Phosphatidylethanolamine of Helicobacter pylori functions as a steroid-binding lipid in the assimilation of free cholesterol and 3β-hydroxl steroids into the bacterial cell membrane

Efficient lipidomic approach for the discovery of lipid ligands for immune receptors by combining LC-HRMS/MS analysis with fractionation and reporter cell assay

C-type lectin receptors (CLRs), which are pattern recognition receptors responsible for triggering innate immune responses, recognize damaged self-components and immunostimulatory lipids from pathogenic bacteria; however, several of their ligands remain unknown. Here, we propose a new analytical platform combining liquid chromatography-high-resolution tandem mass spectrometry with microfractionation capability (LC-FRC-HRMS/MS) and a reporter cell assay for sensitive activity measurements to develop an efficient methodology for searching for lipid ligands of CLR from microbial trace samples (crude cell extracts of approximately 5 mg dry cell/mL). We also developed an in-house lipidomic library containing accurate mass and fragmentation patterns of more than 10,000 lipid molecules predicted in silico for 90 lipid subclasses and 35 acyl side chain fatty acids. Using the developed LC-FRC-HRMS/MS system, the lipid extracts of Helicobacter pylori were separated and fractionated, and HRMS and HRMS/MS spectra were obtained simultaneously. The fractionated lipid extract samples in 96-well plates were thereafter subjected to reporter cell assays using nuclear factor of activated T cells (NFAT)-green fluorescent protein (GFP) reporter cells expressing mouse or human macrophage-inducible C-type lectin (Mincle). A total of 102 lipid molecules from all fractions were annotated using an in-house lipidomic library. Furthermore, a fraction that exhibited significant activity in the NFAT-GFP reporter cell assay contained α-cholesteryl glucoside, a type of glycolipid, which was successfully identified as a lipid ligand molecule for Mincle. Our analytical platform has the potential to be a useful tool for efficient discovery of lipid ligands for immunoreceptors.

Targeted nanotherapeutics for the treatment of Helicobacter pylori infection

Helicobacter pylori infection is involved in gastric diseases such as peptic ulcer and adenocarcinoma. Approved antibiotherapies still fail in 10 to 40% of the infected patients and, in this scenario, targeted nanotherapeutics emerged as powerful allies for H. pylori eradication. Nano/microparticles conjugated with H. pylori binding molecules were developed to eliminate H. pylori by either (i) blocking essential mechanisms of infection, such as adhesion to gastric mucosa or (ii) binding and killing H. pylori through the release of drugs within the bacteria or at the site of infection. Glycan antigens (as Lewis B and sialyl-Lewis X), pectins, lectins, phosphatidylethanolamine and epithelial cell membranes were conjugated with nano/microparticles to successfully block H. pylori adhesion. Urea-coated nanoparticles were used to improve drug delivery inside bacteria through H. pylori UreI channel. Moreover, nanoparticles coated with antibodies against H. pylori and loaded with sono/photosensitizers, were promising for their application as targeted sono/photodynamic therapies. Further, non-specific H. pylori nano/microparticles, but only active in the acidic gastric environment, coated with binders to bacterial membrane, extracellular polymeric substances or to high temperature requirement A protease, were evaluated. In this review, an overview of the existing nanotherapeutics targeting H. pylori will be given and their rational, potential to counteract infection, as well as level of development will be presented and discussed.

Sodium sulfite-driven Helicobacter pylori eradication: Unraveling oxygen dynamics through multi-omics investigation

Due to the emergence and spread of multidrug resistance in Helicobacter pylori (H. pylori), its eradication has become difficult. Sodium sulfite (SS), a widely used food additive for ensuring food safety and storage, has been recognized as an effective nonbactericidal agent for H. pylori eradication. However, the mechanism by which H. pylori adapts and eventually succumbs under low- or no-oxygen conditions remains unknown. In this study, we aimed to evaluate the anti-H. pylori effect of SS and investigated the multiomics mechanism by which SS kills H. pylori. The results demonstrated that SS effectively eradicated H. pylori both in vitro and in vivo. H. pylori responds to the oxygen changes regulated by SS, downregulates the HcpE gene, which is responsible for redox homeostasis in bacteria, decreases the activities of enzymes related to oxidative stress, and disrupts the outer membrane structure, increasing susceptibility to oxidative stress. Furthermore, SS downregulates the content of cytochrome C in the microaerobic respiratory chain, leading to a sharp decrease in ATP synthesis. Consequently, the accumulation of triglycerides (TGs) in bacteria due to oxidative stress supports anaerobic respiration, meeting their energy requirements. The multifaceted death of H. pylori caused by SS does not result in drug resistance. Thus, screening of the redox homeostasis of HcpE as a new target for H. pylori infection treatment could lead to the development of a novel approach for H. pylori eradication therapy.

