Update on molecular pathogenesis of Helicobacter pylori-induced gastric cancer

Abstract

Helicobacter pylori (H. pylori) infection is one of the most prevalent bacterial infections affecting mankind. About half of the world’s population is infected with it. It causes several upper gastrointestinal diseases, including gastric cancer (GC). It has been identified as a major risk factor for GC. GC is one of the most common cancers affecting humans and the third leading cause of cancer-related deaths worldwide. H. pylori infection causes an inflammatory response that progresses through a series of intermediary stages of precancerous lesions (gastritis, atrophy, intestinal metaplasia, and dysplasia) to the final development of GC. Among infected individuals, approximately 10% develop severe gastric lesions such as peptic ulcer disease, 1%-3% progress to GC, and 0.1% develop mucosa-associated lymphoid tissue followed by the development of lymphoma. The bacterium has many virulence factors, including cytotoxin-associated gene A, vacuolating cytotoxin A, and the different outer membrane proteins that cause cancer by different mechanisms. These virulence factors activate cell signaling pathways such as PI3-kinase/Akt, JAK/STAT, Ras, Raf, and ERK signaling that control cell proliferation. Uncontrolled proliferation can lead to cancer. In addition, the repair of DNA damage may also be impaired by H. pylori infection. Reduced DNA repair in combination with increased DNA damage can result in carcinogenic mutations. The accurate identification of pathogenetic pathways is imperative for the development of targeted diagnostic markers and personalized treatments. This scoping review aims to update the readers on the role of H. pylori in the development of GC. It will focus on the molecular mechanisms underpinning gastric carcinogenesis in H. pylori infection. It will highlight the interaction between bacterial virulence factors and host cellular pathways, providing insights into potential therapeutic targets and preventive strategies.

Key Words: Helicobacter pylori; Molecular pathogenesis; Gastric cancer; DNA repair; Mutations

Core Tip: Helicobacter pylori (H. pylori) is a major risk factor for gastric cancer (GC), the third leading cause of cancer-related deaths. H. pylori triggers chronic inflammation, progressing through precancerous stages (gastritis, atrophy, intestinal metaplasia, dysplasia) to GC. Virulence factors like cytotoxin-associated gene A and vacuolating cytotoxin A activate oncogenic signaling pathways (PI3K/Akt, JAK/STAT, Ras/Raf/ERK), promoting uncontrolled cell proliferation and impairing DNA repair, leading to carcinogenic mutations. While 1%-3% of infected individuals develop GC, understanding these molecular mechanisms is crucial for identifying diagnostic markers and developing targeted therapies. This review explores H. pylori's role in gastric carcinogenesis, emphasizing bacterial-host interactions and potential preventive strategies.

INTRODUCTION

Gastric cancer (GC) is a major global public health challenge, and Helicobacter pylori (H. Pylori) is identified as a key etiological factor in about 89% of non-cardia GCs. H. pylori infection is one of the most widespread bacterial infections globally, affecting approximately half of the world’s population[1-3]. This Gram-negative bacterium colonizes the gastric mucosa and is a leading cause of various upper gastrointestinal (GI) diseases, including chronic gastritis, peptic ulcers (PU), and GC[4-6]. Among these, GC remains a significant global health burden, ranking as the third leading cause of cancer-related deaths worldwide. H. pylori has been classified as a Group I carcinogen by the World Health Organization, underscoring its critical role in the development of GC[7]. Despite its high prevalence, only a subset of infected individuals progress to severe outcomes, such as GC or mucosa-associated lymphoid tissue lymphoma, highlighting the complex interplay between bacterial virulence factors, host immune responses, and environmental influences[4-6].

The pathogenesis of H. pylori-induced GC involves a multistep process characterized by chronic inflammation and progressive mucosal injury. The infection initiates a series of precancerous lesions, including gastritis, atrophy, intestinal metaplasia, and dysplasia, which can eventually lead to malignant transformation[8-10]. The principal virulence factors of H. pylori, such as vacuolating cytotoxin A (VacA) and cytotoxin-associated gene A (CagA), play pivotal roles in disrupting host cellular signaling pathways, including PI3K/Akt, JAK/STAT, and Ras/Raf/ERK, which regulate cell proliferation and survival[11]. Additionally, H. pylori infection impairs DNA repair mechanisms and increases DNA damage, creating a mutagenic environment that drives carcinogenesis[12-14]. These molecular insights have opened new avenues for understanding the mechanisms underlying gastric carcinogenesis and identifying potential therapeutic targets[15-17].

This review aims to provide an updated overview of the molecular mechanisms by which H. pylori contributes to the development of GC. It will explore the intricate interactions between bacterial virulence factors and host cellular pathways, shedding light on the processes that drive malignant transformation. By elucidating these pathogenetic pathways, this review seeks to highlight potential diagnostic markers and personalized treatment strategies, offering hope for improved prevention and management of H. pylori-associated gastric diseases, in particular, GC.

METHODOLOGY

This scoping review was conducted following the structured framework developed by Arksey and O’Malley[18], which provides a systematic and transparent approach to mapping key concepts, evidence, and gaps in a broad research area. The framework consists of five key stages: (1) Identifying the research question; (2) Identifying relevant studies; (3) Selecting studies; (4) Charting the data; and (5) Collating, summarizing, and reporting the results. Each stage was carefully executed to ensure a comprehensive and rigorous review of the literature on the role of H. pylori in GC development, with a particular focus on molecular pathogenesis.

