CHOLESTEROL

CHOLESTEROL. Cholesterol is one of the most widely disseminated organic compounds in the animal kingdom. Almost three hundred years ago, Antonio Vallisnieri observed that gallstones were soluble in turpentine or alcohol. Poulletier de la Salle, some thirty years later, demonstrated that the main constituent of gallstones could be crystallized from alcohol. This substance was thought to be a wax until 1815, when Michel Eugène Chevreul showed that it was not saponifiable and gave it the name "cholesterine" derived from the Greek chole, bile, and steros, solid. Soon thereafter, it was isolated from blood, brain, tumors, and egg yolk. The isolated compounds were shown to be identical. In 1843 Vogel found it in atherosclerotic arteries.

The chemical structure of cholesterol was elucidated over the years beginning in 1859. The compound was shown to contain a secondary hydroxyl group and a double bond. The exact empirical formula (C₂₇H₄₆O) was established in 1888 by Friedrich Reinitzer. Proof of structure was obtained chiefly through the brilliant work of Adolf Windaus and Heinrich Wieland. The structure of cholesterol suggested by Windaus and Wieland in the 1920s was incorrect, but that does not detract in any way from their contribution. The true structure was established in the 1930s based on X-ray diffraction data.

There were many suggestions regarding the biological synthesis of cholesterol. The biosynthetic pathway became accessible with the introduction of radioactive carbon in the 1940s. The biosynthetic scheme was generally elucidated by the work of Konrad Bloch, George Popjak, and John Cornforth. It was first shown that cholesterol could be synthesized in mammals and ergosterol in yeast from small organic molecules. Eventually it was shown that all twenty-seven carbon atoms of cholesterol were derived from the two carbon atoms of acetate. The methyl group of acetate contributed fifteen of the twenty-seven carbons of cholesterol and the carboxyl group contributed twelve. The pathway began with the condensation of two acetate residues to give acetoacetate and addition of one more two-carbon moiety to yield hydroxymethylglutaric acid (HMG). HMG lost a carbon atom and the resulting compound rearranged to provide an isoprene unit. Two five-carbon units combined to give a geranyl derivative that added another isoprene to give a farnesyl unit. Two farnesyl units united to provide squalene (C₃₀H₅₀), a hydrocarbon found in the livers of some species of shark that cyclyzed to yield lanosterol, a thirty-carbon atom sterol also found in sheep wool. In a series of rearrangements and demethylations, lanosterol yielded cholesterol. The key step in this complex synthetic pathway involves the reduction of HMG-CoA. Inhibition of HMG-CoA reductase is the basis of a number of potent new serum cholesterol-lowering drugs.

Cholesterol represents about 0.2 percent of the weight of the human body. As Table 1 shows, the bulk of the body's cholesterol is present in two tissues; one is the brain and nerve tissue, the other is muscle. In the brain, cholesterol is thought to act as an insulator, but there have been relatively few studies of the metabolism of brain cholesterol. The next large reservoir of cholesterol is muscle. Between them, nervous tissue and muscle carry 44 percent of the body's cholesterol. The cholesterol in these reservoirs turns over slowly.

Cholesterol is ubiquitous in the human body, where it plays structural and metabolic roles. Together with phospholipid, cholesterol is present in every cell membrane. In the adrenals, cholesterol is converted to adrenocortical hormones such as cortisone. In the gonads,

cholesterol is converted to the appropriate sex hormone—estradiol in women, testosterone in men. The cholesterol in skin is the precursor of 7-dehydrocholesterol, which is ultimately converted to vitamin D. The major catabolic products of cholesterol are the bile acids—cholic and chenodeoxycholic. These are designated as the primary bile acids; they are metabolized in the liver to deoxycholic and lithocholic acids. It has been estimated that over 90 percent of biologically synthesized cholesterol is metabolized to bile acids. In general, the body synthesizes more cholesterol than it ingests.

In 1912 Nicolai Anitschkow showed that cholesterolfed rabbits developed aortic deposits similar to early human atherosclerosis. His experiments presented a possible explanation of human atherosclerosis and that particular debate has not yet abated. Simultaneously with Anitschkow's studies, A. I. Ignatowski demonstrated the atherogenic potential of animal protein, but compared to work on cholesterol and fat there has only been a desultory interest in protein effects.

Since Anitschkow's results were obtained by dietary manipulation, the view that dietary cholesterol was implicated in atherogenesis was accepted generally. With development of simple, rapid methods of cholesterol analysis, it became possible to screen populations for blood cholesterol content. Large epidemiological studies were launched and their results helped to develop the concept of risk factors for heart disease. Currently, the major risk factors are hypercholesterolemia, hypertension, smoking, obesity, and maleness. However, emerging data suggest that homocysteinemia and inflammation (due to infection with cytomegalovirus or chlamydia pneumoniae ) are also important factors.

When cholesterol is ingested, it is emulsified with phospholipid and absorbed. The absorbed lipid circulates in the blood as a water soluble lipid-protein complex called lipoprotein. Initially, absorbed cholesterol is part of a large, triglyceride-rich particle called the chylomicron. In the course of circulation, the triglyceride is removed by activity of cellular lipases and the particles become smaller and their cholesterol content increases. The cholesterol-containing, lipid-protein complex consists of several fractions that are separable by virtue of their hydrated densities. In general terms, the four major fractions are the triglyceride-rich chylomicrons and very low density (VLDL), the cholesterol-rich low density (LDL), and the protein-rich high density (HDL).

Due to development by John Gofman of methods for ultracentrifugal separation of lipoproteins, researchers have been able to isolate and study lipoproteins. The cholesterol-rich low density lipoproteins (LDL) are thought to be major risk factors for coronary disease. It was demonstrated that oxidized LDL is the real villain in coronary disease. It also was shown that LDL can be subfractionated into small, dense and large "fluffy" particles. The small particles appear to infiltrate the artery preferentially. Researchers also know that the process of atherogenesis is not simple and is mediated by an array of small proteins. The high-density lipoproteins are about 50 percent protein. In the simplest terms, LDL facilitates entry of cholesterol into cells and HDL facilitates its removal. LDL receptors on the cell surface facilitate LDL uptake. The proteins of lipoproteins are very important because they provide recognition by cells, and it is now becoming evident that genetic differences in apolipoproteins may dictate susceptibility to disease as well as chances for the efficacy of medication.