Recent Advances in Vitamin D3 Intervention to Eradicate Helicobacter pylori Infection

Helicobacter pylori (HP) infections affect approximately one-third of children worldwide. In China, the incidence of HP infection in children ranges from approximately 30% to 60%. In addition to damaging the gastrointestinal tract mucosa, HP infection in children can negatively affect their growth and development, hematology, respiratory and hepatobiliary system, skin, nutritional metabolism, and autoimmune system. However, the rate of HP eradication also fell considerably from the previous rate due to the presence of drug-resistant HP strains and the limited types of antibiotics that can be used in young patients. Vitamin D3 (VitD3) is a steroid hormone that can reduce inflammation in the stomach mucosa induced by HP and can alleviate and eradicate HP through a variety of pathways and mechanisms, including immune regulation and the stimulation of antimicrobial peptide (AMP) secretion and Ca2+ influx, to reestablish lysosomal acidification; thus, these results provide new strategies and ideas for the eradication of drug-resistant HP strains.

Molecular mechanism of calcitriol enhances membrane water permeability

Helicobacter pylori (H. pylori) exhibits a unique membrane lipid composition, including dimyristoyl phosphatidylethanolamine (DMPE) and cholesterol, unlike other Gram-negative bacteria. Calcitriol has antimicrobial activity against H. pylori, but cholesterol enhances antibiotics resistance in H. pylori. This study explored the changes in membrane structure and the molecular mechanisms of cholesterol/calcitriol translocation using well-tempered metadynamics (WT-MetaD) simulations and microsecond conventional molecular dynamics (CMD) simulations. Calcitriol facilitated water transport across the membrane, while cholesterol had the opposite effect. The differing effects might result from the tail 25-hydroxyl group and a wider range of orientations of calcitriol in the DMPE/dimyristoyl phosphatidylglycerol (DMPG) (3:1) membrane. Calcitriol moves across the bilayer center without changing its orientation along the membrane Z-axis, becomes parallel to the membrane surface at the membrane-water interface, and then rotates approximately 90° in this interface. The translocation mechanism of calcitriol is quite different from the flip-flop of cholesterol. Moreover, calcitriol crossed from one layer to another more easily than cholesterol, causing successive perturbations to the hydrophobic core and increasing water permeation. These results improve our understanding of the relationship between cholesterol/calcitriol concentrations and the lipid bilayer structure and the role of lipid composition in water permeation.

Bacterial lipid biophysics and membrane organization

The formation of lateral microdomains is emerging as a central organizing principle in bacterial membranes. These microdomains are targets of antibiotic development and have the potential to enhance natural product synthesis, but the rules governing their assembly are unclear. Previous studies have suggested that microdomain formation is promoted by lipid phase separation, particularly by cardiolipin (CL) and isoprenoid lipids, and there is strong evidence that CL biosynthesis is required for recruitment of membrane proteins to cell poles and division sites. New work demonstrates that additional bacterial lipids may mediate membrane protein localization and function, opening the field for mechanistic evaluation of lipid-driven membrane organization in vivo.

Sequential isolation of metabolites and lipids from a single sample to achieve multiomics by using TRIzol reagent

Simultaneous extraction of various types of biomolecule from a single sample can be beneficial for multiomics studies of unique specimens. An efficient and convenient sample preparation approach must be developed that can comprehensively isolate and extract biomolecules from one sample. TRIzol reagent is widely used in biological studies for DNA, RNA, and protein isolation. This study evaluated the feasibility of using TRIzol reagent for the simultaneous isolation of not only DNA, RNA, and proteins but also metabolites and lipids from a single sample. Through the comparison of known metabolites and lipids obtained using the conventional methanol (MeOH) and methyl-tert-butyl ether (MTBE) extraction methods, we determined the presence of metabolites and lipids in the supernatant during TRIzol sequential isolation. Finally, we performed untargeted metabolomics and lipidomics to examine metabolite and lipid alterations associated with the jhp0417 mutation in Helicobacter pylori by using the TRIzol sequential isolation protocol and MeOH and MTBE extraction methods. Metabolites and lipids with significant differences isolated using the TRIzol sequential isolation protocol were consistent with those obtained using the conventional MeOH and MTBE extraction methods. These results indicated that TRIzol reagent can be used to simultaneously isolate metabolites and lipids from a single sample. Thus, TRIzol reagent can be used in biological and clinical research, especially in multiomics studies.

