Bioassay guided isolation and identification of anti-inflammatory and anti-microbial compounds from Urtica dioica L. (Urticaceae) leaves

Abstract

The present study describes the anti-inflammatory, anti-microbial activity and lipophilic profile with acute toxicological studies of Urtica dioica. Successive extraction of the leaves with organic solvents of increasing polarity and their screening for anti-inflammatory and anti-microbial activity was assessed. Hexane extract showed good anti-inflammatory and anti-microbial activity; hence it was further fractionated using open silica gel column chromatography into 19 sub fractions which were pooled together according to their thin layer chromatography (TLC) profile to give an overall 5 fractions. Among the 5 fractions, fraction-II (FII) at a dose of 200 mg/kg body-weight (bw) exhibits equipotent anti-inflammatory activity (48.83% after 3 h) as that of the standard drug indomethacin (53.48%) in Wistar rats. FII also showed a potent anti-microbial activity against all the tested bacterial strains and its minimum inhibitory concentration (MIC) value was 125, 15.62, 31.25, 250, 31.25, 125 and 7.81 ìg/ml against Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Shigella flexneri and Salmonella typhi, respectively which was determined by serial tube dilution method. FII was subjected to gas chromatography-mass spectrometry (GC-MS) analysis in search of potent anti-inflammatory and anti-microbial compound(s). 2,4-Di-t-butylphenol (4.56%), neophytadiene (26.97%), butyl tetradecyl ester (9.53%), dibutyl phthalate (7.45%), bis(2-ethyl hexyl) maleate (8.80%), 1,2-benzenedicarboxylic acid (9.89%) and 2-tert-butyl-4,6-bis(3,5-di-tert-butyl-4-hydroxybenzyl)phenol (3.19%) were the major constituents responsible for both anti-inflammatory and anti-microbial activity of hexane extract of U. dioica. Sub-acute oral toxicity of crude n-hexane extract of U. dioica was carried out in Wistar rats at doses of 250, 500, 1000 and 2000 mg/kg bw to assess the safety index. Hematological parameters from blood and other biochemical parameters from serum confirmed its safety at tested concentrations. Our results corroborate the anti-inflammatory and anti-microbial activity of U. dioica, and could justify its use in folk medicine for the treatment of rheumatic arthritis and other infectious diseases.

Key words: Urtica dioica, anti-inflammatory, anti-microbial, minimum inhibitory concentration (MIC), gas chromatography-mass spectrometry (GC-MS), toxicity.