Preparation of antimicrobial reduced lysozyme compatible in food applications

Cytokinetic engineering enhances the secretory production of recombinant human lysozyme in Komagataella phaffii

BACKGROUND

Human lysozyme (hLYZ) is a natural antibacterial protein with broad applications in food and pharmaceutical industries. Recombinant production of hLYZ in Komagataella phaffii (K. phaffii) has attracted considerable attention, but there are very limited strategies for its hyper-production in yeast.

RESULTS

Here through Atmospheric and Room Temperature Plasma (ARTP)-based mutagenesis and transcriptomic analysis, the expression of two genes MYO1 and IQG1 encoding the cytokinesis core proteins was identified downregulated along with higher hLYZ production. Deletion of either gene caused severe cytokinesis defects, but significantly enhanced hLYZ production. The highest hLYZ yield of 1,052,444 ± 23,667 U/mL bioactivity and 4.12 ± 0.11 g/L total protein concentration were obtained after high-density fed-batch fermentation in the Δmyo1 mutant, representing the best production of hLYZ in yeast. Furthermore, O-linked mannose glycans were characterized on this recombinant hLYZ.

CONCLUSIONS

Our work suggests that cytokinesis-based morphology engineering is an effective way to enhance the production of hLYZ in K. phaffii.

Investigating the mechanism of antioxidants as egg white powder flavor modifiers

BACKGROUND

The uses of egg white powder (EWP) are restricted because of its odor. It is necessary to find a method to improve its flavor. In this paper, three different antioxidants - green tea extract (GTE), sodium ascorbate (SA), and glutathione (GSH) - were selected to modify the flavor. The physicochemical and structural properties of EWP were investigated to study the mechanism of the formation and release of volatile compounds.

RESULTS

Antioxidants can modify the overall flavor of EWP significantly, inhibiting the generation or release of nonanal, 3-methylbutanal, heptanal, decanal, geranyl acetone, and 2-pemtylfuran. A SA-EWP combination showed the lowest concentration of 'off' flavor compounds; GTE-EWP and GSH-EWP could reduce several 'off' flavor compounds but increased the formation of geranyl acetone and furans. The changes in the carbonyl content and the amino acid composition confirmed the inhibition of antioxidants with the oxidative degradation of proteins or characteristic amino acids. The results of fluorescence spectroscopy and Fourier transform infrared (FTIR) spectroscopy provided structural information regarding EWP, which showed the release of volatile compounds decreased due to structural changes. For example, the surface hydrophobicity increased and the protein aggregation state changed.

CONCLUSIONS

Antioxidants reduce the 'off' flavor of EWP in two ways: they inhibit protein oxidation and Maillard reactions (they inhibit formation of 3-methylbutanal and 2-pemtylfuran) and they enhance the binding ability of heat-denatured proteins (reducing the release of nonanal, decanal, and similar compounds). © 2023 Society of Chemical Industry.

Novel casein antimicrobial peptides for the inhibition of oral pathogenic bacteria

Milk casein is a rich source of antimicrobial peptides (AMPs) and the most common way to produce AMPs is enzymatic hydrolysis in vitro. In this study, active casein antimicrobial peptide (CAMPs) mixtures were generated by optimized proteolytic cleavage of milk casein. These natural-safe CAMPs mixtures exhibited high activity in the inhibition of Streptococcus mutans and Porphyromonas gingivalis. Morphological characterization suggested the pathogenic bacteria presented incomplete or irregular collapsed membrane surface after the treatment with active CAMPs mixtures. The CAMPs inhibition activity was also effective in the attachment and development of microbial biofilm. Potential CAMPs sequences were unambiguously determined by unbiased proteomic analysis and 301 potential CAMPs were obtained. The activity of 4 novel CAMPs was successfully confirmed by using synthetic standards. This study provides a promising milk CAMPs resource for the development of safe agents in oral bacteria inhibition and functional foods.

