Metabolism Of Medium Chain Fatty Acids Research Articles

EgMADS3 directly regulates EgLPAAT to mediate medium-chain fatty acids (MCFA) anabolism in the mesocarp of oil palm.

EgMADS3, a pivotal transcription factor, positively regulates MCFA accumulation via binding to the EgLPAAT promoter, advancing lipid content in mesocarp of oil palm. Lipids function as the structural components of cell membranes, which serve as permeable barriers to the external environment of cells. The medium-chain fatty acid in the stored lipids of plants is an important renewable energy. Most research on MCFA production in plant lipid synthesis is based on biochemical methods, and the importance of transcriptional regulation in MCFA synthesis and its incorporation into TAGs needs further research. Oil palm is the most productive oil crop in the world and has the highest productivity among the main oil crops. In this study, the MADS transcription factor (EgMADS3) in the mesocarp of oil palm was characterized. Through the VIGS-virus induced gene silencing, it was determined that the potential target gene of EgMADS3 was related to the biosynthesis of medium-chain fatty acid (MCFA). Transient transformation in protoplasts and qRT-PCR analysis showed that EgMADS3 positively regulated the expression of EgLPAAT. The results of the yeast one-hybrid assays and EMSA indicated the interaction between EgMADS3 and EgLPAAT promoter. Through genetic transformation and fatty acid analysis, it is concluded that EgMADS3 directly regulates the mid-chain fatty acid synthesis pathway of the potential target gene EgLPAAT, thus promotes the accumulation of MCFA and improves the total lipid content. This study is innovative in the functional analysis of the MADS family transcription factor in the metabolism of medium-chain fatty acids (MCFA) of oil palm, provides a certain research basis for improving the metabolic pathway of chain fatty acids in oil palm, and improves the synthesis of MCFA in plants. Our results will provide a reference direction for further research on improving the oil quality through biotechnology of oil palm.

The solute carrier SLC25A17 sustains peroxisomal redox homeostasis in diverse mammalian cell lines

Despite the crucial role of peroxisomes in cellular redox maintenance, little is known about how these organelles transport redox metabolites across their membrane. In this study, we sought to assess potential associations between the cellular redox landscape and the human peroxisomal solute carrier SLC25A17, also known as PMP34. This carrier has been reported to function as a counter-exchanger of adenine-containing cofactors such as coenzyme A (CoA), dephospho-CoA, flavin adenine dinucleotide, nicotinamide adenine dinucleotide (NAD+), adenosine 3′,5′-diphosphate, flavin mononucleotide, and adenosine monophosphate. We found that inactivation of SLC25A17 resulted in a shift toward a more reductive state in the glutathione redox couple (GSSG/GSH) across HEK-293 cells, HeLa cells, and SV40-transformed mouse embryonic fibroblasts, with variable impact on the NADPH levels and the NAD+/NADH redox couple. This phenotype could be rescued by the expression of Candida boidinii Pmp47, a putative SLC25A17 orthologue reported to be essential for the metabolism of medium-chain fatty acids in yeast peroxisomes. In addition, we provide evidence that the alterations in the redox state are not caused by changes in peroxisomal antioxidant enzyme expression, catalase activity, H2O2 membrane permeability, or mitochondrial fitness. Furthermore, treating control and ΔSLC25A17 cells with dehydroepiandrosterone, a commonly used glucose-6-phosphate dehydrogenase inhibitor affecting NADPH regeneration, revealed a kinetic disconnection between the peroxisomal and cytosolic glutathione pools. Additionally, these experiments underscored the impact of SLC25A17 loss on peroxisomal NADPH metabolism. The relevance of these findings is discussed in the context of the still ambiguous substrate specificity of SLC25A17 and the recent observation that the mammalian peroxisomal membrane is readily permeable to both GSH and GSSG.

Medium-chain fatty acid oxidation is independent of l-carnitine in liver and kidney but not in heart and skeletal muscle.

