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PubMed1996

Stearic acid unlike shorter-chain saturated fatty acids is poorly utilized for triacylglycerol synthesis and beta-oxidation in cultured rat hepatocytes.

Utilization of stearate as compared to various saturated fatty acids for cholesterol and lipid synthesis and beta-oxidation was determined in primary culture of rat hepatocytes. At 0.5 mmol/L in the medium, stearate (18:0) adequately solubilized by albumin was less inhibitory to cholesterol synthesis from [2-14C] acetate than myristate (14:0) and palmitate (16:0) (68% vs. 91 and 88% inhibition, respectively). The rate of incorporation into cholesterol from [1-14C] stearate (3.0 +/- 0.6 nmol/mg protein/4 h) was 37-, 1.8-, and 7.8-fold of that from myristate, palmitate, and oleate, respectively. Conversely, the rate of [1-14C] stearate incorporation into total glycerolipids was 88-90% lower than that of labeled palmitate, myristate, and oleate. The rate of [1-14C] stearate incorporation into triacylglycerol (3.6 +/- 0.4 nmol/mg protein/4 h) was 6-8% of that from myristate, palmitate, oleate, and linoleate. The rate of stearate incorporation into phospholipids was the lowest among tested fatty acids, whereas the rate of mono- and diacylglycerol synthesis was the highest with stearate treatment. The rate of beta-oxidation as measured by CO2 and acid soluble metabolite production was also the lowest with [1-14C] stearate treatment at 22.7 nmol/mg protein/4 h, which was 35-40% of those from other [1-14C] labeled fatty acids. A greater proportion of stearate than other fatty acids taken up by the hepatocytes remained free and was not metabolized. Clearly, stearate as compared to shorter-chain saturated fatty acids was less efficiently oxidized and esterified to triacylglycerol in cultured rat hepatocytes.

Animals↗
PubMed1969

Gas--liquid chromatography--mass spectrophotometry of hydroxylated octadecanols derived from hydroxylated stearic acids.

A gas-liquid chromatographic-mass spectrometric method of determining the position of oxygen atoms on polyfunctional fatty acids has been explored. The method consists of reduction of keto, hydroperoxy, epoxy, and carboxylic acid groups with LiAlH(4) to the corresponding alcohols; trimethylsilylation with bis(trimethylsilyl)acetamide; and analysis by means of the combined gas-liquid chromatograph-mass spectrometer. The following compounds were analyzed: 9-mono-, 9,10-di-, 9,10,12-tri-, and 9,10,12,13-tetrahydroxystearic acids and the corresponding derivatives of octadecan-1-ol. The reduction products of 9,10-epoxystearic acid and a mixture of linoleic acid 9- and 13-hydroperoxides were also analyzed. The position of the oxygen function in the original molecule can be deduced rapidly and accurately.

Alcohols↗
PubMed1993

Incorporation of stearic acid (18:0) and palmitic acid (16:0) in phospholipid molecular species studied in isolated rat liver cells.

The incorporation of [1-14C]16:0 and [1-14C]18:0 in the molecular species of PC and PE in isolated rat liver cells was studied. More [14C]18:0 than [14C]16:0 was esterified both in PC and PE. Also the chain elongated and desaturated products (16:1, 18:0 and 18:1) were incorporated. The main molecular phospholipid species formed from [14C]18:0 were 18:0-18:2, 18:0-20:4 and 18:0-22:6. 18:0-18:0 species was not detected, independent of the substrate concentration (0.1-0.9 mM). With [14C]16:0 at low substrate concentration (0.1 mM) the dominating species are 16:0-18:2, 16:0-20:4 and 16:0-22:6. These species were detected already after 10 min. The same main species are formed both in PC and PE, but the relative amounts differ. In PC the combination with 18:2 is most abundant for both saturated fatty acid substrates. In PE 18:0-20:4 dominates when 18:0 is the substrate, and 16:0-22:6 when 16:0 is. At higher substrate concentrations (0.4-0.9 mM) 16:0 is also esterified in 16:0-16:0. This molecular species is efficiently degraded in the cells within 2-3 h, in contrast to the other species formed. The results suggest that 16:0 and 18:0 are directly incorporated in the sn-1 position in physiologically important phospholipid molecular species. With an excess of 16:0, 16:0-16:0 is also formed in substantial amounts, but this uncommon species is thereafter removed.

Animals↗
PubMed2002

Glyceride stearic acid content and structure affect the energy available to growing rats.

To better understand the relative absorption of 18:0, specific structured triglycerides (STG) with varied ratios of 18:0 and short-chain organic acids (2:0, 3:0, 4:0) were compared with naturally occurring 18:0 in cocoa butter and to other mono- and diglycerides (DGs) containing 18:0. A bioassay for available fat energy was developed for growing Sprague-Dawley rats fed reduced energy from a control diet containing an American Heart Association (AHA) fat blend to generate 60 or 80% normal growth. The resulting standard growth curve was applied to the test fats, including cocoa butter and six glycerides, which were blended 3:1 with the AHA blend (to ensure EFA sufficiency) and pair-fed to match intake of control rats (AHA diet, 80% normal growth). Available energy from test fats ranged from 30 to 12 kJ/g (7.1 to 2.9 kcal/g) for cocoa butter to 18:0-DG, respectively, with the mean of the four different STG being 22 kJ/g (5.2 kcal/g). Energy available from test fats was negatively related to total 18:0 in the STG (r = -0.90; P < 0.001) and fecal dry weight (r = -0.92; P < 0.001); the effect was greater for monoglyceride (monolong-18:0) than for DG (dilong-18:0) but was not related to fecal 18:0. Compared with monoglyceride-18:0, available energy was increased or decreased when short-chain organic acids (SCOA) were added to form triglycerides, depending on the addition of butyrate or acetate, respectively. The different fat sources altered the available energy without apparent changes in lipoproteins or body composition. Thus, the reduced energy available from a glyceride containing 18:0 is determined by its total 18:0 and reflects the mono- or dilong chain character of the glyceride, its content of SCOA and triglyceride structure or organization per se.

Animals↗