A new study has found that a polymethoxylated flavonoid called nobiletin found in orange peels reduces very low density cholesterol (VLDL and LDL) levels. The researchers, from the Robarts Research Institute of London and Ontario, found that the secretion of LDL and VLDL by human liver cells was significantly inhibited by nobiletin.
They also found that the polymethoxylated flavonoid, with a chemical structure of 3’4’5,6,7,8-hexamethoxyflavone, reduced VLDL levels found in insulin resistance and atherosclerosis.
LDL and VLDL are implicated in cardiovascular disease, because they promote something called lipid peroxidation, which damages the arteries.
This confirms the research by Agricultural Research Service (ARS) scientists who found that 3’4’3,5,6,7,8-heptamethoxyflavone (HMF), another citrus polymethoxylated flavone found in orange peels, inhibited a precursory protein called apoprotein B found within low-density lipoprotein (LDL).
John Manthey, a chemist for the ARS from the USDA’s Winter Haven lab, is a leading citrus peel researcher. He has been researching the orange oils within orange peels for several years.
Citrus peels contain several polymethoxylated flavonoids (PMFs). Nobiletin is a O-methylated flavone. It renders a hydroxyl group that mediates a reaction called O-methylation. Methylation allows for the donation of methyl groups, which provide radical-neutralizing effects, as well as the inhibition of lipid peroxide-friendly LDL cholesterol apoprotein B. Other O-methylated flavones include tangeritin (first found in tangerine oil), wogonin (found in the herb baikal scullcap), and sinensetin, found in the Java tea herb Orthosiphon stamineus.
Citrus peels can contain as much as 70% oil. The oil contains a number of other healthful components including limonene and linalool. Limonene is monoterpene known for its antimicrobial and radical-scavenging abilities.
Most applications of citrus remove the peel and toss it out. In a good year, over 700,000 tons of peel solids are discarded or sold for feed by Florida citrus growers.
Mulvihill EE, Assini JM, Lee JK, Allister EM, Sutherland BG, Koppes JB, Sawyez CG, Edwards JY, Telford DE, Charbonneau A, St-Pierre P, Marette A, Huff MW. Nobiletin attenuates VLDL overproduction, dyslipidemia, and atherosclerosis in mice with diet-induced insulin resistance. Diabetes. 2011 May;60(5):1446-57.
Manthey JA, Bendele P. Anti-inflammatory activity of an orange peel polymethoxylated flavone, 3′,4′,3,5,6,7,8-heptamethoxyflavone, in the rat carrageenan/paw edema and mouse lipopolysaccharide-challenge assays. J Agric Food Chem. 2008 Oct 22;56(20):9399-403.
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