Cytochrome P450 and pharmacokinetics of drugs. Microsomal oxidation increases the reactivity of molecules History of cytochrome p450

Cytochromes P450

The cytochrome P-450 superfamily (CYP-450) is responsible for microsomal oxidation and is a group of enzymes with many isoforms (more than 1000) that not only metabolize drugs, but also participate in the synthesis of steroid hormones, cholesterol, and other substances.

The largest number of cytochromes was found in hepatocytes, as well as in organs such as the intestines, kidneys, lungs, brain, and heart. Based on the homology of the nucleotide and amino acid sequences, cytochrome isoenzymes are divided into families, which, in turn, are divided into subfamilies. Representatives of different families differ in substrate specificity and activity regulators (inductors and inhibitors). Although individual family members may have "cross" specificity and "cross" inducers and inhibitors. Thus, it has been shown that the antiviral drug ritonavir is metabolized by seven enzymes (CYP1A1, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4), and cimetidine inhibits four enzymes (CYP1A2, CYP2C9, CYP2D6, CYP3A4). The most important for drug biotransformation are cytochromes CYP1A1, CYP2A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A5. The relative contribution of various cytochromes and other detoxification phase I enzymes to drug metabolism is shown in Figure 7.2.2.

Each cytochrome P-450 isoenzyme is encoded by its own gene, which is localized on different chromosomes. Some of these genes have closely spaced pseudogenes (non-expressed copies), which significantly complicate genetic testing.

Due to the polymorphism of the metabolism genes, the activity of the corresponding enzymes in different individuals can vary significantly. Depending on these interindividual characteristics, three groups of individuals are distinguished, differing in the activity of a particular metabolic enzyme. These are the so-called "extensive" metabolizers - individuals with a normal rate of metabolism of drugs (the main part of the population), "slow" metabolizers (individuals with a reduced rate of metabolism of certain drugs) and "fast" ("overactive") metabolizers - individuals with an increased rate biotransformation of some drugs. The proportion of "slow" and "fast" metabolizers for individual metabolic enzymes reveals significant interpopulation differences. At the same time, a complete correlation of the genotype and phenotype in the rate of drug metabolism is not always observed, which indicates the need to use biochemical control in the genotyping of metabolic enzymes.

Let us consider the functional features of the polymorphism of the main genes of the CYP-450 cytochrome superfamilies involved in drug metabolism. Detailed information about the properties of metabolic enzymes, their substrate characteristics and genetic polymorphism can be found in a series of domestic monographs and textbooks on clinical pharmacogenetics.

The P-450 CYP1 family metabolizes a relatively small proportion of xenobiotics, the most important of which are polycyclic aromatic hydrocarbons (PAHs), the main components of tobacco smoke.

A particularly important role in this belongs to the CYP1A1 and CYP1A2 genes located on chromosome 15. The expression of both genes is regulated by the complex formed by the Ah receptor with the inducing PAH molecule, which penetrates the nucleus and specifically stimulates the expression of these genes.

CYP1A1 encodes a protein with aryl hydrocarbonate hydroxylase activity that controls the initial metabolism of PAHs, leading to the formation of carcinogens (for example, benzopyrene, which is formed during smoking). The CYP1A1 gene polymorphism is caused by three point mutations: C4887A and A4889G in exon 7 and T6235C in the 3'-flanking region. The G4889(Val)+C6235 substitution is characterized by the appearance of the “fast” allele *2B. It is 3 times more active than the wild-type allele. *2B occurs in up to 7% of Caucasians and is considered a risk factor for lung cancer. It has been shown that in the presence of the *2B allele in smokers, the risk of developing lung cancer increases by more than seven times compared to non-smokers. The risk becomes even greater if, in addition to the *2B allele of the CYP1A1 gene, the smoking individual also has an "inferior" allele of the GSTM1 gene. Alleles *2A (C6235) and *4 (A4887(Asp) occur in the population with a frequency of only 1-3%. At the same time, the *2A allele is associated with a hereditary predisposition to leukemia and resistance to drug therapy for this disease.

The CYP1A2 gene product metabolizes only PAHs, but also compounds such as caffeine, theophylline, etc. It has been shown that the presence of the *1A allele of the CYP1A2 gene inhibits the metabolism of drugs such as caffeine, deazepam, verapamil, methadone, theophylline, estradiol.

The P-450 CYP2 family is represented by a group of functionally most significant enzymes that metabolize a huge number of different drugs. Their activity reveals a pronounced dependence on genetic polymorphism.

The CYP2A subfamily is the most important isoenzyme of this subfamily. It is involved in the conversion of nicotine to cotinine, in the hydroxylation of coumarin and cyclophosamide, and contributes to the metabolism of ritonavir, paracetamol, and valproic acid. CYP2A6 is involved in the bioactivation of tobacco smoke components - nitrosamines, which cause lung cancer. The CYP1A6 gene is located on chromosome 19 at the locus 19q13.2. The gene is mainly expressed in the liver. It has been shown that the *4 allele of the CYP1A6 gene is protective, i.e., it is associated with a lower risk of lung cancer. The presence of *2 and *3 alleles is associated with reduced coumarin metabolism, which is important when dosing this drug due to possible hepatotoxic effects.

