User:PhilipPalermo/sandbox/chem275-2

Methylene cyclopropyl acetic acid (MCPA) is found in lychee seeds and also a toxic metabolite in mammalian digestion after ingestion of hypoglycin. Methylene cyclopropyl acetic acid (MCPA) is a compound found in lychee (Litchi chinensis) seeds. It is also a metabolite in mammalian digestion after ingestion of hypoglycin, a rare and potentially toxic amino acid, chemically related to the common amino acid lysine. Hypoglycin is found in the unripe ackee fruit in Africa.

Dihydrosterculic acid is the major carbocyclic fatty acid in the seed oils of Litchi chinensis. It is a cyclopropene fatty acid; these have been found in many plants of the order Malvales (Sterculiaceae, Malvaceae, Bombaceae and Tiliaceae), in up to 60% of seed oil content, depending on the species but also in leaves, roots and shoots. They are accompanied by small amounts of their cyclopropanoid analogues, i.e. cyclopropyl acetic acid.

Pathophysiology of MCPA
MCPA forms non-metabolizable esters with coenzyme A (CoA) and carnitine, causing a decrease in their bioavailability and concentration in bodily tissue. Both of these cofactors are necessary for the β-oxidation of fatty acids, which in turn is vital for gluconeogenesis. MCPA also inhibits the dehydrogenation of a number of Acyl-CoA dehydrogenases. The inhibition of one in particular, butyryl CoA dehydrogenase (a short-chain acyl-CoA dehydrogenase), causes β-oxidation to cease before fully realized, which leads to a decrease in the production of NADH and Acetyl-CoA. The cascading effect continues, as this decrease in concentration further inhibits gluconeogenesis.



Symptoms
People afflicted with acute poisoning of MCPA will experience symptoms similar to that of Jamaican vomiting sickness. This involves abdominal pains after 2-6 hours followed by vomiting. Poisonings of children and those who are malnourished are at a greater risk of experiencing more severe symptoms such as seizures, comas, or death. When the protoxin Hypoglycin A was orally administered to rats, the subjects displayed signs of lacrimation, depression, and vomiting.

Formation of MCPA after ingestion of hypoglycin A and its toxicity
Hypoglycin A is a water soluble liver toxin, that upon ingestion, leads to hypoglycemia through the inhibition of gluconeogenesis, a metabolic pathway that leads to the generation of glucose from non-carbohydrate carbon sources (i.e. glucogenic amino acids, lactate, and glycerol). In addition, it also limits Acyl and carnitine cofactors, which are instrumental in the oxidation of large fatty acids. Hypoglycin A undergoes deamination, forming α-ketomethylene-cyclopropylpropionic acid (KMCPP), which then forms MCPA through oxidative decarboxylation. Hypoglycin A (and hypoglycin B) is found in the ackee fruit, the national fruit of Jamaica, and, like Litchi chinensis, is a member of the family Sapindaceae. The fruit is rich in fatty acids, zinc, protein, and vitamin A. In the fully ripened arils of the fruit, Hypoglycin A is present at only 0.1ppm, but in the unripened fruit it can exceed a concentration of 1000ppm. Ingestion of the unripened fruit containing such a concentrated dose causes what is known as Jamaican vomiting sickness. Depending on the severity of the case, the symptoms range from headache, rapid heart beat and sweating to dehydration and low blood pressure stemming from intense vomiting, to delirium and coma, and finally seizures and death. The symptoms stemming from lychee poisoning are near identical, both being caused by MCPA, with lychee seeds also containing methylenecyclopropyl glycine (MCPG), a homologue of Hypoglycin A.



Recent poisonings
In 2014, numerous children died in Bihar (the largest producer of lychees in India) after consuming lychees. The vast majority of the fatalities were undernourished children who ate unripened lychees, their preexisting low blood sugar detrimentally amplifying the effects.

In 2019 numerous children also lost their lives due to consumption of litchi fruits.