High density lipoprotein
You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.
| Cardiology Network |
 Discuss High density lipoprotein further in the WikiDoc Cardiology Network |
| Adult Congenital |
|---|
| Biomarkers |
| Cardiac Rehabilitation |
| Congestive Heart Failure |
| CT Angiography |
| Echocardiography |
| Electrophysiology |
| Cardiology General |
| Genetics |
| Health Economics |
| Hypertension |
| Interventional Cardiology |
| MRI |
| Nuclear Cardiology |
| Peripheral Arterial Disease |
| Prevention |
| Public Policy |
| Pulmonary Embolism |
| Stable Angina |
| Valvular Heart Disease |
| Vascular Medicine |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-525-6884
Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [2] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.
High-density lipoproteins (HDL) form a class of lipoproteins, varying somewhat in their size (8–11 nm in diameter), that carry cholesterol from the body's tissues to the liver. About thirty percent of blood cholesterol is carried by HDL.[1]
It is hypothesised that HDL can remove cholesterol from atheroma within arteries and transport it back to the liver for excretion or re-utilization—which is the main reason why HDL-bound cholesterol is sometimes called "good cholesterol", or HDL-C. A high level of HDL-C seems to protect against cardiovascular diseases, and low HDL cholesterol levels (less than 40 mg/dL) increase the risk for heart disease.[1] When measuring cholesterol, any contained in HDL particles is considered as protection to the body's cardiovascular health, in contrast to "bad" LDL cholesterol.
Structure and function
HDL are the smallest of the lipoproteins. They are the densest because they contain the highest proportion of protein. They contain the A class of apolipoproteins.[1] The liver synthesizes these lipoproteins as complexes of apolipoproteins and phospholipid, which resemble cholesterol-free flattened spherical lipoprotein particles. They are capable of picking up cholesterol, carried internally, from cells they interact with. A plasma enzyme called lecithin-cholesterol acyltransferase (LCAT) converts the free cholesterol into cholesteryl ester (a more hydrophobic form of cholesterol) which is then sequestered into the core of the lipoprotein particle eventually making the newly synthesized HDL spherical. They increase in size as they circulate through the bloodstream and incorporate more cholesterol molecules into their structure. Thus it is the concentration of large HDL particles which more accurately reflects protective action, as opposed to the concentration of total HDL particles.[1] This ratio of large HDL to total HDL particles varies widely and is only measured by more sophisticated lipoprotein assays using either electrophoresis (the original method developed in the 1970s), or newer NMR spectroscopy, NMR spectroscopy methods, developed in the 1990s.
HDL particles are not inherently protective. It is only the HDL particles which become the largest (actually picking up and carrying cholesterol) which are protective. There is no reliable relationship between total HDL and large HDL, and more sophisticated analyses which actually measure large HDL, not just total, correlate much better with clinical outcomes.
In the stress response, serum amyloid A, which is one of the acute phase proteins and an apolipoprotein, is under the stimulation of cytokines (IL-1, IL-6) and cortisol produced in the adrenal cortex and carried to the damaged tissue incorporated into HDL particles. At the inflammation site, it attracts and activates leukocytes. In chronic inflammations, its deposition in the tissues manifests itself as amyloidosis.
Men tend to have noticeably lower HDL levels, with smaller size and lower cholesterol content, than women. Men also have an increased incidence of atherosclerotic heart disease.
Historically, beginning in the late 1970's cholesterol and lipid assays were promoted to estimate total HDL-cholesterol because such tests used to be far less expensive, by about 50 fold, than measured lipoprotein particle concentrations and subclass analysis. Over time, with continued research, decreasing costs, greater availability and wider acceptance of other "lipoprotein subclass analysis" assay methods, including NMR spectroscopy, human studies have continued to show a stronger correlation between human clinically obvious cardiovascular events and quantitatively measured large HDL-particle concentrations.
Epidemiology
Epidemiological studies have shown that high concentrations of HDL (over 60 mg/dL) have protective value against cardiovascular diseases such as ischemic stroke and myocardial infarction. Low concentrations of HDL (below 40 mg/dL for men, below 50 mg/dL for women) are a positive risk factor for these atherosclerotic diseases.
