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CELL SUICIDE | Science and life

A living cell is born as a result of the division of the mother cell, goes through life cycles and eventually dies. Cells die «from old age» or any damage. But it turned out that they can die for no apparent reason, spontaneously. And such death is an important protective mechanism of the organism of animals and humans.

Two possible ways of death of a living cell.

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The middle of the 19th century was the time of the birth of cytology, the science of the cell. It was then that it was discovered that a living organism consists of individual cells that constantly multiply — without this there would be neither growth nor development. And it became clear that such a process could not continue indefinitely. Otherwise, the old people would have reached the size of an elephant. Naturally, in order to maintain the constancy of the mass, shape and function of the body, some part of the cells must continuously die. Until recently, it was believed that the process of death is exclusively degenerative: the cell ages, damage accumulates in it, metabolism freezes, it works worse, withers and, finally, dies. It, in essence, was not distinguished from the variant of cell death that occurs during trauma, exposure to poisons, cessation of blood supply, etc. — necrosis. That is, the process of dying off was considered as a catastrophe, and not as a physiologically natural phenomenon. nine0005

However, a century later, scientists realized that everything happens quite differently — cells die for no apparent reason, and such spontaneous death is different from necrosis. The cell lived and lived, and suddenly, for unknown reasons, “died”, and without signs of inflammation and scarring.

The mechanism of programmed cell death is now fully elucidated. The cause of cell death may be its dissolution, or, in scientific terms, lysis. In the 1950s, it was established that there are macroscopic vesicles, lysosomes, inside the cells. They contain digestive enzymes, like those secreted in the stomach and intestines. If the integrity of these vesicles is violated for one reason or another, then the enzymes pour into the protoplasm of the cell and begin to “digest” its contents. This leads to gradual dissolution, disintegration of the cell into parts, and eventually to its death. nine0005

It has also been suggested that programmed cell death may also occur due to an excess of superoxide radicals. The essence of the mechanism is as follows. Cell life requires oxygen, which provides it with energy. The oxygen molecule, as you know, consists of two atoms and is denoted by the symbol O ₂ . If we write its structural formula, we get 0=0. In this form, oxygen is not very reactive. Forgive me, chemists, but to simplify, let’s say that under the action of enzymes in living tissues, molecules of the type -0-0-, atomic oxygen -0-, hydroxyl radicals H-0- or ozone -0-0 are constantly formed from molecules 0=0 -0-, very strong oxidizers. In them, figuratively speaking, oxygen atoms do not hold each other, but have one or two free hands (valences), ready to “grab the hand” of any other atom. nine0005

Under physiological conditions, approximately 5-6% of its molecules from the air oxygen entering the body form such superoxide forms that do not pose a danger in a small amount. But when exposed to radiation, certain poisons, carbon tetrachloride, notorious dioxins, viral diseases and certain metabolic disorders, etc., superoxide radicals are formed in excess. In this case, they begin to oxidize not at all what is required, in particular, the outer and inner membranes of the cells. As many researchers believe, oxidative processes provoke the occurrence of diseases such as sclerosis, hypertension, decreased immunity, cancer, and dementia. Oxidation of the cell membrane disrupts the work of enzymes, making it difficult for ions and nutrients to enter the cell, which leads to incredible confusion in the coordination of cellular mechanisms and ultimately ends in cell death. nine0005

There is another variant of programmed cell death, the so-called «calcium death». It has many reasons, but its essence boils down to the fact that an excess of calcium ions in the intercellular fluid, for one reason or another, enters the protoplasm of the cell, activates a number of enzymes there, which leads first to metabolic disorders, and then to cell decay. .

