Background: Metoprolol (MTP) is a cardio-selective β1-blocker used in hypertension, angina pectoris and chronic heart failure therapies. Serum albumin is the most frequently occurring protein in blood plasma. The binding of ligands to human serum albumin (HSA) has an important effect on pharmacokinetics and final clinical effects.
Objective: The objectives of this study included a detailed analysis of metoprolol – serum albumin interactions in low affinity binding sites, on the surface or within the hydrophobic subdomain of a macromolecule, as well as an analysis of the competition between MTP and fatty acids in binding with protein.
Methods: The analysis of the drug-albumin interaction was based on the observed chemical shifts in combination with correlation Times (T1 -1 = τ) [1/s], 2D NOESY 1H NMR spectra and association constants Ka [M-1]. For the determination of chemical shifts σ [ppm], relaxation times T1 [s] and for the NOESY experiment, the final concentrations of MTP and albumins (in the presence (HSA) and absence of fatty acids (dHSA)) were 5 x 10-3 M and 2 x 10-5 M - 4.55 x 10-4 M, respectively. In order to calculate the association constants, the final concentrations of MTP and both HSA and dHSA were 2.75 x 10-3 M - 6.25 x 10-2 M and 2.5 x 10-4 M, respectively. For the analysis, the MTP proton resonances of aliphatic H17, aromatic (H2/H6 and H3/H5) and the methoxy group H14 were chosen.
Results: Changes in the values of the 1H NMR chemical shift [ppm] are evidence of interaction between MTP, fatted (HSA) and defatted (dHSA) human serum albumin. With an increase of albumin concentration, changes in the chemical shift values were observed for the aromatic protons H2/H6 (Δσ = 0.013 ppm and 0.018 ppm) and H3/H5 (Δσ = 0.015 ppm and 0.019 ppm), the aliphatic proton H17 (Δσ = 0.018 ppm and 0.022 ppm) and the aliphatic protons of the methoxy group H14 (Δσ = 0.019 ppm and 0.022 ppm) for dHSA and HSA, respectively. Greater changes in chemical shifts in the presence of fatty acids (FA) were observed. Changes in the correlation times of MTP aromatic H2/H6 (Δτc = 0.224 1/s and 0.189 1/s) and H3/H5 (Δτc = 0.269 1/s and 0.210 1/s), aliphatic from the methoxy group H14 (Δτc = 0.472 1/s and 0.271 1/s) and aliphatic H17 protons (Δτc = 0.178 1/s and 0.137 1/s) for dHSA and HSA systems, respectively. It confirms the interaction between the drug and albumin are evidence for the dynamics of the process. In the presence of FA the relaxation time of all analyzed MTP proton resonance signals significantly increases (due to the decrease of correlation time). This phenomenon is due to the increase of electron density in the MTP protons' surroundings. Association constants for the MTP-dHSA complex in the low affinity site range between 0.29 x 102 M-1 and 0.47 x 102 M-1. The presence of FA results in a two to three-fold increase of the Ka values of protons from aromatic (H2/H6 and H3/H5), aliphatic H17 and methoxy (H14) groups. In 2D NOESY spectra proton magnetization transfer was observed between cysteine (Cys-34) and aromatic H3/H5 and H2/H6 protons. Cross-peaks were also observed between cysteine and aliphatic protons from the methoxy group.
Conclusion: The selective changes in σ [ppm] and τc [1/s] values indicated the unequal participation of chemical groups of MTP in the interaction with HSA and dHSA. The data obtained suggest that the presence of fatty acids increases the accessibility of low affinity sites of serum albumin to MTP, which results in the higher affinity of albumin towards the drug. The results showed that the main binding site of MTP and fatty acid is probably a low affinity site in subdomain IB, where Cys-34 can be located.
Keywords: Metoprolol, human serum albumin, fatty acids, 1H NMR, β1-blocker, pharmacokinetics.
Human Liver Enzymes Responsible for Metabolic Elimination of Tyramine, a Vasopressor Agent from Daily Food
Drug Metabolism Letters Heme Oxygenase-1 in Lung Disease
Current Drug Targets Editorial [Hot Topic: The Clinical Management and Treatment of Hypertension, Its Pathophysiology and the Clinical Use of Antihypertensive Drugs (Executive Editor: Gregory Y.H. Lip)]
Current Pharmaceutical Design Evidence for a Putative Relationship Between Type 2 Diabetes and Neoplasia with Particular Reference to Breast Cancer: Role of Hormones, Growth Factors and Specific Receptors
Current Drug Targets - Immune, Endocrine & Metabolic Disorders Genes and Hypertension
Current Pharmaceutical Design Epidemiology and Costs of Hypertension-related Disorders
Current Pharmaceutical Design Understanding the Cardiovascular Actions of Soy Isoflavones: Potential Novel Targets for Antihypertensive Drug Development
Cardiovascular & Hematological Disorders-Drug Targets Alzheimers Disease Burdens African-Americans: A Review of Epidemiological Risk Factors and Implications for Prevention and Treatment
Current Psychiatry Reviews Classical Inhibitors of NOX NAD(P)H Oxidases Are Not Specific
Current Drug Metabolism Reductions in Medications with Substantial Weight Loss with Behavioral Intervention
Current Clinical Pharmacology Phytochemical and Pharmacological Activity Profile of Crataegus oxyacantha L. (Hawthorn) - A Cardiotonic Herb
Current Medicinal Chemistry The Mediterranean and other Dietary Patterns in Secondary Cardiovascular Disease Prevention: A Review
Current Vascular Pharmacology Therapeutic Potential of Voltage Gated Calcium Channels
Mini-Reviews in Medicinal Chemistry Synthesis and Antihypertensive Activity of Novel Quinazolin-4(3H)-one Derivatives
Central Nervous System Agents in Medicinal Chemistry Sex Steroid Hormones, Cardiovascular Diseases and The Metabolic Syndrome
Cardiovascular & Hematological Agents in Medicinal Chemistry Delayed Neuroleptic Malignant Syndrome Associated with the Use of Low Dose Risperidone in Conjunction with Cholinergic Drugs-the Dangers of Polypharmacy in the Elderly
Current Drug Therapy Anti-hyperglycemic Properties of a Purified Proteinaceous Protease Inhibitor from Macrotyloma Uniflorum Seeds
Current Topics in Medicinal Chemistry From the Oxygen to the Organ Protection: Erythropoietin as Protagonist in Internal Medicine
Cardiovascular & Hematological Agents in Medicinal Chemistry Mechanisms of Endothelial Dysfunction: Clinical Significance and Preventive Non-Pharmacological Therapeutic Strategies
Current Pharmaceutical Design Hypertension and Ischemic Heart Disease in Women
Current Pharmaceutical Design