Peroxisome-proliferator regulates key enzymes of the tryptophan-NAD+ pathway

Mitochondrial targets in hyperammonemia: Addressing urea cycle function to improve drug therapies

The urea cycle (UC) is a critically important metabolic process for the disposal of nitrogen (ammonia) produced by amino acids catabolism. The impairment of this liver-specific pathway induced either by primary genetic defects or by secondary causes, namely those associated with hepatic disease or drug administration, may result in serious clinical consequences. Urea cycle disorders (UCD) and certain organic acidurias are the major groups of inherited rare diseases manifested with hyperammonemia (HA) with UC dysregulation. Importantly, several commonly prescribed drugs, including antiepileptics in monotherapy or polytherapy from carbamazepine to valproic acid or specific antineoplastic agents such as asparaginase or 5-fluorouracil may be associated with HA by mechanisms not fully elucidated. HA, disclosing an imbalance between ammoniagenesis and ammonia disposal via the UC, can evolve to encephalopathy which may lead to significant morbidity and central nervous system damage. This review will focus on biochemical mechanisms related with HA emphasizing some poorly understood perspectives behind the disruption of the UC and mitochondrial energy metabolism, namely: i) changes in acetyl-CoA or NAD+ levels in subcellular compartments; ii) post-translational modifications of key UC-related enzymes, namely acetylation, potentially affecting their catalytic activity; iii) the mitochondrial sirtuins-mediated role in ureagenesis. Moreover, the main UCD associated with HA will be summarized to highlight the relevance of investigating possible genetic mutations to account for unexpected HA during certain pharmacological therapies. The ammonia-induced effects should be avoided or overcome as part of safer therapeutic strategies to protect patients under treatment with drugs that may be potentially associated with HA.

Identification of Protective Amino Acid Metabolism Events in Nursery Pigs Fed Thermally Oxidized Corn Oil

Feeding thermally oxidized lipids to pigs has been shown to compromise growth and health, reduce energy digestibility, and disrupt lipid metabolism. However, the effects of feeding oxidized lipids on amino acid metabolism in pigs have not been well defined even though amino acids are indispensable for the subsistence of energy metabolism, protein synthesis, the antioxidant system, and many other functions essential for pig growth and health. In this study, oxidized corn oil (OCO)-elicited changes in amino acid homeostasis of nursery pigs were examined by metabolomics-based biochemical analysis. The results showed that serum and hepatic free amino acids and metabolites, including tryptophan, threonine, alanine, glutamate, and glutathione, as well as associated metabolic pathways, were selectively altered by feeding OCO, and more importantly, many of these metabolic events possess protective functions. Specifically, OCO activated tryptophan-nicotinamide adenosine dinucleotide (NAD⁺) synthesis by the transcriptional upregulation of the kynurenine pathway in tryptophan catabolism and promoted adenine nucleotide biosynthesis. Feeding OCO induced oxidative stress, causing decreases in glutathione (GSH)/oxidized glutathione (GSSG) ratio, carnosine, and ascorbic acid in the liver but simultaneously promoted antioxidant responses as shown by the increases in hepatic GSH and GSSG as well as the transcriptional upregulation of GSH metabolism-related enzymes. Moreover, OCO reduced the catabolism of threonine to α-ketobutyrate in the liver by inhibiting the threonine dehydratase (TDH) route. Overall, these protective metabolic events indicate that below a certain threshold of OCO consumption, nursery pigs are capable of overcoming the oxidative stress and metabolic challenges posed by the consumption of oxidized lipids by adjusting antioxidant, nutrient, and energy metabolism, partially through the transcriptional regulation of amino acid metabolism.

Association of Drug-Metabolizing Enzyme and Transporter Gene Polymorphisms and Lipid-Lowering Response to Statins in Thai Patients with Dyslipidemia

Purpose

Statins are increasingly widely used in the primary and secondary prevention of cardiovascular disease. However, there is an inter-individual variation in statin response among patients. The study aims to determine the association between genetic variations in drug-metabolizing enzyme and transporter (DMET) genes and lipid-lowering response to a statin in Thai patients with hyperlipidemia.

Patients and Methods

Seventy-nine patients who received statin at steady-state concentrations were recruited. Serum lipid profile was measured at baseline and repeated after 4-month on a statin regimen. The genotype profile of 1936 DMET markers was obtained using Affymetrix DMET Plus genotyping microarrays.

Results

In this DMET microarray platform, five variants; SLCO1B3 (rs4149117, rs7311358, and rs2053098), QPRT (rs13331798), and SLC10A2 (rs188096) showed a suggestive association with LDL-cholesterol-lowering response. HDL-cholesterol-lowering responses were found to be related to CYP7A1 gene variant (rs12542233). Seven variants, SLCO1B3 (rs4149117, rs7311358, and rs2053098); SULT1E1 (rs3736599 and rs3822172); and ABCB11 (rs4148768 and rs3770603), were associated with the total cholesterol-lowering response. One variant of the ABCB4 gene (rs2109505) was significantly associated with triglyceride-lowering response.

Conclusion

This pharmacogenomic study identifies new genetic variants of DMET genes that are associated with the lipid-lowering response to statins. Genetic polymorphisms in DMET genes may impact the pharmacokinetics and lipid-lowering response to statin. The validation studies confirmations are needed in future pharmacogenomic studies.

Activation of PPARα-catalase pathway reverses alcoholic liver injury via upregulating NAD synthesis and accelerating alcohol clearance

Alcohol metabolism in the liver simultaneously generates toxic metabolites and disrupts redox balance, but the regulatory mechanisms have not been fully elucidated. The study aimed to characterize the role of PPARα in alcohol detoxification. Hepatic PPARα and catalase levels were examined in patients with severe alcoholic hepatitis. Mouse studies were conducted to determine the effect of PPARα reactivation by Wy14,643 on alcoholic hepatotoxicity and how catalase is involved in mediating such effects. Cell culture study was conducted to determine the effect of hydrogen peroxide on cellular NAD levels. We found that the protein levels of PPARα and catalase were significantly reduced in the livers of patients with severe alcoholic hepatitis. PPARα reactivation by Wy14,643 effectively reversed alcohol-induced liver damage in mice. Global and targeted metabolites analysis revealed a fundamental role of PPARα in regulating the tryptophan-NAD pathway. Notably, PPARα activation completely switched alcohol metabolism from the CYP2E1 pathway to the catalase pathway along with accelerated alcohol clearance. Catalase knockout mice were incompetent in alcohol metabolism and hydrogen peroxide clearance and were more susceptible to alcohol-induced liver injury. Hydrogen peroxide-treated hepatocytes had a reduced size of cellular NAD pool. These data demonstrate a key role of PPARα in regulating hepatic alcohol detoxification. Catalase-mediated hydrogen peroxide removal represents an underlying mechanism of how PPARα preserves the NAD pool. The study provides a new angle of view about the PPARα-catalase pathway in combating alcohol toxicity.

