Toxicity of metals

Metals have a ubiquitous distribution and are responsible for accumulation in the food chain. These metals can accumulate in the organs and be excreted through sweat, urine, faeces, peeling of the skin and finally through the hair. the metal is toxic, while the evaluation that offers the fastest results is the analysis of biological fluids, such as urine or blood tests.

The way in which metals come into contact with our body essentially involves the respiratory and skin pathways.
Metals can be divided into:

• ESSENTIALS such as copper, iron, magnesium and zinc (Cu, Fe, Mg, Zn).
• NOT ESSENTIALS such as cadmium, arsenic, lead or mercury (Cd, As, Pb, Hg).

The former are defined as essential metals because they are found inside cells and are necessary for the survival of the cells themselves. For example, iron is found inside hemoglobin (group - EME) and in cytochrome P450.

For all essential metals we must speak of toxicity due to deficiency and excess. The latter are defined as non-essential metals because they should not be found inside our organism. In fact, they do not collaborate in the activity of the cells, as their action is harmful to the cells themselves. In this regard, maximum levels tolerated by our body have been established, within which the metal does not cause any harmful effects. Once this established limit is exceeded, the metal accidentally taken can instead cause toxic effects.
Metals - in addition to being classified into essential and non-essential - can be classified into organic and inorganic. The chemical formula is very important because it determines the bioavailability of the metal for our body. The organic form is very lipophilic, therefore easily absorbed through the skin and through the BEE. The inorganic form of metals, on the other hand, is very water-soluble and has a very slow absorption. Inorganic metals can be equally dangerous, because they pass through the kidneys to be eliminated, so they can cause nephrotoxicity.
In general, the mechanisms by which metals give toxic effects are:

• Interaction with the active sites of enzymes, such as -OH, -SH, -COOH, -NH2 groups. All these groups interact with the metal causing a loss or reduction of enzymatic function.
• They displace an essential metal present in an indispensable enzyme or protein. Lead, for example, can replace iron in intestinal ferritin, or lead can replace calcium in all those enzymes or proteins that are activated by calcium.

The sites of action may vary depending on the affinity between metal and part of our organism. For example, mercury and cadmium prefer renal tissue (nephrotoxic), mercury and lead that of the CNS (neurotoxicity), cadmium and lead that of the reproductive system, while finally aluminum, arsenic, chromium and nickel prefer the respiratory tissue.

The mammalian cell can defend itself from possible excesses of non-essential metals thanks to the presence of a group of proteins called METALLOTIONEIN. These are proteins that chelate or sequester the non-essential metal, thus reducing the possibility that it remains free and exerts its toxic activity. Mainly, the chelated metals are copper, cadmium, zinc, mercury and lead.

One of the toxic effects that metals can have are allergic-type reactions, also known as hypersensitivity reactions. The metals that can cause these reactions are mercury, gold, platinum, beryl, chromium and nickel. There are four reactions that can cause.

• DEGRANULATION OF MASTOCYTES with release of IgE;
• RUPTURE OF RED GLOBULES with release of IgG and IgM (haemolytic anemia);
• FORMATION OF THE ANTIGEN-ANTIBODY COMPLEX with release of IgG and IgM (glomerular nephritis);
• CONTACT DERMATITIS with proliferation of T lymphocytes and release of cytokines which in turn activate TNFα. Contact dermatitis is caused in most cases by chromium and nickel.

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