The research question guiding this review was: What are the molecular mechanisms by which H. pylori infection contributes to the development of GC, and how can these mechanisms inform diagnostic and therapeutic strategies? To address this question, a systematic search was conducted across three major electronic databases-PubMed, Scopus, and Web of Science-to identify relevant studies published within the last decade. The search strategy employed a combination of Medical Subject Headings (MeSH) terms and keywords, including "H. pylori", "Helicobacter pylori", "gastric cancer", "molecular pathogenesis", "CagA", "VacA", "signaling pathways", and "DNA damage". Boolean operators (AND, OR) were used to refine the search and ensure the inclusion of studies addressing both bacterial virulence factors and host cellular responses.

Following the database search, studies were screened based on predefined inclusion and exclusion criteria. Inclusion criteria encompassed peer-reviewed articles published in English, focusing on the molecular mechanisms of H. pylori-induced gastric carcinogenesis and providing insights into bacterial virulence factors, host signaling pathways, or therapeutic targets. Exclusion criteria included studies unrelated to H. pylori or GC, reviews without original data, and studies published before the 10-year period. The selected studies were then carefully scrutinized to extract key information, such as study design, molecular pathways, virulence factors, and therapeutic implications. Data were collated and synthesized to identify common themes, emerging trends, and gaps in the current understanding of H. pylori-associated GC. Finally, the findings were summarized and reported, providing a comprehensive overview of the molecular mechanisms underlying H. pylori-induced gastric carcinogenesis and their potential clinical applications.

BRIEF EPIDEMIOLOGY OF H. PYLORI IN ASIA

In Asia, the prevalence of H. pylori infection varies significantly across countries and even within regions of the same country[1-3]. For instance, Pacific Asian populations such as Chinese, Korean, and Japanese have notably high rates of both H. pylori infection and GC compared to other parts of the world. Conversely, countries like Singapore, Malaysia, Taiwan, and Vietnam demonstrate an intermediate risk due to a lower prevalence of both H. pylori and GC[19].

In South Asia and Middle East, the epidemiology of H. pylori infection presents a distinct scenario, characterized by a high prevalence of H. pylori infection but a relatively low number of GC cases. This contrast might be explained by the genetic diversity of the pathogen and variances in susceptibility among different ethnic groups[20].

H. PYLORI VIRULENCE FACTORS AND THEIR MECHANISMS

H. pylori infection is strongly associated with GI conditions like gastritis, gastric ulcer (GU), duodenal ulcer, and GC, and is classified as a class I carcinogen by the WHO. Numerous virulence factors of H. pylori have been identified, with CagA and the cag PAI playing pivotal roles in the pathogenesis of H. pylori-related diseases, including acute gastritis, GU, and GC. The key virulence factors of H. pylori that contribute to the pathogenicity and GC development, and their mechanisms are listed in Table 1. Other virulence factors, such as VacA and SabA, also mediate H. pylori's pathogenicity. CagA, encoded by the cagA gene, is prevalent in East Asian strains, contributing to epithelial and severe histological damage compared to Western strains. VacA, encoded by the vacA gene, induces cytoplasmic vacuolation in gastric epithelial cells, with toxin activity levels affected by different genotypic combinations. Some other virulence factors involved in the pathogenicity of H. pylori infection and their mechanisms are shown in Table 2. The s1am1 and s1bm1 genotypes are highly virulent and associated with acute gastritis, PU, and GC. Upon entering the gastric lumen, H. pylori undertakes four essential activities for effective colonization and prolonged infection: (1) Surviving in gastric acidic milieu; (2) Approaching epithelial cells by flagella-mediated motility; (3) Attachment to host epithelial cells via bacterial adhesins interacting with epithelial cell surface receptors; and (4) Induction of cellular injury by the toxins’ secretion[21-23] (Figure 1).

Figure 1 The key virulence factors involved in the pathogenicity of Helicobacter pylori infection. BabA: Blood group antigen-binding adhesion A; SabA: Sialic acid-binding adhesion A; NAP: Neutrophil activating protein; Hsp: Heat shock protein; VacA: Vacuolating cytotoxin gene A; CagA: Cytotoxin-associated gene A; T4SS: Type IV secretion system; ROS: Reactive oxygen species; IL: Interleukin; MIP: Macrophage inflammatory protein.

Table 1 Key virulence factors involved in Helicobacter pylori infection.

Key virulence factors	Mechanisms of action
CagPAI and CagA	CagPAI encodes the type IV secretion system and effector protein CagA. CagA is translocated into epithelial cells, where it phosphorylates and triggers signaling cascades associated with gastric cancer pathogenesis
VacA	VacA is a secreted toxin that induces vacuolation in host cells. It affects T cell proliferation, mitochondrial function, apoptosis, IL-8 release, and autophagy. Genetic polymorphisms in VacA influence its activity and are associated with the risk of gastric cancer
Urease	Urease hydrolyzes urea to neutralize stomach acid and maintain an optimal pH for bacterial survival
Flagella	Flagella facilitate bacterial movement and colonization. They also contribute to biofilm formation and modulate the immune response by inducing the release of IL-8
Outer membrane proteins (OMPs)	OMPs like BabA, SabA, and OipA interact with host receptors, promoting long-term colonization, chronic inflammation, and IL-8 secretion

CagA: Cytotoxin-associated gene A; BabA: Blood group antigen-binding adhesion A; SabA: Sialic acid-binding adhesion A; VacA: Vacuolating cytotoxin gene A; IL: Interleukin.

