by Gennady POROSHENKO, Dr. Sc. (Biol.), Research Institute of General Reanimatology, Russian Academy of Medical Sciences (Moscow)

Many congenital diseases are caused by a mutant gene (for example, hemophilia) or chromosome anomalies (Down's syndrome). However, genetic factors, determining our health, play an important role in the development of nonhereditary diseases as well, even such as, for example, pneumonia or myocardial infarction. That is why clinical physicians say that one

should treat not a disease, but a patient. Depending on patients' specific features, the disease can develop or not, its course is different and requires a different approach. Let us discuss these problems from the viewpoint of research, including those carried out recently at the Research Institute of Reanimatology, RAMS.

Cell structure (a diagram).

The normal organism is often compared with a good mechanism: "Works as a clock!" However, it is absolutely incorrect: a mechanism is made of specially prepared separate parts, while a living creature is born as a single whole, forming itself-tissues and organs-in the course of development (differentiation).

The gametes fusing during fertilization bring the code, present in their hereditary system, into the zygote*. Thus, a multicellular formation is developed, with cells which divide, differentiate and acquire distinctive properties. At certain stages some of them become unnecessary and liquidate themselves in accordance with their program.

A LITTLE BIT OF GENETICS

The main character of the play The Petty Bourgeois in Nobility by Jean Baptiste Molière, the great 18th century French comedian, asserts that he has been speaking for 40 years and found out only yesterday that he expressed himself in prose. The situation with genetics is similar. Everyone knows that it is a science of signs, transferred from one generation to another. But a thoughtful scrutiny of the problem shows that it is a science of variability.

The regularities described in 1865 by a Czech naturalist Gregory Mendel, the founder of the heredity theory, show that a tremendous diversity of individuals with different gene sets emerge due to their different combinations in the progeny. It is the so-called combinative variability, and its potentialities are truly great (according to estimates, in order to have two absolutely similar children, to say nothing about homozygotic twins, the parents, differing by all genes, should give birth to more than 2²³ children). In addition, there exists also recombinative variability, caused by the chromosome crossingover during meiosis (sex cell division).

Let us add here mutations, which do not always result from, say, an explosion at the Chernobyl Power Plant (Ukraine) in 1986** or car smog. They often emerge

* Zygote is a diploid (containing a complete double chromosome set) cell forming as a result of fertilization (fusion of two gametes: oocyte and spermatozoon), initial stage of the embryo development.—Ed.

** See: V. Subbotin, "Nuclear Power Safety", Science in Russia, No. 1, 1999.—Ed.

Mitochondrion structure.

spontaneously as a result of cell division "errors" or under the effect of various reactions in the biochemical "boiler" of the organism, etc. At the beginning of the 20th century, Herman Muller, an American geneticist, Nobel Prizewinner of 1946, showed that it was not the mere fact of these transformations, but the increase in their incidence under the effect of this or that external factor that was important.

In a word, the forms of variability are different and create a motley picture, causing the genetic polymorphism of populations-panmixed (freely mating), rather stable communities of individuals of the same species with preset genotypes. However, as a result of, say, geographical isolation or socio-ethnic barriers they are divided into separate subpopulations, in which certain genes can accumulate.

GENETIC POLYMORPHISM AND ITS MANIFESTATIONS

We speak here primarily about numerous genes determining the activities of enzymes responsible for the majority of metabolic processes in the body. The probability of different states in patients exposed to similar factors is not accidental. Recently specialists from the Institute of General Reanimatology, RAMS, in collaboration with their colleagues from the Institute of General Genetics, RAS, demonstrated that the specific features of pneumonia development are largely determined by the gene polymorphism of cytochromes P-450*. Our staff members made similar conclusions also in relation of some other diseases.

In addition, humans react differently to one and the same medical intervention. This problem is best of all studied in relation of drugs, due to which a new trend of research has emerged: pharmacogenetics. It is important to point out that previously a wide spectrum of biochemical values had to be determined for these studies, while today due to the polymerase chain reaction**, it is possible to bring out beforehand the genes, participating in the production of enzymes involved in metabolism of this or that drug.

SOMATIC CELL GENOME DAMAGE

A storm of biochemical transformations emerges in the body during a disease development. From ancient times the physicians believed that the main indicators of inflammation were a dysfunction of the involved organ, erythema (red skin), edema, pain, and fever. The more extensive research led to the understanding of deep physicochemical transformations, associated with this process: the rate of reactions providing normal vital activity and the pH value-the acidity factor of the inner medium (the majority of enzymes work at definite pH values).

Biochemical transformations consist of many stages, with the formation of several intermediate "fragments"—free radicals participating in subsequent reactions and essential for their normal course. However, sometimes these special chemical particles emerge in

* Cytochromes P-450 are the main enzyme proteins involved in the metabolic transformations of many drugs.—Ed.

** Polymerase chain reaction is an experimental method of molecular biology, due to which it is possible to amplify significantly minor concentrations of certain DNA fragments in biological material. It was suggested by Kary Mullise. an American biochemist, in 1983,—Ed.

