Participation of a medium chain acyl-CoA synthetase in glycine conjugation of the benzoic acid derivatives with the electron-donating groups

Hemin Improves Insulin Sensitivity and Lipid Metabolism in Cultured Hepatocytes and Mice Fed a High-Fat Diet

Hemin is a breakdown product of hemoglobin. It has been reported that the injection of hemin improves lipid metabolism and insulin sensitivity in various genetic models. However, the effect of hemin supplementation in food on lipid metabolism and insulin sensitivity is still unclear, and whether hemin directly affects cellular insulin sensitivity is yet to be elucidated. Here we show that hemin enhances insulin-induced phosphorylation of insulin receptors, Akt, Gsk3β, FoxO1 and cytoplasmic translocation of FoxO1 in cultured primary hepatocytes under insulin-resistant conditions. Furthermore, hemin diminishes the accumulation of triglyceride and increases in free fatty acid content in primary hepatocytes induced by palmitate. Oral administration of hemin decreases body weight, energy intake, blood glucose and triglyceride levels, and improves insulin and glucose tolerance as well as hepatic insulin signaling and hepatic steatosis in male mice fed a high-fat diet. In addition, hemin treatment decreases the mRNA and protein levels of some hepatic genes involved in lipogenic regulation, fatty acid synthesis and storage, and increases the mRNA level and enzyme activity of CPT1 involved in fatty acid oxidation. These data demonstrate that hemin can improve lipid metabolism and insulin sensitivity in both cultured hepatocytes and mice fed a high-fat diet, and show the potential beneficial effects of hemin from food on lipid and glucose metabolism.

Characterizing Blood Metabolomics Profiles Associated with Self-Reported Food Intakes in Female Twins

Using dietary biomarkers in nutritional epidemiological studies may better capture exposure and improve the level at which diet-disease associations can be established and explored. Here, we aimed to identify and evaluate reproducibility of novel biomarkers of reported habitual food intake using targeted and non-targeted metabolomic blood profiling in a large twin cohort. Reported intakes of 71 food groups, determined by FFQ, were assessed against 601 fasting blood metabolites in over 3500 adult female twins from the TwinsUK cohort. For each metabolite, linear regression analysis was undertaken in the discovery group (excluding MZ twin pairs discordant [≥1 SD apart] for food group intake) with each food group as a predictor adjusting for age, batch effects, BMI, family relatedness and multiple testing (1.17x10^-6 = 0.05/[71 food groups x 601 detected metabolites]). Significant results were then replicated (non-targeted: P<0.05; targeted: same direction) in the MZ discordant twin group and results from both analyses meta-analyzed. We identified and replicated 180 significant associations with 39 food groups (P<1.17x10^-6), overall consisting of 106 different metabolites (74 known and 32 unknown), including 73 novel associations. In particular we identified trans-4-hydroxyproline as a potential marker of red meat intake (0.075[0.009]; P = 1.08x10^-17), ergothioneine as a marker of mushroom consumption (0.181[0.019]; P = 5.93x10^-22), and three potential markers of fruit consumption (top association: apple and pears): including metabolites derived from gut bacterial transformation of phenolic compounds, 3-phenylpropionate (0.024[0.004]; P = 1.24x10^-8) and indolepropionate (0.026[0.004]; P = 2.39x10^-9), and threitol (0.033[0.003]; P = 1.69x10^-21). With the largest nutritional metabolomics dataset to date, we have identified 73 novel candidate biomarkers of food intake for potential use in nutritional epidemiological studies. We compiled our findings into the DietMetab database (http://www.twinsuk.ac.uk/dietmetab-data/), an online tool to investigate our top associations.

Pea fiber and wheat bran fiber show distinct metabolic profiles in rats as investigated by a 1H NMR-based metabolomic approach