Subfamily CYP2B. All enzymes of this subfamily are induced by phenobarbital. The most significant enzyme is CYP2B6, which metabolizes many cytostatic drugs (cyclophosamide), antivirals (efavirenz and nevirapine), antidepressants (bupropion), anesthetics (propofol) and synthetic opioids (methadone), and is also involved in the metabolism of endogenous steroids. The CYP2B6 gene is located at the same locus as the CYP2A6 gene and is expressed predominantly in the liver. The presence of slow alleles of the CYP2B6 gene (*2, *4, *5, *6) reduces the rate of metabolism of antiviral drugs, which leads to a decrease in clearance and increases the risk of CNS complications.

The CYP2C subfamily plays a key role in the metabolism of many drugs. A common property of these isoenzymes is the presence of 4-hydrolase activity against the anticonvulsant drug mephenytoin.

Especially important for clinical pharmacogenetics is the testing of polymorphism of the CYP2C9 gene, localized in the locus 10q24. The gene is expressed mainly in the liver and is the main metabolizer of angiotensin receptor inhibitors (losartan and irbersartan). Its substrates are also anticoagulants (warfarin), sugar-lowering drugs (glipizide), anticonvulsants (phenytoin, diazepam), antidepressants (amitriptyline, clomipramine, imipramine), proton pump inhibitors (omeprazole), non-steroidal anti-inflammatory drugs (diclofenac, ibuprofen, piroxicam) , tolbutamine . As already mentioned, the CYP2C9 gene polymorphism analysis was the first officially approved genetic test (see above). The number of individuals with reduced activity of this enzyme in the domestic population is up to 20%. At the same time, in order to avoid unwanted side effects, the therapeutic dose of the above drugs in carriers of the *2 and *3 alleles of the CYP2C9 gene must be reduced by 2-4 times.

The CYP2C19 gene is located at the 10q24.1-q24.3 locus and is expressed in the liver. Its protein product is the main enzyme in the metabolism of proton pump inhibitors (omeprazole) and anticonvulsants (proguanil, valproic acid, diazepam, barbiturates). The frequency of its "slow" allele (*2) in the European population ranges from 5 to 200%.

Subfamily CYP2D. Cytochrome CYP2D6 metabolizes about 20% of all known drugs. The CYP2D6 gene is located on chromosome 22 at the locus 22q13.1. The main site of its expression is the liver. Currently, more than 36 alleles have been identified in the CYP2D6 gene, some of them are characterized by the absence of a protein product, while others lead to the appearance of an enzyme with altered properties. Substrates of the CYP2D6 enzyme are drugs widely used in clinical practice, such as beta-blockers, antidepressants, antipsychotropic substances, antiarrhythmics, antipsychotics, antihypertensive drugs, monooxide reductase inhibitors, morphine derivatives, neurotransmitters (dopamines), analgesics, opiates. Taking into account that about 6-10% of Caucasians are slow metabolizers of this enzyme, the need for genetic testing of CYP2D6 in order to adjust the doses of these drugs is obvious. In addition, "functionally weakened" alleles of this gene are associated with a hereditary predisposition to such serious diseases as lung cancer, bowel cancer, etc.

Subfamily CYP2E. Cytochrome CYP2E1 belongs to ethanol-inducible enzymes. Its substrates are carbontetrachloride, dimethylnitrosamine. There is evidence that CYP2E1, along with CYP1A2, is involved in the conversion of paracetamol to N-acetylbenzoquinoneimine, which has a powerful hepatotoxic effect. In addition, it is the most important isoenzyme of a group of cytochromes that oxidize low-density lipoprotein cholesterol, which in turn leads to the formation of atherosclerotic plaques. The CYP2E1 gene is located at the 10q24.3-qter locus and is expressed in the liver of adults. Taq1 polymorphism in the CYP2E1 gene leads to a decrease in the activity of this enzyme. M/M homozygotes for the attenuated allele of the CYP2E1 gene show increased sensitivity to the above drugs due to their delayed detoxification.

Cytochrome P-450 CYP3 family

The CYP3A subfamily is the most numerous. It accounts for about 30% of all cytochrome P-450 isoenzymes in the liver and 70% of all isoenzymes of the gastrointestinal tract wall. The most significant are the CYP3A4 and CYP3A5 enzymes, whose genes are located at the 7q22.1 locus. The CYP3A4 gene is predominantly expressed in the liver, while CYP3A5 is expressed in the gastrointestinal tract.

The CYP3A4 enzyme metabolizes over 60% of all drugs and plays an important role in testosterone and estrogen metabolism. Allelic variants of the CYP3A4 gene are very numerous, but data on their effect on the pharmacokinetics of the respective drugs are contradictory.

The CYP3A5 enzyme metabolizes some of the drugs that CYP3A4 interacts with. It has been shown that the presence of the *3 allele of the CYP3A5 gene leads to a decrease in the clearance of such drugs as alprazolam, midazolam, saquinavir.

