Dicarboxylic acids and glucose utilization in humans: effect of sebacate

Dicarboxylic acids counteract the metabolic effects of a Western diet by boosting energy expenditure

Obesity has reached pandemic proportion not only in the West but also in other countries around the world; it is now one of the leading causes of death worldwide. A Western diet is rich in saturated fats and provides more calories than necessary, contributing to the rise of the obesity rate. It also promotes the development of liver steatosis, insulin resistance, hyperglycemia, and hyperlipidemia. In this issue of the JCI, Goetzman and colleagues describe the effects of consuming dicarboxylic acids (DAs) as an alternative source of dietary fat. The 12-carbon dicarboxylic acid (DC12) was administered to mice at 20% of their daily caloric intake for nine weeks in place of triglycerides. Notably, the change in diet increased the metabolic rate, reduced body fat, reduced liver fat, and improved glucose tolerance. These findings highlight DAs as useful energy nutrients for combatting obesity and treating various metabolic disorders.

IL-6 Linkage to Exercise-Induced Shifts in Lipid-Related Metabolites: A Metabolomics-Based Analysis

Metabolomics profiling and bioinformatics technologies were used to determine the relationship between exercise-induced increases in IL-6 and lipid-related metabolites. Twenty-four male runners (age 36.5 ± 1.8 y) ran on treadmills to exhaustion (2.26 ± 0.01 h, 24.9 ± 1.3 km, 69.7 ± 1.9% VO_2max). Vastus lateralis muscle biopsy and blood samples were collected before and immediately after running and showed a 33.7 ± 4.2% decrease in muscle glycogen, 39.0 ± 8.8-, 2.4 ± 0.3-, and 1.4 ± 0.1-fold increases in plasma IL-6, IL-8, and MCP-1, respectively, and 95.0 ± 18.9 and 158 ± 20.6% increases in cortisol and epinephrine, respectively (all, P < 0.001). The metabolomics analysis revealed changes in 209 metabolites, especially long- and medium-chain fatty acids, fatty acid oxidation products (dicarboxylate and monohydroxy fatty acids, acylcarnitines), and ketone bodies. OPLS-DA modeling supported a strong separation in pre- and post-exercise samples (R2Y = 0.964, Q2Y = 0.902). OPLSR analysis failed to produce a viable model for the relationship between IL-6 and all lipid-related metabolites (R2Y = 0.76, Q2Y = -0.0748). Multiple structure equation models were evaluated based on IL-6, with the best-fit pathway model showing a linkage of exercise time to IL-6, then carnitine, and 13-methylmyristic acid (a marker for adipose tissue lipolysis) and sebacate. These metabolomics-based data indicate that the increase in plasma IL-6 after long endurance running has a minor relationship to increases in lipid-related metabolites.

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.

Dicarboxylic acids, an alternate fuel substrate in parenteral nutrition: an update

Dicarboxylic acids (DA) are formed from the omega-oxidation of monocarboxylic acids when the beta-oxidation of free fatty acids is impaired. Medium-chain DA have the peculiar characteristic of being water soluble due to the presence of two carboxylic terminal groups in the molecule. Contrary to both long- and medium-chain triglycerides which are administered as emulsions, they can be given by a peripheral vein as inorganic salts. DA are beta-oxidized at level of both peroxisomes and mitochondria via carnitine-independent pathway. The products of beta-oxidation of odd-chain DA are acetyl-CoA and malonyl-CoA, which cannot be oxidized further, are used in lipogenesis. Moreover even-chain DA produce acetyl-CoA and succinyl-CoA, which is a gluconeogenetic precursor. Azelaic acid (C9), does not show acute or chronic toxicity effects in animals but much of it is lost in urine (more than 50% of the given dose). Sebacic acid (C10) is lost in urine to a smaller extent (about 12% of the administered dose) and its energy density (6.64 kcal/g) is greater than that of C9 (4.97 kcal/g). Dodecanedioic acid (C12) seems to be the best candidate for parenteral nutrition, because it is eliminated in the urine only in minimal amounts (3.90% of the given dose), it is rapidly utilized by tissues, and it has a high energy density (7.20 kcal/g).

