Isorhamnetin (Methylated Quercetin Metabolite · Cardiovascular Flavonol)
| CAS No. | 480-19-3 |
| Class | Polyphenol · Flavonol · Flavonoid |
| Source | Ginkgo biloba (Leaves); Hippophae rhamnoides (Sea buckthorn berries); onion, dill, coriander, chrysanthemum flowers. Also a human COMT-mediated metabolite of quercetin |
| Claim strength | Moderate |
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Structural relationship to quercetin: Isorhamnetin is 3′-O-methylquercetin — quercetin with a methyl group replacing the 3′-hydroxyl on the B-ring. This single methylation meaningfully shifts properties: greater lipid solubility, higher membrane permeability, and distinct receptor binding characteristics compared to its parent compound. Dual identity: It is both a natural dietary compound (in ginkgo leaves and sea buckthorn berries) and an endogenous human metabolite of quercetin — produced via COMT-mediated methylation in human tissues. Consuming isorhamnetin directly bypasses the methylation step. Ginkgo context: Isorhamnetin is one of the three flavonols quantified in the standardised ginkgo extract (24%/6%) — alongside quercetin and kaempferol glucosides — contributing to the cardiovascular and cognitive evidence base of ginkgo preparations. Sea buckthorn research: Sea buckthorn berries (Hippophae rhamnoides) contain among the highest dietary concentrations of isorhamnetin, and human trials of sea buckthorn for cardiovascular support have specifically studied isorhamnetin as a key active contributor.
Evidence for Cardiovascular Protection, Anti-Adipogenic Activity & Anti-Inflammation
Cardiovascular protection: Inhibits platelet aggregation, reduces LDL oxidation, and improves endothelial function in preclinical models. Cardioprotective in ischaemia-reperfusion models — reduces infarct size. Human trials of sea buckthorn extract document cardiovascular risk marker improvements with isorhamnetin identified as a key contributor. Claim strength: Moderate.
Anti-adipogenic activity: Inhibits adipocyte differentiation in preclinical models by downregulating PPARγ and C/EBPα transcription factors, reducing lipid accumulation in differentiating fat cells. Claim strength: Emerging.
Anti-inflammatory and antioxidant: Inhibits NF-κB activation, COX-2 expression, and pro-inflammatory cytokines. Greater lipid solubility may allow more efficient membrane penetration for lipid-phase antioxidant protection than quercetin. Claim strength: Moderate.
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Isorhamnetin Specification & Formulator Notes
Commercial sources: Most typically encountered as part of standardised ginkgo biloba extract (24%/6%) where it comprises ~one-third of the flavone glycoside fraction. As an isolated compound, produced from sea buckthorn or chrysanthemum extraction. Confirm source and HPLC purity on CoA.
When to use isorhamnetin vs quercetin: Quercetin has the broader and more established clinical evidence base. Isorhamnetin's advantages are better lipid solubility, distinct metabolic fate, and different receptor targeting. For full-spectrum flavonol formulations or sea buckthorn/ginkgo-positioned products, including isorhamnetin alongside quercetin and kaempferol is rational and botanically authentic.
Synergistic pairs: Quercetin (parent compound and metabolic precursor), kaempferol (complete flavonol triad as in ginkgo extract), ginkgo biloba extract (natural flavonol combination source), sea buckthorn extract (natural source with cardiovascular clinical trial evidence).
Frequently Asked Questions — Isorhamnetin
Is isorhamnetin a natural compound or a quercetin metabolite?
It is both — isorhamnetin occurs naturally in ginkgo leaves and sea buckthorn berries as a primary constituent, and is also produced by COMT-mediated methylation of quercetin in human tissues after absorption. Its presence as both dietary compound and endogenous metabolite suggests it is a biologically intended form of quercetin activity.
What role does isorhamnetin play in standardised ginkgo extract?
Ginkgo biloba extract standardised to 24%/6% contains 24% total flavone glycosides — a mixture of quercetin, kaempferol, and isorhamnetin glucosides in roughly equal parts. The clinical evidence for ginkgo in cognitive and cardiovascular support relates to this complete flavonoid mixture alongside the terpene lactone fraction (ginkgolides, bilobalide).
What is the sea buckthorn connection to isorhamnetin?
Sea buckthorn berries contain among the highest concentrations of isorhamnetin in any dietary fruit. Sea buckthorn has a long history in Tibetan, Chinese, and Russian traditional medicine, and has been studied in human trials for cardiovascular support with isorhamnetin specifically identified as a key active contributor alongside the unique fatty acid and carotenoid profile.
Does isorhamnetin have better bioavailability than quercetin?
Isorhamnetin's greater lipid solubility improves membrane penetration and may provide better CNS and tissue access than quercetin. However, the overall bioavailability picture is complex and format-dependent, and quercetin's clinical evidence base is stronger despite lower lipid solubility. Isorhamnetin's advantage is most relevant in CNS-targeted and lipid-phase antioxidant applications.
Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.
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