Mead acid

Mead acid is an omega-9 fatty acid, first characterized by James F. Mead.^[1] Like some other omega-9 polyunsaturated fatty acids animals can make Mead acid de novo. Its elevated presence in the blood is an indication of essential fatty acid deficiency. Mead acid is found in large quantities in cartilage.

Chemistry

Chemically, Mead acid is a carboxylic acid with a 20-carbon chain and three methylene-interrupted cis double bonds. The first double bond is located at the ninth carbon from the omega end. In physiological literature, it is given the name 20:3(n-9). See Fatty Acid#Nomenclature for an explanation of the naming system. In the presence of lipoxygenase, cytochrome p450 or cyclooxygenase Mead acid can form various hydroxy (HETE) and hydoperoxy (HpETE) products .^[2]

Physiology

Two fatty acids, linoleic acid and alpha-linolenic acid, are considered essential in humans and other mammals. Both are 18 carbon fatty acids unlike mead acid, which has 20 carbons. Linoleic is an ω-6 fatty acid whereas linolenic is ω-3 and mead is ω-9.

Under severe conditions of essential fatty acid deprivation, mammals will elongate and desaturate oleic acid to make mead acid, (20:3, n−9).^[3] This also occurs to a lesser extent in vegetarians and semi-vegetarians.^[4][5]

One study examined patients with intestinal fat malabsorption and suspected EFA deficiency. They were found to have blood-levels of Mead acid 1263% higher than reference subjects.^[6]

Role in inflammation

Prostaglandin H synthases (also known as COX) are enzymes known to play a large role in inflammatory processes through oxidation of unsaturated fatty acids. Most notably, the formation of Prostaglandin H2 from arachidonic acid which is very similar in structure to mead acid. When physiological levels of arachidonic acid are low, other unsaturated fatty acids including mead and linoleic acid are oxidized by COX.

Mead acid is also converted to Leukotrienes C3 and D3.^[7]

See also

• Polyunsaturated fatty acid – lists of ω-3, -6 and -9 fatty acids; some others.
• Eicosanoid
• Prostaglandin

References

1. ^ Siegel, George J.; Albers, R. Wayne (2006). Basic neurochemistry: molecular, cellular, and medical aspects, Volume 1 (7th ed.). p. 40. http://books.google.com/books?id=Af0IyHtGCMUC&pg=PA40&dq=James+Mead+mead+acid&hl=en&ei=YCLTToWCEoTrtgf2n-WDCQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDwQ6AEwAg#v=onepage&q=James%20Mead%20mead%20acid&f=false. "One of these is 20:3ω9, termed ‘Mead acid’ after its discovery by James Mead...." 
2. ^ Cyberlipid Center. "PROSTAGLANDINS AND RELATED COMPOUNDS". http://www.cyberlipid.org/prost1/pros0002.htm. Retrieved 2007-10-24. 
3. ^ Lipomics. "Mead acid". http://www.lipomics.com/resources/fatty_acids/20_3n9.htm. Retrieved February 14, 2006. 
4. ^ Phinney, SD, RS Odin, SB Johnson and RT Holman (1990). "Reduced arachidonate in serum phospholipids and cholesteryl esters associated with vegetarian diets in humans". http://intl.ajcn.org/cgi/content/abstract/51/3/385. Retrieved February 11, 2006. 
5. ^ Gerard Hornstra (September 2007). "Essential Polyunsaturated Fatty Acids and Early Human Development" (– ^{Scholar search}). Fats of Life Newsletter. Archived from the original on 2008-06-07. http://web.archive.org/web/20080607194856/http://www.fatsoflife.com/pufa/article.asp?nid=1&edition=this&id=484. Retrieved 2007-10-23. 
6. ^ EN Siguel, KM Chee, JX Gong and EJ Schaefer (October 1, 1987). "Criteria for essential fatty acid deficiency in plasma as assessed by capillary column gas-liquid chromatography". Clinical Chemistry 33 (10): 1869–1873. PMID 3665042. http://www.clinchem.org/cgi/reprint/33/10/1869. Retrieved 2007-10-24. 
7. ^ [1], Conversion of 5,8,11-Eicosatrienoic Acidt o Leukotrienes C3 and D3 Journal of Biological Chemistry (1981) vol. 256, p. 2275