S.J. KONTUREK1, P.C. KONTUREK2, J.W. KONTUREK3,M. PLONKA4 , M. CZESNIKIEWICZ-GUZIK1, T. BRZOZOWSKI1, W. BIELANSKI1

HELICOBACTER PYLORI AND ITS INVOLVEMENT IN GASTRITIS AND PEPTIC ULCER FORMATION

1Department of Clinical Physiology, Jagiellonian University Medical College, Cracow, Poland,2Department of Gastroenterology, University of Erlangen-Nueremberg, Erlangen, Germany,

3Gastroenterology Clinic, Stade Hospital, Germany, 4Department of Anatomy, University of Physical Education, Cracow, Poland

Modern gastroenterology started in early 19th century with the identification by W.Prout of the inorganic (hydrochloric) acid in the stomach and continued through 20th

century with the discoveries by I.P. Pavlov of neuro-reflex stimulation of gastricsecretion for which he was awarded first Nobel Prize in 1904. When concept ofnervism or complete neural control of all digestive functions reached apogeum inEastern Europe, on the other side of Europe (in United Kingdom), E. Edkinsdiscovered in 1906 that a hormone, gastrin, may serve as chemical messenger instimulation of gastric acid secretion, while L. Popielski revealed in 1916 thathistamine is the most potent gastric secretagogue. K. Schwartz, without consideringneural or hormonal nature of gastric secretory stimulation, enunciated in 1910famous dictum; �no acid no ulcer� and suggested gastrectomy as the best medicationfor excessive gastric acid secretion and peptic ulcer. In early 70s, J.W. Black, basingon earlier L. Popielski�s histamine concept, identified histamine-H2 receptors (H2-R)and obtained their antagonists, which were found very useful in the control of gastricacid secretion and ulcer therapy for which he was awarded in 1972 second NobelPrize in gastrology. With discovery by G. Sachs in 1973 of proton pumps and theirinhibitors (PPI), even more effective in gastric acid inhibition and ulcer therapy thanH2-R antagonists, gastric surgery, namely gastrectomy, practiced since first gastricresection in 1881 by L. Rydygier, has been considered obsolete for ulcer treatment.Despite of the progress in gastric pharmacology, the ulcer disease remainedessentially �undefeated� and showed periodic exacerbation and relapses. Thediscovery of spiral bacteria in the stomach in 1983 by B.J. Marshall and R.J. Warren,Australian, clinical researches, awarded in 2005 the Nobel Prize for the third time ingastrology, has been widely considered as a major breakthrough in pathophysiologyof gastritis and peptic ulcer, which for the first time can be definitively cured bymerely eradication of germ infecting stomach. This overview presents themechanism of induction of gastritis and peptic ulcer by the H. pylori infection anddescribes accompanying changes in gastric acid and endocrine secretion as well as

JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY 2006, 57, Supp 3, 29�50

www.jpp.krakow.pl

the effects of germ eradication on gastric secretory functions and gastroduodenalmucosal integrity

K e y w o r d s : gastrology, vagal nerves, gastrin, histamine, peptic ulcer, Helicobacter pylori

INTRODUCTION

Failure of understanding of anatomy and physiology of the digestive systemprevented any progress in gastroenterology for thousand years of antiquity andmedieval time, when major remedies for digestive problems involved diverseprayers to gods, sacrifices and, at best, herbal medicine. The alpha and omega ofmedicine were dogmas coined by ancient Galen and Hippocrates, who believedthat food in the digestive system undergoes ordinary boiling before assimilationby the body. Modern gastroenterology started with the discovery by W. Prout (1)in 1823 of the presence of inorganic hydrochloric acid (HCl) in the stomach andwith ingenious observations by W. Beaumont (2) in 1822 of gastric secretoryfunctions in Alexis St. Martin, a French Canadian traveler, with the permanentpost-shot-gastric fistula that served to Beaumont as a precious �human guineapig� for experimentation on gastric secretion. Since then it became generallyaccepted that gastric HCl (and pepsin) secretion is present in the stomach tocontribute to food digestion as proposed for the first time by Spallanzani (3).Further studies on animals and humans, confirmed that gastric acid secretion isrequired for normal digestion and that it results from the interplay of stimulatoryand inhibitory influences on the gastric parietal cells as suggested before byBeaumont (2).

Gastric acid secretion in healthy stomach and infected by Helicobacter pylori(H. pylori)

The first impressive basic research related to the physiology of gastric HClsecretion originated at the end of 19th and beginning of 20th century from theexperiments performed in St-Petersburg by I. P. Pavlov�s team on �sham-fed�dogs prepared with special vagally innervated gastric pouches or gastric fistulasand with esophageal fistulas (4). Pavlov demonstrated that gastric HCl secretionstarts almost immediately after presentation to hungry animal of appetizing foodor feeding such animals without allowing the food to enter the stomach (�sham-feeding�). Pavlov proposed the concept of nervism or entirely neural control ofgastric secretion (as well as salivary and pancreatic) and this raised wide interestincluding Nobel Foundation at the Karoliska Institute, which offered financialsupport for Pavlov (and closely collaborating with him Polish chemist M.Nencki) and then awarded Pavlov first in gastroenterology Nobel Prize in 1904(Fig. 1). The importance of vagal nerves in sham-feeding induced secretion