In-vitro assessment of a novel plant rhizobacterium, Citrobacter freundii, for degrading and biocontrol of food mycotoxin deoxynivalenol

Deoxynivalenol (DON) is one of the most harmful and well-known toxins present in food and animal feed throughout the world. Citrobacter freundii (C. freundii-ON077584), a novel DON-degrading strain, was isolated from rice root-linked soil samples. The degrading properties, including DON concentrations, incubation pH, incubation temperatures, bacterial concentrations, and acid treatment effect on degradation, were evaluated. At pH 7 and an incubation temperature of 37 °C, C. freundii demonstrated the capability to degrade more than 90% of DON. The degraded products of DON were identified as 3-keto-DON and DOM-1, which were confirmed by High Performance Liquid Chromatography (HPLC) and Ultra-Performance Liquid Chromatography hyphenated with Tandem Mass Spectrometry (UPLC-MS/MS) analyses. The mechanism of DON degradation into 3-keto-DON and DOM-1 by this bacterial strain will be further explored to identify and purify novel degrading enzymes that can be cloned to the microorganism and added to the animal feed to degrade the DON in the digestion tract.

Dietary Lysozyme Alters Sow's Gut Microbiota, Serum Immunity and Milk Metabolite Profile

The aim of current study was to determine variations in sow's gut microbiota, serum immunity, and milk metabolite profile mediated by lysozyme supplementation. Twenty-four pregnant sows were assigned to a control group without supplementation and two treatments with 0.5 kg/t and 1.0 kg/t lysozyme provided in formula feed for 21 days (n = 8 per treatment). Microbiota analysis and metagenomic predictions were based on 16s RNA high-throughput sequencing. Milk metabolome was assessed by untargeted liquid chromatography tandem mass spectrometry. Serum biochemical indicators and immunoglobulins were also determined. Gut microbial diversity of sows receiving 1.0 kg/t lysozyme treatment was significantly reduced after the trial. Spirochaetes, Euryarchaeota, and Actinobacteria significantly increased while Firmicutes showed a remarkable reduction in 1.0 kg/t group compared with control. Lysozyme addition rebuilt sow's gut microbiota to beneficial composition identified by reduced richness of Escherichia coli and increased abundance of Lactobacillus amylovorus. Accordingly, microbial metabolic functions including pyrimidine metabolism, purine metabolism, and amino acid related enzymes were significantly up-regulated in 1.0 kg/t group. Microbial metabolic phenotypes like the richness of Gram-positive bacteria and oxidative stress tolerance were also significantly reduced by lysozyme treatment. Serum alanine transaminase (ALT) activity and IgA levels were significantly down-regulated in the 1.0 kg/t group compared with control, but IgM levels showed a significantly increase in 1.0 kg/t group. Milk metabolites such as L-glutamine, creatine, and L-arginine showed significantly dose-dependent changes after treatment. Overall, lysozyme supplementation could effectively improve the composition, metabolic functions, and phenotypes of sow's gut microbiota and it also benefit sows with better serum immunity and milk composition. This research could provide theoretical support for further application of lysozyme in promoting animal gut health and prevent pathogenic infections in livestock production.

The antimicrobial spectrum of lysozyme broadened by reductive modification

In order to broaden the antimicrobial action spectrum of lysozyme against Gram-negative bacteria, different partially reduced lysozyme derivatives were obtained by reducing the R-S-S-R bonds of lysozyme using the reducing agent Na2SO3. The circular dichroism behavior analysis showed that the tertiary structure of the partially reduced lysozyme molecules became more flexible, leading to an obvious increase in the surface hydrophobicity and the tryptophan fluorescence intensity. Zeta potential analysis indicated that the introduction of SO32- led to a decrease in the surface charges of the reduced lysozyme molecules. Compared with the native lysozyme, the reduced lysozymes not only showed a 1 log increase in the antimicrobial activity against Escherichia coli ATCC 25922 and Salmonella enteritidis ATCC 13076 (P <0.05), but also maintained nearly the same antimicrobial activity against Staphylococcus aureus ATCC 29213 (P >0.05). Overall, the reductive modification with the food-friendly, compatible, and safe reducing agent Na2SO3 has broadened the antimicrobial action spectrum of the modified lysozymes against Gram-negative bacteria, with the enhancement extent depending on the reduction degree and the type of bacterial strains. The integrated results suggest that the Na2SO3-reduced lysozyme can be used as a novel safe potential bactericidal additive for food-processing industry.

