Application of Mono and Trinuclear Cyclometalated Iridium (III) Complexes in Differential Bacterial Imaging and Antimicrobial Photodynamic therapy

The application of transition metal complexes for antimicrobial photodynamic therapy (PDT) has emerged as an attractive alternative in mitigating a broad range of bacterial pathogens, including multidrug-resistant pathogens. In view of their photostability, long excited-state lifetimes, and tunable emission properties, transition metal complexes also contribute as bioimaging agents. In the present work, we designed mono and trinuclear cyclometalated iridium(III) complexes to explore their imaging application and antibacterial potential.  For this, we used Methicillin-resistant S. aureus (MRSA), the most prevalent of community-associated (CA) multidrug-resistant (MDR) bacteria (CA MDR) and Lactococcus lactis (L. lactis) as Gram-positive while Campylobacter jejuni (C. jejuni) and E. coli as Gram-negative bacteria. In addition to differential bioimaging of these bacteria, we assessed the antibacterial effects of both mono and trinuclear Ir(III) complexes under exposure to 427 nm LED light. The data presented herein strongly suggest better efficacy of trinuclear Ir(III) complex over mononuclear complex in imparting photoinduced cell death of MRSA. Based on the safety profile of these complexes, we propose that trinuclear cyclometalated iridium(III) complex hold great promise for selective recognition and targeting MDR bacteria with minimal off-target effect.

Identification and functional characterization of putative ligand binding domain(s) of JlpA protein of Campylobacter jejuni

Among the major Surface Exposed Colonization Proteins (SECPs) of Campylobacter jejuni (C. jejuni), Jejuni lipoprotein A (JlpA) plays a crucial role in host cell adhesion specifically by binding to the N-terminal domain of the human heat shock protein 90α (Hsp90α-NTD). Although the JlpA binding to Hsp90α activates NF-κB and p38 MAP kinase pathways, the underlying mechanism of JlpA association with the cellular receptor remains unclear. To this end, we predicted two potential receptor binding sites within the C-terminal domain of JlpA: one spanning from amino acid residues Q332-A354 and the other from S258-T295; however, the latter exhibited weaker binding. To assess the functional attributes of these predicted sequences, we generated two JlpA mutants (JlpAΔ1: S258-T295; JlpAΔ2: Q332-A354) and assessed the Hsp90α-binding affinity-kinetics by in vitro and ex vivo experiments. Our findings confirmed that the residues Q332-A354 are of greater importance in host cell adhesion with a measurable impact on cellular responses. Further, thermal denaturation by circular dichroism (CD) confirmed that the reduced binding affinity of the JlpAΔ2 to Hsp90α is not associated with protein folding or stability. Together, this study provides a possible framework for determining the molecular function of designing rational inhibitors efficiently targeting JlpA.

Antibacterial activity of hydrophobicity modulated cationic polymers with enzyme and pH-responsiveness

The membrane lipid compositions of prokaryotic and eukaryotic cells are inherently different in many aspects, although some similarities exist in their structure and composition. Therefore, selective targeting of membrane lipids with a compound of therapeutic value, such as an antibacterial copolymer, is often challenging. Hence, developing an ideal copolymer with antibacterial properties demands hydrophobicity/hydrophilicity balance with a high biosafety profile. To integrate hydrophobic/hydrophilic balance and cationic charge in an alternating antibacterial copolymer with enzyme and pH-responsiveness, a lysine appended styrenic monomer was copolymerized with a fatty acid (octanoic acid (OA) or myristic acid (MA)) tethered maleimide monomer via reversible addition-fragmentation chain transfer (RAFT) polymerization. A range of microscopic analyses, including dynamic light scattering (DLS), confirmed the formation of nanoaggregates (size ∼30-40 nm) by these polymers in aqueous solution with positive zeta potential (cationic surface charge). Hydrophobic Nile red (NR) dye was successfully encapsulated in the nanoaggregates, and the in vitro release kinetics of the NR dye were monitored at different pHs and in the presence or absence of esterase/lipase. The in vitro release kinetics of NR revealed ∼85% dye release in the presence of pH 5.5 and lipase, suggesting their suitability for pH/enzyme-triggered therapeutic payload delivery. The standard broth microdilution assay showed significant bactericidal activity against both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria with an MIC50 value <30 μg mL-1. The effect of polymeric nanoaggregates on bacterial morphology and in vitro survival was further confirmed by field emission scanning electron microscopy (FESEM), agar gel disk diffusion assay, and bacterial live/dead cell count. The significantly low hemolytic activity against red blood cells (RBCs) (HC50 >103 μg mL-1) and nontoxic effect on human intestinal epithelial cells (INT 407) (EC50 >500 μg mL-1) ensure that the polymer nanoaggregates are safe for in vivo use and can serve as a potent antibacterial polymer.

