Desaturase Activity and the Risk of Type 2 Diabetes and Coronary Artery Disease: A Mendelian Randomization Study.

Estimated Δ5-desaturase (D5D) and Δ6-desaturase (D6D) are key enzymes in metabolism of polyunsaturated fatty acids (PUFA) and have been associated with cardiometabolic risk; however, causality needs to be clarified. We applied two-sample Mendelian randomization (MR) approach using a representative sub-cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study and public data from DIAbetes Genetics Replication And Meta-analysis (DIAGRAM) and Coronary ARtery DIsease Genome wide Replication and Meta-analysis (CARDIoGRAM) genome-wide association studies (GWAS). Furthermore, we addressed confounding by linkage disequilibrium (LD) as all instruments from FADS1 (encoding D5D) are in LD with FADS2 (encoding D6D) variants. Our univariable MRs revealed risk-increasing total effects of both, D6D and D5D on type 2 diabetes (T2DM) risk; and risk-increasing total effect of D6D on risk of coronary artery disease (CAD). The multivariable MR approach could not unambiguously allocate a direct causal effect to either of the individual desaturases. Our results suggest that D6D is causally linked to cardiometabolic risk, which is likely due to downstream production of fatty acids and products resulting from high D6D activity. For D5D, we found indication for causal effects on T2DM and CAD, which could, however, still be confounded by LD.

Iron-induced derangement in hepatic Δ-5 and Δ-6 desaturation capacity and fatty acid profile leading to steatosis: Impact on extrahepatic tissues and prevention by antioxidant-rich extra virgin olive oil.

The administration of iron induces liver oxidative stress and depletion of long-chain polyunsaturated fatty acids (LCPUFAs), n-6/n-3 LCPUFA ratio enhancement and fat accumulation, which may be prevented by antioxidant-rich extra virgin olive oil (AR-EVOO) supplementation. Male Wistar rats were subjected to a control diet (50 mg iron/kg diet) or iron-rich diet (IRD; 200 mg/kg diet) with alternate AR-EVOO for 21 days. Liver fatty acid (FA) analysis was performed by gas-liquid chromatography (GLC) after lipid extraction and fractionation, besides Δ-5 desaturase (Δ-5 D) and Δ6-D mRNA expression (qPCR) and activity (GLC) measurements. The IRD significantly (p < 0.05) increased hepatic total fat, triacylglycerols, free FA contents and serum transaminases levels, with diminution in those of n-6 and n-3 LCPUFAs, higher n-6/n-3 ratios, lower unsaturation index and Δ5-D and Δ6-D activities, whereas the mRNA expression of both desaturases was enhanced over control values, changes that were prevented by concomitant AR-EVOO supplementation. N-6 and n-3 LCPUFAs were also decreased by IRD in extrahepatic tissues and normalized by AR-EVOO. In conclusion, AR-EVOO supplementation prevents IRD-induced changes in parameters related to liver FA metabolism and steatosis, an effect that may have a significant impact in the treatment of iron-related pathologies or metabolic disorders such as non-alcoholic fatty liver disease.

Dietary fish oil and flaxseed for rabbit does: fatty acids distribution and Δ6-desaturase enzyme expression of different tissues.