Table 2 Some other virulence factors involved in the pathogenicity of Helicobacter pylori infection.

Virulence factors	Mechanisms of action
Lipopolysaccharide	Triggers several signaling pathways
	Induces several inflammatory responses
	Induces immune responses
	Disrupts the mucus secretion
	Shielding the organism against toxic materials
Phospholipase	Activates signaling pathways (e.g., ERK1/2)
	Trigger chronic inflammation
	Enhances bacterial colonization and survival
	Involved in the degradation of lipids and damage to the mucus layer
Heat shock proteins	Enhance adherence to epithelial surfaces
	Involved in urease activation
	Control apoptosis and autophagy
	Help to maintain the structure and properties of the effector proteins
	Protect the cell from reactive oxygen species (ROS)
	Induce the production and release of IL-8, TNF-α and COX-2
Arginase	Prevents bacterial killing
	Prevents T-cell proliferation
	Impair immune responses
	Stimulate apoptosis
	Help the H. pylori to withstand the acidic environment
Superoxide dismutase	Protects the cell from ROS
	Enhances colonization
	Inhibits the production of cytokines
	Stimulates macrophage activation
γ-glutamyl-transferase	Facilitates apoptosis and necrosis
	Induces the release of pro-inflammatory proteins
	Induces the release of ROS
	Stimulates DNA damage
Cholesteryl α-glucosyltransferase (αCgT)	Shields H. pylori from immunological attack
	Stimulates the production of pro-inflammatory proteins (e.g., IL-8)
	Enhances bacterial growth and its resistance to antibiotics

TNF-α: Tumor necrosis factor alpha; IL: Interleukin; Helicobacter pylori: H. pylori.

H. pylori subsists within the acidic gastric environment by employing a method which regulates periplasmic pH through the activity of urease. The urease gene cluster comprises seven genes, which encode the catalytic components (ureA/B), an acid-sensitive urea transporter (ureI), and helper proteins for enzyme assembly (ureE-H). In H. pylori, intracellular urease function is vital for surviving acidic conditions. The ureI channel controls this by allowing urea influx solely in low-pH environments, avoiding harmful pH increases when conditions are less acidic. Outside the cell, urease converts urea into carbon dioxide and ammonia, generating ammonium hydroxide. This reaction buffers the surrounding acidic environment, protecting the bacteria as they traverse the harsh gastric fluid. H. pylori migrates toward the basal aspect of the stomach epithelium, where the pH is near 7.0, aided by the action of 4-7 polar flagella. Increased motility, as observed in certain H. pylori strains, leads to increased bacterial density and a florid inflammatory response in the mucosa of the gastric wall, indicating the flagellum's role as a colonization and virulence factor in the initial phase[24-27].

Bacterial adhesins interact with host cell receptors, facilitating attachment and protecting against displacement by forces like peristalsis and gastric emptying. Notably, BabA and SabA are well-studied adhesins. Many other virulence factors, including neutrophil-activating protein (NAP) and heat shock protein 60 (Hsp60), also play important roles in mediating tissue injury. NAP stimulates the production of oxygen radicals by neutrophils, leading to tissue damage and the release of inflammatory mediators like interleukins (IL)-8, MIP-1a, and MIP-1b, linked with mononuclear cell and neutrophil infiltration into the stomach mucosa following infection by H. pylori. Hsp60 triggers nuclear factor kappa B (NF-κB) activation via TLR2 and MAP kinase signaling pathways, stimulating IL-8 release from human monocytes. Elevated anti-Hsp60 antibody levels are commonly observed in H. pylori-infected individuals, and their concentrations correlate with the severity of gastritis or GC. The prevalence of CagA-positive H. pylori is approximately 60% in Western countries and approaches 90% in Asian populations. The cagPAI, a 40 kb chromosomal DNA segment, harbors over 30 genes, including six homologous to the type IV secretion system (T4SS), facilitating the injection of CagA into the host gastric cell cytoplasm[28-31].

Once translocated, CagA interacts with phosphatidylserine, localizing to the inner surface of the plasma membrane. Upon phosphorylation, CagA interacts with the phosphatase SHP-2, modulating cellular processes such as adhesion, motility, and spreading. Beyond this, CagA triggers cytoskeletal remodeling, alters proliferation, and enhances IL-8 secretion from gastric epithelial cells. Independent of phosphorylation, CagA engages with the hepatocyte growth factor receptor Met, resulting in sustained stimulation of the PI3K/Akt pathway. This signaling cascade drives gastric epithelial proliferation and fosters a pro-inflammatory state linked to chronic gastritis and GC via the activation of NF-κB and β-catenin pathways (Figure 2; Table 3). Furthermore, H. pylori CagA upregulates DNMT1 expression via the AKT–NF-κB pathway, leading to hypermethylation and inactivation of tumor suppressor genes like MGMT in stomach epithelial cells. This mechanism contributes to GC development by promoting aberrant hypermethylation of promoter CpG islands of tumor suppressor genes[28-32].

