Potential Biomarkers for Early Detection of 3-MCPD Dipalmitate Exposure in Sprague-Dawley Rats.

3-Chloro-1,2-propandiol (3-MCPD) dipalmitate is one of the major 3-MCPD esters formed during food processing. In this single-dose study, the metabonomic profile changes in the 48 h after orally administrated 3-MCPD dipalmitate at 1600 mg/kg BW to Sprague-Dawley (SD) rats were determined with liquid chromatography (LC) coupled with mass spectrometry (MS) system. The chemical structures of 12 potential biomarkers for 3-MCPD dipalmitate exposures early detection were detected and tentatively identified from the plasma of SD rats, including indoxyl sulfate, phenol sulfate, p-cresol sulfate, 2-phenylethanol glucuronide, p-cresol glucuronide, p-cresol, allantoin, phenylacetylglycine, pyrocatechol sulfate, phenyllactic acid, 5-hydroxyindoleacetic acid, and creatinine. Taking into account the metabolites identified from SD rats' kidney, liver, testes, and spleen samples, 3-MCPD dipalmitate might potentially disturb the phenylalanine, tryptophan, tyrosine, glycine, fatty acid, and purine metabolisms. The results suggested that the 12 plasma metabolites could be potentially applied in detecting the early exposures of 3-MCPD esters.

Unique Metabolic Features of Adults Discordant for Indices of Insulin Resistance.

PURPOSE: Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and Adipose Insulin Resistance index (ADIPO-IR) values are often concordant. In this study we evaluated whether there are groups discordant for HOMA-IR and ADIPOpalmitate-IR and, if so, what are their defining characteristics. METHODS: The body composition, basal metabolic rate (BMR), fasting plasma lipids, insulin, glucose, and free fatty acid (FFA) palmitate concentrations data of 466 volunteers from previous research studies were abstracted and analyzed. The middle 2 population quartiles for HOMA-IR and Adipose Insulin Resistance index palmitate concentration (ADIPOpalmitate-IR) defined medium HOMA-IR and ADIPOpalmitate-IR (MH and MA), the top and bottom quartiles were defined as high/low HOMA (HH/LH), and high/low ADIPOpalmitate as HA/LA. Because ADIPOpalmitate-IR was significantly greater in women than in men, we established sex-specific quartiles for each index. We identified groups discordant for HOMA-IR and ADIPO-IR (HHMA, LHMA, MHHA, and MHLA). RESULTS: Body fat and fasting triglycerides (TGs) were significantly greater with higher indices in the concordant groups (HHHA > MHMA > LHLA). MHHA differed from MHLA by visceral fat (P < .01) and fasting TGs (P < .05), whereas HHMA differed (P < .01) from LHMA by BMR. By multivariate regression, the group factor contributed to BMR (P < .01) and visceral fat (P < .05). CONCLUSIONS: Adults discordant for HOMA-IR and ADIPO-IR have unique features including differences in visceral fat, TGs, and BMR. This suggests different forms of insulin resistance are present, which should be considered when studying insulin resistance in the future.

In Vivo Effectiveness of Orlistat in the Suppression of Human Colorectal Cancer Cell Proliferation.

BACKGROUND/AIM: Fatty acid synthase (FASN) provides palmitate for cell membrane formation in colorectal cancer (CRC) cells, however, palmitate is also available in the blood of CRC patients. The aim of this study was to examine whether orlistat, a FASN inhibitor, is able to attenuate CRC cell growth despite the availability of extracellular palmitate. MATERIALS AND METHODS: Palmitate concentrations were measured in serum from CRC patients and healthy controls. HT-29 CRC cells were treated with orlistat and palmitate. RESULTS: Treatment of CRC cells with orlistat caused a dose-dependent inhibition of cell proliferation. In turn, delivery of extracellular palmitate at doses lower than those found in the serum of CRC patients reversed inhibition by orlistat concentrations of up to 10 µM. CONCLUSION: Inhibition of CRC cell proliferation by orlistat is reversed by palmitate which is present at high levels in the serum. Therefore, orlistat may be effective in vivo only at high concentrations.