Microbiome-Derived Metabolites in Allogeneic Hematopoietic Stem Cell Transplantation

The gut microbiome has emerged as a major character in the context of hematopoietic stem cell transplantation. The biology underpinning this relationship is still to be defined. Recently, mounting evidence has suggested a role for microbiome-derived metabolites in mediating crosstalk between intestinal microbial communities and the host. Some of these metabolites, such as fiber-derived short-chain fatty acids or amino acid-derived compounds, were found to have a role also in the transplant setting. New interesting data have been published on this topic, posing a new intriguing perspective on comprehension and treatment. This review provides an updated comprehensive overview of the available evidence in the field of gut microbiome-derived metabolites and hematopoietic stem cell transplantation.

Hepatic steatosis induced in C57BL/6 mice by a non-ß oxidizable fatty acid analogue is associated with reduced plasma kynurenine metabolites and a modified hepatic NAD+/NADH ratio

Background

Non-alcoholic fatty liver disease is often associated with obesity, insulin resistance, dyslipidemia, and the metabolic syndrome in addition to mitochondrial dysfunction and nicotinamide adenine dinucleotide (NAD⁺) deficiency. The aim of this study was to investigate how inhibition of mitochondrial fatty acid oxidation using the compound tetradecylthiopropionic acid (TTP) would affect hepatic triacylglycerol level and plasma levels of kynurenine (Kyn) metabolites and nicotinamide.

Methods

12 C57BL/6 mice were fed a control diet, or an intervention diet supplemented with 0.9% (w/w) tetradecylthiopropionic acid for 14 days. Blood and liver samples were collected, enzyme activities and gene expression were analyzed in liver, in addition to fatty acid composition. Metabolites in the tryptophan/kynurenine pathway and total antioxidant status were measured in plasma.

Results

Dietary treatment with tetradecylthiopropionic acid for 2 weeks induced fatty liver accompanied by decreased mitochondrial fatty acid oxidation. The liver content of the oxidized form of NAD⁺ was increased, as well as the ratio of NAD⁺/NADH, and these changes were associated by increased hepatic mRNA levels of NAD synthetase and nicotinamide mononucleotide adenyltransferase-3. The downstream metabolites of kynurenine were reduced in plasma whereas the plasma nicotinamide content was increased. Some effects on inflammation and oxidative stress was observed in the liver, while the plasma antioxidant capacity was increased. This was accompanied by a reduced plasma ratio of kynurenine/tryptophan. In addition, a significant decrease in the inflammation-related arachidonic fatty acid in liver was observed.

Conclusion

Fatty liver induced by short-time treatment with tetradecylthiopropionic acid decreased the levels of kynurenine metabolites but increased the plasma levels of NAD⁺ and nicotinamide. These changes are most likely not associated with increased inflammation and oxidative stress. Most probably the increase of NAD⁺ and nicotinamide are generated through the Preiss Handler pathway and/or salvage pathway and not through the de novo pathway.

The take home message is that non-alcoholic fatty liver disease is associated with the metabolic syndrome in addition to mitochondrial dysfunction and nicotinamide adenine dinucleotide (NAD⁺) deficiency. Inducing fatty liver in mice by inhibition of fatty acid oxidation resulted in a concomitant change in kynurenine metabolites increasing the plasma levels of nicotinamides and the hepatic NAD⁺/NADH ratio, probably without affecting the de novo pathway of kynurenines.

Short-term treatment with a peroxisome proliferator-activated receptor α agonist influences plasma one-carbon metabolites and B-vitamin status in rats

INTRODUCTION

Peroxisome proliferator-activated receptors (PPARs) have been suggested to be involved in the regulation of one-carbon metabolism. Previously we have reported effects on plasma concentrations of metabolites along these pathways as well as markers of B-vitamin status in rats following treatment with a pan-PPAR agonist. Here we aimed to investigate the effect on these metabolites after specific activation of the PPARα and PPARγ subtypes.

METHODS

For a period of 12 days, Male Wistar rats (n = 20) were randomly allocated to receive treatment with the PPARα agonist WY-14.643 (n = 6), the PPARγ agonist rosiglitazone (n = 6) or placebo (n = 8). The animals were sacrificed under fasting conditions, and plasma concentration of metabolites were determined. Group differences were assessed by one-way ANOVA, and planned comparisons were performed for both active treatment groups towards the control group.

RESULTS

Treatment with a PPARα agonist was associated with increased plasma concentrations of most biomarkers, with the most pronounced differences observed for betaine, dimethylglycine, glycine, nicotinamide, methylnicotinamide, pyridoxal and methylmalonic acid. Lower levels were observed for flavin mononucleotide. Fewer associations were observed after treatment with a PPARγ agonist, and the most notable was increased plasma serine.

CONCLUSION

Treatment with a PPARα agonist influenced plasma concentration of one-carbon metabolites and markers of B-vitamin status. This confirms previous findings, suggesting specific involvement of PPARα in the regulation of these metabolic pathways as well as the status of closely related B-vitamins.

PPARα contributes to protection against metabolic and inflammatory derangements associated with acute kidney injury in experimental sepsis

Sepsis-associated acute kidney injury (AKI) is a significant problem in critically ill children and adults resulting in increased morbidity and mortality. Fundamental mechanisms contributing to sepsis-associated AKI are poorly understood. Previous research has demonstrated that peroxisome proliferator-activated receptor α (PPARα) expression is associated with reduced organ system failure in sepsis. Using an experimental model of polymicrobial sepsis, we demonstrate that mice deficient in PPARα have worse kidney function, which is likely related to reduced fatty acid oxidation and increased inflammation. Ultrastructural evaluation with electron microscopy reveals that the proximal convoluted tubule is specifically injured in septic PPARα deficient mice. In this experimental group, serum metabolomic analysis reveals unanticipated metabolic derangements in tryptophan-kynurenine-NAD+ and pantothenate pathways. We also show that a subgroup of children with sepsis whose genome-wide expression profiles are characterized by repression of the PPARα signaling pathway has increased incidence of severe AKI. These findings point toward interesting associations between sepsis-associated AKI and PPARα-driven fatty acid metabolism that merit further investigation.

