Angiotensin-converting enzyme, or ACE, sits at the heart of the renin-angiotensin system, the hormonal cascade that regulates blood volume and vascular tone. When the enzyme clips a small peptide fragment from angiotensin I, it generates angiotensin II, one of the most potent vasoconstrictors in the human body. Angiotensin II narrows blood vessels, prompts the release of aldosterone, and drives up blood pressure. Blocking this conversion is therefore a proven pharmacological strategy, and the degree to which a substance can hamper the enzyme is conventionally expressed as an IC50 value, the concentration needed to halve the enzyme’s activity. In the new study, the 80 percent methanol extract of P. posumbu leaves achieved an IC50 of 298.46 micrograms per millilitre, a figure the authors describe as significant and consistent with a possible role in hypertension management.

The plant itself is far from a household name outside its native range. Polygonum posumbu belongs to the buckwheat family, Polygonaceae, a group of flowering plants known for producing phenolic compounds. In the traditional medicine systems of Manipur and neighbouring regions, preparations of the plant have been used to treat elevated blood pressure, among other ailments. Ethnomedicinal records like these have increasingly become starting points for drug discovery, on the logic that generations of observed use can point researchers toward plants whose chemistry genuinely interacts with human physiology. The Manipur team set out to test that logic rigorously, examining not only antihypertensive activity but also antioxidant and antimicrobial properties, and then asking which molecules in the extract might be responsible.

Preliminary phytochemical screening confirmed the presence of major classes of secondary metabolites, including tannins and alkaloids, both of which are chemically capable of interacting with proteins such as ACE. Tannins, in particular, are polyphenolic compounds that can bind to enzyme active sites, and many dietary polyphenols have been shown in laboratory studies to modulate blood pressure through multiple mechanisms. To go beyond these broad chemical categories, the researchers turned to ultra-high-performance liquid chromatography coupled to Orbitrap mass spectrometry, an analytical platform capable of separating complex mixtures and identifying individual molecules with high precision based on their mass and fragmentation patterns.

The metabolite profiling paid off. The team tentatively identified thirteen compounds with known antihypertensive associations, a list that reads like a highlight reel of plant pharmacology: gallic acid, rosmarinic acid, naringenin, ferulic acid, luteolin, oleanolic acid, quercetin, neochlorogenic acid, kaempferol, caryophyllene oxide, chrysin, ursolic acid, and apigenin. Several of these are flavonoids, a family of polyphenols abundant in fruits, vegetables, and teas that has been repeatedly linked to cardiovascular benefits in dietary studies. Quercetin and kaempferol, for example, have been investigated for their ability to relax blood vessels and reduce oxidative stress, while rosmarinic acid and gallic acid are well-documented antioxidants. The presence of this chemical ensemble, the authors argue, provides a plausible mechanistic foundation for the ACE inhibition and radical-scavenging behaviour observed in their assays.

Antioxidant activity was assessed through six complementary in vitro tests, each probing a different facet of how a substance handles reactive molecules. The extract neutralised the ABTS radical cation with an IC50 of 134.96 micrograms per millilitre and scavenged superoxide anion radicals at an IC50 of 181.98 micrograms per millilitre, both indicating strong free radical quenching capacity. Hydroxyl radical scavenging required a higher concentration, with an IC50 of 482.64 micrograms per millilitre, while nitric oxide scavenging was comparatively weaker at 11.53 milligrams per millilitre. The ferric reducing antioxidant power assay registered 18.66 micromoles of Fe2+ equivalents, and the phosphomolybdenum assay yielded 126 milligrams of ascorbic acid equivalents per gram of extract, confirming substantial overall reducing capacity. Statistical analysis found significant differences across the tested parameters, with p values below 0.001.

Why does antioxidant capacity matter in the context of blood pressure? Oxidative stress, the imbalance created when reactive oxygen species overwhelm cellular defences, is closely intertwined with hypertension. Free radicals can deactivate nitric oxide, a signalling molecule that tells blood vessels to relax, and can damage the endothelial lining of arteries, promoting stiffness and inflammation. A plant extract that both inhibits ACE and mops up reactive radicals would, in principle, attack hypertension from two directions at once, easing vascular constriction while protecting the vessels themselves. This dual action is precisely what the chemical profile of P. posumbu suggests, though the authors are careful to frame these as in vitro findings that warrant further investigation.

The study also documented antibacterial effectiveness against specific microbial strains, adding a third dimension to the extract’s broad-spectrum therapeutic profile. While antimicrobial activity is tangential to blood pressure control, it reinforces the picture of a plant rich in bioactive secondary metabolites, since many of the same phenolic compounds that scavenge radicals and inhibit ACE also disrupt bacterial membranes and metabolism. The authors note that these combined properties point to P. posumbu as a prospective source of naturally occurring bioactive chemicals with antihypertensive, antibacterial, and antioxidant qualities.

As with any laboratory study of a plant extract, important caveats apply. The experiments were conducted entirely in vitro, using plant extracts and purified enzymes rather than living organisms, and the authors explicitly state that no human or animal experiments were involved. An IC50 measured in a test tube does not translate directly into a dose for a patient, because absorption, metabolism, and distribution within the body can dramatically alter how much of each compound actually reaches its target. The identification of the thirteen antihypertensive compounds is described as tentative, meaning the assignments rest on mass spectrometric evidence rather than isolated, purified standards for every molecule. The authors themselves call for further in vivo studies and for the isolation of the active constituents as the necessary next steps.

Nevertheless, the research exemplifies a productive model for modernising ethnobotanical knowledge. By pairing traditional use records with quantitative enzyme assays and high-resolution metabolomics, the Manipur team has converted a folk remedy into a chemically characterised candidate for future drug development. If subsequent animal and clinical studies confirm that the polyphenols in P. posumbu can meaningfully lower blood pressure in living systems, the plant could join the growing roster of botanical sources informing cardiovascular therapeutics. For now, the study stands as a rigorous first step, demonstrating that a plant valued by traditional healers in Northeast India carries a measurable, mechanistically plausible arsenal against hypertension, one of the leading risk factors for death worldwide.

Subject of Research: ACE-inhibitory and antioxidant activity of Polygonum posumbu leaf extract with LC-MS/MS metabolite profiling

Article Title: Polygonum posumbu (an ethnomedicinal plant) extract shows antihypertensive potential via ACE inhibition supported by antioxidant activity and LC-MS/MS metabolite profiling

Article References: Pukhrambam, P. D., Chanu, W. K., Maisnam, J., & Singh, C. B. (2026). Polygonum posumbu (an ethnomedicinal plant) extract shows antihypertensive potential via ACE inhibition supported by antioxidant activity and LC-MS/MS metabolite profiling. BMC Complementary Medicine and Therapies. https://doi.org/10.1186/s12906-026-05552-7

Image Credits: AI Generated

DOI: 10.1186/s12906-026-05552-7

Keywords: Polygonum posumbu, hypertension, ACE inhibition, antioxidant activity, LC-MS/MS, phytochemistry, ethnomedicine, polyphenols, natural products, blood pressure, flavonoids, BMC Complementary Medicine and Therapies