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

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.

Poly(glycerol sebacate)/poly(butylene succinate-butylene dilinoleate) fibrous scaffolds for cardiac tissue engineering

The present article investigates the use of a novel electrospun fibrous blend of poly(glycerol sebacate) (PGS) and poly(butylene succinate-butylene dilinoleate) (PBS-DLA) as a candidate for cardiac tissue engineering. Random electrospun fibers with various PGS/PBS-DLA compositions (70/30, 60/40, 50/50, and 0/100) were fabricated. To examine the suitability of these fiber blends for heart patches, their morphology, as well as their physical, chemical, and mechanical properties were measured before examining their biocompatibility through cell adhesion. The fabricated fibers were bead-free and exhibited a relatively narrow diameter distribution. The addition of PBS-DLA to PGS resulted in an increase of the average fiber diameter, whereas increasing the amount of PBS-DLA decreased the hydrophilicity and the water uptake of the nanofibrous scaffolds to values that approached those of neat PBS-DLA nanofibers. Moreover, the addition of PBS-DLA significantly increased the elastic modulus. Initial toxicity studies with C2C12 myoblast cells up to 72 h confirmed nontoxic behavior of the blends. Immunofluorescence analyses and scanning electron microscopy analyses confirmed that C2C12 cells showed better cell attachment and proliferation on electrospun mats with higher PBS-DLA content. However, immunofluorescence analyses of the 3-day-old rat cardiomyocytes cultured for 2 and 5 days demonstrated better attachment on the 70/30 fibers containing well-aligned sarcomeres and expressing high amounts of connexin 43 in cellular junctions indicating efficient cell-to-cell communication. It can be concluded, therefore, that fibrous PGS/PBS-DLA scaffolds exhibit promising characteristics as a biomaterial for cardiac patch applications.

Early pregnancy urinary biomarkers of fatty acid and carbohydrate metabolism in pregnancies complicated by gestational diabetes

AIMS

Alterations in organic acid biomarkers from fatty acid and carbohydrate metabolism have been documented in type 2 diabetes patients. However, their association with gestational diabetes mellitus (GDM) is largely unknown.

METHODS

Participants were 25 GDM cases and 25 non-GDM controls. Biomarkers of fatty acid (adipate, suberate and ethylmalonate) and carbohydrate (pyruvate, l-lactate and β-hydroxybutyrate) metabolism were measured in maternal urine samples collected in early pregnancy (17 weeks) using liquid chromatography-mass spectrometry methods. Logistic regression were used to calculate odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

GDM cases and controls differed in median urinary concentrations of ethylmalonate (3.0 vs. 2.3μg/mg creatinine), pyruvate (7.4 vs. 2.1μg/mg creatinine), and adipate (4.6 vs. 7.3μg/mg creatinine) (all p-values <0.05). Women in the highest tertile for ethylmalonate or pyruvate concentrations had 11.4-fold (95%CI 1.10-117.48) and 3.27-fold (95%CI 0.72-14.79) increased risk of GDM compared with women in the lowest tertile for ethylmalonate and pyruvate concentrations, respectively. Women in the highest tertile for adipate concentrations, compared with women in the lowest tertile, had an 86% reduction in GDM risk (95%CI 0.02-0.97).

CONCLUSIONS

These preliminary findings underscore the importance of altered fatty acid and carbohydrate metabolism in the pathogenesis of GDM.

Plasma and urine metabolic profiles are reflective of altered beta-oxidation in non-diabetic obese subjects and patients with type 2 diabetes mellitus

OBJECTIVES

The two primary pathophysiological characteristics of patients with type 2 diabetes mellitus (T2DM) are insulin resistance (IR) and beta cell dysfunction. It has been proposed that the development of IR is secondary to the accumulation of triacylglycerols and fatty acids in the muscle and liver, which is in turn thought to be secondary to an enzymatic defect in mitochondrial beta-oxidation. The purpose of the present study was to analyze the molecules of intermediary metabolism to determine if an alteration in mitochondrial function exists in T2DM patients and, if so, to determine whether this alteration is caused by excess nutrients or an enzymatic defect.