This study aimed to examine the effect of pea fiber (PF) and wheat bran fiber (WF) supplementation in rat metabolism. Rats were assigned randomly to one of three dietary groups and were given a basal diet containing 15% PF, 15% WF, or no supplemental fiber. Urine and plasma samples were analyzed by NMR-based metabolomics. PF significantly increased the plasma levels of 3-hydroxybutyrate, and myo-inositol as well as the urine levels of alanine, hydroxyphenylacetate, phenylacetyglycine, and α-ketoglutarate. However, PF significantly decreased the plasma levels of isoleucine, leucine, lactate, and pyruvate as well as the urine levels of allantoin, bile acids, and trigonelline. WF significantly increased the plasma levels of acetone, isobutyrate, lactate, myo-inositol, and lipids as well as the urine levels of alanine, lactate, dimethylglycine, N-methylniconamide, and α-ketoglutarate. However, WF significantly decreased the plasma levels of amino acids, and glucose as well as the urine levels of acetate, allantoin, citrate, creatine, hippurate, hydroxyphenylacetate, and trigonelline. Results suggest that PF and WF exposure can promote antioxidant activity and can exhibit common systemic metabolic changes, including lipid metabolism, energy metabolism, glycogenolysis and glycolysis metabolism, protein biosynthesis, and gut microbiota metabolism. PF can also decrease bile acid metabolism. These findings indicate that different fiber diet may cause differences in the biofluid profile in rats.

Biological system responses to zearalenone mycotoxin exposure by integrated metabolomic studies

This study aims to investigate the effect of zearalenone supplementation on rat metabolism. Rats received biweekly intragastric administration of zearalenone mycotoxin (3 mg/kg body weight) for 2 weeks. Urine and plasma samples after zearalenone administration were analyzed by NMR-based metabolomics. Zearalenone exposure significantly elevated the plasma levels of glucose, lactate, N-acetyl glycoprotein, O-acetyl glycoprotein, and propionate but reduced the plasma levels of tyrosine, branched-chain amino acids, and choline metabolites. Zearalenone supplementation decreased the urine levels of butyrate, lactate, and nicotinate. However, it increased the urine levels of allantoin, choline, and N-methylnicotinamide at 0-8 h after the last zearalenone administration and those of 1-methylhistidine, acetoacetate, acetone, and indoxyl sulfate at 8-24 h after the last zearalenone administration. These results suggest that zearalenone exposure can cause oxidative stress and change common systemic metabolic processes, including cell membrane metabolism, protein biosynthesis, glycolysis, and gut microbiota metabolism.

Liver Patt1 deficiency protects male mice from age-associated but not high-fat diet-induced hepatic steatosis

Patt1 is a newly identified protein acetyltransferase that is highly expressed in liver. However, the role of Patt1 in liver is still unclear. We generated Patt1 liver-specific knockout (LKO) mice and mainly measured the effect of hepatic Patt1 deficiency on lipid metabolism. Hepatic Patt1 deficiency in male mice markedly decreases fat mass and dramatically alleviates age-associated accumulation of lipid droplets in liver. Moreover, hepatic Patt1 abrogation in male mice significantly reduces the liver triglyceride and free fatty acid levels, but it has no effect on liver cholesterol level, liver weight, and liver function. Consistently, primary cultured Patt1-deficient hepatocytes are resistant to palmitic acid-induced lipid accumulation, but hepatic Patt1 deficiency fails to protect male mice from high-fat diet-induced hepatic steatosis. Further studies show that hepatic Patt1 deficiency decreases fatty acid uptake, reduces lipid synthesis, and enhances fatty acid oxidation, which may contribute to the attenuated hepatic steatosis in Patt1 LKO mice. These results demonstrate that Patt1 plays an important role in hepatic lipid metabolism and have implications toward resolving age-associated hepatic steatosis.

Systems responses of rats to aflatoxin B1 exposure revealed with metabonomic changes in multiple biological matrices

Exposure to aflatoxins causes liver fibrosis and hepatocellular carcinoma posing a significant health risk for human populations and livestock. To understand the mammalian systems responses to aflatoxin-B1 (AFB1) exposure, we analyzed the AFB1-induced metabonomic changes in multiple biological matrices (plasma, urine, and liver) of rats using (1)H NMR spectroscopy together with clinical biochemistry and histopathologic assessments. We found that AFB1 exposure caused significant elevation of glucose, amino acids, and choline metabolites (choline, phosphocholine, and glycerophosphocholine) in plasma but reduction of plasma lipids. AFB1 also induced elevation of liver lipids, amino acids (tyrosine, histidine, phenylalanine, leucine, isoleucine, and valine), choline, and nucleic acid metabolites (inosine, adenosine, and uridine) together with reduction of hepatic glycogen and glucose. AFB1 further caused decreases in urinary TCA cycle intermediates (2-oxoglutarate and citrate) and elevation of gut microbiota cometabolites (phenylacetylglycine and hippurate). These indicated that AFB1 exposure caused hepatic steatosis accompanied with widespread metabolic changes including lipid and cell membrane metabolisms, protein biosynthesis, glycolysis, TCA cycle, and gut microbiota functions. This implied that AFB1 exposure probably caused oxidative-stress-mediated impairments of mitochondria functions. These findings provide an overview of biochemical consequences of AFB1 exposure and comprehensive insights into the metabolic aspects of AFB1-induced hepatotoxicity in rats.

