Matos Carla, Lima José L C, Reis Salette, Lopes António, Bastos Margarida
Rede de Química e Tecnologia/Faculdade de Ciências da Saúde, Universidade Fernando Pessoa, Porto, Portugal.
Biophys J. 2004 Feb;86(2):946-54. doi: 10.1016/S0006-3495(04)74170-3.
Isothermal titration calorimetry was used to characterize and quantify the partition of indomethacin and acemetacin between the bulk aqueous phase and the membrane of egg phosphatidylcholine vesicles. Significant electrostatic effects were observed due to binding of the charged drugs to the membrane, which implied the use of the Gouy-Chapman theory to calculate the interfacial concentrations. The binding/partition phenomenon was quantified in terms of the partition coefficient (K(p)), and/or the equilibrium constant (K(b)). Mathematical expressions were developed, either to encompass the electrostatic effects in the partition model, or to numerically relate partition coefficients and binding constants. Calorimetric titrations conducted under a lipid/drug ratio >100:1 lead to a constant heat release and were used to directly calculate the enthalpy of the process, DeltaH, and indirectly, DeltaG and DeltaS. As the lipid/drug ratio decreased, the constancy of reaction enthalpy was tested in the fitting process. Under low lipid/drug ratio conditions simple partition was no longer valid and the interaction phenomenon was interpreted in terms of binding isotherms. A mathematical expression was deduced for quantification of the binding constants and the number of lipid molecules associated with one drug molecule. The broad range of concentrations used stressed the biphasic nature of the interaction under study. As the lipid/drug ratio was varied, the results showed that the interaction of both drugs does not present a unique behavior in all studied regimes: the extent of the interaction, as well as the binding stoichiometry, is affected by the lipid/drug ratio. The change in these parameters reflects the biphasic behavior of the interaction-possibly the consequence of a modification of the membrane's physical properties as it becomes saturated with the drug.
等温滴定量热法用于表征和量化吲哚美辛和阿西美辛在本体水相和卵磷脂囊泡膜之间的分配。由于带电药物与膜的结合，观察到显著的静电效应，这意味着使用古依-查普曼理论来计算界面浓度。结合/分配现象通过分配系数（K(p)）和/或平衡常数（K(b)）进行量化。开发了数学表达式，以涵盖分配模型中的静电效应，或在数值上关联分配系数和结合常数。在脂质/药物比率>100:1的条件下进行的量热滴定导致恒定的热释放，并用于直接计算过程的焓ΔH，以及间接计算ΔG和ΔS。随着脂质/药物比率的降低，在拟合过程中测试了反应焓的恒定性。在低脂质/药物比率条件下，简单分配不再有效，相互作用现象根据结合等温线进行解释。推导了一个数学表达式，用于量化结合常数和与一个药物分子相关的脂质分子数量。所使用的广泛浓度范围强调了所研究相互作用的双相性质。随着脂质/药物比率的变化，结果表明两种药物的相互作用在所有研究体系中都不呈现独特的行为：相互作用的程度以及结合化学计量受到脂质/药物比率的影响。这些参数的变化反映了相互作用的双相行为——这可能是膜在被药物饱和时其物理性质发生改变的结果。
