Pathological conditions caused by disorders of fat metabolism are a vast group. Everyone is familiar with the most “popular” representatives: atherosclerosis, diabetes mellitus, obesity. They provoke the most serious complications, which include coronary heart disease, heart attack, stroke, polyneuropathy and other negative consequences of diabetes.
All diseases are different, but what ties them together in a chain of impaired metabolism is affiliation with leptin, the hormone of fat cells that controls the feeling of satiety and balances a person’s weight. You will learn about the types of proteins, their functional purpose, and the tests that are required to correct the pathological condition in this article.
- Types of lipoproteins.
- Assessment of lipid metabolism.
Types of lipoproteins
Special transport proteins – lipoproteins – carry cholesterol molecules through the bloodstream and are divided into several categories:
- Very low density lipoproteins (VLDL),
- Low-density lipoproteins (LDL),
- High-density lipoproteins (HDL),
- intermediate density lipoproteins (IDL),
- lipoprotein (a).
The dividing line is the amount of cholesterol, triglycerides, and phospholipids that these classes of substances contain. Low-density lipoproteins are the main transporter of cholesterol into cells. The development of vascular atherosclerosis is associated with an increase in its amount. Their high-density counterparts, on the other hand, activate cholesterol withdrawal back and transport it to the liver for optimal utilization.
Fatty tissue is the basis of vital functions of the body: it forms cell membranes, is a source of energy, and protects internal organs from injuries. Normally it is concentrated in the subcutaneous fatty tissue and surrounds the parenchymatous organs. Its balance supports normal human eating behavior through the hormone leptin, which is responsible for normal human weight. In addition, lipids are the source of synthesis of endogenous or internal and exogenous or dietary cholesterol and are responsible for the biochemical processes in the cell, which are related to the transport of cholesterol through the bloodstream and the introduction and release of the biomatter into and out of the cell.
An imbalance in these complex biochemical processes, associated with disruption of cell receptors, underlies the development of atherosclerosis. The state of lipids in the body when the qualitative and quantitative composition of lipoproteins changes is called dyslipidemia. An increase in the concentration of cholesterol in the blood, which can be included in different fractions, is called hyperlipidemia, and a drop in the level of the substance – hypolipidemia. According to the amount of lipoproteins that carry cholesterol in the bloodstream, total cholesterol, and triglycerides, there are five types of hyperlipoproteinemia. This is important when making a diagnosis and prescribing adequate therapy.
Triggers of impaired fat metabolism are thought to be:
- genetic mutations with autosomal dominant inheritance;
- somatic pathologies;
- endocrine disorders;
- abnormal eating behavior.
Mutations occur in genes that control the formation of abnormal receptors responsible for normal fat metabolism. Such mutations in low-density lipoproteins lead to blocked cholesterol transport, prolonging the time LDL stays in the bloodstream. This, in turn, provokes the growth of oxidized forms of low-density lipoproteins with atherogenic properties.
The most serious pathologies that develop against the background of altered lipid metabolism include:
- Primary hyperlipidemia, mediated genetically and divided into several groups.
- Secondary hyperlipidemia – the result of somatic and endocrine primary causes of diseases: diabetes mellitus, obesity, CVD, post-hemodialysis condition, hepatitis, pathology of biliary system, alcoholism, hypothyroidism.
Assessment of lipid metabolism
The only way to understand the state of lipid metabolism is through laboratory blood testing.
Disorders of lipid metabolism and conditions that are associated with it are diagnosed by the following parameters:
- total cholesterol;
- low and high density lipoproteins;
- very low density lipoproteins;
- apolipoprotein A1,
- apolipoprotein B,
- lipoprotein (a);
- fat electrophoresis;
- determination of atherogenicity coefficient;
- genetic tests.
The most common test performed is the determination of total cholesterol. In its essence it is not a substance of the class of fats (lipids), as it might seem, but refers to alcohols. Therefore, it is more correct to call it cholesterol. But both cholesterol and cholesterol are two names for the same biological substance. Total cholesterol is the total amount of a substance that is contained in all the molecules that transport cholesterol: HDL, LDL, LDL-C, LDL-C, and in different ratios. Each of these lipoproteins performs different functions, so both the rise and fall of cholesterol in them can indicate a disturbed lipid metabolism.
The main transporter is low-density lipoproteins (LDL); this fraction has the most cholesterol esters. It is an atherogenic, fat-destroying fraction, “bad cholesterol”. LDL delivers cholesterol to the tissues, including the vascular endothelium. Thus, circulating cholesterol in blood, settles in the place of micro-damage of the vascular wall and forms atherosclerotic plaque. It becomes a trigger for the development of cardiovascular pathologies, affecting, among others, the aorta and coronaries.
Another form of cholesterol is a substance from the high-density lipoprotein fraction, the “good cholesterol” or HDL. This fraction transports excess cholesterol from the cells to the liver, where it is utilized. Chemically, it is absolutely identical to cholesterol, only the carriers are different.
Apolipoprotein A1 is the main protein in “good cholesterol. It ensures the normal movement of fats through the bloodstream. Apolipoprotein B 100 is the leading protein in low- and very-low-density lipoproteins and the high-density fat fraction.
Determining the amount of these proteins helps clarify the diagnosis and assess the risk of cardiovascular disease. Genetic techniques for assessing the condition of fats in the body are based on the detection of apoE gene mutations. This is the most modern and reliable analysis today for determining the degree of risk of forming heart and vascular pathologies.