Photoactivated rose bengal functionalized chitosan nanoparticles produce antibacterial/biofilm activity and stabilize dentin-collagen

Treatment of infected teeth presents two major challenges: persistence of the bacterial-biofilm within root canals after treatment and compromised structural integrity of the dentin hard-tissue. In this study bioactive polymeric chitosan nanoparticles functionalized with rose-bengal, CSRBnp were developed to produce antibiofilm effects as well as stabilize structural-integrity by photocrosslinking dentin-collagen. CSRBnp were less toxic to fibroblasts and had significant antibacterial activity even in the presence of bovine serum albumin. CSRBnp exerted antibacterial mechanism by adhering to bacterial cell surface, permeabilizing the membrane and lysing the cells subsequent to photodynamic treatment. Photoactivated CSRBnp resulted in reduced viability of Enterococcus faecalis biofilms and disruption of biofilm structure. Incorporation of CSRBnp and photocrosslinking significantly improved resistance to degradation and mechanical strength of dentin-collagen (P<0.05). The functionalized chitosan nanoparticles provided a single-step treatment of infected root dentin by combining the properties of chitosan and that of photosensitizer to eliminate bacterial-biofilms and stabilize dentin-matrix.

FROM THE CLINICAL EDITOR

In this study, bioactive polymeric chitosan nanoparticles functionalized with rose-bengal (a photosensitizer), CSRBnp were developed to produce antibiofilm effects as well as stabilize structural-integrity of dental root dentin by photocrosslinking dentin-collagen, leading to efficient elimination of bacterial-biofilms and stabilization of dentin-matrix.

Photodynamic inactivation of biofilm: taking a lightly colored approach to stubborn infection

Microbial biofilms are responsible for a variety of microbial infections in different parts of the body, such as urinary tract infections, catheter infections, middle-ear infections, gingivitis, caries, periodontitis, orthopedic implants, and so on. The microbial biofilm cells have properties and gene expression patterns distinct from planktonic cells, including phenotypic variations in enzymic activity, cell wall composition and surface structure, which increase the resistance to antibiotics and other antimicrobial treatments. There is consequently an urgent need for new approaches to attack biofilm-associated microorganisms, and antimicrobial photodynamic therapy (aPDT) may be a promising candidate. aPDT involves the combination of a nontoxic dye and low-intensity visible light which, in the presence of oxygen, produces cytotoxic reactive oxygen species. It has been demonstrated that many biofilms are susceptible to aPDT, particularly in dental disease. This review will focus on aspects of aPDT that are designed to increase efficiency against biofilms modalities to enhance penetration of photosensitizer into biofilm, and a combination of aPDT with biofilm-disrupting agents.

Xylan-type hemicellulose supported palladium nanoparticles: a highly efficient and reusable catalyst for the carbon–carbon coupling reactions

A heterogeneous catalyst was prepared by depositing palladium nanoparticles onto xylan-type hemicellulose, which is a kind of renewable biopolymer catalyst, and used as an efficient and recyclable catalyst for the Suzuki, Heck, and Sonogashira cross-coupling reactions.

Multiple strategies to activate gold nanoparticles as antibiotics

Widespread antibiotic resistance calls for new strategies. Nanotechnology provides a chance to overcome antibiotic resistance by multiple antibiotic mechanisms. This paper reviews the progress in activating gold nanoparticles with nonantibiotic or antibiotic molecules to combat bacterial resistance, analyzes the gap between experimental achievements and real clinical application, and suggests some potential directions in developing antibacterial nanodrugs.