Tuning the Organelle-Specific Imaging and Photodynamic Therapeutic Efficacy of Theranostic Mono- and Trinuclear Organometallic Iridium(III) Complexes

The organelle-specific localization of mononuclear and trinuclear iridium(III) complexes and their photodynamic behavior within the cells are described herein, emphasizing their structure-activity relationship. Both the IrA2 and IrB2 complexes possess a pair of phenyl-benzothiazole derived from the -CHO moieties of mononuclear organometallic iridium(III) complexes IrA1 and IrB1, which chelates IrCp*Cl (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) to afford trinuclear complexes IrA3 and IrB3. Insights into the photophysical and electrochemical parameters of the complexes were obtained by a time-dependent density functional theory study. The synthesized complexes IrA2, IrA3, IrB2, and IrB3 were found to be nontoxic to human MCF7 breast carcinoma cells. However, the photoexcitation of complexes using LED light could effectively trigger intracellular reactive oxygen species (ROS) generation, leading to cell death. Furthermore, to check the organelle-specific localization of IrA2 and IrB2, we observed that both complexes could selectively localize in the endoplasmic reticulum. In contrast, trinuclear IrA3 and IrB3 accumulate in the nuclei. The photoexcitation of complexes using LED light could effectively trigger intracellular reactive oxygen species (ROS) generation, leading to cell death.

The immune-adjunctive potential of recombinant LAB vector expressing murine IFNλ3 (MuIFNλ3) against Type A Influenza Virus (IAV) infection

BACKGROUND

The conventional means of controlling the recurring pandemics of Type A Influenza Virus (IAV) infections remain challenging primarily because of its high mutability and increasing drug resistance. As an alternative to control IAV infections, the prophylactic use of cytokines to drive immune activation of multiple antiviral host factors has been progressively recognized. Among them, Type III Interferons (IFNs) exhibit a pivotal role in inducing potent antiviral host responses by upregulating the expression of several antiviral genes, including the Interferon-Stimulated Genes (ISGs) that specifically target the virus replication machinery. To harness the immuno-adjunctive potential, we examined whether pre-treatment of IFNλ3, a Type III IFN, can activate antiviral host responses against IAV infections.

METHODS

In the present study, we bioengineered a food-grade lactic acid-producing bacteria (LAB), Lactococcus lactis (L. lactis), to express and secrete functional murine IFNλ3 (MuIFNλ3) protein in the extracellular milieu. To test the immune-protective potential of MuIFNλ3 secreted by recombinant L. lactis (rL. lactis), we used murine B16F10 cells as an in vitro model while mice (BALB/c) were used for in vivo studies.

RESULTS

Our study demonstrated that priming with MuIFNλ3 secreted by rL. lactis could upregulate the expression of several antiviral genes, including Interferon Regulatory Factors (IRFs) and ISGs, without exacerbated pulmonary or intestinal inflammatory responses. Moreover, we also showed that pre-treatment of B16F10 cells with MuIFNλ3 can confer marked immune protection against mice-adapted influenza virus, A/PR/8/1934 (H1N1) infection.

