Assay of the deuterium enrichment of water via acetylene

Metabolic deuterium oxide (D2O) labeling in quantitative omics studies: A tutorial review

Mass spectrometry (MS) is an invaluable tool for sensitive detection and characterization of individual biomolecules in omics studies. MS combined with stable isotope labeling enables the accurate and precise determination of quantitative changes occurring in biological samples. Metabolic isotope labeling, wherein isotopes are introduced into biomolecules through biosynthetic metabolism, is one of the main labeling strategies. Among the precursors employed in metabolic isotope labeling, deuterium oxide (D₂O) is cost-effective and easy to implement in any biological systems. This tutorial review aims to explain the basic principle of D₂O labeling and its applications in omics research. D₂O labeling incorporates D into stable C-H bonds in various biomolecules, including nucleotides, proteins, lipids, and carbohydrates. Typically, D₂O labeling is performed at low enrichment of 1%-10% D₂O, which causes subtle changes in the isotopic distribution of a biomolecule, instead of the complete separation between labeled and unlabeled samples in a mass spectrum. D₂O labeling has been employed in various omics studies to determine the metabolic flux, turnover rate, and relative quantification. Moreover, the advantages and challenges of D₂O labeling and its future prospects in quantitative omics are discussed. The economy, versatility, and convenience of D₂O labeling will be beneficial for the long-term omics studies for higher organisms.

CD57+ Memory T Cells Proliferate In Vivo

A central paradigm in the field of lymphocyte biology asserts that replicatively senescent memory T cells express the carbohydrate epitope CD57. These cells nonetheless accumulate with age and expand numerically in response to persistent antigenic stimulation. Here, we use in vivo deuterium labeling and ex vivo analyses of telomere length, telomerase activity, and intracellular expression of the cell-cycle marker Ki67 to distinguish between two non-exclusive scenarios: (1) CD57+ memory T cells do not proliferate and instead arise via phenotypic transition from the CD57- memory T cell pool; and/or (2) CD57+ memory T cells self-renew via intracompartmental proliferation. Our results provide compelling evidence in favor of the latter scenario and further suggest in conjunction with mathematical modeling that self-renewal is by far the most abundant source of newly generated CD57+ memory T cells. Immunological memory therefore appears to be intrinsically sustainable among highly differentiated subsets of T cells that express CD57.

Calcium-Based Sustainable Chemical Technologies for Total Carbon Recycling

Calcium carbide, a stable solid compound composed of two atoms of carbon and one of calcium, has proven its effectiveness in chemical synthesis, due to the safety and convenience of handling the C≡C acetylenic units. The areas of CaC₂ application are very diverse, and the development of calcium-mediated approaches resolves several important challenges. This Review aims to discuss the laboratory chemistry of calcium carbide, and to go beyond its frontiers to organic synthesis, life sciences, materials and construction, carbon dioxide capturing, alloy manufacturing, and agriculture. The recyclability of calcium carbide and the availability of large-scale industrial production facilities, as well as the future possibility of fossil-resource-independent manufacturing, position this compound as a key chemical platform for sustainable development. Easy regeneration and reuse of the carbide highlight calcium-based sustainable chemical technologies as promising instruments for total carbon recycling.

Comparing DNA enrichment of proliferating cells following administration of different stable isotopes of heavy water

Deuterated water (²H₂O) is a label commonly used for safe quantitative measurement of deuterium enrichment into DNA of proliferating cells. More recently, it has been used for labeling proteins and other biomolecules. Our in vitro - in vivo research reports important stable isotopic labeling enrichment differences into the DNA nucleosides and their isotopologues (e.g. deoxyadenosine (dA) M + 1, dA M + 2, dA M + 3), as well as tumor cell proliferation effects for various forms of commercially available stable heavy water (²H₂O, H₂¹⁸O, and ²H₂¹⁸O). Using an in vitro mouse thymus tumor cell line, we determined that H₂¹⁸O provides superior DNA labeling enrichment quantitation, as measured by GC-positive chemical ionization (PCI)-MS/MS. In addition, at higher but physiologically relevant doses, both ²H₂¹⁸O and ²H₂O down modulated mouse thymus tumor cell proliferation, whereas H₂¹⁸O water had no observable effects on cell proliferation. The in vivo labeling studies, where normal mouse bone marrow cells (i.e. high turnover) were evaluated post labeling, demonstrated DNA enrichments concordant with measurements from the in vitro studies. Our research also reports a headspace-GC-NCI-MS method, which rapidly and quantitatively measures stable heavy water levels in total body water.

Human Stem Cell-like Memory T Cells Are Maintained in a State of Dynamic Flux

Adaptive immunity requires the generation of memory T cells from naive precursors selected in the thymus. The key intermediaries in this process are stem cell-like memory T (TSCM) cells, multipotent progenitors that can both self-renew and replenish more differentiated subsets of memory T cells. In theory, antigen specificity within the TSCM pool may be imprinted statically as a function of largely dormant cells and/or retained dynamically by more transitory subpopulations. To explore the origins of immunological memory, we measured the turnover of TSCM cells in vivo using stable isotope labeling with heavy water. The data indicate that TSCM cells in both young and elderly subjects are maintained by ongoing proliferation. In line with this finding, TSCM cells displayed limited telomere length erosion coupled with high expression levels of active telomerase and Ki67. Collectively, these observations show that TSCM cells exist in a state of perpetual flux throughout the human lifespan.

Application of gas chromatography-tandem mass spectrometry (GC/MS/MS) for the analysis of deuterium enrichment of water

Incorporation of deuterium from deuterium oxide ((2) H2 O) into biological components is a commonly used approach in metabolic studies. Determining the dilution of deuterium in the body water (BW) pool can be used to estimate body composition. We describe three sensitive GC/MS/MS methods to measure water enrichment in BW. Samples were reacted with NaOH and U-(13) C3 -acetone in an autosampler vial to promote deuterium exchange with U-(13) C3 -acetone hydrogens. Headspace injections were made of U-(13) C3 -acetone-saturated air onto a 30-m DB-1MS column in electron impact-mode. Subjects ingested 30 ml (2) H2 O, and plasma samples were collected. BW was determined by standard equation. Dual-energy X-ray absorptiometry scans were performed to calculate body mass, body volume and bone mineral content. A four-compartmental model was used to estimate body composition (fat and fat free mass). Full-scan experiments generated an m/z 45 peak and to a lesser extent an m/z 61 peak. Product fragment ions further monitored included 45 and 46 using selected ion monitoring (Method1), the 61 > 45 and 62 > 46 transition using multiple reaction monitoring (MRM; Method2) and the neutral loss, 62 > 45, transition (Method3). MRM methods were optimized for collision energy (CE) and collision-induced dissociation (CID) argon gas pressure with 6 eV CE and 1.5 mTorr CID gas being optimal. Method2 was used for final determination of (2) H2 O enrichment of subjects because of lower natural background. We have developed a sensitive method to determine (2) H2 O enrichment in BW to enable measurement of FM and FFM.

Normal rates of whole-body fat oxidation and gluconeogenesis after overnight fasting and moderate-intensity exercise in patients with medium-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Impairments in gluconeogenesis have been implicated in the pathophysiology of fasting hypoglycemia in medium-chain acyl-CoA dehydrogenase deficiency. However, whole body glucose and fat metabolism have never been studied in vivo.

METHODS

Stable isotope methodology was applied to compare fat and glucose metabolism between four adult patients with MCADD and four matched controls both at rest and during 1.5 h of moderate-intensity exercise. Additionally, intramyocellular lipid and glycogen content and intramyocellular acylcarnitines were assessed in muscle biopsies collected prior to and immediately after cessation of exercise.

