Conversion Of Stearic Acid Research Articles

Dietary stearate and oleate in the development of hepatic steatosis and obesity

Fatty liver disease or hepatic steatosis, marked by increased accumulation of triglycerides in the liver, is brought on by chronic over-nutrition and increases the risk for secondary conditions such as insulin resistance. Mice with a targeted mutation in the enzyme stearoyl-CoA desaturase 1 (SCD1), which catalyzes the conversion of stearic acid into oleic acid, are lean and protected from diet-induced obesity as well as insulin resistance. This leads us to hypothesize that oleate, the monounsaturated fatty acid product of SCD1, plays a direct role in the development of diet-induced hepatic steatosis. 8-week old male wild-type (WT) and SCD1−/ − mice were fed 20% high-fat diets containing either tristearin or triolein for 7 days. Triolein feeding resulted in significantly greater body weight and adipose tissue gains, as well as greater hepatic triglyceride and cholesteryl ester accumulation in WT and SCD1−/ − mice. Expression of lipogenic genes and the transcription factors SREBP-1c and PGC-1β, as measured by real-time PCR, were increased by triolein feeding in both WT and SCD1−/ − animals. Conversely, activity of the AMP-activated protein kinase (AMPK)- α1 was significantly higher in livers of SCD1−/ − mice after tristearin feeding but was unchanged in WT animals. Taken together, these results suggest that triolein feeding increases lipogenesis in WT and SCD1−/ − animals and downregulates lipid oxidation in SCD1−/ − animals. These data help clarify the roles of specific fatty acids in the modulation of hepatic lipid metabolism. This work has been supported by NIH Grant NIDDK-R0162388 (JMN) and American Heart Association Predoctoral fellowship 0415001Z (HS).

Role of salicylic acid and fatty acid desaturation pathways in ssi2-mediated signaling.

Stearoyl-acyl carrier protein desaturase-mediated conversion of stearic acid to oleic acid (18:1) is the key step that regulates the levels of unsaturated fatty acids (FAs) in cells. Our previous work with the Arabidopsis (Arabidopsis thaliana) ssi2/fab2 mutant and its suppressors demonstrated that a balance between glycerol-3-phosphate (G3P) and 18:1 levels is critical for the regulation of salicylic acid (SA)- and jasmonic acid-mediated defense signaling in the plant. In this study, we have evaluated the role of various genes that have an impact on SA, resistance gene-mediated, or FA desaturation (FAD) pathways on ssi2-mediated signaling. We show that ssi2-triggered resistance is dependent on EDS1, PAD4, EDS5, SID2, and FAD7 FAD8 genes. However, ssi2-triggered defects in the jasmonic acid pathway, morphology, and cell death phenotypes are independent of the EDS1, EDS5, PAD4, NDR1, SID2, FAD3, FAD4, FAD5, DGD1, FAD7, and FAD7 FAD8 genes. Furthermore, the act1-mediated rescue of ssi2 phenotypes is also independent of the FAD2, FAD3, FAD4, FAD5, FAD7, and DGD1 genes. Since exogenous application of glycerol converts wild-type plants into ssi2 mimics, we also studied the effect of exogenous application of glycerol on mutants impaired in resistance-gene signaling, SA, or fad pathways. Glycerol increased SA levels and induced pathogenesis-related gene expression in all but sid2, nahG, fad7, and fad7 fad8 plants. Furthermore, glycerol-induced phenotypes in various mutant lines correlate with a concomitant reduction in 18:1 levels. Inability to convert glycerol into G3P due to a mutation in the nho1-encoded glycerol kinase renders plants tolerant to glycerol and unable to induce the SA-dependent pathway. A reduction in the NHO1-derived G3P pool also results in a partial age-dependent rescue of the ssi2 morphological and cell death phenotypes in the ssi2 nho1 plants. The glycerol-mediated induction of defense was not associated with any major changes in the lipid profile and/or levels of phosphatidic acid. Taken together, our results suggest that glycerol application and the ssi2 mutation in various mutant backgrounds produce similar effects and that restoration of ssi2 phenotypes is not associated with the further desaturation of 18:1 to linoleic or linolenic acids in plastidal or extraplastidal lipids.