The effects of dietary cholesterol became a concern shortly after Anitschkow's observation and warnings regarding excess levels of cholesterol intake, which constitute one of the foundations of dietary therapy. Since cholesterol occurs only in food of animal origin, it was a simple extension to seek an explanation of the role of cholesterol by examining the lipids of food from animal sources. Although no dietary fat is totally saturated or unsaturated, attention also turned to effects of fat saturation.

The amount of cholesterol in the average American diet is in the range of 300–350 mg/day. It used to be much higher. The levels of cholesterol in a number of common animal foods are given in Table 2. It is evident that most muscle contains about the same amount of cholesterol, 81 ± 7 mg/100g. Cholesterol content of butter (per 100 g) is high, but we rarely eat more than 5–10 g of butter per meal. Shrimp is high in cholesterol but very low in fat. Eggs are also high in cholesterol. Continuing research nevertheless indicates that the cholesterol level of a food per se has little effect on serum cholesterol levels. The cholesterolemic effect is a function of dietary fat saturation. It has been shown that the absorption of cholesterol is more a function of the accompanying dietary fat than of cholesterol itself. Saturated dietary fat leads to higher cholesterol levels than does unsaturated fat. This observation is true for most people who are called "non-responders" (to dietary cholesterol). A small number of people are "responders," meaning they absorb more cholesterol, regardless of accompanying fat. In the late 1960s, Keys and Hegsted developed formulas for estimating changes in serum cholesterol based upon changes in dietary fat. There have been a number of more complex formulas developed, but the originals are referred to most often today. Essentially, they found saturated fatty acids to be hypercholesterolemic and unsaturated fatty acids to lower cholesterol. Stearic acid was considered neutral. The polyunsaturated fats lower cholesterol across the board so that HDL cholesterol (the "good" cholesterol) falls as does LDL cholesterol. Oleic acid seems to affect only LDL cholesterol. The reduction in total cholesterol may not be as profound, but the LDL/HDL cholesterol ratio is improved. Recent findings show that the structure of individual triglycerides may also influence their atherogenicity.

In summary, cholesterol is a substance that appears in all cells and also has a number of metabolic functions.

It is synthesized in the body and is part of every cell membrane. Cholesterol is metabolized to adrenocortical or sex hormones, bile acids, and vitamin D. Levels of serum cholesterol are related to risk of coronary disease, but it should be borne in mind that cardiovascular disease is a metabolic disease, not one of cholesterol deposition. Dietary cholesterol is absorbed, but its effects on serum cholesterol are slight. Generally, there is an increase of about 2 mg of serum cholesterol for every 100 mg ingested. Cholesterol should be viewed as a chemical necessary for life and not as a toxic substance. As with so many other aspects of life, moderation is the key.

See also Fats ; Health and Disease.

BIBLIOGRAPHY

Gibbons, G. F., K. A. Mitropoulos, and Nick B. Myant. Biochemistry of Cholesterol. Amsterdam: Elsevier Biomedical Press, 1982.

Howell, Wanda H., et al. "Plasma Lipid and Lipoprotein Responses to Dietary Fat and Cholesterol: A Meta Analysis." American Journal of Clinical Nutrition 65 (1997): 1747–1764.

Keys, Ancel, Joseph T. Anderson, and Francisco Grande. "Serum Cholesterol Response to Changes in Diet, IV: Particular Fatty Acids in the Diet." Metabolism 14 (1965): 776–787.

Kritchevsky, David. Cholesterol. New York: Wiley, 1958.

Kritchevsky, David. "Food Lipids and Atherosclerosis." In Food Lipids and Health, edited by Richard E. McDonald and David B. Min. New York: M. Dekker, 1996.

Leinoneu, M. "Chlamydia pneumoniae and Other Risk Factors for Atherosclerosis." Journal of Infectious Diseases 181, Suppl. 3 (2000): S414–S416.

Myant, Nick B. The Biology of Cholesterol and Related Steroids. London: Heinemann Medical Books, 1981.

Myant, Nick B. Cholesterol Metabolism, LDL, and the LDL Receptor. San Diego, Calif.: Academic Press, Inc., 1990.

David Kritchevsky

CHOLESTEROL

Cholesterol, cholesterol esters, and triglycerides are fats, or lipids. On their own these would not be soluble enough to circulate, so to circulate in blood, these lipids are combined with phospholipids and protein in particles called lipoproteins. Generally, only three lipoproteins—very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)—are found in the serum of fasting persons.

Cholesterol is absorbed from the intestine and transported to the liver where it is taken up by the LDL receptors. Cholesterol from the liver enters the circulation as VLDL and is metabolized to remnant lipoproteins after an enzyme (lipoprotein lipase) removes triglycerides. The remnant lipoproteins are removed by LDL receptors or further metabolized to LDL and then removed by LDL receptors. Cholesterol also is transported from peripheral cells to the liver by HDL. Cholesterol is recycled to LDL and VLDL or is taken up in the liver by an enzyme known as hepatic lipase. Cholesterol is excreted in bile.

LDL is the major cholesterol-containing lipoprotein, the major lipoprotein implicated in the development of atherosclerosis, and the primary target of therapeutic interventions. LDL cholesterol may be increased because of increased dietary saturated fat and cholesterol, obesity, or genetic disorders, or because of other secondary causes such as hypothyroidism, a kidney disorder known as nephrotic syndrome, biliary cirrhosis, and renal failure.

HDL is synthesized in both the liver and intestine and exerts a protective effect on the development of atherosclerotic vascular disease, a condition also sometimes referred to as "hardening of the arteries." HDL reverses cholesterol transport and removes cholesterol from cells to be delivered directly to the liver or indirectly via transfer of other lipoproteins for catabolism (breakdown into simpler substances with the release of energy). HDL also prevents oxidation and aggregation of LDL in the arterial wall. Low HDL cholesterol may be genetically determined or associated with nutritional habits, cigarette smoking, and lack of exercise.

VLDL is a triglyceride-rich lipoprotein synthesized and secreted by the liver. Hypertriglyceridemia is associated with genetic disorders, obesity, heavy alcohol intake, diabetes mellitus, renal failure, and drugs such as estrogens.

