Dietary supplementation with a novel fish oil enriched in very-long-chain-polyunsaturated-fatty-acids improves cardiometabolic risk factors and retinal function in mice

Very-long-chain polyunsaturated fatty acids (VLCPUFA; C24-38) that contain between 5-6 unsaturated double bonds are a unique class of PUFA that are primarily found in the retina, brain and testes. VLCPUFA appear to have important biological roles that cannot be fulfilled by the more common shorter-chain PUFA, but the lack of a suitable dietary source of VLCPUFA have limited research in this field. Typically, fish oils contain only a small amount of VLCPUFA (<1%, w/w), but we were able to produce a fish oil concentrate that contained over 40% by weight of n-3 VLCPUFA, with chain lengths between C24 and C28. A single-dose oral gavage of the VLCPUFA-oil in C57BL/6J mice resulted in a 9-fold increase in plasma levels of C24:5 n-3 by 2 hours. This was followed by a 70% increase in the retinal level of C24:5 n-3 after 8 hours from the gavage. Long-term (8-week) dietary supplementation with 1% or 5% (w/w) of VLCPUFA-oil in chow diet did not cause any adverse changes in the plasma chemistry profile or evidence of histologic injury to multiple tissues. It was found to alter the lipid composition of the liver, brain and eye in 11-month-old C57BL/6J mice. The VLCPUFA supplementation also caused favorable cardiometabolic changes by lowering plasma glucose, insulin, cholesterol and triglyceride levels. Furthermore, mice treated with the VLCPUFA oil had improved electroretinography response and visual performance after 15 consecutive days of oral gavage. Transcriptomic analysis of treated mice revealed significant alternation in genes involved in PPAR signaling pathways. Further in vitro studies demonstrated that the VLCPUFA-oil and chemically synthesized C24:5 n-3 are potent agonists for both PPAR-alpha and gamma. In conclusion, the multiple potential beneficial effects of fish-derived VLCPUFA-oil on eye health and cardiometabolic risk in mice support future efforts to develop VLCPUFA-oil into a novel therapy. Overall design: After mice were fed chow diet supplemented with 0, 1, or 5% VLCPUFA for 8 weeks, total RNA was isolated from liver samples (n = 6/group) using a RNeasy Mini Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions. RNA purity and concentration were assessed using a NanoDropTM spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA). A 4200 TapeStation System (Agilent Technologies, Santa Clara, CA, USA) was used with RNA screentapes to generate RNA integrity numbers (RIN) for RNA samples. All RNA samples selected for RNA-seq library preparation had a RIN greater than 7. RNA-seq libraries were prepared using a TruSeq Stranded mRNA Sample Prep Kit (Illumina, San Diego, CA, USA). RNA seq data was handled as described previously (Brooks et al., 2019).