Medium-chain fatty acid (MCFA) consumption confers a wide range of health benefits that are highly distinct from long-chain fatty acids (LCFAs). A major difference between the metabolism of LCFAs compared with MCFAs is that mitochondrial LCFA oxidation depends on the carnitine shuttle, whereas MCFA mitochondrial oxidation is not. Although MCFAs are said to range from 6 to 14 carbons long based on physicochemical properties in vitro, the biological cut-off length of acyl chains that can bypass the carnitine shuttle in different mammalian tissues is unknown. To define the range of acyl chain length that can be oxidized in the mitochondria independent of carnitine, we determined the oxidative metabolism of free fatty acids (FFAs) from 6 to 18 carbons long in the liver, kidney, heart, and skeletal muscle. The liver oxidized FFAs 6 to 14 carbons long, whereas the kidney oxidized FFAs from 6 to 10 carbons in length. Heart and skeletal muscle were unable to oxidize FFAs of any chain length. These data show that while the liver and kidney can oxidize MCFAs in the free form, the heart and skeletal muscle require carnitine for the oxidative metabolism of MCFAs. Together these data demonstrate that MCFA oxidation independent of carnitine is tissue-specific.NEW & NOTEWORTHY This work demonstrates that the traditional concept of mitochondrial medium-chain fatty acid oxidation as unregulated and independent of carnitine applies only to liver metabolism, and to kidney to a lesser extent, but not the heart or skeletal muscle. Thus, the benefits of dietary medium-chain fatty acids are set by liver metabolic activity and peripheral tissues are unlikely to receive direct benefits from medium-chain fatty acid metabolism, but rather metabolic byproducts of liver's medium-chain oxidative metabolism.

The medium-chain fatty acid decanoic acid reduces oxidative stress levels in neuroblastoma cells

Enhanced oxidative stress is a contributing factor in the pathogenesis of several neurodegenerative disorders such as Alzheimer´s disease. Beneficial effects have been demonstrated for medium-chain fatty acids (MCFAs) nutritionally administered as medium-chain triglycerides (MCTs) or coconut oil (CO). The observed effects on cognitive impairment are generally attributed to the hepatic metabolism of MCFAs, where resulting ketone bodies serve as an alternate energy source to compensate for the impaired glucose utilisation in the human brain. Here we show that the saturated MCFA decanoic acid (10:0) reduces the oxidative stress level in two different neuroblastoma cell lines. Phosphatidylcholine (PC) containing decanoic acid (10:0) (PC10:0/10:0) reduced the cellular H2O2 release in comparison to solvent, L-α-Glycerophosphorylcholine and PC containing the long-chain fatty acid (LCFA) arachidic acid (20:0). This effect seems to be at least partially based on an upregulation of catalase activity, independent of alterations in catalase gene expression. Further, PC10:0/10:0 decreased the intracellular oxidative stress level and attenuated the H2O2-induced cell death. It did not affect the level of the ketone body β-hydroxybutyrate (βHB). These results indicate that decanoic acid (10:0) and possibly MCFAs in general directly reduce oxidative stress levels independent of ketone levels and thus may promote neuronal health.

Abstract 29: Metabolomic Signatures of Sedentary Behavior and Cardiometabolic Traits in US Hispanics/Latinos: Hispanic Community Health Study / Study of Latinos (HCHS/SOL)

Introduction: Sedentary behavior is associated with cardiometabolic risk independent of physical activity, but the underlying mechanisms are not fully understood. Hypothesis: Sedentary behavior may influence serum metabolite profiles which are associated with cardiometabolic risk factors. Methods: The analyses included 2711 participants (43% men) of the HCHS/SOL aged 18 to 74 years, free of CVD and other major chronic diseases. Serum metabolomics was performed using an untargeted approach. Physical activity and sedentary behavior were measured by accelerometer (Actical) for a 7-day period. Survey linear regressions were used to examine associations between sedentary behavior and metabolites. Metabolite scores were calculated by summing up z-scores of significant metabolites within the same sub-pathway. Results: Of 624 known metabolites, 95 were significantly associated with sedentary behavior ( P <0.05 after FDR correction), adjusting for socioeconomic and lifestyle factors including moderate to vigorous physical activity ( Figure 1A ). The majority of significant metabolites were clustered into 7 sub-pathways. Three sub-pathway scores (branched-chain amino acids [BCAA], acylcarnitine and medium-chain fatty acid metabolism) were positively associated with sedentary behavior, while the other 4 sub-pathway scores (acylcholine, plasmalogen, nicotinate, and arginine) were inversely associated with sedentary behavior. Among these scores, the BCAA score showed unfavorable correlations with all cardiometabolic traits including obesity measures, glycemic traits, blood lipids and blood pressure. The acylcholine score showed favorable correlations with obesity measures and glycemic traits, though positive correlations with blood lipids were observed ( Figure 1B) . Conclusions: Our study identified multiple serum metabolites associated with sedentary behavior independent of physical activity, suggesting potential mechanistic links between sedentary behavior and cardiometabolic diseases.

