Helicobacter Pylori, Gastric Ulcers and Cancer

Stomach Pathogen or Immune Regulator?

Helicobacter pylori (Hp) has co-evolved with the human stomach.  Hp has always been passed from mother to child as the child started premasticated solid foods.  The advent of processed baby foods and antibiotics has eliminated Hp in 90% of the US population and coincides with a dramatic rise of allergies, asthma and autoimmune diseases (commonly explained by the hygiene hypothesis.)

Hp Is Stomach-Adapted

Hp is adapted for growth in an acidic environment.  It produces ammonia to neutralize stomach acid. It also provided me with great perplexity in searching for heparin-binding domains in Hp proteins suspected of binding to stomach epithelial cells.  I generalized that pathogens must have proteins on their surfaces that bind to the heparan sulfate proteoglycans of epithelial cells.  I checked candidate Hp proteins and found histidines where I expected to find basic amino acids, either lysine or arginine.  The “duh” moment came when I realized that the pH of the Hp milieu was acidic and hence histidine would have a positive charge and function like the other two basic amino acids.  Hp was adapted to its stomach world.

Is Hp Good or Bad?

I have been trying to incorporate Hp as a pathogen into my view of gut function.  After all, Hp causes stomach ulcers and gastric cancer.  Several studies over the last few years have shown an association between Hp and asthma, but it is a negative association.  Hp seems to provide protection from asthma and I think that it is likely that the protection extends to allergies and autoimmune diseases.  It is also noteworthy that analysis of genetic predisposition to gastric cancer only reveals polymorphism in genes associated with inflammation, e.g. IL-1 or TNF.

Hp Lives on Hydrogen from Gut Biofilms

Further evidence of the integral nature of Hp as part of the natural gut flora is its use of molecular hydrogen (H2) as an energy source, i.e. high energy electrons for its electron transport chain to produce ATP or to power membrane transport.  The source of the hydrogen is Klebsiella in biofilms in the intestines.  The hydrogen diffuses into the intestinal blood supply and is circulated to the stomach lining where it provides energy for Hp.  Attacking gut biofilms may starve Hp and feeding starch (indigestible branch oligosaccharides are unique food source only accessed by Hp pullulanase) enhances Hp hydrogen nutrients.  [Since regulation of the Hp genes is not thoroughly understood, it is also possible that ample starch could shut down nitrogenase and starve the Hp.]

Hp Increases Tregs

Allergies and autoimmune diseases point to problems in self/non-self recognition, i.e. immunological tolerance.  And tolerance is dependent on regulatory T cells.  In this context, it is interesting that Hp stimulates the accumulation of regulatory T cells.  The gut is the major repository of cells of the immune system.  It seems to follow that by elimination of the stomach Treg population by curing Hp infections, the body may be deprived of it major resource to suppress immunological responses to innocuous antigens in foods, pollens, etc. and to self antigens.  Coupling a shortage of Tregs with chronic inflammation may lead to allergies and autoimmune diseases.  Another source of Treg depletion that may further compromise the immune system is circulating LPS, endotoxemia, that is associated with obesity (and leaky gut?)

Biofilm Transformation, Helicobacter, Klebsiella

Helicobacter pylori causes stomach cancer, but it feeds on hydrogen gas produced by Klebsiella pneumoniae in gut biofilms. DNA released by biofilm bacteria not only transfers antibiotic resistance, but it also provides protection against host antibacterial peptides, such a cathelicidins and defensins.

Exploding Labs

When I was working on host/pathogen interactions and plant disease resistance, I also became familiar with research on the formation of the plant equivalent of cancer, crown galls, and symbiotic bacterial nitrogen fixation. I mention this, because this also exposed me to the free-living bacterial nitrogen fixing system in Klebsiella and to the memorable urban legion of exploding labs. As the story goes, as bacteria convert atmospheric nitrogen gas into ammonia, nitrogen fixation, they use high energy electrons, e.g. from ferrodoxin, and lots of ATP, but they also produce hydrogen gas. In labs where they are researching nitrogen fixation, the excess hydrogen gas would accumulate on the ceiling until... boom! Now those labs are properly vented.

Helicobacter Uses Hydrogen as an Energy Source

Helicobacter pylori is considered the most common bacterial pathogen of humans and is the primary cause of ulcers and stomach cancer. H. pylori lives in the stomach by neutralizing stomach acid with ammonia. Another interesting ability of this bacterium is its ability to use hydrogen dissolved in circulating blood as an energy source. The high energy electrons from molecular hydrogen are transported to its electron transport chain, and the energy is used in membrane transport and ATP production. The circulating hydrogen is produced by gut bacteria.

Klebsiella Is not just a Soil Bacterium, Gut Gases

Klebsiella pneumonia is a lung pathogen and it also forms gut biofilms. Presence in the gut and the ability to produce hydrogen gas has some implications for hydrogen utilizing bacteria like H. pylori. Clearly, the stomach of someone with an abundant source of hydrogen fuel in their blood is a better target for H. pylori colonization. This explains why even at age 50, individuals who were exclusively breastfed have a lower incidence of H. pylori and stomach cancer, since even a single bottle of formula can shift an infant to adult, i.e. Klebsiella gut flora.

Klebsiella Needs Carbs to Produce Hydrogen

K. pneumoniae has been associated with Crohn’s Disease and Ankylosing Spondylitis. It grows in gut biofilms and produces pullulanase, an enzyme that can utilize the branched glucosides left over from the action of amylase on plant starch. So K.p. has an untapped food source and it needs lots of ATP to produce hydrogen gas. The nitrogenase needed for nitrogen fixation and hydrogen production is very sensitive to oxygen, so this means that K.p. needs a partially anaerobic environment and must get its energy from fermentation. Fermentation yields much less ATP than respiration using oxygen, which means that K.p. can only produce hydrogen with lots of glucose from starch.

Low Carb Diet Cures Crohn’s Disease

It turns out that the antigen causing Crohn’s disease is the pullulanse (with collagen mimetics.) As you should expect, it has a basic triplet. Eating a low carb diet reduces the flareups of Crohn’s disease, presumably by starving out the K.p.. It is interesting that nitrogenase is the antigen involved in Ankylosing Spondylitis.

Biofilms Promote Transformation and Antibiotic Resistance

Just as a footnote to the benefit of K.p. as a citizen of a biofilm community, H.p. should also live in those biofilms, since that is the source of the hydrogen it uses. Biofilms also stimulate the exchange of DNA, because the quorum sensing chemical signals trigger the release of DNA. The DNA is a component in the matrix that binds bacteria in the biofilm and can work in conjunction with bacterial acidic polysaccharides and host heparan sulfate. These acidic polymers tend to bind the basic antimicrobial peptides, e.g. defensins and cathecidins produced as a major non-adaptive defense against bacteria. Thus, the release of DNA triggered by quorum sensing, builds matrix, facilitates DNA transformation that is the foundation for the spread of antibiotic resistance in gut biofilms and provides resistance against antimicrobial peptides.