Cholesterol: what is it? What is cholesterol? What does cholesterol consist of?

It is found in all tissues and body fluids both in a free state and in the form of esters with fatty acids, mainly linoleic acid (about 10% of total cholesterol). Cholesterol synthesis occurs in all cells of the body. The main transport forms in the blood are α‑, β‑ and preβ‑lipoproteins (or, respectively, high-, low- and very low-density lipoproteins). In blood plasma, cholesterol is found mainly in the form of esters (60-70%). Esters are formed either in cells in a reaction catalyzed by acyl-CoA cholesterol acyltransferase, which uses acyl-CoA as a substrate, or in plasma as a result of the enzyme lecithin cholesterol acyltransferases, which transfers a fatty acid from the second carbon atom of phosphatidylcholine to the hydroxyl group of cholesterol. In blood plasma, the main sources of cholesterol and phosphatidylcholine for the reaction are high- and low-density lipoproteins; most of the plasma cholesterol esters are formed in this way.

To determine the cholesterol level in the blood, the following methods are used:

1. Titrometric.
2. Gravimetric.
3. Nephelometric.
4. Thin layer and gas-liquid chromatography.
5. Polarographic methods allow the determination of total and free cholesterol in the presence of the enzymes cholesterol oxidases and cholesterol esterases.
6. Fluorimetry by reaction with O phthalic aldehyde and other reagents.
7. Enzymatic methods - determination takes place in one test tube, but in several stages: enzymatic hydrolysis of cholesterol esters, oxidation of cholesterol with atmospheric oxygen to form cholest-4-en-3-ol and hydrogen peroxide. The enzymes used are cholesterol oxidase, cholesterol esterase, peroxidase, and catalase. The progress of the reaction can be recorded:

• spectrophotometrically based on the accumulation of cholestenol.
• by the loss of oxygen in the environment.
• By changing the color of the solution, 4‑hydroxybenzoate, 4‑aminophenazone, 4‑aminoantipyrine are used as chromogens - indicators of the progress of reactions.

All these methods are very specific and highly reproducible.

1. Colorimetric methods based on the following color reactions:

• Biol-Croft reaction using potassium persulfate, acetic and sulfuric acid and with the appearance of a red color.
• the Wrigley reaction, based on the interaction of cholesterol with a reagent containing methanol and sulfuric acid.
• Chugaev's reaction, in which a red color appears after the reaction of cholesterol with acetyl chloride and zinc chloride.
• the Liebermann-Burkhard reaction, in which cholesterol is oxidized in a strongly acidic, absolutely anhydrous medium to form conjugated double bonds. As a result, a compound of cholestagexaene with concentrated sulfuric acid of emerald green color is formed with an absorption maximum at 410 and 610 nm. A feature of this reaction is the lack of color stability. In the literature you can find different ratios of ingredients in the Liebermann-Burkhard reagent: the higher the content of acetic anhydride, the faster the reaction proceeds. The reaction is facilitated by sulfosalicylic, paratoluene sulfonic, and dimethylbenzene-sulfonic acids. With cholesterol esters, the reaction proceeds more slowly than with free cholesterol, the rate increases with increasing temperature, and light has a destructive effect on the reaction products. All methods based on the Liebermann-Burkhard reaction are divided into direct and indirect:

• the Kalyani-Zlatkis-Zak reaction, which consists in the appearance of a red-violet color of the solution during the oxidation of cholesterol with ferric chloride in acetic and concentrated sulfuric acids. This reaction is 4-5 times more sensitive than the Liebermann-Burkhard reaction, but less specific.

The unified methods are the colorimetric methods of Ilk and Kalyani-Zlatkis-Zak.

in blood serum using the Ilk method

Principle

Based on the Liebermann-Burkhard reaction: in a strongly acidic environment in the presence of acetic anhydride, cholesterol dehydrates to form greenish-blue colored bischolestadienylmonosulfonic acid.

Normal values

Determination of the amount of total cholesterol
in blood serum using the Zlatkis-Zak method

Principle

Free and ester-bound cholesterol is oxidized by ferric chloride in the presence of acetic, sulfuric and phosphoric acids to form unsaturated products colored violet-red.

