OF ATTRIBUTION OF TO AND MODULATORS OF FUNCTIONAL ACTIVITY OF ABCB1-PROTEIN IN IN VIVO EXPERIMENT

quantity of the substance was determined by HPLC method according to the previously developed procedure. Belonging of Noopept to ABCB1-protein substrates was estimated by comparison of its pharmacokinetic parameters before and after a course of introduction of verapamil (the known inhibitor of the ABCB1-protein) into male rabbits in the dose 20 mg/kg b.w. 3 times a day. The pharmacokinetics of Noopept was studied by the original HPLC method. It was found that the course of Noopept introduction did not lead to any reliable changes in the pharmacokinetic parameters of the ABCB1-protein marker substrate – fexofenadine, which may evidence preservation of the functional activity of the given transport protein at the initial level. It was also found that the pharmacokinetics of Noopept remained unchanged after a course of introduction of ABCB1-protein inhibitor – verapamil – in to the male rabbits, that is, Noopept is not a substrate of the given transport protein. The pharmacokinetics of Noopept was studied by the original HPLC method. It was found that the course of Noopept introduction did not lead to any reliable changes in the pharmacokinetic parameters of the ABCB1-protein marker substrate – fexofenadine, which may evidence preservation of the functional activity of the given transport protein at the initial level. It was also found that the pharmacokinetics of Noopept remained unchanged after a course of introduction of ABCB1-protein inhibitor – verapamil – into the male rabbits, that is, Noopept is not a substrate of the given transport protein.

quantity of the substance was determined by HPLC method according to the previously developed procedure.
Belonging of Noopept to ABCB1-protein substrates was estimated by comparison of its pharmacokinetic parameters before and after a course of introduction of verapamil (the known inhibitor of the ABCB1-protein) into male rabbits in the dose 20 mg/kg b.w. 3 times a day. The pharmacokinetics of Noopept was studied by the original HPLC method.
It was found that the course of Noopept introduction did not lead to any reliable changes in the pharmacokinetic parameters of the ABCB1-protein marker substratefexofenadine, which may evidence preservation of the functional activity of the given transport protein at the initial level. It was also found that the pharmacokinetics of Noopept remained unchanged after a course of introduction of ABCB1-protein inhibitorverapamilin to the male rabbits, that is, Noopept is not a substrate of the given transport protein.
2. Ноопепт не является субстратом ABCB1-белка по результатам тестирования in vivo, что подтверждается отсутствием значимых изменений его концентрации на фоне ингибитора ABCB1-белка -верапамила. In the article the influence of nootropic drug Noopept (N-phenyl-acetyl-L-prolylglycine ethyl ester) on the functional activity of ABCB1-protein is analyzed and attribution of this drug to the transport protein substrates is studied on male Chinchilla rabbits. Functioning of the transport protein was estimated by the pharmacokinetics of its marker substratefexofenadine. Fexofenadine was introduced intragastrically one time in the dose 67,5 mg/kg b.w. before and after 14-day introduction of Noopept in the dose 10 mg/kg b.w. 3 times a day. The quantity of the substance was determined by HPLC method according to the previously developed procedure.
Belonging of Noopept to ABCB1-protein substrates was estimated by comparison of its pharmacokinetic parameters before and after a course of introduction of verapamil (the known inhibitor of the ABCB1-protein) into male rabbits in the dose 20 mg/kg b.w. 3 times a day. The pharmacokinetics of Noopept was studied by the original HPLC method.
It was found that the course of Noopept introduction did not lead to any reliable changes in the pharmacokinetic parameters of the ABCB1-protein marker substratefexofenadine, which may evidence preservation of the functional activity of the given transport protein at the initial level. It was also found that the pharmacokinetics of Noopept remained unchanged after a course of introduction of ABCB1-protein inhibitorverapamilinto the male rabbits, that is, Noopept is not a substrate of the given transport protein.
Keywords: ABCB1-protein, P-glycoprotein, Noopept, fexofenadine, pharmacokinetics, verapamil, substrate. ________________________________________________________________________________ ABCB1-protein (P-glycoprotein) is a membrane ATP-dependent efflux transport protein that removes a wide range of endogenous and exogenous substances including medical drugs of different pharmacological and chemical groups, from a cell [1].