DESIGN AND METHODS

Seventy-seven subjects were recruited and divided into four groups (21 T2DM patients, 17 non-diabetic overweight/obese subjects, 20 offspring of T2DM patients, and 19 healthy subjects). Anthropometric parameters were determined by air plethysmography, and biochemical and metabolic parameters were measured, including 31 acylcarnitines (ACs) and 13 amino acids quantified by MS/MS and 67 organic acids measured by GC/MS.

RESULTS

Patients with T2DM showed elevation of short-chain ACs (C2, C4), a glycogenic amino acid (valine), a glycogenic and ketogenic amino acid (tyrosine), and a ketogenic amino acid (leucine) as well as altered excretion of dicarboxylic acids. T2DM offspring with abnormal glucose tolerance test GTT showed increased levels of C16. Subjects in the obese group who were dysglycemic also showed altered urinary excretion of dicarboxylic acids and lower levels of a long-chain AC (C14:2).

CONCLUSIONS

These results suggest that mitochondrial beta-oxidation is altered in T2DM patients and that the alteration is most likely caused by nutrient overload through a different pathway from that observed in obese subjects.

Use of dicarboxylic acids in type 2 diabetes

Even-number, medium-chain dicarboxylic acids (DAs), naturally occurring in higher plants, are a promising alternative energy substrate. Unlike the homologous fatty acids, DAs are soluble in water as salts. They are β-oxidized, providing acetyl-CoA and succinyl-CoA, the latter being an intermediate of the tricarboxylic acid cycle. Sebacic acid and dodecanedioic acid, DAs with 10 and 12 carbon atoms respectively, provide 6.6 and 7.2 kcal g⁻¹ each; therefore, their energy density is intermediate between glucose and fatty acids. Dicarboxylic acids have been proved to be safe in both experimental animals and humans, and their use has recently been proposed in diabetes. Studies in animals and humans with type 2 diabetes showed that oral administration of sebacic acid improved glycaemic control, probably by enhancing insulin sensitivity, and reduced hepatic gluconeogenesis and glucose output. Moreover, dodecanedioic acid intake reduced muscle fatigue during exercise in subjects with type 2 diabetes, suggesting an improvement of energy utilization and 'metabolic flexibility'. In this article, we review the natural sources of DAs, their fate in animals and humans and their effect in improving glucose metabolism in type 2 diabetes.

Recent advances in synthetic bioelastomers

This article reviews the degradability of chemically synthesized bioelastomers, mainly designed for soft tissue repair. These bioelastomers involve biodegradable polyurethanes, polyphosphazenes, linear and crosslinked poly(ether/ester)s, poly(ε-caprolactone) copolymers, poly(1,3-trimethylene carbonate) and their copolymers, poly(polyol sebacate)s, poly(diol-citrates) and poly(ester amide)s. The in vitro and in vivo degradation mechanisms and impact factors influencing degradation behaviors are discussed. In addition, the molecular designs, synthesis methods, structure properties, mechanical properties, biocompatibility and potential applications of these bioelastomers were also presented.

Design and applications of biodegradable polyester tissue scaffolds based on endogenous monomers found in human metabolism

Synthetic polyesters have deeply impacted various biomedical and engineering fields, such as tissue scaffolding and therapeutic delivery. Currently, many applications involving polyesters are being explored with polymers derived from monomers that are endogenous to the human metabolism. Examples of these monomers include glycerol, xylitol, sorbitol, and lactic, sebacic, citric, succinic, alpha-ketoglutaric, and fumaric acids. In terms of mechanical versatility, crystallinity, hydrophobicity, and biocompatibility, polyesters synthesized partially or completely from these monomers can display a wide range of properties. The flexibility in these macromolecular properties allows for materials to be tailored according to the needs of a particular application. Along with the presence of natural monomers that allows for a high probability of biocompatibility, there is also an added benefit that this class of polyesters is more environmentally friendly than many other materials used in biomedical engineering. While the selection of monomers may be limited by nature, these polymers have produced or have the potential to produce an enormous number of successes in vitro and in vivo.