Nature vs. Nurture: Defining the Effects of Mesenchymal Stromal Cell Isolation and Culture Conditions on Resiliency to Palmitate Challenge.

As MSC products move from early development to clinical translation, culture conditions shift from xeno- to xeno-free systems. However, the impact of isolation and culture-expansion methods on the long-term resiliency of MSCs within challenging transplant environments is not fully understood. Recent work in our lab has shown that palmitate, a saturated fatty acid elevated in the serum of patients with obesity, causes MSCs to convert from an immunosuppressive to an immunostimulatory state at moderate to high physiological levels. This demonstrated that metabolically-diseased environments, like obesity, alter the immunomodulatory efficacy of healthy donor MSCs. In addition, it highlighted the need to test MSC efficacy not only in ideal conditions, but within challenging metabolic environments. To determine how the choice of xeno- vs. xeno-free media during isolation and expansion would affect future immunosuppressive function, umbilical cord explants from seven donors were subdivided and cultured within xeno- (fetal bovine serum, FBS) or xeno-free (human platelet lysate, PLT) medias, creating 14 distinct MSC preparations. After isolation and primary expansion, umbilical cord MSCs (ucMSC) were evaluated according to the ISCT minimal criteria for MSCs. Following baseline characterization, ucMSC were exposed to physiological doses of palmitate and analyzed for metabolic health, apoptotic induction, and immunomodulatory potency in co-cultures with stimulated human peripheral blood mononuclear cells. The paired experimental design (each ucMSC donor grown in two distinct culture environments) allowed us to delineate the contribution of inherent (nature) vs. environmentally-driven (nurture) donor characteristics to the phenotypic response of ucMSC during palmitate exposure. Culturing MSCs in PLT-media led to more consistent growth characteristics during the isolation and expansion for all donors, resulting in faster doubling times and higher cell yields compared to FBS. Upon palmitate challenge, PLT-ucMSCs showed a higher susceptibility to palmitate-induced metabolic disturbance, but less susceptibility to palmitate-induced apoptosis. Most striking however, was that the PLT-ucMSCs resisted the conversion to an immunostimulatory phenotype better than their FBS counterparts. Interestingly, examining MSC suppression of PBMC proliferation at physiologic doses of palmitate magnified the differences between donors, highlighting the utility of evaluating MSC products in stress-based assays that reflect the challenges MSCs may encounter post-transplantation.

Quantitating fatty acids in dried blood spots on a common collection card versus a novel wicking sampling device.

Blood biomarkers of n - 3 polyunsaturated fatty acids can serve as indicators of dietary intake and benefits and/or disease risk. The use of dried blood spots for fatty acid analyses is increasing but most of the reported data is qualitative (relative percentages of total fatty acids). The ability to quantitate concentrations of fatty acids on a common blood spot collection card and a novel wicking device designed to collect 10 µL of blood was compared with a wet blood sample in ten young adult participants. Prior to this comparison, the collection materials were screened for contaminants by gas chromatography with flame ionization and liquid chromatography/tandem mass spectrometry, and the blood volume and blood spot area relationship of the collection card was confirmed using technical replicates. Palmitate and stearate were detected as free fatty acids on both collection materials and as lysophosphatidylcholines on the wicking device. The low amounts (<1.0 µg) did not affect the quantitation of these fatty acids in either material. The relationship between blood volume and blood spot area was linear (r = 0.99, p < 0.001) and it was determined that a 6 mm hole punch contained 9.6 µL of blood. When compared with wet blood, the fatty acid determinations from the dried blood spots were largely similar although there were some minor differences in low abundant fatty acids. Quantitative fatty acid determinations of dried blood spots are possible and should be reported along with relative percentage data to improve interpretation in the future.

Dexamethasone palmitate large porous particles: A controlled release formulation for lung delivery of corticosteroids.

