Folate, or vitamin B9, is best known as an essential nutrient for prenatal development, but inside cells it is the backbone of one-carbon metabolism, a network that shuttles single-carbon units between folate derivatives to manufacture DNA building blocks, support methylation reactions, and maintain redox balance. One branch of this network, the thymidylate cycle, produces dTMP and ultimately dTTP, the nucleotide specifically required for DNA synthesis. Because endothelial cells must divide rapidly during angiogenesis, the growth of new blood vessels, their demand for thymidylate is unusually high. The researchers reasoned that this makes retinal blood vessel growth exquisitely sensitive to folate availability, and that hyperglycemia might exploit that sensitivity to fuel the pathological vessel proliferation seen in diabetic retinopathy.

To test this idea, the team used a remarkable zebrafish model engineered so that intracellular folate deficiency can be switched on at will. A heat shock activates expression of gamma-glutamyl hydrolase, an enzyme that exports folate from cells, and red fluorescence marks the larvae in which the depletion has succeeded. When the researchers induced folate deficiency in these transparent larvae, the branching of the hyaloid vessels that supply the developing retina dropped significantly. Blocking folate metabolism with methotrexate, a classical dihydrofolate reductase inhibitor, produced the same effect, while supplementing with folic acid pushed branching in the opposite direction, increasing it. Retinal vascular development, in other words, tracks folate status closely.

The critical experiment came next. When larvae were bathed in a high-glucose solution, a standard zebrafish approach for modeling hyperglycemia, their retinal hyaloid vessels sprouted excessive branches, mimicking the hyper-angiogenesis of diabetic retinopathy. But when the researchers combined glucose exposure with folate deficiency, or with agents that perturb folate metabolism, including methotrexate, grape seed extract, and the green tea compound epigallocatechin-3-gallate, the glucose-driven vessel overgrowth was significantly blunted. This suggested that an intact, active folate metabolism is required for high sugar to exert its full angiogenic effect, and pointed the investigators toward the specific enzymes that changed under hyperglycemic conditions.

Molecular analysis revealed a clear signature. In the heads of glucose-exposed larvae, the messenger RNA for several one-carbon metabolism enzymes rose, but the standout was thymidylate synthase, or TYMS, the enzyme that converts deoxyuridine monophosphate into thymidylate using a methylene-tetrahydrofolate carrier. TYMS protein levels showed the most prominent increase of any enzyme measured. Crucially, the finding was not a zebrafish quirk: when the researchers exposed RF/6A monkey retinal endothelial cells and HMEC-1 human microvascular endothelial cells to glucose, TYMS protein climbed in both. Even more telling, injecting larvae with synthetic mRNA encoding Tyms, or simply supplying the downstream product dTTP, was enough to increase retinal vessel branching on its own, without any glucose at all.

The team also documented a striking tissue specificity. While TYMS overexpression boosted retinal hyaloid vessel branching, it simultaneously reduced the development of the intersegmental vessels along the trunk and the sub-intestinal vein. Exogenous dTTP reproduced this pattern, promoting retinal branching while leaving trunk vessels untouched. This aligns with the emerging concept of endothelial heterogeneity, in which vessel beds in different tissues have distinct metabolic appetites and signaling contexts. The retina, with its enormous energy demands, appears uniquely responsive to fluctuations in nucleotide supply, whereas trunk vasculature develops under different angiogenic programs governed by VEGF and BMP signaling. A gene set enrichment analysis of transcriptomic data from diabetic mouse retinas independently showed enrichment of folate one-carbon metabolism genes, lending cross-species support to the axis.

Into this mechanistic picture the researchers introduced Mesona chinensis, a botanical species long consumed as the herbal jelly and grass jelly tea of East Asian cuisine, with a documented history of safe dietary use. Phytochemical studies have identified rosmarinic acid, caffeic acid, quercetin glycosides, and astragalin among its constituents. When zebrafish larvae were exposed to the extract, high-performance liquid chromatography revealed a selective drop in dihydrofolate levels, while tetrahydrofolate, 5-methyl-tetrahydrofolate, and 10-formyl-tetrahydrofolate remained largely unchanged. This pointed to a targeted effect on the thymidylate cycle rather than a wholesale depletion of the folate pool. Consistent with that interpretation, adding folic acid or a mixture of other deoxynucleotides failed to reverse the extract’s anti-angiogenic effects, ruling out generalized folate or nucleotide starvation.

The functional results were compelling. Co-treatment with the extract dose-dependently reduced glucose-induced retinal vessel branching in larvae, and it restored the number of vessel branch points when dTTP was withheld from the system, an effect reversed by dTTP supplementation. In cultured endothelial cells, the extract reduced viability in a dose-dependent manner, and dTTP rescued the primate retinal cells. When applied to larvae engineered to overexpress Tyms, the extract tamed both the retinal hyper-branching and the trunk vascular abnormalities caused by excess enzyme. Perhaps most strikingly, larvae exposed to high glucose showed severely impaired optomotor responses, the instinctive swimming that follows moving stripes, with only about 27 percent behaving normally, whereas co-treatment with the extract raised that figure to roughly 84.5 percent. In adult zebrafish given retro-orbital glucose injections, the extract reduced retinal vascular sprouting in the mature vasculature.