A novel role of catalase in cholesterol uptake of Helicobacter pylori

Helicobacter pylori infection is known to be a significant risk factor for the development of gastric cancers in humans. This pathogen exhibits unique biological characteristics in membrane lipid composition. Specifically, H. pylori incorporates exogenous cholesterol into biomembranes and uses cholesterol as the membrane lipid constituents. A previous study by our group demonstrated that phosphatidylethanolamine of H. pylori functions as the cholesterol-binding lipid. It is, however, unclear whether H. pylori is equipped with protein molecules involved in the cholesterol uptake. We, therefore, examined H. pylori proteins that tightly bind to cholesterol. As a consequence, H. pylori catalase (KatA) turned out to be a candidate of the cholesterol uptake-associated protein. In addition, an H. pylori mutant strain that expresses KatA protein lacking catalase activity was significantly lower in total cholesterol contents than the wild-type H. pylori strain. The putative amino acid sequence of KatA found out to contain a number of the cholesterol recognition/interaction amino acid consensus sequence domains (CRAC and CARC domains). These results suggest that H. pylori KatA with normal folding conformation acts as the cholesterol-binding or -storage protein.

Untargeted Microbial Exometabolomics and Metabolomics Analysis of Helicobacter pylori J99 and jhp0106 Mutant

Untargeted metabolomic profiling provides the opportunity to comprehensively explore metabolites of interest. Herein, we investigated the metabolic pathways associated with Jhp0106, a glycosyltransferase enzyme in Helicobacter pylori. Through untargeted exometabolomic and metabolomic profiling, we identified 9 and 10 features with significant differences in the culture media and pellets of the wild-type (WT) J99 and jhp0106 mutant (Δjhp0106). After tentative identification, several phosphatidylethanolamines (PEs) were identified in the culture medium, the levels of which were significantly higher in WT J99 than in Δjhp0106. Moreover, the reduced lysophosphatidic acid absorption from the culture medium and the reduced intrinsic diacylglycerol levels observed in Δjhp0106 indicate the possibility of reduced PE synthesis in Δjhp0106. The results suggest an association of the PE synthesis pathway with flagellar formation in H. pylori. Further investigations should be conducted to confirm this finding and the roles of the PE synthesis pathway in flagellar formation. This study successfully demonstrates the feasibility of the proposed extraction procedure and untargeted exometabolomic and metabolomic profiling strategies for microbial metabolomics. They may also extend our understanding of metabolic pathways associated with flagellar formation in H. pylori.

A short review, effect of dimethyl-β-cyclodextrin on the interaction between Helicobacter pylori and steroidal compounds

The 2,6-di-O-methyl-β-cyclodextrin (dMβCD) is an amphiphilic annular compound consisting of seven dimethyl-glucose molecules. This compound is well known as a solubilizer of lipophilic compounds. Especially, dMβCD extracts cholesterol from the plasma membrane of mammalian cells and releases the cholesterol to the aqueous solution. The experimental use of dMβCD, therefore, serves to investigate the role of cholesterol in the mammalian cell membrane. It is, however, unclear as to how dMβCD extracts cholesterol incorporated into the glycerophospholipid biomembrane. Meanwhile, dMβCD acts as a beneficial compound for Helicobacter pylori and is used as the standard component for supporting the growth of this bacterium in the serum-free culture. However, the detailed mechanism of dMβCD for supporting the growth of H. pylori is still to be clarified. H. pylori is a Gram-negative microaerophilic bacillus recognized as a pathogen concerned with gastrointestinal diseases in human. Previous studies by our group have successfully obtained the H. pylori strains culturable without dMβCD and demonstrated the distinct effects of dMβCD on the interaction between H. pylori and exogenous steroidal compounds. For instance, dMβCD promotes and inhibits the absorption of cholesterol and several steroidal compounds respectively into the biomembranes of H. pylori. In this study we summarized behaviors of dMβCD toward steroidal compounds relevant to H. pylori.