We have optimized a formulation of a prodrug of dexamethasone (DXM), dexamethasone palmitate (DXP) for pulmonary delivery as a dry powder. Formulations were prepared by spray drying DXP with 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) and Hyaluronic Acid (HA) as excipients. Large porous particles around 13 µm were produced with a tap density of 0.05g/cm3 and a Fine particle fraction around 40%. The palmitate moiety favors DXP insertion into DPPC bilayers therefore limiting its in vitro release as shown by differential scanning calorimetry. After administering DXP powder intratracheally to rats by insufflation, bronchoalveolar lavage fluid (BALF) and blood samples were collected up to 24h and DXP and DXM concentrations were determined by HPLC analysis after extraction. PK parameters were evaluated according to a non-compartmental model. We observe that DXP remains for up to 6h in the epithelial lining fluid (ELF) of the lungs at very high concentration. In addition, DXP concentration decreases according to two characteristic times. Consequently, DXM can be detected at rather important concentration in ELF up to 24h. The passage of DXP from the lungs to the bloodstream is very poor whereas DXM seems to be absorbed in the blood more easily. These results suggest that once administered DXP undergoes two different processes: hydrolysis into DXM due to the presence of esterases in the lungs and distribution in the lung tissue. This formulation appears promising to reduce systemic exposure and prolong the effect of the drug locally.

Intramyocellular Ceramides: Subcellular Concentrations and Fractional De Novo Synthesis in Postabsorptive Humans.

We investigated the relationship between insulin resistance markers and subsarcolemmal (SS) and intramyofibrillar (IMF) ceramide concentrations, as well as the contribution of plasma palmitate (6.5-h infusion of [U-13C]palmitate) to intramyocellular ceramides. Seventy-six postabsorptive men and women had muscle biopsies 1.5, 6.5, and 24 h after starting the tracer infusion. Concentrations and enrichment of muscle ceramides were measured by liquid chromatography-tandem mass spectrometry. We found that HOMA of insulin resistance, plasma insulin, and triglyceride concentrations were positively correlated with SS C16:0 and C18:1 ceramide, but not SS C14:0-Cer, C20:0-Cer, C24:0-Cer, and C24:1-Cer concentrations; IMF ceramide concentrations were not correlated with any metabolic parameters. The fractional contribution of plasma palmitate to 16:0 ceramide was greater in SS than IMF (SS, 18.2% vs. IMF, 8.7%; P = 0.0006). Plasma insulin concentrations correlated positively with the fractional contribution of plasma palmitate to SS 16:0 ceramide. The fractional contribution of plasma palmitate to intramyocellular SS 16:0 ceramide was positively correlated with SS C16:0 ceramide concentrations (γ = 0.435; P = 0.002). We conclude that skeletal muscle SS ceramides, especially C16 to C18 chain lengths and the de novo synthesis of intramyocellular ceramide from plasma palmitate are associated with markers of insulin resistance.

Palmitoyl-carnitine production by blood cells associates with the concentration of circulating acyl-carnitines in healthy overweight women.

BACKGROUND: Circulating acyl-carnitines (acyl-CNTs) are associated with insulin resistance (IR) and type 2 diabetes (T2D) in both rodents and humans. However, the mechanisms whereby circulating acyl-CNTs are increased in these conditions and their role in whole-body metabolism remains unknown. The purpose of this study was to determine if, in humans, blood cells contribute in production of circulating acyl-CNTs and associate with whole-body fat metabolism. METHODS AND RESULTS: Eight non-diabetic healthy women (age: 47 ± 19 y; BMI: 26 ± 1 kg·m-2) underwent stable isotope tracer infusion and hyperinsulinemic-euglycemic clamp study to determine in vivo whole-body fatty acid flux and insulin sensitivity. Blood samples collected at baseline (0 min) and after 3 h of clamp were used to determine the synthesis rate of palmitoyl-carnitine (palmitoyl-CNT) in vitro. The fractional synthesis rate of palmitoyl-CNT was significantly higher during hyperinsulinemia (0.788 ± 0.084 vs. 0.318 ± 0.012%·hr-1, p = 0.001); however, the absolute synthesis rate (ASR) did not differ between the periods (p = 0.809) due to ∼30% decrease in blood palmitoyl-CNT concentration (p = 0.189) during hyperinsulinemia. The ASR of palmitoyl-CNT significantly correlated with the concentration of acyl-CNTs in basal (r = 0.992, p < 0.001) and insulin (r = 0.919, p = 0.001) periods; and the basal ASR significantly correlated with plasma palmitate oxidation (r = 0.764, p = 0.027). CONCLUSION: In women, blood cells contribute to plasma acyl-CNT levels and the acyl-CNT production is linked to plasma palmitate oxidation, a marker of whole-body fat metabolism. Future studies are needed to confirm the role of blood cells in acyl-CNT and lipid metabolism under different physiological (i.e., in response to meal) and pathological (i.e., hyperlipidemia, IR and T2D) conditions.