30

documented by showing that vagotomy in dogs eliminated such neurallystimulated gastric acid secretion and, later on, by L. Dragstedt (5), who pioneeredin using vagus section in humans to treat acid-pepsin disorders in peptic ulcer.The K. Schwarz�s (1910) dictum �no acid no ulcer� initiated gastric resections totreat peptic ulcer starting in 1881 with first gastrectomy carried out by Polishsurgeon from Chelmo, L. Rydygier, then professor of Alma Mater Jagiellonica,and almost concomitantly by Austrian surgeon from Vienna, T. Billroth. Withdiscovery by J.S. Edkins in 1906 of antral hormone, gastrin (6), confirmed abouthalf century later by isolation and synthesis of gastrin peptides (17-aminoacid�little gastrin� and 34-aminoacid �big gastrin�) by R. Gregory and H. Tracy (7),the novel neuro-hormonal concept of gastric secretory mechanism wasformulated, indicating that, in addition to vagal nerves, also gastric hormones areinvolved in stimulation of gastric HCl secretion. The discovery in 1916 by L.Popielski, Polish pharmacologist at the Lvov University, a former assistant ofPavlov and fervent supporter of his nervism, that histamine (8), a non-nervousfactor, produced the most powerful gastric acid stimulation opened an alternative,humoral, concept of oxyntic cell stimulation and became an important

31

**W. ProutW. Prout discovereddiscovered in 1823 thein 1823 the presencepresence ofof HClHCl inin humanhuman

stomachstomach and and W. BeaumontW. Beaumont describeddescribed itsits alterationalteration afterafter

feeding;feeding;

*Neural*Neural reflexreflex stimulationstimulation of gastricof gastric andand pancreaticpancreatic secretionsecretion

discovered by discovered by I.P. Pavlow I.P. Pavlow andand awared Nobel prizeawared Nobel prize in 1904, in 1904,

** J.S. EdkinsJ.S. Edkins in 1906 foundin 1906 found thatthat chemicalchemical messenger, gastrin messenger, gastrin

mediatesmediates gastricgastric secretion;secretion;

**K. SchwartzK. Schwartz�s�s dictum �dictum �No acid no ulcer� providedNo acid no ulcer� provided basis for basis for

useuse ofof gastrectomygastrectomy performedperformed alreadyalready in 1881 by in 1881 by L. RydygierL. Rydygier;;

*Histamine, a humoral*Histamine, a humoral substance, presentsubstance, present inin stomachstomach isis potentpotent

gastricgastric HClHCl stimulantstimulant discovered by discovered by L. PopielskiL. Popielski in 1916;in 1916;

**J. FibigerJ. Fibiger �discovered��discovered� SpiropteraSpiroptera carcinoma as a carcinoma as a causecause ofof

gastricgastric carcinomacarcinoma andand gotgot wrongwrong NobelNobel prizeprize forfor itit inin 1926;1926;

** J.W.J.W. BlackBlack identifiedidentified HH22--receptors (Hreceptors (H22--R)R) andand synthesizedsynthesized

theirtheir antagonistsantagonists,, awardedawarded NobelNobel prizeprize inin 1972, 1972, whilewhile andand

proton pump proton pump inhibitorsinhibitors (PPI)(PPI) werewere obtainedobtained byby G. SachsG. Sachs inin

1980,1980, strongstrong inhibitorsinhibitors ofof HClHCl andand effectiveeffective antianti--ulcerulcer drugsdrugs;;

*Discovery*Discovery ofof epidermalepidermal growthgrowth factorfactor (EGF) (EGF) inin salivarysalivary

glandsglands byby S. CohenS. Cohen awardedawarded NobelNobel prizeprize inin 1986;1986;

*Discovery*Discovery ofof H. pyloriH. pylori andand rolerole inin gastritisgastritis andand pepticpeptic ulcerulcer

byby B.J. Marshall & B.J. Marshall & R.J.WarrenR.J.Warren inin 19831983 andand awardedawarded NobelNobel

prizeprize inin 2005. 2005. Awarded Nobel Prize

Prout

Beaumont

Pavlov

Edkins

Rydygier

Schwartz

Popielski

Fibiger

Black

Sachs

Cohen

Marshall Warren

ShortShort historyhistory ofof gastricgastric discoveriesdiscoveries

Fig. 1. Historical background of major discoveries in gastrology without and with (stars) Nobelprize awards

contribution to the development of gastric physiology, apparently depreciatingthe role of nerves and hormones, but favoring histamine as natural gastricsecretagogue, the concept championed later on by C.F. Code (9). Further studies(10, 11) revealed that vagal excitation by sham feeding increased not only gastricHCl secretion but also enhanced release of gastrin (9,10) as well as histamine (12,13), the former being released, at least in part due to the activation of the neuronalgastrin-releasing peptide (GRP), acting on the G-cells and the latter due to theexcitation of enterchromaffin-like (ECL)-cells situated in close vicinity ofparietal cells to stimulate in paracrine fashion histamine-2 receptors (H2-R) ofparietal cells (Fig. 2). It is of interest that H. pylori infected stomach containsunusual form of histamine such as N-alpha-methyl histamine, produced by N-methyl transferase expressed in such H. pylori-infected stomach and being apotent stimulant of gastrin release from antral G-cells (14), thus, there is acomplex vagus-gastrin-histamine interaction, a self-stimulating loop, acting inpositive feedback mechanisms to stimulate gastric acid secretion, particularly