Alpha-Amino-Beta-Carboxy-Muconate-Semialdehyde Decarboxylase Controls Dietary Niacin Requirements for NAD+ Synthesis

NAD⁺ is essential for redox reactions in energy metabolism and necessary for DNA repair and epigenetic modification. Humans require sufficient amounts of dietary niacin (nicotinic acid, nicotinamide, and nicotinamide riboside) for adequate NAD⁺ synthesis. In contrast, mice easily generate sufficient NAD⁺ solely from tryptophan through the kynurenine pathway. We show that transgenic mice with inducible expression of human alpha-amino-beta-carboxy-muconate-semialdehyde decarboxylase (ACMSD) become niacin dependent similar to humans when ACMSD expression is high. On niacin-free diets, these acquired niacin dependency (ANDY) mice developed reversible, mild-to-severe NAD⁺ deficiency, depending on the nutrient composition of the diet. NAD deficiency in mice contributed to behavioral and health changes that are reminiscent of human niacin deficiency. This study shows that ACMSD is a key regulator of mammalian dietary niacin requirements and NAD⁺ metabolism and that the ANDY mouse represents a versatile platform for investigating pathologies linked to low NAD⁺ levels in aging and neurodegenerative diseases.

Identification of activation of tryptophan-NAD+ pathway as a prominent metabolic response to thermally oxidized oil through metabolomics-guided biochemical analysis

Consumption of thermally oxidized oil is associated with metabolic disorders, but oxidized oil-elicited changes in the metabolome are not well defined. In this study, C57BL/6 mice were fed the diets containing either control soybean oil or heated soybean oil (HSO) for 4 weeks. HSO-responsive metabolic events were examined through untargeted metabolomics-guided biochemical analysis. HSO directly contributed to the presence of new HSO-derived metabolites in urine and the decrease of polyunsaturated fatty acid-containing phospholipids in serum and the liver. HSO disrupted redox balance by decreasing hepatic glutathione and ascorbic acid. HSO also activated peroxisome proliferator-activated receptors, leading to the decrease of serum triacylglycerols and the changes of cofactors and products in fatty acid oxidation pathways. Most importantly, multiple metabolic changes, including the decrease of tryptophan in serum; the increase of NAD⁺ in the liver; the increases of kynurenic acid, nicotinamide and nicotinamide N-oxide in urine; and the decreases of the metabolites from pyridine nucleotide degradation in the liver indicated that HSO activated tryptophan-NAD⁺ metabolic pathway, which was further confirmed by the upregulation of gene expression in this pathway. Because NAD⁺ and its metabolites are essential cofactors in many HSO-induced metabolic events, the activation of tryptophan-NAD⁺ pathway should be considered as a central metabolic response to the exposure of HSO.

Peroxisome Proliferator-Activated Receptor Activation is Associated with Altered Plasma One-Carbon Metabolites and B-Vitamin Status in Rats

Plasma concentrations of metabolites along the choline oxidation pathway have been linked to increased risk of major lifestyle diseases, and peroxisome proliferator-activated receptors (PPARs) have been suggested to be involved in the regulation of key enzymes along this pathway. In this study, we investigated the effect of PPAR activation on circulating and urinary one-carbon metabolites as well as markers of B-vitamin status. Male Wistar rats (n = 20) received for 50 weeks either a high-fat control diet or a high-fat diet with tetradecylthioacetic acid (TTA), a modified fatty acid and pan-PPAR agonist with high affinity towards PPARα. Hepatic gene expression of PPARα, PPARβ/δ and the enzymes involved in the choline oxidation pathway were analyzed and concentrations of metabolites were analyzed in plasma and urine. TTA treatment altered most biomarkers, and the largest effect sizes were observed for plasma concentrations of dimethylglycine, nicotinamide, methylnicotinamide, methylmalonic acid and pyridoxal, which were all higher in the TTA group (all p < 0.01). Hepatic Pparα mRNA was increased after TTA treatment, but genes of the choline oxidation pathway were not affected. Long-term TTA treatment was associated with pronounced alterations on the plasma and urinary concentrations of metabolites related to one-carbon metabolism and B-vitamin status in rats.

Regulation of NAD biosynthetic enzymes modulates NAD-sensing processes to shape mammalian cell physiology under varying biological cues

In addition to its role as a redox coenzyme, NAD is a substrate of various enzymes that split the molecule to either catalyze covalent modifications of target proteins or convert NAD into biologically active metabolites. The coenzyme bioavailability may be significantly affected by these reactions, with ensuing major impact on energy metabolism, cell survival, and aging. Moreover, through the activity of the NAD-dependent deacetylating sirtuins, NAD behaves as a beacon molecule that reports the cell metabolic state, and accordingly modulates transcriptional responses and metabolic adaptations. In this view, NAD biosynthesis emerges as a highly regulated process: it enables cells to preserve NAD homeostasis in response to significant NAD-consuming events and it can be modulated by various stimuli to induce, via NAD level changes, suitable NAD-mediated metabolic responses. Here we review the current knowledge on the regulation of mammalian NAD biosynthesis, with focus on the relevant rate-limiting enzymes. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.

Regulation of rat hepatic α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase, a key enzyme in the tryptophan- NAD pathway, by dietary cholesterol and sterol regulatory element-binding protein-2

PURPOSE

Nicotinic acid is one of the older drugs used to treat hyperlipidemia, the greatest risk factor of coronary heart disease. Nicotinic acid is also a precursor of the coenzyme nicotinamide adenine dinucleotide (NAD). In mammals, α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) plays a key role in NAD biosynthesis from tryptophan. However, the relationship between ACMSD and cholesterol metabolism has not been clarified enough yet. The present study was performed to make clear the relationship between ACMSD and cholesterol metabolism using hypercholesterolemic rats and rat primary hepatocytes.

METHODS

Male Sprague-Dawley rats were fed a diet containing cholesterol for 10 days to induce hypercholesterolemia. The NAD levels in the plasma and liver and hepatic ACMSD activity were determined. In vitro study, the expression of ACMSD and the transcriptional factors that regulate cholesterol metabolism were determined using rat primary hepatocytes treated with cholesterol and 25-hydroxycholesterol or simvastatin, a statin medication, by quantitative real-time PCR analysis and Western blotting analysis.

RESULTS

The hepatic NAD level of the hypercholesterolemic group was significantly higher than the control, and the hepatic ACMSD activity of this group was significantly suppressed. There was a significant negative correlation between the hepatic ACMSD activity and liver cholesterol levels. Additionally, in primary rat hepatocytes treated with cholesterol and 25-hydroxycholesterol or simvastatin, ACMSD gene and protein expression was subjected to sterol-dependent regulation. This gene expression changed in parallel to sterol regulatory element-binding protein (SREBP)-2 expression.