A novel bone cement impregnated with silver-tiopronin nanoparticles: its antimicrobial, cytotoxic, and mechanical properties

Post-operatory infections in orthopedic surgeries pose a significant risk. The common approach of using antibiotics, both parenterally or embedded in bone cement (when this is employed during surgery) faces the challenge of the rising population of pathogens exhibiting resistance properties against one or more of these compounds; therefore, novel approaches need to be developed. Silver nanoparticles appear to be an exciting prospect because of their antimicrobial activity and safety at the levels used in medical applications. In this paper, a novel type of silver nanoparticles capped with tiopronin is presented. Two ratios of reagents during synthesis were tested and the effect on the nanoparticles investigated through TEM, TGA, and UV-Vis spectroscopy. Once encapsulated in bone cement, only the nanoparticles with the highest amount of inorganic fraction conferred antimicrobial activity against methicillin resistant Staphylococcus aureus (MRSA) at concentrations as low as 0.1% w/w. No other characteristics of the bone cement, such as cytotoxicity or mechanical properties, were affected by the presence of the nanoparticles. Our work presents a new type of silver nanoparticles and demonstrates that they can be embedded in bone cement to prevent infections once the synthetic conditions are tailored for such applications.

Hypericin encapsulated in solid lipid nanoparticles: phototoxicity and photodynamic efficiency

The hydrophobicity of some photosensitizers can induce aggregation in biological systems, which consequently reduces photodynamic activity. The conjugation of photosensitizers with nanocarrier systems can potentially be used to overcome this problem. The objective of this study was to prepare and characterise hypericin-loaded solid lipid nanoparticles (Hy-SLN) for use in photodynamic therapy (PDT). SLN were prepared using the ultrasonication technique, and their physicochemical properties were characterised. The mean particle size was found to be 153 nm, with a low polydispersity index of 0.28. One of the major advantages of the SLN formulation is its high entrapment efficiency (EE%). Hy-SLN showed greater than 80% EE and a drug loading capacity of 5.22% (w/w). To determine the photodynamic efficiency of Hy before and after encapsulation in SLN, the rate constants for the photodecomposition of two (1)O2 trapping reagents, DPBF and AU, were determined. These rate constants exhibited an increase of 60% and 50% for each method, respectively, which is most likely due to an increase in the lifetime of the triplet state caused by the increase in solubility. Hy-SLN presented a 30% increase in cell uptake and a correlated improvement of 26% in cytotoxicity. Thus, all these advantages suggest that Hy-loaded SLN has potential for use in PDT.

Shining light on materials--a self-sterilising revolution

This review focuses on the development of light activated antimicrobial surfaces. These surfaces kill microbes by the action of light and have potential applications in domestic and healthcare settings. The inspiration for the new self-cleaning surfaces originates from photodynamic therapy where light is used to locate and destroy tumours. The first generation photosensitiser molecules, based on a porphyrin ring structure, could be considered as bioinspired and chemically related to chlorophyll. The review looks at developments of both soft polymeric surfaces with either surface bound or impregnated photosensitiser molecules; and hard inorganic surfaces such as modified titanium dioxide. The bacterial kill mechanisms are looked into with both surface types showing primary microbial kill through a radical induced pathway. The hard inorganic surfaces also show low bacterial adherence by means of a light activated photo-wetting of the surfaces meaning that they are "Easy Clean" and wash off microbes uniformly.

Enhanced photoinactivation of Staphylococcus aureus with nanocomposites containing plasmonic particles and hematoporphyrin

We fabricated composite nanoparticles consisting of a plasmonic core (gold nanorods or gold-silver nanocages) and a hematoporphyrin-doped silica shell. The dual photodynamic and photothermal activities of such nanoparticles against Staphylococcus aureus 209 P were studied and compared with the activities of reference solutions (hematoporphyrin or silica-coated plasmonic nanoparticles). Bacteria were incubated with nanocomposites or with the reference solutions for 15 min, which was followed by CW light irradiation with a few exposures of 5 to 30 min. To stimulate the photodynamic and photothermal activities of the nanocomposites, we used LEDs (405 and 625 nm) and a NIR laser (808 nm), respectively. We observed enhanced inactivation of S. aureus 209 P by nanocomposites in comparison with the reference solutions. By using fluorescence microscopy and spectroscopy, we explain the enhanced antimicrobial effect of hematoporphyrin-doped nanocomposites by their selective accumulation in the vicinity of the bacteria.