Standard feeds are imbalanced in term of n-6/n-3 polyunsaturated fatty acids (PUFA) ratio, with a low proportion of the latter. The reproductive system appears to be strongly affected by administration of n-3 PUFA, and ingredients rich in α-linolenic acid (ALA; i.e. vegetable sources) or EPA and DHA acids (i.e. fish oil) can be included in animal diets to balance PUFA intake. The aim of this study was to evaluate the effect of dietary supplementation with flaxseed (ALA) or fish oil (EPA and DHA) on PUFA metabolism in rabbit does. A total of 60 New Zealand White female rabbits were assigned to three experimental groups: control group, FLAX group fed 10% extruded flaxseed and FISH group fed 3% fish oil. Blood, milk, liver and ovaries were collected from the does to assess the lipid composition; furthermore, FADS2 gene expression was assessed in liver and ovary tissues. Reproductive performance of does was also recorded. The fertility rate and number of weaned rabbits improved with n-3 dietary supplementation: does at first parity showed the lowest reproductive results, but the administration of n-3 reduced the gap between primiparous and multiparous does. Feed consumption and milk production were not affected by the feeding regime. The fatty acid composition of milk, plasma, liver and ovaries were widely influenced by diet, showing higher concentrations of n-3 long-chain PUFA (LCP) in does fed with n-3 enriched diets. FISH diet resulted in the highest n-3 LCP enrichment, whereas in the FLAX group, this increase was lower. Blood and milk showed low levels of LCP, whereas liver and ovaries were the main sites of n-3 LCP synthesis and accumulation. Accordingly, although the liver is the main metabolic centre for LCP synthesis, ovaries also have a prominent role in LCP generation. FADS2 expression in liver and ovary tissue was downregulated by FISH administration. In conclusion, the enrichment of diets with n-3 PUFA could be an effective strategy for improving the reproductive performance of does.

Differentiating the biological effects of linoleic acid from arachidonic acid in health and disease.

Dietary fatty acids are associated with the development of many chronic diseases, such as obesity, diabetes, cardiovascular disease, metabolic syndrome, and several cancers. This review explores the literature surrounding the combined and individual roles of n-6 PUFAs linoleic acid (LA) and arachidonic acid (AA) as they relate to immune and inflammatory response, cardiovascular health, liver health, and cancer. The evidence suggests that a pro-inflammatory view of LA and AA may be over simplified. Overall, this review highlights gaps in our understanding of the biological roles of LA, AA and their complex relationship with n-3 PUFA and the need for future studies that examine the roles of individual fatty acids, rather than groups.

Molecular cloning, tissue expression and regulation of nutrition and temperature on Δ6 fatty acyl desaturase-like gene in the red claw crayfish (Cherax quadricarinatus).

Desaturase enzymes play an important role in the synthesis of unsaturated fatty acids. In this study, a complete cDNA sequence of a Δ6 desaturase-like gene was cloned from the hepatopancreas of the red claw crayfish, Cherax quadricarinatus. The full-length 1885 bp sequence comprises a 5' UTR of 254 bp, 3' UTR of 234 bp, and an open reading frame (ORF) of 1377 bp encoding a 458 amino acid polypeptide (GenBank accession no. MF497442). Bioinformatics analysis revealed three conserved histidine-rich regions, a cytochrome b5 domain at the N-terminus, and a haem binding site (HPGG) in the cytochrome b5 domain, all of which are typical of Δ6 desaturases. Quantitative real-time PCR demonstrated significantly higher expression in the hepatopancreas than other tissues. After feeding crayfish four formulated diets in which fish oil was replaced by 0, 33, 67, or 100% highly unsaturated soybean oil for 8 weeks, Δ6 desaturase-like mRNA expression and enzyme activity were higher than in the fish oil only group. Additionally, a 4-week low temperature treatment at 25, 20, 15, or 9 °C increased Δ6 desaturase mRNA expression and enzyme activity with decreasing water temperature. These results may help us better understand the biosynthesis of unsaturated fatty acids in C. quadricarinatus.

Adding a purple corn extract in rats supplemented with chia oil decreases gene expression of SREBP-1c and retains Δ5 and Δ6 hepatic desaturase activity, unmodified the hepatic lipid profile.

