Increased response of liver microsomal delta 6-desaturase activity to dietary methionine in rats

Existing knowledge on Zn status biomarkers (1963-2021) with a particular focus on FADS1 and FADS2 diagnostic performance and recommendations for further research

The role of Zn in human health was discovered 60 years ago, and despite remarkable research efforts, a sufficiently sensitive and specific biomarker of Zn status is still lacking. Plasma/serum Zn, currently the best available and most accepted population Zn status indicator, responds well to severe Zn deficiency, yet, mild to moderate Zn deficiency states usually remain unrecognized. Identifying early-stage Zn deficiency requires additional robust markers of Zn status. This paper discusses the sensitivity, specificity, and responsiveness of plasma Zn concentrations to Zn interventions. It describes the biochemical and dietary basis for the causal association between Zn and fatty acid desaturases activity, FADS1 and FADS2, based on data collected through studies performed in animals and/or humans. The influence of potential confounders and covariates on the observed relationships is considered. Additional potential Zn biomarkers are discussed and suggestions for further research in this area are provided.

Soy Consumption, but Not Dairy Consumption, Is Inversely Associated with Fatty Acid Desaturase Activity in Young Adults

Past research using hepatic rat microsomes showed that soy protein suppressed delta-6 desaturase activity (D6D) compared to casein (a dairy protein). The effects of soy and dairy on desaturase pathway activity in humans remain poorly investigated. The objective of this analysis was to investigate the association between soy and dairy consumption with plasma fatty acids and estimate the desaturase pathway activity in a multiethnic Canadian population of young adults. We analyzed data from men (n = 319) and women (n = 764) previously collected for the Toronto Nutrigenomics and Health Study. Food frequency questionnaires and plasma fatty acids were assessed. Relationships between soy and dairy beverages and food consumption with estimated desaturase activities were assessed by regression models and by grouping participants according to beverage and food intake data. Weak inverse associations (p ≤ 0.05) were found between soy consumption and the overall desaturation pathway activity, specifically D6D activity. When participants were grouped based on soy and dairy consumption habits, omega-6 LC-PUFAs, as well as various estimates of the desaturase pathway activity, were significantly lower in individuals consuming soy (with or without dairy) compared to individuals consuming only fluid milk and dairy products. In conclusion, soy consumption, not dairy consumption, appears to suppress desaturase pathway activity.

Diet Regulation of Long-Chain PUFA Synthesis: Role of Macronutrients, Micronutrients, and Polyphenols on Δ-5/Δ-6 Desaturases and Elongases 2/5

Deficiencies in the n-3 (ω-3) long-chain PUFAs (LC-PUFAs) EPA and DHA are associated with increased risk for the development of numerous diseases. Although n-3 LC-PUFAs can be obtained by consuming marine products, they are also synthesized endogenously through a biochemical pathway regulated by the Δ-5/Δ-6 desaturase and elongase 2/5 enzymes. This narrative review collates evidence from the past 40 y demonstrating that mRNA expression and activity of desaturase and elongase enzymes are influenced by numerous dietary components, including macronutrients, micronutrients, and polyphenols. Specifically, we highlight that both the quantity and the composition of dietary fats, carbohydrates, and proteins can differentially regulate desaturase pathway activity. Furthermore, desaturase and elongase mRNA levels and enzyme activities are also influenced by micronutrients (folate, vitamin B-12, vitamin A), trace minerals (iron, zinc), and polyphenols (resveratrol, isoflavones). Understanding how these various dietary components influence LC-PUFA synthesis will help further advance our understanding of how dietary patterns, ranging from caloric excesses to micronutrient deficiencies, influence disease risks.

Associations between a fatty acid desaturase gene polymorphism and blood arachidonic acid compositions in Japanese elderly

We investigated whether the single nucleotide polymorphism rs174547 (T/C) of the fatty acid desaturase-1 gene, FADS1, is associated with changes in erythrocyte membrane and plasma phospholipid (PL) long-chain polyunsaturated fatty acid (LCPUFA) composition in elderly Japanese participants (n=124; 65 years or older; self-feeding and oral intake). The rs174547 C-allele carriers had significantly lower arachidonic acid (ARA; n-6 PUFA) and higher linoleic acid (LA, n-6 PUFA precursor) levels in erythrocyte membrane and plasma PL (15% and 6% ARA reduction, respectively, per C-allele), suggesting a low LA to ARA conversion rate in erythrocyte membrane and plasma PL of C-allele carriers. α-linolenic acid (n-3 PUFA precursor) levels were higher in the plasma PL of C-allele carriers, whereas levels of the n-3 LCPUFAs eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) were unchanged in erythrocyte membrane and plasma PL. Thus, rs174547 genotypes were significantly associated with different ARA compositions of the blood of elderly Japanese.