32

Parietal cell

ECL-cell

Gastrin

Ga

str

in

G-cell

Ach

H+

(+)

Ach

(+)(+)

(+)

(+)

(-)

cAMP

Vagal nerve

SST-cell

His

tam

ine

Ca2+

CCK 2-R

M3-R H2-R

SSTR2

M2-R

M1-R

CCK2-R

H+, K+-ATPase

SSTR2

Ach

Protein kinases

Fig. 2. Interaction of gastrin, released from the G-cells, acetylcholine originating from the cholinergicneurons of intramural plexus in gastric mucosa and histamine released from the ECL-cells and actingon parietal cells via H2-receptors. Somatostatin (SST), released from the D cells, inhibits the ECL-celland parietal cell activity, acting via specific SSTR2 receptors (modified from 36)

excessive in subjects with chronic H. pylori infected antral portion of thestomach. An important role in maintenance of the balance between the release ofgastrin from G-cells and histamine from ECL-cells is played by somatostatin(SST), released from the D-cells, present in close vicinity of the G-cells in antralmucosa to exert a tonic inhibitory influence on gastrin release. Whenever theintraluminal; pH drops below 4.0, the H+ ions activate the D-cells to release ofsomatostatin, that in turn reduces gastrin release via SST receptors2 (SSTR2) onD-, ECL and parietal cells (15) (Fig. 3). This complex mechanism controllinggastrin and histamine release involving SST, normally released by D cells in closevicinity of G cells, effectively prevents excessive histamine release andsubsequently gastric acid secretion. This mechanism is deeply impaired by H.pylori infection, that suppresses the D cell activity leading to hypergastrinemiaand subsequently increases gastric acid secretion observed in H. pylori-infected

33

A B

H+

Gastric

DistensionEnteric Neurons

SST

Protein

Digestion

Products

Gastrin

G - Cell

Ach

D - Cell

Vagus

GRP

(+)

(+)

(+)

(+)

(+)

(-)

(+)

Gastrin

Acid

Meal

iv GRP

SST

(-)

(+)

(+)

(+)

H+

P-cell

ECL-cell(+)

(+)

CC

K2-R

Fig. 3. Relation between the activity of vagal nerves and enteric cholinergic and GRP-releasing neuronsand gastrin released from the G-cells (A) in intact and H. pylori infected mucosa. Meal and IV injectionof gastrin-releasing peptide (GRP) induces gastric acid secretion via releasing gastrin and subsequentstimulation of the parietal cells to secrete acid that in turn inhibits further release of antral hormone bystimulating the D-cells and releasing somatostatin (SST). The latter peptide inhibits gastrin release viaSST receptors (SSTR2) and thus attenuates gastric acid secretion (modified from 36)

patients with antrum-predominant gastritis. H. pylori may, also act directly on theECL-cells to release histamine that increases the secretory activity of the parietalcells. When, however, H. pylori infection involves oxyntic gland area and socalled corpus-predominant gastritis develops, the bacteria acts directly on theoxyntic cells to down-regulate the expression of the subunits of the proton pumpsor H+/Na+-ATPase, resulting in hypochlorhydria characteristic for acute H. pyloriinfection and for chronic corpus-predominant gastritis. The overall changes ingastric secretory activity regarding gastrin�histamine�somatostatin interaction onparietal cells in intact and H. pylori-infected stomach are presented on Fig. 4.Thus, usual localization of H. pylori infection in gastric antrum leads to gastricacid hypersecretion due to hypergastrinemia, eventually resulting in duodenalulcer, particularly when islets of gastric metaplasia appear in the duodenum,whereas corpus-predominant H. pylori infection, leading to atrophic gastritis, is

34

LPS

Histamine

Gastrin

+

H+

Nα-mHistamine

GG

DD

SST

PPCORPUS

ANTRUM

GhrelinGrGr

TNFTNFαα

Fig. 4. Interrelationship between gastrin, histamine and somatostatin in control of gastric acidsecretion. Luminal acid directly inhibits the G-cells and gastrin release but stimulates the D-cells torelease somatostatin which by paracrine pathway inhibits gastrin release from the G-cells andindirectly reduces gastric acid secretion. The H. pylori infection of antral mucosa increases gastrinrelease by acting on the G-cells through Nα-methyl-histamine produced by infected mucosa andincrease the release of proinflammatory cytokines that stimulate the G-cells to release gastrin andECL-cells to release histamine, both leading to increased gastric acid secretion.

accompanied by low acid secretion and high plasma gastrin due to lack of normalacid-dependent inhibition of the G-cells and stimulation of D-cells. Under suchconditions, the atrophic gastritis without or with intestinal metaplasia maydevelop and the risk of gastric neoplasia becomes very high so such H. pylori-infected patients require periodical checking (gastroscopy and biopsy) to detectthe possible progression towards the cancerogenesis (Fig. 5).

