MENISPERMACEAE

The Menispermaceae or moonseed family consists of approximately 400 species of tropical climbers. They exhibit simple alternate, often cordate leaves, small unisexual flowers and seeds which are shaped like horseshoes. This family contains many medicinal (Stephania, Tinospora spp.) and/or poisonous species (Anamirta, Chondrodendron spp.). The bright yellow stem of Fibraurea spp. is traditionally used to dye fabric.

Menispermaceae elaborate a wide diversity of terpenes and benzylisoquinoline alkaloids, some are highly poisonous. The tube curare plant (Chondrodendron tomentosum) of South America yields a potent poison called curare (plant extract), which is used by aboriginal people to make poison arrows. Once injected, curare rapidly causes paralysis and death by respiratory failure. This is due to the effect of tubocurarine, a bis-benzylisoquinoline alkaloid which inhibits nerve signals of voluntary muscles. Unlike most alkaloids, tubocurarine is positively charged, it cannot diffuse through the brain and gut effectively. Hence, curare victims remain conscious but locked in their own body. Hunters can safely consume curare tainted meat because the toxin is not orally absorbed. Curare was heavily researched in the 1900s, it has equipped modern anaesthesia with some of the most valuable paralytic drugs (pancuronium, rocuronium etc). Patients can be rendered motionless while unconscious to facilitate delicate surgeries.

Another highly poisonous Menispermaceae product is picrotoxin, which as its name suggest is intensely bitter. Picrotoxin is found in the seeds of Anamirta cocculus, a South Asian vine. It may also be present in the roots of Stephania japonica var. discolor (*dubious claim). Picrotoxin is actually a mixture of two sesquiterpenes (15-carbon natural product) called picrotoxinin and picrotin. Both are potent convulsant which induces seizures and death. In contrast to curare, picrotoxin is orally active, it inhibits the 'chilling' of nerve signals, causing nervous conduction to become hyperdrive. Theoretically, picrotoxin can antagonise (partly) the paralytic effect of curare.

Menispermaceae is a treasure trove of drug discovery. Some Stephania alkaloids like cepharanthine is highly biologically active. It is investigated as a drug to treat alopecia (baldness), leukopenia (low white cell count), and even venomous snakebite.

Stephania japonica var. discolor, leaves.

Stephania japonica var. discolor, seeds.

Stephania japonica var. discolor, matured fruits.