The term «apoptosis» was proposed in 1972 by the American researcher J. Kerr to describe programmed cell death. This word comes from the Greek words «apo» — completeness and «ptosis» — fall and can be translated as «falling leaves.» The essence of the term emphasizes its naturalness, physiology, in contrast to necrosis — death from injury. The life cycle passes, and the fruits fall, the leaves fall. nine0005

Apoptosis is a fundamentally new fundamental concept in cell biology. Kerr and his collaborators formulated the main signs of apoptosis. First, during apoptosis, cell breakdown begins with the nucleus — it shrinks and breaks up into separate fragments. Secondly, the apoptating cell decreases in volume and, as it were, separates from its neighbors. Thirdly, the properties of its membrane change, as a result of which it is easily recognized by macrophages (cell eaters). Fourthly, the preserved membranes form living droplets with functioning organelles in place of the dead cell, which are absorbed by neighboring cells or macrophages. Nothing remains in place of the dead cell. nine0005

Apoptosis is genetically programmed. So far, the genes that initiate suicide are unknown. Most likely, the “killer” genes are asleep, but under the influence of any signals they “wake up”, preparing the cell for spontaneous death. There are a lot of factors that can incite a cell to commit suicide. And the mechanisms of apoptosis in relation to each case are also different.

In a visual form, apoptosis is observed in any tissue that has served its time. So the tail of tadpoles dies, the shape and size of the embryo changes. A decrease in the volume of the mammary gland after the end of lactation occurs without any necrosis, atrophy of the prostate gland after castration too. Dies and what has served its time. In an adult organism, apoptosis occurs constantly. It is most prevalent in short-lived cells such as those lining the intestines, skin cells, and blood cells. nine0005

Apoptosis is a defense mechanism of the body. In a heart attack, a portion of the heart muscle dies as a result of thrombosis. Under the microscope, it can be seen that in the dead muscle tissue, necrotic cells alternate with apoptotic ones. The difference between them is significant, since inflammation and scarring occur at the site of necrosis, and at the site of apoptosis, neighboring cells replace the dead.

Apoptosis protects a person from viral infection. If a living cell is attacked by a virus, it becomes dangerous to its neighbors, because the virus “launches” its DNA into its nucleus. Infected cells multiply and infect neighboring ones. To help fight infection, sometimes the cell «commits suicide» along with dangerous viruses. nine0005

The self-destruction of cells affected by the virus reduces the number of diseased cells, while viral DNA also decays.

Another type of apoptosis is the self-destruction of mutated cells. A mutant cell, not only cancerous, although it is the most dangerous, but also any other, is recognized as alien, and the body «gives the command» for its self-destruction.

And finally: a man hit something. But not much. Yes, hurt. But the cells are damaged, therefore defective. What if microbes get into them? Therefore, damaged defective cells also have to be apoptated so as not to endanger the entire organism. nine0005

An important difference between necrosis and apoptosis is the following: if necrosis is a catastrophic and irreversible death, then apoptosis is just a suggestion from various factors about the expediency of suicide. This means that it is possible to intervene in the development of apoptosis: if necessary, accelerate it, if necessary, slow it down. For example, slow down the atrophy of neurons and accelerate the death of cancer cells.

Apoptosis, as already mentioned, is genetically programmed, so it develops in stages, and does not unfold like a spring. Each stage of it can be controlled with drugs. At 19In 1998, Japanese researchers found that DNA fragmentation during apoptosis begins with its enzymatic cleavage into large fragments. By adding an enzyme activator or blocker, it is possible to regulate apoptosis at the very initial stage — DNA fragmentation, which will allow directing cell suicide in the right direction: for example, activate it in malignant tumors or suppress it in myocardial infarction.

Currently, physiological apoptosis blockers have been identified, in particular growth factors, neutral amino acids, zinc, anti-inflammatory substances, hormones: estrogens, androgens, enzyme blockers (cysteine ​​proteases) and phenobarbital (luminal). nine0005

Now the third, most real. If cell death from apoptosis is reversible, then we can quite fight against it in order to protect at least part of an organ or tissue from death during pathological processes. This can be done, for example, by maintaining the integrity of cell membranes. It is provided by the lipids included in their composition (a special type of animal fats), especially one of the varieties of lipids — phospholipids. In therapy, a whole set of drugs containing phospholipids has been successfully used for a long time. nine0005

The complex lipid preparation Essentiale is especially popular. Amino acids also protect membranes from destruction. Among them are methionine, histidine, cysteine, and the amino acid drug cerebrolysin is used to protect brain nerve cells.

