Give examples of carcinogenic action of products of mushrooms life.

Among products of the mushrooms (mould) metabolism with carcinogenic action, it is most studied aflatoxine B. This mycotoxyne is heterocyclic substance and it is produced by mould Aspergillus fiavum, Carcinogenic action of aflatoxine is shown in very small dozes - 0,02 mg/kg of body weight. For comparison, toxic action of potassium cyanide is shown in the dozes exceeding specified in some tens of time.

With influence of mycotoxynes link development of a primary cancer of a liver in representatives of a tribe Bontu in Africa. A climate of territory on which lives this tribe, is very damp, therefore food is cooked quickly become covered by a mould. By tradition existing in those places such products are suitable to use. Analyses have shown, that in consumed food contains aflatoxine B

16.15. What meaning is put in concept "endogenous carcinogens"?

Endogenous are carcinogens which are formed in an organism from its normal components.

Finally it is not proved, however there are bases to believe, that in an organism during violation of a metabolism can appear carcinogenic polycyclic aromatic hydrocarbons. Their sources can be cholesterol, bilious acids, steroid hormones. In particular, it is shown, that processing of bilious acids in vitro leads to occurrence of methylcholantren - example of PAH possessing strong carcinogenic action.

Besides endogenous carcinogens can appear at violation of an exchange of some amino acids, in particular, trypthophane.

16.16. In what experiences possible participation of hormones in occurrence of malignant tumoral growth is proved?

During violation of regulation of secretion of threefold hormones of adenohypophyse (during violation of feedback mechanisms) their quantity in blood can essentially be increased. Influencing on target-organs, they can stimulate proliferation of cells and development of a tumour.

The similar opportunity is shown in following experiment. Animal is deleted one ovarium, and the second replace in a spleen. Blood from a spleen flows to liver where the estrogen which was formed in ovarium, is destroyed. To a hypophysis blood in which there are not enough estrogen flows. It causes stimulation of formation of honadotroupes. The last, acting on ovarium, strengthen secretion of sexual hormones, however still it is not enough of them in the blood flowing to hypophysis as there is a destruction of estrogen in a liver. Constant stimulating action of honadotroupes on ovarium causes prolipheration its cells and in a plenty of cases development of malignant tumours.

16.17. What are chemical carcinogens of direct and indirect action? Give their comparative characteristic.

Carcinogens of direct action are highly active chemical compounds, in particular lactones, chlorethylamines chlorethylamines, epoxide. They are capable to cooperate directly with structures of cells and to cause development of a tumour. These substances do not demand any transformations in organism for display their carcinogenic action.

Having high reactionary ability, direct carcinogens can not be collected in environment (during interaction with components of an environment they are destroyed). Therefore, from the point of view of hygiene, they do not represent the big danger to the person as factors of the carcinogenesis.

Carcinogens of indirect action are inert substances on the chemical properties. Polycyclic aromatic hydrocarbons, in particular, concern to them, aromatic amines, nitrozo-compaunds, aflatoxines. Possessing the low reactionary ability, the specified carcinogens can be collected in environment and consequently represent greater danger to the person.

These connections substances become carcinogenic in an organism only after some chemical fermentative transformations as a result of which their active forms - actually carcinogens (fig. 53) are formed. In a similar way from PAH are formed epoxide, from aromatic amines - hydroxylamines, from nitrosamines - alcylic radical. These forms of carcinogens influence the genetic device of a cell and cause its transformation into tumoral.

16.18. What properties of chemical substances cause their carcinogenic action?

In 60th years spouses Miller have shown, that carcinogenic action of chemical compounds is connected with presence in their structure positively charged (electrophil) groups. In molecules of carcinogens of direct action such group appears at once at dissolution of substance in water. In case of carcinogens of indirect action electrophil group is formed during fermentative transformations of substance in organism.

So, the products of transformation of PAH containing positively charged group, are epoxide. Spouses Pullman have shown, that epoxide possess carcinogenic properties, in which molecule atom of oxygen is attached to so-called K-zone (from Germany word Krebs- a cancer). It has been established later, that the most carcinogenic are epoxide with atom of oxygen in beat-site molecules PAH (from English b?? - a gulf) (fig. 54). In the image, knowing a chemical structure of molecule of PAH, it is possible to predict carcinogenic properties of substance.

16.19. What stages passes chemical carcinogenesis? What is their essence?

In chemical carcinogenesis allocate three stages: initiation, promotion and a tumoral progression.

The essence of initiation includes influence of chemical carcinogen, there is a transformation of a cell,so its transformation from normal into tumoral.

During the stage of promotion the transformed cell receives stimulus to duplication, the tumour starts to grow. The substances stimulating duplication of transformed cells, have received the name of promotors. They can be not carcinogenic. Very strong promoters are forbol ethers which activate proteinkinase C, taking part in regulation of cellular mitosis.

Between initiation and promotion can pass a lot of time (sometimes years). The majority of the studied chemical carcinogens are full, so show properties either initiators, and promoters.

Tumoral progression is qualitative changes of properties of a tumour during its development. As a rule, tumour gets more and more malignant properties.

16.20. What is an explanation of the phenomenon of a tumoral progression?

Tumoral cells are differed by high variability, therefore their population is non-uniform. There is a constant struggle of cells for a survival in adverse conditions of existence (deficiency of substratum, oxygen, etc.). It is a basis on their natural selection - survive only cells that are most adapted for existence in such conditions. And the most adapted most simply arranged tumoral cells which have lost the specialized functions and have kept only property of boundless division. Thus there is the further malignant tumours ? a mainstream of a tumoral progression.

16.21. What physical factors can matter in occurrence of malignant tumours?

Among factors of the physical nature to etiology of tumours can concern: 1) ionizing radiation; 2) ultra-violet radiation; 3) mechanical influence (long pressure on tissues); 4) a heat.

The role of ionizing radiation is proved in experiment and numerous clinical supervisions. Radiating carcinogenesis has been revealed in 7 years after opening x-ray radiation. Its first victim became the first manufacturer of x-ray tubes of Fricken which checked quality of production on his own hands. He had a cancer of a skin.

While long staying of white rats on the sun, cancer of a skin is developed, that connect with influence of ultra-violet radiation.

Development of a tumour in the field of implantation to animals plates, made of chemically inert material ("plastic" carcinogenesis), occurrence of a cancer in a place of long pressure upon a skin of cangry (a special bag in which inhabitants of India carry coal) are examples of possible value of mechanical factors in carcinogenesis.

At last, frequent occurrence of tumours of an oral cavity at shepherds of mountain areas who drink very hot tea, suggests about a possible role of a heat in development of tumours.

Date: 2016-06-12; view: 97