Backgrounder: Rotenone and Parkinson's Disease
Article URL: http://www.plant.uoguelph.ca/safefood/chem-haz/rotenone.htm
Two papers to be published in the Dec. 2000 issue of Nature Neuroscience and presented at a conference yesterday have raised questions about links between the so-called natural pesticide, rotenone, and Parkinson's disease.
The papers in question are:
Ranjita Betarbet, Todd B. Sherer, Gillian MacKenzie, Monica Garcia-Osuna,
Alexander V. Panov and J. Timothy Greenamyre. (2000) Chronic systemic pesticide
exposure reproduces features of Parkinson's disease. Nature Neuroscience,
Vol. 3, p 1301. http://www.nature.com/neuro/journal/v3/n12/pdf/nn1200_1301.pdf
Benoit I. Giasson and Virginia M.-Y. Lee. (2000) A new link between pesticides and Parkinson's disease, Nature Neuroscience, Vol. 3, p 1227 http://www.nature.com/neuro/journal/v3/n12/pdf/nn1200_1227.pdf
Rotenone is a so-called natural pesticide that has a variety of known and speculated biological effects. Although not widely used by organic growers, rotenone is found in a variety of commercial garden and animal-care products. This latest research underscores the need for specific end-product safety and environment risk assessments, irrespective of process or origin.
Rotenone has been marketed as an organic pesticide (home and commercial use), piscicide (fish toxin) and as an active ingredient for lice and tick control on pets in for several decades. It is often commercially formulated as dusts, powders, and sprays (less than 5% active ingredient) for use in gardens and on food crops. Trade names for products containing rotenone include Chem-Fish, Cuberol, Fish Tox, Sinid and Tox-R Noxfish, Noxfire, Rotacide, Foliafume, Nusyn-Noxfish, PB-Nox, Prentox, Chem-Fish, Rotenone Solution FK-11. It is also marketed as Curex Flea Duster, Derrin, Cenol Garden Dust, Chem-Mite, Cibe Extract and Green Cross Warble Powder. The compound may also be used in formulations with other pesticides such as carbaryl, lindane, thiram, piperonyl butoxide, pyrethrins and quassia.
Rotenone is derived from the root of various plants of the Derris or Lonchocarpus species from Southeast Asia, Central and South America, and can be found in at least 68 species of Legumes. It is available in at least 300 formulated products from a large number of manufacturers and is often made more efficacious by the addition of piperonyl butoxide (PBO), which is another botanical material. Rotenone is expensive compared with synthetic insecticides, but is moderately priced for a botanical. It is the most commonly mentioned of the botanicals in pre-synthetic literature, and is at least somewhat effective against a large number of insect pests. These include: pear psylla, strawberry leafroller, European corn borer, European apple sawfly, cherry fruit fly, apple maggot, cranberry fruitworm, raspberry fruitworm, pea aphid (which is similar to rosy apple aphid), European red mite and two-spotted spider mite, codling moth, plum curculio, Japanese beetle and tarnished plant bug. Rotenone is toxic to ladybird beetles and predatory mites, but non-toxic to syrphid flies that feed on aphids, and to honeybees. Rotenone is rapidly degraded by sunlight, lasting a week or less.
There is evidence of very early usage, as in 1649 it was reported to be used in South America to paralyze fish, which were then netted. In 1848 in Asia, rotenone was cited as used as an insecticide to control leaf eating caterpillars.
Mode of action: Rotenone is a cell respiratory enzyme inhibitor (it acts as a stomach poison in insects (Fields et al, 1991)). Its ultimate mode-of-action involves disruption of cellular metabolism, acting between NAD+ (a coenzyme involved in oxidation and reduction in metabolic pathways) and coenzyme Q (a respiratory enzyme responsible for carrying electrons in some electron transport chains), resulting in failure of the respiratory functions (Ware, 2000). Essentially, Rotenone inhibits a biochemical process at the cellular level making it impossible for the target organism to use oxygen in the release of energy needed for body processes and hence blocks conduction of nerve impulses
Rotenone is a "steroid shaped" molecule that kills insects and it has been used as a fish poison.
