Biomedical subjects

M Beylot

Publications and source records attributed to M Beylot.

At least 19 recordsLinked to original sources

PubMed2005

In vivo expression of carbohydrate responsive element binding protein in lean and obese rats.

ChREBP (Carbohydrate response element binding protein) is considered to mediate the stimulatory effect of glucose on the expression of lipogenic genes. Its activity is stimulated by glucose. Less is known on the control of its expression. This expression could be controlled by nutritional (glucose, fatty acids) and hormonal (insulin) factors. We examined the in vivo nutritional control of ChREBP expression in liver and adipose tissue of Wistar rats. Compared respectively to the fed state and to a high carbohydrate diet, ChREBP mRNA concentrations were not modified by fasting or a high fat diet in rat liver and adipose tissue. FAS and ACC1 mRNA concentrations were on the contrary decreased as expected by fasting and high fat diets and these variations of FAS and ACC1 mRNA were positively related to those of SREBP-1c mRNA and protein, but not of ChREBP mRNA. Therefore i) ChREBP expression appears poorly responsive to modifications of nutritional condition, ii) modifications of the expression of ChREBP do not seem implicated in the physiological control of lipogenesis. To investigate the possible role of ChREBP in pathological situations we measured its mRNA concentrations in the liver and adipose tissue of obese Zucker rats. ChREBP expression was increased in the liver but not the adipose tissue of obese rats compared to their lean littermates. These results support a role of ChREBP in the development of hepatic steatosis and hypertriglyceridemia but not of obesity in this experimental model.

Animals↗

PubMed2004

Metabolism of lipids in human white adipocyte.

Adipose tissue is considered as the body's largest storage organ for energy in the form of triacylglycerols, which are mobilized through lipolysis process, to provide fuel to other organs and to deliver substrates to liver for gluconeogenesis (glycerol) and lipoprotein synthesis (free fatty acids). The release of glycerol and free fatty acids from human adipose tissue is mainly dependent on hormone-sensitive lipase which is intensively regulated by hormones and agents, such as insulin (inhibition of lipolysis) and catecholamines (stimulation of lipolysis). A special attention is paid to the recently discovered perilipins which could regulate the activity of the lipase hormono-sensible. Most of the plasma triacylglycerols are provided by dietary lipids, secreted from the intestine in the form of chylomicron or from the liver in the form of VLDL. Released into circulation as non-esterified fatty acids by lipoprotein lipase, those are taken up by adipose tissue via specific plasma fatty acid transporters (CD36, FATP, FABPpm) and used for triacylglycerol synthesis. A small part of triacylglycerols is synthesized into adipocytes from carbohydrates (lipogenesis) but its regulation is still debated in human. Physiological factors such as dieting/fasting regulate all these metabolic pathways, which are also modified in pathological conditions e.g. obesity.

Adipocytes↗

PubMed2003

Contribution of hepatic de novo lipogenesis and reesterification of plasma non esterified fatty acids to plasma triglyceride synthesis during non-alcoholic fatty liver disease.

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is frequently observed in insulin-resistant subjects and can lead to liver fibrosis and cirrhosis. The abnormalities of lipid metabolism behind this development of excess hepatic TG stores are poorly understood. METHODS: To clarify these mechanisms we measured triglyceride secretion rate and the contributions of hepatic lipogenesis and reesterification of non-esterified fatty acids (NEFA) to this secretion in healthy subjects and in patients with clear evidence of NAFLD. All subjects were studied in the post-absorptive state. Hepatic lipogenesis was measured with deuterated water. NEFA turnover rate, triglyceride secretion rate and the contribution of NEFA reesterification to this secretion were determined with [1-(13)C] palmitate infusion. RESULTS: NAFLD patients had higher NEFA concentrations (p<0.05) but normal NEFA turnover rates (5.23 +/- 0.80 vs 5.91 +/- 0.97 micromol.kg(-1).min(-1) in control subjects, ns). Despite a trend for higher plasma triglyceride levels in patients (p<0.10), triglyceride turnover rates were not increased (0.11 +/- 0.01 micromol.kg(-1).min(-1) in patients vs 0.14 +/- 0.01 in controls, ns). However the contribution of hepatic lipogenesis to triglyceride secretion was largely increased in patients (14.9 +/- 2.7 vs 4.6 +/- 1.1% p<0.01) while that of NEFA reesterification was reduced (25.1 +/- 2.9 vs 52.8 +/- 6.2% p<0.01). CONCLUSION: Enhanced lipogenesis appears as a major abnormality of hepatic fatty metabolism in subjects with NAFLD. Therapeutic measures aimed at decreasing hepatic lipogenesis would therefore be the most appropriate in order to reduce hepatic TG synthesis and content in such patients.