Sulphate-Reducing Bacteria’s Response to Extreme pH Environments and the Effect of Their Activities on Microbial Corrosion

Sulphate-reducing bacteria (SRB) are dominant species causing corrosion of various types of materials. However, they also play a beneficial role in bioremediation due to their tolerance of extreme pH conditions. The application of sulphate-reducing bacteria (SRB) in bioremediation and control methods for microbiologically influenced corrosion (MIC) in extreme pH environments requires an understanding of the microbial activities in these conditions. Recent studies have found that in order to survive and grow in high alkaline/acidic condition, SRB have developed several strategies to combat the environmental challenges. The strategies mainly include maintaining pH homeostasis in the cytoplasm and adjusting metabolic activities leading to changes in environmental pH. The change in pH of the environment and microbial activities in such conditions can have a significant impact on the microbial corrosion of materials. These bacteria strategies to combat extreme pH environments and their effect on microbial corrosion are presented and discussed.

A study of bacteria adhesion and microbial corrosion on different stainless steels in environment containing Desulfovibrio vulgaris

Stainless steel is an important material used in many applications due to its mechanical strength and corrosion-resistant properties. The high corrosion resistance of stainless steel is provided by the passive film. Different stainless steels have different alloy elements and surface properties which could have a significant influence on bacterial attachment to the surface and thus might result in different microbial corrosion behaviours. In this study, the effect of adhesion of sulfate-reducing bacteria (SRB) on corrosion behaviour in artificial seawater on different stainless steels was investigated. Stainless steel materials used were SS 410, SS 420, SS 316 and DSS 2205 and pure chromium. The contact angle was measured to study the effect of surface properties of materials. Adhesion was measured by counting cells attached to the surface of materials. The corrosion behaviour of the materials was measured by electrochemical testing including measuring open circuit potential, electrochemical impedance spectroscopy and potentiodynamic behaviour. The long-term corrosion behaviour of each material was studied after six months of exposure by measuring weight loss and surface analysis with scanning electron microscope with energy-dispersive X-ray analysis. Hydrophobicity had a strong effect on bacterial attachment. Alloying elements e.g. nickel also had shown its ability to attract bacteria to adhere on the surface. However, the corrosion rate of different materials is determined not only by bacterial attachment but also by the stability of the passive film which is determined by the alloying elements, such as Mo and Cr. Chromium showed high resistance to corrosion, possibly due to toxicity on bacterial attachment. The nature of bacterial attachment and corrosion behaviour of the materials are discussed.

Unique responses of Helicobacter pylori to exogenous hydrophobic compounds

Helicobacter pylori is a pathogen responsible for peptic ulcers and gastric cancers in human. One of the unique biological features of this bacterium is a membrane lipid composition significantly differed from that of typical Gram-negative bacteria. Due to its unique lipid composition, the responses of H. pylori to various exogenous lipophilic compounds significantly differ from the responses of typical Gram-negative bacteria to the same lipophilic compounds. For instance, some steroidal compounds are incorporated into the biomembranes of H. pylori through the intermediation of the myristoyl-phosphatidylethanolamine (PE). In addition, H. pylori shows high susceptibility to bacteriolytic action of lipids such as 3-carbonyl steroids, vitamin D, and indene compounds. These lipids are also considered to interact with myristoyl-PE of H. pylori membranes, and to ultimately confer the bactericidal action to this bacterium. In this study we summarize the lipids concerned with H. pylori and suggest the possibility of the development of chemotherapeutic medicines that act on the membrane lipid component of H. pylori.