CAS Number: 83-79-4
Molecular Weight: 394.43
Water Solubility: 15 mg/L @ 100 C, slightly soluble in water
Solubility in Other Solvents: s. in acetone, carbon disulfide and chloroform; s.s in alcohols and carbon tetrachloride
Melting Point: 163 C
Vapor Pressure: <1 mPa @ 20 C
Partition Coefficient: Not Available
Formulations include crystalline preparations (approximately 95% pure), emulsified solutions (approximately 50% pure), and dusts (approximately 0.75 to 5% pure). This profile refers to the crystalline preparation unless otherwise noted. (SEE APPENDIX I)
Rotenone and Parkinson studies:
The link between Rotenoone has been suspected for several
years. In this regard some of the leading work is summarized below. When
rotenone has been injected into animals, tremors, vomiting, inco-ordination,
convulsions, and respiratory arrest have been observed. These effects have not
been reported in occupationally exposed humans (to-date).http://hsis.fedworld.gov/PPH/52841.htm
Postmortem studies and animal models strongly implicate mitochondrial impairment in the pathogenesis of Parkinson's disease. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), an inhibitor of the mitochondrial electron transfer chain, induces Parkinsonism in experimental animals and in humans after inadvertent ingestion. Chronic exposure to rotenone, a common pesticide and potent inhibitor of the electron transfer chain, also produces selective nigrostriatal degeneration and cytoplasmic inclusions reminiscent of Lewy bodies. Mitochondrial dysfunction has numerous consequences, including energetic failure, generation of reactive oxygen species, disregulation of calcium homeostasis and induction of apoptosis, each of which may be important in Parkinson's disease. Secondary consequences of mitochondrial dysfunction may include oxidative damage to cellular components and abnormal protein aggregation. Thus, there is a compelling need to elucidate the role of mitochondrial defects in Parkinson's disease, to define the mechanisms by which mitochondrial impairment kills neurons, and to identify therapeutic strategies to prevent the cell death that accompanies mitochondrial dysfunction.
Complex I dysfunction has been implicated in the pathogenesis of Parkinson's disease and in the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces a Parkinsonian syndrome in experimental animals and humans. Rotenone is an insecticide has been known for several years as a specific inhibitor of complex I.
In particular it has been known since 1997 that systemic administration of rotenone produces selective damage in the striatum and globus pallidus, but not in the substantia nigra. (Ferrante et al, Brain Res 1997 Apr. 4;753(1):157-62). In this specific study the scientists examined the pattern of central nervous system damage produced by i.v. systemic administration of rotenone in rats. Rotenone produced selective damage in the striatum and the globus pallidus, but the substantia nigra was spared. These results are consistent with prior reports suggesting that the selective vulnerability of the substantia nigra to MPTP involves both uptake by the dopamine transporter as well as complex I inhibition, and they show that rotenone produces a unique pattern of central nervous system damage.
In 1999, another study (Greenamyre et al, 1999) knowing that
the reduced activity of complex I of the electron-transport chain had been
implicated in the pathogenesis of both mitochondrial permeability transition
pore-induced Parkinsonism and idiopathic Parkinson's Disease, developed a novel
model of the disease. Using this model it was shown that chronic, systemic
infusion of rotenone, a complex-I inhibitor, selectively killed dopaminergic
terminals and caused retrograde degeneration of substantia nigra neurons over a period of months.
Again in late 1999, M. Friedrich wrote a piece entitled "Rotenone study aids Parkinson research"
(Friedrich, 1999 or http://www.ext.usu.edu/publica/agpubs/pestic/newslet/dec99.htm) in which he described an experimental model which appeared to reproduce the neurochemical, neuropathological, and behavioral features of the disease through chronically exposing laboratory rats to the pesticide rotenone. He further explained that the protocol for the model was simple, the goal being to use low dosages (of rotenone) for long periods of time. He wrote "male rats were given rotenone by continuous infusion via minipumps for anywhere from 2 days to 3 months. The animals became progressively slower in movements and reflexes and more rigid. The results of the investigation indicate that systemic administration of rotenone brings about selective retrograde degeneration and mimics the slowly progressive course of Parkinson Disease. Systemic rotenone infusion may provide an accurate model for the continuously progressive, chronic degeneration that characterizes the disease and may provide a novel and more accurate model to study neuroprotective drugs."