The measurement of levels of LDL cholesterol, HDL cholesterol, and triglycerides in the serum is used to assess risk for atherosclerotic vascular disease. Serum total cholesterol = LDL cholesterol + HDL cholesterol + 1/5 triglycerides. Hypercholesterolemia is a serum total cholesterol of 200 mg/dL or higher. An elevated serum LDL cholesterol is 130 mg/dL or higher. An abnormally low serum HDL cholesterol is 35 mg/dL or lower. Hypertriglyceridemia is serum triglycerides of 190 mg/dL or higher.

An elevated serum total cholesterol, an elevated serum LDL cholesterol, and a low serum HDL cholesterol are risk factors for coronary artery disease, stroke, and peripheral arterial disease in older and younger men and women. The higher the serum total cholesterol, the higher the serum LDL cholesterol, and the lower the serum HDL cholesterol, the greater the incidence of atherosclerotic vascular disease in older and younger men and women.

Elevated serum triglycerides is associated with an increased risk of atherosclerotic vascular disease. However, except for being a weak independent risk factor for new coronary events in elderly women, hypertriglyceridemia is not an independent risk factor for atherosclerotic vascular disease in older or younger men and women.

Because the incidence of atherosclerotic vascular disease is much higher in older men and women than in younger men and women, hypercholesterolemia, an elevated serum LDL cholesterol, and a low serum HDL cholesterol contribute more to the absolute incidence of atherosclerotic vascular disease in older than in younger men and women.

In addition to dyslipidemia, cigarette smoking, hypertension, and diabetes mellitus are major risk factors for atherosclerotic vascular disease. The greater the number and severity of major risk factors, the higher the incidence of atherosclerotic vascular disease.

Persons with dyslipidemia should have secondary causes of dyslipidemia treated, lose weight if obese, and begin dietary treatment. A Step II American Heart Association diet should be used if drug therapy is being considered. The Step II diet contains no more than 30 percent of calories from fat, less than 7 percent of calories from saturated fatty acids, and less than 200 mg of cholesterol daily. Other major risk factors for atherosclerotic vascular disease must be treated.

Increased plasma homocysteine is also an independent risk factor for atherosclerotic vascular disease in older and younger men and women. The presence of both increased plasma homocysteine and dyslipidemia increases independently the incidence of atherosclerotic vascular disease.

Statins are drugs that reduce the synthesis of cholesterol and the secretion of VLDL and increase the activity of LDL receptors. Bile acid– binding resins increase the secretion of bile acids. Nicotinic acid reduces the secretion of VLDL and the formation of LDL and increases the formation of HDL. Fibrates reduce the secretion of VLDL and increase the activity of lipoprotein lipase, thereby increasing the removal of triglycerides.

Older and younger men and women with atherosclerotic vascular disease and a serum LDL cholesterol greater than 125 mg/dL despite dietary treatment should be treated with statin drugs to lower the serum LDL cholesterol to below 100 mg/dL. Statins will decrease serum total and LDL cholesterol and triglycerides, increase serum HDL cholesterol, and reduce in these patients all-cause mortality, cardiovascular mortality, major coronary events, stroke, heart failure, angina pectoris, and peripheral arterial disease. Because mortality rates and cardiovascular events increase with age, statins will reduce all-cause mortality, cardiovascular mortality, and cardiovascular events approximately twice as much in men and women sixty-five years of age and older than in men and women younger than sixty-five years.

Older and younger men and women with atherosclerotic vascular disease and a normal serum LDL cholesterol but a low serum HDL cholesterol should be treated with nicotinic acid or gemfibrozil to reduce cardiovascular events.

Older and younger persons without atherosclerotic vascular disease with a serum LDL cholesterol of 160 mg/dL or higher and two other coronary risk factors (including older age, male gender, smoking, hypertension, diabetes mellitus, low serum HDL cholesterol, and family history), or with a serum LDL cholesterol of 130 mg/dL or higher and a low serum HDL cholesterol, or with a serum LDL cholesterol of 190 mg/dL or higher and no other coronary risk factors should be treated with statins to reduce cardiovascular events.

Wilbert S. Aronow

See also Heart Disease; High Blood Pressure; Stroke.

BIBLIOGRAPHY

Aronow, W. S. "Treatment of Hypercholesterolemia in Older Persons with Coronary Artery Disease." Clinical Geriatrics 7 (1999): 93–100.

Aronow, W. S. "Risk Factors for Coronary Artery Disease, Peripheral Arterial Disease, and Atherothrombotic Brain Infarction in Elderly Persons." In Vascular Disease in the Elderly. Edited by W. S. Aronow, E. A. Stemmer, and S. E. Wilson. Armonk, N.Y.: Futura Publishing Co., 1997. Pages 81–103.

Downs, J. R.; Clearfield, M.; Weis, S.; Whitney, E.; Shapiro, D. R.; Beere, P. A.; Langendorfer, A.; Stein, E. A.; Kruyer, W.; and Gotto, A. M., Jr. "Primary Prevention of Acute Coronary Events with Lovastatin in Men and Women with Average Cholesterol Levels. Results of AFCAPS/TexCAPS." Journal of the American Medical Association 279 (1998): 1615–1622.

Larosa, J. C. "Hyperlipidemia in the Elderly." In Cardiovascular Disease in the Elderly Patient, 2d ed. Edited by D. D. Tresch and W. S. Aronow. New York: Marcel Dekker, Inc., 1999. Pages 129–137.

Miettinen, T. A.; Pyorala, K.; Olsson, A. G.; Musliner, T. A.; Cook, T. J.; Faergeman, O.; Berg, K.; Pedersen, T.; and Kjekshus, J. "Cholesterol-Lowering Therapy in Women and Elderly Patients with Myocardial Infarction or Angina Pectoris. Findings from the Scandinavian Simvastatin Survival Study (4S)." Circulation 96 (1997): 4211–4218.

Cholesterol

Definition

Cholesterol is a fatty substance found in animal tissue and is an important component to the human body. It is manufactured in the liver and carried throughout the body in the bloodstream. Problems can occur when too much cholesterol forms an accumulation of plaque on blood vessel walls, which impedes blood flow to the heart and other organs. The highest cholesterol content is found in meat, poultry, shellfish, and dairy products.