Microbial efflux systems and inhibitors: approaches to drug discovery and the challenge of clinical implementation

Conventional antimicrobials are increasingly ineffective due to the emergence of multidrug-resistance among pathogenic microorganisms. The need to overcome these deficiencies has triggered exploration for novel and unconventional approaches to controlling microbial infections. Multidrug efflux systems (MES) have been a profound obstacle in the successful deployment of antimicrobials. The discovery of small molecule efflux system blockers has been an active and rapidly expanding research discipline. A major theme in this platform involves efflux pump inhibitors (EPIs) from natural sources. The discovery methodologies and the available number of natural EPI-chemotypes are increasing. Advances in our understanding of microbial physiology have shed light on a series of pathways and phenotypes where the role of efflux systems is pivotal. Complementing existing antimicrobial discovery platforms such as photodynamic therapy (PDT) with efflux inhibition is a subject under investigation. This core information is a stepping stone in the challenge of highlighting an effective drug development path for EPIs since the puzzle of clinical implementation remains unsolved. This review summarizes advances in the path of EPI discovery, discusses potential avenues of EPI implementation and development, and underlines the need for highly informative and comprehensive translational approaches.

Denis TG, Hamblin MR. Photodynamic Therapy for Cancer and for Infections: What Is the Difference?

Photodynamic therapy (PDT) was discovered over one hundred years ago when it was observed that certain dyes could kill microorganisms when exposed to light in the presence of oxygen. Since those early days, PDT has mainly been developed as a cancer therapy and as a way to destroy proliferating blood vessels. However, recently it has become apparent that PDT may also be used as an effective antimicrobial modality and a potential treatment for localized infections. This review discusses the similarities and differences between the application of PDT for the treatment of microbial infections and for cancer lesions. Type I and type II photodynamic processes are described, and the structure-function relationships of optimal anticancer and antimicrobial photosensitizers are outlined. The different targeting strategies, intracellular photosensitizer localization, and pharmacokinetic properties of photosensitizers required for these two different PDT applications are compared and contrasted. Finally, the ability of PDT to stimulate an adaptive or innate immune response against pathogens and tumors is also covered.

Shining light on nanotechnology to help repair and regeneration

Phototherapy can be used in two completely different but complementary therapeutic applications. While low level laser (or light) therapy (LLLT) uses red or near-infrared light alone to reduce inflammation, pain and stimulate tissue repair and regeneration, photodynamic therapy (PDT) uses the combination of light plus non-toxic dyes (called photosensitizers) to produce reactive oxygen species that can kill infectious microorganisms and cancer cells or destroy unwanted tissue (neo-vascularization in the choroid, atherosclerotic plaques in the arteries). The recent development of nanotechnology applied to medicine (nanomedicine) has opened a new front of advancement in the field of phototherapy and has provided hope for the development of nanoscale drug delivery platforms for effective killing of pathological cells and to promote repair and regeneration. Despite the well-known beneficial effects of phototherapy and nanomaterials in producing the killing of unwanted cells and promoting repair and regeneration, there are few reports that combine all three elements i.e. phototherapy, nanotechnology and, tissue repair and regeneration. However, these areas in all possible binary combinations have been addressed by many workers. The present review aims at highlighting the combined multi-model applications of phototherapy, nanotechnology and, reparative and regeneration medicine and outlines current strategies, future applications and limitations of nanoscale-assisted phototherapy for the management of cancers, microbial infections and other diseases, and to promote tissue repair and regeneration.

