Electroanalysis of Cytochrome P450 3A4 Catalytic Properties with Nanostructured Electrodes: The Influence of Vitamin B Group on Diclofenac Metabolism: Vitamin B Group Modulates Pharmacological Action of Diclofenac and Exerts Influence on the Electrocatalytic Activity of Cytochrome P450 3A4

Electrochemical transformations catalyzed by cytochrome P450s and peroxidases

Cytochrome P450s (Cyt P450s) and peroxidases are enzymes featuring iron heme cofactors that have wide applicability as biocatalysts in chemical syntheses. Cyt P450s are a family of monooxygenases that oxidize fatty acids, steroids, and xenobiotics, synthesize hormones, and convert drugs and other chemicals to metabolites. Peroxidases are involved in breaking down hydrogen peroxide and can oxidize organic compounds during this process. Both heme-containing enzymes utilize active Fe^IVO intermediates to oxidize reactants. By incorporating these enzymes in stable thin films on electrodes, Cyt P450s and peroxidases can accept electrons from an electrode, albeit by different mechanisms, and catalyze organic transformations in a feasible and cost-effective way. This is an advantageous approach, often called bioelectrocatalysis, compared to their biological pathways in solution that require expensive biochemical reductants such as NADPH or additional enzymes to recycle NADPH for Cyt P450s. Bioelectrocatalysis also serves as an ex situ platform to investigate metabolism of drugs and bio-relevant chemicals. In this paper we review biocatalytic electrochemical reactions using Cyt P450s including C-H activation, S-oxidation, epoxidation, N-hydroxylation, and oxidative N-, and O-dealkylation; as well as reactions catalyzed by peroxidases including synthetically important oxidations of organic compounds. Design aspects of these bioelectrocatalytic reactions are presented and discussed, including enzyme film formation on electrodes, temperature, pH, solvents, and activation of the enzymes. Finally, we discuss challenges and future perspective of these two important bioelectrocatalytic systems.

Human Cytochrome P450 2C9 and Its Polymorphic Modifications: Electroanalysis, Catalytic Properties, and Approaches to the Regulation of Enzymatic Activity

The electrochemical properties of cytochrome P450 2C9 (CYP2C9) and polymorphic modifications P450 2C9*2 (CYP2C9*2) and P450 2C9*3 (CYP2C9*3) were studied. To analyze the comparative electrochemical and electrocatalytic activity, the enzymes were immobilized on electrodes modified with a membrane-like synthetic surfactant (didodecyldimethylammonium bromide (DDAB)). An adequate choice of the type of modified electrode was confirmed by cyclic voltammetry of cytochromes P450 under anaerobic conditions, demonstrating well-defined peaks of reduction and oxidation of the heme iron. The midpoint potential, Emid, of cytochrome P450 2C9 is −0.318 ± 0.01 V, and Emid = −0.324 ± 0.01 V, and Emid = −0.318 ± 0.03 V for allelic variant 2C9*2 and allelic variant 2C9*3, respectively. In the presence of substrate diclofenac under aerobic conditions, cytochrome P450 2C9 and its polymorphic modifications P450 2C9*2 and P450 2C9*3 exhibit catalytic properties. Stimulation of the metabolism of diclofenac by cytochrome P450 2C9 in the presence of antioxidant medications mexidol and taurine was shown.

No effect of lipoic acid on catalytic activity of cytochrome P450 3A4

Objectives α-Lipoic acid is used as an antioxidant in multivitamin formulations to restore the normal level of intracellular glutathione after depletion caused by environmental pollutants or during physiological aging of the body, as a chelating agent, as a dietary supplement, in anti-aging compositions. Lipoic acid (LA) acts as a buffer in cancer therapy and in therapy of diseases associated with oxidative stress. The effect of LA on the catalytic functions of cytochrome P450 3A4 as the main enzyme of the biotransformation of drugs was studied. It was shown that LA in the concentration range of 50-200 μM affects the stage of electron transfer (stage of cytochrome P450 3A4 heme reduction), decreasing the cathodic reduction current by an average of 20 ± 5%. The kinetic parameters (k cat) of the N-demethylation reaction of erythromycin, the antibiotic of the macrolide group, used as a marker substrate for the comparative analysis of the catalytic activity of cytochrome P450 3A4, both in the presence of α-lipoic acid and in the cytochrome P450 3A4-erythromycin complex, amounted to comparable values of 3.5 ± 0.9 and 3.4 ± 0.9 min-1, respectively. Based on these experimental data, we can conclude that there is no significant effect of α-lipoic acid on the catalysis of cytochrome P450 3A4. These results can be projected on the possibility of using α-lipoic acid in complex therapy without negative impact on the enzymatic cytochrome P450 system. Methods The analysis was performed in electrochemical non-invasive model systems for recording the catalytic activity of cytochrome P450 3A4, using screen-printed electrodes, modified with membranous didodecyldimethylammonium bromide. Results It was shown that LA did not affect the N-demethylation of macrolide antibiotic erythromycin. Catalytic constant (k cat) of N-demethylation of erythromycin corresponds to 3.4 ± 0.9 min-1 and in the presence of LA corresponds to 3.5 ± 0.9 min-1. Conclusions Based on the obtained experimental data, we can conclude that there is no significant effect of α-lipoic acid on individual stages and processes of catalysis of cytochrome P450 3A4. LA can be recommended for inclusion in complex therapy as an antioxidant, antitoxic and chelating compound without negative impact on the enzymatic cytochrome P450 3A4 activity of the human body.