Normal values

Determination of total cholesterol content
enzymatic method according to the "Novohol" kit

Principle

Based on the use of coupled enzymatic reactions catalyzed by: 1) cholesterol esterase, which catalyzes the hydrolysis of cholesteryl esters to free cholesterol; 2) cholesterol oxidase, which catalyzes the conversion of cholesterol to cholestenone with the formation of hydrogen peroxide; 3) peroxidase, which catalyzes the oxidation of 4‑aminoantipyrine with hydrogen peroxide in the presence of phenol to form a pink-crimson colored product.

Normal values

Influencing factors

Overestimation of results with colorimetric research methods occurs when there is a high content of bilirubin, hemoglobin, and vitamin A in the sample; with the enzymatic method - oxycorticosteroids and the use of anticoagulants (fluorides, oxalates).

Serum

A significant increase in cholesterol content is observed with hyperlipoproteinemia type IIa (familial hypercholesterolemia), type IIb and III (polygenic hypercholesterolemia, familial combined hyperlipidemia), a moderate increase is observed with hyperlipoproteinemia type I, IV, V, as well as liver diseases (intra- and extrahepatic cholestasis) , kidney diseases, malignant tumors of the pancreas, hypothyroidism, diseases of the cardiovascular system, pregnancy, diabetes.

A decrease is detected in hyperthyroidism, liver cirrhosis, malignant liver tumors, hypoproteinemia and ab-lipoproteinemia.

Cerebrospinal fluid

The accumulation of cholesterol is detected in meningitis, a brain tumor or abscess, cerebral hemorrhages, and multiple sclerosis.

A decrease in values ​​is found in cerebral and cortical atrophy.

Determination of the concentration of free and
esterified cholesterol in blood serum

Free cholesterol is capable of forming sparingly soluble compounds with digitonin, tomatine, and pyridine sulfate. Most often, an aqueous-alcoholic or isopropanol solution of digitonin is used.

Principle

Cholesterol is extracted from whey using isopropyl alcohol, the extract is divided into two parts, and the content of total cholesterol is determined in one. In another portion of the extract, free cholesterol is precipitated with digitonin, the supernatant is discarded, and the precipitate is dissolved and the content of free cholesterol is determined by any method. The content of esterified cholesterol is calculated as the difference between total and free.

Normal values

Clinical and diagnostic value

The cholesterol esterification coefficient is an important functional test of the liver. The decrease in the coefficient is proportional to the decrease in liver function: acute and exacerbation of chronic hepatitis, obstructive jaundice, cirrhosis of the liver. The degree of esterification also depends on the activity of the serum enzyme lecithin-cholesterol acyl-transferase, so storing the sample at room temperature may change the ratio between the free and esterified cholesterol fraction.

Determination of α-cholesterol content

Principle

The separation of α- and β-lipoproteins is based on the selective ability of very low and low density lipoproteins to form insoluble complexes with heparin in the presence of divalent Mn 2+ cations. High-density lipoproteins remain in the supernatant, where the α-cholesterol content is determined by any method.

Determination of α-cholesterol is used to calculate atherogenic index:

Normal values

Clinical and diagnostic value

The increase in α-cholesterol concentration is not clinically significant and is observed in benign conditions. A decrease in α-cholesterol levels indicates a threat of atherosclerosis.

Increasing atherogenic index up to 4 or more is observed in coronary heart disease and atherosclerosis.

Egg yolks contain a lot of cholesterol, so you can fry one white without vegetable oil.

Heart attacks and strokes are the cause of almost 70% of all deaths in the world. Seven out of ten people die due to a blockage in the heart or brain. In almost all cases, the reason for such a terrible end is one - high cholesterol. . as cardiologists call it, it kills millions of people every year.

Conditions for lowering cholesterol

It's easy to conclude. that if you give up these bad habits, put your body in order, then everything will be fine.

• Physical activity is important and necessary, but not all physical exercises are suitable for a person who already has plaque in the arteries.
• Special diet. It is necessary to limit the intake of saturated fats from food, which inevitably increase cholesterol levels. Most of them are found in pork and beef meat, butter, cheese and refined oils. Such products can easily be replaced with chicken, fish, olive or unrefined corn oil. It is not a “low-fat” diet that helps reduce “bad” cholesterol, but a low-carbohydrate diet.
• Significantly increase your intake of foods high in fiber: oats, corn and rice bran, legumes and all vegetables. It is enough to eat some walnuts, wheat germ, a couple of cloves of raw garlic and drink a few cups of green tea every day to quickly reduce blood cholesterol.
• If there is such a hereditary predisposition, then it is all the more necessary to lead a healthy lifestyle and check your cholesterol levels. If you need to use medications, see a doctor.