Antibacterial effect of indene on Helicobacter pylori correlates with specific interaction between its compound and dimyristoyl-phosphatidylethanolamine

Recent studies by our group have suggested that the vitamin D₃ decomposition product VDP1 [(1R,3aR,7aR)-1-[(1R)-1,5-dimethylhexyl]octahydro-7a-methyl-4H-inden-4-one] confers the potent bactericidal action to Helicobacter pylori by targeting the membranal dimyristoyl-phosphatidylethanolamine (di-14:0 PE). In this study we synthesized a new VDP1 derivative to advance further investigation as for the correlative relationship between VDP1 structure and anti-H. pylori activity or PE vesicle collapse induction activity. The derivative VD3-7 [(1R,7aR)-4-fluoro-7a-methyl-1-((R)-6-methylheptan-2-yl)octahydro-1H-indene] retained a fluorine atom in place of the oxygen atom of VDP1. The fluorination of the carbonyl portion of VDP1 forfeited the effective anti-H. pylori activity. We, therefore, prepared Coomassie brilliant blue (CBB)-containing unilamellar vesicles consisting of various PE molecular species, and examined the vesicle collapse induction activity of either VDP1 or VD3-7 by detecting the CBB eluted from the PE unilamellar vesicles. VDP1 strongly induced CBB elution from the unilamellar vesicles of rectus-PE retaining the same two fatty acid side-chains shorter than carbon numbers 14, indicating that VDP1 specifically disrupted the vesicular conformation of those PE unilamellar vesicles. Meanwhile, VD3-7 had no influence on the structural stability of any PE unilamellar vesicles. This study obtained additional evidence that VDP1 acts as a bactericidal agent on H. pylori by targeting the membranal di-14:0 PE.

Helicobacter pylori lipids can form ordered membrane domains (rafts)

Ordered lipid domains (rafts) are generally considered to be features of eukaryotic cells, but ordered lipid domains formed by cholesterol lipids have been identified in bacteria from the genus Borrelia, and similar cholesterol lipids exist in the bacterium Helicobacter pylori. To determine whether H. pylori lipids could form ordered membrane domains, we investigated domain formation in aqueous dispersions of H. pylori whole lipid extracts, individual H. pylori lipids, or defined mixtures of H. pylori lipids and other membrane-forming lipids. DPH (1,6-diphenyl-1,3,5-hexatriene) anisotropy measurements were used to assay membrane order and FRET (Förster resonance energy transfer) was used to detect the presence of co-existing ordered and disordered domains. We found that H. pylori membrane lipid extracts spontaneously formed lipid domains. Domain formation was more stable when lipids were extracted from H. pylori cells grown in the presence of cholesterol. Certain isolated H. pylori lipids (by themselves or when mixed with other lipids) also had the ability to form ordered domains. To be specific, H. pylori cholesteryl-6-O-tetradecanoyl-α-D-glucopyranoside (CAG) and cholesterol-6-O-phosphatidyl-α-D-glucopyranoside (CPG) had the ability to form and/or stabilize ordered domain formation, while H. pylori phosphatidylethanolamine did not, behaving similarly to unsaturated phosphatidylethanolamines. We conclude that specific H. pylori cholesterol lipids have a marked ability to form ordered lipid domains.

Influence of serum vitamin D level on Helicobacter pylori eradication: A multi-center, observational, prospective and cohort study

OBJECTIVES

This study was designed to test whether serum vitamin D levels affected Helicobacter pylori (H. pylori) infection and eradication rates.

METHODS

A multicenter observational prospective cohort study was conducted. A total of 496 H. pylori- positive (H. pylori+ ) and 257 H. pylori-negative (H. pylori- ) patients were enrolled from four hospitals in China. Baseline serum vitamin D levels were measured and a 13 C-urea breath test (UBT) was performed for all the participants. The H. pylori+ patients were divided into two subgroups based on their serum vitamin D levels (<10 or ≥10 ng/mL). A second 13 C-UBT was performed between 4 and 8 weeks after 14-day bismuth-containing quadruple eradication therapies. Factors potentially affecting H. pylori eradication were determined using a questionnaire survey.

RESULTS

Serum vitamin D levels were significantly lower in the H. pylori+ group than in the H. pylori- group ([17.0 ± 6.9] ng/mL vs [19.2 ± 8.0] ng/mL, P = 0.000). H. pylori eradication rate significantly differed between patients with serum vitamin D levels of <10 ng/mL and ≥10 ng/mL (71.7% vs 87.3%, P = 0.005). A multivariate analysis showed that having serum vitamin D level ≥10 ng/mL was an independent risk factor for a successful H. pylori eradication (odds ratio 0.381, 95% confidence interval 0.183-0.791, P = 0.010).

CONCLUSIONS

Serum vitamin D level may affect H. pylori infection and its eradication. Randomized controlled trials are needed to find out whether vitamin D supplements may increase the H. pylori eradication rate.

