Cytolysis: what it is, how it affects the cell, and associated diseases.

Cytolysis is a phenomenon that affects the functioning of cells and even destroys them.

Human beings are an open biological system. As such, we continuously exchange water, waste products, organic matter and nutrients with the environment around us. From the most demanding exercise to the most trivial act requires an exchange with the environment. For example, we lose about 350 milliliters of water per day in the form of vapor through the act of breathing alone.

On the other hand, we also produce about 2 liters of urine per day, a waste substance that helps us to maintain the electrolyte balance in our body. This balance of water and substances is measured by Blood osmolality, a parameter that reflects the concentration of all the chemical particles found in the liquid part of the blood.

The parameter that we quote here is essential for today's topic, because we tell you all about cell cytolysisthat is, what happens when an osmotic imbalance occurs in the cell environment. Don't miss it, as we also discuss its medical connotations beyond the theoretical realm.

Osmosis and its importance

The organic osmosis that happens inside our body rests on a very simple premise: the membranes of our cells are semipermeable. Therefore, in an isotonic medium (the concentration is equal inside and outside the cell), the passage of water between the two environments is balanced. If the medium in which the cell bodies are found is hypertonic (more solutes than in the cytoplasm), water leaves the membrane, and if there is a higher concentration of solutes inside the cell than in the medium (hypotonic medium), the cells "swell" due to the entry of water.

Osmoregulation is the mechanism responsible for actively controlling this from happening. Within our body there are multiple mechanisms that maintain the osmotic pressure of the internal environment, thus preventing the cells of our tissues from gaining or losing excess water. This is where another essential parameter comes into play to understand cytolysis and something different from osmolarity: osmolality..

Osmolality and osmolarity are two sides of the same coin, since they represent the same concept (the measure of the total number of solutes in a solution), only the units used vary. Osmolarity is expressed in osmoles/liter of solution, while osmolality is expressed in osmoles/kilogram of water. For informative purposes, we can use both terms interchangeably to refer to the event that concerns us here, since the differences in body fluids are minimal.

Blood plasma osmolarity is essential for understanding body osmoregulation as a concept, and is calculated as followsand is calculated as follows:

pMSO = 2[Na+] + [glucose] + [urea]. Normal = 290 ± 10 mOsm/kg H2O

In this formula, the 3 solutes most present in blood plasma are taken into account, which are sodium, glucose and urea. When these values are misaligned, we can say (in a simple way) that the blood medium could become hypo- or hyper-osmotic with respect to the environment.which causes certain consequences.

For example, when the kidneys malfunction, there is an increase in hydrostatic pressure in the blood (due to accumulation of water and sodium), which causes water to "leak" from the hyperosmotic medium (blood) to the hyposmotic medium (tissues). Thus, edema and other pathological fluid accumulations can form in the body.

What is cytolysis?

This lengthy explanation may seem unnecessary, but nothing could be further from the truth: cell cytolysis occurs because of an osmotic imbalance in the organism, so it was essential to understand the parameters that condition it. To put it quickly and simply cytolysis is an event that occurs when excess water enters the cell cytoplasm if the medium surrounding the cell is hypotonic, thus causing the cell to swell.thus causing the cell to swell and eventually rupture.

It should be noted that cytolysis only occurs in cells that do not have a cell wall, since this barrier prevents cell bodies from swelling to the point of rupture. Therefore, it only occurs in animals and protozoa, while plants and bacteria are "spared".

The reverse process to cytolysis is plasmolysis, because when the medium is hypertonic, water leaves the cell and the cell dehydrates. There are many causal factors that can trigger both plasmolysis and cytolysis, and we present some of them in the following lines.

Biological agents

In the lytic cycle, viruses end up destroying the cell from within and releasing themselves into the environment. Depending on how we understand the term, we could include this event as cytolysis, since the activity of intracellular viruses causes a drastic rise in internal osmotic pressure, which ultimately causes rupture. Thus, viruses can be released and infect new healthy cells..