CONCLUSION

These results provide the first evidence that ACMSD is associated with cholesterol metabolism, and ACMSD gene expression may be upregulated by SREBP-2.

Hepatic sirtuin 1 is dispensable for fibrate-induced peroxisome proliferator-activated receptor-α function in vivo

Peroxisome proliferator-activated receptor-α (PPARα) mediates metabolic remodeling, resulting in enhanced mitochondrial and peroxisomal β-oxidation of fatty acids. In addition to the physiological stimuli of fasting and high-fat diet, PPARα is activated by the fibrate class of drugs for the treatment of dyslipidemia. Sirtuin 1 (SIRT1), an important regulator of energy homeostasis, was downregulated in fibrate-treated wild-type mice, suggesting PPARα regulation of Sirt1 gene expression. The impact of SIRT1 loss on PPARα functionality in vivo was assessed in hepatocyte-specific knockout mice that lack the deacetylase domain of SIRT1 (Sirt1(ΔLiv)). Knockout mice were treated with fibrates or fasted for 24 h to activate PPARα. Basal expression of the PPARα target genes Cyp4a10 and Cyp4a14 was reduced in Sirt1(ΔLiv) mice compared with wild-type mice. However, no difference was observed between wild-type and Sirt1(ΔLiv) mice in either fasting- or fibrate-mediated induction of PPARα target genes. Similar to the initial results, there was no difference in fibrate-activated PPARα gene induction. To assess the relationship between SIRT1 and PPARα in a pathophysiological setting, Sirt1(ΔLiv) mice were maintained on a high-fat diet for 14 wk, followed by fibrate treatment. Sirt1(ΔLiv) mice exhibited increased body mass compared with control mice. In the context of a high-fat diet, Sirt1(ΔLiv) mice did not respond to the cholesterol-lowering effects of the fibrate treatment. However, there were no significant differences in PPARα target gene expression. These results suggest that, in vivo, SIRT1 deacetylase activity does not significantly impact induced PPARα activity.

Increased conversion of tryptophan to nicotinamide in rats by dietary valproate

Valproic acid (VPA) is a short-chained, branched fatty acid that is widely used in humans as an anticonvulsant and mood stabilizer, and has been reported to increase the liver NAD concentration. We investigated the effects of VPA on the conversion of tryptophan to nicotinamide. Rats were fed diets containing various amounts of VPA (0, 0.5, and 1.0% in the diets) for 14 d, 24-h urine samples were collected, and tryptophan and its catabolites were measured. We found that the conversion of tryptophan to nicotinamide was increased by feeding a diet containing VPA (p<0.01; 0% vs. 1.0% VPA). Of the intermediates formed during the conversion of tryptophan to nicotinamide, the tryptophan to 3-hydroxyanthranilic acid step was not affected by the administration of VPA, while such metabolites beyond quinolinic acid as nicotinamide and its catabolites were significantly increased (p<0.01; 0% vs. 1.0% VPA). This increase was dependent on the intake of VPA.

Kidney tumor biomarkers revealed by simultaneous multiple matrix metabolomics analysis

Metabolomics is increasingly being used in cancer biology for biomarker discovery and identification of potential novel therapeutic targets. However, a systematic metabolomics study of multiple biofluids to determine their interrelationships and to describe their use as tumor proxies is lacking. Using a mouse xenograft model of kidney cancer, characterized by subcapsular implantation of Caki-1 clear cell human kidney cancer cells, we examined tissue, serum, and urine all obtained simultaneously at baseline (urine) and at, or close to, animal sacrifice (urine, tissue, and plasma). Uniform metabolomics analysis of all three "matrices" was accomplished using gas chromatography- and liquid chromatography-mass spectrometry. Of all the metabolites identified (267 in tissue, 246 in serum, and 267 in urine), 89 were detected in all 3 matrices, and the majority was altered in the same direction. Heat maps of individual metabolites showed that alterations in serum were more closely related to tissue than was urine. Two metabolites, cinnamoylglycine and nicotinamide, were concordantly and significantly (when corrected for multiple testing) altered in tissue and serum, and cysteine-glutathione disulfide showed the highest change (232.4-fold in tissue) of any metabolite. On the basis of these and other considerations, three pathways were chosen for biologic validation of the metabolomic data, resulting in potential therapeutic target identification. These data show that serum metabolomics analysis is a more accurate proxy for tissue changes than urine and that tryptophan degradation (yielding anti-inflammatory metabolites) is highly represented in renal cell carcinoma, and support the concept that PPAR-α antagonism may be a potential therapeutic approach for this disease.

The metabonomics of combined dietary exposure to phthalates and polychlorinated biphenyls in mice

Humans undergo simultaneous daily exposure to a multitude of endocrine-disrupting compounds (EDCs). In present study, after combined exposure to endocrine disruptors DEHP and Aroclor 1254 for 12 days, a liquid chromatography/time-of-flight mass spectrometer method combining both reversed-phase (RP) and hydrophilic interaction chromatography (HILIC) separations was carried out to investigate the metabolic responses in mice. The metabolic profiles of endogenous metabolites could differentiate the dose and control groups in both RPLC and HILIC modes. Moreover, the male mice and female mice in different groups could be obviously clustered in their own regions with combined model. Fourteen lysoPCs, PC(18:4/18:1), lysoPE(18:2/0:0), phenylalanine and tryptophan were identified as potential biomarkers for the combined toxicity of DEHP and Aroclor 1254. Different change trends could be observed for the identified lysoPCs, due to their different levels of uptake and metabolism in mice. Moreover, gender-specific differences in several lysoPCs (e.g. lysoPC(18:0), lysoPC(22:6), lysoPC(20:3), and PC(18:4/18:1)) were observed for treated mice. The metabonomic results indicated the combined exposure led to a disturbance of lipid metabolism. The mRNA expressions of PLA2, ACOX1, CPT1, FAS and SCD1 involved in lipid metabolism were investigated. Among them, significant increases of FAS and SCD1 expressions in the liver induced by the exposure could be observed for both male and female mice, contributing to the hepatic lipid accumulation in mice. Besides lipid metabolism, tryptophan metabolism and phenylalanine metabolism may also be involved with the toxic responses to these EDCs. The present study not only improves the understanding of the combined toxicity of phthalates and PCBs but also shows that the metabonomic approach may prove to be a promising technique for the toxicity research of EDCs.