Detection of myocardial medium-chain fatty acid oxidation and tricarboxylic acid cycle activity with hyperpolarized [1-13 C]octanoate.

Under normal conditions, the heart mainly relies on fatty acid oxidation to meet its energy needs. Changes in myocardial fuel preference are noted in the diseased and failing heart. The magnetic resonance signal enhancement provided by spin hyperpolarization allows the metabolism of substrates labeled with carbon-13 to be followed in real time in vivo. Although the low water solubility of long-chain fatty acids abrogates their hyperpolarization by dissolution dynamic nuclear polarization, medium-chain fatty acids have sufficient solubility to be efficiently polarized and dissolved. In this study, we investigated the applicability of hyperpolarized [1-13 C]octanoate to measure myocardial medium-chain fatty acid metabolism in vivo. Scanning rats infused with a bolus of hyperpolarized [1-13 C]octanoate, the primary metabolite observed in the heart was identified as [1-13 C]acetylcarnitine. Additionally, [5-13 C]glutamate and [5-13 C]citrate could be respectively resolved in seven and five of 31 experiments, demonstrating the incorporation of oxidation products of octanoate into the tricarboxylic acid cycle. A variable drop in blood pressure was observed immediately following the bolus injection, and this drop correlated with a decrease in normalized acetylcarnitine signal (acetylcarnitine/octanoate). Increasing the delay before infusion moderated the decrease in blood pressure, which was attributed to the presence of residual gas bubbles in the octanoate solution. No significant difference in normalized acetylcarnitine signal was apparent between fed and 12-hour fasted rats. Compared with a solution in buffer, the longitudinal relaxation of [1-13 C]octanoate was accelerated ~3-fold in blood and by the addition of serum albumin. These results demonstrate the potential of hyperpolarized [1-13 C]octanoate to probe myocardial medium-chain fatty acid metabolism as well as some of the limitations that may accompany its use.

A metabolomic study on the gender-dependent effects of maternal exposure to fenvalerate on neurodevelopment in offspring mice

BackgroundThe general population is widely exposed to fenvalerate. However, the effects of maternal exposure to fenvalerate on neurodevelopment in offspring and the underlying metabolic mechanism are largely unknown. MethodsPregnant mice were exposed to fenvalerate for 11 consecutive days. The forced swimming test (FST) was performed in 35 day-old offspring to investigate the effects of fenvalerate on neurobehavioral responses. Blood serum free T4 and free T3 concentrations were measured using commercial ELISA. Blood and thyroid samples were used for metabolomic analyses with UPLC Q-Exactive. The expression levels of neurotransmitter metaolite receptors were determined in the frontal cortex of offspring using real-time PCR. ResultsThe immobility time, free T4 and free T3, and expression levels of Htr1a and Htr2a were statistically changed in offspring male mice. Metabolomic analysis revealed that the pentose phosphate pathway, starch and sucrose metabolism, glutamic acid metabolism were the key changed pathways in the blood, and thiamine metabolism was the key changed pathway in the thyroid. ConclusionPrenatal exposure to fenvalerate affected neurodevelopment in male offspring mice both via the changed abundances of metabolites involved in glycolysis related metabolism and medium-chain fatty acid metabolism, and the changes in 5-HT receptor expression.

Differential Metabolism of Medium-Chain Fatty Acids in Differentiated Human-Induced Pluripotent Stem Cell-Derived Astrocytes.