Differential modulation by simvastatin of the metabolic pathways in the n-9, n-6 and n-3 fatty acid series, in human monocytic and hepatocytic cell lines

Statins affect the production of long chain polyunsaturated fatty acids (PUFA), both in vitro and in vivo. Various studies have shown the effects of statins on the pattern of n-6 fatty acids (FA), but limited attention has been paid to the n-3 FA. We investigated, in THP-1 and in HepG2 cells, the effects of simvastatin on the conversion of the 18C FA precursors in the n-3 and n-6 series, [1- 14C] α-linolenic acid (α-LNA) and [1- 14C] linoleic acid (LA) respectively, and on the metabolism of [1- 14C] stearic acid (SA). THP-1 cells, as in the case of LA, actively converted α-LNA to its products, and after simvastatin treatment, the total conversion was significantly increased (from 57.2 ± 7.2 to 74.3 ± 8.5%, p < 0.05). HepG2 cells also converted LA and α-LNA, but simvastatin increased significantly only the conversion of LA (9.5 ± 1.9% versus 23.8 ± 5.1%, p < 0.02). SA conversion was similar in untreated cells (about 50%), while statin increased the production of oleic acid in HepG2, but in THP-1 cells there was a decrease. In conclusion, LA, α-LNA and SA are differentially metabolized in THP-1 and in HepG2 cells and their increased conversion by simvastatin is lower in HepG2 than in THP-1. These differences may reflect the distinct features of the two cell lines: monocytes, precursors of phagocytic cells, versus hepatocytes with mainly metabolic functions. Substantial differences concern also cellular FA pools: structural in THP-1 cells, and also depot, resulting in sequestering of the substrates, in HepG2. The greater n-3 FA metabolism in THP-1 cells may have favourable functional effects.

Catalytic wet air oxidation of stearic acid on cerium oxide supported noble metal catalysts

Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy–decarboxylation (RnCOOH + O2 → Rn−1COOH +CO2) yielding essentially CO2 (route A). It may also be oxidized after CC bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO2 (route B). Pt/CeO2 is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via CC bond splitting is much more marked on Ru/CeO2. The catalyst characterization indicates that both noble metal and CeO2 particles remain stable during the reaction.

Oleic acid levels regulated by glycerolipid metabolism modulate defense gene expression in Arabidopsis.

Stearoyl-acyl-carrier-protein-desaturase-mediated conversion of stearic acid (18:0) to oleic acid (18:1) is a key step, which regulates levels of unsaturated fatty acids in cells. We previously showed that stearoyl-acyl-carrier-protein-desaturase mutants ssi2/fab2 carrying a loss-of-function mutation in the plastidial glycerol-3-phosphate (G3P) acyltransferase (act1) have elevated 18:1 levels and are restored in their altered defense signaling. Because G3P is required for the acylation of 18:1 by G3P acyltransferase, it was predicted that reduction of G3P levels should increase 18:1 levels and thereby revert ssi2-triggered phenotypes. Here we show that a mutation in G3P dehydrogenase restores both salicylic acid- and jasmonic acid-mediated phenotypes of ssi2 plants. The G3P dehydrogenase gene was identified by map-based cloning of the ssi2 suppressor mutant rdc8 (gly1-3) and confirmed by epistatic analysis of ssi2 with gly1-1. Restoration of ssi2-triggered phenotypes by the gly1-3 mutation was age-dependent and correlated with the levels of 18:1. Regeneration of G3P pools by glycerol application in ssi2 and ssi2 gly1-3 plants caused a marked reduction in the 18:1 levels, which rendered these plants hypersensitive to glycerol. This hypersensitivity in ssi2 was rescued by the act1 mutation. Furthermore, overexpression of the ACT1 gene resulted in enhanced sensitivity to glycerol. Glycerol application also lowered the 18:1 content in SSI2 plants and converted these into ssi2-mimics. Our results show that 18:1 levels in plastids are regulated by means of acylation with G3P, and a balance between G3P and 18:1 is critical for the regulation of salicylic acid- and jasmonic acid-mediated signaling pathways.