The secret life of NAD+: an old metabolite controlling new metabolic signaling pathways

A century after the identification of a coenzymatic activity for NAD(+), NAD(+) metabolism has come into the spotlight again due to the potential therapeutic relevance of a set of enzymes whose activity is tightly regulated by the balance between the oxidized and reduced forms of this metabolite. In fact, the actions of NAD(+) have been extended from being an oxidoreductase cofactor for single enzymatic activities to acting as substrate for a wide range of proteins. These include NAD(+)-dependent protein deacetylases, poly(ADP-ribose) polymerases, and transcription factors that affect a large array of cellular functions. Through these effects, NAD(+) provides a direct link between the cellular redox status and the control of signaling and transcriptional events. Of particular interest within the metabolic/endocrine arena are the recent results, which indicate that the regulation of these NAD(+)-dependent pathways may have a major contribution to oxidative metabolism and life span extension. In this review, we will provide an integrated view on: 1) the pathways that control NAD(+) production and cycling, as well as its cellular compartmentalization; 2) the signaling and transcriptional pathways controlled by NAD(+); and 3) novel data that show how modulation of NAD(+)-producing and -consuming pathways have a major physiological impact and hold promise for the prevention and treatment of metabolic disease.

An analytical method for the measurement of acid metabolites of tryptophan-NAD pathway and related acids in urine

An analytical method has been developed for the measurements of five urinary acids namely, quinolinic acid, picolinic acid, nicotinic acid, 2-pyridylacetic acid and 3-pyridylacetic acid. The high performance liquid chromatograph-electrospray ionization mass spectrometry was operated in positive polarity under selected ion monitoring mode, with a column flow rate of 0.2 ml/min and an injection volume of 20 microl. The method used isotope-labelled picolinic acid (PA-d(4)) and nicotinic acid (NA-d(4)) as internal standards for the quantification. The sample preparation involved parallel use of two different types of mixed-mode solid phase extraction cartridges (Strata-X-AW for the extraction of quinolinic acid, and Strata-X-C for the remaining acids). Quantitative analysis of five target acids in several human and rat urine samples showed that the levels of acids were relatively uniform among rats while larger variations were observed for human samples.

The crystal structure of human alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase in complex with 1,3-dihydroxyacetonephosphate suggests a regulatory link between NAD synthesis and glycolysis

The enzyme alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) is a zinc-dependent amidohydrolase that participates in picolinic acid (PA), quinolinic acid (QA) and NAD homeostasis. Indeed, the enzyme stands at a branch point of the tryptophan to NAD pathway, and determines the final fate of the amino acid, i.e. transformation into PA, complete oxidation through the citric acid cycle, or conversion into NAD through QA synthesis. Both PA and QA are key players in a number of physiological and pathological conditions, mainly affecting the central nervous system. As their relative concentrations must be tightly controlled, modulation of ACMSD activity appears to be a promising prospect for the treatment of neurological disorders, including cerebral malaria. Here we report the 2.0 A resolution crystal structure of human ACMSD in complex with the glycolytic intermediate 1,3-dihydroxyacetonephosphate (DHAP), refined to an R-factor of 0.19. DHAP, which we discovered to be a potent enzyme inhibitor, resides in the ligand binding pocket with its phosphate moiety contacting the catalytically essential zinc ion through mediation of a solvent molecule. Arg47, Asp291 and Trp191 appear to be the key residues for DHAP recognition in human ACMSD. Ligand binding induces a significant conformational change affecting a strictly conserved Trp-Met couple, and we propose that these residues are involved in controlling ligand admission into ACMSD. Our data may be used for the design of inhibitors with potential medical interest, and suggest a regulatory link between de novo NAD biosynthesis and glycolysis.

Untargeted metabolomic profiling as an evaluative tool of fenofibrate-induced toxicology in Fischer 344 male rats

Peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists such as fenofibrate are used to treat dyslipidemia. Although fenofibrate is considered safe in humans, it is known to cause hepatocarcinogenesis in rodents. To evaluate untargeted metabolic profiling as a tool for gaining insight into the underlying pharmacology and hepatotoxicology, Fischer 344 male rats were dosed with 300 mg/kg/day of fenofibrate for 14 days and the urine and plasma were analyzed on days 2 and 14. A combination of liquid and gas chromatography mass spectrometry returned the profiles of 486 plasma and 932 urinary metabolites. Aside from known pharmacological effects, such as accelerated fatty acid beta-oxidation and reduced plasma cholesterol, new observations on the drug's impact on cellular metabolism were generated. Reductions in TCA cycle intermediates and biochemical evidence of lactic acidosis demonstrated that energy metabolism homeostasis was altered. Perturbation of the glutathione biosynthesis and elevation of oxidative stress markers were observed. Furthermore, tryptophan metabolism was up-regulated, resulting in accumulation of tryptophan metabolites associated with reactive oxygen species generation, suggesting the possibility of oxidative stress as a mechanism of nongenotoxic carcinogenesis. Finally, several metabolites related to liver function, kidney function, cell damage, and cell proliferation were altered by fenofibrate-induced toxicity at this dose.

The physiological action of picolinic Acid in the human brain

Picolinic Acid is an endogenous metabolite of L-tryptophan (TRP) that has been reported to possess a wide range of neuroprotective, immunological, and anti-proliferative affects within the body. However the salient physiological function of this molecule is yet to be established. The synthesis of picolinic acid as a product of the kynurenine pathway (KP) suggests that, similar to other KP metabolites, picolinic acid may play a role in the pathogenesis of inflammatory disorders within the CNS and possibly other organs.

In this paper we review the limited body of literature dealing with the physiological actions of picolinic acid in the CNS and its associated synthesis via the kynurenine pathway in health and disease. Discrepancies and gaps in our current knowledge of picolinic acid are identified highlighting areas of research to promote a more complete understanding of its endogenous function in the brain.

Comprehensive X-ray structural studies of the quinolinate phosphoribosyl transferase (BNA6) from Saccharomyces cerevisiae

Quinolinic acid phosphoribosyl transferase (QAPRTase, EC 2.4.2.19) is a 32 kDa enzyme encoded by the BNA6 gene in yeast and catalyzes the formation of nicotinate mononucleotide from quinolinate and 5-phosphoribosyl-1-pyrophosphate (PRPP). QAPRTase plays a key role in the tryptophan degradation pathway via kynurenine, leading to the de novo biosynthesis of NAD (+) and clearing the neurotoxin quinolinate. To improve our understanding of the specificity of the eukaryotic enzyme and the course of events associated with catalysis, we have determined the crystal structures of the apo and singly bound forms with the substrates quinolinate and PRPP. This reveals that the enzyme folds in a manner similar to that of various prokaryotic forms which are approximately 30% identical in sequence. In addition, the structure of the Michaelis complex is approximated by PRPP and the quinolinate analogue phthalate bound to the active site. These results allow insight into the kinetic mechanism of QAPRTase and provide an understanding of structural diversity in the active site of the Saccharomyces cerevisiae enzyme when compared to prokaryotic homologues.

