Lathyrus

What is the relationship between Copper and the Sweet Pea?

The sweet pea is a member of the Genus, Lathyrus. The plant known as Lathyrus sativus (grass pea) if ingested in sufficient quantity causes a condition know as lathyrism. This condition is has the same signs and symptoms as copper deficiency. The toxin produced by several members of the genus Lathyrus is 3 β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP).

Biology

Scientific Classification: Kingdom - Plantae, Division - Magnoliophyta, Class - Magnoliopsida, Order - Fabales, Family - Fabaceae, Subfamily - Faboideae, Tribe - Vicieae, Genus - Lathyrus

The genus Lathyrus is known as vetchling or wild pea. There are over 100 species of Lathyrus with varying degrees of toxicity. The most common species known to home gardeners is Lathyrus odoratus, the common sweet pea. Much of the popularity of this plant can be attributed to Harry Eckford, gardener for the Earl of Radnor in the late 19th century. He developed over 100 cultivars of the plant before is death in 1906. Today a large number of cultivars are available from seed houses that specialize in their production including Bodger Seeds Ltd. Two of the more common species associated with worldwide poisonings are Lathyrus sativus and Lathyrus cicera. Outwardly, some of the vetches, (genus Vicia) may resemble the members of the genus Lathyrus. With the latter, a good diagnostic feature would be to look at the style which will be flattened with hairs on one side while with vetch flowers, the style will be needle-like but with a ring of hairs about 1 mm wide all around the tip.

Poisonings

Worldwide: Human poisonings are a result of ingestions of large amounts of the Lathyrus sativus or Lathyrus cicera plants in either the raw form or as bread made from flour ground from the seeds of the plants. Both of these species are cultivated for food especially in India and Ethiopia. Pulses by definition are annual leguminous crops yielding from one to twelve grains or seeds of variable size, shape and color within a pod. Pulses are used for food and animal feed. The constituents within pulses may change depending on economics and growing conditions. Lathyrus sativus know as grass pea is an important crop in areas where other food sources are not available because it can survive at low nutrient levels and grows on various different types of soil, including semi-arid regions with low fertility. The plant lives in symbiosis with Rhizobium (nitrogen-fixing bacteria in the root nodules) and in this way adds nitrogen to the soil. In India the plant grows up to 1300 metres above sea level. In Ethiopia it can be cultivated up to 3000 metres above sea level. The yield varies from 900 to 1500 kg per hectare. The plant exhibits important morphologic variations. Osmotic stress increases the concentration of poison. Because of these reasons poisonings with occur generally during times of drought and when cereals are not available. Consequently, outbreaks of lathyrism have occurred repeatedly throughout history and, today, tens of thousands affected during recent epidemics in Ethiopia, India, and Bangladesh, are permanently crippled. In parts of Asia and Africa this disease may cripple as many a 2.5 per cent of the population. One such an epidemic occurred in the 1970's, which left one per cent of the people of the vast Gondar region of Ethiopia permanently crippled. Families, even whole communities, are often deprived of their breadwinners, and unable to continue the struggle against starvation.

Some researchers for the UN have concluded that suppling at least one third of the diet with other cereals substantially lessens the chances of lathyrism.

United States: Human poisonings in the US are rare but animal poisonings are the most common form of poisonings where feed has been tainted with wild peas. Animals, chiefly horses, develop paralysis of their hind legs if they are given Lathyrus regularly as fodder. Interestingly it is now being actively marketed as AC Greenfix, a variety of chickling vetch (Lathyrus sativus L.) also known as a grass pea or grassy peavine as a soil enhancer. AC Greenfix is marketed as "a new annual legume in the United States, developed as a fertilizer alternative to supply green manure Nitrogen for both organic and conventional growers." Claims are that in only 8-10 weeks of growth an average of 80-100 lbs N/acre can be produced.

Chemistry

Lathyrus sativus contains β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), which is thought to cause neuronal damage through excitation of the AMPA-activated receptors although some researchers believe the mechanism is more complex.  Beta-amino-propionitrile (BAPN) found in lathyrus odoratus (our more common garden sweet pea plant) is thought to be responsible for osteolathyrism, which in humans is quite poorly documented. Patients develop bone pain and disfigurement of bones, including vertebrae and pelvis. This is to be distinguished from Kashin-Beck's disease which is related to selenium deficiency.

Clinical Signs and Symptoms

The clinical disease lathyrism can be divided into neurolathyrism and osteolathyrism. Neurolathyrism is a neurodegenerative and irreversible spastic paraparesis that can be crippling. The syndrome is characterized by muscular rigidity, weakness, and paralysis of the leg muscles. In severe cases victims may be reduce to crawling. Young men between the ages of 20 and 30 are primarily affected. As early as 400 BC the Indian physician Charak associated eating triputa (L. sativus) with the occurrence of a neurological syndrome.

The related plant Lathyrus odoratus contains the toxic beta-amino-propionitrile (BAPN). Long-term consumption may lead to skeletal changes. The substance BAPN is an irreversible inhibitor of lysyl oxidase, an enzyme necessary for the covalent cross-linking of tropocollagen molecules during the maturation of mature collagen. A metabolic precursor of BAPN is found in the vegetative parts and unripe seeds of L. sativus. It is probably co-responsible for the osteolathyrism which is sometimes seen after consumption of L. sativus. Interestingly copper deficiency produces a similar syndrome since the lysyl oxidase is a copper containing molecule.

Similar toxin, beta-methylamino-L-alanine, is suspected in causing lytico-bodig, a severe neurological disease endemic in Guam, one of the Mariana Islands in the Pacific Ocean.

References

1. Lambein, F., Y. Kuo, K. Kusama-Eguchi, F. Ikegami, "3-N-oxalyl-L-2,3-diaminopropanoic acid, a multifunctional plant metabolite of toxic reputation" Arikovoc IX:45-52 2007.
2. Yan, ZY, PS Spencer, ZX Li, YF Wang, CY Wang, FM Li, "Lathyrus sativus (gass pea) and its neurotoxin ODAP" Phytochemistry 67(2):107-21 2006.
3. Rao SL. Prevention of neurolathyrism during drought. Lancet 2004;363:657.
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4. Clarke, JC, "Dictionary of Practical Materia Medica"
5. Fikre A, Lambein F, Gheysen G. A life-saving food plant producing more neurotoxin under environmental stress. Commun Agric Appl Biol Sci 2006;71:79-82.
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6. Getahun H, Lambein F, Vanhoorne M, Van der SP. Neurolathyrism risk depends on type of grass pea preparation and on mixing with cereals and antioxidants. Trop Med Int Health 2005;10:169-78.
   Ref ID: PM:15679560
7. Kuo YH, Defoort B, Getahun H, Tekle HR, Lambein F. Comparison of urinary amino acids and trace elements (copper, zinc and manganese) of recent neurolathyrism patients and healthy controls from Ethiopia. Clin Biochem 2007;40:397-402.
   Ref ID: PM:17291478