Figure 2 The main signaling pathways implicated in the pathogenesis of gastric cancer development by Helicobacter pylori virulence factors. This figure was created by BioRender.com (Supplementary material).

Table 3 Signaling pathways activated by Helicobacter pylori infection that promote uncontrolled cell proliferation.

Signaling pathways	Molecular mechanisms involved in gastric cancer induced by H. pylori
STAT3 pathway	H. pylori activates the STAT3 pathway through upregulation of IL-6, CagA-mediated SHP-2 activation, and TLR2 interaction. STAT3 regulates downstream target genes involved in cellular processes such as development, proliferation, differentiation, EMT, invasion, and metastasis
NF-κB pathway	H. pylori activates NF-κB through direct activation by CagA, IKK kinase, and upregulation of pro-inflammatory factors. NF-κB transcriptionally regulates genes involved in cell cycle progression, apoptosis inhibition, and cross-regulates with other tumor signaling pathways
Wnt/β-catenin	H. pylori activates the Wnt/β-catenin pathway through CagA-mediated accumulation and nuclear translocation of β-catenin. Activation of this pathway disrupts cell cycle regulation, inhibits apoptosis, induces EMT, and promotes tumor cell proliferation, motility, and invasion. Cross-regulation between Wnt/β-catenin and other pathways enhances oncogenic effects
Miscellaneous signaling pathways	H. pylori activates additional signaling pathways including the MAPK pathway (ERK, JNK, p38), PI3K/Akt pathway, Hippo pathway, and various other pathways (HGF/Met, TGF-β, Hedgehog, Notch). These pathways are involved in regulating proliferation, survival, migration, invasion, differentiation, apoptosis, stem cell properties, microRNA map, and exhibit complex cross-regulatory interactions with each other and with the classical pathways

Helicobacter pylori: H. pylori.

The mammalian Hippo tumor suppressor signaling pathway plays a critical role in regulating the size and homeostasis of developing organs. Within this pathway, Yes-associated protein (YAP) serves as a key downstream effector, influencing various cellular functions such as proliferation, differentiation, and migration of gastric epithelial cells. Elevated YAP activity or overexpression has been strongly associated with enhanced cell proliferation and anti-apoptotic effects in malignancies. This upregulation shows a significant correlation with disease advancement across multiple cancer types in human patients[33]. Li et al[34] conducted insightful experiments revealing that H. pylori's injection of CagA into cultured stomach epithelial cells stimulates the oncogenic YAP pathway. This leads to a decrease in E-cadherin expression and an upregulation of the epithelial-mesenchymal transition program, thereby fostering gastric carcinogenesis[35-38].

VacA stands as another pivotal virulence factor associated with H. pylori, recognized for its multifaceted impact on host cells, including vacuolization, necrosis, and apoptosis. The VacA complex possesses the ability to integrate into the host cell membrane, exhibiting characteristics of an anionic selective channel. The VacA toxin acts as a channel-forming protein that enables bicarbonate and organic anions to enter host cells, supporting H. pylori colonization by exporting nutrients that promote bacterial growth. Previous studies indicate that VacA can localize to multiple cellular compartments. The toxin is internalized via endocytosis, reaching endosomal membranes, while extracellularly applied VacA directly targets mitochondria, triggering cytochrome C release and apoptotic cell death. Furthermore, VacA activates endoplasmic reticulum stress pathways, promoting both autophagy and apoptosis. H. pylori-driven epithelial cell apoptosis may play a dual role in disease pathogenesis, contributing to both acute gastric damage and the long-term progression to atrophy and malignancy[39,40].

ROLE OF OXIDATIVE STRESS AND CHRONIC INFLAMMATION

Persistent inflammation plays a pivotal role in the development of numerous malignancies, with H. pylori-associated GC representing a prominent example. The infection initiates inflammatory cascades through multiple mechanisms, affecting both the gastric epithelium (the primary site of bacterial contact) and recruited immune cells including neutrophils, macrophages, and lymphocytes that infiltrate the infected tissue[41-43].

Oxidative stress, characterized by an increase in reactive oxygen species (ROS) production, plays a pivotal role in causing damage to gastric epithelial cells and promoting carcinogenesis. ROS can induce oxidative DNA damage, leading to the formation of 8-hydroxy-2′-deoxyguanosine (8-OHdG), a marker associated with DNA damage linked to cancer development[44-48].

As essential effector cells of innate immunity, neutrophils perform critical antimicrobial functions through chemotaxis, phagocytosis, and pathogen elimination. They achieve this through the production of antimicrobial substances like oxidants, proteinases, and antimicrobial peptides[49-51]. ROS and reactive nitrogen species (RNS) produced by neutrophils serve a dual function. They act as antimicrobial agents by directly killing microbial pathogens and also regulate the physiological functions of neutrophils by modulating various molecular pathways. However, in the gastric mucosa infected by H. pylori, ROS and RNS fail to eliminate the bacterium[52]. H. pylori can withstand oxidative stress through defense mechanisms involving the production of antioxidant enzymes such as NapA, catalase, and superoxide dismutase. Interestingly, H. pylori may even contribute to increased oxidative stress in gastric epithelial cells. H. pylori-derived CagA induces the expression of spermine oxidase, an enzyme involved in converting spermine to spermidine, resulting in the production of H₂O₂ as a by-product. Elevated levels of H₂O₂ can lead to ROS accumulation through mitochondrial membrane depolarization and activation of caspase-mediated apoptosis. Elevated levels of ROS/RNS induce multiple forms of DNA lesions, such as point mutations, adduct formation, and single- or double-strand breaks (DSBs). Notably, 8-OHdG, a prominent oxidative DNA lesion, is markedly upregulated in GC tissues. APE1 serves as a critical mediator in oxidative stress responses, participating in both gene expression modulation and the base excision repair (BER) pathway. H. pylori infection can modulate APE1 function, with increased oxidative stress upregulating APE1 levels initially to repair DNA damage, but chronic infection eventually inhibits APE1 expression, leading to genetic instability[53,54].