Protection of membranes and other cell components from overoxidation in a healthy person is provided by natural antioxidants, but in diseases that occur with cell apoptosis, for example, in myocardial infarction, hepatitis, decreased immunity, some diseases of the adrenal glands, antioxidants are not enough and then they are effective antioxidant vitamins, which include (as activity decreases) vitamins E, C, A, and K. In recent years, many effective synthetic antioxidants have been created, including mexidol, emoxipin, ionol, and others. nine0005

Very useful for preventing apoptosis means that reduce the level of calcium inside the cell. They are usually used to treat angina pectoris. With angina pectoris, blood flow to the heart muscle is reduced, which creates all the conditions for apoptosis of its cells. Even in the event that a heart attack cannot be prevented, then with the regular use of calcium-lowering agents, it is limited only to the zone of inevitable necrosis, and cells that have already prepared for suicide in order to save their own kind remain alive. Thus, sometimes it is possible to save at least part of the heart muscle from death. nine0005

The mechanism of apoptosis is just beginning to be studied, and pharmacologists can already offer their effective drugs that can control this process, which is good news.

Dead cell — The Big Encyclopedia of Oil and Gas, article, page 2

Page 2

It is of interest to search for a method for determining dead cells , which died not only as a result of natural processes, but also killed by various physical and chemical agents.
[16]

Behind the layer of lining cells is a ring of dead cells s; they are usually filled with air. The shell of these cells, as well as excretory cells, is thin-walled, but unlike them, it is lignified.
[17]

Typically, the hyphae of endofleod lichens grow between dead bark cells , splitting them into small patches. Whether the hyphae are capable of penetrating the cell wall of the tree’s bark is still unknown.
[18]

To maintain the mechanical stability of the trunk in the wood, dead cells libriform, which differ in wall thickness. The nature of the thin fibrillar spiral structure inherent in the cell walls of wood fibers (tracheid, libriform) is considered in detail in the relevant publications.
[19]

Microscopic examination of the sample determines the number of budding and dead cells . With the normal development of yeast, the number of budding cells is 20 — 25%, and dead — no more than 3 — 5% of their total content in the medium. This yeast from the bottle is the mother culture for small apparatus purity.
[20]

This method takes into account the percentage of live and dead cells .
[21]

As bacteriolytic organisms capable of feeding on dead cells , gliding bacteria, in particular myxobacteria, must first be mentioned. For the digestion of solid particles, they, not being able to introduce solid substances into the cell, form a mucous coordinating moving colony (shwarm), which crawls onto the substrate. Typical bacteriolytic myxobacteria are Cystobacter, Mukhososssh, which does not form fruiting bodies, and also belongs to another group of Lyso-bacter. However, the bacteriolytic loop is mainly carried out by eukaryotic organisms capable of zootrophic and phagotrophic nutrition. It should be noted the bacteriolytic loop caused by viruses — bacteriophages, which cause lysis of living cells infected by them.
[22]

Wood, an object of chemical processing, is dominated by dead cells . In a dead cell, after the death of the protoplast, its shell and cavity remain, filled either with water, usually containing one or another amount of mineral substances, or with air.
[23]

On the other hand, when fluorochromized with acridine orange , dead cells of show bright red luminescence, while living cells show bright green luminescence. This makes it easy to distinguish them from each other. A similar technique is used in the diagnosis of cancer. In this case, the glow of the fluorochrome makes it possible to accurately distinguish healthy cells from cells affected by cancer.
[24]

Acridine orange detected 88 — 100% of dead cells in tap water.
[25]

Pathological resin ducts differ from the usual ones by weak development of the layer of dead cells . Sometimes the lining cells do not form a continuous ring around the canal, and it is closed by adjacent cells of the accompanying parenchyma.
[26]

Tracheids (there are very few of them in birch wood) — dead cells can be identified by bordered pores in the shells.
[28]

This statement is correct, as the sap rises in dead cells of the sapwood, possibly because they are mixed with some living cells.