H. pylori is no ordinary stomach dweller. The World Health Organization has classified it as a Group 1 carcinogen since 1994, and colonization of the gastric mucosa by the spiral-shaped, microaerophilic bacterium remains the single major risk factor for gastric cancer. Its persistence hinges on an arsenal of virulence factors, including outer membrane proteins that function as adhesins, molecular grappling hooks that anchor the bacterium to gastric epithelial cells and allow it to resist clearance by mucus turnover, acid flow, and peristalsis. Chief among these adhesins are BabA, which binds Lewis b blood group antigens; SabA, which recognizes sialyl-Lewis X structures; and HopQ, which latches onto members of the CEACAM glycoprotein family. Adhesion is not merely a docking maneuver: successful binding enables the delivery of additional virulence factors such as urease and the cytotoxins CagA and VacA, and it precedes the chronic inflammation that can progress to metaplasia, dysplasia, and carcinoma.

The therapeutic landscape has grown increasingly hostile. Clarithromycin resistance undermined the classic triple therapy of a proton-pump inhibitor plus amoxicillin and clarithromycin, prompting a shift to bismuth-based quadruple regimens built on tetracycline and metronidazole. Yet metronidazole resistance has now been detected at rates that surpass clarithromycin resistance in multiple territories, threatening the fallback regimen as well. Against this backdrop, researchers at the Federal University of Espírito Santo and the Federal University of Santa Catarina in Brazil set out to test whether a standardized silymarin preparation could attack H. pylori on several fronts at once: growth, adhesion, and inflammation.

Silymarin itself is not a single molecule but a mixture of flavonolignans that can constitute up to 70 percent of the crude extract from milk thistle fruits and seeds. The complex is dominated by the enantiomeric pairs silybinin A and B, which together can account for as much as 70 percent of the mixture, alongside isosilybinin A and B, silychristin, isosilychristin, silydianin, and the flavonoid taxifolin. All carry a flavonoid moiety, which underpins the complex’s celebrated antioxidant activity and its long history of use in hepatoprotection, anti-inflammatory, and antifibrotic formulations. Previous work by some of the same team had already shown that silybinin alone inhibits H. pylori, prompting the question of whether the full phytocomplex might perform even better.

The answer, at least in vitro, appears to be yes. Using the broth microdilution method against the reference strain H. pylori ATCC 43504, a strain known to be amoxicillin-susceptible and metronidazole-resistant, the researchers determined a minimum inhibitory concentration of 128 micrograms per milliliter, achieving 90.46 percent growth inhibition. Critically, the minimum bactericidal concentration matched the MIC, meaning the same dose that halted growth also killed the bacteria outright. For comparison, amoxicillin showed an MIC of 0.0625 micrograms per milliliter while metronidazole required 256 micrograms per milliliter against this resistant strain, confirming the expected susceptibility profile.

Scanning electron microscopy then revealed what the treatment does to the bacterium’s architecture. Untreated cells displayed the archetypal helical morphology with smooth surfaces and intact organization. After exposure to half the MIC of silymarin, the bacteria exhibited surface irregularities, cellular deformation, and the emergence of coccoid-like round forms, a pattern consistent with a membrane-targeted mechanism. The changes resembled, though were less extensive than, the severe membrane disruption caused by amoxicillin, which destroys the cell wall. Prior studies suggest silymarin increases membrane permeability, and its flavonolignans have been linked to interference with protein and RNA synthesis as well as disruption of the enzymes bacteria need for energy production.

Safety and selectivity were addressed before any anti-inflammatory claims could be made. In MTT assays, silymarin showed an IC50 of 46.27 micrograms per milliliter against AGS gastric adenocarcinoma cells and 98.18 micrograms per milliliter against RAW 264.7 macrophages, yielding a selectivity index of 2.12, roughly a twofold preference for killing cancer cells over healthy immune cells. Cisplatin, by contrast, showed almost no selectivity between the two cell types. Importantly, at the concentrations used in the immunological experiments, macrophage viability remained above 90 percent, ensuring that the dramatic reductions in inflammatory mediators were genuine pharmacological effects rather than artifacts of cell death.