RESULTS

At rest, plasma FFA turnover was significantly higher in patients with MCADD, whereas the plasma FFA concentrations did not differ between patients and controls. Blood glucose kinetics did not differ between groups both at rest and during exercise. Palmitate and FFA turnover, total fat and carbohydrate oxidation rates, the use of muscle glycogen and muscle derived triglycerides during exercise did not differ between patients and controls. Plasma FFA oxidation rates were significantly lower in patients at the latter stages of exercise. Free carnitine levels in muscle were lower in patients, whereas no differences were detected in muscle acetylcarnitine levels.

CONCLUSIONS

Whole-body or skeletal muscle glucose and fat metabolism were not impaired in adult patients with MCADD. This implies that MCADD is not rate limiting for energy production under the conditions studied. In addition, patients with MCADD have a higher FFA turnover rate after overnight fasting, which may stimulate ectopic lipid deposition and, as such, make them more susceptible for developing insulin resistance.

A pilot study demonstrating a non-invasive method for the measurement of protein turnover in skin disorders: application to psoriasis

Background

Previous studies of epidermal kinetics in psoriasis have relied on invasive biopsy procedures or the use of radioactive labels. We previously developed a non-invasive method for measuring keratin synthesis in human skin using deuterated water labeling, serial collection of tape strips and measurement of deuterium enrichment in protein by mass spectrometry. This powerful method can be applied to measure other skin proteins and lipids collected by tape stripping. Here, for the first time, we apply this technique to investigate the epidermal kinetics of psoriasis, the first step in defining a kinetic profile for normal skin versus activated or quiescent psoriatic skin.

Methods

Psoriatic subjects were given ²H₂O orally as twice-daily doses for 16–38 days. Affected and unaffected skin was sampled by tape stripping and washing (modified Pachtman method). Proteins were isolated from the tape strips by a method that enriches for keratin. Turnover times were determined by gas chromatography/mass spectrometry. Kinetic data were compared to transepidermal water loss (TEWL).

Results

Deuterium-labeled protein from lesional psoriatic skin appeared at the skin surface within 3–8 days of label administration, whereas labeled protein from non-lesional skin requires 10–20 days to appear. Psoriatic skin had similar rate of growth despite varying anatomic location. Proteins recovered from tape strips were identified by nanoscale liquid chromatography/tandem mass spectrometry. Isolated peptides were >98% from keratin in uninvolved skin and >72% keratin in psoriatic skin. Revealing that one-quarter of all newly synthesized proteins in psoriatic skin are antimicrobial defense and other immune-related proteins. TEWL values were greater in lesional than non-lesional skin, suggesting barrier compromise in psoriatic skin despite increased clinical thickness.

Conclusions

This simple, elegant, and non-invasive method for measuring epidermal protein synthesis, which can also be adapted to measure epidermal lipids, provides a metric that may reveal new insights into the mechanisms and dynamic processes underlying psoriasis and may also provide an objective scale for determining response to therapeutic agents in pre-clinical and clinical trials. This opens a pathway to the non-invasive study of kinetics of protein formation in psoriasis or other skin diseases.

Novel combination of collagen dynamics analysis and transcriptional profiling reveals fibrosis-relevant genes and pathways

Collagen deposition is a key process during idiopathic pulmonary fibrosis; however, little is known about the dynamics of collagen formation during disease development. Tissue samples of early stages of human disease are not readily available and it is difficult to identify changes in collagen content, since standard collagen analyses do not distinguish between 'old' and 'new' collagen. Therefore, the current study aimed to (i) investigate the dynamics of new collagen formation in mice using bleomycin-induced lung fibrosis in which newly synthesized collagen was labeled with deuterated water and (ii) use this information to identify genes and processes correlated to new collagen formation. Lung fibrosis was induced in female C57Bl/6 mice by bleomycin instillation. Animals were sacrificed at 1 to 5 weeks after fibrosis induction. Collagen synthesized during the week before sacrifice was labeled with deuterium by providing mice with deuterated drinking water. After sacrifice, we collected lung tissue for microarray analysis, determination of new collagen formation, and histology. Furthermore, we measured in vitro the expression of selected genes after transforming growth factor (TGF) β₁-induced myofibroblast differentiation. Deuterated water labeling showed a strong increase in new collagen formation already during the first week after fibrosis induction and a complete return to baseline at five weeks. Correlation of new collagen formation data with gene expression data allowed us to create a gene expression signature of fibrosis within the lung and revealed fibrosis-specific processes, among which proliferation. This was confirmed by measuring cell proliferation and collagen synthesis simultaneously using deuterated water incorporation in a separate experiment. Furthermore, new collagen formation strongly correlated with gene expression of e.g. elastin, Wnt-1 inducible signaling pathway protein 1, tenascin C, lysyl oxidase, and type V collagen. Gene expression of these genes was upregulated in vitro in fibroblasts stimulated with TGFβ₁. Together, these data demonstrate, using a novel combination of technologies, that the core process of fibrosis, i.e. the formation of new collagen, correlates not only with a wide range of genes involved in general extracellular matrix production and modification but also with cell proliferation. The observation that the large majority of the genes which correlated with new collagen formation also were upregulated during TGFβ₁-induced myofibroblast differentiation provides further evidence for their involvement in fibrosis.

The role of the carbohydrate response element-binding protein in male fructose-fed rats

By 2030, nearly half of Americans will have nonalcoholic fatty liver disease. In part, this epidemic is fueled by the increasing consumption of caloric sweeteners coupled with an innate capacity to convert sugar into fat via hepatic de novo lipogenesis. In addition to serving as substrates, monosaccharides also increase the expression of key enzymes involved in de novo lipogenesis via the carbohydrate response element-binding protein (ChREBP). To determine whether ChREBP is a potential therapeutic target, we decreased hepatic expression of ChREBP with a specific antisense oligonucleotide (ASO) in male Sprague-Dawley rats fed either a high-fructose or high-fat diet. ChREBP ASO treatment decreased plasma triglyceride concentrations compared with control ASO treatment in both diet groups. The reduction was more pronounced in the fructose-fed group and attributed to decreased hepatic expression of ACC2, FAS, SCD1, and MTTP and a decrease in the rate of hepatic triglyceride secretion. This was associated with an increase in insulin-stimulated peripheral glucose uptake, as assessed by the hyperinsulinemic-euglycemic clamp. In contrast, ChREBP ASO did not alter hepatic lipid content or hepatic insulin sensitivity. Interestingly, fructose-fed rats treated with ChREBP ASO had increased plasma uric acid, alanine transaminase, and aspartate aminotransferase concentrations. This was associated with decreased expression of fructose aldolase and fructokinase, reminiscent of inherited disorders of fructose metabolism. In summary, these studies suggest that targeting ChREBP may prevent fructose-induced hypertriglyceridemia but without the improvements in hepatic steatosis and hepatic insulin responsiveness.

Skeletal muscle insulin resistance promotes increased hepatic de novo lipogenesis, hyperlipidemia, and hepatic steatosis in the elderly

Aging is closely associated with muscle insulin resistance, hyperlipidemia, nonalcoholic fatty liver disease (NAFLD), and type 2 diabetes. We examined the hypothesis that muscle insulin resistance in healthy aging promotes increased hepatic de novo lipogenesis (DNL) and hyperlipidemia by altering the distribution pattern of postprandial energy storage. Healthy, normal weight, sedentary elderly subjects pair-matched to young subjects were given two high-carbohydrate meals followed by ¹³C/¹H magnetic resonance spectroscopy measurements of postprandial changes in muscle and liver glycogen and lipid content, and assessment of DNL using ²H₂O. Net muscle glycogen synthesis was reduced by 45% (P < 0.007) in the elderly subjects compared with the young, reflecting severe muscle insulin resistance. Net liver glycogen synthesis was similar between groups (elderly, 143 ± 23 mmol/L vs. young, 138 ± 13 mmol/L; P = NS). Hepatic DNL was more than twofold higher in the elderly than in the young subjects (elderly, 14.5 ± 1.4% vs. young, 6.9 ± 0.7%; P = 0.00015) and was associated with approximately threefold higher postprandial hepatic triglyceride (TG) content (P < 0.005) and increased fasting plasma TGs (elderly, 1.19 ± 0.18 mmol/L vs. young, 0.74 ± 0.11 mmol/L; P = 0.02). These results strongly support the hypothesis that muscle insulin resistance in aging promotes hyperlipidemia and NAFLD by altering the pattern of postprandial carbohydrate storage away from muscle glycogen and into hepatic DNL.