Data from the landmark Framingham Heart Study showed that for a given level of LDL, the risk of heart disease increases 10-fold as the HDL varies from high to low. Conversely, for a fixed level of HDL, the risk increases 3-fold as LDL varies from low to high.
Recommended range
The American Heart Association, NIH and NCEP provides a set of guidelines for male fasting HDL levels and risk for heart disease.
| Level mg/dL | Level mmol/L | Interpretation |
| <40 | <1.03 | Low HDL cholesterol, heightened risk for heart disease, <50 is the value for women |
| 40–59 | 1.03–1.52 | Medium HDL level |
| >60 | >1.55 | High HDL level, optimal condition considered protective against heart disease |
More sophisticated laboratory methods measure not just the total HDL but also the range of HDL particles, e.g. "lipoprotein subclass analysis", typically divided into several groups by size, instead of just the total HDL concentration as listed above. The largest groups (most functional) of HDL particles have the most protective effects. The groups of smallest particles reflect HDL particles which are not actively transporting cholesterol, thus not protective.
Differential Diagnosis
- HDL cholesterol is a positive cardiac Risk Factors
- 'HDL < 35
- Total cholesterol to HDL ratio in > 5.0 (in men)
- Total cholesterol to HDL ratio in > 4.5 (in women)
- Negative cardiac risk factor if HDL > 60
Decreased
- Apolipoprotein deficiency
- Diabetes Mellitus
- Drugs
- Liver disease
- Menopause
- Obesity
- Puberty in males
- Tangier Disease
- Uremia
Increased
- Drugs
- Moderate alcohol intake
- Regular aerobic exercise
- Weight loss
Raising HDL
Drugs
As of 2006, randomized clinical trials have demonstrated significant reduction of atherosclerosis progression and cardiovascular events with treatments that increase HDL-cholesterol (nicotinic acid or a fibrate).[1]
Pharmacological therapy to increase the level of HDL cholesterol includes use of fibrates and niacin. Consumption of niacin, an immediate release crystalline form of Vitamin B3, can increase HDL levels by 10–30%, and is the most powerful agent currently available to increase HDL-cholesterol.[1][1] [1] The use of statins is effective against high levels of LDL cholesterol, but it has little or no effect in raising HDL-cholesterol. [1] The use of antioxidants in combination with statin and niacin therapy reduces the effectiveness of niacin by 33%. (NIH HATS).
Torcetrapib, a promising new drug developed by Pfizer to raise HDL by inhibition of cholesteryl ester transfer protein (CETP), was terminated after a greater percentage of patients treated with torcetrapib-Lipitor combination died compared with patients treated with Lipitor alone.
Diet and lifestyle
Certain changes in lifestyle can have a positive impact on raising HDL levels:[1]
- Aerobic exercise[1]
- Weight loss
- Smoking cessation
- Using supplements such as omega 3 fish oil
- Limiting intake of dietary fat to 30–35% of total calories
- Removing trans fatty acids from the diet
- Adding monounsaturated and polyunsaturated fats to the diet, and reducing or eliminating saturated fats.
- Drinking 1–2 servings of alcoholic beverages per day
- Adding soluble fiber to diet
See also
References
External links
Lipids: lipoprotein metabolism | |
|---|---|
| General | Chylomicron - HDL - LDL - IDL - VLDL - Lp(a) |
| Apolipoproteins | APOA (1, 2, 5) - APOB - APOC (1, 2, 3, 4) - APOD - APOE - APOH |
| Other | Lipoprotein lipase - HDL (Cholesterylester transfer proteinAcetyl-CoA C-acyltransferase, LCAT) - LDL receptor - Microsomal triglyceride transfer protein - ABCA1 - Lecithin-cholesterol acyltransferase |
| see also disorders | |
de:HDL (Medizin)fr:Lipoprotéine de haute densité it:Lipoproteine ad alta densitàsv:Low density lipoprotein
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