There is a widespread misconception that cholesterol is harmful to the body, and its level in the blood is one of the most important indicators of human health. Many people, in an attempt to maintain their health, adhere to strict diets, eliminating all foods containing cholesterol. However, few people know that it is part of cell membranes, gives them strength and ensures the exchange of substances between the cell and the intercellular substance and regulates the activity of enzymes. Thus, without cholesterol, the normal functioning of our body is impossible.

Despite the importance of cholesterol, excessive consumption of fatty foods of animal origin can lead to increased cholesterol levels in the body, which negatively affects health and can cause serious illness.

Controlling cholesterol levels will help maintain your health for many years, increase the body's natural resistance, increase life expectancy and improve its quality. In this article we will dispel the most common myths about the role of cholesterol in our body and its metabolism. We'll also look at the most effective ways to control your cholesterol levels.

Cholesterol (from the Greek chole - bile and stereo - hard, hard) was first identified in gallstones, hence its name. It is a natural, water-insoluble lipophilic alcohol. About 80% of cholesterol is synthesized in the body (liver, intestines, kidneys, adrenal glands, gonads), the remaining 20% ​​must come from the food we consume.

Circulating in the bloodstream, cholesterol is used, if necessary, as a building material, as well as for the synthesis of more complex compounds. Since it is insoluble in water (and, accordingly, in the blood), its transportation is possible only in the form of complex water-soluble compounds, which are divided into 2 types:

Low-density lipoproteins (LDL)

High density lipoproteins (HDL)

Both of these substances must be in a strictly defined ratio, and their total volume must also not exceed the norm. This can lead to serious cardiovascular diseases.

Functions of cholesterol in the body:

— ensuring the strength of cell walls, regulating their permeability to various molecules;

— synthesis of vitamin D;

- synthesis by the adrenal glands of steroid (cortisone, hydrocortisone), male (androgens) and female (estrogens, progesterone) sex hormones;

- in the form of bile acids, it participates in the formation of bile and the absorption of fats during digestion;

- participates in the formation of new synapses in the brain, thereby improving mental abilities and memory.

In fact, it is not cholesterol as such that causes harm, but its fluctuations outside the normal range. Health problems can be caused by both excess and deficiency in the body.

Negative effects of cholesterol

According to statistics, people who died from cardiovascular diseases had low levels of high-density lipoproteins, but high levels of low-density lipoproteins.

Lipoproteins, if their ratio is incorrect or if their content in the blood is prolonged for a long time, can settle on the walls of blood vessels and cause atherosclerosis.

This dangerous disease occurs when plaques form on the endothelium of blood vessels, which over time grow more and more and accumulate calcium. As a result, the lumen of the vessels narrows, they lose elasticity (stenosis), this leads to a decrease in the supply of oxygen and nutrients to the heart and tissues and the development of angina pectoris (cessation of arterial blood flow to certain parts of the heart due to blockage of the coronary artery, accompanied by pain and discomfort in the chest) . Often, a heart attack or myocardial infarction occurs due to impaired blood supply. The formation of cholesterol plaques leads to damage to the inner wall of blood vessels; a blood clot can form, which can subsequently block the artery or break off and cause an embolism. Also, a vessel that has lost elasticity can burst when pressure in the bloodstream increases.

The role of lipoproteins

HDL is considered a “good” lipoprotein due to its ability to dissolve cholesterol plaques and remove it from artery walls; the higher its percentage relative to LDL (“bad” lipoprotein), the better. LDL transports cholesterol from the organs that synthesize it into the arteries, and when the content of this compound is elevated, these large insoluble molecules aggregate in the form of fatty plaques, attach to the vessels and clog them. Having undergone oxidative processes, cholesterol loses its stability and can easily penetrate into the thickness of the artery walls.

Specific antibodies begin to be produced in large quantities against the resulting oxidized LDL, which leads to severe damage to the artery walls. In addition, cholesterol helps reduce nitric oxide levels, increasing the risk of developing cardiovascular diseases.

Nitric oxide plays an important role in the body:

— dilates blood vessels, lowers blood pressure, prevents the formation of blood clots in the bloodstream;

- plays an important role in the fight against bacteria and viruses that enter the body, destroys cancer cells;

— increases the endurance of muscle tissue;

- participates in the exchange of information between different cells, is a neurotransmitter in synapses.

