Fatty acyl-CoA Concentrations Research Articles

Acute hyperinsulinemia and reduced plasma free fatty acid levels decrease intramuscular triglyceride synthesis

ObjectiveTo investigate the effect of acute hyperinsulinemia and the resulting decrease in plasma free fatty acid (FFA) concentrations on intramuscular TG synthesis. Materials/MethodsU-13C16-palmitate was infused for 3 h in anesthetized rabbits after overnight food deprivation. Arterial blood and leg muscle were sampled during the tracer infusion. Plasma samples were analyzed for free and TG-bound palmitate enrichments and concentrations. The enrichments and concentrations of palmitoyl-CoA and palmitoyl-carnitine as well as the enrichment of palmitate bound to TG were measured in muscle samples. Fractional synthetic rate (FSR) of intramuscular TG was calculated using the tracer incorporation method. The rabbits were divided into a control group and a hyperinsulinemic euglycemic clamp group. Insulin infusion decreased the rate of appearance of plasma free palmitate (2.00±0.15 vs 0.68±0.20μmol⋅kg−1⋅min−1; P<.001), decreased plasma FFA concentration (327±61 vs 72±25nmol/mL; P<.01), decreased the total concentration of intramuscular fatty acyl-CoA plus fatty acyl-carnitine (12.1±1.6 vs 7.0±0.7nmol/g; P<.05), and decreased intramuscular TG FSR (0.48±0.05 vs 0.21±0.06%/h; P<.01) in comparison with the control group. Intramuscular TG FSR was correlated (P<.01) with both plasma FFA concentrations and intramuscular fatty acyl-CoA concentrations. ConclusionsFatty acid availability is a determinant of intramuscular TG synthesis. Insulin infusion decreases plasma and intramuscular fatty acid availability and thereby decreases TG synthesis.

Thioesterase Superfamily Member 2 (Them2) Promotes the Hepatic Oxidation of Plasma Free Fatty Acids

Them2 is a mitochondria‐associated long chain acyl‐CoA thioesterase that hydrolyzes fatty acyl‐CoAs to free fatty acids and CoA in vitro. However, the metabolic role of Them2 in liver remains unclear. Here we utilized chow and high fat fed Them2+/+ and Them2−/− mice to explore regulation of hepatic lipid metabolism by Them2. The absence of Them2 expression reduced total and mitochondrial fatty acyl‐CoA thioesterase activities in liver. This led to a 28% increase in fatty acyl‐CoA concentrations, which was mainly attributable to increases in C16:0, C18:0 and C18:3‐fatty acyl CoA molecular species. Reduced hepatic FGF21 mRNA levels along with decreased plasma β‐hydroxybutyrate concentrations implied that fatty acid oxidation was reduced in livers of Them2−/− mice. Whereas high fat fed Them2+/+ mice developed hepatic steatosis, livers of Them2−/− mice did not accumulate excess triglycerides. In the absence of changes in lipogenic gene expression, this was attributable to increases in hepatic triglyceride secretion rates and decreases in free fatty acid uptake into the liver, as reflected by lower CD36 mRNA levels. Collectively, these findings suggest that the fatty acyl‐CoA thioesterase activity of Them2 in liver promotes oxidation of plasma free fatty acids and reduces their hepatic secretion as triglycerides. Supported by the NIH and AHA.

AMPK and ACC phosphorylation: Effect of leptin, muscle fibre type and obesity

Leptin stimulates fatty acid oxidation via the phosphorylation of AMPK (AMP-activated protein kinase) and ACC (acetyl-CoA carboxylase). Obesity is associated with resistance to the effects of leptin. We determined the action of leptin on AMPKalpha and ACCbeta phosphorylation and lipid metabolism in soleus (SOL) and extensor digitorum longus (EDL) muscles from lean and obese Wistar rats after 1 and 100 nM leptin. Both leptin doses stimulated phosphorylation of AMPKalpha and ACCbeta (P<or=0.05) only in EDL muscles from lean animals. Malonyl-CoA levels were decreased in EDL muscles from lean animals after 1 and 100 nM leptin and significantly after 100 nM leptin in obese animals (P<or=0.05). Long-chain fatty acyl-CoA concentrations were decreased in EDL muscles from both phenotypes after 100 nM leptin. AMPK activation by leptin occurred independently of energy-related metabolites. These data demonstrate that the leptin effect on AMPKalpha and ACCbeta is muscle fibre type dependent and fails in diet-induced obesity.