Size at birth and adult fat mass in twin sheep are determined in early gestation

Size at birth is related to adult health outcomes. Twins are born smaller than singletons; this has been assumed to be secondary to limited nutrient supply in late gestation.We hypothesised that growth trajectory in twins, and the adult consequences of being conceived a twin, are determined in early gestation. Twin pregnancies in sheep were randomised to reduction of one twin on day 42 of a 148 day pregnancy by intra-thoracic KCl (Reductions, n =46) or a sham procedure (Twins, n =22). Singleton-bearing ewes also underwent a sham procedure (n =27). Ewes lambed spontaneously. Linear measures of size at birth were similar in Twins and Reductions, and significantly less than in Singletons. Birthweight was lower in Twins and Reductions than in Singletons, and less in Twins than in Reductions (means (SEM): Singletons, liveborn n =23: 6.59 (0.17) kg; Twins, liveborn n =36: 5.23 (0.16) kg; Reductions, liveborn n =27: 5.76 (0.15) kg; all comparisons P <0.05). Reductions grew most rapidly between birth and weaning (Singletons, 20.0 (0.4) g kg⁻¹ day⁻¹; Twins, 20.0 (0.3) g kg⁻¹ day⁻¹; Reductions, 21.0 (0.3) g kg⁻¹ day⁻¹, P <0.05) and were of similar weight as Singletons by weaning; Twins remained smaller by weaning but grew most rapidly thereafter (Singletons, 1.6 (0.1) g kg⁻¹ day⁻¹; Twins, 2.1 (0.1) g kg⁻¹ day⁻¹; Reductions, 1.6 (0.1) g kg⁻¹ day⁻¹, P <0.01), so that all groups had similar weight at 2 years. However, Twins and Reductions had greater percentage fat mass than Singletons at 2 years (Singletons, 11.1 (1.1)%; Twins, 14.8 (1.2)%; Reductions, 15.5 (1.1)%, P <0.05). Thus, in twins, fetal growth trajectory, linear size at birth and adult fat mass are largely determined in early gestation. If this is also true in humans, there are important implications for interventions aimed at optimising fetal growth and pregnancy outcome.

Reversal of muscle insulin resistance with exercise reduces postprandial hepatic de novo lipogenesis in insulin resistant individuals

Skeletal muscle insulin resistance has been implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and atherogenic dyslipidemia associated with the metabolic syndrome by altering the distribution pattern of postprandial energy storage. We conducted a study to examine this hypothesis by reversing muscle insulin resistance with a single bout of exercise and measuring hepatic de novo lipogenesis and hepatic triglyceride synthesis after a carbohydrate-rich meal. We studied 12 healthy, young, lean, insulin resistant individuals in an interventional, randomized cross-over trial. The response to the ingestion of a carbohydrate-rich meal was studied at rest and after one 45-min bout of exercise on an elliptical trainer. Hepatic de novo lipogenesis was assessed by using (2)H(2)O, and changes in glycogen and fat content in liver and muscle were measured by (13)C and (1)H magnetic resonance spectroscopy, respectively. Exercise resulted in a greater than threefold increase in postprandial net muscle glycogen synthesis (P < 0.001), reflecting improved muscle insulin responsiveness, and a ≈40% reduction (P < 0.05) in net hepatic triglyceride synthesis. These changes in whole body energy storage were accompanied by a ≈30% decrease in hepatic de novo lipogenesis (P < 0.01) and were independent of changes in fasting or postprandial plasma glucose and insulin concentrations. These data demonstrate that skeletal muscle insulin resistance is an early therapeutic target for the treatment and prevention of atherogenic dyslipidemia and NAFLD in young insulin resistant individuals who are prone to develop the metabolic syndrome and type 2 diabetes.

In vivo D2O labeling to quantify static and dynamic changes in cholesterol and cholesterol esters by high resolution LC/MS

High resolution LC/MS-MS and LC/APPI-MS methods have been established for the quantitation of flux in the turnover of cholesterol and cholesterol ester. Attention was directed toward quantifying the monoisotopic mass (M0) and that of the singly deuterated labeled (M+1) isotope. A good degree of isotopic dynamic range has been achieved by LC/MS-MS ranging from 3-4 orders of magnitude. Correlation between the linearity of GC/MS and LC atmospheric pressure photoionization (APPI)-MS are complimentary (r² = 0.9409). To prove the viability of this particular approach, male C57Bl/6 mice on either a high carbohydrate (HC) or a high fat (HF) diet were treated with ²H₂O for 96 h. Gene expression analysis showed an increase in the activity of stearoyl-CoA desaturase (Scd1) in the HC diet up to 69-fold (P < 0.0008) compared with the HF diet. This result was supported by the quantitative flux measurement of the isotopic incorporation of ²H into the respective cholesterol and cholesterol ester (CE) pools. We concluded that it is possible to readily obtain static and dynamic measurement of cholesterol and CEs in vivo by coupling novel LC/MS methods with stable isotope-based protocols.

A potential role for muscle in glucose homeostasis: in vivo kinetic studies in glycogen storage disease type 1a and fructose-1,6-bisphosphatase deficiency

BACKGROUND

A potential role for muscle in glucose homeostasis was recently suggested based on characterization of extrahepatic and extrarenal glucose-6-phosphatase (glucose-6-phosphatase-beta). To study the role of extrahepatic tissue in glucose homeostasis during fasting glucose kinetics were studied in two patients with a deficient hepatic and renal glycogenolysis and/or gluconeogenesis.

DESIGN

Endogenous glucose production (EGP), glycogenolysis (GGL), and gluconeogenesis (GNG) were quantified with stable isotopes in a patient with glycogen storage disease type 1a (GSD-1a) and a patient with fructose-1,6-bisphosphatase (FBPase) deficiency. The [6,6-(2)H(2)]glucose dilution method in combination with the deuterated water method was used during individualized fasting tests.

RESULTS

Both patients became hypoglycemic after 2.5 and 14.5 h fasting, respectively. At that time, the patient with GSD-1a had EGP 3.84 micromol/kg per min (30% of normal EGP after an overnight fast), GGL 3.09 micromol/kg per min, and GNG 0.75 micromol/kg per min. The patient with FBPase deficiency had EGP 8.53 micromol/kg per min (62% of normal EGP after an overnight fast), GGL 6.89 micromol/kg per min GGL, and GNG 1.64 micromol/kg per min.

CONCLUSION

EGP was severely hampered in both patients, resulting in hypoglycemia. However, despite defective hepatic and renal GNG in both disorders and defective hepatic GGL in GSD-1a, both patients were still able to produce glucose via both pathways. As all necessary enzymes of these pathways have now been functionally detected in muscle, a contribution of muscle to EGP during fasting via both GGL as well as GNG is suggested.

Dynamics of glutathione and ophthalmate traced with 2H-enriched body water in rats and humans

We developed a LC-MS-MS assay of the (2)H labeling of free glutathione (GSH) and bound glutathione [GSSR; which includes all DTT-reducible forms, primarily glutathione disulfide (GSSG) and mixed disulfides with proteins] and ophthalmate (an index of GSH depletion) labeled from (2)H-enriched body water. In rats whose body water was 2.5% (2)H enriched for up to 31 days, GSH labeling follows a complex pattern because of different rates of labeling of its constitutive amino acids. In rats infused with [(13)C(2),(15)N-glycine]glutathione, the rate of appearance of plasma GSH was 2.1 micromol.min(-1).kg(-1), and the half-life of plasma GSH/GSSR was 6-8 min. In healthy humans whose body fluids were 0.5% (2)H enriched, the (2)H labeling of GSH/GSSR and ophthalmate can be precisely measured after 4 h, with GSH being more rapidly labeled than GSSR. Since plasma GSH/GSSR derives mostly from liver, this technique opens the way to 2) probe noninvasively the labeling pattern and redox status of the liver GSH system in humans and 2) assess the usefulness of ophthalmate as an index of GSH depletion.