The Sweeping Role of Cholesterol Depletion in the Persistence of Helicobacter pylori Infections

The ability of Helicobacter pylori to persist lifelong in the human gastric mucosa is a striking phenomenon. It is even more surprising since infection is typically associated with a vivid inflammatory response. Recent studies revealed the mechanism by which this pathogen inhibits the epithelial responses to IFN-γ and other central inflammatory cytokines in order to abolish an effective antimicrobial defense. The mechanism is based on the modification and depletion of cholesterol by the pathogen's cholesterol-α-glucosyltransferase. It abrogates the assembly of numerous cytokine receptors due to the reduction of lipid rafts. Particularly, the receptors for IFN-γ, IL-22, and IL-6 then fail to assemble properly and to activate JAK/STAT signaling. Consequently, cholesterol depletion prevents the release of antimicrobial peptides, including the highly effective β-defensin-3. Intriguingly, the inhibition is spatially restricted to heavily infected cells, while the surrounding epithelium continues to respond normally to cytokine stimulation, thus providing a platform of the intense inflammation typically observed in H. pylori infections. It appears that pathogen and host establish a homeostatic balance between tightly colonized and rather inflamed sites. This homeostasis is influenced by the levels of available cholesterol, which potentially exacerbate H. pylori-induced inflammation. The observed blockage of epithelial effector mechanisms by H. pylori constitutes a convincing explanation for the previous failures of T-cell-based vaccination against H. pylori, since infected epithelial cells remain inert upon stimulation by effector cytokines. Moreover, the mechanism provides a rationale for the carcinogenic action of this pathogen in that persistent infection and chronic inflammation represent a pro-carcinogenic environment. Thus, cholesterol-α-glucosyltransferase has been revealed as a central pathogenesis determinant of H. pylori.

The Tnfaip8-PE complex is a novel upstream effector in the anti-autophagic action of insulin

Defective hepatic autophagy is observed in obesity and diabetes, whereas autophagy is inhibited by insulin in hepatocytes. Insulin-induced anti-autophagy is mediated by non-canonical Gαi3 signaling via an unknown mechanism. Previously, we identified the anti-autophagic activity of Tnfaip8 via activation of mammalian target of rapamycin (mTOR) in the nervous system. Here, we demonstrate that insulin temporally induces Tnfaip8, which mediates the anti-autophagic action of insulin through formation of a novel ternary complex including Tnfaip8, phosphatidylethanolamine (PE) and Gαi3. Specifically, an X-ray crystallographic study of Tnfaip8 from Mus musculus (mTnfaip8) at 2.03 Å together with LC-MS analyses reveals PE in the hydrophobic cavity. However, an mTnfaip8 mutant lacking PE does not interact with Gαi3, indicating that the PE component is critical for the anti-autophagic action of mTnfaip8 via interaction with Gαi3. Therefore, the mTnfaip8-PE complex may act as an essential upstream effector via ternary complex formation most likely with active Gαi3 during insulin-induced anti-autophagy.

Hijacking and Use of Host Lipids by Intracellular Pathogens

Intracellular bacteria use a number of strategies to survive, grow, multiply, and disseminate within the host. One of the most striking adaptations that intracellular pathogens have developed is the ability to utilize host lipids and their metabolism. Bacteria such as Anaplasma, Chlamydia, or Mycobacterium can use host lipids for different purposes, such as a means of entry through lipid rafts, building blocks for bacteria membrane formation, energy sources, camouflage to avoid the fusion of phagosomes and lysosomes, and dissemination. One of the most extreme examples of lipid exploitation is Mycobacterium, which not only utilizes the host lipid as a carbon and energy source but is also able to reprogram the host lipid metabolism. Likewise, Chlamydia spp. have also developed numerous mechanisms to reprogram lipids onto their intracellular inclusions. Finally, while the ability to exploit host lipids is important in intracellular bacteria, it is not an exclusive trait. Extracellular pathogens, including Helicobacter, Mycoplasma, and Borrelia, can recruit and metabolize host lipids that are important for their growth and survival.Throughout this chapter we will review how intracellular and extracellular bacterial pathogens utilize host lipids to enter, survive, multiply, and disseminate in the host.