Young, healthy South Asians have enhanced lipogenic sensitivity to dietary sugar.

OBJECTIVE: South Asians have higher rates of type 2 diabetes and cardiovascular disease compared to most other racial/ethnic groups. Increased hepatic de novo lipogenesis (DNL) in response to dietary sugar may accelerate the development of these chronic diseases in this population. STUDY DESIGN: Hepatic DNL in response to a calorically sweetened beverage was measured in an outpatient setting in 15 South Asians and 15 Caucasians with similar and normal body mass indexes, waist circumferences, glucose tolerance and lipid profiles. Blood was sampled before and hourly for 4 h after the ingestion of a single beverage made with glucose (1·5 g/kg) and fructose (1·5 g/kg). The main outcome, DNL, was measured as the increase in %palmitate (16:0) in very low-density lipoprotein (VLDL) triglyceride (TG) over 4 h. RESULTS: After the sugar dose, the increase in %16:0 in VLDL TG was significantly greater in South Asians vs Caucasians (P = 0·01). VLDL and total TG also increased to a significantly greater extent in South Asians (P = 0·04 and <0·001, respectively). Although the fasting and postsugar levels of insulin and glucose did not differ between groups, the DNL response significantly correlated with the insulin response to sugar in South Asians (r = 0·56, P = 0·03). CONCLUSIONS: Hepatic DNL in response to a sugar challenge was greater in healthy, young South Asians compared to Caucasians despite normal indices of insulin sensitivity, and it correlated with the insulin response. These findings suggest an early, insulin-related, gene-nutrient interaction contributing to the high prevalence of diabetes and coronary disease in this population.

Initial hyperinsulinemia and subsequent ß-cell dysfunction is associated with elevated palmitate levels.

BACKGROUND: The prevalence of obesity-related diabetes in childhood is increasing and circulating levels of nonesterified fatty acids may constitute a link. Here, the association between palmitate and insulin secretion was investigated in vivo and in vitro. METHODS: Obese and lean children and adolescents (n = 80) were included. Palmitate was measured at fasting; insulin and glucose during an oral glucose tolerance test (OGTT). Human islets were cultured for 0 to 7 d in presence of 0.5 mmol/l palmitate. Glucose-stimulated insulin secretion (GSIS), insulin content and apoptosis were measured. RESULTS: Obese subjects had fasting palmitate levels between 0.10 and 0.33 mmol/l, with higher average levels compared to lean subjects. While obese children with elevated palmitate (>0.20 mmol/l) had accentuated insulin levels during OGTT, obese adolescents with high palmitate had delayed first-phase insulin response. In human islets exposed to palmitate for 2 d GSIS was twofold enhanced, but after 7 d attenuated. Intracellular insulin content decreased time-dependently in islets cultured in the presence of palmitate and cleaved caspase 3 increased. CONCLUSION: The rapid accentuated and delayed insulin secretory responses observed in obese children and adolescents, respectively, with high palmitate levels may reflect changes in islet secretory activity and integrity induced by extended exposure to the fatty acid.

Increased palmitate intake: higher acylcarnitine concentrations without impaired progression of ß-oxidation.