Paraoxonase is an enzyme responsible for the synthesis of paraoxonase, a blood plasma protein. In addition, the enzyme inactivates organophosphates, organophosphates, carbamates, and acetic acid esters. Some of these substances are chemical warfare agents - sarin, soman, tabun. Of the three known isoforms, PON1 is the most important. Its gene is located at the 7q21.3 locus. The most significant and studied polymorphism is the substitution of glutamine for arginine at position 192 (L/M polymorphism). It has been shown that the M allele is associated with a reduced metabolism of organophosphorus compounds.

The M allele and M/M genotype increase the risk of developing Parkinson's disease, especially in combination with the 5 allele of the GSTP1 gene, and are associated with the formation of atherosclerotic plaques.

Alcohol- and aldehyde dehydrogenases

Alcohol dehydrogenase is a key enzyme in the catabolism of ethanol and other alcohols, oxidizing alcohols to aldehydes. In adults, the ADH1B gene is expressed in the liver. There is a certain dynamics of its expression level depending on age. The ADH1B (ADH2) gene is located at the 4q22 locus. The most studied polymorphism is G141A. It has been shown that the A allele is associated with an increased activity of the enzyme, which leads to an excessive accumulation of intermediate metabolic products - aldehydes, which have a pronounced toxic effect. Individuals with the A allele of the ADH1B gene have an increased sensitivity to ethanol and are less prone to alcoholism.

Two aldehyde dehydrogenases are also present in liver cells: ALDH1 (cytosolic) and ALDH2 (mitochondrial). The ALDH2 gene is located at the 12q24.2 locus; its product plays a key role in the conversion of toxic aldehydes into the corresponding carboxylic acids, which are easily removed from the body. ALDH2 plays an important role in the catabolism of alcohol. It is known that in representatives of the yellow race, alcohol intoxication is due to the absence of ALDH2 in almost 50% of the population. Polymorphism in the ALDH2 gene leads to the replacement of Glu at position 487 of the protein (ALDH2*1 allele) with Lys (ALDH2*2 allele). The ALDH2*2 allele encodes an enzyme with reduced activity. In heterozygotes, the activity of the enzyme is reduced by 10 times. The ALDH2 enzyme has been implicated in the pathogenesis of various alcohol-related cancers - hepatocellular carcinoma, cancer of the esophagus, pharynx, and oral cavity.

Intensive alcohol intake in individuals with unfavorable allelic variants of the ADH1B and ALDH2 genes can lead to the rapid development of hepatic complications: alcoholic disease and liver cirrhosis.

P450 are membrane proteins.

The cytochrome P450 system is involved in the oxidation of numerous compounds, both endogenous and exogenous. Enzymes of this group play an important role in the metabolism of steroids, bile acids, unsaturated fatty acids, phenolic metabolites, as well as in the neutralization of xenobiotics (drugs, poisons, drugs).

Reactions involving the cytochrome P450 system

Cytochrome P450-dependent monooxygenases catalyze the breakdown of various substances through hydroxylation with the participation of the electron donor NADP H and molecular oxygen. In this reaction, one oxygen atom is added to the substrate and the second is reduced to water.

Enzymes of the cytochrome P450 family, unlike other hemoproteins, as a rule, having one type of activity and a strictly defined function, are quite diverse in functions, types of enzymatic activity, and often have low substrate specificity. P450s can exhibit both monooxygenase and oxygenase activity and are therefore sometimes referred to as mixed-function oxidases.

Oxygenase reactions catalyzed by cytochrome P450 are very diverse. One of the most common oxidation reactions of xenobiotics is oxidative dealkylation, accompanied by the oxidation of an alkyl group attached to the N, O or S atoms. This process occurs in the endoplasmic reticulum (EPR) of hepatocytes. Their substrate specificity is low. They most efficiently catalyze the oxidation of non-polar compounds with aliphatic or aromatic rings. P450 of the liver, among other things, is involved in the oxidation of alcohols to the corresponding aldehydes. Hydroxylation of hydrophobic compounds improves their water solubility and promotes excretion through the kidneys. In different people, the set of cytochromes P450 in the EPR differs due to genetic characteristics. In this regard, the study of the P450 enzymatic system is of great importance for pharmacology. All other enzymes of the P450 family are located on * , and their catalytic centers face the matrix.

Another common type of reaction is the hydroxylation of cyclic compounds (aromatic, saturated and heterocyclic hydrocarbons). Enzymes of the P450 family can also catalyze hydroxylation reactions of aliphatic compounds, N-oxidation, oxidative deamination, reduction reactions of nitro compounds.