Cysteine Supplementation Decreases Plasma Homocysteine Concentration in Rats Fed on a Low-Casein Diet in Rats

The effect of dietary supplementation with cysteine on the plasma homocysteine concentration was investigated in rats fed on 10% casein (10C) and 30% casein (30C) diets. The 10C diet significantly increased the plasma homocysteine concentration as compared with the 30C diet. The hyperhomocysteinemia induced by the 10C diet was significantly suppressed by cysteine supplementation even at a 0.3% level, whereas cysteine did not decrease the plasma homocysteine concentration when added to the 30C diet. In contrast, 0.3% methionine supplementation of the 10C diet tended to increase the plasma homocysteine concentration. Cysteine supplementation to rats fed on the 10C diet did not alter the plasma cysteine concentration and the hepatic activities of cystathionine beta-synthase and betaine:homocysteine S-methyltransferase, whereas it significantly decreased the hepatic concentrations of S-adenosylmethionine and betaine. These results suggest that cysteine supplementation might be effective for suppressing the hyperhomocysteinemia induced by a low-protein diet.

Effects of prenatal fish-oil and 5-methyltetrahydrofolate supplementation on cognitive development of children at 6.5 y of age

BACKGROUND

The influence of prenatal long-chain polyunsaturated fatty acids (LC-PUFAs) and folate on neurologic development remains controversial.

OBJECTIVE

The objective was to assess the long-term effects of n-3 (omega-3) LC-PUFA supplementation, 5-methyltetrahydrofolate (5-MTHF) supplementation, or both in pregnant women on cognitive development of offspring at 6.5 y of age.

DESIGN

This was a follow-up study of the NUHEAL (Nutraceuticals for a Healthier Life) cohort. Healthy pregnant women in 3 European centers were randomly assigned to 4 intervention groups. From the 20th week of pregnancy until delivery, they received a daily supplement of 500 mg docosahexaenoic acid (DHA) + 150 mg eicosapentaenoic acid [fish oil (FO)], 400 μg 5-MTHF, or both or a placebo. Infants received formula containing 0.5% DHA and 0.4% arachidonic acid (AA) if they were born to mothers receiving FO supplements or were virtually free of DHA and AA until the age of 6 mo if they belonged to the groups that were not supplemented with FO. Fatty acids and folate concentrations were determined in maternal blood at weeks 20 and 30 of pregnancy, at delivery, and in cord blood. Cognitive function was assessed at 6.5 y of age with the Kaufman Assessment Battery for Children (K-ABC).

RESULTS

We observed no significant differences in K-ABC scores between intervention groups. Higher DHA in maternal erythrocytes at delivery was associated with a Mental Processing Composite Score higher than the 50th percentile in the offspring.

CONCLUSION

We observed no significant effect of supplementation on the cognitive function of children, but maternal DHA status may be related to later cognitive function in children. This trial was registered at clinicaltrials.gov as NCT01180933.

Dietary pea protein stimulates bile acid excretion and lowers hepatic cholesterol concentration in rats

It has been shown that some dietary plant proteins beneficially influence lipid metabolism in animals. The effect of pea protein in this respect however has not yet been investigated. Therefore, we studied the effect of purified pea protein on the lipid metabolism in rats. Twenty-four rats received diets with either 200 g/kg of casein or purified pea protein for 16 days. Concentrations of triacylglycerols in liver, plasma and lipoproteins did not differ between both groups of rats. However, rats fed the pea protein diet had a lower concentration of total cholesterol in the liver and the very low density lipoproteins (VLDL) fraction than rats fed the casein diet (p < 0.05); cholesterol concentration in plasma, low density lipoproteins (LDL) and high density lipoproteins (HDL) did not differ between both groups. Rats fed pea protein moreover had an increased mRNA concentration of cholesterol-7alpha-hydroxylase in the liver and an increased amount of bile acids excreted via faeces compared with rats fed casein (p < 0.05). Concomitantly, mRNA concentrations of sterol regulatory element-binding protein (SREBP)-2 and its target genes 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and LDL receptor in the liver were increased in rats fed pea protein (p < 0.05). The data of this study suggests that pea protein stimulates formation and excretion of bile acids, which leads to a reduced hepatic cholesterol concentration and a reduced secretion of cholesterol via VLDL. An increased gene expression of SREBP-2 and its target genes HMG-CoA reductase and LDL receptor may be a means to compensate for the increased loss of cholesterol for bile acid synthesis.