Biodegradable polyester elastomers in tissue engineering

Tissue engineering often makes use of biodegradable scaffolds to guide and promote controlled cellular growth and differentiation in order to generate new tissue. There has been significant research regarding the effects of scaffold surface chemistry and degradation rate on tissue formation and the importance of these parameters is widely recognised. Nevertheless, studies describing the role of mechanical stimuli during tissue development and function suggest that the mechanical properties of the scaffold will also be important. In particular, scaffold mechanics should be taken into account if mechanical stimulation, such as cyclic strain, will be incorporated into strategies to grow improved tissues or the target tissue to be replaced has elastomeric properties. Biodegradable polyesters, such as polyglycolide, polylactide and poly(lactide-co-glycolide), although commonly used in tissue engineering, undergo plastic deformation and failure when exposed to long-term cyclic strain, limiting their use in engineering elastomeric tissues. This review will cover the latest advances in the development of biodegradable polyester elastomers for use as scaffolds to engineer tissues, such as heart valves and blood vessels.

A tough biodegradable elastomer

Biodegradable polymers have significant potential in biotechnology and bioengineering. However, for some applications, they are limited by their inferior mechanical properties and unsatisfactory compatibility with cells and tissues. A strong, biodegradable, and biocompatible elastomer could be useful for fields such as tissue engineering, drug delivery, and in vivo sensing. We designed, synthesized, and characterized a tough biodegradable elastomer from biocompatible monomers. This elastomer forms a covalently crosslinked, three-dimensional network of random coils with hydroxyl groups attached to its backbone. Both crosslinking and the hydrogen-bonding interactions between the hydroxyl groups likely contribute to the unique properties of the elastomer. In vitro and in vivo studies show that the polymer has good biocompatibility. Polymer implants under animal skin are absorbed completely within 60 days with restoration of the implantation sites to their normal architecture.

Mechanisms for the transport of alpha,omega-dicarboxylates through the mitochondrial inner membrane

alpha,omega-Dicarboxylates have antibacterial properties, have been used in the treatment of hyperpigmentary disorders, are active against various melanoma cell lines, and can also undergo beta-oxidation. Little, however, is known about their transport. In this paper, we examine the mitochondrial transport of alpha, omega-dicarboxylates ranging from oxalate (DC2) to sebacate (DC10). DC2-DC10 are transported by the inner membrane anion channel (IMAC). DC6-DC10 are also transported by an electroneutral mechanism that appears to reflect transport of the acid through the lipid bilayer. At 37 degrees C and pH 7.0, DC10 is transported very rapidly at 3 micromol/min.mg, and respiring mitochondria swell in the K+ salts of these acids. This transport mechanism is probably the major pathway by which the longer dicarboxylates enter cells, bacteria, and mitochondria. We also demonstrate that DC5-DC10 can also be transported by an electroneutral mechanism mediated by tributyltin, a potent inhibitor of IMAC. The mechanism appears to involve electroneutral exchange of a TBT-dicarboxylate-H complex for TBT-OH. Finally, we present evidence that of all the dicarboxylates tested only DC2-DC4 can be transported by the classical dicarboxylate carrier.

Urinary organic acid profiles in obese (ob/ob) mice: indications for the impaired omega-oxidation of fatty acids

As a means of generating an hypothesis to explain genetic obesity of the C57BL/6J ob/ob mouse, we used gas chromatography-mass spectrometry to compare the urinary organic acid profiles of obese (ob/ob) and lean (+/?) mice on both a chow and a chemically simplified diet. More than 60 peaks were found and quantified; 45 peaks were identified. No acid was excreted in greater amounts by lean mice and none was excreted exclusively by either lean or obese mice. When normalized to body weight (obese mice being 40% heavier) and to creatinine excretion (30% greater in obese mice), however, only the daily excretion of malate, 2-hydroxyglutarate, aconitate, 3-hydroxy-3-methylglutarate, oxalate, ethylmalonate, and 4-hydroxyphenylacetate were significantly greater in obese mice. When allowed to eat only an all-fat (Crisco) diet for 4 days, the excretion of adipate rose 10-fold in lean mice, but only threefold in obese mice. Adipate excretion by Zucker rats also increased on the Crisco diet, but was indistinguishable between lean and fatty rats, suggesting that omega-oxidation might be impaired in obese mice but not in fatty rats. This suggestion complements an earlier proposal that a comparative increase in ethylmalonate excretion, which was also characteristic of fatty Zucker rats, might be explained by an increased concentration of butyryl-CoA due to inadequate beta-oxidation. An impairment of omega-oxidation in the obese mouse may also explain why urinary 3-hydroxy-3-methylglutarate, which is derived from short chain products of beta-oxidation, is increased in obese mice but not in fatty rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Biogenesis of dicarboxylic acids in rat liver homogenate studied by 13C labeling