Description

Cholesterol is the Dr. Jekyll and Mr. Hyde of medicine, since it has both a good side and bad side. It is necessary to digest fats from food, make hormones, build cell walls, and participate in other processes for maintaining a healthy body. When people talk about cholesterol as a medical problem, they are usually referring to high cholesterol. This can be somewhat misleading, since there are four components to cholesterol. These are:

• LDL, the so-called bad cholesterol
• HDL, the so-called good cholesterol
• triglycerides, a blood fat lipid that increases the risk for heart disease
• total cholesterol

The U.S. Food and Drug Administration (FDA) estimates that 90 million American adults, roughly one-half of the adult population, have elevated cholesterol levels. High LDL (low-density lipoprotein) is a major contributing factor of heart disease. The cholesterol forms plaque in the heart's blood vessels, which restricts or blocks the supply of blood to the heart, and causes a condition called atherosclerosis. This can lead to a heart attack , resulting in damage to the heart and possibly death.

In 2001, chemical researchers found a link between cholesterol and Alzheimer's disease . Reducing the amount of cholesterol in the cells appears to block attachment of senile plaques to the brain's neurons. (The plaques begin the process that eventually kills brain neurons.) More study remains to test the effects of cholesterol on Alzheimer's.

The population as a whole is at some risk of developing high LDL cholesterol in their lifetimes. Specific risk factors include a family history of high cholesterol, obesity , heart attack or stroke, alcoholism , and lack of regular exercise . The chances of developing high cholesterol increase after the age of 45. One of the primary causes of high LDL cholesterol is too much fat or sugar in the diet, a problem especially true in the United States. Cholesterol also is produced naturally in the liver and overproduction may occur even in people who limit their intake of high cholesterol food. Low HDL and high triglyceride levels also are risk factors for atherosclerosis.

Causes & symptoms

There are no readily apparent symptoms that indicate high LDL or triglycerides, or low HDL. The only way to diagnose a problem is through a simple blood test. However, one general indication of high cholesterol is obesity. Another is a high-fat diet. In 2001, new research involving twins demonstrated that both genetic factors and diet contribute to cholesterol levels.

Diagnosis

High cholesterol often is diagnosed and treated by general practitioners or family practice physicians. In some cases, the condition is treated by an endocrinologist or cardiologist. Total cholesterol, LDL, HDL, and triglyceride levels as well as the cholesterol to HDL ratio are measured by a blood test called a lipid panel. The cost of a lipid panel is generally $40-100 and is covered by most health insurance and HMO plans, including Medicare, providing there is an appropriate reason for the test. Home cholesterol testing kits are available over the counter but test only for total cholesterol. The results should only be used as a guide and if the total cholesterol level is high or low, a lipid panel should be performed by a physician. In most adults the recommended levels, measured by milligrams per deciliter (mg/dL) of blood, are: total cholesterol, less than 200; LDL, less than 130; HDL, more than 35; triglycerides, 30-200; and cholesterol to HDL ratio, four to one. However, the recommended cholesterol levels may vary, depending on other risk factors such as hypertension , a family history of heart disease, diabetes, age, alcoholism, and smoking .

Doctors have always been puzzled by why some people develop heart disease while others with identical HDL and LDL levels do not. New studies indicate it may be due to the size of the cholesterol particles in the

bloodstream. A test called a nuclear magnetic resonance (NMR) LipoProfile exposes a blood sample to a magnetic field to determine the size of the cholesterol particles. Particle size also can be determined by a centrifugation test, where blood samples are spun very quickly to allow particles to separate and move at different distances. The smaller the particles, the greater the chance of developing heart disease. It allows physicians to treat patients who have normal or close to normal results from a lipid panel but abnormal particle size.

Treatment

The primary goal of cholesterol treatment is to lower LDL to under 160 mg/dL in people without heart disease and who are at lower risk of developing it. The goal in people with higher risk factors for heart disease is less than 130 mg/dL. In patients who already have heart disease, the goal is under 100 mg/dL, according to FDA guidelines. Also, since low HDL levels increase the risks

of heart disease, the goal of all patients is more than 35 mg/dL.

In both alternative and conventional treatment of high cholesterol, the first-line treatment options are exercise, diet, weight loss, and stopping smoking. Other alternative treatments include high doses of niacin, soy protein, garlic , algae, and the Chinese medicine supplement Cholestin (a red yeast fermented with rice).

Diet and exercise

Since a large number of people with high cholesterol are overweight, a healthy diet and regular exercise are probably the most beneficial natural ways to control cholesterol levels. In general, the goal is to substantially reduce or eliminate foods high in animal fat. These include meat, shellfish, eggs, and dairy products. Several specific diet options are beneficial. One is the vegetarian diet. Vegetarians typically get up to 100% more fiber and up to 50% less cholesterol from food than non-vegetarians. The vegetarian low-cholesterol diet consists of at least six servings of whole grain foods, three or more servings of green leafy vegetables, two to four servings of fruit, two to four servings of legumes, and one or two servings of non-fat dairy products daily.

A second diet is the Asian diet, with brown rice being the staple. Other allowable foods include fish, vegetables such as bok choy, bean sprouts, and black beans. It allows for one weekly serving of meat and very few dairy products. The food is flavored with traditional Asian spices and condiments, such as ginger , chilies, turmeric , and soy sauce.

Another regimen is the low glycemic or diabetic diet, which can raise the HDL (good cholesterol) level by as much as 20% in three weeks. Low glycemic foods promote a slow but steady rise in blood sugar levels following a meal, which increases the level of HDL. They also lower total cholesterol and triglycerides. Low glycemic foods include certain fruits, vegetables, beans, and whole grains. Processed and refined foods and sugars should be avoided.

Exercise is an extremely important part of lowering bad cholesterol and raising good cholesterol. It should consist of 20-30 minutes of vigorous aerobic exercise at least three times a week. Exercises that cause the heart to beat faster include fast walking, bicycling, jogging, roller skating, swimming, and walking up stairs. There also are a wide selection of aerobic programs available at gyms or on videocassette.

Garlic

A number of clinical studies have indicated that garlic can offer modest reductions in cholesterol. A 1997 study by nutrition researchers at Pennsylvania State University found men who took garlic capsules for five months reduced their total cholesterol by 7% and LDL by 12%. Another study showed that seven cloves of fresh garlic a day significantly reduced LDL, as did a daily dose of four garlic extract pills. Other studies in 1997 and 1998 back up these results. However, two more recent studies have questioned the effectiveness of garlic in lowering "bad cholesterol."