Pharmacological control of gastric acid secretion and ulcer healing

One of the first agents used in the pharmacotherapy of gastritis and pepticulcers were extracts of Atropa belladonna, which eventually resulted in theisolation at the end of 19th century of active principle, atropine. The extracts ofbelladonna and atropine are known to inhibit gastric acid secretion, especiallywhen induced by vagal stimulation (4, 15) but, unfortunately it is accompanied byunpleasant side-effects such as dry mouth, blurred vision or bladder dysfunction.Novel highly specific muscarinic M1-receptor antagonists (M1-RA) such as

35

Fig. 5. Chronic gastric Helicobacter pylori infection results either in antral predominant gastritis withhypergastrinemia and hyperchlohydria leading to duodenal or gastric peptic ulceration, while corpuspredominant H. pylori-induced atrophic gastritis leads to hypochlohydria and increased gastrinrelease, resulting in the cancerogenesis. Most of infected patients (~80%) show only mild mixedgastritis and normal gastric acid secretion without significant gastric diseases (modified from 36).

pirenzepine and telenzepine became available for treatment of acid-pepsindisorders but their clinical usefulness was later found rather limited, particularlythat the target parietal cells are equipped with M3-R, rather than M1-R and thatthey fail to affect histamine-induced gastric acid secretion. Pharmacologicalstudies initiated by J.W. Black et al. (16), who modulating chemically thestructure of histamine, succeeded in development of specific H2R antagonists,which were found to cause not only potent and side-effect free gastric acidinhibition, but also to be effective in acceleration of ulcer healing that brought totheir inventor, Black, a second Nobel prize in gastrology within last century. Itshould be noticed that Black�s pioneering studies were carried on the assumption,originally proposed by L. Popielski (8, 9) that histamine plays a key role in gastricacid secretory mechanism, the concept that was challenged by Johnson�s (17),stating in 1971, few month before synthesis of H2-R antagonists that there is �noroom for histamine� in gastric secretory mechanisms, presumably because ofubiquity of this amine in various organs of the body and failure of inhibitinggastric secretion by suppressing histidine decarboxylase (HDC) activity in rats.Interestingly, these new agents, H2-R antagonists, such as burimamide, metiamideand then cimetidine or ranitidine, were found to inhibit gastric secretion not onlyinduced by histamine, but also by other stimulants of parietal cells includingordinary meal and even vagal excitation (17, 18). These results were initiallyexplained by the interaction of H2R with others such as M3-R and gastrinic(CCK2-R) receptors at the oxyntic cell membrane and this was supported, at leastin part, by in vitro studies on isolated oxyntic cells by Lloyd and Soll (19). Thediscovery of H2-R and their specific antagonists should be considered as themajor breakthrough in the physiology of gastric secretion, reinforcing previousPopielski�s and Code�s assumption concerning significant role of histamine in theregulation of gastric secretion as the �final common chemostimulator� of oxynticcells (9,17) (see Fig. 4). More recent achievements in pharmacological researchled to discovery by G. Sachs and his associates (20) of Na+/K+-ATPase (protonpump) existing in inactive form in cytoplasmic tubulo-vesicles that followingexcitation of oxyntic cells and an increase of intracellular mediators such ascyclic AMP (histamine) or Ca2+ ions (acetylcholine or gastrin) and subsequentincrease in protein kinase activity, are incorporated into the membrane ofintracellular cannaliculi of oxyntic cells resulting in the stimulation of gastric acidsecretion. The discovery of specific proton pump inhibitors (PPI), such asomeprazole, polprazole, lanzoprazole, pantoprazole, esoprazole and others thatwere found to be the most powerful inhibitors of gastric acid secretion, actingindependently of the mode of oxyntic cell stimulation and clinically extremelyuseful in controlling of gastric acid secretion due to higher gastric acid inhibitoryefficacy than that of H2-R antagonists (20-22). Moreover, their biological (gastricinhibitory) half life was found to be remarkable longer, ranging from 14 h forlanzoprazole to 46 h for pantoprazole, when compared to that for histamine H2-Rantagonists. These discoveries apparently undermined, at least from practical

36

point of view, the significance of both vagal nerves, as well as gastrin in the in theconcepts of the gastric secretory stimulation (Fig. 5).

Secretion of gastric acid, constituting major �parietal� component of gastricjuice (17) results from the interaction of numerous stimulatory and inhibitoryneuro-hormonal factors, acting on parietal cells after ingestion of food. It shouldbe mentioned at this point that already A. Vesalius in 1543 (23) identified theunusually �wandering� (vagal) nerves among various intra-abdominal structures.The question was then raised what functions could be attributed to these�wandering� nerves in gastric secretion and food digestion. Pavlov (4) showedexperimentally that vagally stimulated gastric acid secretion induced by e.g. shamfeeding (cephalic phase) or provoked by ordinary feeding can be, at least in part,reduced by vagotomy introduced later on into clinical practice by Dragstedt (5).With the use of microscopy, it was demonstrated that the gastric glands comprisethe parietal (oxyntic � acid producing) as well as peptic (pepsinogen producing)cells. R. Heidenhain (24) of Breslav University, characterized a �third� type ofcells, which adhere to the external surface of epithelial cells, later identified asECL-cells and found to express the histidine decarboxylase (HDC), the importantenzyme responsible for the biosynthesis in the oxyntic mucosa of histamine, themajor stimulus of parietal cells. Naturally, in addition to vagus and histamine,gastrin was considered as major player in the mechanism of gastric acid secretion.