The aim of this investigation is to assess whether long-chain fatty acids can be a substrate for omega-oxidation and the subsequent beta-oxidation to produce medium-chain dicarboxylic acids normally found in urine. Isolated rat liver 10,000 g supernatant and pellet fractions were used as the source of enzymes. The metabolism of palmitate was studied using [1,2,3,4-13C4]hexadecanoic acid as tracer. Selected ion monitoring mass spectrometry was utilized for the determination of isotope enrichments in precursor and products. Palmitate was found to be a good substrate for omega-oxidation; the rate was only slightly slower than decanoate. The beta-oxidation of [1,2,3,4-13C4]hexadecanedioic acid yielded labeled adipic, suberic, and sebacic acids. Isotope distribution in these dicarboxylic acids consisted mostly of unlabeled molecules (M + 0) and molecules labeled with four 13C (M + 4), in agreement with a beta-oxidation initiated equally from both carboxyl ends of the precursor. Significant enrichments (1-8%) with only two 13C labels (M + 2) indicate a partial bidirectional beta-oxidation. The direct metabolic conversion of hexadecanedioate to succinate was documented by the significant enrichment (1.40-1.90%) in M + 4 of succinate. These data indicate that long-chain fatty acids can be a substrate for the production of medium-chain dicarboxylates and the eventual direct conversion to succinate.

Liberation of 14CO2 from [14C]adipic acid and [14C]octanoic acid by adult rats during riboflavin deficiency and its reversal

The purpose of the present study was to test the hypothesis that the already well-established mitochondrial lesion in fatty acid oxidation in riboflavin-deficient experimental animals, might be accompanied by an alteration in vivo in the kinetics of oxidation of labelled adipic acid. This dicarboxylic acid was chosen for testing as a metabolic probe because a block in its oxidation was already apparent from urine analysis of riboflavin-deficient animals, whereas the oxidation of medium- or long-chain monocarboxylic acids seemed to be little affected by deficiency in vivo. Female adult Norwegian hooded rats fed on purified diets containing either 15 mg riboflavin/kg diet (controls) or about 0.4 mg/kg (riboflavin-deficient) received an intragastric dose of either [1,6-14C]adipic acid or [1-14C]octanoic acid. Expired carbon dioxide was then collected in an alkaline trap over 3 h, for determination of radioactivity. This test was repeated at intervals for up to 2 weeks following riboflavin repletion of the deficient animals, and in riboflavin-dosed controls. Whereas the rate and extent of [14C]octanoic acid oxidation was not significantly affected by the deficiency or repletion, the extent of [14C]adipic acid oxidation was markedly and significantly increased during repletion of the deficient animals. The time-course indicated a temporary overshoot, followed by a slow return to the control values over 1-2 weeks. Adipate oxidation was also much less affected by a preceding period of overnight starvation, than was octanoate oxidation. Thus, adipic acid (or a related metabolic probe) may have appropriate properties for the design of a functional test of fatty acid oxidation efficiency, during riboflavin deficiency or allied metabolic conditions in human subjects.