Another very clear example of a biological cytolysis is mediated by Natural Killer (NK) cells, special lymphocytes that detect cancerous and infected cells, attack their plasma membrane and kill them by cytolysis. The NKs recognize the pathogenicity of the cell body being tested by close intercellular contact (immune synapse) and, when they conclude that it is a danger, they induce a cytokine response and trigger the cytolysis already described.

In summary, in all these events there is a "common bridge": there is an attack on the plasma membrane of the affected cell, which results in an osmotic imbalance between the internal and external milieuIn all these events, too much water enters the cell, the cell ruptures, its vital parameters cease and part of the cytoplasm is released into the environment.

Vaginal cytolysis

Another curious case of biological cytolysis is cytolytic vaginosis, caused by the bacterial overgrowth of Lactobacillus in the vaginal mucosa, microorganisms that colonize the female tracts and are generally beneficial to the host. The increase in the proportion of lactobacilli is associated with an acidosis in the vaginal environment (low pH), which results in cytolysis of mucosal surface cells.

This clinical picture presents with symptoms such as itching, vulvar pain, vaginal burning and copious secretions with a "cut milk" appearance. Douching with dissolved sodium bicarbonate is the treatment of choice in these cases, since this chemical substance is alkaline and, therefore, allows the vaginal pH to be balanced.

2. Chemical causes

At this point, we recover the osmotic imbalance. Due to some organic failure, the extracellular medium becomes hypotonic (poor in solutes) and, therefore, to reach an isosmotic state, water enters the cell cytoplasm (which is hyperosmotic with respect to the medium). Water enters the cell in an uncontrolled manner, the cell membrane cannot withstand the pressure and cytolysis occurs..

We could cite several clinical entities that describe why a chemical imbalance occurs in the organism, but they are complex and very difficult to understand without being clear about some advanced medical concepts. For example, patients with heart failure may suffer internal imbalances, resulting in liver damage in the form of cell cytolysis, which in turn leads to an increase in circulating transaminases (which correlate positively in many cases with liver failure).

On the other hand, it appears that cerebrovascular accidents (CVAs) may also be associated with episodes of cytolysis, due to poor nutrient distribution and fluid accumulation.. In summary, failures in certain organs can lead to blood-tissue and medium-cell osmotic imbalance, resulting in cytolysis and other events at the cellular level (such as plasmolysis).

Summary

We know that we have moved into quite technical terrain, but if we want to keep you with a clear idea, this is the following: cytolysis occurs when the cytoplasm of the cell is hypertonic with respect to a hypotonic medium, or what is the same, when inside the cell there are more solutes than on the outside.

This situation can be promoted by viral, bacterial or immunological agents, since they are capable of directly attacking the plasma membrane and thus causing an osmotic imbalance. On the other hand, hypotonic external environment of the cell may be due to chemical imbalances due to organic pathologies, such as cardiac failure and other events.

Bibliographic references:

• Geisbert, T.W.; Young, H.A.; Jahrling, P.B.; Davis, K.J.; Larsen, T.; Kagan, E.; & Hensley, L. E. (2003). Pathogenesis of Ebola hemorrhagic fever in primate models: evidence that hemorrhage is not a direct effect of virus-induced cytolysis of endothelial cells. The American journal of pathology, 163(6), 2371-2382.
• Guevara, A., Santiago, V., & Domínguez, A. (2011). Cytolytic vaginosis: a little known clinical entity. Journal of Obstetrics and Gynecology of Venezuela, 71(1): 45-48.
• Moretta, A., Biassoni, R., Bottino, C., Mingari, M. C., & Moretta, L. (2000). Natural cytotoxicity receptors that trigger human NK-cell-mediated cytolysis. Immunology today, 21(5), 228-234.
• Muñoz-Rodríguez, J., Tricas Leris, J. M., Andreu Solsona, V., & Vilaseca Bellsola, J. (2003, November). Ischemic hepatitis in patients with heart failure. In Anales de medicina interna (Vol. 20, No. 11, pp. 31-33). Aran Ediciones, SL.
• Vergara, U. (2009). Regulatory T lymphocytes and immune response. Advances in Veterinary Sciences, 24(1-2).