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Lipids, cardiovascular disease, and oral contraceptives: a practical perspective
1Wyeth-Ayerst Research and Medical College of Pennsylvania, Philadelphia.
Insights
Lifestyle factors significantly impact lipid levels by influencing the production and metabolism of HDL and LDL. Key enzymes like LCAT and LPL, along with lifestyle choices, regulate these crucial lipoproteins.
Area of Science:
- Lipid metabolism and lipoprotein biochemistry.
Background:
- High-density lipoprotein (HDL) and low-density lipoprotein (LDL) levels are influenced by various lifestyle and physiological factors.
- Understanding lipoprotein production and catabolism is crucial for managing lipid parameters and preventing atherosclerosis.
Purpose of the Study:
- To illustrate the complex interplay between lifestyle factors and lipid metabolism.
- To detail the pathways of HDL and LDL production and the enzymes involved.
Main Methods:
- The study presents a model (Figure 9) based on existing research (Nikkila) to visualize lipoprotein metabolism.
- It maps the influence of diet, exercise, hormones, genetics, drugs, and disease states on HDL and LDL levels.
Main Results:
- HDL is produced in the liver and intestine, with levels affected by diet, exercise, hormones, genetics, drugs, and disease.
- Lecithin-cholesterol acyl transferase (LCAT) and lipoprotein lipase (LPL) are key enzymes in HDL and LDL production.
- Hepatic endothelial lipase catabolizes HDL, and LDL removal is receptor-mediated, with implications for atherosclerosis.
Conclusions:
- Lifestyle modifications and hormonal balances (e.g., in oral contraceptives) can significantly alter HDL and LDL concentrations.
- Defective LDL receptor function can lead to cholesterol accumulation and potentially atherosclerosis.
Abstract:
Figure 9 is an attempt to summate the influences of life-style on lipid parameters. Based on the work of Nikkila, it shows the source of the production of HDL and LDL, the factors that can affect these lipoprotein levels, and where in the cascade of lipoprotein metabolism these factors exert influence. The source of HDL production is the liver and the intestine. At this stage, diet, exercise, hormones, genetics, drugs, and certain disease states can affect HDL levels. Lecithin-cholesterol acyl transferase (LCAT) esterifies HDL-free cholesterol in plasma, and HDL3 is formed that in turn is transformed to HDL2. At the same time, VLDL from the gut and the liver will be converted, under the influence of LPL, to HDL2 and LDL. Thus HDL2 is being formed by the breakdown of VLDL and from the transformation of HDL3 to HDL2. Insulin, exercise, alcohol, fats, drugs, and diet affect lipoprotein lipase and consequently influence levels of LDL and HDL2 indirectly. Progestogens increase and estrogens decrease hepatic endothelial lipase, thus affecting the HDL2 concentration. It is at this point that combination OCs influence HDL2. The balance between estrogen and progestogen in a given contraceptive determines the extent and direction of HDL2 concentration. A separate pathway in the liver also catabolizes HDL2 and HDL3. LDL is generated partly from catabolism of VLDL and is partly secreted from the liver. The removal of LDL is mediated by receptors in both the liver and peripheral tissues. It is here that the Brown-Goldstein theory plays a major role. If LDL receptors are present in an insufficient number or are defective, then the C will accumulate and atherosclerosis may follow. Thus two key enzymes, LCAT and LPL, control the production of HDL2 and LDL, whereas a third enzyme, hepatic endothelial lipase, catabolizes HDL2.