The oxidation of dicarboxylic acid CoA esters via peroxisomal fatty acyl-CoA oxidase

Evidence supporting a common peroxisomal beta-oxidation pathway for the coenzyme A thioesters of medium-chain-length dicarboxylic acids (DCn-CoA) and monocarboxylic acids (MCn-CoA) has been obtained. Using the mono-CoA esters of dodecanedioic acid (DC12-CoA) and lauroyl-CoA (MC12-CoA) as substrates, parallel inductions of activities and parallel increases in specific activities during purification of peroxisomal fatty acyl-CoA oxidase (EC 1.3.99.3) from rat liver after di(2-ethylhexyl)phthalate treatment were seen. The purified enzyme was used for antiserum production in rabbits; antiserum specificity was verified by immunoblot analysis. Coincident losses of oxidase activities with MC12-CoA and DC12-CoA were found in immunotitration experiments with rat liver homogenates, supporting the hypothesis that peroxisomal fatty acyl-CoA oxidase is solely responsible for the oxidation of medium-chain length dicarboxylic acid substrates. Kinetic studies with purified enzyme using the mono-CoA esters of sebacic (DC10-CoA), suberic (DC8-CoA), and adipic (DC6-CoA) acids along with DC12-CoA revealed substrate inhibition. Although these substrates exhibited similar calculated Vmax values, with decreasing chain length, the combination of increasing Km values and decreasing substrate inhibition constant (Ki) caused the maximum obtainable velocity to decrease. These studies offer an explanation for the previously observed limit of the ability of peroxisomes to chain-shorten dicarboxylates and increased urinary excretion of adipic acid when peroxisomal oxidation of dicarboxylic acids is enhanced.

Clinical biochemistry of peroxisomal disorders

Peroxisomes have been shown to participate in a variety of pathological processes. Peroxisomal anomalities are central features of Zellweger's cerebro-hepato-renal syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease and several other genetic metabolic disorders (pseudo-Zellweger syndrome, Leber congenital amaurosis, cerebrotendinous xanthomatosis, rhizomelic chondrodysplasia punctata). In disorders with general loss of peroxisomal functions (Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease) an accumulation of very long-chain fatty acids and pathological bile acids are found. Patients have a defective synthesis of plasmalogens and show increased excretion of dicarboxylic acids of medium chain length and of pipecolic acid in the urine. These anomalities which are due to the lack of peroxisomal enzymes, supply the basis for clinical laboratory tests. The study of these peroxisomal disorders has presented valuable information on the normal function of peroxisomes.

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.

Serum dicarboxylic acids in patients with Reye syndrome

Reye syndrome resembles disorders of fatty acid metabolism. Analysis of serum free fatty acids from 18 patients with Reye syndrome revealed that dicarboxylic acids comprise as much as 55% (range 4% to 55%) of the patients' total free fatty acids; both medium- (6 to 12 carbon lengths) and long-chain (14 to 18 carbon lengths) dicarboxylic acids were identified. Long-chain dicarboxylic acids were not found in any control samples, whereas 86% +/- 4% of the serum dicarboxylic acids were long chain in 10 patients with Reye syndrome in state 3 to 4 coma and 31% +/- 8% in eight patients with a milder illness. The serum concentration of dicarboxylic acids correlated with the clinical state (P less than 0.001) and with the elevation in blood ammonia concentration (r2 = 0.8767). No long-chain dicarboxylic acids were found in the urine. The dicarboxylic acidemia in Reye syndrome may be secondary to the general mitochondrial dysfunction or could indicate that an insult to fatty acid metabolism or the stimulation of omega-oxidation is important in the pathogenesis of the illness. Measurement of serum dicarboxylic acids, especially long chain, may be important in assessing Reye syndrome and may prove useful in distinguishing this from other diseases.

C6-C10-dicarboxylic acids in liver and kidney tissue in normal, diabetic ketotic and clofibrate-treated rats

A combined gas chromatographic-mass spectrometric method (selected ion monitoring) to determine C6-C10-dicarboxylic acids in liver and kidney tissue is reported. Alterations in tissue concentrations of the dicarboxylic acids were reflected in urinary excretions, i.e., diabetic rats with 'ketotic dicarboxylic aciduria' had corresponding elevated concentrations of short-chain dicarboxylic acids in liver and kidney tissue. Stimulation of the enzymes of fatty acid oxidation by clofibrate was, as a sole event, not sufficient to cause elevated tissue concentrations of dicarboxylic acids, nor did it result in dicarboxylic aciduria, probably because of a relative lack in substrate (fatty acids) compared to the diabetic ketotic state, where lipolysis is increased. These results strongly indicate that 'ketotic dicarboxylic aciduria' parallels the activity of the lipid metabolism at cellular level, and that it is not just a matter of renal handling.

