Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, The Netherlands.
AAPS J. 2011 Jun;13(2):284-90. doi: 10.1208/s12248-011-9268-7. Epub 2011 Mar 30.
In the current study, the effect of metal ions in combination with buffers (citrate, acetate, pH 4.5) on the stability of aqueous solutions of oxytocin was investigated. Both monovalent metal ions (Na(+) and K(+)) and divalent metal ions (Ca(2+), Mg(2+), and Zn(2+)) were tested all as chloride salts. The effect of combinations of buffers and metal ions on the stability of aqueous oxytocin solutions was determined by RP-HPLC and HP-SEC after 4 weeks of storage at either 4°C or 55°C. Addition of sodium or potassium ions to acetate- or citrate-buffered solutions did not increase stability, nor did the addition of divalent metal ions to acetate buffer. However, the stability of aqueous oxytocin in aqueous formulations was improved in the presence of 5 and 10 mM citrate buffer in combination with at least 2 mM CaCl(2), MgCl(2), or ZnCl(2) and depended on the divalent metal ion concentration. Isothermal titration calorimetric measurements were predictive for the stabilization effects observed during the stability study. Formulations in citrate buffer that had an improved stability displayed a strong interaction between oxytocin and Ca(2+), Mg(2+), or Zn(2+), while formulations in acetate buffer did not. In conclusion, our study shows that divalent metal ions in combination with citrate buffer strongly improved the stability of oxytocin in aqueous solutions.
在本研究中，考察了金属离子与缓冲液（柠檬酸盐、醋酸盐、pH4.5）组合对催产素水溶液稳定性的影响。所有单价金属离子（Na(+)和 K(+)）和二价金属离子（Ca(2+)、Mg(2+)和 Zn(2+)）均以氯化物盐的形式进行测试。通过 RP-HPLC 和 HP-SEC 测定了在 4°C 或 55°C 下储存 4 周后，缓冲液和金属离子的组合对催产素水溶液稳定性的影响。在醋酸盐或柠檬酸盐缓冲液中添加钠离子或钾离子不会增加稳定性，而在醋酸盐缓冲液中添加二价金属离子也不会增加稳定性。然而，在存在 5 和 10 mM 柠檬酸盐缓冲液的情况下，与至少 2 mM 的 CaCl(2)、MgCl(2)或 ZnCl(2)组合，水溶液中催产素的稳定性得到改善，且取决于二价金属离子的浓度。等温滴定量热测量对稳定性研究中观察到的稳定化效果具有预测性。具有改善稳定性的柠檬酸盐缓冲液配方显示催产素与 Ca(2+)、Mg(2+)或 Zn(2+)之间存在强烈相互作用，而醋酸盐缓冲液配方则没有。总之，本研究表明，二价金属离子与柠檬酸盐缓冲液结合可显著提高催产素在水溶液中的稳定性。
