Mitraphylline

Pharmacology & Research

Mitraphylline is the marker pentacyclic oxindole alkaloid (POA) of cat’s claw (Uncaria tomentosa) — chemically distinct from the Uncaria indole alkaloids such as its co-alkaloid hirsutine. Its own literature is a coherent but entirely preclinical anti-inflammatory/immunomodulatory story — the mechanistic rationale behind cat’s claw’s one genuinely human-anchored use (rheumatoid/osteoarthritis) — plus micromolar cytotoxicity against tumour lines. The load-bearing honesty point: cat’s claw’s clinical trials used the whole/purified extract, not isolated mitraphylline, so the clinical benefit cannot be attributed to this molecule. (One accuracy note: the popular “good POA / bad TOA alkaloid” marketing framing is not supported by the primary literature — both classes occur in both chemotypes.)

1. Anti-inflammatory / immunomodulatory

The best-supported activity and the marker of the anti-inflammatory POA fraction. Oral mitraphylline (30 mg/kg/day) in an LPS mouse model cut IL-1α, IL-1β, IL-17 and TNF-α release ~50% and IL-4 ~40%, comparable to dexamethasone ^{1Reference 1Rojas-Durán R et al. · 2012Anti-inflammatory activity of mitraphylline isolated from Uncaria tomentosa barkView study →}; in primary human monocytes/macrophages it skews toward an M2 (resolving) phenotype ^{2Reference 2Montserrat-de la Paz S et al. · 2015Pharmacological effects of mitraphylline from Uncaria tomentosa in primary human monocytes: skew toward M2 macrophagesView study →}; and in LPS-activated primary human neutrophils it lowers activation and TNF-α/IL-6/IL-8 ^{3Reference 32016Mitraphylline inhibits lipopolysaccharide-mediated activation of primary human neutrophilsView study →}.

Gap: all preclinical, with no human data on the isolated alkaloid — cat’s claw’s RA/OA trials used the whole/purified extract, so the clinical benefit cannot be attributed to mitraphylline alone ^{1Reference 1Rojas-Durán R et al. · 2012Anti-inflammatory activity of mitraphylline isolated from Uncaria tomentosa barkView study →}.

2. Anticancer / cytotoxic

Mitraphylline shows dose-dependent micromolar cytotoxicity against Ewing’s sarcoma (IC50 ~17 µM) and breast (IC50 ~12 µM) lines ^{4Reference 4García Giménez D et al. · 2010Cytotoxic effect of the pentacyclic oxindole alkaloid mitraphylline from Uncaria tomentosa bark on human Ewing’s sarcoma and breast cancer cell linesView study →} and antiproliferative activity in glioma and neuroblastoma ^{5Reference 5García Prado E et al. · 2007Antiproliferative effects of mitraphylline, a pentacyclic oxindole alkaloid of Uncaria tomentosa, on human glioma and neuroblastoma cell linesView study →}, with the broader oxindole-alkaloid fraction inducing apoptosis in leukaemia/lymphoma cells ^{6Reference 6Bacher N et al. · 2006Oxindole alkaloids from Uncaria tomentosa induce apoptosis in proliferating, G0/G1-arrested and bcl-2-expressing acute lymphoblastic leukaemia cellsView study →}.

Gap: cell-line only, with no in-vivo tumour or human data for the isolate — a preclinical signal, not a cancer therapy ^{4Reference 4García Giménez D et al. · 2010Cytotoxic effect of the pentacyclic oxindole alkaloid mitraphylline from Uncaria tomentosa bark on human Ewing’s sarcoma and breast cancer cell linesView study →}.

3. Neuroprotective

Mitraphylline (and isomitraphylline) disaggregated amyloid-β in vitro and were neuroprotective in SH-SY5Y neuroblastoma cells ^{7Reference 72020Neuroprotective potential of the oxindole alkaloids isomitraphylline and mitraphylline in human neuroblastoma SH-SY5Y cellsView study →}.

Gap: a single in-vitro study — and most cat’s claw “neuro” data belong to the Chinese species U. rhynchophylla (a different plant), so do not conflate ^{7Reference 72020Neuroprotective potential of the oxindole alkaloids isomitraphylline and mitraphylline in human neuroblastoma SH-SY5Y cellsView study →}.

