Photostability and photoprotection factor of boldine and glaucine

Abstract

Boldine hydrochloride was more photounstable than boldine after irradiation with UVB (λ = 300 nm). However, photoconsumption quantum yields, for glaucine hydrochloride (6.5 × 10⁻²) and boldine hydrochloride (6.7 × 10⁻²) in air, were quite similar. The photolysis was oxygen dependent in both cases, and the effect over the kinetics after the addition of 2,2,6,6-tetramethyl-1-piperidinyloxy suggested free radicals participation. The fact that the antioxidative capacity of boldine and boldine hydrochloride did not change during the photolysis, suggests that the phenolic structure remains unchanged in the photoproducts, corroborated with the photoproducts analysis. The photoprotection capacity was evaluated before and after irradiation. Results indicate that the values before irradiation are similar for all three compounds, only glaucine increasing its capacity with length of irradiation time.

Introduction

Boldine, (S)-2,9-dihydroxy-1,10-dimethoxy-aporphine, occurs abundantly in the leaves and bark of boldo (Peumus boldus Mol.) a widely distributed native tree of Chile. Infusions of boldo leaves traditionally have been employed in folk medicine for their reportedly chloretic, diuretic, sedative and digestive properties [1], [2]. At low micromolar concentrations, boldine prevents both enzymatic and non-enzymatic mediated damage to biological systems. In vitro, boldine inhibits the free-radical-mediated initiation and propagation of the peroxidative damage induced to various membrane types (such as liver homogenates, hepatic microsomes and ghost erythrocytes) and it blocks the free-radical-dependent lysis of red blood cells and intact hepatocytes [1], [3], [4]. In other words, boldine is a very potent antioxidant substance for biological systems. Boldine undergoes peroxidative free-radical-mediated damage, the boldine molecule acts as an efficient hydroxyl radical scavenger [4].

Glaucine is the dimethoxy analogue of boldine (Scheme 1). The principal difference between both molecules is their solubility, while boldine is hydrosoluble, glaucine is liposoluble. Both molecules are relatively non-toxic [5], [6], [7]. Ca²⁺ channel antagonism by glaucine appears to be responsible for the relaxant effect of glaucine in human isolated bronchus while PDE4 inhibition contributes to the inhibitory effects of glaucine in human granulocytes [8].

We investigated the photoprotector capacity of boldine hydrochloride against UVB using in vitro and in vivo methods. The calculated membrane protection factor, in vitro was higher than octylmethoxycinnamate [9], while the SPF in vivo determined on volunteers was lower than Nivea sun filter [9].

Boldine was found to be photounstable at wavelengths up to λ = 300 nm. Here, we report the photostability and photoprotection capacity of boldine, boldine hydrochloride and glaucine hydrochloride. Three main photoproducts F1, F2 and F3 (Scheme 1) were isolated and characterized from boldine.