Rotenone

Rotenone is an odorless chemical that is used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the roots and stems of several plants such as the jicama vine plant. In mammals, including humans, it is linked to the development of Parkinson's disease.

History
Emmanuel Geoffroy first isolated rotenone from a specimen of Robinia nicou, now called Lonchocarpus nicou, while traveling in French Guiana. He wrote about this research in his thesis, published posthumously in 1895 after his death from a parasitic disease. Researchers later determined that the substance that Geoffroy termed nicouline was identically rotenone.

Uses
Rotenone is used in solution as a pesticide and insecticide, or in emulsified liquid form as a piscicide.

People catch fish by extracting rotenone from plants and releasing it into water. Poisoned fish come to the surface and are easily caught. This method was first practiced by various indigenous tribes who smashed the roots. Fish caught this way can be eaten because rotenone is very poorly absorbed by the gastrointestinal tract of humans, whereas it is lethal to fish because it readily enters the blood stream of the fish through the gills.

Small-scale sampling with rotenone is used by fish researchers studying the biodiversity of marine fishes to collect cryptic, or hidden, fishes, which represent an important component of shoreline fish communities. Rotenone is the most effective tool available because only small quantities are necessary. It has only minor and transient environmental side-effects.

Rotenone is also used in powdered form to reduce parasitic mites on chickens and other fowl. In the United States and in Canada, all uses of rotenone except as a piscicide (fish killer) are being phased out.

Rotenone is sold as an organic pesticide dust for the garden. Unselective in action, it kills potato beetles, cucumber beetles, flea beetles, cabbage worms, raspberry bugs, and asparagus bugs, as well as most other arthropods. Rotenone rapidly bio-degrades under warm conditions so there is minimal harmful residue. A light dusting on the leaves of plants will control insects for several days. It is not known to be harmful to humans when used properly. However, a recent report from the National Institutes of Health finds statistically significant associations between use of either rotenone or paraquat with Parkinson's disease.

Use of Rotenone is controversial as it is not a selective piscicide (kills all species of fish), and in general is not able to kill 100% of the fish from a body of water, thus resulting in eventual return of the species targeted for killing.

Method of action
Rotenone works by interfering with the electron transport chain in mitochondria. To be specific, it inhibits the transfer of electrons from iron-sulfur centers in complex I to ubiquinone. This interferes with NADH during the creation of usable cellular energy (ATP). This is much like the action of amytal.

Presence in plants
Rotenone is produced by extraction from the roots and stems of several tropical and subtropical plant species, especially those belonging to the genus Lonchocarpus or Derris.

Some of the plants containing rotenone:
 * Hoary Pea or Goat’s Rue (Tephrosia virginiana) – North America
 * Jícama (Pachyrhizus erosus) – North America
 * Cubé Plant or Lancepod (Lonchocarpus utilis) – South America
 * The root extract is referred to as Cubé resin
 * Barbasco (Lonchocarpus urucu) – South America
 * The root extract is referred to as Cubé resin
 * Tuba Plant (Derris elliptica) – southeast Asia & southwest Pacific islands
 * The root extract is referred to as Derris or Derris root
 * Jewel Vine (Derris involuta) – southeast Asia & southwest Pacific islands
 * Among the Mizo tribes of India (Derris walchii/D. thyrsiflora) the tender root is eaten as vegetable
 * The root extract is referred to as Derris or Derris root
 * Duboisia – This shrub grows in Australia and bears white clusters of flowers and berry like fruit. The crushed plants were used by the Aboriginals for poisoning fish for food.
 * Verbascum thapsus
 * Cork-Bush (Mundulea sericea) – southern Africa
 * Florida fishpoison tree (Piscidia piscipula) – southern Florida, Caribbean

Toxicity
Rotenone is classified by the World Health Organization as moderately hazardous. It is mildly toxic to humans and other mammals, but extremely toxic to insects and aquatic life including fish. This higher toxicity in fish and insects is due to the fact that the lipophilic rotenone is easily taken up through the gills or trachea, but not as easily through the skin or through the gastrointestinal tract.

The lowest lethal dose for a child is 143 mg/kg. Human deaths from rotenone poisoning are rare because its irritating action causes vomiting. Deliberate ingestion of rotenone can be fatal.

The compound breaks down when exposed to sunlight and usually has a lifetime of six days in the environment. In water rotenone may last six months.

Rotenone is classified by the USDA National Organic Program as a nonsynthetic and was allowed to be used to grow organic produce until 2005, when it was added to the list of prohibited substances due to concerns about its safety. However, it has since been re-approved.

Parkinson's disease
In 2000, it was reported that injecting rotenone into rats causes the development of symptoms similar to those of Parkinson's disease (PD). Rotenone was continuously applied over a period of five weeks, mixed with DMSO and PEG to enhance tissue penetration, and injected into the jugular vein. The study does not directly suggest that rotenone exposure is responsible for PD in humans but is consistent with the belief that chronic exposure to environmental toxins increases the likelihood of the disease.

In addition, studies with primary cultures of rat neurons and microglia have shown that low doses of rotenone (below 10 nM) induce oxidative damage and death of dopaminergic neurons and it is these neurons in the substantia nigra that die in Parkinson's disease. Another study has also described toxic action of rotenone at low concentrations (5 nM) in dopaminergic neurons from acute rat brain slices. This toxicity was exacerbated by an additional cell stressor - elevated intracellular calcium concentration - adding support to the 'multiple hit hypothesis' of dopaminergic neuron death.

It had been known earlier that the neurotoxin MPTP causes PD-like symptoms (in humans and other primates, though not in rats) by interfering with Complex I in the electron transport chain and killing dopaminergic neurons in the substantia nigra. However, further studies involving MPTP have failed to show development of Lewy bodies, a key component to PD pathology. Therefore, the mechanism behind MPTP as it relates to Parkinson's Disease is not fully understood. Because of these developments, rotenone was investigated as a possible Parkinson-causing agent. Both MPTP and rotenone are lipophilic and can cross the blood-brain barrier.

In 2010, a study was published detailing the progression of Parkinson's-like symptoms in mice following chronic intragastric ingestion of low doses of rotenone. The concentrations in the central nervous system were below detectable limits, yet still induced PD pathology.

In 2011, a US National Institutes of Health study showed a link between rotenone use and Parkinson's disease in farm workers.