Phenolic mediated anti-inflammatory properties of a maple syrup extract in RAW 264.7 murine macrophages

The in vitro anti-inflammatory effects of a phenolic-enriched Canadian maple syrup ethyl acetate extract (MS-EtOAc) and 15 purified phenolic constituents were evaluated in a LPS-stimulated RAW 264.7 murine macrophage cell model. MS-EtOAc decreased nitric oxide (NO) and prostaglandin-E2 (PGE2) production at 10-100 μg/mL concentrations. The observed NO inhibition was a direct result of reduced nitric oxide synthase (iNOS) protein and gene expression through suppression of NF-κB transcriptional activation. In addition, MS-EtOAc upregulated cyclooxygenase-2 (COX-2) mRNA and protein expression. Among the 15 pure isolates, (E)-3,3′-dimethoxy-4,4′-dihydroxystilbene was most effective in decreasing both NO and PGE2 levels. However, 4-acetylcatechol, tyrosol, and protocatechuic acid only reduced PGE2 levels. Thus, the potential anti-inflammatory activity of MS-EtOAc can be attributed to its unique combination of compounds and not as a result of a single purified phenolic constituent alone. Future research on the purified phenolic compounds will be useful in understanding the overall in vitro anti-inflammatory effects of maple syrup.