The adaptive immune response to H. pylori involves complex molecular pathways, where locally produced cytokines are essential for maintaining persistent inflammation. During infection, the gastric mucosa shows marked upregulation of Th1-associated [including interferon-γ (IFN-γ)] and Th17-associated cytokines (such as IL-17A and IL-21), whose expression is modulated by antigen-presenting cell-derived mediators, particularly IL-12 and IL-23[55-58].

Studies by D'Elios et al[59] demonstrated the local production of anti-H. pylori IgA and IgG, along with a specific response of Th1 effectors in the gastric antrum of infected patients, leading to increased synthesis of IFN-γ, tumor necrosis factor alpha (TNF-α), and IL-12. This immune response may contribute to the development of PU or H. pylori-related gastric B-cell lymphoma. Circulating anti-H. pylori IgG and IgA antibodies provide reliable serological markers for detecting bacterial infection, representing a convenient non-invasive approach for tracking H. pylori status in patients with premalignant gastric conditions, including atrophy, metaplasia, and dysplasia. Transforming growth factor-β1 (TGF-β1) functions as a potent suppressor of Th1-mediated immunity, modulating inflammatory responses during chronic infection. In H. pylori-infected gastric tissue, elevated expression of Smad7, a negative regulator of TGF-β1 signaling, inhibits the TGF-β1 regulatory cascade. This leads to heightened levels of IFN-γ and T-bet, exacerbating the Th1 immune response and tissue damage. T cell-derived cytokines, such as IL-21 and IL-17A, augment the production of matrix metalloproteinases (MMPs), leading to epithelial damage and mucosal ulceration. IL-21, found at elevated levels in H. pylori-infected gastric mucosa, stimulates the production of MMP-2 and MMP-9 in gastric epithelial cells, exacerbating tissue damage. IL-17A, another cytokine overproduced during H. pylori infection is positively correlated with GC progression and invasiveness. It stimulates the production of inflammatory mediators and MMPs, propagating mucosal inflammation and destruction[59].

Although H. pylori triggers inflammatory responses, it demonstrates remarkable persistence in the gastric mucosa, often surviving for decades. Emerging research reveals that bacterial cholesterol-α-glucosyltransferase activity depletes cellular cholesterol stores in infected epithelial cells. This enzymatic action disrupts IFN-γ-mediated signaling, thereby suppressing host inflammatory defenses and facilitating bacterial immune evasion[60].

HOST RESPONSES AND GENETIC SUSCEPTIBILITY

Host genetic polymorphisms, particularly in genes associated with proinflammatory responses such as IL-1β, IL-1RN, IL-8, IL-10, and TNF-α, play a significant role in influencing the severity of H. pylori-related diseases. These genetic variations can modulate the host immune response to H. pylori infection, impacting disease progression and clinical outcomes[61]. IL-1β is a key proinflammatory cytokine involved in the regulation of immune responses. Polymorphisms in the IL-1β gene have been linked to altered IL-1β expression levels, affecting the intensity of the inflammatory response to H. pylori infection. IL-1 receptor antagonist (IL-1RN) is a natural inhibitor of IL-1β activity. Genetic variations in the IL-1RN gene can influence the balance between IL-1β and its antagonist, thereby modulating the inflammatory response and disease outcome in H. pylori-infected individuals. IL-8 is a chemokine that plays a crucial role in recruiting neutrophils and other inflammatory cells to the site of infection. Genetic polymorphisms in the IL-8 gene can affect its expression levels, influencing the magnitude of the inflammatory response and tissue damage in H. pylori-related diseases. IL-10 is an anti-inflammatory cytokine that regulates immune responses and helps prevent excessive tissue damage. Variations in the IL-10 gene can impact its expression levels, thereby modulating the balance between proinflammatory and anti-inflammatory responses during H. pylori infection. TNF-α is another key proinflammatory cytokine involved in the immune response to H. pylori. Genetic polymorphisms in the TNF-α gene can influence TNF-α production, affecting the intensity of the inflammatory response and disease severity in H. pylori-infected individuals[61,62].

Overall, host genetic polymorphisms in genes related to proinflammatory responses play a crucial role in shaping the immune response to H. pylori infection and determining the severity of associated diseases. Understanding these genetic factors can provide valuable insights into disease pathogenesis and aid in the development of personalized treatment strategies for H. pylori-related conditions.

DYSREGULATION OF DNA REPAIR PATHWAYS

H. pylori impairs host DNA repair mechanisms through multiple pathways, creating genomic instability that drives gastric carcinogenesis. The bacterium's virulence factors, particularly CagA and VacA, play central roles in this process.

