Simple Approach to Enhance Green Tea Epigallocatechin Gallate Stability in Aqueous Solutions and Bioavailability: Experimental and Theoretical Characterizations

Abstract

Because of its antioxidant, antimutagenic, and anti-infectious properties, epigallocatechin gallate (EGCG) is the most interesting compound among the green tea catechins polyphenols. However, its health effects are inconclusive due to its very low bioavailability, largely due to a particular instability that does not allow EGCG to reach the potency required for clinical developments. Over the last decade, many efforts have been made to improve the stability and bioavailability of EGCG using complex delivery systems such as nanotechnology, but these efforts have not been successful and easy to translate to industrial use. To meet the needs of a large-scale clinical trial requiring EGCG in a concentrated solution to anticipate swallowing impairments, we developed an EGCG-based aqueous solution in the simplest way while trying to circumvent EGCG instability. The solution was thoroughly characterized to sort out the unexpected stability outcome by combining experimental (HPLC-UV-mass spectrometry and infrared spectroscopy) and computational (density functional theory) studies. Against all odds, the EGCG-sucrose complex under certain conditions may have prevented EGCG from degradation in aqueous media. Indeed, in agreement with the ICH guidelines, the formulated solution was shown to be stable up to at least 24 months under 2-8 °C and at ambient temperature. Furthermore, considerable improvement in bioavailability in rats, against EGCG powder formulated in hard-gel capsules, was shown after gavage. Thus, the proposed formulation may provide an easily implementable platform to administer EGCG in the context of clinical development.

Keywords: complex; density functional theory; epigallocatechin gallate; formulation; mass spectrometry; oral solution; stability.

Figure 1

Stability of EGCG versus that of equimolar EGCG/sucrose; 1 mL of (a) an equimolar EGCG/sucrose solution (EGCG = 25 mg·mL⁻¹; sucrose = 19 mg·mL⁻¹) and (b) an EGCG-based solution alone (25 mg·mL⁻¹) subjected to a thermal gradient program ranging from 25 to 115 °C at a rate of 5 °C per min. At the end of this exposure, part of each of the residues formed was deposited on a glass slide and the remaining part was analyzed using high-performance liquid chromatography.

Figure 2

(a) Structure and arbitrary numbering of EGCG. (b) Structure and arbitrary numbering of sucrose (inset b).

Figure 3

(a) ATR-FTIR spectra of sucrose (in green) and of the EGCG–sucrose complex (in red). (b) ATR-FTIR spectra of EGCG (in blue) and of the EGCG–sucrose complex (in red).

Figure 4

(a): ESI^- MS spectrum of an EGCG–sucrose solution; (b): ESI^- MS² spectrum of the [EGCG + SUC − H]⁻ product ion (m/z = 799).

Figure 5

Structures of the initial (1, 2 and 3) and the geometrically optimized complexes (1′, 2′ and 3′).

Figure 6

EGCG assay (%) as a function of time and storage conditions.

Figure 7

(a) Chromatogram of the EGCG formulation stored for 17 days at 80 °C. (b,c) Total and enlarged chromatogram of the EGCG formulation stored 6 months at 4 °C (in black), at 25 °C (in green), and at 40 °C (in red). The chromatograms have been normalized on the EGCG peak to compare the chromatographic profiles. The chromatograms of 6 months at 4 °C (in black) and at 25 °C (in green) are almost indistinguishable from each other as the drug products contain similar amounts of degradation products.

Figure 8

EGCG concentration as a function of time and of the formulation.