Flavonoids upregulate gene expression of PPAR-α and underregulate the gene expression of SREBP-1c, and their intake increases the plasmatic concentration of n-3 LC-PUFAs. However, the biological mechanisms underlying these effects have not been elucidated. In this work, the effect of oral supplementation of ALA from chia (Salvia hispanica L.) seed oil and anthocyanins from a purple corn extract (PCE) on gene expression of SREBP-1c, PPAR-α and Δ5 and Δ6 desaturases (Δ5D and Δ6D), the activity of these enzymes in the liver as well as the hepatic lipid profile were evaluated in thirty-six female Sprague Dawley rats whose diet was supplemented with olive oil (OL), chia oil (CH), olive oil and PCE (OL + PCE) or chia oil and PCE (CH + PCE). Gene expression of PPAR-α was significantly higher when supplemented with CH and CH + PCE, SREBP-1c gene expression was higher when supplemented with chia oil. CH supplementation enhanced Δ5D expression whereas no significant differences between treatments were observed concerning Δ6D gene expression. Activities of both desaturases were increased by including olive oil (OL + PCE and OL), and they were found to be higher in CH + PCE respect to CH for both enzymes. The ALA and n-3 LCPUFAs hepatic content was higher with CH, decreasing the levels of AA and n-6 LCPUFAs. It is concluded that the joint action of flavonoids such as anthocyanins and ALA show an anti-adipogenic effect. Desaturase activity was inhibited by ALA and kept by the anthocyanins from PCE, thus anthocyanins would exert a protective effect on the desaturase activity but they would not affect on its gene expression, however, high doses of ALA increased the production of its metabolites, masking the effect of PCE.

Iron-induced pro-oxidant and pro-lipogenic responses in relation to impaired synthesis and accretion of long-chain polyunsaturated fatty acids in rat hepatic and extrahepatic tissues.

OBJECTIVES: Iron is involved in processes involving oxygen transfer and utilization. Excess iron is linked to cardiovascular diseases and some types of cancer. Iron overload is associated with oxidative stress development, and may have important interactions with lipid metabolism in the liver favoring the development and progression of non-alcoholic fatty liver disease. The aim of the study described here was to assess the effect of high intake of iron on oxidative stress-related parameters, lipid metabolism, and levels of long-chain polyunsaturated fatty acids (LCPUFAs) in liver and other tissues of the rat. METHODS: Male Wistar rats (21 d old) were fed an iron-rich diet (200 mg iron/kg diet, IRD) versus a control diet (50 mg iron/kg diet; CD) for 21 d. Samples of erythrocytes, liver, adipose tissue, brain, heart, and testicles were evaluated for fatty acid composition and hepatic biochemical and oxidative stress parameters, Δ-6 and Δ-5 desaturase activities, SREBP-1c and PPAR-α mRNA expression and DNA-binding capacity, and lipolytic, lipogenic, and antioxidant enzymatic activities. RESULTS: The IRD caused liver steatosis and increased activity of plasma transaminases, with higher oxidative stress status in plasma and liver. Liver Δ-6 and Δ-5 desaturase exhibited decreased activity, but enhanced expression in response to the IRD compared with the CD, with lower levels of ω-3 and ω-6 LCPUFAs and higher expression and DNA binding of SREBP-1c, whereas expression and DNA-binding activity of PPAR-α were diminished. CONCLUSIONS: IRD induced oxidative stress and a reduction in the desaturation capacity of the liver, with LCPUFA depletion in the different tissues studied, thus promoting a pro-steatotic condition in the liver.

Role of disturbed fatty acids metabolism in the pathophysiology of diabetic erectile dysfunction.