All the above mentioned gastric secretagogues stimulate �parietal� componentof gastric juice secreted by parietal cells, which are exposed to extremely highacid concentration, reaching within intracellular cannaliculi, about 170 mmol/L.The possible cell damage by this highly concentrated acid is prevented by locallyreleased prostaglandins (PG) released due to constitutively expressed COX-2 inthese cells (25). Non-parietal secretion originating from other than parietal cellsof gastric mucosa contributes to the mucus-alkaline secretion, protecting surfaceepithelium that appears to be mediated by COX-1-PG system existing in normalmucosa to exert gastroprotection and to maintain mucosal integrity (25-32).

The role of H. pylori infection in the development of gastro-duodenal ulcers

The spiral bacterium, has been identified for the first time in gastric sedimentand depicted under microscope in humans with various gastric diseases by W.Jaworski, professor of Cracow Academy in his Handbook of Gastric Diseases (inPolish) over 100 years ago and due to their curved forms named by him Vibriorugula (33) (Fig. 6). Definitive microbiological characterization of this spiralbacteria named initially by mistake Campylobacter pylori, but then properlyidentified as H. pylori should be attributed to Australian clinical researchers, R. J.Warren, pathomorphologist, and B. J. Marshall, gastroenterologist (34), who inearly 1980s proved that bacterium is pathogenic by fulfilling all three Koch�scriteria (isolation of germ, its culture and demonstration of it pathogenicity).Marshall used his own stomach to prove pathogeneicity of bacteria by drinking

37

their pure culture and documenting endoscopically and histologically thedevelopment of acute gastritis cured with antibiotics and bismuth salts. Numerousstudies in various countries showed that the stomach of more than 50% of worldadult population contains H. pylori (35, 36) that exhibits an ability to inducegastritis in all infected subjects and peptic ulcers in about 10-15% of them. H. pyloriis mobile germ due to the presence of flagella and easily moves within thick mucuslayer covering the gastric mucosa to reach the apical membrane of surface epithelialcells and to bind by its adhesin molecules to mucosal glycolipid receptors at thismembrane (Fig. 7). Bacterial genome is now well-studied structure and shown tocontain about 1300 genes. More toxic bacteria are capable of expressing thecytotoxins such as CagA encoded by cagA and VacA encoded by vacA. Thebacterium adhering to mucous cell membrane, is capable to �inject� into cytoplasmof mucosal cells its cytotoxins acting there like �Trojan horse� to induceinflammation (CagA) or to damage its mucosal cell surface and causing its

38

The 2005 Nobel Prize in Physiology or Medicine, October 2005The 2005 Nobel Prize in Physiology or MedicineThe 2005 Nobel Prize in Physiology or Medicine,, October 2005October 2005

The Nobel Assembly at The Nobel Assembly at KarolinskaKarolinska InstituteInstitute has today decided to awardhas today decided to award

The Nobel Prize in Physiology or Medicine for 2005The Nobel Prize in Physiology or Medicine for 2005

jointly to jointly to

Barry J. Marshall and J. Robin WarrenBarry J. Marshall and J. Robin Warren

for their discovery of for their discovery of

""the bacterium the bacterium Helicobacter pyloriHelicobacter pylori and its role in gastritis andand its role in gastritis and

peptic ulcer diseasepeptic ulcer disease""

Walery Jaworski; describedWalery Jaworski; described in 1893in 1893

spiral bacteriaspiral bacteria inin humanhuman stmachstmach

Fig. 6. Nobel laureates in physiology and medicine in 2005. B.J. Marshall and J.R. Warren receivingprize for the discovery of Helicobacter pylori and its role in gastritis and peptic ulcer disease. W.Jaworski (upper panel), who described spiral bacteria in the human stomach 100 years beforeMarshall and Warren should be considered a real discoverer of these bacteria.

vacuolization (VacA) (36, 37). Furthermore, the cytotoxins turn on the mucosalimmunological system, resulting in enhanced expression and release ofproinflammatory cytokines, including interleukin-8 (IL-8), interleukin-1β (IL-1β)and tumor necrosis factor-α (TNF-α) (Fig. 8). It is of interest that H. pyloriinfection interferes with ghrelin releasing cells (Gr-cells), present mainly in oxynticmucosa to decrease usual fasting rise in plasma ghrelin and the appetite as well asto retard the growth of infected children (38,39). Following eradication of H. pylorithe plasma and gastric corpus mucosa content of ghrelin were restoredaccompanied by the improvement of appetite and reduction in dyspeptic symptoms.