CagA disrupts key DNA damage response proteins such as p53 and ATM/ATR, which are critical for detecting and repairing DNA DSBs. By inducing oxidative stress through ROS and RNS, H. pylori causes chronic inflammation, further damaging DNA while simultaneously suppressing repair mechanisms like BER and mismatch repair (MMR). VacA exacerbates this by forming pores in mitochondrial membranes, leading to mitochondrial dysfunction and additional ROS production. Moreover, H. pylori infection promotes epigenetic silencing of DNA repair genes (e.g., MLH1 and MGMT) via hypermethylation, impairing error correction. The combined effects of direct DNA damage, suppressed repair pathways, and inflammation-induced mutations create a permissive environment for oncogenic mutations in genes like TP53 and CDH1 (E-cadherin), accelerating the progression from chronic gastritis to GC. Thus, H. pylori acts as a biological carcinogen not only by inducing inflammation but also by systematically disrupting the host’s genomic safeguards[63].

Dysregulation of DNA repair pathways, including deficiencies of enzymes like PMS2 and ERCC1, has been implicated in the development of H. pylori-associated GC. Understanding the role of these DNA repair enzymes in the pathogenesis of GC associated with H. pylori infection can provide insights into potential therapeutic targets for preventing or treating this malignancy[64,65]. Further investigation is necessary to uncover the mechanisms underlying the dysregulation of DNA repair pathways in H. pylori-infected gastric tissues and their contribution to cancer development. H. pylori infection triggers both inflammatory responses and genotoxic effects in host cells, leading to direct and indirect DNA lesions, including oxidative stress-induced damage and DSBs. Consequently, genetic and/or epigenetic disruptions alter the selection of DNA repair pathways, leading to inaccurate DNA repair, genomic instability, and chromosomal aberrations, all of which can promote gastric carcinogenesis. The cellular DNA damage response employs multiple repair mechanisms, including MMR, BER, nucleotide excision repair, homologous recombination (HR), and both canonical (NHEJ) and alternative end-joining pathways. These repair systems operate in concert with checkpoint signaling that induces cell cycle arrest or apoptosis when DNA damage cannot be properly corrected. Mounting evidence indicates that H. pylori infection dysregulates DNA repair processes through either transcriptional modulation of repair genes or direct functional interference with repair machinery.

The MMR pathway is a crucial mechanism for maintaining genome stability by correcting errors that occur during DNA replication. Dysfunctions in MMR are associated with various diseases, including hereditary non-polyposis colorectal cancer and brain tumors. In human cells, several MMR proteins have been identified. The hMSH2-hMSH6 complex (hMutSα) primarily recognizes base-base mismatches and small insertion-deletion loops, while MutSβ (hMSH2-hMSH3 complex or hMutSβ) targets larger insertion-deletion loops. These complexes, along with MutL homologs (hMLH1, hMLH3, hPMS1, and hPMS2), form the MMR machinery. While hMutLα (hMLH1-hPMS2 complex) is essential for MMR, the functions of hMutLβ and hMutLγ are less understood[66-69].

In eukaryotic cells, defects in DNA MMR are detected as microsatellite instability (MSI), characterized by alterations in simple sequence repeats. MSI is considered a hallmark of MMR deficiencies and is a reliable biomarker for stomach cancer. Notably, MSI-positive GCs demonstrate significantly higher H. pylori colonization rates than their MSI-negative counterparts. This clinical observation suggests potential bacterial-mediated dysregulation of MMR mechanisms during gastric carcinogenesis[70].

Studies have investigated the impact of H. pylori infection on the MMR pathway in GC cell lines. Studies revealed a significant reduction in MLH1, PMS1, PMS2, MSH2, and MSH6 protein levels following H. pylori infection, a phenomenon not mediated by the CagA virulence factor. While MSH2 and MSH6 mRNA expression was correspondingly suppressed, MLH1 transcript levels remained unaffected. Importantly, the expression of MLH1 and MSH2 returned to normal levels after H. pylori eradication, indicating reversible inhibition of MMR gene expression. Further investigations in chronically infected patients with H. pylori before and after eradication treatment showed that bacterial eradication increased MLH1 and MSH2 expression, suggesting that chronic H. pylori infection may have a negative impact on MMR in gastric epithelium, leading to mutation accumulation. Consistent with these findings, studies on human gastric tissue samples revealed lower MLH1-positive epithelial cell nuclei in H. pylori-positive patients compared to uninfected individuals.

Both cell culture and animal model studies consistently showed that H. pylori infection reduces MMR capacity in gastric epithelial cells, evidenced by diminished expression of MMR genes and their protein products, along with impaired repair function. This decrease was not dependent on bacterial virulence factors and led to increased genetic instability. Moreover, H. pylori infection induced the accumulation of DSBs in gastric cells, primarily repaired through error-prone NHEJ rather than HR. This shift in repair mechanism was mediated by the upregulation of NHEJ-related genes and the downregulation of HR-related genes[71,72].

A study identified the upregulation of long, noncoding RNA SNHG17 by H. pylori infection, which increased DSBs by promoting NHEJ over HR repair. SNHG17-mediated recruitment of NONO, involved in NHEJ, and its role as a decoy for miR-3909, which regulates HR, contributed to chromosomal abnormalities associated with GC development. Overall, these findings demonstrate that H. pylori infection induces dysregulation of the MMR pathway, leading to increased genetic instability and promoting gastric carcinogenesis[72,73].

