Abstract
Filamentous fungi are microorganisms that have been increasingly used for obtaining biologically active substances, due to their extraordinary biosynthetic capacity. These fungal metabolites have extensive industrial applications and their production is cheap compared to plants metabolites. The most prominent applications of fungal metabolites are as pigments, antimicrobials, immunosuppressants or immune stimulants, antioxidants, cytotoxic and enzyme inhibitors, among other compounds used in the pharmaceutical or food industry. In recent years, a significant number of natural compounds with antioxidant activity has been reported. Since oxidative stress is related to various diseases, including the neurodegenerative ones, some of these natural metabolites have been screened and presented significant inhibitory activity of acetylcholinesterase (AChE), an enzyme involved in Alzheimer's disease (AD). This enzyme degrades the neurotransmitter acetylcholine, which level is much reduced in AD patients. That disease affects mainly elderly individuals, and with the increase in life expectancy, AD is considered a serious and costly public health problem since treatment is only symptomatic and still limited by price and adverse effects. Therefore, the search for drugs of natural origin, in particular, from fungi to the treatment or prevention of AD has become a huge and urgent need. The vast majority of scientific works that investigate fungal secondary metabolites with regard to possible biological activities, use extracts obtained from the use of solvents such as methanol, ethanol, ethyl acetate, or other, demanding great spent of time, labour, and reagents, generating high volumes of chemical waste, and, at the end, often only a few extracts presents satisfactory results. In view of the urgency of obtaining effective treatment for AD, this study, in an innovative way, targeted, in the biological assays, fermented broths containing secondary metabolites, which provided time optimization and elimination of solvents use, avoiding, therefore, negative impacts to the environment. The aim of this study was to determine the antioxidant potential and AChE inhibitory capacity of fermented broths from different fungi. For this, about 50 filamentous fungi isolated from soil with different macroscopic characteristics were selected. They were grown in culture medium constituted by peptone, sucrose, potassium phosphate dibasic (K2HPO4); sodium nitrate (NaNO3), magnesium sulfate heptahydrate (MgSO4.7H2O); ferrous sulfate heptahydrate (FeSO4.7H2O), potassium chloride (KCl) and cupric sulfate pentahydrate (CuSO4.5H2O), by 28 days at 25 °C. After this period, the broths containing secondary metabolites were screened for assessing their total antioxidant activity by colorimetric phosphomolybdate method and their AChE inhibitory activity. The broth of Hypocrea lixii stood out among the other fungal species, presenting promising results. Even with bioactive compounds very diluted in the medium, this broth presented significant total antioxidant activity (18.22 µg AAE/mL broth) and efficient inhibition of AChE (65.4%) in relation to eserine (positive standard).