Cholestin

Cholestin hit the over-the-counter market in 1997 as a cholesterol-lowering dietary supplement. It is a processed form of red yeast fermented with rice, a traditional herbal remedy used for centuries by the Chinese. Two studies released in 1998 showed Cholestin lowered LDL cholesterol by 20-30%%. It also appeared to raise HDL and lower triglyceride levels. Although the supplement contains hundreds of compounds, the major active LDL-lowering ingredient is lovastatin, a chemical also found in the prescription drug Mevacor. The FDA banned Cholestin in early 1998 but a federal district court judge lifted the ban a year later, ruling the product was a dietary supplement, not a drug. It is not fully understood how the substance works and patients may want to consult with their physician before taking Cholestin. No serious side effects have been reported, but minor side effects, including bloating and heartburn , have been reported.

Other treatments

A study released in 1999 indicated that blue-green algae contains polyunsaturated fatty acids that lower cholesterol. The algae, known as alga Aphanizomenon flosaquae (AFA) is available as an over-the-counter dietary supplement. Niacin, also known as nicotinic acid or vitamin B₃, has been shown to reduce LDL levels by 10-20%, and raise HDL levels by 15-35%. It also can reduce triglycerides. But because an extremely high dose of niacin (2-3 grams) is needed to treat cholesterol problems, it should only be taken under a doctor's supervision to monitor possible toxic side effects. Niacin also can cause flushing when taken in high doses. Soy protein with high levels of isoflavones also have been shown to reduce bad cholesterol by up to 10%. A daily diet that contains 62 mg of isoflavones in soy protein is recommended, and can be incorporated into other diet regimens, including vegetarian, Asian, and low glycemic. In 2003, research revealed that policosanol, a substance made from sugar cane wax or beeswax, lowered LDL cholesterol nearly 27% in study subjects in a Cuban study.

Allopathic treatment

A wide variety of prescription medicines are available to treat cholesterol problems. These include statins such as Mevacor (lovastatin), Lescol (fluvastatin), Pravachol (pravastatin), Zocor (simvastatin), Baycol (cervastatin), and Lipitor (atorvastatin) to lower LDL. A group of drugs called fibric acid derivatives are used to lower triglycerides and raise HDL. These include Lopid (gemfibrozil), Atromid-S (clofibrate), and Tricor (fenofibrate).

A new class of drugs was identified late in 2001 that work differently from the statin drugs. These drugs rely on compounds that bind to a sterol that regulates protein (called SCAP) and speds up removal of cholesterol from the plasma (the fluid part of the blood.) Doctors decide which drug to use based on the severity of the cholesterol problem, side effects, and cost.

Expected results

High cholesterol is one of the key risk factors for heart disease. Left untreated, too much bad cholesterol can clog the blood vessels, leading to chest pain (angina ), blood clots , and heart attacks. Heart disease is the number one killer of men and women in the United States. By reducing LDL, people with heart disease may prevent further heart attacks and strokes, prolong and improve the quality of their lives, and slow or reverse cholesterol buildup in the arteries. In people without heart disease, lowering LDL can decrease the risk of a first heart attack or stroke.

KEY TERMS

Polyunsaturated fats

—A non-animal oil or fatty acid rich in unsaturated chemical bonds not associated with the formation of cholesterol in the blood.

Prevention

The best way to prevent cholesterol problems is through a combination of healthy lifestyle activities, a primarily low-fat and high-fiber diet , regular aerobic exercise, not smoking, and maintaining an optimal weight. In a small 2003 Canadian study, people who ate a low-fat vegetarian diet consisting of foods that are found to help lower cholesterol dropped their levels of LDL cholesterol as much as results from some statin drugs. But for people with high risk factors for heart disease, such as a family history of heart disease, diabetes, and being over the age of 45, these measures may not be enough to prevent the onset of high cholesterol. There are studies being done on the effectiveness of some existing anti-cholesterol drugs for controlling cholesterol levels in patients who do not meet the criteria for high cholesterol but no definitive results are available.

Resources

BOOKS

Bratman, Steven and David Kroll. Natural Pharmacist: Natural Treatments for High Cholesterol. Roseville, CA: Prima Publishing, 2000.

Ingels, Darin. The Natural Pharmacist: Your Complete Guide to Garlic and Cholesterol. Roseville, CA: Prima Publishing, 1999.

Murray, Michael T. Natural Alternatives to Over-the-Counter and Prescription Drugs New York: William Morrow & Co., 1999.

Trubo, Richard. Cholesterol Cures: From Almonds and Antioxidants to Garlic, Golf, Wine and Yogurt. Emmaus, PA: Rodale Press, 1996.

PERIODICALS

"Both Genetics and Diet Influence Cholesterol Levels." Heart Disease Weekly (October 14, 2001).

Carter, Ann. "Cholesterol in Your Diet." Clinical Reference Systems (July 1, 1999): 282.

"Chemical Engineers Suggest Alzheimer Onset Tied to Cholesterol." Pain and Central Nervous System Week (December 24, 2001):3.

"Eating a Vegetarian Diet that Includes Cholesterol-lowering Foods may Lower Lipid Levels as Much as Some Medications." Environmental Nutrition (March 2003):8.

"Researchers Identify New Class of Cholesterol-Lowering Drugs." Heart Disease Weekly (December 23, 2001):14.

Sage, Katie. "Cut Cholesterol with Policosanol: This Supplement Worked Better than a Low-fat Diet in One Study." Natural Health (March 2003):32.

Marandino, Cristin. "The Case for Cholesterol." Vegetarian Times (August 1999): 10.

Schmitt, B.D. "Treating High Cholesterol Levels." Clinical Reference Systems (July 1, 1999): 1551.

VanTyne, Julia, and Davis, Lori. "Drop Your Cholesterol 25 to 100 Points." Prevention (November 1999): 110.

ORGANIZATIONS

National Cholesterol Education Program. NHLBI Information Center, P.O. Box 30105, Bethesda, MD 20824-0105. http://www.nhlbi.nih.gov.

Ken R. Wells

Teresa G. Odle

Cholesterol-Reducing Drugs

Definition

Cholesterol-reducing drugs are medicines that lower the amount of cholesterol (a fat-like substance) in the blood.