Palmitic acid (PA) is associated with higher blood concentrations of medium-chain acylcarnitines (MCACs), and we hypothesized that PA may inhibit progression of FA ß-oxidation. Using a cross-over design, 17 adults were fed high PA (HPA) and low PA/high oleic acid (HOA) diets, each for 3 weeks. The [1-(13)C]PA and [13-(13)C]PA tracers were administered with food in random order with each diet, and we assessed PA oxidation (PA OX) and serum AC concentration to determine whether a higher PA intake promoted incomplete PA OX. Dietary PA was completely oxidized during the HOA diet, but only about 40% was oxidized during the HPA diet. The [13-(13)C]PA/[1-(13)C]PA ratio of PA OX had an approximate value of 1.0 for either diet, but the ratio of the serum concentrations of MCACs to long-chain ACs (LCACs) was significantly higher during the HPA diet. Thus, direct measurement of PA OX did not confirm that the HPA diet caused incomplete PA OX, despite the modest, but statistically significant, increase in the ratio of MCACs to LCACs in blood.

Dipeptidyl peptidase-4 inhibition ameliorates Western diet-induced hepatic steatosis and insulin resistance through hepatic lipid remodeling and modulation of hepatic mitochondrial function.

Novel therapies are needed for treating the increasing prevalence of hepatic steatosis in Western populations. In this regard, dipeptidyl peptidase-4 (DPP-4) inhibitors have recently been reported to attenuate the development of hepatic steatosis, but the potential mechanisms remain poorly defined. In the current study, 4-week-old C57Bl/6 mice were fed a high-fat/high-fructose Western diet (WD) or a WD containing the DPP-4 inhibitor, MK0626, for 16 weeks. The DPP-4 inhibitor prevented WD-induced hepatic steatosis and reduced hepatic insulin resistance by enhancing insulin suppression of hepatic glucose output. WD-induced accumulation of hepatic triacylglycerol (TAG) and diacylglycerol (DAG) content was significantly attenuated with DPP-4 inhibitor treatment. In addition, MK0626 significantly reduced mitochondrial incomplete palmitate oxidation and increased indices of pyruvate dehydrogenase activity, TCA cycle flux, and hepatic TAG secretion. Furthermore, DPP-4 inhibition rescued WD-induced decreases in hepatic PGC-1α and CPT-1 mRNA expression and hepatic Sirt1 protein content. Moreover, plasma uric acid levels in mice fed the WD were decreased after MK0626 treatment. These studies suggest that DPP-4 inhibition ameliorates hepatic steatosis and insulin resistance by suppressing hepatic TAG and DAG accumulation through enhanced mitochondrial carbohydrate utilization and hepatic TAG secretion/export with a concomitant reduction of uric acid production.

Population pharmacokinetic modeling and simulation to guide dose selection for RBP-7000, a new sustained-release formulation of risperidone.

RBP-7000 is a long-acting formulation of risperidone designed for once-monthly subcutaneous injection for the treatment of schizophrenia. The objective was to estimate clinically effective doses of RBP-7000 based on model simulations and on the comparison with other long-acting injectable antipsychotics. A population pharmacokinetic model of RBP-7000 was developed in 90 clinically stable schizophrenic patients having received single/repeated doses of 60, 90, or 120 mg. Model simulations were conducted to compare active moiety plasma exposure after repeated RBP-7000 administrations to the published data of long-acting risperidone injection (Risperdal® Consta®) at 25 and 50 mg, and of paliperidone palmitate (Invega® Sustenna®) at 50 and 100 mg equivalent paliperidone. Predictions of dopamine D2 receptor occupancy were derived from the simulated active moiety concentrations. Simulations showed similar active moiety plasma exposure at steady-state for 90 mg of RBP-7000 and 25 mg of long-acting risperidone. In comparison to risperidone, RBP-7000 reached effective concentrations immediately after the first administration. RBP-7000 at the doses of 60 and 90 mg provided similar active moiety plasma concentrations at steady-state compared to 50 and 100 mg equivalent paliperidone, respectively. These findings provide guidance for dose selection in Phase III clinical trials and suggest potential benefits for RBP-7000 over competitors.

