What is high hdl
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Understanding High HDL: Quantity, Quality, and Functionality
What is High HDL?
High-density lipoproteins (HDL) are often referred to as "good cholesterol" due to their role in transporting cholesterol from the arteries to the liver for excretion. However, the concept of "high HDL" encompasses more than just the quantity of HDL in the blood. It also involves the quality and functionality of these lipoproteins.
HDL Quantity: Serum HDL-C Concentration
The quantity of HDL is typically measured as serum HDL-C concentration (mg/dL). High levels of HDL-C are generally associated with a lower risk of cardiovascular diseases. However, recent studies suggest that merely having high HDL-C levels does not always confer cardiovascular protection . Factors such as age, gender, lifestyle, and disease states can influence HDL-C levels. For instance, regular aerobic exercise and a healthy diet can increase HDL-C, while acute infections and chronic inflammation can decrease it.
HDL Quality: Composition and Morphology
HDL quality refers to the composition and physical characteristics of HDL particles, including their size, shape, and the types of proteins and lipids they contain. High-quality HDL typically has a higher content of apolipoproteins like apoA-I and apoA-II, and lower levels of oxidation and glycation . Dysfunctional HDL, which may result from glycation or oxidation, often has a lower apoA-I content, smaller size, and ambiguous shape, leading to reduced functionality .
HDL Functionality: Beyond Cholesterol Transport
The functionality of HDL is a critical aspect that determines its protective roles. HDL functionality includes several key activities:
Antioxidant and Anti-inflammatory Properties
HDL has strong antioxidant properties, primarily due to enzymes like paraoxonase-1 (PON1), which help prevent the oxidation of low-density lipoproteins (LDL) . HDL also exhibits anti-inflammatory effects, which are crucial in reducing the risk of atherosclerosis and other inflammatory diseases .
Cholesterol Efflux Capacity (CEC)
One of the most important functions of HDL is its ability to promote cholesterol efflux from macrophages, a process that helps remove cholesterol from atherosclerotic plaques. This capacity is a strong indicator of HDL functionality and is inversely associated with cardiovascular disease risk, independent of HDL-C levels .
Emerging Roles in Neurodegenerative and Infectious Diseases
Recent research has expanded the understanding of HDL functionality to include roles in neurodegenerative diseases and infections. HDL has been shown to help remove β-amyloid plaques in Alzheimer's disease and inhibit α-synuclein aggregation in Parkinson's disease . Additionally, HDL's antiviral properties have been highlighted in the context of COVID-19, where native HDL has shown potent antiviral activity against SARS-CoV-2, while glycated HDL loses this functionality .
Conclusion
High HDL is a multifaceted concept that includes not just the quantity of HDL-C but also the quality and functionality of HDL particles. While high HDL-C levels are generally beneficial, the protective effects of HDL are more closely related to its functional properties, such as antioxidant activity, anti-inflammatory effects, and cholesterol efflux capacity. Understanding these aspects can help in developing better therapeutic strategies to harness the full potential of HDL in preventing and treating various diseases.
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