Identification of an Acinetobacter baumannii zinc acquisition system that facilitates resistance to calprotectin-mediated zinc sequestration

Acinetobacter baumannii is an important nosocomial pathogen that accounts for up to 20 percent of infections in intensive care units worldwide. Furthermore, A. baumannii strains have emerged that are resistant to all available antimicrobials. These facts highlight the dire need for new therapeutic strategies to combat this growing public health threat. Given the critical role for transition metals at the pathogen-host interface, interrogating the role for these metals in A. baumannii physiology and pathogenesis could elucidate novel therapeutic strategies. Toward this end, the role for calprotectin- (CP)-mediated chelation of manganese (Mn) and zinc (Zn) in defense against A. baumannii was investigated. These experiments revealed that CP inhibits A. baumannii growth in vitro through chelation of Mn and Zn. Consistent with these in vitro data, Imaging Mass Spectrometry revealed that CP accompanies neutrophil recruitment to the lung and accumulates at foci of infection in a murine model of A. baumannii pneumonia. CP contributes to host survival and control of bacterial replication in the lung and limits dissemination to secondary sites. Using CP as a probe identified an A. baumannii Zn acquisition system that contributes to Zn uptake, enabling this organism to resist CP-mediated metal chelation, which enhances pathogenesis. Moreover, evidence is provided that Zn uptake across the outer membrane is an energy-dependent process in A. baumannii. Finally, it is shown that Zn limitation reverses carbapenem resistance in multidrug resistant A. baumannii underscoring the clinical relevance of these findings. Taken together, these data establish Zn acquisition systems as viable therapeutic targets to combat multidrug resistant A. baumannii infections.

Acinetobacter baumannii is a bacterium responsible for an increasing number of infections in the hospital setting. These infections are particularly challenging because most strains of A. baumannii are resistant to commonly used antibiotics. Unfortunately, there is relatively little known about this organism and how it causes disease, making it difficult to identify new drug targets. In order to address this problem we examined the role for nutrient manganese (Mn) and zinc (Zn) in A. baumannii infections. We have determined that the host protein, calprotectin (CP), contributes to defense against A. baumannii pneumonia through chelation of nutrient Mn and Zn. Moreover, employing purified calprotectin as a probe allowed us to identify a Zn acquisition system in A. baumannii that is required for efficient Zn uptake in vitro and full pathogenesis in vivo. Finally, we demonstrate that inhibiting Zn acquisition can reverse antibiotic resistance mechanisms that rely on Zn-dependent enzymes. Taken together, these results demonstrate the importance of Zn acquisition to A. baumannii pathogenesis and antibiotic resistance, establishing Zn acquisition as a potential target for therapeutic development.

Transition Metal Sequestration by the Host-Defense Protein Calprotectin

In response to microbial infection, the human host deploys metal-sequestering host-defense proteins, which reduce nutrient availability and thereby inhibit microbial growth and virulence. Calprotectin (CP) is an abundant antimicrobial protein released from neutrophils and epithelial cells at sites of infection. CP sequesters divalent first-row transition metal ions to limit the availability of essential metal nutrients in the extracellular space. While functional and clinical studies of CP have been pursued for decades, advances in our understanding of its biological coordination chemistry, which is central to its role in the host-microbe interaction, have been made in more recent years. In this review, we focus on the coordination chemistry of CP and highlight studies of its metal-binding properties and contributions to the metal-withholding innate immune response. Taken together, these recent studies inform our current model of how CP participates in metal homeostasis and immunity, and they provide a foundation for further investigations of a remarkable metal-chelating protein at the host-microbe interface and beyond.

Manganese deficiency or excess caused the depression of intestinal immunity, induction of inflammation and dysfunction of the intestinal physical barrier, as regulated by NF-κB, TOR and Nrf2 signalling, in grass carp (Ctenopharyngodon idella)

Intestinal mucosal immune components and mRNA levels of inflammatory cytokines, tight junction proteins, antioxidant enzymes and related signalling molecules in young grass carp (Ctenopharyngodon idellus) under dietary manganese (Mn) deficiency or excess were investigated. Fish were fed the diets containing graded levels of Mn [3.65-27.86 mg Mn kg(-1) diet] for 8 weeks. The results demonstrated that Mn deficiency significantly decreased the lysozyme and acid phosphatase (ACP) activities, up-regulated tumour necrosis factor α (TNF-α), interleukin 8 and the signalling factor nuclear factor-κB p65, and down-regulated interleukin 10 (IL-10), transforming growth factor β1, inhibitor of signalling factors κB-α and target of rapamycin mRNA levels in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI). However, Mn deficiency did not change the C3 content in the PI, whereas it decreased the C3 contents in the MI and DI. Additionally, Mn depletion also resulted in significantly low mRNA levels for tight junction proteins (claudin-b, claudin-c, claudin-15, occludin and zonula occludens-1), antioxidant enzymes (MnSOD, GPx and CAT) and NF-E2-related factor-2 in the intestines of fish. Excessive Mn exhibited toxic effects similar to Mn deficiency, where optimal Mn contents reversed those indicators. In conclusion, Mn deficiency or excess causes the depression of intestinal immunity, induction of inflammation and dysfunction of the intestinal physical barrier relating to NF-κB, TOR and Nrf2 signalling in grass carp. Furthermore, quadratic regression analysis at 95% maximum response of lysozyme and acid phosphatase activities in the distal intestine of young grass carp revealed the optimum dietary Mn levels to be 8.90 and 8.99 mg kg(-1) diet, respectively.