Down-regulation of alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase by polyunsaturated fatty acids in hepatocytes is not mediated by PPARalpha

BACKGROUND

alpha-Amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) is a key enzyme in NAD biosynthesis from tryptophan. Dietary polyunsaturated fatty acids (PUFA) have been shown to suppress hepatic ACMSD activity and its mRNA level in rat. However the mechanism of the suppressive action has not been clarified yet. Although the phenomena that fatty acids suppress the expression of ACMSD in rat liver have been established in vivo experiment, it is still obscure whether the effect of fatty acids on the expression of the enzyme is caused by its direct or indirect action, because there have been very few investigations performed in vitro.

AIM OF THE STUDY

In this study, to examine whether down-regulation of ACMSD mRNA by PUFA involves peroxisome proliferator-activated receptor (PPAR) alpha mediated mechanism or not, we investigated the effect of PUFA on the ACMSD expression by using primary cultured rat hepatocytes.

METHODS

For this purpose we investigated the effect of PUFA (linoleic acid and eicosapentanoic acid) on the ACMSD mRNA level in primary-cultured rat hepatocytes and compared its effect with that of WY-14,643 (a PPARalpha agonist). After the incubation of hepatocytes with fatty acids, WY-14,643 and/or MK886 (a PPARalpha antagonist), mRNA levels of ACMSD and a peroxisome marker enzyme acyl-CoA oxidase (ACO) were determined by competitive reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS

ACMSD mRNA level in primary hepatocytes were decreased by the incubation with high concentrations of linoleic acid, eicosapentaenoic acid (EPA) and WY-14,643. The appearance of ACO mRNA by WY-14,643 was remarkably increased, and those by linoleic acid and EPA were increased less than that by WY-14,643. Moreover, the suppression of ACMSD mRNA and the augmentation of ACO mRNA by WY-14,643 were inhibited by MK886, but the suppression by PUFA was not substantially affected by MK886.

CONCLUSIONS

The present study suggesting that the mechanism of decrease in ACMSD mRNA level by PUFA was different from that by WY-14,643, and that there would be any pathway other than PPARalpha mediated one for PUFA to regulate ACMSD expression.

Tissue expression and biochemical characterization of human 2-amino 3-carboxymuconate 6-semialdehyde decarboxylase, a key enzyme in tryptophan catabolism

2-amino 3-carboxymuconate 6-semialdehyde decarboxylase (ACMSD, EC 4.1.1.45) plays a key role in tryptophan catabolism. By diverting 2-amino 3-carboxymuconate semialdehyde from quinolinate production, the enzyme regulates NAD biosynthesis from the amino acid, directly affecting quinolinate and picolinate formation. ACMSD is therefore an attractive therapeutic target for treating disorders associated with increased levels of tryptophan metabolites. Through an isoform-specific real-time PCR assay, the constitutive expression of two alternatively spliced ACMSD transcripts (ACMSD I and II) has been examined in human brain, liver and kidney. Both transcripts are present in kidney and liver, with highest expression occurring in kidney. In brain, no ACMSD II expression is detected, and ACMSD I is present at very low levels. Cloning of the two cDNAs in yeast expression vectors and production of the recombinant proteins, revealed that only ACMSD I is endowed with enzymatic activity. After purification to homogeneity, this enzyme was found to be a monomer, with a broad pH optimum ranging from 6.5 to 8.0, a K(m) of 6.5 microM, and a k(cat) of 1.0 s(-1). ACMSD I is inhibited by quinolinic acid, picolinic acid and kynurenic acid, and it is activated slightly by Fe(2+) and Co(2+). Site-directed mutagenesis experiments confirmed the catalytic role of residues, conserved in all ACMSDs so far characterized, which in the bacterial enzyme participate directly in the metallocofactor binding. Even so, the properties of the human enzyme differ significantly from those reported for the bacterial counterpart, suggesting that the metallocofactor is buried deep within the protein and not as accessible as it is in bacterial ACMSD.

Metabolomic and genetic analysis of biomarkers for peroxisome proliferator-activated receptor alpha expression and activation

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear receptor with manifold effects on intermediary metabolism. To define a set of urinary biomarkers that could be used to determine the efficacy of PPARalpha agonists, a metabolomic investigation was undertaken in wild-type and Pparalpha-null mice fed for 2 wk either a regular diet or a diet containing the PPARalpha ligand Wy-14,643 ([4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid), and their urine was analyzed by ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry. Principal components analysis of 6393 accurate mass positive ions revealed clustering as a single phenotype of the treated and untreated Pparalpha (-/-) mice plus two additional discrete phenotypes for the treated and untreated Pparalpha (+/+) mice. Biomarkers of PPARalpha activation were identified from their accurate masses and confirmed by tandem mass spectrometry of authentic compounds. Biomarkers were quantitated from raw chromatographic data using appropriate calibration curves. PPARalpha urinary biomarkers highly statistically significantly elevated by Wy-14,643 treatment included 11beta-hydroxy-3,20-dioxopregn-4-en-21-oic acid (>3700-fold), 11beta,20-dihydroxy-3-oxopregn-4-en-21-oic acid (50-fold), nicotinamide (>2-fold), nicotinamide 1-oxide (5-fold), 1-methylnicotinamide (1.5-fold), hippuric acid (2-fold), and 2,8-dihydroxyquinoline-beta-d-glucuronide (3-fold). PPARalpha urinary biomarkers highly statistically significantly attenuated by Wy-14,643 treatment included xanthurenic acid (1.3-fold), hexanoylglycine (20-fold), phenylpropionylglycine (4-fold), and cinnamoylglycine (9-fold). These biomarkers arise from PPARalpha effects on tryptophan, corticosterone, and fatty acid metabolism and on glucuronidation. This study underscores the power of mass spectrometry-based metabolomics combined with genetically modified mice in the definition of monogenic metabolic phenotypes.

