Guayule
Scientific Name(s): Parthenium argentatum A. Gray Family: Asteraceae (daisies)
Common Name(s): Guayule (pronounced “why-oo-lay”)
Clinical Overview
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Uses of Guayule
Guayale is used in the production of rubber. Its use as a fuel is being investigated.
Guayule Dosing
There are no recent clinical studies of guayule to provide a basis for dosage recommendations.
Contraindications
Contraindications have not yet been identified.
Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.
Guayule Interactions
None well documented.
Guayule Adverse Reactions
Contact with guayule can cause strong erythema. The potency of its allergen (guayulin A) has been equated to that of poison ivy.
Toxicology
Research reveals little or no information regarding toxicology with the use of guayule.
Botany
Guayule is a common shrub native to the Chihuahuan desert of northern Mexico and the adjacent Big Bend region of Texas. The plant can be readily grown in the arid regions of the southwestern US.
History
Guayule had a history as a domestic source of rubber. In the early 1900s, guayule accounted for almost 50% of all the natural rubber consumed in the US and 10% of consumption worldwide. 1 A variety of factors, including the Great Depression and the Mexican Revolution, combined to destroy the industry. The US mounted an intensive research program under the Emergency Rubber Project to identify a domestic source of natural rubber as supplies from Southeast Asia dwindled because of World War II. The work led to the re-evaluation of guayule. The project was ended after the war, following the development of synthetic rubber and the return of cheap Hevea rubber. In 1977, interest in guayule was renewed when the National Research Council noted that the increasing demand for imported natural rubber could result in domestic shortages. The escalating price and variable supply of foreign petroleum, along with the great advantage that guayule can be harvested mechanically, made guayule rubber production attractive from both economic and national security standpoints. 2
Chemistry
The physical and chemical properties of guayule rubber, which is composed of polymeric cisisoprenoid units, are essentially identical to those of Hevea rubber. Guayule rubber is found in parenchymatous cells of the stem and root tissue as a latex. 3 Studies of over 75 native guayule plants have identified at least three prominent plant forms, termed Groups I, II and III, which differ in their leaf shape, trichome morphology and rubber content. 4 Rubber levels range from about 17% in Group I to 6% in Group III. Guayule grows in close association with a related desert plant, P. incanum (mariola). Morphologic and biochemical data indicate the presence of mariola genes in Group II and III guayule, resulting in morphologic changes and decreased rubber content. Group II plants are the most common, and the development of higher rubber-bearing plants should be guided by genetic assessments of guayule stock. Cross-breeding methods have been used to develop improved-yield varieties, and the application of bioinducers can stimulate the production of latex, with a resultant 2- to 6-fold increase in the amount of rubber. 5
The processing of guayule plants leaves behind several by-products that may add to the economic value of guayule rubber production. The process yields large amounts of woody fiber (bagasse), which may serve as a fuel or in the manufacture of paper. To obtain a high-quality rubber, it is necessary to deresinate the crude product. The resin fraction may equal the rubber content. This resin has too high a boiling point to be used as gasoline, but it might be converted to an automotive diesel fuel. 6 Acetone extracts of woody guayule tissue have as their major components sesquiterpene esters composing 10% to 15% of the total, triterpenoids accounting for 27% and fatty acid triglycerides accounting for 7% to 19%. The sesquiterpenes are in part artifacts of heat processing. The major triterpene compounds are C-30 argentatins. Organic acid content varies, but the major aromatic acid is cinnamic acid and the major fatty acid is linoleic acid.
Aqueous extraction yields polysaccharides accounting for 63% of the extract. These are not a good source of fermentable sugars. 7 Guayule had been seen as a potential economic boon to poor native American Indians. Similar to proposals for jojoba, guayule represents an easily grown, economically sound, renewable resource that may be cultivated in economically depressed areas of the southwest.
In recent studies, researchers have found that guayule plants accumulate large amounts of rubber inside the stem tissue parenchyma cells. The rubber particles develop packed within discrete organelles. These are made up mainly of a lipophilic, cis-polyisoprene core, small amounts of lipids and various proteins (most abundant is the M[r]53,000 rubber particle proteins [RPP]). Based on cDNA cloning and spectroscopic analyses, RPP has been placed in the CYP74 family of P450s and further established it as the first P450 localized in rubber particles as well as the first eukaryotic P450 to be identified outside endoplasmic reticulums, mitochondrion or plastids. One researcher has described the sesquiterpenes, guayulins C and D in guayule.
Dosage
There are no recent clinical studies of guayule to provide a basis for dosage recommendations.
Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.
Interactions
None well documented.
Adverse Reactions
Guayule contains a potent contact allergen, long known to pose a hazard to guayule farmers and processing-plant employees. 10 More recent investigations of acetone extracts resulted in the isolation of guayulin-A, a potent elicitor of contact dermatitis. This sesquiterpene cinnamic acid ester induces strong erythema in animals within 24 hours of application in concentrations as low as 0.003% (0.5 nM), which persists for almost 2 weeks. The compound is present in stems and leaves at levels of 0.05% to 0.3%. Guayule processing plants are now designed to minimize worker contact with resins. The allergenicity of guayulin-A may cause unexpected difficulties in the cross-breeding of Parthenium species to develop high-yield strains. Guayule readily undergoes hybridization with mariola and P. tomentosum var. stramonium, close desert relatives. These species contain sesquiterpene lactones that are cytotoxic and produce skin reactions in persons sensitized to other species of Asteraceae. Preliminary investigations of crosses of P. tomentosum with guayule indicate the presence of guayulin-A and stramonin-B (a cytotoxic pseudoguaianolide) in the first generation of experimental hybrids. 11
Toxicology
Research reveals little or no information regarding toxicology with the use of guayule.
Bibliography
1. Maugh TH. Science 1977;196:1189.2. McIntyre D. Rubber World 1979;(Sep):50.
3. Loyd FE. Plant Physiol 1932;7:31.
4. Mehta IJ, et al. Am J Botany 1979;66:796.
5. Yokoyama H, et al. Science 1977;197:1076–7.
6. Lipinsky ES. Science 1978;199:644–5.
7. Schloman WW, et al. J Agr Food Chem 1983;31:873.
8. Pan Z. J Biol Chem 1995;270(15):8487–94.
9. Martinez M, et al. J Nat Prod 1986;49(6):1102–3.
10. Smith LM, Hughes RP. Arch Derm & Syph 1938;38:778.
11. Rodriguez E, et al. Science 1981;211:1444–5.
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