High levels of "bad" HDL have been shown to be detrimental; they can promote heart disease.
Back in 2003 or so, I began reading that HDL was not always good, that it could sometimes promote inflammation.
Here's a study:
HDL And The Inflammatory Response Induced By LDL-derived Oxidized Phospholipids, Arteriosclerosis, Thrombosis, and Vascular Biology, 2001
"It is proposed that LDL-derived oxidized phospholipids and HDL may be part of a system of nonspecific innate immunity and that the detection of proinflammatory HDL may be a useful marker of susceptibility to atherosclerosis."It seems HDL that promotes inflammation is protective and immune-related, in that inflammation is an immune response. But if your inflammation is chronic, as it is with diabetes, heart disease, arthritis, then your pro-inflammatory HDL may also be chronic. And that might not be good.
Move up to 2008, and some types of HDL were being revealed as, not just markers, but able to promote the development of atherosclerosis, and so heart disease:
HDL: Bridging Past And Present With A Look At The Future, FASEB, December 2008
"All of these atheroprotective functions are lost in the post-translational dependent dysfunctional plasma HDLs of subjects with systemic inflammation, coronary heart disease, diabetes, and chronic renal disease. The emerging notion that particle quality has more predictive power than quantity has stimulated further exploration of the HDL proteome, already revealing unsuspected pro- or antiatherogenic proteins/peptides associated with HDL."First author of this study, Angelo Scanu MD:
"For many years, HDL has been viewed as good cholesterol and has generated a false perception that the more HDL in the blood, the better. ... It is now apparent that subjects with high HDL are not necessarily protected from heart problems and should ask their doctor to find out whether their HDL is good or bad."Coincidentally, as I was writing this today I saw this study in The Lancet:
- Some 'Good Cholesterol' Is Actually Bad, Study Shows, ScienceDaily, December, 2008
Plasma HDL Cholesterol And Risk Of Myocardial Infarction: A Mendelian Randomisation Study, The Lancet, May 17, 2012
"Some genetic mechanisms that raise plasma HDL cholesterol do not seem to lower risk of myocardial infarction. These data challenge the concept that raising of plasma HDL cholesterol will uniformly translate into reductions in risk of myocardial infarction."Senior author Sekar Kathiresan:
"It's been assumed that if a patient, or group of patients, did something to cause their HDL levels to go up, then you can safely assume that their risk of heart attack will go down. ... This work fundamentally questions that."I think there is probably more to learn about HDL, and whether therapies to boost it are warranted.
- Not All 'Good Cholesterol' Is 'Good': Raising HDL Not A Sure Route To Countering Heart Disease, ScienceDaily, May 16, 2012
I like how a chameleon changes depending on its environment. Like the chameleon HDL.
Update, May 17, later in the day ... Boy, HDL is a hot topic right now. Here's another study I saw today:
Apolipoprotein C-III As A Potential Modulator Of The Association Between HDL-Cholesterol And Incident Coronary Heart Disease, Journal of the American Heart Association, April 2012.
It just identifies a protein on the HDL membrane, apoC-III, that is pro-inflammatory.
Unfortunately, these studies will be used as a foundation for designing drugs to lower levels of the offending HDL particle. When all along the pro-inflammatory HDL is performing a needed function! Inflammation keeps us alive. It is a complex series of events that attempt to remove harmful stimuli and initiate healing. The problem occurs when pro-inflammatory HDL (or other pro-inflammatory molecules) stick around too long. That happens when we are in a state of chronic disease ... like diabetes, arthritis, kidney disease. How to avoid chronic disease? Don't smoke, manage weight, eat healthfully, stay physically active, get enough sleep, manage stress, laugh and love. Boring but effective.