Amino acid conjugation: contribution to the metabolism and toxicity of xenobiotic carboxylic acids

Despite being the first conjugation reaction demonstrated in humans, amino acid conjugation as a route of metabolism of xenobiotic carboxylic acids is not well characterised. This is principally due to the small number and limited structural diversity of xenobiotic substrates for amino acid conjugation. Unlike CYP and uridine 5'-diphosphate glucuronosyltransferase, which are localised in the endoplasmic reticulum, the enzymes of amino acid conjugation reside in mitochondria. Unique among drug metabolism pathways, amino acid conjugation involves initial formation of a xenobiotic acyl-CoA thioester that is then conjugated principally with glycine in humans. However, formation of the xenobiotic acyl-CoA thioester does not always infer subsequent amino acid conjugation. Evidence is presented that in the absence of glycine conjugation substrates that form acyl-CoA thioesters perturb mitochondrial function. This review discusses literature on the enzymes involved and the concept that xenobiotic substrate selectivity provides a barrier to protect the metabolic integrity of the mitochondria.

Toxicokinetics and biotransformation of 3-(4-methylbenzylidene)camphor in rats after oral administration

3-(4-Methylbenzylidene)camphor (4-MBC) is an UV-filter frequently used in sunscreens and cosmetics. Equivocal findings in some screening tests for hormonal activity initiated a discussion on a possible weak estrogenicity of 4-MBC. In this study, the toxicokinetics and biotransformation of 4-MBC were characterized in rats after oral administration. Male and female Sprague-Dawley rats (n = 3 per group) were administered single oral doses of 25 or 250 mg/kg bw of 4-MBC in corn oil. Metabolites formed were characterized and the kinetics of elimination for 4-MBC and its metabolites from blood and with urine were determined. Metabolites of 4-MBC were characterized by (1)H NMR and LC-MS/MS as 3-(4-carboxybenzylidene)camphor and as four isomers of 3-(4-carboxybenzylidene)hydroxycamphor containing the hydroxyl group located in the camphor ring system with 3-(4-carboxybenzylidene)-6-hydroxycamphor as the major metabolite. After oral administration of 4-MBC, only very low concentrations of 4-MBC were present in blood and the peak concentrations of 3-(4-carboxybenzylidene)camphor were approximately 500-fold above those of 4-MBC; blood concentrations of 3-(4-carboxybenzylidene)-6-hydroxycamphor were below the limit of detection. Blood concentration of 4-MBC and 3-(4-carboxybenzylidene)camphor peaked within 10 h after 4-MBC administration and then decreased with half-lives of approximately 15 h. No major differences in peak blood levels between male and female rats were seen. In urine, one isomer of 3-(4-carboxybenzylidene)hydroxycamphor was the predominant metabolite [3-(4-carboxybenzylidene)-6-hydroxycamphor], the other isomers and 3-(4-carboxybenzylidene)camphor were only minor metabolites excreted with urine. However, urinary excretion of 4-MBC-metabolites represents only a minor pathway of elimination for 4-MBC, since most of the applied dose was recovered in feces as 3-(4-carboxybenzylidene)camphor and, to a smaller extent, as 3-(4-carboxybenzylidene)-6-hydroxycamphor. Glucuronides of both metabolites were also present in feces, but partly decomposed during sample workup and were thus not quantified. The results show that absorbed 4-MBC undergoes extensive first-pass biotransformation in rat liver resulting in very low blood levels of the parent 4-MBC. Enterohepatic circulation of glucuronides derived from the two major 4-MBC metabolites may explain the slow excretion of 4-MBC metabolites with urine and the small percentage of the administered doses recovered in urine.