Changes in hepatic gene expression related to innate immunity, growth and iron metabolism in GH-transgenic amago salmon (Oncorhynchus masou) by cDNA subtraction and microarray analysis, and serum lysozyme activity

Growth hormone (GH) transgenic amago salmon (Oncorhynchus masou) were generated with a construct containing the sockeye salmon GH1 gene fused to the metallothionein-B (MT-B) promoter from the same species. This transgene directed significant growth enhancement with transgenic fish reaching approximately four to five times greater weight than control salmon in F(2) and F(3) generations. This drastic growth enhancement by GH transgene is well known in fish species compared with mammals, however, such fish can show morphological abnormalities and physiological disorders like other GH transgenic animals. GH is known to have many acute effects, but currently there are no data describing the chronic effects of over-expression of GH on various hepatic genes in GH transgenic fish. Hepatic gene expression is anticipated to play very important roles in many physiological functions and growth performance of transgenic and control salmon. To examine these effects, we performed subtractive hybridization (using cDNA generated from liver RNA) in both directions to identify genes both increased and decreased in transgenic salmon relative to controls (576 clones were isolated and sequenced in total). Heme oxygenase, vitelline envelope protein, Acyl-coA binding protein, NADH dehydrogenase, mannose binding lectin-associated serine protease, hemopexin-like protein, leucyte-derived chemotaxin2 (LECT2), and many other genes were obtained in higher clone frequencies suggesting enhanced expression. In contrast, complement C3-1, lectin, rabin, alcohol dehydrogenase, Tc1-like transposase, Delta6-desaturase, and pentraxin genes were obtained in lower frequencies. Microarray analysis was also performed to obtain quantitative expression data for these subtracted cDNA clones. Analysis of fish across seasons was also conducted using both F(2) and F(3) salmon. Results of the microarray data essentially corresponded with those of the subtraction data when both F(2) and F(3) fish were completely immature, but the expression pattern was changed when fish approached maturation. Genes showing enhanced expression in GH transgenic fish in F(2) and F(3) by array analysis were vitelline envelope protein, hemopexin-like protein, heme-oxygenase, inter alpha-trypsin inhibitor, LECT2, GTP cyclohydrolase I feedback regulatory protein (GFRP), and bikunin. Reduced expression genes were lectin, Delta6-desaturase, apolipoprotein, and pentraxin. In particular, lectin was found to be highly suppressed in all F(2) and immature F(3) salmon. Further, serum lysozyme activity, one of innate immunity, was significantly (p<0.05) decreased in both F(2) and F(3) GH transgenic fish. These results indicate that the GH transgene fish had altered hepatic gene expression relating to iron-metabolism, innate immunity, reproduction, and growth.

Methionine-Induced Elevation of Plasma Homocysteine Concentration Is Associated with an Increase of Plasma Cholesterol in Adult Rats

BACKGROUND AND AIMS

Dietary methionine affects cholesterol metabolism in growing rats. Methionine effects on adult rats and mechanisms by which methionine alters the lipid metabolism are not fully elucidated. We investigated possible mechanisms by which dietary methionine acts on lipid metabolism of adult rats.

METHODS

Male adult rats were divided into three groups (n=10) and were fed casein-based diets differing in methionine concentration (low-methionine diet: 0.96 g/kg; adequate-methionine diet: 2.22 g/kg, high-methionine diet: 6.82 g/kg) for 4 weeks. Concentrations of triacylglycerols and cholesterol in plasma and lipoproteins, concentration of homocysteine in plasma, concentration of cholesterol in liver, fecal lipid excretion, expression of hepatic HMG-CoA reductase, phosphatidylethanolamine N-methyltransferase 2 (PEMT-2) and of LDL receptor were measured.

RESULTS

Rats fed the high-methionine diet had higher plasma homocysteine concentrations than rats fed the low-methionine diet (p<0.05). Although concentrations of cholesterol in plasma and lipoproteins were not different between the groups, there was a distinct positive correlation between circulating plasma homocysteine and plasma cholesterol (R(2)=0.55, p<0.001). The fecal excretion of cholesterol and bile acids was not altered by dietary methionine. The relative mRNA concentration of HMG-CoA reductase and of LDL receptor remained unaffected by dietary methionine. Gene expression of PEMT-2 was higher in rats fed the high-methionine diet than in rats fed the other diets (p<0.05).

CONCLUSION

The results demonstrate that dietary methionine contributes to a rise in circulating homocysteine concentration which positively correlates with the concentration of plasma cholesterol. However, the effects of methionine on cholesterol metabolism of adult rats were relatively weak.