BACKGROUND: Vasculogenic erectile dysfunction (VED) is considered as a common complication among people with type 2 diabetes (T2D). We tested whether changes in fatty acid (FAs) classes measured in erythrocytes are associated with increased risk of diabetic VED along with related risk factors. METHODS: We assessed erythrocyte FAs composition, lipid peroxidation parameters and inflammatory cytokines among 72 T2D men with VED, 78 T2D men without VED and 88 healthy volunteers with similar age. Biochemical, hepatic, lipid and hormonal profiles were measured. RESULTS: T2D people with VED had significant decrease in the indexes of Δ6-desaturase and elongase activities compared to the other studied groups. The same group of participants displayed lower erythrocytes levels of dihomo-γ-linolenic acid (C20:3n-6) (P < .001), precursor of the messenger molecule PGE1 mainly involved in promoting erection. Moreover, absolute SFAs concentration and HOMA IR levels were higher in T2D people with VED when compared to controls and associated with impaired NO concentration (1.43 vs 3.30 ng/L, P < .001). Our results showed that IL-6 and TNF-α were significantly increased and positively correlated with MDA levels only in T2D people with VED (r = 0.884, P = .016 and r = 0.753, P = .035; respectively) suggesting a decrease in the relative availability of vasodilator mediators and an activation of vasoconstrictors release. CONCLUSION: Our findings show that the deranged FAs metabolism represents a potential marker of VED in progress, or at least an indicator of increased risk within men with T2D.

Δ6-fatty acid desaturase and fatty acid elongase mRNA expression, phagocytic activity and weight-to-length relationships in channel catfish (Ictalurus punctatus) fed alternative diets with soy oil and a probiotic.

A time-course feeding trial was conducted for 120 days on juvenile channel catfish (Ictalurus punctatus) to study the effects of diets differing in oil source (fish oil or soy oil) and supplementation with a commercial probiotic. Relative levels of Δ6-fatty acid desaturase (Δ6-FAD) and fatty acid elongase (FAE) expression were assessed in brain and liver tissues. Both genes showed similar expression levels in all groups studied. Fish weight-to-length relationships were evaluated using polynomial regression analyses, which identified a burst in weight and length in the channel catfish on day 105 of treatment; this increase was related to an increase in gene expression. Mid-intestinal lactic acid bacterium (LAB) count was determined according to morphological and biochemical criteria using API strips. There was no indication that intestinal LAB count was affected by the modified diets. The Cunningham glass adherence method was applied to evaluate phagocytic cell activity in peripheral blood. Reactive oxygen species (ROS) generation was assessed through the respiratory burst activity of spleen macrophages by the NBT reduction test. Probiotic-supplemented diets provided a good substrate for innate immune system function; the phagocytic index was significantly enhanced in fish fed soy oil and the probiotic, and at the end of the experimental period, ROS production increased in fish fed soy oil. The substitution of fish oil by soy oil is recommended for food formulation and will contribute to promoting sustainable aquaculture. Probiotics are also recommended for channel catfish farming as they may act as immunonutrients.

Screening and molecular identification of overproducing γ-linolenic acid fungi and cloning the delta 6-desaturase gene.

This research aims at isolating and identifying γ-linolenic acid (GLA)-producing fungi in the traditional Chinese salt-fermented soybean food, Douchi, from Yongchuan, People's Republic of China. In this study, Rhizopus oryzae DR3 was identified as a novel fungal species that produces large amounts of GLA. A full-length cDNA, designated as RoD6 D, with high homology to fungal △6 fatty acid desaturase genes was isolated from R. oryzae by using the rapid amplification of cDNA ends method. It had an open reading frame of 1,176 bp encoding a deduced polypeptide of 391 amino acids. Bioinformatics analysis characterized the putative RoD6 D protein as a typical membrane-bound desaturase, including three conserved histidine-rich motifs, a hydropathy profile, and a cytochrome b5 -like domain in the N-terminus. When the coding sequence was expressed in the Saccharomyces cerevisiae strain INVScl, the encoded product of RoD6 D exhibited △6 fatty acid desaturase activity that led to the accumulation of GLA. The results show that Douchi contains a large natural diverse composition, and some strains could be selected as starters for functional fermented foods. This study has also laid a foundation for developing functional Douchi products for further research.

Cloning, functional characterization and nutritional regulation of Δ6 fatty acyl desaturase in the herbivorous euryhaline teleost Scatophagus argus.