Purification, characterization, and mass spectrometric sequencing of a medium chain acyl-CoA synthetase from mouse liver mitochondria and comparisons with the homologues of rat and bovine

Medium chain acyl-CoA synthetases catalyze the first reaction of amino acid conjugation of many xenobiotic carboxylic acids and fatty acid metabolism. This paper reports studies on purification, characterization, and the partial amino acid sequence of mouse liver enzyme. The medium chain acyl-CoA synthetase was isolated from mouse liver mitochondria. The purified enzyme catalyzes this reaction not only for straight medium chain fatty acids but also for aromatic and arylacetic acids. Maximal activity was found with hexanoic acid. High activities were obtained with benzoic acid having methyl, pentyl, and methoxy groups in the para- or meta-positions of the benzene ring. However, the enzyme was less active with valproic acid and ketoprofen. Salicylic acid exhibited no activity. The medium chain acyl-CoA synthetases from mouse and bovine liver mitochondria were subjected to in-gel tryptic digestion, followed by LC-MS/MS sequence analysis. The amino acid sequence of each tryptic peptide of mouse liver mitochondrial medium chain acyl-CoA synthetase differed from that from bovine liver mitochondria only in one or two amino acids. LC-MS/MS analysis provided the information about these differences in amino acid sequences. In addition, we compared the properties of this protein with the homologues from rat and bovine.

The L513S polymorphism in medium-chain acyl-CoA synthetase 2 (MACS2) is associated with risk factors of the metabolic syndrome in a Caucasian study population

Enzymes of the medium-chain acyl-CoA synthetase (MACS) family catalyze the ligation of medium chain fatty acids with CoA to produce medium-chain-acyl-CoA. At least four members of the MACS gene family are clustered on human chromosome 16p12. Association studies in the Japanese Suita cohort of MACS polymorphisms and various phenotypes revealed the contribution of the Leu513Ser polymorphism in MACS2 to multiple risk factors of the metabolic syndrome. Here, we investigated the association between this polymorphism and different risk factors in the Caucasian Metabolic Intervention Cohort Kiel. Seven hundred and sixteen male subjects aged 45-65 years were recruited for a standard oral glucose tolerance test and the postprandial assessment of metabolic parameters after an oral metabolic tolerance test (oMTT; 1017 kcal, 51.6% fat, 29.6% carbohydrates, 11.9% protein). The MACS2 Leu513Ser polymorphism was determined by TaqMan-Assay in 705 subjects. Postprandial triglyceride levels following oMTT [area under the curve (AUC)] were significantly higher in subjects carrying the Ser allele compared to subjects homozygous for the Leu allele (1690 +/- 100 mg x h/dL versus 1514 +/- 39 mg x h/dL, p = 0.04). Significant differences between genotype groups were also found for fasting (108 +/- 1.9 mg/dL versus 104 +/- 0.66 mg/dL, p = 0.04) and postprandial (AUC 535 +/- 11 versus 512 +/- 4.0, p = 0.02) glucose levels as well as for high-density-lipoprotein, body mass index, waist circumference, systolic and diastolic blood pressure. Carriers of the Ser allele also show an increased risk of impaired glucose metabolism (OR: 1.48, 95% confidence interval: 0.98-2.27, p = 0.07), adiposity (1.8, 1.16-2.81, p = 0.01) and hypertension (1.5, 0.99-2.17, p = 0.06). In conclusion, our results suggest an involvement of the MACS2 Leu513Ser polymorphism in the development of the metabolic syndrome in Caucasian population. Additionally, the higher triglyceride and glucose levels after an oMTT support a possible functional impact of the polymorphism in vivo.

Possible mechanism for species difference on the toxicity of pivalic acid between dogs and rats