The infection strongly affects gastric acid secretion by altering the gastrin-somatostatin ratio as well as damaging the mucus-alkaline coat at the mucoussurface and the quality of adherent mucus gel, resulting in acute and then chronicgastritis and ulcerations (Fig. 9). The induction of COX-2-PG system by thisbacterium may limit the mucosal cell damage due to released PG, but the H.pylori infection results also in the generation of proinflammatory substances,

39

Helicobacter pylori Person to person Person to person

transmissiontransmission of Hp;of Hp;

GastroGastro--oraloral andand fecofeco--

oraloral transmissionstransmissions

areare alsoalso postulatedpostulated

Urease

Virulence

factors

Mobile

bacteria

Adhesins

Gastric

Mucosa

Mucus

ChemokinesRecrutment

& activation

of PMN

ROS

releaseAnty-Hp

IgG i IgA

Immuno-

mediated

response

Activation of T

lymphocytes

IFNγ

IL-2

Cell

damageInflammatory

mediators

Immune

complex

.formation

Acute/

Chronic

Gastritis

Peptic ulcer Gastric cancer

Virulence factors of H. pylori (Hp);Hp gastric colonization factors;

Flagellae (mobility),

Urease

Adhesion factors (Adhesin proteins

coded by BabA & BabB genes

Factors damaging mucosa;

NH3 - urease product

Lipopolisacharides (LPS)

Chemokines (factors recruiting and

activating leukocytes)

Cytotoxins (CagA & VagA) released

by Hp carrying cytotoxin associated

gene A (cagA & vacA);

Proinflammatory proteins of outer Hp

membrane (OipA),

Heat shock proteins (HspA, HspB),

Proteases hydrolysing mucus

proteins

Phospholipase A2, hydrolysing

mucus and cell membrane

phospholipides ,

NO synthase (NOS), releasing NO,

that may damage host cells

Receptors

Associated Conditions

Fig. 7. Schematic presentation of the H. pylori, its colonization of the stomach, induction ofimmune gastric response (gastritis) and development of gastric or duodenal ulcers without or withcomplication such as bleeding.

including reactive oxygen species (ROS), that, unlike PG belong to damagingproinflammatory �team�. It becomes evident that the eradication of the bacteriumrestores, at least in part, the disturbed mucosal integrity and reverses the courseof gastritis. Administration of mucosal barrier breaker such as aspirin or ethanolusually results in bleeding erosions or exacerbation of chronic gastric ulcerations(30,32). Considering duodenal mucus-alkaline secretion in response to topical H+,delivered into duodenal bulb by H. pylori infected stomach, it should beemphasized that the duodenal mucosa behaves somehow differently than gastricmucosa in response to topical acid. Isenberg and his colleagues (31, 40) andKaunitz and Akiba (26) using chambered human or animal duodenum, confirmedearlier proposal that, unlike gastric mucosa, where tight epithelial cells constitutethe main component of gastric mucosal barrier against H+, in the duodenum, H+

easily penetrates the duodenocytes, but does not damage them, though transientlydecreases their intracellular pH (pH). This strongly activates the basolateral Na+-HCO3

- cotransporters, allowing for massive inward movement through baso-lateral membrane of HCO3

- from the extracellular space, leading to activation ofthe HCO3/Cl exchangers in apical membrane of duodenocytes and resulting in amarked stimulation of HCO3

- secretion together with mucus gel that is capable of

40

Effects on

cell junctions

vacA

cag PAI

oipA dupA

babAcagA

CagA

CagA

Cytoskeletal

changes

Proliferation

CagA

- P

VacA

Cell damageOther bacterial

components

Nod1

NF B

Pro-inflammatory

cytokine expression

INFLAMMATION

Fig. 8. The activation and expression of Helicobacter pylori cytotoxins (CagA and VacA) andexpression of other genes (oipA, dupA an babA) result in mucosal cell damage andproinflammatory cytokine formation.

neutralization of H+ ions entering the duodenal lumen, thereby securing duodenalmucosal neutrality and integrity (Fig. 10).

Sjoblom and Flemstrom (41) provided evidence that, neurally releasedmelatonin and neuronal VIP, participate in the mechanism of the stimulation ofduodenal mucus-alkaline secretion by topical H+-activating the vago-vagalreflexes and their brainstem centers, also essential for the control of gastric,duodenal or pancreatic secretion (32, 42). The neuronal pathway involved inactivation of gastro-duodenal mucus-alkaline secretion with the contribution ofmelatonin was confirmed by Reiter et al. (43), just reinforcing Sjoblom andFlemstrom (41) idea implicating melatonin in gastro-duodenal protective system.As shown by Isenberg et al (40), the H. pylori infection reduces duodenal HCO3

-

mucus secretion (despite of increasing mucosal PGE2 generation) and this allowsfor excessive penetration of gastric H+ and other irritants into the mucosa, causingdamage of duodenocytes with subsequent formation of gastric metaplastic isletsin duodenum. This mechanism leads to the formation of the �locus minoris

41

Fig. 9. The possible long-term effects of H. pylori infection of the stomach and the percentage ofvarious pathologies resulting from this infection.

resistentiae� for duodenal H. pylori infection and, finally, to the ulcerdevelopment in duodenum. This occurs when duodenitis, combined withdisorders of duodenal mucus-alkaline secretion caused by H. pylori infection,takes place and when complex mechanism controlling this secretion is deeplyaltered by this infection (Fig. 10).

As shown on Figs 11, the prevalence of H. pylori infection estimated by W.£aszewicz (35) on about 18 000 subjects and Bielanski�s studies including about20 000 subjects of southern part of Poland (46-48), reached similar values. Theinfection rate shows similar trends regarding the influence of the age, but inBielanski�s studies extending up to 80 years of age, some tendency of theinfection rate to decline at age above 50 years and this could be due either to thedevelopment in these patients of atrophic gastritis and/or the translocation of thebacteria from the gastric surface into the mucosal cells without showing H. pyloripositivity in UBT or CLO (46).