Δ9 -desaturase activity in the mammary gland of lactating dairy cows

The Δ9 -desaturase system (steroyl-CoA desaturase) involves the addition of a cis double bond between carbons 9 and 10 of fatty acids. The conversion of stearic acid (C18:0) to oleic acid (cis-9 C18:1) is the predominant precursor:product of this enzyme system; conversion of saturated fatty acids (SFA) to mono-unsaturated fatty acids (MUFA) is important in determining the fluidity of milk. In previous studies (Lock &amp; Garnsworthy 2001), we have shown that more than 50% of the oleic acid occurring in milk is produced in the mammary gland via Δ9 -desaturase. We also found that the conversion of trans-11 C18:1 to cis-9, trans-11 conjugated linoleic acid (CLA) accounted for ~80% of milk fat CLA. Increasing the activity of Δ9 -desaturase offers the opportunity of increasing the MUFA content of milk, especially oleic acid, while decreasing its SFA content, as well as increasing the CLA content of milk. Lock &amp; Garnsworthy, (2001) also reported that there were significant differences between individual cows with regard to milk fat CLA content. In an earlier study (Lock &amp; Garnsworthy, 2000) we found that the CLA content of milk varied throughout the year, with highest values occurring when cows received fresh pasture. In view of the significant contribution of Δ9 -desaturase to the CLA and MUFA content of milk, the objective of the work reported here was to investigate individual animal and dietary variation in Δ9 -desaturase activity in the mammary gland of lactating dairy cows.

Selection of fatty acid auxotrophs from the oleaginous yeast Cryptococcus curvatus and production of cocoa butter equivalents in batch culture

A search was carried out for mutants, defective in the conversion of stearic acid to oleic acid in effort to improve the quality of lipids produced by Cryptococcus curvatus ATCC, 20509. Mutants were selected as unsaturated fatty acid (Ufa) auxotrophs. After treatment of parent organism with Ethyl methanesulfonate (EMS), 11 oleate-requiring auxotrophs were isolated. Only 3 of them were real unsaturated fatty acid (Ufa) mutants, while the other 8 were designated as fatty acid synthetase (Fas) mutants. The amount of saturated fatty acid (SFA) was about 65.2 % in the lipids extracted from an Ufa mutant named UfaM3 and it was significantly higher than that of the wild-type (WT) (46.6 %) and similar to that of cocoa butter (60.4 %).

Synthesis of mono‐ and diglycerides in water‐in‐oil microemulsions

AbstractEnzyme‐catalyzed esterification was carried out in single‐phase, oil‐continuous microemulsions. The lipozyme was solubilized, along with glycerol and water, in the aqueous core of water/diethylhexyl sodium sulfosuccinate/hydrocarbon microemulsion system. Upon addition of fatty acid, mono‐ and diglycerides were formed, due to the esterification reaction taking place at the interface of the droplets in the microemulsion. The initial rate of conversion of oleic acid increases with oil chainlength of the continuous phase whereas final conversion is maximum for hexane. The conversion of stearic acid is 30% whereas conversion of oleic acid is 70%. The percent conversion of various fatty acids in the same continuous medium increases with fatty acid chainlength. The oleic acid/glycerol ratio is an important parameter for optimum conversion of oleic acid into glycerides. The yield can be increased by subsequent addition of glycerol after equilibrium is reached. High‐performance liquid chromatography analysis of samples from microemulsions shows the presence of mono‐ and diglycerides. Possible mechanisms for the abovementioned effects are discussed.

Isolation and characterization of fatty acid auxotrophs from the oleaginous yeast Apiotrichum curvatum

In order to improve the economic value of lipids produced by the oleaginous yeast strain Apiotrichum curvatum ATCC 20509, a search was made for mutants defective in the conversion of stearic acid to oleic acid. Mutants could be selected as unsaturated fatty acid auxotrophs, since unsaturated fatty acids are essential componenets in membrane lipids. After treatment of A. curvatum wild-type with N-methyl-N′-nitro-N⇔-nitrosoguanidine, 58 fatty-acid-requiring mutants were isolated. On the basis of (1) the growth response to saturated and unsaturated fatty acids and (2) the fatty acid composition of lipids produced by these mutants, it was concluded that only 18 of them were real unsaturated fatty acid (Ufa) mutants, while the other 40 were designated as fatty acid synthetase (Fas) mutants. It is further shown that Ufa mutants of A. curvatum are able to produce high amounts of lipids consisting of more than 90% triacylglycerols with a percentage of saturated fatty acids resembling that of cocoa butter, when grown in the presence of relatively small amounts of oleic acid in the growth medium. This may offer an economically favourable alternative in comparison with other methods that have been developed for the production of cocoa butter equivalents by microorganisms.