CONCLUSION

Since the primary target for IAV infections is the upper respiratory and gastrointestinal tract, immune activation without affecting the tissue homeostasis suggests the immune-adjunctive potential of IFNλ3 against IAV infections.

Multimodal Biofilm Inactivation Using a Photocatalytic Bismuth Perovskite-TiO2-Ru(II)polypyridyl-Based Multisite Heterojunction

Infectious bacterial biofilms are recalcitrant to most antibiotics compared to their planktonic version, and the lack of appropriate therapeutic strategies for mitigating them poses a serious threat to clinical treatment. A ternary heterojunction material derived from a Bi-based perovskite-TiO₂ hybrid and a [Ru(2,2'-bpy)₂(4,4'-dicarboxy-2,2'-bpy)]²⁺ (2,2'-bpy, 2,2'-bipyridyl) as a photosensitizer (RuPS) is developed. This hybrid material is found to be capable of generating reactive oxygen species (ROS)/reactive nitrogen species (RNS) upon solar light irradiation. The aligned band edges and effective exciton dynamics between multisite heterojunctions are established by steady-state/time-resolved optical and other spectroscopic studies. Proposed mechanistic pathways for the photocatalytic generation of ROS/RNS are rationalized based on a cascade-redox processes arising from three catalytic centers. These ROS/RNS are utilized to demonstrate a proof-of-concept in treating two elusive bacterial biofilms while maintaining a high level of biocompatibility (IC₅₀ > 1 mg/mL). The in situ generation of radical species (ROS/RNS) upon photoirradiation is established with EPR spectroscopic measurements and colorimetric assays. Experimental results showed improved efficacy toward biofilm inactivation of the ternary heterojunction material as compared to their individual/binary counterparts under solar light irradiation. The multisite heterojunction formation helped with better exciton delocalization for an efficient catalytic biofilm inactivation. This was rationalized based on the favorable exciton dissociation followed by the onset of multiple oxidation and reduction sites in the ternary heterojunction. This together with exceptional photoelectric features of lead-free halide perovskites outlines a proof-of-principle demonstration in biomedical optoelectronics addressing multimodal antibiofilm/antimicrobial modality.

A combined protocol for isolation of T6SS-positive Campylobacter jejuni and assessment of interspecies interaction

The bacterial Type VI Secretion System (T6SS) functions as a nanomachine used by many gut pathogens. In the present protocol, we outlined how such molecular activities during interspecies interaction can be demonstrated at a population level. To this end, we first present a comprehensive protocol for isolation, identification, and functional characterization of T6SS-positive Campylobacter jejuni. Further, we developed straightforward techniques for unraveling how the T6SS targets prey populations and host cells when growing with or without environmental stressors.

For complete details on the use and execution of this protocol, please refer to Gupta et al. (2021).

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A technique for isolation and identification of C. jejuni from its primary host

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Molecular and Functional characterization of C. jejuni T6SS

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Protocol for direct visualization of T6SS-dependent interspecies interaction

Bioengineering of LAB vector expressing Haemolysin co-regulated protein (Hcp): a strategic approach to control gut colonization of Campylobacter jejuni in a murine model