HDL not only removes cholesterol from the blood back to the liver, but also prevents the oxidation of LDL.

Signs of increased cholesterol levels in the body

Increased cholesterol levels are associated with impaired lipid (fat) metabolism. This can be a symptom not only of atherosclerosis, but also of other serious diseases:

- liver;

— kidneys (chronic renal failure, glomerulonephritis);

- pancreas (chronic pancreatitis);

- diabetes mellitus (a serious disease associated with impaired synthesis of the islets of Langerhans by beta cells in the pancreas);

— hypothyroidism (decreased synthesis of hormones by the thyroid gland);

- obesity.

Symptoms of atherosclerosis are caused by a narrowing of the lumen of blood vessels as a result of prolonged and persistent elevated cholesterol levels, and deterioration of blood circulation in different parts of the bloodstream.

Main symptoms:

- angina pectoris (sudden discomfort or pain in the chest that occurs during physical activity or emotional stress);

- shortness of breath;

- arrhythmia (heart rhythm disturbance);

- cyanosis and swelling of peripheral parts of the body (fingers, toes);

- periodic leg cramps (intermittent claudication);

- memory impairment, inattention;

- decreased intellectual abilities;

- yellow-pink lipid deposits in the skin (xanthomas), most often observed on the skin of the eyelids and in the ankle joints.

The impact of HDL and LDL levels on our health

Still, the opinion is that the total level of lipoproteins HDL and LDL affects the state of health and their increase entails dire consequences for the functioning of the entire body. However, this statement is not entirely true. Yes, the above diseases will be accompanied by an increased content of lipoproteins in general, but what is much more important is the exact ratio of “good” HDL and “bad” LDL in the blood. It is the violation of this proportion that leads to health problems. When determining the content of lipoproteins in the blood, 4 indicators are taken into account: the total amount of cholesterol, the level of HDL, LDL and triglycerides.

Norms

Total cholesterol in the blood - 3.0 - 5.0 mmol/l;

With the threat of atherosclerosis, total cholesterol rises to 7.8 mmol/l;

LDL at men- 2.25 - 4.82 mmol/l;

LDL in women- 1.92 - 4.51 mmol/l;

HDL at men- 0.72 - 1.73 mmol/l;

HDL at women- 0.86 - 2.28 mmol/l;

Triglyceridesin men- 0.52 - 3.7 mmol/l;

Triglyceridesamong women- 0.41 - 2.96 mmol/l.

The most indicative is the ratio of HDL and LDL against the background of total cholesterol levels. In a healthy body, HDL is much higher than LDL.

The most effective treatments for high cholesterol

There are many drugs that lower cholesterol levels in cases where this indicator poses a serious threat to health, or already at the beginning of the development of atherosclerosis. It is necessary to pay tribute, an important part of which is proper nutrition. In such cases, diet and moderate physical activity will help not only bring all blood counts back to normal, but will also completely heal and rejuvenate your body.

For a faster therapeutic effect, pharmacological drugs are used:

— Statins- the most popular drugs, the principle of their action is to inhibit the synthesis of cholesterol in the liver by blocking the corresponding enzymes. They are usually taken once a day before bed (at this time the active production of cholesterol in the body begins). The therapeutic effect occurs after 1-2 weeks of systematic use; long-term use does not cause addiction. Side effects may include nausea, abdominal and muscle pain, and in rare cases there may be individual sensitivity. Drugs of the statin group can reduce cholesterol levels by 60%, but if they are taken for a long time, it is necessary to regularly take tests for AST and ALT every six months. The most common statins are cerivastatin, fluvastatin, lovastatin.

— Fibrates stimulate the production of HDL, recommended for triglyceride levels of 4.5 mmol/l. It is highly not recommended to use it with statins. Side effects manifest themselves in the form of gastrointestinal disorders, flatulence, nausea, vomiting, and abdominal pain. Representatives of this group of drugs: clofibrate, fenofibrate, gemfibrozil.

— Bile acid sequestrants. This group of drugs is not absorbed into the blood, but acts locally - it binds to bile acids, which are synthesized from cholesterol, and removes them from the body naturally. The liver begins to increase the production of bile acids, using more cholesterol from the blood; a visible positive effect occurs a month after starting medication; simultaneous use of statins is possible to enhance the effect. Long-term use of drugs can lead to impaired absorption of fats and vitamins, and increased bleeding is possible. Side effects: flatulence, constipation. These drugs include: colestipol, cholestyramine.