Microsomal desaturation of stearic acid in relation to lymphocyte activation

The conversion of stearic acid to oleic acid (Δ 9-desaturase) was followed in mouse thymocytes stimulated by either concanavalin A or concanavalin A + interleukin-2 resulting in different rates of cell proliferation. To estimate the plasma membrane turnover of oleic acid as compared to that of a saturated fatty acid, double-label experiments ([ 14C]oleic acid, [ 3H]palmitic acid) were performed. Following an inhibition Δ 9-desaturase was found to be activated from the fourth hour of stimulation. In the early period of cell activation this process proved to be independent of protein synthesis, whereas in the stage of proliferation it was dependent on it. Increased membrane fluidity in the first 30 min of activation is not likely due to enrichment of oleic acid. Cell proliferation and microsomal desaturation seem to be coupled and an increasing amount of oleic acid is at least one of the factors resulting in increased fluidity of the surface membrane of proliferating cells.

Tritium release assay for oleic acid desaturation

The “tritium release” assay for the enzymic conversion of stearic acid into oleic acid introduced by Talamo and Bloch in 1969 (1) represented a major advance in the measurement of enzymic fatty acid desaturation. By measuring the release of tritium from the 9- and 10-positions of erythro-[9,10 3H 2]stearic acid into water instead of isolating the oleic acid chromatographically, the processing time can be reduced from about 2–3 hr to 5–10 min per assay. Recently, Johnson and Gurr (2) showed that the release of tritium does not represent an absolute measure of enzymic activity due to a primary kinetic isotope effect discriminating against tritium. In that paper we recorded the magnitude of the isotope effect, described the synthesis and use of threo-[9,10 3H 2]stearic acid, which increases the sensitivity of the assay, and demonstrated that release of tritium from this substrate was proportional to the formation of oleic acid. Because of the considerable interest in this laboratory in the biosynthesis of linoleic acid in plants, we have developed the principle of the tritium release assay to be applicable to the assay of the plant enzyme which converts oleic acid into linoleic acid. This has necessitated the synthesis of the appropriate oleic acid labeled with tritium in the 12- and 13-positions and this is described in some detail. In this paper we have been less concerned with the mechanistic details of the isotope effect than with the practical details involved in the use of the method and have discussed at some length some of its inherent advantages and disadvantages.

Inhibition of desaturation of stearic acid in livers of rats fed ethionine.

AbstractThe effect of ethionine on the conversion of stearic acid to oleic acid was studied. Rats were fed essential fatty acid (EFA) deficient diet for three weeks, after which time half the animals were fed 0.25% DL‐ethionine for nine additional days. Seventeen hours prior to killing, they were fed a slurry of the diet containing 18‐14C‐stearic acid. Liver triglycerides and phospholipids were extracted and separated and their fatty acid composition and the distribution of radioactivity between stearic and oleic acid was determined. In the tissues studied, oleic acid was maintained at control levels in ethionine‐fed rats, but eicosatrienoic acid was significantly depressed. Distribution of radioactivity and specific activity of oleic acid in the triglycerides and phospholipids were significantly reduced by the analogue. In vitro studies of desaturation and chain elongation reactions, with liver microsomes, using 18‐14C‐stearic and 1‐14C‐linoleic acids as substrates, showed that ethionine depressed the synthesis of oleic acid from stearic and γ‐linolenic from linoleic acid. Elongation of linoleic adie to a 20∶2 fatty acid was unaffected by ethionine. Therefore, the results showed that ethionine inhibited desaturation of stearic to oleic acid in vivo and in vitro and probably also impaired the desaturation of oleic to octadeca‐6, 9‐dienoic acid. Maintenance of control levels of oleic acid in the tissues of ethionine‐fed, EFA deficient rats suggested the presence of synthetic pathways for oleic acid other than via desaturation of stearic acid.

The conversion of stearic acid to oleic in freshly secreted milk

The conversion of stearic acid to oleic in freshly secreted milk

Conversion of stearic acid into oleic acid in adipose tissue

Conversion of stearic acid into oleic acid in adipose tissue

Biosynthesis of fatty acids in the roach Eurycotis floridana

After ingestion of [1- 14C]acetate, fatty acids of the roach Eurycotis floridana show a labelling pattern consistent with biosynthesis by condensation of C 2 units. Oleic acid is efficiently synthesized by direct conversion of stearic acid. Synthesis of a C 18 dienoic acid may occur at a very low rate. Oleic acid constitutes about half of the total fatty acid content, and palmitic is the most abundant saturated acid. There is only a trace of fatty acids of chain length greater than C 18; arachidonic acid is entirely absent.