MOLECULAR HETEROGENEITY OF GC

GC is a molecularly heterogeneous disease, and H. pylori-induced tumors exhibit distinct molecular features that influence both pathogenesis and treatment response[74]. The TCGA study identified four major GC subtypes, with H. pylori-associated cancers most commonly falling into the chromosomal instability (CIN) group, characterized by TP53 mutations and intestinal-type histology[75]. Similarly, the ACRG classification by Cristescu et al[76] linked H. pylori-driven cancers to the MSS/TP53- and MSS/TP53+ subtypes, both associated with worse outcomes compared to MSI-high tumors. H. pylori-induced GC is most commonly associated with intestinal-type histology, CIN, and specific molecular changes such as TP53 mutations, epigenetic silencing, and inflammatory gene signatures. Understanding these molecular traits can help refine treatment strategies and identify which patients benefit most from targeted therapies or immune modulation.

POTENTIAL THERAPEUTIC TARGETS AND PREVENTION STRATEGIES

Eradication therapy

The eradication of H. pylori infection is a cornerstone in the prevention of GC, as chronic infection is a major risk factor for the development of gastric adenocarcinoma. Current eradication therapies typically involve a combination of antibiotics (such as clarithromycin, amoxicillin, or metronidazole) and proton pump inhibitors. While these regimens have shown success in reducing H. pylori colonization and associated inflammation, their effectiveness in preventing GC varies depending on factors such as the timing of intervention, antibiotic resistance, and the extent of pre-existing gastric damage. Studies have demonstrated that eradication therapy is most effective in preventing GC when administered before the onset of precancerous lesions, such as atrophic gastritis or intestinal metaplasia. However, in advanced stages of gastric carcinogenesis, eradication alone may not be sufficient to reverse the damage, highlighting the need for early detection and treatment of H. pylori infection[77,78].

Several key randomized controlled trials (RCTs) have shown that H. pylori eradication therapy is most effective in preventing GC when administered before the development of precancerous lesions such as atrophic gastritis or intestinal metaplasia. In the Shandong intervention trial[79], a double-blind, factorial RCT with over 3000 participants evaluated the effects of antibiotics, vitamins, and garlic on precancerous lesions and found a significant reduction in lesion progression, especially when eradication was performed early. The Wong et al[80] study randomized 1630 individuals in a high-risk Chinese population to receive H. pylori treatment or placebo and demonstrated a reduced incidence of GC primarily in those without baseline intestinal metaplasia or dysplasia. Similarly, Ma et al[81] followed a Chinese cohort over 15 years and found that early eradication significantly reduced GC incidence, particularly in participants without precancerous changes. Finally, the Fukase et al[82] trial, conducted in Japanese patients with early GC post-endoscopic resection, showed that eradication reduced the risk of metachronous GC by 66%. Across all studies, the primary outcome was the incidence or progression of GC, and the study designs were robust, long-term RCTs with histological or clinical endpoints to assess cancer risk.

Precancerous gastric lesions, including atrophic gastritis and intestinal metaplasia, are assessed histologically using validated staging systems. The Operative Link on Gastritis Assessment (OLGA) system, as described by Rugge et al[83], quantifies the severity and topographic extent of gastric atrophy by scoring biopsies from the antrum and corpus. This staging correlates well with GC risk. Capelle et al[84] further validated that intestinal metaplasia, when used in place of atrophy, provides equally reliable staging within the OLGA framework.

In large trials like the Shandong Intervention Trial by You et al[79] and the 15-year follow-up study by Ma et al[81], gastric mucosal biopsies were evaluated using the Updated Sydney System, which semiquantitatively scores atrophy and intestinal metaplasia (none, mild, moderate, marked) across multiple gastric sites. These studies demonstrated that eradication of H. pylori before the onset or in early stages of these lesions significantly reduces progression and the risk of GC.

Several studies and meta-analyses have explored whether different antibiotic regimens for H. pylori eradication vary in their GC prevention efficacy. While Ma et al[81] demonstrated that H. pylori eradication (regardless of regimen) significantly reduces GC incidence over 15 years, Liou et al[85] provided evidence that bismuth quadruple and concomitant therapies achieved significantly higher eradication rates than standard triple therapy. Although GC outcomes were not directly compared across regimens in Liou et al's study, improved eradication correlates with better cancer prevention[85]. Lee et al[86] confirmed through meta-analysis that H. pylori eradication significantly lowers GC risk, though regimen-specific comparisons were limited. The American College of Gastroenterologists guidelines[87] recommend tailored therapy based on local antibiotic resistance, highlighting that higher eradication efficacy, particularly in resistant regions, is key to maximizing cancer prevention. While GC prevention is more dependent on successful eradication than the specific regimen, comparative studies have shown that newer regimens (bismuth quadruple, concomitant) yield significantly better eradication rates, especially in areas with high resistance, indirectly improving cancer prevention outcomes.

Antibiotic resistance, particularly to clarithromycin, is a major factor reducing the success rate of H. pylori eradication, with treatment failure occurring in areas where resistance exceeds 15%[87,88]. The Maastricht VI/Florence consensus recommends avoiding standard triple therapy in high-resistance regions and favoring regimens like bismuth quadruple or concomitant therapy. To mitigate resistance-related failure, strategies include tailored therapy based on susceptibility testing and adopting novel acid suppression approaches, such as vonoprazan-based dual therapy, which demonstrated high eradication rates even in resistant strains[89].