Lipopolysaccharide neutralizing peptide-porphyrin conjugates for effective photoinactivation and intracellular imaging of gram-negative bacteria strains

A simple and specific strategy based on the bioconjugation of a photosensitizer protophophyrin IX (PpIX) with a lipopolysaccharide (LPS) binding antimicrobial peptide YI13WF (YVLWKRKRKFCFI-Amide) has been developed for the effective fluorescent imaging and photodynamic inactivation of Gram-negative bacterial strains. The intracellular fluorescent imaging and photodynamic antimicrobial chemotherapy (PACT) studies supported our hypothesis that the PpIX-YI13WF conjugates could serve as efficient probes to image the bacterial strains and meanwhile indicated the potent activities against Gram-negative bacterial pathogens especially for those with antibiotics resistance when exposed to the white light irradiation. Compared to the monomeric PpIX-YI13WF conjugate, the dimeric conjugate indicated the stronger fluorescent imaging signals and higher photoinactivation toward the Gram-negative bacterial pathogens throughout the whole concentration range. In addition, the photodynamic bacterial inactivation also demonstrated more potent activity than the minimum inhibitory concentration (MIC) values of dimeric PpIX-YI13WF conjugate itself observed for E. coli DH5a (~4 times), S. enterica (~8 times), and other Gram-negative strains including antibiotic-resistant E. coli BL21 (~8 times) and K. pneumoniae (~16 times). Moreover, both fluorescent imaging and photoinactivation measurements also demonstrated that the dimeric PpIX-YI13WF conjugate could selectively recognize bacterial strains over mammalian cells and generate less photo damage to mammalian cells. We believed that the enhanced fluorescence and bacterial inactivation were probably attributed to the higher binding affinity between dimeric photosensitizer peptide conjugate and LPS components on the surface of bacterial strains, which were the results of efficient multivalent interactions.

Laser for treatment of aphthous ulcers on bacteria cultures and DNA

Low-intensity red lasers are proposed for treatment of oral aphthous ulcers based on biostimulative effects. However, effects of low-intensity lasers at fluences used in clinical protocols on DNA are controversial. The aim of this work was to evaluate the effects of low-intensity red laser on survival and induction of filamentation of Escherichia coli cells, and induction of DNA lesions in bacterial plasmids. Escherichia coli cultures were exposed to laser (660 nm, 100 mW, 25 and 45 J cm(-2)) to study bacterial survival and filamentation. Also, bacterial plasmids were exposed to laser to study DNA lesions by electrophoretic profile and action of DNA repair enzymes. Data indicate that low-intensity red laser: (i) had no effect on survival of E. coli wild type, exonuclease III and formamidopyrimidine DNA glycosylase/MutM protein but decreased the survival of endonuclease III deficient cultures; (ii) induced bacterial filamentation, (iii) there was no alteration in the electrophoretic profile of plasmids in agarose gels, (iv) there was no alteration in the electrophoretic profile of plasmids incubated with formamidopyrimidine DNA glycosylase/MutM protein and endonuclease III enzymes, but it altered the electrophoretic profile of plasmids incubated with exonuclease III. Low-intensity red laser at therapeutic fluences has an effect on the survival of E. coli endonuclease III deficient cells, induces bacterial filamentation in E. coli cultures and DNA lesions targeted by exonuclease III.

Concepts and principles of photodynamic therapy as an alternative antifungal discovery platform

Opportunistic fungal pathogens may cause superficial or serious invasive infections, especially in immunocompromised and debilitated patients. Invasive mycoses represent an exponentially growing threat for human health due to a combination of slow diagnosis and the existence of relatively few classes of available and effective antifungal drugs. Therefore systemic fungal infections result in high attributable mortality. There is an urgent need to pursue and deploy novel and effective alternative antifungal countermeasures. Photodynamic therapy (PDT) was established as a successful modality for malignancies and age-related macular degeneration but photodynamic inactivation has only recently been intensively investigated as an alternative antimicrobial discovery and development platform. The concept of photodynamic inactivation requires microbial exposure to either exogenous or endogenous photosensitizer molecules, followed by visible light energy, typically wavelengths in the red/near infrared region that cause the excitation of the photosensitizers resulting in the production of singlet oxygen and other reactive oxygen species that react with intracellular components, and consequently produce cell inactivation and death. Antifungal PDT is an area of increasing interest, as research is advancing (i) to identify the photochemical and photophysical mechanisms involved in photoinactivation; (ii) to develop potent and clinically compatible photosensitizers; (iii) to understand how photoinactivation is affected by key microbial phenotypic elements multidrug resistance and efflux, virulence and pathogenesis determinants, and formation of biofilms; (iv) to explore novel photosensitizer delivery platforms; and (v) to identify photoinactivation applications beyond the clinical setting such as environmental disinfectants.

