Ribes nigrum leaf extract: antioxidant capacity and redox balance regulation mechanism in microglial cells

This study focuses on the investigation of the antioxidant and anti-inflammatory activity of extracts from Ribes nigrum leaves on BV-2 microglial Wt and Acyl-CoA oxidase 1 deficient (Acox1^−/−) cell line models, useful for the investigation of some neurodegenerative disorders. Investigations showed the presence of high quantity of phenolic compounds in this extract, among which flavan-3-ols, flavonols, furanocoumarins, hydroxycinnamates, quercetin, and quercetin derivatives were major components, which are known for their biological activity in various test systems. The MTT test revealed the 0.125 mg/mL concentration of R. nigrum extract as the highest non-toxic. The investigated extract showed high antioxidant activity in chemical-based tests. The antioxidant potential of the R. nigrum leaf extract was furtherly explored using the BV-2 microglial cell line models. Moreover, the extract was found to alter the activity of the main antioxidant enzyme, catalase and fatty acid oxidation enzyme, Acyl-CoA oxidase 1 (ACOX1) as well as the expression of appropriate genes in Wt and Acox1^−/− BV-2 microglial cells such as Cat, iNos, Il-1β, Tnf-α, and Abcd1. In Wt cells, the treatment with R. nigrum leaf extract ACOX1 activity was downregulated after 24 hours of treatment, meanwhile the catalase activity remains unchanged. The further treatment leaded to the downregulation of catalase and the upregulation of ACOX1 activity. However, in Acox1^−/− cells, which represent a model of oxidative stress, an increase in catalase activity was observed only after 48 hours of treatment, indicating an alternative mode of action of the extract. It was also observed the reduced ROS and NO formation in cells, indicating the pronounced antioxidant capacity of R. nigrum extract in the investigated cell-models.