Mechanism of action (Pathogenesis)
How exactly do statins work? The entire process unfolds in hepatocytes and consists of a clear sequence of biochemical reactions:
- Enzyme blockade. The drug competitively and reversibly inhibits HMG-CoA reductase.
- Cessation of synthesis. Normally, cholesterol is formed via the chain: acetyl-CoA $\rightarrow$ mevalonic acid $\rightarrow$ cholesterol. Statins interrupt this pathway at the stage of mevalonate formation. Intracellular cholesterol stores in the liver drop sharply.
- Compensatory reaction. The liver tries to compensate for the deficiency and increases the number (expression) of low-density lipoprotein (LDL) receptors on its cell membranes.
- Blood clearance. Due to receptor up-regulation, receptor-dependent endocytosis is enhanced: hepatocytes actively uptake atherogenic LDL from the bloodstream. Additionally, the liver reduces the release of VLDL.
Result: a powerful lipid-lowering effect (reduction of atherogenic fractions) and a concomitant increase in the level of "good" HDL.
Classification and chemical structure
Statins are classified according to their source of origin and structural features, which directly determines their pharmacological properties.
- Natural: lovastatin. It is isolated from the fungus culture Aspergillus terreus.
- Semi-synthetic: simvastatin and pravastatin (chemical derivatives of lovastatin). Their structure contains a hydronaphthalene ring (responsible for binding to the enzyme) and an oxyacid side chain (mimicking mevalonate).
- Synthetic: fluvastatin (a mevalonolactone derivative). Contains a fluorophenylindole moiety that binds to the coenzyme A site.
It is critically important to distinguish drugs by their pharmacological status:
- Prodrugs: lovastatin and simvastatin. These are inactive lactones. To start working, they must undergo hydrolysis in the body and convert into active $\beta$-hydroxy acids.
- Active substances: pravastatin and fluvastatin. They initially contain an oxyacid in their structure and are pharmacologically active immediately after administration.
Pharmacokinetic features
When administered orally, statins are characterized by low bioavailability (ranging from less than 5% for lovastatin and simvastatin to 24% for fluvastatin). This is due to the active uptake of the drugs by the liver during the first pass (presystemic metabolism).
Food intake affects absorption differently:
- Improves: in lovastatin.
- Does not affect: in simvastatin.
- Worsens: in pravastatin and fluvastatin.
Penetration through histohematic barriers (blood-brain barrier, placenta) depends on the lipophilicity of the molecule. Lovastatin and simvastatin cross the barriers well, whereas fluvastatin, pravastatin, and atorvastatin practically do not overcome them.
Pleiotropic effects
The anti-atherosclerotic action of statins is not only due to lipid lowering. They possess a number of additional (pleiotropic) properties that protect the cardiovascular system:
- Endothelial protection and vasodilation: protection of the vascular wall from oxidized LDL and stimulation of NO synthase expression (increased nitric oxide production).
- Antithrombotic action: reduction of thrombin levels, suppression of platelet aggregation, and activation of fibrinolysis.
- Antiproliferative effect: inhibition of vascular smooth muscle cell proliferation (due to enzyme inhibition in angiomyocytes).
- Anti-inflammatory and anti-ischemic action (increased exercise tolerance).
Pharmacological profile of atorvastatin
Atorvastatin stands out as the most effective drug in the group. Despite high absorption (80%), its bioavailability is only 14% due to presystemic metabolism.
It is metabolized in the liver with the participation of the CYP3A4 isoenzyme. As a result, active metabolites are formed ($\beta$-oxidation products, ortho- and parahydroxylated derivatives) which continue to inhibit HMG-CoA reductase for 20–30 hours. The drug is excreted predominantly via bile (half-life is 14 hours).
Specific effects of atorvastatin:
- Stabilization and regression of atherosclerotic plaques.
- Reduction of C-reactive protein levels.
- Antiarrhythmic action and increased cardiac output (improved coronary blood flow).
- Improvement of psychological well-being due to the normalization of cerebral circulation.
Briefly: answers to topical questions
With which drugs is it dangerous to combine statins due to the high risk of developing rhabdomyolysis?
Statins are contraindicated for combination with fibric acid derivatives (fibrates) due to the risk of muscle damage.
When co-administered with statins, adverse effects on muscle tissue are additive, which can lead to myopathies, myalgia, and rhabdomyolysis.
Which cytochrome P450 isoenzymes, besides CYP3A4, are involved in the metabolism of statins?
In addition to the CYP3A4 isoenzyme, the CYP3A5 isoenzyme is involved in the metabolism of certain statins.
These isoenzymes belong to the same cytochrome P450 subfamily, which is the most extensive and metabolizes the majority of drugs.
- CYP3A4 / CYP3A5 — act as the enzymatic target for lovastatin metabolism.
At the same time, the biotransformation of atorvastatin in the liver proceeds predominantly with the participation of CYP3A4, forming active ortho- and parahydroxylated derivatives that retain their pharmacological effect.
To avoid confusing prodrugs (inactive lactones) with active forms, remember the phrase "Lazy Statins" — Lovastatin and Simvastatin. They need time to activate.
Class and exam questions
Why are statins recommended to be taken at bedtime?
This is due to the body's circadian rhythms. The peak of endogenous cholesterol synthesis in the liver occurs at night, so evening administration ensures maximum enzyme inhibition.
How to properly combine statins with bile acid sequestrants?
It is necessary to strictly observe the time interval to avoid impaired absorption. The statin is taken either 1 hour before the sequestrant or 4 hours after it.
Which side effects of statins pose the greatest danger?
The most serious threat is muscle tissue damage, which can manifest as myopathy and rhabdomyolysis. Additionally, the drugs exhibit dose-dependent hepatotoxicity (elevation of hepatic transaminases).
What else to study on this topic
- Detailed analysis of types IIa and IIb hyperlipoproteinemias, which are the main indications.
- The relationship of chemical structure (SAR) with affinity for HMG-CoA reductase.
- Differences in the time to reach maximum concentration (Tmax) among various representatives.
- Mechanisms of atorvastatin metabolism via the CYP3A4 cytochrome system.
- The effect of lipophilicity on the penetration of statins across the blood-brain barrier.
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