In a high dose toxicity study of pivalic acid (PA), PA caused skeletal muscle disorder in dog, and a significant increase of pivaloyl carnitine (PC) was observed in canine muscle, but not in rat muscle. In order to understand species difference of the toxicity of PA, we compared the in vitro metabolism of PA among dog, rat and rabbit, especially focussing on the carnitine conjugate. Canine muscle showed low, but significant carnitine conjugating activity, while that of rat was negligible. Canine kidney mitochondria had significant activity in the pivaloyl CoA synthesis (7 nmol/mg protein/h), but muscle mitochondria showed only trace activity. Both kidney and muscle mitochondria displayed similar carnitine acyltransferase activity (2-3 nmol/mg protein/h) towards pivaloyl CoA. On the other hand, with respect to the activity of carnitine acyltransferase in the reverse direction using PC as substrate, canine muscle mitochondria showed higher activity than that of kidney mitochondria. This means that PC is not the final stable metabolite, but is converted easily to pivaloyl CoA in canine muscle. These results suggest one of the possible mechanisms for canine selective muscle disorder to be as follows. Only canine muscle can metabolize PA to its carnitine conjugate slowly, but significantly. In canine muscle, PC is not the final stable metabolite; it is easily converted to pivaloyl CoA. As carnitine conjugation is thought to be the only detoxification metabolic route in canine muscle, under certain circumstances such as carnitine deficiency, the risk of exposure with toxic pivaloyl CoA might increase and the CoASH pool in canine muscle might be exhausted, resulting in toxicity in canine muscle.

Elucidation of the mechanism of inhibition of cyclooxygenases by acyl-coenzyme A and acylglucuronic conjugates of ketoprofen

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit the cyclooxygenase (COX) isoforms which accounts for their clinical effects. The differential inhibition of COX-1 and COX-2 is not sufficient to explain the absence of a correlation between in vitro and in vivo effects, especially for 2-aryl-propionates, thus indicating the participation of metabolites. Conjugates to glucuronic acid and to coenzyme-A are mainly produced, and have been shown to be chemically reactive. Therefore, we studied the interaction of the ketoprofen metabolites with the COX enzymes. After incubation with bovine pulmonary artery endothelial cells (BPAEC), COX-1 was inhibited stereoselectively by S-ketoprofen acylglucuronide, and more significantly by CoA-thioester. After washing-out the medium, COX-1 activity was essentially recovered, indicating a reversible inhibition. In LPS-stimulated J774.2 cells, COX activity (mainly inducible COX-2) was inhibited reversibly and stereospecifically by S-ketoprofen glucuronide, whereas it disappeared totally and was not recovered after incubation with CoA-thioester. Correspondingly, inhibition of purified COX-2 with this compound was observed to be rapid and irreversible. Using an anti-ketoprofen antibody, COX immunoprecipitated from cells exhibited adduct formation for COX-2 but not for COX-1. This was observed after incubation with CoA-thioester, and, surprisingly, also with glucuronide. Molecular docking gave support to explain this discrepancy: the glucuronide was found to establish a strong interaction with Y115 located in the membrane binding domain, whereas the thioester was preferentially bound to the active site of the enzyme. Overall, our results suggest a contribution of CoA-thioester metabolites of carboxylic NSAIDs to their pharmacological action by irreversibly and selectively inhibiting COX-2.

Nitrile pathway involving acyl-CoA synthetase: overall metabolic gene organization and purification and characterization of the enzyme

Two open reading frames (nhpS and acsA) were identified immediately downstream of the previously described Pseudomonas chlororaphis B23 nitrile hydratase (NHase) gene cluster (encoding aldoxime dehydratase, amidase, the two NHase subunits, and an uncharacterized protein). The amino acid sequence deduced from acsA shows similarity to that of acyl-CoA synthetase (AcsA). The acsA gene product expressed in Escherichia coli showed acyl-CoA synthetase activity toward butyric acid and CoA as substrates, with butyryl-CoA being synthesized. From the E. coli transformant, AcsA was purified to homogeneity and characterized. The quality of the recombinant protein was verified by the NH2-terminal amino acid sequence and the results of matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The apparent Km values for butyric acid, CoA, and ATP were 0.32 +/- 0.04, 0.37 +/- 0.02, and 0.22 +/- 0.02 mm, respectively. AcsA was shown to be a short-chain acyl-CoA synthetase, according to the catalytic efficiencies (kcat/Km) for various acids. The substrate specificity of AcsA was similar to those of aldoxime dehydratase, NHase, and amidase, the genes of which coexist in the same orientation in the gene cluster. P. chlororaphis B23 grew when cultured in a medium containing butyraldoxime as the sole carbon and nitrogen source. The activities of aldoxime dehydratase, NHase, and amidase were detected together with that of acyl-CoA synthetase under the culture conditions used. Moreover, on culture in a medium containing butyric acid as the sole carbon source, acyl-CoA synthetase activity was also detected. Together with the adjacent locations of the aldoxime dehydratase, NHase, amidase, and acyl-CoA synthetase genes, these findings suggest that the four enzymes are sequentially correlated with one another in vivo to utilize butyraldoxime as a carbon and nitrogen source. This is the first report of an overall "nitrile pathway" (aldoxime-->nitrile-->amide-->acid-->acyl-CoA) comprising these enzymes.