In vivo dynamics of stable chronic lymphocytic leukemia inversely correlate with somatic hypermutation levels and suggest no major leukemic turnover in bone marrow

Although accumulating evidence indicates that chronic lymphocytic leukemia (CLL) is a disease with appreciable cell dynamics, it remains uncertain whether this also applies to patients with stable disease. In this study, (2)H(2)O was administered to a clinically homogeneous cohort of nine stable, untreated CLL patients. CLL dynamics in blood and bone marrow were determined and compared with normal B-cell dynamics in blood from five healthy individuals who underwent a similar (2)H(2)O labeling protocol. Average CLL turnover rates (0.08-0.35% of the clone per day) were approximately 2-fold lower than average B-cell turnover rates from healthy individuals (0.34-0.89%), whereas the rate at which labeled CLL cells in blood disappeared (0.00-0.39% of B cells per day) was approximately 10-fold lower compared with labeled B cells from healthy individuals (1.57-4.24% per day). Leukemic cell turnover variables inversely correlated with the level of somatic hypermutation of the CLL clone (IgVH mutations). Although CLL cells in bone marrow had a higher level of label enrichment than CLL cells in blood, no difference between proliferation rates and proapoptotic and antiapoptotic profiles of CLL cells from these compartments was observed. These data suggest that, in stable disease, there is a biological relationship between the degree of somatic hypermutation of the CLL clone and its dynamics in vivo. Furthermore, in contrast to lymph nodes, the bone marrow does not seem to be a major CLL proliferation site.

Fasting adaptation in idiopathic ketotic hypoglycemia: a mismatch between glucose production and demand

In order to study the pathophysiology of hypoglycemia in idiopathic ketotic hypoglycemia (KH), glucose kinetics during fasting in patients with KH were determined. A fasting test was performed in 12 children with previously documented KH. Besides determination of glucoregulatory hormones, plasma ketones, FFA and alanine, the rates of endogenous glucose production (EGP), glucose uptake, gluconeogenesis (GNG) and glycogenolysis (GGL) were quantified using the [6,6-(2)H(2)] glucose isotope dilution method and the deuterated water method. The five youngest subjects (age 2.5-3.9 years) became hypoglycemic (glucose <3.0 mmol/l) during the test. Mean differences in glucose kinetics between overnight fasting and the end of the test in the hypoglycemic vs. the normoglycemic subjects were: EGP: -31.9% vs. -17.9% (p = 0.007), GGL: -66.2% vs. -50.8% (p = 0.465) and GNG 6.8% vs. 19.5% (p = 0.465). Plasma alanine levels were significantly lower (p = 0.028) at the end of the test in the hypoglycemic subjects. Plasma ketones and FFA levels were in the normal range for fasting duration in all subjects. We conclude that hypoglycemia in KH is caused by the inability to sustain an adequate EGP during fasting in view of the higher glucose requirement in young children. The decrease in GGL is not accompanied by a significant increase in GNG, possibly because of a limitation in the supply of alanine. Our results support the hypothesis that KH represents the lower tail of the Gaussian distribution of fasting tolerance in children.

Sparse production but preferential incorporation of recently produced naive T cells in the human peripheral pool

In mice, recent thymic emigrants (RTEs) make up a large part of the naïve T cell pool and have been suggested to be a distinct short-lived pool. In humans, however, the life span and number of RTEs are unknown. Although (2)H(2)O labeling in young mice showed high thymic-dependent daily naïve T cell production, long term up- and down-labeling with (2)H(2)O in human adults revealed a low daily production of naïve T cells. Using mathematical modeling, we estimated human naïve CD4 and CD8 T cell half-lives of 4.2 and 6.5 years, respectively, whereas memory CD4 and CD8 T cells had half-lives of 0.4 and 0.7 year. The estimated half-life of recently produced naïve T cells was much longer than these average half-lives. Thus, our data are incompatible with a substantial short-lived RTE population in human adults and suggest that the few naïve T cells that are newly produced are preferentially incorporated in the peripheral pool.

Very young children with uncomplicated falciparum malaria have higher risk of hypoglycaemia: a study from Suriname

OBJECTIVE

To measure glucose kinetics and the influence of age, nutritional status and fasting duration in children with uncomplicated falciparum malaria (UFM) under the age of 5 years.

METHODS

Plasma glucose concentration, endogenous glucose production (EGP) and gluconeogenesis (GNG) were measured using [6,6-(2)H(2)]glucose and (2)H(2)O in 17 very young (<3 years) and 7 older (3-5 years) Surinamese children with UFM admitted to the Distrikt Hospital Stoelmanseiland and Diakonessen Hospital Paramaribo over 17 months.

RESULTS

Plasma glucose concentration was lower in the group of very young children than in the older children (P = 0.028). There were no differences in EGP and GNG between the groups. Overall GNG contributed 56% (median, range 17-87%) to EGP, with no differences between the groups (P = 0.240). Glucose clearance was lower in the older children (P = 0.026). Glucose concentration did not differ between children with weight for length/height less than -1.3 SD and children with weight for length/height greater than -1.3 SD (P = 0.266). Plasma glucose concentration was not predicted by fasting duration (P = 0.762).

CONCLUSIONS

Our data suggest a higher risk of hypoglycaemia in very young children with uncomplicated malaria as plasma glucose concentration was lower in this study group. Since this could not be attributed to an impaired EGP, and because glucose clearance was lower in the older children, we presume that older children were better capable of reducing glucose utilization during fasting. Studies on glucose kinetics are feasible in very young children with malaria and give more insight in the pathophysiology of hypoglycaemia.

Measurement of cell proliferation by heavy water labeling

DNA replication occurs almost exclusively during S-phase of the cell cycle and represents a simple biochemical metric of cell division. Previous methods for measuring cell proliferation rates have important limitations. Here, we describe experimental protocols for measuring cell proliferation and death rates based on the incorporation of deuterium ((2)H) from heavy water ((2)H(2)O) into the deoxyribose moiety of purine deoxyribonucleotides in DNA of dividing cells. Label incorporation is measured by gas chromatography/mass spectrometry. Modifications of the basic protocol permit analysis of small cell samples (down to 2,000 cells). The theoretical basis and operational requirements for effective use of these methods to measure proliferation and death rates of cells in vivo are described. These methods are safe for use in humans, have technical and interpretation advantages over alternative techniques and can be used on small numbers of cells. The protocols enable definitive in vivo studies of the fraction or absolute number of newly divided cells and their subsequent survival kinetics in animals and humans.

Low Utilization of Circulating Glucose after Food Withdrawal in Snell Dwarf Mice

Glucose metabolism is altered in long-lived people and mice. Although it is clear that there is an association between altered glucose metabolism and longevity, it is not known whether this link is causal or not. Our current hypothesis is that decreased fasting glucose utilization may increase longevity by reducing oxygen radical production, a potential cause of aging. We observed that whole body fasting glucose utilization was lower in the Snell dwarf, a long-lived mutant mouse. Whole body fasting glucose utilization may be reduced by a decrease in the production of circulating glucose. Our isotope labeling analysis indicated both gluconeogenesis and glycogenolysis were suppressed in Snell dwarfs. Elevated circulating adiponectin may contribute to the reduction of glucose production in Snell dwarfs. Adiponectin lowered the appearance of glucose in the media over hepatoma cells by suppressing gluconeogenesis and glycogenolysis. The suppression of glucose production by adiponectin in vitro depended on AMP-activated protein kinase, a cell mediator of fatty acid oxidation. Elevated fatty acid oxidation was indicated in Snell dwarfs by increased utilization of circulating oleic acid, reduced intracellular triglyceride content, and increased phosphorylation of acetyl-CoA carboxylase. Finally, protein carbonyl content, a marker of oxygen radical damage, was decreased in Snell dwarfs. The correlation between high glucose utilization and elevated oxygen radical production was also observed in vitro by altering the concentrations of glucose and fatty acids in the media or pharmacologic inhibition of glucose and fatty acid oxidation with 4-hydroxycyanocinnamic acid and etomoxir, respectively.