Medium-chain triglyceride (MCT) ketogenic diets increase ketone bodies, which are believed to act as alternative energy substrates in the injured brain. Octanoic (C8:0) and decanoic (C10:0) acids, which produce ketone bodies through β-oxidation, are used as part of MCT ketogenic diets. Although the ketogenic role of MCT is well-established, it remains unclear how the network metabolism underlying β-oxidation of these medium-chain fatty acids (MCFA) differ. We aim to elucidate basal β-oxidation of these commonly used MCFA at the cellular level. Human-induced pluripotent stem cell-derived (iPSC) astrocytes were incubated with [U-13C]-C8:0 or [U-13C]-C10:0, and the fractional enrichments (FE) of the derivatives were used for metabolic flux analysis. Data indicate higher extracellular concentrations and faster secretion rates of β-hydroxybutyrate (βHB) and acetoacetate (AcAc) with C8:0 than C10:0, and an important contribution from unlabeled substrates. Flux analysis indicates opposite direction of metabolic flux between the MCFA intermediates C6:0 and C8:0, with an important contribution of unlabeled sources to the elongation in the C10:0 condition, suggesting different β-oxidation pathways. Finally, larger intracellular glutathione concentrations and secretions of 3-OH-C10:0 and C6:0 were measured in C10:0-treated astrocytes. These findings reveal MCFA-specific ketogenic properties. Our results provide insights into designing different MCT-based ketogenic diets to target specific health benefits.

[Formation in the phylogenesis of three pulls of cells with expressed different absorption and metabolism of fatty acids. Insulin and medium chains fatty acids.]

Somatic cells at the early stages of phylogenesis realized the metabolism of long-chain fatty acids (FA), primarily palmitic saturated FA. It dominated the construction of a bilayer cell membrane and as a substrate for oxidation in mitochondria during energy production. Later, polyene FAs became involved in the construction of the cell membrane, the membranes of intracellular organelles, and became the substrate for the synthesis of biologically active eicosanoids. At later stages of phylogenesis, the metabolism of medium-chain FAs is activated and the formation of ketone bodies as a substrate, which is available for oxidation by the mitochondria of the formed cells of the nervous tissue in the absence of first substrate glucose. In the later stages of phylogenesis, insulin initiated: a) the transformation of carnivorous ancestors of the species Homo sapiens in the ocean into a herbivorous species while living on land; b) the formation of the new biological function of locomotion and c) the dominance of the oleic variant of the metabolism of long-chain fatty acids with higher kinetic parameters of mitochondria oxidation. Metabolites of medium chain FA have become humoral mediators of metabolism and the formation of feedback mechanisms in the function of trophology and cognitive biological function. The formation of an oleic variant of the metabolism of fatty acids under the action of insulin led to the improvement of the energy supply of cells and the high kinetic parameters of many species of herbivorous mammals, including Homo sapiens. The species Homo sapiens was not omnivorous (Omnivores); the insulin's regulatory action during life on land has turned it into a herbivorous species (Herbivore), but with a carnivorous (Carnivore) (fish-eating) past. Seven metabolic pandemics (1. atherosclerosis and atheromatosis; 2. metabolic arterial hypertension; 3. metabolic syndrome; 4. insulin resistance syndrome; 5. obesity; 6. nonalcoholic fatty liver disease and 7. endogenous hyperuricemia) are only functional disorders and can be, in most cases, eliminated. From the standpoint of the phylogenetic theory of general pathology, atherosclerosis and atheromatosis of the arteries have no great future. As soon, as the majority of individuals of the Homo sapiens species realize that in phylogenesis they have formed as herbivores and stop eating excessive amounts of meat food, exogenous palmitic FA, the incidence in the population will begin to decrease. Patients are still obliged to justify the binary, biological name of the species - reasonable man. Prevention and other metabolic pandemics, diseases of civilization, can be discussed. It takes time, an understanding of what happens by the doctors, diligence and the desire of patients to be healthy.

Intestinal Metabolites Are Profoundly Altered in the Context of HLA-B27 Expression and Functionally Modulate Disease in a Rat Model of Spondyloarthritis.