Mechanisms

Target / pathway	Effect	Relevant to
TNF-α; IL-1α/IL-1β; IL-17	suppressed release (~50%, LPS mouse)	anti-inflammatory
IL-6 / IL-8	reduced (human neutrophils)	anti-inflammatory
Monocyte → macrophage polarisation	skewed to M2 (resolving)	immunomodulation
Neutrophil activation (CD16⁺CD62L⁻)	diminished after LPS	anti-inflammatory
Pro-apoptotic (tumour lines)	dose-dependent growth inhibition, µM range	anticancer (preclinical)
Amyloid-β aggregation	disaggregated in vitro	neuroprotective (preclinical)

NF-κB is the widely-cited upstream node for cat’s claw’s cytokine effects, but the isolated-mitraphylline studies demonstrate the downstream cytokine outputs rather than assaying NF-κB directly — stated honestly, not over-claimed.

Pharmacokinetics

Mitraphylline’s pharmacokinetics are poorly characterised, with no isolated-compound human data (Cmax, half-life, bioavailability). It is a low-abundance oxindole alkaloid — total oxindole alkaloids in cat’s claw bark are on the order of tenths of a percent and vary widely by chemotype, part and season ^{9Reference 9Heitzman ME et al. · 2005Ethnobotany, phytochemistry and pharmacology of Uncaria (Rubiaceae)View study →} — so isolate exposure from crude preparations is small. Oral 30 mg/kg was pharmacologically active in mice ^{1Reference 1Rojas-Durán R et al. · 2012Anti-inflammatory activity of mitraphylline isolated from Uncaria tomentosa barkView study →}, implying some oral absorption, but there is no formal ADME. A 2024 study found U. tomentosa extract and its major constituents (including mitraphylline) modulate multispecific drug transporters, flagging herb–drug-interaction potential ^{8Reference 82024Modulation of multispecific transporters by Uncaria tomentosa extract and its major phytoconstituentsView study →} — though the frequently-cited CYP3A4/protease-inhibitor interaction is a whole-extract finding, not demonstrated for isolated mitraphylline.

Clinical trials

There are no trials of isolated mitraphylline. Human cat’s claw trials (rheumatoid arthritis, knee osteoarthritis, breast-cancer chemo-adjuvant) all used whole/purified/freeze-dried extract and cannot be attributed to this single alkaloid.

Last checked: July 2026.

Toxicity & Safety

Mitraphylline has a [low] toxicity verdict on the available preclinical data — it showed no cytotoxicity against normal murine peritoneal macrophages up to 100 µM, so its tumour-line cytotoxicity (IC50 ~12–17 µM) is comparatively selective ^{1,4Reference 1Rojas-Durán R et al. · 2012Anti-inflammatory activity of mitraphylline isolated from Uncaria tomentosa barkView study →Reference 4García Giménez D et al. · 2010Cytotoxic effect of the pentacyclic oxindole alkaloid mitraphylline from Uncaria tomentosa bark on human Ewing’s sarcoma and breast cancer cell linesView study →}. There are no genotoxicity, organ-toxicity or human safety data for the isolate, and the main practical concern is a theoretical herb–drug interaction via transporter/CYP modulation at the extract level ^{8Reference 82024Modulation of multispecific transporters by Uncaria tomentosa extract and its major phytoconstituentsView study →}. This is a chemically distinct molecule from kratom’s mitragynine, and kratom’s opioid pharmacology must not be attributed to it.

Pregnancy & lactation

Avoid. Cat’s claw (U. tomentosa) is traditionally cautioned/contraindicated in pregnancy (historical Amazonian contraceptive/abortifacient use), and there are no reproductive-safety data for isolated mitraphylline — so it is best avoided in pregnancy and lactation.

Dosage

There is no established dose for isolated mitraphylline — it is not used as a standalone supplement but functions as the standardisation marker for cat’s claw pentacyclic-chemotype extracts (products are standardised to POA content), not as a dosed ingredient, so no human dosing guidance exists.

References