Relationship between hepatic/visceral fat and hepatic insulin resistance in nondiabetic and type 2 diabetic subjects

BACKGROUND AND AIMS

Abdominal fat accumulation (visceral/hepatic) has been associated with hepatic insulin resistance (IR) in obesity and type 2 diabetes (T2DM). We examined the relationship between visceral/hepatic fat accumulation and hepatic IR/accelerated gluconeogenesis (GNG).

METHODS

In 14 normal glucose tolerant (NGT) (body mass index [BMI] = 25 +/- 1 kg/m(2)) and 43 T2DM (24 nonobese, BMI = 26 +/- 1; 19 obese, BMI = 32 +/- 1 kg/m(2)) subjects, we measured endogenous (hepatic) glucose production (3-(3)H-glucose) and GNG ((2)H(2)O) in the basal state and during 240 pmol/m(2)/min euglycemic-hyperinsulinemic clamp, and liver (LF) subcutaneous (SAT)/visceral (VAT) fat content by magnetic resonance spectroscopy/magnetic resonance imaging.

RESULTS

LF was increased in lean T2DM compared with lean NGT (18% +/- 3% vs 9% +/- 2%, P < .03), but was similar in lean T2DM and obese T2DM (18% +/- 3% vs 22% +/- 3%; P = NS). Both VAT and SAT increased progressively from lean NGT to lean T2DM to obese T2DM. T2DM had increased basal endogenous glucose production (EGP) (NGT, 15.1 +/- 0.5; lean T2DM, 16.3 +/- 0.4; obese T2DM, 17.2 +/- 0.6 micromol/min/kg(ffm); P = .02) and basal GNG flux (NGT, 8.6 +/- 0.4; lean T2DM, 9.6 +/- 0.4; obese T2DM, 11.1 +/- 0.6 micromol/min/kg(ffm); P = .02). Basal hepatic IR index (EGP x fasting plasma insulin) was increased in T2DM (NGT, 816 +/- 54; lean T2DM, 1252 +/- 164; obese T2DM, 1810 +/- 210; P = .007). In T2DM, after accounting for age, sex, and BMI, both LF and VAT, but not SAT, were correlated significantly (P < .05) with basal hepatic IR and residual EGP during insulin clamp. Basal percentage of GNG and GNG flux were correlated positively with VAT (P < .05), but not with LF. LF, but not VAT, was correlated with fasting insulin, insulin-stimulated glucose disposal, and impaired FFA suppression by insulin (all P < .05).

CONCLUSIONS

Abdominal adiposity significantly affects both lipid (FFA) and glucose metabolism. Excess VAT primarily increases GNG flux. Both VAT and LF are associated with hepatic IR.

The role of skeletal muscle insulin resistance in the pathogenesis of the metabolic syndrome

We examined the hypothesis that insulin resistance in skeletal muscle promotes the development of atherogenic dyslipidemia, associated with the metabolic syndrome, by altering the distribution pattern of postprandial energy storage. Following ingestion of two high carbohydrate mixed meals, net muscle glycogen synthesis was reduced by approximately 60% in young, lean, insulin-resistant subjects compared with a similar cohort of age-weight-body mass index-activity-matched, insulin-sensitive, control subjects. In contrast, hepatic de novo lipogenesis and hepatic triglyceride synthesis were both increased by >2-fold in the insulin-resistant subjects. These changes were associated with a 60% increase in plasma triglyceride concentrations and an approximately 20% reduction in plasma high-density lipoprotein concentrations but no differences in plasma concentrations of TNF-alpha, IL-6, adiponectin, resistin, retinol binding protein-4, or intraabdominal fat volume. These data demonstrate that insulin resistance in skeletal muscle, due to decreased muscle glycogen synthesis, can promote atherogenic dyslipidemia by changing the pattern of ingested carbohydrate away from skeletal muscle glycogen synthesis into hepatic de novo lipogenesis, resulting in an increase in plasma triglyceride concentrations and a reduction in plasma high-density lipoprotein concentrations. Furthermore, insulin resistance in these subjects was independent of changes in the plasma concentrations of TNF-alpha, IL-6, high-molecular-weight adiponectin, resistin, retinol binding protein-4, or intraabdominal obesity, suggesting that these factors do not play a primary role in causing insulin resistance in the early stages of the metabolic syndrome.

The effect of pioglitazone on the liver: role of adiponectin

OBJECTIVE

Diabetic hyperglycemia results from insulin resistance of peripheral tissues and glucose overproduction due to increased gluconeogenesis (GNG). Thiazolidinediones (TZDs) improve peripheral insulin sensitivity, but the effect on the liver is less clear. The goal of this study was to examine the effect of TZDs on GNG.

RESEARCH DESIGN AND METHODS

Twenty sulfonylurea-treated type 2 diabetic subjects were randomly assigned (double-blind study) to receive pioglitazone (PIO group; 45 mg/day) or placebo (Plc group) for 4 months to assess endogenous glucose production (EGP) (3-(3)H-glucose infusion), GNG (D2O technique), and insulin sensitivity by two-step hyperinsulinemic-euglycemic clamp (240 and 960 pmol/min per m2).

RESULTS

Fasting plasma glucose (FPG) (10.0 +/- 0.8 to 7.7 +/- 0.7 mmol/l) and HbA1c (9.0 +/- 0.4 to 7.3 +/- 0.6%) decreased in the PIO and increased in Plc group (P < 0.05 PIO vs. Plc). Insulin sensitivity increased approximately 40% during high insulin clamp after pioglitazone (P < 0.01) and remained unchanged in the Plc group (P < 0.05 PIO vs. Plc). EGP did not change, while GNG decreased in the PIO group (9.6 +/- 0.7 to 8.7 +/- 0.6 micromol x min(-1) x kg(ffm)(-1)) and increased in the Plc group (8.0 +/- 0.5 to 9.6 +/- 0.8) (P < 0.05 PIO vs. Plc). Change in FPG correlated with change in GNG flux (r = 0.63, P < 0.003) and in insulin sensitivity (r = 0.59, P < 0.01). Plasma adiponectin increased after pioglitazone (P < 0.001) and correlated with delta FPG (r = -0.54, P < 0.03), delta GNG flux (r = -0.47, P < 0.05), and delta insulin sensitivity (r = 0.65, P < 0.005). Plasma free fatty acids decreased after pioglitazone and correlated with delta GNG flux (r = 0.54, P < 0.02). From stepwise regression analysis, the strongest determinant of change in FPG was change in GNG flux.

CONCLUSIONS

Pioglitazone improves FPG, primarily by reducing GNG flux in type 2 diabetic subjects.

