Benzodiazepines are psychotropic drugs extensively used as hypnotics and anxiolytics [1]. Due to their high lipophilicity, they are able to partition into biological membranes and are accumulated mainly in high lipidcontaining tissues [2]. Two aspect of the electrochemical behavior of benzodiazepines derivatives are discussed in this presentation: their partition coefficients between water and 1,2-dichloroethane, to be used in structure–activity relationships and their interactions with membrane components. Quantitative structure–activity relationships (QSAR) have been used extensively in the last few decades to correlate the biological activity of drugs with physicochemical parameters such as solubility, the partition coefficient in oil / water systems (log P), the electronic effect of substituents, electron density, steric effects. These correlations are very important in providing a rational approach to the design of new drugs [3]. For this reason, much attention has been focused on the determination of the lipophilicity of drugs by different methods. Electrochemical methods applied to the interface between two immiscible electrolyte solutions (ITIES) has been used to examine kinetic and analytical aspects of the transport of various drugs [4], to determine partition coefficients from transfer potentials [5] and to clarify the electrochemical behavior of structurally specific and nonspecific drugs [6]. Biological studies lead to the conclusion that different substituents at position 7 of the benzene ring and position 2´ of the aryl ring produce important changes in the potency, rate of absorption and other pharmacological parameters [7]. The transfer potentials of a series of benzodiazepines, across the water/1,2 – dichloroethane interface, were determined with the aim to correlate the partition coefficient of these compounds with the presence of different substituents at positions 7 and 2. Related to the second aspect mentioned above, the interaction of Flunitrazepam (FNTZ) with phospholipids present in biological membranes was analyzed. FNTZ is a benzodiazepine widely administered as anxiolytic drug. Although the pharmacological action of FNTZ is related to the binding of this compound to specific site in biological membranes, it also interacts non – specifically with lipidic components, reaching high concentrations in biomembranes and altering its structural properties [8]. The last behavior arises as a result of the hydrophobic nature of FNTZ and may affect its biological activity [2]. For this reason, studies devoted to understand these non – specific interactions were carried out by several authors employing biomembranes and different membrane models. In this way the partition coefficient of FNTZ, determined in a synaptosomal membrane/buffer system [9] and the pKa value of membrane – bound FNTZ significantly lower than that measured in the bulk [2] indicate the tendency of this drug to penetrate into natural and model membranes (micelles, lipid - water monolayer or bilayers) and to localize at the polar head group region of monolayer or bilayer. For many years, electrochemical measurements applied to liquid – liquid interfaces modified by the adsorption of a lipid monolayer have provided information about the interaction of inorganic ions and biological compounds with membranes as well as about their transfer across these membranes [10 - 13]. The use of this kind of system to study the effect of FNTZ on the packing properties of a monolayer formed by the adsorption of zwitterionic or anionic phospholipid molecules at the liquid/liquid interface is shown in this presentation. The effect of FNTZ on phospholipid + cholesterol mixed monolayer is also analyzed. The influence of chemical variables (cations present in the aqueous phase, pH, and polar head group of phospholipids) is analyzed. The combination of EIS experiments and cyclic voltammetry employing a test cation such as TEA+, allowed us to evaluate the permeability and the compactness of the monolayer.
