Grapefruit’s Antioxidant Ingredients Beneficial for Diabetes
Naringenin, an antioxidant derived from the bitter flavor of grapefruits and other citrus fruits, may cause the liver to break down fat while increasing insulin sensitivity, a process that naturally occurs during long periods of fasting.
A team of researchers from the Hebrew University of Jerusalem and Massachusetts General Hospital (MGH) report that naringenin activates a family of small proteins, called nuclear receptors, causing the liver to break down fatty acids. In fact, the compound seems to mimic the actions of other drugs, such as the lipid-lowering Fenofibrate and the anti-diabetic Rosiglitazone, offering the advantages of both. If the results of this study extend to human patients, this dietary supplement could become a staple in the treatment of hyperlipidemia, type-2 diabetes, and perhaps metabolic syndrome. The report appears in this week issue of the online journal PLoS ONE.
“It is a fascinating find,” said the researchers of the Hebrew University of Jerusalem “We show the mechanism by which naringenin increases two important pharmaceutical targets, PPARa and PPAR?, while blocking a third, LXRa. The results
are similar to those induced by long periods of fasting.”
The liver is the main organ responsible for the regulation of carbohydrate and lipid levels in the blood. Following a meal, the
blood is flushed with sugars, which activate LXRa, causing the liver to create fatty acids for long-term storage. During fasting,
the process is reversed; fatty acids are released by fat cells, activate PPARa in the liver, and are broken down to ketones.
A similar process, involving PPAR?, increases sensitivity to insulin.
“It is a process which is similar to the Atkins diet, without many of the side effects,” they added… “The liver behaves as if fasting,
breaking down fatty acids instead of carbohydrates.”
“Dual PPARa and PPAR? agonists, like naringenin, were long sought after by the pharmaceutical industry, but their development was plagued by safety concerns. Interestingly, naringenin is a dietary supplement with a clear safety record. Evidence suggests it might actually protect the liver from damage.”
Grapefruit’s bitter taste is caused the presence of the flavonoid naringin, which is broken down in the gut into naringenin. Earlier evidence has shown the compound has cholesterol lowering properties and may ameliorate some of the symptoms associated with diabetes. The researchers demonstrated that the compound activates PPARa and PPAR? by dramatically increasing the levels of a co-activator peptide of both, called PGC1a. At the same time, naringenin bound directly to LXRa, blocking its activation. These effects culminated with increased fatty acid oxidation and the inhibition of vLDL (‘bad cholesterol’) production.
The research was supported by grants from the National Institutes of Health (NIH) and European Research Council (ERC).
This work was supported by the National Institute of Diabetes and Digestive and Kidney Diseases (K01DK080241), a European Research Council starting grant (TMIHCV 242699), and the Harvard Clinical Nutrition Research Center (P30-DK040561). Resources were provided by the BioMEMS Resource Center (P41 EB-002503), Shriners Burns Hospital, and the Alexander Silberman Institute of Life Sciences.
“Transcriptional Regulation of Human and Rat Hepatic Lipid
Metabolism by the Grapefruit Flavonoid Naringenin”
Public Library of Science (2010, August 27). Grapefruit’s
bitter taste holds a sweet promise for diabetes therapy.