Post-H. pylori eradication, the gastric mucosa experiences a significant reduction in inflammatory mediators, oxidative stress, epithelial proliferation, and microbial imbalance, all of which lower the risk of GC, especially when intervention occurs before advanced precancerous changes develop. Following H. pylori eradication, inflammatory markers and microbial dysbiosis in the gastric microenvironment are significantly reduced, which contributes to lowering GC risk. Schulz et al[90] showed that eradication restores a healthier gastric microbiota composition, reducing pro-inflammatory bacterial species. Nakajima et al[91] demonstrated that eradication can partially reverse epigenetic alterations, such as CDH1 gene methylation, which are key drivers in gastric carcinogenesis. Additionally, Tahara[92] highlighted that persistent inflammation promotes oxidative DNA damage and mutagenesis; thus, resolving inflammation post-eradication helps stabilize the mucosa and suppress neoplastic transformation.

Evidence suggests that H. pylori eradication can still provide prognostic benefit and partially reverse gastric mucosal damage even in advanced stages of gastric carcinogenesis. According to Wang et al[93], eradication significantly improves gastric atrophy and shows limited but possible regression of intestinal metaplasia, especially in less extensive cases. Shin et al[94] demonstrated that eradication reduces aberrant DNA methylation over a 10-year period, suggesting reversal of molecular damage associated with cancer progression. Additionally, Choi et al[95] found that eradication therapy significantly lowers the risk of metachronous GC after endoscopic resection of early GC, highlighting its role in improving long-term outcomes even when precancerous changes are already present.

Vaccine development

Vaccine development represents a promising strategy for the primary prevention of H. pylori-induced GC. Research has focused on identifying immunogenic antigens, such as urease, VacA, and CagA, which play critical roles in H. pylori pathogenesis. Advances in vaccine technology, including the use of recombinant proteins, DNA vaccines, and mucosal delivery systems, have shown potential in eliciting robust immune responses in preclinical models. However, challenges remain in translating these findings into effective human vaccines, including the need for long-lasting immunity and the ability to overcome the bacterium's immune evasion strategies. Despite these hurdles, ongoing clinical trials and innovative approaches, such as multi-epitope vaccines and adjuvants, continue to drive progress in this field[96-99].

Targeted molecular therapy

The molecular mechanisms underlying H. pylori-induced carcinogenesis provide opportunities for targeted therapies aimed at disrupting specific pathways involved in GC development. Key pathways include the NF-κB and MAPK signaling cascades, which are activated by H. pylori virulence factors such as CagA and promote inflammation and cell proliferation. Additionally, targeting oxidative stress and DNA damage responses, which are exacerbated by chronic infection, may help mitigate carcinogenic processes. Small molecule inhibitors, monoclonal antibodies, and epigenetic modulators are being explored as potential therapeutic agents to block these pathways. Combining targeted molecular therapies with eradication regimens or vaccines could enhance the prevention and treatment of H. pylori-associated GC, offering a multifaceted approach to reducing the global burden of this disease[96].

Understanding H. Pylori’s molecular mechanisms can pave the way for targeted therapies and preventive strategies by pinpointing key virulence factors, host-pathogen interactions, and immune evasion strategies. For example, targeting toxins like CagA and VacA, which disrupt host cell signaling and promote inflammation and cancer, could involve developing inhibitors that block their secretion through the T4SS or neutralizing their effects with monoclonal antibodies. Additionally, since H. pylori relies on urease to survive stomach acid, small-molecule urease inhibitors could jeopardise its colonization. Disrupting bacterial adhesion molecules like BabA and SabA, could prevent infection using synthetic analogs that competitively block these interactions. Furthermore, since H. pylori forms biofilms that enhance antibiotic resistance, quorum-sensing inhibitors or biofilm-disrupting agents could improve treatment efficacy. On the host side, modulating immune responses, such as balancing Treg/Th17 activity or manipulating TLR/NLR signaling, could reduce chronic inflammation without eliminating protective immunity. Meanwhile, vaccine development using CagA, VacA, or urease subunits, along with engineered probiotics that competitively exclude H. pylori, could offer preventive solutions. Finally, personalized approaches, such as screening for high-risk strains (CagA+/VacA+) or detecting early molecular biomarkers, could enable preemptive treatment before malignancy develops. By leveraging these molecular insights, researchers can design more effective, tailored interventions to combat H. pylori infections and their devastating consequences, including GC[100-102].

CONCLUSION

In conclusion, H. pylori infection represents a significant risk factor for a spectrum of gastroduodenal pathologies, encompassing PUs and gastric adenocarcinoma. This bacterium employs a multifaceted pathogenesis strategy. H. pylori utilizes urease activity to neutralize gastric acid, facilitating colonization. Flagella enable motility towards the epithelium, where adherence occurs via bacterial adhesins. Virulence factors like CagA disrupt cellular homeostasis and trigger chronic inflammation. Furthermore, H. pylori infection can compromise DNA repair mechanisms, promoting mutagenesis. Host genetic polymorphisms also influence disease susceptibility. Elucidating these intricate mechanisms underlying H. pylori pathogenesis is paramount for developing targeted therapies to eradicate the infection and prevent its associated gastric diseases.