— Cholesterol absorption inhibitors interfere with the absorption of lipids from the intestine. Drugs in this group can be prescribed to people who have contraindications to taking statins, since they are not absorbed into the blood. In Russia, only 1 drug from the group of cholesterol absorption inhibitors is registered - ezetrol.

The above measures are used in advanced cases, when it is necessary to quickly reduce cholesterol levels, and lifestyle changes cannot quickly produce the desired effect. But even when taking pharmacological agents, do not forget about prevention and harmless natural supplements, which, with long-term regular use, will help you prevent cardiovascular diseases in the future.

Folk remedies that help lower blood cholesterol levels

— Niacin (nicotinic acid, vitamin PP, vitamin B 3). The mechanism of action has not been fully studied, but experiments show that after just a few days of taking increased doses of the vitamin, the level of LDL and triglycerides in the blood decreases noticeably, but the amount of HDL increases up to 30%. Unfortunately, it does not reduce the risk of cardiovascular complications and attacks. For maximum effectiveness, you can combine niacin with other treatment methods.

— . Contained in fish oil and seafood, as well as cold-pressed (unrefined) vegetable oils. They have a positive effect on the nervous system, prevent rickets during the period of active growth, help lower cholesterol and blood pressure, improve blood circulation, strengthen blood vessels and give them elasticity, prevent their thrombosis, and participate in the synthesis of hormone-like substances - prostaglandins. Regular intake of sources of essential fatty acids will have a miraculous effect on the functioning of the entire body, in particular, it will help prevent the development of atherosclerosis.

— Vitamin E. An extremely strong antioxidant that prevents the breakdown of LDL and the formation of fatty plaques. For a positive effect to occur, it is necessary to constantly consume the vitamin in appropriate doses.

— Green tea contains polyphenols - substances that affect lipid metabolism, they reduce the level of “bad” cholesterol and increase the content of “good” cholesterol. In addition, tea contains antioxidants.

- Garlic. Fresh garlic is recommended to be consumed to reduce cholesterol levels and prevent the formation of clots in blood vessels (thin the blood). The active components of garlic are sulfur-containing compounds, in particular alliin.

— Soy protein. They are similar in action to estrogens - they reduce the likelihood of atherosclerosis. Genistein prevents LDL oxidation due to its antioxidant properties. In addition, soy stimulates the production of bile, thereby helping to remove cholesterol from the body.

— Vitamins B 6 (pyridoxine), B 9 (folic acid), B 12 (cyanocobalamin). A sufficient amount of these vitamins in the diet contributes to the proper functioning of the heart muscle and significantly reduces the risk of developing atherosclerosis and coronary heart disease.

What factors contribute to increased cholesterol levels and the development of atherosclerosis?

Most often, atherosclerosis affects people who have neglected their health for a long time. The sooner you change your lifestyle, the less likely you are to develop serious illnesses. Here are 4 main factors that contribute to high blood cholesterol:

— Passive lifestyle. With low mobility and lack of physical activity, the level of “bad” cholesterol increases, creating a threat of developing cardiovascular diseases.

— Obesity. Lipid metabolism disorders are closely related to high cholesterol levels. People who are overweight are prone to various diseases of the cardiovascular system.

— Smoking. Leads to narrowing of arteries, increased blood viscosity, thrombosis, and entails a risk of heart disease.

— Consumption of fatty animal products in large quantities leads to an increase in LDL.

— Heredity. The predisposition to high cholesterol levels is genetically transmitted. Therefore, people whose relatives suffer from this pathology should carefully monitor their health.

A healthy lifestyle as a method of combating cholesterol

As you maintain a healthy diet and an active lifestyle, your risk of developing various diseases decreases. This especially applies to people at risk. By changing your lifestyle, you improve the functioning of the whole body, even despite the tendency to any pathologies, internal defense mechanisms can easily cope with the threat.

Active sports improve metabolism, train the heart muscle at the same time as skeletal muscles, promote a better blood supply to all organs and systems (during physical activity, blood from the depot goes into the general channel, this contributes to better saturation of organs with oxygen and nutrients).

Sports exercises also lead to strengthening the walls of blood vessels and prevent the development of varicose veins.