Background

Campylobacter jejuni (C. jejuni) is accountable for more than 400 million cases of gastroenteritis each year and is listed as a high-priority gut pathogen by the World Health Organization (WHO). Although the acute infection of C. jejuni (campylobacteriosis) is commonly treated with macrolides and fluoroquinolones, the emergence of antibiotic resistance among C. jejuni warrants the need for an alternative approach to control campylobacteriosis in humans. To this end, vaccines remain a safe, effective, and widely accepted strategy for controlling emerging and re-emerging infectious diseases. In search of a suitable vaccine against campylobacteriosis, recently, we demonstrated the potential of recombinant Haemolysin co-regulated protein (Hcp) of C. jejuni Type VI secretion system (T6SS) in imparting significant immune-protection against cecal colonization of C. jejuni; however, in the avian model. Since clinical features of human campylobacteriosis are more complicated than the avians, we explored the potential of Hcp as a T6SS targeted vaccine in a murine model as a more reliable and reproducible experimental host to study vaccine-induced immune-protection against C. jejuni. Because C. jejuni primarily utilizes the mucosal route for host pathogenesis, we analyzed the immunogenicity of a mucosally deliverable bioengineered Lactic acid bacteria (LAB), Lactococcus lactis (L. lactis), expressing Hcp. Considering the role of Hcp in both structural (membrane-bound) and functional (effector protein) exhibition of C. jejuni T6SS, a head-to-head comparison of two different forms of recombinant LAB vectors (cell wall anchored and secreted form of Hcp) were tested and assessed for the immune phenotypes of each modality in BALB/c mice.

Results

We show that regardless of the Hcp protein localization, mucosal delivery of bioengineered LAB vector expressing Hcp induced high-level production of antigen-specific neutralizing antibody (sIgA) in the gut with the potential to reduce the cecal load of C. jejuni in mice.

Conclusion

Together with the non-commensal nature of L. lactis, short gut transit time in humans, and the ability to express the heterologous protein in the gut, the present study highlights the benefits of bioengineered LAB vectors based mucosal vaccine modality against C. jejuni without the risk of immunotolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13099-021-00444-2.

Molecular characterization of Bu-1 and TLR2 gene in Haringhata Black chicken

Haringhata Black is the only registered indigenous poultry genetic resource of West Bengal till date. Molecular characterization of HB revealed that Bu-1 to be highly glycoylated transmembrane protein unlike mammalian Bu-1, whereas TLR2 of HB chicken was observed to be rich in Leucine rich repeat. HB chicken was observed to be genetically close to chicken of Japan, while distant to chicken breed of UK and Chicago. Avian species wise evolution study indicates genetic closeness of HB chicken with turkey. Differential mRNA expression profile for the immune response genes (TLR2, TLR4 and Bu1 gene) were studied for HB chicken with respect to other chicken breed and poultry birds, which reveals that HB chicken were better in terms of B cell mediated immunity and hence better response to vaccination. Hence HB chicken is one of the best poultry genetic resources to be reared under backyard system where biosecurity measures are almost lacking.

Blocking the attachment of cancer cells in vivo with DNA aptamers displaying anti-adhesive properties against the carcinoembryonic antigen

The formation of metastatic foci occurs through a series of cellular events, initiated by the attachment and aggregation of cancer cells leading to the establishment of micrometastases. We report the derivation of synthetic DNA aptamers bearing anti-adhesive properties directed at cancer cells expressing the carcinoembryonic antigen (CEA). Two DNA aptamers targeting the homotypic and heterotypic IgV-like binding domain of CEA were shown to block the cell adhesion properties of CEA, while not recognizing other IgV-like domains of CEACAM family members that share strong sequence and structural homologies. More importantly, the pre-treatment of CEA-expressing tumour cells with these aptamers prior to their intraperitoneal implantation resulted in the prevention of peritoneal tumour foci formation. Taken together, these results highlight the effectiveness of targeting the cell adhesion properties of cancer cells with aptamers in preventing tumour implantation.

