Abstract:
Psidium guajava L. (Guava, Myrtaceae) is a fruit tree widely distributed in Sri Lanka and reported to have anti-inflammatory properties. The objective of the present study is to investigate in vitro Lipoxygenase related anti- inflammatory and antioxidant properties of leaf extract of P. guajava.The air-dried, powdered leaves of P. guajava were extracted with ethanol using cold extraction technique. Anti-inflammatory activity was determined by Lipoxygenase enzyme inhibitory (LOXEI) assay. Antioxidant activity was determined by DPPH free radical scavenging, Ferric Reducing Antioxidant Power (FRAP), Ferrous Iron Chelating (FIC) and Oxygen Radical Absorbance Capacity (ORAC) assays. The Total Phenolic Content (TPC) and Total Flavanoid Content (TFC) were also determined. The total ethanol leaf extract showed a marked LOXEI activity, having IC50 value of 42.98 ±
0.45 µg/mL in comparison to quercetin (35.01±0.82 µg/mL). The extract
exhibited high DPPH free radical scavenging (IC50=15.00±0.36 µg/mL,
Trolox: 5.29±0.09 µg/mL) and low FIC activity (IC50=2684.34±34.30 µg/mL, EDTA-2Na: 13.07±0.64 µg/mL). The FRAP of the extract was found to be 2170.00 ± 89.10mg Trolox Equivalents (TE)/ g and ORAC value was 936.51±63.49 mg TE/g, which is comparable to that of green tea extract (1662.82±0.22 mg TE/g). The TPC and TFC were found to be 125.83±4.60 mg Gallic Acid Equivalents (GAE)/g and 13.73±1.25 mg Quercetin
Equivalents (QE)/g, respectively. The LOXEI activity and antioxidant
activity of leaf extract were significantly different from their reference standards (P<0.05). The present study implies that the leaf of P. guajava could be used as a health food and as a source of new drug leads for further research