Purpose

Cholesterol is a chemical that can both benefit and harm the body. On the good side, cholesterol plays important roles in the structure of cells and in the production of hormones. But too much cholesterol in the blood can lead to heart and blood vessel disease. To complicate matters, not all cholesterol contributes to heart and blood vessel problems. One type, called high-density lipoprotein (HDL) cholesterol, or "good cholesterol," actually lowers the risk of these problems. The other type, low-density lipoprotein (LDL) cholesterol, or "bad cholesterol," is the type that threatens people's health. The names reflect the way cholesterol moves through the body. To travel through the bloodstream, cholesterol must attach itself to a protein. The combination of a protein and a fatty substance like cholesterol is called a lipoprotein.

Many factors may contribute to the fact that some people have higher cholesterol levels than others. A diet high in certain types of fats is one factor. Medical problems such as poorly controlled diabetes, an underactive thyroid gland, an overactive pituitary gland, liver disease or kidney failure also may cause high cholesterol levels. And some people have inherited disorders that prevent their bodies from properly using and eliminating fats. This allows cholesterol to build up in the blood.

Treatment for high cholesterol levels usually begins with changes in daily habits. By losing weight, stopping smoking, exercising more and reducing the amount of fat and cholesterol in the diet, many people can bring their cholesterol levels down to acceptable levels. However, some may need to use cholesterol-reducing drugs to reduce their risk of health problems.

Description

There are four different classes of cholesterol lowering drugs:

Bile acid sequesterants are drugs that act by binding with the bile produced by the liver. Bile helps the digestion and absorption of fats in the intestine. By blocking the digestion of fats, bile acid sequesterants prevent the formation of cholesterol. Drugs in this class include: cholestyramine (Questran); colestipol (Colestid); and colesevalam (Welchol).

HMG-CoA inhibitors, often called "statins," are drugs that block an enzyme called "3-hydroxy-3-methyl-glutaryl-coenzyme A reductase." This blocks one of the steps in converting fat to cholesterol. These are the most effective cholesterol lowering agents available and in recent years have received increased attention for their benefits beyond helping patients with high cholesterol. In 2003, researchers reported that people with heart failure but no coronary artery disease received benefits after only 14 weeks of statin therapy. In addition, some research has connected the drugs to reduced risk for depression and dementia. Drugs in this group include: atorvastatin (Lipitor); cerivastatin (Baycol); fluvastatin (Lescol); lovastatin (Mevacor); pravastatin (Pravachol); simvastatin (Zocor); and the newest approved drug rosuvastatin (Crestor).

Fibric acid derivatives include clofibrate (Atromid-S); gemfibrozil (Lopid); and fenofibrate (Tricor). Although these drugs are less effective than the statins at lowering total cholesterol, they may be able to lower the low-density lipoprotein (LDL) cholesterol while raising the high-density lipoprotein (HDL) cholesterol. They probably act by inhibiting lipoprotein lipase activity.

Niacin, or vitamin B-3, also is effective in lowering cholesterol levels. Although the normal vitamin dose of niacin is only 20 mg, the dose required to reduce cholesterol levels is at least 500 mg each day. Niacin probably helps reduce cholesterol by inhibiting very low density lipoprotein (VLDL) secretion in the bloodstream.

Recommended dosage

The recommended dosage depends on the type of cholesterol-reducing drug used. The prescribing physician or the pharmacist who filled the prescription can advise about the correct dosage.

Cholesterol-reducing drugs should be taken exactly as directed and doses should not be missed. Double doses should not be taken to make up for a missed dose.

Physicians may prescribe a combination of cholesterol-reducing drugs, such as pravastatin and colestipol. Following the directions for how and when to take the drugs is very important. The medicine may not work properly if both drugs are taken at the same time of day.

Niacin should not be taken at the same time as an HMG-CoA inhibitor, as this combination may cause severe muscle problems. If niacin is taken in an over-the-counter form, both the prescribing physician and pharmacist should be informed. There are no problems when the niacin is taken in normal doses as a vitamin.

The prescription should not be stopped without first checking with the physician who prescribed it. Cholesterol levels may increase when the medicine is stopped, and the physician may prescribe a special diet to make this less likely.

Precautions

Seeing a physician regularly while taking cholesterol-reducing drugs is important. The physician will check to make sure the medicine is working as it should and will decide whether it is still needed. Blood tests and other medical tests may be ordered to help the physician monitor the drug's effectiveness and check for side effects.

For most people, cholesterol-reducing drugs are just one part of a whole program for lowering cholesterol levels. Other important elements of the program may include weight loss, exercise, special diets, and changes in other habits. The medication should never be viewed as a substitute for other measures ordered by the physician. Cholesterol-reducing drugs will not cure problems that cause high cholesterol; they will only help control cholesterol levels.

People over 60 years of age may be unusually sensitive to the effects of some cholesterol-reducing drugs. This may increase the chance of side effects.

Anyone who is taking an HMG-CoA reductase inhibitor should notify the health care professional in charge before having any surgical or dental procedures or receiving emergency treatment.

Special conditions

People who have certain medical conditions or who are taking certain other medications may have problems if they take cholesterol-reducing drugs. Before taking these drugs, the prescribing physician should be informed of any of the following conditions:

ALLERGIES. Anyone who has had unusual reactions to cholesterol-reducing drugs in the past should inform the prescribing physician before taking the drugs again. The physician also should be told about any allergies to foods, dyes, preservatives, or other substances.

PREGNANCY. Studies of laboratory animals have shown that giving high doses of gemfibrozil during pregnancy increases the risk of birth defects and other problems, including death of the unborn baby. The effects of this drug have not been studied in pregnant women. Women who are pregnant or who may become pregnant should check with their physicians before using gemfibrozil.

Cholesterol-reducing drugs in the group known as HMG-CoA reductase inhibitors (such as lovastatin, fluvastatin, pravastatin and simvastatin) should not be taken by women who are pregnant or who plan to become pregnant soon. By blocking the production of cholesterol, these drugs prevent a fetus from developing properly. Women who are able to bear children should use an effective birth control method while taking these drugs. Any woman who becomes pregnant while taking these drugs should check with her physician immediately.