A toll-like receptor 3 ligand enhances protective effects of vaccination against Marek's disease virus and hinders tumor development in chickens

Marek's disease (MD) is caused by Marek's disease virus (MDV). Various vaccines including herpesvirus of turkeys (HVT) have been used to control this disease. However, HVT is not able to completely protect against very virulent strains of MDV. The objective of this study was to determine whether a vaccination protocol consisting of HVT and a Toll-like receptor (TLR) ligand could enhance protective efficacy of vaccination against MD. Hence, chickens were immunized with HVT and subsequently treated with synthetic double-stranded RNA polyriboinosinic polyribocytidylic [poly(I:C)], a TLR3 ligand, before or after being infected with a very virulent strain of MDV. Among the groups that were HVT-vaccinated and challenged with MDV, the lowest incidence of tumors was observed in the group that received poly(I:C) before and after MDV infection. Moreover, the groups that received a single poly(I:C) treatment either before or after MDV infection were better protected against MD tumors compared to the group that only received HVT. No association was observed between viral load, as determined by MDV genome copy number, and the reduction in tumor formation. Overall, the results presented here indicate that poly(I:C) treatment, especially when it is administered prior to and after HVT vaccination, enhances the efficacy of HVT vaccine and improves protection against MDV.

A Toll-like receptor 3 agonist (polyI:C) elicits innate host responses in the spleen and lungs of chickens

Double-stranded (ds) RNA interacts with host Toll-like receptor (TLR-3), leading to the induction of anti-viral host responses. The present study was designed to compare different routes of administration of a synthetic dsRNA (polyI:C) for induction of innate responses in chicken spleen and lungs. Chickens were treated with polyI:C via the aerosol, intra-air sac (i.a.s.), and intramuscular (IM) routes. Spleen and lungs were collected at 0, 2, 6, 12, and 24 h post-treatment and the expression of innate defence genes was quantified by real-time reverse transcriptase polymerase chain reaction (RT-PCR). There was an up-regulation of interferon (IFN)-β, TLR-3, and Toll/interleukin 1 receptor domain-containing adaptor protein inducing IFN-β (TRIF) at 6 h post-treatment in the spleen via IM administration of polyI:C. There was also an increase in the expression of TLR-3 and TRIF in the spleen at 2 h post-treatment via the i.a.s. route. The expression of IFN-α and TRIF was upregulated at 6 h post-treatment via the i.a.s. route in the lungs. Overall, our results indicate that administration of polyI:C can locally and systemically induce the expression of innate response genes depending on the route.

A focused immune response targeting the homotypic binding domain of the carcinoembryonic antigen blocks the establishment of tumor foci in vivo

Metastatic forms of cancers remain the main cause of death in cancer patients. In this study, we demonstrate that directing a sustained antibody response towards the homotypic binding function of CEA interferes with the implantation and development of tumor foci in CEA-expressing transgenic (CEA.Tg) mice. Specifically, vaccinating CEA.Tg mice with a recombinant, altered self-form of the CEA Ig V-like N domain led to the production of circulating IgG1 and IgG2a antibodies that inhibited CEA-mediated adhesion of murine carcinoma expressing CEA (MC38.CEA) and mediated antibody-dependent lysis of tumor cells. Moreover, vaccinated CEA.Tg mice were resistant to the development of tumor nodules in the lungs and the peritoneal cavity, suggesting that mounting a focused antibody response to the CEA N domain may represent a simple therapeutic strategy to control the establishment of metastatic foci in cancer patients.

Co-immunization with interlukin-18 enhances the protective efficacy of liposomes encapsulated recombinant Cu-Zn superoxide dismutase protein against Brucella abortus

Brucellosis is a worldwide zoonotic disease caused by Brucella abortus and a number of closely related species. Brucellosis has severe impact on the health and economic prosperity of the developing countries due to the persistent nature of infection and unavailability of effective control measures. The Cu-Zn superoxide dismuatse (SOD) protein of Brucella have been extensively studied as a major antigen involved in bacterial evading mechanism of host defence. Being a critical pro-inflammatory cytokine interleukin-18 (IL-18) plays key role in induction of immune mediated protection against intracellular pathogens. In the present study, we aimed to investigate the immunogenic potential of fusogenic liposomes (escheriosomes) encapsulated recombinant Cu-Zn SOD (rSOD) protein alone or in combination with recombinant IL-18 (rIL-18). Escheriosomes encapsulated rSOD mediated immune responses were further increased upon co-immunization with rIL-18. Furthermore, immunization with escheriosomes encapsulated rSOD alone or in combination with rIL-18, increased resistance in mice against challenge with B. abortus 544.