Marine fish are generally unable or have low ability for the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFA) from C18 PUFA precursors, with some notable exceptions including the herbivorous marine teleost Siganus canaliculatus in which such a capability was recently demonstrated. To determine whether this is a unique feature of S. canaliculatus or whether it is common to the herbivorous marine teleosts, LC-PUFA biosynthetic pathways were investigated in the herbivorous euryhaline Scatophagus argus. A putative desaturase gene was cloned and functionally characterized, and tissue expression and nutritional regulation were investigated. The full-length cDNA was 1972 bp, containing a 1338 bp open-reading frame encoding a polypeptide of 445 amino acids, which possessed all the characteristic features of fatty acyl desaturase (Fad). Functional characterization by heterologous expression in yeast showed the protein product of the cDNA efficiently converted 18:3n-3 and 18:2n-6 to 18:4n-3 and 18:3n-6, respectively, indicating Δ6 desaturation activity. Quantitative real-time PCR showed that highest Δ6 fad mRNA expression was detected in liver followed by brain, with lower expression in other tissues including intestine, eye, muscle, adipose, heart kidney and gill, and lowest expression in stomach and spleen. The expression of Δ6 fad was significantly affected by dietary lipid and, especially, fatty acid composition, with highest expression of mRNA in liver of fish fed a diet with a ratio of 18:3n-3/18:2n-6 of 1.72:1. The results indicated that S. argus may have a different LC-PUFA biosynthetic system from S. canaliculatus despite possessing similar habitats and feeding habits suggesting that LC-PUFA biosynthesis may not be common to all marine herbivorous teleosts.

Fish oil replacement in current aquaculture feed: is cholesterol a hidden treasure for fish nutrition?

Teleost fish, as with all vertebrates, are capable of synthesizing cholesterol and as such have no dietary requirement for it. Thus, limited research has addressed the potential effects of dietary cholesterol in fish, even if fish meal and fish oil are increasingly replaced by vegetable alternatives in modern aquafeeds, resulting in progressively reduced dietary cholesterol content. The objective of this study was to determine if dietary cholesterol fortification in a vegetable oil-based diet can manifest any effects on growth and feed utilization performance in the salmonid fish, the rainbow trout. In addition, given a series of studies in mammals have shown that dietary cholesterol can directly affect the fatty acid metabolism, the apparent in vivo fatty acid metabolism of fish fed the experimental diets was assessed. Triplicate groups of juvenile fish were fed one of two identical vegetable oil-based diets, with additional cholesterol fortification (high cholesterol; H-Chol) or without (low cholesterol; L-Chol), for 12 weeks. No effects were observed on growth and feed efficiency, however, in fish fed H-Col no biosynthesis of cholesterol, and a remarkably decreased apparent in vivo fatty acid ß-oxidation were recorded, whilst in L-Chol fed fish, cholesterol was abundantly biosynthesised and an increased apparent in vivo fatty acid ß-oxidation was observed. Only minor effects were observed on the activity of stearyl-CoA desaturase, but a significant increase was observed for both the transcription rate in liver and the apparent in vivo activity of the fatty acid Δ-6 desaturase and elongase, with increasing dietary cholesterol. This study showed that the possible effects of reduced dietary cholesterol in current aquafeeds can be significant and warrant future investigations.

Identification and functional analysis of a Δ6-desaturase gene and the effects of temperature and wounding stresses on its expression in Microula sikkimensis leaves.

A Δ6-desaturase gene was isolated from Microula sikkimensis. Sequence analysis indicated that the gene, designated MsD6DES, had an open reading frame of 1,357 bp and encoded 448 amino acids. Heterologous expression in tobacco indicated that MsD6DES can use endogenous substrates to synthesize γ-linolenic acid (GLA, 18:3(Δ 6,9,12)) and octadecatetraenoic acid (OTA, 18:4(Δ 6,9,12,15)). MsD6DES transcripts were distributed in all tested tissues, with high expression levels in seeds and young leaves. The effects of temperature and wounding stresses on MsD6DES expression were analyzed. The results indicated that temperature regulates MsD6DES at the transcriptional level. MsD6DES expression increased first, reaching a maximum 4 h after low-temperature treatment. A slight increase in MsD6DES transcript levels was also observed under high temperature. We found that the response of MsD6DES to temperature stress was different from those of fungi and algae. In addition, MsD6DES was found to be wound-inducible.