Antibacterial Activity of Hen Egg White Lysozyme Denatured by Thermal and Chemical Treatments

The aim of this study was to increase the antibacterial spectrum of modified hen egg white lysozyme (HEWL) with thermal and chemical treatments against Gram-negative bacteria. The antibacterial activity of heat-denatured HEWL and chemical denatured HEWL against Gram-negative and Gram-positive bacteria was evaluated in 15 h of incubation tests. HEWL was denatured by heating at pH 6.0 and pH 7.0 and chemical denaturing was carried out for 1.0, 1.5, 2.0, and 4.0 h with DL-Dithiothreitol (DTT). HEWL modified by thermal and chemical treatments was characterized using the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) electrophoresis method. Heat-denatured HEWL lytic activity against Micrococcus lysodeikticus lessened with increasing temperature and time of incubation with the chemical agent (DTT). The loss of lytic activity in modified HEWL suggests that the mechanism of action of the antibacterial activity is not dependent on the lytic activity. Thermal and chemical treatments of HEWL enabled the production of oligoforms and increased antibacterial activity over a wider spectrum. Heat-denatured HEWL at pH 6.0 and chemically-denatured HEWL increased the HEWL antibacterial spectrum against Gram-negative bacteria (Escherichia coli ATCC 25922). HEWL at 120 °C and pH 6.0 (1.0 mg/mL) inhibited 78.20% of the growth of E. coli. HEWL/DTT treatment for 4.0 h (1.0 mg/mL) inhibited 68.75% of the growth E. coli. Heat-denatured HEWL at pH 6.0 and pH 7.0 and chemically-denatured HEWL (1.0, 1.5, 2.0, and 4.0 h with DTT) were active against Gram-positive bacteria (Staphylococcus carnosus CECT 4491T). Heat-denatured and chemical-denatured HEWL caused the death of the bacteria with the destruction of the cell wall. LIVE/DEAD assays of fluorescent dye stain of the membrane cell showed membrane perturbation of bacteria after incubation with modified HEWL. The cell wall destruction was viewed using electron microscopy. The results obtained in this study suggest that heat-denatured HEWL at pH 6.0 and chemical-denatured HEWL treatments increase the HEWL antibacterial activity against Gram-negative bacteria.

Ochratoxin A reduction ability of biocontrol agent Bacillus subtilis isolated from Korean traditional fermented food Kimchi

In the present study, a new biocontrol strain, Bacillus subtilis KU-153, was isolated from the Korean traditional fermented food Kimchi and evaluated for its ability to reduce the ochratoxin A (OTA) content in culture medium. A 16 S rRNA gene sequencing analysis revealed the identity of newly isolated strain KU-153 as B. subtilis. The growth kinetic study of B. subtilis KU-153, in terms of the OTA reduction in culture medium, confirmed its biocontrol efficacy. To verify its ability to reduce the OTA content in culture medium, bacterial extracts (intracellular and extracellular) of B. subtilis were separated and compared with whole B. subtilis cells (viable and heat-killed). No reduction in the OTA content was observed in culture medium with extracellular and intracellular extracts, while viable and heat-killed cells of B. subtilis showed significant levels (p < 0.05) of OTA reduction in culture medium. Interestingly, B. subtilis heat-treated cells showed a higher OTA reduction (45%) than viable cells (22%). Further, B. subtilis heat-treated cells were assessed for their ability to reduce OTA levels in artificially contaminated red wine samples that resulted in an OTA reduction of approximately 90%, suggesting the biocontrol potential of the newly isolated strain B. subtilis KU-153 on OTA reduction.

Dextran-Conjugated Lysozymes Inhibit the Growth of Shigella sonnei and Viral Hemorrhagic Septicemia Virus

Lysozyme is well known as a natural antimicrobial agent, but its function is limited in that it only combats Gram-positive bacteria. We investigated the inhibitory effects of dextran-conjugated lysozymes (DLs) against some strains of Gram-negative bacteria and viral hemorrhagic septicemia virus (VHSV). The Maillard reactions of the DL were performed at various pHs (3.0, 7.0, and 8.5) in the presence of saturated KBr solution for 1, 3, 5, 7, and 9 days. The growth inhibition effects against Gram-negative bacterial strains, such as Escherichia coli, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Shigella sonnei, and Shigella flexneri were found only in some DLs. DLs incubated at pH 7.0 for 9 days strongly inhibited growth of S. sonnei (92.9%). Fathead minnow (FHM) cells were infected with VHSV. DLs treated at all pHs for 1 day resulted in more than 80% viability of VHSV-infected FHM cells. The results of this study suggest that our DLs can be useful in food preservatives, pharmaceuticals, or aquatic feed due to their inhibitory effects against pathogenic bacteria and viral infections.