Cholestyramine and colestipol will not directly harm an unborn baby, because these drugs are not taken into the body. However, the drugs may keep the mother's body from absorbing vitamins that she and the baby need. Pregnant women who take these drugs should ask their physicians whether they need to take extra vitamins.

BREASTFEEDING. Because cholestyramine and colestipol interfere with the absorption of vitamins, women who use these drugs while breastfeeding should ask their physicians if they need to take extra vitamins.

Women who are breastfeeding should talk to their physicians before using gemfibrozil. Whether this drug passes into breast milk is not known. But because animal studies suggest that it may increase the risk of some types of cancer, women should carefully consider the safety of using it while breastfeeding.

HMG-CoA reductase inhibitors (such as lovastatin, pravastatin, fluvastatin and simvastatin) should not be used by women who are breastfeeding their babies.

OTHER MEDICAL CONDITIONS. Cholesterol-reducing drugs may make some medical problems worse. Before using these drugs, people with any of these medical conditions should make sure their physicians are aware of their conditions:

• stomach problems, including stomach ulcer
• constipation
• hemorrhoids
• gallstones or gallbladder disease
• bleeding problems
• underactive thyroid
• heart or blood vessel disease

In addition, people with kidney or liver disease may be more likely to have blood problems or other side effects when they take certain cholesterol-reducing drugs. And some drugs of this type may actually raise cholesterol levels in people with liver disease.

Patients with any of the following medical conditions may develop problems that could lead to kidney failure if they take HMG-CoA reductase inhibitors:

• treatments to prevent rejection after an organ transplant
• recent major surgery
• seizures (convulsions) that are not well controlled

People with phenylketonuria (PKU) should be aware that sugar-free formulations of some cholesterol-reducing drugs contain phenylalanine in aspartame. This ingredient can cause problems in people who have phenylketonuria.

USE OF CERTAIN MEDICINES. Cholesterol-reducing drugs may change the effects of other medicines. Patients should not take any other medicine that has not been prescribed or approved by a physician who knows they are taking cholesterol-reducing drugs.

Side effects

Gemfibrozil

Studies in animals and humans suggest that gemfibrozil increases the risk of some types of cancer. The drug may also cause gallstones or muscle problems. Patients who need to take this medicine should ask their physicians for the latest information on its benefits and risks.

Patients taking gemfibrozil should check with a physician immediately if any of these side effects occur:

• fever or chills
• severe stomach pain with nausea and vomiting
• pain in the lower back or side
• pain or difficulty when urinating
• cough or hoarseness

HMG-CoA reductase inhibitors

These drugs may damage the liver or muscles. Patients who take the drugs should have blood tests to check for liver damage as often as their physician recommends. Any unexplained pain, tenderness or weakness in the muscles should be reported to the physician at once.

All cholesterol-reducing drugs

Minor side effects such as heartburn, indigestion, belching, bloating, gas, nausea or vomiting, stomach pain, dizziness and headache usually go away as the body adjusts to the drug and do not require medical treatment unless they continue or they interfere with normal activities.

Patients who have constipation while taking cholesterol-reducing drugs should bring the problem to a physician's attention as soon as possible.

Additional side effects are possible. Anyone who has unusual symptoms while taking cholesterol-reducing drugs should get in touch with his or her physician.

Interactions

Cholesterol-reducing drugs may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes cholesterol-reducing drugs should let the physician know all other medicines he or she is taking and should ask whether the possible interactions can interfere with drug therapy. Examples of possible interactions are listed below.

Some cholesterol-reducing drugs may prevent the following medicines from working properly:

• thyroid hormones
• water pills (diuretics)
• certain antibiotics taken by mouth, such as tetracyclines, penicillin G and vancomycin
• the beta-blocker Inderal, used to treat high blood pressure
• digitalis heart medicines
• phenylbutazone, a nonsteroidal anti-inflammatory drug

Taking some cholesterol-reducing drugs with blood thinners (anticoagulants) may increase the chance of bleeding.

KEY TERMS

Cell— The basic unit that makes up all living tissue.

Cholesterol— Fatty substance found in tissue. Necessary to maintain a healthy body.

Enzyme— A type of protein, produced in the body, that brings about or speeds up chemical reactions.

Hormone— A substance that is produced in one part of the body, then travels through the bloodstream to another part of the body where it has its effect.

Phenylketonuria— (PKU) A genetic disorder in which the body lacks an important enzyme. If untreated, the disorder can lead to brain damage and mental retardation.

Pituitary gland— A pea-sized gland at the base of the brain that produces many hormones that affect growth and body functions.

Combining HMG-CoA reductase inhibitors with gemfibrozil, cyclosporine (Sandimmune) or niacin may cause or worsen problems with the kidneys or muscles.

Resources

BOOKS

Nesto, R. W., and L. Christensen. Cholesterol-Lowering Drugs: Everything You and Your Family Need to Know. New York: Morrow, William & Co, 2000.

PERIODICALS

"Cholesterol Drug Helps Heart Failure Patients Without High Cholesterol." Heart Disease Weekly August 24, 2003: 33.

"Link to Cholesterol Drugs Disputed." Cardiovascular Week September 29, 2003: 73.

Mechcatie, Elizabeth. "FDA Okays Rosuvastatin for Hypercholeterolemia: Most Potent Statin to Date." Internal Medicine News September 1, 2003: 30-31.

Cholesterol

History

Properties and occurrence

Cholesterol in the human body

Cholesterol and health

Resources

Cholesterol (sometimes also known as cholesterin) is the principle sterol (an ester of a fatty acid and an aromatic [ring structure] complex alcohol) found in all animal tissues. Cholesterol is found in humans in both free and esterified forms. It was first isolated from humans in gallstones. Cholesterol is now commercially obtained from cattle spinal cords or from lanosterol—the fatty coating of sheep wool. High levels of cholesterol have been implicated in some forms of atherosclerosis (a disease caused by the thickening of arterial walls).

Cholesterol is a complex organic compound with the molecular formula C₂₇H₄₆O. It is a member of the biochemical family of compounds known as the lipids. Other lipids, such as waxes, fats, and oils, share not a structural similarity (as is the case with most families of compounds), but a physical property; they are all insoluble in water, but are soluble in organic liquids.

