The effects of Tween-80 on the integrity of solutions of capsaicin: Useful information for performing tussigenic challenges

Abstract

Background. Because variable results of capsaicin challenges may be due to the incomplete solubility of capsaicin, we sought to determine if the use of Tween-80 in solutions of capsaicin improves actual concentrations of freshly prepared and stored solutions. Methods. Capsaicin solutions ranging from 0.5-128 μM were mixed with and without Tween-80. Samples of various concentrations were then stored under 4 environmental conditions: 4°C, protected from light; room temperature, protected from light; room temperature, exposed to light; -20°C. All samples were analyzed initially, and at 2 and 4 months. Results. While freshly prepared solutions with Tween-80 had consistently higher concentrations than those prepared without Tween-80 (83% vs. 69%), Tween-80 does not facilitate complete solubility. For solutions stored at 4°C and protected from light, there was a significant decrease after 2 months in low concentration solutions of both the Tween-80 and non-Tween-80 solutions. Both Tween-80 and non-Tween-80 containing solutions significantly decreased in concentration after 2 months when stored at room temperature and protected from light, room temperature and exposed to light, and -20°C. Concentrations of solutions made of 4 μM or higher are stable when stored at 4°C and protected from light for 4 months. Conclusion. While the inherent difficulty of forcing capsaicin into solution cannot be eliminated, it can be improved with Tween-80. However, the addition of Tween-80 does not prevent the breakdown of stored capsaicin solutions. We recommend preparing and storing capsaicin solutions according to the methods and results of this study. © 2008 Kopec et al; licensee BioMed Central Ltd.