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Pathogenesis of Atherosclerosis and Hyperlipoproteinemia

Atherosclerosis et hyperlipoproteinaemia

For medical students2 min readUpdated 2026-10-10

Atherosclerosis is a chronic condition that develops due to a pronounced imbalance between the delivery of lipids to peripheral tissues and their subsequent reverse transport back to the liver. The primary biochemical consequence of this systemic disorder is hyperlipoproteinemia—a pathological elevation in the plasma levels of various lipoprotein classes. Depending on which lipid fractions predominate, varying degrees of risk for vascular bed damage are established.

Core pathogenesisImbalance between lipid delivery to tissues and return to the liver

ClassificationFredrickson classification defines 5 types of hyperlipoproteinemias

Typical patternDecreased HDL levels combined with increased LDL levels

High-risk therapyStatins, fibrates, bile acid sequestrants, nicotinic acid

Fundamentals of Atherosclerosis Pathogenesis

The atherosclerotic process does not occur spontaneously; it is triggered by a profound disturbance of lipid metabolism in the body. Under normal physiological conditions, there is a strict and balanced equilibrium between the volume of lipids delivered to cells to meet their metabolic needs and the volume transported back to the liver for subsequent disposal.

The foundation of this pathology is precisely the imbalance of this transport mechanism. The classic clinical and laboratory blood profile in progressive atherosclerosis demonstrates characteristic changes: a notable decrease in high-density lipoprotein (HDL) levels alongside a simultaneous increase in low-density lipoprotein (LDL) concentration.

The direct result of this biochemical shift is hyperlipoproteinemia (HLP)—an excessive content of lipoproteins in the plasma. Modern medicine distinguishes five main types of HLP, which differ in their lipid fraction composition. It is fundamentally important to understand that not every one of these five types leads to the development of atherosclerosis.

Fredrickson Classification: High and Moderate Risk

For the clinical evaluation of vascular event probability and the selection of treatment strategy, all types of hyperlipoproteinemias are traditionally categorized by their degree of atherogenic risk.

High Atherogenic Risk Group:

Type IIa: Characterized by a sharp increase in cholesterol (Ch ++) and the LDL fraction. The basis of this disorder is a genetic defect in the LDL receptor or the specific Apo B-100 protein. Pharmacotherapy includes statins and bile acid sequestrants.
Type IIb: Two atherogenic fractions—LDL and VLDL—increase simultaneously in the blood plasma. In addition, cholesterol (Ch ++) and triglyceride (TG ++) levels are significantly elevated. The exact molecular defect for this type is currently unknown. Pharmacotherapy is comprehensive and includes fibrates, statins, and nicotinic acid preparations.

Moderate Atherogenic Risk Group:

Type III: The blood concentration of IDLs rises (also referred to in literature as $\beta$-VLDL or floating $\beta$-VLDL). Concurrently, an increase in Ch (++) and TG (++) is recorded. The cause lies in an Apo E protein defect, which disrupts the normal clearance of remnants. The main drugs for treatment are fibrates.
Type IV: An isolated increase in VLDL is observed with a moderate rise in cholesterol (Ch +) and a marked surge in triglycerides (TG ++). As with Type IIb, the primary defect has not been established. The primary prescribed drug class is fibrates.

Group Without Atherogenic Risk

There are specific lipid profile disorders which, despite pronounced laboratory alterations, do not lead to atherosclerotic plaque formation and belong to the non-atherogenic risk group.

Type I: Manifests as a massive surge in triglyceride levels (TG +++) and the appearance of chylomicrons with a relatively minor elevation in cholesterol (Ch +). This pathology is directly linked to a defect in the enzyme lipoprotein lipase or the Apo C-II protein. Specific pharmacological agents for correcting this type are not indicated.
Type V: According to the presented classification data, this type is accompanied by an elevation in HDL levels. The molecular defect leading to this condition has not been identified. Specific medical pharmacotherapy in this case is either not required or not specified in standard protocols.

Mnemonic

For quick memorization of pharmacotherapy in high-risk types (IIa and IIb), use the mnemonic SSFN: Statins and Sequestrants (for IIa), plus Fibrates and Niacin (added for IIb).

Frequently asked questions

What is the mechanism of action of statins used in type IIa and IIb hyperlipoproteinemias?

The mechanism of action of statins involves the inhibition of HMG-CoA reductase, which is the key enzyme in cholesterol synthesis. This process occurs inside hepatocytes, leading to the suppression of endogenous cholesterol production in the liver. As a result, cellular uptake of cholesterol from the blood is enhanced, effectively lowering its plasma level.

Which specific drugs belong to the bile acid sequestrants group?

Bile acid sequestrants include the following polymeric agents:

Cholestyramine — a typical representative of the sequestrant group.
Colestipol — binds bile acids in the intestinal lumen, which may impair the absorption of fat-soluble vitamins.
Colesevelam — adsorbs bile acids in the intestine and interrupts their enterohepatic circulation.

Through what mechanism do fibrates lower triglyceride levels in type III and IV hyperlipoproteinemias?

Fibrates lower triglyceride levels by activating nuclear receptors and stimulating lipoprotein lipase activity. The mechanism includes:

Activation of PPAR$\alpha$ receptors (peroxisome proliferator-activated receptors).
Upregulation and increased expression of endothelial lipoprotein lipase (LPL).
Acceleration of the catabolism (breakdown) of triglyceride-rich particles: VLDL, IDL, and chylomicrons.

These processes result in a pronounced decrease in plasma triglyceride levels.

What is the main cause of the development of atherosclerosis?

The core of the disorder lies in an imbalance between lipid delivery to peripheral tissues and their return to the liver. A typical pattern includes decreased HDL and increased LDL.

Are all types of hyperlipoproteinemias equally dangerous and do they cause atherosclerosis?

No, the classification distinguishes 5 types that differ in risk degree. Types I and V belong to the non-atherogenic risk group and do not provoke the development of the disease.

What molecular defect is characteristic of type III hyperlipoproteinemia?

Type III features an Apo E protein defect. This leads to a severe impairment in the clearance of lipoprotein remnants in the body.

How does the pharmacotherapy of type IIa differ from type IIb?

For type IIa, statins and bile acid sequestrants are prescribed. For type IIb, fibrates and nicotinic acid are added to statins because VLDL and triglycerides are additionally elevated.

Go deeper

Pharmacodynamics of statins and bile acid sequestrants in the treatment of hyperlipoproteinemias.
Mechanism of action of fibrates and nicotinic acid derivatives.
The role of LDL receptors and the Apo B-100 protein in cellular metabolism.
Functions of the enzyme lipoprotein lipase and the Apo C-II protein in chylomicron metabolism.
Biochemical differences between floating $\beta$-VLDL (IDL) and other fractions.