Molecular identification and characterization of two medium-chain acyl-CoA synthetases, MACS1 and the Sa gene product

In this study, we identified and characterized two murine cDNAs encoding medium-chain acyl-CoA synthetase (MACS). One, designated MACS1, is a novel protein and the other the product of the Sa gene (Sa protein), which is preferentially expressed in spontaneously hypertensive rats. Based on the murine MACS1 sequence, we also identified the location and organization of the human MACS1 gene, showing that the human MACS1 and Sa genes are located in the opposite transcriptional direction within a 150-kilobase region on chromosome 16p13.1. Murine MACS1 and Sa protein were overexpressed in COS cells, purified to homogeneity, and characterized. Among C4-C16 fatty acids, MACS1 preferentially utilizes octanoate, whereas isobutyrate is the most preferred fatty acid among C2-C6 fatty acids for Sa protein. Like Sa gene transcript, MACS1 mRNA was detected mainly in the liver and kidney. Subcellular fractionation revealed that both MACS1 and Sa protein are localized in the mitochondrial matrix. (14)C-Fatty acid incorporation studies indicated that acyl-CoAs produced by MACS1 and Sa protein are utilized mainly for oxidation.

Inhibitory effect of quinolone antimicrobial and nonsteroidal anti-inflammatory drugs on a medium chain acyl-CoA synthetase

The inhibitory effects of quinolone antimicrobial agents and nonsteroidal anti-inflammatory drugs on purified mouse liver mitochondrial medium chain acyl-CoA synthetase catalyzing the first reaction of glycine conjugation were examined, using hexanoic acid as a substrate. Enoxacin, ofloxacin, nalidixic acid, diflunisal, salicylic acid, 2-hydroxynaphthoic acid, and 2-hydroxydodecanoic acid, which do not act as substrates, were potent inhibitors. Diflunisal, nalidixic acid, salicylic acid, 2-hydroxynaphthoic acid, and 2-hydroxydodecanoic acid inhibited competitively this medium chain acyl-CoA synthetase with K(i) values of 0.6, 12.4, 19.6, 13.4, and 15.0 microM, respectively. Enoxacin and ofloxacin inhibited this medium chain acyl-CoA synthetase in a mixed-type manner with K(i) values of 23.7 and 38.2 microM, respectively. Felbinac, which is a substrate, inhibited the activity of this medium chain acyl-CoA synthetase for hexanoic acid (IC50 = 25 microM). The concomitant presence of enoxacin and felbinac strongly inhibited this medium chain acyl-CoA synthetase. These findings indicate that medium chain acyl-CoA synthetases may be influenced by quinolone antimicrobial and nonsteroidal anti-inflammatory drugs.

Expression of rat liver long-chain acyl-CoA synthetase and characterization of its role in the metabolism of R-ibuprofen and other fatty acid-like xenobiotics

Our investigations of fatty acid metabolism and epimerization of the 2-arylpropionic acid derivative, R-ibuprofen, resulted in the successful purification of an acyl-CoA synthetase from rat liver microsomes that catalyzes the formation of both palmitoyl-CoA and R-ibuprofenoyl-CoA. To investigate whether R-ibuprofenoyl-CoA synthetase and long-chain acyl-CoA synthetase (LACS) are identical enzymes, we cloned the cDNA from LACS into the pQE30 expression vector and transformed the construct into Escherichia coli M15[pREP4]. Induction of the bacterial protein synthesis with 0.2 mM isopropyl-beta-D-galactoside resulted in a strong, time-dependent increase in LACS protein as determined by Western blot analysis using a polyclonal rabbit anti-LACS antibody. Incubations of the recombinantly expressed protein with palmitic acid as physiological LACS substrate or R-ibuprofen in the presence of Mg2+, ATP, and CoA resulted in a 5-fold increase in the thioesterification of both substrates. Western blot analysis using tissue homogenates of rat liver, heart, kidney, lung, brain, and ileum showed that LACS was found in every tissue investigated, with the greatest expression in the liver. Similar results were obtained with activity measurements using R-ibuprofen and palmitic acid as substrates. Northern blot analysis revealed a hybridization with a 3.8-kb mRNA transcript in rat liver, heart, and kidney, but no signal was observed in lung, brain and ileum, suggesting the expression of different LACS isoform(s) in these organs. In summary, our results further show that R-ibuprofenoyl-CoA synthetase and long-chain acyl-CoA synthetase are identical enzymes that are involved in the metabolism of various xenobiotics.

