Effective use of reducing agents and nanoparticle encapsulation in stabilizing catechins in alkaline solution

Catechins are an important class of dietary flavonoids with promising use as therapeutic agents due to their potent antioxidant activity and diverse biological properties. However, catechins are highly unstable in alkaline solutions, such as those present in some biological fluids and experimental protocols. In this study, we optimised, evaluated and compared the effectiveness of the reducing agents ascorbic acid (AA), dithiothreitol (DTT), tris(2-carboxyethyl)phosphine (TCEP), as well as encapsulation in chitosan–tripolyphosphate nanoparticles for their potential to protect (+)-catechin and (−)-epigallocatechin gallate from degradation in potassium hydrogen phosphate buffer (pH 7.4). TCEP provided greater protection than did either AA or DTT against degradation. Combining AA and TCEP provided even greater protection than TCEP alone. The levels of (+)-catechin and (−)-epigallocatechin gallate remaining after a 24 h incubation in the presence of AA and TCEP were 88.3 ± 0.1% and 73.4 ± 2.5%, respectively, compared to 19.2 ± 1.1% and undetectable levels, respectively, in their absence. Encapsulation in chitosan–tripolyphosphate nanoparticles protected the catechins. It took 8 and 24 h for the non-encapsulated and encapsulated (+)-catechin, respectively, to degrade to 50% of their initial levels, and the corresponding values for the non-encapsulated and encapsulated (−)-epigallocatechin gallate were 10 and 40 min, respectively. These results demonstrate that the reducing agents TCEP and AA, and encapsulation in chitosan–tripolyphosphate nanoparticles, have a role to play in the in vitro and in vivo stabilization of catechins, respectively.