Effects of aliphatic dioic acids and glycerol-1,2,3-tris(dodecanedioate) on D-glucose-stimulated insulin release in rat pancreatic islets

Aliphatic dioic acids have been proposed as alternative nutrients in selected clinical situations. In this study, their possible insulinotropic action was investigated in isolated rat pancreatic islets prepared from fed rats. Azelaic acid, sebacic acid and tridecanedioic acids, when tested at a 10·0 mM CONCENTRATION, WERE FOUND TO AUGMENT INSULIN RELEASE EVOKED BY d-glucose (7·0 mm) in the pancreatic islets. Likewise, glycerol-1,2,3-tris(dodecanoedioate), when used at concentrations close to 1·0 mm, increased the secretory response to the hexose. It is speculated that these findings may extend to insulin-producing cells, the knowledge that aliphatic dioic acids or their esters may act as energy substrates, e.g. in parenteral nutrition.

Approximate linear confidence and curvature of a kinetic model of dodecanedioic acid in humans

Dicarboxylic acids with an even number of carbon atoms have been proposed as an alternate energy substrate for enteral or parenteral nutrition in the acutely ill patient, due to their water solubility and their yielding TCA cycle intermediates upon beta-oxidation. In the present work, a nonlinear compartmental model of the kinetics of dodecanedioic acid is developed, and its parameters are estimated from time concentration experimental observations obtained from six healthy volunteers undergoing a per os administration of 3 g of the substance. Although the model is linear in the transfer of the free substance from plasma to the tissues, the exchange between gut and plasma compartments is represented as a saturable function. Albumin binding is then incorporated to obtain the final model in terms of the measured total concentrations. Estimates of the model's structural parameters were computed for each experimental subject, and the usual single-subject approximate confidence regions for the parameters were derived by inversion of the Hessian at the optimum. To verify the applicability of this approximation, the nonlinearity of the expectation surface at the optimum was measured by computing the normal (intrinsic) component of curvature. Because the model curvature was excessive in all subjects, the usual approximation could not be trusted to provide acceptable approximations to the parameter confidence regions. A suitable Monte Carlo simulation yielded empirical joint parameter distributions from which the approximate parameter variances could finally be obtained.

A new HPLC method for the direct analysis of triglycerides of dicarboxylic acids in biological samples

Dicarboxylic acids (DA) are alternate lipid substrates recently proposed in parenteral nutrition. Two new derivatives of DA, a triglyceride of sebacic (TGC10) and one of dodecanedioic (TGC12) acid have been synthesised in order to reduce the amount of sodium given with the unesterified forms. The present paper describes a rapid and direct high-performance liquid chromatographic method (HPLC) for the analysis of these substances in both plasma and urine. Thirty-six male Wistar rats were rapidly injected with 64 mg of TGC10 or 53 mg of TGC12. The triglycerides and their products of hydrolysis were measured in plasma samples taken at different times. For the dose of 500 ng the intra-assay variations ranged from 6. 80+/-0.35% for TGC10 to 18.6+/-3.20% for TGC12 and the inter-assay variations were from 4.44+/-2.21% for TGC10 to 15.0+/-6.72% for TGC12. The detection limit for both triglycerides was 5 ng. This rapid and direct HPLC method could have practical implications in monitoring the concentration of both triglycerides and free forms of DA in biological samples of patients who might benefit from the administration of these substances during parenteral nutrition regimens.