Restoring redox balance enhances contractility in heart trabeculae from type 2 diabetic rats exposed to high glucose.

Hearts from type 2 diabetic (T2DM) subjects are chronically subjected to hyperglycemia and hyperlipidemia, both thought to contribute to oxidizing conditions and contractile dysfunction. How redox alterations and contractility interrelate, ultimately diminishing T2DM heart function, remains poorly understood. Herein we tested whether the fatty acid palmitate (Palm), in addition to its energetic contribution, rescues function by improving redox [glutathione (GSH), NAD(P)H, less oxidative stress] in T2DM rat heart trabeculae subjected to high glucose. Using cardiac trabeculae from Zucker Diabetic Fatty (ZDF) rats, we assessed the impact of low glucose (EG) and high glucose (HG), in absence or presence of Palm or insulin, on force development, energetics, and redox responses. We found that in EG ZDF and lean trabeculae displayed similar contractile work, yield of contractile work (Ycw), representing the ratio of force time integral over rate of O2 consumption. Conversely, HG had a negative impact on Ycw, whereas Palm, but not insulin, completely prevented contractile loss. This effect was associated with higher GSH, less oxidative stress, and augmented matrix GSH/thioredoxin (Trx) in ZDF mitochondria. Restoration of myocardial redox with GSH ethyl ester also rescued ZDF contractile function in HG, independently from Palm. These results support the idea that maintained redox balance, via increased GSH and Trx antioxidant activities to resist oxidative stress, is an essential protective response of the diabetic heart to keep contractile function.

Development and comparison of intramuscularly long-acting paliperidone palmitate nanosuspensions with different particle size.

The main purpose of this study was to develop and compare the pharmacokinetic behavior of two paliperidone palmitate (PP) nanosuspensions with different particle size after intramuscular (i.m.) administration. PP nanosuspensions were prepared by wet media milling method and the mean particle size of nanosuspension was controlled as 1,041 ± 6 nm (A) and 505 ± 9 nm (B), respectively. The morphology of nanosuspensions was observed by scanning electron microscope (SEM). Differential scanning calorimeter (DSC) and powder X-ray diffraction (PXRD) confirmed the crystallinity of PP in nanosuspensions. The physical and chemical stabilities of nanosuspensions A and B were investigated by particle analyzer and HPLC after storage for 2 months at 25°C, 4°C and mechanical shaking condition. No obvious change in particle size and chemical degradation of drug were observed. Following single-dose i.m. administration to beagle dogs, the release of paliperidone lasted for nearly 1 month. The Tmax of nanosuspensions A and B was 6 (d) and 10 (d). The AUC0-t and Cmax of nanosuspensions A was 2.0-fold and 1.8-fold higher than nanosuspensions B (p<0.05). The results demonstrated that PP nanosuspensions formulation had long-acting effect. Nanosuspension A with a larger particle size performed better than nanosuspension B. As a result, it is important to design appropriate particle size of nanosuspensions for i.m. administration in order to produce larger therapeutic effect.

Bed rest worsens impairments in fat and glucose metabolism in older, overweight adults.

BACKGROUND: The effects of bed rest on the dysregulation of fatty acid and glucose metabolism have not been addressed in the older population. OBJECTIVE: We examined the effect of 10 days of bed rest on fatty acid kinetics and hepatic and peripheral insulin resistance in aging. METHODS: We utilized an octreotide, basal glucagon replacement, multistage insulin infusion, and the concomitant infusion of [6,6 (2)H2]glucose to derive insulin-mediated suppression of glucose production and insulin-stimulated glucose disposal in nine older, overweight individuals (body mass index 28.1 ± 1.7 kg m(-2); 39.9% ± 1.9% fat). During the multistage insulin infusion, we also infused [1-(13)C]palmitate to examine free fatty acid rate of appearance (R(a)). RESULTS: Body weight, % body fat, and energy metabolism did not change with bed rest. There was a significant decrease (-2291 ± 316 cm(3)) in visceral fat, and no change in abdominal subcutaneous fat with bed rest. Insulin-mediated suppression of glucose production was modest prior to bed rest and was further reduced (>15% ± 2%) by bed rest. There was also a minor decrease in the insulin-mediated suppression of free fatty acid R(a) after bed rest and, as a consequence, a small variation in plasma free fatty acid from pre- to post-bed rest in the first stage of the multistage insulin infusion. There was also a significant bed rest-induced decline (>2.0 ± 0.6 mg kg FFM(-1) min(-1)) in insulin-stimulated glucose disposal. CONCLUSIONS: Preexisting impairments in insulin sensitivity are worsened by bed rest and seem linked to alterations in the regulation of free fatty acid in older, overweight individuals.