HLA-B27-associated spondyloarthritides are associated with an altered intestinal microbiota and bowel inflammation. We undertook this study to identify HLA-B27-dependent changes in both host and microbial metabolites in the HLA-B27/β2 -microglobulin (β2 m)-transgenic rat and to determine whether microbiota-derived metabolites could impact disease in this major model of spondyloarthritis. Cecal contents were collected from Fischer 344 33-3 HLA-B27/β2 m-transgenic rats and wild-type controls at 6 weeks (before disease) and 16 weeks (with active bowel inflammation). Metabolomic profiling was performed by high-throughput gas and liquid chromatography-based mass spectrometry. HLA-B27/β2 m-transgenic rats were treated with the microbial metabolites propionate or butyrate in drinking water for 10 weeks, and disease activity was subsequently assessed. Our screen identified 582 metabolites, of which more than half were significantly altered by HLA-B27 expression at 16 weeks. Both microbial and host metabolites were altered, with multiple pathways affected, including those for amino acid, carbohydrate, xenobiotic, and medium-chain fatty acid metabolism. Differences were even observed at 6 weeks, with up-regulation of histidine, tyrosine, spermidine, N-acetylmuramate, and glycerate in HLA-B27/β2 m-transgenic rats. Administration of the short-chain fatty acid propionate significantly attenuated HLA-B27-associated inflammatory disease, although this was not associated with increased FoxP3+ T cell induction or with altered expression of the immunomodulatory cytokines interleukin-10 (IL-10) or IL-33 or of the tight junction protein zonula occludens 1. HLA-B27 expression was also associated with altered host expression of messenger RNA for the microbial metabolite receptors free fatty acid receptor 2 (FFAR2), FFAR3, and niacin receptor 1. HLA-B27 expression profoundly impacts the intestinal metabolome, with changes evident in rats even at age 6 weeks. Critically, we demonstrate that a microbial metabolite, propionate, attenuates development of HLA-B27-associated inflammatory disease. These and other microbiota-derived bioactive mediators may provide novel treatment modalities in HLA-B27-associated spondyloarthritides.

Hepatic-portal oleic acid inhibits feeding more potently than hepatic-portal caprylic acid in rats

In several human and animal studies, medium-chain triglycerides decreased food intake more than did long-chain triglycerides. It is possible that faster uptake and metabolism of medium-chain fatty acids in the liver is responsible for this difference. To test this hypothesis we compared the feeding effects of hepatic portal vein (HPV) infusion of the medium-chain fatty acid caprylic acid (CA) with those of the long-chain fatty acid oleic acid (OA). Contrary to our expectation, six-h HPV infusion of 14 μg/min (50 nmol/min) OA robustly inhibited feeding, whereas infusion of 22 or 220 μg/min (150 and 1500 nmol/min) CA failed to have any effect on feeding. Only a much larger dose of CA, 1100 μg/min (7500 nmol/min) inhibited feeding similarly to 14 μg/min OA. The increased feeding-inhibitory potency of OA did not appear to be due to differences in stimulation of hepatic fatty acid oxidation because equimolar (50 nmol/min) doses of OA (14 μg/min) and CA (7 μg/min) did not differentially affect post-infusion levels of β-hydroxybutyrate. Stress, inflammation, acute hepatotoxicity or oxidative stress also do not appear to account for the increased feeding-inhibitory potency of HPV OA because plasma concentrations of the stress hormones corticosterone and epinephrine, the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-α, the liver enzymes γ-glutamyl transferase and alanine aminotransferase and as well as hepatic levels of malondialdehyde and glutathione were all similar after HPV infusion of saline or of 50 nmol/min OA or CA.

8-cyclopentadienyltricarbonyl 99mtc 8-oxooctanoic acid: a novel radiotracer for evaluation of medium chain fatty acid metabolism in the liver.

8-Cyclopentadienyltricarbonyl 99mTc 8-oxooctanoic acid (99mTc-CpTTOA; 1a) was synthesized for evaluation of medium chain fatty acid metabolism in the liver. 99mTc-CpTTOA was prepared in high radiochemical yield (50-63%) by a double ligand transfer reaction of methyl 8-ferrocenyl-8-oxooctanoate and Na99mTcO4 in the presence of CrCl3 and Cr(CO)6, followed by hydrolysis. This radiotracer was shown to be stable (>90% at 6 h) when incubated with human serum. Aqueous extraction of the radioactivity from the liver and blood samples of mice suggested that 99mTc-CpTTOA was mainly metabolized via beta-oxidation in the liver, and the radioactivity was retained longer in CCl4-treated mice than in control mice, possibly due to impaired beta-oxidation in the former. Planar images of rats injected with 99mTc-CpTTOA showed accumulation of the radioactivity in the liver, kidneys, and bladder with rapid hepatic clearance as a function of time. Analysis of the metabolites from the liver and urine samples of rats further supported that 99mTc-CpTTOA was metabolized to 4-cyclopentadienyltricarbonyl 99mTc 4-oxobutanoic acid (99mTc-CpTTBA; 1c) via beta-oxidation. The results suggested that this radiotracer might be of valuable use in the evaluation of fatty acid metabolism in the liver.