A Label-Free Fluorescent Array Sensor Utilizing Liposome Encapsulating Calcein for Discriminating Target Proteins by Principal Component Analysis

A new fluorescent arrayed biosensor has been developed to discriminate species and concentrations of target proteins by using plural different phospholipid liposome species encapsulating fluorescent molecules, utilizing differences in permeation of the fluorescent molecules through the membrane to modulate liposome-target protein interactions. This approach proposes a basically new label-free fluorescent sensor, compared with the common technique of developed fluorescent array sensors with labeling. We have confirmed a high output intensity of fluorescence emission related to characteristics of the fluorescent molecules dependent on their concentrations when they leak from inside the liposomes through the perturbed lipid membrane. After taking an array image of the fluorescence emission from the sensor using a CMOS imager, the output intensities of the fluorescence were analyzed by a principal component analysis (PCA) statistical method. It is found from PCA plots that different protein species with several concentrations were successfully discriminated by using the different lipid membranes with high cumulative contribution ratio. We also confirmed that the accuracy of the discrimination by the array sensor with a single shot is higher than that of a single sensor with multiple shots.

Antibacterial activity of hen egg white lysozyme modified by heat and enzymatic treatments against oenological lactic acid bacteria and acetic acid bacteria

The antimicrobial activity of heat-denatured and hydrolyzed hen egg white lysozyme against oenological lactic acid and acetic acid bacteria was investigated. The lysozyme was denatured by heating, and native and heat-denatured lysozymes were hydrolyzed by pepsin. The lytic activity against Micrococcus lysodeikticus of heat-denatured lysozyme decreased with the temperature of the heat treatment, whereas the hydrolyzed lysozyme had no enzymatic activity. Heat-denatured and hydrolyzed lysozyme preparations showed antimicrobial activity against acetic acid bacteria. Lysozyme heated at 90°C exerted potent activity against Acetobacter aceti CIAL-106 and Gluconobacter oxydans CIAL-107 with concentrations required to obtain 50% inhibition of growth (IC50) of 0.089 and 0.013 mg/ml, respectively. This preparation also demonstrated activity against Lactobacillus casei CIAL-52 and Oenococcus oeni CIAL-91 (IC50, 1.37 and 0.45 mg/ml, respectively). The two hydrolysates from native and heat-denatured lysozyme were active against O. oeni CIAL-96 (IC50, 2.77 and 0.3 mg/ml, respectively). The results obtained suggest that thermal and enzymatic treatments increase the antibacterial spectrum of hen egg white lysozyme in relation to oenological microorganisms.

Modified lysozymes as novel broad spectrum natural antimicrobial agents in foods

In recent years much attention and interest have been directed toward application of natural antimicrobial agents in foods. Some naturally occurring proteins such as lactoperoxidase, lactoferrin, and lysozyme have received considerable attention and are being considered as potential antimicrobial agents in foods. Lysozyme kills bacteria by hydrolyzing the peptidoglycan layer of the cell wall of certain bacterial species, hence its application as a natural antimicrobial agent has been suggested. However, limitations in the action of lysozyme against only Gram-positive bacteria have prompted scientists to extend the antimicrobial effects of lysozyme by several types of chemical modifications. During the last 2 decades extensive research has been directed toward modification of lysozyme in order to improve its antimicrobial properties. This review will report on the latest information available on lysozyme modifications and examine the applicability of the modified lysozymes in controlling growth of Gram-positive and Gram-negative bacteria in foods. The results of modifications of lysozyme using its conjugation with different small molecule, polysaccharides, as well as modifications using proteolytic enzymes will be reviewed. These types of modifications have not only increased the functional properties of lysozyme (such as solubility and heat stability) but also extended the antimicrobial activity of lysozyme. Many examples will be given to show that modification can decrease the count of Gram-negative bacteria in bacterial culture and in foods by as much as 5 log CFU/mL and in some cases essentially eliminated Escherichia coli. In conclusion this review demonstrates that modified lysozymes are excellent natural food preservatives, which can be used in food industry.

PRACTICAL APPLICATION

The subject described in this review article can lead to the development of methods to produce new broad-spectrum natural antimicrobial agents, based on modification of chicken egg white lysozyme, which might potentially replace the currently used synthetic food preservatives.