Human cytochrome P450 genes

Family	Functions	Compound	Titles
CYP1	metabolism of drugs and steroids (especially estrogen)	3 subfamilies, 3 genes, 1 pseudogene	CYP1A1, CYP1A2, CYP1B1
CYP2	drug and steroid metabolism	13 subfamilies, 16 genes, 16 pseudogenes	CYP2A6 , CYP2A7 , CYP2A13 , CYP2B6 , CYP2C8 , CYP2C9 , CYP2C18 , CYP2C19 , CYP2D6 , CYP2E1 , CYP2F1 , CYP2J2 , CYP2R1 , CYP2S1 , CYP2U1 , CYP2W1
CYP3	drug and steroid metabolism (including testosterone)	1 subfamily, 4 genes, 2 pseudogenes	CYP3A4, CYP3A5, CYP3A7, CYP3A43
CYP4	arachidonic acid metabolism	6 subfamilies, 12 genes, 10 pseudogenes	CYP4A11 , CYP4A22 , CYP4B1 , CYP4F2 , CYP4F3 , CYP4F8 , CYP4F11 , CYP4F12 , CYP4F22 , CYP4V2 , CYP4X1 , CYP4Z1
CYP5	synthesis of thromboxane A 2	1 subfamily, 1 gene	CYP5A1 (thromboxane synthase A 2)
CYP7	bile acid biosynthesis, participation in steroid metabolism	2 subfamilies, 2 genes	CYP7A1, CYP7B1
CYP8	various	2 subfamilies, 2 genes	CYP8A1 (prostacyclin synthesis), CYP8B1 (bile acid biosynthesis)
CYP11	steroid biosynthesis	2 subfamilies, 3 genes	CYP11A1, CYP11B1, CYP11B2
CYP17	steroid biosynthesis, 17-alpha hydroxylase	1 subfamily, 1 gene	CYP17A1
CYP19	steroid biosynthesis (aromatase, which synthesizes estrogen)	1 subfamily, 1 gene	CYP19A1
CYP20	not installed	1 subfamily, 1 gene	CYP20A1
CYP21	steroid biosynthesis	2 subfamilies, 1 gene, 1 pseudogene	CYP21A2
CYP24	biodegradation of vitamin D	1 subfamily, 1 gene	CYP24A1
CYP26	hydroxylation of retinolic acid	3 subfamilies, 3 genes	CYP26A1, CYP26B1, CYP26C1
CYP27	various	3 subfamilies, 3 genes	CYP27A1 (bile acid biosynthesis), CYP27B1 (vitamin D3 activating 1-alpha-hydroxylase vitamin D3), CYP27C1 (function not established)
CYP39	7-alpha-hydroxylation of 24-hydroxycholesterol	1 subfamily, 1 gene	CYP39A1
CYP46	cholesterol 24-hydroxylase	1 subfamily, 1 gene	CYP46A1
CYP51	cholesterol biosynthesis	1 subfamily, 1 gene, 3 pseudogenes	CYP51A1 (14-alpha demethylase lanosterol)

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Notes

1. , With. 180-181.
2. , With. 310-311.
3. Danielson P.B.(English) // Current drug metabolism. - 2002. - Vol. 3, no. 6. - P. 561-597. - PMID 12369887 .to correct
4. Ortiz de Montellano, Paul R. Cytochrome P450: structure, mechanism, and biochemistry. - 3rd edition. - New York: Kluwer Academic/Plenum Publishers, 2005. - ISBN 0-306-48324-6 .
5. , With. 348-349.
6. .

Literature

• D. Nelson, M. Cox. Fundamentals of Lehninger's biochemistry: in 3 volumes - M .: BINOM, 2014. - V. 2. - S. 348-349. - 636 p. - ISBN 978-5-94774-366-1.
• Britton G.. - Moscow: Mir, 1986. - 422 p. - 3050 copies.
• Jan Kolman, Klaus-Heinrich Rehm.= Taschenatlas der Biochemie. - Moscow: Mir, 2000. - 470 p. - 7000 copies.
• Ponomarenko T. M., Sychev D. A., Chikalo A. O., Berdnikova N. G., Kukes V. G.// Pharmacokinetics and Pharmacodynamics. - 2012. - No. 1. - S. 25-28.

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An excerpt characterizing Cytochrome P450

