Effect of UV Irradiation on Interactions ofα-Lipoic Acid with Free Radicals

Abstract

Changes of antioxidant properties ofα-lipoic acid (LA) after UV irradiation were studied. LA is the typical drug used in diabetic neuropathy. Quenching of free radicals is an important factor of therapy by using this substance.α-Lipoic acid is exposed to UV irradiation during the storage. The aim of our studies was to examine the effect of UV irradiation on the interactions of LA with free radicals. Theα-lipoic acid was irradiated by UVA 315–400 nm light during 10 to 110 minutes by intervals of 10 minutes. The electron paramagnetic resonance spectroscopy was used as the experimental technique. The antioxidant properties of LA were spectroscopically confirmed. The strong effect of UV irradiation on interactions ofα-lipoic acid with free radicals was observed. It was pointed out that interactions of LA with free radicals decrease after its exposition on UV. The interactions of LA with free radicals were higher after the sample irradiation during 10 minutes than for the samples irradiated longer (20–110 minutes). The results are important for problems connected with photomedicine; they pointed out thatα-lipoic acid should not be stored on UV exposition. Application of electron paramagnetic resonance spectroscopy to characterize interactions of pharmacological substance with free radicals was confirmed.

UV‐irradiation influence on free radical formation and radical scavenging ability of caffeic acid—EPR, UV‐Vis, and colorimetric examination

“…Probably free radicals formed by UV‐irradiation in caffeic acid were responsible for the stronger quenching of EPR lines of DPPH by irradiated samples relative to nonirradiated one. The quenching of EPR lines of DPPH by interactions with free radicals were also observed by us for Echinacea (Ramos & Pilawa, 2015), morus (Kurzeja, Stec, Ramos, Pilawa, & Pawłowska‐Góral, 2013), and α‐lipoic acid (Ramos et al, 2013).…”

“…This effect was characteristic for high amounts of free radicals in the samples and low distances between unpaired electrons (Eaton et al, 1998;Wertz & Bolton, 1986). Broad EPR lines were also observed by us for UVirradiated α-lipoic acid (Ramos, Pepli nski, & Pilawa, 2013). increased with increasing of microwave power (Figure 6a-c), because of excitation of unpaired electrons of free radicals to the higher energy levels.…”

“…This effect was characteristic for high amounts of free radicals in the samples and low distances between unpaired electrons (Eaton et al, 1998; Wertz & Bolton, 1986). Broad EPR lines were also observed by us for UV‐irradiated α‐lipoic acid (Ramos, Pepliński, & Pilawa, 2013).…”

“…Shape of EPR spectra of UV-irradiated caffeic acid changed with increasing of microwave power. All the tested shape parame- Echinacea (Ramos & Pilawa, 2015), morus (Kurzeja, Stec, Ramos, Pilawa, & Pawłowska-G oral, 2013), and α-lipoic acid (Ramos et al, 2013).…”