Adult↗

PubMed2001

Effects of isoenergetic high-carbohydrate compared with high-fat diets on human cholesterol synthesis and expression of key regulatory genes of cholesterol metabolism.

BACKGROUND: High-carbohydrate diets improve plasma cholesterol concentrations but increase triacylglycerol concentrations; the latter effect increases the risk of cardiovascular disease (CVD). Triacylglycerol concentrations increase only during very-high-carbohydrate diets consisting mainly of simple sugars. OBJECTIVE: We compared the CVD risk profile, cholesterol metabolism, and glucose tolerance of 7 healthy subjects during 2 isoenergetic diets: a high-fat, low-carbohydrate diet (HF diet) and a moderately high-carbohydrate, low-fat diet (HC diet). DESIGN: In a randomized crossover study, we measured the effects of the HF diet [40% carbohydrate and 45% fat (15% saturated, 15% monounsaturated, and 15% polyunsaturated)] and HC diet [55% carbohydrate (mainly complex) and 30% fat (10% saturated, 10% monounsaturated, and 10% polyunsaturated)] (3 wk each) on plasma lipid concentrations, oral glucose tolerance, cholesterol synthesis rate, and the messenger RNA (mRNA) concentrations of beta-hydroxy-beta-methylglutaryl coenzyme A (HMG-CoA) reductase, the LDL receptor, and the LDL-receptor-related protein (LRP). RESULTS: Compared with the HF diet, the HC diet lowered total, LDL, and HDL cholesterol (P < 0.05 for all) without modifying the ratio of LDL to HDL cholesterol; triacylglycerol concentrations were unchanged. Lower cholesterol concentrations occurred despite a higher cholesterol synthesis rate (P < 0.05) and higher HMG-CoA reductase mRNA concentrations (P < 0.05). LDL receptor mRNA concentrations were unchanged, LRP mRNA concentrations were lower (P < 0.01), and oral glucose tolerance was better (P < 0.05) with the HC diet. CONCLUSION: The beneficial effects of the HC diet on glucose tolerance and plasma cholesterol concentrations without increases in triacylglycerol show that this diet had favorable effects on both insulin sensitivity and the plasma lipid profile.

Adult↗

PubMed2001

Hepatic lipogenesis and cholesterol synthesis in hyperthyroid patients.

To determine the effect of hyperthyroidism on hepatic lipogenesis and cholesterol synthesis we measured these metabolic pathways (deuterated water method) in euthyroid and hyperthyroid subjects investigated in the postabsorptive state. Hyperthyroid patients had increased concentrations of glucose (P < 0.05), insulin (P < 0.05), nonesterified fatty acids (P < 0.01), and triglycerides (P < 0.05) and decreased levels of plasma cholesterol (P < 0.01). The contribution of hepatic lipogenesis to plasma triglycerides was largely increased in hyperthyroid subjects (23.0 +/- 1.8% vs. 7.5 +/- 0.2%; P < 0.001), whereas the fractional synthetic rate of cholesterol was moderately higher (5.0 +/- 0.8% vs. 3.3 +/- 0.2%; P < 0.05). mRNA levels of beta-hydroxy-beta-methyl glutaryl-coenzyme A reductase, measured in circulating mononuclear cells, were increased (P < 0.05), whereas those of low density lipoprotein (LDL) receptor and LDL receptor-related protein were unchanged. Sterol responsive element binding protein-1c mRNAs were undetectable in mononuclear cells from both groups of subjects. The large stimulation of hepatic lipogenesis in hyperthyroid patients is probably explained by both a direct action of thyroid hormones and the increase in insulin. It could contribute to their moderate rise in triglycerides levels. The decreased plasma cholesterol level is observed despite an enhanced synthetic rate and is thus related to an increased clearance rate. The lack of increased expression of LDL receptor and LDL receptor-related protein suggests that other receptors are implicated.