Bacteriophage therapy against staphylococci

The emergence of the multi-drug-resistant Staphylococcus aureus strains has prompted interest in alternatives to conventional drugs. Among the possible options one of the most promising is the therapeutic use of bacteriophages. Over the recent decades, increasing amount of literature has validated the use of bacteriophages for therapy and prophylaxis against drug-resistant staphylococci. This work attempts to review the current knowledge on bacteriophages and their usages for treatment of staphylococcal diseases.

Identification and characterization of the two-component cell lysis cassette encoded by temperate bacteriophage phiPYB5 of Lactobacillus fermentum

AIMS

To characterize the two-component cell lysis cassette comprised of holin (Hyb5) and endolysin (Lyb5) encoded by Lactobacillus fermentum temperate bacteriophage phiPYB5, and illustrate the potential application of Lyb5 as therapeutic agents.

METHODS AND RESULTS

The hyb5-lyb5 cassette was cloned from the genome library of phiPYB5, and the hyb5, lyb5 and hyb5-lyb5 cassette were expressed in E. coli BL21, respectively. The molecular weight of Hyb5 indicated by SDS-PAGE was 19 kDa, and Lyb5 was 45 kDa. Both Hyb5 and Lyb5 protein could induce cell lysis alone, resulting in the leakage of beta-galactosidase. However, the Hyb5-Lyb5 cassette lysed the host cells more rapidly and extensively. By zymogram analysis, Lyb5 exhibited a broad lytic spectrum.

CONCLUSIONS

Overexpression of hyb5, lyb5 and hyb5-lyb5 cassette were carried out in E. coli and Lyb5 exhibited a broad lytic spectrum.

SIGNIFICANCE AND IMPACT OF THE STUDY

The Lyb5 produced in E. coli exhibited a broad lytic spectrum against Gram-positive strains including Staphylococcus aureus as well as Gram-negative strains such as Salmonella typhi, suggesting that Lyb5 provides a potential alternative of diagnostic tools and therapeutic agents.

Lysozyme transgenic goats' milk influences gastrointestinal morphology in young pigs

Transgenesis provides a method of expressing novel proteins in milk to increase the functional benefits of milk consumption. Transgenic goats expressing human lysozyme (hLZ) at 67% of the concentration in human breast milk were produced, thereby enhancing the antimicrobial properties of goats' milk. The objective of this study was to investigate the impact of pasteurized milk containing hLZ on growth, the intestinal epithelium, and an enteropathogenic Escherichia coli (EPEC) infection in young weaned pigs. Pigs were placed into 4 groups and fed a diet of solid food and either control (nontransgenic) goats' milk or milk from hLZ-transgenic goats. Growth was assessed by weight gain. Nonchallenged pigs were necropsied after 6 wk, whereas the remaining pigs were necropsied at 7 wk following bacterial challenge. We determined the numbers of total coliforms and E. coli and examined small intestinal histology for all pigs. Complete blood counts were also determined pre- and postchallenge. Challenged pigs receiving hLZ milk had fewer total coliforms (P = 0.029) and E. coli (P = 0.030) in the ileum than controls. hLZ-fed pigs also had a greater duodenal villi width (P = 0.029) than controls. Additionally, nonchallenged hLZ-fed pigs had fewer intraepithelial lymphocytes per micron of villi height (P = 0.020) than nonchallenged controls. These results indicate that the consumption of pasteurized hLZ goats' milk has the potential to improve gastrointestinal health and is protective against an EPEC in young weaned pigs. These same benefits may occur in young children if they were to consume milk from hLZ-transgenic goats.

Quantitative electrochemiluminescence detection of proteins: Avidin-based sensor and tris(2,2'-bipyridine) ruthenium(II) label