Difference of the liver and kidney in glycine conjugation of ortho-substituted benzoic acids

The relative importance of the liver and kidney for glycine conjugation of ortho-substituted benzoic acids was investigated. Glycine conjugation of ortho-substituted benzoic acids was investigated in mouse liver and kidney mitochondria. The extent of glycine conjugation of benzoic acids with the halogen group decreased in the order F > Cl > Br > I. The conjugation of salicylic acid with glycine took place in only the kidney. 2-Methoxybenzoic acid exhibited no activity in the liver and kidney. The difference in glycine conjugation of ortho-substituted benzoic acids was observed between liver and kidney. The kidney was more active in glycine conjugation of ortho-substituted acids than the liver. In addition, the relationship between glycine conjugation and the chemical structure of ortho-substituted acids was examined in the liver and kidney. The size of the substituent had a far greater influence over glycine conjugation in the liver and kidney. Glycine conjugation was also dependent on the substituent electronegativity. It may be important that the substrates undergoing glycine conjugation contain a flat region coplanar to the carboxylate group.

The distribution of aminoacylase I among mammalian species and localization of the enzyme in porcine kidney

Aminoacylase I (Acy-1, EC 3.5.1.14) is found in many mammalian tissues, with highest activities occurring in kidney. The enzyme hydrolyzes a variety of N-acylated amino acids; however, the physiological role and the exact cellular localization of Acy-1 are still a matter of debate. The comparison of Acy-1 activities in kidney and liver homogenates of 11 mammalian species showed that the enzyme is most abundant in true herbivores such as sheep and cattle as well as in omnivores, while activities were very low in both rodents and the cat. Acy-1 activity was not detected in livers of dogs of five different breeds. Using in situ hybridization of porcine kidney sections with DIG-labeled RNA probes, Acy-1 mRNA was shown to be evenly distributed throughout the tubular system, while glomeruli and the interstitium were free of stain. During subcellular fractionation, porcine Acy-1 behaved like a typical cytosolic enzyme. Commonly, Acy-1 is thought to catalyze hydrolytic reactions, i.e., the formation of free amino acids from acylated derivatives. Based on the present results and literature data, we propose a novel hypothesis, i.e., that Acy-1 catalyzes the synthesis (rather than the hydrolysis) of hippurate that is formed as a detoxification product of aromatic compounds.

Characterization of a renal medium chain acyl-CoA synthetase responsible for glycine conjugation in mouse kidney mitochondria

Glycine conjugation of a series of benzoic acid derivatives was investigated in mouse kidney mitochondria. The chlorine and methyl substitutions in the para- and meta-positions of the benzene ring yielded an increase in glycine conjugation. The acids with a methoxy group showed a low degree of glycine conjugation. In addition, the acids with nitro or amino groups were conjugated to a slight extent with glycine. The in vitro conjugation of salicylic acid with glycine occurred not in liver but in kidney. The specificity of the renal medium chain acyl-CoA synthetase catalyzing the first reaction of glycine conjugation was also examined. The enzyme accepted not only medium chain fatty acids but also aromatic and arylacetic acids. The highest activity was shown with hexanoic acid. High activities were observed for benzoic acid derivatives with alkyl and alkoxyl groups in the para- and meta-positions of the benzene ring. An ortho-substituted acid exhibited no activity. In addition, the enzyme was less active with valproic acid, tranexamic acid, indomethacin and ketoprofen. The enzyme was inhibited by diflunisal, 2-hydroxydodecanoic acid and salicylic acid, which did not act as substrates. There was a poor correlation between the activity of the medium chain acyl-CoA synthetase and glycine conjugation of eleven substituted benzoic acids. These findings suggest that the present medium chain acyl-CoA synthetase is involved in glycine conjugation of the substituted acids in mouse kidney mitochondria, but there may be a larger contribution of another isoenzyme.