Relative oral bioavailability of glycidol from glycidyl fatty acid esters in rats.

In order to quantify the relative bioavailability of glycidol from glycidyl fatty acid esters in vivo, glycidyl palmitoyl ester and glycidol were orally applied to rats in equimolar doses. The time courses of the amounts of glycidol binding to hemoglobin as well as the excretion of 2,3-dihydroxypropyl mercapturic acids were determined. The results indicate that glycidol is released from the glycidyl ester by hydrolysis and rapidly distributed in the organism. In relation to glycidol, there was only a small timely delay in the binding to hemoglobin for the glycidol moiety released from the ester which may be certainly attributed to enzymatic hydrolysis. In both cases, however, an analogous plateau was observed representing similar amounts of hemoglobin binding. With regard to the urinary excretion of mercapturic acids, also similar amounts of dihydroxypropyl mercapturic acids could be detected. In an ADME test using a virtual double tag (³H, ¹4C) of glycidyl palmitoyl ester, a diverging isotope distribution was detected. The kinetics of the ¹4C-activity reflected the kinetics of free glycidol released after hydrolysis of the palmitoyl ester. In view of this experimental data obtained in rats, it is at present justified for the purpose of risk assessment to assume complete hydrolysis of the glycidyl ester in the gastrointestinal tract. Therefore, assessment of human exposure to glycidyl fatty acid ester should be regarded as an exposure to the same molar quantity of glycidol.

Equivalence of arterial and venous blood for [11C]CO2-metabolite analysis following intravenous administration of 1-[11C]acetate and 1-[11C]palmitate.

PURPOSE: Sampling of arterial blood for metabolite correction is often required to define a true radiotracer input function in quantitative modeling of PET data. However, arterial puncture for blood sampling is often undesirable. To establish whether venous blood could substitute for arterial blood in metabolite analysis for quantitative PET studies with 1-[(11)C]acetate and 1-[(11)C]palmitate, we compared the results of [(11)C]CO2-metabolite analyses performed on simultaneously collected arterial and venous blood samples. METHODS: Paired arterial and venous blood samples were drawn from anesthetized pigs at 1, 3, 6, 8, 10, 15, 20, 25 and 30min after i.v. administration of 1-[(11)C]acetate and 1-[(11)C]palmitate. Blood radioactivity present as [(11)C]CO2 was determined employing a validated 10-min gas-purge method. Briefly, total blood (11)C radioactivity was counted in base-treated [(11)C]-blood samples, and non-[(11)C]CO2 radioactivity was counted after the [(11)C]-blood was acidified using 6N HCl and bubbled with air for 10min to quantitatively remove [(11)C]CO2. RESULTS: An excellent correlation was found between concurrent arterial and venous [(11)C]CO2 levels. For the [(11)C]acetate study, the regression equation derived to estimate the venous [(11)C]CO2 from the arterial values was: y=0.994x+0.004 (r(2)=0.97), and for the [(11)C]palmitate: y=0.964x-0.001 (r(2)=0.9). Over the 1-30min period, the fraction of total blood (11)C present as [(11)C]CO2 rose from 4% to 64% for acetate, and 0% to 24% for palmitate. The rate of [(11)C]CO2 appearance in venous blood appears similar for the pig model and humans following i.v. [(11)C]-acetate administration. CONCLUSION: Venous blood [(11)C]CO2 values appear suitable as substitutes for arterial blood samples in [(11)C]CO2 metabolite analysis after administration of [(11)C]acetate or [(11)C]palmitate ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: Quantitative PET studies employing 1-[(11)C]acetate and 1-[(11)C]palmitate can employ venous blood samples for metabolite correction of an image-derived tracer arterial input function, thereby avoiding the risks of direct arterial blood sampling.