Partitioning of energy during lactation of primiparous beef cows1

For a beef cow to continue in an annual production cycle, she must rebreed within 3 mo after calving. Malnutrition during this period frequently results in failure of the cow to become pregnant. The energetic needs of the cow are increased by lactation, and additional energy is required for growth of the primiparous cow. Determining energy expenditures during the first 40 to 60 d postpartum is critical to developing feed programs that will allow cows to become pregnant with a second calf. Sixty-seven balance trials were conducted on 25 MARC III cows (4-breed composite: (1/4) Hereford, (1/4) Angus, (1/4) Red Poll, and (1/4) Pinzgauer) that were between 3 and 53 d in milk. Cows' BW were 481 +/- 4 kg. Metabolizable energy intake ranged from 14.8 to 28.9 Mcal/d. Milk yields ranged from 4.7 to 13.3 kg/d. Recovered energy (RE) increased linearly with increased ME intake. Forty-seven observations were obtained with cows in negative tissue energy (TE) balance, and 20 observations were obtained with cows in positive TE balance. Estimated zero RE from regression analysis of RE on ME intake was 146 kcal of ME/kg of BW(0.75). Efficiency of conversion of ME to lactation energy (LE) was 72%. The efficiency for conversion of ME to TE and the conversion of TE to LE was 78%. Our findings suggest that, even though their milk production is lower, the overall efficiency of energy retention in young beef cows is similar to that of dairy cows.

Reproducibility of gas chromatography–mass spectrometry measurements of 2H labeling of water: Application for measuring body composition in mice

Deuterium-labeled water (2H2O) has emerged as a novel isotope tracer. Following the administration of 2H2O, it is possible to study the dynamics of carbohydrate, protein, lipid, and DNA and to determine body composition. Those studies require reliable measurements of the 2H labeling of water. Although simple gas chromatography-mass spectrometry (GC-MS) methods have been developed for measuring the 2H enrichment of biological fluids, investigators have not reported on the intra- and/or interdaily variability of the measurements. We have experimentally examined the reproducibility of one GC-MS method for measuring the 2H labeling of water. Briefly, hydrogen (deuterium) atoms in water were exchanged with those bound to acetone, and the 2H labeling of acetone was then determined under electron impact ionization. We found that the coefficient of variation is generally less than 0.5% when water is labeled between 0 and 2.8 mole percentage excess 2H. We demonstrated that this highly reproducible result allows one to use 2H2O and the "acetone method" to measure physiological parameters such as body composition in mice.

Development of a novel method for measuring in vivo breast epithelial cell proliferation in humans

Cell proliferation plays an important role in all stages of carcinogenesis. Currently, no safe, direct, in vivo method of measuring breast epithelial cell (BEC) proliferation rates in humans exists. Static immunohistochemical markers of cell proliferation, such as Ki-67 and PCNA indices, have technical limitations including high inter-lab variability, inaccuracy in the presence of agents that cause G1/S cell cycle block and inadequate sensitivity in post-menopausal women with low BEC proliferation rates. We describe here a safe, direct method of measuring BEC proliferation rates in vivo in women using heavy water ((2)H(2)O) labeling coupled with mass spectrometric analysis. Proliferation of normal and tumor BEC was measured from breast tissue biopsies in women undergoing mastectomy (n = 11) and normal BEC from healthy volunteers (n = 16). Women took heavy water (50-150 ml per day) for 1-4 weeks. Pre-menopausal women had significantly higher proliferation rates than post-menopausal women (0.7 +/- 0.1 versus 0.2 +/- 0.1 new cells per day, respectively), and tumor BEC had different proliferation rates than normal BEC from the same breast. The method is analytically reproducible and remains sensitive in the range of low proliferation rates. In summary, this novel method of measuring BEC proliferation in vivo holds promise for assessing the effects of anti-proliferative chemopreventive and chemotherapeutic agents.

Physiologic and pharmacologic factors influencing glyceroneogenic contribution to triacylglyceride glycerol measured by mass isotopomer distribution analysis

An imbalance between triacylglycerol synthesis and breakdown is necessary for the development of obesity. The direct precursor for triacylglycerol biosynthesis is alpha-glycerol phosphate, which can have glycolytic and glyceroneogenic origins. We present a technique for determining the relative glyceroneogenic contribution to triacylglyceride glycerol by labeling the glycerol moiety with 2H2O. The number of hydrogen atoms (n) incorporated from H2O into C-H bonds reflects the metabolic source of alpha-glycerol phosphate and can be calculated by combinatorial analysis of the distribution of mass isotopomers in triacylglyceride glycerol. Three physiological settings with potential effects on glyceroneogenesis and glycolysis were studied in rodents. Adipose tissue acylglyceride glycerol in mice fed a low carbohydrate diet had significantly higher values of n than in mice fed a high carbohydrate diet, suggesting an increased contribution from glyceroneogenesis of from 17 to 50% on the low carbohydrate diet. Similarly, mice administered rosiglitazone had a significant relative increase in glyceroneogenesis (from 17 to 53%), indicated by an increase in adipose acylglyceride glycerol n. Fructose infusion in overnight fasted rats rapidly lowered plasma triacylglyceride glycerol n, reflecting a decreased contribution from glyceroneogenesis (from 66 to 34%) presumably because of increased glycolytic input. In conclusion, we demonstrate that the number of C-H atoms derived from cellular H2O in triacylglyceride glycerol is an informative indicator of alpha-glycerol phosphate origin and, ultimately, triacylglycerol metabolism. Under certain physiological conditions, glyceroneogenesis can be up-regulated in adipose (e.g. low carbohydrate diet) or down-regulated in liver (e.g. fructose infusion). Additionally, stimulation of glyceroneogenesis by rosiglitazone in adipose tissue may be an important factor in the antilipolytic actions of thiazolidinediones.

Adiponectin and glucose production in patients infected with Plasmodium falciparum

Infections are often complicated by an increase in glucose production due to stimulation of the secretion of glucose counter-regulatory hormones and cytokines. Adiponectin, a fat-derived hormone with insulin-sensitizing properties, could play a regulatory role in the degree of stimulation of glucose production by the infectious agent. Therefore, we investigated the possible correlation between glucose production and plasma adiponectin levels in 25 subjects: 7 patients with cerebral malaria, 6 with uncomplicated malaria, and 12 matched controls. Glucose production was significantly higher in patients with malaria compared to healthy controls (P < .001). Adiponectin levels were not different between the patients with malaria and the control group. However, patients with cerebral malaria had significantly higher values for adiponectin than the patients with uncomplicated malaria (P < .005). Glucose production and gluconeogenesis were positively correlated to plasma adiponectin in the patients (r = 0.835, P < .001 and r = 0.846, P < .001, respectively), whereas these correlations were absent in the controls (r = -0.329, NS and r = -0.028, NS, respectively). In conclusion, adiponectin levels were not different between patients with malaria and their matched controls. However, patients infected with Plasmodium falciparum who have higher glucose production also have higher adiponectin levels. In healthy subjects such a correlation was not found. As adiponectin is known to inhibit glucose production, stimulation of adiponectin secretion during infection could be intended to restrain the glucose production stimulating properties of hormones and cytokines secreted during infection.

In Vivo Measurement of Microtubule Dynamics Using Stable Isotope Labeling with Heavy Water

Microtubules are dynamic polymers with central roles in the mitotic checkpoint, mitotic spindle assembly, and chromosome segregation. Agents that block mitotic progression and cell proliferation by interfering with microtubule dynamics (microtubule-targeted tubulin-polymerizing agents (MTPAs)) are powerful antitumor agents. Effects of MTPAs (e.g. paclitaxel) on microtubule dynamics have not yet been directly demonstrated in intact animals, however. Here we describe a method that measures microtubule dynamics as an exchange of tubulin dimers into microtubules in vivo. The incorporation of deuterium ((2)H(2)) from heavy water ((2)H(2)O) into tubulin dimers and polymers is measured by gas chromatography/mass spectrometry. In cultured human lung and breast cancer cell lines, or in tumors implanted into nude mice, tubulin dimers and polymerized microtubules exhibited nearly identical label incorporation rates, reflecting their rapid exchange. Administration of paclitaxel during 24 h of (2)H(2)O labeling in vivo reduced (2)H labeling in polymers while increasing (2)H in dimers, indicating diminished flux of dimers into polymers (i.e. inhibition of microtubule dynamic equilibrium). In vivo inhibition of microtubule dynamics was dose-dependent and correlated with inhibition of DNA replication, a stable isotopic measure of tumor cell growth. In contrast, microtubule polymers from sciatic nerve of untreated mice were not in dynamic equilibrium with tubulin dimers, and paclitaxel increased label incorporation into polymers. Our results directly demonstrate altered microtubule dynamics as an important action of MTPAs in vivo. This sensitive and quantitative in vivo assay of microtubule dynamics may prove useful for pre-clinical and clinical development of the next generation of MTPAs as anticancer drugs.

