Pokeweed

Scientific Name(s): Phytolacca americana L. Family: Phytolaccaceae

Common Name(s): American nightshade , cancer jalap , cancerroot , chongras , coakum , pokeberry , crowberry , garget , inkberry , pigeonberry , poke , red ink plant , scoke

Uses

Young pokeweed leaves and berries may be eaten as food, but only after being cooked properly by boiling in several changes of water.

Dosing

At doses of 1 g, dried pokeweed root is emetic and purgative. At lower doses of 60 to 100 mg/day, the root and berries have been used to treat rheumatism and for immune stimulation; however, there are no clinical trials that support these uses or doses.

Contraindications

Contraindications have not yet been identified.

Pregnancy/Lactation

Documented adverse effects. Avoid use. Uterine stimulant with toxic constituents; is reputed to affect menstrual cycle.

Interactions

None well documented.

Adverse Reactions

GI distress, possibly leading to severe toxicities (see Toxicology).

Toxicology

Ingestion of poisonous parts of the plant may cause severe stomach cramping, nausea with persistent diarrhea and vomiting, slow and difficult breathing, weakness, spasms, hypotension, severe convulsions, and death.

Botany

Pokeweed is an ubiquitous plant found in areas such as fields, along fences, and in damp woods. Pokeweed is indigenous to eastern North America, and widely naturalized in Europe, the West Indies, and Asia. This vigorous shrub-like perennial can grow up to 4 m from a heavy tap root. The reddish stem has large pointed leaves that taper at both ends. 1 The flowers are numerous, in small and greenish-white racemes, developing into clusters of juicy, purple-black berries that mature from July to September.

History

Pokeweed leaves and roots have been used in folk medicine for the treatment of chronic rheumatism and arthritis, and as an emetic and purgative. 2 The plant has also been used to treat edema, 3 skin cancers, catarrh, dysmenorrhea, mumps, ringworm, scabies, tonsillitis, and syphilis. Poke greens, the young immature leaves, are commercially canned and sold under the name “poke salet.” The juice of the berries has been employed as an ink, a dye, and as a coloring agent in wine. 4

Chemistry

The toxic components of the plant are saponins based on the triterepene genins phytolaccagenin, jaligonic acid, phytolaccagenic acid (phytolaccinic acid), esculentic acid, and pokeberrygenin. 3 These include phytolaccosides A, B, D, E, and G, and phytolaccasaponins B, E, and G. 5 , 6 The saponins are present in cell culture as well. 7 The free triterpenes also have been isolated from different plant parts. 3 , 8 In addition, poke root has been found to contain sterols, including alpha-spinasterol. 9

Several neolignans have been isolated from seeds, including americanins A, B, and D 10 , 11 ; americanol A; isoamericanol A 12 ; and the methyl esters and ethers of the latter compounds. 13

A 4 kDa antifungal peptide, PAFP-s, has been elucidated from the seeds, 14 and its solution structure as a knottin-type peptide determined by nuclear magnetic resonance. 15 , 16

Numerous proteins of poke have been studied for a variety of reasons. The cysteine proteases phytolacains G and R are found in fruits and are 25 and 23 kDa in size, respectively. 17 , 18 , 19 Mitogenic proteins with the ability to bind specific carbohydrates (di-N-acetylchitobiose) have been recognized and isolated from poke roots for decades. 20 The pokeweed lectins C, D1, and D2 have been thoroughly characterized by x-ray crystallography and contain multiple chitin-binding domains. 21 , 22

The most medically interesting group of proteins from poke are pokeweed antiviral proteins (PAP). Different isoforms of PAP are present in seeds and in leaves at different growth stages. All proteins are approximately 30 kDa in size and are homologous to ribosome inactivating proteins such as ricin. 23