Safety was a key differentiator. At concentrations that suppressed glucose-driven retinal angiogenesis, the extract produced no detectable developmental toxicity, while methotrexate and 5-fluorouracil caused reduced survival, body curvature, yolk sac and pericardial edema, and failed swim bladder inflation in the larvae. Molecular docking analysis further suggested that quercetin, a flavonoid present in the extract, binds the TYMS active site with a predicted energy more favorable than that of the natural substrate dUMP or the clinical inhibitor FdUMP, forming hydrogen bonds with Ser216 and hydrophobic contacts with Phe225 and Leu221, although the authors emphasize this is hypothesis-generating modeling rather than proof. Quercetin alone partially recapitulated the extract’s vascular effects in larvae.

The authors are careful about the limits of the work. The 100 millimolar glucose used in zebrafish immersion exceeds human physiological levels, though the TYMS upregulation was independently confirmed in mammalian cells at 10 millimolar glucose, within the clinically relevant range. Osmotic controls were omitted, long-term chronic exposure studies remain to be done, and the full chemical composition of the extract was not characterized chromatographically. No mammalian diabetic retinopathy model or clinical cohort has yet validated the findings, and the experimental concentrations cannot be translated directly into dietary recommendations. Still, the study establishes a mechanistic foundation for a genuinely novel idea: that a common, traditionally consumed food plant may modulate a chemotherapy-linked metabolic enzyme to protect the retina from sugar-driven vessel overgrowth, offering a gentler, diet-based complement to injections for millions at risk of diabetic blindness.

Subject of Research: The role of folate-mediated one-carbon metabolism and thymidylate synthase in diabetic retinopathy and the anti-angiogenic potential of Mesona chinensis extract

Article Title: Modulating Folate Metabolism and Thymidylate Synthase in Diabetic Retinopathy: Zebrafish Insights and the Prophylactic Potential of Mesona chinensis

Article References: Jao, S.-W., Yu, H.-H., Lee, G.-H., Ma, T.-W., Chang, Y.-S., Tang, M.-J., Chen, B.-H., & Fu, T.-F. (2026). Modulating Folate Metabolism and Thymidylate Synthase in Diabetic Retinopathy: Zebrafish Insights and the Prophylactic Potential of Mesona chinensis. Journal of Agriculture and Food Research, Article 103355. https://doi.org/10.1016/j.jafr.2026.103355

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103355

Keywords: diabetic retinopathy, folate metabolism, thymidylate synthase, one-carbon metabolism, Mesona chinensis, zebrafish model, angiogenesis, quercetin, hyperglycemia, retinal vasculature, functional foods, endothelial cells

The research team enrolled 131 women who were scheduled to undergo surgery for breast conditions spanning the full spectrum of disease severity: 23 women with benign breast disease, 47 with high-risk or non-invasive lesions, and 61 with invasive breast cancer. The median age of participants was 59 years. Before any surgical intervention, each participant provided a preoperative stool sample, giving the investigators a snapshot of the gut microbial community in a window when the disease status was known but treatment had not yet altered the biology being measured. This design allowed the researchers to compare microbial profiles across diagnostic categories while also testing how body size influenced those profiles.

Technically, the study relied on shallow shotgun metagenomic sequencing, an approach that sequences the collective genomes of all microbes present in a sample rather than targeting a single marker gene. Taxonomic profiling was carried out with Sourmash version 4.2.4 against the GTDB v207 reference database, a comprehensive and evolutionarily consistent catalog of bacterial and archaeal genomes. Functional profiling was performed using HUMAnN 3.6, which maps detected gene families onto MetaCyc metabolic pathways. This dual strategy is important because knowing which species are present does not necessarily reveal what those microbes are doing; by interrogating the functional gene content, the team could ask whether the metabolic capabilities of the gut community shifted with body mass index independently of which particular organisms carried those genes.

The results revealed a clear signal tied to body size. Alpha diversity, a measure of how many distinct microbial species coexist within a single individual and how evenly they are distributed, differed across the three diagnosis groups and inversely correlated with increasing body mass index, with the Inverse Simpson index reaching statistical significance at p equal to 0.025. In practical terms, women with higher BMI tended to harbor less diverse gut communities, a pattern consistent with prior observations that obesity is associated with a contraction of microbial richness. Beta diversity, which quantifies differences in community composition between individuals, also varied significantly by both diagnosis group and BMI, indicating that the overall architectural layout of the gut ecosystem shifted along both axes.