Kinetics of dodecanedioic acid triglyceride in rats

The kinetics of the triglyceride of dodecanedioic acid (TGDA) has been investigated in 30 male Wistar rats after a rapid intravenous bolus injection. TGDA and its product of hydrolysis, nonesterified dodecanedioic acid (NEDA), were measured in plasma samples taken at different times using an improved high-performance liquid chromatographic method. The 24-h urinary excretion of TGDA was 1.54 +/- 0.37 micromol, corresponding to approximately 0.67% of the administered amount. Several kinetics models were considered, including central and peripheral compartments for the triglyceride and the free forms and expressing transports between compartments with combinations of linear, carrier-limited, or time-varying mechanisms. The parameter estimates of the kinetics of TGDA and of NEDA were finally obtained using a three-compartment model in which the transfer of TGDA to NEDA was assumed to be linear, through a peripheral compartment, and the tissue uptake of NEDA was assumed to be carrier limited. TGDA had a large volume of distribution ( approximately 0.5 l/kg body wt) with a fast disappearance rate from plasma (0.42 min-1), whereas NEDA had a very small volume of distribution ( approximately 0.04 l/kg body wt) and a tissue uptake with maximal transport rate of 0.636 mM/min. In conclusion, this first study on the triglyceride form of dodecanedioic acid indicates that it is rapidly hydrolyzed and that both triglyceride and nonesterified forms are excreted in the urine to a very low extent. The tissue uptake rate of NEDA is consistent with the possibility of achieving substantial energy delivery, should it be added to parenteral nutrition formulations. Furthermore, the amount of sodium administered with the triglyceride form is one-half of that necessary with the free diacid.

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.

Dodecanedioic acid infusion induces a sparing effect on whole-body glucose uptake, mainly in non-insulin-dependent diabetes mellitus

Even-numbered dicarboxylic acids (DA) have been proposed as an alternative fuel substrate in parenteral nutrition. In particular, dodecanedioic acid (C12) shows a rapid plasma clearance from tissues, a very low urinary excretion compared with other DA and a high oxidation rate. The aim of the present study was to investigate the effect of C12 infusion on insulin-stimulated glucose uptake in patients with non-insulin-dependent diabetes mellitus (NIDDM) compared with healthy volunteers. A primed-constant infusion of C12 (0.39 mmol/min) was administered over 240 min, and at 120 min a 2 h euglycaemic hyperinsulinaemic clamp was performed. Blood specimens were sampled every 30 min and fractioned urines were collected over 24 h. The levels of C12 were measured by HPLC. Indirect calorimetry was performed continuously during the entire session. Body composition was assessed in all subjects studied to obtain fat-free mass (FFM) values. Whole-body glucose uptake decreased significantly during C12 infusion in both groups, although this effect was much more evident (P < 0.01) in NIDDM patients (52.4 (SD 15.8) % decrease compared with saline) than in controls (25.9 (SD 12.1) % decrease). The M value (mumol/kgFFM per min) was reduced by C12 to lower levels in NIDDM patients than in normal controls (12.6 (SD 3.9) v. 25.9 (SD 4.5), P < 0.01). Urinary excretion of C12 over 24 h was significantly lower in NIDDM patients than in controls (4.26 (SD 0.30) mmol v. 5.43 (SD 0.48), P < 0.01), corresponding to less than 3% of the administered dose. The infusion of C12 decreased non-protein RQ significantly in both groups of patients. In conclusion, this study shows, for the first time, that C12 significantly reduces glucose uptake in both normal controls and NIDDM patients, although this sparing effect on glucose uptake is much more pronounced in diabetic patients. These data suggest that C12 decreases glucose uptake and oxidation, mainly through a mechanism of substrate competition. Thus, it might be a useful alternative substrate in enteral or parenteral nutrition, sparing glucose utilization and increasing glycogen stores, in those clinical conditions, like NIDDM, where reduced insulin-induced glucose uptake and oxidation are observed.

Kinetics of dodecanedioic acid and effect of its administration on glucose kinetics in rats

Dodecanedioic acid (C12), a saturated aliphatic dicarboxylic acid with twelve C atoms, was given as an intraperitoneal bolus to male Wistar rats, with the aim of evaluating C12 suitability as an energy substrate for parenteral nutrition. The 24 h urinary excretion of C12 was 3.9% of the administered dose. C12 kinetics were investigated by a one-compartment model with saturable tissue uptake and reversible binding to plasma albumin. The analysis of plasma concentration and urinary excretion data from different animals yielded the population means of the kinetic parameters: renal clearance was 0.72 ml/min per kg body weight (BW) (much smaller than inulin clearance in the rat), and maximal tissue uptake was 17.8 mumol/min per kg BW corresponding to 123.7 J/min per kg BW. These results encourage the consideration of C12 as a possible substrate for parenteral nutrition. To investigate the effect of C12 administration on glucose kinetics, two other groups of rats, one treated with an intraperitoneal bolus of C12 and the other with saline, were subsequently given an intravenous injection of D[-U-14C]glucose in a tracer amount. Radioactivity data of both control and C12-treated rats were analysed by means of a two-compartment kinetic model which takes into account glucose recycling. The estimates of glucose pool size (2.3 mmol/kg BW) and total-body rate of disappearance (82.1 mumol/min per kg BW) in control rats agreed with published values. In C12-treated rats, the rate of disappearance appeared to be reduced to 36.7 mumol/min per kg BW and the extent of recycling appeared to be negligible.

