Urinary excretion of C4--C10-dicarboxylic acids and antiketogenic properties of adipic acid in ketogenic-stimulated rats due to diabetes, long-chain and short-chain monocarboxylic acids

The biochemistry and physiology of long-chain dicarboxylic acid metabolism

Mitochondrial β-oxidation is the most prominent pathway for fatty acid oxidation but alternative oxidative metabolism exists. Fatty acid ω-oxidation is one of these pathways and forms dicarboxylic acids as products. These dicarboxylic acids are metabolized through peroxisomal β-oxidation representing an alternative pathway, which could potentially limit the toxic effects of fatty acid accumulation. Although dicarboxylic acid metabolism is highly active in liver and kidney, its role in physiology has not been explored in depth. In this review, we summarize the biochemical mechanism of the formation and degradation of dicarboxylic acids through ω- and β-oxidation, respectively. We will discuss the role of dicarboxylic acids in different (patho)physiological states with a particular focus on the role of the intermediates and products generated through peroxisomal β-oxidation. This review is expected to increase the understanding of dicarboxylic acid metabolism and spark future research.

Integrative analyses of TEDDY Omics data reveal lipid metabolism abnormalities, increased intracellular ROS and heightened inflammation prior to autoimmunity for type 1 diabetes

BACKGROUND

The Environmental Determinants of Diabetes in the Young (TEDDY) is a prospective birth cohort designed to study type 1 diabetes (T1D) by following children with high genetic risk. An integrative multi-omics approach was used to evaluate islet autoimmunity etiology, identify disease biomarkers, and understand progression over time.

RESULTS

We identify a multi-omics signature that was predictive of islet autoimmunity (IA) as early as 1 year before seroconversion. At this time, abnormalities in lipid metabolism, decreased capacity for nutrient absorption, and intracellular ROS accumulation are detected in children progressing towards IA. Additionally, extracellular matrix remodeling, inflammation, cytotoxicity, angiogenesis, and increased activity of antigen-presenting cells are observed, which may contribute to beta cell destruction. Our results indicate that altered molecular homeostasis is present in IA-developing children months before the actual detection of islet autoantibodies, which opens an interesting window of opportunity for therapeutic intervention.

CONCLUSIONS

The approach employed herein for assessment of the TEDDY cohort showcases the utilization of multi-omics data for the modeling of complex, multifactorial diseases, like T1D.

Urine dicarboxylic acids change in pre-symptomatic Alzheimer's disease and reflect loss of energy capacity and hippocampal volume

Non-invasive biomarkers will enable widespread screening and early diagnosis of Alzheimer’s disease (AD). We hypothesized that the considerable loss of brain tissue in AD will result in detection of brain lipid components in urine, and that these will change in concert with CSF and brain biomarkers of AD. We examined urine dicarboxylic acids (DCA) of carbon length 3–10 to reflect products of oxidative damage and energy generation or balance that may account for changes in brain function in AD. Mean C4-C5 DCAs were lower and mean C7-C10 DCAs were higher in the urine from AD compared to cognitively healthy (CH) individuals. Moreover, mean C4-C5 DCAs were lower and mean C7-C9 were higher in urine from CH individuals with abnormal compared to normal CSF amyloid and Tau levels; i.e., the apparent urine changes in AD also appeared to be present in CH individuals that have CSF risk factors of early AD pathology. In examining the relationship between urine DCAs and AD biomarkers, we found short chain DCAs positively correlated with CSF Aβ₄₂, while C7-C10 DCAs negatively correlated with CSF Aβ₄₂ and positively correlated with CSF Tau levels. Furthermore, we found a negative correlation of C7-C10 DCAs with hippocampal volume (p < 0.01), which was not found in the occipital volume. Urine measures of DCAs have an 82% ability to predict cognitively healthy participants with normal CSF amyloid/Tau. These data suggest that urine measures of increased lipoxidation and dysfunctional energy balance reflect early AD pathology from brain and CSF biomarkers. Measures of urine DCAs may contribute to personalized healthcare by indicating AD pathology and may be utilized to explore population wellness or monitor the efficacy of therapies in clinical trials.