Enhancement of immunogenicity of a virosome-based avian influenza vaccine in chickens by incorporating CpG-ODN

Influenza virosomes are virus-like particles, representing a platform for vaccine development. In this study, we examined the immunogenicity of avian influenza virosomes with or without inclusion of recombinant chicken interferon-gamma (rChIFN-γ) or CpG-ODN in chickens. Immunization with virosomes adjuvanted with CpG-ODN elicited the highest haemagglutination inhibition antibody titres, as well as IgG and IgA serum antibody responses. Moreover, Virosomes+CpG-ODN formulation induced an antigen-specific spleen cell proliferation and IFN-γ expression. In conclusion, our results demonstrated that virus-specific antibody- and cell-mediated responses may be induced in chickens immunized with virosomes and these responses can be enhanced by incorporating CpG-ODN in the virosome vaccine formulation.

Liposomised recombinant ribosomal L7/L12 protein protects BALB/c mice against Brucella abortus 544 infection

Brucella abortus, a facultative intracellular pathogen, is of tremendous zoonotic importance because of its ability to induce spontaneous abortion in cattle and other livestock. It is also known to cause persistent undulant fever, endocarditis, arthritis, osteomyelitis and meningitis in humans. The available vaccines against this dreadful infection suffer from limitations like short-term immunity, increased risk of hypersensitivity and low prophylactic index in the recipients. In the present study, we have demonstrated that liposomal form of a recombinant ribosomal L7/L12 protein, a B-T cell antigen of B. abortus, activates strong immune response in the host. In contrast, free antigen generates moderate immune response in the immunised animals. The liposomisation of rL7/L12 protein causes tremendous increase in cell-mediated immune response in terms of delayed type hypersensitivity, T-cell proliferation and up-regulation in type I cytokine expression, etc. Moreover, the liposome encapsulated antigen elicited stronger humoral immune response as compared to standard vaccine (S-19) or IFA-L7/L12 combination in the immunised animals. The effectiveness of liposome-based vaccine was also substantiated by better systemic clearance of bacterial load after challenging the animals with B. abortus 544 pathogen. The results of the present study suggest the potential of liposome-based rL7/L12 antigen as prospective and efficient candidate vaccine capable of eliciting both cell mediated as well as humoral immune responses against experimental murine brucellosis.

Co-administration of immunomodulator tuftsin and liposomised nystatin can combat less susceptible Candida albicans infection in temporarily neutropenic mice

In order to develop a prospective chemotherapeutic agent against opportunistic infections, it is important to know that host factors such as degree of immunological debility as well as recovery of immune functions to normality may contribute significantly to a successful elimination of the pathogens. We demonstrated previously that concomitant delivery of antimicrobial agents and immunomodulators to the pathogen harbouring-host contributes to the complete elimination of the deep-seated fungal infections (aspergillosis and candidiasis) in animals with normal immune status. Considering that neutropenic hosts are the main targets of such infections, it can be argued about the potential of the immunomodulator-based therapy in subjects with non-functional immune system. To resolve the hypothesis, we studied the role of immunomodulator tuftsin against experimental murine candidiasis in temporarily neutropenic Balb/c mice. The neutropenic mice were challenged with an isolate of Candida albicans that was showing less susceptibility to both free and liposomised-amphotericin B. The co-administration of tuftsin increased the efficiency of liposomised-polyene antibiotics (nystatin and amphotericin B) against experimental murine candidiasis in immunocompromised Balb/c mice. Pretreatment with liposomised tuftsin prior to C. albicans infection clearly enhanced protection against candidiasis, suggesting a prophylactic role of tuftsin in normal and temporarily neutropenic animals.