Don't forget the importance of proper nutrition. You should not abuse strict diets. The body must receive all the nutrients it needs in optimal proportions, vitamins and minerals, and fiber. The diet should contain sufficient quantities of vegetables, fruits, cereals, lean meat, sea and ocean fish, unrefined vegetable oils, milk and fermented milk products. If there is a lack of any vitamins in the diet, it is worth periodically taking medications containing them to prevent vitamin deficiencies.

Quitting smoking will reduce the risk of developing not only atherosclerosis, but also a number of other diseases, such as bronchitis, stomach ulcers, and cancer.

Sport is the best remedy for stress and depression; it strengthens the nervous system. Regular physical activity, be it a jog in the park or 3 hours of exercise in the gym, helps relieve the negativity and irritation that has accumulated throughout the day; many athletes experience euphoria during training. It has been experimentally proven that active people are much less susceptible to stress than those who lead a sedentary lifestyle.

Conclusion

As you can already see, cholesterol is an extremely important compound that performs a number of vital functions. It is necessary for our life, but its amount in the body should not exceed normal limits. An imbalance in the ratio of high- and low-density lipoproteins entails serious consequences.

The best method of treatment is timely prevention. The most effective method to prevent high blood cholesterol levels is a healthy lifestyle.

When you give up bad habits and start adhering to the above rules, you will completely forget about your health problems.

Cholesterol. Myths and deception.

(hereinafter referred to as “X.”) is an organic compound from the class of steroids Steroids- a class of organic compounds widespread in nature. These include vitamins D, sex hormones, and adrenal hormones (corticosteroids). They are part of the molecules of steroid glycosides, including cardiac glycosides. Many steroids are obtained by chemical and microbiological synthesis.; the most important sterol in animals and humans. First isolated from gallstones (hence the name: Greek chole - bile). Colorless crystals with a melting point of 149 °C, insoluble in water, highly soluble in non-polar organic solvents.

A characteristic chemical property of cholesterol is the ability to form molecular complexes with many salts, acids, amines, proteins and neutral compounds such as saponins, vitamin D 3 (cholecalciferol), etc. Cholesterol is present in almost all living organisms Organism(from the medieval Latin organizo - arrange, impart a slender appearance) - a living being that has a set of properties that distinguish it from inanimate matter. Most organisms have a cellular structure. The formation of a complete organism is a process consisting of differentiation of structures (cells, tissues, organs) and functions and their integration both in ontogenesis and phylogenesis., including bacteria Bacteria- a group of microscopic, predominantly unicellular organisms. Globular (cocci), rod-shaped (bacillus, clostridia, pseudomonads), convoluted (vibrones, spirilla, spirochetes). Capable of growing both in the presence of atmospheric oxygen (aerobes) and in its absence (anaerobes). Many bacteria are causative agents of diseases in animals and humans. There are bacteria necessary for the normal process of life (Escherichia coli is involved in the processing of nutrients in the intestines, but when it is detected, for example, in urine, the same bacterium is considered to be the causative agent of kidney and urinary tract infections). and blue-green algae.

The chromium content in plants is usually low (with the exception of seed oils). In vertebrates, large amounts of chromium are contained in lipids Lipids(from the Greek “fat”), a large group of natural organic compounds, including fats and fat-like substances. Contained in all living cells. They form an energy reserve for the body, participate in the transmission of nerve impulses, in the creation of water-repellent and thermal insulating covers, etc. nervous tissue (where it is associated with the structural components of the myelin sheath), eggs and cells, in (the main organ of chromium biosynthesis), in the adrenal glands Adrenal glands- paired endocrine glands. The adrenal cortex secretes corticosteroid hormones, as well as partially male and female sex hormones, while the medulla secretes adrenaline and norepinephrine. The adrenal glands play an important role in regulating metabolism and in adapting the body to unfavorable conditions. Damage to the adrenal glands leads to diseases (Addison's disease, Itsenko-Cushing's disease, etc.)., in sebum and in cell walls. In plasma, cholesterol is found in the form of esters with higher fatty acids (oleic and others) and serves as a carrier during their transport: the formation of these esters occurs in the walls with the participation of the enzyme Enzymes(from the Latin "leaven") - biological catalysts present in all living cells. They carry out the transformation of substances in the body, thereby directing and regulating metabolism. By chemical nature they are proteins.
Each type of enzyme catalyzes the transformation of certain substances (substrates), sometimes only a single substance in a single direction. Therefore, numerous biochemical reactions in cells are carried out by a huge number of different enzymes. Enzyme preparations are widely used in medicine. cholesterol esterase. Most organisms (with the exception of some annelids, mollusks, echinoderms, and sharks) are capable of synthesizing chromium from squalene.