Distinction between urinary acids originating from nutrition and those produced in the human body

A simple procedure to distinguish between urinary acids originating from nutrition and beverages and those produced from compounds stored in the body is described. Acids originating from nutrition disappear in urine samples after a few days of a zero diet, whereas those produced from body compounds do not. The zero diet can be substituted by a diet of peeled rice and water.

The microsomal dicarboxylyl-CoA synthetase

Dicarboxylic acids are products of the omega-oxidation of monocarboxylic acids. We demonstrate that in rat liver dicarboxylic acids (C5-C16) can be converted into their CoA esters by a dicarboxylyl-CoA synthetase. During this activation ATP, which cannot be replaced by GTP, is converted into AMP and PPi, both acting as feedback inhibitors of the reaction. Thermolabile at 37 degrees C, and optimally active at pH 6.5, dicarboxylyl-CoA synthetase displays the highest activity on dodecanedioic acid (2 micromol/min per g of liver). Cell-fractionation studies indicate that this enzyme belongs to the hepatic microsomal fraction. Investigations about the fate of dicarboxylyl-CoA esters disclosed the existence of an oxidase, which could be measured by monitoring the production of H2O2. In our assay conditions this H2O2 production is dependent on and closely follows the CoA consumption. It appears that the chain-length specificity of the handling of dicarboxylic acids by this catabolic pathway (activation to acyl-CoA and oxidation with H2O2 production) parallels the pattern of the degradation of exogenous dicarboxylic acids in vivo.

Effect of Reye's syndrome serum on isolated chinchilla liver mitochondria

A general impairment of liver mitochondrial enzymes is central to Reye's syndrome (RS). The respiration of isolated liver mitochondria was measured after the addition of concentrated normal serum or RS serum derived from 12 patients. RS serum stimulates oxygen consumption in isolated rat liver mitochondria. This effect is due to the oxidation of uric acid by peroxisomes contaminating the preparation and a stimulation of mitochondrial respiration (1.05 +/- 0.14 nmol of O2/min X mg of protein; control 0.30 +/- 0.08 nmol O2/min X mg). The stimulation of respiration occurs in the presence of all respiratory substrates, is dependent on the amount of serum added, and represents an uncoupling of oxidative phosphorylation. RS serum reduces ATP formation by 15-76%. The uncoupling effect correlates with the amount of free fatty acid in the serum sample and resembles the effect induced by the addition of a dicarboxylic fatty acid. Dicarboxylic fatty acids, especially long-chain dicarboxylic acids, impair ATP formation. Dicarboxylic acids were found in the serum of all RS patients and comprised as much as 54% of the total serum free fatty acids. 90% of the serum dicarboxylic acids were of 16-18 carbon lengths. The amount of dicarboxylic acids in the RS serum corresponded directly with the reduction in ATP formation by the RS serum. This demonstrates that dicarboxylic acids occur in RS and may be important in the general impairment of mitochondrial function in RS and other disorders where they are present.

Urinary excretion of dicarboxylic acids from patients with the Zellweger syndrome. Importance of peroxisomes in beta-oxidation of dicarboxylic acids

The urinary excretion of adipic acid, suberic acid and sebacic acid from two patients with the cerebrohepato-renal syndrome of Zellweger was studied. The patients had a complete lack of peroxisomes in the liver as judged by electron microscopy. In the non-ketotic state, the total excretion of free and conjugated adipic acid, suberic acid and sebacic acid was increased by about 100%, 200% and 350%, respectively, as compared to the corresponding excretion from six healthy infants of the same age. The excretion of free dicarboxylic acid was increased to a considerably lesser extent than the free + conjugated dicarboxylic acid. In view of the presence of adipic acid in urine of the Zellweger patients, it is concluded that peroxisomes are not obligatory for beta-oxidation of medium-chain dicarboxylic acids in vivo. The relative accumulation of suberic acid and sebacic acid as compared to adipic acid is, however, consistent with a relative block in the conversion of suberic acid and sebacic acid into adipic acid in patients with the Zellweger syndrome.