It is of interest that the prevalence of H. pylori infection in Poland decreased byabout 30% during last 10 years when the eradication procedure has been widelyapplied in ulcer therapy. At the same time, the incidence of ulcers without H. pyloriinfection or the use of non-steroidal anti-inflammatory drugs (NSAID) also tended

42

Du

od

en

alm

uc

osa

pH=2

Mucus-gel

thickness

CGRP NO

COX-1

NSAIDs

CNS(Brain-Gut Axis)

SE

NS

OR

S (

VR

-1)

Vasodilation

Capsaicin

cNOS L-NNA

HH++

pH=7

PG

HCO3-

+

+

+

+

++

+

++

+

HCO3-

pCO2

+ +

Neurotransmitters

H. pylori

COX-2

PG

Fig. 10. Mechanisms controlling the duodenal alkaline secretion.

to increase so that the ratio of these �idiopathic� ulcers to total number of ulcersignificantly increased (47, 48). Despite of the decline in H. pylori prevalence, therate of ulcer complications such as bleeding and perforation did not changedramatically as compared to the period when no eradication therapy has beenapplied. According to the opinion of Blaser (49) the fall in H. pylori prevalenceoccurs all over the world due to improvement of living standard levels, but it isaccompanied by the increase in the occurrence of gastro-esophageal reflux disease(GERD), Barrett�s esophagus and esophageal carcinoma (Fig. 12).

The H. pylori infection appears to interfere with the expression and releasefrom the oxyntic mucosa of ghrelin, and this may result in the decrease of appetiteand retardation of the growth in children (38, 39). Following the eradication ofthe H. pylori the release of ghrelin has been restored and this was accompaniedby the improvement of appetite and decrease of dyspeptic symptoms (Fig. 13).

Concerning the risk of H. pylori infection, numerous conditions increase suchrisk including the low socio-economic status, poor sanitary conditions, uncleanwater and smoking as well as the direct exposure nurses to endoscopicinstruments or gastric contents (51).

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Fig. 11. Mean H. pylori infection rate in various countries of the world and in Poland, in which theinfection rate averages 58.29% for the entire adult Polish population (35).

Brain-gut axis in gastroduodenal mucosal damage caused by H. pylori, NSAIDand other irritants

The question remains whether H. pylori-induced gastric and duodenalmucosal damage is merely a local phenomenon or whether it also involves theextragastric, namely neuro-hormonal mechanisms. To answer this question,several tools were employed in experimental animals; 1) inactivation of sensoryafferent nerves that serve to signal the brain the changes occurring in thegastrointestinal tract by using animals injected with large neurotoxic dose ofcapsaicin; 2) surgical vagotomy to eliminate the transmission of signals from theGI tract to central nervous system (CNS) through the sensory vagal fibers, whichconstitute over 90% of total vagal fibers, and which supply the gastro-duodenalarea that is crucial for the H. pylori-induced inflammatory changes andulcerogenesis; 3) intracerebral application of various hormonal substances todetermine whether the CNS centers can influence the gastric H+-secretory patternand gastro-duodenal mucus-HCO3

- responses to topical irritant application suchas H. pylori or aspirin and 4) determination of expression of cFOS in intrinsic and

44

INF

EC

TIO

No

rD

ISE

AS

ER

are

Co

mm

on

H. pylori infection

Gastric adenocarcinoma

GERD

Barrett�s

esophagus

Esophageal

carcinoma

1900 1950 2000

Y e a rModified from Blaser, 2005

Fig. 12. During last decades the H. pylori prevalence and the occurrence of distal gastric cancer aredeclining, while there is an increase in the gastro-duodenal reflux disease (GERD), esophagitis andcancer of the proximal part of the stomach.

extrinsic neurons involved in the transmission of gut-brain-gut signals (30).Using such wide spectrum of physiological and pharmacological tools, severalresearchers, including our group, were able to reveal that the gastro-duodenalmucosa is equipped with a variety of neuronal sensors that respond to the actionof luminal irritants such as H. pylori produced cytotoxic substances, especiallycytotoxin CagA, VacA and ammonia, luminal acid, ethanol, various drugs e.g.NSAID or even physiological changes such as chemical ingredients of food, itsosmolarity and pH as well as motility and tension of the GI tract wall. Throughactivation of chemo-, osmo-, mechano- and noci-receptors of gastroduodenalmucosa, the afferent nerves may mediate short local or intramural and long, vago-vagal or extramural (axonal and spinal or cerebral) reflexes triggered by luminalH+ or H. pylori and affecting, among others, also the mucus-HCO3

- secretion, thegastro-duodenal mucosal barriers, and mucosal integrity as well as mucosal

45

Mucosal

barrier

Mucosal protection

Gastrin- H+

H. pylori

Motility

(MMC)

Brain-gut

axis

GHRELIN

Food

intake

Control of food intakeControl of food intake && H. pyloriH. pylori

H. pylori

infection

Fig. 13. The gastric infection with H. pylori results in the decrease in the expression and the releaseof ghrelin, gastric hormone stimulating appetite and enhancing the body growth.