Beyond lipids, pharmacological PPARalpha activation has important effects on amino acid metabolism as studied in the rat

PPARalpha agonists have been characterized largely in terms of their effects on lipids and glucose metabolism, whereas little has been reported about effects on amino acid metabolism. We studied responses to the PPARalpha agonist WY 14,643 (30 micromol x kg(-1) x day(-1) for 4 wk) in rats fed a saturated fat diet. Plasma and urine were analyzed with proton NMR. Plasma amino acids were measured using HPLC, and hepatic gene expression was assessed with DNA arrays. The high-fat diet elevated plasma levels of insulin and triglycerides (TG), and WY 14,643 treatment ameliorated this insulin resistance and dyslipidemia, lowering plasma insulin and TG levels. In addition, treatment decreased body weight gain, without altering cumulative food intake, and increased liver mass. WY 14,643 increased plasma levels of 12 of 22 amino acids, including glucogenic and some ketogenic amino acids, whereas arginine was significantly decreased. There was no alteration in branched-chain amino acid levels. Compared with the fat-fed control animals, WY 14,643-treated animals had raised plasma urea and ammonia levels as well as raised urine levels of N-methylnicotinamide and dimethylglycine. WY 14,643 induced changes in a number of key genes involved in amino acid metabolism in addition to expected effects on hepatic genes involved in lipid catabolism and ketone body formation. In conclusion, the present results suggest that, in rodents, effects of pharmacological PPARalpha activation extend beyond control of lipid metabolism to include important effects on whole body amino acid mobilization and hepatic amino acid metabolism.

A metabonomics study of the hepatotoxicants galactosamine, methylene dianiline and clofibrate in rats

The efficacy of high-resolution (1)H nuclear magnetic resonance ((1)H-NMR) spectroscopy-based metabonomics was studied in a model of rat liver toxicity. Hepatotoxicities were induced in male rats using methylene dianiline, clofibrate and galactosamine. Twenty-four-hr urine from days 1 to 5 after treatment were subjected to (1)H-NMR evaluation of the biochemical effects. Blood were also taken at Days 2, 3 and 5 to examine biochemical changes associated with hepatotoxicities, and histopathological changes were evaluated at termination. Increases in liver enzymes were observed in animals treated with methylene dianiline or galactosamine, and histopathological analysis revealed changes associated with hepatobiliary damage and hepatocellular necrosis in methylene dianiline- and galactosamine-treated animals, respectively. Principal component analysis and statistical Spotfire analyses were used to visualize similarities and differences in urine biochemical profiles produced by (1)H-NMR spectra. The biochemical effects of methylene dianiline and galactosamine were characterized by elevated levels of glucose, fructose, beta-hydroxybutyrate, alanine, acetoacetate, lactate and creatine and decreased levels of hippurate, 2-oxoglutarate, citrate, succinate, trimethylamine-N-oxide, taurine and N-acetylglutamate in rat urine. Clofibrate treatment elevated the levels of N-methylnicotinamide and 3,4-dihydroxymandelate and decreased the levels of 2-oxoglutarate and N-acetylaspartate. This work shows that combinations of (1)H-NMR and pattern recognition are powerful tools in the evaluation of the biochemical effects of xenobiotics in liver.

Regulation of mouse hepatic alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase, a key enzyme in the tryptophan-nicotinamide adenine dinucleotide pathway, by hepatocyte nuclear factor 4alpha and peroxisome proliferator-activated receptor alpha

Nicotinamide adenine dinucleotide (NAD) plays a critical role in the maintenance of cellular energy homeostasis. alpha-Amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) is the key enzyme regulating de novo synthesis of NAD from l-tryptophan (Trp), designated the Trp-NAD pathway. Acmsd gene expression was found to be under the control of both hepatocyte nuclear factor 4alpha (HNF4alpha) and peroxisome proliferator-activated receptor alpha (PPARalpha). Constitutive expression of ACMSD mRNA levels were governed by HNF4alpha and downregulated by activation of PPARalpha by the ligand Wy-14,643 ([4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid]), as revealed by studies with hepatic HNF4alpha-null mice and PPARalpha-null mice, respectively. Transient transfection and electrophoretic mobility shift analyses showed an HNF4alpha binding site in the Acmsd gene promoter that directed transactivation of reporter gene constructs by HNF4alpha. The Acmsd promoter was not responsive to PPARalpha in transactivation assays. Wy-14,643 treatment decreased HNF4alpha protein levels in wild-type, but not PPARalpha-null, mouse livers, with no changes in HNF4alpha mRNA. These results show that Wy-14,643, through PPARalpha, post-transcriptionally down-regulates HNF4alpha protein levels, leading to reduced expression of the HNF4alpha target gene Acmsd.

Gene expression profiling of the PPAR-alpha agonist ciprofibrate in the cynomolgus monkey liver

Fibrates, such as ciprofibrate, fenofibrate, and clofibrate, are peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists that have been in clinical use for many decades for treatment of dyslipidemia. When mice and rats are given PPARalpha agonists, these drugs cause hepatic peroxisome proliferation, hypertrophy, hyperplasia, and eventually hepatocarcinogenesis. Importantly, primates are relatively refractory to these effects; however, the mechanisms for the species differences are not clearly understood. Cynomolgus monkeys were exposed to ciprofibrate at various dose levels for either 4 or 15 days, and the liver transcriptional profiles were examined using Affymetrix human GeneChips. Strong upregulation of many genes relating to fatty acid metabolism and mitochondrial oxidative phosphorylation was observed; this reflects the known pharmacology and activity of the fibrates. In addition, (1) many genes related to ribosome and proteasome biosynthesis were upregulated, (2) a large number of genes downregulated were in the complement and coagulation cascades, (3) a number of key regulatory genes, including members of the JUN, MYC, and NFkappaB families were downregulated, which appears to be in contrast to the rodent, where JUN and MYC are reported to upregulated after PPARalpha agonist treatment, (4) no transcriptional signal for DNA damage or oxidative stress was observed, and (5) transcriptional signals consistent with an anti-proliferative and a pro-apoptotic effect were seen. We also compared the primate data to literature reports of hepatic transcriptional profiling in PPARalpha-treated rodents, which showed that the magnitude of induction in beta-oxidation pathways was substantially greater in the rodent than the primate.

Transcriptional regulation of lipid metabolism by fatty acids: a key determinant of pancreatic beta-cell function

BACKGROUND: Optimal pancreatic beta-cell function is essential for the regulation of glucose homeostasis in both humans and animals and its impairment leads to the development of diabetes. Type 2 diabetes is a polygenic disease aggravated by environmental factors such as low physical activity or a hypercaloric high-fat diet. RESULTS: Free fatty acids represent an important factor linking excess fat mass to type 2 diabetes. Several studies have shown that chronically elevated free fatty acids have a negative effect on beta-cell function leading to elevated insulin secretion basally but with an impaired response to glucose. The transcription factors PPARalpha, PPARgamma and SREBP-1c respond to changing fat concentrations in tissues, thereby coordinating the genomic response to altered metabolic conditions to promote either fat storage or catabolism. These transcription factors have been identified in beta-cells and it appears that each may exert influence on beta-cell function in health and disease. CONCLUSION: The role of the PPARs and SREBP-1c as potential mediators of lipotoxicity is an emerging area of interest.

