E. coli Lipopolysaccharide: acute oral toxicity study in mice

Oral administration of a recombinant modified RBD antigen of SARS-CoV-2 as a possible immunostimulant for the care of COVID-19

BACKGROUND

Developing effective vaccines against SARS-CoV-2 that consider manufacturing limitations, equitable access, and acceptance is necessary for developing platforms to produce antigens that can be efficiently presented for generating neutralizing antibodies and as a model for new vaccines.

RESULTS

This work presents the development of an applicable technology through the oral administration of the SARS-CoV-2 RBD antigen fused with a peptide to improve its antigenic presentation. We focused on the development and production of the recombinant receptor binding domain (RBD) produced in E. coli modified with the addition of amino acids extension designed to improve antigen presentation. The production was carried out in shake flask and bioreactor cultures, obtaining around 200 mg/L of the antigen. The peptide-fused RBD and peptide-free RBD proteins were characterized and compared using SDS-PAGE gel, high-performance chromatography, and circular dichroism. The peptide-fused RBD was formulated in an oil-in-water emulsion for oral mice immunization. The peptide-fused RBD, compared to RBD, induced robust IgG production in mice, capable of recognizing the recombinant RBD in Enzyme-linked immunosorbent assays. In addition, the peptide-fused RBD generated neutralizing antibodies in the sera of the dosed mice. The formulation showed no reactive episodes and no changes in temperature or vomiting.

CONCLUSIONS

Our study demonstrated the effectiveness of the designed peptide added to the RBD to improve antigen immunostimulation by oral administration.

Genome-wide high-throughput screening of interactive bacterial metabolite in the algal population using Escherichia coli K-12 Keio collection

Algae-bacteria interaction is one of the main factors underlying the formation of harmful algal blooms (HABs). The aim of this study was to develop a genome-wide high-throughput screening method to identify HAB-influenced specific interactive bacterial metabolites using a comprehensive collection of gene-disrupted E. coli K-12 mutants (Keio collection). The screening revealed that a total of 80 gene knockout mutants in E. coli K-12 resulted in an approximately 1.5-fold increase in algal growth relative to that in wild-type E. coli. Five bacterial genes (lpxL, lpxM, kdsC, kdsD, gmhB) involved in the lipopolysaccharide (LPS) (or lipooligosaccharide, LOS) biosynthesis were identified from the screen. Relatively lower levels of LPS were detected in these bacteria compared to that in the wild-type. Moreover, the concentration-dependent decrease in microalgal growth after synthetic LPS supplementation indicated that LPS inhibits algal growth. LPS supplementation increased the 2,7-dichlorodihydrofluorescein diacetate fluorescence, as well as the levels of lipid peroxidation-mediated malondialdehyde formation, in a concentration-dependent manner, indicating that oxidative stress can result from LPS supplementation. Furthermore, supplementation with LPS also remarkably reduced the growth of diverse bloom-forming dinoflagellates and green algae. Our findings indicate that the Keio collection-based high-throughput in vitro screening is an effective approach for the identification of interactive bacterial metabolites and related genes.

Dietary Toll-Like Receptor Stimulants Promote Hepatic Inflammation and Impair Reverse Cholesterol Transport in Mice via Macrophage-Dependent Interleukin-1 Production

Background: The mechanisms connecting dietary intake of processed foods with systemic inflammatory markers and cardiovascular risk remain poorly defined. We sought to compare the abundance of pro-inflammatory stimulants of innate immune receptors in processed foods with those produced by the murine ileal and caecal microbiota, and to explore the impact of their ingestion on systemic inflammation and lipid metabolism in vivo. Methods and results: Calibrated receptor-dependent reporter assays revealed that many processed foods, particularly those based on minced meats, contain pro-inflammatory stimulants of Toll-like receptor (TLR)-2 and TLR4 at concentrations which greatly exceed those produced by the endogenous murine ileal microbiota. Chronic dietary supplementation with these stimulants, at concentrations relevant to those measured in the Western diet, promoted hepatic inflammation and reduced several markers of reverse cholesterol transport (RCT) in mice. Hepatocytes were found to be insensitive to TLR2- and TLR4-stimulants directly, but their secretion of functional cholesterol acceptors was impaired by interleukin (IL)-1β released by TLR-responsive hepatic macrophages. Hepatic macrophage priming by high-fat diet enhanced the impairment of RCT by ingested endotoxin, and this was reversed by macrophage depletion via clodronate liposome treatment, or genetic deficiency in the IL-1 receptor. Conclusion: These findings reveal an unexpected mechanism connecting processed food consumption with cardiovascular risk factors, and introduce the food microbiota as a potential target for therapeutic regulation of lipid metabolism.