Accumulated Metabolites of Hydroxybutyric Acid Serve as Diagnostic and Prognostic Biomarkers of Ovarian High-Grade Serous Carcinomas

Ovarian cancer is a heterogeneous disease of low prevalence, but poor survival. Early diagnosis is critical for survival, but it is often challenging because the symptoms of ovarian cancer are subtle and become apparent only during advanced stages of the disease. Therefore, the identification of robust biomarkers of early disease is a clinical priority. Metabolomic profiling is an emerging diagnostic tool enabling the detection of biomarkers reflecting alterations in tumor metabolism, a hallmark of cancer. In this study, we performed metabolomic profiling of serum and tumor tissue from 158 patients with high-grade serous ovarian cancer (HGSOC) and 100 control patients with benign or non-neoplastic lesions. We report metabolites of hydroxybutyric acid (HBA) as novel diagnostic and prognostic biomarkers associated with tumor burden and patient survival. The accumulation of HBA metabolites caused by HGSOC was also associated with reduced expression of succinic semialdehyde dehydrogenase (encoded by ALDH5A1), and with the presence of an epithelial-to-mesenchymal transition gene signature, implying a role for these metabolic alterations in cancer cell migration and invasion. In conclusion, our findings represent the first comprehensive metabolomics analysis in HGSOC and propose a new set of metabolites as biomarkers of disease with diagnostic and prognostic capabilities.

Comparison between dodecanedioic acid and long-chain triglycerides as an energy source in liquid formula diets

BACKGROUND

Dicarboxylic acids (DA) are water-soluble substances with high-energy density proposed as an alternative lipid substrate for nutrition purposes. The aim of the present study was to investigate the interaction between glucose and DA or long-chain triglyceride (LCT) metabolism after oral administration.

METHODS

Two test meals containing either dodecanedioic acid (C12, the 12-atom DA) or LCT, together with glucose and amino acids, were each administered to five healthy volunteers. Tracer amounts of 14C-dodecanedioic acid were added to the C12 meal to recover expired traced CO2 and estimate the minimum rate of C12 oxidation. Glucose, insulin, and C12 plasma levels were measured for 360 minutes after the test meal. Indirect calorimetry was performed for the duration of the study.

RESULTS

LCTs proved ineffective in promoting their own oxidation after oral administration. On the contrary, C12 was promptly oxidized, a minimum of 21.9%+/-8.3% of the administered amount giving rise to the recovered expired CO2. This difference in metabolic fate was reflected in a sparing effect on glucose: suprabasal respiratory quotient and suprabasal carbohydrate oxidation were significantly (p < .05) lower under C12 administration than under LCT administration, with a difference of 0.024+/-0.015 in respiratory quotient (RQ) and a difference of 0.791+/-0.197 kJ/min in carbohydrate oxidation. In particular, carbohydrate oxidation increased by 54% over basal with LCT but only by 28% with C12 administration. RQ increased over basal by 5.8% with LCT but only by 3.0% with C12 administration.

CONCLUSIONS

These results show a fundamental metabolic difference between conventional lipids and DAs, which is the basis for a possible role of DAs in clinical nutrition. The fate of spared glucose is likely to be storage in glycogen form when dodecanedioic acid is made available as an energy source.

Skeletal muscle mitochondrial beta-oxidation of dicarboxylates

(1) The oxidation of [U-14C]hexadecanedionoyl-mono-CoA by rat skeletal muscle mitochondrial fractions is carnitine dependent and is inhibited by cyanide. (2) [U-14C]hexadecanedionoyl-mono-CoA was oxidised at a rate 8% of that of [U-14C]hexadecanoyl-CoA. (3) Oxidations were saturable and no substrate inhibition was observed. (4) We demonstrate the formation of dicarboxylyl-mono-CoA esters and the corresponding carnitine derivatives. (5) We conclude that, although skeletal muscle mitochondria are capable of the beta-oxidation of dicarboxylic acids, this is unlikely to be of great physiological significance.

