Evaluation of antioxidant potential of essential oil and methanolic extract from the leaves of Didymocarpus pedicellatus R.Br.: An endemic Himalayan herb

Didymocarpus pedicellatus R.Br. (Family: Gesneriaceae) is an important medicinal herb used to treat renal diseases, particularly kidney stones in Asian countries. Leaf is the medicinally most utilized part of this plant possessing antiseptic, diuretic and anti-urolithiatic properties. The present study was conducted to investigate the chemical composition and antioxidant capacity of the essential oil and methanolic extract obtained from the leaves of D. pedicellatus. The essential oil yield was 0.05% while the yield for methanolic leaf extract was found to be 18.87%. GC-MS analysis of the essential oil led to the identification of twenty-nine compounds comprising 95.07% area of the total oil, with humulene oxide (39.58%), α-humulene (23.24%) and caryophyllene oxide (8.59%) being the major components. The essential oil exhibited significant antioxidant activity as demonstrated by 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay (IC₅₀ value 46.38 μg/mL) and metal chelating activity (IC₅₀ value 74.67 μg/mL). This may be attributed to its high sesquiterpene content (86.93%) and low concentration of monoterpenes (1.48%). The methanolic leaf extract was rich in phenols (14.23 ± 0.12 μg GAE/mg), flavonoids (27.09 ± 0.30 μg QE/mg) and also exhibited strong antioxidant activity (DPPH assay, IC₅₀ value 33.22 μg/mL; Metal chelating activity, IC₅₀ value 60.42 μg/mL). The major components of the methanolic leaf extract identified through GC-MS analysis were squalene (17.68%), flavanone, 4',5,6,7,8-pentamethoxy (11.75%), α-sitosterol (9.02%), neophytadiene (8.45%) and phytol (5.69%) accounting for 52.59% of the total area. The presence of these bioactive compounds may contribute significantly to the strong antioxidant potential of the leaf extract. The results of this study suggests that the leaves of D. pedicellatus have low essential oil content but contain significant amounts of other phytochemicals extractable with polar solvents like methanol, which could be further explored for their pharmacological and medicinal potential.