Associations between manganese exposure and multiple immunological parameters in manganese-exposed workers healthy cohort

BACKGROUND

Manganese (Mn) ions play a crucial role in the immune response. The immunotoxicity of Mn is rarely reported compared with the neurotoxicity of Mn.

OBJECTIVES

The purpose of this study was to investigate the associations between chronic Mn exposure and immunological parameters in occupational Mn-exposed workers.

METHODS

A total of 538 workers were selected from the follow-up of manganese-exposed workers healthy cohort (MEWHC) in 2017. We divided the workers into the low-exposure group and the high-exposure group by the cutoff of the manganese-time weighted average (Mn-TWA) setting at 0.15 mg/m³. We examined serum immunological parameters by the immunoturbidimetric method and leukocyte counts and ratios in blood routine. Then we used the generalized linear model analyses and spline analyses to explore the associations between external exposure of Mn and multiple immunological parameters adjusted for variables. Based on the epidemiological analyses, we used Elisa (enzyme-linked immune sorbent assay) to detect plasma complement C3 of Mn-exposed rats.

RESULTS

In male workers, the mean value of complement C3 was 1.20 ± 0.16 g/L in the high-exposure group, which was significantly lower as compared to the low-exposure group (1.25 ± 0.18 g/L, P = 0.023). The generalize linear models' analyses showed that complement C3 value had a significantly negative association with external exposure of Mn included adjustment for variables (β = -0.04, P = 0.035). Moreover, in male rats, the high-exposure group also had a lower level of complement C3 compared with the low-exposure group (P < 0.001). None significant association was observed in immunological parameters among female workers and rats (all P > 0.05).

CONCLUSIONS

Mn exposure from inhalable dust was associated with decreased complement C3 among occupationally Mn-exposed male individuals but not in female workers, which was further confirmed by the rat model. Further research into the possible mechanism of C3 reduction is needed in the future.

General toxicology of MnDPDP

Purpose: To investigate the general toxicology of mangafodipir trisodium (MnDPDP, Teslascan).

Material and Methods: Studies were performed in accordance with standard methods and in compliance with regulations current at the time of conduct.

Results: Single-dose studies in rodents and dogs showed that MnDPDP was tolerated at doses of approximately 2000 μmol/kg, approximately 400 times a single imaging dose of 5 μmol/kg. The single dose tolerance of MnDPDP was approximately 10 times greater than MnCl2. A good safety profile of MnDPDP was also shown in repeat-dose studies (3 weeks), in which the no-observed-adverse-effect level for the rat, monkey and dog was 116, 29 and 10 μmol/kg, respectively. The local tolerance studies indicated that no adverse local tissue reactions are likely to occur after i.v. injection. Other studies indicate that accidental spillage of MnDPDP onto the skin is not expected to lead to significant systemic exposure, or to local irritation or hypersensitivity. MnDPDP was not genotoxic in a battery of several different tests.

Conclusion: MnDPDP was shown to have a good safety profile suitable as an hepatobiliary MR contrast agent for i.v. administration.

[Sensitization to industrial chemical allergens in bronchial asthma in children in environmental pollution]

Examination covered 41 children with bronchial asthma varying in severity, who live in ecologically hazardous industrial area. High incidence of sensibilization to industrial chemical allergens (chromium, nickel, formaldehyde and sometimes manganese and beryllium) appeared to be a feature of the examinees. Effect of IgE binding, a specific in vitro provocation test, identified pathogenic role of sensibilization to industrial allergens polluting environment. Clinical and immunologic principles revealed are basis for safe, specific and informative laboratory methods diagnosing sensibilization to industrial chemical allergens in ecologic, epidemiologic and clinical pediatric investigation.

2D Differential Metallic Immunopotentiators Drive High Diversity and Capability of Antigen-specific Immunity Against Tumor

The therapeutic efficacy of vaccines for treating cancers in clinics remains limited. Here, a rationally designed cancer vaccine by placing immunogenically differential and clinically approved aluminum (Al) or manganese (Mn) in a 2D nanosheet (NS) architecture together with antigens is reported. Structurally optimal NS with a high molar ratio of Mn to Al (MANS-H) features distinctive immune modulation, markedly promoting the influx of heterogeneous innate immune cells at the injection site. Stimulation of multiple subsets of dendritic cells (DCs) significantly increases the levels, subtypes, and functionalities of antigen-specific T cells. MANS-H demonstrates even greater effectiveness in the production of antigen-specific antibodies than the commercial adjuvant (Alhydrogel) by priming T helper (Th)2 cells rather than T follicular helper (Tfh) cells. Beyond humoral immunity, MANS-H evokes high frequencies of antigen-specific Th1 and CD8+ cell immunity, which are comparable with Quil-A that is widely used in veterinary vaccines. Immunized mice with MANS-H adjuvanted vaccines exert strong potency in tumor regression by promoting effector T cells infiltrating at tumor and overcoming tumor resistance in multiple highly aggressive tumor models. The engineered immunogen with an intriguing NS architecture and safe immunopotentiators offers the next clinical advance in cancer immunotherapy.