The most important biochemical function of chromium in vertebrates is its transformation into a hormone in the placenta, corpus luteum, and adrenal glands; this transformation opens the chain of biosynthesis of steroid sex hormones and corticosteroids Corticosteroids- hormones produced by the adrenal cortex. They regulate mineral metabolism (the so-called mineralocorticoids - aldosterone, cortexone) and the metabolism of carbohydrates, proteins and fats (the so-called glucocorticoids - hydrocortisone, cortisone, corticosterone, which also affect mineral metabolism). They are used in medicine when they are deficient in the body (for example, Addison's disease), as anti-inflammatory and antiallergic agents.. Another direction of cholesterol metabolism in vertebrates is the formation of bile acids and D3. In addition, chromium is involved in the regulation of cell permeability and protects red blood cells from the action of hemolytic poisons. In insects, chromium supplied with food is used for the biosynthesis of ecdysones.

In a number of animals, the constant level of cholesterol in the body is regulated according to the feedback principle: when excess cholesterol is taken from food, its biosynthesis in the cells of the body is inhibited (suppressed). In humans, this control mechanism is absent, so the content of chromium in the blood (normally 150 - 200 mg%) can increase noticeably, especially at the age of 30 - 60 years with fatty. This contributes to blockage of the bile ducts, fatty infiltration of the liver, the formation of gallstones, and the deposition of atherosclerotic plaques in cells containing chromium.

Cholesterol is excreted from the body of animals mainly through excrement (in the form of coprosterol). In the pharmaceutical industry, chromium serves as a raw material for the production of many steroid drugs. The main source of chromium is the spinal cord Spinal cord- a section of the central nervous system located in the spinal canal, which is involved in most reflexes. In humans, it consists of 31-33 segments, each of which has 2 pairs of nerve roots: the anterior ones - the so-called motor ones, through which impulses from the cells of the spinal cord are transmitted to the periphery (to the skeletal muscles, vascular muscles, internal organs) and the posterior ones - the so-called sensitive, through which impulses from receptors in the skin, muscles, and internal organs are transmitted to the spinal cord. The anterior and posterior roots, connecting with each other, form mixed spinal nerves. The most complex reflex reactions of the spinal cord are controlled by the brain. slaughtered cattle. (E. P. Serebryakov)

For more information on cholesterol, see the literature:

• Biosynthesis of lipids. Symposium VII, M., 1962 (Proceedings of the V International Biochemical Congress, vol. 7);
• Myasnikov A.L., and, M., 1965;
• Heftman E.M., Biochemistry of steroids, trans. from English, M., 1972;
• Schwartzman A., Cholesterol and the heart, N.Y., 1965.

Find something else interesting:

Cholesterol

Cholesterol or cholesterol is a steroid found only in animal organisms. Belongs to the class of sterols (steryls). Sterols are characterized by the presence of a hydroxyl group at position 3, as well as a side chain at position 17. In cholesterol, all rings are in the trans position; in addition, it has a double bond between the 5th and 6th carbon atoms. Therefore, cholesterol is an unsaturated alcohol:

Core formed by hydrogenated phenanthrene (rings A, B and C) and cyclopentane (ring D). Cyclopentaneperhydrophenanthrene (common structural basis of steroids)

The ring structure of cholesterol is characterized by significant rigidity, while the side chain is relatively flexible. So, cholesterol contains an alcohol hydroxyl group at C-3 and a branched aliphatic chain of 8 carbon atoms at C-17. The chemical name for cholesterol is 3-hydroxy-5,6-cholestene. The hydroxyl group at C-3 can be esterified with a higher fatty acid, resulting in the formation of cholesterol esters (cholesterides)

More than 50% of cholesterol is synthesized in the liver, 15-20% is synthesized in the small intestine, the rest of the cholesterol is synthesized in the skin, adrenal cortex, and gonads. In the cytoplasm, cholesterol is found predominantly in the form of esters with fatty acids, forming vacuoles. In blood plasma, both unesterified and esterified cholesterol are transported as part of lipoproteins. About 1 g of cholesterol is synthesized in the body per day; 300-500 mg comes with food. It is a component of cell membranes, a precursor in the synthesis of bile acids, steroid hormones, and vitamin D.