The thermostability of two kinds of recombinant ∆6-fatty acid desaturase with different N-terminal sequence lengths in low temperature.

Two recombinant Rhizopus stolonifer ∆6-fatty acid desaturase enzymes with different-length N-termini were cloned and expressed in Saccharomyces cerevisiae strain INVScl: LRsD6D begins with the sequence of the N-terminal of the R. stolonifer ∆6-fatty acid desaturase native, encoding a deduced polypeptide of 459 amino acids (M-S-T-L-D-R-Q-S-I-F-T-I-K-E-L-E-S-I-S-Q-R-I-H-D-G-D-E-E-A-M-K-F), whereas SRsD6D begins with the amino acid sequence of the predicted ORF, encoding a deduced polypeptide of 430 amino acids (M-K-F) and LRsD6D is longer than SRsD6D by 29 amino acids (M-S-T-L-D-R-Q-S-I-F-T-I-K-E-L-E-S-I-S-Q-R-I-H-D-G-D-E-E-A). Bioinformatic analysis characterized the two recombinant ∆6-fatty acid desaturase enzymes with different-length N-termini, including three conserved histidine-rich motifs, hydropathy profile, and a cytochrome b5-like domain in the N-terminus. When the coding sequence was expressed in S. cerevisiae strain INVScl, the coding produced ∆6-fatty acid desaturase activity exhibited by RsD6D, leading to a novel peak corresponding to γ-linolenic acid methyl ester standards, which was detected with the same retention time. The residual activity of LRsD6D was 74 % at 15 °C for 4 h and that of SRsD6D was 43 %. Purified recombinant LRsD6D was more stable than SRsD6D, indicating that the N-terminal extension, containing mostly hydrophobic residues, affected the overall stability of recombinant LRsD6D.

Cloning and tissue distribution of a fatty acyl Δ6-desaturase-like gene and effects of dietary lipid levels on its expression in the hepatopancreas of Chinese mitten crab (Eriocheir sinensis).

Fatty acyl Δ6-desaturase is the rate-limiting enzyme in the biosynthetic pathway of highly unsaturated fatty acids (HUFAs) in vertebrates. In this report, a fatty acyl Δ6-desaturase-like cDNA was cloned from the hepatopancreas of Eriocheir sinensis (Chinese mitten crab) and characterized by performing rapid-amplification of cDNA ends. The 2278-bp long full-length cDNA encodes a polypeptide with 442 amino acids. Gene expression analysis via real-time quantitative polymerase chain reaction revealed that the fatty acyl Δ6-desaturase-like transcripts are widely distributed in various tissues, with high expression levels in the hepatopancreas and cranial ganglia. This study focuses on the nutritional regulation of genes involved in the HUFA biosynthetic pathway in Chinese mitten crab. A feeding trial was performed whereby crablets were fed for 238 d with four different diets: control diet without oil lipids (added with 3% basic lipid of the fundamental diets); fish oil diet (FO; added with 3% of the fundamental diets); soybean oil diet (SO; added with 3% of the fundamental diets); and FO/SO diet (1:1; added with 3% of the fundamental diets). The hepatopancreas of crabs sampled at 168 d and 238 d to determine the effects on fatty acyl Δ6-desaturase-like mRNA expression. The results show that the expression of fatty acyl Δ6-desaturase-like is higher in the hepatopancreas of crabs fed with SO diet than those fed with FO diet. Furthermore, gene expression increased by 2.45-fold in the hepatopancreas of crabs fed with SO after 238 d than those fed after 168 d but remained steady for those fed with FO after 238 d.