The biogenesis of dicarboxylic acid in rats given hypoglycin

The metabolic origin of dicarboxylic acids which are produced as a result of hypoglycin poisoning (Jamaican vomiting sickness) was investigated. 14C- and 3H-labelled palmitic acid was administered with hypoglycin to rats, and radioactivity was measured in urinary dicarboxylic acids that were isolated by gas-liquid chromatography. Both isotopes were incorporated into adipic and sebacic acids, indicating a precursor-product relationship. Glutaric acid was, essentially, unlabelled. Preferential incorporation of C-16, relative to C-1 of palmitate, while not evident from data for fraction of isotopic dose incorporated, could be deduced by comparing ratios of 14C:3H in precursor with those ratios in products. It thus appears that omega-oxidation of the fatty acid intervenes predominantly at an intermediate stage of chain-shortening, when inhibition of beta-oxidation by hypoglycin becomes more pronounced.

Cyanide-insensitive and clofibrate enhanced beta-oxidation of dodecanedioic acid in rat liver. An indication of peroxisomal beta-oxidation of N-dicarboxylic acids

The beta-oxidation rate of dodecanedioic acid in rat liver homogenates (600 X g supernatant fraction) was determined by simultaneous measurements of the C6-C12-dicarboxylic acids, i.e., adipic, suberic, sebacic and dodecanedioic acids, in relation to time in assays incubated with dodecanedioic acid. Measurements were performed by a combined gas chromatographic-mass spectrometric technique, i.e., selected ion-monitoring. The beta-oxidation rate was registered as the consumption rate of dodecanedioic acid and as the initial rise in the concentrations of C6-C10-dicarboxylic acids. The beta-oxidation rate of C8-C12-dicarboxylic acids was increased many times in homogenates from clofibrate-treated rats. Moreover, it was unexpectedly found that 2.0 mM cyanide was unable to inhibit the beta-oxidation rate of the dicarboxylic acids in vitro, but in fact caused a minor increase in the rate of beta-oxidation in homogenates from both normal and clofibrate-treated rats. It was concluded that the present results strongly indicate the existence of a peroxisomal beta-oxidation of dicarboxylic acids.

The biological origin of ketotic dicarboxylic aciduria. II. In vivo and in vitro investigations of the beta-oxidation of C8-C16-dicarboxylic acids in unstarved, starved and diabetic rats

The beta-oxidation of C8-C16-dicarboxylic acids to short-chain dicarboxylic acids was investigated in vivo and in rat liver homogenate. The beta-oxidation in vivo was evaluated from the excretions of C6-C10-dicarboxylic acids in urine from rats given C8-C16-dicarboxylic acids. Correspondingly, the beta-oxidation in vitro was determined from the rise in concentration of C6-C10(12)-dicarboxylic acids in the postnuclear (600Xg) fraction of rat liver homogenates incubated with C8-C16-dicarboxylic acids. The results showed that C10-C14-dicarboxylic acids were far better substrates for beta-oxidation than were C8- and C16-dicarboxylic acids. In particular, hexadecanedioic acid could only be beta-oxidized to a minor degree, and, in contrast to the other dicarboxylic acids, it was toxic for starved rats. The activity of the lipid metabolism (unstarved, starved and diabetic ketotic rats) was of decisive significance for the quantity and pattern of the C6-C10-dicarboxylic acids present both in vivo and in vitro, since adipic acid was increased and sebacic acid decreased with increasing lipid catabolism, i.e. the adipic: sebacic acid ratio increased with increasing rates of beta-oxidation. On comparison with earlier investigations on the chain-length dependency of the omega-oxidation of monocarboxylic acids it was concluded that the biological origin of the ketotic C6-C8 -dicarboxylic aciduria is C10-C14-monocarboxylic acids, and that an elevated beta-oxidation rate is important for the formation of C6-C8-dicarboxylic aciduria.

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.