Flaxseed Consumption Reduces Blood Pressure in Patients With Hypertension by Altering Circulating Oxylipins via an α-Linolenic Acid–Induced Inhibition of Soluble Epoxide Hydrolase

In a randomized, double-blinded, controlled clinical trial, participants with peripheral arterial disease (75% hypertensive) consumed 30 g of milled flaxseed/d for 6 months. The flaxseed group exhibited significant reductions in systolic (−10 mm Hg) and diastolic (−7 mm Hg) blood pressure. Flaxseed contains the n3 fatty acid α-linolenic acid. Plasma α-linolenic acid increased with ingestion of flaxseed and was inversely associated with blood pressure. However, the antihypertensive mechanism was unclear. Oxylipins derived from polyunsaturated fatty acids regulate vascular tone. Therefore, the objective was to examine whether flaxseed consumption altered plasma oxylipins in a manner that influenced blood pressure. Plasma of FlaxPAD (Flaxseed for Peripheral Arterial Disease) participants underwent solid phase extraction and high-performance liquid chromatography–mass spectrometry/mass spectrometry analysis. The flaxseed group exhibited significant decreases in 8 plasma oxylipins versus control. Six of these (5,6-, 8,9-, 11,12-, 14,15-dihydroxyeicosatrienoic acid and 9,10- and 12,13-dihydroxyoctadecenoic acid) were products of soluble epoxide hydrolase, a pharmacological target for antihypertensive treatment. Patients exhibiting a decrease in total plasma soluble epoxide hydrolase–derived oxylipins, exhibited a significant decrease in systolic blood pressure (mean [95% confidence interval], −7.97 [−14.4 to −1.50] mm Hg) versus those who exhibited increased plasma soluble epoxide hydrolase–derived oxylipins (+3.17 [−4.78 to 11.13] mm Hg). These data suggest that a flaxseed bioactive may have decreased blood pressure via soluble epoxide hydrolase inhibition. Using a soluble epoxide hydrolase inhibitor screening assay, increasing concentrations of α-linolenic acid decreased soluble epoxide hydrolase activity ( P =0.0048; ρ=−0.94). In conclusion, α-linolenic acid in flaxseed may have inhibited soluble epoxide hydrolase, which altered oxylipin concentrations that contributed to the antihypertensive effects in patients with peripheral arterial disease. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00781950