Cytotoxicity characterizes the degree of toxic effect of chemical substances and living cells on body cells. Through their influence, the human cell is damaged or even killed. In this process, many different processes lead to the destruction of body cells.
What is cytotoxicity?
Cytotoxicity characterizes the degree to which chemical substances and living cells have a toxic effect on body cells. The term cytotoxicity is derived from Greek, where it means cell poison. In this context, many substances are toxic to the body’s cells, and some can even lead to cell death. For example, there are many chemicals that can interfere with the metabolism of cells and thereby alter it. Chemical cell poisons include certain organic acids, hydrogen peroxide or ethanol (alcohol). Many dangerous substances are also known from everyday life, such as inorganic acids, highly concentrated alkalis, chlorinated hydrocarbons and many more. Many biological poisons are also known. For example, snake venoms, fungus toxins and many other plant and animal toxins have cytotoxic effects. In the process of evolution, new cytotoxins were produced all the time. They serve in part to defend against attack and, in the context of hunting, to kill prey. However, not only chemical but also biological cytotoxics have evolved. To defend against infections, the immune system has developed a sophisticated system of defense against bacteria, fungi or viruses. In this process, not only the cells of the microorganisms themselves must be killed, but also the cells of the body that they attack. Therefore, cytotoxics include T cells, natural killer cells, neutrophil granulocytes or macrophages.
Function and task
The cytotoxicity of certain substances and cells possesses great importance in the context of biological development. The immune system in particular has developed some strategies to protect the body from microbial invaders. These include bacteria, fungi and also viruses. Infected cells further damage the organism and must be killed by the defense mechanisms of the immune system. Bacteria are already confronted with various defense substances before they enter the body and are partly killed. If this first immune reaction is sufficient to stop the entry of the bacteria, the production of cytotoxic substances and immune cells against the bacteria already ends here. However, infected body cells must be eliminated by the influence of T cells, natural killer cells and macrophages. Furthermore, the organism produces antibodies that bind with antigens located on the cell surfaces. In these cases, the cytotoxic action of immune cells and antibodies serves the health of the whole organism. The fight against viruses can also only work by destroying the infected cells. In this process, violent inflammatory reactions develop, which are manifested by pain and fever. The entire disease process during an infection can be understood as a cytotoxic reaction. When drugs are used, the cytotoxic properties of the corresponding substances are also often exploited. Often these are cytostatic effects to kill specific pathological cells in the body. This applies in particular to tumor cells, which divide without restriction. Cytostatic agents often mediate their cytotoxic effects through their influence on nucleic acid production. If, for example, the formation of nitrogen bases is inhibited, cell growth comes to a standstill due to a lack of nucleic acid production. This mainly affects fast-growing cells such as tumor cells. Therefore, the effect of these drugs, which are used as part of chemotherapy, is specifically directed against cancer cells. The side effects are based on the concomitant slowing of the growth of mucosal and immune cells.
Diseases and medical conditions
However, cytotoxins do not only mediate positive effects. For example, there are many biological agents that can lead to the killing of all body cells and thus to the death of the entire body. Examples include snake venoms, fungal toxins, and many other plant as well as animal toxins. For the poison-producing organisms, this means a biological advantage over the damaged organisms. Furthermore, there are many chemical substances that have a cell-damaging effect by interfering with the metabolism of the cell.Some cytotoxins already have a destructive effect on cell membranes. Still other toxins inhibit nucleic acid metabolism and thus lead to the destruction of the cell. The mechanisms of action are very broad. The cytotoxicity can be represented by a cytotoxicity scale. Thus, there are gradations from 0 to 3. At 0, the substance is not toxic. At level 1, there is slight inhibition by a weakly toxic material. Level 2 again means significant inhibition by moderately toxic material. Strongly toxic materials are counted as level 3. The cytotoxicity of a substance can be determined by the so-called cell viability. Cell viability represents the number of living cells in a cell population. The fewer living cells there are, the lower the cell viability and the more toxic the substance being tested for toxicity. In this process, the total cell count is determined using a counting chamber or flow cytometer, among other methods. Certain staining methods can then be used to determine the living cells. This method can be used to determine the concentration of a substance at which cell viability is reduced by 50 percent. This is then the IC50 value. At this concentration, 50 percent of the cells die. This value can be used to estimate the effectiveness of chemotherapeutic agents or disinfectants. If the IC50 value is exceeded when these agents are used, the toxicity to the entire body predominates. Significant adverse health effects occur, which can also lead to death.