Adult↗

PubMed2001

Study of the regulation by nutrients of the expression of genes involved in lipogenesis and obesity in humans and animals.

Dietary digestible carbohydrates are able to modulate lipogenesis, by modifying the expression of genes coding for key lipogenic enzymes, like fatty acid synthase. The overall objective of the Nutrigene project (FAIR-CT97-3011) was to study the efficiency of various carbohydrates to modulate the lipogenic capacity and relevant gene expression in rat and human species (control and obese subjects) and to understand the underlying molecular mechanisms involved in the regulation of lipogenic genes by carbohydrates. Key cellular mediators (namely SREBP-1c and 2, AMP activated protein kinase, cholesterol content) of the regulation of lipogenic gene expression by glucose and/or insulin were identified and constitute new putative targets in the development of plurimetabolic syndrome associated with obesity. In humans, hepatic lipogenesis and triglyceride synthesis, assessed in vivo by the use of stable isotopes, was promoted by a high-carbohydrate diet in non obese subjects, and in non alcoholic steatotic patients, but was not modified in the adipose tissue of obese subjects. Non digestible/fermentable carbohydrates, such as fructans, were shown to decrease hepatic lipogenesis in non obese rats, and to lessen hepatic steatosis and body weight in obese Zucker rats. If confirmed in obese humans, this would allow the development of functional food able to counteract the metabolic disturbances linked to obesity.

Adipose Tissue↗

PubMed2000

In vivo measurement of gluconeogenesis in animals and humans with deuterated water: a simplified method.

The contribution of gluconeogenesis to glucose production can be measured by comparing after ingestion of deuterated water the enrichment in deuterium of the hydrogen bound to carbon 5 of glucose with that of hydrogen bound to carbon 2 or with the deuterium enrichment of plasma water. The method developed by Landau et al. for measuring deuterium enrichment on carbon 5 by gas chromatography-mass spectrometry analysis is tedious and time consuming. We developed a simpler procedure for measuring this deuterium enrichment. Deuterium enrichment on carbons 5 and 6 of glucose is measured using the 1,2-5, 6-diisopropylidene-3-O-acetyl-a-furanosyl derivative. Enrichment in position 6 is measured using the hexamethylenetetramine procedure and subtracted from the enrichment on carbons 5 and 6 to obtain the specific enrichment on carbon 5. We tested first this method in post-absorptive and fasted rats (plasma water enrichment 0.6%) infused simultaneously with [6,6-(2) H(2) ] glucose in order to obtain not only the percent contribution of gluconeogenesis, but also glucose turnover rate and absolute gluconeogenesis flux. In post-absorptive and starved rats gluconeogenesis represented respectively 46.7+/-2.0% and 94.1+/-2.0% of glucose production and a flux of 31.1+/-1.8 and 38.9+/-0.9 micromol/kg/min. The method was then used in humans. The contribution in the post-absorptive state of gluconeogenesis to glucose appearance measured in control and type 2 diabetic subjects (plasma water enrichment 0.23-0.38%) was 40. 7+/-5.0% and 65.7 +/-3.3% (p<0.05) respectively. In conclusion this simplified method appears useful for in vivo studies of gluconeogenesis.

Adult↗

PubMed2000

Insulin sensitivity of glucose and fat metabolism in severe sepsis.