FFAs are not involved in regulation of gluconeogenesis and glycogenolysis in adults with uncomplicated P. falciparum malaria

In normal subjects, elevation of plasma free fatty acid (FFA) levels stimulates gluconeogenesis (GNG) and inhibits glycogenolysis (GLY). In adults with uncomplicated Plasmodium falciparum malaria, GNG is increased and GLY decreased. To test the hypothesis that FFAs are regulators of GNG and GLY in uncomplicated falciparum malaria, we investigated the effect of inhibition of lipolysis by acipimox in 12 patients with uncomplicated falciparum malaria. Six of them were given acipimox, and six served as controls. Also as controls, six matched healthy subjects were studied on two occasions with and without acipimox. After 16 h of fasting, glucose production and GNG were significantly higher in the malaria patients compared with the healthy controls (P = 0.003 and < 0.0001, respectively), whereas GLY was significantly lower (P < 0.001), together with elevated plasma concentrations of cortisol and glucagon. During the study, glucose production in patients declined over time (P < 0.0001), without a statistically significant difference between the acipimox-treated and untreated patients. In controls, however, with acipimox the decline was less outspoken compared with nontreated controls (P = 0.005). GNG was unchanged over time in patients as well as in healthy controls, and no influence of acipimox was found. In patients, GLY declined over time (P < 0.001), without a difference between acipimox-treated and untreated patients. In contrast, in controls treated with acipimox, no change over time was found, which was statistically different from the decline in untreated controls (P = 0.002). In conclusion, in falciparum malaria, FFAs are not involved in regulation of glucose production, nor of GNG or GLY.

Influence of prolonged starvation on glucose kinetics in pregnant patients infected with Plasmodium falciparum

Hypoglycaemia is a recognised complication of malaria in pregnancy, but its pathophysiology is not well understood. We studied the influence of fasting on glucose production and gluconeogenesis by infusion of [6,6-(2)H(2)]glucose and ingestion of (2)H(2)O in 20 female subjects, eight pregnant patients with uncomplicated falciparum malaria, six pregnant controls matched for age and trimester and six non-pregnant controls matched for age. Infection with Plasmodium falciparum induced a significant increase in glucose production (16.7+/-0.3 vs. 12.4+/-0.8 micromol/kg/min; P=0.002) and gluconeogenesis (12.5+/-0.6 vs. 8.2+/-0.7 micromol/kg/min; P=0.001) without a change in the glucoregulatory hormone milieu, compared to the healthy pregnant controls. Extension of the fast from 20.30 to 24.30 h resulted in a rate of decline of glucose production that was similar in patients with malaria and healthy pregnant subjects, a decline that was steeper compared to the non-pregnant subjects (-0.283 and -0.426 vs. -0.065 micromol/kg/min/h; P=0.037). The plasma glucose concentration measured at 20.30 h of fasting in the malaria patients was intermediate between the value found in the pregnant and the non-pregnant controls (4.01+/-0.2 mmol/l) while it was significantly lower in the non-infected pregnant women compared to non-pregnant controls (3.59+/-0.14 vs. 4.70+/-0.29 mmol/l; P=0.009). Plasma glucose concentration declined at a similar rate in patients with malaria and pregnant controls but faster compared to the non-pregnant controls (-0.078 and -0.093 vs. -0.044 mmol/l/h; P < 0.05). We conclude that fasting is a major risk factor for hypoglycaemia in pregnancy. Non-severe Plasmodium falciparum infection in pregnant women results in higher glucose production and higher glucose levels, thereby, compared to healthy pregnant patients, delaying of the occurrence of hypoglycaemia due to fasting. The exact mechanism of hypoglycaemia in fasting pregnant women remains to be elucidated.

Gluconeogenesis in humans with induced hyperlactatemia during low-intensity exercise

We studied the role of lactate in gluconeogenesis (GNG) during exercise in untrained fasting humans. During the final hour of a 4-h cycle exercise at 33-34% maximal O(2) uptake, seven subjects received, in random order, either a sodium lactate infusion (60 micromol x kg(-1) x min(-1)) or an isomolar sodium bicarbonate infusion. The contribution of lactate to gluconeogenic glucose was quantified by measuring (2)H incorporation into glucose after body water was labeled with deuterium oxide, and glucose rate of appearance (R(a)) was measured by [6,6-(2)H(2)]glucose dilution. Infusion of lactate increased lactate concentration to 4.4 +/- 0.6 mM (mean +/- SE). Exercise induced a decrease in blood glucose concentration from 5.0 +/- 0.2 to 4.2 +/- 0.3 mM (P < 0.05); lactate infusion abolished this decrease (5.0 +/- 0.3 mM; P < 0.001) and increased glucose R(a) compared with bicarbonate infusion (P < 0.05). Lactate infusion increased both GNG from lactate (29 +/- 4 to 46 +/- 4% of glucose R(a), P < 0.001) and total GNG. We conclude that lactate infusion during low-intensity exercise in fasting humans 1). increased GNG from lactate and 2). increased glucose production, thus increasing the blood glucose concentration. These results indicate that GNG capacity is available in humans after an overnight fast and can be used to sustain blood glucose levels during low-intensity exercise when lactate, a known precursor of GNG, is available at elevated plasma levels.

Lactate disposal via gluconeogenesis is increased during exercise in patients with mitochondrial myopathy due to complex I deficiency

This study evaluated lactate disposal via gluconeogenesis as well as effects of FFA availability on gluconeogenesis via pyruvate (GNG(PYR)) in patients with mitochondrial myopathy due to complex I deficiency (CID). The rates of GNG(PYR) were measured in three CID patients and six healthy controls at rest and during 90 min cycle exercise, using the deuterium-labeled water method. All subjects served as their own control: on one occasion they were studied in the fasting state, and on the second occasion they received an infusion of triacylglycerol plus heparin. At rest, the fractional rate of gluconeogenesis from pyruvate was higher in patients than in controls in the fasting state. Triacylglycerol infusion was associated with increased rates of GNG(PYR) at rest in controls (p < 0.05) but not in patients. Circulating lactate and pyruvate levels were increased 3-fold during exercise in the CID patients. During exercise, GNG(PYR) increased in the CID patients (p < 0.01) and remained unchanged in controls, resulting in 85% and 72% higher absolute rates of GNG(PYR) in the patients than in the controls during fasting and triacylglycerol infusion, respectively. During exercise, rates of GNG(PYR) were not different between fasting and triacylglycerol infusion within both groups. Our data show that 1) GNG(PYR) is increased during exercise in CID patients; 2) increased pyruvate availability contributes to the higher rates of GNG(PYR) in the CID patients; and 3) exogenous infusion of fatty acids is not associated with increased rates of GNG(PYR) in CID patients at rest or during exercise. GNG(PYR) is a significant mechanism of lactate disposal in exercising CID patients, but triglyceride infusion does not enhance their lactate disposal through this mechanism.