microcirculation (30). The space limitation of this review does not allow for thedetailed presentation of the evidence, obtained, in part, from animalexperimentations, supporting the involvement of extragastric neuro-reflexes inthe maintenance of gastro-duodenal mucosal integrity but it is of interest that e.g.experimental chronic gastric ulcers in rats infected with H. pylori or with gastricmucosal damage by acidified aspirin or ethanol are greatly augmented followingcapsaicin-induced inactivation of afferent sensory nerves or vagotomy. This couldbe interpreted that both sensory afferent and vagal efferent nerves are involvednot only in the pathogenesis of gastro-duodenal mucosal lesions but also arerequired for normal course of their healing and for the maintenance of mucosalintegrity (30). In humans with H. pylori infected stomach, the course of post-eradication ulcer healing probably also involves the long vago-vagal reflexesinitiated by activation of gastric mucosal sensors by H. pylori-released cytotoxinsand inflammatory products such as the reactive oxygen species (ROS) as well as

46

HCl/pepsinHCl/pepsin

Fig. 14. The healing process of acute or chronic gastric ulcerations induced by the H. pyloriinfection involves a variety of growth factors and the products of cyclooxygenase (COX) or nitricoxide synthase (NOS) products that counteract the deleterious effects of this infection.

various growth factors including EGF, TGFα, bFGF, VEGF generated in gastricmucosa under the influence of H. pylori infection but enhancing mucosalregeneration and ulcer healing. Also the clot filling the ulcer niche is rich sourceof various growth factors produced by platelets as well as by microphages andinteracting with the damage by ulcer mucosa to enhance its regeneration and ulcerhealing (Fig. 14). Also the development and subsequent repair of aspirin- andethanol-induced gastric mucosal lesions may involve the brain-gut axis, startingwith the irritation of mucosal chemo-receptors by noxious chemicals and theirmucosal toxic products such as ROS (32). This is supported by experimentalevidence that inactivation of sensory afferent fibers with capsaicin orsubdiaphragmatic vagotomy, eliminating the activity of both afferent and efferentvagal pathways, greatly delays ulcer healing and worsens the lesion induced byvarious local irritants (30-32). Mucosal lesions and ulcerations induced either byH. pylori infection and aspirin, ethanol or ischemia-reperfusion, have beenthought to involve predominantly local mechanism related to the activation ofCOX-2-PG system and various growth factors assuring spontaneous healing ofgastric lesions (Fig. 14). However, based on studies with ulcer healing afterinactivation of afferent sensory fibers with neurotoxic dose of capsaicin or byvagotomy, it is tempting to assume that brain-gut axis is involved in pathogenesisof H. pylori induced ulcer formation and in healing of these ulcers via neuralmediation of local mucosal changes including gastric blood flow at ulcer area(30). This does not to exclude the contribution in mucosal repair processes oflocal anti-ulcer and protective humorals such as COX-2-PG, growth factors,gastrin, somatostatin, ghrelin, melatonin etc., that may modify the final outcomeof H. pylori-induced ulcer healing, and repair processes involving both localfactors and neural brain-gut axis (32).

Concluding remarks

1. H. pylori infection interferes with the release and action on parietal cells ofbasic secretagogues such as histamine, gastrin and somatostatin, resulting ingastric acid hypersecretion, when the infection is localized in gastric antrum, orin hypochlorhydria when such infection involves gastric corpus, resulting incorpus-predominant chronic gastritis.

2. Duodenal ulcer, which is causally related to the H. pylori infection in antralmucosa, is usually accompanied by hyperchlorhydria caused by an excessiverelease of gastrin from the G-cells due to deficient somatostatin release from theantral D-cells as well as due to excessive histamine release from the ECL-cellscaused by their stimulation by endogenous gastrin induced by the action on Nα-methyl histamine, present in H. pylori infected stomach.

3. Gastric ulcer is usually accompanied by reduced corpus mucosal integrityand altered mucosal barrier as well as reduced gastric acid secretion caused bydown-regulation of the expression of compound units of the proton pumps andreduced acid secretory activity of oxyntic cells. Following H. pylori eradication,

47

gastric acid tends to increase depending upon the improvement of the mucosalintegrity and secretory activity of oxyntic cells.

4. Neuro-hormonal pharmacology of the stomach and duodenum succeeded indiscovery and clinical use of potent inhibitors of gastric acid secretion such as H2-R antagonists and PPI, that abolish all modes of gastric secretory stimulation but,concomitantly, result in hypergastrinemia that stimulates the growth of H. pyloripromoting spreading the infection towards the proximal part of the stomach withsubsequent development of corpus-predominant atrophic gastritis andcancerogenesis.

4. The eradication of H. pylori abolishes hyperchlorhydria andhypergastrinemia in duodenal ulcer patients and is successful in healing andprevention of ulcer recurrence as well as in prevention of the H. pylori-relatedgastric cancerogenesis.

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Author�s address: Prof. Dr S.J. Konturek, Department of Clinical Physiology JagiellonianUniversity College of Medicine, Cracow, Poland. Fax; 012-4211578; Tel; 012-4211006. E-mail: mpkontur@cyf-kr.edu.pl

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