In order to quantify the changes in insulin sensitivity, particularly of endogenous glucose production and fat metabolism, in patients with severe sepsis, a prospective study was conducted in five normal subjects and in five patients with severe sepsis hospitalized in an intensive care unit. The responses of endogenous glucose production, glucose utilization, plasma fatty acids and ketone body concentrations to progressive increase in plasma insulin levels (exogenous insulin infusion rates of 0, 0.5, 1 and 2 m-units x min(-1) x kg(-1)) were measured using the isoglycaemic clamp technique. Total glucose turnover was determined with D-[6,6-(2)H(2)]glucose. In each group, plasma glucose was maintained at basal levels (control subjects, 4.32+/-0.22 mmol x l(-1); patients with sepsis, 7.10+/-2.29 mmol x l(-1); P<0.05). Plasma insulin concentrations were comparable in the two groups at an insulin infusion rate of 0.4 m-unit x min(-1) x kg(-1) for controls and 0.5 m-unit x min(-1) x kg(-1) for patients with sepsis, but differed following infusion at 2 m-unit x min(-1) x kg(-1) (control subjects, 102+/-13.4 m-units x l(-1); patients with sepsis, 124.8+/-19.7 m-units x l(-1); P<0.05). Endogenous glucose production was completely suppressed in control subjects by the first insulin infusion (0.4 m-unit x min(-1) x kg(-1)), but was only suppressed during infusion at 1 m-unit x min(-1) x kg(-1) insulin in patients with sepsis. The glucose utilization rate increased significantly with exogenous insulin infusion in control subjects, but did not increase in patients with sepsis. Plasma non-esterified (free) fatty acid and ketone body levels were significantly decreased in both groups by the infusion of exogenous insulin, but the sensitivity of lipolysis was impaired in patients with sepsis. In conclusion, sepsis impaired to a varying extent the action of insulin on endogenous glucose production, glucose utilization, lipolysis and ketogenesis. Whole-body glucose uptake was the most affected, with a total lack of response to the elevated insulin levels obtained in this study. Suppression of endogenous glucose production and lipolysis could only be achieved with higher doses of insulin than those required in normal subjects.

Adult↗

PubMed1999

Thermogenic effect of slight hyperglycemia during a lipid infusion.

Resistance to the glucoregulatory action of insulin is a common finding in obesity and may affect thermogenesis. In 13 healthy subjects, we studied the influence of acute insulin resistance induced by a lipid infusion on thermogenesis without any glucose load (n = 4) or during a euglycemic-hyperinsulinemic clamp (n = 5) and an oral glucose tolerance test (OGTT, n = 8). When substrates were not administered at the same time, the energy cost of storage was significantly (P < .05) lower for lipids (3.9%+/-0.9%) than for glucose (11.9%+/-0.5% during the clamp and 14.9%+/-4.0% during the OGTT, NS). The lipid infusion decreased glucose storage during the clamp (control, 3.99+/-0.40 mg x kg(-1) x min(-1); lipid infusion, 0.92+/-0.39; P < .05) but increased it during the OGTT (control, 1.76+/-0.22 mg x kg(-1) x min(-1); lipid infusion, 2.94+/-0.27; P < .05). Infused lipids were stored more (clamp, 3.31+/-0.16; OGTT, 2.65+/-0.11 mg x kg(-1) x min(-1); P < .01) and oxidized less (clamp, 0.64+/-0.21; OGTT, 1.02+/-0.09 mg x kg(-1) x min(-1); P < .05) during the clamp than during the OGTT. When lipids were infused, the energy cost of substrate storage was lower during the clamp versus the OGTT (clamp, 3.2%+/-0.8%; OGTT, 7.3%+/-1.0%; P < .05). This effect was attributed to a lipid-induced impairment of glucose tolerance, which overcomes the inhibitory effect of lipid infusion on glucose storage observed in euglycemia. A slight elevation of plasma glucose in response to a lipid infusion impairs thermogenesis by redirecting the storage of substrates from lipids to glucose, which has a higher energy cost.

Adult↗

PubMed1999

Noninvasive tracing of human liver metabolism: comparison of phenylacetate and apoB-100 to sample glutamine.

The labeling pattern of hepatic glutamine during infusion of [3-13C]lactate provides information on liver intermediary metabolism and allows us to correct apparent gluconeogenic rates for isotopic dilution in the oxaloacetate (OAA) pool. Liver glutamine can be sampled by its conjugation with phenylacetate to form phenylacetylglutamine (PAGN) but also by purifying the glutamine of the apolipoproteinB-100 of very low-density lipoprotein (apoB-100-VLDL). We compared these methods in normal and non-insulin dependent diabetes subjects. We tested also whether apoB-100-VLDL alanine enrichment could solve the problem of dilution of gluconeogenic precursor enrichments between peripheral blood and liver (prehepatic dilution). In both normal and diabetic subjects, the labeling patterns of glutamine obtained from PAGN or apoB-100-VLDL were comparable. Therefore, metabolic fluxes and correction factors for dilution in the OAA pool were also comparable. With both methods, gluconeogenic rates were not increased in diabetic patients. Use of the enrichment of apoB-100-VLDL alanine to correct for prehepatic dilution led to high estimates of gluconeogenesis; it remains uncertain whether this enrichment provides a correct estimate of liver pyruvate enrichment.