Earlier this year, knowing from a previous study, that rotenone, a complex I inhibitor, induced a rapid accumulation of DOPAL and DOPET in the medium of cultured PC12 cells an experiment was done that showed results indicating that accumulation of DOPAL was responsible for the potentiated rotenone-induced toxicity following combined inhibition of ALDH and ARs. Since complex I dysfunction is reported to be involved in the pathogenesis of Parkinson's disease, DOPAL potentiation of the deleterious effects of complex I inhibition may contribute to the specific vulnerability of dopaminergic neurons to injury. (Lamensdorf et al, 2000)
Regulatory Commercial Notes:
In the U.S., 10 rotenone products were withdrawn or canceled at the request of the registrants in 1999. The products can be sold for another year, and end-users can continue to use the pesticides according to the label (which has been voluntarily canceled for food uses). In1997, AgrEvo -- due to the high cost of re-registration -- deleted from their label the usage on domestic pets. (FR Vol. 61, 12-3-96).
Fields, P.G Arnason, J.T., Philogene B.J., Aucoin R.R, Morand P., Soucy-Breau C.(1991) Phototoxins as Insecticides and Natural Plant Defenses. Mem. ent. Soc. Can . IS9: 29-38
Friedrich M. (1999) Rotenone study aids Parkinson research, JAMA Dec 15;282(23):p2200
Greenamyre JT, MacKenzie G, Peng TI, Stephans SE (1999) Mitochondrial dysfunction in Parkinson's disease.
Biochem Soc Symp 1999;66:85-97
Lamensdorf I, Eisenhofer G, Harvey-White J, Nechustan A, Kirk K, Kopin IJ (2000) 3,4 Dihydroxyphenylacetaldehyde potentiates the toxic effects of metabolic stress in PC12 cells. Brain Res Jun 23;868(2):191-201
Ware G.W. (2000) AN INTRODUCTION TO INSECTICIDES (3rd Edition) In E. B. Radcliffe and W. D. Hutchison [eds.], Radcliffe's IPM World Textbook, URL: http://ipmworld.umn.edu,
Added Notes on General Toxicity:
When compared to most botanicals, rotenone is the most toxic to humans and other mammals. The acute oral LD50 is from 601500 mg/kg. In small doses it may be irritating or numbing to mucous membranes.
Acute toxicity: Local effects on the body include conjunctivitis, dermatitis, sore throat, and congestion. Ingestion produces effects ranging from mild irritation to vomiting. Inhalation of high doses can cause increased respiration followed by depression and convulsions. The compound can cause a mild rash in humans and is a strong eye irritant to rabbits. The oral LD50 of rotenone ranges from 132 to 1500 mg/kg in rats. The reported LD50 of rotenone in white mice is 350 mg/kg. A spray of 5% rotenone in water was fatal to a 100-pound pig when exposed to 250 cubic centimeters (mL) of the airborne mixture. In rats and dogs exposed to rotenone in dust form, the inhalation fatal dose was uniformly smaller than the oral fatal dose. Rotenone is believed to be moderately toxic to humans with an oral lethal dose estimated from 300 to 500 mg/kg. Human fatalities are rare, perhaps because rotenone is usually sold in low concentrations (1 to 5% formulation) and because its irritating action causes prompt vomiting. The mean particle size of the powder determines the inhalation toxicity. Rotenone may be more toxic when inhaled than when ingested, especially if the mean particle size is very small and particles can enter the deep regions of the lungs.
Chronic toxicity: Growth retardation and vomiting resulted from chronic exposures of rats and dogs. Rats fed diets containing rotenone at doses up to 2.5 mg/kg for 2 years developed no pathological changes that could be attributed to rotenone. Dogs fed doses of rotenone up to 50 mg/kg/day for 28 days experienced vomiting and excessive salivation, but no decreased weight gain. Dogs fed rotenone for six months at doses up to 10 mg/kg/day had reduced food consumption and therefore reduced weight gain. At the highest dose, blood chemistry was adversely affected, possibly due to gastointestinal lesions and chronic bleeding. Examination of 35 tissue types revealed only one type of lesion that might have been associated with exposure to the test chemical: lesions of the GI tract.
Reproductive effects: Pregnant rats fed 10 mg/kg/day on
days 6 through 15 of gestation experienced decreased fecundity, increased fetal
resorption, and lower birthweight. Very high maternal mortality was seen at this
dose. The 2.5 mg/kg/day dose produced no observable maternal toxicity or adverse
effect on fetal development. Fetotoxicity and failure of offspring are reported
in guinea pigs at doses of 4.5 and 9.0 mg/kg/day for an unspecified period. Thus
reproductive effects seem unlikely in humans at expected exposures. Teratogenic
effects: Pregnant rats fed 5 mg/kg/day produced a significant number of young
with skeletal deformities. The effects were not observed at the 10 mg/kg/day
level, so the data do not provide convincing evidence of teratogenicity because
the effects do not appear to be dose-related. Thus, the evidence for
teratogenicity is inconclusive. Mutagenic effects: The compound was determined
to be nonmutagenic to bacteria and yeast and in treated mice and rats. However,
it was shown to
cause mutations in some cultured mouse cells. In summary, the data regarding the mutagenicity of rotenone are inclusive.