ABCB1-protein localizes on the membranes of epithelial cells of small intestinal mucosa and of the proximal tubules of nephron, of hepatocytes and endothelial cells of histohematic barriers. The transporter prevents absorption in the intestine of medical drugs that are its substrates, participates in their dis-tribution and facilitates their excretion into the bile and urine. Thus, the functional activity of this transport protein determines the pharmacokinetics of medical drugs -substrates of ABCB1-protein, and, finally, determines the effectiveness and safety of pharmacotherapy [2]. High activity of ABCB1-protein makes treatment with the substrate substance ineffective, and its low activity leads to overdosage.
Noopept (N-phenyl-acetyl-L-prolylglycine ethyl ester), a dipeptide analog of pyracetam, is a modern original nootropic and neuroprotective drug developed in V.V. Zakusov Research Institute of Pharmacology. Noopept is used in treatment for chronic ischemic brain damages, schizophrenia, epilepsy [3].
In the scientific literature no research is found on estimation of the attribution of Noopept to substrates, inductors and inhibitors of ABCB1-protein. However, based on the chemical structure and physical properties of Noopept it is possible to suggest participation of ABCB1protein in its pharmacokinetics, or the ability of the drug to modulate its functional activity. Earlier among the modulators of the transporter, substances of peptide nature were found [4]. The mechanism of alteration of the functional activity of ABCB1-protein by substances of peptide nature is described. It consists in their direct interaction with parts of the protein molecule with modification of its spatial structure [5].
The aim of the work is estimation of the influence of Noopept on the functional activity of ABCB1-protein and determination of belonging of the drug to the transport protein substrates.

Materials and methods
The research was conducted on 12 viripotent male Chinchilla rabbits of 3500-4300 g mass [6]. The work with the animals was conducted according to the good laboratory practice (Supplement to the Order of Ministry of Health and Social Development of Russian Federation of August 23, 2010, 708н).
The animals were divided to 2 series: in the first series (n=6) the influence of Noopept on the functional activity of ABCB1-protein was studied, in the second series (n=6) belonging of Noopept to the transporter substrates was determined.
The animals of the first series received fexofenadine (coated tablets, Telfast, 180 mg, Aventis Pharma, Italy) intragastrically one time in the dose 67,5 mg/kg b.w. [7] before and after 14-day introduction of Noopept (Noopept tablets, 10 mg, ZAO (CJSC) «LEK-KO», Russia) in the dose 10 mg/kg b.w. 3 times a day, and also on the 5 th day after its withdrawal [8]. The last introduction of Noopept was in the morning 20 min. before introduction of the marker substrate, to evaluate the direct influence of the drug on ABCB1-protein (the period of time was determined by T max of Noopept -15 min.). After that blood was taken from the marginal veins of the rabbits' ears into heparinized test tubes in the quantity 5 ml with subsequent centrifugation at 3000 rpm for 10 min. to obtain plasma. Concentration of fexofenadine in the blood plasma was determined by HPLC method on «Stayer» chromatograph (Russia) according to the earlier described procedure [9].
The second series animals received the test drug Noopept intragastrically in the dose 50 mg/kg b.w. in the form of suspension prepared on purified water one time before and after introduction of ABCB1-protein inhibitor. Blood samples were taken in 5, 10, 20, 30, 45, 60 and 90 min after introduction of the test drug [10] with the subsequent analysis of its pharmacokinetics by HPLC method. «Stayer» chromatograph was used with UV-spectrophotometric detector with 206 nm wavelength. Composition of the mobile phase: deionized water -acetonitrile -glacial acetic acid (50 -50 -0.1). Chromatographic column Phenomenex Synergi 4u Polar-RP 80A (250 х 4.6, 4 μm). The inhibitor to ABCB1-protein was verapamil (coated tablets, 80 mg, OAO (JSC) Valenta Pharmacevtica, Russia) given in the dose 20 mg/kg b.w. 3 times a day [7] in 14-day course. The last introduction of verapamil was conducted in the morning 1 hour before introduction of Noopept (the time is determined by T max of verapamil 1-2 h).
Pharmacokinetic parameters of fexofenadine and Noopept were calculated by noncompartmental method using Kinetica 5.0 program.