Those effects were substantial. When macrophages were stimulated with H. pylori and treated with 50 micrograms per milliliter of silymarin, production of tumor necrosis factor-alpha fell by 80.82 percent, interleukin-6 dropped by 76.24 percent, and nitric oxide plummeted by 97.50 percent. Each mediator matters: TNF-alpha activates the NF-kappaB pathway that amplifies the inflammatory cascade and has been implicated in gastric carcinogenesis, while IL-6 drives a feedback loop between macrophages and gastric epithelial cells that promotes cancer, and sustained nitric oxide generates reactive nitrogen species capable of oxidative DNA damage. Notably, the complex outperformed pure silybinin on nitric oxide suppression, 97.50 percent versus 73.33 percent in earlier work, hinting at additive or synergistic contributions from the full flavonolignan mixture.

Adhesion assays added a third dimension to the picture. Using fluorescence-labeled H. pylori and AGS gastric cells, the team found that silymarin inhibited bacterial attachment in a concentration-dependent manner, with the highest tested dose of 256 micrograms per milliliter reducing adhesion by 25.87 percent. That figure is moderate, but it sits within the range reported for other natural anti-adhesive agents, including green tea epigallocatechin gallate, cranberry proanthocyanidins, and garlic-derived organosulfur compounds. Because attachment is the critical first step in colonization, even partial interference could impair the establishment of infection, and blocking adhesin binding sites may also indirectly dampen the expression of virulence factors such as VacA and CagA.

To probe the mechanism, the researchers turned to molecular docking, individually fitting all eight major silymarin constituents into the crystal structures of BabA, SabA, and HopQ. Isosilybinin A scored highest against BabA, forming hydrogen bonds with residues CYS189 and SER244; isosilychristin performed best against SabA, interacting with LYS152 and GLN159; and silychristin led against HopQ through contacts with SER135, ILE130, and ILE242. The results were validated with a consensus docking strategy using AutoDock Vina, since no co-crystallized small-molecule inhibitors exist for these adhesins. Encouragingly, the key residues targeted are highly conserved across H. pylori strains, and their substitution is known to cripple adhesin function. The authors caution that docking was performed on isolated compounds rather than the whole extract, so the computational results support plausible ligand-target interactions but do not fully explain the activity of the intact phytocomplex.

Physicochemical predictions rounded out the evaluation. All eight compounds showed mildly lipophilic logP values between 0.85 and 1.85 with satisfactory aqueous solubility, and all complied with Lipinski’s rule of five, the classical benchmark for oral drug-likeness. That profile is consistent with silymarin’s decades of oral use as a phytotherapeutic agent. Taken together, the study positions the milk thistle complex as a genuinely multifunctional candidate against H. pylori, one that simultaneously curbs bacterial growth, disrupts cellular architecture, suppresses three major inflammatory mediators, and undermines the adhesion machinery the pathogen depends on. The work remains at the in vitro and computational stage, and clinical translation will require further validation, but it offers a compelling case that an ancient herbal remedy may hold modern answers to one of medicine’s most stubborn gastric adversaries.

Subject of Research: Antibacterial, anti-inflammatory, and anti-adhesive effects of silymarin from milk thistle against Helicobacter pylori

Article Title: Effect of silymarin on Helicobacter pylori growth and adhesion: in vitro and in silico evaluation

Article References: Majeski, V. Z., Bittencourt, M. L. F., Tregnago, P. H., Loose, D. N., Federico, L. B., Kitagawa, R. R., & Ribeiro Gonçalves, R. D. C. (2026). Effect of silymarin on Helicobacter pylori growth and adhesion: in vitro and in silico evaluation. Frontiers in Natural Products, 5, Article 1890760. https://doi.org/10.3389/fntpr.2026.1890760

Image Credits: AI Generated

DOI: 10.3389/fntpr.2026.1890760

Keywords: silymarin, Helicobacter pylori, milk thistle, flavonolignans, antibacterial, anti-inflammatory, molecular docking, adhesins, gastric cancer, natural products, antibiotic resistance, Silybum marianum