Intermediates of peroxisomal beta-oxidation of [U-14C]hexadecanedionoate. A study of the acyl-CoA esters which accumulate during peroxisomal beta-oxidation of [U-14C]hexadecanedionate and [U-14C]hexadecanedionoyl-mono-CoA

1. The oxidation of [U-14C]hexadecanedionoyl-mono-CoA was stimulated by CoA, by carnitine in the absence of CoA and by the presence of an NAD(+)-regenerating system. 2. Substrate inhibition was observed with respect to [U-14C]hexadecanedionoyl-mono-CoA at concentrations greater than 35 microM. 3. Acetyl-CoA and the dicarboxyl-CoA esters of chain length C6-16 were detected by HPLC under standard incubation conditions. 4. In the absence of the NAD(+)-regenerating system, 2-enoyl-CoA and 3-hydroxacyl-CoA esters were detected. 5. In general, the peroxisomal beta-oxidation of dicarboxylates is very similar to that of monocarboxylates [Bartlett, K., Hovik, R., Eaton, S., Watmough, N. J. & Osmundsen, H. (1990) Biochem. J. 270, 175-180] except that chain shortening does not proceed beyond C6. 6. We conclude that the peroxisomal beta-oxidation of dicarboxylates is regulated by the redox state of the peroxisomal matrix and CoA availability.

Formation and degradation of dicarboxylic acids in relation to alterations in fatty acid oxidation in rats

Dicarboxylic acids are excreted in urine when fatty acid oxidation is increased (ketosis) or inhibited (defects in beta-oxidation) and in Reye's syndrome. omega-Hydroxylation and omega-oxidation of C6-C12 fatty acids were measured by mass spectrometry in rat liver microsomes and homogenates, and beta-oxidation of the dicarboxylic acids in liver homogenates and isolated mitochondria and peroxisomes. Medium-chain fatty acids formed large amounts of medium-chain dicarboxylic acids, which were easily beta-oxidized both in vitro and in vivo, in contrast to the long-chain C16-dicarboxylic acid, which was toxic to starved rats. Increment of fatty acid oxidation in rats by starvation or diabetes increased C6:C10 dicarboxylic acid ratio in rats fed medium-chain triacylglycerols, and increased short-chain dicarboxylic acid excretion in urine in rats fed medium-chain dicarboxylic acids. Valproate, which inhibits fatty acid oxidation and may induce Reye like syndromes, caused the pattern of C6-C10-dicarboxylic aciduria seen in beta-oxidation defects, but only in starved rats. It is suggested, that the origin of urinary short-chain dicarboxylic acids is omega-oxidized medium-chain fatty acids, which after peroxisomal beta-oxidation accumulate as C6-C8-dicarboxylic acids. C10-C12-dicarboxylic acids were also metabolized in the mitochondria, but did not accumulate as C6-C8-dicarboxylic acids, indicating that beta-oxidation was completed beyond the level of adipyl CoA.

The participation of soluble factors in the omega-oxidation of fatty acids in the liver of the sheep

The removal of soluble components from an ovine hepatic microsomal preparation decreased the omega-hydroxylation of dodecanoic and hexadecanoic acids. The results suggest that one or more soluble components play a role in the microsomal omega-hydroxylation of fatty acids. The possible roles in the reaction of catalase (known to stimulate the microsomal desaturations of fatty acids and alkylglycerols) and superoxide dismutase were investigated. The addition of these enzymes to the complete (but not the washed) microsomal preparation stimulated both the initial omega-hydroxylation reaction and the subsequent dehydrogenation reactions of the omega-oxidation pathway. The similarity of the effects of catalase and superoxide dismutase and stimulation of two different steps of the omega-oxidation pathway suggest that these agents are acting indirectly by removing active oxygen species rather than directly on the enzymes of microsomal fatty acid omega-hydroxylation.

Products and intermediates of the beta-oxidation of [U-14C]hexadecanedionoyl-mono-CoA by rat liver peroxisomes and mitochondria

1. The synthesis of [U-14C]hexadecanedionoyl-mono-CoA is described. 2. The beta-oxidation of [U-14C]hexadecanedionoyl-mono-CoA by purified rat liver peroxisomes and mitochondria is demonstrated. 3. The products of mitochondrial beta-oxidation of [U-14C]hexadecanedionoyl-mono-CoA include ketone bodies, citrate and acetylcarnitine. 4. Tetradecadionoyl-mono-CoA, hexadec-2-enedionyl-mono-CoA and hexadionoyl-mono-CoA were the only detectable intermediates formed by mitochondrial beta-oxidation, whereas acetyl-CoA and all saturated even-numbered intermediates of chain length C6-C16 were generated by peroxisomal beta-oxidation. 5. Hexadecanedionoyl-mono-CoA and hexadecanoyl-CoA were equally effective substrates for peroxisomal beta-oxidation, but hexadecanedionoyl-mono-CoA was a relatively poorer substrate for the mitochondrial pathway.