Adult↗

PubMed1999

Modifications of citric acid cycle activity and gluconeogenesis in streptozotocin-induced diabetes and effects of metformin.

To better define the modifications of liver gluconeogenesis and citric acid cycle, or Krebs' cycle, activity induced by insulin deficiency and the effects of metformin on these abnormalities, we infused livers isolated from postabsorptive or starved normal and streptozotocin-induced diabetic rats with pyruvate and lactate (labeled with [3-13C]lactate) with or without the simultaneous infusion of metformin. Lactate and pyruvate uptake and glucose production were calculated. The 13C-labeling pattern of liver glutamate was used to calculate, according to Magnusson's model, the relative fluxes through Krebs' cycle and gluconeogenesis. These relative fluxes were converted into absolute values using substrate balances. In normal rats, starvation increased gluconeogenesis, the flux through pyruvate carboxylase-phosphoenolpyruvate carboxykinase (PC-PEPCK), and the ratio of PC to pyruvate dehydrogenase (PDH) flux (P < 0.05); metformin induced only a moderate decrease in the PC:PDH ratio. Livers from postabsorptive diabetic rats had increased lactate and pyruvate uptakes (P < 0.05); their metabolic fluxes resembled those of starved control livers, with increased gluconeogenesis and flux through PC-PEPCK. Starvation induced no further modifications in the diabetic group. Metformin decreased glucose output from the liver of starved diabetic rats (P < 0.05). The flux through PC-PEPCK and also pyruvate kinase were decreased (P < 0.05) by metformin in both groups of diabetic rats. In conclusion, insulin deficiency increased in this model of diabetes gluconeogenesis through enhanced uptake of substrate and increased flux through PC-PEPCK; metformin decreased glucose production by reducing the flux through PC-PEPCK.

Animals↗

PubMed1998

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.

Acetone↗

PubMed1998

Non-invasive tracing of liver intermediary metabolism in normal subjects and in moderately hyperglycaemic NIDDM subjects. Evidence against increased gluconeogenesis and hepatic fatty acid oxidation in NIDDM.

To test whether gluconeogenesis is increased in non-insulin-dependent diabetic (NIDDM) patients we infused (post-absorptive state) healthy subjects and NIDDM patients with [6,6-2H2]glucose (150 min) and [3-13C]lactate (6 h). Liver glutamine was sampled with phenylacetate and its labelling pattern determined (mass spectrometry) after purification of the glutamine moiety of urinary phenylacetylglutamine. After correction for 13CO2 re-incorporation (control test with NaH13CO3 infusion) this pattern was used to calculate the dilution factor (F) in the hepatic oxaloacetate pool and fluxes through liver Krebs cycle. NIDDM patients had increased lactate turnover rates (16.18+/-0.92 vs 12.14+/-0.60 micromol x kg(-1) x min(-1), p < 0.01) and a moderate rise in glucose production (EGP) (15.39+/-0.87 vs 12.52+/-0.28 micromol x kg(-1) x min(-1) , p = 0.047). Uncorrected contributions of gluconeogenesis to EGP were 31+/-3 % (control subjects) and 17+/-2 % (NIDDM patients). F was comparable (1.34+/-0.02 and 1.39 0.09, respectively) and the corrected percent and absolute contributions of gluconeogenesis were not increased in NIDDM (25+/-3 % and 3.8+/-O.5 micromol x kg(1) x min[-1]) compared to control subjects (41+/-3 % and 5.1+/-0.4 micromol x kg(-1) x min(-1]). The calculated pyruvate carboxylase over pyruvate dehydrogenase activity ratio was comparable (12.1+/-2.6 vs 11.2+/-1.4). Lastly hepatic fatty oxidation, as estimated by the model, was not increased in NIDDM (1.8+/-0.4 vs 1.6+/-0.1 micromol x kg(-1) x min[-1]). In conclusion, in the patients studied we found no evidence of increased hepatic fatty oxidation, or, despite the increased lactate turnover rate, an increased gluconeogenesis.