Immunomodulation by gastrointestinal carbon black nanoparticle exposure in ovalbumin T cell receptor transgenic mice

Humans could become exposed to carbon black nanoparticles (CBNPs) in consumer products or an occupational setting. In rodent models, acute respiratory, subcutaneous, and direct immune cell exposure to CBNPs has been shown to enhance allergic sensitization to co-administered ovalbumin (OVA) protein from chicken egg. However, little is known about the effects of ingested CBNPs on immunological responses and oral tolerance to food antigens. We hypothesized that ingestion of CBNPs would enhance the development of food allergy to OVA. Allergy prone DO11.10 mice were orally exposed to CBNPs every second day for 2 weeks (total dose 10.8 (LOW) or 108 μg (HI)), with and without (±) co-administered OVA. Systemic immune parameters were measured at necropsy. Exposure to OVA resulted in significant increases in serum anti-OVA IgG1, anti-OVA IgM, and anti-OVA IgA antibodies relative to vehicle control. Immunophenotyping revealed a reduction in the number of OVA-specific CD4⁺T helper cells upon OVA ± CBNP^HI treatment in the spleen. Yet, secretion of the allergy-associated Th2 cytokines IL-4, IL-9, and IL-13 was greater in OVA_323-339 peptide-pulsed splenocytes from OVA + CBNP^HI-treated mice compared with control. Transcriptome analysis at necropsy of splenocytes from OVA + CBNP^HI dose mice compared with OVA mice revealed increases in the allergy associated genes Il4 and Stat6 and decreases in Csf3r and Retnlg. Although oral exposure to high-dose CBNPs did not impact OVA-specific antibody production relative to OVA, we did observe increased expression of genes and cytokines associated with allergy in peripheral splenocytes. This work suggests that CBNP gastrointestinal exposure may potentiate allergy pathways.

From bench to bed and back again: phage therapy of childhood Escherichia coli diarrhea

Over the last 20 years, the Nestlé Research Center in Switzerland and the International Center for Diarrhoeal Diseases Research in Bangladesh have explored the efficacy of alternative biological agents for the treatment of diarrheal diseases. This paper reviews the work of this collaborative effort, particularly on Escherichia coli phage therapy (PT), and discusses the development of the project, starting with the isolation of T4-like coliphages from the stool of diarrhea patients, their pilot plant amplification and purification, and the constitution and testing of a cocktail of T4-like phages in mice. A series of phase I clinical trials has demonstrated the safety of PT. Oral phage given without protection survived gastric passage and was recovered in the feces. Oral T4 phage cocktail was then tested in parallel to a commercial phage product in a phase II randomized, placebo-controlled single-center trial in Bangladeshi children hospitalized with acute E. coli diarrhea. It was found that oral phage did not perform better than the current standard of care by oral rehydration/zinc treatment. Furthermore, fecal E. coli pathogen titers were low and mixed infections were found to be frequent. Microbiota analysis showed a correlation between diarrhea and increased levels of Streptococcus, which raises fundamental questions on the causative agent of diarrhea that may explain PT clinical failure.

Amplification and purification of T4-like escherichia coli phages for phage therapy: from laboratory to pilot scale

We investigated the amplification and purification of phage preparations with respect to titer, contamination level, stability, and technical affordability. Using various production systems (wave bags, stirred-tank reactors, and Erlenmeyer flasks), we obtained peak titers of 10(9) to 10(10) PFU/ml for T4-like coliphages. Phage lysates could be sterilized through 0.22-μm membrane filters without titer loss. Phages concentrated by differential centrifugation were not contaminated with cellular debris or bacterial proteins, as assessed by electron microscopy and mass spectrometry, respectively. Titer losses occurred by high-speed pelleting of phages but could be decreased by sedimentation through a sucrose cushion. Alternative phage concentration methods are prolonged medium-speed centrifugation, strong anion-exchange chromatography, and ultrafiltration, but the latter still allowed elevated lipopolysaccharide contamination. T4-like phages could not be pasteurized but maintained their infectivity titer in the cold chain. In the presence of 10 mM magnesium ions, phages showed no loss of titer over 1 month at 30°C.

Ingestion of bacterial lipopolysaccharide inhibits peripheral taste responses to sucrose in mice

A fundamental role of the taste system is to discriminate between nutritive and toxic foods. However, it is unknown whether bacterial pathogens that might contaminate food and water modulate the transmission of taste input to the brain. We hypothesized that exogenous, bacterially-derived lipopolysaccharide (LPS), modulates neural responses to taste stimuli. Neurophysiological responses from the chorda tympani nerve, which innervates taste cells on the anterior tongue, were unchanged by acute exposure to LPS. Instead, neural responses to sucrose were selectively inhibited in mice that drank LPS during a single overnight period. Decreased sucrose sensitivity appeared 7days after LPS ingestion, in parallel with decreased lingual expression of Tas1r2 and Tas1r3 transcripts, which are translated to T1R2+T1R3 subunits forming the sweet taste receptor. Tas1r2 and Tas1r3 mRNA expression levels and neural responses to sucrose were restored by 14 days after LPS consumption. Ingestion of LPS, rather than contact with taste receptor cells, appears to be necessary to suppress sucrose responses. Furthermore, mice lacking the Toll-like receptor (TLR) 4 for LPS were resistant to neurophysiological changes following LPS consumption. These findings demonstrate that ingestion of LPS during a single period specifically and transiently inhibits neural responses to sucrose. We suggest that LPS drinking initiates TLR4-dependent hormonal signals that downregulate sweet taste receptor genes in taste buds. Delayed inhibition of sweet taste signaling may influence food selection and the complex interplay between gastrointestinal bacteria and obesity.