Vitamin B-6 restriction impairs fatty acid synthesis in cultured human hepatoma (HepG2) cells.

Vitamin B-6 deficiency has been reported to alter n-6 and n-3 fatty acid profiles in plasma and tissue lipids; however, the mechanisms underlying such metabolic changes remain unclear. The objective of this study was to determine the effects of vitamin B-6 restriction on fatty acid profiles and fatty acid synthesis in HepG2 cells. Cells were cultured for 6 wk in media with four different vitamin B-6 concentrations (10, 20, 50, and 2,000 nM added pyridoxal, representing deficient, marginal, adequate, and supraphysiological conditions) that induced a range of steady-state cellular concentrations of pyridoxal phosphate. Total cellular lipid content was greatest in the deficient (10 nM pyridoxal) medium. The percentage of arachidonic acid and the ratio of arachidonic acid to linoleic acid in the total lipid fraction were ~15% lower in vitamin B-6-restricted cells, which suggests that vitamin B-6 restriction affects n-6 fatty acid interconversions. Metabolic flux studies indicated significantly lower fractional synthesis rate of oleic acid and arachidonic acid at 10, 20, and 50 nM pyridoxal, whereas that of eicosapentaenoic acid was lower in the cells cultured in 10 nM pyridoxal. Additionally, relative mRNA expressions of Δ5 and Δ6 desaturases were 40-50% lower in vitamin B-6-restricted cells. Overall, these findings suggest that vitamin B-6 restriction alters unsaturated fatty acid synthesis, particularly n-6 and n-3 polyunsaturated fatty acid synthesis. These results and observations of changes in human plasma fatty acid profiles caused by vitamin B-6 restriction suggest a mechanism by which vitamin B-6 inadequacy influences the cardiovascular risk.

Molecular cloning and functional characterization of a Δ6-fatty acid desaturase gene from Rhizopus oryzae.

The objective was to screen for and isolate a novel enzyme with the specific activity of a Δ6-fatty acid desaturase from Rhizopus oryzae. In this study, R. oryzae was identified as a novel fungal species that produces large amounts of γ-linolenic acid. A full-length cDNA, designated here as RoD6D, with high homology to fungal Δ6-fatty acid desaturase genes was isolated from R. oryzae by using the rapid amplification of cDNA ends method. It had an open reading frame of 1176 bp encoding a deduced polypeptide of 391 amino acids. Bioinformatics analysis characterized the putative RoD6D protein as a typical membrane-bound desaturase, including three conserved histidine-rich motifs, a hydropathy profile, and a cytochrome b5 -like domain in the N terminus. When the coding sequence was expressed in the Saccharomyces cerevisiae strain INVScl, the encoded product of RoD6D exhibited Δ6-fatty acid desaturase activity that led to the accumulation of γ-linolenic acid. The corresponding genomic sequence of RoD6D was 1565 bp in length, with five introns. This is the first report on the characterization and gene cloning of a Δ6-fatty acid desaturase of R. oryzae from Douchi.

Tissue-specific sex differences in docosahexaenoic acid and Δ6-desaturase in rats fed a standard chow diet.

Docosahexaenoic acid (DHA, 22:6n-3) is higher in the blood and tissues of females relative to males, but the underlying mechanism is not clear. The present study examined the expression of enzymes involved in the biosynthesis of DHA from short-chain n-3 polyunsaturated fatty acids in male and female rats (n = 6 for each sex). Rats were maintained on an AIN-93G diet and sacrificed at 14 weeks of age after an overnight fast. Plasma, erythrocytes, liver, heart, and brain were collected for fatty acid composition analysis and the determination of enzyme and transcription factor expression by RT-PCR and immunoblotting. Females had higher DHA concentrations in the total lipids of liver, plasma, erythrocyte, and heart (53%, 75%, 36%, and 25% higher, respectively, compared with males) with no sex differences in brain DHA concentrations. The mRNA content of Δ5-desaturase, Δ6-desaturase, and elongase 2 was 1.0-, 1.4-, and 1.1-fold higher, respectively, in the livers of female rats compared with males, with no differences in the hearts or brains. The protein content of Δ6-desaturase was also higher in females. Higher hepatic mRNA of sterol-regulatory element-binding protein 1-c and estrogen receptor α in the females suggests that lipogenic and estrogen signaling mechanisms are involved. The sex difference in DHA concentration is tissue specific and is associated with higher Δ6-desaturase expression in females relative to males, which appears to be limited to the liver.