The obtained results were processed using StatSoft Statistica 7.0 program. The statistical significance of the differences between the pharmacokinetic parameters was evaluated on the basis of the concept of the lognormal distribution of data. The test pharmacokinetic parameters were compared using dispersion analysis of repeated measurements (ANOVA) after taking their logarithms. Statistically significant were assumed the differences at the meaning of p<0.05. Additionally, two-tailed 90% confidence interval of the ratio of the mean geometrical values of the pharmacokinetic parameters with introduction of the test substances (verapamil and Noopept) to the parameters of intact animals was calculated. According to recommendations of Drug Evalua-tion and Research Center of U.S. Food and Drug Administration [11], the differences between pharmacokinetic parameters are considered significant if the two-tailed 90% confidence interval of their ratio lies beyond the range 0,8-1,25 (80-125%). The obtained results are given in the tables as the geometrical mean and its 95% confidence interval.

Results and Discussion
14-Day introduction of Noopept to the male rabbits did not cause any statistically significant changes in any of the test pharmacokinetic parameters of fexofenadine (tabl. 1).
14-Day introduction of ABCB1-protein inhibitor -verapamil -did not lead to any reliable changes in the pharmacokinetics of Noopept in comparison with the initial parameters (tabl. 2). Note: the data are presented as the geometrical mean and its 95% confidence interval Note: the data are presented as the geometrical mean and its 95% confidence interval Fexofenadine is H 1 -histamin receptor blocker of the III generation which is recommended by FDA as the marker substrate of ABCB1-protein; it is not metabolized in an organism, and its absorption in the intestine, distribution and elimination depend on the functioning of the transporter. Thus, the changes of the concentration of fexofenadine in blood characterizes the functional activity of ABCB1-protein [7,11,12].
Absence of any statistically significant alterations in the pharmacokinetics of fexofenadine after a course of administration of Noopept into rabbits shows that the rate of absorption of the marker substrate in the intestine and the intensity of its excretion did not change that means preservation of the functional activity of ABCB1-protein at the initial level.
Earlier in vitro was found that Noopept (10 μM) increases DNA-binding activity of HIF-1 [13] -transcription factor that enhances expression of ABCB1-protein [14]. Our results do not agree with these data probably because we used Noopept in normal intact animals and studied functioning of the transporter at the level of the whole organism and not in cell culture.
A probable reason for absence of the influence of Noopept on the functional activity of ABCB1-protein at the level of the whole organism found in our research, may be its short halflife period which, according to the literature, in rabbits is 0,3±0,03 h [10] which minimizes the probability for its direct interaction with the transport protein and for changing its activity. Besides, at the level of the whole organism ABCB1-protein is under the influence of many factors (surrounding cells, hormonal background, etc.) that are absent in vitro.
Belonging of medical drugs to ABCB1protein substrates is estimated in vivo in the following way. Pharmacokinetics of the test drug is estimated before and after administration of the classic inhibitor and inductor of ABCB1-protein.
If after a course of introduction to male rabbits of the transporter inhibitor (verapamil) the concentration of the test substance in plasma increases and its excretion decreases, and after a course of introduction of ABCB1-protein inductor (rifampicin) the opposite dynamics is observed, the conclusion is made about the drug belonging to the transport protein substrates [15]. In this work the maximal concentration of Noopept in blood plasma after its oral administration into intact animals in the dose 50 mg/kg b.w. was 44,43 (25,20; 78,33) ng/ml. Here, if Noopept belongs to ABCB1-protein substrates, introduction of rifampicin will further decrease its concentration in plasma that will not permit its detection by the method used by us. Because of this limitation, in our work only the transport protein inhibitor was introduced -verapamil, which increases concentration of the test substrates in blood.
Lack of any reliable differences between pharmacokinetic parameters of Noopept before and after a course of introduction of verapamil into rabbits means that the test drug is not a substrate of ABCB1-protein, and the involvement of the given transporter into the processes of absorption, distribution and excretion of the test substance produces no significant influence on its pharmacokinetics.
Independence of Noopept pharmacokinetics of ABCB1-protein functioning, as well as absence of any influence of the drug on the functional activity of the transporter permits to safely administer the drug together with drugs that are substrates of the transport protein (digoxin, dabigatran etexilate, talinolol, etc.) without correction of its dose with the minimal probability for undesired drug-drug interactions. Conclusions 1. A course of Noopept introduction in 10 mg/kg b.w. dose 3 times daily to male rabbits within 14 days does not lead to any changes in the functional activity of ABCB1protein that is estimated by pharmacokinetics of its marker substrate fexofenadine.
2. By the results of in vivo testing, Noopept is not a substrate of ABCB1-protein that is confirmed by absence of any significant changes in its concentration after introduction of ABCB1-protein inhibitor -verapamil.
In relation to this article reported no potential conflicts of interest.