In vivo absorption of medium-chain fatty acids by the rat colon exceeds that of short-chain fatty acids

Short-chain fatty acids (SCFAs) are main fuels of the colonic epithelium, and are avidly absorbed by the colon of animal and man. The current knowledge on colonic metabolism and absorption of medium-chain fatty acids (MCFAs) is limited. In some clinical situations, colonic absorption of high-energy substances could compensate for reduced absorptive capacity because of a shortened or malfunctioning small bowel. We evaluated and compared colonic absorption and metabolism of MCFAs (octanoate, decanoate, and dodecanoate), SCFAs (acetate and butyrate), and long-chain fatty acids (LCFAs) (oleate). Rats were surgically operated on to cannulate a 7-cm segment of proximal colon, isolate the vasculature, and cannulate the right colic vein draining this segment. The lumen was perfused with (14)C-labeled substrates for 100 minutes. Right colic vein blood was analyzed for total (14)C, (14)CO(2), and metabolites by scintillation counting and high-performance liquid chromatography. The transport from the colonic lumen to mesenteric blood of substrate carbon from MCFAs exceeded by 2-13-fold that of SCFAs and LCFAs. The CO(2) production from the oxidation of MCFAs was as high as or higher than that from SCFAs. CO(2) produced from the LCFA, oleate, was lower than from SCFAs or MCFAs. In addition to CO(2), ketone bodies were major metabolites of SCFAs and MCFAs. Ketogenesis from butyrate and the MCFAs was significantly higher than from acetate and oleate. A substantial proportion (50%-90%) of all substrates was absorbed without being metabolized. The colonic epithelium serves to absorb and partially metabolize MCFAs. For patients with a compromised small-bowel function, colonic absorption of MCFAs could represent an important way of receiving calories.

Medium chain fatty acid metabolism and energy expenditure: Obesity treatment implications

Fatty acids undergo different metabolic fates depending on their chain length and degree of saturation. The purpose of this review is to examine the metabolic handling of medium chain fatty acids (MCFA) with specific reference to intermediary metabolism and postprandial and total energy expenditure. The metabolic discrimination between varying fatty acids begins in the GI tract, with MCFA being absorbed more efficiently than long chain fatty acids (LFCA). Subsequently, MCFA are transported in the portal blood directly to the liver, unlike LCFA which are incorporated into chylomicrons and transported through lymph. These structure based differences continue through the processes of fat utilization; MCFA enter the mitochondria independently of the carnitine transport system and undergo preferential oxidation. Variations in ketogenic and lipogenic capacity also exist. Such metabolic discrimination is supported by data in animals and humans showing increases in postprandial energy expenditure after short term feeding with MCFA. In long term MCFA feeding in animals, weight accretion has been attenuated. These differences in metabolic handling of MCFA versus LCFA are considered with the conclusion that MCFA hold potential as weight loss agents.

Interaction of salicylate and ibuprofen with the carboxylic acid: CoA ligases from bovine liver mitochondria.