Both the countess and Sonya understood that Moscow, the fire of Moscow, whatever it was, of course, could not matter to Natasha.
The count again went behind the partition and lay down. The countess went up to Natasha, touched her head with her upturned hand, as she did when her daughter was sick, then touched her forehead with her lips, as if to find out if there was a fever, and kissed her.
- You are cold. You're all trembling. You should go to bed,” she said.
- Lie down? Yes, okay, I'll go to bed. I'm going to bed now, - said Natasha.
Since Natasha was told this morning that Prince Andrei was seriously wounded and was traveling with them, she only in the first minute asked a lot about where? How? is he dangerously injured? and can she see him? But after she was told that she was not allowed to see him, that he was seriously injured, but that his life was not in danger, she obviously did not believe what she was told, but convinced that no matter how much she said, she would be answer the same thing, stopped asking and talking. All the way, with big eyes, which the countess knew so well and whose expression the countess was so afraid of, Natasha sat motionless in the corner of the carriage and was now sitting in the same way on the bench on which she sat down. She was thinking about something, something she was deciding or had already decided in her mind now - the countess knew this, but what it was, she did not know, and this frightened and tormented her.
- Natasha, undress, my dear, lie down on my bed. (Only the countess alone was made a bed on the bed; m me Schoss and both young ladies had to sleep on the floor in the hay.)
“No, mom, I’ll lie down here on the floor,” Natasha said angrily, went to the window and opened it. The groan of the adjutant was heard more distinctly from the open window. She stuck her head out into the damp night air, and the countess saw her thin shoulders tremble with sobs and beat against the frame. Natasha knew that it was not Prince Andrei who was moaning. She knew that Prince Andrei was lying in the same connection where they were, in another hut across the passage; but this terrible unceasing groan made her sob. The Countess exchanged glances with Sonya.
"Lie down, my dear, lie down, my friend," said the countess, lightly touching Natasha's shoulder with her hand. - Well, go to bed.
“Ah, yes ... I’ll lie down now, now,” said Natasha, hastily undressing and tearing off the strings of her skirts. Throwing off her dress and putting on a jacket, she tucked her legs up, sat down on the bed prepared on the floor and, throwing her short, thin braid over her shoulder, began to weave it. Thin long habitual fingers quickly, deftly took apart, weaved, tied a braid. Natasha's head, with a habitual gesture, turned first to one side, then to the other, but her eyes, feverishly open, fixedly stared straight ahead. When the night costume was over, Natasha quietly sank down on a sheet spread on hay from the edge of the door.
“Natasha, lie down in the middle,” said Sonya.
“No, I’m here,” Natasha said. "Go to bed," she added with annoyance. And she buried her face in the pillow.
The countess, m me Schoss, and Sonya hurriedly undressed and lay down. One lamp was left in the room. But in the yard it was getting brighter from the fire of Maly Mytishchi, two miles away, and the drunken cries of the people were buzzing in the tavern, which was broken by the Mamonov Cossacks, on the warp, in the street, and the incessant groan of the adjutant was heard all the time.
For a long time Natasha listened to the internal and external sounds that reached her, and did not move. At first she heard her mother's prayer and sighs, the creaking of her bed under her, the familiar whistling snore of m me Schoss, Sonya's quiet breathing. Then the Countess called Natasha. Natasha did not answer her.
“He seems to be sleeping, mother,” Sonya answered quietly. The Countess, after a pause, called again, but no one answered her.
Soon after, Natasha heard her mother's even breathing. Natasha did not move, despite the fact that her small bare foot, knocked out from under the covers, shivered on the bare floor.
As if celebrating the victory over everyone, a cricket screamed in the crack. The rooster crowed far away, relatives responded. In the tavern, the screams died down, only the same stand of the adjutant was heard. Natasha got up.
- Sonya? are you sleeping? Mother? she whispered. No one answered. Natasha slowly and cautiously got up, crossed herself and carefully stepped with her narrow and flexible bare foot on the dirty cold floor. The floorboard creaked. She, quickly moving her feet, ran like a kitten a few steps and took hold of the cold bracket of the door.
It seemed to her that something heavy, evenly striking, was knocking on all the walls of the hut: it was beating her heart, which was dying from fear, from horror and love, bursting.
She opened the door, stepped over the threshold and stepped onto the damp, cold earth of the porch. The chill that gripped her refreshed her. She felt the sleeping man with her bare foot, stepped over him and opened the door to the hut where Prince Andrei lay. It was dark in this hut. In the back corner, by the bed, on which something was lying, on a bench stood a tallow candle burnt with a large mushroom.
In the morning, Natasha, when she was told about the wound and the presence of Prince Andrei, decided that she should see him. She didn't know what it was for, but she knew that the date would be painful, and she was even more convinced that it was necessary.
All day she lived only in the hope that at night she would see him. But now that the moment had come, she was terrified of what she would see. How was he mutilated? What was left of him? Was he like that, what was that unceasing groan of the adjutant? Yes, he was. He was in her imagination the personification of that terrible moan. When she saw an indistinct mass in the corner and took his knees raised under the covers by his shoulders, she imagined some kind of terrible body and stopped in horror. But an irresistible force pulled her forward. She cautiously took one step, then another, and found herself in the middle of a small cluttered hut. In the hut, under the images, another person was lying on benches (it was Timokhin), and two more people were lying on the floor (they were a doctor and a valet).
The valet got up and whispered something. Timokhin, suffering from pain in his wounded leg, did not sleep and looked with all his eyes at the strange appearance of a girl in a poor shirt, jacket and eternal cap. The sleepy and frightened words of the valet; "What do you want, why?" - they only made Natasha come up to the one that lay in the corner as soon as possible. As terrifying as this body was, it must have been visible to her. She passed the valet: the burning mushroom of the candle fell off, and she clearly saw Prince Andrei lying on the blanket with outstretched arms, just as she had always seen him.
He was the same as always; but the inflamed complexion of his face, the brilliant eyes fixed enthusiastically on her, and especially the tender childish neck protruding from the laid back collar of his shirt, gave him a special, innocent, childish look, which, however, she had never seen in Prince Andrei. She walked over to him and, with a quick, lithe, youthful movement, knelt down.
He smiled and extended his hand to her.