Adult↗

PubMed1998

Influence of human obesity on the metabolic fate of dietary long- and medium-chain triacylglycerols.

The metabolic fate of an oral long-chain-triacylglycerol (LCT) load and of a mixed oral LCT and medium-chain-triacylglycerol (MCT) load was followed for 6 h in eight control and eight obese subjects with normal postabsorptive triacylglycerol concentrations. Labeled triacylglycerol and indirect calorimetry were used. Results showed that LCTs were less oxidized in obese than in control subjects (3.2+/-0.5 compared with 6.0+/-0.4 g, P < 0.01). Moreover, the amount of LCT oxidized was negatively correlated with fat mass (r = -0.77, P < 0.01). Appearance in plasma of dietary triacyglycerol-derived long-chain fatty acids was blunted in obese subjects and it was negatively related to fat mass (r = -0.84, P < 0.01) and positively to LCT oxidation (r = 0.70, P < 0.01). On the contrary, MCT oxidation was not altered in obese subjects compared with control subjects. Furthermore, the proportion of MCTs oxidized was higher in both groups compared with LCTs (x+/-SEM: 57.5+/-2.6% compared with 15.2+/-1.6%, P < 0.01, n = 16). Our conclusion is that obesity is associated with a defect in the oxidation of dietary LCTs probably related to an excessive uptake by the adipose tissue of meal-derived long-chain fatty acids. MCTs, the oxidation of which is not altered in obesity, could therefore be of interest in the dietary treatment of obesity.

3-Hydroxybutyric Acid↗

PubMed1998

Role of human liver lipogenesis and reesterification in triglycerides secretion and in FFA reesterification.

To measure 1) the contribution of hepatic de novo lipogenesis (DNL) and plasma free fatty acid (FFA) reesterification to plasma triglyceride (TG) secretion and 2) the role of oxidation and hepatic and extrahepatic reesterification in FFA utilization, five normal subjects drank deuterate water and were infused (postabsorptive state) with [1-13C]palmitate and [1,2,3-2H5]glycerol. Total lipid oxidation (Lox) was measured by indirect calorimetry. FFA oxidation (2.76 +/- 0.65 mumol.kg.-1.min-1) accounted for 45% of FFA turnover rate (Rt) (1.04 mumol.kg-1.min-1) and 91% of Lox; FFA reesterification was 3.27 +/- 0.54 mumol.kg-1.min-1. Fractional and absolute TG Rt were 0.21 +/- 0.02 h-1 and 0.11 +/- 0.05 mumol.kg-1.min-1. DNL accounted for 3.9 +/- 0.9% of TG secretion, and hepatic FFA reesterification accounted for 49.4 +/- 5.7%; this last process represented a utilization of FFA of 0.16 +/- 0.02 mumol.kg-1.min-1. We conclude that, in the postabsorptive state, 1) DNL and FFA reesterification account for only 50-55% of TG secretion, the remaining presumably being provided by stored lipids or lipoproteins taken up by liver, 2) most reesterification occurs in extrahepatic tissues, and 3) oxidation and reesterification each contribute about one-half to FFA utilization; FFA oxidation accounts for almost all Lox.

Adult↗

PubMed1998

Mechanisms of glucose intolerance during triglyceride infusion.

Lipid infusions may affect glucose tolerance by effects on glucose production or utilization. We performed double-labeled oral glucose tolerance tests with and without a lipid infusion in eight normal subjects. During the lipid infusion, plasma glucose and insulin levels were higher, showing some insulin resistance. The increased glucose level was due to a higher total glucose appearance rate, partly reproducible by a control infusion of glycerol [saline 1,181 +/- 71 mg . kg-1 . 330 min-1 vs. lipid 1,388 +/- 100 (P < 0.05) vs. glycerol 1,276 +/- 126 (NS)]. The tracer-determined appearance rate of exogenous glucose was higher with lipid infusion but was probably overestimated because of higher 13C recycling into glucose. Residual systemic glucose production was increased but was reproducible by the glycerol infusion. Total glucose disposal was increased. This was observed despite a lower stimulation of total glucose oxidation as measured by indirect calorimetry, whereas oxidation of exogenous glucose was normal after correction for the lipid-induced modification of excretion rate of 13CO2. Accordingly, glucose nonoxidative disposal was increased. These moderate modifications of glucose metabolism (increased appearance, increased nonoxidative disposal, and lower total oxidation) have been reported in starvation-induced or spontaneously impaired glucose tolerance. Further impairment, especially decreased nonoxidative glucose disposal, seems to be required to produce non-insulin-dependent diabetes mellitus.

