Comparative antioxidant, antiproliferative and cytotoxic potentials of Piliostigma thonningii (Schum.) Milne-Redh. and Delonix regia (Boj. ex Hook) Raf. (Fabaceae) stem bark
Methanol extract and solvent fractions of Piliostigma thonningii (Schum.) Milne-Redh. and Delonix regia (Boj. ex Hook) Raf. (Fabaceae) stem barks were investigated for antiproliferative effect on guinea corn (Sorghum bicolor) seeds, cytotoxicity on tadpoles (Raniceps ranninus), in vitro 2,2-diphenyl-1-picrylhydraxyl (DPPH) radical scavenging and ferric reducing power activities. All tested agents of both plants at 0.25 - 5.0 mg/ml gave significant decreases in mean radicle length of guinea corn seeds (antiproliferative action) which was concentration-dependent. Growth inhibition ranking at 72 h for both plants at the most active concentration, 5 mg/ml was: aqueous fraction > methanol extract > chloroform fraction. However, the aqueous fraction of D. regia (95.3% inhibition) was more active than that of P. thonningii (62.6%). With the cytotoxic assay, the chloroform fractions (LC50, 5.0 mg/ml and 6.0 mg/ml respectively, for P. thonningii and D. regia) were more active than their aqueous fractions. Extracts and fractions of these plants yielded inactive DPPH radical scavenging activity at the tested concentrations of 20 - 100 µg/ml. In the concentration-dependent ferric reducing power model, the methanol extracts of both plants were more active than their partitioned fractions as antioxidant agents at 100 µg/ml. Although D. regia stem bark was richer in phenols (0.321 - 0.339 mg gallic acid equivalent /g) and flavonoids (0.041 - 0.046 mg quercetin equivalent /g) than P. thonningii, phenolic contents of these plants were five-six times more than that of their flavonoids. Data reported herein showed that D. regia was a better antioxidant, cytotoxic and antiproliferative plant than P. thonningii . These findings hereby justify the folkloric use of P. thonningii and D. regia in the treatment of oxidative stress-induced diseases.
Keywords: Piliostigma thonningii, Delonix regia, antiproliferative activity, cytotoxicity, antioxidant assay