Silica nanoparticles functionalized with porphyrins and analogs for biomedical studies

This review focus on the preparation of silica nanoparticles functionalized with porphyrins and related compounds. It is aimed to highlight their features as photosensitizers in the area of photodynamic therapy. In this field, photosensitizers have been covalently and non-covalently linked to silica nanoparticles, in order to study their photophysical and biological properties. Another fascinating scenario for photosensitizer-silica nanoparticles hybrids involves the possibility of including metal cores for conditioning the uptake in the target cells, allowing most of the times the combination of therapies and in certain conditions to facilitate the removal and reutilization of the photosensitizer in environmental applications.

All you need is light: antimicrobial photoinactivation as an evolving and emerging discovery strategy against infectious disease

The story of prevention and control of infectious diseases remains open and a series of highly virulent pathogens are emerging both in and beyond the hospital setting. Antibiotics were an absolute success story for a previous era. The academic and industrial biomedical communities have now come together to formulate consensus beliefs regarding the pursuit of novel and effective alternative anti-infective countermeasures. Photodynamic therapy was established and remains a successful modality for malignancies but photodynamic inactivation has been transformed recently to an antimicrobial discovery and development platform. The concept of photodynamic inactivation is quite straightforward and requires microbial exposure to visible light energy, typically wavelengths in the visible region, that causes the excitation of photosensitizer molecules (either exogenous or endogenous), which results in the production of singlet oxygen and other reactive oxygen species that react with intracellular components, and consequently produce cell inactivation. It is an area of increasing interest, as research is advancing i) to identify the photochemical and photophysical mechanisms involved in inactivation; ii) to develop potent and clinically compatible photosensitizer; iii) to understand how photoinactivation is affected by key microbial phenotypic elements (multidrug resistance and efflux, virulence and pathogenesis determinants, biofilms); iv) to explore novel delivery platforms inspired by current trends in pharmacology and nanotechnology; and v) to identify photoinactivation applications beyond the clinical setting such as environmental disinfectants.

Antimicrobial peptide-modified liposomes for bacteria targeted delivery of temoporfin in photodynamic antimicrobial chemotherapy

Photodynamic antimicrobial chemotherapy (PACT) and antimicrobial peptides (AMPs) are two promising strategies to combat the increasing prevalence of antibiotic-resistant bacteria. To take advantage of these two strategies, we integrated a novel antimicrobial peptide (WLBU2) and a potent generation II photosensitizer (temoporfin) into liposomes by preparing WLBU2-modified liposomes, aiming at bacteria targeted delivery of temoporfin for PACT. WLBU2 was successfully coupled to temoporfin-loaded liposomes using a functional phospholipid. The delivery of temoporfin to bacteria was confirmed by fluorescence microscopy and flow cytometry, thus demonstrating that more temoporfin was delivered to bacteria by WLBU2-modified liposomes than by unmodified liposomes. Consequently, the WLBU2-modified liposomes eradicated all methicillin-resistant Staphylococcus aureus (MRSA) and induced a 3.3 log(10) reduction of Pseudomonas aeruginosa in the in vitro photodynamic inactivation test. These findings demonstrate that the use of AMP-modified liposomes is promising for bacteria-targeted delivery of photosensitizers and for improving the PACT efficiency against both gram-positive and gram-negative bacteria in the local infections.