Sphingomyelinase inhibitory and free radical scavenging potential of selected Nigerian medicinal plant extracts

Ceramides from sphingolipid breakdown, and other sphingolipid metabolites, mediate cellular signalling in infectious and other diseases. Therefore, inhibitors of sphingomyelinases (SMases), hold promise as prospective therapeutic agents. Considering the potential therapeutic utility, this in vitro study explored the sphingomyelinase inhibitory, and free radical scavenging potential of five Nigerian medicinal plant leaf extracts, purported to have efficacy against diseases, including HIV/AIDS. The extracts’ sphingomyelinase inhibitory potencies were assessed colorimetrically and theirfree radical scavenging capabilities were assayed by the ability to quench 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical and superoxide anion (O₂.‐) radical. Considering their IC₅₀ (μg/ml) values, the extracts inhibited the biochemical activity of sphingomyelinase in a dose-dependent manner, relative to imipramine the standard inhibitor (IC₅₀ 38.5 ± 2.4 μg/ml). With Aloe vera as least inhibitory, inhibition increased as follows: Aloe vera

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(Asphodelaceae) (1132 ± 10.8) < Senna siamea

(Fabaceae) (992.2 ± 11.2) < Azadirachta indica

(Meliaceae) (984 ± 7.4) < Landolphia owariensis

(Apocynaceae) (146.3 ± 9.4) < Stachytarpheta angustifolia

(Verbenacae) (100.3 ± 8.7). DPPH radical scavenging relative to ascorbic acid standard increased as: A. indica < A. vera < S. siamea < S. angustifolia < L. owariensis; and superoxide anion quenching, relative to standard rutin increased as: A. vera < S. angustifolia < L. owariensis < S. siamea < A. indica.These results showed thatthe most potent SMase inhibitor was S. angustifolia; whereas, for DPPH radical scavenging and superoxide inhibition, the most potent of the five extracts were L. owariensis and A. indica respectively.These extracts deserve further investigation into their biological effects.