Complications in the group of patients with outpatient pneumonia.

excess, and they start reacting with compounds they are not intended for, including genetic structures, which they impair and disturb their functioning. A lot of viruses directly enter into the genome of blood cells or other tissues.

In certain cases mutagenic factors can overcome the barrier, which protects areas, where sex cells are formed, a majority of which is probably still unknown to us. The genome is damaged too (the totality of genes in a single set of chromosomes of sex cells). In other words, it becomes not only the subject, but also the object of the process of a disease.

At present the specialists are well informed about the molecular structure of the gene: a section of twisted "spiral" from two complementary (supplementing each other) DNA strands. Though, of course, we have a rather primitive scheme of its work. But even this is a great achievement of science, which allows to understand many things in nature.

Many diseases are associated with a release of hormones connected with an inflammatory process, the temperature and pH of the medium are changed, chains of free radicals are formed, and all this has an impact on the functioning and structure of the cellular genetic system. Our recent studies have shown that pneumonia and myocardial infaction are accompanied by significant disorders of reparation (restoration of the natural structure) of DNA. Development of critical and terminal states (states between life and death)* in laboratory animals and humans is associated with significant disorders in the structure of the blood cell chromosome system. In a series of studies, staff members of the Tomsk State University demonstrated mutagenic effects of many diseases (severe blood loss, measles, and other infections).

Besides, we must take into consideration the fact that such effects are not directional, a possible mutagenesis remains heterodirectional. Moreover, the treatment and a complex of rehabilitation measures after serious diseases should include obligatory measures to restore morphological and functional integrity of the genetic system, particularly for patients in critical and terminal states. No doubt, the organism has a genome stability support system, but under these conditions the functions of some genes are upset and directly damaged.

GENOME PROTECTION

Today the majority of scientists focus their attention on the role of the organism, in which spontaneous or induced mutagenesis can develop. It has been found that this process can progress or, vice versa, be reduced to a negligible level (even to complete absence of manifestations), depending on the genotype and functional state of the patient.

Studies of chemical reactions associated with this process, as our specialists have shown, help reveal key moments when human organism influences it. For example, the mutagen (agent causing mutations) gets into the body through the gastrointestinal, pulmonary, ophthalmic mucosal membranes or the skin. Then it gets into circulation, where it becomes bound to some of plasma components (liquid part of the blood), for example, with one of the plasma proteins (for some time "deactivating" and protecting this mutagen from destruction by enzymatic systems) and is disseminated in the body with this protein.

Reaching a "target" cell, the mutagen penetrates through its membrane, and when inside, it meets a potent "army" of enzymes, realizing metabolic transformations of xenobiotics (alien substances). As a result, numerous quinones, oxides, and other highly active free radicals form at first, after which there start processes leading to the formation of inert water-soluble compounds.

Eventually the mutagen or its metabolites (intermediate metabolic products) penetrate into the cell nucleus and cause primary DNA damage. At this moment the mechanisms of its reparation (restoration of its structure) start operating to eliminate the defect and if they

* See: G. Poroshenko, "Medicine of Critical States", Science in Russia, No. 5, 2004; "Between Life and Death". Ibid., No. 1, 2006.—Ed.

Spontaneous DNA synthesis in healthy people (1), patients with acute pneumonia (2) and myocardial infarction (3).

work effectively and accurately, the success is inevitable—mutation as such does not take place.

It is well-known that DNA reparation is regulated by some genes. However, many other factors, including diseases (myocardial infarction, tuberculosis, pneumonia, etc.) are also essential for restoration of DNA structure. If no gene reparation takes place, such gene modified cells are eliminated by immune or other mechanisms (apoptosis).

Mutagenic compounds and their metabolites are, as a rule, eliminated from the body via natural routes. However, some of them, that pose a threat for human health, can linger in some cells and cause their changes, while harmless ones can transform into harmful ones under the effect of enzymes or microorganisms. All this indicates that a medical intervention, for example, prescription of diuretics and other drugs, can accelerate their elimination in order to minimize the risk or grave-ness of the disease.

One of the basic characteristics of critical states is hypoxia, when the vital organs are deprived of oxygen. This condition involves disorders in electron transport in the mitochondria* and production of macroergic compounds**, functions of outer and inner membranes, stimulation of apoptosis (programmed cell death), etc. However, attempts to restore oxygen supply to tissues and organs result in more intense formation of free radicals, which leads to modification of the activities of enzymes servicing the DNA, and eventually in the formation of mutations. Presumably, one of the signs of a critical state is a damaged genetic system of somatic (non-sexual) cells. This state involves relaxation of immunological factors, tells on the disease course and quality of the patient's recovery.

Let us point out that determination of the degree of damage inflicted to the genetic system of somatic cells can serve as a prognostic method through the choice of treatment methods to reduce the level of these disorders.

* Mitochondria arc cell elements, on whose membrane a free electron passes from hydrogen to oxygen, as a result of which macroergic compounds are formed.—Ed.

** Macroergic compounds are organic compounds of living cells, containing energy-rich (macroergic) bonds. They are formed by photosynthesis, chemosynthesis. and biological oxidation.—Ed.