Grewia mollis Leaf Extracts and Fractions Demonstrated Good Inhibitory Activity on Pro-Inflammatory Enzymes and with Lower Cytotoxicity in vitro

Introduction: Plant extracts are used to treat illnesses, promote health, and maintain general well-being in traditional medicine. Grewia mollis Juss (Malvaceae) is one of the medicinal herbs that is used traditionally to treat chronic diseases and related pain because currently used anti-inflammatory drugs may cause severe side effects, and naturally occurring compounds with reduced cytotoxicity could be explored for therapeutic goals.

Materials and methods: Dried leaf of G. mollis was extracted with aqueous and organic solvents and partitioned based on polarity using solvent-solvent methods. The extracts were tested in anti-inflammatory assays against cyclooxygenases and lipoxygenase, and the safety profile was determined in a cell-based in-vitro assay.

Results: The n-hexane fraction of G. mollis leaf extracts had significant activity against both COX-1 (IC₅₀ =0.97±1.9 µg/mL) and COX-2 (IC₅₀ =1.13±0.2 µg/mL) better than the indomethacin positive control (IC₅₀ =1.3±0.6 and 1.52±0.2 µg/mL), respectively (p≤ 0.05). Also, all the extracts and fractions of G. mollis tested inhibited the activity of 15-LOX (IC₅₀ =12.48±2.9 to 29.43±9.9 µg/mL) better than the quercetin reference control (IC₅₀ =61.82±5.5 µg/mL), with the butanol fraction demonstrating the best anti-15 LOX action (IC₅₀ =12.48±2.9 µg/mL). Furthermore, all the extracts and fractions of G. mollis had relatively lower cytotoxicity on vero monkey kidney cells (LD₅₀ =30.56-479±0.07 µg/mL) compared to the doxorubicin positive control (LD₅₀ =2.59 µg/mL), but the selectivity index (SI=1.04-1.89) determination suggested that some of the extracts may contain toxic constituents.

Conclusion: Organic extracts of the leaves of Grewia mollis contained bioactive molecules with potent action on COX-2 and 15-LOX. Targeted high-resolution high-performance liquid chromatographic (HPLC) methods have streamlined and enhanced bioactive compound isolation and purification process. This allows for the separation of undesirable compounds that could cause metabolic cytotoxicity in the plant extract mixtures. The method could be used to develop an alternative therapeutic strategy to manage pain associated with chronic inflammation where the use of NSAID is problematic.

Keywords: 15-LOX; COX; Grewia mollis; anti-inflammatory; pain; plant extracts.