In vitro antisickling and antioxidant studies on selected medicinal plants
This study evaluated the in-vitro inhibition of polymerization of haemoglobin and antioxidant activity of the methanolic extract of the whole plant of Mitracarpus villosus Cham. (Rubiaceae) (MVW), the leaf of Senna siamea Lam. (Caesalpinioideae) (SSL), the aerial parts of Lantana camara Linn. (Verbenaceae)(LCA), Emilia coccinea Sims. (Lamiaceae)(ECA), Amaranthus viridis Linn. (Amaranthaceae)(AVA), A. hybridus Linn. (Amaranthaceae)(AHA), A. spinosus Linn. (Amaranthaceae)(ASA), the flower of Lagenaria breviflora Benth.(LBF)(Cucurbitaceae) and the fruit of Citrullus lanatus sub sp mucosospermus Thunb. (CLFM) (Cucurbitaceae). This was with a view to providing scientific basis for the use of the plants in the management of sickle cell disease. The antisickling property of the test extracts was estimated by inhibition of polymerization of HbS molecules using the sodium metabisulphite (Na2S2O5). Absorbance of the antisickling assay mixture which includes HbS blood, Na2S2O5 with or without the test extracts or isolated compounds was recorded using a T70 UV/VIS spectrophotometer at 700 nm. The antioxidant activity was estimated by the use of 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay and thin layer chromatography (TLC) bioautography. The absorbance of the antioxidant assay mixture which includes methanol, the extract with or without DPPH was measured using T70 UV-VIS Spectrophotometer with absorbance recorded at 517 nm. Ascorbic acid served as the positive control. The extract with the most significant activities (p< 0.05) in both test models was recollected, extracted and partitioned to dichloromethane and ethylacetate fractions. The fractions were subsequently subjected to repeated chromatographic separation for isolation of compounds. The isolated compounds were also subjected to the bioassay tests. The result showed that ECA and MVW demonstrated the most significant (p<0.05) activities in both test models. The polymerization inhibitory activity and free radical scavenging activity of ECA were estimated to be 100.32 ± 0.02 % and 95.68 ± 0.07 % while MVW had 91.62 ± 0.02 % and 91.74 ± 0.05 % respectively. Chromatographic separation of the dichloromethane and ethylacetate fractions resulted in the isolation of psychorubrin (3-hydroxy-3, 4-dihydro-1H-benzo[g]isochromene-5, 10-dione) and two other unidentified compounds E4 and D1. Psychorubrin was identified by 1H and 13C NMR and by comparison with literature data. Compounds E4 had the highest polymerization inhibitory effect (87.85 ± 0.87 %) and antioxidant activity (87.99 ± 0.18 %) compared with vanillic acid (96.71 ± 0.90 %) and ascorbic acid (98.90 ± 0.04 %) at the maximum concentration of 4 mg/ml and 3.125 mg/ml respectively. Psychorubrin had a moderate polymerization inhibitory effect (59.64 ± 0.49 %) as well as antioxidant activity (46.90 ± 0.45 %). The study concluded that the plant extracts have both antisickling and antioxidant activities with the extract of Mitracarpus villosus having the highest activity.