Quantification of the concentration and 13C tracer enrichment of long-chain fatty acyl-coenzyme A in muscle by liquid chromatography/mass spectrometry

Recent diabetes and obesity research has been focused on the role of intracellular lipids in insulin resistance. Fatty acyl-coenzyme A (CoA) esters play a central role in the trafficking of intracellular lipids, but there has not previously been a method with which to quantify their kinetics using tracer methodology. We have therefore developed a high-performance liquid chromatography (HPLC)–mass spectrometry method to simultaneously measure the 13C stable isotopic enrichment of palmitoyl-acyl-CoA ester and the concentrations of five individual long-chain fatty acyl-CoA esters extracted from muscle tissue samples. The long-chain fatty acyl-CoA can be effectively extracted from frozen muscle tissue samples and baseline separated by a reverse-phase HPLC with the presence of a volatile reagent—triethylamine. Negative ion electrospray mass spectrometry with selected ion monitoring was used to analyze the fatty acyl-CoAs to achieve reliable quantification of their concentrations and 13C isotopic enrichment. Applying this protocol to rabbit muscle samples demonstrates that it is a sensitive, accurate, and precise method for the quantification of long-chain fatty acyl-CoA concentrations and enrichment.

Skeletal muscle lipid metabolism with obesity

The objectives of this study were to 1). examine skeletal muscle fatty acid oxidation in individuals with varying degrees of adiposity and 2). determine the relationship between skeletal muscle fatty acid oxidation and the accumulation of long-chain fatty acyl-CoAs. Muscle was obtained from normal-weight [n = 8; body mass index (BMI) 23.8 +/- 0.58 kg/m(2)], overweight/obese (n = 8; BMI 30.2 +/- 0.81 kg/m(2)), and extremely obese (n = 8; BMI 53.8 +/- 3.5 kg/m(2)) females undergoing abdominal surgery. Skeletal muscle fatty acid oxidation was assessed in intact muscle strips. Long-chain fatty acyl-CoA concentrations were measured in a separate portion of the same muscle tissue in which fatty acid oxidation was determined. Palmitate oxidation was 58 and 83% lower in skeletal muscle from extremely obese (44.9 +/- 5.2 nmol x g(-1) x h(-1)) patients compared with normal-weight (71.0 +/- 5.0 nmol x g(-1) x h(-1)) and overweight/obese (82.2 +/- 8.7 nmol x g(-1) x h(-1)) patients, respectively. Palmitate oxidation was negatively (R = -0.44, P = 0.003) associated with BMI. Long-chain fatty acyl-CoA content was higher in both the overweight/obese and extremely obese patients compared with normal-weight patients, despite significantly lower fatty acid oxidation only in the extremely obese. No associations were observed between long-chain fatty acyl-CoA content and palmitate oxidation. These data suggest that there is a defect in skeletal muscle fatty acid oxidation with extreme obesity but not overweight/obesity and that the accumulation of intramyocellular long-chain fatty acyl-CoAs is not solely a result of reduced fatty acid oxidation.

Regulation of Lipogenesis and the Total Activities of Lipogenic Enzymes in a Primary Culture of Hepatocytes from Prenatal and Early Postnatal Chicks

Abstract Hepatocytes prepared from the livers of 18- or 19-day-old chick embryos and maintained in culture medium containing serum for 3 days exhibited marked induction of the lipogenic pathway. Incorporation of [U-14C]glucose into fatty acids and the total activities of malic enzyme, fatty acid synthetase, and ATP-citrate lyase increased by 1000-, 47-, 21-, and 4.5-fold, respectively. When l-triiodothyronine was added to the culture medium, the activities increased a total of 2500-, 140-, 40-, and 8-fold, respectively. The increases in the rate of fatty acid synthesis and total activity of malic enzyme were inhibited by bovine serum albumin, human thyroxin-binding prealbumin, and rabbit anti-thyroxin serum. Inhibition was reversed by adding a large amount of l-triiodothyronine. Thus, thyroid hormone was a major serum factor causing induction of the lipogenic pathway. Oxidation of [1-14C]acetate to CO2 and the total activity of NADP-isocitrate dehydrogenase were not affected by incubating the cells with or without l-triiodothyronine. The activity of lactate dehydrogenase decreased during the culture period. This induction of the lipogenesis pathway quantitatively mimics changes in the pathway which occur when newly hatched chicks are fed a high carbohydrate mash diet. Glucagon, cAMP, and free stearate also inhibited the induction of lipogenesis and its associated enzymes. These compounds also inhibit fatty acid synthesis and elevate fatty acyl-CoA levels in freshly prepared hepatocytes. Hence, glucagon and free fatty acids exert both long and short term regulation over fatty acid synthesis, possibly via changes in the intracellular concentration of fatty acyl-CoA.