Carcinogenic effects: Studies in rats and hamsters have provided limited evidence for carcinogenic activity of rotenone. No evidence of carcinogenic activity was seen in hamsters at oral doses as high as 120 mg/kg/day for a period of 18 months. Studies of two species of rats evidenced no statistically significant cancerous changes in any organ site, including mammary glands, at oral doses of up to 75 mg/kg/day for 18 months. Significant increases in mammary tumors have been reported in albino rats with intraperitoneal doses of 1.7 mg/kg/day for 42 days, and in Wistar rats at approximately 1.5 mg/kg/day orally for 8 to 12 months. In the latter study, however, higher dose rates (3.75 and 7.5 mg/kg/day) over the same period did not produce increased tumors. Thus, the evidence for carcinogenicity is inconclusive.
Organ toxicity: Chronic exposure may produce changes in the liver and kidneys as indicated by the animal studies cited above.
Fate in humans and animals: Absorption in the stomach and intestines is relatively slow and incomplete, although fats and oils promote its uptake. The liver breaks down the compound fairly effectively . Animal studies indicate that possible metabolites are carbon dioxide and a more water-soluble compound that can be excreted in the urine. Studies indicated that approximately 20% of the applied oral dose (and probably most of the absorbed dose) may be eliminated from animal systems within 24 hours. Related symptomatic occupational exposures in humans involving flea-control dips were identified. Responsible active ingredients were rotenone/pyrethrin (five cases); rotenone, (one case ). Eight workers developed moderate health effects that required some form of treatment, and 18 developed minor health effects (minimally bothersome symptoms that resolved rapidly). Among the workers with moderate health effects two were cased by rotenone/pyrethrin
Effects on birds: Rotenone is slightly toxic to wildfowl. The LD50 values for rotenone in mallards and pheasants are (greater than) 2000 mg/kg and 1680 mg/kg respectively. A dietary LC50 of 4500 to 7000 ppm is reported in Japanese quail.
Effects on aquatic organisms: Since rotenone is used as a fish toxin (piscicide), it follows that it is very highly toxic to fish. Reported 96-hour LC50s were 0.031 mg/L in rainbow trout, 0.0026 mg/L in channel catfish, and 0.023 mg/L in bluegill for the 44% pure formulation. Aquatic invertebrates have a wide range of sensitivity to rotenone with 48-hour EC50 values ranging from 0.002 to 100 mg/L. The compound is not expected to accumulate appreciably in aquatic organisms. The bioconcentration factor for rotenone in the sunfish is 181 times the ambient water concentration. In addition the highly toxic nature of this substance to aquatic organisms means that there is little survival of the organisms that accumulate the compound.
Effects on other organisms: The compound is nontoxic to bees. However, it is toxic to bees when used in combination with pyrethrum.
Breakdown in soil and groundwater: Rotenone is rapidly broken down in soil and in water. The half-life in both of these environments is between 1 and 3 days. It does not readily leach from soil, and it is not expected to be a groundwater pollutant. Rotenone breaks down readily by exposure to sunlight. Nearly all of the toxicity of the compound is lost in 5 to 6 days of spring sunlight or 2 to 3 days of summer sunlight. Breakdown in water: Rotenone is rapidly broken down in soil and in water. The half-life in both of these environments is between 1 and 3 days. It does not readily leach from soil, and it is not expected to be a groundwater pollutant. Rotenone breaks down readily by exposure to sunlight. Nearly all of the toxicity of the compound is lost in 5 to 6 days of spring sunlight or 2 to 3 days of summer sunlight.
Breakdown in vegetation: Rotenone is a highly active but
short-livedphotosensitizer. This means that an organism consuming the compound
develops a strong sensitivity to the sun for a short time. A number of
photodecomposition products are formed when bean leaves are exposed to light. It
is also sensitive to heat, with much of the rotenone quickly lost at high