Notably, the study found no significant differences in microbial diversity based on age, menopausal status, or mammographic breast density. This last finding is particularly interesting because breast density is itself a well-established breast cancer risk factor, and some investigators have hypothesized that the gut microbiome might influence density through estrogen metabolism. The absence of a density signal in this cohort suggests that, at least in this population of women already undergoing breast surgery, body mass index may be the dominant host characteristic shaping the gut microbial landscape, overshadowing factors that have historically attracted more attention in the microbiome-breast cancer literature.

At the level of individual taxa, higher BMI was associated with enrichment of species belonging to three genera in particular: Dorea, Blautia, and Streptococcus. These are not obscure organisms. Blautia in particular has repeatedly surfaced in obesity research, including earlier work linking the genus to visceral fat accumulation in adults. Dorea has likewise been flagged in large taxonomic surveys of adiposity in American adults. The convergence of these findings across independent cohorts strengthens the case that these organisms are not random passengers but consistent companions of the obese metabolic state, possibly thriving on the altered nutrient availability, bile acid profiles, and inflammatory milieu that characterize excess adiposity.

The functional analysis proved even more provocative. When the researchers profiled microbial metabolic pathways, they found that higher BMI was associated with greater relative abundance of genes involved in NAD biosynthesis, folate metabolism, and aromatic amino acid metabolism. Each of these pathways has plausible connections to cancer biology. NAD is a cofactor indispensable for energy metabolism, DNA repair, and cell survival, and tumor cells are notoriously dependent on NAD-generating pathways; drugs targeting NAMPT, a key enzyme in the NAD salvage route, are under active investigation as cancer therapeutics. Folate metabolism is central to one-carbon chemistry and nucleotide synthesis, making it a classic target of chemotherapy. Aromatic amino acid metabolism encompasses the handling of tryptophan, tyrosine, and phenylalanine, and the kynurenine branch of tryptophan catabolism has been implicated in immunosuppression within the breast tumor microenvironment.

Perhaps the most conceptually striking result emerged when the team cross-referenced their most significant taxonomic and functional findings. That integrative analysis suggested that enrichment of Blautia species, acting through tryptophan metabolism, might provide a mechanistic bridge to the observed increase in NAD biosynthesis pathways. The logic is biologically coherent: certain gut bacteria can convert tryptophan into metabolites that feed into de novo NAD synthesis, and prior work has shown that bacteria can boost mammalian host NAD metabolism by engaging alternative biosynthesis routes. If the obesity-associated expansion of Blautia indeed channels more tryptophan-derived substrate into NAD-generating pathways, it could conceivably alter the systemic metabolic environment in ways that influence breast tissue biology, although the authors are careful to frame this as a hypothesis-generating observation rather than a demonstrated causal chain.

The study’s authors emphasize that these findings do not prove that the gut microbiome causes breast cancer, nor do they establish the direction of causality between BMI, microbial composition, and disease status. The cross-sectional design captures associations at a single time point, and the cohort consists of women already undergoing surgery for breast conditions, which may limit generalizability to healthy populations. Nevertheless, the work provides a concrete rationale for future longitudinal studies that could track whether obesity-associated microbial signatures precede malignant transformation, and whether interventions such as weight loss or dietary modification can reshape the gut microbiome in ways that reduce risk. Indeed, related ongoing research is already exploring how weight loss and omega-3 supplementation modulate the microbiome in women at increased breast cancer risk.

What makes this study resonate beyond the specialist literature is the way it reframes obesity as not merely a hormonal or inflammatory risk factor but also an ecological one. The human gut is a metabolic organ in its own right, and the microbes it hosts process dietary compounds, synthesize vitamins, regulate immune signaling, and metabolize estrogens that circulate to distant tissues including the breast. By documenting that body mass index leaves a detectable fingerprint on both the taxonomy and the functional repertoire of this internal ecosystem in women across the benign-to-malignant disease spectrum, the Mayo Clinic team has laid groundwork for a future in which microbiome profiles might one day help stratify breast cancer risk, or in which microbial pathways such as tryptophan-fueled NAD biosynthesis become targets for prevention strategies aimed at the interface between body weight and tumor biology.

Subject of Research: Associations between body mass index, gut microbial taxa, and microbial functional pathways in women with benign and malignant breast disease

Article Title: Body mass index-associated gut microbial taxa and functional pathways in women with benign and malignant breast disease

Article References: Sample, J. W., Johnson, S., Hoskin, T. L., Redaelli, M., Walther-Antonio, M. R., Chen, J., Degnim, A. C., & Hieken, T. J. (2026). Body mass index-associated gut microbial taxa and functional pathways in women with benign and malignant breast disease. Breast Cancer Research and Treatment, 219(2), Article 4. https://doi.org/10.1007/s10549-026-08065-6

Image Credits: AI Generated

DOI: 10.1007/s10549-026-08065-6

Keywords: breast cancer, obesity, body mass index, gut microbiome, microbiome, Blautia, Dorea, Streptococcus, tryptophan metabolism, NAD biosynthesis, folate metabolism, breast density