Discovery and Anti-Inflammatory Activity of a Cyanobacterial Fatty Acid Targeting the Keap1/Nrf2 Pathway

The monounsaturated fatty acid 7( )-9-keto-hexadec-7-enoic acid ( ) and three structurally related analogues with different oxidation states and degrees of unsaturation ( - ) were discovered from a marine benthic cyanobacterial mat collected from Delta Shoal, Florida Keys. Their structures were elucidated using NMR spectroscopy and mass spectrometry. The structure of contained an α, -unsaturated carbonyl system, a key motif required for the activation of the Keap1/Nrf2-ARE pathway that is involved in the activation of antioxidant and phase II detoxification enzymes. Compounds - were screened in ARE-luciferase reporter gene assay using stably transfected HEK293 cells, and only significantly induced Nrf2 activity at 32 and 10 µM, whereas - were inactive. As there is crosstalk between inflammation and oxidative stress, subsequent biological studies were focused on to investigate its anti-inflammatory potential. Compound induced , a well-known target gene of Nrf2, and suppressed transcript levels, which translated into reduced levels of nitric oxide in LPS-activated mouse macrophage RAW264.7 cells, a more relevant model for inflammation. RNA sequencing was performed to capture the effects of on a global level and identified additional canonical pathways and upstream regulators involved in inflammation and immune response, particularly those related to multiple sclerosis. A targeted survey of marine cyanobacterial samples from other geographic locations, including Guam, suggested the widespread occurrence of . Furthermore, the previous isolation of from marine diatoms and green algae implied a potentially important ecological role across marine algal eukaryotes and prokaryotes. The previous isolation from sea lettuce raises the possibility of dietary intervention to attenuate inflammation and related disease progression.