There are a limited range of drugs available to treat type 2 diabetes (T2D) and insulin resistance (IR) that are efficacious and inexpensive. In West Africa, extracts of Hymenocardia acida are frequently used. However, few objective studies have yet attested to their efficacy. Here we evaluated the potential for extracts of H. acida to overcome IR in muscle in vitro.
Crude extracts of H. acida were prepared in methanol (MeOH) and chloroform (CHCL3). The methanolic extract was also subjected to a further solid phase extraction (SPE) on C18 silica using ratios of MeOH:dH2O from 0 to 100%, yielding 15 sub-fractions. Sub-fractions were dried and analysed using proton nuclear magnetic resonance (1H-NMR) spectroscopy. The effect of crude extracts or SPE sub-fractions 13 on the viability of differentiated L6 myotubes was then assessed using resazurin. Subsequently, myotubes were treated with palmitic acid (PA) to generate IR and incubated with extracts or sub-fractions at concentrations across a 100-fold range that did not impair viability. Their effects on insulin sensitivity were assessed using uptake of 3H-2-deoxyglucose uptake±insulin.
Treatment with PA had the expected effect to abolish insulin-stimulated glucose uptake in L6 myotubes. Co-incubation with the MeOH extract at 200 μg/ml significantly restored insulin sensitivity of glucose uptake by 63% (P=0.041), while the CHCL3 extract was not effective. SPE sub-fractions 13 were identified as potentially containing bioactive compounds, due to the presence of peaks on 1H-NMR trace, indicative of the presence of un-/partially-substituted benzene rings in their chemical structure. However, treatment with these sub-fractions did not modify insulin-stimulated glucose uptake in myotubes.
Thus, methanolic extracts of H. acida have shown promise in ameliorating IR in skeletal muscle cells, representing the key tissue mediating insulin-stimulated glucose disposal. Further work must aim to identify the active substance(s) responsible and their mechanism of action.