The Effects Of Algal Oil Supplementation On Fatty Acid Metabolism And Gut Microbiota Of Healthy Rats

Many studies have reported the important biochemical and nutritional functions of DHA（docosahexaenoic acid;22:6n-3）,highlighting its benefits in cognitive and visual functions.Given raising concerns over low DHA intakes,algal oil produced in tightly controlled fermentation facilities can offer a source of DHA that are pure and sustainable.Moreover,evidence is accumulating that dietary fatty acids intake also helps to shape the composition of gut microbiota.However,the impacts of DHA algal oil on fatty acid metabolism in tissues and gut microbiota compositions is limited.This study was conducted to investigate the DHA algal oil on fatty acid metabolism in tissues and gut microbiota.The results from this study may be used to further investigate these factors which will also contribute to the wide application of DHA algal oil.Healthy male rats were randomly divided into five groups（n=8）.A,B and C groups were administered 51.37 mg/kg/day of the three kinds of commercial DHA algal oil products including DHA algal oil（represented by A）and two kinds of DHA algal oil,which were encapsulated by microencapsulation technology（represented by B and C respectively）,while control group administered normal saline for 28-day intervention.Baseline and post-intervention samples were analysed for serum metabolic markers and tissue fatty acid composition and fecal microbiota composition.Fatty acid composition in tissues was measured using gas chromatography and mass spectrometry（GC-MS）,whereas the facal microbial composition was assessed using 16S rRNA high-throughput sequencing technology.The results showed that the A,B and C had no significant effect on the body weight gain and food intake of rats after 28-day intervention.And A decreased the levels of serum high-density lipoprotein cholesterol（HDL-C）,low-density lipoprotein cholesterol（LDL-C）and total cholesterol（TC）on the 28^th day;The absorption of B was the fastest within 24h,followed by C.On the 28^th day,A,B and C groups increased the DHA content in the liver,heart,epididymal fat pad and plasma of rats;A had the best absorption in the plasma,heart,epididymal fat pad and liver of rats,while B and C had the best absorption in the brain and retina of rats.On the 28^th day,A and C groups increased the ratio of n-3 polyunsaturated fatty acids（n-3 PUFAs）to n-6 polyunsaturated fatty acids（n-6 PUFAs）in the plasma,and decreased the 22:4n-6 content in the heart;A,B and C groups increased the content of EPA（eicosapentanoic acid;20:5n-3）and n-6 DPA（docosapentaenoic acid;22:5n-6）and increased the ratio of n-3 PUFAs to n-6 PUFAs in the liver and heart;B and C groups increased the ratio of n-3 PUFAs to n-6 PUFAs in the brain;C group increased the ratio of n-3 PUFAs to n-6PUFAs in the retina;B group decreased the content of n-3 DPA（docosapentaenoic acid;22:5n-3）in the retina.From the point of view of gut microbiota,on the 14^th day,C group increased the relative abundance of Firmicutes at phylum level;A group increased the abundance of Bacteroides,while B group increased the abundance of Coprococcus.On the28^th day,A group increased the total number of OTUs and the number of unique OTUs and increasedα-diversity;B and C groups increased the relative abundance of Bacteriodetes at phylum level;A group increased the abundance of Bacteroides;B group increased the abundance of Parabacteroides,Desulfovibrio,Parabacteroides distasonis,Bacteroides uniformis and Bacteroides caccae;C group increased the abundance of Parabacteroides distasonis,Parabacteroides,Bacteroides uniformis,Bacteroides and Blautia.The effect of DHA algal oil on fatty acid metabolism provides a reference for studying the metabolic direction of long chain polyunsaturated fatty acids including DHA;microencapsulation of DHA algal oil provides a new and effective way to increase DHA levels in brain and retina.Meanwhile,DHA algal oil consumption altered the gut microbial community suggesting the possible effects of DHA on health.