Cholesterol is a molecule with seven rings and important, necessary functions in the body. For example, it structurally augments the cell membrane, which surrounds and protects the cell. It also is the precursor to steroid hormones such as adrenalin, testosterone and estrogen. High concentrations in the blood are linked to adverse health conditions, however. Statins, also known as HMG-CoA inhibitors, are a group of drugs used to treat high cholesterol.
Types of Cholesterol
According to "Physiology" by Linda Costanzo, cholesterol travels through the blood attached to proteins. This is because cholesterol is not very soluble in liquid solutions such as blood, so they don't dissolve. The proteins bind to cholesterol so they can be transported through the blood. These protein and cholesterol complexes are called lipoproteins. Different types of lipoproteins include chylomicrons; very low density lipoproteins, or VLDL; low density lipoprotein, or LDL; intermediate density lipoprotein, or IDL; and high density lipoprotein, or HDL. The most important of these are generally thought to be the LDL and HDL particles. LDL is known as "bad" cholesterol because it deposits cholesterol on the blood vessel walls, leading to cardiovascular disease. HDL is known as "good" cholesterol because it returns cholesterol to the liver to be broken down. and excreted from the body.
Cholesterol and Disease
According to "Harrison's Principles of Internal Medicine" by Dr. Anthony Fauci, high cholesterol levels have been associated with a number of diseases. The lipid hypothesis proposes that high levels of LDL cholesterol deposit plaques called atheroma on the walls of blood vessels, causing them to become hard and narrow. This restricts blood flow to the heart. The plaque can also rupture, causing blood to clot in the vessel and cutting off blood flow at that vessel. If it happens in the heart, this causes a heart attack. If it occurs in the brain, it causes a stroke.
Statins
Statins include such drugs as atorvastatin, lovastatin, simvastatin and pravastatin among others. They are used mostly to decrease levels of LDL cholesterol to decrease the risk of cardiovascular disease. They also have the effect of lowering blood fat, or triglyceride, levels and raising beneficial HDL cholesterol.
Mechanism of Action
According to "Basic and Clinical Pharmacology" by Dr. Bertram Katzung, statins inhibit an enzyme in the liver called HMG-CoA reductase. This enzyme converts the chemical HMG-CoA into the chemical mevalonate, which is a precursor to cholesterol. Therefore, HMG-CoA reductase helps to synthesize cholesterol in the liver. Statins have a similar structure to HMG-CoA and bind to the enzyme HMG-CoA reductase so it makes less mevalonate--and, hence, less cholesterol. The effect is for statins to decrease the amount of cholesterol made by the liver and encourage the liver to scoop up cholesterol from the blood. They also may have positive effects on the blood vessel walls and the immune system.
Side Effects
Statins are associated with some side effects--though they only occur in a minority of patients--including nausea, constipation or diarrhea. Some people experience muscle aches, cramping or muscle breakdown. Liver tests are also performed periodically on users because in a very small number of people, statins cause liver damage.
References
- "Physiology (fourth edition)"; Linda Costanzo; 2009
- "Harrison's Principles of Internal Medicine(17th edition)"; Dr. Anthony Fauci et al; 2008
- "Basic and Clinical Pharmacology (11th edition)"; Bertram Katzung; 2009
