title: Attenuation of oxidative stress in U937 cells by polyphenolic-rich bark fractions of Burkea africana and Syzygium cordatum.
abstract: BACKGROUND
  Oxidative stress has been implicated in the progression of various diseases, which may result in the depletion of endogenous antioxidants. Exogenous supplementation with antioxidants could result in increased protection against oxidative stress. As concerns have been raised regarding synthetic antioxidant usage, the identification of alternative treatments is justified. The aim of the present study was to determine the antioxidant efficacy of Burkea africana and Syzygium cordatum bark extracts in an in vitro oxidative stress model.
  
  
  METHODS
  Cytotoxicity of crude aqueous and methanolic extracts, as well as polyphenolic-rich fractions, was determined in C2C12 myoblasts, 3T3-L1 pre-adipocytes, normal human dermal fibroblasts and U937 macrophage-like cells using the neutral red uptake assay. Polyphenolic content was determined using the Folin-Ciocalteau and aluminium trichloride assays, and antioxidant activity using the Trolox Equivalence Antioxidant Capacity and DPPH assays. The extracts efficacy against oxidative stress in AAPH-exposed U937 cells was assessed with regards to reactive oxygen species generation, cytotoxicity, apoptosis, lipid peroxidation and reduced glutathione depletion.
  
  
  RESULTS
  B. africana and S. cordatum showed enrichment of polyphenols from the aqueous extract, to methanolic extract, to polyphenolic-rich fractions. Antioxidant activity followed the same trend, which correlated well with the increased concentration of polyphenols, and was between two- to three-fold stronger than the Trolox antioxidant control. Both plants had superior activity compared to ascorbic acid in the DPPH assay. Polyphenolic-rich fractions were most toxic to the 3T3-L1 (IC50's between 13 and 21 μg/ml) and C2C12 (IC50's approximately 25 μg/ml) cell lines, but were not cytotoxic in the U937 and normal human dermal fibroblasts cultures. Free radical-induced generation of reactive oxygen species (up to 80%), cytotoxicity (up to 20%), lipid peroxidation (up to 200%) and apoptosis (up to 60%) was successfully reduced by crude extracts of B. africana and the polyphenolic-rich fractions of both plants. The crude extracts of S. cordatum were not as effective in reducing cytotoxic parameters.
  
  
  CONCLUSIONS
  Although oxidative stress was attenuated in U937 cells, cytotoxicity was observed in the 3T3-L1 and C2C12 cell lines. Further isolation and purification of polyphenolic-fractions could increase the potential use of these extracts as supplements by decreasing cytotoxicity and maintaining antioxidant quality.
authors.forename: Werner
authors.initials: W
authors.lastname: Cordier
authors.forename: Mary
authors.initials: M
authors.lastname: Gulumian
authors.forename: Allan Duncan
authors.initials: AD
authors.lastname: Cromarty
authors.forename: Vanessa
authors.initials: V
authors.lastname: Steenkamp
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology; D007887:Fabaceae / Q000737:chemistry*; D005609:Free Radicals; D006801:Humans; D015227:Lipid Peroxidation / Q000187:drug effects; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects*; D024301:Plant Bark / Q000737:chemistry; D010936:Plant Extracts / Q000494:pharmacology*; D059808:Polyphenols / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D027842:Syzygium / Q000737:chemistry*; D020298:U937 Cells
chemical_list: D000975:Antioxidants; D005609:Free Radicals; D010936:Plant Extracts; D059808:Polyphenols; D017382:Reactive Oxygen Species; D001205:Ascorbic Acid