Stereoselective disposition of tiaprofenic acid enantiomers in rats

The pharmacokinetics and metabolic chiral inversion of the S(+)- and R(-)-enantiomers of tiaprofenic acid (S-TIA, R-TIA) were assessed in vivo in rats, and in addition the biochemistry of inversion was investigated in vitro in rat liver homogenates. Drug enantiomer concentrations in plasma were investigated following administration of S-TIA and R-TIA (i.p. 3 and 9 mg/kg) over 24 hr. Plasma concentrations of TIA enantiomers were determined by stereospecific HPLC analysis. After administration of R-TIA it was found that 1) there was a time delay of peak S-TIA plasma concentrations, 2) S-TIA concentrations exceeded R-TIA concentrations from approximately 2 hr after dosing, 3) Cmax and AUC(0-infinity) for S-TIA were greater than for R-TIA following administration of S-TIA, and 4) inversion was bidirectional but favored inversion of R-TIA to S-TIA. Bidirectional inversion was also observed when TIA enantiomers were incubated with liver homogenates up to 24 hr. However, the rate of inversion favored transformation of the R-enantiomer to the S-enantiomer. In conclusion, stereoselective pharmacokinetics of R- and S-TIA were observed in rats and bidirectional inversion in rat liver homogenates has been demonstrated for the first time. Chiral inversion of TIA may involve metabolic routes different from those associated with inversion of other 2-arylpropionic acids such as ibuprofen.

Molecular specificity of a medium chain acyl-CoA synthetase for substrates and inhibitors: conformational analysis

Amino acid conjugation is an important route of detoxification of xenobiotic and endogenous carboxylic acids. The specificity of the purified medium chain acyl-CoA synthetase catalyzing the first reaction of amino acid conjugation was investigated further for substrates and inhibitors. Molecular modeling techniques were applied to derive the molecular characteristics of substrates and inhibitors for the medium chain acyl-CoA synthetase. The purified enzyme accepted not only straight medium chain fatty acids but also aromatic acids. Of the arylacetic acids, activity was obtained with naphthylacetic acids, whereas introduction of a methyl group at the alpha-position caused loss of activity. High activity was also observed with cyclohexanoic acid. Diflunisal, 2-hydroxydodecanoic acid, and nalidixic acid inhibited the medium chain acyl-CoA synthetase activity for hexanoic acid, with Ki values of 0.8, 4.4, and 12.3 microM, respectively. The inhibitory carboxylic acids were competitive with respect to hexanoic acid. The hydroxyl or ketone (oxo) groups at the beta-position of carboxylic acids were an important determinant for inhibitory activity. All substrates and inhibitors contained a flat hydrophobic region coplanar to the carboxylate group. In addition, the substrates had negative values for charge on the carbon in the beta-position of carboxylic acids.

Inhibition of a medium chain acyl-CoA synthetase involved in glycine conjugation by carboxylic acids

Molecular characteristics of carboxylic acids were investigated for the ability to inhibit a purified medium chain acyl-CoA synthetase, using hexanoic acid as a substrate. Salicylic acid, 4-methylsalicylic acid, 2-hydroxynaphtoic acid, and 2-hydroxyoctanoic acid, which do not act as substrates for the medium chain acyl-CoA synthetase, were potent as inhibitors. Valproic acid was not an inhibitor. Salicylic acid, 2-hydroxynaphthoic acid, and 2-hydroxyoctanoic acid inhibited the medium chain acyl-CoA synthetase with Ki values of 37, 5.2, and 500 microM, respectively. 4-Methylsalicylic acid was more potent than salicylic acid. The inhibitory carboxylic acids were competitive with respect to hexanoic acid. The distance of the hydroxyl group from the carboxylic acid group of the benzene ring influenced the inhibitory activity. The hydroxyl group on the carbon adjacent to the carboxylic acid group was required for inhibitory activity. In addition, there was a good correlation between the lipophilicity of the carboxylic acids and the Ki values, suggesting that the lipophilicity of the carboxylic acids is a major determinant for inhibition of the medium chain acyl-CoA synthetase.