Hirsutine

Hirsutine’s classic and best-characterised signal. In isolated rat aorta it produces dose-dependent, endothelium-independent relaxation of noradrenaline- and high-K⁺-induced contraction, acting mainly as a voltage-dependent Ca²⁺-channel blocker and also reducing intracellular Ca²⁺-store release ^{2,3Reference 21991AnimalCa²⁺-channel-blocking effects of hirsutine, an indole alkaloid from the Uncaria genus, in the isolated rat aortaView study →Reference 31992AnimalEffects of hirsutine, an antihypertensive indole alkaloid from Uncaria rhynchophylla, on intracellular calcium in rat thoracic aortaView study →}; in cardiac tissue it is negatively chronotropic and antiarrhythmic, prolonging action-potential duration in SA node, atrium and ventricle ^{4Reference 41999Effects of hirsutine and dihydrocorynantheine on the action potentials of sino-atrial node, atrium and ventricleView study →}, building on the original Uncaria “hypotensive principle” work ^{1Reference 1Endo K et al. · 1983Hypotensive principles of Uncaria hooksView study →}.

Gap: all in-vitro/animal (rat isolated tissue), with no human isolate blood-pressure or arrhythmia trial and modest (µM-range) potency ^{2,4Reference 21991AnimalCa²⁺-channel-blocking effects of hirsutine, an indole alkaloid from the Uncaria genus, in the isolated rat aortaView study →Reference 41999Effects of hirsutine and dihydrocorynantheine on the action potentials of sino-atrial node, atrium and ventricleView study →}.

The genuine hook beyond cardiovascular. Against dengue virus, hirsutine inhibits a late step of the lifecycle (assembly/budding/release, not replication) across serotypes at low-µM EC50 ^{5Reference 5Hishiki T et al. · 2017Hirsutine, an indole alkaloid of Uncaria rhynchophylla, inhibits a late step in the dengue-virus lifecycleView study →}; against influenza A (H3N2) it was reported more potent than ribavirin, a finding echoed in the total-synthesis literature that titles it “the active anti-influenza A virus indole alkaloid” ^{6Reference 62021Highly efficient enantioselective total synthesis of the active anti-influenza-A-virus indole alkaloid hirsutineView study →}.

Gap: in-vitro/cell-culture only, with the influenza figure a secondary/older report and no in-vivo antiviral or human data ^{5,6Reference 5Hishiki T et al. · 2017Hirsutine, an indole alkaloid of Uncaria rhynchophylla, inhibits a late step in the dengue-virus lifecycleView study →Reference 62021Highly efficient enantioselective total synthesis of the active anti-influenza-A-virus indole alkaloid hirsutineView study →}.

Hirsutine was identified as an anti-metastatic phytochemical targeting NF-κB (p65) and suppressing MMP-2/MMP-9 in a murine breast-cancer model ^{7Reference 72014Identification of hirsutine as an anti-metastatic phytochemical by targeting NF-κB activationView study →}, induces mitochondrial-permeability-transition-dependent apoptosis via ROCK1/PTEN/PI3K/GSK3β in lung cancer cells ^{8Reference 82018Hirsutine induces mPTP-dependent apoptosis through the ROCK1/PTEN/PI3K/GSK3β pathway in human lung cancer cellsView study →}, and is antiproliferative in Jurkat leukaemia cells ^{9Reference 92021Inhibitory effect and mechanism of hirsutine on the proliferation of T-cell leukaemia Jurkat clone E6-1 cellsView study →}.

Gap: cell-line and single-mouse-model level, with no isolate clinical oncology data — do not imply clinical use ^{7,8Reference 72014Identification of hirsutine as an anti-metastatic phytochemical by targeting NF-κB activationView study →Reference 82018Hirsutine induces mPTP-dependent apoptosis through the ROCK1/PTEN/PI3K/GSK3β pathway in human lung cancer cellsView study →}.

Hirsutine crosses the blood-brain barrier (low but measurable brain levels in mice) ^{11Reference 112020AnimalTissue distribution of hirsutine and hirsuteine in mice by UHPLC-MSView study →}, giving biological plausibility.

Gap: essentially no direct hirsutine neuroprotection dataset — the well-documented Uncaria neuroprotection belongs to the sibling alkaloids rhynchophylline/isorhynchophylline, so this is speculative for hirsutine ^{11Reference 112020AnimalTissue distribution of hirsutine and hirsuteine in mice by UHPLC-MSView study →}.