Identification and characterization of a vitamin D₃ decomposition product bactericidal against Helicobacter pylori

This study demonstrated that the vitamin D₃ decomposition product VDP1 exerts an antibacterial action against Helicobacter pylori but not against other bacteria. Treatment with VDP1 induced a collapse of cell membrane structures of H. pylori and ultimately lysed the bacterial cells. A unique dimyristoyl phosphatidylethanolamine in the membrane lipid compositions contributed to the interaction of VDP1 with H. pylori cells. In separate experiments, VDP1 had no influence on the viability of the human cancer cell lines MKN45 and T47D and lacked any vitamin D₃-like hormonal action against the latter. In both ¹H and ¹³C NMR analyses, the spectra patterns of VDP1 corresponded with those of Grundmann's ketone. These results suggest that VDP1 (or Grundmann's ketone-type indene compound) may become a fundamental structure for the development of new antibacterial substances with selective bactericidal action against H. pylori.

Antibacterial activity of a novel synthetic progesterone species carrying a linoleic acid molecule against Helicobacter pylori and the hormonal effect of its steroid on a murine macrophage-like cell line

Helicobacter pylori, a pathogen responsible for gastric and duodenal diseases, absorbs various steroid compounds into the cell membrane even though some are toxic to this bacterium. An earlier study by our group has demonstrated that progesterone is bactericidal to H. pylori. In this study, we newly synthesized a steroid compound, 17α-hydroxyprogesterone linoleic acid ester (17hPL), to examine antibacterial activity against H. pylori. As expected, 17hPL acted as a bactericidal agent to H. pylori and had no effect on the survival of other common bacterial species. This steroidal substance interacted with phosphatidylethanolamine (PE) on the outer membrane of H. pylori to induce the release of PE from the bacterial cell membrane and to ultimately lyse the bacterial cells. One of the hormonal effects of progesterone is the inhibition of nitric oxide (NO) production from mouse macrophages activated by lipopolysaccharide (LPS). We therefore examined the inhibition effect of 17hPL on the NO production of RAW 264.7 cells, a murine macrophage-like cell line, stimulated with LPS and demonstrated that 17hPL is relatively weaker in its capability to inhibit NO production in LPS-activated cells than progesterone. These results suggest the possibility that 17hPL could be an oral medicine for selectively treating patients infected with H. pylori.

The sodium/proline transporter PutP of Helicobacter pylori

Helicobacter pylori is cause of chronic gastritis, duodenal ulcer and gastric carcinoma in humans. L-proline is a preferred energy source of the microaerophilic bacterium. Previous analyses revealed that HpputP and HpputA, the genes that are predicted to play a central role in proline metabolism as they encode for the proline transporter and proline dehydrogenase, respectively, are essential for stomach colonization. Here, the molecular basis of proline transport in H. pylori by HpPutP was investigated experimentally for the first time. Measuring radiolabeled substrate transport in H. pylori and E. coli heterologously expressing HpputP as well as in proteoliposomes reconstituted with HpPutP, we demonstrate that the observed proline transport in H. pylori is mediated by HpPutP. HpPutP is specific and exhibits a high affinity for L-proline. Notably, L-proline transport is exclusively dependent on Na⁺ as coupling ion, i.e., Na⁺/L-proline symport, reminiscent to the properties of PutP of E. coli even though H. pylori lives in a more acidic environment. Homology model-based structural comparisons and substitution analyses identified amino acids crucial for function. HpPutP-catalyzed proline uptake was efficiently inhibited by the known proline analogs 3,4-dehydro-D,L-proline and L-azetidine-2-carboxylic acid.