For Prince Andrei, seven days have passed since he woke up at the dressing station in the Borodino field. All this time he was almost in constant unconsciousness. The fever and inflammation of the intestines, which were damaged, in the opinion of the doctor who was traveling with the wounded, must have carried him away. But on the seventh day he ate a piece of bread with tea with pleasure, and the doctor noticed that the general fever had decreased. Prince Andrei regained consciousness in the morning. The first night after leaving Moscow was quite warm, and Prince Andrei was left to sleep in a carriage; but in Mytishchi the wounded man himself demanded to be carried out and to be given tea. The pain inflicted on him by being carried to the hut made Prince Andrei moan loudly and lose consciousness again. When they laid him down on the camp bed, he lay with his eyes closed for a long time without moving. Then he opened them and whispered softly: “What about tea?” This memory for the small details of life struck the doctor. He felt his pulse and, to his surprise and displeasure, noticed that the pulse was better. To his displeasure, the doctor noticed this because he was convinced from his experience that Prince Andrei could not live, and that if he did not die now, he would only die with great suffering a few time later. With Prince Andrei they carried the major of his regiment Timokhin, who had joined them in Moscow, with a red nose, wounded in the leg in the same Battle of Borodino. They were accompanied by a doctor, the prince's valet, his coachman and two batmen.
Prince Andrei was given tea. He drank greedily, looking ahead at the door with feverish eyes, as if trying to understand and remember something.
- I don't want any more. Timokhin here? - he asked. Timokhin crawled up to him along the bench.
“I'm here, Your Excellency.
- How is the wound?
– My then with? Nothing. Here you are? - Prince Andrei again thought, as if remembering something.
- Could you get a book? - he said.
- Which book?
– Gospel! I have no.
The doctor promised to get it and began to question the prince about how he felt. Prince Andrei reluctantly but reasonably answered all the doctor's questions and then said that he should have put a roller on him, otherwise it would be awkward and very painful. The doctor and the valet raised the overcoat with which he was covered, and, wincing at the heavy smell of rotten meat spreading from the wound, began to examine this terrible place. The doctor was very dissatisfied with something, he altered something differently, turned the wounded man over so that he again groaned and, from pain during the turning, again lost consciousness and began to rave. He kept talking about getting this book as soon as possible and putting it there.

Drapkina O.M.

i>Academician Ivashkin V.T.: – Oksana Mikhailovna, you have the opportunity to make your presentation “Cytochrome P450 and pharmacokinetics of drugs”. Please!

Professor Drapkina O.M.:– Today it fell to me to talk about cytochrome P450 and possible drug interactions. And, basically, I will, I will say right away, touch on the issue of the interaction of proton pump inhibitors and clopidogrel. Lots of posts on this topic. In general, everything is still not completely clear, but I will try to present my point of view on this problem.

So, if we are talking about drug interactions, then we can or should first, apparently, define that drug interactions are a change in the pharmacological effect of one or more drugs (drugs) with their simultaneous or sequential use.

And just as in general in life all interactions can be divided, so can drug interactions, into:

• sensitizing effect;
• additive action;
• those moments when the summation of the action occurs;
• and potentiation of effects.

This all belongs to the class of synergism, when a friendly reaction of drugs occurs, or antagonism.

Types of drug interactions are also divided according to clinical pharmacokinetics into:

- pharmaceutical, which implies various interactions outside the body;

- pharmacokinetic - this is a change in the pharmacokinetic characteristics of medicinal substances;

- pharmacodynamic, when there is a change in one of the drugs used.

All the drugs that our patient uses, that we use with you, go through the same path. These are two phases.

Phase I is the oxidation phase. And just here the cytochrome P450 system takes on a big role, or the main role.

And phase II, in which several such subphases can also be distinguished, ending with methylation and conjugation with various substances presented on the slide.

I must say that the cytochrome P450 system is a very complex system, it is a system of microsomal oxidation. If, or because of, this system, we continue to live and live long, and strive for our patients to live long, because the main way of detoxification and metabolism of drugs, and, in addition, this is the main way and the main opportunity to make substances soluble and eliminate them from the body.

The main localization is the liver, although this system is present in some other organs. And, as I said, the main task is to make complex systems, make substances less toxic and better soluble so that they are excreted by the kidneys.

I will try to briefly illustrate how cytochrome P450 works. This is a powerful system. It is so powerful that it can break an oxygen atom, i.e. O 2 , divide it into two electrons, and insert one electron into a xenobiotic, or into a drug that is poorly soluble. So, we have a poorly soluble substance, or a xenobiotic, there is oxygen O 2, and there is a universal reducing agent NADP + H +. This H + is also needed in order for an additional proton to be given. And as a result of transformation through the cytochrome P450 system, we see that as a result of this reaction, water is formed, the oxidized reducing agent NADP and already a xenobiotic, in which the oxygen proton and electron are built. This xenobiotic can already be excreted as a soluble substance.

The main work in this large family, consisting of various cytochrome P450 isoforms, of course, the main work falls on CYP3A4, which is almost 34%. But today I will focus more on the isoform that is responsible for 8% of metabolism and proton pump inhibitor, for the most part, it is also metabolized with the help of cytochrome and its CYP2C19 isoform. It is also metabolized by cytochrome and its CYP2C19 isoform.