Blood Glucose↗

PubMed1997

Measuring lipogenesis and cholesterol synthesis in humans with deuterated water: use of simple gas chromatographic/mass spectrometric techniques.

Lipogenesis and cholesterol synthesis can be studied by measuring the incorporation into fatty acids and cholesterol of deuterium from deuterated water. This has been previously achieved in human subjects using low levels of deuterium enrichment in plasma water, and thus in fatty acids and cholesterol. For the measurement of enrichment in lipids, this required the use of isotope ratio mass spectrometry, a tedious and time-consuming technique. It is shown that these measurements can be performed using the much simpler gas chromatography/mass spectrometry if higher, but always safe, deuterium enrichments in plasma water are obtained. Normal subjects ingested deuterated water in order to obtain stable enrichment in plasma water of 0.3% during a 60 h period. Enrichment in palmitate of plasma triglycerides (TG) plateaued (0.6-0.76%) whereas plasma cholesterol enrichment increased progressively [0.32 +/- 0.08% (12 h) to 0.78 +/- 0.18% (60 h)]. Endogenous synthesis was estimated to contribute, in post-absorptive subjects, 8-10% of the plasma TG pool and 3-5% of plasma free cholesterol pool. These data agree with results obtained previously using isotope ratio mass spectrometry. The present method will be useful for studies of normal and abnormal lipid metabolism in humans.

Cholesterol↗

PubMed1997

Glucose production and gluconeogenesis in postabsorptive and starved normal and streptozotocin-diabetic rats.

Using a 3-hour primed-continuous infusion of [3-3H]glucose and [2-13C]glycerol, we measured glucose production, gluconeogenesis from glycerol, and total gluconeogenesis (using mass isotopomer distribution analysis [MIDA] of glucose) in postabsorptive and starved normal and streptozotocin-diabetic rats. In normal rats, 48 hours of starvation increased (P < .01) the percent contribution of both gluconeogenesis from glycerol (from 14.4% +/- 1.8% to 25.5% +/- 4.0%) and total gluconeogenesis (from 52.2% +/- 3.9% to 89.8% +/- 1.3%) to glucose production, but the absolute gluconeogenic fluxes were not modified, since glucose production decreased. Diabetic rats showed increased glucose production in the postabsorptive state; this decreased with starvation and was comparable to the of controls after 48 hours of starvation. Gluconeogenesis was increased in postabsorptive diabetic rats (69.0% +/- 1.3%, P < .05 v controls). Surprisingly, this contribution of gluconeogenesis to glucose production was not found to be increased in 24-hour starved diabetic rats (64.4% +/- 2.4%). These rats had significant liver glycogen stores, but gluconeogenesis was also low (42.8% +/- 2.1%) in 48-hour starved diabetic rats deprived of glycogen stores. Moreover, in 24-hour starved diabetic rats infused with [3-13C]lactate, gluconeogenesis was 100% when determined by comparing circulating glucose and liver pyruvate enrichment, but only 47% +/- 3% when calculated from the MIDA of glucose. Therefore, MIDA is not a valid method to measure gluconeogenesis in starved diabetic rats. This was not explained by differences in the labeling of liver and kidney triose phosphates: functional nephrectomy of starved diabetic rats decreased glucose production, but gluconeogenesis calculated by the MIDA method was only 48% +/- 3.3%. We conclude that (1) diabetic rats have increased glucose production and gluconeogenesis in the postabsorptive state; (2) starvation decreases glucose production and increases the contribution of gluconeogenesis, but MIDA is not an appropriate method in this situation; and (3) the kidneys contribute to glucose production in starved diabetic rats.

Animals↗