The inborn errors of mitochondrial fatty acid oxidation

To date, seven inborn errors of mitochondrial fatty acid oxidation have been identified. A total of about 100 patients in the world have been reported. Clinically the beta-oxidation defects are more often characterized by episodic hypoglycaemia leading to a coma mimicking Reye's syndrome. The hypoglycaemia is non-ketotic since the synthesis of ketone bodies is deficient. Periods of decompensation occur when carbohydrate supply is poor, e.g. prolonged fasting, vomiting, or increased caloric requirements, as and when lipid stores are used. Defects in beta-oxidation have also been reported to be one cause of sudden infant death syndrome. The diagnosis of these inborn errors is by biochemical investigation since where symptoms suggest such a defect, the precise aetiology cannot be assessed. The biochemical diagnosis is based firstly on identification of abnormal plasma and of urinary metabolites during acute attacks. Derivatives of the omega-oxidation and omega-1-oxidation of medium chain fatty acids have been identified, as well as acylglycine and acylcarnitine conjugates. These metabolites are nearly always absent when patients are in good clinical condition. Secondly, the diagnosis must be based on the identification of the enzymatic defects: this involves global assays which allow a localization of the 'level' of the defect (i.e. the oxidation of long, medium or short chain fatty acids) and specific measurement of enzyme activities (acyl-CoA dehydrogenases and electron carriers: ETF and ETF-DH). The diagnosis of these disorders is of prime importance because of the severity of the clinical symptoms. These can be prevented, in some cases, by an appropriate diet (a high carbohydrate, low fat diet, sometimes supplemented with L-carnitine). In other cases, genetic counselling can be offered.

Urinary profiles of organic acids and volatile metabolites during the starvation process in rats

Capillary gas chromatographic procedures were used to quantify the volatile and acidic compound profiles in the urinary samples of Sprague-Dawley rats during the starvation and refeeding periods. Numerous metabolites, identified through mass spectrometry, showed significant variations due to these physiological processes. Correlations are attempted with the previously studied biochemical processes in diabetic animals.

Chemoreceptively active compounds in secretions, excretions and tissue extracts of marine mammals

Semen, prostate glandular extract, perianal glandular secretion, urine, feces and blood from Atlantic bottlenose dolphins, Tursiops truncatus, were analyzed chemically by gas chromatography. A fecal sample from a California sea lion, Zalophus californianus, was analyzed similarly. Acids, esters, amino acids, amines, steroids, esters, sugars and alcohols were among the compounds revealed in the analyses. Twenty-two identified compounds can be detected gustatorily in aqueous solutions of sufficient concentration by humans. The chemical compositions of samples from Tursiops are similar to those from humans and other mammals.

The effects of physiological state and plane of nutrition on the concentrations of microsomal cytochromes and the omega-oxidation of fatty acids in various tissues of the sheep (Ovis aries)

The omega-oxidation activities and electron transport components of the microsomal fractions of tissues from pregnant, non-pregnant and lactating sheep on different planes of nutrition have been examined. Differences from the rat system were found, and between the non-pregnant and late pregnant sheep. The hepatic microsomal activity of omega-oxidation was approximately doubled by fasting for 5 days, but was unaltered by pregnancy or lactation per se. This increase was not caused by an increase in the specific activity of the omega-hydroxy fatty acid dehydrogenases. The results are discussed in relation to the glucose stresses of pregnancy in ruminants.

Chromatographic profiling of urinary volatile and organic acid metabolites of normal and diabetic C57BL/Ks mice

Capillary gas chromatography and gas chromatography-mass spectrometry were used to examine the urinary volatile and organic acid metabolites in normal and diabetic C57BL/Ks male mice. Quantitative differences in the excretion of these metabolites were assessed in the animals from 5 to 24 weeks of age. Statistically significant differences were examined with respect to known metabolic abnormalities in the diabetic animals and to the possible toxic effects of elevated levels of certain metabolites. A number of aldehyde metabolites and aromatic acids, as well as most other organic acids, were found at consistently higher levels in diabetic urine. Several ketone metabolites, linalool, and 2-sec.-butylthiazoline were found at consistently low levels throughout the study.