Quantitative electrochemiluminescence (ECL) detection of a model protein, bovine serum albumin (BSA) was achieved via biotin-avidin interaction using an avidin-based sensor and a well-developed ECL system of tris(2,2'-bipyridine) ruthenium(II) derivative as label and tri-n-propylamine (TPA) as coreactant. To detect the protein, avidin was linked to the glassy carbon electrode through passive adsorptions and covalent interaction with carboxylate-terminated carbon nanotubes that was used as binder to immobilize avidin onto the electrode. Then, biotinylated BSA tagged with tris(2,2'-bipyridine) ruthenium(II) label was attached to the prepared avidin surface. After binding of BSA labeled with tris(2,2'-bipyridine) ruthenium(II) derivative to the surface-immobilized avidin through biotin, ECL response was generated when the self-assembled modified electrode was immersed in a TPA-containing electrolyte solution. Such double protein labeling protocol with a biotin label for biorecognition and ruthenium label for ECL detection facilitated the detection of protein compared to the classical double antibody sandwich format. The ECL intensity was linearly proportional to the feed concentration of BSA over two orders of magnitude in the range of 15nM to 7.5microM. The detection limit was estimated to be 1.5nM. Further application to the lysozyme analysis was carried out to validate the present approach for an effective and favorable protocol for the quantitative detection of proteins. The dynamic range of lysozyme was from 0.001gL(-1) to 0.1gL(-1) and the detection limit was 0.1mgL(-1). Electrochemical impedance and cyclic voltammetric measurements along with some necessary control experiments were conducted to characterize the successful formation of self-assembled modified electrodes and to grant the whole detection process.

Enzymatic lysis of microbial cells

Cell wall lytic enzymes are valuable tools for the biotechnologist, with many applications in medicine, the food industry, and agriculture, and for recovering of intracellular products from yeast or bacteria. The diversity of potential applications has conducted to the development of lytic enzyme systems with specific characteristics, suitable for satisfying the requirements of each particular application. Since the first time the lytic enzyme of excellence, lysozyme, was discovered, many investigations have contributed to the understanding of the action mechanisms and other basic aspects of these interesting enzymes. Today, recombinant production and protein engineering have improved and expanded the area of potential applications. In this review, some of the recent advances in specific enzyme systems for bacteria and yeast cells rupture and other applications are examined. Emphasis is focused in biotechnological aspects of these enzymes.

A novel lysozyme from Xanthomonas oryzae phage ϕXo411 active against Xanthomonas and Stenotrophomonas

In this study, a bacteriophage of Xanthomonas oryzae pv. oryzae designated as varphiXo411 was isolated. Random sequencing of its genome revealed that it is closely related to another X. oryzae phage, Xp10. A cloned fragment carries the lysozyme gene, lys411. The deduced protein, Lys411, shares 92% identity with Xp10 lysozyme, which contains an extra 46 aa at the N-terminus. Lys411 shows over 40% identities to several other phage lysozymes. The His-tagged protein, Lys411H, expressed in Escherichia coli largely formed as inclusion bodies. The insoluble protein was solubilized in urea and purified by passing through a His-bind column, and the lytic activity was then restored by a refolding process. The optimal assay conditions determined for Lys411H are in 0.1M potassium phosphate buffer, pH 6.6 containing 1 mM CuCl(2) at 25 degrees C. Lysis assays using different bacterial cells as the substrates indicate that Lys411H is the first lysozyme active against both Xanthomonas and Stenotrophomonas maltophilia. This suggests that Lys411 can be a candidate to be developed into a therapeutic agent for treating S. maltophilia infections, in addition to the potential use in control of the plant diseases caused by Xanthomonas. By analogy to the situation in Xp10, we predict that varphiXo411 has no holin, the protein required for lysozyme export, and the N-terminal signal-arrest-release sequence of Lys411 can accommodate its own export to the periplasm.

Antimicrobial proteins and peptides: anti-infective molecules of mammalian leukocytes

Phagocytic leukocytes are a central cellular element of innate-immune defense in mammals. Over the past few decades, substantial progress has been made in defining the means by which phagocytes kill and dispose of microbes. In addition to the generation of toxic oxygen radicals and nitric oxide, leukocytes deploy a broad array of antimicrobial proteins and peptides (APP). The majority of APP includes cationic, granule-associated (poly)peptides with affinity for components of the negatively charged microbial cell wall. Over the past few years, the range of cells expressing APP and the potential roles of these agents have further expanded. Recent advances include the discovery of two novel families of mammalian APP (peptidoglycan recognition proteins and neutrophil gelatinase-associated lipocalin), that the oxygen-dependent and oxygen-independent systems are inextricably linked, that APP can be deployed in the context of novel subcellular organelles, and APP and the Toll-like receptor system interact. From a clinical perspective, congeners of several of the APP have been developed as potential therapeutic agents and have entered clinical trials with some evidence of benefit.