Antioxidant enzymes stimulation in Aspergillus parasiticus by Lentinula edodes inhibits aflatoxin production

Abstract

Biosynthesis of aflatoxins, toxic metabolites produced by Aspergillus parasiticus, is correlated to the fungal oxidative stress and cell ageing. In this paper, the mechanism underlying the aflatoxin-inhibiting effect of the Lentinula edodes culture filtrates was studied by analysing their anti-oxidant activity and beta-glucan content. Mushroom beta-glucans are pharmacologically active compounds stimulating anti-oxidant responses in animal cells. L. edodes lyophilised filtrates stimulate A. parasiticus anti-oxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase) and aflatoxin inhibition was better correlated with beta-glucan content than with anti-oxidant activity of the filtrates. RT-PCR analyses on treated mycelia showed a delay in the activation of aflR, and norA, genes of aflatoxin cluster and a synchronous activation of hsf2-like, a homologue of a yeast transcription factor involved in oxidative stress responses. The first evidence of hsf2-like in A. parasiticus and its activation during aflatoxin biosynthesis is reported. L. edodes filtrates could play a role as external stimulus affecting the anti-oxidant status in the fungal cell that, in turn, leads to aflatoxin inhibition. In the fungal cell, beta-glucans present in the filtrates could stimulate the activation of transcription factors related to anti-oxidant response and anti-oxidant enzyme activity with a contemporaneous delay of aflatoxin genes transcription, which led to a marked reduction of aflatoxin production. This research suggests new perspectives to set suitable strategies against aflatoxins and L. edodes could be considered a promising tool.

Aflatoxins: Mechanisms of Inhibition by Antagonistic Plants and Microorganisms

“…Recently, mushrooms have been explored as potential control agents for AF contamination (Reverberi et al, 2005;Zjalic et al, 2006). Reverberi et al (2005) concluded that culture filtrate and purified -glucans from Lentinula edodes, an edible basidiomycetous mushroom native to East Asia, significantly inhibited AF production by A. parasiticus without affecting fungal growth. Their RT-PCR analyses of treated A. parasiticus mycelia showed a delay in activation of AF biosynthetic pathway genes aflR and norA as well as a simultaneous activation of hsf2-like, a transcription factor involved in oxidative stress responses.…”

“…It has been shown that oxidative stress is a prerequisite and stimulatory factor for AF biosynthesis (Jayashree and Subramanyam, 2000;Reverberi et al, 2005). Oxidative stress is a result of exposure of fungal cells to ROS such as superoxide anion (O 2 · -), hydrogen peroxide (H 2 O 2 ), hydroxyl radicals (HO˙) and lipoperoxides (LOOH), which are formed from unsaturated fatty acids.…”

Fungi a source with huge potential for 'mushroom pharmaceuticals'

“…Some studies suggested that mushrooms could be used also as inhibitors of mycotoxins production. Culture filtrates from Lentinula edodes and Trametes versicolor have revealed promising aflatoxin-inhibiting effects (Reverberi et al, 2005;Zjalic et al, 2006).…”

Effects of β-glucan on some environmental toxins: An overview

“…In testing the mechanisms involved in the aflatoxin-inhibiting effects of Lentinula edodes cultures, the authors demonstrated that these cultures act as an external stimulus affecting the anti-oxidant status in the fungal cells, which subsequently inhibits aflatoxin. Glucan present in cultures activates the transcription factors related to the anti-oxidant response 16 . Based on this study, glucan acts not "only" by absorption of mycotoxins but directly reduces aflatoxin production.…”