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

The research team, led by Hussein S. Mohamed of Beni-Suef University in Egypt together with collaborators across Egypt, Iraq and Saudi Arabia, conducted the work under genuine semiarid field conditions rather than in the more forgiving environment of a greenhouse. They compared two botanical varieties of milk thistle: the purple-flowered Silybum marianum var. marianum, abbreviated Sm-mar, and the white-flowered Silybum marianum var. albiflorum, or Sm-alb. Half of the plants were inoculated with arbuscular mycorrhizal fungi while the other half grew uninoculated as controls, allowing the researchers to isolate the effect of the symbiosis on everything from flower head counts to the molecular composition of the harvested seeds.

The yield results were unambiguous. Inoculated plants of the white-flowered variety produced roughly 13 percent more capitula, the spiny flower heads that contain the seeds, compared with about 8 percent more in the purple-flowered variety. More dramatic still were the changes in seed size and weight: thousand-seed weight rose by approximately 20 percent in Sm-mar and by 36 percent in Sm-alb. Taken together, these effects translated into overall seed yield gains of around 9 percent for the purple-flowered variety and a remarkable 27 percent for the white-flowered one. For a medicinal crop grown under water-limited conditions, yield improvements of this magnitude achieved without synthetic fertilizers represent a meaningful agronomic advance.

What makes the study particularly valuable is that the researchers did not stop at yield. They carried out a detailed metabolic audit of the seeds, examining primary metabolites such as sugars, organic acids and amino acids, as well as the secondary metabolites responsible for the plant’s pharmacological reputation. The carbon and nitrogen profiles of the seeds shifted in a clearly variety-dependent manner. In the white-flowered Sm-alb, glucose and fructose levels surged by up to about 136 percent and sucrose climbed by 37 percent relative to uninoculated controls. In the purple-flowered Sm-mar, the increases in individual sugars were more moderate and were instead accompanied by a shift toward higher starch accumulation, suggesting the two genotypes channel fungal-derived carbon into different storage forms.

The amino acid pools of the seeds also responded to the fungal partnership. Lysine, an essential amino acid that human and animal diets must supply externally, rose by roughly 50 percent in Sm-mar and 46 percent in Sm-alb under inoculation. The white-flowered variety additionally showed smaller but consistent increases in several other free amino acids. The authors are careful to frame these findings as evidence of improved seed amino acid pools rather than a direct demonstration of enhanced nitrogen nutrition status, a distinction that reflects the complexity of tracing nitrogen flows through a living symbiosis. Even so, the enrichment of essential amino acids has obvious implications for the nutritional value of milk thistle seed meal, which is already used in animal feed applications.

The headline result for pharmacology concerns silymarin, the signature complex of flavonolignans concentrated in milk thistle seeds that has been studied for decades for its hepatoprotective, antioxidant and anti-inflammatory properties. Here the two varieties diverged in an intriguing way. In the purple-flowered Sm-mar, total silymarin increased by about 36 percent, driven largely by rises in silybin, the most pharmacologically prominent component, along with a doubling of minor flavonolignans such as silydianin and silychristin. The white-flowered Sm-alb showed a more modest 12 percent increase in total silymarin with smaller changes in individual components. In other words, the purple variety proved the stronger silymarin responder, while the white variety excelled elsewhere.

Bulk phenolic chemistry told a similarly split story. Total phenolics and total flavonoids actually decreased slightly, by 15 to 16 percent, in the purple-flowered variety under mycorrhizal treatment, yet they increased by 11 percent and 34 percent respectively in the white-flowered one. This divergence underscores a principle that is increasingly recognized in plant-microbe research: mycorrhizal fungi do not simply push secondary metabolism in one direction. Instead, they reconfigure metabolic priorities in ways that depend on the genotype, the environment and the specific biosynthetic pathways involved. A decline in total phenolics can coexist with an increase in a targeted, high-value compound class such as the silymarin flavonolignans, as the Sm-mar results demonstrate.

Crucially, these compositional shifts translated into measurable changes in bioactivity. Ferric reducing antioxidant power, a standard assay of a sample’s capacity to neutralize oxidizing agents, increased by 26 percent in Sm-mar and by 65 percent in Sm-alb. Extracts from inoculated plants also inhibited the oxidation of low-density lipoprotein, the lipoprotein particle central to cardiovascular disease pathology, and reduced red blood cell hemolysis more effectively than extracts from control plants in both varieties. The antimicrobial results were perhaps the most eye-catching of all: activity against the most responsive bacterial strains rose by up to 160 percent in the white-flowered variety, while antifungal activity against Aspergillus flavus, a notorious food-contaminating fungus and producer of aflatoxins, increased by 41 percent in Sm-mar and 119 percent in Sm-alb.

The broader significance of the work lies in its demonstration that a single, low-input intervention can upgrade a medicinal crop on multiple axes at once. Arbuscular mycorrhizal fungi are increasingly promoted as biofertilizers for sustainable agriculture because they improve nutrient uptake, enhance drought tolerance and reduce the need for chemical inputs, but evidence that they can also raise the therapeutic quality of a crop’s harvest is far scarcer than evidence for yield effects alone. By documenting simultaneous gains in yield, amino acid nutrition, silymarin content, antioxidant capacity and antimicrobial potency under real field conditions, the study strengthens the case for integrating mycorrhizal inoculation into the cultivation protocols of medicinal plants, particularly in semiarid regions where conventional fertilization is both costly and environmentally risky.

There is also a practical lesson for growers and breeders in the variety-specific responses. The white-flowered Sm-alb generally exhibited larger relative improvements in yield and in several bioactivity parameters, making it an attractive candidate for farmers seeking maximum output from inoculated fields, whereas the purple-flowered Sm-mar showed the stronger relative enrichment in silymarin flavonolignans, the compounds most directly associated with liver-supportive supplements. Matching fungal inoculation to the right genotype, and choosing the genotype according to whether the goal is biomass, seed quantity or pharmaceutical concentration, could allow producers to tailor milk thistle cultivation to specific market demands. As demand for plant-derived hepatoprotective compounds continues to grow, the humble fungi threading through the soil may prove to be among the most important partners the medicinal crop industry has.

Subject of Research: Effects of arbuscular mycorrhizal fungal inoculation on seed yield, silymarin content and bioactivity in two varieties of milk thistle under semiarid field conditions

Article Title: Arbuscular mycorrhizal fungi improve seed yield, silymarin content and bioactivity in two varieties of milk thistle (Silybum marianum)

Article References: S. Mohamed, H., A. Abdelrheem, D., Z. Al-Saffar, A., Sonbol, H., Magdy Korany, S., A. Alsherif, E., M. Almutairi, M., M. Mahmoud, A., & Yousry A. Mohamed, M. (2026). Arbuscular mycorrhizal fungi improve seed yield, silymarin content and bioactivity in two varieties of milk thistle (Silybum marianum). Plant Biosystems, 160(5), Article 278. https://doi.org/10.1007/s44473-026-00275-6

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00275-6

Keywords: arbuscular mycorrhizal fungi, milk thistle, Silybum marianum, silymarin, seed yield, flavonolignans, antioxidant activity, antimicrobial activity, biofertilizer, medicinal plants, secondary metabolism, sustainable agriculture