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.

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.

Indene Compounds Synthetically Derived from Vitamin D Have Selective Antibacterial Action on Helicobacter pylori.

Helicobacter pylori infects the human stomach and is closely linked with the development of gastric cancer. When detected, this pathogen can be eradicated from the human stomach using wide-spectrum antibiotics. However, year by year, H. pylori strains resistant to the antibacterial action of antibiotics have been increasing. The development of new antibacterial substances effective against drug-resistant H. pylori is urgently required. Our group has recently identified extremely selective bactericidal effects against H. pylori in (1R,3aR,7aR)-1-[(1R)-1,5-dimethylhexyl]octahydro-7a-methyl-4H-inden-4-one (VDP1) (otherwise known as Grundmann's ketone), an indene compound derived from the decomposition of vitamin D3 and proposed the antibacterial mechanism whereby VDP1 induces the bacteriolysis by interacting at least with PtdEtn (dimyristoyl-phosphatidylethanolamine [di-14:0 PtdEtn]) retaining two 14:0 fatty acids of the membrane lipid constituents. In this study, we synthesized new indene compounds ((1R,3aR,7aR)-1-((2R,E)-5,6-dimethylhept-3-en-2-yl)-7a-methyloctahydro-4H-inden-4-one [VD2-1], (1R,3aR,7aR)-1-((S)-1-hydroxypropan-2-yl)-7a-methyloctahydro-1H-inden-4-ol [VD2-2], and (1R,3aR,7aR)-7a-methyl-1-((R)-6-methylheptan-2-yl)octahydro-1H-inden-4-ol [VD3-1]) using either vitamin D2 or vitamin D3 as materials. VD2-1 and VD3-1 selectively disrupted the di-14:0 PtdEtn vesicles without destructing the vesicles of PtdEtn (dipalmitoyl-phosphatidylethanolamine) retaining two 16:0 fatty acids. In contrast, VD2-2, an indene compound lacking an alkyl group, had no influence on the structural stability of both PtdEtn vesicles. In addition, VD2-1 and VD3-1 exerted extremely selective bactericidal action against H. pylori without affecting the viability of commonplace bacteria. Meanwhile, VD2-2 almost forfeited the bactericidal effects on H. pylori. These results suggest that the alkyl group of the indene compounds has a crucial conformation to interact with di-14:0 PtdEtn of H. pylori membrane lipid constituents whereby the bacteriolysis is ultimately induced.

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 (1)H and (13)C 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.