Levocarnitine for the Treatment of Polymorbid Patients

Effective and safe treatment of patients with polymorbidity is an urgent task of modern healthcare. Of particular difficulty is the treatment of patients with cardiovascular comorbidity, which requires an integrated approach to the treatment and development of a special, so-called patient-oriented approach. Modern scientific evidence proposes the use of levocarnitine, as part of complex therapy to increase its effectiveness. So, it was shown that levocarnitine can have a beneficial effect on blood pressure in patients with hypertension, especially those who are overweight and obese. Levocarnitine is also effective in the treatment of heart failure, which has been studied in several clinical studies, which demonstrated its ability to increase the ejection fraction of the left ventricle, stroke volume of blood and other indicators. Optimization of the bioavailability of nitrogen oxide (NO) and a decrease in systemic oxidative stress while taking levocarnitine plays an important positive role in complex therapy in patients with coronary artery disease: exertional angina and post-infarction cardiosclerosis, reducing the number of anginal attacks. Since levocarnitine has powerful antioxidant effects, it also has the neuroprotective effect found in in vitro studies in animal experiments. In case of impaired renal function, due to accelerated elimination and impaired reabsorption, a deficiency of levocarnitine in the body tissues develops, and therefore the US Food and Drug Administration (US FDA) decided on the possibility of using levocarnitine in patients on hemodialysis. Thus, taking into account the positive effects of levocarnitine in a number of frequently combined diseases, it can be considered as the drug of choice in the treatment of patients with polymorbidity.

The influence of taurine and L-carnitine on 6 β-hydroxycortisol/cortisol ratio in human urine of healthy volunteers

Background Cytochrome P450s (CYPs, EC 1.14.14.1) are the main enzymes of drug metabolism. The functional significance of CYPs also includes the metabolism of foreign chemicals and endogenic biologically active compounds. The CYP3A4 isoform contributes to the metabolism of about half of all marketed medicinal preparations. The aim of this study was to investigate the effects of two biologically active compounds: 2-aminoethane-sulfonic acid (taurine) and 3-hydroxy-4-trimethylaminobutyrate (L-carnitine) on urinary 6β-hydroxycortisol/cortisol (6β-OHC/cortisol) metabolic ratio as a biomarker of the CYP3A4 activity of healthy volunteers. Taurine is used for the treatment of chronic heart failure and liver disease. Cardiologists, nephrologists, neurologists, gerontologists in addition to the main etiopathogenetic therapies, use L-carnitine. The quantification of the 6β-OHC/cortisol metabolic ratio as a biomarker of CYP3A4 activity in human urine was used for the assessment of CYP3A4 catalytic activity as a non-invasive test. Methods The study included 18 healthy male volunteers (aged from 18 to 35 years old). The volunteers took taurine in a dose of 500 mg twice a day or L-carnitine in a dose of 2.5 mL 3 times a day for 14 consecutive days. The test drug was given 20 min before meals. The collection of urine samples was performed before and after 3, 7, 10, and 14 days after taurine intake. The metabolic ratio of 6β-OHC/cortisol in morning spot urine samples was studied by the liquid chromatography/mass spectroscopy (LC/MS) method. Results The ratio of 6-6β-OHC/cortisol was used as a biomarker to study the taurine and L-carnitine influence on CYP3A4 metabolism of cortisol. The ratio of urinary 6β-OCH/cortisol in the morning urine samples of volunteers before the beginning of taurine therapy (baseline ratio) was 2.71 ± 0.2. Seven days after the administration of taurine in a dose of 500 mg twice a day, the 6β-OCH/cortisol ratio was 3.3 ± 0.2, which indicated the increased catalytic activity of CYP3A4 towards cortisol. As for the L-carnitine supplementation, analysis of the 6β-OCH/cortisol ratio in the urine for 14 days did not show any significant changes in this baseline ratio, indicating the lack of L-carnitine influence on the catalytic activity of CYP3A4 to cortisol. Conclusions The results obtained demonstrated the influence of taurine on 6β-OCH/cortisol metabolic ratio as a biomarker of CYP3A4 catalytic activity to cortisol. L-carnitine did not affect the activity of CYP3A4. The lack of a clinically meaningful effect of L-carnitine was established.