History of discovery. In 1769, Pouletier de la Salle obtained a dense white substance (“adipose wax”) from gallstones, which had the properties of fats. Cholesterol was isolated in its pure form by the chemist, member of the National Convention and Minister of Education Antoine Fourcroy in 1789. In 1815, Michel Chevreul, who also isolated this compound, called it cholesterol (“chole” - bile, “sterol” - fatty). In 1859, Marcelin Berthelot proved that cholesterol belongs to the class of alcohols, after which the French renamed cholesterol “cholesterol.” A number of languages ​​(Russian, German, Hungarian, etc.) retain the old name - cholesterol.

Cholesterol synthesis starts with acetyl-CoA. Cholesterol biosynthesis can be divided into four stages. In the first step (1), mevalonate (C6) is formed from three molecules of acetyl-CoA. In the second step (2), the mevalonate is converted into “active isoprene,” isopentenyl diphosphate. In the third step (3), six isoprene molecules polymerize to form squalene (C30). Finally, squalene cyclizes with the elimination of three carbon atoms and is converted to cholesterol (4). The diagram shows only the most important intermediate products of biosynthesis.

1. Formation of mevalonate. The conversion of acetyl-CoA to acetoacetyl-CoA and then to 3-hydroxy-3-methylglutaryl-CoA (3-HMG-CoA) corresponds to the pathway of ketone body biosynthesis (for details, see Fig. 305), however, this process does not occur in mitochondria, but in the endoplasmic reticulum (ER). 3-HMG-CoA is reduced with the cleavage of coenzyme A with the participation of 3-HMG-CoA reductase, a key enzyme in cholesterol biosynthesis (see below). At this important stage, by repressing the biosynthesis of the enzyme (effectors: hydroxysterols), as well as due to the interconversion of the enzyme molecule (effectors: hormones), regulation of cholesterol biosynthesis is carried out. For example, phosphorylated reductase is an inactive form of the enzyme; insulin and thyroxine stimulate the enzyme, glucagon inhibits; Dietary cholesterol also inhibits 3-HMG-CoA reductase.

2 . Formation of isopentenyl diphosphate. Mevalonate, due to decarboxylation with the consumption of ATP, is converted into isopentenyl diphosphate, which is the structural element from which all isoprenoids are built.

3 . Formation of squalene. Isopentenyl diphosphate undergoes isomerization to form dimethylallyl diphosphate. Both C5 molecules condense into geranyl diphosphate and, as a result of the addition of the next isopentenyl diphosphate molecule, form farnesyl diphosphate. When the latter dimerizes in a head-to-head manner, squalene is formed. Farnesyl diphosphate is also the starting compound for the synthesis of other polyisoprenoids, such as dolichol and ubiquinone.

4. Cholesterol formation. Squalene, a linear isoprenoid, cyclizes with the consumption of oxygen into lanosterol, a C30-sterol, from which three methyl groups are cleaved in subsequent steps catalyzed by cytochrome P450, resulting in the formation of the final product - cholesterol. The described biosynthesis pathway is localized in the smooth ER. The synthesis occurs due to the energy released during the breakdown of coenzyme A derivatives and energy-rich phosphates. The reducing agent in the formation of mevalonate and squalene, as well as in the last stages of cholesterol biosynthesis, is NADPH + H+. This pathway is characterized by the fact that intermediate metabolites can be divided into three groups: coenzyme A derivatives, diphosphates, and highly lipophilic compounds (from squalene to cholesterol) associated with sterol transporters.

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Esterification of cholesterol. In some tissues, the hydroxyl group of cholesterol is esterified to form more hydrophobic molecules, cholesterol esters. The reaction is catalyzed by the intracellular enzyme ACHAT (acylCoA: cholesterol alyltransferase). The esterification reaction also occurs in the blood in HDL, where the enzyme LCAT (lecithin: cholesterol acyltransferase) is located. Cholesterol esters are the form in which they are stored in cells or transported in the blood. In the blood, about 75% of cholesterol is in the form of esters.

Used Books

Berezov. Korovkin.

http://www.xumuk.ru/biochem/174.html

http://biokhimija.ru/lipidny-obmen/cholesterin.html

http://ru.wikipedia.org/wiki/%D0%A5%D0%BE%D0%BB%D0%B5%D1%81%D1%82%D0%B5%D1%80%D0%B8%D0 %BD