Co-evolution of sphingomyelin and the ceramide transport protein CERT

Life creates many varieties of lipids. The choline-containing sphingophospholipid sphingomyelin (SM) exists ubiquitously or widely in vertebrates and lower animals, but is absent or rare in bacteria, fungi, protists, and plants. In the biosynthesis of SM, ceramide, which is synthesized in the endoplasmic reticulum, is transported to the Golgi region by the ceramide transport protein CERT, probably in a non-vesicular manner, and is then converted to SM by SM synthase, which catalyzes the reaction of phosphocholine transfer from phosphatidylcholine (PtdCho) to ceramide. Recent advances in genomics and lipidomics indicate that the phylogenetic occurrence of CERT and its orthologs is nearly parallel to that of SM. Based on the chemistry of lipids together with evolutionary aspects of SM and CERT, several concepts are here proposed. SM may serve as a chemically inert and robust, but non-covalently interactive lipid class at the outer leaflet of the plasma membrane. The functional domains and peptidic motifs of CERT are separated by exon units, suggesting an exon-shuffling mechanism for the generation of an ancestral CERT gene. CERT may have co-evolved with SM to bypass a competing metabolic reaction at the bifurcated point in the anabolism of ceramide. Human CERT is identical to the splicing variant of human Goodpasture antigen-binding protein (GPBP) annotated as an extracellular non-canonical serine/threonine protein kinase. The relationship between CERT and GPBP has also been discussed from an evolutionary aspect. Moreover, using an analogy of "compatible (or osmoprotective) solutes" that can accumulate to very high concentrations in the cytosol without denaturing proteins, choline phospholipids such as PtdCho and SM may act as compatible phospholipids in biomembranes. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

The outer surface lipoprotein VolA mediates utilization of exogenous lipids by Vibrio cholerae

Previous work from our laboratory showed that the Gram-negative aquatic pathogen Vibrio cholerae can take up a much wider repertoire of fatty acids than other Gram-negative organisms. The current work elaborated on the ability of V. cholerae to exploit an even more diverse pool of lipid nutrients from its environment. We have demonstrated that the bacterium can use lysophosphatidylcholine as a metabolite for growth. Using a combination of thin-layer chromatography and mass spectrometry, we also showed that lysophosphatidylcholine-derived fatty acid moieties can be used for remodeling the V. cholerae membrane architecture. Furthermore, we have identified a lysophospholipase, VolA (Vibrio outer membrane lysophospholipase A), required for these activities. The enzyme is well conserved in Vibrio species, is coexpressed with the outer membrane fatty acid transporter FadL, is one of very few surface-exposed lipoprotein enzymes to be identified in Gram-negative bacteria and the first instance of a surface lipoprotein phospholipase. We propose a model whereby the bacterium efficiently couples the liberation of fatty acid from lysophosphatidylcholine to its subsequent metabolic uptake. An expanded ability to scavenge diverse environmental lipids at the bacterial surface increases overall bacterial fitness and promotes homeoviscous adaptation through membrane remodeling.

Our understanding of how bacteria utilize environmental lipid sources has been limited to lipids such as fatty acids and cholesterol. This narrow scope may be attributed to both the intricate nature of lipid uptake mechanisms and the diversity of lipid substrates encountered within an ecological niche. By examining the ability of the pathogen Vibrio cholerae to utilize exogenous lipids, we uncovered a surface-exposed lipoprotein (VolA) that is required for processing the prevalent host lipid lysophosphatidylcholine. VolA functions as a lipase liberating a fatty acid from exogenous lysophospholipids. The freed fatty acid is then transported into the cell, serving as a carbon source, or shunted into phospholipid synthesis for membrane assembly. A limited number of surface-exposed lipoproteins have been found in Gram-negative organisms, and few have enzymatic function. This work highlights the ability of bacteria to exploit exogenous lipids for both maintenance of the membrane and carbon source acquisition.

Detoxification of 7-dehydrocholesterol fatal to Helicobacter pylori is a novel role of cholesterol glucosylation

The glucosylation of free cholesterol (FC) by Helicobacter pylori cells has various biological significances for the survival of this bacterium. H. pylori cells with glucosylated FC are capable of evading host immune systems, such as phagocytosis by macrophages and activation of antigen-specific T cells, and surviving in the gastric mucosal tissues for long periods. An additional role of cholesterol glucosylation in the survival of H. pylori which is distinct from the role of escaping the host immune system, however, has yet to be identified. This study demonstrated that 7-dehydrocholesterol (7dFC), an FC precursor, is a toxic compound fatal to H. pylori cells, but the cell membrane of H. pylori is capable of absorbing this toxic sterol via glucosylation. In contrast to the case with 7dFC, no toxicity to H. pylori cells was detected from the glucosylated 7dFC. In addition, cgt gene mutant H. pylori cells that cannot glucosylate cholesterols had higher susceptibility to the toxic action of 7dFC than wild-type H. pylori cells. These results indicate that the cgt gene product of H. pylori serves to detoxify the sterol fatal to this bacterium and to permit this toxic sterol as a cell membrane lipid component. In summary, this study defined a novel role of cholesterol glucosylation in H. pylori.