The biological origin of ketotic dicarboxylic aciduria. In vivo and in vitro investigations of the omega-oxidation of C6-C16-monocarboxylic acids in unstarved, starved and diabetic rats

The conversion of radioactive C6-C16-monocarboxylic acids to urinary adipic, suberic, sebacic and 3-hydroxybutyric acids was investigated in vivo in unstarved, starved and diabetic ketotic rats. Hexanoic, octanoic and decanoic acids were converted to C6-, C6-C8- and C6-C10-dicarboxylic acids, respectively, in fed and 72-h-starved rats. Lauric acid was converted to C6-C8-dicarboxylic acids in starved rats but not in unstarved rats. Decanoic and lauric acids were converted to relatively high amounts of C6-C8-dicarboxylic acids compared with myristic acid in myristic acid in ketotic diabetic rats, while radioactivity from [1-14C]-and [16-(14)] palmitic acid was not incorporated into C6-C8-dicarboxylic acids in diabetic ketotic rats. C6-C12-monocarboxylic acids in hydrolysed rat adipose tissue wee determined by gas-liquid chromatography-mass spectrometry (selected ion monitoring). Decanoic and lauric acids were found in amounts of 7.6-9.1 and 85.9-137.5 micrometers/100 mg tissue, respectively, whereas the amounts of hexanoic and octanoic acids were negligible. It is concluded that the biological origin of the C6-C8-dicarboxylic aciduria seen in ketotic rats are C10-C14-monocarboxylic acids, which are initially omega-oxidised solely or partly as free acids and subsequently beta-oxidised to adipic and suberic acids. The in vitro omega-oxidation of C6-C16-monocarboxylic acids to corresponding dicarboxylic acids in the 100,000 Xg supernatant fraction of rat liver homogenate was measured by selected ion monitoring. 0.09, 0.14, 16.1, 5.8, 7.0 and -6.9% of, respectively, hexanoic, octanoic, decanoic, lauric, myristic and palmitic acid were omega-oxidised to dicarboxylic acids of corresponding chain lengths after 90 min of incubation, when correction for the production of dicarboxylic acids in control assays was made. An in vitro production of C12-C16-dicarboxylic acids was detected in all assays ()including control assays), probably formed from"endogenous' monocarboxylic acids preexistent in the homogenate. Ths "endogenous' production of dicarboxylic acids was inhibited by C10-C16-monocarboxylic acids, where palmitic acid had the strongest effect. In fact, palmitic acid inhibited its own omega-oxidation when added in concentrations above 0.6 mM. Starvation of rats for 72 h did not alter the "endogenous' in vitro production of hexadecanedioic acid.

C6--C10-dicarboxylic aciduria in starved, fat-fed and diabetic rats receiving decanoic acid or medium-chain triacylglycerol. An in vivo measure of the rate of beta-oxidation of fatty acids

Administration of decanoic acid to rats resulted not only in elevated urinary excretions of the C10-dicarboxylic acid (sebacic acid), but also in highly elevated excretions of the beta-oxidation products C8- and C6-dicarboxylic acids (suberic and adipic acids). Activation of the lipid metabolism by starvation, fat-feeding and experimental diabetes increased the excretions of adipic acid and decreased the excretions of sebacic acid, i.e. the rate of oxidation of fatty acids was correlated to the adipic : sebacic acid ratio in urine. Compared with nondiabetic unstarved rats the adipic : sebacic acid ratio was elevated 2--3-, 8--16-, 5--19-, and 22--88-times in rats which were, respectively, starved for 2 days, 4 days, on a fat-diet for 4 days, and ketotic due to streptozotocin-induced diabetes. All rats with ratios above 10 were ketotic (urinary excretions of 3-hydroxybutyric acid over 500 microgram/mg creatinine) and all rats with ratios below 4 were nonketotic, while ketosis was a variable finding in rats with intermediary ratios. Similar changes in the ratio of excreted dicarboxylic acids were found when medium-chain triacylglycerols were fed instead of decanoic acid.