NAD levels in the rat primary cultured hepatocytes affected by peroxisome-proliferators

The effect of peroxisome-proliferators (PPs) on the NAD level in primary cultured rat hepatocytes was investigated and compared with that in the liver of rat administered with PPs. Various PPs, including fibrates, phthalate esters and steroid, increased NAD level in the cultured hepatocytes as in whole animal with a little exception. The NAD level decreased after once reaching the peak by the addition of most PPs. The gradual decrease of NAD observed in primary cultured hepatocytes, was partially inhibited by the addition of poly(ADP-ribose) polymerase and/or NAD glycohydrolase inhibitors. In the presence of these inhibitors, the increase of NAD by PPs still remained. The mechanism of increasing NAD level by PPs will be due to the stimulation of tryptophan (Trp)-NAD biosynthesis, with the possibility of the transcriptional regulation of genes related to Trp-NAD pathway by PPs. This in vitro system, therefore, can be used to clarify detailed mechanism of the stimulation of hepatic NAD biosynthesis in rats administered PPs.

Effects of dietary di(2-ethylhexyl)phthalate, a putative endocrine disrupter, on enzyme activities involved in the metabolism of tryptophan to niacin in rats

We have reported that the conversion ratio of tryptophan to niacin increased with increasing dietary concentration of di(2-ethylhexyl)phthalate (DEHP); the conversion ratio was about 2.0% in the control rat, which increased by about 30% in the rat fed with 3.0% DEHP diet. In this study, we investigated whether this abnormal increase in the conversion ratio by DEHP occurred through the alteration of the enzyme activities involved in the metabolism of tryptophan to niacin. Rats were fed with a diet containing 0%, 0.1%, 0.5%, or 1.0% DEHP for 21 days. The nine kinds of enzyme activities involved in the biosynthesis and catabolism in the liver and kidney were measured. Based on previous findings that the formation of quinolinic acid and its' metabolites significantly increased with DEHP administration, we proposed that the activity of 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase would be inhibited by DEHP intake. However, we found that the activities in the liver and kidney did not decrease in the rat fed with DEHP-containing diet. We discuss the discrepancy between the metabolite results and the enzyme activities.

The effects of Eucalyptus terpenes on hepatic cytochrome P450 CYP4A, peroxisomal Acyl CoA oxidase (AOX) and peroxisome proliferator activated receptor alpha (PPARalpha) in the common brush tail possum (Trichosurus vulpecula)

Eucalyptus leaves contain a high proportion of essential oils comprising of a complex mixture of monoterpenes such as 1,8-cineole, alpha-pinene, d-limonene and p-cymene. In this study, hepatic levels of microsomal lauric acid hydroxylase and peroxisomal cyanide-intensive palmitoyl coenzyme A oxidative activities were examined in livers of possums given an artificial diet consisting of the above monoterpenes for 10 days. These values were compared with those of possums fed a control diet containing only fruits and cereals. Peroxisomal cyanide-intensive palmitoyl coenzyme A oxidative activity was significantly higher in livers of treated possums relative to that of control possums (2.96+/-0.93 vs. 0.98+/-0.88 nmol/mg protein per min, P<0.01) (mean+/-S.D., n=4). A small increase in microsomal lauric acid hydroxylase activity was observed in the treated possum in comparison with the control group (4.40+/-0.85 vs. 3.60+/-0.48 nmol/mg protein per min) (mean+/-S.D., n=4). A higher NAD/ NADP ratio was observed in treated possums as compared with control possums (4.73+/-0.65 vs. 3.51+/-0.64 nmol/mg protein per min, P<0.05) (mean+/-S.D., n=4). No other statistically significant differences in pyridine nucleotide contents were found between control and treated possums. Northern blot analysis of mRNA from rat, human, terpene treated and control possum livers, using the corresponding koala cDNA probes, detected a more intense acyl CoA oxidase (AOX) mRNA band in livers of terpene fed possums. Negligible differences in the intensity of CYP4A and PPARalpha mRNA bands were observed between the two groups. These data suggest that Eucalyptus terpenes elevate hepatic AOX expression in possums.

Identification of a toxic mechanism of the plasticizers, phtahlic acid esters, which are putative endocrine disrupters: time-dependent increase in quinolinic acid and its metabolites in rats fed di(2-ethylhexyl)phthalate

We have reported that the administration of di(2-ethylhexyl)phthalate (DEHP) increased the formations of quinolinic acid (QA) and its lower metabolites on the tryptophan-niacin pathway. To discover the mechanism involved in disruption of the tryptophan-niacin pathway by DEHP, we assessed the daily urinary excretion of QA and its lower metabolites, and enzyme activities on the tryptophan-niacin pathway. Rats were fed with a niacin-free, 20% casein diet or the same diet supplemented with 0.1% DEHP or 0.043% phthalic acid and 0.067% 2-ethylhexanol added for 21 days. Feeding of DEHP increased the urinary excretions of QA and its lower metabolites in a time-dependent manner, and the increase of these excretions reached a peak at 11 days, but feeding of phthalic acid and 2-ethylhexanol had no effect. Feeding of DEHP, however, did not affect any enzyme activity including alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD), affecting the formation of QA, on the tryptophan-niacin pathway.

Cytochrome P450 4A, peroxisomal enzymes and nicotinamide cofactors in koala liver

We have examined hepatic levels of microsomal lauric acid hydroxylase activity and cyanide-insensitive palmitoyl coenzyme A oxidative activity in koala (Phascolarctos cinereus) and tammar wallaby (Macropus eugenii) and compared our results to those determined in rat. Microsomal lauric acid hydroxylation was significantly higher in koala than in tammar wallaby or rat. However, cyanide-insensitive palmitoyl-CoA oxidation was absent in the koala. We have also determined the hepatic nicotinamide cofactors in these species. Hepatic nicotinamide-adenine dinucleotide (NAD) and the ratio of NAD/nicotinamide-adenine dinucleotide phosphate (NADP) were higher in koala than in tammar wallaby and rat liver. Reverse transcription of koala liver mRNA, followed by polymerase chain reaction using primers based on highly conserved areas in the CYP4A family led to the cloning of a partial, near full length, cDNA clone with approximately 70% nucleotide and deduced amino acid sequence identity to human CYP4A11. The CYP has been named CYP4A15.