Significance of L-carnitine in internal medicine

The review presents the results of a number of experimental and clinical studies proving the prospects of using L-carnitine in the clinic of internal diseases. Due to the antioxidant and antihypoxant properties, the additional use of L-carnitine in addition to the main etiopathogenetic therapy is prescribed by cardiologists, nephrologists, neurologists, gerontologists. Experimental studies we conducted earlier showed no effect of L-carnitine on the activity of the P450 CYP 3A4 system, which reduces the likelihood of drug-drug interaction at the level of metabolism of drugs metabolized by P450 3A4. When using L-carnitine as part of complex pharmacotherapy, the drug has an increased safety profile in comorbid patients taking L-carnitine. Keywords: L-carnitine, P450 CYP 3А4, chronic heart failure, myocardial infarction, chronic renal failure, inter-drug interaction, antioxidant, antihypoxant.

[Electrochemical methods for biomedical investigations]

In the review, authors discussed recently published experimental data concerning highly sensitive electrochemical methods and technologies for biomedical investigations in the postgenomic era. Developments in electrochemical biosensors systems for the analysis of various bio objects are also considered: cytochrome P450s, cardiac markers, bacterial cells, the analysis of proteins based on electro oxidized amino acids as a tool for analysis of conformational events. The electroanalysis of catalytic activity of cytochromes P450 allowed developing system for screening of potential substrates, inhibitors or modulators of catalytic functions of this class of hemoproteins. The highly sensitive quartz crystal microbalance (QCM) immunosensor has been developed for analysis of bio affinity interactions of antibodies with troponin I in plasma. The QCM technique allowed real-time monitoring of the kinetic differences in specific interactions and nonspecific sorption, with out multiple labeling procedures and separation steps. The affinity binding process was characterized by the association (ka) and the dissociation (kd) kinetic constants and the equilibrium association (K) constant, calculated using experimental data. Based on the electroactivity of bacterial cells, the electrochemical system for determination of sensitivity of the microbial cells to antibiotics cefepime, ampicillin, amikacin, and erythromycin was proposed. It was shown that the minimally detectable cell number corresponds to 106 CFU per electrode. The electrochemical method allows estimating the degree of E.coli JM109 cells resistance to antibiotics within 2-5 h. Electrosynthesis of polymeric analogs of antibodies for myoglobin (molecularly imprinted polymer, MIP) on the surface of graphite screen-printed electrodes as sensor elements with o- phenylenediamine as the functional monomer was developed. Molecularly imprinted polymers demonstrate selective complementary binding of a template protein molecule (myoglobin) by the "key-lock" principle.

Electrocatalytic cycle of P450 cytochromes: the protective and stimulating roles of antioxidants

This study reports the investigation of the catalytic activity of isolated cytochromes from the cytochrome P450 superfamily. Electrochemically driven CYP reactions may have practical relevance, providing a useful tool for drug assay studies.

[Role of antioxidants in electro catalytic activity of cytochrome P450 3A4]

The electrochemical analysis of cytochrome Р450 3А4 catalytic activity has shown that vitamins C, A and Е influence on electron transfer and Fe3+/Fe2+ reduction process of cytochrome Р450 3А4. These data allow to assume possibility of cross effects and interference of vitamins-antioxidants with drugs metabolised by cytochrome Р450 3А4, at carrying out of complex therapy. This class of vitamins shows antioxidant properties that lead to increase of the cathodic current corresponding to heme reduction of this functionally significant haemoprotein. Ascorbic acid of 0.028-0.56 mM concentration stimulates cathodic peak (an electrochemical signal) of cytochrome Р450 3А4. At the presence of diclofenac (Voltaren) - a typical substrate of cytochrome Р450 3А4 - the increase growth of a catalytic current testifying to an electrocatalysis and stimulating action of ascorbic acid is observed. In the presence of vitamins A and Е also is registered dose-dependent (in a range of 10-100 M) increase in a catalytic current of cytochrome Р450 3А4: the maximum increase corresponds to 229 ± 20% for 100 M of vitamin A, and 162±10% for 100 M of vitamin E. Vitamin E in the presence of P450's inhibitor itraconazole doesn't give essential increase in a reductive current, unlike retinol (vitamin A). This effect can manifest substrate properties of tocopherol (vitamin E). The electrochemical approach for the analysis of catalytic activity of cytochrome Р450 3А4 and studies of influence of biologically active compounds on an electrocatalysis is the sensitive and effective sensor approach, allowing to use low concentration of protein on an electrode (till 10-15 mol/electrode), to carry out the analysis without participation of protein redox partners, and to reveal drug-drug or drug-vitamins interaction in pre-clinical experiments.