Uptake of dodecanedioic acid by isolated rat liver

The uptake of dodecanedioic acid (C12); a dicarboxylic acid with 12 carbon atoms, was studied in the isolated perfused rat liver. Fifty mumol of C12 were injected as a bolus into the perfusing liver solution. The concentration of C12 in perfusate samples taken over 2 h from the beginning of the experiments were analyzed by high performance liquid chromatography. An in vitro experimental session was performed to determine the binding curve of C12 to defatted bovine serum albumin. These data were then used to compute the perfusate C12 free fraction. The number of binding sites on the albumin molecule was equal to 4.29 +/- 0.21 (S.E.), while the affinity constant was 6.33 +/- 0.87 x 10(3). M-1. Experimental values of perfusate C12 concentration versus time were individually plotted and fitted to a monoexponential decay for each liver perfused. The predicted C12 concentration at time zero averaged 0.354 +/- 0.0375 mumol/ml. Prom this value the apparent volume of distribution of C12 was obtained and corresponded to 153.02 +/- 14.56 ml. The disappearance rate constant from the perfusate was 0.0278 +/- 0.0030 min-1. The C12 half life was 26.6 +/- 2.3 min. The mean hepatic clearance from the perfusate was 4.08 +/- 0.38 ml/min. In conclusion, C12 is quickly taken up by the liver so that in about 100 min it was completely cleared from the perfusate.

Plasma clearance and oxidation of dodecanedioic acid in humans

BACKGROUND

Dicarboxylic acids are water-soluble, contrary to monocarboxylic acids, and have a metabolic pathway intermediate between those of lipids and carbohydrates. Our goal was to investigate the plasma turnover and oxidation rate of dodecanedioic acid (C12) in eight healthy male volunteers.

METHODS

A simultaneous infusion of both cold (0.24 mmol/min corresponding to 0.396 kcal/min) and radiolabeled (1.62 microCi/min) C12 free acid was performed. Blood specimens were sampled over a period of 360 minutes, and 24-hour urine samples were collected to measure the levels of C12 by high-performance liquid chromatography and liquid scintillation. Indirect calorimetry was continuously performed, and expired 14CO2 was collected. Binding of C12 in human plasma was determined in separate experiments using equilibrium dialysis.

RESULTS

A linear one-compartment model was used to describe the kinetics of labeled C12. Its volume of distribution was 139.02 +/- 10.84 mL/kgbw (mean +/- SE), and its plasma elimination constant was 0.01 +/- 0.004 min-1. The 24-hour urinary excretion of C12 was 3.14 +/- 0.96 mmol, corresponding to about 7% of the administered dose. The amount of C12 oxidized, expressed as percent oxidation, was equal to 35.44 +/- 1.64%. The mean basal value of npRQ (0.80 +/- 0.006) significantly (p < .02) decreased during the infusion to 0.78 +/- 0.01, which is a value close to that theoretically calculated (0.77). The oxidation of free fatty acids was significantly increased at the end of the C12 infusion, whereas the glucose oxidation was reduced to about 50%.

CONCLUSIONS

The experimental data suggest that C12 might represent a fuel substrate immediately available for tissue energy requirements, because a relevant amount of C12 is promptly oxidized. Its prompt oxidation and its conversion to succinic acid support the use of dodecanedioic acid in parenteral nutrition, especially in insulin-resistance conditions in which glucose uptake and oxidation is impaired.