Menhaden oil, but not safflower or soybean oil, aids in restoring the polyunsaturated fatty acid profile in the novel delta-6-desaturase null mouse.

BACKGROUND: Polyunsaturated fatty acids (PUFA) have diverse biological effects, from promoting inflammation to preventing cancer and heart disease. Growing evidence suggests that individual PUFA may have independent effects in health and disease. The individual roles of the two essential PUFA, linoleic acid (LA) and α-linolenic acid (ALA), have been difficult to discern from the actions of their highly unsaturated fatty acid (HUFA) downstream metabolites. This issue has recently been addressed through the development of the Δ-6 desaturase knock out (D6KO) mouse, which lacks the rate limiting Δ-6 desaturase enzyme and therefore cannot metabolize LA or ALA. However, a potential confounder in this model is the production of novel Δ-5 desaturase (D5D) derived fatty acids when D6KO mice are fed diets containing LA and ALA, but void of arachidonic acid. OBJECTIVE: The aim of the present study was to characterize how the D6KO model differentially responds to diets containing the essential n-6 and n-3 PUFA, and whether the direct provision of downstream HUFA can rescue the phenotype and prevent the production of D5D fatty acids. METHODOLOGY: Liver and serum phospholipid (PL) fatty acid composition was examined in D6KO and wild type mice fed i) 10% safflower oil diet (SF, LA rich) ii) 10% soy diet (SO, LA+ALA) or iii) 3% menhaden oil +7% SF diet (MD, HUFA rich) for 28 days (n = 3-7/group). RESULTS: Novel D5D fatty acids were found in liver PL of D6KO fed SF or SO-fed mice, but differed in the type of D5D fatty acid depending on diet. Conversely, MD-fed D6KO mice had a liver PL fatty acid profile similar to wild-type mice. CONCLUSIONS: Through careful consideration of the dietary fatty acid composition, and especially the HUFA content in order to prevent the synthesis of D5D fatty acids, the D6KO model has the potential to elucidate the independent biological and health effects of the parent n-6 and n-3 fatty acids, LA and ALA.

DHA and EPA reverse cystic fibrosis-related FA abnormalities by suppressing FA desaturase expression and activity.

Patients and models of cystic fibrosis (CF) exhibit consistent abnormalities of polyunsaturated fatty acid composition, including decreased linoleate (LA) and docosahexaenoate (DHA) and variably increased arachidonate (AA), related in part to increased expression and activity of fatty acid desaturases. These abnormalities and the consequent CF-related pathologic manifestations can be reversed in CF mouse models by dietary supplementation with DHA. However, the mechanism is unknown. This study investigates this mechanism by measuring the effect of exogenous DHA and eicosapentaenoate (EPA) supplementation on fatty acid composition and metabolism, as well as on metabolic enzyme expression, in a cell culture model of CF. We found that both DHA and EPA suppress the expression and activity of Δ5- and Δ6-desaturases, leading to decreased flux through the n-3 and n-6 PUFA metabolic pathways and decreased production of AA. The findings also uncover other metabolic abnormalities, including increased fatty acid uptake and markedly increased retroconversion of DHA to EPA, in CF cells. These results indicate that the fatty acid abnormalities of CF are related to intrinsic alterations of PUFA metabolism and that they may be reversed by supplementation with DHA and EPA.