Acute hyperinsulinemia and reduced plasma free fatty acid levels decrease intramuscular triglyceride synthesis.

OBJECTIVE: To investigate the effect of acute hyperinsulinemia and the resulting decrease in plasma free fatty acid (FFA) concentrations on intramuscular TG synthesis. MATERIALS/METHODS: U-(13)C(16)-palmitate was infused for 3 h in anesthetized rabbits after overnight food deprivation. Arterial blood and leg muscle were sampled during the tracer infusion. Plasma samples were analyzed for free and TG-bound palmitate enrichments and concentrations. The enrichments and concentrations of palmitoyl-CoA and palmitoyl-carnitine as well as the enrichment of palmitate bound to TG were measured in muscle samples. Fractional synthetic rate (FSR) of intramuscular TG was calculated using the tracer incorporation method. The rabbits were divided into a control group and a hyperinsulinemic euglycemic clamp group. Insulin infusion decreased the rate of appearance of plasma free palmitate (2.00±0.15 vs 0.68±0.20 µmol⋅kg(-1)⋅min(-1); P<.001), decreased plasma FFA concentration (327±61 vs 72±25 nmol/mL; P<.01), decreased the total concentration of intramuscular fatty acyl-CoA plus fatty acyl-carnitine (12.1±1.6 vs 7.0±0.7 nmol/g; P<.05), and decreased intramuscular TG FSR (0.48±0.05 vs 0.21±0.06%/h; P<.01) in comparison with the control group. Intramuscular TG FSR was correlated (P<.01) with both plasma FFA concentrations and intramuscular fatty acyl-CoA concentrations. CONCLUSIONS: Fatty acid availability is a determinant of intramuscular TG synthesis. Insulin infusion decreases plasma and intramuscular fatty acid availability and thereby decreases TG synthesis.

Measuring plasma fatty acid oxidation with intravenous bolus injection of 3H- and 14C-fatty acid.

Accurate measures of plasma FA oxidation can improve our understanding of diseases characterized by impaired FA oxidation. We describe and compare the 24 h time-courses of FA oxidation using bolus injections of [1-(14)C]palmitate versus [9,10-(3)H]palmitate under postabsorptive, postprandial, and walking conditions. Fifty-one men and 95 premenopausal women participated in one condition (postabsorptive, postprandial, or walking), one tracer ((14)C- or (3)H-labeled), and an acetate or palmitate study. Groups were matched for sex, age, and body mass index (BMI). At 24 h, cumulative [(3)H]acetate recovery as (3)H(2)O was 80 ± 6%, 78 ± 2%, and 81 ± 6% in the postabsorptive, postprandial, and walking conditions, respectively (not significant). Model-predicted maximum [1-(14)C]acetate recovery as expired (14)CO(2) was 59 ± 12%, 52 ± 8%, and 65 ± 10% in the postabsorptive, postprandial, and walking condition, respectively (one way ANOVA, P = 0.12). When corrected with the corresponding acetate recovery factors, 24 h time-courses of FFA oxidation were similar between [1-(14)C]palmitate and [9,10-(3)H]palmitate in all three conditions. In contrast to previous meal ingestion studies, an acetate-hydrogen recovery factor was needed to achieve comparable oxidation rates using an intravenous bolus of [(3)H]palmitate. In conclusion, intravenous boluses of [9,10-(3)H]palmitate versus [1-(14)C]palmitate gave similar estimates of 24 h cumulative FFA oxidation in age-, sex- and BMI-matched individuals.