title: Xanthine oxidase inhibitory activities of extracts and flavonoids of the leaves of Blumea balsamifera.
abstract: BACKGROUND
  Blumea balsamifera DC (Compositae) leaves have been recommended for use as a folk medicine in the treatment of various diseases related to urolithiasis in southeast Asia. Phytochemical studies of this plant revealed it contains four classes of flavonoids (e.g., flavonols, flavones, flavanones, and dihydroflavonol derivatives).
  
  
  OBJECTIVE
  In view of the broad pharmacological activity of flavonoids, this study was carried out to determine the xanthine oxidase (XO) inhibitory and enzymatically produced superoxide radical scavenging activity of different organic extracts and that of the isolated flavonoids from B. balsamifera leaves.
  
  
  METHODS
  The inhibitory activity of XO was assayed spectrophotometrically at 295 nm. The superoxide radicals scavenging activity was assessed by NBT reduction method, spectrophotometrically at 560 nm. A dose response curve was plotted for determining IC₅₀ values.
  
  
  RESULTS
  The methanol extract (IC₅₀ = 0.111 mg/mL) showed higher XO inhibitory activity than the chloroform (0.138 mg/mL) and pet-ether extracts (0.516 mg/mL). IC₅₀ values of scavenging of superoxide radicals for extracts decreased in the order of: methanol (0.063 mg/mL) > chloroform (0.092 mg/mL) > pet-ether (0.321 mg/mL). The XO inhibitory activity of the isolated flavonoids and reference compounds tested decreased in the order of: allopurinol > luteolin > quercetin > tamarixetin > 5,7,3',5'-tetrahydroxyflavanone > rhamnetin > luteolin-7-methyl ether > blumeatin > dihydroquercetin-4'-methyl ether > dihydroquercetin-7,4'-dimethyl ether > L-ascorbic acid.
  
  
  CONCLUSIONS
  The results indicated that the flavone derivatives were more active than the flavonol derivatives. The flavanone derivatives were moderately active and the dihydroflavonol derivatives were the least. The higher flavonoid content of extracts contributed to their higher XO inhibitory activity.
authors.affiliation: Dubai Pharmacy College, P.O. BOX 19099, Dubai, United Arab Emirates. nessa1995@yahoo.com
authors.forename: Fazilatun
authors.initials: F
authors.lastname: Nessa
authors.forename: Zhari
authors.initials: Z
authors.lastname: Ismail
authors.forename: Nornisah
authors.initials: N
authors.lastname: Mohamed
mesh_terms: D019659:Asteraceae / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D005419:Flavonoids / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000008:administration & dosage / Q000302:isolation & purification / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008518:Medicine, East Asian Traditional; D010936:Plant Extracts / Q000008:administration & dosage / Q000494:pharmacology*; D018515:Plant Leaves; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors*
chemical_list: D005419:Flavonoids; D016166:Free Radical Scavengers; D010936:Plant Extracts; D014969:Xanthine Oxidase