The so called bad cholesterol (LDL) inhibits the breakdown of fat in cells of peripheral deposits, according to a study from the Swedish medical university Karolinska Institutet. [
LDL cholesterol is known to be raised by trans fats (hydrogenated oils) in the diet. “Peripheral” fat deposits are those in the arms, legs, head, and buttocks.]
The discovery reveals a novel function of LDL as a regulator of fat turnover besides its well-established detrimental effects in promoting atherosclerosis [plaque buildup on inside of arteries]. The study, which is a collaboration of two research groups at Karolinska Institutet, is published in the open-access journal PLoS ONE.* It shows that LDL cholesterol slows the rate of fat breakdown (i.e., lipolysis) in adipocytes, the peripheral cells responsible for fat storage. Previously, it has been known that release of free fatty acid from the peripheral fat to the blood stream increases the synthesis of LDL precursors in the liver.
"The results of our study provide evidence of a reciprocal link between the liver and peripheral fat regulating fat turnover," says study-initiator Dr. Johan Bjorkegren. The discovery also opens up for new theories for the well-established association between blood lipids and the metabolic syndrome. [A group of risk factors, including high blood pressure, obesity, high cholesterol, & insulin resistance, that if present increase risk of diabetes and cardiovascular disease.]
"If proven of general physiological importance, therapies lowering LDL, as for instance Statins, may also affect the turnover of peripheral fat," continues Dr Bjorkegren.
The study and has been performed on cell cultures and tissues from humans as well as mouse models with different levels of LDL. The inhibitory effect was also shown to be dependent on LDL receptors on the surface of the fat cells.
"The exact intracellular mechanism for how the binding of LDL to the surface of the fat cells inhibits the breakdown of intracellular fat remains to be revealed," says project leader Dr. Josefin Skogsberg.
* The full text of this publication is available free at PubMedCentral. See: “ApoB100-LDL Acts as a Metabolic Signal from Liver to Peripheral Fat Causing Inhibition of Lipolysis in Adipocytes," PLoS ONE, Nov 20, 2008, by Johan Björkegren [E-mail: firstname.lastname@example.org], Josefin Skogsberg [E-mail: email@example.com], et al.