Its features are such that it makes up a little, only about 1% of the pool of liver cytochromes, while, as shown in the previous slide, it metabolizes about 8% of drugs. It is characterized by genetic polymorphism and its metabolism has been studied mainly with omeprazole, so the next two slides will present the kinetics and conversion of omeprazole. Studied there are works with other substrates, which are presented on this slide. But for our clinic, of course, the metabolism of warfarin is of greatest interest, since there are more and more such patients with atrial fibrillation, propranolol, and proton pump inhibitors.

So we can say, or model the situation, that there are three possible patterns of drug-drug interactions.

The first is when the drug and the second drug, which is a cytochrome inducer (for example, phenobarbital), lead to an acceleration of metabolism and a decrease in the plasma lifetime of the drug that is shown first on this slide.

The second situation is when a person uses a cytochrome inhibitor (for example, fluoroquinolones) together with a drug or with a drug. This leads to a slowdown in metabolism and an increase in the "life" time in the blood plasma.

There is also such a situation when two drugs are metabolized in the same isoform of the cytochrome P450 CYP system, drug 1 and drug 2, and in this case, the metabolism of both drugs is slowed down. This is exactly the scheme today, to a greater extent, I will consider.

I have already said that cytochrome P450 is CYP2C19, its marker agent is omeprazole, and therefore the effect of omeprazole on the cytochrome P450 system has been very well studied. It is known to inhibit what it induces and is metabolized.

There are different omeprazoles. We know dextrorotatory and levorotatory. But in fact, despite the many publications that levorotatory isomers have slightly different properties and a slightly different metabolism. Cytochrome P450, namely the CYP2C19 isoform, is responsible for both the metabolism of omeprazole, both the dextrorotatory and levorotatory isomer, which we know as esomeprazole.

As I said, the contribution of genetic polymorphisms is important. This is approximately 3% of the population. This leads to the fact that the concentration of omeprazole increases in the blood plasma, and, accordingly, the greater the concentration of omeprazole, the greater the risk of drug interactions, for example, with clopidogrel, which is also metabolized by the cytochrome P450 system precisely by the CYP2C19 isoform.

Recent studies have shown that the life of a person with acute coronary syndrome may also depend on the activity of this cytochrome, therefore, people with reduced cytochrome P450 metabolism have a more severe prognosis and a higher risk of stent thrombosis of repeated myocardial infarctions. In the Caucasian race, this is approximately 2%, and Mongoloids have slightly more such slow metabolizers.

If we now touch on the pharmacokinetics of clopidogrel, then we also know that this is an inactive substance, and in order to turn into an active thiol derivative of clopidogrel, clopidogrel needs to go through the liver to this inactive substance, through the CYP2C19 system, turning at an intermediate stage into 2 -oxo-clopidogrel. And only then this thiol derivative can irreversibly bind to receptors on platelets induced by ATP.

Thus, it turns out that the pharmacodynamic interaction of clopidogrel, which was illustrated a few slides earlier, depends not only on the fact that the same cytochrome isoform is loaded, but also on the dose. The higher, for example, the dose of omeprazole or another proton pump inhibitor, the lower the dose of the active metabolite of clopidogrel, respectively, the greater the risk of thrombosis in these patients.

The question arises: what to do? You can not use clopidogrel, for example, in patients. Or it is worth replacing clopidogrel with aspirin. Omeprazole may be omitted or omeprazole may be substituted with other proton pump inhibitors (PPIs). It seems to me that we will answer the first two questions, especially the first question, in the negative. It is impossible to replace or not use clopidogrel, because statistics show that more and more stents are being installed, there are also many coronary heart diseases with various complications. Therefore, all the data, here is one of the studies - the CURE study, showed that, nevertheless, the use of two-component platelet therapy (clopidogrel + aspirin) reduces the risk of developing acute myocardial infarction by 31%. The same or similar data were found in the ACAPRI study, when it was shown at the very beginning that clopidogrel was as effective as aspirin.

The second question is: is there a clinically significant interaction between PPIs and aspirin? It turns out that in 2011, work was published that showed that clinical interactions are also possible between aspirin and proton pump inhibitors. And this study showed that about 50,000 patients with acute myocardial infarction, if they took PPIs, the risk of acute myocardial infarction increased by 46%.

And finally, clopidogrel. It is believed, especially after the ACAPRI study, that clopidogrel is just as effective and appears to be safer. But, nevertheless, even this slightly greater safety is still associated with the fact that there is a risk of developing gastroduodenal ulcers. The risk especially increases with the combined use of clopidogrel and aspirin, it is 7 times higher. And, accordingly, PPIs can certainly help here.

The feasibility of prophylactic administration of proton pump inhibitors has been proven in many studies. Here are the statistics too. PPI against the background of the use of non-steroidal anti-inflammatory drugs reduces gastrointestinal bleeding by 37%. And we see that low doses of aspirin in patients, which we, roughly speaking, covered with proton pump inhibitors, also reduce the risk of bleeding, on average, by about a third.