Cholesterol belongs more specifically to a class of compounds known as the steroids. Most steroids are naturally occurring compounds that play critical roles in plant and animal physiology and biochemistry. Other steroids include sex hormones, certain vitamins, and adrenocorticoid hormones. All steroids share a common structural unit, a four-ring structure known as the perhydrocyclopentanophenanthrene ring system or, more simply, the steroid nucleus.

History

Although cholesterol had been isolated as early as 1770, productive research on its structure did not begin until the twentieth century. Then, in about 1903, German chemist Adolf Windaus (1876–1959) decided to concentrate on finding the molecular composition of the compound. Windaus eventually worked out a detailed structure for cholesterol, an accomplishment that was partially responsible for his earning the 1928 Nobel Prize in chemistry.

Later research showed that the structure proposed by Windaus was in error. By the early 1930s, however, additional evidence from x-ray analysis allowed Windaus’ long-time colleague, German chemist Heinrich Wieland, (1877–1957), along with others, to determine the correct structure for the cholesterol molecule.

The next step in understanding cholesterol, synthesizing the compound, was not completed for another two decades. In 1951, American chemist Robert B. Woodward (1917–1979) completed that line of research when he synthesized cholesterol starting with simple compounds. For this accomplishment and his other work in synthesizing large molecule compounds, Woodward was awarded the 1965 Nobel Prize in chemistry.

Properties and occurrence

Cholesterol crystallizes from an alcoholic solution as pearly white or pale yellow granules or plates. It is waxy in appearance and has a melting point of 299.3°F (148.5°C) and a boiling point of 680°F (360°C) (with some decomposition). It has a specific gravity of 1.067. Cholesterol is insoluble in water, but slightly soluble in alcohol and somewhat more soluble in ether and chloroform.

Cholesterol occurs in almost all living organisms with the primary exception of microorganisms. Of the cholesterol found in the human body, about 93% occurs in cells and the remaining 7% in the circulatory system. The brain and spinal cord are particularly rich in the compound. About 10% of the former’s dry weight is due to cholesterol. An important commercial source of the compound is spinal fluid taken from cattle. Cholesterol is also found in myelin, the material that surrounds nerve strands. Gallstones are nearly pure cholesterol.

The concentration of cholesterol in human blood varies rather widely, from a low of less than 200 mg/dL (milligrams per deciliter) to a high of more than 300 mg/dL. It is also found in bile, a source from which, in fact, it gets its name: chole (Greek for bile) and stereos (Greek for solid).

Cholesterol in the human body

Cholesterol is a critically important compound in the human body. It is synthesized in the liver and then used in the manufacture of bile, hormones, and nerve tissue.

It is also a part of the human diet. A single egg yolk for example, contains about 250 mg of cholesterol. Organ meats are particularly rich in the compound. A 3-oz (85 g) serving of beef liver, for example, contains about 372 mg of cholesterol, and a similar-size serving of calves’ brain has about 2, 700 mg of the compound. Because diets differ from culture to culture, the amount of cholesterol an individual consumes differs widely around the world. The average European diet includes about 500 mg of cholesterol a day, but the average Japanese diet includes only about 130 mg a day. The latter fact reflects a diet in which fish rather than meat tends to predominate.

The human body contains a feedback mechanism that keeps the serum concentration of cholesterol approximately constant. The liver itself manufactures about 600 mg of cholesterol a day, but that output changes depending on the intake of cholesterol in the daily diet. As a person consumes more cholesterol, the liver reduces its production of the compound. If one’s intake of cholesterol greatly exceeds the body’s needs, excess cholesterol may then precipitate out of the blood and be deposited on arterial linings.

Cholesterol and health

Some of the earliest clues about possible ill effects of cholesterol on human health came from the research of Russian biologist Nikolai in the 1910s. Anitschkow (1885–1964) fed rabbits a diet high in cholesterol and found that the animals became particularly susceptible to circulatory disorders. Post-mortem studies of the animals found the presence of plaques (clumps) of cholesterol on their arterial walls.

Since Anitschkow’s original research, debate has raged over the relationship between cholesterol intake and circulatory disease, particular atherosclerosis (the blockage of coronary arteries with deposits of fatty material). Over time, it has become increasingly obvious that high serum cholesterol levels do have some association with such diseases. A particularly powerful study in forming this conclusion has been the ongoing Framingham Study, conducted since 1948 by the National Heart Institute in the Massachusetts town that has given its name to the research. Among the recommendations evolving out of that study has been that a reduced intake of cholesterol in one’s daily diet is one factor in reducing the risk of heart disease.

The cholesterol-heart disease puzzle is not completely solved. One of the remaining issues concerns the role of lipoproteins in the equation. Since cholesterol is not soluble in water, it is transported through the blood stream bound to molecules containing both

KEY TERMS

Bile —A greenish yellow liquid, secreted by the liver and stored in the gall bladder, that aids in the digestion of fats and oils in the body.

Circulatory system —The body system that circulates blood pumped by the heart through the blood vessels to the body tissues.

Lipid —A family of biochemical compounds soluble in many organic solvents, but not in water.

Steroids —A group of organic compounds that belong to the lipid family and that include many important biochemical compounds including the sex hormones, certain vitamins, and cholesterol.

Synthesis —A chemical process by which some new substance is produced by reacting other substances with each other

fat and protein components, called lipoproteins. These lipoproteins are of two kinds, high-density lipoproteins (HDLs) and low-density lipoproteins (LDLs). For some time, researchers have thought that LDL is particularly rich in cholesterol and, therefore, bad, while HDL is low in cholesterol and, therefore, good. While this analysis may be another step in the right direction, it still does not provide the final word on the role of cholesterol in the development of circulatory diseases.

See also Lipid; Nervous system.

Resources

BOOKS

Betteridge, John. Clinicians’ Guide to Lipids and Coronary Heart Disease. London, UK, and Arnold, NY: Oxford University Press, 2003.

Teaque, Michael L. Your Health Today: Choices in a Changing Society. Boston, MA: McGraw Hill, 2007.

OTHER

American Heart Association. “Cholesterol.” <http://www.americanheart.org/presenter.jhtml?identifier=4488> (accessed October 5, 2006).

National Heart, Lung, and Blood Institute. “Live Healthier, Live Longer: Cholesterol Counts For Everyone.” <http://www.nhlbi.nih.gov/chd/> (accessed October 5, 2006).

David E. Newton