The intracellular localization of an enzymatic defect of lipid metabolism in diabetic rats

The conversion of stearic acid to oleic acid has been studied in homogenates and other subcellular fractions of adipose tissues and liver of untreated and insulin-treated diabetic rats and rats maintained on a fat-free diet. The synthesis of the monounsaturrated fatty acid is an oxygenase reaction requiring molecular oxygen and DPNH or TPNH. The site of the reaction has been localized to the microsomes. In diabetes, the microsomal enzymatic conversion of strearate to oleate stops. This defect in lipid metabolism, which is separable from the overall depression of lipid biosynthesis, is corrected by insulin therapy.

Effect of Oleic Acid on the Delay of Sexual Maturity in Chickens Caused By Sterculia Foetida Oil

It has recently been shown that feeding 200 mg. of S. foetida oil per day to sexually maturing pullets resulted in retardation of comb, ovary, and oviduct development (Schneider et al., 1962). Also noted in these experiments were lack of egg production, enlargement of the gall bladder and liver, and a decrease in the iodine number of the omental fat. Evans et al. (1961) showed that feeding either cottonseed oil or S. foetida seeds (both of which contain Halphen-reactive cyclopropene fatty acids) to laying hens produced eggs which had a higher percentage of stearic acid and a lower percentage of oleic acid.Both of these investigations indicated that the cyclopropene fatty acids apparently interfered in some manner with the conversion of stearic acid to oleic acid even though they are present only in small amounts. What role this metabolic derangement might have on sexual maturity is unknown. However, Panos et al….

Glyceride hydrolysis and glycerol fermentation by sheep rumen contents.

SUMMARY: Microbial hydrolysis of triglycerides was observed when these were incubated anaerobically at 37° with sheep rumen contents. The extent of hydrolysis was variable, but was often considerable(<90 %)when linseed oil was used as substrate. The free fatty acids liberated were analysed by gas chromatography and, as compared with the acids present initially in glyceride combination, they were less unsaturated because of microbial hydrogenation. Linolenic acid was particularly effectively hydrogenated. No synthesis of long-chain fatty acids took place during the incubations and, apart from the possibility that in some experiments a limited conversion of stearic acid to palmitic acid took place, there was no evidence of significant degradation of long-chain acids. Glycerol liberated during the hydrolysis was completely metabolized, in part to volatile fatty acids, largely propionic acid. No mono- or diglycerides were detected as intermediates in the lipolysis of triglycerides. Analysis of the contents of the rumen, abomasum and small intestine of each of two slaughtered sheep, one of which had previously been fed on a diet rich in linseed oil, showed that most of the total higher fatty acids present in each of these three portions of the alimentary tract was in the form of free acids. It is concluded that microbial lipolysis results in the pre-digestion of much of the lipids ingested by the sheep as part of its feed.

Die enzymatische Dehydrierung der Stearinsäure zu Ölsäure

AbstractWe tried to prove the conversion of stearic acid into oleic acid by liver extracts. The method described by LE BRETON and co‐workers results in enzyme preparations from rat liver which decolorize methylenblue very rapidly but do not dehydrogenate stearic to oleic acid.After fractionation of liver cell particles in sucrose solution we were able to prove the existence of a dehydrogenase in the supernatant containing microsomes and cytoplasma, which converts 14C stearic acid into oleic acid. The mytochondrial fraction showed no activity.

On the mechanism of enzyme action. XLVIII. Investigation of the fat of Fusarium lini Bolley by means of urea adducts

The usefulness of urea adducts for the fractionation of natural fatty acids has been demonstrated. Stearic acid has been isolated and identified from the fat of Fusarium lini Bolley by purification of the solid fraction obtained from the urea adduct of its fatty acids. The conversion of stearic acid to fatty material with a higher iodine value has provided further evidence for the enzymatic formation of unsaturated fatty acids in Fusarium lini Bolley by means of the action of a fatty acid dehydrogenase system.