P), the electronic effect of substituents, electron density, steric effects. These correlations are very important in providing a rational approach to the design of new drugs [3]. For this reason, much attention has been focused on the determination of the lipophilicity of drugs by different methods. Electrochemical methods applied to the interface between two immiscible electrolyte solutions (ITIES) has been used to examine kinetic and analytical aspects of the transport of various drugs [4], to determine partition coefficients from transfer potentials [5] and to clarify the electrochemical behavior of structurally specific and nonspecific drugs [6]. Biological studies lead to the conclusion that different substituents at position 7 of the benzene ring and position 2´ of the aryl ring produce important changes in the potency, rate of absorption and other pharmacological parameters [7]. The transfer potentials of a series of benzodiazepines, across the water/1,2 – dichloroethane interface, were determined with the aim to correlate the partition coefficient of these compounds with the presence of different substituents at positions 7 and 2. Related to the second aspect mentioned above, the interaction of Flunitrazepam (FNTZ) with phospholipids present in biological membranes was analyzed. FNTZ is a benzodiazepine widely administered as anxiolytic drug. Although the pharmacological action of FNTZ is related to the binding of this compound to specific site in biological membranes, it also interacts non – specifically with lipidic components, reaching high concentrations in biomembranes and altering its structural properties [8]. The last behavior arises as a result of the hydrophobic nature of FNTZ and may affect its biological activity [2]. For this reason, studies devoted to understand these non – specific interactions were carried out by several authors employing biomembranes and different membrane models. In this way the partition coefficient of FNTZ, determined in a synaptosomal membrane/buffer system [9] and the pKa value of membrane – bound FNTZ significantly lower than that measured in the bulk [2] indicate the tendency of this drug to penetrate into natural and model membranes (micelles, lipid - water monolayer or bilayers) and to localize at the polar head group region of monolayer or bilayer. For many years, electrochemical measurements applied to liquid – liquid interfaces modified by the adsorption of a lipid monolayer have provided information about the interaction of inorganic ions and biological compounds with membranes as well as about their transfer across these membranes [10 - 13]. The use of this kind of system to study the effect of FNTZ on the packing properties of a monolayer formed by the adsorption of zwitterionic or anionic phospholipid molecules at the liquid/liquid interface is shown in this presentation. The effect of FNTZ on phospholipid + cholesterol mixed monolayer is also analyzed. The influence of chemical variables (cations present in the aqueous phase, pH, and polar head group of phospholipids) is analyzed. The combination of EIS experiments and cyclic voltammetry employing a test cation such as TEA+, allowed us to evaluate the permeability and the compactness of the monolayer.References
1.- J.F. Tallman, S.M. Paul, P. Skolnick, D.W. Gallager, Science 207 (1980) 274.
2.- D.AGarcía, M.A Perillo, Biochim. Biophys. Acta 1418 (1999) 221.
3.- C. Hansch, The use of substituent constant in structure–activity studies, in: E.J. Ariens (Ed.),
Physico-Chemical Aspect of Drug Action, Pergamon Press, UK, 1968 Proceedings of the Third
International Pharmacological Meeting.
4.- F. Reymond, G. Steyaert, A. Pagliara, P.A. Carrupt, B. Testa, H.H. Girault, Helv. Chim. Acta 79 (1996) 1651.
5.- L.M.A. Monzón, L.M. Yudi, J. Electroanal. Chem. 495 (2001)146.
6.- K. Arai, M. Oshawa, F. Kusu, K. Takamura, Bioelectrochem. Bioenerg. 31 (1993) 65.
7.- J. Nelson, G. Chouinard, in: A. Baskys, G. Remington (Eds.), Brain Mechanism and Psychotropic Drugs,
CRC Press, Boca Raton, USA, 1996.
8.- M.A. Perillo, D.A. García, Colloids and Surfaces B: Biointerfaces 20 (2001) 63.
9.- M.A. Perillo, D.A. García, Biomedical Chromat. 6 (1992) 183.
10.- A. Malkia, P. Liljeroth, K. Kontturi, Electrochem. Commun. 5 (2003) 473.
11.- T. Kakiuchi, T. Kondo, M. Katani, M. Senda, Langmuir 8 (1992) 169.
12.- S.G. Chesniuk, S.A. Dassie, L.M. Yudi, A.M. Baruzzi, Langmuir 14 (1998) 5226.
13.- S. Fantini, V. Clohessy, K. Gorgy, F. Fusalba, C. Johans, K. Kontturi, V.J. Cunnane, European J. of
Pharmaceutical Sciences 18 (2003) 251.
Pharmaceutical Sciences 18 (2003) 251.
