efficiency of antibiotics in polymeric nanoparticles determines how much antimicrobial agent can be delivered to the biofilm.
3 Targeted delivery to biofilms
- Functionalizing drug delivery nanoparticles with targeting ligands could be beneficial to achieve accumulation of the nanoparticles close to the bacterial cells and to promote close contact of the nanocarrier with the bacteria.
- Targeting can also be beneficial in environments with high shear forces, such as the oral cavity, where only short exposure times can be achieved (e.g. mouthwash).
- A distinction can be made between specific and non‐specific targeting.
- Non‐ specific targeting mainly relies on charge based interactions and hydrogen bonding of the nanocarrier with the biofilm.
- While biofilm targeting strategies have extensively been developed for liposomal drug delivery systems, to the best of our knowledge no studies regarding the specific targeting of polymer or lipid‐polymer hybrid nanoparticles have been published to date.
3.1. Non‐specific targeting
- Jones and coworkers established that phosphatidylinositol (PI) and to a lesser extent DPPG caused the adsorption of liposomes to biofilms formed by bacteria recovered from the skin and the oral cavity. [75].
- All the liposomes tested showed a certain degree of inhibition of the bacterial growth, but only for low drug to PLGA PCL Ciprofloxacin Levofloxacin 0.17‐0.24 ND.
- ND ND Stearylamine (SA) is another compound that can be used for the targeting of biofilm bacteria.
- More liposomes are adsorbed at lower ionic strength, at higher temperatures and when the bacteria are more hydrophobic.
- Over time, more and more liposomes adsorb onto the biofilm, increasing the penicillin G concentration in the biofilm and slowing penicillin G release from the liposomes. [73].
3.2 Specific targeting
- Another targeting possibility is the use of immunoliposomes which carry covalently bound antibodies on the outer surface.
- The immunoliposomes strongly adsorbed to S. oralis biofilms and showed decreased affinity to other oral commensal bacteria tested (S. gordonii, S. sanguis C104 and S. salivarius DBD and 8618), indicating that targeting of an antimicrobial agent to a specific organism can be achieved.
- Furthermore, the affinity of the DPPC:PI:DPPE‐ anti S. oralis immunoliposomes was compared to that of DPPC:Chol:SA cationic liposomes and DPPC:PI anionic liposomes.
- One example is concanavalin A (Con‐A), which selectively binds to α‐mannopyranosyl and α‐glucopyranosyl residues that can be found in the extracellular polysaccharide matrix of many biofilms.
- The latter involves the use of a photosensitizer that produces reactive oxygen species (ROS) upon exposure to light.
4 Triggered release inside biofilms
- Triggered release of the antibiotic from nanoformulations in close proximity to the biofilm bacteria is another approach to increase the local concentration of antibiotics in the biofilm.
- The ability of nanoparticles to penetrate into the biofilm is a first aspect that needs to be investigated.
- The interaction of phospholipid liposomes with mixed bacterial biofilms and their use in the delivery of bactericide, Colloids and Surfaces a‐ Physicochemical and Engineering Aspects, 186 (2001) 43‐53. [81].
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