Anthocyanins Extracted from Black Soybean Seed Coat and Mulberry Rescue Retinal Degeneration Induced by N-methyl-N-nitrosourea in Rats

Abstract

Purpose: : Anthocyanins are known to have antioxidant effects and thus may play an important role in the prevention of various degenerative diseases. In this study, we examined the effect of anthocyanins extracted from black soybean seed coat and mulberry in an animal model for retinal degeneration (RD), which is one of the leading causes of photoreceptor cell death.

Methods: : Retinal degeneration was induced in Sprague-Dawley rats by an intraperitoneal injection of N-methyl-N-nitrosourea (MNU) (50 mg/Kg), a DNA methylating agent, which causes selective retinal pigment epithelium damage with secondary photoreceptor cell death. Anthocyanins extracted from black soybean seed coat (50 mg/Kg) and mulberry (50 mg/Kg) were administered daily, orally (p.o.) for 1 week (wk), 2 wks and 4 wks after MNU injection. Electroretinogram (ERG) recordings and morphological analyses were performed.

Results: : In control rats damaged by MNU, ERG recordings showed a significant time-dependent reduction in both a- and b-wave amplitudes, compared with normal animals. In the MNU-injected rats with the administration of anthocyanins from black soybean seed coat and mulberry for 4 wks, significant increases were detected in both a-and b-waves, while in the MNU-injected rats given anthocyanins for 1 wk and 2 wks, the increase in ERG responses was not significant. Thus, anthocyanins from black soybean seed coat and mulberry appeared to be more effective when applied for long duration. This corresponds to morphological results showing that photoreceptors and the outer nuclear layer (ONL) thickness were well preserved after dosage > 2 wks. In addition, retinal inflammation, evaluated by immunolabeling with an antibody to GFAP, was markedly reduced in anthocyanin-treated retinas.

Conclusions: : These results demonstrate that anthocyanins extracted from black soybean seed coat and mulberry may protect retinal neurons from MNU-induced damages both structurally and functionally. It suggests that anthocyanins from black soybean seed coat and mulberry may be used as a useful supplement to modulate RD.

Keywords: retinal degenerations: cell biology • apoptosis/cell death • electroretinography: non-clinical