Uses and Pharmacology

Antiviral

PAPs have been extensively studied for their biochemical mechanism and antiviral activity. They are able to enzymatically depurinate adenine (A4324) and several other residues of ribosomal RNA via a specific RNA N-glycosidase activity. The consequence of this activity in a living cell is cessation of protein synthesis. The proteins are bound within the plant cell wall matrix and do not interfere with the plant's ribosomes unless the cell is injured. 24 PAP isoforms are also able to depurinate viral RNA of HIV-1, which blocks replication of the virus within host cells, 25 a property not shared by all ribosome-inactivating proteins. Ricin, for example, is inactive as an antiviral, but PAPs are active against a broad spectrum of plant and animal viruses, including poliovirus, herpes simplex, influenza, cytomegalovirus, and HIV. 25 The specificity for viral versus host cell RNA appears to reside in PAP's ability to bind to RNA cap structures. 26 It has been shown that cap binding and rRNA depurination can be uncoupled because mutation of a conserved asparagine residue blocks rRNA depurination but not cap binding. 27 The same study showed that PAP is retrotranslocated through the endoplasmic reticulum into the cellular cytosol. High resolution x-ray crystallogrphic structures of PAP-III and PAP-S have been published. 28 , 29

The antiviral properties of PAP have prompted its development as a microbicide for sexually transmitted diseases such as HIV. PAP-I had no adverse effects on semen used for artificial insemination of rabbits, and pups born via insemination with treated semen were entirely normal. 30 Likewise, neither human spermatazoa nor female genital tract epithelial cells were adversely affected by PAP. 31 As a topical microbicide, PAP would be administered vaginally in a gel formulation. Consequently, PAP was evaluated in a 13-week subchronic and reproductive toxicity study in mice. No adverse effects on the vaginal mucosa or on reproductive success were found in examination of numerous end points. 32 However, in rabbits, moderate to marked vaginal irritation was noted in some animals, but it was not dose-dependent in intensity. 33

It should be emphasized that the above studies were conducted on purified proteins and that crude extracts of poke cannot be substituted in therapy because of their acutely toxic properties.

Other

The saponins showed anti-inflammatory activity in a rat paw edema model at doses 10-fold lower than the LD 50 ; however, the toxicity of the saponins precludes their use in inflamation. 34 Poke extracts were found to have inhibitory activity in a model of diabetic nephropathy. 35 The sterol alpha-spinasterol was isolated as the active principle. 9 Some of the neolignans of poke promote neurite outgrowth in rat cortical neuron cultures. 12 , 13

Dosage

At doses of 1 g, dried pokeweed root is emetic and purgative. At lower doses of 60 to 100 mg/day, the root and berries have been used to treat rheumatism and for immune stimulation. However, there are no clinical trials that support these uses or doses. 36 , 37 , 38

Pregnancy/Lactation

Documented adverse effects. Avoid use. Uterine stimulant with toxic constituents; is reputed to affect menstrual cycle. 39

Interactions

None well documented.

Adverse Reactions

GI distress, possibly leading to severe toxicities, can occur (see Toxicology).

Toxicology

Pokeweed poisonings were common in eastern North America during the 19th century, especially from the use of tinctures as antirheumatic preparations and from ingestion of berries and roots that were mistaken for parsnip, Jerusalem artichoke, or horseradish. 36

All parts of pokeweed are toxic except the aboveground leaves sprouting in the early spring. The poisonous principles are found in highest concentrations in the rootstock, less in the mature leaves and stems, and least in the fruits. Young leaves, if collected before acquiring a red color, are edible if boiled for 5 minutes, rinsed, and reboiled. Berries are toxic when raw but edible when cooked.

Ingestion of poisonous parts of the plant may cause severe stomach cramping, nausea with persistent diarrhea and vomiting, slow and difficult breathing, weakness, spasms, hypotension, severe convulsions, and death. 40 However, less than 10 uncooked berries are generally harmless to adults. Several investigators have reported deaths in children following the ingestion of uncooked berries or pokeberry juice. 40 , 41 Severe poisonings have been reported in adults who ingested mature pokeweed leaves 42 and following the ingestion of tea brewed from one-half teaspoonful of powdered pokeroot. 36

A case of toxicity in campers who ingested properly cooked young shoots has been reported by the Centers for Disease Control and Prevention. Sixteen of the 51 cases exhibited case-definitive symptoms (vomiting followed by any 3 of the following: nausea, diarrhea, stomach cramps, dizziness, headache). These symptoms persisted for up to 48 hours (mean, 24 hours). 43 Poisoning also may occur when the toxic components enter the circulatory system through cuts and abrasions in the skin. Symptoms of mild poisoning generally last 24 hours. In severe cases, gastric lavage, emesis, and symptomatic and supportive treatment have been suggested. 40 The FDA classifies pokeweed as an herb of undefined safety that has demonstrated narcotic effects.

Bibliography

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