Thus, the recommendations that we are now given suggest that a PPI (not omeprazole) is indicated for patients with coronary artery stents receiving clopidogrel, who are over 65 years of age, who have had a history of peptic ulcer disease and who have other factors of increased risk of gastrointestinal bleeding. This, in fact, is the CRUSADE scale that Professor Zateyshchikov spoke about today. Many meta-analyses have been carried out. And in fact, now in the recommendations, it is also given to the desire of the doctor, which PPI to choose, but, nevertheless, those meta-analyses presented on this slide indicate that, nevertheless, PPIs reduce the activity of clopidogrel and to a lesser extent degrees affect the kinetics of cytochrome P450 CYP2C19, namely rabeprazole and pantoprazole.

The interaction effect has been noted in many works. I have collected several of them. The first is a study in 26 patients that was initially, clopidogrel at a loading dose along with lansoprazole, resulted in a 13% decrease in clopidogrel concentrations.

Another prospective study - patients (there are already 300 of them) with acute coronary syndrome, after angioplasty, clopidogrel with pantoprazole - a statistically insignificant decrease in the effect of clopidogrel on platelets.

Finally, a retrospective study of more than 16,000 patients undergoing angioplasty, clopidogrel with PPIs also showed an increased risk of reaching the combined endpoint.

The following study is a rather famous study Ho and co-authors, also a retrospective cohort study, patients with acute coronary syndrome. They were followed for 3 years. They received clopidogrel for 3 years. An increase in mortality and repeated ACS were noted, i.e. myocardial infarctions, in the group of patients who received PPIs together with clopidogrel, by 25%.

In Canada, these data have also been confirmed. More than 13,000 patients with ACS. An increase in mortality was observed against the background of the use of clopidogrel in conjunction with a PPI (it was omeprazole) by 40%. The exception was patients who received rabeprazole and pantoprazole, which had a lesser effect on CYP2C19, and there was also no increase in mortality against the background of H2-blockers.

In addition, there were studies that showed changes in platelet function, suppression of platelet function, against the background of the use of clopidogrel along with aspirin, and then omeprazole was added to this combination. So in these patients who received omeprazole, by the 7th day there was a significant increase in platelet reactivity. Thus, rabeprazole and pantoprazole are, in my opinion, the drugs that should be used in patients on dual antiplatelet therapy.

And also a few confirmations. The Sharara study, which decided to aim to see if clopidogrel with rabeprazole or clopidogrel with esoprazole, affects antiplatelet properties. It turned out that the percentage of patients in whom vasoreactivity changed was greater in the clopidogrel plus omeprazole group.

And the next study, the last one I will focus on. The researchers set out to look at the effect of rabeprazole on the antiplatelet properties of clopidogrel. We know rabeprazole as pariet being evaluated in our clinical practice. Platelet reactivity index was assessed. And it turned out, when we looked, compared the placebo group, the omeprazole group and the rabeprazole group, that there were no changes, i.e. changes are not statistically significant. However, when we looked at and evaluated patients who responded well to clopidogrel therapy, it turned out that in the rabeprazole group, this change in platelet reactivity index was almost the same as in placebo. But in omeprazole it was 43.2%. A small figure (-47.3% and -43.2%), however, it had a statistically significant characteristic, which indicated that in the omeprazole group the platelet reactivity index was indeed changed.

Thus, if a patient comes to us with dual platelet therapy, then the risk of NSAIDs and antiplatelet drugs should first be assessed. We divide them into high-risk patients, moderate-risk patients, and low-risk patients when there are no risk factors. So, high risk. Complicated ulcer history, multiple risk factors. Moderate risk is age over 65, high dose of NSAIDs.

And accordingly, summing up all these recommendations, I propose the following scheme. PPIs when taking antiplatelet agents, I want to say again - rabeprazole, pariet, should be prescribed to all patients with a history of ulcerative complications, without bleeding, people with a history of gastrointestinal bleeding, all those who are currently receiving dual antiplatelet therapy, concomitant anticoagulant therapy and has one of the risk factors, for example, age, treatment with corticosteroids, or having manifestations of gastroesophageal reflux disease.

What is a 21st century patient? We mainly deal with patients over 65 years of age. And what is this patient like? In this patient, almost everything that can be blocked is blocked. With calcium channel blockers, and beta-blockers, and drugs that affect the renin-angiotensin-aldosterone system, we blocked the corresponding receptors. Aspirin and clopidogrel are cyclooxygenase and platelets are also blocked. God forbid if these patients are still obese, and God forbid if he is on drugs that lower the levels of orlistat (a pancreatic lipase inhibitor). GMC-CoA reductase is also blocked with rosuvastatin, and blocked with metformin. Therefore, more than 50 patients who come to us over 6 years old take more than 5 drugs. Accordingly, drug interactions are inevitable here. And of course, in this case it is better to choose the drug that will not or will interfere to a lesser extent with the work of cytochrome P450. And therefore, in this course between Scylla and Charybdis, in a patient with dual antiplatelet therapy or even with single platelet therapy, on the one hand, ulcers and bleeding, on the other hand, a decrease in coronary events, rabeprazole (pariet) can probably help. Thank you for your attention!

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