Effect of physiological hyperinsulinemia on gluconeogenesis in nondiabetic subjects and in type 2 diabetic patients

Gluconeogenesis (GNG) is enhanced in type 2 diabetes. In experimental animals, insulin at high doses decreases the incorporation of labeled GNG precursors into plasma glucose. Whether physiological hyperinsulinemia has any effect on total GNG in humans has not been determined. We combined the insulin clamp with the (2)H(2)O technique to measure total GNG in 33 subjects with type 2 diabetes (BMI 29.0 +/- 0.6 kg/m(2), fasting plasma glucose 8.1 +/- 0.3 mmol/l) and in 9 nondiabetic BMI-matched subjects after 16 h of fasting and after euglycemic hyperinsulinemia. A primed-constant infusion of 6,6-(2)H-glucose was used to monitor endogenous glucose output (EGO); insulin (40 mU. min(-1). m(-2)) was then infused while clamping plasma glucose for 2 h (at 5.8 +/- 0.1 and 4.9 +/- 0.2 mmol/l for diabetic and control subjects, respectively). In the fasting state, EGO averaged 15.2 +/- 0.4 micromol. min(-1). kg(-1)(ffm) (62% from GNG) in diabetic subjects and 12.2 +/- 0.7 micromol. min(-1). kg(-1)(ffm) (55% from GNG) in control subjects (P < 0.05 or less for both fluxes). Glycogenolysis (EGO - GNG) was similar in the two groups (P = NS). During the last 40 min of the clamp, both EGO and GNG were significantly (P < 0.01 or less, compared with fasting) inhibited (EGO 7.1 +/- 0.9 and 3.6 +/- 0.5 and GNG 7.9 +/- 0.5 and 4.5 +/- 1.0 respectively) but remained significantly (P < 0.05) higher in diabetic subjects, whereas glycogenolysis was suppressed completely and equally in both groups. During hyperinsulinemia, GNG micromol. min(-1). kg(-1)(ffm) in diabetic and control subjects, was reciprocally related to plasma glucose clearance. In conclusion, physiological hyperinsulinemia suppresses GNG by approximately 20%, while completely blocking glycogenolysis. Resistance of GNG (to insulin suppression) and resistance of glucose uptake (to insulin stimulation) are coupled phenomena. In type 2 diabetes, the excess GNG of the fasting state is carried over to the insulinized state, thereby contributing to glucose overproduction under both conditions.

In vivo effects of uncoupling protein-3 gene disruption on mitochondrial energy metabolism

To clarify the role of uncoupling protein-3 (UCP3) in skeletal muscle, we used NMR and isotopic labeling experiments to evaluate the effect of UCP3 knockout (UCP3KO) in mice on the regulation of energy metabolism in vivo. Whole body energy expenditure was determined from the turnover of doubly labeled body water. Coupling of mitochondrial oxidative phosphorylation in skeletal muscle was evaluated from measurements of rates of ATP synthesis (using (31)P NMR magnetization transfer experiments) and tricarboxylic acid (TCA) cycle flux (calculated from the time course of (13)C enrichment in C-4 and C-2 of glutamate during an infusion of [2-(13)C]acetate). At the whole body level, we observed no change in energy expenditure. However, at the cellular level, skeletal muscle UCP3KO increased the rate of ATP synthesis from P(i) more than 4-fold under fasting conditions (wild type, 2.2 +/- 0.6 versus knockout, 9.1 +/- 1.4 micromol/g of muscle/min, p < 0.001) with no change in TCA cycle flux rate (wild type, 0.74 +/- 0.04 versus knockout, 0.71 +/- 0.03 micromol/g of muscle/min). The increased efficiency of ATP production may account for the significant (p < 0.05) increase in the ratio of ATP to ADP in the muscle of UCP3KO mice (5.9 +/- 0.3) compared with controls (4.5 +/- 0.4). The data presented here provide the first evidence of uncoupling activity by UCP3 in skeletal muscle in vivo.

The effects of carbohydrate variation in isocaloric diets on glycogenolysis and gluconeogenesis in healthy men

To evaluate the effect of dietary carbohydrate content on postabsorptive glucose metabolism, we quantified gluconeogenesis and glycogenolysis after 11 days of high carbohydrate (85% carbohydrate), control (44% carbohydrate), and very low carbohydrate (2% carbohydrate) diets in six healthy men. Diets were eucaloric and provided 15% of energy as protein. Postabsorptive glucose production was measured by infusion of [6,6-2H2]glucose, and fractional gluconeogenesis was measured by ingestion of 2H2O. Postabsorptive glucose production rates were 13.0 +/- 0.7, 11.4 +/- 0.4, and 9.7 +/- 0.4 micromol/kg x min after high carbohydrate, control, and very low carbohydrate diets, respectively (P < 0.001 among the three diets). Gluconeogenesis was about 14% higher after the very low carbohydrate diet (6.3 +/- 0.2 micromol/kg x min; P = 0.001) compared to the control diet, but was not different between the high carbohydrate and control diets (5.5 +/- 0.3 vs. 5.5 +/- 0.2 micromol/kg x min). The rates of glycogenolysis were 7.5 +/- 0.5, 5.9 +/- 0.3, and 3.4 +/- 0.3 micromol/kg x min, respectively (P < 0.001 among the three diets). We conclude that under eucaloric conditions in healthy subjects, dietary carbohydrate content affects the rate of postabsorptive glucose production mainly by modulation of glycogenolysis. In contrast, dietary carbohydrate content affects the postabsorptive rate of gluconeogenesis minimally, as evidenced by only a slight increase in gluconeogenesis during severe carbohydrate restriction.

Assay of low deuterium enrichment of water by isotopic exchange with [U-13C3]acetone and gas chromatography-mass spectrometry

A sensitive assay of the 2H-enrichment of water based on the isotopic exchange between the hydrogens of water and of acetone in alkaline medium is described and validated. For low 2H-enrichments (0.008 to 0.5%), the sample is spiked with [U-13C3]acetone and NaOH. After exchange, 2H-enriched [U-13C3]acetone is extracted with chloroform and assayed by gas chromatography-mass spectrometry. With some instruments, ion-molecule reactions, resulting in increased baseline enrichment, are minimized by lowering the electron ionization energy from the usual 70 to 10 eV. The 2H-enrichment of water is amplified nearly sixfold in the M4/M3 ratio of [U-13C3]acetone. For high 2H-enrichments (0.25 to 100%), the use of unlabeled acetone suffices. After exchange, the mass isotopomer distribution of acetone is analyzed, yielding the 2H-enrichment of water. The assay with [U-13C3]acetone allows measuring the 2H-enrichment of water even in biological samples containing acetone. This technique is more rapid and economical than the classical isotope ratio mass spectrometric assay of the enrichment of hydrogen gas derived from the reduction of water.

Tracing gluconeogenesis with deuterated water: measurement of low deuterium enrichments on carbons 6 and 2 of glucose

The contribution of gluconeogenesis to glucose production in vivo can be measured by enriching body water with 0.5% 2H2O and measuring the glucose labeling ratio C6/C2 (Landau et al., J. Clin. Invest. 95, 172-178, 1995). We present further refinements of the measurements of the 2H enrichments on C6 and C2 of glucose. The transfer of 2H from C6 of glucose to hexamethylenetetramine (HMT) and extraction in preparation for gas chromatography-mass spectrometry can be done in a single test tube, without distillation of the intermediate formaldehyde. In addition, extraction of small amounts of HMT is greatly improved by making a HMT-iodine adduct. For C2, glucose is reduced to sorbitol, and 2H on C2 is transferred enzymatically to [U-13C3]pyruvate, forming [U-13C3,2-2H]lactate. The latter is assayed by negative chemical ionization gas chromatography-mass spectrometry of the pentafluorobenzyl derivative. The natural enrichment of the [U-13C3]lactyl ion is only 0.4%, allowing measurements of 2H enrichment down to 0.1%. These techniques were used in dogs infused with 2H2O and in isolated rat livers perfused with buffer containing 1 to 5% 2H2O. Our data reveal a difference in the rate of labeling of C6 and C2 of glucose in vivo. Lastly, in cows infused with [6,6-2H2]glucose, we show that the turnover of glucose can be economically measured by assaying low tracer enrichment (down to 0.1%) via hexamethylenetetramine.