Neither salicylate nor ibuprofen was a substrate or inhibitor of the long-chain fatty acid:CoA ligase. In contrast, all three xenobiotic-metabolizing medium-chain fatty acid:CoA ligases (XL-I, XL-II, and XL-III) had activity toward salicylate. The K(m) value for salicylate was similar for all three forms (2 to 3 microM), but XL-II and XL-III had higher activity at Vmax. For ibuprofen, only XL-III catalyzed its activation, and it had a K(m) for ibuprofen of 36 microM. Studies of salicylate inhibition of XL-I, XL-II, and XL-III revealed that it inhibited the benzoate activity of all three forms with K1 values of ca. 2 microM, which is in agreement with the K(m) values obtained with salicylate as substrate. Kinetic analysis revealed that salicylate conjugation by all three forms is characterized by substrate inhibition when salicylate exceeds ca. 20 microM. Substrate inhibition was more extensive with XL-I and XL-III. Previous work on the ligases employed assay concentrations of salicylate in the range of 0.1 to 1.0 mM, which are clearly inhibitory, particularly toward XL-I and XL-III. Thus, activity was not properly measured in previous studies, which accounts for the fact that salicylate conjugation was only found with one form, which is most likely XL-II since it has the highest Vmax activity and shows the least amount of substrate inhibition. Studies with ibuprofen indicated that it inhibited XL-I, XL-II, and XL-III, with KI values being in the range of 75-125 microM. The short-chain ligase was inhibited by both salicylate and ibuprofen with KI values of 93 and 84 microM, respectively. It was concluded that pharmacological doses of salicylate, but not ibuprofen, will affect the metabolism of medium-chain fatty acids and carboxylic acid xenobiotics and that the previously described mitochondrial ibuprofen:CoA ligase activity is attributable to XL-III.

Interaction between valproate and branched‐chain amino acid metabolism

Structural similarities between valproate metabolites and metabolites formed from the beta-oxidation of branched-chain amino acids (isoleucine, leucine, and valine) suggest that valproate may utilize key enzymes of branched-chain amino acid metabolism. Genetic deficiencies in these enzymes may decrease beta-oxidation of valproate and increase formation of valproate hepatotoxic metabolites. We attempted to determine if valproate interacts with branched-chain amino acid enzymes and also evaluated the effect of valproate on the urinary excretion of the straight-chain fatty acids butyrate (C4), valerate (C5), and hexanoate (C6). We collected dosage interval urine samples from three groups of 10 valproate patients: (1) valproate monotherapy, (2) valproate with carbamazepine, and (3) valproate with phenytoin. We also collected 12-hour urine samples from 10 normal volunteers who served as controls. Valproate caused a significant increase in the excretion of the deaminated acid metabolites of valine, isoleucine, and leucine. There were also significant increases in the excretion of the isoleucine metabolites 2-methylbutyrate and 2-methyl-3-OH-butyrate in the valproate patients. Valproate caused a significant increase in the excretion of all three of the straight-chain fatty acids evaluated, and valproate appears to inhibit the four types of acyl-CoA dehydrogenases involved in branched-chain amino acid and short- and medium-chain fatty acid metabolism.

EFFECT OF MEDIUM CHAIN TRIGLYCERIDE (MCT) ADMINISTRATION ON CARNITINE METABOLISM IN THE ANESTHESIZED PIGLET AND CULTURED KIDNEY EPITHELIAL CELLS

To test the hypothesis that carnitine plays a role in medium chain fatty acid metabolism, blood, urine, liver and bile specimens were collected from anesthesized neonatal piglets prior to, and after 30, 60, 120 and 180 minutes of a continuous intravenous infusion of MCT (1 g/kg-h). Interval fractional tubular reabsorption was calculated throughout the infusion. 3H-L-Carnitine uptake was determined in cultured renal tubular epithelial (Cos-l) cells incubated with increasing amounts of octanoic acid.Results: The ketogenic response to MCT administration was associated with a rise in esterified (15.2-->40.9 μM), particularly acetylcamitine (11.4-->26.2 μM), and a fall in free carnitine plasma concentrations (34.6-->14.4 μM). The appearance in the plasma, bile and liver of butyryl-, hexanoyl-, octanoyl- and decanoylcarniune and the greater than 4-fold increase in ratios of plasma free fatty acids/β-hydroxybutyratc and lactate/pyruvate suggested overloading of both β- and Krebs cycle oxidative pathways. The fractional tubular reabsorption of free carnitine decreased from 96.5% to 48.7% with MCT loading, and was associated with a 6-fold increase of free carnitine excretion. Uptake of 3H-L-Carnitine into Cos-1 cells decreased in a dose-dependent manner with increasing octanoic acid concentration. The results suggest that MCT loading has profound effects on carnitine metabolism affecting intracellular esterifications and renal tubular reabsorption.